Gas Cleaning Technology Research Articles

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.

Evaluating ammonia as green fuel for power generation: A thermo-chemical perspective

Energy storage will be necessary for a future power system with high penetration of renewable sources, mainly, wind and solar, to ensure the stability of the grid. In this context, power-to-chemicals is a promising concept for a medium/long-term storage horizon and a wide range of capacities. Within this alternative, ammonia rises as one of the fuels with the highest potential in a scenario targeting decarbonization. The first step is the production of ammonia using renewable energy sources, followed by its transformation into energy. This second area requires a deeper analysis at process scale in order to introduce this technology into the future power system. In this work, an assessment of an ammonia-based power plant is presented, focusing on the thermo-chemical route. A combined cycle is evaluated, considering different gas clean-up technologies to recover valuable components and comply with environmental restrictions. As a result, the total efficiency of the power facility reaches about 40%, limited by the maximum temperature allowed in the gas turbine. The influence of the price of ammonia is also evaluated due to the paramount importance of this parameter. The production cost ranges from 0.2 to 0.6€/kWh, with the lowest level corresponding to a scenario in which there is a significant reduction in the cost of renewable power generation and electrolysis technology. Therefore, the feasibility of the use of ammonia as an energy storage alternative is demonstrated, providing a powerful platform for the implementation of a power grid with high penetration of fluctuating sources.

Large-scale applications and challenges of adsorption-based carbon capture technologies

This paper introduces adsorption processes with scaled sizes for post-combustion carbon capture, pre-combustion carbon capture, and direct air capture (DAC). Technical characteristics, separation performances, and operating energy consumptions of adsorption-based pilot plants for carbon capture are analyzed. Opportunities and challenges of adsorption-based carbon capture processes in future development are illustrated. Adsorption-based post-combustion carbon capture is a relatively mature technology, which can be applied to retrofitted power plants. However, in order to commercialize this technology, quantities of research and development resources are still needed. Researches on adsorption-based post-combustion carbon capture should focus on the following three aspects: (1) Low-temperature adsorbents with excellent CO2 working capacities, kinetics, and stabilities, (2) low energy consumption cycles using steam purge, and (3) contactors with low gas-solid mass transfer resistances. The warm gas clean-up technology based on pressure swing adsorption (PSA) is a research hotspot for pre-combustion carbon capture. At present, many warm gas clean-up pilot plants are being built worldwide, and in the meantime, some bottlenecks appear. First, the CO2 working capacities of elevated temperature adsorbents are still lower than those of low temperature adsorbents. The recently reported molten salt-promoted magnesium oxide achieves a very high working capacity through the bulk phase chemical absorption, but a carbon capture prototype needs to be established to verify its cyclic stability. Achieving both high purity and high recovery of warm gas clean-up consumes a large amount of high temperature steam. Although multi-train PSA configuration can reduce the energy consumption, it also increases the operating complexity and equipment investment. In addition to CO2, the removal of other impurities such as H2S, COS, HCl, and heavy metals in syngas/reforming gas should be considered. The sorption enhanced reforming with oxy-fuel regeneration process based on high temperature adsorbents can achieve CO2 enrichment in the regeneration reactor. However, pilot plants for this technology are currently lacking, and so detailed techno-economic analysis is still needed to assess its capture cost. Although DAC is a relatively new concept and is still in the early stage for large-scale commercial application, the synergy between DAC and conventional carbon capture technologies can mitigate climate change effects in the long run. The development of DAC technologies needs to pay special attention to the pressure drop problems. Novel gas-solid contactors using structural adsorbents can effectively reduce the power consumption of the fan. Steam purge under subatomospheric pressures reduces the regeneration temperature of DAC, and thus makes the utilization of renewable energy and industrial waste heat for regeneration becoming possible. When steam purge is used, the cyclic stability of the adsorbents should be concerned. For instance, polyamine impregnated adsorbents are prone to amine leakage in the presence of steam. Therefore, the development of hydrothermally stable DAC adsorbents is significantly important.

Solution to the Problem of Precipitation of High-Resistivity Ashes by Electrostatic Precipitators

The innovative and highly effective Russian electrostatic precipitators of the EGAV type were created in order to solve problems associated with the reduction of ash emissions at coal power plants. The new electrostatic precipitators ensured an increase in precipitation effectiveness to 99.87% in the same overall housing sizes along with a reduction in emissions up to 16 times, with actual emissions ranging from 12.6 to 119 mg/m3 (under standard conditions). The technical solutions for intensifying electrostatic precipitation realised in EGAV precipitators increase particle drift velocity to the precipitating electrode by 65%. The application of the EGAV type electrostatic precipitators for removing high-resistivity ashes from flue gases led to the required reduction of emissions during the modernization of the acting electrostatic precipitators. The cost of reconstructing the gas-cleaning unit with the application of innovative electrostatic precipitators turned to be less than with the use of a combined electrostatic precipitator or a bag filter. The new electrical cleaning technology also formed a scientific basis for the innovative development of other promising gas-cleaning technologies.

Determining kinetic constants for reactions of zinc oxide sorbents with syngas components

Hot gas clean-up (HGC) technology uses special zinc oxide based sorbents. Sorbent attrition is one of the negative factors that should be improved. The current study has determined that one of the main reasons of sorbent reduction is interaction with syngas components, namely, carbon monoxide, hydrogen, methane and carbon (side reactions). In this study, kinetics of main reaction (h2s adsorption by zinc oxide) and side reactions were considered and compared. Models of chemical processes and mechanisms were considered as well. Complicated nature of HGC process was researched. It is stated that the process can run in three different phases (gas, solid, dust). Methods of TGA data calculation are presented and compared with literature. In syngas where hydrogen sulphide concentration is much lower than concentration of hydrogen and carbon monoxide, main reaction is dominant at temperatures near 300–500 °C. At 650 °C main reaction takes the second place after H2 reduction, and at 850°C it is the third after CO reduction (with diffusion resistance of product shell). Hydrogen reduction is more active than carbon monoxide reduction, that is why CO/H2 ratio in syngas should be increased for rising the HGC operation temperature. A wide range of processes (main and side reactions) was considered with the use of the same materials, equipment and methods.

Simulation of elevated temperature solid sorbent CO2 capture for pre-combustion applications using computational fluid dynamics

CO2 adsorption is one of the warm gas cleanup technologies under development for integrated gasification combined cycle (IGCC) applications. Computational Fluid Dynamics (CFD) can be a practical and powerful tool for reactor design for and optimization of the CO2 adsorption process. In this present work, CFD simulation was developed in commercially available ANSYS Fluent software and validated for solid sorbent CO2 capture to investigate pressure swing adsorption (PSA) for CO2 separation from syngas with all the auxiliary operating steps. The adsorption equilibrium and kinetics were incorporated into ANSYS by user defined functions (UDFs) for source terms in Navier–Stokes equations. The CFD model well predicted the CO2 breakthrough curve and temperature change. It was shown that in demo reactor operation, at the end of adsorption step, only half of the sorbent was loaded with CO2, while most of the loaded CO2 was released during the desorption step. Further optimization of sorbent packing and cycle operation can be done with assistance of this CFD model to maximize bed loading, and used to design the commercial size reactors.

Modelling of Substitute Natural Gas production via combined gasification and power to fuel

The combination of water electrolysis and solid fuel gasification offers the substitution of Air Separation Unit, the reduction or elimination of water gas shift catalytic system and acid gas removal technology. Subsequently, the direct utilisation of CO2, which otherwise would be emitted during production and its conversion to valuable fuels in combination with energy storage are achieved. Steam gasification and steam-oxygen gasification in different operating conditions and scales are combined with electrolysers with the aim to define optimum efficiencies towards SNG production and reduction of direct CO2 emissions. Modelling and comparison of 6 different cases for steam and steam-oxygen gasification process, gas cleaning and conditioning technologies focusing on tar removal, activated carbon, water gas shift, and acid gas removal technologies with potassium carbonate and MDEA are investigated. Capture ratios are balanced with and without water gas shift reactor according to the requirements of SNG synthesis. The efficiency of gasification and power to SNG ranges between 57.67% and 63.43% for the optimum cases with low pressure steam/oxygen gasification and electrolysers sized according to oxygen demand and according to the oversized electrolysers case respectively. The overall energy conversion resulted in an energy conversion efficiency of 72.83% and 73.51% with the production of steam.

Integration of chemical looping oxygen production and chemical looping combustion in integrated gasification combined cycles

Energy penalty is the primary economic challenge facing CO2 capture technology. This work aims to address this challenge through a novel power plant configuration, capable of achieving 45.4% electric efficiency from coal with a 95% CO2 capture efficiency. The COMPOSITE concept integrates chemical looping oxygen production (CLOP) and packed bed chemical looping combustion (PBCLC) reactors into an integrated gasification combined cycle (IGCC) power plant. Hot gas clean-up technology is implemented to boost plant efficiency. When commercially available cold gas clean-up technology is used, the plant efficiency reduces by 2%-points, but remains 2.3%-points higher than a comparative PBCLC-IGCC power plant and 8.1%-points higher than an IGCC power plant with pre-combustion CO2 capture. It was also shown that the COMPOSITE power plant performance was not sensitive to changes in the performance of the CLOP reactors, implying that uncertainties related to this novel process component do not reduce the potential of the COMPOSITE concept. The outstanding efficiency obtained for this concept is made possible by a complex and highly integrated plant configuration, whose operability and techno-economic feasibility must be demonstrated.

Influence of operational parameters on the performance of gas clean-up technology with a moving granular bed filter

This paper describes new design and test procedures of an inlet gas system that is part of a moving granular bed filter. A series of experiments is conducted to demonstrate the collection efficiency of this method under different operating conditions. In addition, the dynamic model and the flow analysis of gas in the inlet gas system and filter bed are discussed. Several parameters are considered, including uniform flow of gas, geometry of inlet gas system, and position of flow-corrective insert in filter bed, to understand the performance of the new filter system. The filtration superficial velocity, mass flow rate of filter granules, and baffle length and baffle angle of inlet gas system are controlled during the test process. The pressure drop, collection efficiency, flow velocity profile of gas, and size distribution of dust particulates are measured simultaneously. The trend in uniform gas flow behaviors can be useful for application in different cross-flow filter systems for gas clean-up. The results of this study are expected to serve as a basis for future research.

Economic assessment of packed bed chemical looping combustion and suitable benchmarks

CO2 capture and storage (CCS) must be deployed on a large scale if global temperature rise is to be limited to 2°C. To facilitate such a rapid expansion, it is crucial that costs are reduced from today’s levels. Energy penalty is the biggest single contributor to the cost of CCS. This work therefore presents an economic assessment of the packed bed chemical looping combustion (PBCLC) concept for near-zero emission power production with minimal energy penalty. Results showed that the PBCLC concept integrated into an integrated gasification combined cycle (IGCC) power plant resulted in similar CO2 avoidance costs as a supercritical pulverized coal plant with CCS: 66 €/ton (including CO2 transport and storage). Relative to an unabated IGCC plant, the CO2 avoidance cost was 34 €/ton, significantly lower than the costs of an IGCC power plant with pre-combustion CO2 capture (47 €/ton). Moderate sensitivities to uncertainties regarding the PBCLC oxygen carrier material lifetime and reactor cost were observed. The promise of the PBCLC concept therefore strongly depends on future cost reductions from IGCC power plants (e.g. through hot gas clean-up and advanced gas turbine technology). Finally, a sensitivity analysis to future policy developments showed that today’s CCS technology is already cost competitive with unabated power plants under policy developments consistent with the 2°C global temperature rise goal.

Catalytic abatement of biomass tar: a technological perspective of Ni-based catalysts

Heterogeneous catalysis has a fundamental role in the development of both gasification and gas cleanup technologies for the production of synthesis gas (syngas) and renewable hydrogen. In this review, a technological perspective of Ni-based catalysts is presented giving particular attention to the interaction of different tars molecules present in tar mixture and to catalyst deactivation by coke deposition and sulphur poisoning. For the effective development of these technologies, several challenges have been still to be undertaken, so that, are outlined in this review: (i) optimization of catalyst formulation; (ii) catalyst stability; (iii) resistance to the different contaminants present in biomass feedstocks; (iv) activity in more complex mixtures, coupling the knowledge available with model mixture and evidence eventual interaction that might be detrimental in start-up and shut-down operations; (v) tests in real biomass tar and in pilot plants; (vi) determination of mechanisms and kinetics for the complex reaction network and coke deposition; and (vii) development of effective regeneration steps applicable in real industrial applications.

Technical Discussion over Three Means of Waste Management

The present investigation is an effort to compare between three different ways of waste management: Recycling/ re-use, incineration and composting. Re-use gives the impression to have more beneficial factors than the other methods. Nevertheless, incineration is regarded as an effective alternative that converts waste into energy, hence improves the economy and preserve the environment by the use of modern gas-cleaning technology. Recycling has been found to be of less social demand, and composting has higher negative environmental impact and deals with smaller amounts of waste for longer periods of time.

Investigation of cryogenic technique for synthetic natural gas upgrading

Bio-LNG which is produced by liquefaction of synthetic natural gas from biomass (bio-SNG) is a valuable renewable fuel as it has high energy density and transportability. Cryogenic technology is a promising option for integration of the gas upgrading and liquefaction systems with the main biomass gasification and methane synthesis plant. This study investigates the feasibility of this technology for future commercial bio-SNG production plants based on indirect gasification technology, similar to that adopted by Göteborg Energi for the GoBiGas project. Simulation program Aspen Plus and pinch analysis tool Pro_PI are used to compare conventional gas cleaning and liquefaction technology and cryogenic technology. The cryogenic unit achieves the targeted product specifications and capacity, and the calculated performance is comparable to published data for commercial units. The results show that the integrated plant with cryogenic technology has a higher power requirement than the plant with conventional technology. Cryogenic technology is still under development, therefore there is a high potential for performance improvement by application of energy efficiency measures. In addition, high purity liquid CO2 is produced at very low temperature as a by-product which could generate additional revenue.

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.

Hot gas clean-up technology of dust particulates with a moving granular bed filter

The purpose of this study is to investigate the efficiency and stability of moving granular bed filter (MGBF) in high-temperature environment with various operation conditions. Experiments were carried out to study the influence of various parameters, such as test temperature, mass flow rate of filter granules and filtration superficial velocity. The experimental facilities include an air fan, flow ducts, heaters of gas and filter granules, a screw feeder of dust particulates, a measurement system for size distribution of dust particulates, a filter granules supply device, a rotary valve, and a granular bed filter filled with filter granules. The results of this study indicate that this type of method can be useful to applications in different cross-flow filter systems for gas clean-up. From the results, with the conditions of filtration superficial velocities at 0.2 and 0.35 m/s, and the mass flow rate of filter granules at 0.01 kg/s, the better collection efficiency and the smaller-sized distribution of dust particulates were obtained for the case with operating temperature of 20 °C. The experimental results show that an average increase in operation temperature of 100 °C resulted in a decrease in average collection efficiency of 1.74%. The focus in the current study is essentially the development of an MGBF that can be applied in the industrial environment. The results are expected to serve as the basis for future research.

Wet vs. Dry Top Gas Cleaning Technology for Blast Furnaces

At the moment the top gas from blast furnaces is commonly cleaned by wet gas cleaning technology which consists of a gravity separator for coarse dedusting and a scrubber for fine dedusting. Dry type top gas cleaning, consisting of a gravity separator and a bag filter, shows a number of technical and economic benefits compared to the wet technology. An example is the approximately 30 % higher energy output at the top gas recovery turbine due to the lower temperature and pressure loss of the dry gas cleaning technology. In this paper both technologies are compared with each other, and the respective advantages and disadvantages are discussed.

Present technologies for hydrogen sulfide removal from gaseous mixtures

Natural gas, refinery gas, and coal gas contain acid gases such as hydrogen sulfide (H 2 S) and carbon dioxide that must be removed from the gas stream due to the toxicity of H 2 S and to prevent corrosion to piping and production facility caused by the acid gases. In this article, current technologies for the acid gas removal are selected and reviewed. The review includes absorption, adsorption, conversion of H 2 S into elemental sulfur, and membrane reactor for H 2 S decomposition and desulfurization. Recently, hollow fiber membrane contactor has been in the limelight of research in H 2 S absorption from gaseous mixture due to its potential to overcome problems such as foaming and loading. Recent trends on Claus tail gas cleanup technologies are highlighted due to the recent progress in membrane technology. The article also suggests current research on the acid gas removal technology using catalytic membrane reactor. The interest on finding suitable active component and support and studying the membrane structure for enhanced removal of acid gases is likely to be rekindled in the near future.

Analysis of Membrane and Adsorbent Processes for Warm Syngas Cleanup in Integrated Gasification Combined-Cycle Power with CO2 Capture and Sequestration

Integrated gasification combined cycle (IGCC) with CO2 capture and sequestration (CCS) offers a promising approach for cleanly using abundant coal reserves of the world to generate electricity. The present state-of-the-art synthesis gas (syngas) cleanup technologies in IGCC involve cooling the syngas from the gasifier to room temperature or lower for removing sulfur, carbon dioxide, and other pollutants, leading to a large efficiency loss. Here we assess the suitability of various alternative syngas cleanup technologies for IGCC with CCS through computational simulations. We model multicomponent gas separation for CO2 capture in IGCC using polymeric membranes and H2 separation from the syngas using both Pd-alloy based composite metallic membranes and polymeric membranes. In addition, we develop a pressure swing adsorption model to estimate the energy efficiency of regenerable sorbent beds for CO2 capture. We use our models with Aspen Plus simulations to identify promising design and operating conditions for membrane and adsorption processes in an IGCC plant. On the basis of our analysis, the benefits of warm gas cleanup are not as great as previously reported in the literature, and only CO2 separations performed using H2-permeable Pd-alloy membranes and CO2 adsorbents produce overall higher heating value (HHV) efficiencies higher than that of Selexol. In addition, many of the technologies surveyed require a narrow operating range of process parameters in order to be viable alternatives. We identify desired material properties of membranes and thermodynamic properties of sorbents that are needed to make these technologies successful, providing direction for ongoing experimental efforts to develop these materials.

System Analysis of Thermochemical-Based Biorefineries for Coproduction of Hydrogen and Electricity

Fuels derived from biomass feedstocks are a particularly attractive energy resource pathway given their inherent advantages of energy security via domestic fuel crop production and their renewable status. However, there are numerous questions regarding how to optimally produce, distribute, and utilize biofuels such that they are economically, energetically, and environmentally sustainable. Comparative analyses of two conceptual 2000 tons/day thermochemical-based biorefineries are performed to explore the effects of emerging technologies on process efficiencies. System models of the biorefineries, created using ASPEN Plus®, include all primary process steps required to convert a biomass feedstock into hydrogen, including gasification, gas cleanup and conditioning, hydrogen purification, and thermal integration. The biorefinery concepts studied herein are representative of “near-term” (approximately 2015) and “future” (approximately 2025) plants. The near-term plant design serves as a baseline concept and incorporates currently available commercial technologies for all nongasifier processes. Gasifier technology employed in these analyses is centered on directly heated, oxygen-blown, fluidized-bed systems that are pressurized to nearly 25 bars. The future plant design employs emerging gas cleaning and conditioning technologies for both tar and sulfur removal unit operations. A 25% increase in electric power production is observed for the future case over the baseline configuration due to the improved thermal integration while realizing an overall plant efficiency improvement of 2 percentage points. Exergy analysis reveals that the largest inefficiencies are associated with the (i) gasification, (ii) steam and power production, and (iii) gas cleanup and purification processes. Additional suggestions for improvements in the biorefinery plant for hydrogen production are given.

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.