Experimental Study On Preheated Combustion Of Pulverized Semi-coke

Coal occupies the dominant position in China's energy structure,and the low-grade coal dominated by lignite and sub bituminous coal accounts for more than 55%of total coal reserves.As the low-grade coal efficient cascade use of intermediate product,semi-coke has the characteristics of high calorific value,low content of moisture and volatile,resulting in high ignition point,low combustion rate,burn dif-ficult.After years of development preheated combustion technology has proven to be a great potential for efficient clean combustion of low-volatile fuels.Based on pre-liminary research on preheated combustion,this paper studies the relationship be-tween the nitrogen release of semi-coke and the characteristics of the particles,dis-sects thoroughly the mechanism of the migration and transformation of nitrogen ele-ments,and analyzes the cold flow field characteristics in the furnace under the op-posed arrangement and quadrilateral arrangement of the preheated burner.In the 30kW semi-coke preheated combustion experimental system,with the in-crease of the air equivalent ratio in the circulating fluidized bed preheated burner,a large amount of oxygen enters the semi-coke particles through the pores and reacts with the fixed carbon.The consumption of the internal carbon structure of the parti-cles leads to the decrease of the strength,the collapse of the internal pores,and part of the small holes to synthesize the large pores,which increases the pore size and the specific surface area,thus promoting the release of nitrogen.In the combustion pro-cess of the down-fired combustor,the particles burn violently and the temperature is the highest in the range of D100-D400(distance from the top of the down-fired com-bustor 100mm-400mm).The high temperature and the intense combustion reaction consume a lot of carbon structure,which causes the carbon skeleton to become brittle,the pore to be ruptured and collapsed,the particle size and the specific surface area to be decreased significantly,and nitrogen to be released strongly.With the decrease of the secondary air equivalent ratio,in the D100-D400 range the increase in reduction strength contributes to more nitrogen to be reduced and NOx reduction.On the cold experimental system of preheated burner opposed arrangement,due to the asymmetry of the inlet position of the cyclone,the outgoing primary air flow is eccentric.And then through a duct elbow,the centrifugal force also causes primary air deflecting,so that the air flowing into the furnace is deflected toward the side wall,further the second air,the third air and the entire furnace flow field deflection.When the both cyclone are axially symmetrically arranged,the corresponding two primary air jet are also axisymmetric distributions.And when centrally symmetrically ar-ranged,the two air jet are distributed centrally.Once the primary air duct is rectangu-lar,the jet will flow vertically to eliminate deflection.On the cold experimental system of preheated burner quadrilateral arrangement,the four primary air enters the furnace in a vertical flow,forming a symmetrical tan-gential rotation.Secondary air 1 jet has a strong rigidity,so the tangential rotation is more obvious at the nozzle section.Due to the rising effect of main air flow,the flow of the secondary air 2 and the secondary air 3 is rotationally rising.In the furnace structure,there is almost no material deposition.Increasing the cross section average jet velocity of the primary wind,secondary air 2 and secondary air 3,the tangential diameter is reduced first and then unchanged.This is because the tangential diameter is also related to the shape and angle of the nozzle.When the jet velocity increases to a certain extent,the tangential diameter is no longer affected by it.This paper provides theoretical basis and design support for reduction of NOx emission and engineering application for preheated combustion technology.