A heat storage structure and method for a combined heat and power central heating system

Abstract

A heat storage structure and method for a combined heat and power (CHP) centralized heating system, relating to a CHP centralized heating system, includes a primary heat exchange station connected to the CHP plant, a primary heating network, a secondary heat exchange station, a secondary heating network, and heat users. The primary side of the primary heat exchange station is connected to the steam pipeline and condensate recovery device of the CHP plant, and the secondary side of the primary heat exchange station is connected to the primary heating network; the primary side of the secondary heat exchange station is connected to the primary heating network; the heat users are connected to the secondary heating network; and a heat storage structure and method for a combined heat and power (CHP) centralized heating system is located L meters away from the primary heat exchange station. A primary heat storage return water valve is installed on the primary heating network. The heat storage method includes: when the temperature rise rate of the primary heating network supply water is greater than S, the opening of the primary heat storage return water valve is increased; when the temperature drop rate of the primary heating network supply water is greater than S, the opening of the primary heat storage return water valve is decreased; when the temperature rise rate or temperature drop rate of the primary heating network supply water is less than or equal to S, the primary heat storage return water valve remains unchanged. This invention has a small footprint and low investment, and can store or release heat as needed.

Description

Technical Field

[0001] This invention relates to centralized heating systems in cogeneration plants, and more particularly to a heat storage structure and method for a centralized heating system in a cogeneration plant. Background Technology

[0002] We know that centralized heating uses hot water or steam generated by a centralized heat source as the heat medium, and supplies heat to production, heating, and domestic users in a town or larger area through a heat network. Centralized heating has advantages such as high heat load, large heat source scale, high thermal efficiency, saving fuel and labor, and small land area. In 2021, the State Council issued the "Guiding Opinions on Accelerating the Establishment and Improvement of a Green, Low-Carbon, and Circular Economic System" (Guofa

[2021] No. 4), proposing to actively develop clean cogeneration centralized heating in county towns in northern regions and steadily promote biomass-coupled heating.

[0003] Combined heat and power (CHP) district heating is a major form of urban district heating, primarily aimed at energy conservation and is a recognized energy-saving and environmentally friendly technology. According to statistics from the Ministry of Housing and Urban-Rural Development, in 2021, CHP accounted for the majority of urban district heating in my country, representing approximately 67% of the total district heating volume.

[0004] The existing combined heat and power (CHP) centralized heating system includes a heat exchange station connected to the power plant, a primary heating network, a secondary heat exchange station, a secondary heating network, and heat users. The primary inlet of the heat exchanger in the heat exchange station is connected to the steam pipeline of the power plant, and the primary outlet is connected to the condensate recovery device. The secondary outlet and inlet of the heat exchanger in the heat exchange station are connected to the supply and return water pipelines of the primary heating network, respectively. Specifically, the secondary inlet of the heat exchanger in the heat exchange station is connected to the return water pipeline of the primary heating network via a variable frequency circulating pump, and the secondary outlet of the heat exchanger in the heat exchange station is connected to the supply water pipeline of the primary heating network. The primary-side inlet and outlet of the secondary heat exchange station are connected to the supply and return water pipes of the primary heating network via pipelines, respectively. The secondary-side outlet and inlet of the secondary heat exchange station are connected to the supply and return water pipes of the secondary heating network, respectively. The secondary-side inlet of the heat exchanger (within the station) is connected to the return water pipe of the secondary heating network via a variable frequency circulating pump. Heat users (indoor heat dissipation equipment) are connected to the supply and return water pipes of the secondary heating network. The primary and secondary heating networks are equipped with supply water temperature sensors, supply water pressure sensors, heat meters, return water temperature sensors, and return water pressure sensors, respectively. The temperature data collected by the supply and return water temperature sensors at each level of the heating network controls the water flow rate at each level, achieving a balance between heat supply and demand.

[0005] In recent years, large thermal power units have been gradually upgraded to implement combined heat and power (CHP) centralized heating. To improve thermal energy utilization efficiency and reduce cold source losses, generators are generally modified to operate under low-pressure cylinder cut-off, enabling them to operate in condensation mode during the non-heating season and under back pressure during the heating season. CHP centralized heating operates under two different modes: "heat-driven power generation" and "electricity-driven heat generation," which cannot simultaneously balance the supply and demand of heat and electricity loads in the heating network and the power grid.

[0006] The State Grid's dispatching operation time generally includes two peak periods, two valley periods, and two normal periods per day. For example: Peak periods: 6:00-11:00 and 18:00-23:00, totaling 10 hours; Valley periods: 1:00-6:00 and 13:00-18:00, totaling 10 hours; Normal periods: 11:00-13:00 and 23:00-1:00, totaling 4 hours. When the grid dispatching operation time is during the peak period, the generating units need to operate with increased power load, resulting in increased steam output and a greater heat supply. The heating system cannot absorb the peak-shaving heat on its own, and the heat is wasted by releasing it into the atmosphere. Thermal storage tanks are used for heat storage, but these require large volumes and numerous tanks, occupying a large area and requiring a huge investment. When the grid dispatching operation time is during the valley period, the generating units need to operate with reduced power load, resulting in decreased steam output and a smaller heat supply. This cannot meet the heat demand of the heating system, leading to insufficient heat source. Thermal storage electric boilers or natural gas boilers are needed to supplement the peak-shaving heat, which also requires a large investment. Summary of the Invention

[0007] The purpose of this invention is to overcome the shortcomings of the prior art and provide a heat storage structure and method for a combined heat and power centralized heating system that requires little floor space and investment and can store or release heat as needed.

[0008] The technical solution adopted by this invention to overcome the shortcomings of the prior art is as follows:

[0009] A heat storage structure for a combined heat and power (CHP) centralized heating system includes a primary heat exchange station connected to a power plant, a primary heating network, a secondary heat exchange station, a secondary heating network, and heat users. The primary inlet of the heat exchangers in the primary heat exchange station is connected to the steam pipeline of the power plant, and the primary outlet is connected to a condensate recovery device. The secondary inlet of the heat exchangers in the primary heat exchange station is connected to the return water pipeline of the primary heating network via a primary variable frequency circulating pump and a flow meter. The secondary outlet of the heat exchangers in the primary heat exchange station is connected to the supply water pipeline of the primary heating network. The primary inlet of the heat exchangers in the secondary heat exchange station... The outlet and return water are respectively connected to the supply and return water pipes of the primary heating network via pipelines. The secondary side outlet of the heat exchanger in the secondary heat exchange station is connected to the supply water pipe of the secondary heating network, and the secondary side inlet of the heat exchanger in the secondary heat exchange station is connected to the return water pipe of the secondary heating network via a secondary variable frequency circulating pump. Heat users (indoor heat dissipation equipment) are connected to the supply and return water pipes of the secondary heating network. The feature is that a primary heat storage return water valve is installed between the supply and return water pipes of the primary heating network at a distance of L meters from the first heat exchange station. The value range of L (m) is: V × H 峰 ×3600≤L≤V×(H 峰 +2 H p平 ) × 3600,

[0010] Among them, H 峰 (h) represents the duration of the peak power grid period, H p平 V represents the duration of the normal power grid period, and V (m / s) represents the flow velocity of the medium in the pipeline of the primary heating network.

[0011] The formula for calculating V (m / s) in this invention is: V = (0.354 × G) 计算 ×υ) / D 2 Among them, G 计算 (t / h) represents the calculated flow rate of the primary pipeline network, υ(m 3 / kg) is the specific volume of water in the pipeline; D (m) is the inner diameter of the return water pipeline of the primary heating network.

[0012] The G described in this invention 计算 The formula for calculating (t / h) is: G 计算 =(0.86×A×q) / (T1-T2) / 1000, where A(m 2 ) represents the heating area, q (W / m²) 2 T1 (°C) is the calculated heat consumption index, and T2 (°C) is the calculated supply water temperature of the primary heating network.

[0013] The present invention is further improved, and the formula for calculating V (m / s) is: V = (0.354 × G) 实际 ×υ) / D 2 G 实际This refers to the actual flow rate of the primary pipeline network during peak hours or the average actual flow rate of the primary pipeline network during peak and off-peak hours. Typically, G... 实际 Based on experience, it is set to 1.1 G. 计算 1.15 G 计算 1,2 G 计算 Or 1.3 G 计算 It has a better heat storage effect.

[0014] In this invention, pressure sensors and temperature sensors are installed on the primary and secondary pipes of the first heat exchange station and each secondary heat exchange station. Pressure sensors and temperature sensors are also installed on the water supply and return pipes of the primary heating network on both sides before and after the primary heat storage return water valve, for real-time monitoring of heating data at various points in the heating system.

[0015] The water supply pipeline of the primary heating network described in this invention includes a main water supply pipeline and a branch water supply pipeline, and the return water pipeline includes a main return water pipeline and a branch return water pipeline; the branch water supply pipeline and the branch return water pipeline are used for the connection between the primary side of the heat exchanger in the secondary heat exchange station and the main water supply pipeline and the main return water pipeline; the primary heat storage return water valve is installed between the main water supply pipeline and the main return water pipeline.

[0016] In a further improvement of this invention, the water supply pipeline of the primary heating network includes a main water supply pipeline and branch water supply pipelines, and the return water pipeline includes a main return water pipeline and branch return water pipelines. The primary side inlet and outlet of the heat exchangers in the secondary heat exchange stations are connected to the main water supply pipeline and main return water pipeline via branch water supply pipelines and branch return water pipelines, respectively. The primary heat storage return water valve is installed between the branch water supply pipelines and branch return water pipelines in the secondary heat exchange stations. A primary heat storage return water valve is also installed between the branch water supply pipelines and branch return water pipelines in n secondary heat exchange stations within a range of L meters from the primary heat exchange station. This structure can be constructed within the secondary heat exchange station, facilitating the installation and control of the primary heat storage return water valves. It is simple, easy to implement, and low in cost. When the peak flow rate changes are small, one or more primary heat storage return water valves can be controlled to open, resulting in high flow control accuracy.

[0017] The invention is further improved by installing a secondary heat storage return water valve at the rear of the water supply and return water pipes of the secondary heating network. The high-temperature water in the water supply pipe of the secondary heating network can flow back to the secondary side inlet of the heat exchanger in the secondary heat exchange station through the secondary heat storage return water valve and the return water pipe for secondary heat storage.

[0018] The above-mentioned heat storage method for a combined heat and power (CHP) centralized heating system is characterized by comprising the following steps:

[0019] Step 1: When the temperature rise rate of the primary heating network supply water is greater than S, control the opening of the primary heat storage return water valve to increase so that the temperature rise rate of the primary heating network supply water is less than or equal to S.

[0020] Step 2: When the temperature drop rate of the primary heating network supply water is greater than S, control the opening of the primary heat storage return water valve to be smaller, so that the temperature drop rate of the primary heating network supply water is less than or equal to S.

[0021] Step 3: When the temperature rise rate or temperature drop rate of the primary heating network supply water is detected to be ≤S, the primary heat storage return water valve remains in place.

[0022] During the adjustment process of the primary thermal storage return water valve, when three boundary conditions t3=t4 and ΔP are met... J =ΔP 最小 G1 运行 =G1 最大 Under any one of the following conditions, the primary heat storage return water valve reaches its maximum allowable opening.

[0023] Where: S is the maximum allowable rate of increase or decrease in the primary heating network water supply temperature at the secondary side outlet of the heat exchanger in the heat exchange station.

[0024] ΔP J The pressure difference between the primary supply and return water pipelines of the heat exchanger in the most unfavorable secondary heat exchange station is the value of the pressure difference.

[0025] ΔP 最小 This refers to the minimum available pressure difference between the primary supply and return water pipelines of the heat exchangers in a secondary heat exchange station.

[0026] G1 运行 The flow rate is the operating flow rate of the primary heating network, expressed in t / h, and is collected by a flow meter installed on the secondary side of the heat exchanger in the primary heat exchange station.

[0027] G1 最大 This represents the maximum flow rate of the primary heating network, expressed in t / h.

[0028] t3 (°C) is the return water temperature of the primary heating network after heat storage. It is the temperature at which the high-temperature water in the primary heating network supply pipe enters the primary heating network return water pipe and mixes after the primary heat storage return water valve is opened.

[0029] t4 is the safe boundary temperature of the return water pipeline.

[0030] In this invention, when the primary heat storage return water valve is installed between the supply branch pipe and the return branch pipe in the secondary heat exchange station, a primary heat storage return water valve is installed between the supply branch pipe and the return branch pipe in each of the n secondary heat exchange stations (each of the n secondary heat exchange stations) within a distance of L (m) from the primary heat exchange station (a total of n primary heat storage return water valves); in the heat storage method of the cogeneration centralized heating system, during the adjustment (opening degree increases or decreases) of the (n) primary heat storage return water valves, (the automatic control system can determine in real time) when the i-th primary heat storage return water valve satisfies the three boundary conditions t3=t4, ΔP iJ =ΔP 最小G i 1 运行 =G i 1 最大 Under any one of the following conditions, the i-th primary thermal storage return water valve reaches its maximum allowable opening (the opening cannot continue to increase, such as when t3 > t4, ΔP...). iJ <ΔP 最小 G i 1 运行 >G i 1 最大 At that time, the opening degree of the i-th primary heat storage return water valve needs to be reduced by 3%.

[0031] ΔP iJ The pressure difference between the primary supply and return water pipelines of the heat exchanger in the most unfavorable secondary heat exchange station is the value of the pressure difference.

[0032] ΔP 最小 This refers to the minimum available pressure difference between the primary supply and return water pipelines of the heat exchangers in a secondary heat exchange station.

[0033] G i 1 运行 The operating flow rate of the primary heating network is expressed in t / h.

[0034] G i 1 最大 This represents the maximum flow rate transmission capacity of the primary heating network, expressed in t / h.

[0035] t3 (°C) is the return water temperature of the primary heating network after heat storage. It is the temperature at which the high-temperature water in the primary heating network supply pipe enters the primary heating network return water pipe and mixes after the primary heat storage return water valve is opened.

[0036] t4 is the safe boundary temperature of the return water pipeline.

[0037] During operation, when the primary heat storage return water valve reaches its maximum allowable opening and the temperature rise rate of the primary heating network water supply exceeds S, the flow rate on the primary side of the heat exchange station is controlled.

[0038] In this invention, n primary heat storage return water valves can be controlled to open or close simultaneously, or they can be controlled to open or close sequentially. Preferably, when the temperature rise rate of the primary heating network supply water is >S, the first or first group of primary heat storage return water valves closest to the heat exchange station are opened first. When the first or first group of primary heat storage return water valves reaches the maximum allowable opening, and the temperature rise rate of the primary heating network supply water is >S, the second or second group of primary heat storage return water valves behind the first or first group of primary heat storage return water valves are opened. The primary heat storage return water valves are opened sequentially from closest to farthest from the heat exchange station. When the temperature drop rate of the primary heating network supply water is detected to be greater than S, the last or a group of primary heat storage return water valves that are furthest from the heat exchange station are controlled to close first. When the last or a group of primary heat storage return water valves are completely closed, and the temperature drop rate of the primary heating network supply water is greater than S, the first or a group of primary heat storage return water valves before the last or a group of primary heat storage return water valves are controlled to close. The primary heat storage return water valves are controlled to close sequentially from farthest to closest according to their distance from the heat exchange station.

[0039] This invention is further improved by the following: During peak hours, when the primary heat storage return water valve reaches its maximum allowable opening, if the temperature rise rate of the primary heating network supply water at the secondary side outlet of the heat exchanger in the heat exchange station is still greater than S, the secondary heat storage return water valve is opened. High-temperature water from the secondary heating network supply pipe enters the secondary heating network return water pipe to form high-temperature return water, thus achieving heat storage in the secondary heating network. As the flow rate in the secondary heating network gradually increases, the opening of the primary side electric regulating valve of the secondary heat exchange station is increased, and the primary side flow rate increases synchronously; the operating frequency of the secondary variable frequency circulating pump is also increased synchronously. During the frequency conversion process of the secondary variable frequency circulating pump, two boundary conditions are simultaneously satisfied: maintaining G2... 运行 ≤G2 最大 Maintain a constant pressure difference ΔP2 (m) at the inlet and outlet of the heat exchanger on the secondary side within the secondary station. During off-peak hours, when the temperature drop rate of the primary heating network supply water exceeds S, firstly, control the secondary heat storage return water valve to close, thereby reducing the flow rate within the secondary heating network. Simultaneously, the operating frequency of the secondary variable frequency circulating pump will decrease, maintaining a constant pressure difference ΔP2 (m) at the inlet and outlet of the heat exchanger on the secondary side within the secondary station. The high-temperature return water will flow to the secondary side inlet of the heat exchanger within the secondary heat exchange station, absorb a small amount of heat within the secondary heat exchange station, and then reach the predetermined temperature before entering the secondary heating network supply water pipeline to meet the user's heating needs. When all secondary heat storage return water valves are closed, and the temperature drop rate of the primary heating network supply water exceeds S, the primary heat storage return water valve will close.

[0040] ΔP2 is the pressure difference between the inlet and outlet of the heat exchanger on the secondary side in the secondary heat exchange station;

[0041] G2 运行 This refers to the operating flow rate of the secondary heating network.

[0042] G2 最大 This represents the maximum flow transmission capacity of the secondary heating network.

[0043] During the opening of the primary thermal storage return water valve, the flow rate within the primary heating network gradually increases. This increase is equal to the flow rate of the primary thermal storage return water valve, causing a gradual increase in the operating resistance loss of the primary heating network's supply and return water pipelines. Simultaneously, the operating frequency of the primary variable frequency circulating pump at the first station is gradually increased through the automatic control system. During the pump frequency conversion process, two boundary conditions are simultaneously satisfied: maintaining G1... 运行 ≤G1 最大 Maintain a constant pressure difference ΔP1 (m) at the inlet and outlet of the heat exchanger on the secondary side within the first heat exchange station.

[0044] ΔP1 is the pressure difference between the inlet and outlet of the heat exchanger on the secondary side within the heat exchange station.

[0045] G1 运行 This refers to the operating flow rate of the primary heating network.

[0046] G1 最大 This represents the maximum flow transmission capacity of the primary heating network.

[0047] The primary thermal storage return water valve can be synchronously controlled by the PLC controller (automatic control system). The thermal storage return water valve adjustment and control method adopts the time and opening ratio method. The automatic control system monitors various relevant operating parameters in real time, and through edge computing and fuzzy control, selects a 2-second time interval and a 3% valve opening principle (the automatic control program can modify the time and opening ratio) to control the opening of the connected electric regulating valve step by step.

[0048] The heat storage structure and method of the present invention can store excess heat generated during peak periods of power grid operation in the return water pipeline of the centralized heating system. When the heat generated during off-peak periods of power grid operation is insufficient, the heat stored in the return water pipeline of the centralized heating system can be promptly replenished to the supply water pipeline of the centralized heating system. Compared with the prior art, it has the advantages of simple structure, convenient operation, small footprint, and low investment. Attached Figure Description

[0049] Figure 1 This is a schematic diagram of the structure of Embodiment 1 of the present invention.

[0050] Figure 2 This is a schematic diagram of the structure of Embodiment 2 of the present invention.

[0051] Figure 3 This is a schematic diagram of the structure of Embodiment 1 of the present invention connected to a thermal power plant. Detailed Implementation

[0052] like Figure 1The heat storage structure of the combined heat and power (CHP) centralized heating system shown includes a heat exchange station 2 connected to the power plant, a primary heating network, a secondary heat exchange station 10, a secondary heating network, and heat users 12. The primary inlet of the heat exchanger in heat exchange station 2 is connected to the steam output pipeline 1 of the power plant, and the primary outlet is connected to a condensate recovery device, which can be a water tank or a storage pool. The secondary inlet of the heat exchanger in heat exchange station 2 is connected to the return water pipeline of the primary heating network via a primary variable frequency circulating pump 3 and a flow meter 6. The heat exchanger in heat exchange station 2... The secondary side outlet of the heat exchanger is connected to the water supply pipeline of the primary heating network; the primary side inlet and outlet of the heat exchanger in the secondary heat exchange station 10 are connected to the water supply pipeline and return pipeline of the primary heating network respectively via pipelines; the secondary side outlet of the heat exchanger in the secondary heat exchange station 10 is connected to the water supply pipeline of the secondary heating network; the secondary side inlet of the heat exchanger in the secondary heat exchange station 10 is connected to the return pipeline 11 of the secondary heating network via a secondary variable frequency circulating pump; the indoor heat dissipation equipment of the heat user 12 is connected to the water supply pipeline and return pipeline 11 of the secondary heating network. Pressure and temperature sensors are installed on the water supply pipes of the primary heating network upstream of the primary heat storage return water valve, and on the return water pipes. Pressure and temperature sensors are also installed on the water supply pipes and return water pipes of the primary heating network downstream of the primary heat storage return water valve. Pressure sensors 5 and temperature sensors 4 are installed on the primary and secondary side pipes of the heat exchange station 2 and each secondary heat exchange station. Specifically, pressure and temperature sensors are installed on the inlet water / gas pipes connecting the primary side of the heat exchange station to the steam output pipe 1 of the thermal power plant; pressure and temperature sensors are installed on the outlet water pipes connecting the primary side of the heat exchanger in heat exchange station 2 to the condensate recovery device; and pressure sensors are installed on the water supply pipes of the primary heating network on the secondary side of the heat exchanger in heat exchange station 2. Pressure sensors and temperature sensors are installed on the return water pipes of the primary heating network on the secondary side of the heat exchanger in the first heat exchange station 2, and on the pipes connecting the primary side of each secondary heat exchange station to the supply water pipe of the primary heating network, and on the pipes connecting the primary side of each secondary heat exchange station to the return water pipe of the primary heating network, and on the pipes connecting the secondary side of each secondary heat exchange station to the supply water pipe of the secondary heating network, and on the pipes connecting the secondary side of each secondary heat exchange station to the return water pipe of the secondary heating network. The pressure sensors and temperature sensors can be installed individually or as integrated remote monitoring instruments. The above structure is the same as the prior art and will not be described in detail. The feature of this invention is that a primary heat storage return water valve 8 is installed between the supply water pipe and the return water pipe of the primary heating network at a distance of L meters from the first heat exchange station; from Figure 1As can be seen from the diagram, the primary heating network's water supply pipelines include a main water supply pipeline 7 and branch water supply pipelines, and the return water pipelines include a main return water pipeline 9 and branch return water pipelines. The branch water supply pipelines and branch return water pipelines are used to connect the primary side of the heat exchangers in the secondary heat exchange station to the main water supply pipeline and the main return water pipeline. The primary heat storage return water valve 8 is installed between the main water supply pipeline and the main return water pipeline. L is the length of the main water supply pipeline or the main return water pipeline. The inlet and outlet of the primary heat storage return water valve 8 are connected to the main water supply pipeline 7 and the main return water pipeline 9 of the primary heating network, respectively. The unit of L is meters, and its value range is: V×H. 峰 ×3600≤L≤V×(H 峰 +2 H p平 )×3600, usually V×H is chosen 峰 ×3600≤L≤V×(H 峰 + H p平 ) × 3600; where, H 峰 (h) represents the duration of a peak period in the power grid, H p平 V is the duration of a normal period in the power grid, and V (m / s) is the flow velocity of the medium in the return water pipe of the primary heating network.

[0053] The formula for calculating V (m / s) is: V = (0.354 × G) 计算 ×υ) / D 2 ,

[0054] Among them, G 计算 (t / h), is the calculated flow rate of the primary pipeline network; υ(m 3 / kg), where D (m) is the specific volume of the water medium in the pipeline; D (m) is the inner diameter of the (return water) pipeline of the primary heating network. The G... 计算 The formula for calculating (t / h) is: G 计算 =(0.86×A×q) / (T1-T2) / 1000; where A (m 2 ) represents the heating area; q (W / m²) 2 T1 (°C) is the calculated heat consumption index; T2 (°C) is the calculated supply water temperature of the primary heating network; T2 (°C) is the calculated return water temperature of the primary heating network.

[0055] The preferred formula for calculating V (m / s) is: V = (0.354 × G 实际 ×υ) / D 2 G 实际 This refers to the actual flow rate of the primary pipeline network during peak hours and the average actual flow rate of the primary pipeline network during peak and off-peak hours. Typically, G... 实际 Based on experience, it is set to 1.1 G. 计算 1.15G 计算 1,2 G 计算 Or 1.3 G 计算It has a better heat storage effect.

[0056] The heat storage method of the combined heat and power (CHP) district heating system in this embodiment includes the following steps:

[0057] Step 1: When the temperature rise rate (the rate of temperature increase) of the primary heating network supply water temperature (usually monitored in real time by a temperature sensor installed on the pipe at the secondary side outlet of the heat exchanger in the first heat exchange station) is greater than S, the automatic control system controls the opening of the primary heat storage return water valve to increase, so that the temperature rise rate of the primary heating network supply water temperature is less than or equal to S; the high-temperature hot water in the supply water pipe of the primary heating network enters the return water pipe, stores heat to form high-temperature return water, and realizes heat storage in the primary heating network.

[0058] Step 2: When the temperature drop rate of the primary heating network supply water is greater than S, the automatic control system controls the opening of the primary heat storage return water valve to decrease, so that the temperature drop rate of the primary heating network supply water is less than or equal to S.

[0059] Step 3: When the temperature rise rate or temperature drop rate of the primary heating network supply water is detected to be ≤S, the primary heat storage return water valve remains unchanged in opening degree.

[0060] During the adjustment (opening degree increases or decreases) of the primary thermal storage return water valve, the automatic control system can determine in real time whether the three boundary conditions t3=t4 and ΔP are met. J =ΔP 最小 G1 运行 =G1 最大 Under any of the following conditions, the primary heat storage return water valve reaches its maximum allowable opening, and the opening cannot continue to increase, such as when t3 > t4 and ΔP... J <ΔP 最小 G1 运行 >G1 最大 At this time, the opening degree of the primary heat storage return water valve needs to be reduced by 10%;

[0061] Where: S is the maximum allowable rate of temperature rise and fall of the primary heating network water supply at the secondary side outlet of the heat exchanger in the first heat exchange station, in ℃ / h, generally taken as 4-6℃ / h.

[0062] ΔP J ΔP represents the pressure difference between the primary supply and return water pipelines of the heat exchanger at the most unfavorable point (the point furthest from the primary heat storage return water valve) within the secondary heat exchange station; J =P J 1-P J 2, P J 1 represents the primary side operating water supply pressure of the heat exchanger in the most unfavorable secondary heat exchange station, P. J2 represents the primary side operating return water pressure of the heat exchanger in the most unfavorable secondary heat exchange station; pressure sensors are installed at the primary side inlet and outlet of the heat exchanger in the most unfavorable secondary heat exchange station to collect the pressure.

[0063] ΔP 最小 This is the minimum available pressure difference value for the primary side supply and return water pipelines of the heat exchanger in the secondary heat exchange station; the unit is meters (m), and it is a set value, typically 8-12, preferably 10-11.

[0064] G1 运行 The flow rate of the primary heating network is measured in t / h and is obtained by installing a flow meter at the secondary side inlet of the heat exchanger in the primary heat exchange station.

[0065] G1 最大 This represents the maximum flow rate transport capacity of the primary heating network, expressed in t / h; it is obtained from the hydraulic calculations of the primary network.

[0066] t3 (°C) is the return water temperature of the primary heating network after heat storage. A temperature sensor is installed on the return water pipe before the primary heat storage return water valve to collect the temperature remotely. It is the temperature of the high-temperature water in the primary heating network supply pipe mixed in the primary heating network return water pipe after the primary heat storage return water valve is opened.

[0067] t4 is the safe boundary temperature of the return water pipeline at the installation location of the primary heat storage return water valve, i.e., the highest allowable temperature, in °C, and is generally taken as 70-80 °C.

[0068] like Figure 2The heat storage structure of the combined heat and power (CHP) centralized heating system shown includes a primary heat exchange station 2 connected to the power plant, a primary heating network, a secondary heat exchange station 10, a secondary heating network, and heat users 12. The primary inlet of the heat exchanger in the primary heat exchange station 2 is connected to the steam output pipeline 1 of the power plant, and the primary outlet is connected to a condensate recovery device, which is a water storage tank. The secondary inlet of the heat exchanger in the primary heat exchange station 2 is connected to the return water pipeline of the primary heating network via a primary variable frequency circulating pump 3 and a flow meter 6. The secondary outlet of the heat exchanger in the primary heat exchange station 2 is connected to the supply water pipeline of the primary heating network. The primary inlet and outlet of the heat exchanger in the secondary heat exchange station 10 are connected to the supply water pipeline and return water pipeline of the primary heating network, respectively, via pipelines. The secondary outlet of the heat exchanger in heat station 10 is connected to the water supply pipe of the secondary heating network, and the secondary inlet of the heat exchanger in secondary heat exchange station 10 is connected to the return water pipe 11 of the secondary heating network via a secondary variable frequency circulating pump; the indoor heat dissipation equipment of heat user 12 is connected to the water supply and return water pipes 11 of the secondary heating network; pressure sensors 5 and temperature sensors 4 are respectively installed on the primary and secondary pipes of the heat exchange head station 2 and each secondary heat exchange station; pressure sensors and temperature sensors are respectively installed on the water supply and return water pipes of the primary heating network on both sides before and after the primary heat storage return water valve. The pressure sensors and temperature sensors can be set separately or integrated into a remote monitoring instrument; the above structure is the same as the prior art and will not be described again. The feature of this invention is that a primary heat storage return water valve is installed between the water supply and return water pipes of the primary heating network at a distance of L meters from the heat exchange head station; from Figure 2 As can be seen from the diagram, the primary heating network's water supply pipelines include a main water supply pipeline 7 and a branch water supply pipeline 13, and the return water pipelines include a main return water pipeline 9 and a branch return water pipeline 14. The branch water supply pipeline 13 and the branch return water pipeline 14 are used to connect the primary side of the heat exchanger in the secondary heat exchange station to the main water supply pipeline and the main return water pipeline. The primary heat storage return water valve 15 is installed between the branch water supply pipeline 13 and the branch return water pipeline 14 before the secondary heat exchange station 10 (where water flows from front to back in the water supply pipeline). L is the sum of the lengths of the main water supply pipeline and the branch water supply pipeline, or the sum of the lengths of the main return water pipeline and the branch return water pipeline. The lengths of the water supply pipeline and the return water pipeline are usually equal. The inlet and outlet of the primary heat storage return water valve 15 are connected to the branch water supply pipeline 13 and the branch return water pipeline 14 of the primary heating network, respectively. The unit of L is meters, and its value range is: V×H. 峰 ×3600≤L≤V×(H 峰 +2 H p平 )×3600, usually V×H is chosen 峰 ×3600≤L≤V×(H 峰 + H p平 ) × 3600; where, H 峰 (h) represents the duration of a peak period in the power grid, Hp平 V (m / s) represents the duration of a normal period in the power grid (one), and V (m / s) represents the medium velocity in the return water pipe of the primary heating network. The primary side inlet and outlet of the heat exchanger in the secondary heat exchange station 10 are connected to the main supply pipe 7 and the main return pipe 9 via supply branch pipe 13 and return branch pipe 14, respectively. The primary heat storage return water valve is installed between the supply and return branch pipes in the secondary heat exchange station. A primary heat storage return water valve 15 is installed between the supply and return branch pipes in n secondary heat exchange stations after the first heat exchange station (a total of n primary heat storage return water valves 15). This structure can be constructed within the secondary heat exchange station, facilitating the installation and control of the primary heat storage return water valve. It is simple, easy to implement, and low in cost. When the peak flow rate changes are small, one or more primary heat storage return water valves can be controlled to open, resulting in high flow control accuracy. Each pair...

[0069] In a further improvement, a secondary heat storage return water valve 16 is installed at the rear (end) of the water supply and return water pipes of the secondary heating network. The inlet and outlet of the secondary heat storage return water valve 16 are connected to the water supply and return water pipes of the secondary heating network, respectively. The high-temperature water in the water supply pipe of the secondary heating network can flow back to the secondary side inlet of the heat exchanger in the secondary heat exchange station through the secondary heat storage return water valve and the return water pipe for secondary heat storage.

[0070] In this embodiment, a primary heat storage return valve is installed between the water supply branch pipe and the return water branch pipe in each of the n secondary heat exchange stations within a distance of L (m) from the primary heat exchange station, for a total of n primary heat storage return valves.

[0071] The heat storage method of the combined heat and power (CHP) district heating system in this embodiment includes the following steps:

[0072] Step 1: When the temperature rise rate of the primary heating network supply water is greater than S, the automatic control system controls the opening of the primary heat storage return water valve to increase, so that the temperature rise rate of the primary heating network supply water is less than or equal to S; the high-temperature hot water in the supply water pipe of the primary heating network enters the return water pipe, stores heat to form high-temperature return water, and realizes heat storage in the primary heating network.

[0073] Step 2: When the temperature drop rate of the primary heating network water supply is greater than S, the automatic control system controls the opening of the primary heat storage return water valve to decrease, so that the temperature drop rate of the primary heating network water supply is less than or equal to S.

[0074] Step 3: When the temperature rise rate or temperature drop rate of the primary heating network supply water is detected to be ≤S, the primary heat storage return water valve remains unchanged in opening degree.

[0075] During the adjustment process of the primary thermal storage return water valve, the automatic control system performs real-time judgment and control. When three boundary conditions t3=t4 and ΔP are met, J =ΔP 最小 G1运行 =G1 最大 Under any of the following conditions, the primary heat storage return water valve reaches its maximum allowable opening, and the opening cannot continue to increase, such as when t3 > t4 and ΔP... J <ΔP 最小 G1 运行 >G1 最大 At this time, the opening degree of the primary heat storage return water valve needs to be reduced by 10%;

[0076] Where: S is the maximum allowable rate of temperature rise and fall of the primary heating network water supply at the secondary side outlet of the heat exchanger in the first heat exchange station, in ℃ / h, generally taken as 4-6℃ / h.

[0077] During the adjustment of n primary thermal storage return water valves, the automatic control system can perform real-time judgment and control. When the i-th primary thermal storage return water valve satisfies the three boundary conditions t3=t4, ΔP iJ =ΔP 最小 G i 1 运行 =G i 1 最大 Under any one of the following conditions, the i-th primary thermal storage return valve reaches its maximum allowable opening, and the opening cannot continue to increase; if t3 > t4, ΔP iJ <ΔP 最小 G i 1 运行 >G i 1 最大 At this time, the opening degree of the i-th primary heat storage return water valve needs to be reduced by 3%;

[0078] ΔP iJ ΔP represents the pressure difference between the primary supply and return water pipelines of the heat exchanger in the most unfavorable secondary heat exchange station. iJ =P iJ 1-P iJ 2, P iJ 1 represents the primary side operating water supply pressure of the heat exchanger in the most unfavorable secondary heat exchange station, P. iJ 2 represents the primary side operating return water pressure of the heat exchanger in the most unfavorable secondary heat exchange station; pressure sensors are installed at the primary side inlet and outlet of the heat exchanger in the most unfavorable secondary heat exchange station to collect the pressure.

[0079] ΔP 最小 This is the minimum available pressure difference value for the primary side supply and return water pipelines of the heat exchanger in the secondary heat exchange station; the unit is meters (m), and it is a set value, typically 8-12, preferably 10-11.

[0080] G i 1 运行 The flow rate of the primary heating network is measured in t / h and is collected by a flow meter installed at the secondary side outlet of the heat exchanger in the first heat exchange station.

[0081] G i 1 最大 This represents the maximum flow rate transport capacity of the primary heating network, expressed in t / h, and is obtained from the hydraulic calculation results of the primary network.

[0082] t3 (°C) is the return water temperature of the primary heating network after heat storage. A temperature sensor is installed on the return water pipe before the primary heat storage return water valve to collect the temperature remotely. It is the temperature of the high-temperature water in the primary heating network supply pipe mixed in the primary heating network return water pipe after the primary heat storage return water valve is opened.

[0083] t4 is the safe boundary temperature of the return water pipeline at the installation location of the primary heat storage return water valve, i.e., the highest allowable temperature, in °C, and is generally taken as 70-80 °C.

[0084] In this embodiment, n primary heat storage return water valves can be controlled to open or close simultaneously, or they can be controlled to open or close sequentially. Preferably, when the temperature rise rate of the primary heating network water supply is >S, the first or first group of primary heat storage return water valves closest to the heat exchange station are opened first. When the first or first group of primary heat storage return water valves reaches the maximum allowable opening, and the temperature rise rate of the primary heating network water supply is >S, the second or second group of primary heat storage return water valves behind the first or first group of primary heat storage return water valves are opened. The primary heat storage return water valves are opened sequentially from closest to farthest from the heat exchange station. When the temperature drop rate of the primary heating network supply water is detected to be greater than S, the last or a group of primary heat storage return water valves that are furthest from the heat exchange station are controlled to close first. When the last or a group of primary heat storage return water valves are completely closed, and the temperature drop rate of the primary heating network supply water is greater than S, the first or a group of primary heat storage return water valves before the last or a group of primary heat storage return water valves are controlled to close. The primary heat storage return water valves are controlled to close sequentially from farthest to closest according to their distance from the heat exchange station.

[0085] This invention is further improved so that during peak hours, when all primary heat storage return water valves reach their maximum allowable opening, if the temperature rise rate of the primary heating network supply water at the secondary side outlet of the heat exchanger in the first heat exchange station is still greater than S, the automatic control system controls the secondary heat storage return water valve to open. High-temperature water from the secondary heating network supply pipe enters the secondary heating network return water pipe to form high-temperature return water, thus achieving heat storage in the secondary heating network. As the flow rate in the secondary heating network gradually increases, the automatic control system controls the primary side electric regulating valve of the secondary heat exchange station to increase its opening, and the primary side flow rate increases synchronously. The automatic control system also controls the secondary variable frequency circulating pump to increase its operating frequency synchronously. During the frequency conversion process of the secondary variable frequency circulating pump, two boundary conditions are simultaneously satisfied: maintaining G2... 运行 ≤G2 最大The system maintains a constant pressure difference ΔP2 (m) at the inlet and outlet of the heat exchanger on the secondary side within the secondary station. During off-peak hours, when the temperature drop rate of the primary heating network's water supply exceeds S, the automatic control system first closes the secondary heat storage return water valve, reducing the flow rate within the secondary heating network. Simultaneously, the automatic control system controls the secondary variable frequency circulating pump to reduce its operating frequency, maintaining a constant pressure difference ΔP2 (m) at the inlet and outlet of the heat exchanger on the secondary side within the secondary station. The high-temperature return water flows to the secondary inlet of the heat exchanger in the secondary heat exchange station, absorbs a small amount of heat within the station, and then reaches the predetermined temperature before entering the secondary heating network's water supply pipeline to meet user heating needs. When all secondary heat storage return water valves are closed, and the temperature drop rate of the primary heating network's water supply exceeds S, the primary heat storage return water valve is then closed.

[0086] ΔP2 is the pressure difference between the inlet and outlet of the heat exchanger on the secondary side in the secondary heat exchange station, in meters (m).

[0087] G2 represents the operating flow rate of the secondary heating network, measured in t / h, and is collected by a flow meter installed on the secondary side outlet pipe of the heat exchanger within the secondary station.

[0088] G2 最大 This represents the maximum flow rate of the secondary heating network, expressed in t / h, and is obtained from hydraulic calculations of the secondary network.

[0089] During the opening of the primary thermal storage return water valve, the flow rate within the primary heating network gradually increases. This increase is equal to the flow rate of the primary thermal storage return water valve, causing a gradual increase in the operating resistance loss of the primary heating network's supply and return water pipelines. Simultaneously, the operating frequency of the primary variable frequency circulating pump at the first station is gradually increased through the automatic control system. During the pump frequency conversion process, two boundary conditions are simultaneously satisfied: maintaining G1... 运行 ≤G1 最大 Maintain a constant pressure difference ΔP1 (m) at the inlet and outlet of the heat exchanger on the secondary side within the first heat exchange station.

[0090] ΔP1 is the pressure difference between the inlet and outlet of the heat exchanger on the secondary side within the heat exchange station (in meters).

[0091] G1 运行 The flow rate is the operating flow rate of the primary heating network, expressed in t / h, and is collected by a heat meter installed at the secondary side outlet of the heat exchanger in the primary heat exchange station.

[0092] G1 最大 This represents the maximum flow rate of the primary heating network, expressed in t / h, and is obtained from hydraulic calculations of the primary network.

[0093] The thermal storage return water valve can be synchronously controlled by the PLC controller of the automatic control system. The adjustment and control method of the thermal storage return water valve adopts the time and opening ratio method. The automatic control system monitors various relevant operating parameters in real time. Through edge computing and fuzzy control, the valve opening is selected according to the principle of 3% valve opening with a 2-second time interval. The automatic control program can modify the time and opening ratio to control the opening of the connected electric regulating valve step by step.

[0094] The heat storage structure and method of the present invention can store excess heat generated during peak periods of power grid operation in the return water pipeline of the centralized heating system. When the heat generated during off-peak periods of power grid operation is insufficient, the heat stored in the return water pipeline of the centralized heating system can be promptly replenished to the supply water pipeline of the centralized heating system. Compared with the prior art, it has the advantages of simple structure, convenient operation, small footprint, and low investment.

Claims

1. A heat storage structure for a combined heat and power (CHP) centralized heating system, comprising a primary heat exchange station connected to a power plant, a primary heating network, a secondary heat exchange station, a secondary heating network, and heat users. The primary inlet of the heat exchanger in the primary heat exchange station is connected to the steam pipeline of the power plant, and the primary outlet is connected to a condensate recovery device. The secondary inlet of the heat exchanger in the primary heat exchange station is connected to the return water pipeline of the primary heating network via a primary variable frequency circulating pump and a flow meter. The secondary outlet of the heat exchanger in the primary heat exchange station is connected to... The primary heating network's water supply pipeline is connected; the primary-side inlet and outlet of the heat exchanger in the secondary heat exchange station are respectively connected to the primary heating network's water supply and return pipelines via pipelines; the secondary-side outlet of the heat exchanger in the secondary heat exchange station is connected to the secondary heating network's water supply pipeline; the secondary-side inlet of the heat exchanger in the secondary heat exchange station is connected to the secondary heating network's return pipeline via a secondary variable frequency circulating pump; heat users are connected to the secondary heating network's water supply and return pipelines; its characteristic is that... A primary heat storage return valve is installed between the supply and return water pipes of the primary heating network located L meters away from the first heat exchange station. The value of L is in the range of V×H. 峰 ×3600≤L≤V×(H 峰 +2 H p平 ) × 3600, where H 峰 H represents the duration of the peak power grid period, measured in hours (h). p平 V represents the duration of the normal power grid period, V represents the flow velocity of the medium in the pipeline of the primary heating network, and L represents the length of the pipeline.

2. The heat storage structure of the combined heat and power centralized heating system according to claim 1, characterized in that, The formula for calculating V is: V = (0.354 × G) 计算 ×υ) / D 2 Among them, G 计算 The calculated flow rate of the primary pipeline network is expressed in t / h, and υ is the specific volume of the water medium in the pipeline, expressed in cubic meters per second. 3 / kg; D is the inner diameter of the return water pipe of the primary heating network, in meters.

3. The heat storage structure of the combined heat and power centralized heating system according to claim 2, characterized in that... The G 计算 The formula for calculating G is: 计算 =(0.86×A×q) / (T1-T2) / 1000, where A is the heating area in m². 2 q is the calculated heat consumption index, with units of W / m³. 2 T1 is the calculated supply water temperature of the primary heating network, in °C; T2 is the calculated return water temperature of the primary heating network, in °C.

4. The heat storage structure of the combined heat and power centralized heating system according to claim 1, characterized in that, The formula for calculating V is: V = (0.354 × G) 实际 ×υ) / D 2 G 实际 The flow rate is either the actual flow rate of the primary pipeline during peak hours or the average actual flow rate of the primary pipeline during peak and off-peak hours, in tons per hour (t / h). υ represents the specific volume of the water medium in the pipeline, in cubic meters per second (m³). 3 / kg; D is the inner diameter of the return water pipe of the primary heating network, in meters.

5. The heat storage structure of the combined heat and power centralized heating system according to any one of claims 1-4, characterized in that... Pressure sensors and temperature sensors are installed on the primary and secondary pipes of the first heat exchange station and each secondary heat exchange station, respectively. Pressure sensors and temperature sensors are also installed on the water supply and return pipes of the primary heating network on both sides before and after the primary heat storage return water valve.

6. The heat storage structure of the combined heat and power centralized heating system according to claim 5, characterized in that, The primary heating network includes a main water supply pipeline and branch water supply pipelines, and a return water pipeline includes a main return water pipeline and branch return water pipelines. The branch water supply pipelines and branch return water pipelines are used to connect the primary side of the heat exchanger in the secondary heat exchange station to the main water supply pipeline and the main return water pipeline. The primary heat storage return water valve is installed between the main water supply pipeline and the main return water pipeline.

7. The heat storage structure of the combined heat and power centralized heating system according to claim 5, characterized in that, The primary heating network includes a main water supply pipeline and branch water supply pipelines, and a return water pipeline includes a main return water pipeline and branch return water pipelines. The primary side inlet and outlet of the heat exchanger in the secondary heat exchange station are connected to the main water supply pipeline and the main return water pipeline via branch water supply pipelines and branch return water pipelines, respectively. The primary heat storage return water valve is installed between the branch water supply pipelines and the branch return water pipelines in the secondary heat exchange station. A primary heat storage return water valve is installed between the branch water supply pipelines and the branch return water pipelines in n secondary heat exchange stations within a range of L meters from the primary heat exchange station.

8. A method for storing heat in a heat storage structure of a combined heat and power centralized heating system according to claim 1 or 6, characterized in that... Includes the following steps: Step 1: When the temperature rise rate of the primary heating network supply water is greater than S, control the opening of the primary heat storage return water valve to increase so that the temperature rise rate of the primary heating network supply water is less than or equal to S. Step 2: When the temperature drop rate of the primary heating network supply water is greater than S, control the opening of the primary heat storage return water valve to be smaller, so that the temperature drop rate of the primary heating network supply water is less than or equal to S. Step 3: When the temperature rise rate or temperature drop rate of the primary heating network supply water is detected to be ≤S, the primary heat storage return water valve remains in place. During the adjustment process of the primary thermal storage return water valve, when three boundary conditions t3=t4 and ΔP are met... J =ΔP 最小 G1 运行 =G1 最大 Under any one of the following conditions, the primary heat storage return water valve reaches its maximum allowable opening. Where: S is the maximum allowable rate of increase or decrease in the primary heating network water supply temperature at the secondary side outlet of the heat exchanger in the heat exchange station. ΔP J The pressure difference between the primary supply and return water pipelines of the heat exchanger in the most unfavorable secondary heat exchange station; ΔP 最小 This refers to the minimum available pressure difference between the primary supply and return water pipelines of the heat exchangers in a secondary heat exchange station. G1 运行 The flow rate of the primary heating network is measured in t / h and is collected by a flow meter installed on the secondary side of the heat exchanger in the first heat exchange station. G1 最大 This represents the maximum flow rate transmission capacity of the primary heating network, expressed in t / h. t3 is the return water temperature of the primary heating network after heat storage. It is the temperature of the high-temperature water in the primary heating network supply pipe mixed in the primary heating network return water pipe after the primary heat storage return water valve is opened. t4 is the safe boundary temperature of the return water pipeline.

9. A method for storing heat in a heat storage structure of a combined heat and power (CHP) centralized heating system according to claim 7, characterized in that... Includes the following steps: Step 1: When the temperature rise rate of the primary heating network supply water is greater than S, the automatic control system controls the opening of the primary heat storage return water valve to increase, so that the temperature rise rate of the primary heating network supply water is less than or equal to S; the high-temperature hot water in the supply water pipe of the primary heating network enters the return water pipe, stores heat to form high-temperature return water, and realizes heat storage in the primary heating network. Step 2: When the temperature drop rate of the primary heating network water supply is greater than S, the automatic control system controls the opening of the primary heat storage return water valve to decrease, so that the temperature drop rate of the primary heating network water supply is less than or equal to S. Step 3: When the temperature rise rate or temperature drop rate of the primary heating network supply water is detected to be ≤S, the primary heat storage return water valve remains unchanged in opening degree. Where: S is the maximum allowable rate of temperature rise and fall of the primary heating network water supply at the secondary side outlet of the heat exchanger in the first heat exchange station, in ℃ / h, and is taken as 4-6℃ / h. During the adjustment process of the primary thermal storage return water valve, when the i-th primary thermal storage return water valve satisfies the three boundary conditions t3=t4, ΔP iJ =ΔP 最小 G i 1 运行 =G i 1 最大 Under any one of the following conditions, the i-th primary heat storage return water valve reaches its maximum allowable opening. ΔP iJ The pressure difference between the primary supply and return water pipelines of the heat exchanger in the most unfavorable secondary heat exchange station; ΔP 最小 This refers to the minimum available pressure difference between the primary supply and return water pipelines of the heat exchangers in a secondary heat exchange station. G i 1 运行 This refers to the operating flow rate of the primary heating network. G i 1 最大 This represents the maximum flow transmission capacity of the primary heating network. t3 is the return water temperature of the primary heating network after heat storage. It is the temperature of the high-temperature water in the primary heating network supply pipe mixed in the primary heating network return water pipe after the primary heat storage return water valve is opened. t4 is the safe boundary temperature of the return water pipeline.

Images