Biomass Of Low-temperature Pyrolysis Carbonization And Reburning Denitration Characteristics Experimental Study

With the excessive consumption of fossil fuels such as coal and oil, it has created a series of worldwide issues that restrict the development of the global economy, like energy source shortage, environment pollution, greenhouse effect caused by CO2emission, and so on. Combination of biomass low temperature pyrolysis carbonization and rebuming for NOX reduction can not only control NOx reduction effectively, but also reduce SO2and CO2emission in fuel combustion. Meanwhile, it also makes large-scale utilization of biomass. However, how to obtain low-cost and high efficient biomass char is one of the keys to success. Though biomass has obvious advantages compared with other renewable energy, there are some drawbacks such as widely distributed, high moisture content, perishability, low energy density, little susceptible of storing and transport, and seasonality problem of biomass yield. Therefore, it is very important to carry out experimental study of biomass low temperature pyrolysis carbonization and rebuming for NOx reduction, which has great theoretical value and application prospect.In this paper, four kinds of biomass, named mulberry twig (MT), rice straw (RS), wood chip and bamboo were selected as the tested biomass for proximate analysis, ultimate analysis, calorific value analysis, and minor elements analysis. Then, the experiments of MT and RS with TGA were carried out, and calculated pyrolysis reaction kinetics parameters by non-isothermal method (Coats-Redfem) and isothermal method. The results indicated that:1) Biomass had high moisture, high volatile content and low fixed carbon content. In addition, there was obvious difference in ash content between xylophyta and herbaceous plant. It was a low calorific value clean energy, which had low carbon content, high oxygen and hydrogen content, and low nitrogen and sulfur content compared to coal.2) The pyrolysis of biomass was a typical endothermic-exothermic-endothermic process.3) The mass loss increased with the increase in pyrolysis temperature and residence time at each section, and high pyrolysis temperature was beneficial to form the gaseous product.4) The activation energy obtained by using Coats-Redfem model was between35.17kJ·mol-1and53.13kJ·mol-1, while it was between38.49kJ·mol-1and63.52kJ·mol-1by using isothermal method. The results of them were similar.Biomass chars prepared by fixed bed, screw-type and grate type experimental facilities were tested for the analysis of micro-morphology, hydrophobicity and grindability. The distribution of low temperature pyrolysis products, mass and energy yields of solid product and energy density influenced by operating parameters were obtained. The results indicated that:1) With the pyrolysis temperature and residence time increasing, apparent volume of biomass char was shrinking down, and biomass char was more brownish in color, low moisture and volatile content, high fixed carbon and ash content, increased in carbon content, decreased in oxygen and hydrogen content and trace changes in nitrogen and sulfur content than the raw biomass.2) The surface and structure of biomass char were broken. Large structure breaks into small pieces and the surface sediments increase. The porosity and the degree of thermal degradation increased with the increasing of pyrolysis temperature. Hydrophobicity and grindability of biomass char were improved greatly.3) The mass yield of biomass char decreased’with the increasing of the pyrolysis temperature and residence time, but it was varied between the mass yield of liquid and gaseous product.4) The mass and energy yields of MT and RS chars decreased with the increasing of the pyrolysis temperature and residence time, and the energy yield was always higher than the mass yield. Meanwhile, the energy density of them increased.Mixture of wood chips char and sawdust (WC-A), rice straw (RS), mulberry twig char (MT-250/30) and bamboo char (BB-275/30) were selected as reburning fuels for experimental studies on reburning with biomass/biomass char for NOx reduction. The effects, such as types of reburning fuels, partical size, the reburning zone temperature, initial concentration of NO, residence time in reburning zone and SR2were analyzed. The mechanism of NO reduction was discussed. The results indicated that:1) WC-A behaved the best performance in NO reduction, followed by RS and BB-275/30, and MT-250/30had little effect.2) Under the standard working condition, the NO removal efficiency were63.4%and60.5%for WC-A of0～200μm and0～450μm, and a smaller particle size is beneficial to NO reduction, while the release of SO2was obvious faster.3) The NO removal efficiency increased with the increasing of the reburning zone temperature, and it had the highest efficiency at the temperature of1250℃, which was64.9%. While the temperature increased from1050℃to1150℃, the NO removal efficiency increased11%, and it only increased1.5%when the temperature increased to1250℃.4) The NO removal efficiency decreased with the decreasing of initial concentration of NO.5) The NO removal efficiency increased with the increasing of residence time in reburning zone, but beyond the resident time limit, NO removal efficiency increased slowly, and it would be comparatively uneconomical.5) The NO removal efficiency decreased with the increasing of SR2, while the NO removal efficiency of64.5%at SR2=0.7was the highest, and the SR2 of0.8～0.9was recommended.