I have been testing different feed streams, coal, MSW waste stream, biomass, oil shale, tire crumbs, etc. both systematically based on equilibrium analysis and high fidelity based on CFD the maximum that I have achieved is nearly 60% for the gasifier and 45% when I used it in IGCC or much lower in the IGPlasmaCC. Has anyone achieved higher efficiency in the IGCC? And can I share our findings with them?
I should caution that you have to be careful when you throw efficiency numbers around - you may be referring to fuel LHV going to MWe or possibly just the LHV efficiency so you should always state what is your efficiency basis.
The efficiency losses in IGCC come from having to heat the feed up to extreme temperatures such as 2500 F in order to gasify all of the carbon. Using a very low ash coal and highly reactive carbon-source would improve efficiency. All of the other losses come from thermodynamic inefficiencies in heat transfer and the limiting practical efficiency of steam turbines, gas turbines, compressors and generators. Conducting heat transfer at lower temperature differentials, with smaller approaches in exchangers, with higher temperatures in turbine inlets, using higher pressure steam, etc. would all lead to efficiency gains but at the expense of exotic (or non existent) materials, longer , higher surface area exchangers, improved exch. tube surface treatments, possibly lowered reliability, etc. Improvements in air separation could also improve the efficiency, if you are including that in your calculations. Some more complicated bottoming cycles using multiple fluids instead of just steam,various reheat schemes, and many other things have been looked at (refer to EPRI studies). Turbine manufacturers GE and Siemens are developing more efficient gas turbines e.g. FlexEfficiency 60 model (known as the 7F 7-series) with a claimed 61% efficiency.
Looking at non-IGCC power plants, efficiency improvements were made over a number of decades by increasing the steam pressures to critical, supercritical and eventually to what is now referred to as ultra-supercritical. These advancements were made possible partly by improvemnts in metallurgy of the steam tubes and also in refractories used in the boilers. Similar improvements will occur over time in IGCC.
Dennis Leppin, P.E.
Institute Fellow, Gas Technology Institute
As the proximate material analysis of the feedstock consists of moisture, volatile, fixed carbon and Ash, the moisture and Ash takes up a considerable latent/ sensible heat. Thus a feedstock with lower moisture and ash contents is your best bed to improve your efficiency and weather you based on LHV or HHV. Reducing the gasification temperature using different catalysis is another option to lower the wasted sensible heat. I also agree with Dennis is to obtain the top of the range IGCC units, including gas and steam turbines, heat exchangers, and regenerate heat as much as you can. Including the heat due the sulfur stripping and gas clean up/separation stage. Overall, 60% is what FUTUREGEN were targeting and thought it was very optimistic (http://en.wikipedia.org/wiki/FutureGen)
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