Study On Heat Storage And Release Characteristics Of Heat Storage Tank And Matching On Capacity And Peak-load Regulation Ability Of Combined Heat And Power Units

At this stage,central heating has become the main heating method in China's cities and towns.Combined heat and power units account for a large proportion in the heating industry.The rapid development of central heating has led to a rapid increase in the central heating and heating load,which requires the unit to increase the heating load.On the other hand,the generators require deep peak-load regulation and absorption of renewable energy for power generation,which will result in a decrease in the heating load provided by the system.Therefore,how to solve the contradiction problem of heat supply and demand has become the key to the thermoelectric unit.The heat storage technology can store the excess heat of the system during the low period,and then release it during the peak period,which can effectively meet the user's heat demand.It can adjust the system heat supply according to the fluctuation of the external heating load.At the same time,adding heat storage technology to the system can also improve the peak-load regulation ability of the system and provide a basis for the utilization of other renewable energy sources,such as solar energy and wind energy.In addition,heat storage technology can replace the peak heat source,to reduce the start and stop frequency of unit,which can effectively reduce the primary energy consumption and protect the ecological environment.This paper mainly uses numerical simulation and theoretical calculation to study the heat storage and release performance of heat storage tanks,the influencing factors and their influence on the peak-load regulation of the unit,and lay the foundation for the wide application of heat storage tanks.In this paper,the actual heat storage tank in a power plant is taken as the research object.The Gambit software is used to geometrically model and mesh the heat storage tank,and the independence and reliability of grid verification are verified.The variation of thermocline during the heat storage and release process is studied.When the heat storage is performed,the thermocline will gradually move down until all the water is discharged through the lower water distributor.It indicates that the heat storage process is over.When the heat release is performed,the thermocline gradually moves up until it flows out through the upper water distributor.As the heat storage and release time increases,the thickness of the thermocline also becomes thicker due to the increase in the mixing time of the hot and cold water.At the same time,the influence of various factors on the thermocline of the heat storage tank is studied:increasing the aspect ratio of the tank,will increase the thickness of the thermocline,but the volume occupied by the thermocline will decrease due to the reduction of the cross-sectional area.Therefore,the actual available heat of the tank is increased.Increasing the water supply temperature and the water supply flow,will reduce the thickness of the thermocline in the tank,to increase the actual available heat in the tank.Increasing the diameter and number of the openings of the water distributor,will accelerate the formation of the thermocline and reduce the thickness.The thickness of the thermocline formed by different types of water distributors is different,and the thickness of the ramp layer is ordered as:octagonal<split<straight.Secondly,the variation of the velocity field in the heat storage tank is studied by numerical simulation.As the inlet distance increases,the flow uniformity gradually becomes better due to the influence of the resistance.In addition.since the opening portion of the split type water distributor is relatively dense,the maximum flow velocity is mainly distributed in the middle portion,and this portion is the most uniform.At the same time,the effects of various factors on the performance of the heat storage tank are studied,including the aspect ratio,the temperature and flow of water supply,and the diameter,number and type of the openings of the water distributor.Studies have shown that increasing the aspect ratio of the tank,the uniformity of water flow in the tank will be better,but the heat storage time will increase,which will reduce the heat storage efficiency.The change of the water supply temperature will have little effect on the flow uniformity of the water flow in the tank.But the heat storage capacity,time and efficiency will be increased with the increasing of water supply temperature.The flow uniformity in the tank will be decreased with the increasing of water supply flow,but the heat storage time will be decreased while the efficiency will be increased.The increasing of diameter and number of the water distributor openings,will improve the flow uniformity and efficiency,but the heat storage time will be decreased.In terms of the type of water distributor,the uniform flow and efficiency order are:octagonal>split>straight.But the manufacturing and use of the split type water distributor is convenient.In practical applications,the tank aspect ratio,water supply temperature,flow,and the specific structure of the water distributor should be selected in accordance with engineering requirements.Finally,mathematical models of the instantaneous and daily peak-load regulation ability of the unit before and after heat storage are established,and the affecting factors are found.For the operating conditions and actual heating load requirements of different units in China,the operating conditions of the heat storage tank are obtained.The relationship between the daily peak-load regulation capacity of different units and the capacity of the heat storage tank is obtained.The research shows that the daily peak-load regulation capacity of the unit increases with the increasing of the capacity of the heat storage tank,and finally reaches the maximum daily peak-load regulation capacity.The calculation shows that the maximum daily peak-load regulation capacity after heat storage can account for 57.37%of the unit rated capacity,which is 1.77 times of the peak-load regulation capacity before heat storage.By calculating the instantaneous peak-load regulation of different units before and after heat storage in our country,it is found that the instantaneous peak-load regulation after heat storage is significantly higher than that before heat storage.The maximum instantaneous peak-load regulation after heat storage would increase with the increasing of unit capacity.At the same time,the relationship between the maximum instantaneous peaking capacity of different units and the heat release per unit time of the heat storage tank is obtained.The calculation shows that the instantaneous peak-load regulation capacity of the unit after heat storage can account for 40.0%of the unit rated capacity.In the actual project,the capacity of the heat storage tank can be selected by the daily peak-load regulation capacity.The heat release per unit time of the heat storage tank can be selected by the instantaneous peak-load regulation capacity,to provide the basis for the off-design operation of regenerative tank.