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Bubbling Fluidized Bed or Stoker — Which is the Right Choice for Your Renewable Energy Project ?
| Content Provider | Semantic Scholar |
|---|---|
| Author | DeFusco, J. P. McKenzie, P. A. Fick, M. D. |
| Copyright Year | 2007 |
| Abstract | Current market conditions are providing multiple economic and environmental drivers to promote the use of renewable fuels including: A Federal renewable energy tax credit; State mandated Renewable Portfolio Standards (RPS) programs; Voluntary green up programs; Displacement of higher cost fossil fuels; and Biomass based power as CO2 neutral. A viable renewable fuel in many parts of the country is wood-based biomass. There are many ways to drive useful energy out of biomass fuels. In regard to power production and or combined heat and power applications, a proven method is to convert the chemical energy in the biomass to thermal energy via gasification or combustion. This energy is transferred to a working fluid such as steam, which in turn drives a turbine generator, and/or provides heat to an industrial process. This paper will explore two different technologies available to convert the energy in wood biomass to do useful work in a power plant application. Both options involve the use of a steam generator. The fuel in both cases is identical – it is assumed to be whole tree chips and primarily the low value attributes of the tree, which would be the tree tops, trimmings and bark. It is assumed that the high value section of the tree will be further refined to make lumber, furniture, or other higher quality, valued-added products, and not utilized for power production. For the purpose of this analysis, we assumed a constant fuel moisture content. Also, we did not consider any non-biomass fuels such as tire derived fuel (TDF), coal, or petcoke; the later two would normally drive the technology toward Circulating Fluidized Bed (CFB). For outputs of between 15 and 100 MWe and the conditions we have outlined, there are two conventional, commercially available technologies that could be considered – Bubbling Fluidized Bed (BFB) technology and Stoker technology. While the boiler systems and designs are similar, there are distinct differences. This paper will explore the differences between these technologies in the areas of technical features, capital cost and Operating and Maintenance (O&M) costs. The results of this evaluation can be utilized to pick the appropriate technology for a specific project, given the same or similar design conditions. Review of stoker technology Stoker technology has been around for more than one hundred years, and was the means by which most of the early solid-fuel boilers were fired. These early generation boilers were “stoked” by an operator or “fireman” shoveling fuel in by hand. Ash was later removed by manually raking the grate. Modern stoker units for wood firing are normally mechanical rotating grates or water/air-cooled vibrating grates depending on the fuel moisture content. Fuel is typically introduced into the boiler through multiple fuel chutes. Air is supplied under the grate as well as above via an overfire air (OFA) system. Depending on the fuel moisture content, the combustion air is pre-heated to 350 to 650F. The combustion zone temperature is typically neither measured nor controlled and can range from 2200 to over 3000F. Due to high shaft velocities in the lower furnace and the “throwing” of fuel onto the grate for proper distribution with the stoker combustion process, a modern stoker unit will have unburned fuel “carried over” and out of the furnace. This “carryover” occurs by virtue of entrainment of unburned wood particles in the flue gas moving up through the furnace shaft. The unburned combustible loss leaving the boiler can be as high as 4 to 6% on a fuel efficiency basis. If not recovered, this unburned fuel results in efficiency losses, which increases the required fuel consumption and equipment costs. In order to recover what would have been a loss, stoker-fired boilers typically include carbon re-injection systems that recycle the J.P. DeFusco, P.A. McKenzie and M.D. Fick The Babcock & Wilcox Company Barberton, Ohio, U.S.A. Presented to: CIBO Fluid Bed Combustion XX Conference May 21 23, 2007 Lexington, Kentucky, U.S.A. BR-1802 |
| File Format | PDF HTM / HTML |
| Alternate Webpage(s) | https://www.babcock.com/zh-cn/products/-/media/809ad04de4e144ccbaae37718f1558c2.ashx |
| Language | English |
| Access Restriction | Open |
| Content Type | Text |
| Resource Type | Article |
