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The use of domestic high-ash coal reserves contributes to the security of energy supply, and therefore high-ash coal is expected to remain as a key energy source in several countries (e.g., India, Turkey) for at least the next 30-40 years. However, the use of high-ash coals for energy production (currently performed mainly via combustion processes) poses a number of technical and economic challenges, e.g., low efficiency and environmental issues. Gasification is an attractive option, since it allows a more efficient, more environmentally friendly conversion of the coal. In particular, integrated gasification combined cycle (IGCC) offers high efficiency, reduced emissions and potential for the implementation of CO 2 capture. With the aim of optimising the design and operation of high-ash coal fluidised-bed gasification processes, this paper studies the effect of temperature and partial pressure on the conversion and reactivity of coke from an Indian high-ash coal under CO 2 and steam gasification conditions using thermogravimetric analysis. Moreover, additional steam gasification tests have been carried out in order to determine the conversion rate under realistic fluidised-bed gasification conditions (e.g., coal ash as bed material, coal particle size, heating rate, bed hydrodynamics, gasification atmosphere), thus taking into account the effect of mass and heat transfer phenomena. Results of isothermal TGA tests have shown that coke reactivity increases at higher temperatures and/or partial pressures of gasifying agent. The experimental data have been fitted to two conversion models (shrinking core and volumetric). The determination of kinetic parameters (reaction order b, pre-exponential factor A and activation energy E a) has been carried out at three conversion levels: X = 0.2, X = 0.5, and X = 0.8. In the case of CO 2 gasification, the reaction order b ranges between 0.2 and 0.8, although at temperatures of 850-900°C, the reaction order has a value around 0.6. In the case of steam gasification, the reaction order ranges between 0 and 1.1, and increases with reaction temperature. Fluidised-bed steam gasification tests have shown that approximately 23-27% of the carbon contained in the coal (~40-45% of the overall coal, considering also hydrogen and oxygen released in the gas) is quickly converted during the devolatilisation stage. Between 12 and 22% of the carbon contained in the remaining coke is converted to gas within the first 25 min of steam gasification. Finally, 55-80% of the carbon in the coke remaining after steam gasification is converted during the first 25 min of oxidation with air. Conversion of the high-ash coal is favoured at higher steam partial pressures and/or higher gasification temperatures. The conversion rate under fluidisedbed conditions is significantly lower than that obtained in TGA tests at similar temperature and steam partial pressure values. Differences in coal particle size, heating rate during devolatilisation, inhibition issues, and other fluid-dynamic effects influence the re...

In recent years, Mid-Infrared spectroscopy has garnered lot of attention from researchers and industries due to the availability of industrial grade room temperature Intra-band and Quantum Cascade Lasers. These lasers are repeatable in their performance and along with Near-Infrared Lasers, it has opened the entire Infra-red spectral band for industrial applications. This enabled widespread applications of tunable laser absorption spectroscopy for real-time, in-situ and non-invasive gas sensing. Though several spectroscopy techniques are currently available, Mid-Infrared Absorption Spectroscopy offers us a unique advantage of measurement of trace gas concentrations of few gases which has very weak transitions in Near-Infrared region. The objectives of this chapter are to discuss about the spectroscopy technique commonly used for Mid-Infrared Lasers, a comparative study with other techniques, noise and some challenges remaining for industrial applications.

The development of a harsh environment ammonia slip sensor based on tunable diode laser absorption spectroscopy is presented. A hybrid optical sensor design, through combination of wavelength modulation spectroscopy (WMS) and alignment control, is proposed as an approach towards reliable in-situ measurements in misalignment prone harsh environments. 1531.59 nm, 1553.4 nm and 1555.56 nm are suggested as possible absorption lines for trace ammonia measurement (<1ppm at 10m path length at 500K) in gas turbine exhaust conditions. Design and performance of the alignment control system are presented in detail. Effect of misalignment related measurement degradation is investigated and significant improvement in measurement fidelity is demonstrated through the use of the hybrid optical sensor design.

Techniques using a tunable diode laser (TDL) and multiple broadband lasers have been developed and tested for measuring the steam quality or steam wetness fraction. The steam wetness fraction was estimated using a ratiometric technique combining measured absorbance of water and water vapor overtone transitions in the near infrared spectral band. Using these techniques we were able to measure a wide variation in steam quality ranging from saturated steam condition to 80% mass fraction of steam with less than 1% error. Our sensor can be tailor-made to suit cost, sensitivity, and operating conditions as per requirements, and could be used eventually for measuring the quality of steam in the low pressure stage of steam turbines.