Abstract: An electrolyzer system comprises electrolyzer elements (101) each comprising an electrolyzer stack (104) constituted by electrolysis cells. Furthermore, each electrolyzer element comprises a water inlet (106), a hydrogen separator tank (107) having a hydrogen outlet (108), an oxygen separator tank (109) having an oxygen outlet (110), and a channel system (111) for conducting electrolyte from the hydrogen separator tank and from the oxygen separator tank to the electrolyzer stack. The electrolyzer stacks of the electrolyzer elements are electrically connected to each other so that direct voltage of the electrolyzer system is a sum of direct voltages of the electrolyzer stacks of two or more of the electrolyzer elements. The water inlets, the hydrogen outlets, and the oxygen outlets of different ones of the electrolyzer elements are galvanically separated from each other. This enables the direct voltage of the electrolyzer system to have a desired value with low stray electric currents.

Abstract: An apparatus for estimating electrical properties of an electrolyzer includes a data processing system for estimating electrical values, for example a membrane resistance, of the electrolyzer based on a difference voltage, a current, and an initial value and an attenuation time constant of a double-layer capacitance voltage of the electrolyzer during a shutdown of the electrolyzer. The difference voltage is a difference between a voltage of the electrolyzer and a total reversible voltage of the electrolyzer. The initial value and the attenuation time constant of the double-layer capacitance voltage are estimated based on values of the difference voltage when the current is zero and thus the difference voltage equals the double-layer capacitance voltage. The electrical values can be estimated even if a stepwise interruption of the current of the electrolyzer is not possible.

Abstract: A system for alkaline water electrolysis includes electrolysis cells, a hydrogen separator tank, a first piping from the electrolysis cells to the hydrogen separator tank, an oxygen separator tank, a second piping from the electrolysis cells to the oxygen separator tank, and a third piping for conducting liquid electrolyte from the hydrogen separator tank and from the oxygen separator tank back to the electrolysis cells. The system includes an ultrasound source for applying ultrasound on the liquid electrolyte contained by the first piping. The ultrasound enhances the separation of dissolved hydrogen gas from the liquid electrolyte contained by the first piping, and thus energy efficiency of the alkaline water electrolysis is improved. Furthermore, a safe control range of the alkaline water electrolysis is broadened because crossover of hydrogen gas to an oxygen side of the system is reduced.

Abstract: A system for an electrochemical process includes an electrochemical reactor, a converter bridge for supplying direct current to electrodes of the electrochemical reactor, and serial inductors connected to alternating voltage terminals of the converter bridge. The converter bridge includes bi-directional controllable switches between the alternating voltage terminals and direct voltage terminals of the converter bridge. Forced commutation of the bi-directional controllable switches enables reduction of current ripple in the direct current supplied to the electrochemical reactor. The forced commutation enables also to control a power factor of an alternating voltage supply of the system.

Abstract: the screw compressor with a variable rotational speed of the screw compressor, the rotational speed of the screw compressor having a speed profile in which the rotational speed is changed stepwise such that between stepwise changes the rotational speed of the screw compressor is kept substantially constant for a time period, repeating the speed profile until the pressure of the pressure vessel reaches a set pressure value, determining pressure of the pressure vessel, power consumption of the screw compressor drive and mass flow rate during the pressurising when the rotational speed of the screw compressor is kept substantially constant, calculating energy efficiency of the screw compressor drive as a function of pressure of the pressure vessel and rotational speed of the screw compressor on the on the basis of the determined pressure of the pressure vessel and power consumption of the screw compressor drive.