CN112484023A

CN112484023A - Two-stage series material returning device of circulating fluidized bed boiler and temperature adjusting method

Info

Publication number: CN112484023A
Application number: CN202011542352.1A
Authority: CN
Inventors: 叶忠; 李书平; 蒋志康; 郭佳明; 王贤朕
Original assignee: Hangzhou Boiler Group Co Ltd
Current assignee: Hangzhou Boiler Group Co Ltd
Priority date: 2020-12-24
Filing date: 2020-12-24
Publication date: 2021-03-12

Abstract

The invention discloses a two-stage series material returning device and a temperature adjusting method of a circulating fluidized bed boiler, wherein a first-stage material returning device and a second-stage material returning device are connected in series; the second grade returning charge ware has arranged the heat-transfer surface as required including not hard up room, normal returning charge pipe and bypass overflow pipe not hard up indoor portion, and not hard up indoor through normal returning charge pipe and bypass overflow pipe intercommunication furnace, one-level returning charge ware entry end intercommunication cyclone. The device and the temperature adjusting 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, dust accumulation, slag bonding and the like of the heating surface in the boiler when the circulating fluidized bed boiler burns biomass fuel, and are beneficial to realizing the high parameterization of the biomass fluidized bed boiler. Meanwhile, the temperature of the working medium is adjusted by adjusting the normal return air volume; the bed temperature is adjusted by controlling the bypass material returning air quantity. In addition, the circulating ash can return to the hearth through the bypass overflow pipe, so that the problem of emergency shutdown caused by interruption of a circulating ash loop when a normal return pipe or a heat exchange surface fails is solved.

Description

Two-stage series material returning device of circulating fluidized bed boiler and temperature adjusting method

Technical Field

The invention relates to the field of circulating fluidized bed boilers, in particular to a two-stage series material returning device of a circulating fluidized bed boiler and a temperature adjusting method, which are applied to biomass power generation equipment.

Background

With the continuous and rapid development of society, fossil fuels with limited reserves cannot meet the increasing energy demand. Therefore, how to realize efficient utilization of renewable energy such as biomass has become a focus of attention all over the world. At present, combustion power generation is the main way of high-efficiency utilization of biomass. However, due to the characteristics of fuels containing chlorine and high alkali content, the biomass is combusted by a conventional circulating fluidized bed boiler, and phenomena such as high-temperature corrosion, ash accumulation, slag bonding and the like of a heating surface in the boiler are easy to occur. The method not only causes the reduction of the thermal efficiency of the boiler, the frequent and regular inspection and replacement of the high-temperature heating surface and the increase of the operation and maintenance cost of the power plant, but also is an important reason that the high-parameter of the fuel boiler cannot be realized, and is a main obstacle for realizing the efficient combustion and utilization of the biomass.

The bed temperature adjusting method of the circulating fluidized bed boiler mainly comprises two methods: firstly, the feeding amount of the feeder is adjusted, and secondly, the primary air quantity at the bottom of the furnace is adjusted. The feeding amount has great hysteresis on bed temperature adjustment, and the main reason is that a feeding port has a certain distance from a bed layer, and a certain time is needed for ignition when fuel enters a furnace. The primary air of the circulating fluidized bed has two functions, namely fluidizing air and combustion air. Therefore, the influence of primary air on the bed temperature can present two opposite trends, the air quantity is increased, the heat quantity taken away by the flue gas from the dense-phase zone is increased, and the bed temperature is reduced; at the same time, the combustion oxygen amount supplied to the fuel particles also rises, the gas-solid turbulence is more intense, the combustion heat release amount is increased, and the bed temperature rises. The two methods for adjusting the bed temperature need field debugging personnel to comprehensively judge and adjust according to the actual situation on the spot, the experience is very strong, and once the debugging personnel make a judgment error, the detonation phenomenon is likely to occur, so that the bed temperature is rapidly increased, and serious consequences such as bed coking are caused.

The water spraying temperature reduction is one of steam temperature regulating methods, and the principle is that the water supply is directly mixed with superheated steam or reheated steam to achieve the purpose of regulating the steam temperature. The circulating fluidized bed boiler unit has the advantages of simple structure, large temperature adjusting range, high temperature reduction speed and the like, and is widely applied to modern circulating fluidized bed boiler units. However, the temperature adjusting mode directly changes the thermodynamic cycle state of the working medium, the thermal economy of the whole unit can be reduced, and particularly, the reduction of the thermal economy of the unit is more obvious when the reheat steam with lower pressure parameters is sprayed. Relevant studies have shown that for every 1% share of reheater desuperheater water in a 300MW train, the train efficiency is relatively reduced by 0.2% and the standard coal consumption is increased by 0.6 g/(kWh). When the boiler operates for a long period, the energy loss caused by the temperature reduction of the reheater by spraying water is huge.

In order to realize stable and efficient combustion and long-period continuous operation of the biomass circulating fluidized bed boiler, the shutdown risk caused by out-of-control bed temperature regulation is reduced, energy waste caused by water spraying and temperature reduction of a reheater is avoided, and a novel material returning device, a reheating steam temperature regulation mode and a bed temperature regulation mode which are reasonable in structure, stable and reliable are urgently needed to be developed.

Disclosure of Invention

The invention aims to solve the technical problem of providing a two-stage series material returning device and a temperature adjusting method for a circulating fluidized bed boiler, so that the separation of the combustion process and the heat exchange process of the circulating fluidized bed boiler is realized, the problems of high-temperature corrosion, ash accumulation, slag bonding and the like of the heating surface in the boiler when biomass fuel is used by the circulating fluidized bed boiler are fundamentally solved, and the high parameterization of the biomass circulating fluidized bed boiler is facilitated. Meanwhile, the temperature of the working medium 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 quantity.

The invention adopts the following technical scheme:

a two-stage series material returning device of a circulating fluidized bed boiler comprises a primary material returning device and a secondary material returning device, wherein the primary material returning device and the secondary material returning device are connected in series; the secondary material returning device comprises a loosening chamber, a normal material returning pipe and a bypass overflow pipe, wherein a heat exchange surface is arranged in the loosening chamber as required, the loosening chamber is communicated with the hearth through the normal material returning pipe and the bypass overflow pipe, the inlet end of the primary material returning device is communicated with the cyclone separator, and the bottom of the primary material returning device is provided with a primary fluidized air port; a loose tuyere is arranged at the bottom of the heat exchange chamber; a normal material returning air port is arranged at the bottom of the normal material returning pipe; and a bypass return tuyere is arranged at the bottom of the bypass overflow pipe.

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 in the heat exchange chambers as required.

Preferably, the heat exchange surface types include evaporators, superheaters and reheaters.

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

Preferably, the inlet of the bypass overflow is above the uppermost surface of the heat exchange surface.

The temperature regulating method of the two-stage series material returning device of the circulating fluidized bed boiler comprises the following specific flow steps:

1) after the flue gas enters the cyclone separator, the separated circulating ash falls into a first-stage material returning device. The primary fluidized air enters from the primary fluidized air port, so that the circulating ash flows into the secondary material returning device;

2) opening a loose air port and a normal return air port of each heat exchange chamber of the secondary material returning device, closing a bypass return air port, fluidizing circulating ash in each heat exchange chamber by loose air, fluidizing circulating ash in a normal return pipe by normal return air, and returning the circulating ash to a hearth through the normal return pipe after heat exchange with a heat exchange surface;

3) when the temperature of the working medium of the heat exchange surface is adjusted, the normal return air volume is adjusted, the circulating ash inlet volume of each heat exchange chamber is distributed, and the heat exchange volume adjustment of the circulating ash and the heat exchange surface in each heat exchange chamber is further realized;

4) when the normal return pipe fails or the bed temperature needs to be adjusted, the bypass return air port is opened, the bypass return air fluidizes circulating ash in the bypass return pipe, and the circulating ash does not participate in heat exchange and directly returns to the hearth through the bypass overflow pipe.

The invention has the beneficial effects that:

firstly, the separation of the combustion process and the heat exchange process is realized, the combustion process is carried out in the hearth, the heat exchange process is carried out in the heat exchange chamber, the direct contact between a heating surface and high-temperature flue gas containing chlorine and high alkali content is avoided, and the high-temperature corrosion of the heating surface is prevented;

secondly, the flow rate of circulating ash in the heat exchange chamber is low, so that on one hand, the heat exchange chamber plays a role in flushing a hot surface of a pipe to avoid ash accumulation and slag bonding on the hot surface, on the other hand, the hot surface is completely soaked in the circulating ash, each part can be well contacted with high-temperature circulating ash, and the heat exchange efficiency is greatly enhanced;

thirdly, heat exchange surfaces can be arranged in the heat exchange chamber as required, the purpose of adjusting the temperature of the working medium is achieved by adjusting the amount of circulating ash entering the heat exchange chamber, and energy loss caused by water spraying and temperature reduction is avoided;

fourthly, the bed temperature is adjusted by adjusting the amount of circulating ash entering the heat exchange chamber and controlling the opening and closing state of the bypass return air. An easy-to-operate adjusting method is added on the basis of the traditional bed temperature adjusting method, so that the risk of severe fluctuation of the bed temperature is reduced, and the operation reliability of the boiler is improved;

fifthly, the circulating ash can return to the hearth through the bypass overflow pipe, and boiler shutdown caused by interruption of a circulating ash circulation loop when a normal return pipe or a heat exchange surface fails is avoided.

Drawings

FIG. 1 is a schematic diagram of a structure of the present invention.

In the figure, 100, a primary material returning device, 200, a secondary material returning device, 201, a loosening chamber, 202, a heat exchange surface, 203, a normal material returning pipe, 204, a bypass overflow pipe, 300, a hearth, 400, a cyclone separator, 500, a primary fluidized air port, 601, a loosening air port, 602, a normal material returning air port, 603 and a bypass material returning air port.

Detailed Description

The technical solution of the present invention is further described in detail by the following embodiments with reference to the accompanying drawings.

Example (b): as shown in fig. 1, a two-stage series material returning device of a circulating fluidized bed boiler comprises a first-stage material returning device 100 and a second-stage material returning device 200. The first-stage material returning device 100 and the second-stage material returning device 200 are connected in series, and the second-stage material returning device 200 is composed of a loosening chamber 201, a normal material returning pipe 203 and a bypass overflow pipe 204. The primary material returning device 200, the loosening chamber 201 and the hearth 300 are equal in width and are all composed of membrane water-cooled walls, and refractory plastic materials are laid on the periphery and the top of the primary material returning device.

The loosening chamber 201 is divided into 3 heat exchange chambers with equal width by partition plates, the heat exchange chambers on two sides are provided with high-temperature superheaters, and the heat exchange chamber in the middle is provided with a reheater. Each heat exchange chamber outlet is provided with 2 normal return pipes 203 and a bypass overflow pipe 204. The normal return pipe 203 and the bypass overflow pipe 204 are symmetrically arranged along the central 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.

The bottom of the first-stage material returning device 100 is provided with a first-stage fluidization air port 500, the bottom of the heat exchange chamber is provided with a loosening air port 601, the bottom of the normal material returning pipe 203 is provided with a normal material returning air port 602, and the bottom of the bypass overflow pipe 204 is provided with a bypass material returning air port 603.

1) after the flue gas enters the cyclone separator 400, the separated circulating ash falls into the first-stage material returning device 100. The primary fluidizing air enters from the bottom of the primary material returning device 100 through the primary fluidizing air port 500, so that circulating ash flows into the secondary material returning device 200.

2) The loose tuyere 601 and the normal return tuyere 602 of each heat exchange chamber of the secondary material returning device 200 are opened, the bypass return tuyere 603 is closed, the loose air entering from the loose tuyere 601 fluidizes the circulating ash in each heat exchange chamber, the normal return air entering from the normal return tuyere 602 fluidizes the circulating ash in the normal return pipe 203, and the circulating ash exchanges heat with the heat exchange surface 202 and then returns to the hearth 300 through the normal return pipe 203.

3) Reheat steam temperature adjustment process: the air quantity of a normal return pipe 203 connected with the reheater heat exchange chamber is increased, so that the circulating ash entering quantity of the reheater heat exchange chamber is increased, the heat exchange quantity in the reheater heat exchange chamber is increased, and the temperature of reheated steam is increased. In a similar way, the air quantity of the normal return pipe 203 connected with the heat exchange chamber of the reheater is reduced, and the temperature of the reheated steam can be reduced.

4) The bed temperature adjusting process: and opening a bypass return air port 603 of the heat exchange chamber of the high-temperature superheater, fluidizing the circulating ash in the bypass return pipe 204 by the bypass return air, and directly returning part of the circulating ash from the primary material returning device to the hearth 300 through the bypass return pipe 204 without exchanging heat with the high-temperature superheater. The air quantity of the bypass return material is adjusted, so that the circulating ash quantity entering the hearth 300 through the bypass return material pipe 204 is changed, the circulating ash temperature is changed, and further bed temperature adjustment is realized.

5) When the normal return pipe 203 breaks down, the bypass return tuyere 603 is opened, so that the circulating ash returns to the hearth 300 through the bypass overflow pipe 204, and the continuous and stable return of the device is ensured.

The above-described embodiments are only preferred embodiments of the present invention, and are not intended to limit the present invention in any way, and other variations and modifications may be made without departing from the spirit of the invention as set forth in the claims.

Claims

1. A two-stage series material returning device of a circulating fluidized bed boiler comprises a first-stage material returning device (100) and a second-stage material returning device (200), and is characterized in that the first-stage material returning device (100) and the second-stage material returning device (200) are connected in series; the secondary material returning device (200) comprises a loosening chamber (201), a normal material returning pipe (203) and a bypass overflow pipe (204), a heat exchange surface (202) is arranged in the loosening chamber (201) as required, the loosening chamber (201) is communicated with a hearth (300) through the normal material returning pipe (203) and the bypass overflow pipe (204), the inlet end of the primary material returning device (100) is communicated with a cyclone separator (400), and the bottom of the primary material returning device (100) is provided with a primary fluidized air port (500); a loose tuyere (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 tuyere (603) is arranged at the bottom of the bypass overflow pipe (204).

2. A two-stage series-connection material returning device of a circulating fluidized bed boiler, according to the claim 1, characterized in that the loosening chamber (201) is divided into a plurality of heat exchange chambers, a plurality of normal material returning pipes (203) and bypass overflow pipes (204) are arranged at the outlet of each heat exchange chamber, and heat exchange surfaces (202) are arranged in the heat exchange chambers according to the requirement.

3. A circulating fluidized bed boiler two-stage series feed back device according to claim 1, characterized in that the types of heat exchange surfaces (202) comprise an evaporator, a superheater and a reheater.

4. A circulating fluidized bed boiler two-stage series feed back device according to claim 1, characterized in that the inlet of the normal feed back 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).

5. The temperature regulating method of the two-stage series material returning device of the circulating fluidized bed boiler according to any one of claims 1 to 4, which is characterized by comprising the following specific process steps:

1) after the flue gas enters the cyclone separator (400), separated circulating ash falls into a first-stage material returning device (100); the primary fluidized air enters from the primary fluidized air port (500) to make the circulating ash flow into the secondary material returning device (200);

2) opening a loose air port (601) and a normal material returning air port (602) of each heat exchange chamber of the secondary material returning device (200), closing a bypass material returning air port (603), fluidizing circulating ash in each heat exchange chamber by loose air, fluidizing circulating ash in the normal material returning pipe (203) by normal material returning air, and returning the circulating ash to the hearth (300) through the normal material returning pipe (203) after heat exchange with the heat exchange surface (202);

3) when the working medium of the heat exchange surface (202) is adjusted in temperature, the circulating ash entering amount of each heat exchange chamber is distributed by adjusting the normal material returning air quantity of each normal material returning air port (602), and further the heat exchange amount adjustment of the circulating ash in each heat exchange chamber and the heat exchange surface (202) is realized;

4) when the bed temperature is adjusted, opening a bypass return air port (603), and controlling the circulating ash amount returned to the hearth (300) by a bypass overflow pipe (204) by adjusting the bypass return air volume so as to adjust the bed temperature;

5) when the normal return pipe fails, the bypass return tuyere is opened, and the circulating ash directly returns to the hearth (300) through the bypass overflow pipe.