The invention relates to a device for splitting water into hydrogen and oxygen by thermolysis , that is , by decomposition at elevated temperature .

The invention al so pertains to a process for spl itting water into hydrogen using the above device .

Background of the Invention

US patent No . 7 , 935 , 254 discloses a device for the thermolysis or thermal decomposition of water . The splitting of water into hydrogen and oxygen takes place in a device comprising a reactor having a heating system, a first reactor outlet for hydrogen, a second reactor outlet for oxygen, at least one water inlet and at least one oxygen filter, a hydrogen filter, an oxygen extraction pump, a hydrogen extraction pump and a water inj ection pump .

Summary of the Invention

The main goal of the invention is to improve the above device , in particular for reducing the energy needed to split the water and for increasing the yield of oxygen and hydrogen produced .

To this ef fect , the inventor has developed a device for splitting water into hydrogen and oxygen, comprising :

- a reactor having a heating system, a first reactor outlet , a second reactor outlet , at least one water inlet and at least one oxygen filter,

- at least one hydrogen filter,

- an oxygen extraction pump, a hydrogen extraction pump, at least one water inj ection pump, the particularity of this device being that it further comprises a hydrogen separation chamber located outside the reactor and containing the hydrogen filter ( s ) .

The invention also deals with a process for splitting water into hydrogen and oxygen, comprising the following steps :

- getting a device according to invention,

- connecting the water inlets to a source of water,

- connecting the heating system,

- controlling the heating system and the pumps so as to keep the temperature in the reaction chamber at more than 2000 ° C, the temperature in the hydrogen separation chamber at less than 1000 ° C and the exit temperatures of hydrogen and oxygen at less than 100 ° C, and

- recovering oxygen and hydrogen at the oxygen and the hydrogen outlets , respectively .

Other features and advantages of the invention will now be described in detail in the following description, which refers to the single appended figure that schematically shows an embodiment of the device of the invention .

Detailed description of the invention

An embodiment of the invention is shown in the appended figure .

The device for splitting water into hydrogen and oxygen, comprises , like the device of the above-mentioned prior art :

- a reactor 1 having a heating system 2 , a first reactor outlet 3 , a second reactor outlet 4 , at least one water inlet 5 and at least one oxygen filter 6 ,

- at least one hydrogen filter 7 ,

- an oxygen extraction pump 8 , a hydrogen extraction pump 9 , at least one water inj ection pump 10 . According to the invention, the device further comprises a hydrogen separation chamber 11 which is located outside the reactor 1 and contains the hydrogen filter ( s ) 7 .

Preferably several hydrogen filters 7 and several oxygen filters 6 are used . They may be connected to a hydrogen mani fold 25 and an oxygen mani fold 26 .

The hydrogen and oxygen filters 7 , 6 may consi st in straight hollow tubes arranged hori zontally, in order to avoid a signi ficant temperature gradient between the ends of the tubes which preferably are integrated in the walls of the hydrogen separation chamber 11 and the reactor 1 .

The filters 7 , 6 for hydrogen and oxygen may both be made of the same material which preferably is a known mixed ionic-electronic conducting (MIEC ) ceramic membrane that can withstand very high temperatures . Another advantage of such filtering membranes is that when used at about 850 ° C they extract only molecular hydrogen whereas at about 2250 ° C they extract only molecular oxygen .

The device preferably comprises three heat exchangers in order to avoid energy losses and reuse the thermal energy of the gases to heat the liquid or gaseous water .

The heat exchangers are for example typical shell and tube heat exchangers and they each have an inlet and an outlet for a first circuit and an inlet and an outlet for a second circuit .

As can be seen in the figure , the inlet 31 of the first circuit of a first heat exchanger 15 is connected to a first external water inlet 12 via the water inj ection pump 10 and the outlet 13 of the first circuit of the first heat exchanger 15 is connected to the inlet 14 of a first circuit of a second heat exchanger 16 , whereas the inlet 17 of the second circuit of the first heat exchanger 15 is connected to an outlet 18 of the hydrogen separation chamber 11 via the hydrogen extraction pump 9 and the outlet 19 of the second circuit of the first heat exchanger 15 is a hydrogen outlet of the device .

Thus the first heat exchanger 15 allows on one hand, to reduce the exit temperature of the hydrogen extracted from the hydrogen separation chamber to less than 100 ° C and preferably to about 50 ° C and, on the other hand, to trans fer the energy recovered from the exiting hydrogen to the liquid low temperature ( about 20 ° C ) water entering through the first external water inlet 12 .

The outlet 20 of the first circuit of the second heat exchanger 16 is connected to a second water inlet 21 of the reactor 1 and the inlet 22 of the second circuit of the second heat exchanger 16 is connected to the first reactor outlet 3 of the reactor 1 and the outlet 23 of the second circuit of the second heat exchanger 16 is connected to an inlet 24 of the hydrogen separation chamber 11 .

Therefore , the second heat exchanger 16 uses the heat of the mixture of hydrogen and steam coming from the reactor 1 to further heat the already heated water or steam coming from first heat exchanger 15 . At the same time , it cools the steam before it enters the hydrogen separation chamber 11 so that the hydrogen splitting can take place through the MIEC membrane filters 7 at a lower temperature of about 850 ° C . The separated hydrogen collected by the hydrogen separation chamber outlet 18 connected to the membrane filters 7 via the mani fold 25 can subsequently be pumped by the hydrogen extraction pump 9 and sent to the first heat exchanger 15 .

The second reactor outlet 4 of the reactor 1 is connected to the oxygen filters 6 via the mani fold 26 and to the inlet 27 of the first circuit of the third heat exchanger 28 and the outlet 29 of the first circuit of the third heat exchanger 28 is connected to the oxygen extraction pump 8 which is connected to the oxygen outlet 30 of the device ,

- the inlet 36 of the second circuit of the third heat exchanger 28 is connected to a second external water inlet 32 via a second water inj ection pump 33 and

- the outlet 34 of the second circuit of the third heat exchanger 28 is connected to the water inlet 5 of the reactor 1 .

As a result , the third heat exchanger 28 uses the heat of the oxygen coming from the reactor 1 to heat the cold water ( about 20 ° C ) entering from water inlet 32 and at the same time it cools the exiting oxygen to a temperature less than 100 ° C and preferably to about 50 ° C .

The oxygen molecules arrive at the filter wall where they split in 0-ions (Wagner' s law) which enter and hop into the vacancies/electron holes towards the center of the filter . When leaving the inside wall of the filter, they reconstitute into molecules which are sucked out through the opened end of the filter ( the other end of the filter being closed) .

The experiments that have been carried out by the inventor have demonstrated that the net energy needed to split 9 kg o f water into 1 kg of H2 and 8 kg of O2, both obtained with a purity of 99 , 99% , is smaller than 45 kWh .

The first and second external water inlets 12 , 32 may be connected to a common general external water inlet 35 .

The device of the invention is preferably provided with means for controlling the pumps , the heating system and optionally the partial pressures of hydrogen and oxygen .

The means are generally electronic means , in particular a computer implementing an appropriate software to control and optimi ze the splitting temperature of water and to increase the oxygen and hydrogen yields by acting on the heating system 2 , on the oxygen and hydrogen extraction pumps 8 , 9 , on the water inj ection pumps 10 , 33 and optionally on the partial pressures of the gases .

The computer maintains the balance between inj ected power and energy and the stable temperature in the reactor by checking the gas exit volumes and the water/ steam inj ection .

When the device has reached a stable condition, the gas mixture in the reactor is made of 94 % steam, about 4 % H2 and about 2 % O2 , with traces of OHy H ⁺ , and some H and 0 atoms ) .

As to the heating system, it comprises any appropriate burner, for example a known ultrahigh temperature (UHT ) burner having an inlet connected to a mixture of a fuel and a comburent , and an outlet for the exhaust gases . It is activated by starting the combustion of the mixture .

The temperature must be suf ficient high to cause the thermolysis of water in the reactor . Therefore , the fuel is generally composed of a combustible gas selected in the group consisting of unleaded gasoline , hydrogen, methanol , ethanol , methane , ethane , butane , propane and acetylene , the latter being preferred .

The comburent i s air or oxygen, the latter being preferred .

Preferably the burner is supplied with a mixture of a fuel as above and oxygen as a part of the oxygen produced by device itsel f . Better results in terms of energy consumption are even obtained when the oxygen provided to the burner is still hot . The device may then be provided with an oxygen duct connecting the oxygen outlet of the device to the inlet of the burner in order to recirculate a part of the oxygen produced by the device to the inlet of the burner .

According to a preferred embodiment of the invention, the heat losses are minimi zed to the extreme by placing the device inside a vessel having a double wall and preferably an external ceramic insulation . Inside the vessel , all hot components are advantageously insulated by special ceramics having low heat conductivity ( close to the 0 .2 W/m ² for water ) . The insulation is preferably arranged with wall at distances that choke the heat waves at a frequency corresponding to the temperatures in the delta space .

According to another preferred embodiment , the vessel has two walls ( optionally insulated on the external side by a ceramic layer ) separated by a space which is connected to a general water inlet 35 and the first and second external water inlets 12 , 32 . This feature of fers a very advantageous ef fect : the vessel acts as a whole cooling system because the water entering from the general water inlet circulates within the space between the walls before reaching the external water inlets 12 , 32 of the device . During that circulation the water absorbs heat , which on one hand, reduces the heat reaching the external wall of the vessel , and on the other hand, warms the water which thus needs less energy to reach the temperature needed for its splitting . Therefore the energy (heat ) lost by radiation of the external wall of the vessel is only 1 . 5-2 % , the other energy loss being due to temperature of the gases ( oxygen and hydrogen) exiting the vessel through the oxygen and hydrogen outlets 30 , 19 .

Process for splitting water into hydrogen and oxygen

The process according to the invention comprises the following steps :

- getting a device according to the invention,

- connecting the external water inlets 22 , 32 to a source of water,

- activating the heating system 2 , - controlling the heating system 2 and the flows through the pumps 8,9,10,33 to keep the temperature in the reactor 1 at more than 2000°C, preferably at a minimum of 2250°C, the temperature in the hydrogen separation chamber 11 at less than 1000°C, preferably at a maximum of 850°C, and the exit temperatures of hydrogen and oxygen at less than 100°C, preferably at a maximum of 50°C, and recovering oxygen and hydrogen at the oxygen and the hydrogen outlets 30,19, respectively.

According to a preferred embodiment, the heating system 2 is fed with a combustible gas, preferably acetylene, and oxygen, in order to ensure that a temperature exceeding 2200°C is reached.

In addition the combustion of oxygen will reduce the flue gases of up to 75% in comparison with air, while diminishing the production of carbon dioxide of up to 75%.

The oxygen can advantageously be a part of the oxygen produced by the device which is recirculated to the heating system 2.

The oxygen duct connecting the oxygen outlet of the device to the inlet of the burner is preferably inside the vessel in order to avoid losses of thermal energy.