Research On Control Logic And Threshold Of Automatic Block Valves In Gas Pipelines

Most of block valves for gas pipelines have the function of automatic closing based on pressure reduction.The correct closing action depends on the control logic and threshold adopted by the valve.The operating threshold of block valves has an empirical value,the pressure reduction should not be less than 0.15 MPa/min for the period 120 seconds.However,the generality of this empirical value for all pipelines in all cases is doubtful.In order to improve the correct closing action rate of block valve,it is necessary to study the control logic of block valve and the corresponding threshold setting.SPS software is used to simulate the pipeline leakage condition dynamically.The method of simulating leakage based on SPS using BV valve is deduced.Secondary development of SPS based on VB.net has realized the function of batch simulation of leakage condition.Compressor start-stop,valve shut-off and more than 4000 kinds of leakage conditions is simulated.The influence of leakage caliber,location,diffusion time,operation pressure and pressure reduction rate algorithm on pressure reduction setting values is analyzed.The results show that the current empirical setting value of pressure reduction can only detect leakage conditions of more than half caliber,it is not suitable for Shanxi-Beijing Third Line.Different pipelines should set different threshold combinations according to their own conditions.According to the relationship between the calculated value of the pressure reduction at block valve and the influencing factors,the control logic of the block valve based on SCADA system and the basic principle of selecting the corresponding threshold value of the pressure reduction are determined,so as to improve the reliability of the action of block valve and the detection rate of the leakage condition.