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Show - m g per m 3 - k9N0x per tonne of clinker, or cement product Each kiln has a characteristic exhaust gas flow rate to allow conversion to a mass based criterion; older kilns - 2900-3700 m3/tonne, preheater/precalciners - 2200-2500 m3/tonne). NOx EMISSION CONTROL TECHNOLOGIES Several methods of NOx reduction were assessed, although only some of these have been proven commercially. These include both combustion technologies which reduce or prevent emissions at their point of generation, and post-combustion methods which reduce emissions already generated. Combustion and Operational Modifications Process optimization through combustion modifications (COM) was one of the first options to considered for reducing emissions. Improvements to be considered include; improved process control and automation systems, reduced excess air and firing temperature, improved raw mix design, and optimized clinker cooling and air preheat, and most other modifications which improve thermal efficiency. These low cost options should be maximized, but must be evaluated against degradation of clinker quality, and possible increases in other emissions. Low-NO, burners This is one of the main areas of interest in environmental performance of cement kilns. The use of Low-NOx burners is being studied internationally by research organizations and cement companies. Although the concepts of a staged burning zone with exit gas recirculation are commonly used for LNBs in power boilers, the higher temperatures required in kiln pyroprocessing make these methods more difficult to apply for an acceptable quality of clinker. Four types of Low-NOx burners (3 coal, 1 gas) were described in the Radian study, with a wide variety of results (5-30% N O x reduction) on installed systems, depending upon; - the initial baseline NOx emission - whether excess air could be kept to design low values, to maintain efficiency - length of testing time, and resulting clinker quality - emissions of other pollutants Figure 7 LNB: Pi Hard R O T A F L A M * low N O , burner for pulverized coal liquid and gas fuels. (Source: Ref. $) 15 |