Tar Destruction Research Articles

The Use of the Catalysts Based on Coal Ash Microsphere and Chrysotile in the Thermal Destruction of Primary Coal Tar

In order to evaluate the possibility of using different catalysts prepared for the hydrogenation process of primary coal tar, the method of differential thermal analysis was used, which allows to determine the kinetic parameters of thermal destruction, such as the rate constant, activation energy, and pre-exponential multiplier. The effect of catalysts on characteristics of mass loss during heating of "Shubarkol Komir" JSC primary coal tar at a constant speed (20 K/min) in a nitrogen medium has been considered. Microsphere, NiO/microsphere, CoO/microsphere, chrysotile and NiCo/chrysotile have been taken as catalytic additives. In the presence of the catalysts, the rate of thermal destruction of primary coal tar increases in the following order: CoO/microsphere < NiO/microsphere < NiCo/chrysotile. While microsphere catalysts extend the range of thermal destruction, chrysotile catalysts lead to the rapid completion of the destruction process. This fact is characterized by the formation of bonds between catalytic additives and primary coal tar. It is important to determine such parameters that affect on the activation energy and macrokinetics of the thermal decomposition process for prediction of catalyst activity during hydrogenation of heavy hydrocarbon raw materials.

Investigation into application of biochar as a catalyst during pyrolysis-catalytic reforming of rice husk: The role of K specie and steam in upgrading syngas quality

This study investigated the role of K and steam in upgrading syngas quality over biochar in a two-stage fixed-bed reactor. The integration of K-char catalyst and steam greatly increased syngas (H2+CO) and H2 production. The syngas products yield (19.76 mmol/gbiomass) and a H2 yield (11.14 mmol/gbiomass) were achieved when K-char was used as catalyst in the presence of steam. In general, four ways could be concluded to promote volatiles reforming to improve syngas quality by K and steam: Firstly, K and steam interaction with biochar increased the surface area and developed the porous structure of biochar, providing the pyrolytic intermediates with full complete contact with the char surface, and improving the chance of contact with the active sites. Secondly, the condensation reactions of biochar were inhibited by K and steam, thus preventing the reduction of active groups on the aromatic ring of biochar. Thirdly, K and steam promoted the formation of O-containing groups with high reactive activity on the char surface, such as –COO and –CO. Moreover, volatile K migrated in biochar matrix during catalytic reforming, and steam inhibited the release of K in biochar, resulting in more K retaining on the char surface in the form of -COK and -COOK acting as the active sites, which ultimately improved the catalytic activity of biochar, and promoted tar destruction and hydrocarbon reforming.

Experimental research on hydrogen-rich syngas yield by catalytic biomass air-gasification over Ni/olivine as in-situ tar destruction catalyst

This research focuses on investigating the air-gasification process of pine sawdust using a fluidized bed unit with Ni/olivine as an in-situ tar destruction catalyst. The goal is to eliminate tar production and obtain high-quality synthesis gas. Consequently, the effects of reaction conditions and catalyst properties on the producer gas composition, the lower heating value (LHV) of the yielded synthesis gas (syngas), char conversion efficiency (CCE), and cold gas efficiency (GE) are comprehensively explored. The conclusions indicate that higher temperatures favor the H2 and CO production and result in an evident decrease of CH4 and C2H4, which is responsible for the increasing gas LHV. The tar capture efficiency (TCE) increases by increasing the equivalence ratio (ER); however, a reverse trend obtains for gas LHV because of a significant decline in the combustible gas contents. The results also reveal that when using Ni/olivine as the bed material, GE reaches an optimum value of 72.4% at equivalence ratio (ER) of 0.21 and then lowers down with a further increase in ER to 0.39 due to the enhanced char combustion reaction. The tar yield (1.3–6.8 g/Nm3) significantly decreases with temperature, whereas H2 concentration (14.1–29.8 vol %), CCE (51.3–89.1%), GE (44.8–86.1%) and gas LHV (5.13–7.19 MJ/Nm3) promote at high temperature. Compared to raw-olivine, the lower heating value (LHV) of the producer gas slightly increases under the same conditions (T = 800 °C and ER = 0.21) when the bed material is Ni/olivine. The conclusions obtained help to provide reliable theoretical guidance for operating condition optimization of biomass catalytic air-gasification with Ni/olivine as bed material in a fluidized bed reactor.

Thermocracking of a heavy fraction of the oil residue in a mixture with shale

The process of tar thermal cracking in a mixture with crushed oil shale to obtain components of motor fuels and raw materials for the process of thermal cracking is investigated in this paper. The optimization results of technological parameters (shale concentration, temperature, and duration) are presented and the material balance (mass.%) of the process is made. It was found that during single-stage processing under relatively mild conditions (5 MPa, 425C, feed space velocity of 1.0 h-1), a deep destruction of tar is achieved (the yield of the gasoline fraction from boiling point to 200C is ~12 wt.%; medium distillates with boil. point 200370C-43-44 mass.%; raw materials for thermal cracking with boil. point above 370C ~15-16 wt.% on per the original tar). The generating coke-like products and the V and Ni contained in the raw materials are deposited on the mineral part of the shale and removed from the reaction zone with the liquid products of the process.

Valorization of fluid petroleum coke for efficient catalytic destruction of biomass gasification tar

Large volumes of waste petroleum coke stockpiled in open yard not only represent a huge loss of valuable material but also pose a significant risk to the environment. This work proposed an innovative strategy for waste petroleum coke valorization by exploring its catalytic performance of biomass gasification tar destruction. Waste petroleum coke was firstly activated by potassium hydroxide (KOH) to obtain high specific surface area as well as low sulfur and ash contents. Petroleum coke derived catalyst showed superior performance than a commercial activated carbon derived catalyst for destruction of naphthalene as the tar model compound. The petroleum coke derived catalyst exhibited 99.1% naphthalene destruction efficiency at 800 °C but deactivated quickly under N2 atmosphere. Under H2 and steam atmospheres, the catalytic activities were 98.6% and 96.5% for 8 h, respectively. To study the correlation between catalytic performance and the structure of carbon catalyst, elemental analysis, scanning electron microscope (SEM) analysis, transmission electron microscope (TEM) analysis, X-ray powder diffraction (XRD) analysis, Brunauer-Emmett-Teller method (BET) analysis, Fourier transform infrared (FTIR) spectroscopy, temperature programmed oxidation (TPO) analysis and Raman spectroscopy were performed on both fresh and spent catalysts. Results demonstrated that the hydrogen-rich groups (small rings and amorphous carbon) and oxygen-containing groups may account for the good resistance to coke deposition under H2 and steam atmospheres.

Comparatively investigation of real MSW and biomass tar treatment by a rotating gliding arc

Effective tar removal is the bottleneck in gasification application with municipal solid waste (MSW) and biomass as feedstocks. Herein, a rotating gliding arc plasma reactor equipped with a specific designed swirling generator and pre-heating systems is firstly proposed to treat real tar rather than tar surrogates. The composition of MSW and biomass tar is comparatively analyzed. The influence of vapor concentration, CO2 concentration and the discharge current on the destruction efficiency and distribution of gas products are systematically emphasized. The destruction efficiency of major components from both MSW and biomass tar can reach up to over 90%. The order of destruction efficiency of the components tends to be η (Monocyclic species) > η (Bicyclic species) > η (Tricyclic species). Amongst, species with oxygen-containing functional group such as –OH is prone to be destructed compared with those aromatic hydrocarbon species. Similar changing trend of MSW and biomass tar destruction efficiency dependent on operating parameters is detected, with slight differences attributed to the differences of element and group content.

Destruction of gasification tar over Ni catalysts in a modified rotating gliding arc plasma reactor: Effect of catalyst position and nickel loading

In this study, a modified rotating gliding arc (RGA) plasma reactor with fan-shaped swirl generator coupled with Ni/γ-Al2O3 catalyst was investigated for the steam reforming of gasification tar from waste materials, taking toluene as the tar surrogate. The system performance was evaluated in terms of tar conversion, energy efficiency, yield of product gas, as well as synergistic capability of plasma catalysis, with particular attention on the effects of specific energy input (SEI), positioning of the catalysts, and Ni loading of catalysts. Different characterizations of catalysts including N2 adsorption-desorption, XRD, H2-TPR, and TEM were conducted to study the properties of catalysts. Incorporation of catalyst placed sufficiently far from the anode increased toluene conversion which indicated the synergy between plasma and catalysis for tar conversion. A toluene conversion of up to 91.9% can be achieved with a distance of 62 mm between the catalyst and the anode, which was 21% higher than that in the plasma alone system. The toluene conversion can be further increased to 94.7% when the Ni loading was increased from 4% to 16%. The synergistic capability of plasma catalysis was demonstrated from an enhanced toluene conversion and the increased formation of value-added fuel gases such as H2, CO, and CH4, together with simultaneously a selective reduction in CO2 formation, especially when the Ni loading was 4% and 8%. Identification of liquid by-products also revealed the synergy between plasma and catalysis which transformed bi-radical HCCH into gaseous products, prohibiting the formation of indene and naphthalene.

Catalytic steam co-gasification of biomass and coal in a dual loop gasification system with olivine catalysts

A dual loop gasification system (DLG) has been previously proposed to facilitate tar destruction and H2-rich gas production in steam gasification of biomass. To sustain the process auto-thermal, however, additional fuel with higher carbon content has to be supplied. Co-gasification of biomass in conjunction with coal is a preferred option. Herein, the heat balance of the steam co-gasification of pine sawdust and Shenmu bituminous coal in the DLG has been analyzed to verify the feasibility of the process with the help of Aspen Plus. Upon which, the co-gasification experiments in the DLG have been investigated with olivine as both solid heat carriers and in-situ tar destruction catalysts. The simulation results show that the self-heating of the DLG in the co-gasification is achieved at the coal blending ratio of 28%, gasification circulation ratio of 19 and reforming circulation ratio of 20 when the gasifier temperature 800 °C, reforming temperature 850 °C, combustor temperature 920 °C and S/C 1.1. The co-gasification experiments indicate that the tar is efficiently destructed in the DLG at the optimized reformer temperature and with olivine catalysts.

Role of O-containing functional groups in biochar during the catalytic steam reforming of tar using the biochar as a catalyst

Tar formation is practically unavoidable during gasification. Catalytic tar forming is one of the most promising techniques for producing high-quality syngas at a commercial scale. Biochar has great potential to be used as a catalyst for the removal of tar from the syngas produced from the pyrolysis/gasification of biomass. The structure of biochar is a critical factor affecting its catalytic performance. This study investigates the role of O-containing functional groups in biochar during steam reforming of tar using biochar as a catalyst. Mallee wood biochar (106–250 μm) was activated in H2O for different times (0–50 min) and then used as a catalyst for the steam reforming of tar at 800 °C. The chemical structural features of biochars were characterized with Raman spectroscopy and X-ray photoelectron spectroscopy (XPS). It was found that H2O activation increased the concentration of O-containing functional groups, mainly the aromatic CO structures in biochar, which enhanced the catalytic destruction of tar. During the catalytic reforming of tar, the content of aromatic CO groups decreased while the catalyst activity decreased. It is believed that the aromatic CO functional groups in biochar play a vital role in the steam reforming of tar.

Plasma reforming of naphthalene as a tar model compound of biomass gasification

The contamination of producer gas with tars from biomass gasification remains a significant challenge in the bioenergy industry and a critical barrier, limiting the commercial applications of biomass gasification. Non-thermal and non-equilibrium plasma offers an unconventional and emerging technology for the effective reduction of problematic tars from gasification. In this study, we investigated plasma reforming of naphthalene as a two-ring tar model compound using a gliding arc discharge (GAD) reactor with/without steam. The influence on the plasma conversion of naphthalene based on the inlet naphthalene concentration, discharge power and steam-to-carbon ratio was examined to understand the effects of these operating parameters on the destruction of tar, gas selectivity/yield and energy efficiency. Adding H2O in the plasma process generates oxidative OH radicals, creating additional reaction routes for the step-wised oxidation of naphthalene and its fragments towards the CO, CO2 and water. The optimum ratio (2.0) of steam-to-carbon was identified to achieve the highest naphthalene conversion (84.8%), C2H2 yield (33.0%), total gas yield (72.2%) and energy efficiency (5.7 g/kWh). The effect of the amount of steam on the plasma reduction of tars was dependent on the balance between two opposite effects due to the presence of steam: positive effect of OH radicals and the negative effect of electron attachment on water molecules. Introducing an appropriate amount of steam to the plasma reduction of naphthalene also substantially minimized the formation of by-products and enhanced the carbon balance. Plausible reaction mechanisms for the plasma decomposition of naphthalene were proposed through a comprehensive analysis of gaseous and condensable products combined with plasma spectroscopic diagnostics.

Catalytic steam‐gasification of biomass in a fluidized bed reactor

AbstractBACKGROUNDThe depletion of fossil fuels and the increasing demands for clean energy, make biomass energy a promising sustainable alternative to fossil fuels. Biomass gasification is a promising pathway for producing gas and other valuable products using biomass materials (wood residue, agricultural waste, bagasse, etc.).RESULTSThe tar cracking and char conversion increased slowly at lower temperatures (750–800 °C) and rapidly at higher temperatures (800–900 °C). The results also indicated that a reduction in the biomass particle size leads to a slight improvement in the gasification characterstics. With increasing steam–biomass ratio, gas yield increased while the yield of tar and char showed an opposite trend.CONCLUSIONIncreasing temperature and steam introduction significantly promoted tar destruction and gas production. In terms of catalytic activity, both catalysts showed good performance regarding the destruction of tars but dolomite was more active than olivine. © 2018 Society of Chemical Industry

Steam reforming of toluene and naphthalene as tar surrogate in a gliding arc discharge reactor.

Steam reforming of mixed toluene and naphthalene as tar surrogate has been investigated in an AC gliding arc discharge plasma, with particular emphasis on better understanding the effect of steam and CO2 on the reaction performance. Results show that H2, C2H2 and CO are the major gas products in the plasma steam reforming of tar for energy recovery. The addition of a small amount of steam remarkably enhances the conversions of both toluene and naphthalene, from 60.4% to 76.1% and 57.6% to 67.4%, respectively, as OH radicals formed by water dissociation create more reaction pathways for the conversion of toluene, naphthalene and their fragments. However, introducing CO2 to this process has a negative effect on the tar reforming. Optical emission spectroscopic diagnostics has shown the formation of a variety of reactive species in the plasma process. Trace amounts of monocyclic and bicyclic aromatic condensable by-products are also detected. The destruction of toluene and naphthalene can be initiated through the collisions of tar surrogates with energetic electrons, N2 excited species, OH and O radicals etc. Further optimization of the plasma tar destruction is still needed because the complexity of the tar component in a practical gasifier could decrease the tar conversions.

Destruction of Toluene, Naphthalene and Phenanthrene as Model Tar Compounds in a Modified Rotating Gliding Arc Discharge Reactor

Tar removal is one of the greatest technical challenges of commercial gasification technologies. To find an efficient way to destroy tar with plasma, a rotating gliding arc (RGA) discharge reactor equipped with a fan-shaped swirling generator was used for model tar destruction in this study. The solution of toluene, naphthalene and phenanthrene is used as a tar surrogate and is destroyed in humid nitrogen. The influence of tar, CO2 and moisture concentrations, and the discharge current on the destruction efficiency is emphasized. In addition, the combination of Ni/γ-Al2O3 catalyst with plasma was tested for plasma catalytic tar destruction. The toluene, naphthalene and phenanthrene destruction efficiency reached up to 95.2%, 88.9%, and 83.9% respectively, with a content of 12 g/Nm3 tar, 12% moisture, 15% CO2, and a flow rate of 6 NL/min, whereas 9.3 g/kW·h energy efficiency was achieved. The increase of discharge current is advantageous in terms of decreasing black carbon production. The participation of Ni/γ-Al2O3 catalyst shows considerable improvement in destruction efficiency, especially at a relatively high flow rate (over 9 NL/min). The major liquid by-products are phenylethyne, indene, acenaphthylene and fluoranthene. The first two are majorly converted from toluene, acenaphthylene is produced by the co-reaction of toluene and naphthalene in the plasma, and fluoranthene is converted by phenanthrene.

Development of renewable biomass energy by catalytic gasification: Syngas production for environmental management

ABSTRACTGasification is a process in which biomass is decomposed into small quantities of solid char and ash and large quantities of gaseous products in the presence of one or more fluidizing agents. In this paper, a lab scale fluidized bed gasifier was used to explore the effects of different kinds of calcined dolomites (CD-1, CD-2, and CD-3) on tar conversion and composition during air-steam gasification of biomass. Results showed that all dolomites have a good performance in terms of tar reduction but CD-2 is more reactive than two other dolomites with respect to tar destruction. When the temperature was lower than 850◦C, conversion of tar was relatively low; however, with temperature increasing further (>850 ◦C), tar conversion was greatly enhanced.

Syngas production from air-steam gasification of biomass with natural catalysts

Biomass has a great potential for production of syngas and chemicals; however, it has stood in the shadow of natural gas (NG) and coal due to technical problems and issues such as tar formation. In this paper, syngas production from catalytic air–steam gasification of biomass in a fluidized bed was investigated. To enhance the yield of produced syngas and reduce its tar content by cracking, limestone, calcined dolomite, and olivine were used as catalyst. The maximum mole fraction of H2 was found to be 49.1 vol% at 1000 °C and a steam/biomass ratio (S/B) of 1.0 with dolomite present. Compared to olivine and dolomite, calcined dolomite was proved to be more effective for gas production and tar destruction. The results also showed that the particle size has a weak influence on gasifier performance, with only a slight decrease in tar content with decreasing biomass particle size.

Applicability of a kinetic model for catalytic conversion of tar and light hydrocarbons using process-activated ilmenite

This work evaluates further the applicability of a previously formulated kinetic model that describes the conversion of tar and light hydrocarbons during the catalytic upgrading of a raw gas derived via biomass gasification. The model is based on the mechanism through which tar and light hydrocarbons are converted, and the distribution of CO/CO2 and tar/light hydrocarbons as the products of the destruction of the parent tar and light hydrocarbons. Furthermore, the model uses a pseudo tar to represent all the in situ-formed tar and light hydrocarbons. The experiments used an ilmenite catalyst that was activated in the Chalmers 12-MWth boiler, and a mature tar-containing raw gas that was produced in the Chalmers 2–4-MWth dual fluidized bed biomass gasifier. The temperature levels (800 °C and 850 °C) and ilmenite particle size ranges (45–90 µm and 125–180 µm) were investigated. Through fitting the model to the experimental data, the composition of the upgraded gas as a function of gas–solid contact time was derived for the operating conditions studied. The previously proposed conversion network for tar and light hydrocarbons, and the empirical model coefficients for ilmenite (125–180 µm) at 850 °C were validated. Overall, the obtained results confirm that the proposed model is able to describe the upgrading process. Further development of the proposed model and application of the results obtained for ilmenite in designing gas upgrading strategies are discussed.

Gasification of low-rank coal for hydrogen-rich gas production in a dual loop gasification system

A dual loop gasification (DLG) system consisting of three separated reactors and two bed material circulation loops has been proposed for steam gasification of low-rank coal to obtain hydrogen-rich gas with low tar content. The system decouples the gasification process into fuel gasification, tar destruction and residual char combustion, which occur in three independent reactors correspondingly, i.e. a gasifier, a reformer and a combustor. Both the gasifier and the reformer are separately interconnected with the single combustor, forming two bed material circulation loops in parallel. In this way, both the gasifier and the reformer could be operated individually under optimized conditions. With Shenmu bituminous coal as feedstock and calcined olivine as both solid heat carrier and in-situ tar destruction catalyst, the performance of the system for the steam gasification of the coal has been investigated. It has been found that the tar was effectively removed under higher reformer temperature and in the presence of the olivine catalyst, and the coal gasification was promoted at higher gasifier temperature, S/C and ER.

Exploiting the Photocatalytic Effect of Microwave–Metal Discharges for the Destruction of a Tar Model Compound

Microwave–metal (MW–metal) discharges can induce multiple effects, including heating, plasma, and light effects, which may open new pathways for enhancing chemical reactions via plasma- and photocatalysis. Heating and plasma effects have been researched extensively, with applications explored thoroughly. However, the photocatalytic effect of MW–metal discharges has been scarcely investigated. In this study, the photocatalytic effect of MW–metal discharges for the destruction of tar was investigated by comparing the conversion of a model tar compound under MW–metal discharges alone and under the synergetic effect of MW–metal discharges and a photocatalyst. Toluene was selected as the model tar compound, and anatase-type TiO2 was used as the photocatalyst. The experimental results show that anatase-type TiO2 can use the ultraviolet (UV) light emitted by MW–metal discharges to assist in the decomposition of toluene. Moreover, the discharge atmosphere plays an important role in discharge light characteristics...

Hydrogen and syngas production by catalytic gasification of algal biomass (Cladophora glomerata L.) using alkali and alkaline-earth metals compounds

ABSTRACTThe steam gasification of algal biomass (Cladophora glomerata L.) in presence of alkali and alkaline-earth metal compounds catalysts was studied to enhance the yield of syngas and reduce its tar content through cracking and reforming of condensable fractions. The commercial catalysts used include NaOH, KHCO3, Na3PO4 and MgO. The gasification runs carried out with a research scale, biomass gasification unit, show that the NaOH has a strong potential for production of hydrogen, along with the added advantages of char converting and tar destruction, allowing enhancement of produced syngas caloric value. When the temperature increased from 700°C to 900°C, the tar content in the gas sharply decreased, while the hydrogen yield increased. Increasing steam/biomass ratio significantly increased hydrogen yield and tar destruction; however, the particle size in the range of 0.5–2.5 mm played a minor role in the process.

Destruction of tar during volatile-char interactions at low temperature

This study aims to investigate the mechanisms of tar destruction during volatile-char interactions at low temperature (400–700°C). A bio-char was subjected to interactions with biomass volatiles at different temperatures (400–700°C). The results indicate that tar is converted into gaseous and solid products (coke) during volatile-char interactions and the proportion of coke formed on the bio-char from the total converted tar steadily increases with increasing temperature. The non-aromatic structures (e.g. aliphatic and/or O-containing structures) in tar are mainly converted into gases by catalytic cracking and/or reforming reactions on char, while the aromatic structures in tar primarily go through condensation/polymerisation reactions to form coke on char surface. The UV-fluorescence spectroscopic results imply that the non-aromatic structures in tar are easier converted on char than aromatic structures at low temperature (e.g. 400–500°C) and the conversion of aromatic structures through coke formation on char will be enhanced at higher temperature (e.g. 600–700°C). The Raman spectroscopic results show that some O-containing species in tar molecules are transferred to the char and form additional O-containing structures into the entire char matrix during the volatile-char interactions.