Interim Report FYDP Final 86

7/28/2019 Interim Report FYDP Final 86

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CHAPTER 7: INSTRUMENTATION AND CONTROL

7.1 INTRODUCTION

Control in process industries refers to the regulation of all aspects of the process.

Precise control of level, temperature, pressure and flow is important in many process

applications. Refining, combining, handling, and otherwise manipulating fluids to

profitably produce end products can be a precise, demanding, and potentially hazardous

process. Small changes in a process can have a large impact on the end result. Variations

in proportions, temperature, flow, turbulence, and many other factors must be carefully

and consistently controlled to produce the desired end product with a minimum of raw

materials and energy. Process control technology is the tool that enables manufacturers to

keep their operations running within specified limits and to set more precise limits to

maximize profitability, ensure quality and safety.

Process control refers to the methods that are used to control process variables

when manufacturing a product. For example, factors such as the proportion of one

ingredient to another, the temperature of the materials, how well the ingredients are

mixed, and the pressure under which the materials are held can significantly impact the

lit f d d t



lit f d d t

The overriding motivation for modern control systems is safety, which encompasses

the safety of people, environment, and equipment. The safety of plant personal and

people in the community is the highest priority in any plant operation. The design of a

process and associated control systems must always make human safety the prime

objective.

ii. Profit

When people, the environment and plant equipment are properly protected,

control objectives focus on the profit motive. Automatic control systems offer strong

benefits in this intention. Plant wide control objectives motivated by profit include

meeting final product specifications, minimizing waste production, minimizing

environmental impact, minimizing energy use and maximizing overall production

rate. Product specification sets by customers are an essential priority. Example

product specifications range from maximum or minimum values for density, viscosity

or component concentration, to specification on thickness or even color.

iii. Production Rate and Quality



In this chapter, there will be concise description of control strategies for two major

equipments and three minor equipments which are:

• Reactor

• Distillation column

• Heat exchanger

• Pump

• Compressor

7.2 REACTOR CONTROL SYSTEM

The main purpose of the reactor is to provide an area where ethylene and benzene

could react to produce ethylbenzene via liquid phase reaction. Since the reactor is the

main equipment that converts the feed into product, it is crucial that we perform a proper

control around the reactor so that we produce consistent quality product.

The first requirement for a successful control of a reactor is to establish proper

stoichiometry in order to control flow of the reactants (composition control) in proportions required as to satisfy the reaction chemistry (Perry’s, 1997). In this plug flow

reactor, R-101, benzene to ethylene is fed in ratio of 4:1 to guarantee that product



3. Safety

• Provide the safeguards against the process runaway reaction and maintain the safe

operation

• To maximize catalyst and prolong its life cycle

The fail-close valves are employed especially in the case of failure, that is when the

reactor’s internal temperature is becoming too high, the coolant would still be flowing in

the cooling coils via the fail-close valve and vice versa. This is vital to ensure that the

coolant would be flowing to cool down the reactor rather than letting it overheated. A

pressure safety valve, PSV is installed on the reactor to discharge excessive pressure

whenever necessary.

Table 1: Summary of Control Strategy for Reactor

Measured

Variable

Manipulated

Variable

Disturbances Type of Controller

Feed’s flow

rate at R-101

Benzene and

ethylene

flowrate

Compositional

changes in

benzene and

th l

Ratio control



Symbols:

FT – Flow Transmitter

RC – Ratio Controller

FC – Flow Controller

LC – Level Controller

LT – Level Transmitter

Title: Instrumentation and Control Strategy for

Reactor

Note: N/A

Project : Ethylbenzene Plant

Designer: GROUP 9 Date: 03-10-2010



As the reaction scheme requires a stringent control to be exercised in terms of reactants’

compositions to attain optimal yield, therefore a ratio control is chosen to ensure that this

requirement is fulfilled. This ratio control is a special type of feedforward control. Its

objective is to maintain the ratio of (4:1). Therefore it measures the disturbance in which,

is coming from both benzene and ethylene streams in this case.

Secondly, as the reactions involved in the whole process are entirely in liquid phase,

hence, the level of liquid resulted is among the main concern. Therefore, the simple

feedback control scheme is proposed to provide better control of the liquid level. The

liquid level from the reactor is measured and transmitted electronically to a level

controller. The controller compares the measured value to the set point and takes the

appropriate corrective action by sending signal to the control valve.

Thirdly, as the reactor chosen is operating isothermally and that, the reactions carried out

inside it are exothermic in nature, therefore temperature control is significant. For that

reason, cascade control is ideally proposed and has the following features:

1. The output signal of the master controller serves as the set point for the slave

controller.

2 The two feedback control loops are nested with secondary control loop (slave



7.3 DISTILLATION COLUMN CONTROL STRATEGY

This section will introduce the control strategy of distillation column. There are three

distillation columns in Ethylbenzene Plant with different top and bottom products. The

common operation of a distillation column is based on the production of a vapor phase by

boiling the liquid mixture, and condenses the vapor allowing some liquid or reflux to

return to the column. However, only the control system for C-102 is explained in detail in

this report. The other two of distillation columns will be having similar control strategy.

The control system for this column is designed with following control objectives:

1. Feedrate

• To maintain the federate to the distillation column at desired value. It is

achieved by the feed flow is controlled.

2. Column pressure

• To control the pressure of top tray at desired value. It is achieved by

manipulating the flowrate of cooling water. If the cooling water is

increased, then more vapor is condensed at the pressure is reduced.

3. Column Temperature



Table 1: Summary of Control Strategy for Distillation Column

MeasuredVariable

ManipulatedVariable


Column

pressure

Flowrate of

cooling water

Change of

temperaturecooling water

Feedback control

Column

temperature

Steam flow rate

to reboiler

Pressure of steam

flow

Cascade control

Liquid level indistillation

column

Bottom productflowrate Distillate flowrate Feedback and overridecotrol

Top product

composition

Reflux rate Column

temperature

Feedfforward and

feedback

Feedrate Feed flowrate Pressure of feed

flowrate

feedback



Symbols:

PT – Pressure Transmitter

PC – Pressure Controller

TT – Temperature Transmitter ll


Distillation Column

Note: N/A

P j t Eth lb l t



manipulated. But the disturbance is the pressure of the steam flowrate itself. Since the

disturbance variable is associated with the manipulated variable, cascade control is the

best way to overcome it. It consists of primary control loop of which control the column

temperature and secondary control loop which control the steam pressure. If disturbance

in a supply pressure occurs, the pressure controller will act very quickly to hold the steam

pressure at it set point before it upsets the master set point.

Liquid level of the distillation control is simply control by flow controlled. However, the

problem exists here is that the safety concerns. Suppose the base level in a distillation

column is normally held by bottoms product withdrawal. A temperature in the stripping

section is held by steam to the reboiler. Situations can arise where the base level

continues to drop even with the bottoms flow at zero (vapor boilup is greater than the

liquid rate from tray 1). If no corrective action is taken, the reboiler may boil dry and the

bottoms pump could lose suction. Thus, override control is taking place in this matter.

When the level drops below the permitted level, then the temperature controller takes

place in spite of the level controller. The feedrate to the distillation column is also simply

feedback control.

The other parameter most likely to be controlled is the composition of the tops product.

the reason is that the final product come from the top of the column and it is important to



The purpose of performing a control system for heat exchanger is to maintain the desired

temperature of its outlet stream either by providing the heating or cooling utility. The

outlet stream of the heat exchanger will be compared with the set point. If the

temperature is not at the desired level, the controller will take action by manipulating the

flow rate of the utility. In the plant, there are two heat exchangers and two coolers; the

detail description is shown in Table X below. All the heat exchanger and cooler used

same control system. The objective is to control the outlet temperature at the desired set

point. The type of controller being use is cascade controller.

1. Temperature outlet stream

• Cascade control is implemented with the temperature control as the

primary loop and flow control as the secondary loop.

Measured

Variable

Manipulated

Variable


Temperature of

at liquid at

outlet stream

Flowrate of

steam into heat

exchanger

Changes in steam

flowrate

Cascade controller

- (TIC) master loop

To maintain the temperature in the heat exchanger output process stream by manipulating



Symbols:

PT – Pressure Transmitter

PC – Pressure Controller TT – Temperature Transmitter

TC – Temperature Controller

Title: Instrumentation and Control Strategy for Heat

Exchanger

Note: N/A

Project : Ethylbenzene plant




Pumps are used to transfer liquids from one point to another and woked based on the

principle of pressure difference. It should be noted that all the pumps that are used in our

plant are of minor pumps, where they are working to hike the pressure of supply streams,

and that their content and flow are abundant and will not dry out. Therefore, we will only

allocate a pressure gauge on both of the inlet and outlet of the pump.

Table 5: Summary of Control Strategies for Pump

Control

Variable

Measured

Variable

Manipulated

Variable


1. Inlet

flowrate

Pressure

differenceacross pump

Recycle line

flowrate

Changes in the

inlet’s flowrate

Feedforward control

2. Inlet

pressure

Flowrate of

pump outlet

Pump speed Change in the

inlet flowrate

Close loop ration

control



7.6 COMPRESSOR CONTROL STRATEGY

The main use of a compressor is to increases the pressure of a vapor stream.

Compressor is a single phase unit as it cannot process mixed-phased stream that will

destroy its blades.

Table 6: Summary of Control Strategies for Compressor

Control

Variable

Measured

Variable

Manipulated

Variable


1. Inlet

flowrate

Pressure

across

compressor

and pressure

across

restriction

orifice

Recycle line

flowrate

Changes in the

inlet’s flowrate

Feedforward control

2. Inlet

pressure

Flowrate of

compressor

Compressor

speed

Change in the

inlet flowrate

Close loop ration

control



Symbols:

PG – Pressure Gauge

FT - Flow Transmitter

FC – Flow Controller


Compressor

Note: N/AProject : Ethylbenzene Plant




8.1 Hazard and Operability Studies (HAZOP)

8.1.1 Description

A Hazard and Operability (HAZOP) study is a structured and systematic examination of

a planned or existing process or operation in order to identify and evaluate problems that

may represent risks to personnel or equipment, or prevent efficient operation. The

HAZOP technique was initially developed to analyze chemical process systems, but haslater been extended to other types of systems and also to complex operations and to

software systems. A HAZOP is a qualitative technique based on guide-words and is

carried out by a multi-disciplinary team (HAZOP team) during a set of meetings.

The HAZOP study should preferably be carried out as early in the design phase as

possible - to have influence on the design. On the other hand; to carry out a HAZOP we

need a rather complete design. As a compromise, the HAZOP is usually carried out as a

final check when the detailed design has been completed. A HAZOP study may also be

conducted on an existing facility to identify modifications that should be implemented to

reduce risk and operability problems.

8 1 2 Prerequisite



To ensure high success rates, we need to provide accuracy of drawings and data used as a

basis for the study, utilize experience and skills of the HAZOP team leader, technical

skills and insights of the team, ability of the team to use the HAZOP approach as an aid

to identify deviations, causes, and consequences, ability of the team to maintain a sense

of proportion, especially when assessing the severity of the potential consequences.

8.1.4 HAZOP Study Procedures



been done for three process lines, in which HAZOP assessments are performed on two

major equipments and one minor equipment. The three equipments are:

• Node 1: Reactor (R-101)

• Node 2: Distillation Column (C-102)

• Node 3: Heat Exchanger (E-1)

Although the basic HAZOP Analysis approach is well established, the way that it is

employed may vary from organization to organization. Table lists guide words that are

commonly used in HAZOP Analysis.

8.1.5 Guidewords

Table 8: List of basic HAZOP guidewords

GUIDEWORDS MEANING No (not, none) None of the design intent is achieved

More (more of, higher) Quantitative increase in a parameter

Less (less of, lower) Quantitative decrease in a parameter



Process Section: Reactor R-101

Intention: To transport raw materials into the reactor, R-101.

Node 1: Stream S7Process parameter: Flow

Table 8: HAZOP Analysis for Node 1 - Flow

Guide

word

Deviation Possible causes Possible consequences Required actions

No No flow • Use of fail closed typed

control valve

• Fracture of pipe

• No feedstock supplied, no product

produced as no reaction taken place

• Reactor shutdown

• Employ fail opened typed control

valve

• Install emergency shutdown (ESD)

valve or shutdown plant immediately

Less Less flow • Leakage in piping

• Blockage in pumps

• Control valve failed

partially opened/closed

position

• Reduced rate of reaction

• Inconsistent production rate

• Reduced amount of process fluids to R-

101

• Install flow indicator

• Install low flow or low level alarm to

R-101

• Install check valve to stream S-7

More More

flow

• Control valve fails open • Increased amount of process fluids to

R-101 and over spillage


• Install high flow alarm and relief valve

104



Reverse Reverse

flow

• Backflow due to

backpressure in reactor

• Reduced amount of feedstock, thus

reduced yielded product

• Install check valve or flow indicator

and alarm to acknowledge the changes

in flow

• Regular inspection and maintenance of

valve

Process parameter: Pressure

Table 10: HAZOP Analysis for Node 1 - Pressure

Guide word Deviation Possible causes Possible consequences Required actions

Less Less

pressure

• Leakage in pipeline • Reverse flow

• Loss of raw material,

desired reaction cannot

be achieved

• Install pressure indicator

• Install low pressure alarm

• Install ESD valve

More More

pressure

• Control valve fails open • High pressure and could

lead to overpressure

(pressure build-ups) in R-

101

• Runaway reaction

• Install pressure indicator and high

pressure alarm


• Install relief valve

Process parameter: Temperature

105



Table 9: HAZOP Analysis for Node 1 - Temperature

Guide

word


Less Less

temperatur

e

•Temperature indicator

fails

•Heat exchanger

failure/ inefficient

• Optimal reaction scheme cannot be

attained

• Reduced yield

• Inspect, maintain temperature

indicator and replace it promptly if it

fails

• Inspect and maintain heat exchanger

periodically

More More

temperatur

e

•Temperature indicator

fails

•External heating

• High pressure in reactor

• Uncontrolled and excessive heat release

surrounding R-101

• Install temperature indicator and

high temperature alarm

• Instruct operator by procedures

• Install cooling water flow meter

• Check heat exchanger

Process Section: Distillation Column C-102

Intention: To transport process materials from separator C-101 to separator C-102.

106



Node 2: Stream S11

Process parameter: Flow

Table 11: HAZOP Analysis for Node 2 - FlowGuide

word


No No flow • Control valve fails

closed.

• Column C-101

empty.

• Fracture pipe.

• Isolation valve

closed.

• No process material to separator.

• No ethylbenzene produced.

• Plant shutdown.

• Release of hazardous material.

• Use control valve fails open.

• Install low flow alarm to alert

operator

• Install hazardous substance detector

and alarm.

Less Less flow • Pipe leaking.

• Control valve failed

in partially open

position.

• Blockage in pipe or

pump.

• Less process material to separator.

• Ethylbenzene production rate decrease.


• Install low flow or low level alarm to

S-11.

More More flow • Control valve fails

open

• Air pressure to drive

• Increased amount of process material to

C-102.

• Over spillage.


• Install high flow alarm

• Install relief valve at reactor

107



valve fails

• Incorrect instrument

reading.

• Overpressure in separator.

Reverse Reverse

flow

• Backflow due to

backpressure in

reactor

• Reduced amount of feedstock, thus

reduced yielded product.

• Desired flow could not be achieved.

• Plant shutdown

• Install check valve.

• Regular inspection and maintenance

of valve.

Process parameter: Temperature

Table 12: HAZOP Analysis for Node 2 - Temperature


108



Less Less

temperature

•Heat exchanger failure.

•Temperature control error.

• Cooling water control

valves fails closed.

• Possible thermal

runaway

•

Decrease product yield

• Install low temperature alarm.

• Adequate pipe installation.

More More

temperature

•External heating

•Heat exchanger failure.

•Temperature control error.

• Cooling water control

valves fails closed.

• High pressure in

distillation column.

• Uncontrolled and

excessive heat release.

• Desired product cannot

be separated

• Install temperature indicator and high

temperature alarm

• Install cooling water flow meter.

Process parameter: Pressure

Table 13: HAZOP Analysis for Node 2 - Pressure


109



Less Less

pressure

• Leakage/rupture in

pipeline.

• Compressor malfunction.

• Control valve fails close.

• Reverse flow

• Loss of raw material.

• Desired reaction cannot

be achieved

• Install pressure indicator

• Install low pressure alarm

More More

pressure

• Control valve fails open.

• Compressor malfunction.

• Build up pressure in C-

101.

• Runaway reaction • Install pressure indicator and high

pressure alarm


• Install PSV.

110



Process Section: Heat Exchanger E-1

Intention: To transport materials to transkylation reactor, R-102

Node 3: Stream S19

Table 14: HAZOP Analysis for Node 3

Parameter Deviation Possible causes Possible consequences Required Actions

Flow No flow • Upstream flow

disrupted

• Heater, its line and

downstream line

rupture

• Line blockage

• No feed to R-102, less yield

• Release of hazardous and flammable

material

(a) Install control valve that fails open

(b) Install low flow alarm at R-102 inlet

(c) Install hazardous substance detector and

alarm

More flow • Leakage in the heat

exchanger tubes

causing mixture of product of

ethylbenzene streamwith the feed of

transkylation reactor

• Mixture of ethylbenzene with

transkylation feed stream affects the

reaction and produce less product

• Decrease temperature of feed to R-102

• Overflow of reactor and release of

hazardous material

(d) Install high flow alarm at reactor inlet

• Covered by (c)

Less Flow • Line fracture, leakage

(flange/valve and heat

exchanger shell)

• Failure of charge pump

• Flow return to the mixer

• Low feed flow to the reactor

• Feed loss and release

(e) Install bypass valve

• Covered by (a)Covered by (b)

111



Reverse

flow• Heat exchanger/Line

rupture leading to low pressure and no flow

• No/Low feed

• Potential flow back to mixer

• Feed loss and release of hazardous and

flammable material

(f) Install check valve

• Covered by (a)

• Covered by (b)

Temperature Higher

temperature• Heat exchanger failure

• Faulty transmitter

• Change of reactant phase (g) Install high/low temperature indicator

alarm at reactor inlet

(h) Regular patrolling and inspection of the

heat exchanger

(i) Install two transmitter

Lower

temperature• Heat exchanger failure

• Faulty transmitter

• Hot stream temperature

at inlet heat exchanger

is too low

• Reactor conversion cannot be achieved

• Low reaction rate is achieve Covered (g), (h) and (i)

112



Pressure Lower

pressure• Equipment/line rupture

leading to less/no flow

•

Clogging in pipe

• Loss and spillage of feed


material

• Less feed to the reactor

• Bring damage to the equipment

(j) Install low/high pressure alarm at pump

(water line) outlet

(k) Install a pressure relief valve on pipeline

• Covered by (c)

Higher pressure

• Blockage at reactor

inlet

• Overpressure will lead to line rupture

• Spurge flow into reactor

• Pressure build up in the reactor

• Covered (c) , (j) and (k)

No pressure • Equipment/line rupture

leading to no flow

• Loss and spillage of product


material

• No feed to reactor

• Reversible flow occur

• Covered (c) , (j) and (k)

113



8.2 PLANT LAYOUT

8.2.1 Introduction

Plant layout and construction design must be considered early in the design work to

ensure economical construction and efficient operation of the completed plant. This

section of the report provides the basic information and safety justifications on the

plant layout designed for the newly proposed ethyl benzene plant.

In general, the layout shows the basic arrangement of main production site,

supporting buildings and few important safety aspects. However, the plant layout

adopted may affect the safe operation of the completed plant and if needed, any

possible modification or extension must be accepted. Plant layout is often a

compromise between a numbers of factors such as:

• The need to keep distances for transfer of materials between plant/storage units to

a minimum to reduce costs and risks

• The geographical limitations of the site

• Interaction with existing or planned facilities on site such as existing roadways,

drainage and utilities routings

• Interaction with other plants on site



8.2.2 Plant Layout Consideration Factors

Based on the previous factors stated, the factor to design plant layout for the ethyl

benzene has been narrowed down to several factors as followed. Thus, to ensure that the

final design for plant layout is complied with all the factors that has been discussed

earlier.

a. Cost - Minimization of construction cost is done by adopting shortest run of

connecting pipe between equipment. The cost is also reduced by having the least

amount of structural steel work. The most important thing is to have an

arrangement for best operation and maintenance.

b. Operation - Equipment such as valves, sample points and instruments are

considered as frequently attended equipments. They are located not far away from

control room, with convenient positions and heights, to ease the operator’s job.

Also, sufficient working and headroom space are provided to allow easy access to

equipments.

c Maintenance - When laying out the plant some considerations were made



d. Safety - Among the safety consideration that we have when laying out this plant

are:

• Operators have 3 escape routes if anything occurs in the main process unit

• To minimize fire from spread, flammables handling process units are

separated from each other

• Process vessels with substantial inventories of flammable liquids are

located at grade

• Elevated areas will have at least one stairway

• Storage farm which stores the flammable materials are located at safe

distance from the main process area

• Equipment subject to explosion hazard is set away from occupied

buildings and areas.

8.2.3 Site Layout



8.2.3.1 Non-Process Area

The non-process area usually occupies a smaller fraction of the overall plant site area. All

the facilities in the non-process area should be located in a logical manner that considers

site terrain, accessibility to roads, soil bearing capability and the climate including the

wind direction and other unusual weather condition. This is important to avoid any

undesired incident due to explosion or fire from the process zone that will be easily

spread to the non-process area.

Taking this into account, the entire process area where the reaction and separation occurs

is surrounded with a buffer zone to ensure that surrounding buildings or sites are not

affected in case of an emergency. Among the buildings or units in the non-process areaare:

a) Guard posts

Guard posts are located at the entrance of the site in order to ensure that only

authorized personnel gets access into the plant. There are three guard posts that aresituated at the crucial entrances in the plant:



material spillage at the plant. With this, the public are less exposed to the

danger of chemicals exposure or accidents with the trucks.

b) Administration building

The administration block is built near the parking area which acts as assembly area

for staffs as well to ensure the staffs can arrive faster at the assembly point during an

emergency. Based on the plant layout, the administration building is placed far from

the process area in order to protect the staffs and visitors from any potential hazards.

c) Canteen

The canteen is located across the administration building for easy access to the

employees and visitors, and far away from the process area to avoid contaminant in

food and ensure safety of the public. The location is so strategic that in order to avoid

the food supplier from being exposed to the process area allowing them to move in

and out easily.

There are other facilities that located in the non-process area including prayer hall,

clinic and parking lot. Prayer hall is located near cafeteria for Muslims employees to perform their prayers during breaks. Clinic and parking lot is located side by side just

next to Gate 4 for the staffs and visitors benefits.



area guard post is to ensure that all the personnel will obey to the plant rule and

regulations.

b) Control building

All the control valves for the whole process area will be controlled and monitored

from this central control building. The control building is designed with blast proof

construction and has emergency backup power and is air conditioned in order to save

and secure the vital documents of the process that it houses during emergency.

c) Laboratory

The quality of the purity of ethyl benzene is tested after the product is recovered to

determine whether it meets the specifications or not. All the results will be sent to the

control room and some adjustments in controlling will be made, if needed. The

distance between laboratory and control room is not too far. Laboratory staffs will

also perform analysis of the waste of the process before being channeled to

wastewater treatment and flare system; or being released to atmosphere.

d) Waste treatment plants

The waste stream from the separation area will flow into the waste treatment plant to



f) Separation site

The main objective of this treatment unit is to separate between the products,

byproducts and unreacted reactants to be recycled back to the transalkylation reactor.

Its location is at a distance away from the reactor site and next to laboratory. The

units are arranged on the production line from high pressure to low pressure so as to

ease the flow of product. The units are properly spaced among each other for

maintenance and also for safety.

g) Utilities site

This unit will supply cooling water, high pressure steam and nitrogen to the main

process unit. Its location is perfectly suitable to give the most economical run of pipe

to and from the process unit.

h) Storage Vessels and Drums

This unit stores vessels and drums containing products that are going to bedistributed locally, chemical substance, lubricants and catalyst used for the process.

It also stores chemicals needed for the waste treatment plant It is situated near the



Ample area is allocated at the process area for future expansion in case the

management decides to increase production rate or other crucial considerations. They

occupy enough space for further expansion, whether for process reaction or

producing the plant’s own utility such as cooling water and steam.

k) Pump house and Compressor house

Pump house and compressor house are located just beside the reactor site to house

the pumps and compressor that are used in the production and distribution of the

product, ethyl benzene to customers.

l) Loading area

Loading area is where the trucks deliver the chemicals used in running of the plant

and also load the products that are going to be distributed locally. Thus, it is directly

located to the storage.

m) Flare area

Flare is used to burn excess gas that is emitted from the process units as well as to

burn some of the waste gas from waste treatment area. The flare is located in thesame area for wastewater treatment plant and far from the process area and

administration complex for this purpose



M a i n r o a d

Chemical Storage Units

Reactor System

L o a d i n g a n d u n l o a d i n g

b a y

Utility Sections

Gate 1Gate 2

Gate 3

Flare

Raw materials

Future expansion site 2 / Assembly area 2

Future expansion

site 1 / Assembly

Area 1

Training

Center/Seminar /Conference Room

Administration and Technical Services

Parking Canteen

Prayer Hall

Clinic

Main Power Supply

Guard House

Wastewater treatment

plant

Laboratory

Future expansion site 3

Fire station

Separation Section

Maintenance

Warehouse

Control building

Minor Equipments

Housing

Gate 4

Figure 2: Plant Layout of Ethylbenzene Production Plan

122



CHAPTER 9: WASTE WATER TREATMENT

9.1 Introduction

Waste is unwanted or unusable materials. Waste is directly linked to human

development, both technologically and socially. The compositions of different wastes

have varied over time and location, with industrial development and innovation beingdirectly linked to waste materials. Wastewater is any water that has been adversely

affected in quality by anthropogenic influence. It comprises liquid waste discharged by

domestic residences, commercial properties, industry, and/or agriculture and can

encompass a wide range of potential contaminants and concentrations.

In a chemical plant, the wastewater is defined as a combination of the liquid or

water that carries waste removed from commercial and industrial establishment.

Wastewater, one of the major contributors to the increasingly heated environmental

problem consists of toxic contaminants that may lead to direct fatal of all organisms

including aquatic or land inhibited animals and even human beings. Non-biodegradable

toxic waste is absorbed into the body system via food chain, which consequently leads to

serious disease such as cancer, food poisoning and others.



Wastewater from Ethylbenzene production plant comprises of unused reactants

and byproducts from the process side due to process divergence. The most appropriate

wastewater treatment to be applied is the one that meets the recommended

microbiological and chemical quality guidelines both at low cost and with minimal

operational and maintenance requirements.

9.2 Laws and Regulations on Industrial Waste (Malaysia)

Generally, all industries in Malaysia must comply with the law and

regulations stated in the Environmental Quality Act 1974 (EQA 1974). Basically,

this is an Act relating to the prevention, abatement, control of pollution and

enhancement of the environment, and for purposes connected therewith. This act

includes 34 regulations, which covers three (3) auxiliary regulations that aresignificant to the plant environmental issues:

i. Environmental Quality (Clean Air) Regulation 1978

ii. Environmental Quality (Sewage and Industrial Effluent) Regulation 1979

iii. Environmental Quality (Scheduled Waste) Regulation 1989.iv. Other closely related regulations

(a) Environmental Quality (Compounding of Offences) Rules 1978



According to Environmental Quality (Scheduled Wastes) Regulations 1989, solid wastes

are categorized in 107 categories in the First Schedule wastes. It consists of two parts:

i. Part I: Scheduled Wastes from Non-Specific Sources

ii. Part II: Scheduled Wastes from Specific Sources

In the schedule, proper reference likes tagging with a specific number is required to make

it easier for classification. It is important for plant management to classify the waste

accordingly before proceed with the treatment. Each treatment differs for different kind

of waste. Therefore, they must follow the guidelines stated in the regulations on waste

collection, packaging, labeling, and transportation of the wastes for further treatment and

disposal. Based on the regulation, schedule waste shall be treated at prescribed premises

or at on-site treatment facilities only.

9.2.2 Liquid Waste

As for the effluent discharge from the industry, it needs to comply with the

Environmental Quality (Sewage and Industrial Effluents) Regulations, (Regulation 8(1)Third Schedule, Standards A, EQ 1979). In this context, industrial effluent means liquid

water or wastewater produced by reason of the production processes taking place at any



Table 15: Plant Wastewater and Standard A Values of EQA

Parameter Unit Standard A Plant wastewaterTemperature ˚C 40 70.00

BOD5 at 20˚C ppm 20 100-200

COD ppm 50 1000-1500

Suspended solids ppm 50 < 100

9.2.3 Gaseous Waste

The gaseous emission limits from the chemical industry must comply with the

Environmental Quality (Clean Air) Regulations, 1977. The primary source of the gas

emission of Ethylbenzene production plant is from the purge gas of benzene side product.

The Clean Air Act that was enacted in 1970 includes the National Emission Standards for Hazardous Air Pollutants. This standard controls air emission levels of harmful toxins

like benzene. It was reported that benzene exposure significantly increased one's risk of

developing leukemia by adding benzene to the list of toxic air pollutants. Oil refineries

and other industrial operations must comply with federal and state environmental law in

regards to benzene emissions.



Treatment

Stage

Description

Preliminary Removal of any constituents from wastewater which can clog or

damage pumps, or interfere with subsequent treatment processes.

Primary Removal of organic and inorganic solids by the physical processes of

sedimentation and flotation.

Secondary Removal of colloidal and dissolved organic and inorganic solids of

effluent from primary treatment. The secondary treatment process

consists of the biological treatment of wastewater by utilizing many

different types of microorganisms in a controlled environment.

Tertiary and/or

Advanced

Removal of dissolved organic matter that cannot be removed by

secondary treatment.

9.3.1 Physical Methods

Physical methods include processes where no gross chemical or biological changes are

carried out and strictly physical phenomena are used to improve or treat the

wastewater. Physical treatment is usually the first step in a larger wastewater treatment

process. In general, the mechanisms involved in physical treatment do not result in



process. In filtration process, sewage is passed through filters to separate the

contaminating solids from the water. Sand filter is a common filter used in this process.

9.3.2 Chemical Methods

In chemical water treatment, chemicals are used to treat wastewater in order to improve

water quality. The most common method to treat water using chemicals is chlorination,

wherein chlorine, a strong oxidizing chemical is used to kill the bacteria and slow downthe rate of decomposition of the wastewater. Bacterial kill is achieved when vital

biological processes are affected by the chlorine. Ozone, an oxidizing disinfectant, is

another oxidizing agent used to treat polluted water . These oxidizing agents affect the

biological growth process of bacteria, thus making the water usable.

Neutralization is another chemical process used in many industrial wastewater treatment

operations. Neutralization consists of acid and basis to adjust the pH levels back to

neutrality. Lime is one of example of base used in the neutralization of acid wastes.

Coagulation consists of the addition of a chemical. There are small particulates in

wastewater where suspended in water forming a colloid. These particles carry the samecharges, and repulsion prevents them from combining into larger particulates to settle.

Thus by adding a chemical reaction will occur and forms an insoluble end product that

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In the biological water treatment process, microorganisms, mostly bacteria are used to

biochemical decomposition of wastewaters to stable end products. More

microorganisms, or sludges, are formed and a portion of the waste is converted to carbon

dioxide, water and other end products. There are two sub-divisions of biological waste

treatment which are aerobic and anaerobic, based on availability of dissolved oxygen. In

the aerobic process, bacteria consumes the organic matter and helps convert it to carbon

dioxide in the presence of oxygen, while in the anaerobic process, sludge is fermented at

a particular temperature in the absence of oxygen. Another aerobic process is

composting, where sludge is mixed with carbon sources such as sawdust to treat

wastewater.

Table 17: Summary of Treatment Methods

Properties Physical Chemical Biological

Types of

process

Sedimentation,

aeration and filtration

Chlorination,

neutralization,

coagulation, and carbon

adsorption

Aerobic

Anaerobic

Advantage Simple andinexpensive process

to separate solid and

Capable to improvewater quality using

chemical reaction and it

Consume thecontaminants in

wastewater using



There are three levels of wastewater treatment applied in the Ethylbenzene production

plant which are preliminary, primary, secondary and tertiary (or advanced). In the

preliminary treatment, any constituents which can clog or damage pumps, or interfere

with subsequent treatment processes are removed from the wastewater. Then it proceed

with the primary treatment which involve sedimentation, and is the process by which

about 30 to 50 percent of the suspended solid materials in raw wastewater are removed.

The purpose of preliminary treatment is to protect the operation of the wastewater

treatment plant. This is achieved by removing from the wastewater any constituents

which can clog or damage pumps, or interfere with subsequent treatment processes. The

organic matter remaining after primary treatment is extracted by biological secondary

treatment processes to meet effluent standards. Secondary treatment commonly is carried

out using activated-sludge processes, trickling filters, or rotating biological contactors.

Tertiary wastewater treatment is additional treatment that follows primary and secondary

treatment processes. It is employed when primary and secondary treatment cannot

accomplish all that is required.

9.4.1 Preliminary Treatment



treatment units. Flow equalization and mechanical mixing in the collection sump will

level out the hydraulics load on treatment units.

9.4.2 Primary Treatment

Primary treatment is designed to remove organic and inorganic solids by the physical

processes of sedimentation and flotation. Approximately 25 to 50% of the incoming

biochemical oxygen demand (BOD5), 50 to 70% of the total suspended solids (SS), and

65% of the oil and grease are removed during primary treatment. Some organic nitrogen,

organic phosphorus, and heavy metals associated with solids are also removed during

primary sedimentation but colloidal and dissolved constituents are not affected.

Primary treatment devices reduce the velocity and disperse the flow of wastewater. In

primary treatment the velocity of flow is reduced to 1 to 2 feet per minute to maintain a

quiescent condition so that the material denser than water will settle out and material less

dense than water will float to the surface. The solids that remain in suspension as well as

dissolved solids will usually be biochemically treated in subsequent processes for

physical separation and removal in the final (secondary) settling tanks.

Further the settling rate of a particle depends on the strength and freshness of the



process consists of the biological treatment of wastewater by utilizing many different

types of microorganisms in a controlled environment. In most cases, secondary treatment

uses aerobic biological treatment processes to remove biodegradable dissolved and

colloidal organic matter. Aerobic biological treatment is performed in the presence of

oxygen by aerobic microorganisms (principally bacteria) that metabolize the organic

matter in the wastewater, thereby producing more microorganisms and inorganic end-

products (principally CO2, NH3, and H2O). Several aerobic biological processes are used

for secondary treatment differing primarily in the manner in which oxygen is supplied to

the microorganisms and in the rate at which organisms metabolize the organic matter.

The microorganisms must be separated from the treated wastewater by sedimentation to

produce clarified secondary effluent. The sedimentation tanks used in secondary

treatment, often referred to as secondary clarifiers, operate in the same basic manner as

the primary clarifiers described previously. The biological solids removed during

secondary sedimentation, called secondary or biological sludge, are normally combined

with primary sludge for sludge processing.

9.4.4 Tertiary and/or Advance Treatment

Advanced Wastewater Treatment may be broken into three major categories



(e.g.chemical addition to primary clarifiers or aeration basins to remove phosphorus) or

used in place of secondary treatment (e.g., overland flow treatment of primary effluent).

9.5 Solid Waste

Some examples of possible solid waste obtained from this plant are residue, spent catalyst

and suspended solids. Residues are materials remaining from burning or heat reaction of

coke and combustible or volatile waste. Suspended particles from source of steam (water)

and particulates from equipments and piping lines also contribute to the solid waste..

According to Environmental Pollution Act, the waste can be classified as hazardous as

the waste exhibits the following characteristics: ignitability, corrosivity, reactivity, and

toxicity. Solid waste consist mainly the sludge removed from the liquid waste after

biological treatment and little amount of spent catalyst. Suspended solids can be removed

by settling and sedimentation using clarifiers. The characteristics of solids and sludge

produced during wastewater treatment are summarized in Table 18



Scum/greaseFloatable material from primary and secondary

settling tanks

Primary sludge Usually grey and slimy with foul odour.

Activated sludge Generally has a brownish, flocculants appearance

Digested sludgeBrown and has a flocculants appearance but

usually no offensive odour.

Environmental Quality (Scheduled Wastes) Regulations 1989 requires that scheduled

wastes be treated and disposed of at facilities approved by Department of Environment

(DOE). Presently most local authorities in Malaysia dispose solid wastes in landfills.

Incineration has always been viewed as a risk in terms of costs and effectiveness. The

existing Town and Planning Act do not allow the use of incinerators in urban areas.

Landfills cover 60 to 90 percent of the served areas, and are projected to cover up to 70 to

95 percent in the near future. 80 percent of the waste disposal sites had less than 2 years

of operating life remaining in 1990, emphasizing the urgency for municipalities to secure

new landfills before the existing ones is exhausted.

One of the disposal areas of scheduled wastes for Peninsular Malaysia is provided byKualiti Alam Sdn Bhd. The company owns and operates the Integrated Scheduled Waste

Management Centre (WMC) at Bukit Nanas Negeri Sembilan The waste treatment



Stream (S) Component Composition Amount (kg/hr)

S27 Ethyl Benzene 0.02 22.57

Diethyl Benzene 0.05 56.43Ethyl Toluene 0.01 11.29

Triethyl Benzene 0.31 349.86

Diphenyl Ethane 0.62 699.73

The estimated amount of wastewater that will be entering the wastewater treatment

system is 1128.59 kg/hr. After completing the wastewater treatment, then only the treated

water will be drained back into South China Sea.

Table 20: Plant Wastewater and Standard B Values of EQA

Parameter Unit Standard B Plant wastewaterTemperature ˚C 40 39

PH value 5.5-9.0 6.0-8.0

BOD5 at 20˚C ppm 50 100-200

COD ppm 100 150-250

Suspended solids ppm 100 < 100

Others None



Therefore, total estimated gaseous waste in the plant is 6438.63 kg/hr. National emission

standard or limits have been established pertaining to particular source of gas emissions

with respect to the country regulation itself. Therefore, an efficient and sophisticated

degree of control must be implemented for industrial emission.

These gases must be vented to avoid dangerously high pressure in the operating

equipment, from plant start up and from emergency shutdown. The system for safely

venting process equipment during these situations is called emergency relief systems.

Such system usually has many safety valves tied into one collection system. They are

designed with large pipes to ensure large volume can be handled at low pressure. The

lines lead to a water seal drum and to a flare stack, where the gaseous such as benzene are

flared at a safe height above the process area.

Flare tips use steam to create a turbulent mixing between air and the stack gas at the top.

It also provides some cooling of the flare tip and stack. The flammable gas is ignited at

the top by a continuous pilot. The main control that needs to be maintained along the

flaring process is the control of proper steam flow. This is because with proper steam

flow, smokeless operation can be maintained at all conditions of gas flow, which providean almost complete combustion of gaseous.

The flaring process may results in some smoke emissions to the atmosphere In order to





Figure 3: Process Flow Diagram of Wastewater Treatment System for Ethyl Benzene PlantUntreated Waste Water

Treated Water

Equalization

138

Documents

Interim Report FYDP Final 86