The Fouling Behavior of Rice Husk Ash in Fluidized-Bed Combustion. 2. Pilot-Scale and Full-Scale Measurements

Abstract

This paper is the second in a series of two on the slagging and fouling behavior of rice husk when fired alone or in combination with other fuels in a fluidized-bed boiler. The first paper involved the fuel properties of rice husk, as investigated by a variety of laboratory methods. In this second paper, we report the results of fireside fouling measurements when burning rice husk alone and together with eucalyptus bark in various ratios. This study is based on short-term (3−10 h) deposit samples taken with air-cooled deposit probes in the superheater region of a large-scale (157 MWth) bubbling fluidized-bed (BFB) boiler burning rice husk and eucalyptus bark. Using an entrained-flow type of pilot furnace, we further made more, systematic measurements of the influence of the fuel mixture ratio on the fouling tendency of the fly ash formed. Burning of rice husk alone did not result in any detectable fouling, neither in the pilot furnace nor on the deposit probes in the superheater area of the fluidized-bed boiler. After deposit samplings with durations of up to 10 h during 100% rice husk firing, the deposit sampling probe had not collected more than ∼95 mg of deposit material. The combustion of eucalyptus bark alone caused significant fouling. Here, the corresponding amount of deposit was ∼90 mg after 10 h of sampling. The fouling tendency of mixtures of rice husk and bark showed a nonlinear dependence on the fuel mixture ratio. The results suggest that the rice husk ash acted as an erosive, cleaning agent in the fly ash mix.

Assessment of the rice husk lean-combustion in a bubbling fluidized bed for the production of amorphous silica-rich ash

“…In the case of fluidized beds, where the turbulences and convections conditions are important, the ash morphology resembles the natural state, as observed previously by other researchers in RH combustion in a bubbling fluidized bed [24].…”

Ash Deposition in Biomass Combustion or Co-Firing for Power/Heat Generation

“…The ash elemental compositions are also commonly reported as oxides, in their highest oxidation states, which reflect the principal inorganic compositions. Furthermore, SEM is a particularly powerful analytical technique for the examination of the microstructure of ashes and deposits [50][51][52]. XRD is commonly used for the identification of the major crystalline phases in deposits [47,53,54].…”

“…Research efforts have been put into attempting to understand the mechanisms involved in the formation [15,44,48,55,56], slagging/fouling [52] and corrosion [35] of the ash deposits during biomass combustion or co-firing. During combustion processes, ash is formed from the fuel-bound inorganic materials through a combination of complex chemical and physical processes.…”

Bed agglomeration characteristics of rice straw combustion in a vortexing fluidized-bed combustor

“…Bed temperature is the key factor for defluidization. The most convenient and effective method of preventing defluidization is to keep the bed temperature from rising above the melting point of the eutectic compositions, which prevents the melting phenomenon (Skrifvars et al, 2005;Yu et al, 2011). As the bed temperature decreases, CO emission also increases to much higher levels than the norms of the regulation (Bahillo et al, 2004;Baron et al, 2002).…”