| Industrial gases are referenced as "industrial blood",and cryogenic distillation air separation units(ASU)is the mainstream technology for large-scale production of highpurity oxygen,nitrogen,argon and other gas products.According to statistics,the energy consumption of the ASU accounts for about 10%-20% of the total system energy consumption in the steel and coal chemical industry.Under the requirements of "Carbon Emission Peak by 2030" and "Carbon Neutralization by 2060",reduction of the energy consumption of ASU is imperative.Although a lot of optimization research have been conducted on the air compressor in the past few decades,the current energy consumption of the compression module still accounts for about 80% of the total energy consumption in the ASU,and more than 60% of the compression work is dissipated in the form of compression heat without being utilized.Compression heat recovery is thought of great significance for the energy saving in the ASU.Focusing on the characteristics of the compression heat,this paper aims to explore the efficient and appropriate system structure,safe and effective operation scheme,and dynamic model with high precision and short calculation time,so as to provide theoretical reference for the practical application of compression heat recovery in the ASU.The main works are as follows:(1)A global performance comparison method is developed,and an operation method based on pinch-point temperature difference is proposed,thus maximuming system energy saving performance with structure and operation optimization.Compression heat in the ASU is produced in intermediate process,which is with the characteristics of low grade,fluctuating and lacked of direct heat utilization applicaiton.A global performance comparison method is proposed,along with an operation method based on pinch-point temperature difference(PPTDO)to maximum the system performance.According to the optimization results,the oraganic Rankine-mechanically coupled vapor compression-heat recovery system(ORC-m-VCR)is the structure with global optimal comprehensive performance,which has the best energysaving,economic and environmental protection performance under all design conditions.It is observed that the proposed PPTDO has the optimal energy-saving performance under all design conditions,whose duty ratio reaches 100%,illustrating a capacity of normal operation throughout the year.(2)The organic Rankine-mechanically coupled vapor compression test bench is designed and built.The influence laws of the system performance and dynamic response characteristics are analyzed,and the key parameters affecting the operation and performance are revealed.Organic Rankine-mechanically coupled vapor compression technology is the key technology for ORC-m-VCR to realize practical application.In this paper,an organic Rankine-mechanically coupled vapor compression test bench is designed and built,and the off-design experiments are carried out.According to the experimental results and sensitivity analysis,the operation parameters of the ORC are mainly affected by the working fluid flow rate of the ORC,while those of the VCR are mainly affected by the throttle valve opening,and the rotational speed is mainly affected by the auxiliary generator torque and the throttle valve opening.In terms of system performance,the throttle valve opening and hot water flow rate are the key parameters affecting the cooling capacity,while the throttle valve opening and working fluid flow rate of the ORC are the key parameters affecting the system COP.System COP can reach a maximum value of 0.61.In terms of dynamic response,this experimental system responds quickly under variable working conditions,as the delay time of each condition is less than 10 s,while the response time is less than 45 s.(3)An improved heat exchanger model combined with a dynamic simulation scheme of BP neural network algorithm is proposed when the process of ORC-mVCR is complex and parameter decoupling is hard.The dynamic characteristics of the ORC-m-VCR during annual operations are predicted.Dynamic modelling is an effective method to predict the actual system operation characteristics.However,the structure of the ORC-m-VCR is complicated and the operation parameter decoupling is difficult,which rises the difficulty of dynamic modelling with longer calculation time and lower accuracy.In this paper,an improved lumped-parameter heat exchanger model with density zoning averaged is put forward.A dynamic simulation scheme combined with BP neural network algorithm for predicting the performance of the mechanically coupled expansion-compressor is also proposed.This dynamic model shortens the lag time from about 100 s to about 20 s,and the average relative error is less than 10%.When the 60,000 Nm3/h grade ORC-mVCR runs annual,the temperatures basically fluctuate near the design values,and the response time is about 4-8 min.The annual energy saving of the system is about 13.75 GWh,while the annual average energy saving ratio and heat recovery ratio is about 7.4%and 76.4%,respectively,equivalent to CO2 emission reduction of about 9.9 Mt,demonstrating great energy saving and environmental protection potential. |
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