An air preheater

Abstract

The present invention discloses an air preheater, particularly an air preheater for the coal-to-gas process that heats the air temperature to above 500 °C. Both tube sheets of the air preheater have effective cooling and measures to make the air flow evenly, ensuring that the air is evenly distributed in the shell side, especially at the tube sheets, providing uniform and effective cooling for the tube sheets, and avoiding failure caused by severe thermal stress due to temperature difference.

Description

Technical Field

[0001] The present invention relates to an air preheater, and particularly to an air preheater for coal-to-gas process that heats air temperature to above 500°C. Background Art

[0002] Coal-to-gas is a process in which coal is heated to a certain temperature under anoxic conditions to be transformed into gas and other by-products, and the heat for heating the coal is provided by the combustion of a part of the coal. The gas temperature after the reaction in the reactor is very high and carries a large amount of heat energy, while the delivered finished gas needs to be maintained at about normal temperature. Therefore, there are many heat energy recovery devices designed in the process, which can not only recover heat energy but also reduce the gas temperature to the required temperature. The air preheater is one of the heat energy recovery devices in the process, and its function is to heat the air used for coal combustion in the reactor. The higher the temperature to which the air is heated, it means that the less coal needs to be burned under the same furnace temperature, that is, the more energy-efficient the whole system is.

[0003] Currently, the well-known air preheaters include, one is the traditional fixed tube sheet shell-and-tube air preheater. Due to structural limitations, this kind of air preheater is not applicable to working conditions above 500°C; the other is the shell-and-tube air preheater with an expander installed on each heat exchange tube, which is applicable to working conditions above 500°C and has a mature application in the carbon black production line. However, in the coal-to-gas process, the flow ratio of air and gas leads to a short and thick design of the air preheater, with a small number of baffles, and the air cannot be guaranteed to be evenly distributed in the shell side, forming a flow dead zone. When the equipment works, it bears serious temperature difference thermal stress, especially the tube sheet. The air forms a flow dead zone in the area opposite to the inlet side, and this uneven flow distribution causes uneven heating of the tube sheet, resulting in serious temperature difference thermal stress and the tube sheet failing within a short time. Therefore, there is an urgent need for an improved new air preheater that is applicable to high-temperature working conditions above 500°C and does not suffer from failure caused by serious uneven thermal stress. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide an air preheater, in which both side tube sheets of the air preheater have effective measures for cooling and making the air flow evenly. The beneficial effects are: ensuring the uniform distribution of air in the shell side, especially at the tube sheet, providing uniform and effective cooling for the tube sheet, and avoiding failure caused by serious temperature difference thermal stress.

[0005] To solve the above problems, an air preheater of the present invention includes heat exchange tubes, baffles, a housing, a hot-side tube sheet, a cold-side tube sheet, an expander, a first smoke box, a second smoke box, an air inlet, an air outlet, a diverter plate, and a bypass pipe. The hot-side tube sheet is located on the high-temperature flue gas side and is a double-layer tube sheet with forced cooling air introduced into its interior. The cold-side tube sheet is located on the low-temperature flue gas side, and a diverter plate is provided between the adjacent baffles. The diverter plate diverts a part of the air to the cavity near the cold-side tube sheet and introduces it to a certain position in the middle of the housing through the bypass pipe to converge with the other part of the air. Therefore, both tube sheets are effectively cooled, avoiding severe uneven thermal stress, and thus ensuring the safe operation of the equipment. BRIEF DESCRIPTION OF THE DRAWINGS

[0006] The following further details the specific embodiments of the present invention with reference to the drawings, where:

[0007] Figure 1 is a schematic diagram of the present invention. SPECIFIC EMBODIMENTS

[0008] Figure 1 A schematic diagram showing the present invention. An air preheater of the present invention includes heat exchange tubes, baffles, a housing, a hot-side tube sheet, a cold-side tube sheet, an expander, a first smoke box, a second smoke box, an air inlet, an air outlet, a diverter plate, and a bypass pipe. The hot-side tube sheet is composed of a first tube sheet, a second tube sheet, a sleeve tube, a cooling air inlet pipe, and a cooling air outlet pipe. The specific embodiments are as follows:

[0009] Multiple heat exchange tubes 1 pass through the staggered baffles 2 according to a certain arrangement rule. The tube bundle composed of the heat exchange tubes 1 and the baffles 2 is placed in a cylindrical housing 3. One end of the housing 3 is provided with a hot-side tube sheet 4, and the other end is provided with a cold-side tube sheet 5. Both tube sheets have tube holes corresponding to the positions and quantities of the heat exchange tubes. Both ends of the heat exchange tubes 1 respectively pass through the tube holes of the two tube sheets, one end of which is connected to the outside of the hot-side tube sheet 4, and the other end is installed with an expander 6, and the expander 6 is connected to the outside of the cold-side tube sheet 5. The outside of the hot-side tube sheet 4 is connected to a first smoke box 7, which is the high-temperature flue gas inlet, and the outside of the cold-side tube sheet 5 is connected to a second smoke box 8, which is the low-temperature flue gas outlet. The side of the housing 3 is opened and connected to an air inlet 9 within the range between the cold-side tube sheet 5 and its adjacent baffle, and the side of the housing 3 is opened and connected to an air outlet 10 within the range between the hot-side tube sheet 4 and its adjacent baffle.

[0010] A flow dividing plate 11 is provided between the cold side tube sheet 5 and the adjacent baffle plate. The flow dividing plate 11 is a baffle plate in the shape of a complete circle, which divides the air entering from the air inlet 9 into two streams. One or more holes are opened in the side surface of the shell 3 on the opposite side of the air inlet within the range between the cold side tube sheet 5 and the flow dividing plate 11 and are respectively connected to bypass pipes 12. The other ends of the bypass pipes 12 lead to somewhere in the middle of the shell 3. One stream of air flows through the cavity on the side of the flow dividing plate 11 close to the cold side tube sheet 5, then flows into the bypass pipe 12 and returns to the inside of the shell from somewhere in the middle of the shell 3 to converge with the other stream of air flowing in a baffle pattern inside the shell.

[0011] The hot side tube sheet 4 is composed of tube sheet one 401, tube sheet two 402, sleeve pipes 403, cooling air inlet pipes 404, and cooling air outlet pipes 405. Tube sheet one 404 and tube sheet two 402 are two parallel tube sheets with a certain distance between them. Tube holes are opened at the same positions on the two tube sheets, and the sleeve pipes 403 are inserted into the tube holes. The sleeve pipes 403 are respectively connected to the outsides of tube sheet one 401 and tube sheet two 402. A cooling air inlet pipe 404 is provided around the gap formed by the two tube sheets. One or more tube holes are opened at a certain position in the center of tube sheet two 402 and are connected to the cooling air outlet pipe 405. The cooling air enters the gap formed by tube sheet one 401, tube sheet two 402, and sleeve pipes 403 from the cooling air inlet pipe 404 and flows out from the cooling air outlet pipe 405 at the center. Tube sheet two 402 is the inner side of the hot side tube sheet 4 and is connected to the shell 3. Tube sheet one 401 is the outer side of the hot side tube sheet 4 and is connected to the first smoke box 8. The cooling air outlet pipe 405 passes through one or more baffle plates inside the shell, so that the cooling air converges with the preheated air.

Claims

1. An air preheater, comprising heat exchange tubes, baffles, a housing, a hot-side tube sheet, a cold-side tube sheet, an expander, a first smoke box, a second smoke box, an air inlet, an air outlet, a diverter plate, and a bypass pipe. The hot-side tube sheet is composed of a first tube sheet, a second tube sheet, a sleeve tube, a cooling air inlet pipe, and a cooling air outlet pipe, and is characterized in that: A flow dividing plate is provided between the cold-side tube sheet and the adjacent baffle plate. The flow dividing plate is a baffle plate in the shape of a complete circle, which divides the air entering from the air inlet into two streams. One or more holes are opened in the side surface of the shell on the opposite side of the air inlet within the range between the cold-side tube sheet and the flow dividing plate and are respectively connected to bypass pipes. The other ends of the bypass pipes lead to a certain position in the middle of the shell. One stream of air flows through the cavity on the side of the flow dividing plate close to the cold-side tube sheet, then flows into the bypass pipe and returns to the inside of the shell from a certain position in the middle of the shell to converge with the other stream of air that flows in a zigzag manner inside the shell; Both ends of the heat exchange tubes respectively pass through the tube holes of the hot-side tube sheet and the cold-side tube sheet. One end thereof is connected to the outside of the hot-side tube sheet, and an expander is installed at the other end, and the expander is connected to the outside of the cold-side tube sheet; Tube sheet one and tube sheet two are two parallel tube sheets with a certain distance between them. Tube holes are opened at the same positions on the two tube sheets, and sleeve tubes are inserted into the tube holes. The sleeve tubes are respectively connected to the outside of tube sheet one and tube sheet two. Cooling air inlet pipes are provided around the gap formed by the two tube sheets. One or more tube holes are opened at a certain position in the center of tube sheet two and are connected to the cooling air outlet pipe. Cooling air enters the gap formed by tube sheet one, tube sheet two and the sleeve tubes from the cooling air inlet pipe and flows out from the cooling air outlet pipe at the center.

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