Steam storage systems for flexible biomass CHP plants - Evaluation and initial model based calculation

Within the present study a novel concept for the demand-oriented power generation of a solid-biomass fueled combined heat and power (CHP) plant is investigated. The integration of a novel steam storage system into the plants process enables a decoupling of the steam (boiler) and the power generation (steam turbine). By buffering the steam, the power output of the turbine can be adjusted without changing the rated thermal capacity of the plant. The storage system consist of combination of steam accumulator and concrete storage. An initial model based simulation study is performed to identify the fundamental behavior of this system, integrated in a biomass CHP plant. The operation principle has proved their technical feasibility and seems to be applicable at a commercial scale. According to the modelling results flexible short term power generation in a time range from 15 min to several hours is applicable. A load-range of almost the plant's rated capacity can be achieved. The properties of the proposed concept are competitive to available energy storage systems

Mixing in biogas digesters: correlations between laboratory experiments on artificial substrate and simulations with computational fluid dynamics

Energy demand for mixing of biomass digesters is a crucial parameter in design and operation of biogas plants. Optimization of flow characteristics in the fermentation process is usually focused on the stirrers where their placement, shape and number, as well as their rotational speed and switching sequence are all important decision variables for overall energy efficiency planning. Digester stirring was analyzed in cylindrical transparent physical digester models located in the laboratories of Technische Hochschule Ingolstadt. Real biomass was substituted with chemical substrates based on cellulose exhibiting transparency, physico-chemical stability, ease of use and rheological behavior comparable to real biomass. The motion of the liquid within the tanks was investigated with pulsed laser PIV (Particle Image Velocimetry). The optical measurements of the flow velocity allow to measure flow fields in a non-invasive way. In order to gain more insight into the theoretical concepts of mixing and flow patterns within digesters the results of the laboratory experiments were verified with computer simulations using a commercial computational fluid dynamics (CFD) software tool StarCCM +

Investigation of fluid dynamic in a scale-down laboratory digester

Mixing is a crucial process in biogas plants and is required to maintain uniform concentrations of biomass in the digester. However, mixing requires high energy inputs and hence energy efficient design and operation of the mixing process is of vital importance. At the design stage the shape, number and placement of stirrers are important decision variables. At the operational stage the rotational speed and the switching sequence are important to guarantee substrate uniformity whilst avoiding unnecessary over-mixing. In our laboratories at the Technische Hochschule Ingolstadt we set-up a 1:12 scale digester model. The digester is made of transparent plexiglass allowing us to carry out optical measurements

Optimization of the mixing system in biodigesters with computational fluid dynamics (CFD)

Up to 50 % of a biogas plants parasitic energy consumption is actually caused by the mixing system. Therefore the optimization of the mixing-system is an essential method to increase the overall efficiency of the biogas plant. Various influences onto the mixing characteristic such as the type, number, positioning and geometry of the stirrer as well as the (influential) substrate rheology have to be considered. For comprehensive investigations on digester mixing, laboratory experiments in combination with numerical calculations are a promising approach. Under defined conditions, a high flexibility allows various investigations and evaluations. The non-Newtonian, shear thinning behavior of biogas substrate strongly influences digester mixing. While the use of real biogas substrate in laboratory is critical, the creation of a consistent model substrate with similar physical properties, which enables comparable experimental results, should be preferred. The main objective of the presented project, which is funded by the German Ministry of Education and Science, is to optimize biogas digester mixing with highest benefit at lowest cost in general