Development and testing of tube type wet ESP for the removal of particulate matter and tar from producer gas

This paper reports the development and testing of a state-of-the-art tube type wet electro-static precipitator (ESP) for cleaning producer gas generated through the process of biomass gasification. A wet ESP facilitates the removal of fine particulate matter (less than 1 micron) and tar with the added advantage of low internal power consumption. A tube type wet ESP was designed from first principles and simulations were carried out to prove its performance. Later on a full-fledged wet ESP was designed to process 100 Nm³/hr of gas, and was tested with an existing open top down draft biomass gasification system. Maximum particulate matter removal efficiency of 83% and tar removal efficiency of 62% was achieved. The results were encouraging to the tune that the particulate matter and tar levels were found below the permissible limits (50 mg/Nm³) for naturally aspirated reciprocating engines and thus the proof of concept was established. Nevertheless, the performance fell short of the permissible limits for turbo-charged reciprocating engines. The cause of the same has been identified and further development work is in progress.     

Thermodynamic analysis of combined unit of biomass gasifier and tar steam reformer for hydrogen production and tar removal

A combined unit of biomass gasifier and tar steam reformer (CGR) was proposed in this study to achieve simultaneous tar removal and increased hydrogen production. Tar steam reforming calculations based on thermodynamic equilibrium were carried out by using Aspen Plus software. Thermodynamic analysis reveals that when selecting appropriate operating conditions, exothermic heat available from the gasifier could sufficiently supply to the heat-demanding units including feed preheaters, steam generator and reformer. The effects of gasification temperature (T_gs), reforming temperature (T_ref) and steam-to-biomass ratio (S:BM) on percentages of tar removal and improvement of H₂ production were investigated. It was reported that the CGR system can completely remove tar and increase H₂ production (1.6 times) under thermally self-sufficient condition. The increase of H₂ production is mainly via the water–gas shift reaction.     

Roles of AAEMs in catalytic reforming of biomass pyrolysis tar and coke accumulation characteristics over biochar surface for H2 production

Coke formation is a significant challenge in catalytic tar reforming. AAEMs are essential in the conversion and decomposition of tar catalyzed by biochar. In this paper, four biochar catalysts with different K and Ca contents were prepared by acid washing and loading, and the coke accumulation characteristics in catalytic tar reforming at 650 °C were investigated using a single-stage reaction system. The gas-liquid-solid products were characterized by GC-MS, Raman, N₂ adsorption, FTIR and TG. The results suggest that K-loaded biochar has a maximum tar reforming capacity of 94.9%, while H-form biochar has a tar removal efficiency of only 27.8%. The micropore area in biochar is considerably reduced and the average pore size is increased after coke deposition. While K-loaded biochar retains the highest micropore area, it also exhibits a smaller increase in average pore size. The loading of K/Ca affects the growth structure of the coke, resulting in an increased number of O-containing structures in it. The coke on the Raw biochar surface is mainly small aromatic ring structures and aliphatic structures, thus increasing the intensity of the vibrational peaks corresponding to aromatic = C–H and aliphatic C–H on it. The coke on K-loaded biochar has a large proportion of aliphatic structures, which also contributes to the reduced graphitization of it after reforming. The AAEMs-free biochar surface preferentially removes tar components carrying O-containing groups. K-loaded biochar preferentially catalyzes the reforming of mono-aromatic ring components in tar. Ca-loaded biochar preferentially removes the mono-aromatic ring components, while being less selective for the removal of tar components containing hydroxyl groups and polyaromatic ring components. The loading of K/Ca promotes the dehydrogenation of the tar fraction during reforming, while only K catalyzes the deoxygenation of tar components. H-form biochar has no appreciable catalytic activity on CH₄ cracking. AAEMs have a catalytic activity on CH₄ cracking. K is particularly effective in improving tar conversion and hydrogen production of biochar.     

A novel process simulation model for hydrogen production via reforming of biomass gasification tar

Process modeling and simulation are very important for new designs and estimation of operating variables. This study describes a new process for the production of hydrogen from lignocellulosic biomass gasification tars. The main focus of this research is to increase hydrogen production and improve the overall energy efficiency of the process. In this study, Aspen HYSYS software was used for simulation. The integration structure presented in this research includes sections like tar reforming and ash separation (Ash), combined heat and power cycle (CHP), hydrogen sulfide removal unit (HRU), water-gas shift (WGS) reactor, and gas compression as well as hydrogen separation from a mixture of gases in pressure swing adsorption (PSA). It was found that the addition of CHP cycle and the use of the plug flow reactor (PFR) model, firstly, increased the overall energy efficiency of the process by 63% compared to 29.2% of the base process. Secondly it increased the amount of hydrogen production by 0.518 kmol (H2)/kmol Tar as compared with 0.475 of the base process. Process analysis also demonstrated that the integrated process of hydrogen production from biomass gasification tars is carbon neutral.     

A novel utilized method of tar derived from biomass gasification for fabricating binder-free all-solid-state hybrid supercapacitors

As an industrial pollutant, tar derived from biomass gasification is used as the precursor for fabricating a novel carbon-metal hydroxides composite electrode. A slurry (the mixture of tar, KOH and melamine) is daubed uniformly onto the nickel foam, which is directly carbonized to form NPC@LDH electrode material. This electrode is further coated with NiCo-LDH nanosheets using an electrodeposition method to form NF@NPC@LDH. The newly made NF@NPC@LDH electrode exhibits a high specific capacity of 9.6 F cm⁻² at a current density of 2 mA cm⁻² and good rate performance (55.3% retention). Furthermore, a hybrid NF@NPC@LDH//NF@PC all-solid-state supercapacitor is fabricated, and the device exhibits high energy density of 1.28 mWh cm⁻³ at a power density of 8.04 mW cm⁻³, low resistance and good cycling stability.     

Catalytic decomposition of tar derived from biomass pyrolysis using Ni-loaded chicken dropping catalysts

The Ni-loaded chicken droppings (Ni/CD) and chicken dropping ash (Ni/CDA) were prepared by the impregnation method and applied as catalysts for biomass tar decomposition at low temperature (450 °C) under N₂ and steam/N₂ conditions. The prepared samples and the supports were characterized by N₂ adsorption measurements, X-ray diffraction, H₂ temperature-programmed reduction, and X-ray photoelectron spectroscopy. The results reveal that Ni/CD and Ni/CDA showed higher catalytic activity for tar decomposition, in terms of producing hydrogen-rich gas, relative to commercial Ni/Al₂O₃ under N₂ conditions. This higher activity was caused by lower interactions of Ni with the support and the presence of additional reduced Ni. In the case of steam reforming, Ni/CDA also showed higher hydrogen yield and a lower amount of carbon deposition than Ni/Al₂O₃. This result indicates that a hydrophilic hydroxyapatite in the CDA support promoted the water–gas shift reaction to suppress carbon deposition and increase hydrogen yield.     

Tar removal from biomass pyrolysis gas in two-step function of decomposition and adsorption

Tar content in syngas pyrolysis is a serious problem for fuel gas utilization in downstream applications. This paper investigated tar removal, by the two-step function of decomposition and adsorption, from the pyrolysis gas. The temperature of the tar decomposition process was fixed at 800 °C both with and without steam, with air as the reforming agent. Both steam and air had a strong influence on the tar decomposition reaction. The reduction of the gravimetric tar mass was 78% in the case of the thermal cracking, whereas, it was in the range of 77–92% in the case of the steam and air forming. Under conditions of tar decomposition, the gravimetric tar mass reduced, while the yield of the combustible gaseous components in the syngas increased. Synchronously, the amount of light tars increased. This should be eliminated later by fixed-bed adsorption. Three adsorbents (activated carbon, wood chip, and synthetic porous cordierite) were selected to evaluate the adsorption performance of light tars, especially of condensable tar. Activated carbon showed the best adsorption performance among all light tars, in view of the adsorption capacity and breakthrough time. On the other hand, activated carbon decreased the efficiency of the system due to its high adsorption performance with non-condensable tar, which is a combustible substance in syngas. Synthetic porous cordierite showed very low adsorption performance with almost all light tars, whereas, wood chip showed a high adsorption performance with condensable tar and low adsorption performance with non-condensable tar. When compared with other adsorbents, wood chip showed a prominent adsorption selectivity that was suitable for practical use, by minimizing the condensable tar without decreasing the efficiency of the system.     

The performance of nickel-loaded lignite residue for steam reforming of toluene as the model compound of biomass gasification tar

Tars should be removed from biomass gasification systems so as not to damage or clog downstream pipes or equipment. In this paper, lignite insoluble residue (LIR) after extraction of humic acids was used as the support to prepare a nickel-loaded LIR (Ni/LIR) catalyst. This novel catalyst Ni/LIR was tested in steam reforming of toluene as a model compound of biomass tar conducted in a laboratory-scale fixed bed reactor. When compared to the reactions without catalyst or with Ni/Al₂O_3, Ni/LIR was confirmed as an active catalyst for toluene conversion at a relatively low temperature of 900 K. The investigated reforming parameters during the experiments in this research were selected as reaction temperature at a range of 850–950 K, steam/carbon molar ratio at a range of 2–5 mol/mol, and a space velocity from 1696 to 3387 h^?1. It was concluded that, under optimum conditions, significant amount of syngas yields, acceptable Ni/LIR consumption and more than 95% of toluene conversion can be obtained from the biomass Ni/LIR catalytic gasification system.     

Evaluation of sorbents for high temperature removal of tars,hydrogen sulphide,hydrogen chloride and ammonia from biomass-derived syngas by using Aspen Plus

Biomass gasification is a promising technology to produce secondary fuels or heat and power, offering considerable advantages over fossil fuels. An important aspect in the usage of producer gas is the removal of harmful contaminants from the raw syngas. Thus, the object of this study is the development of a simulation model for a gasifier including gas clean-up, for which a fluidized-bed gasifier for biomass-derived syngas production was considered, based on a quasi-equilibrium approach through Gibbs free energy minimisation, and including an innovative hot gas cleaning, constituted by a combination of catalyst sorbents inside the gasification reactor, catalysts in the freeboard and subsequent sorbent reactors, by using Aspen Plus software. The gas cleaning chain simulates the raw syngas clean-up for several organic and inorganic contaminants, i.e. toluene, benzene, naphthalene, hydrogen sulphide, hydrogen chloride and ammonia. The tar and inorganic contaminants final values achieved are under 1 g/Nm³ and 1 ppm respectively.     

Catalytic reforming of biomass primary tar from pyrolysis over waste steel slag based catalysts

Steel slag (SS) contains high amounts of metal oxides and could be applied as the catalyst or support material for the reforming of biomass derived tar. In this research, steel slag supported nickel catalysts were prepared by impregnation of a small amount of nickel (0–10 wt%) and calcination at 900 °C, and then tested for the catalytic reforming of biomass primary tar from pine sawdust pyrolysis. The steel slag after calcination was mainly composed of Fe₂O₃ and MgFe₂O₄, and granular NiO particles was formed and highly dispersed on the surface of nickel loaded steel slag which lead to a porous structure of the catalysts. The steel slag showed good activity on converting biomass primary tar into syngas, and its performance can be further enhanced by the loading of nickel. The yield of H₂ increased significantly with the increase of nickel loading amount, while excessive nickel loading resulted in the decrease in CO and CH₄ yields and significant increase in CO₂ yield. The presence of steam contributed to enhancing the tar steam reforming as well as reactions between steam and produced gases, while decrease the contact probability between the reactants and the active sites of catalysts, leading to a little decrease in tar conversion efficiency but significant increase in syngas yield. The iron and nickel oxides were reduced by the syngas (CO and H₂) from the biomass pyrolysis, and stable and porous structure was formed on the surface of the nickel loaded catalysts during tar reforming.     

Desulfurization and tar reforming of biogenous syngas over Ni/olivine in a decoupled dual loop gasifier

For the production of bio-SNG (substitute natural gas) from syngas of biomass steam gasification, trace amounts of sulfur and tar compounds in raw syngas must be removed. In present work, biomass gasification and in-bed raw gas upgrading have been performed in a decoupled dual loop gasifier (DDLG), with aggregation-resistant nickel supported on calcined olivine (Ni/olivine) as the upgrading catalyst for simultaneous desulfurization and tar elimination of biogenous syngas. The effects of catalyst preparation, upgrading temperature and steam content of raw syngas on sulfur removal were investigated and the catalytic tar reforming at different temperatures was evaluated as well. It was found that 850 °C calcined Ni/olivine was efficient for both inorganic-sulfur (H₂S) and organic-sulfur (thiophene) removal at 600–680 °C and the excellent desulfurization performance was maintained with wide range H₂O content (27.0–40.7%). Meanwhile, tar was mostly eliminated and H₂ content increased much in the same temperature range. The favorable results indicate that biomass gasification in DDLG with Ni/olivine as the upgrading bed material could be a promising approach to produce qualified biogenous syngas for bio-SNG production and other syngas-derived applications in electric power, heat or fuels.     

Main issues of the impact of tar,H2S,HCl and alkali metal from biomass-gasification derived syngas on the SOFC anode and the related gas cleaning technologies for feeding a SOFC system: A review

Biomass gasification has acquired considerable interest as a sustainable and environmentally friendly way to produce heat, hydrogen or electricity from agro-industrial wastes or other kinds of biomass. A very effective solution for the achievement of high electrical efficiency (up to 55%) is the integration of biomass gasification with solid oxide fuel cell (SOFC) technology, including the necessary gas cleanup to avoid degradation of the SOFC. For this reason, this paper first shows in detail the risk and the impact of carbon deposition, exposure to tar, hydrogen sulphide, hydrogen chloride and alkali metals on SOFC anode and then, considering the tolerance limit for inorganic and organic contaminants (<1 ppmv for H₂S, HCl and alkali and <10 ppmv for tar), offers an overview of the most relevant and effective technologies to remove these contaminants and to feed safely a SOFC system.     

Preparation of high-activity coal char-based catalysts from high metals containing coal gangue and lignite for catalytic decomposition of biomass tar

The potential of using high metals containing coal gangue and lignite to prepare high-activity coal char-based catalysts is investigated for effective biomass tar decomposition. Loose structure and rough surface are formed for these char-based catalysts with heterogeneous distribution of a large number of inorganic particles. In the biomass tar decomposition, the performance of the coal char-based catalysts is significantly influenced by the content of the metals in the raw materials and coal gangue char (GC) with the ash content as high as 50.80% exhibits the highest activity in this work. A high biomass tar conversion efficiency of 93.5% is achieved at 800 °C along with a significant increase in the fuel gas product. During the five-time consecutive tests, the catalytic performance of GC increases a little at the second or third times reuse and remains relatively stable, showing the remarkable stability of the catalyst in biomass tar decomposition applications.     

The influence of different chemical compositions in biomass on gasification tar formation

To elucidate the relationship between biomass composition and tar formation, forest residue sawdust, rich in lignin, and agriculture waste cornstalks, rich in cellulose, were gasified in a spout-fluidized bed reactor from 700 °C to 900 °C. Gel permeation chromatography (GPC) coupled with a photodiode array detector (PDA) and gas chromatography – mass spectrometry (GC–MS) were used to analyze the tar character. The GPC results showed that the molecular mass distribution of the gasified tars were unchanged, only the amount of each component changed when the temperature increased during gasification. The amount of heaviest molecular mass components decreased, while the lighter components increased with temperature. Sawdust tar and cornstalks tar both showed aromatic character, while cornstalks tar contained more aliphatic compounds than sawdust tar. The tar formation mechanism has been proposed from the experimental data analysis.     

Production of renewable hydrogen by steam reforming of tar from biomass pyrolysis over supported Co catalysts

Co catalyst supported on BaAl₁₂O₁₉ (BA) showed higher activity in the steam reforming of tar from the pyrolysis of biomass than those supported on Al₂O₃, ZrO₂, SiO₂, MgO, and TiO₂. Characterization results indicate that the Co metal particles supported on BA had high dispersion, although the surface area of Co/BA was small. High dispersion of Co metal particles on BA can account for the high steam reforming activity, and this high dispersion is related to the strong basicity of the BA surface. Strong basicity of BA and high dispersion of Co metal particles on BA are connected to high H₂O reactivity to form H₂, probably at the interface between Co metal and BA. In addition, the Co/BA catalyst exhibited higher reusability through the coke combustion and the subsequent reduction treatment than the Co/Al₂O₃ catalyst. This is attributed to the suppression of the solid reaction between the oxidized Co and BA.     

Effect of selected representative biomass gasification tar compounds on Ni-GDC solid oxide fuel cells

Contaminants as particulate matter, sulfur, chlorine and tar should be removed from biosyngas to avoid damaging solid oxide fuel cells. However, there is no sufficient information on tar effect since they might be potentially used as a fuel, or they might cause performance losses and irreversible damages. Therefore, this study aims to assess whether tar can be reformed inside the SOFC and used as fuel. Short-duration experiments were conducted on Ni-GDC cells operating with simulated biosyngas containing different concentrations of representative tar compounds from biomass gasification. While benzene and ethylbenzene could be regarded as additional fuels even at concentrations as high as 15 g/Nm³, naphthalene and phenanthrene act as contaminants for the SOFC electrochemical and catalytic reactions, even at concentrations of 0.3 and 0.05 g/Nm³. However, the effect on these reactions appeared almost completely reversible. Solid carbon deposited on the SOFC ceramic housing in proximity of the inlet. Post-mortem analysis should be performed to asses the tar effect on the cell anode.     

Perovskite-based catalysts for tar removal by steam reforming: Effect of the presence of hydrogen sulfide

One of the greatest problems in biomass gasification processes is the conditioning of the produced synthesis gas, which contains various contaminants, including tar and hydrogen sulfide. Nickel catalysts, designed for steam reforming of aliphatic hydrocarbons (natural gas and nafta), are usually deactivated by coke deposition and sulfur poisoning. In this work, nickel and/or manganese catalysts derived from perovskites were prepared by the citrate method and characterized by X-ray diffraction, N₂ physisorption and temperature programmed reduction. The catalysts were evaluated in the steam reforming of toluene, used as tar model compound, in the absence of H₂S at 700 °C and in the presence of 50 ppm H₂S at 800 °C. LaNi_0.5Mn_0.5O₃ catalyst showed higher activity and stability in the absence of H₂S. LaMnO₃ catalyst, although less active in the absence of H₂S, showed increased stability in the presence of H₂S, with conversion of about 60%. H₂ production was only observed in the absence of H₂S.     

Effect of biomass leaching on H2 production,ash and tar behavior during high temperature steam gasification (HTSG) process

The effect of biomass water leaching on H₂ production, as well as, prediction of ash thermal behavior and formation of biomass tar during high temperature steam gasification (HTSG) of olive kernel is the main aim of the present work. Within this study raw olive kernel samples (OK₁, OK₂) and a pre-treated one by water leaching (LOK₂) were examined with regard to their ash fouling propensity and tar concentration in the gaseous phase. Two temperatures (T = 850 and 950 °C) and a constant steam to biomass ratio (S/B = 1.28) were chosen in order to perform the steam gasification experiments. Results indicated that considering the samples' ash thermal behavior, it seemed that water leaching improved the fusibility behavior of olive kernel; however, it proved that water leaching does not favour tar steam reforming, while at the same time decreases the H₂ yield in gas product under air gasification conditions, due to possible loss of the catalytic effect of ash with water leaching.     

Experimental study of Ni/MgO catalyst in carbon dioxide reforming of toluene,a model compound of tar from biomass gasification

An experimental study of Ni/MgO solid solution catalyst in CO₂ reforming of toluene was conducted in this paper. Experimental parameters were reduction temperature, reaction temperature, CO₂/toluene mole ratio, and toluene feed rate.