Correlation of Sub-micrometer Ash Formation from Pulverized Biomass Combustion with Ash Composition

For the development of sustainable energy and a great reduction of CO2 emission into the atmosphere, renewable energy has been rapidly installed and used in the last two decades. Many biomass power plants have been built and operated because the combustion of biomass is considered to be renewable and carbon neutral. In this review, the following topics are summarized: (1) economic values of bioproducts, (2) many restrictions of biomass power generation systems such as (i) very low energy efficiency from solar power to electricity, (ii) limiting amount of resource, and (iii) requirement of fuel cost for operation, and (3) characteristics of combustion technologies including drawbacks and the following strong points: (i) high power, (ii) high-temperature heat generation, and (iii) utilization for hygiene or sanitation purposes. The reduction of simple combustion and the noble use of combustion technology by effectively utilizing these strongpoints are required to greatly reduce CO2 emission even if renewable biomass is used. Next-generation biomass power generation systems integrated with variable renewable energy and energy storage system for non-steady-state operation are proposed as a promising method to balance the intermittent electricity supply by variable renewable energy and electricity demands.

Section: Characterization Of Combustion Technologymentioning

confidence: 99%

Valorization of Biomass Power Generation System: Noble Use of Combustion and Integration with Energy Storage

Fushimi

2021

“…A challenge in burning biomass in PF boilers is its content of alkali metals. Higher alkali contents might lead to increased ash deposition and aerosol formation . Gaseous alkali salts from biomass combustion are transferred with the flue gas and deposited on boiler surfaces, accelerating corrosion and deactivation of the SCR catalyst. − The use of fuel additives is a promising technique to solve this problem in PF boilers .…”

Section: Introductionmentioning

confidence: 99%

Modeling Potassium Capture by Aluminosilicate, Part 1: Kaolin

Hashemi

Wang²,

Jensen

et al. 2021

Additives rich in Si and Al such as kaolin may be applied in PF biomass boilers to fix alkali metals in species that are more benign than the alkali salts released in biomass combustion. In this study, models for the reaction of gas-phase potassium salts with kaolin particles are developed for the conditions appearing in PF boilers such as short residence times, high temperatures, and small size of the additive particles. The reaction between gaseous potassium components and kaolin particles has been modeled with a shrinking core model (SCM) and a uniform conversion model (UCM). The SCM takes into account the effects of chemical kinetics, diffusion in a gas film surrounding the particle, diffusion in a product layer, and thermochemical equilibrium on the reaction progress. The UCM covers diffusion in a gas film surrounding the particles, chemical kinetics, and thermochemical equilibrium. Both models are able to accommodate the effects of change in temperature, particle size, reaction time, and potassium component concentration. Literature data from experiments in an entrained flow-reactor (EFR) at 800−900 °C were used to derive the chemical kinetic rate coefficients of the reaction between kaolin and KOH. The models were then evaluated against experimental data for alkali salts of KCl, KOH, K 2 CO 3 , and K 2 SO 4 covering temperatures of 800−1450 °C, kaolin particle sizes of 4−14 μm, residence times of 0.8−1.9 s, and salt/additive molar ratios of 0.05−0.96. The evaluation indicated that both SCM and UCM were suitable for a wide range of conditions, but the UCM captured the effect of particle size better. The modeling outcomes suggested that if the reaction time was long enough, the thermochemical equilibrium would be the major limitation in capturing potassium by kaolin at high temperatures and high potassium concentrations. At lower temperatures, however, the conversion was mainly limited by chemical kinetics. The mass-transfer limitation was less critical under the investigated conditions. The developed models can account for the reaction of gas-phase potassium salts with kaolin at local conditions relevant to PF boilers using biomass.

“…In solid fuel combustion, the ultrafine PM 0.1 or PM 0.2 emission (denoting the aerodynamic diameter less than 0.1 or 0.2 μm) is extremely hazardous due to the enrichment of toxic species. − Even worse, the ultrafine fraction is more likely to escape from the dust removal devices . Extensive research efforts have been devoted to understanding the ultrafine PM formation and revealed a vaporization-nucleation pathway. − It was reported that, compared with bituminous coal, the low-rank lignite is more prone to generate PM 0.2 which is dominant by the alkali and alkaline earth metallic (AAEM) elements. , Likewise, ultrafine PM from burning biomass and sewage sludge is composed of fuel-dependent volatilized mineral species containing alkali (Na and K), S, Cl, and P. − Nevertheless, it remains a challenge to predict ultrafine PM yields in practical combustors due to the complex interactions of multiple species.…”

Section: Introductionmentioning

confidence: 99%

Ultrafine Particle Formation in Pulverized Coal, Biomass, and Waste Combustion: Understanding the Relationship with Flame Synthesis Process

Huang

Gao

et al. 2019

The adverse effect of ultrafine particulate matter (PM) from the combustion of solid fuels calls for fundamental insights to guide effective control strategies. In this work, we investigated the ultrafine PM formation from burning several solid fuel samples, with special emphasis on the relationship with an emerging field of flame synthesis. Diluted fly ash was sampled and characterized in a bench-scale flat-flame burner at the early stage (∼40 ms) and in a 25 kW quasi-one-dimensional combustor at the burnout stage (∼1.5 s). Then, the population balance model framework was transplanted from the community of flame aerosol synthesis to simulate the particle size distributions (PSDs). From the experiments, unimodal submicron PSDs were revealed for the combustion of coal, rice husk, and sewage sludge under 40 ms of residence time and a postflame ambience of 1500 K and 20 vol % O 2 . The compositional analysis reveals both the contributions from Na/K/P/S and from refractory species are important for ultrafine PM formation. This vaporization-nucleation mechanism highlights the similarity between solid fuel combustion and flame synthesis. However, the dif ference is raised by the medium and coarse mode PM that only appears in solid fuel combustion. The volatilized mineral and the ultrafine PM can be scavenged via coagulation, and the scavenged ratio takes ∼10−60% of the total volatilized minerals for different coal samples. This ratio is inversely correlated with the volatilized minerals on a basis of ash input.