System structure for improving heat efficiency of unit by reconstructing steam source of air heater

Abstract

The utility model discloses a system structure for improving heat efficiency of a unit through steam air heater steam source reconstruction, air preheaters are arranged on a primary air pipeline and a secondary air pipeline, a primary air steam air heater is further arranged on the primary air pipeline on the upstream sides of the air preheaters, and a secondary air steam air heater is further arranged on the secondary air pipeline; the system further comprises a pressure matcher, the steam extraction source input end of the pressure matcher is connected with the upstream side of the steam exhausting and condensing device, the driving steam source input end of the pressure matcher is connected with a steam exhausting pipeline or a regenerative steam extraction pipeline of the intermediate-pressure cylinder, and the steam output end of the pressure matcher is connected with the heat exchange medium input end of the primary air steam air heater. The steam output end of the pressure matcher is further connected with the heat exchange medium input end of the secondary air steam air heater. The low-pressure cylinder is used for exhausting steam, cold source loss is reduced, a boiler air heater steam source is replaced, heat economy of the unit is improved, a thermodynamic system is innovated and reconstructed, and technical and economic feasibility is high.

Description

Technical Field

[0001] This utility model belongs to the field of coal-fired power generation technology, specifically relating to a system structure for improving the thermal efficiency of a generator unit by reconfiguring the steam source of a heater. Background Technology

[0002] Under the "dual carbon" target, deeply exploring the thermal economy of coal-fired power units and achieving high efficiency under all operating conditions is one of the key focuses of the new generation of coal-fired power plants. Unit efficiency mainly depends on boiler efficiency and turbine absolute internal efficiency. In modern units, boiler thermal efficiency is generally around 94.5%, with flue gas heat loss being the largest component of boiler heat loss, accounting for approximately 70-80%. Therefore, the core of improving boiler thermal efficiency is to find ways to reduce flue gas temperature or maximize the recovery and utilization of flue gas heat.

[0003] The absolute internal efficiency of a steam turbine reflects the actual thermal efficiency of the turbine unit's thermodynamic cycle. The heat input from the boiler to the turbine, after deducting the portion used for power generation, is lost as a cold source loss—the heat released into the environment by the exhaust steam from the turbine's low-pressure cylinder through the condenser. The absolute efficiency of a steam turbine is generally around 50%, with cold source losses accounting for approximately 50%. Therefore, fully utilizing the energy (mainly latent heat) of the turbine's low-pressure cylinder exhaust steam and reducing cold source losses are important directions for improving the efficiency of coal-fired power units. However, the low-pressure cylinder exhaust steam is waste steam after power generation, with low grade, making it difficult to utilize effectively.

[0004] Power plant boilers generally use an ambient temperature of 25℃ as the air input design temperature. When the ambient temperature is lower than the air design temperature or the boiler flue gas temperature decreases, causing the overall temperature of the cold end of the air preheater to be lower than the limit, it is generally necessary to put in a steam heater to increase the air inlet temperature of the air preheater and ensure that the overall temperature of the cold end of the air preheater is not lower than the limit requirement, so as to avoid cold end corrosion and ash accumulation blockage.

[0005] Steam-powered air heaters are typically located upstream of the air preheater on the wind side, or on the fan outlet or inlet duct. In engineering, a comprehensive consideration must be given to the power source, piping and equipment system resistance, and condensate return. The steam source is generally taken from the unit's auxiliary steam header. The auxiliary steam source usually comes from the exhaust steam of the intermediate-pressure cylinder (fourth-stage or fifth-stage extraction), with a pressure generally around 1 MPa.a. The extracted steam has a high grade; extracting steam from between stages reduces the work flow for the air heaters, resulting in less power generation and thus an increase in the unit's coal consumption rate. Taking a 660MW air-cooled unit as an example, under winter conditions and rated output, a single unit's air heater consumes approximately 20t / h of steam, resulting in a reduction of 4100kW in power generation, equivalent to an increase of 50kJ / kWh in heat consumption and approximately 1.8g / kWh in coal consumption.

[0006] Therefore, an improved system structure needs to be designed to improve the thermal efficiency of coal-fired power generating units in winter environments. Utility Model Content

[0007] The technical problem to be solved by this utility model is to provide a system structure for improving the thermal efficiency of the unit by reconstructing the steam source of the heater, thereby solving the problem of low thermal efficiency and increased coal consumption for power generation in the existing unit under winter conditions. By innovating and reconstructing the heat source of the heater, the heat of the turbine exhaust steam is fully utilized, the loss of cold source is reduced, and the thermal economy of the unit is improved.

[0008] According to the technical solution of this utility model, this utility model provides a system structure for improving the thermal efficiency of a unit by reconfiguring the steam source of a heater. It includes a boiler, a high-pressure cylinder, a medium-pressure cylinder, a low-pressure cylinder, and a steam exhaust condenser connected in sequence. It also includes a primary air duct and a secondary air duct, with air preheaters installed on both the primary and secondary air ducts. Upstream of the air preheaters, a primary air steam heater is installed on the primary air duct, and a secondary air steam heater is installed on the secondary air duct. Furthermore, it includes a pressure matching device. The steam source input end of the pressure matching device is connected to the upstream side of the steam exhaust condenser. The driving steam source input end of the pressure matching device is connected to the steam exhaust duct or the regenerative steam extraction duct of the medium-pressure cylinder. The steam output end of the pressure matching device is connected to the heat exchange medium input end of the primary air steam heater, and the steam output end of the pressure matching device is also connected to the heat exchange medium input end of the secondary air steam heater.

[0009] Furthermore, the driving steam source input end of the pressure matcher is connected to the four-section or five-section extraction steam pipeline of the intermediate pressure cylinder.

[0010] Furthermore, a primary air heating regulating valve is installed in the pipeline upstream of the heat exchange medium input end of the primary air steam heater; a secondary air heating regulating valve is installed in the pipeline upstream of the heat exchange medium input end of the secondary air steam heater.

[0011] Furthermore, the heat exchange medium output end of the primary air steam heater is connected to the heater condensate collection system, and the heat exchange medium output end of the secondary air steam heater is also connected to the heater condensate collection system.

[0012] Furthermore, a primary air fan is installed on the primary air duct, and the primary air fan is located upstream of the primary air steam heater; a supply air fan is installed on the secondary air duct, and the supply air fan is located upstream of the secondary air steam heater.

[0013] Furthermore, the high-temperature flue gas output end of the boiler is sequentially connected to an air preheater, an electrostatic precipitator, an induced draft fan, a desulfurization and dust removal tower, and a chimney.

[0014] Compared with the prior art, the beneficial technical effects of this utility model are as follows:

[0015] This invention proposes a rationally designed pressure matching device to extract low-pressure cylinder exhaust steam using appropriately sized high-pressure steam, producing medium-pressure steam as the steam source for a steam heater. Conventional steam heaters use fourth- or fifth-stage extraction steam, utilizing the sensible and latent heat of the extracted steam to heat boiler cold air. This invention utilizes the steam produced from the low-pressure cylinder exhaust steam extracted by the pressure matching device as the heater's steam source to heat boiler cold air. While utilizing the heat (mainly latent heat) from the low-pressure cylinder exhaust steam, the replaced conventional heater steam continues to generate electricity in the turbine, improving unit thermal efficiency. This invention fully utilizes low-pressure cylinder exhaust steam, reduces cold source losses, and replaces the boiler heater's steam source, aiming to improve unit thermal economy. It is applicable not only to newly built units but also to existing units, without limitations on unit parameters, capacity, or cold-end type. It represents an innovation and restructuring of the thermal system, with strong technical and economic feasibility, making it worthy of development and promotion. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of the system structure provided by this utility model.

[0017] Explanation of reference numerals in the attached figures:

[0018] 1. Boiler; 2. High-pressure cylinder; 3. Medium-pressure cylinder; 4. Low-pressure cylinder; 5. Exhaust steam condenser; 6. Primary air duct; 7. Secondary air duct; 8. Air preheater; 9. Primary air steam heater; 10. Secondary air steam heater; 11. Pressure matching device; 12. Primary air heating regulating valve; 13. Secondary air heating regulating valve; 14. Electrostatic precipitator; 15. Exhaust fan; 16. Desulfurization and dust removal tower; 17. Chimney. Detailed Implementation

[0019] This utility model provides a system structure for improving the thermal efficiency of a generator unit by reconstructing the steam source of the heater, which solves the problems of low thermal efficiency and increased coal consumption in power generation of existing units in winter. By innovating and reconstructing the heat source of the heater, the heat of the turbine exhaust steam is fully utilized, the loss of cold source is reduced, and the thermal economy of the unit is improved.

[0020] Please see Figure 1 This utility model discloses a system structure for improving the thermal efficiency of a generator unit through steam source reconfiguration in a heater. The system includes a boiler 1, a high-pressure cylinder 2, a medium-pressure cylinder 3, a low-pressure cylinder 4, and an exhaust condenser 5, all connected in sequence. It also includes a primary air duct 6 and a secondary air duct 7. The high-pressure cylinder 2, medium-pressure cylinder 3, low-pressure cylinder 4, and generator are components of a steam turbine. The primary air duct 6 and secondary air duct 7 are directly or indirectly connected to the boiler 1.

[0021] The above structure is a common structure (part of it) in existing coal-fired power generating units. The main improvement of this utility model is that a pressure matching device 11 is also provided. An air preheater 8 is provided on the primary air duct 6 and the secondary air duct 7. Upstream of the air preheater 8, a primary air steam heater 9 is also provided on the primary air duct 6, and a secondary air steam heater 10 is also provided on the secondary air duct 7. The steam source input end of the pressure matching device 11 is connected to the upstream side of the exhaust steam condensing device 5. The driving steam source input end of the pressure matching device 11 is connected to the exhaust steam duct or the regenerative steam extraction duct of the intermediate pressure cylinder 3. The steam output end of the pressure matching device 11 is connected to the heat exchange medium input end of the primary air steam heater 9. The steam output end of the pressure matching device 11 is also connected to the heat exchange medium input end of the secondary air steam heater 10.

[0022] Specifically, for example, the driving steam source input end of the pressure matching device 11 is connected to the exhaust steam pipeline of the intermediate pressure cylinder 3, which is equivalent to connecting to the exhaust side of the intermediate pressure cylinder or to the pipeline between the intermediate pressure cylinder and the low pressure cylinder; another example is that the driving steam source input end of the pressure matching device 11 is connected to the regenerative extraction steam pipeline of the intermediate pressure cylinder 3. The regenerative extraction steam pipeline has the existing structure of the intermediate pressure cylinder and is used to extract steam from the corresponding position of the intermediate pressure cylinder and lead it to the regenerative system. More specifically, the driving steam source input end of the pressure matching device 11 is connected to the four-section or five-section extraction steam pipeline in the regenerative extraction steam pipeline of the intermediate pressure cylinder 3.

[0023] Pressure matching devices are mature industrial equipment in power plants. One application of pressure matching devices is the water jet ejector used for vacuuming the unit. Their working principle involves using high-pressure driving steam as a power source, which is injected through a nozzle to form a high-speed jet stream. A low-pressure zone is created at the throat, creating a pressure difference between the low-pressure steam being pumped in and the high-pressure steam. After mixing and diffusion of the high and low-pressure steam, the output pressure is higher than the pressure of the pumped low-pressure steam, thus achieving the purpose of pressurizing the low-pressure steam. In this invention, a pressure matching device is used, with the exhaust steam from the medium-pressure cylinder as the driving steam source, to extract the exhaust steam (waste steam) from the low-pressure cylinder, producing product steam with suitable parameters. This product steam is then used as the steam source for the steam heater, replacing the four-stage (or five-stage) steam extraction, thereby improving the unit's thermal economy. In low-temperature winter conditions, the primary and secondary cold air are first heated by the steam heater, and then further heated by the air preheater 8.

[0024] The pressure matching device needs to be specifically matched and designed based on the parameters of the driving steam source, the extraction steam source, and the required product steam parameters (pressure, flow rate, etc.). In specific projects, a reasonable pressure matching device system needs to be set up according to the characteristics of the unit's regenerative system, the parameter requirements of the boiler air heater, and the economic efficiency of investment. This includes the selection of the driving steam source for the pressure matching device and the number of pressure matching device stages. In the illustrated embodiment, the number of pressure matching device stages is one; in other embodiments, if the product parameters of the primary pressure matching device cannot meet the requirements, a secondary pressure matching device can be added in series. The secondary pressure matching device uses the product steam of the primary pressure matching device as the extraction steam source. The driving steam source of the secondary pressure matching device can be the same as or different from that of the primary pressure matching device. The steam output end of the secondary pressure matching device is then connected to the heat exchange medium input end of the primary air steam heater 9 and the secondary air steam heater 10.

[0025] More specifically, a primary air heating regulating valve 12 is installed in the pipeline upstream of the heat exchange medium input end of the primary air steam heater 9, and a secondary air heating regulating valve 13 is installed in the pipeline upstream of the heat exchange medium input end of the secondary air steam heater 10. Both the primary air heating regulating valve 12 and the secondary air heating regulating valve 13 can be electric valves. The primary air heating regulating valve 12 and the secondary air heating regulating valve 13 are respectively installed on two branch pipes of the steam output end pipeline of the pressure matching device 11. By adjusting the primary air heating regulating valve 12 and the secondary air heating regulating valve 13, the on / off state and flow rate can be controlled, thereby controlling the heating of cold air by the primary air steam heater 9 and the secondary air steam heater 10.

[0026] The heat exchange medium output end of the primary air steam heater 9 is connected to the heater condensate collection system, and the heat exchange medium output end of the secondary air steam heater 10 is connected to the heater condensate collection system to collect the condensate after heat exchange. It can also be connected to the water circulation system of the whole unit, for example, to the downstream side of the exhaust steam condensing device 5.

[0027] A primary air fan is installed on the primary air duct 6, located upstream of the primary air steam heater 9, thus forming primary cold air. The primary cold air undergoes its first heating after passing through the primary air steam heater 9, and then undergoes its second heating after passing through the air preheater 8, forming primary hot air. Primary hot air is generally used to transport pulverized coal into the boiler furnace and to provide oxygen.

[0028] A blower is installed on the secondary air duct 7, located upstream of the secondary air steam heater 10, thus forming secondary cold air. This secondary cold air undergoes its first heating after passing through the secondary air steam heater 10, and then its second heating after passing through the air preheater 8, forming secondary hot air. This secondary hot air is generally used to be introduced into the boiler furnace and mixed with the primary air, providing oxygen for combustion and enhancing airflow turbulence and mixing of pulverized coal to ensure complete combustion.

[0029] In the illustrated embodiment, the high-temperature flue gas output end of boiler 1 is sequentially connected to an air preheater 8, an electrostatic precipitator 14, an induced draft fan 15, a desulfurization and dust removal tower 16, and a chimney 17. The air preheater 8 uses high-temperature flue gas to heat the primary and secondary air, and the flue gas is discharged into the atmosphere after treatment.

[0030] The main concept and beneficial technical effects of this utility model are as follows. Looking at the power plant's combustion system and steam-water system, the boiler inputs cold air from the environment, which is a relatively low-energy-grade input link and also a working medium that can effectively utilize the exhaust steam from the turbine's low-pressure cylinder. Assuming that heating the boiler's cold air from ambient temperature to 50°C requires a steam pressure of approximately 0.012 MPa.a, while atmospheric pressure is 0.1 MPa.a, the extraction steam pressure of the No. 7 low-pressure heater in the air-cooled unit is 0.097 MPa.a, the exhaust back pressure of the air-cooled unit is generally 0.01 MPa.a, and the exhaust back pressure of the wet-cooled unit is generally 0.005 MPa.a. It can be seen that the steam grade required for heating the cold air is very low, comparable to the exhaust back pressure of the air-cooled unit.

[0031] Taking the steam source reconfiguration of a certain unit's air heater as an example. The steam air heater is arranged on the primary and secondary cold air ducts, both located between the fan and the air preheater. The conventional steam source scheme for the air heater uses intermediate-pressure cylinder exhaust (four-stage extraction), i.e. Figure 1 The system includes AGBC (secondary air heater) and AGBD (primary air heater) circuits. A pressure matching device is installed, using the exhaust steam from the intermediate-pressure cylinder as the driving steam source, and extracting the exhaust steam from the low-pressure cylinder (waste steam) to produce product steam with suitable parameters, which is used as the steam source for the steam heaters, replacing the four-stage extraction steam. When designing the pressure matching device, the required product steam pressure and mass flow rate are based on the steam parameters used by the heaters. Since the required steam pressure is very low, the design boundary is mainly to meet the mass flow rate requirement. That is, the product steam from the pressure matching device serves as the steam source for the heaters, namely EFGBC (secondary air heater) and EFHD (primary air heater). Preliminary calculations show that the unit's coal consumption is reduced by approximately 1.2 g / kWh compared to the traditional scheme. In northern regions, coal-fired units have heaters operating for more than 50% of the year, resulting in significant annual coal savings.

[0032] Furthermore, this solution can be implemented by simply modifying the existing unit structure, for example... Figure 1As shown, the newly constructed piping associated with the pressure matching device 11 (the piping containing the primary air heating regulating valve 12 and the secondary air heating regulating valve 13) can be connected to the existing piping, and then... Figure 1 The existing pipeline section shown by the dashed line can be sealed off using valves or other methods.

[0033] In summary, this utility model makes full use of low-pressure cylinder exhaust steam and reduces cold source loss to replace the steam source of the boiler heater, aiming to improve the thermal economy of the unit. It is applicable not only to newly built units but also to existing units, and does not restrict unit parameters, capacity, cold end type, etc. It is an innovation and reconstruction of the thermal system, with strong technical and economic feasibility, and is worth developing and promoting.

[0034] Finally, it should be noted that: the above only provides a detailed explanation of the main improvements of this utility model; the remaining parts not described in detail are common knowledge or can be achieved by using existing technology or similar technical solutions, and therefore need not be elaborated upon; the above embodiments are only used to illustrate the technical solutions of this utility model, and not to limit it; obviously, the described embodiments are some embodiments of this utility model, not all embodiments. Based on the embodiments of this utility model, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this utility model; for ease of description, only the parts related to the utility model are shown in the accompanying drawings. In the absence of conflict, the embodiments and features in the embodiments of this utility model can be combined with each other; modifications to the technical solutions described in the foregoing embodiments, or equivalent substitutions of some technical features, do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of this utility model.

Claims

1. A system structure for improving the thermal efficiency of a generator unit by reconfiguring the steam source of a heater, comprising a boiler (1), a high-pressure cylinder (2), a medium-pressure cylinder (3), a low-pressure cylinder (4), and a steam exhaust condenser (5) connected in sequence, and further comprising a primary air duct (6) and a secondary air duct (7), characterized in that, An air preheater (8) is installed on the primary air duct (6) and the secondary air duct (7). On the upstream side of the air preheater (8), a primary air steam heater (9) is also installed on the primary air duct (6), and a secondary air steam heater (10) is also installed on the secondary air duct (7). A pressure matching device (11) is also included. The steam source input end of the pressure matching device (11) is connected to the upstream side of the exhaust steam condensing device (5). The driving steam source input end of the pressure matching device (11) is connected to the exhaust steam duct or the regenerative steam extraction duct of the intermediate pressure cylinder (3). The steam output end of the pressure matching device (11) is connected to the heat exchange medium input end of the primary air steam heater (9). The steam output end of the pressure matching device (11) is also connected to the heat exchange medium input end of the secondary air steam heater (10).

2. The system structure for improving unit thermal efficiency through heater steam source reconfiguration according to claim 1, characterized in that, The driving steam source input end of the pressure matching device (11) is connected to the four-section or five-section extraction steam pipeline of the intermediate pressure cylinder (3).

3. The system structure for improving unit thermal efficiency through heater steam source reconfiguration according to claim 1, characterized in that, A primary air heating regulating valve (12) is installed in the pipeline upstream of the heat exchange medium input end of the primary air steam heater (9); a secondary air heating regulating valve (13) is installed in the pipeline upstream of the heat exchange medium input end of the secondary air steam heater (10).

4. The system structure for improving unit thermal efficiency through heater steam source reconfiguration according to claim 1, characterized in that, The heat exchange medium output end of the primary air steam heater (9) is connected to the heater condensate collection system, and the heat exchange medium output end of the secondary air steam heater (10) is connected to the heater condensate collection system.

5. The system structure for improving unit thermal efficiency through heater steam source reconfiguration according to claim 1, characterized in that, A primary air fan is installed on the primary air duct (6), and the primary air fan is located upstream of the primary air steam heater (9); a blower is installed on the secondary air duct (7), and the blower is located upstream of the secondary air steam heater (10).

6. The system structure for improving unit thermal efficiency through heater steam source reconfiguration according to any one of claims 1-5, characterized in that, The high-temperature flue gas output end of the boiler (1) is connected in sequence to the air preheater (8), the electrostatic precipitator (14), the induced draft fan (15), the desulfurization and dust removal tower (16) and the chimney (17).

Images