| With the overuse of fossil fuel,the climatic and environmental problems have become increasingly serious,so it is imperative to adjust the energy structure.Gradually reducing the proportion of coal-fired power plants and substantially increasing the proportion of renewable energy based on wind and light have become the main development direction of future power system.Due to the randomness,intermittency and volatility of renewable energy,it has become a hot research focus on finding a low-cost peak shaving method.With this background,power energy storage technology has attracted more and more attention because of its time-sharing storage/release characteristics.Compressed air energy storage technology is one of the large-scale power energy storage technologies that can be commercialized in the future.It has the characteristics of large system capacity,low operation cost,long service life and less constraints on construction site selection.which leads to its good application prospects.On the basis of introducing the technology status of compressed air energy storage,the concept of hydraulic compressed air energy storage system is established by controlling the flow of liquid to obtain compressed gas.There are four subsystems:isothermal compression,virtual pumped storage,adaptive hydraulic potential energy transfer device and constant pressure gas storage.During the operation,the temperature of the gas is almost constant.And this system has the characteristics of hydraulic turbine generation with the fixed water head,multi-area matching of hydraulic piston and efficient gas transmission and storage.The principle analysis,system design and operation strategy of each subsystem are studied in this paper,and the experimental model of the hydraulic compressed air energy storage system is built.Finally,the design scheme and operation strategy of the system are verified by physical experiments using PLC control.The main research contents are as follows:(1)The thermodynamic process in the operation of the hydraulic compressed air energy storage system is studied.The work processes of different gas-liquid and the calculation methods of its corresponding losses are compared through theoretical derivation.Based on the control of gas temperature,the hydraulic compressed energy storage technology realizes the approximate isothermal process of the gas-liquid work.By choosing the work path of the multi-variable process,the efficient operation scheme of the hydraulic compressed air energy storage system based on the Carnot cycle under multi-heat source conditions is proposed.The system runs in the Carnot cycle,the gas is compressed isothermally under the low temperature heat source and expanded isothermally under the high temperature heat source,so the overall power generation efficiency of this system has been improved.(2)The highly efficient temperature control technology in the process of gas-liquid work is studied.By comparing the applicable conditions of three basic heat transfer modes,including heat conduction,heat radiation and heat convection,the convective heat transfer with higher heat transfer efficiency under the condition of direct contact between two-phase fluid is chosen as the system scheme.Besides,combining with the mass transfer principle of packed tower in chemical industry,the hydraulic compression technology based on forced gas-liquid circulation is proposed.In this technology,packed material are used to improve the heat transfer area and to a forced gas-liquid external circulation is added to enhance the two-phase flow.So the approximate isothermal process is realized.In view of the performance redundancy of high-pressure vessels in the design of pressure vessels,a hierarchical relay compression scheme is proposed,which enables the gas to enter pressure vessels with different pressure grades in turn with the change of gas pressure,the construction cost is reduced by limiting the compression ratio of each grade to reduce the volume of high-pressure vessels.Each pressure vessel is alternately connected with the other vessel of both sides during operation,so the gas work and migration process are carried out simultaneously which realizes the uninterrupted operation of compression/expansion process.So as to improve the utilization efficiency of hydraulic equipment.Finally,the feasibility of the proposed scheme is verified by simulation calculation.(3)The virtual pumping technology is studied.By controlling the gas pressure and liquid circulation flow in the pressure vessels,the concept of virtual water head and virtual water volume is introduced,and the virtual pumping method of hydraulic compressed air energy storage system is put forward,which can make hydraulic equipment run efficiently under the cooperation with pressure vessels without terrain restriction.The load regulation strategy of the hydraulic controlled compressed air energy storage system in power generation mode and energy storage mode is proposed,so the operation efficiency of hydraulic equipment keeps high when the system power changes.By adjusting the speed and head of hydraulic unit simultaneously,the operation efficiency of the hydraulic unit is improved.Finally,the feasibility of the proposed scheme is verified by simulation calculation.(4)Hydraulic transformer is used to realize high-efficiency potential energy transfer and constant-pressure network is construct to improve the operation efficiency of hydraulic equipment.A group of multi-stage hydraulic cylinders with equal sequence piston area is used to replace a group of single-stage hydraulic cylinders with fixed piston area.On this basis,a high-efficiency hydraulic potential energy transfer strategy based on constant-pressure network and hydraulic transformer is proposed.At the same time,the number of hydraulic cylinders is reduced as much as possible,so the cost of construction and maintenance is saved.Both hydraulic equipment and hydraulic equipment are connected to the constant pressure network to regulate the flow rate of the constant pressure network,which can reduce the idling loss of hydraulic equipment caused by the change of direction of hydraulic equipment when they are directly connected,so the operation efficiency of hydraulic equipment is effectively improved.Finally,the feasibility of the proposed scheme is verified by simulation calculation.(5)According to the requirement of experiment,a physical experimental platform with 10 kW power transmission and 1.6MPa pressure level is designed and built.The design of system control programming based on Schneider M218 PLC is studied.The control schemes are provided for each link of the hydraulic compressed air energy storage system and the overall operation schemes.Finally,the correctness of the design scheme and operation strategy of each part of the hydraulic compressed air energy storage system proposed in this paper is verified by the operation of the physical system. |
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