Disclosed are a system and method for purifying hydrogen, and a system for producing hydrogen by water electrolysis. The system for purifying hydrogen includes three dryers, and the three dryers share one regeneration cycle module. This significantly reduces a quantity of regeneration cycle modules, and therefore, manufacturing cost of the system is relatively low. In addition, a first gas-gas heat exchanger (4) is arranged in a regeneration cycle system, so that heat exchange can be performed between low-temperature regeneration hydrogen before regeneration and high-temperature regeneration tail gas after regeneration. In this way, residual heat of the high-temperature regeneration tail gas can be fully utilized, and power consumption of a subsequent heater and regeneration cooler can be significantly reduced. Therefore, energy consumption of the system is relatively low.

Aspects of the present invention relate to a gas treatment apparatus (1) for treating a process gas. The gas treatment apparatus (1) includes a primary treatment unit (2) and a secondary treatment unit (3), the primary and secondary treatment units (2, 3) being configured to treat the process gas. The primary treatment unit (2) includes a primary process gas inlet (10) for receiving the process gas, a first and a second primary adsorber (12, 13) for treating the process gas, and at least one primary process gas outlet for discharging the treated process gas from the first and the second primary adsorbers (12, 13). The secondary treatment unit (3) includes a secondary process gas inlet (30) for receiving the process gas, at least one secondary adsorber (32, 33) for treating the process gas, and at least one secondary process gas outlet (31) for discharging the treated process gas from the at least one secondary adsorber (32, 33) to the primary treatment unit (2). The primary treatment unit (2) is selectively configurable in a first operating mode and a second operating mode. When operating in the first operating mode, the primary process gas inlet (10) is connected to the first primary adsorber (12) to supply the process gas to the first primary adsorber (12) for treatment; and the second primary adsorber (13) is connected to the at least one secondary process gas outlet (31) to receive treated process gas from the secondary treatment unit (3) for regenerating the second primary adsorber (13). When operating in the second operating mode, the primary process gas inlet (10) is connected to the second primary adsorber (13) to supply the process gas to the second primary adsorber (13) for treatment; and the first primary adsorber (12) is connected to the at least one secondary process gas outlet (31) to receive treated process gas from the secondary treatment unit (3) for regenerating the first primary adsorber (12). Aspects of the present invention also relate to a method of controlling a gas treatment apparatus (1) to treat a process gas; and a liquid air energy storage plant.

Disclosed herein is a system including at least two adsorbent bed containing vessels in adsorption mode, where one has a high pressure PI and one has a low pressure P3, and at least one adsorbent bed containing vessel in regeneration mode. The vessel that is in regeneration mode may have a pressure P2 that is intermediate to the pressures PI and P3 of each of the vessels that are in adsorption mode. The system may be configured to introduce a gas feed stream into the high pressure (P3) vessel to generate a first product stream, followed by passing a slip stream from the first product stream, to act as a regeneration gas, into the vessel that in regeneration mode, followed by passing the regeneration gas into the low pressure (P3) vessel, without passing through a compressor, to generate a second product stream.