A heat supply system and method for cascaded utilization of energy

Abstract

The present invention discloses a heat supply system for cascaded utilization of energy, which includes a coal-fired steam boiler, a steam turbine, an exhaust steam waste heat recovery mechanism, a primary flue gas waste heat recovery mechanism, a secondary flue gas waste heat recovery mechanism, a sewage waste heat recovery mechanism, a primary network circulation mechanism and a secondary network circulation and heat exchange mechanism; and also discloses a heat supply method for cascaded utilization of energy. Specifically, by using the above heat supply system, the effect of cascaded utilization of the waste heat and exhaust steam generated in the production process of the heat supply system is achieved as a whole, reducing energy waste; and by extracting the low-grade heat in sewage to supplement heat to the heat supply system, the demand for coal combustion for heat supply is reduced, and thus the pollutant emissions of the coal-fired boiler are reduced; at the same time, each waste heat recovery device adopts a parallel connection mode. If a certain device fails, it will not affect the overall heat supply effect, improving the stability of the entire system.

Description

Technical Field

[0001] The present invention relates to the technical field of heating, energy conservation and environmental protection, and more specifically, to a heating system and method for cascaded utilization of energy. Background Art

[0002] At present, the centralized heating technology has been relatively maturely developed in China, gradually replacing the traditional separate boiler heating method, and most heating systems can relatively quickly adapt to the heat load fluctuations caused by the sharp change of outdoor temperature by increasing the coal consumption. Moreover, most centralized heating provides energy by burning coal. With the development of society, non-renewable energy represented by coal and oil is increasingly scarce. Therefore, it is urgent to improve the energy utilization rate. At the same time, a large amount of pollutants are emitted into the environment during the coal combustion in the heating process, and the resulting environmental pollution problems are also increasing day by day. Therefore, how to reduce environmental pollution problems while improving the energy utilization rate is the key to the development of the current centralized heating technology.

[0003] To solve the above technical problems, those skilled in the art have proposed technical improvements to the traditional centralized heating system, but there are still technical defects. For example, Patent CN102261694 A discloses an energy-saving heating system for a thermal power plant. Before the return water of the heat network enters the water-water heat exchanger, it is divided into two paths. One path of the return water of the heat network first enters the absorber of the first absorption heat pump, then is connected in series with the absorbers of each intermediate absorption heat pump, and finally enters the condenser of the last absorption heat pump. The other path of the return water of the heat network is connected in parallel to the subcoolers of each absorption heat pump and finally merged and sent out hot water. Although more waste heat of the condensate steam of the power plant can be utilized for heating, in order to reach the standard supply water temperature, multiple absorption heat pumps need to be set, increasing the equipment investment; and this system only utilizes the condensate waste heat and does not extract other forms of waste heat, and the energy utilization rate needs to be further improved.

[0004] Therefore, how to provide a heating system and method for cascaded utilization of energy to reduce the coal consumption and pollutant emissions of the entire heating system is an urgent problem to be solved by those skilled in the art. Summary of the Invention

[0005] In view of this, the present invention provides a heating system and method for cascaded utilization of energy, which cascades and utilizes the waste heat and exhausted steam generated in the production process of the heating system to reduce energy waste; extracts the low-grade heat in the sewage to supplement the heating system, reducing the pollutant emissions of the coal-fired boiler; at the same time, each waste heat recovery device adopts a parallel connection method. If a certain device fails, it will not affect the overall heating effect, improving the stability of the entire system.

[0006] In order to achieve the above object, the present invention adopts the following technical solutions:

[0007] A heat supply system for cascaded utilization of energy, characterized by comprising a coal-fired steam boiler, a steam turbine, an exhaust steam waste heat recovery mechanism, a primary flue gas waste heat recovery mechanism, a secondary flue gas waste heat recovery mechanism, a sewage waste heat recovery mechanism, a primary network circulation mechanism and a secondary network circulation and heat exchange mechanism;

[0008] The high-temperature steam outlet of the coal-fired steam boiler is connected to the steam turbine, and the flue gas outlet is sequentially connected to the primary flue gas waste heat recovery mechanism and the secondary flue gas waste heat recovery mechanism through a flue;

[0009] The steam turbine is drivingly connected to the secondary flue gas waste heat recovery mechanism;

[0010] The exhaust steam waste heat recovery mechanism is connected upstream to the steam turbine and downstream to the coal-fired steam boiler; meanwhile, the exhaust steam waste heat recovery mechanism is connected upstream to the primary flue gas waste heat recovery mechanism, the secondary flue gas waste heat recovery mechanism and the sewage waste heat recovery mechanism, and downstream to the primary network circulation mechanism;

[0011] The upstream of the primary flue gas waste heat recovery mechanism, the secondary flue gas waste heat recovery mechanism and the sewage waste heat recovery mechanism are respectively connected to the primary network circulation mechanism;

[0012] The primary network circulation mechanism is connected to the secondary network circulation mechanism and forms a closed loop.

[0013] The beneficial effects of the above preferred technical solutions are as follows: A heat supply system for cascaded utilization of energy disclosed by the present invention first uses the primary flue gas waste heat recovery mechanism, the secondary flue gas waste heat recovery mechanism and the sewage waste heat recovery mechanism to preliminarily heat the primary network return water, and then uses the exhaust steam waste heat recovery mechanism to further heat it, so that the obtained primary network supply water can meet the temperature supply requirements, cascadingly utilize the waste heat and exhaust steam generated in the production process of the heat supply system, and reduce energy waste; and, by extracting the low-grade heat in the sewage through the sewage waste heat recovery mechanism to supplement the heat supply system, the demand for extracting heat by coal combustion is reduced, thereby reducing the pollutant emissions of the coal-fired boiler. At the same time, the primary flue gas waste heat recovery mechanism, the secondary flue gas waste heat recovery mechanism and the sewage waste heat recovery mechanism are connected in parallel. If a certain device fails, it will not cause the entire heat supply system to collapse, improving the operation stability of the entire heat supply system.

[0014] Preferably, the exhaust steam waste heat recovery mechanism includes a steam pipe, a steam-water heat exchanger and a condensate pipe;

[0015] The steam pipe is connected to the steam outlet of the steam turbine and the hot water inlet pipe of the steam-water heat exchanger;

[0016] The cold outlet pipe of the steam-water heat exchanger is connected to the return water pipe of the coal-fired steam boiler through the condensate pipe. The cold inlet pipe of the steam-water heat exchanger is respectively connected to the primary flue gas waste heat recovery mechanism, the secondary flue gas waste heat recovery mechanism, and the sewage waste heat recovery mechanism. The hot outlet pipe of the steam-water heat exchanger is connected to the primary network circulation mechanism.

[0017] The beneficial effects of the above preferred technical solution are as follows: Through the mutual cooperation of the steam pipe, the steam-water heat exchanger, and the condensate pipe, the low-temperature exhaust steam generated by the steam turbine can be recovered and utilized for waste heat, and the primary network return water that has been preliminarily heated can be further heated, so as to obtain the primary network supply water that meets the temperature supply requirements.

[0018] Further preferably, the primary flue gas waste heat recovery mechanism includes a primary desulfurization water bed, a primary desulfurization slurry circulation pump, a primary heat exchanger, and a steam-water heat exchanger circulation pump;

[0019] The flue gas inlet of the primary desulfurization water bed is connected to the flue gas outlet of the coal-fired steam boiler through the flue. The flue gas outlet of the primary desulfurization water bed is connected to the secondary flue gas waste heat recovery mechanism through the flue. The desulfurization slurry outlet pipe of the primary desulfurization water bed is connected to the hot inlet pipe of the primary heat exchanger through the primary desulfurization slurry circulation pump. The desulfurization slurry inlet pipe of the primary desulfurization water bed is connected to the cold outlet pipe of the primary heat exchanger;

[0020] The cold inlet pipe of the primary heat exchanger is connected to the primary network circulation mechanism. The hot outlet pipe of the primary heat exchanger is connected to the cold inlet pipe of the steam-water heat exchanger through the steam-water heat exchanger circulation pump.

[0021] The beneficial effects of the above preferred technical solution are as follows: Through the mutual cooperation of the primary desulfurization water bed, the primary desulfurization slurry circulation pump, the primary heat exchanger, and the steam-water heat exchanger circulation pump, the present invention can perform preliminary desulfurization treatment on the flue gas, and can preliminarily recover the heat in the flue gas generated by the coal-fired steam boiler, so as to preliminarily heat the primary network return water and avoid energy waste.

[0022] Further preferably, the secondary flue gas waste heat recovery mechanism includes a secondary desulfurization water bed, a secondary desulfurization slurry circulation pump, a secondary heat exchanger, an intermediate water pipe, an intermediate water circulation pump, and a compression heat pump;

[0023] The flue gas inlet of the secondary desulfurization water bed is connected to the flue gas outlet of the primary desulfurization water bed through the flue. The flue gas outlet of the secondary desulfurization water bed is connected to the chimney through the flue. The desulfurization slurry outlet pipe of the secondary desulfurization water bed is connected to the hot inlet pipe of the secondary heat exchanger through the secondary desulfurization slurry circulation pump. The desulfurization slurry inlet pipe of the secondary desulfurization water bed is connected to the cold outlet pipe of the secondary heat exchanger;

[0024] The cold water inlet pipe of the secondary heat exchanger is connected to the intermediate water pipe, and the hot water outlet pipe of the secondary heat exchanger is connected to the hot water inlet pipe of the compression heat pump through the intermediate water circulation pump;

[0025] The cold water outlet pipe of the compression heat pump is connected to the intermediate water pipe, the cold water inlet pipe of the compression heat pump is connected to the primary network circulation mechanism, the hot water outlet pipe of the compression heat pump is connected to the cold water inlet pipe of the steam-water heat exchanger, and the compression heat pump is driven by the steam turbine.

[0026] The beneficial effects of the above preferred technical solutions are as follows: In the present invention, through the mutual cooperation of the secondary desulfurization water bed, the secondary desulfurization slurry circulation pump, the secondary heat exchanger, the intermediate water pipe, the intermediate water circulation pump and the compression heat pump, the flue gas can be further desulfurized, so that the gas discharged through the chimney is safe and environmentally friendly, avoiding environmental pollution, and further recovering and utilizing the heat in the flue gas, improving the energy utilization rate and saving energy.

[0027] Further preferably, the sewage waste heat recovery mechanism includes an absorption heat pump, a sewage channel, a sewage pipe and a water pump;

[0028] The hot water inlet pipe of the absorption heat pump is connected to the sewage channel, the cold water outlet pipe of the absorption heat pump is connected to the sewage channel through the sewage pipe, the cold water inlet pipe of the absorption heat pump is connected to the primary network circulation mechanism through the water pump, and the hot water outlet pipe of the absorption heat pump is connected to the cold water inlet pipe of the steam-water heat exchanger.

[0029] Among them, the sewage in the sewage channel is derived from domestic sewage preliminarily treated by a sewage treatment plant. The function of the absorption heat pump is to extract heat from a low-grade heat source and transfer it to a high-grade heat source. The current sewage inlet temperature of the absorption sewage source heat pump is about 12°C, and the return water temperature is about 7°C.

[0030] The beneficial effects of the above preferred technical solutions are as follows: In the present invention, through the mutual cooperation of the absorption heat pump, the sewage channel, the sewage pipe and the water pump, the low-grade heat in the sewage is extracted and heat is supplemented to the heating system, thereby reducing the demand for extracting heat by burning coal, and further reducing the pollutant emissions of the coal-fired boiler.

[0031] Further preferably, the primary network circulation mechanism includes a heat network heat exchanger, a primary network water supply pipe, a primary network circulation pump and a primary network return water pipe;

[0032] The hot water inlet pipe of the heat network heat exchanger is connected to the hot water outlet pipe of the steam-water heat exchanger through the primary network circulation pump and the primary network water supply pipe. The cold water outlet pipe of the heat network heat exchanger is connected to the cold water inlet pipe of the primary heat exchanger, the cold water inlet pipe of the compression heat pump and the water pump through the primary network return water pipe, and the heat network heat exchanger is connected to the secondary network circulation heat exchange mechanism and forms a closed loop.

[0033] Further preferably, the secondary network circulation mechanism includes a secondary network circulation pump, a secondary network water supply pipe, a heat user, and a secondary network water return pipe; the upstream of the secondary network circulation pump is connected to the hot water outlet pipe of the heat network heat exchanger, and the downstream is connected to the heat user through the secondary network water supply pipe; the heat user is connected to the cold water inlet pipe of the heat network heat exchanger through the secondary network water return pipe.

[0034] Further preferably, the primary desulfurization slurry circulation pump, the steam-water heat exchanger circulation pump, the secondary desulfurization slurry circulation pump, the intermediate water circulation pump, the primary network circulation pump, and the secondary network circulation pump are variable-frequency circulation pumps.

[0035] The beneficial effects of the above preferred technical solutions are: Since the primary desulfurization slurry circulation pump, the secondary desulfurization slurry circulation pump, the intermediate water circulation pump, the primary network circulation pump, and the secondary network circulation pump are variable-frequency circulation pumps, the pipe flow can be controlled by setting the power of the variable-frequency circulation pump.

[0036] Preferably, the desulfurization slurry inlet pipe and the desulfurization slurry outlet pipe are made of stainless steel to prevent the desulfurization slurry from corroding the pipe.

[0037] The present invention also discloses a heat supply method for cascaded utilization of energy. Using the above heat supply system for cascaded utilization of energy, it includes the following steps:

[0038] (1) The high-pressure steam generated by the coal-fired steam boiler is input into the steam turbine to do work and then discharges low-temperature exhaust steam. The low-temperature exhaust steam is transported through a steam pipe to the steam-water heat exchanger for heat exchange, and the obtained condensed water flows back to the coal-fired steam boiler through a condensate pipe for heating;

[0039] (2) The flue gas generated by the combustion of coal in the coal-fired steam boiler is transported through a flue to the primary desulfurization water bed for primary desulfurization treatment and heats the primary desulfurization slurry. Then, the primary desulfurization slurry circulation pump is started, and the heated primary desulfurization slurry is transported to the primary heat exchanger to exchange heat with the primary network return water, and the cooled primary desulfurization slurry flows back to the primary desulfurization water bed. The primary heat exchanger simultaneously raises the temperature of the primary network return water to form primary supply water; and at the same time, the steam-water heat exchanger circulation pump is started to make the primary supply water transported to the steam-water heat exchanger to exchange heat with the low-temperature exhaust steam;

[0040] (3) The flue gas after primary desulfurization treatment enters the secondary desulfurization water bed for secondary desulfurization treatment, and the secondary desulfurization slurry is heated. Then, the secondary desulfurization slurry circulation pump is started to transport the heated secondary desulfurization slurry to the secondary heat exchanger to exchange heat with the intermediate water, and the cooled secondary desulfurization slurry is returned to the secondary desulfurization water bed. The secondary heat exchanger simultaneously raises the temperature of the intermediate water. And the intermediate water circulation pump is started to transport the heated intermediate water to the compression heat pump to exchange heat with the return water of the primary network and then be cooled. The cooled intermediate water flows back to the secondary heat exchanger for heating. The compression heat pump operates under the drive of the steam turbine to heat the return water of the primary network to obtain the primary water supply, and the primary water supply is transported to the steam-water heat exchanger to exchange heat with the low-temperature exhaust steam. And the flue gas after complete desulfurization is transported to the chimney through the flue for external discharge;

[0041] (4) The sewage in the sewage channel is transported through the sewage pipe to the absorption heat pump to exchange heat with the return water of the primary network and then be cooled. The cooled sewage flows back to the sewage channel through the sewage pipe. The absorption heat pump simultaneously heats the return water of the primary network to obtain the primary water supply, and the primary water supply is transported to the steam-water heat exchanger to exchange heat with the low-temperature exhaust steam;

[0042] (5) The primary water supply is transported to the steam-water heat exchanger to exchange heat with the low-temperature exhaust steam and then is heated to obtain the primary network water supply. Then, the primary network circulation pump is started to make the primary network water supply be transported through the primary network water supply pipe to the heat network heat exchanger to exchange heat with the secondary network return water. After cooling, the primary network return water is transported through the primary network return water pipe to the primary heat exchanger, the absorption heat pump, and the compression heat pump for heating respectively. The heat network heat exchanger simultaneously heats the secondary network return water to obtain the secondary network water supply. And the secondary network circulation pump is started simultaneously to make the secondary network water supply be transported through the secondary network water supply pipe to the heat user for heating. After cooling, the secondary network return water flows back to the heat network heat exchanger through the secondary network return water pipe.

[0043] Further preferably, in step (1), the pressure of the high-pressure steam is 3.11 - 3.96 Mpa, and the temperature is 430 - 480 °C. The pressure of the low-temperature exhaust steam is 0.12 Mpa, and the temperature is 190 °C;

[0044] In step (2), the temperature of the heated primary desulfurization slurry is 120 - 132 °C, and the temperature of the cooled primary desulfurization slurry is 84 - 96 °C. The temperature of the primary water supply is 45 - 50 °C;

[0045] In step (3), the temperature of the heated secondary desulfurization slurry is 26 - 32 °C, and the temperature of the cooled secondary desulfurization slurry is 19 - 25 °C. The temperature of the heated intermediate water is 19 - 20 °C, and the temperature of the cooled intermediate water is 15 - 16 °C. The temperature of the primary water supply is 50 - 55 °C;

[0046] In step (4), the temperature of the sewage in the sewage channel is 12°C, the temperature of the cooled sewage is 7°C, the return water temperature of the primary network is 40°C, and the primary supply water temperature is 50 - 55°C;

[0047] In step (5), the supply water temperature of the primary network is 90 - 95°C, and the return water temperature of the primary network is 40 - 45°C; the supply water temperature of the secondary network is 45 - 50°C, and the return water temperature of the secondary network is 35 - 40°C.

[0048] The beneficial effects of the above preferred technical solutions are as follows: A heat supply method for cascaded utilization of energy disclosed in the present invention utilizes the above heat supply system for cascaded utilization of energy. The operation method is simple and the overall regulation is convenient. The waste heat and exhausted steam generated in the production process of the heat supply system are utilized in a cascaded manner, reducing energy waste; at the same time, the low-grade heat in the sewage can be extracted to supplement heat to the heat supply system, reducing the demand for coal combustion; and each waste heat recovery device is connected in parallel. If a certain device fails, it will not affect the overall heat supply effect, improving the stability of the entire system.

[0049] As can be seen from the above technical solutions, compared with the prior art, the present invention discloses a heat supply system and method for cascaded utilization of energy, having the following beneficial effects:

[0050] (1) The primary flue gas waste heat recovery mechanism and the secondary flue gas waste heat recovery mechanism are respectively used to preliminarily heat the heating water. At the same time, the sewage waste heat recovery mechanism extracts the low-grade heat in the sewage to preliminarily heat the heating water, and then the exhausted steam generated after the steam turbine drives the compression heat pump to do work is used to further heat the heating water for heating, realizing the cascaded utilization of waste heat and exhausted steam, avoiding energy waste, and saving 10% of energy and reducing 12% of pollutant emissions compared with the traditional heat supply system on the basis of ensuring heat supply compliance;

[0051] (2) The primary flue gas waste heat recovery mechanism, the secondary flue gas waste heat recovery mechanism, and the sewage waste heat recovery mechanism are connected in parallel. If a certain device fails, it will not affect the overall heat supply effect, improving the stability of the operation of the heat supply system. BRIEF DESCRIPTION OF THE DRAWINGS

[0052] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the drawings in the following description are only the embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained according to the provided drawings without creative efforts.

[0053] Figure 1 The attached drawing is a schematic structural diagram of a heat supply system for cascaded utilization of energy provided in Embodiment 1 of the present invention.

[0054] In the figure: 1 is a coal-fired steam boiler, 2 is a steam turbine, 3 is a steam pipe, 4 is a steam-water heat exchanger, 5 is a condensate pipe, 6 is a primary desulfurization water bed, 7 is a primary desulfurization slurry circulation pump, 8 is a primary heat exchanger, 9 is a secondary desulfurization water bed, 10 is a secondary desulfurization slurry circulation pump, 11 is a secondary heat exchanger, 12 is an intermediate water pipe, 13 is an intermediate water circulation pump, 14 is a compression heat pump, 15 is an absorption heat pump, 16 is a sewage channel, 17 is a sewage pipe, 18 is a water pump, 19 is a heat network heat exchanger, 20 is a primary network supply water pipe, 21 is a primary network circulation pump, 22 is a primary network return water pipe, 23 is a secondary network circulation pump, 24 is a secondary network supply water pipe, 25 is a heat user, 26 is a secondary network return water pipe, 27 is a flue, 28 is a chimney, and 29 is a steam-water heat exchanger circulation pump. Specific implementation mode

[0055] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0056] Embodiment 1

[0057] Embodiment 1 of the present invention discloses a heat supply system for cascaded energy utilization, including a coal-fired steam boiler, a steam turbine, an exhaust steam waste heat recovery mechanism, a primary flue gas waste heat recovery mechanism, a secondary flue gas waste heat recovery mechanism, a sewage waste heat recovery mechanism, a primary network circulation mechanism, and a secondary network circulation and heat exchange mechanism.

[0058] The high-temperature steam outlet of the coal-fired steam boiler is connected to the steam turbine, and the flue gas outlet is sequentially connected to the primary flue gas waste heat recovery mechanism and the secondary flue gas waste heat recovery mechanism through a flue.

[0059] Among them, the exhaust steam waste heat recovery mechanism includes a steam pipe, a steam-water heat exchanger, and a condensate pipe; the steam pipe is connected to the steam outlet of the steam turbine and the hot water inlet pipe of the steam-water heat exchanger; the cold water outlet pipe of the steam-water heat exchanger is connected to the return water pipe of the coal-fired steam boiler through the condensate pipe, the cold water inlet pipe of the steam-water heat exchanger is respectively connected to the primary flue gas waste heat recovery mechanism, the secondary flue gas waste heat recovery mechanism, and the sewage waste heat recovery mechanism, and the hot water outlet pipe of the steam-water heat exchanger is connected to the primary network circulation mechanism.

[0060] More specifically, the primary flue gas waste heat recovery mechanism includes a primary desulfurization water bed, a primary desulfurization slurry circulation pump, a primary heat exchanger, and a steam-water heat exchanger circulation pump; the flue gas inlet of the primary desulfurization water bed is connected to the flue gas outlet of the coal-fired steam boiler through a flue, the flue gas outlet of the primary desulfurization water bed is connected to the secondary flue gas waste heat recovery mechanism through a flue, the desulfurization slurry outlet pipe of the primary desulfurization water bed is connected to the hot water inlet pipe of the primary heat exchanger through the primary desulfurization slurry circulation pump, and the desulfurization slurry inlet pipe of the primary desulfurization water bed is connected to the cold water outlet pipe of the primary heat exchanger; the cold water inlet pipe of the primary heat exchanger is connected to the primary network circulation mechanism, and the hot water outlet pipe of the primary heat exchanger is connected to the cold water inlet pipe of the steam-water heat exchanger through the steam-water heat exchanger circulation pump.

[0061] Furthermore, the secondary flue gas waste heat recovery mechanism includes a secondary desulfurization water bed, a secondary desulfurization slurry circulation pump, a secondary heat exchanger, an intermediate water pipe, an intermediate water circulation pump, and a compression heat pump; the flue gas inlet of the secondary desulfurization water bed is connected to the flue gas outlet of the primary desulfurization water bed through a flue, the flue gas outlet of the secondary desulfurization water bed is connected to the chimney through a flue, the desulfurization slurry outlet pipe of the secondary desulfurization water bed is connected to the hot water inlet pipe of the secondary heat exchanger through the secondary desulfurization slurry circulation pump, and the desulfurization slurry inlet pipe of the secondary desulfurization water bed is connected to the cold water outlet pipe of the secondary heat exchanger; the cold water inlet pipe of the secondary heat exchanger is connected to the intermediate water pipe, and the hot water outlet pipe of the secondary heat exchanger is connected to the hot water inlet pipe of the compression heat pump through the intermediate water circulation pump; the cold water outlet pipe of the compression heat pump is connected to the intermediate water pipe, the cold water inlet pipe of the compression heat pump is connected to the primary network circulation mechanism, the hot water outlet pipe of the compression heat pump is connected to the cold water inlet pipe of the steam-water heat exchanger, and the compression heat pump is driven by a steam turbine.

[0062] In addition, the sewage waste heat recovery mechanism includes an absorption heat pump, a sewage channel, a sewage pipe, and a water pump; the hot water inlet pipe of the absorption heat pump is connected to the sewage channel, the cold water outlet pipe of the absorption heat pump is connected to the sewage channel through the sewage pipe, the cold water inlet pipe of the absorption heat pump is connected to the primary network circulation mechanism through the water pump, and the hot water outlet pipe of the absorption heat pump is connected to the cold water inlet pipe of the steam-water heat exchanger.

[0063] Among them, the sewage in the sewage channel is sourced from domestic sewage that has been preliminarily treated by a sewage treatment plant. The function of the absorption heat pump is to extract heat from a low-grade heat source and transfer it to a high-grade heat source. The current sewage inlet temperature of the absorption sewage source heat pump is about 12°C, and the return water temperature is about 7°C.

[0064] The primary network circulation mechanism includes a heat network heat exchanger, a primary network water supply pipe, a primary network circulation pump, and a primary network return pipe; the hot water inlet pipe of the heat network heat exchanger is connected to the hot water outlet pipe of the steam-water heat exchanger through the primary network circulation pump and the primary network water supply pipe, and the cold water outlet pipe of the heat network heat exchanger is connected to the cold water inlet pipe of the primary heat exchanger, the cold water inlet pipe of the compression heat pump, and the water pump through the primary network return pipe. Moreover, the heat network heat exchanger is connected to the secondary network circulation and heat exchange mechanism and forms a closed loop.

[0065] The secondary network circulation mechanism includes a secondary network circulation pump, a secondary network water supply pipe, heat users, and a secondary network water return pipe; the upstream of the secondary network circulation pump is connected to the hot water outlet pipe of the heat network heat exchanger, and the downstream is connected to the heat users through the secondary network water supply pipe; the heat users are connected to the cold water inlet pipe of the heat network heat exchanger through the secondary network water return pipe.

[0066] To further optimize the technical solution, the primary desulfurization slurry circulation pump, the steam-water heat exchanger circulation pump, the secondary desulfurization slurry circulation pump, the intermediate water circulation pump, the primary network circulation pump, and the secondary network circulation pump are selected as variable-frequency circulation pumps, so that the pipe flow can be controlled by setting the power of the variable-frequency circulation pump.

[0067] To further optimize the technical solution, the desulfurization slurry inlet pipe and the desulfurization slurry outlet pipe are made of stainless steel to prevent the desulfurization slurry from corroding the pipe.

[0068] Operating principle:

[0069] First, after the coal burns in the coal-fired steam boiler, the condensed water is heated to generate high-pressure steam, which is then input into the steam turbine to drive the compression heat pump to do work and generate low-temperature waste steam. The low-temperature waste steam passes through the steam outlet of the steam turbine and is transported through the steam pipe to the hot water inlet pipe of the steam-water heat exchanger. After heat exchange and cooling in the steam-water heat exchanger, condensed water is obtained, and then it flows back to the coal-fired steam boiler through the cold water outlet pipe of the steam-water heat exchanger, the condensate pipe, and the return water pipe of the coal-fired steam boiler to continue heating;

[0070] Second, the flue gas generated by the coal combustion in the coal-fired steam boiler is transported through the flue gas outlet of the coal-fired steam boiler, the flue, and then through the flue gas inlet of the primary desulfurization water bed to the primary desulfurization water bed for primary desulfurization treatment, and at the same time, the primary desulfurization slurry can be heated; then start the primary desulfurization slurry circulation pump, and transport the heated primary desulfurization slurry through the desulfurization slurry outlet pipe of the primary desulfurization water bed and the hot water inlet pipe of the primary heat exchanger to the primary heat exchanger to exchange heat with the primary network return water. The cooled primary desulfurization slurry flows back to the primary desulfurization water bed through the cold water outlet pipe of the primary heat exchanger and the desulfurization slurry inlet pipe of the primary desulfurization water bed. The primary heat exchanger simultaneously heats up the primary network return water to form primary supply water; and at the same time, start the steam-water heat exchanger circulation pump, so that the primary supply water is transported through the hot water outlet pipe of the primary heat exchanger and the cold water inlet pipe of the steam-water heat exchanger to the steam-water heat exchanger to exchange heat with the low-temperature waste steam;

[0071] Again, the flue gas after primary desulfurization treatment enters the secondary desulfurization water bed for secondary desulfurization treatment, and the secondary desulfurization slurry is heated. Then, the secondary desulfurization slurry circulation pump is started to transport the heated secondary desulfurization slurry to the secondary heat exchanger for heat exchange with the intermediate water, and the cooled secondary desulfurization slurry is returned to the secondary desulfurization water bed. At the same time, the secondary heat exchanger heats up the intermediate water; and the intermediate water circulation pump is started to transport the heated intermediate water to the compression heat pump for heat exchange with the return water of the primary network and then cooled. The cooled intermediate water flows back to the secondary heat exchanger for heating. The compression heat pump operates under the drive of the steam turbine to heat the return water of the primary network to obtain the primary water supply, and the primary water supply is transported to the steam-water heat exchanger for heat exchange with the low-temperature exhaust steam;

[0072] In addition, the sewage in the sewage channel is transported through the sewage pipe to the absorption heat pump for heat exchange with the return water of the primary network and then cooled. The cooled sewage flows back to the sewage channel through the sewage pipe. At the same time, the absorption heat pump heats the return water of the primary network to obtain the primary water supply, and the primary water supply is transported to the steam-water heat exchanger for heat exchange with the low-temperature exhaust steam;

[0073] Finally, the primary water supply is transported to the steam-water heat exchanger for heat exchange with the low-temperature exhaust steam and then heated up to obtain the primary network water supply; then the primary network circulation pump is started to make the primary network water supply be transported through the primary network water supply pipe to the heat network heat exchanger for heat exchange with the return water of the secondary network. After cooling, the primary network return water is transported through the primary network return water pipe to the primary heat exchanger, the absorption heat pump and the compression heat pump for heating respectively. At the same time, the heat network heat exchanger heats the return water of the secondary network to obtain the secondary network water supply; and the secondary network circulation pump is started at the same time to make the secondary network water supply be transported through the secondary network water supply pipe to the heat user for heating. After cooling, the secondary network return water flows back to the heat network heat exchanger through the secondary network return water pipe.

[0074] The present invention first uses the primary flue gas waste heat recovery mechanism, the secondary flue gas waste heat recovery mechanism, and the sewage waste heat recovery mechanism to preliminarily heat the return water of the primary network circulation, and then uses the exhaust steam waste heat recovery mechanism to further heat it, so that the obtained primary network water supply can meet the supply temperature requirements, and the waste heat and exhaust steam generated in the production process of the heating system are utilized in a cascade manner, reducing energy waste. Moreover, the sewage waste heat recovery mechanism is used to extract the low-grade heat in the sewage and supplement it to the heating system, reducing the demand for extracting heat by coal combustion, thereby reducing the pollutant emissions of the coal-fired boiler. At the same time, the primary flue gas waste heat recovery mechanism, the secondary flue gas waste heat recovery mechanism, and the sewage waste heat recovery mechanism are connected in parallel. If a certain device fails, it will not affect the overall heating effect, improving the stability of the overall heating system.

[0075] Embodiment 2

[0076] Embodiment 2 of the present invention discloses a heating method for cascade utilization of energy, which adopts the heating system for cascade utilization of energy disclosed in Embodiment 1, and includes the following steps:

[0077] (1) The high-pressure steam generated by the coal-fired steam boiler is input into the steam turbine to do work and then the low-temperature exhausted steam is discharged. The low-temperature exhausted steam is transported through the steam pipe to the steam-water heat exchanger for heat exchange, and the condensed water obtained is returned to the coal-fired steam boiler for heating through the condensate pipe. Among them, the pressure of the high-pressure steam is 3.11 - 3.96 Mpa and the temperature is 430 - 480 °C, and the pressure of the low-temperature exhausted steam is 0.12 Mpa and the temperature is 190 °C;

[0078] (2) The flue gas generated by the combustion of coal in the coal-fired steam boiler is transported through the flue to the first-stage desulfurization water bed for the first-stage desulfurization treatment, and the first-stage desulfurization slurry is heated to 120 - 132 °C. Then, the first-stage desulfurization slurry circulation pump is started, and the heated first-stage desulfurization slurry is transported to the first-stage heat exchanger to exchange heat with the first-stage network return water and then cooled to 84 - 96 °C. The cooled first-stage desulfurization slurry is returned to the first-stage desulfurization water bed. The first-stage heat exchanger simultaneously raises the temperature of the first-stage network return water to 45 - 50 °C to form the primary water supply. At the same time, the steam-water heat exchanger circulation pump is started to make the primary water supply transported to the steam-water heat exchanger to exchange heat with the low-temperature exhausted steam;

[0079] (3) The flue gas after the first-stage desulfurization treatment enters the second-stage desulfurization water bed for the second-stage desulfurization treatment, and the second-stage desulfurization slurry is heated to 26 - 32 °C. Then, the second-stage desulfurization slurry circulation pump is started to transport the heated second-stage desulfurization slurry to the second-stage heat exchanger to exchange heat with the intermediate water and cooled to 19 - 25 °C. The cooled second-stage desulfurization slurry is returned to the second-stage desulfurization water bed. The second-stage heat exchanger simultaneously raises the temperature of the intermediate water to 19 - 20 °C. And the intermediate water circulation pump is started to transport the heated intermediate water to the compression heat pump to exchange heat with the first-stage network return water and then cooled to 15 - 16 °C. The cooled intermediate water is returned to the second-stage heat exchanger for heating. The compression heat pump operates simultaneously driven by the steam turbine to heat the first-stage network return water to 50 - 55 °C to obtain the primary water supply, and the primary water supply is transported to the steam-water heat exchanger to exchange heat with the low-temperature exhausted steam;

[0080] (4) The sewage with a temperature of 12 °C in the sewage channel is transported through the sewage pipe to the absorption heat pump to exchange heat with the first-stage network return water and then cooled to 7 °C. The cooled sewage is returned to the sewage channel through the sewage pipe. The absorption heat pump simultaneously heats the first-stage network return water at 40 °C to 50 - 55 °C to obtain the primary water supply, and the primary water supply is transported to the steam-water heat exchanger to exchange heat with the low-temperature exhausted steam;

[0081] (5) The primary water supply is transported to the steam-water heat exchanger, where it exchanges heat with the low-temperature exhausted steam and is heated to 90 - 95 °C to obtain the supply water of the primary network. Then, the primary network circulation pump is started, and the supply water of the primary network is transported through the supply pipe of the primary network to the heat network heat exchanger, where it exchanges heat with the return water of the secondary network and is cooled to 40 - 45 °C. After cooling, the return water of the primary network is transported through the return pipe of the primary network to the primary heat exchanger, the absorption heat pump, and the compression heat pump for heating. The heat network heat exchanger simultaneously heats the return water of the secondary network to 45 - 50 °C to obtain the supply water of the secondary network. At the same time, the secondary network circulation pump is started, and the supply water of the secondary network is transported through the supply pipe of the secondary network to the heat user for heating and is cooled to 35 - 40 °C. After cooling, the return water of the secondary network is returned to the heat network heat exchanger through the return pipe of the secondary network.

[0082] Example 3

[0083] Taking the heating system of a certain heating company as an example in Example 3 of the present invention, the heat source of the company is a 60 MW coal-fired steam boiler, the heating area is 1 million square meters, and the indoor standard temperature is 18 °C. The heating system using cascaded energy utilization disclosed in Example 1 is adopted, and a heating method using cascaded energy utilization is specifically disclosed, including the following steps:

[0084] (1) The high-pressure steam generated by the coal-fired steam boiler is input into the steam turbine to do work and then discharges low-temperature exhausted steam. The low-temperature exhausted steam is transported through the steam pipe to the steam-water heat exchanger for heat exchange, and the obtained condensed water is returned to the coal-fired steam boiler through the condensate pipe for heating. Among them, the pressure of the high-pressure steam is 3.12 Mpa and the temperature is 480 °C, and the pressure of the low-temperature exhausted steam is 0.12 Mpa and the temperature is 190 °C.

[0085] (2) The flue gas generated by the coal combustion in the coal-fired steam boiler is transported through the flue to the primary desulfurization water bed for primary desulfurization treatment, and the primary desulfurization slurry is heated to 132 °C. Then, the primary desulfurization slurry circulation pump is started, and the heated primary desulfurization slurry is transported to the primary heat exchanger to exchange heat with the return water of the primary network and is cooled to 86 °C. The cooled primary desulfurization slurry is returned to the primary desulfurization water bed, and the primary heat exchanger simultaneously heats the 42 °C return water of the primary network to 52 °C to form the primary water supply. At the same time, the steam-water heat exchanger circulation pump is started, and the primary water supply is transported to the steam-water heat exchanger to exchange heat with the low-temperature exhausted steam.

[0086] (3) The flue gas after primary desulfurization treatment enters the secondary desulfurization water bed for secondary desulfurization treatment, and the secondary desulfurization slurry is heated to 32°C. Then, the secondary desulfurization slurry circulation pump is started to transport the heated secondary desulfurization slurry to the secondary heat exchanger to exchange heat with the intermediate water and cool it to 19°C. The cooled secondary desulfurization slurry returns to the secondary desulfurization water bed, and the secondary heat exchanger simultaneously heats the intermediate water to 19°C. And the intermediate water circulation pump is started to transport the heated intermediate water to the compression heat pump to exchange heat with the return water of the primary network and cool it to 15°C. The cooled intermediate water flows back to the secondary heat exchanger for heating. The compression heat pump operates simultaneously driven by the steam turbine to heat the 42°C return water of the primary network to 52°C to obtain the primary water supply. The primary water supply is transported to the steam-water heat exchanger to exchange heat with the low-temperature exhaust steam. The fully desulfurized flue gas is transported to the chimney through the flue for external discharge;

[0087] (4) The sewage at 12°C in the sewage channel is transported through the sewage pipe to the absorption heat pump to exchange heat with the return water of the primary network and cool it to 7°C. The cooled sewage flows back to the sewage channel through the sewage pipe. The absorption heat pump simultaneously heats the 40°C return water of the primary network to 52°C to obtain the primary water supply. The primary water supply is transported to the steam-water heat exchanger to exchange heat with the low-temperature exhaust steam;

[0088] (5) The 52°C primary water supply is transported to the steam-water heat exchanger to exchange heat with the low-temperature exhaust steam and is heated to 93°C to obtain the primary network water supply. Then, the primary network circulation pump is started to make the primary network water supply be transported through the primary network water supply pipe to the heat network heat exchanger to exchange heat with the 37°C return water of the secondary network and cool it to 40°C. The obtained primary network return water is transported to the primary heat exchanger, the absorption heat pump, and the compression heat pump for heating respectively. The heat network heat exchanger simultaneously heats the return water of the secondary network to 45°C to obtain the secondary network water supply. And the secondary network circulation pump is started simultaneously to make the secondary network water supply be transported through the secondary network water supply pipe to the heat user for heating and cooled to 37°C. After cooling, the obtained secondary network return water flows back to the heat network heat exchanger. It is actually measured that at this secondary network supply and return water temperature, the indoor temperature of the heat user reaches 24°C.

[0089] In this specification, each embodiment is described in a progressive manner. The key point of each embodiment is to illustrate the differences from other embodiments. For the same or similar parts among the embodiments, reference can be made to each other. For the device disclosed in the embodiment, since it corresponds to the method disclosed in the embodiment, the description is relatively simple. For the relevant parts, reference can be made to the description in the method part.

[0090] The foregoing description of the disclosed embodiments enables those skilled in the art to implement or use the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Thus, the present invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A heat supply system for cascaded utilization of energy, characterized in that, it includes a coal-fired steam boiler, a steam turbine, an exhaust steam waste heat recovery mechanism, a primary flue gas waste heat recovery mechanism, a secondary flue gas waste heat recovery mechanism, a sewage waste heat recovery mechanism, a primary network circulation mechanism and a secondary network circulation and heat exchange mechanism; The high-temperature steam outlet of the coal-fired steam boiler is connected to the steam turbine, and the flue gas outlet is sequentially connected to the primary flue gas waste heat recovery mechanism and the secondary flue gas waste heat recovery mechanism; The steam turbine is drivingly connected to the secondary flue gas waste heat recovery mechanism; The upstream of the exhaust steam waste heat recovery mechanism is connected to the steam turbine, and the downstream is connected to the coal-fired steam boiler; meanwhile, the upstream of the exhaust steam waste heat recovery mechanism is connected to the primary flue gas waste heat recovery mechanism, the secondary flue gas waste heat recovery mechanism and the sewage waste heat recovery mechanism, and the downstream is connected to the primary network circulation mechanism; The upstream of the primary flue gas waste heat recovery mechanism, the secondary flue gas waste heat recovery mechanism and the sewage waste heat recovery mechanism are respectively connected to the primary network circulation mechanism; The primary network circulation mechanism is connected to the secondary network circulation mechanism and forms a closed loop; The exhaust steam waste heat recovery mechanism includes a steam pipe, a steam-water heat exchanger and a condensate pipe; The steam pipe is connected to the steam outlet of the steam turbine and the hot water inlet pipe of the steam-water heat exchanger; The cold water outlet pipe of the steam-water heat exchanger is connected to the return water pipe of the coal-fired steam boiler, the cold water inlet pipe of the steam-water heat exchanger is respectively connected to the primary flue gas waste heat recovery mechanism, the secondary flue gas waste heat recovery mechanism and the sewage waste heat recovery mechanism, and the hot water outlet pipe of the steam-water heat exchanger is connected to the primary network circulation mechanism; The primary flue gas waste heat recovery mechanism includes a primary desulfurization water bed, a primary desulfurization slurry circulation pump, a primary heat exchanger and a steam-water heat exchanger circulation pump; The flue gas inlet of the primary desulfurization water bed is connected to the flue gas outlet of the coal-fired steam boiler, the flue gas outlet of the primary desulfurization water bed is connected to the secondary flue gas waste heat recovery mechanism, the desulfurization slurry outlet pipe of the primary desulfurization water bed is connected to the hot water inlet pipe of the primary heat exchanger, and the desulfurization slurry inlet pipe of the primary desulfurization water bed is connected to the cold water outlet pipe of the primary heat exchanger; The cold water inlet pipe of the primary heat exchanger is connected to the primary network circulation mechanism, and the hot water outlet pipe of the primary heat exchanger is connected to the cold water inlet pipe of the steam-water heat exchanger; The secondary flue gas waste heat recovery mechanism includes a secondary desulfurization water bed, a secondary desulfurization slurry circulation pump, a secondary heat exchanger, an intermediate water pipe, an intermediate water circulation pump and a compression heat pump; The flue gas inlet of the secondary desulfurization water bed is connected to the flue gas outlet of the primary desulfurization water bed, the flue gas outlet of the secondary desulfurization water bed is connected to the chimney, the desulfurization slurry outlet pipe of the secondary desulfurization water bed is connected to the hot water inlet pipe of the secondary heat exchanger, and the desulfurization slurry inlet pipe of the secondary desulfurization water bed is connected to the cold water outlet pipe of the secondary heat exchanger; The cold water inlet pipe of the secondary heat exchanger is connected to the intermediate water pipe, and the hot water outlet pipe of the secondary heat exchanger is connected to the hot water inlet pipe of the compression heat pump; The cold water outlet pipe of the compression heat pump is connected to the intermediate water pipe, the cold water inlet pipe of the compression heat pump is connected to the primary network circulation mechanism, and the hot water outlet pipe of the compression heat pump is connected to the cold water inlet pipe of the steam-water heat exchanger; The sewage waste heat recovery mechanism includes an absorption heat pump, a sewage channel, a sewage pipe, and a water pump; The hot water inlet pipe of the absorption heat pump is connected to the sewage channel, the cold water outlet pipe of the absorption heat pump is connected to the sewage channel, the cold water inlet pipe of the absorption heat pump is connected to the primary network circulation mechanism, and the hot water outlet pipe of the absorption heat pump is connected to the cold water inlet pipe of the steam-water heat exchanger; The desulfurized slurry inlet pipe and the desulfurized slurry outlet pipe are made of stainless steel.

2. A heat supply system for cascaded utilization of energy according to claim 1, wherein, The primary network circulation mechanism includes a heat network heat exchanger, a primary network water supply pipe, a primary network circulation pump, and a primary network return pipe; The hot water inlet pipe of the heat network heat exchanger is connected to the hot water outlet pipe of the steam-water heat exchanger through the primary network circulation pump and the primary network water supply pipe. The cold water outlet pipe of the heat network heat exchanger is respectively connected to the cold water inlet pipe of the primary heat exchanger, the cold water inlet pipe of the compression heat pump, and the water pump through the primary network return pipe. And the heat network heat exchanger is connected to the secondary network circulation and heat exchange mechanism and forms a closed loop.

3. A heat supply system for cascaded utilization of energy according to claim 2, wherein, The secondary network circulation and heat exchange mechanism includes a secondary network circulation pump, a secondary network water supply pipe, a heat user, and a secondary network return pipe; Upstream of the secondary network circulation pump is connected to the hot water outlet pipe of the heat network heat exchanger, and downstream is connected to the heat user through the secondary network water supply pipe; the heat user is connected to the cold water inlet pipe of the heat network heat exchanger through the secondary network return pipe.

4. A heat supply system for cascaded utilization of energy according to any one of claims 1 to 3, wherein, The primary desulfurized slurry circulation pump, the steam-water heat exchanger circulation pump, the secondary desulfurized slurry circulation pump, the intermediate water circulation pump, the primary network circulation pump, and the secondary network circulation pump are selected as variable frequency circulation pumps.

5. A heat supply method for cascaded utilization of energy, wherein, Using the heat supply system for cascaded utilization of energy according to any one of claims 1 to 4, includes the following steps: (1) The high-pressure steam generated by the coal-fired steam boiler is input into the steam turbine to do work and then discharges low-temperature exhaust steam. The low-temperature exhaust steam is transported through the steam pipe to the steam-water heat exchanger for heat exchange, and the obtained condensed water is returned to the coal-fired steam boiler through the condensate pipe for heating; (2) The flue gas generated by the combustion of coal in the coal-fired steam boiler is transported through the flue to the primary desulfurization water bed for primary desulfurization treatment and heat the primary desulfurized slurry. Then start the primary desulfurized slurry circulation pump to transport the heated primary desulfurized slurry to the primary heat exchanger to exchange heat with the primary network return water and then cool it. The cooled primary desulfurized slurry flows back to the primary desulfurization water bed, and the primary heat exchanger simultaneously heats up the primary network return water to form primary supply water; And simultaneously start the steam-water heat exchanger circulation pump to transport the primary supply water to the steam-water heat exchanger to exchange heat with the low-temperature exhaust steam; (3) The flue gas after primary desulfurization treatment enters the secondary desulfurization water bed for secondary desulfurization treatment, and the secondary desulfurization slurry is heated. Then, the secondary desulfurization slurry circulation pump is started to transport the heated secondary desulfurization slurry to the secondary heat exchanger to exchange heat with the intermediate water, and the cooled secondary desulfurization slurry returns to the secondary desulfurization water bed. The secondary heat exchanger simultaneously raises the temperature of the intermediate water. And the intermediate water circulation pump is started to transport the heated intermediate water to the compression heat pump to exchange heat with the return water of the primary network and then be cooled. The cooled intermediate water flows back to the secondary heat exchanger for heating. The compression heat pump operates simultaneously under the drive of the steam turbine to heat the return water of the primary network to obtain the primary water supply. The primary water supply is transported to the steam-water heat exchanger to exchange heat with the low-temperature exhaust steam. And the flue gas after complete desulfurization is transported to the chimney through the flue for external discharge. (4) The sewage in the sewage channel is transported through the sewage pipe to the absorption heat pump to exchange heat with the return water of the primary network and then be cooled. The cooled sewage flows back to the sewage channel through the sewage pipe. The absorption heat pump simultaneously heats the return water of the primary network to obtain the primary water supply. The primary water supply is transported to the steam-water heat exchanger to exchange heat with the low-temperature exhaust steam. (5) The primary water supply is transported to the steam-water heat exchanger to exchange heat with the low-temperature exhaust steam and then is heated to obtain the primary network water supply. Then, the primary network circulation pump is started to make the primary network water supply be transported through the primary network water supply pipe to the heat network heat exchanger to exchange heat with the return water of the secondary network. After cooling, the obtained primary network return water is respectively transported to the primary heat exchanger, the absorption heat pump, and the compression heat pump for heating. The heat network heat exchanger simultaneously heats the return water of the secondary network to obtain the secondary network water supply. And the secondary network circulation pump is started simultaneously to make the secondary network water supply be transported through the secondary network water supply pipe to the heat user for heating. After cooling, the obtained secondary network return water flows back to the heat network heat exchanger through the secondary network return water pipe.

6. A multi-source complementary heating method for cascaded utilization of energy according to claim 5, characterized in that, in step (1), the pressure of the high-pressure steam is 3.11 - 3.96 Mpa and the temperature is 430 - 480 °C, and the pressure of the low-temperature exhaust steam is 0.12 Mpa and the temperature is 190 °C; in step (2), the temperature of the heated primary desulfurization slurry is 120 - 132 °C, and the temperature of the cooled primary desulfurization slurry is 84 - 96 °C; the temperature of the primary water supply is 45 - 50 °C; in step (3), the temperature of the secondary desulfurization slurry after heating is 26 - 32 °C, and the temperature of the cooled secondary desulfurization slurry is 19 - 25 °C; the temperature of the heated intermediate water is 19 - 20 °C, and the temperature of the cooled intermediate water is 15 - 16 °C; the temperature of the primary water supply is 50 - 55 °C; in step (4), the temperature of the sewage in the sewage channel is 12 °C, the temperature of the cooled sewage is 7 °C, the temperature of the return water of the primary network is 40 °C, and the temperature of the primary water supply is 50 - 55 °C; In step (5), the supply water temperature of the primary network is 90 - 95 °C, and the return water temperature of the primary network is 40 - 45 °C; the supply water temperature of the secondary network is 45 - 50 °C, and the return water temperature of the secondary network is 35 - 40 °C.

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