BAT Guide on Fertiliser Processes

8/13/2019 BAT Guide on Fertiliser Processes

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Fertiliser and Carbon Black Processes, CARDS 2004 project Further Approximation of

Croatian Legislation with the Environmental Acquis

1

BAT GUIDANCE NOTE

FERTILISER AND CARBON

BLACK PROCESSES


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Contents

INTRODUCTION......................................................................................................................................3

1 BACKGROUND TO THE GUIDANCE NOTES.................................................................................3

2 GLOSSARY.............................................................................................................................................5

3 BACKGROUND - FERTILISER AND CARBON BLACK PROCESSES .....................................10

THE MOST SIGNIFICANT ISSUES ARE: ..........................................................................................12

EMISSIONS OF N2O FROM THE PRODUCTION OF NITRIC ACID. ....................................12

COMMON ISSUES..................................................................................................................................12

PRODUCTION OF AMMONIA ..............................................................................................................13

PRODUCTION OF NITRIC ACID .........................................................................................................13

PRODUCTION OF SULPHURIC ACID ...............................................................................................14

PHOSPHATE ROCK GRINDING AND PREVENTION OF ROCK DUST DISPERSION ............14

PRODUCTION OF PHOSPHORIC ACID ............................................................................................14

4 COMMON TECHNIQUES FOR ALL PROCESSES .......................................................................16

5 AMMONIA PLANT..............................................................................................................................17

6 NITRIC ACID PLANTS.......................................................................................................................20

7 UREA PLANT .......................................................................................................................................23

8 SULPHURIC ACID PLANT................................................................................................................27

9 PHOSPHORIC ACID PLANT.............................................................................................................30

10 CALCIUM AMMONIUM NITRATE (CAN) PLANTS ..................................................................33

11 NITROGEN PHOSPHOROUS POTASSIUM (NPK) PLANTS.....................................................35

12 WASTE AND WASTEWATER.........................................................................................................40

13 CARBON BLACK PLANT ................................................................................................................40


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INTRODUCTION

1 BACKGROUND TO THE GUIDANCE NOTES

A key feature of the IPPC Directive is the requirement to base permits on the use of BestAvailable Technique(s) (BAT). Best Available Techniques are defined in theEnvironment Protection Act. In summary BAT means; all techniques, includingtechnology, planning, construction, maintenance, operation and decommission, whichare applicable in practice under acceptable technical and economical conditions and arethe most effective for the provision of a high level of protection for the environment as awhole. From October 2007 all Installations should receive an Integrated Permit settingemission limits based on BAT. This series of Guidelines has been produced to assistthe determination of BAT.

This is one of a series of notes describing the Best Available Techniques (BAT)conclusions for industry sectors. The notes are all aimed at providing a strong frameworkfor consistent and transparent regulation of processes and installations. A number ofGuides reporting on horizontal issues have also been prepared. The Guide on Fertiliserand Carbon Black Processes is document number xxxxxxxx and this should be referredto when setting permit conditions.

When determining BAT for a new installation, the BAT conclusions given in theBREFs, or more advanced techniques where applicable should be used. TheBAT Associated Emission Levels (BATAELs) should not be exceeded whenemission limit values are set at a local level and the lower value of any range

should be used. When determining BAT for an existing installation it is possible to decide on a

derogation that takes into account the environmental costs and benefits and setslightly more relaxed limit values at a local level. A range of factors may be takeninto consideration when deciding the most appropriate techniques to provide thebest protection for the environment as a whole. The objective is to set permitconditions in order that the installation shall approach as closely as possible thestandards that would be set for a new plant, but taking into account the cost-effectiveness, time-scale and practicality of making changes to the existing plant.Annex IV to the IPPC Directive lists the considerations to be taken into accountwhen determining BAT at a local level.

When assessing the applicability of the BAT or the associated emission levels for

an existing installation, departures or derogations may be justified which areeither stricter or less strict than BAT as described in the BREFs. The mostappropriate technique depends upon local factors and a local assessment of thecosts and benefits of the available options may be needed to establish the bestoption. The justification for departing from the BAT conclusions must be robustand must be recorded.

Departures may be justified on the grounds of environmental costs and benefitsand local conditions such as the technical characteristics of the installationconcerned, its geographical location and the local environmental conditions butnot on grounds of individual company profitability.

All processes are subject to BAT. In general terms, what is BAT for one processin a sector is likely to be BAT for a comparable process; but in each case it is in


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practice for regulators (subject to appeal) to decide what is BAT for the individualprocess and the regulator should take into account variable factors (such asconfiguration, size and other individual characteristics or the process) and the

locality (such as proximity of particularly sensitive receptors. Ultimately whatconstitutes BAT is site specific but this guidance note comprises guidance for thegenerality of processes in the sector and careful regard should be had to it, inorder to maximise consistency of permits as appropriate.

This guidance is for:o Regulators: who must have regard to the guidance when determining

applications and reviewing extant authorisations and permits,o Operators: who are best advised also to have regard to it when making

applications, and in the subsequent operation of their process,o Members of the public: who may be interested to know what is

considered to be appropriate conditions for controlling emissions for thegenerality of processes in this particular industry sector.

The guidance is based on the state of knowledge and understanding at the timeof writing of:

o Fertiliser and Carbon Black Processes,o their potential impact on the environment, ando how Fertiliser and Carbon Black Processes come within the aims of the

IPPC Directive.

In addition to the BREFs, Guidance published by other Countries has been usedand these Guidance Notes may also provide additional information.

The note may be amended from time to time in order to keep abreast withdevelopments in BAT: including improvements in techniques, and newunderstanding of environmental impacts and risks. Such changes may be issuedin a complete revision of this document, or in separate additional guidance notes

which address specific issues. The following Croatian Guidelines should also be consulted to give a full

understanding of the issues:

BAT Assessment

Energy Efficiency

Monitoring Techniques

Noise

Decommissioning

Waste Minimisation

Environmental Management Systems

Contaminated Land Assessment

Fugitive Emissions

Wastewater/waste gas treatment


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2 GLOSSARY

A

ACES Advanced Process for Cost and Energy Saving

ADEME Agence de l'Environnement et de la Matrise de l'Energie

AG Aktiengesellschaft

aMDEA Activated Methyl Diethanolamine

AN Ammonium Nitrate (NH4NO3)

ANS Ammonium Nitrate Solution

APC Advanced Process Control

ASN Ammonium Sulphate Nitrate

BBAT Best Available Techniques

BFW Boiler Feed-water

BOD Biochemical Oxygen Demand

BPL Bone Phosphate of Lime

BREF BAT Reference Document

C

CAN Calcium Ammonium Nitrate (KAN in Croatian)

CEFIC European Chemical Industry Council

CDM Clean Development Mechanism emission reduction projects,where an industrialised country invests in an emission reductionproject in a developing country

CHF Swiss francs

CIS Commonwealth of Independent States Armenia, Azerbaijan,Belarus, Georgia, Kazakhstan, Kyrgyzstan, Moldova, Russia,Tajikistan, Ukraine, and Uzbekistan

CN Calcium Nitrate Ca(NO3)2

CNTH Calcium Nitrate Tetra Hydrate Ca(NO3)2.4H2O

COD Chemical Oxygen Demand

Conversion rate The SO2conversion rate for the production of H2SO4 is defined as

follows:(SO2in SO2out) x 100 (%)

Conversion rate =SO2in

See also Section Pogreka! Izvor reference nije pronaen.

Combination of At least two

D

DAP Diammonium Phosphate (NH4)2HPO4


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DeNOx Abatement system to remove nitrogen oxides (NOx)

DeN2O Abatement system to remove nitrous oxide (N2O)

DH Dihydrate processDHH or DH/HH Di-hemihydrate recrystallisation process with double-stage filtration

E

EFMA European Fertilizer Manufacturers Association

EGTEI Expert Group of Techno Economic Issues this group is workingunder the umbrella of United Nations/Economic Commission forEurope

EIPPCB European IPPC Bureau

EMAS Eco-Management and Audit Scheme

EMS Environmental Management System

EA Environment Agency

EPER European Pollutant Emission Register

ERM Environmental Resources Management

ESP Electrostatic Precipitator

EU European Union

EUR Euro

H

H/H Dual high/high pressure nitric acid plants, see Pogreka! Izvorreference nije pronaen.

HDH-1 Hemi-dihydrate recrystallisation process single-stage filtration

HDH-2 Hemi-dihydrate recrystallisation process double-stage filtration

HDS Hydrodesulphurisation unit

HEA High Efficiency Absorption

HH Hemihydrate

HHV High Heating Value amount of heat released by a specifiedquantity (initially at 25 C) once it is combusted and the productshave returned to a temperature of 25 C.

HMTA Hexamethylene Tetramine

HP High Pressure steam

HRC Hemihydrate Recrystallisation process

I

IDR Isobaric Double Recycling process

IRMA Institut Rgional des Materiaux Avancs

IEF Information Exchange Forum

IFA International Fertiliser Industry Association

InfoMil Dutch information centre for environmental licensing andenforcement

IPCC Intergovernmental Panel on Climate Change


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IPPC Integrated Pollution Prevention Control

ISO 14001 International Standards Organization environmental management

J

JI Joint Implementation emission reduction projects, where anindustrialised country invests in another industrialised country. Bothcountries must be Kyoto protocol signatory states

L

L/M Dual Low/Medium pressure nitric acid plants, see Pogreka! Izvorreference nije pronaen.

LEL Low Explosion Limit

LHV Low Heating Value amount of heat released by combusting a

specified quantity (initially at 25 C or another reference state) andreturning the temperature of the combustion products to 150 C.

Low NOxburner Technology to reduce NOx emissions from combustion, by modifyingthe introduction of air and fuel, to retard their mixture, reduce theoxygen availability and the peak flame temperature. It delays theconversion of fuel-bound nitrogen to NOx and the formation ofthermal NOx, while maintaining the high combustion efficiency

LP Low Pressure steam

LPG Liquefied Petroleum Gas

M

M/H Dual Medium/High pressure nitric acid plants, see Pogreka! Izvorreference nije pronaen.

M/M Dual Medium/Medium pressure nitric acid plants, see Pogreka!Izvor reference nije pronaen.

MAN Magnesium Ammonium Nitrate

MAP Monoammonium Phosphate NH4.H2PO4

MEA Mono Ethanolamine

MP Medium Pressure

Multipurpose plant Installation for production of NPK, AN/CAN and phosphatefertilisers, using the same line of equipment and abatement system

N

New installation As opposed to an existing installation or a substantial change of anexisting installation

NLG Dutch Guilders

NG Natural Gas

NPK Compound/multinutrient fertiliser

NSCR Non Selective Catalytic Reduction

O


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P

PAPR Partially Acidulated Phosphate RockPRDS Pressure Reduction and De-superheating

PSA Pressure Swing Adsorption gas separation process in which theadsorbent is regenerated by rapidly reducing the partial pressure ofthe adsorbed component, either by lowering the total pressure or byusing a purge gas

PTFE Polytetrafluoroethylene

R

R & D Research and Development

RIZA Dutch Institute for Inland Water Management and Waste Water

TreatmentRTD Research and Technology Development

S

S. A. Sociedad Annima

SCR Selective Catalytic Reduction

SNCR Selective Non-Catalytic Reduction

SSD Self-Sustaining Decomposition

SSP Single Superphosphates

Substantial change According to the IPPC Directive, a substantial change in operation

shall mean a change in operation which, in the opinion of thecompetent authority, may have significant negative effects onhuman beings or the environment

T

TAK-S Technischer Arbeitskreis Schwefel

TSP Triplesuperphosphates

TWG Technical Working Group

U

UAN Urea Ammonium Nitrate

UBA Umweltbundesamt Federal Environmental Agency

UNEP United Nations Environment Programme

UNFCCC United Nations Framework Convention on Climate Change

Urea CO(NH2)2

USD US dollar

V

VSCC Vertical Submerged Carbamate Condenser

VOC Volatile Organic Compounds


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W

WESP Wet Electrostatic PrecipitatorWSA Wet gas Sulphuric Acid (Topse)


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3 BACKGROUND - FERTILISER AND CARBON BLACK PROCESSES

Fertiliser production currently accounts for about 2 3 % of the total global energyconsumption. Nitrogen fertilisers account for a large majority of this consumption. Mostof the energy for fertiliser production is required for fixation of atmospheric nitrogen tomanufacture ammonia. Considerable energy is also required for the conversion ofammonia to urea.

Amongst the LVIC-AAF industries, the production of sulphuric acid and nitric acid arecandidates for exporting energy as high, medium, or low pressure steam or as hot water.The main pollutants emitted to air are NOx, SO2, H2S, HF, NH3 and dust. These are,depending on the particular source, usually emitted at high volume flows. In theproduction of HNO3, considerable amounts of the greenhouse gas N2O are generated.

In the table 2.1 below an overview of raw materials and the major environmental issuesconcerning mineral fertiliser production is given.

Production process Raw material Major issues

NH3 (intermediateproduct)

Hydrocarbon feed, water, air Energy consumption

Air: NOx, NH3, H2S

Waste water

Urea, UAN NH3, CO2 Energy consumption

Air: NH3, dust

Waste water: NH3, urea

CAN AN, CaCO3 Air: NH3, dust Waste water

HNO3 Air, NH3 Energy export

Air: N2O, NOx

H2SO4 SO2, air Energy export

Air: SO2, SO3/ H2SO4mist

H3PO4 Phosphate rock, H2SO4 Air: HF, H2SiF6, dust

Phosphogypsum

Waste water

H2SiF6 By- product from H3PO4

production

Air: HF, dust

Waste waterAN NH3, HNO3 Air: NH3, dust

Waste water

MAP NH3, H3PO4 Ammonia, dust, HF

NPK Phosphate rock, SSP/TSPNH3, H2SO4, H3PO4, HNO3

Air: NH3, NOx, HF, HCl,dust

Waste water

Carbon black Coal, gas SO2, NOx, dust

Energy export

Bentonite clay products Bentonite clay Dust


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Table 3.1: Overview of raw materials and the major environmental issues concerning mineral

fertiliser


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The most significant issues are:

Emissions of N2O from the production of nitric acid.

Energy consumption.

The amount of residue produced, 4 5 tonnes of phosphogysum are generatedper tonne P2O5manufactured in the production of H3PO4.

One issue is the radioactivity in different phosphate rocks due to the naturalpresence of the radioactive isotope of phosphorus.

The presence of As and Cd in the phosphate rock which will report to thephosphogysum residue.

Most of the energy for fertiliser production is required by the fixation of atmosphericnitrogen to manufacture ammonia. Considerable energy is also required for theconversion of ammonia to urea. For the manufacture of ammonium nitrate, theconversion of ammonia to nitric acid provides a net energy gain which can be used, forexample, to produce electrical energy via a steam turbine. The neutralisation ofammonia with nitric acid to produce ammonium nitrate also releases energy. In the caseof phosphate fertilisers, energy is required for the mining of the ore, for the production ofphosphoric acid, for the further processing into finished products and for pollutioncontrol.

Although fertiliser production will always consume large amounts of energy in processes

requiring high temperatures and pressures, the industry has become more energyefficient through improved design. Ammonia factories built in 1990 used some 30 percent less energy per tonne of nitrogen than those designed around 1970. Energy use ina new plant, using natural gas in a reforming process, including raw materials, can nowbe lower than 30 GJ/tonne NH3, compared with 75 GJ/tonne for the processes prevalentin the early 1960s. Partial oxidation processes use considerably more energy thanreforming processes. In 1995, the average for all plants in the US fertiliser industry wasabout 40 GJ/tonne.

Common issues

BAT is to carry out regular energy audits for the whole production site, to monitor key

performance parameters and to establish and to maintain mass balances for nitrogen,P2O5, steam, water and CO2. Minimisation of energy losses is carried out by generallyavoiding steam pressure reduction without using the energy or by adjusting the wholesteam system in order to minimise the generation of excess steam. Excess thermalenergy should be used on-site or off-site and, if local factors prevent that, as a lastoption, steam might be used for generating electrical power only.

BAT is to improve the environmental performance of the production site by acombination of recycling or re-routing mass streams, efficiently sharing equipment,increasing heat integration, preheating of combustion air, maintaining heat exchanger


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efficiency, reducing waste water volumes and loads by recycling condensates, processand scrubbing waters, applying advanced process control systems and by maintenance.

Production of ammonia

BAT for new installations is to apply conventional reforming or reduced primaryreforming or heat exchange autothermal reforming. In order to achieve the appropriateNOxconcentration emission levels, techniques such as SNCR at the primary reformer (ifthe furnace allows the required temperature/retention time windows), low NOx burners,ammonia removal from purge and flash gases or low temperature desulphurisation forautothermal heat exchange reforming, should be applied.

BAT is to carry out routine energy audits. Techniques to achieve the energyconsumption levels are extended preheating of the hydrocarbon feed, preheating of

combustion air, installation of a second generation gas turbine, modifications of thefurnace burners (to assure an adequate distribution of gas turbine exhaust over theburners), rearrangement of the convection coils and addition of additional surface, pre-reforming in combination with a suitable steam saving project. Other options areimproved CO2 removal, low temperature desulphurisation, isothermal shift conversion(mainly for new installations), use of smaller catalyst particles in ammonia converters,low pressure ammonia synthesis catalyst, use of sulphur resistant catalyst for shiftreaction of syngas from partial oxidation, liquid nitrogen wash for final purification of thesynthesis gas, indirect cooling of the ammonia synthesis reactor, hydrogen recoveryfrom the purge gas of the ammonia synthesis or the implementation of an advancedprocess control system. In partial oxidation, sulphur is recovered from flue-gases, e.g. byapplying a combination of a Claus unit with tail gas treatment to achieve BAT associated

emission levels and efficiencies given in the BREF on Oil and Gas Refineries. BAT is toremove NH3 from process condensates, e.g. by stripping. NH3 is recovered from purgeand flash gases in a closed loop. The full text provides guidance on how to handlestartup/shutdown and other abnormal operating conditions.

Production of nitric acid

BAT is to use recoverable energy: co-generated steam and/or electrical power. BAT is toreduce emissions of N2O by applying a combination of the following techniques:

optimising the filtration of raw materials

optimising the mixing of raw materials

optimising the gas distribution over the catalyst monitoring catalyst performance and adjusting the campaign length

optimisation of the NH3/air ratio

optimising the pressure and temperature of the oxidation step

N2O decomposition by extension of the reactor chamber in new plants

catalytic N2O decomposition in the reactor chamber

combined NOxand N2O abatement in tail gases.

BAT is to reduce emissions during startup and shutdown conditions. BAT is to reduceemissions of NOxand to achieve the appropriate emission levels by applying one or acombination of the following techniques:


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optimisation of the absorption stage

combined NOxand N2O abatement in tail gases

SCR addition of H2O2to the last absorption stage.

Production of sulphuric acidBAT is to use recoverable energy: co-generated steam, electrical power, hot water. Theoptions to achieve the appropriate conversion rates and emission levels are theapplication of double contact/double absorption, single contact/single absorption, theaddition of a 5th catalyst bed, using a caesium promoted catalyst in bed 4 or 5, thechange over from single to double absorption, wet or combined wet/dry processes,regular screening and replacement of the catalyst (especially in catalyst bed 1), thereplacement of brick-arch converters by stainless steel converters, improving raw gascleaning (metallurgical plants), improving air filtration, e.g. by two stage filtration (sulphurburning), improving sulphur filtration, e.g. by applying polishing filters (sulphur burning),maintaining heat exchanger efficiency or tail gas scrubbing (provided that by-productscan be recycled on-site).

BAT is to continuously monitor the SO2levels required to determine the SO2conversionrate and the SO2 emission level. The options to achieve appropriate SO3/H2SO4 mistemission levels are the use of sulphur with a low impurity content (in case of sulphurburning), adequate drying of inlet gas and combustion air (only for dry contactprocesses), the use of a larger condensation area (only for the wet catalysis process),adequate acid distribution and circulation rate, applying high performance candle filtersafter absorption, controlling concentration and temperature of the absorber acid orapplying recovery/abatement techniques in wet processes, such as ESP, WESP or wetscrubbing. BAT is to minimise or abate NOxemissions. BAT is to recycle exhaust gasesfrom product H2SO4stripping to the contact process.

Phosphate rock grinding and prevention of rock dust dispersionBAT is to reduce dust emissions from rock grinding, e.g. by application of fabric filters orceramic filters and to achieve dust emission levels of 2.5 10 mg/Nm3. BAT is to preventdispersion of phosphate rock dust by using covered conveyor belts, indoor storage, andfrequently cleaning/sweeping the plant grounds and the quay.

Production of phosphoric acidBAT for existing installations using a wet process is to achieve P2O5efficiencies of 94.0 98.5 %, e.g. by applying one or a combination of the following techniques:

dihydrate process or improved dihydrate process

increasing the residence time

recrystallisation process

repulping

double-stage filtration

recycling the water from the phosphogypsum pile

selection of phosphate rock.


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BAT for new installations is to achieve P2O5 efficiencies of 98.0 % or higher, e.g. byapplying a hemi-dihydrate recrystallisation process with double-stage filtration. BAT forthe wet process is to minimise the emissions of P2O5 by applying techniques like

entrainment separators (where vacuum flash coolers and/or vacuum evaporators areused), liquid ring pumps (with recycling of the ring liquid to the process) or scrubbingwith recycling of the scrubbing liquid.

BAT is to reduce fluoride emissions by the application of scrubbers with suitablescrubbing liquids and to achieve fluoride emission levels of 1 5 mg/Nm3expressed asHF. BAT for wet processes is to market the generated phosphogypsum and fluosilicicacid, and, if there is no market, to dispose of it. Piling of phosphogypsum requiresprecautionary measures and recycling of water from these piles. BAT for wet processesis to prevent fluoride emissions to water, e.g. by the application of an indirectcondensation system or by a scrubbing with recycling or marketing the scrubbing liquid.BAT is to treat waste water by applying a combination of the following techniques:

neutralisation with lime

filtration and optionally sedimentation

recycling of solids to the phosphogypsum pile.

Other BREFs that may be relevant include:

Large Combustion Plants, July 2006;

Large Volume Inorganic Chemicals - Ammonia, Acids and Fertilisers, August 2007;

Large Volume Inorganic Chemicals - Solids and Others - industry, August 2007;

Industrial Cooling Systems, December 2001;

Common Waste Water and Waste Gas Treatment / Management Systems in theChemical Sector, February 2003;

Emissions from Storage, July 2006;

Energy efficiency, June 2008;

General Principles of Monitoring, July 2003;

Economics and Cross-Media Effects, July 2006.

The following sections contain the BAT conclusions that are particularly relevant to theproduction of fertilisers in Croatia and each process is described and the conclusions aregiven.


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4 COMMON TECHNIQUES FOR ALL PROCESSES

In the BREF Large Volume Inorganic Chemicals - Ammonia, Acids and Fertilisers (LVIC AAF) a number of BAT techniques are specified, which are common for a productionsite as a whole. In the table 3.1 below an assessment is presented of the BATconclusions.

BAT conclusions

To carry out regular energy audits for the whole production

Energy audits

Advanced process control

SNCR at the primary reformer

Preheating of combustion air

Low NOx burners

Selective catalytic reduction of NOx(SCR)

Maintaining heat exchanger efficiency

Monitoring of key performance parameters

To monitor key performance parameters and to establish and to maintain massbalances for nitrogen, P2O5, steam, water, CO2

To minimise energy losses by: avoiding steam pressure reduction without using the energy

adjusting the whole steam system in order to minimise excess steamgeneration

using excess thermal energy on- or off-site

using steam for generating only electrical power, if local factors prevent theuse of excess thermal energy on-site or off-site

To improve the environmental performance of the production site by acombination ofthe following techniques: recycling or re-routing mass streams efficiently sharing equipment increasing heat integration preheating of combustion air

maintaining heat exchanger efficiency

reducing waste water volumes and loads by recycling condensates, processand scrubbing waters

applying advanced process control systems maintenance

To implement and adhere to an Environmental Management System (EMS)

Table 4.1: BAT Conclusions for common techniques


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5 AMMONIA PLANT

Ammonia is mainly produced as an intermediate product for the production of urea andnitric acid. Ammonia is synthesised from nitrogen and hydrogen by the followingreaction:

N2+ 3H22NH3

The best available source of nitrogen is from atmospheric air. The hydrogen requiredcan be produced from various feedstocks but currently it is derived mostly from fossilfuels. Depending of the type of fossil fuel, two different methods; steam reforming orpartial oxidation; are mainly applied to produce the hydrogen for ammonia production:.

There has been limited development work of the partial oxidation process in integratedplant concepts. At present, a typical plant is a blend of techniques offered by differentlicensors assembled by the selected contractor. The steam reforming process is themost efficient and the primary energy consumption of the processes is shown in table4.1 below.

Feedstock ProcessNet primary energyconsumption GJ/t NH3

Natural gas Steam reforming 28

Heavyhydrocarbons

Partial oxidation 38

Coal Partial oxidation 48

Table 5.1: Net primary energy consumption for the available processes

The block diagram of a steam reforming process (Kellogg process), which uses naturalgas as raw material is shown in the following figure 4.1 below.


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Figure 5.1: The Kellogg process

The conclusions from the LVIC-AAF BAT are given in table 4.2


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BAT conclusions Associated emission

Air emissions

SNCR at the primary reformerLow NOx burners

Ammonia removal from purge and flash gases in closedloop

Low temperature desulphurisation for autothermal heatexchange reforming

NOxemissions 90 230 mg/Nm3NOxas

NO2-0,29 0,32 kg/tonne NH3

Ammonia

Waste water emission

Stripping of ammonia from process condensates

Energy related issues

Preheating of the hydrocarbon feed

Preheating of combustion air

Installation of a second generation gas turbine

Modifications of the furnace burners to assure an adequatedistribution of gas turbine exhaust over the burners

Rearrangement of the convection coils and use of additionalsurface

Pre-reforming in combination with a suitable steam savingproject

Improved CO2removal

Low temperature desulphurisationIsothermal shift conversion (for new installations)

Use of smaller catalyst particles in ammonia converters

Low pressure ammonia synthesis catalyst

Use of a sulphur resistant catalyst for shift reaction ofsyngas from partial oxidation

Liquid nitrogen wash for final purification of the synthesisgas

Indirect cooling of the ammonia synthesis reactor

Hydrogen recovery from the purge gas of the ammoniasynthesis

Implementation of an advanced process control system

Startup/shutdown and other abnormal operating conditionsTo carry out routine energy audits

Net energy consumption 27,6-31,8 GJ/tonne NH3

Table 5.2: BAT conclusions for ammonia production


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6 NITRIC ACID PLANTS

Liquid ammonia is oxidised to nitrogen oxides and cooled down, the nitrogen oxidesreact with water to form nitric acid. NH3is reacted with air on a catalyst in the oxidationsection. Nitric oxide and water are formed in this process according to the mainequation:

4 NH3+ 5 O2 4 NO + 6 H2O

Nitrous oxide, nitrogen and water are formed simultaneously in accordance with thefollowing equations:

4 NH3 + 3 O22 N2 + 6 H2O

4 NH3 + 4 O22 N2O + 6 H2O

The yield of nitric oxide (NO) depends on pressure and temperature as indicated in table5.1 below.

Pressure in bar Temperature (C) NO yield (%)

6.5 900 940 95

Table 6.1: NO dependence on pressure and temperature

The reaction is carried out in the presence of a catalyst. The catalyst typically consists ofseveral woven or knitted gauzes formed from wire containing approximately 90 %platinum alloyed with rhodium for greater strength and sometimes containing palladium.

The most relevant emission are emissions to air of NOxand N2O. N2O is a strong globalwarming gas. The emissions to water are limited.

Block diagrams for two Nitric acid plants are shown in the following two figures.


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Figure 6.1: Block diagram of Nitric acid plant A

Figure 6.2: Block diagram of Nitric acid plant B


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Emissions to air

Optimisation of the absorption stage

Combined NOxand N2O abatement in tail gasesApplying SCR

Addition of H2O2to the last absorption stage

To reduce emissions during startup and shutdownconditions

Emission of NO2 5-90 ppmv/150 ppmv,

NH3 slip from SCR < 5 ppmv

Air emissions of N2O

Optimising the filtration of raw materials

Optimising the mixing of raw materials

Optimising the gas distribution over the catalyst

Monitoring catalyst performance and adjusting thecampaign length

Optimisation of the NH3/air ratio

Optimise pressure and temperature of the oxidation step

Catalytic N2O decomposition in the reactor chamber

Combined NOxand N2O abatement in tail gases

Waste water emissions

Waste water process


To use recoverable energy: co-generated steam and/orelectrical power

Table 6.2: BAT conclusions for nitric acid production


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7 UREA PLANT

The commercial synthesis of urea is achieved by the reaction of ammonia and carbondioxide at high pressure forming ammonium carbamate, which is then dehydrated byapplying heat, forming urea and water:

Both reactions take place in the liquid phase in the same reactor and are in equilibrium.The yield depends on various operating parameters. The most typical productionconditions are summarised in Table 6.1. Reaction 1 is fast and exothermic andessentially goes to completion under the industrial reaction conditions used. Reaction 2is slower and endothermic and does not go to completion. The conversion (on a CO2basis) is usually in the order of 50 80 %. The conversion increases with increasingtemperature and NH3/CO2 ratio and decreases with increasing H2O/CO2 ratio. Theproduction parameters are given in table 6.1

Parameter Unit

Pressure 140 250 bar

Temperature 180 210 C

NH3/CO2ratio 2.8:1 4:1 molar ratio

Retention time 20 30 minutes

Table 7.1: Typical urea production parameters

Several side reactions may occur in urea synthesis. The most relevant equilibriumreactions are

hydrolysis of urea: CO(NH2)2+ H2O NH2COONH42 NH3+ CO2

formation of biuret: 2 CO(NH2)2NH2CONHCONH2+ NH3

formation of isocyanic acid: CO(NH2)2NH4NCO NH3+ HNCO.

The hydrolysis reaction is the reverse reaction of the urea formation and only takesplace in the presence of water. Acids or alkaline solutions can also accelerate the rate ofhydrolysis. In practice, residence times of urea solutions with low NH3 content at high

temperatures must be minimised. Biuret must be limited in fertiliser urea (preferablymaximum of 1.2 %), since biuret might cause crop damage, notably during foliagespraying. In technical urea (e.g. used in the production of synthetic resins), the biuretcontent is generally up to 0.3 0.4 % or much lower (even


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stripping (still at high pressure) and subsequent depressurisation/heating of the ureasolution or combinations of both.Various strategies have been developed to realise total recycling processes, these

include:

conventional processes without stripping

CO2stripping processes, e.g. by Stamicarbon or Toyos ACES process

NH3stripping processes, e.g. by Snamprogetti

the Isobaric Double Recycling process (IDR), applying stripping with NH3and CO2,by Montedison.

Finally, the urea solution from the synthesis/recycling stages of the process isconcentrated via evaporation or crystallisation to a urea melt for conversion to a solidprilled or granular product for use as a fertiliser or technical grade. In some cases, ureais produced solely for melamine production.

Relevant emissions to air include dust and ammonia. Relevant emissions to water areammonia and urea.

The block diagram of a Urea Plant is shown in the next figure 6.1 and the BATconclusions in table 6.2.


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Figure 7.1: Block diagram of a Urea Plant


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General environmental performance

Apply plate bank product cooling

Redirecting urea fines to the concentrated urea solution

Select proper size of screens and mills, e.g. roller or chainmills

Apply surge hoppers for granulation recycle control

Apply product size distribution measurement

Monitoring key performance parameters

NH3 consumption per tonne of urea 570-600 kg/tonne

Air emissions

Treat exhaust gases from wet section by scrubbing andrecycle NH3 to the process

Reduce dust and ammonia from prilling and/or granulationand re-use the liquids on-site

Ammonia concentration from prilling tower 3 - 35 mg/Nm3

Dust concentration from prilling tower 15 - 55 mg/Nm3

Ammonia concentration after absorber Not specified by BAT

Ammonia in vents Not specified by BAT


Re-use or treatment of process water

NH3 concentration in effluent < 10 mg/l

Urea concentration in effluent < 5 mg/l


Applying or upgrading of stripping technology

Increase heat integration of stripping plants

Applying combined condensation and reaction technology

Table 7.2: BAT conclusions for Urea production


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8 SULPHURIC ACID PLANT

H2SO4is produced from SO2, which is derived from various sources such as combustionof elemental sulphur or roasting of metal sulphides. SO2is then converted into SO3in agas phase chemical equilibrium reaction, using a catalyst:

SO2+ O2SO3 H0= -99 kJ/mole

as this is an exothermic process, a decrease in temperature by removal of the heatwill favour the formation of SO3

increased oxygen concentration

SO3removal (as in the case of the double absorption process)

increased pressure

catalyst selection, to reduce the working temperature (equilibrium)

longer reaction time.

Optimising the overall system behaviour requires a balance between reaction velocityand equilibrium. However, this optimum also depends on the SO2 concentration in theraw gas and on its variability. Consequently, each process is more or less specific for aparticular SO2source.

Finally, sulphuric acid is obtained from the absorption of SO3and water into H2SO4(witha concentration of at least 98 %). For an example of a final absorber. The efficiency ofthe absorption step is related to:

the H2SO4concentration of the absorbing liquid (98.5 99.5 %)

the temperature range of the liquid (normally 70 120 C)

the technique of acid distribution

the raw gas humidity (mist passes the absorption equipment)

the mist filter

the temperature of incoming gas

the co-current or counter-current character of the gas stream in the absorbing liquid.

. Relevant emissions to air include SO2 and SO3/ H2SO4. Water emissions go to thesewage system.

The block diagram of a double absorption/double contact Sulphuric Acid Plant is shown

in the next figure 7.1 and the BAT conclusions in table 7.1.


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Figure 8.1: Block diagram of a double absorption/double contact Sulphuric Acid Plant


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Double contact/double absorptionAddition of a 5thcatalyst bed

Using a caesium promoted catalyst in bed 4 or 5

Wet or combined wet/dry processes

Regular screening and replacement of catalyst, especiallyof catalyst bed 1

Replace brick-arch converters by stainless steel converters

Improve air filtration, e.g. by two stage filtration (sulphurburning)

Improve sulphur filtration, e.g. by applying polishing filters(sulphur burning)

Maintaining heat exchanger efficiency

Tail gas scrubbing, provided that by-products can berecycled on-site

Conversion rate 99.8 99.92 %

Air emissions of SO2 and SO3/H2SO4

To continuously monitor the SO2 levels required todetermine the SO2 conversion rate and the SO2 emissionlevel

Use of sulphur with a low impurity content (in case ofsulphur burning)

Adequate drying of inlet gas and combustion air (only fordry contact processes)

Use of larger condensation area (only for wet catalysisprocess)

Adequate acid distribution and circulation rate

Applying high performance candle filters after absorption

Control concentration and temperature of the absorber acid

To minimise or abate NOxemissions 20 mg/m3

To recycle exhaust gases from product H2SO4 stripping tothe contact process

30 mg/kg

SO2emission,Daily average

30 770 mg/Nm3

SO3/ H2SO4emission,

Yearly average

10 35 mg/Nm3


See above


To use recoverable energy: co-generated steam, electricalpower, hot water

Table 8.1: BAT conclusions for sulphuric acid production


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9 PHOSPHORIC ACID PLANT

There are three possible subgroups of wet processes depending on which acid is usedfor the acidulation, i.e. HNO3, HCl or H2SO4. The wet digestion of phosphate rock withH2SO4 is the preferred process in terms of volume. For descriptions of specific wetprocesses using H2SO4, see:

The tri-calcium phosphate from the phosphate rock reacts with concentrated H2SO4 toproduce H3PO4and the insoluble salt calcium sulphate.

Ca3(PO4)2+ 3 H2SO42 H3PO4+ 3 CaSO4

The insoluble calcium sulphate is filtered from the H3PO4. The reaction between

phosphate rock and H2SO4is restricted by an insoluble layer of calcium sulphate whichforms on the surface area of the rock. This restriction is minimised by contacting thephosphate rock with recirculated H3PO4, thereby converting as much of it as possible tothe soluble mono calcium phosphate, followed by precipitation as calcium sulphate withH2SO4.

Ca3(PO4)2+ 4 H3PO43 Ca(H2PO4)2

3 Ca(H2PO4)2+ 3 H2SO43 CaSO4+ 6 H3PO4

The operating conditions are generally selected so that the calcium sulphate will be

precipitated as the di or hemihydrate form, i.e. 26 32 % P2O5 at 70 80 C for

dihydrate precipitation and 40 52 % P2O5at 90 110 C for hemihydrate precipitation.Circulation of the reactor contents provides the necessary mixing. The phosphoric acid isseparated from the calcium sulphate.

Compound fertilisers can be produced in four, basically different, ways:

production by the mixed acid route, without phosphate rock digestion

production by the mixed acid route, with phosphate rock digestion

production by the nitrophosphate route (ODDA process)

mechanical blending or compactation of single or multi-nutrient components (notincluded in the figure).

Raw materials include rock phosphate and sulphuric acid to form phosphoric acid. Thechemical equation of phosphoric acid (H3PO4)production is:

Ca10F2(PO4)6 + 10H2SO4 + 20H2O 6H3PO4 + 10CaSO4*2H2O+ 2HF

Relevant emissions to air include dust, HF and SiF4. Water emissions may containphosphorus, sulphate, fluorides and metals.

Phosphogypsum is produced as solid waste and may contain cadmium that is present inthe raw materials.


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The block diagram of a phosphoric acid plant is shown in following figure 8.1 and theBAT conclusions in table 8.1.

PHOSPHATEROCK

GRINDING

REACTOR

S

C

R

U

B

B

E

R

FILTER

WASTE GASES

PHOSPHATE

ROCK

H2SO4

(EMISSION TO AIR)

(EMISSION TO AIR)PHOSPHATE DUST

(VACUUM)

PHOSPHOGYPSUMRETURN PHOSPH. ACID

WEAK

PHOSPHORIC

ACID

WASH

WATER

RETURN WATER FROM

PHOSPHOGYPSUM STACKMAKE-UP

WATER

(29% P2O5)

SEPARATOREVAPORATOR

CIRCULATION

PUMP

H

E

A

T

E

X

C

H

A

N

G

E

R

F

L

O

U

R

I

N

E

S

C

R

U

B

B

E

R

STRONG

PHOSPHORIC

ACID

WEAK

PHOSPHORICACID

STEAM

CONDENSATE

H2SiF6

MAKE-UP

WATER

VACUUM

SYSTEM

(54% P2O5)

Reaction and filtration section

Concentration section

Figure 9.1block diagram of a phosphoric acid plant


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Dihydrate process or improved dihydrate processIncreasing the residence time

Recrystallisation process /Double-stage filtration

Repulping

Recycling the water from the phosphogypsum pile

Selection of phosphate rock

Market the generated Phosphogypsum (if possible) andfluosilicic acid

P2O5 efficiency 94 98,5 %

Precautionary measures concerning phosphogypsum pileand recycling water from these piles

Reduce dust emissions from rock grinding, e.g. byapplication of fabric filters or ceramic filters

Dust emission from grinding 2.5 10 mg/Nm3

Prevent dispersion of phosphate rock dust by using coveredconveyor belts, indoor storage

Frequently cleaning/sweeping the plant grounds and thequay

Reduce fluoride emissions by application of scrubbers withsuitable scrubbing liquids

Fluoride emission into air 1 5 mg/Nm3expressedas HF


Entrainment separators, where vacuum flash coolers and/orvacuum evaporators are used

Liquid ring pumps with recycling of the ring liquid to theprocess

Scrubbing with recycling of the scrubbing liquid

Prevent fluoride emissions to water by application of indirectcondensation system or by a scrubbing with recycling ormarketing the scrubbing liquid

Treat waste water by applying a combination of thefollowing techniques:

Neutralisation with lime

Filtration and optionally sedimentation

Recycling of water and solids to the phosphogypsumpile

Table 9.1: BAT conclusions for phosphoric acid production


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10 CALCIUM AMMONIUM NITRATE (CAN) PLANTS

AN (NH4NO3) is produced by neutralising 50 70 wt-% aqueous HNO3 with gaseousNH3:

NH3+ HNO3 NH4NO3

The reaction is highly exothermic and proceeds rapidly. The heat produced is often usedto generate steam. The obtained AN solution can be concentrated by evaporation. Mostapplied production processes comprise three main operations: neutralisation,evaporation and solidification (prilling or granulation).

The exothermic neutralisation of HNO3with NH3gas produces ANS (ammonium nitratesolution) and steam. The HNO3 is normally preheated in corrosion-resistant equipment,

particularly if the concentration of nitric acid is at the lower end of the 50 70 % range.Preheating using steam or hot condensate from the AN process is the most effective useof this excess heat.

The ANS is normally concentrated in an evaporator to the water content required for theparticular product finishing. The water concentration is normally below 1 % for a prilledproduct and up to 8 % for some granulation processes.

Relevant emissions to air include NH3and dust. Water emissions may contain ammoniaand nitrate. The most relevant details of the process are listed below:

The block diagrams of two calcium ammonium nitrate plants are shown in the following

figures 9.1 and 9.2 and the BAT conclusions in table 9.1.


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Figure 10.1: Block diagrams of a calcium ammonium nitrate plant

Figure 10.2: Block diagrams of an alternative calcium ammonium nitrate plant


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BAT conclusions


To optimise the neutralisation/evaporation stage by a combination of:

Using the heat of reaction to preheat the HNO3and/or to vapourise NH3

Operating the neutralisation at an elevated pressure and exporting steam

Using the generated steam for evaporation of water from ANS

Recovering residual heat for chilling process water

Using the generated steam for the treatment of process condensates

Using the heat of the reaction for additional water evaporation

To effectively and reliably control pH, flow and temperature

To improve environmental performance of the finishing section by one or acombination of:


Recycling of warm air

Select proper size of screens and mills, e.g. roller or chain millsApply surge hoppers for granulation recycle control

Apply product size distribution measurement and control

Air emissions(1)

To reduce dust emissions from dolomite grinding to levels < 10 mg/Nm 3 byapplying, e.g. fabric filters.


To minimise waste water volumes by recycling washing and rinsing waters andscrubbing liquors into the process, e.g. by using residual heat for waste waterevaporation

To treat the remaining waste water volumes

To recycle process water on-site or offsite and to treat the remaining wastewater in a biological treatment plant or using any other technique achieving anequivalent removal efficiency.

Table 10.1: Bat conclusions for CAN production

(1) Please note that the BREF indicates that no conclusions could be drawn for emissions to air fromneutralization, evaporation, granulation, prilling, drying, cooling and conditioning because of aninsufficient data basis.

11 NITROGEN PHOSPHOROUS POTASSIUM (NPK) PLANTS

The production of NPK fertilisers by digestion of phosphate rock with HNO3in the ODDAprocess produces calcium nitrate tetra hydrate (CNTH, Ca(NO3)2

. 4 H2O) as a by-product. The conversion of CNTH with NH3 and CO2 results in the production ofammonium nitrate and lime, which can both be used for the production of CAN.

For the conversion, NH3 and CO2 are dissolved in an NH4NO3 solution, which iscirculated in a carbonising column, and forms ammonium carbonate according to:

2 NH3+ CO2+ H2O (NH4)2CO3


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The reaction is exothermic and the heat is removed by cooling. Also CNTH is dissolvedin a NH4NO3solution and both solutions react according to:

Ca(NO3)2+ (NH4)2CO32 NH4NO3+ CaCO3

On completion, excess (NH4)2CO3 is neutralised with HNO3 and the approx. 65 %NH4NO3 (AN) solution is separated (belt filter) from the CaCO3 (lime) and concentratedin a two stage evaporator (e.g. falling film type) using steam.

Alternatively, the CNTH may be converted into commercial calcium nitrate fertiliser.

Relevant emission to air include NH3, NOx, HF, HCl, dust. Water emissions may containphosphorus, sulphate, fluorides and metals.

The block diagrams of two typical NPK plants are shown in the following figures 10.1

and 10.2 and the BAT conclusions in table 10.1.


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Figure 11.1: Block diagram of a typical NPK plant using the mixed acid route


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Figure 11.2: Block diagram of a typical NPK plant




Recycling of warm air

Select proper size of screens and mills, e.g. roller or chainmills

Apply surge hoppers for granulation recycle control

Apply online product size distribution measurements forgranulation recycle control


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Air emissions

Reduce dust emissions from rock grinding, e.g. byapplication of fabric filters or ceramic filters and to achievedust emission levels of 2.5 10 mg/Nm3

Prevent dispersion of phosphate rock dust by using coveredconveyor belts, indoor storage, and frequentlycleaning/sweeping the plant grounds and the quay

Minimise the NOxload in exhaust gases from phosphate rockdigestion by one or a combination of:

Accurate temperature control

Proper rock/acid ratio

Phosphate rock selection

Reduce emissions air from phosphate rock digestion, sandwashing and CNTH filtration by applying, e.g. multistagescrubbing

NOx emission from phosphate rock digestion, sand washingand CNTH filtration

100 425 mg/Nm3

Fluoride emission from phosphate rock digestion, sandwashing and CNTH filtration

0,3 5 mg/Nm3

To reduce emission levels air from neutralisation,granulation, drying, coating and cooling by applying thefollowing techniques:

Dust removal, such as cyclones and/or fabric filters

Wet scrubbing, e.g. combined scrubbing

To reduce emission levels air from neutralisation,granulation, drying, coating and cooling by applying theabove techniques and to achieve the emission levels orremoval efficiencies listed below:

NH3 emission from neutralisation, granulation, drying,coating and cooling

5- 30 mg/Nm3

Fluoride emission from neutralisation, granulation, drying,coating and cooling (as HF)

1 -5mg/Nm3

Dust emission from neutralisation, granulation, drying,coating and cooling

10 - 25mg/Nm3

HCl emission from neutralisation, granulation, drying,coating and cooling

4 - 23mg/Nm3

Waste water emissionsTo minimise waste water volumes by recycling washing andrinsing waters and scrubbing liquors into the process, e.g. byusing residual heat for waste water evaporation

To treat the remaining waste water volumes

Table 11.1: BAT conclusions for NPK production


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12 WASTE AND WASTEWATER

Wastewater is produced by all of the process reported above. Wastewater treatment is

reported in the horizontal guideline on Waste gas and waste water treatment. Twomethods are used in Croatia and meet the requirements of BAT:

Ion exchange to recover water and ammonia and nitric acid which are reused.

Treatment of fluorides with lime.

There are also wastewater and other facilities including a waste disposal facility for thePhosphor Gypsum residue.

Cadmium levels should be controlled by strict quality limits on the phosphate rocksupplies. In Croatia the limit is 70 grams per tonne. The disposal site should be treatedas a landfill and use monitoring boreholes to assess the potential leakage of contents

and leachate.

Water used to transport the residue should be returned to the process and re-used.

13 CARBON BLACK PLANT

The heart of a furnace black plant is the furnace in which the carbon black is formed.The primary feedstock is injected, usually as an atomised spray, into a high temperaturezone of high energy density, which is achieved by burning a secondary feedstock(natural gas or oil) with air.

The oxygen, which is in excess with respect to the secondary feedstock, is not sufficientfor complete combustion of the primary feedstock, the majority of which is, therefore,pyrolysed to form carbon black at 1200 1900 C.

The reaction mixture is then quenched with water and further cooled in heat exchangers,and the carbon black is collected from the tail-gas by a filter system.

The primary feedstock, preferably petrochemical or carbo-chemical heavy aromatic oils,some of which begin to crystallise near ambient temperature, is stored in open to air,vented and heated tanks equipped with circulation pumps to maintain a homogeneousmixture. The primary feedstock is pumped to the reactor via heated and/or insulatedpipes to a heat exchanger, where it is heated to 150 - 250 C to obtain a viscosity

appropriate for atomisation. Various types of spraying devices are used to introduce theprimary feedstock into the reaction zone.

As the carbon black structure can be influenced by the presence of alkali metal ions inthe reaction zone, alkali metal salts, preferably aqueous solutions of potassium salts(e.g. potassium carbonate, hydroxide or chloride), are often added to the oil in the oilinjector. Alternatively, the additives may be sprayed separately into the combustionchamber. In special cases, other additives, e.g. alkaline-earth metal compounds, whichincrease the specific surface area, are introduced in a similar manner.


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The energy to break C-H bonds is supplied by feedstock, which provides the reactiontemperature required for the specific grades. Natural gas, petrochemical oils and othergases, e.g. coke oven gas or vaporised liquid petroleum gas may be used as secondary

feedstock. Depending on the type of secondary feedstock, special burners are also usedto obtain fast and complete combustion. The required air is preheated in heatexchangers by the hot carbon black containing gases leaving the reactor. This savesenergy and thus improves the carbon black yield. Preheated air temperatures of 500 700 C are common.

The properties of carbon blacks depend on the ratios of primary feedstock, secondaryfeedstock and air, which therefore must be carefully controlled. The particle size of thecarbon black generally decreases with increasing amounts of excess air relative to theamount needed for the complete combustion of the secondary feedstock. Since theexcess air reacts with the primary feedstock, a greater amount of air leads to higher oilcombustion rates, resulting in rising temperatures in the reaction zone. As a

consequence, the nucleation velocity and the number of particles formed increase, butthe mass of each particle and the total yield decrease.

The yields, which depend on the carbon black type and the type of primary feedstock,range between 40 and 65 % for some types of carbon black. High surface area pigmentblacks with markedly smaller particle size than rubber blacks give lower yields(10 - 30 %). Other parameters influencing carbon black quality are the manner in whichthe oil is injected, atomised, and mixed with the combustion gases, the type and amountof additives, the preheating temperature of the air and the quench position.

Furthermore, traces of sulphur compounds (H2S, CS2 and COS) and nitrogencompounds (HCN, NOX, NH3) are present in these gases. The amount of these

compounds depends on the composition of the feedstock and the processing conditions.The combustible gases normally include 6 12 vol-% carbon monoxide, 6.5 14 vol-%hydrogen, small amounts of methane and other hydrocarbons. The lower heating valuelies between 1.7 and 3.8 MJ/m3. The gas is normally burned for environmental reasons,and a portion of its energy is used, e.g. for heating dryer drums and for the production ofsteam and/or electricity. At many plants, the remaining portion of the tail-gas iscombusted using a flare.

The mixture of gas and carbon black leaving the reactor is cooled to 250 350 C inheat exchangers by counter-flowing combustion air and then conducted into thecollecting system. Formerly, a combination of electro-flocculators and cyclones orcyclones and filters were used. Currently, simpler units are preferred. Generally, the

collecting system consists of only one high performance bag filter with severalchambers, which are periodically purged by counter-flowing filtered gas or by pulse-jets.Occasionally, an agglomeration cyclone is installed between the heat exchanger and thefilter.

Fluffy carbon black has an extremely low bulk density of 20 60 g/l. To facilitatehandling and further processing by the customer, it must be compacted. Densification byoutgassing a process by which the carbon black is passed over porous, evacuateddrums is the weakest form of compacting and allows the carbon black to retain itspowdery state. This form of compacting is used for certain pigment blacks, which mustretain easy dispersibility. Other pigment blacks and rubber blacks are compacted bypelletisation. Two processes are used: dry and wet pelletisation.


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The block diagram of a Carbon Plant is shown in the following figure 11.1 and the BATconclusions in table 11.1.

Figure 13.1: Block diagram of a Carbon Plant


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Use low sulphur feedstock with a sulphur content in the

range of 0.5 - 1.5 % as a yearly averageSpecific emission level 10 50 kg SOx (as SO2)

per tonne of rubber gradecarbon black produced, asa yearly average

Preheat air required in the process to save energy

Maintain optimum operational parameters in the carbonblack collecting system

Utilise the energy content of the tail-gas

Apply primary DeNOx techniques

Emission in the range of 0.6 1.0 g NOx/Nm3as an hourly

average at 3 % O2 normal production

Reduce NOxemissions from flares

Apply fabric filters for the air conveying system, ventcollection system and dryer purge gas

Dust in off gas from conveying and vent collector systems10-30 mg/Nm3as a half-hour average

Dust in off gas from dryer purge filter

Documents

BAT Guide on Fertiliser Processes