Sulfuric acid drying treatment system for methane chloride gas

Abstract

The invention provides a methane chloride gas sulfuric acid drying treatment system which is provided with a methane chloride inlet pipe, a sulfuric acid drying agent inlet pipe and a methane chloride outlet pipe, and the methane chloride inlet pipe is provided with a methane chloride gas flowmeter; the sulfuric acid drying agent inlet pipe is provided with a sulfuric acid metering pump, an acid inlet heat exchanger and a sulfuric acid flowmeter, and a cold medium inlet pipe of the acid inlet heat exchanger is provided with a cold medium inlet valve; the methane chloride outlet pipe is provided with a gas phase thermometer; the methane chloride gas flowmeter and the sulfuric acid flowmeter are electrically connected with the sulfuric acid metering pump, and the running power of the sulfuric acid metering pump is controlled by the flow ratio of methane chloride to sulfuric acid; the gas phase thermometer is electrically connected with the cold medium inlet valve, and the gas phase temperature of the drying system controls the opening and closing degree of the cold medium inlet valve. The method has the beneficial effects that the magnitude order of the acid mist content in the dried gas is reduced, so that the corrosion rate of downstream devices and pipelines is remarkably reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of chemical equipment, and in particular to a sulfuric acid drying treatment system for methyl chloride gas. Background Art

[0002] In the current process chain of methane chloride production plants, methyl chloride gas generated by the hydrochlorination reaction system serves as the core feedstock for the thermal chlorination system. Its quality and stability directly determine the economic viability and safety of the entire production plant. Upon exiting the hydrochlorination reactor, this gas inevitably carries with it a significant proportion of by-product water. Failure to effectively remove this water will pose a critical risk to the subsequent thermal chlorination process. In this context, the sulfuric acid drying tower, a key barrier for water removal, has a chain reaction effect on the thermal chlorination system. Residual water in the dried methyl chloride gas first triggers a hydrolysis side reaction in the thermal chlorination reactor. Methyl chloride reacts with water under a catalytic environment to produce methanol and highly corrosive hydrochloric acid. This, on the one hand, results in a yield loss of over 5% for the main product. On the other hand, the generated hydrochloric acid gas, under high temperature and high pressure, causes pitting corrosion on the reactor walls, with a measured corrosion rate of up to 0.5 mm / year. The cumulative effect of this corrosion process has shortened the plant's operating cycle from the designed 12 months to less than three months, resulting in three additional unplanned maintenance outages annually.

[0003] Existing sulfuric acid drying tower control strategies suffer from systemic shortcomings, manifesting primarily in two interrelated weaknesses. First, in terms of acid inlet control, operators currently rely entirely on manual adjustment of the concentrated sulfuric acid flow rate via on-site valves. This extensive control approach proves insufficient for addressing fluctuations in the moisture load of the feed gas. Secondly, shortcomings in temperature control are equally significant. The current approach focuses solely on maintaining the bottom liquid temperature at 15-35°C, effectively allowing for dangerous fluctuations in the gas-liquid microinterface within the tower. This submicron-sized acid mist, flowing through the compressor unit, condenses into a liquid film in the negative pressure zone created by the high-speed rotation of the impeller, which then undergoes an electrochemical corrosion reaction with carbon steel. Furthermore, this vapor-phase acid mist reacts synergistically with residual moisture to create a hydrofluoric acid microenvironment within the heat exchanger tubes, tripling the rate of intergranular corrosion of stainless steel fittings.

[0004] The above problems reflect the essential defects of the current control methods - the lack of a feedforward linkage mechanism between the acid inlet flow rate and the inlet moisture content, the neglect of the spatial distribution monitoring of the tower temperature field, and the lack of real-time feedback control of the outlet gas acid mist concentration. Summary of the Invention

[0005] To solve the problem of acid mist corrosion of equipment after methyl chloride finished gas is dried; The invention provides a chloromethane gas sulfuric acid drying treatment system. The drying treatment system is provided with a chloromethane inlet pipe, a sulfuric acid desiccant inlet pipe and a chloromethane outlet pipe, wherein the chloromethane inlet pipe is provided with a chloromethane gas flowmeter; the sulfuric acid desiccant inlet pipe is provided with a sulfuric acid metering pump, an acid inlet heat exchanger and a sulfuric acid flowmeter; the cold medium inlet pipe of the acid inlet heat exchanger is provided with a cold medium inlet valve; the chloromethane outlet pipe is provided with a gas phase thermometer; the chloromethane gas flowmeter and the sulfuric acid flowmeter are electrically connected to the sulfuric acid metering pump, and the flow ratio of chloromethane to sulfuric acid controls the operating power of the sulfuric acid metering pump; the gas phase thermometer is electrically connected to the cold medium inlet valve, and the gas phase temperature of the drying system controls the opening and closing degree of the cold medium inlet valve.

[0006] Furthermore, the drying treatment system is provided with two-stage drying towers, including a primary drying tower and a secondary drying tower connected in series.

[0007] Furthermore, the first-level drying tower is provided with a circulation pipeline utilizing sulfuric acid desiccant, and the circulation pipeline is provided with a tower circulation pump and a tower heat exchanger.

[0008] Furthermore, the secondary drying tower is provided with a circulation pipeline utilizing sulfuric acid desiccant, and the circulation pipeline is provided with a second-tower heat exchanger and a second-tower circulation pump.

[0009] Furthermore, the first-level drying tower is provided with a gas-connected pipe and a liquid-connected pipe to communicate with the second-level drying tower.

[0010] As a preferred solution, the methyl chloride outlet pipe is provided with a post-drying demister.

[0011] As a preferred solution, an APC control system is also included to control the flow ratio of methyl chloride to sulfuric acid.

[0012] The beneficial effects of the present invention are: 1. This invention utilizes real-time data from a chloromethane gas flowmeter and a sulfuric acid flowmeter, allowing the APC system to precisely adjust the sulfuric acid metering pump power, achieving dynamic molar ratio control of the feed gas to concentrated sulfuric acid injection, completely eliminating the hysteresis caused by manual adjustments. A synchronous temperature feedback system directly controls the opening of the cold medium inlet valve of the acid inlet heat exchanger using a gas phase thermometer, creating a closed-loop response within seconds and effectively suppressing heat accumulation within the tower.

[0013] 2. The present invention constructs a gradient dehydration environment through a series-connected double-tower structure. The first drying tower promptly removes the reaction heat generated by water absorption to achieve preliminary dehydration; the second drying tower performs deep refining, and the liquid redistribution system between the two towers automatically adjusts the sulfuric acid circulation volume of the two towers according to the acid concentration.

[0014] 3. The present invention reduces the acid mist content in the dried gas by an order of magnitude, significantly reducing the corrosion rate of downstream equipment and pipelines. Through a triple guarantee mechanism of "flow ratio feedforward to stabilize dehydration efficiency - temperature feedback to block acid mist generation - and composite demisting physical interception," it lays the technical foundation for the long-term, high-load operation of methane chloride plants. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] In order to make the content of the present invention more clearly understood, the present invention is further described in detail below based on specific embodiments and in conjunction with the accompanying drawings, wherein Figure 1 It is a structural schematic diagram of the present invention.

[0016] The reference numerals in the accompanying drawings are: 1. Sulfuric acid metering pump; 2. Acid inlet heat exchanger; 3. Secondary drying tower; 4. Second tower heat exchanger; 5. Second tower circulation pump; 6. Sulfuric acid flowmeter; 7. Post-drying demister; 8. Gas phase thermometer; 9. First tower circulation pump; 10. First tower heat exchanger; 11. First drying tower; 12. Methyl chloride gas flowmeter; 13. Cold medium inlet valve. DETAILED DESCRIPTION

[0017] To illustrate the features of the present invention, the present invention will be further described below with reference to the accompanying drawings and embodiments.

[0018] Example: See also Figure 1 This embodiment provides a sulfuric acid drying treatment system for chloromethane gas, comprising a first-stage drying tower 11 and a second-stage drying tower 3 installed in series. The bottom of the first-stage drying tower 11 is connected to a first-tower circulation pump 9 and a first-tower heat exchanger 10 via a pipeline to form a circulation loop. The bottom of the second-stage drying tower 3 is similarly provided with a second-tower circulation pump 5 and a second-tower heat exchanger 4 to form an independent circulation system. Gas-to-liquid pipes and liquid-to-gas pipes connect the two towers to achieve material intercommunication. A chloromethane gas flowmeter 12 is installed on the chloromethane inlet pipe at the raw gas inlet end. A sulfuric acid metering pump 1, an acid inlet heat exchanger 2, and a sulfuric acid flowmeter 6 are installed on the sulfuric acid desiccant inlet pipe of the concentrated sulfuric acid supply path. A cold medium inlet valve 13 is installed on the cold medium inlet pipe of the acid inlet heat exchanger 2. A gas phase thermometer 8 and a post-drying demister 7 are installed on the chloromethane outlet pipe at the dried gas output end.

[0019] In this embodiment, all metering and control equipment are integrated through the DCS system. The signal lines of the methyl chloride gas flowmeter 12 and the sulfuric acid flowmeter 6 are connected to the input end of the APC controller, and the APC output end is connected to the power regulation module of the sulfuric acid metering pump 1. The signal output of the gas phase thermometer 8 is directly interlocked with the opening controller of the cold medium inlet valve 13.

[0020] In the present embodiment, when chloromethane flow is 2370kg / h, chloromethane flow and sulfuric acid feed flow ratio are set at about 3.5, and now sulfuric acid acid inlet flow is about 285kg / h;When system load increases, chloromethane flow is brought up to 2610kg / h, sulfuric acid metering pump speed increases automatically, and sulfuric acid acid inlet flow automatically increases to 315kg / h, meets system load sulfuric acid demand, can automatically increase sulfuric acid flow without manual adjustment, before and after system load adjustment, chloromethane gas sampling analysis, water content does not change significantly;After acid inlet pipeline increases cold water heat exchanger, control drying two towers gas temperature between 18-20 ℃, at this temperature, sulfuric acid content in gas phase can be reduced. By sampling analysis, after adjustment, gas phase sulfate radical is reduced to 0.0258% by 0.0646%, and chloromethane gas moisture is reduced to 0.0045% by 0.0066%.

[0021] The above embodiments and accompanying drawings are intended only to illustrate the technical solutions of the present invention and are not intended to limit the present invention. The present invention has been described in detail with reference to preferred embodiments. Those skilled in the art should understand that any changes, modifications, additions, or substitutions made by those skilled in the art within the spirit and scope of the present invention do not depart from the spirit of the present invention and are intended to fall within the scope of the claims. Other related technical structures not fully disclosed in the present invention constitute prior art in the art.

Claims

1. A chloromethane gas sulfuric acid drying treatment system, wherein the drying treatment system is provided with a chloromethane inlet pipe, a sulfuric acid desiccant inlet pipe and a chloromethane outlet pipe, characterized in that: The chloromethane inlet pipe is provided with a chloromethane gas flow meter (12); The sulfuric acid desiccant inlet pipe is provided with a sulfuric acid metering pump (1), an acid inlet heat exchanger (2), and a sulfuric acid flow meter (6); the cold medium inlet pipe of the acid inlet heat exchanger (2) is provided with a cold medium inlet valve (13); The monochloromethane outlet pipe is provided with a gas phase thermometer (8); The methyl chloride gas flow meter (12) and the sulfuric acid flow meter (6) are electrically connected to the sulfuric acid metering pump (1), and the flow ratio of the methyl chloride to the sulfuric acid controls the operating power of the sulfuric acid metering pump (1); The gas phase thermometer (8) is electrically connected to the cold medium inlet valve (13), and the gas phase temperature of the drying system controls the opening and closing degree of the cold medium inlet valve (13).

2. The sulfuric acid drying treatment system for methyl chloride gas according to claim 1, characterized in that: The drying treatment system is provided with two-stage drying towers, including a first-stage drying tower (11) and a second-stage drying tower (3) connected in series.

3. The sulfuric acid drying treatment system for methyl chloride gas according to claim 2, characterized in that: The primary drying tower (11) is provided with a circulation pipeline for utilizing sulfuric acid desiccant, and the circulation pipeline is provided with a tower circulation pump (9) and a tower heat exchanger (10).

4. The sulfuric acid drying treatment system for methyl chloride gas according to claim 2, characterized in that: The secondary drying tower (3) is provided with a circulation pipeline utilizing sulfuric acid desiccant, and the circulation pipeline is provided with a second-tower heat exchanger (4) and a second-tower circulation pump (5).

5. The sulfuric acid drying treatment system for methyl chloride gas according to claim 2, characterized in that: The first-stage drying tower (11) is provided with a gas-connected pipe and a liquid-connected pipe, respectively, to communicate with the second-stage drying tower (3).

6. The sulfuric acid drying treatment system for methyl chloride gas according to claim 1, characterized in that: The monochloromethane outlet pipe is provided with a post-drying demister (7).

7. The sulfuric acid drying treatment system for methyl chloride gas according to claim 1, characterized in that: It also includes an APC control system that controls the flow ratio of methyl chloride and sulfuric acid.

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