Plate fin heat exchanger for SOFC

Heat exchangers in Solid Oxide Fuel Cell (SOFC)

A typical Solid Oxide Fuel Cell (SOFC) power generation system consists of a fuel processing unit, a fuel cell power generation unit, and an energy recovery unit. Figure 1 illustrates an example of a power generation system operating at atmospheric pressure with natural gas as the fuel. The air is compressed by a compressor, overcoming system resistance, and enters the air heat exchanger for preheating before reaching the cathode of the fuel cell. Natural gas, compressed by a compressor to overcome system resistance, enters the mixer (reformer) and mixes with the superheated steam generated in the steam generator (heat exchanger). The resulting fuel gas enters the gas heat exchanger, raising its temperature before reaching the anode of the fuel cell. The gases at the anode and cathode undergo electrochemical reactions within the fuel cell, generating electrical energy while the heat produced from the electrochemical reactions heats the incompletely reacted anode and cathode gases. The partially reacted gases from the anode and the remaining oxidizer from the cathode enter the combustor for combustion. The high-temperature gases produced by combustion are utilized not only to preheat the fuel and air but also to provide the heat required for the steam generator. The combustion products after the steam generator still contain valuable thermal energy, which can be further utilized through a waste heat recovery unit to supply hot water or for heating purposes.

Figure 1: Power Generation System Operating at Atmospheric Pressure with Natural Gas as Fuel

As you can see, in the SOFC power generation system, the heat exchanger plays a significant role, with its efficiency, volume, and lifespan determining the size and longevity of the SOFC.

Technical Requirements for Heat Exchangers

The main technical challenges of heat exchangers in SOFC lie in the large temperature difference (up to 400°C or above). Additionally, the heat exchanger undergoes frequent cycling during startup. Therefore, the heat exchanger needs to exhibit excellent resistance to thermal shocks and maintain high-temperature resistance (above 850°C). Specific technical specifications are detailed in the table below.

Table 1: Conventional Technical Specifications of Heat Exchangers in SOFC

(Note: kPa A represents kilopascal absolute pressure)

The plate heat exchanger adopts a diffusion welding process. Let us see their features;

Diffusion-welded plate-fin heat exchanger features

1. The diffusion-welded plate-fin heat exchanger utilizes the vacuum diffusion welding process. This process requires no addition of any welding material, and the solid-state bonding between materials maintains the physical properties of the parent material. This effectively addresses issues related to high temperature, thermal shock, and overall lifespan.
2. The plate-fin structure adopted in the diffusion-welded plate-fin heat exchanger significantly enhances heat exchange efficiency, resolving challenges associated with the excessive size of the heat exchanger.
3. The diffusion-welded plate-fin heat exchanger can be designed as a multi-pass flow heat exchanger, integrating multiple heat exchangers in the SOFC power generation system into a single unit. This not only ensures the effective operation of the SOFC power generation system but also reduces the number of components.
4. The diffusion-welded plate-fin heat exchanger provides material options, including stainless steel series and high-temperature alloy series.