Bed Of Silica Sand Research Articles

Experimental Study of Sinkhole Propagation Induced by a Leaking Pipe Using Fibre Bragg Grating Sensors.

Sinkhole formation caused by leaking pipes in karst soluble rocks is a significant concern, leading to infrastructure damage and safety risks. In this paper, an experiment was conducted to investigate sinkhole formation in dense sand induced by a leaking pipe. Fibre Bragg grating (FBG) sensors were used to record the strain. A balloon was gradually deflated within a bed of wet silica sand to create an underground cavity. Eighteen FBG sensors, with a wavelength range between 1550 nm and 1560 nm, were embedded horizontally and vertically in the physical model at different levels to monitor deformation at various locations. A leaking pipe was installed to induce the collapse of the formed arch above the cavity. The strain measurements suggested the following four phases in the sinkhole formation process: (1) cavity formation, (2) progressive weathering and erosion, (3) catastrophic collapse, and (4) subsequent equilibrium conditions. The results showed differences in the strain signatures and distributions between the horizontal and vertical measurements. During the critical phase of the sinkhole collapse, the horizontal measurements primarily showed tension, while the vertical measurements indicated compression. This investigation demonstrates the effectiveness of FBGs as advanced monitoring tools for sinkhole precursor identification. The study also suggests using FBGs in geotechnical monitoring applications to improve the understanding and mitigation of sinkholes and related geohazards.

Efficiency of Backwashing in Removing Solids from Sand Media Filters for Drip Irrigation Systems

Sand media filters are especially recommended to prevent emitter clogging with loaded irrigation waters, but their performances rely on backwashing. Despite backwashing being a basic procedure needed to restore the initial filtration capacity, there is a lack of information about the solid removal efficiency along the media bed depth. An experimental filter with a 200 mm silica sand bed height was used to assess the effect of two operation velocities (30/45 and 60/75 (filtration/backwashing) m h−1) and two clogging particles (inorganic sand dust and organic from a reclaimed effluent) on the efficiency of backwashing for removing the total suspended solids retained in different media bed slices. The average solid removal backwashing efficiency was greater with organic particles (78%) than with inorganic ones (64%), reaching its maximum at a 5–15 mm bed depth. A higher operation velocity increased the solid removal efficiency by 16%, using organic particles, but no significant differences were observed with inorganic particles. The removal efficiencies across the media bed were more uniform with organic particles (63–89%) than with inorganic (40–85%), which makes it not advisable to reduce the media height when reclaimed effluents are used. This study may contribute to future improvements in sand media filter design and management.

Experimental analysis of a novel confined bed system for thermal energy storage

Thermal energy storage (TES) is an essential subsystem for the uniform operation of concentrated solar power (CSP) plants. A sensible heat storage system based on a novel confined bed of small particle size granular material was experimentally evaluated. The bed of regular silica sand was mechanically confined between a bottom and a top perforated plate gas distributor, to prevent the motion of particles even for gas velocities above the minimum fluidization velocity of the solids, operating the bed under a fixed or packed bed regime. The discharge process of the confined bed was experimentally analyzed, preheating the granular material at 300–320 °C and supplying various volumetric flow rates of cold air through the bottom distributor. During the discharge process, the temperature of the bed was segregated, obtaining a high temperature zone at the top region and a low temperature zone at the bottom region of the bed. These regions are separated by a thermocline that evolves in the upwards direction as the discharge process progresses. The temperature distribution in the bed and the total pressure drop of the TES system were monitored during the tests. For all cases, the temperature of the bed at different heights evolves as in a fixed bed, confirming the proper confinement of the granular material. The thermocline velocity depends on the volumetric flow rate of cold air, obtaining a discharge time for the temperature located at the exit of the system of around 50, 40, and 30 min for air volumetric flow rates of 700, 900, and 1100 Nlpm, respectively, using 55 kg of regular silica sand as granular material. The experimental results of the evolution and distribution of temperature in the bed were compared with an analytical model of the process for a fixed/packed bed regime of operation, resulting in a good agreement between the experimental measurements and the numerical predictions.

The use of kaolin and dolomite bed additives as an agglomeration mitigation method for wheat straw and miscanthus biomass fuels in a pilot-scale fluidized bed combustor

Renewable biomass fuels are frequently used for power generation. Biomass ash causes bed agglomeration in fluidized bed boilers due to the formation of alkali silicate melts. Very few prior studies have tested dolomite and kaolin bed additives for agglomeration mitigation with agricultural biomasses. In this work, pelletized miscanthus and wheat straw were tested in a pilot-scale 65kWth fluidized bed combustor with varying dosages of dolomite and kaolin on a silica sand bed. Neither additive improved defluidization time with wheat straw, whereas additive use at all dosages prevented bed defluidization with miscanthus. Agglomerates were studied through a novel, detailed SEM/EDX analysis across structural features. SEM/EDX analysis presented evidence of chemical reaction between both additives and fuels. Potassium in ash migrated into kaolin particle at depths of up to 60 μm. With dolomite, calcium and magnesium raised melt temperatures. Thermochemical modelling of the ash and additive combinations predicted that additive use would substantially reduce ash melt formation. It is proposed that the wheat straw pellet acted as a “ready-made” agglomerate structure due to release of molten ash to the pellet surface which bed material then sticks to, hence the lack of change to defluidization time regardless of additive use. Future studies into this behaviour would improve additive use.

The combustion of waste, industrial glycerol in a fluidised bed

Large quantities of glycerol are produced as a somewhat useless, industrial by-product, when producing biodiesel. Thus, the combustion of this waste (containing glycerol, less volatile, non-glyceride oils, ash and water) in a fluidised bed has been investigated. The fuel entered the bottom of the bed (on its axis) as bubbles of vapour, which rose up the bed, surrounded by bubbles of fluidising air. While more difficult to burn than medicinal glycerol, continuous burning of the waste was sustained for a total of ∼ 4 h in a bed of silica sand (500 – 710 μm) at 750°C, fluidised by air. However, after ∼ 4 h, fluidisation ceased, because the silica sand agglomerated into globules a few mm wide, probably cemented by a eutectic of K2SO4 and KOH; this industrial glycerol did originally contain potassium and sulphate ions, from its manufacture. Under similar conditions, when burning the waste in a bed of fluidised alumina (Al2O3) particles (355 – 425 μm), the bed de-fluidised after almost ½ h, and then sintered into a cake, again possibly cemented by the potassium salts K2SO4 and KOH. As for combustion, there was evidence that waste glycerol can be burned in a fluidised bed of SiO2 particles autonomously, without supplying heat. In such a fluidised bed, it appeared that glycerol vapour, inside a bubble, first decomposes thermally, yielding CO and H2. The less volatile oils were slower to evaporate and decompose. Combustion of the waste fuel with air occurred in a bed of SiO2 particles only to a limited extent in rising bubbles, depending on the bed’s depth. Otherwise, burning occurred above the fluidised particles, just as a mixture of methane or propane in air burns, when fluidising a hot bed of silica particles. The role of the particles is to inhibit combustion by scavenging radicals.

The heat transfer coefficient associated with a moving packed bed of silica particles flowing through parallel plates

Concentrating Solar Power (CSP) with thermal energy storage has the potential to be a renewable energy technology with long duration, inexpensive energy storage. Higher temperature operation increases the conversion efficiency and reduces the cost of energy storage. Several emerging CSP designs utilize particles as the solar receiver due to their high temperature stability and low cost. In some designs, the particles are also used as the thermal energy storage (TES) media. In either configuration, an energy transfer is required between the hot particles and the working fluid in the power cycle in a Particle-to-Fluid Heat Exchanger (PtFHX). Understanding the heat transfer between a moving packed bed and a stationary surface is critical to the successful design of a PtFHX.In this paper, a test facility is described in which a moving packed bed of silica sand with particle size 100–600 μm is introduced into the channel formed by two parallel plates, one of which is heated. The effective static thermal conductivity of the particles used for the test are separately measured over the entire range of test temperatures. The inlet and outlet bulk temperatures of the particle flow are measured as are the surface temperatures at several axial locations along the centerline of the plate. The result is the measurement of heat transfer coefficient as a function of temperature for several velocities. The uncertainty of the measurements is presented and the results are compared to model results found in the literature.

Fate of trace elements in Oxygen Carrier Aided Combustion (OCAC) of municipal solid waste

Oxygen Carrier Aided Combustion is a novel fluidized bed concept for burning waste. This study analyzed solid samples from an industrial OCAC application using municipal solid waste and the oxygen carrier ilmenite. The presence of oxygen carriers impacts the ash chemistry, which can influence corrosion and ash characteristics. By investigating samples obtained from industrial applications, unique and highly relevant information on the solid-state chemistry and the fate of important elements can be obtained. In total, 20 bottom ashes and 17 fly ashes were sampled over a period of 38 days. In a preceding study, the surface interaction between ilmenite and Zn, Cu and Pb was investigated. In this paper, the distribution of these elements throughout the particle cross-section and the influence of residence time has been studied using XRD, SEM-EDX and XPS. The results show that Zn is incorporated in the Fe-rich ash layer over time in the form of Zn ferrites, while Cu accumulates inside the ilmenite particles with time, and Cr is enriched in the magnetically separated bottom ash. Low concentrations of Pb were detected in the bottom ashes, suggesting that a significant part is released in the gas phase. The influence of temperature, bed material and reduction potential were evaluated using multicomponent, multiphase equilibrium calculations. It is shown that an ilmenite bed is less prone to form melts in comparison to a bed of silica sand and that the addition of sulfur could decrease the volatilization of Pb.

Sewage sludge ashes as a primary catalyst for the abatement of tar in biomass gasification: Bubbling versus spouted‐fluidized bed configuration

AbstractSewage sludge (SS) ashes, rich in iron and calcium, have been tested as a primary catalyst during air gasification of commercial wood pellets in a pre‐pilot scale fluidized bed (FB) reactor. The shifting from a conventional fluidized bed to a spouted‐fluidized bed configuration has been assessed on the catalyst performance. Specifically, at constant total air inlet flow rate, two different values of the air flow rate in a central spouting nozzle have been adopted, which correspond to 20% and 37.5% of the total inlet gas flow rate. Under the conventional fluidized bed configuration (i.e., bubbling regime), SS ashes exhibit good performance in term of tar reduction (about 20% decrease compared to a bed of inert silica sand), without significantly affecting the syngas composition. Concerning the transition to the spouted‐fluid bed configuration, the gas‐solid contact efficiency is enhanced at lower air flow rates through the central nozzle, with respect to the FB regime, leading to better gasification performance in terms of tar reduction (around 40% less) and syngas quality. A slightly worse gasification performance is obtained at high values of air flow rate in the central nozzle, due to a progressive increase of gas bed bypassing. Furthermore, moving from the conventional FB configuration to the spouted‐fluid bed one dramatically boosts the elutriation rate of carbon fines as well as the attrition of catalyst particles.

Effects of (Co-)Combustion Techniques and Operating Conditions on the Performance and NO Emission Reduction in a Biomass-Fueled Twin-Cyclone Fluidized-Bed Combustor

This work studied the potential of using two (co-)combustion techniques to reduce NO emission in a novel twin-cyclone combustor with a swirling fluidized bed. Prior to a (co-)combustion study, cold-state hydrodynamic tests were performed to investigate the flow regimes and hydrodynamic characteristics of a silica sand bed employed in this reactor. Static bed height of 20 cm was found suitable to ensure bubbling fluidization of the swirling bed during (co-)firing experiments. In the (co-)combustion study, rice husk (a base fuel) was first co-fired with high-moisture sugarcane bagasse (sharing 15% of the total heat input) using an air staging technique, whereas in the second group of experiments, the base fuel was combusted alone with flue gas recirculation. Detailed investigations of (co-)combustion and emission characteristics of the two proposed techniques was performed with a 100 kW heat input to the combustor for variable operating parameters: 30–60% excess air, 0–0.3 secondary-to-total air ratio in the tests for air staging, and 5– 20% fraction of the recycling flue gas when using the second technique. In all test runs, both (co-)combustion techniques ensured NO reducing conditions in the lower combustor’s chamber, leading eventually to the NO emission reduction, compared to burning the base fuel alone. At optimal operating parameters, the combustor showed high (~ 99%) combustion efficiency and reduction of NO emission: by 30% for husk-bagasse co-firing with air staging, and by 38% when burning rice husk with flue gas recirculation, as compared to conventional combustion of the base fuel.

Rotation-assisted Abrasive Fluidised Bed Machining of AlSi10Mg parts made through Selective Laser Melting Technology

Poor surface quality represents one of the most critical drawbacks of metal parts produced by powder bed-based Additive Manufacturing (AM) technologies, such as Selective Laser Melting (SLM) and Electron Beam Melting (EBM). Among the several post-process surface finishing treatments, Fluidised Bed Machining (FBM) could represent an intriguing and cost effective option for the treatment of complex AM metal parts. This work illustrates the results of the preliminary tests carried out by means of the FBM technology in which an external contribution of rotational speed of the samples was introduced. Rotation of the samples was considered in order to increase the relative speed and energy dissipation between the parts and the fluidised abrasive particles, with the aim to increase the process efficiency in terms of surface roughness reduction. For the experiments, AlSi10Mg alloy square flat samples were built in vertical direction by means of SLM technology and dipped into an abrasive fluidized bed of silica sand. The preliminary tests were carried out by adopting a minimum fluidization regime of the abrasives and establishing, through the rotation of the samples, two values of mean superficial tangential speed of 1 m/s and 2 m/s. The effect of the latter was investigated in combination with different impact angles, considering a process time of 30 min. The surfaces were characterized quantitatively by means of confocal microscopy and weight loss measurements, while SEM images were acquired in order to observe the real morphology evolution after the treatment. The experimental results suggested a slight surface modification and roughness reduction for the investigated FBM process conditions, due to a low energy transfer from the abrasives to the surfaces. On the other hand, the results shown also that a greater surface smoothing effect was achieved when increasing the tangential speed and adopting low impact angles.

The influence of fluidized bed co-combustion of cassava rhizome and eucalyptus bark on the combustor performance and time-related physiochemical changes of the bed material

Pelletized cassava rhizome (base fuel with elevated fuel-N and potassium contents) and high-moisture eucalyptus bark (secondary/reburn fuel) were co-fired in a 200 kW fluidized-bed combustor with a silica sand bed, using fuel staging and reburning techniques to mitigate NO emission. Detailed analyses of (co-)combustion and emission characteristics of the combustor were performed for variable operating parameters: 0–0.25 energy fraction of eucalyptus bark, 20–80% excess air (for each fuel option), and 0.1–0.4 secondary-to-total air ratio (in reburning tests at fixed excess air). High CO and CxHy in a secondary/reburn zone of the combustor led to enhanced decomposition of NO in this zone for both co-firing techniques. With optimal operating parameters, a noticeable NO emission reduction (25% when using fuel staging and 50% for reburning), at some increase in the CO and CxHy emissions, compared to burning the base fuel alone, can be achieved at high (∼99%) combustion efficiency. However, a small proportion of silica sand was subjected to agglomeration in both techniques within ∼8 h. Two alternative bed materials (alumina sand and alumina/silica sand mixture) were therefore employed to inhibit bed agglomeration during long-term co-firing tests for reburning under optimal operating conditions. No evidences of bed agglomeration were found in these 30 h reburning tests with the alternative bed materials. However, the bed materials showed the time-domain changes in their physiochemical characteristics, as found with SEM−EDS and XRF techniques. A carryover of fine Al-rich particles from the beds with alumina sand and alumina/silica sand mixture gradually diminished bed resistance to agglomeration.

Influence of water saturation and particle size on methane hydrate formation and dissociation in a fixed bed of silica sand

In this work, the effects of water saturation and particle size on methane hydrate formation and dissociation in a fixed bed of silica sand were investigated. The experiments were carried out at 277.15 K with the initial pressure fixed at 8 MPa. Three water saturations (50%, 70%, and 90%) and two particle sizes (0.18-0.25 mm and 0.3-0.9 mm) of silica sand were used. The results indicated that water conversion to methane hydrates increased with the decrease of water saturation. 70% was found to be an optimum water saturation due to the largest hydrate amount and the highest gas uptake obtained using the small particle size of silica sand (0.18-0.25 mm). In addition, hydrate formation rate and gas uptake obtained using small particle size of silica sand were larger, and gas recovery and hydrate dissociation rate were higher in the dissociation experiments using the small particle size of silica sand. Therefore, the medium water saturation (70%) and small particle size (0.18-0.25 mm) are favorable for methane hydrate formation and dissociation in the fixed bed of silica sand.

Reducing polycyclic aromatic hydrocarbon and its mechanism by porous alumina bed material during medical waste incineration

In this paper, porous alumina was used as an alternative bed material to reduce polycyclic aromatic hydrocarbon (PAH) and monocyclic aromatic hydrocarbons (MAH) emission during medical waste incineration in a fluidized bed combustor (FBC). In order to understand the reduction mechanisms of MAH and PAH, porous alumina, nonporous alumina, and silica sand (180–250 μm and 250–320 μm) were used as the bed materials. In comparison to the silica sand (180–250 μm) bed material, the reduction efficiencies of ∑MAH, ∑PAH and ∑PAH toxic equivalent (TEQ) by porous alumina bed material were in sequence as 91.57%, 58.90% and 73.23% during medical waste incineration under 800 °C. There were three mechanisms for the reduction of PAH under porous alumina bed materials. Firstly, the evolution rate of hydrocarbon was reduced by porous alumina due to its low heat transfer coefficient. Secondly, porous alumina bed materials could absorb more gaseous hydrocarbon and prolong the residence time of hydrocarbon in the diluted zone of FBC due to its higher BET. Lastly, the oxidization of the gaseous hydrocarbon was accelerated by porous alumina due to its catalytic effect. Thus, less light hydrocarbon, MAH and PAH were formed during medical waste incineration. The experimental results also indicated that the heat transmission, catalytic effect, and adsorption effect of porous alumina bed materials respectively accounted for 22.8%, 29.2% and 20.9% of the ∑PAH reduction.

Product gas composition for steam-oxygen fluidized bed gasification of dried sewage sludge, straw pellets and wood pellets and the influence of limestone as bed material

This is a study on gasification of low cost biogenic fuels for synthesis gas production with assessment of the gas composition and impurity concentrations. Experiments were carried out in a 20 kW fuel input bubbling fluidized bed facility with steam and oxygen as gasification agents. Dried sewage sludge, straw pellets and, for reference, wood pellets were used as fuels. The influence of limestone as low cost bed material acting as in-situ tar cracking catalyst and sulfur sorbent was analyzed. In terms of product gas quality and the influence of limestone as bed material, it can be summarized: (i) Regarding permanent gases, all fuels yielded comparable gas composition and output on water and ash free basis. The gas contains 40% H2 and 20% CO (dry mole fraction) and is thus suitable for synthesis. (ii) The gravimetric tar concentration of the product gases varied between 15 and 28 g m−³ for experiments with inert silica sand or ash bed, but could be reduced significantly by addition of calcined limestone to below 6 g m−³. As a novel approach, also the elemental composition of the gravimetric tar was analyzed. (iii) Since straw and sewage sludge contain significant amounts of nitrogen, sulfur and chlorine, the concentrations of H2S, NH3 and HCl in the syngas have been measured by wet chemical methods for these fuels. Limestone acts as sulfur sorbent and it was shown, that the H2S content of the product gas could be lowered significantly, reducing the effort of downstream gas cleaning.

Pyrolysis of Cynara cardunculus L. samples – Effect of operating conditions and bed stage on the evolution of the conversion

The effect of different parameters on the pyrolysis of Cynara cardunculus L. was studied through an innovative technique based on a precision scale, capable of measuring the time evolution of the biomass samples mass during their thermochemical conversion process while moving freely inside a fluidized bed. A silica sand bed reactor, operated under different values of excess gas velocity and reactor temperature, was employed to hold the pyrolysis reaction of cardoon particles of three different size ranges. The pyrolysis was accelerated for higher excess gas velocities, obtaining pyrolysis times as short as 17.3 s for experiments conducted under bubbling fluidized bed regimes, compared to 185.9 s required to complete the pyrolysis of the same sample in a fixed bed configuration. Similarly, the effect of increasing the reactor temperature promoted faster heating rates across the fuel samples, especially under fixed bed configurations, for which the pyrolysis time is reduced from 321.7 s to 132.0 s when increasing the bed temperature from 450 to 650 °C. Regarding the biomass particle size, small sizes are preferred to minimize the conduction thermal resistance inside the fuel particles and, thus, reduce pyrolysis times and increase volatile yields for the pyrolysis in a bubbling fluidized bed reactor. The opposite result was found when the pyrolysis took place in non-bubbling beds, where the use of larger particles is beneficial to accelerate the biomass pyrolysis reaction.

Demonstration of gas-hydrate assisted carbon dioxide storage through horizontal injection in lab-scale reservoir

Abstract Depleted hydrocarbon reservoirs are known to provide an opportunity for CO2 sequestration. A new 5300 cm3 stainless steel high pressure chamber (crystallizer), employing horizontal CO2 injection, is used to demonstrate the sequestration of CO2, via hydrate crystallization, in depleted hydrocarbon reservoirs. The crystallizer was employed to carry out laboratory injection trials. A bed of silica sand with a porosity of 0.35 and a water saturation of 0.22 was used in these experiments. CO2 is sequestered into the crystallizer by constant flow rate (1200 cm3/h) followed by constant pressure CO2 injection. This method has been shown to increase CO2 hydrate formation compared to only using constant pressure CO2 injection. Experimental pressures (pressure targets) ranging from 2.2 MPa to 3.2 MPa at 277 K are investigated. A total storage density of 126.6 kg·m−3 is found 24 h after the start of injection at a pressure target of 3.2 MPa.

Influence of thermal stimulation on the methane hydrate dissociation in porous media under confined reservoir

The kinetics of methane gas hydrate under confined environment in porous media have been studied for understanding the formation and dissociation behavior under this condition. We have developed a replica of natural hydrate-bearing atmosphere in a laboratory scale experimental set-up and examined the silica sand size effect on the formation and gas recovery in the presence of both pure water and seawater under confined reservoir conditions. Four sizes of silica sand particles were used in the present study (S1 (0.16mm), S2 (0.46mm), S3 (0.65mm) and S4 (0.92mm)). The formation experiments were done with 70% water saturation both for pure water and seawater. All these experiments were carried out at 277.15K and 8MPa. It is perceived that the gas consumption in the presence of smaller size sand particles is higher as compared to the larger size. The total consumption of methane gas during hydrate formation has been found to be less in the presence of seawater as compared to pure water. Subsequently, dissociation experiments have been carried out under confined reservoir conditions using thermal stimulation from 277.15K to 303.15K for 2h. Gas recovery and dissociation rates are found to be higher in the smaller size silica sand bed in pure water as compared to bigger ones and seawater. Also, the maximum rate of dissociation was occurred at the near-equilibrium condition of pure methane hydrate system. Further insights into the dissociation behavior of methane hydrate under confined reservoir conditions have also been presented.

An experimental study on hydrogen enriched gas with reduced tar formation using pre-treated olivine in dual bed steam gasification of mixed biomass compost

The study investigated the effects of pre-treated olivine in dual bed steam gasification (DBSG) of biomass compost in order to produce H2 enriched synthesis gas with significantly reduced tar formation. The DBSG employed circulating fluidized bed (CFB) of silica sand as first stage and fixed catalytic bed of pre-treated olivine as second stage. The mixed biomass compost contained 15–20 wt. % of agri-residues (mainly wheat straw) and 80–85 wt. % of cow manure. The study compared the synthesis gas distribution and tar reductions using pre-treated olivine in the DBSG scheme with Ni–Al based DBSG scheme. The effects of operating condition on the synthesis gas distribution and tar formation are studied such as: (i) effect of steam to biomass ratio, (ii) effects of relative oxidation (relox), (iii) operating temperature of the reactor, (iv) performance and comparison of employed catalysts, and (v) yield of synthesis gas together with carbon conversion efficiency. Experimental analysis showed that H2 concentration obtained from pre-treated olivine based DBSG is considerably higher than H2 produced from compared gasification schemes. The H2 production is favoured at higher temperatures and higher SBR under the influence of pre-treated olivine catalyst. However, the conditions are less advantageous for the production of CO and CH4. Among all experiments, the synthesis gas composition obtained at SBR = 1.40 and at 800 °C consisted of highest H2 concentration (35 vol.% d.n.f) in the pre-treated olivine DBSG. Higher steam to biomass ratio (SBR) resulted in lower cold gas energy efficiency and lower heating value of the synthesis gas mainly due to large steam content in the gas. The tar removal efficiency of 98% is achieved with the pre-treated olivine DBSG system. The total tar content is significantly reduced (≈ 40%) in the DBSG with pre-treated olivine. Higher relative oxidation resulted in increased concentration of CO2 in the synthesis gas due to increased partial oxidation of organic matter in the gasifier. The pre-treated olivine catalyst in the DBSG consistently promoted the process of steam reforming and tar cracking and thus improved the quality of the syngas by limiting the tar contents.

Impact of fixed bed reactor orientation, liquid saturation, bed volume and temperature on the clathrate hydrate process for pre-combustion carbon capture

Hydrate based gas separation (HBGS) process is a promising technology for carbon capture from pre-combustion streams of power generation. Recently, fixed bed reactor (FBR) configuration has been reported to significantly enhance the kinetics of hydrate formation for the HBGS process. In this work, silica sand bed reactor was employed along with 5.56 mol% THF solution to capture CO2 from fuel gas mixture (CO2/H2) at 6.0 MPa, to investigate the effects of reactor orientation (vertical, horizontal), liquid saturations in the bed (50%, 75%, 100%), and fixed bed volume. Horizontal configuration showed a major improvement in terms of gas uptake and normalized rate of hydrate formation than vertical configuration, due to the larger cross sectional area in the horizontal configuration. 50% liquid saturation performed better than the other saturations from water utilization perspective, whereas 100% saturation was better from space utilization perspective. While bed volume did not influence the kinetics of hydrate formation much, smaller bed volume showed better dissociation kinetics. In addition, the effect of operating temperatures (279.2 K, 282.2 K and 285.2 K) were evaluated for a chosen configuration. Operating temperature of 282.2 K presented slightly lower performance compared with 279.2 K, but had the advantage of energy saving. The short induction time and high CO2 composition in hydrate phase (more than 91%) further enhanced the potential and feasibility of employing this horizontal FBR configuration for pre-combustion CO2 capture with the use of THF.

Precombustion CO2 capture using a hybrid process of adsorption and gas hydrate formation

In this study, a fixed bed of pulverized coal particles was employed to enhance the precombustion CO2 capture from fuel gas (40 mol% CO2/H2). The performance of the HAHF (hybrid adsorption-hydrate formation) process occurred in the fixed bed was evaluated at different liquid saturations and operation pressures. The experiments were carried out at 274.2 K with the pressure varying from 3.0 MPa to 6.0 MPa. 1.0 mol% THF (tetrahydrofuran) solution instead of liquid water was used to saturate the fixed bed and reduce the hydrate phase equilibrium conditions. The results indicated that gas hydrate nucleation in the fixed bed was quickly induced by gas adsorption in coal particles. The HAHF process was dominated by hydrate formation as the fixed bed saturation increased, and the CO2 recovery and separation factor were increased. Gas consumption during the HAHF process was promoted with the increase of operation pressure, but the CO2 recovery and separation factor decreased. In the fixed bed of coal particles saturated by 1.0 mol% THF solution the highest gas uptake obtained was 51.9 mmol of gas/mol of water, which was comparable with that obtained in the fixed bed of silica sand in the presence of 5.53 mol% THF. Therefore, compared with the hydrate based gas separation process, the hybrid adsorption-hydrate formation process proposed in this study could be a viable option for CO2 capture from fuel gas.