Bench-scale Fixed-bed Reactor Research Articles

Release of K, Cl, and S during combustion and co-combustion with wood of high-chlorine biomass in bench and pilot scale fuel beds

Studies of the release of critical ash-forming elements from combustion of biomass are typically conducted with small sample masses under well controlled conditions. In biomass combustion on a grate, secondary recapture and release reactions in the fuel-bed may affect the overall release and partitioning of these elements. Earlier work by the authors on the release of K, Cl, and S from a high-chlorine biomass (corn stover) in a lab-scale setup is, in the present work, supplemented with novel results from a bench-scale fixed bed reactor and a 100kW moving grate pilot facility. The results from the bench-scale reactor indicate that S and K release are not significantly affected by secondary reactions, while Cl is partly recaptured by secondary reactions in the char. A linear increase in K-release was observed from 50% at 906°C to almost 80wt.% at 1234°C when firing only corn stover. A similar release profile was observed for Cl, from 65% to nearly 100%. Complete release of S was achieved at 1234°C with a linear increase from 70% at 906°C. Co-combustion of corn stover with low-Cl wood chips served to increase the bed temperature, resulting in complete and close to complete release of Cl and S, respectively. An increase in the relative K-release was observed when increasing the wood chip fraction from 40% to 100% (energy basis). Pilot scale flue gas results indicate that the share of Cl released as HCl decreases towards 0% as the share of wood chips is increased towards 100%. Hence, co-combustion of corn stover with wood chips is expected to decrease the absolute release of KCl due to the lower feedstock quantity of Cl, however, increase the relative release of Cl as KCl.

Hydrogen from acetic acid as the model compound of biomass fast-pyralysis oil over Ni catalyst supported on ceria–zirconia

Hydrogen production from catalytic steam reforming of model compound acetic acid of bio-oil was investigated under atmospheric pressure in a bench-scale fixed-bed reactor and a series of Ni catalysts supported on ceria–zirconia were prepared via co-precipitation with varying contents of Ni and Ce loading. Simultaneously, effects of reaction temperature, and molar ratio of steam to carbon fed, liquid hourly space velocity (LHSV) were also explored. The results indicated that the 12Ni/7.5Ce-Zr-O catalyst was superior to other catalysts with different Ni and Ce loading. At T = 650 °C, S/C = 3, LHSV = 2.8 h−1, the reaction over Ni catalyst supported on ceria–zirconia turns out that the highest activity and the maximum hydrogen selectivity of 83.4% and the minimum methane selectivity of 0.39% are attained. Besides, Ni catalyst supported on ceria–zirconia shows good stability during 25 h continuous reaction without any deactivation.

Kinetics of thermal hydrocracking of heavy oils under moderate hydroprocessing reaction conditions

Thermal hydrocracking (non-catalytic) of a heavy oil residue was studied in a bench-scale fixed-bed reactor unit. The reaction temperature and the ratio of total mass flow to inert material volume were varied from 380 to 420°C and from 0.23 to 0.65gTcmSiC-3h-1 respectively, at constant hydrogen-to-oil ratio (890m3/m3) and pressure (100kg/cm2). The reactor was loaded with silicon carbide as inert material. The results from the simulated distillation of the feed and of the products were used to calculate conversion of vacuum residue and the yield of each specific fraction (vacuum gasoil, middle distillates, naphtha and gases). The lumping approach was used to study the kinetics of the hydrocracking reaction. The results confirm that hydrocracking reactions proceed by cascade mechanism from the heavier fractions to the lighter fractions. Naphtha does not hydrocrack to form gases at the operating conditions studied. The reaction order that better fits the experimental data of vacuum residue conversion is two with activation energy of 42kcal/mol.

Hg Removal Characteristics of Noncarbon Sorbents in a Fixed-Bed Reactor

This research targeted the development of a low-cost, high-effidenry sorbent for mercury capture in flue gas. Six non-carbon-based carriers and various impregnating substances including Nal, CuCl 2 , CuBr, and FeCl 3 were investigated in this study. The performances of the prepared sorbents were tested in a bench-scale fixed-bed reactor at 140 °C in N 2 atmosphere. Some sorbents demonstrated the mercury capture capabilities similar to that of a commercial active carbon sorbent (Norit Darco LH).

Experimental and Modeling Study of Continuous Catalytic Transesterification to Biodiesel in a Bench-Scale Fixed-Bed Reactor

A 500 h endurance test of continuous catalytic transesterification to biodiesel was conducted in a bench-scale fixed-bed reactor. A designed cylinder shape of KF/Ca–Mg–Al hydrotalcite catalyst was stable through the test with high catalytic activity and mechanical strength, converting palm oil to biodiesel with a conversion of more than 95%. Conditions effects on transesterification under relative high pressure (1.0 MPa) were investigated and a one-dimensional heterogeneous model of a fixed-bed reactor was developed to describe the reaction-mass transfer behaviors of continuous catalytic transesterification in a bench-scale fixed-bed reactor. With the given reactor size, optimum conditions were proposed as a LHSV (liquid hourly space velocity) of 0.76–0.25 h–1, molar ratio of methanol-to-oil of 9.16–13.7, and temperature of 338–347 K.

Calcium Looping Process (CLP) for Enhanced Steam Methane Reforming

Carbon dioxide (CO2) capture using calcium-based sorbents for post- and pre-combustion applications has the potential to become a viable technology. When applied to a pre-combustion system, the presence of calcium sorbents facilitates process intensification by combining the CO2 removal step with the reactions generating the fuel gas [syngas, hydrogen (H2), etc.] in a single step. Such a process is also capable of producing a high-purity sequestration-ready CO2 stream. The enhanced steam methane reforming (SMR) using the Calcium Looping Process (CLP) has been investigated in this work. The CLP comprises three reactors: the carbonation reactor or carbonator where the thermodynamic constraint of the reforming and water gas shift (WGS) reaction is overcome by the incessant removal of the CO2 product resulting in the production of high-purity H2, the calciner where the calcium sorbent is regenerated and a sequestration-ready CO2 stream is produced, and the hydrator where the regenerated sorbent is reactivated to improve its multicyclic performance. The exothermic carbonation and WGS reaction convert the highly endothermic SMR into a heat neutral process, thus reducing the temperature of reforming from >900 to 650 °C. Experiments conducted using methane in a bench-scale fixed bed reactor have indicated that high purity H2 (∼95–99%, dry basis) can be produced using the CLP with in situ CO2 capture. Attempts to maintain the sorbent reactivity over multiple cycles using hydration have yielded encouraging results.

Use of Fe2O3-Containing Industrial Wastes As the Oxygen Carrier for Chemical-Looping Combustion of Coal: Effects of Pressure and Cycles

Chemical-looping combustion (CLC), employing metal oxide(s) as the oxygen carrier for solid fuels (such as coal and biomass) combustion, is of growing interest thanks to its low cost of CO2 capture and the high system conversion efficiency. In this work, Fe2O3-containing wastes from the steel industry were applied as the oxygen carrier for chemical looping combustion with a Chinese bituminous coal in a bench-scale fixed-bed reactor. The performance of Fe2O3-containing industrial wastes was estimated with comparison to that of two other commercial iron ores (MAC iron ore from Australia and CVRD iron ore from Brazil). Effects of the operating pressure of the system (from 0.1 to 0.5 MPa) and cycle number (0–20) on the performance of the oxygen carriers were extensively studied, in terms of overall gas composition, carbon conversion, and its conversion rate. The Fe2O3-containing industrial wastes were remarkably sensitive with the operating pressure, as more pyrolysis gases and char gasification products were converted under higher pressure leading to higher concentration of CO2 and lower concentrations of CO and CH4. The elevated pressure also increased the carbon conversion and the overall reaction rate. The reactivity and porosity of the Fe2O3-containing industrial wastes under atmospheric pressure were notably enhanced by the reduction cycles, giving the concentration of 99% CO2 and the carbon conversion 81.41% after 20 cycles. Comparatively, the Fe2O3-containing industrial wastes exhibited better performance as oxygen carrier than the other two iron ores (MAC iron ore and CVRD iron ore), while the two iron ores behaved similarly to the Fe2O3-containing industrial waste with regard to the variation of operating pressure and cycles. It could be concluded that the Fe2O3-containing industrial wastes would be the outstanding oxygen carrier for chemical-looping combustion of coal over the other two iron ores.

Gas-phase elemental mercury removal by novel carbon-based sorbents

To develop cost-effective carbon-based sorbents used in gas-phase elemental mercury removal, the performance of commercial bamboo charcoal (BC) produced from renewable bioresource of bamboo and modified BC was investigated with a bench-scale fixed-bed reactor. The simple impregnation method was used to modify the BC using ZnCl 2, NH 3·H 2O and HNO 3 separately. BET, XPS, elemental analysis and FT-IR were used to determine the pore structure and surface chemistry of the sorbents. The characterization of the physical and chemical properties of sorbents in relation to Hg 0 adsorption capacity provided important information on the Hg 0 adsorption mechanism. This suggested that the modified BCs have excellent adsorption potential for elemental mercury at a relatively higher temperature of 140 °C except for the NH 3·H 2O impregnated BC. The amount of Hg 0 absorbed depends on the concentration of impregnant used. The impregnation has increased the sorbents’ active sites for mercury adsorption and the specific reaction mechanism has been further analyzed.

OPTIMIZATION STRATEGY FOR A FISCHER-TROPSCH SYNTHESIS BENCH-SCALE REACTOR: EFFECT OF OBJECTIVE ELEMENTS ON OPTIMIZATION PERFORMANCE

A mathematical model of Fischer-Tropsch synthesis over an iron-based catalyst was developed for a bench-scale fixed-bed reactor. Parametric sensitivity analysis found that inert fraction, H2/CO ratio, and inlet and wall temperatures are effective manipulated variables. Three optimization strategies, with different combinations of objective functions and manipulated variables, were suggested to optimize conditions using the genetic algorithm, and it was shown by the comparison that maximization of CO conversion and C5+ productivity guaranteed both maximum production by amount of catalyst and sustainable operation by maintaining peak temperatures below an allowable limit, even without including maximum temperature as an objective function.

Premium quality renewable diesel fuel by hydroprocessing of sunflower oil

Hydroprocessing of neat sunflower oil was carried out at 360–420 °C and 18 MPa over a commercial hydrocracking catalyst in a bench scale fixed bed reactor. In the studied experimental range, products consisted exclusively of hydrocarbons that differed significantly in composition. While the concentration of n-alkanes exceeded 67 wt.% in the reaction products collected at 360 °C, it decreased to just 20 wt.% in the product obtained at 420 °C. Consequently, the fuel properties of the latter product were very similar to those of standard (petroleum-derived) diesel fuel. Particularly, it exhibited excellent low-temperature properties (cloud point −11 °C; CFPP −14 °C). Reaction products obtained at 400 and 420 °C were blended into petroleum-derived diesel fuel in three concentration levels ranging from 10 to 50 wt.% and the fuel properties of these mixtures were evaluated. Diesel fuel mixtures containing the product of sunflower oil hydrocracking at 420 °C showed very good low-temperature properties including cloud point (−8 °C) and CFPP (−15 °C) that was further lowered to −25 °C due to addition of flow improvers.

Influence of the catalytic support on the industrial Fischer–Tropsch synthetic diesel production

A range of cobalt catalysts supported on alumina, titania, bentonite and the newer silicon carbide was examined for catalytic activity and product selectivity in the Fischer–Tropsch reaction. Experiments were carried out on a bench scale fixed bed reactor. TPR results showed that Co/TiO 2 and Co/bentonite were easier to reduce than Co/Al 2O 3 and Co/SiC based catalyst. Particle size depended on nature of support and specific area. Catalyst Co/SiC provided good catalytic results at temperatures higher than 235 °C whereas Co/bentonite showed high catalytic activity at low temperatures. However, Co/bentonite was found to enhance the formation of oxygenated compounds. Hydrocarbon distribution was influenced by the support. Co/Al 2O 3 shifted to lighter hydrocarbon than Co/TiO 2 and Co/bentonite. Co/SiC yielded to higher molecular weight hydrocarbons products distribution as compared with Co/alumina catalyst.

Influence of alkali promoters on synthetic diesel production over Co catalyst

The effects of the addition of alkali metal and alkali-earth metal promoters over cobalt based catalyst on Fischer–Tropsch activity and on hydrocarbon product distribution were studied. The influence of promoters on the reducibility and cobalt particle size was studied by different techniques, including N2 adsorption, X-ray diffraction, temperature-programmed reduction, temperature-programmed desorption and acid–base titrations. Experiments were carried out on a bench scale fixed bed reactor and catalysts were prepared by incipient wetness impregnation. It was observed that the addition of small amounts of these promoters (0.5wt%) improved the cobalt oxide reducibility by reducing the formation of cobalt aluminate species. The interaction between cobalt oxide and promoted support was reduced and larger cobalt oxide particles were formed on the surface. A positive correlation between basicity and particle size was observed with the exception of K promoted sample. Furthermore, CO conversion and C5+ selectivity were found to be also influenced by the addition of promoters. An enhanced dispersion that provides abundant catalytically active sites was observed on promoted catalyst. The addition of Ca to the cobalt based catalyst greatly improved the diesel selectivity. However Ca promoted catalyst yield a higher amount of methane at 242°C than the Na sample.

Fischer–Tropsch diesel production over calcium-promoted Co/alumina catalyst: Effect of reaction conditions

The effects of reaction conditions on the Fischer–Tropsch activity and product distribution of an alkali-earth metal promoted cobalt based catalyst were studied. The influence of the promoter on the reducibility and cobalt particle size was studied by different techniques, including N 2 adsorption, X-ray diffraction, temperature-programmed reduction, temperature-programmed desorption and acid–base titrations. Experiments were carried out on a bench-scale fixed bed reactor and catalysts were prepared by incipient wetness impregnation. It was observed that addition of a small amount of calcium oxide as a promoter (0.6 wt.%) improved the cobalt oxide reducibility and reduced the formation of cobalt-aluminate species. A positive correlation between basicity and particle size was observed. In terms of FTS results, CO conversion and C 5 + selectivity were found to be enhanced by the addition of this promoter. It was important to note that the addition of calcium shifted the distribution to mainly C 16–C 18 hydrocarbons fraction, which could be greatly considered for a diesel formulation. Furthermore, the variation of the reaction conditions seemed to influence product distribution in a lesser extent than unpromoted catalyst. Also, a displacement of hydrocarbon distribution to higher molecular weight with decreasing space velocity and temperature was observed. Moreover, the addition of calcium to the cobalt based catalyst was found to greatly maintain selectivity to C 5 + for a wide range of H 2/CO molar ratios.

Catalytic pyrolysis of Arab Heavy residue and effects on the chemistry of asphaltene

In an attempt to understand the changes in asphaltene structure during pyrolysis, hydrothermal reactions were performed on Arab Heavy atmospheric residue using FCC catalyst, ZSM-5 zeolite, hydrocracking catalyst (HC-1) and hydroprocessing (NiMo) catalyst in a bench-scale fixed bed reactor. The effect of four different catalysts on pyrolysis reactions showed that the cracking of residue is affected by catalyst type. All four catalysts used in this study are good for achieving hydrocracking selectivity and were found to be effective in conversion of large asphaltene molecules into smaller moieties. Detailed analyses of asphaltenes were carried out using IR, NMR and HP-GPC techniques. These analyses indicated that the mean molecular weight distribution of residue and asphaltenes decreased after pyrolysis reactions indicating the breaking up of larger molecules. The NMR showed the increase of aromatics carbon and aromatic proton contents in asphaltene obtained from all reactions except when using ZSM-5 catalyst. IR analysis showed that there were significant changes in the chemistry of asphaltenes after the pyrolysis of residue. The pyrolysis reactions were performed and the following reaction conditions were maintained; reaction time: 1 h, temperature 400 °C, feed amount (Arab Heavy residue): 10 g, catalyst amount: 5% of feed (0.5 g) and hydrogen gas pressure: 900–1300 psi. The compositional data generated by this work will enhance the understanding of asphaltene structure that will be of great value in improved refining practices, geochemical studies and in assessing performance properties of asphalt.

Regenerable Multifunctional Sorbent Development for Sulfur and Chloride Removal from Coal-Derived Synthesis Gas

A large number of components in coal form corrosive and toxic compounds during coal gasification processes. These contaminants have to be reduced to the parts-per-million range to use the fuel gas in an integrated gasification combined cycle. Even more stringent requirements are expected if the fuel gas is to be used in fuel cell or chemical production applications. Impurity removal may be even more cost-effective if multiple impurities can be removed in a minimum number of steps. To accomplish this goal, a regenerable sorbent capable of removing both hydrogen chloride (HCl) and hydrogen sulfide (H2S) was investigated. The results of the thermogravimetric analyzer tests and bench-scale fixed-bed flow reactor tests conducted with the sorbent to evaluate the feasibility of both H2S and HCl sorption will be discussed in this paper.

Improvement of the stability of a ZrO 2-modified Ni–nano-CaO sorption complex catalyst for ReSER hydrogen production

A Ni–nano-CaO sorption complex catalyst was modified with ZrO 2 to improve its stability for use in hydrogen production from steam methane reforming (SMR). Nano-ZrO 2 was introduced into a support containing nano-CaCO 3 and Al 2O 3. The sorption complex catalyst, ZrO 2–Ni–nano-CaO, was prepared by infusing Ni into the ZrO 2–nano-CaO support, followed by calcination. The catalyst was evaluated with a bench-scale fixed bed reactor under the following reaction conditions: a temperature of 600 °C, a steam–carbon mole ratio of 4:1, a gas hourly space velocity of 1800 h −1, and a regeneration temperature of 800 °C. The reaction was performed under an atmosphere of nitrogen. The ZrO 2-modified sorption complex catalyst could achieve 20 cyclic runs of ReSER hydrogen production, while the sorption complex catalyst without the ZrO 2 modification rapidly deactivated after three cyclic runs. Brunauer–Emmer–Teller analysis showed that the catalyst surface area of the new catalyst had increased. Furthermore, the addition of ZrO 2 could prevent the formation of NiAl 2O 4 in the sorption complex catalyst, which we believe to be the main cause of the improvement in the catalyst stability.

Chemical-Looping Combustion of Coal with Metal Oxide Oxygen Carriers

The combustion and reoxidation properties of direct coal chemical-looping combustion (CLC) over CuO, Fe2O3, Co3O4, NiO, and Mn2O3 were investigated using thermogravimetric analysis (TGA) and bench-scale fixed-bed flow reactor studies. When coal is heated in either nitrogen or carbon dioxide (CO2), 50% of weight loss was observed because of partial pyrolysis, consistent with the proximate analysis. Among various metal oxides evaluated, CuO showed the best reaction properties: CuO can initiate the reduction reaction as low as 500 °C and complete the full combustion at 700 °C. In addition, the reduced copper can be fully reoxidized by air at 700 °C. The combustion products formed during the CLC reaction of the coal/metal oxide mixture are CO2 and water, while no carbon monoxide was observed. Multicycle TGA tests and bench-scale fixed-bed flow reactor tests strongly supported the feasibility of CLC of coal by using CuO as an oxygen carrier. Scanning electron microscopy (SEM) images of solid reaction products indicated some changes in the surface morphology of a CuO−coal sample after reduction/oxidation reactions at 800 °C. However, significant surface sintering was not observed. The interactions of fly ash with metal oxides were investigated by X-ray diffraction and thermodynamic analysis. Overall, the results indicated that it is feasible to develop CLC with coal by metal oxides as oxygen carriers.

Influences of minerals transformation on the reactivity of high temperature char gasification

Two Chinese coals were used in this study and coal chars were prepared at different temperatures. High temperature gasification of coal chars with CO 2 was investigated in a bench scale fixed-bed reactor and the transformations of minerals from these two coals were also studied from 1100 to 1500 °C. Mineral matters produced at different temperature and ash generated after gasification were collected and analyzed by XRD and FTIR. It was found that the iron oxides were only catalytic mineral matters existing at high temperature. And gasification behaviors above ash melting temperature were different for different mineral composition, especially the content and form of iron oxide, which not only accelerates the gasification reaction, but also reduces the influence caused by melting minerals.

Hydrogen production from bio-oil aqueous fraction with in situ carbon dioxide capture

This paper presents the results of the investigation on steam reforming bio-oil aqueous fraction coupled with in situ carbon dioxide capture for hydrogen production. Experiments were carried out in a bench-scale fixed-bed reactor with calcined dolomite as the sorbent. The effects of temperature and water to bio-oil ratio on hydrogen production are reported. In the presence of calcined dolomite, maximum hydrogen yield of 75% was obtained among without sorbent, with CaO and with calcined dolomite at 600 °C, whereas hydrogen content was 83%, a little lower than that of 85% when CaO was used. Hydrogen content varies little at different water to bio-oil ratios and hydrogen yield was the greatest at the water to bio-oil ratio of 1:1. After regeneration of the sorbent, hydrogen content was back to the initial level but the hydrogen yield dropped.

Removal of Vapor-Phase Elemental Mercury by Oil-Fired Fly Ashes

The vapor-phase elemental mercury removal efficiency of the heavy-oil-fired fly ash (HOFA) discharged from heavy-oil-fired power plants was first tested to evaluate its suitability as a base material for the development of a low-cost novel sorbent to capture vapor-phase mercury in coal combustion flue gases. Raw, CO2-activated, and sulfur-impregnated HOFAs were prepared and tested. The morphology, specific surface area, particle size, and chemical composition were analyzed for the tested samples. A bench-scale fixed-bed reactor system was used to determine the mercury removal efficiencies of the HOFAs and commercially available activated carbons for comparison. The CO2-activated HOFA showed slightly higher mercury removal efficiency than the raw HOFA, resulting from the increase of active sorption sites by the enlarged surface area. The mercury removal efficiencies of the HOFAs modified by the sulfur impregnation process significantly increased with increasing sulfur content and were comparable to those o...