| 1. |
|
|
| 2. |
- Kuba, Matthias, et al.
(författare)
-
A review on bed material particle layer formation and its positive influence on the performance of thermo-chemical biomass conversion in fluidized beds
- 2021
-
Ingår i: Fuel. - : Elsevier. - 0016-2361 .- 1873-7153. ; 291
-
Forskningsöversikt (refereegranskat)abstract
- Bed material particle layer formation plays a significant role in thermo-chemical conversion of biomass. The interaction between biomass ash and bed material in fluidized bed conversion processes has been described for a variety of different applications and spans from fundamental research of formation mechanisms to effects of this layer formation on long-term operation in industrial-scale. This review describes the current state of the research regarding the mechanisms underlying layer formation and the positive influence of bed material particle layer formation on the operation of thermo-chemical conversion processes. Thus, the main focus lies on its effect on the catalytic activity towards gasification reactions and the impact on oxygen transport in chemical looping combustion. The review focuses on the most commonly investigated bed materials, such as quartz, feldspar or olivine. While the most relevant results for both the underlying mechanisms and the subsequently observed effects on the operation are presented and discussed, knowledge gaps where further research is necessary are identified and described.
|
|
| 3. |
- Kuba, Matthias, et al.
(författare)
-
Deposit build-up and ash behavior in dual fluid bed steam gasification of logging residues in an industrial power plant
- 2015
-
Ingår i: Fuel processing technology. - : Elsevier BV. - 0378-3820 .- 1873-7188. ; 139, s. 33-41
-
Tidskriftsartikel (refereegranskat)abstract
- A promising way to substitute fossil fuels for production of electricity, heat, fuels for transportation and synthetic chemicals is biomass steam gasification in a dual fluidized bed (DFB). Using lower-cost feedstock, such as logging residues, instead of stemwood, improves the economic operation. In Senden, near Ulm in Germany, the first plant using logging residues is successfully operated by Stadtwerke Ulm. The major difficulties are slagging and deposit build-up. This paper characterizes inorganic components of ash forming matter and draws conclusions regarding mechanisms of deposit build-up. Olivine is used as bed material. Impurities, e.g., quartz, brought into the fluidized bed with the feedstock play a critical role. Interaction with biomass ash leads to formation of potassium silicates, decreasing the melting temperature. Recirculation of coarse ash back into combustion leads to enrichment of critical fragments. Improving the management of inorganic streams and controlling temperature levels is essential for operation with logging residues. (C) 2015 Elsevier B.V. All rights reserved.
|
|
| 4. |
- Kuba, Matthias, et al.
(författare)
-
Mechanism of Layer Formation on Olivine Bed Particles in Industrial-Scale Dual Fluid Bed Gasification of Wood
- 2016
-
Ingår i: Energy & Fuels. - : American Chemical Society (ACS). - 0887-0624 .- 1520-5029. ; 30:9, s. 7410-7418
-
Tidskriftsartikel (refereegranskat)abstract
- Utilization of biomass as feedstock in dual fluidized bed steam gasification is a promising technology for the substitution of fossil energy carriers. Experience from industrial-scale power plants showed an alteration of the olivine bed material due to interaction with biomass ash components. This change results mainly in the formation of Ca-rich layers on the bed particles. In this paper, a mechanism for layer formation is proposed and compared to the better understood mechanism for layer formation on quartz bed particles. Olivine bed material was sampled at an industrial-scale power plant before the start of operation and at predefined times after the operation had commenced. Therefore, time-dependent layer formation under industrial-scale conditions could be investigated. The proposed mechanism suggests that the interaction between wood biomass ash and olivine bed particles is based on a solid-solid substitution reaction, where Ca2+ is incorporated into the crystal structure. As a consequence, Fe2+/3+ and Mg2+ ions are expelled as oxides. This substitution results in the formation of cracks in the particle layer due to a volume expansion in the crystal structure once Ca2+ is incorporated. The results of this work are compared to relevant published results, including those related to quartz bed particles
|
|
| 5. |
- Kuba, Matthias, et al.
(författare)
-
Surface characterization of ash-layered olivine from fluidized bed biomass gasification
- 2021
-
Ingår i: Biomass Conversion and Biorefinery. - : Springer. - 2190-6815 .- 2190-6823. ; 11:1, s. 29-38
-
Tidskriftsartikel (refereegranskat)abstract
- The present study aims to present a comprehensive characterization of the surface of ash-layered olivine bed particles from dual fluidized bed gasification. It is well known from operation experience at industrial gasification plants that the bed material is activated during operation concerning its positive influence on gasification reactions. This is due to the built up of ash layers on the bed material particles; however, the chemical mechanisms are not well understood yet. Olivine samples from long-term operation in an industrial-scale gasification plant were investigated in comparison to fresh unused olivine. Changes of the surface morphology due to Ca-enrichment showed a significant increase of their surface area. Furthermore, the Ca-enrichment on the ash layer surface was distinctively associated to CaO being present. The presence of CaO on the surface was proven by adsorption tests of carbon monoxide as model compound. The detailed characterization contributes to a deeper understanding of the surface properties of ash layers and forms the basis for further investigations into their influence on gasification reactions.
|
|
| 6. |
- Kuba, Matthias, et al.
(författare)
-
Thermal stability of bed particle layers on naturally occurring minerals from dual fluid bed gasification of woody biomass
- 2016
-
Ingår i: Energy & Fuels. - Washington : American Chemical Society (ACS). - 0887-0624 .- 1520-5029. ; 30:10, s. 8277-8285
-
Tidskriftsartikel (refereegranskat)abstract
- The use of biomass as feedstock for gasification is a promising way of producing not only electricity and heat but also fuels for transportation and synthetic chemicals. Dual fluid bed steam gasification has proven to be suitable for this purpose. Olivine is currently the most commonly used bed material in this process due to its good agglomeration performance and its catalytic effectiveness in the reduction of biomass tars. However, as olivine contains heavy metals such as nickel and chromium, no further usage of the nutrient-rich ash is possible, and additional operational costs arise due to necessary disposal of the ash fractions. This paper investigates possible alternative bed materials and their suitability for dual fluid bed gasification systems focusing on the behavior of the naturally occurring minerals olivine, quartz, and K-feldspar in terms of agglomeration and fracturing at typical temperatures. To this end, samples of bed materials with layer formation on their particles were collected at the industrial biomass combined heat and power (CHP) plant in Senden, Germany, which uses olivine as the bed material and woody biomass as feedstock. The low cost logging residue feedstock contains mineral impurities such as quartz and K-feldspar, which become mixed into the fluidized bed during operation. Using experimental and thermochemical analysis, it was found that the layers on olivine and K-feldspar showed a significantly lower agglomeration tendency than quartz. Significant fracturing of particles or their layers could be detected for olivine and quartz, whereas K-feldspar layers were characterized by a higher stability. High catalytic activity is predicted for all three minerals once Ca-rich particle layers are fully developed. However, quartz may be less active during the buildup of the layers due to lower amounts of Ca in the initial layer formation.
|
|
| 7. |
- Vargas Falla, Ana Maria, et al.
(författare)
-
Kuba är under stor press
- 2013
-
Ingår i: Sydsvenskan. - 1652-814X.
-
Tidskriftsartikel (populärvet., debatt m.m.)abstract
- Möjligheten för kubaner att resa utomlands är en viktig symbolfråga och en av de rättigheter som det kubanska folket efterfrågat. Att fler reformer genomförs på Kuba den närmaste tiden är, som vi ser det, självklart. Utvecklingen går inte att skruva tillbaka. Sannolikt är resereformen bara början på ett liberalare Kuba. Det kommer ytterligare att aktualiseras när de som styrt landet sedan revolutionen 1959 måste ersättas inom de närmaste åren. De reformer som skedde innan den nya resereformen antogs fokuserade på ekonomisk liberalism. Resereformen är ett trendbrott genom att den fokuserar på medborgerliga rättigheter. Förhoppningsvis är det ett steg på vägen också mot ökad åsiktsfrihet, pressfrihet och rätten att fritt välja politiska ledare.
|
|
| 8. |
|
|
| 9. |
|
|
| 10. |
- Bozaghian Bäckman, Marjan, et al.
(författare)
-
Bed material performance of quartz, natural K-feldspar, and olivine in bubbling fluidized bed combustion of barley straw
- 2024
-
Ingår i: Fuel. - : Elsevier. - 0016-2361 .- 1873-7153. ; 364
-
Tidskriftsartikel (refereegranskat)abstract
- The present study investigates how three different silicate-based bed materials behave in bubbling fluidized bed combustion of a model agricultural residue with respect to ash composition, namely barley straw. Quartz, natural K-feldspar, and olivine were all used in combustion at 700 °C, and the resulting layer formation and bed agglomeration characteristics were determined. Based on this, a general reaction model for bed ash from agricultural residues was proposed, taking into account the reactivity of the different silicates investigated towards the main ash-forming elements K, Ca, and Si. The proposed reaction model links bed material interaction with K-rich bed ash to the degree of polymerization of the silicate bed material, where addition reactions occur in systems with high polymerization, predominately in quartz, and substitution reactions dominate for depolymerized silicates such as K-feldspar and olivine.
|
|
