Study On The Flammability Limit Of H₂/CO Syngas At O₂/CO₂ Atmosphere

Controlling CO2 emission has become an inevitable and urgent problem in the world.Among them,O2/CO2 combustion technology and clean coal gasification technology are the most promising energy saving and emission reduction technologies at present.The former uses pure oxygen as an oxidant and the product after fuel combustion as a circulating dilution gas.Through circulating combustion,the final products are only H2O and CO2 with higher concentration.After cooling,gas-liquid separation plant can be used to achieve CO2 enrichment.The latter obtain clean industrial syngas after gasification of raw coal and treatment of impurity gas.Its main components are H2 and CO,and its clean utilization is also a hot spot of current research.The combustion characteristic of gas fuel in O2/CO2 atmosphere is not clear,this paper studies one of the parameters in the combustion characteristics of H2/CO syngas at O2/CO2 atmosphere,namely the flammability limit.And three aspects of experimental measurement,prediction calculation and numerical simulation are studied,so as to supplement the basic data of combustion characteristics of H2/CO syngas at O2/CO2 atmosphere.The specific research content is as follows:The flammability limit of H2/CO syngas,pure H2 and CO at O2/CO2 atmosphere or O2/N2 atmosphere were measured by using 5L cylindrical closed vessel.The effect of the type of diluted gas,concentration of diluted gas,concentration of O2 and ratio of H2/CO on the flammability limit of H2/CO syngas was analyzed.The results showed that the dilution gas inhibited the ignition of H2,CO and H2/CO syngas.The higher the concentration of dilution gas is,the stronger the inhibition effect is,and the inhibition effect of CO2 is stronger than N2;O2 concentration promotes the ignition of gaseous fuel,and the higher the O2 concentration is,the stronger the promotion effect is;the larger the proportion of H2 in H2/CO syngas,the larger its flammability range,and this rule is more obvious in O2/CO2 atmosphere.The prediction model of the flammability limit of H2/CO syngas,pure H2 and CO at O2/CO2 atmosphere were re-deduced by using Ma’s thermal theory and the Le Chatelier formula.The prediction model of CO is in good agreement with the experimental value;the prediction model of H2 and H2/CO syngas has a good agreement at upper flammability limit only,while the predicted value at lower flammability limit is generally smaller than the experimental value.For H2/CO syngas,the gap between the predicted value and the experimental value at lower flammability limit gradually increases with the increase of the proportion of H2.These deviations are mainly due to the assumption of adiabatic flame temperature in the thermal theory of Ma.In addition,the Le formula has certain limitations for the prediction of the lower flammability limit of H2/CO syngas at two atmospheres.When the proportion of H2 in syngas is greater than 50%,the prediction is consistent,the relative error is within 10%and the maximum error is 8.854%.When the proportion of H2 is less than 50%,the error is larger,the relative error is within 20%,and the maximum error is 17.388%.In order to further improve the prediction accuracy of the flammability limit,the numerical model of the combustion process of H2/CO syngas in the O2/CO2 atmosphere in a cylindrical closed container was established by using Fluent software.The range of the simulation value of flammability limit of H2/CO syngas is obtained by using the 7%pressure appreciation discriminant method.The results show that the H2/CO syngas’s simulation value of flammability limit changing with the dilution gas concentration were basically identical with the experimental situation;in this paper,the absorption coefficient term is calculated using the modified WSGG model to accurately simulate the effect of radiant heat loss on the flammability limit of H2/CO syngas.The results show that the existence of radiant heat loss can inhibit the combustion of H2/CO syngas,and the effect of radiant heat loss on the flammability limit of H2/CO syngas in O2/CO2 atmosphere is greater than that in O2/N2 atmosphere.