| During the transportation process of oil tankers,due to the strong volatility of the light hydrocarbon components in the crude oil in the storage tank,a large amount of VOCs(volatile organic compounds)gas is inevitably generated.VOCs gas not only causes serious environmental pollution,but also brings losses in oil quality,economic benefits,and other aspects.Therefore,it is particularly important to effectively recover and treat VOCs gas.Based on the determination of the two-stage VOCs gas condensation and recovery process plan for cascade refrigeration and nitrogen expansion refrigeration,this article first establishes a model through HYSYS software for process simulation analysis,determines the parameter range of each control point,and provides data reference for subsequent control system design;Secondly,a condensation recovery control system scheme with a PLC controller as the core was designed according to the project requirements.At the same time,hardware design selection,programming and debugging of upper and lower computers were completed.Then,through experimental research,the effectiveness of the control system and the accuracy of the process simulation results were verified.Finally,an improvement plan was proposed to address the shortcomings of the experiment,and the effects before and after the improvement were compared and analyzed through simulation.The main content is as follows:The condensation recovery process and low-temperature heat exchanger testing plan were sorted out,and the process was simulated using HYSYS software to complete the characteristic analysis of the simulation results.The simulation results showed that when the system condensation temperature was below-166 ℃,the methane recovery rate in the treated oil and gas reached 98.52%,and the exhaust emissions met the national standard requirements.A control system architecture was designed based on the simulation parameter range and system control requirements.The overall scheme of the oil and gas condensation recovery control system was designed,which consists of a gas parameter control subsystem,a cascade refrigeration control subsystem,a nitrogen expansion refrigeration control subsystem,and an upper control computer.The control system adopts Siemens S7-1200 series PLC as the controller for each subsystem,which controls the main pipeline,nitrogen expansion unit,and cascade unit respectively.On this basis,the software and hardware design and selection of the control system were completed.The Botu software was used to program the lower computer PLC,including subroutines such as data acquisition,refrigeration temperature setting and delayed start,pneumatic valve control,unit emergency stop,alarm and protection,frequency converter and magnetic levitation controller control.At the same time,the Jiekong configuration software was used to complete the upper computer program and design the upper computer control interface,Designed functional interfaces such as database operation settings,alarm information queries,historical data queries,real-time and historical curve queries.Secondly,some control cabinets were connected,communicated,and debugged,and experimental research on condensation recovery was completed.After multi-stage condensation,the raw gas achieved complete recovery of non methane total hydrocarbons,with a methane recovery rate of 96.2%.Finally,in response to the shortcomings in the experimental process,this article also proposes several improvement plans.Proposed adding nitrogen circulation pipelines to reduce nitrogen consumption during pre cooling;An improved scheme for controlling lowtemperature heat exchangers using fuzzy PID algorithm was proposed;It was proposed to increase pre cooled heat exchangers to reduce system energy consumption,and a joint simulation was conducted using MATLAB and HYSYS to analyze and compare the total energy consumption and energy loss before and after optimization. |
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