Research On Thermal Efficiency Model And Its Application On Energy Efficiency Optimization Of Whole Cement Kiln System

Calcination of cement clinker consumes a lot of heat energy,and energy conservation is one of the long-term goals of the cement industry.Feasible energy saving measures include traditional methods such as improving the process flow,carrying out technical transformation,and new methods such as implementing intelligent optimization control.Their essence is to improve the thermal efficiency of the clinker burning process.Existing research on thermal efficiency of cement clinker calcination process mostly focused on single equipment or local sections,and their original data were obtained mainly by relying on thermal calibration or laboratory testing,which can only be used for static evaluation,and cannot meet the requirements for real-time and continuity of thermal efficiency models in optimal operation and intelligent control.In this paper,research object of thermal efficiency was extended to the whole kiln system,and thermal efficiency mechanism model,thermal efficiency dynamic calculation model and thermal efficiency prediction model of the whole kiln system were develop,thus to meet the specific requirements of different energy conservation measures on the thermal efficiency model.The three model were based on the operation data of the production line and have been applied in many cement production lines in China,and the conclusions are as follows:（1）Research scope of the whole kiln system included raw fuel drying,waste heat utilization,clinker burning,etc.,and was divided into three subsystems by reference to the process flow.Then,the mechanism model of the whole kiln system thermal efficiency was developed according to the correlation between each subsystem and the thermal efficiency of the whole kiln system.According to the mechanism model,the thermal efficiency of clinker burning subsystem has the greatest impact on thermal efficiency of the whole kiln system(φ_qy);among the three sub units of the clinker burning subsystem,the thermal efficiency of the decomposition and calcination unit has the greatest influence.（2）The dynamic calculation model can realize real-time acquisition of thermal efficiency value based on DCS data and a small amount of laboratory value.Dynamic calculation model can provide direct basis for optimizing production operation,and the average value of operating parameters corresponding to different thermal efficiency intervals can also be obtained according to historical data,thus the DCS parameters corresponding to high thermal efficiency can be taken as the control target value of production parameters.Taking a domestic 12000 t/d production line as an example,φ_qy obtained under the typical working condition（raw meal mill and coal mill are all in operation）is up to 72.78%;higherφ_qy could be obtained by increasing feed quantity,decreasing calcination temperature in calciner and increasing air flow in high temperature section of cooler.（3）Using the temperature of the clinker as the output variable,mechanism prediction model A,multiple linear regression prediction model B,and RBF prediction model C were established to achieve real-time prediction of thermal efficiency based only on a small amount of DCS data.The real-time prediction of thermal efficiency could be realized based on only a small amount of DCS data,calculation amount was significantly reduced and the real-time performance of prediction models were greatly improved.Among the three models,model B and model C have better prediction effects than model A,and fewer independent variables are used.（4）Mechanism model in this paper can be used to provide direct guidance for the formulation of optimization plans.Taking a domestic 12000 t/d production line as an example,the main reason for the low thermal efficiency of the whole kiln system is the low thermal efficiency of the preheating unit and cooling unit;φ_Qy can be improved by measures such as improving the material distribution box and optimizing the tertiary air duct.Mechanism model can also be used to determine the optimal process route.According to the actual operation data of the production line,the thermal efficiency can be greatly improved from 9.98%to 51.82%when the direct utilization process of waste heat such as drying slag is used to replace the indirect utilization process of waste heat such as waste heat power generation in the waste heat utilization link;The thermal efficiency of the preheating unit can be increased from 54.98%to62.04%by adopting the high solid gas ratio form instead of the traditional five stage double series form.（5）Thermal efficiency mechanism model of the whole kiln system and the linear regression prediction model B were integrated into the clinker firing process optimization control system in one 12000 t/d cement clinker production line.Comparative test shows that,under intelligent optimization control conditions,the heat consumption of clinker burning can be reduced by 44.89 k J/kg.cl.