Circulating fluidized bed boiler system and control method
By introducing molten salt heat storage and heat release loops into the circulating fluidized bed boiler, the problem of rapid bed temperature drop during fire suppression was solved, enabling long-cycle fire suppression and heat preservation with low fuel consumption and rapid start-up.
Patent Information
- Application Number
- CN202610703668.5
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2026-05-21
- Publication Date
- 2026-07-10
Smart Images
Figure CN122359693A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of thermal power generation technology, and more specifically, to a circulating fluidized bed boiler system and control method. Background Technology
[0002] As an important piece of equipment in thermal power units, circulating fluidized bed boilers exhibit good performance in load regulation due to their large bed heat capacity.
[0003] During off-peak hours in the power grid, to meet grid dispatch requirements, generating units often need to undergo shutdown operations, which involves suspending the boiler combustion process while maintaining high-temperature bed material, thus placing the boiler in a hot standby state. Existing circulating fluidized bed boilers typically consist of a furnace, cyclone separator, return valve, various stages of superheaters, reheater, economizer, air preheater, main steam pipeline, coal feeder, and blowers. During shutdown, coal feeding is stopped and the main blower is shut down, keeping the furnace in a closed state and relying on the bed material's own heat storage to maintain the temperature. During startup, the decision to add fuel oil for combustion is made based on the bed temperature, and the coal feed and air volume are gradually increased to restore normal operation.
[0004] However, during the initial firing phase, although the furnace is sealed after the blower stops, natural heat dissipation still occurs through the furnace walls and dampers, causing the bed temperature to drop continuously. Once the bed temperature falls below the allowable coal feeding temperature, coal cannot be directly fed to start the furnace, and fuel oil must be added for combustion assistance, resulting in excessive fuel oil consumption during the start-up phase. Summary of the Invention
[0005] The purpose of this invention is to provide a circulating fluidized bed boiler system to alleviate the technical problems of short firing time and excessive fuel consumption during the start-up phase in existing circulating fluidized bed boilers.
[0006] The present invention provides a circulating fluidized bed boiler system, comprising: a boiler body, a molten salt heat storage circuit, and a molten salt heat release circuit.
[0007] The boiler body has a furnace, a main steam pipe and a water-cooled air chamber. The main steam pipe is connected to the steam outlet of the furnace, and the water-cooled air chamber is connected to the primary air inlet of the furnace.
[0008] The molten salt thermal storage circuit includes a thermal storage heat exchanger, a high-temperature molten salt tank, and a low-temperature molten salt tank. The steam inlet of the thermal storage heat exchanger is connected to the main steam pipeline through a bypass pipe. The molten salt outlet of the thermal storage heat exchanger is connected to the inlet of the high-temperature molten salt tank, and the molten salt inlet of the thermal storage heat exchanger is connected to the outlet of the low-temperature molten salt tank. This circuit is used to convert excess steam heat energy during boiler load reduction into sensible heat of molten salt and store it in the high-temperature molten salt tank. The steam outlet of the thermal storage heat exchanger is connected to a condensate drainage system.
[0009] The molten salt heat release circuit includes a feedwater heat exchanger and a radiator. The molten salt inlet of the feedwater heat exchanger and the molten salt inlet of the radiator are both connected to the outlet of the high-temperature molten salt tank. The molten salt outlet of the feedwater heat exchanger and the molten salt outlet of the radiator are both connected to the inlet of the low-temperature molten salt tank. The feedwater outlet of the feedwater heat exchanger is connected to the feedwater inlet of the boiler body. The air outlet of the radiator is connected to the water-cooled air chamber.
[0010] Furthermore, both the heat storage heat exchanger and the feedwater heat exchanger are shell-and-tube heat exchangers.
[0011] Furthermore, the high-temperature molten salt tank and the low-temperature molten salt tank are separate and independently configured dual-tank structures.
[0012] Furthermore, the radiator is connected in series or in parallel to the primary air fan outlet duct and is located in the air preheater bypass.
[0013] The outlet of the radiator is connected to the water-cooled air chamber.
[0014] The air duct is equipped with regulating valves for adjusting the flow rate and temperature of the hot air entering the furnace.
[0015] Furthermore, the circulating fluidized bed boiler system also includes a control system.
[0016] The control system is electrically connected to the boiler body, the molten salt heat storage circuit, and the molten salt heat release circuit.
[0017] Furthermore, the radiator is a finned tube gas-liquid heat exchanger, and its air outlet temperature is adjustable from 500°C to 550°C.
[0018] Furthermore, both the high-temperature molten salt tank and the low-temperature molten salt tank have an insulation layer on their outer walls.
[0019] A heat tracing system is provided between the high-temperature molten salt tank and the low-temperature molten salt tank.
[0020] Furthermore, the boiler body also includes an economizer.
[0021] The flue gas inlet of the economizer is connected to the flue gas outlet of the furnace, and the water outlet of the economizer is connected to the water inlet of the furnace.
[0022] The water side of the feedwater heat exchanger is connected to the water side pipeline of the boiler body to send the heated working fluid back to the boiler body.
[0023] Furthermore, the boiler body also includes a cyclone separator, a return valve, a low-temperature superheater, a low-temperature reheater, a high-temperature superheater, an air preheater, and a coal feeder.
[0024] The flue gas outlet of the furnace is connected to the inlet of the cyclone separator, and the material outlet of the cyclone separator is connected to the return port of the furnace via the return valve. The flue gas outlet of the cyclone separator is sequentially connected to the flue gas side of the high-temperature superheater, the low-temperature reheater, the low-temperature superheater, the economizer, and the air preheater. The air outlet of the air preheater is connected to the water-cooled air chamber via a duct. The outlet of the coal feeder is connected to the coal feed port of the furnace.
[0025] The main steam pipe is connected to the steam outlet of the high-temperature superheater.
[0026] The present invention also aims to provide a control method for a circulating fluidized bed boiler system, applied to the provided system, comprising the following steps: When the boiler reduces its load, the excess high-temperature and high-pressure steam generated by the boiler is introduced into the heat storage heat exchanger to heat the low-temperature molten salt from the low-temperature molten salt tank to form high-temperature molten salt and store it in the high-temperature molten salt tank.
[0027] During boiler pressure preservation, the high-temperature molten salt in the high-temperature molten salt tank is respectively transported to the feedwater heat exchanger and the radiator. The feedwater heat exchanger is controlled to heat the boiler feedwater to maintain the steam drum pressure and temperature, and the radiator is controlled to heat the primary air to compensate for the heat loss of the furnace bed material, so that the bed temperature is locked above the allowable coal feeding temperature.
[0028] When the boiler starts up quickly, the flow rate of high-temperature molten salt delivered to the radiator is increased, and high-temperature combustion air is sent into the furnace. At the same time, coal is directly fed to achieve oil-free or low-oil hot start-up, and the steam drum is kept in a hot standby state by the feedwater heat exchanger to complete the turbine start-up and grid connection.
[0029] Beneficial effects: The circulating fluidized bed boiler system provided by this invention, by setting up a molten salt heat storage circuit and a molten salt heat release circuit, utilizes a heat exchanger to convert the thermal energy of excess steam into sensible heat of molten salt and stores it in a high-temperature molten salt tank during the boiler load reduction phase, thus reserving an external heat source for fire suppression and heat preservation. During the fire suppression and heat preservation phase, the feedwater is heated by a feedwater heat exchanger to maintain the steam drum pressure and temperature, while high-temperature air is introduced into the furnace through radiators to actively compensate for the natural heat loss of the bed material through the furnace walls and dampers, continuously maintaining the bed temperature above the allowable coal feeding temperature. This breaks the limitations of traditional circulating fluidized bed boilers that rely solely on the bed material's own heat storage to maintain fire suppression and experience a continuous drop in bed temperature, significantly extending the fire suppression and heat preservation time. Furthermore, because the bed temperature is locked above the allowable coal feeding temperature during fire suppression, the boiler can be directly ignited upon restart, requiring no or only a small amount of fuel oil, thereby effectively reducing fuel oil consumption during startup. Attached Figure Description
[0030] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.
[0031] Figure 1 This is a schematic diagram of the connection relationship of a circulating fluidized bed boiler system provided in an embodiment of the present invention.
[0032] icon: 1-Furnace; 2-Cyclone separator; 3-Return valve; 4-Low-temperature superheater; 5-Low-temperature reheater; 6-Economizer; 7-Air preheater; 8-High-temperature superheater; 9-Main steam pipe; 10-Coal feeder; 11-Primary air fan; 12-Feed water heat exchanger; 13-Heat storage heat exchanger; 14-Radiator; 15-High-temperature molten salt tank; 16-Low-temperature molten salt tank. Detailed Implementation
[0033] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.
[0034] Therefore, the following detailed description of the embodiments of the invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the invention without inventive effort are within the scope of protection of the invention.
[0035] 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.
[0036] 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.
[0037] Furthermore, terms such as "horizontal" and "vertical" 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 than "vertical," and does not mean that the structure must be completely horizontal, but can be slightly tilted.
[0038] 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, or a connection within two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.
[0039] The present invention will now be described in further detail with reference to specific embodiments and accompanying drawings.
[0040] Please combine Figure 1 The circulating fluidized bed boiler system provided in this embodiment includes a boiler body, a molten salt heat storage circuit, and a molten salt heat release circuit.
[0041] The boiler body has a furnace 1, a main steam pipe 9, and a water-cooled air chamber. The main steam pipe 9 is connected to the steam outlet of the furnace 1 and is used to transport the steam generated in the furnace 1 to the outside. The water-cooled air chamber is located at the bottom of the furnace 1 and is connected to the primary air inlet of the furnace 1. It is used to introduce primary air into the furnace 1 to keep the bed material in a fluidized state.
[0042] The molten salt thermal storage circuit includes a thermal storage heat exchanger 13, a high-temperature molten salt tank 15, and a low-temperature molten salt tank 16. The steam inlet of the thermal storage heat exchanger 13 is connected to the main steam pipe 9 via a bypass pipe, and the steam outlet of the thermal storage heat exchanger 13 is connected to a condensate drainage system, forming a steam-side passage. On the molten salt side, the molten salt outlet of the thermal storage heat exchanger 13 is connected to the inlet of the high-temperature molten salt tank 15, and the molten salt inlet of the thermal storage heat exchanger 13 is connected to the outlet of the low-temperature molten salt tank 16, forming a molten salt circulation path. The low-temperature molten salt tank 16 is used to store unheated molten salt at a temperature of approximately 280°C. The high-temperature molten salt tank 15 is used to store heated molten salt at a temperature of approximately 550°C to 565°C.
[0043] When the boiler reduces its load, the power grid dispatching center issues a deep peak shaving or shutdown command, requiring the unit load to be reduced below the minimum stable combustion load. At this time, the high-pressure regulating valve of the steam turbine is gradually closed to reduce the power generation load, and simultaneously the regulating valve at the inlet of the thermal storage heat exchanger 13 is opened, introducing excess high-temperature, high-pressure steam from the main steam pipeline 9 into the thermal storage heat exchanger 13 through a bypass pipeline. Inside the thermal storage heat exchanger 13, the high-temperature steam on the steam side exchanges heat with the low-temperature molten salt on the molten salt side. After releasing heat, the steam condenses into water, which is then recovered to the deaerator or high-pressure heater via a condensate drain system. The low-temperature molten salt absorbs heat and heats up to approximately 565°C, subsequently being stored in the high-temperature molten salt tank 15. Through this process, excess steam heat that might otherwise be wasted through bypass discharge or reduced-parameter operation is stored in the form of sensible heat from the molten salt, achieving energy recovery during the load reduction process.
[0044] The molten salt heat release circuit includes a feedwater heat exchanger 12 and a radiator 14. The molten salt inlets of both the feedwater heat exchanger 12 and the radiator 14 are connected to the outlet of the high-temperature molten salt tank 15, and the molten salt outlets of both the feedwater heat exchanger 12 and the radiator 14 are connected to the inlet of the low-temperature molten salt tank 16, thus forming a complete molten salt circulation path from the high-temperature molten salt tank 15 to the two heat-using devices and back to the low-temperature molten salt tank 16. On the feedwater side, the feedwater outlet of the feedwater heat exchanger 12 is connected to the feedwater inlet of the boiler body. On the air side, the air outlet of the radiator 14 is connected to the water-cooled air chamber.
[0045] During boiler shutdown, the blower is shut down, and the furnace 1 is in a closed state. The heat stored in the bed material is naturally dissipated through the furnace walls and the gaps in the dampers, and the bed temperature drops at a rate of 10°C to 20°C per hour. At this time, the molten salt exothermic circuit is activated for active heat preservation: on the one hand, the high-temperature molten salt in the high-temperature molten salt tank 15 is transported to the feedwater heat exchanger 12 to heat the boiler feedwater to near the steam drum saturation temperature. The heat is transferred to the steam drum and heating surfaces through continuous small-flow water replenishment or natural circulation, maintaining the steam drum pressure within 50% to 80% of the rated pressure, keeping the steam drum in a hot standby state, and reducing the alternating thermal stress during the shutdown-start process. On the other hand, the high-temperature molten salt is transported to the radiator 14, where the primary air is heated to 500°C to 550°C, forming high-temperature hot air that is sent into the water-cooled air chamber and then into the furnace 1. High-temperature hot air penetrates through the fixed bed layer, transferring heat to the bed material and refractory materials, compensating for the natural heat loss of the furnace body, and maintaining the bed temperature above the allowable coal feeding temperature of 550℃. As a result, the traditional method, which originally relied solely on the heat storage of the bed material itself and the fire suppression time was usually no more than 1.5 hours, can be extended to more than 24 hours, achieving long-cycle fire suppression and heat preservation.
[0046] In this embodiment, both the heat storage heat exchanger 13 and the feedwater heat exchanger 12 are shell-and-tube heat exchangers.
[0047] A shell-and-tube heat exchanger consists of a shell and tubes. One medium flows inside the tubes, while another medium flows inside the shell, with heat transfer occurring through the tube walls. In the heat storage heat exchanger 13, high-temperature steam flows through the shell side, while low-temperature molten salt flows through the tubes. The heat from the steam is transferred to the molten salt through the tube walls, causing the molten salt temperature to rise.
[0048] In the feedwater heat exchanger 12, the high-temperature molten salt flows through the shell side, while the feedwater flows through the tube side. The heat from the molten salt is transferred to the feedwater through the tube wall, raising the feedwater temperature to near the steam drum saturation temperature. Shell-and-tube heat exchangers are characterized by their robust structure and adaptability to high-temperature and high-pressure conditions. They are suitable for heat exchange between steam and molten salt and between molten salt and feedwater in this embodiment, helping to ensure stable system operation during shutdown and startup.
[0049] As an feasible approach, plate heat exchangers or heat pipe heat exchangers can also be selected to meet different operating conditions.
[0050] In this embodiment, both the high-temperature molten salt tank 15 and the low-temperature molten salt tank 16 are separate, independently configured dual-tank structures.
[0051] The low-temperature molten salt tank 16 is used to store low-temperature molten salt that has not absorbed heat, and its temperature is maintained at approximately 280°C. The high-temperature molten salt tank 15 is used to store high-temperature molten salt that has absorbed heat, and its temperature is maintained at approximately 550°C to 565°C.
[0052] In this embodiment, both the low-temperature molten salt tank 16 and the high-temperature molten salt tank 15 are driven by molten salt pumps to flow molten salt. During the heat storage stage, the low-temperature molten salt pump transports the low-temperature molten salt from the low-temperature molten salt tank 16 to the heat storage heat exchanger 13 to absorb heat before entering the high-temperature molten salt tank 15. During the heat release stage, the high-temperature molten salt pump transports the high-temperature molten salt from the high-temperature molten salt tank 15 to the feedwater heat exchanger 12 and the radiator 14 respectively to release heat, after which the molten salt temperature decreases and returns to the low-temperature molten salt tank 16.
[0053] In this embodiment, the high-temperature molten salt tank 15 and the low-temperature molten salt tank 16 are separated into two tanks to store the high-temperature molten salt and the low-temperature molten salt separately. This avoids heat loss caused by mixing hot and cold molten salt in the same tank and keeps the high-temperature molten salt at a high temperature. This provides a stable high-temperature heat source during the heat release phase and helps to maintain the stability of the thermal parameters for water heating and air heating.
[0054] In this embodiment, the radiator 14 is connected in series or in parallel to the outlet duct of the primary air fan 11 and is located in the bypass of the air preheater 7. The outlet of the radiator 14 is connected to the water-cooled air chamber. The outlet duct of the primary air fan 11 is provided with a regulating valve for adjusting the flow rate and temperature of the hot air entering the furnace.
[0055] Under normal operating conditions, the air output from the primary air fan 11 is heated by the air preheater 7 and then sent into the water-cooled air chamber for combustion and fluidization. During the pressure-down and heat preservation stage, the air preheater 7 stops working when the boiler is shut down. At this time, the bypass air duct where the radiator 14 is located is opened, so that the cold air output by the primary air fan 11 at low speed bypasses the air preheater 7 and enters the radiator 14. It is heated to 500°C to 550°C by the high-temperature molten salt, forming high-temperature hot air, which is then directly sent into the water-cooled air chamber.
[0056] In this embodiment, the airflow and temperature entering the radiator 14 can be precisely controlled by the regulating valve on the outlet duct of the primary air fan 11. When the average bed temperature drops to a preset threshold, the opening of the regulating valve is increased to increase the flow rate of the hot air entering the furnace and enhance heat compensation. When the bed temperature rises back to the allowable temperature range for coal feeding, the opening of the regulating valve is reduced or switched to an extremely low flow rate maintenance state to save high-temperature molten salt consumption and reduce fan power consumption. Since the hot air bypasses the air preheater 7 and is directly sent into the furnace, the heat dissipation path is short, the heat loss is small, and the hot air temperature is stable and controllable, enabling continuous and stable heat supply to the bed material during the fire suppression period.
[0057] In this embodiment, the circulating fluidized bed boiler system also includes a control system, which is electrically connected to the boiler body, the molten salt thermal storage circuit, and the molten salt heat release circuit. The control system collects operating parameters such as temperature, pressure, and flow rate from the boiler body, the molten salt thermal storage circuit, and the molten salt heat release circuit, and issues commands to the actuators in each circuit according to preset control logic to coordinate the operating status of the three circuits.
[0058] Specifically, in this embodiment, the control system comprehensively determines the boiler's operating stage by collecting pressure signals from the main steam pipeline 9, bed temperature signals from the furnace 1, steam drum pressure signals, and liquid level and temperature signals from the high-temperature molten salt tank 15 and the low-temperature molten salt tank 16. During the load reduction and heat storage stage, the control system automatically adjusts the opening of the regulating valve on the steam bypass pipeline and the speed of the low-temperature molten salt pump to control the heating rate and storage volume of the molten salt. During the heat preservation stage, the control system adjusts the flow rate of high-temperature molten salt delivered to the feedwater heat exchanger 12 and the radiator 14 according to changes in bed temperature and steam drum pressure. During the rapid start-up stage, the control system coordinates the air volume, molten salt flow rate, and coal feed rate according to a preset start-up curve to ensure a smooth heating and pressurization process. This unifies and coordinates the originally dispersed and independent heat storage and heat release operations, reducing manual intervention and improving the system's response speed and operational stability.
[0059] Specifically, in this embodiment, the radiator 14 is a finned tube gas-liquid heat exchanger, and its air outlet temperature is adjustable from 500°C to 550°C. A finned tube gas-liquid heat exchanger has fins installed on the outer surface of the heat exchange tubes, expanding the contact area with the air. In this system, high-temperature molten salt flows inside the tubes, while air sweeps across the outer surface of the fins. The heat from the molten salt is conducted through the tube wall to the fins, and then transferred by the fins to the flowing air.
[0060] When radiator 14 is operating, high-temperature molten salt is transported from high-temperature molten salt tank 15 to the tube-side inlet of radiator 14 via molten salt pump, and transfers heat to the tube wall and fins during its flow within the tubes. Simultaneously, cold air output from primary fan 11 enters the air side of radiator 14, is heated while flowing across the finned tube bundle, and is then discharged from the air outlet. By adjusting the molten salt flow rate and air flow rate, the air outlet temperature of radiator 14 can be controlled within the range of 500℃ to 550℃ to adapt to different bed temperature compensation requirements.
[0061] The finned tube structure significantly increases the heat exchange area on the air side, compensating for the low gas heat transfer coefficient and enabling the radiator 14 to achieve efficient air heating within a compact volume. Simultaneously, the outlet air temperature is adjusted to above 500℃, exceeding the minimum bed temperature required for coal feeding. This effectively compensates for heat loss from the bed material during fire suppression and locks the bed temperature within a suitable range, providing temperature assurance for subsequent direct coal feeding startup.
[0062] In this embodiment, both the high-temperature molten salt tank 15 and the low-temperature molten salt tank 16 are provided with an insulation layer on their outer walls, and a heat tracing system is provided between the high-temperature molten salt tank 15 and the low-temperature molten salt tank 16.
[0063] The insulation layer can be made of aluminum silicate fiber blanket, rock wool board, or other high-temperature resistant insulation materials and laid on the outer wall of the tank. In this embodiment, the insulation layer is specifically an aluminum silicate fiber blanket, which can prevent the heat of the molten salt inside the tank from being lost to the external environment through the tank wall. The insulation layer of the high-temperature molten salt tank 15 can reduce the natural loss of heat of the molten salt during storage, allowing the high-temperature molten salt to maintain a usable temperature above 550°C for a longer period of time. Similarly, the insulation layer of the low-temperature molten salt tank 16 can prevent the molten salt from solidifying due to excessively low temperature.
[0064] Because the molten salt between the high-temperature molten salt tank 15 and the low-temperature molten salt tank 16 gradually decreases in temperature due to heat dissipation as it flows through pipes, valves, and other equipment during circulation, there is a risk of molten salt solidifying and clogging the pipelines. Therefore, in this embodiment, a heat tracing system is installed between the high-temperature molten salt tank 15 and the low-temperature molten salt tank 16. Specifically, the heat tracing system in this embodiment is an electric heat tracing cable, which is laid along the molten salt flow path on the outer wall of the pipes and at the valves. It maintains the molten salt temperature above its freezing point through external heating, preventing localized cooling that could lead to freezing. The combined use of the insulation layer and the heat tracing system maintains the temperature stability of the molten salt system from both passive insulation and active heating perspectives, ensuring the reliability of the heat storage and release circuits during long-term operation.
[0065] In this embodiment, the boiler body also includes an economizer 6. The flue gas inlet of the economizer 6 is connected to the flue gas outlet of the furnace 1, and the feedwater outlet of the economizer 6 is connected to the feedwater inlet of the furnace 1. In normal operation mode, low-temperature feedwater from the feedwater pump enters the economizer 6, exchanges heat with the high-temperature flue gas discharged from the furnace, absorbs the waste heat of the flue gas to raise its temperature, and is then sent to the water-cooled wall or steam drum of the furnace 1.
[0066] The water side of the feedwater heat exchanger 12 is connected to the water side pipeline of the boiler body to return the heated working fluid to the boiler body. Specifically, in this embodiment, the feedwater side pipeline of the feedwater heat exchanger 12 can be connected in parallel to the inlet feedwater pipeline of the economizer 6, so that part or all of the low-temperature feedwater first passes through the feedwater heat exchanger 12, is heated by the high-temperature molten salt, and then enters the economizer 6 or is directly sent to the steam drum. During the shutdown period, there is no high-temperature flue gas flow in the conventional flue gas passage, the economizer 6 stops working, and the feedwater heat exchanger 12 independently provides the heated working fluid to the boiler body using the heat of the high-temperature molten salt to maintain the temperature of the steam drum and the heating surface.
[0067] In this structure, the feedwater heat exchanger 12 is compatible with the original feedwater system of the boiler body. It can operate without participating in the work during normal boiler operation and without increasing system resistance, and can also operate independently as a backup heat source during the fire suppression period, which improves the system integration and operational flexibility.
[0068] As an feasible approach, an independent circulation pipeline can also be set up, drawing water from the steam drum downcomer, heating it through the feedwater heat exchanger 12, and then returning it to the steam drum to form an independent hot water circulation.
[0069] In this embodiment, the boiler body also includes a cyclone separator 2, a return valve 3, a low-temperature superheater 4, a low-temperature reheater 5, a high-temperature superheater 8, an air preheater 7, and a coal feeder 10.
[0070] The flue gas outlet of the furnace 1 is connected to the inlet of the cyclone separator 2. The high-temperature flue gas generated by combustion in the furnace 1 and the solid bed material particles it carries enter the cyclone separator 2 from the flue gas outlet.
[0071] In the cyclone separator 2, solid materials and flue gas undergo gas-solid separation. The separated solid materials are returned to the return port of the furnace 1 via the return valve 3 at the bottom of the cyclone separator 2. The return valve 3 acts as an airlock during the material return process, continuously and stably feeding the separated high-temperature bed material particles back to the furnace 1, while preventing the high-temperature flue gas in the furnace 1 from flowing back into the cyclone separator 2 through the return pipeline, thus ensuring reliable material circulation and a stable amount of bed material in the furnace.
[0072] The separated high-temperature flue gas flows out from the flue gas outlet of cyclone separator 2 and passes through the following components sequentially along the flue gas flow path: First, it enters the flue gas side of high-temperature superheater 8, where it exchanges heat with the superheated steam inside the tubes. The flue gas flowing out of high-temperature superheater 8 enters the flue gas side of low-temperature reheater 5, heating the reheated steam inside the tubes. The flue gas flowing out of low-temperature reheater 5 enters the flue gas side of low-temperature superheater 4, heating the saturated steam inside the tubes. The flue gas flowing out of low-temperature superheater 4 enters the flue gas side of economizer 6, heating the boiler feedwater. The flue gas flowing out of economizer 6 finally enters the flue gas side of air preheater 7, heating the primary and secondary air before being discharged. Along the working fluid flow path, the feedwater first enters economizer 6 to absorb heat and increase its temperature before being sent to the water-cooled wall or steam drum of furnace 1. The saturated steam generated in the steam drum is heated sequentially by low-temperature superheater 4 and high-temperature superheater 8 to become high-temperature superheated steam, which is then sent out through the main steam pipe 9. The reheated steam is then heated by low-temperature reheater 5 before being sent out.
[0073] On the air side, the air outlet of the air preheater 7 is connected to the water-cooled air chamber via a duct, sending the preheated air into the furnace 1 to participate in combustion and fluidization. The outlet of the coal feeder 10 is connected to the coal feed port of the furnace 1, used to quantitatively deliver coal fuel into the furnace 1. The main steam pipe 9 is connected to the steam outlet of the high-temperature superheater 8, which further heats the saturated steam into high-temperature superheated steam, which is then sent to the steam turbine or bypassed to the heat storage heat exchanger 13 via the main steam pipe 9.
[0074] In this embodiment, the flue gas path is arranged sequentially along the high-temperature superheater 8, the low-temperature reheater 5, the low-temperature superheater 4, the economizer 6, and the air preheater 7. The working fluid path is arranged sequentially along the economizer 6, the low-temperature superheater 4, and the high-temperature superheater 8, thus forming a complete combustion, heat transfer, and steam-water circulation system for the circulating fluidized bed boiler. Based on this, the molten salt heat storage circuit is connected to the main steam pipeline 9 via a bypass pipe, and the molten salt heat release circuit is connected in parallel to the feedwater system and the primary air system via the feedwater heat exchanger 12 and the radiator 14, respectively. Working in coordination with the various components of the boiler body, this achieves long-cycle heat preservation and rapid start-up functions.
[0075] The circulating fluidized bed boiler system control method provided in this embodiment is applied to the above system and specifically includes the following steps: When the boiler reduces its load, the excess high-temperature and high-pressure steam generated by the boiler is introduced into the heat storage heat exchanger to heat the low-temperature molten salt from the low-temperature molten salt tank to form high-temperature molten salt and store it in the high-temperature molten salt tank.
[0076] During boiler heat preservation, the high-temperature molten salt in the high-temperature molten salt tank is transported to the feedwater heat exchanger and radiator respectively. The feedwater heat exchanger is controlled to heat the boiler feedwater to maintain the steam drum pressure and temperature, and the radiator is controlled to heat the primary air to compensate for the heat loss of the furnace bed material, so that the bed temperature is locked above the allowable coal feeding temperature.
[0077] When the boiler starts up quickly, the flow rate of high-temperature molten salt delivered to the radiator is increased, and high-temperature combustion air is sent into the furnace. At the same time, coal is directly fed to achieve oil-free or low-oil hot start-up, and the steam drum is kept in a hot standby state by controlling the feedwater heat exchanger to complete the turbine start-up and grid connection.
[0078] Specifically, during the boiler load reduction phase, when the power grid dispatch issues a deep peak shaving or shutdown command, and the unit load needs to be reduced below the minimum stable combustion load, the high-pressure regulating valve of the steam turbine is gradually closed to reduce the power generation load, and the regulating valve at the inlet of the thermal storage heat exchanger 13 is opened simultaneously. The control system maintains a constant main steam header pressure. When the steam consumption of the steam turbine is less than the current steam production of the boiler, the steam flow to the thermal storage heat exchanger 13 is automatically increased, introducing the excess high-temperature and high-pressure steam into the thermal storage heat exchanger 13. At the same time, the low-temperature molten salt pump is started to transport the low-temperature molten salt in the low-temperature molten salt tank 16 to the thermal storage heat exchanger 13. After the molten salt absorbs heat and heats up to the set high temperature value, it is stored in the high-temperature molten salt tank 15. The water after the steam releases heat and condenses is recovered to the deaerator or the steam side of the high-pressure heater through the condensate expansion tank. As the load decreases, the coal feed and total air volume are gradually reduced according to conventional logic, and the combustion side transitions smoothly. After the thermal storage is completed, the coal feed is stopped, and the boiler enters the shutdown preparation state. This stage stores excess steam heat as sensible heat in molten salt, thus reserving an external heat source for subsequent heat preservation and heat treatment.
[0079] During the boiler's heat preservation and cooling phase, coal feeding is stopped, the main blower is shut down, and the boiler enters a heat preservation state. At this time, the molten salt exothermic circuit is activated. On the feedwater side, high-temperature molten salt from the high-temperature molten salt tank 15 is transported to the feedwater heat exchanger 12 to heat the boiler feedwater. The steam drum pressure is maintained within 50% to 80% of normal operating pressure through continuous small-flow water replenishment or natural circulation, keeping the steam drum and heating surfaces in a hot standby state. On the air side, when the average bed temperature drops to a preset threshold, the bypass duct of radiator 14 is opened, and high-temperature molten salt is transported to radiator 14. The primary air fan 11 operates at a low speed, and the cold air delivered is heated by radiator 14 to form high-temperature hot air at 500°C to 550°C, which is then sent into the water-cooled air chamber and into the furnace 1. The airflow into the furnace is controlled below the critical fluidizing airflow. The hot air permeates through the fixed bed layer, transferring heat to the bed material and refractory material. When the average bed temperature rises back to the allowable coal feeding temperature range, reduce the molten salt flow rate of radiator 14 or stop heating. Through the above-mentioned water supply insulation and hot air supplementary heating measures, the bed temperature is continuously locked above the allowable coal feeding temperature, and the fire suppression time can be extended to more than 24 hours.
[0080] During the boiler's rapid start-up phase, upon receiving the grid connection command, the flow rate of high-temperature molten salt supplied to radiator 14 is increased, and the primary air fan 11 is fully activated, sending a large amount of high-temperature combustion air (above 500°C) into the furnace 1. Since the bed temperature has been maintained above the permissible coal feeding line during the pressure-down period, and the inlet air temperature is high, pulverized coal can be directly added into the furnace 1 for ignition, requiring no or only a small amount of fuel oil. Simultaneously, because the steam drum pressure has been maintained at a high level by the feedwater heat exchanger 12 during the pressure-down period, the turbine can quickly start up and connect to the grid. This phase utilizes the high bed temperature and high steam drum pressure maintained during the pressure-down period to achieve rapid hot start-up with little or no oil, shortening the start-up response time, reducing start-up fuel consumption, and minimizing the power consumption of prolonged fluidization heating during cold or warm start-ups.
[0081] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features. These modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.
Claims
1. A circulating fluidized bed boiler system, characterized in that, include: The boiler body has a furnace (1), a main steam pipe (9) and a water-cooled air chamber. The main steam pipe (9) is connected to the steam outlet of the furnace (1), and the water-cooled air chamber is connected to the primary air inlet of the furnace (1). The molten salt heat storage circuit includes a heat storage heat exchanger (13), a high-temperature molten salt tank (15), and a low-temperature molten salt tank (16). The steam inlet of the heat storage heat exchanger (13) is connected to the main steam pipeline (9) through a bypass pipe. The molten salt outlet of the heat storage heat exchanger (13) is connected to the inlet of the high-temperature molten salt tank (15). The molten salt inlet of the heat storage heat exchanger (13) is connected to the outlet of the low-temperature molten salt tank (16). It is used to convert the excess steam heat energy when the boiler is reduced in load into sensible heat of molten salt and store it in the high-temperature molten salt tank (15). The steam outlet of the heat storage heat exchanger (13) is connected to the condensate system. The molten salt heat release circuit includes a feedwater heat exchanger (12) and a radiator (14). The molten salt inlet of the feedwater heat exchanger (12) and the molten salt inlet of the radiator (14) are both connected to the outlet of the high-temperature molten salt tank (15). The molten salt outlet of the feedwater heat exchanger (12) and the molten salt outlet of the radiator (14) are both connected to the inlet of the low-temperature molten salt tank (16). The feedwater outlet of the feedwater heat exchanger (12) is connected to the feedwater inlet of the boiler body. The air outlet of the radiator (14) is connected to the water-cooled air chamber.
2. The circulating fluidized bed boiler system according to claim 1, characterized in that, Both the heat storage heat exchanger (13) and the water supply heat exchanger (12) are shell-and-tube heat exchangers.
3. The circulating fluidized bed boiler system according to claim 1, characterized in that, The high-temperature molten salt tank (15) and the low-temperature molten salt tank (16) are separate and independently set up as a dual-tank structure.
4. The circulating fluidized bed boiler system according to claim 1, characterized in that, The radiator (14) is connected in series or in parallel to the outlet air duct of the primary air fan (11) and is located in the bypass of the air preheater (7); The outlet of the radiator (14) is connected to the water-cooled air chamber; The air duct is equipped with regulating valves for adjusting the flow rate and temperature of the hot air entering the furnace.
5. The circulating fluidized bed boiler system according to claim 1, characterized in that, The circulating fluidized bed boiler system also includes a control system; The control system is electrically connected to the boiler body, the molten salt heat storage circuit, and the molten salt heat release circuit.
6. The circulating fluidized bed boiler system according to claim 1, characterized in that, The radiator (14) is a finned tube gas-liquid heat exchanger, and its air outlet temperature is adjustable from 500°C to 550°C.
7. The circulating fluidized bed boiler system according to claim 1, characterized in that, The outer walls of both the high-temperature molten salt tank (15) and the low-temperature molten salt tank (16) are provided with heat insulation layers; A heat tracing system is provided between the high-temperature molten salt tank (15) and the low-temperature molten salt tank (16).
8. The circulating fluidized bed boiler system according to any one of claims 1-7, characterized in that, The boiler body also includes an economizer (6); The flue gas inlet of the economizer (6) is connected to the flue gas outlet of the furnace (1), and the water outlet of the economizer (6) is connected to the water inlet of the furnace (1). The water side of the feedwater heat exchanger (12) is connected to the water side pipeline of the boiler body to send the heated working fluid back to the boiler body.
9. The circulating fluidized bed boiler system according to claim 8, characterized in that, The boiler body also includes a cyclone separator (2), a return valve (3), a low-temperature superheater (4), a low-temperature reheater (5), a high-temperature superheater (8), an air preheater (7), and a coal feeder (10). The flue gas outlet of the furnace (1) is connected to the inlet of the cyclone separator (2), and the material outlet of the cyclone separator (2) is connected to the return port of the furnace (1) via the return valve (3); the flue gas outlet of the cyclone separator (2) is sequentially connected to the flue gas side of the high-temperature superheater (8), the low-temperature reheater (5), the low-temperature superheater (4), the economizer (6), and the air preheater (7); the air outlet of the air preheater (7) is connected to the water-cooled air chamber via a duct; the outlet of the coal feeder (10) is connected to the coal feed port of the furnace (1); The main steam pipe (9) is connected to the steam outlet of the high-temperature superheater (8).
10. A control method for a circulating fluidized bed boiler system, characterized in that, The application of the circulating fluidized bed boiler system as described in any one of claims 1 to 9 includes the following steps: When the boiler reduces its load, the excess high-temperature and high-pressure steam generated by the boiler is introduced into the heat storage heat exchanger to heat the low-temperature molten salt from the low-temperature molten salt tank to form high-temperature molten salt and store it in the high-temperature molten salt tank. During boiler heat preservation, the high-temperature molten salt in the high-temperature molten salt tank is respectively transported to the feedwater heat exchanger and the radiator. The feedwater heat exchanger is controlled to heat the boiler feedwater to maintain the steam drum pressure and temperature, and the radiator is controlled to heat the primary air to compensate for the heat loss of the furnace bed material, so that the bed temperature is locked above the allowable coal feeding temperature. When the boiler starts up quickly, the flow rate of high-temperature molten salt delivered to the radiator is increased, and high-temperature combustion air is sent into the furnace. At the same time, coal is directly fed to achieve oil-free or low-oil hot start-up, and the steam drum is kept in a hot standby state by the feedwater heat exchanger to complete the turbine start-up and grid connection.