Emission characteristics of a lean-premixed ammoniaatural-gas gas-turbine combustor and effect of secondary ammonia injection

摘要

To develop an NH_(3)atural gas-fired gas-turbine combustor with minimal modifications to a natural gas-fired combustor, the effect of co-firing NH_(3) with natural gas on emission characteristics and combustion efficiency is investigated experimentally under atmospheric pressure. In this experiment, a lean premixed combustor that has basically the same structure and same size as those of an actual 2 MW-class gas-turbine combustor is used and the effects of equivalence ratio, NH_(3) mixing ratio, and NH_(3) injection method were evaluated. The results of NH_(3)atural gas/air premixed combustion show that NO emission shows a local maximum at a certain NH_(3) mixing ratio, when equivalence ratio is fixed. The NH_(3) mixing ratio where this maximal NO emission occurs shifts to higher ratios, when equivalence ratio is increased towards stoichiometric condition. At the same time, the maximal NO emission increases. The variation of NO_(x) concentration can be explained by the change in the selective non-catalytic reduction (SNCR) effect, which depends on temperature and NH_(3) concentration in the flame. In particular, the influence of NH_(3) concentration on the SNCR effect appears to be stronger than that of temperature. On the other hand, concentrations of N_(2)O and unburnt NH_(3) increase with increasing NH_(3) mixing ratio in the very lean case, when decreasing flame temperature approaches the lean flame blow-off limit. When NH_(3) is directly injected into the lean premixed flame of natural gas, NO and N_(2)O concentrations are simultaneously reduced; this is attributed to the local increase of NH_(3) concentration and flame temperature. Finally, it is proposed to consider NO_(x) as unburnt component in the calculation of combustion efficiency. When NH_(3) is fired, the enthalpy content of NO_(x) is very high, and its influence on combustion efficiency cannot be ignored. It is also found that NH_(3) direct injection is effective in increasing combustion efficiency, achieving more than 99.6% of the combustion efficiency even if the enthalpy of NO_(x) is considered.