FIELD OF THE INVENTION
The present invention relates to a process of producing hydrogen-rich gas in a
counter-current reactor from molten metallurgical slag and water/steam.
BACKGROUND OF THE INVENTION
With depleting fossil fuels based energy sources and their adverse impact on the
environment, efforts are being directed to shift to low carbon energy economy.
In this context, hydrogen is being considered as of the most important energy
source and carrier. However, according to the known techniques, hydrogen is
mainly generated through steam reforming of hydrocarbons, and electrolysis of
water. However, hydrogen produced by these known processes is expensive and
not environment friendly, as it involves use of hydrocarbons, electricity, or other
chemicals which has direct or indirect association with greenhouse gas
emissions.
Steel industry, accounts for 2-3% of world's energy demand and, generates ~
100 Mt of slag at temperatures 1400-1700 °C. Presently, the slag is disposed
either by granulation or by water quenching, a substantial amount of thus
releasing sensible energy of slag to the environment in the form of steam. At the
same time, these prior art practices pollute the water with alkalies and other
particulate matter.
Amongst the efforts globally being persued to reduce its energy intensity,
processes directed to recover energy from the rejected heat in slag are exhibiting
the highest rate of success. T. Akiyama et al. (2000) reviewed the methods for
recovery of waste heat from slag. One such application is to generate steam that
can be used for electricity generation. Steam generated through this process is a
low pressure steam and entails major design and safety concerns. Another
method to recover energy from the molten slag, to pre-heat air has been
disclosed in U.S. Patent No. 4,311,3239. Owing to low specific heat of air and
huge volume of air required to recover this energy from slag hence, makes this
technology economically unviable. It is further known that phase change
materials like Cu, Be, Mn, MgF2, Na20 (melting point> 1300 °C) have the ability
to store energy in the form of latent heat for melting and can later be released at
their melting point after their solidification. However, these materials have not
been commercially successful because of their cost and possibility of
contamination with slag.
Waste heat of molten slag can also act as a heat source for endothermic
reactions to produce hydrogen. One such method is disclosed in U.S Patent No.
1,592,861 and U.S. Patent No. 0,030,130360. In these processes, steam reacts
with carbonaceous material to produce hydrogen, carbon monoxide and carbon
dioxide. In another US Patent No. 4,388,084, molten iron bath is used for coal
gasification. All these known processes use carbonaceous material to generate
hydrogen and have direct C02 emissions.
WIPO/2007/125537 disclosed a technique to generate hydrogen rich gas using
the waste heat of molten metallurgical slag and steel plant waste. To improve
the hydrogen generation efficiency, reducing agents like coal or carbon bearing
materials can be used. WIPO/2007/036953 describes a process where thermo-
chemical decomposition of water takes place using sensible waste heat and
chemical of molten slag. In this process, lower oxides such as Feo, CrO etc. react
with oxygen to produce higher oxides like Fe203 G2O3 etc., thus improving the
hydrogen yield.
In the above prior patents, water comes in contact with the molten slag in a
container in stagnant. Because of the heat transfer from slag to steam, too layer
of the slag gets solidified and prevents energy transfer from bulk phase to the
gas phase of the slag. This solidified slag layer poses a hindrance to the
penetration of oxygen in the slag layer. Hence, there is a need to devise a
process, where new slag surface is regenerated continuously. This invention
describes a novel process where, a counter-current process is developed (where
slag surface is continuously generated.
OBJECTS OF THE INVENTION
It is therefore, an object of the invention to propose a process of producing
hydrogen-rich gas in a counter-current reactor from molten metallurgical slag
and water/stream, which eliminates the disadvantages of prior art.
Another object of the invention is to propose a process of producing hydrogen-
rich gas in a counter-current reactor from molten metallurgical slag and
water/steam, which eliminates the use of carbon-bearing materials.
It is therefore an object of the invention is to propose a process of producing
hydrogen-rich gas in a counter-current reactor from molten metallurgical slag
and water/steam, which is enabled to continuously regenerate new slag surface
to eliminate the oxygen penetration hindrance into the slag layer.
Yet another object of the invention is to propose a process of producing
hydrogen-rich gas in a counter-current reactor from molten metallurgical slag
and water/steam, where the contact time and reaction surface between the slag
and steam is enhanced to recover waste heat and chemical energy of molten
slag in the form of hydrogen-rich gas and steam.
A further object of the invention is to propose a device to generate hydrogen-rich
gas and steam by reacting molten metallurgical slag and water/steam reach in a
counter-current fashion.
A still further object of the invention is to propose a process of producing
hydrogen-rich gas in a counter-current reactor from molten metallurgical slag
and water/steam, which is capable of recovering the sensible and chemical heat
of the molten slag.
SUMMARY OF THE INVENTION
The present invention describes a process where hydrogen-rich gas and steam
are produced when molten metallurgical slag and water/steam reach in counter-
current manner.
According to the invention, molten slag after being discharged from a furnace is
allowed to flow on an inclined surface for granulation. Controlled water/steam is
sprayed on the running slag through a series of nozzle housed inside a semi-
cylindrical reactor. Product gases and steam are collected through a conical gas
collection hood, to be used as an energy source and/or energy carrier. Residence
time of steam/water in the reactor is increased by fixing baffles at specific
locations selected through computational fluid dynamic studies. Steam curtains
are provided at the inlet and outlet of the reactor to prevent air ingress including
leakage of hydrogen-rich gas from the reactor.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
The invention is now described in further details with the help of the
accompanied drawings in which, Figure 1, shows a device according to the
invention for producing hydrogen-rich gas with steam using waste heat of molten
metallurgical slag. Figure-2 shows a side view of the device of Figure-1.
DETAILED DESCRIPTION OF THE INVENTION
In the present invention, waste heat of molten metallurgical slag is recovered by
thermo-chemical decomposition of water to generate hydrogen rich gas/steam.
In this step molten slag provides the energy for the endothermic thermal and/or
catalytic splitting of the water/steam.
Molten slag in the present invention refers to the blast furnace slag, steel making
slag, EAF slag, ferro alloys slag, titania slag, non-ferrous slags, and/or any
combination of thereof.
The disclosed counter-current process is developed by considering the following
parameters:
• Simple, safe and low cost system which can be adapted by any
metallurgical industry with minimum obstruction to the existing operations
• Reaction chamber should have sufficient strength to bear the extremely
high radiation and should provide the maximum surface area for the
reaction
• Reactor should be inclined to ensure sufficient residence time of the slag
in the reactor, without disturbing the granulation/quenching process
• Reactor configuration provides recirculation of steam in the reactor to
increase the reaction efficiency
• Configuration to allow easy removal of the product gas from the reactor
• Reactor ensures prevention of ingress of air in to the reactor and product
gas leakage from the reactor
Important features of the reactor are described in the following section and in
Figures 1.2.
1) Reactor Hood/Chamber:
A semi-cylindrical chamber made of stainless steel (a) capable of spraying
water/steam on the slag surface through a plurality of nozzles (2,3) with desired
water/steam flow profile, at required flow rate. A plurality of baffles (4) are
provided in the reactor at pre-determined distance with inclination decided based
on the computational studies. The baffles (4) are located at distance where the
flow profile of the nozzles (2,3) do not interact and generate turbulence and
recirculation in the product gas. Design of the baffles is also optimized to
increase the residence time of steam in the reactor and enhance the steam slag
contact. Water enters the reactor from a slag inlet area (B) and is preheated by
the radiation from the slag in stainless steel tubes (5). Hence, a high quality
steam is released from the nozzles (2,3), thereby increasing the overall process
efficiency.
To minimize the air ingress and/or gas leakage to/from the reactor, a provision
has been made to create steam curtains (6,7) at the slag inlet and outlet. A high
pressure/low pressure region generated inside the reactor at the slag inlet/exit,
which facilitates the gas leakage and/or air ingress, is restricted/minimized with
the help of these curtains hence, a high purity hydrogen gas is produced. A
plurality of ceraboard pads (8,9) are also provided at the slag inlet/exit to further
reduce the gas leakage. Gas leakage along the reactor length is reduced by a
sand locking arrangement of the hood in channel trays (10).
2. Gas Collection System
It comprises of a conical section (11), mounted on the top of the reaction hood
at the slag inlet side B to collect the product gas. Location, shape and
dimensions of the hood are optimized based on the gas flow profiles and prevent
air ingress and/or gas leakage in to the reactor. The conical design ensures a
smooth and safe collection of the product gas. The conical hood of the device is
connected to a flexible stainless steel hose (12), which extends to a steam
condensation unit, instrumentation for flow measurement, gas analysis
temperature and pressure measurement (not shown in the drawing). The other
auxiliaries for gas collection such as blowers, suction pumps, buffer tanks may
also be included.
3. Instrumentation and Control System
A control system has been provided for process control and data acquisition
system. Electronic sensors are fixed on various locations for continuous
monitoring of temperature, pressure, water and gas flow, gas composition
analysis.
In the present invention, hydrogen rich gas and steam is generated form a
flowing slag system as compared to the conventional batch type process.
Referring to Figure 2, the molten slag once discharged from the furnace is
allowed to flow on an inclined surface (runner) (13) for slag granulation or
quenching. Along the length of the runner (13) rests a semi-cylindrical chamber
(preferably made of stainless steel) that forms an enclosed space (reactor) for
the controlled thermal-chemical decomposition of water/steam. Molten slag
enters (side B) the chamber at high temperature greater than the slag solidus
temperature.
Water enters the device from side B and runs along the reactor length in the
stainless steel tubes. Water gets preheated by the radiation from the slag and is
released in to the reactor through the plurality of nozzles (2,3) placed at pre-
determined location and inclination based on the computational fluid dynamic
studies. Hydrogen-rich gas and steam are collected from side B by the conical
gas collection hood which is connected to a steam condensation unit to generate
hydrogen-rich gas. To increase the thermo-chemical splitting efficiency and
residence time of steam, a plurality of baffles (4) are provided at pre-determined
location and inclination in the reactor.
At both the ends (side A and B) of the chamber a steam curtain (6,7) is formed
by dripping water on the slag surface. Steam curtain (6,7) prevents the ingress
of the air in to the reactor and/or prevents the generated gas escape from the
reactor. Along the length of the reactor gas leakage and or air ingress is checked
by resting the device on trays, filled with sand or granulated slag. To reduce the
heat loss to the surrounding atmosphere from the device peripherals, insulating
material may be used to cover up the walls from outside.
The device is installed with necessary instrumentation such as valves, flow
measurement, controllers, pressure indicator, pyrometer, thermocouples, gas
analyzer for real time monitoring of the process parameters. The process
described in this invention enables the efficient recovery of sensible and chemical
energy of the molten slag in the form of hydrogen-rich gas and steam, where the
reactants interact in a counter-current manner.
It is to be noted, that carbonaceous flux can also be injected in the existing
setup to prevent the recombination reaction between the hydrogen and oxygen
and maximize the hydrogen yield. At the same time, this setup can also be used
to generate various gas streams by i.e. hydrogen gas, steam, hydrocarbons by
altering the input stream combination to the reactor and recovering the waste
heat of slag, based on the plant requirement and techno-economic parameters.
WE CLAIM
1. A device for recovery of waste heat and chemical energy of molten slags
in the form of hydrogen-rich gas and steam in a counter-current reactor,
consisting of:
• an inclined surface for flow of molten slag;
• a semi-cylindrical reactor resting on the inclined surface where, molten
slag and water/steam react in a counter-current manner;
• a conical hood assembly for product gas collection;
• a plurality of nozzles with profiles circular and/or planar housed in the
reactor at determined locations to spray water/steam onto the slag
surface;
• a plurality of baffles at selected location to increase the residence time
and thermo-chemical splitting of hydrogen;
• at least two steam curtains dispose each at the slag inlet and outlet of
the reactor to prevent air, ingress and gas leakage in and from the
reactor respectively; and
• channel trays to prevent the air ingress and gas leakage in and from
the reactor respectively along the reactor length.
2. The device as claimed in claim 1, wherein the device is enabled a
continuous or semi-continuous production of hydrogen-rich gas and/or
steam.
3. The device as clamed in claim 1, wherein the device is configured to
accommodate high temperature metallurgical slag to produce hydrogen-
rich gas and/or steam.
4. The device as claimed in claim 1, wherein the reactor geometry is
alterable corresponding to the desired rate of increase in the waste heat
recovery in the form of hydrogen rich gas.
5. The device as claimed in claim 1, wherein the plurality of baffle is
disposed to achieve desired water/steam flow profiles and increase the
process efficiency.
6. The device as claimed in claim 1, wherein the plurality of nozzles allow
generation of steam curtains for isolation of the reactor interior from
ambient conditions which prevents escape of product gas or ingress of air
into the device.
7. The device as claimed in claim 1, comprising slag runners for slag
granulation and quenching.
8. The device as claimed in any of the preceding claims, wherein the device
chamber is made of stainless steel.
9. A process for recovery of waste-heat and chemical energy of molten slags
in the form of hydrogen-rich gas and steam in a counter-current manner,
comprising the steps of :-
- allowing molten slag on discharge from a furnace to flow on an incliner
runner for slag granulation or quenching, an enclosed space acting as
a reactor being formed by a substantially semi-cylindrical chamber
resting along the length of the runner;
- inputting the molten slag from a second side of the chamber at a
temperature above 1400°C, and exiting through a first side of the
chamber at temperature higher than that of the slag solidus;
- supplying water via stainless tubes to the second side of the chamber
to run along the reactor length, the water picking up radiated heat
from the molten slag;
- a plurality of nozzles disposed at different computed locations and at
various computed inclination to spray said pre-heated water into the
reactor generating hydrogen-rich gas and steam;
- a conical gas collection hood connected through its proximal end to the
second side of the chamber for collection of the generated gas and
steam, the distal end of the hood connected to a steam-condensation
unit to produce hydrogen-rich gas.
10.The process as claimed in claim 9, wherein the molten slag comprises one
of blast-furnace slag, steel making slag, EAF slag, ferro-alloy slag, titania
slag, non-ferrous slag, and/or combination thereof.

This invention relates to a device for recovery of waste heat and chemical energy of molten slags in the form of hydrogen-rich gas and steam in a counter-current reactor, consisting of: an inclined surface for flow of molten slag; a semi-cylindrical reactor resting on the inclined surface where, molten slag and water/steam react in a counter-current manner; a conical hood assembly for product gas collection; a plurality of nozzles with profiles circular and/or planar housed in the reactor at determined locations to spray water/steam onto the slag surface; a plurality of baffles at selected location to increase the residence time and thermo-chemical splitting of hydrogen; at least two steam curtains dispose each at the slag inlet and outlet of the reactor to prevent air, ingress and gas leakage in and from the reactor respectively; and channel trays to prevent the air ingress and gas leakage in and from the reactor respectively along the reactor length.