| 1. |
- Berguerand, Nicolas, 1978, et al.
(författare)
-
Producer Gas Cleaning in a Dual Fluidized Bed - a Comparative Study of Performance with Ilmenite and a Manganese Oxide as Catalysts
- 2012
-
Ingår i: Biomass Conversion and Biorefinery. - : Springer Science and Business Media LLC. - 2190-6815 .- 2190-6823. ; 2:3, s. 8-252
-
Tidskriftsartikel (refereegranskat)abstract
- Secondary catalytic gas conditioning is one strategy to eliminate tars formed in a producer gas during biomass gasification. However, most catalysts tend to lose their tar reforming activity after short period of operation due to carbon formation. A novel technique for catalytic gas cleaning based on two interconnected fluidized beds has been investigated; this technique can be applied to all types of gasifiers. The idea is to reform the tar components into useful molecules - even at high tar contents - by means of a circulating catalyst. More precisely, the producer gas is cleaned with catalyst in one of the reactors, referred to as the fuel reactor (FR), while the catalyst is continuously regenerated in another reactor, the air reactor (AR). The system described here is coupled with the Chalmers 2-4 MWth biomass gasifier while the AR is fed with nitrogen-diluted air. The effect of different catalysts on both the tar content and the gas composition was investigated. Some of the tested materials do not only reform tars, they also influence the H2/CO-ratio in a beneficial manner; in particular, ratios closer to 3 in the reformed gas are favorable if subsequent methanation is implemented. In this paper, comparative results based on testing with manganese- and iron-based catalysts are presented. The former is a manufactured catalyst while the latter is a natural ore. Results suggest that both show satisfying ability for regeneration from carbon deposits. Higher temperature enhances tar decomposition during experiment with both catalysts. Moreover, the iron-based catalyst enhances water gas shift activity, which in turns impacts the total amount of produced gas. On the other hand, the manganese-based catalyst seems to display higher propensity for tar conversion.
|
|
| 2. |
- Berguerand, Nicolas, 1978, et al.
(författare)
-
Producer Gas Cleaning in a Dual Fluidized Bed Reformer using Two Catalysts
- 2011
-
Ingår i: Compendium of the International Conference on Polygeneration Strategies11. ; , s. 9-
-
Konferensbidrag (refereegranskat)abstract
- The most elegant method to remove tars out of producer gas from biomass gasification is catalytic hot gas cleaning. However, most catalysts are poisoned after short operation due to carbon formation or by other contaminants on their active sites. A novel technique for catalytic gas cleaning based on two interconnected fluidized beds has been investigated. The idea is to reform the tar components into useful molecules by means of a circulating catalyst, also called oxygen carrier in the following. The producer gas is cleaned in one of the reactors, referred to as the fuel reactor (FR), while it is continuously regenerated in the air reactor (AR). The two reactors are separated by loop seals in such a way that gas leakage is prevented between the reactors while solid circulation occurs. By varying the circulation rate of material in the system, the residence time in the raw gas stream and the frequency of regeneration can be adjusted. Meanwhile, the required amount of oxygen for partial oxidation of the tars is transferred. The system described here is coupled with its FR to the Chalmers 2-4 MWth biomass gasifier while the AR is fed with nitrogen-diluted air. In preliminary tests, the effect of different catalysts on both the tar content and the gas composition was investigated. Some of the tested materials do not only reform tars, they also influence the H2/CO-ratio in a beneficial manner. In this paper, comparative results based on testing with manganese and iron based catalysts are presented. Results suggest that both show satisfying ability for regeneration from carbon deposits. Higher temperature enhances tar removal during experiment with both catalysts. Moreover, the iron-based catalyst enhances water gas shift activity, which in turns impacts the total amount of produced gas. On the other hand, the manganese-based catalyst seems to express higher propensity for tar conversion. These observations elicit an interesting flexibility of the process as a judicious set of catalyst in coordination with pertinent operating conditions can be chosen to achieve desired purposes.
|
|
| 3. |
- Berguerand, Nicolas, 1978, et al.
(författare)
-
Use of Nickel Oxide as a Catalyst for Tar Elimination in a Chemical-Looping Reforming Reactor Operated with Biomass Producer Gas
- 2012
-
Ingår i: Industrial & Engineering Chemistry Research. - : American Chemical Society (ACS). - 1520-5045 .- 0888-5885. ; 51:51, s. 16610-16616
-
Tidskriftsartikel (refereegranskat)abstract
- 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.
|
|
| 4. |
|
|
| 5. |
- Lind, Fredrik, 1978, et al.
(författare)
-
Ilmenite and Nickel as Catalysts for Upgrading of Raw Gas Derived from Biomass Gasification
- 2013
-
Ingår i: Energy & Fuels. - : American Chemical Society (ACS). - 1520-5029 .- 0887-0624. ; 27:2, s. 997-1007
-
Tidskriftsartikel (refereegranskat)abstract
- Two metal oxides, naturally occurring ilmenite (iron titanium oxide) and manufactured nickel oxide supported on an α-Al2O3 matrix (NiO/AL2O3), were compared as catalysts for secondary biomass gas upgrading. The experiments were conducted in a Chemical-Looping Reforming (CLR) reactor, which combines biomass gas upgrading with continuous regeneration of coke deposits. The CLR system was fed with a tar-rich producer gas from the Chalmers 2–4 MW biomass gasifier, and the possibilities to reduce the tar fraction and to increase the yield of hydrogen were evaluated for temperatures between 700°C and 880°C. A system-wide molar balance was established, to enable calculations of tar removal efficiency on a mass basis; these results were further compared with those for the more widely used tar-to-reformed gas ratio, yielding tar concentrations in units of gtar/Nm3gas. Both materials exhibited activity with respect to tar decomposition and increased the yield of hydrogen. In addition, both tar removal and hydrogen production were increased with increases in temperature. All the phenolic compounds and a large proportion of the one-ring branched tars were decomposed at 800ºC by the two catalysts, despite the fact that the tar load in the raw gas was as high as 30 gtar/Nm3gas. Results from the mole balance showed that it is important to specify on what basis the tar removal efficiency is calculated. The tar removal efficiency was calculated to 95% for the Ni/Al2O3 catalyst at 880°C and to 60% for the ilmenite catalyst at 850°C on tar-to-reformed gas basis. When the produced permanent gases were removed from the reformed gas the same calculations yielded the tar removal efficiency of 86% and 42% respectively. The testing of serial samples of the effluent stream from the regeneration reactor for carbon oxides showed that coke was removed from the catalyst, and no deactivation by coke deposits was detected during the 8 hours of operation of the CLR reactor.
|
|
| 6. |
- Maric, Jelena, 1983, et al.
(författare)
-
Using a manganese ore as catalyst for upgrading biomass derived gas
- 2013
-
Ingår i: International Conference on Polygeneration Strategies, Wien.
-
Konferensbidrag (refereegranskat)abstract
- Secondary catalytic tar cleaning has been evidenced as a promising technology for upgrading gas derived from biomass gasification. When applying this technology downstream a biomass gasifier, the tar fraction in the raw gas can be reduced and the content of hydrogen can be increased. In this work, experiments have been conducted in a Chemical-Looping-Reforming (CLR) reactor. The present reactor system features a circulating fluidized bed as the reformer section, which offers a higher gas-solids contact time than a bubbling bed configuration previously tested. All experiments were performed using raw gas from the Chalmers 2-4 MWth biomass gasifier as feedstock to the reactor system. The catalyst inventory consisted of a natural manganese ore and its activity was evaluated at three different temperature levels - 800oC, 850oC and 880oC - and with an oxygen content of 2.2%, corresponding to a theoretical air-to-fuel ratio of 0.06. Experimental results showed that the manganese ore exhibits catalytic activity with respect to tar conversion and a tar reduction of as much as 72% was achieved at 880oC. Moreover, this material showed high activity towards hydrogen production.
|
|
| 7. |
- Thunman, Henrik, 1970, et al.
(författare)
-
Using an oxygen-carrier as bed material for combustion of biomass in a 12-MWth circulating fluidized-bed boiler
- 2013
-
Ingår i: Fuel. - : Elsevier BV. - 0016-2361. ; 113, s. 300-309
-
Tidskriftsartikel (refereegranskat)abstract
- 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 40 wt.% 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 12 wt.% 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. © 2013 Elsevier Ltd. All rights reserved.
|
|
| 8. |
- Berguerand, Nicolas, 1978, et al.
(författare)
-
Batch Testing of Solid Fuels with Ilmenite in a 10 kWth Chemical-Looping Combustor
- 2010
-
Ingår i: Fuel. - : Elsevier BV. - 0016-2361. ; 89:8, s. 1749-1762
-
Tidskriftsartikel (refereegranskat)abstract
- Batch experiments were conducted in a 10 kWth chemical-looping combustor for solid fuels using ilmenite, an iron titanium oxide, as the oxygen carrier with two solid fuels: a petroleum coke from Mexico and a bituminous coal from South Africa. The purpose of these batch tests was to attain detailed information on fuel conversion, complementary to previous continuous operation of the unit. At steady-state, a fuel batch of typically 25 g was introduced in the fuel reactor and gas concentrations were measured at the outlet of both air and fuel reactors. The fuel reactor was fluidized with steam and the amount of bed material was typically 5 kg. The fuel introduced devolatilizes rapidly while the remaining char is gasified and the resulting syngases H2 and CO react with the oxygen carrier. Operation involved testing at different fuel reactor temperatures from 950 to 1030°C, and investigation of the influence of particle circulation between air and fuel reactors. The fuel conversion rate was increased at higher temperature: at 950°C the instantaneous rate of conversion for petroleum coke averaged at 17.4 %/min while at 1030°C, the value was 40 %/min. For the much more reactive South African coal, the averaged rate at 970°C was 47 %/min and increased to 101 %/min at 1000°C. For petroleum coke testing with particle circulation, the oxygen demand - defined as oxygen lacking to fully convert the gases leaving the fuel reactor - was typically 12-14% for the gasified char including H2S, in line with previous experiments with the same unit and fuel. If only syngases are considered, the oxygen demand for char conversion was 8.4-11%. Similar or even lower values were seen for the char of South African coal. This is in line with expectations, i.e. that it is possible to reach fairly high conversion, although difficult to reach complete gas conversion with solid fuel. It was also seen that the volatiles pass through the system essentially unconverted, an effect of feeding the fuel from above. Moreover, the oxygen demand for char conversion decreased with increasing temperature. Finally, the CO2 capture - defined as the proportion of gaseous carbon leaving the fuel reactor to total gaseous carbon leaving the system - decreased at higher particle circulation and a correlation between capture and circulation index was obtained.
|
|
| 9. |
- Berguerand, Nicolas, 1978, et al.
(författare)
-
Chemical Looping Combustion of Solid Fuels in a 10 kWth Unit
- 2011
-
Ingår i: Oil and Gas Science and Technology. - : EDP Sciences. - 1294-4475 .- 1953-8189. ; 66:2, s. 181-191
-
Tidskriftsartikel (refereegranskat)abstract
- Chemical Looping Combustion of Solid Fuels in a 10 kW(th) Unit - The present study is based on previous results from batch experiments which were conducted in a 10 kW(th), chemical looping combustor for solid fuels using ilmenite, an iron titanium oxide, as the oxygen carrier with two solid fuels: a Mexican petroleum coke and a South African bituminous coal. These experiments involved testing at different fuel reactor temperatures, up to 1030°C, and different particle circulation rates between the air and fuel reactors. Previous results enabled modeling of the reactor system. In particular, it was possible to derive a correlation between measured operational data and actual circulation mass flow, as well as a model that describes the carbon capture efficiency as a function of the residence time and the char reactivity. Moreover, the kinetics of char conversion could be modeled and results showed good agreement with experimental values. The purpose of the present study was to complete these results by developing a model to predict the conversion of syngas with ilmenite in the fuel reactor. Here, kinetic data from investigations of ilmenite in TGA and batch fluidized bed reactors were used. Results were compared with the actual conversions during operation in this 10 kW(th) unit.
|
|
| 10. |
- Markström, Pontus, 1980, et al.
(författare)
-
The Application of a Multistage-Bed Model for Residence-Time Analysis in Chemical-Looping Combustion of Solid Fuel
- 2010
-
Ingår i: Chemical Engineering Science. - : Elsevier BV. - 0009-2509. ; 65:18, s. 5055-5066
-
Tidskriftsartikel (refereegranskat)abstract
- The behavior of a 10 kW chemical-looping combustor for solid fuels, normally operated in continuous mode, has been studied by addition of fuel batches. From analysis of gas leaving the air reactor, it was possible to determine the residence time and residence-time distribution of particles in the fuel reactor. Knowing the solids inventory in the fuel reactor, the circulation mass flow could be directly correlated to measured operational data, i.e. pressure drop, temperature and gas flow in air reactor riser. Using results for carbon-capture efficiency and residence-time distribution, a model was developed which could determine a mass-based reaction-rate constant for char conversion. The reaction-rate constant of a Mexican petroleum coke at both 950°C and 970°C was calculated to 8.2 wt%/min and 28.8 wt%/min, respectively. The reaction-rate constant of a South African coal at 950°C was calculated to 26.1 wt%/min. This reaction-rate constant could also be determined independently from the conversion rates of char during the batch tests. The results showed a good agreement between the two approaches, indicating that the model well describes the behavior of the unit. From the determination of the circulation mass flow, and comparison with previous testing with different circulation, it was also possible to estimate the limit for which the ilmenite was unable to supply sufficient oxygen to achieve good conversion. This limit was compared to theoretical limits for ilmenite as well as the limit set by a heat balance. It was concluded that the latter will be the one setting the limit.
|
|
