CROSS REFERENCE
A generic principle for the production for the production of hydrogen gas using
waste heat of molten slag including an system for carrying out the process of the
invention is disclosed in WO 2007/3695 and WO 2007/125537, Indian Patent
Application 803/Kol/07, all of which are incorporated by way of reference.
FIELD OF INVENTION
The invention relates to a method for safely harvesting hydrogen gas by reacting
molten slag having reducing agents with one of water and steam to form
hydrogen-rich gas that can be reused as a fuel. The invention further relates to a
system for carrying out the method.
BACKGROUND OF INVENTION
In metal extraction and processing industries such as the production of iron and
steel, stainless steel, nonferrous metals, a large volume of slag is generated
during the extraction and refining processes. The high temperature molten slag
is commonly quenched by a 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 / emitted in the environment and also these practices
pollute the water which is used for quenching of the slag. Presently, the global

warming, rise in the demand of energy, depleting natural resources (coal, oil and
nature gas) are a major concern to mankind. Therefore, there is an urgent need
for development of a new technology for conservation and recovery of energy,
which is wasted, in industrial practice. For example, more than 50 % of heat
generated in the power plants and heating applications is wasted. The excessive
use of fossil fuels is a major source of green house gas emission and global
warming. The alternative to fossil fuels is hydrogen, solar, wind, geothermal, etc.
These energy resources have the potential to control and reduce the emission of
green house gases.
Hydrogen technology: Worldwide, the electrolytic process is used for production
of hydrogen gas. Currently, this method is employed for generation of high purity
hydrogen. The cost of hydrogen produced by this method is significantly higher
and therefore it is predominantly used only in specialty applications such as
semiconductor manufacture.
Steam-methane reforming process is used widely for the hydrogen production.
This process is the most energy-efficient commercialized technology currently
available, and is most cost-effective when applied to large and constant loads.
Partial oxidation of fossil fuels in large gasifiers is another method of hydrogen
production. It involves the reaction of a fuel with a limited supply of oxygen to
produce a hydrogen mixture, which is then purified. Its primary by-product is
carbon dioxide.

However, these commercial processes employed for production of hydrogen gas
are based on either fossil fuels (coal, natural gas, methane, etc.) or electricity
(part of which comes from thermal power plants). Also the product gas produced
by these techniques, except electrolysis of water, comprises H2 and CO / CO2.
The use of hydrogen produced by these techniques therefore only shifts the
emission of CO2 from end applications (vehicles, etc.) to the production plants
(hydrogen production plants / power plants). Therefore, current hydrogen
production processes are not completely clean or green until additional processes
for separation and sequestration of CO2 are developed and incorporated in the
commercial hydrogen production plants. However, these new techniques
invariably increase the cost of hydrogen. Therefore, most of the commercial
hydrogen production processes are not considered as renewable. Emerging
methods hold the promise of producing hydrogen without carbon dioxide
emissions, but all of these are still in early stages of development. Some of these
technologies are thermo-chemical water-splitting using nuclear and solar heat,
photolytic (solar) processes (photo-electrochemical, electrolysis), and biological
techniques [4]. However, the capital investment and cost of production of energy
resources such as nuclear, solar thermal, solar PV, wind, tidal, etc. make these
techniques commercially less attractive.
Energy required for endothermic reactions of hydrogen production is supplied by
adding excess fossil fuel and oxygen or air in the reactor. The waste heat
generated in metallurgical industries (such as molten slag or liquid metal) can be
a potential alternative source for these endothermic reactions of hydrogen
generation. A method for the production of water gas by contacting steam with

carbon in a bath of molten metal is disclosed in U.S. Pat. No. 1,592,861 and U.S.
Pat application 0030130360. In this process, the steam reacts with carbon and
dissociates into hydrogen and carbon monoxide at temperatures of 900 to 1200
C. The carbon input to reaction is adjusted to generate carbon monoxide and to
minimize CO2 formation. In another patent (U.S. Pat. No. 4,388,084) molten iron
bath is used for the gasification of coal by using coal, oxygen and steam at a
temperature of about 1500° C. In this process a ratio of hydrogen to carbon
monoxide in the product gas is about 0.5:1. T. Akiyama et al. (2000) reviewed
the methods for recovery of waste heat of molten slag. The use of molten slag
bath for gasification and decomposition of fuel is explained in U.S. Pat. No.
2,953,445. In this invention a water gas composition is obtained wherein the
ratio of hydrogen to carbon monoxide is about 0.38:1. Although many
techniques (as described above) are developed for hydrogen gas formation using
waste heat, the product gas in these techniques still comprises sizable amount of
CO and / or CO2 (with H2:CO in the range of 0.3:1 to 1:1) as in these techniques
large volume of carbonaceous material is used as a reductant. This type of
product gas generates greenhouse gases at the end applications or purification
stages. Therefore, it would be advantageous to have a method that can minimize
or eliminate the use of carbonaceous material and thereby abate greenhouse gas
emission. The product gas with high H2:CO can also be used for the production
of high-value hydrocarbons.

OBJECTS OF THE INVENTION
It is therefore an object of the invention to propose an improved method for
harvesting hydrogen gas adaptable as fuel by reacting molten slag with one of
water and steam.
Another object of the invention is to propose an improved method for harvesting
hydrogen gas adaptable as fuel by reacting molten slag with one of water and
steam, which is a semi - continuous process for removing of waste heat of
molten slag to form hydrogen gas.
A still another object of the invention is to propose an improved method for
harvesting hydrogen gas adaptable as fuel by reacting molten slag with one of
water and steam, which is adaptable as a continuous process for recovering of
hydrogen gas in large metal producing plant.
Yet another object of the invention is to propose an improved method for
harvesting hydrogen gas adaptable as fuel by reacting molten slag with one of
water and steam, which is capable of utilizing additional reducing agent to
improve the efficiency.

A further object of the invention is to propose an improved method for
harvesting hydrogen gas adaptable as fuel by reacting molten slag with one of
water and steam, which is capable of recovering even the sensible heat of the
molten slag to make the process further cost-effective.
A still further object of the invention is to propose a system for producing
hydrogen gas by reacting the molten slag with one of water and steam.
Yet further object of the invention is to propose a system for producing hydrogen
gas by reacting the molten slag with one of water and steam, which is capable of
producing and safe collection of hydrogen gas by catalytic thermo-chemical
decomposition of water and/or steam.
SUMMARY OF THE INVENTION
The present disclosure provides a simple, low cost innovative process, in which,
water / steam and a small amount of carbonaceous flux are contacted with
molten slag to generate hydrogen-rich gas. The present disclosure describes an
improved and safe process for recovery of waste heat of molten slag in the form
of hydrogen gas and steam and a corresponding system to carryout the method.
The process is simple and can be easily incorporated in commercial metal
extraction and refining production units.

The invention further provides innovative intra-process parameters for example,
a) collecting the hydrogen gas safely in the collection tank by using steam
envelop, which is one of the input materials in step one and / or the by-
product of water vaporization, as a carrier and protecting medium for
hydrogen gas stream,
b) adaptability of the molten slag as the heat source (for steps one and two),
oxygen absorber (in step two), and as a catalyst (for reactions in steps one
and two),
c) recovering the sensible heat of the molten slag at lower temperature in the
form of steam to use for heating and power generating applications; and
d) application of a semi-continuous process for production of hydrogen gas and
steam using waste heat of the molten slag.
An exemplary embodiment of the present invention provides a novel method for
recovery of waste heat of molten slag to form the hydrogen gas at higher
temperature (> 1250°C) in first step and steam at lower temperatures (<
1250°C) by adapting a specially developed system / set-up. The hydrogen gas
and steam generated in two steps can be used directly for heating applications in

the plant or for generation of power. The hydrogen gas can also be used in
combination with CO gas formed in other operations for production of methanol
or higher hydrocarbon fuels.
An advantageous embodiment of the present invention provides a semi-
continuous process for recovering of waste heat of molten slag in the form of
hydrogen gas and / or steam which is simple, cost effective and environment
friendly.
According to a further advantageous embodiment of this invention, there is also
provided a system for production and safe collection of hydrogen gas by catalytic
thermo-chemical decomposition of water and / or steam by using waste heat of
molten gas.
The present invention basically constitutes thermo-chemical decomposition of
water and / or steam by using the heat of the molten slag to form hydrogen and
oxygen. The oxygen formed in the reaction is absorbed by reducing agents
present in the slag or / and added separately in the reactor, which minimizes the
recombination of the oxygen and hydrogen in the product gas.
These together with other objects of the invention, along with the various
features of novelty, which characterize the invention, are pointed out in the
claims annexed to and forming a part of this disclosure. For better understanding
of the invention, its operating advantages and the specific objects attained by its

uses, reference should be had to the accompanying drawings and descriptive
matter in which there is illustrated preferred embodiments of the invention.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWING
The invention is explained in greater details with the accompanying drawing:
Figure 1, schematically illustrates the complete assembly of the system according
to an embodiment of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
According to the present invention, waste heat of molten slag in a first step is
recovered by contacting water and / or steam with molten slag having reducing
agents. In this step, the molten slag provides the energy for the endothermic
water decomposition reaction (1) and form of the hydrogen and oxygen gas.

Simultaneously, the reducing agent present within the slag reacts with the
oxygen formed in the decomposition reaction and thereby minimizes the
recombination reaction. This oxygen capture reaction (2), and reduces the partial
pressure (thermodynamic activity) of oxygen in the reactor and thereby
enhances the rate of the water / steam decomposition reaction.


where Mx0y represent combination of various types of reductant (for example,
metallic: x = 1, y = 0, monoxides: x = 1, y = 1, etc.) present in the molten slag
and MaOb represent higher oxides (e.g. a=l & b=2, a=2 & b=3, etc.).
The molten slag in the present invention can include blast furnace slag, steel
making slag, EAF slag, slag generated in ferroalloys plant, titania slag, non-
ferrous plant slag, and/or any combination thereof. In a preferred case, the
molten slag includes steel making slag (preferably LD-steel making slag). The
steel making slag may be described as a CaO-SiO2-FeO ternary slag with MnO,
MgO, AI2O3, Fe, etc as a minor constituents, but it should be noted that the
present invention is not limited thereto. Optionally molten slag can be pre-
treated to get the required properties (for example removal of the solidified mass
/ pieces), if required, although this is not critical to the reactions involved in this
invention.
Flux addition. Although the reductants in the slag are primarily responsible and
sufficient for water decomposition and oxygen capture, additional carbonaceous
fluxes may be provided in the reactor to capture any oxygen (via reaction 3),
which is not arrested by the reductant in the molten slag (reaction 2) and also
for further reduction of oxygen partial pressure in the reactor.


According to the present invention, the part of CO also reacts with steam and
generates hydrogen (reaction 4) due to presence of excess steam in the reaction
zone.

The composition of product gas in terms of H2, CO, CO2, and H2O depends on
the amount of flux and water (steam) and on reaction thermodynamic and
kinetics at given temperatures. The production of H2 is optimized by operating
within phase regions that establish a high activity of reductants. This applies
both to the reductants present in the slag and flux. However, the present
invention does not exclude operation in the other regions of phase equilibrium
and different types of slag systems.
The carbonaceous flux can include coal, coke, & their fines, used oil, tar or a
similar substance, pet coke, plant waste, municipal waste, hazardous waste,
biomass, tires and/or any combination thereof. In a preferred embodiment, the
carbonaceous material includes coal and the following description refers to coal
as the carbonaceous material, although it will be understood that the present
invention is not limited thereto. Optionally carbonaceous flux can be pre-treated

to achieve required quality / properties (e.g. particle size, reactivity, etc.), if
required, although the pre-treatment of the flux is not critical to the reactions
involved in this invention.
Thus, one advantage of utilizing this double protection scheme (the use of
reductant in slag and the use of a flux) according to this invention is that the
exothermic oxidation reactions (2 & 3) not only help to reduce and control the
oxygen partial pressure (thermodynamic activity) but also provide additional heat
to endothermic reactions (1 & 4). The oxidation reactions reduce the oxygen
partial pressure in the reaction zone, which also enhances the rate of water
decomposition reaction.
In short, the fundamental principle of this invention is a thermo-chemical cycle
developed for decomposition of the water and / or steam by using the high
temperature molten slag generated in metal industries. The process not only
uses the sensible heat of the slag but also utilizes its chemical energy and
catalytic properties for decomposition of water and arresting the recombination
reactions of decomposition products. The carbonaceous fluxes can also be
employed in this process for enhancing the rate of reactions and kinetics. The
overall reaction of hydrogen gas formation can be presented as:


where A represents the amount of water / steam added in the system, x is the
amount of C available in the flux, y is the amount of reductant (metallic and or /
lower oxide species) in the slag and z is the amount of CO2 formed by reaction
of C & CO with oxygen or water. The present invention also includes oxidation
reactions of lower oxides other than MO and formation of higher oxide other
than M2O3 as oxygen sink.
In the second step of this-inventive process, when the hydrogen formation
reaction subsides due to the decrease in the slag temperature, the water and /
or steam input to the reactor and other system parameters (pressure, collector,
etc.) are readjusted to generate the high temperature and / or high pressure
steam as a product. This steam can be used as input to the first step of the
inventive process and / or for other heating and power generation applications.
Production of the steam continues as long as the energy of slag is available and
is dictated by economics, at which point the process is terminated.
According to the present invention, the recovery of waste heat of molten slag in
the form of hydrogen results in a very high ratio of hydrogen to carbon
monoxide and can be controlled. This is more advantageous than hydrogen gas
produced in the prior arts, except water electrolysis, and hence this innovative
process is a superior alternative for recovery of waste heat of slag and for
production of clean / green energy source.

The methanol and / or bio-diesel is produced by a catalytic reaction of hydrogen
and CO at high temperature. In an embodiment of the present invention the
hydrogen product gas and CO gas generated / separated from other waste gases
coming out from metal industries is used to form methanol or a higher hydro-
carbon by adjusting the H2:CO ratio and using waste heat of slag or other
sources within metal industries. According to this part of invention, the overall
reaction is illustrated as:

HYDROGEN PRODUCING SYSTEM OF THE INVENTION
The system is one of the major embodiments of present invention. A non-limiting
schematic representation of a complete assembly of the system is shown in
Figure 1. Some of the important points considered for designing the system for
hydrogen harvesting are:
1) simple, safe and low cost system which can be incorporated in industry /
plant with minimum disturbance to existing operations,

2) reaction chamber should have enough strength to hold molten slag and also
provide maximum surface area of slag with minimum heat loss to
environment,
3) profile of the reaction chamber should provide better steam/water - slag
contact and maximum residence time,
4) configuration should facilitate smooth flow of product gas away from reaction
zone and flow of steam / water towards slag surface,
5) configuration should also provide facility to contact fresh product gas with
carbonaceous flux for further oxygen removal and steam decomposition
reactions,
6) product gas collector means should collect the hydrogen gas in steam jacket
till it reaches the collection tank where steam is separate from hydrogen gas
by condensation, and
7) system should have provision for easy discharge of the solidified slag after
recovery of the waste heat.

The important features of the system (Fig 1), in present invention, are described
below by means of a non-limiting example:
1. Slag Box: A slag box (1) is designed to hold the high temperature molten
slag. The inventors found that a typical content for the box (1) is between 5
and 50 tonnes, for instance about 10 tonnes of slag. The slag box (1) is
preferably made of steel plate and an additional structure (not shown) is
provided at the bottom of the box (1) as a stiffener to hold the high
temperature molten slag. The slag box (1) is fixed on the bottom platform,
via at least two side hinges on the front end and a plurality of flat resting
pads at the rear bottom side. A provision (2) for fitting the box (1) is made at
the bottom of the backside for tilting the slag box (1) and removal of the
slag. A slanted shape on the front side assists for easy disposal of the slag.
The top edge of the box (1) is preferably shaped such that a reaction hood
(3) rests on the edge during the hydrogen harvesting. The other designs /
mechanisms for slag holding and disposal (such as moving slag box, lifting
box by crane for slag discharge, etc) are not excluded from the scope of the
present invention.
2. Reaction hood: The reaction hood (3) is capable of spraying water and / or
steam and fluxes on the molten slag surface at a required flow rate and also
collect the product gas safely with minimum air infiltration. The function of
the hood (3) is to isolate the reaction chamber from the surrounding
atmosphere. Means such as ceramic wool and / or similar material pads may
be provided on the base of the hood (3) for proper resting of the reaction

hood (3) on the slag box (1) and for complete insulation to avoid any air
infiltration inside the reaction chamber. A plurality of nozzles (4) are provided
on the walls of the reaction hood (3) for spraying / injecting water and / or
steam. The nozzles (4) allow water / steam to sprinkle upon the entire
surface area of the molten slag in the slag box (1). The nozzles (4) are
connected via inlet pipes to a central water / steam inlet pipe (5). The flow
rate and pressure of the water / steam is controlled by a water inlet valve (6)
and monitored by an on-line flow meter and a pressure transducer. Flux
chambers (7) are provided on the side wall of the hood (3) for spraying the
desired quantity of the flux on the slag surface for thermo-chemical
decomposition reaction of water. In a preferable embodiment, the number of
flux chambers (7) used is at least 2, and preferably at most 6. A suitable
number of the flux chambers (7) is 4. Pneumatically operated sliding gate
valves may be provided for each flux chamber (7) to a) open the gate for
discharging the flux inside the chamber and b) to keep the chamber closed.
The other designs / mechanisms for water - slag reactions (such as counter
current heat exchanger, granulation, etc) are not excluded from the scope of
the present invention.
3. Gas collection device: It comprises of a plurality of collection sections (8)
which are preferably conical in shape and which are located on the top of the
reaction hood (3) for collection of product gas mixture and steam from the
reaction chamber. In a preferable embodiment, the number of collection
sections (8) used is at least 2, and preferably at most 6. A suitable number of

collection sections (3) appears to be 4. The location and shape of the
collection sections (8) is designed for complete, smooth and safe collection of
the product gas from the reaction hood (3). The proper collection of the gas
from all the sides is essential for maintaining uniform pressure inside the
reaction chamber and also to avoid generation of any excess pressure and /
or backpressure. The conical sections (8) are connected to a central gas
collection pipeline through flexible stainless steel tubes. The flexible tubes are
provided for compensating the upward and downward movement of the hood
(3). The gas is collected in a tank (9). The gas is collected using water
displacement technique. The system may be provided with means for venting
excess steam / gas from gas collection device, such as an excess steam valve
(10). Water inlet (11) and outlet valves (12), gas inlet valve (13), compound
gauge, explosive diaphragm, sampling valve, gas flow and pressure sensor,
etc. are provided in the gas collection device for proper and safe collection
and storage of the hydrogen gas. The other designs / mechanisms for gas
collection (such as blowers, suction pumps, condenser - buffer tanks, etc) can
also be included in the present invention.
4. Instrumentation & Control system: A central control panel is provided for
operating the system and also for monitoring and acquisition of data.
Electronic sensors are fixed on various locations of the system for continuous
monitoring of the temperature and pressure inside reaction zone, and flow
rate of water and / or steam and product gases. An on-line hydrogen gas
analyzer is provided near the gas inlet valve (13) on the gas collection tank.

The sensors are connected to the central control panel for data acquisition
and monitoring. The advanced automatic control device can also be
incorporated in the system for better process control and safe operations.
The system, described in present invention, enables the maximum recovery
of the waste energy of the molten slag in the form of hydrogen gas and
steam. However, it will be appreciated that other types of system can also be
utilized in accordance with the present invention. The selection and type of
system is dictated by properties of slag (temperature, fluidity, composition,
etc.), scale, economics and plant operations, at which maximum heat
recovery is possible with required safety and minimum operational problems.
In the present invention, one of the standard procedures used for hydrogen
harvesting in a batch type process with single slag box and reaction hood is
described below: Before starting the operation a complete safety check of the
system and the surrounding area is conducted. The slag box (1) is dried properly
for removing any traces of moisture or water on the surface. The required
amount of the flux is charged in the flux chambers (7) attached to reaction hood
(3). The gas collection tank (9) is filled completely with water and any pockets of
entrapped air are removed. When the entire system is ready for the operation,
the reaction hood (3) is turned away from the slag box (1), and an amount of
high temperature molten slag, e.g. about 10 tonnes, is provided in the slag box
(1). After providing the slag in the slag-box (1), the reaction hood (3) is rotated
and placed on the top of the slag box. When the hood (3) is in proper position
above the slag box (1), the flux chamber or chambers (7) are opened and flux

materials is sprayed over the hot surface of the molten slag in the slag box (1).
The flux can be sprayed on the surface for instance by using high pressure inert
gas or by screw mechanism. After that, water is sprinkled on the slag surface by
operating the water or steam inlet valve (6). The product gas emerging from the
reaction hood (3) is used to purge residual air entrapped in the system and after
purging the gas is collected in the gas collection tank (9) by opening the gas inlet
valve (13) and water outlet valve (12) simultaneously. Throughout the process
the flow rate of water / steam and product gas, temperature of the slag surface
and product gas stream, pressure of the reaction hood (3) and gas collection
tank (9) is monitored and recorded. The concentration of hydrogen in the
product gas is monitored during the process. The gas inlet valve (13) is closed
when the concentration of the hydrogen in product gas drops below a required
limiting level, which is dictated by the end applications of products and economic
criteria of the operations. The excess product gas and steam is then diverted to
other piping system by opening excess steam valve (10). In this second stage
the product gas which comprises of HT and or HP steam is collected separately
for other applications. When slag temperature drop to below the set limit, which
also depends on the operating parameters, end applications, and economic
parameters, the reaction hood (3) is turned away from the slag box (1) and then
the slag is removed from the slag box (1). After complete removal of the slag
from the slag box (1), the system is made ready for the next cycle as described
above. The procedure described is used for system used in present invention. It
be noted that other methodology / procedures can also be utilized in accordance
with the present invention and are not excluded in the present invention.

COMMERCIAL PROCESS TECHNOLOGY
In most of the metal processing industries, slag is generated in batches or
discharged / tapped after specific time intervals. Therefore supply of the molten
slag is not continuous. Hence, designing a continuous process is complex.
However, a semi-continuous or continuous process is desirable for the
generation of hydrogen gas and or steam for the downstream process such as
power generation. One of the embodiments of present invention is a continuous
or semi-continuous process for the production of hydrogen gas and/or steam. In
this process, a series of slag boxes and a series of reaction hood stations are
designed and arranged in a specific sequence. The slag boxes move in sequence,
first the molten slag is poured at a slag station in the slag box and then the slag
box moves to the next station where the reaction hood is placed on the top of
slag box and the hydrogen rich product gas is collected as described in above
section. When the temperature of the slag or the concentration of hydrogen in
the product gas drops below a limiting value the slag box moves to the next
station where a second reaction hood is placed on the slag box. At this stage
additional fixtures are attached to make slag box and reaction hood to get
required / desired quality (temperature and pressure) of the product gas i.e.
steam. Part of the steam generated in this second stage can be used in the
hydrogen harvesting reaction hoods of the first stage. The other part of the
steam along with product gas can be used for end applications such as power
generation using combined cycle power generators. The other applications (such
as captive applications in metal industry) of the product gas and steam are not
excluded in the present invention. When the temperature of the slag drops below

a limiting value, the slag box is moved to a slag cooling station where it is further
cooled by using water stream and the hot water generated during this process is
used as input for steam harvesting reaction hoods. When the slag cools down,
the slag box moves to a knocking station where the slag is removed from the
slag box and the slag box is made ready after which it goes back to the first
station. The process is based on fixed slag box and moving reactions hoods can
also be used for applying the present invention. The choice of process will be
determined by the existing plant operations and techno-economic viability.
It is particularly noteworthy, in accordance with the foregoing description, that
essentially the same system can be utilized to produce various gas streams i.e.
hydrogen gas, steam, and hydrocarbons by simply altering the input stream
combination to the reactor and recovering the waste heat of slag, based on the
plant requirement and techno-economic parameters.
STEEL PLANTS (Example -1)
In a preferred case, the molten slag includes steel making slag (LD). The molten
LD is poured in the slag box (1) and then the reaction hood (3) is placed on the
slag box. The flux stored in flux chamber is sprayed on the molten slag in slag
box (1). The flux in this preferred embodiment comprises of coal, and the water
and/or steam is sprayed on the surface on the molten LD slag. When the
steam/water droplets enter the reaction hood, they get heated by radiation
energy of the slag and attend a high temperature. The rise in the temperature of

water or steam in the reaction hood also increases their pressure and thereby
increase the retention time and contact period with the molten slag. At the
reaction interface on the surface of the molten slag, part of the steam
decomposes into hydrogen and oxygen via reaction (1). The slag not only
provides the energy required for the endothermic reaction 1 but also acts as a
catalyst. Simultaneously the reductants in the slag, in this case Fe metal (steel)
and FeO, react with oxygen and form higher oxides i.e. Fe3O4, Fe2O3 via
reactions;

These oxidation reactions are exothermic in nature and provide additional energy
to the reaction front where the water decomposition takes place. The part of the
oxygen which does not react with the reductant in the slag and/or escape the
reaction interface is locked/captured by the reductant present in the
carbonaceous flux via reaction 7. Since the thermodynamic activity of FeO and
metallic Fe in the slag is very high at high temperatures, it enhances the rate of

the oxidation reactions. In should be noted that the present invention also
exploits the thermodynamics properties of the slag. At high temperatures, the
products of oxidation reactions (7 & 8) Fe3O4 & Fe2O3 form thermodynamically
more stable compounds with other constituents of slag i.e. x-CaO.ySiC2.zFe2O3
and thereby locks the free or unreacted lime in the steel making slag. The steel
making slag is mainly used as construction materials (road filler, etc.) and in
these applications the presence of free lime degrades the properties of the end
products. Free lime reacts with water or moisture and swells. The process, in the
present invention, partly locks the free lime and thus improves the properties of
the slag for end application. The LD slag at 1500°C contains about 8.3 GJ/ton
energy. The energy release in the temperature range of 1500 to 1250°C is of the
order of 500 MJ/ton which can be recovered by the present invention with
minimum loss of energy as the product of the recovery is high energy carrier, H2.
A further drop in the slag temperature from 1250 to 600°C will release about 1.7
GJ/ton of slag, which is recovered in the form of HT and/or HP steam. The
results of experiments carried out using system and method described in present
invention are given in the example. The ratio of the hydrogen and other
combustible gases (CO) in the product gas can be controlled by adjusting the
steam and/or water input and flux to the reactor. The product gas generated in
this invention can be used in a number of applications within steel plant and for
other market applications. For example, the hydrogen gas with and without other
combustible waste gases formed in the steel plant such as coke oven gas, blast
furnace gas and LD gas, can be used as fuel to reheating furnaces in the steel
plant, the purified hydrogen gas can be used a protecting medium in annealing
furnaces. The combination of the hydrogen gas and steam and other
combustible waste gases can also be used for power generation applications or

generation of hydrocarbons such as methane, methanol, etc. The use of
hydrogen gas as substitute to CNG, LPG for these applications can also be used
to reduce green house gas emission emissions. This will generate additional
saving in terms of carbon credits.
Examples: The experiments were carried out using this novel system and using
high temperature steel making LD slag. In one trial 3 tonnes of steel slag was
poured in the slag box and 1 kg carbonaceous flux (off grade coke lumps and
coke breeze) was used. About 2 Nm3 product gas containing > 60 vol %
hydrogen was collected successfully and safely in 4 minutes of time. The typical
composition of product gas is as follows: 60 - 72% vol. H2, 4-10 vol % CO, 1 -
4 vol. % CO2, 1 - 4 vol. % O2, < 3 % CmHn, Bal N2.
Ferro-chrome plant f Example - 2)
The ferro-chrome is produced by smelting-reduction of chromite ore in
submerged arc furnace (SAF). In this process, chromite ore, coke (as a
reductant) and quartzite (as a flux) are charged in the SAF. The energy required
for endothermic smelting and reduction is supplied by electric arc. This high
temperature reaction generated large volumes of molten slag and also CO gas.
This extremely power intensive process uses 3300 - 4500 kWh power per ton of
FeCr. Therefore, application of the present invention in ferro-chrome plant is
advantageous to recover the waste heat or waste energy. The tapping
temperature of molten slag is much higher (> 1650°C) than that of LD slag. In

addition to this, the specific slag rate of typical ferro-chrome process is about 1.1
- 1.2 ton slag / ton of FeCr as compared to an LD-steel plant (0.12 - 0.15 ton LD
slag / ton of crude steel). The typical FeCr slag composition is 30 - 35 % SiO2/
25- 28 % AI2O3/ 20 - 25 % MgO, and 8 - 12 % Cr2O3, 1 - 5 % FeO and minor
quantities of K, Ti, Mn oxides. However, other compositions of slag formed
during production of ferrochrome are not excluded in the present invention. The
higher temperature molten slag (with high fluidity) is processed using the system
and method disclosed in present invention. The molten ferro-chrome slag also
contains significant quantity of metallic FeCr and lower oxides of Fe and Cr (FeO,
CrO). The Cr and CrO are very strong oxidizers and hence enhance the rate of
water decomposition via

Where x= 1, 2, & 3 and y= 2, 3 & 4.
These oxidation reactions are highly exothermic in nature and provide additional
energy to the reaction front where water decomposition takes place. The coke
breeze and other carbonaceous waste generated / available in the FeCr plant can

be employed as flux. The small coke particles (from the furnace charge) get
trapped in the slag and come out with slag during tapping. The presence of
these unreacted coke particles also enhances the rate of hydrogen generation
and also reduces the requirement of additional flux. The vertical counter-current
heat exchanger type reactor (slag comes from top and steam from bottom) can
also be employed in this process due to high fluidity and high temperature of
molten FeCr slag. The hydrogen gas and steam produced by recovery of waste
heat of molten slag, along with CO gas from SAF can be used for production of
electricity / power by CCGT, which can be reused in SAF. The hydrogen and
steam can also be used for other applications (such as in sintering furnace,
charge pre-heating furnace, ladle pre-heating, etc.) in FeCr plant. Similarly, the
system and method disclosed in the present invention can be used in other ferro-
alloys plants (FeMn, FeSi, etc.) and other metal processing plants based on arc
furnace process.
TITANIA SLAG PLANTS(EXAMPLE - 3)
The Titania slag is produced from ilmenite concentrates by smelting in DC
plasma or arc furnace using coke or other forms of carbon as the reductant.
Carbon requirements are about 125 to 150% of the stoichiometric amount based
on the total reduction of iron oxides contained in the concentrate. The calcium
oxide or lime flux is added, if required, in an amount equivalent to about 2 to 5%
by weight of the ilmenite charged. The operating and tapping temperatures of
titania slag are extremely high (> 1700°C). The reduction of titanium dioxide to
lower valency titanium oxide also takes place during smelting process at high

temperature. The molten titania slag (1700 - 1800°C temperature) is tapped in
the ladle and then quenched in water for further beneficiation via acid leaching.
In this process, latent heat of slag is wasted. Globally about 3.5 million tonnes of
titania slag is produced. This is also an extremely power intensive process and
uses ~ 2100 - 2500 kWh power per ton of slag. Therefore, application of the
present invention in titania slag plant is most meaningful / advantageous to
conserve / recover the waste heat /energy. The sensible heat of molten titania
slag can be used for production of hydrogen gas by using the innovative system
and process disclosed in present invention. In this process titania slag acts as
heat sources and sub-oxides of Ti in the slag also take part in the decomposition
reaction (1) by reacting with nascent oxygen via one of the reactions (11):

The exothermic oxidation reaction provides additional energy required and also
reduces the oxygen partial pressure of the system and thereby enhances the rate
of formation of hydrogen gas. Titanium oxides 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 Ti-oxide in the slag thereby
enhances the water decomposition reaction. In addition to catalytic activity of
slag, the presence of molten iron and carbon impurities present in the slag also
assist the decomposition reaction and arrest the recombination reaction.
Oxidation of Ti sub-oxides to TiO2 also beneficial for the end application of the
slag in chlorination process which is used for production of pigment grade TiO2.

Typical composition of titania slag is 85 - 95 % TiO2/ 1 - 3 % FeO, 0.5 - 1.5 %
AI2O3, 1 - 3 % SiO2, and minor quantity of oxides of Mn, Mg, Cr, Ca, etc.
However, the processing of titania slag with other compositions is also included
in this invention.
Thus, a novel system and process disclosed in present invention can be
employed easily and safely for recovery of waste heat in the form of hydrogen
and steam.
Although the foregoing description of the present invention has been shown and
described with reference to particular embodiments and applications thereof, it
has been presented for purposes of illustration and description and is not
intended to be exhaustive or to limit the invention to the particular embodiments
and applications disclosed. It will be apparent to those having ordinary skill in the
art that a number of changes, modifications, variations, or alterations to the
invention as described herein may be made, none of which depart from the spirit
or scope of the present invention. The particular embodiments and applications
were chosen and described to provide the best illustration of the principles of the
invention and its practical application to thereby enable one of ordinary skill in
the art to utilize the invention in various embodiments and with various
modifications as are suited to the particular use contemplated. All such changes,
modifications, variations, and alterations should therefore be seen as being
within the scope of the present invention as determined by the appended claims
when interpreted in accordance with the breadth to which they are fairly, legally,
and equitably entitled.

WE CLAIM
1. An improved method for safely harvesting hydrogen gas by reacting molten
slag with one of water and steam comprising the steps of:
- providing molten slag in a reactor vessel, said molten slag
comprising a reducing agent for scavenging the thermo-chemically
produced oxygen;
- closing the reactor vessel to prevent entry of atmospheric oxygen
into the reactor vessel during the thermo-chemical dissociation of
H2O;
- optionally providing additional reducing agent for scavenging
thermo-chemically produced oxygen, wherein the reducing agent is
preferably in a solid form;
- contacting the molten slag in the reactor vessel with H2O to thermo-
chemically dissociate the H2O into hydrogen and oxygen to create a
gaseous product stream comprising said hydrogen and said oxygen;
- allowing the reducing agent to react with the oxygen to scavenge
the oxygen from said gaseous product stream to prevent H2O-
recombination;

- collecting the hydrogen from said stream by using a steam envelope
and water displacement technique.
2. The method as claimed in claim 1, wherein said molten slag is one of, or a
mixture of blast furnace slag, desulphurisation slag of steel making,
converter slag of steel making, ferrochrome or ferromanganese slag in
submerged arc furnace and titania slag.
3. An improved system for safe harvesting of hydrogen gas by thermo-
chemical dissociation of H2O comprising the steps of :

- a reactor vessel for containing molten slag;
- means for (1,2) providing molten slag into the reactor vessel;
means for (5,6) providing water, steam or a mixture thereof onto
the molten slag;
- means for (7) providing additional reducing agent onto the molten
slag;
- means for forming an enclosed reaction chamber for the thermo-
chemical dissociation of H2O, said means comprising a hood (3)
positionable over the slag box (1);

- means for (8,9) collecting a gaseous product stream comprising the
thermo-chemically formed hydrogen from the reaction chamber;
and
- means for (10,11,12,13) preventing access of atmospheric oxygen
to the reaction chamber during the thermo-chemical dissociation of
H2O.

4. An improved system as claimed in claim 3, wherein the molten slag is
poured in the slag box (1) and then the reaction hood (3) is placed on the
slag box (1) and the flux stored in at least one flux chamber (7) is sprayed
on the molten slag in the slag box (1).
5. An improved system as claimed in claim 3, wherein the gas collection tank
(9) is filled completely with water and all pockets of entrapped air are
removed.
6. An improved system as claimed in claim 3, wherein the reaction hood (3)
is rotated and placed on the top of the slag box (1) after providing the
slag in the slag-box (1) and the flux chambers (7) are opened and flux
materials is sprayed over the hot surface of the molten slag in the slag
box (1) by using high pressure inert gas or by screw mechanism.

7. An improved system as claimed in claim 3, wherein, water or steam is
sprinkled on the slag surface by operating the water / steam inlet valve
(6) and the product gas emerging from the reaction hood (3) is used to
purge residual air entrapped in the system and after purging, the gas is
collected in the gas collection tank (9) by opening the gas inlet valve (13)
and water outlet valve (12) simultaneously.
8. An improved system as claimed in claim 3, wherein, the flow rate of water
/ steam and product gas, temperature of the slag surface and product gas
stream, pressure of the reaction hood (3) and gas collection tank (9) and
the concentration of hydrogen produced is monitored and recorded.
9. An improved system as claimed in claim 3, wherein, the gas inlet valve
(13) is closed when the concentration of the hydrogen in product gas
drops below a required limiting level, which is dictated by the end
applications of products and economic criteria of the operations and the
excess product gas and steam is then diverted to other piping system by
opening the excess steam valve (10).
10. An improved system as claimed in claim 3, wherein the product gas
which comprises HT and or HP steam is collected separately for other
applications.

11. An improved system as claimed in claim 3, wherein, under a condition
that the slag temperature drops below the set limit, the reaction hood (3)
is turned away from the slag box (1) and then the slag is removed from
the slag box (1).
12. The method as claimed in claim 1, wherein said method is a continuous or
semi-continuous process for the production of hydrogen gas and/or
steam.
13. An improved system as claimed in claim 3, wherein, when under
continuous process said system further comprises a series of slag boxes
and a series of reaction hood stations and arranged in a specific
sequence.
14. An improved method for safely harvesting hydrogen as claimed in claim
12, wherein under continuous process the slag boxes move in sequence,
the molten slag is first poured at a slag station in the slag box and then
the slag box moves to the next station where the reaction hood is placed
on the top of the slag box and the hydrogen rich product gas is collected
till the temperature of the slag or the concentration of hydrogen in the
product gas drops below a limiting value and the slag box moves to the
next station where a second reaction hood is placed on the slag box.

15. An improved method for safely harvesting hydrogen gas by reacting molten
slag with one of water and steam, as substantially described and illustrated
herein with reference to the accompanying drawings.
16. An improved system for safe harvesting of hydrogen gas by thermo-
chemical dissociation of H2O, as substantially described and illustrated
herein with reference to the accompanying drawings.
Dated this 23rd day of May, 2008

An improved method for safely harvesting hydrogen gas by reacting molten
slag with one of water and steam comprising the steps of:
- providing molten slag in a reactor vessel, said molten slag comprising a reducing agent for scavenging the thermo-chemically produced oxygen;
- closing the reactor vessel to prevent entry of atmospheric oxygen into the reactor vessel during the thermo-chemical dissociation of
H2O;
- optionally providing additional reducing agent for scavenging thermo-chemically produced oxygen, wherein the reducing agent is
preferably in a solid form;
- contacting the molten slag in the reactor vessel with H2O to thermo-
chemically dissociate the H2O into hydrogen and oxygen to create a gaseous product stream comprising said hydrogen and said oxygen;
- allowing the reducing agent to react with the oxygen to scavenge the oxygen from said gaseous product stream to prevent H2O-
recombination;
- collecting the hydrogen from said stream by using a steam envelope and water displacement technique.