Energy performance of Power-to-Liquid applications integrating biogas upgrading, reverse water gas shift, solid oxide electrolysis and Fischer-Tropsch technologies

Marco Marchese, Emanuele Giglio, Massimo Santarelli, Andrea Lanzini
2020 Energy Conversion and Management: X  
Please cite this article as: M. Marchese, E. Giglio, M. Santarelli, A. Lanzini, Energy performance of Power-to-Liquid applications integrating biogas upgrading, reverse water gas shift, solid oxide electrolysis and Fischer-Tropsch technologies, Energy Conversion and Management: X (2020), doi: https://doi.Abstract 11 Power-to-liquid (P2L) pathways represent a possible solution for the conversion of carbon 12 dioxide into synthetic value-added products. The present work analyses different
more » ... s different power-to-liquid 13 options for the synthesis of Fischer-Tropsch (FT) fuels and chemicals. The FT section is integrated 14 into a complete carbon capture and utilization route. The involved processes are a biogas upgrading 15 unit for CO 2 recovery, a reverse water gas shift, a solid oxide electrolyser and a Fischer-Tropsch 16 reactor. 17 The upgrading plant produces about 1 ton/h of carbon dioxide. The recovered CO 2 is fed to 18 either a reverse water gas shift reactor or a solid oxide electrolysis unit operating in co-electrolysis 19 mode for the generation of syngas. The produced syngas is fed to a Fischer-Tropsch reactor at 501 20 K and 25 bar for the synthesis of the Fischer-Tropsch products, which are further separated into 21 different classes based on their boiling point to yield light gas, naphtha, middle distillates, light 22 waxes and heavy waxes. The developed process model uses a detailed carbide kinetic model to 23 describe the formation of paraffins and olefins based on real experimental data. The effect of 24 Fischer-Tropsch off-gas recirculation has been studied against a one-through option. Finally, 25 energy integration of each configuration plant is provided. Results from process simulations show 26 that the best model configurations reach a plant efficiency of 81.1% in the case of solid oxide 27 electrolyser as syngas generator, and 71.8% in the case of reverse water gas shift option, with a 28 global carbon reduction potential of 79.4% and 81.7%, respectively. Abbreviations ASR Area-specific resistance (Ωcm 2 ) ATR Auto thermal reactor CCU Carbon capture and utilization CGO Gallium-doped ceria CPOX Partial oxidation CRP Carbon reduction potential DAC Direct air capture FT Fischer-Tropsch LHV Low Heating Value LSC Lanthanum strontium cobaltite MEA Monoethanolamine Ni Nickel OCV Open circuit voltage P2G Power to gas P2L Power to liquid RR Recirculation rate RU Reactant utilization RWGS Reverse water gas shift SMR Steam methane reforming SOE Solid oxide electrolyser SOEC Solid oxide electrolysis cell TN Thermoneutral YSZ Yttria-stabilized zirconia 4 35 1 Introduction 36 Since the Paris agreement of the COP21, increasing effort has been spent in implementing 37 solutions that can reduce greenhouse gases emissions towards the environment. Thus, alongside 38 the deployment of renewable energy technologies, the study of novel applications that can store 39 such energy meanwhile utilizing CO 2 of industrial processes as raw material has gained much 40 attention [1]. 41 Means for on-site carbon dioxide reuse include power-to-gas (P2G) and power-to-liquid (P2L) 42 applications. These concepts consider exploiting CO 2 as a useful commodity, shifting it from a 43 low-value resource to high-value product, meanwhile storing energy from renewable electricity 44 [2,3]. In the framework of P2G and P2L routes, different steps are required to transform carbon 45 dioxide into further products. CO 2 can be captured from the flue gas of industrial and energy plants 46 burning fossil fuels through highly energy-intensive chemical or physical capture processes, 47 upgrading of biogas, or even from the air with direct air capture technologies (DAC) [4-6]. 48 Furthermore, the captured molecule can be transformed into synthetic products through 49 thermochemical or electrochemical processes. These processes enable methane and syngas 50 synthesis in the case of P2G, while P2L final outcomes can include Fischer-Tropsch fuels and 51 chemicals, methanol, dimethyl ether (DME) and formic acid [7-9]. 52 In the present work, we focus on P2L chains presenting a Fischer-Tropsch reactor (FT). The 53 FT technology has risen in scientific interest as an effective application to be inserted into carbon 54 capture and utilization (CCU) plants, capable of delivering the so-called syncrude [10]: a broad 55 mixture of synthetic hydrocarbons that can replace oil extracted from the ground. Syncrude 56 accounts for hydrocarbons ranging from carbon number C 1 to C 80+ , in the form of n-paraffins, α-57 olefins, with a lower content of alcohols and aromatic compounds [11]. Hence, the great potential 58 of the FT processes is the displacement opportunity of wide-ranging hydrocarbons of fossil origin. 5 59 Transportation sector utilizing gasoline, diesel and jet fuels, and the chemical industry utilizing 60 long-chain hydrocarbons as a feedstock for chemical products can be inserted into a circular 61 economy concept, where the use of fossil material is avoided in favour of recycled CO 2 [12,13]. 62 The input to the Fischer-Tropsch process is synthesis gas, namely syngas that is a mixture of 63 CO 2 , H 2 , CO and H 2 O mainly. To obtain it, the captured carbon dioxide can be converted into CO 64 through thermochemical or electrochemical devices. Thus, reverse water gas shift reactors 65 (RWGS), autothermal reactors (ATR), partial oxidation reactors (CPOX), steam methane 66 reformers (SMR) or solid oxide electrolysis cells (SOEC) can be employed. Specifically, RWGS 67 and SOEC can directly convert carbon dioxide to CO with the aid of hydrogen or steam, whereas 68 CPOX, ATR and SMR use methane (or other hydrocarbons) for the syngas generation [14,15]. 69 Once the syngas is fed to the Fischer-Tropsch reactor, the description of the FT products 70 distribution becomes a key aspect in evaluating the whole system performance. Different kinetic 71 approaches can be used. The overall FTS synthesis can be described by a single equation like a 72 modification of the Anderson-Flory-Shultz theory or power-law kinetics [16]. Selectivity models 73 can provide information on the reactants consumption rates and specific groups of FT compounds 74 [17]. Finally, mechanistic kinetic models allow for the identification of reactants consumption 75 rates as well as products generation rates. A recent review comprising the FT kinetics, beyond the 76 scope of this work, is provided by Santos et al. [18]. A different amount of information can be 77 extracted from the PtL models, depending on the modelling approach employed for the FTS. For 78 instance, Cinti et al. [19] applied in their work on SOEC+FT the AFS distribution at a fixed chain 79 growth probability α=0.94, with a modification to account for olefins and paraffins formation. In 80 this regard, they could identify 5 main molecules representative of the paraffins, 4 for the olefins 81 and a clustered molecule to account for C 30+ waxes. Fazeli et al. [20] employed a one-step reaction 82 rate to describe the FT synthesis, with weight distribution based on lumped species experimental 83 data. Selvatico et al. [21], instead, used detailed kinetics for olefins and paraffins, but only up to 6 84 carbon number C 30 , thus excluding the heaviest FT fractions of interest if targeting long-chain 85 hydrocarbons like C 30+ waxes. 86 As far as P2L routes are concerned, different solutions have been proposed in literature. Herz 87 et al. [22] created a possible SOEC+FT process model with SOE stacks operating in co-electrolysis 88 mode, calculating a maximum process efficiency of 68.1%. Rafiee et al. [23] reached a carbon 89 efficiency (i.e., efficiency of carbon utilization) of 68.2% for a system that captured CO 2 from flue 90 gases, combining it together with an ATR and an FT reactor. Vidal et al. [24] studied the 91 integration of a DAC with low temperature electrolysis, RWGS and FT reactors, reaching 94% 92 carbon efficiency and 47% plant efficiency. In fact, different studies on the integration of FT 93 reactors with syngas generation units for P2L systems can be found. However, to the best of our 94 knowledge, not many studies include a full process integrated with the carbon capture one, and 95 seldom focusing on a detailed products separation analysis, too. For instance, Tagomori et al. [25] 96 stated the need of properly designing and evaluating the process of distillation of the FT products. 97 In the present work, we provide a P2L system analysis from the capture of CO 2 to the generation 98 and separation of the synthetic products. We investigate the coupling between a solvent-based 99 biogas upgrading process and the Fischer-Tropsch reactor with two concurrent technologies for 100 syngas generation: one proven and commercially available technology like the RWGS reactor; one 101 less commercialized technology but with high CO 2 conversion potential like the SOEC under co-102 electrolysis. To the authors knowledge, only one report (Comidy et al. [26]) is available in the 103 open literature that provides some insight on the direct comparison of a P2L with RWGS against 104 a P2L with SOEC technologies feeding a Fischer-Tropsch reactor. However, their analysis focused 105 on the production of light FT fuels for on-board consumption on aircraft carriers. Furthermore, 106 they stated that no experimental validation of any of their employed technologies was assessed. In 107 this work, we include a mechanistic kinetic description based on the carbide FTS mechanisms of 108 paraffins and olefins up to carbon number C 80 , experimentally validated for the Fischer-Tropsch 7 109 reactor and presented in another research work (Marchese et al. [27]). Specifically, the model 110 provides detailed information about the production rate of each of the heaviest FT fraction 111 compounds, that are generally clustered into one single C 30+ pseudo-component [21], from which 112 exact FTS heat of reaction is evaluated. Finally, our model includes in the analysis two distillation 113 towers: the first needed to separate waxes, the second to distillate the lighter FT products. With 114 this work, we seek to maximize the synthesis of middle distillates and waxes fractions, maximize 115 the CO 2 conversion and minimize the thermal requirements of the process. Each system is 116 thermally integrated allowing a sensible reduction in the thermal energy needs of the highly 117 energy-intensive MEA process. Lastly, considerations about the technology readiness level of each 118 device are given. 119 2 Methodology 120 2.1 Plant layout 121 A biogas upgrading unit based on chemical scrubbing and separating CO 2 from CH 4 was chosen 122 as the source for carbon dioxide. Two different process configurations were then studied, with 123 variation in the syngas generation unit. The recovered CO 2 from the biogas upgrading section was 124 fed to either an RWGS reactor or a SOEC stack operating under co-electrolysis conditions for the 125 synthesis gas generation. In the case of the RWGS solution, a low-temperature electrolysis unit 126 was also inserted to deliver the required hydrogen for the process. The resulting syngas was 127 dehydrated and supplied to a Fischer-Tropsch reactor for the syncrude synthesis. The syncrude 128 was further upgraded into several chemical classes, based on their boiling point: gas, naphtha, 129 middle distillates, light waxes and heavy waxes. To increase the targeted Fisher-Tropsch products 130 yield, each configuration also accounted for a recirculation solution of the Fischer-Tropsch off-131 gases back to the syngas generation unit inlet. The conditions at 0% recirculation rate (0% RR) of 132 the off-gases were considered as the reference. Finally, the effect of gas pressurization before the
doi:10.1016/j.ecmx.2020.100041 fatcat:24sbftv7u5f6fbwfstofgb3hwu