Assessment Of Safety Protection Capability And Relief Load Management Of Pressure System Under Overpressure Conditions

Pressure is one of the most important operating parameters in petrochemical production.Pressure exists in pressure vessels,operating equipment,heat exchangers or piping systems,and then pressure equipment is formed.Pressure system is a production or storage system consisting of equipments with the same pressure level.It is very important to ensure the safe operation of pressure system.In the production process,overpressure ignition and explosion accidents often occur due to fire,man-made operation errors,all power failure and other conditions.The results of material leakage and device damage caused by ignition and explosion seriously endanger the safety of people's lives and property,and bring irreparable adverse effects on the environment.Therefore,when the pressure system is facing the possible risk of overpressure,it is helpful to prevent overpressure accidents by evaluating the overpressure safety protection capability of the equipment in the pressure system and managing the relief load.Based on the background of wax oil hydrotreating unit,this thesis deals with the whole process of pressure equipment from overpressure to discharge to treatment system,and divides it into three stages: upstream pressure system of wax oil hydrotreating plant area;middle pressure relief device,such as regular pressure relief valve and blasting disc;downstream pressure relief treatment system,including large pressure relief system.Gas Emission and Flare System.The pressure relief device in the middle reaches and the pressure relief processing system in the downstream are collectively called the pressure relief system.In this thesis,the pressure relief device is used as a link,and the pressure system is closely linked with the pressure relief system.By establishing a wax oil hydrotreating plant model with 15 pressure devices,considering the correlation of the upper,middle and lower stages,the safety assessment and load management are carried out from the overall point of view of pressure relief.The main work is as follows:(1)At the upstream pressure system level,when the pressure equipment is at risk of overpressure due to various accident conditions,and assuming that the protective layer(such as interlocking function)before the relief device fails,it is necessary to evaluate the safety protection capability of the pressure equipment to prevent the occurrence of accidents.In the wax oil hydrotreating unit,the cold and low pressure separator under the condition of artificial operation error is selected as the typical overpressure equipment,and the overpressure protection strategy is determined.The pressure channeling process between the cold and high pressure separator and the cold and low pressure separator is studied.A method for calculating the flow threshold of gas-liquid two-phase channeling pressure in cold-high pressure separator is proposed,and a flash and cavitation model is introduced to analyze the detailed characteristics of gas-liquid phase change during steady-state channeling pressure.According to API520 standard,the size of pressure relief valve on cold-low pressure separator is checked and the safety protection capability is evaluated.Finally,Aspen-Plus is used to simulate the channeling pressure process,and the simulation results and analysis are obtained.The results were consistent.(2)At the level of upstream pressure relief device,the influence of single relief device and multiple relief devices on downstream processing system is analyzed.Aiming at the situation of multiple pressure relief devices releasing at the same time,the concept of maximum load is introduced to determine its judgment mode;the artificial and event dynamic factors are analyzed,and the total discharge amount superposition algorithm of multiple pressure relief devices releasing at the same time is proposed;all combinations of pressure relief devices are listed,and the calculation and verification function of Aspen-Flarenet is used to carry out numerical simulation to determine the independence.Maximum load under working conditions,clear the priority order of pressure equipment that affects the maximum load,lay the foundation for the subsequent load management of the torch system.(3)At the level of downstream discharge treatment,further theoretical analysis is made on simultaneous pressure relief of multiple discharge devices.Based on the maximum load theory algorithm,the maximum independent load is determined,and Aspen-Flarenet is used to optimize the design of the torch system;the associated accident conditions are introduced,and by increasing the IPF safety instrumentation loop,the discharge capacity of torch exceeding the maximum load is managed around Mach number,back pressure and noise,and the best treatment method is found,which is used as the existing torch.The pressure relief system adds assistant decision-making means of safety interlocking device.