Study of Fuel cell- Turboexpander Hybrid System for Gass Pressure Reducing Stations

In this research, it is tried to study fuel cell turbo-expander hybrid system for gas pressure reduction stations. This research is based on thermodynamic equations for the behavior of hybrid systems in various conditions. Gas pressure reducing stations reduce gas pressure from 5000 kPa to around 1000 kPa. This pressure reduction is performed by expansion a valve that does not produce any energy. Electricity can be produced and injected to the grid by adding a turbo-expander and fuel cell in a gas reducing station. In winter, due to low temperature and high pressure of inlet gas, gas freezing can causes damage in turbo-expander and expansion valve, for this reason a boiler is used in cold months to produce heat for increasing the inlet gas temperature. Since fuel cell can generate considerable heat during its operation, it can be used for preheating the inlet gas and lower the fuel consumption. The results show that pressure reduction station which consisted of a fuel cell and a turbine has 5 to 10% more efficiency than a pressure reducing station which consisted of a fuel cell and expansion valves; however the amount of fuel consumption is equal for both systems. For pressure reduction station with fuel cell, the fuel consumption is very higher than the pressure reduction station without fuel cell; because more fuel will be consumed for electricity. The results show that more efficiency can be obtained by using the fuel cell in pressure reducing station and thus fuel consumption will be more reduced compared with a combined cycle power plant