Steam-water system and method for extending the hot standby cycle of circulating fluidized bed unit

Abstract

This application discloses a steam-water system and method for extending the hot standby period of a circulating fluidized bed (CFB) unit, comprising: a boiler and an external bed assembly. The external bed assembly includes at least one external bed unit, each external bed unit including multiple external beds connected in series or parallel, with each external bed corresponding to a cyclone separator. Each external bed unit includes a superheater external bed unit, the external bed of which has a second superheater. The first superheater is one of a medium-temperature superheater and a high-temperature superheater, and the second superheater is the other of a medium-temperature superheater and a high-temperature superheater. A high-temperature reheater is installed inside the furnace. Alternatively, the external bed unit includes a superheater external bed unit and a high-temperature reheater external bed unit, the external bed of which has a high-temperature reheater. This system can extend the hot standby period of a CFB unit, achieving a smooth transition from a hot standby state to a high-load operation state.

Description

Technical Field

[0001] This application relates to the field of circulating fluidized bed technology, and more specifically, to a steam-water system and method for extending the hot standby cycle of a circulating fluidized bed unit. Background Technology

[0002] Among various coal-fired power boiler types, circulating fluidized bed (CFB) boilers have the inherent conditions to participate in peak shaving in the range of 20% to 100% rated load due to their wide fuel adaptability, good combustion stability, large load adjustment range and low pollutant control cost. At the same time, the large amount of high-temperature bed material and refractory and wear-resistant components enriched in the CFB furnace endow the system with significant thermal inertia and heat storage capacity, enabling it to maintain extremely low output operation of the unit in the form of furnace shut-down (hot standby) for a short period of time, and can quickly switch to load increase state as needed.

[0003] With the solidification of the "high output of photovoltaic power during the day - load recovery in the evening" pattern due to the high proportion of new energy connections, thermal power units need to maintain a near-zero output standby state for longer periods during the daytime, while ensuring parameter recoverability and safety margins when the system needs them. Under standby conditions, the thermal boundary of ultra-supercritical CFB units changes significantly: after coal shutdown and reduced ventilation, furnace heat release and circulating ash flux decline rapidly, and steam temperature drops significantly over time; to ensure the safe operation of the turbine, the main steam temperature is usually required not to fall below the limit value. Once the main steam parameters fall below the safety window, standby operation is terminated.

[0004] Current engineering practice shows that, under the constraints of no external auxiliary heat source and keeping the turbine generator on standby, the sustained combustion time of ultra-supercritical CFB units is typically only about 1 to 2 hours. This is because the current steam-water system layout and operation strategy of ultra-supercritical CFB units are still dominated by rated load and conventional start-up and shutdown, without system optimization design based on the heat source decay characteristics of long-cycle combustion. The typical current practice is that the intermediate and final stage superheaters are still located in the upper part of the furnace. After coal supply is stopped and air volume is reduced, the gas temperature and heat flux in the upper part of the furnace drop rapidly. The intermediate and final stage superheaters directly face low heat source conditions, resulting in insufficient heat absorption and a rapid decrease in main steam temperature over time.

[0005] Therefore, how to extend the compression time of circulating fluidized bed units to adapt to the deep peak shaving needs of the power grid has become a technical problem that urgently needs to be solved by those skilled in the art. Summary of the Invention

[0006] In view of this, the purpose of this application is to disclose a steam-water system for extending the hot standby cycle of a circulating fluidized bed unit, thereby extending the hot standby time of the circulating fluidized bed unit to meet the deep peak shaving requirements of the power grid.

[0007] Another core aspect of this application is the disclosure of a method for extending the hot standby period of a circulating fluidized bed unit, which employs the aforementioned steam-water system for extending the hot standby period of a circulating fluidized bed unit.

[0008] To achieve the above objectives, this application provides the following technical solution:

[0009] A steam-water system for extending the hot standby cycle of a circulating fluidized bed unit includes: a boiler and an external bed assembly. The boiler includes a furnace, a steam-water separator, a cyclone separator, and a tail flue. A water-cooled screen and a first superheater are installed in the furnace. A low-temperature superheater, a low-temperature reheater, and an economizer are installed in the tail flue. The economizer is connected to the furnace. The water-cooled screen is connected to the steam-water separator. The steam-water separator is connected to the cyclone separator. The cyclone separator is connected to the low-temperature superheater.

[0010] The external bed assembly includes at least one external bed unit, each external bed unit includes multiple external beds, and the external beds are connected in series or in parallel. Each external bed corresponds to one of the cyclone separators.

[0011] The external bed unit includes a superheater external bed unit, the external bed of the superheater external bed unit having a second superheater, the first superheater being one of a medium-temperature superheater and a high-temperature superheater, the second superheater being the other of the medium-temperature superheater and the high-temperature superheater, and a high-temperature reheater being provided in the furnace; or, the external bed unit includes the superheater external bed unit and a high-temperature reheater external bed unit, the external bed of the high-temperature reheater external bed unit having the high-temperature reheater;

[0012] The low-temperature superheater, the medium-temperature superheater, and the high-temperature superheater are connected in sequence, and the low-temperature reheater and the high-temperature reheater are connected; the boiler's return feeder is connected to the furnace and each of the external beds respectively.

[0013] Optionally, in the steam-water system for extending the hot standby cycle of the circulating fluidized bed unit, the first superheater is the high-temperature superheater, the external bed assembly includes a superheater external bed unit, the external bed unit includes a medium-temperature superheater external bed unit, and the medium-temperature superheater external bed unit includes at least one.

[0014] Optionally, in the steam-water system for extending the hot standby cycle of the circulating fluidized bed unit, the external bed assembly includes a high-temperature reheater external bed unit, wherein each external bed of the high-temperature reheater external bed unit is connected in series or in parallel.

[0015] Optionally, in the steam-water system for extending the hot standby cycle of the circulating fluidized bed unit, the external bed unit of the medium-temperature superheater includes two connected units.

[0016] Optionally, in the steam-water system for extending the hot standby cycle of the circulating fluidized bed unit, the first superheater is the medium-temperature superheater, and the external bed unit includes a high-temperature superheater external bed unit.

[0017] Optionally, in the steam-water system for extending the hot standby cycle of the circulating fluidized bed unit, the external bed unit further includes an external bed unit with a medium-temperature superheater, which is connected to the external bed unit with a high-temperature superheater.

[0018] Optionally, in the steam-water system for extending the hot standby cycle of the circulating fluidized bed unit, the external bed unit further includes a high-temperature reheater external bed unit, the low-temperature reheater is connected to the high-temperature reheater external bed unit, and each external bed of the high-temperature reheater external bed unit is connected in series or in parallel.

[0019] Optionally, in the steam-water system for extending the hot standby cycle of the circulating fluidized bed unit, a first water spray desuperheater is provided on the connecting pipe between the low-temperature superheater and the medium-temperature superheater, and a second water spray desuperheater is provided on the connecting pipe between the medium-temperature superheater and the high-temperature superheater.

[0020] Optionally, in the steam-water system for extending the hot standby cycle of the circulating fluidized bed unit, a third water spray desuperheater is provided on the inlet pipe of the low-temperature reheater, and a fourth water spray desuperheater is provided on the connecting pipe between the low-temperature reheater and the high-temperature reheater.

[0021] Optionally, in the steam-water system for extending the hot standby cycle of the circulating fluidized bed unit, the tail flue is equipped with a flue gas regulating baffle.

[0022] A method for extending the hot standby period of a circulating fluidized bed unit, employing the aforementioned steam-water system for extending the hot standby period of a circulating fluidized bed unit, includes the following steps:

[0023] Before the fire is shut down, the system is checked to confirm that the boiler's water-cooled walls, evaporator screens, and all levels of superheating and reheating circuits have minimum flow. The opening of the cone valve of the external bed is increased by the control unit in preset increment steps until the static accumulation height of the bed material in the external bed is raised to the preset height, and the fire shut-down baseline data is recorded.

[0024] When switching to the fire suppression and standby state, in response to the power grid dispatch command, the boiler load is reduced to the fire suppression inlet load, the opening of the cone valve of the external bed is gradually reduced, and then the coal feeder, primary air fan and secondary air fan are shut down in sequence so that the boiler enters the fire suppression and shut-down state.

[0025] In the hot standby mode, when the rate of temperature drop of the superheated steam and the temperature difference between the inlet and outlet tube bundles of the heat exchanger of the external bed exceed a preset threshold, the air supply system of the external bed is started until the rate of temperature drop of the superheated steam and the temperature difference between the inlet and outlet tube bundles of the heat exchanger of the external bed are within the preset threshold, and then the air supply system of the external bed is shut down.

[0026] Once the fire is reignited, and a load increase command is received, the fluidizing air, induced draft air, primary air, secondary air, and coal feeding system of the external bed are started sequentially, and the cone valve and ash return system of the external bed are gradually opened.

[0027] As can be seen from the above scheme, the steam-water system for extending the hot standby period of the circulating fluidized bed unit disclosed in this application moves at least one of the medium-temperature superheater and high-temperature superheater located in the furnace to the external bed outside the boiler. During the rapid load reduction stage when the unit transitions from deep adjustment to hot standby mode, it can reduce the amount of ash returned to the furnace and increase the amount of circulating ash entering the external bed, so that the heat of the circulating ash can be directionally migrated and enriched to the external bed, ensuring sufficient heat source in the external bed during long-term hot standby. The high-temperature bed material heat storage in the external bed is used as a thermal buffer for unit restart, which can form a stable steam temperature platform in the initial stage of startup, realizing a smooth switch from hot standby mode to hot standby and load increase mode. It can effectively suppress the wall temperature gradient and temperature change rate during hot standby and restart, reduce thermal stress and start-up fatigue, and improve the economy and reliability under frequent start-up and shutdown conditions.

[0028] The method for extending the hot standby period of a circulating fluidized bed unit disclosed in this application has the same technical effect as the system for extending the hot standby period of a circulating fluidized bed unit, and will not be described in detail here. Attached Figure Description

[0029] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0030] Figure 1 This is a schematic diagram of the steam-water system for extending the hot standby cycle of circulating fluidized bed combustion, as disclosed in an embodiment of this application. Figure 1 ;

[0031] Figure 2 This is a schematic diagram of a system for extending the hot standby cycle of circulating fluidized bed combustion, as disclosed in an embodiment of this application. Figure 2 ;

[0032] Figure 3 This is a schematic diagram of a system for extending the hot standby cycle of circulating fluidized bed combustion, as disclosed in an embodiment of this application. Figure 3 ;

[0033] Figure 4 This is a schematic diagram of a system for extending the hot standby cycle of circulating fluidized bed combustion, as disclosed in an embodiment of this application. Figure 4 ;

[0034] Figure 5 This is a schematic diagram of a system for extending the hot standby cycle of circulating fluidized bed combustion, as disclosed in an embodiment of this application. Figure 5 ;

[0035] Figure 6 This is a schematic diagram of a system for extending the hot standby cycle of circulating fluidized bed combustion, as disclosed in an embodiment of this application. Figure 6 ;

[0036] Figure 7 This is a schematic diagram of the external beds connected in series as disclosed in the embodiments of this application;

[0037] Figure 8 This is a schematic diagram of the parallel connection of external beds disclosed in an embodiment of this application.

[0038] Among them, 100 is the furnace, 110 is the water-cooled screen, 120 is the high-temperature superheater, 130 is the high-temperature reheater, 140 is the medium-temperature superheater, 141 is the first medium-temperature superheater, 142 is the second medium-temperature superheater, 143 is the third medium-temperature superheater, and 144 is the fourth medium-temperature superheater.

[0039] 200 is an external bed assembly, and 210 is an external bed;

[0040] 300 is a steam-water separator, 310 is a water storage tank, and 320 is an expansion tank;

[0041] 400 is a cyclone separator;

[0042] 500 is the tail flue, 510 is the low-temperature superheater, 520 is the low-temperature reheater, and 530 is the economizer. Detailed Implementation

[0043] The core of this application is to disclose a steam-water system for extending the hot standby cycle of circulating fluidized bed units, thereby extending the hot standby time of the circulating fluidized bed units to meet the deep peak shaving requirements of the power grid.

[0044] Another core aspect of this application is the disclosure of a method for extending the hot standby period of a circulating fluidized bed unit, which employs the aforementioned steam-water system for extending the hot standby period of a circulating fluidized bed unit.

[0045] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0046] Under closed-fire conditions, the thermal boundary of ultra-supercritical CFB units changes significantly. After coal shutdown and reduced airflow, furnace heat release and circulating ash flux decline rapidly, and steam temperature drops significantly over time. To ensure safe turbine operation, the main steam temperature is typically required not to fall below the limit value. Once the main steam parameters fall below the safety window, closed-fire operation terminates. Therefore, as the closed-fire time increases, the inability of main steam and reheat steam parameters to meet the safe operation requirements of the turbine becomes the main factor limiting the closed-fire duration.

[0047] For current circulating fluidized bed (CFB) units, the intermediate and final superheaters are still located in the upper part of the furnace 100. After coal shutdown and reduced air supply, the gas temperature and heat flux in the upper part of the furnace 100 drop rapidly. The intermediate and final superheaters directly face low heat source conditions, resulting in insufficient heat absorption and a rapid decrease in main steam temperature over time. This application is proposed against this background, moving the intermediate and final superheaters from the furnace 100 to an external bed 210, and introducing circulating ash from the boiler into the external bed 210 to heat the steam and maintain the main steam parameters during long-cycle shutdown and hot standby processes.

[0048] like Figures 1-6 As shown in the embodiment of this application, a steam-water system for extending the hot standby cycle of a circulating fluidized bed unit is disclosed, including a boiler and an external bed assembly 200. The boiler includes a furnace 100, a steam-water separator 300, a cyclone separator 400, and a tail flue 500. A water-cooled screen 110 and a first superheater are installed in the furnace 100. A low-temperature superheater 510, a low-temperature reheater 520, and an economizer 530 are installed in the tail flue 500. The economizer 530 is connected to the furnace 100 through a steam-water circulation pipeline system. The water-cooled screen 110 is connected to the steam-water separator 300. The steam-water separator 300 is connected to the cyclone separator 400. The cyclone separator 400 is connected to the low-temperature superheater 510.

[0049] The external bed assembly 200 includes at least one external bed unit, and each external bed unit includes multiple external beds 210. The external beds 210 are connected in series or in parallel. Each external bed 210 corresponds to a cyclone separator 400, that is, the number of external beds 210 is the same as the number of cyclone separators 400.

[0050] In some specific embodiments, the external bed unit includes a superheater external bed unit, the external bed 210 of which has a second superheater. The first superheater is one of an intermediate-temperature superheater 140 and a high-temperature superheater 120, and the second superheater is the other of the intermediate-temperature superheater 140 and the high-temperature superheater 120. A high-temperature reheater 130 is disposed within the furnace 100. In other specific embodiments, the external bed unit includes a superheater external bed unit and a high-temperature reheater external bed unit, the external bed 210 of which has a high-temperature reheater 130. In this embodiment, the high-temperature reheater 130 is moved outside the furnace, and one of the intermediate-temperature superheater 140 and the high-temperature superheater 120 is disposed within the furnace 100, while the other is located within the external bed 210.

[0051] The low-temperature superheater 510, medium-temperature superheater 140, and high-temperature superheater 120 are connected in sequence, while the low-temperature reheater 520 and high-temperature reheater 130 are connected. The boiler's return feeders are connected to the furnace 100 and each external bed 210, meaning that part of the circulating ash returns to the furnace 100, and the other part is fed into the external beds 210. The circulating ash heats the steam. Each external bed 210 is equipped with a conical valve, and the amount of circulating ash can be adjusted by regulating the opening of the conical valve. The number of return feeders corresponds one-to-one with the cyclone separators 400. It should be noted that the arrows in the figure indicate the direction of medium flow.

[0052] Specifically, such as Figure 1 As shown, feedwater passes through economizer 530, where it is heated by flue gas and its temperature rises. It then enters the boiler drum, where it continues to flow through the water-cooled walls and water-cooled screens 110 in the furnace 100, where it is heated to become a steam-water mixture. This mixture is then introduced into the steam-water separator 300 via the outlet header and steam-water outlet pipe for steam-water separation. The separated water re-enters the boiler drum for recirculation, while excess water or water requiring temporary storage falls into the water storage tank 310, which is connected to the expansion tank 320. The separated saturated steam is led out from the steam connection pipe at the top of the steam-water separator 300. The saturated steam is introduced into the cyclone separator 400, where it is heated. It then enters the low-temperature superheater 510 in the tail flue duct 500, and subsequently enters the medium-temperature superheater 140 and the high-temperature superheater 120 in sequence, where it is heated by the flue gas to form superheated steam that meets preset parameters.

[0053] Steam discharged from the high-pressure cylinder of the steam turbine is introduced into the inlet header of the low-temperature reheater 520 in the tail flue 500, flows counter-currently upward through the tube bundle of the low-temperature reheater, and is drawn out from the outlet header of the low-temperature reheater 520. It is then led to the inlet header of the high-temperature reheater 130 through the connecting pipes on both sides of the boiler. After flowing counter-currently upward through the high-temperature reheater 130, the reheated steam that meets the preset parameters is led from the outlet header of the high-temperature reheater 130 to the intermediate-pressure cylinder of the steam turbine.

[0054] The steam-water system for extending the hot standby period of a circulating fluidized bed unit disclosed in this application involves moving at least one of the medium-temperature superheater 140 and the high-temperature superheater 120, which are located inside the furnace 100, to an external bed 210 outside the boiler. During the rapid load reduction phase when the unit transitions from deep adjustment to hot standby mode, this reduces the amount of ash returned to the furnace and increases the amount of circulating ash entering the external bed 210. This allows the heat from the circulating ash to migrate directionally to and accumulate in the external bed 210, ensuring sufficient heat source within the external bed 210 during long-term hot standby. Utilizing the high-temperature bed material heat storage in the external bed 210 serves as a thermal buffer for unit restart, a stable steam temperature platform can be formed in the initial stage of startup. This enables a smooth transition from hot standby to high-load operation, effectively suppressing the wall temperature gradient and temperature change rate during the high-load restart process, reducing thermal stress and start-up fatigue, and improving economy and reliability under frequent start-up and shutdown conditions.

[0055] The system disclosed in this application for extending the hot standby period of a circulating fluidized bed unit transfers the intermediate and final stage heat exchangers from the flue gas side of the furnace to the external bed side, so that the intermediate and final stage heat exchange is transferred from the rapid decay channel on the gas side to the controllable channel on the solid side. Furthermore, through full immersion heat exchange and pre-heat storage, the rate of decrease of steam parameters during the hot standby stage can be effectively slowed down, thus extending the hot standby time of the unit.

[0056] It should be noted that the steam-water system for extending the hot standby period of circulating fluidized bed units disclosed in this application is mainly for ultra-supercritical circulating fluidized bed (CFB) units with a rated power generation capacity of 700MW-1000MW.

[0057] This application pertains to the arrangement of four cyclone separators 400 behind the furnace 100, see [reference]. Figure 1 and Figure 2 Six cyclone separators 400 are arranged on the front and rear walls of the furnace 100 (three on the front wall and three on the rear wall), see [reference]. Figures 3-6 A total of eight cyclone separators 400 are arranged on the front and rear walls of the furnace 100, that is, four cyclone separators 400 are arranged on each of the front and rear walls of the furnace 100, to illustrate the scheme of the embodiment of this application. This application focuses on the structure of the steam and water system side.

[0058] In some specific embodiments, the first superheater is a high-temperature superheater 120, and the external bed assembly 200 includes a superheater external bed unit, which includes a medium-temperature superheater external bed unit, with at least one medium-temperature superheater external bed unit. For example... Figure 1As shown in the figure, the furnace 100 is equipped with a high-temperature superheater 120 and a high-temperature reheater 130. The medium-temperature superheater 140 is placed in the external bed 210. There is one external bed unit for the superheater. The number of external beds 210 is the same as the number of cyclone separators 400, which is four units. The four external beds 210 are arranged in series. Of course, the four external beds 210 can also be arranged in parallel.

[0059] Saturated steam is introduced into the cyclone separator 400, then into the low-temperature superheater 510 of the tail flue 500, and then into the medium-temperature superheaters 140 of four external beds 210 connected in series. Finally, the superheated steam that meets the preset parameters is discharged from the outlet of the high-temperature superheater 120.

[0060] In some specific embodiments, the external bed assembly 200 includes a high-temperature reheater external bed unit, wherein the various external beds 210 of the high-temperature reheater external bed unit are connected in series or in parallel. For details, see [link to relevant documentation]. Figure 5 The external bed unit shown in the figure includes an external bed unit for a medium-temperature superheater and an external bed unit for a high-temperature reheater. Each external bed unit includes three external beds 210. The external bed 210 of the external bed unit for the medium-temperature superheater has a medium-temperature superheater 140, and the external bed 210 of the external bed unit for the high-temperature reheater has a high-temperature reheater 130. It is matched with the arrangement of six cyclone separators 400. The external beds 210 of each external bed unit are connected in series. A high-temperature superheater 120 is provided in the furnace 100. The superheated steam flowing out from the low-temperature superheater 510 enters the three external beds 210 connected in series, each with a medium-temperature superheater 140, and then enters the high-temperature superheater 120 provided in the furnace 100. The superheated steam that meets the preset parameters flows out from the outlet of the high-temperature superheater 120. The superheated steam flowing out of the low-temperature reheater 520 enters the high-temperature reheater 130 of the external bed 210. After flowing through three external beds 210 connected in series, the reheated steam that meets the preset parameters is discharged through the outlet of the high-temperature reheater 130.

[0061] In some specific embodiments, see Figure 3To better control the temperature of the main steam, the superheater external bed unit shown in the figure has two units, i.e., a two-stage intermediate temperature superheater 140 connected in series. Each superheater external bed unit includes three external beds 210, and each external bed 210 is equipped with an intermediate temperature superheater 140, matching the configuration of six cyclone separators 400. For easy distinction, the intermediate temperature superheater 140 of the external bed 210 arranged on the front wall (right side) of the furnace 100 is named the first intermediate temperature superheater 141, and the intermediate temperature superheater 140 of the external bed 210 arranged on the rear wall (left side) of the furnace 100 is named the second intermediate temperature superheater 142. A high temperature superheater 120 and a high temperature reheater 130 are installed inside the furnace 100. Saturated steam is introduced into the cyclone separator 400, then into the low-temperature superheater 510 of the tail flue 500, and then sequentially into three series-connected first medium-temperature superheaters 141, followed by three series-connected second medium-temperature superheaters 142. From the second medium-temperature superheater 142 in the external bed 210, the steam is then led to the high-temperature superheater 120 in the furnace 100. Finally, superheated steam meeting preset parameters is discharged from the outlet of the high-temperature superheater 120. The two-stage series connection of the medium-temperature superheaters 140 allows the superheated steam to absorb heat in stages, facilitating temperature adjustment.

[0062] In some specific embodiments, the first superheater is a medium-temperature superheater 140, and the external bed unit includes a high-temperature superheater external bed unit, that is, the medium-temperature superheater 140 is disposed inside the furnace 100, and the high-temperature superheater 120 is disposed in the external bed 210. For details, see [link to specific embodiments]. Figure 2 The external bed 210 shown in the figure includes four units connected in series, matched with four cyclone separators 400. Each external bed 210 is equipped with a high-temperature superheater 120, and a high-temperature reheater 130 is located inside the furnace 100. That is, the furnace 100 has a medium-temperature superheater 140 and a high-temperature reheater 130 inside. The superheated steam drawn from the low-temperature superheater 510 is first drawn from the connecting pipes on both sides of the boiler to the inlet header of the medium-temperature superheater 140 at the top of the furnace 100. After flowing through the heating surface of the medium-temperature superheater 140, it is drawn from the connecting pipes on both sides of the boiler to the inlet header of the high-temperature superheater 120 in the external bed 210 outside the furnace. After flowing through the four high-temperature superheaters 120 arranged in series, the superheated steam that finally meets the preset parameters is drawn out from the outlet header of the high-temperature superheater 120 of the external bed 210.

[0063] Based on the above embodiments, the external bed unit further includes an intermediate-temperature superheater external bed unit, which is connected to the high-temperature superheater external bed unit. For details, see [link to documentation]. Figure 4The external bed unit shown in the figure includes two units. One external bed unit is a medium-temperature superheater external bed unit, located on the rear wall side of the furnace 100. The other external bed unit is a high-temperature reheater external bed unit, located on the front wall side of the furnace 100. Each external bed unit has three external beds 210. The furnace 100 contains a medium-temperature superheater 140 and a high-temperature reheater 130. For distinction, the medium-temperature superheater 140 is located within the furnace 100. The intermediate temperature superheater 143 is named the third intermediate temperature superheater 143, and the intermediate temperature superheater 140 set in the external bed 210 is named the fourth intermediate temperature superheater 144. After passing through the low temperature superheater 510, the steam enters the third intermediate temperature superheater 143 set in the furnace 100, and then enters the high temperature superheater 120 of the external bed 210 through the fourth intermediate temperature superheater 144. Finally, the superheated steam that meets the preset parameters is discharged from the outlet of the high temperature superheater 120.

[0064] In some specific embodiments, in order to maintain better steam quality during the hot standby period of the reheating process and to shorten the restart load time while effectively extending the reheating duration, the external bed unit also includes a high-temperature reheater external bed unit. The low-temperature reheater 520 is connected to the high-temperature reheater external bed unit, and each external bed 210 of the high-temperature reheater external bed unit is connected in series to maintain the temperature of the reheated steam during the reheating process. For details, see [link to specific documentation]. Figure 6 The furnace 100 shown in the figure is equipped with a medium-temperature superheater 140. The external bed unit includes a high-temperature superheater external bed unit and a high-temperature reheater external bed unit. Each external bed unit includes three external beds 210 connected in series. A high-temperature superheater 120 is installed in the external bed 210 of the high-temperature superheater external bed unit, and a high-temperature reheater 130 is installed in the external bed 210 of the high-temperature reheater external bed unit. The superheated steam flowing out of the low-temperature superheater 510 flows sequentially through the medium-temperature superheater 140 located in the furnace 100, and then flows through the high-temperature superheater 120 of the three external beds 210 connected in series. The superheated steam that meets the preset parameters flows out from the outlet of the high-temperature superheater 120. The reheated steam flowing out of the low-temperature reheater 520 passes through the high-temperature reheater 130 of the three external beds 210 connected in series, and the reheated steam that meets the preset parameters flows out from the outlet of the high-temperature reheater 130.

[0065] In some specific embodiments, in order to regulate the temperature of the superheated steam, a first water spray desuperheater is installed on the connecting pipe between the low-temperature superheater 510 and the medium-temperature superheater 140, and a second water spray desuperheater is installed on the connecting pipe between the medium-temperature superheater 140 and the high-temperature superheater 120. That is, the two-stage water spray desuperheater configuration enables two-stage water spray desuperheating of the superheated steam. The first water spray desuperheater controls the inlet steam temperature of the medium-temperature superheater 140, and the second water spray desuperheater adjusts the inlet steam temperature of the high-temperature superheater 120. The two-stage water spray desuperheater configuration ensures that the temperature of the superheated steam meets a preset value. Figure 1 As shown in the figure, the location of the desuperheating water is the location where the water spray desuperheater is installed. The specific structure of the water spray desuperheater can be referred to the existing water spray desuperheater. This application does not involve structural improvements to the water spray desuperheater, and the structure and working principle of the water spray desuperheater will not be described in detail here.

[0066] In some specific embodiments, to protect the reheater tube panel and increase the sensitivity of reheat steam temperature regulation, the reheat system is also equipped with a water spray desuperheater. Specifically, a third water spray desuperheater is installed on the inlet pipe of the low-temperature reheater 520 as an emergency water spray desuperheater, and a fourth water spray desuperheater is installed on the connecting pipe between the low-temperature reheater 520 and the high-temperature reheater 130 as a micro-spray desuperheater. Figures 1-6 The location of the desuperheating water marked on the reheat system shown is the location of the water spray desuperheater.

[0067] In addition, in order to regulate the temperature of the reheat steam, a flue gas regulating baffle is installed in the tail flue 500. By adjusting the flue gas regulating baffles in the flue of the low-temperature superheater 510 and the low-temperature reheater 520 in the tail flue 500, the opening of the baffle is adjusted by utilizing the relationship between the flue gas flow rate and the reheat steam outlet temperature, thereby controlling the amount of flue gas flowing through the reheater side and the superheater side, and achieving the purpose of regulating the temperature of the reheat steam.

[0068] It should be noted that, Figures 1-6 The external bed 210 shown is arranged in series on one side, but it can also be arranged in parallel. The specific arrangement can be determined according to the actual situation. Figure 7 and Figure 8 As shown in the figure, taking an example with a total of eight external beds 210, four external beds 210 are installed on the front wall side and four on the rear wall side of the furnace 100. Figure 7 The four external beds 210 on one side of the furnace 100 shown are arranged in series. Figure 8 The four external beds 210 shown are arranged in a series and then in parallel configuration. The arrangement of the external beds 210 can be determined according to the actual situation.

[0069] Furthermore, this application also discloses a method for extending the hot standby cycle of a circulating fluidized bed unit, employing the aforementioned steam-water system for extending the hot standby cycle of a circulating fluidized bed unit, including the following steps:

[0070] Step S1: System check before ignition suppression;

[0071] The boiler's water-cooled walls, water-cooled screen 110, and all levels of superheating and reheating circuits are confirmed to have minimum flow. The control unit increases the opening of the conical valve of the external bed 210 in preset increments until the static accumulation height of the bed material in the external bed 210 reaches a preset height. The bed pressure of the external bed 210 is used as the monitoring basis to ensure that the steam heating surface within the external bed 210 is completely immersed in the high-temperature bed material, and the pressure-reducing baseline data is recorded. Specifically, the conical valve of the external bed 210 refers to the conical valve between the return feeder and the external bed 210. By adjusting the opening of the conical valve, the amount of circulating ash entering each external bed 210 can be adjusted. Increasing the opening of the conical valve of the external bed 210 reduces the proportion of circulating ash returning to the furnace 100, allowing circulating ash to preferentially enter the external bed 210, thus achieving the directional migration and enrichment of heat from the furnace 100 to the external bed 210. After completion, record the superheated steam temperature, reheated steam temperature, regulating stage temperature, bed temperature and bed pressure of external bed 210, and the temperature difference between the inlet and outlet tube bundles of the heat exchanger of external bed 210 to form the pressure-fire baseline data.

[0072] Step S2: Switching between hot standby and pressure-fired states;

[0073] In response to the grid dispatch command, the boiler load is reduced to the pressure-reducing inlet load, and the opening of the cone valve of the external bed 210 is gradually reduced. Subsequently, the coal feeder, primary air fan, and secondary air fan are shut down in sequence, so that the boiler enters the shut-off pressure-reducing state. In this state, the external bed 210 does not supply air normally, and the steam heating surface inside relies on the heat storage of the bed material for heat exchange through conduction and natural convection.

[0074] Step S3: Preheating and heating.

[0075] When the rate of temperature drop of the superheated steam and the temperature difference between the inlet and outlet tube bundles of the heat exchanger of the external bed 210 exceed a preset threshold, the air supply system of the external bed 210 is started. Preferably, the air supply system of the external bed 210 is started through the control system (DCS system). Preferably, the air cap of the external bed 210 is opened for a short time for 5 to 10 seconds, and the air volume is 1 to 2 times the initial fluidization air volume of the external bed 210 to form a short, rapid and stop disturbance to disperse the material layer and homogenize heat transfer until the rate of temperature drop of the superheated steam and the temperature difference between the inlet and outlet tube bundles of the heat exchanger of the external bed 210 are within the preset threshold, and then the air supply system of the external bed 210 is shut down.

[0076] Step S4: Restart the fire;

[0077] Upon receiving the load increase command, the fluidizing air, induced draft air, primary air and secondary air of the external bed 210, as well as the coal feeding system, are started in sequence. The cone valve and ash return system of the external bed 210 are gradually opened to match the temperature of the superheated steam with the temperature of the steam turbine.

[0078] The method for extending the hot standby period of a circulating fluidized bed (CFB) unit disclosed in this application involves, before the CFB unit enters the hot standby mode, implementing solid-side pre-charging during the rapid load reduction phase. This is achieved by reducing the proportion of circulating ash returning to the furnace 100 and increasing the ash inlet and air distribution in the external bed 210, allowing the available solid bed material heat to migrate and accumulate from the furnace 100 to the external bed 210. During the hot standby phase, timely pulse air supply ensures the timely release of heat and uniform heat exchange within the external bed 210. Steam parameters are well controlled during the hot standby phase, enabling the ultra-supercritical CFB boiler to extend the hot standby time to over 3 hours and respond rapidly during the start-up phase.

[0079] It should be noted that the various embodiments in this specification mainly describe the differences from other embodiments, and the same or similar parts between the various embodiments can be referred to each other.

[0080] In the description of the embodiments of this application, it should be noted that, unless otherwise explicitly specified and limited, the terms "connected" and "linked" 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. Those skilled in the art can understand the specific meaning of the above terms in the embodiments of this application based on the specific circumstances.

[0081] Hereinafter, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature.

[0082] References to "one embodiment" or "some embodiments" as described in this specification mean that one or more embodiments of this application include a specific feature, structure, or characteristic described in connection with that embodiment. Therefore, the phrases "in one embodiment," "in some embodiments," "in other embodiments," "in still other embodiments," etc., appearing in different parts of this specification do not necessarily refer to the same embodiment, but rather mean "one or more, but not all, embodiments," unless otherwise specifically emphasized. The terms "comprising," "including," "having," and variations thereof mean "including but not limited to," unless otherwise specifically emphasized.

[0083] This document uses specific examples to illustrate the principles and implementation methods of this application. The descriptions of the embodiments above are only for the purpose of helping to understand the core ideas of this application. It should be noted that those skilled in the art can make several improvements and modifications to this application without departing from the principles of this application, and these improvements and modifications also fall within the protection scope of the claims of this application.

Claims

1. A steam-water system for extending the hot standby cycle of a circulating fluidized bed unit, characterized in that, include: A boiler and external bed assembly (200), the boiler including a furnace (100), a steam-water separator (300), a cyclone separator (400) and a tail flue (500), the furnace (100) being provided with a water-cooled screen (110) and a first superheater, the tail flue (500) being provided with a low-temperature superheater (510), a low-temperature reheater (520) and an economizer (530), the economizer (530) being connected to the furnace (100), the water-cooled screen (110) being connected to the steam-water separator (300), the steam-water separator (300) being connected to the cyclone separator (400), and the cyclone separator (400) being connected to the low-temperature superheater (510); The external bed assembly (200) includes at least one external bed unit, each external bed unit includes multiple external beds (210), each external bed (210) is connected in series or in parallel, and each external bed (210) corresponds to the cyclone separator (400); The external bed unit includes a superheater external bed unit, the external bed (210) of the superheater external bed unit has a second superheater, the first superheater is one of a medium-temperature superheater (140) and a high-temperature superheater (120), the second superheater includes the other of the medium-temperature superheater (140) and the high-temperature superheater (120), and a high-temperature reheater (130) is provided in the furnace (100); or, the external bed unit includes the superheater external bed unit and the high-temperature reheater external bed unit, the external bed (210) of the high-temperature reheater external bed unit has the high-temperature reheater (130). The low-temperature superheater (510), the medium-temperature superheater (140), and the high-temperature superheater (120) are connected in sequence, and the low-temperature reheater (520) and the high-temperature reheater (130) are connected; the boiler return feeder is connected to the furnace (100) and each of the external beds (210) respectively.

2. The steam-water system for extending the hot standby cycle of a circulating fluidized bed unit as described in claim 1, characterized in that, The first superheater is the high-temperature superheater (120), and the external bed assembly (200) includes a superheater external bed unit, which includes a medium-temperature superheater external bed unit, and the medium-temperature superheater external bed unit includes at least one.

3. The steam-water system for extending the hot standby cycle of a circulating fluidized bed unit as described in claim 2, characterized in that, The external bed assembly (200) includes a high-temperature reheater external bed unit, wherein each external bed (210) of the high-temperature reheater external bed unit is connected in series or in parallel.

4. The steam-water system for extending the hot standby cycle of a circulating fluidized bed unit as described in claim 2, characterized in that, The intermediate-temperature superheater external bed unit comprises two connected units.

5. The steam-water system for extending the hot standby cycle of a circulating fluidized bed unit as described in claim 1, characterized in that, The first superheater is the medium-temperature superheater (140), and the external bed unit includes a high-temperature superheater external bed unit.

6. The steam-water system for extending the hot standby cycle of a circulating fluidized bed unit as described in claim 5, characterized in that, The external bed unit also includes a medium-temperature superheater external bed unit, which is connected to the high-temperature superheater external bed unit.

7. The steam-water system for extending the hot standby cycle of a circulating fluidized bed unit as described in claim 5, characterized in that, The external bed unit also includes a high-temperature reheater external bed unit. The low-temperature reheater (520) is connected to the high-temperature reheater external bed unit. Each external bed (210) of the high-temperature reheater external bed unit is connected in series or in parallel.

8. The steam-water system for extending the hot standby cycle of a circulating fluidized bed unit as described in claim 1, characterized in that, The connecting pipe between the low-temperature superheater (510) and the medium-temperature superheater (140) is provided with a first water spray desuperheater, and the connecting pipe between the medium-temperature superheater (140) and the high-temperature superheater (120) is provided with a second water spray desuperheater.

9. The steam-water system for extending the hot standby cycle of a circulating fluidized bed unit as described in claim 8, characterized in that, The inlet pipe of the low-temperature reheater (520) is equipped with a third water spray desuperheater, and the connecting pipe between the low-temperature reheater (520) and the high-temperature reheater (130) is equipped with a fourth water spray desuperheater.

10. The steam-water system for extending the hot standby cycle of a circulating fluidized bed unit as described in any one of claims 1-9, characterized in that, The tail flue (500) is equipped with a flue gas regulating baffle.

11. A method for extending the hot standby period of a circulating fluidized bed unit, employing a steam-water system for extending the hot standby period of a circulating fluidized bed unit as described in any one of claims 1-10, comprising the steps of: Before the fire is extinguished, the system is checked to confirm that the water-cooled wall, evaporator, and each stage of superheating circuit and reheating circuit of the boiler have minimum flow. The opening of the cone valve of the external bed (210) is increased by the control unit in a preset increment step until the static accumulation height of the bed material of the external bed (210) is raised to the preset height, and the fire extinguishing baseline data is recorded. When switching to the fire-stopping standby state, in response to the grid dispatching command, the boiler load is reduced to the fire-stopping inlet load, the opening of the cone valve of the external bed (210) is gradually reduced, and then the coal feeder, primary air fan and secondary air fan are shut down in sequence so that the boiler enters the fire-stopping state. When the temperature drop rate of the superheated steam and the temperature difference between the inlet and outlet tube bundles of the heat exchanger of the external bed (210) exceed a preset threshold, the air supply system of the external bed (210) is started until the temperature drop rate of the superheated steam and the temperature difference between the inlet and outlet tube bundles of the heat exchanger of the external bed (210) are within the preset threshold, and then the air supply system of the external bed (210) is shut down. Once the fire is reignited and a load increase command is received, the fluidizing air, induced draft air, primary air and secondary air of the external bed (210) and the coal feeding system are started in sequence, and the cone valve and ash return system of the external bed (210) are gradually opened.

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