Design Considerations of Oxy-Fuel Fired Supercritical Pressure Circulating Fluidized Bed Boilers

2006 ◽  
Author(s):  
Prabir K. Halder
Keyword(s):  
Heat Transfer ◽  
Fluidized Bed ◽  
Flue Gas ◽  
Circulating Fluidized Bed ◽  
Fuel Combustion ◽  
Cfb Boiler ◽  
Design Considerations ◽  
Effective Manner ◽  
The Impact ◽  
Fluidized Bed Boilers

Researchers around the globe are focussing on the capture and storage of carbon dioxide generated from the combustion of coal in boilers for power generation. Oxygen fired boilers have the advantage of creating CO2 rich flue gas which enables the CO2 to be captured in a more cost effective manner compared to post combustion capture of CO2 from an air fired boiler. This paper discusses design considerations for oxy-fuel fired supercritical circulating fluidized bed boilers. A 420 MWe supercritical CFB boiler firing coal with oxygen has been considered for the study. An analytical/semi-empirical model has been developed to model fuel combustion and heat transfer in the furnace and convection pass. The fuel burns with oxygen supplied at the bottom of the bed and the fluidization velocity and bed temperature is controlled by flue gas recirculation. The model is used to design the boiler and determine its performance characteristics. The heating surfaces, recirculation ratios and other parameters have been designed to achieve the required boiler capacity. The impact of the CO2 rich flue gas on CFB boiler design is compared with conventional air blown CFB boilers. The study reveals that oxy-fuel combustion in a CFB combustor does not alter the heat transfer characteristics when compared with combustion with air. In the convection bank, oxyfuel combustion increases both convective and radiative components of heat transfer, thereby reducing the size of the heat transfer banks required.

Heat-Transfer Model of the Rotary Ash Cooler Used in Circulating Fluidized-Bed Boilers

2010 ◽  
Vol 24 (4) ◽  
pp. 2570-2575 ◽  
Author(s):  
Wei Wang ◽  
Xiaodong Si ◽  
Hairui Yang ◽  
Hai Zhang ◽  
Junfu Lu
Keyword(s):  
Heat Transfer ◽  
Fluidized Bed ◽  
Circulating Fluidized Bed ◽  
Heat Transfer Model ◽  
Transfer Model ◽  
Fluidized Bed Boilers

The Performance of a Loop Seal in a CFB Boiler

2006 ◽  
Vol 128 (2) ◽  
pp. 135-142 ◽  
Author(s):  
Andreas Johansson ◽  
Filip Johnsson ◽  
Bengt-Åke Andersson
Keyword(s):  
Heat Transfer ◽  
Flow Pattern ◽  
Fluidized Bed ◽  
Scaling Laws ◽  
Circulating Fluidized Bed ◽  
Vertical Direction ◽  
Scale Model ◽  
Corrosive Environment ◽  
Cfb Boiler ◽  
Load Conditions

High in-bed heat transfer and low corrosive environment imply that the loop seal of a circulating fluidized bed (CFB) boiler is an advantageous location for superheaters. In order to increase the knowledge on the flow pattern and the heat transfer distribution to the tubes within a loop seal, measurements were performed in the loop seal of a 30MW CFB boiler as well as in a 1∕3 scaled-down seal operated according to simplified scaling laws. The scale model measurements show that the solids recirculation flux can be maintained with a substantial decrease of the fluidization flow in the seal compared to that currently used at full load conditions. It was also possible to significantly decrease the fraction of the bottom of the seal that was fluidized without affecting the solids flux through the seal. A gradient in the solids flow were detected in the vertical direction.

Co-Firing Coal, Biomass and Waste Fuels in Circulating Fluidized Bed Boilers to Reduce CO2 Emissions

2011 ◽  
Author(s):  
Ronald Hancharik
Keyword(s):  
Fluidized Bed ◽  
Co2 Emissions ◽  
Carbon Footprint ◽  
Circulating Fluidized Bed ◽  
Heating Surface ◽  
Energy Sources ◽  
Cfb Boiler ◽  
Design Considerations ◽  
Technical Challenges ◽  
Operating History

The combustion of CO2 neutral solid fuels like biomass and waste-based fuels with circulating fluidized bed (CFB) boiler designs has become an accepted way to generate electric power and process steam to reduce global CO2 emissions (i.e. reduce “carbon footprint”) and hence to reduce the potential impact on climate change. In the European Union, for example, there is a co-combustion directive to encourage the use of biomass and waste as energy sources with the co-firing of coal. Quite often biomass and waste combustion in CFB’s have unique technical challenges when compared to fossil fuels. The technical challenges of firing these CO2 neutral fuels do impact CFB boiler design and may impact plant lifecycle and reliability when compared to coal. Among these are combustion bed agglomeration, furnace and heating surface slagging, and new forms of corrosion potential. However, when co-firing these CO2 neutral fuels with coal, these challenges can be tempered in a positive way through inherent changes in the flue gas chemistry and other design considerations. Co-firing makes sense. In addition to reducing the carbon footprint of a boiler project through use of biomass and waste, these energy sources can have a significant positive impact on plant financials owing to low cost supply. However these fuels can have wide variations in availability and energy content over the course of the many years of a boiler’s life. As such, maintaining coal as a supplemental fuel or back-up fuel also provides significant benefit in terms of guaranteeing the energy input supply and thereby securing plant availability. This benefit can help lower project financial risk and improve financial attractiveness and viability. This paper describes this type of boiler, its design considerations and operating history. Highlighted herein is the operating facility in Pori, Finland, commissioned in 2008, which is a 60 MWe CFB boiler burning peat, biomass and recycled waste fuel (RDF) with coal as a back-up fuel. Other facilities with similar design and with operating history of over 10 years are included as reference.

Experimental Study on Microstructure of Fly-Ash from Circulating Fluidized Bed Boilers

2011 ◽  
Vol 354-355 ◽  
pp. 413-416
Author(s):  
Yan Jin ◽  
Cui Ying Feng ◽  
Juan Juan Liu
Keyword(s):  
Fly Ash ◽  
Fluidized Bed ◽  
Adsorption Isotherms ◽  
Circulating Fluidized Bed ◽  
Nitrogen Adsorption ◽  
Cfb Boiler ◽  
Nitrogen Adsorption Isotherms ◽  
Pore Types ◽  
Adsorption Desorption ◽  
Fluidized Bed Boilers

Circulating fluidized bed (CFB) combustion techniques have been widely used in China. In order to improve CFB boiler performance it is necessary to study on microstructures of fly-ash. With the help of nitrogen adsorption instrument and scanning electron microscopy, the pore structure of fly-ash in circulating fluidized bed boilers are studied by nitrogen adsorption/desorption isotherms of fly-ash, hysteresis loop and pore distribution. The results indicated that different particle sizes of fly-ash in CFB boilers are of similar nitrogen adsorption isotherms, pore types and the pore size distribution, and the most probable pore radius of fly-ash is about 2nm. Adsorption isotherms of fly-ash is the second type, and the macro-porous and meso-porous types are tapered hole, parallel plate slit hole and the ink bottle shape hole. And meso-pore in proportion is the largest. Micro-pores are not discovered in fly-ash from CFB boilers.

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