Hot Gas Cleanup Research Articles

Catalytic decomposition of nitrogen-containing heterocyclic compounds with highly dispersed iron nanoparticles on carbons

Decomposition of pyrrole or pyridine with iron catalysts supported on carbons has been studied with a cylindrical quartz-made pulse reactor, into which liquid pyrrole or pyridine is injected as a pulse, in order to develop a novel hot gas cleanup method of removing the nitrogen present in tar as N2. The catalyst is mainly prepared by heating FeOOH precipitated onto powdery cellulose from FeCl3 solution. Nanoscale iron catalysts with the average particle sizes of 25–30nm can promote decomposition reactions of the N-containing heterocyclic compounds in inert gas at >500°C and provide N2 yields of 40–45% after the almost complete decomposition of pyrrole at 600°C or pyridine at 650–700°C. Iron catalyst with the mean size of 100–500nm, prepared from Fe(NO3)3 impregnated with a commercial activated carbon, is also active for the decomposition of the heterocyclic N-compounds, but it is almost inactive for N2 formation, the yields being as low as less than 2% in all cases. The increase in the number of pulses lowers the catalytic activity of iron nanoparticles for N2 formation, whereas in situ H2 treatment at 500°C after reaction can restore it to the almost original state. On the basis of the above-mentioned results, it is likely that the activity of iron catalyst for N2 formation from pyrrole or pyridine is very sensitive to the iron particle size, and the in situ H2 treatment is effective for recovery of the decreased catalytic performance.

Investigations on the influence of steam on the release of sodium, potassium, chlorine, and sulphur species during high temperature gasification of coal

Basic investigations on the release of alkali metal, chlorine, and sulphur species form a crucial element in designing control measures and to develop hot gas cleaning strategies for coal gasification systems. Together with other experimental approaches a large body of useful data has already been delivered in this area, but the underlying reaction mechanisms are not yet sufficiently understood. Therefore, release experiments were done in lab-scale with six hard coals and four lignites at 1400°C, 1atm and a gas stream of He/7.5% O2 and He/7.5% O2 and additional steam, respectively. The molecular beam mass spectrometry technique used for hot gas analysis is well established and is able to detect and differentiate key chemical species released during the different phases of gasification. Main species detected by MBMS were 23Na+, 34H2S+, 36HCl+, 39K+/39NaO+, 56KOH+, 58NaCl+, 64SO2+, and 74KCl+. The release of these inorganic species occurred for the most part during devolatilisation phase and is strongly influenced by steam. Especially, the amount of alkali metal hydroxide compounds increased significantly under the influence of steam.

Fabrication of nickel filter by uniaxial pressing process for gas purification: ceramic coating effect for hot gas cleaning

A nickel filter for hot gas cleaning was successfully fabricated by pressing micron-size nickel powder. The deposition of the alumina coating on nickel powder having a particle size distribution of 2 to 10 &mgr;m is the first step in the fabrication procedure. The raw nickel powder and alumina modified nickel powder were pressed in a cylindrical metal mold under a pressure of 42 MPa and then heat treated in the temperature ranges of 450–900°C and 1100–1400°C, respectively, for 10 h in pure hydrogen to endow them with thermal stability and mechanical strength. SEM, mercury porosimetry and the air permeation test showed that the alumina coating on the surface of the nickel powder hindered the sintering and agglomeration of nickel up to 1200°C, while the pore structure of the un-modified nickel filter was destroyed at 550°C. We believe that the nickel filter developed herein could be applied not only to high temperature processes, such as solid fuel gasification for the reliable and environmentally sound operation of subsequent processes, but also provide energy savings and more effective whole process optimization.

Upgrading of Raw Gas from Biomass and Waste Gasification: Challenges and Opportunities

The depletion of fossil fuel-based resources and concerns for increasing emissions of CO2 call for new ways of producing environmentally-friendly substitutes for motor fuels and chemicals. Thermo-chemical conversion of biomass and waste using gasification is a strong candidate to meet these challenges. For efficient and cost-effective application of this technique, novel solutions for hot gas cleaning are needed. This review highlights some important areas for improvement of upgrading technologies for pressurised fluidised bed gasification systems using biomass as a fuel.

Laboratory investigations on chemical hot gas cleaning of inorganic trace elements for the “UNIQUE” process

The UNIQUE project aims at integrating the fluidized bed steam gasification of biomass and the hot gas cleaning and conditioning system into one reactor vessel. This paper outlines thermodynamic calculations and lab-scale experimental investigations on alkali removal and sour gas control. The results show that the alkali concentration in gasifier derived gases can be limited to values below 100ppbv using aluminosilicates. The H2S concentration can be limited to values above 100ppmv using conventional Ca or Cu based sorbents and to values below 1ppmv by a new Ba containing sorbent developed by Forschungszentrum Jülich. In addition, the Ba containing sorbent can also limit the HCl concentration to values below 1ppmv.

Precious metal catalysts in the clean-up of biomass gasification gas part 2: Performance and sulfur tolerance of rhodium based catalysts

Rh, Pt, and Pt-Rh catalysts on modified commercial zirconia support (m-ZrO 2) were screened for the clean-up of gasification gas from tar, methane, and ammonia both in the absence and presence of H 2S while varying the Rh metal content from 0.5 to 5 w-%. Our goal was to optimize the composition of the Rh/m-ZrO 2 catalyst in view of the production of ultra clean gas applicable for liquid biofuels synthesis. In the presence of 100 ppm sulfur, increasing Rh concentration from 0.5 to 5 w-% did not greatly improve the activity of the catalyst. The bimetallic Pt/Rh/m-ZrO 2 catalyst was also less active than the 0.5 w-% Rh/m-ZrO 2 catalyst. Furthermore, the Rh/m-ZrO 2 catalyst regained its performance at the set point of 800 °C when the sulfur feed was turned off even after exposures to 500–1000 ppm sulfur. Our data allow us to suggest that in the presence of sulfur, the active sites responsible for the reforming reactions are poisoned, but less impact occurs on sites responsible for oxidation reactions. Furthermore, the screening experiments allow to suggest that the Rh/m-ZrO 2 catalyst could be applicable to hot gas cleaning in the presence of sulfur (> 50 ppm) at above 800 °C using a moderate gas hourly space velocity of approximately 3400 1/h. Since biomass gasification gas generally contains sulfur, the 0.5 w-% Rh/m-ZrO 2 catalyst could be a promising option for gasification gas clean-up applications at temperatures above 800 °C where it reduces tar to very low levels.

Gasification of Woodchips from the San Rossore Natural Reserve Maintenance for Chp Application: a Case Study Analysis

This work aims at analyzing a complete biomass gasification chain for CHP purposes. The biomass production step is related to an existing scenario, the woodchips produced from the maintenance of the S.Rossore natural reserve. Two different gas cleaning systems are taken into account, a wet gas clean-up and a hot gas clean-up (based on a dolomite bed with air injection for tar cracking). Performance indicators are calculated according to an inventory of the energy and mass fluxes. The results show that the most significant energy loss of the wet gas clean-up is due to syngas cooling, while for the hot tar clean-up part of the syngas sensible heat is recovered, however this is a benefit only if a suitable heat demand is available in the plant. Since part of the syngas chemical energy is lost in the dolomite bed in the hot clean-up, the overall energy efficiency of this chain is lower compared to the wet gas clean-up. The main advantage of the hot clean-up is the reduction of the wastewater.

Steam gasification of Miscanthus X Giganteus with olivine as catalyst production of syngas and analysis of tars (IR, NMR and GC/MS)

Abstract Steam gasification of Miscanthus X Giganteus (MXG) at high heating rate in a fluidised bed reactor with the use of olivine as catalyst was investigated. The effects of temperature (815–880 °C) on the yields and the compositions of syngas and tars were determined. The experimental results show that the gas yields and the content of H 2 increase with the temperature, while the yields of tar, char and the content of CO, CO 2 and CH 4 in the product gas decrease. Noteworthy is that about 1.1 m 3 of dry gas (at ambient conditions) per kg of dry ash free biomass were obtained with about 46% of H 2 and 24% of CO by volume at 880 °C. The tars composition was determined by FTIR, NMR and GC/MS. The identification of different compounds shows mainly the presence of simple molecules. This may be facilitating the possibility of complete tar reforming process (hot gas cleaning), to improvement of the syngas yield and the decrease of the formation of pollutants.

High Temperature Sorption of Arsenic in Gasification Atmosphere

Modern gasification technologies need to have low concentrations of impurities in the process gas for their failure-free operation. Therefore, hot gas cleaning is required. Molecular beam mass spectrometry was used to determine the gas purity downstream different materials for the sorption of arsenic at 800 °C. Additionally, thermodynamic calculations regarding the release and the removal of arsenic using SimuSage were performed. The calculations showed that copper-containing sorbents should be suitable for cleaning of arsenic-laden gases. This could be confirmed by sorption experiments, where also high surface alumina appeared as an adequate sorbent material. Fly ash from lignite combustion is also capable for arsenic retention, whereas zeolites, clay minerals, and lime did not interact with arsenic.

Structured exergy analysis of an integrated gasification combined cycle (IGCC) plant with carbon capture

In order to identify approaches for integrated gasification combined cycle (IGCC) plant optimization it is necessary to analyse where and why the losses in the process occur. Therefore a structured exergy analysis of an IGCC with carbon capture was performed to identify losses on a plant, subsystem and individual component level. The investigation of the IGCC base case revealed an exergetic efficiency of 40%. Thus, 60% of the whole fuel exergy is lost in the process. On the subsystem level it was found that the major loss contributor is the combined cycle followed by the gas treatment section and the gasification island. Furthermore, it was demonstrated that the significance of the losses is higher in upstream processes than in downstream processes. On the individual component level it is shown that 80% of all exergy losses in the plant are caused by just 4 components. Since two of them are related to the gas conditioning an advanced hot gas clean-up (HGCU) system was proposed which improves exergy efficiency of the IGCC plant by 5.2%-points. However, assuming an ideal IGCC process an exergy efficiency of 54.1% was calculated demonstrating significant potential for further optimization of the technology.

Sulfur removal property of activated-char-supported Fe–Mo sorbents for integrated cleaning of hot coal gases

An integrated hot coal gas cleaning process is proposed with emphasis on simultaneous removal of multiple impurities including sulfur containing species, NOx precursors, mercury and tarry materials. Activated-char-supported sorbents were synthesized by gasifying Fe and Mo impregnated Chinese lignite coal in steam (15%, vol) at 1100K for 15min. Sulfur removal properties of the sorbent samples were examined by sulfidation experiments using simulated coal gases (with 4700ppmv H2S and 470ppmv COS) at a space velocity of 1000h−1 using a fixed-bed quartz reactor at the temperature range of 673–873K. The SEM with EDS and XRD were used to examine the physical and chemical changes in the sorbents during sulfidation. The active metal oxides components were dispersed in the char matrix as nano-size particles resulting in a high reactivity of the sorbents towards H2S and COS contained in coal gases. Under the conditions in this study, the sorbents can effectively remove H2S and COS from the simulated coal gases with high efficiency. Sulfur removal is influenced by the level of iron-loading. The presence of Mo along with Fe in the char-supported sorbents can significantly increase the desulfurization efficiency.

Catalytic decomposition of ammonia in simulated coal-derived gas over supported nickel catalysts

As a hot gas clean-up technology for integrated coal gasification combined-cycle (IGCC) power plants, the catalytic decomposition of ammonia using simulated coal-derived gas was studied. Based on the selective catalytic oxidation of ammonia to nitrogen and water, the characteristics of five kinds of supported nickel catalysts were investigated. Ammonia decomposition experiments were carried out at 0.9 MPa, and the surface properties of the catalysts were investigated through surface area measurement, the temperature programmed desorption of ammonia (NH 3-TPD), carbon analysis, XRD analysis, and transmission electron microscope (TEM) observation. The results showed that a nickel catalyst supported on ZSM-5 zeolite has the highest activity and selectivity for ammonia decomposition to nitrogen without carbon deposition from 250–400 °C among the tested catalysts.

Thermal plasma-sprayed nickel catalysts in the clean-up of biomass gasification gas

Plasma spraying is a potential catalyst preparation method for hot gas clean-up which requires very durable catalytic coatings. In this work, the multi-layer composite coating powders consisted of a gibbsite or boehmite core together with a hydrotalcite coating. We used the coating powders in the preparation of the powder form Ni catalysts, which were characterized by XRD, BET, XPS, and XRF. The coating powders were also used in the preparation of plasma sprayed metal substrate supported Ni catalysts. Selected plasma-sprayed nickel containing catalysts were characterized by XRD and SEM. In addition, for comparative purposes we prepared and used a ceramic monolithic Ni catalyst on modified ZrO2. The performance of all catalysts were studied in the clean-up of synthetic gasification gas, i.e. the decomposition of tar, ammonia, and methane, at 700 and 900°C, without and with the addition of H2S. Catalysts with a gibbsite-core showed higher activity and better sulfur resistance than those with a boehmite-core. The high activity of the gibbsite-core Ni catalyst with a sulfur-containing gas together with the promising mechanical and thermal strength makes the plasma spraying method an interesting alternative for gas clean-up catalysts in biomass gasification processes.

A model on desulfurization characteristics of an entrained bed-bubbling bed hot gas cleanup system for IGCC

A mathematical model has been developed to predict performance of a continuous entrained-bed and bubbling fluidized-bed hot gas desulfurization system in IGCC. The model combines the particle residence time with the kinetic rate in each reactor. The model has been applied to the KIER’s laboratory scale fluidized bed process. The present model provided a reasonable fit in predicting experimental results that the outlet concentration of H 2S from the desulfurizer and SO 2 from the regenerator increased nearly proportionally to the inlet concentration of H 2S to the desulfurizer. The model also could predict well the outlet concentration of O 2 from the regenerator to decrease as the inlet concentration of H 2S to the desulfurizer increased. The present model predicted with reasonable accuracy mean diameter of bed particles and sulfur content of particles in desulfurizer and regenerator.

A review on research and development of iron-based sorbents for removal of hydrogen sulfide from hot coal gases

In poly-generation and integrated gasification-combined cycle (IGCC) systems for clean energy conversion, it is essential to remove impurities such as sulfur species from hot coal gases prior to entering the subsequent units. This paper provides a comprehensive review on previous studies on high temperature removal of hydrogen sulfide from high temperature coal gases using iron-based sorbents. A two-step desulphurization process for hot coal gas cleanup is highlighted, which is integrated with direct production of elemental sulfur during regeneration of iron-based sorbents in the primary desulphurization step. Different kinetic modeling approaches for sulfidation and regeneration were compared. Limited research on activated carbon supported sorbents was also briefly summarized.

Thermochemical production of liquid fuels from biomass: Thermo-economic modeling, process design and process integration analysis

A detailed thermo-economic model combining thermodynamics with economic analysis and considering different technological alternatives for the thermochemical production of liquid fuels from lignocellulosic biomass is presented. Energetic and economic models for the production of Fischer–Tropsch fuel (FT), methanol (MeOH) and dimethyl ether (DME) by means of biomass drying with steam or flue gas, directly or indirectly heated fluidized bed or entrained flow gasification, hot or cold gas cleaning, fuel synthesis and upgrading are reviewed and developed. The process is integrated and the optimal utility system is computed. The competitiveness of the different process options is compared systematically with regard to energetic, economic and environmental considerations. At several examples, it is highlighted that process integration is a key element that allows for considerably increasing the performance by optimal utility integration and energy conversion. The performance computations of some exemplary technology scenarios of integrated plants yield overall energy efficiencies of 59.8% (crude FT-fuel), 52.5% (MeOH) and 53.5% (DME), and production costs of 89, 128 and 113 € MWh −1 on fuel basis. The applied process design approach allows to evaluate the economic competitiveness compared to fossil fuels, to study the influence of the biomass and electricity price and to project for different plant capacities. Process integration reveals in particular potential energy savings and waste heat valorization. Based on this work, the most promising options for the polygeneration of fuel, power and heat will be determined in a future thermo-economic optimization.

Catalytic Activity in Naphthalene Reforming of Two Types of Catalytic Filters for Hot Gas Cleaning of Biomass-Derived Syngas

The catalytic activity in the reforming of naphthalene of two different types of catalytic filter candles for biomass-derived syngas cleaning are presented and compared at superficial velocities of 72 and 90 m/h, respectively. The tests were performed in a laboratory setup on a fixed catalyst bed and small sections of full size candles. In a 50 h long-term test of the first candle type of fixed bed design, complete naphthalene conversion was found at 800 °C, 100 ppmv H2S, and an average superficial velocity of 135 m/h for the integrated Ni catalyst. Doubling the naphthalene concentration from 5 to 10 g/Nm3 has also led to complete conversion in a short-term test at a superficial velocity of 90 m/h. Because of easier manufacturing of the second candle type, several candles of a catalytic layer design were prepared by using different MgO-containing support materials and adjusting NiO loadings between 35 and 194 wt %. As compared to previous work, a conversion increase from 58 to 74% was achieved at 800 °C, ...

Preparation and Characterization of Porous Composite Filter Medium by Polytetrafluoroethylene Foam Coating

The high costs of ceramic and Teflon filter media for hot gas cleaning has limited their industrial applications. This paper presents a foam coating technology that can be used to produce an inexpensive and highly efficient filter for industrial applications. A new apparatus was designed and built that coats porous glass mats with liquid-phase polytetrafluoroethylene (PTFE). The machine generates bubbles, enables the formation of uniform micropores less than 45 μm in diameter, and produces a product with air permeability greater than 5.5 cm3/cm2/sec. The resulting filter was found to be thermally stable up to 270 °C without any visible distortion and was comparable in dust collection efficiency to other commercial filter media. In addition, its de-dusting efficiency was greater than 85%, which is similar to that of other test filter media.

Operation of solid oxide fuel cell on biomass product gas with tar levels >10 g Nm −3

This work assesses experimentally the feasibility of feeding a high tar load product gas from biomass gasification to a planar solid oxide fuel cell (SOFC) for renewable electricity generation. The SOFC had a nickel gadolinium-doped ceria anode (Ni-GDC) and the gasifier was a pilot scale circulating fluidized bed, employing hot gas-cleaning to remove particulates, HCl and H 2S. The SOFC operated for several hours on either pre-reformed gas (reduced tar levels < 0.5 g Nm −3) as well as on high tar-laden wood gas (tar levels > 10 g Nm −3) i.e. with no pre-reforming of tars. The tests were carried out at low fuel utilization U f of around 20% at a current density j = 130 mA cm −2. In all cases stable continuous SOFC performance was established. Post experimental examination of the SOFC showed that the anode was not affected by carbon deposition or other impurity accumulation.

Biomass gasification for DRI production

The Direct Reduction process can be carried out using syngas from biomass. Mathematical models of the integrated process gasification plus direct reduction have been used to evaluate flow rate, temperature and composition of the gas in the various steps of the whole process. Fluidised bed gasification and operation with technological oxygen at high pressures is the proposed solution to produce syngas. Best candidates for such application are biomass from forest and wood industry and agricultural residues. Both of such type of biomass are present and distributed in many European areas in such amount to make industrially possible their use, taking into account the logistic requirements. A cost between 30-60 €/t DRI is roughly estimated. The characteristics of the syngas implies the adoption of purification steps, before the use of the syngas in the shaft furnace, using technologies permitting hot gas cleaning, to save energy efficiency of the process.