FIELD OF INVENTION
The present invention relates to an on-board hydrogen generation system for underwater application; more particularly as submarines. The present invention more particularly relates to hydrolyser for onboard hydrogen generation using sodium borohydride (NaBH4) hydrolysis for end use in Submarine Air Independent Propulsion System.

BACKGROUND OF THE INVENTION
Hydrogen gas is used as fuel for fuel cells of submarines and under water vehicles. A compact, high-density, controllable source of hydrogen gas is required. Hydrogen gas cylinders are too heavy and bulky, while liquid hydrogen requires cryogenic cooling. Metal hydride systems are limited to 1-3% hydrogen by weight; are endothermic (that is, as hydrogen is evolved, the container gets colder, which reduces the hydrogen vapor pressure); the hydrogen evolution rate is not controllable or adjustable (so that an oversized amount of hydride is necessary).

Hydrogen generation is the first subsystem in the process train. The hydrogen flows in to fuel cell stacks where it is consumed along with oxygen to form water and unregulated DC power.

Hydrogen generation when carried out in an ‘underwater’ setting requires conformity with various platform restrictions. The technical operation system requirements are way different than terrestrial operations.

Submarines and underwater platforms depend on batteries and other stored form of energy for propulsion power. While the land based systems have flexibility of choice of power systems and can harness the oxygen in atmosphere for burning of fuel, this is not possible for a submerged system. Conventional submarines use hybrid power systems comprising of the lead acid batteries which serve as the power supply system for propulsion needs when underwater. Diesel engines provide for onboard recharging of batteries, possible only during snorkeling. The system therefore has restricted indiscretion.

US7938077 relates to hydrogen generation apparatus. The said apparatus comprising a hydrolysis reaction compartment, a mass of solid lithium hydride disposed in the compartment, inlet and outlet means for passing sea water through the compartment to generate steam, lithium hydroxide and hydrogen gas, a condenser for condensing the steam and lithium hydroxide, and a tank for collecting the hydrogen gas, the tank having outlet means for discharging the hydrogen gas to a vehicle propulsion means.

DE202004020537 relates to underwater drive system for submarine that uses stores of oxygen and hydrogen that are fed to fuel cell and waste heat from fuel cell to warm metal hydride hydrogen store to release hydrogen. The energy supply system of this prior art comprises one or more fuel cell an array of metal hydride hydrogen stores.

US3210157 relates to generation of hydrogen by reacting of water with an alkali metal borohydride, an alkaline earth metal borohydride or water soluble amine boranes.

US5372617 relates to hydrogen generator for generation of hydrogen gas by a substantially stoichiometric hydrolysis reaction between water and a hydride.
There exists a need of hydrogen generation on-demand to fuel fuel-cells to quench underwater power requirement for propulsion. Further that the hydrogen generation system be compact with low noise and vibrations and do not generate gaseous by-product.

The inventors of the present invention have devised a hydrolyser with in-built heat exchanger system for on-board hydrogen generation with sodium borohydride hydrolysis. The on-board hydrogen generation system of the present invention provides continuous supply of hydrogen when dived. The present invention also provides for killing the hydrolysis reaction as safety measures in emergency.

Uniqueness of the hydrogen generation system of the present invention:-
• Underwater marine platform is dynamic in nature owing to sea conditions and hence agitation was done through recirculation of the slurry instead of a stirrer. This also reduces the underwater vibrations which is highly critical for Submarine systems.
• The recirculation method is also used for heat transfer through conformal inbuilt heat exchangers as the hydrolysis reaction is exothermic. This keeps external piping minimal and enhances safety (from leaking through piping) apart from the compactness.
• Under dynamic motion due to sea conditions, the level of the liquid inside the H2 generator is difficult to monitor, due to sloshing effect, for deciding when to unload part of the liquor. The present configuration, while operation, always fills the space by forced circulation leaving a small amount of liquid in the suction side of the recirculation pumps and thus allows easy level monitoring.

OBJECTS OF THE INVENTION

It is an object of the present invention to provide hydrolyser for an onboard hydrogen generation system for underwater application.

It is an object of the present invention to provide hydrolyser for generation of hydrogen gas from borohydride hydrolysis.

It is another object of the present invention to provide hydrolyser for onboard hydrogen generation system for underwater application with in-built heat exchangers.

It is further an object of the present invention to provide a compact hydrolyser using recirculation based borohydride hydrolysis.

It is yet another object of the present invention to provide for onboard hydrogen generation to allow longer underwater endurance.

It is yet another object of the present invention to provide continuous supply of hydrogen to fuel fuel-cells in power generation unit in Air independent propulsion system.

SUMMARY OF THE INVENTION

According to an aspect of the present invention there is provided a method of generating hydrogen from on-board hydrogen generation system comprising fuel tank, catalyst tank, compact vessel with in-built heat exchangers, intermediate tank, spent storage tank, pressure control means wherein, the said method comprising the steps of:
a. pumping the fuel solution and caustic solution from fuel tank and catalyst from catalyst tank to the compact vessel with in-built heat exchangers;
b. hydrolyzing borohydride in fuel solution in presence of catalyst in the said compact vessel for generating hydrogen at higher rate than required;
c. discharging the resultant borax solution formed as byproduct in step b, intermittently to intermediate tank wherein the trace borohydride in borax solution is converted to hydrogen, the resultant residual hydrogen then joins to the main hydrogen line and remainder is discharged to spent storage tank;
d. hydrolyzing reaction in step b, resulting in increase in pressure; which activates the pressure control means to stop the fuel solution feed in step a;
e. as hydrogen is consumed by phosphoric acid fuel cell (c), the pressure in the compact vessel falls thereby restarting the fuel solution feed;
f. providing the said compact vessel with conformal heat exchanger for heat removal and reactant mixing;
g. providing the said compact vessel with top mounted heat exchanger for cooling product hydrogen;
h. providing the said compact vessel with non-conventional heat exchanger coils for removal of heat and reactor temperature maintenance comprising shell side circulating borate solution and tube side circulating de-mineralized water.
BRIEF DESCRIPTION OF ACCOMPANYING DRAWINGS
Figure 1: Schematic diagram of hydrogen system of the present invention with hydrolyser.
Figure 2: Schematic and Isometric view of Heat Exchanger
Figure 3: Top view of Heat Exchanger
DETAILED DESCRIPTION
The following description with reference to the accompanying drawings is provided to assist in a comprehensive understanding of exemplary embodiments of the invention. It includes various specific details to assist in that understanding but these are to be regarded as merely exemplary.

The present invention is described in connection with such embodiments, but the invention is not limited to any embodiment. The scope of the invention is limited only by the claims and the invention encompasses numerous alternatives, modifications and equivalents. Numerous specific details are set forth in the following description in order to provide a thorough understanding of the invention. These details are provided for the purpose of example and the invention may be practiced according to the claims without some or all of these specific details. For the purpose of clarity, technical material that is known in the technical fields related to the invention has not been described in detail so that the invention is not unnecessarily obscured.

The present invention relates to hydrolyser for onboard hydrogen generation system for underwater application using recirculation based borohydride hydrolysis, more particularly sodium borohydride (NaBH4) hydrolysis process.

Capacity or scale of hydrogen generation by sodium borohydride hydrolysis process is first time developed in the present invention. In the present invention process of sodium borohydride hydrolysis, aqueous solution of sodium borohydride (NaBH4) is used for generating hydrogen by dosing it inside reactor system along with Catalyst in form of NiCl2 or CoCl2 solution which get converted inside the reactor in presence of NaBH4 to Ni / NiB or Co/CoB particles which act like a catalyst. Sodium borohydride reacts with water to generate hydrogen and borate slurry in presence of this catalyst. Hydrolysis reaction is exothermic in nature and generated heat is dissipated by pumping the NaBH4 / catalyst /product liquor slurry through a heat exchanger which could be cooled by water or even air. The slurry after heat exchanger is flashed into the same vessel from which it was pumped out.

In an embodiment of the present invention, there is provided a method and materials for the generation of hydrogen gas from storage materials. In particular, the present invention relates to generation of hydrogen gas by contacting water with sodium borohydride in the presence of a catalyst, such as cobalt or nickel.

In a major embodiment of the present invention, the components of hydrolyser of the present invention are as follows:
• The agitation to ensure uniform mixing and heat transfer to keep temperature of the slurry in control is achieved by re-circulating the NaBH4 /catalyst and product slurry through a heat exchanger and a pumping device.
• The main vessel which holds the catalyst / NaBH4 feed and NaBO2 product also acts like a gas-liquid separator and a buffer tank for the hydrogen.
• The system generates no gaseous by product and hence is ideal for underwater or enclosed area hydrogen generation.
• The hydrogen generated is filtered using micro filters and is transferred to fuel cell section for electricity production. Hydrolysis reaction take place inside reactor system is as follows

• Product hydrogen cooling coming out of the main vessel is done by finned tube heat exchanger integrated at top of reaction vessel for process compaction and outlet temperature is maintained by Demineralize water circulation. Schematic diagram for hydrogen generation from sodium borohydride hydrolysis process is depicted in figure 1. Design was done considering the submarine environment conditions of tilting, shock, noise, vibration etc.
Working of the Hydrolyser of the Present Invention:
Figure 1 is the schematic representation of onboard hydrogen generation from sodium borohydride solution with hydrolyser of the present invention. Sodium borohydride is dissolved in mixed caustic solution stored inside fuel tank and pumped to the main vessel containing suspended catalyst (catalyst tank) particles and reaction byproduct borax solution which is called borate slurry. The borate slurry along with reaction mass is recirculated through a pump (recirculation pump) to a heat exchanger and is returned to the vessel where the hydrogen is flashed and separated from the slurry. The hydrogen separated in the vessel is cooled and passed through an alkali line mist separation filter train followed by an acid scrubber. The clean gas is finally taken to fuel cell system.

Product borate solution intermittently discharge through hydrolyser to an intermediate tank and finally to spent storage tank. Intermediate borate tank is kept to allow conversion of trace NaBH4 in the borate slurry and this residual hydrogen generated joins the main hydrogen line. Two stage pressure regulators provided to supply constant amount of hydrogen to fuel cells irrespective of the pressure in the main vessel.

The hydrolyser of the present invention is compacted by placing the conformal heat exchanger system inside the main vessel for heat removal and reactant mixing. The product hydrogen cooling is done in the same single vessel through a top mounted heat exchanger so that condensate forms can roll back into the main vessel. Non-conventional heat exchanger coil is designed for removing reaction heat and maintaining reactor temperature as shown in figure 2 and 3. Water is used for cooling purpose.

Shell side is used for borate solution and tube side is used for de-mineralize water circulation. Tube bundle is made concentric to shell boundary to achieve process requirements, easy integration and maintenance purpose. Inspection nozzles are provided to check health of tubes.
In the embodiment of the present invention the fuel solution is selected from zinc borohydride (ZnBH4), potassium borohydride (KBH4), calcium borohydride (CaBH4), lithium aluminum hydride (LiAlH4), sodium boron trimethoxy hydride (NaBH(OCH3)3), or sodium borohydride (NaBH4). Most preferred being sodium borohydride (NaBH4).

In the embodiment of the present invention the catalyst is selected from aqueous solution of NiCl2 or CoCl2

According to an embodiment of the present invention there is provided a method of generating hydrogen from on-board hydrogen generation system comprising fuel tank, catalyst tank, compact vessel with in-built heat exchangers, intermediate tank, spent storage tank, pressure control means wherein, the said method comprising the steps of:
a. pumping the fuel solution and caustic solution from fuel tank and catalyst from catalyst tank to the compact vessel with in-built heat exchangers;
b. hydrolyzing borohydride in fuel solution in presence of catalyst in the said compact vessel for generating hydrogen at higher rate than required;
c. discharging the resultant borax solution formed as byproduct in step b, intermittently to intermediate tank wherein the trace borohydride in borax solution is converted to hydrogen, the resultant residual hydrogen then joins to the main hydrogen line and remainder is discharged to spent storage tank;
d. hydrolyzing reaction in step b, resulting in increase in pressure; which activates the pressure control means to stop the fuel solution feed in step a;
e. as hydrogen is consumed by phosphoric acid fuel cell (c), the pressure in the compact vessel falls thereby restarting the fuel solution feed;
f. providing the said compact vessel with conformal heat exchanger for heat removal and reactant mixing;
g. providing the said compact vessel with top mounted heat exchanger for cooling product hydrogen;
h. providing the said compact vessel with non-conventional heat exchanger coils for removal of heat and reactor temperature maintenance comprising shell side circulating borate solution and tube side circulating de-mineralized water.

Accordingly, those of ordinary skill in the art will recognize that various changes and modifications of the embodiments described herein can be made without departing from the scope of the invention. In addition, descriptions of well-known functions and constructions are omitted for clarity and conciseness

CLAIMS:
1. A method of generating hydrogen from on-board hydrogen generation system comprising fuel tank, catalyst tank, compact vessel with in-built heat exchangers, intermediate tank, spent storage tank, pressure control means wherein, the said method comprising the steps of:
a. pumping the fuel solution and caustic solution from fuel tank and catalyst from catalyst tank to the compact vessel with in-built heat exchangers;
b. hydrolyzing borohydride in fuel solution in presence of catalyst in the said compact vessel for generating hydrogen at higher rate than required;
c. discharging the resultant borax solution formed as byproduct in step b, intermittently to intermediate tank wherein the trace borohydride in borax solution is converted to hydrogen, the resultant residual hydrogen then joins to the main hydrogen line and remainder is discharged to spent storage tank;
d. hydrolyzing reaction in step b, resulting in increase in pressure; which activates the pressure control means to stop the fuel solution feed in step a;
e. as hydrogen is consumed by phosphoric acid fuel cell (c), the pressure in the compact vessel falls thereby restarting the fuel solution feed;
f. providing the said compact vessel with conformal heat exchanger for heat removal and reactant mixing;
g. providing the said compact vessel with top mounted heat exchanger for cooling product hydrogen;
h. providing the said compact vessel with non-conventional heat exchanger coils for removal of heat and reactor temperature maintenance comprising shell side circulating borate solution and tube side circulating de-mineralized water.

2. The method of generating hydrogen from on-board hydrogen generation system as claimed in claim 1 (a) wherein the said fuel solution is selected from zinc borohydride (ZnBH4), potassium borohydride (KBH4), calcium borohydride (CaBH4), lithium aluminum hydride (LiAlH4), sodium boron trimethoxy hydride (NaBH(OCH3)3), or sodium borohydride (NaBH4).

3. The method of generating hydrogen from on-board hydrogen generation system as claimed in claim 1 (a) wherein the said catalyst is selected from aqueous solution of NiCl2 or CoCl2.