Energy Efficiency Evaluation,Diagnosis And Scheduling Of Ethylene Cracking Production

Cracking equipment is the core of ethylene production process,whose energy consumption accounts for about 60% of the total energy consumption in the production process.Therefore,energy consumption reduction and energy efficiency level improvement of the cracking equipment are of great significance to reduce the total energy consumption in the ethylene production process.However,there are still some problems to be addressed for the energy efficiency management of the cracking production in the theoretical research and practical application at present,such as inadequate coupling analysis of multi-media energy and material flows,insufficient energy efficiency evaluation under multiple production condition,rough diagnosis granularity,imperfect energy efficiency scheduling optimization and so on,which have limited the energy efficiency level improvement of the cracking production in China.For this purpose,this paper focuses on the energy efficiency evaluation,diagnosis and scheduling of cracking production,and considering the specific problems and actual production demand,systematically proposes the energy efficiency management schemes integrating energy efficiency evaluation,diagnosis and scheduling.The main research work is as follows:Aiming at the technic characteristics of multi-energy medium,multi-energy flow and multi-material flow cross coupling,which leads to the energy efficiency management problems with multi-spatial level,multi-production dimension and multi-time scale characteristic of energy efficiency index,the cracking production is divided into process level,device level and component level according to the spatial structure and composition relationship when focusing on the whole production process,independent device and internal components in turn.Then,the object boundary is defined level by level and the energy flow attributes are classified according to their roles in production.Starting from the energy flow conversion,material flow transformation,and material flow and energy flow coupling,a three-level six-dimension twoscale energy efficiency index system is established,which lays a foundation for the follow-up research on comprehensive energy efficiency evaluation,diagnosis and scheduling under different levels.In terms of the energy efficiency evaluation of cracking furnace under multi-medium energy flow and multi-working condition,an energy efficiency evaluation scheme based on double virtual dynamic benchmark is proposed.Firstly,the inputs and outputs of production decision-making units are redesigned according to device-level indexes.Then,the changes of energy efficiency indexes caused by multi-working condition and multi-dimension characteristic of energy efficiency indexes caused by multi-energy flow are integrated to improve the integrity of energy efficiency evaluation results.On this basis,the energy efficiency optimization models based on the energy efficiency benchmark soft-sensing models of cracking furnace are established to solve the upper and lower energy efficiency benchmarks dynamically adjusted with the change of working conditions,so as to obtain the influence of operation condition changes on the energy efficiency evaluation of cracking furnace under different working conditions.Compared with previous working condition classification method,the proposed evaluation scheme can directly evaluate the energy efficiency of cracking production under multiple working conditions at the same time,and provide the energy efficiency evaluation results reflecting the operation level.The actual results show that the evaluation scheme supports the multi-index and multi-working-condition energy efficiency evaluation of cracking furnace,and can give improvement directions of energy efficiency from multiple perspectives.In view of the diagnosis problem of low energy efficiency of cracking furnace caused by alternating or simultaneous occurrence of fault and abnormal operation and the efficiency fluctuation of internal three chambers,a two-level energy efficiency diagnosis scheme is proposed.Based on device-level diagnosis indexes,fault and operation criteria together with joint criteria are established to identify three types of inefficiency.Combined with inefficiency index type analysis,minimum loss models are established for solving the non-fault and operation standards,so as to separate different contributions of fault and abnormal operation by calculating the energy efficiency deviation value.On this basis,the partial differential and stepby-step transformation methods are applied to determine the abnormal output,operation conditions and their contributions.Then,through the energy efficiency correlations between the furnace and three chambers,the partial differential based on the component-level energy efficiency standards is used to determine the abnormal chambers and their contributions.The final diagnosis results are given by combining the two-level anomaly analysis.The actual case has verified that the proposed diagnosis scheme is more effective than the traditional one,which can locate the bottleneck factors more accurately and provide more effective energy-saving improvement strategy.Aiming at the energy efficiency scheduling problem of cracking furnace group with DRC structure under the interdependence of production arrangement and operation setting,a multiobjective energy efficiency scheduling scheme based on multi-flow allocation,multi-parameter setting and DRC coordinated operation is proposed.Firstly,based on process-level indicators and scheduling requirements,energy efficiency scheduling indexes are proposed to measure the overall energy efficiency level of the cracking process within a long period.Then,to determine the correlations among the multi material and energy flows,and multi operation conditions in the cracking furnace with DRC independent operation capability,a total cracking model with radiation chamber as the minimum unit is constructed according to kinetics analysis.Finally,combined with the constraints of scheduling rules,a scheduling model including steam heat recovery and exhaust heat loss is established,and a multi-objective evolutionary algorithm is used to solve the model on the basis of introducing variable mapping,penalty function and relaxation factor.The case study confirms the effectiveness of the proposed scheduling scheme,which achieves the optimal balance among multi-flow allocation,multi-parameter setting and DRC coordinated operation in the long-term cracking process.After scheduling,the net energy input of cracking process is reduced by 3.37% and 2.63% respectively,and the energy loss is reduced by 1.56% under the same product output and conversion rate.