Single element technology
The main feature of the Uhde membrane technology is the unique single-cell element otherwise known as the single element, which comprises an anode compartment made completely from titanium, a membrane, a cathode compartment made from nickel and an individual sealing system with external flanges.
The seal system comprises a PTFE frame gasket (reusable) and Goretex® sealing cords. The external steel flanges, which have electrically insulated bolting with spring washers, guarantee that the single element remains leak-proof throughout its entire service life.
|The single element comprises an anode half shell, a cathode half shell, a membrane and a sealing system with external flanges.|
Very slightly trapezoidal anodic and cathodic channels are located in the upper section of both the anode and cathode compartment. This design has the following advantages:
- Brine and chlorine on the anode side as well as caustic and hydrogen on the cathode side are transported to the upper end of the compartments. The thorough supply of liquid to these sections ensures proper function of the membrane.
- A higher degree of safety is achieved as both compartments are flooded even when the electrolysis cells are in stand-by operation mode. The liquid level in the compartments is always high enough to ensure that the membrane is fully submerged, thus preventing any exchange of gases via the membrane in the upper part of the electrolysis cell.
- The foamy gas-liquid mixture is separated completely inside the channels, resulting in an outlet flow of two homogeneous phases. This total separation of gas and liquid reduces the internal differential pressure fluctuation within the electrolysis cell to a minimum, ensuring an even longer lifetime of the membrane.
Single elements are assembled and tested in the workshop outside the cell room where they can be stored for months. In case of maintenance of a single element from the cell room it can be quickly and easily replaced by another one taken from the store.
Ultra pure brine enters the anode compartment via an external tube with a nozzle and is distributed across the whole width of the compartment via an internal feed pipe.
A downcomer plate utilises the gas lift effect to create a high degree of internal brine circulation, thus ensuring ideal distribution with uniform density and temperature within the compartment. Depleted brine and chlorine leave the compartment via a discharge pipe.
In the cathode compartment there is also a feed pipe, which in this case is used to distribute caustic soda, and a discharge pipe, via which the products, hydrogen and caustic soda (32%), leave the single element.
Since there is only a small difference in the caustic soda concentration at the inlet and at the outlet of the cathode compartment, and as hydrogen and caustic soda are more easily separated than brine and chlorine, the cathode compartment is not equipped with a downcomer plate.
The UHDE BM 2.7 bipolar membrane electrolyser is a modular concept, with a number of advantages including low investment costs, low energy consumption and a long service life. The single elements are suspended in a frame and are pressed against each other by a clamping device to form a ,,bipolar rack". Slight pressure by spring loaded pressure bolts is exerted on the stack prior to start-up to ensure optimal electrical contact between the elements. In contrast to conventional electrolysers with a filter press design, no heavy duty pressers or track rods are needed to seal the electrolyser. The elements are all sealed individually beforehand which leads to increased operational reliability.
The single elements are arranged in series to form an electrolyser. A parallel connection is used on the electrolyte and product side whilst the serial configuration is used for the electrical side. The electrolysis current (direct current) is fed across contact strips from the cathode half shells to the anode half shells of the adjacent single elements in the electrolyser. Internal plate conductors arranged in the half shells ensure uniform current distribution to the anodes and cathodes.
All the elements are connected to the inlet and outlet headers arranged underneath the electrolyser by flexible, transparent PTFE tubes (see picture). The inlet tubes with smaller cross-sections ensure that a constant stream of electrolyte is supplied to the half-shells, whilst the tubes with larger cross-sections (corrugated hoses) carry the chlorine gas with anolyte and hydrogen gas with catholyte away from the cell. This fail-safe connection system can be used to check each individual cell for proper functioning by observing the colour and flow of the product streams in these tubes.
Between 20 and 90 elements can be connected to form a stack. Several of these stacks connected in series create a membrane electrolyser.
All this ensures: highest possible operational reliability, easy maintenance, timely cost-optimised membrane replacement and electrode recoating, no additional investments needed for back-up electrolysers, minimal loss of production.
Chlorine consumer table