Horizontal Flow Agitators for Bioreactor Mixing
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Solution Overview
Problem
In biogas production, the use of vertically driven central agitators in tall, narrow fermenters is inefficient due to localized mixing patterns creating 'caverns' around the propeller, leading to suboptimal substrate conversion and reduced methane production, along with increased energy consumption and potential for floating layers that hinder gas escape.
Innovation Solution
A control unit monitors various process variables, including gas flow rate, viscosity, and floating layer formation, to adjust agitator power input, composition, and flow behavior, optimizing the operation of agitators, feed systems, and recirculation units to maximize methane production and minimize energy use.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If vertically driven central agitators are used in tall, narrow fermenters, then mixing is achieved in the vertical direction, but localized mixing patterns create 'caverns' around the propeller leading to suboptimal substrate conversion and reduced methane production
Solution Approach 1:
The patent inverts the conventional vertical mixing approach by using horizontal flow agitators that generate predominantly horizontal flow patterns instead of vertical flow. This inversion eliminates the formation of stagnant caverns around the propeller and ensures more uniform substrate distribution throughout the fermenter, thereby improving substrate conversion efficiency and methane production.
Solution Approach 2:
The patent applies local quality by positioning multiple horizontal flow agitators at different heights and locations within the fermenter to create localized mixing zones that collectively achieve uniform overall mixing. This distributed approach ensures that every region of the fermenter receives adequate mixing action, eliminating dead zones and improving substrate conversion throughout the entire volume.
2Ease of operation
If vertically driven central agitators are used, then mixing is achieved, but energy consumption increases
Solution Approach 1:
The patent inverts the conventional vertical mixing approach to horizontal flow generation, which reduces energy consumption by creating more efficient flow patterns that utilize the natural geometry of the fermenter better, reducing the power required for effective mixing.
Solution Approach 2:
The patent employs multiple agitators that can operate in a coordinated periodic manner, where not all agitators need to run at full power simultaneously. This periodic and coordinated operation reduces overall energy consumption while maintaining effective mixing throughout the fermenter volume.
3Ease of operation
If vertically driven central agitators are used, then mixing is achieved, but floating layers form that hinder gas escape
Solution Approach 1:
The patent inverts the vertical flow pattern to horizontal flow generation, which prevents the formation of stable floating layers on the surface. The horizontal flow patterns create continuous surface agitation that disrupts floating layer formation, allowing biogas to escape efficiently without being trapped by floating substrate layers.
Solution Approach 2:
The patent uses multiple distributed agitators that create localized flow patterns throughout the fermenter, including at the surface level. This distributed approach ensures that floating layers are continuously disrupted at multiple locations, preventing their accumulation and maintaining efficient gas escape pathways throughout the entire fermenter volume.
4Ease of manufacture
If container diameter is increased to reduce height-to-diameter ratio below 0.5, then central vertical agitators become uneconomical, but edge-arranged agitators are needed instead
Solution Approach 1:
The patent segments the single central agitator into multiple smaller horizontal flow agitators distributed around the edge and at different heights within the fermenter. This segmentation makes the system more economical for large-diameter containers while the coordinated operation of these segmented units achieves the required mixing performance without excessive complexity.
Solution Approach 2:
The patent transitions from a single vertical dimension of mixing (central vertical agitator) to a three-dimensional distributed arrangement of horizontal flow agitators. This dimensional change allows the system to effectively mix large-diameter containers by utilizing both radial and vertical distributions of mixing elements, reducing overall system complexity compared to scaling up a single central agitator.
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, increases biogas yield, reduces energy consumption, and prevents floating layers from forming, thereby optimizing the bioreactor's efficiency and methane production.
Implementation Method 1
The fermentation substrates used for biogas production typically exhibit shear-thinning flow properties. Shear-thinning means that the dynamic viscosity of the fermentation substrate decreases with increasing shear rate.
Implementation Method 2
Viscosity is therefore not a fixed value but a function. A corresponding viscosity is established for every induced shear rate. Consequently, the viscosity varies locally within the container. It depends on the locally present shear rates.
Implementation Method 3
In the immediate vicinity of the propeller, the local viscosity of diaphragmatic fermentation substrates decreases. With increasing distance from the propeller, the shear rate decreases and the viscosity increases accordingly.
Data Source
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AI summary
The invention relates to a method and a facility for producing biogas from organic matter. A container (1) is charged with substrate by means of a delivery system (13). At least one stirring mechanism (2) is arranged in the container (1). The feedback value of at least one measurable variable is recorded and transmitted to a control unit (4). A reference variable is provided in the control unit (4). The control unit (4) calculates the deviation of the feedback value from the reference value. Actuating variables which modify the power input of the stirring mechanism (2) and/or the composition of the container contents and/or the flow behaviour of the container contents are varied as a function of this deviation.