The Numerical Simulation of the Flow Field in a Cold Model of Five-stage Cyclone Preheater and Precalciner System

The flow field in a cold model of 2500 t/d five-stage cyclone preheater and precalciner system was numerically simulated. Renault stress model (RSM) turbulent model was adopted to simulate the flow field, and a hybrid mesh scheme was selected to generate calculation mesh. With the first order upwind difference, finite-volume method was used to convert turbulent equations into difference equations pressure-velocity coupling which were solved by the classic simple algorithm, and during the course of numerical solution, mesh self-adapting technology was applied. The main flow field structures of the whole system and each part of the cold model were studied by analyzing the simulation results.

Numerical Simulation of Sludge Combustion in TTF Precalciner

The research method of computational fluid dynamics(CFD)is used to study the technology of burning sludge in cement precalciner.The simulation results show that the flow field in the TTF precalciner is stable,the spray effect is good,and no raw meal collapse occurs.The special structure of the TTF(Trinal-sprayed)precalciner allows the pulverized coal and sludge to fully exchange heat with the flue gas and burn.When there is no sludge burning in the furnace,the decomposition rate can reach 92.1%,and the maximum temperature of the precalciner can reach 1600 K.When the moisture content of the sludge is constant,as the amount of sludge increases,the overall furnace temperature shows a downward trend and the minimum temperature at the precalciner outlet can be reduced to 1080 K.The phenomenon shows that sludge has a great influence on furnace temperature.In order to ensure that the decomposition rate of the raw meal is not less than 85%,the decomposition rate of the raw meal under different conditions is calculated.It was found that the sludge input can be about S-20%when the mositure content of the sludge is 50%.Moreover,when the water content of the sludge is 60%,the burning amount of sludge cannot be higher than S-20%,which ensures the normal decomposition of cement.The addition of sludge reduces the temperature in the precalciner and further inhibits the generation of thermal NO_(x).The reduction of CO content produced by incomplete combustion of pulverized coal indicates that CO suppresses the production of fuel-type NO_(x).The NO_(x) concentration at the gooseneck is as low as 522 mg/Nm3.Additionally,it was also found that when the sludge input is fixed,the NO_(x) concentration decreases with the moisture content of the sludge increasing,indirectly proving the inhibitory effect of H2O on NO_(x).

Technological Characters and Improvements on Type SLC-S Precalciner Kiln

In this paper the problems on SP kiln period is discussed, whichlead to low CaCO_3 decarbon- ation rate in the hot meal, so that kilncoating is vulnerable and material frequently falls off and blocksthe pre- heater. Excellent effects are achieved when skipping the SPkiln period, neglecting the function of the dividing gate below theC4 preheater and sending the material completely into the calciner.

Numerical Simulation of Co-Combustion of Pulverized Coal and Different Proportions of Refused Derived Fuel in TTF Precalciner

Based on the theory of computational fluid dynamics(CFD),pulverized coal combustion alone,and the co-combustion of pulverized coal and refuse-derived fuel(RDF)in a Trinal-sprayed calciner(TTF)precalciner were simulated.The results revealed that when coal was used as a single fuel,the velocity field in the precalciner had good symmetry,and formed three spray effects and multiple recirculation zones.The main combustion zone was distributed in the lower tertiary air and pulverized coal area,and the highest temperature reached up to 1,500 K.According to the simulation results,the predicted decomposing rate of raw meal was 90.12%,which is in good agreement with the actual measured result.In addition,with the increase in RDF content,the average temperature of the furnace,the decomposition rate of the raw meal,and the NO_(x) concentration all exhibited a downward trend.Under the condition of ensuring the normal operation of the precalciner,blending with 20%RDF is the most reasonable strategy,and the NO_(x) emissions decreased by approximately 16%.

Numerical Simulation of Urea Based SNCR Process in a Trinal-Sprayed Precalciner

In order to study the combustion characteristics,NOx emission and NH3 slip in a new trinal-sprayed precalciner,the simulations of combustion and aqueous urea solution based selective non-catalytic reduction(SNCR)process were conducted by computational fluid dynamics in this precalciner,the effects of different injection heights,different injection flow rates and stratified injection under different flow rates on SNCR process were studied.The results showed that the flow field was symmetrically distributed in the precalciner,and the flue gas from the rotary kiln formed the recirculation region on both sides of the cone body,which increased the residence time of the solid particles.The temperature was mainly between 1100 K and 1250 K in the middle and upper column of the precalciner,which met the demand of the pulverized coal combustion and raw material decomposition.The concentration of NO at the outlet of the precalciner was 559 ppm,moreover,different injection heights and different injection flow rates had a strong influence on NOX removal efficiency and NH3 slip.The aqueous urea solution should be injected at SNCR-1 to prolong the residence time of NH3,and injection flow rate had an optimal flow rate but not the higher the better.When the injection flow rate under stratified injection was 0.019 kg/s,which could play a better optimization role on NO removal efficiency on the basic of the injection flow rate.In consideration of cost effective,a stratified injection with an injection flow rate of 0.019 kg/s and an injection height of 20 m,25 m and 30 m was suggested as a compromise of a satisfactory NOx reduction rates and reasonable NH3 slip.Under this condition,numerical simulation result showed that NOx concentration at the outlet of precalciner was 297.27 mg/Nm3 and NH3 slip was 4.67 mg/Nm3,meeting emission standard.

Composite Control of Precalciner Exit Temperature in Cement Rotary Kiln

A composite control strategy for the precalciner exit temperature in cement kiln is introduced based on a mathematical model. In this model, the raw meal flow, coal powder flow and wind flow are taken as three input variables, the clinker fow and exit teperature of cement kiln are output variables, and other influencing factors are considered as disturbance. A composite control system is synthesied by integrating self learning PID, fuzzy and feedforward function into a combined controller, and the arithmetics for the self learning PID controller, fuzzy controller and feedforward controller are elaborated respectively. The control strategy has been realized by software in real practice at cement factory. Application results show that the composite control technology is superior to the general PID control in control effect, and is suitable to the industrial process control with slow parameter variation, nonlinearity and uncertainty.

Effects of Co-Firing Biomass and Pulverized Coal on NO Reduction in Cement Precalciner

With increased awareness of the large-scale CO_(2) emissions from the cement industry,there has been growing focus on greenhouse gas reduction strategies.Among all these strategies,fuel substitution using biomass fuel is extensively used to achieve CO_(2) zero-emission in cement production.Due to the avoidable high-temperature-generated thermal nitrogen oxides during cement production,research on the impact of biomass application on nitrogen oxide emissions shall be carried out.Three types of biomass fuel and bituminous coal were used to investigate the NO reduction characteristics under different O_(2) concentrations on experimental benches.It was found that the change in oxygen concentration from 9% to 1% increased the reaction time in the reactor from 555 s to 1425 s,which means the increase in oxygen concentration can lead to shorter reaction time,and correspondingly,the existing time of nitric oxide in the flue gas is also shortened,but the peak value of nitric oxide rises,during the process of O_(2) concentration changing from 1% to 9%,the peak NO concentration in the flue gas increased from 5.4×10^(-5) to 1.05×10^(-4).An increase in O_(2) concentration greatly reduces the total reduction of NO and the minimum change in NO concentration.The peak NO concentration during the combustion process of corn stalk is 4.56×10^(-4),which is approximately 7 times higher than that of coal,and it is caused by the high amount of N in corn stalk.The addition of raw meal has an inhibitory effect on the reduction of NO:after adding raw meal,the effective reduction time of NO by fuel decreased by about 20%,but adding raw meal raises CO_(2) concentration of fuel gas in the early stage of reaction.

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.

Numerical Simulation and Optimization of Staged Combustion and NO_x Release Characteristics in Precalciner

In order to study the combustion characteristics in a precalciner, the temperature and composition field in a typical Trinal-sprayed calciner were numerically analysed. The results obtained by simulation were compared to actual measurements and the simulated results were in good agreement with the measured ones. The results indicated that the aerodynamic flow field in the precalciner is satisfactory, and a symmetrical reflux occurs in the shrinkage zone of the precalciner because of air staging, which can increase the residence time of the solid particles. The temperature distribution in the furnace is uniform, and the average temperature is greater than 1200 K, which can satisfy the conditions for the pulverised coal combustion and raw material decomposition. The mass fraction distribution of oxygen, carbon monoxide, and carbon dioxide in the precalciner is closely related to the temperature distribution. The concentration of nitrogen oxides(NO_x) exhibits a trend of increasing, decreasing and then increasing, and finally tending to a stable level. Within a certain velocity range, the average temperature in the precalciner and the decomposition efficiency of the raw material increase as the flue gas velocity increases. When the flue gas velocity is 24 m/s, the overall performance of the precalciner is optimal.

Modeling De-No_(x) by Injection Ammonia in High Temperature Zone of Cement Precalciner

The quantity of NO_(x) emission from cement production is second only to thermal power generation and vehicle exhaust.In this paper,a phenomenon found by Taniguchi is used to achieve NO_(x) reduction in the cement precalciner.Based on his results,it is proposed to reduce NO_(x) that ammonia is injected in the high-temperature and lean-oxygen zone(HT-DeNO_(x))during pulverized coal combustion.For a large cement precalciner(3200 t/d),numerical simulation is used to evaluate the technology of HT-DeNO_(x) combined with the traditional selective non-catalytic reduction(SNCR)method.The results indicate that NH3 and HCN in HT-DeNO_(x) can reduce NO during the reaction process.With very little ammonia injection(normalized stoichiometric ratio NSR=0.1,the normalized stoichiometric ratio),the efficiency of NO reduction by HT-DeNO_(x) is 27.72%.Combining SNCR(NSR=1.1)and HT-DeNO_(x)(NSR=0.1),the reduction efficiency will be improved to 60.05%,compared with 50.83%efficiency when using only SNCR at NSR=1.2.

Influence of Characteristics of Alumina-silicate Raw Materials on the Formation Process of Clinker

The traditional alumina-silicate raw materials, for example, clays, in the precalcining technique of cement production, have been replaced by low grade and high silica content sandstones, shales, and industrial waste residues, including fly ashes, slag, and others. The results are the change of compositions and characteristics of raw materials applied and a great effect on cement calcination process and clinker formation. In this work, the cement clinker formation process of different alumina-silicate raw materials to replace clay raw material was studied by chemical analysis, X-ray diffraction, differential thermal analysis, and high temperature microscope based on the characteristics of the alumina-silicate raw materials. The formation heat of the clinker was determined by the acid dissolution method. Influence of different alumina-silicate raw materials on the clinker burnability and formation process was studied. The results show that the changing of alumina- silicate raw materials, especially using industrial waste residues, can reduce the formation temperature of high temperature liquid phases, improve the burnability of raw materials, reduce the formation temperature and formation heat of clinker. And this study also observed the formation temperature and transformation of high temperature liquid phases in the heating process of raw materials by high temperature microscope.

Optimization of Fuel In-Situ Reduction(FISR)Denitrification Technology for Cement Kiln using CFD Method

Nitrogen oxides(NO_(x))from cement industry have drawn more and more attention and the existing denitrification technologies can hardly meet the increasingly stringent emission requirements in China.In our previous work,fuel in-situ reduction(FISR)method was proposed to cut cement NO_(x)emission.With the pilot-scale precalciner in the previous experiment as objection,optimization of FISR method was conducted using CFD method.The results demonstrated that NO_(x)emission decreased by 69.86%after adopting FISR method.The effects of initial concentrations of NO and O_(2)in kiln gas,feeding location of the first-stage tertiary(tertiary air-I)and cement raw meal(CRM)were further investigated.With increasing initial NO concentration,NO_(x)emission increased linearly,while the reduction rate of NO in kiln gas maintained above 80%.When O_(2)content in kiln gas is more than 4%,oxygen would more significantly promote the formation of NO_(x)and inhibit the reduction of NO.The dimensionless locations of tertiary air-I and CRM were introduced.The simulation results showed that the optimal dimensionless locations are 0.6 and 1.6 for tertiary air-I and CRM,respectively.The outputs achieved in this study will provide a strong support for the practical application of FISR method in cement industry.