How is the conversion rate of syngas in the methanol synthesis tower controlled?
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I have just started working in the coal chemical industry, and I would like to ask those with more experience: what conditions are controlled in the methanol synthesis tower of a methanol synthesis unit in order to regulate the conversion rate of syngas? Is the outlet temperature controlled by the steam drum nearby? Thank you
The conversion rate of syngas is influenced by many factors, such as temperature, pressure, gas composition, space velocity, and catalyst. In the early stage of catalyst activity, the temperature is appropriately reduced and the space velocity is increased to control the reaction, whereas the opposite is true in the later stage.
The syngas conversion rate, under certain temperatures and pressures as well as a specific catalyst activity, is related to the space velocity and the volume of gas fed into the reactor. Once the general air velocity and the amount of gas entering the tower are determined, the conversion rate is also relatively fixed; it cannot be adjusted manually. If artificial adjustment is necessary, the only options are to adjust the airspeed, as well as using methods such as increasing or decreasing the approach path, thereby adjusting the amount of reaction.
Yes, the exit temperature of the synthesis tower is regulated by the pressure in the steam drum. There are many factors that affect the conversion rate: temperature, pressure, space velocity, and catalyst performance. When the gas supply is limited, the space velocity is low, resulting in a high conversion rate; a higher temperature also leads to a higher conversion rate. A higher pressure facilitates the forward reaction in synthesis, thereby increasing the conversion rate as well
How can the drum pressure be controlled? Also, is it true that the higher the drum pressure, the lower the outlet temperature of the synthesis product?
During normal operation, the outlet temperature of the synthesis tower is primarily regulated by the pressure in the steam drum; it can also be adjusted by controlling the volume of syngas, as well as the main split ratio and space velocity. During normal production, the factor that affects the conversion rate is mainly the space velocity.
What does airspeed mean as well? I used to only know that separation towers have a concept of space velocity; these two concepts of space velocity are definitely different
Simply put, it is the volume of gas entering the tower divided by the amount of catalyst loaded, which is the space velocity. Generally, once the gas reaches the synthesis stage, its loading rate is fixed; the circulation path valves as well as the pressure in the gas tank usually do not change arbitrarily. So in our factory, the conversion rate is determined by adjusting the hydrogen-to-carbon ratio for purification. The volume capacity determines the quality of the gasification medium.
The control of the synthesis conversion rate, with the tower type and catalyst remaining constant, relies mainly on temperature, gas composition, and circulation volume for adjustment. In the initial stage, the catalyst is primarily controlled by the circulation rate and gas composition. Later on, the temperature needs to be adjusted based on the catalyst’s activity in order to maintain a good conversion rate.
The synthesis conversion rate also needs to take into full account comprehensive factors such as system pressure, yield, and energy consumption; it is not possible to focus solely on increasing the conversion rate.
Conversion rate merely reflects the level of catalyst activity under the same process conditions; there is no need to pay excessive attention to it. When the catalyst is active, the conversion rate is high, and vice versa. Therefore, as long as the temperature is kept within the optimal activity range of the catalyst and the pressure is increased as much as possible within the designed range, high yields can be achieved.
In practical operations, the control of synthetic conversion rate relies on temperature, as the tower type, synthesis pressure, gas composition, and production load (amount of fresh gas) remain essentially constant, with catalyst activity being primarily determined by temperature. In the initial stage, the catalyst is primarily controlled by the circulation rate and gas composition ； Later on, the temperature can be adjusted based on the catalyst’s activity to ensure a high conversion rate. In reproduction, the key is to control the temperature of the catalyst throughout its entire usage period, raising the temperature appropriately in order to maximize the contribution per ton of catalyst over its whole lifespan.
The drum pressure is primarily used to control the pressure inside the synthesis tower. The pressure within the synthesis tower, catalyst activity, space velocity, and the amount of inert gases in the process gas are all important indicators of the conversion rate in synthesis. Of course, pressure and temperature cannot be adjusted arbitrarily; when the catalyst has high activity, the pressure and temperature should remain relatively low. As the catalyst’s activity decreases, it is necessary to increase the pressure and temperature appropriately
The higher the drum pressure, the higher the outlet temperature. When raising the temperature, the pressure in the steam drum must be increased
The higher the pressure, the higher the steam temperature in the drum, the higher the bed temperature, and consequently the higher the outlet temperature as well.
In practical operations, the conversion rate seems to be less important; it is mainly the bed temperature, pressure, and hydrogen-to-carbon ratio that determine the production capacity. Furthermore, if there is too much carbon dioxide in the feed gas, the bed temperature will drop, resulting in a lower outlet temperature. Increasing the space velocity also lowers the bed temperature, but the conversion rate will certainly be low as well. The initial space velocity of the catalyst can be higher, while it should be reduced later on, allowing the feed gas to react on the catalyst for a longer period of time and thereby increasing the yield.