David Tee Liang

Modeling of CO2 capture by three typical amine solutions in hollow fiber membrane contactors

Abstract A theoretical simulation was performed to study CO 2 capture by absorption in a hollow fiber membrane contactor. Three typical alkanolamine solutions of 2-amino-2-methyl-1-propanol (AMP), diethanolamine (DEA) and methyldiethanoamine (MDEA) were employed as absorbents in the analysis. The effects of different sorption systems, operating conditions and membrane characteristics on the removal behavior of CO 2 were investigated. Simulation results indicate that AMP and DEA solutions have much higher CO 2 absorption fluxes than MDEA solution, but the concentrations of both AMP and DEA drop dramatically due to depletion. It implies that the separation efficiency and the consumption of absorbents should be taken into consideration simultaneously in terms of absorbent selection in practice applications. The liquid flow velocity, initial liquid concentration and the fiber length as well as fiber radius have significant impacts on the CO 2 absorption by AMP and DEA because of their instantaneous reactions with CO 2 . The reaction kinetics of MDEA with CO 2 has been found to be the controlling factor in the process of CO 2 capture in the membrane contactor. Theoretical solution also confirms that the non-wetted mode of operation is favored, by taking the advantage of higher gas diffusivity in order to optimize CO 2 capture performance.

Aerobic granulation under the combined hydraulic and loading selection pressures.

Two SBR reactors were set up to investigate the feasibility of aerobic granulation under the combined selection pressures of hydraulic shear force and substrate loading. Aerobic granulation was studied at superficial upflow air velocity of 3.2 and 2.4 cm/s under an organic loading rate (OLR) range of 6.0-15.0 kg COD/m3d. Good reactor performance and well granule characteristics were achieved in a wide OLR range from 6.0 high up to 15.0 kg COD/m3d at 3.2 cm/s. While under the velocity of 2.4 cm/s, stable operation was limited in the OLR range of 6.0-9.0 kg COD/m3d and failed to operate with granule deterioration under further higher OLRs. The optimal combination of hydrodynamic shear force and loading selection pressure was demonstrated to be an important factor that influence aerobic granulation and govern the granule characteristics and reactor performance.

Characteristics of rapidly formed hydrogen‐producing granules and biofilms

The physicochemical and microbiological characteristics of rapidly formed hydrogen‐producing granules and biofilms were evaluated in the present study. Microbial species composition was examined using the 16S rDNA‐based separation and sequencing techniques, and spatial distribution and internal structure of microbial components were evaluated by examining the confocal laser scanning microscope (CLSM) images. Phylogenetic analysis indicated that a pure culture of Clostridium pasteurianum‐like bacterium (98% similarity) was found in microbial community of granules and biofilms. It is postulated that containing such a species favored the rapid immobilization of hydrogen‐producing culture. Manure granules and biofilms secreted 24–35 mg extracellulous proteins and 142–175 mg extracellulous polysaccharides in each gram of culture (in VSS). Such a high productivity of extracellulous polymers (ECP), a bio‐glue to facilitate cell‐to‐cell and/or cell‐to‐substratum interaction, may work as the driving forces for the immobilization of C. pasteurianum. As abundant proteins were noted in the granule cores, it can be derived that rapid formation of the hydrogen‐producing granules could be due to the establishment of precursor protein‐rich microbial nuclei. Biotechnol. Bioeng.

Formation of bed agglomeration in a fluidized multi-waste incinerator☆ ☆

Abstract A case study was carried out to investigate the bed agglomeration observed in a fluidized bed incinerator when burning blends of three wastes (carbon soot, biosludge and fuel oil). Several instrumental approaches were employed (i.e. XRF, SEM, XRD, and ICP-AES) to identify the bed materials (fresh sand and degrader sand) and clinkers formed in the full-scale incinerator tests. Several elements (V, Al, S, Na, Fe, Ni, P, and Cl), which normally are associated with the formation of low melting point compounds, were found in the waste blends at high content levels. The clinker bridges were identified to be associated with Al, Fe, V, K, Na, S, Ni, and Si elements. The effects of temperature and blending ratio were investigated in a muffle furnace. Carbon soot is believed to be more susceptible to the clinker formation than the other two fuels. Thermodynamic multi-phase multi-component equilibrium calculations predict that the main low melting point species could be Al 2 (SO 4 ) 3 , Fe 2 (SO 4 ) 3 , Na 2 SO 4 , NaCl, Na 2 SiO 3 and V 2 O 5 . This information is useful to understand the chemistry of clinker formation. Also, it helps to develop methods for the control and possible elimination of the agglomeration problem for the design fuels.

Use of activated carbon as a support medium for H2S biofiltration and effect of bacterial immobilization on available pore surface

The use of support media for the immobilization of microorganisms is widely known to provide a surface for microbial growth and a shelter that protects the microorganisms from inhibitory compounds. In this study, activated carbon is used as a support medium for the immobilization of microorganisms enriched from municipal sewage activated sludge to remove gas-phase hydrogen sulfide (H2S), a major odorous component of waste gas from sewage treatment plants. A series of designed experiments is used to examine the effect on bacteria-immobilized activated carbon (termed “biocarbon”) due to physical adsorption, chemical reaction, and microbial degradation in the overall removal of H2S. H2S breakthrough tests are conducted with various samples, including microbe-immobilized carbon and Teflon discs, salts-medium-washed carbon, and ultra-pure water-washed carbon. The results show a higher removal capacity for the microbe-immobilized activated carbon compared with the activated carbon control in a batch biofilter column. The increase in removal capacity is attributed to the role played by the immobilized microorganisms in metabolizing adsorbed sulfur and sulfur compounds on the biocarbon, hence releasing the adsorption sites for further H2S uptake. The advantage for activated carbon serving as the support medium is to adsorb a high initial concentration of substrate and progressively release this for microbial degradation, hence acting as a buffer for the microorganisms. Results obtained from surface area and pore size distribution analyses of the biocarbon show a correlation between the available surface area and pore volume with the extent of microbial immobilization and H2S uptake. The depletion of surface area and pore volume is seen as one of the factors which cause the onset of column breakthrough. Microbial growth retardation is due to the accumulation of metabolic products (i.e., sulfuric acid); and a lack of water and nutrient salts in the batch biofilter are other possible causes of column breakthrough.

Isolation and characterization of sulphur‐oxidizing Thiomonas sp. and its potential application in biological deodorization

Aims:  To isolate and characterize a sulphur‐oxidizing bacterial strain from activated sludge and to evaluate its potential application in biological deodorization.

Case Studies: Problems Solving in Fluidized Bed Waste Fuel Incineration

Fluidized bed combustion technology has been widely used as the new, flexible, multi-fuel boiler for waste combustion and energy recovery from low-grade fuels. However, problems such as low thermal efficiency, high emissions and bed agglomeration etc., are still encountered in operation of fluidized beds. Valuable experiences were gained from the two case studies recently conducted regarding wastes combustion in industrial-scale fluidized beds. In the first case, the performance of a fluidized bed combustor for energy recovery from oil sludge was evaluated during the commercial trials. Apart from the sludge characterization and bed material analysis, the combustion efficiency, solid flow balance, on-stack emission of CO, SOx , NOx were addressed, as well as the fluidization quality. Although the system was operated with good combustion efficiency (>99.9%), sulfur dioxide emission (>1,000ppm) was found to be substantially higher than the allowable discharge limit. It was recommended to increase limestone feed rate in order to meet the SO2 emission standard and subsequently, installation of a cyclone is suggested to remove the potential significant increase in ash and fine particles. The second case study focused on the bed agglomeration observed in a fluidized bed incinerator where burning blend of three wastes (i.e., carbon soot, biosludge and fuel oil) are involved. To understand the mechanisms and chemistry related, several analytical approaches are employed to identify the bed materials (fresh sand and degrader sand) and clinkers formed from full-scale incinerator tests. The formation of clinker is believed to follow the mechanism of partial melting and/or reactive liquid sintering. The effects of temperature and blending ratio are tested in a muffle furnace. Carbon soot is believed to be more susceptible than the other two fuels. Thermodynamic multi-Phase multi-Component Equilibrium (TPCE) calculations predict that the main low melting point species are predominant under oxidizing condition, suggesting that reducing conditions might be favorable to restrain the bed agglomeration. This study provides valuable information for the better understanding of the chemistry related to clinker formation; it also helps in developing methods for the control and possible elimination of the bed agglomeration problem for the design fuels.Copyright

Control of mercury vapor emissions from combustion flue gas

GOAL, SCOPE AND BACKGROUND Mercury (Hg) emission from combustion flue gas is a significant environmental concern due to its toxicity and high volatility. A number of the research efforts have been carried out in the past decade exploiting mercury emission, monitoring and control from combustion flue gases. Most recently, increasing activities are focused on evaluating the behavior of mercury in coal combustion systems and developing novel Hg control technologies. This is partly due to the new regulatory requirement on mercury emissions from coal-fired combustors to be enacted under the U.S. Title III of the 1990 Clean Air Act Amendments. The aim of this review work is to better understand the state-of-the-art technologies of flue gas mercury control and identify the gaps of knowledge hence areas for further opportunities in research and development. MAIN FEATURES This paper examines mercury behaviors in combustion systems through a comprehensive review of the available literature. About 70 published papers and reports were cited and studied. RESULTS AND DISCUSSION This paper summarizes the mechanisms of formation of mercury containing compounds during combustion, its speciation and reaction in flue gas, as well as subsequent mobilization in the environment. It also provides a review of the current techniques designed for real-time, continuous emission monitoring (CEM) for mercury. Most importantly, current flue gas mercury control technologies are reviewed while activated carbon adsorption, a technology that offers the greatest potential for the control of gas-phase mercury emissions, is highlighted. CONCLUSIONS AND RECOMMENDATIONS Although much progress has been achieved in the last decade, techniques developed for the monitoring and control of mercury from combustion flue gases are not yet mature and gaps in knowledge exist for further advancement. More R&D efforts are required for the effective control of Hg emissions and the main focuses are identified.