Field Study on Ash Behavior during Circulating Fluidized-Bed Combustion of Biomass. 1. Ash Formation

Abstract

Ash formation was studied experimentally during combustion of forest residue and willow in a 35 MW circulating fluidized-bed co-generation plant. Ash particles and vapors were sampled downstream of the process cyclone at flue gas temperatures of 810-850 °C. Inorganic vapors and fly ash particles were collected separately on filters. Size-classified fly ash particle samples were collected with an impactor. Elemental analysis methods and electron microscopy were used for ash characterization. During combustion of forest residue, about 30-40% of the total ash and a similar percentage of Ca and P was attached on the bed-material particles and were eventually removed from the bed along with bottom ash. K was retained with a higher efficiency (about 50%). S and Cl were volatilized in the furnace and were not retained in the bed. During combustion of forest residue, 80% of S had already reacted with species present in supermicrometer ash particles when detected after the process cyclone at 810-850 °C. When willow was combusted, about one-half of the sulfur remained as SO 2 . More than one-half of the particlephase S was present as alkali sulfate fine particles that were almost nonexistent during forest residue combustion. Cl was present as gaseous species (KCl and presumably HCl) at 810-850 °C with both fuels.

Formation and Emission of Submicron Particles in Pulverized Olive Residue (Orujillo) Combustion

“…In this case, as essentially all the mineral matter entering the EFR is collected in the cyclone or the BLPI, approximately 3% of the inorganic matter in the fuel is emitted in the form of particles smaller than 1 µm. This value is comparable with published submicron fraction measurements in FBC plants at locations prior to the process cyclone (Valmari et al 1999). The supermicron mode is also shifted to larger diameters with respect to previous results for biomass-fired boilers, the type of combustion being again responsible for this fact.…”

The Effect of Traction Sanding on Urban Suspended Particles in Finland

“…It was not possible to identify separately these sources. Their chemical composition resembled also that of fly ash from different combustion sources (see Ganor et al, 1998;Valmari et al, 1999;Lighty et al, 2000), and on the other hand that of bitumen mixed with minerals possibly from filler or stone materials of the asphalt, based on analysis made for this study. The fly ash can originate from the residential area where the houses are heated mainly with oil and wood.…”

“…However, coarse spherical particles usually found in fly ash (Kindratenko et al, 1994;Xie et al, 1994) were not present. On the other hand the temperature for the formation of compact spherical particles may not have been high enough (Valmari et al, 1999) in the residential boilers. Some of the particles might also have been agglomerates of mineral particles that had been 'contaminated' e.g.…”

Combustion Aerosols: Factors Governing Their Size and Composition and Implications to Human Health

“…Studies have been conducted of industrial-scale biomass combustion, especially in fluidized bed boilers. 199,200 The ash formation processes during suspension firing of wood sawdust and sanderdust have been shown to be similar to the mechanism for pulverized coal combustion, 201 as indicated in Figure 3. The supermicron particles are predominantly Ca, but also contain Fe, Al, Mn, and Si.…”