3.2 Task guidance sheets for furnaces
TASK GUIDANCE SHEET 7
FURNACES:
ROTARY FURNACE
CLASSIFICATION OF THE MATERIAL ACCORDING TO DIOXIN FORMATION
Scale (0-5): 4
0=MOST DANGEROUS 5= SAFEST
CHARACTERISTICS
TYPICAL CHARGE
Pig iron
Returns
Iron Scrap
Packed sheet
Steel scrap
Chips
50%
40%
5%
-
5%
-
The 90% of the scrap are pig iron and returns which have not a high risk of dioxin formation. For
more details see the task guidance sheets of each raw material.
DIOXIN EMISSION IN ROTARY FURNACES
Because of the furnace characteristics normally clean raw materials are used and therefore there is a
not high emission rate of dioxins. However, as dioxins are semivolatile compounds they can be
emitted as gas or particles so sometimes a depuration system is required not to exceed the
emission limit value as occurs for Foundry 1. A bigger furnace size and so, a higher
production rate does not involve a higher emission rate. The gas line and process design are
the main influence in the dioxin formation (see recommendations in the following lines).
FOUNDRIES
Dioxin emission rate
ng I-TEQ/Nm3
WITHOUT DEPURATION SYSTEM
0.02 - 0.10
WITH DEPURATION SYSTEM
≈0.002
Emission limit value 0.1 ng I-TEQ/Nm3
RECOMMENDATIONS
DIOXIN CAPTURE SYSTEM
According to current legislation, specific dioxin capture systems are not required because they
have been measured low emission rates.
PROCESS DESIGN: GAS LINE
It is very important that gas lines should be designed to avoid dioxin formation by ‘de novo’ synthesis
(occurred when gases reach temperatures between 250-450 ºC with low cooling rate). However, this
phenomenon is almost impossible to avoid in cases where interchangers or long lines are required. In
these cases it must be taken into account a special waste treatment and handling. When possible,
exhausts quenching is recommended.
PROCESS PARAMETERS CONTROL
 The main parameter to check is that charged raw materials should be clean.
This sheet is part of the Good Practice Guide on prevention of dioxin formation in iron foundries and it is for public use.
This guide offers advices, recommendations and individual data to perform correctly the melting process in furnaces
used in iron foundries, in order to minimize dioxin formation. All the data included in this guide have been obtained from
the Diofur Project, carried out under EU’s Sixth Framework Programme.
TASK GUIDANCE SHEET 8
FURNACES:
BLAST CUPOLA
CLASSIFICATION OF THE MATERIAL ACCORDING TO DIOXIN FORMATION
Scale (0-5): 1
0=MOST DANGEROUS 5= SAFEST
CHARACTERISTICS
TYPICAL CHARGE
Pig iron
Returns
Iron Scrap
Packed sheet
Steel scrap
Chips
15%
40%
15%
0%
20%
10%
The use of iron scrap and chips containing oil and paintings is a chlorine source for the dioxins
formation. For more details see the task guidance sheets of each raw material.
DIOXIN EMISSION IN CUPOLA FURNACES
This type of furnace has the higher potential risk of dioxin formation. The high rates of
charged chips, iron scrap and steel scrap provide oil and paintings, which are the major source of
chlorine for dioxin formation. For blast cupolas it is absolutely necessary a depuration system in
order to capture dioxins condensed and adsorbed on particles. A bigger furnace size and so, a
higher production rate does not involve a higher emission rate. The gas line and process
design are the main influence in the dioxin formation (see recommendations in the following lines).
FOUNDRIES
Dioxin emission rate
ng I-TEQ/Nm3
WITHOUT DEPURATION SYSTEM + NO CONTROL OF PROCESS
PARAMETERS
4.0 - 7.0
WITH DEPURATION SYSTEM + CONTROL OF PROCESS
PARAMETERS
0.0010 - 0.5000
WITH DEPURATION SYSTEM + CONTROL OF PROCESS
PARAMETERS + ABATEMENT SYSTEM
0.0001 - 0.0600*
*See explanatory note at the end of the document
Emission limit value 0.1 ng I-TEQ/Nm3
RECOMMENDATIONS
DIOXIN CAPTURE SYSTEM
According to current legislation, in order to assure emission rates below the established limit of it is
necessary to install dioxin capture systems especially in HBC. In CBC it has to be studied if it
is possible to control the situation controlling the process and its parameters.
PROCESS DESIGN: GAS LINE
It is very important that gas lines should be designed to avoid dioxin formation by ‘de novo’ synthesis
(occurred when gases reach temperatures between 250-450 ºC with low cooling rate). However, this
phenomenon is almost impossible to avoid in cases where exchangers or long lines are required. In
these cases it must be taken into account a special waste treatment and handling. When possible,
exhausts quenching is recommended.
PROCESS PARAMETERS CONTROL
 The main parameters to check are: the use of cleanest possible raw materials, to have a
steady and continuous process, to have enough temperature at the stack to allow the spraying
of water. However the control of these parameters could not be enough to assure an
emission rate below the target. For those cases an end of pipe solution would be necessary.
This sheet is part of the Good Practice Guide on prevention of dioxin formation in iron foundries and it is for public use.
This guide offers advices, recommendations and individual data to perform correctly the melting process in furnaces
used in iron foundries, in order to minimize dioxin formation. All the data included in this guide have been obtained from
TASK GUIDANCE SHEET 9
FURNACES:
INDUCTION FURNACE
CLASSIFICATION OF THE MATERIAL ACCORDING TO DIOXIN FORMATION
Scale (0-5): 5
0=MOST DANGEROUS 5= SAFEST
CHARACTERISTICS
TYPICAL CHARGE
Pig iron
Returns
Iron Scrap
Packed sheet
Steel scrap
Chips
15%
50%
-
30%
5%
-
Due to the limited possibility of alloying, the induction furnace charge generally consists of clean
material. For more details see the task guidance sheets of each raw material.
DIOXIN EMISSION IN INDUCTION FURNACES
As well as using clean charge, the furnace does not produce a ducted high temperature flue-gas
stream that cools down slowly. Therefore, there are no potential sources of chlorine and de-novo
synthesis is not likely to occur. The BREF document on Smitheries and Foundries mentions that
induction furnaces show a low risk of dioxin formation and therefore they have not been measured
emission rates from this type of furnace in the Diofur project (main data source of this Good Practice
Book). The following table includes data from the BREF document:
Dioxin emission rate
ng I-TEQ/Nm3
Foundries
WITH DEPURATION SYSTEM
0.003 - 0.010
Emission limit value 0.1 ng I-TEQ/Nm3
RECOMMENDATIONS
DIOXIN CAPTURE SYSTEM
According to current legislation, specific dioxin capture systems are not required because they
have been measured low emission rates.
PROCESS DESIGN: GAS LINE
For this type of furnaces, it is not produce a ducted high temperature flue-gas stream that cools down
slowly so the process design does not affect to the dioxin formation. However a non common designs
involving long ducts and other parameters where slow cooling processes could occur should be
avoided.
PROCESS PARAMETERS
 Process parameter values related to a normal furnace working day assure emissions below the
limit.
This sheet is part of the Good Practice Guide on prevention of dioxin formation in iron foundries and it is for public use.
This guide offers advices, recommendations and individual data to perform correctly the melting process in furnaces
used in iron foundries, in order to minimize dioxin formation. All the data included in this guide have been obtained from
the Diofur Project, carried out under EU’s Sixth Framework Programme.
TASK GUIDANCE SHEET 10
FURNACES:
ELECTRIC ARC FURNACE
CLASSIFICATION OF THE MATERIAL ACCORDING TO DIOXIN FORMATION
Scale (0-5): 3
0=MOST DANGEROUS 5= SAFEST
CHARACTERISTICS
TYPICAL CHARGE
Pig iron
Returns
Iron Scrap
Packed sheet
Steel scrap
Chips
5%
50%
10%
5%
20%
10%
The risk of dioxin formation is due to the use of polluted charge with oil and paintings mainly iron
scrap, steel scrap and chips. However these type of raw materials represent around 40% so the risk
is lower than for blast furnaces.
DIOXIN EMISSION IN ELECTRIC ARC FURNACES
This type of furnaces represents a mid-low emission rate of dioxins. However, as dioxins are
semivolatile compounds they can be emitted as gas or particles so sometimes a depuration
system is required not to exceed the emission limit value. A bigger furnace size and so, a
higher production rate does not involve a higher emission rate. The gas line and process
design are the main influence in the dioxin formation (see recommendations in the following lines).
FOUNDRIES
Dioxin emission rate
ng I-TEQ/Nm3
WITHOUT DEPURATION SYSTEM
0.035 - 0.800
WITH DEPURATION SYSTEM
0.002 - 0.040
Emission limit value 0.1 ng I-TEQ/Nm3
RECOMMENDATIONS
DIOXIN CAPTURE SYSTEM
According to current legislation, specific dioxin capture systems are not required because they
have been measured low emission rates.
PROCESS DESIGN: GAS LINE
It is very important that gas lines should be designed to avoid dioxin formation by ‘de novo’ synthesis
(occurred when gases reach temperatures between 250-450 ºC with low cooling rate). However, this
phenomenon is almost impossible to avoid in cases where interchangers or long lines are required. In
these cases it must be taken into account a special waste treatment and handling. When possible,
exhausts quenching is recommended.
PROCESS PARAMETERS CONTROL
 The main parameter to check is that charged raw materials should be clean.
This sheet is part of the Good Practice Guide on prevention of dioxin formation in iron foundries and it is for public use.
This guide offers advices, recommendations and individual data to perform correctly the melting process in furnaces
used in iron foundries, in order to minimize dioxin formation. All the data included in this guide have been obtained from
the Diofur Project, carried out under EU’s Sixth Framework Programme.
4. Mind map: focusing the most important issues
This tool helps to the foundrymen to focus on the most important issues to achieve low
dioxin emissions:
4.1 Cupolas
4.2 Rotary furnaces
Use uniform charge
Charge in the correct order
Raw material
Minimize or eliminate oil, paintings or plastics
Avoid contamination during storage
Eliminate mould sand on returns
Optimize combustible/comburent ratio
Control the refractory wear
Furnace
Use gaseous fuel
Adjust well the burner support and the furnace
Rotary Furnace
Heat exchanger
Rapid cooling between 450-250ºC
Optimize duct diameters
Gas line
Avoid long and horizontal ducts
Keep ducts clean
Exhausts
< 5 mg/Nm3
Repair faulty equipment
Bag house
Dry
Keep good working order
Implement procedures
Dust
removal
Tightness
Sleeves
Cyclone
Wet
Supports
4.3 Electric Arc furnaces
5. Check list: concepts to check before the production
A check list is a list of items to be checked, noted or remembered. In this case this tool has
been included in order to help the verifying of the process to the foundrymen. Checking one
per one the foundrymen can mark the parameters which do not fulfil the recommendation.
After finishing the checking, it will be easy to change the parameters previously marked.
Therefore this tool has the purpose of helping the foundrymen to identify the problems,
pamateres… to check before starting the process.
CHECK LIST FOR GOOD OPERATION AND DIOXIN MINIZATION
IN CUPOLAS
PART 1: COMMON FOR EVERY FOUNDRY
CHECKING RAW MATERIALS FOR ALL TYPE OF FURNACES
MATERIAL STORING PLACE
□ Do the raw materials arrive clean? It is important if we could choose a clean
supplier.
□ Do you store each material always in the same storing place? It is very important not
to pollute clean raw materials with residues of oil, paintings… of previously stored
materials.
□ Are the storing places clean? Do you clean them frequently?
RETURNS
□ Are they free of mould sand (binder residues)?
SCRAPS (Steel or iron)
□ Are they free of oil, grease, plastic, wood and paintings?
□ If they are oily, greasy… is it possible to carry on a cleanliness procedure?
PIG IRON
□ Are the storing places clean? Do you clean them frequently?
□ If not, is it possible to clean them?
MACHINING CHIPS
□ Are they free of oil? (Not usual for induction furnaces)
COKE FOR CUPOLAS
□ Is it dry? Avoid too wet cokes.
□ Is the ash content low enough? It has to be as low as possible.
□ Is the fine fraction of coke low? It has to be as low as possible.
□ Is the breakage index low enough? It is necessary a good MICUM index
LIQUID OR GASEOUS FUELS FOR RFs or POST COMBUSTORS
□ Is the fuel in liquid form? It is interesting using as gaseous for reducing some dioxin
formations.
CHECKING THE DESIGN AND EQUIPMENT OF THE GAS LINE
GAS LINE
□ Are duct diameters optimized / minimized?
□ Are avoided long and horizontal ducts that can lead to problems with memory
effect?
□ Do you keep the ducts clean?
□ If not, is it possible to clean them?
EXHAUST TREATMENT
□ Do you have post-combustors?
□ Do you remove dry dust (with dry or wet systems) before the post combustor or
stack?
□ Do you use water sprays or air/air exchangers for the cooling process?
POST COMBUSTION
□ Do you eliminate CO? CO is a precursor of dioxins.
□ Do you need to implement burners? Implement them if necessary. Minimize them
due to energy and new dioxins source reasons.
□ Do you cool the gases before the fabric filter? At least to avoid burnings.
COOLING SYSTEM 1: QUENCHING BY SPRAYED WATER
□ Do you use a permanent spraying even having low temperature in exhausts?
□ Is the cooling process until 100ºC quick enough? It is necessary a quick pass
between 250 and 450ºC temperature window to avoid de-novo synthesis; dioxin
reformation.
□ Have you removed deposits or quencher pipes? It is necessary to remove them
(sludge included) in order to avoid memory effect.
COOLING SYSTEM 2: EXCHANGERS AT THE STACK
□ Do you cool gases before removing the dusts? Do you cool them quick enough?
□ Do you keep clean the exchangers? Do you remove deposits or sludges?
□ Do you keep clean the ducts?
□ If not, is it possible to clean them?
DUST REMOVAL 1: DRY SYSTEM
□ Is the cyclone effective? It is necessary an effective cyclone to limit the presence of
coarse particles rich in unburned matter, as well as to avoid burnings.
□ Do you have a bag filter? Do you have an effective cleaning?
□ Are dust removers sized to filter stack gases in process peaks (of volume flow,
temperature, dust load…)?
□ Do you follow strictly supplier recommendations for operation set-points?
□ Do you check regularly the equipment? In case of failures, do you repair it
immediately?
□ Do you fulfil the lowest goals of particle emission (<5 mg/Nm3) included in Foundry
BREF?
DUST REMOVAL 2: WET SYSTEM
□ Is it efficient enough for your process? They are in general less efficient and more
problematic than dry systems.
EQUIPMENT MAINTENANCE
□ Do you carry out preventive maintenance of the equipment?
□ Do you keep it in good working conditions?
TRAINING
□ Are the operators informed of the risks associated to dioxin formation and emission?
□ Have the operators been trained in prevention of dioxin emissions? (Satisfactory
furnace operation, checking of the stack gas treatment systems…)
SUPERVISION
□ Do you have checking procedures?
□ Do you have operation procedures in accordance with recommendation of technical
sheets?
WASTE MANAGEMENT
□ Do you store removed dust correctly? Big bags or closed containers avoid rain and
diffuse emissions.
□ Do you analyze periodically the dioxin content of the removed dust?
□ In case of having dioxins, do you handle removed dust as hazardous waste?
PART 2: CHECKING EACH TYPE OF FURNACE
CHECKING THE CUPOLA FURNACE
CHARGE
□ Is it uniform?
□ Has it got a good distribution?
THERMAL EFFICIENCY
□ Will O2 injection improve your energy efficiency? It could be interesting using an
optimized oxygen injection.
□ Is there a secondary row of nozzles?
PRODUCTION ORGANIZING
□ Try to minimize interruptions in the melting (stoppage), unburned gases, memory
effect...
□ Is furnace operation regular?
□ Are air losses avoided along the process?
CHECKING THE ROTARY FURNACE
CHARGE
□ Is the charge uniform? Uniform charge allows an easier melting, saving fuel and
time.
THERMAL EFFICIENCY
□ Do you charge the materials in the correct order? A correct order of the charge
means thermal efficiency.
□ Is it optimized the combustible (fuel or natural gas)/comburent (air or O2) ratio?
□ Have you got an oxyburner?
□ Is well kept the adjustment between the burner support and the furnace during the
melting operation? Little maladjustments mean increasing needs of fuel and
decreasing efficiencies.
FURNACE MAINTENANCE
□ Is well controlled the refractory wear, in particular, at the exhausts outlet zone?
Uncontrolled wears mean exhaust scapes to the plant with a high dust generation
containing dioxins.
CHECKING THE ELECTRIC ARC FURNACES
CHARGE
□ Is the charge uniform? Uniform charge allows an easier melting, saving fuel and
time. Strongly recommend mixing of the charge with various sizes of pieces.
THERMAL EFFICIENCY
□ Do you charge the materials in the correct order? A correct order of the charge
means thermal efficiency.
□ Have you got an oxyburner? It's necessary, if you use it as heat booster in melting
process.
FURNACE MAINTENANCE
▫
Is well controlled the refractory wear, in particular, at the exhausts outlet zone?
Uncontrolled wears mean exhaust escapes to the plant with dust and other
pollutants generation.
▫
Have you got indirect exhaust gases? If yes, during melting period check leakliness
of hood and collecting pipe of the dedusting installation.
▫
Did you check the condition of the graphite electrodes before the melting? Bad
condition of electrodes induces increase of energy consumption and possibility of
dioxin formation.