What are the conditions for transforming the gas to be fed into the low-temperature methanol wash?
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Some say that after the sulfidation process in the shift converter is completed and loading begins on the converter, gas can be directed to the low-temperature methanol wash unit. I believe that doing this would cause significant fluctuations in the performance of the low-temperature methanol wash unit, after all, the converter itself isn’t yet stable! Others suggest waiting until the production process becomes stable before sending gas to the low-temperature methanol wash; this way, the impact on subsequent processes is reduced, but the venting time increases, leading to higher energy consumption! But I still think the latter is better! Dear sea friends, please share your opinions!
I personally think the latter is better, right? ~! Firstly, the pressure during driving isn’t high enough to allow for low-pressure air supply; moreover, the load keeps increasing after vulcanization is complete~! Unless you want people with low thyroid levels to be extremely busy~! Conditions for switching to low-temperature methanol washing gas flow: After the conversion process reaches stability, 1. Confirm that the conditions for introducing gas into the low-temperature section are met; 2. Increase the system pressure by 0.1 MPa above that of the low-temperature section using the conversion pressure control valve; 3. Verify that the system is in proper working condition; 4. Use the bypass valve to equalize the pressures across all valves involved in gas delivery. The following are the steps for starting up the conversion process, written arbitrarily for reference only. For switching to low-temperature methanol washing gas flow: 1. Slowly increase the pressure in the conversion section from 3.0 mPa to 6.1 mPa, or slightly above the pressure indicated by PI060, using the PV108 pressure control valve; 2. Confirm that section 146 of the low-temperature methanol washing unit is ready to operate under the required conditions; 3. Ensure that AV104 shows CO levels of at least 20.46%, H2 levels of at least 46.75%, and a temperature of 30–40°C in TI115; 4. Open the EV106 bypass valve. Once the pressures in both sections are equal, fully open the EV106 valve and close its bypass valve. Meanwhile, gradually close the PV108 valve and set it to maintain a pressure 0.1 mPa higher than the system pressure, then put it in automatic mode.
From the perspective of reducing startup time, it is possible to direct the gas flow to the methanol scrubber during the process of changing the gas flow direction; this will shorten the time required for gas diversion as well as the time needed to reach a low temperature. Firstly, the pressure of the nitrogen used for flushing in our plant’s methanol washing unit is 3.2 Mpa. As lw37062370 mentioned above, gas can be fed into the methanol washing unit when the pressure exceeds 3.3 Mpa. After the gas is introduced following the completion of the shift sulfidation process, the greatest risk associated with feeding gas to the methanol wash unit is overheating of the shift reactor. If the shift reactor overheats, the process gas entering it is shut off, which in turn cuts off the gas supply to the methanol wash unit; as a result, the operating conditions that have just been adjusted in the methanol wash unit must be abandoned. As long as the transformation control is properly managed to prevent overheating, methanol washing for gas purification can be carried out. Let’s think in reverse: what harm can it cause to the methanol washing process if the transformation does not properly adjust the pressure and the air-fuel ratio? The gas guiding pressure for methanol washing also increases gradually. Therefore, the pressure increase does not pose any harm to the methanol washing process, allowing it to adjust the liquid level of T1 and the methanol circulation rate more easily. The proportion of the modified gas is not appropriate. When we adjust the operating conditions of the transformation process, the process gas is vented, and the same occurs during methanol washing; therefore, there is no talk of waste. Less CO2 enters the methanol scrubber, less CO2 is absorbed by methanol, and thus the amount of CO2 released is low. There is no harm in this either; it will not cause fluctuations in the CO2 product tower, nor will it affect the hydrogen sulfide concentration tower. Early gas introduction can also provide cooling capacity for the methanol wash earlier. I can’t think of any harm that could be caused to the methanol wash!
I tend to agree with the conclusion above. Our system pressure is 3.2 MPa, and when the methanol washing cycle is used for cooling, the pressure in tower C1 is increased only to 2.0 MPa – as long as the circulation can be maintained, that’s sufficient. Therefore, when the pressure in the shift reactor is slightly higher than that in the methanol washing unit, regardless of whether the composition of the shift gas is within normal ranges or not, we carry out pressure equalization by directing gas through the methanol washing unit; this helps save some time. However, when the amount of carbon dioxide in the shift gas is low, it doesn’t provide much assistance in cooling the methanol washing unit
The latter is better; although it consumes a lot of energy, such energy consumption is necessary for the safety of the subsequent systems. After all, safety should come first in chemical operations! ! Conditions for venting gas in low-temperature methanol washing: 1. The minimum circulation rate of methanol in the system must be maintained for stable operation. 2. The temperature of methanol entering the washing tower is around -20°C. 3. The regeneration system is now functioning properly. 4. The methanol/water separation system is operating normally. 5. Methanol spraying and nitrogen stripping have been in operation for over half an hour. 6. The ammonia scrubber has been put into operation and is working properly.
I have a question: if the transformation is unstable and gas is allowed to pass through, could that introduce ammonia into the methanol washing process? It is still possible for the operating conditions to be unstable
Replying to the person above: The ammonia scrubber has been put into use during gas introduction! Additionally, the rapid sequential transfer of gas between the reformer and the methanol wash unit does not mean that gas from the reformer is sent to the methanol wash unit as soon as it is produced; rather, this process starts only after the reformer has reached a stable state. It’s just that the gas has not yet been fully adjusted to meet the required standards – this is based on empirical values. After all, under such an economic situation, it’s necessary to find a balance between savings and speed and safety!
The CO content in your modified gas composition is so high, at 20%, and I wonder what products you are producing.
If your system operates at such low pressures for an extended period of time, it will cause significant damage to the low-temperature methanol wash tower. This is because the pressure at the outlet of the methanol-poor pump is very high; under normal operating conditions, the pressure in the wash tower should be as high as 5.0 MPa. By operating at such a low pressure of 2.0 MPa, the backpressure is too low. It is recommended that you not keep the pressure too low when the temperature drops. When nitrogen is available. At present, some manufacturers do not have their own medium-pressure nitrogen compressors; instead, they rely on nitrogen vaporization compressors, which cannot ensure a consistent flow rate. As a result, the pressure in the scrubber tower becomes too low during cooling.
Since there is no high-pressure nitrogen, only the 3.2 bar of nitrogen provided by the recycle gas compressor is available, and even with pressurization it may not be possible to maintain that pressure; therefore I estimate that we generally won’t be able to keep it at 3.2 bar either. So the methanol cycle can only be operated at low pressure.
The normal operating pressure for our methanol washing process is 3.2 MPa. In addition, the methanol-poor pump that delivers fluid to the washing tower passes through a flow control valve as well; therefore, I think the impact of pressure differences on the washing tower is limited!
I believe it is safer and more reliable to wait until the shift conversion operation is running normally before introducing gas into the low-temperature methanol wash. Additionally, during low-temperature conversion sulfidation, hydrogen sulfide levels are high, which can contaminate the decarboxylation solvent, resulting in losses that outweigh any benefits.
What the original poster mentioned about a 20% change in the carbon monoxide content at the outlet refers to the production of methanol! For typical coal-to-methanol production plants, the required concentration of carbon monoxide at the shift outlet is around 19.5%!