3 category 3: carbonization and coal gasification

3 CATEGORY 3: CARBONIZATION AND COAL GASIFICATION

Producing high purity carbon substances from gasses or by modifying other carbon rich

solids falls under Category 3. These processes primarily rely on heat to drive off the

volatiles in the raw material in an oxygen starved atmosphere thereby reducing the

compounds to carbon.

The raw material needs to be high in carbon limiting it to carbonaceous materials such

as biomass, coal and hydrocarbon oils. The processes used are mostly derived from

pyrolysis which is the application of high temperatures to a substance in the presence

of little or no oxygen. This vaporizes the volatiles components of the material without

combusting the carbon. Coal pyrolysis at high temperature is called carbonization.

The main products gained from the various raw materials are:

• Carbon black from oil

• Coke from coal

• Char (or charcoal) from biomass

These products can be bonded and shaped into more usable forms, a well-known

South African example being charcoal briquettes used in food preparation which is

made from char that has been bonded and compressed into the desired shape.

Tar production is also under this category which deals with the separation of the

volatiles off of the heavy oils using heat.

The APPA scheduled activities that are covered in this category are:

3. Gas Liquor Processes (Sub-category 3.1)

16. Tar Processes (Sub-category 3.3)

18. Benzene Processes

25. Acid Sludge Processes

34. Gas, Coke and Charcoal Processes

64. Carbon Black Processes (Subcategory 3.4)

3.1 SUB-CATEGORY 3.1: COMBUSTION INSTALLATIONS

3.1.1 APPLICABILITY

Combustion installations not used primarily for steam raising or electricity generation

All combustion installations (except test or experimental installations)

Sub-category 3.1 covers combustion processes involved in carbonization processes and

coal gasification that are not used for heat or steam generation purposes. These will

include all combustion installations not covered by any of the other subcategories. The

combustion flue gas will need to comply with this subcategory if it falls in carbonization

and coal gasification processes while the process it is heating may need to comply with

an appropriate sub-category (Sub-category 3.3: Tar Production is an example).

For combustion processes primarily used for heat and steam generation refer to Sub-

category 1.1. For combustion processes involved in liquid and gaseous fuel production

from coal and crude oil refer to Sub-category 2.1.

3.1.2 PROCESS OVERVIEW

This sub-category is a generalised combustion sub-category. The combustion will follow

the same steps as the other combustion processes in that:

• A fuel is processed and fed to a combustor of some description, where;

• Heat is liberated either to promote a reaction or to heat up a process or

material; and

• Combustion emissions are generated and should be channelled through

appropriate abatement equipment and released to atmosphere within the

emission limits.

The descriptions that can be given are therefore extremely varied and are not limited

to a single setup type. General examples of such combustion processes may include:

• Drying raw materials before feeding to other processes;

• Pre-heating of materials before being sent to other processes; and

• Application of heat to keep tar and other highly viscous substances in a fluid

state to facilitate storage or transfer to transport containers.

Figure 3-1: Combustion Process

3.1.3 ATMOSPHERIC EMISSIONS

Typical pollutants emitted to atmosphere from this process include (but are not

necessarily limited to):

• Particulate Matter* (ash and soot)

• Sulphur Dioxide (SO2)*

• Oxides of Nitrogen (NOx)*

• Carbon Monoxide (CO)

• Metals (In the case of coal use, particulate matter may contain some metals)

* Regulated by the NEMAQA emission standards

The atmospheric emissions are expected to be primarily from the combustion of flue

gases and are generally released to the atmosphere using a flue stack. Before releasing

to atmosphere the flue gas can be cleaned using a variety of methods, depending on

the target pollutant, common examples are:

• Scrubber: PM, SO2, NOx

• Cyclone: PM

• Baghouse: PM

• Electrostatic Precipitator: PM

Improper handling and disposal of the ash obtained from the combustor and the fly ash

from the abatement could lead to particulate matter emissions. The bottom ash

removed from the boiler and the fly ash removed from the flue gas may either be sold

as a product if they meet the end-user’s specifications or they may be disposed of in

ash dams or landfills. Improper handling of ash or improper management of the

disposal area may lead to fugitive particulate emissions.

3.1.4 SPECIAL ARRANGEMENTS

Compounds containing sulphur recovered from gases, to be used for combustion, with:

• A recovery efficiency of not less than 90%; or

• The remaining content of sulphur-containing compounds to be less than 1000

mg/Nm3 measured as hydrogen sulphide, whichever is strictest.

3.2 SUB-CATEGORY 3.2: COKE PRODUCTION AND COAL GASSIFICAITON

3.2.1 APPLICABILITY

Coke production, coal gasification and by-product recovery from these operations

All installations

Sub-category 3.2 covers coal gasification and coking processes which has a direct

relation to APPA scheduled process No. 34: Gas, Coke and Charcoal Processes (also

linked to Sub-category 3.4).

Coke is produced by the application of high temperatures to coal in the absence of

oxygen. The coal is heated until all the volatile components are removed. The porous

carbon rich material which remains is referred to as coke and is largely used as a

reducing agent for production of ferro-alloys. Coke may also be produced from other

carbonaceous materials such as petroleum, however coal is the primary source of coke

in South Africa.

Coal gasification is undertaken by heating coal in the presence of steam and a

controlled amount of oxygen to produce gases which are captured, processed and

split into a product and waste gases. The gas produced may be used for its calorific

value and/or as a reducing agent.

3.2.2 PROCESS OVERVIEW – COKE PRODUCTION

Figure 3-2: Coal Coking Process

Figure 3-3: Photograph of a coke oven battery showing the chambers, the coal tower

and the coke oven gas collecting main (IPPC, 2001)

Coke is the non-volatile component of coal that has been fused together by the

application of heat in the absence of oxygen. Coke is used in high temperature

applications and as a reducing agent in metallurgical and ore treatment processes.

The raw material used for this process is normally referred to as coking coal. Various

types of coal (i.e. coals with different compositions) are used to produce the coke

product.

3.2.2.1 Receiving and Handling of Raw Materials

Coal is typically received via locomotive or road truck unless the coking plant is located

close to the mine, in which case delivery by overland conveyor may be possible.

Coking plants are generally located at the site of use rather than at the source of

coking coal. Conveyor belts transfer the coal to silos or mixing bins where the various

types of coal are stored.

Refer to Sub-category 5.1 for further detail on bulk coal handling systems and

associated emissions.

3.2.2.2 Pre-Processing

The coal is transferred from the silos/mixing bins to a crusher where it is crushed to a pre-

selected size. The desired size depends on the response of the coal to coking reactions

and the ultimate coke properties required.

The coal is then mixed and blended. According to US-EPA AP42 sometimes water and

oil are added to control the bulk density of the mixture. The prepared coal mixture is

transported to storage vessels or prepared for feeding to the coke oven battery. Coal is

then fed into a trolley (charging car), and transferred to the coking oven. The coal may

also be transported by various forms of conveyor (e.g. belt conveyors, pneumatic

conveyors etc.).

3.2.2.3 Feeding and Processing

The coke production process follows these general steps:

• Charging - The coal is placed in the coke oven;

• Heating/Firing and Cooking – The oven is heated and the volatiles (coal gas,

moisture and coal tars) are driven off leaving behind the non-volatile carbon

and ash fusing to form coke;

• Pushing - When the coking is completed the coke is pushed out from the ovens;

and

• Quenching – the hot coke is quenched with water. After quenching, the coke

can be transported to stockpiles and silos.

The coal is typically charged from the top. To minimize the escape of gases from the

oven during charging, steam aspiration may be used to draw gases from the space

above the charged coal into the collecting main. The material is then mechanically

levelled in the oven. This levelling process aids in uniform coking and provides a clear

vapour space for the gases that evolve during coking to flow to the gas collection

system. The doors are then closed and sealed.

A coking plant generally consists of a battery of individual coke oven chambers

separated by heating walls. The heating walls have cavities in which gas is combusted

to provide heat. In some cases fuel is combusted externally and the hot combustion

gasses are passed into the heating walls. Coke oven gas is often used as a fuel but

other fuels may be used to meet the total energy need.

The carbonisation process starts immediately after coal charging. The volatile materials

driven off (volatile organics, water, H2S etc.) account for about 8 - 20% of the charged

coal, this varies depending on the coal composition and residence time in the oven.

The raw coke oven gas (COG) is exhausted into a collecting main and passed onto gas

cleaning processes. The high calorific content of this gas means that after gas cleaning

it can be used as a fuel.

COG has a relatively high calorific content due to the presence of hydrogen, methane,

carbon monoxide and hydrocarbons and thus can be used as a fuel for the coking

process. Furthermore COG contains valuable products such as tar, light oil (mainly

consisting of BTEX (benzene, toluene, ethyl benzene and xylenes), sulphur and

ammonia. Thus various by-products can be recovered from the gas. In this case the

valuable by-products are separated from the gas stream using various methods such as

condensation and absorption.

Upon completion of the coking process, the coke oven is opened and the coke is

pushed out into a container. The coke is still at an elevated temperature and upon

contact with air the coke may begin to burn. Thus it is transported to a quenching

station where it is sprayed with water. Dry quenching can also be used, in which case

the coke is transported to a dry quenching chamber which is sealed and an inert

quenching gas (e.g. nitrogen) is circulated through the chamber. This process has the

advantage of being able to recover heat for use elsewhere, while preventing the

generation of liquid effluent.

3.2.2.4 Atmospheric Emissions

Pollutants from these processes will depend a lot on the quality of the coal used as well

as the process parameters but typically will contain the following pollutants:

• Hydrogen sulphide (H2S)*

• Carbon monoxide (CO)

• Ammonia (NH3)

• VOCs (including benzene, toluene, xylene, and PAHs)

• Particulate matter

• Metals (In the case of coal use, particulate matter may contain some metals)


Pre-coking atmospheric emissions are expected to be primarily from materials handling

fugitives and will largely be particulate matter. The coking oven emissions may be

significant and direct emissions are typically fugitive emissions from:

• Improper/imperfect sealing of ovens;

• Fugitive oven emissions during charging; and

• Fugitive oven emissions during pushing and from the hot coke.

Gas recovery allows the COG to be re-used as an energy source and/or produce by-

products. Once cleaned the off-gasses and are generally released to the atmosphere

after combustion, or by-products are recovered. Common cleaning methods applied

include:

• Cooling/Condensing: drop out H2O, tar and organics with low boiling points; and

• Scrubber: PM, SO2, H2S, NOx

3.2.2.5 Further Sources of Information

For further information refer to:

1) EC IPPC 2001 Production of Iron and Steel

2) US-EPA AP 42 chapter 12.2.

3) IFC EHS Guidelines Integrated Steel Mills

3.2.3 PROCESS OVERVIEW – COAL GASIFICATION

Figure 3-4: Coal gasification process

3.2.3.1 Receiving and Handling of Raw Materials

Coal is typically received via locomotive or road truck unless the plant is located close

to the mine in which case delivery by overland conveyor may be possible. Conveyor

belts transfer the coal to silos or mixing bins for storage prior to processing.

Refer to Sub-category 5.1 for further detail on bulk coal handling systems and

associated emissions.

3.2.3.2 Pre-Processing

The coal is transferred from the silos/mixing bins to a crusher where it is crushed to a

preselected size as required by the gasification plant. The coal may be mixed and

blended depending on the desired raw material specification for gasification.

3.2.3.3 Gasification

Coal gasification is undertaken by heating coal in the presence of steam and a

controlled amount of oxygen. The primary aim of this process is to produce syngas (also

known as synthesis gas or synthetic gas) which can be processed to produce various

other products or directly used as a gaseous fuel or reductant. The gas produced may

be used for its calorific value and/or as a reducing agent.

The key steps in the gasification process are as follows:

• Gasification: the partial combustion of coal with limited oxygen supplied, and

steam, which creates a mixture of CO, CO2, H2, and CH4, as well as volatiles, and

some H2S depending on the composition of the coal. This product is generally

referred to as ’raw gas’ or ‘crude syngas’;

C + O2 + H2O → H2 + CO + CH4 + CO2*

Carbon (in coal) + Oxygen + Steam → Syngas

• Gas Cooling: the gas is cooled to condense and remove the less volatile

components. The material removed may be further processed to produce

organic by-products;

• Gas cleaning: particulate removal and if necessary removal of other undesired

impurities;

• Shift conversion: excess carbon monoxide in the raw gas is catalytically "shifted"

(converted) to carbon dioxide to obtain the desired ratio of hydrogen-to-carbon

monoxide required for downstream production of methane (Fischer-Tropsch

process);

• Acid gas removal: The cleaned syngas is then sent through an absorption

process where H2S and CO2 are removed, from which elemental sulphur can

further be produced (using the Claus process for example, refer to Section Error!

Reference source not found.); and

* Note that the chemical equation is not balanced and is for illustration only

• The clean gas is then fed to other processes for use, such as the Fischer-Tropsch

process for gas-to-liquids processes (refer to Category 2), as a reductant, or as a

gaseous fuel.

A number of reactions occur during gasification to produce syngas. These include:

� The gasification of the carbon takes place by the reaction:

C + H2O (steam) + Heat → CO + H2

� Hydrogen is also produced by the "water gas reaction";

CO + H2O → CO2 + H2 + Heat

� Some carbon also reacts with carbon dioxide to form carbon monoxide:

C + CO2 + Heat → 2CO

� Methane is produced by the hydrogasification reaction:

C + 2H2 → CH4 + Heat

� Some carbon is completely combusted with oxygen to produce CO2, providing

significant amounts of heat which drives the other reactions and can also be

recovered to produce steam to feed the gasifier:

C + O2 → CO2 + Heat

The oxygen required for gasification can either be fed as pure oxygen or as air. In case

where pure oxygen is used an air separation process is required.

Several by-product streams may be produced; these include, but are not limited to:

• Tars;

• Waxes;

• Oils;

• Sulphur; and

• Ammonia.

The volatiles removed during the gas cleaning phase can be separated to yield

specific products such as ammonia and phenol. The remaining off gasses from the

volatile recovery and sulphur recovery will be sent to abatement and released from a

stack.


Pollutants from these processes will depend a lot on the quality of the coal used as well

as the process parameters but typically will contain the following pollutants:

• Particulate matter


• Hydrogen sulphide (H2S)*

• Heavy Metals (in particulate matter)

• Carbonyl sulphide (COS)


Pre-processing atmospheric emissions are expected to be primarily from materials

handling and crushing fugitives and will largely be particulate matter.

The gasification process will generally result in interment release of gaseous and

particulate matter from the coal feed chamber when it is opened to input coal. This

may be prevented or reduced by the use of lock chamber which allows gas in the

chamber to be purged in to the gasifier or syngas stream before opening to take in a

batch of coal.

Ash quenching will result in the entrainment of ash particulate matter in steam and

vapour and may be significant if not abated. Before releasing to atmosphere the ash

quenching flue gas may require abatement to target particulate matter:

• Scrubber: PM,

• Cyclone: PM

Improper disposal of the ash obtained from the gasifier may lead to particulate matter

emissions when the disposed ash slurry has dried out.



1) US-EPA AP 42 chapter 11.11 Coal Conversion

2) IFC EHS Guidelines Environmental, Health and Safety Guidelines for Coal

Processing

3) IPPC Guidance for the Gasification, Liquefaction and, Refining Sector


The following special arrangements shall apply:

• Charging must be carried out "on the main" with additional draught in the

ascension or riser pipes produced by high-pressure water jets in the goosenecks.

Even coal feeding must be ensured using screw feeders or rotary valve feeders.

Telescopic seals are to be used around the charging holes. Visible emissions are

limited to 12 sec per charge

• For pushing, evacuation from the coke guide and the quench car using

stationary ducting and gas cleaning or any other technology yielding the

equivalent or better results is required.

• For quenching, the quench tower must have suitable baffles; quench water must

have less than 50 mg/litre suspended solids and no floating oil.

• A battery and door frame maintenance system approved by the licensing

authority must be operated. No more than 4% of doors may show visible leaks;

no more than 2.5% of gas off-take pipes may show visible leaks.

• Measurement inspection procedures for visible leaks from doors, standpipes and

from charging shall be carried out weekly for each battery using method EPA

303 from Table 1 and records submitted to the licensing authority on a quarterly

basis.

The licensing authority may set alternative standards and/or control measures for the

reduction of hydrogen sulphide emissions.

3.3 SUB-CATEGORY 3.3: TAR PRODUCTION

3.3.1 APPLICABILITY

Processes in which tar, creosote or any other product of distillation of tar is distilled or

heated in any manufacturing process.

All installations

Sub-category 3.3 covers all tar distillation and heating processes which directly covers

APPA scheduled process No. 16: Tar Processes.

If the tar is heated using fuel combustion the flue gasses of the combustion process will

fall under Sub-category 3.1, while any gasses evaporated from the tar will fall under this

category.

Note that Sub-category 5.8: Macadam Preparation is specific to preparation of road

surface material.

3.3.1.1 Disambiguation

Tar is a dark, oily, viscous material, consisting mainly of hydrocarbons produced by the

pyrolysis organic materials. There are various types of tar and these are named based

on the material from which they originate:

• Wood Tar - produced by the pyrolysis of wood

• Coal Tar - produced by the pyrolysis of coal

• Peat Tar - produced by the pyrolysis of peat

Creosote is obtained from the distillation of tar.

Bitumen is derived from petroleum, it has similar properties to tar but is not referred to as

tar. Bitumen use in any manufacturing process is covered in this sub-category.


3.3.2.1 Tar Distillation

Figure 3-5: Simplified tar distillation process

Tar can be obtained from organic materials, typically coal or wood (often pine) during

gasification and carbonizing reactions. Further processing is done by simply distilling the

tar into various fractions which can be done in batches (preferred as it is quite viscous)

or continuously and typically only has one separation of the tar into heavy and light

mixtures.

3.3.2.1.1 Receiving and Pre-processing

Being a viscous liquid, tar is generally delivered by road or rail tanker if the source is

distant from the processing site. If the process is on the same site as the source then

delivery is likely to be via pipeline. The tar is typically stored in a heated vessel. The heat

may be supplied from combustion, steam or electrical heating. In the case of

combustion related heating refer to Sub-category 3.1.

Emissions will largely be limited to VOCs emitted during handling or from storage vessel

vents.

3.3.2.1.2 Processing and Product Storage

The basic process steps are:

• The tar is preheated to make it easier to pump and sent to the distillation vessel;

• The vessel is heated to a set temperature that will cause the lighter compounds

to evaporate out of the mixture leaving the heavier compounds; and

• The lighter compounds are condensed and sent to further processing to yield

other products while the tar is discharged from the distillation vessel to product

storage. Creosote may be one of these products and is generally made of

compounds (oils) that are denser than water.

Emissions from the distillation are found in the light component and are made up mostly

of volatile organic compounds. These may be captured or may be burned to produce

the heat in the vessel. In the case that it is combusted it will fall under the appropriate

combustion Sub-category 3.1.

The products are stored in various types of vessels as described in Section 3.3.5 below.

These are discussed in detail in Sub-category 2.2: Storage and Handling of Petroleum

Products. These vessels may also be heated to keep the material viscosity at a desirable

level.


Two main sources of emissions will be present here:

• Combustion products (covered under Sub-category 3.1); and

• VOC’s from the handling and storage of raw tar and distillate.

Aside from the combustion emission, the atmospheric emissions will largely be made up

of various VOCs. These may be fugitive releases from seals, couplings, and handling

activities, but may also be vapours vented during filling or to relieve pressure build-up in

storage vessels.

VOCs can be treated either destructively, using methods like flaring, or by absorption

and or adsorption scrubbers. Vapours may also be captured, condensed and returned

to bulk storage.

If the distilled VOC’s are not efficiently captured through condensation, they will be

released to the atmosphere and be a considerable source of emission. If the heating is

done using combustion then the emissions thereof will fall under Sub-category 3.1.

3.3.4 FURTHER SOURCES OF INFORMATION


1) UK DEFRA Secretary of State's Guidance for Bitumen and Tar Processes

3.3.5 TRANSITIONAL AND SPECIAL ARRANGEMENTS

The following transitional and special arrangements shall apply:

• Leak detection and repair (LDAR) program approved by licensing authority to

be instituted, within one year after publication date of the Section 21 Notice.

• Storage vessels for liquids shall be of the following type:

• For vapour pressures up to 14kPa: Fixed roof tank vented to atmosphere

• Above 14kPa, below 91kPa: External floating roof tank with primary and

secondary rim seals for tank diameter larger than 20m, or fixed roof tank with

internal floating deck fitted with primary seal, or fixed roof tank with vapour

recovery system.

• Above 91kPa: Pressure vessel.

• The roof legs, slotted pipes and/or dipping well on floating roof tanks (except

domed floating roof tanks or internal floating roof tanks) shall have sleeves fitted

to minimise emissions.

• Relief valves on pressurised storage should undergo periodic checks for internal

leaks. This can be carried out using portable acoustic monitors or if venting to

atmosphere with an accessible open end, tested with a hydrocarbon analyser

as part of an LDAR programme.

• Loading/unloading (except rail loading and unloading): All liquid products with a

vapour pressure above 14 kPa shall be loaded/unloaded using bottom loading,

with the vent pipe connected to a gas balancing line. Vapours expelled during

loading operations must be returned to the loading tank if it is of the fixed roof

type where it can be stored prior to vapour recovery or destruction. Where

vapour balancing is not possible, a recovery system utilising adsorption,

absorption and condensation and/or incineration of the remaining VOC, with a

collection efficiency of at least 95 % shall be fitted.

• The actual temperature in the tank must be used for vapour pressure

calculations.

• Alternative control measures that can achieve the same or better results may be

used.

3.4 SUB-CATEGORY 3.4: CHAR, CHARCOAL AND CARBON BLACK

PRODUCTION

3.4.1 APPLICABILITY

Char, charcoal and carbon black production (excluding electrode paste production)

All installations

Sub-category 3.4 covers processes producing char, charcoal and carbon black,

except electrode paste production which is covered by Sub-category 3.5. This section

covers the following APPA scheduled processes:

34. Gas, Coke and Charcoal Processes

64. Carbon Black Processes

For processes focussed on the liquid and fuel production from carbonaceous materials

refer to Category 2.


3.4.2.1 Char and charcoal production

Figure 3-6: Simplified Char/Charcoal production

Char is the high carbon residue that remains after slow pyrolysis of carbonaceous

materials. During this slow pyrolysis, moisture and VOCs are driven off leaving the solid

material behind which fuses together. This can be achieved by burning carbonaceous

materials with a partial lack of oxygen or by heating it in the absence of oxygen by

heating the material in an airtight vessel. Charcoal is similar to char except that it

comes exclusively from woody materials (e.g. wood from trees such as wattle and pine,

or softwoods such as peanut shells, fruit pits etc.).

Char and charcoal are typically used as solid fuels and/or as reductants in other

processes.

Production is typically undertaken as follows:

• Coal or biomass is crushed or chipped to the desired size and charged to the

carbonization chamber;

• The material is combusted at a very slow rate using a controlled amount of

oxygen to drive off the volatiles and leave behind the carbonaceous material

which is collected at the bottom of the chamber. A slow combustion rate is

achieved by lighting the material and then restricting the available air once the

material is burning; and

• The volatiles also burn and along with the flue gas are sent to abatement and

ultimately released through a stack.

The material may also be heated indirectly, in which case the volatiles can then be

returned as a fuel if heating the material being processed. Emissions from these

processes are the particulates (which are collected and added to the product stock

pile) and gases in the flue gas, as the bottom solids are the product (char or charcoal).

The products may be further processed to produce various size grades via screening or

agglomerated to produce briquettes. Briquettes are from by crushing/grinding the

product, followed by application of a binder (e.g. maize starch, molasses) and then

pressing into the desired shape and dried.


Atmospheric emission from receiving, pre-processing, post processing, and storage will

largely be fugitive particulate matter.

Atmospheric emissions from the processing will consist of combustion products and

volatile matter:

• Volatile organic compounds including polycyclic aromatic hydrocarbons (PAH)*

• Particulate matter*


• Sulphur dioxide and reduced sulphurs (SO2 and H2S - where coal is used)

• Heavy metals (where coal is used)

• Oxides of nitrogen (NOx - limited due to the reducing atmosphere, unless off-gas

is flared)

*Regulated by the NEMAQA emission standards

The atmospheric emissions are expected to be primarily from the combustion flue gases

and are released to the atmosphere using a flue stack. Before releasing to atmosphere

the flue gas may require abatement using a variety of methods, depending on the

target pollutant, common examples are:


• Cyclone: PM

• Baghouse: PM


3.4.2.3 Carbon Black Production

Figure 3-7: Carbon black process

The main uses of carbon black are as a reinforcing agent in rubber compounds (e.g.

tyres and shoe soles to improve abrasion resistance) and as a black pigment in printing

inks, surface coatings, paper, and plastics.

Carbon black is produced from the pyrolysis of hydrocarbon fuels, usually specific oils,

gas, and some vegetable oils. Pyrolysis is the partial combustion of the feed material

and is achieved by blowing the feed material directly into hot gases with limited

oxygen available. This results in the formation of fine particles of unburnt carbon called

carbon black.

The basic process steps are as follows:

• Feed stock is sprayed into a chamber with hot gasses blowing through it. The hot

gasses are generated in a separate combustion chamber using a secondary

fuel source if necessary such as natural gas;

• The hot gases pyrolyse the feedstock to produce fine carbon black particles;

• The reaction mixture is then quenched with water and can be further cooled in

heat exchangers;

• Some of the carbonized particulate matter falls to the bottom however the

particles are very fine and remain entrained in the flue. The carbon black may

then be separate from the flue gas using cyclone separators and bag filters;

• The hot flue gasses may pass through heat exchangers to recover energy before

proceeding to abatement equipment; and

• The carbon black (the particulates) is then further processed to produce pellets

or briquettes to allow for easy handling, storage and transportation.

Emissions from these processes are the gaseous pollutants in the flue as well as the

particulate matter that is not gathered as the product, carbon black.

Carbon black may also be produced through thermal cracking, in this case the feed

material is heated externally, however this method is much less common than pyrolysis

by partial combustion. According to European Commission 95% of global production of

carbon black is through pyrolysis of petrochemical oils, coal tar oils and natural gas*.


Atmospheric emissions from these processes will consist of combustion products:

* IPPC Reference Document on Best Available Techniques for the Manufacture of Large Volume

Inorganic Chemicals - Solids and Others industry August 2007.

• Volatile organic compounds including polycyclic aromatic hydrocarbons (PAH)*


• Carbon dioxide (CO2)

• Heavy metals


Aromatic hydrocarbons produce higher yields and are thus preferred to aliphatic

hydrocarbons, hence the emission of PAHs (polycyclic aromatic hydrocarbons).

The atmospheric emissions are expected to be primarily from the combustion flue gases

and are released to the atmosphere using a flue stack. Before releasing to atmosphere

the flue gas may require abatement using a variety of methods, depending on the

target pollutant, common examples are:


• Cyclone: PM

• Baghouse: PM


Fugitive emissions are also expected from various equipment and material handling

processes. Carbon black particles are very fine and thus easily entrainable in air.


1) IPPC Best Available Techniques for the Manufacture of Large Volume Inorganic

Chemicals - Solids and Others industry

2) EPA AP 42 chapter 6.1 Carbon Black


None

3.5 SUB-CATEGORY 3.5: ELECTRODE PASTE PRODUCTION

3.5.1 APPLICABILITY

Electrode paste production

All installations

Carbon electrode paste is used in submerged arc furnaces for delivering electricity

to the charge mix. The paste forms a self-baking electrode, and allows for

continuous feed of the electrode as it is consumed in the furnace, unlike solid

carbon electrodes which may need to be fed in batches.

While Sub-category 3.5 is a carbonizing process it deals specifically with the

production of carbon electrode paste. For processes dealing with char, charcoal

and carbon black production please refer to Sub-category 3.4 and for coke

production (including petroleum coke, which is the precursor of this process) refer to

Sub-category 3.2


3.5.2.1 Petroleum, coke and anthracite calcination

Figure 3-2: Petroleum, coke and anthracite calcination process

Petroleum coke can be calcined to produce a carbon electrode paste by driving

off VOCs and moisture, the coke left behind is a high purity carbon. This high purity

carbon can then be mixed with a plasticizer (improves workability), resin and water

and baked in a mould to make a carbon electrode for use in electric arc furnaces.

The paste production process is as follows:

• Petroleum coke or high grade anthracite (crushed) is introduced into a kiln

that heats up the material using a gas flame;

• This bakes the material and drives off any volatiles and moisture leaving

behind high purity carbon;

• The calcined carbon is collected at the end of the kiln and sent to a mixer

along with a bonding agent (resin), a plasticizer (makes it easier to mould)

and water, forming the paste. Coal tar pitch is often used to produce the

paste; and

• The paste is then either directly poured into a mould or packaged and sold to

an electrode manufacturer.

Emissions from this process include both the volatiles driven off and the particulate

matter that escapes to the atmosphere as rotary kilns cause finer particulates to get

suspended in the flue gas. The particulate matter is usually abated and mixed into

the product as it will be of a similar composition.


Atmospheric emissions from these processes will consist of combustion products in

the flue gas:

• Volatile organic compounds (VOCs)

• Oxides of nitrogen (NOx)



• Carbon dioxide (CO2)

• Sulphur dioxide and other reduced sulphurs (H2S, SO2)

• Heavy metals (in the particulate matter)


The atmospheric emissions are expected to be primarily from the combustion flue

gases and are generally released to the atmosphere using a flue stack. Before

releasing to atmosphere the flue gas can be cleaned using a variety of methods,

depending on the target pollutant, common examples are:


• Cyclone: PM

• Baghouse: PM


The fly ash removed from the flue gas may either be sold as a number of products if

it meets the end-user’s specifications or they may be disposed of in ash dams or

landfills. Improper handling of ash or improper management of the disposal area

may lead to fugitive particulate emissions.


None

3 category 3: carbonization and coal gasification

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