| China is one of the largest agricultural countries in the world. Approximately,0.71 billion tons of various crop residues are generated annually.50%-60% crop residues are not used, which are ussally burnt in open field, leading to serious air pollution and fire disaster, Crop stalks can be used to make densified biomass briquetting fuel (DBBF), which is one of effective ways to use crop stalks and widely used in rural areas in China. However, DBBF is facing a bottle-neck problem with igniting. DBBF is a kind of densified biomass with high density (0.8-1.4g/cm3), which is very difficult to be ignited. Farmers normally need to take 20 to 30 minutes for successfully igniting cooking stoves. In addition, long-time ignition causes thick smoke and harmful gases emission, posing serious environmental pollution and threat to people's health. And it seriously affected the further promotion of DBBF. Therefore, it is imperitive to develop efficiency, affordable, and environmentally friendly ignition-assisting agents. Densified corn stover briquetting fuel(DCBF) was used as the experimental material for type LLA-6 household cooking stove. The research was conducted to:develop ignition-assisting agents, study on ignition characteristics, DCBF combustion characteristics and numerical simulation.1. Development of ignition-assisting agents and study on igniting and emission characteristics.25 kinds of ignition-assisting agents were developed by mixing waste engine, waste diesel oil, and industrial alcohol at different volume ratios. ED15 and DA51 achieved better igniting results. ED 15 with 9mL dosage and DA51 with 8mL dosage took 40 and 53 seconds to successfully ignite the DCBF, which were 30-40 times shorter than those without using ignition-assisting agent. ED 15 and DA51 showed similar emission and combustion characteristics in terms of O2, CO, CO2, NOx, and SO2 emissions, and fume gases temperature and combustion efficiency. The average concentrations of CO, CO2, NOx, and SO2 for ED 15 and DA51 at all dosages met the requirements by Beijing local standard. Compared to other agent and other dosages, ED15 at the dosage of 9mL achieved similar combustion efficiency but emitted less pollutants, therefore, is recommended for practical application.2. Experimental study on analyses on the combustion characteristics of DCBF. The thermal performance, temperature, and combustion weight loss were measured and analyszed. The results showed that thermal efficiency of type LLA-6 stove was only 20% and could not reach to Beijing local standard(thermal efficiency≥35%). The reaction mechanism of combustion of DCBF was obtained by the "volatile mix rate scanning method". The results showed that the reaction mechanism belonged to three-dimensional,3D, sphericity symmetry, D4 Deceleratory a-t curves in the rapid heating stage and the cooling stage during the combustion of DCBF process. The mechanisms function expression of integral form was ; The reaction mechanism belonged to chemical reaction, F2, Deceleratory a-t curves in the rapid heating inflection point and constant temperature stage. The mechanisms function expression of integral form was . Combustion results without wind condition was obviously better than that of with wind condition through temperature monitoring of different positions in the stove. Pollution emission concentrations met the requirement of Beijing local standard "General Technical Requirements of Household Biomass Stoves" (DB11/T 540-2008) through monitoring various pollutants. Pollutants emission of DCBF with wind was slightly higher than that of no wind. Therefore, combustion results was optimal in no wind conditions with a dosage of 9 mL.3. Numerical simulation on DCBF combustion characteristic. Model Fluent, Turbulent, and Finite-Rate were used to simulate DCBF combustion characteristics. The numerical simulation results showed that CO2 concentrations in stove, stove mouth and exhaust pipe were 18.4%,9% and 15%, respectively. No any chemical reaction was found in the combustion device, meaning that the combustion device did not play any role in ignition assisting. (2) Closed vent of combustion-assisting device was favourable to be the improving on combustion. The temperature was 990-1020K in combustion-assisting device and 1020K at stove mouth. The temperatures of stove mouth without secondary inlet were 19.86%,29.86%,37.67%,39.59% and 39.73% higher than those with inlet at stove, respectively, when ventilation holes was closed 0 row,1 row,2 rows,3 rows and 4 rows. The type LLA-6 stove achieved the best combustion results without combustion-assisting device. The heat loss from the combustion device (q2) and the second inlet(q3) were 19.21%. The thermal efficiency could be increasing from 20% to 39.21% if the combustion-assisting device was taken away and the second inlet was closed.Therefore, it is recommended to use ignition-assisting agent ED15 with a dosage of 9 mL for the ignition of DCBF. The thermal efficiency could reach to 39.21% at no wind and no combustion-assisting device.
|
PDF Full Text Request