- WATER DESALINATION AND HYDROGEN PRODUCTION COUPLED BLOCK -


Desalination unit.

It is a modular plant for industrial-scale desalination of sea water and brackish drilling water, which use applied technologies and methodologies to recover distilled drinking water. We select the method of Multiple Effect Distillation (MED) because it offers the advantages as follows:
* It has excellent performance at relatively low temperatures.
* It is quite economic.
* It presents a few (not many) technical problems.
* It has minimal staff requirements.
* It has no specialized personnel requirements.
* More particular, in the case of evaporators at vertical MED provision, it is required the minimum heat exchange surface.
* It has already been implemented previously in commercial facilities combined with conventional fuels and other renewable energy sources.
* Moreover, it provides full advantage of waste brine for the production of high quality sea salt with the method of solar ponds.
The desalination plant consists of the following sections:
* Vertical evaporation columns of 3 levels.
* Linear Fresnel Reflector (LFR).
* Auxiliary equipment for water heating.
* Storage tanks for distilled water.
Key features:
* Temperature range 70/60/50 C.
* Required energy input 2 kwh/m3.
* Inlet of seawater 8 m3/h.
* Discarded brine 3 m3/h.
* Produced water salinity index <10TBS.
* Brine output 0.27 kg salt / kg solution.

Hydrogen unit.

A) PRODUCTION METHOD
We choose the commercial hydrogen production method by water electrolysis, where water breaks down to its key elements hydrogen and oxygen via electricity application. The unit uses technology of bipolar electrolytes which produce hydrogen at high pressure (up to 30 bar). The electrolytes' columns consist by bipolar plates/electrodes made of inert metal and they are connected to DC voltage feeders. Moreover, in order to facilitate the flow of electrical current in the device, a small quantity of NaOH typically is added in the water without directly involve in the reactions taking place at the electrodes. In practice this is an electrolysis of a NaOH solution corresponding indirectly to water electrolysis. The water which flows in electrolysis is distilled because it is inert and contains no ions. It passes through an ion exchange column so that its conductivity falls to 5 μS/cm. The electrolyzer is the only user of electrical power of the device that can absorb large power changes. When the power is reduced, so the production of hydrogen is reduced accordingly. In case of any abnormality, the unit stops its operation automatically, decompression is applied and the system is filled with nitrogen. The advantages of this process is the high purity of hydrogen produced for industrial or other use. Purity percentage is 99.9% for H2 and 99.8% for O2. Hydrogen can be used as an alternative fuel in properly modified catalytic burners, gas boilers, gas turbines and internal combustion engines. A parallel commercial use of oxygen takes place in industry and medicine.
B) ELECTRICAL ENERGY
We use small-scale hydroelectric plants for electricity generation through groups of Archimedes Screw Hydro Turbines to harness the potential energy of water. We select the Archimedes Screw Hydro Turbines because they can be installed in places with small height differences and they continue to operate under conditions of reduced water supplies. This makes the method applicable to hundreds of sites in rivers so far considered unusable. The usual production rates are 20-5,000 Nm3/h. For production of about 500 Nm3/h, the power of 2 MW of electricity is needed. Purity percentage is 99.9% for H2 and 99.8% for O2. The hydropower plant consists of the following sections:
* System of artificial lakes (reservoirs) which are built in places with small height differences (1-10 m) and water supply (0.5-5.5 m3/sec).
* Water-feeding pipes.
* Canals for acceleration of water flow.
* Positions of Archimedes Screw Hydro Turbine groups.
* Electrolytes protection system.
For the reliable operation we must be careful to maintain and protect the electrodes, because they are sensitive to possible damage. Especially in the use of renewable energy it is important to avoid the destruction of the electrodes due to disorders of the incoming power by the network. The shelf life of simple electrodes into changing networks is a few hours. Therefore, electrolytes usually are operated in nominal loads. When electrolytes are disabled, we apply protection voltage to avoid the corrosion of the electrodes.
C) STORAGE
We choose to store hydrogen in the form of CGH2 (compressed hydrogen gas). Currently the storage of hydrogen as a compressed gas is the simplest, the most common and effective method of storage. To store hydrogen efficiently in volume and weight, we must compress it with 20-100 MPa. Because of the low molecular mass, conventional compressors are not used but piston compressors instead. The produced hydrogen is stored in cylindrical tanks made of durable material.
D) COOLING SYSTEMS
The electrolysis unit and hydrogen compressor require cooling with cold water at 9-13 C. Proper cooling is essential for the safe operation of the plant. The minimum water pressure required for proper feeding of the machines is about 3 bar in an adjustable closed loop water cooling system which increases the safety of the installation.