Lower Gasification Temperature Research Articles

Effect of the Ca/P ratio of Ni-loaded hydroxyapatite on the catalytic decomposition of biomass tar at low temperatures

Ni-loaded catalysts using hydroxyapatite (HAp) supports with various Ca/P ratios are promising biomass tar decomposition catalysts at low gasification temperatures (i.e., 450 °C), and that variations in the Ca/P ratio of the HAp support allow tuning of the Ni dispersion state and catalytic activity.

Atom economy or product yield to determine optimal gasification conditions in biomass-to-olefins biorefinery

Biorefinery design uses various metrics for achieving biomass conversion with process efficiency and biochemical selectivity. A common optimization strategy targets the product yield expecting favorable waste reductions. As a green-chemistry metric, atom economy offers a novel approach to achieving mass efficiency by simultaneously computing products and waste. A comparison between the product yield and atom economy presumes different optimal operating conditions. This study applied atom economy to a biomass-to-olefins process to elucidate metric differences. An initial revision of the stoichiometric conditions determined the ideal product and waste generations. A realistic simulation predicted the mass flows to olefins via gasification, methanol synthesis, and methanol-to-olefins conversion. The gasifier operating conditions were modified to clarify interactions among the atom economy, reaction temperature, and steam-to-biomass mass ratio (S/B). The optimal atom-economic and product-yield conditions differed; a lower gasification temperature and atom-economic (S/B) ratio enhanced the olefins-to-waste ratio. The atom economy indicated that CO2 and H2O are inefficient transport molecules for releasing oxygen in biomass. Both wastes consume at best 33% g/g of feedstock carbon or hydrogen, complying to olefin and intermediate H/C ratios. A comprehensive revision of the energy performance is required to complement the atom economy as a performance indicator.

A parametric study to optimize the temperature of hazelnut and walnut shell gasification for hydrogen and methane production

In this study, hazelnut and walnut shells were gasified with steam in a lab-scale updraft fixed bed reactor. Operating temperature effects on syngas composition were investigated experimentally. It is aimed to optimize the temperature of gasification for producing hydrogen and methane gases. Gasification was carried out at 600 °C, 650 °C, 700 °C, 750 °C and 800°C. The experimental results showed that the amount of hydrogen content in syngas increased with increasing temperature but amount of methane content decreased during both fuels' gasification. The optimum gasification temperatures of hazelnut and walnut shells were obtained as 750 °C and 800°C for producing hydrogen in syngas, respectively. On the other hand, lower gasification temperatures than 700 °C favored the methane content instead of hydrogen in syngas. Optimum temperature for methane production from hazelnut shells was obtained as 600 °C and for walnut shells was obtained as 650 °C. These findings make it possible to arrange the required composition of desired syngas content for different usage areas like hydrogen/methane utilization or chemicals production.

The Combined Impact of Ni-Based Catalysts and a Binary Carbonate Salts Mixture on the CO2 Gasification Performance of Olive Kernel Biomass Fuel

In the present work, the individual or synergistic effect of Ni-based catalysts (Ni/CeO2, Ni/Al2O3) and an eutectic carbonate salt mixture (MS) on the CO2 gasification performance of olive kernels was investigated. It was found that the Ni/CeO2 catalyst presented a relatively superior instant gasification reaction rate (Rco) compared to Ni/Al2O3, in line with the significant redox capability of CeO2. On the other hand, the use of the binary eutectic carbonate salt mixture (MS) lowered the onset and maximum CO2 gasification temperatures, resulting in a notably higher carbon conversion efficiency (81%) compared to the individual Ni-based catalysts and non-catalytic gasification tests (60%). Interestingly, a synergetic catalyst-carbonate salt mixture effect was revealed in the low and intermediate CO2 gasification temperature regimes, boosting the instant gasification reaction rate (Rco). In fact, in the temperature range of 300 to 550 °C, the maximum Rco value for both MS-Ni/Al2O3 and MS-Ni/CeO2 systems were four times higher (4 × 10−3 min−1 at 460 °C) compared to the individual counterparts. The present results demonstrated for the first time the combined effect of two different Ni-based catalysts and an eutectic carbonate salt mixture towards enhancing the CO production rate during CO2 gasification of olive kernel biomass fuel, especially in the devolatilization and tar cracking/reforming zones. On the basis of a systematic characterization study and lab-scale gasification experiments, the beneficial role of catalysts and molten carbonate salts on the gasification process was revealed, which can be ascribed to the catalytic activity as well as the improved mass and heat transport properties offered by the molten carbonate salts.

Numerical investigation of biomass and liquefied natural gas driven oxy-fuel combustion power system

Biomass as carbon-neutral renewable energy is beneficial for carbon emission reduction in power sectors. A biomass gasification integrated natural gas combined cycle is proposed in this study. Oxy-fuel combustion is utilized to realize CO2 capture with cold energy of liquefied natural gas applied for power consumption reduction. CO2 and H2O in the flue gas are separated and adopted as gasifying agents. The composition of natural gas and gasification syngas injected into the combustion chamber is restricted by the heat value and H2 concentration. The biomass mixing ratio and global energy efficiency under different gasification conditions are evaluated using Aspen Plus software. Increasing CO2 and decreasing H2O flow rate in gasifying agents are positive for increasing biomass mixing ratio which can achieve a maximum of 0.33. Gasification temperature increased from 650 °C to 950 °C causes an evident enhancement in energy efficiency. On the contrary, both biomass mixing ratio and energy efficiency are less sensitive to gasification pressure, particularly at low gasification temperature. The integrated system reaches the highest energy efficiency of 0.520 with a biomass mixing ratio of 0.10. Accordingly, the electricity cost is estimated to be 0.102 $/kWh, and the net CO2 emission considering fuel production is 91.0 g/kWh.

The integration of low temperature supercritical water gasification with continuous in situ nano-catalyst synthesis for hydrogen generation from biomass wastewater

A continuous hydrothermal process is demonstrated, for the first time, that can operate at low gasification temperature (430 °C) and residence time (20 s) by combining supercritical water gasification (SCWG) and partial oxidation with in situ synthesis of virgin metal oxide nano-catalyst. Using olive wastewater as the feedstock, this gasification study experimentally investigated the impact of multiple variables: (1) COD feed concentration, (2) the in situ synthesis of different metal oxide nano-catalysts, (3) the partial oxidation coefficient (ɳ) and (4) the nano-catalyst precursor solution concentration. The optimum conditions for the generation of hydrogen and methane from olive wastewater were a feed COD of 38.6 g/L, ɳ = 0.8, and 60 mM precursor concentration for the in situ synthesis of Fe2O3 nano-catalyst. These optimised conditions were further investigated using spent lees and stillage. The efficiency of hydrogen and methane yields and COD reduction were in the order of stillage > spent lees > olive wastewater. The highest hydrogen molar selectivity, hydrogen and methane yields at 18.8 %, 17 and 11.4 mol/(kg biomass) respectively were obtained with stillage feedstock. Gasification, COD and TOC reduction efficiencies were 68.8–71.7 %, 72.6–76.5 % and 53.9–55.7 % respectively, with this process. Importantly, this novel gasification approach prevents any performance drop or catalyst deactivation during continuous operation. This study exemplifies that the co-generation of catalyst during SCWG is a promising and economically feasible direction for large-scale continuous generation of hydrogen and methane from different types of biomass wastewater at < 450 °C, whilst lowering its COD and TOC. (249 words)

Proposal and assessment of a solar-coal thermochemical hybrid power generation system

The thermochemical complementarity is an efficient path to improve the utilization efficiency of coal and address the intermittence of solar energy. In this paper, a solar-coal thermochemical hybrid power generation system based on supercritical water gasification is proposed, and the feature is that the low gasification temperature of 650 °C makes it feasible to use concentrated solar energy to provide reaction heat for the gasification process. The energy and exergy analysis methods are used to evaluate the thermodynamic performance of the system with a net power output of 500 MW. The results show that the net power generation efficiency and exergy efficiency of the proposed system can reach 53.06 % and 52.24 %, respectively, which are approximately 6.94 and 6.83 percentage points higher than those of the reference system. The significant role of thermochemical method is that the chemical energy of syngas produced by the proposed system is 851.57 MW, which is increased by approximately 29.70 %. Through the energy utilization diagram analysis, it is found that the key to performance improvement is that the exergy destruction of the fuel conversion process and heat exchange process are decreased by 10.36 % and 54.68 %, respectively. Finally, the proposed system has better performance and lower exergy destruction. The solar thermal energy of low energy level is converted into syngas chemical energy of high energy level, and the upgrading of solar energy is achieved. In addition, the proposed system is simpler, and eliminates the air separation unit and syngas purification unit. This work provides a promising method for the complementary utilization of solar energy and coal.

Modelling of an Integrated Plasma Gasification Combined Cycle power plant using Aspen Plus

The development of a steady-state model of an Integrated Plasma Gasification Combined Cycle (IPGCC) power plant is presented here. The model includes the plasma gasifier, syngas conditioning units, and the power generation unit. Furthermore, the model of each component implemented in Aspen Plus is described in detail (thermodynamic method, chemical reactions, and operative conditions). The proposed model was validated by comparing the plasma gasification results with experimental and numerical data from the literature; the relative error was 6.23% and 5.24%, respectively. The model was then used to perform a two-part sensitivity analysis. In the first part, simulations with municipal solid waste (MSW) with a moisture content varying from 20% to 60% were performed. The moisture content increment reduced the torch-specific power consumption by 53%. However, because of the increasing specific fuel consumption, the thermal efficiency of the IPGCC power plant also decreased by 28% as the MSW moisture content increased from 20% to 60%. In the second part, it was determined that the IPGCC power plant reached the best performance (32.5%) when a high plasma temperature (5000 °C) and a low gasification temperature (2000 °C) were used. At these highest efficiency conditions, the 1000 t/day IPGGC power plant’s net power generation was 62 MWe.

Comparative evaluation of microwave and conventional gasification of different coal types: Experimental reaction studies

Effects of gasifier conditions (microwave or conventional) on the gasification characteristics of four different types of coal are evaluated by analysis of gaseous species generated during pyrolysis and gasification reactions. Four different coal samples are tested: a lignite (Mississippi), a low-ash subbituminous (Wyodak), a high-ash subbituminous (Usibelli), and a low volatile bituminous (Pocahontas #3). Gas composition, overall yields, carbon conversion efficiency, and cold gas efficiency are evaluated to compare gasification reactivity of the different coal types under microwave and conventional heating. During microwave pyrolysis (Ar atmosphere), greater selectivity of syngas species (H2 + CO) and greater overall non-condensable gas yields are observed, compared to conventional pyrolysis for all coals tested. The high yield of syngas during microwave pyrolysis is attributed to primary pyrolysis gases subsequently gasifying the char of the same sample to produce greater amounts of H2 and CO. During microwave gasification (CO2 atmosphere), selective heating and formation of hotspots within the coal enable the reverse Boudouard reaction to occur at a low bulk gasification temperature of 700 °C, which is less favorable under thermal gasification at this temperature. Yields of syngas are much higher under microwave gasification of all coals. Carbon conversion is found to have a linear correlation with volatile matter of the parent coal. Carbon conversion and cold gas efficiency are highest for coals gasified under microwave irradiation, and gasification reactivity of the four coals was determined to be dependent on the coal type.

Effect of auto thermal biomass gasification on the sintering of simulated ashes

Ash sintering is an essential factor for the competitiveness of biomass gasification. Compared to conventional air biomass gasification, the gasification temperature is reduced in the auto thermal biomass gasification, as the utilisation of thermal compensation for the CaO carbonation reaction, which ultimately could suppress the extent of ash sintering. This work firstly investigated the inhibition effect of this process on the sintering of simulated ashes (silica, potassium oxide and alumina) in a lab-scale fixed bed reactor. The results indicate that the alumina particles are present under different CO2 concentrations, gasification temperature and CaO/ biomass ratios. However, silica and potassium oxides react with CaO and disappear at high temperatures. Among the three simulated ashes, alumina particles are relatively stable in the auto thermal biomass gasification. The average particle size decreases from 116.9 µm to 64.9 µm and 93.8 µm when CaO/alumina ratio is 2 and 5, respectively, indicating the increase of CaO addition under the flue gas atmosphere could inhibit the sintering degree of simulated ash. Meanwhile, the reaction between CaO and CO2 in the carrier gas can reduce the formation of calcium silicate. Therefore, compared with conventional biomass gasification, auto thermal biomass gasification is favourable to restrain the degree of ash sintering because of the relatively low gasification temperature.

Hydrogen-rich gas production from steam co-gasification of banana peel with agricultural residues and woody biomass

Steam co-gasification of banana peel with other biomass, i.e., Japanese cedar wood, rice husk and their mixture, was carried out for the hydrogen-rich gas production in a fixed-bed reactor. For the co-gasification process, the banana peels were physically mixed with rice husk, Japanese cedarwood and their mixture respectively by different mixing weight ratios. The effects of reaction temperature and the addition amount of banana peel on the gas production yield were investigated by comparing the experimental data with the calculated ones based on the individual biomass gasification at the same condition. It was found that the banana peel with a high content of alkali and alkaline earth metal (AAEM) species exhibited not only high gasification reactivity but also a significant enhancing catalytic effect on the co-gasification process at the low temperature, especially with the biomass containing no silica species. The high content of silica species in the rice husk had a negative effect on the gasification reactivity of banana peel during the co-gasification since it could hinder the release of AAEM from the biomass and/or lead to the possible formation of inactive alkaline silicates. However, the combination of these three samples with the suitable weight ratio could improve the gasification performance at the low temperature due to the synergetic effect provided by high contents of potassium and calcium from banana peel and cedarwood respectively. Moreover, the addition of calcined seashells as the CaO source could further improve the gas production yield, especially the hydrogen gas yield at a relatively low gasification temperature of 750 ℃.

Influence of Different Catalysts on Coal Char-CO2 Gasification

The influence of catalyst Fe(NO3)3, CaO and composite catalysts on the thermostatic gasification process of char-CO2 at atmospheric pressure were studied in this paper. The experimental conclusions Indicate that the catalytic effect of CaO is stronger than that of Fe(NO3)3 at relatively low gasification temperatures. As the gasification temperature increases, the catalytic gap between the two catalysts decreases. The catalytic effect of the composite catalyst at lower gasification temperatures is between the single component catalysts CaO and Fe(NO3)3. When the gasification temperature exceeds 850°C, the promoting effect of the composite catalyst is better than that of the to single-component catalysts. After adding composite catalyst, the time of the coal char is shorter by 103 minutes than the original char, which is shortened by 18 minutes compared with the two single-component catalysts, and the gasification temperature is lowered by 100°C, lower than 120°C of one-component CaO, and higher than 90°C of Fe(NO3)3.

Experimental investigation on the air gasification of olive cake at low temperatures

In this work, the impacts of temperature, equivalence ratio, contact-time, and torrefaction on air gasification of olive cake at low temperatures were experimentally investigated. Both raw and hydrolysed olive cake feedstocks were considered. The yields of main fuel gas products, the gas LHV, and cold gas efficiency (CGE) were adopted as the indicators to evaluate the gasification performance. The experimental work was conducted in fixed bed reactor. Higher CO, CH4 and H2 yields and CGE were obtained for an equivalence ratio of 0.3 and a temperature of 700 °C. The main difference between gasification of raw and hydrolysed olive cake samples were the higher yields of fuel gas in hydrolysed sample, likely due to the higher lignin content. The main difference between non-torrefied and torrefied samples was observed on CO and CH4 yields and CGE. At the same operating conditions, the CO and CH4 yields increased with torrefaction, while H2 yield decreased. Gasification of torrefied-raw olive cake increased by 14.1% and 95.3% the CO and CH4 yields. Finally, important differences on results were found when metal-loaded samples were tested. This study demonstrated that both hydrolysed and raw olive cake samples are high quality gasification feedstock to achieve a good CGE also at relatively low gasification temperatures.

A perspective on sodium-induced agglomeration of Zhundong coal gasification: Experiments and calculations

In order to provide basic knowledge for the gasification utilization of low-rank Zhundong (ZD) coal in the process of circulating fluidized bed (CFB), this study focuses on gasification reactivity and ash related agglomeration of ZD coal mainly induced by sodium transformation. Typical ZD coal was pyrolyzed in a horizontal tube reactor by a rapid pyrolysis method at 900 °C. Isothermal and non-isothermal thermogravimetric analyses were used to study the gasification reactivity of ZD char under CO2 atmosphere. The effect of temperature, ranging from 850 °C to 1050 °C, on isothermal gasification was investigated, and the obtained gasification residues were analyzed to observe microscope morphology and evaluate agglomeration degree. The ternary system relationship of Na2O–SiO2–Al2O3 at each gasification temperature was calculated with FactSage to compare with the experimental results. The results show that: the gasification reactivity of ZD coal char is greatly affected by the gasification temperature. Higher temperature can increase the average specific gasification rate, thus shorten the reaction time that the carbon conversion reaches equilibrium. The gasification reactivity of coal char is proved to be better at higher temperature. The agglomeration characteristics were also affected by the gasification temperature. There is almost no melting and agglomeration phenomenon for 850 °C gasification residue, while a strong tendency to agglomeration is showed in other samples. However, when the mass fraction of local CaO on the surface of large particles is more than 40%, the melting phenomenon can be alleviated. According to the Na2O–SiO2–Al2O3 phase diagram, the positions of ZD coal and ZD char are located near the complete Slag-liq region, indicating that using ZD coal and ZD char at the operation temperature of CFB above 950 °C has strong risk of slagging, and a relatively lower gasification temperature, ∼900 °C, is suitable for ZD coal/char gasification.

Rootcrops processing waste management by Pyrolysis conversion

The waste products derived from the commercial processing of root crops are the soiled peels, trimmings, root tissues, and by-products like pulp fibers obtained from the finishing operations. These bulky waste products create the management problems of safe storage and environmentally sound disposal. Processing the wastes from cassava was found to be the most suitable for pyrolysis conversion from among the rootcrops considered. Results showed that, of the four (4) cassava waste forms, larger briquette was found to have the highest vinegar yield conversion at 1.842L per kg while the shred form had the lowest at 1.203L per kg. The rate of vinegar production was also fastest from the briquettes at 2.388L per h and lowest from the raw form at 1.544L per h. Better vinegar yields were therefore associated with solid fuel forms, smaller bed porosity, smaller surface reaction area, and lower gasification temperature. Other factors that also affected vinegar production were the loading rates, air supply conditions, and heat exchanger efficiency. In this study, the available Logarithmic Mean Temperature Difference (LMTD) was only 45.67°C, indicative of poor performance of the exchanger unit. The heat exchanger unit’s design can be improved in future experiments by using good thermal conducting materials, reconfiguration, and increasing the conductor interface area. This should result in higher vinegar yields.

A Detailed One-Dimensional Hydrodynamic and Kinetic Model for Sorption Enhanced Gasification

Increased installation of renewable electricity generators requires different technologies to compensate for the associated fast and high load gradients. In this work, sorption enhanced gasification (SEG) in a dual fluidized bed gasification system is considered as a promising and flexible technology for the tailored syngas production for use in chemical manufacturing or electricity generation. To study different operational strategies, as defined by gasification temperature or fuel input, a simulation model is developed. This model considers the hydrodynamics in a bubbling fluidized bed gasifier and the kinetics of gasification reactions and CO2 capture. The CO2 capture rate is defined by the number of carbonation/calcination cycles and the make-up of fresh limestone. A parametric study of the make-up flow rate (0.2, 6.6, and 15 kg/h) reveals its strong influence on the syngas composition, especially at low gasification temperatures (600–650 °C). Our results show good agreement with the experimental data of a 200 kW pilot plant, as demonstrated by deviations of syngas composition (5–34%), lower heating value (LHV) (5–7%), and M module (23–32%). Studying the fuel feeding rate (22–40 kg/h), an operational range with a good mixing of solids in the fluidized bed is identified. The achieved results are summarized in a reactor performance diagram, which gives the syngas power depending on the gasification temperature and the fuel feeding rate.

A comprehensive study on influence of operating parameters on agglomeration of ashes during biomass gasification in a laboratory-scale gasification system

Ash residues produced from biomass gasification could agglomerate and cause severe ash-related problems. The objectives of this study were to determine the impacts of different operating parameters (including equivalent ratio (ER), residence time (RT), and gasification temperature (GT)) on ash deposits during corncob gasification and to further elucidate ash agglomeration mechanisms. The results indicated that the major difference between the ashes in gasifier and the cyclone fly ash (CFA) in mineralogy was that the CFA had a higher content of potassium-bearing compounds, particularly sylvite and potassium silicates, the contents of which could be as high as 47.33 wt% and 12.61 wt%, respectively. Compared with the gasifier fine ash (GFA), the microstructure of gasifier slagging block (GSB) seemed to be much denser and could be divided into three types, skeleton structure, porous texture, and dense structure. However, the melting of CFA was more severe than that of the gasifier ashes. During gasification, a higher ER and a higher GT favored the capture of more volatile species such as K, Ca, S and Cl in the cyclone while a lower GT and an increased RT favored the retention of Si, Al and Fe in the bottom residues. Moreover, when the ER was increased, less silicate minerals could be concentrated on the CFA. With regards to the operations performed at different times, no obvious variation in the ash mineralogy was observed. The ER had little influence on fly ash morphology while the slagging degree of fly ash could be enhanced with the increasing of RT.

Promoting effect of biomass ash additives on high-temperature gasification of petroleum coke: Reactivity and kinetic analysis

The effect of biomass ash (rice straw ash (RSA) and cotton straw ash (CSA)) on the gasification reactivity and the evolution of physicochemical structure of petcoke char was investigated. The catalytic effect of CSA was significantly higher than that of RSA, and the catalytic effect of biomass ash was enhanced at lower gasification temperature and for higher blending ratio of biomass ash. The promoting effect of biomass ash was related to the increase of active AAEM content, the decrease of order degree of carbon structure and the development of surface structure in char gasification after biomass ash addition, which was more significant for CSA, at lower temperature and for higher blending ratio. Moreover, the shrinking core model was suitable for char gasification, and the additions of RSA and CSA reduced the activation energy of petcoke char gasification from 199.84 kJ mol−1 to 159.85 kJ mol−1 and 62.75 kJ mol−1, respectively.

Influence of coal ash on CO2 gasification reactivity of corn stalk char

The effect of added coal ash on the gasification behavior of corn stalk char by using the thermalgravimetric analysis and a lab-scale horizontal fixed bed furnace was investigated. For comparison, synthetic ash with different chemical composition was used for studying the effect of difference ash composition on promoting/inhibiting the gasification reactivity. The results show that the slagging-control preferred coal ash additive has a negative impact on the gasification performance. Interestingly, a relatively less slagging-control preferred coal ash additive has a beneficial impact on promoting the gasification performance under low gasification temperature. This could be due to the difference composition between the two coal ash additives, where the former coal ash type has much lower content in the calcium and iron. In addition, the findings in the synthetic ash suggest that iron can have a better performance in promoting gasification than calcium/magnesium. Two types of coal ash show an inhibiting effect under higher temperature due to temperature might be the dominant factor and the restraining effect of additive. These observations are also supported by the evolution of char structure by using the Raman spectroscopy. Further, the modified random pore model can correlate well with the gasification kinetics data.

Effect of torrefaction on steam gasification of starchy food waste

This work compares the gasification of the raw and the torrefied leftover rice to understand the effect of torrefaction on steam gasification of starchy food waste at various temperatures. Torrefaction experiments were first performed at 240–300 °C to study the effect of torrefaction temperature on fuel properties of torrefied leftover rice. Then, gasification experiments of the raw and torrefied leftover rice sample were conducted in a fixed-bed reactor at 600–1000 °C and a steam/carbon (S/C) molar ratio of 2. It is found that the raw leftover rice can be completely converted into volatile products at 600 °C, but with a high tar yield of 20.4% and a low cold gas efficiency (CGE) of 60.5%. A further increase in gasification temperature to 700 °C greatly reduces the tar yield to 1.9% thus substantially increases the CGE to 94.9%. Further comparisons with the existing data from other feedstocks demonstrate that the raw leftover rice is a high-quality gasification feedstock which can achieve a high CGE at a low gasification temperature (i.e., 700 °C). In contrast, the gas yield of the torrefied leftover rice is low at low temperatures, but increases with gasification temperature due to enhanced char reforming reactions. This leads to the CGE of the torrefied leftover rice increasing from 16.7% at 600 °C to 91.1% at 1000 °C. It should be noted that the CGE of the torrefied leftover rice at 1000 °C is even higher than that of the raw leftover rice, due to increased coke formation from the raw leftover rice at high temperatures, most likely via the hydrogen abstraction and carbon addition reactions. While for the torrefied leftover rice, its coke formation is mainly attributed to the tar polymerization reactions. The results show that the gasification of torrefied leftover rice at high temperatures (>900 °C) generates high-quality syngas suitable for the synthesis of chemical products.