Multi-effect rectification system for acetic acid dehydration process

Abstract

The utility model relates to a multi-effect rectification system for an acetic acid dehydration process, which comprises at least two acetic acid dehydration towers, the tower kettle discharge of the previous acetic acid dehydration tower is connected with the feed of the next acetic acid dehydration tower, and the tower kettle reboiler of the previous acetic acid dehydration tower is connected with the tower top of the next acetic acid dehydration tower for heat exchange. Wastewater is extracted from the tops of all the acetic acid dehydrating towers; a to-be-treated water-containing acetic acid raw material is input into the feeding hole of the first acetic acid dehydrating tower, and acetic acid is extracted from the tower bottom of the last acetic acid dehydrating tower. The acetic acid dehydrating towers are sequentially connected, high-temperature steam at the top of the next tower exchanges heat with the reboiler at the bottom of the current tower, so that the reboiler at the bottom of the current tower obtains heat, meanwhile, the high-temperature steam at the top of the next tower is completely liquefied, consumption of external heating media or cold sources is effectively reduced, energy consumption of the whole process is reduced, and the production cost is reduced. Therefore, the operation cost is greatly reduced.

Description

Technical Field

[0001] The utility model relates to a multi-effect distillation system for acetic acid dehydration process. Background Art

[0002] Acetic acid is an important organic chemical with wide applications in production and life. Acetic acid can be used in the synthesis of various chemicals such as vinyl acetate, acetate ester, acetic anhydride, terephthalic acid, and chloroacetic acid. At the same time, it is widely used in the fields of medicine, pesticides, dyes, synthetic fibers, and water treatment.

[0003] The main synthesis routes of acetic acid include acetaldehyde oxidation method, ethylene oxidation method, naphtha / n-butane oxidation method, ethane catalytic oxidation method, methanol carbonylation synthesis method, etc. Among them, the methanol carbonylation synthesis method has rich and easily available raw materials, mild reaction conditions, simple process, and high product yield, and it is a commonly used process for newly launched projects at present.

[0004] When acetic acid is used as a solvent in the synthesis of some chemicals, a large amount of water will be generated in some reactions. In order to recycle and reuse acetic acid as a solvent, an acetic acid dehydration tower is usually used to separate water and acetic acid. Since the mass ratio of acetic acid and water in the whole system is very large, the energy consumption of the acetic acid dehydration tower accounts for a large part of the whole process.

[0005] Most of the existing acetic acid dehydration towers use an azeotropic agent (such as acetate esters) for azeotropic dehydration (such as CN115317949B). Its advantage is that it can greatly reduce the energy consumption compared with directly distilling and separating acetic acid and water. However, there will be a loss of the azeotropic agent in this scheme. The price of the azeotropic agent is generally high, and using the azeotropic agent will increase the material cost, and finally the effect of reducing the cost is limited.

[0006] In the existing distillation technology, the heat source and the refrigerant both come from external utilities, resulting in large energy consumption. Therefore, a multi-effect distillation system for acetic acid dehydration process with more energy-saving and lower cost is proposed. Content of the Utility Model

[0007] Aiming at the deficiencies of the existing technology, the technical problem to be solved by the utility model is to provide a multi-effect distillation system for acetic acid dehydration process, which has lower energy consumption, realizes heat exchange between towers, and greatly reduces the production cost.

[0008] The technical solution adopted by the utility model to solve the above technical problem is:

[0009] The utility model provides a multi-effect distillation system for an acetic acid dehydration process, which is characterized in that the system includes at least two acetic acid dehydration towers. The bottom discharge of the previous acetic acid dehydration tower is connected to the feed of the next acetic acid dehydration tower, and the reboiler at the bottom of the previous acetic acid dehydration tower is connected to the top of the next acetic acid dehydration tower for heat exchange. The waste water is taken out from the top of all acetic acid dehydration towers. The feed port of the first acetic acid dehydration tower inputs the acetic acid raw material containing water to be treated, and the acetic acid is taken out from the bottom of the last acetic acid dehydration tower.

[0010] Further, there are heavy components in the acetic acid raw material containing water to be treated. At this time, the system also includes an acetic acid product tower. The reboiler at the bottom of the last acetic acid dehydration tower is connected to the top of the acetic acid product tower for heat exchange. The acetic acid is taken out from the top of the acetic acid product tower, and the heavy components are taken out from the bottom. And the feed port of the acetic acid product tower is connected to the bottom discharge of the last acetic acid dehydration tower.

[0011] Further, there are no heavy components in the acetic acid raw material containing water to be treated. At this time, the system does not need an acetic acid product tower, and the qualified acetic acid is taken out from the bottom of the last acetic acid dehydration tower. At this time, an external heat source is provided for the last acetic acid dehydration tower.

[0012] Further, the tower diameter of the acetic acid dehydration tower is 0.2 m to 9 m, and the tower height is 10 m to 80 m; the tower diameter of the acetic acid product tower is 0.2 m to 9 m, and the tower height is 10 m to 80 m.

[0013] Further, the pressure and temperature of each tower connected in sequence increase, and the top temperature of the next tower is higher than the bottom temperature of the previous tower.

[0014] Further, corresponding condensers, reflux tanks and reflux pumps are equipped at the top of each acetic acid dehydration tower, and reboilers are equipped at the bottom of each acetic acid dehydration tower.

[0015] Further, when there is an acetic acid product tower and the gas phase at the top of the acetic acid product tower is not enough to meet the heat required by the reboiler of the last acetic acid dehydration tower, two parallel reboilers are equipped at the bottom of the last acetic acid dehydration tower. One of the reboilers exchanges heat with the top of the acetic acid product tower, and the other reboiler uses an external heat source.

[0016] Further, corresponding condensers, reflux tanks and reflux pumps are equipped at the top of the acetic acid product tower, and a reboiler is equipped at the bottom of the acetic acid product tower.

[0017] Further, the water content in the acetic acid raw material containing water to be treated is less than 15% by mass, and two acetic acid dehydration towers are arranged in the system.

[0018] Compared with the prior art, the beneficial effects of the utility model are:

[0019] 1. The utility model uses multiple acetic acid dehydration towers connected in sequence. The high-temperature steam at the top of the next tower exchanges heat with the reboiler at the bottom of the current tower, enabling the reboiler at the bottom of the current tower to obtain heat. At the same time, the high-temperature steam at the top of the next tower is completely liquefied, effectively reducing the consumption of external heat medium or cold source, lowering the energy consumption of the entire process, and thus greatly reducing the operating cost. Compared with other industrial energy-saving designs, this method has less investment, is practical and reliable, and has remarkable effects. Compared with the acetic acid dehydration device with conventional non-heat exchange design, the utility model can save about 40 - 70% of energy.

[0020] 2. The utility model combines multiple acetic acid dehydration towers with an acetic acid product tower, capable of processing water-containing acetic acid raw materials with heavy components at low energy consumption and low cost.

[0021] 3. For the different water contents and different heavy component contents of common water-containing acetic acid, the utility model can expand or streamline the system equipment, with more flexible settings and better meeting the actual needs. Brief Description of the Drawings

[0022] Figure 1 It is a schematic structural diagram of a multi-effect rectification system for the acetic acid dehydration process in Embodiment 1 of the utility model.

[0023] Figure 2 It is a schematic structural diagram of a multi-effect rectification system for the acetic acid dehydration process in Embodiment 2 of the utility model.

[0024] In the figure, 1 - the first acetic acid dehydration tower; 2 - the reboiler of the first acetic acid dehydration tower; 3 - the condenser of the first acetic acid dehydration tower; 4 - the reflux drum of the first acetic acid dehydration tower; 5 - the reflux pump of the first acetic acid dehydration tower; 6 - the bottom pump of the first acetic acid dehydration tower; 7 - the second acetic acid dehydration tower; 8 - the reboiler of the second acetic acid dehydration tower; 9 - the reflux drum of the second acetic acid dehydration tower; 10 - the reflux pump of the second acetic acid dehydration tower; 11 - the bottom pump of the second acetic acid dehydration tower; 12 - the third acetic acid dehydration tower; 13 - the first reboiler of the third acetic acid dehydration tower; 14 - the second reboiler of the third acetic acid dehydration tower; 15 - the reflux drum of the third acetic acid dehydration tower; 16 - the reflux pump of the third acetic acid dehydration tower; 17 - the bottom pump of the third acetic acid dehydration tower; 18 - the acetic acid product tower; 19 - the reboiler of the acetic acid product tower; 20 - the reflux drum of the acetic acid product tower; 21 - the reflux pump of the acetic acid product tower; 22 - the bottom pump of the acetic acid product tower. Detailed Embodiments

[0025] The following further explains the utility model in conjunction with embodiments and drawings, but does not limit the protection scope of this application with this.

[0026] In the present utility model, it can be divided into two parts in sequence: acetic acid dehydration and light component removal, and acetic acid heavy component removal. The water-containing acetic acid enters the acetic acid dehydration and light component removal part as raw material, and then the light components are removed to obtain crude acetic acid. In the acetic acid heavy component removal part, the heavy components are removed from the crude acetic acid to obtain qualified acetic acid products. The acetic acid dehydration and light component removal part is completed by multiple acetic acid dehydration towers (such as acetic acid dehydration tower 1, acetic acid dehydration tower 7, acetic acid dehydration tower 12, etc.), and the acetic acid heavy component removal part is completed by the acetic acid product tower.

[0027] When the water content is relatively low (when the water content is 15% - 80% when the water content is high, and less than 15% is considered to have a low water content) and there are heavy components, it can be completed by two acetic acid dehydration towers, and the acetic acid heavy component removal part is completed by the acetic acid product tower. The pressure and temperature of each tower connected in sequence increase, and the top temperature of the latter tower is higher than the bottom temperature of the previous tower, and there is a temperature difference, so that the top gas phase of the latter tower serves as the heat source for the previous tower.

[0028] When the water content is high and there are heavy components, the bottom temperature of acetic acid dehydration tower 1 < the top temperature of acetic acid dehydration tower 7, the bottom temperature of acetic acid dehydration tower 7 < the top temperature of acetic acid dehydration tower 12, the bottom temperature of acetic acid dehydration tower 12 < the top temperature of acetic acid product tower 18, and between each pair, the one with the higher temperature provides part or all of the required heat for the one with the lower temperature.

[0029] When the water content is low and there are heavy components, the bottom temperature of acetic acid dehydration tower 1 < the top temperature of acetic acid dehydration tower 7, the bottom temperature of acetic acid dehydration tower 7 < the top temperature of acetic acid product tower 18, and between each pair, the one with the higher temperature serves as the heat source for the one with the lower temperature.

[0030] The temperature difference between each pair is 5°C - 50°C, and preferably the temperature difference is 10°C - 30°C.

[0031] When there are heavy components in the water-containing acetic acid raw material, the acetic acid product tower is used to remove the heavy components; when there are no heavy components in the water-containing acetic acid raw material, the acetic acid product tower can be not set in the system, and at this time, an external heat source is provided for the last acetic acid dehydration tower.

[0032] In the present utility model, the tower diameter of the acetic acid dehydration tower used is 0.2m - 9m, and the tower height is 10m - 80m; the tower diameter of the acetic acid product tower is 0.2m - 9m, and the tower height is 10m - 80m, which can be selected according to the actual situation.

[0033] For the convenience of startup and adjustment, a reboiler using steam as the heat source can also be set in acetic acid dehydration tower 1 or acetic acid dehydration tower 7.

[0034] The temperature difference is the driving force for heat transfer in the heat exchanger. According to the basic heat transfer equation:

[0035] Q = KAΔtm

[0036] wherein, Q — heat transfer rate, W

[0037] K — proportionality coefficient, W / m2·°C

[0038] A — heat transfer area, m 2

[0039] Δtm — heat transfer driving force, °C

[0040] The heat transfer driving force comes from the temperature difference between the hot stream and the cold stream. If the temperature difference is too small, it is easy to cause temperature cross and affect heat transfer, and the heat transfer area of the heat exchanger will be very large, which is unreasonable from an economic perspective; in order to build the temperature difference between different towers, the pressure needs to be controlled. If the pressure difference between the two towers is blindly increased just to expand the temperature difference between the two towers, it is also unreasonable from an economic perspective. Therefore, the temperature difference between the top and bottom of the two towers that need heat exchange is limited within the range of 5 to 50 °C.

[0041] The top pressure of the first acetic acid dehydration tower 1 is -100 kPa(G) to atmospheric pressure, the top temperature is 30 to 80 °C, and the bottom temperature is 50 to 100 °C; the top pressure of the second acetic acid dehydration tower 7 is -70 kPa(G) to 30 kPa(G), the top temperature is 65 to 120 °C, and the bottom temperature is 75 to 130 °C;

[0042] When the water content is relatively high, the top pressure of the third acetic acid dehydration tower 12 is -50 kPa(G) to 50 kPa(G), the top temperature is 85 to 135 °C, and the bottom temperature is 100 to 150 °C; the top pressure of the acetic acid product tower 18 is atmospheric pressure to 100 kPa(G), the top temperature is 110 to 160 °C, and the bottom temperature is 130 to 180 °C;

[0043] When the water content is relatively low, the top pressure of the acetic acid product tower 18 is -50 kPa(G) to 50 kPa(G), the top temperature is 90 to 140 °C, and the bottom temperature is 105 to 165 °C.

[0044] In the present utility model, the mass fraction of acetic acid in the raw material is between 20% and 95%.

[0045] Select the tower internals according to the different physical properties of the gas phase and liquid phase of each tower, and it can be selected according to the following formula:

[0046] Flow parameter

[0047] wherein, L — liquid load, kmol / s

[0048] V — gas load, kmol / s

[0049] ρ g—— Gas density, kg / m 3

[0050] ρ l —— Liquid density, kg / m 3

[0051] When FP = 0.02 - 0.3, the packed tower has higher efficiency than the tray tower. In the process of the present utility model, the FP values of each tower are all between 0.02 - 0.25, and it is more suitable to use a packed tower. When using a packed tower, the internals of the tower include packing, packing support rings, liquid distributors, etc. In addition, the packed tower has better separation effect at the same tower height, and the pressure drop of the whole tower is smaller, making it easier to meet the heat exchange system in the present utility model. In the following embodiments, a packed tower is selected.

[0052] The number of theoretical plates of each acetic acid dehydration tower in the present utility model can be the same, and the number of theoretical plates of the acetic acid product tower can be set according to the types and contents of the heavy components in the feed.

[0053] The system of the present utility model exchanges heat and pressurizes step by step, so that a suitable temperature difference is formed between the towers, constituting a multi-effect heat exchange network. The next tower has a higher pressure and temperature than the current tower, making the top temperature of the next tower higher than the bottom temperature of the current tower, and the temperature difference is not less than 5°C; in the process, the high-temperature steam at the top of the next tower exchanges heat with the reboiler at the bottom of the current tower, enabling the reboiler at the bottom of the current tower to obtain heat, and at the same time, the high-temperature steam at the top of the next tower is completely liquefied; effectively reducing the consumption of external heat medium or cold source, reducing the energy consumption of the whole process, and thus greatly reducing the operating cost.

[0054] Example 1

[0055] This example is used for acetic acid dehydration treatment when the water content is greater than 15% and there are heavy components. The multi-effect distillation system for the acetic acid dehydration process includes the first acetic acid dehydration tower 1, the second acetic acid dehydration tower 7, the second acetic acid dehydration tower 12, and the acetic acid product tower 18, a total of 4 towers, all equipped with corresponding condensers, reflux phase separation tanks, and reboilers;

[0056] The feed of the first acetic acid dehydration tower 1 is the acetic acid raw material containing water; the bottom discharge of the first acetic acid dehydration tower 1 is connected to the feed of the second acetic acid dehydration tower 7. The top of the first acetic acid dehydration tower 1 is refluxed and taken out as wastewater, and the reboiler at the bottom of the first acetic acid dehydration tower 1 is connected to the top of the second acetic acid dehydration tower 7 for heat exchange;

[0057] The bottom discharge of the second acetic acid dehydration tower 7 is connected to the feed of the third acetic acid dehydration tower 12. The top of the second acetic acid dehydration tower 7 is refluxed and taken out as wastewater, and the reboiler at the bottom of the second acetic acid dehydration tower 7 is connected to the top of the third acetic acid dehydration tower 12 for heat exchange;

[0058] The bottom discharge of the third acetic acid dehydration tower 12 is connected to the feed of the acetic acid product tower 18, and the top reflux of the third acetic acid dehydration tower 12 is taken out as wastewater; the reboiler at the bottom of the third acetic acid dehydration tower 12 is connected to the top of the acetic acid product tower 18, and part of the required heat is provided by the top gas phase of the acetic acid product tower 18.

[0059] The bottom discharge of the acetic acid product tower 18 is taken out as heavy components, and the top reflux of the acetic acid product tower 18 is taken out as acetic acid product.

[0060] The specific treatment process is as follows: the acetic acid raw material containing water is sent to the first acetic acid dehydration tower 1. The first acetic acid dehydration tower 1 is equipped with a reboiler for the first acetic acid dehydration tower 2, and the top gas phase of the second acetic acid dehydration tower 7 is used as the heat source for the reboiler; the top pressure of the first acetic acid dehydration tower 1 is -100 kPa(G) to atmospheric pressure, where G represents gauge pressure, the top temperature is 30 - 80 °C, and the bottom temperature is 50 - 100 °C; the top gas phase of the first acetic acid dehydration tower 1 enters the condenser 3 of the first acetic acid dehydration tower for condensation, with circulating water as the refrigerant for the condenser. The condensed liquid enters the reflux drum 4 of the first acetic acid dehydration tower. The material in the reflux drum 4 of the first acetic acid dehydration tower is transported by the reflux pump 5 of the first acetic acid dehydration tower. Part of it is returned as reflux to the top of the first acetic acid dehydration tower 1, and the other part is taken out as wastewater.

[0061] The material at the bottom of the first acetic acid dehydration tower 1 is transported by the bottom pump 6 of the first acetic acid dehydration tower into the second acetic acid dehydration tower 7. The second acetic acid dehydration tower 7 is equipped with a reboiler for the second acetic acid dehydration tower 8, and the top gas phase of the third acetic acid dehydration tower 12 is used as the heat source for the reboiler; the top pressure of the second acetic acid dehydration tower 7 is -70 kPa(G) to 30 kPa(G), the top temperature is 65 - 120 °C, and the bottom temperature is 75 - 130 °C; the top gas phase of the second acetic acid dehydration tower 7 enters the reboiler 2 of the first acetic acid dehydration tower for condensation. The condensed liquid enters the reflux drum 9 of the second acetic acid dehydration tower. The material in the reflux drum 9 of the second acetic acid dehydration tower is transported by the reflux pump 10 of the second acetic acid dehydration tower. Part of it is returned as reflux to the top of the second acetic acid dehydration tower 7, and the other part is taken out as wastewater.

[0062] The material at the bottom of the second column of the acetic acid dehydration tower (Column 7) is transported through the bottom pump of the second column of the acetic acid dehydration tower (Pump 11) into the third column of the acetic acid dehydration tower (Column 12). The third column of the acetic acid dehydration tower (Column 12) is equipped with two reboilers. Among them, the first reboiler of the third column of the acetic acid dehydration tower (Reboiler 13) uses steam as the heat source, and the second reboiler of the third column of the acetic acid dehydration tower (Reboiler 14) uses the top gas phase of the acetic acid product tower (Tower 18) as the reboiler heat source; the top pressure of the third column of the acetic acid dehydration tower (Column 12) is -50 kPa(G) to 50 kPa(G), the top temperature is 85 to 135 °C, and the bottom temperature is 100 to 150 °C; the top gas phase of the third column of the acetic acid dehydration tower (Column 12) enters the reboiler of the second column of the acetic acid dehydration tower (Reboiler 8) for condensation, and the condensed liquid enters the reflux drum of the third column of the acetic acid dehydration tower (Reflux Drum 15). The material in the reflux drum of the third column of the acetic acid dehydration tower (Reflux Drum 15) is transported through the reflux pump of the third column of the acetic acid dehydration tower (Pump 16). Part of it is returned as reflux to the top of the third column of the acetic acid dehydration tower (Column 12), and the other part is taken out as wastewater.

[0063] The material at the bottom of the third column of the acetic acid dehydration tower (Column 12) is transported through the bottom pump of the third column of the acetic acid dehydration tower (Pump 17) into the acetic acid product tower (Tower 18). The acetic acid product tower (Tower 18) is equipped with one acetic acid product tower reboiler (Reboiler 19), using steam as the reboiler heat source; the top pressure of the acetic acid product tower (Tower 18) is normal pressure to 100 kPa(G), the top temperature is 110 to 160 °C, and the bottom temperature is 130 to 180 °C; the top gas phase of the acetic acid product tower (Tower 18) enters the second reboiler of the third column of the acetic acid dehydration tower (Reboiler 14) for condensation, and the condensed liquid enters the reflux drum of the acetic acid product tower (Reflux Drum 20). The material in the reflux drum of the acetic acid product tower (Reflux Drum 20) is transported through the reflux pump of the acetic acid product tower (Pump 21). Part of it is returned as reflux to the top of the acetic acid product tower (Tower 18), and the other part is taken out as acetic acid product; the material at the bottom of the acetic acid product tower (Tower 18) is transported through the bottom pump of the acetic acid product tower (Pump 22) and taken out as heavy components.

[0064] The pressure and temperature of each tower connected in sequence increase, and the top temperature of the latter tower is higher than the bottom temperature of the previous tower.

[0065] Example 2

[0066] This example is used for acetic acid dehydration treatment when the water content is less than 15% and there are heavy components. The multi-effect distillation system of the acetic acid dehydration process includes the first column of the acetic acid dehydration tower (Column 1), the second column of the acetic acid dehydration tower (Column 7), and the acetic acid product tower (Tower 18), a total of 3 towers, all equipped with corresponding condensers, reflux phase separation drums, and reboilers;

[0067] The feed of the first column of the acetic acid dehydration tower (Column 1) is the acetic acid raw material containing water; the bottom discharge of the first column of the acetic acid dehydration tower (Column 1) is connected to the feed of the second column of the acetic acid dehydration tower (Column 7). The top of the first column of the acetic acid dehydration tower (Column 1) is refluxed and taken out as wastewater. The reboiler at the bottom of the first column of the acetic acid dehydration tower (Column 1) is connected to the top of the second column of the acetic acid dehydration tower (Column 7) for heat exchange;

[0068] The bottom discharge of the second acetic acid dehydration tower 7 is connected to the feed of the acetic acid product tower 18. The top of the second acetic acid dehydration tower 7 is refluxed and taken out as wastewater. The reboiler at the bottom of the second acetic acid dehydration tower 7 is connected to the top of the acetic acid product tower 18 for heat exchange;

[0069] The bottom discharge of the acetic acid product tower 18 is taken out as heavy components. The top of the acetic acid product tower 18 is refluxed and taken out as acetic acid product.

[0070] The specific process is as follows: The water-containing acetic acid is sent to the first acetic acid dehydration tower 1. The first acetic acid dehydration tower 1 is equipped with a reboiler for the first acetic acid dehydration tower 2, and the gas phase at the top of the second acetic acid dehydration tower 7 is used as the heat source for the reboiler; the top pressure of the first acetic acid dehydration tower 1 is -100 kPa(G) to atmospheric pressure, where G represents gauge pressure, the top temperature is 30 to 80 °C, and the bottom temperature is 50 to 100 °C; the gas phase at the top of the first acetic acid dehydration tower 1 enters the condenser 3 for the first acetic acid dehydration tower to be condensed, with circulating water as the refrigerant for the condenser. The condensed liquid enters the reflux drum 4 for the first acetic acid dehydration tower. The material in the reflux drum 4 for the first acetic acid dehydration tower is transported by the reflux pump 5 for the first acetic acid dehydration tower. Part of it is returned as reflux to the top of the first acetic acid dehydration tower 1, and the other part is taken out as wastewater.

[0071] The material at the bottom of the first acetic acid dehydration tower 1 is transported by the bottom pump 6 for the first acetic acid dehydration tower and enters the second acetic acid dehydration tower 7. The second acetic acid dehydration tower 7 is equipped with a reboiler for the second acetic acid dehydration tower 8, and the gas phase at the top of the acetic acid product tower 18 is used as the heat source for the reboiler; the top pressure of the second acetic acid dehydration tower 7 is -70 kPa(G) to 30 kPa(G), the top temperature is 65 to 120 °C, and the bottom temperature is 75 to 130 °C; the gas phase at the top of the second acetic acid dehydration tower 7 enters the reboiler 2 for the first acetic acid dehydration tower to be condensed. The condensed liquid enters the reflux drum 9 for the second acetic acid dehydration tower. The material in the reflux drum 9 for the second acetic acid dehydration tower is transported by the reflux pump 10 for the second acetic acid dehydration tower. Part of it is returned as reflux to the top of the second acetic acid dehydration tower 7, and the other part is taken out as wastewater.

[0072] The material at the bottom of the second acetic acid dehydration tower 7 is transported by the bottom pump 11 for the second acetic acid dehydration tower and enters the acetic acid product tower 18. The acetic acid product tower 18 is equipped with a reboiler 19 for the acetic acid product tower, and steam is used as the heat source for the reboiler; the top pressure of the acetic acid product tower 18 is -50 kPa(G) to 50 kPa(G), the top temperature is 90 to 140 °C, and the bottom temperature is 105 to 165 °C; the gas phase at the top of the acetic acid product tower 18 enters the reboiler 8 for the second acetic acid dehydration tower to be condensed. The condensed liquid enters the reflux drum 20 for the acetic acid product tower. The material in the reflux drum 20 for the acetic acid product tower is transported by the reflux pump 21 for the acetic acid product tower. Part of it is returned as reflux to the top of the acetic acid product tower 18, and the other part is taken out as acetic acid product; the material at the bottom of the acetic acid product tower 18 is transported by the bottom pump 22 for the acetic acid product tower and taken out as heavy components.

[0073] Example 3:

[0074] Acetic acid with a water content of 40 wt% and a recombinant component content of 2.5 wt% is sent to the first acetic acid dehydration tower 1. One acetic acid dehydration tower first reboiler 2 is installed in the first acetic acid dehydration tower 1, and the gas phase at the top of the second acetic acid dehydration tower 7 is used as the reboiler heat source; the top pressure of the first acetic acid dehydration tower 1 is -50 kPa(G), the top temperature is 42 °C, and the bottom temperature is 60 °C; the gas phase at the top of the first acetic acid dehydration tower 1 enters the first acetic acid dehydration tower condenser 3 for condensation. Circulating water is used as the condenser refrigerant. The condensed liquid enters the first acetic acid dehydration tower reflux drum 4. The material in the first acetic acid dehydration tower reflux drum 4 is transported by the first acetic acid dehydration tower reflux pump 5. Part of it is returned as reflux to the top of the first acetic acid dehydration tower 1, and the other part is taken out as wastewater.

[0075] The material at the bottom of the first acetic acid dehydration tower 1 is transported by the first acetic acid dehydration tower bottom pump 6 and enters the second acetic acid dehydration tower 7. One acetic acid dehydration tower second reboiler 8 is installed in the second acetic acid dehydration tower 7, and the gas phase at the top of the third acetic acid dehydration tower 12 is used as the reboiler heat source; the top pressure of the second acetic acid dehydration tower 7 is -30 kPa(G), the top temperature is 83 °C, and the bottom temperature is 95 °C; the gas phase at the top of the second acetic acid dehydration tower 7 enters the first acetic acid dehydration tower reboiler 2 for condensation. The condensed liquid enters the second acetic acid dehydration tower reflux drum 9. The material in the second acetic acid dehydration tower reflux drum 9 is transported by the second acetic acid dehydration tower reflux pump 10. Part of it is returned as reflux to the top of the second acetic acid dehydration tower 7, and the other part is taken out as wastewater.

[0076] The material at the bottom of the second acetic acid dehydration tower 7 is transported by the second acetic acid dehydration tower bottom pump 11 and enters the third acetic acid dehydration tower 12. Two reboilers are installed in the third acetic acid dehydration tower 12. Among them, the first reboiler 13 of the third acetic acid dehydration tower uses steam as the heat source, and the second reboiler 14 of the third acetic acid dehydration tower uses the gas phase at the top of the acetic acid product tower 18 as the reboiler heat source; the top pressure of the third acetic acid dehydration tower 12 is 10 kPa(G), the top temperature is 107 °C, and the bottom temperature is 118 °C; the gas phase at the top of the third acetic acid dehydration tower 12 enters the second acetic acid dehydration tower reboiler 8 for condensation. The condensed liquid enters the third acetic acid dehydration tower reflux drum 15. The material in the third acetic acid dehydration tower reflux drum 15 is transported by the third acetic acid dehydration tower reflux pump 16. Part of it is returned as reflux to the top of the third acetic acid dehydration tower 12, and the other part is taken out as wastewater.

[0077] The material at the bottom of the 12th tower of the acetic acid dehydration tower three-tower is transported into the acetic acid product tower 18 through the acetic acid dehydration tower three-tower bottom pump 17. One acetic acid product tower reboiler 19 is set in the acetic acid product tower 18, with steam as the reboiler heat source; the top pressure of the acetic acid product tower 18 is 70 kPa(G), the top temperature is 132 °C, and the bottom temperature is 158 °C; the gas phase at the top of the acetic acid product tower 18 enters the acetic acid dehydration tower three-tower second reboiler 14 for condensation, and the condensed liquid enters the acetic acid product tower reflux drum 20. The material in the acetic acid product tower reflux drum 20 is transported through the acetic acid product tower reflux pump 21. Part of it is returned as reflux to the top of the acetic acid product tower 18, and the other part is taken out as acetic acid product; the material at the bottom of the acetic acid product tower 18 is transported through the acetic acid product tower bottom pump 22 and taken out as heavy components.

[0078] In this embodiment, the tower diameter of the acetic acid dehydration tower is 1.6 m and the tower height is 30 m, and the tower diameter of the acetic acid product tower is 1.2 m and the tower height is 20 m.

[0079] Under the same feeding conditions, the energy consumption comparison between the system of the present utility model and the acetic acid dehydration equipment with conventional non-heat exchange design (the heat source and refrigerant both come from external public works) is as follows:

[0080] Energy consumption kW Proportion of energy consumption reduction Conventional rectification 6279 Example 3 2163 66％

[0081] Matters not described in the present utility model are applicable to the prior art.

Claims

1. A multi-effect distillation system for an acetic acid dehydration process, characterized in that, The system includes at least two acetic acid dehydration towers. The bottom discharge of the previous acetic acid dehydration tower is connected to the feed of the next acetic acid dehydration tower. The bottom reboiler of the previous acetic acid dehydration tower is connected to the top of the next acetic acid dehydration tower for heat exchange. Waste water is withdrawn from the top of all acetic acid dehydration towers. The feed port of the first acetic acid dehydration tower inputs the acetic acid raw material containing water to be treated. Acetic acid is withdrawn from the bottom of the last acetic acid dehydration tower.

2. The system according to claim 1, characterized in that There are heavy components in the acetic acid raw material containing water to be treated. At this time, the system further includes an acetic acid product tower. The bottom reboiler of the last acetic acid dehydration tower is connected to the top of the acetic acid product tower for heat exchange. Acetic acid is withdrawn from the top of the acetic acid product tower, and heavy components are withdrawn from the bottom. The feed port of the acetic acid product tower is connected to the bottom discharge of the last acetic acid dehydration tower.

3. The system according to claim 1, wherein There are no heavy components in the acetic acid raw material containing water to be treated. At this time, the system does not require an acetic acid product tower. Qualified acetic acid is withdrawn from the bottom of the last acetic acid dehydration tower. At this time, an external heat source is provided for the last acetic acid dehydration tower.

4. The system according to claim 2, wherein The tower diameter of the acetic acid dehydration tower is 0.2 m to 9 m, and the tower height is 10 m to 80 m; the tower diameter of the acetic acid product tower is 0.2 m to 9 m, and the tower height is 10 m to 80 m.

5. The system according to claim 1, wherein The pressure and temperature of each tower connected in sequence increase, and the top temperature of the next tower is higher than the bottom temperature of the previous tower.

6. The system according to any one of claims 1-5, characterized in that A corresponding condenser, reflux drum and reflux pump are equipped at the top of each acetic acid dehydration tower, and a reboiler is equipped at the bottom of each acetic acid dehydration tower.

7. The system according to claim 6, wherein When there is an acetic acid product tower and the gas phase at the top of the acetic acid product tower is not sufficient to meet the heat required by the bottom reboiler of the last acetic acid dehydration tower, two parallel reboilers are equipped at the bottom of the last acetic acid dehydration tower. One of the reboilers exchanges heat with the top of the acetic acid product tower, and the other reboiler uses an external heat source.

8. The system according to claim 3, wherein A corresponding condenser, reflux drum and reflux pump are equipped at the top of the acetic acid product tower, and a reboiler is equipped at the bottom of the acetic acid product tower.

9. The system according to claim 1, wherein The water content in the acetic acid raw material containing water to be treated is less than 15% by mass, and two acetic acid dehydration towers are set in the system.

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