Application of Pre- and Co-Processing in Cement Production

Transcription

1 A GIZ-Holcim Public Private Partnership managed by FHNW Version v3.1 Contact Date Introduction Alternative raw materials and fuels are waste-derived mineral and organic (combustible) materials which can, to the advantage of all stakeholders, be used in the cement production process to substitute natural raw materials and fuels. Thus, their use contributes to resource conservation, waste management and reduction, as well as to improved societal and environmental outcomes. For optimal use in cement kilns (co-processing with "zero additional emissions"), alternative fuels and raw materials often require preparatory processes (preprocessing), and need to be fed into the kiln via appropriate feed points and in adequate proportions. Also, to optimize pre- and co-processing and to prove that cement kilns are not abused for the elimination of special wastes or overloaded with "conventional" alternative materials, AFR quality and cement kiln emission control systems need to be implemented. provides an introduction to these issues. Learning Targets Public sector stakeholders have a basic knowledge of pre- and co-processing waste-derived combustible and mineral materials in the cement industry. In particular, they understand and are able to discuss why well-managed AFR (alternative fuels (AF) and alternative raw materials (AR) together = AFR)) utilization is advantageous to all stakeholders, does not increase cement plant emissions and warrants regulatory attention to its source materials, products and emissions.

2 Content List of contents slide 3 Alternative fuels (AF) and raw materials (AR) Pre-processing of AF Co-processing of AF Pre- and co-processing of AFR Environmental aspects of pre-processing Environmental aspects of co-processing, AFR in cement kilns 1 Five main types of waste used as AF (and the ash as AR) slide 4 Alternative fuels are normally classed first as non-hazardous or hazardous, with each group subdivided into five types (from liquids to lumps) each. The ten characteristics are essential for the selection of appropriate feed points to the kiln system and the achievable substitution rates. Gaseous wastes exist but are rarely used in the cement industry. 2 Another practical approach to alternative fuel classification slides 5, 6 From a business point of view it makes sense to distinguish AFRs derived from (normally) uncritical materials from those produced from potentially or clearly critical materials, since the latter demand considerably more efforts in terms of pre-processing, OHS, analysis and control. 3 Materials not to be used in a cement kiln slide 7 Holcim maintains this list of materials not accepted as AFRs in their kilns. Besides the hard facts there are also soft factors, including business promotion and product protection) backing up this list. 4 AFR utilization in the Holcim Group slides 14, 15 Slides 14 and 15 give an impression of the development of the Holcim AFR sector. Competitors generally operate using lower average AFR levels but exhibit similar development patterns. In general, an average substitution level of 50% is achievable. A GIZ-Holcim Public Private Partnership managed by FHNW v3.1, of 6

3 There is obviously considerable unrealised development potential in an industry that requires limited additional investment to deliver substantial returns. 5 What does hazardous mean? slides 19, 20 It is very important to understand that the term "hazardous" refers to properties of the waste prior to co-processing. After, although the combustion gases include components that require special care (e.g., NOx, CO2, etc.), no hazardous qualities remain in the final product. 6 Select the correct fuel feed points slide 21 As displayed in slide 21, a modern kiln system has three AF feed points. Historic kiln systems still in use in some areas may including a long kiln (L = 30 to 40 diameters), and are sometimes equipped with mid-kiln feed points to allow coarse or lump fuel feed (which cannot travel through long kilns chain systems). 7 Do not overload the feed points slide 22 For reasons relating mainly to process technology, depending on the AF type and the feed point, upper limits apply to AF substitution rates. Locally applicable limits have to be determined by trial and error. 8 Dealing with alternative raw materials slide 25 Alternative raw materials are often hydrocarbon contaminated soils or mineral matter. Simply added these to the normal raw materials would produce organic emissions in the preheater due to roasting-off. Such materials therefore often need thermal pretreatment (drying and roasting off of volatile organics in separate equipment) prior to their use as raw materials. 9 Environmental aspects of pre-processing slide 26 Pre-processing plants also have environmental impacts. The most important are odour emissions and leakage/water management. It therefore makes sense to implement such plants some distance from residential areas. A GIZ-Holcim Public Private Partnership managed by FHNW v3.1, of 6

4 10 Main statement about environmental aspects of co-processing slides 27 to 33 (These slides are self explanatory: no additional comments are necessary.) 11 Consequences of non-compliance with rules/regulations slide 34 Besides the cited effects of basic rule violations (e.g., environmental, OHS degradation) misuse of the kiln system can damage its operational capacity and stability, with further effects regarding maintenance and kiln availability. These risks act as strong arguments for cement plant operators to adhere closely to regulations. FAQ Q: There are five main families of alternative fuels. What about gaseous alternative fuels? Gaseous alternative fuels do exist, but unfortunately usually in quantities too small to justify their use in cement production. The best known is landfill gas from engineered landfills. However, this gas is generally used as fuel for electrical generators. Q: The alternative fuel utilization rate in the Holcim Group appears to plateau between 10 and 15%. Individual companies, however, reach 50% and individual plants even 100%. Can you explain these differences? The low-hanging fruits have long been harvested: the easiest alternative fuels to use have all been spoken for. In addition, a new group of countries (e.g., India and China) with no alternative fuel records presently dilute the Holcim figures. AFR business development is increasingly complex and time consuming: developing countries often place a relatively low priority on environmental protection and waste management, as they often either are unaware of the importance of waste management, or simply lack the means to pay for it. Another problem is long transport distances and related costs. Substitution rates of 50% or higher are normally possible in any cement plant with an adequate alternative fuel mix and appropriate pre-processing levels. Full (100%) AF use is possible if the fuel mix includes approximately 50% liquid alternative fuels. Q: What is the difference between pre- and co-processing? Pre-processing includes all process steps required to produce waste-derived alternative fuels or raw materials for reliable use in the co-processing stage (cement kiln). Reliability includes constant mass and energy flow. These can be assured by crushing/grinding, drying, homogenizing and adequate design of storage and extraction equipment. Co-processing involves the use of pre-processed alternative fuel as a component in A GIZ-Holcim Public Private Partnership managed by FHNW v3.1, of 6

5 FAQ the fuel mix of the respective industrial process. It also includes the use of special kiln feed equipment, which is essential for efficient co-processing. Q: Do you really believe in the "zero additional emissions" statement? Please detail! Mercury and chlorine emissions may increase if the total input is increased. Sulphur emissions may increase or decrease depending on the amount of volatile sulphur contained in the raw materials. CO emissions (often not regulated in the cement industry) and sometimes VOCs may increase if fuel feed points are overloaded. NOx emissions may actually decrease if alternative fuels (fed to the main firing) carry moisture and mineral matter or need higher excess air factors, all of which have a flame cooling effect. There are other, mostly minor effects. The net environmental benefits of reduced NOX and CO2 emissions, as well as of improved waste management, far outweigh the few possible negative effects. Q: Is there also a potential for emission reduction? Details? Yes (see question above). This holds particularly true if the total system is considered. For example, how would co-processing emissions to air, water and soil compare to those that would result from other available processes, e.g., digestion or open fires in unsecured landfills or back yards. Q: How can we recognize / prevent wrong feed point selection and feed point overload? This is comparatively simple to accomplish if the feed technicians know how to react to increased CO and VOC numbers from the continuous emission monitoring equipment. Countermeasures can include the use of finer fuel, improved dosing, input reduction or correction of excess air factors. Q: There was an instruction about quality assurance of alternative fuels. What about quality assurance of products of the industry? Cement plants are mass producers of a comparatively cheap product. Producing out-of-specs materials is out of question. Cement plants therefore need and do have elaborate quality assurance systems. These are normally sufficient to also deal with effects from alternative fuels. Q: Why are some people against waste incineration in general and against co-processing in particular? A: Most wastes are simply raw materials in problematic places and forms. Ideally, these should be reused as raw materials (see "waste hierarchy"). Therefore, some people accept incineration only as a last link in the waste management chain, A GIZ-Holcim Public Private Partnership managed by FHNW v3.1, of 6

6 FAQ demanding higher-priority implementation of the upstream links. They perceive coincineration as a door opener to direct incineration, which bypasses the desired waste hierarchy. Q: Bypass systems have been mentioned. What exactly are they? Bypass systems are used to partially bypass process stages, thus preventing the enrichment (by extraction) of undesired compounds/elements. Some cement kiln systems include preheater bypass systems to limit the enrichment of (mainly) chlorines in the kiln system. Cement kiln systems should also include a DOM (direct operation mode) dust bypass to limit enrichments of some compounds in the external dust circuit. In both types of bypass system the extracted materials are fed back into the system i.e., into the cement mill for incorporation into the final product. Q: Transportation and pre-processing (handling) of hazardous materials can be critical. What improvements are possible in this sector? Collection and transportation should only be contracted to efficient, well-established, professionally oriented companies with clean vehicle fleets. Pre-processing of hazardous materials needs to strictly follow the rules of a wellestablished and monitored OHS system. Both systems should be subject to regular internal and external audits. References & further information Holcim Course on Cement Manufacturing Holcim Course on Environment Holcim-GIZ Guideline on Co-Processing Waste Materials in Articles in business sector publications A GIZ-Holcim Public Private Partnership managed by FHNW v3.1, of 6