Tar Content In Producer Gas Research Articles

Mathematical modeling of tar conversion on downdraft biomass gasification processes

AbstractThe article concerns some problems associated with the use of low‐grade fuels for the production of syngas in fixed‐bed gasifiers. Syngas is typically used to feed internal combustion engines in small power systems. Gas quality can be understood as its various characteristics, such as calorific value, the content of individual components (for example, hydrogen), low tar and soot content, and so forth. Achieving these quality criteria often requires specific conditions for the gasification process, in addition, some of them may be limited by additional requirements that are associated with thermal stability or fuel conversion requirements. When evaluating the technical and economic characteristics of gasification‐based power plants, the optimal efficiency does not always correspond to the higher efficiency of the gasification process and the quality of producer gas. In this regard, the aim is to develop optimization methods for different criteria and to create regime maps that cover physically achievable options. Novel mathematical models of tar conversion are proposed, allowing investigation of the dependencies of tar yield on gasification conditions, including the addition of catalysts or staged air supply. Computational tools based on thermodynamic and kinetic models make it possible to solve some of these problems, first of all, to consider and compare the efficiency of various methods for reducing tar content in producer gas (staged gasification, fuel mixing, thermal, and catalytic methods of tar elimination). The choice of relatively simple mathematical models allows us to conduct numerical calculations in a wide range of conditions and to optimize the parameters of biofuel conversion plants. This approach allows a more flexible choice of gasifier operating conditions, including its work as a part of a power unit. Optimal parameters are calculated for specific conditions: secondary air ratio (1–20%) and fraction of catalytic material (5–10%). The results may be used in the analysis and choice of biofuel gasification conditions at small power plants.

Partial oxidation of biomass gasification tar with oxygen transport membranes

Dual phase oxygen transport membranes were directly integrated into the producer gas stream of a low temperature circulating fluidized bed (LT-CFB) gasifier for partial oxidation of tar. Ce0.9Gd0.1O1.95–La0.6Sr0.4FeO3-d composite membranes were prepared by extrusion and dip-coating, co-sintered and infiltrated with electro-catalysts. These were investigated in two different set-ups: i) a membrane test rig, and ii) a partial oxidation testing unit connected to a biomass gasifier. The stability and performance of the membrane were tested in two different gas-streams; i) H2 and ii) producer gas. An oxygen flux of 1.5 Nml∙cm−2∙min−1 was measured in an air/H2 gradient at 850 °C through a 10 cm long membrane with a diameter of 10 mm, whereas a lower oxygen flux of 0.5 Nml∙cm−2∙min−1 was measured for the air/producer gas case. The producer gas contained ca. 2000 mg Nm−3 of primary tar. Analysis of the gas and the tar composition at the output of the membrane unit demonstrated that it contributed to the partial oxidation of the primary tar, resulting in a twofold increase of H2, CH4 and CO in the producer gas. This successful integration of oxygen transport membranes demonstrated that these membranes can reduce the tar content in producer gas from biomass gasifiers.

Absorption of Tar Content in Producer Gas using Used Cooking Oil in a Packed-bed Column

<span lang="EN-US">The tar content in producer gas may cause crusting on the engine if it is utilized as a fuel gas, thus it needs to be removed. This study aims to determine the liquid phase mass transfer coefficient in process of removing tar from producer gas in a packed-bed contactor column. This process is carried out continuously using used-cooking oil as absorbent. This was carried out by contacting the producer gas as a product of cacao pod-husk gasification at temperature range of 491-940<sup>o</sup>C at a certain counter-current flow rate with used-cooking oil in a column with a Raschig ring packing bed. The study used packed-bed materials with specific surface areas of 29.3927 m<sup>2</sup>/m<sup>3</sup>, 49.7532 m<sup>2</sup>/m<sup>3</sup>, 95.4113 m<sup>2</sup>/m<sup>3</sup>, 96.8182 m<sup>2</sup>/m<sup>3</sup>, 101.6840 m<sup>2</sup>/m<sup>3</sup>, and 105.0128 m<sup>2</sup>/m<sup>3</sup>, and with the linear velocity of used-cooking oil ranging from 0.0229 m/s to 0.0827 m/s. A mass transfer coefficient mathematical model has been constructed based on the research results. The model applies to the ranges (As.dt), (D<sub>L</sub>/dt.v<sub>L</sub>), and (µ<sub>L</sub> / ρ<sub>L</sub>.v<sub>L</sub>.dt) from 2.2397 to 8.0020, 2.26.10-10 to 1.72.10-9, and 0.0331 to 0.3102, respectively, with an average error of 9.33%. The average tar removed was 87%</span>

Feasible tar cleaning method of producer gas from palm kernel shell and mahogany fruit shell gasification

Palm kernel shells and mahogany fruit shells are technically possible to be converted into producer gas by means of air gasification process for several purposes, such as fuel gas, liquid fuels, or chemicals processes after specific treatments. Tar as the most significant impurity in the producer gas should be minimized to prevent blockage or chocking in the downstream flow of the system and to produce high purity gas. This research examines producer gas cleaning system which consists of scrubber, elutriator pipe, and shell-and-tube heat exchanger to produce low tar content producer gas in a fixed-bed gasifier using both feedstocks. This system is coupled with a fixed-bed gasifier using air as gasifying agent at feedstock capacity of 25 kg/h. It is found that gasification of palm kernel shell produced more tar at 92.67 ppm compared with mahogany fruit shell at 26.87 ppm. Furthermore, this system demonstrated high performance in reducing tar content in producer gas up to value of 8.67 ppm and 10.00 ppm for palm kernel shell and mahogany fruit shell gasification respectively.

Co–gasification of coal/biomass blends in 50 kWe circulating fluidized bed gasifier

This paper reports gasification of coal/biomass blends in a pilot scale (50 kWe) air-blown circulating fluidized bed gasifier. Yardsticks for gasification performance are net yield, LHV and composition and tar content of producer gas, cold gas efficiency (CGE) and carbon conversion efficiency (CCE). Net LHV decreased with increasing equivalence ratio (ER) whereas CCE and CGE increased. Max gas yield (1.91 Nm3/kg) and least tar yield (5.61 g/kg of dry fuel) was obtained for coal biomass composition of 60:40 wt% at 800 °C. Catalytic effect of alkali and alkaline earth metals in biomass enhanced char and tar conversion for coal/biomass blend of 60:40 wt% at ER = 0.29, with CGE and CCE of 44% and 84%, respectively. Gasification of 60:40 wt% coal/biomass blend with dolomite (10 wt%, in-bed) gave higher gas yield (2.11 Nm3/kg) and H2 content (12.63 vol%) of producer gas with reduced tar content (4.3 g/kg dry fuel).

Performance and Emission Characteristics of Producer Gas Operated Dual Fuel Diesel Engine with Cooling Cleaning System

The performance and emission characteristics of liquid fuel-producer gas operated dual-fuel engine depend on the quality of producer gas (PG) as tar content and temperature. In the present work cooling cleaning system has been adopted for the gasifier-engine system to reduce the tar content and cool the PG before inducting into the combustion chamber of the diesel engine. The experiments were conducted on 5.2 kW, DI, 4 strokes, diesel engine operated at 1500 rpm. It has been observed, improved performance and reduced emission levels for the dual-fuel operation of the engine with the use of cooling cleaning system. Experimental results showed that the brake thermal efficiency increased by 2-12% for the diesel/HOME-PG dual-fuel engine operation and tar content of PG was reduced from 320mg/Nm3 to about 55mg/Nm3 entering to the engine. Also, the emission levels were reduced, such as hydrocarbon 11.1%-19% and carbon monoxide 10.5%-20% compared to the wet filter provided with the gasifier-engine system. However, NOx emission levels were increased by 8% because of higher temperature due to the combustion of improved quality of PG. The temperature of the PG after the cooling cleaning system was reduced to 310C-340C which is the requirement for the diesel engine operation.

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%.

Gasification of dried sewage sludge in a newly developed three-stage gasifier: Effect of each reactor temperature on the producer gas composition and impurity removal

Gasification of dried sewage sludge was performed in a newly developed three-stage gasifier consisting of an auger as well as fluidized and fixed bed reactors to produce a producer gas with low-levels of contaminants. The auger reactor was designed to generate tar in advance, thereby enhancing the tar destruction in the fluidized bed gasifier and fixed-bed reactor. In the study, the effects of each reactor temperature and activated carbon as an impurity absorbent were mainly investigated. The reaction temperatures of the auger and fixed bed reactors were shown to have a strong influence on the tar removal, while that of the fluidized bed reactor mainly affected the producer gas composition. The three-stage gasifier clearly decreased the tar content in producer gas and condensed tar and increased the H2 production. In an experiment performed with activated carbon at the auger reactor temperature of ∼710 °C and the fluidized bed and fixed bed reactor temperatures of ∼830 °C, the tar and H2 contents in producer gas were only 22 mg/Nm3 and ∼29 vol%, respectively. Activated carbon clearly reduced the NH3 and H2S contents in producer gas. The minimum NH3 and H2S contents were 324 and 346 ppmv, respectively.

Air gasification of PVC (polyvinyl chloride)-containing plastic waste in a two-stage gasifier using Ca-based additives and Ni-loaded activated carbon for the production of clean and hydrogen-rich producer gas

A plastic waste containing polyvinyl chloride was gasified in a two-stage gasifier consisting of a fluidized bed reactor and tar-cracking zone to produce a hydrogen-rich producer gas with low tar and HCl contents. In particular, this study investigated the effects of calcined Ca-based additives, especially oyster shells, and a Ni-loaded activated carbon on the chlorine and tar removal. Additionally, a ∼3 h gasification of the plastic waste was performed using a distributor with a large hole size to confirm the gasification stability. In the experiments, where 900 g activated carbon was applied, all the producer gases were free of tar. The maximum H2 content (30 vol.%) in the producer gas was obtained with 900 g of Ni-loaded activated carbon. Chlorine in the feed material was mainly distributed in char and condensate liquid. The HCl contents in the producer gases obtained with the calcined Ca-based additives including oyster shells were under 1 ppm. The ∼3 h gasification revealed that the gasification was stable in terms of tar content in producer gas and producer gas composition.

Experimental study of wood downdraft gasification for an improved producer gas quality through an innovative two-stage air and premixed air/gas supply approach

This study conducted experiments on three different downdraft gasification approaches: single stage, conventional two-stage, and an innovative two-stage air and premixed air/gas supply approach. The innovative two-stage approach has two nozzle locations, one for air supply at combustion zone and the other located at the pyrolysis zone for supplying the premixed gas (air and producer gas). The producer gas is partially bypassed to mix with air and supplied to burn at the pyrolysis zone. The result shows that producer gas quality generated by the innovative two-stage approach improved as compared to conventional two-stage. The higher heating value (HHV) increased from 5.4 to 6.5MJ/Nm3. Tar content in producer gas reduced to less than 45mg/Nm3. With this approach, gas can be fed directly to an internal combustion engine. Furthermore, the gasification thermal efficiency also improved by approximately 14%. The approach gave double benefits on gas qualities and energy savings.

Flaming pyrolysis model of the fixed bed cross draft long-stick wood gasifier

The future industrial development of biomass energy depends on the application of renewable energy technology in an efficient manner. Of all the competing technologies under biomass, gasifiers are considered to be one of most viable applications. The use of biomass fuel, especially biomass wastes, for distributed power production can be economically viable in many parts of the world through gasification of biomass. Since biomass, is a clean and renewable fuel, gasification gives the opportunity to convert biomass into clean fuel gas or synthesis gas for industrial uses. The preparation of feedstock for a gasifier requires time, energy and labour and this has been a setback for gasifier technology development. The present work is focused on gasification of long-stick wood as a feed material for gasifiers. This application makes reduction not only in the cost but also on the power consumption of feed material preparation. A 50 m 3/h capacity gasifier was fabricated in the cross draft mode. The cross draft mode makes it possible to produce low tar content in producer gas. This cross draft mode operates with 180 W of blower supply for air to produce 10 kW of thermal output. The initial bed heights of the long-stick wood and charcoal are 58 cm and 48 cm respectively. Results were obtained for various flow conditions with air flow rates ranging from 20 to 30 m 3/h. For modelling, the flaming pyrolysis time for long-stick wood in the gasifier is calculated to be 1.6 min. The length of the flaming pyrolysis zone and char gasification zone is found to be 34 cm and 30 cm respectively. The rate of feed was between 9 and 10 kg/h. Continuous operation for 5 h was used for three runs to study the performance. In this study we measured the temperature and pressure in the different zones as a function of airflow. We measured the gas flow and efficiency of the gasifier in order to determine its commercial potential for process and power industries.

Tar content and composition in producer gas of fluidized bed gasification of wood—Influence of temperature and pressure

AbstractIn thermochemical biomass conversion processes, especially gasification, the tar content, and composition is a major subject. Because of the various processes examined at VUT, this work picks up the opportunity to compare the different tar amounts and its composition at different temperatures and process parameters. Gasification of biomass was carried out at the 100‐kW steam‐blown dual fluidized bed gasifier pilot plant III (800–870°C) and the 70‐kW air‐blown pressurized research unit (800–900°C; 1–5 bar) at VUT. Olivine is a catalyst for tar conversion; hence it was used as bed material in steam gasification and also in pressurized air gasification. For better understanding of tar formation during thermochemical conversion of biomass, the tar content and composition in the producer gas were analyzed with a gas chromatograph coupled with a mass spectrometer.Basic differences between the two thermochemical conversion processes occurred especially at higher temperatures or higher pressures. The tar composition was shifted to higher molecular tars such as polyaromatic hydrocarbons. Decreasing tar amounts were found at higher temperatures or higher pressures. Therefore, in future, an optimization of gasification processes should be easier to accomplish, which means lower tar content in the producer gas, which results in a better utilization of the biomass. © 2009 American Institute of Chemical Engineers Environ Prog, 2009