Tar and Condensable Hydrocarbons in Indirect Gasification Systems

Biomass gasification, which is a primary process step in the production of biofuels, yields a combustible gas mixture (raw gas). This raw gas consists of a wide range of species, from permanent gases to condensable hydrocarbons, which are collectively known as tar. Considered as the Achilles heel of biomass gasification, tar starts to condense at temperatures of around 350°C, causing blockage and fouling of downstream equipment. In addition to creating operational difficulties, tar is responsible for a loss of efficiency if it is not successfully converted into permanent gases. Consequently, there is a need to understand the concepts underlying tar formation and evolution, so as to guide efforts towards reducing its yield, as well as towards facilitating its removal once formed. This requires accurate quantification of all the components of the produced raw gas to evaluate the behavior of the tar. However, as the produced gas comprise such a wide range of species, several different measurement techniques are required. In this work, the effects of catalytic materials on tar were investigated in two different systems. The observed responses motivated the development of improved measurement systems, directed to fulfilling the mass balance of the gasifier. These systems were subsequently implemented to map the behaviors of the various species of the raw gas, for a range of process parameters, and to derive a reaction scheme for all the condensable species. The concepts of primary and secondary measures were studied by introducing a catalytic material directly into the Chalmers dual fluidized bed (DFB) gasifier (primary measure) and by utilizing an additional reactor for catalytic reforming of the raw gas (secondary measure). Overall, both measures resulted in significantly decreased levels of tar. However, the composition of the remaining tar differed for the two measures, as did the added amounts of oxygen. The SPA method for tar measurement was evaluated for reproducibility, which was found to be well within 10% for the majority of the measured species. In addition, the detection limits of the SPA method have been extended throughout this work and currently extend from benzene to coronene. A high-temperature reactor, for thermal cracking of all the gas species into CO, CO2, H2, and H2O, was constructed to measure the total elemental yields of C, H, O, and N in the raw gas. This measurement allowed a mass balance for the system to be constructed, which combined with the cold gas and tar measurements, was used to obtain information regarding the yields and composition of previously unmeasured condensable species. This group contained a level of carbon similar to that found in the SPA-measured tar, thereby underlining the need for quantification through standard measurements. ii The developed measurement equipment was used to map the behavior of the gasifier under various temperatures, residence times, and steam-to-fuel ratios. The performed measurements showed that not only are the previously unmeasured species important for fulfilling the mass balance of the gasifier, but also for describing the formation of SPA-measureable tar. Subsequent modeling of the tar formation and evolution for the measured cases revealed that a substantial fraction of these species tends to form tertiary SPA tar directly, as these species are reformed. Furthermore, it was shown that additional factors, presumably related to the aging of the bed material, can significantly affect the reactivity of the gasifier and should be quantified to improve the functionality of the model

ZEITLUPE Promotes ABA-Induced Stomatal Closure in Arabidopsis and Populus.

Plants balance water availability with gas exchange and photosynthesis by controlling stomatal aperture. This control is regulated in part by the circadian clock, but it remains unclear how signalling pathways of daily rhythms are integrated into stress responses. The serine/threonine protein kinase OPEN STOMATA 1 (OST1) contributes to the regulation of stomatal closure via activation of S-type anion channels. OST1 also mediates gene regulation in response to ABA/drought stress. We show that ZEITLUPE (ZTL), a blue light photoreceptor and clock component, also regulates ABA-induced stomatal closure in Arabidopsis thaliana, establishing a link between clock and ABA-signalling pathways. ZTL sustains expression of OST1 and ABA-signalling genes. Stomatal closure in response to ABA is reduced in ztl mutants, which maintain wider stomatal apertures and show higher rates of gas exchange and water loss than wild-type plants. Detached rosette leaf assays revealed a stronger water loss phenotype in ztl-3, ost1-3 double mutants, indicating that ZTL and OST1 contributed synergistically to the control of stomatal aperture. Experimental studies of Populus sp., revealed that ZTL regulated the circadian clock and stomata, indicating ZTL function was similar in these trees and Arabidopsis. PSEUDO-RESPONSE REGULATOR 5 (PRR5), a known target of ZTL, affects ABA-induced responses, including stomatal regulation. Like ZTL, PRR5 interacted physically with OST1 and contributed to the integration of ABA responses with circadian clock signalling. This suggests a novel mechanism whereby the PRR proteins-which are expressed from dawn to dusk-interact with OST1 to mediate ABA-dependent plant responses to reduce water loss in time of stress

ZEITLUPE Promotes ABA-Induced Stomatal Closure in Arabidopsis and Populus.

Plants balance water availability with gas exchange and photosynthesis by controlling stomatal aperture. This control is regulated in part by the circadian clock, but it remains unclear how signalling pathways of daily rhythms are integrated into stress responses. The serine/threonine protein kinase OPEN STOMATA 1 (OST1) contributes to the regulation of stomatal closure via activation of S-type anion channels. OST1 also mediates gene regulation in response to ABA/drought stress. We show that ZEITLUPE (ZTL), a blue light photoreceptor and clock component, also regulates ABA-induced stomatal closure in Arabidopsis thaliana, establishing a link between clock and ABA-signalling pathways. ZTL sustains expression of OST1 and ABA-signalling genes. Stomatal closure in response to ABA is reduced in ztl mutants, which maintain wider stomatal apertures and show higher rates of gas exchange and water loss than wild-type plants. Detached rosette leaf assays revealed a stronger water loss phenotype in ztl-3, ost1-3 double mutants, indicating that ZTL and OST1 contributed synergistically to the control of stomatal aperture. Experimental studies of Populus sp., revealed that ZTL regulated the circadian clock and stomata, indicating ZTL function was similar in these trees and Arabidopsis. PSEUDO-RESPONSE REGULATOR 5 (PRR5), a known target of ZTL, affects ABA-induced responses, including stomatal regulation. Like ZTL, PRR5 interacted physically with OST1 and contributed to the integration of ABA responses with circadian clock signalling. This suggests a novel mechanism whereby the PRR proteins-which are expressed from dawn to dusk-interact with OST1 to mediate ABA-dependent plant responses to reduce water loss in time of stress

Utagerande barn i förskolan : En kvalitativ studie om förskollärares bemötande av barn med utagerande beteende

Syftet med denna studie är att skapa en ökad kunskap om vilka strategier som används av verksamma förskollärare i arbetet med att stötta utagerande barn i 4 till 5-årsåldern. Syftet är också att undersöka varför dessa strategier används. De forskningsfrågor som den kvalitativa studien utgår ifrån är: Vilka strategier beskriver förskollärare att de använder sig av i bemötandet av utagerande barn och varför? Vilka faktorer påverkar förskollärares möjligheter och förutsättningar i att stödja utagerande barn i sin verksamhet? Fyra verksamma förskollärare har intervjuats för att få svar på forskningsfrågorna. Resultatet visar att förskollärarna främst använder sig av ett lågaffektivt bemötande av utagerande barn. De orsaker som förskollärarna menar ligger bakom ett utagerande beteende ligger främst inom barnet själv. Resultatet visar också att det inte är optimala förutsättningar för att bemöta dessa barn på det sätt förskollärarna önskar och att de faktorer som påverkar förutsättningarna negativt till största delen inte kan påverkas av förskollärarna själva

Tar and Condensable Hydrocarbons in Indirect Gasification Systems

Biomass gasification, which is a primary process step in the production of biofuels, yields a combustible gas mixture (raw gas). This raw gas consists of a wide range of species, from permanent gases to condensable hydrocarbons, which are collectively known as tar. Considered as the Achilles heel of biomass gasification, tar starts to condense at temperatures of around 350\ub0C, causing blockage and fouling of downstream equipment. In addition to creating operational difficulties, tar is responsible for a loss of efficiency if it is not successfully converted into permanent gases. Consequently, there is a need to understand the concepts underlying tar formation and evolution, so as to guide efforts towards reducing its yield, as well as towards facilitating its removal once formed. This requires accurate quantification of all the components of the produced raw gas to evaluate the behavior of the tar. However, as the produced gas comprise such a wide range of species, several different measurement techniques are required. In this work, the effects of catalytic materials on tar were investigated in two different systems. The observed responses motivated the development of improved measurement systems, directed to fulfilling the mass balance of the gasifier. These systems were subsequently implemented to map the behaviors of the various species of the raw gas, for a range of process parameters, and to derive a reaction scheme for all the condensable species.The concepts of primary and secondary measures were studied by introducing a catalytic material directly into the Chalmers dual fluidized bed (DFB) gasifier (primary measure) and by utilizing an additional reactor for catalytic reforming of the raw gas (secondary measure). Overall, both measures resulted in significantly decreased levels of tar. However, the composition of the remaining tar differed for the two measures, as did the added amounts of oxygen.The SPA method for tar measurement was evaluated for reproducibility, which was found to be well within 10% for the majority of the measured species. In addition, the detection limits of the SPA method have been extended throughout this work and currently extend from benzene to coronene. A high-temperature reactor, for thermal cracking of all the gas species into CO, CO2, H2, and H2O, was constructed to measure the total elemental yields of C, H, O, and N in the raw gas. This measurement allowed a mass balance for the system to be constructed, which combined with the cold gas and tar measurements, was used to obtain information regarding the yields and composition of previously unmeasured condensable species. This group contained a level of carbon similar to that found in the SPA-measured tar, thereby underlining the need for quantification through standard measurements.iiThe developed measurement equipment was used to map the behavior of the gasifier under various temperatures, residence times, and steam-to-fuel ratios. The performed measurements showed that not only are the previously unmeasured species important for fulfilling the mass balance of the gasifier, but also for describing the formation of SPA-measureable tar. Subsequent modeling of the tar formation and evolution for the measured cases revealed that a substantial fraction of these species tends to form tertiary SPA tar directly, as these species are reformed. Furthermore, it was shown that additional factors, presumably related to the aging of the bed material, can significantly affect the reactivity of the gasifier and should be quantified to improve the functionality of the model

Gasification Reaction Pathways of Condensable Hydrocarbons

Dual fluidized bed (DFB) gasification of biomass generates numerous species with large differences in-size and boiling point. At the heavier (tar) end, the produced species range from benzene to coronene: In this work, a method for elucidating the pathways of tar evolution is, applied to previously presented measurements that satisfy the carbon, balance of the Chalmers 2-4-MW DFB gasifier. In addition to quantifying the cold gas and tar, the measurements yield information regarding the amount and C, O, H composition of unknown condensable species (UCS). The reaction pathways were identified by means of fitting a model to the performed measurements. The employed solver varies freely the reaction rate coefficients of three global reactions (mimicking dissociation and reactions with hydrogen and steam) per modeled group, as well as the carbon distribution coefficients within a predefined reaction scheme. The mature tar (excluding primary tar) spectrum is divided into phenols, furans, benzene, naphthalene, pyrene, and one-, two-, and three-ring aromatic components. In addition, UCS that are considered to contain primary tar are divided into four subgroups, to encompass two levels of reactivity with varying composition. Ultimately, the solver converges, yielding a reaction scheme that is based on the findings of earlier works and that describes the creation of mature tar from UCS. Furthermore, the importance of individual reaction routes is discerned for the pertinent measurements. Thus, it is demonstrated that the maturation of secondary tar species (e.g., toluene and phenol) is not in itself sufficient to describe the formation of the tar spectrum

Polisens bemötande : Polismannens upplevelse i bemötandet med rattfylleristen

Att bilkörning och alkohol inte hör ihop kan nog de flesta skriva under på. Vad vi kan konstatera via statistik är att förare som åker dit för rattfylla har ökat. I Västerbottens län vid polismyndigheten i Skellefteå påbörjades ett projekt 1999 tillsammans med beroendeenheten samt socialtjänsten som kom att kallas ”Skelleftemodellen”. Den gick ut på att erbjuda personer som gjort sig skyldig till rattfylleri hjälp och stöd att ta itu med sina alkoholproblem. Syftet med detta projekt var att minska antalet påverkade förare i trafiken genom att minska återfallen. Modellen går idag under namnet SMADIT och är riksomfattande. Vi har i vårt arbete valt att fokusera på den enskilda polismannens bemötande med den misstänkta rattfylleristen. Hur upplever polismannen sitt bemötande med rattfylleristen samt vilka faktorer påverkar polismannens bemötande? Som vi ser det handlar det till viss del om att kunna sälja in en produkt till rattfylleristen, att få denna att tacka ja till hjälp med sitt eventuella alkoholmissbruk. Den enskilda polisens bemötande spelar, utifrån vårt arbete, en stor roll för om rattfylleristen tackar ja eller nej till fortsatt hjälp

Gasification Reaction Pathways of Condensable Hydrocarbons

Dual fluidized bed (DFB) gasification of biomass generates numerous species with large differences in-size and boiling point. At the heavier (tar) end, the produced species range from benzene to coronene: In this work, a method for elucidating the pathways of tar evolution is, applied to previously presented measurements that satisfy the carbon, balance of the Chalmers 2-4-MW DFB gasifier. In addition to quantifying the cold gas and tar, the measurements yield information regarding the amount and C, O, H composition of unknown condensable species (UCS). The reaction pathways were identified by means of fitting a model to the performed measurements. The employed solver varies freely the reaction rate coefficients of three global reactions (mimicking dissociation and reactions with hydrogen and steam) per modeled group, as well as the carbon distribution coefficients within a predefined reaction scheme. The mature tar (excluding primary tar) spectrum is divided into phenols, furans, benzene, naphthalene, pyrene, and one-, two-, and three-ring aromatic components. In addition, UCS that are considered to contain primary tar are divided into four subgroups, to encompass two levels of reactivity with varying composition. Ultimately, the solver converges, yielding a reaction scheme that is based on the findings of earlier works and that describes the creation of mature tar from UCS. Furthermore, the importance of individual reaction routes is discerned for the pertinent measurements. Thus, it is demonstrated that the maturation of secondary tar species (e.g., toluene and phenol) is not in itself sufficient to describe the formation of the tar spectrum

Assessment of the Solid-Phase Adsorption Method for Sampling Biomass-Derived Tar in Industrial Environments

Low-temperature gasification of biomass is a primary process step for production of biofuels or electricity using gas-fired engines or turbines. In addition to the desired product gas, the raw gas produced through gasification inevitably contains condensable hydrocarbons, known collectively as tar. The amount and composition of the tar have relevance for the efficiencies of the downstream processes. Tar can be measured using both online and off-line methods. However, many of these methods currently lack information regarding their implementation and accuracy levels for large-scale systems. In this work, the Solid-Phase Adsorption (SPA) method for measuring tar in industrial applications is evaluated. The individual steps of the method were examined for their effects on the overall performance of the analysis. Sample collection was found to be the most prominent source of error, and this was mainly due to human factors. Omitting to determine the temperature and pressure of the sampled gas contributed to this error, as the sampled volume of gas under normal conditions could not be correctly calculated. Inconsistencies in the treatment and storage of the collected samples were shown to affect the more volatile species with boiling points similar to that of benzene. The gas chromatography (GC) analysis was performed with satisfying accuracy. However, the reliability of the estimations of the average composition and dew-point of the tar mixture were dependent upon the amount of the identified species. The current implementation of the SPA method yields values with a relative standard deviation within 10% for the majority of the compounds in a given sample. However, in line with the result of previous studies, the tar species with boiling points between those of benzene and xylene (i.e., the BTX compounds) were measured with a lower accuracy than those of heavier tars