Device for separating crude methanol and recovering methanol in esterification reaction by combination method and rectification method
Technical Field
The invention belongs to the field of methanol recovery, and particularly relates to a device and a rectification method for separating crude methanol and recovering methanol in an esterification reaction by a combination method.
Background
Methanol is one of the most basic organic raw materials, is saturated monohydric alcohol with the simplest structure in the world at present, has the relative molecular weight of 32.04 and the boiling point of 64.7 ℃, is commonly used as an organic solvent, is also used as a basic raw material in the industries of pesticides, medicines, plastics manufacturing and the like, and has extremely wide application range.
In recent years, due to breakthrough success of multiple technologies in methanol application, the market demand is accelerated rapidly, China is a large methanol-producing country and is also the largest methanol consuming country in the world, by the end of 2017, the apparent consumption of the methanol market in China reaches 5420 ten thousand tons, the self-supporting rate exceeds 90%, and under the condition that the operating rate of a methanol device stably rises, the acceleration of the methanol-producing capacity in 2018 is also accelerated synchronously, so that the problems brought by the acceleration are increasingly highlighted.
Methanol plants are rapidly increasing in scale and the energy saving problem becomes increasingly important. In the current methanol refining industry, the adopted mode is rectification, the rectification of methanol is a key link for obtaining high-quality methanol, but the problem of high energy consumption always exists, the traditional mode mostly adopts a double-tower structure consisting of a light component removal tower and a rectification tower, although the reaction flow is simple, the initial investment is less, the energy consumption is very high, the cost is higher, the profit margin is not ideal, and the energy-saving requirement of green chemistry is not met.
The existing rectification modes, such as double-effect rectification or multi-effect rectification, have the defect that the existing rectification modes cannot avoid any flow direction mode. Taking multi-effect rectification as an example, the equipment investment cost is inevitably increased along with the increase of the effect number and the increase of the number of the towers, one aspect is that the heat transfer temperature difference of the heat exchangers between adjacent effects is reduced because of the increase of the effect number, and the heat exchange area is required to be increased for achieving the purpose of good heat exchange, so the investment cost of the heat exchangers is increased. And because the pressure is increased in the rectifying process, a reboiler must use a high-quality heat source, so that a new requirement is provided for the reboiler, and in addition, the operation of a multi-effect rectifying system is relatively difficult, and the effect is not ideal when the system is applied to actual production. The technical key point of the double-effect rectification process lies in the recovery and reuse of the condensation potential of the product steam on the top of the tower, the production control key lies in the energy distribution proportion of the pressurizing tower and the main tower, and the double-effect rectification process flow is modified on the basis of the single-tower rectification flow, and needs to additionally increase the investment of fixed equipment, so that the operation cost is increased.
Disclosure of Invention
The invention provides a device and a rectification method for separating crude methanol and recovering methanol in esterification reaction by a combined method aiming at the problems.
The technical scheme adopted by the invention is as follows: a recovery unit for separating crude methanol and esterification reaction methanol by a combined method, wherein the tower top of a low-pressure tower is sequentially connected with a temporary condenser, a high-pressure tower heat exchanger, a low-pressure tower reflux tank and a high-pressure tower through pipelines, and the outlet of the low-pressure tower reflux tank is also connected with the low-pressure tower; the tower bottom of the low-pressure tower is connected with the high-pressure tower through a pipeline, and the tower bottom of the low-pressure tower is sequentially connected with the low-pressure tower heat exchanger and the low-pressure tower through pipelines; the top of the high-pressure tower is sequentially connected with the low-pressure tower heat exchanger, the high-pressure tower reflux tank and the high-pressure tower through pipelines, and a product is extracted at the outlet of the high-pressure tower reflux tank; the tower bottom of the high-pressure tower is connected with a high-pressure tower heat exchanger, a temporary reboiler and the high-pressure tower through pipelines, and a fusel oil discharge pipeline is arranged at the tower bottom of the high-pressure tower; the bottom of the high-pressure tower is also provided with a process wastewater discharge pipeline.
The recovery device for separating the crude methanol and the esterification reaction methanol by the combined method has the advantages that the temporary condenser can be detached after the device runs stably.
The recovery device for separating the crude methanol and the esterification reaction methanol by the combined method has the advantages that the temporary reboiler can be detached after the device is stably operated.
A rectification method of any one of the recovery device for the combined separation of the crude methanol and the esterification reaction methanol,
1) when the device does not reach the steady state: the first-stage crude methanol enters the low-pressure tower and then sequentially enters the high-pressure tower, the high-pressure tower heat exchanger and the temporary reboiler through pipelines, at the moment, no heat exchange medium exists in the high-pressure tower heat exchanger, so the first-stage crude methanol is heated by the temporary reboiler, the heated first-stage crude methanol returns to the high-pressure tower for rectification, the rectified methanol at the tower top returns to the high-pressure tower after passing through the low-pressure tower heat exchanger and the high-pressure tower reflux tank,
heating a part of first-stage crude methanol at the bottom of the low-pressure tower by a low-pressure tower heat exchanger, returning the heated first-stage crude methanol to the low-pressure tower, pre-rectifying the heated first-stage crude methanol in the low-pressure tower to obtain second-stage crude methanol, sequentially feeding the second-stage crude methanol into a temporary condenser, a high-pressure tower heat exchanger and a low-pressure tower reflux tank through pipelines, wherein a cooling medium in the high-pressure tower heat exchanger is insufficient for cooling the second-stage crude methanol, so that the temporary condenser is adopted for condensing the second-stage crude methanol, the distillate enters the high-pressure tower for rectification after refluxing in the low-pressure tower reflux tank, and the reflux liquid returns to the low-pressure tower;
2) when the device reaches a steady state: the first-stage crude methanol enters a low-pressure tower for pre-rectification, the second-stage crude methanol at the top of the tower enters a high-pressure tower heat exchanger for heat exchange and then enters a low-pressure tower reflux tank for separation, one part of the crude methanol enters the high-pressure tower, and the other part of the crude methanol refluxes into the low-pressure tower; one part of first-stage crude methanol at the bottom of the low-pressure tower exchanges heat through a low-pressure tower heat exchanger and then flows back to the low-pressure tower, and the other part of the first-stage crude methanol enters the high-pressure tower;
the second-stage crude methanol treated by the low-pressure tower enters a high-pressure tower for rectification, the rectified methanol steam at the top of the high-pressure tower enters a high-pressure tower reflux tank after heat exchange by a low-pressure tower heat exchanger, the distillate is extracted as a product after separation by the high-pressure tower reflux tank, and the reflux liquid flows back into the high-pressure tower; one part of the product at the bottom of the high-pressure tower returns to the high-pressure tower after heat exchange by the high-pressure tower heat exchanger, and the other part of the product is extracted as fusel oil; the process wastewater is discharged through a process wastewater pipeline.
In the rectification method of the recovery device for separating the crude methanol and the esterification reaction methanol by the combined method, the feed plate of the crude methanol entering the low-pressure tower is the 11 th plate.
The rectification method of the recovery device for separating the crude methanol and the esterification reaction methanol by the combined method has the following operating parameters of the low-pressure tower: the operation absolute pressure at the top of the tower is 50-60kPa, the operation temperature at the top of the tower is 46.7-51.8 ℃, the operation absolute pressure at the bottom of the tower is 80-100kPa, the operation temperature at the bottom of the tower is 61.8-67.5 ℃, and the reflux ratio is 0.7-1.5.
The rectification method of the recovery device for separating the crude methanol and the esterification reaction methanol by the combined method has the following operating parameters of the high-pressure tower: the operation absolute pressure at the top of the tower is 190-230kPa, the operation temperature at the top of the tower is 81.4-86.9 ℃, the operation absolute pressure at the bottom of the tower is 220-270kPa, the operation temperature at the bottom of the tower is 122.5-129.2 ℃, and the reflux ratio is 1.9-2.5.
The invention has the beneficial effects that:
1. the high-efficiency double-effect coupling design ensures that the whole system realizes self-sufficiency of energy, the energy is efficiently utilized, and the aim of saving energy is fulfilled.
2. The final product of the invention is provided by a high-pressure tower, and the low-pressure tower is used for pre-rectification of the crude methanol, so that the purity and yield of the refined methanol product are improved on one hand, and the stability of the quality of the output product can be ensured on the other hand.
3. The invention uses the temporary condenser and the temporary reboiler, makes up the defect of poor stability in the early stage of the double-effect coupling heat exchanger, and promotes the system to quickly reach a stable state. In addition, compared with multi-effect rectification, the combined form of two towers and two tanks improves the product separation quality, improves the yield, and simultaneously reduces the equipment cost and the cost.
Drawings
FIG. 1 is a process flow diagram of the present invention.
The designations in the figures illustrate the following: 1-low pressure column; 2-low pressure column heat exchanger; 3-a high pressure column; 4-high pressure column reflux drum; 5-high pressure column heat exchanger; 6-temporary reboiler; 7-temporary condenser; 8-low pressure column reflux drum.
Detailed Description
The invention is further illustrated by the following specific examples, but is not limited thereto.
Example 1
A recovery unit for separating crude methanol and methanol of esterification reaction by a combined method, wherein the tower top of a low pressure tower 1 is sequentially connected with a temporary condenser 7, a high pressure tower heat exchanger 5, a low pressure tower reflux tank 8 and a high pressure tower 3 through pipelines, and the outlet of the low pressure tower reflux tank 8 is also connected with the low pressure tower 1; the tower bottom of the low-pressure tower 1 is connected with the high-pressure tower 3 through a pipeline, and the tower bottom of the low-pressure tower 1 is sequentially connected with the low-pressure tower heat exchanger 2 and the low-pressure tower 1 through pipelines; the top of the high-pressure tower 3 is sequentially connected with the low-pressure tower heat exchanger 2, the high-pressure tower reflux tank 4 and the high-pressure tower 3 through pipelines, and a product is extracted at the outlet of the high-pressure tower reflux tank 4; the tower bottom of the high-pressure tower 3 is connected with a high-pressure tower heat exchanger 5, a temporary reboiler 6 and the high-pressure tower 3 through pipelines, and a fusel oil discharge pipeline is arranged at the tower bottom of the high-pressure tower 3; the bottom of the high-pressure tower 3 is also provided with a process wastewater discharge pipeline.
A rectification method for a recovery device for separating crude methanol and esterification reaction methanol by a combined method comprises the following steps:
firstly, when the device does not reach a steady state:
the crude methanol or the methanol remaining from the esterification reaction is used as the first-stage crude methanol.
The method comprises the following steps that first-stage crude methanol enters a low-pressure tower 1 from an 11 th plate, the first-stage crude methanol is gathered at the bottom of the low-pressure tower 1 under the action of gravity and is conveyed to a high-pressure tower 3 through a tower bottom pipeline, the first-stage crude methanol at the bottom of the high-pressure tower 3 sequentially enters a high-pressure tower heat exchanger 5 and a temporary reboiler 6 through pipelines, no medium serving as a first-stage crude methanol heat source exists in the high-pressure tower heat exchanger 5, therefore, the temporary reboiler 6 is arranged between the high-pressure tower heat exchanger 5 and the high-pressure tower 3 and is used for heating the first-stage crude methanol, methanol steam returns to the high-pressure tower 3 through a pipeline and is rectified in the high-pressure tower 3, the rectified methanol enters a low-pressure tower heat exchanger 2 through a tower top pipeline of the high-pressure tower 3 and enters a high-pressure tower reflux tank 4 after providing a heat source for the low-pressure tower heat exchanger 2, distillate is extracted as a product, and the distillate enters the high-pressure tower 3 for rectification again.
A part of first-stage crude methanol at the bottom of the low-pressure tower 1 enters a low-pressure tower heat exchanger 2 for heat exchange and then returns to the low-pressure tower 1, and is pre-rectified in the low-pressure tower 1, second-stage crude methanol enters a temporary condenser 7, a high-pressure tower heat exchanger 5 and a low-pressure tower reflux tank 8 in sequence through a tower top pipeline of the low-pressure tower 1, at the moment, a cooling medium in the high-pressure tower heat exchanger 5 cannot completely cool the pre-rectified methanol, so the temporary condenser 7 is arranged between the low-pressure tower 1 and the high-pressure tower heat exchanger to cool the second-stage crude methanol, the cooled second-stage crude methanol enters the low-pressure tower reflux tank 8 through a pipeline, reflux liquid enters the low-pressure tower 1 for pre-rectification again, and distillate enters the high-pressure tower 3 for rectification again,
secondly, when the device reaches a stable state:
the operation absolute pressure at the top of the low-pressure tower 1 is set to be 50-60kPa, the operation temperature at the top of the low-pressure tower is set to be 46.7-51.8 ℃, the operation absolute pressure at the bottom of the low-pressure tower is set to be 80-100kPa, the operation temperature at the bottom of the low-pressure tower is set to be 61.8-67.5 ℃, and the reflux ratio is set to be 0.7-1.5. The operation absolute pressure at the top of the high-pressure tower is set to be 190-86.9 kPa, the operation temperature at the top of the high-pressure tower is set to be 81.4-86.9 kPa, the operation absolute pressure at the bottom of the tower is set to be 220-129.2 kPa, the operation temperature at the bottom of the tower is set to be 122.5-129.2 ℃, and the reflux ratio is set to be 1.9-2.5.
And (5) removing the temporary condenser 7 and the temporary reboiler 6 after the device is stably operated.
The first-stage crude methanol enters a low-pressure tower 1 from the 11 th plate, part of the first-stage crude methanol passes through a low-pressure tower heat exchanger 2, the first-stage crude methanol is heated by the low-pressure tower heat exchanger 2 and then returns to the low-pressure tower 1 again, and pre-rectification is carried out in the low-pressure tower 1; the other part of the first-stage crude methanol enters the high-pressure tower 3 for rectification. The second-stage crude methanol enters a high-pressure tower heat exchanger 5 through a pipeline at the top of the low-pressure tower 1 for heat exchange and then enters a low-pressure tower reflux tank 8, the distillate enters a high-pressure tower 3 for rectification, and the reflux liquid returns to the low-pressure tower 1 through a pipeline for pre-rectification again.
A part of first-stage crude methanol and pre-rectified methanol are rectified in a high-pressure tower 3, the rectified methanol enters a low-pressure tower heat exchanger 2 for heat exchange and then enters a high-pressure tower reflux tank, distillate is extracted as a product, reflux liquid returns to the high-pressure tower 3 for rectification again, a part of methanol at the bottom of the high-pressure tower 3 passes through a high-pressure tower heat exchanger 5 as a cooling medium and then returns to the high-pressure tower 3 for rectification, and the other part of methanol is discharged as fusel oil. The process wastewater is discharged through a process wastewater pipeline.