A water and heat co-generation and co-transmission system for cascaded utilization of steam heat and a working method thereof

Abstract

The present invention discloses a water and heat co-production and co-transmission system and a working method for cascade utilization of steam heat. The present invention sends the three-stage extraction steam of the steam turbine unit into the steam cooler, heats the product water desalinated by the multi-effect distillation seawater desalination device, obtains high-temperature product water and supplies it, and realizes the co-transmission of water and heat to the outside. On the one hand, it avoids the increase of irreversible losses caused by the extraction steam with high superheat directly entering the feedwater heater for heat exchange. On the other hand, it realizes the co-transmission of water and heat from the power plant to the outside, enriching the diversity of the products supplied to the outside of the power plant. Compared with the water and heat distribution system, it simplifies the system pipeline layout and reduces the pipeline construction and maintenance costs.

Description

Technical Field

[0001] The invention belongs to the technical field of centralized heating and seawater utilization, and in particular relates to a water and heat co-generation and co-transmission system for cascaded utilization of steam heat and a working method. Background Art

[0002] Central heating is a way of organizing energy regional production by building centralized heat sources in industrial production areas and urban residential areas to provide production and living heat to enterprises and residents in and around the area. Central heating can save fuel, is easy to scale up, mechanize, and can centrally solve problems such as smoke pollution and ash fuel stacking. It has obvious economic, environmental and social benefits and has become one of the important infrastructures for modern urban construction.

[0003] However, the coverage rate of centralized heating in my country is still at a low level. Only the main towns in the northern provinces have built centralized heating systems. There are basically no centralized heating facilities in the southern towns and the vast rural areas of my country. They can only rely on independent heating methods such as natural gas stoves, air conditioners, electric stoves and honeycomb coal for heating. The coverage rate of centralized heating in developed countries such as Finland and Denmark is as high as 90%, and the national average is also above 60%. The future development of the real estate industry, the increase in urbanization rate, the removal of regional small boilers and the construction and reconstruction of pipelines in old urban areas have created huge and continuous demand for the centralized heating market. my country's centralized heating industry has a very broad development prospect.

[0004] On the other hand, with the rapid development of clean energy power generation such as wind and light, thermal power units are gradually transforming from the dominant position of electricity supply in the power system to a bottom-line position of supply guarantee. In order to improve the profitability and survival competitiveness of power plants, thermal power units need to transform from a single power supply to a comprehensive energy supply base such as electricity, heat, steam, cold, and water, and enrich the diversity of external supply products. For coastal power plants, combining seawater desalination with the thermal cycle of power generation and using the power plant's exhaust steam to provide the steam required for seawater desalination can greatly reduce the cost of seawater desalination and increase the profitability of power plants. For power plants with a variety of external supply products, how to reasonably couple the production process of each product with the thermal cycle of coal-fired units to reduce the total energy consumption of the system is an effective way to achieve energy conservation and emission reduction and increase profits in power plants.

[0005] The three-stage steam extraction of coal-fired power generation units is generally the first stage of steam extraction after reheating. The steam superheat is relatively high. If it directly enters the corresponding feedwater heater to heat the feedwater, the large temperature difference between the heat exchange between the two will lead to an increase in irreversible losses. The present invention proposes a water and heat co-production and delivery system and method for cascade utilization of steam heat, which uses three-stage steam extraction from coal-fired power generation units to heat seawater desalination product water, and realizes external water and heat delivery based on high-temperature product water. On the one hand, it avoids the increase in irreversible losses caused by the high-superheated extraction steam directly entering the feedwater heater for heat exchange. On the other hand, it realizes the external water and heat delivery of the power plant, enriching the diversity of external products of the power plant. Compared with the water and heat distribution system, it simplifies the system pipeline layout and reduces the pipeline construction and maintenance costs. Summary of the invention

[0006] The purpose of the present invention is to overcome the above-mentioned shortcomings and provide a water and heat co-production and co-transmission system and working method for the cascade utilization of steam heat. The present invention not only avoids the increase of irreversible losses caused by the extraction steam with high superheat directly entering the feedwater heater for heat exchange, but also realizes the co-transmission of water and heat from the power plant to the outside, enriches the diversity of the power plant's external supply products, simplifies the system pipeline layout, and reduces the pipeline construction and maintenance costs.

[0007] In order to achieve the above-mentioned purpose, a water and heat co-generation and co-transmission system for stepwise utilization of steam heat includes a boiler, the steam outlet of the boiler is connected to a high-pressure cylinder through a pipeline, the exhaust steam outlet of the high-pressure cylinder is connected to the boiler through a pipeline, the secondary heating steam outlet of the boiler is connected to an intermediate-pressure cylinder through a pipeline, the steam outlet of the intermediate-pressure cylinder is connected to a low-pressure cylinder through a pipeline, and the low-pressure cylinder is connected to a generator;

[0008] The exhaust steam outlet of the low-pressure cylinder is connected to the condenser and the multi-effect distillation seawater desalination device through a pipeline. The condenser is cooled by seawater. The condensate outlet of the condenser is connected to the condensate pump, the condensate pump is connected to the low-pressure heater group, the low-pressure heater group is connected to the deaerator, the deaerator is connected to the feed water pump, the feed water pump is connected to the high-pressure heater group, and the high-pressure heater group is connected to the boiler;

[0009] The seawater outlet of the condenser is connected to a multi-effect distillation seawater desalination device through a pipeline. The multi-effect distillation seawater desalination device is used to separate seawater into concentrated brine and product water. The product water outlet of the multi-effect distillation seawater desalination device is connected to a steam cooler and a delivery pipeline through a pipeline.

[0010] The first-stage steam extraction outlet of the intermediate pressure cylinder is connected to the steam cooler and the high-pressure heater group through a pipeline, the four-stage steam extraction outlet of the intermediate pressure cylinder is connected to the deaerator through a pipeline, the steam outlet of the steam cooler is connected to the high-pressure heater group through a pipeline, and the high-temperature product water outlet of the steam cooler is connected to the user side through a transmission pipeline.

[0011] A first valve is provided on the connecting pipeline between the low-pressure cylinder and the multi-effect distillation seawater desalination device;

[0012] A second valve is arranged on the connecting pipeline between the seawater outlet of the condenser and the multi-effect distillation seawater desalination device.

[0013] A third valve is provided on the connecting pipeline between the first stage extraction steam of the intermediate pressure cylinder and the steam cooler;

[0014] A fourth valve is provided on the connecting pipeline between the first stage extraction steam of the medium pressure cylinder and the high pressure heater group;

[0015] A fifth valve is provided on the connecting pipeline between the steam outlet of the steam cooler and the high-pressure heater group.

[0016] A sixth valve is provided on the connecting pipeline between the product water outlet of the multi-effect distillation seawater desalination device and the steam cooler;

[0017] A seventh valve is provided on the connecting pipeline between the product water outlet of the multi-effect distillation seawater desalination device and the delivery pipeline.

[0018] The user side includes a heat exchange device, which is connected to the delivery pipeline. The heat exchange device is used to exchange heat between the high-temperature product water sent from the delivery pipeline and the return water of the urban heating network, transfer the heat to the heating network water, and become normal-temperature product water, which is then supplied to the water plant or other fresh water users;

[0019] An eighth valve is provided on the connecting pipeline between the delivery pipeline and the heat exchange device;

[0020] A ninth valve is arranged on the connecting pipeline between the delivery pipeline and the water plant.

[0021] The low-pressure heater group includes a first low-pressure heater, a second low-pressure heater, a third low-pressure heater and a fourth low-pressure heater;

[0022] The condensate outlet of the condensate pump is connected to the upstream of the first low-pressure heater, and the second low-pressure heater, the third low-pressure heater and the fourth low-pressure heater are connected in sequence downstream of the first low-pressure heater. The first-stage extraction steam, the second-stage extraction steam and the third-stage extraction steam of the low-pressure cylinder are connected to the third low-pressure heater, the second low-pressure heater and the first low-pressure heater respectively as heat sources, and the third-stage extraction steam of the medium-pressure cylinder is connected to the fourth low-pressure heater as a heat source.

[0023] The high-voltage heater group includes a first high-voltage heater, a second high-voltage heater and a third high-voltage heater;

[0024] The first high-pressure heater is connected to a feed water pump upstream, the second high-pressure heater and the third high-pressure heater are connected in sequence downstream of the first high-pressure heater, the third high-pressure heater is connected to a boiler, the first-stage extraction steam of the intermediate-pressure cylinder is connected to the first high-pressure heater as a heat source, and the first-stage extraction steam and the second-stage extraction steam of the high-pressure cylinder are connected to the third high-pressure heater and the second high-pressure heater respectively as heat sources.

[0025] A working method of a water and heat co-generation and co-transmission system for cascaded utilization of steam heat, comprising the following steps:

[0026] When the seawater desalination device is started, part of the heated seawater in the cooling water outlet of the condenser enters the multi-effect distillation seawater desalination device as raw seawater, and part of the exhaust steam of the low-pressure cylinder enters the multi-effect distillation seawater desalination device as a driving heat source. After the raw seawater and the exhaust steam complete multi-stage distillation in the multi-effect distillation seawater desalination device, the raw seawater is separated into concentrated brine and product water;

[0027] When the unit is supplying heat to the outside at the same time, the first-stage extraction steam from the intermediate pressure cylinder enters the steam cooler to heat the product water, and then enters the first high-pressure heater to heat the feed water. The high-temperature product water at the outlet of the steam cooler enters the transmission pipeline and is transported to the user side.

[0028] When the unit does not supply heat to the outside, the product water at the outlet of the multi-effect distillation seawater desalination device is directly sent into the transmission pipeline and transported to the user side.

[0029] When the seawater desalination device is started, the first valve and the second valve 22 are opened;

[0030] When the unit is supplying heat to the outside at the same time, open the third valve, the fifth valve, the sixth valve and the eighth valve, and close the fourth valve, the seventh valve and the ninth valve;

[0031] When the unit does not supply heat to the outside, close the third valve, the fifth valve, the sixth valve and the eighth valve, and open the fourth valve, the seventh valve and the ninth valve.

[0032] On the user side, the high-temperature product water exchanges heat with the return water of the city heating network in the heat exchange device, transfers the heat to the heating network water, becomes normal-temperature product water, and then supplies it to the water plant or other fresh water users;

[0033] On the user side, the product water is transported to the water plant or other fresh water users through the ninth valve.

[0034] Compared with the prior art, the present invention sends the three-stage extraction steam of the steam turbine unit into the steam cooler to heat the product water desalinated by the multi-effect distillation seawater desalination device to obtain high-temperature product water, thereby realizing the simultaneous delivery of water and heat to the outside. On the one hand, it avoids the increase of irreversible losses caused by the extraction steam with high superheat directly entering the feedwater heater for heat exchange. On the other hand, it realizes the simultaneous delivery of water and heat from the power plant to the outside, enriching the diversity of products supplied to the outside of the power plant. Compared with the water and heat distribution system, it simplifies the system pipeline layout and reduces the pipeline construction and maintenance costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 is a system diagram of the present invention;

[0036] Among them, 1. boiler, 2. high-pressure cylinder, 3. medium-pressure cylinder, 4. low-pressure cylinder, 5. first generator, 6. condenser, 7. condensate pump, 8. first low-pressure heater, 9. second low-pressure heater, 10. third low-pressure heater, 11. fourth low-pressure heater, 12. deaerator, 13. feed water pump, 14. first high-pressure heater, 15. second high-pressure heater, 16. third high-pressure heater, 17. multi-effect distillation desalination device, 18. steam cooler, 19. transmission pipeline, 20. heat exchange device, 21. first valve, 22. second valve, 23. third valve, 24. fourth valve, 25. fifth valve, 26. sixth valve, 27. seventh valve, 28. eighth valve, 29. ninth valve. DETAILED DESCRIPTION

[0037] The present invention will be further described below in conjunction with the accompanying drawings.

[0038] See also Figure 1 , a water and heat co-generation and co-transmission system for cascade utilization of steam heat, comprising a boiler 1, the steam outlet of the boiler 1 is connected to a high-pressure cylinder 2 through a pipeline, the exhaust steam outlet of the high-pressure cylinder 2 is connected to the boiler 1 through a pipeline, the secondary heating steam outlet of the boiler 1 is connected to an intermediate-pressure cylinder 3 through a pipeline, the steam outlet of the intermediate-pressure cylinder 3 is connected to a low-pressure cylinder 4 through a pipeline, and the low-pressure cylinder 4 is connected to a generator 5;

[0039] The exhaust steam outlet of the low-pressure cylinder 4 is connected to the condenser 6 and the multi-effect distillation seawater desalination device 17 through a pipeline. The condenser 6 is cooled by seawater. The condensate outlet of the condenser 6 is connected to the low-pressure heater group. A condensate pump 7 is provided on the connecting pipeline between the condenser 6 and the low-pressure heater group. The low-pressure heater group is connected to the deaerator 12. The deaerator 12 is connected to the high-pressure heater group. The high-pressure heater group is connected to the boiler. A feed water pump 13 is provided on the connecting pipeline between the deaerator 12 and the high-pressure heater group.

[0040] The seawater outlet of the condenser 6 is connected to a multi-effect distillation desalination device 17 through a pipeline. The multi-effect distillation desalination device 17 is used to separate seawater into concentrated brine and product water. The product water outlet of the multi-effect distillation desalination device 17 is connected to a steam cooler 18 and a delivery pipeline 19 through a pipeline.

[0041] The first-stage steam extraction outlet of the intermediate pressure cylinder 3 is connected to the steam cooler 18 and the high-pressure heater group through a pipeline, the four-stage steam extraction outlet of the intermediate pressure cylinder 3 is connected to the deaerator 12 through a pipeline, the steam outlet of the steam cooler 18 is connected to the high-pressure heater group through a pipeline, and the high-temperature product water outlet of the steam cooler 18 is connected to the user side through a delivery pipeline 19.

[0042] A first valve 21 is provided on the connecting pipeline between the low-pressure cylinder 4 and the multi-effect distillation desalination device 17; a second valve 22 is provided on the connecting pipeline between the seawater outlet of the condenser 6 and the multi-effect distillation desalination device 17. A third valve 23 is provided on the connecting pipeline between the first-stage extraction steam of the medium-pressure cylinder 3 and the steam cooler 18; a fourth valve 24 is provided on the connecting pipeline between the first-stage extraction steam of the medium-pressure cylinder 3 and the high-pressure heater group; a fifth valve 25 is provided on the connecting pipeline between the steam outlet of the steam cooler 18 and the high-pressure heater group. A sixth valve 26 is provided on the connecting pipeline between the product water outlet of the multi-effect distillation desalination device 17 and the steam cooler 18; a seventh valve 27 is provided on the connecting pipeline between the product water outlet of the multi-effect distillation desalination device 17 and the delivery pipeline 19.

[0043] The user side includes a heat exchange device 20, which is connected to the delivery pipeline 19. The heat exchange device 20 is used to exchange heat between the high-temperature product water delivered by the delivery pipeline 19 and the return water of the urban heating network, and transfer the heat to the heating network water to become normal temperature product water. The product water after heat exchange is supplied to the water plant or other fresh water users; an eighth valve 28 is provided on the connecting pipeline between the delivery pipeline 19 and the heat exchange device 20; and a ninth valve 29 is provided on the connecting pipeline between the delivery pipeline 19 and the water plant.

[0044] The low-pressure heater group includes a first low-pressure heater 8, a second low-pressure heater 9, a third low-pressure heater 10 and a fourth low-pressure heater 11; the first low-pressure heater 8 is connected to the condensate outlet of the condensate pump 7 upstream, and the first low-pressure heater 8 is connected to the second low-pressure heater 9, the third low-pressure heater 10 and the fourth low-pressure heater 11 in sequence downstream, and the first-stage extraction steam, the second-stage extraction steam and the third-stage extraction steam of the low-pressure cylinder 4 are connected to the third low-pressure heater 10, the second low-pressure heater 9 and the first low-pressure heater 8 as heat sources respectively. The third-stage extraction steam of the medium-pressure cylinder 3 is connected to the fourth low-pressure heater 11 as a heat source.

[0045] The high-pressure heater group includes a first high-pressure heater 14, a second high-pressure heater 15 and a third high-pressure heater 16; the first high-pressure heater 14 is connected to the feed water pump 13 upstream, and the first high-pressure heater 14 is connected to the second high-pressure heater 15 and the third high-pressure heater 16 downstream in sequence, the third high-pressure heater 16 is connected to the boiler 1, the first-stage extraction steam of the intermediate pressure cylinder 3 is connected to the first high-pressure heater 14 as a heat source, and the first-stage extraction steam and the second-stage extraction steam of the high-pressure cylinder 2 are connected to the third high-pressure heater 16 and the second high-pressure heater 15 as heat sources respectively.

[0046] The conveying pipeline 19 is provided with a heat-insulating layer to reduce the heat loss of the high-temperature product water during the conveying process.

[0047] The working method of the present invention is as follows:

[0048] The new steam at the outlet of boiler 1 enters the high-pressure cylinder 2 to expand and do work, and then returns to boiler 1 for secondary heating, and then enters the medium-pressure cylinder 3 and the low-pressure cylinder 4 in sequence to expand and do work, driving the first generator 5 to generate electricity. The exhaust steam of the low-pressure cylinder 4 enters the condenser 6 for condensation, and then passes through the condensate pump 7, the first low-pressure heater 8, the second low-pressure heater 9, the third low-pressure heater 10, the fourth low-pressure heater 11, and then passes through the deaerator 12 and the feedwater pump 13, and then enters the first high-pressure heater 14, the second high-pressure heater 15, the third high-pressure heater 16, and finally returns to boiler 1 to complete the steam-water cycle of the coal-fired generator set.

[0049] When the seawater desalination device is started, the first valve 21 and the second valve 22 are opened, and part of the heated seawater in the cooling water outlet of the condenser 6 enters the multi-effect distillation seawater desalination device 17 as raw seawater, and part of the exhaust steam of the low-pressure cylinder 4 enters the multi-effect distillation seawater desalination device 17 as a driving heat source. After the raw seawater and the exhaust steam complete multi-stage distillation in the multi-effect distillation seawater desalination device 17, the exhaust steam condenses and releases heat and returns to the outlet of the condenser 6, and the raw seawater is separated into concentrated brine and product water;

[0050] When the unit supplies heat to the outside at the same time, the third valve 23, the fifth valve 25, the sixth valve 26 and the eighth valve 28 are opened, and the fourth valve 24, the seventh valve 27 and the ninth valve 29 are closed. The first-stage extraction steam of the intermediate pressure cylinder 3 enters the steam cooler 18 to heat the product water, and then enters the first high-pressure heater 14 to heat the feed water. The high-temperature product water at the outlet of the steam cooler 18 enters the transmission pipeline 19 and is transported to the user side; on the user side, the high-temperature product water exchanges heat with the return water of the urban heating network in the heat exchange device 20, transfers the heat to the heating network water, becomes normal temperature product water, and then supplies the water plant or other fresh water users.

[0051] When the unit does not supply heat to the outside, the third valve 23, the fifth valve 25, the sixth valve 26 and the eighth valve 28 are closed, the fourth valve 24, the seventh valve 27 and the ninth valve 29 are opened, and the product water at the outlet of the multi-effect distillation seawater desalination device 17 is directly sent to the delivery pipeline 19 and delivered to the user side. On the user side, the product water is delivered to the water plant or other fresh water users through the ninth valve 29.

Claims

1. A water and heat co-production and co-transmission system for cascaded utilization of steam heat, characterized in that: The invention comprises a boiler (1), wherein the steam outlet of the boiler (1) is connected to a high-pressure cylinder (2) via a pipeline, the exhaust steam outlet of the high-pressure cylinder (2) is connected to the boiler (1) via a pipeline, the secondary heating steam outlet of the boiler (1) is connected to a medium-pressure cylinder (3) via a pipeline, the steam outlet of the medium-pressure cylinder (3) is connected to a low-pressure cylinder (4) via a pipeline, and the low-pressure cylinder (4) is connected to a generator (5); The exhaust outlet of the low-pressure cylinder (4) is connected to the condenser (6) and the multi-effect distillation seawater desalination device (17) through a pipeline. The condenser (6) is cooled by seawater. The condensate outlet of the condenser (6) is connected to the condensate pump (7). The outlet of the condensate pump (7) is connected to the low-pressure heater group. The low-pressure heater group is connected to the deaerator (12). The deaerator (12) is connected to the feed water pump (13). The feed water pump (13) is connected to the high-pressure heater group. The high-pressure heater group is connected to the boiler. The seawater outlet of the condenser (6) is connected to a multi-effect distillation seawater desalination device (17) via a pipeline. The multi-effect distillation seawater desalination device (17) is used to separate seawater into concentrated brine and product water. The product water outlet of the multi-effect distillation seawater desalination device (17) is connected to a steam cooler (18) and a delivery pipeline (19) via a pipeline. The first-stage steam extraction outlet of the intermediate pressure cylinder (3) is connected to the steam cooler (18) and the high-pressure heater group through a pipeline, the four-stage steam extraction outlet of the intermediate pressure cylinder (3) is connected to the deaerator (12) through a pipeline, the steam outlet of the steam cooler (18) is connected to the high-pressure heater group through a pipeline, and the high-temperature product water outlet of the steam cooler (18) is connected to the user side through a delivery pipeline (19); A third valve (23) is provided on a connecting pipeline between the first-stage steam extraction of the medium-pressure cylinder (3) and the steam cooler (18); A fourth valve (24) is provided on the connecting pipeline between the first stage extraction steam of the medium pressure cylinder (3) and the high pressure heater group; A fifth valve (25) is provided on the connection pipeline between the steam outlet of the steam cooler (18) and the high-pressure heater group; The low-pressure heater group comprises a first low-pressure heater (8), a second low-pressure heater (9), a third low-pressure heater (10) and a fourth low-pressure heater (11); The first low-pressure heater (8) is connected upstream to the condensate outlet of the condensate pump (7), the first low-pressure heater (8) is connected downstream in sequence to the second low-pressure heater (9), the third low-pressure heater (10) and the fourth low-pressure heater (11), the first-stage extraction steam of the low-pressure cylinder (4) is connected to the third low-pressure heater (10), the second-stage extraction steam is connected to the second low-pressure heater (9), the third-stage extraction steam is connected to the first low-pressure heater (8), and the third-stage extraction steam of the medium-pressure cylinder (3) is connected to the fourth low-pressure heater (11); The high-voltage heater group includes a first high-voltage heater (14), a second high-voltage heater (15) and a third high-voltage heater (16); The first high-pressure heater (14) is connected to the feed water pump (13) upstream, and the first high-pressure heater (14) is connected to the second high-pressure heater (15) and the third high-pressure heater (16) downstream in sequence, the third high-pressure heater (16) is connected to the boiler (1), the first-stage extraction steam of the intermediate-pressure cylinder (3) is connected to the first high-pressure heater (14) as a heat source, and the first-stage extraction steam and the second-stage extraction steam of the high-pressure cylinder (2) are connected to the third high-pressure heater (16) and the second high-pressure heater (15) as heat sources, respectively.

2. The water and heat co-generation and co-transmission system for cascaded utilization of steam heat according to claim 1 is characterized in that: A first valve (21) is provided on a connecting pipeline between the low-pressure cylinder (4) and the multi-effect distillation seawater desalination device (17); A second valve (22) is provided on the connecting pipeline between the seawater outlet of the condenser (6) and the multi-effect distillation seawater desalination device (17).

3. The water and heat co-generation and co-transmission system for cascaded utilization of steam heat according to claim 1 is characterized in that: A sixth valve (26) is provided on the connecting pipeline between the product water outlet of the multi-effect distillation seawater desalination device (17) and the steam cooler (18); A seventh valve (27) is provided on the connecting pipeline between the product water outlet of the multi-effect distillation seawater desalination device (17) and the delivery pipeline (19).

4. The water and heat co-generation and co-transmission system for cascaded utilization of steam heat according to claim 1 is characterized in that: The user side includes a heat exchange device (20), the heat exchange device (20) is connected to the delivery pipeline (19), and the heat exchange device (20) is used to exchange heat between the high-temperature product water delivered by the delivery pipeline (19) and the return water of the urban heating network, and transfer the heat to the heating network water to become normal-temperature product water, and the product water is supplied to the water plant or other fresh water users; An eighth valve (28) is provided on the connecting pipeline between the delivery pipeline (19) and the heat exchange device (20); A ninth valve (29) is provided on the connecting pipeline between the delivery pipeline (19) and the water plant.

5. The working method of the water and heat co-generation and co-transmission system for cascaded utilization of steam heat as claimed in claim 1 is characterized in that: The following steps are involved: When the seawater desalination device is started, part of the heated seawater in the cooling water outlet of the condenser (6) enters the multi-effect distillation seawater desalination device (17) as raw seawater, and part of the exhaust steam of the low-pressure cylinder (4) enters the multi-effect distillation seawater desalination device (17) as a driving heat source. After the raw seawater and the exhaust steam complete multi-stage distillation in the multi-effect distillation seawater desalination device (17), the raw seawater is separated into concentrated brine and product water. When the unit is supplying heat to the outside at the same time, the first-stage extraction steam of the intermediate pressure cylinder (3) enters the steam cooler (18) to heat the product water, and then enters the first high-pressure heater (14) to heat the feed water. The high-temperature product water at the outlet of the steam cooler (18) enters the delivery pipeline (19) and is delivered to the user side. When the unit does not supply heat to the outside, the product water at the outlet of the multi-effect distillation seawater desalination device (17) is directly sent to the transmission pipeline (19) and is transported to the user side.

6. The working method of the water and heat co-generation and co-transmission system for cascaded utilization of steam heat according to claim 5 is characterized in that: When the seawater desalination device is started, the first valve (21) and the second valve 22 are opened; When the unit is supplying heat to the outside at the same time, the third valve (23), the fifth valve (25), the sixth valve (26) and the eighth valve (28) are opened, and the fourth valve (24), the seventh valve (27) and the ninth valve (29) are closed; When the unit does not supply heat to the outside, the third valve (23), the fifth valve (25), the sixth valve (26) and the eighth valve (28) are closed, and the fourth valve (24), the seventh valve (27) and the ninth valve (29) are opened.

7. The working method of a water and heat co-generation and co-transmission system for cascaded utilization of steam heat according to claim 5 is characterized in that: On the user side, the high-temperature product water exchanges heat with the return water of the city heating network in the heat exchange device (20), transfers heat to the heating network water, becomes normal-temperature product water, and is then supplied to the water plant or other fresh water users; On the user side, the product water is transported to the water plant or other fresh water users through the ninth valve (29).

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