Fuel Cell And Gas-Turbine Hybrid – A Better Way of Power Production

With every passing day, the amount of gases and by that the heat emitted by power generation stations to the environment is increasing. We all know that it is practically impossible to stop generating and hence the only way left out is improvisation. Using a fuel cell and gas-turbine hybrid is one of such ways.

A fuel cell basically produces electrical energy trough electrochemical reactions. However, it produces energy with much more efficiency than heat engines because it eliminates all moving parts thus reducing frictional losses. The average efficiency of a fuel cell ranges from 40 to 60%. After the production of electricity, the fuel cells give out hot exhaust gases. If these hot gases are let away as it is, much amount of precious energy is lost. But if a compressor is used to extract this waste of energy can be avoided. High Temperature Fuel Cells (HTFCs), such as Solid Oxide Fuel Cells (SOFC) and Molten Carbonate Fuel Cells (MCFC) are best options Hybrid operation. A typical fuel cell is shown in the following figure:



The fuel cell – gas turbine hybrid can be modeled in a variety of ways. For instance, for Solid Oxide Fuel Cells (SOFC) the air supplied should be first pressurized through the compressor of the turbine. The pressurized air along with the fuel (say natural gas) is then fed to the fuel cell. The pressurized air feed helps in improving the fuel cell efficiency and the energy density. The electrochemical reactions result in direct electricity production and the cell emits exhaust gases. The gas turbine then can be arranged to extract this thermal energy to drive compressors which provide compressed air to the fuel cell, thus completing a loop. The enthalpy, still remaining can be expanded through a number of turbine stages thus producing additional power with the help of shaft connected generators. This arrangement is as shown in this figure:



The salient advantages of use of such a hybrid system are many. To list a few, fuel to electrical energy conversion efficiencies approaching 80% can be achieved using this system. The wastage of energy in the form of hot gases can be very well utilized.  In addition to this, the fuel cells have an extremely low NO_x emission rate so the systems are environment friendly.