Supercritical fluidization reaction system for co-processing flue gas

Abstract

The invention discloses a supercritical fluidized reaction system for co-processing flue gas, which comprises a reactor, the reactor is connected with a gas-solid separation device, the gas-solid separation device is connected with a material return valve, the material return valve is connected with the reactor, an evaporation heating surface and a high-temperature heating surface are arranged in the reactor, the gas-solid separation device is connected with a tail flue, and the high-temperature heating surface is connected with the tail flue. A flue gas preheater and a mixed preheater are arranged in the tail flue, a flue gas generator is connected with a flue gas booster fan, the flue gas booster fan is connected with the flue gas preheater and the mixed preheater, the flue gas preheater is connected with a reactor through a secondary air duct, an air booster fan is connected with the mixed preheater, and the mixed preheater is connected with a secondary air duct. And the mixed preheater is connected with the reactor through a primary air duct. The system has the beneficial effects that dioxin, CO, NOX and SO2 in flue gas are removed through the fluidized reaction system, and high-quality steam can be generated for power generation while ultralow emission is achieved; the reactor adopts supercritical parameters, the power generation efficiency is higher, and the economical efficiency is better.

Description

Technical Field

[0001] The present application belongs to the technical field of flue gas treatment, and specifically relates to a supercritical fluidized reaction system for collaboratively treating flue gas. Background Art

[0002] In recent years, with the rapid growth of my country's economy, the contradiction between economic development and resources and environment has become increasingly acute, and pollutant emission reduction has become one of my country's current important tasks. The steel industry is a basic industry of the national economy. A large amount of flue gas is generated during the sintering process, with an average of about 4000m 3 / ton of ore. Sintering flue gas contains a large amount of NO x , SO2, CO, dioxins and other pollutants cause serious environmental pollution.

[0003] At present, in order to achieve ultra-low emissions from sintering flue gas, the mainstream process is a combination of wet desulfurization + SCR (selective catalytic reduction) denitrification process. The SCR denitrification process has requirements for flue gas temperature, and it is necessary to use MGGH (flue gas heat exchanger), GGH (flue gas reheater) and hot air furnace and other equipment to heat the flue gas after desulfurization. If dioxins are to be further treated, additional adsorption devices are required. The mainstream process equipment requires huge investment and high energy consumption, and does not generate any economic benefits. The market is in urgent need of a method that can efficiently, stably and low-costly treat NO in steel sintering flue gas. x , SO2, CO, dioxins and other pollutants.

[0004] Patent "CN114733318B" proposes a method for treating sintering flue gas, which uses a vacuum pressure swing adsorption device to remove N2 from the sintering flue gas, and then heats the sintering flue gas; the heated sintering flue gas is sprayed from the tuyere into the working oxygen blast furnace, and at the same time, oxygen-enriched air and pulverized coal are sprayed into the oxygen blast furnace at the tuyere to remove SO2 and NO in the sintering flue gas. x It is reduced in an oxygen blast furnace, thereby achieving denitration and desulfurization. The energy consumption of the vacuum pressure swing adsorption device of this method is high and the economic efficiency is poor.

[0005] Patent "CN112325307B" proposes a rapid cooler for sintering flue gas incinerators, which solves the problem of slow flue gas cooling speed in existing vertical rapid coolers, which easily leads to the synthesis of dioxins and damages the environment. The device is designed for a drum boiler, with low working fluid parameters and low power generation efficiency.

[0006] The existing technology has proposed a method for treating sintering flue gas from a systematic perspective, but all of them have problems such as low working fluid parameters and poor economy, and do not involve the field of supercritical fluidized bed reactor design for treating sintering flue gas. Summary of the invention

[0007] In order to improve the economy of sintering flue gas treatment technology, the present application proposes a supercritical fluidized bed reaction system for collaboratively treating sintering flue gas, and provides key parameters such as the heat absorption share on the working fluid side, the excess oxygen coefficient on the flue gas and air side, and the primary and secondary air distribution of the supercritical fluidized bed reactor for treating sintering flue gas, thereby improving the working fluid parameters of the prior art to supercritical, achieving higher power generation efficiency and better economy.

[0008] The purpose of this application is achieved through the following technical solutions:

[0009] A supercritical fluidized bed reaction system for collaboratively treating flue gas comprises a reactor, wherein the upper portion of the reactor is connected to a gas-solid separation device, the lower portion of the gas-solid separation device is connected to a return valve, the return valve is connected to the middle and lower portion of the reactor, the reactor, the gas-solid separation device and the return valve form a main circulation loop, an evaporation heating surface and a high-temperature heating surface are arranged inside the reactor, the upper portion of the gas-solid separation device is connected to a tail flue, a flue gas preheater and a mixed preheater are arranged inside the tail flue, a flue gas generator is connected to a flue gas booster fan, the flue gas booster fan is respectively connected to the flue gas preheater and the mixed preheater, the flue gas preheater is connected to the middle and lower portion of the reactor through a secondary air duct, the air booster fan is connected to the mixed preheater, and the mixed preheater is connected to the wind chamber at the bottom of the reactor through a primary air duct.

[0010] Furthermore, the fume generator produces sintering fume.

[0011] Furthermore, the internal temperature of the reactor is between 850 and 920° C., so as to remove dioxins and CO from the flue gas.

[0012] Furthermore, the reaction system adopts SNCR+SCR system to remove NO in flue gas. X .

[0013] Furthermore, the reaction system adopts in-furnace + tail desulfurization to remove SO2 in the flue gas.

[0014] Furthermore, the temperature of the main circulation loop is maintained between 850 and 920°C, the heat absorption ratio of the main circulation loop is 40% to 50%; the heat absorption ratio of the tail flue is 50% to 60%; the heat absorption ratio of the evaporation heating surface in the main circulation loop is 37% to 40%; the heat absorption ratio of the gas-solid separation device and the return valve is 0 to 2%; and the heat absorption ratio of the high-temperature heating surface is 3% to 8%.

[0015] Furthermore, the evaporation heating surface is a membrane water-cooled wall structure independent of the water-cooled intermediate partition wall or evaporation screen, and the mass flow rate is not less than 500kg / m 2 ·s.

[0016] Furthermore, the excess oxygen coefficient is between 1.25 and 1.5.

[0017] Furthermore, the proportion of primary air is between 40% and 50%, the proportion of primary air at the furnace bottom does not exceed 40%, the proportion of secondary air is between 50% and 60%, and the proportion of lower secondary air does not exceed 50%.

[0018] Furthermore, the hybrid preheater adopts an anti-corrosion material with internal enamel coating.

[0019] Furthermore, the sintering flue gas consumption of primary and secondary air is determined according to the ratio of flue gas to the total air consumption; the flue gas is preferentially preheated as secondary air through a flue gas preheater and then sent to the reactor. When the sintering flue gas volume is large, the remaining flue gas is preheated as primary air through a mixed preheater and then sent to the reactor.

[0020] Furthermore, the hybrid preheater is arranged downstream of the flue gas relative to the flue gas preheater.

[0021] Furthermore, a low-temperature heating surface, a feedwater heater, a flue gas preheater and a mixed preheater are arranged in sequence along the flow direction inside the tail flue.

[0022] Beneficial effects of this application:

[0023] 1. Use fluidized bed reaction system to remove dioxins, CO and NO from sintering flue gas X , SO2, while achieving ultra-low emissions of sintering flue gas, it can generate high-quality steam for power generation and has certain economic benefits.

[0024] 2. The reactor adopts supercritical parameters, which has higher power generation efficiency and better economy than the existing technology.

[0025] The aforementioned main scheme of the present application and its further options can be freely combined to form multiple schemes, all of which are schemes that can be adopted and claimed for protection in the present application; and in the present application, (non-conflicting options) can also be freely combined with each other and with other options. After understanding the scheme of the present application, those skilled in the art can understand that there are many combinations based on the prior art and common knowledge, all of which are technical schemes to be protected by the present application, and they are not exhaustively listed here. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 It is a schematic diagram of the structure of this application.

[0027] In the figure: 1-primary air duct, 2-secondary air duct, 3-air distribution plate, 4-reactor, 5-gas-solid separation device, 6-return valve, 7-tail flue, 8-starting system, 9-flue gas booster fan, 91-flue gas generator, 10-air booster fan, 11-evaporation heating surface, 14-high temperature heating surface, 13-low temperature heating surface, 21-feed water heater, 31-flue gas preheater, 32-mixed preheater. DETAILED DESCRIPTION

[0028] The following non-limiting examples are provided to illustrate the present application.

[0029] Embodiment 1

[0030] refer to Figure 1 As shown, a supercritical fluidized bed reaction system for collaboratively treating flue gas includes a primary air duct 1, a secondary air duct 2, an air distribution plate 3, a reactor 4, a gas-solid separation device 5, a return valve 6, a tail flue 7, a starting system 8, a flue gas booster fan 9, a flue gas generator 91, an air booster fan 10, an evaporating heating surface 11, a high-temperature heating surface 14, a low-temperature heating surface 13, a feed water heater 21, a flue gas preheater 31 and a mixed preheater 32.

[0031] The upper part of the reactor 4 is connected to the gas-solid separation device 5, the lower part of the gas-solid separation device 5 is connected to the return valve 6, the return valve 6 is connected to the middle and lower part of the reactor 4, and the reactor 4, the gas-solid separation device 5 and the return valve 6 form a main circulation loop. The reactor 4 is provided with an evaporation heating surface 11 and a high-temperature heating surface 14, and the wind chamber at the bottom of the reactor 4 is provided with an air distribution plate 3. The fuel inside the reactor 4 reacts with the oxygen in the sintering flue gas, and a large amount of heat is released to maintain the temperature of the reactor between 850 and 920°C. At the same time, this high temperature environment is used to burn CO in the sintering flue gas and decompose dioxins. The gas-solid separation device 5 is used to separate the bed material of the fluidized reactor, and the separated bed material is sent back to the reactor 4.

[0032] The upper part of the gas-solid separation device 5 is connected to the tail flue 7, and a flue gas preheater 31 and a mixed preheater 32 are arranged inside the tail flue 7. Specifically, a low-temperature heating surface 13, a feed water heater 21, a flue gas preheater 31 and a mixed preheater 32 are arranged in sequence inside the tail flue 7 along the flow direction, so as to absorb the heat of the flue gas in the tail flue 7 for recycling.

[0033] The flue gas generator 91 produces sintering flue gas. The flue gas generator 91 is connected to the flue gas booster fan 9. The flue gas booster fan 9 is connected to the flue gas preheater 31 and the mixed preheater 32 in two ways. The flue gas preheater 31 is connected to the middle and lower part of the reactor 4 through the secondary air duct 2. The air booster fan 10 is connected to the mixed preheater 32. The mixed preheater 32 is connected to the bottom wind chamber of the reactor 4 through the primary air duct 1.

[0034] The internal temperature of reactor 4 is between 850 and 920°C, which is used to remove dioxins and CO from the sintering flue gas. The reaction system adopts SNCR+SCR system to remove NO from the sintering flue gas. X The reaction system adopts in-furnace + tail desulfurization to remove SO2 in sintering flue gas.

[0035] The oxygen content of sintering flue gas is generally between 14% and 16%, which is lower than the oxygen content of air, so the amount of flue gas produced by combustion is greater. In order to maintain the temperature of the main circulation loop of the fluidized reaction system, the heat brought into the tail flue 7 by the flue gas is higher than that of the fluidized reactor with air-assisted combustion. When the temperature of the main circulation loop is maintained between 850 and 920°C, the heat absorption ratio of the main circulation loop heating surface of the supercritical fluidized reactor with air-assisted combustion is 60% to 75%, the heat absorption ratio of the tail flue heating surface is 25% to 40%, and the heat absorption ratio of the evaporation heating surface is generally between 37% and 45%.

[0036] This embodiment uses sintering flue gas with low oxygen concentration as the combustion-supporting gas. Compared with conventional air as the combustion-supporting gas, in order to ensure that the temperature of the main circulation loop is maintained between 850 and 920°C, the heat absorption ratio of the tail heating surface is greater. Therefore, the heat absorption ratio of the main circulation loop is 40% to 50%; the heat absorption ratio of the tail flue is 50% to 60%; the heat absorption ratio of the evaporation heating surface 11 in the main circulation loop is 37% to 40%; the heat absorption ratio of the gas-solid separation device 5 and the return valve 6 is 0 to 2%; the heat absorption ratio of the high-temperature heating surface 14 is 3% to 8%. The heat absorption ratio of the remaining heating surfaces is designed as needed, and the geometric dimensions of the heating surfaces at each level are designed according to the heat absorption and layout determined by the above heat absorption ratio.

[0037] To ensure hydrodynamic safety, the evaporation heating surface 11 is a membrane water-cooled wall structure independent of the water-cooled intermediate partition wall or evaporation screen, and the mass flow rate is not less than 500kg / m 2 ·s.

[0038] The oxygen content of sintering flue gas is relatively low, and the combustion efficiency is relatively low if the conventional excess oxygen coefficient is below 1.25. Therefore, the excess oxygen coefficient in this embodiment is set between 1.25 and 1.5.

[0039] Too low oxygen concentration in the dense phase of the fluidized reaction system will reduce the combustion efficiency, while too high oxygen content will cause NO X The original emission is increased, taking into account the combustion efficiency and NO X For original emission, the proportion of primary air is between 40% and 50%, the proportion of primary air at the bottom of the furnace (the air used for combustion in fluidized bed boilers is usually primary air and secondary air, and the primary air at the bottom of the furnace is mainly used for fluidization of bed materials and provides a certain amount of oxygen for fuel combustion) does not exceed 40%, and the proportion of secondary air (the role of secondary air is to supplement the oxygen used for combustion and to disturb the flue gas in the furnace to strengthen the reaction) is between 50% and 60%, and the proportion of lower secondary air (the secondary air is divided into upper and lower secondary air, which is to control the NO generated by fuel combustion X , the less secondary wind, NO X The less, but it has a negative impact on combustion and needs to be considered comprehensively) the proportion shall not exceed 50%.

[0040] The sintering flue gas contains a certain amount of SO2, which will corrode the inside of the mixed preheater. Therefore, the mixed preheater 32 adopts an anti-corrosion material with internal enamel coating.

[0041] Sintering flue gas contains certain alkali metals, which will react with SO3 to form low melting point salts at high temperature. A large proportion of sintering flue gas entering the primary air will corrode and block the air distribution plate cap. The sintering flue gas consumption of primary and secondary air is determined according to the proportion of flue gas in the total air consumption; the flue gas is first preheated as secondary air through the flue gas preheater 31 and then sent to the reactor 4. When the sintering flue gas volume is large, the remaining flue gas is preheated as primary air through the mixed preheater 32 and then sent to the reactor 4; at the same time, the air distribution plate 3 adopts an anti-corrosion and anti-clogging cap.

[0042] The temperature of sintering flue gas is generally above 120°C. In order to reduce the exhaust temperature of the reactor, the mixed preheater 32 is arranged downstream of the flue gas relative to the flue gas preheater 31.

[0043] The supercritical fluidized bed reactor of this embodiment is not only suitable for sintering flue gas, but also suitable for treating other low-oxygen flue gas containing dioxins, CO, NO X , SO2 waste gas.

[0044] Embodiment 2

[0045] refer to Figure 1 As shown, a supercritical fluidized bed reaction system for collaboratively treating flue gas includes a primary air duct 1, a secondary air duct 2, an air distribution plate 3, a reactor 4, a gas-solid separation device 5, a return valve 6, a tail flue 7, a starting system 8, a flue gas booster fan 9, a flue gas generator 91, an air booster fan 10, an evaporating heating surface 11, a high-temperature heating surface 14, a low-temperature heating surface 13, a feed water heater 21, a flue gas preheater 31 and a mixed preheater 32.

[0046] The upper part of the reactor 4 is connected to the gas-solid separation device 5, the lower part of the gas-solid separation device 5 is connected to the return valve 6, the return valve 6 is connected to the middle and lower part of the reactor 4, and the reactor 4, the gas-solid separation device 5 and the return valve 6 form a main circulation loop. The reactor 4 is provided with an evaporation heating surface 11 and a high-temperature heating surface 14, and the wind chamber at the bottom of the reactor 4 is provided with an air distribution plate 3. The fuel inside the reactor 4 reacts with the oxygen in the sintering flue gas, and a large amount of heat is released to maintain the temperature of the reactor between 850 and 920°C. At the same time, this high temperature environment is used to burn CO in the sintering flue gas and decompose dioxins. The gas-solid separation device 5 is used to separate the bed material of the fluidized reactor, and the separated bed material is sent back to the reactor 4.

[0047] The upper part of the gas-solid separation device 5 is connected to the tail flue 7, and a flue gas preheater 31 and a mixed preheater 32 are arranged inside the tail flue 7. Specifically, a low-temperature heating surface 13, a feed water heater 21, a flue gas preheater 31 and a mixed preheater 32 are arranged in sequence inside the tail flue 7 along the flow direction, so as to absorb the heat of the flue gas in the tail flue 7 for recycling.

[0048] The flue gas generator 91 produces sintering flue gas. The flue gas generator 91 is connected to the flue gas booster fan 9. The flue gas booster fan 9 is connected to the flue gas preheater 31 and the mixed preheater 32 in two ways. The flue gas preheater 31 is connected to the middle and lower part of the reactor 4 through the secondary air duct 2. The air booster fan 10 is connected to the mixed preheater 32. The mixed preheater 32 is connected to the bottom wind chamber of the reactor 4 through the primary air duct 1.

[0049] The internal temperature of reactor 4 is 900℃, which is used to remove dioxins and CO from sintering flue gas. The reaction system adopts SNCR+SCR system to remove NO from sintering flue gas. X The reaction system adopts in-furnace + tail desulfurization to remove SO2 in sintering flue gas.

[0050] In this embodiment, the oxygen content of the sintering flue gas is 15.5%, the temperature of the main circulation loop is maintained at 900°C, the heat absorption ratio of the main circulation loop is 46%, the heat absorption ratio of the tail flue is 54%, the heat absorption ratio of the evaporation heating surface 11 in the main circulation loop is 38%, the gas-solid separation device 5 and the return valve 6 adopt an insulating structure, and the heat absorption ratio is 0; the heat absorption ratio of the high-temperature heating surface 14 is 8%. The heat absorption ratio of the remaining heating surfaces is designed as needed, and the geometric dimensions of the heating surfaces at each level are designed according to the heat absorption amount determined by the above heat absorption ratio and the layout position.

[0051] To ensure hydrodynamic safety, the evaporation heating surface 11 is a membrane water-cooled wall structure independent of the water-cooled intermediate partition wall or evaporation screen, with a mass flow rate of 550kg / m 2 ·s. The excess oxygen coefficient is 1.35. The primary air ratio is 45%, the bottom primary air (the air used for fluidized bed boiler combustion is usually primary air and secondary air. The bottom primary air is mainly used for fluidization of bed materials and provides a certain amount of oxygen for fuel combustion) ratio is 40%, the secondary air (the role of secondary air is to supplement the oxygen used for combustion and to disturb the flue gas in the furnace to strengthen the reaction) ratio is 55%, and the lower secondary air (the secondary air is divided into upper and lower secondary air, which is to control the NO generated by fuel combustion) ratio is 55%. X , the less secondary wind, NO X The less, but it has a negative impact on combustion and needs to be considered comprehensively) the proportion is 46%.

[0052] The sintering flue gas contains a certain amount of SO2, which will corrode the inside of the mixed preheater. Therefore, the mixed preheater 32 adopts an anti-corrosion material with internal enamel coating.

[0053] Sintering flue gas accounts for 55% of the total air consumption, all of which is sent to the reactor as secondary air, and primary air is air. The mixed preheater 32 is arranged downstream of the flue gas preheater 31.

[0054] The supercritical fluidized bed reactor of this embodiment is not only suitable for sintering flue gas, but also suitable for treating other low-oxygen flue gas containing dioxins, CO, NO X , SO2 waste gas.

[0055] Embodiment 3

[0056] refer to Figure 1 As shown, a supercritical fluidized bed reaction system for collaboratively treating flue gas is different from Example 2 in that sintering flue gas accounts for 80% of the total air volume, so sintering flue gas accounting for 55% of the total air volume is sent to the reactor as secondary air, and the remaining 25% of the sintering flue gas and 20% of the air are sent to the reactor as primary air, and the air distribution plate of reactor 4 adopts an anti-corrosion and anti-clogging wind hood.

[0057] The supercritical fluidized bed reactor of this embodiment is not only suitable for sintering flue gas, but also suitable for treating other low-oxygen flue gas containing dioxins, CO, NO X , SO2 waste gas.

[0058] The rest is the same as in the second embodiment.

[0059] The aforementioned basic examples and their further selected examples can be freely combined to form multiple embodiments, all of which are embodiments that can be adopted and claimed for protection in this application. In the scheme of this application, each selected example can be arbitrarily combined with any other basic examples and selected examples.

[0060] The above description is only a preferred embodiment of the present application and is not intended to limit the present application. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present application should be included in the protection scope of the present application.

Claims

1. A supercritical fluidized bed reaction system for collaboratively treating flue gas, comprising a reactor (4), characterized in that: The upper part of the reactor (4) is connected to the gas-solid separation device (5), the lower part of the gas-solid separation device (5) is connected to the return valve (6), the return valve (6) is connected to the middle and lower part of the reactor (4), the reactor (4), the gas-solid separation device (5) and the return valve (6) form a main circulation loop, the reactor (4) is provided with an evaporation heating surface (11) and a high-temperature heating surface (14), the upper part of the gas-solid separation device (5) is connected to the tail flue (7), and the tail flue (7) is provided with a flue gas preheating device (11). The smoke generator (91) is connected to the smoke booster fan (9), the smoke booster fan (9) is connected to the smoke preheater (31) and the mixed preheater (32), the smoke preheater (31) is connected to the middle and lower part of the reactor (4) through the secondary air duct (2), the air booster fan (10) is connected to the mixed preheater (32), and the mixed preheater (32) is connected to the bottom wind chamber of the reactor (4) through the primary air duct (1).

2. The supercritical fluidized bed reaction system for collaboratively treating flue gas according to claim 1, characterized in that: The fume generator (91) produces sintering fume.

3. The supercritical fluidized bed reaction system for collaboratively treating flue gas according to claim 1, characterized in that: The internal temperature of the reactor (4) is between 850 and 920°C, which is used to remove dioxins and CO from the flue gas; the reaction system adopts the SNCR+SCR system, which is used to remove NO from the flue gas. X ; The reaction system adopts furnace + tail desulfurization to remove SO2 in flue gas.

4. The supercritical fluidized bed reaction system for collaboratively treating flue gas according to claim 1 or 3, characterized in that: The temperature of the main circulation loop is maintained between 850 and 920°C, the heat absorption ratio of the main circulation loop is 40% to 50%; the heat absorption ratio of the tail flue is 50% to 60%; the heat absorption ratio of the evaporation heating surface (11) in the main circulation loop is 37% to 40%; the heat absorption ratio of the gas-solid separation device (5) and the return valve (6) is 0 to 2%; and the heat absorption ratio of the high-temperature heating surface (14) is 3% to 8%.

5. The supercritical fluidized bed reaction system for collaboratively treating flue gas according to claim 1, characterized in that: The evaporation heating surface (11) is a membrane water-cooled wall structure independent of the water-cooled intermediate partition wall or evaporation screen, and the mass flow rate is not less than 500kg / m 2 ·s.

6. The supercritical fluidized bed reaction system for collaboratively treating flue gas according to claim 1, characterized in that: The excess oxygen coefficient is between 1.25 and 1.

5.

7. The supercritical fluidized bed reaction system for collaboratively treating flue gas according to claim 1 or 6, characterized in that: The proportion of primary air is between 40% and 50%, the proportion of primary air at the furnace bottom does not exceed 40%, the proportion of secondary air is between 50% and 60%, and the proportion of lower secondary air does not exceed 50%.

8. The supercritical fluidized bed reaction system for collaboratively treating flue gas according to claim 1, characterized in that: The hybrid preheater (32) is made of an anti-corrosion material with internal enamel coating.

9. The supercritical fluidized bed reaction system for collaboratively treating flue gas according to claim 1, characterized in that: The sintering flue gas consumption of primary and secondary air is determined according to the ratio of flue gas to the total air consumption; the flue gas is preferentially used as secondary air and preheated by a flue gas preheater (31) before being sent to the reactor (4); when the sintering flue gas volume is large, the remaining flue gas is used as primary air and preheated by a mixed preheater (32) before being sent to the reactor (4).

10. The supercritical fluidized bed reaction system for collaboratively treating flue gas according to claim 1, characterized in that: The mixed preheater (32) is arranged downstream of the flue gas relative to the flue gas preheater (31); the low-temperature heating surface (13), the feed water heater (21), the flue gas preheater (31) and the mixed preheater (32) are arranged in sequence along the flow direction inside the tail flue (7).

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