Reference documents

Activity

Emissions from Storage (EFS)

Storage and handling of raw materials and products

General Principles of Monitoring (MON)

Emissions monitoring

Waste Treatments Industries (WT)

Waste treatment

Energy Efficiency (ENE)

General energy efficiency

Economic and Cross-media Effects (ECM)

Economics and cross-media effects of techniques

Term used

Definition

New plant

A plant introduced on the site of the installation following the publication of these BAT conclusions or a complete replacement of a plant on the existing foundations of the installation following the publication of these BAT conclusions

Existing plant

A plant which is not a new plant

Major upgrade

An upgrade of the plant/kiln involving a major change in the kiln requirements or technology, or replacement of the kiln

‧Use of waste as fuel and/or raw material‧

The term covers the use of:

Term used

Definition

White cement

Cement falling under the following PRODCOM 2007 code: 26.51.12.10 – White Portland cement

Special cement

Special cements falling under the following PRODCOM 2007 codes:

Dolime or calcinated dolime

A mixture of calcium and magnesium oxides produced by the decarbonation of dolomite (CaCO3.MgCO3) with a residual CO2 content of the product exceeding 0,25 % and the bulk density of the commercial product well below 3,05 g/cm3. The free content as MgO is usually between 25 % and 40 %.

Sintered dolime

A mixture of calcium and magnesium oxides used solely for the production of refractory bricks and other refractory products, with a minimum bulk density of 3,05 g/cm3

Term used

Definition

NOx expressed as NO2

The sum of nitrogen oxide (NO) and nitrogen dioxide (NO2) expressed as NO2

SOx expressed as SO2

The sum of sulphur dioxide (SO2) and sulphur trioxide (SO3) expressed as SO2

Hydrogen chloride expressed as HCl

All gaseous chlorides expressed as HCl

Hydrogen fluoride expressed as HF

All gaseous fluorides expressed as HF

ASK

Annular shaft kiln

DBM

Dead burned magnesia

I-TEQ

International toxicity equivalent

LRK

Long rotary kiln

MFSK

Mixed feed shaft kiln

OK

Other kilns

For the lime industry this covers:

OSK

Other shaft kiln (shaft kilns other than ASK and MFSK)

PCDD

Polychlorinated dibenzo-p-dioxin

PCDF

Polychlorinated dibenzofuran

PFRK

Parallel flow regenerative kiln

PRK

Rotary kiln with preheater

Activities

Reference conditions

Kiln activities

Cement industry

10 % oxygen by volume

Lime industry (2)

11 % oxygen by volume

Magnesium oxide industry (dry process route) (3)

10 % oxygen by volume

Non-kiln activities

All processes

No correction for oxygen

Lime hydrating plants

As emitted

(no correction for oxygen and for dry gas)

Daily average value

Average value over a period of 24 hours measured by the continuous monitoring of emissions

Average over the sampling period

Average value of spot measurements (periodic) of at least 30 minutes each, unless otherwise stated

Technique

a

Select an appropriate location for noisy operations

b

Enclose noisy operations/units

c

Use vibration insulation of operations/units

d

Use internal and external lining made of impact-absorbent material

e

Use soundproofed buildings to shelter any noisy operations involving material transformation equipment

f

Use noise protection walls and/or natural noise barriers

g

Use outlet silencers to exhaust stacks

h

Lag ducts and final blowers which are situated in soundproofed buildings

i

Close doors and windows of covered areas

j

Use sound insulation of machine buildings

k

Use sound insulation of wall breaks, e.g. by installation of a sluice at the entrance point of a belt conveyor

l

Install sound absorbers at air outlets, e.g. the clean gas outlet of dedusting units

m

Reduce flow rates in ducts

n

Use sound insulation of ducts

o

Apply the decoupled arrangement of noise sources and potentially resonant components, e.g. of compressors and ducts

p

Use silencers for filter fans

q

Use soundproofed modules for technical devices (e.g. compressors)

r

Use rubber shields for mills (avoiding the contact of metal against metal)

s

Construct buildings or growing trees and bushes between the protected area and the noisy activity

Technique

a

Process control optimisation, including computer-based automatic control

b

Using modern, gravimetric solid fuel feed systems

Technique

Applicability

a

Continuous measurements of process parameters demonstrating the process stability, such as temperature, O2 content, pressure and flowrate

Generally applicable

b

Monitoring and stabilising critical process parameters, i.e. homogenous raw material mix and fuel feed, regular dosage and excess oxygen

Generally applicable

c

Continuous measurements of NH3 emissions when SNCR is applied

Generally applicable

d

Continuous measurements of dust, NOx, SOx, and CO emissions

Applicable to kiln processes

e

Periodic measurements of PCDD/F and metal emissions

f

Continuous or periodic measurements of HCl, HF and TOC emissions.

g

Continuous or periodic measurements of dust

Applicable to non-kiln activities.

For small sources (< 10 000 Nm3/h) from dusty operations other than cooling and the main milling processes, the frequency of measurements or performance checks should be based on a maintenance management system.

Process

Unit

BAT-associated energy consumption levels (4)

Dry process with multistage preheating and precalcination

MJ/tonne clinker

2 900 – 3 300 (5)  (6)

Technique

Applicability

a

Applying improved and optimised kiln systems and a smooth and stable kiln process, operating close to the process parameter set points by applying:

Generally applicable. For existing kilns, the applicability of preheating and precalcination is subject to the kiln system configuration

b

Recovering excess heat from kilns, especially from their cooling zone. In particular, the kiln excess heat from the cooling zone (hot air) or from the preheater can be used for drying raw materials

Generally applicable in the cement industry.

Recovery of excess heat from the cooling zone is applicable when grate coolers are used.

Limited recovery efficiency can be achieved on rotary coolers

c

Applying the appropriate number of cyclone stages related to the characteristics and properties of raw material and fuels used

Cyclone preheater stages are applicable to new plants and major upgrades.

d

Using fuels with characteristics which have a positive influence on the thermal energy consumption

The technique is generally applicable to the cement kilns subject to fuel availability and for existing kilns subject to the technical possibilities of injecting the fuel into the kiln

e

When replacing conventional fuels by waste fuels, using optimised and suitable cement kiln systems for burning wastes

Generally applicable to all cement kiln types

f

Minimising bypass flows

Generally applicable to the cement industry

Technique

a

Using power management systems

b

Using grinding equipment and other electricity based equipment with high energy efficiency

c

Using improved monitoring systems

d

Reducing air leaks into the system

e

Process control optimisation

Technique

a

Apply quality assurance systems to guarantee the characteristics of wastes and to analyse any waste that is to be used as raw material and/or fuel in a cement kiln for:

b

Control the amount of relevant parameters for any waste that is to be used as raw material and/or fuel in a cement kiln, such as chlorine, relevant metals (e.g. cadmium, mercury, thallium), sulphur, total halogen content

c

Apply quality assurance systems for each waste load

Technique

a

Use appropriate points to feed the waste into the kiln in terms of temperature and residence time depending on kiln design and kiln operation

b

To feed waste materials containing organic components that can be volatilised before the calcining zone into the adequately high temperature zones of the kiln system

c

To operate in such a way that the gas resulting from the co-incineration of waste is raised in a controlled and homogeneous fashion, even under the most unfavourable conditions, to a temperature of 850 °C for 2 seconds

d

To raise the temperature to 1 100 °C, if hazardous waste with a content of more than 1 % of halogenated organic substances, expressed as chlorine, are co-incinerated

e

To feed wastes continuously and constantly

f

Delay or stop co-incinerating waste for operations such as start-ups and/or shutdowns when appropriate temperatures and residence times cannot be reached, as noted in a) to d) above

Technique

Applicability

a

Use a simple and linear site layout of the installation

Applicable to new plants only

b

Enclose/encapsulate dusty operations, such as grinding, screening and mixing

Generally applicable

c

Cover conveyors and elevators, which are constructed as closed systems, if diffuse dust emissions are likely to be released from dusty material

d

Reduce air leakages and spillage points

e

Use automatic devices and control systems

f

Ensure trouble-free operations

g

Ensure proper and complete maintenance of the installation using mobile and stationary vacuum cleaning.

h

Ventilate and collect dust in fabric filters:

i

Use closed storage with an automatic handling system:

j

Use flexible filling pipes for dispatch and loading processes, equipped with a dust extraction system for loading cement, which are positioned towards the loading floor of the lorry

Technique

a

Cover bulk storage areas or stockpiles or enclose them with screening, walling or an enclosure consisting of vertical greenery (artificial or natural wind barriers for open pile wind protection)

b

Use open pile wind protection:

c

Use water spray and chemical dust suppressors:

d

Ensure paving, road wetting and housekeeping:

e

Ensure humidification of stockpiles:

f

Match the discharge height to the varying height of the heap, automatically if possible or by reduction of the unloading velocity, when diffuse dust emissions at the charging or discharging points of storage sites cannot be avoided

Technique (7)

Applicability

a

Electrostatic precipitators (ESPs)

Applicable to all kiln systems

b

Fabric filters

c

Hybrid filters

Technique (8)

Applicability

a

Electrostatic precipitators (ESPs)

Generally applicable to clinker coolers and cement mills.

b

Fabric filters

Generally applicable to clinker coolers and mills

c

Hybrid filters

Applicable to clinker coolers and cement mills.

Technique (9)

Applicability

a

Primary techniques

Applicable to all types of kilns used for cement manufacturing. The degree of applicability can be limited by product quality requirements and potential impacts on process stability

Applicable to all rotary kilns, in the main kiln as well as in the precalciner

Generally applicable to long rotary kilns

Generally applicable to rotary kilns subject to final product quality requirements

Generally applicable to all kilns

b

Staged combustion (conventional or waste fuels), also in combination with a precalciner and the use of optimised fuel mix

In general, can only be applied in kilns equipped with a precalciner. Substantial plant modifications are necessary in cyclone preheater systems without a precalciner.

In kilns without precalciner, lump fuels firing might have a positive effect on NOx reduction depending on the ability to produce a controlled reduction atmosphere and to control the related CO emissions

c

Selective non-catalytic reduction (SNCR)

In principle, applicable to rotary cement kilns. The injection zones vary with the type of kiln process. In long wet and long dry process kilns it may be difficult to obtain the right temperature and retention time needed. See also BAT 20

d

Selective catalytic reduction (SCR)

Applicability is subject to appropriate catalyst and process development in the cement industry

Kiln type

Unit

BAT-AEL

(daily average value)

Preheater kilns

mg/Nm3

< 200 – 450 (10)  (11)

Lepol and long rotary kilns

mg/Nm3

400 – 800 (12)

Technique

a

To apply an appropriate and sufficient NOx reduction efficiency along with a stable operating process

b

To apply a good stoichiometric distribution of ammonia in order to achieve the highest efficiency of NOx reduction and to reduce the NH3 slip

c

To keep the emissions of NH3 slip (due to unreacted ammonia) from the flue-gases as low as possible taking into account the correlation between the NOx abatement efficiency and the NH3 slip

Parameter

Unit

BAT-AEL

(daily average value)

NH3 slip

mg/Nm3

< 30 – 50 (13)

Technique (14)

Applicability

a

Absorbent addition

Absorbent addition is, in principle, applicable to all kiln systems, although it is mostly used in suspension preheaters. Lime addition to the kiln feed reduces the quality of the granules/nodules and causes flow problems in Lepol kilns. For preheater kilns it has been found that direct injection of slaked lime into the flue-gas is less efficient than adding slaked lime to the kiln feed

b

Wet scrubber

Applicable to all cement kiln types with appropriate (sufficient) SO2 levels for manufacturing the gypsum

Parameter

Unit

BAT-AEL (15)  (16)

(daily average value)

SOx expressed as SO2

mg/Nm3

< 50 – 400

Technique

a

Manage CO trips in order to reduce the ESP downtime

b

Continuous automatic CO measurements by means of monitoring equipment with a short response time and situated close to the CO source

Technique

a

Using raw materials and fuels with a low chlorine content

b

Limiting the amount of chlorine content for any waste that is to be used as raw material and/or fuel in a cement kiln

Technique

a

Using raw materials and fuels with a low fluorine content

b

Limiting the amount of fluorine content for any waste that is to be used as raw material and/or fuel in a cement kiln

Technique

Applicability

a

Carefully selecting and controlling of kiln inputs (raw materials), i.e. chlorine, copper and volatile organic compounds

Generally applicable

b

Carefully selecting and controlling kiln inputs (fuels), i.e. chlorine and copper

Generally applicable

c

Limiting/avoiding the use of wastes which contain chlorinated organic materials

Generally applicable

d

Avoid feeding fuels with a high content of halogens (e.g. chlorine) in secondary firing

Generally applicable

e

Quick cooling of kiln flue-gases to lower than 200 °C and minimising residence time of flue-gases and oxygen content in zones where the temperatures range between 300 and 450 °C

Applicable to long wet kilns and long dry kilns without preheating. In modern preheater and precalciner kilns, this feature is already inherent

f

Stop co-incinerating waste for operations such as start-ups and/or shutdowns

Generally applicable

Technique

a

Selecting materials with a low content of relevant metals and limiting the content of relevant metals in materials, especially mercury

b

Using a quality assurance system to guarantee the characteristics of the waste materials used

c

Using effective dust removal techniques as set out in BAT 17

Metals

Unit

BAT-AEL

(average over the sampling period (spot measurements, for at least half an hour))

Hg

mg/Nm3

< 0,05 (18)

Σ (Cd, Tl)

mg/Nm3

< 0,05 (17)

Σ (As, Sb, Pb, Cr, Co, Cu, Mn, Ni, V)

mg/Nm3

< 0,5 (17)

Technique

Applicability

a

Reuse collected dusts in the process, wherever practicable

Generally applicable but subject to dust chemical composition

b

Utilise these dusts in other commercial products, when possible

The utilisation of the dusts in other commercial products may not be within the control of the operator

Technique

a

Process control optimisation, including computer-based automatic control

b

Using modern, gravimetric solid fuel feed systems and/or gas flow meters

Technique

Applicability

a

Continuous measurements of process parameters demonstrating the process stability, such as temperature, O2 content, pressure, flow rate and CO emissions

Applicable to kiln processes

b

Monitoring and stabilising of critical process parameters, e.g. fuel feed, regular dosage and excess oxygen

c

Continuous or periodic measurements of dust, NOx, SOx, CO emissions and NH3 emissions when SNCR is applied

Applicable to kiln processes

d

Continuous or periodic measurements of HCl and HF emissions in case wastes are co-incinerated

Applicable to kiln processes

e

Continuous or periodic measurements of TOC emissions or continuous measurements in case wastes are co-incinerated

Applicable to kiln processes

f

Periodic measurements of PCDD/F and metal emissions

Applicable to kiln processes

g

Continuous or periodic measurements of dust emissions

Applicable to non-kiln processes

For small sources (<10 000 Nm3/h) the frequency of the measurements should be based on a maintenance management system

Technique

Description

Applicability

a

Applying improved and optimised kiln systems and a smooth and stable kiln process, operating close to the process parameter set points, through:

Maintaining kiln control parameters close to their optimum values has the effect of reducing all consumption parameters due to, among other things, reduced numbers of shutdowns and upset conditions.

The use of optimised grain size of stone is subject to raw material availability

Technique (a) II is applicable only to long rotary kilns (LRK)

b

Using fuels with characteristics which have a positive influence on thermal energy consumption

The characteristics of fuels, e.g. high calorific value and low moisture content can have a positive effect on the thermal energy consumption

The applicability depends on the technical possibility to feed the selected fuel into the kiln and on the availability of suitable fuels (e.g. high calorific value and low humidity) which may be impacted by the energy policy of the Member State

c

Limiting excess air

A decrease of excess air used for combustion has a direct effect on fuel consumption since high percentages of air require more thermal energy to heat up the excess volume.

Only in LRK and PRK the limitation of excess air has an impact on thermal energy consumption.

The technique has a potential of increasing TOC and CO emission

Applicable to LRK and PRK within the limits of a potential overheating of some areas in the kiln with consequent deterioration of the refractory lifetime

Kiln type

Thermal energy consumption (19)

GJ/tonne of product

Long rotary kilns (LRK)

6,0 – 9,2

Rotary kilns with preheater (PRK)

5,1 – 7,8

Parallel flow regenerative kilns (PFRK)

3,2 – 4,2

Annular shaft kilns (ASK)

3,3 – 4,9

Mixed feed shaft kilns (MFSK)

3,4 – 4,7

Other kilns (OK)

3,5 – 7,0

Technique

a

Using power management systems

b

Using optimised grain size of limestone

c

Using grinding equipment and other electricity based equipment with high energy efficiency

Technique

Applicability

a

Specific quarrying, crushing and well directed use of limestone (quality, grain size)

Generally applicable in the lime industry; however, stone processing is dependent on the limestone quality

b

Selecting kilns applying optimised techniques which allow for operating with a wider range of limestone grain sizes to make optimum use of quarried limestone

Applicable to new plants and major upgrades of kiln.

Vertical kilns can in principle only burn coarse limestone pebbles. Fine lime PFRK and/or rotary kilns can operate with smaller limestone grain sizes

Technique

a

Apply a quality assurance system to guarantee and control the characteristics of wastes and to analyse any waste that is to be used as fuel in the kiln for:

b

Control the amount of relevant components for any waste that is to be used as fuel, such as total halogen content, metals (e.g. total chromium, lead, cadmium, mercury, thallium) and sulphur

Technique

a

To use appropriate burners for feeding suitable wastes depending on kiln design and kiln operation

b

To operate in such a way that the gas resulting from the co-incineration of waste is raised in a controlled and homogeneous fashion and even under the most unfavourable conditions, to a temperature of 850 °C for 2 seconds

c

To raise the temperature to 1 100 °C if hazardous wastes with a content of more than 1 % of halogenated organic substances, expressed as chlorine, are co-incinerated

d

To feed wastes continuously and constantly

e

To stop feeding waste for operations such as start-ups and/or shutdowns when appropriate temperatures and residence times cannot be reached, as mentioned in (b) and (c) above

Technique

a

Enclosure/encapsulation of dusty operations, such as grinding, screening and mixing

b

Use of covered conveyors and elevators, which are constructed as closed systems, if dust emissions are likely to be released from dusty material

c

Use of storage silos with adequate capacity, level indicators with cut out switches and with filters to deal with dust-bearing air displaced during filling operations

d

Use of a circulation process which is favoured for pneumatic conveying systems

e

Material handling in closed systems maintained under negative pressure and dedusting of the suction air by a fabric filter before being emitted into the air

f

Reduction of air leakage and spillage points, completion of installation

g

Proper and complete maintenance of the installation

h

Use of automatic devices and control systems

i

Use of continuous trouble-free operations

j

Use of flexible filling pipes equipped with a dust extraction system for loading lime which are positioned at the loading floor of the lorry

Technique

a

Enclose storage locations using screening, walling or vertical greenery (artificial or natural wind barriers for open pile wind protection)

b

Use product silos and closed, fully-automated raw material storages. These types of storage are equipped with one or more fabric filters to prevent diffuse dust formation in loading and unloading operations

c

Reduce diffuse dust emissions at stockpiles by using sufficient humidification of stockpile charging and discharging points and the use of conveyor belts with adjustable height. When using humidification or spraying measures/techniques, the ground can be sealed and the surplus water can be gathered, and if necessary this can be treated and used in closed cycles

d

Reduce diffuse dust emissions at charging or discharging points of storage sites if they cannot be avoided, by matching the discharge height to the varying height of the heap, if possible automatically, or by reduction of the unloading velocity

e

Keep the locations wet, especially dry areas, using spraying devices and clean them by cleaning lorries

f

Use vacuum systems during removal operations. New buildings can easily be equipped with stationary vacuum cleaning systems, while existing buildings are normally better fitted with mobile systems and flexible connections

g

Reduce diffuse dust emissions arising in areas used by lorries, by paving these areas when possible and keeping the surface as clean as possible. Wetting the roads can reduce diffuse dust emissions, especially during dry weather. Good housekeeping practices can be used in order to keep diffuse dust emissions to a minimum

Technique (20)  (21)

Applicability

a

Fabric filter

Generally applicable to milling and grinding plants and subsidiary processes in the lime industry; material transport; and storage and loading facilities. The applicability of fabric filters in hydrating lime plants may be limited by the high moisture and low temperature of the flue-gases

b

Wet scrubbers

Mainly applicable to hydrating lime plants

Technique

Unit

BAT-AEL

(daily average or average over the sampling period (spot measurements for at least half an hour))

Fabric filter

mg/Nm3

< 10

Wet scrubber

mg/Nm3

< 10 – 20

Technique (22)

Applicability

a

ESP

Applicable to all kiln systems

b

Fabric filter

Applicable to all kiln systems

c

Wet dust separator

Applicable to all kiln systems

d

Centrifugal separator/cyclone

Centrifugal separators are only suitable as pre-separators and can be used to pre-clean the flue-gases from all kiln systems

Technique

Unit

BAT-AEL

(daily average value or average over the sampling period (spot measurements for at least half an hour))

Fabric filter

mg/Nm3

< 10

ESP or other filters

mg/Nm3

< 20 (23)

Technique

Applicability

a

Careful selection and control of substances entering the kiln

Generally applicable

b

Reducing the pollutant precursors in fuels and, if possible, in raw materials, i.e.

Generally applicable in the lime industry subject to local availability of raw materials and fuels, the type of kiln used, the desired product qualities and the technical possibility of feeding the fuels into the selected kiln

c

Using process optimisation techniques to ensure an efficient absorption of sulphur dioxide (e.g. efficient contact between the kiln gases and the quicklime)

Applicable to all lime plants.

In general, complete process automation is not achievable due to uncontrollable variables, i.e. quality of the limestone

Technique

Applicability

a

Primary techniques

Generally applicable in the lime industry subject to fuel availability which may be impacted by the energy policy of the Member State and to the technical possibility to feed a certain type of fuel into the selected kiln

Optimisation of process and process control can be applied in lime manufacturing but is subject to the final product quality

Low NOX burners are applicable to rotary kilns and to annular shaft kilns presenting conditions of high primary air. PFRKs and other shaft kilns have flameless combustion, thus rendering low NOX burners not applicable to this kiln type

Not applicable to shaft kilns.

Applicable only to PRK but not when hard burned lime is produced. The applicability may be limited by constraints imposed by the type of final product, due to possible overheating in some areas of the kiln and consequent deterioration of the refractory lining

b

SNCR (24)

Applicable to Lepol rotary kilns. See also BAT 46

Kiln type

Unit

BAT-AEL

(daily average value or average over the sampling period (spot measurements for at least half an hour), stated as NO2)

PFRK, ASK, MFSK, OSK

mg/Nm3

100 – 350 (25)  (27)

LRK, PRK

mg/Nm3

< 200 – 500 (25)  (26)

Technique

a

To apply an appropriate and sufficient reduction efficiency along with a stable operating process

b

To apply a good stoichiometric ratio and distribution of ammonia in order to achieve the highest efficiency of NOx reduction and to reduce the ammonia slip

c

To keep the emissions of NH3 slip (due to unreacted ammonia) from the flue-gases as low as possible, taking into account the correlation between the NOx abatement efficiency and the NH3 slip.

Technique

Applicability

a

Process optimisation to ensure an efficient absorption of sulphur dioxide (e.g. efficient contact between the kiln gases and the quicklime)

Process control optimisation is applicable to all lime plants

b

Selecting fuels with a low sulphur content

Generally applicable, subject to fuel availability in particular for use in long rotary kilns (LRK), due to high SOx emissions

c

Using absorbent addition techniques (e.g. absorbent addition, dry flue-gas cleaning with a filter, wet scrubber, or activated carbon injection) (28)

Absorbent addition techniques are, in principle, applicable in the lime industry; however, this technique had not yet been applied in the lime sector in 2007. Particularly for rotary lime kilns further investigation is required in order to assess its applicability

Kiln type

Unit

BAT-AEL (29)  (30)

(daily average value or average over the sampling period (spot measurements for at least half an hour), SOx expressed as SO2)

PFRK, ASK, MFSK, OSK, PRK

mg/Nm3

< 50 – 200

LRK

mg/Nm3

< 50 – 400

Technique

Applicability

a

Selecting, raw materials with a low content of organic matter

Generally applicable to the lime industry within the constraints of the local availability and composition of raw materials, the type of kiln used and the quality of the final product

b

Using process optimisation techniques to achieve a stable and complete combustion

Applicable to all lime plants.

In general, complete process automation is not achievable due to uncontrollable variables, i.e. quality of the limestone

Kiln type

Unit

BAT-AEL (31)  (32)

(daily average value or average over the sampling period (spot measurements for at least half an hour))

PFRK, OSK, LRK, PRK

mg/Nm3

< 500

Technique

a

Manage CO trips in order to reduce the ESP downtime

b

Continuous automatic CO measurements by means of monitoring equipment with a short response time and situated close to the CO source

Technique

a

Applying general primary techniques and monitoring (see also BAT 30 and 31 in Section 1.3.1, and BAT 32 in Section 1.3.2)

b

Avoid feeding raw materials with a high content of volatile organic compounds into the kiln system (except for hydraulic lime production)

Kiln type

Unit

BAT-AEL (33)

(daily average value or average over the sampling period (spot measurements for at least half an hour))

LRK, PRK

mg/Nm3

< 10

ASK, MFSK (34), PFRK (34)

mg/Nm3

< 30

Technique

a

Using conventional fuels with a low chlorine and fluorine content

b

Limiting the amount of chlorine and fluorine content for any waste that is to be used as fuel in a lime kiln

Emission

Unit

BAT-AEL

(daily average value or the average value over the sampling period (spot measurements, for at least half an hour))

HCl

mg/Nm3

< 10

HF

mg/Nm3

< 1

Technique

a

Selecting fuels with a low chlorine content

b

Limiting the copper input through the fuel

c

Minimising the residence time of the flue-gases and the oxygen content in zones where the temperatures range between 300 and 450 °C

Technique

a

Selecting fuels with a low content of metals

b

Using a quality assurance system to guarantee the characteristics of the waste fuels used

c

Limiting the content of relevant metals in materials, especially mercury

d

Using one or a combination of dust removal techniques as set out in BAT 43

Metals

Unit

BAT-AEL

(average over the sampling period (spot measurements for at least half an hour))

Hg

mg/Nm3

< 0,05

Σ (Cd, Tl)

mg/Nm3

< 0,05

Σ (As, Sb, Pb, Cr, Co, Cu, Mn, Ni, V)

mg/Nm3

< 0,5

Technique

Applicability

a

Reuse the collected dust or other particulate matter (e.g. sand, gravel) in the process

Generally applicable whenever practicable

b

Utilise dust, off-specification quicklime and off-specification hydrated lime in selected commercial products

Generally utilised in different kinds of selected commercial products, whenever practicable

Technique

Applicability

a

Continuous measurements of process parameters demonstrating the process stability, such as temperature, O2 content, pressure, flow rate

Generally applicable to kiln processes

b

Monitoring and stabilising critical process parameters, i.e. raw material and fuel feed, regular dosage and excess oxygen

c

Continuous or periodic measurements of dust, NOx, SOx and CO emissions

Generally applicable to kiln processes

d

Continuous or periodic measurements of dust emissions

Applicable to non-kiln processes.

For small source (< 10 000 Nm3/h) the frequency of the measurements or performance check should be based on a maintenance management system

Technique

Description

Applicability

a

Applying improved and optimised kiln systems and a smooth and stable kiln process by applying:

Heat recovery from flue-gases by the preliminary heating of the magnesite can be used in order to reduce fuel energy use. Heat recovered from the kiln can be used for drying fuels, raw materials and some packaging materials

Process control optimisation is applicable to all kiln types used in the magnesia industry.

b

Using fuels with characteristics which have a positive influence on thermal energy consumption

The characteristics of fuels, e.g. high calorific value and low moisture content have a positive effect on the thermal energy consumption

Generally applicable subject to availability of the fuels, the type of kilns used, the desired product qualities and the technical possibilities of injecting the fuels into the kiln.

c

Limiting excess air

The excess oxygen level to obtain the required quality of the products and for optimal combustion is usually in practice about 1 – 3 %

Generally applicable

Technique

a

Using power management systems

b

Using grinding equipment and other electricity based equipment with high energy efficiency

Technique

a

Simple and linear site layout

b

Good housekeeping of buildings and roads, along with proper and complete maintenance of the installation

c

Watering of raw material piles

d

Enclosure/encapsulation of dusty operations, such as grinding and screening

e

Use of covered conveyors and elevators, which are constructed as closed systems, if dust emissions are likely to be released from dusty material

f

Use of storage silos with adequate capacities and equipping them with filters to deal with dust-bearing air displaced during filling operations

g

A circulation process is favoured for pneumatic conveying systems

h

Reduction of air leakage and spillage points

i

Use of automatic devices and control systems

k

Use of continuous trouble-free operations

Technique (36)

Applicability

a

Fabric filters

Generally applicable to all units in the magnesium oxide manufacturing process, especially for dusty operations, screening, grinding and milling

b

Centrifugal separators/ cyclones

Because of the system-dependent limited degree of separation, cyclones are mainly applicable as preliminary separators for coarse dust and flue-gases

c

Wet dust separators

Generally applicable

Technique (37)

Applicability

a

Electrostatic precipitators (ESPs)

ESPs are mainly applicable in rotary kilns. They are applicable for flue-gas temperatures above the dew point and up to 370 – 400 °C

b

Fabric filters

Fabric filters for dust removal from flue-gases can, in principle, be applied for all units in the magnesium oxide manufacturing process. They can be used for flue-gas temperatures above the dew point and up to 280 °C.

For the production of caustic calcined magnesia (CCM) and sintered/dead burned magnesia (DBM), due to the high temperatures, the corrosive nature and the high volume of the flue-gases occurring from the kiln firing process, special fabric filters with high temperature-resistant filter material have to be used. However, experience from the magnesia industry producing DBM shows that no suitable equipment is available for flue-gas temperatures of approximately 400 °C for magnesia production

c

Centrifugal separators/ cyclones

Because of the system-dependent limited degree of separation, cyclones are mainly applicable as preliminary separators for coarse dust and flue-gases

d

Wet dust separators

Generally applicable

Technique

Applicability

a

Careful selection and control of the substances entering the kiln in order to reduce the pollutant precursors, i.e.:

Generally applicable subject to availability of raw materials and fuels, the type of kiln used, the desired product qualities and the technical possibility of injecting the fuels into the selected kiln.

Waste materials can be considered as fuels in the magnesia industry but had not yet been applied in the magnesia industry in 2007

b

Using process optimisation measures/techniques to ensure a smooth and stable kiln process, operating close to the stoichiometric required air

Process control optimisation is applicable to all kiln types used in the magnesia industry. However, a highly sophisticated process control system may be necessary

Technique

Applicability

a

Appropriate fuel selection along with a limited nitrogen content in the fuel

Generally applicable subject to fuels availability

b

Process optimisation and improved firing technique

Generally applicable in the magnesia industry

Technique

Description

a

Selecting raw materials with a low content of organic matter

A part of CO emissions results from the organic matter of raw materials thus selection of raw materials with low organic content can reduce CO emissions

b

Process control optimisation

A complete and correct combustion is essential to reduce CO emissions. Air supply from cooler and primary air as well as the draught of the stack fan can be controlled in order to keep an oxygen level of between 1 (sinter) and 1,5 % (caustic) during the combustion. A change of air and fuel charge can reduce CO emissions. Furthermore, CO emissions can be decreased by changing the depth of the burner

c

Feeding fuels controlled, constantly and continuously

Controlled fuel addition includes, e.g.:

Technique

a

Manage CO trips in order to reduce the ESP downtime

b

Continuous automatic CO measurements by means of monitoring equipment with a short response time and situated close to the CO source

Technique

Applicability

a

Process optimisation techniques

Generally applicable

b

Selecting fuels with a low sulphur content

Generally applicable subject to availability of low sulphur fuels which may be impacted by the energy policy of the Member State. The selection of fuel also depends on the quality of the final product, technical possibilities and economic considerations

c

A dry absorbent addition technique (sorbent addition into the flue gas stream such as reactive MgO grades, hydrated lime, activated carbon, etc.), in combination with a filter (38)

Generally applicable

d

Wet scrubber (38)

The applicability may be limited in arid areas by the large volume of water necessary and the need for waste water treatment and the related cross-media effects

Parameter

Unit

BAT-AEL (39)  (40)

(daily average value or average over the sampling period (spot measurements for at least half an hour))

SOX expressed as SO2

mg/Nm3

< 50 – 400 (41)

Technique

a

To select suitable wastes for the process and the burner

b

To apply quality assurance systems to guarantee and control the characteristics of wastes and to analyse any waste that is to be used for:

c

To control the amount of relevant parameters for any waste that is to be used, such as total halogen content, metals (e.g. total chromium, lead, cadmium, mercury, thallium) and sulphur

Technique

Description

a

Electrostatic precipitators

Electrostatic precipitators (ESPs) generate an electrostatic field across the path of particulate matter in the air stream. The particles become negatively charged and migrate towards positively charged collection plates. The collection plates are rapped or vibrated periodically, dislodging the material so that it falls into collection hoppers below. It is important that ESP rapping cycles be optimised to minimise particulate re-entrainment and thereby minimise the potential to affect plume visibility.

ESPs are characterised by their ability to operate under conditions of high temperatures (up to approximately 400 °C) and high humidity. The major disadvantages of this technique are their decreased efficiency with an insulating layer and a build-up of material that may be generated with high chlorine and sulphur inputs. For the overall performance of ESPs, it is important to avoid CO trips

Even though there are no technical restrictions on the applicability of ESPs in the various processes in the cement industry, they are not often chosen for cement mill dedusting because of the investment costs and the efficiency (relatively high emissions) during start-ups and shutdowns

b

Fabric filters

Fabric filters are efficient dust collectors. The basic principle of fabric filtration is to use a fabric membrane which is permeable to gas but which will retain the dust. Basically, the filter medium is arranged geometrically. Initially, dust is deposited both on the surface fibres and within the depth of the fabric, but as the surface layer builds up, the dust itself becomes the dominating filter medium. Off-gas can flow either from the inside of the bag outwards or vice versa. As the dust cake thickens, the resistance to gas flow increases. Periodic cleaning of the filter medium is therefore necessary to control the gas pressure drop across the filter. The fabricfilter should have multiple compartments which can be individually isolated in case of bag failure and there should be sufficient of these to allow adequate performance to be maintained if a compartment is taken off line. There should be ‘burst bag detectors’ in each compartment to indicate the need for maintenance when this happens. Filter bags are available in a range of woven and non-woven fabrics. Modern synthetic fabrics can operate at quite high temperatures of up to 280 °C.

The performance of fabric filters is mainly influenced by different parameters, such as compatibility of the filter medium with the characteristics of the flue-gas and the dust, suitable properties for thermal, physical and chemical resistance, such as hydrolysis, acid, alkali, and oxidation and process temperature. Moisture and temperature of the flue-gases have to be taken into consideration during the selection of the technique.

c

Hybrid filters

Hybrid filters are the combination of ESPs and fabric filters in the same device. They generally result from the conversion of existing ESPs. They allow the partial reuse of the old equipment

Technique

Description

a

Primary measures/techniques

The addition of water to the fuel or directly to the flame by using different injection methods, such as injection of one fluid (liquid) or two fluids (liquid and compressed air or solids) or the use of liquid/solid wastes with a high water content reduces the temperature and increases the concentration of hydroxyl radicals. This can have a positive effect on NOx reduction in the burning zone

Designs of low NOx burners (indirect firing) vary in detail but essentially the fuel and air are injected into the kiln through concentric tubes. The primary air proportion is reduced to some 6 – 10 % of that required for stoichiometric combustion (typically 10 – 15 % in traditional burners). Axial air is injected at high momentum in the outer channel. The coal may be blown through the centre pipe or the middle channel. A third channel is used for swirl air, its swirl being induced by vanes at, or behind, the outlet of the firing pipe. The net effect of this burner design is to produce very early ignition, especially of the volatile compounds in the fuel, in an oxygen-deficient atmosphere, and this will tend to reduce the formation of NOx.

The application of low NOx burners is not always followed by a reduction of NOx emissions. The set-up of the burner has to be optimised

In long wet and long dry kilns, the creation of a reducing zone by firing lump fuel can reduce NOx emissions. As long kilns usually have no access to a temperature zone of about 900 – 1 000 °C, mid-kiln firing systems can be installed in order to be able to use waste fuels that cannot pass the main burner (for example tyres).

The rate of the burning of fuels can be critical. If it is too slow, reducing conditions can occur in the burning zone, which may severely affect product quality. If it is too high, the kiln chain section can be overheated – resulting in the chains being burned out. A temperature range of less than 1 100 °C excludes the use of hazardous waste with a chlorine content of greater than 1 %

The addition of mineralisers, such as fluorine, to the raw material is a technique to adjust the clinker quality and allow the sintering zone temperature to be reduced. By reducing/lowering the burning temperature, NOx formation is also reduced

Optimisation of the process, such as smoothing and optimising the kiln operation and firing conditions, optimising the kiln operation control and/or homogenisation of the fuel feedings, can be applied for reducing NOx emissions. General primary optimisation measures/techniques, such as process control measures/techniques, an improved indirect firing technique, optimised cooler connections and fuel selection, and optimised oxygen levels have been applied

b

Staged combustion (conventional or waste fuels), also in combination with a precalciner and the use of optimised fuel mix

Staged combustion is applied at cement kilns with an especially designed precalciner. The first combustion stage takes place in the rotary kiln under optimum conditions for the clinker burning process. The second combustion stage is a burner at the kiln inlet, which produces a reducing atmosphere that decomposes a portion of the nitrogen oxides generated in the sintering zone. The high temperature in this zone is particularly favourable for the reaction which reconverts the NOx to elementary nitrogen. In the third combustion stage, the calcining fuel is fed into the calciner with an amount of tertiary air, producing a reducing atmosphere there, too. This system reduces the generation of NOx from the fuel, and also decreases the NOx coming out of the kiln. In the fourth and final combustion stage, the remaining tertiary air is fed into the system as ‘top air’ for residual combustion

c

SNCR

Selective non-catalytic reduction (SNCR) involves injecting ammonia water (up to 25 % NH3), ammonia precursor compounds or urea solution into the combustion gas to reduce NO to N2. The reaction has an optimum effect in a temperature window of about 830 to 1 050 °C, and sufficient retention time must be provided for the injected agents to react with NO

d

SCR

SCR reduces NO and NO2 to N2 with the help of NH3 and a catalyst at a temperature range of about 300 – 400 °C. This technique is widely used for NOx abatement in other industries (coal fired power stations, waste incinerators). In the cement industry, basically two systems are considered: low dust configuration between a dedusting unit and stack, and a high dust configuration between a preheater and a dedusting unit. Low dust flue-gas systems require the reheating of the flue-gases after dedusting, which may cause additional energy costs and pressure losses. High dust systems are considered preferable for technical and economical reasons. These systems do not require reheating, because the waste gas temperature at the outlet of the preheater system is usually in the right temperature range for SCR operation

Technique

Description

a

Absorbent addition

Absorbent is either added to the raw materials (e.g. hydrated lime addition) or injected into the gas stream (e.g. hydrated or slaked lime (Ca(OH)2), quicklime (CaO), activated fly ash with a high CaO content or sodium bicarbonate (NaHCO3)).

Hydrated lime can be charged into the raw mill together with the raw material constituents or directly added to the kiln feed. The addition of hydrated lime offers the advantage that the calcium-bearing additive forms reaction products that can be directly incorporated into the clinker-burning process.

Absorbent injection into the gas stream can be applied in a dry or wet form (semi-dry scrubbing). The absorbent is injected into the flue-gas path at temperatures close to the water dew point, which results in more favourable conditions for SO2 capture. In cement kiln systems, this temperature range is usually reached in the area between the raw mill and the dust collector

b

Wet scrubber

The wet scrubber is the most commonly used technique for flue-gas desulphurisation in coal-fired power plants. For cement manufacturing processes, the wet process for reducing SO2 emissions is an established technique. Wet scrubbing is based on the following chemical reaction:

SOx are absorbed by a liquid/slurry which is sprayed in a spray tower. The absorbent is generally calcium carbonate. Wet scrubbing systems provide the highest removal efficiencies for soluble acid gases of all flue-gas desulphurisation (FGD) methods with the lowest excess stoichiometric factors and the lowest solid waste production rate. The technique requires certain amounts of water with a consequent need for waste water treatment

Technique

Description

a

ESP

A general description of ESPs is provided in Section 1.5.1.

ESPs are suitable for use at temperatures above the dew point and up to 400 °C. Furthermore, it is also possible to use ESPs close to, or below, the dew point. Because of high volume flows and relatively high dust loads, mainly rotary kilns without preheaters but also rotary kilns with preheaters are equipped with ESPs. In the case of combination with a quenching tower, excellent performance can be achieved

b

Fabric filter

A general description of fabric filters is provided in Section 1.5.1.

Fabric filters are well suited for kilns, milling and grinding plants for quicklime as well as for limestone; lime hydrating plants; material transport; and storage and loading facilities. Often a combination with cyclone prefilters is useful. The operation of fabric filters is limited by the flue-gas conditions such as temperature, moisture, dust load and chemical composition. There are various fabric materials available to resist mechanical, thermal and chemical wear to meet those conditions

c

Wet dust separator

With wet dust separators, dust is eliminated from off-gas streams by bringing the gas flow into close contact with a scrubbing liquid (usually water), so that the dust particles are retained in the liquid and can be rinsed away. There are a number of different types of wet scrubbers available for dust removal. The main types that have been used in lime kilns are multi-cascade/multistage wet scrubbers, dynamic wet scrubbers and venturi wet scrubbers. The majority of wet scrubbers used on lime kilns are multi-cascade/multistage wet scrubbers.

Wet scrubbers are chosen when the flue-gas temperatures are close to, or below the dew point. They may also be chosen when space is limited. Wet scrubbers are sometimes used with higher temperature gases, in which case, the water cools the gases and reduces their volume

d

Centrifugal Separator/cyclone

In a centrifugal separator/cyclone, the dust particles to be eliminated from an off-gas stream are forced out against the outer wall of the unit by centrifugal action and then eliminated through an aperture at the bottom of the unit. Centrifugal forces can be developed by directing the gas flow in a downward spiral motion through a cylindrical vessel (cyclonic separators) or by a rotating impeller fitted in the unit (mechanical centrifugal separators). However, they are only suitable as pre-separators because of their limited particle removal efficiency and they relieve ESPs and fabric filters from high dust loading, and reduce abrasion problems

Technique

Description

a

Burner design (low NOx burner)

The low NOx burners are useful for reducing the flame temperature and thus reducing thermal and (to some extent) fuel derived NOx. The NOx reduction is achieved by supplying rinsing air for lowering the flame temperature or pulsed operation of the burners. Low NOx burners are designed to reduce the primary air portion which leads to lower NOx formation whereas common multi-channel burners are operated with a primary air portion of 10 to 18 % of the total combustion air. The higher portion of the primary air leads to a short and intensive flame by the early mixing of hot secondary air and fuel. This results in high flame temperatures along with a creation of a high amount of NOx formation which can be avoided by using low NOx burners

b

Air staging

A reducing zone is created by reducing the oxygen supply in the primary reaction zones. High temperatures in this zone are particularly favourable for the reaction which reconverts the NOx to elementary nitrogen. At later combustion zones, the air and oxygen supply is increased to oxidise the gases formed. Effective air/gas mixing in the firing zone is required to ensure that CO and NOx are both maintained at low levels.

In 2007, air staging had never been applied in the lime sector

c

SNCR

Nitrogen oxides (NO and NO2) from the flue-gases are removed by selective non-catalytic reduction and converted into nitrogen and water by injecting a reducing agent into the kiln which reacts with the nitrogen oxides. Ammonia or urea is typically used as the reducing agent. The reactions occur at temperatures of between 850 and 1 020 °C, with the optimal range typically between 900 to 920 °C

Technique

Description

a

Absorbent addition techniques

The technique involves the addition of an absorbent in dry form directly into the kiln (fed or injected) or in dry or wet form (e.g. hydrated lime or sodium bicarbonate) into the flue-gases in order to remove SOx emissions. When absorbent is injected into the flue-gases, a sufficient residence time between the injection point and the dust collector (fabric filter or ESP) must be provided in order to obtain an efficient absorption.

For rotary kilns, absorption techniques may include:

Measure/Technique

Description

a

Electrostatic precipitators (ESPs)

A general description of ESPs is provided in Section 1.5.1

b

Fabric filters

A general description of fabric filters is provided in Section 1.5.1

Fabric filters receive high particle retention, typically over 98 % and up to 99 % depending on the particle size. This technique offers the best efficiency on particle collection in comparison to other dust abatement measures/techniques used in the magnesia industry. However, because of the high temperatures of the kiln flue-gases, special filter materials which can tolerate high temperatures have to be used.

In DBM manufacturing, filter materials operating with temperatures of up to 250 °C are used, such as PTFE (Teflon) filter material. This filter material shows good resistance to acids or alkalis and a lot of corrosion problems have been solved

c

Cyclones (centrifugal separator)

A general description of cyclones is provided in Section 1.6.1. They are robust equipment and they have a wide operational temperature range with a low energy requirement. Because of the system-dependent limited degree of separation, cyclones are mainly used as preliminary separators for coarse dust and flue-gases

d

Wet dust separators

General description of wet dust separators (also called wet scrubbers) is provided in Section 1.6.1

Wet dust separators can be divided into various types according to their design and working principles, such as the venturi type. This type of wet dust separator has a number of applications in the magnesia industry, including when gas is directed through the narrowest section of the venturi tube, the ‘venturi neck’, and gas velocities of between 60 and 120 m/s can be achieved. The washing fluids which are fed into the venturi tube neck are diffused into a mist of very fine droplets and are intensively mixed with the gas. The particles separated onto the water droplets become heavier and can be readily drawn off using a drop separator installed in this venturi wet dust separator

Technique

Description

a

Absorbent addition technique

The technique involves the injection of an absorbent in dry or wet form (semi-dry scrubbing) into the flue-gases in order to remove SOx emissions. A sufficient gas residence time between the injection point and the dust collector is very important to obtain highly efficient absorption. Reactive MgO grades can be used as efficient absorbents for SO2 in the magnesia industry. Despite the lower efficiency compared to other absorbents, the use or reactive MgO grades has a double advantage as it lowers the investment costs and also the filter dust is not contaminated by other substances and can be reused in place of raw materials for the production of magnesia or employed as a fertiliser (magnesium sulphate) minimising waste generation

b

Wet scrubber

In the wet scrubbing technique, SOx are absorbed by a liquid/slurry which is sprayed countercurrently to the flue-gases in a spray tower. The technique requires an amount of water between 5 and 12 m3/tonne product, with a consequent need for a waste water treatment