|Abstract or Summary
- This report presents the analysis of ceramic heat
exchangers for use in a combined-cycle, wood-fired power
plant. The combined-cycle system investigated is
characterized by having a wood-fueled combustor, an
indirect-fired gas turbine, and a Rankine steam cycle.
The direct use of low-grade fuels, such as wood, in
present gas turbines will present difficulties due to
corrosion and erosion of the turbine components from the
particulate matter in the exhaust gases. This difficulty
can be overcome by indirectly firing the gas turbine with
the transfer of energy from the combustion gases to the
compressor air by means of a heat exchanger. Gas turbines
suitable for this type of power plant operate at their
maximum efficiency at the rated turbine inlet temperature,
typically in the range of 1750 F. Modern ceramics exhibit
excellent high temperature strength, and hence a ceramic
heat exchanger is considered a very suitable candidate for such applications.
In the power plant considered, air enters the heat
exchanger at 540 F where it is heated to the turbine inlet
temperature. Since a compact unit with low leakage was
desired, a multiple gas-side pass, cross-flow heat
exchanger was selected for the present application.
A model was developed to simulate the ceramic heat
exchanger. This model was used to size a heat exchanger
for the power plant.
The influence of the ceramic heat exchanger on the
overall power plant performance were analyzed. The other
plant components were simulated by using a computer code
developed during previous studies of this power plant.
The ceramic heat exchanger system was compared with a
metallic heat exchanger system. Since leakage was
recognized as a major difficulty in ceramic heat
exchangers, the effects of leakage on the overall plant
performance was analyzed. Finally, the ceramic heat
exchanger system was compared to other possible methods of
obtaining a high turbine inlet temperature.
The results of the study indicate that the use of a
ceramic heat exchanger has good potential for this type of
power plant. It was also observed that losses due to heat
exchanger leakage justify further research towards the
development of better sealing arrangements, for high
temperature and high pressure applications.