A peak regulation system using boiler secondary air heat storage

Abstract

The application discloses a kind of peak shaving system using boiler secondary air heat storage, comprising: air preheater, boiler flue, secondary air duct, secondary air heater, steam turbine medium pressure cylinder;The boiler flue and secondary air duct are respectively set through air preheater, and the heating of secondary air in secondary air duct is completed by flue gas in boiler flue through air preheater;The secondary air duct is also set through secondary air heater, and the steam inlet end of the steam turbine medium pressure cylinder is provided with steam extraction pipeline, the steam extraction pipeline is connected with the secondary air heater, and the boiler reheated steam is introduced into the secondary air heater, to heat the secondary air in secondary air duct, by adjusting the steam extraction amount of boiler reheated steam in steam extraction pipeline to change the steam inlet amount of steam turbine medium pressure cylinder, to realize the rapid change of corresponding boiler load. The system of the application improves the variable load rate of coal-fired unit;And the system of the application does not increase additional heat storage device and medium, and the system is simple, and the cost is relatively low.

Description

Technical Field

[0001] This invention belongs to the field of power plant boilers, and particularly relates to a peak-shaving system that utilizes boiler secondary air heat storage. Background Technology

[0002] In recent years, the vigorous development of renewable energy sources such as wind and solar power has led to increasingly prominent issues of wind and solar curtailment in areas rich in such resources due to the temporal and spatial differences between wind and solar resources and residential electricity consumption. As coal-fired power units are the main force for peak shaving in the power system, improving their peak shaving capacity is one of the most direct and effective means to solve the problem of wind and solar curtailment.

[0003] The peak-shaving capacity of coal-fired power units includes both low-load operation capability and rapid load change capability. Currently, most coal-fired power units have a load change rate of 1% to 2% per minute. Improving this rate is limited by various factors, such as the pulverizing system response rate, combustion delay, and heat transfer delay. To improve the load change rate of coal-fired power units, the industry has developed adjustment methods such as hot water thermal storage, molten salt thermal storage, feedwater throttling, and condensate throttling. However, thermal storage methods are costly, and feedwater and condensate throttling methods are limited by the steam drum water level and deaerator water level, resulting in limited adjustment range. Summary of the Invention

[0004] The purpose of this invention is to overcome the problems of the prior art by disclosing a peak-shaving system that utilizes boiler secondary air heat storage, thereby further improving the boiler load change rate.

[0005] The objective of this invention is achieved through the following technical solution:

[0006] A peak-shaving system utilizing boiler secondary air heat storage, the peak-shaving system comprising: an air preheater, a boiler flue, a secondary air duct, a secondary air heater, and a steam turbine intermediate-pressure cylinder;

[0007] The boiler flue and the secondary air duct are respectively installed through the air preheater, and the flue gas in the boiler flue heats the secondary air in the secondary air duct through the air preheater.

[0008] The secondary air duct also passes through a secondary air heater. The steam inlet end of the intermediate pressure cylinder of the steam turbine is provided with an extraction steam pipeline. The extraction steam pipeline is connected to the secondary air heater and introduces boiler reheat steam into the secondary air heater to heat the secondary air in the secondary air duct. By adjusting the amount of boiler reheat steam extracted from the extraction steam pipeline, the amount of steam entering the intermediate pressure cylinder of the steam turbine can be changed, so as to achieve a rapid change in the corresponding boiler load.

[0009] According to a preferred embodiment, the extraction steam pipeline is provided with an extraction steam regulating valve for controlling the amount of steam extracted from the steam inlet end of the intermediate pressure cylinder of the steam turbine.

[0010] According to a preferred embodiment, the peak-shaving system further includes: a deaerator and a low-pressure heater;

[0011] The exhaust end of the secondary air heater is connected to the deaerator and the low-pressure heater via the deaerator extraction pipeline and the low-pressure heater extraction pipeline, respectively.

[0012] According to a preferred embodiment, the deaerator extraction steam regulating valve is provided on the deaerator extraction steam pipeline.

[0013] According to a preferred embodiment, the low-pressure heater extraction steam line is provided with a low-pressure heater extraction steam regulating valve.

[0014] According to a preferred embodiment, the deaerator is also connected to the intermediate pressure cylinder of the steam turbine, and a first regulating valve is provided on the corresponding connecting pipeline.

[0015] According to a preferred embodiment, the low-pressure heater is also connected to the intermediate-pressure cylinder of the steam turbine, and a second regulating valve is provided on the corresponding connecting pipeline.

[0016] According to a preferred embodiment, when the system is in steady-state operation, the first regulating valve and the second regulating valve are fully closed, the reheat steam extraction rate is adjusted using the extraction steam regulating valve, and the flow distribution is adjusted through the deaerator extraction steam pipeline and the low-pressure heater extraction steam pipeline to make the outlet water temperature of the deaerator and the outlet condensate temperature of the low-pressure heater consistent with the standard condition unit.

[0017] According to a preferred embodiment, when it is necessary to rapidly increase the load, the extraction steam regulating valve is quickly closed to directly increase the steam intake of the intermediate pressure cylinder of the steam turbine, thereby increasing the output of the intermediate pressure cylinder of the steam turbine and achieving a rapid increase in load.

[0018] Close the low-pressure steam extraction regulating valve slightly and open the deaerator steam extraction regulating valve wider to increase the proportion of reheat steam entering the deaerator and slow down the rate of deaerator water level drop.

[0019] When the deaerator water level continues to drop, open the first regulating valve to directly extract steam from the intermediate pressure cylinder and adjust the deaerator water level to a safe value.

[0020] According to a preferred embodiment, when a rapid load reduction is required, the extraction steam regulating valve is quickly opened to directly reduce the steam intake of the intermediate pressure cylinder of the turbine, thereby reducing the output of the intermediate pressure cylinder and achieving a rapid load reduction. At this time, the deaerator water level rises rapidly. By opening the low-pressure heater extraction steam regulating valve and closing the deaerator extraction steam regulating valve, the proportion of reheat steam extraction entering the deaerator is reduced. When the deaerator is unable to maintain the water level due to excessive reheat steam extraction, the feedwater flow rate to the water pump is increased to adjust the deaerator water level to a safe value.

[0021] The aforementioned main solution of the present invention and its various further alternative solutions can be freely combined to form multiple solutions, all of which are solutions that can be adopted and are claimed by the present invention. Those skilled in the art, after understanding the solution of the present invention, will realize that there are many combinations based on existing technology and common knowledge, all of which are technical solutions to be protected by the present invention, and will not be exhaustively listed here.

[0022] The beneficial effects of this invention are:

[0023] The peak-shaving system of this invention addresses the problem of low load change rate during conventional coal-fired power unit operation by adding a secondary air heater. A portion of the reheat steam is extracted to heat the hot secondary air, ensuring the effective utilization of thermal energy. At the same time, during load changes, the amount of reheat steam extracted is adjusted to quickly change the steam intake of the intermediate pressure cylinder of the turbine, thereby achieving rapid load change.

[0024] Compared with conventional regenerative systems, this invention uses reheated steam to heat the secondary air, and replaces the deaerator extraction steam and low-pressure heater extraction steam with the heated exhaust steam. The amount of steam extracted from the intermediate-pressure cylinder remains unchanged, but the extraction point is advanced, increasing the degree of regeneration, improving the efficiency of the thermal system, increasing the total enthalpy of the extracted steam, and also increasing the heat storage capacity of the regenerative system.

[0025] Compared to thermal storage systems equipped with additional heat storage media, this patent does not require additional heat storage devices or media, resulting in a simpler and lower-cost system. It allows for priority adjustment of the steam extraction rate from the low-pressure heater (approximately 53%), making it easier to maintain a stable deaerator water level during rapid load changes compared to condensate throttling methods. Attached Figure Description

[0026] Figure 1 This is a schematic diagram of the peak-shaving system of the present invention;

[0027] Among them, 1-air preheater, 2-boiler flue, 3-primary air duct, 4-secondary air duct, 5-steam turbine intermediate pressure cylinder, 6-deaerator, 7-low pressure heater, 8-first regulating valve, 9-deaerator extraction steam regulating valve, 10-second regulating valve, 11-low pressure heater extraction steam regulating valve, 12-secondary air heater, 13-extraction steam regulating valve. Detailed Implementation

[0028] The following specific examples illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that, unless otherwise specified, the following embodiments and features described therein can be combined with each other.

[0029] It should be noted that similar labels and letters in the following figures indicate similar items. Therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures.

[0030] In the description of this invention, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, or the orientation or positional relationship commonly used when the product of this invention is in use. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this invention. In addition, the terms "first," "second," "third," etc., are only used to distinguish descriptions and should not be construed as indicating or implying relative importance.

[0031] Furthermore, terms such as "horizontal," "vertical," and "sag" do not imply that components must be absolutely horizontal or suspended, but rather that they can be slightly tilted. For example, "horizontal" simply means that its direction is more horizontal relative to "vertical," and does not mean that the structure must be completely horizontal, but can be slightly tilted.

[0032] In the description of this invention, it should also be noted that, unless otherwise explicitly specified and limited, the terms "set," "install," "connect," and "link" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0033] Furthermore, it should be noted that, unless otherwise specified, the structures, connections, positions, power sources, etc. involved in this invention are all things that a person skilled in the art can know without creative effort based on the prior art.

[0034] refer to Figure 1 As shown, this invention discloses a peak-shaving system utilizing boiler secondary air heat storage. The peak-shaving system of this invention includes an air preheater 1, a boiler flue 2, a primary air duct 3, a secondary air duct 4, a turbine intermediate-pressure cylinder 5, a deaerator 6, a low-pressure heater 7, a first regulating valve 8, a deaerator extraction steam regulating valve 9, a second regulating valve 10, a low-pressure heater extraction steam regulating valve 11, a secondary air heater 12, and an extraction steam regulating valve 13.

[0035] The arrangement sequence of air preheater 1, boiler flue 2, primary air duct 3, secondary air duct 4, intermediate pressure cylinder of steam turbine 5, deaerator 6, and low-pressure heater 7 is the same as that of conventional units. Based on conventional coal-fired units, the following are added: first regulating valve 8, deaerator extraction steam regulating valve 9, second regulating valve 10, low-pressure heater extraction steam regulating valve 11, secondary air heater 12, and extraction steam regulating valve 13.

[0036] Air preheater 1 is located at the tail end of the boiler. The boiler flue duct 2, primary air duct 3, and secondary air duct 4 are connected to air preheater 1 via three gas channels. The flue gas heats the primary and secondary air in air preheater 1. Before the reheated steam from the boiler enters the intermediate-pressure cylinder 5 of the turbine, a steam extraction channel is provided. A portion of the reheated steam is extracted and enters the secondary air heater 12, where it heats the secondary air. The amount of reheated steam extracted is regulated by the steam extraction regulating valve 13.

[0037] After heat exchange, the reheated steam exhaust is divided into two streams and enters the deaerator and low-pressure heater 7 respectively. The distribution of the two steam streams is controlled by the deaerator extraction steam regulating valve 9 and the low-pressure heater extraction steam regulating valve 11.

[0038] The deaerator 6 is also connected to the intermediate-pressure cylinder 5 of the steam turbine, and a first regulating valve 8 is provided on the corresponding connecting pipeline; the low-pressure heater 7 is also connected to the intermediate-pressure cylinder 5 of the steam turbine, and a second regulating valve 10 is provided on the corresponding connecting pipeline. The first regulating valve 8 and the second regulating valve 10 are closed when the reheat steam extraction rate reaches its maximum, and can be selectively opened when the reheat steam extraction rate decreases, in order to regulate the water level and temperature of the deaerator 6.

[0039] In practical operation, the thermal system of a subcritical coal-fired power unit typically consists of three high-pressure heaters, one deaerator, and three low-pressure heaters. The working fluid temperature, from highest to lowest, is sequentially assigned to high-pressure heaters No. 1, 2, and 3, the deaerator, and low-pressure heaters No. 5, 6, and 7. Condensate from the condenser, after being pressurized by the condensate pump, sequentially enters low-pressure heaters No. 7, 6, and 5, and then the deaerator. The working fluid at the deaerator outlet is called boiler feedwater, which, after being heated by the feedwater pump, sequentially enters high-pressure heaters No. 3, 2, and 1, and finally the boiler economizer. For working fluid temperature matching, this invention focuses on the deaerator and low-pressure heater No. 5.

[0040] Deaerator: The function of a deaerator is to remove oxygen from boiler condensate. The working fluids entering the deaerator are condensate from the low-pressure heater and superheated steam extracted from the intermediate-pressure cylinder of the turbine. The working fluid leaving the deaerator, as boiler feedwater, is pressurized by the feedwater pump and then sequentially enters the high-pressure heater (usually three stages), the economizer, and finally the steam drum. The working principle of the deaerator is that superheated steam mixes with condensate, heating the condensate to the saturation temperature corresponding to the deaerator's operating pressure, removing dissolved oxygen and other gases from the condensate, and preventing and reducing corrosion of boiler feedwater pipes, economizer, and other auxiliary equipment.

[0041] Low-pressure heaters: The function of low-pressure heaters is to heat the condensate from the condenser. Steam drum boilers typically have three stages of low-pressure heaters connected in series. The working fluid entering the low-pressure heaters is condensate that has been pressurized by the condensate pump and superheated steam extracted from the intermediate or low-pressure cylinder of the turbine. The two working fluids do not mix directly. After heat exchange, the condensate enters the next stage of low-pressure heater and finally enters the deaerator. The extracted superheated steam cools down and condenses, becoming condensate that ultimately enters the condenser.

[0042] Control methods:

[0043] When the system is running in normal steady state, the first regulating valve 8 and the second regulating valve 10 are fully closed. The extraction steam regulating valve 13 is used to regulate the amount of reheat steam extracted, and the deaerator extraction steam regulating valve 9 and the low-pressure heater extraction steam regulating valve 11 are used to regulate the flow distribution so that the deaerator outlet water temperature and the low-pressure heater outlet condensate temperature are consistent with those of conventional units.

[0044] When a rapid increase in load is required, the extraction steam regulating valve 13 can be quickly closed to directly increase the steam intake of the intermediate-pressure cylinder, thereby increasing the output of the intermediate-pressure cylinder and achieving a rapid increase in load. If the deaerator water level drops rapidly, the low-pressure heater extraction steam regulating valve 11 can be closed and the deaerator extraction steam regulating valve 9 can be opened to increase the proportion of reheat steam extraction into the deaerator. This means prioritizing a reduction in the steam extraction from the low-pressure heater to slow the rate of deaerator water level decline. If reheat steam extraction alone cannot maintain the deaerator water level, the first regulating valve 8 can be opened to directly extract steam from the intermediate-pressure cylinder, adjusting the deaerator water level to a safe value.

[0045] When a rapid load reduction is required, the extraction steam regulating valve 13 can be quickly opened to directly reduce the steam intake of the intermediate-pressure cylinder, thereby reducing the output of the intermediate-pressure cylinder and achieving a rapid load reduction. If the deaerator water level rises rapidly, the low-pressure heater extraction steam regulating valve 11 can be opened wider while the deaerator extraction steam regulating valve 9 can be closed slightly to reduce the proportion of reheat steam extraction entering the deaerator. This prioritizes increasing the extraction steam from the low-pressure heater to slow the rate of increase in the deaerator water level. If excessive reheat steam extraction cannot maintain the deaerator water level, the feedwater flow rate of the feedwater pump should be increased to adjust the deaerator water level to a safe value.

[0046] It should be noted that the increase in the load change rate of coal-fired units by this invention is also limited by the deaerator water level and cannot be increased indefinitely. It can be used in conjunction with condensate throttling, and on the basis of condensate throttling, secondary air thermal storage and deaerator water level regulation means are added, so the load regulation range is greater.

[0047] The peak-shaving system of this invention addresses the problem of low load change rate during conventional coal-fired power unit operation by adding a secondary air heater. A portion of the reheat steam is extracted to heat the hot secondary air, ensuring the effective utilization of thermal energy. At the same time, during load changes, the amount of reheat steam extracted is adjusted to quickly change the steam intake of the intermediate pressure cylinder of the turbine, thereby achieving rapid load change.

[0048] Compared with conventional regenerative systems, this invention uses reheated steam to heat the secondary air, and replaces the deaerator extraction steam and low-pressure heater extraction steam with the heated exhaust steam. The amount of steam extracted from the intermediate-pressure cylinder remains unchanged, but the extraction point is advanced, increasing the degree of regeneration, improving the efficiency of the thermal system, increasing the total enthalpy of the extracted steam, and also increasing the heat storage capacity of the regenerative system.

[0049] Compared to thermal storage systems equipped with additional heat storage media, this patent does not require additional heat storage devices or media, resulting in a simpler and lower-cost system. It allows for priority adjustment of the steam extraction rate from the low-pressure heater (approximately 53%), making it easier to maintain a stable deaerator water level during rapid load changes compared to condensate throttling methods.

[0050] Example

[0051] Taking a 330MW subcritical boiler as an example, before the reheat steam (pressure 3.156MPa, temperature 538℃, flow rate 861230kg / h) from the boiler enters the intermediate pressure cylinder 5 of the steam turbine, a steam extraction channel is set up to extract part of the reheat steam (flow rate 88000kg / h) into the secondary air heater 12. The reheat steam heats the hot secondary air from 340℃ to 376℃ in the secondary air heater 12.

[0052] The reheated steam exhaust (temperature 350℃) after heat exchange is divided into two streams and enters deaerator 6 (flow rate 41000kg / h) and low-pressure heater 7 (flow rate 47000kg / h) respectively.

[0053] Control methods:

[0054] When the system is operating in normal steady state, the first regulating valve 8 and the second regulating valve 10 are fully closed. The reheat steam extraction rate is regulated by the extraction steam regulating valve 13, and the flow distribution is regulated by the deaerator extraction steam regulating valve 9 and the low-pressure heater extraction steam regulating valve 11. Under 330MW operating conditions, the deaerator outlet water temperature is 180℃ and the low-pressure heater outlet condensate temperature is 148℃.

[0055] When a rapid load increase is required, the extraction steam regulating valve 13 can be quickly closed to directly increase the steam intake of the intermediate-pressure cylinder, thereby increasing the output of the intermediate-pressure cylinder and achieving a rapid load increase. Correspondingly, the secondary air temperature drops from 376℃ to a minimum of 340℃, the low-pressure heater outlet water temperature drops to a minimum of 114℃, and the deaerator water level drops rapidly. At this time, the low-pressure heater extraction steam regulating valve 11 can be closed and the deaerator extraction steam regulating valve 9 can be opened to increase the proportion of reheat steam extraction into the deaerator, that is, to prioritize reducing the steam extraction from the low-pressure heater to slow down the rate of deaerator water level decline. If the deaerator water level cannot be maintained by reheat steam extraction alone, the first regulating valve 8 can be opened to directly extract steam from the intermediate-pressure cylinder or the feedwater flow rate can be reduced to adjust the deaerator water level to a safe value.

[0056] When a rapid load reduction is required, the extraction steam regulating valve 13 can be quickly opened to directly reduce the steam intake of the intermediate-pressure cylinder, thereby reducing the output of the intermediate-pressure cylinder and achieving a rapid load reduction. Correspondingly, the secondary air temperature drops from 376℃ to a maximum of 410℃, the low-pressure heater outlet water temperature drops to a maximum of 180℃, and the deaerator water level rises rapidly. At this time, the low-pressure heater extraction steam regulating valve 11 can be opened wider and the deaerator extraction steam regulating valve 9 can be closed to reduce the proportion of reheat steam extraction entering the deaerator, that is, to prioritize increasing the extraction steam volume of the low-pressure heater to slow down the rate of rise in the deaerator water level. If too much reheat steam extraction cannot maintain the deaerator water level, the feedwater flow rate can be increased to adjust the deaerator water level to a safe value.

[0057] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A peak-shaving system utilizing boiler secondary air heat storage, characterized in that, The peak-shaving system includes: an air preheater (1), a boiler flue (2), a secondary air duct (4), a secondary air heater (12), and a turbine intermediate-pressure cylinder (5). The boiler flue (2) and the secondary air duct (4) are respectively set through the air preheater (1). The flue gas in the boiler flue (2) heats the secondary air in the secondary air duct (4) through the air preheater (1). The secondary air duct (4) also passes through the secondary air heater (12). The steam inlet end of the intermediate pressure cylinder (5) of the steam turbine is provided with a steam extraction pipeline. The steam extraction pipeline is connected to the secondary air heater (12) and introduces boiler reheat steam into the secondary air heater (12) to heat the secondary air in the secondary air duct (4). By adjusting the amount of boiler reheat steam extracted from the steam extraction pipeline, the amount of steam entering the intermediate pressure cylinder of the steam turbine can be changed, so as to achieve a rapid change in the corresponding boiler load. The peak-shaving system also includes: a deaerator (6) and a low-pressure heater (7); The exhaust end of the secondary air heater (12) is connected to the deaerator (6) and the low-pressure heater (7) via the deaerator extraction pipeline and the low-pressure heater extraction pipeline, respectively. The deaerator (6) is also connected to the intermediate pressure cylinder (5) of the steam turbine, and a first regulating valve (8) is provided on the corresponding connecting pipeline. The low-pressure heater (7) is also connected to the intermediate-pressure cylinder (5) of the steam turbine, and a second regulating valve (10) is provided on the corresponding connecting pipeline. The extraction pipeline is equipped with an extraction regulating valve (13) to control the amount of steam extracted from the steam inlet of the intermediate pressure cylinder (5) of the steam turbine. The deaerator extraction steam regulating valve (9) is provided on the deaerator extraction steam pipeline. The low-pressure heater extraction pipe is equipped with a low-pressure heater extraction regulating valve (11).

2. The peak-shaving system as described in claim 1, characterized in that, When the system is in steady state, the first regulating valve (8) and the second regulating valve (10) are fully closed. The amount of reheat steam extracted is adjusted by the extraction steam regulating valve (13). The flow distribution is adjusted by the extraction steam pipeline of the deaerator and the extraction steam pipeline of the low-pressure heater, so that the outlet water temperature of the deaerator (6) and the outlet condensate temperature of the low-pressure heater (7) are consistent with those of the conventional unit.

3. The peak-shaving system as described in claim 1, characterized in that, When it is necessary to rapidly increase the load, quickly close the extraction steam regulating valve (13) to directly increase the steam intake of the intermediate pressure cylinder (5) of the steam turbine, increase the output of the intermediate pressure cylinder (5) of the steam turbine, and achieve rapid load increase; Close the low-pressure steam extraction regulating valve (11) and open the deaerator steam extraction regulating valve (9) to increase the proportion of reheat steam extraction entering the deaerator (6) and slow down the rate of decrease in the deaerator water level. When the water level in the deaerator (6) continues to drop, the first regulating valve (8) is opened to directly extract steam from the intermediate pressure cylinder and adjust the water level in the deaerator (6) to a safe value.

4. The peak-shaving system as described in claim 1, characterized in that, When it is necessary to quickly reduce the load, the extraction steam regulating valve (13) is opened quickly to directly reduce the steam intake of the intermediate pressure cylinder (5) of the steam turbine, reduce the output of the intermediate pressure cylinder (5) of the steam turbine, and achieve a rapid reduction in load. At this time, the water level in the deaerator (6) rises rapidly. By opening the low-pressure steam extraction regulating valve (11) and closing the deaerator steam extraction regulating valve (9), the proportion of reheat steam extracted into the deaerator (6) is reduced. When the deaerator (6) is unable to maintain the water level due to excessive reheat steam extraction, the feed water flow rate of the feed water pump is increased to adjust the deaerator water level to a safe value.

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