Turning NGCC Into IGCC: Cycle Retrofitting Issues
The increase in price of natural gas and the need for a cleaner technology to generate electricity has motivated the power industry to move towards Integrated Gasification Combined Cycle (IGCC) plants. The system uses a low heating value fuel such as coal or biomass that is gasified to produce a mixture of hydrogen and carbon monoxide. The potential for efficiency improvement and the decrease in emissions resulting from this process compared to coal-fired power plants are strong evidence to the argument that IGCC technology will be a key player in the future of power generation. In addition to new IGCC plants, and as a result of new emissions regulations, industry is looking at possibilities for retrofitting existing natural gas plants. This paper studies the feasibility of retrofitting existing gas turbines of Natural Gas Combined Cycle (NGCC) power plants to burn syngas, with a focus on the water/steam cycle design limitations and necessary changes. It shows how the gasification island processes can be treated independently and then integrated with the power block to make retrofitting possible. This paper provides a starting point to incorporate the gasification technology to current natural gas plants with minor redesigns.
Gasification of hay in a bench scale fluidised bed reactor with emphasis on the suitability for gas turbines
Thermal gasification of pasture plants (hay) is so far considered as difficult mainly due to the high amount of inorganics (ash, alkalis). Under certain circumstances it could be an additional resource for power production. There has been some experiments to test hay in gasification plants but most lack inorganic analysis. A bubbling fluidized bed was set up and gasification experiments with extensive analysis of the gas composition was conducted. Dolomite, silica and alumina particles were used as bed material. Silica proved to work successfully at 700 degrees C. Ash experiments showed that at higher temperatures silica forms compounds that melt and lead to unstable gasification conditions. Dolomite proved to be not stable enough for fluidised bed conditions, since it was ground down to smaller particles and subsequently entrained. Alumina was the best bed material tested, which was used up to 750 degrees C with good results. The longest run was 10 h at 750 degrees C without defluidisation. Despite the low temperature in the process the bulk tar concentration was low. The heating value of the gas was good (4-6 MJ m(-3)). The concentration of sodium and potassium in the syngas after the warm gas filter at 400 C is low enough towards a cofiring IGCC application with 10% energy input from hay. (C) 2012 Elsevier Ltd. All rights reserved.
Mechanical behaviour and durability of high volume fly ash cementitious composites
The purpose of this research is to separate different morphological particles of ASTM class F fly ash, and study their effect on mechanical behaviour and durability of high volume cementitious mixtures. In this research wet separation of raw fly ash is carried out, which resulted in three layers of different morphological particles. The first layer of particles float, comprise of about 1-5% of fly ash, is identified as cenospheres or hollow spheres. The second layer of particles is measured to be 55-60% of raw fly ash and consisting of porous spherical and rounded particles rich in Si and Al. The third layer particles is measured to be about 35-40% of raw fly ash. High volume fly ash cementitious composites containing second or third layer particles are tested under compression and bending, highlighting a higher strength and ductility in comparison to cementitious ones containing raw fly ash particles. KEYWORDS. Cementitious matrix; Raw fly ash; Second layer particles; Third layer particles.