Hot Gas Cleanup Research Articles

Preparation, microstructure and properties of cordierite-mullite-corundum porous ceramics for high-temperature gas-solid separation

In order to obtain ceramic materials for high-temperature gas-solid separation, the cordierite-mullite-corundum porous ceramics were prepared by particle stacking and pore-forming agent method, with bauxite as aggregate and in-situ synthesized cordierite as binder. Designed four-factor four-level orthogonal experiments for the first time to improve the porosity of the samples. The phase composition and microstructure of the samples were studied by XRD, SEM and other testing methods. The results show that: X6 sample (firing temperature of 1340 °C, 50 wt% binder, aggregate coarse, medium and fine mass percentage 30:50:20, plus 20 wt% charcoal powder, 10 wt% graphite) has the best comprehensive performance, with porosity of 41.51 % and bending strength of 17.88 MPa. Pore size distribution range from 10 to 40 μm. Corundum and mullite, with excellent high-temperature properties formed by the aggregate, are tightly bonded together by cordierite, contributing to the strength of the porous ceramics. The addition of pore-forming agent improves the porosity and forms a stable and uniform pore structure in the porous ceramics. The high porosity and large connected pore size reduce the viscous resistance of the porous ceramics to the gas, improve the filtration performance of the material, and make it expected to be applied in the field of hot gas clean-up.

Modelling and assessment of a sorption enhanced gasification system coupled with hydrothermal carbonization, hot gas cleaning, and plasma to produce pure H2 from biomass

Concerns about energy security, energy prices and climate change led scientific research towards sustainable solutions to fossil fuel as renewable energy sources coupled to hydrogen as energy vector and carbon capture and conversion technologies. Among the technologies investigated in the last decades, biomass gasification acquired great interest owing to the possibility to obtain low cost and CO2 negative emission hydrogen production from a large variety of everywhere available organic wastes. Upstream and downstream treatment were then studied in order to maximize hydrogen yield, reduce the content of organic and inorganic contaminants under the admissible levels for the technologies which are coupled with, capture, and convert carbon dioxide. However, studies which analyse a whole process made of all those technologies is still missing. In order to fill this lack, the present paper investigated the coexistence of Hydrothermal Carbonization (HTC), Sorption Enhance Gasification (SEG), Hot Gas Cleaning (HGC), and CO2 conversion by Dielectric Barrier Discharge (DBD) plasma reactor for H2 production from biomass waste by means of Aspen Plus software. The proposed model aimed to identify and optimise the performance of the plant by varying operating parameters (such as temperature, CaO/biomass ratio, separation efficiency, etc.). The carbon footprint of the global plant is 2.3 kg CO2/kg H2, lower than the latest limit value imposed by the European Commission to consider hydrogen as “clean”, that was set to 3 kg CO2/kg H2. The hydrogen yield referred to the whole plant is 250 gH2/kgBIOMASS.

Performance evaluation of an innovative 100 kWth dual bubbling fluidized bed gasifier through two years of experimental tests: Results of the BLAZE project

In this work, the results of two years of experimental tests on an innovative dual bubbling fluidized bed gasifier are reported. These are related to the activities of the BLAZE project (Horizon 2020) for the integration of steam biomass gasification and solid oxide fuel cell. Several tests were carried out on the pilot-scale reactor at various operating conditions, and in this work the results are reported in terms of dry gas composition and yield, organic and inorganic contaminants (tar, particulate matter, H2S). The compact design of the gasifier (a single reactor with two concentric chambers and in-situ hot gas cleaning and conditioning) reduces the heat losses and produces close to nitrogen-free syngas. Preliminary tests using a filter candle filled with conventional catalyst, installed in the freeboard of the gasifier, show that the tar content dropped to about 2 g/Nm3, and the H2 concentration increased up to 41%vol,dry.

Review of Porous Ceramics for Hot Gas Cleanup of Biomass Syngas Using Catalytic Ceramic Filters to Produce Green Hydrogen/Fuels/Chemicals

Biomass gasification is one of the most promising routes to produce green hydrogen, power, fuels, and chemicals, which has drawn much attention as the world moves away from fossil fuels. Syngas produced from gasification needs to go through an essential gas cleanup step for the removal of tars and particulates for further processing, which is one of the cost-inducing steps. Existing hot gas cleanup strategies involve the particulate removal step followed by catalytic tar reforming, which could be integrated into a single unit operation using porous ceramics owing to their advantages including high-temperature resistance, high corrosion resistance, flexibility, and robust mechanical integrity. Ceramic filters have proven to be effective at filtering particulates from hot gas streams in various applications including combustion, incineration, gasification, and pyrolysis. These materials have also been evaluated and used to an extent as catalyst support to remove contaminants such as nitrogen oxides (NOx), volatile organic compounds (VOC), and in particular, tars, however, the use of these ceramic materials to remove both tars and particulates in one unit has not received much attention, although it has a promising potential to be a cost-effective hot gas cleanup strategy. Thus, this review presents the ability of catalytic ceramic filters to boost energy efficiency by converting unwanted byproducts while simultaneously eliminating PM in a single unit and is shown to be valuable in industrial processes across the board. This article presents a comprehensive and systematic overview and current state of knowledge of the use of porous ceramics for catalytic hot gas filtration applications with an emphasis on biomass syngas cleanup. In addition, a similar strategy for other applications such as combustion exhaust streams is presented. Prospects and challenges of taking this approach, and the necessary research and development to advance the novel use of reactive ceramic filters within biomass-fed thermal systems are presented. Major challenges include the low surface area of the ceramic filter media and high-pressure drop across the filter media, which can be overcome by wash coating or dip coating mechanisms and porosity tailored to meet the requirements. Owing to limited R&D efforts in this area, a systematic approach toward developing these integrated hot gas filtration systems is much needed, which will ultimately contribute to cost-effective green hydrogen production.

Hydrogen sulfide removal from simulated synthesis gas using a hot gas cleaning system

This study investigated the removal, adsorption, and regeneration performances of simulated H2S produced from rice straw gasification in a hot gas cleaning system with combination of three types of adsorbents including zeolite, calcined dolomite and activated carbon. These experiments were conducted at 250 ℃ hot gas cleaning system and simulated synthesis gas containing hydrogen sulfide (H2S) concentration at 200 ppm. The experimental results indicated that the tested H2S removal efficiency and adsorbed capacity were observed to be adsorbed in decreasing order: activated carbon > calcined dolomite > zeolite. The adsorption capacities of zeolite, calcined dolomite, and activated carbon are 2.22, 3.16, 5.88 mg S/g adsorbents, respectively. In this research, the calcined dolomite shows poor adsorption-regeneration ability due to its deactivation by H2S. However, the tested zeolite and activated carbon could be fully regenerated at 350 °C with a stable sulfur adsorption capacity during four adsorption-regeneration cycles. These results gained from this study could significantly support researchers obtaining more information about the synthesis gas contaminants removal during hot gas temperature operation process.

Novel nickel ceramic filter for hot gas cleanup of tars from syngas

Tars, defined as hydrocarbons having molecular weights above that of benzene, have been considered to be one of the major impurities in syngas preventing largescale commercialization of biomass gasification. Catalytic tar removal has shown the most promise in reforming/eliminating tars compared to physical and thermal techniques. Nickel based catalytic filter was developed using porous ceramic support, which acts both as a particulate filter and tar reformer, resulting in process intensification. The relatively high surface area of the ceramic filter (100 m2/g) makes it an ideal catalyst support. Nickel based ceramic catalysts were prepared using incipient wetness method and evaluated for tar removal effectiveness using naphthalene as a tar simulant. Influence of nickel loading, steam/carbon ratios, and temperatures on steam reforming activity of the catalyst was performed. Promising results were obtained with naphthalene conversions of 76% using a 15 wt% nickel filter over 2 h with very minimal pressure drop across the catalytic filter, offering a promising potential of using catalytic ceramic filters for integrated tar and particulate removal applications.

Synergic Effects of Bed Materials and Catalytic Filter Candle for the Conversion of Tar during Biomass Steam Gasification

This work concerns the activities of the European project BLAZE that aims to integrate a pilot-scale gasifier unit with a Solid Oxide Fuel Cell (SOFC). The objective is to identify the optimal operating conditions for a gasifier and hot gas cleaning and conditioning unit to produce H2-rich syngas with contaminants levels within the limits for the safe operation of the SOFC (750 mg/Nm3 and 75 mg/Nm3 for toluene and naphthalene, respectively). Experimental tests were carried out on a bench-scale gasification plant with a catalytic filter candle placed in the freeboard, to study the influence of temperature (1032 up to 1137 K), bed materials (olivine or olivine/dolomite 80/20%), and a nickel-based catalyst. The tests with a ceramic filter candle filled with catalyst and the mixture of olivine and dolomite in the bed gave the best results in terms of gas composition and gas yield, but the tar content was still higher than the limits for the SOFC. To increase the residence time of the gas in the catalytic bed a new metallic filter candle was tested. This candle, with almost the same external volume, allowed doubling the amount of catalyst used. Under these conditions, the content of toluene and naphthalene was reduced below 150 and 50 mg/Nm3, respectively.

Enhancing the catalytic performance of Ni based catalysts in toluene reforming at low temperature by structuring on SiC extrudates

Catalytic structuration on SiC extrudates improves the catalytic performance of Ni based catalysts in toluene reforming, and provides promising materials for hot gas cleaning in biomass gasification.

Filtration characteristics with parameter variation for dust removal from syngas

BackgroundGranular bed filter technology is a newly emerging field, and the science is in its infancy. There is a lack of background information on these consistencies. This study provides new insights into clean processing, which is useful in hot gas cleanup technology. MethodsWe employed a moving granular bed filter, which is evaluated in two separate performance studies: (1) optimization of particle removal efficiency and bed pressure drop under different movement velocities of silica sand; and (2) high temperature model simulation conducted dust and Silica sand flow rates and superficial velocity. Besides, this evaluated the filter system's dynamic characteristics by measuring variations in the outlet concentration and size distribution of dust particulates. Significant findingsThe results indicated that the filtered dust in the silica sand considerably affected the dust via inertial impaction and diffusion. With higher movement velocity of silica sand, the higher specific resistance coefficient of k1 and k2 caused better performance of collection mechanism, thereby enhancing the removal efficiency. Consequently, this study observations indicated that at a high movement velocity of silica sand, the gas velocity favors dust attachment on the silica sand particle surface, facilitating dust removal.The purpose of this study is to investigate the efficiency of moving granular bed filter (MGBF) in high-temperature environment under different operation conditions. The effects of the test temperature and movement velocities of silica sand on the dust size distribution and removal efficiency were studied; further, an experimental system comprising a high-temperature environment of 600 °C was established for a filter system. The removal efficiency was enhanced at a test temperature of 25 °C when considering a gas velocity of 500 mm/s and a movement velocity of silica sand of 1.95 mm/s. The test results showed that an improvement in the movement velocity of silica sand decreased the temperature of the bed, increasing the removal efficiency. Furthermore, this study could be used in different high-temperature filter systems for gas cleanup.

Study of the heat transfer characteristics and waste heat recovery of hot gas with coagulative particles flowing through a moving granular bed filter (MGBF)

The moving granular bed filter is a promising technology for handling the challenges of hot gas clean-up and waste heat recovery in various fields. The purpose of this study was to investigate the heat transfer characteristics and waste heat recovery of a moving granular bed filter during hot gas clean-up. The novelty of this study lies in its investigation of the heat transfer performance of coagulative particles. Experiments were carried out to study the influence of the flue gas inlet temperature, granular velocity, and filtration superficial velocity. The results revealed that increasing the superficial velocity and inlet temperature and reducing the granular velocity are beneficial for improving the heat storage capacity of granules in terms of single factor. However, moderate granular velocity and superficial velocity are recommended to achieve a high waste heat recovery efficiency considering multiple factors. In the present study, a granular velocity of 2 cm∙min−1 and a superficial velocity of 0.3 m∙s−1 are optimal. The superficial velocity is the main factor affecting the comprehensive heat transfer coefficient. The results reveal that the melting and solidification processes of the coagulative particles affect the heat transfer. They also reveal that improving the heat transfer performance is necessary for enhancement of waste heat recovery. The focus of the present study is essentially the development of a moving granular bed filter that contains coagulative particles for use in the metallurgy industry. The results are significant for the design and evaluation of a moving granular bed filter in practical applications that can improve energy efficiency.

Techno-Economic Assessment of Chemical Looping Gasification of Biomass for Fischer–Tropsch Crude Production with Net-Negative CO2 Emissions: Part 2

This work presents a techno-economic analysis of a novel gasification system, chemical looping gasification (CLG), used as the primary gasification process for biofuel production through Fischer–Tropsch synthesis (FTS). Two different gas cleaning process configurations, cold-gas cleanup and hot-gas cleanup process trains, are explored, along with off-gas utilization possibilities, to study their influence on the process economics of an integrated CLG–FT process plant. Off-gas recirculation to increase Fischer–Tropsch (FT) crude production has a significant influence on reducing the levelized production costs for FT crude. The results indicate that the specific production cost estimated for a CLG–FT plant with a hot-gas cleanup train is roughly 10% lower than the case with a cold-gas cleanup train, while the total plant costs remain relatively the same for all plant configurations. In addition to this, the former has a considerably higher overall system energy efficiency of 63%, roughly 18% more than the latter, considering the co-production of FT crude, district heating, and electricity. The specific investment costs range from 1.5 to 1.7 M€2018/MWLHV, and the specific FT crude production cost ranges from 120 to 147 €2018/MWhFT. Roughly 60% of total carbon fed to the process is captured, enabling net-negative CO2 emissions. A CO2 price for negative emissions would significantly reduce the specific fuel production costs and would, hence, be competitive with fossil-based liquid fuels.

Energy and exergy analysis of different biomass gasification coupled to Fischer-Tropsch synthesis configurations

The aim of this work is to evaluate the energy and exergy efficiencies at the system and subsystem level of different Integrated biomass Gasification coupled to Fischer-Tropsch synthesis (IGFT) configurations. The combination of the first and second law analysis provides a comprehensive understanding of the different analyzed systems and, in particular, of the peculiarities of hot gas cleaning. Four Aspen Plus models were developed: 1) air-based gasification, cold gas cleaning (CGC), FT synthesis; 2) air-based gasification, hot gas cleaning (HGC), FT synthesis; 3) steam-based gasification, CGC, FT synthesis; 4) steam-based gasification, HGC, FT synthesis. The results highlight the higher energy and exergy efficiency of the configurations that use hot gas cleaning system or steam as gasification agent, with the highest values (52.0% and 55.5%) achieved by the fourth configuration. The gasification part of the process shows the highest exergy irreversibilities, both in terms of exergy destruction and exergy loss, due to the large chemical exergy degradation and to the char production. The results of this work provide further evidence towards the feasibility of renewable biofuels production. Moreover, this analysis gives a more comprehensive understanding of the optimal IGFT technologies to maximize the energy and exergy efficiency.

Removal of hydrogen chloride from simulated coal gasification fuel gases using honeycomb-supported natural soda ash

In this study, we examined the HCl absorption performance of cheap natural soda ash loaded on a honeycomb support as a hot-gas cleanup method. Air-blown and oxygen-blown coal gasification fuel gases were used to simulate the gas composition. The effect of fuel gas composition on the HCl removal performance of the prepared absorbent was studied. It was found that the removal performance in an inert atmosphere was maintained in the presence of H2. On the other hand, the performance deteriorated in the presence of CO due to carbon deposition from the disproportionation reaction of CO. When CO2 was added to the CO, carbon deposition was suppressed in the air-blown gas and the HCl removal performance recovered. The performance recovery for an oxygen-blown gas was smaller than that for an air-blown gas. However, when the amount of CO2 added to the oxygen-blown gas was increased, the removal performance improved. The HCl removal performance of the absorbent was dependent on the initial HCl concentration and treatment temperature in the following order: 2000 ppm < 1000 ppm < 500 ppm, and 400 °C < 600 °C ≈ 500 °C. Recycled absorbents were prepared by loading natural soda ash once again on the recovered honeycomb supports that had been washed with water. Their HCl removal performance was similar to the fresh absorbent regardless of air-blown or oxygen-blown gasification. Thus, honeycomb supports were recyclable.

Design and experimental tests of an Imbert type downdraft gasifier prototype and clean-up system for small-scale biomass-based power generation

This paper addresses the design, development and experimental tests of a prototype of fuel gas generation system based on biomass gasification for small-scale applications, around 5 kW. It comprises the small scale downdraft gasifier and the gas cleaning system aiming to clean-up the producer gas to be used in the upstream Internal Combustion Engine (ICE). The design of the downdraft gasifier prototype follows the methodologies that have been reported on the available literature. However, since these methodologies apply to gasifiers with larger rated powers, the adopted methodology is based on the extrapolation of the main parameters used for larger gasifiers design. For runing the ICE the producer gas requires to have a specific gas composition with an acceptable range of impurities. Therefore, a clean-up system was proposed following three stages: in first instance a hot gas clean-up using a cyclone designed to eliminate particles and compounds; then a heat exchanger was used for cooling the gas to condensate tars and water; finally a cold gas clean-up is performed by filtration using two filter steps: the first one using organic material (biomass) and the second one using a polypropylene cartridge filter. Experimental tests were performed using the developed imbert downdraft gasifier prototype, using pellets as feedstock. The preliminary results allow verifying several drawbacks that will difficult an effective integration of the developed prototype for small scale power generation applications based on ICE using low density feedstock.

Exergy Analysis of Coal-Based Series Polygeneration Systems for Methanol and Electricity Co-Production.

This paper quantifies the exergy losses of coal-based series polygeneration systems and evaluates the potential efficiency improvements that can be realized by applying advanced technologies for gasification, methanol synthesis, and combined cycle power generation. Exergy analysis identified exergy losses and their associated causes from chemical and physical processes. A new indicator was defined to evaluate the potential gain from minimizing exergy losses caused by physical processes—the degree of perfection of the system’s thermodynamic performance. The influences of a variety of advanced technical solutions on exergy improvement were analyzed and compared. It was found that the overall exergy loss of a series polygeneration system can be reduced significantly, from 57.4% to 48.9%, by applying all the advanced technologies selected. For gasification, four advanced technologies were evaluated, and the largest reduction in exergy loss (about 2.5 percentage points) was contributed by hot gas cleaning, followed by ion transport membrane technology (1.5 percentage points), slurry pre-heating (0.91 percentage points), and syngas heat recovery (0.6 percentage points). For methanol synthesis, partial shift technology reduced the overall exergy loss by about 1.4 percentage points. For power generation, using a G-class gas turbine decreased the overall exergy loss by about 1.6 percentage points.

Energy Analysis of an Integrated Plant: Fluidized Bed Steam Gasification of Hydrothermally Treated Biomass Coupled to Solid Oxide Fuel Cells

An innovative process based on hydrothermal carbonization, gasification, and solid oxide fuel cells (SOFCs) technologies was developed using a commercial process simulation software called ASPEN Plus. The object of this work is to study plant efficiency under various operating conditions. The hydrothermal pre-treatment (HTC) at 200 and 250 °C was modelled as a black box based on the experimental results. The gasifier was modelled as a single reactor vessel with both the fluidized bed steam gasification of solid fuel and the hot gas cleaning system. The SOFC was modelled as a simple grey box with the ASPEN Plus blocks. The effect of HTC temperature and steam/carbon (S/C) ratio on the syngas composition and yield and plant efficiency was studied. The results show that the gasification of hydrochar obtained at 200 °C with S/C ratio of 0.6 gives the best results, namely an energy output of SOFC equal to 1.81 kW/kgBiomass, and overall process efficiency of 36%.

Catalytic Tar Conversion in Two Different Hot Syngas Cleaning Systems

Tar in the product gas of biomass gasifiers reduces the efficiency of gasification processes and causes fouling of system components and pipework. Therefore, an efficient tar conversion in the product gas is a key step of effective and reliable syngas production. One of the most promising approaches is the catalytic decomposition of the tar species combined with hot syngas cleaning. The catalyst must be able to convert tar components in the synthesis gas at temperatures of around 700 °C downstream of the gasifier without preheating. A Ni-based doped catalyst with high activity in tar conversion was developed and characterized in detail. An appropriate composition of transition metals was applied to minimize catalyst coking. Precious metals (Pt, Pd, Rh, or a combination of two of them) were added to the catalyst in small quantities. Depending on the hot gas cleaning system used, both transition metals and precious metals were co-impregnated on pellets or on a ceramic filter material. In the case of a pelletized-type catalyst, the hot gas cleaning system revealed a conversion above 80% for 70 and 110 h. The catalyst composed of Ni, Fe, and Cr oxides, promoted with Pt and impregnated on a ceramic fiber filter composed of Al2O3(44%)/SiO2(56%), was the most active catalyst for a compact cleaning system. This catalyst was catalytically active with a naphthalene conversion of around 93% over 95 h without catalyst deactivation.

A Review of Hot Gas Cleaning Techniques for Hydrogen Chloride Removal from Biomass-Derived Syngas

Considering the pressing challenges of supply security and climate change, advanced processes to produce electricity and biofuels from biomass have to be developed. Biomass gasification is a very promising technology, but there is a lack of comprehensive reviews, specifically on the technologies for hydrogen chloride hot gas cleanup, which are necessary in order to work at the same temperature and respect the limits of advanced downstream components. In this review, the Cl content of the main biomasses in Europe is given, and data on syngas content and the tolerance of downstream equipment are highlighted. Hot gas cleaning technologies, which have the advantage of improved thermal efficiency are reviewed, analyzing the thermodynamic and primary and secondary methods. This review identifies NaAlO2 and Na2CO3 within 450–550 °C as the most effective sorbents, which are able to reduce the concentration of HCl below 1 ppm. Nevertheless, H2S cannot be simultaneously removed and has to be removed first, because it reduces the HCl adsorption sorbent capacity.

Sewage and textile sludge co-gasification using a lab-scale fluidized bed gasifier

This research aims to evaluate the hydrogen production and removal ability of impurity (e.g. tar and NH3) generated from sewage and textile sludge co-gasification using lab-scale fluidized-bed gasifier with an integrated hot-gas cleaning system. The gasification temperature and equivalence ratio (ER) were controlled at 850 °C and 0.2, as well as the hot gas cleaning system operated at 250 °C with the combination of zeolite, calcined dolomite, and activated carbon. Experimental results indicated that the H2 and CO yield in co-gasification of the tested sludge ranged from 2.12 to 2.45 mol/kg and from 2.83 to 3.98 mol/kg, respectively. The overall energy content of produced gas ranged between 2.40 and 2.63 MJ/kg, and cold gas efficiency (CGE) was nearly 15%. The impurities of produced gas were effectively mitigated by the hot-gas cleaning system, which could remove approximately 90% of the heavy fraction tar, up to 77% of total tar, and about 35% of ammonia. In summary, the combination of the fluidized-bed gasifier and the hot-gas cleaning system had been well developed for purifying the syngas produced from the tested sludge, and it could be applied to other organic wastes in the future.

Carbon-negative hydrogen: Exploring the techno-economic potential of biomass co-gasification with CO2 capture

The hydrogen economy is receiving increasing attention as a complement to electrification in the global energy transition. Clean hydrogen production is often viewed as a competition between natural gas reforming with CO2 capture and electrolysis using renewable electricity. However, solid fuel gasification with CO2 capture presents another viable alternative, especially when considering the potential of biomass to achieve negative CO2 emissions. This study investigates the techno-economic potential of hydrogen production from large-scale coal/biomass co-gasification plants with CO2 capture. With a CO2 price of 50 €/ton, the benchmark plant using commercially available technologies achieved an attractive hydrogen production cost of 1.78 €/kg, with higher CO2 prices leading to considerable cost reductions. Advanced configurations employing hot gas clean-up, membrane-assisted water-gas shift, and more efficient gasification with slurry vaporization and a chemical quench reduced the hydrogen production cost to 1.50–1.62 €/kg with up to 100% CO2 capture. Without contingencies added to the pre-commercial technologies, the lowest cost reduces to 1.43 €/kg. It was also possible to recover waste heat in the form of hot water at 120 °C for district heating, potentially unlocking further cost reductions to 1.24 €/kg. In conclusion, gasification of locally available solid fuels should be seriously considered next to natural gas and electrolysis for supplying the emerging hydrogen economy.