Experimental Study on Preheated Combustion of Pulverized Semi-coke

In a test rig,pulverized semi-coke was preheated to 850℃in a circulating fluidized bed(CFB)and then cornbusted at 1100℃in a down-fired combustor(DFC).Experiments were conducted to reveal the effects of three secondary air nozzle cases(co-axial jet,top circular jet and wall circular jet)on the NO emission.The results show that the optimized secondary air nozzle can reduce NO emission.O_2 concentration profile is the major factor affecting NO generation and emission,which is led by the secondary air nozzle.The lower O_2 concentration led to the generation of lower initial NO.The NO emission at the exit of the DFC was reduced from 189 to 92mg/m^3(@6%O_2)with the decrease of initial generation.The peak of NO at 100 mm below the nozzle should be attributed to the oxidization of NH_3 in the syngas,rather than the oxidization of fuel-N in the char.The low and well-distributed O_2 concentration contributes to the reduction of initial NO,which helps to reduce the NO emission.The combustion effieiencies of the eases of the co-axial jet,the top circular jet,and the wall circular jet are97.88%,98.94%and 98.74%,respectively.

Numerical Investigation of Fuel Dilution Effects on the Performance of the Conventional and the Highly Preheated and Diluted Air Combustion Furnaces

This numerical study investigates the effects of using a diluted fuel （50% natural gas and 50% N2） in an industrial furnace under several cases of conventional combustion （air with 21% O2 at 300 and 1273 K） and the highly preheated and diluted air （1273 K with 10% O2 and 90% N2） combustion （HPDAC） conditions using an in-house computer program. It was found that by applying a combined diluted fuel and oxidant instead of their uncombined and/or undiluted states, the best condition is obtained for the establishment of HPDAC＇s main unique features. These features are low mean and maximum gas temperature and high radiation/total heat transfer to gas and tubes; as well as more uniformity of theirs distributions which results in decrease in NOx pollutant formation and increase in furnace efficiency or energy saving. Moreover, a variety of chemical flame shape, the process fluid and tubes walls temperatures profiles, the required regenerator efficiency and finally the concentration and velocity patterns have been also qualitatively/quantitatively studied.

Coal-Biomass Preheating Combustion Characteristics in Cement Precalciner.Part 1:Preheating of Coal/Biomass

The co-combustion of biomass and coal can positively impact the environment and reduce the cost of power generation.However,biomass fuels have many limitations.Circulating fluidized bed(CFB)preheating combustion is suitable for co-combusting coal and biomass because of better fuel adaptability.In the cement industry,fuel combustion and raw meal decomposition in precalciners affect cement quality and cause pollutant emissions.The preheating combustion method used in precalciners can improve combustion performance and reduce NO_(x)emissions.This study investigated the preheating characteristics of a coal-biomass mixed fuel in a cement precalciner.The effects of load,biomass type,and biomass proportion on the preheated fuel and the conditions of the CFB were investigated.The results indicated that a lower load reduces the combustible components in gaseous and solid preheated fuels.However,due to the gas volume remains constant under different loads,a lower load also increases temperature and intensifies the reaction.The carbon chain and microscopic structural activities of preheated fuels are considerably enhanced,facilitating their combustion in precalciners and reducing nitrogen oxides in rotary kilns.Furthermore,adding biomass can improve the reactivity of a fuel subjected to preheating.Thus,biomass fuels(e.g.,rice husks)exhibit high combustion efficiency,and thus high energy utilization.The present study achieved better pore structure and molecular activity using preheated fuel from a CFB preheater.In addition,the improvement of pore structure and molecular activity increases with the proportion of the biomass.

Dome Combustion Hot Blast Stove for Huge Blast Furnace

In Shougang Jingtang 5 500m 3 huge blast furnace ( BF ) design , dome combustion hot blast stove ( DCHBS ) technology is developed.DCHBS process is optimized and integrated , and reasonable hot blast stove ( HBS ) technical parameters are determined.Mathematic model is established and adopted by computational fluid dynamics ( CFD ) .The transmission theory is studied for hot blast stove combustion and gas flow , and distribution results of HBS velocity field , CO density field and temperature field are achieved.Physical test model and hot trail unit are established , and the numeral calculation result is verified through test and investigation.3-D simulation design is adopted.HBS process flow and process layout are optimized and designed.Combustion air two-stage high temperature preheating technology is designed and developed.Two sets of small size DCHBSs are adopted to preheat the combustion air to 520-600℃.With the precondition of BF gas combustion , the hot blast stove dome temperature can exceed 1 420 ℃. According to DCHBS technical features , reasonable refractory structure is designed.Effective technical measures are adopted to prevent hot blast stove shell intercrystalline stress corrosion.Hot blast stove hot pipe and lining system are optimized and designed.After blowing in , the blast temperature keeps increasing , and the monthly average blast temperature reaches 1 300℃ when burning single BF gas.

Characteristics of Preheating Combustion of Power Coal with High Coking Properties

Yankuang coal with the high coking property is difficult to use through direct combustion.The main purpose of this paper is to study the combustion characteristics and NO_(x)emissions of this type of coal using preheating combustion technology.The experimental results show that after the pulverized coal is preheated,the char residue characteristic is significantly reduced from 5 to 1.During the preheating process,the preheating temperature is stable at about 910°C,and the particle size of char after preheating is reduced,and the pore structure and specific surface areas are increased.The combustion temperature of preheated fuel is stable at around 1100℃,and the combustion efficiency can reach more than 99%under different conditions.Changing the structure of the secondary air nozzles during the preheating combustion process can influence the characteristics of NO_(x)emissions.The NO_(x)emission of the central nozzle is about 112 mg/Nm~(3)lower than that of the annular nozzle.Changing the tertiary air distribution modes can reduce the final NO_(x)emissions to 215 mg/Nm~3(@6%O_2),and the corresponding conversion ratio of fuel N to the final NO_(x)is 4.2%.The results of this experiment prove that the Yankuang coal can achieve stable combustion by preheating combustion technology,and this proposed a new way for the utilization of Yankuang coal.

Experimental study on conversion path of sulfur in coal slime preheating combustion

In this study,coal slime was mainly utilized to conduct experiments on a 30 kW preheating combustion test rig to analyze the conversion pathway of sulfur during the experiment,aiming at reducing slime pollution,controlling sulfur emission reasonably,and providing theoretical support for the preheating combustion technology.The results showed that after the coal slime was preheated,a large number of elements were released.The maximum release rates for H and S were 94.0%and 73.3%,respectively.The released S was converted into the sulfur-containing gases like H_(2)S,COS,CS_(2),and the rest existed in the solid in the five forms of mercaptan,thiophene,sulfoxide,sulfone,and sulfate.Besides,during the combustion process,the gas was oxidized continuously and finally converted into SO2,leaving only the sulfate in the fly ash.In the preheating combustion process,26.7%of the S was released from the coal,73.3%of the S was retained in the semi-coke,and the final SO2 emission concentration of combustion was 959 ppm.