Numerical Simulation Study On The Effect Of Different Coal Injection Locations On NO_x Formation In NST Calciner

Calciner is the core equipment of new suspension precalciner?NSP?kiln.The situation of its operation directly affects the output of cement and the heat consumption of clinker.According to the work experience about thermal condition calibration of mine over the past few years,the working situation,such as the distribution of air,coal and raw meal inside the calciner are not very clear in cement industry.The distribution of temperature field,pressure field and gas composition was a major obstacle to the development of precalciner kiln.This work investigated the effect of coal injection site and different coal a/b ratio on NOx generation of NST calciner of a cement plant using CFD simulation,which aims to provide a theoretical basis and direction for NOx reduction of calciner.The main part of NST Calciner's diameter is 7 m,tertiary air enters the calciner with 15^o.The inlet method of tertiary air made the gas of calciner rotate one and half distance and air velocity distribution extremely uneven,low concentration zone was formed in the calciner.Before the raw meal was added,the high temperature zone of the calciner mainly existed at heights of 0.28D⁰.57D,0.57D¹D and 3.71D⁵.14D.The NO mainly existed at heights of 0.28D⁰.57D and 1.14D²D with relatively high concentration of O₂.The calcination of raw meal was 91.7%under normally operational conditions.Affected by the tertiary air inlet method,bias flows at different coal injection angles were observed.When the angle movement is 15°,high calcination of raw meal and low NO emission are obtained.However,severe local high-temperature phenomenon occured at heights of 2D².71D.With the increase of the angle movement,Pulverized coal particles which close to the tertiary wind exhibited larger rotation angle and more turbulent movement of coal particle b which removed from tertiary wind were observed.In the upper part of the tertiary air duct,the kiln gas carrying pulverized coal“collided”with the tertiary air in zone a of the blanking tube,leading to long residence time and intense combustion of the pulverized coal.As the height increased,kiln gas showed more stronger effect on the movement of pulverized coal on the b side of jetting coal pipe and the chaos degree of the movement of pulverized coal increased.At the height of 3.86 m,the calcination of the raw meal was the largest and the NO emission also reached the maximum.When the height increased to 4.86 m,The raw meal obtained the lowest calcination,only 89.7%which barely reached a reasonable value,but the NO exhibited the minimum emission.Based on the investigation of different coal a/b ratio,The NO emission from the calciner were mainly determined by pulverized coal on the side of the jetting coal pipe a which was close to the tertiary air duct.When the amount of pulverized coal increased,the NO emission increased and the pulverized coal showed poor combustion in the lower part of calciner,resulting in an increase in O₂ concentration in the upper part and delaying the formation of NO.Based on the experimental results of the CFD simulations,the structural characteristics of NST calciner and the formation mechanism of NOx were further understood,providing a reference for the improvement and operation of this calciner as well as the NOx reduction of calciner.