| The issues of energy and environmental protection are the focus of serious attention in the current society.During the calcining process of cement clinker,a large amount of low-temperature waste gas is emitted,which contains about 30%of the total heat consumption of the calcination of cement clink,if this part of heat can be recycled,it is of great significance for energy conservation and environmental protection.Due to the high concentration of fly ash in the flue gas from the cement kiln,problems such as abrasion and accumulation of ash may occur after the flue gas is introduced into the waste heat boiler,which will have adverse effects on the efficiency of waste heat recovery and the life of the waste heat boiler.In the paper,a simulation model is established on the basis of the SP waste heat boiler's superheater of a 5000 t/d new dry process cement production line,the flow,heat transfer and ash accumulation characteristics of it are studied further in order to provide technical support for the efficient operation of HRSG.The specific research contents and conclusions were as follows:(1)The flue gas flow and heat transfer characteristics in the superheater area of the cement kiln SP waste heat boiler are simulated.The distribution rules of the flow field,temperature field and pressure field in the superheater area are obtained,the results show that the heat transfer coefficient Nu between superheater and flue gas,the convection heat transfer coefficient h,the pressure drop ?P between the inlet and outlet of superheater,etc.gradually increase with the increase of the inlet velocity of the flue gas,and the reliability of numerical simulation method is verified by the measured data and empirical formulas.(2)Based on the velocity and ash accumulation criterion,UDF is used to compile the source code for determining fly ash accumulation.(3)The influence of flow parameters such as fly ash particle size,flue gas velocity,dust content in flue gas and flue gas temperature,etc.on the characteristics of fly ash particles accumulation is studied.The results show that in the scope of the study,the deposition of the particles with small size on the wall surfaces of each row of heat exchange tube bundles is relatively random,and the deposition rate of large-size particles along the flow direction of the flue gas tends to decrease as a whole,with the increase of the flow velocity of the flue gas,the deposition rate of small size fly ash is on the rise,while the deposition rate of large-size fly ash decreases,with the increase of dust content and fuel gas temperature,the deposition rate of fly ash increases.(4)The influence of structural parameters such as the arrangements of the superheater's tube bundles,shape and pitch,etc.on the deposition characteristics of fly ash particles is studied.The results show that the deposition rate of the circular tube is greater than that of the elliptical tube,and the deposition rate of aligned arrangement is larger than that of staggered arrangement.The use of staggered elliptical tubes can effectively reduce the deposition rate of fly ash particles,the increase of the horizontal pitch can reduce the accumulation of ash effectively,while the increase of the vertical pitch can reduce the accumulation of ash slightly.(5)The technical scheme of installing a shutter separator above the superheater to reduce the deposition of fly ash particles on the wall of the heat exchange tube bundle is proposed,and the optimized structural parameters of the shutter separator are obtained through simulation and orthogonal analysis method:the blade angle is 27° the spacing is 190mm,the covering distance is 300mm,and the number of blocks is 6.The results show that after installing the optimized shutter separator,the fly ash deposition rate is reduced by 68.86%,and the system resistance loss is increased by 268Pa. |
PDF Full Text Request