Cement, Energy and Environment

- The waste type and composition will determine the adequate feeding point; i.e. the main burner or the secondary burner in precalciner/preheater will ensure temperature > 900 °C. No waste should be fed as part of raw mix feed if it contains organics, and no waste feed during start-up and shutdown. Handling and feed systems should be appropriate to the waste used and must ensure stable and controlled input to the kiln. The operator should assess risks from fugitive emissions; equipment failure modes and appropriate safeguards should be incorporated into the design to prevent environmental pollution , health, and safety problems. Automated monitors should be employed to alert operators in the event of a waste handling problem. A pressure transducer located in the waste piping at the entrance of the kiln should be provided to turn off the waste fuel pump automatically in the even of a sudden pressure drop due to pipe rupture or pump failure. Interlocks should be provided to stop the flow of waste automatically if either normal f:.:el or feed supply or combustion airflow is interrupted (fans stopped or reduced), or if carbon monoxide levels indicate problems with combustion efficiency. The feed point for wastes into the kiln should be selected according to the nature (and, if relevant, hazardous characteristics) of the wastes used. Gaseous, liquid, and finely pulverized alternative fuels can be fed to the kiln system via any of the feed points mentioned in the previous chapter. Coarse crushed and lump fuels can be fed to the transition chamber or to the mid-kiln valve only (with some exceptions). Hazardous wastes should be introduced in the high-temperature combustion zone of the kiln system, i.e. the main burner, the precalciner burner, the secondary firing at the preheater, or the mid-kiln (for long dry and wet kilns). The following is valid: Persistent organic pollutants and highly chlorinated organic compounds should be introduced at the main burner to ensure complete combustion due to the high combustion temperature and long retention time. Other feed points are appropriate only where test have shown high destruction and removal efficiency rates; Alternative raw materials with volatile organic components should not be introduced with other raw materials in the process , unless tests have shown that undesired emissions at the stack do not occur; such raw materials can be fed through a double or triple flap arrangement into the kiln inlet; Mineral inorganic wastes free of organic compounds can be added to the raw meal or raw slurry preparation system. Mineral wastes containing significantly quantities of organic components are introduced via the solid fuels handling system, i.e. directly to the main burner, to the secondary firing or, rarely, to the calcining zone of long wet or dry kilns; Mineral additions such as granulated blast furnace slag, fly ash from thermal power plants or industrial gypsum can be fed to the cement mill. Operations and process control Operating requirements should be developed to specify the acceptable composition of the waste feed, including acceptable variations in the physical and/or chemical properties of the waste. For each waste, the operating requirements should specify acceptable operating limits for feed rates , temperatures, retention time, oxygen etc. For start-up, shutdown , or upset conditions of the kiln, written instructions should be issued, describing conditions of use of wastes. Kiln operators should know and understand these instructions. The general principle of good operational control of the kiln system using conventional fuels and raw materials should be applied . In particular, all relevant process parameters should be measured recorded and evaluated continuously and may cover: a) Free lime: b) Oxygen concentration; c) Carbon concentration . Continuous emission measurements monoxide To monitor the process and accurately quantify the emissions, continuous emission measurements are recommended for the following parameters: a) Exhaust volume; b) Humidity; c) Temperatures; d) Particulate matter; e) 0 2 f) NO. g) so2 81