| 1. |
- Bonmann, Marlene, 1988, et al.
(author)
-
Sub-millimetre wave range-Doppler radar as a diagnostic tool for gas-solids systems - solids concentration measurements
- 2023
-
In: Advanced Powder Technology. - : Elsevier BV. - 0921-8831 .- 1568-5527. ; 34:1
-
Journal article (peer-reviewed)abstract
- Current non-intrusive measurement techniques for characterising the solids flow in gas-solids suspensions are limited by the low temporal or low spatial resolution of the sample volume, or in the case of optical methods, by a short range of sight. In this work, a sub-millimetre wave range-Doppler radar is developed and validated for non-intrusive sensing of solids concentrations in a gas-solids particle system with known characteristics. The radar system combines favourable features, such as the ability to see through at optical frequencies opaque materials, to measure the local solids velocity and the reflected radar power with a spatial resolution of a few cubic centimetres over distances of a few metres. In addition, the radar hardware offers flexibility in terms of installation. After signal processing, the output of the radar is range-velocity images of the solids flowing along the radar’s line-of-sight. The image frame rate can be close to real-time, allowing the solids flow dynamics to be observed. While the well-established Doppler principle is used to measure the solids velocity, this paper introduces a method to relate the received radar signal power to the solids volumetric concentrations (cv) of different particulate materials. The experimental set-up provides a steady stream of free-falling solids that consist of glass spheres, bronze spheres or natural sand grains with known particle size distributions and with particle diameters in the range of 50–300 µm. Thus, the values of cv found using the radar measurements are validated using the values of cv retrieved from closure of the mass balance derived from the measured mass flow rate of the solids stream and the solids velocity. The results show that the radar system provides reliable measurements of cv, with a mean relative error of approximately 25 % for all the tested materials, particle sizes and mass flow rates, yielding values of cv ranging from 0.2 × 10-4 m3/m3 up to 40 × 10-4 m3/m3 and solids velocities within the range of 0–4.5 m/s. This demonstrates the ability of the radar technology to diagnose the solids flow in gas-solids suspensions using a unique combination of penetration length, accuracy, and spatial and time resolution. In future work, the radar technique will be applied to study non-controlled solids flow at a larger scale, and to understand flow conditions relevant to industrial reactor applications, e.g., fluidised bed, entrained flow, and cyclone units.
|
|
| 2. |
- Guio Perez, Diana Carolina, 1985, et al.
(author)
-
Radar-based measurements of the solids flow in a circulating fluidized bed
- 2023
-
In: Fuel. - 0016-2361. ; 345
-
Journal article (peer-reviewed)abstract
- The aim of this work is to demonstrate the value of radar technology for studying experimentally the solids flows in gas-solids fluidized beds. The work presents original results regarding the solids concentration and velocity acquired in a non-intrusive manner from a cold flow model. The tailored radar setup operates at submillimeter wave frequencies (0.34 THz) and can measure the location of solids with a spatial resolution of 1/8 mm−1 in the direction of the radar beam, and of 40–60 mm across the radar beam. The solids velocity in the direction of the beam propagation is determined through measurement of the Doppler shift caused by the reflection of the transmitted radar signal by solids moving in relation to the antenna. The measurements were performed in both the horizontal and vertical directions in the riser of a circulating fluidized bed (cross-sectional area of 0.45 m2 and height of 3.1 m) operated with glass beads (mean particle size of 106 µm, and particle density of 2,486 kg/m3) and using air at ambient temperature as the fluidization agent, with superficial velocities in the range of 0.3–1.3 m/s. The measurements are used to assess the validity of the technique and are not intended to characterize the unit fluid dynamically. The solids concentrations derived from the radar measurements follow the qualitative trends derived from pressure-drop measurements, resembling the expected changes that occur in the concentration profiles as the fluidization velocity increases. Concentrations in the range from 10-6 m3/m3 to 10-1 m3/m3 are measurable. In quantitative terms, for low concentrations of solids (<5·10-3 m3/m3, approximately) the radar measurements exhibited the ability to provide more consistent measurements of the solids concentration than those obtained from pressure transducers, for which the small pressure differences lead to unstable and even negative values for solids concentrations. The two measurement methods were in quantitative agreement for solids volume fractions higher than the threshold. Concentrations ≥ 1·10-1 m3/m3, though measurable, strongly attenuate the radar signal, thereby reducing the beam penetration to a depth of centimeters. For each position along the radar beam, the distribution of solids velocity measured from the Doppler effect was found to be within the expected ranges and allowed observations of solids back-mixing. The radar technique applied in this work is a promising technique for detailed characterization of the solids flow in fluidized beds, offering high spatial and temporal resolutions, allowing the determination of both solids velocity and concentration, and having a reasonably high penetration depth.
|
|
| 3. |
- Larsson, Anton, 1984, et al.
(author)
-
Zero-dimensional modeling of indirect fluidized bed gasification
- 2010
-
In: 13th International Conference on Fluidization.
-
Conference paper (peer-reviewed)abstract
- Zero-dimensional models has been developed to investigate mass balance and fuel (biomass) conversion in Chalmers 2-4 MWfuel indirect fluidized bed gasifier. The input to the model is measured concentrations and flows. The model shows that the conversion factor of the water gas shift reaction is around 40 %.
|
|
| 4. |
- Thunman, Henrik, 1970, et al.
(author)
-
Advanced biofuel production via gasification – lessons learned from 200 man-years of research activity with Chalmers’ research gasifier and the GoBiGas demonstration plant.
- 2018
-
In: Energy Science and Engineering. - : Wiley. - 2050-0505. ; 6:1, s. 6-34
-
Journal article (peer-reviewed)abstract
- This paper presents the main experiences gained and conclusions drawn from the demonstration of a first-of-its-kind wood-based biomethane production plant (20-MW capacity, 150 dry tonnes of biomass/day) and 10 years of operation of the 2–4-MW (10–20 dry tonnes of biomass/day) research gasifier at Chalmers University of Technology in Sweden. Based on the experience gained, an elaborated outline for commercialization of the technology for a wide spectrum of applications and end products is defined. The main findings are related to the use of biomass ash constituents as a catalyst for the process and the application of coated heat exchangers, such that regular fluidized bed boilers can be retrofitted to become biomass gasifiers. Among the recirculation of the ash streams within the process, presence of the alkali salt in the system is identified as highly important for control of the tar species. Combined with new insights on fuel feeding and reactor design, these two major findings form the basis for a comprehensive process layout that can support a gradual transformation of existing boilers in district heating networks and in pulp, paper and saw mills, and it facilitates the exploitation of existing oil refineries and petrochemical plants for large-scale production of renewable fuels, chemicals, and materials from biomass and wastes. The potential for electrification of those process layouts are also discussed. The commercialization route represents an example of how biomass conversion develops and integrates with existing industrial and energy infrastructures to form highly effective systems that deliver a wide range of end products. Illustrating the potential, the existing fluidized bed boilers in Sweden alone represent a jet fuel production capacity that corresponds to 10% of current global consumption.
|
|
| 5. |
- Alamia, Alberto, 1984, et al.
(author)
-
Process Simulation of Dual Fluidized Bed Gasifiers Using Experimental Data
- 2016
-
In: Energy & Fuels. - : American Chemical Society (ACS). - 1520-5029 .- 0887-0624. ; 30:5, s. 4017-4033
-
Journal article (peer-reviewed)abstract
- Process simulation of a dual fluidized bed (DFB) gasifier is challenging, owing to the high degree of freedominherent to the operation of the double-reactor system and the complexity of the reactions therein. We propose a method forsimulation of the gasifier based on the analysis of experimental data and of the total uncertainty associated with them. The overallaim is to use data from the large amount of pilot and demonstration gasifiers in the analysis and optimization of gasification-basedprocesses. In the method proposed a set of fuel conversion variables and their associated uncertainties are calculated using astochastic approach that takes into account the effect of unclosed mass balance, incomplete characterization of the raw gascompounds and measurement errors. Subsequently, these fuel conversion variables are used to simulate the gasifier in a flowsheetmodel developed in Aspen Plus. The results include the evaluation of critical parameters, such as, gasifier efficiency, chargasification, and tar yield and their uncertainties, which depend highly on the measurement system. The method is applied todata sets derived from several measurement setups, and the results are validated with total carbon measurements. The resultsshow that detection of ≥95% of the carbon in the raw gas is necessary to maintain the uncertainty level at
|
|
| 6. |
- Berdugo Vilches, Teresa, 1985, et al.
(author)
-
Bed material as a catalyst for char gasification: The case of ash-coated olivine activated by K and S addition
- 2018
-
In: Fuel. - : Elsevier BV. - 0016-2361. ; 224, s. 85-93
-
Journal article (peer-reviewed)abstract
- In this paper, the ability of an ash-coated olivine to catalyze the steam gasification of biomass-derived char is investigated in a laboratory reactor. The olivine investigated is a sample from the Chalmers dual fluidized bed gasifier and it has been activated by the in-bed addition of S and K 2 CO 3 . The char and bed material samples were analyzed by Scanning Electron Microscopy coupled with Energy Dispersive X-ray Spectroscopy (SEM-EDS). It is shown that the ash layer coating of the olivine can catalyze the steam gasification of char by transferring catalytic potassium (K) to the char particles. The mobilities of the catalytic species from the olivine ash-layer are discussed. This work furthers the current understanding of the catalytic activities of ash-coated bed material particles during the thermochemical conversion of carbonaceous feedstocks in fluidized beds. In addition, it complements the existing literature on catalytic bed materials, which to date have focused on tar removal and improving gas quality.
|
|
| 7. |
- Berdugo Vilches, Teresa, 1985, et al.
(author)
-
Comparing Active Bed Materials in a Dual Fluidized Bed Biomass Gasifier: Olivine, Bauxite, Quartz-Sand, and Ilmenite
- 2016
-
In: Energy & Fuels. - : American Chemical Society (ACS). - 1520-5029 .- 0887-0624. ; 30:6, s. 4848-4857
-
Journal article (peer-reviewed)abstract
- Active bed materials are in this work investigated for in situ gas upgrading of biomass-derived gas. Previous research on in situ gas upgrading has focused on assessing gas quality, in terms of the concentrations of tar and permanent gases. Other aspects of fuel conversion, such as char conversion and the impact of oxygen transport on the final gas, are not as well documented in the literature on gasification. In this paper, the overall biomass conversion in a dual fluidized bed biomass gasifier is investigated in the presence of the catalytic material olivine and the alkali-binding material bauxite. The impact of these materials on fuel conversion is described as the combination of four effects, which are induced by the bed material: thermal, catalytic, ash-enhanced catalytic effect, and oxygen transport. Quartz-sand and ilmenite are here used as the reference materials for the thermal and the oxygen transport effects, respectively. Olivine and bauxite show activity toward tar species compared to quartz-sand. After 1 week of operation and exposure to biomass ash, the activities of olivine and bauxite toward tar species increase further, and the water gas shift reaction is catalyzed by both materials. Additionally, bauxite shows a stronger ability to increase char conversion than olivine. Under the conditions tested, olivine and bauxite have some degree of oxygen transport capacity, which is between those of quartz-sand and ilmenite. The oxygen transport effect is higher for bauxite than for olivine; nevertheless, the catalytic activities of the materials result in higher yields of H-2 than in a similar case with quartz-sand. The implications of the findings for the operation of dual fluidized bed gasifiers are discussed.
|
|
| 8. |
- Berdugo Vilches, Teresa, 1985, et al.
(author)
-
Influence of in-bed catalysis by ash-coated olivine on tar formation in steam gasification of biomass
- 2018
-
In: Energy & Fuels. - : American Chemical Society (ACS). - 1520-5029 .- 0887-0624. ; 32:9, s. 9592-9604
-
Journal article (peer-reviewed)abstract
- The use of catalytic bed materials has become a state-of-the-art solution to control the concentration of tar in fluidized bed biomass steam gasifiers. Ash-coated olivine is commonly applied as bed material, owing to its relatively high catalytic activity towards tar species. However, the mechanisms and conversion pathways influenced by the ash-coated olivine when applied as an in-bed catalyst are still not well understood. The present work aims at proving that the ash-layered olivine prevents the formation of biomass-derived tar at an early stage of their formation. Tests with olivine at different stages of activation and at different temperatures are carried out in the Chalmers 2-4MWth DFB gasifier. Detailed characterization of the tar and light hydrocarbon fractions are presented and discussed in relation to the sources of aromatic species. It is concluded that the ash-coated olivine prevents the formation of aromatic tar species by promoting the steam reforming of early tar precursors. Gas-phase interactions of the early tar precursors and bed material contribute to the tar reduction observed. The results indicate that olivine interferes the cyclization routes involving C2H2 and C3 hydrocarbons.
|
|
| 9. |
- Berdugo Vilches, Teresa, 1985, et al.
(author)
-
Mapping the effects of potassium on fuel conversion in industrial-scale fluidized bed gasifiers and combustors
- 2021
-
In: Catalysts. - : MDPI AG. - 2073-4344. ; 11:11
-
Journal article (peer-reviewed)abstract
- Potassium (K) is a notorious villain among the ash components found in the biomass, being the cause of bed agglomeration and contributing to fouling and corrosion. At the same time, K is known to have catalytic properties towards fuel conversion in combustion and gasification environments. Olivine (MgFe silicate) used as gasifier bed material has a higher propensity to form catalytically active K species than traditional silica sand beds, which tend to react with K to form stable and inactive silicates. In a dual fluidized bed (DFB) gasifier, many of those catalytic effects are expected to be relevant, given that the bed material becomes naturally enriched with ash elements from the fuel. However, a comprehensive overview of how enrichment of the bed with alkali affects fuel conversion in both parts of the DFB system is lacking. In this work, the effects of ash-enriched olivine on fuel conversion in the gasification and combustion parts of the process are mapped. The work is based on a dedicated experimental campaign in a Chalmers DFB gasifier, wherein enrichment of the bed material with K is promoted by the addition of a reaction partner, i.e., sulfur, which ensures K retention in the bed in forms other than inactive silicates. The choice of sulfur is based on its affinity for K under combustion conditions. The addition of sulfur proved to be an efficient strategy for capturing catalytic K in olivine particles. In the gasification part, K-loaded olivine enhanced the char gasification rate, decreased the tar concentration, and promoted the WGS equilibrium. In the combustion part, K prevented full oxidation of CO, which could be mitigated by the addition of sulfur to the cyclone outlet.
|
|
| 10. |
- Berdugo Vilches, Teresa, 1985, et al.
(author)
-
Shedding light on the governing mechanisms for insufficient CO and H2 burnout in the presence of potassium, chlorine and sulfur
- 2020
-
In: Fuel. - : Elsevier BV. - 0016-2361. ; 273
-
Journal article (peer-reviewed)abstract
- Based on the experiences of insufficient burnout in industrial fluidized bed furnaces despite adequate mixing and availability of oxidizer, the influence of potassium on CO and H2 oxidation in combustion environments was investigated. The combustion environments were provided by a laminar flame burner in a range relevant to industrial furnaces, i.e. 845 °C to 1275 °C and excess air ratios ranging from 1.05 to 1.65. Potassium, in the form of KOH, was homogeneously introduced into the hot gas environments to investigate its effect on the radical pool. To quantitatively determine key species that are involved in the oxidation mechanism (CO, H2, KOH, OH radicals, K atoms), a combination of measurement systems was applied: micro-gas chromatography, broadband UV absorption spectroscopy and tunable diode laser absorption spectroscopy. The inhibition effect of potassium on CO and H2 oxidation in excess air was experimentally confirmed and attributed to the chain-terminating reaction between KOH, K atoms and OH radicals, which enhanced the OH radical consumption. The addition of chlorine or sulfur could reduce the concentrations of KOH and K atoms and consequently eliminated the inhibition on CO and H2 oxidation. Existing kinetic mechanisms underestimate the inhibiting effect of potassium and they fail to predict the effect of temperature on CO and H2 concentration when potassium and sulfur co-exist. This work advances the need to revise existing kinetic mechanisms to fully capture the interplay of K and S in the oxidation of CO and H2 in industrial fluidized bed furnaces.
|
|
