| Nitrogen Oxides(NOx) is one of the major air pollutants, which causes severe hazard to both people's health and the environment. The current status of NOx emissions in China is so grim that reducing NOx emissions from coal-fired boilers has become an essential. Reburning is one of the most promising methods to reduce NOx emissions for its economy and efficiency. Using biomass as reburning fuel can not only reduce the use of coal, but can also reduce NOx emissions efficiently. It is of great significance for solving the energy crisis and environmental pollution problems in China.In order to fully understand the process of NOx reduction by biomass under reburning conditions, three kinds of biomasses cotton straw, rice straw and biosludge were selected as the reseaching objects. Systematic studies were carried out in a fixed bed reactor. Firstly, experimental studies on NO reduction process by the biomasses and their chars were carried out. The influences of biomass type, reburning zone O2 concentration, temperature and intial NO concentration on NO reduction were investigated. The results showed that obvious NO reduction could be achieved by the biomasses. NO reduction efficiency of cotton straw was the most efficient, rice straw was medium, biosludge was the lowest. Decreasing O2 concentration and increasing temperature in the reburning zone, NO reduction efficiency increased. When using biomass chars as rebuning fuels, cotton straw char showed the best NO reduction ability, rice straw char was medium, biosludge char performanced relatively bad. NO reduction efficiency of biomass chars increased when certain low concentration of O2 existed in the reburnig zone and the reburning temperature increased. The contribution of heterogeneous reaction was small in NO reduction by cotton straw and rice straw, while it played a major role in NO reduction by biosludge.Subsequently, experimental studies on NO reduction process by gases from biomass pyrolysis were also carried out in the fixed bed reactor. The influences of reburning conditions on NO reduction were investigated. Meanwhile, numerical simulation utilizing a kinetic modeling software for the reburning process was carried out, too. The results showed that the O2 concentration in the reburning zone was an important variable that affected NO reduction, there was an optimal O2 concentration for the highest NO reduction efficiency. When the reburning temperature increasesd in a certain rage, the NO reduction efficiency increased significantly. The modeling results revealed that CH4, CO and H2 in biomass pyrolysis gas have contributed to the reduction of NO, among which CH4 played an major role. |
