Extent Of Gasification Research Articles

On the primary pyrolysis products of torrefied oak at extremely high heating rates in a wire mesh reactor

Torrefaction is a key process for biomass energy densification ahead of its utilisation in pyrolysis, gasification or combustion, and therefore the changes it originates have been the subject of multiple studies. Most of them employ low heating rates, in the range of thermogravimetric analysers (TGA), typically below 1 °C s−1 or high rates (100–1000 °C s−1) in reactors where tars undergo considerable secondary reactions following release from a particle and the temperature history of the sample is not well defined, such as entrained flow or fluidised beds. This study aims to analyse the behaviour of torrefied lignocellulosic biomass (oak) under fast pyrolysis in with very controlled temperature history and absence of secondary reactions between evolving volatiles and chars in a wire mesh reactor (WMR), which allows determination of primary products. To this end, oak was firstly torrefied in a grey-King reactor to provide samples from mild to severe torrefaction (210–300 °C). The raw and torrefied oaks were pyrolyzed/gasified, at 1000 °C s−1 and 850 °C in the WMR using He and CO2 atmospheres. All samples showed high volatile production, in excess of 80 wt.%, but with a clear drop with increasing torrefaction temperature. The char yields from the WMR in CO2 were lower than in He, reflecting a degree of char gasification. However, char deactivation at the higher torrefaction temperatures caused a sharp decrease in the extent of gasification from 32 wt.% for Raw Oak to 6 wt.% for oak torrefied at 300 °C (Oak-300). This is a consequence of the predominance of chemical effects such as enrichment of carbon, which increased from 46.5 wt.% for Raw Oak to 54.3 wt.% in Oak-300 and depletion of oxygen, which led to greater aromaticity and structural order in the char with torrefaction temperature, over physical changes observed by scanning electron microscopy (SEM) revealing increasing porosity.

Hydrogen production by supercritical water gasification of valine over Ni/activated charcoal catalyst modified with Y, Pt, and Pd

Hydrogen production by supercritical water gasification (SCWG) of valine as a model for protein was examined in a fixed-bed reactor at 28 MPa. The effect of reaction temperature (500–710 °C), type of catalyst (AC, Ni–Y/AC, Ni–Pt/AC, and Ni–Pd/AC), and LHSV (24–72 h−1) on the extent of gasification and gas composition was investigated. Total gas yield increased with increasing temperature up to 710 °C while carbon gasification efficiency (CGE) reached the highest value of 98.1% at 600 °C over the Ni–Y/AC catalyst. The three Ni-based catalysts promoted hydrogen formation reactions greater than the AC. In particular the Ni–Pt/AC and Ni–Pd/AC catalysts effectively reformed C2+ hydrocarbons intermediates to H2 and CO2. The Ni–Y/AC catalyst at 650 °C completely destroyed nitrogen-containing organic intermediates such as amines in the liquid effluent. The presence of Pt and Pd significantly suppressed the crystallization of Ni metal supported on AC in supercritical water.

Steam Gasification of Different Brown Coals Catalysed by the Naturally Occurring Calcium Species

The effects of the constituents of mineral matter in brown coals from different deposits of Kansk-Achinsk, Lenaand from Yallourn Basins on the structural parameters and steam gasification reactivities of respective coal chars at moderate temperature and at low and high pressure were studied in this paper. The data on how the preliminary decationization with diluted hydrochloric, acetic and sulphuric acids affect char gasification reactivities are presented. The importance of surface area and crystallinity of chars and the presence of naturally occurring metals on gasification reactivity is considered. Quantitative correlations between the calcium contents and the extents of gasification are revealed. The gasification results obtained in a flow reactor with steam stream and in an autoclave reactor at high pressure of gaseous products are compared. The catalytic effect of dispersed calcium oxide-carbonate particles produced from the naturally occurring calcium containing carboxylates was shown to be a key factor for char gasification reactivity, the effect in the flow reactor being much larger as compared to that in the autoclave reactor. This was mainly related to different forms of catalytically active calcium species and to the composition of the gaseous reaction mixture.

Effect of operating conditions in Chemical-Looping Combustion of coal in a 500 Wth unit

Chemical-Looping Combustion, CLC, is one of the most promising processes to capture CO2 at low cost. It is based on transferring the oxygen from air to the fuel by using a solid oxygen-carrier that circulates between two interconnected fluidized-bed reactors: the fuel- and the air-reactor.In this work, CLC with coal was investigated in a continuous 500Wth rig using ilmenite as oxygen-carrier and Colombian bituminous coal as fuel. In the fuel-reactor the oxygen-carrier is reduced by the volatile matter and coal gasification products.The effect of operating conditions such as the solids circulation rate and oxygen-carrier residence time, the coal flow feed and the steam flow as gasification agent were investigated on the combustion efficiency and extent of gasification. The influence of using CO2 as gasification agent was assessed by doing experiments with different CO2–H2O mixtures.The results obtained are valid for the scale-up of a CLC process with coal. They indicate that it is feasible to decrease the gasification agent flow to lower values than the corresponding stoichiometric for the gasification, and that some of the steam as gasification agent can be replaced by CO2 recirculated from the fuel-reactor outlet. Low circulation rate of solids improved coal conversion.

Effect of metal addition to Ni/activated charcoal catalyst on gasification of glucose in supercritical water

Activated charcoal supported nickel-based catalysts such as Ni/AC, Ni–Y/AC, Ni–Fe/AC, and Ni–Co/AC were formulated and their catalytic activity for the gasification of glucose in supercritical water were investigated using a packed-bed reactor at 650 °C, 28 MPa. A set of glucose gasification experiments was also carried out without catalyst and with AC to provide baseline data. Loading of small amounts of Y to the Ni/AC catalyst appeared to increase both the extent of gasification and hydrogen yield while loading of Fe or Co metal to the Ni/AC catalyst did not give any positive effect on the gasification results. Effect of catalyst composition, temperature, reactant concentration, and reactor residence time on the glucose gasification with the Ni–Y/AC catalyst was examined. Catalyst analysis indicates that adding of Y into the Ni/AC catalyst inhibited carbon formation to a great extent, thereby maintaining catalytic activity of the Ni metal for H2 formation reactions.

Ilmenite as oxygen carrier in a chemical looping combustion system with coal

Chemical-Looping Combustion, CLC, is one of the most promising technologies to capture at a low cost the CO2 in fossil-fuelled power plants. CLC is based on the transfer of the oxygen from air to the fuel by using a solid oxygen-carrier that circulates between two interconnected fluidized reactors: the fuel- and the air-reactor. The CO2 capture is inherent to this process, as the air does not get mixed with the fuel. The selection of the oxygen-carrier is a key factor for the CLC technology development. Ilmenite is a low cost natural mineral which is promising for its large scale industrial use as oxygen-carrier with solid fuels. In this work, the CLC technology with a Colombian bituminous coal was investigated in a continuous rig using ilmenite as oxygen-carrier. The plant was basically composed of two interconnected fluidized-bed reactors joined by a loop seal, a riser for solids transport from the air- to the fuel-reactor, a cyclone and a solid valve to control the solids flow rate. This work is focused on the study of the fuel-reactor within the process. The behavior of the fuel-reactor has been evaluated. The effect of the temperature and coal particle size was investigated, on the combustion efficiency as well as on the extent of gasification in the fuel-reactor. The experiments were done at 820–950 °C in the fuel-reactor. A particular feature of this plant is that the solids circulation rate can be also controlled. The fluidizing gas was water steam, which acts also as gasifying agent. Since this plant does not have carbon stripper, it is really focused on the study of the gasification and combustion of coal in the FR within the CLC process. The results obtained are valid for the scale-up of a CLC process fuelled with coal. The results show that ilmenite has a good behavior as oxygen-carrier and that optimization of the CLC technology with solid fuels can lead to energy production with high CO2 capture efficiencies.

Hydrogen Production by SCWG Treatment of Wastewater from Amino Acid Production Process

The organic wastewater obtained from an amino acid production process was treated by supercritical water gasification (SCWG) method for achieving water purification and hydrogen production. A set of SCWG experiments was also carried out with glucose and valine solutions as model compounds for reducing sugars and amino acids present in the wastewater, respectively. The effect of temperature (600—700 °C) and different catalysts (activated charcoal (AC), Ni/AC, and Ni―Y/AC) on the extent of gasification and gas composition was investigated in a continuous-flow reactor at 28 MPa and 12 h ―1 LHSV. Complete gasification of organic compounds in the wastewater was achieved in the presence of the supported nickel catalysts, resulting in the formation of gaseous products with high hydrogen contents. Alkaline salts present in the wastewater feed contributed to hydrogen formation reactions. Solid product formed during the SCWGs of the wastewater feed was identified as one of main obstacles for a possible commercial design and a schematic concept was suggested for its removal.

Pyrolysis and CO2 Gasification of Chinese Coals in a High-Pressure Wire-Mesh Reactor under Conditions Relevant to Entrained-Flow Gasification

A high-pressure wire-mesh reactor has been successfully re-commissioned to operate at high temperatures (up to 2000 °C) and pressures (up to 30 bara) for characterization of coal samples under conditions relevant to entrained-flow gasification. A sample of coal supplied by the Thermal Power Research Institute (China) has been tested. Pyrolysis yields increased as the temperature increased and decreased as the pressure increased. The extent of gasification at low temperature (1000 °C for 1 s) must have been low, because the weight losses in CO2 and helium did not differ greatly. Nevertheless, the gasification yields at high temperature (1500 °C and 1 s) were significant, and near-complete conversion of the sample occurred in CO2. Non-isothermal thermogravimetric analysis of residual char clearly showed an increased thermal deactivation with increased temperature and pressure. The coupled use of the high-pressure wire-mesh reactor and the thermogravimetric analyzer has potential as a laboratory tool to assess the reactivity of coals to be used in entrained-flow gasifiers.

High-pressure pyrolysis and CO 2-gasification of coal maceral concentrates: conversions and char combustion reactivities

The gasification behaviour of maceral concentrates was examined in a fixed-bed and a wire-mesh reactor. ‘Extents of gasification’ were calculated by subtracting sample weight loss during pyrolysis (He) from weight loss in CO 2-gasification. The effect of holding time (10 and 200 s) and pressure (1 and 20 bar) on conversions and on combustion reactivities of chars were studied. During short hold-time gasification experiments (10 s), liptinites gave the highest conversions, followed by the vitrinites and the inertinites. Vitrinite conversions decreased sharply above 90% elemental-C content. Extents of gasification were found to be in the order: vitrinites>liptinites>inertinites. However, at 200 s, a marked increase in inertinite conversion translated into a clear change of relative ordering to: inertinites>vitrinites>liptinites. The high gasification reactivities of inertinites at longer times appear to be related to a more rigid and porous structure, but the late surge suggests that an induction period is needed. More detailed time series data are required. Relative combustion reactivities of chars were generally observed to decrease with (i) pressure, (ii) time at temperature and (iii) increasing elemental carbon content. The data indicated that orders of gasification reactivities may be predicted from the order of combustion reactivities of pyrolysis chars. Inertinite concentrate chars were more reactive. However, the difference in reactivity between inertinite chars and other samples was reduced when the inertinites were heated rapidly—possibly owing to melting at the higher heating rates.

CO 2 and steam-gasification in a high-pressure wire-mesh reactor: the reactivity of Daw Mill coal and combustion reactivity of its chars

Interrelationships between extents of coal gasification, char gasification and combustion reactivities have been examined as a function of CO 2 and steam pressure and holding time. Experiments have been carried out in a high-pressure wire-mesh reactor equipped with a steam injection facility. Evidence has been presented linking minima in weight loss vs. reactive gas pressure curves with deactivation as a result of secondary char deposition. At longer times, extents of gasification were about 2–3 times higher in steam compared to CO 2. With increasing reactivity of the ambient gas, the minimum in the weight loss vs. pressure curve appears only at the shortest reaction times. At higher pressures, reactivities between zero and 10 s were lower than those between 10 and 20 s. These data are novel and support the suggestion that a relatively unreactive layer of re-polymerised tar tends to slow down the gasification of the main body of the char in the initial stages – until it is itself consumed. Combustion reactivities of pyrolysis and gasification chars decrease with increasing pressure. When exposed to a temperature of 1000°C, combustion reactivities of chars were found drop rapidly within about 10 s to relatively low and stable values. The end values were independent of pressure and composition of the reactive gas. The results are relevant to the design of pilot and commercial scale reactors. On the basis of limited available evidence, it appears that secondary char deposition caused by tar re-polymerisation plays an increasingly significant effect with increasing particle size.

Pyrolysis and Gasification in a Bench-Scale High-Pressure Fluidized-Bed Reactor

A bench-scale high-pressure fluidized-bed reactor designed for pyrolysis, gasification, and combustion experiments (up to 1000 °C, 40 bar) has been constructed and commissioned. The system is intended to generate fuel reactivity data rapidly and cheaply, under realistic experimental conditions; it is relatively simple to construct and capable of operation by a single researcher. The reactor body (Incoloy Alloy 800HT, 34 mm i.d., 504 mm long) serves as the resistance heater and is designed to withstand the reaction pressure, obviating use of a “cold” pressure casing. The reactor is lined with a loosely fitting quartz tube to limit corrosion and catalytic effects. Sample (up to 2000 mg) is held between two air actuated valves and injected batchwise (“single-slug”) through a water-cooled probe. The design of the reactor allows determination of tar/oil and char yields. Exhaust gases are passed through a dryer before entering the analytical stage. The present report focuses on equipment design and preliminary data from pyrolysis and gasification experiments with Daw Mill coal (UK) at up to 1000 °C and 30 bar. Extents of gasification were calculated by subtraction of total volatile yields in CO2 from mass loss during pyrolysis in helium, performed under otherwise identical conditions. Combustion reactivities of chars were determined in an atmospheric pressure TGA instrument. A number of design adjustments have been described, enabling total volatile yields from the FB reactor to match those from a high-pressure wire-mesh reactor. As expected, tar yields from the fluidized-bed reactor were significantly lower than those from the wire-mesh instrument, due to longer residence times of volatiles in the bed of solids and the reactor freeboard.

Adsorption Properties of Activated Carbons Obtained from Polymer Wastes

Non-activated carbon has been prepared by carbonizing waste products manufactured from phenol formaldehyde at 1073 K in a nitrogen atmosphere. Activated carbons were obtained by gasifying the non-activated product with air at 673 K, or with steam at 1173 K, to different levels of burn-off. The adsorption of nitrogen at 77 K and of carbon dioxide at 298 K was measured for all the carbons prepared using volumetric apparatus. The adsorption of iso-octane and α-pinene at 320 K was carried out gravimetrically using silica spring balances. The adsorption of methylene blue and of phenol from their aqueous solutions was determined spectrophotometrically. The adsorption of ammonia from its aqueous solution at 308 K was determined colorimetrically. The surface area of the activated carbons increased with increasing percentage burn-off to reach a maximum and then decreased with further increase in percentage burn-off. Gasification with oxidizing gases changed the porosity of the carbon with the change depending on the extent of gasification. The adsorption of iso-octane and α-pinene increased with increasing percentage burn-off as a result of pore widening. The low burn-off carbons obtained from phenol formaldehyde wastes are characterized by extremely high surface areas and microporosity, and a high CO/CO2 ratio on outgassing. The carbons exhibit high phenol adsorption capacities. Ammonia adsorption is favoured on carbons of a low CO/CO2 ratio.

Penetration of sodium catalysts in activated carbon: effect on the porous structure and reactivity in air, carbon dioxide and steam

The effect of the penetration of sodium compounds on the porous structure and reactivity of activated carbon was studied. Loadings of NaCl, NaOH or Na 2CO 3 were effected from the solid phase by heating above their melting points or from an NaOH aqueous solution. The heat treatment, addition order and solution concentration were varied; a heat-treated carbon was also used as support. The samples were structurally characterized by gas adsorption (N 2, −196 °C; CO 2, 25 °C), mercury porosimetry and helium pycnometry. The reactivity of the carbon was determined in air at 400 °C and in CO 2 and steam at 900 °C. The loading method had a marked influence on the structure of the carbon, including the porosity distribution. A better agreement was found between the specific surface area and the total pore volume than between these properties and the micropore volume. The catalytic activity was much lower for NaCl than for NaOH or Na 2CO 3. As for NaOH, the reactivity was greatly dependent on the loading method. Its variation with temperature and concentration was consistent with the ash level and the micropore volume for the gasifications in CO 2 and steam; in air, the extent of gasification seemed to be determined by the porosity distribution; the reactivity increased for samples prepared with solid NaOH with regard to those obtained using a NaOH solution. The behaviour was similar with Na 2CO 3.

Structure and active surface area of carbon fibers

The surface characteristics and oxidation rates of two carbon fibers, T-300 (PAN) and VSB-32 (pitch), before and after graphitization at 2973 K, are reported. The as-received (AR) and graphitized (GR) fibers have insignificant open porosity, small BET areas (<0.7 m 2/g), and small concentrations of alkali metals. Attempts have been made to measure values of apparent active surface areas (AASA) using oxygen chemisorption techniques at 573 K. For the T-300 AR fiber, AASA increases as the measurements are repeated on the same sample, and the value finally approaches the initial BET area because carbon gasification occurs during the measurements. Extrapolation of AASA values to zero-level gasification yields the true active surface area (TASA), 0.075 m 2/g. A similar trend has been observed with the T-300 GR fiber, and the TASA, obtained by extrapolation, at a starting oxygen pressure below 2.67 K Pa, is 0.024 m 2/g. However, at higher pressures, a second group of active sites, whose area is 0.067 m 2/g, is observed. With the VSB-32 AR and GR fibers, the extent of gasification below 0.67 K Pa is insignificant, and the TASA and AASA are similar; they amount to 0.029 and 0.019 m 2/g respectively. Furthermore, there is no indication of a second group of active site at higher chem-isorption pressures.

Catalytic gasification of metallurgical coke by carbon dioxide using potassium salts

The catalytic gasification of metallurgical coke by carbon dioxide with potassium salts is studied from the view-point of the catalytic activity of the salts, the optical texture of the coke and its reactivity, monitoring weight losses and the detail of topographical change induced in the coke surface by gasification. The activity of the catalyst and the reactivity of the coke were found to be dependent upon the anion of the salt and optical texture of the coke. Potassium metal may be produced in situ in the gasification reactions and has a significant role in the mechanism of catalytic gasification. The reactivity of a coke and its performance in a blast furnace must be associated both with extents of gasification and development of pits and fissures which could promote a weakening of the coke.

Gasification of polyethylene over solid catalysts. 4. Gasification over sodium X zeolite and silica-alumina in a fixed bed tubular flow reactor.

Gasification-degradation reactions of polyethylene (PE) over NaX zeolite and silica-alumina (SA) catalysts were studied in a fixed bed flow reactor system at 452-526°C and under 19.7-37.5g-cat•min/g-PE. The initial values in terms of the extent of gasification (RgF) at 25.0g-cat•min/g-PE were 0.23 and 0.41 at 477°C over NaX and SA, respectively. These values of RgFwere significantly greater than 0.015 for thermal degradation. However, these catalysts were deactivated by coke deposition and the RgFafter 2.5 hours was 33-55% of the initial value of NaX or 65-69% of that of SA. Product distribution in terms of carbon number for SA was almost independent of process time and reaction temperature, but the ratio of olefin to paraffin for the C3 fraction and that for C4 fraction increased gradually with process time and reaction temperature. For NaX, the fractions in the C1-C3 range increased, but other fractions and ratios decreased with increasing process time, while the increase in the reaction temperature caused a complex change in product distribution. The isobutane produced was 1-5mol% or 10-14mol% of the total gaseous products formed over NaX and SA. The main products formed over both of these catalysts were C3 and C4 olefins. The apparent activation energy was 25.2kcal/mol for NaX and it was 14.7kcal/mol for SA. The activity of these catalysts was reduced by pyridine poisoning. Moreover the poisoning of SA catalyst with sodium ion caused sharp drops in the activity levels and brought about marked changes in product distribution. The product distribution obtained over a Na-poisoned SA was quite similar to that over NaX. From the results obtained in the present study, it was suggested that the gasification-degradation reaction of PE over SA proceeded through the carbonium ion mechanism, while the gasification-degradation reaction involved over NaX was complex, competitive reactions of both the radical and carbonium ion mechanisms.

Gasification: Part I. Isothermal, kinetic control model for a solid with a pore size distribution

AbstractA model describing the development of specific surface area, volume, porosity, and mean pore radius of a porous solid with extent of gasification is developed based on consideration of pore size growth, initiation of new pores, and coalescence of adjacent pores. Use of population balances and formulation of the properties as moments of the pore size distribution leads to a mathematically simple, closed set of equations for kinetically controlled gasification. The model successfully predicts maximums in specific surface area and number of pores observed by Kawahata and Walker (1962) in the activation of devolatilized anthracite by CO2 in a fluidized bed.