Heat And Power Synergic Dispatch And Optimal Configuration Of Clean Heat Sources For District Energy System

With the rapid development of renewable energy in China(especially the wind power)and the urgency of promoting clean heating improvements,the conventional heat and power synergic dispatch is facing many new problems.Based on such backgrounds,the main research objectives of this thesis can be divided into: 1)improving the operating flexibility of existing combined heat and power(CHP)units by fully utilizing the heat storage capacities of district heating networks(DHN).Thus,the wind curtailments and operating costs can be reduced significantly.2)proposing a two-layer configuration optimization model of additional clean heating devices with specific conditions,including hourly available wind energy,time-of-use power prices,waste heat resources,and energy flow structures of district energy system(DES).It could provide theoretical support for the economic and efficient utilization of renewable energy in the district heating system(DHS).Generally,the thermodynamic processes of DHN can be regarded as a time series combination of many steady-state operating conditions.Based on the mass and energy conservation,and specific flow distribution of DHN,a steady-state thermal simulation model(with related matrices)and the analytic temperature expressions of all nodes have been proposed.In order to decouple the complex thermodynamic relationships between primary and secondary DHN and ensure the heating quality of all end users in the process of DHN’s short-time charging and discharging,the constant heat supply control system has been introduced into each substation.On this basis,two kinds of typical charging(discharging)processes of the primary network were analyzed,and the theoretical formula for calculating the comprehensive heat storage capacity of primary DHN with the constant flow regulation mode was proposed.As an important part of the DHS,primary DHN has a great potential to provide considerable short-term heat storage capacities for the DHS economic dispatch.Furthermore,the majority of extraction-condensing CHP units was released into the air,however,such condensing waste heat was an ideal low-temperature heat source for heat pumps.Based on the typical structure of DES in three-northern areas in China.In this thesis,a novel heat and power synergic dispatch model based on DHN free heat storage and waste heat recycling(using electric heat pump)was proposed.The corresponding complete mathematical description and calculation processes were also given.Theoretically,short-term heat storage from the primary DHN relaxed the constraint from an equation of heat balance into an inequation of supply temperatures,thus expanding the feasible region of the optimization problem in which the better operating schedules could be found with lower wind energy curtailments and primary energy consumption.In addition,regarding the hourly on-off status of each unit as the prior information,the proposed heat and power synergic dispatch can be simplified to a high-dimensional linear programming,which can be solved efficiently and quickly by the off-the-shelf optimization tool Linprog.In order to evaluate the effects of free heat storage from the existing primary DHN and waste heat recycling based on additional electric heat pumps quantitatively,multi-scenario case studies of the test DES have been simulated in this paper.The results based on four operating dispatch schemes,three daily wind power output modes,and five heat load levels show that: 1)Opposite variation mode of daily available wind power brings the maximum regulation pressure to the district power grid(DPG).The use of heat storage from pipes and recycle the free heat from existing primary DHN will cause 7% of the total wind curtailment rate.In contrast,using heat storage from pipes only will eliminate wind curtailment completely.2)Utilizing the heat storage capacity of pipes or recycling the residual heat from CHP can significantly reduce the wind curtailment rate.However,equipping electric heat pump to recycle the residual heat will have better effect.3)Making full use of the existing heat storage capacity of primary DHN can always achieve a better wind power integration,regardless of whether additional heat pumps are introduced into the DES.According to the combination of additional clean-heating devices(e.g.,electric boiler,heat pump,displacement storage accumulator,and charging/discharging pump),the clean-heating improvements of a typical DES can be divided into seven categories.In this thesis,maximizing the net benefits during a whole heating season is proposed as the optimization objective.Multi-scenario case studies of the test DES illustrated that: 1)Improvement scheme one has the largest economic potential in which two types of electric heating devices(electric boiler and heat pump)and heat storage equipment have been added.2)For different improvement schemes,the lower wind curtailment rates were not consistent with the larger net benefits during a whole heating season.However,improvement schemes which added the electric heat pump had larger net benefits.3)The optimal configuration of additional clean-heating devices was most sensitive to the change of their own economic parameters,and the increase of any economic parameters will lead to the lower net benefits of cleanheating improvements and higher wind power curtailment rates.In some regions where possess considerable waste heat resources and time-ofuse electricity price policy,conducting the clean-heating improvements(introducing waste heat recycling and storage equipment)on the basis of conventional DHS could bring consideration economic benefits.In this thesis,a two-layer optimization model was proposed,which was based on traditional economic dispatch model of DHS search for the optimal configurations of additional devices(i.e.,waste heat recycling equipment,electric heat pump,and low-temperature DSA)by using Genetic Algorithms(GAs)and Pattern Search.Case studies show that: 1)Compared with GAs,the computational efficiency and accuracy of Pattern Search was better.2)After introducing waste heat recycling devices with optimal configurations,the total heat supply from coal-fired and gas boilers reduced significantly,with the total operating cost of the test DHS decreased by 13.8%.3)The amount of waste heat resources had a great impact on the optimal configuration of the renovation project and the comprehensive income of the heating season.