Optimized analysis of compressed air energy storage and its application in low temperature waste heat

Energy storage is particularly important as the demand for smart grids and new energy storage increases. The energy storage is mainly divided into two types: chemical energy storage and nuclear physical energy storage. At this stage, chemical battery energy storage and pumped storage are dominant in various energy storage, but due to their own and environmental constraints, development is greatly affected. . For the rest of the energy storage, only the compressed air storage has a higher maturity.

The compressed air storage energy is operability, the storage capacity is huge, the environment is environmentally friendly, and it is not restricted by the terrain. The medium is safe and easy to obtain, which is one of the most potential energy storage methods.

1 Compressed air energy storage process optimization analysis Compressed air energy storage based on the principle of absorption and release of energy when compressing and expanding air medium, using the corresponding equipment to transform and store energy, the whole process is a thermodynamic process. The whole process of compressed air storage is not unique, and the energy storage efficiency of different cycle processes is very different. The compressed air storage process is optimized from a thermodynamic process.

A1e4 cycle: including al isothermal compression process, 1e isobaric expansion process, e4 isothermal expansion process; a3ef cycle: a3 adiabatic compression process, 3e isobaric expansion process, ef adiabatic expansion process; abcdef cycle: ab adiabatic compression, bc isobaric Cooling, cd secondary adiabatic compression, de isothermal heating expansion process, ef is adiabatic expansion process; temperature e4 is isothermal expansion, 45 is adiabatic expansion.

The compressed energy storage process obtains the same amount of energy as the area enveloped by the curve. Among them, a1e4 cycle stores the most energy. The analysis shows that the isothermal compression in the compression stage is the most efficient, but the compression in practical applications keeps the constant temperature impossible. Therefore, multi-stage adiabatic compression plus isostatic cooling method is used to approach isothermal compression. In practice, two to three stages are selected for air compression. While 1e is an isostatic expansion, it can make full use of other heat sources to impart energy to the compressed air and increase the initial energy of expansion. In the expansion work phase, it is known that the isothermal expansion obtains the highest energy, so that the existing waste heat can be fully utilized to ensure that the expansion approximates the isothermal expansion. According to the comprehensive analysis, the compressed air energy storage flow uses isothermal and similar isothermal compression expansion as the means of storage and work. In the process, low-grade heat energy is used as much as possible to obtain the maximum energy storage efficiency.

According to the above theoretical analysis, the optimal compressed air energy storage process is isothermal compression and isothermal expansion, so the optimal process is abcde45: ab, cd adiabatic compression, bc equal pressure drop de isostatic pressure e4 isothermal expansion, 45 adiabatic expansion .

2 Application of compressed air energy storage in ultra-low temperature waste heat At present, China's energy utilization rate is not high. The total waste heat resources of various industries account for about 17% to 67% of the total fuel consumption. The waste heat resources that can be recycled are about waste heat. 60% of the total resources. The low temperature heat source with a temperature of about 200C accounts for a large proportion. The waste heat utilization system used at this stage, the mainstream technology is the third generation waste heat utilization system, mainly for the utilization of 180500C high temperature and 330380C medium temperature waste heat. For the ultra-low temperature waste heat resource of about 200C, the utilization efficiency will be greatly reduced. Compressed air for better heat utilization will achieve better results.

The optimal process abcde45 for compressed air storage is the thermodynamic cycle of waste heat utilization. The rest of the heat is mainly concentrated in the isostatic heating stage before expansion. At this time, the compressed air is in the high pressure and low temperature state, and the heat is transferred by the heat transfer. The air makes the initial energy of the expansion of the compressed air higher, thereby increasing the amount of power generation to achieve the purpose of utilizing the waste heat resources. The efficiency is calculated as follows: n = W adiabatic + W isobaric + WQ n heat - heat utilization efficiency; W - adiabatic expansion released work, W isobaric isostatic expansion released work, W compression multi-stage compression consumed work Q, i is the heat absorbed from the outside of the system during the isostatic expansion stage, assuming that the highest pressure reached by compression starts from atmospheric pressure until 3Mpa. It is known from the public that for 200C low temperature waste heat, the heat utilization efficiency is not the higher the final pressure. Well, the trend is to increase and then decrease, so a certain residual heat temperature has a reasonable maximum expansion pressure point, so it needs to be continuously optimized. Medium 200C low-grade heat source, the utilization rate of thermal energy is up to 453%, which is very high compared with the current 13%~25% waste heat utilization rate. In addition, the air compression technology has also been greatly developed, the US SustahX The company has successfully solved the problem of isothermal compression, and the efficiency of compression and expansion will be greatly improved.

The energy storage efficiency of compressed air energy storage varies with heat utilization. Therefore, in the process of energy storage, it is necessary not only to start from the aspects of equipment manufacturing, but also to consider the optimization of its cycle process.

Compressed air energy storage can be innovatively combined with waste heat utilization, using its dielectric properties and energy storage principle to capture lower quality waste heat resources and improve waste heat utilization.

Xu Yujie and so on. Analysis of characteristics of integrated air-energy storage and power generation systems with complementary wind and light M. China Electrical Engineering Journal, 2012. Wu Guofang, Lu Lei. Thermal efficiency and exergy efficiency of a pure low temperature waste heat power generation system. New Century Cement Guide

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