GoBiGas demonstration – a vital step for a large-scale transition from fossil fuels to advanced biofuels and electrofuels

This report summarises the technical and economic demonstration of the GoBiGas-project, a first-of-its-kind industrial demonstration of advanced biofuel production via gasification. The principal result of the GoBiGas demonstration is an advanced biofuel plant with a production capacity of 20 MW of biomethane* from woody biomass, which shows that the technology is commercially mature and is ready for large-scale deployment

Experimental Investigation of Volatiles-Bed Contact in a 2-4 MWth Bubbling Bed Reactor of a Dual Fluidized Bed Gasifier

The use of catalytic bed materials in fluidized bed gasifiers represents a promising primary measure to decrease the tar content of biomass-derived raw gas. For effective application of such in-bed catalysts, extensive contact must be established between the volatile matter released from the fuel particles and the bed material. However, the extent of the contact and, consequently, the potential of in-bed tar removal techniques are not well understood. In this work, the fraction of volatile matter that interacts with the bed in a large (i.e., throughput of 300-400 kg/h biomass) bubbling bed gasifier is quantified experimentally and the effect of fluidization velocity is investigated. The results show that a higher fluidization velocity enhances gas-solid contact, with 48-69% of the volatile matter coming in contact with the bed within the range of 6-10 times the minimum fluidization (umf)

EVALUATION OF FLUID DYNAMICS IN A HOT AND A COLD SYSTEM OF INTERCONNECTING FLUIDISED BEDS

Operation controllability and fluid dynamics were evaluated in a system of interconnecting fluidised beds. Results indicate that the solid circulation is controllable and possible to determine from pressure measurements. Sufficient gas tightness of the loop-seals and flexibility in controlling of solid fluxes was indicated

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 H<SUB>2</SUB>/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 CO<SUB>2</SUB> 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

Integration aspects for synthetic natural gas production from biomass based on a novel indirect gasification concept

An innovative indirectly heated biomass gasification unit has been recently built at Chalmers University of Technology as an integrated extension of a standard circulating fluidised bed (CFB) boiler for heat and power production. The gasification medium can be varied between steam, oxygen, combustion flue gases or recirculated syngas. In this paper a process for production of synthetic natural gas (SNG) based on this biomass gasification technique is proposed and investigated with emphasis on evaluation of possible heat integration options. Special attention is given to possible options for cogeneration of heat and power. The increase in electricity production from the power cycle is achieved by two means: combusting the non-reacted char from gasification in the boiler and extracting high temperature excess heat from the syngas to SNG conversion steps. It is shown that the amine-based CO2 separation stage is a large heat sink. The reduction of the steam demand for the CO2 absorbent regeneration stripper is of crucial importance to have a maximum of high temperature excess heat available from the gasification process to be used in the steam power cycle. The cold gas efficiency for SNG production comparing biomass input to SNG output is about 60 % for the proposed process. This performance indicator however does not consider the electricity production increase. The balance between SNG yield and increased electricity production is mainly dependant on the gasification efficiency since the amount of char from gasification that is used in the boiler directly influences the yield of synthetic natural gas

Advanced Gas Cleaning using Chemical-Looping Reforming (CLR)

When using a fluidized bed gasification technology to gasify biomass for the downstream synthesis to biofuels or chemicals, the biggest challenge is associated with the reforming of hydrocarbons into desirable gas components. These unwanted hydrocarbons are formed during the primary conversion step of the biomass. They range from ethylene to larger aromatic components or even methane if it is not the desired product, and introduce numerous problems to the operation, but also require additional process steps that significantly influence the competitiveness of the overall process. An efficient way to tackle this problem is to provide catalytic surfaces for hydrocarbon reforming directly inside the gasifier by using a catalytic bed material and/or in one or several secondary reactors. In this work, a concept based on this principle and named Chemical-Looping Reforming (CLR) is presented and it is discussed how this concept has the potential to be implemented for both primary and secondary reforming of hydrocarbons

Validation of the oxygen buffering ability of bed materials used for ocac in a large scale cfb boiler

Fluidized bed combustion is widely considered an advantageous technology managing moist and heterogeneous fuels due to the heat storage in the bed material and its favorable conditions regarding fuel and oxygen mixing throughout the combustion chamber. Even though mixing is often regarded as sufficient, the technology remains sensitive to variations in load and heterogeneity of fuels, leading to an uneven distribution of oxygen in time and space of the furnace. The remedy has nearby exclusively been related to the supply of air, particularly considering a surplus of air and positioning of injection ports. An applicable combustion concept, oxygen carrier aided combustion (OCAC), has been developed and demonstrated in the Chalmers 12 MWth circulating fluidized bed boiler. The novelty of this concept is that it targets the distribution of oxygen inside the combustion chamber on contrary to prior accepted remedies. The rational is to replace the regularly used inert bed material by an oxygen carrying metal oxide which can take up oxygen where it is abundant and subsequently release it to combust unburned gases at oxygen depleted zones. Thus, the bed material functions as a buffer of oxygen allowing for lower surpluses of air and better ability to handle load variations and heterogeneous fuels. This work contains the modeling of a system where inert bed material is compared to an oxygen carrier with the aim to show the effects of its oxygen-buffering ability. To a system with constant fuel feed, a pulse of instantaneous fuel increase is modeled. The outcome of the model was then verified by the results of experimental work conducted in Chalmers 12 MWth CFB boiler. The results consistently show that the introduced oxygen carrying bed material does have an oxygen-buffering ability and the distribution of oxygen is considerably improved throughout the combustion chamber. Due to the enhanced distribution of oxygen the system is less sensitive to fluctuations in load and fuel heterogeneity. As the infrastructure of plants where the concept would be applicable are already in place, the use of active bed material for oxygen carrier aided combustion has great potential to reach full scale commercialization in a near future. Furthermore, naturally occurring ores that contain considerable amount of metals such as iron and manganese have proven to be promising candidates as oxygen carriers. Owing to the possibility of using natural ores, in place of manufactured materials, economic feasibility of the concept is promising

Behaviour of biomass particles in a large scale (2-4MWth) bubbling bed reactor

Biomass is regarded as an interesting fuel for energy-related processes owing to its renewable nature. However, the high volatile content of biomass adds a number of difficulties to the fuel conversion and process operation. In the context of fluidized bed reactors, several authors have observed that devolatilizing fuel particles tend to float on the surface of a gas-fluidized bed of finer solids. This behaviour, known as segregation, leads to undesired effects such as poor contact between volatiles and bed material. Previous investigations on segregation of gas-emitting particles in fluidized beds are conducted in small units and they are often operated at rather low gas velocities, typically between the minimum fluidization velocity (umf) and 2·umf. Therefore, it is not known to what extent such results are of relevance for industrial scale units and for higher fluidization velocities that are commonly used in large bubbling beds. In this work the behaviour of biomass particles in a large scale bubbling bed reactor is investigated. Tests were conducted at a wide range of fluidization velocities with three different bed materials of varying particle size and density. The fuel was wood pellets and the fluidization medium was steam, which makes the findings relevant for indirect gasification, chemical looping combustion (CLC) and bubbling bed combustion applications. The experiments were recorded by means of a digital video camera and the digital images were subsequently analysed qualitatively. The results show high level of segregation at fluidization velocity up to 3.5umf. Beyond this point fuel mixing was significantly enhanced by increasing fluidization velocities. At the highest fluidization velocity tested (i.e. >8umf), a maximum degree of mixing was achieved

Fuel Quality Analysis for Biogas Utilization in Heavy Duty Dual Fuel Engines

The perspective of using gas form biomass gasification as fuel for dual fuel (DF) engines, without refine it all the way to synthetic natural gas (SNG) has been investigated. The initial gas from gasification contains of a blend of various components which are not commonly present in natural gas (NG). The operability of these components in a heavy duty DF engine has been assessed and compared to those of NG. Three parameters have been used to define the quality of the fuel: Lower Heating Value (LHV), Methane Number (MN) and Lower Flammability Limit (LFL)

Investigation of steam regeneration strategies for industrial-scale temperature-swing adsorption of benzene on activated carbon

Large-scale separation of substances present at low concentrations is readily performed by adsorption in packed beds that requires recurring energy-intensive regeneration of the adsorbent. The present work uses numerical simulations previously developed for industrial-scale packed-bed benzene sorption on activated carbon with temperature-swing regeneration by steam to investigate the influence of steam properties and regeneration strategy on total energy performance and breakthrough behaviour. It is shown that using saturated steam lowers both the steam mass and energy consumption during regeneration of a fixed amount of benzene, whereas using superheated steam returns the bed to a more fresh-like state after each regeneration stage. The most promising variation tried implies a 19% reduction in the energy consumption. Furthermore, the importance of accounting for the real industrial cycling conditions in the optimization of packed-bed adsorbers is highlighted. It is shown that the participation of different sections of the bed during adsorption varies with the regeneration strategy, but is never as localized as predicted from a model for a fresh bed without cycling. Finally, the present results also show that the effluent purity attained during regeneration increases when high-temperature saturated steam is used, e.g. a 60-degree increase in steam temperature raises the purity by 11%