Philippe Mathieu

Performance Analysis of a Biomass Gasifier

Abstract This paper presents an original modelling of the biomass gasification process and more particularly the wood gasification. Gasification is one of the more efficient ways to convert the energy embedded in the biomass. In the long term, the use of this rather new technology will reduce the too high pressure on the natural resources and that especially in the developing countries. The model based on the minimisation of the Gibbs free energy is performed in the ASPEN PLUS process simulator. The processes occurring in the gasification are here uncoupled in pyrolysis, combustion, Boudouard reaction, and gasification. In the first part of the paper the model is described and the physical meaning of the relevant parameters are given. In the second part, the results of a sensitivity analysis with respect to the oxygen factor, the air temperature, the oxygen content in air, the operating pressure and the injection of steam are presented. From this study, the following conclusions are derived: there exists a critical air temperature above which the preheating is no longer efficient, there is an optimum oxygen factor, the oxygen enrichment of air plays an efficient role under a certain value and the operating pressure has only a slight positive effect on the process efficiency.

Comparison of two CO2 removal options in combined cycle power plants

In this paper, two concepts of CO2 removal in CC are compared from the performance point of view. The first concept has been proposed in the framework of the European Joule II pro- gramme and is based on a semi-closed gas turbine cycle using CO2 as the working fluid and a combus- tion with pure oxygen generated in an air separation unit. This is a zero emission system as the excess CO2 produced in the combustion process is totally captured without the need of costly and energy con- suming devices. The second concept calls for a partial recirculation of the flue gas at the exit of the heat recovery boiler of a CC. The remaining flow is sent to a CO2 scrubber. Ninety percent of the CO2 is removed in an absorber/stripper device. The two systems are compared to a state-of-the-art CC when the most advanced technology is used, namely a 9FA type gas turbine and a three pressure level and heat recovery boiler. Our results show also that the CO2 semi-closed CC cycle performances are not very dependent on the configuration of the heat recovery boiler and that the recirculated gas CC per- formances are only slightly sensitive to the recirculation ratio. A high value of this latter mainly gives a significant reduction of the size and hence of the cost of the CO2 scrubber. From the performance point of view, the results show that the system eAciency with partial recirculation and a CO2 scrubber is always higher by 2-3% points than the CO2-based CC eAciency in comparable conditions. # 1998 Published by Elsevier Science Ltd. All rights reserved CO2 removal CO2/O2 combustion CO2 semi-closed cycle Flue gas recirculation The objective of this study is to assess the impact of CO2 removal and transportation on de- sign and performance of a natural gas-fired gas turbine plant. Two diAerent concepts were ana- lysed; one including downstream removal of CO2 from combined cycle power plant flue gas and one with air separation prior to a CO2-based power cycle with near stoichiometric oxygen com- bustion. These alternatives are compared to a standard natural gas fired combined cycle where no measures are taken in order to reduce the CO2 emissions. The two mentioned options are considered here for a comparison because the Norwegian and Belgian research teams under the leaderships of O. Bollard and Ph. Mathieu, developed respect- ively a modelling of the CC with flue gas partial recirculation and of the semi-closed CO2-based power cycle. In the semi-closed cycle option, the big advantage is the 100% extraction of the excess CO2 produced in the combustion process from the CO2 working fluid with a simple valve, hence without an energy consuming and costly device like the MEA scrubber but on the other hand it requires an ASU. This is a zero CO2 emission concept.

Condensation of ammonia by homogeneous nucleation in supersonic nozzles

Abstract The problem of the condensation of ammonia, mixed with an inert gas (air or helium), during a supersonic expansion in a nozzle is studied theoretically. In the absence of particle coalescence phenomena, the condensation zone in a slowly divergent straight nozzle may be divided into a nucleation zone and growth zone. A new formulation of the system of the differential equations which replaces the equation governing the condensate mass fraction is proposed. This formulation involves the calculation of quantities related to the description of the particle size distribution: the mean size, the number of particles per unit time, the second and third centered relative moments. The three latter quantities are conserved in the growth zone, leading to some substantial numerical advantages. Profiles of the flow quantities, such as the condensate mass fraction and the particle-size distributions, are obtained in the case of a stationary one-dimensional flow. The influences of the value of the inert gas mass fraction in the nozzle reservoir, of the nature of the inert gas and of the form of the expression of the nucleation rate are examined. Theoretical results are compared with experimental data and a good agreement is observed.

Zero Emission Technologies: An Option for Climate Change Mitigation

The present paper briefly explores the scientific, technical and economical characteristics of Zero Emission Technologies, with a particular emphasis on the E-MATIANT cycle. It is shown that this latter provides a cost-effective option to mitigate CO2 emissions, with a cost of electricity generation comparable to the one of advanced coal/gas fired power plants with CO2 capture and competitive with renewable wind energy. The important energy policy question of whether it is more cost-effective to upgrade an existing plant with a capture unit or to build a ZET is also addressed by introducing the concept of Mitigation Cost.

The Use of Gaseous Fuels on Aero-Derivative Gas Turbine Engines

In this paper, the use of various gaseous fuels in aero-derivative gas turbine engines is analysed. The gases investigated are natural gas and three coal synthetic gases of calorific values which are significantly lower than that of natural gas.The analysis is carried out employing natural gas fuel as a yardstick for comparison. Due to the lower calorific values of synthetic gases, the mass flow balance between compressors and turbines is altered. This in turn affects the matching of the components and the overall performance of a gas turbine engine. The engines examined are a single spool gas generator with a free power turbine and the double engine described in a previous paper.The main conclusion drawn from this analysis is that, for a given power output, the use of synthetic gases will result in an erosion of surge margins and in a reduction of the overall efficiency of the power plant.Copyright

Use of Artificial Neural Networks for the Simulation of Combined Cycle Transients

Due to techno-economic assets, the demand of combined cycles (CC) is currently growing. Nowadays, in a diversified electricity mix, these plants are often used on a load cycling duty or in the intermediate load range. The ability to start quickly and reliably may be a decisional criterion for the selection of the plant, in addition to the design performance, the cost and the pollutant emissions. Therefore, together with the simulation of CC transients, a proper monitoring system aimed at keeping high plant performance during the transients is required.With the help of advanced measurement and monitoring devices, artificial intelligence (AI) techniques as expert systems (ES) and neural networks (NN) can fulfill this duty.The goal of this paper is to show that a NN technique can be used reliably to obtain the response of a complex energetic system, such as CCs, during a slow transient and consequently as part of an on-line monitoring system.In this work, a CC power plant is simulated by dividing it into three blocks, which are representative of the three main elements of the CC: namely the gas turbine (GT), the heat recovery steam generator (HRSG) and the steam turbine (ST). To each of them a NN is associated. Once the training and testing of the NNs is carried out, the blocks are then arranged in a series cascade, the output of a block being the input of the subsequent one. With this solution, the NN-based system is able to produce the transient response of a CC plant when the input information are the GT inlet parameters.The transient data, not easy to obtain from measurements on existing plants, are provided by the CCDYN simulator (Dechamps, 1995). The performance obtained by the NN based system are observed to be in good agreement with those given by CCDYN, the latter being validated on the basis of measurements in an existing plant. The NN code, providing the departures of the measured data from the predicted ones, can be considered as a proper system for on-line monitoring and diagnosis.Copyright

CO2 Emissions Mitigation from Power Generation Using Capture Technologies

Technologies for capturing CO2 from power generation, that is separating CO2 from other components in a gaseous or liquid mixture, are examined from a triple point of view: of impacts of capture on performance, of costs and of pollutant emission. It is shown that there is currently no winner among the main three capture options, namely post-combustion removal of CO2 from flue gas, pre-combustion carbon removal from fuel and from oxy-combustion power systems. Although postand pre-combustion capture is an available technology in industrial applications, it must still be scaled up to the size of large power plants and from that point of view the three options are not at the same stage of development. Pilot plants are expected to be in operation in the period 2010–2015, especially in European funded projects, Europe being in the forefront of reducing strongly CO2 emissions from power plants.

Future of Combined-Cycle Plants in Belgium

In this paper we investigate the possible penetration of combined-cycle plants in the Belgian electricity generation system after the Belgian Government has not considered as appropriate the construction of a next nuclear plant at the present time. First the characteristic features of the Belgian production capabilities are given. The share of gas turbines, turbojets and already existing combined-cycle plants and their operation modes are emphasized. Then, alternative options to nuclear energy are presented, i.e. repowering of existing plants and construction of new combined-cycle plants. The potentialities of gas turbines and CC plants as well as their future in Belgium are investigated.Finally we discuss the equipment plan for the Belgian generation system proposed by the management committee of the electrical plant operators.From the results of our research about repowering, gas turbines and new CC plants, we derive recommendations for the future production means in Belgium.Copyright