1. What is the difference between co-processing and incineration of waste material?
Co-processing means the substitution of primary fuel and raw material by waste materials in industrial processes. Incineration is primarily a disposal technology to reduce waste volumes, to reduce the potential negative impact of the waste material and to a certain extent recover energy.
2. Can co-processing only be applied in the cement industry?
Co-processing can also be applied in other industrial processes such as lime or steel production and power stations or any other large combustion plants.
3. How does the cement industry protect residents and employees from potential risks associated with co-processing?
On the basis of an occupational health & safety system all required preventive measures such as operational control and monitoring will be taken to minimize the potential risk for the employees and the residents.
4. Does co-processing adversely affect a cement plant’s atmospheric emissions?
The use of AFR doesn’t affect negatively the quality of the emissions of a cement kiln stack if some basic rules are observed such as selection of correct feed points and control/limitation of the input of volatile metals. This applies for non-hazardous as well as for hazardous waste.
5. Is there a link between co-processing and the reduction of green house relevant CO2 emissions?
Co-processing can reduce the green house relevant CO2 emissions, if the waste material being used would instead have been burned without energy recovery or being disposed in an uncontrolled manner.
6. Which waste material is not suitable for co-processing?
Electronic waste, entire batteries, infectious & biol. active medical waste, mineral acids, corrosives, explosives, asbestos, radioactive waste, unsorted municipal waste are not suitable for co-processing. Reasons for excluding them are the risk of excessive emissions, health and safety provisions, negative impact on kiln operation, or the observation of the general waste hierarchy principles
7. Which measures at a cement plant can provide confidence of its daily operation to the neighborhood community?
With the control of the waste input, continuous monitoring of the most important emission parameters, adequate operational controls and a regular and transparent reporting to the authorities the basis for trust to the neighborhood communities can be build-up. Information of the emission and quality of waste input should also be made available to the community in the framework of a comprehensive stakeholder engagement program.
8. Which waste materials are most suitable for co-processing?
There is a wide range of waste material suitable for co-processing, ranging from animal fat to sludge’s from water treatment plants. However, the most common solid wastes are papers, cartons, plastics, textiles, packaging material, tires, and wood. There are liquid waste byproducts such as used oil, solvents, or paint sludge’s as end-of-line products from the transport sector or derivates from industrial activities. Obsolete pesticides and other organic waste material can also be co-processed in cement plants.
9. Why is pre-processing required for certain waste material?
Some types of waste cannot be used directly as AFR, but must undergo a preparation process. This step delivers a product that complies with the technical specifications of cement production and guarantees that environmental standards are met.
10. Does co-processing of waste material generate dioxins and furans?
Independent of the use of alternative fuels any chlorine introduced to the kiln system in the presence of organic material may cause the formation of small quantities of dioxins and furans in combustion processes. Due to the long residence time, the high temperatures in the kiln and the rapid cooling of the exhaust gas dioxins and furans emissions are generally very low during steady kiln conditions. In Europe, cement production is not a significant source of dioxins and furans emissions. Cement kilns typically can easily comply with an emission limit of 0.1 ng TEQ/Nm3.
11. Can POP’s be disposed in cement kilns?
The main concern for co-processing hazardous waste containing POP’s is the formation of dioxins and furans. Due to the long residence time and the high temperatures in the cement kiln all organic compounds will be destroyed. Feeding the waste to the main burner (or to the preheater / precalciner) and good process control are prerequisites for the POP destruction. Rapid cooling of the exhaust gas together with the low temperature in the gas cleaning device avoids the novo synthesis of dioxins and furans.
12. Are test burns needed for any kind of waste material to be co-processed?
Test burns with non-hazardous AFR are not a regulatory requirement but are sometimes done to evaluate the behavior of the process, the influence on main atmospheric emissions and the cement clinker quality when feeding AFR to the kiln. Test burns with hazardous compounds require however professional supervision and independent verification. The Stockholm and the Basel Convention will require a destruction efficiency test for kilns aiming to treat POPs or POPs containing waste.
13. How can it be avoided that clinker becomes a sink for heavy metals?
Extensive investigations have shown that the effect of AFR on the heavy metal content of clinker is marginal on a statistical basis. The one exception is the widespread use of tires which will raise zinc levels. With the careful input control and the limitation of the heavy metal content in the waste used for AFR, an accumulation of these pollutants in the clinker can be avoided.
14. Why has the waste generator to pay for the disposal of his waste in the cement kiln although waste is a resource for the cement industry?
The polluter-pays-principle must be the basis for the economical and financial analysis of co-processing. This means that those who are producing waste (e.g. industry) or are responsible for its handling (e.g. municipality) have to take care for its best environmental sound management. Co-processing means additional investments and costs for the cement industries and is only attractive if the production costs can be reduced compared to traditional fuels and raw materials.
15. What are the adequate limit values of emissions in development countries or countries in transition compared to industrialized countries?
Each country must define the pollutants and adequate limit values for industrial emissions taking into consideration the overall economic and industrial development but as well environmental targets. The European Waste Incineration Directive (2000/76/EC) could be taken as a reference in the discussion of the definition of the limit values. There should be comparable environmental standards between industrialized and developing countries.
16. How must waste material be handled during pre-processing if it contains VOC?
Wastes containing volatile organic components must be stored and handled in a way to allow suppression or containment of these components (such as closed tanks or containers, proper air ventilation etc.). Common reduction techniques for captured VOC emissions include nitrogen traps, biological treatment, activated carbon and thermal treatment.
17. How can NOx emissions be reduced?
Primary operational measures such as low-NOx burner and calciners or water injection can reduce NOx emissions to a limited extent. Best available technology to reduce NOx emissions are selective non-catalytic reduction (SNCR) with ammonia or urea injection in an appropriate temperature window. Using this technology NOx emissions below 800 mg/Nm3 with existing suspension preheater / precalciner kilns, and even less than 500 mg/Nm3 with new SP/PC kilns are achievable.
18. What happens to the dust from the de-dusting equipment?
Dust collected in the gas cleaning devices can be partially or totally recycled to the manufacturing process (to the kiln or to the cement mill). If local standards or technical specifications do not allow recycling, other solutions such as the use of the dust for soil or waste stabilization or for agricultural purposes must be evaluated. If landfilling is needed, the landfill design must correspond to latest state-of-the-art technology.
19. Is there a perspective for co-processing of municipal waste unsorted/specific components/the rest after elaborate sorting of the waste?
Unsorted municipal waste should not be used for co-processing as it is too heterogeneous. The combustible part of municipal waste after a separation process can be used as alternative fuel in co-processing if the content of pollutants is below the limit values.
20. Does co-processing attract waste from other regions or stimulate transboundary waste shipment?
The Basel Convention bans transboundary shipment of hazardous-waste from the OECD to non-OECD countries for final disposal. The transboundary shipment of hazardous waste among non-OECD member countries, from non-OECD to OECD member countries and among OECD countries is allowed but certain rules must be followed. To be in line with the key objectives of the Basel Convention transboundary shipment of hazardous waste for co-processing shall be consistent with their environmental sound management and the disposal should be as close as possible to their source of generation.
21. Is there a risk that countries permitting co-processing will become a playground for dumping all kind of waste?
The background of the permitting process is avoiding environmental, operational and OH&S risks from co-processing. But it requires capacity building and open communication within the involved authorities, the cement plant operators and the other involved parties. Generic permits shall only be issued for homogeneous waste including waste coming from pre-processing facilities, for example solid substitute fuels (impregnated sawdust, refuse derived fuels, fluff) or liquid substitute fuels. Other waste requires individual permits.
22. Can co-processing replace land filling as waste disposal alternative and if yes, should authorities prohibit sanitary landfill at all?
Co-processing is only one element in a country’s waste management scheme. In the general waste hierarchy, energy or material recovery are preferred options compared to landfilling. However, not all waste material is suitable for co-processing. For those waste material conventional disposal options such as landfilling might be an alternative.
23. What’s the impact from heavy metal when feeding it to kilns? Is the degree of HM leaching from cement products still acceptable?
The behavior of heavy metals in the cement kiln system is well understood. While some volatile or semi-volatile metals such as mercury, thallium or cadmium are mainly adsorbed to the dust in the gas cleaning devices, most of the metals will be incorporated in the mineral structure of the clinker. Scientific studies have demonstrated that release of metals from hardened concrete structures is well below applicable limit values such as drinking water standards. The input of more “leachable” metals such as chromium must be controlled and limited.
24. Can hazardous waste co-processing be applied in all cement plants (in term of kiln size and cement production technology)
Co-Processing requires a certain standard of technology. Most common are modern dry preheater / precalciner kiln but also wet kiln are suitable for co-processing. Adequate feed point selection and operational controls are prerequisites for co-processing. For example, alternative fuels containing stable toxic components should preferably be fed to the main burner to ensure complete combustion due to the high temperature and the long retention time. Old shaft kilns are not well suited for co-processing.
25. Are the environmental impacts from landfills (leaching, gases) not easier to control in comparison to the more complex technology of co-processing?
Various life cycle analyses demonstrate that co-processing has less negative environmental impacts than landfill. Co-processing doesn’t release any toxic substances to water and soil. The substitution with AFR avoids the negative environmental impact of mining fossil fuels and conserves natural resources. No additional emissions compared to traditional cement production will be created.