Unless otherwise stated, the BAT conclusions presented in this section can be applied to all installations in the cement industry.
| Technique | |
|---|---|
| a | Process control optimisation, including computer-based automatic control |
| b | Using modern, gravimetric solid fuel feed systems |
Careful selection and control of substances entering the kiln can reduce emissions. The chemical composition of the substances and the way they are fed in the kiln are factors that should be taken into account during the selection. Substances of concern may include the substances mentioned in BAT 11 and in BAT 24 to 28.
| 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. |
The selection between continuous or periodic measurements mentioned in BAT 5(f) is based on the emission source and the type of pollutant expected.
In this type of kiln system, exhaust gases and recovered waste heat from the cooler can be used to preheat and precalcine the raw material feed before entering the kiln, providing significant savings in energy consumption.
Applicable to new plants and major upgrades, subject to raw materials moisture content.
See Table 1.
BAT-associated energy consumption levels for new plants and major upgrades using dry process kiln with multistage preheating and precalcination
| a Levels do not apply to plants producing special cement or white cement clinker that require significantly higher process temperatures due to product specifications. | ||
| b Under normal (excluding, e.g. start-ups and shutdowns) and optimised operational conditions. | ||
| c The production capacity has an influence on the energy demand, with higher capacities providing energy savings and smaller capacities requiring more energy. Energy consumption also depends on the number of cyclone preheater stages, with more cyclone preheater stages leading to lower energy consumption of the kiln process. The appropriate number of cyclone preheater stages is mainly determined by the moisture content of raw materials. | ||
| Process | Unit | BAT-associated energy consumption levelsa |
|---|---|---|
| Dry process with multistage preheating and precalcination | MJ/tonne clinker | 2 900 – 3 300b c |
| 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: I. process control optimisation, including computer-based automatic control systems II. modern, gravimetric solid fuel feed systems III. preheating and precalcination to the extent possible, considering the existing kiln system configuration | 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 |
Several factors affect the energy consumption of modern kiln systems such as raw materials properties (e.g. moisture content, burnability), the use of fuels, with different properties, as well as the use of a gas bypass system. Furthermore, the production capacity of the kiln has an influence on the energy demand.
Technique 7c: the appropriate number of cyclone stages for preheating is determined by the throughput and the moisture content of raw materials and fuels which have to be dried by the remaining flue-gas heat because local raw materials vary widely regarding their moisture content or burnability
Technique 7d: conventional and waste fuels can be used in the cement industry. The characteristics of the fuels used, such as adequate calorific value and low moisture content, have a positive influence on the specific energy consumption of the kiln.
Technique 7f: the removal of hot raw material and hot gas leads to a higher specific energy consumption of about 6 – 12 MJ/tonne clinker per percentage point of removed kiln inlet gas. Hence, minimising the use of gas bypass has a positive effect on energy consumption.
The reduction of the clinker content of cement and cement products can be achieved by adding fillers and/or additions, such as blast furnace slag, limestone, fly ash and pozzolana in the grinding step in accordance with the relevant cement standards.
Generally applicable to the cement industry, subject to (local) availability of fillers and/or additions and local market specificities.
The employment of cogeneration plants for the production of steam and electricity or combined heat and power plants can be applied in the cement industry by recovering waste heat from the clinker cooler or kiln flue-gases using the conventional steam cycle processes or other techniques. Furthermore, excess heat can be recovered from the clinker cooler or kiln flue-gases for district heating or industrial applications.
The technique is applicable in all cement kilns if sufficient excess heat is available, if appropriate process parameters can be met, and if economic viability is ensured.
| 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: I. constant quality II. physical criteria, e.g. emissions formation, coarseness, reactivity, burnability, calorific value III. chemical criteria, e.g. chlorine, sulphur, alkali and phosphate content and relevant metals content |
| 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 |
Different types of waste materials can replace primary raw materials and/or fossil fuels in cement manufacturing and will contribute to saving natural resources.
| 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 |
This section concerns dust emissions arising from dusty operations other than those from kiln firing, cooling and the main milling processes. This covers processes such as the crushing of raw materials; raw material conveyors and elevators; the storage of raw materials, clinker and cement; the storage of fuels and the dispatch of cement.
For dusty operations, dry flue-gas cleaning with a filter usually consists of a fabric filter. A description of fabric filters is provided in Section 1.5.1.
The BAT-AEL for channelled dust emissions from dusty operations (other than those from kiln firing, cooling and the main milling processes) is < 10 mg/Nm3, as the average over the sampling period (spot measurement, for at least half an hour).
It should be noted that for small sources (< 10 000 Nm3/h) a priority approach, based on the maintenance management system, regarding the frequency for checking the performance of the filter has to be taken into account (see also BAT 5).
| a A description of the techniques is given in Section 1.5.1. | ||
| Techniquea | Applicability | |
|---|---|---|
| a | Electrostatic precipitators (ESPs) | Applicable to all kiln systems |
| b | Fabric filters | |
| c | Hybrid filters | |
The BAT-AEL for dust emissions from flue-gases of kiln firing processes is <10 – 20 mg/Nm3, as the daily average value. When applying fabric filters or new or upgraded ESPs, the lower level is achieved.
| a A description of the techniques is given in Section 1.5.1 | ||
| Techniquea | 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. |
The BAT-AEL for dust emissions from the flue-gases of cooling and milling processes is <10 – 20 mg/Nm3, as the daily average value or average over the sampling period (spot measurements for at least half an hour). When applying fabric filters or new or upgraded ESPs, the lower level is achieved.
| a A description of the techniques is provided in Section 1.5.2. | ||
| Techniquea | Applicability | |
|---|---|---|
| a | Primary techniques | |
I.Flame cooling | 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 | |
II.Low NOx burners | Applicable to all rotary kilns, in the main kiln as well as in the precalciner | |
III.Mid-kiln firing | Generally applicable to long rotary kilns | |
IV.Addition of mineralisers to improve the burnability of the raw meal (mineralised clinker) | Generally applicable to rotary kilns subject to final product quality requirements | |
V.Process optimisation | 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 |
See Table 2.
BAT-associated emission levels for NOx from the flue-gases of kiln firing and/or preheating/precalcining processes in the cement industry
| a The upper level of the BAT-AEL range is 500 mg/Nm3, if the initial NOx level after primary techniques is > 1 000 mg/Nm3. | ||
| b Existing kiln system design, fuel mix properties including waste and raw material burnability (e.g. special cement or white cement clinker) can influence the ability to be within the range. Levels below 350 mg/Nm3 are achieved at kilns with favourable conditions when using SNCR. In 2008, the lower value of 200 mg/Nm3 has been reported as a monthly average for three plants (easy burning mix used) using SNCR. | ||
| c Depending on initial levels and NH3 slip. | ||
| Kiln type | Unit | BAT-AEL(daily average value) |
|---|---|---|
| Preheater kilns | mg/Nm3 | < 200 – 450a b |
| Lepol and long rotary kilns | mg/Nm3 | 400 – 800c |
| 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 |
SNCR is generally 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 19.
See Table 3.
BAT-associated emission levels for NH3 slip in the flue-gases when SNCR is applied
| a The ammonia slip depends on the initial NOx level and on the NOx abatement efficiency. For Lepol and long rotary kilns, the level may be even higher. | ||
| Parameter | Unit | BAT-AEL(daily average value) |
|---|---|---|
| NH3 slip | mg/Nm3 | < 30 – 50a |
| a A description of the techniques is provided in Section 1.5.3 | ||
| Techniquea | 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 |
Depending on the raw materials and the fuel quality, levels of SOx emissions can be kept low not requiring the use of an abatement technique.
If necessary, primary techniques and/or abatement techniques such as absorbent addition or wet scrubber can be used to reduce SOx emissions.
Wet scrubbers have already been operated in plants with initial unabated SOx levels higher than 800 – 1 000 mg/Nm3.
See Table 4.
BAT-associated emission levels for SOx from the flue-gases of kiln firing and/or preheating/precalcining processes in the cement industry
| a The range takes into account the sulphur content in the raw materials. | ||
| b For white cement and special cement clinker production, the ability of clinker to retain fuel sulphur might be significantly lower leading to higher SOX emissions. | ||
| Parameter | Unit | BAT-AELa b(daily average value) |
|---|---|---|
| SOx expressed as SO2 | mg/Nm3 | < 50 – 400 |
The technique consists of optimising the raw milling process so that the raw mill can be operated to act as SO2 abatement for the kiln. This can be achieved by adjusting factors such as:
raw material moisture
mill temperature
retention time in the mill
fineness of the ground material.
Applicable if the dry milling process is used in compound mode.
| 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 |
For safety reasons, due to the risk of explosions, ESPs will have to shut down during elevated CO levels in the flue-gases. The following techniques prevent CO trips and, therefore, reduce ESP shutdown times:
control of the combustion process
control of the organic load of raw materials
control of the quality of the fuels and fuel feeding system.
Disruptions predominantly happen during the start-up operation phase. For safe operation, the gas analysers for ESP protection have to be on-line during all operational phases and the ESP downtime can be reduced by using a backup monitoring system maintained in operation.
The continuous CO monitoring system needs to be optimised for reaction time and should be located close to the CO source, e.g. at a preheater tower outlet, or at a kiln inlet in the case of a wet kiln application.
When hybrid filters are used, the grounding of the bag support cage with the cell plate is recommended.
| 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 |
The BAT-AEL for the emissions of HCl is <10 mg/Nm3, as the daily average value or average over the sampling period (spot measurements, for at least half an hour).
| 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 |
The BAT-AEL for the emissions of HF is <1 mg/Nm3, as the daily average value or average over the sampling period (spot measurements, for at least half an hour).
| 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 |
The BAT-AEL for the emissions of PCDD/F from the flue-gases of the kiln firing processes is <0,05 – 0,1 ng PCDD/F I-TEQ/Nm3, as the average over the sampling period (6 – 8 hours).
| 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 |
See Table 5.
BAT-associated emission levels for metals from the flue-gases of kiln firing processes
| a Low levels have been reported based on the quality of the raw materials and the fuels. | ||
| b Low levels have been reported based on the quality of the raw materials and the fuels. Values higher than 0,03 mg/Nm3 have to be further investigated. Values close to 0,05 mg/Nm3 require consideration of additional techniques (e.g. lowering of the flue-gas temperature, activated carbon). | ||
| Metals | Unit | BAT-AEL(average over the sampling period (spot measurements, for at least half an hour)) |
|---|---|---|
| Hg | mg/Nm3 | < 0,05b |
| Σ (Cd, Tl) | mg/Nm3 | < 0,05a |
| Σ (As, Sb, Pb, Cr, Co, Cu, Mn, Ni, V) | mg/Nm3 | < 0,5a |
| 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 |
Collected dust can be recycled back into the production processes whenever practicable. This recycling may take place directly into the kiln or kiln feed (the alkali metal content being the limiting factor) or by blending with finished cement products. A quality assurance procedure might be required when the collected dusts are recycled back into the production processes. Alternative uses may be found for material that cannot be recycled (e.g. additive for flue-gas desulphurisation in combustion plants).