CN115155253A - Automatic control system for carbon dioxide content of coal-to-methanol synthesis gas - Google Patents
Automatic control system for carbon dioxide content of coal-to-methanol synthesis gas Download PDFInfo
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- CN115155253A CN115155253A CN202210777647.XA CN202210777647A CN115155253A CN 115155253 A CN115155253 A CN 115155253A CN 202210777647 A CN202210777647 A CN 202210777647A CN 115155253 A CN115155253 A CN 115155253A
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- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
- B01D53/14—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols by absorption
- B01D53/18—Absorbing units; Liquid distributors therefor
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- C—CHEMISTRY; METALLURGY
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- C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
- C07C29/00—Preparation of compounds having hydroxy or O-metal groups bound to a carbon atom not belonging to a six-membered aromatic ring
- C07C29/15—Preparation of compounds having hydroxy or O-metal groups bound to a carbon atom not belonging to a six-membered aromatic ring by reduction of oxides of carbon exclusively
- C07C29/151—Preparation of compounds having hydroxy or O-metal groups bound to a carbon atom not belonging to a six-membered aromatic ring by reduction of oxides of carbon exclusively with hydrogen or hydrogen-containing gases
- C07C29/152—Preparation of compounds having hydroxy or O-metal groups bound to a carbon atom not belonging to a six-membered aromatic ring by reduction of oxides of carbon exclusively with hydrogen or hydrogen-containing gases characterised by the reactor used
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- G—PHYSICS
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- G01K—MEASURING TEMPERATURE; MEASURING QUANTITY OF HEAT; THERMALLY-SENSITIVE ELEMENTS NOT OTHERWISE PROVIDED FOR
- G01K13/00—Thermometers specially adapted for specific purposes
- G01K13/02—Thermometers specially adapted for specific purposes for measuring temperature of moving fluids or granular materials capable of flow
- G01K13/024—Thermometers specially adapted for specific purposes for measuring temperature of moving fluids or granular materials capable of flow of moving gases
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N33/00—Investigating or analysing materials by specific methods not covered by groups G01N1/00 - G01N31/00
- G01N33/0004—Gaseous mixtures, e.g. polluted air
- G01N33/0009—General constructional details of gas analysers, e.g. portable test equipment
- G01N33/0027—General constructional details of gas analysers, e.g. portable test equipment concerning the detector
- G01N33/0036—Specially adapted to detect a particular component
- G01N33/004—Specially adapted to detect a particular component for CO, CO2
Abstract
The invention discloses an automatic control system for carbon dioxide content in coal-to-methanol synthesis gas, which utilizes the principle that the carbon dioxide content in the methanol synthesis gas is in direct proportion to the carbon dioxide content in purified gas at the outlet of a washing tower of a low-temperature methanol washing section, and the carbon dioxide content in purified gas at the outlet of the washing tower of the low-temperature methanol washing section is in direct proportion to the difference between the temperature of the purified gas at the outlet of the washing tower and the temperature of poor methanol, and realizes the automatic control of the carbon dioxide content in the methanol synthesis gas by adjusting the difference between the temperature of the purified gas at the outlet of the washing tower and the temperature of poor methanol, thereby reducing the fluctuation range of the carbon dioxide content and the hydrogen-carbon ratio of the methanol synthesis gas, improving the yield and the quality of methanol, prolonging the service life of a synthesis catalyst, reducing the consumption of a device, reducing the labor intensity of process operators, and having the characteristics of high automation level, convenient use, stable control, strong practicability and the like.
Description
Technical Field
The invention relates to the technical field of control of carbon dioxide content of coal-to-methanol synthesis gas, in particular to an automatic control system for carbon dioxide content of coal-to-methanol synthesis gas.
Background
In the production of methanol from coal, the crude gas rich in carbon monoxide and hydrogen prepared by a coal gasification device is firstly converted into hydrogen and carbon dioxide by the carbon monoxide part in the crude gas in a carbon monoxide conversion section, and then most of the carbon dioxide is removed in a low-temperature methanol washing section, thus finally preparing the methanol synthesis feed gas containing hydrogen, carbon monoxide and carbon dioxide. The methanol synthesis raw material gas is subjected to the following reaction to generate methanol under the action of a synthesis catalyst in a synthesis process: 2H 2 ＋CO=CH 3 OH、3H 2 ＋CO 2 =CH 3 OH＋H 2 O。
The content of hydrogen, carbon monoxide and carbon dioxide in the methanol synthesis raw material gas must meet a certain proportion requirement, and is generally expressed by a hydrogen-carbon ratio f, wherein f = (n (H) 2 ）-n（CO 2 ））/（n（CO）+n（CO 2 )). The hydrogen-carbon ratio f = 2.05-2.15 of fresh gas entering the synthesis system and the hydrogen-carbon ratio f = 3.5-4.5 of recycle synthesis gas entering the synthesis tower are required. Although carbon dioxide in the methanol synthesis gas is not a main raw material, proper amount of carbon dioxide in the synthesis gas can be controlled to slow down CO and H 2 The intensity of the reaction is favorable for stabilizing the temperature of a catalyst bed layer, prolonging the service life of the catalyst, improving the selectivity of the catalyst, promoting the improvement of the yield of the methanol, reducing the occurrence of side reactions, reducing the content of by-products in the crude methanol, improving the product quality and reducing the energy consumption of methanol rectification. However, excessive carbon dioxide content can cause the reduction of the synthesis rate of CO, the reduction of the yield of methanol, the increase of the water content in crude methanol and the increase of the operation cost of rectification. It is generally preferred to control the carbon dioxide content of the gas entering the synthesis column to be in the range of 3.0 to 5.0% (vol%).
The content of hydrogen and carbon monoxide in the methanol synthesis gas is controlled by a conversion section, and the content of carbon dioxide is controlled by a low-temperature methanol washing section. In the existing production process of methanol from coal, a secondary line with an adjusting valve is usually arranged at the upper part of a washing tower at a low-temperature methanol washing section to control the content of carbon dioxide in synthesis gas, for example, the invention patent of 201320387484.0, a low-temperature methanol washing tower capable of slightly adjusting the concentration of carbon dioxide, namely the method is adopted to control the content of carbon dioxide. However, the sulfur content in the gas at the upper part of the washing tower of part of manufacturers is high, and the content of carbon dioxide in the synthesis gas is controlled by using a secondary line arranged at the upper part of the washing tower, so that the sulfur content of the synthesis gas exceeds the standard, and a synthesis catalyst is poisoned, so that the secondary line is not used for controlling the content of carbon dioxide. Besides, the means for controlling the content of the carbon dioxide also comprises adjusting the flow of the lean methanol in the washing tower, and adjusting the opening of an ammonia cooler at the three-section outlet of the washing tower, a circulating methanol cooler and a two-section circulating methanol bypass adjusting valve. However, the on-line analyzer for the components of the synthesis gas configured by some existing manufacturers needs a certain time (for example, about 5 minutes) to obtain an analysis value, analysis data cannot be displayed in real time, an operator can only perform manual adjustment according to the analysis data reported discontinuously, automatic control cannot be realized, and the on-line analyzer has the defects of lag in adjustment, frequent adjustment, poor control precision, poor stability, large workload of the operator and the like, so that the fluctuation of the carbon dioxide content and the hydrogen-carbon ratio of the synthesis gas is large, the yield, the quality and the consumption of a methanol product are influenced, and the service life of a synthesis catalyst is also influenced in a serious case. Therefore, a set of automatic control system for the carbon dioxide content of the methanol synthesis gas is developed, and the system has great practical value.
Disclosure of Invention
Aiming at the problems and the defects in the prior art, the invention provides a novel automatic control system for the carbon dioxide content in a coal-to-methanol synthesis gas.
The invention solves the technical problems through the following technical scheme:
the invention provides an automatic control system for carbon dioxide content of coal-to-methanol synthesis gas, which comprises a conversion gas precooler, a conversion gas separator, a four-section washing tower, a circulating methanol cooler, an ammonia cooler between sections of the washing tower and a synthesis gas compressor, and is characterized by also comprising a synthesis gas on-line analyzer arranged on a pipeline between the synthesis gas compressor and the methanol synthesis tower and a master controller electrically connected with the synthesis gas on-line analyzer, wherein the top of the four-section washing tower is provided with a purified gas temperature measuring instrument;
the main controller is provided with a methanol synthesis gas carbon dioxide content control target value input frame, a temperature difference control target value input frame, a methanol synthesis gas carbon dioxide content actual value and target value deviation set value input frame, a temperature difference controller given value plus decrement input frame, a bypass regulating valve opening set value input frame and a lean methanol flow controller given value plus decrement input frame, wherein the range value input by the methanol synthesis gas carbon dioxide content actual value and target value deviation set value input frame corresponds to the addition and subtraction amount input by the temperature difference controller given value addition and subtraction amount input frame one by one, the opening range input by the bypass regulating valve opening set value input frame corresponds to the addition and subtraction amount input by the lean methanol flow controller given value plus decrement input frame one by one, and the lean methanol flow controller is provided with a lean methanol flow target value in advance;
the on-line analysis instrument of the synthesis gas is used for analyzing the actual carbon dioxide content in the methanol synthesis gas in real time, the lean methanol flow controller is used for acquiring the actual flow of lean methanol in real time, the temperature difference controller is used for calculating the actual temperature difference based on the real-time purified gas temperature value of the purified gas temperature measuring instrument and the real-time lean methanol temperature value of the lean methanol temperature measuring instrument, and the bypass regulating valve controller is used for acquiring the opening degree of the methanol bypass regulating valve in real time;
the main controller is used for calculating the difference between the actual carbon dioxide content value and the target value to be controlled input in the methanol synthesis gas carbon dioxide content control target value input frame, automatically selecting the range to which the difference input in the methanol synthesis gas carbon dioxide content actual value and target value deviation set value input frame belongs according to the difference, selecting the corresponding increment and decrement input in the temperature difference controller given value increment and decrement input frame according to the selected range, and adding the temperature difference control target value input in the temperature difference control target value input frame and the increment and decrement corresponding to the selected range to obtain a new temperature difference control target value;
the temperature difference controller is used for comparing the actual temperature difference value with a new temperature difference control target value, driving the bypass adjusting valve controller to adjust the opening of the bypass adjusting valve, enabling the actual temperature difference value to approach the new temperature difference control target value continuously, automatically selecting the range to which the opening belongs, which is input in the opening set value input frame of the bypass adjusting valve, according to the opening of the bypass adjusting valve, selecting the corresponding increment and decrement input by the methanol-poor flow controller given value and decrement input frame according to the selected range, and adding the methanol-poor flow target value input in advance by the methanol-poor flow controller with the increment and decrement corresponding to the selected range to obtain a new methanol-poor flow target value;
the poor methanol flow controller is used for comparing the actual poor methanol flow value with the new poor methanol flow target value and automatically adjusting the opening of the poor methanol flow regulating valve, so that the actual poor methanol flow value continuously approaches to the new poor methanol flow target value.
Preferably, the system further comprises a purified gas on-line analyzer disposed on a pipeline between the shift gas pre-cooler and the synthesis gas compressor, for analyzing H in the purified gas 2 、CO、CO 2 And H 2 The content of S substance.
The positive progress effects of the invention are as follows: the invention utilizes the principle that the carbon dioxide content in the methanol synthesis gas is in direct proportion with the carbon dioxide content in the purified gas at the outlet of the washing tower of the low-temperature methanol washing section, and the carbon dioxide content in the purified gas at the outlet of the washing tower of the low-temperature methanol washing section is in direct proportion with the difference between the temperature of the purified gas at the outlet of the washing tower and the temperature of poor methanol, overcomes the difficulties that an on-line analyzer of the methanol synthesis gas cannot analyze in real time and data lags behind, realizes automatic control of the carbon dioxide content in the methanol synthesis gas by adjusting the difference between the temperature of the purified gas at the outlet of the washing tower and the temperature of poor methanol, reduces the fluctuation range of the carbon dioxide content and the hydrogen-carbon ratio of the methanol synthesis gas, can improve the yield and the quality of methanol, prolong the service life of a synthesis catalyst, reduce the consumption of a device, and reduce the labor intensity of process operators, and has the characteristics of high automation level, convenient use, stable control, strong practicability and the like, thereby providing an advanced carbon dioxide content control system for preparing the methanol synthesis gas from coal.
Drawings
Fig. 1 is a schematic structural diagram of an automatic control system for carbon dioxide content in a coal-to-methanol synthesis gas according to a preferred embodiment of the present invention.
FIG. 2 is a diagram of the interface of the general controller according to the preferred embodiment of the present invention.
Detailed Description
In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are some, but not all, embodiments of the present invention. All other embodiments, which can be obtained by a person skilled in the art without any inventive step based on the embodiments of the present invention, are within the scope of the present invention.
As shown in fig. 1 and fig. 2, the present embodiment provides an automatic control system for carbon dioxide content in coal-to-methanol synthesis gas, which includes a shift pre-cooler 1, a shift gas separator 2, a four-stage scrubber 3, a circulating methanol cooler 4, a scrubber inter-stage ammonia cooler 5, a synthesis gas compressor 6, a purified gas on-line analyzer 8 (e.g., position number AI 201), a synthesis gas on-line analyzer 9 (e.g., position number AT 301), and a general controller 10, wherein a purified gas temperature measuring instrument 7 (e.g., position number TI 201) is disposed AT the top of the four-stage scrubber 3, low-temperature lean methanol is introduced into the top of the four-stage scrubber 3 through a lean methanol flow regulating valve 15 (e.g., position number FV 201), the lean methanol flow regulating valve 15 is controlled by a lean methanol flow controller 16 (e.g., position number FIC 201), a lean methanol temperature measuring instrument 14 (e.g., position number TI 202) is disposed on a pipeline where the lean methanol flow regulating valve 15 is disposed, the purified gas on-line analyzer 8 is disposed on a pipeline between the shift pre-cooler 1 and the synthesis gas compressor 6, and the pipeline between the synthesis gas compressor 6. The synthesis gas on-line analyzer 9 is electrically connected with a master controller 10, a purified gas temperature measuring instrument 7 (TI 201) and a poor methanol temperature measuring instrument 14 (TI 202) are both electrically connected with a temperature difference controller 17 (TDIC 201), a methanol bypass regulating valve 12 (HV 201) is arranged between the two sections of the four-section washing tower 3 and an input pipeline of the ammonia cooler 5 between the sections of the washing tower, the methanol bypass regulating valve 12 is controlled by a bypass regulating valve controller 13 (HIC 201), the master controller 10 is electrically connected with the temperature difference controller 17, the temperature difference controller 17 is electrically connected with the bypass regulating valve controller 13, and the bypass regulating valve controller 13 is electrically connected with a poor methanol flow controller 16.
The hardware part of the equipment is shown in figure 1, the conversion gas from the conversion section firstly enters the shell pass of a conversion gas precooler 1 of a low-temperature methanol washing section, is cooled by low-temperature tail gas, carbon dioxide and purified gas of the tube pass of the conversion gas precooler 1, and enters the bottom of a four-section washing tower 3 after water, methanol and other liquid substances are separated by a conversion gas separator 2, the conversion gas passes through a plurality of layers of floating valve tower plates in four sections of the four-section washing tower 3 from bottom to top, all sulfides and most carbon dioxide are absorbed by low-temperature poor methanol solution added from the top of the tower, and the gas coming out of the top of the tower is called purified gas (namely fresh methanol synthesis gas). Purified gas enters a tube pass of the conversion gas precooler 1, cold energy is transferred to conversion gas of a shell pass of the conversion gas precooler 1, and the conversion gas enters a synthesis gas compressor 6 to be boosted and then is conveyed to a methanol synthesis tower to produce crude methanol. The low-temperature lean methanol added from the top of the four-section washing tower 3 is heated after absorbing carbon dioxide in the fourth section, enters the circulating methanol cooler 4 outside the tower through the multilayer float valve tower plate in the fourth section and the liquid accumulating disc at the bottom of the fourth section to remove absorption heat, returns to the top of the third section to absorb carbon dioxide, enters the washing tower inter-section ammonia cooler 5 and the circulating methanol cooler 4 outside the tower through the multilayer float valve tower plate in the third section and the liquid accumulating disc at the bottom of the third section to remove absorption heat, and returns to the top of the second section to absorb carbon dioxide again. The carbon-rich methanol at the bottom of the second section is divided into two paths, one path returns to the first section to absorb sulfide, the other path goes to a flash tank of a subsequent flash system, and the sulfur-rich methanol after absorbing sulfide comes out from the bottom of the four-section washing tower 3 and goes to the flash tank of the subsequent flash system.
Further, the online purifier gas analyzer 8 (AI 201) may analyze H in the purifier gas 2 、CO、CO 2 And H 2 S and the like, and the analysis data is updated once about 5 minutes. The on-line analyzer 9 for the synthesis gas can analyze H in the gas entering the methanol synthesis tower 2 、CO、CO 2 、N 2 、CH 4 And (5) waiting for substances, and updating the analysis data once in about 5 minutes.
As shown in fig. 2, the overall controller 10 is provided with a control target value input box 18 for the carbon dioxide content of the methanol synthesis gas (AIC 301_ 3), a control target value input box 19 for the temperature difference between the purge gas and the lean methanol (TDIC 201) of the scrubber tower, an input box 20 for the actual carbon dioxide content of the methanol synthesis gas (AIC 301_3. Pv) and a target value deviation set value, an input box 21 for the addition and subtraction of the given value of the temperature difference controller (tdic201. Sp), an input box 22 for the opening of the bypass regulating valve (hic 201. Op), an input box 23 for the addition and subtraction of the given value of the lean methanol flow controller (fic201. Sp), a range value input by the actual carbon dioxide content of the methanol synthesis gas and the target value deviation set value input box 20 corresponds to the addition and subtraction of the given value input box 21, an opening range input by the opening of the bypass regulating valve set value input box 22 corresponds to the addition and subtraction of the given value of the lean methanol flow controller 23, and the lean methanol flow controller 16 is preset with a target value of the lean methanol flow.
Further, the actual value of the carbon dioxide content of the methanol synthesis gas and the value of the deviation set value input box 20 of the target value and the value of the opening set value input box 22 of the bypass regulating valve are not constant, and can be increased or decreased according to the actual operation condition. The numerical values in the operation interface are only used for demonstration and do not represent actual operation data.
The working principle of the automatic control system for the carbon dioxide content of the methanol synthesis gas is as follows:
the method overcomes the difficulties that a methanol synthesis gas on-line analyzer cannot analyze in real time and analyze data lag by utilizing the principle that the carbon dioxide content in the methanol synthesis gas is in direct proportion to the carbon dioxide content in the purified gas at the outlet of the washing tower of the low-temperature methanol washing section and the carbon dioxide content in the purified gas at the outlet of the washing tower of the low-temperature methanol washing section is in direct proportion to the difference between the temperature of the purified gas at the top of the washing tower and the temperature of poor methanol, and realizes the automatic control of the carbon dioxide content in the methanol synthesis gas by adjusting the difference between the temperature of the purified gas at the top of the washing tower and the temperature of poor methanol in advance.
Further, the carbon dioxide content in the purge gas determines the carbon dioxide content in the methanol synthesis gas, the higher the carbon dioxide content in the purge gas, the higher the carbon dioxide content in the methanol synthesis gas and vice versa. However, the carbon dioxide content of the same purified gas and the carbon dioxide content of the methanol synthesis gas are not always the same, and therefore, the carbon dioxide content of the purified gas cannot be targeted for control and can be used only as reference data, depending on factors such as the plant operation load, the activity of the synthesis catalyst, and the content of inert gas in the synthesis gas.
Further, the methanol-poor temperature measured by the methanol-poor temperature measuring instrument 14 and the purified gas temperature measured by the purified gas temperature measuring instrument 7 under different operating conditions are changed, but the difference between the purified gas temperature value and the methanol-poor temperature value determines the carbon dioxide content in the purified gas, and the higher the difference is, the higher the carbon dioxide content is, and vice versa.
Further, the difference between the purge gas temperature value measured by the purge gas temperature measuring instrument 7 and the methanol lean temperature value measured by the methanol lean temperature measuring instrument 14 is inversely proportional to the methanol lean flow rate, the higher the methanol lean flow rate is, the lower the temperature difference is, and vice versa.
Further, the difference between the purge gas temperature value measured by the purge gas temperature measuring instrument 7 and the methanol-poor temperature value measured by the methanol-poor temperature measuring instrument 14 is proportional to the opening degree of the bypass adjusting valve 12, and the larger the opening degree of the bypass adjusting valve 12 is, the higher the temperature difference is, and vice versa.
Since frequent adjustment of the lean methanol flow controller 16 affects the stability of the whole low-temperature methanol washing section, the opening of the bypass regulating valve 12 is used as a main regulation for controlling the temperature difference, and the lean methanol flow is used as an auxiliary regulation for controlling the temperature difference.
The operation process and the working process of the automatic control system for the carbon dioxide content of the methanol synthesis gas are as follows:
the target value to be controlled is input in a control target value input box 18 for the carbon dioxide content of the methanol synthesis gas, and a value corresponding to the target value input in the input box 18 is input in a control target value input box 19 for the temperature difference between the purge gas of the washing tower and the lean methanol. The correspondence between syngas carbon dioxide content and temperature difference requires a certain period of empirical summary by skilled and operating personnel.
The numerical values in different ranges are input into an input box 20 for the deviation set value between the actual value of the carbon dioxide content of the methanol synthesis gas and the target value, and the numerical value of the temperature difference controller set value which is required to be changed and corresponds to the input box 20 is input into an input box 21 for the given value plus-minus quantity of the temperature difference controller of the purified gas and the lean methanol. The numerical values to be input are related to the experience of technicians and operators, and can be cured through groping and summarizing.
The values of the different ranges are input in the bypass regulator valve opening setting value input box 22, and the value of the lean methanol flow controller set value to be changed corresponding to the input box 22 is input in the lean methanol flow controller set value plus decrement input box 23. The numerical values to be input are related to the experience of technicians and operators, and can be cured through groping and summarizing.
After the numerical value input is finished, the bypass regulating valve controller 13, the temperature difference controller 17 and the poor methanol flow controller 16 are put into cascade connection in sequence, and the automatic control system for the carbon dioxide content of the methanol synthesis gas is put into operation. During the trouble shooting of the on-line analyzer 9 for the synthetic gas, the temperature difference controller 17 is set to be automatic or manual, namely, the automatic control system for the carbon dioxide content of the methanol synthetic gas is released.
After the automatic control system for the carbon dioxide content of the methanol synthesis gas is put into operation, the on-line synthesis gas analyzer 9 is used for analyzing the actual carbon dioxide content of the methanol synthesis gas in real time, the lean methanol flow controller 16 is used for acquiring the actual flow of lean methanol in real time, the temperature difference controller 17 is used for calculating the actual temperature difference based on the real-time purified gas temperature value of the purified gas temperature measuring instrument 7 and the real-time lean methanol temperature value of the lean methanol temperature measuring instrument 14, and the bypass regulating valve controller 13 is used for acquiring the opening of the methanol bypass regulating valve 12 in real time.
The main controller 10 is used for calculating the difference between the actual carbon dioxide content value and the target value to be controlled input in the control target value input box 18 of the carbon dioxide content of the methanol synthesis gas, automatically selecting the range to which the difference between the actual carbon dioxide content of the methanol synthesis gas and the target value input in the deviation set value input box 20 belongs according to the difference, selecting the corresponding increment and decrement input in the given value increment and decrement input box 21 of the temperature difference controller according to the selected range, and adding the temperature difference control target value input in the temperature difference control target value input box 19 and the increment and decrement corresponding to the selected range to obtain the new temperature difference control target value.
The temperature difference controller 17 is used for comparing the actual temperature difference value with a new temperature difference control target value, driving the bypass regulating valve controller 13 to regulate the opening degree of the bypass regulating valve 12, so that the actual temperature difference value continuously approaches the new temperature difference control target value, automatically selecting the range to which the opening degree input in the bypass regulating valve opening degree set value input frame 22 belongs according to the opening degree of the bypass regulating valve 12, selecting the corresponding increment and decrement input by the methanol-poor flow controller set value increment and decrement input frame 23 according to the selected range, and adding the methanol-poor flow target value input in advance by the methanol-poor flow controller 16 with the increment and decrement corresponding to the selected range to obtain the new methanol-poor flow target value.
The lean methanol flow controller 16 is configured to compare the actual lean methanol flow value with the new lean methanol flow target value, and automatically adjust the opening of the lean methanol flow control valve 15, so that the actual lean methanol flow value continuously approaches the new lean methanol flow target value.
The present invention is described below with reference to a specific example so that those skilled in the art can better understand the technical solution of the present invention:
as shown in figure 1, the conversion gas from the conversion section with the temperature of 30-40 ℃ and the carbon dioxide content of 38-41% (vol%) enters the shell pass of a conversion gas precooler 1 of a low-temperature methanol washing section, is cooled to-30-34 ℃ by low-temperature tail gas, carbon dioxide and purified gas of the tube pass of the conversion gas precooler 1, enters the bottom of a four-section washing tower 3 after liquid substances such as water, methanol and the like are separated by a conversion gas separator 2, the conversion gas passes through four sections of floating valve tower plates from bottom to top, all sulfides and most carbon dioxide are absorbed by low-temperature poor methanol solution with the temperature of-54-60 ℃ added from the top of the tower, the gas coming out of the top of the tower is called purified gas (namely fresh methanol synthesis gas), the temperature is-48-53 ℃, and the carbon dioxide content is 2-3% (vol%). Purified gas enters a tube pass of the conversion gas precooler 1, the temperature of the conversion gas which transfers cold energy to a shell pass of the conversion gas precooler 1 is raised to 21-27 ℃, the temperature of the conversion gas enters a synthesis gas compressor 6 to be raised and then is conveyed to a methanol synthesis tower to produce crude methanol, and after the purified gas is mixed with circulating gas of the methanol synthesis tower, the content of carbon dioxide is controlled to be 3-5% (vol%).
During the device start-up period, because the fluctuation of technological parameters of each section is large, the operation is unstable, the automatic control system for the carbon dioxide content of the methanol synthesis gas is not used, the related poor methanol flow controller 16 and the bypass regulating valve controller 13 are manually or automatically controlled, and the automatic control system for the carbon dioxide content of the methanol synthesis gas can be used after the technological parameters of the low-temperature methanol washing section and the methanol synthesis section are basically adjusted and stabilized.
The operation of the automatic control system for carbon dioxide content in methanol synthesis gas according to the present invention is described below with reference to the data in FIG. 2:
the target value of the carbon dioxide content AIC301_3 of the methanol synthesis gas to be controlled is input in a control target value input box 18 of the carbon dioxide content of the methanol synthesis gas: 4.0%, inputting the target value of the temperature difference TDIC201 between the purge gas and the lean methanol in the purge gas and lean methanol control target value input box 19: 6.5 ℃.
In the "AIC301 — 3. Pv-target value" input box 20 (the input box of the deviation of the actual value of the carbon dioxide content of the methanol synthesis gas from the target value set value) are sequentially input from left to right: 0.5, 0.5-0.3, 0.3-0.1, 0.1-0.1, -0.1-0.3, -0.3-0.5 and less than-0.5, and sequentially input in a TDIC201.SP input box 21 (a temperature difference controller given value addition and subtraction input box) from left to right: -1.5, -1.0, -0.5, 0, +0.5, +1.0, +1.5.
In the HIC201 opening degree input box 22 (i.e., the bypass regulator valve opening degree setting value input box), sequentially input from left to right are: the values >90, >80, >70, <30, <20, <10, <20 > are sequentially input from left to right in the fic201.Sp input block 23 (the methanol lean flow controller given value plus decrement input block): -2.0, -1.0, +2.0.
After the numerical value input is finished, the bypass regulating valve controller 13, the temperature difference controller 17 and the poor methanol flow controller 16 are put into cascade connection in sequence, and the automatic control system for the carbon dioxide content of the methanol synthesis gas is put into operation.
For example, the carbon dioxide content AIC301 — 3.PV of the methanol synthesis gas analyzed by the current on-line syngas analyzer 9 is 3.8% (vol%), the lean methanol flow target value (SP value) of the lean methanol flow controller 16 is 200t/h, the lean methanol flow actual value (PV value) is 199.5t/h, the temperature difference target value (SP value) of the temperature difference controller 17 is 6.5 ℃, the temperature difference actual value (PV value) is 6.0 ℃, and the opening degree of the bypass regulator valve controller 13 is 60%. The "AIC301_3. Pv-target value" was calculated to be-0.2 (i.e., 3.8-4.0= -0.2), and the temperature difference SP value of the temperature difference controller 17 was increased from 6.5 ℃ (i.e., the value input in the input box 19) to 7.0 ℃ in the range of "-0.1 to-0.3" of the "AIC301_3. Pv-target value" input box 20, corresponding to "+0.5" in the tdic201.SP input box 21. The temperature difference controller 17 compares the current temperature difference PV value "6.0 ℃ with the new temperature difference SP value" 7.0 ℃, gradually opens the opening of the bypass regulating valve controller 13 from the current 60%, so that the circulating methanol entering the ammonia cooler 5, the circulating methanol cooler 4 and the second section from the outlet of the three sections of the washing tower is reduced, the temperature of the purified gas outlet measured by the purified gas temperature measuring instrument 7 rises, and the actual temperature difference value continuously approaches the SP value "7.0 ℃ from the current" 6.0 ℃. After the actual value of the temperature difference has risen, the carbon dioxide in the purge gas will rise, so that the carbon dioxide content in the methanol synthesis gas gradually rises from the current 3.8% (vol%) to approach the target value of 4.0% (vol%). When the opening degree of the bypass regulating valve 12 controlled by the bypass regulating valve controller 13 is gradually increased from 60% to 70.1%, the flow target value (SP value) of the methanol-poor flow controller 16 is reduced from 200t/h to 199t/h corresponding to-1.0 "in the FIC201.SP input box 23 in the range of" >70 "in the HIC201 opening degree input box 22, and the methanol-poor flow controller 16 gradually reduces the opening degree of the methanol-poor flow regulating valve 15 according to the current flow PV value 199.5t/h, so as to reduce the methanol-poor flow and enable the new flow PV value to gradually approach the flow SP value. After the lean methanol flow rate is reduced, the outlet temperature of the purified gas measured by the purified gas temperature measuring instrument 7 is increased, and the PV value of the temperature difference is continuously close to the SP value of 7.0 ℃ from the current' 6.0 ℃, so that the carbon dioxide in the purified gas is increased, and the carbon dioxide content in the methanol synthesis gas is gradually increased from the current 3.8% (vol%) to the target value of 4.0% (vol%). After about 5 minutes, the on-line analyzer 9 for the synthesis gas analyzes new data, and the adjustment of the next period is performed according to the carbon dioxide content of the methanol synthesis gas in the master controller. Before new analysis data comes out, the temperature difference SP value of the temperature difference controller 17 is kept unchanged, but the opening degrees of the bypass regulating valve 12 and the lean methanol flow regulating valve 15 are continuously adjusted, so that the PV value of the temperature difference controller 17 is infinitely close to the SP value all the time, and thus, the automatic control of the carbon dioxide content of the methanol synthesis gas is realized.
While specific embodiments of the invention have been described above, it will be appreciated by those skilled in the art that these are by way of example only, and that the scope of the invention is defined by the appended claims. Various changes and modifications to these embodiments may be made by those skilled in the art without departing from the spirit and scope of the invention, and these changes and modifications are within the scope of the invention.
Claims (2)
1. The system is characterized by further comprising a synthesis gas on-line analyzer arranged on a pipeline between the synthesis gas compressor and the methanol synthesis tower and a controller electrically connected with the synthesis gas on-line analyzer, wherein a purified gas temperature measuring instrument is arranged at the top of the four-section washing tower, low-temperature poor methanol is introduced into the top of the four-section washing tower through a poor methanol flow regulating valve, the poor methanol flow regulating valve is controlled by a poor methanol flow controller, a poor methanol temperature measuring instrument is arranged on a pipeline where the poor methanol flow regulating valve is arranged, the purified gas temperature measuring instrument and the poor methanol temperature measuring instrument are electrically connected with a temperature difference controller, a methanol bypass regulating valve is arranged between the second section of the four-section washing tower and an input pipeline of the ammonia synthesis gas cooler between the sections of the washing tower and controlled by a bypass regulating valve controller, the total controller is electrically connected with the temperature difference controller, the temperature difference controller is electrically connected with the bypass regulating valve, and the poor methanol bypass regulating valve is electrically connected with the methanol flow controller;
the main controller is provided with a methanol synthesis gas carbon dioxide content control target value input frame, a temperature difference control target value input frame, a methanol synthesis gas carbon dioxide content actual value and target value deviation set value input frame, a temperature difference controller given value plus decrement input frame, a bypass regulating valve opening set value input frame and a lean methanol flow controller given value plus decrement input frame, wherein the range value input by the methanol synthesis gas carbon dioxide content actual value and target value deviation set value input frame corresponds to the addition and subtraction amount input by the temperature difference controller given value addition and subtraction amount input frame one by one, the opening range input by the bypass regulating valve opening set value input frame corresponds to the addition and subtraction amount input by the lean methanol flow controller given value plus decrement input frame one by one, and the lean methanol flow controller is provided with a lean methanol flow target value in advance;
the on-line analysis instrument of the synthesis gas is used for analyzing the actual carbon dioxide content in the methanol synthesis gas in real time, the lean methanol flow controller is used for acquiring the actual flow of lean methanol in real time, the temperature difference controller is used for calculating the actual temperature difference based on the real-time purified gas temperature value of the purified gas temperature measuring instrument and the real-time lean methanol temperature value of the lean methanol temperature measuring instrument, and the bypass regulating valve controller is used for acquiring the opening degree of the methanol bypass regulating valve in real time;
the master controller is used for calculating the difference value between the actual carbon dioxide content value and the target value to be controlled input in the methanol synthesis gas carbon dioxide content control target value input frame, automatically selecting the range to which the difference value input in the methanol synthesis gas carbon dioxide content actual value and target value deviation set value input frame belongs according to the difference value, selecting the corresponding increment and decrement input in the temperature difference controller given value increment and decrement input frame according to the selected range, and adding the temperature difference control target value input in the temperature difference control target value input frame and the increment and decrement corresponding to the selected range to obtain a new temperature difference control target value;
the temperature difference controller is used for comparing the actual temperature difference value with a new temperature difference control target value, driving the bypass adjusting valve controller to adjust the opening of the bypass adjusting valve, enabling the actual temperature difference value to approach the new temperature difference control target value continuously, automatically selecting the range to which the opening belongs, which is input in the opening set value input frame of the bypass adjusting valve, according to the opening of the bypass adjusting valve, selecting the corresponding increment and decrement input by the methanol-poor flow controller given value and decrement input frame according to the selected range, and adding the methanol-poor flow target value input in advance by the methanol-poor flow controller with the increment and decrement corresponding to the selected range to obtain a new methanol-poor flow target value;
the poor methanol flow controller is used for comparing the actual poor methanol flow value with the new poor methanol flow target value and automatically adjusting the opening of the poor methanol flow regulating valve, so that the actual poor methanol flow value continuously approaches to the new poor methanol flow target value.
2. The carbon dioxide content of coal-to-methanol synthesis gas of claim 1The system is characterized by further comprising a purified gas online analyzer, wherein the purified gas online analyzer is arranged on a pipeline between the transformation gas precooler and the synthesis gas compressor and is used for analyzing H in the purified gas 2 、CO、CO 2 And H 2 The content of S substance.
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