A combined heat exchanger system and heat exchange method for styrene plant waste heat recovery

Abstract

This invention belongs to the technical field of styrene plant technology and discloses a combined heat exchanger system and method for waste heat recovery in styrene plants. The system includes an evaporator, a preheater, a superheater, and a shell. The evaporator is a horizontal heat exchanger, with evaporation heat exchange tubes positioned close to the bottom of the shell and completely submerged in the boiler feedwater within the shell. The preheater is also a horizontal heat exchanger, with preheating heat exchange tubes positioned near the top of the shell, and the distance between the preheating heat exchange tubes and the top of the shell is greater than or equal to the space required for water vapor to accumulate at the top of the shell. The superheater is a vertical heat exchanger. This invention employs a combination of vertical and horizontal heat exchangers, achieving the recovery and utilization of waste heat from high-temperature reaction products while overcoming the drawbacks of horizontal combined heat exchangers. This not only contributes to energy conservation and consumption reduction but also reduces equipment investment costs.

Description

Technical Field

[0001] This invention belongs to the technical field of styrene plant technology, and more specifically, relates to a combined heat exchanger system and heat exchange method for waste heat recovery in styrene plants. Background Technology

[0002] Styrene, an important petrochemical raw material, is mainly used in the production of various chemical products such as synthetic rubber, synthetic resins, and polystyrene. With rapid economic development, the demand for styrene is increasing year by year. Simultaneously, due to the continuous commissioning of new styrene plants each year, the production capacity of styrene plants is also increasing annually. The main styrene production processes are ethylbenzene dehydrogenation, SM / PO, and C8 extraction. Among these, ethylbenzene dehydrogenation is currently the most widely used technology in styrene plants, accounting for approximately 80% of global styrene production capacity.

[0003] In the ethylbenzene dehydrogenation process, the temperature of the reaction products generated from the dehydrogenation reactor is about 600°C. In order to fully recover and utilize the waste heat in the reaction products, a combined heat exchanger is usually used to exchange heat between the high-temperature reaction products and the reaction raw materials and boiler feedwater. This can heat the reaction raw materials and also produce a portion of low-pressure steam as a byproduct.

[0004] Most commonly used combined heat exchangers are horizontal, using multiple shell-and-tube heat exchangers connected in series. The problems with this technical solution are: (1) The horizontal series structure results in long equipment size, large footprint, and high load requirements on the civil engineering foundation; (2) The heat exchanger uses a single-pass fixed tube sheet heat exchanger. Under high temperature conditions, the tube sheet and heat exchange tubes are heated unevenly in the vertical direction, resulting in excessive temperature stress, which can easily cause tube sheet deformation failure and heat exchange tube pull-out problems. Summary of the Invention

[0005] The purpose of this invention is to address the problems existing in the prior art by providing a combined heat exchanger system and method for waste heat recovery in styrene plants. This invention employs a combination of vertical and horizontal heat exchangers, achieving the recovery and utilization of waste heat from high-temperature reaction products while overcoming the drawbacks of horizontal combined heat exchangers. This not only contributes to energy conservation and consumption reduction but also reduces equipment investment costs.

[0006] To achieve the above objectives, the first aspect of the present invention provides a combined heat exchanger system for waste heat recovery in a styrene plant, the system comprising an evaporator, a preheater, a superheater, and a shell;

[0007] The shell consists of three parts: a left end cap, a middle cylinder, and a right end cap; the top of the shell is provided with multiple cylinder shell-side outlets, and a wire mesh demister is fixedly installed on the inner wall of the shell below each cylinder shell-side outlet; the bottom of the shell is provided with multiple cylinder shell-side inlets.

[0008] The evaporator is a horizontal heat exchanger, including an evaporator tube box and evaporator heat exchange tubes arranged sequentially from left to right; the evaporator heat exchange tubes are arranged close to the bottom of the shell and are completely submerged in the boiler feedwater inside the shell; the evaporator tube box is located outside the shell and has an evaporator tube inlet and an evaporator tube outlet.

[0009] The preheater is a horizontal heat exchanger, comprising a preheating tube box and preheating heat exchange tubes arranged sequentially from right to left; the preheating heat exchange tubes are located close to the top of the shell inside the shell, and the distance between the preheating heat exchange tubes and the top of the shell is greater than or equal to the space height required for water vapor to accumulate at the top of the shell; the preheating tube box is located outside the shell, and the preheating tube box is provided with a preheater tube side outlet and a preheater tube side inlet; the preheater tube side inlet is connected to the reaction raw material supply device;

[0010] The superheater is a vertical heat exchanger, comprising an upper superheated tube box, a superheated shell, and a lower superheated tube box connected sequentially from top to bottom. Multiple vertical heat exchange tubes are arranged inside the superheated shell. A shell-side outlet is located on the portion of the superheated shell near the inlet end of the multiple vertical heat exchange tubes, and a shell-side inlet is located on the portion of the superheated shell near the outlet end of the multiple vertical heat exchange tubes. The shell-side outlet of the superheater is connected to the feed inlet of the dehydrogenation reactor, and the shell-side inlet of the superheater is connected to the tube-side outlet of the preheater via a first connecting pipe. One end of the lower superheated tube box is connected to the outlet end of the vertical heat exchange tubes, and the other end is connected to the tube-side inlet of the evaporator via a second connecting pipe. One end of the upper superheated tube box is connected to the product outlet of the dehydrogenation reactor, and the other end is connected to the inlet end of the vertical heat exchange tubes.

[0011] According to the present invention, preferably, the left end cap is an eccentric conical shell with an inclination angle ranging from 20° to 60°.

[0012] According to the present invention, preferably, the right end cap is an elliptical end cap.

[0013] According to the present invention, preferably, the top of the shell is provided with two shell-side outlets; the bottom of the shell is provided with two shell-side inlets and two supports.

[0014] In this invention, the wire mesh demister is fixedly installed on the inner wall of the shell below the outlet of each cylinder by welding.

[0015] In this invention, the evaporator is a two-pass U-tube heat exchanger (i.e., it has one inlet end and one outlet end of an evaporation heat exchange tube). According to this invention, preferably, the evaporation tube box is connected to the other end of the left end cap through a first flange and thus disposed outside the shell, and the evaporation tube plate is held between the two flanges of the first flange; the inlet end and outlet end of the evaporation heat exchange tube are fixed on the evaporation tube plate; the evaporation tube box is divided into an upper evaporation tube box and a lower evaporation tube box by an evaporation partition plate horizontally disposed inside the evaporation tube box (i.e., the evaporator is divided into two passes); the upper evaporation tube box is connected to the inlet end of the evaporation heat exchange tube and is provided with the evaporator tube-side inlet, and the lower evaporation tube box is connected to the outlet end of the evaporation heat exchange tube and is provided with the evaporator tube-side outlet.

[0016] In this invention, the evaporative heat exchange tube is disposed close to the bottom of the shell and is completely submerged in the boiler feedwater inside the shell, which allows the evaporative heat exchange tube to fully heat the boiler feedwater.

[0017] According to the present invention, preferably, the evaporative heat exchange tube is a U-shaped tube.

[0018] According to the present invention, preferably, the inlet end and outlet end of the evaporation heat exchange tube are welded to the evaporation tube plate.

[0019] According to the present invention, preferably, the bottom of the shell is provided with a plurality of equally spaced evaporation support plates, which are used to support the evaporation heat exchange tubes to be disposed close to the bottom of the shell inside the shell.

[0020] According to the present invention, preferably, the evaporator tube outlet is connected to an external system.

[0021] In this invention, the preheater is a two-pass U-tube heat exchanger (i.e., it has one inlet end and one outlet end of a preheating heat exchange tube). According to this invention, preferably, the preheating tube box is connected to the other end of the right end cap through a second flange and thus disposed outside the shell, and the preheating tube plate is clamped between the two flanges of the second flange; the inlet end and outlet end of the preheating heat exchange tube are fixed on the preheating tube plate; the preheating tube box is divided into an upper preheating tube box and a lower preheating tube box by a preheating partition plate horizontally disposed inside the preheating tube box (i.e., the preheater is divided into two passes); the upper preheating tube box is connected to the outlet end of the preheating heat exchange tube and is provided with the preheater tube-side outlet, and the lower preheating tube box is connected to the inlet end of the preheating heat exchange tube and is provided with the preheater tube-side inlet.

[0022] According to the present invention, preferably, the preheating heat exchange tube is a U-shaped tube.

[0023] According to the present invention, preferably, the inlet end and outlet end of the preheating heat exchange tube are welded to the preheating tube sheet.

[0024] According to the present invention, preferably, the upper part of the shell is provided with a support beam, which is used to support the preheating heat exchange tube, thereby realizing that the preheating heat exchange tube is located close to the top of the shell inside the shell and the distance between the preheating heat exchange tube and the top of the shell is greater than or equal to the space height required for water vapor to accumulate at the top of the shell; the upper part of the shell is provided with a plurality of equally spaced preheating support plates, which support the preheating heat exchange tube on the support beam.

[0025] In this invention, the evaporation heat exchange tube, evaporation tube sheet, preheating heat exchange tube and preheating tube sheet can all be pulled out from the shell. After being pulled out, a person can enter the shell through the first flange and the second flange for maintenance, and there is no need to set a separate inspection hole on the shell.

[0026] In this invention, as a preferred embodiment, the superheater is a vertical single-pass fixed tube sheet heat exchanger. According to this invention, preferably, the superheater shell is further provided with a plurality of horizontally arranged baffles at equal intervals, and the plurality of vertical heat exchange tubes pass vertically through the baffles.

[0027] The superheated shell is connected in the middle by an expansion joint, which is used to compensate for the thermal expansion difference between the vertical heat exchange tubes and the superheated shell; the top and bottom of the superheated shell are respectively fixedly connected to an upper tube sheet and a lower tube sheet; the upper superheated tube box is connected to the upper tube sheet through an upper tube box flange; the lower superheated tube box is connected to the lower tube sheet through a lower tube box flange; the inlet end and outlet end of the vertical heat exchange tube are respectively fixed to the upper tube sheet and the lower tube sheet.

[0028] In this invention, as a preferred embodiment, the superheater is a vertical single-pass internal packed floating tube sheet heat exchanger. According to this invention, preferably, the superheater shell is further provided with a plurality of horizontally arranged baffles at equal intervals, and the plurality of vertical heat exchange tubes pass vertically through the baffles.

[0029] An upper tube sheet is fixedly connected to the top of the superheated shell; a lower tube sheet is built into the bottom of the superheated shell, and a packing device is provided between the lower tube sheet and the superheated shell. The packing device is used to prevent leakage of the shell-side medium in the superheated shell caused by the movement of the lower tube sheet within the superheated shell; the upper superheated tube box is connected to the upper tube sheet via an upper tube box flange; the lower superheated tube box is connected to the bottom of the superheated shell via a lower tube box flange; the inlet and outlet ends of the vertical heat exchange tubes are fixed to the upper tube sheet and the lower tube sheet, respectively.

[0030] Preferably, the packing device includes packing, a packing gland, and fasteners; the packing gland is used to compact and fix the packing between the lower tube sheet and the inner wall of the superheated shell; the fasteners are used to fix the packing gland to the bottom plate surface of the lower tube sheet.

[0031] A second aspect of the present invention provides a combined heat exchange method for waste heat recovery in a styrene plant, the method employing the aforementioned system and comprising the following steps:

[0032] Boiler feedwater enters the bottom of the shell from the shell side inlet and is vaporized into water vapor under the heating effect of the evaporation heat exchange tubes, flowing towards the top of the shell;

[0033] The water vapor reaching the top of the shell, part of which is filtered by the wire mesh demister and flows out of the shell through the shell-side outlet; the other part exchanges heat with the reaction material entering the preheating heat exchange tube from the preheater tube-side inlet. The water vapor is cooled and condenses into liquid water and falls back to the bottom of the shell. The reaction material is initially heated and flows into the superheater shell side through the preheater tube-side outlet, the first connecting pipe and the superheater shell-side inlet in sequence.

[0034] In the superheater, the initially heated reaction feedstock exchanges heat with the dehydrogenation reaction products entering the vertical heat exchange tubes from the upper superheater tube box within the superheater shell side. The initially heated reaction feedstock is then reheated and enters the feedstock inlet of the dehydrogenation reactor from the superheater shell side outlet. The dehydrogenation reaction products are cooled and flow sequentially through the lower superheater tube box, the second connecting pipe, and the evaporator tube side inlet into the evaporation heat exchange tubes, serving as a heat source for the gasification of the boiler feedwater.

[0035] In this invention, as a preferred embodiment, the water vapor that flows out of the shell through the shell side outlet after being filtered by the wire mesh demister is transported to subsequent related equipment for use.

[0036] According to the present invention, preferably, within the shell side of the superheater, the reactants after initial heating undergo baffled flow under the action of baffles, and exchange heat with the dehydrogenation reaction products entering the vertical heat exchange tubes from the upper superheater tube box.

[0037] According to the present invention, preferably, after the dehydrogenation reaction products in the evaporator heat exchange tube are used as a heat source to vaporize the boiler feedwater, the dehydrogenation reaction products are cooled again and discharged from the system through the evaporator tube outlet, and then transported to other related equipment.

[0038] In this invention, as a preferred embodiment, an upper tube sheet and a lower tube sheet are welded to the top and bottom of the superheated shell, respectively; the inlet end and outlet end of the vertical heat exchange tube are welded to the upper tube sheet and the lower tube sheet, respectively; the upper superheated tube box and the lower superheated tube box are each independently a conical structure.

[0039] The beneficial effects of the technical solution of the present invention are as follows:

[0040] (1) Compared with the prior art, the combined heat exchanger system of the present invention adopts a combination of vertical heat exchanger and horizontal heat exchanger, which effectively reduces the equipment volume, makes the equipment more compact, and occupies less space;

[0041] (2) The present invention uses high-temperature reaction products as heat source, and the high-temperature waste heat can be fully recovered and utilized, and continuously heats the reaction raw materials and produces water vapor as a by-product, thus truly achieving the goal of energy saving and consumption reduction.

[0042] (3) The superheater of the present invention adopts a vertical structure, which makes the tube sheet and heat exchange tubes more uniformly heated in the radial direction, the tube sheet is not easy to deform, and the heat exchange tubes are not easy to be pulled off.

[0043] (4) The superheater of the present invention adopts the form of an expansion joint in the shell side or a packing device built into the shell, which effectively reduces the temperature stress between the tube and the shell side.

[0044] (5) The heat exchange tubes of the evaporator and preheater of the present invention are all U-shaped tube structures. During operation, the heat exchange tubes can freely expand and contract, and there is no temperature difference stress between the tube and the shell side.

[0045] (6) The reaction raw materials of the present invention are heated in two stages by a preheater and a superheater, so that the reaction raw materials are fully heated and the utilization efficiency of residual heat in the reaction products is improved.

[0046] Other features and advantages of the present invention will be described in detail in the following detailed description section. Attached Figure Description

[0047] The above and other objects, features and advantages of the present invention will become more apparent from the more detailed description of exemplary embodiments of the invention in conjunction with the accompanying drawings, wherein the same reference numerals generally represent the same components in the exemplary embodiments of the invention.

[0048] Figure 1 A schematic diagram of a combined heat exchanger system for waste heat recovery in a styrene plant, provided in Embodiment 1 of the present invention, is shown.

[0049] Figure 2 A schematic diagram of a combined heat exchanger system for waste heat recovery in a styrene plant, provided in Embodiment 2 of the present invention, is shown.

[0050] Figure 3 A schematic diagram of a packing device for a combined heat exchanger system for waste heat recovery in a styrene plant, provided in Embodiment 2 of the present invention, is shown.

[0051] The annotations in the attached figures are explained as follows:

[0052] E1. Superheater; 1. Upper superheater tube sheet; 2. Upper tube sheet; 3. Superheater shell-side outlet; 4. Superheater shell; 5. Expansion joint; 6. Vertical heat exchange tube; 7. Baffle plate; 8. Lower tube sheet; 9. Lower superheater tube sheet; 10. Superheater shell-side inlet; 11. Second connecting tube; 36. First connecting tube; 37. Packing; 38. Packing gland; 39. Fasteners;

[0053] E2, Evaporator; 12, Evaporator tube-side inlet; 13, Evaporator tube box; 14, Evaporator tube sheet; 15, First flange; 16, Evaporator partition plate; 17, Evaporator tube-side outlet; 18, Evaporator support plate; 19, Evaporator heat exchange tube;

[0054] E3, Preheater; 22, Preheater tube inlet; 23, Preheater partition plate; 24, Preheater tube box; 25, Preheater tube outlet; 26, Preheater tube sheet; 27, Second flange; 29, Support beam; 30, Preheater support plate; 31, Preheater heat exchanger tube;

[0055] 20. Shell side inlet; 21. Support; 28. Right end cap; 32. Wire mesh demister; 33. Shell side outlet; 34. Intermediate shell; 35. Left end cap. Detailed Implementation

[0056] Preferred embodiments of the invention will now be described in more detail. While preferred embodiments of the invention are described below, it should be understood that the invention can be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided so that the invention will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art.

[0057] Example 1

[0058] This embodiment provides a combined heat exchanger system for waste heat recovery in a styrene plant, such as... Figure 1 As shown, the system includes an evaporator E2, a preheater E3, a superheater E1, and a shell;

[0059] The shell consists of three parts: a left end cap 35, a middle cylinder 34, and a right end cap 28. The left end cap 35 is an eccentric conical shell with an inclination angle ranging from 20° to 60°. The right end cap 28 is an elliptical end cap. The top of the shell has two cylinder shell-side outlets 33, and a wire mesh demister 32 is welded to the inner wall of the shell below each cylinder shell-side outlet 33. The bottom of the shell has two cylinder shell-side inlets 20 and two supports 21.

[0060] The evaporator E2 is a horizontal two-pass U-tube heat exchanger, including an evaporator tube box 13 and evaporator heat exchange tubes 19 arranged sequentially from left to right. The evaporator heat exchange tubes 19 are arranged close to the bottom of the shell and are completely submerged in the boiler feedwater within the shell. The other end of the evaporator tube box 13 is connected to the left end cap 35 via a first flange 15 and is located outside the shell. An evaporator tube plate 14 is held between the two flanges of the first flange 15. The inlet and outlet ends of the evaporator heat exchange tubes 19 are welded to the evaporator tube plate 14. The evaporator tube box 13 is divided into an upper evaporator tube box and a lower evaporator tube box by an evaporation partition plate 16 arranged horizontally within the evaporator tube box 13. The upper evaporator tube box is connected to the inlet end of the evaporator heat exchange tubes 19 and is provided with an evaporator tube-side inlet 12. The lower evaporator tube box is connected to the outlet end of the evaporator heat exchange tubes 19 and is provided with an evaporator tube-side outlet 17. The evaporator tube-side outlet 17 is connected to the outside of the system.

[0061] The bottom of the shell is provided with a plurality of equally spaced evaporation support plates 18, which are used to support the evaporation heat exchange tube 19 which is set close to the bottom of the shell inside the shell.

[0062] The preheater E3 is a horizontal two-pass U-tube heat exchanger, comprising a preheating tube box 24 and preheating heat exchange tubes 31 arranged sequentially from right to left. The preheating heat exchange tubes 31 are positioned close to the top of the shell, and the distance between the preheating heat exchange tubes 31 and the top of the shell is greater than or equal to the space required for water vapor to accumulate at the top of the shell. The other end of the preheating tube box 24 is connected to the right end cap 28 via a second flange 27 and is thus positioned outside the shell. The two ends of the second flange 27... A preheating tube sheet 26 is clamped between flanges; the inlet and outlet ends of the preheating heat exchange tube 31 are welded to the preheating tube sheet 26; the preheating tube box 24 is divided into an upper preheating tube box and a lower preheating tube box by a preheating partition 23 horizontally arranged inside the preheating tube box 24; the upper preheating tube box is connected to the outlet end of the preheating heat exchange tube 31 and is provided with a preheater tube side outlet 25; the lower preheating tube box is connected to the inlet end of the preheating heat exchange tube 31 and is provided with a preheater tube side inlet 22.

[0063] The upper part of the shell is provided with a support beam 29, which is used to support the preheating heat exchange tube 31, thereby ensuring that the preheating heat exchange tube is located close to the top of the shell and the distance between the preheating heat exchange tube and the top of the shell is greater than or equal to the space height required for water vapor to accumulate at the top of the shell; the upper part of the shell is provided with a plurality of equally spaced preheating support plates 30, which support the preheating heat exchange tube on the support beam 29;

[0064] The superheater E1 is a single-pass fixed tube sheet heat exchanger, comprising an upper superheated tube box 1, a superheated shell 4, and a lower superheated tube box 9 connected sequentially from top to bottom. The superheated shell 4 contains multiple vertical heat exchange tubes 6 and several horizontally arranged baffles 7 at equal intervals. The multiple vertical heat exchange tubes 6 pass vertically through the baffles 7. A superheater shell-side outlet 3 is located near the inlet end of the multiple vertical heat exchange tubes 6, and a superheater shell-side inlet 10 is located near the outlet end of the multiple vertical heat exchange tubes 6. The superheater shell-side outlet 3 is connected to the feed inlet (not shown) of the dehydrogenation reactor, and the superheater shell-side inlet 10 is connected to the preheater tube-side outlet 25 via a first connecting pipe 36. The middle of the superheated shell 4 is connected via an expansion joint 5 (U-shaped). The expansion joint 5 is used to compensate for the thermal expansion difference between the vertical heat exchange tube 6 and the superheated shell 4; the top and bottom of the superheated shell 4 are respectively welded with an upper tube sheet 2 and a lower tube sheet 8; the upper superheated tube box 1 and the lower superheated tube box 9 are each independently conical structures; the upper superheated tube box 1 is connected to the upper tube sheet 2 through an upper tube box flange; the lower superheated tube box 9 is connected to the lower tube sheet 8 through a lower tube box flange; the inlet end and outlet end of the vertical heat exchange tube 6 are respectively welded to the upper tube sheet 2 and the lower tube sheet 8; furthermore, one end of the lower superheated tube box 9 is connected to the outlet end of the vertical heat exchange tube 6, and the other end is connected to the evaporator tube side inlet 12 through a second connecting pipe 11; one end of the upper superheated tube box 1 is connected to the product outlet (not shown) of the dehydrogenation reactor, and the other end is connected to the inlet end of the vertical heat exchange tube 6.

[0065] Example 2

[0066] This embodiment provides a combined heat exchanger system for waste heat recovery in a styrene plant, such as... Figure 2 , 3 As shown, the only difference between this embodiment and Embodiment 1 is that:

[0067] The superheater E1 is a vertical single-pass floating tube sheet heat exchanger with built-in packing, comprising an upper superheated tube box 1, a superheated shell 4, and a lower superheated tube box 9 connected sequentially from top to bottom. The superheated shell 4 contains multiple vertical heat exchange tubes 6 and several horizontally arranged baffles 7 at equal intervals. The multiple vertical heat exchange tubes 6 pass vertically through the baffles 7. A superheater shell-side outlet 3 is located near the inlet end of the multiple vertical heat exchange tubes 6, and a superheater shell-side inlet 10 is located near the outlet end of the multiple vertical heat exchange tubes 6. The superheater shell-side outlet 3 is connected to the feed inlet of the dehydrogenation reactor, and the superheater shell-side inlet 10 is connected to the preheater tube-side outlet 25 via a first connecting pipe 36.

[0068] The top of the superheated shell 4 is welded with an upper tube sheet 2; the bottom of the superheated shell 4 is internally fitted with a lower tube sheet 8, and a packing device is provided between the lower tube sheet 2 and the superheated shell 4. The packing device is used to prevent leakage of the shell-side medium in the superheated shell caused by the movement of the lower tube sheet in the superheated shell (that is, the lower tube sheet can slide freely in the superheated shell under high temperature conditions, and the shell-side medium in the superheated shell will not leak into the tube side); the packing device includes packing 37, a packing gland 38, and fasteners 39; the packing gland 38 is used to compact and fix the packing 37 between the lower tube sheet 8 and the inner wall of the superheated shell 4; the fasteners 39 are used to fix the packing gland 38 to the bottom plate surface of the lower tube sheet 8;

[0069] The upper superheated tube box 1 and the lower superheated tube box 9 are each independently conical structures; the upper superheated tube box 1 is connected to the upper tube sheet 2 via an upper tube box flange; the lower superheated tube box 9 is connected to the lower tube sheet 8 via a lower tube box flange; the inlet and outlet ends of the vertical heat exchange tube 6 are respectively welded to the upper tube sheet 2 and the lower tube sheet 8; furthermore, one end of the lower superheated tube box 1 is connected to the outlet end of the vertical heat exchange tube 6, and the other end is connected to the evaporator tube inlet 12 via a second connecting pipe 11; one end of the upper superheated tube box 1 is connected to the product outlet of the dehydrogenation reactor, and the other end is connected to the inlet end of the vertical heat exchange tube 6.

[0070] Example 3

[0071] This embodiment provides a combined heat exchange method for waste heat recovery in a styrene plant. The method uses the system described in Embodiment 1 and includes the following steps:

[0072] Boiler feedwater enters the bottom of the shell from the shell side inlet 20 and is vaporized into water vapor under the heating action of the evaporation heat exchange tube 19, flowing towards the top of the shell;

[0073] The water vapor reaching the top of the shell, part of which is filtered by the wire mesh demister 32 and flows out of the shell through the shell-side outlet 33 (that is, in this embodiment, a part of water vapor is produced as a byproduct, realizing the full recovery and utilization of waste heat); the other part exchanges heat with the reaction raw materials entering the preheating heat exchange tube 31 from the preheater tube-side inlet 22. The water vapor is cooled and condensed into liquid water and falls back to the bottom of the shell. After the reaction raw materials are initially heated, they flow into the superheater E1 shell side through the preheater tube-side outlet 25, the first connecting pipe 36 and the superheater shell-side inlet 10 in sequence.

[0074] In the superheater E1, the reactants after initial heating undergo baffle flow in the shell side of the superheater under the action of the baffle 7, and exchange heat with the dehydrogenation reaction products entering the vertical heat exchange tube 6 from the upper superheater tube box 1. The reactants after initial heating are reheated and enter the feed inlet of the dehydrogenation reactor from the shell side outlet 3 of the superheater. The dehydrogenation reaction products are cooled and flow into the evaporation heat exchange tube 19 in sequence through the lower superheater tube box 9, the second connecting pipe 11 and the evaporator tube side inlet 12, serving as a heat source for gasifying the boiler feedwater.

[0075] The products of the dehydrogenation reaction in the evaporator heat exchange tube 19 are used as a heat source to vaporize the boiler feedwater. The products of the dehydrogenation reaction are then cooled again and discharged from the system through the evaporator tube outlet 17.

[0076] The various embodiments of the present invention have been described above. These descriptions are exemplary and not exhaustive, nor are they limited to the disclosed embodiments. Many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the described embodiments.

Claims

1. A combined heat exchanger system for waste heat recovery in a styrene plant, characterized in that, The system includes an evaporator, a preheater, a superheater, and a shell; The shell consists of three parts: a left end cap, a middle cylinder, and a right end cap; the top of the shell is provided with multiple cylinder shell-side outlets, and a wire mesh demister is fixedly installed on the inner wall of the shell below each cylinder shell-side outlet; the bottom of the shell is provided with multiple cylinder shell-side inlets. The evaporator is a horizontal heat exchanger, including an evaporator tube box and evaporator heat exchange tubes arranged sequentially from left to right; the evaporator heat exchange tubes are arranged close to the bottom of the shell and are completely submerged in the boiler feedwater inside the shell; the evaporator tube box is located outside the shell and has an evaporator tube inlet and an evaporator tube outlet. The preheater is a horizontal heat exchanger, comprising a preheating tube box and preheating heat exchange tubes arranged sequentially from right to left; the preheating heat exchange tubes are located close to the top of the shell inside the shell, and the distance between the preheating heat exchange tubes and the top of the shell is greater than or equal to the space height required for water vapor to accumulate at the top of the shell; the preheating tube box is located outside the shell, and the preheating tube box is provided with a preheater tube side outlet and a preheater tube side inlet; the preheater tube side inlet is connected to the reaction raw material supply device; The superheater is a vertical heat exchanger, comprising an upper superheated tube box, a superheated shell, and a lower superheated tube box connected sequentially from top to bottom. Multiple vertical heat exchange tubes are arranged inside the superheated shell. A shell-side outlet is located on the portion of the superheated shell near the inlet end of the multiple vertical heat exchange tubes, and a shell-side inlet is located on the portion of the superheated shell near the outlet end of the multiple vertical heat exchange tubes. The shell-side outlet of the superheater is connected to the feed inlet of the dehydrogenation reactor, and the shell-side inlet of the superheater is connected to the tube-side outlet of the preheater via a first connecting pipe. One end of the lower superheated tube box is connected to the outlet end of the vertical heat exchange tubes, and the other end is connected to the tube-side inlet of the evaporator via a second connecting pipe. One end of the upper superheated tube box is connected to the product outlet of the dehydrogenation reactor, and the other end is connected to the inlet end of the vertical heat exchange tubes.

2. The combined heat exchanger system for waste heat recovery in a styrene plant according to claim 1, wherein, The left end cap is an eccentric conical shell with an inclination angle ranging from 20º to 60º. The right end cap is an elliptical end cap; The top of the shell has two shell-side outlets; the bottom of the shell has two shell-side inlets and two supports.

3. The combined heat exchanger system for waste heat recovery in a styrene plant according to claim 1, wherein, The evaporator tube box is connected to the other end of the left end cap via a first flange and is thus disposed outside the shell, with the evaporator tube plate sandwiched between the two flanges of the first flange; the inlet and outlet ends of the evaporator heat exchange tube are fixed to the evaporator tube plate; the evaporator tube box is divided into an upper evaporator tube box and a lower evaporator tube box by an evaporation partition plate horizontally disposed inside the evaporator tube box; the upper evaporator tube box is connected to the inlet end of the evaporator heat exchange tube and is provided with the evaporator tube inlet, and the lower evaporator tube box is connected to the outlet end of the evaporator heat exchange tube and is provided with the evaporator tube outlet.

4. The combined heat exchanger system for waste heat recovery in a styrene plant according to claim 3, wherein, The evaporation heat exchange tube is a U-shaped tube; The inlet and outlet ends of the evaporation heat exchange tube are welded to the evaporation tube plate; The bottom of the shell is provided with several equally spaced evaporation support plates, which are used to support the evaporation heat exchange tubes to be closely attached to the bottom of the shell inside the shell. The evaporator tube outlet is connected to the outside of the system.

5. The combined heat exchanger system for waste heat recovery in a styrene plant according to claim 1, wherein, The preheating tube box is connected to the other end of the right end cap via a second flange and is thus disposed outside the shell, with the preheating tube plate sandwiched between the two flanges of the second flange; the inlet and outlet ends of the preheating heat exchange tube are fixed to the preheating tube plate; the preheating tube box is divided into an upper preheating tube box and a lower preheating tube box by a preheating partition plate horizontally disposed inside the preheating tube box; the upper preheating tube box is connected to the outlet end of the preheating heat exchange tube and is provided with the preheater tube side outlet, and the lower preheating tube box is connected to the inlet end of the preheating heat exchange tube and is provided with the preheater tube side inlet.

6. The combined heat exchanger system for waste heat recovery in a styrene plant according to claim 5, wherein, The preheating heat exchange tube is a U-shaped tube; The inlet and outlet ends of the preheating heat exchange tube are welded to the preheating tube sheet; The upper part of the shell is provided with a support beam, which is used to support the preheating heat exchange tube, thereby enabling the preheating heat exchange tube to be positioned close to the top of the shell inside the shell, and the distance between the preheating heat exchange tube and the top of the shell is greater than or equal to the space height required for water vapor to accumulate at the top of the shell; the upper part of the shell is provided with a plurality of equally spaced preheating support plates, which support the preheating heat exchange tube on the support beam.

7. The combined heat exchanger system for waste heat recovery in a styrene plant according to claim 1, wherein, The superheated shell is also provided with several horizontally arranged baffles at equal intervals, and the multiple vertical heat exchange tubes pass vertically through the baffles. The superheated shell is connected in the middle by an expansion joint, which is used to compensate for the thermal expansion difference between the vertical heat exchange tubes and the superheated shell; the top and bottom of the superheated shell are respectively fixedly connected to an upper tube sheet and a lower tube sheet; the upper superheated tube box is connected to the upper tube sheet through an upper tube box flange; the lower superheated tube box is connected to the lower tube sheet through a lower tube box flange; the inlet end and outlet end of the vertical heat exchange tube are respectively fixed to the upper tube sheet and the lower tube sheet.

8. The combined heat exchanger system for waste heat recovery in a styrene plant according to claim 1, wherein, The superheated shell is also provided with several horizontally arranged baffles at equal intervals, and the multiple vertical heat exchange tubes pass vertically through the baffles. An upper tube sheet is fixedly connected to the top of the superheated shell; a lower tube sheet is built into the bottom of the superheated shell, and a packing device is provided between the lower tube sheet and the superheated shell. The packing device is used to prevent leakage of the shell-side medium in the superheated shell caused by the movement of the lower tube sheet within the superheated shell; the upper superheated tube box is connected to the upper tube sheet through an upper tube box flange; the lower superheated tube box is connected to the bottom of the superheated shell through a lower tube box flange; the inlet and outlet ends of the vertical heat exchange tubes are fixed to the upper tube sheet and the lower tube sheet, respectively.

9. The combined heat exchanger system for waste heat recovery in a styrene plant according to claim 8, wherein, The packing device includes packing, a packing gland, and fasteners; the packing gland is used to compact and fix the packing between the lower tube sheet and the inner wall of the superheated shell; the fasteners are used to fix the packing gland to the bottom plate surface of the lower tube sheet.

10. A combined heat exchange method for waste heat recovery in a styrene plant, characterized in that, The method employs the system described in any one of claims 1-9 and includes the following steps: Boiler feedwater enters the bottom of the shell from the shell side inlet and is vaporized into water vapor under the heating effect of the evaporation heat exchange tubes, flowing towards the top of the shell; The water vapor reaching the top of the shell, part of which is filtered by the wire mesh demister and flows out of the shell through the shell-side outlet; the other part exchanges heat with the reaction material entering the preheating heat exchange tube from the preheater tube-side inlet. The water vapor is cooled and condenses into liquid water and falls back to the bottom of the shell. The reaction material is initially heated and flows into the superheater shell side through the preheater tube-side outlet, the first connecting pipe and the superheater shell-side inlet in sequence. In the superheater, the initially heated reaction feedstock exchanges heat with the dehydrogenation reaction products entering the vertical heat exchange tubes from the upper superheater tube box within the superheater shell side. The initially heated reaction feedstock is then reheated and enters the feedstock inlet of the dehydrogenation reactor from the superheater shell side outlet. The dehydrogenation reaction products are cooled and flow sequentially through the lower superheater tube box, the second connecting pipe, and the evaporator tube side inlet into the evaporation heat exchange tubes, serving as a heat source for the gasification of the boiler feedwater.

11. The combined heat exchange method for waste heat recovery in a styrene plant according to claim 10, wherein, Within the shell side of the superheater, the reactants after initial heating undergo baffled flow under the action of baffles, and exchange heat with the dehydrogenation reaction products that enter the vertical heat exchange tubes from the upper superheater tube box. The products of the dehydrogenation reaction in the evaporator heat exchange tube are used as a heat source to vaporize the boiler feedwater. The products of the dehydrogenation reaction are then cooled again and discharged from the system through the tube outlet of the evaporator.

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