|Abstract or Summary
- This thesis presents thermodynamic evaluations of various biomass-fueled combined-cycle power plants using a computer model developed for simulating such plants. The combined-cycle systems Investigated are characterized by having a wood-fueled combustor, an indirect-fired gas turbine, and a steam cycle. This work was part of a larger biomass energy project at Oregon State University. The systems evaluated consisted of a "base case" design and five variations thereof. The base case itself includes a fuel preparation section with fuel drying, a combustor, an indirect-fired gas turbine system, a waste heat recovery boiler, and a Rankine cycle steam system. An Important facet of this design Is that hot combustion gases as well as the exhaust gases from the waste heat recovery boiler are used to dry the fuel. Variations of the base case that were investigated included (I) elimination of the use of hot combustion gases for drying, (II) steam Injection Into the gas turbine, (III) boosting the indirect-fired gas turbine inlet temperature with a trimburner, (iv) eliminating fuel drying, and (v) a combination of (III) and (iv). The simulation model developed consists of an main program and component models. The main program solves the simultaneous nonlinear algebraic equations that arise in modeling steady state thermal systems. The equations of the process in each component are evaluated In the respective component model. The unknown variables require initial guesses at the start of simulation and are solved by iteration using successive substitution until convergence is reached. The results of the simulations allowed the various systems to be compared with regard to efficiency, power output, total heat transfer area, and irreversibility. The various systems have similar net efficiencies, although those using a trimburner have a net efficiency about 2% higher than the others. In fact, the efficiency of the fossil fuel used in the trimburner is about 42%. The power output of the various systems, like the efficiency, is about the same except for those that utilize the trimburner. AlI of the systems without the trimburner have essentially the same overalI irreversibility. But some of the systems have very large mixing irreversibilities and others have greater irreversibilities in the heat exchanger. The occurance of the irreversibilities In the heat exchangers corresponds with smaller heat transfer areas. Total heat transfer area changed by as much as 6000 square feet (30%) from one system to another. These thermal analysis results show that detailed economic evaluations are necessary to fuIly determine the relative desirability of the systems.