This paper investigates the potential energetic utilization of wheat chaff via combustion and necessary process steps such as pretreatment and pellet production as an example of stramineous biomass. Chaff is one out of three main fractions during harvesting and remains usually on the field. Vice versa, it is a potentially so far unexploited biomass resource, which could serve as renewable energy source. Simultaneously, exploiting wheat chaff could intensify the economic benefit of agricultural land use. The combustion application requires choosing an applicable firing system adjusted to the properties of chaff. The economic feasibility of the combustion application depends strongly on the technical effort, which depends on the fuel. Chaff consists mainly of husks and straw. Due to the low ash melting point and the high chlorine content of straw, it can be advantageous for the combustion to remove short straw from the chaff by sieving. To evaluate the combustion properties of presorted and original chaff the elemental composition, the net calorific value, the volatiles and ash content and the ash melting behavior were determined. The efficient logistic of chaff is decisive for its economic exploitation. This is in conflict with the low bulk density of chaff and the resulting high storage volume. Compressing chaff into pellets optimizes its handling. This vital step for an economic exploitation of chaff was therefore investigated by this study. Parameters such as water content of the feed, addition of binders and the geometry of the pressing die bores influence the pelletizing success significantly. Thus, these parameters were investigated in this study. The resulting pellets were characterized with standardized methods and compared to the requirements of EnPlus standards in terms of mechanical durability, amount of fines, bulk density and final moisture content. Finally, combustion experiments in a Large-scale Oven for Kinetics Investigation characterized the burnout behavior of the produced pellets. This was compared to pine wood pellets as conventional fuel. The performed investigations show that the pellet production and the subsequent combustion of wheat chaff pellets is a feasible approach for an energetic utilization.

This review studies unwanted precipitation reactions, which can occur in SO2 absorption processes using a magnesium hydroxide slurry. Solubility data of potential salts in the MgO-CaO-SO2-H2O system are evaluated. The reviewed data can serve as a reliable basis for process modeling of this system used to support the optimization of the SO2 absorption process. This study includes the solubility data of MgSO3, MgSO4, Mg(OH)2, CaSO3, CaSO4, and Ca(OH)2 as potential salts. The solubility is strongly dependent on the state of the precipitated salts. Therefore, this review includes studies on the stability of different forms of the salts under different conditions. The solubility data in water over temperature serve as a base for modeling the precipitation in such system. Furthermore, influencing factors such as pH value, SO2 content and the co-existence of other salts are included and available data on such dependencies are reviewed. Literature data evaluated by the International Union of Pure and Applied Chemistry (IUPAC) are revisited and additional and newer studies are supplemented to obtain a solid base of accurate experimental values. For temperatures higher than 100 °C the available data are scarce. For a temperature range from 0 to 100 °C, the reviewed investigations and data provide a good base to evaluate and adapt process models for processes in order to map precipitations issues accurately.

This work assesses the thermodynamic modeling of the MgO-CaO-CO 2 -SO 2 -H 2 O-O 2 system using the electrolyte NRTL activity coefficient model, primarily focusing on the solubility of potential salts in the system. The assessment includes the SO 2 -H 2 O and SO 2 -Mg(OH) 2 vapor−liquid equilibria as well as the precipitation of Mg(OH) 2 , Ca(OH) 2 , MgSO 3 , CaSO 3 , MgSO 4 , CaSO 4 , and their hydrate forms. The analysis covers a temperature range of 0 to 100 °C and focuses on calculations at atmospheric pressure. The performed calculations assess the necessity of defining equilibrium constants K eq as a function of temperature to describe the chemical equilibria accurately. The SO 2 solubility in water is studied for a pressure range of 0.545 to 1.788 bar. The SO 2 -Mg(OH) 2 absorption equilibrium is studied for a SO 2 partial pressure range of 0.00963 to 1.101325 bar and a MgO concentration of up to 14.5 kg/m 3 H 2 O. The results are evaluated using experimentally determined data from the literature. The study shows that the model recognizes all reported precipitation forms in the correct temperature range in chemically stable systems. The solubility of Mg(OH) 2 is calculated with a deviation from literature data of <6% for a temperature range of 70 to 90 °C and a maximum deviation of −40% for temperatures close to 0 °C. The calculated Ca(OH) 2 solubility at the complete studied temperature range deviates less than 11% from the literature data. The model also recognizes the pH dependency of the solubility of both hydroxides. The calculated solubility of MgSO 3 hexahydrate deviates less than 1% from literature data, and the calculated solubility of MgSO 3 trihydrate shows a maximum deviation from literature data of 20% at temperatures up to 90 °C. The solubility of CaSO 3 hemihydrate is predicted with a deviation of <1% at a temperature range of 70 to 100 °C and a deviation of <30% for temperatures higher than 20 °C. The model predicts the solubility of MgSO 4 monohydrate with a maximum deviation from literature data of 20% and overestimates the solubility of MgSO 4 heptahydrate by up to 118% compared to literature data. The solubility of CaSO 4 monohydrate is calculated with a deviation from literature data of <2%, and the solubility of CaSO 4 dihydrate with a deviation of <7%. The model's accuracy in predicting the SO 2 solubility in water variates strongly depending on which literature data points it is compared to. The smallest deviation from literature data is 1% compared to data measured at 60 °C and a pressure of 1.377 bar. The highest deviation is 60% compared to data measured at 90 °C and atmospheric pressure. The study shows that the experimental data in literature describing the SO 2 absorption in an Mg(OH) 2 solution are scarce. This leads to a limited ability to evaluate thermodynamic models based on experimental data. The model describes the SO 2 absorption in Mg(OH) 2 with a deviation between 8 and 52% compared to available literature data.