An accurate formulation of energy conservation to model pyrolysis of a biomass particle needs to account for variations in the heat of reaction with temperature, usually neglected in most past studies. It is shown that by including this effect in a pyrolysis model with three parallel reactions yielding char, gas and tar, a wide range of experimental data can be accurately predicted. In particular, through comprehensive comparisons of the simulation results with various measurements, a consistent and single value of 25 kJ/kg is obtained for enthalpy of pyrolysis, which represents a lumped heat of volatiles and char formation at a reference temperature. It is found that the kinetic parameters of Chan et al. [W.C. Chan, M. Kelbon, B.B. Krieger, Fuel 64 (1985) 1505–1513] and Thurner and Mann [F. Thurner, U. Mann, Ind. Eng. Chem. Process Des. Dev. 20 (1981) 482–488] provide reasonable agreement between the model predictions and experiments compared to other reported kinetic constants. These comparisons also indicate that inclusion of tar cracking reactions to yield additional light gases does not give a better prediction of the process parameters. The presented thermo-kinetic model is capable of successfully predicting various experimental observations such as the internal temperature peak reported in some past studies. It is shown that the sensible heat released due to the conversion of virgin biomass to the reaction products is responsible for this phenomenon. Simulation results reveal that a temperature peak at an internal location of the particle may occur when the corresponding local temperature reaches the particle surface temperature while the local biomass conversion is not finalized yet.
PYROLYSIS OF BIOMASS PARTICLE
COMBUSTION OF BIOMASS PARTICLE
A detailed one-dimensional model for combustion of a single biomass particle is developed. It accounts for particle heating up, pyrolysis, char gasification and oxidation and gas phase reactions within and in the vicinity of the particle. The biomass pyrolysis is assumed to take place through three competing reactions yielding char, light gas and tar. The model is validated using different sets of experiments reported in the literature. Special emphasis is placed on examination of the effects of pyrolysis kinetic constants and gas phase reactions on the combustion process which have not been thoroughly discussed in previous works. It is shown that depending on the process condition and reactor temperature, correct selection of the pyrolysis kinetic data is a necessary step for simulation of biomass particle conversion. The computer program developed for the purpose of this study enables one to get a deeper insight into the biomass particle combustion process. Typical numerical results related to the combustion of 1 mm wood particle in air are illustrated in these figures.
FLUIDIZED BED FOR H2 PRODUCTION
This study examined transport phenomena involving the reaction of cupric chloride (CuCl2) particles and superheated steam within a fluidized bed as part of a thermochemical hydrogen production plant. The study was carried out by performing hydrodynamics and mass transport analysis, which was necessary for analyzing the mass transport of the reaction in a fluidized bed. In the first part, the effects of superficial velocity, bed inventory, particle diameter and spherecity on bed height, average bubble diameter and bed voidage were investigated through a newly developed solution procedure. In the second step, the conversion of steam as a fluidizing gas and conversion of CuCl2 were numerically investigated using a new non-catalytic gas-solid reaction model, proposed in past literature but here updated for the purposes of the present study. The results were illustrated considering two cases of kinetics models for the consumption of particles: Volumetric Model (VM) and Shrinking Core Model (SCM). Consistent results in terms of the conversion of reactants versus superficial velocity, bed inventory and bed temperature were obtained by developing new solution algorithms based on each of the above kinetic models. The methodology presented in this study was useful in the next phases of the research when building an experimental apparatus and estimating the optimal values of reactor parameters.
COMPARATIVE ASSESSEMENT OF HYDROGEN PASSENGER TRAINS
This study examined a comparative assessment in terms of CO2 emissions from a hydrogen passenger train in Ontario, Canada, particularly comparing four specific propulsion technologies: (1) conventional diesel internal combustion engine (ICE), (2) electrified train, (3) hydrogen ICE, and (4) hydrogen PEM fuel cell (PEMFC) train. For the electrified train, greenhouse gases from electricity generation by natural gas and coal-burning power plants are taken into consideration. Several hydrogen production methods were also considered in this analysis, i.e., (1) steam methane reforming (SMR), (2) thermochemical copper-chlorine (Cu-Cl) cycle supplied partly by waste heat from a nuclear plant, (3) renewable energies (solar and wind power) and (4) a combined renewable energy and copper-chlorine cycle. The results show that a PEMFC power train fuelled by hydrogen produced from combined wind energy and a copper-chlorine plant is the most environmentally friendly method, with CO2 emissions of about 9% of a conventional diesel train or electrified train that uses a coal-burning power plant to generate electricity. Hydrogen produced with a thermochemical cycle is a promising alternative to further reduce the greenhouse gas emissions. By replacing a conventional diesel train with hydrogen ICE or PEMFC trains fuelled by Cu-Cl based-hydrogen, the annual CO2 emissions are reduced by 2,260 and 3318 tonnes, respectively. A comparison with different types of automobile commuting scenarios to carry an equivalent number of people as a train was also conducted. On an average basis, only an electric car using renewable energy-based electricity that carries more than three people may be competitive with hydrogen trains.
HYBRID GAS TURBINE POWER PLANT
In this project, the performance of a high-temperature solid oxide fuel cell combined with a conventional recuperative gas turbine (GT-SOFC) plant was examined. Individual thermodyanmic models were developed for each component. The overall system performance was then analyzed by employing the thermodyanmic model developed to evaluate the thermal efficiency of the plant. It was found that increasing the turbine inlet temperature results in decreasing the thermal efficiency of the cycle, whereas it improves the total specific power output. A comparison between the GT-SOFC plant and a traditional GT cycle, based on identical operating conditions, was also made. The superior performance of a GT-SOFC, in terms of thermal efficiency and environmental impact (lower CO2emissions), over a traditional GT cycle was evident. It has about 27.8% higher efficiency than a traditional GT plant. In this case, the thermal efficiency of the integrated cycle becomes as high as 60.55% at the optimum compression ratio.
OPTIMIZATION OF GT-SOFC POWER CYCLE
Optimum pressure ratios of a regenerative gas turbine power plant with a solid oxide fuel cell were investigated. The thermodynamic optimization of this system was numerically studied using models of RGT plant and solid oxide fuel cell. The component efficiencies and the total pressure drop within each configuration were taken into account. The hybrid system was studied for a turbine inlet temperature (TIT) of 1250 – 1450 K and 10–20% total pressure drop in the system. The maximum thermal efficiency was found to be at a pressure ratio of 3–4, which was consistent with other studies. A higher TIT leads to a higher optimum pressure ratio. No significant effect of pressure drop on the optimum pressure ratio was observed. The maximum work output of the hybrid system may take place at a pressure ratio at which the compressor outlet temperature is equal to the turbine downstream temperature. The work output increases with increasing the pressure ratio up to a point after which it starts to vary slightly. The pressure ratio at this point was suggested to be the optimal because the work output is very close to its maximum and the thermal efficiency is as high as a little less than 60%.
SHELL AND TUBE STEAM CONDENSER
Through development of the fundamental equations of Film Theory, condensation of steam in the presence of air in a TEMA ‘E’ type shell and one-path tube condenser was modeled. The interaction between heat and mass transfer and hydrodynamics in the shell-side was taken into consideration. A comparison of the predictions of the model with experimental data revealed excellent accuracy of the formulation. The consistency of the method was validated by generating the profiles of the temperature drop and pressure drop of the gas flowing through the baffles, at various air leakages. Additionally, the effects of air leakage and upstream cooling water temperature were investigated to observe how they influence the total condensation rate, shell-side gas temperature and pressure drops. The results show that the total condensation rate decreases 5% and 20.5% at an air leakage of 1% and 5%, respectively, compared to a case with pure vapor. Also, increasing the inlet cooling water temperature from 46.50C to 48.50C leads to 16.2% reduction in the total condensation rate, i.e., 8.1% per 10C. However, this ratio is higher at high temperatures. For example, as the cooling water temperature rises from 500C to 510C under identical process conditions, the total condensation rate decreases 11.7% (per 10C).
ENTROPY ANALYSIS OF HEAT ENGINES
The objective of this study was to find out whether there is any relationship between the entropy produced by a heat engine and its thermal efficiency or power output. Two classes of heat engines are considered. The first group consists of some simple and endo-reversible models of power plants including Curzon-Ahlborn engine, Novikov engine, and Carnot Vapor cycle. The second group includes irreversible Brayton, Otto and Diesel cycles. The operational regimes at maximum thermal efficiency, maximum power output and minimum entropy production are compared for each engine. The results show that thermal efficiency inversely correlates with entropy production in an endo-reversible engine; that is, an increase in thermal efficiency is equivalent to a decrease in entropy production. On the other hand, in irreversible engines, maximum power output, maximum thermal efficiency and minimum entropy production are found to be three different operational regimes. A reduction in the cycle entropy production is neither equivalent to an increase in its thermal efficiency; nor to an increase in its power. However, under the assumption of constant heat input, the above three optimization criteria lead to an identical operational condition.