Combustion Characteristic Research Of Drying Lignite Mixed With Biomass Under Oxy-fuel Atmosphere

In this paper, the mixed combustion characteristics of upgradedHulunbeier lignite and biomass (cotton stalk) in air and in oxy-fuel (CO2/O2=75%/25%) atmosphere was carried out by two methods: experiments and simulations, andit focused on the combustion characteristics comparison of the two kinds ofatmosphere. The upgraded lignite was dried by air and steam in fluid-bed, the dryingtemperatures of110℃,135℃,160℃. Experimental methods used were FTIRanalysis and thermal gravimetric analysis. Based on a1.2MWt laboratory furnace,using Fluent software simulate the mixed combustion of different proportions ligniteand cotton stalks in the two atmosphere.Fourier infrared analysis experiment of dried lignite of different medium atdifferent drying temperature was carried out, the result showed: the organic structureof dried Hulunbeier lignite changed. When air as the drying medium, theoxygen-containing functional groups of lignite decreased when the temperature was110℃,but when the temperature is higher than135℃， the content ofoxygen-containing functional groups increased, lignite was oxidized and the organicstructure changed. When steam as the drying medium, the aromatic of ligniteincreased with temperature increased, the oxygen-containing functional group contentdecreased, water retention capacity and lignite spontaneous combustion tendencydecreased, lignite organic structure change was smaller.Cotton pyrolysis mainly occurred in275-500℃, the activation energy was55.8kJ/mol. Through the analysis of pyrolysis parameters and kinetic parameters foundthat the activity of raw coal was the best and air-dried lignite was the worst. Theactivation energy of steam-dried lignite and its re-absorption lignite were both lowerthan air-dried lignite and this proved the application of steam-dried lignite enhanced.Pyrolysis experiment results and the Fourier infrared analysis results are the same.The experimental results of mixed fuel combustion showed that with theincreasing of biomass mixture ratio, the comprehensive combustion characteristic,flammability and burnout characteristic were better in both air and oxy-fuelatmosphere, which showed that the join of biomass could improve the combustioncharacteristic of dried lignite. The combustion activation energy of mixed fuel burnedin air decreased with the increasing amount of biomass. With the increased amount ofbiomass in CO2/O2atmosphere, the activation energy of high-temperature period andthe average activation energy decreases, but the low-temperature period activationenergy increased. Because of the higher oxygen content in CO2/O2atmosphere thanthat of air, the ignition temperature and the corresponding temperature of maximumcombustion rate advanced. Burnout temperature lowered when the amount of biomassblended was less, while the amount of biomass blending high rose, and burnout rate offuel is reduced. Its flammability index and comprehensive combustion characteristics index tended to increase compared to the air, indicated that oxy-fuel atmosphere couldpromote mixed fuel ignition, and the combustion characteristics was good but theburnout characteristic was bad.Simulation results showed that the temperature of lignite burned in oxy-fuel wasa little worse than in air, and the peak temperature appeared slightly delay than that ofair and the flame length is short, but the overall level of radiation force was betterthan in air. In the oxy-fuel atmosphere lignite mixed with biomass5:5, the peak andoutlet temperature was higher than that in the air, and the average radiation force wasbetter than air. In the oxy-fuel atmosphere, with the increase of biomass mixingproportion, the cross-sectional average temperature of mixed fuel combustiondecreased, and the average radiation force decreased, and the CO2concentrationreduced, while the moisture concentration increased.