The fan-turbine unit (FTU)

The anode off-gas recirculator, the so-called fan-turbine unit (FTU), is designed and optimized to increase the efficiency and lifetime of Solid Oxide Fuel Cell (SFOC) systems.

The fan-turbine unit (FTU): the fan is on the left side, the turbine on the right side, and the stainless steel shaft is coated with diamond-like carbon (DLC), featuring two herringbone-grooved journal bearings. The Swiss five centime diameter is 17 mm.

This FTU consists of a small-scale AOR fan, a steam turbine, and a shaft with gas film bearings. The entire unit is manufactured by milling, turning, and surface finishing operations (i.e., grinding and honing) exclusively. The unit design is focused on low manufacturing cost, high lifetime, as well as oil-free and explosion-proof operation.

Top view of the radial anode off-gas recirculation fan without mounted spinner featuring holes for balancing (left) and the logarithmic fan volute (right).

Fan: The radial inducer-less fan with a tip diameter of 19.2 mm features backward-curved prismatic blades (four main blades and four splitter blades). It is designed for SOFCs with up to 10 kW of electrical power. The design point is as follows:

  • Pressure rise: 70 mbar
  • Mass flow rate: 4.8 kg/h (anode off-gas mixture at 200 °C and 1.05 bar)
  • Rotational speed: 175 krpm

Optical microscopy (left) of the turbine stator and rotor (digitally mirrored) and overview of turbine stator and rotor (upside-down) with turbine inducer (right).

Turbine: The radial-inflow, partial-admission (21 %), and low-reaction (15 %) steam turbine has a diameter of 15 mm. It consists of 59 prismatic rotor blades with a radial chord of 1 mm and a blade height of 0.6 mm. The design point is as follows:

  • Expansion ratio: 1.9
  • Mass flow rate: 2.1 kg/h of water vapor (at 220 °C and 2.2 bar)
  • Rotational speed: 175 krpm
  • Power: 36 Watt
Side view of the radial anode off-gas recirculation fan with mounted spinner, the diamond-like carbon (DLC) coated shaft with an 8mm diameter featuring two herringbone-grooved journal bearings.

Shaft: The shaft features one single-sided spiral-grooved thrust and two herringbone-grooved journal gas film bearings. Nominally, these bearings operate with water vapor at temperatures of up to 240 °C and a rotational speed of up to 250 krpm.