9.8B shows the response curve with respect to sulfate and MWE concentrations. This would indicate that pH values above 7.5 were beyond the range required for the growth of SRB.įig. However, a subsequent increase resulted in a significant decrease in sulfate reduction. Similarly, an increase in pH from 6.5 to 7.5 resulted in an increase in sulfate reduction.
However, a further increase in sulfate concentration resulted in a decrease in sulfate reduction, suggesting it was inhibitory to SRB growth above 1500 mg/L. An increase in sulfate concentration from 500 mg/L to 1500 mg/L resulted in an increase in sulfate reduction. The response surface plot with respect to sulfate concentration and pH is pre sented in Fig. The response surface curve on sulfate reduction with respect to the mutual effects of process parameters such as: (A) sulfate concentration versus pH (B) sulfate concentration versus MWE concentration (C) pH versus MWE concentration. Then lower RPN numbers were used in eliminating the failures.įigure 9.8. RPN analysis took all the possible failure modes and effects into account.įirst, the highest RPN numbers were selected in reducing the failures to make the biggest impact in the process improvement. Also, this implies that assuming biocrude has a higher heating value of 34 MJ/kg, as much as 360 GJ of energy can be made available onsite annually via the direct combustion of the biocrude product with the insoluble solid (biochar) suitable for use as cheap adsorbents and soil additives, as discussed briefly in Section 10.1. It is clear that up to 670 and 110 tons/year of biochar and biocrude can be generated if 5000 tons of high moisture digestate (96.98% wt water) are made available per year. From Table 10.6, it is clear that the proposed HTL-based one-step digestate processing approach will facilitate not only the comprehensive treatment of the digestate, but the proposed pathway will also enable the generation of useful products of not only biocrude but biochar as well. Table 10.6 also shows that experimentally determined maximum biocrude yield was close to the predicted optimum biocrude yield with a relative absolute deviation of only 4.7%. At the conclusion of the experiment, the final reactor pressure recorded was measured as 17 MPa. Under the specified conditions of the temperature, initial pressure, and holding time necessary for maximum biocrude production, the yields of the insoluble solid (biochar), soluble solids present in the post-HTL water, and the gas phase products were determined to be 44.6 wt%, 10.3 wt%, and 38.1 wt%, respectively. Reactor design specifications such as the reactor geometry and heating rate vary significantly in the literature.Īs shown in Table 10.6, the experimentally determined results for the optimum biocrude yield are 7.0 wt% on a dry basis. The variability of the optimum initial pressure and reaction time reported in the literature is clearly a reflection of the dependence of the pressure and reaction time on the peculiar reactor design and performance. However, variations in the optimum initial reactor pressure and reaction time were observed in the literature. , and Jindal and Jha reported optimal target temperatures of 300☌, 295☌, and 280☌ respectively. Previous hydrothermal liquefaction studies demonstrated maximum biocrude production at temperatures close to 290☌. A review of the literature suggests that the experimentally determined optimal target temperature for the maximum biocrude yield from the high moisture digestate in this chapter is similar to the optimal target temperature conditions reported in most previous studies in the literature. (10.30) and applying the optimization module of the Minitab software, the target temperature, reaction time (inclusive of holding time), and initial pressure for the maximum biocrude yield have been determined to be 290☌, 83 min (inclusive of heating time), and 5 MPa, respectively. Using the fitted relations presented in Eq. John Birch, in Advances in Eco-Fuels for a Sustainable Environment, 2019 10.4.2 The operating conditions for a maximum biocrude yield
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