| 1. |
- Alevanau, Aliaksandr, 1965-
(författare)
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Study of the Apparent Kinetics of Biomass Gasification Using High-Temperature Steam
- 2010
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Among the latest achievements in gasification technology, one may list the development of a method to preheat gasification agents using switched ceramic honey combs. The best output from this technology is achieved with use of water steam as a gasification agent, which is heated up to 1600 °C. The application of these temperatures with steam as a gasification agent provides a cleaner syngas (no nitrogen from air, cracked tars) and the ash melts into easily utilised glass-like sludge. High hydrogen content in output gas is also favourable for end-user applications.Among the other advantages of this technology is the presumable application of fixed-bed-type reactors fed by separately produced and preheated steam. This construction assumes relatively high steam flow rates to deliver the heat needed for endothermic reactions involving biomass. The biomass is to be heated uniformly and evenly in the volume of the whole reactor, providing easier and simpler control and operation in comparison to other types of reactors. To provide potential constructors and exploiters of these reactors with the kinetic data needed for the calculations of vital parameters for both reactor construction and exploitation, basic experimental research of high-temperature steam gasification of four types of industrially produced biomass has been conducted.Kinetic data have been obtained for straw and wood pellets, wood-chip charcoal and compressed charcoal of mixed origin. Experiments were conducted using two experimental facilities at the Energy and Furnace Division of the Department of Material Science and Engineering (MSE) at the School of Industrial Engineering and Management (ITM) of the Royal Institute of Technology (KTH) and at the Combustion Laboratory of the Mechanical Engineering Department of the University of Maryland (UMD), USA.The experimental facility at the Energy and Furnace Division has been improved with the addition of several constructive elements, providing better possibilities for thermo-gravimetric measurements.The obtained thermo-gravimetric data were analysed and approximated using several models described in the literature. In addition, appropriate software based on the Scilab package was developed. The implementation of the isothermal method based on optimisation algorithms has been developed and tested on the data obtained under the conditions of a slow decrease of temperature in experiments with the char gasification in small-scale experimental facilities in the Energy and Furnace Division.The composition of the gases generated during the gasification of straw and wood pellets by high-temperature steam has been recorded and analysed for different experimental conditions.
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| 2. |
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| 3. |
- Li, Jun, et al.
(författare)
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Volumetric combustion of biomass for CO2 and NOx reduction in coal-fired boilers
- 2012
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Ingår i: Fuel. - : Elsevier BV. - 0016-2361 .- 1873-7153. ; 102, s. 624-633
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Tidskriftsartikel (refereegranskat)abstract
- To meet the urgent environmental targets, substituting coal with biomass has been considered to be an effective and promising method over the last decades. In this paper, a new concept of volumetric combustion is proposed and further developed to achieve 100% fuel switching to biomass in large scale coal-fired boilers. Volumetric combustion not only changes the in-furnace flow but also affects the combustion reactions by the intensive mixing and internal recirculation of the flue gases. Firstly, the volumetric combustion properties of the wood pellets were investigated experimentally. An Aspen model was then used to thermodynamically describe and study the volumetric combustion with three different types of fuel, and the emission properties of CO2 and NOx were compared. Finally, two applications of volumetric combustion were discussed. It is concluded that the wood pellets ignited and combusted much faster than the coal pellets and had a larger combustion volume when combusted under lower oxygen concentration conditions, and the ignition time was almost independent of the oxygen concentration when the oxidizer was preheated to 1000 degrees C. In addition, the NOx emissions decreased as the recirculation ratio of the flue gas increased, and as the percentage of biomass used in co-firing increased, the amount of flue gas that needs to be recycled for reduction of NOx decreased. Thus, the volumetric combustion is beneficial as it reduces the operation cost of NOx reduction. The volumetric combustion would be an attractive technology for co-firing a large proportion of biomass in coal-fired boilers with high boiler efficiency and effective emissions reduction.
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| 4. |
- Lucas, Carlos, et al.
(författare)
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Mathematical model of biomass gasification using high temperature air in fixed beds
- 2007
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Ingår i: Progress in Computational Fluid Dynamics, An International Journal. - 1468-4349 .- 1741-5233. ; 7:1, s. 58-67
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Tidskriftsartikel (refereegranskat)abstract
- A mathematical model has been formulated for predicting the main chemical and physical processes taking place during the fixed-bed gasification of biomass fuels using high temperature air (up to 1000 degrees C). Predicted gas species concentrations profiles and their maximum values are in good agreement with measurements. The results also show that when the temperature of feed gas (air) is increased a higher gasification rate, higher molar fractions of fuel gases (CO, H-2 and CmHn) are obtained, thus resulting in a higher LHV. At a high flow rate of the feed gases, the peaks of the fuel gas concentrations are slightly increased, and the gasification rate is strongly increased. A smaller particle size of the biomass fuels leads to higher peak values of the fuel gas species molar fractions, and a more stable gasification zone for a relatively long period of time.
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| 5. |
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| 6. |
- Ponzio, Anna, et al.
(författare)
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Combustion of coal in high temperature oxygen diluted and oxygen enriched conditions
- 2006
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Ingår i: A and WM, Annual International Conference on Incineration and Thermal Treatment Technologies, IT3. - 0923204849 - 9780923204846 ; , s. 202-216
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Konferensbidrag (refereegranskat)abstract
- In this investigation, coal pellets were combusted using a high temperature oxidizer (600-1000°C), both in oxygen diluted and oxygen enriched conditions, using a small scale batch reactor able to preheat the oxidizer to 1000°C. The combustion process and flame are described and mass, temperature and heating rate as function of time for different oxidizer compositions and temperature discussed. The results show that high temperature conditions gives the highest mass loss rates. The influence of oxygen concentration on mass loss rate is more evidenced for enriched conditions and/or lower oxidizer temperatures. Diluted conditions are associated with large flames while a typical flame downstream from the sample was almost absent for oxygen concentrations above 50%. Ignition time is highly dependent on oxygen concentration only when a 600°C oxidizer was used while almost independent when a 1000°C oxidizer was used.
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| 7. |
- Ponzio, Anna, et al.
(författare)
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Combustion of solid fuels under the conditions of high temperature and various oxygen concentration
- 2007
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Ingår i: Challenges on Power Engineering and Environment - Proceedings of the International Conference on Power Engineering 2007, ICOPE 2007. - Berlin, Heidelberg : Springer Berlin Heidelberg. - 9787308055956 ; , s. 871-876
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Konferensbidrag (refereegranskat)abstract
- This work investigated the combustion phenomena of solid fuels, coal and wood pellets with use of high temperature oxidizers (873-1273 K), both in oxygen diluted and oxygen enriched conditions. The combustion process and flame are described and mass, temperature and heating rate as function of time for different oxidizer compositions and temperature are discussed. The results show that high temperature conditions give the highest mass loss rates. The influence of oxygen concentration on mass loss rate is more evidenced for enriched conditions and/or lower oxidizer temperatures. Diluted conditions are associated with large flames while a typical flame downstream from the sample was almost absent for oxygen concentrations above 50%. Ignition time is highly dependent on oxygen concentration only when a 873 K oxidizer was used while almost independent when a 1273 K oxidizer was used.
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| 8. |
- Ponzio, Anna, et al.
(författare)
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Development of a thermally homogeneous gasifier system using high-temperature agents
- 2006
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Ingår i: Clean Air. - 1561-4417. ; 7:4, s. 363-379
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Tidskriftsartikel (refereegranskat)abstract
- An advanced twin component gasification system, named Thermally Homogenous Gasification (THG), is developed. Development, testing and numerical simulations of the THG have shown that increased temperature of the gasification agent, results in a higher gasification rate, higher ignition front rate, higher molar fraction of combustible species in the product gas (CO, H2 and CmHn), and consequently a higher LHV. Moreover, there exists a critical gasification agent temperature above which preheating is no longer efficient if the purpose is to maximise the yield of gaseous products.
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| 9. |
- Ponzio, Anna, et al.
(författare)
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Effect of operating conditions on tar and gas composition in high temperature air/steam gasification (HTAG) of plastic containing waste
- 2006
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Ingår i: Fuel processing technology. - : Elsevier BV. - 0378-3820 .- 1873-7188. ; 87:3, s. 223-233
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Tidskriftsartikel (refereegranskat)abstract
- In this work, the high temperature air/steam gasification (HTAG) technique has been tested for a fuel in pellet form made from waste material of woody and plastic origin. The feedstock was gasified in an updraft fixed bed reactor by mixtures of air and steam (102 Nm(3)/h, 4% to 82% steam) preheated to 1400 degrees C, a temperature well above the fluid temperature of the feedstock. The produced gas was analyzed with respect to composition, including a detailed characterization of the tar. Lower heating values up to 9.5 MJ/Nm(3) and gas yields as high as 3.4 Nm(3)/kg were reported, indicating the process to be highly efficient for waste-to-energy applications. The composition of the tars, suggested extensive cracking as a result of the high temperatures of the outgoing gas.
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| 10. |
- Ponzio, Anna, et al.
(författare)
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Ignition of single coal particles in high-temperature oxidizers with various oxygen concentrations
- 2008
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Ingår i: Fuel. - : Elsevier BV. - 0016-2361 .- 1873-7153. ; 87:6, s. 974-987
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Tidskriftsartikel (refereegranskat)abstract
- In this investigation, coal pellets were combusted using a high temperature oxidizer with varying oxygen concentration, using a small scale batch reactor able to preheat the oxidizer to 1273 K. In base of the experimental results, the influence of oxygen concentration on the ignition mechanism, the solid temperature inside the particle at the moment of ignition, the mass lost at the moment of the ignition and ignition time is analyzed and discussed. A theoretical basis for the division of the conditions tested into three ignition regimes is developed and a formula for the prediction of the ignition time directly from the material and oxidizer temperature and oxygen concentration is proposed.
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| 11. |
- Ponzio, Anna, et al.
(författare)
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Nitrogen release during thermochemical conversion of single coal pellets in highly preheated mixtures of oxygen and nitrogen
- 2009
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Ingår i: Fuel. - : Elsevier BV. - 0016-2361 .- 1873-7153. ; 88:6, s. 1127-1134
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Tidskriftsartikel (refereegranskat)abstract
- In this investigation, single coal particles (pellets) were combusted in highly preheated oxidants (8731273 K) with oxygen concentrations ranging from 0% to 100%, using a small scale' batch reactor. In base of the experimental results, the influence of oxygen concentration and oxidizer temperature on total mass conversion, the release of fuel nitrogen and the fraction of fuel nitrogen that is oxidized to NOx, is discussed. For oxygen concentration 5-21%, the rate of the thermochemical conversion was shown to be almost independent oxygen concentration when oxidant temperatures of 1073-1273 K were used. The opposite was true for an oxidant temperature of 873 K. Thus there appears to be an oxidant temperature above which devolatilisation is controlled by convective heat transfer rather than reaction. Further it was shown that the release of fuel nitrogen was promoted by an increased oxygen concentration (from 5% to 21% at 1273 K) and an increase of oxidant temperature (from 1073 K to 1273 K at 21% oxygen). An estimate of the devolatilisation of nitrogen from the measured pellet temperature indicated that the devolatilisation of nitrogen is significantly delayed with respect to other components. In fact, during the very initial part of the thermochemical conversion, most released nitrogen appeared to follow the route via char rather than via devolatilisation. Favorable conditions for No reduction thanks to a prompt devolatilisation contemporarily to a release of fuel nitrogen via the char route was believed to be one of the explanation for the evidenced low ratios between NOx emissions and fuel nitrogen released, particularly in the beginning of the experiment. The fact that the amount of released fuel nitrogen that is oxidized to NOx was shown to decrease with increasing oxidant temperatures from 1073 K to 1273 K supports this interpretation, though a higher temperature of the oxidant creates higher devolatilisation rates.
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| 12. |
- Ponzio, Anna, 1975-
(författare)
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Thermally homogenous gasification of biomass/coal/waste for medium or high calorific value syngas production
- 2008
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Today’s problems with emissions of green house gases, land filling of waste and depletion of the oil reserves calls for new energy systems based on alternative fuels like biomass and waste. Gasification is an attractive technology for the use of such solid fuels. Conventional gasification, in the vast majority of cases, uses in-reactor heat release from combustion of part of the feedstock, possibly coupled with a limited preheating of the agent, to obtain the necessary temperatures in the gasifier bed. During recent years, a new gasification technology, using highly preheated gasification agents (> 1273 K), has been developed. The extra heat brought into the process by the high temperature agent reduces the amount of feedstock that has to be oxidized to supply the necessary heat and the use of highly preheated agents has previously proven to have several positive effects on the fuel gas quality.In difference to the previous work on gasification with highly preheated agents, this thesis primarily focuses on the fundamental aspects namely, mass conversion, heating and ignition. It starts by considering single fuel particles or thin beds of fuel particles inserted into highly preheated agents. Mass conversion, heating and ignition are reported in function of the temperature and oxygen concentration of the agent and formulas for the prediction of ignition time and ignition mechanism are developed. The perspective is then widened to include the whole gasifier bed. Simulations of fixed bed batch gasification using highly preheated agents are performed with a mathematical model and used to study how the high agent temperature influences the mass conversion, devolatilisation front rate and the temperature distribution in the fixed fuel bed. Further, the gas quality and gasification efficiency are studied by means of large scale experiment. Ultimately, a thermodynamic analysis of the whole autothermal gasification system, including both a regenerative preheating system and the gasifier, is made.The particle study reports results from experiments with wood and coal and agents consisting of mixtures of nitrogen and oxygen in various proportions. It is shown that an increase in agent temperature from 873 K to 1273 K make the conversion process faster, mostly due to an early onset of the devolatilisation (fast drying) but also due to an increased devolatilisation rate (at least in the case of wood). The time to ignition also decreases significantly, particularly so between 873 and 1073 K. Further, it is shown that the higher the agent temperature, the more pronounced was also the tendency of the coal particles to heat significantly faster in oxygen diluted conditions (5,10 and 21% oxygen) than in inert (0% oxygen) or oxygen rich conditions (30, 50, 80 and 100% oxygen). An increase in agent temperature is also shown to reduce the dependency of the process on the oxygen concentration, at least in diluted conditions (5-21% oxygen). The results also indicate that for coal an increase in the oxygen concentration, specifically in the region above the atmospheric concentration, leads to a decreased dependency on the agent temperature. It is finally shown in the experiments with agent temperatures of 1073 and 1273 K that a flame is promptly formed even in very low concentrations of oxygen.The gasifier study reports results from simulation of batch air gasification and experiments in both batch and continuous up-draft fixed bed gasifier with wood and waste derived fuel and air and mixtures of air and steam. It is shown that the conversion process is faster the higher the air temperature. In particular somewhere between air temperatures of 623 K and 803 K the process behaviour changes. In fact, the devolatilisation rate is significantly increased in this region while it increases less sharply with air temperature below and above this temperature window. The temperature distribution in the bed shows less sharp gradients at high temperature (> 803 K) than at low temperatures (< 623 K). It is also showed experimentally and in fairly large scale that the use of highly preheated air for the gasification of biomass and waste derived fuels can produce - in continuous mode – relatively high yields of product syngas with relatively high fractions of combustible gases and probably also low content of tar. The efficiency of the gasification under these conditions, even when the extra heat input in the preheated agent is considered in the computation of the gasification efficiency, is shown to be comparable to that of conventional gasification techniques. The results also shows that with the use of steam in the agent, the content of hydrogen can be further increased with respect to gasification with only preheated air.In base of the results of the particle study and the gasifier study it is shown that a there exists two regimes of operation in function of the agent temperature, separated by the minimum agent temperature to guarantee spontaneous ignition regardless of the particle temperature. The value of this temperature depend on material properties and the kinetics of the reaction, thus also on the oxygen concentration. When agent temperatures below the minimum agent temperature to guarantee spontaneous ignition regardless of the particle temperature are used, the drying and devolatilisation are mainly controlled by the heat released by reactions. The heating of the fuel particles and their devolatilisation are relatively slow and the devolatilisation rate is highly oxygen dependent. In a fixed bed, the devolatilisation front rate is low and the bed is characterised by significant temperature gradients.When the agent temperature is higher than the minimum agent temperature to guarantee spontaneous ignition regardless of the particle temperature, the drying and devolatilisation are mainly controlled by the convective heat transfer from the preheated agent and the released volatiles ignite very fast even in diluted conditions. This results in very efficient heat transfer to the fuel particles. In the fixed fuel bed the process is characterized by a high devolatilisation front rate. Thus, the temperature gradients in the bed are significantly reduced and the gasification can be said to be thermally homogeneous. Thanks to high rates of heat transfer and mass conversion, the heating value of the dry produced syngas is high with high concentrations of combustible species. The ignition of the volatiles and the high temperatures all along the bed presumably contributes to the reduction of the tar content even in up-draft configurations. The high temperatures also allows for operation with reduced air – to – fuel ratios which further increased the value of the produced gas (thanks to less dilution by nitrogen).The system study presents a concept for an autothermal system including both preheating and gasification. Results from a thermodynamic analysis of such a system are reported. Autothermal operation of a thermally homogeneous gasifier is possible only in a twin component system in which the gasifier is coupled to a preheating system able to reach preheating temperatures well above the minimum agent temperature to guarantee spontaneous ignition regardless of the particle temperature. It is shown that to reach certain temperature levels of the gasification air, heat exchange between product gas and air is not enough and the preheating system has to improve the temperatures involved, for example by burning part of the produced gas in a regenerative preheater. Further, it is shown that in comparison to gasifier without such a system for additional preheating, the autothermal Thermally Homogeneous Gasification system has the ability to significantly improve the gas quality (in terms of heating value of the dry gas) without losing energy- or exergy efficiency to an appreciable extent.
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| 13. |
- Yang, Weihong, et al.
(författare)
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Performance analysis of a fixed-bed biomass gasifier using high-temperature air
- 2006
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Ingår i: Fuel processing technology. - : Elsevier BV. - 0378-3820 .- 1873-7188. ; 87:3, s. 235-245
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Tidskriftsartikel (refereegranskat)abstract
- Gasification of biomass using high-temperature agents (air/steam) has been proven to have many features superior to those of conventional gasification using low-temperature agents. In this work, an experimental fixed-bed gasifier is utilized to investigate the gasification of biomass using high-temperature air up to 1473 K. A mathematical model has been formulated for the prediction of the main chemical and physical processes and is used to study the influence of temperature, oxygen concentration and flow rate of the feed gas. Predicted gas species concentration profiles and their maximum values are in reasonable agreements with the measurements. The results show that: (a) When the temperature of feed gas is increased, a higher gasification rate, a higher ignition front rate, and higher molar fractions of fuel gases (CO, H-2 and CmHn), thus a higher LHV are obtained. (b) Increased oxygen concentration leads to higher peak values of the fuel gas concentrations, a higher gasification rate, and a larger ignition front rate.
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| 14. |
- Zock, Jan-Paul, et al.
(författare)
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Distribution and determinants of house dust mite allergens in Europe : the European Community Respiratory Health Survey II
- 2006
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Ingår i: Journal of Allergy and Clinical Immunology. - : Elsevier BV. - 0091-6749 .- 1097-6825. ; 118:3, s. 682-690
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Tidskriftsartikel (refereegranskat)abstract
- Background: Several studies in European homes have described allergen levels from the house dust mite species Dermatophagoides pteronyssinus and to a lesser extent Dermatophagoides farinae, but geographic comparisons of exposure levels and risk factors have been hampered by a lack of standardized methods. Objective: To study the distribution and determinants of the major house dust mite allergens Der p 1 and Der f 1 in 10 European countries using a common protocol. Methods: During home visits with 3580 participants of the European Community Respiratory Health Survey II from 22 study centers, mattress dust was sampled and analyzed for Der p 1, Der f 1, and Der 2 allergen. Information on housing characteristics was obtained by both observations and interview. Results: Der 1 and Der 2 allergens were detectable (>= 0.1 mu g/g) in 68% and 53% of the samples, respectively. Large differences in allergen levels between study centers were observed, and geographic patterns for Der p 1 and Der f 1 were different. Low winter temperatures reduced Der p 1 rather than Der f 1. Important risk factors for high allergen levels included an older mattress, a lower floor level of the bedroom, limited ventilation of the bedroom, and dampness for Der p 1 but not for Der f 1. Conclusion: There are large qualitative and quantitative differences of house dust mite allergen levels in Europe, which can partly be explained by geographic and housing characteristics. Clinical implications: Mite allergen exposure may be reduced by replacing the mattress regularly and increasing ventilation of the bedroom, particularly in winter.
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| 15. |
- Zock, Jan-Paul, et al.
(författare)
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Domestic use of hypochlorite bleach, atopic sensitization, and respiratory symptoms in adults
- 2009
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Ingår i: Journal of Allergy and Clinical Immunology. - : Elsevier BV. - 0091-6749 .- 1097-6825. ; 124:4, s. 731-738
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Tidskriftsartikel (refereegranskat)abstract
- BACKGROUND: Professional use of hypochlorite (bleach) has been associated with respiratory symptoms. Bleach is capable of inactivating allergens, and there are indications that its domestic use may reduce the risk of allergies in children. OBJECTIVE: To study the associations between household use of bleach and atopic sensitization, allergic diseases, and respiratory health status in adults. METHODS: We identified 3626 participants of the European Community Respiratory Health Survey II in 10 countries who did the cleaning in their homes and for whom data on specific serum IgE to 4 environmental allergens were available. Frequency of bleach use and information on respiratory symptoms were obtained in face-to-face interviews. House dust mite and cat allergens in mattress dust were measured in a subsample. Associations between the frequency of bleach use and health outcomes were evaluated by using multivariable mixed logistic regression analyses. RESULTS: The use of bleach was associated with less atopic sensitization (odds ratio [OR], 0.75; 95% CI, 0.63-0.89). This association was apparent for specific IgE to both indoor (cat) and outdoor (grass) allergens, and was consistent in various subgroups, including those without any history of respiratory problems (OR, 0.85). Dose-response relationships (P < .05) were apparent for the frequency of bleach use and sensitization rates. Lower respiratory tract symptoms, but not allergic symptoms, were more prevalent among those using bleach 4 or more days per week (OR, 1.24-1.49). The use of bleach was not associated with indoor allergen concentrations. CONCLUSION: People who clean their homes with hypochlorite bleach are less likely to be atopic but more likely to have respiratory symptoms.
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