A heat exchanger and a methanol rectification system using the heat exchanger

Abstract

The present invention provides a methanol rectification system, which applies a heat exchanger and includes a crude alcohol preheater, a crude distillation column, a pressurized column, and a rectification column that are sequentially connected through pipelines. A steam buffer tank is connected to the crude distillation column and the pressurized column through pipelines. A first reboiler and a second reboiler are respectively connected to the pipelines where the steam buffer tank is connected to the crude distillation column and the pressurized column. A third reboiler is connected to the pipeline where the pressurized column is connected to the rectification column. A liquid delivery pump is connected to the pipeline where the crude distillation column is connected to the pressurized column. Both the first reboiler and the second reboiler are connected to a condensate tank through pipelines. The condensate tank is connected to the crude alcohol preheater through a pipeline. The bottom of the rectification column is connected to a heat exchanger through a pipeline. The present invention solves the problems of low heat utilization rate of the methanol rectification system and small total amount of heat recovery for the entire device in the prior art, and has the effect of improving the utilization rate of the total amount of waste heat.

Description

Technical Field

[0001] The present invention relates to the technical field of methanol rectification, and particularly relates to a heat exchanger and a methanol rectification system applying the heat exchanger. Background Art

[0002] At present, in domestic methanol production plants, especially some small-scale methanol production plants, there is a common phenomenon of high steam consumption in methanol rectification. Generally, at least 2.5 t of steam (0.35 MPa) is consumed for every 1 t of refined methanol produced, and even exceeds 3.0 t. The steam cost consumed in methanol rectification accounts for more than 80% of the methanol rectification cost (water, electricity, steam). Therefore, it has certain practical significance to study the reduction of steam consumption in methanol rectification.

[0003] The bottom temperature of the main rectification tower in the methanol rectification system is 104 - 110 °C. The residual liquid produced by rectification is sent out for treatment through a residual liquid pump. Since the residual liquid has a high temperature and an acidic pH value of 4.5 - 5.5, if directly sent out, it will not only cause heat loss, but also easily cause erosion corrosion and thinning of the residual liquid pipeline. Therefore, it is urgent to design a heat exchanger with strong heat exchange capacity to utilize the heat energy of the residual liquid; for example, a methanol recovery tower or a waste heat utilization system for a methanol rectification tower disclosed in the patent document CN212395918 absorbs the heat energy of the steam at the top of the methanol rectification tower through an absorption heat pump, and then uses the absorbed heat energy to heat the liquid at the bottom of the tower to achieve the full utilization of the remaining heat. However, the working energy consumption of the heat pump is high and the investment cost is high. Ordinary heat exchangers cannot fully utilize the heat of the residual liquid, and in the methanol rectification system, only the waste heat at the top of the methanol rectification tower is utilized, and the total amount of recovered heat is limited. Summary of the Invention

[0004] Aiming at the deficiencies in the prior art, the present invention provides a heat exchanger and a methanol rectification system applying the heat exchanger, which solve the problems of low heat utilization rate in the existing methanol rectification system and small total amount of heat recovery for the entire device.

[0005] According to an embodiment of the present invention, a heat exchanger includes a shell, a feed pipe fixedly connected to the top of the shell, and a discharge pipe fixedly connected to the bottom of the shell. Inside the shell, a first heat exchange group, a second heat exchange group, and a third heat exchange group are fixedly connected in sequence from top to bottom. The first heat exchange group and the third heat exchange group are horizontally fixedly installed at the inner top and inner bottom of the shell respectively through two parallel first tube sheets and third tube sheets. The second heat exchange group is fixedly installed obliquely at the inner middle of the shell through a second tube sheet. A connecting pipe for sequentially connecting the inside of the first heat exchange group, the second heat exchange group, and the third heat exchange group is fixedly connected to the side wall of the shell. Heat exchange tubes perpendicular to the corresponding tube sheets are fixedly connected inside the first heat exchange group, the second heat exchange group, and the third heat exchange group. A heat source pipe and a liquid outlet pipe are fixedly connected to the side wall of the shell. The heat source pipe is communicated with the inside of the third heat exchange group, and the liquid outlet pipe is communicated with the inside of the first heat exchange group.

[0006] Preferably, a plurality of second heat exchange groups are fixedly installed inside the housing.

[0007] Preferably, the heat exchange tubes in the first heat exchange group pass through the first tube sheet at the top, and the length of the heat exchange tubes passing through the first tube sheet decreases from the middle of the first tube sheet to the periphery.

[0008] Preferably, a methanol rectification system uses the above heat exchanger, and includes a crude alcohol preheater, a crude distillation column, a pressurizing column, and a rectification column that are sequentially connected by pipelines and are used for rectifying methanol. It also includes a steam buffer tank. The steam buffer tank is connected to a first reboiler and a second reboiler through pipelines. The first reboiler and the second reboiler are respectively connected to the crude distillation column and the pressurizing column through circulation pipelines. A third reboiler is connected to the pipeline connecting the pressurizing column and the rectification column. Liquid delivery pumps for transporting condensed water and methanol are connected to each pipeline. Both the first reboiler and the second reboiler are connected to a condensate tank through pipelines. The condensate tank is connected to the crude alcohol preheater through a pipeline. A heat exchanger is connected to the pipeline between the crude distillation column and the pressurizing column. The bottom of the rectification column is connected to a heat exchanger through a pipeline. The heat source pipe of the heat exchanger is connected to the bottom of the rectification column, and the feed pipe of the heat exchanger is connected to the bottom of the crude distillation column.

[0009] The outer wall of the condensate tank is coated with a layer of heat insulation cotton.

[0010] Compared with the prior art, the present invention has the following beneficial effects:

[0011] 1. The heat exchanger heats the methanol flowing through the heat exchange tubes by setting multiple heat exchange groups. The residual liquid enters the heat exchanger through the heat source pipe. The flow direction of the residual liquid is opposite to the flow direction of the methanol in the heat exchanger. The heat energy of the residual liquid is used in multiple stages to heat the methanol liquid with a temperature lower than that of the residual liquid; the heat exchange tubes in the second heat exchanger are inclined relative to the axis of the housing, so that the methanol slides down along the side wall of the housing of the heat exchange tube, and the tube pass of the heat exchange tube is relatively increased, making full use of the heat energy of the residual liquid flowing through the heat exchange group and improving the utilization rate of heat.

[0012] 2. The energy-saving and emission-reducing methanol rectification system transports the high-temperature condensed water in the first reboiler and the second reboiler to the crude alcohol preheater through the condensate tank, so that the crude alcohol is heated before entering the crude distillation column, reducing the consumption of steam in the crude distillation column; the heat exchanger uses the residual liquid of the rectification column to heat the methanol after crude distillation, reducing the consumption of steam in the rectification column and at the same time reducing the temperature of the residual liquid, which can slow down the corrosion of the residual liquid pipeline. Overall, the waste heat is fully utilized, the consumption of steam is reduced, and energy conservation and emission reduction are achieved. Description of the Drawings

[0013] Figure 1 It is the production process diagram of the embodiment of the present invention.

[0014] Figure 2Schematic diagram of the internal structure of the heat exchanger in the embodiment of the present invention.

[0015] In the above-mentioned drawings: 1, steam buffer tank; 2, first reboiler; 3, crude distillation column; 4, crude alcohol preheater; 5, second reboiler; 6, pressurized column; 7, third reboiler; 8, rectification column; 9, infusion pump; 10, condensate tank; 200, heat exchanger; 201, housing; 202, feed pipe; 203, discharge pipe; 204, heat source pipe; 205, connecting pipe; 206, heat exchange pipe; 207, liquid outlet pipe; 210, first heat exchange group; 211, first tube sheet; 220, second heat exchange group; 221, second tube sheet; 230, third heat exchange group; 231, third tube sheet. Detailed implementation manners

[0016] The technical solutions in the embodiments of the present invention will be further described below with reference to the drawings and embodiments.

[0017] As Figure 2 shown, in order to fully utilize the residue of the rectification column, an embodiment of the present invention proposes a heat exchanger, which includes a housing 201, a feed pipe 202 fixedly connected to the top of the housing 201, and a discharge pipe 203 fixedly connected to the bottom of the housing 201. Inside the housing 201, a first heat exchange group 210, a second heat exchange group 220, and a third heat exchange group 230 are fixedly connected in sequence from top to bottom. The first heat exchange group 210 and the third heat exchange group 230 are horizontally fixedly installed at the inner top and inner bottom of the housing 201 through two parallel first tube sheets 211 and third tube sheets 231 respectively. The second heat exchange group 220 is obliquely fixedly installed in the middle of the housing 201 through a second tube sheet 221. A connecting pipe 205 for sequentially connecting the inside of the first heat exchange group 210, the second heat exchange group 220, and the third heat exchange group 230 is fixedly connected to the side wall of the housing 201. Heat exchange pipes 206 perpendicular to the corresponding tube sheets are fixedly connected in the first heat exchange group 210, the second heat exchange group 220, and the third heat exchange group 230. A heat source pipe 204 and a liquid outlet pipe 207 are fixedly connected to the side wall of the housing 201. The heat source pipe 204 communicates with the inside of the third heat exchange group 230, and the liquid outlet pipe 207 communicates with the inside of the first heat exchange group 210.

[0018] The residual liquid enters the housing 201 through the heat source pipe 204, and methanol enters the interior of the housing 201 through the feed pipe 202. The residual liquid heats the methanol through the heat exchange pipe 206 in the third heat exchange group 230, the second heat exchange group 220, and the first heat exchange group 210. The flow direction of the residual liquid is opposite to that of the methanol, and the heat energy in the residual liquid is fully utilized by convection; the second tube sheet 221 is inclined and installed in the housing 201, so that the heat exchange pipe 206 fixedly installed on the second tube sheet 221 is inclined, so that methanol flows down from the side wall of the heat exchange pipe 206, so that the methanol flowing through the heat exchange pipe 206 absorbs heat sufficiently, and at the same time increases the heat exchange time of methanol, fully utilizing the heat energy of the residual liquid. At the same time, the inclined heat exchange pipe 206 increases the tube pass of methanol flowing through the heat exchange pipe 206.

[0019] As Figure 2 shown, to increase the number of heat exchange pipes 206 in the second heat exchange group 220, in another embodiment of the present invention, multiple groups of second heat exchange groups 220 are fixedly installed in the housing 201; when the heat exchange pipe 206 in the second heat exchange group 220 is relatively long, due to the inclined setting of the heat exchange pipe 206, the number of heat exchange pipes 206 installed on the second tube sheet 221 is reduced, thereby reducing the contact area between the heat exchange pipes 206 in the second heat exchange group 220 and the residual liquid. By providing multiple groups of second heat exchange groups 220 in the housing 201 and increasing the number of heat exchange pipes 206 in the second heat exchange group 220, the total area of the heat exchange pipes 206 in the second heat exchange group 220 can be increased, thereby improving the heat exchange efficiency of the second heat exchange group 220.

[0020] As Figure 2 shown, to prevent methanol from passing through the heat exchange pipes 206 in the middle of the first heat exchange group 210 and reducing the utilization rate of heat, the heat exchange pipes 206 in the first heat exchange group 210 pass through the top first tube sheet 211, and the length of the heat exchange pipes 206 passing through the first tube sheet 211 decreases from the middle of the first tube sheet 211 to the periphery; part of the methanol passes through the heat exchange pipes 206 in the middle of the first tube sheet 211, and the remaining methanol falls on the first tube sheet 211. As the amount of methanol on the first tube sheet 211 increases, the methanol flows into the heat exchange pipes 206 at the edge of the first tube sheet 211 and gradually extends towards the middle of the first tube sheet 211.

[0021] As Figure 1As shown in the figure, in order to improve the utilization rate of waste heat in the rectification device, an embodiment of the present invention proposes a methanol rectification system. Applying the above-mentioned heat exchanger 200, it includes a raw alcohol preheater 4, a rough distillation column 3, a pressurizing column 6, and a rectification column 8 that are sequentially connected by pipelines and used for rectifying methanol. It also includes a steam buffer tank 1. The steam buffer tank 1 is connected to a first reboiler 2 and a second reboiler 5 through pipelines. The first reboiler 2 and the second reboiler 5 are respectively connected to the rough distillation column 3 and the pressurizing column 6 through circulation pipelines. A third reboiler 7 is connected to the pipeline connecting the pressurizing column 6 and the rectification column 8. Liquid delivery pumps 9 for transporting condensate and methanol are connected to each pipeline. Both the first reboiler 2 and the second reboiler 5 are connected to a condensate tank 10 through pipelines. The condensate tank 10 is connected to the raw alcohol preheater 4 through a pipeline. A heat exchanger 200 is connected to the pipeline between the rough distillation column 3 and the pressurizing column 6. The bottom of the rectification column 8 is connected to a heat exchanger 200 through a pipeline. The heat source pipe 204 of the heat exchanger 200 is connected to the bottom of the rectification column 8. The feed pipe 202 of the heat exchanger 200 is connected to the bottom of the rough distillation column 3. Methanol first passes through the raw alcohol preheater 4 and then enters the rough distillation column 3. The condensate obtained after the steam used for heating methanol in the first reboiler 2 and the second reboiler 5 is liquefied is transported to the condensate tank 10 through a pipeline. Then, the liquid delivery pump 9 transports the condensate in the condensate tank 10 to the raw alcohol preheater 4. The raw alcohol preheater 4 uses the heat in the condensate to heat methanol. The heated methanol enters the rough distillation column 3, reducing the amount of steam used for heating methanol in the rough distillation column 3, thereby achieving energy conservation. At the same time, the bottom residue generated during the methanol rectification in the rectification column 8 is transported to the heat exchanger 200 through the liquid delivery pump 9. The methanol after rough distillation is transported to the heat exchanger 200 through a pipeline. The residue and methanol perform heat exchange in the heat exchanger 200, making full use of the heat in the residue. After the heat exchange of methanol is completed, it enters the rectification column 8 after passing through the pressurizing column 6 and the third reboiler 7, realizing the rectification of methanol.

[0022] As a preferred embodiment, in order to reduce the heat energy loss of the condensate in the condensate tank 10, the outer wall of the condensate tank 10 is coated with a layer of heat insulation cotton; the heat insulation cotton is used to reduce the heat energy loss of the condensate in the condensate tank 10.

[0023] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that the technical solutions of the present invention can be modified or equivalently replaced without departing from the purpose and scope of the technical solutions of the present invention, and they should all be covered within the scope of the claims of the present invention.

Claims

1. A heat exchanger, comprising a housing (201), a feed pipe (202) fixedly connected to the top of the housing (201), and a discharge pipe (203) fixedly connected to the bottom of the housing (201), characterized in that: Inside the housing (201), a first heat exchange group (210), a second heat exchange group (220), and a third heat exchange group (230) are fixedly connected in sequence from top to bottom. The first heat exchange group (210) and the third heat exchange group (230) are horizontally and fixedly installed at the inner top and inner bottom of the housing (201) respectively through two parallel first tube sheets (211) and third tube sheets (231). The second heat exchange group (220) is obliquely and fixedly installed in the middle part of the housing (201) through a second tube sheet (221). A connecting pipe (205) for sequentially communicating the interiors of the first heat exchange group (210), the second heat exchange group (220), and the third heat exchange group (230) is fixedly connected to the side wall of the housing (201). Heat exchange tubes (206) perpendicular to the corresponding tube sheets are fixedly connected inside the first heat exchange group (210), the second heat exchange group (220), and the third heat exchange group (230). A heat source pipe (204) and a liquid outlet pipe (207) are fixedly connected to the side wall of the housing (201). The heat source pipe (204) communicates with the interior of the third heat exchange group (230), and the liquid outlet pipe (207) communicates with the interior of the first heat exchange group (210); the heat exchange tubes (206) in the first heat exchange group (210) pass through the first tube sheet (211) at the top, and the length of the heat exchange tubes (206) passing through the first tube sheet (211) decreases from the middle of the first tube sheet (211) to the periphery.

2. The heat exchanger according to claim 1, wherein: Multiple groups of second heat exchange groups (220) are fixedly installed inside the housing (201).

3. A methanol rectification system, applying the heat exchanger described in claim 1 or 2, comprises a raw alcohol preheater (4), a rough distillation column (3), a pressurized column (6) and a rectification column (8) which are connected in sequence through pipelines and are used for rectifying methanol. The system further comprises a steam buffer tank (1). The steam buffer tank (1) is connected to a first reboiler (2) and a second reboiler (5) through pipelines. The first reboiler (2) and the second reboiler (5) are respectively connected to the rough distillation column (3) and the pressurized column (6) through circulation pipelines. A third reboiler (7) is connected to the pipeline connecting the pressurized column (6) and the rectification column (8). Liquid delivery pumps (9) for transporting condensed water and methanol are connected to each pipeline. It is characterized in that: Both the first reboiler (2) and the second reboiler (5) are connected to a condensate tank (10) through pipelines. The condensate tank (10) is connected to a crude alcohol preheater (4) through a pipeline. A heat exchanger (200) is connected to the pipeline between the crude distillation column (3) and the pressurized column (6). The bottom of the rectification column (8) is connected to a heat exchanger (200) through a pipeline. The heat source pipe (204) of the heat exchanger (200) is connected to the bottom of the rectification column (8), and the feed pipe (202) of the heat exchanger (200) is connected to the bottom of the crude distillation column (3).

4. A methanol rectification system according to claim 3, characterized in that: The outer wall of the condensate tank (10) is coated with a layer of heat insulation cotton.

Images