What is the effect of temperature after water cooling on synthesis?

The low cooling temperature and high methanol content in the circulating gas affect the synthesis conversion rate.

The gas exiting the tower after being cooled by the water cooler has most of its methanol and water condensed into liquids; this gas then enters a separator where crude methanol is separated out. The effective gas resulting from this process contains approximately 0.611% methanol vapor. If the temperature of the gas entering the separator increases, the concentration of methanol vapor rises, and this will affect the quality of the methanol produced when the gas is sent to the synthesis tower under pressure. The increase in by-products causes problems for distillation. At the same time, compressors are prone to causing liquid slugging. It’s unnecessary when the temperature is too low; it wastes a large amount of cooling water.

The temperature of the gas after cooling with synthetic water affects the condensation of methanol and water vapor in the gas. As the temperature of the gas after cooling rises, the amount of methanol that remains uncondensed in the syngas increases accordingly. This methanol not only raises the power consumption of the recycle compressor but also prevents the methanol synthesis reaction from proceeding toward the formation of products inside the synthesis tower. Conversely, as the temperature of the gas after cooling with synthetic water decreases, the condensation effect of methanol improves accordingly. However, when the gas temperature drops to 20 degrees, the improvement in methanol’s condensation effect is not significant. Therefore, an excessively low cooling temperature is uneconomical for production; generally, it is sufficient to maintain the temperature of the gas after cooling with synthetic water between 25 and 40 degrees during operation.

It affects the separation efficiency and the alcohol content in the recycled gas, thereby impacting the catalyst yield

If the temperature of the gas after cooling in the synthesis process is controlled too high, it will affect the condensation of methanol and water vapor in the gas. As the temperature of the gas after cooling increases, the amount of methanol that remains uncondensed in the syngas also increases. This methanol not only raises the power consumption of the circulation compressor but also hinders the reaction for methanol synthesis into products within the synthesis tower. However, it is not necessary to keep the temperature of the gas after cooling with synthetic water at too low a level. As the temperature of the gas after cooling with synthetic water decreases, the efficiency of methanol condensation increases accordingly; but when the gas temperature drops below 20 degrees Celsius, the increase in methanol condensation efficiency is not significant. Therefore, pursuing excessively low water cooling temperatures is not economical; it not only increases the requirements for water condenser equipment but also raises the consumption of cooling water.

The methanol synthesis reaction is a reversible exothermic reaction; a decrease in temperature facilitates the reaction to proceed in the direction of methanol formation, thereby increasing the conversion rate.

The separation efficiency is poor, which increases the methanol content in the recycled gas. This has two drawbacks: 1) It poses a risk to the compressor, as liquid can easily reach the blades and damage them; 2) It enters the synthesis tower, reducing the efficiency of methanol synthesis and suppressing its production, leading to a decrease in conversion rates!

An increase in alcohol content leads to the following adverse effects: (1) an increase in the equilibrium methanol level at the inlet of the synthesis tower, resulting in a decrease in the net synthesis yield. (2) Increased side reactions during synthesis reduce the quality of methanol; wax formation can cause blockages in the water cooling systems and separators, leading to a decrease in the efficiency of heat exchange equipment. (3) The system circulation rate increases, leading to a rise in pressure, which in turn increases the power consumption for compressing the raw material gas/syngas in the system. (4) The load on the alcohol washing tower increases, leading to greater losses of methanol in the vented gas and environmental pollution.

Excessively high temperature after water cooling: 1) An increase in the methanol content in the circulating air raises the power consumption of the compressor, and liquid slugging incidents may also occur. 2) A high methanol content in the circulating gas leads to an increase in side reactions during the reaction in the synthesis tower, which may cause wax formation in the water cooler and an increased load on the alcohol washing tower. Too low water cooling temperature: 1) The condensation effect is not significant below 20 degrees Celsius. The water consumption for circulation is high. It’s not economical. 2) When it is too low, it may also cause a decrease in the temperature of the gas entering the tower.

1. At high temperatures, the crude methanol circulating in the system cannot be completely condensed, which deteriorates the synthesis reaction and poses a risk of liquid slugging for the compressor. 2. At low temperatures, the effect is not very significant, and energy is wasted; therefore, the temperature is generally maintained around 36 degrees.