Thermal Economic Analysis of Compressed Air Storage System

+ Thermodynamic Analysis of Thermal Cycle + Compressed Air Energy Storage System Lu Yuanwei, Liu Guanglin, Ma Chongfang, Lu Pengfei (Department of Heat Transfer Enhancement and Process Energy Conservation of the School of Environmental and Energy Engineering, Beijing University of Technology. The principle is: in the electricity valley, After being compressed in two stages, the air is stored in the air storage chamber at normal temperature, and the electric energy is converted into air compression energy storage. In this process, the heat released by air cooling is discharged into the atmosphere; when the electricity peaks, the air is first passed through the heat recovery heat exchanger. After the waste heat of the gas turbine exhaust gas is heated, it enters the steam turbine (AT) to do work, and then mixes with the natural gas in the combustion chamber to enter the gas turbine (GT) for work, and turns into a cycle. The supercritical compressed air energy storage system studied in this paper adopts the mode proposed by 5, considering To the system working parameters, the energy storage system uses two-stage compression and intermediate cooling to reduce the compression work of the system. The expander adopts two-stage expansion to work, as shown in the figure. The working principle of the system is: when the electricity is low Low-cost electric energy is used for compressed air for energy storage. The air is first compressed by a low-pressure compressor (LP) and then stored at a high temperature. After heat exchange and heat storage in the device (HS1), it enters the high pressure compressor (HP) for compression, and then enters the high and low temperature heat storage heat exchangers (HS1, HS2) for heat exchange and energy storage. Finally, the throttling valve is throttled to cool down. The liquid storage tank stores air in a liquid form; at the peak of power consumption, the air is pressurized by the working medium pump P, and then enters the low-temperature and high-temperature heat storage heat exchanger for heating, and then enters the high-pressure steam turbine (HT) to expand work and then passes through the high temperature. The heat storage heat exchanger heats up. Finally, it enters the low pressure expander (LT) to work. It is a cyclic process.

The biggest difference between supercritical compressed air energy storage system and CAES is that the storage medium of supercritical compressed air energy storage system is atmospheric pressure low temperature liquid air stored in low temperature irrigation, which solves the problem that CAES system working medium is stored in normal temperature and high pressure state. The special geographical conditions of the space are limited, and the gas turbine is not required to be set. The system process is relatively simple, which greatly reduces the initial investment of the system. Secondly, the natural gas combustion exothermic work process of the CAES system is the core of the whole system, and supercritical compression. The air storage system does not have this process. The heat required for the working fluid to expand and work in the system comes from the heat stored in the heat accumulator during the compressed air storage process. It can also use other waste heat or solar energy to increase the energy. The use of energy.

The system is divided into different subsystems, as shown in the dashed box.

The circled circle number is the number of the subsystem, the number pipe number is the number of the physical fire flow of the subsystem, and the arrow is the flow direction of the working fluid.

2 Thermal Economics Matrix Analysis 2.1 Thermal Economics Thermal economics (tobacco economics) is an analytical method that combines thermodynamic analysis with economic factors, that is, considering the physical and economic environment of the system. The basic idea is to use the material, energy and cash that interact within the system and the system as the flow, and build a relationship of mass balance, energy balance and cash balance, so as to obtain information about the evaluation system. The models of thermoeconomic analysis mainly include accounting model, optimization model, structural system model and symbolic smoke economic model. The symbolic smoke economic model is also called the matrix model. It is based on the efficiency defined by the second law of thermodynamics. The unit price of smoke reflects the loss inside the system and the cost of obtaining the unit product smoke. It is the thermal economics of the former several models. New achievements. This study uses the matrix model to analyze the economics of the system.

2.2 Main parameters of the system Table 1 GT10B parameters Numerical rated electrical efficiency /%34.2 Fuel type Natural gas (q=37680k/m3) Net power P/MW23.4 Pressure ratio 14:1 Exhaust temperature / K816 exhaust flow / kg.s180.4 The air temperature and pressure (t=27°C, =0.1MPa) are used as the reference point. The air mass flow rate in CAES is 78.8kg/s, and the mass flow rate of natural gas is 1.6kg/s. The efficiency of the two-stage compressor is 85%, the compression ratio is 8; the efficiency of steam turbine (AT) is 80%, the expansion ratio is 4.5. The working parameters of the gas storage chamber are P=6.4MPa and t=32C. The supercritical compressed air energy storage system takes the working medium. The mass flow rate is 1kg/s, and the working fluid pump efficiency is 0.75. The working medium is stored in the liquid storage tank in the liquid state after the throttle valve = 6.4 MPa and temperature t C, respectively, and the pressure and temperature are respectively For MPa, t=-194.5C. The resistance loss of the pipe network of the system is 0.1 MPa, and the outlet pressure of the working fluid pump is 6.3 MPa. The supercritical compressed air system compressor and air expansion efficiency are 85% and 80%, The pressure ratio is 8 and 7.9 respectively. The heat transfer temperature difference of the heat exchanger is 6C. CAES is simulated by the model GT10B gas turbine. The specific parameters are shown in Table 1.

2.3 Establishment of Mathematical Model The relationship between each turbulence and subsystem can be represented by the event matrix AiX, where i represents the number of subsystems in the system and represents the number of smoke streams in the system. For the CAES system, the number of subsystems is i = 6, and the number of smoke streams is = 14. If the element 0 in the matrix indicates that the first stream is not related to the subsystem i, if the element in the matrix = 1 indicates the inflow of the first stream Subsystem i, if an element in the matrix. =%1 indicates the first stream of the outflow subsystem i. The calculation results are analyzed. For the specific calculation, refer to 9. The matrix A is expressed as: since each subsystem can only establish one cash balance equation, it can list 6 cash. The equation, and the number of cash flow of the demand solution is 14, so that the system calculation results need to be supplemented with -i, that is, eight equations, and the equation complements the principle of 08: (1) the unit cost from the external input system turbulence According to the market price, 2) for the multi-product output subsystem, according to the principle that the smoke cost of each product unit is equal; (3) if the “fuel” of the subsystem is a double-line flow, the two turbulent unit fires that constitute the double-line flow The cost is equal to 4) If the smoke flow is an internal product, it is calculated on the principle that the unit price is equal.

According to the above principle, the supplementary equation required for solving is established, that is, according to principle (1), in the subsystems 1, 2 and 6 in the system, the unit smoke flow cost of the input subsystem is calculated according to the market price, and the subsystem is 1 For example, the supplementary equation is: according to principle (2), two supplementary equations are established for the principle of equal product unit price of subsystems 4 and 5 of multi-products, and the supplementary system of subsystem No. 4 can be established in the research system. The equation is: according to principle (3), the “fuel” of the subsystem is a two-line flow, and the unit price of the input and output subsystems is equal. Three equations can be established in the research system, considering the intercooler and post-cooling. The function of the device is not divided into subsystems, but the unit price of the smoke flow of the input and output coolers is equal, and the two equations and subsystem 3 can be added to establish a supplementary equation: there is no internal product in the research system, according to the above 3 The principle can establish the 8 equations required. The natural gas price is 2 yuan / m3, the output price of the supercritical compressed air energy storage system is 0.475 SkW-h), which is lower than the CAES system output price 0.531SKkW.h), and both are lower than the peak and valley electricity price of 0.753 yuan / ( kWh), indicating that the supercritical compressed air storage system is more economical.

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