FIELD OF THE INVENTION:
The present invention relates to a method for assessing the suitability of a coal and/or coal blend or more particularly a technique based on a Composite Burnout Potential (CBP) for burnout behaviour of coal during injection for improving combustion performance of coal blends.
The invention further discloses a Composite Burnout Potential (CBP) model which determines the optimum value of CBP of coal and/or coal blend which eventually improves the burnout of coal at a constant oxygen concentration in blast air which will enable improved combustion.
BACKGROUND OF THE INVENTION:
The improvements in productivity, reduction in coke consumption and increased level of coal injection within the blast furnaces have been accelerated due to the steel industry being a very competitive global industry. It can be expected that further improvements in these areas of operations to reduce cost will continue. This is achieved internationally by replacing part of metallurgical coke by injecting the cheaper coal in blast furnace.
The combustion behaviour of coal particles (pulverized coal injection, PCI) within a short residence time in a blast furnace can be difficult to assess by using any single coal parameter. It is influenced by several ways e.g. particle size, fuel ratio, mode of injection lances, blast gas composition, temperature, coal properties including volatile matter, carbon structure, ash content, rank and maceral composition.

Unexpectedly, few low VM coals from different origins displayed better combustion performance. This unexpected combustion behavior cannot be completely understood in terms of current understanding of coal organic and inorganic properties. On the other hand, it has also been reported that burnout efficiency did not change linearly with increase in volatile matter of coal blends. However, there is relatively little research on selections of PCI coals based on fundamental aspects of combustion are far from complete.
To overcome the problems identified above, it is felt necessary to explore the critical factors affecting burnout behaviour of coal and/or coal blends belonging from different geological origins and optimize the combustion performance of difficult to burn coals by characterization of coal properties.
Hence, the main object of the present invention is to explore the critical factors affecting coal and/or coal blends belonging from different geological origins and optimize the combustion performance of difficult to burn coals by intrinsic properties of coal. Accordingly, the present invention provides a process which has been simulated as per the pulverized coal injection.
OBJECTIVES OF THE INVENTION:
The principal object of the present invention is based on Composite Burnout Potential (CBP) is to provide optimization the combustion performances of selected coal and/or coal blend by intrinsic properties of coal.
Another object of the present invention based on CBP is to provide a mechanism in which the composite burnout potential of the coal is maintained to maximize the burnout efficiency by keeping the constant oxygen concentration in the blast air stream.

Further object of the present invention based on Composite Burnout Potential (CBP) is to provide variation and optimization of excess oxygen concentration over and above the stichiometrically required air for complete combustion of carbon and particle size distribution of coal used in pulverized coal injection in Blast Furnace.
Another object of the present invention based on CBP is using of pulverized coal (PCI) in modern blast furnaces for lowering the coke rate through replacing part of metallurgical coke by injecting coal in blast furnace.
Further object of the present invention based on CBP for assessing the suitability of a coal and/or coal blend in blast furnace, is facilitation of smooth operation of blast furnace and reducing the cost of hot metal.
Another object of the present invention is to develop a Composite Burnout Potential (CBP) based in the intrinsic properties of coal model which has been correlated with combustibility of coal and/or coal blend to ensure proper utilization of heat with proper combustion of coal particles.
Another object of the present invention based on CBP is to provide a method for assessing the suitability of coal and/or coal blend in blast furnace, which is economic and environment friendly.
SUMMARY OF THE INVENTION:
According to this present invention, there is provided a novel method based on Composite Burnout Potential (CBP) selecting a particular coal and/ or coal blend can be represents as:



where VM is the volatile matter, IM is inherent matter, C is elemental carbon %, H is the elemental hydrogen % and O is elemental oxygen %;
said method comprises the steps of: a) providing an electrically heated vertical tube furnace of 2.5 m height; b) feeding dried pulverized coal and/or coal blend through a vibratory feeder at top of the electrically heated vertical furnace along with primary air; c) injecting a secondary air stream which enters the furnace circumferentially; d) collection of a coal sample from the furnace through a water cooled probe.
- said pulverized coal injection gradecoals can be divided in two
distinguish groups viz., i) coals/coal blends having CBP <2.5 is poor PCI
grade coal which exivits poor burnout efficiency; ii) coals/coal blends
having CBP > 2.5 is good PCI grade coals/coal blends which show
burnout efficiency.
- said three different level of oxygen concentration such as 21%, 25% and 31%, was injected into the furnace during the combustion process.
- said a positive correlation between CBP and burnout of individual coal with correlation coefficients such as 0.671% to 0.776%, 0.688% to 0.785% and 0.566% to 0.765% for three different oxygen levels.

- said CBP value of coal varies from -0.03 to 4.9, minimum CBP value of Coal–N is – 0.03 and Coal C has maximum CBP value is 4.90.
- said source of pure oxygen stream was equipped with a flow regulator and a rotameter to allow required variations in oxygen flow.
- said dried pulverized coal was fed through the vibratory feeder at the rate of 1.5 kg/h when the temperature was 1000°C.
- said burnout efficiency of the coal and/or coal blend increases for the same particle size with the increase in the level of oxygen concentration in the supplied stream of pure oxygen into the furnace.
- said burnout efficiency of coal and/or coal blend gets increased the use of coal having finer particles below 72 micron.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS:
Figure 1 illustrates schematic diagram of drop tube furnace.
Figure 2 illustrates process flow for selection of coals.
Figure 3 illustrates Coal Burnout potential (CBP) of individual coals.
Figure 4 illustrates relation between CBP and burnout of different coal coals.
Figure 5 illustrates relation between CBP and burnout of different coal blends.
Figure 6 illustrates relation between CBP and burnout of coals/coal blends.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT OF THE INVENTION:
The present invention provides a novel method for determining burnout efficiency of a coal and/or coal blend in blast furnace based on a Composite Burnout potential (CBP).

CBP is a combination of statistical and mathematical methods that ate useful for selection of coals. In this technique, the main objective is to optimize the proportion of high and low rank of coal in a coal blend that is influenced by various properties. The calculation of CBP is based on the interpolation of the range of selected properties which is used in this model. Mathematically CBP can be represents as:

wherein VM is the volatile matter, IM is inherent matter, C is elemental carbon %, H is the elemental hydrogen % and O is elemental oxygen %.
Therefore, CBP of coal blend can be expressed as:
CBP of coal blend = Σ (CBP of coal x Wtp)
Where, Wtp is the proportion of individual coal. The method comprises the steps:
a) providing an electrically heated vertical tube furnace of 2.5 m height;
b) feeding dried pulverized coal and/or coal blend through a vibratory feeder at top of the electrically heated vertical furnace along with primary air;

c) injecting a secondary air stream which enters the furnace
circumferentially;
d) mixing a pure oxygen stream to said secondary air stream before
injecting the secondary air stream to the furnace; and
e) collection of a coal sample from the furnace through a water cooled
probe.
A controlled flow of required primary air is provided to maintain the coal flow velocity similar to PCI process in blast furnace. Also, preheated secondary air stream was maintained separately to enter the furnace circumferentially. The 20% excess air quantity of preheated secondary air was maintained over the stichiometric requirement for the charged fuel. Pure oxygen was being supplied by industrial oxygen cylinder. The oxygen stream was equipped with flow regulator and rotameter to enable the required variation in oxygen flow and take reading thereof.
The coal sample was pulverized in a ball mill to different fineness and various particle size distributions were measured by standard sieve analysis.
A table has been given for different operating parameters of drop tube furnace which were maintained for evaluating the burnout efficiency of coal and/or coal blends.


Figure 1 discloses a schematic diagram of drop tube furnace.
A model also has prepared for assessing the suitability of coal based on Composite Burnout Potential (CBP) and named on CBP model.
CBP model has been used for selecting the least expensive coals/coal blends which will comply with the minimum requirements of blast furnace. It appears that the CBP of coal is an important coefficient for predicting the combustibility of PCI coal in blast furnaces. This may be due to the fact that coal having lower CBP value, the volatile matter contains considerable quantities of saturated hydrocarbons and when it goes high the volatile matter is rich in unsaturated hydrocarbons i.e., in high volatile matter coals (low rank), the CBP value being less, the volatile matter contains considerable amount of saturated hydrocarbons and in higher rank coals the volatile matter is rich in unsaturated hydrocarbons. Unsaturated hydrocarbons decompose thermally or deposit soot more easily than the saturated hydrocarbons.

Coefficient of Composite Burnout Potential (CBP)
Burnout Potential (BP) of coal depends on its individual properties which is important for combustion. In an effort to broaden the scope of coal selection, the authors have developed a novel technique based on a coefficient, named as Composite Burnout Potential (CBP). CBP model has been used for selecting cheap coal blends that would still comply with the minimum requirements of blast furnaces. The CBP index takes into account the various properties of the coals and their proportions in a given coal blend. This methodology is necessary since each of these parameters represents different aspects of the combustion phenomena with its varying importance. Some of these parameters also have inter dependencies.
Development of CBP Model
CBP is a combination of statistical and mathematical methods that are useful for selection of coals. In this technique, the main objective is to optimize the properties. The calculation of CBP is based on the selected properties which is used in this model. Mathematically CBP can be represents as:



Note: VM is the volatile matter, IM is inherent matter, C is elemental carbon %, H is the elemental hydrogen % and O is elemental oxygen %.
Therefore, CBP of coal blend can be expressed as:
CBP of coal blend = Σ (CBP of coal x Wtp)
Where, Wt is the proportion of individual coal.
Input Sheet
CBP consist of 6 inputs variables which are determined from proximate and chemical analysis. The functional relationship between the input variables like ash, volatile matter (VM), inherent moisture (IM), elemental carbon (c), elemental hydrogen (H) and elemental oxygen (O) the corresponding coal and/or coal blend burnout has been mapped using an adaptive CBP model.
Output Sheet
In the output sheet, coal and/or coal blend quality with respect to ash, VM, IM, C, H and O resultant burnout with respect to burnout potential of all properties.
In an embodiment of the present invention through the said process with increase in oxygen concentration to a particular percentage, the burnout efficiency of the high rank coal has increased for the same particle size distribution.
In another embodiment of the present invention the said process with increase in grinding time i.e. increase of finer particles below 72 micron.
The burnout efficiency of the high rank coal has increased for the same oxygen concentration.

CBP of coals/coal blends
The CBP model was developed with the use of thirteen different origins of coals and twenty seven coal blends covering wide range of properties. All coals and coal blends were selected for combustion study in drop tube furnace in two different phases. In the first phase, 13 individual coals were selected for combustion study in DTF at 3 different level of oxygen concentration. In the second phase, based on individual combustibility behaviour 27 binary coal blends were designed for combustibility experiments in DTF with similar operating conditions. A positive relationship between coal/blend burnout and blend CBP was found. A brief flow diagram showing the steps followed in CBP model development is given in Figure 2. The calculated CBP of all individual coals are shown in Figure 3. It is noted from Figure 3 that the CBP value of the coal varies from -0.03 to 4.90. Coal N is having the least CBP value of -0.03, while Coal C is having the maximum CBP value of 4.90. A strong positive correlation between CBP and burnout efficiency is also observed from the results.
Figures 4-6 show the calculated CBP value and burnout of coal and/or coal blends at three different oxygen levels viz., 21%, 25% and 31%. Result shows that increasing CBP value of coal and/or coal blend increases in burnout.
Figure 4 shows the relationship between CBP of individual coal and burnout efficiency. The result shows a positive correlation between the CBP and burnout of individual coal at drop tube furnace at three different oxygen levels viz., 21%, 25% and 31% with correlation coefficient 0.724%, 0.720% and 0.754% respectively. It appears that the CBP of coal is an important coefficient for predicting the combustibility of PCI coal in blast furnaces. This may be due to the fact that coal having

lower CBP value, the volatile matter contains considerable quantities of saturated hydrocarbons and when it goes high the volatile matter is rich in unsaturated hydrocarbons i.e., in high volatile matter coals (low rank), the CBP value being less, the volatile matter contains considerable amount of saturated hydrocarbons and in higher rank coals the volatile matter is rich in unsaturated hydrocarbons. Unsaturated hydrocarbons decompose thermally or deposit soot more easily than the saturated hydrocarbons.
Figure 5 shows the relationship between CBP of coal blends and burnout. A positive correlation between CBP and burnout was observed at all three different oxygen levels viz., 21%, 25% and 31% with correlation coefficient 0.671%, 0.688% and 0.566% respectively.
Figure 6 shows a good relationship between CBP of coals and coal blends and burnout. The similar increasing trend was observed as again at all three different oxygen levels viz., 21%, 25% and 31% with correlation coefficient 0.776%, 0.785% and 0.765% respectively. Therefore, the effect of an increase in oxygen enrichment on coal combustion efficiency is very limited, as can clearly be seen in Fig. 4-6. Consequently, CBP coefficient of coal and/or coal blend is an important parameter for predicting the burnout behaviour of coals/coal blends.
It is also interesting to note from the figure that the coal can be divided into two distinct groups: coals with CBP <2.5 give poor burnout efficiency, coal with CBP >2.5 which give god burnout efficiency (≥60%). Consequently, burnout efficiency seems to have a strong dependence of CBP in the full range tested, which includes a wide variety of PCI coals; but, such dependence is especially strong in coals with CBP>3, where CBP variations could imply a substantial burnout improvement in marginal coals. The optimum CBP value of near 2.5 is supported by the

experimental burnout efficiency of coal and/or coal blend produced at a pilot scale level (drop tube furnace). Hence, it may be concluded that the CBP of coal, blend and coal and/or coal blend is in close proximity with the burnout efficiency.

Table 2 presents the relevant properties of thirteen individual coals from different origins. The selected coals are from different sources with wide property variation starting from low volatile (Coal N) to high volatile (Coal C). The other properties such as ash content, VM, Ro and GCV of the selected coals varies from 7.10-15.42%, 5.10-35.40%, 0.67-2.01% and 6350-7650 kcal/kg, respectively. The HGI value of the selected coals varies from 48 to 104. Results show that there is some similarity with the trend as reflected in the rank parameter except coal E and coal J. The

operating parameters of the tested coal and/or coal blends samples selected for the DTF tests are described in Table 1.
The following example is given by way of illustration of the present invention and should not be construed to limit the scope of the present invention.
Example 1:
The coals used in the study were characterized through physical, chemical and petrographic analysis (Table 1). After characterization of individual coals, CBP values were calculated with the help of the model developed. Total forty coal and/ or coal blends were used for developing this model.
Combustion tests in drop tube furnace
The combustion experiments were carried out in a vertical drop tube furnace (DTF). The DTF consists of a ceramic tube of length 2500 mm and ID 100 mm. The overall length of furnace is divided in five zones. All the five zones were heated electrically and the temperature in all the zones could be raised up to 1100°C. In each zone, there is a provision of sample collection through water- cooled probe. This especially designed water-cooled probe having vacuum pump and cyclone was used for collection of solid samples. The schematic diagram of DTF is shown in Figure 1.
The dried pulverized coal was fed through the vibratory feeder at the rate of 1.5 kg/h when the temperature of combustor was about 1000°C. Experiments were conducted at constant coal feed rate of 1.5 kg/h of DTF at three different oxygen concentration viz. 21%, 25% and 31%. The primary air and different quantity of preheated secondary air were feed in to the combustor for different run of DTF. Desired oxygen concentrations in the air required for combustion for various DTF runs were maintained

by additional, commercially available oxygen cylinders. Required oxygen supply to meet the combustion studies were maintained by standard regulator and observing the flow in a rotameter. Char samples were collected from second port of drop tube furnace for each test under different O2 enrichment for evaluation of the burnout efficiency (BE).
The chemical analysis of the coals and char samples was determined to calculate the burnout efficiency. BE was calculated as per following empirical relation:

Where Ao is the dry ash % of the parent coal and Ac is the dry ash % of the char.
The present invention is based on novel combustibility assessing technique of the pulverized coal injection in blast furnace is composed of the CBP technique through the intrinsic properties of coal and/or coal blends. The process wherein a new coefficient named as Composite Burnout Potential (CBP) of coal and/or coal blend is proposed for identifying suitable/cheaper coal and/or coal blend for blast furnace injection. The process wherein CBP value has been correlated with combustibility of coal and/or coal blend, namely, burnout to ensure proper utilization of heat with proper combustion of coal particles. The method wherein the combustion of pulverized coal injection claims that CBP technique has been validated in vertical drop tube furnace (2.5 m height). The method wherein the oxygen concentration during combustion of the pulverized coal injection claims not playing significant importance which is reflects from Figures 3-5. The process wherein the pulverized coal injection coals can be divided into two distinct groups: Coals with CBP <2.5 give poor burnout efficiency, Coal with CBP >2.5 which give god burnout efficiency (≥60%). Another object of the present

invention is to provide a guideline for assessing the burnout of coal and/or coal blend. Consequently, burnout efficiency seems to have a strong dependence of CBP in the full range tested, which includes a wide variety of PCI coals; but, such dependence is especially strong in coals with CBP>3, where CBP variations could imply a substantial burnout improvement in marginal coals. As wherein the optimum CBP value of near 2.5 is supported by the experimental burnout efficiency of coal and/or coal blend produced at a pilot scale level (drop tube furnace), which seem to be reasonable judging from reported experiences.
The non-limiting advantages of the present invention are listed below:
1. Optimal utilization of inferior combustible coal as a PCI in blast
furnaces. 2. Reduction in hot metal cost and increasing raw material (coal) security.
3. Designing and optimization of proportion of coals in coal blend to insure proper utilization of heat.
4. The findings are useful to the control and optimization of PCI operation and reduce the cost of hot metal.

WE CLAIM:
1. A novel method based on Composite Burnout Potential (CBP) selecting a particular coal and/ or coal blend can be represents as:

where VM is the volatile matter, IM is inherent matter, C is elemental carbon %, H is the elemental hydrogen % and O is elemental oxygen %;
said method comprises the steps of:
a) providing an electrically heated vertical tube furnace of 2.5 m
height;
b) feeding dried pulverized coal and/or coal blend through a vibratory feeder at top of the electrically heated vertical furnace along with primary air;
c) injecting a secondary air stream which enters the furnace circumferentially;

d) collection of a coal sample from the furnace through a water cooled probe.
2. The process as claimed in claim 1, wherein pulverized coal injection gradecoals can be divided in two distinguish groups viz., i) coals/coal blends having CBP <2.5 is poor PCI grade coal which exivits poor burnout efficiency; ii) coals/coal blends having CBP > 2.5 is good PCI grade coals/coal blends which show burnout efficiency.
3. The method as claimed in any of the preceding claims, wherein three different level of oxygen concentration such as 21%, 25% and 31%, was injected into the furnace during the combustion process.
4. The method as claimed in any of the preceding claims shows a positive correlation between CBP and burnout of individual coal with correlation coefficients such as 0.671% to 0.776%, 0.688% to 0.785% and 0.566% to 0.765% for three different oxygen levels.

5. The method as claimed in claim 1, wherein the CBP value of coal varies from -0.03 to 4.9, minimum CBP value of Coal–N is – 0.03 and Coal C has maximum CBP value is 4.90.
6. The method as claimed in any of the preceding claims, wherein said source of pure oxygen stream was equipped with a flow regulator and a rotameter to allow required variations in oxygen flow.
7. The method as claimed in claim 1, wherein said dried pulverized coal was fed through the vibratory feeder at the rate of 1.5 kg/h when the temperature was 1000°C.
8. The method as claimed in any of the preceding claims, wherein the burnout efficiency of the coal and/or coal blend increases for the same particle size with the increase in the level of oxygen concentration in the supplied stream of pure oxygen into the furnace.

9. The method as claimed in any of the preceding claims, wherein the burnout efficiency of coal and/or coal blend gets increased the use of coal having finer particles below 72 micron.