Performance Assessment of a Hybrid Solid Oxide Fuel Cell-Gas Turbine Combined Heat and Power System

Abstract

In this chapter, a comprehensive thermodynamic modeling of a hybrid solid oxide fuel cell-gas turbine (SOFC-GT) is conducted. A heat recovery steam generator is used to produce saturated water for the heating purpose. This saturated hot water can be used in an absorption chiller system to meet the cooling load of the system. In order to model the hybrid system, chemical and electrochemical analyses of SOFCs and other components are carried out through energy and exergy analyses. The results of a hybrid system are compared to a gas turbine power generation system in order to investigate the effect of fuel cell on the system performance. Based on the model results, exergy efficiency of a hybrid SOFC-GT is higher than the one for conventional gas turbine and steam generator cycle. To enhance the understanding of the results in this study, a complete parametric study is performed and the results are presented. The results of this study, show that an increase in fuel cell stack temperature and compressor pressure ratio increases the efficiency; however an increase in fuel cell current density and gas turbine inlet temperature (GTIT) decreases the efficiency. In addition, an increase in HRSG steam pressure and a decrease in HRSG pinch point temperature results in an increase in system exergy efficiency.

Nomenclature

A B, C, D, E:

Constants in Eq. (20.6)

$\dot{E}$ :

Exergy rate (kW)

F:

Faraday constant (C/kmol)

h:

Enthalpy (kJ/kg)

I:

Current (A)

i:

Current density (A/cm²)

i_a,s :

Anode limiting current density (A/cm²)

i_o :

Exchange current density (A/cm²)

K:

Equilibrium constant

L:

Length (m)

LHV:

Lower heating value (kJ/kg)

m:

Mass flow rate (kg/s)

P:

Pressure (bar)

P_main :

Steam pressure (bar)

$\dot{Q}$ :

Heat rate (kJ)

R:

Universal gas constant (kJ/(kmol K))

r_c :

Compressor pressure ratio

T:

Temperature (K)

TIT:

Gas turbine inlet temperature (K)

T_o :

Ambient temperature (K)

T_sat :

Saturation temperature (K)

V:

Voltage (Volt)

V_o :

Standard voltage

$\dot{W}$ :

Power (kW)

x:

Concentration

γ:

Specific heat ratio

η:

Efficiency

ρ:

Ohmic resistance per length (Ω/m)

a:

Air anode

AC:

Air compressor

act:

Activation

AP:

Air preheater

c:

Cathode

ch:

Chemical

conc:

Concentration

D:

Destruction

e:

Electrolyte

FC:

Fuel cell

g:

Flue gas

GT:

Gas turbine

i:

Components index in mixture or interconnector

in:

Inlet

N:

Nernst

Ohm:

Ohmic

out:

Outlet