Two-Stage Anaerobic Digester for High Solids Mixing
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Anaerobic digestion systems face challenges in processing high-solids feedstocks, as they are difficult to mix and require dilution, which increases digester volume and reduces reaction rates.
Innovation Solution
A two-stage anaerobic digester system with a tank-in-tank configuration, where the first stage operates as a raceway with circulating digestate and the second stage as a stirred reactor, allowing for partial digestion and further reduction of solids content, facilitating mixing and reducing dilution needs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of stationary object
If high-solids feedstock is processed without dilution, then digester volume is reduced, but mixing becomes extremely difficult
Solution Approach 1:
The digester is divided into two separate stages: a first stage for initial digestion and a second stage for completion of digestion. This segmentation allows each stage to be optimized for its specific function, with the first stage handling high-solids feedstock and the second stage receiving partially digested material that is easier to mix and process.
Solution Approach 2:
The first stage digester is positioned inside the second stage digester, creating a tank-in-tank configuration. This nested arrangement allows both digesters to occupy the same overall footprint, reducing the total volume required while maintaining separate processing zones for different solids concentrations.
2Ease of operation
If high-solids feedstock is diluted to improve mixing, then reaction rate decreases and digester volume increases
Solution Approach 1:
The digestion process is segmented into two stages with different solids concentrations. The first stage operates with high-solids feedstock (up to 30% total solids) to maintain high reaction rates, while the second stage receives partially digested material with lower solids content that is easier to mix, thus avoiding the need to dilute the original feedstock.
Solution Approach 2:
The system changes the solids concentration parameter progressively through the two stages. The first stage handles high-solids material, and as digestion proceeds, the solids concentration naturally decreases, making the material progressively easier to mix in the second stage without requiring external dilution.
3Ease of operation
If two separate tanks are used for two-stage digestion, then mixing is improved, but device complexity increases
Solution Approach 1:
The first stage digester is nested within the second stage digester, creating a compact tank-in-tank configuration. This reduces the overall footprint and structural complexity compared to using two completely separate tanks, while still maintaining separate processing zones for effective two-stage digestion.
Solution Approach 2:
The two digesters are combined into a single integrated unit where the first stage is positioned inside the second stage. This merging reduces the number of external structures, piping connections, and support systems needed compared to two completely separate tanks, thereby reducing overall system complexity.
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 configuration enables efficient processing of high-solids feedstocks with minimal dilution, reducing hydraulic retention time and digester volume, while maintaining effective mixing and biogas production, suitable for large-scale applications.
Implementation Method 1
In a first stage, substrate being digested in the digester, called digestate, circulates in one direction around an endless loop
Implementation Method 2
The outer ring provides the first stage, where partial digestion occurs. The internal cylindrical portion is the second stage of the digester, where the digestion is completed.
Data Source
Figure 1
Figure 2
Figure 3A~3B
AI summary
A multi-stage anaerobic digester is designed to treat a high solids, stackable feedstock. The system may also receive a pumpable feedstock such as a slurry or sludge. In a first stage, the digestate circulates in one direction around a raceway such that the digestate may pass a feed inlet multiple times before leaving the first tank. An optional side stream loop withdraws fibrous material from near the top of the reaceway and return digestate with chopped fibers, preferably lower and further along the raceway. An outlet from the raceway located near, but upstream of the feed inlet discharges partially digested substrate to a second stage, which is operated as a stirred tank reactor. The two stages may be provided in a single tank with an internal wall separating a ring shaped outer portion from a cylindrical inner portion. The digester may be operated in a thermophilic temperature range.