FIELD OF INVENTION
The present invention relates to an apparatus and an improved method of
more uniform steam curing of steel making slag with efficient radial distribution of
steam. More particularly the invention relates to a process for the curing of steel
making slag including reduction of free alkaline earth oxide with volume expansion
less than 2% by artificial means using steam at variable conditions of pressure and
temperature in shorter time in comparison to the open steam curing to obtain a
product applicable for use in road construction.
The present invention involves the penetration of steam through slag at
predetermined pressure and temperature and at optimum bed height of steel
making slag to induce a hydration reaction for leaching out the free alkaline earth
oxide present in slag in the form of slaked lime and use of condensate as
neutralising agent.
BACKGROUND OF THE INVENTION
Steelmaking slag is generated by the process that turns pig iron produced by
a blast furnace into tough and highly workable steel. In this procedure the furnace is

filled with hot and/or cold metal and additives to obtain steel with desired
characteristics. Then the melted steel and impurities are separated from the
furnace, with the impurities consisting mainly of silicon, manganese, phosphorus,
and some iron in the form of liquid oxides. Combined with lime and dolomite lime,
those impurities create steel slag mostly cooled naturally – air cooled – or cooling
can be accelerated by sprinkling water.
Expansion characteristic is a big problem when steel slag is used as road bed
material. It is a phenomenon where the free alkaline earth oxide contained in steel
slag, although in a very small quantity, reacts with water and forms slaked lime, its
volume becoming approximately twice its original. The presence of free calcium
oxide, accounting for more than 2%, causes another adverse property of steel slag,
namely, the appearance of white powder in the form of sediment. Free alkaline
earth oxide from leachate is bound with water, creating slaked lime, Ca(OH)2,
which, when exposed to atmospheric conditions, reacts with carbon dioxide, CO2
creating limestone (CaCO3). It settles down in the form of white powder and may
cause obstructions in the drainage systems and water retention. Those obstructions
are particularly dangerous in the case of freezing, which renders large damage to
pavement structure.

Physical properties of slag also play an important role in the utilization of slag
in asphalt mixtures. Sharp edges, a proper grain shape, and rough surface texture
also contribute to better adhesiveness of aggregate binder and grain, and increase
the coefficient of internal friction of bituminous overlay more than any other natural
aggregate. Those physical properties, in addition to the proper granulometric
composition, increase shear tightness of mixtures and resistance to appearance of
rut. It is for this reason that those mixtures are most frequently used in places
where great wear resistance and good adhesiveness of pavement is required, such
as roads in industrial installations, parking spaces exposed to heavy freight vehicles
and junctions. Due to the high specific weight and density of slag it also increases
the specific weight and density of asphalt mixes in comparison to the natural
aggregates.
The current practices available for curing of slag are natural weathering,
curing through water, open steam curing and pressurised steam curing. The curing
of slag by natural weathering requires 12-24 months which results into high space
requirement. The combine process of natural weathering and steam curing of steel
making slag needs 1-3 months for natural weathering followed by steam curing of

10hrs. The total processing time is not shortened due to the inclusion of natural
weathering.
Curing of slag by using water requires 3-6 months which results into high
space requirement and generation of large amount of leachate with alkaline
properties. In industrial application the handling or discharge of this large quantity
of alkaline leachate is a difficult task.
Open steam curing process needs a week to stabilise the steel making slag.
However, since the high pressure steam is spouted to slag stored at atmospheric
pressure through the perforated pipes installed at the bottom of the pit. Therefore,
non-uniform stabilization of slag persists because only the enthalpy of steam is
utilised not temperature. It has no system for recovery of flash steam which is
generated during the process.
The pressurised method for steam curing of steel making slag stabilizes the
slag within 5hrs. however, since the capital cost associated with this process is very
high. Therefore, application of this technology at industrial scale needs large capital
investment.

The objective of this study is to develop a method for the curing of steel
making slag under semi closed condition which will have less capital investment than
pressurised steam curing and this method will generate the slag with more uniform
stabilization of slag in comparison to open steam curing.
Prior Art:
Conventional open steam curing process as shown in Fig.1 is as follows:
1. Steel making slag stored at atmospheric condition will be charged to a slag
stabilizing pit, dimensions of which are decided on the basis of capacity and
bulk density of slag and it will be covered from three sides.
2. Steam will be supplied from the bottom through the perforated pipes.
3. Steam will react with free alkaline earth oxide present in slag and hydration
reaction will occur.
4. No reuse of condensate in the current process.
OBJECTS OF THE INVENTION
Therefore, it is an object of the invention to propose an apparatus and an
improved method of more uniform steam curing of steel making slag with efficient
radial distribution of steam which is capable of achieving more uniform curing of
steel making slag with less capital investment compared to prior Art.

Another object of the invention is to propose an apparatus and an improved
method of more uniform steam curing of steel making slag with efficient radial
distribution of steam which is able to reduce free alkaline earth oxide with volume
expansion less than 2% by artificial means using steam at variable conditions of
pressure and temperature in shorter time compared to the prior Arts.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Fig.1. : Shows a conventional open steam curing process of prior Arts.
Fig.2. : Shows a schematic diagram of proposal semi-closed open steam curing
process according to the invention.
Fig.3. : Shows a semi-closed vessel design for open steam curing according to
the invention.
Fig.4. : Shows relationship between volume expansion and bed height at
constant pressure.
Fig.5. : Shows % reduction in chemical components of treated slag w.r.t feed
slag.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE
INVENTION
The process for open steam curing of steel making slag with more
uniform stabilized slag, less steam consumption and less amount of condensate
generation is carried out in an apparatus which is a semi closed vessel of a
cylindrical robust structure (V) having a lid (1) at the top for charging the slag and a
gate at the front for unloading the cured slag. The lid (1) at the top of the vessel
makes it fully semi or fully closed system. A moisture separator to remove any
moisture present in steam, is connected by a pipe to the lower portion of the vessel.
A steam generator is connected through a pipe to the moisture separator. A pipe is
configured at the bottom of the vessel to discharge the hot condensate. Woven net
(7) is provided to separate fragile slag from the condensate. One vent line (2) is
disposed to pass the excess steam from the vessel. The vessel is provided with
stiffening ring (3) to make the vessel structure more robust so that it can handle the
weight of slag as well as steam. Steam is injected via inlet line (4) having quick
release coupling. A condensate drain plug (5) is disposed at the bottom of the
structure to release the condensate during steam curing. The apparatus/vessel (V) is
provided with a pressure relief valve (6) to meet any emergency situation due to
accumulation of steam inside the vessel. A mixing tank (12) is provided to neutralize
alkaline hot condensate with acidic effluent maintaining a value of pH7. A perforated

disc plate with triangular pitch perforations is configured at the bottom of the vessel
(V) which ensures the radial distribution of steam as well as less blockage of
perforation with fragile slag. A nozzle arrangement on the middle of the bottom disc
supplies the steam throughout the slag bed and such type of arrangement provides
uniform stabilization of slag. This present invention provides a method for steam
curing of processed slag or Bias oxygen furnace slag with less capital investment
than pressurised steam curing process and more uniform stabilized slag with less
steam consumption than conventional open steam curing process. This method
comprises the steps of through a conveyor belt (8), charging of slag at normal
temperature crushed and grind to the size of 6 - 80mm into the vessel which
constitutes 9% - 90% or more of total volume of vessel. The half top of the vessel
can be closed tight enough to maintain the pressure substantially higher than
atmosphere.
The apparatus is a semi closed vessel (V) for the steam-curing of steel
making slag. At the bottom vessel has disc type arrangement from which steam is
supplied, the nozzle arrangement in the middle of the disc supplies the steam to the
perforated pipe and through the perforated pipe arrangements in the disc steam is
supplied to the rest of the area of the vessel which provides uniform stabilization of
slag. Keeping the interior of the said vessel under a condition pressurised upto 2.5-
3.5 kg/cm2 for 24 to 72hrs.

The steam is supplied to the vessel from the bottom after passing through a
moisture separator (10) to remove any moisture present in steam.
The pressure of the said vessel is brought in equalisation with the
atmosphere and the slag is discharged from the vessel and collected in a storage
tank (11).
The high pH condensate is supplied to a mixing tank (12) to use it as a
neutralizing agent for acidic industrial effluent as coagulant used for oil and grease
removal from industrial effluent work more effectively at pH7.
According to the above method free alkaline earth oxide present in slag
converts into hydrated lime and leached out from slag which prohibits the swollen
effect of processed slag or Bias oxygen furnace slag.
The temperature of processed slag charged to the said vessel can be higher
than atmospheric temperature, but it is at such a level which allows the slag to be
handled by belt conveyor. Since, the rate of hydration reaction increases with the
increase in temperature and the saturation temperature of the steam is based on
saturation pressure of steam. Therefore the pressure of the steam should be higher
so the pressure was kept in the range of 2.5-3.5 Kg/cm2.

Moreover, as the saturation pressure increases the rising rate of saturation
temperature decreases. Therefore, it is acceptable to keep the maximum
temperature in the vessel at 3Kg/cm2 to obtain the steam aged slag with volume
expansion less than 2%.
The temperature of the condensate discharged during this process becomes
gradually lower than the saturated steam temperature as sensible heat of steam is
supplied to the slag. The continuous discharge of the hot condensate (13) is
essential to avoid the decrease in steam temperature and to avoid the deposition of
slaked lime on the walls of the vessel and perforated plate.
An invention comprising the steps of charging normal temperature slag
crushed to the size varying from 6 - 80mm in a vessel which is half lid open at the
top. The slag constitutes the volume varying from 9% - 90% or more of the total
volume of the vessel to maintain different bed height of slag. The half top of the
vessel can be closed tight enough to maintain a pressure substantially higher than
atmosphere. Uniform stabilization of slag has been ensured by designing the vessel
with a triangular pitch perforated plate at the bottom and perforated cylindrical type
arrangement in the middle of it. The plate and cylindrical pipe arrangement both
have triangular pitch perforations to avoid the dead zone during penetration of

steam through slag. In the half closed vessel the saturated steam is supplied from a
circular disc at the bottom of the vessel. Circular disc has been divided into eight
equal parts with perforated pipes containing particular size of holes at a certain gap
and holes at the periphery of the disc with a nozzle arrangement in the middle to
supply the steam in the cylindrical pipe. The interior pressure of the vessel was kept
in the pressure range varying from 2.5-3.5 kg/cm2 for 24 to 72hrs. After the
experiment the vessel was brought down to atmospheric pressure and slag was
discharged. The condensate generated during the process is continuously
discharged from the bottom of the vessel through a steam trap and used as a
neutralizing agent by mixing it with acidic water to maintain the pH at 7. The
pressure is maintained in the vessel by pressure reducing valve attached to the
steam header.
ADVANTAGES OF THE PRESENT INVENTION OVER PRIOR ART:
1. The innovation is to provide a further improved method and develop an
apparatus with radial distribution of steam for the uniform curing of steel making
slag with less capital investment than pressurised steam curing and more uniformed
stabilised slag in comparison to the open steam curing.

2. A perforated stem distribution system is placed centrally above the bottom
plate for equal radial steam distribution inside the pit.
3. As the present invention is semi closed, steam gets sufficient time to
penetrate through processed slag or Bias oxygen furnace slag and thus overall
curing time is lesser compare to open steam curing. Due to uniform distribution of
steam the curing of processed slag is uniform throughout the bed.
4. In the semi closed system the distribution of steam throughout the slag bed
is uniform thus there is hardly any temperature gradient between any two points
along the bed.
5. As the system is semi closed the flash steam generation is less and better
utilization of the steam takes place.
6. The high pH condensate is supplied to a mixing tank to neutralize the acidic
industrial effluent as coagulant used for oil and grease removal from industrial
effluent work more effectively at pH7.

7. To develop a complete close loop unit which leads to sustainable and
environment friendly “zero discharge uniform processed slag or Bias oxygen furnace
slag stabilisation process”.
Variation of volume expansion with bed heights at different pressure is shown
in figure 4. Here, a polymeric relationship was developed between volume expansion
and bed height at constant pressure in a predetermined pressure range. This
polymeric relationship has correlation coefficient >98% which is giving volume
expansion less than 2% at the pressure of 3.0 Kg/cm2 for the bed height of 2m.
Fig.5 shows a percentage reduction with respect to treated sample at
pressure 3 Kg/cm2 and temp 1400C and Bed height 2m. The figure represents %
reduction in chemical composition of treated slag in comparison to the feed steel
making slag at the optimised condition of pressure 3Kg/cm2, corresponding
saturation temperature of 1400C and at the bed height of 2m. It can be easily
depicted from this example that at the optimised conditions 79.10% reduction in
free alkaline earth oxide has been observed.

WE CLAIM
1. An apparatus and an improved method of more uniform steam curing of steel
making slag with efficient radial distribution of steam, the said apparatus
comprising;
a semi closed cylindrical vessel (V) having a lid (1) semi closing the vessel (V)
at the top for charging slag;
a moisture separator for removing any moisture present in steam disposed at
the lower portion of the vessel;
a steam generator connected to the moisture separator through a pipe for
supplying steam;
a pipe disposed at the bottom of the vessel for discharging hot condensate;
a woven net (7) provided for separating fragile slag from the condensate
(13);
a vent line disposed at the top of the vessel for allowing excess steam to pass
from the vessel (V);
a plurality of stiffening ring (3) provided for making the vessel structure more
rigid for handling the weight of slag and steam;
an inlet line (4) having quick release coupling disposed for injection of steam;
a condensate drain plug disposed at the bottom of the structure for releasing
the condensate during steam curing;

a pressure relief valve for meeting any emergency situation due to
accumulation of steam inside the vessel; Characterized in that,
a mixing tank is provided to neutralize alkaline hot condensate with acidic
effluent maintaining a pH value of 7 wherein a perforated disc plate with triangular
pitch perforations disposed at the bottom of the vessel (V) for ensuring radial
distribution of steam as well as less blockage of perforation with fragile slag when
the steam penetrates the slag at predetermined pressure and temperature and at
optimum bed height of steel making slag for inducing a hydration reaction for
leaching out the free alkaline earth oxide present in slag in the form of slaked lime.
2. An apparatus as claimed in claim 1, wherein the said apparatus carries out
the process of steam curing of steel making slag maintain an interior pressure of the
said apparatus in the range varying from 2.5 — 3.5kg/cm2 for 24 to 72 hrs at a bed
height of 2m.
3. An apparatus as claimed in claim 1, wherein the said apparatus is equipped
with a nozzle arrangement on the middle of the bottom disc for supplying steam
throughout the slag bed for providing uniform stabilization of slag.

4. An improved method of more uniform steam curing of steel making slag
carried out in the apparatus claimed in claim 1, comprising the steps of;
crushing and grinding the slag to a size of 6-80 mm;
charging the slag into the apparatus (V) at normal temperature through a
conveyor belt (8);
closing the half top (1) of the vessel (V) tight enough to maintain the
pressure substantially higher than atmosphere; wherein,
generated steam is supplied to the vessel form a nozzle type arrangement
disposed in the middle of a disc type arrangement provided at the bottom of the
vessel (V) ensuring uniform stabilization of slag, the said steam being passed
through a moisture separator (10) before supplying to the vessel (V) when the
interior of the apparatus/vessel (V) is maintained under a pressure of 2.5 –
3.5kg/cm2 for a period of 24 to 72 hrs. at a bed height of 2m. when the high pH
condensate (13) is supplied to a mixing tank (12) to use it as a neutralizing agent
for acidic industrial effluent wherein free alkaline earth oxide present in slag is
converted into hydrate lime and leached out from slag when the pressure of the said
vessel (V) is made equal to atmospheric pressure when the slag is discharged from
the vessel and collected in storage tank (11).

5. The method of steam curing of steel making slag as claimed in claim 4,
wherein the charged slag constitutes the volume varying from 9% -- 90% or more
of the total volume of the vessel (V).
6. The method of steam curing of steel making slag as claimed in claim 4,
wherein the volume expansion of slag is less than 2% at pressure of 3.0 kg/cm2 for
the bed height of 2m.