3 category 3: carbonization and coal gasification
TRANSCRIPT
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)
* Regulated by the NEMAQA emission standards
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.
3.2.3.4 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:
• Particulate matter
• Carbon monoxide (CO)
• Hydrogen sulphide (H2S)*
• Heavy Metals (in particulate matter)
• Carbonyl sulphide (COS)
* Regulated by the NEMAQA emission standards
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.
3.2.3.5 Further Sources of Information
For further information refer to:
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
3.2.4 SPECIAL ARRANGEMENTS
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 PROCESS OVERVIEW
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.
3.3.3 ATMOSPHERIC EMISSIONS
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
For further information refer to:
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 PROCESS OVERVIEW
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.
3.4.2.2 Atmospheric Emissions
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*
• Carbon monoxide (CO)
• 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:
• Scrubber: PM, SO2, NOx
• Cyclone: PM
• Baghouse: PM
• Electrostatic Precipitator: 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*.
3.4.3 ATMOSPHERIC EMISSIONS
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)*
• Particulate matter*
• Carbon dioxide (CO2)
• Heavy metals
*Regulated by the NEMAQA emission standards
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:
• Scrubber: PM, SO2, NOx
• Cyclone: PM
• Baghouse: PM
• Electrostatic Precipitator: 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.
3.4.3.1 Further Sources of Information
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
3.4.4 SPECIAL ARRANGEMENTS
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 PROCESS OVERVIEW
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.
3.5.3 ATMOSPHERIC EMISSIONS
Atmospheric emissions from these processes will consist of combustion products in
the flue gas:
• Volatile organic compounds (VOCs)
• Oxides of nitrogen (NOx)
• Carbon monoxide (CO)
• Particulate matter*
• Carbon dioxide (CO2)
• Sulphur dioxide and other reduced sulphurs (H2S, SO2)
• Heavy metals (in the particulate matter)
*Regulated by the NEMAQA emission standards
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:
• Scrubber: PM, SO2, NOx
• Cyclone: PM
• Baghouse: PM
• Electrostatic Precipitator: 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.
3.5.4 SPECIAL ARRANGEMENTS
None