Monitoring and Process Control of Anaerobic Digestion Plants. Copyright: Torsten Reinelt

Ammonia, as a major inhibitor of the biogas process, is an important target of process monitoring. Ammonium salts, which are frequently used in laboratory experiments, are shown to lead to misleading results. Stable isotope analysis of the biogas was used to assess the major methanogenic pathway, confirming that ammonium chloride is a less effective biogas inhibitor than urea.

An online mid-infrared spectroscopic gas sensor with a microelectromechanical system-based interferometer was developed for assessing biogas concentration. The sensor response was evaluated and tests were performed on a pilot-scale digester and at a landfill site. The possible role of this sensor is discussed in the context of the shifting function of anaerobic digestion in the energy market.

A microbial electrochemical sensor for the quantification of volatile fatty acids is integrated in a real anaerobic digestion process. The sensor signal correlates with the acetate concentration in the process but the sensor stability is affected by the process conditions. Potential inhibitors in the anaerobic digestion process are examined to explain the observed loss of function.

The flexible production of biogas makes it a promising candidate to become the first renewable on-demand energy source. One interesting possibility to enable on-demand supply of biogas is to control the output itself via system operation. A non-dispersive infrared absorption spectroscopy setup using an alternative, gas-based detector scheme based on the photoacoustic effect is proposed.

Linking multiple biogas storages often causes problems on large-scale biogas plants, especially when they operate demand-driven gas consumers. Methods for the correct design and control of the gas system in biogas plants are reported and illustrated by reference to two specific large-scale industrial biogas plants, in order to overcome these problems by using a dedicated gas management system.

Currently, several biogas plants are started in Poland, using pig slurry as the main substrate. However, there is no up-to-date data on the commissioning of installations using this substrate. The start-up of agricultural biogas plants on a laboratory scale was simulated using pig slurry and maize silage. Similar running conditions like for real-scale biogas installation were assessed.

Anaerobic digestion is a promising technology for biowaste management. A highly important target is the overall process control of such plants. The hydrolysis in the first stage for the treatment of biowaste is optimized using the digestate recirculation from the second stage. An advanced management system is proposed with pH sensors to control the process within the optimal range.

In order to assess the contribution of molecules to anaerobic digestion performances, the application of near-infrared spectroscopy and partial least square b coefficient analysis is proposed as a fast and economical approach. Powerful tools are provided to investigate the influence of the molecules on anaerobic digestion performances which can be extended to other fields of application.

The mixing process in biogas plants is crucial to effectiveness. Difficult test conditions at full scale mean that experiments must be conducted at lab-scale. To cover flow characteristics, scale-up conditions have to be defined to transfer findings from the model to the original scale. Similarity laws are applied to find conditions necessary for achieving equal mixing processes at different scales.

The digestibility of liquid digestate and digestate compost was evaluated using batch reactors in an anaerobic digestion plant. In these experiments, digestate compost turned out to be an interesting substrate for anew anaerobic digestion which can be employed in times of worsening reactor performance because of seasonal changes in the quantity and quality of the feed material.

The monitoring of online and offline process parameters allows the efficient operation of anaerobic treatment plants but also requires a profound knowledge of the involved biological processes and regular maintenance and calibration of the sensor technology. Process monitoring and analytical methods at a field-scale biogas facility treating slaughterhouse wastewater are discussed.

Estimating the methane yield of substrates in continuous anaerobic digestion processes usually requires either complex substrate analysis or labor-intensive laboratory-scale continuous reactors. By modifying simple batch assays and applying the acquired kinetic rates and specific methane yields to mass flow models, satisfactory estimation of continuous process yields was achieved.

External forces during supercooling of melt-emulsified particles influence the size, shape, and stability of crystalline alkane dispersions. With increasing mechanical treatment during the crystallization, especially in higher alkane emulsions, the stability of the dispersions decreased due to morphological changes within solidifying droplets.

Chemical looping combustion (CLC) is an attractive technology because it allows fuel combustion with inherently pure CO₂ separation. Two basic approaches to CLC, coal direct (CD) and coal gasification, are combined into cycle power generation systems and simulated by using the ASPEN Plus software. The CD-CLC combined cycle results in excellent system performance with high CO₂ capture efficiency.

The coupling of concentration polarization, transmembrane solute and solvent fluxes and osmotic pressures was studied by solving the continuity, Navier-Stokes and solute transfer equations. Solvent permeation was found to rise with the value of membrane solute permeability. There is an optimal value of inlet pressure which leads to maximum solute rejection at a given feed concentration.

Sulfonated polymers have applications in water softening, acid catalysis, and measuring mass transfer rates. Herein, mass transfer coefficients for laminar flow were determined in a 3D-printed tubular reactor and a fixed bed of spherical particles, both modified by sulfonation, and the obtained values showed good agreement with correlations in the literature.

High-purity distillation columns exhibit issues in terms of nonlinearity, interactions, directionality, structural variance, and ill-conditioning for the control systems, leading to poor controller performance. The effects of these challenges on the performance of model predictive control in operations in near-azeotropic regions are evaluated via setpoint tracking and disturbance rejection.

Ionic liquids often contain considerable shares of moisture which exert a significant effect on their viscosity. Alterations of viscosity during mixing still mean a major challenge for the prediction of substance properties. The influence of water content on the rheological behavior of ionic liquids is evaluated and an estimation approach is proposed.

Process integration of unit operations is an important field of current research activities in academia and industry. Integrated distillation equipment like the Petlyuk column exhibits significant energy-saving potential. A pilot-plant scale Petlyuk column was operated for three reference systems, and a non-equilibrium simulation model was validated using the presented experimental data.

In order to achieve high lactic acid conversion associated with a high-purity final product without the need of a further purification step, a reactive and functional poly(styrenesulfonic acid)-carboxymethylcellulose blend catalytic membrane was developed and applied in a pervaporation-aided membrane reactor for ethyl lactate production. Excellent acid conversion could be realized.

The catalytic performance of the Zr(SO₄)₂ catalyst was investigated for esterification of oleic acid with methanol. The effects of relevant reaction parameters like methanol-to-oleic acid molar ratio, reaction temperature, and catalyst amount versus reaction time were examined. The kinetics of esterification was studied by applying pseudo-homogeneous and Eley-Rideal models to experimental data.

Emergency relief vent lines for polymerization reactors typically need to be sized for a two-phase flow of gas and highly viscous liquid phase. No experimental data are available and the empirical models are not validated in this region. The two-phase pressure drop in a vertically upward straight pipe was measured and the results were compared to literature models.

SO₂ is one of the major causes of acid rain and is mainly generated from coal combustion systems. SO₂ is removed from flue gas by using a system composed of a rotating packed bed and an electric-field device. The effects of operating conditions on SO₂ removal efficiency and gas-phase overall volumetric mass-transfer coefficient are revealed.

A correlation between the liquid product distribution and the H₂ selectivity during catalytic depolymerization of kraft lignin is proposed, which can be used to predict the composition of the liquid products based on H₂ selectivity detection or to convert kraft lignin to the desired liquid products. Different solvents, temperatures, and catalysts are viable options for this relationship.

Consistent initialization issues in the Laplace transform treatment for nontrivial chemical engineering systems are addressed. Two application examples of a surge tank and a condenser that contain interacting capacities are used for illustration. The accuracy of the approach over approach is verified and the popular approach is found to be inconsistent and inexact.