Operating Strategy Study Of Coal-fired Generating Units With Molten Salt Heat Storage

In this paper,coal-fired generating units are coupled with heat storage devices,the structural parameters of the devices are optimized and the effects of the operating parameters on the characteristics of the heat charging processes and discharging processes are studied under the optimal structural parameters,and the peaking capacity and exergy of the coal-fired generating units coupled with heat storage devices are analyzed.Firstly,the regression equation of heat storage and structural parameters of heat storage device at a specific moment is fitted in a certain range based on regression orthogonal test,and the simulation results of regression test are highly accurate and meet the requirements of significance test and misfit test,and the heat storage of heat storage device can be predicted under any structural parameters.The optimal structural parameters obtained by solving the regression equation,which is that the radius of high-temperature steam pipe,fin thickness,and fin length is 12.823 mm,10 mm,and 20 mm respectively.On this basis,the effects of changing the operating parameters on the heat charging and discharging characteristics of the heat storage device are investigated.In the heat charging process,the increase of mass flow rate and the increase of inlet temperature can make the molten salt achieve faster melting,its complete melting time is shortened,and the outlet temperature,heat storage and heat storage rate are increased.With the increase of inlet temperature or mass flow rate,the melting performance is gradually slowed down,and the significant degree of influence of inlet temperature interval 5K on melting is less than the significant degree of influence of mass flow rate interval 0.03kg/s on melting.In addition,the efficiency of the exergy increases with the delay of time,and the phenomenon that the efficiency of the exergy increases with the increase of the mass flow rate only occurs at the early stage of melting and the late stage of melting,and the difference of the efficiency of the exergy between different flow rates is not significant in the rest of the time;while the increase of the inlet temperature leads to the decrease of the efficiency of the exergy,and the release of the exergy of the high temperature steam and the storage of the molten salt both increase with the increase of the inlet temperature.In the discharging process,the increase of mass flow rate and the decrease of inlet temperature can make the molten salt solidify faster,the complete solidification time is shortened,the outlet temperature is lowered,the discharging heat,the discharging rate,the molten salt release humidity and the low-temperature steam storage humidity are increased,and the increase of solidification performance gradually slows down with the increase of mass flow rate,while the increase of discharging performance gradually slows down with the decrease of inlet temperature,and the increase of discharging performance starts to increase after reaching the critical point.Finally,by coupling the thermal storage device with the coal-fired generating units and proposing four thermal charging schemes and two discharging schemes,the best operating strategy for coal-fired generating units equipped with thermal storage devices is as follows: in thermal storage operation,the best peaking performance scheme is to set the steam extraction point at the entrance of the high-pressure cylinder and the return point at the entrance of the low-pressure cylinder;in discharging operation,the best peaking performance scheme is to use the thermal storage device instead of the high-pressure heater;In the heat storage and discharging cycle operation,in order to make the coal-fired generating units coupled with heat storage devices both reduce power loss and add new peaking capacity to help the grid accommodate more renewable power,the steam extraction point is set at the inlet of the medium-pressure cylinder and the return point is set at the inlet of the low-pressure cylinder during heat storage operation,and the heat storage device is used instead of the high-pressure heater during discharging operation.