Fixed-bed Gasifier Research Articles

Exergy Analysis of a Fixed-Bed, Batch Type Rice Husk Fuelled Downdraft Gasifier

This paper treats exergy analysis of rice husk at various loading rates of 1 kg, 1.5 kg and 2 kg of feedstock, using a batch type, fixed-bed gasifier, equipped with a gas filtering system and between the operating temperatures of 690 K and 1100 K, operated for the whole year. Exergy analysis is a thermodynamic technique which uses conservation of mass and energy principles to design thermal systems with maximum efficiency and it is based on First and Second law of thermodynamics. Formulas from literature and previous researches as well as Microsoft Excel 2007 were used to make calculations and graphically interpret the results. The exergoeconomic analysis is based on location specific and national data collected from official sources. A MATLAB based hybrid model developed from a combination of other studies is used to generate the exergoeconomic analysis results. Methane was found with the highest total exergies where values of exergies were varying between 1110126 kJ and 1066279 kJ for 2kg; 1037525 kJ and 1004639 kJ for 1.5 kg and finally, 965559.3kJ and 943635.6kJ for a feedstock mass of 1 kg between 690 K and 960 K respectively. From the overall results obtained, the gasification efficiency can be improved by increasing the temperature with an addition of heat in the process. The R2 values of 0.999 to 1 show the true behavior and similarities of the graphs and highlighting the enormous exergy destruction rate in the process. The CO2, CO and NOx capture/avoidance increases the plant efficiency by producing more electricity thereby increasing the financial potential of the plant. From the total exergies of CO2, CO and NOx, $0.156/kg, $0.20/kg and $12.335/kg could be made when sold respectively. The total exergies of gases considerably assist in the exergoeconomic analysis of the gasification plant, when the environmental aspect is considered.

Simulation studies on the co-production of syngas and activated carbon from waste tyre gasification using different reactor configurations

• Waste tyre gasification was evaluated in three different reactor configurations. • Fluidized bed, fixed bed and rotary kiln reactors were evaluated. • Fixed bed reactor was the most suitable reactor configuration for syngas production. • Fluidized bed reactor was the most suitable for activated carbon production. • Coproduction of syngas and activated carbon was most suitable in fluidized reactor. Gasification is one of the most efficient thermo-chemical conversion processes for transforming waste tyres into syngas and high-valued solid carbon products such as activated carbon (AC). This study evaluated the co-production of syngas and AC in three reactor configurations: fluidized bed, fixed bed, and rotary kiln at the systems level. A single-stage steam gasification and char activation process was simulated using Aspen Plus V10 software. The effects of gasification parameters such as equivalence ratio (ER) and steam-to-fuel ratio (SFR) were investigated and compared. The best conditions for the co-production of syngas and AC in the reactors were evaluated and compared. Brunauer-Emmett-Teller (BET) computational analysis was used to predict the surface area of the AC. The fluidized bed gasifier has the potential to produce syngas with a low heating value (LHV) of 6.67 MJ/Nm 3 , cold gas efficiency (CGE) of 82.4% LHV , AC with BET surface area of 698.63 m 2 /g and a carbon conversion ratio (CCR) of 92.5%, the fixed bed gasifier has a syngas LHV of 6.25 MJ/Nm 3 , CGE of 85.9% LHV , AC with BET surface area of 432.51 m 2 /g and CCR of 97.3% and the rotary kiln gasifier has a syngas LHV of 5.96 MJ/Nm 3 , CGE of 74% LHV , AC with BET surface area of 661.73 m 2 /g and CCR of 93%.

Hydrogen production from co-gasification of Çan lignite and sorghum biomass in a fixed-bed gasifier: CFD modeling

Hydrogen production from co-gasification of Çan lignite and sorghum biomass in a fixed-bed gasifier: CFD modeling

Multi-objective optimization of an integrated biomass waste fixed-bed gasification system for power and biochar co-production

In this work, an integrated biomass waste gasification combined heat and power (CHP) system is simulated and analyzed based on a multi-scale first-principles numerical model, which consists of a 1D fixed-bed gasifier model and a 1D hybrid peripheral fragmentation and shrinking-core biomass particle model. The simulations are based on a 15kW gasification CHP system and the numerical model is validated by two different groups of experimental data, and the maximum deviation is 2.56% in syngas H2 composition prediction. A multi-objective optimization framework of the integrated biomass waste gasification CHP system is formulated that considers 3 objectives: economic benefit, greenhouse gas emission, and potential health impact caused by PM emission. The best-compromised solution from the Pareto front leads to $142.8/day economic benefit, 694.3 kg CO2eq/day mitigation, and 57.67 Singapore Pollutant Standards Index score. The impacts of the three objectives on decision variables (i.e., feedstock flowrate, feedstock moisture content, and equivalent ratio) are analyzed by investigating 21 different weighted single-objective problems.

Enhancement of syngas production via co-gasification and renewable densified fuels (RDF) in an open-top downdraft gasifier: Case study of Indonesian waste

The global increase in world population is followed with a rise in waste generation and energy needs in various sectors. Organic waste, also known as biomass, is the most substantial contribution of the waste generation and it also can be utilized in energy generation. Therefore, the purpose of this study is to analyze the syngas production from co-gasification using Renewable Densified Fuels (RDF) with gasification temperature, lower heating and gas emission values, on the performance of the biomass co-gasification process in an open-top downdraft fixed bed gasifier. In this study organic waste used woods, coconut fibers and rice husks in pellets to blend the compositions of raw materials during the co-gasification process. The method used is the co-gasification technique with feed pellets WCF (wood-coconut fiber) and RH (rice husk) in various compositions, for example: 100% WCF, with 0% of RH, 75 WCF: 25 RH, 50 WCF: 50RH, 25 WCF: 75RH and all 100% RH with 0WCF. Furthermore, the syngas testing was directly measured on the burner with TCD type Shimadzu 8A gas chromatography. The result showed that the highest reactor temperature in the pyrolysis zone is 700 °C–900 °C which was significantly stable at 800 °C with oxidation temperature of 1000 °C–1100 °C. Furthermore, the result of the synthetic gas showed that the highest lower heating value of 100% WCF pellet composition at 3.582 kJ/Nm3 and lower heating value of RDF blending composition (75:25) at 3.392 kJ/Nm3. The increase in pellet fuels also leads to a rise in the LHV syngas value. These results produced a visually low tar content and ash particles in all compositions by approximately 30–35% of the initial mass, with the lowest ash in 100% WCF pellets composition at 0.25 g.

Gasification of mixed waste at high temperature to enhance the syngas efficiency and reduce gaseous emissions and tar production

ABSTRACT The brisk escalation in population, energy demand and waste production are the pivotal dilemma confronted world wide. Thus, gasification could be considered as a favorable, economical and ecofriendly technique to resolve this issue. In this study, upstream fixed bed gasifier was used in the process to convert the refuse derived fuel (RDF) into syngas. It was employed at high temperature of about 900°C with steam-to-biomass ratio of 2.0 and 3 min of residence time. Results showed that the calorific value of RDF was about 4340 Kcal/kg of RDF and carbon conversion efficiency was about 46.31%. The quality and composition of syngas was also determined at different operating conditions.The hydrogen gas was highest in concentration to about 27.01% followed by CO 25.79%, CO2 19.20% and then CH4 11.50%. Moreover, gaseous emissions were also monitored which depicted the level of SO2 at 500 mg/Nm3, NO2 at a100 mg/Nm3, H2S at 7 mg/Nm3, Cl2 at 95 mg/Nm3, particulate matter at 480 mg/Nm3 and smoke about 20%. All of these were under the prescribed limits recommended by Pakistan Environmental Quality Standards (PEQs) and US-EPA.

Development of a simplified gas ultracleaning process: experiments in biomass residue-based fixed-bed gasification syngas

For the realization of small-scale biomass-to-liquid (BTL) processes, low-cost syngas cleaning remains a major obstacle, and for this reason a simplified gas ultracleaning process is being developed. In this study, a low- to medium-temperature final gas cleaning process based on adsorption and organic solvent-free scrubbing methods was coupled to a pilot-scale staged fixed-bed gasification facility including hot filtration and catalytic reforming steps for extended duration gas cleaning tests for the generation of ultraclean syngas. The final gas cleaning process purified syngas from woody and agricultural biomass origin to a degree suitable for catalytic synthesis. The gas contained up to 3000 ppm of ammonia, 1300 ppm of benzene, 200 ppm of hydrogen sulfide, 10 ppm of carbonyl sulfide, and 5 ppm of hydrogen cyanide. Post-run characterization displayed that the accumulation of impurities on the Cu-based deoxygenation catalyst (TOS 105 h) did not occur, demonstrating that effective main impurity removal was achieved in the first two steps: acidic water scrubbing (AWC) and adsorption by activated carbons (AR). In the final test campaign, a comprehensive multipoint gas analysis confirmed that ammonia was fully removed by the scrubbing step, and benzene and H2S were fully removed by the subsequent activated carbon beds. The activated carbons achieved > 90% removal of up to 100 ppm of COS and 5 ppm of HCN in the syngas. These results provide insights into the adsorption affinity of activated carbons in a complex impurity matrix, which would be arduous to replicate in laboratory conditions.

Production of synthesis gas from biomass residues by staged fixed-bed gasification - results from pilot test campaigns

Fluidized-bed and entrained-flow gasification systems are developed for large-scale synthesis gas applications with at least 100 MW biomass input. However, there is also a market need for smaller-scale plants, which could be better integrated into energy production systems and local biomass logistics. The staged fixed-bed (SXB) gasifier described in this paper targets a size range of 10-50 MW of feedstock input. The primary gasification stage occurs in an updraft fixed bed. The tar-containing updraft gas is further processed in the secondary gasification zone, where gas temperature is raised from 200-500 °C to 750-900 °C by feeding secondary oxygen through a specially designed catalytic distributor zone. The composition and tar content of the resulting raw gas is similar to that of fluidized-bed gasifiers. Consequently, hot gas filtration, catalytic reforming and final gas cleaning technologies, similar to those recently developed and demonstrated for fluidized-bed gasifiers, can be applied. The results from the 0.5 MW pilot gasification tests carried out with wood, bark and sunflower husk pellets are presented in this paper.

Performance investigation of a non-combustion heat carrier biomass gasifier for various reforming methods of pyrolysis products

ABSTRACT Conventional biomass gasifiers such as fixed bed gasifiers, fluidized bed gasifiers, and entrained flow gasifiers have been widely studied in the literature covering biomass gasification systems. However, there are few published studies on non-combustion heat carrier biomass gasifier technology in the literature. Therefore, further studies are needed to reveal potential advantages, disadvantages, and possible improvement opportunities for this gasifier type. In this work, we investigate the effects of various operating parameters: reformation temperature, steam-to-biomass ratio, and steam-to-oxygen ratio on important performance indicators of non-combustion biomass gasifiers. To estimate the pyrolysis products, we use stoichiometric methods based on published data in the literature. The reforming of pyrolysis products is estimated using the Gibbs free energy minimization method using Aspen Plus. In addition, calculator blocks, sensitivity blocks, and design specifications are used to obtain the results. The results reveal that the desired hydrogen to carbon monoxide ratio can be obtained for steam reforming and autothermal reforming of pyrolysis products while a low hydrogen-to-carbon ratio (less than 1.5) is obtained for partial oxidation of pyrolysis products. However, partial oxidation can be beneficial in increasing the heating value of the syn-gas. The results presented in this study will be useful in improving the current configuration of non-combustion heat carrier biomass gasifiers. In future studies, the effects of gasifying agents on the tar content of the syn-gas, impurities in the syn-gas, start-up time of the gasifier, and size of the gasifier should be investigated.

Pilot-scale development of pressurized fixed-bed gasification for synthesis gas production from biomass residues

Advanced transportation biofuels have been the focus of intensive development since the early 2000s, and gasification in combination with synthesis technologies represents a flexible production pathway to deliver fuels for heavy-duty transport sectors that are difficult to electrify. This article is related to the pilot-scale development of a process concept aiming to smaller-scale production plants than are feasible with fluidized-bed gasifiers. Five test weeks with a total gasification time of 347 h were realized at a pilot plant that consisted of the pressurized staged fixed-bed gasifier, raw gas cooling to 500–600 °C, filtration with robust metal filters, and catalytic reforming of tars and methane. The gasifier combined an updraft primary stage and a catalytically enhanced secondary stage where most of the updraft tars were decomposed. The tar content of the product gas, 2–12 g/m3, was of the same order of magnitude as determined previously for fluidized-bed gasifiers. Consequently, similar filtration and reforming methods could be successfully applied. After the reformer, the contents of C2-hydrocarbon gases and high-molecular-weight tars were negligible.

Effect of Equivalent Ratio on Thermal Energy and Exhaust Gas Properties from Gasification of Oil Palm Empty Fruit Bunch using Household Gasifier

This study investigated the effect of equivalent ratio on thermal energy and exhaust gas properties obtained from gasification of oil palm empty fruit bunch by using a household gasifier. The fixed bed household gasifier was designed, fabricated and tested. The chopped oil palm empty fruit bunch (EFB) was used as feedstock and its feeding rate was fixed at 11 kg/hr. The studied equivalent ratios (ERs) of air were 0.1, 0.3, 0.5, 0.7, and 1, respectively. Then, the flame temperature of syngas firing and flue gases properties were determined. The results obtained from study showed that the gasification process was obtained if the ERs were 0.3 and 0.5. When the gasifier was operated at ERs of 0.7 and 1, the process was changed to be combustion. At ER of 0.5, it was the suitable condition for fixed bed gasifier due to this condition provided low ash content, low carbon monoxide, and moderate thermal energy.

Comparison of BGL and Lurgi gasification for coal to liquid fuels (CTL): Process modeling, simulation and thermodynamic analysis

Fixed bed gasifiers are widely used for the production of clean alternative fuels, chemicals and electricity. Of the commercialized fixed bed gasifiers, BGL and Lurgi gasifiers are the most typical. In this paper, modeling, simulation and comparison of the coal to liquid fuels (CTL) process with BGL/Lurgi gasifier are conducted. For a typical CTL process with feeding rate of 852.74 t coal (dry)/h, Case BGL can produce Fischer-Tropsch (FT) liquids of 212.61 t/h, while Case Lurgi can produce 168.48 t/h. Case BGL demonstrates higher energy efficiency (44.91%) than Case Lurgi (41.21%) due to the higher syngas yield of BGL gasifier. The corresponding exergy efficiencies are 44.65% for Case BGL and 40.27% for Case Lurgi, respectively. The exergy losses of the subsystems are quantitatively analyzed and the measures to reduce exergy losses are proposed. The techno-economic and CO2 emission analysis are investigated. Finally, the performances of fixed bed and entrained flow gasifiers for CTL process are compared. It is found that gasification has an important influence on the thermodynamic efficiency, economics, and CO2 emission, and this research is useful for gasifier selection in the CTL process.

Emission of species of environmental and process concern during simulated oxy-fuel gasification

The release of species of environmental concern during simulated oxy-fuel gasification in a laboratory scale fluidised bed have been investigated. Fluidising gases containing a high partial pressure of CO2 and in some tests, steam, were used. The species considered are tars, H2S and NH3 and the aim has been to gain an understanding of the impact of the gasifer operating conditions on their release. This is part of a programme of work on the potential of oxy-fuel gasification as a means of enabling the use of coal to continue as a source of energy, whilst capturing the CO2 for sequestration to minimise the impact on climate change.It has been shown that the tars released during pyrolysis are efficiently destroyed during their passage through the hot, char containing bed. The measured emission of tar was very low, particularly when compared to a conventional fixed bed gasifier. The extent of S release as H2S depends on the fuel-S and ash-Ca contents, and on the operating conditions. Increasing the partial pressure of CO2, steam and raising the temperature increased the proportion of S released. Adding dolomite, to retain S, decreased the emission level at atmospheric pressure, provided the temperature was above 950 °C. The use of this method to reduce S emissions at elevated pressure would require careful consideration, as the high partial pressure of CO2 in the fluidising gas can prevent the calcination of the dolomite and therefore reduce its effectiveness. Steam was found to increase the proportion of fuel-N converted to NH3 and the concentration also depended on the bed temperature. A peak in the concentration was noted at 850 °C, due to the opposing impacts on increased release as the temperature was raised and increasing equilibration of NH3 to N2 and H2.

Composition of phenolic compounds in wastewater from the fixed-bed gasification of Baishihu coal

Crude phenols extracted using organic solvent from the wastewater of a typical fixed-bed gasification process was used as a raw material, and the distillation range was analyzed. The wide and narrow fractions of the raw material derived from distillation range analysis were cut using a real boiling point distillation device. The phenolic compounds in the different fractions were then qualitatively and quantitatively analyzed by gas chromatography after derivatization pretreatment. The yield of the < 290 °C fraction was 68.50% (mass fraction). A total of 33 effective phenolic compounds were identified in this fraction, and the percentage of identified phenols was nearly 80%. The contents of eight phenolic compounds were high, with phenol being the most abundant (26.34%) followed by catechol (13.44%). The contents of the remaining six abundant phenols ranged from 4% to 8%. The sum of the contents of m-cresol and p-cresol exceeded 12%, and the content of 5-indenol was nearly 8%. The yield of the fraction rich in low-grade phenols (< 230 °C) was 35.40%. The content of phenol in this fraction was more than 40%, the total content of cresol was over 23%, and the total content of m-cresol and p-cresol was nearly 20%. At room temperature, the 235–245 °C and 245–260 °C fractions were white crystals in which the catechol content was approximately 50%, and the 5-indenol content was more than 10%. The contents of these two high-value-added phenolic compounds are low in typical coal tar, making them difficult to extract. However, due to their strong polarity and good water solubility, catechol and 5-indenol are enriched in gasification wastewater by water selection, allowing their further extraction.

Electrifying with High-Temperature Water Electrolysis to Produce Syngas from Wood via Oxy-Gasification, Leading to Superior Carbon Conversion Yield for Methanol Synthesis

Due to concerns regarding fossil greenhouse gas emissions, biogenic material such as forest residues is viewed nowadays as a valuable source of carbon atoms to produce syngas that can be used to synthesise biofuels such as methanol. A great challenge in using gasified biomass for methanol production is the large excess of carbon in the syngas, as compared to the H2 content. The water–gas shift (WGS) reaction is often used to add H2 and balance the syngas. CO2 is also produced by this reaction. Some of the CO2 has to be removed from the gaseous mixture, thus decreasing the process carbon yield and maintaining CO2 emissions. The WGS reaction also decreases the overall process heat output. This paper demonstrates the usefulness of using an extra source of renewable H2 from steam electrolysis instead of relying on the WGS reaction, for a much higher performance of syngas production from gasification of wood in a simple system with a fixed-bed gasifier. A commercial process simulation software is employed to predict that this approach will be more efficient (overall energy efficiency of about 67%) and productive (carbon conversion yield of about 75%) than relying on the WGS reaction. The outlook for this process that includes the use of the solid oxide electrolyser technology appears to be very promising because the electrolyser has the dual function of providing all of the supplemental H2 required for syngas balancing and all the O2 required for the production of a suitable hot raw syngas. This process is conducive to biomethanol production in dispersed, small plants using local biomass for end-users from the same geographical area, thus contributing to regional sustainability.

Numerical simulation of gasification with a one-dimensional particle submodel for char structure evolution

The exact knowledge of reaction rate, diameter, and density of a char particle is important for precise computational fluid dynamics (CFD) simulations of gasifiers. Most of the present research treats char particles as homogeneous with respect to density and composition. Diameter and density evolve according to power law relations, which are empirical and hard to validate. In this work, char particles are subdivided into multiple homogeneous shell–like volume elements. It allows the calculation of a density profile within the particle and hence profiles of specific surface area and effective diffusivity. This one–dimensional approach is directly compared to the common modeling approach based on Thiele modulus and power law relations. Both have been implemented into a two-dimensional CFD simulation of a lab–scale fixed bed gasifier. Simulations are carried out with particle sizes of 100 µm and 1 mm at temperatures of 800 °C up to 1800 °C with carbon dioxide and water vapor at 1 atm and 50 atm total pressure. The smaller diameter is relevant for entrained flow gasifiers. The reaction rate can accurately be described by the common approach with slight modifications. However, larger deviations of up to 13% and 42% remain for diameter and density in regimeII. Future work can either employ the presented shell model or adopt the proposed modifications to the common approach.

Primary fragmentation behavior of refuse derived fuel pellets during rapid pyrolysis

Primary fragmentation during rapid pyrolysis is considered to be the critical size reduction mechanism as it determines the particle size distribution and char conversion rates in the fixed bed gasifier. This study aims to investigate the primary fragmentation behavior of Refuse Derived Fuel (RDF) pellets during a rapid pyrolysis process. RDF pellets consisted of different blending ratios of cardboard and polyethylene (PE) were produced by a single-pellet densification process. Pyrolysis tests at temperature ranges of 500–700 °C were performed for each pellet type, and the number and particle size of the fragmented particles were analyzed. The results demonstrate that the different composition of RDF causes different particle binding mechanisms that behave differently during pyrolysis. Densification of cardboard particles can maintain the structure of the pellet char at higher temperatures compared to PE, due to the more stable lignin binding mechanism. A modified Fragmentation Ratio (FR) is introduced to quantify the degree of fragmentation. It is shown that a raise of the concentration of PE from 25 to 75 wt% increases the FR value by up to 4.2 times, whereas an increase in pyrolysis temperature from 500 to 700 °C only slightly changes the FR values. It can be concluded that the type of materials in the RDF pellet has a more dominating effect on the fragmentation compared to the pyrolysis temperature. Further, the volatile matter content of pellets shows a linear correlation with the FR value, whereas no clear relation is found in the case of the pellet's mechanical strength.

The study of palm kernel shell updraft gasification for supplying heat to an asphalt mixing plant

Air-gasification converts biomass using air into combustible gaseous components which also known as producer gas. The combustion of those gases provides energy for any purposes. In an asphalt mixing plant, this technology is implemented using palm kernel shell as feedstock to generate heat for aggregate heating as a part of hot-mixed asphalt production. Both Cold Gas Efficiency (CGE) and Carbon Conversion Efficiency (CCE) are the common performance indicators of such process. This study examines a performance of an updraft fixed-bed gasifier to convert the shell into producer gas in supplying heat for increasing aggregate temperature from ambient to about 145 – 165°C at capacity of 800 kg/min. The feedstock flowrate was set at 990 kg/hour and equivalence ratios were varied at 0.04, 0.05 and 0.08. Because the gasification reactions were in equilibrium, the producer gas composition for calculating the CGE was predicted using thermodynamic model with minimizing Gibbs free energy. The feedstock and solid residue of the process were analysed to determine the carbon content for calculating the CCE. It is indicated that the performance of the gasification operation for supplying heat in an asphalt mixing plant is limited by operating conditions.

Steam gasification characteristics of char pellets of typical technical solid wastes

Steam gasification performance of char pellets for typical technique solid waste (gloves, paper towel, coveralls, sawdust and their mixture) in nuclear power plant were examined between 700 °C and 900 °C at four steam concentrations (20 %, 40 %, 60 % and 80 %) in a lab-scale fixed-bed gasifier. There was certain synergistic effect in mixture gasification. The average percentage of solid residues for mixture char pellets was 32 % at the steam concentration of 20 %, which fell down about 71 % with lifting the steam concentration to 80 %. The activation energy of the mixture char pellets was 82.7 kJ mol−1. The kinetic parameters of steam gasification for all samples were well estimated based on shrinking core model. The maximum mass reduction ratio of mixture char through gasification was 98 %. The total maximum mass reduction ratios of primary samples through further gasification treatment were over 98 % that was much higher than that only through pyrolysis.

Techno-Economic Assessment of a Gasification Plant for Distributed Cogeneration in the Agrifood Sector

This research work presents a techno-economic analysis of a biomass gasification plant fueled with residues from the olive oil and almond industries for combined heat and power generation in the agrifood sector. The experimental plant consists of a downdraft fixed bed gasifier, a producer gas cleaning and cooling system and a spark-ignition engine–generator set as a power generation unit, which generates about 10–12 kW of rated electric power. With an average consumption between 13–14 kg/h of exhausted olive pomace pellets as feedstock, the producer gas volumetric flow rate was 31 Nm3/h (vol. %: 19.2 H2, 12.9 CO, 1.9 CH4, 19.2 CO2, 46.7 N2). The average cold gas efficiency was nearly 63%. This work also addresses the characterization and potential application of the carbonaceous solid residue (biochar), discharged from the gasifier at 1.7 kg/h. Finally, an economic feasibility analysis was developed, wherein the payback period ranges between 5–9 years.