Carbon Recovery in A Dual Fluidized Bed Gasifier

As the concept of a circular economy gains acceptance and awareness of climate change and its disastrous consequences increases, the ways in which we produce the carbon-based goods upon which so much of our economy depends need to change. Society must end its reliance on fossil carbon resources and shift to renewable sources that enable the establishment of a carbon cycle. Plastic and biogenic wastes should become our main sources of carbon for new materials. This would simultaneously address the critical issues related to the current deficit of recycling and robust collection systems, which currently entails immense loss of value and represents a threat to the environment. The biomass waste would also compensate for inevitable leakage from the carbon cycle and enable overall-negative CO2 emissions.Technologies are needed that are capable of extracting efficiently the carbon from these new sources. This will be challenging given the expected heterogeneous nature of such sources. In this context, the Dual Fluidized Bed (DFB) gasification process is an attractive technology owing to its flexibility. This thesis investigates the possibility for carbon recovery in DFB gasification processes. The various configurations in which a DFB gasification unit can be designed and operated are discussed, with respect to their carbon balances. In addition, as the valorization of waste materials is a critical aspect of the circular economy, the use of such materials in DFB processes, beyond the consideration of carbon extraction, is considered. These materials may possess properties that can enhance the carbon recovery of the existing process or around which an entire process can be devised.To illustrate the challenges related to optimizing carbon recovery in DFB gasification processes, and the possible uses and impacts of waste materials in those processes, experiments were carried out in the Chalmers University of Technology DFB gasifier. The first set of experiments was aimed at increasing carbon recovery in the form of valuable products in a regular DFB gasifier by increasing the catalytic activity of the bed towards the reforming of non-valuable compounds, in this case tar. This was achieved by circulating the flue gas ash, which is a waste material produced by the process, back into the system. The second set of experiments was designed to investigate the feasibility and carbon balance of Chemical-Looping Gasification (CLG), which is a DFB gasification technology whereby an oxygen carrier produces the heat needed for the gasification reaction. The CLG technology, which potentially enables carbon recovery into a single, undiluted stream, was explored for two cases. The first case involved CLG of biomass using a waste from the steel-making industry as the oxygen carrier. The second case entailed CLG of Automotive Shredder Residue (ASR), a plastic-containing waste the high ash content of which leads to the formation of an oxygen-carrying bed material.The results presented in this thesis reveal that the fate of the CO2 in the raw gas is a critical issue, both in regular DFB gasification with an active bed and in CLG. As the activity of the bed material increases, as achieved by circulating the flue gas ash, the carbon is transferred from both non-valuable and valuable products to CO2 in the raw gas, owing to the action of the water-gas shift. In the case of CLG, the oxygen transport from the bed material results in significant oxidation of H2 and CO, predominantly, thereby transferring carbon to CO2, which becomes the main carbon output from the process. However, the oxygen transport is also identified as the key parameter for solving a crucial issue in CLG, i.e., the achievement of complete conversion of the fuel in the fuel reactor. The gasification of ASR in the Chalmers gasifier led to an oxygen-carrying bed, which may facilitate operation in CLG mode, provided that the oxygen transport level is increased. The possibilities to achieve this are discussed in this thesis. In terms of the selection and operation of DFB gasification processes, the results of this work have the following implications: (i) for regular DFB gasification, the catalytic activity and temperature levels should be carefully selected, based on the comparison of the energy cost of separation of the CO2 from the raw gas on the one hand, and the destruction or valorization of non-valuable products on the other hand; and (ii) for CLG, the process should be designed to maximize the conversion of the fuel in the fuel reactor, while minimizing the oxidation of the raw gas. The viability of CLG in terms of producing simultaneously chemical precursors and CO2 that is ready for sequestration should be assessed by comparing with the alternative process, i.e., DFB gasification with oxyfuel combustion

Strategies for Complete Recovery of Carbon in Dual Fluidized Bed Gasifiers

To establish a circular economy and curtail our dependency on fossil resources, technologies are needed to extract carbon from biomass and plastic waste. Dual fluidized bed (DFB) gasification is a carbon-extracting technology that offers flexibility in terms of its inputs, outputs, design, and operational conditions. This thesis investigates the carbon distribution produced by DFB gasification and explores the possibilities to achieve total carbon recovery. The various configurations under which DFB gasification can be designed and operated to facilitate the total recovery of carbon are compared on a theoretical basis. Thus, insights into the carbon distribution and energy demands of each configuration are obtained. A method to increase the catalytic activity of the bed in the DFB gasifier so as to enhance the recovery of valuable forms of carbon is experimentally demonstrated, based on the use of a waste generated from the process. However, it is shown that increasing the catalytic activity is not always beneficial for carbon recovery. The development of oxygen transport along with the catalytic activity, a phenomenon that had been reported but never investigated, is here demonstrated. Taking advantage of the oxygen transport properties of certain bed materials to facilitate the total recovery of carbon is the basis for the chemical-looping gasification (CLG) technology, a DFB gasification configuration. The parameters that affect fuel conversion, an essential aspect of CLG, are investigated for a plastic waste that generates its own oxygen-carrying bed material. Oxygen transport is shown to be the most important parameter for the process. Based on these experiments, the numerous challenges associated with CLG are discussed. Finally, a process through which negative-emissions steel is produced, based on the integration of DFB gasification into a CLG configuration with direct reduction (DR) of iron, is proposed and evaluated. Compared with the traditional steelmaking route and alternative DR routes, the proposed process is found to be the most-competitive for carbon prices >60 €/tCO2, which corresponds to both the price for CO2 emissions and the revenue associated with negative emissions. Most of the data used in this work were obtained from experiments conducted at a scale relevant to the industry

Production of negative-emissions steel using a reducing gas derived from dfb gasification

A dual fluidized bed (DFB) gasification process is proposed to produce sustainable reducing gas for the direct reduction (DR) of iron ore. This novel steelmaking route is compared with the established process for DR, which is based on natural gas, and with the emerging DR technology using electrolysis-generated hydrogen as the reducing gas. The DFB-DR route is found to produce reducing gas that meets the requirement of the DR reactor, based on existing MIDREX plants, and which is produced with an energetic efficiency comparable with the natural gas route. The DFB-DR path is the only route considered that allows negative CO2 emissions, enabling a 145% decrease in emissions relative to the traditional blast furnace–basic oxygen furnace (BF–BOF) route. A reducing gas cost between 45–60 EUR/MWh is obtained, which makes it competitive with the hydrogen route, but not the natural gas route. The cost estimation for liquid steel production shows that, in Sweden, the DFB-DR route cannot compete with the natural gas and BF–BOF routes without a cost associated with carbon emissions and a revenue attributed to negative emissions. When the cost and revenue are set as equal, the DFB-DR route becomes the most competitive for a carbon price >60 EUR/tCO2

Dual Fluidized Bed Gasification Configurations for Carbon Recovery from Biomass

Techniques that produce chemicals and fuels from sustainable carbon sources will have to maximize the carbon recovery to support circularity. In dual fluidized bed (DFB) gasification, to facilitate carbon recovery, the CO2\ua0from the flue gas can be concentrated using pure oxygen as an oxidant. The heat required by the process can also be provided electrically or by oxidizing an oxygen-carrying bed material, rather than combusting part of the char, thereby concentrating all of the carbon in the syngas. In this work, the three configurations of oxyfuel, electrical, and chemical-looping gasification (CLG) are compared to each other, as well as to the standard or “air” configuration, which corresponds to the combustion of char with air and the separation of CO2\ua0from both the flue gas and syngas. The configurations are compared based on their carbon distributions and energy demands for CO2\ua0separation. We show that the air and oxyfuel configurations lead to similar carbon distributions, whereas the CLG configuration gives the lowest carbon recovery in the form of an end product. The oxyfuel and CLG configurations show the lowest energy demands for CO2\ua0separation, while the air configuration exhibits the highest. The electrical configuration has the lowest potential to benefit from heat integration to cover this energy demand. An investigation into the optimal gasification temperature for the air and oxyfuel configurations shows that there is no driver for operation at high temperatures

Circular use of plastics-transformation of existing petrochemical clusters into thermochemical recycling plants with 100% plastics recovery

Plastics represent a serious waste-handling problem, with only 10% of the plastic waste (PW) generated world-wide being recycled. The remainder follows a linear economy model, involving disposal or incineration. Thermochemical recycling provides an opportunity to close the material cycle, and this work shows how this can be achieved using the existing petrochemical infrastructure. The transformation of a generic petrochemical cluster based on virgin fossil feedstocks into a cluster that is based on PW has the following proposed sequence: (1) the feedstock is partially replaced (45% on carbon basis) by PW; (2) the feedstock is totally replaced by PW; (3) the process undergoes electrification; and (4) oxy-combustion and carbon capture and storage are introduced to achieve 100% carbon recovery in the form of monomers or permanent storage. An alternative transformation pathway that includes the introduction of biomass is also considered. The energy and carbon balances of the proposed implementation steps are resolved, and cost estimates of the savings related to the feedstock and required investments are presented. The main conclusion drawn is that switching the feedstock from virgin fossil fuels to PW (Implementation steps 1 and 2) confers economic advantages. However, the subsequent transformation steps (Implementation steps 3 and 4) can only be justified if a value is assigned to the environmental benefits, e.g., CO2 savings, increased share of biogenic carbon in plastic products, increasing recycling quotas, and/or the potential of the process to compensate for the intermittency of renewable power. It is also discussed how utilisation of the diverse compositions of PW streams by additional processes can meet the other demands of a chemical cluster

Bim and Mcl-1 exert key roles in regulating JAK2V617F cell survival

<p>Abstract</p> <p>Background</p> <p>The JAK2^V617Fmutation plays a major role in the pathogenesis of myeloproliferative neoplasms and is found in the vast majority of patients suffering from polycythemia vera and in roughly every second patient suffering from essential thrombocythemia or from primary myelofibrosis. The V617F mutation is thought to provide hematopoietic stem cells and myeloid progenitors with a survival and proliferation advantage. It has previously been shown that activated JAK2 promotes cell survival by upregulating the anti-apoptotic STAT5 target gene Bcl-xL. In this study, we have investigated the role of additional apoptotic players, the pro-apoptotic protein Bim as well as the anti-apoptotic protein Mcl-1.</p> <p>Methods</p> <p>Pharmacological inhibition of JAK2/STAT5 signaling in JAK2^V617Fmutant SET-2 and MB-02 cells was used to study effects on signaling, cell proliferation and apoptosis by Western blot analysis, WST-1 proliferation assays and flow cytometry. Cells were transfected with siRNA oligos to deplete candidate pro- and anti-apoptotic proteins. Co-immunoprecipitation assays were performed to assess the impact of JAK2 inhibition on complexes of pro- and anti-apoptotic proteins.</p> <p>Results</p> <p>Treatment of JAK2^V617Fmutant cell lines with a JAK2 inhibitor was found to trigger Bim activation. Furthermore, Bim depletion by RNAi suppressed JAK2 inhibitor-induced cell death. Bim activation following JAK2 inhibition led to enhanced sequestration of Mcl-1, besides Bcl-xL. Importantly, Mcl-1 depletion by RNAi was sufficient to compromise JAK2^V617Fmutant cell viability and sensitized the cells to JAK2 inhibition.</p> <p>Conclusions</p> <p>We conclude that Bim and Mcl-1 have key opposing roles in regulating JAK2^V617Fcell survival and propose that inactivation of aberrant JAK2 signaling leads to changes in Bim complexes that trigger cell death. Thus, further preclinical evaluation of combinations of JAK2 inhibitors with Bcl-2 family antagonists that also tackle Mcl-1, besides Bcl-xL, is warranted to assess the therapeutic potential for the treatment of chronic myeloproliferative neoplasms.</p

Effect of ash circulation on the performance of a dual fluidized bed gasification system

During gasification of biomass, ash forming elements are released from the fuel and some of these elements can have a positive impact on the quality of the gas produced. In a dual fluidized bed (DFB) gasifier, a significant amount of these components are found in the fly ash from the gasification and combustion reactors. In order to increase carbon conversion and bed material recovery, these streams are generally circulated back to the combustor for the raw gas fly ash and in some cases to the gasifier for the flue gas fly ash. The impact on the gasification performance has, however, not been investigated. Circulation of flue gas coarse ash was carried out in the Chalmers gasifier, with the aim of assessing the impact on gas quality, in particular in term of tar yields, and how it relates to the flow and properties of ash streams. The coarse ash was first enhanced by an injection of untreated olivine in a fine particle size and was then recirculated, yielding a direct decrease in tar concentration. This effect persisted after the recirculation and the bed activity was seen to increase with time, at a higher rate than a reference aging experiment. Both the internal bed material cycle and the external fly ash loop were found to get enriched in ash components, which was linked to the activity gains observed. These results show the potential of continuous fly ash recirculation as an activity enhancer in industrial dual fluidized bed gasification systems

Development of Oxygen Transport Properties by Olivine and Feldspar in Industrial-Scale Dual Fluidized Bed Gasification of Woody Biomass

In dual fluidized bed (DFB) gasification, the interaction of the bed material with the fuel ash leads to the development of a bed catalytic activity toward tar-abating reactions. However, the formation of ash layers may also be detrimental to the process, especially in terms of the uncontrolled transport of oxygen from the combustor to the gasifier. A few previous studies investigating the development of catalytic activity in bed materials have also reported the development of oxygen transport, although the latter was not the focus of these studies. This work verifies that olivine and feldspar, which are bed materials with limited and no intrinsic oxygen transport capacities, respectively, develop the capacity to transport oxygen by interacting with the fuel ash. We correlate this development in oxygen transport to the development of bed catalytic activity. Our results imply that the volatile species that are released by the bed material to the gas phase in the gasifier contribute to the developed oxygen transport. Sulfur is proposed as one of the components of these volatile species, and its potential contribution is investigated. For feldspar, the results support the notion that sulfur is involved in the transport of oxygen, both as a volatile species and as a species remaining within the ash layer. The results also suggest that other species, including volatile ones, are involved. These aspects are investigated based on experimental results obtained from the Chalmers gasifier - a semi-industrial-scale DFB gasifier - and are isolated in laboratory-scale experiments