Uendo Lee

Long-term operation of biomass-to-liquid systems coupled to gasification and Fischer–Tropsch processes for biofuel production

Long-term operation of the biomass-to-liquid (BTL) process was conducted with a focus on the production of bio-syngas that satisfies the purity standards for the Fischer-Tropsch (FT) process. The integrated BTL system consisted of a bubbling fluidized bed (BFB) gasifier (20 kW(th)), gas cleaning unit, syngas compression unit, acid gas removing unit, and an FT reactor. Since the raw syngas from the gasifier contains different types of contaminants, such as particulates, condensable tars, and acid gases, which can cause various mechanical problems or deactivate the FT catalyst, the syngas was purified by passing through cyclones, a gravitational dust collector, a two-stage wet scrubber (packing-type), and a methanol absorption tower. The integrated system was operated for 500 h over several runs, and stable operating conditions for each component were achieved. The cleaned syngas contained no sulfur compounds (under 1 ppmV) and satisfied the requirements for the FT process.

Economic analysis of biomass power generation schemes under renewable energy initiative with Renewable Portfolio Standards (RPS) in Korea

An economic analysis of biomass power generation was conducted. Two key technologies--direct combustion with a steam turbine and gasification with a syngas engine--were mainly examined. In view of the present domestic biomass infrastructure of Korea, a small and distributed power generation system ranging from 0.5 to 5 MW(e) was considered. It was found that gasification with a syngas engine becomes more economically feasible as the plant size decreases. Changes in the economic feasibilities with and without RPS or heat sales were also investigated. A sensitivity analysis of each system was conducted for representative parameters. Regarding the cost of electricity generation, electrical efficiency and fuel cost significantly affect both direct combustion and gasification systems. Regarding the internal rate of return (IRR), the heat sales price becomes important for obtaining a higher IRR, followed by power generation capacity and electrical efficiency.

Transient behavior of devolatilization and char reaction during steam gasification of biomass.

Steam gasification of biomass is a promising method for producing high quality syngas for polygeneration. During the steam gasification, devolatilization and char reaction are key steps of syngas production and the contributions of the two reactions are highly related to gasification conditions. In this study, the transient characteristics of devolatilization and char reaction in biomass steam gasification were investigated by monitoring cumulative gas production and composition changes in terms of reaction temperature and S/B ratio. Contribution of each reaction stage on the product gas yield was studied in detail. The results provide important insight for understanding the complex nature of biomass gasification and will guide future improvements to the biomass gasification process.

Production of bio-oil rich in acetic acid and phenol from fast pyrolysis of palm residues using a fluidized bed reactor: Influence of activated carbons.

In this study, palm residues were pyrolyzed in a bench-scale (3kg/h) fast pyrolysis plant equipped with a fluidized bed reactor and bio-oil separation system for the production of bio-oil rich in acetic acid and phenol. Pyrolysis experiments were performed to investigate the effects of reaction temperature and the types and amounts of activated carbon on the bio-oil composition. The maximum bio-oil yield obtained was approximately 47wt% at a reaction temperature of 515°C. The main compounds produced from the bio-oils were acetic acid, hydroxyacetone, phenol, and phenolic compounds such as cresol, xylenol, and pyrocatechol. When coal-derived activated carbon was applied, the acetic acid and phenol yields in the bio-oils reached 21 and 19wt%, respectively. Finally, bio-oils rich in acetic acid and phenol could be produced separately by using an in situ bio-oil separation system and activated carbon as an additive.

Behavior of heavy metals in air pollution control devices of 2,400 kg/h municipal solid waste incinerator

We analyzed the behavior of heavy metals, such as Cd, Cr, Cu, Ni, Pb, Zn, and Hg, in air pollution control devices of a municipal solid waste incinerator. For this study, a municipal solid waste incinerator with a burning capacity of 2,400 kg/h was selected. A semi-dry reactor (SDR), fabric filter, and wet scrubber were installed to serve as air pollution control devices. Flue gas was sampled upstream and downstream of each air pollution control device to determine the heavy metal concentrations therein. Ash was collected from the furnace, boiler, SDR, and fabric filter to determine the heavy metal concentration in the ash produced by each device. Each heavy metal was found to have a different fate in the incinerator and air pollution control devices. Cd and Pb were mostly present in the fabric filter ash, whereas Cr, Cu, and Ni were most prevalent in the bottom ash of the furnace and boiler, and Zn was present in the bottom and fabric filter ash at a ratio of 7: 3. However, only a few percent of Hg was identified in the ash from the furnace, boiler, SDR, and fabric filter; the majority of Hg passed through the fabric filter and existed in an oxidized form. The wet scrubber exhibited high control efficiency for oxidized mercury, and the injection of commercial activated carbon at a rate of 0.2 g/Sm3 resulted in 93.2% mercury removal efficiency.