The main objective of this investigation is to obtain experimental data for the sulfuric acid hydrolysis of cotton and mechanically pretreated cotton fibres. These data indicate that some glycosidic bonds of cellulose have very high accessibility to catalytic ions. It was also shown that milling increases the accessibility of some glycosidic bonds of cellulose and decreases the volume of the crystalline regions of cotton. From the glucose yield versus time data, it was found that the effect of milling on the rate of cellulose depolymerization depends on the reactivity and accessibility of the glycon rings of cellulose. It was also found that at 1OO°C, the rate of cellulose depolymerization was not affected by the extraction of cotton wax and this was related to a rolling up process of cotton wax caused by melting. The kinetic constants of glucose degradation and cellobiose hydrolysis have been determined for the stochastic simulation of cellulose depolymerization which is the subject of the second part of this work.

The main objective of this investigation is to obtain an optimum value for the flue gas recirculation ratio in a 620 MW-Natural Gas Combined Cycle (NGCC) power plant with a 100% excess air in order to have a composition of the exhaust gas suitable for an effective absorption by amine solutions. To reach this goal, the recirculated flue gas is added to the secondary air (dilution air) used for cooling the turbine. The originality of this work is that the optimum value of a Flue Gas Recirculation (FGR) ratio of 0.42 is obtained from the change of the slope related to the effects of flue gas recirculation ratio on the molar percentage of oxygen in the exhaust gas. Compared to the NGCC power plant without flue gas recirculation, the molar percentage of carbon dioxide in the flue gas increases from 5% to 9.2% and the molar percentage of oxygen decreases from 10.9% to 3.5%. Since energy efficiency is the key parameter of energy conversion systems, the impact of the flue gas recirculation on the different energy inputs and outputs and the overall efficiency of the power plant are also investigated. It is found the positive effects of the flue gas recirculation on the electricity produced by the steam turbine generator (STG) are more important than its cooling effects on the power output of the combustion turbine generator (CTG). The flue gas recirculation has no effects on the water pump of the steam cycle and the increase of energy consumed by the compressor of flue gas is compensated by the decrease of energy consumed by the compressor of fresh air. Based on the Low heating value (LHV) of the natural gas, the flue gas recirculation increases the overall efficiency of the power plant by 1.1% from 57.5% from to 58.2%.

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