Study On Optimization Design And Peak-shaving Characteristics Of The Solar-aided Combined Heat And Power System

Under the vision of "Carbon peak and carbon neutrality",it has become inevitable to vigorously develop renewable energy and promote the construction of an energy supply system dominated by clean and low-carbon energy sources.In Northern China,coal-fired combined heat and power(CHP)units are widely used to solve the problem of large area central heating due to their high energy utilization efficiency.However,during the heating season,the electrical output of CHP units operating in heat-controlled operation mode is restricted by heat load,and the CHP unit flexibility is decreased.It restricts the further development of renewable power e.g.,photovoltaic and wind power.Introducing solar energy into the CHP unit not only reduces coal consumption,but also improves the flexibility of the CHP unit.The solar-aided combined heat and power(SA-CHP)system is researched in this thesis.The thermal characteristics,peak-shaving performances,and operating characteristics are analyzed.And the collaborative optimization of capacity and operation strategy is also studied.The main research contents and conclusions are summarized as follows.Firstly,based on the modular modeling method,the static simulation model of the SA-CHP system is built,including sub-models of the solar field,thermal energy storage(TES)system,boiler,steam turbine,and other key equipment.The model can be applied to simulate the thermodynamic performances of the SA-CHP system.Considering that the SA-CHP system has two kinds of energy inputs and two energy products,solar fractions to the electrical and thermal outputs of the SA-CHP system are evaluated by the solar contribution evaluation method,which is based on the exergy balance.The solar and coal exergy distributions and exergy destruction distributions of SA-CHP systems with typical integration schemes and operation modes are obtained and analyzed.In order to increase the calculation speed of solar fractions,according to the exergy analysis results,a new solar fraction calculation method,considering the differences of solar fraction between the high-pressure cylinder and medium-pressure cylinder,is proposed.Secondly,the influences of the proportion of introducing solar energy to replace the high-pressure extraction steam and to directly supply heat on the feasible operation region and peak-shaving capacity are studied.The feasible operation region of the CHP unit introducing solar energy is obtained.The result shows that introducing solar heat to directly supply heat has more benefits in improving the peak down-regulation ability of CHP units while replacing the high-pressure extraction steam with the solar heat has more benefits in improving the peak up-regulation ability of CHP units.For a 330 MWe CHP unit,under the rated heating power condition,compared with the original CHP unit,through flexibly adjusting the proportion of introducing solar energy to replace the high-pressure extraction steam,the peak regulation range of the SA-CHP system is increased from 179.3 MWe～292.8 MWe to 116.3 MWe～344.2 MWe.In addition,both the peak-shaving,capacity and primary energy utilization ratio of CHP units using integrated solar energy heat-power decoupling method and two conventional heat-power decoupling methods integrating the electric boiler and the heat storage tank are compared.The results show that in terms of improving peak-shaving ability,the sequences from largest to smallest are integrated with the-electric boiler,solar energy or the heat storage tank,respectively.In terms of primary energy utilization ratio,the sequences from largest to smallest are integrated with the heat storage tank,solar energy or the electric boiler,respectively.Thirdly,to maximize the wind power consumption,an operation strategy of the SACHP system is proposed.Based on this operation strategy,the daily and annual performances of the SA-CHP system cooperating with a wind farm are simulated and analyzed.Results show that,compared to the reference system,curtailed wind power and standard coal consumption of the SA-CHP system are reduced by 202.69 MWh(93.34%)and 80.83 t(4.11%)on the heating season typical day.And the standard coal consumption of the SA-CHP system is reduced by 98.59 t(6.77%)on the non-heating season typical day.Based on annual performance simulation,the key equipment capacity of the SA-CHP system is optimized based on the enumeration method for maximizing the net annual revenue.The optimized result indicates that when the thermal energy storage capacity and the solar field size are 2 h and 21.48×104 m2(152 Loops),respectively,the SA-CHP system has the highest net annual revenue of 1.83 M$.Finally,to include wind power capacity to decision variables of capacity optimization,in this paper,a multi-source(i.e.,wind,solar and coal)complementary cogeneration(MCC)system with a 330 MWe SA-CHP subystem as the core is constructed.A bi-level capacityoperation collaborative optimization method is proposed to simultaneously optimize capacity configuration and annual load dispatch of the MCC system.The optimized result shows that the thermal energy storage capacity,solar field size,and wind farm capacity of the best compromise solution are 4 h,28.68×104 m2,and 84 MWe,respectively.The corresponding CO2 emissions and net present value are 167.14×104 t/y and 142.41 M$,respectively.Compared to the optimization method with a fixed operation strategy,the optimal MCC system optimized by the collaborative optimization method can obtain higher wind power output,higher net present value,and lower CO2 emissions.Besides,based on the best compromise solution,the effects of capacity parameters on economic performance,environmental performance,and wind power consumption of the MCC system are analyzed.