Tar In Producer Gas Research Articles

Investigation of different configurations of alumina packed bed reactor for coke free conversion of benzene

Conversion of producer gas tar without coke generation is a great challenge. This study investigates conversion of tar model benzene using different configurations of highly non-porous ɣ-Al2O3 packed bed reactor at 1000–1100 0C. The configurations comprised of different positions (relative to top (P1), center (P2) and bottom (P3) of reactor furnace), heights (5, 13 and 25 cm) and particles sizes (0.5, 3 and 5 mm) of alumina packed bed. Steam and CO2 were used as reforming media for tested benzene concentrations (0.4–1.8 vol%). The results showed benzene conversions of 48–91% with negligible steady thin coke generation using a packed bed (height: 25 cm, particles size: 3 mm) at P1. Whereas, relative high benzene conversions of 63–93 and 68–95% at P2 and P3 respectively with unsteady thick coke generation at benzene concentrations greater than 0.4 vol% increased differential upstream pressures (DUPs) of beds. Similar unsteady coke generation at benzene concentrations greater than 0.8 vol% and temperature of 1100 0C was observed with packed beds of heights of 5 and 13 cm, and particles size of 0.5 mm at P1. Generation of unsteady coke with condensed structure as evidenced by its characterization was attributable to increased benzene polymerization and reduced bed surface gasification reactions due to improperly installed packed bed. Developed kinetic model predicted well the generated coke. As conclusion, properly installed alumina packed bed pertaining to tar concentration and other experimental conditions may inhibit coke generation during tar conversion.

Tar cracking enhancement by air sparger installation in the combustion zone of the downdraft gasifier

In the present article, experimental studies are performed on Imbert downdraft gasifier using two different air distribution systems (two-nozzle and air-sparger) for the combustion zone. A novel air distribution system (air-sparger) is designed to supply uniform air across the combustion zone for achieving uniform temperature and enhancing the tar cracking. The effect of operating parameters (Equivalence ratio, temperature, air flow rate, and biomass consumption) on the tar cracking and producer gas compositions are investigated. Tar is measured in the producer gas before and after the gas cleaning units using a stack monitoring system. The experiments are performed by varying the airflow rate between 3 and 7 Nm3 h−1, and the equivalence ratio varies from 0.24 to 0.38. The operating parameters and air-sparger have significantly influenced the zone's temperature, producer gas composition, and the tar content in the producer gas. The maximum temperature of the combustion zone and reduction zone increases from 764 to 975 °C and 467 to 760 °C respectively with the air-sparger compared to the two-nozzle conventional air distribution system at the airflow rate of 7 Nm3 h−1. The lower heating value of the producer gas and the cold gas efficiency of the gasifier increased from 4.28 to 4.37 MJ Nm−3 and 48.55–55.05%, respectively, with the air-sparger. The incorporation of air-sparger reduces tar in producer gas from 23.95 to 0.97 g Nm−3 before gas cleaning unit at the airflow rate of 7 Nm3 h−1. Air-sparger has shown the adequate potential to enhance tar cracking and improve the overall gasifier performance.

Effects of biochar and ash outflow during updraft partial gasification on process parameters in a moving bed reactor

The present paper concerns the partial updraft gasification of wheat–rye straw pellets, using air as a gasification agent. The aim of this paper is to examine the impact of biochar and ash outflow during the updraft gasification process on the parameters of the latter. For this purpose, a series of five experiments with different parameters of biochar and ash outflow and a reference experiment were carried out with a constant amount of supplied air. The results of the research show that higher volumetric outflows of biochar and ash increase the calorific value (from 6.7 to 7.4 MJ/Nm3) and production (from 34.8 to 40.3 Nm3/h) of the producer gas, as well as the rate of fuel feed rate (from 30 to 43 kg/h). Reductions in the yield of gas (from 1.16 to 0.94 Nm3/kgfuel), equivalence ratio (from 0.125 to 0.087), and cold gas efficiency (from 44.7 to 40.2%) were observed. The content of gravimetric tar in producer gas was typical of updraft gasification and fluctuated within a range of 65‒125 g/Nm3.

Refining of producer gas using sand filters: An experimental study

The presence of tar in producer gas is a major bottleneck in wide application of biomass gasifier. The tar mitigation can be accomplished by physical methods, catalytic methods and thermal cracking method. The physical tar cracking method is done by passing the gas through sand filter or oil scrubber. In this study the tar refinement using sand filter has been attempted. The issued gas from biomass gasifier was passed across the sand filter positioned at the downstream of the gasifier. Initially experiments were carried out with 100 g of sand and then the quantity of sand was increased up to 500 g in steps of 100 g. As the sand quantity was increased the tar refinement increased from 16.5% to 38%. This experimental study indicated that there is further scope for tar refinement and improving the calorific value of producer gas using the catalytic tar mitigation methods.

Studies for removal of tar from producer gas in small scale biomass gasifiers using biodiesel

Biomass gasification based electricity generation systems are emerging as an important component of the decentralised energy supply systems in rural India. Each type of gasifier has different reaction conditions, temperature, residence time, pressure, feedstock, reactor design, and therefore the tar and particulate matter (PM) compositions and concentrations are found to vary. A field study was conducted on a 35 kWe downdraft gasifier to measure and characterize the tar in producer gas using GC-MS, for rice husk and pine needles as the two biomass feeds. Use of water-based scrubbers for removal of tar and PM is prevalent, however it is often the case that such clean-up is not adequate for meeting the engine manufacturers’ requirements for the quality of intake gas. Limited attempts have been reported for the use of organic solvent based gas cleaning in small scale downdraft gasifiers in the range 15–50 kWe. In the present work, toluene, naphthalene and phenol were selected as representative compounds of tar, and methyl oleate was selected to represent biodiesel as an organic solvent. A bench scale packed bed scrubber was designed for 95% removal of toluene. An 86–97% removal of toluene from the gas stream was achieved, and similar results were obtained for phenol and naphthalene. Further experiments were carried out with actual producer gas from a 1 kWe downdraft wood gasifier. Pongamia pinnata based biodiesel was used as the solvent, and 88–92% of the tar removal from the producer gas stream was achievable.

Effects of Oxygen Enrichment in Air Oxidants on Biomass Gasification Efficiency and the Reduction of Tar Emissions

This study applied oxygen-enrichment conditions to remove tar (the main problem in biomass gasification) and increase gasification efficiency. Experiments on oxygen-enrichment conditions were conducted at oxygen concentrations of 21%, 25%, 30%, and 35% in oxidants. This was expected to increase the partial oxidation reaction in gasification reactions, thus leading to thermal decomposition of tar in producer gas. The decomposed tar was expected to be converted into syngas or combustible gases in the producer gas. The results were as follows: Tar-reduction efficiency was 72.46% at 30% oxygen enrichment compared to the standard 21% enrichment condition. In addition, the concentrations of syngas and combustible gases in the producer gas tended to increase. Therefore, the 30% oxygen-enrichment condition was optimal, resulting in 78.00% for cold gas efficiency and 80.24% for carbon conversion efficiency. The application of oxygen enrichment into the lab-scale gasification system clearly reduced the concentration of tar and tended to increase some indexes of gasification efficiency, thus suggesting the usefulness of this technique in large-scale biomass gasification operations.

A statistical analysis on tar reduction in producer gas for IC engine application

ABSTRACT The automobile sector attained a boom in the last decade; this made the necessity for more fuel consumption. To meet the demand, many alternate fuel systems are introduced. Among that, producer gas blend carbonated fuels are highly recommended. Since, it is adaptive to the current internal combustion engines with modified carburetor. This paper aims to investigate the production of producer gas from wood and the methods to filter the tar content in it. The chemical-catalytic method is the cost- and eco-effective way to reduce the tar in producer gas. Therefore, a new Ni-based TiO2-supported catalysts are synthesised to improve the efficiency of the tar cracking. The catalytic system is affected by other factors such as bed temperature, catalyst weight, gas feed rate and gas residence time (GRT). The design of experiments is framed with L27 design table and the response is optimised using the Taguchi methodology. The derived regression equation attained 98.4% of adequacy in response prediction and the identified optimaltar cracking efficiency is 99.46% for Ni-Pr/TiO2 catalyst.

Optimisation of catalytic system for tar mitigation in biomass producer gas

ABSTRACTThe producer gas from biomass gasification is an upcoming power-generating technique for meeting the power requirements of the rural society. The performance of the biomass gasifier can be raised by mitigating tar in producer gas. Tar is highly carcinogenic and tends to condense at room temperature, which results in blocking and fouling of the downstream equipment. In this research, nano-structured SiO2-supported Ni pellets are used as catalysts to reduce the tar content in producer gas from a biomass gasifier. Further, Cerium (Ce) and Praseodymium (Pr) are reinforced with Ni–SiO2 pellets to improve the catalytic activity for tar mitigation. The Taguchi methodology is employed to rank and predict the optimal catalytic factor among the catalyst weight, gas feed rate (GF) and bed temperature (BT) for the tar cracking. The experimentation is done according to the L9 design table and the mathematical model for tar concentration is developed with the adequacy (R2) of 99.93%. The optimal catalytic system with 9 g of Pr, 0.01 l/s GF and 775°C of BT has reduced the tar concentration from 27 to 0.17 mg/Nm3, i.e. the efficiency of tar mitigation achieved is around 99.3%.

Gas cleaning with molten tin for hydrogen sulfide and tar in producer gas generated from biomass gasification

Hot gas cleaning of producer gas generated from a gasification process has many advantages in terms of thermal efficiency, gas-quality improvement, compact gas-cleaning devices, and economic feasibility. In this study, the characteristics of molten tin as a working fluid for hot gas cleaning were examined. To evaluate the hot gas cleaning performance of molten tin, the producer gas generated from the gasification of empty fruit bunch pellets was tested with a molten-tin-based gas cleaning system connected to the downstream of the gasifier. Gas chromatographic analysis of the producer gas shows that the removal efficiencies of hydrogen sulfide and non-condensable tar were about 97% and 80%, respectively, in a molten tin bed maintained at 400 °C. The results suggest that molten tin could be used as a multifunctional gas-cleaning medium for the simultaneous removal of tar and hydrogen sulfide from the producer gas.

Detailed Measurement Uncertainty Analysis of Solid-Phase Adsorption—Total Gas Chromatography (GC)-Detectable Tar from Biomass Gasification

Thermochemical gasification offers an attractive solution for the conversion of low-grade biomass and waste. However, practical experiences of the gasification processes reveal that the formation of tar is troublesome to continuous operation. Therefore, tar measurement protocols and tar reduction systems are priorities in the development of effective biomass gasification. Results of tar measurements often raise questions regarding their reliability and accuracy, because of calibration, sampling, and discrimination issues. The present work evaluates the solid phase adsorption (SPA)–gas chromatography (GC) measurement system for tar in product gas by comparing the mass spectroscopy detector (MSD) and flame ionization detector (FID) and their associated measurement uncertainty. The measurand is defined as the total GC detectable tar in a normal cubic meter of dry product gas when employing the common quantitation method, “quantitation as naphthalene”. The GC-FID measurements were significantly higher than th...

Design and development of a bench scale vegetable oil based wet packed bed scrubbing system for removing producer gas tar compounds

The overall goal of this study was to design, fabricate and evaluate a vegetable oil based wet packed bed scrubbing system to study the removal of model producer gas tar compounds, i.e., benzene, toluene, and ethylbenzene. The designed column was 0.5m diameter by 1.1m tall and contained 6-mm raschig rings. Soybean and canola oils were used as solvents. These oils were not statistically (p>0.05) different in removal efficiencies of benzene, toluene and ethylbenzene. Packing specific constants of Billet and Schultes (1999) correlation (CV=0.80 and CL=2.40) were found experimentally. These constants can be used to predict height equivalent to a theoretical plate (HETP) of laboratory or pilot scale vegetable oil based wet packed bed scrubbing systems. The pressure drop across the column was in the range of 6.7 to 18.8mm of water column.

Vegetable oil as a solvent for removing producer gas tar compounds

The objective of this study was to evaluate the performance of vegetable oil as a solvent in a wet packed bed scrubbing system for removing model producer gas tar compounds. Solvent type, column bed height, solvent temperature and solvent flow rate were varied to assess the performance in terms of tar removal efficiency. Soybean and canola oils were used as solvents. Benzene, toluene and ethylbenzene were used as model tar compounds. Testing was conducted using a bench scale packed bed column, 5.25cm diameter by 1.1m height, filled with 6-mm raschig rings as packing material. Statistical analysis showed that soybean and canola oils provide comparable removal efficiencies of tar compounds. The analysis also revealed that bed height and solvent temperature had highly significant effects on tar removal efficiencies. Bed height, solvent temperature and solvent flow rate had highly significant effects on liquid holdup and pressure drop across the column.

Solubility enhancement of producer gas tar compounds in water using sodium dodecyl sulfate as a surfactant

The overall goal of this study was to improve the solubility of tar compounds in water using a surfactant, sodium dodecyl sulfate (SDS). The solubility experiments were performed using 100-ml media bottles. Benzene, toluene, ethylbenzene, styrene, and p-xylene were used as model tar compounds because these compounds are sparingly soluble in water. The solubility of tar compounds was measured using UV/VIS spectrophotometer. Statistical analysis showed that solubilities of tar compounds improved significantly (p<0.0001) using SDS above the critical micelle concentration. Experimental results showed that the solubility of benzene, toluene, ethylbenzene, styrene and p-xylene increased 4 to 14, 9 to 33, 19 to 69, 18 to 83 and 29 to 135 fold, respectively, as SDS concentration increased from 0, i.e., water as control to 15, 30, 45 and 60g/L at solvent temperature of 20°C. Results also showed that solubilities of benzene, toluene and ethylbenzene decreased as the solvent temperature increased.

Equilibrium stage based model of a vegetable oil based wet packed bed scrubbing system for removing producer gas tar compounds

This study was aimed to develop and validate equilibrium stage based absorption model to investigate the removal of model producer gas tar compounds using vegetable oil as a solvent. The absorption model was developed using split (φ/γ) approach and a “RadFrac” block in Aspen Plus™. The model used Peng–Robinson equation of state (EOS) and non-random two-liquid (NRTL) activity coefficient model to predict the fugacity coefficients (φ) for vapor phase and activity coefficients (γ) for liquid phase. The developed model was validated using the extreme conditions of the experimental test range. The model predictions showed best fits with the experimental data within 6% for benzene, 4% for toluene, and 2% for ethylbenzene at the solvent temperature of 30°C. Packing specific constants of Billet and Schultes (1999) correlation (Ch=2.52 and CP,0=2.93) were found experimentally. These constants can be used to predict pressure drop across the column for vegetable oil based wet packed bed scrubbing systems. The average deviation of predicted pressure drop across the column compared to experimental data was within 5%. The developed absorption model and packing specific constants would be beneficial in the design, optimization, and economic evaluation of vegetable oil based wet packed bed scrubbing systems.

Effect of Sample Aging on the Accuracy of the International Energy Agency's Tar Measurement Protocol

The Working Group of the Biomass Gasification Task of the International Energy Agency (IEA) Bioenergy Agreement has developed a protocol for sampling and analysis of tar and particulates from biomass gasifiers, which is commonly accepted as a standard for reliable measurement of tar in producer gas. The methodology is dependent upon dissolving tar in a solvent for subsequent recovery by evaporation or distillation. This paper investigates whether storage of the tar/solvent sample prior to analysis affects the accuracy of the tar measurement. On the basis of the results of this study, we recommend that samples be analyzed within a few hours of collection and never be stored longer than 24 h.

Softeners for Rubber Based on Shale Thermal Dissolution Products

The source of raw materials for manufacturing softeners for rubber is extended through applying a nonwaste process of thermal dissolution of ordinary or enriched shale in crude producer-gas tar. The resulting products are less expensive than the conventional high-melting oil asphalts and oils.

A physico-chemical study of the action of lime on coal-tars

The action of lime on coal tars, especially the vertical retort and producer gas tars, has beenstudied physicochemically. The reaction finds its use in the preparation of fuel briquette binders and road surfacing materials. Lime-treated and normal tars have been studied by means of the microscope, the ultramicroscope and the electron-microscope. Lime-treated tar has been distilled and the distillate and residue compared with those of the normal tar. The distillation residue from the limetreated tar was not pitch but a porous coke-like material. The X-ray diffraction patterns of the pitch and this coke-like residue have been compared. Finally, an attempt has been made to explain the increase in viscosity and binding power of a producer gas or vertical retort tar on treatment with lime on the basis of the experimental evidence.