| As the greenhouse effect becoming more and more serious,the reduction of CO2 emission is promoted for the environmental necessity.Our research group proposed an Oxy-coal combustion steam system of near-zero emissions（OCCSS）based on the clean energy system（CES）technology,which is expected to achieve efficient use of coal without pollutants emissions during power generation process.The combustion of OCCSS has characteristics of high temperature,high pressure,high-oxygen and high water vapor concentration,and there is no research conducted under this combustion atmosphere.The purpose of this paper is to use numerical simulation to research the flame speed of syngas under this “Four High” combustion atmosphere.According to optically thin radiation model,we modified the energy equation of PREMIX code in CHEMKIN Ⅱ package,and the PLANK average gas absorption coefficient was fitted according to Grosshandler.The numerical results simulated by the radiation model we modified,the radiation model modified by FAN rong and adiabatic model respectively were compared with Natarajan J’s experimental data.The result shows that the radiation model we modified has the best agreement with the experimental data.With our modified PREMIX code,we compared the numerical simulation results by the GRI 3.0 mechanism,San Diego mechanism,Davis and Li mechanism with the experimental data measured by Purdue University when they explored the flame speed of syngas diluted by water vapor under high temperature.It shows that the Davis mechanism has a better agreement with the measurements than the others.The combustion and radiation intensity with oxygen are greater than that with air.Because of the easier reacting of OH + H2 = H + H2 O than the reacting of R28:CO + OH = CO2 + H and R29: CO + OH = CO2 + H,H2 combusts totally prior to CO.Both the increasing of pressure and water vapor concentration will raise the radiation heat loss,resulting in reducing the flame temperature.When the H2 content of syngas is less than 5%,adding water vapor will make the flame speed increase first and then decrease.For the syngas with H2 content more than 10%,adding water vapor.will make the flame speed decrease monotonically.The increasing of H2 concentration will raise the flame speed of syngas,and it is the result of the competition between reaction R1 H + O2 = O + OH which produces OH and reaction R28 CO + OH = CO2 + H which consumes OH.The intensity of R1 is great when the content of H2 is high in syngas,while the intensity of R28 is weak.This is the reason why H2 can promote the flame speed of syngas. |
