Title:
A novel method for production of hydrogen gas by catalytic thermo-
chemical decomposition of water using waste heat of metallic slag
Field of invention:
This invention relates to a novel method of generating hydrogen gas
from water / steam using waste heat of metallic slag.
Cross-reference to related applications
This application is a co-pending application of Indian patent
application No. 387/KOL/06 filed on April 28th, 2006, entitled: Set up
for production of Hydrogen gas by thermo chemical decomposition of
water using steel plant slag and waste materials, which is a co-
pending application of patent application No. 900/KOL/05 filed on
September 30th, 2005 entitled: A method of generating hydrogen gas
and also relates to co-generation of oxygen oxides of carbon and
other gases. Each of the foregoing are incorporated herein by
reference in their entirety.

Background of invention:
Currently commercial processes for production of hydrogen gas use
either fossil fuels (coal, natural gas, etc.) or electricity. These
processes generate CO2 gas and hence require additional process
for separation and sequestration of CO2 which increase the cost of
production of hydrogen. Therefore, most of the commercial hydrogen
production processes are not considered as renewable as these
technologies merely shift the source of pollution from a distributed
one (like cars, households for example) to a more concentrated
source like a hydrogen producing plants or thermal power plants. On
the other hand, the capital investment and cost of production of other
energy resources such as nuclear, solar energy, solar PV, wind, tidal,
etc. make these techniques commercially less attractive.
In metal extraction and processing industries such as iron and steel,
stainless steel, nonferrous metals, a large volume of slag is
generated during extraction and refining processes. The molten slag
are commonly quenched by stream of water and disposed. Present
techniques which are used for slag disposal are not environmental
friendly as large amount of heat / energy is lost in the form of steam
in the environment and also these processes pollute the water used

for quenching of the slag. The innovative process is developed which
will reduce the cost of production of hydrogen by provide the cheap
energy source for hydrogen production and will also help to recover,
store and reuse the energy from metallic slag.
Objects of the invention:
An object of this invention is to propose a novel method of producing
hydrogen gas by catalytic thermo-chemical decomposition of water /
steam.
Another object of this invention is to propose a novel method of
producing hydrogen gas from water in presence of catalytic fluxes.
Further object of this invention is to propose a novel method of
producing hydrogen gas from water wherein waste heat and catalytic
properties of metallic slag are used for the thermo-chemical
decomposition of water / steam.
Still further object of this invention is to propose a novel method of
producing hydrogen gas from water / steam which is simple and cost
effective.

Statement of invention:
According to this invention there is provided a method for producing
hydrogen gas using waste heat of metallic slag comprising the steps
of:
providing metallic a slag;
subjecting the slag to the step of thermo-chemical decomposition of
water / steam;
collecting the hydrogen gas obtained from the said decomposition
reaction.
Detailed description of the invention:
A novel method is developed for production of hydrogen gas by water
/ steam and slag reactions. In this novel process, slag not only
provides sensible heat for endothermic water decomposition reaction
but also acts as a catalyst and arrests the reverse reactions between
hydrogen and oxygen gas. The temperature required for the
decomposition of water / steam in presence of metallic slag is above
1500°C. The lower oxides of metals in the slag react with oxygen gas
in the product gas mix and form very stable higher oxides and
thereby reduce the thermodynamic activity of oxygen.

Thermal decomposition of pure water in presence of slag:
The sensible heat of molten metallic slag can be used for the thermo-
chemical decomposition of water. In this process slag acts as heat
sources and sub oxides of metal in the slag also take part in the
decomposition reaction (1) by reacting with nascent oxygen via
reaction (2):

The exothermic oxidation reaction (2) provides additional energy
required for reaction (1) and also reduces the oxygen partial pressure
of the system and thereby enhances the rate of formation of
hydrogen gas. Metallic and oxide compounds are widely employed as
catalyst in many chemical processes such as methane decomposition
process, which is used for production of hydrogen gas. The presence
of the lower oxides in the slag thereby enhances the water
decomposition reaction. In addition to catalytic activity of slag, the
presence of molten metal and carbon impurities in the slag also assist
the decomposition reaction and arrest the recombination reaction.
The metallic slag is one or mixture of following slag:
a) Slag generated during stainless steel making operation
containing 20-30 Wt % silicon oxide, 20-36 Wt % aluminum
oxide and 15-36 Wt % magnesium oxide and other minor
impurities.

b) Titania slag generated after smelting of ilmenite or Fe-Ti-
oxides containing 80-90 Wt % titanium oxide, 8- 15 Wt %
iron oxide, 1 - 3 Wt % silicon oxide and other minor
impurities.
c) Slag generated during production of ferroalloys such as
FeCr, FeMn, FeSi, FeV, FeTi, etc. of various compositions.

WE CLAIM
1. A method for producing hydrogen gas using waste heat of metallic slag
comprising the steps of:
- providing metallic slag having temperature at least above 1500°C
generated in a metal extraction and steel production process;
- subjecting the slag to a step of thermo-chemical decomposition by
injecting water/steam which generate oxygen and hydrogen gases;
- collecting the hydrogen gas generating in said decomposition reaction;
characterised in that the presence of metallic suboxides (TiO, MnO, FeO
or CrO) in the slag act as a catalyst in the decomposition reaction of
water/steam in presence of high heat energy of the molten slag to
produce hydrogen gas, in that the exothermic decomposition reaction
enhances the process of hydrogen formation by reducing partial pressure
of the oxygen, and in that the presence of molten iron and carbon
impurities in the slag disables a recombination reaction while enhancing
the decomposition reaction.

2. The method as claimed in claim 1, wherein said metallic slag acts as a catalyst in
the decomposition reaction.
3. The method as claimed in claim 1, wherein said metallic slag is one or mixture of
generated slag in the process of:
a) Slag generated during stainless steel making operation containing
20-30 wt% silicon oxide, 20-36 wt% aluminum oxide and 15-36
wt% magnesium oxide and other minor impurities.

b) Titania slag generated after smelting of ilmenite or Fe-Ti-oxides
containing 80-90 wt% titanium oxide, 8-15 wt% iron oxide, 1-3%
silicon oxide and other minor impurities.
c) Slag generated during production of ferroalloys such as FeCr,
FeMn, FeSi, FeV, FeTi etc. of various compositions.

4. The method as claimed in claim 1, wherein said metallic slag is the source of
heat for the thermo-chemical decomposition of water.
5. The method as claimed in claim 1, wherein the oxidation of sub-oxides of metals
in the slag results from the exothermic reaction which provides additional energy
and also reduces the partial pressure of the oxygen to enhance the rate of
formation of hydrogen gas.

A method for producing hydrogen gas using waste heat of metallic
slag comprising the steps of: providing metallic a slag; subjecting the
slag to the step of thermo-chemical decomposition of water / steam;
collecting the hydrogen gas obtained from the said decomposition
reaction.