Pressure equalization for hydrogen production PSA units

Only after the forward flow is completed does the adsorption front reach the tower outlet. The number of voltage equalization cycles is low, and the qualified hydrogen has not been fully recovered.

Given the number of voltage equalization attempts, won’t the pressures be different after they finally achieve voltage equalization?

Equalization voltage refers to three instances of voltage rise and three instances of voltage drop. I don’t know about yours. The pressure between the last two towers in pressure equalization is equal, but each time of pressure equalization, it is not applied to one specific tower.

With fewer voltage equalization cycles, some hydrogen has to be released during the reverse discharge phase, resulting in a low yield. The number of voltage equalization cycles is high, which results in more hydrogen accumulating at the top during these cycles, and thus more hydrogen can be recovered and reused.

With fewer voltage equalization cycles, some hydrogen has to be released during the reverse discharge phase, resulting in a low yield. The more times voltage equalization is performed, the more hydrogen accumulates at the top during voltage reduction, and thus more of it can be recovered and reused.

A lower number of pressure equalization cycles results in a lower recovery rate – this concept is easy to understand. Those new to PSA might find it a bit difficult to grasp, but in fact, if we set aside complex concepts related to adsorption such as the adsorption front, a simple comparison will make it clear. There are now three empty tanks, A/B/C, all with the same volume – for example, 10 m3 each. Tank A is at a high pressure of 1.0 MPaG, tank B is at 0.5 MPaG, while tank C is at atmospheric pressure. All three tanks contain hydrogen. To improve the efficiency of hydrogen recovery, it can be understood as follows: try to transfer as much hydrogen as possible from tank A to tanks B and C; the lower the pressure in tank A, the better. Both A and B are pressurized at once, and the final pressure is (1+0.5)/2=0.75 MPaG. At this point, the pressure in tank A drops by only 0.25 MPa, meaning that only 25% of the hydrogen gas is recovered. What should be done? After one pressure equalization, Tank A (at 0.75 MPaG) is then pressure-equalized with Tank C once more; the final pressure becomes (0.75 + 0)/2 = 0.375 MPa. In this way, 62.5% of the hydrogen gas is recovered, resulting in a significantly higher yield. . . The poster can simply create a table to find out; the yield for secondary or tertiary pressure equalization can be calculated by oneself. Generally speaking, the number of pressure equalization cycles in PSA processes should not be too high, as too many such cycles will lead to an increase in the number of adsorption towers. Each additional pressure equalization cycle requires an extra tank as well as an additional set of programmable control valves, which in turn means more adsorbent is needed. This increases the cost of project construction. Moreover, more pressure equalization cycles result in energy waste. The number of pressure equalization cycles in PSA installations must be carefully considered; it rarely exceeds four times. Four cycles are usually used in larger installations where there are a large number of adsorption towers.

Yes, the more times pressure equalization is performed, the higher the yield of hydrogen; multiple pressure equalizations can effectively utilize the dead space in the bed~~

Of course, this is the manufacturer’s control procedure: the appropriate pressure is applied to equalize the pressure in each tower~~

I understand what you mean. My idea is that, for a tower, after it has been equalized three times and four times. Are the pressures of the two equal? In other words, the voltage drop for each of the three equalization steps is larger, while the voltage drop for the four steps is smaller. Does that mean we just have to wait in the end?

No matter how many times equalization is performed, as long as the final pressure remains the same, theoretically the amount of hydrogen recovered from the dead space is the same, and the yield is likewise identical. . Of course, the fewer voltage equalization cycles there are, the greater the voltage drop per cycle will be. The voltage drop during equalization should not be too large either, and the equalization time needs to be controlled properly – it cannot be too fast, as this is detrimental to the adsorbent.