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RAPID RISK ASSESSMENT OF

RAMAGUNDAM FERTILIZER COMPLEX

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RAPID RISK ASSESSMENT PROJECT : RAMAGUNDAM FERTILIZER COMPLEX

OWNER : CONSORTIUM OF EIL, NFL AND FCI

CONSULTANT : ENGINEERS INDIA LTD.

A 11.11.14 ISSUED AS DRAFT NC DK GG

Rev. No Date Purpose Prepared by Reviewed by Approved by




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PREFACE

Consortium of M/S Engineers India Ltd, NFL and FCI have proposed for setting up of new

Ammonia/Urea Fertilizer Complex at Ramagundam Unit, Ramagundam Mandal, District

Karimnagar of Telangana state. The new plant consists of ammonia and urea section along with

associated offsite and utility facilities within the premises of existing Ramagudam Fertilizer

complex. Ammonia plant will be single stream having a capacity of 2200 MTPD. The plant will

be designed to use NG/RLNG as feed and fuel. The Urea plant will be single stream having

capacity of 3850 MTPD prilled urea. New CPP of capacity 29.1 MW (Normal)/34.6 MW (Max)

and (GTG+HRSG) will be installed. Nearest ports are Krishnapatanam, Kakinada. This Report

pertains to New Ammonia and Urea facilities. Licensor for the new facilities KBR for Ammonia

and Stamicarbon for Urea were considered.




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EXECUTIVE SUMMARY

TABLE OF CONTENTS

1. INTRODUCTION

1.1 OBJECTIVE

1.2 SCOPE OF WORK

2. SITE CONDITIONS

2.1 SITE_LOCATION_AND_VICINITY

2.2 METEOROLOGICAL CONDITIONS

2.3 ATMOSPHERIC PARAMETERS

2.4 WIND SPEED AND DIRECTION

2.5 WEATHER_CATEGORY

3. PROCESS DESCRIPTION

3.1 AMMONIA UNIT

3.2 UREA UNIT

3.3 OFFSITES

3.4 CPP

4. HAZARDS ASSOCIATED WITH THE PROJECT

4.1 CATEGORIES OF RISK ASSOCIATED WITH THE PROJECT

4.2 HAZARDS ASSOCIATED WITH MATERIALS HANDLED

5. HAZARD IDENTIFICATION

5.1 FAILURE MODE ANALYSIS

5.2 GENERAL

5.3 MODES OF FAILURE

5.4 SELECTED FAILURE CASES

6. CONSEQUENCE_ANALYSIS

6.1 CONSEQUENCE ANALYSIS MODELING

6.2 SIZE AND DURATION OF LEAK

6.3 DAMAGE CRITERIA DUE TO VARIOUS SCENARIOS




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6.4 HAZARD ASSESSMENT

7. CONCLUSIONS AND RECOMMENDATIONS

8. GLOSSARY

9. REFERENCES




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EXECUTIVE SUMMARY

A Rapid Risk Assessment of the risks envisaged at the proposed Fertilizer complex at

Ramagundam has been carried out by Engineers India Limited. The present report provides the

details of the consequences and recommendations for the risks involved. After modeling the

possible leak scenarios, consequence analysis shows that hazards due to high concentration of

ammonia cater the risks on a significance scale. Overall, even if some contribution of flammable

mixtures is found from natural gas and ammonia, it is clearly seen that toxic hazards of ammonia

dictate the risk profile both inside and outside the plant. The consequences due to minor leaks

which bear a higher probability are confined inside the complex. The consequences due to major

leaks like large holes and catastrophic ruptures reach outside the fertilizer complex which can

affect the outside population also. Even though these scenarios have a very low probability of

occurrence, appropriate disaster management plan should be employed for the protection of

population inside and outside the complex. It is highly recommended to provide gas detectors

along with emergency alarm wherever applicable. Water curtains are to be provided at critical

locations to dilute the toxic vapors of ammonia released. Breathing apparatus should be made

available for the plant personnel in the event of major ammonia leak in the facility. Control

rooms and other buildings should be positively pressurized and kept airtight to prevent the entry

of toxic gases.




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1. INTRODUCTION

Ramagundam Fertilizer, a consortium of M/s Engineers India Ltd., NFL and FCI have proposed

for setting up of new Ammonia/Urea Fertilizer Complex at Ramagundam Unit, Ramagundam

Mandal, Karimnagar District, Telangana. The proposal consists of new ammonia and urea plant

along with associated offsite and utility facilities within the premises of existing Ramagundam

Fertilizer complex. Ammonia plant is a single stream having a capacity of 2200 MTPD. The

plant is designed to use NG/RLNG as feed and fuel. The urea plant is a single stream having

capacity of 3850 MTPD prilled urea. New captive power plant of 29.1 MW (Normal)/34.6MW

(Max.) (GTG + HRSG) will be installed to cater the extra power requirements. Nearest ports

located are Krishnapatanam and Kakinada

1.1 OBJECTIVE

The objectives of the Rapid Risk Assessment study are to identify all potential failure cases,

which might affect the population and property in the vicinity of the facilities, and provide

information necessary in developing strategies to prevent accidents and formulate the disaster

management plan.

The main objectives of the study are:

a) Identification of failure cases within the installations.

b) Evaluate process hazards emanating from the identified potential accident scenarios.

c) Analyze the damage effects to surroundings due to such incidents.

d) Suggest mitigating measures to reduce the hazard / risk.

The results are useful in developing a meaningful emergency plan and also serve as a powerful

training tool.

1.2 SCOPE OF WORK

The study covers the following units and associated piping and equipment as sources of hazards/

vulnerability:




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Ammonia Unit

Natural gas compression

Reforming section

Shift section

CO2 removal section

Methanation and Purification section

Ammonia synthesis section

Ammonia recovery

Process condensate stripping section

Urea Unit

Ammonia and CO2 compression section

Urea Synthesis section

Recirculation section

Evaporation and MP section

Prilling section

Condensation section

Urea desorption section

CPP

GTG

HRSG

OFFSITES

Ammonia Storage tanks

Tank manifold




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2. SITE CONDITIONS

This chapter depicts the location of Ramagundam fertilizer complex. It also indicates the

meteorological data, which will be used for the Rapid Risk Assessment study.

2.1 SITE, LOCATION AND VICINITY

Ramagundam city is Municipal corporation and mandal in the district of Karimnagar, located in

the northern region of the state of Telangana in India.

Ramagundam, known as the City of Energy is located on the banks of Godavari River about 250

km (155 mi) north east of state capital, Hyderabad. It is situated at latitude of 18.46o and

longitude of N 79.45 o E and approximately 156 m above mean sea level.

2.2 METEOROLOGICAL CONDITIONS

The consequences of released flammable or toxic material are largely dependent on the

prevailing weather conditions. For the assessment of major scenarios involving release of

flammable or toxic materials, the most important meteorological parameters are those that affect

the atmospheric dispersion of the escaping material. The crucial variables are wind direction,

wind speed, atmospheric stability and temperature. Rainfall does not have any direct bearing on

the results of the risk Assessment; however, it can have beneficial effects by absorption /

washout of released materials. Actual behavior of any release would largely depend on

prevailing weather condition at the time of release.

For the present Risk Assessment study, Meteorological data of Ramagundam have been taken

from the Climatological Tables of Observatories in India (1961-1990) published by Indian

Meteorological Department.

2.3 ATMOSPHERIC PARAMETERS

The Climatological data which have been used for the Risk Assessment study is summarized

below:

http://en.wikipedia.org/wiki/Karimnagar_district�

http://en.wikipedia.org/wiki/Telangana�

http://en.wikipedia.org/wiki/India�

http://en.wikipedia.org/wiki/Godavari_River�

http://en.wikipedia.org/wiki/Hyderabad,_India�




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Table 2.3.1: Atmospheric parameters

S. No Parameter Average value considered for study

1. Ambient Temperature (OC) 32.1

2. Atmospheric Pressure (mm Hg) 760

3. Relative Humidity (%) 68

4. Solar Radiation flux (kW/m2) 0.7

2.4 WIND SPEED AND WIND DIRECTION

Based on the Meteorological data provided at the IMD table, it is observed that calm weather

can be experienced for 38-42% of the time in a year. Wind speed in the range of 2-5 m/s blows

58-62% of the time, and wind speed more than 5 m/s was not apparent during any part of the

year. Hence as a conservative approach, wind speed of 1 m/s would account for the calm

weather and 2 m/s for the rest of the time. Both the wind speeds are observed in almost equal

proportions during every part of the year. The predominant wind direction was observed from

west followed by south accounting for 13% and 9% respectively with calm weather observed for

around 41% of the year.

Table 2.4-1: Average mean wind speed (m/s)

Month Jan Feb Mar April May June July Aug Sep Oct Nov Dec

km/h 3.4 4.2 4.8 6.3 6.1 6.8 5.4 4.2 3.4 2.7 2.4 2.5

m/s 0.944 1.167 1.334 1.75 1.69 1.889 1.5 1.167 0.944 0.75 0.667 0.694

2.5 WEATHER CATEGORY

One of the most important characteristics of atmosphere is its stability. Stability of atmosphere is

its tendency to resist vertical motion or to suppress existing turbulence. This tendency directly

influences the ability of atmosphere to disperse pollutants emitted into it from the facilities. In

most dispersion scenarios, the relevant atmospheric layer is that nearest to the ground, varying in

thickness from a few meters to a few thousand meters. Turbulence induced by buoyancy forces

in the atmosphere is closely related to the vertical temperature gradient.




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Temperature normally decreases with increasing height in the atmosphere. The rate at which the

temperature of air decreases with height is called Environmental Lapse Rate (ELR). It will vary

from time to time and from place to place. The atmosphere is said to be stable, neutral or

unstable according to ELR is less than, equal to or greater than Dry Adiabatic Lapse Rate

(DALR), which is a constant value of 0.98°C/100 meters.

Pasquill stability parameter, based on Pasquill – Gifford categorization, is such a meteorological

parameter, which describes the stability of atmosphere, i.e., the degree of convective turbulence.

Pasquill has defined six stability classes ranging from `A' (extremely unstable) to `F' (stable).

Wind speeds, intensity of solar radiation (daytime insulation) and nighttime sky cover have been

identified as prime factors defining these stability categories. Table 3.3-3 indicates the various

Pasquill stability classes.

Table 2.5.1: Pasquill stability classes

Surface Wind Speed

(meter/s)

Day time solar radiation Night time cloud cover

Strong Medium Slight Thin < 3/8 Medium 3/8 Overcast >4/8

< 2 A A – B B - - D

2 – 3 A – B B C E F D

3 – 5 B B – C C D E D

5 – 6 C C – D D D D D

> 6 C D D D D D

Legend: A = Very unstable, B = Unstable, C = moderately unstable, D = Neutral, E =

moderately stable, F = stable

When the atmosphere is unstable and wind speeds are moderate or high or gusty, rapid

dispersion of pollutants will occur. Under these conditions, pollutant concentrations in air will be

moderate or low and the material will be dispersed rapidly. When the atmosphere is stable and

wind speed is low, dispersion of material will be limited and pollutant concentration in air will

be high.




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Stability category for the present study is identified based on the cloud amount and wind speed.

Table 2.5.2: Average all cloud amount (oktas of sky)

Jan Feb Mar April May June July Aug Sep Oct Nov Dec

1.6 1.55 1.55 2.2 2.85 5.4 6.5 6.35 5.15 3 2.25 1.85

For risk Assessment the representative average annual weather conditions are assessed based on

the following:

Wind speed less than 2 m/s would be experienced for 38-42% of the time in a year. In order to

realize the worst hazardous distances, weather stability of “F” was selected with wind speed 1

m/s for consequence analysis. Wind speed of 2-5 m/s can be realized for the remaining part of

the year. Cloud cover for these months is in the ranges of 2.2 to 6.5 oktas. This results in

stability class of D foe wind speeds of 2-5 m/s. As a conservative approach minimum velocity, 2

m/s has been selected with stability class D for risk Assessment. Average wind speed of greater

than 4 m/s can be realized in the month of June. Cloud cover for this month is 3.8. From this

information stability class of “D” was selected with wind speed 5 m/s for risk assessment.

Discussions, conclusions and recommendations pertaining to consequence analysis are based on

the worst weather condition. The consequence results are reported in tabular form for all the

weather conditions and are represented graphically for worst weather condition.

In the present study, the entire range of representative wind speeds, both during the day and

night, and cloud amount have been considered.

Table 2.5.3: Weather Conditions

Wind Speed Pasquill Stability

1 F

2 D




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3. PROCESS DESCRIPTION

3.1 AMMONIA UNIT- KBR

The key process features of KBR Ammonia purifier process are feed gas flexibility, mild

primary reforming, secondary reforming with excess air, mild reformed gas boiler conditions, a

gas turbine driven high efficiency process air compressor, cryogenic removal of excess nitrogen

and inerts from syngas, efficient synthesis scheme with a single horizontal converter and unitized

chiller. Purifier process also produces required CO2 by-product flow to convert the entire 2200

MTPD NH3 product to urea. The purifier process is inherently low energy consuming process

due to its unique parameters and integration as below. All of the process features in this plant

have been in operation in numerous KBR Purifier plants. Each of these features is discussed in

the following paragraphs.

Feed Gas Flexibility:

The KBR Purifier process uses a cryogenic nitrogen wash step to remove impurities from the

makeup synthesis gas. The process is uniquely able to handle variations in the composition of the

natural gas feed, including variations in hydrocarbon contents, N2 content and CO2 content. The

Purifier has the ability to absorb the variations in the raw synthesis, and maintain a stable

composition of the makeup gas to the synthesis loop.

Conversely, in a conventional plant, the flow rate of process air to the secondary reformer needs

to be controlled carefully to obtain the required H2 to N2 ratio in the makeup gas to the synthesis

loop.

With the ability to vary the flow rate of the process air, the loads on the air compressor,

secondary reformer and cryogenic Purifier were adjusted to maintain high ammonia capacity.

Unlike in the conventional process, the primary reformer’s operation has little impact during feed

gas composition variation. Operationally the whole plant is adjusted easily with varying feed gas

composition just by adjusting process air flow. Therefore, the plant has been able to maintain

high capacity during variations in the feed gas composition and is proven operationally flexible

due to this unique process.




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Mild Primary Reforming:

Primary reforming is carried out at a much lower temperature than in conventional ammonia

process. The methane content of the process gas going to the secondary reformer is much higher

than in conventional ammonia plant. More of the reforming is shifted to the secondary reformer,

which is more suitable to the temperatures involved and in which essentially 100 percent of the

heat is recovered. The radiant duty in the primary reformer is thus greatly reduced.

Integrated Reforming Furnace & Gas Turbine:

Radiant duty of the primary reformer furnace in the Purifier Process is only about 60% whereas

power requirement of the process air compressor is about 1.5 times more of that in a

conventional ammonia plant. Due to this unique combination, the oxygen content of the gas

turbine exhaust provides a good match with the requirement of combustion air to the primary

reformer furnace burners. The exhaust of the gas turbine driver of the process air compressor is

thus integrated with the primary reformer furnace.

The gas turbine driven air compressor is started-up standalone without requiring imported steam

thus required capacity of the OSBL package boiler is significantly less. Not only installed cost is

reduced this way but energy efficiency of the ammonia plant as well as the whole complex is

significantly increased with such integration as commercially proven in numerous Purifier plants.

Ammonia plat exports steam to urea plant/ CO2 compressor steam turbine and offsite users and

meets all their demand by aforementioned integration as well as due to the fact that process

steam consumption in Purifier process reforming is less due to lower S/C ratio enabled due to

higher allowable CH4 slip exit the secondary reformer.

Ramagundam Power & Steam Integration with the Urea/OSBL:

The power & steam of Ramagundam complex is integrated with the Captive Power Plant (CPP)

to maximize overall energy efficiency. Purifier process due to its integrated furnace-gas turbine

feature and lower ISBL steam consumption along with the gas turbine based CPP are able to

meet the entire steam and power demand of the whole complex including CO2 compressor steam

turbine urea process and offsite. The configuration of CPP plant will have a gas turbine driven

generator (GTG) and steam turbine driven generator (STG). Heat recovery from the GT exhaust




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is maximized and steam is generated at different pressure levels. Ramagundam will require MP

steam from OSBL only during it start-up & emergency, however start up steam is less, only

about 90t/h as air compressor does not require steam for its start up. Unlike in conventional

plants, Purifier plant does not require huge MP steam during trip of secondary reformer which is

a big relief while managing the transient operations.

Secondary Reforming with Excess Air:

In a conventional secondary reformer, the quantity of air is limited to the amount that is required

to produce a 3-to-1 ratio of H2 to N2 in the synthesis gas. With the Purifier process, the H2/N2

ratio is controlled at the Purifier so that extra air can be used in the secondary reformer. The

extra air provides additional reaction heat. Nearly 100 percent of the heat released in this vessel

is recovered compared to 40 to 50 percent in the radiant zone of the primary reformer. Therefore

shift of the duty from primary to secondary reformer makes the process more efficient.

In addition, because of the downstream Purifier, the allowable methane leakage is much higher

than in conventional plants, which further relaxes the reforming load by lowering the secondary

reformer outlet temperature. These two features result in much milder reforming conditions that

are advantageous in terms of both steady and reliable operations and longer equipment life.

The extra un-reformed methane, together with surplus N2 and most of the argon are recovered in

the Purifier system later in the process sequence, and returned to the reformer furnace as fuel.

Mild Reformed Gas Boiler Conditions:

Reformed gas (RG) boiler in Purifier process operates under significantly mild conditions of

inert gas temperature as well as heat flux. Typically RG boilers exit the secondary reformer may

be prone to failure due to severe high inlet temperature and high heat flux. Purifier process

enables to operate it at more than 100OC cooler which minimizes the process severity and thus

enhances equipment reliability.

More CO2 production for Urea Plant:

Since Purifier Process uses excess process air in the secondary reformer, more CO2 is produced

in the reforming section compared to a conventional process. Consequently, all the required CO2




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for conversion of 2200 MTPD ammonia to urea, is produced from the CO2 removal unit as by-

product, even with light feed natural gas composition as in Ramagundam. In a conventional

ammonia plant, the CO2 production will always be shorter then required by urea plant which will

need to be made up by either having a large surplus syngas or by recovering Co2 from the

furnace flue gas which is not required in case of Purifier process.

Optimally Integrated 2-stage OASE Process based CO2 removal:

A 2-stage OASE process based CO2 removal system, licensed from BASF, has been optimally

integrated into the Purifier process based ammonia flow sheet. As explained later, KBR’s

Purifier Ammonia Process allows using lower steam/carbon ratio in the reformer mixed feed and

as a consequence the higher methane slip from the secondary reformer can be removed by the

cryogenic unit. The Reboiler heat duty available in the purifier process is well matched with low

Reboiler duty required for solvent regeneration in a 2-stage OASE process. KBR was first in the

ammonia industry to incorporate a 2-stage OASE (former aMDEA) process (a 1980’s Purifier

process based plant) and has a leading position ever since for integration and execution of this

CO2 removal technology.

Cryogenic Purification Unit:

The cryogenic purification unit is the heart of the KBR Purifier Process. In this unit, essentially

all the methane and about 60 percent of the argon in the raw synthesis gas are removed together

with the excess nitrogen as waste gas. This waste gas is returned to the primary reformer furnace

as fuel after it has been used to regenerate the driers. The product from this unit is a highly pure

synthesis gas. The synthesis gas contains H2 and N1 in ratio of 3 without any water or carbon

oxides, which are poisons for the synthesis catalyst, and inert content is about 0.2 percent.

Most of the net cooling required by the Purifier is provided by a gas expander, which causes a

modest pressure drop in the synthesis gas stream. Further cooling is provided by low-pressure

vaporization of the waste gas described above. The Purifier has two controls. The energy balance

is controlled by the amount of work removed from the system by the expander. The material

balance is controlled by a valve in the line on the liquid from the bottom of the column. This

valve is controlled by a hydrogen analyzer on the purified process gas exit the cryogenic system.




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The highly pure and dry synthesis gas produced in the Purifier permits the operation of the

synthesis loop at lower pressure for the same level of refrigeration, thereby saving syngas

compressor power. This also leads to a very efficient ammonia synthesis process scheme with

savings in both syngas and refrigeration compressor power.

The cryogenic step allows a higher concentration of methane in the raw synthesis gas leaving the

secondary reformer since methane is removed from the syngas in the Purifier and used as fuel.

Thus, the secondary reformer outlet temperature is typically lower by more than 100°C than in a

conventional plant, and primary reformer radiant heat input as well as outlet gas temperature is

significantly less. Also, since higher methane content is allowed exit the secondary reformer, a

lower steam/carbon ratio in the primary reformer mixed feed (than in conventional process) can

be used. The lower S/C ratio maximizes MP steam export to the OSBL which makes the plant

more efficient. Complete removal of all traces of water and carbon dioxide lengthens the life of

the synthesis catalyst.

Another key advantage of the Purifier is that it stabilizes the operation of the plant by ' separating

the front end of the plant from the back end. First, it permits setting the hydrogen-to-nitrogen

ratio in the synthesis loop independently of the secondary reformer operation. Second, it

effectively compensates for any problems or upsets in the front end. For example, during

instances when the CO or the C02 leakage is higher than design, the CO and CO; will be

converted to methane in the methanator and all methane will be removed in the Purifier. The

synthesis loop operation will not be affected.

In a conventional ammonia process the above flexibility is not available. For example, the

process air rate must be carefully controlled in the front end of the plant to maintain a three- to-

one hydrogen-to-nitrogen ratio in the makeup gas to the synthesis loop. Also, during instances of

higher than normal CO or CO; leakages, the synthesis loop purge rate would have to be

increased to maintain the design loop inert level.

Finally, the Purifier also acts as a purge gas recovery unit as the entire loop purge is recycled to

this unit for hydrogen recovery as required. Purge gas from other existing ammonia units within

the complex can also be processed in this unit for increased ammonia production with minimal

added investment.




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During plant start-up, the Purifier can be cooled down during the same time period when the

synthesis converter is heated up. Operators of Purifier plants report that the Purifier does not

extend the total start-up time of the plant. During a short shutdown, the inventory of liquid

nitrogen in the Purifier will keep the system cold, allowing quick restart. If preferred any time,

ammonia plant can be operated in Purifier bypass mode.

High Production Rates through Extended End of Run & Turnaround Flexibility:

Unlike in conventional ammonia plants, purifier plant can maintain production rates with rising

methane slip from reformers or rising CO slip from shift converter as consequent rising inerts

(methane) in make-up gas are removed in the purifier cold box. This is possible only in Purifier

process where all the make-up gas to synloop is processed through the cold box. Production rates

are thus maintained through extended operations of catalysts to end of runs which benefits the

owner greatly on plant life cycle basis. It provides much needed flexibility in planning plant

turnaround. Such details are compared in an attached published paper

Efficient KBR synthesis Scheme:

Since the makeup gas from the Purifier contains no carbon oxides and water, which are poisons

to the synthesis catalyst, it can be directly fed to the converter, joining with the recycle gas. Also,

the make-up syngas has little inert with negligible CH4 which provides a low inert synthesis loop

with high partial pressure of reactants H2 and N2. This process scheme has two advantages.

First, refrigeration requirements will be lower than other schemes, in which the moisture

containing makeup gas is mixed with converter effluent to first pass through the chilling train

before going back to the converter.

Second, the ammonia converter capacity is increased because of lower ammonia content in the

feed as a result of mixing the ammonia free makeup gas with the recycle gas. The low inert level

in the makeup gas also permits operation of the synthesis loop at lower pressures for a given

level of refrigeration, saving syngas compressor power.

Due to very low inert contents in a syn-loop based on purifier process, loop pressure is

significantly lower and required conversion is achieved in a single converter using lesser

catalyst. Thus, efficient ammonia plant with lesser compression power is achieved with




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significantly less CAPEX. Attached published paper compares impact of make-up gas quality on

various types of syn-loops.

In the KBR synthesis scheme, ammonia synthesis is carried out in a single horizontal, three bed

converter.

Refrigeration in the synloop uses unitized chiller. This exchanger takes the place of several

refrigeration chillers and a recycle exchanger, thereby eliminating expensive high-pressure

piping and fittings and significantly reducing the pressure drop compared to the sum of

individual chiller pressure drops. The basic concept of this unit is the use of concentric tubes and

a compartmentalized shell to replace several equipment items with one. The converter effluent

flows through the annuli of the concentric tubes, with the recycle gas flowing through the inner

tubes. Refrigeration ammonia at four different temperatures and pressures boils on the shell side

in four compartments. Thus the converter effluent is simultaneously cooled by two media, the

recycle gas and ammonia refrigeration.

Due to highly pure synthesis loop makeup gas feed from the purifier, the life of the ammonia

synthesis catalyst is estimated as 18 years compared to only 10 years typical for that in the

conventional synthesis loop. Significantly higher catalyst life is typically found in purifier plants

in industry.

The synloop also incorporates high-pressure steam generation which improves overall heat

integration and improves energy efficiency by exporting steam for OSBL usage.

3.2 UREA UNIT- STAMICARBON

The Ammonia and CO2 from ammonia unit caters to Stamicarbon’s Urea melt of 3850 MTPD

which is based on the Pool Condenser Concept. Ammonia and carbon dioxide are introduced to

the high pressure synthesis using a high-pressure ammonia pump and a carbon dioxide

compressor. The ammonia then drives an ejector, which conveys a carbamate solution into the

pool condenser. In the high-pressure stripper, the carbon dioxide, entering the synthesis as a feed,

flows counter-current to the urea solution leaving the reactor. On the shell side, the high-pressure

stripper is heated with steam. The off-gas of the high-pressure stripper, containing the carbon

dioxide, together with the dissociated carbamate, is then fed into the pool condenser. In the pool




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condenser, ammonia and carbon dioxide are condensed to form carbamate, and a substantial part

of the conversion to urea is already established here. The heat released by condensation and

subsequent formation of carbamate is used to produce re-usable low-pressure steam.

After the pool condenser, the remaining gases and a urea carbamate liquid enter the vertical

reactor. Here, the final part of the urea conversion takes place. The urea solution then leaves the

top of the reactor (via an overflow funnel) before being introduced into the high-pressure

stripper. Ammonia and carbon dioxide conversions in the synthesis section of a Stamicarbon

carbon dioxide stripping plant are high, reducing the need for a medium pressure stage to recycle

any unconverted ammonia and carbon dioxide. As a result, the Stamicarbon CO2 stripping

process is the only commercial available process that does not require a medium-pressure

recirculation stage downstream from the high-pressure stripper. Gases leaving the reactor are fed

into the high-pressure scrubber. Here, the gases are washed with the carbamate solution from the

low-pressure recirculation stage. The enriched carbamate solution is then fed into the high-

pressure ejector and, subsequently, to the pool condenser. Inert gases, containing some ammonia

and carbon dioxide, are then released into the 4-bar absorber.

Low-pressure recirculation section

This stage recovers the ammonia and carbon dioxide still present in the urea solution coming

from the high-pressure stripper. Thanks to the low ammonia and carbon dioxide concentrations

in the stripped urea solutions, the Stamicarbon CO2 stripping process is the only process that

requires just one single low-pressure recirculation stage. Coming out of the stripper, the urea

solution is fed into the dissociation heater, where most of the ammonia and carbon dioxide are

removed. The heat required for this heater is derived from the condensation of the low-pressure

steam produced in the urea synthesis. The ammonia and carbon dioxide are then fed into the low-

pressure carbamate condenser, where they are condensed. Because the ratio between ammonia

and carbon dioxide in the recovered gases is optimal, the quantity of water needed to dilute the

resultant ammonium carbamate solution can be kept to a minimum, maximizing conversion

figures for the urea plant. The resultant carbamate solution is fed, via a high-pressure carbamate

pump, back to the synthesis as a scrubbing agent in the high-pressure scrubber.




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Before entering the urea solution tank, part of the water present in the urea solution is evaporated

by further preflashing in two steps (atmospheric and sub-atmospheric). The vent gas from the

recirculation stage is practically free from ammonia because it is scrubbed in an atmospheric

absorber.

Evaporation section

Waste-water treatment section before the entire urea production process is complete; the urea

solution present in the urea solution tank must be concentrated. The urea solution is therefore

sent to an evaporation section. The topology of this evaporation section depends on the applied

finishing section (prilling, granulation or pastillation). Depending on the requirements of the

finishing section, the evaporation section may, for example, consist of two consecutive

evaporators, where the water in the urea solution is evaporated under vacuum conditions. The

remaining urea melt has a urea concentration varying from 96 to 99.7wt%, depending on the

requirements of the downstream finishing section.

Waste-water treatment section

The process condensate coming from the evaporation section, together with other process

effluents such as sealing water from stuffing boxes, contains ammonia and urea. All of the

process condensate is collected in the ammonia water tank. From this tank, the water is fed to the

top part of the desorber. In the top part of the desorber, the bulk of ammonia and carbon dioxide

are stripped off from the water phase by using the off-gas from the bottom part of the desorber as

a stripping agent. The descending effluent still contains urea and some ammonia. To remove this

urea, this effluent is then fed to the hydrolyzer. The hydrolyzer is a liquid-filled column. In the

hydrolyser, the urea, at elevated pressure and temperature, is dissociated into ammonia and

carbon dioxide by the application of heat (steam) and retention time. The process condensate

feed is kept in counter-current contact with the steam in order to obtain extremely low urea

content in the hydrolyzer effluent. The remaining ammonia and carbon dioxide in the effluent of

the hydrolyzer are stripped off with steam at a reduced pressure in the bottom part of the

desorber. The off-gases leaving the top part of the Desorber are recycled to the synthesis section

after being condensed in the reflux condenser. The purity of the remaining water satisfies




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requirements for boiler feed water make-up or cooling water make-up - which means that

Stamicarbon urea plants do not produce a waste-water stream.

This is followed by the adiabatic expansion and MP section and prilling section. Steam and

condensate system ensure that overall energy consumption is optimized.

3.3 Offsites

Two ammonia storage tanks of storage capacity 15000 m3 and 5000 m3 along with the tank

manifold are envisaged in the north side of the complex. Waste water generated in the ammonia

and urea plants will be treated in the new ETP

3.4 CPP

New CPP of 29.1 MW (normal)/ 34.6 MW (max) (GTG + HRSG) will be installed.

4. HAZARDS ASSOCIATED WITH THE PROJECT

The new manufacturing facility handles various hazardous materials like Natural gas, Ammonia,

Carbon monoxide, carbon dioxide and various other hydrocarbons which have a potential to

cause fire, explosion and release/leakage of toxic chemicals may lead to major hazards.

There are various modes in which flammable and toxic chemicals can leak into atmosphere

causing adverse affects. It may be a small leak from gaskets of the flanged joints, failure of the

pipeline or even catastrophic failure of storage tanks.

4.1 CATEGORIES OF RISKS ASSOCIATED WITH THE COMPLEX

The manufacture of anhydrous liquid ammonia involves processing of hydrocarbons under high

temperature, high pressure conditions in the presence of various catalysts, chemicals etc. Typical

risks are as follows:

a) Ammonia Plant:

Fire / Explosion Risks

Glands/seal leaks in valves, pumps, compressors handling hydrogen, natural gas,

naphtha, synthesis gas etc. Hose/pipe failure, leakage from flanged joints carrying combustible gases, vapours,

liquids.




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High / Low Temperature Exposure Risks

Burns due to contact with hot surfaces of pipelines, equipments, etc. or leaking

steam lines, process fluids at high temperature. Frost bite due to contact with anhydrous liquid ammonia at -33 deg. C Burns due to contact with pyrophoric catalyst

Toxic Chemicals Exposure Risks

Asphyxia due to inhalation of simple asphyxiants like CO2 , N2, H2, CH4, naphtha

etc. and chemical asphyxiants like CO, NH3, Nickel carbonyl, V2O5, Hydrazine, NOx, SOx, H2S etc.

Acute toxicity due to inhalation of catalyst dusts containing heavy metals like Ni, Cr, CO, Mo, Fe, Zn, Alumina etc. and silica gel molecular sieves, insulation fibers/dusts.

Corrosive / Radioactive Chemicals Exposure Risks

Severe burns, damage to eyes, skin and body tissues due to contact with anhydrous

ammonia

b) Urea Plant

The manufacture of urea involves reaction of Ammonia and Carbon dioxide under high temperature & pressure and subsequent recovery and concentration of the solution at various pressure stages. Typical risks are as follows: Fire / Explosion Risks

Ammonia leaks from glands/ pump seals or flanged joints piping resulting in formation explosive mixtures in air. Accumulation of H2 may take place in HP Section in case CO2 purity from

Ammonia Plant is not within allowable limits. Ignition of this accumulated H2 can occur due to dissipation of static charge.

High / Low Temperature Exposure Risks

Refer to risks in Ammonia Plant


Asphyxia due to inhalation of simple Exposure risk asphyxiants like CO2, N2, chemical asphyxiant and ammonia. Solution of Urea, Ammonium carbamate and ammonium carbonate containing high NH3 content.

Irritation due to inhalation of urea dust. Corrosive / Radioactive Chemicals Exposure Risks

Severe burns, damage to eyes, skin and body tissues due to contact with anhydrous ammonia, conc. Urea and Ammonium carbamate solutions.

c) Power Plant

The captive Power Plant involves generation of steam in N.G./Naphtha-fired boilers and utilizing

the steam in Urea and Ammonia plants. Typical risks are as follows:




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Explosion and fire risks associated with storage and handling of B Class (Naphtha) and Natural gas handling pipelines (Refer off site Facilities).

Fire Box explosion in Boiler High / Low Temp. Exposure Risks

Burns due to contact with hot surfaces of pipelines, equipments, etc. or leaking steam lines

Toxic Chemical Exposure Risk

Asphyxia due to inhalation of SOX and NOx. Irritation due to inflammation caused by inhalation of Natural gas and the

Naphtha vapors

d) Offsite Facilities

The offsite facilities consist of integrated units for water and effluent treatment, inert gas

generation, cooling towers, storage of ammonia, supply / distribution of utilities like compressed

air, water, etc. Potential risks in the above offsite facilities are essentially on account of handling

of corrosive, toxic and reactive chemicals as well as inflammable petroleum products.


Gland / Seal leaks in valves, pumps, compressor, handling naphtha, N.G., ammonia hydrogen, syngas etc.

Hose / pipe failure, leakage from flanged joints in pipes conveying petroleum products, ammonia, hydrogen, syngas, etc.

Leakage of petroleum products during tanker unloading operations Overheating / pressurization of storage tanks Improper earthing/ lightning protection of storage tanks and pipelines Improper sealing of floating roof tanks In adequate / improper breather valves leading to tank failures.

High / Low Temp. Exposure Risks

Burns due to contact with hot surfaces of pipe lines, equipments, etc or leaking steam lines.

Heat radiation burns from high intensity flames from the flare stack. Frost bite due to contact with anhydrous liquid ammonia at – 33 °C


Asphyxia due to inhalation of simple asphyxiants like N2, H2, Naphtha, etc. and Chemical asphyxiants like Cl2, NH3, NOx, Sox, etc.

Toxicity due to inhalation of catalyst dust containing heavy metals like Ni, Pd, Alumina etc. and perlite / insulation fibers, silica gel dust

Corrosive Chemicals Exposure Risks

Severe burners, damage to eyes, skin & body tissues due to contact with corrosive chemicals like anhydrous liquid Ammonia, Sulphuric acid, Hydrochloric acid, etc.

NOTE: All the above categories have been listed for representative purpose only. Risk

study will not be carried out for all the cases




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4.2 HAZARDS ASSOCIATED WITH MATERIALS HANDLED

AMMONIA:

It is a colorless gas with a sharp, strong odor similar to “smelling salts” which is readily

detectable at 20 ppm and is highly toxic gas, its IDLH being 300 ppm. It is also a combustible

gas which can explode under certain circumstances, although its lower explosive limit is rather

high being of the order of 16%. Anhydrous Ammonia is an irritating, flammable, and colorless

liquefied compressed gas packaged in cylinders under its own vapor pressure of 114 psig at 70oF.

Ammonia can cause severe eye, skin and respiratory tract burns and is severely irritating to nose,

throat, and lungs. Vapor contact may cause irritation and burns. Contact with liquid may cause

freezing of the tissue accompanied by corrosive caustic action and dehydration. Ammonia

Overexposure may also cause central nervous system effects including unconsciousness and

convulsions.

CARBON MONOXIDE:

Carbon monoxide is a poisonous, flammable and odorless high-pressure gas which acts on blood,

causing damage to central nervous system (CNS) and could be fatal even with adequate oxygen.

It can form explosive mixtures with air at 12.5-74% concentration. Self-contained breathing

apparatus must be worn by rescue workers. Depending on the concentration and duration of

exposure, inhalation may cause headache, drowsiness, dizziness, excitation, rapid breathing,

pallor, cyanosis, excess salivation, nausea, vomiting, hallucinations, confusion, angina,

convulsions, and unconsciousness. IDLH of CO is 1200 ppm.

The binding of CO with hemoglobin producing decreasing the oxygen carrying capacity of

blood, this is appear to be the principle mechanism of the toxic action of low-level carbon

monoxide exposure. Carbon monoxide reduces blood oxygen- carrying capacity, causing

dizziness, weakness and headache. Concentrations above 1000 ppm can be fatal within one hour.

UREA:

Urea is a colorless to white, prismatic crystals or white crystalline powder. It is almost odorless,

may gradually develop slight odor of ammonia, especially in the presence of moisture. It has a

saline cooling taste and melting point of 132.7o C.




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It causes redness and irritation of skin and eyes. Adverse reactions include headache, nausea,

vomiting, syncope, disorientation, transient confusion and electrolyte depletion (hyponatremia

and hypokalemia). Urea is irritating to tissues, it causes pain at site of infusion and necrosis may

result if extravasations occur.

Urea is artificially released to the environment through direct application to soil as a nitrogen-

released fertilizer. If released to the atmosphere, urea will degrade rapidly in the vapour phase by

reaction with photo-chemically produced hydroxyl radicals. If released to soil, urea is hydrolyzed

to ammonium through soil urease activity. The rate of hydrolysis can be fast (24 hrs), however, a

number of variables (such as increasing the pellet size of the fertilizer) can decrease the

degradation rate from days to weeks. If released to water, urea can degrade readily through biotic

hydrolysis. The presence of naturally- occurring phytoplankton increases the degradation rate

because phytoplankton use urea as a nitrogen source and because urea is decomposed by

phytoplankton photosynthesis. Degradation of urea occurs much faster in sunlight than in dark

water. Biodegradation is expected to be the major fate process in the aquatic ecosystem. Urea

can biodegrade readily with the release of CO2 and ammonia.

NATURAL GAS

Sudden release of gas under pressure can cause a physical explosion with material in the vicinity

of failure (soil) hurling in all directions. Accidental release of gases from a high-pressure source

usually results in a turbulent jet. If ignited, this would form a jet flame. Such a flame

impingement causes structural weakness and in turn can cause extensive damage and failure.

Thermal radiation due to jet fire can cause various degrees of burns on human body and would

pose a potential radiation hazard. Moreover, their effects on inanimate objects like equipment,

piping or vegetation also need to be evaluated to assess the impact.

Low pressure vapour release or impinged release will normally spread out in the direction of

wind. If it finds an ignition source before being dispersed below Lower Flammability Limit

(LFL), a flash fire is likely to occur and the flame may travel back to source of leak. Any person

caught in the flash fire is likely to suffer fatal burn injury. In consequence analysis the distance to

LFL value is usually taken to indicate the area, which may be affected by flash fire. Any other

combustible materials within the flash fire distance are also likely to catch fire and secondary fire




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may ensue. In the area close to source of hydrocarbon leak, there is a possibility of oxygen

depletion.

5. HAZARD IDENTIFICATION

5.1 Failure Mode Analysis

There are various modes in which flammable and toxic chemicals can leak into atmosphere causing

adverse affects. It may be small leaks from gaskets of the flanged joints, or guillotine failure of a pipeline

of even catastrophic failure of the storage tank. Some typical modes of failures and their possible causes

are discussed below:

S. No Failure Mode Probable Cause Remarks

1.

Flange /

Gasket failure

Incorrect gasket Incorrect

installation.

Attention to be paid during selection

and installation of gaskets.

2. Weld failure It is normally due to poor quality

of welds

Welding to be done by certified

welders with right quality of

welding rods. Inspection and

radiography must also be done.

3. Pipe corrosion

erosion or

failure due to

stress

Sometimes fabrication or

installation leaves stress in the

pipes. Erosion or corrosion also is

sometimes the cause.

Pipes material of construction

should be selected correctly. Design

should take care of erosion effects.

And installation of pipes should not

leave any stress.

4. Over

pressurization

of pipeline

Over pressurization can occur due

to failure of SRV or incorrect

operation.

Necessary procedures should be

there to prevent.

5. Deficient

installation of

pipes

Pipes design and installation is

sometimes not as per appropriate

standard.

It must be ensured that installation is

as per correct standards completely.

6. Leaks from

valve

Leaks from glands, bonnets or

failures valves spindle is

Right selection of valves and their

maintenance should be ensured.




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sometimes the cause.

7. Instruments

failure

Multifarious instruments are used

for control of process parameters.

Any such instrument failure can

cause mishap.

Reliability of instruments working

must be ensured through proper

selection and maintenance.

8. Failures of

protective

system

Protective system like SRV,

bursting discs, vent header, drain

lines etc. are provided to take care

of abnormal conditions.

Reliability of protective system must

be ensured highest through

inspection and proper maintenance.

9. Operational

effort

Plant operational parameters

should not be exceeded beyond

the permissible limits.

Operating procedures must be

complete and strictly followed.

10.

Other failures There are external other reasons

causing the failures.

Design and operating philosophy

must consider all possible reasons.

5.2 GENERAL

Identification of hazards is of primary significance in the analysis. A classical definition of

hazard states that hazard is the characteristic of system/plant/process that presents potential for

an accident. Hence all the components of a system/plant/process need to be thoroughly examined

in order to assess their potential for initiating or propagating an unplanned event/sequence of

events, which can be termed as an accident.

In Risk Assessment terminology a hazard is something with the potential to cause harm. Hence

the Hazard Identification step is an exercise that seeks to identify what can go wrong at the major

hazard installation or process in such a way that people may be harmed. The output of this step is

a list of events that need to be passed on to later steps for further analysis.

The potential hazards posed by the facility were identified based on the past accidents, lessons

learnt and a checklist method. This list includes the following elements.

• Catastrophic rupture of pressure vessel.




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• “Guillotine-Breakage” of pipe-work

• Small hole, cracks or instrument tapping failure in piping and vessels.

• Flange leaks.

• Leaks from pump glands and similar seals.

5.3 MODES OF FAILURE

There are various potential sources of large leakage, which may release hazardous chemicals and

hydrocarbon materials into the atmosphere. These could be in form of gasket failure in flanged

joints, bleeder valve left open inadvertently, instrument tubing giving away, pump seal failure,

guillotine failure of equipment/ pipeline or any other source of leakage. Operating experience

can identify lots of these sources and their modes of failure. A list of general equipment and

pipeline failure mechanisms is as follows:

Material/Construction Defects

• Incorrect selection or supply of materials of construction

• Incorrect use of design codes

• Weld failures

• Failure of inadequate pipeline supports

Pre-Operational Failures

• Failure induced during delivery at site

• Failure induced during installation

• Pressure and temperature effects

• Overpressure

• Temperature expansion/contraction (improper stress analysis and support design)




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• Low temperature brittle fracture (if metallurgy is incorrect)

• Fatigue loading (cycling and mechanical vibration)

Corrosion Failures

• Internal corrosion (e.g. ingress of moisture)

• External corrosion

• Cladding/insulation failure (e.g. ingress of moisture)

• Cathodic protection failure, if provided

Failures due to Operational Errors

• Human error

• Failure to inspect regularly and identify any defects

External Impact Induced Failures

• Dropped objects

• Impact from transport such as construction traffic

• Vandalism

• Subsidence

• Strong winds

Failure due to Fire

• External fire impinging on pipeline or equipment

• Rapid vaporization of cold liquid in contact with hot surfaces

5.4 SELECTED FAILURE CASES




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A list of selected failure cases was prepared based on process knowledge, engineering judgment,

experience, past incidents associated with such facilities and considering the general mechanisms

for loss of containment. A list of cases has been identified for the consequence analysis study

based on the following.

• Cases with high chance of occurrence but having low consequence:

Example of such failure cases includes two-bolt gasket leak for flanges, seal failure for pumps,

sample connection failure, instrument tapping failure, drain/vent failure etc. The consequence

results will provide enough data for planning routine safety exercises. This will emphasize the

area where operator's vigilance is essential.

• Cases with low chance of occurrence but having high consequence (The example

includes catastrophic failure of lines, process pressure vessels, pressurized storages etc.)

This approach ensures at least one representative case of all possible types of accidental failure

events, is considered for the consequence analysis. Moreover, the list below includes at least one

accidental case comprising of release of different sorts of highly hazardous materials handled in

the onshore oil/gas production facilities. Although the list does not give complete failure

incidents considering all equipments, units, but the consequence of a similar incident considered

in the list below could be used to foresee the consequence of that particular accident.




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Selected failure cases and likely consequences) outlines the failure cases those selected for

facilities of onshore oil/gas production facilities at Ramagundam Fertilizer Complex:

S. No Equipment Failure case Associated hazards

Ammonia Unit

1. NG at B/L Instrument tapping failure, 20 mm

Flammable

2. NG Compressor Discharge Instrument tapping failure, 20 mm Flammable

3. HTS Effluent Large hole in bottom, 50 mm Flammable/ Toxic

4. Converter effluent Catastrophic Failure Flammable/ Toxic

5. HP ammonia scrubber vapour Instrument tapping failure, 20 mm Flammable/ Toxic

6.

Process condensate Instrument tapping failure, 20 mm Toxic

7. Large hole in bottom, 50 mm Toxic

8. HP Ammonia scrubber liquid

Large hole in bottom, 50 mm Flammable/ Toxic

9. Catastrophic failure Flammable/ Toxic

Urea Plant

10. Ammonia at B/L Instrument tapping failure, 20 mm Flammable/ Toxic

11.

HP Ammonia pump 10 mm failure Flammable/ Toxic

12. Instrument tapping failure, 20 mm Flammable/ Toxic

13. Reactor Large hole in bottom, 50 mm Flammable/ Toxic

14. HP Carbamate pump Pump seal failure, 10 mm Flammable/ Toxic

CPP

15. Gas Turbine generator Instrument tapping failure, 20 mm Flammable




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S. No Equipment Failure case Associated hazards

Offsites

16.

Ammonia Storage Tank Tank Manifold leak Flammable/ Toxic

17. Tank on Fire Flammable

6. CONSEQUENCE ANALYSIS

The Risk assessment study has been carried out using the risk assessment software program

‘PHAST’ ver. 7.0 developed by DNV.

Consequence analysis involves the application of the mathematical, analytical and computer

models for calculation of the effects and damages subsequent to a hydrocarbon / toxic release

accident.

Computer models are used to predict the physical behavior of hazardous incidents. The model

uses below mentioned techniques to assess the consequences of identified scenarios:

• Modeling of discharge rates when holes develop in process equipment/pipe work

• Modeling of the size & shape of the flammable/toxic gas clouds from releases in the

atmosphere

• Modeling of the flame and radiation field of the releases that are ignited and burn as jet

fire, pool fire, flash fire and fire ball.

• Modeling of the explosion fields of releases which are ignited away from the point of

release

The different consequences (Flash fire, pool fire, jet fire and Explosion effects) of loss of

containment accidents depend on the sequence of events & properties of material released

leading to the either toxic vapor dispersion, fire or explosion or both.




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6.1 CONSEQUENCE ANALYSIS MODELLING

DISCHARGE RATE

The initial rate of release through a leak depends mainly on the pressure inside the equipment,

size of the hole and phase of the release (liquid, gas or two-phase). The release rate decreases

with time as the equipment depressurizes. This reduction depends mainly on the inventory and

the action taken to isolate the leak and blow-down the equipment.

DISPERSION

Releases of gas into the open air form clouds whose dispersion is governed by the wind, by

turbulence around the site, the density of the gas and initial momentum of the release. In case of

flammable materials the sizes of these gas clouds above their Lower Flammable Limit (LFL) are

important in determining whether the release will ignite. In this study, the results of dispersion

modeling for flammable materials are presented LFL quantity.

FLASH FIRE

A flash fire occurs when a cloud of vapors/gas burns without generating any significant

overpressure. The cloud is typically ignited on its edge, remote from- the leak source. The

combustion zone moves through the cloud away from the ignition point. The duration of the

flash fire is relatively short but it may stabilize as a continuous jet fire from the leak source. For

flash fires, an approximate estimate for the extent of the total effect zone is the area over which

the cloud is above the LFL.

JET FIRE

Jet fires are burning jets of gas or atomized liquid whose shape is dominated by the momentum

of the release. The jet flame stabilizes on or close to the point of release and continues until the

release is stopped. Jet fire can be realized, if the leakage is immediately ignited. The effect of jet

flame impingement is severe as it may cut through equipment, pipeline or structure. The damage

effect of thermal radiation is depended on both the level of thermal radiation and duration of

exposure.




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POOL FIRE

A cylindrical shape of the pool fire is presumed. Pool-fire calculations are then carried out as

part of an accidental scenario, e.g. in case a hydrocarbon liquid leak from a vessel leads to the

formation of an ignitable liquid pool. First no ignition is assumed, and pool evaporation and

dispersion calculations are being carried out. Subsequently late pool fires (ignition following

spreading of liquid pool) are considered. If the release is bunded, the diameter is given by the

size of the bund. If there is no bund, then the diameter is that which corresponds with a minimum

pool thickness, set by the type of surface on which the pool is spreading.

VAPOR CLOUD EXPLOSION

A vapor cloud explosion (VCE) occurs if a cloud of flammable gas burns sufficiently quickly to

generate high overpressures (i.e. pressures in excess of ambient). The overpressure resulting

from an explosion of hydrocarbon gases is estimated considering the explosive mass available to

be the mass of hydrocarbon vapor between its lower and upper explosive limits.

BOILING LIQUID EXPANDING VAPOUR EXPLOSION (BLEVE)

BLEVE occur when pressurized vessels containing volatile liquids, in particular liquefied gases,

are engulfed by external fires causing catastrophic rupture of the vessel and the formation of a

disastrous fireball.

TOXIC RELEASE

The aim of the toxic risk study is to determine whether the operators in the plant, people

occupied buildings and the public outside are likely to be affected by toxic substances. Toxic gas

cloud e.g. H2S, chlorine, Benzene etc is undertaken to the Immediately Dangerous to Life and

Health concentration (IDLH) limit to determine the extent of the toxic hazard created as the

result of loss of containment of a toxic substance.

6.2 SIZE AND DURATION OF RELEASE

Leak size considered for selected failure cases are listed below




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Leak Size for selected failure scenario

Pump seal/ Flange gasket failure 10 mm hole size

Instrument tapping failure 20 mm hole size

Large hole 50 mm, complete rupture of 2” drain line

Catastrophic failure Complete rupture of pressure vessels

The discharge duration is taken as 10 minutes for continuous release scenarios as it is considered

that it would take plant personnel about 10 minutes to detect and isolate the leak.

Ref [5] AICHE, CCPS, Chemical process Quantitative Risk Analysis

6.3 DAMAGE CRITERIA DUE TO VARIOUS SCENARIOS

In order to appreciate the damage effect produced by various scenarios, physiological/physical

effects of the blast wave, thermal radiation or toxic vapor exposition are discussed.

LFL OR FLASH FIRE

Hydrocarbon vapor released accidentally will spread out in the direction of wind. This mixture

(hydrocarbon and air) finds an ignition source before being dispersed below lower flammability

limit (LFL), a flash fire is likely to occur and the flame will travel back to the source of leak.

Any person caught in the flash fire is likely to suffer fatal burn injury. Therefore, in consequence

analysis, the distance of LFL value is usually taken to indicate the area, which may be affected

by the flash fire.

Flash fire (LFL) events are considered to cause direct harm to the population present within the

flammability range of the cloud. Fire escalation from flash fire such that process or storage

equipment or building may be affected is considered unlikely.




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THERMAL HAZARD DUE TO POOL FIRE, JET FIRE AND FIRE BALL

Thermal radiation due to pool fire, jet fire or fire ball may cause various degrees of burn on

human body and process equipment. Table 7.4-2 tabulates the damage effect due to thermal

radiation intensity.

Damage due to incident thermal radiation intensity

Incident radiation intensity

(KW/m²) Type of damage

37.5 Sufficient to cause damage to process equipment

32.0 Maximum flux level for thermally protected tanks

containing flammable liquid

12.5 Minimum energy required for piloted ignition of wood,

melting of plastic tubing etc.

8.0 Maximum heat flux for un-insulated tanks

4.0

Sufficient to cause pain to personnel if unable to reach cover

within 20 seconds. However blistering of skin (1st degree

burns) is likely.

The hazard distances to the 37.5 kW/m2, 32 kW/m2, 12.5 kW/m2, 8 kW/m2 and 4 kW/m2

radiation levels, selected based on their effect on population, buildings and equipment were

modeled using PHAST.

VAPOR CLOUD EXPLOSION:

In the event of explosion taking place within the plant, the resultant blast wave will have

damaging effects on equipment, structures, building and piping falling within the overpressure

distances of the blast. Tanks, buildings, structures etc. can only tolerate low level of

overpressure. Human body, by comparison, can withstand higher overpressure. But injury or




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fatality can be inflicted by collapse of building of structures. Table 7.4-3 illustrates the damage

effect of blast overpressure.

Damage Effects of Blast Overpressure

Blast Overpressure (psi) Damage Level

5.0 Major structure damage (assumed fatal to people inside

building or within other structures)

3.0 Oil storage tank failure

2.5 Eardrum rupture

2.0 Repairable damage, pressure vessels remain intact, light

structures collapse

1.0 Window pane breakage possible, causing some injuries

The hazard distances to the 5 psi, 3 psi and 2 psi overpressure levels, selected based on their

effects on equipment, buildings and population were modeled using PHAST.

TOXIC HAZARD:

The inhalation of toxic gases can give rise to effects, which range in severity from mild irritation

of the respiratory tract to death. Lethal effects of inhalation depend on the concentration of the

gas to which people are exposed and on the duration of exposure. Mostly this dependence is

nonlinear and as the concentration increases, the time required to produce a specific injury

decreases rapidly.

The hazard distances to Immediately Dangerous to Life and Health concentration (IDLH) limit is

selected to determine the extent of the toxic hazard created as the result of loss of containment of

a toxic substance.




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6.4 HAZARD ASSESSMENT:

Natural Gas line Instrument tapping failure at B/L

Weather

Jet Fire radiation (kW/m2)

Distance, m

Overpressure (psi)

distances, m

Toxic front

distance, m

4 12.5 37.5 2 3 5

1F 24.88 19.77 15.53 36.36 34.92 33.6 -

2D 24.91 19.89 15.71 26 24.65 23.4 -

In order to find out the major consequences due to flammable effects of natural gas in the unit

battery limit, instrument tapping failure in the natural gas line is considered for study. The

thermal radiation due to jet fire of 37.5kW/m2 is limited to 16m around the battery limit. The

overpressure distances suggest that the blast pressure of 5 psi would extend up to a distance

within 34 m but the effect is well within the complex.

NG Compressor Discharge Instrument tapping failure

Weather

Pool Fire radiation (kW/m2) Distance, m

Overpressure (psi) distances, m

Toxic front distance, m

4 12.5 37.5 2 3 5

1F 24.62 19.56 15.33 26.24 24.82 23.54 -

2D 24.64 19.68 15.52 25.94 24.59 23.37 -

In order to find out the major consequences due to flammable effects of natural gas in the unit,

instrument tapping failure in the natural gas compressor discharge line is considered for study.

The thermal radiation due to jet fire of 37.5kW/m2 is limited to 16m radius. The overpressure

distances suggest that the blast pressure of 5 psi could extend up to a distance of 24 m but the

effect is well within the complex.

HTS Effluent Large hole in bottom, 50 mm




Doc No.: A512-04-41-RRA-0001

Rev. No: A

Weather


Distance, m

Overpressure (psi)

distances, m

Toxic (NH3) front

distance, m

4 12.5 37.5 2 3 5 IDLH=300 ppm

1F 13.43 7.8 0 35.75 29.09 26.66 10.83

2D 13.64 8.1 0 30.16 27.86 25.762 16.43

In order to find out the major consequences due to flammable and toxic effects of ammonia in

the HTS section, large hole in HTS effluent bottom line is considered for study. The thermal

radiation due to jet fire of 12.5kW/m2 is limited to 8m radius. The overpressure distances

suggest that the blast pressure of 5 psi could extend up to a distance of 27 m but the effect is well

within the complex. The toxic front gets diluted very quickly after reaching a distance of 17m.

Process condensate large hole in bottom

Weather

Jet Fire radiation (kW/m2) Distance, m


Toxic (CO) front distance, m

4 12.5 37.5 2 3 5 IDLH=1200 ppm

1F 18.5 12.45 2.42 160.1 155.55 151.39 1099

2D 18.65 12.7 2.51 102.78 99.89 97.246 673

In order to find out the flammable and toxic effects of CO in the unit, large hole in the process

condensate line is considered for study. The thermal hazard due to jet fire radiation of 37.5

kW/m2 shows that the effect is limited within a diameter of 20m and within the unit. The

overpressure distances suggest that the blast pressure of 5 psi could extend up to a distance

within 150m radius but the effect is well within the complex. The toxic front travels a long way

during 1F condition when compared to 2D, extending its effect outside the complex.




Doc No.: A512-04-41-RRA-0001

Rev. No: A

HP Ammonia scrubber liquid large hole in bottom

Weather


Distance, m

Overpressure (psi)

distances, m

Toxic (NH3) front

distance, m

4 12.5 37.5 2 3 5 IDLH=300 ppm

1F 269 235 - 203 195.5 188.75 3939

2D 255 221 - 190 183.5 177.2 3779

In order to find out the flammable and toxic effects of ammonia in the Ammonia recovery unit,

large hole in the HP Ammonia Scrubber liquid line is considered for study. The thermal hazard

due to jet fire radiation is limited within the range of 12.5kW/m2 and the effect is seen outside

the unit but well within the complex. The overpressure distances suggest that the blast pressure

of 5 psi could extend up to a distance within 188 m radius but the effect is well within the

complex. The toxic front travels a long way extending its effect way outside the complex.

Because of the pressure of ammonia released, the toxic vapors travel a long way extending its

effect outside the complex.

Catastrophic failure of HP Ammonia scrubber

Weather

Overpressure (psi) distances, m Toxic (NH3) front distance,

m

2 3 5 IDLH=300 ppm

1F 231.122 192.39 156.99 6672

2D 231.35 192.57 157 2417


the Ammonia recovery unit, catastrophic failure of HP Ammonia Scrubber line is considered for

study. The overpressure distances suggest that the blast pressure of 5 psi could extend up to a

distance within 177 m but the effect is well within the complex. The toxic front travels a long

way during 1F condition when compared to 2D, extending its effect way outside the complex.

Because of the pressure of ammonia and amount of inventory released, the toxic vapors travel a

long way extending its effect outside the complex.




Doc No.: A512-04-41-RRA-0001

Rev. No: A

Instrument tapping failure of Ammonia line at B/L

Weather


Distance, m

Overpressure (psi)

distances, m

Toxic (NH3) front

distance, m

4 12.5 37.5 2 3 5 IDLH=300 ppm

1F 84.31 73.33 - 24.79 23.71 22.72 1528

2D 79.6 69.30 - 24.63 23.58 22.62 1085


the battery limit, instrument tapping failure on Ammonia line is considered for study. The

thermal hazard due to jet fire radiation is limited within the range of 12.5kW/m2 and the effect is

seen outside the unit but well within the complex. The overpressure distances suggest that the

blast pressure of 5 psi could extend up to a distance within 23 m but the effect is well within the

unit. The toxic front travels a long way during 1F condition when compared to 2D, extending its

effect outside the complex. Because of the pressure of ammonia released, the toxic vapors travel

a long way extending its effect outside the complex.

HP Ammonia pump 10 mm failure

Weather


Distance, m

Overpressure (psi)

distances, m

Toxic (NH3) front

distance, m

4 12.5 37.5 2 3 5 IDLH=300 ppm

1F 64.17 55.70 - 13.5 12.71 11.98 1289.45

2D 60.55 52.74 - 13.37 12.6 11.9 869

In order to find out the consequences due to minor leaks in ammonia, 10 mm failure of HP

Ammonia pump is considered for study. The thermal hazard due to jet fire radiation is limited

within the range of 12.5kW/m2 and the effect is seen a little outside the unit but well within the

complex. The overpressure distances suggest that the blast pressure of 5 psi could extend up to a

distance within 12 m but the effect is well within the unit. The toxic front travels a long way

during 1F condition when compared to 2D, extending its effect outside the complex. Because of

the pressure of ammonia released, the toxic vapors travel a long way extending its effect outside

the complex.




Doc No.: A512-04-41-RRA-0001

Rev. No: A

HP Ammonia pump Instrument tapping failure

Weather


Distance, m

Overpressure (psi)

distances, m

Toxic (NH3) front

distance, m

4 12.5 37.5 2 3 5 IDLH=300 ppm

1F 119 104 - 37.1 35.1 34 2259.6

2D 112 98 - 36.88 35.3 33.9 2001


the HP Ammonia section in urea plant, instrument tapping failure on Ammonia line is considered

for study. The thermal hazard due to jet fire radiation is limited within the range of 12.5kW/m2

and the effect is seen outside the unit but well within the complex. The overpressure distances

suggest that the blast pressure of 5 psi could extend up to a distance within 34 m but the effect is

well within the unit. The toxic front travels a long way during 1F condition when compared to

2D, extending its effect outside the complex. Because of the pressure of ammonia released, the

toxic vapors travel a long way extending its effect outside the complex.

Large hole in bottom of the Reactor

Weather

Pool Fire radiation (kW/m2)

Distance, m

Overpressure (psi)

distances, m

Toxic (NH3) front

distance, m

4 12.5 37.5 2 3 5 IDLH=300 ppm

1F - - - - - - 331.95

2D - - - - - - 274.96


the reactor, 50 mm large hole in the synthesis reactor is considered for study. The released

mixture because of the high temperature in the reactor flashes and disperses quickly reducing the

toxic front, limiting its effect within the complex.




Doc No.: A512-04-41-RRA-0001

Rev. No: A

Instrument tapping failure of HP Carbamate pump discharge line

Weather


Distance, m

Overpressure (psi)

distances, m

Toxic (NH3) front

distance, m

4 12.5 37.5 2 3 5 IDLH=300 ppm

1F 84 - - - - - 1581

2D 79 - - - - - 1417

In order to find out the toxic consequences of ammonia in the recirculation section, instrument

tapping failure in HP Carbamate pump discharge line is considered for study. Ammonia because

of the high pressure release carries the toxic front to longer distances, in this case outside the

complex.

Instrument tapping failure, 20 mm of Gas Turbine generator

Weather

Pool Fire radiation (kW/m2)

Distance, m

Overpressure (psi)

distances, m

Toxic front

distance, m

4 12.5 37.5 2 3 5

1F 24.88 19.77 15.53 36.36 34.92 33.61 -

2D 24.91 19.90 15.72 26 24.65 23.40 -

The consequences due to minor to major leaks of natural gas in the power plant are studied

considering an instrument tapping failure in the GTG discharge line. The thermal hazard due to

jet fire radiation is limited to a distance of 16 m. The overpressure distances suggest that the blast

pressure of 5 psi could extend up to a distance within 34 m but the effect is well within the plant.




Doc No.: A512-04-41-RRA-0001

Rev. No: A

Tank Manifold leak of Ammonia Storage tank

Weather


Distance, m

Overpressure (psi)

distances, m

Toxic (NH3) front

distance, m

4 12.5 37.5 2 3 5 IDLH= 300 ppm

1F 103.34 87.74 - 60.93 58.46 56.2 1691

2D 92.71 82.76 - 59.93 57.68 55.63 1033

The consequences due to minor to major leaks of ammonia in the offsite storage facilities are

studied considering an instrument tapping failure in the tank manifold. The thermal hazard due to

jet fire radiation is limited within the range of 12.5kW/m2 and the effect is seen to a distance of

88 m. This being affecting the storage tank area, it has to be ensured that the tanks are properly

insulated. The overpressure distances suggest that the blast pressure of 5 psi could extend up to a

distance within 56 m but the effect is well within the unit. The toxic front travels a long way

during 1F condition when compared to 2D, extending its effect outside the complex. Because of

the pressure of ammonia released, the toxic vapors travel a long way extending its effect outside

the complex.

Ammonia Storage tank on fire

The consequences due to major fire in ammonia storage tanks in the offsite storage facilities are

studied considering a tank on failure. The thermal hazard due to pool fire radiation of range of 32

kW/m2 is seen to a distance of 32 m. Ammonia stored at refrigerated conditions vaporizes at

ambient temperature the moment it comes outside.

In the case of catastrophic rupture of the storage tank a large amount of liquid ammonia would

get released. The foundation of the storage tank rests on pipes. The released ammonia liquid

Weather

Pool Fire radiation (kW/m2) Distance, m


Toxic front distance, m

4 8 32 2 3 5

1F X X 18

NA NA NA NA

2D X X 24

NA NA NA NA




Doc No.: A512-04-41-RRA-0001

Rev. No: A

would flow underneath the storage tank and surrounding dyke area. It is considered that the dyke

is leak proof and the entire contents of the tank be held within the dyke and the pit underneath

the tank in the event of catastrophic rupture of the tank. The presence of the dyke confines the

liquid ammonia within the dyke area.

As the liquid from the ruptured tank falls on the dyke at its boiling point and evaporates, the

release of ammonia vapor becomes continuous till the time the liquid inventory becomes

exhausted or the boil-off of the ammonia is terminated by external protective actions. The

vaporized ammonia would then form a cloud, which being heavier than air would travel along

the ground.

7. CONCLUSIONS AND RECOMMENDATIONS

i. As discussed in SECTION- 8, the risk level emanating from the fertilizer complex on

account of large holes (50 mm leaks) and rupture of vessel extend beyond the complex

limit. The level of individual risk of fatality would be considerably larger on the outside

than the inside of the complex. Hence to reduce the risk level outside the complex, it is

recommended to provide water curtains at strategic location facing the villages outside

the complex. The location can be near units handling toxic chemicals like Ammonia unit,

urea unit, and ammonia storage tank area. This should be operable from both local and

remote in case of emergency. The idea of the curtain is to arrest/dilute the toxic vapor

release from different sources inside the complex itself. Adequate contingency planning

should be devised and put into effect in case of any major hazardous release as the curtain

provided might not be 100% sufficient.

ii. Implement and maintain a specific Emergency (Disaster) Management Plan providing

guidance on emergency measures to protect both operators and local communities in the

event of toxic ammonia releases extending outside the complex.

iii. Disaster management plan has to be designed for the scenarios where the effect goes

outside the complex envisaging the risk involved and all plant personnel should be aware

of the same

iv. Early detection and warning system should be provided in the event of leak so that people

can move indoors, close doors, windows and ventilation to reduce chances of exposure of

high ammonia concentration and escape dreadful injury.




Doc No.: A512-04-41-RRA-0001

Rev. No: A

v. Adequate wind socks should be provided at strategic locations to notify people of the

wind direction so that they can escape accordingly in case of emergency.

vi. Ramagundam Fertilizer complex does not cause any domino effect on nearby industrial

equipment as the major hazards are mainly due to toxic release.

vii. Equipment failures can be prevented by adequate design, good operating and

maintenance practices etc. Frequency of testing of equipment has a great role in reducing

failure frequency. Higher the frequency, greater the reliability.

viii. Corrosion monitoring of piping and equipment should be done periodically to forewarn

against possible failures and plant preventive maintenance. It is advisable to keep updated

with the latest corrosion prevention and maintenance techniques.

ix. The acceptable individual risk to plant personnel is apparently higher than to public as

plant personnel are involved in daily operations, maintenance and emergency situations.

However, Ramagundam Fertilizer should endeavor to adopt all safe practices and

conform to regulations to keep the accident frequency at the minimum.

x. Ramagundam Fertilizer with the help of local authorities should check and prevent the

population growth around the plant boundary especially on the eastern and northern side.

xi. It is highly recommended to provide gas detectors along with emergency alarm wherever

applicable.

xii. Location of manning stations like operator cabin, sub station, control room etc. have to

decided in compliance with the safety regulations, standards and specifications as

applicable

xiii. Positive pressurization of the control room and other building and keeping them airtight to prevent the entry of toxic gases.

xiv. Ammonia detectors to be provided at the inlet of HVAC system to automatically shutdown the HVAC air intake and close fresh air suction dampers.

xv. Provide an alternative breathing air system within the control room for actuation in the event of major ammonia leaks in the facility.

xvi. Urea plant should be provided with prilling towers based on natural draft so as to

minimize urea dust emissions.

xvii. Use refrigerated storage for large quantities of liquid ammonia since the initial release of

ammonia in the case of atmospheric storage is slower than in case of pressurized

ammonia storage systems




Doc No.: A512-04-41-RRA-0001

Rev. No: A

xviii. Catastrophic failure of storage tank is unforeseen since the tank is a double containment

construction wherein outer shell is also designed for retention of the liquid content in the

event of inner shell failure. Assuming proper safety instrumented functions are applied to

this system, catastrophic failure is a remote possibility. Possible causes that could lead to

catastrophic rupture are natural disaster like earthquakes or any acts of extreme terrorism.

xix. In case of any sabotage act like terrorism or hostile conditions like war, etc., it is

recommended that the security be tightened around the plant and the ammonia stock

should be kept as minimum as possible.

xx. All plant personnel should be made well aware of TRAINING IN FIRE FIGHTING &

SAFETY AND OHSAS-18001

xxi. Provision of muster locations at different locations with suitable protection means (e.g.

enclosed areas designed to protect people against a toxic gas cloud)

.

8. GLOSSARY

CASUALTY:

Someone who suffers serious injury or worse i.e. including fatal injuries. As a rough guide

fatalities are likely to be half the total casualties. But this may vary depending on the nature of

the event.

HAZARD A chemical or physical condition with the potential of causing damage.

FLAMMABILITY LIMITS in fuel-air systems, a range of compositions exists inside which a

(UFL – LFL) flame will propagate substantial distance from an ignition source. The limiting fuel

concentrations are termed as Upper flammability or explosives limit (Fuel concentrations

exceeding this are too rich) and Lower flammability or explosives limit (Fuel concentrations

below this are too lean).

FLASH FIRE The burning of a vapor cloud at very low flame propagation speed. Combustion

products are generated at a rate low enough for expansion to take place easily without significant

overpressure ahead or behind the flame front. The hazard is therefore only due to thermal effects.




Doc No.: A512-04-41-RRA-0001

Rev. No: A

POOL FIRE The combustion of material evaporating from a layer of liquid at the seat of the

fire.

JET FIRE The combustion of material emerging from an orifice with a significant momentum.

OVERPRESSURE Maximum pressure above atmosphere pressure experiences during the

passage of a blast wave from an explosion expressed in this report as pounds per square inch

(psi).

EXPLOSION A rapid release of energy, which causes a pressure discontinuity or shock wave

moving away from the source. An explosion can be produced by detonation of a high explosive

or by the rapid burning of a flammable gas cloud. The resulting overpressure is sufficient to

cause damage inside and outside the cloud as the shock wave propagation into the atmosphere

beyond the cloud. Some authors use the term deflagration for this type of explosion

DOMINO EFFECT The effect that loss of containment of one installation leads to loss of

containment of other installations

EVENT TREE A logic diagram of success and failure combinations of events used to

identify accident sequences leading to all possible consequences of a given initiating event.

TLV “Threshold limit value” is defined as the concentration of the substance in air that can be

breathed for five consecutive 8 hours work day (40 hours work week) by most people without

side effect.

STEL “Short Term Exposure Limit” is the maximum permissible average exposure for the time

period specified (15 minutes).

IDLH “Immediate Dangerous to Life and Health” is the maximum concentration level from

which one could escape within 30 minutes without any escape impairing symptoms.

PASQUILL CLASS Classification to qualify the stability of the atmosphere, indicated by a

letter ranging from A, for very unstable, to F, for stable.

FREQUENCY The number of times an outcome is expected to occur in a given period of

time.




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Rev. No: A

9. REFERENCES

1. Classification of hazardous locations, A. W. Cox, F. P. Lees and M. L. Ang, Published by

the Institute of Chemical engineers, U. K.

2. The reference manual, Volume-II, Cremer & Warner Ltd. U. K. (Presently Entec).

3. Risk analysis of six potentially hazardous industrial objects in the Rijnmond area; A pilot

study. A report to the Rijnmond Public Authority. D. Riedel publishing company, U. K.

4. Loss prevention in the process industries, Hazard identification, Assessment and Control,

Frank. P. Lees (Vol. I, II & III), Published by Butterworth-Heinemann, U. K.

5. AICHE, CCPS, Chemical process Quantitative Risk Analysis

6. Guideline for Quantitative Risk assessment, ‘Purple book’.

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