Research On Principle And Optimization Method Of Stepless Flow Control For Reciprocating Compressor And Its Application

Reciprocating compressor is widely used in petroleum,chemical industry,natural gas transportation and other industries.It is a high energy consuming equipment of enterprises.The reciprocating compressor has fixed compression volume which always mismatches with the changing gas demand of the system.As a result,a large number of compressors depend on the return valve for flow regulation.It causes large amount of excessive gas flows back to the intake pipeline through the return valve after being compressed.However,this control scheme is extremely inefficient as the backflow gas is re-compressed and the compression work is totally wasted.Therefore,for reciprocating compressor,it is necessary to continuously adjust its exhaust gas volume,so that compressor equipment can meet the requirements of efficient operation under different gas flow conditions.Existing energy-saving gas regulation technologies and related systems have problems such as high costs,rigid mode of use,and blockade of technological achievements,which limits their popularization and application in China.Therefore,it is of great significance and value to realize the high performance(high efficiency,adaptive working conditions)operation of domestic compressor units by developing the energy-saving flow regulation technology of compressor,which features low-cost,wide application range,high reliability,and high flexibility.In this paper,we started from the mechanism of inlet valve backflow regulation.The thermodynamic circulation characteristics of compressor and movement law of air valve under the condition of regulating air flow by reflux were studied theoretically and experimentally based on fluid dynamics.The stepless regulation and control method of reciprocating compressor was improved,a set of stepless flow control device was designed based on the principle of electro-hydraulic separation key parameters of the control system were optimized.The relevant theoretical research results have been verified by experiments and practical applications,and good application results have been achieved.Firstly,a theoretical calculation model of reciprocating compressor under variable load condition was established in which characteristics of gas back-flow adjustment by delaying the closing of intake valves and dynamic balance of compressor pressure between all stages were introduced into the calculation model.Each valve was modelled as an independent open and close component in the model.The calculation and analysis of internal flow,valve dynamics and thermodynamic circulation characteristics of compressor chamber under complex working conditions with variable flow load were performed.The mechanism and characteristic of inlet valve backflow regulation was revealed by comparing the experimental results with the simulation results.Secondly,a new stepless regulation method by optimum combination of uniform load reflux regulation in each single cycle,differential load reflux regulation in double cycles and differential load reflux regulation by duty cycle adjustment in multi-cycles was put forward.Range of highly efficient and stable operating conditions of the compressor unit and the applicable compressor speed range were further broadened.The working cycle characteristics of compressor with a small number of air valves involved in backflow were analyzed through the model for capacity regulation by inlet valve backflow.A method of regulating air flow capacity based on dynamic adaptive adjustment of inlet valve flow area was proposed,and an algorithm for compensating and correcting the backflow deviation of the partial inlet valve,based on the control timing sequence,was developed.It breaks through the limitation that only with all inlet valves involved in backflow can the air load be accurately controlled,which realizes the optimization of stepless regulation of air volume with the least air valve.A dynamic pressure prediction model for the buffer chamber of multistage compressor was constructed.It can predict the steady-state characteristics of pressure at all stages and the dynamic response characteristics with step,which lays a foundation for stepless flow regulation of multistage compressors.In view of the multi-stage multi-cylinder compressor under partial capacity condition,the pressure change of each stage is a multi-coupling,time-varying and non-linear process,and a nested multi-loop pressure control method was proposed for the multi-stage compressor pressure system.Then,taking a DW2/12 type reciprocating compressor as the research object,a design scheme of stepless flow control system for reciprocating compressor in which the air valve hydraulic unloading mechanism was designed to separate from the electrical components was proposed.The hardware control system design adopted the framework of using one electrical component to drive several hydraulic actuators,which can realize high efficiency,energy saving and stable regulation of compressor unit under full capacity regulation range.A prototype of the stepless capacity control system for reciprocating compressors and relevant experimental test platform were built on which a large number of experiments were carried out on the performance of control system,stepless gas regulation and control method,and operation characteristics under conditions of different flow capacity.The experimental results verify the correctness and feasibility of the research results in flow regulation principle and control method.Then,the effects of key parameters,such as actuator unload force,ejection displacement,ejection phase,withdrawal speed,actuator assembly error and unloading fork reset spring,on the internal flow,valve dynamics and thermodynamic circulation characteristics of the compressor chamber were further analyzed.The system structure parameters and operation parameters were optimized on the premise of complete function and energy saving effect,aiming at low processing cost,low energy consumption and long service life,to improve the applicability of the control system to the unit and avoid the adverse effects of variable flow regulation on the unit and process.Finally,the research results of this paper have been applied to reciprocating compressors in some petrochemical enterprises in China,and good application results have been achieved.The research results of gas regulation of reciprocating compressors in this paper have been further validated.