Abstract
Biomass with a large amount of moisture is well-suited to be processed by supercritical water gasification, SCWG. The precipitation of inorganics, together with char formation and re-polymerization, can cause reactor plugging and stop the process operations. When plugging occurs, sudden injections of relatively large mass quantities take place, influencing the mass flow dynamics significantly in the process. Reactor plugging is a phenomenon very well observed during SCWG of industrial feedstock, which hinders scale-up initiatives, and it is seldom studied with precision in the literature. The present study provides an accurate evaluation of continuous tubular reactor dynamics in the event of sudden injections of water. An interpretation of the results regarding water properties at supercritical conditions contributes to comprehending mass and heat transfer when plugging occurs. Experiments are then compared to SCWG of a biomass sample aiming to give key insights into heat transfer and fluid dynamics mechanisms that could help develop operational and control strategies to increase the reliability of SCWG. In addition, a simplified model is presented to assess the effect of material integrity on burst-event likelihood, which states that SCWG is safe to operate, at 250 bar and 610 °C, in tubular reactors made of 0.22 wall thickness-to-diameter ratio Inconel-625 with superficial microfractures smaller than 30 µm. We also suggest improvement opportunities for the safety of SCWG in continuous operation mode.
Highlights
The world population is forecasted to be over 9 billion by 2040 [1], and sustainable development measures are needed
Supercritical water gasification of biomass is currently limited to small scales due to the challenges of complicated process kinetics, salt corrosion and plugging, and wet biomass feed handling, especially in continuous mode
A better understanding of the continuous process is required to address these issues within the supercritical water medium, which dominates the fluid dynamics of the system
Summary
The world population is forecasted to be over 9 billion by 2040 [1], and sustainable development measures are needed. One of the most important aspects of sustainable development is reducing the adverse outcomes of electricity production processes [2]. The energy need for the same population is increasing, and by 2040 it is estimated to be 150 trillion megawatt-hours per year [3]. It is reported that the yearly biomass availability could be estimated to be in the range of the equivalent of 1011 tons of oil [4]. There are still many different industrial processes dealing with biomass, and large quantities of organic waste or industrial streams are available for energy production without deforestation. Biological processes need long retention times to give favorable conversions to bio-methane [7], which is a disadvantage to fully meeting the future demand of biogas
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