Essential Valves in Methanol Production: A Comprehensive Guide

Introduction

Methanol is an important organic chemical raw material and high-quality fuel, widely used in fine chemicals, plastics, pharmaceuticals, fertilizers and other fields. Compared to ethanol, it is also an important organic solvent with superior solubility and is suitable for paint formulations. Methanol has the advantages of safety, low cost, complete combustion, high utilization efficiency, environmental protection, etc. It is a promising clean energy and a potential substitute for gasoline. In addition, methanol can be biofermented into methanol protein, which is rich in vitamins and proteins, and is a cost-effective and nutrient-rich feed additive. Therefore, methanol plays an important role in the national economy.

Overview of Valve Applications

In methanol production plants, the application of valves varies significantly based on the specific conditions of the medium in the pipelines. This overview will focus on the distinctive valves used in the methanol production process.

1. Gasification System

The gasification system's medium conditions are characterized by:

1. Solid Particles in Some Pipelines:
   • Examples: Coal slurry and black water pipelines.
   • Solid particles can cause wear on pipeline components. Thus, structural designs should minimize flow resistance, and sealing materials should be wear-resistant. Suitable valves include ball valves with special hard alloy coating on the sealing surfaces. Wafer check valves with the valve core in the middle of the flow path are not recommended.
2. High-Temperature, High-Pressure Oxygen Pipelines:
   • High-pressure oxygen is a strong oxidizer, requiring clean (degreased) valves and smooth transitional structures to reduce particle impact surfaces. Ball valves are recommended for shutoff, and wafer double plate check valves are not advised. Valve materials should meet requirements for unrestricted flow rates.
3. Pipelines with Carbon Monoxide and Hydrogen Sulfide:
   • Example: Raw synthesis gas pipelines.
   • These harmful media necessitate reliable sealing valves like gate valves or globe valves, with low emission measures considered.
4. Hydrogen-Containing Pipelines:
   • Valves should have reliable sealing, such as gate or globe valves, with low emission measures.
5. Pipelines with Carbon Dioxide:
   • Below dew point conditions, consider CO₂'s electrochemical corrosion on metal materials, influenced by medium flow rate and pattern. Valves with good flow characteristics are preferred.
6. High-Pressure Steam Pipelines:
   • Pressure-sealed bonnet and welded connection valves are recommended, with bypass considerations for large-diameter valves. For high-pressure steam erosion, Y-pattern globe valves are advisable.

2. Purification System

The purification system's medium conditions include:

1. Hydrogen, Carbon Monoxide, Carbon Dioxide, and Hydrogen Sulfide in the Conversion Section:
   • Operating at high temperatures, valve materials must resist hydrogen corrosion. The medium requires reliable sealing and low emission design.
2. High Concentrations of Hydrogen Sulfide and Carbon Dioxide:
   • Operating below dew point temperatures, consider wet hydrogen sulfide's impact on valve materials, including anti-sulfide stress cracking treatment. The presence of wet CO₂ necessitates valves with favorable flow characteristics.
3. Low-Temperature Medium Conditions:
   • Example: Pipelines with temperatures as low as -75°C.
   • Valve materials must account for low-temperature brittleness, and extended bonnet designs are recommended to avoid damage from freezing at the stem packing area.

3. Synthesis System

Based on the corrosion characteristics, the synthesis system is divided into:

1. Medium-Temperature Pipelines:
   • Example: Reactor inlet and outlet pipelines.
   • Conditions: Medium pressure (approximately 5.2 MPa) and medium temperature (approximately 250°C), with media including hydrogen, carbon monoxide, carbon dioxide, and methanol. Valves must resist hydrogen corrosion, suitable for handling hydrogen and carbon monoxide.
2. Low-Temperature Pipelines (Below Dew Point):
   • Example: Gas-liquid separation system pipelines.
   • Conditions include CO₂ corrosion and organic acids from methanol synthesis by-products. Valves should resist the combined effects of CO₂, hydrogen, and corrosive media.

4. Distillation System

The distillation system features relatively mild conditions with lower pressure and temperature. The main medium, methanol, does not significantly corrode metal materials. Despite the presence of CO₂ and organic acids at the distillation column top, their low concentrations do not necessitate special valve types or materials.

Conclusion

Valves in methanol production must be selected according to the specific medium conditions of each section of the device, considering factors such as wear resistance, seal reliability, corrosion resistance and structural design to minimize flow resistance and particle impact. The right valve selection ensures efficient and safe operation of methanol production.

FAQs

1. What are the main considerations when selecting valves for high-pressure oxygen pipelines?
   • Clean (degreased) valves, smooth transitional structures to reduce particle impact, and materials suitable for unrestricted flow rates.
2. Why are ball valves recommended for pipelines containing solid particles?
   • Ball valves minimize flow resistance and have wear-resistant sealing surfaces.
3. What are the challenges of using valves in hydrogen-containing pipelines?
   • Ensuring reliable sealing and low emission measures.
4. How does carbon dioxide affect valve selection in low-temperature conditions?
   • Electrochemical corrosion requires materials that resist such effects, and valves with good flow characteristics are preferred.
5. What special design considerations are needed for valves used in low-temperature environments?
   • Extended bonnet designs to prevent damage from freezing at the stem packing area.