Modularized smoke tube type steam generator

Abstract

The utility model relates to a modularized smoke tube type steam generator, which is different from a known multi-channel smoke tube type steam boiler and consists of a plurality of smoke tube type gas-steam heat exchange modules (1, 2 and 3). In this way, the smoke tube type steam boiler with the evaporation capacity larger than 20 tons per hour can be manufactured. In order to reduce the exhaust gas temperature, an independent water loop smoke tube type gas-water heat exchange module (4) is connected behind the smoke tube type gas-steam heat exchange modules (1, 2 and 3). All the heat exchange tubes (8) of the smoke tube type heat exchange modules (1, 2, 3 and 4) are coaxially aligned, the number, the length and the diameter of the heat exchange tubes (8) can be changed according to needs, the heat exchange tubes can be conveniently cleaned through a compressed air gun (38), and therefore the modularized smoke tube type steam generator is particularly suitable for biomass fuel such as straw.

Description

Technical Field

[0001] This invention belongs to the field of steam boilers, specifically a modular flue-tube steam generator suitable for biomass fuels such as straw. Background Art

[0002] Water-tube steam boilers are generally used for high-power, high-pressure steam, while flue-tube steam boilers are the preferred choice for low-power, low-pressure steam because they are typically more efficient. Flue-tube steam boilers generally require a heavier pressure-bearing shell and cannot usually be manufactured on-site like water-tube steam boilers. This limits their output power due to transport weight constraints. Therefore, in practical applications, there are almost no flue-tube steam boilers with an evaporation capacity exceeding 10 tons / hour.

[0003] Especially in biomass combustion systems, the advantage of flue-tube steam boilers lies in the fact that dust deposits in the tubes of flue-tube heat exchangers are easier to remove than those on the outside of water-tube heat exchanger tubes. Furthermore, flue-tube steam boilers have a higher water content, which better serves as an energy buffer. Therefore, the stringent requirements for shutdown and startup speeds of industrial steam boilers with frequently changing loads are relatively reduced, making this point particularly important.

[0004] To improve efficiency, flue-tube steam boilers are generally designed as multi-channel boilers with different tube diameters. Reversing the airflow direction between channels not only increases the draft requirements but also makes it impossible to concentrate the airflow across all tubes. Therefore, flue-tube steam boilers are typically used for coal, natural gas, or oil-fired boilers, as these fuels usually do not require continuous ash removal and maintenance.

[0005] Multi-channel flue-tube steam boilers are generally composed of a series of compact, type-certified units. Due to their complex design, they cannot currently be manufactured on automated production lines, nor can they be customized to order. Steam generators consisting of multiple gas-steam modules designed according to CN201811060700.4 are only suitable for water-tube steam boilers and not for flue-tube steam boilers.

[0006] Known flue-tube steam boilers typically have only one water chamber. The low-temperature feedwater, once introduced into the chamber, quickly mixes with the existing high-temperature water that determines the flue gas temperature. This premature mixing of high and low-temperature water leads to reduced efficiency. To use low-temperature water for flue gas cooling, an economizer must be installed downstream. If dust purification of biomass fuels such as straw is required, a separate device is needed, but its location is currently unclear.

[0007] Increasing the flue gas velocity to avoid ash accumulation would consume more electricity. Rising fuel prices require more in-depth optimization of boiler design. To achieve this, designers must be able to freely determine the specifications and dimensions of flue-tube steam boilers, which is difficult to achieve in traditional multi-channel flue-tube steam boilers.

[0008] To improve boiler efficiency and combustion quality, it is considered to recycle the flue gas from the boiler tail end to preheat and dry straw bales. However, to ensure that the straw bales do not fall apart, the temperature of the drying flue gas should not exceed 115°C. However, the known feedwater economizer cannot do this. Therefore, the known flue-tube steam boilers cannot produce steam and hot water at the same time. Summary of the Invention

[0009] The objective of this invention is to design a modular flue-tube steam generator suitable for biomass fuels such as straw, with a steam evaporation capacity of more than 10 tons / hour. Its design and construction are simple and can be automated in a factory for road transport by ordinary heavy-duty trucks or exported in containers. The surface of its flue-tube heat exchanger is easy to clean during operation, and the exhaust temperature is much lower than that of known modular flue-tube steam generators. This allows designers to optimize the design and select all heat-related specifications as needed.

[0010] The modular flue-tube steam generator of the present invention is composed of multiple cylindrical, horizontally placed, sequentially arranged, pressure-resistant flue-tube heat exchange modules. The heat exchange tubes of the flue-tube steam generator are arranged in a parallel and longitudinal horizontal manner.

[0011] In the modular flue-tube steam generator of the present invention, the steam chambers of the gas-steam heat exchange modules are interconnected via steam pipes, and the water storage chambers are interconnected via an overflow pipe located outside the modular flue-tube heat exchange device. To overcome the slight displacement caused by the possible thermal expansion of the heat exchange modules, the overflow pipe is provided with a bend.

[0012] To minimize the temperature of the flue gas after heat exchange, one or more flue-tube gas-water heat exchange modules with the same outer diameter, coaxial arrangement, and number of heat exchange tubes can be connected downstream of the modular flue-tube gas-steam heat exchange module, or an economizer can be connected.

[0013] The modular flue-tube steam generator of this invention is supplied with hot water by an independent hot water circuit. The thermal energy of the hot water can be used to preheat feedwater, preheat combustion air, dry fuel, or provide heating. The first flue-tube gas-steam heat exchange module is equipped with the heat exchange tubes with the largest diameter. In subsequent flue-tube heat exchange modules, heat exchange tubes with smaller diameters can be used sequentially.

[0014] Since the number of heat exchange tubes in each flue-tube heat exchange module is the same, heat exchange tubes of different diameters can be used within the same flue-tube heat exchange module to optimize flow rate. All flue-tube heat exchange modules are securely connected by horizontal fixing rods that extend to the entire length of the modular flue-tube steam generator of this invention.

[0015] The horizontal fixed tie rod is arranged in the insulation layer outside the pressure-resistant shell of the modular flue-type steam generator. Therefore, the temperature difference between the pressure-resistant shell and the horizontal fixed tie rod is always very small and has little effect on the tensile stress of the horizontal fixed tie rod.

[0016] Since the modular flue-tube steam generator of the present invention may be relatively long, its potential thermal expansion must be considered, and such thermal expansion generally only occurs in the direction of the heat exchange flue gas flow. One end of the first flue-tube gas-steam heat exchange module is fixed to a fixed bracket connected to the equipment foundation on one side of the heat exchange flue gas inlet chamber. The other support points of the modular flue-tube heat exchange module of the present invention are arranged on a movable bracket with rollers below to prevent thermal expansion.

[0017] To ensure precise alignment of the flue-tube heat exchange modules during assembly, each roller-equipped movable bracket is mounted on a support plate with numerous adjusting screws. To ensure even load distribution on the equipment foundation and prevent deformation of the flue-tube heat exchange modules, the torque of these adjusting screws is adjusted using a torque wrench to ensure they all have approximately the same torque.

[0018] If hygroscopic dust from straw burning accumulates between the vertical orifice plates of a flue-type heat exchange module, the conformal spaces between these plates are at risk of corrosion. Therefore, these spaces need to be filled with a hardened material, such as very fine-grained cement mortar, to prevent corrosion. Attached Figure Description

[0019] Figure 1 A simplified side view of a modular flue-type steam generator is shown.

[0020] Figure 2 The cross-section of a flue-type heat exchange module mounted on a drum is shown.

[0021] Figure 3 A side view of the transition area between two flue-type heat exchange modules is shown.

[0022] Figure 4 The illustration shows the situation where the conformal space of the flue-type heat exchange module is filled with materials such as cement mortar.

[0023] Figure 5 A side cross-sectional view of the heat exchange flue gas inlet chamber with a compressed air gun is shown.

[0024] In the diagram: 1-First flue-type gas-steam heat exchange module, 2-Second flue-type gas-steam heat exchange module, 3-Third flue-type gas-steam heat exchange module, 4-Flue-type gas-water heat exchange module, 5-Equipment foundation, 6-Pressure-resistant outer shell, 7-Water level sensor, 8-Heat exchange tube, 9-Heat exchange feed water, 10-Steam pipe, 11-Overflow pipe, 12-Steam chamber, 13-Water storage chamber, 14-Heat exchange flue gas inlet chamber, 15-Heat exchange flue gas exhaust chamber, 16-Insulated flexible connection, 17-Exhaust fan, 18-Fixed bracket, 19 - Reinforcing rib, 20 - Movable bracket with rollers, 21 - Columnar roller, 22 - Steel plate, 23 - Leveling layer, 24 - Adjusting screw, 25 - Horizontal fixing rod, 26 - Insulation layer, 27 - Sealing strip, 28 - Rubber tube, 29 - Cement mortar injection hole, 30 - Cement mortar, 31 - Cement mortar funnel, 32 - Cement mortar vibrator, 33 - Compressed air gun channel, 34 - Water-cooled wall, 35 - Heat insulation layer, 36 - Heat-resistant ceramic layer, 37 - Ball valve, 38 - Compressed air gun, 39 - Support plate. DETAILED DESCRIPTION

[0025] The present invention will be described in detail through an embodiment, which is a modular flue-tube steam generator with a steam output of approximately 17 tons / hour at a pressure of 1.25 MPa.

[0026] according to Figure 1 The modular flue-tube steam generator consists of a first flue-tube gas-steam heat exchange module (1), a second flue-tube gas-steam heat exchange module (2), a third flue-tube gas-steam heat exchange module (3), and a flue-tube gas-water heat exchange module (4). They are arranged sequentially on a completely horizontal equipment foundation (5).

[0027] All flue-type heat exchange modules (1, 2, 3, 4) have a pressure-resistant housing (6), and they should also contain other legally mandated safety equipment and devices as well as their respective overflow pipes (11), and in particular their respective water level sensors (7).

[0028] All the flue-tube heat exchange modules (1, 2, 3, 4) contain the same number of heat exchange tubes (8), which have different diameters. However, each heat exchange tube (8) in all the flue-tube heat exchange modules (1, 2, 3, 4) is arranged sequentially and coaxially aligned. Only straight-line flow is possible within the heat exchange tubes (8), and no deviation is allowed. Therefore, the modular flue-tube steam generator of this embodiment can be considered a single-pass boiler, allowing compressed air to be used to clean the surface of all heat exchange tubes (8) at once.

[0029] The heat exchange feedwater (9) is fed into the third flue gas-steam heat exchange module (3). In this embodiment, the flue gas-water heat exchange module (4) can help achieve low-temperature flue gas exhaust. However, if the flue gas-water heat exchange module (4) is not used, an economizer module can be arranged to replace the third flue gas-steam heat exchange module (3) or the flue gas-water heat exchange module (4). Alternatively, the third flue gas-steam heat exchange module (3) and the flue gas-water heat exchange module (4) can be used to preheat the feedwater of the steam generator of the present invention. Here, the economizer module is shorter in length but has the same diameter as the flue gas-steam heat exchange modules (1, 2). In this embodiment, the length of all flue heat exchange modules (1, 2, 3, 4) is 3.5 meters.

[0030] In this invention, the flue-type gas-steam heat exchange modules (1, 2, 3) are interconnected on one side of the steam chamber (12) through steam pipes (10). The large-diameter steam pipes (10) can achieve a very small pressure difference between the steam chambers (12), so the water level in the flue-type gas-steam heat exchange modules (1, 2, 3) is not affected.

[0031] The flue-type gas-steam heat exchange modules (1, 2, 3) on one side of the water storage chamber (13) are interconnected through an overflow pipe (11). In this embodiment, the diameter of the overflow pipe (11) is set to 160 mm. Thus, the water flow velocity between the third flue-type gas-steam heat exchange module (3) and the second flue-type gas-steam heat exchange module (2) is less than 0.23 m / s, resulting in very small pressure loss and no impact on the water level. The water level of the third flue-type gas-steam heat exchange module (3) will be slightly higher than that of the second flue-type gas-steam heat exchange module (2), while the water level of the first flue-type gas-steam heat exchange module (1) is the lowest. However, when setting the water level sensor (7), only the millimeter-level water level difference is considered.

[0032] All the flue-type heat exchange modules (1, 2, 3, 4) have an outer diameter of 2.95 meters, making them suitable for road transport. The heaviest of these, the first flue-type gas-to-steam heat exchange module (1), weighs approximately 16.5 tons and is suitable for use in non-special transport vehicles.

[0033] In this embodiment, all flue-tube heat exchange modules (1, 2, 3, 4) contain 183 heat exchange tubes (8). The first flue-tube gas-steam heat exchange module (1) contains only DN100 (φ108 mm) heat exchange tubes (8), and the second flue-tube gas-steam heat exchange module (2) contains only DN80 (φ89 mm) heat exchange tubes (8). To optimize the second flue-tube gas-steam heat exchange module (3) and the flue-tube gas-water heat exchange module (4) in this embodiment, heat exchange tubes (8) with diameters of φ89 mm and φ76 mm are selected. It can be seen that, according to the present invention, the designer can set the flue gas velocity, the number of heat exchange modules and the number of heat exchange tubes (8) as needed. The diameter, length and material of the heat exchange tubes (8) can also be changed, so as to optimize the design of the entire modular flue-tube steam generator.

[0034] Hot flue gas at 720-920℃ (850℃ in this embodiment) enters the modular flue gas generator through the heat exchange flue gas inlet chamber (14), and is then discharged through the heat exchange flue gas outlet chamber (15) via the thermal expansion flexible connection (16) and the induced draft fan (17).

[0035] The modular flue-tube steam generator is securely connected to the equipment foundation (5) on one side of the heat exchange flue gas inlet chamber (14) via a fixed bracket (18) and reinforcing ribs (19). Other movable brackets (20) with rollers rest on columnar rollers (21), thereby enabling the modular flue-tube steam generator to overcome thermal expansion along the gas flow direction. Each flue-tube gas-steam heat exchange module (1, 2, 3) includes a water level sensor (7), and a signal from one of the water level sensors (7) will activate the heat exchange feedwater (9).

[0036] Figure 2 The cross-section of the flue-type heat exchange module mounted on the drum is shown. 183 heat exchange tubes (8) are supported by a movable bracket (20) with rollers and a columnar roller (21). The steel plate (22) arranged on the equipment foundation (5) is corrected and leveled by a leveling layer (23) composed of hardened material.

[0037] The precise positioning of all the tube heat exchange modules (1, 2, 3, 4) is accomplished by a support plate (39) with a large number of adjusting screws (24). The torque of the adjusting screws (24) is adjusted with a torque wrench. This not only ensures that all the tube heat exchange modules (1, 2, 3, 4) are accurately close together, but also ensures that the weight load is evenly distributed, thereby preventing the tube heat exchange modules (1, 2, 3, 4) from deforming.

[0038] All the flue-tube heat exchange modules (1, 2, 3, 4) are interconnected by horizontal fixing rods (25) that extend along the entire length of all the flue-tube heat exchange modules (1, 2, 3, 4). The horizontal fixing rods (25) are located in the insulation layer (26) outside the pressure-resistant shell (6), so the temperature of the horizontal fixing rods (25) is always close to the temperature of the pressure-resistant shell (6), and their thermal expansion is almost synchronized. The horizontal fixing rods (25) are made of spring steel and can be pre-tightened with a torque wrench. Their tensile stress remains positive even when the temperature changes, and their thermal expansion stress is always lower than the allowable value of spring steel.

[0039] All the flue-type heat exchange modules (1, 2, 3, 4) are connected to each other only by tension and generate force only in the longitudinal direction. They will not generate local forces in the vertical direction, thus affecting the safe operation of these pressurized heat exchange modules.

[0040] Figure 3 A side view of the connection area between two flue-tube heat exchange modules connected by a horizontal fixed tie rod (25) is shown. The load of the modular flue-tube steam generator is distributed across the entire cylindrical roller (21). There is a sealing strip (27) and a sealing ring (not shown in this figure) between the two flue-tube heat exchange modules, so that cement mortar (30) can be filled into the conformal space between the two flue-tube heat exchange modules.

[0041] An overflow pipe (11) of a certain length is used to balance the water level between the flue-type gas-steam heat exchange modules (1, 2, 3). The overflow pipe (11) arranged on the outside of the insulation layer (26) has a certain degree of curvature to overcome the thermal expansion deformation of the flue-type heat exchange module.

[0042] Figure 4 The method of filling the conformal space between the flue-type heat exchange modules (1, 2, 3, 4) with cement mortar (30) is shown. Filling the hollow conformal space can prevent the accumulation of hygroscopic dust generated by biomass combustion and causing corrosion.

[0043] After all the flue-type heat exchange modules (1, 2, 3, 4) are installed, the rubber tube (28) is passed through all the heat exchange tubes (8) and pressurized. After sealing the overlapping part of the heat exchange tubes (8), the tube is passed through the insulation layer (26) and the pressure-resistant shell (6) to make a cement mortar injection hole (29). With the help of the cement mortar vibrator (32), the cement mortar (30) is filled into the hollow conformal space through the cement mortar injection hole (29), compacted and the air is discharged.

[0044] Figure 5A side cross-sectional view of the heat exchange flue gas inlet chamber (14) with a compressed air gun (38) is shown. 850°C heat exchange flue gas enters the first flue-tube gas-steam heat exchange module (1) through the heat exchange flue gas inlet chamber (14). The heat exchange flue gas inlet chamber (14) is made of steel and is equipped with a double-layer water-cooled wall (34). The inner lining consists of a heat insulation layer (35) and a heat-resistant ceramic layer (36).

[0045] On the opposite side of each heat exchange tube (8), there is a compressed air gun channel (33) with a ball valve (37). When the ball valve (37) is opened and the compressed air gun (38) is pushed in, the compressed air can be sprayed out through the compressed air gun (38) to clean the dust on the surface of the heat exchange tube (8).

[0046] In this embodiment, the waste heat of the flue gas generated after steam is generated in the flue-tube gas-water heat exchange module (4) can be recovered and converted into hot water, thereby further utilizing the waste heat of the flue gas. The modular flue-tube steam generator of the present invention has a simple design and construction, can realize automated production, reduce manufacturing costs and improve equipment quality, thereby expanding the market for flue-tube steam boilers and improving product competitiveness.

[0047] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A modular flue-tube steam generator, comprising a flue-tube gas-steam heat exchange module, a flue-tube gas-water heat exchange module, a pressure-resistant shell, heat exchange tubes, steam pipes, a steam chamber, a water storage chamber, and other safety and control devices as required by law; characterized in that, The modular flue-tube steam generator consists of several cylindrical, horizontally placed, sequentially arranged flue-tube gas-steam heat exchange modules (1, 2, 3). The heat exchange tubes (8) of these flue-tube gas-steam heat exchange modules (1, 2, 3) are interconnected. The steam chambers (12) of the flue-tube gas-steam heat exchange modules (1, 2, 3) are interconnected through steam pipes (10). Their water storage chambers (13) are interconnected through curved overflow pipes (11) arranged outside the flue-tube gas-steam heat exchange modules (1, 2, 3).

2. A modular flue-tube steam generator according to claim 1, characterized in that, A flue-type gas-to-steam heat exchange module (4) is arranged after the flue-type gas-to-water heat exchange module (1, 2, 3). This module has the same outer diameter and the same arrangement and number of heat exchange tubes (8) as the flue-type gas-to-steam heat exchange module (1, 2, 3). The water around these heat exchange tubes (8) comes from an independent water loop.

3. A modular flue-tube steam generator according to claim 2, characterized in that, All the flue-type heat exchange modules (1, 2, 3, 4) are connected together by horizontally extending, prestressed horizontal fixing rods (25) that extend along the entire length of the modular flue-type steam generator and are arranged between the pressure-resistant shell (6) and the insulation layer (26).

4. A modular flue-tube steam generator according to claim 1, characterized in that, All the flue-tube heat exchange modules (1, 2, 3, 4) contain heat exchange tubes (8) of different diameters, and the diameter of the heat exchange tubes in each flue-tube heat exchange module (1, 2, 3, 4) can also be different.

5. A modular flue-tube steam generator according to claim 1, characterized in that, The first flue gas-steam heat exchange module (1) is fixed on a fixed bracket (18) connected to the equipment foundation (5) on one side of the heat exchange flue gas inlet chamber (14). The other supports of the modular flue steam generator are supported on a movable bracket (20) with rollers carried by columnar rollers (21).

6. A modular flue-tube steam generator according to claim 1, characterized in that, The cylindrical roller (21) rolls on the support plate (39), the precise position of the support plate (39) in the vertical direction is determined by a plurality of adjusting screws (24), the torque of the adjusting screws (24) is adjusted by a torque wrench.

7. A modular flue-tube steam generator according to claim 1, characterized in that, The hollow, conformal space between the flue-type heat exchange modules (1, 2, 3, 4) is densely filled with cement mortar (30).

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