A two-stage series return material device and temperature control method for a circulating fluidized bed boiler

Abstract

The invention discloses a two-stage series return material device and temperature control method for a circulating fluidized bed boiler, comprising a first-stage return material device and a second-stage return material device connected in series; the second-stage return material device comprises a loosening chamber, a normal return material pipe and a bypass overflow pipe, a heat exchange surface is arranged as required inside the loosening chamber, the loosening chamber is connected to the furnace through the normal return material pipe and the bypass overflow pipe, and the inlet end of the first-stage return material device is connected to a cyclone separator. The device and the temperature control method realize the separation of the combustion process and the heat exchange process of the circulating fluidized bed boiler, fundamentally solve the problems of high-temperature corrosion, ash accumulation, slagging and the like of the heating surface in the furnace when the circulating fluidized bed boiler burns biomass fuel, and help to realize the high parameterization of the biomass fluidized bed boiler. At the same time, the working medium temperature is adjusted by adjusting the normal return material air volume; the bed temperature is adjusted by controlling the bypass return material air volume. In addition, the circulating ash can be returned to the furnace through the bypass overflow pipe, avoiding the emergency shutdown problem caused by the interruption of the circulating ash loop when the normal return material pipe or the heat exchange surface fails.

Description

Technical Field

[0001] The invention relates to the field of circulating fluidized bed boilers, in particular to a two-stage series material return device and a temperature control method for a circulating fluidized bed boiler, which are applied to biomass power generation equipment. Background Art

[0002] With the rapid development of society, the limited reserves of fossil fuels can no longer meet the growing energy demand. Therefore, how to achieve efficient utilization of renewable energy such as biomass has become the focus of worldwide attention. At present, combustion power generation is the main way to efficiently utilize biomass. However, due to the fuel characteristics of biomass with high chlorine and alkali content, the use of conventional circulating fluidized bed boilers is prone to high-temperature corrosion, ash accumulation, and slagging on the heating surface in the furnace. This not only leads to a decrease in the thermal efficiency of the boiler, the need for regular inspection and replacement of the high-temperature heating surface, and an increase in the operation and maintenance costs of the power plant, but also is an important reason why such fuel boilers cannot be highly parameterized, and is a major obstacle to the efficient combustion and utilization of biomass.

[0003] At present, there are two main methods for adjusting the bed temperature of circulating fluidized bed boilers: one is to adjust the feed rate of the feeder, and the other is to adjust the primary air volume at the bottom of the furnace. There is a huge lag in the feed rate to adjust the bed temperature. The main reason is that the feed port is a certain distance away from the bed layer, and it takes a certain amount of time for the fuel to enter the furnace and ignite. The primary air of the circulating fluidized bed has two functions, one is fluidization air, and the other is combustion air. Therefore, the effect of the primary air on the bed temperature will show two opposite trends. As the air volume increases, the heat taken away by the flue gas from the dense phase area increases, and the bed temperature decreases; at the same time, the amount of combustion oxygen provided to the fuel particles will also increase, the gas-solid turbulence will be more intense, the combustion heat will increase, and the bed temperature will rise. These two methods of adjusting the bed temperature require the on-site commissioning personnel to make comprehensive judgments and adjustments based on the actual situation on site. They are very empirical. Once the commissioning personnel make a mistake in judgment, it is very likely that deflagration will occur, resulting in a rapid increase in bed temperature and serious consequences such as coking of the bed layer.

[0004] Water spraying is one of the steam temperature regulation methods. Its principle is to use feed water to mix directly with superheated steam or reheated steam to achieve the purpose of regulating steam temperature. Because of its advantages such as simple structure, large temperature regulation range and fast temperature reduction speed, it is widely used in modern circulating fluidized bed boiler units. However, this temperature regulation method directly changes the thermodynamic cycle state of the working fluid, which will reduce the thermal economy of the entire unit, especially when water is sprayed on reheated steam with lower pressure parameters, the thermal economy of the unit will decrease more significantly. Relevant studies have shown that for every 1% increase in the reheater cooling water volume in a 300MW unit, the unit efficiency will decrease by 0.2% and the standard coal consumption will increase by 0.6g / (kWh). When the boiler is running for a long period of time, the energy loss caused by reheater water spraying is huge.

[0005] In order to achieve stable and efficient combustion of biomass circulating fluidized bed boilers, long-term continuous operation, reduce the risk of shutdown due to uncontrolled bed temperature regulation, and avoid energy waste from reheater water spraying and cooling, it is urgent to develop a new type of return device with a reasonable structure, stable and reliable, and a reheat steam temperature and bed temperature regulation method. Summary of the invention

[0006] The technical problem to be solved by the present invention is to provide a two-stage series return device and temperature control method for a circulating fluidized bed boiler, so as to separate the combustion process from the heat exchange process of the circulating fluidized bed boiler, fundamentally solve the problems of high temperature corrosion, ash accumulation, slagging, etc. of the heating surface in the furnace when the circulating fluidized bed boiler burns biomass fuel, and help to achieve high parameterization of the biomass circulating fluidized bed boiler. At the same time, the working medium temperature is adjusted by adjusting the amount of circulating ash entering the heat exchange chamber. In addition, the bed temperature is adjusted by adjusting the bypass return air volume.

[0007] The present invention adopts the following technical solution:

[0008] A two-stage series return device for a circulating fluidized bed boiler comprises a primary return device and a secondary return device, wherein the primary return device and the secondary return device are connected in series; the secondary return device comprises a loosening chamber, a normal return pipe and a bypass overflow pipe, a heat exchange surface is arranged inside the loosening chamber as required, the loosening chamber is connected to the furnace through the normal return pipe and the bypass overflow pipe, the inlet end of the primary return device is connected to a cyclone separator, a primary fluidizing air port is arranged at the bottom of the primary return device; a loosening air port is arranged at the bottom of the heat exchange chamber; a normal return air port is arranged at the bottom of the normal return pipe; and a bypass return air port is arranged at the bottom of the bypass overflow pipe.

[0009] Preferably, the loosening chamber is divided into a plurality of heat exchange chambers, a plurality of normal return pipes and bypass overflow pipes are arranged at the outlet of each heat exchange chamber, and heat exchange surfaces are arranged inside the heat exchange chamber as required.

[0010] Preferably, the types of heat exchange surfaces include evaporators, superheaters and reheaters.

[0011] Preferably, the inlet of the normal return pipe is lower than the lowest lower surface of the heat exchange surface.

[0012] Preferably, the inlet of the bypass overflow pipe is higher than the highest upper surface of the heat exchange surface.

[0013] The temperature control method of the two-stage series return device of the circulating fluidized bed boiler has the following specific process steps:

[0014] 1) After the flue gas enters the cyclone separator, the separated circulating ash falls into the primary return material. The primary fluidizing air enters from the primary fluidizing air port, causing the circulating ash to flow into the secondary return material;

[0015] 2) Open the loosening air port and normal return air port of each heat exchange chamber of the secondary return material device, and close the bypass return air port. The loosening air fluidizes the circulating ash in each heat exchange chamber, and the normal return air fluidizes the circulating ash in the normal return pipe. After the circulating ash exchanges heat with the heat exchange surface, it returns to the furnace through the normal return pipe;

[0016] 3) When the working medium of the heat exchange surface is adjusted in temperature, the normal return air volume is adjusted to distribute the circulating ash entering each heat exchange chamber, thereby realizing the regulation of the heat exchange between the circulating ash in each heat exchange chamber and the heat exchange surface;

[0017] 4) When the normal return pipe fails or the bed temperature needs to be adjusted, open the bypass return air port. The bypass return air fluidizes the circulating ash in the bypass return pipe. The circulating ash no longer participates in heat exchange and directly returns to the furnace through the bypass overflow pipe.

[0018] The beneficial effects of the present invention are:

[0019] Firstly, the present invention realizes the separation of the combustion process and the heat exchange process. The combustion process is carried out in the furnace, and the heat exchange process is carried out in the heat exchange chamber, so as to avoid direct contact between the heating surface and the high-temperature flue gas containing high chlorine and alkali content, thereby preventing high-temperature corrosion of the heating surface;

[0020] Secondly, the circulating ash velocity in the heat exchange chamber is low, which, on the one hand, plays a role in flushing the hot surface of the tube to prevent ash accumulation and slagging on the heating surface tube, and on the other hand, the heating surface is completely immersed in the circulating ash, and each part can be in good contact with the high-temperature circulating ash, greatly enhancing the heat exchange efficiency;

[0021] Thirdly, the heat exchange surface can be arranged in the heat exchange chamber as needed, and the temperature of the working medium can be adjusted by adjusting the amount of circulating ash entering the heat exchange chamber, thus avoiding energy loss caused by water spray cooling;

[0022] Fourthly, the bed temperature is adjusted by adjusting the circulating ash volume entering the heat exchange chamber and controlling the opening and closing state of the bypass return air. An easy-to-operate adjustment method is added on the basis of the traditional bed temperature adjustment method to reduce the risk of drastic fluctuations in bed temperature and improve the reliability of boiler operation;

[0023] Fifth, the circulating ash can return to the furnace through the bypass overflow pipe, avoiding boiler shutdown caused by interruption of the circulating ash circulation loop when the normal return pipe or heat exchange surface fails. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 A structural schematic diagram of the present invention.

[0025] In the figure, 100, the first-stage returner, 200, the second-stage returner, 201, the loosening chamber, 202, the heat exchange surface, 203, the normal return pipe, 204, the bypass overflow pipe, 300, the furnace, 400, the cyclone separator, 500, the first-stage fluidizing air port, 601, the loosening air port, 602, the normal return air port, 603, the bypass return air port. DETAILED DESCRIPTION

[0026] The technical solution of the present invention is further described in detail below through specific embodiments and in conjunction with the accompanying drawings.

[0027] Example: As shown in the attached Figure 1 As shown, a two-stage series return device for a circulating fluidized bed boiler includes a primary return device 100 and a secondary return device 200. The primary return device 100 and the secondary return device 200 are connected in series, and the secondary return device 200 is composed of a loosening chamber 201, a normal return pipe 203 and a bypass overflow pipe 204. The primary return device 200 and the loosening chamber 201 are as wide as the furnace 300, and are all composed of membrane water-cooled walls, with refractory plastics laid around and on the top.

[0028] The loosening chamber 201 is divided into three heat exchange chambers of equal width by partitions. High-temperature superheaters are arranged in the heat exchange chambers on both sides, and reheaters are arranged in the middle heat exchange chamber. Two normal return pipes 203 and a bypass overflow pipe 204 are arranged at the outlet of each heat exchange chamber. The normal return pipe 203 and the bypass overflow pipe 204 are arranged symmetrically along the center line of the boiler. The inlet of the normal return pipe 203 of each heat exchange chamber is lower than the lowest lower surface of the high-temperature superheater / reheater, and the inlet of the bypass overflow pipe 204 is higher than the highest upper surface of the high-temperature superheater / reheater.

[0029] A primary fluidizing tuyere 500 is arranged at the bottom of the primary return device 100 , a loosening tuyere 601 is arranged at the bottom of the heat exchange chamber, a normal return tuyere 602 is arranged at the bottom of the normal return pipe 203 , and a bypass return tuyere 603 is arranged at the bottom of the bypass overflow pipe 204 .

[0030] The temperature control method of the two-stage series return device of the circulating fluidized bed boiler has the following specific process steps:

[0031] 1) After the flue gas enters the cyclone separator 400, the separated circulating ash falls into the primary return material 100. The primary fluidizing air enters from the bottom of the primary return material 100 through the primary fluidizing air port 500, so that the circulating ash flows into the secondary return material 200.

[0032] 2) Open the loosening air port 601 and the normal return air port 602 of each heat exchange chamber of the secondary return device 200, and close the bypass return air port 603. The loosening air entering from the loosening air port 601 fluidizes the circulating ash in each heat exchange chamber, and the normal return air entering from the normal return air port 602 fluidizes the circulating ash in the normal return pipe 203. After the circulating ash exchanges heat with the heat exchange surface 202, it returns to the furnace 300 through the normal return pipe 203.

[0033] 3) Reheat steam temperature adjustment process: Increase the air volume of the normal return pipe 203 connected to the reheater heat exchange chamber to increase the amount of circulating ash entering the reheater heat exchange chamber, increase the heat exchange in the reheater heat exchange chamber, and increase the reheat steam temperature. Similarly, reducing the air volume of the normal return pipe 203 connected to the reheater heat exchange chamber can reduce the reheat steam temperature.

[0034] 4) Bed temperature adjustment process: Open the bypass return air port 603 of the high-temperature superheater heat exchange chamber, and the bypass return air fluidizes the circulating ash in the bypass return pipe 204. Part of the circulating ash from the first-stage return device does not exchange heat with the high-temperature superheater, but directly returns to the furnace 300 through the bypass return pipe 204. The bypass return air volume is adjusted to change the amount of circulating ash entering the furnace 300 through the bypass return pipe 204, and the circulating ash temperature changes, thereby achieving bed temperature adjustment.

[0035] 5) When the normal return pipe 203 fails, the bypass return air port 603 is opened to allow the circulating ash to return to the furnace 300 through the bypass overflow pipe 204, thereby ensuring continuous and stable return of materials in the device.

[0036] The above-described embodiment is only a preferred solution of the present invention and does not limit the present invention in any form. There are other variations and modifications without exceeding the technical solution described in the claims.

Claims

1. A temperature control method for a two-stage series return device of a circulating fluidized bed boiler, characterized in that: The two-stage series return material device of the circulating fluidized bed boiler comprises a first-stage return material device (100) and a second-stage return material device (200), wherein the first-stage return material device (100) and the second-stage return material device (200) are connected in series; the second-stage return material device (200) comprises a loosening chamber (201), a normal return material pipe (203) and a bypass overflow pipe (204), wherein the loosening chamber (201) is divided into a plurality of heat exchange chambers, and a plurality of normal return material pipes (203) and bypass overflow pipes (204) are arranged at the outlet of each heat exchange chamber, and a heat exchange surface (202) is arranged inside the heat exchange chamber as required, and the loosening chamber (201) The furnace (300) is connected to the furnace (300) through a normal return pipe (203) and a bypass overflow pipe (204); the inlet end of the first-stage return device (100) is connected to the cyclone separator (400); a first-stage fluidizing air port (500) is arranged at the bottom of the first-stage return device (100); a loosening air port (601) is arranged at the bottom of the heat exchange chamber; a normal return air port (602) is arranged at the bottom of the normal return pipe (203); and a bypass return air port (603) is arranged at the bottom of the bypass overflow pipe (204); The inlet of the normal return pipe (203) is lower than the lowest lower surface of the heat exchange surface (202), and the inlet of the bypass overflow pipe (204) is higher than the highest upper surface of the heat exchange surface (202); The specific process steps of the temperature control method of the two-stage series return device of the circulating fluidized bed boiler are as follows: 1) After the flue gas enters the cyclone separator (400), the separated circulating ash falls into the primary return material device (100); the primary fluidizing air enters from the primary fluidizing air port (500), causing the circulating ash to flow into the secondary return material device (200); 2) Open the loosening air port (601) and the normal return air port (602) of each heat exchange chamber of the secondary return device (200), and close the bypass return air port (603). The loosening air fluidizes the circulating ash in each heat exchange chamber, and the normal return air fluidizes the circulating ash in the normal return pipe (203). After the circulating ash exchanges heat with the heat exchange surface (202), it returns to the furnace (300) through the normal return pipe (203); 3) When the working medium of the heat exchange surface (202) is adjusted in temperature, the normal return air volume of each normal return air port (602) is adjusted to distribute the amount of circulating ash entering each heat exchange chamber, thereby achieving the regulation of the heat exchange amount between the circulating ash in each heat exchange chamber and the heat exchange surface (202); 4) When adjusting the bed temperature, the bypass return air port (603) is opened, and the amount of circulating ash returned to the furnace (300) through the bypass overflow pipe (204) is controlled by adjusting the bypass return air volume, thereby adjusting the bed temperature; 5) When the normal return pipe fails, the bypass return air port is opened, and the circulating ash is directly returned to the furnace (300) through the bypass overflow pipe.

2. The temperature control method of a two-stage series return device for a circulating fluidized bed boiler according to claim 1 is characterized in that: The types of heat exchange surfaces (202) include evaporators, superheaters and reheaters.

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