CN110327647B - Improved three-tower three-effect crude methanol refining process method - Google Patents
Improved three-tower three-effect crude methanol refining process method Download PDFInfo
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Abstract
The invention provides an improved three-tower triple-effect crude methanol refining process method, which comprises a pre-rectifying tower, a first rectifying tower and a second rectifying tower, wherein the heat of a refined methanol gas phase extracted from the top of the first rectifying tower firstly meets the reboiling load at the bottom of the second rectifying tower, a non-condensable gas phase after heat exchange and the refined methanol gas phase extracted from the top of the second rectifying tower flow in parallel, and then a strand of gas is separated out to ensure that the heat of the gas phase meets the reboiling load at the bottom of the pre-rectifying tower. The invention can further reduce the energy consumption of the system, reduce the load of the three towers and avoid the difficult transformation of the traditional three-tower methanol rectification process system.
Description
Technical Field
The invention belongs to the technical field of chemical material purification process methods and equipment, and particularly relates to an improved crude methanol refining method and system.
Background
The rectification of crude methanol is a conventional process method for obtaining high-purity methanol products at present, and a traditional three-tower methanol rectification (concurrent double-effect rectification) process is usually adopted, namely, the crude methanol is rectified and separated sequentially through a pre-rectification tower, a pressurized rectification tower and an atmospheric rectification tower. In order to reduce the energy consumption of methanol rectification, the applicant proposed a three-tower three-effect crude methanol refining process method in 2018, so that the refined methanol gas-phase heat extracted from the top of a pressurized rectifying tower firstly meets the reboiling load of the bottom of an atmospheric rectifying tower, and the residual refined methanol gas-phase heat provides part of heat for reboiling at the bottom of a pre-rectifying tower. The heat distribution of the two parts of heat can ensure that the heat of the gas-phase material at the top of the pressurized rectifying tower is reasonably distributed and utilized, and the energy consumption of the system is reduced. On one hand, the heat of the reboiler at the bottom of the pre-rectifying tower is provided by the gas phase at the top of the pressurized rectifying tower, so that the heat required by the reboiler at the bottom of the pre-rectifying tower is possibly insufficient, and the heat exchange capacity is limited, on the other hand, the load of the pressurized rectifying tower is possibly increased, and a higher requirement is provided for the capacity increasing capacity of the pressurized rectifying tower, but the capacity increasing capacity of the pressurized rectifying tower in the existing factory is limited, so that the requirement for the capacity increasing capacity is difficult to meet. The defects enable the effect of the three-tower three-effect crude methanol refining process method to be exerted in the aspect of reducing the energy consumption of the system to be limited, and the comprehensive energy consumption is reduced to be limited.
Disclosure of Invention
The invention aims to provide an improved three-tower triple-effect crude methanol refining process method, which can further reduce the energy consumption of a system, reduce the load of three towers and avoid the difficulty in reforming the traditional three-tower methanol rectification process system.
The improved three-tower triple-effect crude methanol refining process method comprises a pre-rectifying tower, a first rectifying tower and a second rectifying tower, wherein the heat of a refined methanol gas phase extracted from the top of the first rectifying tower firstly meets the reboiling load at the bottom of the second rectifying tower, a non-condensable gas phase after heat exchange and the refined methanol gas phase extracted from the top of the second rectifying tower flow in parallel, and then a strand of gas is separated out to enable the heat to meet the reboiling load at the bottom of the pre-rectifying tower.
The process route enables the heat at the top of the first rectifying tower to be utilized twice, and provides the total heat for reboiling at the bottom of the second rectifying tower and partial heat for the reboiler at the bottom of the pre-rectifying tower respectively. Meanwhile, as the non-condensable gas phase obtained after heat exchange of the refined methanol gas phase extracted from the top of the first rectifying tower and the refined methanol gas phase obtained from the top of the second rectifying tower are in parallel flow, the heat at the top of the second rectifying tower can be fully utilized and insufficient heat can be effectively supplemented, the heat utilization efficiency in the system is further improved, the heat supply load of the first rectifying tower is effectively reduced, and the requirement on the capacity increasing requirement of the first rectifying tower is reduced. The reboiling heat at the bottom of the first rectifying tower is provided by external steam, so the process route can realize the three-effect utilization of the heat of the external steam: the external steam heat is firstly used for reboiling at the bottom of the first rectifying tower, and is regarded as a first effect; the reboiling heat obtained by the first rectifying tower is transferred to the gas phase at the top of the tower through the reaction in the tower, and the gas phase at the top of the tower is used for reboiling at the bottom of the second rectifying tower, so that the second effect is considered; the two effects are regarded as three effects by using the noncondensable gas after heat transfer to be sequentially used for reboiling at the bottom of the pre-rectifying tower. The heat efficiency is exerted to the maximum extent by the triple-effect utilization of the external steam, the total amount of steam consumed by the system is effectively reduced, and the energy consumption of the system is saved.
Specifically, after crude methanol enters a pre-rectifying tower, light components and a small amount of gaseous methanol are extracted from the top of the pre-rectifying tower, and an aqueous methanol solution A is extracted from the bottom of the pre-rectifying tower and enters a first rectifying tower; the refined methanol gas phase material extracted from the top of the first rectifying tower is sent to the bottom of the second rectifying tower and provides reboiling heat for the second rectifying tower, and the material after heat exchange is divided into at least three: the first strand is taken as reflux liquid to flow back into a first rectifying tower, the second strand is taken as a product to be extracted, and the third strand is taken as non-condensable gas to flow in parallel with a refined methanol gas phase extracted from the top of the second rectifying tower; the aqueous methanol solution B extracted from the bottom of the first rectifying tower enters a second rectifying tower; the refined methanol gas phase material extracted from the top of the second rectifying tower and the material which is used as the third non-condensable gas phase after providing reboiling heat for the second rectifying tower are divided into three parts again after flowing in parallel: the first stream is sent to the bottom of the pre-rectifying tower and provides reboiling heat for the pre-rectifying tower, the second stream becomes reflux liquid and flows back to the second rectifying tower, and the third stream becomes a product and is extracted; and the wastewater material is extracted from the bottom of the second rectifying tower, and the fusel material is extracted from the side line.
Wherein, the bottom of the pre-rectifying tower is provided with at least two reboiling devices, preferably three reboiling devices, one of the reboiling devices exchanges heat with one strand of the refined methanol gas-phase material extracted from the top of the second rectifying tower, and the other reboiling devices exchanges heat with external steam (namely the reboiling heat is provided by the external steam). When the system is started, due to insufficient heat in the system, the reboiling heat at the bottom of the pre-rectifying tower is mainly provided by external steam, and after the system runs stably, the reboiling heat at the bottom of the pre-rectifying tower can be completely provided by the refined methanol gas-phase material extracted from the top of the second rectifying tower.
And the refined methanol gas-phase material extracted from the top of the second rectifying tower is firstly condensed and then treated as a liquid-phase material without providing reboiling heat to the bottom of the pre-rectifying tower, namely split flows are respectively formed into the second reflux liquid and the third product.
Wherein fusel is also extracted from the middle lower part of the second rectifying tower, the water content of the fusel is 65-76w%, the extraction temperature is 105-122 ℃, and the pressure is 170-265 kPa. The design of the fusel extraction line is beneficial to reducing the load of the second atmospheric distillation tower, improving the refining efficiency of the methanol, further reducing the energy consumption, and the recovered fusel can be further treated to obtain resource recycling.
In order to meet the requirement of the reboiling load of the top gas produced by the first rectifying tower and the second rectifying tower relative to the bottom of the system, the design pressure of the three towers can adopt two combination modes:
the first method is as follows: the pre-rectifying tower is operated at normal pressure, the first rectifying tower is operated under pressure, the second rectifying tower is operated under pressure, the operating pressure of the first rectifying tower is higher than that of the second rectifying tower, and the operating pressures of the first rectifying tower and the second rectifying tower are both higher than the conventional design pressure. Specifically, the design pressure of the three-tower is preferably that the operation pressure of the pre-rectifying tower is 103-160kPa, the operation pressure of the first rectifying tower is 790-1100kPa, and the operation pressure of the second rectifying tower is 180-350 kPa.
The second method comprises the following steps: the pre-rectifying tower is operated under reduced pressure, the first rectifying tower is operated under pressure, the second rectifying tower is operated under pressure, the operating pressure of the first rectifying tower is higher than that of the second rectifying tower, and the operating pressure of the second rectifying tower is higher than that of the conventional design but lower than that of the second rectifying tower in the first mode. Specifically, the design pressure of the three-tower is preferably that the operation pressure of the pre-rectifying tower is 40-92kPa, the operation pressure of the first rectifying tower is 650-1150kPa, and the operation pressure of the second rectifying tower is 150-220 kPa.
The optimized control of the process conditions further optimizes and reduces the energy consumption of the system under the condition of ensuring the purity of the refined methanol. Therefore, the scheme optimizes the process condition control parameters of the three towers:
for the first mode: the number of the tower plates of the pre-rectifying tower is 50-58, the temperature extracted from the tower top is 60-65.2 ℃, the pressure is 110-4.8 and the reflux ratio is 3.5-4.8, the temperature extracted from the tower bottom is 75-85 ℃, and the pressure is 136-160 kPa; the number of the tower plates of the first rectifying tower is 70-95 layers, the temperature of the tower top is 115-145 ℃, the pressure is 890-1050kPa, the reflux ratio is 1.5-2.9, the temperature of the tower bottom is 145-155 ℃, and the pressure is 950-1045 kPa; the number of the second rectifying tower plates is 85-95 layers, the temperature of the tower top extraction is 70-105 ℃, the pressure is 180-260kPa, the reflux ratio is 1.3-2.2, the tower bottom extraction temperature is 115-129 ℃, and the pressure is 220-290 kPa.
For the second mode: the number of the tower plates of the pre-rectifying tower is 45-58, the temperature extracted from the top of the pre-rectifying tower is 42-49 ℃, the pressure is 50-60kPa, the reflux ratio is 2.5-4.6, the temperature extracted from the bottom of the pre-rectifying tower is 55-68 ℃, and the pressure is 70-92 kPa; the number of the tower plates of the first rectifying tower is 70-95 layers, the temperature of the tower top is 105-132 ℃, the pressure is 690-742kPa, the reflux ratio is 1.4-2.9, the temperature of the tower bottom is 125-145 ℃, and the pressure is 720-815 kPa; the number of the second rectifying tower plates is 85-95 layers, the temperature of the tower top is 65-85 ℃, the pressure is 150-210kPa, the reflux ratio is 1.4-2.9, the temperature of the tower bottom is 110-120 ℃, and the pressure is 150-195 kPa.
The gas-phase material extracted from the top of the pre-rectifying tower is sequentially subjected to primary condensation and secondary condensation, the condensed liquid phase subjected to secondary condensation is subjected to gas-liquid separation, the condensed liquid phase subjected to primary condensation and the separated liquid phase obtained by gas-liquid separation flow in parallel and serve as reflux liquid to flow back into the pre-rectifying tower, a small amount of non-condensable gas returns to secondary condensation operation after flow-parallel, and the non-condensable gas phase subjected to secondary condensation and the separated gas phase obtained by gas-liquid separation are subjected to subsequent treatment (such as flare system treatment). The secondary condensation is adopted to improve the condensation recovery efficiency and reduce the loss rate of methanol. This design may be satisfactory for operation of the pre-rectification column in an atmospheric design, including operation under the conditions described above in mode one.
Further, for the pre-rectifying tower needing decompression operation, the noncondensable gas phase subjected to secondary condensation can be subjected to gas-liquid separation together with the condensed liquid phase subjected to secondary condensation after being subjected to tertiary condensation, the separated gas phase obtained by gas-liquid separation is subjected to subsequent treatment after being subjected to tertiary condensation, and the material subjected to tertiary condensation enters subsequent treatment again through a vacuum pump which is connected with an adjusting valve in parallel; and the third condensation is normal-temperature condensation, and the fourth condensation is low-temperature condensation. The third condensation and the fourth condensation are added, so that the condensation recovery efficiency can be further improved, the pressure at the top of the pre-rectifying tower can be reduced through the connection of a vacuum pump, the pre-rectifying tower operated under normal pressure is improved to be capable of performing reduced pressure operation, and the method is effectively suitable for the operating requirements of the working conditions in the second mode. In addition, the design can also adjust the strength of the vacuum pump by the adjusting valve, or completely close the vacuum pump, so that the pre-rectifying tower can recover the condition of normal pressure operation under the condition that the vacuum pump does not play a role, namely, the operation under the working condition in the first mode can be simultaneously met.
Additionally, the feed composition of the crude methanol may be: 50-97w% of methanol, 1.5-2.5w% of light component impurities and 7.5-13.5w% of heavy component impurities; the methanol content in the gas phase material extracted from the top of the pre-rectifying tower is 18-28w%, and the methanol content in the aqueous methanol solution A extracted from the bottom of the pre-rectifying tower is 70-85 w%; the content of methanol in the water-containing methanol solution B extracted from the bottom of the first rectifying tower is 50-75 w%. The optimized control of the feeding and discharging components ensures that the purification efficiency can be optimized while the purity of the refined methanol is ensured and the energy consumption is reduced.
Compared with the prior art, the invention has the following advantages:
(1) the secondary utilization of the heat at the top of the first pressurizing tower can be realized, the triple-effect heat utilization of external steam is formed, the heat utilization efficiency is greatly improved, and the energy consumption of a methanol rectification system is effectively reduced. Compared with the disclosed common three-tower triple-effect rectification process (the heat of the tower bottom reboilers of the atmospheric rectification tower and the pre-rectification tower is provided by the gas phase at the tower top of the pressurized rectification tower), the heat energy is fully utilized, the overall load of the first rectification tower is obviously reduced, and the heating capacity of preheating is improved.
(2) In the process, the comprehensive energy consumption of each ton of refined methanol can be reduced to 0.71 ton of steam, and compared with the steam consumption of the disclosed common three-tower triple-effect rectification process of 0.85-0.90 ton, the steam consumption is reduced by 24.1%.
(3) Because the capacity increasing capability of the pressurizing towers of different factories is different, the tower diameter and the heat exchange area of a reboiler of some equipment are limited, the gas-liquid flux of the internal parts of the tower is limited, and the implementation difficulty of the disclosed transformation scheme of the ordinary three-tower triple-effect rectification process route is higher. Compared with the traditional three-tower concurrent double-effect process and the common three-tower triple-effect rectification process, the invention avoids the requirement of larger capacity-increasing transformation on the first rectification tower, can realize equipment transformation by adding simple equipment such as a reboiler, a condenser, a vacuum pump and the like, can greatly reduce the difficulty of implementing the transformation of new process projects, better adapts to various working conditions simultaneously, and effectively improves the energy-saving level of the existing factory.
Drawings
The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate an embodiment of the invention and, together with the description, serve to explain the invention and not to limit the invention. In the drawings:
FIG. 1 is a process flow diagram of example 1 of the present invention.
FIG. 2 is a process flow diagram of example 2 of the present invention.
Wherein the coarse blue line is dominated by liquid phase process flow and the fine powder line is dominated by gas phase process flow.
Detailed Description
For a better understanding of the present invention, reference is made to the following detailed description taken in conjunction with the accompanying drawings. The following examples illustrate details of the process for the purpose of describing the invention in detail and are not intended to unduly limit the invention.
Example 1 (mode one)
As shown in FIG. 1, crude methanol (40 ℃, 0.5MPa, 120 m)3The material R1) is preheated by a first preheater M4 and enters a pre-rectifying tower M1, the material is fully contacted with gas and liquid through 52 layers of efficient DVST tower plates or a plurality of sections of fillers in the tower, light components in crude methanol and a small part of methanol are extracted from the top of the pre-rectifying tower M1 in a gaseous form, the content of the methanol in gas-phase materials extracted from the top of the tower is about 22 percent, the temperature extracted from the top of the tower is 62.9 ℃, the pressure is 119kPa, the gas-phase materials extracted from the top of the tower sequentially enter a first condenser M5 and a second condenser M6 for secondary condensation, condensate obtained after the secondary condensation enters a gas-liquid separator M7, and non-condensable gas (CO, CO) is separated2、H2、N2、CH4Multi-carbon alkane, ethyl acetate, dimethyl ether, etc. at 40 deg.C, 0.12MPa, 3.0-50.0m3H) the condensed non-condensable gas is combined with the condensed non-condensable gas of the second condenser M6 and enters a subsequent post-treatment and torch system, the condensate separated by the gas-liquid separator M7 and the condensate condensed by the first condenser M5 both enter the first reflux tank M8, the liquid in the first reflux tank M8 serving as reflux enters a tower plate on the top 52 layer of the pre-rectifying tower M1 for reflux, the reflux ratio is 4.0 to control the methanol carrying-out amount, and a small amount of non-condensable gas in the first reflux tank M8 returns to enter the second condenser M6 for continuous condensation.
At least two reboilers, in this case three reboilers, namely a reboiler M9, a reboiler M10 and a reboiler M11, are connected in parallel to the bottom of the pre-rectifying column M1. The reboiler M9 and reboiler M11 are conventionally supplied with heat via external steam lines, respectively. One side of one reboiler M11 is provided with a buffer tank M12, one strand (about 95 ℃, 99.95% methanol, 0.26Mpa and material R5) of gas-phase materials extracted from the top of the second rectifying tower M3 enters the buffer tank M12, then is thermally coupled (heat exchanged) with the reboiler M11 to be cooled to form condensate, and the condensate returns to a third reflux tank M21 of the second rectifying tower M3.
Aqueous methanol solution A (material R2) is extracted from the bottom of the pre-rectifying tower M1, wherein the content of methanol is about 83 percent, the temperature of the extraction at the bottom of the tower is 80 ℃, and the pressure is 1.41kg/cm2. The aqueous methanol solution A is preheated by a second preheater M13 and then enters the middle-lower part of a tower plate of a first rectifying tower M2, and the feeding temperature is 125 ℃. At least one reboiler, in this case two reboilers M14 and M15, are connected in parallel to the bottom of the first rectification column M2, and they supply heat through external steam lines. Gas-liquid mass transfer and heat transfer are carried out on gas-liquid in the first rectifying tower M2 through a high-efficiency DVST tower plate or filler, refined methanol (135 ℃, 99.98% methanol, 0.9902Mpa and material R4) from the top of the tower enters a shell pass of a reboiler M19 at the bottom of the second rectifying tower M3 for heat exchange, and condensate after the refined methanol is subjected to heat exchange returns to the second reflux tank M16. The refined methanol condensate in the second reflux tank M16 is divided into two parts: the first stream enters a top layer 1 tower plate of a first rectifying tower M2 for reflux, and the reflux ratio is 2.2; the second strand is cooled for the second time by a first cooler M17 and a second cooler M18 in sequence and then enters a product storage tank; the refined methanol noncondensable gas in the second reflux tank M16 and the refined methanol gas phase extracted from the top of the second rectifying tower M3 are in cocurrent.
Aqueous methanol solution B (material R3) is extracted from the bottom of the first rectifying tower M2, wherein the content of the methanol is about 70 percent, the temperature of the extracted liquid at the bottom of the tower is 145 ℃, and the pressure is 10.45kg/cm2. The aqueous methanol solution B entered the second rectification column M3 above the mid-lower tray at a feed temperature of 145 ℃. In the second rectifying tower M3, gas-liquid heat transfer and mass transfer are carried out on the gas-liquid through a high-efficiency tray or a filler, and water, ethanol, fusel and the like in the methanol are fully removed. The gas phase material extracted from the top of the second rectifying tower M3 is refined methanol (99.95% methanol, material R6), and the pressure extracted from the top of the second rectifying tower M3 is 2.1kg/cm2. After the refined methanol material and the refined methanol noncondensable gas in the second reflux tank M16 flow in parallel, the refined methanol material is divided into two streams: one stream (material R5) enters a buffer tank M12 and then is thermally coupled with a reboiler M11 to form condensate which returns to the first stageThree reflux drums M21, one was also fed to the third reflux drum M21 after being condensed by the fifth condenser M20. The material in the third reflux drum M21 also divides into two streams: one strand returns to the top layer 1 tower plate of the second rectifying tower M3 for reflux, the reflux ratio is 1.95, the temperature of the reflux liquid is 90 ℃, and the other strand enters a product storage tank after being cooled by a third cooler M22.
The middle lower part of the second rectifying tower M3 is provided with a fusel (material R8) outlet, and the enriched fusel such as ethanol is sent to a fusel tank region through a fifth cooler M23 and a second buffer tank M24(40 ℃, 70% of water and 0.167Mpa) in sequence.
The wastewater material (material R7) is extracted from the bottom of the second rectifying tower M3, the content of methanol is reduced to below 0.1%, the temperature extracted from the bottom of the tower is 124 ℃, and the pressure is 2.3kg/cm2And then cooled by a fourth cooler M25 and sent to a subsequent waste treatment system for treatment.
In the above process, the compositions of the relevant materials are shown in table 1.
TABLE 1 composition of materials w%
By adopting the scheme, a certain 60 ten thousand tons/year crude methanol refining factory is reformed, and crude methanol is fed at 96.7 t/h. The purity of refined methanol before modification is 99.9%, the energy consumption of the system is 56.85MKcal/h, the methanol extraction amount is 84.1t/h, and the steam consumption of a single ton of refined methanol is 1.37. The purity of the refined methanol after transformation is 99.95 percent of methanol, the energy consumption of the system is 30.61MKcal/h, the extraction amount of the methanol is 84.1t/h, and the steam consumption of a single ton of the refined methanol is 0.727. Compared with the traditional process, the energy consumption of the system is reduced by 46.9%.
Example 2 (mode two)
As shown in FIG. 2, crude methanol (40 ℃, 0.5MPa, 120 m)3H, feed R1) is preheated by a first preheater M4 into a pre-rectification column M1 and passed through the columnThe gas-liquid full contact of inner 52 layers of high-efficiency DVST tower plates or a plurality of sections of fillers, light components in crude methanol and a small part of methanol are extracted from the top of a pre-rectifying tower M1 in a gaseous form, the content of the methanol in gas-phase materials extracted from the top of the tower is about 28%, the temperature extracted from the top of the tower is 48 ℃, the pressure is 60kPa, the gas-phase materials extracted from the top of the tower sequentially enter a first condenser M5 and a second condenser M6 for secondary condensation, condensate after the secondary condensation enters a gas-liquid separator M7, noncondensable gas after the secondary condensation enters a gas-liquid separator M7 through the third condenser M26, the noncondensable gas after separation in the gas-liquid separator M7 enters a fourth condenser M27 and then is sent to a torch system for subsequent treatment through a vacuum pump M28, a regulating valve M29 is connected to the vacuum pump M28 in parallel and used for regulating the material flow of the vacuum pump M28 and the noncondensable gas (CO, CO and CO) from the M282、H2、N2、CH4Multi-carbon alkane, ethyl acetate, dimethyl ether, etc. at 40 deg.C, 0.12MPa, 3.0-50.0m3H) entering a flare system for subsequent post-treatment. The condensate separated by the gas-liquid separator M7 and the condensate condensed by the first condenser M5 both enter the first reflux tank M8, the liquid in the first reflux tank M8 is used as reflux and enters a tower plate on the top 52 layers of the pre-rectifying tower M1 for reflux, the reflux ratio is 4.1 to control the entrainment amount of methanol, and a small amount of non-condensable gas in the first reflux tank M8 returns to enter the second condenser M6 for continuous condensation.
At least two reboilers, in this case three reboilers, namely a reboiler M9, a reboiler M10 and a reboiler M11, are connected in parallel to the bottom of the pre-rectifying column M1. The reboiler M9 and reboiler M11 are conventionally supplied with heat via external steam lines, respectively. One side of one reboiler M11 is provided with a buffer tank M12, one strand (about 80 ℃, 99.96% methanol, 0.17Mpa and material R5) of gas-phase materials extracted from the top of the second rectifying tower M3 enters the buffer tank M12, then is thermally coupled (heat exchanged) with the reboiler M11 to be cooled to form condensate, and the condensate returns to a third reflux tank M21 of the second rectifying tower M3.
Aqueous methanol solution A (material R2) is extracted from the bottom of the pre-rectifying tower M1, wherein the content of methanol is about 84%, the temperature extracted from the bottom of the tower is 62.8 ℃, and the pressure is 0.82kg/cm2. Aqueous methanol solutionA enters the middle-lower part of a tray of the first rectifying tower M2 after being preheated by a second preheater M13, and the feeding temperature is 122 ℃. At least one reboiler, in this case two reboilers M14 and M15, are connected in parallel to the bottom of the first rectification column M2, and they supply heat through external steam lines. Gas-liquid mass transfer and heat transfer are carried out on gas-liquid in the first rectifying tower M2 through a high-efficiency DVST tower plate or filler, refined methanol (122 ℃, 99.99% methanol, 0.702Mpa and material R4) from the top of the tower enters a shell pass of a reboiler M19 at the bottom of the second rectifying tower M3 for heat exchange, and condensate after the refined methanol is subjected to heat exchange returns to the second reflux tank M16. The refined methanol condensate in the second reflux tank M16 is divided into two parts: the first stream enters a top layer 1 tower plate of a first rectifying tower M2 for reflux, and the reflux ratio is 2.2; the second strand is cooled for the second time by a first cooler M17 and a second cooler M18 in sequence and then enters a product storage tank; the refined methanol noncondensable gas in the second reflux tank M16 and the refined methanol gas phase extracted from the top of the second rectifying tower M3 are in cocurrent.
The bottom of the first rectifying tower M2 produces aqueous methanol solution B (material R3), wherein the content of methanol is about 73 percent, the temperature of the bottom produced is 133 ℃, and the pressure is 7.85kg/cm2. The aqueous methanol solution B entered the second rectification column M3 above the mid-lower tray at a feed temperature of 132 ℃. In the second rectifying tower M3, gas-liquid heat transfer and mass transfer are carried out on the gas-liquid through a high-efficiency tray or a filler, and water, ethanol, fusel and the like in the methanol are fully removed. The gas phase material extracted from the top of the second rectifying tower M3 is refined methanol (99.96% methanol, material R6), and the pressure extracted from the top of the second rectifying tower M3 is 1.56kg/cm2. After the refined methanol material and the refined methanol noncondensable gas in the second reflux tank M16 flow in parallel, the refined methanol material is divided into two streams: one (material R5) enters a buffer tank M12, and then is thermally coupled with a reboiler M11 to form condensate which returns to a third reflux tank M21, and the other (material) enters a third reflux tank M21 after being condensed by a fifth condenser M20. The material in the third reflux drum M21 also divides into two streams: one strand returns to the top layer 1 tower plate of the second rectifying tower M3 for reflux, the reflux ratio is 1.9, the temperature of the reflux liquid is 70 ℃, and the other strand enters a product storage tank after being cooled by a third cooler M22.
The middle lower part of the second rectifying tower M3 is provided with a fusel (material R8) outlet, and the enriched fusel such as ethanol is sent to a fusel tank area through a fifth cooler M23 and a second buffer tank M24(40 ℃, 70% of water and 0.197Mpa) in sequence.
The wastewater material (material R7) is extracted from the bottom of the second rectifying tower M3, the content of methanol is reduced to below 0.1%, the temperature extracted from the bottom of the tower is 115 ℃, and the pressure is 1.75kg/cm2And then cooled by a fourth cooler M25 and sent to a subsequent waste treatment system for treatment.
The compositions of the relevant materials in the above process are shown in table 2.
TABLE 2 composition of the materials w%
By adopting the scheme, a certain 60 ten thousand tons/year crude methanol refining factory is improved, and 96.72t/h crude methanol is fed. The purity of refined methanol before modification is 99.92%, the energy consumption of the system is 56.85MKcal/h, the methanol extraction amount is 84.1t/h, and the steam consumption of a single ton of refined methanol is 1.37. The purity of the refined methanol after transformation is 99.98 percent of methanol, the energy consumption of the system is 31.76MKcal/h, the extraction amount of the methanol is 83.9t/h, and the steam consumption of a single ton of the refined methanol is 0.735. Compared with the traditional process, the energy consumption of the system is reduced by 46.3 percent.
The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents, improvements and the like that fall within the spirit and principle of the present invention are intended to be included therein.
Claims (7)
1. An improved three-tower triple-effect crude methanol refining process method comprises a pre-rectifying tower, a first rectifying tower and a second rectifying tower, wherein the heat of a refined methanol gas phase extracted from the top of the first rectifying tower firstly meets the reboiling load at the bottom of the second rectifying tower, a non-condensable gas phase after heat exchange and the refined methanol gas phase extracted from the top of the second rectifying tower flow in parallel, and then a strand of gas is separated out to ensure that the heat of the gas phase meets the reboiling load at the bottom of the pre-rectifying tower;
the design pressure of the three towers adopts one of the following two modes:
the first method is as follows: the operation pressure of the pre-rectifying tower is 103-160kPa, the operation pressure of the first rectifying tower is 790-1100kPa, the operation pressure of the second rectifying tower is 180-350kPa, the operation pressure of the first rectifying tower is higher than that of the second rectifying tower, and the operation pressures of the first rectifying tower and the second rectifying tower are higher than the conventional design pressure;
the second method comprises the following steps: the operating pressure of the pre-rectifying tower is 40-92kPa, the operating pressure of the first rectifying tower is 650-1150kPa, the operating pressure of the second rectifying tower is 150-220kPa, the operating pressure of the first rectifying tower is higher than that of the second rectifying tower, and the operating pressure of the second rectifying tower is higher than the conventional design pressure but lower than that of the second rectifying tower in the first mode;
for mode one or mode two: for a pre-rectifying tower needing pressure reduction operation, gas-phase materials extracted from the top of the pre-rectifying tower are subjected to primary condensation and secondary condensation in sequence, a condensed liquid phase subjected to secondary condensation is subjected to gas-liquid separation, the condensed liquid phase subjected to primary condensation and a separated liquid phase obtained by gas-liquid separation are subjected to parallel flow to serve as a reflux liquid and flow back to the pre-rectifying tower, a small amount of non-condensable gas returns to the secondary condensation operation after parallel flow, the non-condensable gas phase subjected to secondary condensation is subjected to gas-liquid separation together with the condensed liquid phase subjected to secondary condensation after being subjected to tertiary condensation, the separated gas phase obtained by gas-liquid separation is subjected to subsequent treatment after being subjected to fourth condensation, the materials subjected to fourth condensation are subjected to subsequent treatment again through a vacuum pump, and the vacuum pump is connected with an adjusting valve in parallel; wherein the third condensation is normal temperature condensation, the fourth condensation is low temperature condensation,
the refining process method of the crude methanol comprises the following steps: after crude methanol enters a pre-rectifying tower, light components and a small amount of gaseous methanol are extracted from the top of the pre-rectifying tower, and an aqueous methanol solution A is extracted from the bottom of the pre-rectifying tower and enters a first rectifying tower; the refined methanol gas phase material extracted from the top of the first rectifying tower is sent to the bottom of the second rectifying tower and provides reboiling heat for the second rectifying tower, and the material after heat exchange is divided into at least three: the first strand is taken as reflux liquid to flow back into a first rectifying tower, the second strand is taken as a product to be extracted, and the third strand is taken as non-condensable gas to flow in parallel with a refined methanol gas phase extracted from the top of the second rectifying tower; the aqueous methanol solution B extracted from the bottom of the first rectifying tower enters a second rectifying tower; the refined methanol gas phase material extracted from the top of the second rectifying tower and the material which is used as the third non-condensable gas phase after providing reboiling heat for the second rectifying tower are divided into three parts again after flowing in parallel: the first stream is sent to the bottom of the pre-rectifying tower and provides reboiling heat for the pre-rectifying tower, the second stream becomes reflux liquid and flows back to the second rectifying tower, and the third stream becomes a product and is extracted; and the wastewater material is extracted from the bottom of the second rectifying tower, and the fusel material is extracted from the side line.
2. The improved three-tower three-effect crude methanol refining process as claimed in claim 1, characterized in that the bottom of the pre-rectifying tower is provided with three reboiling devices, one of which exchanges heat with one of the gas phase materials of the refined methanol extracted from the top of the second rectifying tower, and the other reboiling devices exchange heat with external steam.
3. The improved three-tower three-effect crude methanol refining process as claimed in claim 1, wherein the refined methanol gas phase material extracted from the top of the second rectifying tower, which does not provide reboiling heat to the bottom of the pre-rectifying tower, is first condensed and then treated as a liquid phase material.
4. The improved three-tower three-effect crude methanol refining process as claimed in claim 1, wherein fusel alcohol is further extracted from the middle lower part of the second distillation tower, the water content of the fusel alcohol is 65-76w%, the extraction temperature is 105-122 ℃, and the pressure is 170-265 kPa.
5. The improved three-tower three-effect crude methanol refining process according to claim 1, characterized in that,
for the first mode: the number of the tower plates of the pre-rectifying tower is 50-58, the temperature extracted from the tower top is 60-65.2 ℃, the pressure is 110-4.8 and the reflux ratio is 3.5-4.8, the temperature extracted from the tower bottom is 75-85 ℃, and the pressure is 136-160 kPa; the number of the tower plates of the first rectifying tower is 70-95 layers, the temperature of the tower top is 115-145 ℃, the pressure is 890-1050kPa, the reflux ratio is 1.5-2.9, the temperature of the tower bottom is 145-155 ℃, and the pressure is 950-1045 kPa; the number of the tower plates of the second rectifying tower is 85-95 layers, the temperature of the tower top is 70-105 ℃, the pressure is 180-260kPa, the reflux ratio is 1.3-2.2, the temperature of the tower bottom is 115-129 ℃, and the pressure is 220-290 kPa;
for the second mode: the number of the tower plates of the pre-rectifying tower is 45-58, the temperature extracted from the top of the pre-rectifying tower is 42-49 ℃, the pressure is 50-60kPa, the reflux ratio is 2.5-4.6, the temperature extracted from the bottom of the pre-rectifying tower is 55-68 ℃, and the pressure is 70-92 kPa; the number of the tower plates of the first rectifying tower is 70-95 layers, the temperature of the tower top is 105-132 ℃, the pressure is 690-742kPa, the reflux ratio is 1.4-2.9, the temperature of the tower bottom is 125-145 ℃, and the pressure is 720-815 kPa; the number of the second rectifying tower plates is 85-95 layers, the temperature of the tower top is 65-85 ℃, the pressure is 150-210kPa, the reflux ratio is 1.4-2.9, the temperature of the tower bottom is 110-120 ℃, and the pressure is 150-195 kPa.
6. The improved three-tower three-effect crude methanol refining process according to claim 1, characterized in that,
for the first mode: gas-phase materials extracted from the top of the pre-rectifying tower are sequentially subjected to primary condensation and secondary condensation, gas-liquid separation is carried out on a condensed liquid phase after the secondary condensation, the condensed liquid phase after the primary condensation and a separated liquid phase obtained by the gas-liquid separation flow in parallel to be used as reflux liquid to flow back into the pre-rectifying tower, a small amount of non-condensable gas returns to secondary condensation operation after the parallel flow, and the non-condensable gas phase after the secondary condensation and the separated gas phase obtained by the gas-liquid separation are subjected to subsequent treatment.
7. The improved three-tower three-effect crude methanol refining process of claim 1, wherein the feed composition of the crude methanol is: 50-97w% of methanol, 1.5-2.5w% of light component impurities and 7.5-13.5w% of heavy component impurities; the methanol content in the gas phase material extracted from the top of the pre-rectifying tower is 18-28w%, and the methanol content in the aqueous methanol solution A extracted from the bottom of the pre-rectifying tower is 70-85 w%; the content of methanol in the water-containing methanol solution B extracted from the bottom of the first rectifying tower is 50-75 w%.
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| CN112811976B (en) * | 2021-01-12 | 2023-01-13 | 江苏扬农化工集团有限公司 | Method for recovering solvent in aqueous phase of epoxy chloropropane prepared by hydrogen peroxide method |
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| CN113979840B (en) * | 2021-11-29 | 2023-06-20 | 中国成达工程有限公司 | Three-tower differential pressure thermal coupling rectification method for separating methanol from dimethyl carbonate and phenol |
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