Co-firing of cassava rhizome and eucalyptus bark in a fluidized-bed combustor using a reburning method to reduce NOx emissions

Thammasat University 2018

Cassava rhizome and eucalyptus bark are promising bioenergy resources in Thailand. Based on the availability and calorific values, the domestic annual energy potentials of these biomass residues account for about 45 PJ and 50 PJ, respectively. However, individual burning of these biomass fuels in a fluidized-bed combustion system are associated with some operational problems, such as (i) noticeable NO emission during combustion of cassava rhizome with its elevated fuel-N and (ii) flame instability when firing high-moisture bark. Furthermore, elevated potassium contents in fuel-ash indicate a propensity of both fuels for bed agglomeration when fired individually in a fluidized bed of silica/quartz sand. In this thesis work, pelletized cassava rhizome (a base fuel) and shredded eucalyptus bark (a reburn fuel) were co-fired in a 200 kW fluidized-bed combustor, using a reburning technique to reduce NO emission from the combustor. At the first stage of the study, the selected fuels were (co-)combusted at the constant heat input to the reactor, using conventional bed material (silica sand), for variable operating conditions. In this test series, the energy fraction of the secondary fuel (EF2) varied within 0–0.25, with excess air (EA) of 20–80% (at fixed EF2) and secondary-to-total air ratio (SA/TA) of 0.10–0.25 (at fixed EA). During a test run at fixed operating parameters, the temperature and gas concentrations (O2, CO, CxHy as CH4, and NO) were measured along the axial and radial directions inside the combustor, as well as at stack, to investigate combustion and emission characteristics of the reactor. A cost-based optimization technique was used to quantify the optimal operating parameters: EF2 = 0.15, EA ≈ 60%, and SA/TA ≈ 0.25, to minimize the "external" (emission) costs of the combustor. Under these operating conditions, a 50% NO emission reduction is achievable, compared to burning the base fuel alone. However, when using silica sand as the bed material, a fairly

Biomass; Fluidized bed; Reburning; NOx reduction; Optimization; Bed agglomeration; Time-related bed behavior; Text

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TULIB 164591
1346250931

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