Because of the adverse effect of CO₂ from fossil fuel combustion on the earth’s ecosystems, the most cost‐effective method for CO₂ capture is an important area of research. The predominant process for CO₂ capture currently employed by industry is chemical absorption in amine solutions. A dynamic model for the de‐absorption process was developed with monoethanolamine (MEA) solution. Henry’s law was used for modelling the vapour phase equilibrium of the CO₂, and fugacity ratios calculated by the Peng–Robinson equation of state (EOS) were used for H₂O, MEA, N₂ and O₂. Chemical reactions between CO₂ and MEA were included in the model along with the enhancement factor for chemical absorption. Liquid and vapour energy balances were developed to calculate the liquid and vapour temperature, respectively.

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Interaction of free oxygen in bio-gasification is a sparsely studied area, apart from the common argument of oxygen being toxic and inhibitory for anaerobic micro-cultures. Some studies have, however, revealed increased solubilisation of organic matter in the presence of some free oxygen in anaerobic digestion. This article analyses these counterbalancing phenomena with a mathematical modelling approach using the widely accepted biochemical model ADM 1. Aerobic oxidation of soluble carbon and inhibition of obligatory anaerobic organisms are modelled using standard saturation type kinetics. Biomass dependent first order hydrolysis kinetics is used to relate the increased hydrolysis rate with oxygen induced increase in biomass growth. The amended model, ADM 1-Ox (oxygen), has 25 state variables and 22 biochemical processes, presented in matrix form. The computer aided simulation tool AQUASIM 2.1 is used to simulate the developed model. Simulation predictions are evaluated against experimental data obtained using a laboratory batch test array comprising miniature anaerobic bio-reactors of 100 ml total volume each, operated under different initial air headspaces giving rise to the different oxygen loading conditions. The reactors were initially fed with a glucose solution and incubated at 35 Celsius, for 563 hours. Under the oxygen load conditions of 22, 44 and 88 mg/L, the ADM1-Ox model simulations predicted the experimental methane potentials quite adequately. Both the experimental data and the simulations suggest a linear reduction of methane potential with respect to the increase in oxygen load within this range

A state estimator and various model-based control systems have been designed for a real anaerobic digestion (AD) pilot reactor fed with dairy manure. The model used is a modified Hill model which is a relatively simple dynamical AD process model. The state estimator is an Unscented Kalman Filter (UKF) which uses only methane gas flow measurement to update its states. The model and the state estimates are used in different control systems. One of the control systems aims at controlling the methane gas flow to a setpoint. Simulations indicate that the setpoint tracking performance of a predictive control system is considerably better comparing with PI control, while disturbance compensation is not much better. Consequently, assuming the setpoint is constant, the PI controller competes well with the predictive controller. A successful application of predictive control of the real reactor is presented. Also, three different control systems aiming at retaining the reactor at an operating point where the volatile fatty acids (VFA) concentration has a maximum, safe value are designed. A simulation study indicates that the best control solution among the three alternatives is PI control based on feedback from estimated VFA.

The flexible generation of electrical energy is heavily dependent on hydropower. Advanced control systems may offer an enhanced operational security. During power system disturbances, a generator may need to operate beyond its limits to maintain a stable operation. This increased performance can be obtained if the total thermal capacity of the generator is exploited by applying optimal control theory in the automatic voltage regulator (AVR). A low order model is required for online implementation and prediction of critical thermal stresses in the machine. Periodic extension of the generator capability diagram has been historically overlooked. In this contribution, a thermal network for air-cooled hydrogenerators for use in real-time monitoring and optimal control is proposed and validated. The thermal model is extended with a heat exchanger model. The dynamic model is developed from an energy balance of the system and verified through FEM simulations and temperature measurements in a case study. Transient simulation results of the online low order model are in good agreement with measurements. Finally, a satisfactory simulator speed is obtained which confirms the feasibility of this approach in real-world applications.