Design method for continuous bioreactors in series with recirculation and productivity optimization

Study on the Nonlinear Dynamics of the Continuous Stirred Tank Reactors

Chemical processes often exhibit nonlinear dynamics and tend to generate complex state trajectories, which present challenging operational problems due to complexities such as output multiplicity, oscillation, and even chaos. For this reason, a complete knowledge of the static and dynamic nature of these behaviors is required to understand, to operate, to control, and to optimize continuous stirred tank reactors (CSTRs). Through nonlinear analysis, the possibility of output multiplicity, self-sustained oscillation, and torus dynamics are studied in this paper. Specifically, output multiplicity is investigated in a case-by-case basis, and related operation and control strategies are discussed. Bifurcation analysis to identify different dynamic behaviors of a CSTR is also implemented, where operational parameters are identified to obtain self-oscillatory dynamics and possible unsteady-state operation strategy through designing the CSTR as self-sustained periodic. Finally, a discussion on codimension-1 bifurcations of limits cycles is also provided for the exploration of periodic forcing on self-oscillators. Through this synergistic study on the CSTRs, possible output multiplicity, oscillatory, and chaotic dynamics facilitates the implementation of novel operation/control strategies for the process industry.

Experimental research of efficiency of semi-continuous and periodic biogas production processes by using chicken manure bioloadings

Semi-continuous and periodic biogas production processes were investigated. Dry chicken manure containing 40.0 ± 0.5% volatile solids (VS) was used for the production of bioloading. Semi-continuous operation bioreactor and periodic bioreactor were used to implement research. Bioloading was additionally supplemented with newly prepared parts by removing 10% of decomposed mass and by adding the same amount of preheated mass every 7 days (semi-continuous process). The process was periodic when the mass was completely decomposed (after 45 days of the experiment) and fully removed (bioreactor was loaded with a new portion of raw material to 100% of the working volume again). Total duration of both experiments was 90 days. The results show that biogas production by semi-continuous process is more effective than periodic process due to higher total biogas yield (up to 39.7%) and higher methane yield (up to 33.5%). The maximum concentration of CH₄ was determined during the periodic biogas production process, but the difference was only up to 2.1% (68.9% and 66.8%, respectively). Since the produced biogas had quite high average CO₂ and H₂ S concentrations (<40.0% and 2.1 g/m³ , respectively), it is recommended to use filter-adsorbers or biofilters. According to the results, semi-continuous type bioreactor is more effective than periodic. PRACTITIONER POINTS: Maximum CH₄ concentration in biogas, produced during periodic process, is 2.1% higher than during the semi-continuous process. Average CH₄ concentration in biogas, produced during periodic and semi-continuous process, reaches 52.7% and 53.0%, respectively. Biogas and methane yield (during periodic process) is 39.7% and 33.5% lower than during the semi-continuous process. CH₄ concentration decreases (after supplement) about 6.0%-7.0% (during the semi-continuous process), but increases to the next cyclic bioloading supplement. Semi-continuous biogas production process is more efficient than periodic.