FIELD OF THE INVENTION
The present invention generally relates to conversion of poor combustible coals
(especially higher rank) to Pulverized Coal Injection in Blast furnace. More
particularly, the present invention relates to a process of optimization of oxygen
concentration in blast air and particle size distribution of fuel for injection into a
blast furnace to improve combustion of fuel.
BACKGROUND OF THE INVENTION
The main aspect of the competitive iron making is to reduce the cost and
increase the performance of blast furnace. This is achieved internationally by
replacing part of metallurgical coke by injecting the cheaper coal in blast furnace.
Since cheaper coal having the poor combustibility and also it's not suitable for
prior art blast furnace design which interalia limits especially residence time
leading to incomplete combustion of the coal particle during injection. The
degree of combustion is greatly influenced by the particle size and oxygen
enrichment of coal. The larger the particle size of the coal to be burnt, the
smaller is the surface area of the coal available for reaction with oxygen and the
longer is the time required for complete combustion. Therefore, particle size is a
decisive factor for a degree of carbon combustion because of the recognition that
optimum particle size enhances the degree of combustion. Hence it is necessary
to optimize the particle size and oxygen concentration in poor combustible coal
(i.e. high rank coal) to improve the combustion degree of coal. Coal combustion
can be improved by increasing the supply of oxygen to the individual coal grains
and by adding combustion-promoting agent.

Therefore, coal injection in the prior art blast furnaces is de-limited primarily due
to the processes in the lower part of the furnace.
The process of combustion of coal, within a bed, or as pulverized coal in a
suspension is primarily a matter of combustion of carbon with sequential or
parallel combustion of volatile matter (VM). It is not, however, exactly known as
to whether or not oxidation begins to contribute to the temperature rise before
or after the loss of VM. The amount of VM evolved during combustion may not
correspond to the parameters determined by analysis of coal for example,
proximate and chemical analysis.
Based on the above mentioned disadvantages of prior art, the present inventors
recognized that it is necessary to characterize a coal in such a manner to first
assess the combustibility of coal similar to blast furnace design. To determined
the effect of oxygen enrichment and particle size distribution of high rank coal, a
bench-scale experimentation is conducted to diagnise the effect of oxygen
enrichment and particle size distribution on the combustion behavior of PCI coal
in electrically heated vertical furnace (2.5 m height).
OBJECTS OF THE INVENTION
It is therefore an object of the invention is to propose a process of optimization
of oxygen concentration in blast air and particle size distribution of fuel for
injection into a blast furnace to improve combustion of fuel.
Another object of the invention is to propose a process of optimization of oxygen

concentration in blast air and particle size distribution of fuel for injection into a
blast furnace to improve combustion of fuel, which allows poor combustable coal
to be used in blast furnace with improved combustability.
A further object of the invention is to propose a process of optimization of
oxygen concentration in blast air and particle size distribution of fuel for injection
into a blast furnace to improve combustion of fuel, which reduces the cost of hot
metal produced in a blast furnace.
SUMMARY OF THE INVENTION
Accordingly, there is provided a process of optimization of oxygen concentration
in blast air and particle size distribution of fuel for injection into a blast furnace to
improve combustion of fuel, comprising the steps of: feeding of high rank coal in
a particle size distribution from top portion of an electrically heated vertical
furnace alongwith a controlled flow of primary air to carry the coal particles
inside the furnace; injecting a pre-heating secondary air circumferentially into
the furnace including excess air quantity about 20% over the stochiometric
requirements; and supplying a pure oxygen stream with desired variable in
oxygen flow, wherein the burnout efficiency of the high rank coal is increased.
The present inventors consider that novelty of the invention lies in providing an
enhanced ignition and combustion conditions for high rank coal by creating a
zone of high oxygen concentration within the blast air stream. The inventive step
resides in the mechanism in which the particle size distribution of the coal is

maintained to maximize the burnout efficiency by keeping the constant oxygen
. concentration in the blast air stream.
Accordingly, there is provided a process of injecting high rank coal through blast
air stream in a blast furnace. As per the inventive process a variation and
optimization of excess oxygen concentration over a stoichiometrically required air
for complete combustion of carbon is first determined, and particle size
distribution of coal used in pulverized coal injection in the Blast Furnace, is
decided.
The inventors recognized that optimization of oxygen concentration in the blast
air and particle size distribution of the fuel for subsequent passage into the blast
furnace allow an improved combustion of a particular coal/fuel. The present
inventors further concluded that by increasing the combustibility of poor coal, the
poor coal can be used in blast furnace for Pulverised Coal Injection (PCI), which
interalia reduces the PCI cost and hence reduces the hot metal cost.
DETAILED DESCRIPTION OF THE INVENTION
The invention provides an enhanced ignition and combustion conditions for high
rank coal by creating a zone of high oxygen concentration within the blast air
stream. Further, the invention provides a particle size distribution so as to
enhance ignition and combustion of the fuel along with high oxygen
concentration in the blast air stream supplied to the blast furnaces for complete
combustion.

Accordingly, the present invention provides a process which first obtains the
input parameters of pulverized coal injection, for example, residence time of
pulverized coal in blast furnace. The process is implemented in the context of an
electrically heated vertical tube furnace similar to blast furnace PCI tuyere.
Pulverized coal is fed from top of the electrically heated vertical furnace along
with primary air to carry the coal particles inside the furnace. A controlled flow of
required primary air is provided to maintain the coal flow velocity similar to
pulverized coal injection (PCI) process in blast furnace. Further, preheated
secondary air stream is separately maintained to inject into the furnace
circumferentially. 20% excess air quantity of preheated secondary air over the
stochiometric requirement is maintained for the charged fuel. A separate stream
of pure oxygen is added to the secondary air line before supplying to the
furnace. Pure oxygen is supplied from an industrial oxygen cylinder. The oxygen
stream is controlled by a flow regulator and a rotameter to allow required
variation in oxygen flow and take reading thereof.
The coal sample is pulverized in a ball mill to different fineness and various
particle size distributions are measured by a standard sieve analysis.
In an embodiment of the present invention, oxygen concentration is increased to
a particular percentage to enhance the burnout efficiency of the high rank coal
for prior art particle size distribution.
In another embodiment of the present invention, the grinding time is increased
which interalia, increases finer particles distribution below 200 micron. The
burnout efficiency of the high rank coal is found to be increased for the same
oxygen concentration.

Table 1 and Table 2 show that the effect of different oxygen concentration and
particle size distribution on burnout efficiency of coal in an electrically heated
vertical furnace. The following examples are given by way of illustration of the
present invention which should not be construed to limit the scope of the present
invention.
Result shows that by increasing oxygen concentration from normal atmospheric
condition to 27.2 LPM in similar operating conditions, the burnout efficiency
increases approximately by 3% (Table 1). The similar increasing trend is
observed when the coal particle size distribution of injected coal is optimized.
Table 1: Effect of different oxygen concentration on burnout efficiency at similar
operating parameters



The main advantages of the present invention are
1. Use of poor combustible coal as a PCI in blast furnaces.
2. Reduction in hot metal cost and increasing raw material (coal) security.

WE CLAIM
1. A process of optimization of oxygen concentration in blast air and particle
size distribution of fuel for injection into a blast furnace to improve
combustion of fuel, comprising the steps of:
- feeding of high rank coal in a particle size distribution from top portion
of an electrically heated vertical furnace alongwith a controlled flow of
primary air to carry the coal particles inside the furnace;
- injecting a pre-heating secondary air circumferentially into the furnace
including excess air quantity about 20% over the stochiometric
requirements; and
supplying a pure oxygen stream with desired variable in oxygen flow,
wherein the burnout efficiency of the high rank coal is increased.
2. The process as claimed in claim 1, wherein the desired concentration is
27.2 LPM, and wherein the burn-out efficiency is achieved at 97.08%.
3. The process as claimed in claim 1, wherein when the particle size
distribution of the finer particles of the high rank coal is below 200 micron,
the burnout efficiency is achieved at 93.84%.

ABSTRACT

The invention relates to a process of optimization of oxygen concentration in
blast air and particle size distribution of fuel for injection into a blast furnace to
improve combustion of fuel, comprising the steps of: feeding of high rank coal in
a particle size distribution from top portion of an electrically heated vertical
furnace alongwith a controlled flow of primary air to carry the coal particles
inside the furnace; injecting a pre-heating secondary air circumferentially into
the furnace including excess air quantity about 20% over the stochiometric
requirements; and supplying a pure oxygen stream with desired variable in
oxygen flow, wherein the burnout efficiency of the high rank coal is increased.