Biogas Fermenter Flushing for Safe Dry Loading
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Solution Overview
Problem
In biogas plants using dry fermentation, there is a risk of creating explosive biogas/air mixtures during the unloading and loading of fermenters, necessitating safe shutdown and startup procedures to prevent accidents.
Innovation Solution
The biogas plant employs a method where the biogas/exhaust gas mixture is flushed with carbon dioxide and later fresh air to reduce methane concentration, allowing safe unloading and loading by separating the biogas line when methane levels fall below predetermined limits, and using an exhaust chimney for low-methane mixtures, ensuring personnel safety.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Duration of action of stationary object
If the fermenter is unloaded and loaded during shutdown, then the fermenter can be maintained for long-term operation, but there is a risk of creating explosive biogas/air mixtures
Solution Approach 1:
The system performs preliminary flushing actions with carbon dioxide and fresh air before unloading and loading operations. The control device activates the exhaust gas blower and purge gas inlet to replace biogas with inert carbon dioxide, then with fresh air, reducing methane concentration to safe levels before personnel access the fermenter. This preliminary action eliminates the explosive hazard while enabling continuous operation.
Solution Approach 2:
Carbon dioxide serves as an intermediary substance to replace biogas in the fermenter before unloading. The exhaust gas from the combined heat and power plant, rich in carbon dioxide, is introduced through the purge gas inlet to displace biogas. This intermediary approach safely reduces methane concentration without requiring direct air contact during the transition phase.
2Reliability
If biogas production is stopped during shutdown, then safety can be ensured, but productivity is reduced
Solution Approach 1:
The system maintains continuous biogas production and utilization by implementing a multi-stage shutdown procedure. While one fermenter is being unloaded and loaded, other fermenters continue producing biogas that is fed to the combined heat and power plant. The controlled flushing and gas replacement procedures minimize interruption time, allowing rapid resumption of biogas production after loading, thus maintaining overall system productivity.
Solution Approach 2:
The control device initiates preliminary gas replacement procedures using carbon dioxide from the combined heat and power plant exhaust before complete shutdown. This allows the system to maintain power generation from existing biogas reserves while safely preparing the fermenter for loading, minimizing total downtime and maintaining productivity continuity across the multi-fermenter system.
3Reliability
If the biogas line is separated when methane concentration falls below limits, then safety is improved, but device complexity increases
Solution Approach 1:
The control device continuously monitors methane concentration in the biogas line using sensors and automatically controls the separation and reconnection of gas lines based on real-time measurements. When methane concentration falls below predetermined safety limits during flushing, the control device automatically closes valves to separate the biogas line. When safe levels are restored, the system automatically reconnects. This feedback-controlled automation manages the increased device complexity while ensuring reliable safety operations.
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 method maintains biogas production and utilization during shutdown, prevents explosive mixtures, and ensures safe operation by controlling gas composition, allowing for risk-free unloading and reloading of fermenters.
Implementation Method 1
the biogas/exhaust gas mixture from the fermenter to be switched off continues to be fed to the biogas consumer until the quality of this mixture drops below a predetermined level
Implementation Method 2
The fermenter to be switched off is then flushed with fresh air instead of exhaust gas containing carbon dioxide and the exhaust gas/biogas/fresh air mixture is discharged via the exhaust chimney
Implementation Method 3
Only when the methane concentration in the biogas outlet falls below an upper limit value is the biogas line leading to the biogas consumer separated from the biogas outlet
Implementation Method 4
The resulting biogas can be used in a combined heat and power plant to generate electricity and heat
Data Source
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AI summary
This document describes a biogas plant for producing biogas from biomass with at least one digester, a method for safely shutting down a digester, and a method for safely starting a digester. To unload spent biomass and load fresh biomass, the individual digesters must be shut down periodically, meaning biogas production must be stopped. For safety reasons, it is essential to prevent the formation of an explosive biogas/air mixture during the unloading and loading of the individual digesters. Purging the digester with carbon dioxide-containing exhaust gas during shutdown prevents the formation of an explosive biogas/air mixture and maintains biogas production for as long as possible. This means that the biogas/exhaust gas mixture from the digester being shut down continues to be supplied to the biogas consumer until its quality falls below a predetermined level.Only when the methane concentration in the biogas outlet falls below an upper limit is the biogas pipeline leading to the biogas consumer disconnected from the biogas outlet. Afterwards, the biogas/exhaust gas mixture, now containing only a small amount of methane, is discharged via an exhaust stack.