For synthetic catalyst reduction, is it necessary to vent the gas from the outlet of the synthesis tower or the recycle gas?
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Ammonia is injected in the initial stage to prevent freezing, and the syngas is vented at the inlet of the circulation section; in other words, the gas exiting the synthesis tower does not enter the syngas compressor and thus does not participate in the circulation. The advantage is: 100% of the water evaporated from the coal is retained, and the rest is released. No moisture will enter the synthesis tower anymore. May I ask: We already have liquid ammonia injected, an ammonia cooler is in place, and the water has been almost completely separated – is it still necessary to add more? Allow the gas exiting the synthesis tower to return directly to the compressor to participate in the cycle, before entering the synthesis tower again; this increases the volume of gas and leads to more complete reduction.
The gas exiting the synthesis tower must be returned to the circulation machine; otherwise, how can the circulation machine be connected, and where would the circulation volume come from? Without this circulation volume, it’s not possible to ensure an adequate supply of gas for the electric furnace’s safe operation. During reduction, we generally use a punching valve to supply fresh gas, which is then discharged at the vent behind the tower to maintain system pressure balance. During reduction, it is necessary to maintain stable pressure and temperature; excessive fluctuations can easily cause the catalyst to break down, reducing its service life. Try to reduce the ammonia cooling temperature so that the water generated during reduction can be cooled and separated, thereby keeping the water vapor entering the tower as low as possible.
The method of venting behind the tower is generally not used to reduce the water vapor concentration in the gas entering the tower. The main purpose of venting is to maintain the H2 content in the recycle gas; throughout the reduction process, it is essential that the H2 level in the recycle gas remains above 75%. As the reduction reaction proceeds, H2 is continuously consumed, so it is necessary to replenish gas to keep the H2 level in the system at the desired level.
I’ve heard of this thing LZ mentioned for the first time; it’s possible that the gas entering the synthesis tower contains trace amounts of water. But it’s not possible to release all of the gas. If the system pressure rises or the hydrogen content changes significantly, some of the gas can be released to adjust things. Using this thing to adjust the humidity level must be extremely costly! If that’s the case, the synthesis system won’t need to be filled with ammonia. But how is this amount of water measured? Isn’t measurement necessary?
There should be no need for that; LZ wants to control the hydrogen content, water vapor, and circulation rate. All of you have replied in great detail. Otherwise, how can the temperature be maintained, and the heating and water discharge rates controlled? Moreover, the entire process takes over a hundred hours – what a waste.
At the initial stage of catalyst reduction, using a one-time gas flow has several advantages: 1) it helps to effectively reduce the water vapor concentration at the inlet of the synthesis tower; 2) it prevents impurities such as catalyst ash from entering the compressor and causing damage to it; 3) by allowing only fresh gas to flow in, the concentration of inert gases, water vapor, and ammonia at the inlet of the synthesis tower remains low, which is conducive to the progress of the reduction reaction. As the reduction process progresses, the pressure and the amount of gas flowing through need to be increased gradually. Raising the compressor speed alone is no longer sufficient at this point, so it is necessary to gradually close the vent valve in order to increase the amount of gas circulating
During the heating and reduction process, the gas needs to be circulated; the purpose of venting is merely to reduce the amount of inert gases in the circulating gas, thereby ensuring efficient hydrogen reduction. Generally, this is achieved by using a make-up gas valve in conjunction with venting – gas is added while venting occurs – to maintain stable synthesis pressure and thus stabilize the temperature of the catalyst layer.
The purpose of venting is to maintain an H2 content of over 75%. The water vapor concentration is controlled by adjusting the temperature during the reduction process; if the water vapor concentration is high, the temperature must be kept constant for several hours. Once the concentration stabilizes and decreases, the temperature can be increased gradually. Additionally, ammonia cooling is used to separate the moisture that enters the tower. The water vapor concentration should be kept at 2 g/Nm3
The purpose of heating and reducing the synthetic catalyst is to remove oxygen as water, but in order to prevent water from being reintroduced into the synthesis tower and causing repeated oxidation-reduction reactions, it is also necessary to maintain a low concentration of water vapor entering the tower. Therefore, high water output and low vapor concentration in the feed water to the tower are the key factors for raising the catalyst temperature. In the early stage of reduction, heating is achieved through the heat generated by the electric furnace; the smaller the gas flow rate, the higher the temperature. To ensure the safety of the electric furnace, it is necessary to control the system pressure properly. In this sense, it is acceptable to vent either at the inlet of the circulation pump or at the outlet of the synthesis tower.