Experimental Study Of Characteristics For Semi-char Co-firing With Bituminous Coal

Semi-char can be a new type of fuel with high calorific value,but its volatile content is very low and close to anthracite,which makes it difficult to ignite and has poor combustion stability.Generally,it is rarely burned directly alone.In order to improve the ignition characteristics of semi-char and make it more widely used,it is necessary to mix flammable bituminous coal with high volatile content as auxiliary fuel,and use blended-coal technology in combustion.To this end,a thermal state experiment was conducted for shenmu semi-char co-firing with shenhua bituminous coal in a 350 k W pulverized coal-fired pilot-scale furnace to investigate the effect of primary air characteristics?primary air velocity and primary air temperature?on ignition,NO_x emission and burnout characteristics for co-combustion of bituminous coal and pyrolyzed semi-char.A thermal state experiment was conducted in a 350 k W pulverized coal-fired pil ot-scale furnace under the condition that the total thermal power of the test system,excess air coefficient,blending ratio of semi-char,primary air temperature,and othe r parameters remained unchanged as well as coal powder concentration remained un iform only to change the primary air velocity.The experimental results showed that under different primary air velocities,the axial temperature of the p rimary combustion zone all experienced a process of first increasing,then briefly decreasing,then gradually increasing,and finally becoming stable as well as the radial temperature distribution of the primary combustion zone was basically symmetrical.The overall temperature of the primary combustion zone was highest and the ignition characteristics became best for the ignition distance reducing to 188 mm when the primary air velocity was 20m/s.The ignition delay was caused if the primary air velocity was too high or too low.When the primary air velocity was 14m/s,the ignition distance was 292 mm.The ignition distance was 334 mm and the combustion became dispersed when the primary air velocity was 23m/s.The axial flue gas distribution in the primary combustion zone indicated that the O₂ distributions at the axial positions for the four groups were basically the same :they all had been rapidly decreasing and finally went down to zero.The CO 2 emission was lowest,and the CO production as NO production for the early period was highest when the primary air velocity was 20m/s.But the pre-ignition made the reduction of NO the most advanced so that the time and zone of the NO reduction became best,which made the NO emission at the exit of the primary combustio n zone got lowest to 300.41 mg·m^-3@6% O₂;The distribution of O₂ and EGA gas analysis were employed to estimate the ignition point of the blend fuel.It was found that the CO analysis method was inaccurate,and the ignition point obtained by O 2 analysis method was more advanced than that for axial temperature second-derivative method.NO analysis method achieved better results on analyzing the ignition of the blend fuel when the primary air velocity was 20m/s.The analysis believes that the cause of this result mainly depends on some factors such as the combustion conditions,the rise rate of furnace temperature,the order of gas release and so on.The burnout ratio for co-combustion of bituminous coal and pyrolyzed semi-char was highest when the primary air velocity was 20m/s,and the burnout ratio decreased if the primary air velocity became too low or too high.The experimental results of primary air temperature showed that as the primary air temperature increased,the higher the overall temperature of the primary combustion zone,the better the ignition characteristics and the smaller the ignition distance.But it had little effect on the improvement of the ignition characteristics if still increasing primary air temperature after 120?;The higher the primary air temperature,the lower the NO production,and the lower the NO emission at the exit of the primary combustion zone;When the primary air temperature was 120?,150?,and 180?,the ignition distance obtained by the NO analysis method was relatively close to that got by axial temperature second-derivative method;The burnout ratio for co-combustion of bituminous coal and pyrolyzed semi-char increased when the primary air temperature became higher.