Water pipe and fire pipe combined type waste heat boiler structure and waste heat recovery method

Abstract

The invention relates to a water pipe and fire pipe combined type waste heat boiler structure and a waste heat recovery method, the structure comprises a steam pocket, and further comprises a water pipe type evaporator arranged in a flue gas / coal gas high-temperature area and a fire pipe type economizer arranged in a flue gas / coal gas low-temperature area, and the water pipe type evaporator and the fire pipe type economizer are independently arranged; flue gas / coal gas sequentially flows through the water pipe type evaporator and the fire pipe type economizer and then is exhausted, the water pipe type evaporator absorbs heat of a high-temperature area of the flue gas / coal gas, and the fire pipe type economizer absorbs heat of a low-temperature area of the flue gas / coal gas. On the basis of the water pipe evaporator, the fire pipe type economizer is adopted, the waste heat utilization efficiency is improved, cost is saved, and efficient utilization of waste heat is achieved; the fire tube type economizer is located in a low-temperature area of smoke / coal gas, the heating intensity is small, the working environment is relatively good, tube plate crack accidents are not prone to occurring, and equipment operation is safe and reliable.

Description

Technical Field

[0001] The present invention relates to the technical field of coal gas / smoke waste heat utilization, and in particular to a water tube and fire tube combined waste heat boiler structure and a waste heat recovery method. Background Art

[0002] In industrial heating, smelting and other process production, energy such as oil, coal and natural gas are widely used, and these processes will produce different forms of secondary energy - waste heat. The emission of high-temperature coal gas or flue gas not only increases heat loss, but also damages and even pollutes the natural environment. With the gradual strengthening of energy-saving and environmental protection awareness, the exploration and research of high-temperature flue gas waste heat recovery has become a major research direction in the current environmental protection industry. Therefore, the utilization of flue gas waste heat is imperative.

[0003] Prior art 1: A pressurized waste heat boiler and heating method combining water tubes and fire tubes, which recovers high temperature positive pressure waste heat flue gas, mainly provides a combustion device with an inlet temperature of 800-500°C, a waste heat pressure generally between 0.3-0.5MPa, and dust-containing raw coal gas. It has the following disadvantages:

[0004] Disadvantage 1: In this technology, the fire tube boiler is used in the high-temperature flue gas area. The flue gas conditions at the upper and lower tube plates where the fire tubes are rooted are poor. Tube plate cracks are easily generated under high temperature, affecting the safe and stable operation of the equipment.

[0005] Disadvantage 2: This technology does not use threaded steel pipes in the fire tube boiler, the heat exchange intensity is relatively low, and the required equipment volume and floor space will increase.

[0006] Prior art 2: A modular sub-high temperature medium pressure vertical waste heat boiler using the tail gas generated by the combustion of an annular heating gasifier as the medium, including a drum, a high temperature superheater, a low temperature superheater, an evaporator I, an evaporator II, an evaporator III, an economizer, and an air preheater. This waste heat boiler is a single drum vertically placed, vertical π-shaped flue arranged natural circulation sub-high temperature medium pressure waste heat boiler, using 580℃ flue gas to generate sub-high temperature medium pressure steam, each heating surface component is modularly assembled in the factory and shipped, and connecting pipes, expansion joints, etc. are installed on the construction site. It has the following disadvantages:

[0007] Disadvantage 1: Economizer water pipes are arranged horizontally, which is easy to accumulate dust, affect heat transfer, reduce heat transfer coefficient, and reduce boiler thermal efficiency.

[0008] Disadvantage 2: The economizer structure is a water pipe structure, and the outer wall is sealed with fire-resistant and thermal insulation materials. The on-site construction period is long and the sealing is poor, which can easily cause air leakage into the flue gas system.

[0009] Prior art three: a self-deoxidizing and anti-corrosion calcining furnace waste gas waste heat boiler system, the system has a high-temperature flue gas inlet at the front end and a low-temperature flue gas outlet at the rear end, and a fire tube evaporator, a superheater, a water tube evaporator, an economizer and a deoxygenating evaporator are sequentially arranged in the system along the flue gas flow direction. It has the following disadvantages: in the fire tube evaporator, the fire tube is arranged horizontally, which is easy to accumulate dust, affect heat transfer, reduce the heat exchange coefficient, and cause the furnace to stop in serious cases, affecting safe and stable operation.

[0010] Prior art 4: A vertical water-fire tube waste heat boiler with a vertically distributed furnace body, and the following components arranged in the furnace body and arranged in sequence from bottom to top: a water drum, in which a fluid is stored; a smoke inlet and outlet chamber, in which a membrane wall is arranged, and the smoke inlet and outlet chamber is divided into two chambers by a connected membrane wall partition wall; an evaporator, which includes an evaporator cylinder and two groups of vertically arranged threaded smoke pipes arranged in the evaporator cylinder; a smoke rotating chamber, which is respectively connected to the two groups of threaded smoke pipes to achieve the circulation and rotation of smoke; a steam drum, in which the upper end of the membrane wall structure of the rotating chamber passes through the bottom wall of the steam drum, and a steam outlet for extracting steam is provided on the steam drum. It has the following disadvantages:

[0011] Disadvantage 1: The water-fire tube boiler is an integrated type and is not suitable for use in working environments with certain height restrictions.

[0012] Disadvantage 2: The fire tube tube sheet operates in a high temperature environment, which is prone to tube sheet crack accidents, affecting the safe use of the equipment.

[0013] Disadvantage 3: The flue gas flows in the evaporator in a double process, and there is a large temperature difference in the lower tube plate, which causes uneven heating of the lower tube plate, affecting the safe use of the equipment. At the same time, the water side of the double process is heated disorderly and the outlet temperature of the water side is uneven.

[0014] Therefore, the inventor, relying on many years of experience and practice in related industries, proposes a water tube and fire tube combined waste heat boiler structure and a waste heat recovery method to overcome the defects of the prior art. Summary of the invention

[0015] The purpose of the present invention is to provide a water tube and fire tube combined waste heat boiler structure and a waste heat recovery method to solve the problems of low heat exchange efficiency and poor safety in the prior art. The present invention combines the water tube heating surface structure with the fire tube heating surface structure, that is, on the basis of the water tube evaporator, a fire tube economizer is adopted. The water tube evaporator absorbs heat from the high temperature zone of the flue gas / coal gas, and the fire tube economizer absorbs heat from the low temperature zone of the flue gas / coal gas, thereby improving the utilization efficiency of waste heat, saving costs, and realizing efficient utilization of waste heat; the fire tube economizer is in the low temperature zone of the flue gas / coal gas, the heating intensity is small, the working environment is relatively good, it is not easy to cause tube plate crack accidents, and the equipment operation is safe and reliable.

[0016] The objective of the present invention is achieved in this way. A water tube and fire tube combined waste heat boiler structure includes a steam drum, a water tube evaporator arranged in the high temperature zone of the flue gas / coal gas, and a fire tube economizer arranged in the low temperature zone of the flue gas / coal gas, wherein the water tube evaporator and the fire tube economizer are arranged independently of each other; wherein the flue gas / coal gas flows through the water tube evaporator and the fire tube economizer in sequence and is then discharged, the water tube evaporator absorbs heat from the high temperature zone of the flue gas / coal gas, and the fire tube economizer absorbs heat from the low temperature zone of the flue gas / coal gas.

[0017] In a preferred embodiment of the present invention, the water-tube evaporator includes a first flue and a first heat exchange medium channel, and the fire-tube economizer includes a second flue and a second heat exchange medium channel, the first flue is connected to the second flue; both ends of the first heat exchange medium channel are respectively connected to the steam drum, the outlet of the second heat exchange medium channel is connected to the steam drum, and the inlet of the second heat exchange medium channel is used to connect to the medium supply part.

[0018] In a preferred embodiment of the present invention, the second flue of the fire-tube economizer is vertically arranged, and both ends of the second flue are respectively connected to the tube sheet.

[0019] In a preferred embodiment of the present invention, the second flue adopts a threaded smoke pipe structure to increase airflow disturbance and increase the residence time of smoke / coal gas in the second flue.

[0020] In a preferred embodiment of the present invention, the fire tube economizer includes a second outer shell, and the second heat exchange medium channel is penetrated in the second outer shell; the inner cavity of the second outer shell constitutes the second heat exchange medium channel, and the inlet of the second heat exchange medium channel and the outlet of the second heat exchange medium channel are arranged on the side wall of the second outer shell, and the outlet of the second heat exchange medium channel is located above the inlet of the second heat exchange medium channel.

[0021] In a preferred embodiment of the present invention, the outlet of the second heat exchange medium channel is connected to the steam drum through a water supply outlet pipe; the inlet of the second heat exchange medium channel is used to connect to the medium supply part through a water supply inlet pipe.

[0022] In a preferred embodiment of the present invention, the water-tube evaporator includes a first outer shell, the inner cavity of the first outer shell constitutes the first flue; the first heat exchange medium channel is arranged in the first outer shell, the inlet of the first heat exchange medium channel is connected to the steam drum through a downcomer, and the outlet of the first heat exchange medium channel is connected to the steam drum through a riser.

[0023] In a preferred embodiment of the present invention, a water pipe bundle is arranged in the first shell, the water pipe bundle constitutes the first heat exchange medium channel, and the high-temperature gas or flue gas flowing through the inner cavity of the first shell flushes the water pipe bundle to perform heat exchange.

[0024] In a preferred embodiment of the present invention, the first flue is connected to the second flue through a transition section flue.

[0025] The object of the present invention can also be achieved in this way. A waste heat recovery method is implemented using the aforementioned water tube and fire tube combined waste heat boiler structure; it includes: high-temperature flue gas / coal gas enters the first flue of the water tube evaporator, exchanges heat with the heat exchange medium in the first heat exchange medium channel of the water tube evaporator, the cooled flue gas / coal gas continues to flow through the second flue of the fire tube economizer, and exchanges heat with the heat exchange medium in the second heat exchange medium channel of the fire tube economizer; the flue gas / coal gas cooled by two heat exchanges is discharged from the water tube and fire tube combined waste heat boiler structure.

[0026] As described above, the water tube and fire tube combined waste heat boiler structure and waste heat recovery method of the present invention have the following beneficial effects:

[0027] The present invention combines the water tube heating surface structure with the fire tube heating surface structure, that is, on the basis of the water tube evaporator, a fire tube economizer is adopted. The water tube evaporator absorbs the heat in the high temperature zone of the flue gas / coal gas, and the fire tube economizer absorbs the heat in the low temperature zone of the flue gas / coal gas. The waste heat recovery is realized through two forms of heat exchange, and the waste heat of the high temperature flue gas / coal gas is efficiently recovered. The thermal efficiency of the whole system is improved by reducing the exhaust temperature. The fire tube economizer of the present invention is under the low temperature condition of the flue gas / coal gas, and it is not easy to produce tube plate crack accidents. The operation is safe and reliable, and the service life is longer. The fire tube economizer has good sealing performance and no external air leakage, which can ensure the high quality of coal gas and flue gas. The water tube evaporator and the fire tube economizer of the present invention adopt a split structure, and different layout structures can be adopted to cope with different working environments. The present invention can effectively realize the waste heat recovery and utilization of medium and high temperature coal gas or flue gas, and achieve energy saving and emission reduction. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] The following drawings are only intended to illustrate and explain the present invention, and are not intended to limit the scope of the present invention.

[0029] in:

[0030] Figure 1 It is a schematic diagram of the water tube and fire tube combined waste heat boiler structure of the present invention.

[0031] In the figure:

[0032] 1. Steam drum;

[0033] 2. Water tube evaporator;

[0034] 3. Fire tube economizer;

[0035] 4. Water supply outlet pipe;

[0036] 5. Water supply inlet pipeline;

[0037] 6. Transition section flue;

[0038] 7. Downcomer;

[0039] 8. Riser. DETAILED DESCRIPTION

[0040] In order to have a clearer understanding of the technical features, purposes and effects of the present invention, specific embodiments of the present invention are now described with reference to the accompanying drawings.

[0041] The specific embodiments of the present invention described herein are only used to explain the purpose of the present invention and cannot be understood as limiting the present invention in any way. Under the guidance of the present invention, technicians can conceive of any possible variations based on the present invention, which should be considered to belong to the scope of the present invention. It should be noted that when an element is referred to as "arranged on" another element, it can be directly on the other element or there can also be a central element. When an element is considered to be "connected" to another element, it can be directly connected to the other element or there may be a central element at the same time. The terms "installed", "connected" and "connected" should be understood in a broad sense, for example, it can be a mechanical connection or an electrical connection, or it can be the internal communication of two elements, it can be directly connected, or it can be indirectly connected through an intermediate medium. For ordinary technicians in this field, the specific meanings of the above terms can be understood according to the specific circumstances. The terms "vertical", "horizontal", "up", "down", "left", "right" and similar expressions used herein are only for illustrative purposes and do not represent the only implementation method.

[0042] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those generally understood by those skilled in the art to which this application belongs. The terms used herein in the specification of this application are only for the purpose of describing specific embodiments and are not intended to limit this application. The term "and / or" used herein includes any and all combinations of one or more related listed items.

[0043] like Figure 1As shown, the present invention provides a water tube and fire tube combined waste heat boiler structure, including a steam drum 1. The present invention also includes a water tube evaporator 2 arranged in the high temperature zone of the flue gas / coal gas and a fire tube economizer 3 arranged in the low temperature zone of the flue gas / coal gas. The high temperature and low temperature in this article are relative descriptions. The temperature of the flue gas / coal gas passing through the water tube evaporator 2 is higher than the temperature of the flue gas / coal gas passing through the fire tube economizer 3. In a specific embodiment, the temperature of the flue gas / coal gas in the high temperature zone is greater than or equal to 350°C, and the temperature of the flue gas / coal gas in the low temperature zone is less than 350°C; the water tube evaporator 2 and the fire tube economizer 3 are independently arranged; wherein, the flue gas / coal gas flows through the water tube evaporator 2 and the fire tube economizer 3 in sequence and is discharged, the water tube evaporator 2 absorbs the heat of the high temperature zone (high temperature section) of the flue gas / coal gas, and the fire tube economizer 3 absorbs the heat of the low temperature zone (low temperature section) of the flue gas / coal gas. The fire-tube economizer 3 is arranged after the water-tube evaporator 2. The fire-tube economizer 3 is in the low-temperature area of ​​the flue gas / coal gas, with low heat intensity and relatively good working environment. It is not easy to cause tube sheet crack accidents, and the equipment runs safely and reliably.

[0044] When the flue gas / coal gas in the high temperature zone (high temperature section) passes through the water tube evaporator 2, it exchanges heat with its internal heat exchange medium (low temperature water from the drum), and the temperature of the flue gas / coal gas decreases. Its high temperature heat heats the low temperature heat exchange medium from the drum 1 into high temperature steam and then returns to the drum 1 to be delivered to the heat user; after being cooled by the water tube evaporator 2, the temperature of the flue gas / coal gas in the low temperature zone (low temperature section) continues to decrease after passing through the fire tube economizer 3. The heat absorbed by the fire tube economizer 3 heats its internal heat exchange medium (cold water) into hot water and delivers it to the drum 1. The present invention realizes waste heat recovery through two forms of heat exchange.

[0045] The present invention combines the water tube heating surface structure with the fire tube heating surface structure, that is, a fire tube economizer 3 is used on the basis of the water tube evaporator 2. The water tube evaporator 2 absorbs the heat in the high temperature zone of the flue gas / coal gas, and the fire tube economizer 3 absorbs the heat in the low temperature zone of the flue gas / coal gas. The waste heat recovery is realized through two forms of heat exchange, and the waste heat of the high temperature flue gas / coal gas is efficiently recovered. The thermal efficiency of the whole system is improved by reducing the exhaust temperature. The fire tube economizer 3 of the present invention is in the low temperature condition of the flue gas / coal gas, and it is not easy to produce tube plate crack accidents. The operation is safe and reliable, and the service life is longer. The fire tube economizer 3 has good structural sealing, no external air leakage, and can ensure the high quality of coal gas and flue gas. The water tube evaporator 2 and the fire tube economizer 3 of the present invention adopt a split structure, and different layout structures can be adopted to cope with different working environments.

[0046] Furthermore, the water-tube evaporator 2 includes a first flue and a first heat exchange medium channel, the fire-tube economizer 3 includes a second flue and a second heat exchange medium channel, the first flue is connected to the second flue; both ends of the first heat exchange medium channel are respectively connected to the steam drum 1, the outlet of the second heat exchange medium channel is connected to the steam drum 1, and the inlet of the second heat exchange medium channel is connected to the medium supply part.

[0047] Furthermore, the second flue of the fire-tube economizer 3 is vertically arranged, and both ends of the second flue are connected to the tube sheet respectively. The second flue is vertically arranged, and ash is not easy to accumulate in the second flue (flue pipe).

[0048] The fire tube economizer 3 recovers the heat of low-temperature coal gas or flue gas. It is arranged vertically. The flue gas or coal gas is constantly flushed to play a self-cleaning role. The heating surface is not easy to accumulate dust. A high flow rate can be appropriately used to improve the heat exchange efficiency and save costs. The flue gas / coal gas goes inside the second flue, without external air leakage, which can ensure the high quality of coal gas or flue gas and avoid the risk of explosion.

[0049] The working environment of the fire tube economizer 3 is relatively good, which reduces the possibility of cracks between the second flue (smoke tube, fire tube) and the tube plate, and is safer and more reliable to use.

[0050] Furthermore, the second flue adopts a threaded smoke pipe structure to increase airflow disturbance and increase the residence time of smoke / coal gas in the second flue, thereby increasing the heat exchange coefficient, improving the heat exchange efficiency and saving manufacturing costs.

[0051] Furthermore, the fire tube economizer 3 includes a second outer shell, and a second heat exchange medium channel is penetrated in the second outer shell; the inner cavity of the second outer shell constitutes the second heat exchange medium channel, and the inlet and outlet of the second heat exchange medium channel are arranged on the side wall of the second outer shell, and the outlet of the second heat exchange medium channel is located above the inlet of the second heat exchange medium channel.

[0052] The second outer shell is a steel cylinder with cooling water inside. The outer wall temperature is low, which saves outer wall insulation materials, does not require refractory materials, and has low insulation costs.

[0053] Further, if Figure 1 As shown, the outlet of the second heat exchange medium channel is connected to the steam drum through the water supply outlet pipe 4; the inlet of the second heat exchange medium channel is connected to the medium supply part through the water supply inlet pipe 5.

[0054] The fire tube economizer 3 adopts a vertical fire tube (threaded smoke tube) structure. The upper and lower parts of the fire tube are respectively connected to the tube plate. The water side adopts a steel cylinder. The fire tube is a threaded steel pipe. The coal gas or flue gas flows inside the pipe, and the low-temperature water flows outside the pipe on the inside of the second outer shell (steel cylinder). When the flue gas passes through the fire tube economizer 3, it exchanges heat with the cold water in the second heat exchange medium channel, absorbs the heat in the flue gas or coal gas, reduces the temperature of the flue gas or coal gas, and improves the thermal efficiency of the waste heat boiler.

[0055] The coal gas from the fire tube economizer 3 enters the subsequent process after being cooled, and is sent to the gas tank and other equipment through the fan for storage and utilization. The flue gas from the fire tube economizer 3 is discharged into the atmosphere after being purified.

[0056] The flue gas / coal gas flows in the fire tube economizer 3 in a single flow path, and the flow path is simple and clear, and uneven heating of the tube sheet and uneven outlet temperature on the water side are not likely to occur.

[0057] Further, if Figure 1 As shown, the water-tube evaporator 2 includes a first outer shell, the inner cavity of which constitutes a first flue; a first heat exchange medium channel is arranged in the first outer shell, the inlet of the first heat exchange medium channel is connected to the steam drum 1 through the downcomer 7, and the outlet of the first heat exchange medium channel is connected to the steam drum 1 through the upcomer 8.

[0058] Furthermore, a water pipe bundle is arranged in the first shell. In one embodiment, the water pipe bundle adopts a serpentine pipe structure. The water pipe bundle constitutes a first heat exchange medium channel. The high-temperature gas or flue gas flowing through the inner cavity of the first shell flushes the water pipe bundle to perform heat exchange.

[0059] Further, if Figure 1 As shown, the first flue is connected to the second flue through the transition section flue 6. During the flow of flue gas / coal gas, due to flow reversal and other reasons, dust in the flue gas / coal gas falls into the transition section flue 6 between the water tube evaporator 2 and the fire tube economizer 3, and the dust can be recycled, while reducing the emission of smoke dust to meet the emission requirements.

[0060] The present invention provides a waste heat recovery method, which is implemented using the aforementioned water tube and fire tube combined waste heat boiler structure; it includes: high-temperature flue gas / coal gas enters the first flue of the water tube evaporator 2, exchanges heat with the heat exchange medium in the first heat exchange medium channel of the water tube evaporator 2, the cooled flue gas / coal gas continues to flow through the second flue of the fire tube economizer 3, and exchanges heat with the heat exchange medium in the second heat exchange medium channel of the fire tube economizer 3; the flue gas / coal gas cooled by the second heat exchange is discharged from the water tube and fire tube combined waste heat boiler structure.

[0061] The temperature of the heat exchange medium exchanged by the fire-tube economizer 3 is lower than the temperature of the heat exchange medium exchanged by the water-tube evaporator 2, that is, the medium supply part supplies cold water to the second heat exchange medium channel, and the cold water in the second heat exchange medium channel is heated by the low-temperature flue gas / coal gas to form hot water and flows to the drum 1; the hot water in the drum 1 flows to the first heat exchange medium channel of the water-tube evaporator 2, and the hot water in the first heat exchange medium channel is heated by the high-temperature flue gas / coal gas to form high-temperature steam and flows to the drum 1, and the high-temperature steam is transported to the heat user;

[0062] As described above, the water tube and fire tube combined waste heat boiler structure and waste heat recovery method of the present invention have the following beneficial effects:

[0063] The present invention combines a water tube heating surface structure with a fire tube heating surface structure, that is, on the basis of a water tube evaporator, a fire tube economizer is used, and waste heat recovery is achieved through two forms of heat exchange, and high-temperature flue gas / coal gas waste heat is efficiently recovered, and the thermal efficiency of the entire system is improved by lowering the exhaust temperature. The fire tube economizer of the present invention is under low temperature conditions of flue gas / coal gas, and is not prone to tube sheet crack accidents. It is safe and reliable to operate and has a longer service life. The fire tube economizer has good sealing properties and no external air leakage, which can ensure the high quality of coal gas and flue gas. The water tube evaporator and the fire tube economizer of the present invention adopt a split structure, and different layout structures can be adopted to cope with different operating environments. The present invention can effectively realize the waste heat recovery and utilization of medium and high temperature coal gas or flue gas, and achieve energy conservation and emission reduction.

[0064] The above description is only an illustrative embodiment of the present invention and is not intended to limit the scope of the present invention. Any equivalent changes and modifications made by any person skilled in the art without departing from the concept and principle of the present invention shall fall within the scope of protection of the present invention.

Claims

1. A water tube and fire tube combined waste heat boiler structure, including a steam drum, characterized in that: It also includes a water-tube evaporator arranged in the high-temperature zone of the flue gas / coal gas and a fire-tube economizer arranged in the low-temperature zone of the flue gas / coal gas, and the water-tube evaporator and the fire-tube economizer are arranged independently of each other; wherein, the flue gas / coal gas flows through the water-tube evaporator and the fire-tube economizer in sequence and is then discharged, the water-tube evaporator absorbs heat from the high-temperature zone of the flue gas / coal gas, and the fire-tube economizer absorbs heat from the low-temperature zone of the flue gas / coal gas.

2. The water tube and fire tube combined waste heat boiler structure according to claim 1, characterized in that: The water-tube evaporator includes a first flue and a first heat exchange medium channel, and the fire-tube economizer includes a second flue and a second heat exchange medium channel, the first flue is connected to the second flue; both ends of the first heat exchange medium channel are respectively connected to the steam drum, the outlet of the second heat exchange medium channel is connected to the steam drum, and the inlet of the second heat exchange medium channel is used to connect to the medium supply part.

3. The water tube and fire tube combined waste heat boiler structure according to claim 2, characterized in that: The second flue of the fire-tube economizer is vertically arranged, and both ends of the second flue are respectively connected to the tube sheet.

4. The water tube and fire tube combined waste heat boiler structure according to claim 3, characterized in that: The second flue adopts a threaded smoke pipe structure to increase airflow disturbance and increase the residence time of smoke / coal gas in the second flue.

5. The water tube and fire tube combined waste heat boiler structure according to claim 4, characterized in that: The fire tube economizer includes a second shell, and the second heat exchange medium channel is penetrated in the second shell; the inner cavity of the second shell constitutes the second heat exchange medium channel, and the inlet of the second heat exchange medium channel and the outlet of the second heat exchange medium channel are arranged on the side wall of the second shell, and the outlet of the second heat exchange medium channel is located above the inlet of the second heat exchange medium channel.

6. The water tube and fire tube combined waste heat boiler structure according to claim 5, characterized in that: The outlet of the second heat exchange medium channel is connected to the steam drum through a water supply outlet pipe; the inlet of the second heat exchange medium channel is used to connect to the medium supply part through a water supply inlet pipe.

7. The water tube and fire tube combined waste heat boiler structure according to claim 2, characterized in that: The water-tube evaporator includes a first shell, the inner cavity of which constitutes the first flue; the first heat exchange medium channel is arranged in the first shell, the inlet of the first heat exchange medium channel is connected to the steam drum through a downcomer, and the outlet of the first heat exchange medium channel is connected to the steam drum through a riser.

8. The water tube and fire tube combined waste heat boiler structure according to claim 7, characterized in that: A water pipe bundle is arranged in the first shell, and the water pipe bundle constitutes the first heat exchange medium channel. High-temperature gas or flue gas flowing through the inner cavity of the first shell flushes the water pipe bundle to perform heat exchange.

9. The water tube and fire tube combined waste heat boiler structure according to claim 2, characterized in that: The first flue is connected to the second flue through a transition section flue.

10. A waste heat recovery method, characterized in that: The water tube and fire tube combined waste heat boiler structure as described in any one of claims 2 to 9 is adopted for implementation; comprising: high-temperature flue gas / coal gas enters the first flue of the water tube evaporator, exchanges heat with the heat exchange medium in the first heat exchange medium channel of the water tube evaporator, the cooled flue gas / coal gas continues to flow through the second flue of the fire tube economizer, and exchanges heat with the heat exchange medium in the second heat exchange medium channel of the fire tube economizer; the flue gas / coal gas cooled by two heat exchanges is discharged from the water tube and fire tube combined waste heat boiler structure.

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