Technology
An innovative approach
Producing renewable hydrogen with less electrical energy
By using concentrated solar radiation as a heat source through the solid particle receivers’ technology and in particular the innovative centrifugal receiver CentRec® developed and patented by DLR in combination with the innovative Hybrid Sulphur Cycle technology concept, green hydrogen can be produced at lower electrical cost than with the state-of-the-art electrolysis technology.
The Technology
The Testing Facility
The HySelect Technology will be implemented at two sites. At the Jülich heliostat field, next to the large-scale solar tower of DLR, a thermochemical test plant will be build. The centrifugal particle receiver used for HySelect, has already been installed in the in the frame of another project (HEHTRES). The HySelect chemical plant as well as the innovative HySelect electrolyser will be implemented at the Grillo plant in Duisburg.
The DLR Solar Plant
Particle Receiver
HySelect Jülich
HySelect Duisburg
The Technology
The Hybrid Sulphur Cycle
The ambition of HySelect is to close the technical gaps and provide the missing links in the overall, complete HyS cycle technology concept, for a realistic overall evaluation of the technology and its scaleup.
Particle Receiver
In the HySelect project, solar radiation is concentrated onto a so-called centrifugal particle receiver with 750 kW thermal power which is mounted on top of the DLR solar tower facility. Small ceramic particles as the absorber medium pass through the receiver and get thereby heated up to 900-1000 °C. The basic concept of the receiver is a rotating cylinder with an inclined rotation axis. Particles are fed into the receiver and forced against the inner cylinder wall by centrifugal forces, where they form a thin, but optically dense particle film. While slowly moving along the wall towards the receiver outlet, the film is gradually heated by incoming solar radiation.
High Density Storage
The heated particles can be directly stored in an insulated tank for later use, allowing the generation of dispatchable power. Due to the large temperature span from 300 °C to 700 °C between hot and cold state of the particles the volumetric storage density is about 2.5 times higher than current solutions. Together with low-cost particles this results in reduced specific storage costs (about 50 % of current solutions).
Cold Storage Tank
After passing the thermal reactor, the cooled particles are stored in a cold storage tank. Both, the cold and hot storage tanks are sized large enough to smooth out the variable energy inputs.
Chemical Reactor
The Sulphuric Acid Splitting (SAS) reactor is allothermally heated with solar-heated particles and spatially decoupled from the centrifugal particle solar receiver (HySelect Pilot Plant). The decomposition of the Sulphuric Acid (SA, H2SO4) at 250 kW thermal reactor results in the formation of water vapour (H2O), sulphur dioxide (SO2) and oxygen (O2).
Gas Separation
In the gas separation and treatment unit, O2 is separated from SO2.
Sulphuric Acid Storage
Processed SA will be stored at Grillo site.
Sulphuric Acid Concentration
Use of a commercial unit capable of processing SA with required concentrations for the SA reactor.
Sulphur dioxide Depolarised Electrolyser
The SO2 Depolarized Electrolyser (SDE) is a breakthrough in the production of renewable hydrogen (H2) in comparison to the state-of-the-art electrolysis technology. The overall reaction involves the oxidation of SO2 and water at the anode side resulting in the production of H2SO4 and H2 at the cathode side. In general, SDE would only require 25-60 % of the electrical energy and performs at an operating voltage range between 0.5 V to 1.2 V which is much lower than that for Polymer Electrolyte Membrane (PEM) water electrolyser, varying from 1.6 V to 2 V.
Sulphur Dioxide Storage
Storage of clean SO2 for use in the Sulphur dioxide Depolarized Electrolyser (SDE) at Grillo site.
Hydrogen
The HySelect process allows an average renewable hydrogen production rate of 2.38 kg per day per m² receiver area.
Transportation Jülich to Duisburg
The products of the SAS reactor are transported by truck to HySelect Duisburg site, approximately 100 km distance away from HySelect Jülich site.
Transportation Duisburg to Jülich
Transportation of fresh SA from HySelect Duisburg site to HySelect Jülich site for use in the SAS reactor.
Electricity
Electricity consumption from renewable energy sources is significantly lower than for current state-of-the-art electrolyser technology.
The Technology
The Hybrid Sulphur Cycle
The ambition of HySelect is to close the technical gaps and provide the missing links in the overall, complete HyS cycle technology concept, for a realistic overall evaluation of the technology and its scaleup.
The Technology
Frequently Asked Questions
Here you can find all important questions regarding the HySelect Technology and testing plant.
What does "HySelect" stand for?
Efficient water splitting via a flexible solar-powered Hybrid thermochemical-Sulphur dioxide depolarised Electrolysis Cycle.
How is the concentrated solar energy produced?
Movable mirrors closely arranged over a large area capture sunlight, bundle it and direct it to a receiver, where the concentrated solar energy can be used e.g. for thermochemical reactions.
What is the concentrated solar energy used for in HySelect?
The concentrated solar energy is used to heat dark particles (e.g. sand-like bauxite ceramic solid particles) in a rotating solar particle receiver through direct irradiation in a solar tower. The moving solid particle streams act as an inexpensive heat transfer fluid (HTF) that can also be used as a heat storage medium. Downstream of the solar receiver, the hot solid particles are used for the allothermal performance of sulphur-based thermochemistry: the sulphur trioxide splitting reaction together with the preceding sulphuric acid decomposition. The obtained sulphur dioxide is then used in the SDE to re-generate sulphuric acid closing its cycle.
What is meant by Sulphur dioxide Depolarized Electrolysis (SDE)?
It is the electrochemical oxidation of sulphur dioxide (SO2) with water to yield hydrogen at the cathode (negatively polarised electrode) and sulfuric acid at the anode (positively polarised electrode). In this so-called electrolysis process, a certain potential difference has to be applied between the two electrodes, which are placed separately from each other through a polymer membrane in an electrolyte solution (sulphurous acid, formed by mixing water and SO2), while an external circuit ensures the transfer of electrons from the anode to the cathode.
What is the advantage of SDE in comparison to water electrolysis?
The theoretical cell potential for the sulphur dioxide depolarized electrolysis (SDE) is only 0.17 V compared to 1.23 V for conventional water electrolysis. This means that the SDE offers a promising alternative to conventional electrolytical water splitting because of significantly reduced amounts of electrical power required.
How pure is the produced hydrogen via SDE?
Hydrogen purity is mainly affected by SO2 carry-over from anode to cathode, where hydrogen is produced. Therefore, the suppression of SO2 carry-over is essential and represents a separate investigation task in the HySelect project in order to test new membrane materials and purification systems.
What is the role of sulphuric acid in the overall process?
The overall process comprises the so-called hybrid sulphur cycle consisting of 2 reaction steps – a thermochemical and an electrochemical one – in order to recycle sulphur as the central element. In the thermochemical step, sulphuric acid is first decomposed to water (steam) and sulphur trioxide (SO3), which is then catalytically dissociated to sulphur dioxide (SO2) and oxygen (O2) at higher temperatures. Sulphur dioxide and water serve as educts for the electrochemical step, the second step, in the sulphur dioxide depolarised electrolysis, where hydrogen is formed and the initially used sulphuric acid is re-generated (recycled).
Is there a potential risk for environmental harm through the use of sulphur compounds (sulphur oxides and sulphuric acid)?
Sulphuric acid is the world´s most produced chemical. Hence, its safe use can build on a high degree of decades of industrial experience and operational safety and environmental impact have already been addressed to a large extent. Mature SOx emission capture/neutralization techniques can be applied in the HySelect process preventing environmental harm and ensuring that the sulphur containing compounds remain in the process cycle. Potential emissions of SO2 may be effectively captured through elaborated filters from other sectors (H2SO4 production).