Indirect Gasification Research Articles

Influence of bulk solids cross-flow on lateral mixing of fuel in dual fluidized beds

In typical dual fluidized bed systems — used e.g. in chemical looping combustion or indirect gasification of biomass for production of second-generation biofuels — the bulk solids are continuously circulating between a tall high-velocity riser and a bubbling bed. This circulation results in a solids cross-flow in the bubbling bed, which creates a net convective solids flow. The aims of this paper are to describe this convective flow by means of mathematical modeling and to investigate the effect of the cross-flow of bulk solids on the lateral mixing of fuel particles.Experiments relevant for industrial conditions are carried out in a fluid dynamically downscaled cold flow model of an existing indirect gasifier. It is found that the velocity field of the bulk solids induced by the solids cross-flow can be described by a potential function obtained from a diffusion equation. As for the fuel particles, their slip respect to the bulk solids cross-flow is quantified using a cross-flow impact factor, θ, which is found to be a linear function of fluidization velocity and in the range 0.18–0.68 for the conditions investigated. Finally, we conclude that the fuel mixing in fluidized beds with a significant cross-flow of bed material can be described by a convection–diffusion equation.

Optimal Production of Dimethyl Ether from Switchgrass-Based Syngas via Direct Synthesis

A conceptual optimal design for the production of dimethyl ether (DME) and/or power from switchgrass is proposed. A superstructure is formulated embedding two different gasification technologies, direct and indirect, two reforming modes, partial oxidation or steam reforming, gas cleaning, and composition adjustment. Next, DME is produced following direct synthesis, a novel one-step technology. The unreacted gas can be either recycled or used within a Brayton cycle for the simultaneous production of DME and power. The problem is formulated as a mixed integer nonlinear programming problem. The optimal topology involves indirect gasification followed by steam reforming. DME production is favored over power for current electricity prices. Thus, the investment cost for the production of 197 kt/yr of DME adds up to $133 million, at a price of $0.31/kg.

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.

Technoeconomic Analysis for the Production of Mixed Alcohols via Indirect Gasification of Biomass Based on Demonstration Experiments

An integrated biomass-to-mixed alcohol process was demonstrated at the pilot scale, including indirect gasification, tar and hydrocarbon reforming, gas conditioning, and gas to liquids operations. Additional bench-scale experiments were conducted to gather insights into reforming and fuel synthesis operations under more extensive conditions. Data from these experiments were combined with tools and knowledge owned by industrial partners—Rentech and The Dow Chemical Company—to validate a conceptual commercial-scale cellulosic ethanol refinery. Results suggest that both reforming and mixed alcohol processes are scalable and economical, with a modeled mature plant ethanol production cost of $0.54/L ($0.82/L of gasoline equivalent). Sustainability metrics for the conversion process are also presented.

Comparing direct and indirect fluidized bed gasification: Effect of redox cycle on olivine activity

Fluidized bed gasification processes are generally considered a good choice for biomass and waste because of its fuel flexibility. Furthermore, it is a relatively low‐temperature highly efficient process operating at 700–900°C compared with, for example, coal‐based entrained flow processes that mostly operate at 1400–1600°C. Indirect fluidized bed gasification is becoming increasingly popular for some applications due to the possibility of producing a N2‐free gas without the need for an air separation unit, as well as complete conversion of the fuel. ECN has developed MILENA indirect gasification, in which gasification and combustion are physically separated, but both reactors are placed in the same vessel. This article aims to compare the performance of olivine as bed material in direct‐ and indirect (MILENA) gasification. With this purpose, oxidation/reduction cycles have been simulated in a direct gasifier to determine the effect of olivine preoxidation in terms of tar destruction and oxygen transport. Results show that olivine preoxidation mainly enhances the capacity of oxygen transport of the bed material, which adds up to the catalytic effect of iron in olivine towards tar destruction. Oxygen transport capacity of olivine has been quantified as ER = 0.25 at the maximum initial CO2 peak, and it has been estimated that 20–25% wt of iron in olivine is able to transfer oxygen during the first 10 min operation. On the other hand, it has been found that MILENA operating conditions are equivalent to the point of initial maximum peak of CO2 in the devolatilization stage. This means that oxygen transport capacity of olivine is kept at its maximum due to the continuous combustion/gasification cycles, and olivine is kept activated by cyclical migration of iron into the surface and subsequent fast reduction. The effect of oxygen transport on the overall heat balance of the MILENA gasifier is equivalent to oxidation of additional fuel in the combustor. © 2014 American Institute of Chemical Engineers Environ Prog, 33: 711–720, 2014

Environmental and exergetic evaluation of hydrogen production via lignocellulosic biomass gasification

Abstract Gasification is a promising pathway for the conversion of biomass into energy products. In particular, the syngas generated through biomass gasification is of great interest for hydrogen production. Based on an overview of technological options, a base-case system for hydrogen production via biomass gasification is defined, and its environmental and thermodynamic performance is evaluated through a life cycle assessment and an exergetic analysis. The case study involves poplar gasification in a low-pressure char indirect gasifier, catalytic tar destruction, cold wet gas cleaning, syngas conversion and hydrogen purification. The calculated exergetic efficiency of the plant is 48%, a value comparable to that of conventional coal gasification technologies for hydrogen production. The total exergy loss of the plant (mainly associated with the flue gas streams) is found to be 4.6% of the fuel exergy provided to the overall plant, while 47% of the overall fuel exergy vanishes as exergy destruction within the individual components of the plant. The life cycle assessment of the system covers from poplar cultivation to hydrogen purification. Seven impact potentials are considered: cumulative energy demand, global warming, ozone layer depletion, photochemical oxidant formation, land competition, acidification and eutrophication. The life-cycle energy balance of the system suggests a relatively promising energy performance. Poplar cultivation and harvesting, biomass pre-treatment and syngas cleaning are identified as the subsystems with the largest contributions to the environmental impacts. Measures to enhance the environmental and energy performance of the system should focus on minimizing the poplar feedstock demand, improving the logistical planning for biomass supply, reducing the natural gas demand of the steam reforming subsystem, and optimizing the electricity demand of the gas cleaning subsystem. Lower consumption levels of fertilizers and diesel for poplar cultivation and harvesting should also be achieved.

Biomass-based hydrogen for oil refining: Integration and performances of two gasification concepts

In this work, two biomass-to-hydrogen concepts are designed and their integration with a large European refinery is investigated. One concept is based on indirect, atmospheric steam gasification while the second is based on pressurized direct oxygen-steam-blown gasification. The technologies chosen for gas cleaning, upgrading and hydrogen separation also differ in the two concepts. Heat integration and poly-generation opportunities are identified by means of process integration tools and four system configurations are identified. These are compared in terms of energy and exergy performances and potential for reduction of fossil CO2 emissions at the refinery. It is found that the performance of the biomass-to-hydrogen concepts can be improved by up to 11% points in energy efficiency and 9% points in exergy efficiency. The design based on indirect gasification appears the most efficient according to both energy and exergy efficiencies. All configurations yield potential significant reductions of fossil CO2 emissions at the refinery.

Optimal coupling of a biomass based polygeneration system with a concentrated solar power facility for the constant production of electricity over a year

In this paper we address the integration of a polygeneration system based on biomass with a concentrated solar power facility for the constant production of electricity over a year long. The process is modelled as a superstructure embedding two different gasification technologies, direct and indirect, and two reforming modes, partial oxidation or steam reforming followed by gas cleaning and three alternatives for the syngas use, water gas shift reactor (WGSR) to produce hydrogen, a furnace for thermal energy production and an open Brayton cycle. We couple this system with a concentrated solar plant that uses tower technology, molten salts and a regenerative Rankine cycle. The problem is formulated as a multi-period mixed-integer non linear programming problem (MINLP). The optimal integration involves the use of indirect gasification, steam reforming and a Brayton cycle to produce 340MW of electricity at 0.073€/kWh and 97kt/yr of hydrogen as a credit.

Thermodynamic analysis of biomass gasification with CO2 recycle for synthesis gas production

Thermodynamic analysis of biomass gasification with recycled CO2 was investigated in this work to determine optimum operation mode and CO2/C ratio. Gasification System Efficiency (GSE), which takes into account the energy demand in the system, and CO2 emission per syngas production (CO2/Sg) were calculated to evaluate the performance of the gasification system. Considering the production of syngas at a H2/CO ratio of 1.5, it was revealed that indirect gasification using biomass as fuel is the most efficient and environmental-friendly operation mode. The recycled CO2 proves to increase syngas production. However, when considering the additional energy demand required for processing the CO2 recycle, it was demonstrated that there are only some ranges of operating conditions (high pressure and low temperature) which offer the benefit of the CO2 recycle. The optimum CO2/C was reported to be around 0.1–0.2 for pressurized and low temperature gasification.

CO2–steam mixture for direct and indirect gasification of rice straw in a downdraft gasifier: Laboratory-scale experiments and performance prediction

This paper explored the feasibility of CO2 as alternative gasifying agent of steam to obtain higher thermal efficiency in biomass gasification. The effect of the gasifying agent on gas evolution and thermal efficiency was examined by using a lab scale downdraft gasifier. The results were also compared with the output of pyrolysis with N2. The reaction atmosphere in indirect and direct gasification was simulated by carrying out the experiments without and with O2 presence. The reaction conditions were varied in the temperature range from 750°C to 950°C by changing the CO2 molar fraction in gasifying agent to the ratio of 0, 30 and 60vol.% in balance with steam. 40vol.% of N2 fraction was kept during O2 free experiments, while 31.7vol.% of N2 and 8.3vol.% O2 were kept during the experiments with the presence of O2. At all examined condition, gasification yielded more combustible gas than pyrolysis. Furthermore, high CO2 fraction in gasifying agent generally resulted in low H2 yield and high CO yield. These substitutions mostly lowered the energy yield of the producer gas, but in the other hand also reduced the preheating energy of gasifying agent. Thus, optimizations of these changes were investigated for gaining highest thermal efficiency of the gasification process. Highest thermal efficiency of the process without O2 was 52% under N2 (40vol.%)–CO2 (60vol.%) atmosphere at the temperature of 850°C. For the process with O2, where the part of gasifying agent preheating energy supplied by the biomass partial combustion, the highest thermal efficiency was 60% under the CO2 (60vol.%)–O2 (8.3vol.%)–N2 (31.7vol.%) atmosphere at the temperature of 950°C. CO2 utilization as a gasifying agent potentially increases the thermal efficiency of biomass conversion process compared with pyrolysis or conventional indirect and direct gasification, i.e. pure-steam gasification and O2–steam gasification.

Life-cycle performance of indirect biomass gasification as a green alternative to steam methane reforming for hydrogen production

The environmental performance of hydrogen production via indirect gasification of poplar biomass was evaluated following a Life Cycle Assessment approach. Foreground data for the study were provided mainly from process simulation. The main subsystems and processes that contribute to the environmental impacts were identified. Thus, poplar production and direct emissions to air from the processing plant were found to be the main sources of environmental impact. Furthermore, a favourable (positive) life-cycle energy balance was estimated for the gasification-based system.The environmental profile of hydrogen from poplar gasification was compared with that calculated for hydrogen from conventional steam methane reforming according to inventory data also obtained through process simulation. Gasification-derived biohydrogen was generally found to be a promising hydrogen fuel, with reduced greenhouse gas emissions and a low non-renewable energy demand. However, its suitability depends on the evaluated impact categories. Moreover, the biomass demand should be minimized to enhance the efficiency of the system.

Using an oxygen-carrier as bed material for combustion of biomass in a 12-MWth circulating fluidized-bed boiler

The initial experiences of using an oxygen-carrying metal oxide, ilmenite, in the 12-MWth circulating fluidized bed (CFB) boiler/gasifier system at Chalmers University of Technology are presented. The rationale for the addition of ilmenite to the solids inventory is that ilmenite has the ability to alternately take up and release oxygen, and thereby improve the distribution of oxygen throughout the furnace. As a consequence, less air is needed to maintain low emissions from carbon monoxide (CO) and unreacted hydrocarbons (HC) during the combustion of volatile-rich fuels, such as biomass. One of the conducted experiments involved only the boiler, and the reference case corresponded to operation solely with silica-sand as the bed material, while in an additional three cases, ilmenite in various amounts was added to make up to 40wt.% of the total bed inventory. During the experiments, the concentrations of CO and nitric oxide (NO) in the convection path of the boiler were measured. The addition of ilmenite to the silica-sand decreased the concentrations of CO and NO by 80% and 30%, respectively. Additional experiments were performed in which a concentrated stream of raw gas produced in the indirect gasifier was injected into the freeboard of the boiler. In one experiment, only silica-sand was used, while 12wt.% ilmenite was added to the bed material in a separate experiment. The concentrations of CO and HC were measured at three different heights in the boiler and at nine positions over a cross-section of the furnace. The concentrations of CO and total HC in the furnace cross-section during concomitant gasification operation were reduced by the addition of ilmenite.

Exergy-based comparison of indirect and direct biomass gasification technologies within the framework of bio-SNG production

Atmospheric indirect steam-blown and pressurised direct oxygen-blown gasification are the two major technologies discussed for large-scale production of synthetic natural gas from biomass (bio-SNG) by thermochemical conversion. Published system studies of bio-SNG production concepts draw different conclusions about which gasification technology performs best. In this paper, an exergy-based comparison of the two gasification technologies is performed using a simplified gasification reactor model. This approach aims at comparing the two technologies on a common basis without possible bias due to model regression on specific reactor data. The system boundaries include the gasification and gas cleaning step to generate a product gas ready for subsequent synthesis. The major parameter investigated is the delivery pressure of the product gas. Other model parameters include the air-to-fuel ratio for gasification as well as the H2/CO ratio in the product gas. In order to illustrate the thermodynamic limits and sources of efficiency loss, an ideal modelling approach is contrasted with a model accounting for losses in, e.g. the heat recovery and compression operations. The resulting cold-gas efficiencies of the processes are in the range of 0.66–0.84 on a lower heating value basis. Exergy efficiencies for the ideal systems are from 0.79 to 0.84 and in the range of 0.7 to 0.79 for the systems including losses. Pressurised direct gasification benefits from higher delivery pressure of the finished gas product and results in the highest exergy efficiency values. Regarding bio-SNG synthesis however, a higher energetic and exergetic penalty for CO2 removal results in direct gasification exergy efficiency values that are below values for indirect gasification. No significant difference in performance between the technologies can be observed based on the model results, but a challenge identified for process design is efficient heat recovery and cogeneration of electricity for both technologies. Furthermore, direct gasification performance is penalised by incomplete carbon conversion in contrast to performance of indirect gasification concepts.

Hydrogen for oil refining via biomass indirect steam gasification: energy and environmental targets

The energy and CO2 consequences of substitution of a fossil-fuel-based hydrogen production unit with a biomass-based process in a large European refinery are studied in this study. In the base case, the biomass-based process consists in atmospheric, steam–blown indirect gasification of air-dried woody biomass followed by necessary upgrading steps. The effect of gradually substituting the current refinery hydrogen production unit with this process on global energy and CO2 targets is estimated first. Few process concepts are studied in further detail by looking at different degrees of heat integration with the remaining refinery units and possible polygeneration opportunities. The proposed process concepts are compared in terms of energy and exergy performances and potential reduction in refinery CO2 emission also taking into account the effect of marginal electricity. Compared to the base case, an increase by up to 8 % points in energy efficiency and 9 % points in exergy efficiency can be obtained by exploiting process integration opportunities. According to energy efficiency, steam production appears the best way to use excess heat available in the process while electricity generation through a heat recovery steam cycle appears the best option according to exergy efficiency results. All investigated cases yield to significant reduction in CO2 emissions at the refinery. It appears in particular that maximal emission reduction is obtained by producing extra steam to cover the demand of other refinery units if high efficiency marginal electricity scenarios are considered.

Pa-206 海水を含んだゴムノキの密閉型ガス化炉による間接ガス化(2.技術,ポスターセッション1)

Pa-206 海水を含んだゴムノキの密閉型ガス化炉による間接ガス化(2.技術,ポスターセッション1)

Pa-205 密閉型ガス化炉によるヒノキの間接ガス化における水分率と圧力の影響(2.技術,ポスターセッション1)

Pa-205 密閉型ガス化炉によるヒノキの間接ガス化における水分率と圧力の影響(2.技術,ポスターセッション1)

Use of Nickel Oxide as a Catalyst for Tar Elimination in a Chemical-Looping Reforming Reactor Operated with Biomass Producer Gas

A secondary tar-cleaning process based on Chemical-Looping Reforming (CLR) was investigated for upgrading biomass producer gas, derived from the Chalmers University of Technology 2-4 MW indirect gasifier. The experiments were conducted in a bench-scale CLR reactor using a manufactured nickel oxide (NiO) catalyst. Although Ni is a well-documented and efficient steam-reforming catalyst, it is susceptible to rapid deactivation under tar-rich conditions. The aim of this study was to explore the advantages of CLR as a gas-cleaning application, a process which offers continuous regeneration of the carbon deposits on catalysts. The tar-reforming performance of this Ni material and its influence on the gas composition and in particular its potential to increase the H2/CO ratio, were studied. The system was tested at reforming temperatures that ranged from 700°C to 880°C and at oxygen concentrations of 1.0% and 2.2% in the inlet feed to regenerator section. The results confirm the strong ability of the catalyst to reform tars. Higher process temperatures clearly promoted tar conversion, with 96% overall conversion at 880°C (99% if benzene is excluded), as compared with 45% conversion at 700°C. The hydrogen production was favored when temperature was raised. Though, a maximum ratio H2/CO of 2.2 was observed at 750°C. Finally, no time-on-stream deactivation of the catalyst in the CLR was observed during the test, which lasted almost 7 hours.

Life-Cycle Assessment of Bioethanol from Pine Residues via Indirect Biomass Gasification to Mixed Alcohols*

Abstract The goal of this study was to estimate the greenhouse gas (GHG) emissions and fossil energy requirements from the production and use (cradle-to-grave) of bioethanol produced from the indirect gasification thermochemical conversion of loblolly pine (Pinus taeda) residues. Additional impact categories (acidification and eutrophication) were also analyzed. Of the life-cycle stages, the thermochemical fuel production and biomass growth stages resulted in the greatest environmental impact for the bioethanol product life cycle. The GHG emissions from fuel transportation and process chemicals used in the thermochemical conversion process were minor (less than 1 percent of conversion emissions). The net GHG emissions over the bioethanol life cycle, cradle-to-grave, was 74 percent less than gasoline of an equal energy content, meeting the 60 percent minimum reduction requirement of the Renewable Fuels Standard to qualify as an advanced (second generation) biofuel. Also, bioethanol had a 72 percent lower acidification impact and a 59 percent lower eutrophication impact relative to gasoline. The fossil fuel usage for bioethanol was 96 percent less than gasoline, mainly because crude oil is used as the primary feedstock for gasoline production. The total GHG emissions for the bioethanol life cycle analyzed in this study were determined to be similar to the comparable scenario from the Greenhouse Gases, Regulated Emissions, and Energy Use in Transportation model. A sensitivity analysis determined that mass allocation of forest establishment burdens to the residues was not significant for GHG emissions but had significant effects on the acidification and eutrophication impact categories.

Integrated Process Configuration for High-Temperature Sulfur Mitigation during Biomass Conversion via Indirect Gasification

Sulfur present in biomass often causes catalyst deactivation during downstream operations after gasification. Early removal of sulfur from the syngas stream post-gasification is possible via process rearrangements and can be beneficial for maintaining a low-sulfur environment for all downstream operations. High-temperature sulfur sorbents have superior performance and capacity under drier syngas conditions. The reconfigured process discussed in this paper is comprised of indirect biomass gasification using dry recycled gas from downstream operations, which produces a drier syngas stream and, consequently, more-efficient sulfur removal at high temperatures using regenerable sorbents. A combination of experimental results from NREL’s fluidizable Ni-based reforming catalyst, fluidizable Mn-based sulfur sorbent, and process modeling information show that using a coupled process of dry gasification with high-temperature sulfur removal can improve the performance of Ni-based reforming catalysts significantly.

Small-scale production of synthetic natural gas by allothermal biomass gasification

The gasification of biomass can be coupled to a downstream methanation process that produces synthetic natural gas (SNG). This enables the distribution of bioenergy in the existing natural gas grid. A process model is developed for the small-scale production of SNG with the use of the software package Aspen Plus (Aspen Technology, Inc., Burlington, MA, USA). The gasification is based on an indirect gasifier with a thermal input of 500 kW. The gasification system consists of a fluidized bed reformer and a fluidized bed combustor that are interconnected via heat pipes. The subsequent methanation is modeled by a fluidized bed reactor. Different stages of process integration between the endothermic gasification and exothermic combustion and methanation are considered. With increasing process integration, the conversion efficiency from biomass to SNG increases. A conversion efficiency from biomass to SNG of 73.9% on a lower heating value basis is feasible with the best integrated system. The SNG produced in the simulation meets the quality requirements for injection into the natural gas grid. Copyright © 2012 John Wiley & Sons, Ltd.