The invention generally relates to assessing the thermoplastic behaviour of different metallurgical coal through known High Temperature Microscope. More particularly, the invention relates to an improved method to accurately determine the swelling properties of coal and identification of thermoplastic zone.
BACKGROUND OF THE INVENTION
According to the prior art technique, the crucible swelling number (CSN) is the measure of coking potential of coal. In CSN studies, coal is expanded by rapid heating. The shape of the expanded coal is then compared with predetermined and pre-stored shape of coal as per coking potential. These values start from 0 and continue up to 9 as per different coking potential of coal. CSN 0 is considered as non coking coal whereas CSN 9 is considered as the prime coking coal.
A known instrument (plastometer) allows measurement of “resistance to rotation of a stirrer immersed in a mass of coal (-72 mesh)”, which is subjected to a preset heating regime. With increasing of temperature, the stirrer speed is increased until at some point when the coal resolidifies and the stirrer is halted (Fig.1). The plastic properties of the samples are then measured by the resistance to motion of the fluid mass in a plastometer.

Crucible swelling Number (CSN) Apparatus
This test has been performed using standard IS 1353: 1993, in which 1 gm of
sample (-0.212 mm size) is taken in a translucent squat shaped silica crucible
and the sample is levelled by tapping the crucible at least 12 times. The crucible
is covered with a lid and heated under standard conditions by a gas burner. After
the test, the shape of coke button is compared with a standard chart and
accordingly, the crucible swelling number (1 to 9) is assigned to the coal sample
(Fig. 2).
For some non-coking and solvent extracted coal, the conventional swelling and
plasticity experimentation do not work properly due to the insensitivity or abrupt
changes in plastic phase of those coals.
OBJECTS OF THE INVENTION
It is therefore an object of the invention to propose an improved method to accurately determine the swelling properties of coal and identification of thermoplastic zone.
Another object of the invention is to propose an improved method to accurately determine the swelling properties of coal and identification of thermoplastic zone, which allows development of plastic phase regime including kinetic information of the thermoplastic zone.

SUMMARY OF THE INVENTION
Accordingly, there is provided an improved method to accurately determine the swelling properties of coal and identification of thermoplastic zone. As per the improved method of invention, a standard heating microscope is used to visualize the change in contact angle, sintering, softening and melting temperature of powdered materials during heating. The sample is prepared by compressing the powder material to form a soldering tablet which is then applied to the substrate material to be tested. The substrate is positioned in the middle of a tube furnace where the external thermos-element is located. The sample structure is heated up in the furnace to around 800 0C. Images of the sample are captured by a camera which produces a very sharp image with high contrast. No distortions occur even when the soldering material during the heating is liquefied quickly. As the coal in powdered form passes through the thermoplastic stages, it exhibited swelling and plastic properties, which are visualized and determined from the high temperature sharp images. Any changes in the swelling behavior is also noted from change in area of the images. A good correlation can be found between change in area and thermoplastic behavior of coal. The present invention is also applicable to the coal having very low fluidity or coals having fluidity different from the conventional limit. The method is useful for the evaluating both swelling and plastic region of the coals. All the results developed

from the swelling data are found to be in good agreement to determine the fluidity order and CSN value of coals. All the results are quite similar with the conventional approach and hence can be used further for correlating and evaluating the coking potential and thermoplastic property of coal.
This method of the invention is much cheaper and requires less time and can be an alternative to plastometers and crucible swelling number (CSN ) apparatus where the determination of fluidity of non-caking coals is quite difficult.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Figure 1 Plasticity curve for coal drawn based on the plastometer data. Figure 2 Standard button images from crucible swelling number (CSN) test. Figure 3 Flow diagram of the method of present invention. Figure 4 Deformation images of coal pellets at initial and maximum swelling
under High Temperature Microscope. Figure 5 Change in area of coal pellets vs Temperature
Figure 6 Comparison of Fludity (Plastometer) and Area change (High Temperature Microscope.
DETAILED DESCRIPTION OF THE INVENTION
A detailed flow diagram of the experimental procedure is given in figure 3:
Figure 3 Flow diagram of the method of present invention. At the beginning
coal sample must be taken in around -100 mesh size. A coal button is formed

from the powdery coal samples which is placed on a sample holder. The Sample holder with the sample is placed in a furnace having automatic image capture devices with the progress of heating. Capturing of snapshots is done at each 30C increase in temperature. Captured images is processed by a known image processing software. Inert heating environment must be maintained throughout the heating. Heating rate is kept around 30C/minute. Deformed area is recorded automatically along with the snapshots. The degree of deformation provides a direct correlation with coking potential. Increase in area exactly correlates with the standard CSN practice. The temperature corresponding to the maximum area gives data/gradation on coking property. First derivative of the increase in area correlates directly with the standard plastometer data for determination of coal fluidity. Almost for all type of coal quantification in terms of coking potential is possible by this method.
As coal enter into the plastic zone, a change in shape of button can be observed, which is due to the rapid changes in intra bond co-ordination. It is believed that there may be enhancement of coal volume per unit mass as some rapid chemical transformation occurs in that zone. An idea, to observe this phenomenon through high temperature microscope is so conceived that it may give some insight to thermoplastic behavior of coal by capturing the change of shape of cylindrical coal pellet. It was observed that raw coal fluidity varied from 330 to

5500C depending on the nature of coal. It was also found from the result in Table 1 that the major thermoplastic behaviors of coals always existed around that zone only. In this experiment, cylindrical pellets of coal of 3 mm diameter and height were made. These coal pellets were then placed individually under the furnace with a constant heating rate of 30C/min. The entire pellet image was captured by a robust microscope. As the temperature increased, the microscope started capturing images with a pre-specified time interval. An image processing software was attached which calculated instantaneously the change in area, shape factor and the contact angle of the pellet with the exact temperature record. Fig. 4 shows the deformation point identified by the machine itself. Fig. 5 shows the change in area with the temperature. It was observed that the change in area ceased exactly around 450 0C, which is theoretically the plastic phase of the coal. A differential graph of change in area also supported the fact that the entire swelling characteristics occurred between 330 to 530 oC. As the coal passed through plastic stage the volume of the pellet got changed accordingly, which was instantaneously captured by the image and got analyzed by the image processing software. This change in area actually indicated that more thermoplasticity induced more swelling tendency of the pellet. A very good correlation is observed between the variation in coal and the percentage change in area during heating. Coal O has got the maximum swelling as the percentage

of change in area is elevated to 149 (Table 2). The temperature at which maximum swelling occurred was found to be around 450 o C which is also the highest temperature in comparison to others. Coal W comes in the second in position. It got the swelling value of area of 133%. The temperature of maximum swelling occurred also stood second in position (442 oC). Coal N is placed 3rd in position. It has got swelling of 118% at the temperature around 440 o C. Coal M has very poor swelling tendency (~ 106% ) and the maximum swelling temperature is also substantially lower than others ( 421oC). The main interesting feature that can be easily observed was the change in area due to the swelling of button exactly followed the same trend as shown by CSN values. The order of the swelling can be rearranged as Coal O> Coal W> Coal N> Coal M. This proved the fact that this equipment can be used to study the swelling phenomena for evaluating the coking potential of coal.
The above findings encouraged us to drive for further study of finding out thermoplastic zone of coal. The change in area can also be modified as per the data obtained from the plastometer. The initial change is the swelling or softening point which can be visualized by calculating the first derivative of the area. It is quite obvious that the point where the differential area started rising from the zero value is the initial softening point of coal (Fig. 5). The differential

area started increasing and finally got a maximum value. This value shows a little lagging behind than the maximum swelling temperature. However, for deriving a correlation with plastometer data the maximum swelling temperature was considered for the study. So the temperature at the maximum increase in area represents the maximum fluidity zone. Now similar to initial point the solidification temperature is considered where differential area got a minimum value. Beyond that point, differential area exhibit constant decrease in area which is basically just the reduction in weight by constant devlolatilization (Fig5). So solidification temperature can be considered as the point where the rate of change in area got a constant value. Now this data can also be compared with the conventional fluidity data obtained from the plastometer (Fig. 6). Although, the trend in the graph shows the same features as obtained from plastometer, a shift towards low temperature zone is observed. This may be due to the difference in working principle of those equipment’s. Plastometer basically portray the change in viscosity whereas current approach captures the swelling nature of coal in plasticity.

WE CLAIM :
1. An improved method to accurately determine the swelling properties of
coal and identification of thermoplastic zone, comprising the steps of :
- forming a coal pellet with powdery coal sample of - 100 mesh size;
- placing the coal pellet with coal sample in a tube furnace having external thermos element;
- heating the sample structure in the furnace to around 8000C, maintaining an inert heating environment;
- providing a heating microscope at a spaced- apart location from the furnace to visualize the change in contact angle, sintering, softening and melting temperature of the sample during the heating in the furnace; and
- capturing images of the sample with the progress of heating, the captured images being processed by a known image processing software in respect of area, shape factor and contact angle wherein the capturing of images of the sample structure is made at each 30C increase in heating temperature, wherein the heating rate is maintained around 30C/minute, and wherein the deformed area on the sample structure is automatically marked in real time on the captured images.

2. The method as claimed in claim 1, wherein the raw coal fluidity exhibited a variation between 330 to 5500C.
3. The method as claimed in claim 1, wherein the change in area corresponding to heating ceases at 4500C which being the normal plastic phase of coal.

4. The method as claimed in claim 1, wherein the maximum swelling is occurring at a temperature between 421°C to 450°C.