Experimental And Numerical Study Of The NO_x Reduction By Gas Reburning And SNCR

Coal combustion in power plant is a major source of NO_x emission, so the NO_x control of power plant has become more and more necessary. Among all of the NO_x control technologies, reburning and SNCR technology are accepted abroadly, for the characteristic of low operating cost and high NO_x reduction efficiency respectively. However these two technologies also have some weaknesses. The NO_x reduction efficiency of reburning is too low to satisfy the increasingly strict requirement of environmental protection. The high operating cost and the narrow "temperature window" have also limited the application of SNCR technology. So overcoming the weaknesses of these technologies is very important for the development of the NO_x reduction industry.In this paper, a test system with multi-function such as fuel reburning and nitrogen agent injection is built up. In the test system, the temperature of each reaction zone can be controlled separately and the reductive process of NO_x can be simulated in furnace, which provides test prerequisite condition for the study of gas reburning and SNCR technology.First, the main influencing factors of gas reburning are studied by test and numerical simulation. At the low temperature (<1100℃), the NO_x reduction efficiency of liquid gas reburning is better than that of the natural gas reburning, but when the temperature exceeds 1100℃, the natural gas reburning is better. Thus natural gas is fit for using as a reburning fuel under high temperature condition. Under reducing atmosphere, the NO_x reduction efficiency can be improved by increasing the reburning zone temperature, augmenting the reburning fuel scale and prolonging the reburning time. Reburning zone excess air coefficient (α₂) has optimal value, which is 0.8 in test.Then, the main influencing factors of SNCR process are studied by test and numerical simulation. The NO_x reduction effect of ammonia SNCR process is better than the urea SNCR process. Improving the mixing of reaction zone can shorten the reaction time, decrease optimal reaction temperature and reduce the quantity of nitrogen agent demanded in reaction.The reduction of NO_x by ammonia and urea has been investigated experimentally in the presence of various additives, such as sodium carbonate (NaCO₃), ethanol, methyl acetate and glycerol. All the additives can enlarge the width of SNCR "temperature window" where NO_x abatement occurs without compromising significantly the maximum efficiency of the process. The width of the temperature windows is 1.2-1.83 times larger.In the end, the hybrid process of gas reburning and SNCR has been investigated experimentally. 85% NO_x reduction is obtained by combining gas reburning with SNCR process, which is 10-20 more percentage points than gas reburning. The quantity of nitrogen agent demanded in the hybrid process is only 1/3 of the SNCR process, which improve the economical efficiency greatly.In this paper, gas reburning and SNCR are studied experimentally and numerically. The economy and effective NO_x control methods are gained through reaction condition optimization, additives injection and reburning and SNCR combination.