Bench-scale Unit Research Articles

Efficiency analysis of the electrocoagulation and electroflotation treatment of poultry slaughterhouse wastewater using aluminum and graphite anodes.

The application of electrocoagulation (EC) and electroflotation (EF) was investigated for the treatment of poultry slaughterhouse wastewater in a bench scale unit cell electrolyzer with different EC-to-EF ratios at current densities of 3, 9, and 15mAcm-2. The EC-to-EF ratio was controlled by current reversal using aluminum and graphite electrodes. The electrochemical treatment showed satisfactory removal efficiencies for Al coagulant loads greater than 51.8mgL-1. The 4/5 EC to EF ratio (69.1mgL-1 Al and 32.2NmLL-1 additional EF gas) and 3/5 (51.8mgL-1 Al/64NmLL-1 additional EF gas) presented the best results for the removal of COD (76-85%), color (93-99%), and turbidity (95-99%), with the additional benefit of reducing the electrode consumption and sludge disposal costs proportionally to the EC-to-EF ratio. The effects of the EC-to-EF ratio and the current density on efficiency of the electrochemical treatment for the removal of COD, apparent color, turbidity, TSS, TSD, and NH3-N were discussed in the light of the physicochemical and electrochemical processes underlying the removal mechanism for each parameter. In particular, the blow-off mechanism seems to play an important role in the NH3-N removal, whereas indirect electrooxidation mechanism accounts for a fraction of the soluble COD removal for the electrodes configuration used in the treatment.

Catalytic pyrolysis of crude glycerol over shaped ZSM-5/bentonite catalysts for bio-BTX synthesis

Ex-situ catalytic pyrolysis of crude glycerol for the synthesis of bio-based benzene, toluene and xylenes (bio-BTX) was performed in a tandem micro-reactor (TMR), a batch gram scale reactor and a continuous integrated bench scale unit using ZSM-5/bentonite extrudates. A bio-BTX yield of 8.1 wt.% (14.6% carbon yield) based on crude glycerol was obtained over the fresh catalysts (Cat-F) in the bench scale unit (crude glycerol feed rate of 200 g h−1, pyrolysis temperature of 520 °C and catalytic upgrading temperature of 536 °C). Catalyst activity was shown to be a function of the time on stream (TOS) and after 4.7 h the activity dropped with about 8%. After an oxidative regeneration step to remove coke, the activity of the regenerated catalysts (Cat-R1) was recovered to 95% of the original catalyst activity. After 11 reaction-regeneration cycles, the bio-BTX yield decreased to 5.4 wt.% (9.7% carbon yield) over Cat-R11. The fresh, deactivated and regenerated ZSM-5/bentonite catalysts were characterized in detail using nitrogen physisorption, XRD, ICP-AES, EA, TEM-EDX, TGA, NH3-TPD, pyridine-IR and solid MAS NMR. Coke (10.5 wt.% over Cat-D) was mostly deposited on ZSM-5 planes, and not only decreased the number of Lewis and Brönsted acid sites, but also blocked the pores, resulting in catalyst deactivation. Coke removal was effectively performed using an oxidative treatment. However, exchange of cations (e.g., Na) of the bentonite and possibly also from the crude glycerol feed with protons of ZSM-5 was observed, leading to irreversible deactivation. Furthermore, the layered structure of bentonite collapsed due to the removal of interlamellar water and dehydroxylation.

Advantages of confining the fountain in a conical spouted bed reactor for biomass steam gasification

A study was carried out on the advantages of inserting a fountain confiner in conical spouted beds for biomass steam gasification and the results (gas yield and composition, tar content, carbon conversion efficiency and H2 production) are compared with those obtained under conventional spouting regime. The experiments were carried out in a bench scale unit operating in continuous regime under the same gasification conditions in all the configurations (850 °C, S/B ratio of 2 and olivine as primary catalyst). The gaseous product was analyzed by on-line gas chromatography and micro-gas chromatography, and the tars by gas chromatography-mass spectrometry. The use of a fountain confiner allows enhancing process versatility, increasing gas velocity over the minimum spouting one, increasing the fountain height and reducing olivine particle size (enhanced fountain regime). Thus, as a result of a better gas-solid contact, tar content was reduced from 49.2 g Nm−3 without fountain confiner to 20.6 g Nm−3 under enhanced fountain regime, with the reduction of heavy PAHs being especially remarkable. In the same line, a great improvement in process conversion efficiency was attained under the enhanced fountain regime, with gas production reaching a value of 1.3 m3 kg−1 and that of H2 production 5.0 wt%.

A new structure of permeable pavement for mitigating urban heat island

The urban heat island (UHI) effect has been a great threat to human habitation, and how to mitigate this problem has been a global concern over decades. This paper addresses the cooling effect of a novel permeable pavement called evaporation-enhancing permeable pavement, which has capillary columns in aggregate and a liner at the bottom. To explore the efficiency of mitigating the UHI, bench-scale permeable pavement units with capillary columns were developed and compared with conventional permeable pavement. Criteria of capillary capacities of the column, evaporation rates, and surface temperature of the pavements were monitored under simulated rainfall and Shanghai local weather conditions. Results show the capillary column was important in increasing evaporation by lifting water from the bottom to the surface, and the evaporation-enhancing permeable pavement was cooler than a conventional permeable pavement by as much as 9.4°C during the experimental period. Moreover, the cooling effect of the former pavement could persist more than seven days under the condition of no further rainfall. Statistical analysis result reveals that evaporation-enhancing permeable pavement can mitigate the UHI effect significantly more than a conventional permeable pavement.

Effect of adsorbent heterogeneity on performance of a PSA process for bulk gas separation: a parametric simulation

The effect of adsorbent heterogeneity on the performance of an adiabatic pressure swing adsorption (PSA) process for separation of bulk C2H4 from an inert gas (helium) using the BPL carbon as the adsorbent was numerically estimated employing a detailed mathematical model for the process. The heterogeneous Toth model was used to describe the equilibrium adsorption isotherms for C2H4 and a linear driving force model was used to describe the adsorbate mass transfer rate in the simulation. The variations in the isosteric heat of adsorption of C2H4 with adsorbate loading was included in the simulation. The study indicates that adsorbent heterogeneity negatively affects the key process performance variables by increasing the bed size factor and reducing the helium recovery. Actual performance data for a PSA process using a bench or pilot scale unit is required to reliably estimate the complexity introduced by adsorbent heterogeneity.

Treatment of Typical Organic Pollutants in Textile Wastewater by Direct Contact Membrane Distillation

Direct contact membrane distillation technology was considered as a promising and efficient technology for the treatment of textile wastewater. In this study, hydrophobic polytetrafluoroethylene and polyvinylidene fluoride membranes for the treatment of selected model compounds of textile wastewater (e.g., phenol, aniline, and sulfanilic acid) were explored comparatively in a bench-scale direct contact membrane distillation technology test unit. The effect of various operational parameters including temperature, flow rate, and concentration on the rejection performance was investigated systematically. The results indicated that an increased feed temperature and a faster cross flow velocity contributed positively to the direct contact membrane distillation performance. Limited rejection for phenol and aniline was witnessed, which can be due to their relatively lower boiling point. A > 99% of sulfanilic acid rejection was obtained under the same conditions. Furthermore, the polytetrafluoroethylene membrane always presented enhanced performance compared with the polyvinylidene fluoride samples. In brief, the direct contact membrane distillation process could be potentially used as a promising technique for the treatment of textile wastewater.

Influence of the support on Ni catalysts performance in the in-line steam reforming of biomass fast pyrolysis derived volatiles

The influence the support has on the performance of Ni catalysts used in the reforming of biomass fast pyrolysis volatiles has been assessed. Accordingly, five catalysts have been prepared by wet impregnation method, namely Ni/Al2O3, Ni/SiO2, Ni/MgO, Ni/TiO2 and Ni/ZrO2. These catalysts have been characterized by nitrogen adsorption/desorption, X-ray fluorescence spectroscopy, temperature programmed reduction and X-ray diffraction techniques. The pyrolysis-reforming runs have been performed in a bench scale unit operating in continuous regime. The biomass (pine wood sawdust) pyrolysis step has been carried out in a conical spouted bed reactor at 500 °C, with the volatiles produced (a mixture of gases and bio-oil) being reformed in-line on the prepared catalysts in a fluidized bed reactor at 600 °C. Remarkable differences have been observed amongst the catalyst prepared, with Ni/Al2O3, Ni/MgO and Ni/ZrO2 being those leading to the most encouraging results, whereas Ni/TiO2 and, especially Ni/SiO2, having a limited reforming activity. The performance of each catalyst has been related to its properties determined in the characterization.

Experimental study of the adsorber performance in a multi-stage fluidized bed system for continuous CO2 capture by means of temperature swing adsorption

Most recently, a new reactor design of a continuous temperature swing adsorption (TSA) CO2 capture process has been proposed by the authors of this work. The reactor design incorporates interconnected multi-stage fluidized bed columns that act as adsorber and desorber in the TSA process. In the course of this work, a comprehensive parameter variation was performed in the TSA bench scale unit, to study the adsorber performance. Results show that by decreasing the operating temperatures in the adsorber to 42 °C, the dynamic CO2 loading of the adsorbent could be increased to 7.4 wt%. The flexibility of the process was investigated in respect to different CO2 concentrations of the treated flue-gas as well as different adsorber feed-gas velocities. Increasing the CO2 concentrations of the adsorber feed-gas leads to an increase of the CO2 capture rate and dynamic CO2 loading of the adsorbent. At the maximum CO2 concentration of 12 vol%CO2, the capture rate reached its maximum of 64 kgCO2·day−1. Furthermore, the flue-gas feeding rate could be increased to 0.87 m·s−1 which successfully demonstrated a turndown ratio of 2.7. However, large gas bubbles observed at adsorber feed-gas velocities exceeding 0.69 m·s−1 make insufficient gas-solids contact likely, which in turn explains a reduction of the dynamic CO2 loading of the adsorbent at these conditions. For high CO2 feeding rates, the capture efficiency dropped because of an insufficient heat transfer surface area and a limitation in the achievable sorbent circulation rates. In conclusion, the parameter study revealed a high operating flexibility of the TSA CO2 capture process and delivered a valuable basis for further improvements of the TSA reactor design.

Design, process simulation and construction of a 100 kW pilot-scale CO2 membrane rig: Improving in situ CO2 capture using selective exhaust gas recirculation (S-EGR)

Carbon capture and storage (CCS) from natural gas-fired systems is an emerging field and many of the concepts and underlying scientific principles are still being developed. Preliminary studies suggest this approach can boost the CO2 content in the feed gas up to 3 times compared to the ‘no recycle’ case (CO2 concentration increased to 18% vs. 6%), with a consequent reduction in flow to the post-combustion capture unit by a factor of three compared to conventional, non-S-EGR. For this project, Cranfield University developed a pilot-scale 100 kW CO2 membrane rig facility in order to investigate simultaneously EGR and S-EGR technologies, the latter being achieved by using a CO2 sweep air polymeric membrane. A bench-scale membrane rig has also been developed to investigate the permeability and selectivity of different polymeric membranes to CO2. Currently a small-scale polydimethylsiloxane (PDMS) membrane module is also being investigated to study its selectivity/permeability. The tests include exploring the performance improvement of the PDMS membrane using different operating conditions with a view to developing scale-up procedures for the membrane unit for the actual 100 kW pilot-scale rig.Process simulations were performed using Aspen Plus software to predict the behaviour of the pilot-scale rig using a model developed based on empirical parameters (i.e., mass transfer coefficient of CO2 through the membrane and permeance), measured in the bench-scale membrane test unit. The results show that CO2 concentrations of up to 14.9% (comparable to CO2 level in coal combustion) can be achieved with 60% EGR, with a 90% CO2 removal efficiency of the membrane units. However, the results generated with the membrane model in which specific permeance values to PDMS were applied, predicted concentrations of CO2 in flue gases up to 9.8% (v/v) for a selective recycle of 60%. The study shows that the S-EGR technique is an effective method that can provide similar conditions to that of a coal-fired power plant for the post-combustion capture system operating on natural gas-fired units, but also highlights the fact that more research is required to find more suitable materials for membranes that optimise the CO2 removal efficiencies from the flue gas.

Combination of lauroyl arginate ethyl and nisin for biofouling control in reverse osmosis processes

Lauroyl arginate ethyl (LAE) is a non-oxidizing biocide effective in controlling biofouling in reverse osmosis (RO) processes. However, the operating concentrations of LAE should be lowered to reduce the possible adsorption of LAE onto RO membranes and to reduce operational costs. This study investigated combinations of LAE with another non-oxidizing biocide, nisin, to overcome such practical limitation of LAE in a bench-scale RO unit operated with full recirculation with the model bacteria Staphylococcus aureus ATCC6538 and Pseudomonas aeruginosa PA14. Several combinations of LAE and nisin (e.g. 1mg/L LAE+2mg/L nisin) were more effective in killing bacteria than LAE or nisin treatment alone, possibly due to permeability synergy. Furthermore, in a bench-scale RO unit operated with full recirculation and model bacteria, flux declines were more effectively moderated by dosing LAE and nisin together compared with the dosing of LAE or nisin alone. LAE dosing alone showed rapid flux decline in the early operational period, while nisin dosing alone demonstrated the lowest flux at the end of the operation. In conclusion, combinations of LAE and nisin appear more effective to mitigate biofouling developed on membranes than LAE or nisin alone.

Laboratory to bench-scale evaluation of an integrated CO2 capture system using a thermostable carbonic anhydrase promoted K2CO3 solvent with low temperature vacuum stripping

An advanced post-combustion CO2 capture process with combined attributes of a thermostable carbonic anhydrase (CA) enzyme catalyst, low-enthalpy K2CO3 solvent, and vacuum stripping utilizing low exergy steam was evaluated from laboratory concept to application performance testing in an integrated 30 standard liters per minute gas flow bench-scale system operated for 500 h. Laboratory concept studies were performed using a wetted wall column to characterize solvent CO2 absorption kinetics and using a recirculating temperature loop to evaluate CA thermo-stability. Wetted wall column tests showed a dramatic 5-fold increase in CO2 mass transfer coefficient when combining 2 g/L CA with aqueous 23.5 wt% K2CO3 solvent. Further increasing the CA concentration resulted in a gradual increase in mass transfer coefficient until a performance plateau was observed beyond a 4 g/L CA dose. Operating temperature had limited impact on CO2 capture over the range 30–50 °C. Surface tension measurements of 23.5 wt% K2CO3 solvent exhibited a gradual decrease with increasing CA concentration. Thermo-stability tests in a temperature cycling loop designed to mimic the temperature swings between absorption and desorption showed that CA longevity could be extended by decreasing the total cycle time spent at high temperature. Parametric tests in the bench-scale unit resulted in a CO2 capture efficiency increase of 4.6-fold when increasing the CA concentration from zero to 2.5 g/L. Capture efficiency increased with higher reboiler duty (i.e. reboiler temperature) and lower absorber temperature. Tests with a 30 °C absorber temperature delivered >90% capture. Variation in solvent flow rate had little impact on capture efficiency because the reaction closely reached equilibrium at the top of the absorber. The integrated bench-scale system operated successfully for an accumulated 500 h under conditions of 40 °C absorber temperature and stripper at 35 kPa pressure with an approximate 77 °C stripper bottom temperature, delivering an average 84% CO2 capture with 23.5 wt% K2CO3-based solvent containing 2.5 g/L CA. Dissolved CA replenishment and conventional process controls were demonstrated as straightforward approaches to maintain system performance of this benign, low-temperature, CA-promoted process for CO2 capture.

Modeling, simulation and kinetic parameter estimation for diesel hydrotreating

The modeling and simulation of hydrotreating (HDT) reactors can provide relevant information about optimal operating conditions, reactor design and formulation of catalysts to achieve cleaner fuels. This study developed a phenomenological model to estimate the kinetic parameters for the HDT process using the design of experiments technique. The catalytic tests were carried out in a bench-scale unit with diesel as feedstock under similar conditions to those of the industrial units and commercial nickel-molybdenum on alumina (NiMo/γ-Al2O3) as catalyst. The reactor temperature was varied from 330 to 380°C and liquid hourly space velocity (LHSV) from 0.5 to 1.5h−1, keeping constant hydrogen to oil ratio (H2/oil) and pressure at 800stdm3/m3 and 90bar, respectively. The unknown parameters are estimated from experimental data by minimization of the unweighted least-squares function, using a non-linear optimization method (complex algorithm). The proposed model was able to reproduce different operating conditions with good adjustment and accuracy. Relative deviations below 4% for the experimental data and model prediction were achieved. Statistical parameters, p values, and confidence intervals confirmed the good quality of the estimated kinetic parameters. Internal diffusion resistances were present during hydrodesulfurization (HDS) and hydrodenitrogenation (HDN) reactions. The hydrogen consumption for HDS was higher than for HDN reaction. Finally, the proposed experimental design with 12 catalytic tests was satisfactory to obtain the desired results in a reliable way.

Effect of feeding frequency and organic loading rate on biomethane production in the anaerobic digestion of rice straw

World energy demand is growing and the negative effects of greenhouse gases (GHGs) and climate change are being felt more acutely. Accordingly, technologies that reduce GHG releases and produce renewable energy, such as anaerobic digestion (AD) with combined heat and power (CHP) systems, are potentially attractive for agricultural wastes, including rice straw (RS). Asia produces over 500 Mt of RS per year that is usually burned, wasting potential energy, causing air pollution and GHGs, and having negative health impacts. Therefore, making RS AD options more attractive is urgently needed. This paper shows biomethane (CH4) yields from infrequently fed RS AD units, which match better with RS harvest production cycles, can be very efficient at specific CH4 production without the need for co-digestion. Using Biomethane Potential (BMP) data to guide AD reactor conditions, five feeding frequencies (FFs) were operated for over 250days in bench-scale units, ranging from five feeds per seven days (5/7; frequent) to one feed per 21days (1/21; infrequent), using OLRs of 1gVS/L/d and 2gVS/L/d. Highest specific methane yields (148±6.3mL CH4/g VS/d) were observed at 1/21 FF and the lower OLR. In contrast, highest volumetric yields were seen for a FF of 1/7 at 2gVS/L/d (276±10.6mL CH4/L/d), although AD units failed at this OLR for FFs of 1/14 and 1/21 due to volatile fatty acids accumulation. This study shows RS AD is feasible without co-digestion, producing biogas that can be coupled with CHP technology to provide renewable energy. However, less frequent feeding regimes performed better than more frequent feeding regimes, suggesting infrequently-fed batch AD units may be a better option for biomethane production, especially for rural locations.

Enhancements in mass transfer for carbon capture solvents part II: Micron-sized solid particles

The mass transfer of CO2 into amine-based carbon capture solvents was improved with the addition of heterogeneous micron- and nano-sized particle additives. Enhancement in CO2 removal rate was determined in a stirred reactor with a flat steady gas-liquid interface and in a small packed-bed absorption column. The screening of several particle types in the stirred reactor indicated that carbon particles are best suited to enhance the rate of CO2 diffusion in 30wt.% monoethanolamine (MEA), and tests in the small packed-bed absorption column showed improved CO2 mass transfer in three solvents, MEA, piperazine (PZ), and hexanediamine (HDA), upon addition of nano-sized activated carbon particles. The enhancement of CO2 capture efficiency and KG increases with increasing solvent kinetics, in order of methyldiethanolamine (MDEA)<MEA<PZ<HDA, confirming the particle additives have a larger impact on kinetically faster, liquid-side diffusion limited, solvents. The combined benefits of the particle additives were then demonstrated on an absorption-desorption integrated bench-scale CO2 capture unit, in both MEA and the thermally stable advanced amine blend: 1-amino-2-propanol (A2P)/2-amino-2-methyl-1-propanol (AMP). The combined system translated to an overall 26% reduction in energy penalty for CO2 capture on the CAER Bench-scale unit.

Experimental comparison of two bench scale units for fast and intermediate pyrolysis

Comparison of different literature results for fast pyrolysis of biomass is difficult due to the variety in feedstock, process conditions, analyses, and detail of the provided data. The presented experiments represent a concerted effort to directly compare two bench scale units (10kgh−1) for fast and intermediate pyrolysis on the basis of the same set of biomass feedstock and the same pyrolysis reactor temperature. Hybrid poplar, wheat straw, a blend (hybrid poplar/wheat straw/forest thinnings) and beech wood have been used as feedstocks. Organic liquid yields for intermediate pyrolysis are 17–21 % and that of fast pyrolysis 26–51 %. The advantage of higher organic liquid yields from fast pyrolysis decreases with the ash content of biomass due to catalytically active minerals. It is concluded that the importance of the primary pyrolysis temperature level and the hot vapour residence time is significantly reduced with increasing ash content of the biomass. Carbon balances show that ash is not only increasing the total char yield as inorganic material, but also leads to a higher fraction of carbon material being retained in the char. Analyses of the liquid fractions reveal that pyrolytic degradation appears generally more evolved for the case of intermediate pyrolysis. Moreover, it was observed that there is a correlation between the ratio of CO to CO2 in the permanent gas after pyrolysis and the yield of organic liquids (dry basis). This correlation differs between the two processes and is suitable to predict the organic liquid yield based on permanent gas measurements. Three of the four feedstocks were supplied as part of a Round Robin Test organized by International Agency Bioenergy Task 34 ‘Direct thermal liquefaction’ and the obtained results can be directly compared even beyond the scope of this work.

Evaluation of the heat duty of catalyst-aided amine-based post combustion CO2 capture

The role of a solid acid catalyst in reducing the heat duty for solvent regeneration in post-combustion CO2 was elucidated for the first time using two types of solid acid catalysts (HZSM-5 and γ-Al2O3) in the desorber of a bench scale unit for CO2 capture with 5mol/L MEA solution at the catalyst bed temperature maintained at 85°C using 15SLPM of feed gas with composition of 15% CO2 in N2. The process performance was evaluated in terms of the cyclic capacity, absorption efficiency and heat duty. The results show that HZSM-5 and γ-Al2O3 facilitated CO2 desorption from a CO2-loaded MEA solution by increasing both the cyclic capacity and absorption efficiency, thereby lowering the heat duty. HZSM-5 (predominantly a proton donor catalyst) facilitated the carbamate breakdown by providing a free proton, and increased the absorption efficiency by 38% while reducing the heat duty by 42% as compared to the non-catalytic condition. γ-Al2O3 (predominantly an electron accepter catalyst) improved absorption efficiency by 23.6% and reduced heat duty by 30% over that of the non catalytic conditions. Based on energy distribution analysis, when a catalyst was used, sensible heat decreased while the heat of desorption and heat of vaporization had insignificant changes. A statistical analysis was performed to show which characteristics of the catalysts had the most influence on process performance by testing five catalytic conditions (HZSM-5, γ-Al2O3, HY, silica-alumina, and no catalyst) with widely different catalytic properties. The resulting correlations indicate that the acid strength of the catalyst had the most important role in facilitating CO2 desorption from a CO2-loaded MEA solution followed by the Brønsted acid/Lewis acid (B/L) ratio.

A multi-stage fluidized bed system for continuous CO2 capture by means of temperature swing adsorption – First results from bench scale experiments

Most recently, the authors of this work introduced a reactor design for a new post-combustion CO2 capture process that is based on continuous temperature swing adsorption. The system comprises two interconnected multi-stage fluidized bed columns that enable counter-current contact of adsorbent and gas streams in the adsorption and desorption step. The system further allows for effective heat management through indirect heat exchange with the fluidized adsorbent material in each stage. Based on the proposed reactor design, a fully integrated bench scale unit (BSU) has been constructed and put into operation to study the process experimentally. The BSU is designed to capture 90% of the CO2 present in synthetic flue gas mixtures at a maximum capture rate of 35kgCO2,capt per day using amine-functionalized adsorbent materials. First results obtained from continuous CO2 capture experiments showed that the design capture targets can be reached with this unit. Despite the fact that only five fluidized bed adsorption stages were implemented, CO2 was not detected at the adsorber outlet during the initial minutes of the experiments, indicating that gas-solids contact is sufficient and adsorption kinetics are fast. However, in the initial CO2 capture experiments it was not possible to achieve the desired operating temperatures within the desorber and the CO2 capture capacity of the unit seemed to be limited by heat transfer. Installation of heat exchangers with a higher surface area entailed an improved capture performance. It was thus concluded that performance limitations of the TSA BSU lie within its heat transfer properties rather than within the prevailing adsorption conditions.

Integrated Bench-Scale Parametric Study on CO2 Capture Using a Carbonic Anhydrase Promoted K2CO3 Solvent with Low Temperature Vacuum Stripping

A bench-scale unit was fabricated and used to investigate use of carbonic anhydrase (CA) promoted K2CO3 solvent as an option for CO2 capture from coal-fired power plants. Bench-scale parametric tests were performed at various CA concentrations, solvent flow rates, and reboiler duties. The CO2 capture efficiency significantly increases, and regeneration energy requirement decreases, with increasing CA concentrations up to 2.5 g/L, with capture performance leveling off at higher enzyme doses (up to 4 g/L). Thus, at higher enzyme doses, the capture efficiency is equilibrium rather than kinetically controlled at the top of absorber, when using solvent regenerated via vacuum stripping at high (>35%) lean carbonate to bicarbonate (CTB) conversion levels, which limits the driving force for CO2 absorption. The CO2 capture efficiency also increases when reboiler duty was increased from 0.85 to 1.1 kW, although this also increases the regeneration energy penalty. In contrast, the effect of solvent flow rate on CO2 capture efficiency is less pronounced. Further improvements to the CO2 capture process using CA promoted K2CO3 solvent with low temperature vacuum stripping could be potentially advanced by lowering vacuum pressure, improving strategies for increasing rich CTB conversion (e.g., advanced packing column and optimized L/G ratio), and decreasing absorption temperature.

Experimental study on capture of carbon dioxide and production of sodium bicarbonate from sodium hydroxide

Global warming due to greenhouse gases is an issue of great concern today. Fossil fuel power plants, especially coal-fired thermal power plants, are a major source of carbon dioxide emission. In this work, carbon capture and utilization using sodium hydroxide was studied experimentally. Application for flue gas of a coal-fired power plant is considered. Carbon dioxide, reacting with an aqueous solution of sodium hydroxide, could be converted to sodium bicarbonate (NaHCO3). A bench-scale unit of a reactor system was designed for this experiment. The capture scale of the reactor system was 2 kg of carbon dioxide per day. The detailed operational condition could be determined. The purity of produced sodium bicarbonate was above 97% and the absorption rate of CO2 was above 95% through the experiment using this reactor system. The results obtained in this experiment contain useful information for the construction and operation of a commercial-scale plant. Through this experiment, the possibility of carbon capture for coal power plants using sodium hydroxide could be confirmed. Keywords: Carbon Capture, Carbon Utilization, Sodium Bicarbonate

Release behavior of Hg, Se, Cr and As during oxy-fuel combustion using Loy Yang brown coal in a bench-scale fluidized bed unit

This experimental study investigates, for the first time, the fate of trace elements (Hg, Se, Cr and As) during combustion of Loy Yang brown coal in a large bench-scale oxy-fuel fluidized bed. The results indicated that up to 70%, 28%, 7% and 2% of total As, Cr, Se, and Hg respectively were retained in the collected ash at 15–30% oxygen concentration in the oxy-fuel combustion atmosphere at around 850°C. With the increase in oxygen concentration in oxidant, the Hg adsorption in ash was found to decrease. Compared to bed ashes, higher Hg adsorption was observed in fly ashes containing higher carbon content. Therefore, a higher level of Hg capture is expected in oxy-fuel circulating fluidized bed combustion due to the circulating materials having higher carbon content.