Most fuel cell systems are operated with scroll compressors, side channel compressors or displacement compressors. Displacement compressors can be further divided into various subtypes (rotary vane, piston, diaphragm, and wobbling disc compressors, etc.). These compressors are already used in the automotive sector for air conditioners. Although the technology is widely available and already industrialized, it is limited in terms of miniaturisation and efficiency optimization. Displacement compressors are available for practically the entire range of pressure ratios and mass flows.
It is true that side channel compressors can be miniaturised by increasing their rotational speed; however, this principle decreases efficiency, which further decreases for greater pressure ratios. Side channel compressors can only be used at low pressure ratios, typically in the range of 1 to 1.3.
Scroll compressors also belong to the displacement compressor group; however, they are listed separately. Scroll compressors have medium to high efficiency, depending greatly on the manufacturing tolerances. Miniaturisation by increasing rotational speed is only possible to a limited extent, since the rotational speed will be limited by the design of the rotor.
Turbo compressors have the highest efficiency. They can also be miniaturized by increasing rotational speed. However, their operating range is limited since speed, mass flow and pressure ratio cannot be selected arbitrarily. Pressure ratios up to approx. 2.5 are possible for single-stage fuel cells with typical mass flows.
In terms of weight (and size), the oil-free turbo compressor from Celeroton performs better than well-established fuel cell compressors by a factor of 3 to 17. Side channel compressors perform second best with a factor of 3 and are therefore very often used in mobile fuel cell systems; however, they are suitable for fuel cell applications only to a limited degree, since they have about half the efficiency of turbo compressors. With constant tank filling and fuel cells, the power consumption of compressors equipped with Celeroton technology can be halved from approximately 20% of the output power of the fuel cell to about 10%, thus increasing the range of the vehicle by about 10%. As an example, the following table shows a 5 kW fuel cell and its operating point. For a given constant driving distance, a compressor with Celeroton technology consumes 1,260 kWh less energy than a side channel compressor with a running time of 3,000 hrs. If the hydrogen cycle is included from production (electrolysis, approx. 70% efficiency) via the conversion in the fuel cell (fuel cell, approx. 50% efficiency), the energy saving increases “from the socket” to about 3,600 kWh.
Despite the high rotational speeds of oil-free turbo compressors (CT-17-1000.GB) of Celeroton at a rated speed of 280,000 rpm), they do guarantee high dynamics.