A steam-air preheater system based on cascaded utilization of energy

Abstract

The present invention discloses a steam air preheater system based on cascaded energy utilization, which includes 3 steam heating stages and 6 drain heating stages; the 3 steam heating stages are respectively a low-pressure steam heating stage, a medium-pressure steam heating stage, and a high-pressure steam heating stage along the air inlet direction; the 6 drain heating stages include 3 drain low-temperature heating stages, 2 drain medium-temperature heating stages, and 1 drain high-temperature heating stage. According to different heat source qualities, the present invention uses 9 heating stages to heat air, realizing cascaded energy utilization and improving the energy utilization efficiency; after the thermal energy of each stage of steam is cascadedly utilized, the heat load impact of the drain on the deaerator is reduced, effectively preventing the self-boiling of the deaerator and reducing the operation risk of the boiler; the cold air is heated in multiple stages with low temperature rise, effectively alleviating the influence of load fluctuations on the air temperature and ensuring the stable operation of the incineration system.

Description

Technical Field

[0001] The invention relates to the technical field of waste incineration power generation, in particular to a steam air preheater system. Background Art

[0002] Air preheater is an air heating device that uses waste heat to increase the temperature of air entering the furnace to facilitate combustion. Its main functions are to increase the theoretical combustion temperature of the fuel, ensure the furnace temperature, and improve the combustion efficiency. Since there are many acidic gases in the flue gas of the boiler of the garbage incineration power plant, it is very easy to cause low-temperature corrosion at low temperatures, so steam air preheaters that heat the air with steam are generally used. The steam air preheater system has a great impact on the stable combustion of garbage, the stability of the thermal system, and the thermal efficiency of the whole plant.

[0003] The conventional steam air preheater in the waste incineration power plant is a two-stage heating: the first stage is a low-pressure heating section, the heat source is the first-stage extraction steam of the steam turbine; the second stage is a high-pressure heating section, the heat source is superheated main steam or saturated steam in the drum. Conventional steam air preheaters have the following disadvantages: 1) The two-stage heating is adopted, the energy is not fully utilized, the thermal efficiency is low, and energy is wasted; 2) When the boiler load changes, the air temperature of each heating section often does not reach the design temperature; 3) The heat of the drain is not fully utilized, and the large amount of heat carried in the drain is directly vaporized and enters the deaerator, causing the deaerator to boil spontaneously, reducing the deoxidation effect and affecting the safe operation of the boiler. Summary of the invention

[0004] The present invention aims to provide a highly efficient and stable steam air preheater system based on cascaded energy utilization.

[0005] The specific technical solution of the present invention is:

[0006] A steam-air preheater system based on cascaded energy utilization, comprising 3 steam heating stages and 6 drain heating stages. The 3 steam heating stages are, in the air inlet direction, a low-pressure steam heating stage, a medium-pressure steam heating stage, and a high-pressure steam heating stage. The steam sources of each heating stage are respectively from the second-stage extraction steam of the steam turbine, the first-stage extraction steam of the steam turbine, and the saturated steam in the boiler drum; the 6 drain heating stages include 3 low-temperature drain heating stages, 2 medium-temperature drain heating stages, and 1 high-temperature drain heating stage. In the air inlet direction, they are a low-pressure low-temperature drain heating stage, a medium-pressure low-temperature drain heating stage, a high-pressure low-temperature drain heating stage, a medium-pressure medium-temperature drain heating stage, a high-pressure medium-temperature drain heating stage, and a high-pressure high-temperature drain heating stage. The heat sources of each drain heating stage are respectively from the drains of the corresponding-pressure steam heating stages. The layout relationship between each steam heating stage and the drain heating stage in the air inlet direction is as follows: 1 low-pressure steam heating stage is arranged after 3 low-temperature drain heating stages, 1 medium-pressure steam heating stage is arranged after 2 medium-temperature drain heating stages, and 1 high-pressure steam heating stage is arranged after 1 high-temperature drain heating stage. The heat exchange process of each stage of steam is as follows: The saturated steam from the boiler drum condenses into saturated drain after releasing heat in the high-pressure steam heating stage. The saturated drain enters the high-pressure high-temperature drain heating stage to further release heat and form subcooled drain. The subcooled drain then enters the deaerator after releasing heat through the two stages of the high-pressure medium-temperature drain heating stage and the high-pressure low-temperature drain heating stage; The superheated steam from the first-stage extraction steam of the steam turbine condenses into saturated drain after releasing heat in the medium-pressure steam heating stage. The saturated drain enters the medium-pressure medium-temperature drain heating stage to further release heat and form subcooled drain. The subcooled drain then enters the deaerator after releasing heat through the medium-pressure low-temperature drain heating stage; The superheated steam from the second-stage extraction steam of the steam turbine condenses into saturated drain after releasing heat in the low-pressure steam heating stage. The saturated drain enters the low-pressure low-temperature drain heating stage to further release heat and form subcooled drain and then enters the deaerator.

[0007] The beneficial effects of the present invention are as follows: The system is safe, reliable, stable, and efficient. Nine heating stages are used to heat the air according to different heat source qualities, realizing cascaded energy utilization, improving the energy utilization efficiency, and achieving the purpose of energy conservation and consumption reduction; Through the cascaded utilization of the heat energy of each stage of steam, the heat of the end drain is greatly reduced, reducing the thermal load impact of the drain on the deaerator, effectively preventing the self-boiling of the deaerator, and reducing the operation risk of the boiler; The cold air is heated in multiple stages with low temperature rise, effectively alleviating the influence of load fluctuations on the air temperature and ensuring the stable operation of the incineration system. Brief Description of the Drawings

[0008] Figure 1 It is a schematic diagram of a steam-air preheater system based on cascaded energy utilization of the present invention.

[0009] Figure 2 It is a schematic diagram of the equipment structure of the system of the present invention.

[0010] In the figure: 1 - low-pressure drain low-temperature heating stage, 2 - medium-pressure drain low-temperature heating stage, 3 - high-pressure drain low-temperature heating stage, 4 - low-pressure steam heating stage, 5 - medium-pressure drain medium-temperature heating stage, 6 - high-pressure drain medium-temperature heating stage, 7 - medium-pressure steam heating stage, 8 - high-pressure drain high-temperature heating stage, 9 - high-pressure steam heating stage. Detailed implementation mode

[0011] As shown in the Figure 1 A steam-air preheater system based on cascaded utilization of energy, as shown in the figure, includes a low-pressure drain low-temperature heating stage 1, a medium-pressure drain low-temperature heating stage 2, a high-pressure drain low-temperature heating stage 3, a low-pressure steam heating stage 4, a medium-pressure drain medium-temperature heating stage 5, a high-pressure drain medium-temperature heating stage 6, a medium-pressure steam heating stage 7, a high-pressure drain high-temperature heating stage 8, and a high-pressure steam heating stage 9. The saturated steam from the steam drum condenses into saturated drain water after releasing heat in the high-pressure steam heating stage 9, and the saturated drain water enters the high-pressure drain high-temperature heating stage 8 to further release heat and form subcooled drain water, which then enters the deaerator after releasing heat through the two stages of the high-pressure drain medium-temperature heating stage 6 and the high-pressure drain low-temperature heating stage 3; the superheated steam from the first-stage extraction steam of the steam turbine condenses into saturated drain water after releasing heat in the medium-pressure steam heating stage 7, and the saturated drain water enters the medium-pressure drain medium-temperature heating stage 5 to further release heat and form subcooled drain water, which then enters the deaerator after releasing heat through the medium-pressure drain low-temperature heating stage 2; the superheated steam from the second-stage extraction steam of the steam turbine condenses into saturated drain water after releasing heat in the low-pressure steam heating stage 4, and the saturated drain water enters the low-pressure drain low-temperature heating stage 1 to further release heat and form subcooled drain water and enter the deaerator.

[0012] During use, cold air enters from the inlet end of the air preheater and sequentially passes through the low-pressure drain low-temperature heating stage 1, the medium-pressure drain low-temperature heating stage 2, the high-pressure drain low-temperature heating stage 3, the low-pressure steam heating stage 4, the medium-pressure drain medium-temperature heating stage 5, the high-pressure drain medium-temperature heating stage 6, the medium-pressure steam heating stage 7, the high-pressure drain high-temperature heating stage 8, and the high-pressure steam heating stage 9. After nine-stage heating, the outlet air temperature of the air preheater reaches the design value.

[0013] Example 1, a waste incineration power generation project with a primary air temperature of 220°C and main steam parameters of 4.0 MPa / 400°C. The saturated steam (5.1 MPa / 266°C) from the steam drum is condensed into saturated drain water (5.1 MPa / 266°C) after releasing heat in the high-pressure steam heating stage 9, and the saturated drain water (5.1 MPa / 266°C) enters the high-pressure drain water high-temperature heating stage 8 to further release heat and form subcooled drain water (5.1 MPa / 215°C). The subcooled drain water (5.1 MPa / 215°C) is depressurized to 2.1 MPa and then releases heat in the high-pressure drain water medium-temperature heating stage 6 to form medium-temperature drain water (2.1 MPa / 140°C). The medium-temperature drain water (2.1 MPa / 140°C) is depressurized to 1.0 MPa and then releases heat in the high-pressure drain water low-temperature heating stage 3 to form low-temperature drain water (1.0 MPa / 90°C) and enters the deaerator; the superheated steam (1.0 MPa / 264°C) from the first-stage extraction steam of the steam turbine is condensed into saturated drain water (1.0 MPa / 184°C) after releasing heat in the medium-pressure steam heating stage 7, and the saturated drain water (1.0 MPa / 184°C) enters the medium-pressure drain water medium-temperature heating stage 5 to further release heat and form subcooled drain water (1.0 MPa / 140°C). The subcooled drain water (1.0 MPa / 140°C) releases heat in the medium-pressure drain water low-temperature heating stage 2 to form low-temperature drain water (1.0 MPa / 90°C) and enters the deaerator; the superheated steam (0.4 MPa / 186°C) from the second-stage extraction steam of the steam turbine is condensed into saturated drain water (0.4 MPa / 151°C) after releasing heat in the low-pressure steam heating stage 4, and the saturated drain water (0.4 MPa / 151°C) enters the low-pressure drain water low-temperature heating stage 1 to further release heat and form subcooled drain water (0.4 MPa / 90°C) and enters the deaerator. The primary air cold air (25°C) enters from the inlet end of the air preheater and is sequentially heated to 35.4°C by the low-pressure drain water low-temperature heating stage 1, to 38.7°C by the medium-pressure drain water low-temperature heating stage 2, to 43.9°C by the high-pressure drain water low-temperature heating stage 3, to 130°C by the low-pressure steam heating stage 4, to 133°C by the medium-pressure drain water medium-temperature heating stage 5, to 141°C by the high-pressure drain water medium-temperature heating stage 6, to 175°C by the medium-pressure steam heating stage 7, to 180.9°C by the high-pressure drain water high-temperature heating stage 8, and to 220°C by the high-pressure steam heating stage 9. Compared with the conventional two-stage steam air preheater scheme in this case, the overall plant thermal efficiency is relatively increased by about 0.8%; all drain waters enter the deaerator at a temperature of 90°C after multi-stage temperature reduction. Compared with the way that the drain water of the conventional scheme directly enters the deaerator in a saturated water state, this scheme greatly reduces the heat load impact of the drain water on the deaerator; the cold air can stably reach the design value (220°C) after nine-stage segmented heating, and has stronger load fluctuation resistance ability compared with the conventional scheme.

[0014] Example 2: A waste incineration power generation project with a primary air temperature of 220°C and main steam parameters of 4.0 MPa / 450°C. The air preheater system process is the same as in Case 1. Compared with the conventional two-stage steam air preheater scheme, the overall plant thermal efficiency of this case is relatively increased by about 1.3%.

[0015] Example 3: A waste incineration power generation project with a primary air temperature of 220°C and main steam parameters of 6.4 MPa / 485°C. The air preheater system process is the same as in Case 1. Compared with the conventional two-stage steam air preheater scheme, the overall plant thermal efficiency of this case is relatively increased by about 1.1%.

Claims

1. A method for using a steam-air preheater system based on cascaded energy utilization, characterized in that, It includes 3 steam heating stages and 6 drain heating stages. The 3 steam heating stages are, in the air inlet direction, a low-pressure steam heating stage, a medium-pressure steam heating stage, and a high-pressure steam heating stage respectively. The 6 drain heating stages include 3 low-temperature drain heating stages, 2 medium-temperature drain heating stages, and 1 high-temperature drain heating stage. In the air inlet direction, they are a low-pressure low-temperature drain heating stage, a medium-pressure low-temperature drain heating stage, a high-pressure low-temperature drain heating stage, a medium-pressure medium-temperature drain heating stage, a high-pressure medium-temperature drain heating stage, and a high-pressure high-temperature drain heating stage respectively. The heat sources of each drain heating stage come from the drains of the steam heating stages with corresponding pressures respectively. The layout relationship between each steam heating stage and the drain heating stage in the air inlet direction is as follows: 1 low-pressure steam heating stage is arranged after 3 low-temperature drain heating stages, 1 medium-pressure steam heating stage is arranged after 2 medium-temperature drain heating stages, and 1 high-pressure steam heating stage is arranged after 1 high-temperature drain heating stage. The heat exchange processes of each stage of steam are as follows: The saturated steam from the boiler steam drum is condensed into saturated drain after releasing heat through the high-pressure steam heating stage. The saturated drain enters the high-pressure high-temperature drain heating stage to release heat further and forms subcooled drain. The subcooled drain then enters the deaerator after releasing heat through the two stages of the high-pressure medium-temperature drain heating stage and the high-pressure low-temperature drain heating stage. The superheated steam from the first-stage extraction steam of the steam turbine is condensed into saturated drain after releasing heat through the medium-pressure steam heating stage. The saturated drain enters the medium-pressure medium-temperature drain heating stage to release heat further and forms subcooled drain. The subcooled drain then enters the deaerator after releasing heat through the medium-pressure low-temperature drain heating stage. The superheated steam from the second-stage extraction steam of the steam turbine is condensed into saturated drain after releasing heat through the low-pressure steam heating stage. The saturated drain enters the low-pressure low-temperature drain heating stage to release heat further and forms subcooled drain, which then enters the deaerator.

2. The method for using a steam-air preheater system based on cascaded energy utilization according to claim 1, characterized in that: The steam sources of the respective heating stages of the low-pressure steam heating stage, the medium-pressure steam heating stage, and the high-pressure steam heating stage come from the second-stage extraction steam of the steam turbine, the first-stage extraction steam of the steam turbine, and the saturated steam of the boiler steam drum respectively.

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