High space and investment demand
A separate hydrolysis stage and an independent digester require additional foundations, vessels, pipework and technical equipment.
Compact technical solution for bioenergy plants
Combined hydrolysis and anaerobic digestion reactor
The reactor combines a centrally arranged hydrolysis vessel with a surrounding anaerobic digester, post-digester or digestate store. Hydrolysis and methane fermentation remain spatially separated while sharing structural, thermal and gas-related functions.
Initial challenge
Separate process stages often require additional vessels, heating surfaces and structures
Additional heat demand
Hydrolysis and fermentation require different stable temperature levels. Separate heating systems increase investment, maintenance and energy consumption.
Unused hydrolysis gases
Hydrolysis gases can contain oxygen, hydrogen and vapours of short-chain fatty acids. Inappropriate handling wastes energy and process potential.
Retrofitting existing vessels
Existing digesters or open digestate stores can often be converted into efficient gas-tight process stages only with considerable structural effort.
Operating principle
Central hydrolysis vessel inside the surrounding substrate vessel
Spatially separated reaction zones
The corrosion-resistant hydrolysis vessel is arranged centrally inside a larger vessel for fermentation substrate. Both stages remain materially and biologically separated.
Aerobic or mildly aerobic hydrolysis
Metered air or oxygen supply through air lances or via the vortex generated by the central agitator enables demand-based hydrolysis.
Integrated heating function
The wall of the hydrolysis vessel is partly designed as a hot-water heating surface. It heats the hydrolysis stage and simultaneously transfers heat to the surrounding digester.
Use of hydrolysis gases
Oxygen-containing hydrolysis gases are routed into the gas space of the surrounding digester. The oxygen can support biological hydrogen-sulphide removal, while hydrogen and fatty-acid vapours can contribute to further biogas formation.
Flexible use of the surrounding vessel
The surrounding vessel can be operated as a main digester, post-digester or heated gas-tight digestate store.
Batch operation and longer minimum retention time
With at least two apparatus units, hydrolysis and fermentation can be operated alternately in batch mode. This enables defined hydrolysis periods, longer minimum anaerobic retention times and thermophilic hygienisation.
Design features
Multiple functions in a compact vessel combination
Corrosion-resistant hydrolysis vessel
The central reaction zone is made of corrosion-resistant materials suitable for the acidic and oxygen-containing hydrolysis conditions.
Central support for the roof
The hydrolysis vessel can also serve as a structural central support for a rigid roof or the supporting system of a gas-storage membrane.
Maintenance during operation
Immersion sleeves for mixing equipment allow replacement or maintenance without completely emptying the reaction zones when operated appropriately.
Suitable for new plants and retrofits
The solution can be integrated into new plants or used to upgrade existing digesters, post-digesters and previously open digestate stores.
Client benefits
Lower construction effort and improved use of biological process stages
Compact plant layout
Hydrolysis and fermentation are implemented within one combined vessel geometry without mixing the biological reaction zones.
Reduced heating equipment
The heated wall of the hydrolysis vessel also controls the temperature of the surrounding substrate zone. Separate heating surfaces in the outer vessel can be omitted.
Improved hydrolysis of fibrous feedstocks
Defined temperature, aeration and treatment time improve the biological breakdown of lignocellulosic feedstocks and can increase methane yield.
More stable anaerobic digestion
Upstream hydrolysis can reduce viscosity and floating-layer formation, accelerate carbon degradation and protect the methanation stage against over-acidification.
Energy use of hydrolysis gases
Hydrolysis gases are not discharged unused but are integrated into the anaerobic process and, where appropriate, into biological gas desulphurisation.
Retrofitting open digestate stores
Existing digestate stores can be upgraded with a central hydrolysis vessel, heating and a gas-tight roof to form an additional biologically active gas-producing stage.
Technical background
The technical solution presented is based on European patent application EP 2 982 739 A1. Vessel volumes, heating surfaces, corrosion protection, mixing systems, gas routing and safety equipment must be designed specifically for the project, site and feedstock.
Technical project assessment