| The China-Kazakhstan Crude Oil Pipeline is the first onshore transnational crude oil import pipeline in China,with a design import capacity of 20 million tons per year,which has five major characteristics of " multiple oil sources,long distance,large drop,pump to pump process,low throughput ".Up to now,it has supplied 146 million tons of crude oil to China,with annual throughput accounting for about 20% of China onshore crude oil imports,which plays a very important role of ensuring the balance of national energy supply and energy consumption,as well as the source security.There exist several main problems in pipeline actual production: the large drop pipeline sections produce the phenomenon of slack flow after crossing certain high points.A long-term low throughput operation makes the energy consumption in the system increase year by year.The main energy consuming oil pump unit lacks the scientific energy-saving monitoring evaluation and analysis system.The oil transportation task allocation and scheme formulation in the planning period are only based on experience.And the non-linear problems are caused by accident conditions.The steady-state water hammer hazard is difficult to avoid,which seriously affects the safe and economic operation of the pipeline.Therefore,it is necessary to carry out in-depth study on energy saving of operation and advanced protection strategy of water hammer in China-Kazakhstan Crude Oil Pipeline system.Aiming at the Atasu-Alashankou section(AA pipeline)of China-Kazakhstan Crude Oil Pipeline,on the basis of oil physical property test,the prediction models of density,specific heat capacity and viscosity are established.The thermal and hydraulic analysis models of the pipeline are corrected by correcting the total heat transfer coefficient and hydraulic friction coefficient respectively,which can meet the accuracy requirements of engineering application.Taking the phenomenon of slack flow caused by large fluctuation of pipeline in consideration,the critical pressure control method is proposed,that is to say,by controlling the pressure at the end of the pipe to be higher than the critical pressure caused by underflow,the phenomenon of underflow can be avoided when the pipe crosses the high point.In terms of this method,a control and calculation program for slack flow of China-Kazakhstan Crude Oil Pipeline is compiled and verified through SPS simulation software.The relative error is less than 0.3%.The program is integrated with the on-site SCADA and ESD control system to realize the automatic calculation and adjustment of the end pressure of the pipeline under the conditions of different throughput and different oil properties,so as to ensure the safe operation of the pipeline.The multi-level energy efficiency evaluation system of China-Kazakhstan Crude Oil Pipeline system is constructed,and the analytic hierarchy process is used to determine that the oil pumping station or pump unit should be the key unit of energy saving monitoring and technical transformation of the system.The measured data points of 16 pump units in four pumping stations along the China-Kazakhstan Crude Oil Pipeline are preliminarily screened and twice accurately eliminated,and the least square method and image translation method are used.According to GB/T 31453-2015 "Specification for Energy Saving Monitoring of Oilfield Production System" and other national or industrial standards,the test and calculation method of energy consumption index of pipeline oil pump unit is given,which can be used to evaluate the energy consumption level of pipeline system and continuously track the performance change of pump unit.A comprehensive evaluation method of multi-indexes energy saving monitoring is proposed,in which the entropy weight method is used to determine the weight of each index,and then the gray correlation method is used The method is used to determine the close degree between the pump unit state and the ideal state,so as to make a reasonable evaluation of the overall operation of the pump unit in the oil transportation system,in order to identify the weak unit equipment the weak unit equipment.The reason why the pump unit with the lower correlation degree ranking does not meet the requirements of the qualified limit value is analyzed,and the adaptive impeller cutting transformation and permanent magnet speed regulation technology are put forward,the energy saving effect of 8.1% and 7% of the pump efficiency can be enhanced respectively.Based on the idea of dynamic programming,taking the operation electricity charge as the objective function,combined with the actual operation situation of China-Kazakhstan Crude Oil Pipeline,considering the constraints of inlet pressure,outlet pressure,whole line hydraulic pressure and pump power,a mathematical model of pipeline system operation optimization is established.The multi-stage process is transformed into a series of single-stage problems,which are solved one by one by using the relationship between each stage.The steady-state optimization software of China-Kazakhstan Crude Oil Pipeline is developed by Visual Basic Language,which includes basic data information module,daily average throughput optimization module and monthly throughput optimization module.Daily average throughput optimization can generate the optimal pump start-up scheme and operation parameters under different months,different throughput and different ground temperature conditions,and compare the energy consumption and cost before and after the optimization of typical working conditions,which can save 41424 k Wh per day of electricity and 26900 yuan per day of electricity cost.The monthly throughput optimization module can give the optimal off load and off load days of the month,taking the monthly total throughput of 1 million tons as an example,compared with the daily average transmission,the monthly optimization can save 16500 yuan in electricity cost,and the economic benefit is obvious.The operation scheme of pump station,pipeline operation pressure and reaction time after the accident are comprehensively considered,the water hammer simulation conditions of China-Kazakhstan Crude Oil Pipeline are selected.The transient simulations of the water hammer process caused by 17 accident conditions,such as the power failure of the pumping station,the emergency closing of the ESD valve and the BVS isolation valve,are carried out by using the SPS simulation software,and the pressure of the whole pipeline from unsteady state to steady state is obtained.On the basis of numerical prediction of the specific location and experience time of water hammer wave arriving at the pipeline,the cancellation strategies of pressurization wave and decompression wave at different positions of the pipeline are formulated,and the step-by-step adjustment scheme and control logic of water hammer protection are formed.Aiming at the 14 possible restart processes triggered by the advanced protection logic of water hammer under the simulated conditions of China-Kazakhstan Crude Oil Pipeline,the numerical simulation is also carried out.The step-by-step adjustment scheme and control logic of water hammer protection under restart condition are proposed.The sequence of pump start-up and the pressure change of the whole line are strictly controlled according to this method,which can realize the safe operation of the whole production cycle after the water hammer control of the pipeline system.In this paper,the control method of critical pressure of slack flow with large drop,the comprehensive evaluation method of Entropy Weight-Grey Correlation energy saving monitoring for pump units,the modeling and solving method of dynamic programming optimization operation of long-distance crude oil pipeline in tight line pumping process,the step-by-step adjustment scheme and control logic of water hammer condition protection are proposed,which can provide theory and technology for pipeline enterprises to scientifically formulate transportation scheme,improve transportation efficiency and reduce operation risk support. |
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