A boiler for a corrosion-resistant flue gas waste heat recovery device

Abstract

This invention provides a boiler with a corrosion-resistant flue gas waste heat recovery device. The boiler includes a horizontal flue, within which the flue gas waste heat recovery device is installed. The device includes a flue gas cooling mechanism, dividing the cooling pipes into an upstream and downstream section along the flue gas flow direction. The upstream and downstream cooling pipes are made of different materials; the downstream cooling pipes have stronger corrosion resistance than the upstream cooling pipes. This invention addresses the issue of low-temperature corrosion due to the need for condensate in the downstream section. By separating the upstream and downstream cooling pipes and using different materials for different situations, the cost can be significantly reduced while efficiently absorbing waste heat and recovering water.

Description

Technical Field

[0001] The invention relates to a method and a device for utilizing waste heat of flue gas, and mainly relates to the technical field of heat exchange of waste heat boilers or heat exchangers. Background Art

[0002] In reality, steel mills, cement plants, etc., there are technical problems of energy saving and waste heat utilization. Therefore, how to use the exhaust flue gas to recover heat energy with the highest efficiency is a topic that technicians are constantly reforming. In the steel production process, the energy consumption of the sintering process accounts for about 10% of the total energy consumption, second only to the ironmaking process. In the total energy consumption of the sintering process, nearly 50% of the heat energy is discharged into the atmosphere in the form of sensible heat of sintering machine flue gas and cooler exhaust gas. Since the temperature of the sintering cooler exhaust gas is not high, this part of the heat is usually not recovered, or only a simple heat exchanger is used to absorb the waste heat, which not only has low recovery efficiency, but also generates less steam.

[0003] The current flue gas waste heat utilization technology usually mixes two or more flue gases of different temperatures in advance and then enters the waste heat boiler or heat exchanger for heat exchange. This method does not fully utilize the high-quality heat of the high-temperature flue gas, resulting in a very low energy utilization rate of the flue gas.

[0004] The Chinese invention patent with the publication number CN101017059A discloses a method and device for utilizing flue gas waste heat, which separates multiple flue gases of different temperatures into a waste heat boiler or heat exchanger through channels / inlets, and cools the high-temperature flue gas through a high-temperature heat exchange surface / zone / cavity. When the temperature drops to the same temperature as the low-temperature flue gas, the high-temperature flue gas is mixed and flows through the low-temperature heat exchange surface together, so that the waste heat of flue gases of different temperatures can be recycled to the maximum extent. The invention method is to separate multiple flue gases of different temperatures into channels to enter a boiler or heat exchanger, and cool the high-temperature flue gas through a high-temperature heat exchange surface / zone / cavity. When the temperature drops to the same temperature as the low-temperature flue gas, the high-temperature flue gas is mixed, wherein the temperature difference between the high and low-temperature flue gases is greater than 50°C, so that the waste heat of the flue gas can be recycled to the maximum extent. The present invention also includes a device for realizing the above method, which is composed of a high-temperature flue gas inlet, a low-temperature flue gas inlet, a high-temperature heat exchange surface / zone / cavity, a low-temperature heat exchange surface / zone / cavity, a mixed heat exchange surface / zone / cavity and a flue gas discharge port. The Chinese invention patent application with publication number CN101598506A discloses a hot and cold water exchange device using waste heat from exhaust gas. It includes an exhaust gas pool, an air intake pipe and a heating water pipe. The exhaust gas pool is inserted with the air intake pipe, hot exhaust gas is passed through the air intake pipe, and the heating water pipe is a multi-channel spirally curved circulating water pipe. The two ends of the heating water pipe extend from the exhaust gas pool (1), one end is a water inlet, and the other end is a water outlet. The exhaust gas pool is filled with water, and the air outlet of the air intake pipe and the circulating water pipe are immersed under the water surface. The Chinese invention patent with publication number CN105485915A discloses a flue gas waste heat recovery device for oil-fired and gas-fired boilers to solve the problem that the existing flue gas waste heat recovery device occupies a large area and is difficult to install. The support pipe, inner wall and outer wall are coaxially arranged from inside to outside, the inner chamber is between the support pipe and the inner wall, the outer chamber is between the inner wall and the outer wall, the economizer annular header is arranged at the upper end of the inner wall and the outer wall, the bottom flue is arranged at the lower end of the inner wall and the outer wall, the lower end of the smoke outlet is communicated with the inner chamber, and the upper end is communicated with the atmosphere, the inner ring side wall of the economizer annular header is provided with an annular smoke inlet communicated with the smoke inlet channel, the upper end of the economizer tube bundle is communicated with the economizer annular header, and the lower end is communicated with the bottom flue, the upper end of the light tube air preheater tube bundle is communicated with the smoke outlet, and the lower end is communicated with the bottom flue, a plurality of inner chamber flue baffles are spirally arranged in the inner chamber from top to bottom, and a plurality of outer chamber flue baffles are spirally arranged between the upper tube plate and the lower tube plate in the outer chamber from bottom to top. The present invention is used for oil and gas boilers.

[0005] The above invention realizes the flue gas waste heat recovery and utilization boiler, and the principle is feasible, but there are still the following problems: 1. The boiler flue system requires large modifications and high investment, which increases the footprint of the flue gas treatment system; 2. The system has many devices, complex structures, high control difficulties, and high operating failure rates; 3. Multiple water pumps are installed in the system, which increases the system energy consumption and wet flue gas water recovery costs; 4. There is a lack of recovery of water vapor in the flue gas. Summary of the invention

[0006] In view of the shortcomings of the prior art, the present invention provides a boiler equipped with a low-energy flue gas waste heat recovery device. The device transforms the horizontal flue of the boiler and uses the heat of the saturated wet flue gas itself to achieve natural convection between ambient air and saturated wet flue gas without generating additional energy consumption, thereby cooling the saturated wet flue gas and achieving the purpose of saturated wet flue gas waste heat and water recovery. The device can reduce the investment and operating costs of the flue gas waste heat recovery process.

[0007] In order to achieve the above object, the technical solution of the present invention is as follows:

[0008] A boiler with a corrosion-resistant flue gas waste heat recovery device, the boiler comprises a horizontal flue, a flue gas waste heat recovery device is arranged in the horizontal flue, the flue gas waste heat recovery device comprises a flue gas cooling mechanism, the cooling mechanism comprises a cooling pipe arranged in a vertical direction, the upper and lower ends of the cooling pipe are respectively connected to a cooling pipe convergence plate and pass through the tube holes of the cooling pipe convergence plate, air enters from the tube holes at the lower end of the cooling pipe and flows out from the tube holes at the upper end by natural convection, the flue gas exchanges heat with the cooling pipe through the cooling pipe; along the flue gas flow direction, the cooling pipe is divided into an upstream part and a downstream part, the cooling pipe materials of the upstream part and the downstream part are different; the corrosion resistance of the downstream cooling pipe is stronger than that of the upstream cooling pipe.

[0009] As an improvement, the corrosion resistance of the cooling pipes in the downstream part along the flow direction of the flue gas is getting better and better.

[0010] As an improvement, by separating the upstream cooling pipe from the downstream cooling pipe, the upstream cooling pipe and the downstream cooling pipe can be replaced separately.

[0011] As an improvement, the upstream part can make full use of waste heat, which can greatly improve the efficiency of waste heat utilization and output high-temperature air. The downstream can utilize waste heat and recover water to output low-temperature air. It can realize waste heat utilization at different temperatures and output air at different temperatures. At the same time, the waste heat utilization and water recovery can also be separated.

[0012] As an improvement, a plurality of flue gas cooling pipes are fixed to a cooling pipe bundling plate to form a flue gas cooling mechanism; the flue gas cooling mechanism is inserted from the upper wall of the horizontal flue of the boiler so that the flue gas cooling pipes pass through the horizontal flue of the boiler, and the cooling pipe bundling plate is assembled and connected to the upper wall of the horizontal flue of the boiler using a flange.

[0013] As an improvement, the drain outlet is located at the geometric center of the bottom surface of the condensate collection tank and is connected to the outside through pipes and valves to discharge the condensate.

[0014] Compared with the prior art, the present invention has the following advantages:

[0015] 1. The present invention separates the upstream and downstream cooling pipes so that different materials can be set according to different situations, which can greatly reduce the cost while absorbing waste heat and recycling water with high efficiency.

[0016] 2. Small transformation and simple structure: The present invention is based on the flue gas indirect condensation technology, and only the original horizontal flue of the boiler is transformed, with a small investment. Compared with the existing technology, there is no need to add equipment such as spray towers, and the area occupied by the flue gas treatment system will not be increased.

[0017] 3. Low energy consumption: The present invention utilizes the heat of saturated wet flue gas to drive the ambient air to have natural convection with it, thereby realizing the waste heat recovery of wet flue gas and water recovery. Compared with the prior art, it does not require the use of energy-consuming equipment such as water pumps, thus reducing the cost of recovering water from wet flue gas.

[0018] 4. The present invention changes the distribution density of the downstream cooling pipes, so that the overall water distribution is uniform, avoiding the situation where some of the water on the cooling pipes are dry and some are too much, thereby ensuring the service life of the pipes and sufficient condensation and recovery of water. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 , Figure 2 This is a schematic diagram of the structure of the invented low-energy wet flue gas heat recovery device.

[0020] Figure 3 It is a schematic diagram of the cooling tube bundling plate structure and the arrangement of the flue gas cooling tubes of the present invention.

[0021] Figure 4 It is a schematic diagram of the condensed water collection mechanism of the present invention.

[0022] Figure 5 Schematic diagram of flue gas condensation mechanism.

[0023] Figure 6 It is a schematic diagram of the structure of the present invention installed on the horizontal flue of a boiler.

[0024] The reference numerals in the accompanying drawings are as follows:

[0025] 1: Cooling pipe convergence plate; 2: Condensate collection tank; 3: Flue gas cooling pipe; 3-1: Air inlet; 3-2: Air outlet; 4: Drain outlet; 5: Boiler horizontal flue; 5-1: Flue gas inlet; 5-2: Flue gas outlet. DETAILED DESCRIPTION

[0026] The specific implementation modes of the present invention are described in detail below with reference to the accompanying drawings.

[0027] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0028] It should be noted that all directional indications (such as up, down, etc.) in the embodiments of the present invention are only used to explain the relative position relationship, movement status, etc. between the components under a certain specific posture (as shown in the accompanying drawings). If the specific posture changes, the directional indication will also change accordingly.

[0029] In addition, in the present invention, the descriptions such as "first", "second", etc. are only used for descriptive purposes and cannot be understood as indicating or implying their relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" or "second" may explicitly or implicitly include at least one of the features.

[0030] Furthermore, the technical solutions between the various embodiments of the present invention may be combined with each other, but this must be based on the fact that they can be implemented by ordinary technicians in the field. When the combination of technical solutions is mutually contradictory or cannot be implemented, it should be deemed that such combination of technical solutions does not exist and is not within the scope of protection required by the present invention.

[0031] A boiler provided with a low-energy consumption flue gas waste heat recovery device, the boiler comprising a horizontal flue 5, the horizontal flue 5 being provided with a flue gas waste heat recovery device, the flue gas waste heat recovery device being as Figure 1 As shown, it includes a flue gas cooling mechanism, which includes a cooling pipe 3 arranged in a vertical direction. The upper and lower ends of the cooling pipe 3 are respectively connected to the cooling pipe bundling plate 1 and pass through the tube holes of the cooling pipe bundling plate 1. Air enters from the tube holes at the lower end of the cooling pipe and flows out from the tube holes at the upper end by natural convection. The flue gas passes through the cooling pipe to exchange heat with the cooling pipe.

[0032] The invention has small modification and simple structure. It is based on flue gas indirect condensation technology and only requires modification on the original horizontal flue of the boiler, so the investment is small. Compared with the prior art, there is no need to add equipment such as spray towers, and the area occupied by the flue gas treatment system will not be increased.

[0033] As an improvement, Figure 6As shown, the convergence plate at the upper end of the cooling tube is arranged on the outer surface of the upper end of the flue, and the convergence plate at the lower end of the cooling tube is a box structure, the upper side of the box is open, and the other sides are closed, and the lower side of the box is arranged on the outer surface of the lower end of the flue, a certain distance away from the outer surface of the lower end, and the lower surface of the box is provided with pipe holes, and the middle part of the lower surface of the box is provided with a drain outlet 4.

[0034] The Chinese invention patents with publication numbers CN 110124465 B, CN 111974177 A, and CN 110124500 B all use a water collection tower combined with condensed water circulation to achieve wet flue gas water recovery and utilization, which is feasible in principle. However, the following problems still exist: 1. The boiler flue system requires large modifications, high investment, and increases the floor space of the flue gas treatment system. 2. There are many devices in the system, the structure is complex, the control is difficult, and the operating failure rate is high. 3. Multiple water pumps are set in the system, which increases the system energy consumption and the cost of wet flue gas water recovery.

[0035] The present invention is provided with a flue gas water condensation recovery device, which has small modification and simple structure. The present invention is based on the flue gas indirect condensation technology, and only the original horizontal flue of the boiler is modified, so the investment is small. Compared with the prior art, there is no need to add equipment such as a spray tower, and the floor space of the flue gas treatment system will not be increased. It can realize the recovery of waste heat and the recovery of water in humid air at the same time. It is a great improvement over the recovery system of the prior art.

[0036] As an improvement, the interior of the several flue gas cooling tubes 3 is an air flow channel, the bottom end is an air inlet, the top end is an air outlet, and runs through the flue.

[0037] As an improvement, the temperature of the wet flue gas is 50℃~55℃, the relative humidity is 100%, and the temperature difference between the ambient air and the wet flue gas is 35℃~80℃.

[0038] As an improvement, the cooling pipe 3 is divided into an upstream part and a downstream part along the flue gas flow direction, and the box structure (condensate recovery box) is arranged in the downstream part. The air in the upstream cooling pipe exchanges heat with the flue gas by forced convection, and the air in the downstream part exchanges heat with the flue gas by natural convection.

[0039] The present invention divides the cooling pipe into two parts. The upstream part fully utilizes the waste heat, which can greatly improve the waste heat utilization efficiency and output high-temperature air. The downstream part can utilize the waste heat and recover water. Output low-temperature air, which can realize the waste heat utilization of different temperatures and output air of different temperatures. At the same time, the waste heat utilization and water recovery can be separated to ensure the full recovery of heat and water and improve the waste heat recovery efficiency.

[0040] As an improvement, a temperature sensor is set in the upstream flue gas to detect the temperature of the flue gas, and the air flow entering the upstream cooling pipe is controlled by the detected flue gas temperature. By detecting the flue gas temperature, condensed water is avoided from being generated upstream, which affects the heat recovery and water collection.

[0041] As an improvement, if the detected temperature of the upstream flue gas is lower than the set value, the controller controls the fan to reduce the air flow entering the upstream cooling pipe, and if the detected temperature of the upstream flue gas is higher than the set value, the controller controls the fan to increase the air flow entering the upstream cooling pipe. By automatic control, the upstream flue gas temperature is kept above the dew point to avoid the formation of water condensation. Preferably, the temperature setting value is higher than the dew point temperature.

[0042] As an improvement, the cooling pipe materials of the upstream and downstream parts are different. The corrosion resistance of the downstream cooling pipe is stronger than that of the upstream cooling pipe. Because the downstream needs condensed water, there is a problem of low-temperature corrosion. By separating the upstream and downstream cooling pipes, different materials are set according to different situations, which can greatly reduce costs while efficiently absorbing waste heat and recycling water.

[0043] As an improvement, along the flow direction of the flue gas, the distribution density of the cooling pipes in the downstream part is getting larger and larger. The present invention changes the distribution density of the downstream cooling pipes, so that the water is evenly distributed on the whole, avoiding the distribution of water on some cooling pipes being dry and some being too much, thereby ensuring the service life of the pipes and sufficient condensation and recovery of water.

[0044] As an improvement, along the flow direction of the flue gas, the cooling tube distribution density of the downstream part is increasing. The above arrangement can further ensure uniform distribution of condensed water.

[0045] As an improvement, the corrosion resistance of the cooling pipe in the downstream part is getting better and better along the flow direction of the flue gas. This is mainly because the downstream temperature is low, which may lead to insufficient cooling moisture. Therefore, by increasing the corrosion resistance of the cooling pipe in the downstream, the overall corrosion resistance can be increased, further reducing costs and increasing service life.

[0046] By separating the upstream and downstream cooling pipes, the upstream and downstream cooling pipes can be replaced separately. For example, the downstream corrosion performance leads to a short cooling pipe life, so the replacement frequency is high. By separating the upstream and downstream, the overall replacement is avoided and the efficiency is improved.

[0047] As an example, Figure 1-6As shown, a low-energy consumption wet flue gas heat and water recovery device includes a flue gas cooling mechanism and a condensed water collection mechanism. The flue gas cooling mechanism is composed of a cooling pipe convergence plate 1 and a plurality of flue gas cooling pipes 3, and the condensed water collection mechanism includes a condensed water collection tank 2 and a drain port 4. The low-energy consumption wet flue gas water recovery device is arranged in the boiler horizontal flue 5, and can be modified on the original horizontal flue, assembled and connected with the horizontal flue 5 through a flange, or manufactured with a new flue.

[0048] The flue gas cooling pipes 3 are arranged in a staggered manner, at 90° to the flow direction of the wet flue gas. The arrangement of the flue gas cooling pipes is as follows: Figure 3 shown.

[0049] like Figure 5 As shown, a plurality of flue gas cooling tubes 3 are fixed to the cooling tube convergence plate 1 to form a flue gas cooling mechanism. The flue gas cooling mechanism is inserted from the upper wall of the boiler horizontal flue 5, so that the flue gas cooling tube 3 passes through the boiler horizontal flue 5, and the cooling tube convergence plate 1 is assembled and connected to the upper wall of the boiler horizontal flue 5 by flange. The condensate collection mechanism is assembled and connected to the lower wall of the boiler horizontal flue 5 by flange, and each flue gas cooling tube is matched with the tube bundle mounting hole of the condensate collection tank to ensure the airtightness of the flue gas flow channel. The drain port 4 is located at the geometric center of the bottom surface of the condensate collection tank, and is connected to the outside through pipelines and valves to discharge condensate.

[0050] The specific process of recovering heat and water is as follows:

[0051] The saturated wet flue gas after wet desulfurization flows into the boiler horizontal flue 5 from the flue gas inlet 5-1. The air in the flue gas cooling pipe 3 is heated by the saturated wet flue gas in the boiler horizontal flue 5. The ambient air is heated and its density decreases accordingly. The density difference between the air in the flue gas cooling pipe 3 and the ambient air below the air inlet 3-1 causes the air to generate an upward self-generated ventilation force. The ambient air spontaneously flows in from the air inlet 3-1 and flows out from the air outlet 3-2. The ambient air and the saturated wet flue gas form natural convection. The saturated wet flue gas continuously releases heat during the convection heat exchange process. The water vapor therein releases the latent heat of vaporization and condenses into water on the surface of the flue gas cooling pipe 3. Since the flue gas cooling pipe 3 is at 90 degrees to the direction of flue gas flow, the condensed water on the outer surface of the flue gas cooling pipe 3 flows into the condensed water collection tank 2 under the action of gravity and is discharged through the drain port 4 to complete the water recovery. Example

[0052] Taking a 600 MW unit with a flue gas volume of 200 Nm3 / h and a flue gas flow rate of 15 m / s as an example, the flue gas inlet temperature is 50°C and the relative humidity is 100%. The low-energy flue gas water recovery device of the present invention is used, and the device uses a flue gas cooling pipe of size DN 40. The flue gas cooling pipe is arranged in a staggered manner, with a total of 16 rows of tube bundles (39 tubes in the first row, 38 tubes in the second row, and a total of 616 flue gas cooling pipes). The device can achieve a water recovery of 5.13 t / day in spring / autumn (ambient air temperature 10°C); a water recovery of 4.59 t / day in summer (ambient temperature 20°C); and a water recovery of 5.98 t / day in winter (ambient temperature -20°C).

[0053] The amount of water recovered by the low-energy flue gas water recovery device using flue gas cooling tubes of different diameters is shown in Table 1.

[0054] Table 1 Water recovery capacity of low energy consumption wet flue gas water recovery device (t / day)

[0055]

[0056] (Note: Spring / Autumn temperature is 10℃, Summer temperature is 20℃, Winter temperature is -20℃;

[0057] When DN 32 steel pipes are selected, there are 45 pipes in the first row and 44 pipes in the second row, for a total of 712 pipes in the installation;

[0058] When DN 40 steel pipes are selected, there are 39 pipes in the first row and 38 pipes in the second row, for a total of 616 pipes in the installation;

[0059] When DN 50 steel pipes are selected, there are 31 pipes in the first row and 10 pipes in the second row, for a total of 488 pipes in the installation;

[0060] When DN 70 steel pipes are selected, there are 25 pipes in the first row and 24 pipes in the second row, for a total of 392 pipes.

[0061] Although the present invention has been disclosed as above with preferred embodiments, the present invention is not limited thereto. Any person skilled in the art can make various changes and modifications without departing from the spirit and scope of the present invention, so the protection scope of the present invention shall be subject to the scope defined by the claims.

Claims

1. A boiler with a corrosion-resistant flue gas waste heat recovery device, the boiler comprising a horizontal flue, a flue gas waste heat recovery device being arranged in the horizontal flue, the flue gas waste heat recovery device comprising a flue gas cooling mechanism, the cooling mechanism comprising a cooling pipe arranged in a vertical direction, the upper and lower ends of the cooling pipe being respectively connected to a cooling pipe convergence plate and passing through the pipe holes of the cooling pipe convergence plate, air enters through the pipe holes at the lower end of the cooling pipe and flows out from the pipe holes at the upper end by natural convection, the flue gas exchanges heat with the air through the cooling pipe; along the flue gas flow direction, the cooling pipe is divided into an upstream part and a downstream part, the cooling pipe materials of the upstream part and the downstream part are different; the corrosion resistance of the downstream cooling pipe is stronger than that of the upstream cooling pipe; the convergence plate at the upper end of the cooling pipe is arranged on the external surface of the upper end of the flue, the convergence plate at the lower end of the cooling pipe is a box structure, the upper end of the box is open, the other sides are closed, and the lower end of the box is arranged on the external surface of the lower end of the flue, At a certain distance from the outer surface of the lower end, a pipe hole is arranged on the lower surface of the box body, and a drain outlet is arranged in the middle of the lower surface of the box body; the box body structure is arranged in the downstream part, and the air of the cooling pipe of the upstream part exchanges heat with the flue gas by forced convection, and the air of the downstream part exchanges heat by natural convection; along the flow direction of the flue gas, the distribution density of the cooling pipes in the downstream part becomes larger and larger, and along the flow direction of the flue gas, the distribution density of the cooling pipes in the downstream part becomes larger and larger, and the amplitude of the increasing distribution density of the cooling pipes in the downstream part continues to increase; a temperature sensor is arranged in the flue gas in the upstream part to detect the temperature of the flue gas, and the air flow rate entering the cooling pipe of the upstream part is controlled by the detected flue gas temperature; if the detected temperature of the upstream flue gas is lower than the set value, the controller controls the fan to reduce the air flow rate entering the cooling pipe of the upstream part, and if the detected temperature of the upstream flue gas is higher than the set value, the controller controls the fan to increase the air flow rate entering the cooling pipe of the upstream part.

2. The boiler according to claim 1, characterized in that Along the flow direction of the flue gas, the corrosion resistance of the cooling pipe in the downstream part becomes better and better.

3. The boiler according to claim 1, characterized in that By separating the upstream and downstream cooling pipes, the upstream and downstream cooling pipes can be replaced individually.

4. The boiler according to claim 3, characterized in that The upstream part can make full use of waste heat to greatly improve the efficiency of waste heat utilization and output high-temperature air. The downstream can utilize waste heat and recover water to output low-temperature air. It can realize waste heat utilization at different temperatures and output air at different temperatures. At the same time, waste heat utilization and water recovery can also be separated.

5. The boiler according to claim 1, characterized in that: A plurality of cooling pipes are fixed to the cooling pipe convergence plate to form a flue gas cooling mechanism; the flue gas cooling mechanism is inserted from the upper wall of the boiler horizontal flue so that the cooling pipes pass through the boiler horizontal flue, and the cooling pipe convergence plate is assembled and connected with the upper wall of the boiler horizontal flue by using a flange.

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