Heat source optimizing device for reboiler of methanol pre-rectifying tower

Abstract

The utility model discloses a heat source optimizing device for a reboiler of a methanol pre-rectifying tower, which comprises the pre-rectifying tower and the reboiler, and is characterized in that a branch pipeline is separated from the crude methanol discharge of a tower kettle and is connected with a negative pressure flash tank, and the crude methanol in the negative pressure flash tank is subjected to gas-liquid separation through flash evaporation; the bottom of the negative-pressure flash tank is connected with a methanol circulating pump, and a liquid-phase material is conveyed to a first heat exchanger at the top of the tower and returns to the negative-pressure flash tank after exchanging heat with steam at the top of the tower; a gas-phase material in the negative-pressure flash tank enters a compressor, is compressed and heated and then returns to the tower kettle of the pre-rectifying tower; according to the utility model, the process is improved by combining flash evaporation of a tower kettle discharge part with heat pump rectification, and meanwhile, the flash evaporation liquid is recycled to recycle steam heat at the top of the tower, so that the steam consumption of a reboiler of the methanol pre-rectifying tower and the use amount of circulating water at the top of the tower are effectively reduced, meanwhile, the reboiler does not need to be added, and the compression ratio of a heat pump compressor can be reduced.

Description

Technical Field

[0001] The utility model belongs to the technical field of methanol refining and relates to a heat source optimization device for a reboiler of a methanol pre-distillation tower. Background Art

[0002] In the methanol production process, crude methanol is first produced from various raw materials such as coal, natural gas, coke oven gas, CO2, and biomass. The most common process for producing refined methanol from crude methanol is distillation. Distillation can be performed using different process methods, including double-tower distillation, "3+1" distillation towers, multi-effect distillation (high-pressure or negative-pressure towers), and heat pump distillation.

[0003] Double-tower distillation is adopted by many medium and small methanol production enterprises in my country, especially joint methanol enterprises, due to its low investment, short construction period and simple operation. The steam consumption for distillation of one ton of methanol is about 1.5 tons. Three-tower distillation is an advanced, efficient and low-energy process developed to reduce the loss of methanol in distillation and improve heat utilization efficiency. The methanol vapor at the top of the pressure tower is used as the heat source for heating the bottom of the atmospheric tower. The methanol vapor itself is condensed as reflux and extraction of the pressure tower. The atmospheric tower increases the side line extraction of fusel alcohol to reduce the accumulation of heavy components, which leads to an increase in the ethanol content in the top methanol product. The side line extraction and bottom material of the atmospheric tower are used as feed to the recovery tower to recover methanol from fusel alcohol and wastewater. The methanol recovery rate is improved, and the steam consumption for distillation of one ton of methanol can be controlled at about 1.1 tons. In recent years, driven by the increasing demand for energy conservation and consumption reduction, as well as higher product quality, the dominant "3+1" distillation tower technology has been expanded to include a high-pressure or negative-pressure tower. This provides an additional thermal coupling stage and a product output tower, resulting in improved methanol quality and lower energy consumption. Steam consumption per ton of methanol distilled is now around 0.8 tons. This increase in equipment volume has led to increased investment, increased operational difficulty, and decreased stability.

[0004] The conventional practice in heat pump distillation is to compress and heat the overhead vapor, using it as a heat source for the bottom of the tower. This consumes electricity to raise the pressure of the overhead vapor to heat the bottom of the tower. This process requires adding a heat exchanger to the bottom of the tower and ensuring a sufficient temperature difference to ensure heat transfer. The greater the temperature difference between the top of the tower and the bottom of the tower, the higher the compression ratio required by the heat pump, which in turn increases the space occupied by the compressor unit and the energy consumption. Summary of the Invention

[0005] The purpose of this utility model is to provide a reboiler heat source optimization device for a methanol pre-distillation tower. This device further reduces energy consumption by combining partial flash evaporation of the tower bottom discharge with a heat pump distillation process, while simultaneously circulating the flashed liquid to absorb the heat of overhead steam. This effectively reduces reboiler steam consumption and overhead circulating water usage. This also eliminates the need for a spare reboiler, reducing equipment footprint, and can also lower the compression ratio of the heat pump compressor, reducing energy consumption.

[0006] In order to achieve the above-mentioned purpose of the invention, the technical solution adopted by the present utility model is:

[0007] A heat source optimization device for a methanol pre-distillation tower reboiler comprises a pre-distillation tower and a reboiler, and is characterized in that a branch pipeline is branched from the crude methanol discharge from the tower bottom to be connected to a negative pressure flash tank, and the crude methanol in the negative pressure flash tank is subjected to gas-liquid separation by flash evaporation; the bottom of the negative pressure flash tank is connected to a methanol circulation pump, which sends liquid-phase material to a first heat exchanger at the top of the tower, and returns to the negative pressure flash tank after heat exchange with the steam at the top of the tower; the gaseous phase material in the negative pressure flash tank enters a compressor, is compressed and heated, and then returns to the tower bottom of the pre-distillation tower.

[0008] Furthermore, the top of the pre-distillation tower includes a first heat exchanger and a second heat exchanger connected in series, and the top steam enters the reflux tank after being cooled by the first heat exchanger and the second heat exchanger.

[0009] Furthermore, the first heat exchanger is a membrane heat exchanger.

[0010] Furthermore, the second heat exchanger is a circulating water heat exchanger.

[0011] Furthermore, the pressure of the negative pressure flash tank is 50-100 kPa (absolute pressure), and the liquid phase temperature is 58-65°C.

[0012] Furthermore, a heavy component extraction outlet is provided at the outlet of the methanol circulation pump, so that part of the flash liquid can be sent to the product separation tower of the subsequent process to avoid the accumulation of heavy components in the negative pressure flash tank.

[0013] The utility model discloses a heat source optimization device for the reboiler of a methanol pre-distillation tower. By optimizing the heat pump distillation process, the liquid in the tower bottom is directly flashed with negative pressure, and the methanol vapor at the top of the tower is used to heat the crude methanol after the decompression of the tower bottom, so as to achieve self-gasification. The gas is then pressurized and heated by a compressor and then directly returned to the tower bottom as a heat source, thereby replacing the steam consumption of the steam reboiler.

[0014] Beneficial effects: The heat source optimization device for the reboiler of the methanol pre-distillation tower of the present invention uses partial flash evaporation of the tower bottom discharge combined with a heat pump to replace the steam heating of the reboiler, thereby improving the heat pump distillation process. At the same time, the flash liquid is circulated and heat-exchanged with the steam at the top of the tower to recover heat. The heated part of the tower bottom liquid is vaporized, effectively reducing the steam consumption of the reboiler. The steam at the top of the tower is condensed after heat exchange, reducing the amount of circulating water at the top of the tower. Due to the use of the tower bottom heat pump process, there is no need for a spare reboiler. After flash evaporation and pressure raising, the steam directly enters the tower bottom, reducing the equipment footprint and heat transfer temperature difference restrictions, and can reduce the compression ratio of the heat pump compressor and reduce energy consumption. Specifically including:

[0015] (1) The steam consumption of the reboiler in the pre-distillation tower can be reduced by 80-90% by using a combination of a negative pressure flash tank, a circulating pump, a heat exchanger and a compressor;

[0016] (2) Improvements to the heat pump eliminate the need for a reboiler. Since the crude methanol flash heating process is used in the tower bottom, the medium itself does not mix. The crude methanol vapor that flashes after the decompression of the liquid absorbs the heat of the steam at the top of the tower and is then pressurized and incorporated into the tower bottom. This is of great significance for optimizing the equipment with limited layout in the renovation project. Other equipment can be arranged in the nearby open space.

[0017] (3) After the methanol vapor at the top of the tower is cooled and condensed by the crude methanol in the bottom of the tower, it can replace the cooling circulating water of most of the original primary coolers, and the amount of circulating water used is greatly reduced. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 A schematic structural diagram of a heat source optimization device for a methanol pre-distillation tower reboiler according to the present invention;

[0019] Among them, 1. Reboiler; 2. Heavy component; 3. Bottom discharge; 4. Negative pressure flash tank; 5. Methanol circulation pump; 6. Pre-distillation tower; 7. First heat exchanger (membrane heat exchanger); 8. Second heat exchanger (circulating water heat exchanger); 9. Reflux tank; 10. Compressor; 11. Non-condensable gas. DETAILED DESCRIPTION

[0020] The specific implementation methods of the present invention are described in detail below. However, it should be noted that the protection scope of the present invention is not limited by these specific implementation methods, but is determined by the claims.

[0021] like Figure 1 As shown, the heat source optimization device of the methanol pre-distillation tower reboiler of the utility model includes a pre-distillation tower 6 and a reboiler 1, and is characterized in that a branch pipeline is separated from the crude methanol discharge from the tower bottom to connect to the negative pressure flash tank 4, and the crude methanol in the negative pressure flash tank 4 is separated into gas and liquid by flash evaporation; the bottom of the negative pressure flash tank 4 is connected to a methanol circulation pump 5, and the liquid phase crude methanol is sent to the first heat exchanger 7 at the top of the tower, and the crude methanol returns to the negative pressure flash tank 4 after heat exchange with the steam at the top of the tower; the gaseous phase material in the negative pressure flash tank 4 enters the compressor 10, is compressed and heated, and then returns to the bottom of the pre-distillation tower 6.

[0022] The top of the pre-distillation tower 6 includes a first heat exchanger 7 and a second heat exchanger 8 connected in series. The first heat exchanger 7 is a membrane heat exchanger, and the second heat exchanger 8 is a circulating water heat exchanger. The overhead steam is cooled by the first heat exchanger 7 and the second heat exchanger 8 before entering the reflux tank 9.

[0023] The pre-distillation tower 6 uses steam to enter the reboiler 1 to start up. After stabilization, a branch is separated from the tower bottom discharge pipeline 3 to enter the negative pressure flash tank 4. The methanol content of the tower bottom discharge 3 is 80-95%, the temperature is 70-80 degrees, and the pressure is 130-200kPa (absolute pressure). The pressure of the negative pressure flash tank 4 is controlled by the compressor 10 speed or the reflux valve, generally controlled at 50-100kPa (absolute pressure). The liquid at the bottom of the negative pressure flash tank 4 is 58-65 degrees and is sent to the first heat exchanger 7 at the top of the tower through the methanol circulation pump 5. In order to avoid the accumulation of heavy components in the negative pressure flash tank 4, a stream of heavy component 2 material is drawn out from the outlet of the methanol circulation pump 5 and enters the subsequent product separation tower. In the first heat exchanger 7, the circulating methanol is heated to 72-78 degrees by the methanol vapor at the top of the tower and then returns to the negative pressure flash tank 4 for gas-liquid separation. The gaseous methanol enters the compressor 10, and after the pressure and temperature are increased, it returns to the pre-distillation tower 6. After the top of the tower is condensed by the first heat exchanger 7, the methanol follows the original process. After passing through the second heat exchanger 8, the non-condensable gas 11 is discharged, and the liquid enters the reflux tank 9. The liquid methanol returns to the pre-distillation tower 6 as tower reflux.

[0024] The outlet temperature of the first methanol heat exchanger 7 at the top of the tower can be controlled by the flow rate of the circulating methanol pump 5. The accumulation of heavy components will affect the efficiency of the first heat exchanger 7 and the evaporation amount of the negative pressure flash tank 4, and needs to be discharged continuously. The liquid level of the negative pressure flash tank 4 is controlled by the tower bottom discharge 3 pipeline branch of the pre-distillation tower 6, and the pressure of the negative pressure flash tank 4 is controlled by the speed of the compressor 10.

Claims

1. A methanol pre-distillation tower reboiler heat source optimization device, comprising a pre-distillation tower (6) and a reboiler (1), characterized in that: A branch pipeline is branched from the crude methanol discharge (3) at the bottom of the tower to be connected to a negative pressure flash tank (4), and the crude methanol in the negative pressure flash tank (4) is subjected to gas-liquid separation by flash evaporation; the bottom of the negative pressure flash tank (4) is connected to a methanol circulation pump (5), which sends the liquid phase material to the first heat exchanger (7) at the top of the tower, and returns to the negative pressure flash tank (4) after heat exchange with the steam at the top of the tower; the gas phase material in the negative pressure flash tank (4) enters the compressor (10), is compressed and heated, and then returns to the bottom of the pre-distillation tower (6).

2. The methanol pre-distillation tower reboiler heat source optimization device according to claim 1, characterized in that: The top of the pre-distillation tower (6) comprises a first heat exchanger (7) and a second heat exchanger (8) connected in series. The steam from the top of the tower is cooled by the first heat exchanger (7) and the second heat exchanger (8) and then enters the reflux tank (9).

3. The methanol pre-distillation tower reboiler heat source optimization device according to claim 2, characterized in that: The first heat exchanger (7) is a membrane heat exchanger.

4. The methanol pre-distillation tower reboiler heat source optimization device according to claim 2, characterized in that: The second heat exchanger (8) is a circulating water heat exchanger.

5. The heat source optimization device for the reboiler of the methanol pre-distillation tower according to claim 1, characterized in that: The pressure of the negative pressure flash tank (4) is 50-100 kPa, and the liquid phase temperature is 58-65°C.

6. The heat source optimization device for the reboiler of the methanol pre-distillation tower according to claim 1, characterized in that: The outlet of the methanol circulation pump (5) is provided with a heavy component (2) extraction outlet.

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