A device and method for the resource utilization and combustion of low-calorific-value fuels

Abstract

This invention discloses a device and method for the resource-based combustion and utilization of low-calorific-value fuels, relating to the field of low-calorific-value fuel combustion technology. It includes a circulating fluidized bed incinerator, a cyclone separator, a tail flue structure, and a waste heat recovery and utilization structure. The circulating fluidized bed incinerator includes a furnace, with an upper dilute phase zone and a lower dense phase zone. The furnace outlet is connected to the cyclone separator, which is connected to the circulating ash inlet at the bottom of the furnace. The tail flue structure is equipped with a convective heat exchange device. The waste heat recovery and utilization structure includes a flue gas outlet. This invention solves the problem of utilizing low-calorific-value coal and coal-based solid waste in the combustion field, while simultaneously producing hot water and steam with certain temperature and pressure, which can be used for steam turbine power generation, district heating, or industrial steam, generating certain economic benefits.

Description

Technical Field

[0001] This invention relates to the field of low-calorific-value fuel combustion technology, and in particular to a device and method for the resource-based combustion and utilization of low-calorific-value coal and coal-based solid waste. Background Technology

[0002] The coal industry is a vital foundational industry related to my country's economic lifeline and energy security, playing a crucial role in the national economy. However, the mining, processing, and utilization of coal generate a large amount of waste residue, which, if indiscriminately dumped, not only causes serious environmental pollution but also represents a huge waste of resources. During the mining, processing, and utilization of coal, a type of low-calorific-value fuel is produced, and the resource-efficient combustion and utilization of this low-calorific-value fuel has always been an important issue of concern within the industry.

[0003] These low-calorific-value fuels mainly fall into two categories: low-calorific-value coals, such as coal gangue, coal shale, coal slime, and washed middlings; and coal-based solid wastes, primarily high-carbon general solid wastes produced as byproducts of coal chemical projects, such as coal gasification ash, fine ash, and furnace slag. These low-calorific-value fuels are characterized by high moisture content, high ash content, extremely low volatile matter, and low net calorific value on an as-received basis.

[0004] Currently, the main application of low-calorific-value coals such as coal gangue, coal slime, and middlings in the combustion field is through CFB boilers for power generation or heating. However, existing technologies can only handle low-calorific-value coals with an as-received lower heating value (ORF) ranging from 2400 kcal / kg to 3400 kcal / kg (inclusive). For coal gangue and coal shale with an ORF of less than 2400 kcal / kg, it is necessary to blend them with medium-calorific-value coals with an ORF of not less than 4300 kcal / kg. Current technologies are still lacking in the combustion application of low-calorific-value coals with an ORF of less than 2400 kcal / kg. These low-calorific-value coal gangue and coal shale are currently mainly used for land reclamation, roadbed materials, brick making, and as a blending material for cement clinker. Middlings and coal slime, with relatively higher calorific values, are generally blended into medium- and high-calorific-value coals as fuel.

[0005] Coal-based solid waste, such as coal gasification ash and slag, generally has a calorific value of less than 2400 kcal / kg. Currently, its utilization in the combustion field is also blank. As solid waste, it generally needs to be specially designed and constructed in accordance with the specifications for landfill treatment, which not only increases the cost of manpower, material resources and financial resources, but also causes a great waste of carbon resources in coal-based solid waste and damages the environment. Summary of the Invention

[0006] The purpose of this invention is to provide a device and method for the resource utilization of low-calorific-value fuels through combustion, which solves the problem of utilizing low-calorific-value coal and coal-based solid waste in the field of combustion. At the same time, it co-produces hot water and steam with certain temperature and pressure, which can be used for steam turbine power generation, district heating or industrial steam, generating certain economic benefits.

[0007] To achieve the above objectives, the present invention provides the following solution:

[0008] This invention provides a device for the resource utilization and combustion of low-calorific-value fuels, including a circulating fluidized bed incinerator, a cyclone separator, a tail flue structure, and a waste heat recovery and utilization structure;

[0009] The circulating fluidized bed incinerator includes a furnace chamber, the upper part of which is a dilute phase zone and the lower part of which is a dense phase zone. The feed inlet of the circulating fluidized bed incinerator is located in the middle and lower part of the furnace chamber, and the outlet of the circulating fluidized bed incinerator is located in the dilute phase zone.

[0010] The outlet of the furnace is connected to the cyclone separator, the cyclone separator is connected to the circulating ash inlet at the bottom of the furnace, a convection heat exchange device is provided in the tail flue structure, the inlet of the tail flue structure is connected to the cyclone separator, and the outlet of the tail flue structure is connected to the inlet of the waste heat recovery and utilization structure.

[0011] The waste heat recovery and utilization structure is equipped with a flue gas outlet.

[0012] Preferably, the furnace of the circulating fluidized bed incinerator has a rectangular cross-section and is an integral structure cast with refractory castable. The lower end of the furnace in the dense phase zone tapers into a conical structure, and several feed inlets are located on the front wall of the lower middle part of the furnace.

[0013] Preferably, the furnace of the circulating fluidized bed incinerator has a rectangular cross-section, the inner wall of the furnace is provided with a membrane water-cooled wall, the surface of the membrane water-cooled wall in the lower middle part of the dilute phase zone forms an evaporation heating surface, refractory castable is laid between the inner wall of the furnace and the outer wall of the remaining membrane water-cooled walls, the lower end of the furnace in the dense phase zone tapers into a conical structure, and several feed inlets are provided on the front wall in the lower middle part of the furnace.

[0014] Preferably, the tail flue structure includes a first flue structure and a second flue structure. The inlet of the first flue structure is connected to the cyclone separator, the outlet of the first flue structure is connected to the inlet of the second flue structure, and the outlet of the second flue structure is connected to the inlet of the waste heat recovery and utilization structure. The convection heat exchange device includes a first convection heat exchange tube group, an evaporator, a second convection heat exchange tube group, and an air preheater arranged sequentially from the inlet of the first flue structure to the outlet of the first flue structure. A first fly ash discharge pipe is provided at the lower end of the first flue structure, and a second fly ash discharge pipe is provided at the lower end of the second flue structure.

[0015] Preferably, the inlet header of the second convection heat exchanger tube group is connected to the feedwater pipeline, the outlet header of the second convection heat exchanger tube group is connected to the inlet header of the evaporator, the outlet header of the evaporator is connected to the steam drum and the downcomer from the steam drum, the downcomer is connected to the inlet header of the membrane water-cooled wall of the furnace, and the outlet header of the membrane water-cooled wall is connected to the steam drum via a top connecting pipe; the inlet header of the first convection heat exchanger tube group is connected to the saturated steam outlet pipe from the steam drum, and the working fluid in the first convection heat exchanger tube group is sent out through the outlet header of the first convection heat exchanger tube group after heat exchange through the first convection heat exchanger tube group.

[0016] Preferably, the inlet header of the second convection heat exchanger tube assembly is connected to the feedwater pipeline, the outlet header of the second convection heat exchanger tube assembly is connected to the steam drum via a water guide pipe, the steam drum is connected to the inlet header of the membrane water-cooled wall of the furnace via a downcomer, the upper outlet of the downcomer is connected to the inlet header of the evaporator, the outlet header of the membrane water-cooled wall is connected to the steam drum via a top connecting pipe, the outlet header of the evaporator is connected to the steam drum, and the inlet header of the first convection heat exchanger tube assembly is connected to the steam drum via a saturated steam outlet pipe.

[0017] Preferably, an ignition combustion chamber is provided at the lower end of the furnace, and an air distribution structure is provided between the ignition combustion chamber and the furnace.

[0018] The outlet at the lower part of the cyclone separator is connected to the circulating ash inlet at the lower part of the furnace through a return structure. The bottom of the return structure is provided with a fluidizing air inlet and a circulating ash discharge pipe.

[0019] The waste heat recovery and utilization structure includes a waste heat recovery box and a heat exchange tube. One end of the waste heat recovery box is connected to the second flue structure, and the other end of the waste heat recovery box is connected to the flue gas outlet. The heat exchange tube is installed in the waste heat recovery box and is used to exchange heat with the flue gas entering the box.

[0020] Preferably, the system further includes a fuel processing structure, which comprises a filter press, a mesh belt drying structure, a regenerator, a heater, and a crushing structure. The mesh belt drying structure includes a drying chamber and a belt drive structure. The conveyor belt of the belt drive structure has through holes. The outlet of the filter press is connected to the feed inlet at the top of the drying chamber. The air outlet at the top of the drying chamber is connected to the regenerator. The regenerator is connected to the heater. The heater is connected to the air inlet at the bottom of the drying chamber.

[0021] Preferably, a pulverizer is installed inside the drying chamber. The inlet of the pulverizer is connected to the feed inlet, and the outlet of the pulverizer corresponds to the belt drive structure. Low-calorific-value fuel enters the pulverizer through the feed inlet and the inlet of the pulverizer, and after being pulverized, falls into the belt drive structure through the outlet of the pulverizer.

[0022] The present invention also provides a method for the combustion and utilization of low-calorific-value fuels using the aforementioned low-calorific-value fuel resource utilization device, comprising the following steps:

[0023] Low-calorific-value fuels are processed to meet the requirements for fuel to be fed into the furnace.

[0024] The bed material is heated, and low-calorific-value fuel is fed into the furnace of the circulating fluidized bed incinerator. As the low-calorific-value fuel continues to burn, the high-temperature flue gas carrying fly ash rises continuously in the furnace. After reaching the top of the furnace, the flue gas flow direction changes and flows out of the circulating fluidized bed incinerator from the furnace outlet, entering the cyclone separator. The particles captured by the cyclone separator enter the furnace through the return structure to continue to participate in combustion, while the particles not captured by the cyclone separator enter the tail flue structure for heat exchange.

[0025] When no evaporation heating surface is arranged in the furnace, the operating method on the working fluid side is as follows: feedwater enters the inlet header of the second convection heat exchanger tube group through the feedwater pipe, and after being heated by the second convection heat exchanger tube group, it enters the lower water side of the steam drum through the water guide pipe. The lower water side of the steam drum is connected to the downcomer. The hot water of the second convection heat exchanger tube group enters the downcomer and then enters the inlet header of the evaporator through the downcomer outlet connecting pipe. It exchanges heat with the external flue gas in the evaporator. The steam-water mixture after heat exchange enters the steam drum through the connecting pipe for steam-water separation. The separated saturated steam is sent to the first convection heat exchanger tube group for heat exchange through the saturated steam outlet pipe.

[0026] When evaporation heating surfaces are arranged inside the furnace, the operating methods on the working fluid side are divided into two types:

[0027] In the first method, feedwater enters the inlet header of the second convection heat exchanger tube group through the feedwater pipe. After being heated by the second convection heat exchanger tube group, it first enters the evaporator through the inlet header of the evaporator. Convection heat exchange occurs through the transverse flow of flue gas over the evaporator tube bundles. After the working fluid absorbs heat in the evaporator, a portion of the evaporator tube bundle containing a steam-water mixture enters the steam drum through the connecting pipe for steam-water separation. The separated saturated steam enters the first convection heat exchanger tube group for heat exchange through the saturated steam outlet pipe. The remaining portion of the evaporator tube bundle containing hot water with increased temperature enters the downcomer through the upper interface of the downcomer and flows into the lower inlet header of the membrane water-cooled wall in the furnace. The working fluid in the membrane water-cooled wall tubes flows upward and undergoes convection and radiation heat exchange with the hot flue gas in the furnace. The steam-water mixture after heat exchange enters the steam drum through the top connecting pipe for steam-water separation. The separated saturated steam enters the first convection heat exchanger tube group for heat exchange through the saturated steam outlet pipe. The water separated from the steam drum flows back into the downcomer and membrane water-cooled wall for further heat exchange.

[0028] The second method involves feeding water into the inlet header of the second convection heat exchanger tube group via a feed water pipe. After being heated by the second convection heat exchanger tube group, the water enters the lower water side of the steam drum through a water guide pipe. The lower water side of the steam drum is connected to the downcomer. The hot water from the second convection heat exchanger tube group is divided into two parts after entering the downcomer. One part of the hot water enters the inlet header of the evaporator through the upper outlet connecting pipe of the downcomer, where it exchanges heat with the external flue gas. The steam-water mixture after heat exchange enters the steam drum through the connecting pipe for steam-water separation. The separated saturated steam is sent to the first convection heat exchanger tube group through the saturated steam outlet pipe. Heat exchange occurs through the heat pipe assembly; the remaining hot water continues to flow along the downcomer into the lower inlet header of the membrane water-cooled wall. The working fluid inside the membrane water-cooled wall flows upward and exchanges convective and radiative heat with the hot flue gas in the furnace. The steam-water mixture after heat exchange enters the steam drum through the top connecting pipe for steam-water separation. The separated saturated steam enters the first convective heat exchange tube assembly through the saturated steam outlet pipe. The water separated in the steam drum flows back into the downcomer and repeats the above process until it completely absorbs heat and becomes saturated steam, which then enters the first convective heat exchange tube assembly through the saturated steam outlet pipe.

[0029] The present invention achieves the following technical effects compared to the prior art:

[0030] This invention, by setting up a cyclone separator, allows unburned carbon in the fly ash exiting the furnace to undergo secondary combustion within the cyclone separator, further improving the incinerator's burnout rate. Through a convective heat exchange device in the tail flue structure and a waste heat recovery and utilization structure, the calorific value of the fuel is recovered and utilized, co-producing hot water and steam at a certain temperature and pressure. These can be used for steam turbine power generation, district heating, or industrial steam, generating certain economic benefits. Attached Figure Description

[0031] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0032] Figure 1 This is a schematic diagram of the low-calorific-value fuel resource utilization and combustion device of the present invention;

[0033] Figure 2 This is a schematic diagram of the fuel processing structure of the present invention;

[0034] The components are as follows: 100-Low calorific value fuel resource utilization and combustion device; 1-Fuel processing structure; 2-Ignition combustion chamber; 3-Feed inlet; 4-Circulating fluidized bed incinerator; 5-Evaporation heating surface; 6-Cyclone separator; 7-Return material structure; 8-Air distribution structure; 9-Furnace; 10-First convection heat exchange tube group; 11-Evaporator; 12-Second convection heat exchange tube group; 13-SCR denitrification reserved position; 14-Air preheater; 15-Waste heat recovery and utilization structure; 16-First flue structure; 17-Second flue structure; 18-First fly ash discharge pipe; 19-Second fly ash discharge pipe; 20-Circulating ash discharge pipe; 21-Fluidized air inlet; 101-Filter press; 102-Dehumidification dryer; 103-Crushing structure; 104-Belt drying structure; 105-Waste heat dehumidification structure; 106-Regenerative cooler; 107-Heater. Detailed Implementation

[0035] 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. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0036] The purpose of this invention is to provide a device and method for the resource utilization of low-calorific-value fuels through combustion, which solves the problem of utilizing low-calorific-value coal and coal-based solid waste in the field of combustion. At the same time, it co-produces hot water and steam with certain temperature and pressure, which can be used for steam turbine power generation, district heating or industrial steam, generating certain economic benefits.

[0037] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0038] Example 1

[0039] like Figures 1-2As shown: This embodiment provides a low-calorific-value fuel resource utilization device 100, including a circulating fluidized bed incinerator 4, a cyclone separator 6, a tail flue structure and a waste heat recovery and utilization structure 15;

[0040] The circulating fluidized bed incinerator 4 includes a furnace 9, the upper part of which is a dilute phase zone and the lower part of which is a dense phase zone. The feed inlet 3 of the circulating fluidized bed incinerator 4 is located in the middle and lower part of the furnace 9, and the outlet of the circulating fluidized bed incinerator 4 is located in the dilute phase zone.

[0041] The outlet of the furnace 9 is connected to the cyclone separator 6, and the cyclone separator 6 is connected to the circulating ash inlet at the bottom of the furnace 9. The tail flue structure includes a first flue structure 16 and a second flue structure 17. The inlet of the first flue structure 16 is connected to the cyclone separator 6, and the outlet of the first flue structure 16 is connected to the inlet of the second flue structure 17. The outlet of the second flue structure 17 is connected to the inlet of the waste heat recovery and utilization structure 15. In the first flue structure 16, from the inlet to the outlet, a first convection heat exchange tube group 10, an evaporator 11, and a second convection heat exchange tube group 12 are arranged in sequence. The first convection heat exchange tube group 10 is a high-temperature convection heat exchange tube group, and the second convection heat exchange tube group 12 is a low-temperature convection heat exchange tube group. An air preheater 14 is arranged in the second flue structure 17. The waste heat recovery and utilization structure 15 is provided with a flue gas outlet.

[0042] In this embodiment, due to the characteristics of the low-calorific-value fuel entering the furnace, such as low calorific value, high moisture content, high ash content, and extremely low volatile matter content, it is difficult to ignite and maintain stable combustion. It has been determined that the ignition temperature of coal-based solid waste is 800℃, and it will not ignite when the temperature is below 800℃. In order to achieve stable combustion of low-calorific-value coal and coal-based solid waste in the furnace 9, the furnace 9 temperature range is designed to be 900℃~1100℃ (inclusive of the two endpoints), the bed temperature of the lower dense phase zone of the furnace 9 is 900℃~1100℃ (inclusive of the two endpoints), and the upper dilute phase zone and outlet temperature of the furnace 9 is 900℃~950℃ (inclusive of the two endpoints). The furnace 9 contains evaporative heating surfaces 5, arranged differently from those in conventional coal-fired circulating fluidized bed boilers. Conventional coal-fired circulating fluidized bed boilers, due to the combustion of medium- to high-calorific-value coal, have good ignition characteristics and can achieve stable combustion at relatively low furnace temperatures. Therefore, the entire furnace is covered by a membrane water-cooled wall structure, and the membrane water-cooled walls constitute the entire evaporative heating surface. However, low-calorific-value fuels have very low calorific-values. To ensure the furnace 9 temperature reaches 900℃~1100℃, the arrangement of evaporative heating surfaces 5 within the furnace 9 must be reduced or eliminated. Instead, evaporators 11 are arranged in the first flue structure 16. Therefore, in this embodiment, the furnace 9 may or may not contain evaporative heating surfaces 5. When the evaporation heating surface 5 is arranged, the entire inner wall of the furnace 9 in this embodiment is provided with a membrane water-cooled wall, which is arranged around the furnace wall of the furnace 9. The evaporation heating surface 5 is formed only on the surface of the membrane water-cooled wall in the middle and lower part of the dilute phase zone. The area of ​​the evaporation heating surface 5 accounts for 0-30% of the total area of ​​the furnace 9. The outer wall of the remaining membrane water-cooled wall of the furnace 9 is covered with refractory castable between it and the inner wall of the furnace 9. When the evaporation heating surface 5 is not arranged, the furnace 9 adopts an integral structure cast from refractory castable.

[0043] In this embodiment, the inlet header of the second convection heat exchanger tube group 12 is connected to the feedwater pipeline, and the outlet header of the second convection heat exchanger tube group 12 is connected to the inlet header of the evaporator 11. A portion of the evaporation tube bundle of the evaporator 11 is connected to the connecting pipe of the steam drum (the steam drum is located on the support platform at the top of the furnace 9), and another portion of the evaporation tube bundle is connected to the downcomer pipe from the steam drum. The lower outlet of the downcomer pipe is connected to the inlet header at the lower end of the furnace membrane water-cooled wall, and the outlet header at the upper end of the membrane water-cooled wall is connected to the steam drum through the top connecting pipe. The inlet header of the first convection heat exchanger tube group 10 is connected to the saturated steam outlet pipe from the steam drum. The working fluid in the tubes of the first convection heat exchanger tube group 10 becomes qualified main steam after heat exchange by the first convection heat exchanger tube group 10, and is sent to the user or the steam turbine generator set in the plant area through the main steam valve of the outlet header pipe of the first convection heat exchanger tube group 10.

[0044] Alternatively, the inlet header of the second convection heat exchanger tube group 12 is connected to the feedwater pipeline, the outlet header of the second convection heat exchanger tube group 12 is connected to the steam drum through a water guide pipe, the steam drum is connected to the membrane water-cooled wall of the furnace 9 through a downcomer, wherein the upper inlet of the downcomer is connected to the steam drum, the upper outlet of the downcomer is connected to the inlet header of the evaporator 10 through a connecting pipe, the lower outlet of the downcomer is connected to the inlet header of the membrane water-cooled wall, the upper outlet header of the membrane water-cooled wall is connected to the steam drum through a connecting pipe, the outlet header of the evaporator 10 is connected to the steam drum through a connecting pipe, and the inlet header of the first convection heat exchanger tube group 10 is connected to the steam drum through a saturated steam outlet pipe.

[0045] In this embodiment, the dense phase zone includes a bed section and a conical connecting section arranged from top to bottom. The front and rear walls of the furnace 9 at the lower end of the dense phase zone taper at a certain angle with the vertical line, forming a conical structure that is larger at the top and smaller at the bottom. Several feed inlets 3 are symmetrically arranged in the middle and lower front wall of the furnace 9 along the horizontal direction. Low-calorific-value coal and coal-based solid waste that meet the requirements for fuel entering the furnace are transported to the feed inlets 3 by feeding devices such as screw feeders, weighing belt feeders, and pneumatic conveying devices. Under the action of gravity and coal-pulling air, they are sent into the bed section of the dense phase zone of the furnace 9 for ignition and combustion. The height of the feed inlets 3 is 1.5m to 15.0m above the air distribution structure 8. The number of feed inlets 3 is set to 2 to 8 depending on the fuel processing capacity, and they are arranged in single or double layers. This arrangement can make the low-calorific-value fuel evenly spread on the entire bed surface.

[0046] In this embodiment, an ignition combustion chamber 2 is provided at the lower end of the furnace 9. The ignition combustion chamber 2 is lined with a certain thickness of refractory castable. An air distribution structure 8 is provided between the ignition combustion chamber 2 and the furnace 9. Because low-calorific-value fuels have low calorific value, extremely low volatile matter, and high moisture content, they are difficult to ignite. To ensure better ignition and stable combustion of low-calorific-value fuels within the furnace 9, this embodiment optimizes the hot air temperature design. The designed hot air temperature is 160℃~300℃ (inclusive of both endpoints), with a more optimal design temperature of 165℃~200℃ (inclusive of both endpoints). The design of the number, height, and hot air temperature of the feed inlets 3 effectively ensures thorough mixing of the low-calorific-value fuels with the primary air, which is beneficial for the ignition and combustion of the low-calorific-value fuels and for maintaining the bed temperature.

[0047] The design of the feed inlet 3 and the furnace 9, as well as the air distribution, ensures that the temperature range of the furnace 9 in the circulating fluidized bed incinerator 4 is 900℃~1100℃, the design temperature of the bed layer in the lower dense phase zone of the furnace 9 is 900℃~1100℃, and the design temperature of the upper dilute phase zone and the outlet of the furnace 9 is 900℃~950℃. This temperature ensures the stable combustion of low-calorific-value solid waste with characteristics such as low calorific value (370kcal / kg~2400kcal / kg), high moisture content, high ash content, extremely low volatile matter content, and non-ignition at temperatures below 800℃ in the circulating fluidized bed incinerator 4.

[0048] In this embodiment, the cross-section of the furnace 9 of the circulating fluidized bed incinerator 4 is rectangular, the width of the furnace 9 is greater than its depth, and the height of the furnace 9 is designed to be 31m to 33m. By designing the ratio of the primary air volume to the total air volume and the ratio of the opening area of ​​the air distribution structure 8 to the total area (referring to the sum of the opening area and the non-opening area of ​​the air distribution structure 8), the flue gas velocity in the furnace 9 is controlled at 3m / s to 4m / s, and the residence time of the flue gas in the furnace 9 reaches 8s to 10s. This can effectively extend the residence time of low-calorific-value fuel in the furnace 9.

[0049] In this embodiment, the outlet at the lower part of the cyclone separator 6 is connected to the circulating ash inlet at the lower part of the furnace 9 through the return structure 7. The bottom of the return structure 7 is provided with a fluidizing air inlet 21 and a circulating ash discharge pipe 20.

[0050] In this embodiment, the cyclone separator 6 is designed as a high-temperature insulated cyclone separator or a water-cooled cyclone separator. The separation efficiency of the cyclone separator 6 is >99.5%, and the ash circulation ratio is 175-230 (inclusive of the two endpoint values). Due to the high ash content in low-calorific-value fuels, the amount of circulating ash is 2-4 times that of conventional coal-fired circulating fluidized bed boilers. Material circulation can be established without adding auxiliary bed material during the operation of the incinerator. The volatile matter content in low-calorific-value fuels is extremely low, and the amount of fly ash at the outlet of the furnace 9 is extremely large. Unburned carbon in the fly ash will undergo secondary combustion in the cyclone separator 6, further improving the burnout rate of the incinerator. This embodiment can realize the internal circulation of circulating materials within the furnace 9 and the external circulation of circulating materials between the furnace 9 and the cyclone separator 6. A large amount of circulating ash can repeatedly participate in the combustion reaction, minimizing the carbon content in the fly ash. In this embodiment, the carbon content of the fly ash after combustion is no more than 5% (mass fraction), and the carbon content of the bottom ash is no more than 1% (mass fraction).

[0051] In this embodiment, two second convection heat exchanger tube groups 12 can be provided, with a 3m to 5m reserved space 13 for SCR denitrification between the two second convection heat exchanger tube groups 12. A conical hopper is provided at the lower end of the first flue structure 16, and a first fly ash discharge pipe 18 is provided at the lower end of the conical hopper. A conical hopper is provided at the lower end of the second flue structure 17, and a second fly ash discharge pipe 19 is provided at the lower end of the conical hopper.

[0052] The first convection heat exchange tube group 10, the evaporator 11, the second convection heat exchange tube group 12, and the air preheater 14 constitute a convection heat exchange device. Due to the high fly ash content in the flue gas, the thermal efficiency coefficient decreases when the hot flue gas exchanges heat with the convection heat exchange device. The thermal efficiency coefficient of conventional coal-fired boiler heat exchangers is 0.6 to 0.7, while the thermal efficiency coefficient of the convection heat exchange device in this embodiment is 0.5 to 0.7 (including the two endpoint values). The heat exchange area of ​​the convection heat exchange device is 20% to 30% larger. The width and depth dimensions of the tail flue, which is composed of the first flue structure 16 and the second flue structure 17, do not change much, but the height dimension is 20% to 30% larger.

[0053] In this embodiment, an evaporator 11 is arranged between the first convection heat exchange tube group 10 and the second convection heat exchange tube group 12 of the first flue structure 16 as the remaining heat-receiving surface for evaporation, to meet the heat exchange requirements of the working fluid evaporation heat of the incinerator. The flue gas temperature at the location of the evaporator 11 is 750℃~420℃ (inclusive of the two endpoints). The evaporator 11 includes several parallel evaporator tube bundles, which are connected end to end in a serpentine arrangement. The evaporator tube bundles can be arranged in a straight line or staggered. Each evaporator tube bundle is perpendicular to the front wall of the first flue structure 16. The inlet and outlet of the evaporator 11 are both connected to the header. Each evaporator tube bundle is made of seamless steel pipe with a diameter of 32mm~42mm (inclusive of the two endpoints) and a wall thickness of 3mm~7mm (inclusive of the two endpoints). The material of the evaporator tube bundle can be carbon steel pipe or low alloy steel pipe, with 20G preferred. The flue gas flows laterally across the evaporator tube bundle of the evaporator 11, absorbing heat from the flue gas through convection to change the working fluid inside the evaporator tube bundle from a liquid phase to a gas phase. When no evaporation heating surface 5 is arranged in the furnace 9, the evaporator 11 heats the water in the evaporator tube bundle into a steam-water mixture through heat exchange with the flue gas; when the evaporation heating surface 5 is arranged in the furnace 9, depending on the number of evaporation heating surfaces 5 and the operating method on the working fluid side, the evaporator 11 heats the water in the evaporator tube bundle into hot water or a steam-water mixture at a higher temperature through heat exchange with the flue gas.

[0054] In this embodiment, the flue gas temperature at the outlet of the air preheater 14 is 140℃~170℃ (inclusive of the two endpoints), containing a large amount of flue gas waste heat. The waste heat recovery and utilization structure 15 can recover and utilize this part of the flue gas waste heat. The waste heat recovery and utilization structure 15 includes a waste heat recovery box and fluoroplastic heat exchange tubes. One end of the waste heat recovery box is connected to the second flue structure 17, and the other end of the waste heat recovery box is connected to the flue gas outlet. The heat exchange tubes are installed in the waste heat recovery box. The heat exchange medium can be one of cooling water, hot water, or heat transfer oil. The heat exchange tubes are used to exchange heat with the flue gas entering the box. After heat exchange, the flue gas temperature drops to 75℃~85℃ (inclusive of the two endpoints). The recovered flue gas heat can heat the cooling water to hot water with a temperature of not less than 90℃, which can be used as the heat source for the heater 107 in the waste heat type dehumidification structure 105. It can also be used to heat the feedwater of the circulating fluidized bed incinerator 4, heat the circulating water of the heating network to increase part of the centralized heating area, or meet other industrial needs.

[0055] This embodiment enables the stable combustion of low-calorific-value fuels such as low-calorific-value coal and coal-based solid waste in a circulating fluidized bed incinerator 4. The high-temperature flue gas generated from the combustion of these fuels exchanges heat with the heat exchange tubes and the evaporative heating surfaces 5 within the furnace 9, producing hot water and steam at specific temperatures and pressures. The hot water can be used for district heating, with a pressure of 0.4 MPa to 2.5 MPa (inclusive) and a temperature of 95°C to 180°C (inclusive). The steam can be used for turbine power generation, district heating, or industrial steam use, with a pressure of 0.4 MPa to 14 MPa (inclusive) and a steam temperature of 151°C to 540°C (inclusive).

[0056] In this embodiment, a fuel processing structure 1 is also included. The fuel processing structure 1 includes a filter press 101, a mesh belt drying structure 104, a regenerative cooler 106, a heater 107, and a crushing structure 103. The regenerative cooler 106 and the heater 107 form a waste heat dehumidification structure 105. The mesh belt drying structure 104 and the waste heat dehumidification structure 105 form a dehumidification dryer 102. The dehumidification dryer 102 is used for drying low-calorific-value fuels. The filter press 101 is a plate and frame filter press, which is used for... The mechanical filter press for low-calorific-value fuels includes a mesh belt drying structure 104 comprising a drying chamber and a belt drive structure. The belt drive structure has through holes on its conveyor belt and can be configured in two stages. The outlet of the filter press 101 is connected to the feed inlet at the top of the drying chamber. The air outlet at the top of the drying chamber is connected to the regenerator 106. The regenerator 106 is connected to the heater 107. The heater 107 is connected to the air inlet at the bottom of the drying chamber. The crushing structure 103 is connected to the dry material outlet at the bottom of the drying chamber.

[0057] In this embodiment, a pulverizer is installed inside the drying chamber. The inlet of the pulverizer is connected to the feed inlet, and the outlet of the pulverizer corresponds to the belt drive structure. Low-calorific-value fuel enters the pulverizer through the feed inlet and the inlet of the pulverizer. After being pulverized, it falls into the belt drive structure through the outlet of the pulverizer.

[0058] Low-calorific-value fuels have high moisture content, which directly affects their ignition characteristics and stable combustion in the circulating fluidized bed incinerator 4. When the operating flexibility of the circulating fluidized bed incinerator 4 is >60% B-MCR, low-calorific-value fuels with a moisture content of no more than 55% do not require dehydration treatment before combustion. However, low-calorific-value fuels with a moisture content >55% require mechanical filtration and dehydration drying through the plate and frame filter press and dehumidifier 102 in the fuel processing structure 1 to reduce the moisture content to below 55%, which meets the stable combustion requirements of the circulating fluidized bed incinerator 4. When the operating flexibility of the circulating fluidized bed incinerator 4 is 30% to 60% (inclusive of both endpoints) B-MCR (maximum continuous evaporation rate), it is necessary to mechanically filter and dehydrate the low-calorific-value fuel through the plate and frame filter press and dehumidifier 102 in the fuel processing structure 1 to reduce the moisture content of the low-calorific-value fuel to 10% to 30% (mass fraction, inclusive of both endpoints) to meet the stable combustion requirements of the circulating fluidized bed incinerator 4.

[0059] Specifically, the low-calorific-value fuel containing water first enters the plate and frame filter press for mechanical filtration. The low-calorific-value fuel after filtration becomes a mud cake and then enters the dehumidification dryer 102 for closed-loop waste heat drying. Low-calorific-value fuel in the form of mud cakes enters the mesh belt drying structure 104 through the feed inlet of the drying chamber. After being crushed by the pulverizer, it falls onto the two-stage belt drive structure. By adjusting the conveying speed of the conveyor belt of the mesh belt drying structure 104 in the dehumidifying dryer 102, the moisture content of the low-calorific-value fuel can be reduced to 10% to 55% (mass fraction, including both endpoints). 80°C dry hot air is sent in through the air inlet at the bottom of the mesh belt drying structure 104, passing through the low-calorific-value fuel from bottom to top, heating the low-calorific-value fuel on the conveyor belt. The moisture in the low-calorific-value fuel evaporates, and the dry hot air carries the evaporated moisture from the low-calorific-value fuel to become 60°C humid hot air, which flows out from the air outlet at the top of the mesh belt drying structure 104. The dried low-calorific-value fuel is sent out from the dry material outlet at the bottom. The dry fuel temperature is <50°C, and it can be directly stored or subjected to further fuel processing without cooling. After the 60°C humid air flows out of the mesh belt drying structure 104, it enters the waste heat dehumidification structure 105 for condensation and heating. The 60°C humid air first enters the regenerative cooler 106, where 30°C cooling water cools the humid air, causing the moisture in the humid air to condense and be discharged. The cooled and dry air after condensation and dehumidification enters the heater 107, where hot water at a temperature of not less than 90°C is introduced to heat the cooled and dry air. After being heated to 80°C, the hot dry air is sent back to the mesh belt drying structure 104, forming a closed-loop circulation of the air medium.

[0060] The heat source of the heater 107 in the waste heat dehumidification structure 105 comes from the waste heat of the flue gas at the outlet of the air preheater 14 of the second flue structure 17. The waste heat of the flue gas is converted into hot water with a temperature of not less than 90°C through the waste heat recovery and utilization structure 15, which serves as the heat source in the heater 107. This not only reduces the exhaust heat loss of the low-calorific-value fuel resource utilization device 100, but also makes reasonable use of the waste heat, greatly improving the thermal efficiency of the entire system.

[0061] The particle size of the fuel entering the furnace is a crucial factor affecting the combustion efficiency, ash circulation ratio, and air distribution of the circulating fluidized bed incinerator 4. Simultaneously, the fuel particle size directly influences the heating rate of the fuel particles on the bed; larger particles result in a lower heating rate. Typically, gasification ash, fly ash, and slag, which are coal-based solid wastes, are high-carbon fly ash produced after coal combustion or high-temperature gasification. Their particle size ranges from 10μm to 500μm (inclusive of both endpoints), and they do not require crushing and directly meet the particle size requirements for entering the furnace. For low-calorific-value coal, screening and crushing are required via the crushing structure 103 in the fuel processing structure 1 to break the coal into coal powder with a particle size of 0–10mm (excluding 0mm but including the 10mm endpoint), meeting the particle size requirements for entering the furnace. Gasification ash, fly ash, and slag, which are high-carbon fly ash produced after coal combustion or gasification, typically have a particle size of 10μm to 500μm and can directly meet the particle size requirements for entering the furnace. Moisture content requirement: Moisture content ≤ 55% (mass fraction).

[0062] This embodiment can process low-calorific-value fuels (i.e., low-calorific-value coal and coal-based solid waste) with a net calorific value ranging from 370 kcal / kg to 2400 kcal / kg that cannot be purely burned using existing combustion technologies. Industrial analysis of these fuels shows a net moisture content ranging from 5% to 55%, a net ash content ranging from 25% to 75%, and a net volatile matter content ranging from 1% to 15%. This embodiment achieves a breakthrough in the resource utilization of low-calorific-value fuels in the combustion field, and can co-produce steam and hot water. It has advantages such as stable combustion, simple operation, high carbon burnout rate, and high equipment thermal efficiency.

[0063] This embodiment demonstrates that low-calorific-value coal can be stably burned and continuously operated in a circulating fluidized bed incinerator 4 after simple crushing, maximizing the recovery and utilization of carbon resources in the low-calorific-value coal and achieving the goal of energy conservation and carbon reduction. The circulating fluidized bed incinerator 4 can directly burn coal-based solid waste such as gasification ash, fine ash, and slag, further burning the residual carbon in the coal-based solid waste, maximizing the combustion value of the residual carbon, achieving the goal of energy conservation and carbon reduction, while also saving land resources required for landfilling these coal-based solid wastes, saving enterprises the cost of solid waste treatment and avoiding environmental pollution. While helping enterprises treat low-calorific-value coal and coal-based solid waste, it also generates high-temperature flue gas from the carbon in the low-calorific-value coal and coal-based solid waste through combustion. The heat of the high-temperature flue gas is transferred through a convection heat exchanger. The combined heat and power generation system produces hot water and steam, which can be used for steam turbine power generation, district heating, or industrial steam, bringing significant economic benefits to enterprises. It has achieved a technological breakthrough in the resource utilization of low-calorific-value coal (with a net calorific value of less than 2400 kcal / kg) and coal-based solid waste in the combustion field, and there are already industrial-scale utilization projects implemented to date. The circulating fluidized bed incinerator 4 has a high burnout rate, with the carbon content of the fly ash after combustion not exceeding 5% (mass fraction) and the carbon content of the bottom ash not exceeding 1% (mass fraction), and the thermal efficiency of the entire unit is not less than 90%. Through the convective heat exchange device in the tail flue structure of the circulating fluidized bed incinerator 4 and the waste heat recovery and utilization structure 15, the calorific value of the fuel is recovered and utilized, and the thermal efficiency of the entire circulating fluidized bed incinerator is not less than 90%.

[0064] This embodiment solves the technical problem of stable combustion of low-calorific-value fuels that are directly fed into the furnace without pressure filtration and drying when the moisture content of the received base is no more than 55%; it solves the technical problem of stable combustion of low-calorific-value coal with a received base low calorific value of 370kcal / kg to 2400kcal / kg as fuel in the circulating fluidized bed incinerator 4; it solves the technical problem of stable combustion of gasification ash, fine ash, and slag as fuel in the circulating fluidized bed incinerator 4 through residual carbon reburning; it increases the material circulation ratio of the circulating fluidized bed incinerator 4, which can quickly heat fly ash and overcome the problem of insufficient reactivity; it extends the residence time in the fly ash bed, improves the burnout rate, and reduces the carbon content of fly ash and bottom ash, maximizing energy saving and carbon reduction; based on the co-production of hot water and steam by the convection heat exchange device in the tail flue structure, a waste heat recovery and utilization structure 15 is added, which further reduces the exhaust temperature of the incinerator while recovering waste heat from the flue gas, greatly improving the thermal efficiency of the entire incinerator.

[0065] Example 2

[0066] The low-calorific-value fuel resource utilization method using the low-calorific-value fuel resource utilization device 100 of Embodiment 1 includes the following steps:

[0067] The first step is to process the low-calorific-value fuel to meet the requirements for fuel to be fed into the furnace, as follows:

[0068] When the production of low-calorific-value fuels that need to be processed is large enough to maintain the incinerator load at no less than 60% B-MCR, low-calorific-value fuels with a moisture content of no more than 55% do not need to be dried and dehydrated by the filter press 101 and the dehumidifying dryer 102. Low-calorific-value coal needs to be screened and crushed by the crushing structure 103. After being crushed into coal powder of 0mm to 10mm, it can be directly fed into the furnace for combustion. Coal-based solid wastes do not need to be crushed and can be directly fed into the furnace for combustion.

[0069] Low-calorific-value fuels with a moisture content exceeding 55% need to have their moisture content reduced to below 55% before being processed using the aforementioned fuel crushing method. Specifically, the drying method involves the fuel with a moisture content exceeding 55% first undergoing mechanical filtration in a filter press 101. The filtered fuel forms a sludge cake, which then enters a dehumidifying dryer 102 for closed-loop waste heat drying. The sludge cake-like fuel enters the mesh belt drying structure 104 through the filter cake inlet, is crushed, and falls onto a two-stage horizontal perforated belt conveyor structure. 80°C hot air is introduced from the bottom inlet of the mesh belt drying structure 104, passing upwards through the fuel and heating it. The moisture in the fuel evaporates, and the hot air carrying the evaporated moisture becomes 60°C humidified air, which flows out from the upper outlet of the mesh belt drying structure 104. The dried fuel is then discharged from the lower dry material outlet. Fuel with a temperature <50℃ can be stored directly or processed further without cooling. 60℃ humid air flows out of the mesh belt drying structure 104 and enters the waste heat dehumidification structure 105 for condensation and heating. The 60℃ humid air first enters the regenerative cooler 106, where 30℃ cooling water cools the humid air, causing the moisture in the humid air to condense and be discharged. The cooled and dehumidified air then enters the heater 107, where hot water at a temperature not less than 90℃ is introduced to heat the air. After being heated to 80℃, the hot air is sent back to the mesh belt drying structure 104, forming a closed-loop circulation of the air medium. The heat source for the heater 107 in the waste heat dehumidification structure 105 comes from the waste heat of the flue gas at the outlet of the air preheater of the circulating fluidized bed incinerator 4. The waste heat is converted into hot water at a temperature not less than 90℃ through the waste heat recovery and utilization structure 15, which serves as the heat source for the heater 107.

[0070] When the output of low-calorific-value solid waste that needs to be treated is insufficient, and the incinerator load can only be maintained at 30% to 60% B-MCR, the water content in the low-calorific-value fuel needs to be reduced to 10% to 30% by the filter press 101 and dehumidification dryer 102 in the fuel treatment structure 1. The drying and crushing methods for low-calorific-value fuel are the same as those described above.

[0071] The second step involves the operation of the combustion system, which consists of a circulating fluidized bed incinerator and a cyclone separator: The bed material is heated, and low-calorific-value fuel is fed into the furnace of the circulating fluidized bed incinerator. As the low-calorific-value fuel continues to burn, the high-temperature flue gas carrying fly ash rises continuously within the furnace. Upon reaching the top of the furnace, the flue gas flow direction changes, exiting the circulating fluidized bed incinerator from the furnace outlet and entering the cyclone separator. Particles captured by the cyclone separator return to the furnace through the return structure to continue combustion. Particles not captured by the cyclone separator enter the tail flue structure for heat exchange, as detailed below:

[0072] Bed material is laid in the upper bed section of the air distribution structure 8. The primary air regulating valve is opened (the primary air outlet of the air preheater 14 is connected to the ignition combustion chamber 2 through the primary air hot flue, and the primary air regulating valve is set in a suitable position in the primary air hot flue). Primary air is evenly sent from the ignition combustion chamber 2 to the dense phase zone bed section of the furnace 9 through the air distribution structure 8, and the bed material is evenly blown into a fluidized state. The ignition fuel of the circulating fluidized bed incinerator 4 can be light diesel oil, natural gas, etc. The ignition burner in the ignition combustion chamber 2 is opened to ignite and heat the bed material. The bed material temperature gradually rises. When the temperature is >600℃, auxiliary combustion coal is added from the feed inlet 3. At the same time, the secondary air regulating valve is opened (the secondary air outlet of the air preheater 14 is connected to the secondary air box arranged in the dense phase zone of the furnace 9 through the secondary air hot flue, and the secondary air regulating valve is set in a suitable position in the secondary air hot flue). The auxiliary combustion coal particles enter the fluidized bed material and are heated, undergoing crushing, pyrolysis, and combustion reactions. Stable combustion of coal continues, and the bed material temperature continues to rise. Since the ignition temperature of low-calorific-value fuels is not less than 800℃ and they will not ignite below 800℃, when the bed temperature is ≥800℃, the input of auxiliary combustion coal is gradually reduced. At the same time, low-calorific-value coal and coal-based solid waste that meet the requirements for fuel entering the furnace are transported to the feed inlet 3 of the circulating fluidized bed incinerator 4 through a screw feeder. Under the action of gravity and coal-feeding air, they are sent into the dense phase zone bed section of the furnace 9 for ignition and combustion. At this time, the air required for combustion is gradually heated by the air preheater 14. The primary hot air meets the air required for the ignition and combustion of low-calorific-value fuels and is evenly sent from the ignition combustion chamber 2 into the dense phase zone bed section of the furnace 9 through the air distribution structure 8. The secondary hot air supplements the air required for the continued combustion of low-calorific-value fuels. As the load of the circulating fluidized bed incinerator 4 gradually increases, the input of low-calorific-value fuels is gradually increased until the load of the circulating fluidized bed incinerator 4 reaches the rated load. At this time, the input of auxiliary combustion coal is stopped, and stable combustion is achieved.

[0073] The flue gas produced by combustion carries a large amount of bed material and coke particles produced by pyrolysis out of the dense phase zone of furnace 9. Secondary air supplements the air required for subsequent combustion. During the upward flow of the airflow, a large number of particles carried by the flue gas will agglomerate. The agglomerated particle clusters have a high terminal velocity, which makes the upward velocity of the particles much lower than the empty tower velocity. Particle clusters with terminal velocities lower than the empty tower velocity adhere to the wall and form a downward flow. During the downward process, the particle clusters are dispersed by the upward airflow, and the particles flow upward again to form particle clusters. This process greatly prolongs the residence time of the particles in the ignition combustion chamber 2, providing conditions for the complete combustion of carbon. This process constitutes the internal circulation of the circulating fluidized bed incinerator 4.

[0074] As the low-calorific-value fuel continues to burn, the high-temperature flue gas carrying a large amount of fly ash rises continuously within the furnace 9. Upon reaching the top of the furnace, the flue gas flow direction changes, exiting the circulating fluidized bed incinerator 4 from the outlet of the furnace 9 and entering the cyclone separator 6. Due to the high ash content and extremely low volatile matter of the low-calorific-value fuel, a large amount of unburned carbon in the fly ash undergoes secondary combustion in the cyclone separator 6. Most of the fine particles are captured by the cyclone separator 6 along with the particle clusters, and the Roots blower provides fluidization for the captured fine particles. The required fluidizing air is sent into the return structure 7 through the fluidizing air inlet 21. The fine particles are sent into the dense phase zone bed section of the furnace 9 under the action of the fluidizing air to continue to participate in combustion. These fine particles constitute the circulating ash. This process constitutes the external circulation of the circulating fluidized bed incinerator 4. The remaining fine particles are sent out with the flue gas through the central cylinder of the cyclone separator 6 and enter the first flue structure 16 and the second flue structure 17 in sequence to exchange heat with the convective heat exchange devices arranged in the first flue structure 16 and the second flue structure 17.

[0075] Because the low-calorific-value fuel has a very high ash content, coupled with the extremely high separation efficiency of the cyclone separator 6, the circulating ash volume of the circulating fluidized bed incinerator 4 is very large. Apart from the bed material added when the circulating fluidized bed incinerator 4 is started up, no additional bed material is needed to establish material circulation during the stable operation phase.

[0076] When the amount of low-calorific-value fuel to be processed decreases, the load on the circulating fluidized bed incinerator 4 drops, the bed temperature decreases, and the combustion of low-calorific-value fuel is affected, resulting in a decrease in combustion efficiency. At this time, the valve of the circulating ash discharge pipe 20 at the bottom of the return structure 7 is opened to artificially reduce the amount of circulating ash returning to the furnace 9. More than 50% of the heat generated by the low-calorific-value fuel during combustion in the bed is carried away by the circulating ash, and the remaining heat maintains the bed temperature. After the circulating ash decreases, the heat carried away by the circulating ash decreases, and the bed temperature rises. When the load on the circulating fluidized bed incinerator 4 increases, the valve of the circulating ash discharge pipe 20 is closed, and the circulating ash is slowly increased to the amount required for the rated load, so that the bed temperature is always maintained at the design temperature. Through this operation method, the operating flexibility of the circulating fluidized bed incinerator 4 can achieve stable combustion within 60% to 110% B-MCR.

[0077] When no evaporation heating surface 5 is arranged in the furnace 9, the operation method on the working fluid side is as follows: the feedwater enters the inlet header of the second convection heat exchanger tube group 12 through the feedwater pipe, and after being heated by the second convection heat exchanger tube group 12, it enters the lower water side of the steam drum through the water guide pipe. The lower water side of the steam drum is connected to the downcomer. The hot water of the second convection heat exchanger tube group 12 enters the downcomer and then enters the inlet header of the evaporator 11 through the downcomer outlet connecting pipe. It exchanges heat with the external flue gas in the evaporator 11. The steam-water mixture after heat exchange enters the steam drum through the connecting pipe for steam-water separation. The separated saturated steam is sent to the first convection heat exchanger tube group 10 for heat exchange through the saturated steam outlet pipe.

[0078] When evaporation heating surfaces are arranged inside the furnace, the operating methods on the working fluid side are divided into two types:

[0079] In the first method, feedwater enters the inlet header of the second convection heat exchanger tube group 12 through the feedwater pipeline. After being heated by the second convection heat exchanger tube group 12, it first enters the evaporator 11 through the inlet header of the evaporator 11. Convection heat exchange occurs through the transverse flow of flue gas through the pipes of the evaporator 11. After the working fluid completes heat absorption in the evaporator 11, a portion of the evaporator tube bundle containing a steam-water mixture enters the steam drum through the connecting pipe for steam-water separation. The separated saturated steam enters the first convection heat exchanger tube group 10 for heat exchange through the saturated steam outlet pipe; the remaining evaporator tubes... The hot water with increased temperature inside the bundle tubes enters the downcomer through the upper interface of the downcomer and flows into the lower inlet header of the membrane water-cooled wall in the furnace 9. The working fluid inside the membrane water-cooled wall flows from bottom to top and exchanges heat with the hot flue gas in the furnace 9 through convection and radiation. The steam-water mixture after heat exchange enters the steam drum through the top connecting pipe for steam-water separation. The separated saturated steam enters the first convection heat exchange tube group 10 for heat exchange through the saturated steam outlet pipe. The water separated from the steam drum flows back into the downcomer and the membrane water-cooled wall for heat exchange again.

[0080] The second method involves feeding water into the inlet header of the second convection heat exchanger tube group 12 via a feed water pipe. After being heated by the second convection heat exchanger tube group 12, the water enters the lower water side of the steam drum through a water guide pipe. The lower water side is connected to the downcomer. The hot water from the second convection heat exchanger tube group 12 is divided into two parts after entering the downcomer. One part of the hot water enters the inlet header of the evaporator 11 through the upper outlet connecting pipe of the downcomer, where it exchanges heat with the external flue gas. The steam-water mixture after heat exchange enters the steam drum through the connecting pipe for steam-water separation. The separated saturated steam is sent to the first convection heat exchanger through the saturated steam outlet pipe. Heat exchange occurs in tube group 10; the remaining hot water continues to enter the lower inlet header of the membrane water-cooled wall through the downcomer. The working fluid inside the membrane water-cooled wall flows upward and exchanges convective and radiative heat with the hot flue gas in the furnace 9. The steam-water mixture after heat exchange enters the steam drum through the top connecting pipe for steam-water separation. The separated saturated steam enters the first convective heat exchange tube group 10 through the saturated steam outlet pipe for heat exchange. The water separated in the steam drum flows back into the downcomer and repeats the above process until it completely absorbs heat and becomes saturated steam, which then enters the first convective heat exchange tube group 10 through the saturated steam outlet pipe. Due to the high ash content of low-calorific-value fuels, the high-temperature flue gas entering the tail flue structure has a high fly ash content. The fly ash is very fine, which makes it easier for ash to accumulate on the convective heating surface of the tail flue structure, affecting heat transfer. Therefore, soot blowers need to be installed at the locations where ash easily accumulates in the pipes of the evaporator 11. These can be steam soot blowers, sonic soot blowers, shock wave soot blowers, etc. The soot blowers are opened periodically to blow away the accumulated ash on the heating surface. The fly ash blown off falls into the conical hopper at the bottom of the first flue structure 16 and the second flue structure 17 for temporary storage. The valves of the first fly ash discharge pipe 18 and the second fly ash discharge pipe 19 are opened periodically for cleaning.

[0081] This specification uses specific examples to illustrate the principles and implementation methods of the present invention. The descriptions of the above embodiments are only for the purpose of helping to understand the method and core ideas of the present invention. Furthermore, those skilled in the art will recognize that, based on the ideas of the present invention, there will be changes in the specific implementation methods and application scope. Therefore, the content of this specification should not be construed as a limitation of the present invention.

Claims

1. A device for the resource utilization and combustion of low-calorific-value fuels, characterized in that, This includes a circulating fluidized bed incinerator, a cyclone separator, a tail flue structure, and a waste heat recovery and utilization structure; The circulating fluidized bed incinerator includes a furnace chamber, the upper part of which is a dilute phase zone and the lower part of which is a dense phase zone. The feed inlet of the circulating fluidized bed incinerator is located in the middle and lower part of the furnace chamber, and the outlet of the circulating fluidized bed incinerator is located in the dilute phase zone. The outlet of the furnace is connected to the cyclone separator, the cyclone separator is connected to the circulating ash inlet at the bottom of the furnace, a convection heat exchange device is provided in the tail flue structure, the inlet of the tail flue structure is connected to the cyclone separator, and the outlet of the tail flue structure is connected to the inlet of the waste heat recovery and utilization structure. The waste heat recovery and utilization structure is equipped with a flue gas outlet; The inner wall of the furnace is provided with a membrane water-cooled wall, and the surface of the membrane water-cooled wall in the middle and lower part of the dilute phase region forms an evaporation heating surface. The tail flue structure includes a first flue structure and a second flue structure. The inlet of the first flue structure is connected to the cyclone separator, the outlet of the first flue structure is connected to the inlet of the second flue structure, and the outlet of the second flue structure is connected to the inlet of the waste heat recovery and utilization structure. The convection heat exchange device includes a first convection heat exchange tube group, an evaporator, a second convection heat exchange tube group, and an air preheater arranged sequentially from the inlet of the first flue structure to the outlet of the first flue structure. A first fly ash discharge pipe is provided at the lower end of the first flue structure, and a second fly ash discharge pipe is provided at the lower end of the second flue structure. The inlet header of the second convection heat exchanger tube assembly is connected to the feed water pipeline, and the outlet header of the second convection heat exchanger tube assembly is connected to the inlet header of the evaporator. The outlet header of the evaporator is connected to the steam drum and a downcomer pipe from the steam drum. The downcomer pipe is connected to the inlet header of the membrane water-cooled wall of the furnace. The outlet header of the membrane water-cooled wall is connected to the steam drum via a top connecting pipe. The inlet header of the first convection heat exchanger tube assembly is connected to the saturated steam outlet pipe from the steam drum. The working fluid in the first convection heat exchanger tube assembly exchanges heat with the first convection heat exchanger tube assembly and then passes through the first pair of tubes. The heat exchanger tube assembly is discharged from the outlet header; or, the inlet header of the second convection heat exchanger tube assembly is connected to the feedwater pipeline, the outlet header of the second convection heat exchanger tube assembly is connected to the steam drum via a water guide pipe, the steam drum is connected to the inlet header of the membrane water-cooled wall of the furnace via a downcomer, the outlet of the upper part of the downcomer is connected to the inlet header of the evaporator, the outlet header of the membrane water-cooled wall is connected to the steam drum via a top connecting pipe, the outlet header of the evaporator is connected to the steam drum, and the inlet header of the first convection heat exchanger tube assembly is connected to the steam drum via a saturated steam outlet pipe.

2. The low-calorific-value fuel resource utilization device according to claim 1, characterized in that, The furnace of the circulating fluidized bed incinerator has a rectangular cross-section. Refractory castable is laid between the inner wall of the furnace and the outer wall of the remaining membrane water-cooled walls. The lower end of the furnace in the dense phase zone tapers into a conical structure. Several feed inlets are located on the front wall of the lower middle part of the furnace.

3. The low-calorific-value fuel resource utilization device according to claim 1, characterized in that, An ignition and combustion chamber is provided at the lower end of the furnace, and an air distribution structure is provided between the ignition and combustion chamber and the furnace. The outlet at the lower part of the cyclone separator is connected to the circulating ash inlet at the lower part of the furnace through a return structure. The bottom of the return structure is provided with a fluidizing air inlet and a circulating ash discharge pipe. The waste heat recovery and utilization structure includes a waste heat recovery box and a heat exchange tube. One end of the waste heat recovery box is connected to the second flue structure, and the other end of the waste heat recovery box is connected to the flue gas outlet. The heat exchange tube is installed in the waste heat recovery box and is used to exchange heat with the flue gas entering the box.

4. The low-calorific-value fuel resource utilization device according to claim 1, characterized in that, It also includes a fuel processing structure, which comprises a filter press, a mesh belt drying structure, a regenerator, a heater, and a crushing structure. The mesh belt drying structure includes a drying chamber and a belt drive structure. The conveyor belt of the belt drive structure has through holes. The outlet of the filter press is connected to the feed inlet at the top of the drying chamber. The air outlet at the top of the drying chamber is connected to the regenerator. The regenerator is connected to the heater. The heater is connected to the air inlet at the bottom of the drying chamber.

5. The low-calorific-value fuel resource utilization device according to claim 4, characterized in that, The drying chamber is equipped with a pulverizer. The inlet of the pulverizer is connected to the feed inlet, and the outlet of the pulverizer corresponds to the belt drive structure. Low-calorific-value fuel enters the pulverizer through the feed inlet and the inlet of the pulverizer. After being pulverized, it falls into the belt drive structure through the outlet of the pulverizer.

6. A method for the combustion and utilization of low-calorific-value fuel using the low-calorific-value fuel resource utilization device according to any one of claims 1-5, characterized in that, Includes the following steps: Low-calorific-value fuels are processed to meet the requirements for fuel to be fed into the furnace. The bed material is heated, and low-calorific-value fuel is fed into the furnace of the circulating fluidized bed incinerator. As the low-calorific-value fuel continues to burn, the high-temperature flue gas carrying fly ash rises continuously in the furnace. After reaching the top of the furnace, the flue gas flow direction changes and flows out of the circulating fluidized bed incinerator from the furnace outlet, entering the cyclone separator. The particles captured by the cyclone separator enter the furnace through the return structure to continue to participate in combustion, while the particles not captured by the cyclone separator enter the tail flue structure for heat exchange. When evaporation heating surfaces are arranged inside the furnace, the operating methods on the working fluid side are divided into two types: In the first method, feedwater enters the inlet header of the second convection heat exchanger tube group through the feedwater pipe. After being heated by the second convection heat exchanger tube group, it first enters the evaporator through the inlet header of the evaporator. Convection heat exchange occurs through the transverse flow of flue gas over the evaporator tube bundles. After the working fluid absorbs heat in the evaporator, a portion of the evaporator tube bundle containing a steam-water mixture enters the steam drum through the connecting pipe for steam-water separation. The separated saturated steam enters the first convection heat exchanger tube group for heat exchange through the saturated steam outlet pipe. The remaining portion of the evaporator tube bundle containing hot water with increased temperature enters the downcomer through the upper interface of the downcomer and flows into the lower inlet header of the membrane water-cooled wall in the furnace. The working fluid in the membrane water-cooled wall tubes flows upward and undergoes convection and radiation heat exchange with the hot flue gas in the furnace. The steam-water mixture after heat exchange enters the steam drum through the top connecting pipe for steam-water separation. The separated saturated steam enters the first convection heat exchanger tube group for heat exchange through the saturated steam outlet pipe. The water separated from the steam drum flows back into the downcomer and membrane water-cooled wall for further heat exchange. The second method involves feeding water into the inlet header of the second convection heat exchanger tube group via a feed water pipe. After being heated by the second convection heat exchanger tube group, the water enters the lower water side of the steam drum through a water guide pipe. The lower water side of the steam drum is connected to the downcomer. The hot water from the second convection heat exchanger tube group is divided into two parts after entering the downcomer. One part of the hot water enters the inlet header of the evaporator through the upper outlet connecting pipe of the downcomer. It exchanges heat with the external flue gas in the evaporator. The steam-water mixture after heat exchange enters the steam drum through the connecting pipe for steam-water separation. The separated saturated steam is sent to the first convection heat exchanger tube group for heat exchange through the saturated steam outlet pipe. The remaining hot water continues to enter the lower inlet header of the membrane water-cooled wall through the downcomer. The working fluid inside the membrane water-cooled wall flows upward and exchanges heat with the hot flue gas in the furnace through convection and radiation. The steam-water mixture after heat exchange enters the steam drum through the top connecting pipe for steam-water separation. The separated saturated steam enters the first convection heat exchange tube group through the saturated steam outlet pipe for heat exchange. The water separated in the steam drum flows back into the downcomer and repeats the process of hot water entering the downcomer and being divided into two parts until it completely absorbs heat and becomes saturated steam, which then enters the first convection heat exchange tube group through the saturated steam outlet pipe.

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