The measurement of flyash and bottom ash flow rates from a circulating fluidized bed boiler

Abstract

The measurement of the flow rates offtyash and bottom ashfiom a Circulating Fluidized Bed (CFB) boiler has a number of uses. Among these are the requirements of boiler pe$rmance testing, the devehpment ofparticle population modeb for assessing key chemical interactions taking place in the combustion chamber, and the partitioning of key species between flyash and bottom ash. Identification of partitioning of key species betweenfl ash and bottom ash in key parameters of boih operation.Current methodsfor the computing of the flow rates of these ash streams include the measurement of the flow rates offeed solids, one ash stream flow rate, and infevence of the otherfiom a material balance. This is effort intensive and as such, not routinely feasible.Offered here is a methodfor computing the flow rates of ash streams through measurement of the solid feed rates to the system, and solving material balances around inorganic solid (total ash), cahium, and/ or su&, using these material balances as a simple set of simultaneous equations. This methodpermits the calculation of the ash stream flow rates without the direct measurement of either, and can bepracticed on a routine basi s. (com bustibles, calcium, sulficr) can t ' ead to improvements INTROMlcTONThere are several key parameters related to the performance of circulating fluidized bed (CFB) boilers that are influenced by the nature of the particles making u p the bed inventory. Among these are the amount and characteristics of bed particles that can be maintained in the combustion chamber, which can affect heat transfer 111, and ultimately heat rate. Another is the distribution and characteristics of sorbent particles within the system [21, which can affect sorbent consumption, and ultimately compliance costs.CFB boilers classify bed particles into flyash and bottom ash streams according to their gas flow resistance (size, density). As such, the ash split (the relative contributions of flyash and bottom ash to the composite ash flow from the boiler) will be impacted by the responses of feed particles to the chemical and physical stimuli encountered in the system 131. Lastly, there are interactions among bed particles and with the boiler that can adversely impact availability. Included among these are erosion of pressure parts and bed agglomeration.These considerations all relate to the transformations to which the feed particles are subjected during their residence in the system. Included among the transformations are combustion of fuel particles, calcination, sulfation, and reductive decomposition of sorbent particles, and attrition. Fuel, sorbent, and possibly inert bed particles are fed to a CFB boiler. The transformations exhibited by individual classes of particles have been elucidated in many cases. Among the results of relevant studies have been attrition of relatively low ash content coal char particles through percolative fragmentation [4,51. Similarly, the combustion of relatively high ash fuel particles has seen some attention [4,61 and a "shrinking core" me...

Characterization of Fly Ashes from Circulating Fluidized Bed Combustion (CFBC) Boilers Cofiring Coal and Petroleum Coke

“…Recently, there have been several publications on properties or utilizations of CFBC fly ashes − and fly ashes from cofiring PC and coal 5-7,13 but few on fly ashes originating from cofiring PC and coal in a CFBC boiler. Only Anthony and his co-researchers have presented some investigations on such fly ashes, but they mostly focused on fouling and agglomeration in boilers ,, and on vanadium compounds in the fly ashes …”

Effect of Heterogeneity in Coal Ash Chemical Composition on the Onset of Conditions Favorable for Agglomeration in Fluid Beds

“…They mentioned the significance of particle-level heterogeneities in ash composition and used gravity separated Rosebud coal fractions in the study of deposition on heat transfer surfaces in pulverized coal fired boilers. This concept was further applied to the fluidized bed industry by Rozelle et al [23]. in their models to predict the flow rates of fly ash and bottom ash from a CFB boiler.…”

Modeling of particle size distribution of limestone in sulfur capture in air and oxy-fuel circulating fluidized bed combustion

“…The partitioning of calcium and sulfur between bottom ash and fly ash in a CFB boiler has been studied. 51 Oxy-firing is a promising technology leading to high concentration of CO 2 in flue gases allowing its effective separation for sequestration. [52][53][54][55][56][57][58][59] There are some differences in sulfur capture in air-firing and oxy-firing as the gas atmosphere and temperature defines the sulfur capture mechanism.…”