Fuel Gas Cleaning Research Articles

Recent research progress in the study of catalytic CO oxidation by gas phase atomic clusters

Oxidation of CO into CO2 is a major solution to reduce CO emission into the atmosphere and to remove CO in fuel gas cleanup. Furthermore, CO oxidation serves as a prototypical reaction for heterogeneous catalysis. This review provides an overview and an update on how to study catalytic CO oxidation at a strictly molecular level by performing well-controlled gas-phase experiments in combination with quantum chemistry calculations. The advances in the unique catalytic reactivity of single-atom cluster catalysts are emphasized. The catalytically active sites and various mechanistic aspects in the redox couples N2O/CO and O2/CO for the seemingly simple oxidation reaction are described.

Thermodynamic analysis of engineering solutions aimed at raising the efficiency of integrated gasification combined cycle

Raising the efficiency and environmental friendliness of electric power generation from coal is the aim of numerous research groups today. The traditional approach based on the steam power cycle has reached its efficiency limit, prompted by materials development and maneuverability performance. The rival approach based on the combined cycle is also drawing nearer to its efficiency limit. However, there is a reserve for efficiency increase of the integrated gasification combined cycle, which has the energy efficiency at the level of modern steam-turbine power units. The limit of increase in efficiency is the efficiency of NGCC. One of the main problems of the IGCC is higher costs of receiving and preparing fuel gas for GTU. It would be reasonable to decrease the necessary amount of fuel gas in the power unit to minimize the costs. The effect can be reached by raising of the heat value of fuel gas, its heat content and the heat content of cycle air. On the example of the process flowsheet of the IGCC with a power of 500 MW, running on Kuznetsk bituminous coal, by means of software Thermoflex, the influence of the developed technical solutions on the efficiency of the power plant is considered. It is received that rise in steam-air blast temperature to 900°C leads to an increase in conversion efficiency up to 84.2%. An increase in temperature levels of fuel gas clean-up to 900°C leads to an increase in the IGCC efficiency gross/net by 3.42%. Cycle air heating reduces the need for fuel gas by 40% and raises the IGCC efficiency gross/net by 0.85-1.22%. The offered solutions for IGCC allow to exceed net efficiency of analogous plants by 1.8-2.3%.

A review on the fuel gas cleaning technologies in gasification process

The product gas produced from gasification of solid fuel contains various impurities such as particulates, toxin gases, tar, vapours of heavy metals, etc. Presence of tar is a major issue which requires to be addressed before the use of gas product in the downstream process. Tar causes problems in the process equipment like flow channels, power generating units, etc. Generally gasification technology is adapted for the utilization of low grade coal, municipal solid waste, agro-waste, bio-waste, etc., which generates toxic and emits various hazardous compounds of chlorine, sulphur, nitrogen and heavy metals like Mn, Cd and Hg. Various alkali metals like Na, K, etc., generated through the gasification of wastes also create problem in the downstream processes when condensed at low temperature. The key challenge to commercializing gasification technology is to generate a clean fuel gas which meets the global emission standards. This paper provides a comprehensive overview of the fuel gas cleaning methods those are used to remove the contaminants and gas impurities generated from various types of reactor for gasification of coal or biomass.

Corrosion of alumina and mullite hot gas filter candles in gasification environment

Reliable fuel gas cleaning is required to meet environmental regulations as well as to prevent corrosion and erosion of downstream components. The aggressive process environment in biomass-gasification power generation systems or in biofuels production systems causes corrosion in the ceramic hot gas filter candles used to clean the fuel gas. Therefore, in order to improve the reliability and durability of filters, the influence of steam, ash, hydrogen sulfide, and alkaline metals on the corrosion processes was studied for alumina and mullite filter candles fabricated by Pall Schumacher. Exposure to these contaminants effects the chemical composition of the binder phases resulting in exchange of alkaline metals and alkaline earth metals. Analyses by energy dispersive X-ray spectroscopy demonstrate the negative effect of silicon containing binder phases. These effects are discussed and it is shown that the usage of silicon-free binder phases in hot gas filter candles for gasification processes is promising.

Efficiency enhancement in IGCC power plants with air-blown gasification and hot gas clean-up

Air-blown IGCC systems with hot fuel gas clean-up are investigated. In detail, the gas clean-up station consists of two reactors: in the first, the raw syngas exiting the gasifier and passed through high-temperature syngas coolers is desulfurized by means of a zinc oxide-based sorbent, whereas in the second the sulfided sorbent is duly regenerated. The hot fuel gas clean-up station releases H2S-free syngas, which is ready to fuel the combustion turbine after hot gas filtration, and a SO2-laden stream, which is successively treated in a wet scrubber.A thermodynamic analysis of two air-blown IGCC systems, the first with cold fuel gas clean-up and the second with hot fuel gas clean-up, both with a state-of-the-art combustion turbine as topping cycle, shows that it is possible to obtain a really attractive net efficiency (more than 51%) for the second system, with significant improvements in comparison with the first system. Nevertheless, higher efficiency is accomplished with a small reduction in the power output and no sensible efficiency improvements seem to be appreciated when the desulfurization temperature increases. Other IGCC systems, with an advanced 1500°C-class combustion turbine as the result of technology improvements, are investigated as well, with efficiency as high as 53%.

Catalytic formation of carbonyl sulfide during warm gas clean-up of simulated coal-derived fuel gas with Pd/γ-Al2O3 sorbents

Coal gasification processes, such as the Integrated Gasification Combined Cycle (IGCC), will increase in importance due to the expanding concern over CO2 emissions and global climate change. During the development of a Pd/γ-Al2O3 sorbent for warm (200°C) fuel gas cleanup, the catalytic formation of carbonyl sulfide (COS), was observed. This is attributed to a heterogeneous reaction involving fuel gas components (CO/CO2/H2/H2S/H2O) and Pd/γ-Al2O3. The concentration of COS increases 200-fold when exposed to the Pd/γ-Al2O3 sorbent. A Langmuir–Hinshelwood reaction mechanism is proposed and a kinetic model is developed based on experimental results. The effect of γ-Al2O3, a common catalyst for hydrolysis of COS, and H2O on the COS concentration is discussed.

Removal of tar component over cracking catalysts from high temperature fuel gas

Five catalysts were evaluated for removal of tar components in high temperature fuel gas cleaning. 1-Methylnaphthalene was chosen as a model of the tar components. The NiMo catalyst having the highest surface area exhibited the highest activity of tar removal among the five catalysts. The effects of reaction temperature and space velocity on tar removal were studied in the range of 250–650 °C and 3000–9000 h −1, respectively. A lumped kinetic model was developed to describe the removal process. A sequential method to estimate the rate constants in the lumped kinetic model was adopted, which greatly simplifies the data treatments. Kinetic constants and activation energies were determined by a nonlinear regression program. The results showed that the predicted yields were very close to the experimental ones.

Liquid Tin Irrigated Packed Bed for Hot Fuel Gas Desulfurization

Hot fuel gas cleaning for gasification of coal can increase the energy efficiency by minimizing the loss of thermal energy. The current hot gas desulfurization studies focus on the development of various metal oxide sorbents. This paper presents a novel approach using liquid tin as a nonwetting scrubbing medium in a countercurrent packed bed. The H2S removal efficiency of liquid tin was investigated in a 200 mm high reactor for various tin and gas flow rates, bed heights, and H2S concentration at operating temperatures of 300−400 °C. For tested conditions, gas transfer unit heights of 0.084−0.181 m were obtained at H2S concentration of 1000 ppm, which corresponded to an H2S removal efficiency of up to 91% in the small test reactor. These results are promising since higher efficiencies can be achieved at larger scales. The effects of thermal equilibrium and interaction with other gases are also discussed. Further studies are required on various aspects including higher operating temperatures, larger flow rates, and the regeneration of tin using zinc.

Mixed zirconia–alumina supports for Ni/MgO based catalytic filters for biomass fuel gas cleaning

Localized, small scale renewable energy generation by biomass gasification will only find widespread use if simple and efficient technology is available for removing undesired impurities such as particles and tar from the producer gas in order to avoid serious operating problems in the downstream equipment and coupled diesel engine. This work focuses on the further improvement of a novel one-step cleanup with a catalytic candle filter by using alternative ZrO 2 or ZrO 2–Al 2O 3 mixed supports in order to improve the activity of Ni-based catalysts at lower temperatures. Porous α-alumina filter materials were prepared with the urea method to deposit 2.5 wt.% Al 2O 3 or ZrO 2, or a combination of ZrO 2 and Al 2O 3 to increase the surface area, followed by 1 wt.% Ni and 0.5 wt.% MgO deposition. The surface area increases with the number of deposition cycles of ZrO 2 or ZrO 2–Al 2O 3, but was lower than for pure Al 2O 3 deposition. Uniform distributions of the zirconia secondary support and the active ingredients such as Ni and MgO throughout the sample could be obtained. Tar conversion achieved from the three types of supports: ZrO 2, Al 2O 3 and a mixed ZrO 2–Al 2O 3 are generally similar, except at high velocity and low temperature where the mixed support is best. As an example, for the mixed oxide deposit of 1.20 wt.% ZrO 2 + 1.28 wt.% Al 2O 3 followed by 0.46 wt.% MgO + 0.996 wt.% Ni at 900 °C, 2.5 cm/s, with 15 g/Nm 3 benzene or 5 g/Nm 3 naphthalene loading in presence of 100 ppm H 2S, conversions of benzene and naphthalene were 95% and 99.5% respectively, which is extremely promising, since the surface area of these new ZrO 2 based materials is lower than with pure alumina and leaves room for significant improvement. Extended time testing over 170 h under the condition of 15 g/Nm 3 benzene and 5 g/Nm 3 naphthalene fed together at 900 °C and in presence of 100 ppm H 2S, showed 99.2–99.6% benzene conversion and 100% naphthalene conversion, even at lower temperature (850 °C) a good activity was still achieved in comparison with our previously developed catalysts.

Streamer corona plasma for fuel gas cleaning: comparison of energization techniques

Tar (heavy hydrocarbon or Poly Aromatic Hydrocarbon (PAH)) removal from biomass derived fuel gas is one of the biggest obstacles in its utilization for power generation. We have investigated pulsed corona as a method for tar removal. Our previous experimental results indicated an energy consumption of 200–250 J/L at an optimum gas temperature of 400 °C. One of the challenges in scaling up a process based on pulsed corona is the availability of high power pulsed power sources. To overcome this, a newer method of streamer corona generation by an alternative “DC/AC” power source is investigated. Energy consumption for tar removal process is used as a basis for comparing the two methods for its chemical efficiency. Results indicate the pulsed corona system and DC/AC system to have similar efficiency.

A high-temperature pulsed corona plasma system for fuel gas cleaning

Tars in fuel gases create serious obstacles for gasification. This paper describes a pulsed corona plasma system for tar removal from the fuel gas. Experiments were performed under gaseous temperatures of up to 500°C. Effects of the gaseous temperature on the electrical matching and tar removal are reported.

Catalytic cracking of tar component from high-temperature fuel gas

The cracking removal of tar component in high-temperature fuel gas cleanup is one of the most crucial problems in developing cleanest advanced power technology. Five catalysts were evaluated to tar component removal from high-temperature fuel gas in a fixed-bed reactor. 1-Methylnaphthalene was chosen as a model of tar component. The Y-zeolite and NiMo catalysts were found to be the most effective catalysts. Two catalysts almost removed 100% tar component at 550 °C. The process variables, temperature and space velocity, have very significant effects on tar component removal with catalysts. The long-term durability shows that two catalysts maintain more than 95% removal conversion at 550 °C in 168 h. The combustion study of coke deposited on catalysts by thermal gravimetric analysis technology shows that very small amount buildup of coke appears on two catalysts surface. Using a first-order kinetic model, the apparent energies of activation and pre-exponential factors for tar component removal reaction and coke combustion on catalysts were obtained for the most active catalysts.

Modeling the Thermal Destruction of Toluene (C7H8) as Tar-Related Species for Fuel Gas Cleanup

Thermal destruction of vaporized toluene in the presence of a [N2 + H2O + O2] in air and [N2 + H2 + H2O] gas mixtures are examined. Toluene (P[C7H8] = 0.93−1.85 kPa) is used as model species present in tar-related volatile organic compounds from advanced thermochemical conversion technologies. Experiments were performed in a nonisothermal tubular flow reactor at a total pressure of ca. 101.3 kPa, temperature range of 973−1223 K. In presence of oxygen-containing molecules (molar ratios of [H2O + O2]/C7H8 were varied between 1.78 and 3.52), a first-order reaction rate could express the effects of temperature and residence time. Thermal destruction of toluene in [N2 + H2 + H2O] gas mixture ([H2 + H2O]/C7H8 = 3.52, and 0.40 < τ < 0.90 s) was studied as reference. Activation energies of the thermal destruction of toluene are: 356 ± 5 kJ mol-1 in [N2 + H2O + O2] atmosphere and 250 ± 10 kJ mol-1 in [N2 + H2 + H2O] gas mixture. A chemical reaction network and a free-radical mechanism have been suggested to expla...

Chemical Processes in Tar Removal from Biomass Derived Fuel Gas by Pulsed Corona Discharges

Cleaning or conditioning of fuel gas from biomass gasification is perhaps one of the main obstacles for utilization of biomass as a source of power generation. Various methods exist, but, so far, none of them have been reported to be reliable for long-term operation. In our present research, we try to couple our advancements in pulsed power technology for industrial applications to the application mentioned. Here we focus on the chemical processes that occur during pulsed corona fuel gas cleaning. Experimental results at 200°C show that the main process for tar (heavy aromatic hydrocarbons) removal is mainly via oxidation.

KVAERNER SECURES €30 MILLION IN CONTRACTS

Since the mid-1980s, TPS Termiska Processer AB has been working on the development of an atmospheric-pressure gasification process. A major aim at the start of this work was the generation of fuel gas from indigenous fuels to Sweden (i.e. biomass). As the economic climate changed and awareness of the damage to the environment caused by the use of fossil fuels in power generation equipment increased, the aim of the development work at TPS was changed to applying the process to heat and power generation from feedstocks such as biomass and solid wastes. Compared with modern waste incineration with heat recovery, the gasification process will permit an increase in electricity output of up to 50%. The gasification process being developed is based on an atmospheric-pressure circulating fluidised bed gasifier coupled to a tar-cracking vessel. The gas produced from this process is then cooled and cleaned in conventional equipment. The energy-rich gas produced is clean enough to be fired in a gas boiler (and, in the longer term, in an engine or gas turbine) without requiring extensive flue gas cleaning, as is normally required in conventional waste incineration plants. Producing clean fuel gas in this manner, which facilitates the use of efficient gas-fired boilers, means that overall plant electrical efficiencies of close to 30% can be achieved. TPS has performed a considerable amount of pilot plant testing on waste fuels in their gasification/gas cleaning pilot plant in Sweden. Two gasifiers of TPS design have been in operation in Grève-in-Chianti, Italy since 1992. This plant processes 200 tonnes of RDF (refuse-derived fuel) per day. It is planned that the complete TPS gasification process (including the complete fuel gas cleaning system) be demonstrated in several gas turbine-based biomass-fuelled power generating plants in different parts of the world. It is the aim of TPS to prove, at commercial scale, the technical feasibility and economic advantages of the gasification process when it is applied to solid waste fuels. This aim shall be achieved, in the short-term, by employing the cold clean product gas in a gas boiler and, in the longer-term, by firing the gas in engines and gas turbines. A study for a 90 MWth waste-fuelled co-generation plant in Sweden has shown that, already today, gasification of solid waste can compete economically with conventional incineration technologies.

KVAERNER SECURES €30 MILLION IN CONTRACTS

Since the mid-1980s, TPS Termiska Processer AB has been working on the development of an atmospheric-pressure gasification process. A major aim at the start of this work was the generation of fuel gas from indigenous fuels to Sweden (i.e. biomass). As the economic climate changed and awareness of the damage to the environment caused by the use of fossil fuels in power generation equipment increased, the aim of the development work at TPS was changed to applying the process to heat and power generation from feedstocks such as biomass and solid wastes. Compared with modern waste incineration with heat recovery, the gasification process will permit an increase in electricity output of up to 50%. The gasification process being developed is based on an atmospheric-pressure circulating fluidised bed gasifier coupled to a tar-cracking vessel. The gas produced from this process is then cooled and cleaned in conventional equipment. The energy-rich gas produced is clean enough to be fired in a gas boiler (and, in the longer term, in an engine or gas turbine) without requiring extensive flue gas cleaning, as is normally required in conventional waste incineration plants. Producing clean fuel gas in this manner, which facilitates the use of efficient gas-fired boilers, means that overall plant electrical efficiencies of close to 30% can be achieved. TPS has performed a considerable amount of pilot plant testing on waste fuels in their gasification/gas cleaning pilot plant in Sweden. Two gasifiers of TPS design have been in operation in Grève-in-Chianti, Italy since 1992. This plant processes 200 tonnes of RDF (refuse-derived fuel) per day. It is planned that the complete TPS gasification process (including the complete fuel gas cleaning system) be demonstrated in several gas turbine-based biomass-fuelled power generating plants in different parts of the world. It is the aim of TPS to prove, at commercial scale, the technical feasibility and economic advantages of the gasification process when it is applied to solid waste fuels. This aim shall be achieved, in the short-term, by employing the cold clean product gas in a gas boiler and, in the longer-term, by firing the gas in engines and gas turbines. A study for a 90 MWth waste-fuelled co-generation plant in Sweden has shown that, already today, gasification of solid waste can compete economically with conventional incineration technologies.

Fuel Gas Cleanup Parameters in Air-Blown IGCC

Fuel gas cleanup processing significantly influences overall performance and cost of IGCC power generation. The raw fuel gas properties (heating value, sulfur content, alkali content, ammonia content, “tar” content, particulate content) and the fuel gas cleanup requirements (environmental and turbine protection) are key process parameters. Several IGCC power plant configurations and fuel gas cleanup technologies are being demonstrated or are under development. In this evaluation, air-blown, fluidized-bed gasification combined-cycle power plant thermal performance is estimated as a function of fuel type (coal and biomass fuels), extent of sulfur removal required, and the sulfur removal technique. Desulfurization in the fluid bed gasifier is combined with external hot fuel gas desulfurization, or, alternatively with conventional cold fuel gas desulfurization. The power plant simulations are built around the Siemens Westinghouse 501F combustion turbine in this evaluation. [S0742-4795(00)00502-0]

Energy recovery from solid waste fuels using advanced gasification technology

Since the mid-1980s, TPS Termiska Processer AB has been working on the development of an atmospheric-pressure gasification process. A major aim at the start of this work was the generation of fuel gas from indigenous fuels to Sweden (i.e. biomass). As the economic climate changed and awareness of the damage to the environment caused by the use of fossil fuels in power generation equipment increased, the aim of the development work at TPS was changed to applying the process to heat and power generation from feedstocks such as biomass and solid wastes. Compared with modern waste incineration with heat recovery, the gasification process will permit an increase in electricity output of up to 50%. The gasification process being developed is based on an atmospheric-pressure circulating fluidised bed gasifier coupled to a tar-cracking vessel. The gas produced from this process is then cooled and cleaned in conventional equipment. The energy-rich gas produced is clean enough to be fired in a gas boiler (and, in the longer term, in an engine or gas turbine) without requiring extensive flue gas cleaning, as is normally required in conventional waste incineration plants. Producing clean fuel gas in this manner, which facilitates the use of efficient gas-fired boilers, means that overall plant electrical efficiencies of close to 30% can be achieved. TPS has performed a considerable amount of pilot plant testing on waste fuels in their gasification/gas cleaning pilot plant in Sweden. Two gasifiers of TPS design have been in operation in Grève-in-Chianti, Italy since 1992. This plant processes 200 tonnes of RDF (refuse-derived fuel) per day. It is planned that the complete TPS gasification process (including the complete fuel gas cleaning system) be demonstrated in several gas turbine-based biomass-fuelled power generating plants in different parts of the world. It is the aim of TPS to prove, at commercial scale, the technical feasibility and economic advantages of the gasification process when it is applied to solid waste fuels. This aim shall be achieved, in the short-term, by employing the cold clean product gas in a gas boiler and, in the longer-term, by firing the gas in engines and gas turbines. A study for a 90 MWth waste-fuelled co-generation plant in Sweden has shown that, already today, gasification of solid waste can compete economically with conventional incineration technologies.

98/02867 Application of gasification to the conversion of wood, urban and industrial wastes: Abatzoglou, N. K. et al. Dev. Thermochem. Biomass Convers., 1997, 2, 960–972

Air-blown IGCC systems with hot fuel gas clean-up are investigated. In detail, the gas clean-up station consists of two reactors: in the first, the raw syngas exiting the gasifier and passed through high-temperature syngas coolers is desulfurized by means of a zinc oxide-based sorbent, whereas in the second the sulfided sorbent is duly regenerated. The hot fuel gas clean-up station releases H2S-free syngas, which is ready to fuel the combustion turbine after hot gas filtration, and a SO2-laden stream, which is successively treated in a wet scrubber.A thermodynamic analysis of two air-blown IGCC systems, the first with cold fuel gas clean-up and the second with hot fuel gas clean-up, both with a state-of-the-art combustion turbine as topping cycle, shows that it is possible to obtain a really attractive net efficiency (more than 51%) for the second system, with significant improvements in comparison with the first system. Nevertheless, higher efficiency is accomplished with a small reduction in the power output and no sensible efficiency improvements seem to be appreciated when the desulfurization temperature increases. Other IGCC systems, with an advanced 1500 °C-class combustion turbine as the result of technology improvements, are investigated as well, with efficiency as high as 53%.

A Direct Coal-Fired Combustion Turbine Power System Based on Slagging Gasification With In-Situ Gas Cleaning

Westinghouse began the development of a compact, entrained, slagging gasifier technology utilizing in-situ fuel gas cleaning for combustion turbine power cycles in 1986. The slagging gasifier is air-blown, and produces a hot, low-heating value fuel gas that can be combusted and quenched to combustion turbine inlet temperatures while maintaining low levels of NOx emissions. The U.S. Department of Energy sponsored engineering studies and pilot testing during the period 1986 to 1992. This work has shown that the technology has promise, although performance improvements are required in some key areas. A major challenge has been the development of insitu removal of sulfur, alkali vapor, and particulate to low enough levels to permit its use in combustion turbine power systems without additional, external gas cleaning. This paper reviews the Westinghouse slagging gasifier, direct coal-fired turbine power generation concept; the pilot test results; and the current development activities that Westinghouse is engaged in.