Hot Gas Cleanup Research Articles

Observation of dust release behavior from ceramic filter elements

The dust-releasing behavior from a ceramic candle filter, which is a key technology of the hot gas cleaning system in advanced coal power generation processes such as pressurized fluidized bed combustion and integrated gasification combined cycle, is discussed based on the observation of the dust-releasing process using a high-speed video camera and the measurement of time change of pressure inside the filter. Time changes of dust-released area and geometrical characteristics and motion of released dust cake fragments were investigated by analyzing photo images from the video camera, compared with the time change and distribution of pressure inside the filter. In order to discuss the influence of porosity of the dust layer, a consolidated dust layer was prepared by clean air filtration at an elevated filtration velocity after the dust filtration. The dust-releasing process was found to be a multi-mode process, i.e. release occurred in a short time after the injection of cleaning air, followed by one or two intermittent releases afterwards. The amount of dust released by the first strike increased with tank pressure. The dust-releasing behavior was sensitive to the cake porosity: the mean size and perimeter of cake fragments increased with porosity and tank pressure for the consolidated dust layer. The initial radial velocity of cake fragment released just after the first strike increased with tank pressure and was almost independent of the filter location.

Biomass and fossil fuel conversion by pressurised fluidised bed gasification using hot gas ceramic filters as gas cleaning

Gasification of biomass and fossil fuels, hot gas cleanup using a ceramic filter and combustion of LCV product gas in a combustor were performed using a 1.5 MWth test rig (pressurised bubbling fluidised bed gasifier) at Delft University and a 10– 50 kWth system at Stuttgart University (DWSA) in the framework of experimental research on efficient, environmentally acceptable large-scale power generators based on fluidised bed gasification. The influence of operating conditions (pressure, temperature, stoichiometric ratio) on gasification (gas composition, conversion grades) was studied. The gasifiers were operated in a pressure range of 0.15– 0.7 MPa and maximum temperatures of ca. 900°C. The Delft gasifier has a 2 m high bed zone (diameter: 0.4 m ) followed by a freeboard approximately 4 m high (diameter: 0.5 m ). The IVD gasifier has a diameter of 0.1 m and a reactor length of 4 m . Carbon conversions during wood, miscanthus and brown coal gasification experiments were well above 80%. Fuel-nitrogen conversion to ammonia was above ca. 50% and the highest values were observed for biomass. The results are in line with other investigations with biomass bottom feeding. Deviation occurs compared with top feeding. Measurements are compared with simulation results of a reaction-kinetics-based model, using ASPEN PLUS, related to emission of components like fuel-nitrogen-derived species. Data from literature regarding initial biomass flash pyrolysis in the gasification process are used in the gasifier model and will be compared with simulation results from the FG-DVC model. Measurements and model predictions were in reasonably good agreement with each other.

Influence of Fly Ash on High Temperature Desulfurization Using Iron Oxide Sorbent

The understanding of the influence of the deposited dust on the desulfurization performance of sorbent is of significance for developing a combined process for simultaneous desulfurization and dust removal in hot gas cleanup. In this paper, the influence of fly ash from a fluidized-bed coal gasifier on the desulfurization performance of iron oxide sorbent made by a kind of waste material containing iron oxide was systematically evaluated in the temperature range of 400 °C to 550 °C in a fixed-bed reactor. The results showed that fly ash could interact with the sorbent and adversely influence the sulfur capacity and sulfidation rate of the sorbent. The interaction was promoted with increasing sulfidation temperature and quantity of fly ash. But below 450 °C, the interaction becomes negligible. Kinetic studies were conducted using the grain model. Deposition of fly ash on the surface of the sorbent could cause the hindering of mass transfer and the decrease of the effective diffusivities. In addition, the mechanism of influence was discussed. It was found that the reaction of carbon with iron oxide and the sintering of minerals in fly ash with components of sorbent at higher temperature plays an important role in causing the fly ash to be influential.

Gas flow and particle deposition in the hot-gas filter vessel of the Pinon Pine project

Advanced pressurized fluidized bed combustors (PFBC) and integrated gasification combined cycles (IGCC) as economical clean coal technologies for the 21st century have attracted considerable attention. The success of these advanced coal energy systems hinges on effective and reliable commercial-scale filtration of gases at very high temperatures. The Pinon Pine hot-gas filtration system is the first industrial-scale application of an advanced particle filtration system in the United States. The system currently is becoming operational and will provide significant practical insights into operation of the industrial-scale hot-gas cleaning process. This study is concerned with a computer simulation of hot-gas flow and particle transport and deposition in the Pinon Pine filter vessel. The FLUENT™ code is used for evaluating the gas mean velocity, mean pressure, and the state of turbulence in the filter vessel. The 748 filters arranged into four tiers are modeled as four effective cylindrical filters. The particle equation of motion that includes the nonlinear drag and the gravity is used. The particle deposition patterns are evaluated, and the effect of particle size is studied. The results show that, for clean filters, the particle deposition rate of particles on different tiers depends on particle size. These differences could lead to nonuniform cake compositions and thicknesses on the candle filters in different tiers.

Future prospects for production of methanol and hydrogen from biomass

Technical and economic prospects of the future production of methanol and hydrogen from biomass have been evaluated. A technology review, including promising future components, was made, resulting in a set of promising conversion concepts. Flowsheeting models were made to analyse the technical performance. Results were used for economic evaluations. Overall energy efficiencies are around 55% HHV for methanol and around 60% for hydrogen production. Accounting for the lower energy quality of fuel compared to electricity, once-through concepts perform better than the concepts aimed for fuel only production. Hot gas cleaning can contribute to a better performance. Systems of 400 MW th input produce biofuels at US$ 8–12/GJ, this is above the current gasoline production price of US$ 4–6/GJ. This cost price is largely dictated by the capital investments. The outcomes for the various system types are rather comparable, although concepts focussing on optimised fuel production with little or no electricity co-production perform somewhat better. Hydrogen concepts using ceramic membranes perform well due to their higher overall efficiency combined with modest investment. Long-term (2020) cost reductions reside in cheaper biomass, technological learning, and application of large scales up to 2000 MW th. This could bring the production costs of biofuels in the US$ 5–7/GJ range. Biomass-derived methanol and hydrogen are likely to become competitive fuels tomorrow.

Analysis of Steady-State Filtration and Backpulse Process in a Hot-Gas Filter Vessel

The need to develop a technology for clean and efficient electric power generation has led to the development of advanced pressurized fluidized bed combustors (PFBC) and integrated gasification combined cycles (IGCC). The effective filtration of hot gases for removal of ash and sulfur sorbent, however, is the key to the success of these advanced coal energy systems. Recently, attention has been given to the use of ceramic candle filters for hot-gas cleaning. The ash cake formation on these filters needs to be removed by the backpusle for their successful operation. In this paper, steady-state filtration as well as the transient gas flow during the backpulse process in the integrated gasification and cleanup facility (IGCF) (located at the National Energy Technology Laboratory, NETL) is studied. The steady-state filtration condition is first evaluated, using a compressible heat-conducting flow analysis. Particle transport patterns are studied, and the deposition patterns of 1-30 w m particles on the cerami...

Preparation of activated carbon-supported ferrite for absorbent of hydrogen sulfide at a low temperature

An efficient absorbent of hydrogen sulfide for hot gas cleaning was developed. In order to increase the efficiency of the absorbent, activated carbon-supported ferrite was prepared and the absorption behavior of the absorbent was examined using a fixed-bed reactor and a thermogravimetric balance. Activated carbon-supported ferrites could be prepared at a much lower calcination temperature (400 °C) than the typical preparation temperature of ca. 1000 °C for a dry process. These ferrites have high surface areas up to 663 m 2/g. Breakthrough behavior was obtained with a fixed-bed flow reactor, with almost complete absorption of hydrogen sulfide from 5000 ppm to nearly zero level being achieved at an absorption temperature of 400 °C. The results obtained with a thermogravimetric balance indicated that the initial hydrogen sulfide absorption rate of the activated carbon-supported ferrite was about ten times higher than that of the ferrite prepared by the dry process.

Biomass gasification with air in fluidized bed. hot gas cleanup with selected commercial and full-size nickel-based catalysts

Biomass gasification with air in fluidized bed. hot gas cleanup with selected commercial and full-size nickel-based catalysts

セラミックチューブフィルターの開発

The Pressurized Fluidized Bed Combustion (PFBC) combined cycle has become a subject of world attention in terms of better plant operation, improved plant efficiency, lower flue gas emission and fuel flexibility.The 71MWe PFBC combined cycle power plant at Wakamatsu, Electric Power Development Company (EPDC) (funded by Ministry of International Trade and Industry (MITI) and Center of Coal Utilization Japan (CCUJ)) achieved approximately 11, 500h accumulative operation while extremely low dust emission (<0.2mg/m3N) was succeeded by a hot gas cleaning system combining cyclones and full scale Ceramic Tube Filter (CTF). The gas turbine installed at the downstream of the CTF was thus completely protected from the possible severe erosion problem with fly ash. Two different configurations of cyclones and CTF were examined in Phases 1 (Conventional PFBC) and Phase2 (Ash Re-circulating PFBC) where several coals, petroleum coke, and two kinds of domestic limestone as absorbent were tested successfully.CTF is one of key technology for hot gas cleaning. Its major items to be concerned such as the reliability of filter element and dust seal mechanism, the pressure drop performance, the optimization for reverse cleaning conditions and system maintenance-ability are summarized in this paper. Since it's most concerned how long the filter tubes made from Cordierite material can really survive in the commercial use, its life time is confirmed at least several years, based on the physical/chemical analysis of the used filter (approximately 8, 000h) and the accelerated corrosion test with potassium and/or sulfur dioxide gas flow. Increased resistance of gas passage at the seal portion improved the seal between ceramic filter element and metallic parts, avoiding dust leakage. The on-site inspection tool for the filter elements to find any damage suffered and the watching system of plant stability during operation were developed to avoid the catastrophic filter breakage. In conclusion, CTF was confirmed to be applicable for the commercial use.The future perspective and the application of CTF system are discussed to respond the strong demands for the better environment and the higher efficiency plant using coal.

Predicting the pressure drop across hot gas filter (CTF) installed in a commercial size PFBC system

The 71 MWe PFBC combined cycle power plant at Wakamatsu, Electric Power Development Company (EPDC) (funded by the Ministry of International Trade and Industry (MITI) and the Center of Coal Utilization Japan (CCUJ)) achieved 11,500 h accumulative operation while establishing extremely low dust emission (<1 mg/m3 N) with a hot gas cleaning system combining cyclones and ceramic tube filter (CTF). Two different configurations of cyclones and CTF were examined in Phases 1 and 2, where several coals and domestic limestone as absorbents were used.The pressure drop across the filter (ΔPc) was continuously observed to predict its maximum value (ΔPmax) under operating conditions. The ΔPmax value consisted of irreversible (ΔPbase) and reversible (ΔPown) drops with cleaning as the following equation shows,ΔPmax=ΔPbase+ΔPown=f(facevelocity,gasviscosity,thickness/permeability,dustconcentration)+dΔPc/dt×twhere: dΔPc/dt, mean rate of ΔPc increase during cleaning interval; t, reverse cleaning interval time.The pressure drop across the regenerator (ΔPregenerator) was monitored to calculate the changing face velocity of each compartment according to the Fanning equation. Both pressure drops (ΔPbase and ΔPown) were successfully estimated by the face velocity calculated for both phases. Dust concentration to the filter in both phases was found to improve the predictability of the base line one (ΔPbase).The conditioned filter material was proven to be stable, showing a constant drop depending on the operating condition. The particle size of ashes on the filter must be considered in order to obtain better prediction of the maximum pressure drop in the future.

Kinetics of ammonia decomposition in hot gas cleaning

Kinetics of ammonia decomposition in hot gas cleaning

Hot gas cleanup technologies for coal burning PFBC system for high efficient power generation

Hot gas cleanup technologies for coal burning PFBC system for high efficient power generation

00/03473 Conversion of biomass and biomass-coal mixtures — gasification, hot gas cleaning and gas turbine combustion

00/03473 Conversion of biomass and biomass-coal mixtures — gasification, hot gas cleaning and gas turbine combustion

00/03472 Conversion of biomass and biomass-coal mixtures-gasification, hot gas cleaning and gas turbine combustion

We evaluated orientation dependence in the etching rate of single-crystal silicon for tetramethyl-ammonium-hydroxide (TMAH) water solutions. Etching rates for a number of crystallographic orientations were measured for a wide range of etching conditions, including TMAH concentrations of 10–25% and temperatures of 70–90°C. We found significantly different characteristics from those for KOH water solutions. Firstly, different types of orientation dependence in etching rate were found around (111) between TMAH and KOH. This means the bonding energy of the silicon crystal lattice is not a single factor that dominates orientation dependence, and there exist different etching mechanisms for the two etchants. Secondly, effects of the circulation of etchants on the etching rates were not negligible in TMAH in contrast to KOH system.

Catalytic Hot Gas Cleaning of Fuel Gas from an Air-Blown Pressurized Fluidized-Bed Gasifier

Catalytic ammonia decomposition and tar reduction by a Ni catalyst were studied using a feed gas from a pilot-scale pressurized fluidized-bed gasifier. Tests were conducted in a tubular fixed-bed reactor with a space time of about 3 s at 800−900 °C and 12 atm. Ammonia removals of 35−95% and light tar conversions of 90−95% were observed. The amount of the light hydrocarbons was found to have a negative effect on the ammonia decomposition. An ammonia concentration in the fuel gas, gas residence time, and catalytic bed temperature also had a significant influence on the ammonia removal efficiency. After the catalyst, CO2 and CO approached equilibrium values, but the content of H2 and H2O was lower because of reactions with tar. The heating value of the fuel gas remained the same. The gasification efficiency increased by about 10%, mainly because of catalytic tar cracking. Deactivation of the catalyst was not observed in the fuel gas containing 50−150 ppm H2S and about 10 g/Nm3 tar.

Biomass Gasification with Air in Fluidized Bed. Hot Gas Cleanup with Selected Commercial and Full-Size Nickel-Based Catalysts

Three selected commercial, full-size steam-reforming catalysts for naphthas, BASF G1-50, ICI 46-1, and Topsøe R-67, are tested at pilot-scale level for hot gas cleanup in biomass gasification in a fluidized bed. Gas composition and tar content in the flue gas are measured before and after the catalytic bed. Variations of the catalytic bed in H2, CO, CO2, CH4, and H2O contents are reported for different operating conditions. Tar conversions and an apparent first-order kinetics constant for the overall tar removal reaction are calculated. Tar contents at the exit of the catalytic reactor as low as 10 mg/mn3 are obtained in a test of 50 h-on-stream without noticeable catalyst deactivation. Important variations in tar conversion with space time in the catalytic bed, with H2O/C* in the flue gas, and with the equivalence ratio in the upstream gasifier are observed. These results obtained at the pilot-scale level and with the use of full-sized commercial catalysts are an important forward step in demonstrating the technical feasibility of the overall biomass gasification process.

00/00889 The Vermont biomass gasifier project—medium heating value gas for electric power applications

The Vermont Biomass Gasifier Project is part of a major DOE initiative to demonstrate indirect gasification of renewable biomass for electricity production. The Vermont Project has been undertaken to demonstrate the integration of the Battelle Columbus Laboratories (Battelle) indirectly-heated gasifier with a high-efficiency gas turbine. The demonstration and validation of this gasification/gas turbine system is being performed at the existing 50 MW wood-fired McNeil Power Generating Station in Burlington, Vermont, thereby significantly reducing the time scale for deployment and the necessary capital investment for DOE and the Vermont project partnership. The development and commercialization of this technology is important for several reasons: (1) it does not require a hot-gas clean-up for gas turbine operation, thus removing this technical hurdle from the commercialization path; (2) it is the only US biomass gasification system that has successfully powered a gas turbine, supporting its near-term viability for commercial deployment; and (3) it produces a medium-heating-value gas without employing an oxygen plant, thus allowing the use of existing unmodified industrial gas turbines. Gasifier construction was completed in late 1997; commissioning and parametric testing was completed during the spring and summer of 1998. This paper discusses the results of this testing and presents plans formore » both the next phase of testing and prospects for near-term commercialization.« less

Biomass gasification as a means for avoiding fouling and corrosion during combustion

Gasification of biomass at 600–800°C can produce an effluent gas for use in a combustor for power production after removal of the solid products of gasification by hot gas cleanup (e.g., aspen wood). This will avoid the fouling and/or corrosion often found in biomass combustion. Biomasses which form liquids below 800°C (e.g., wheat straw) require the use of additives which raise the lowest temperatures for the presence of inorganic liquids to over 800°C. This alternative path for avoiding the fouling and corrosion found during combustion of many biomasses probably can be applied to a broad range of analogous materials.

Biomass Gasification in Fluidized Bed: Where To Locate the Dolomite To Improve Gasification?

Calcined dolomites (OCa.OMg) are often used for hot gas cleanup in biomass gasification processes in a fluidized bed. Two locations are envisaged for such dolomite: in the same gasifier bed (mixed with silica sand) or in a secondary bed, downstream from the gasifier. Previous results obtained under very similar circumstances are here analyzed to determine which is the best location (regarding its chemical usefulness for tar elimination) of the dolomite. Gas and tar yields and gas compositions are here given for the two locations of the dolomite, and it is made both for gasification with air and with steam−O2 mixtures. It is demonstrated how the effectiveness of the dolomite in the second reactor is only a little bit higher than for the in-bed location. This small increase in effectiveness is mainly found in gasification with H2O−O2 mixtures, there no having noticeable chemical differences (between the two locations of the dolomite) in gasification with air.

Kinetics of Ammonia Decomposition in Hot Gas Cleaning

Reduction in the amount of ammonia in fuel gas from biomass gasification was studied. Experiments were carried out in a fixed-bed reactor dt 200-1000 degrees C, 21 atm. A kinetic model for ammonia decomposition was developed. The partial pressure of hydrogen in the fuel gas was a key factor to model ammonia decomposition. Activation energies in the empty reactor, on carbon, and in a sand bed were similar, 130-140 kJ/mol. The frequency factors for carbon and sand were 10 times as large as for the empty reactor. The activation energy for a Ni-based catalyst was 111-113 kJ/mol. Carbon deposit deactivated the Ni-based catalyst. High temperature was found to be essential for avoiding carbon fouling and for achieving high ammonia removal efficiency. Estimation of the ammonia reduction for fuel gas showed that a moderate amount of ammonia could be removed by use of the Ni-based pellets at 800 degrees C. (Less)