Weekly Topic 4.26, Issue 24: Methanol-related control systems

The level interlock for the synthesis drum operates on a 2-out-of-2 shutdown principle. The gas-liquid separator for crude methanol in the synthesis section uses a 3-out-of-2 system for level control; due to the very large pressure difference across its level, there is a high risk of cross-pressure, which requires stringent instrument interlocks!

The typical interlocks in a methanol system include the drum liquid level, the temperature of the synthesis tower, and the liquid level of the high-pressure separator; what else are there? Instrument control relies most on redundancy

Various interlocks for compressors: oil pressure, shaft displacement and vibration, motor bearing temperature, interlocks for dry-seal systems, and so on

Due to the high content of catalyst particles in crude methanol and the large pressure difference before and after the valve, an angle valve is used as the level control valve in the crude methanol gas-liquid separator. I’m not sure what type of valves are used in other devices

Generally, there is a interlock between the synthesis drum liquid level and gas production, so it isn’t used very often

The compressor has issues such as vibration, displacement, and bearing temperature; the dry gas seal features an exhaust pressure interlock； Synthesis is mainly controlled by the drum liquid level, catalyst hotspot temperature, separator liquid level, etc ； Distillation mainly involves interlocks for the liquid levels in various towers and reflux tanks ； In the actual production process, things become much easier for everyone if the flow meters and control valves are in good working condition

The gate valves installed on site here have flow direction arrows marked on them. I’m not sure why; aren’t there requirements regarding the installation direction of gate valves? I don’t know why, but if anyone knows, please let me know

In the compression section, there are mainly interlocks such as hydraulic pressure and water pressure

I think it’s sufficient to provide interlocks for the drum and the separator; only a low liquid level interlock is needed, and there’s no need for a high-level interlock on the separator.

The compressor inlet separator and the inter-stage separator should be equipped with high liquid level interlocks, as well as interlocks for parameters such as the displacement, vibration, oil pressure, and vacuum level of the compressor and the receiver. The steam drum is equipped with high and low level interlocks, interlocks for the converted process gas, interlocks for the fuel gas, and a general interlock for the conversion process ； Interlocks such as high liquid level interlock for the synthetic methanol separator, high liquid level interlock for the flash tank, and overall synthesis interlock. Interlock for low pump flow, overall system shutdown interlock, etc. Interlocks should adopt a hierarchical system, with levels and types determined based on their importance. Operational permissions for interlocks at each level should be defined, and ensuring the safety and stability of both the system and personnel should be the primary principle in selecting interlocks. Initially, as many interlocks as possible should be installed; adjustments can then be made after the system starts operating, based on its actual conditions, with further interlocks being added gradually.