Horizontal Agitators for Biogas Fermenter Mixing
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Solution Overview
Problem
In biogas production, the use of vertically driven central agitators in tall fermenters is inefficient for mixing substrates with pseudoplastic flow properties, leading to localized mixing and reduced usable reactor volume, resulting in lower methane production due to uneven viscosity and shear rates.
Innovation Solution
Implementing a system with multiple agitators positioned to create a common mixing zone, using measurement data to optimize power input and substrate composition, and varying agitator speed to maintain optimal average speed and viscosity for efficient mixing, minimizing energy expenditure and maximizing methane yield.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If vertically driven central agitators are used in tall fermenters, then mixing is performed, but the mixing is localized and usable reactor volume is reduced
Solution Approach 1:
The single central vertical agitator is segmented into multiple horizontal agitators distributed throughout the fermenter volume. Each horizontal agitator creates localized mixing zones that collectively cover the entire reactor volume, eliminating the cavern effect and ensuring uniform substrate distribution throughout the fermentation medium.
Solution Approach 2:
The mixing approach transitions from vertical agitation (single dimension) to horizontal agitation (perpendicular dimension). This dimensional change allows the agitators to generate flow patterns that effectively mix the pseudoplastic substrate across the entire cross-section of the fermenter, maximizing the usable reactor volume.
2Productivity
If agitators work locally in caverns, then mixing occurs in small volumes, but energy expenditure increases and methane yield decreases
Solution Approach 1:
Multiple localized mixing zones created by individual horizontal agitators merge to form a unified mixing system. The flow fields generated by adjacent agitators interact and combine, creating a continuous mixing pattern throughout the fermenter that prevents energy waste in isolated caverns while maximizing methane production from the entire substrate volume.
Solution Approach 2:
The horizontal agitators operate continuously to maintain uniform mixing throughout the fermenter volume, preventing the formation and dissipation cycles characteristic of vertical agitators in pseudoplastic media. This continuous useful action ensures consistent substrate availability to microorganisms, maximizing methane yield while minimizing energy expenditure.
3Stability of the object's composition
If vertically driven central agitators are used, then mixing is attempted, but viscosity distribution remains uneven due to pseudoplastic flow properties
Solution Approach 1:
Each horizontal agitator creates a localized mixing zone with optimized flow characteristics suited to the pseudoplastic properties of the substrate. The horizontal configuration generates shear rates that effectively reduce viscosity in the immediate vicinity of each agitator, and the distributed arrangement ensures uniform viscosity distribution throughout the entire fermenter volume.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach enhances substrate conversion and mixing efficiency, increasing the effective reactor volume and methane production while reducing energy consumption and preventing the formation of floating layers that impede gas escape.
Implementation Method 1
Shear rates are generated by the movement of the propeller of an agitator. In the area around the propeller, the local viscosity decreases with structurally viscous fermentation substrates.
Implementation Method 2
The fermentation substrates used for biogas production usually have pseudoplastic flow properties. Particle viscosity means that the dynamic viscosity of the fermentation substrate decreases with increasing shear rate.
Implementation Method 3
As the distance from the propeller increases, the shear rate decreases and the viscosity increases accordingly. As a result, the propeller primarily sucks in fermentation substrate from areas close to the propeller, in which the fermentation substrate has a low viscosity. These areas close to the propeller are referred to as caverns.
Data Source
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AI summary
The invention relates to a method and a facility for producing biogas. The biogas is obtained from organic matter. A container (1) is charged with substrate by means of a delivery system (13). At least two stirring mechanisms (2) are arranged in the container (1). The fans (3) of the stirring mechanisms (2) are rotated and generate in the container (1) mostly horizontal currents of the container contents. The fan diameter, the fan geometry and the position of the fans (3) are chosen such that a shared mixing zone of the medium is generated in the container (1). According to the invention, data for determining the mean speed and/or the viscosity of the medium in the mixing zone are recorded. These data are transmitted to a control unit (4). The control unit (4) varies actuating variables which modify the power input of the stirring mechanism (2) into the mixing zone and/or the composition and/or the flow behaviour of the container contents.