Claims:WE CLAIM:

1. Pellet charging system in muffle furnace to generate effective sample pellet quality comprising:

pellet charging container having a peripheral wall contiguous to the base for supporting pellets ;

said pellet charging container apart from peripheral heat transfer into pellets provided with blank core/central portion blocking any pellet feed therein in zone of poor heat transfer and further favouring radiation heat transfer therein for better consistent pellet heating and effective sampling.

2. Pellet charging system in muffle furnace as claimed in claim 1 comprising said peripheral wall and said blank core/central portion are connected to provide for thin ring layer arrangement of pellets for heating.

3. Pellet charging system in muffle furnace as claimed in anyone of claims 1 or 2 supporting there between said peripheral wall and the blank core/central region a thin ring of pellets 15 to 80 mm preferably about 70 mm depth to accommodate preferably about 5-7 pellets of mean size 10-12 mm.

4. Pellet charging system in muffle furnace as claimed in anyone of claims 1 to 3 supporting there between said peripheral wall and the blank core/central region up to 1-4 layers that too with centre blocking.

5. Pellet charging system in muffle furnace as claimed in anyone of claims 1 to 4 comprising of elevation from bottom to provide space in the bottom to increase possibility of convective heat transfer preferably through passage of hot air supplied from bottom.

6. Pellet charging system in muffle furnace in as claimed in anyone of claims 1 to 5 comprising of cage like construction for effective heat transfer.

7. Pellet charging system in muffle furnace as claimed in anyone of claims 1 to 6 comprising a substantially cylindrical basket type container with a concentric said core central blank having an elevated base with total height of the basket in the range of 150 to 350 preferably about 250 mm and height from the elevated base in the region of 50 to150 preferably about 100 mm.

8. Pellet charging system in muffle furnace as claimed in anyone of claims 1 to 7 wherein said container, base and central core blank are obtained of high temperature material based rods.

9. Pellet charging system in muffle furnace as claimed in anyone of claims 1 to 8 comprising container/basket outer diameter ranging from 100 to 350 mm preferably about 220mm and said concentric core/center blank having diameter of 50 to 250 mm preferably about 80mm.

10. A method of sampling of pellets to ascertain pellet quality such as cold crushing strength comparable to actual plant environment involving the pellet charging system in muffle furnace as claimed in anyone of claims 1 to 9 comprising:

loading of said pellets in thin layer there between said container internal wall and said core/central blank maintaining core/ center part of the of the container/basket completely blank to facilitate efficient heat transfer and effective sampling.

11. A method as claimed in claim 10 comprising providing a thin ring of pellets 15 to 80 mm preferably about 70 mm depth to accommodate preferably about 5-7 pellets of mean size 10-12 mm.

12. A method as claimed in anyone of claims 10 or 11 comprising providing there between said peripheral wall and the blank core/central region a thin ring of pellets 15 to 80 mm preferably about 70 mm depth to accommodate preferably about 5-7 pellets of mean size 10-12 mm.

Dated this the 29th June, 2019
Anjan Sen
Of Anjan Sen & Associates
(Applicant’s Agent)
IN/PA-199

, Description:FIELD OF THE INVENTION

Present invention relates to pellet heating in muffle furnace. More particularly, the present invention is directed to pellet charging system in muffle furnace for pellet heating to achieve best possible sample pellet quality which can be reproduced on plant scale operation. The invention is related to the feeding arrangement of pellets inside the muffle furnace so that the desired output of the pellet quality can be achieved after heating the pellets through designed heat treatment cycle.

BACKGROUND OF THE INVENTION
Use of pilot plants or lab scale experiments is always a desirable tool to predict the performance of the system with any given change in input feed or process parameter. For industry like pellet plant, this becomes more critical as there is practically no control over input properties as input is a natural occurring mineral (e.g. iron ore) whose properties vary from source to source or many time, within the sources itself over a period of time.

Few pilot scale pellet furnaces are commercially available which involves huge setup in terms of space required and capital cost. There are commercial ‘pilot scale pellet machines’ available which uses a cylindrical pot which is properly filled in close packing in above equipment. These pilot scale furnaces use hot air flow thus utilising convection & radiation both for heat transfer to the pellet surface. These are very complex systems and involves capital investment along with a lot of space to accommodate gas heating & control mechanisms.

More widely used practice involves use of muffle furnaces of different capacity. Green pellets are charged in these muffle furnaces either using a basket or crucibles. Major disadvantage of these systems is the fact that their results shows a wide variation in terms of pellet properties (i.e. CCS- cold crushing strength) within a batch. This happens primarily due to non-uniform heating across the cross section. Pellets exposed to the heat source gets overheated whereas pellets placed inside receive less heat.

There has been thus a need to developing method and means for pellet heating in muffle furnace to attain uniform and consistent sample pellet properties which would corroborate with actual operating condition in plant scale. Contrary to the existing disadvantage of wide variation within a batch and poorer average properties compared to the pellet plant, this invention attempts to arrive at a solution incorporating specific arrangement of pellets inside the muffle furnace.

OBJECTS OF THE INVENTION

The basic object of the preset invention aims at providing a pellet charging system in muffle furnace resolving the major drawback of simple muffle furnace system of high standard deviation in pellet properties and non-uniform heating of pellets.

A further object of the present invention is directed to provide a pellet carging system in muffle furnace which is able to produce pellets with properties matching very close to the actual plant output.

A still further object of the present invention is directed to provide a pellet charging system and heating arrangement in muffle furnace which further helps to do blend optimization experiments offline with much higher confidence level compared to earlier arrangement.

Yet another object of the present invention is directed to provide a simple yet reliable pellet charging system and heating arrangement in muffle furnace partially substituting the need for a costly and resource intensive pellet simulator furnace for blend optimization studies.

SUMMARY OF THE INVENTION
The basic aspect of the present invention is directed to pellet charging system in muffle furnace to generate effective sample pellet quality comprising:

Pellet charging container having a peripheral wall contiguous to the base;

Said pellet charging container apart from peripheral heat transfer into pellets provided with blank core/central portion blocking any pellet feed therein in zone of poor heat transfer and further favoring radiation heat transfer therein for better consistent pellet heating and effective sampling.

A further aspect of the present invention is directed said pellet charging system in muffle furnace comprising said peripheral wall and said blank core/central portion are connected to provide for thin ring layer arrangement of pellets for heating.

A still further aspect of the present invention is directed to said pellet charging system in muffle furnace supporting there between said peripheral wall and the blank core/central region a thin ring of pellets 15 to 80 mm preferably about 70 mm depth to accommodate preferably about 5-7 pellets of mean size 10-12 mm.

A still further aspect of the present invention is directed to said pellet charging system in muffle furnace supporting there between said peripheral wall and the blank core/central region up to 1-4 layers that too with centre blocking.

Another aspect of the present invention is directed to said pellet charging system in muffle furnace comprising of elevation from bottom to provide space in the bottom to increase possibility of convective heat transfer preferably through passage of hot air supplied from bottom.

Yet another aspect of the present invention is directed to said pellet charging system in muffle furnace comprising of cage like construction for effective heat transfer.

A further aspect of the present invention is directed to said pellet charging system in muffle furnace comprising a substantially cylindrical basket type container with a concentric said core central blank having an elevated base with total height of the basket in the range of 150 to 350 preferably about 250 mm and height from the elevated base in the region of 50 to150 preferably about 100 mm.

A still further aspect of the present invention is directed to said pellet charging system in muffle furnace wherein said container, base and central core blank are obtained of high temperature sustaining material based rods.

A still further aspect of the present invention is directed to said pellet charging system in muffle furnace comprising container/basket outer diameter ranging from 100 to 350mm preferably about 220mm and said concentric core/center blank having diameter of 50 to 250 preferably about 80mm.

Another aspect of the present invention is directed to a method of sampling of pellets to ascertain pellet quality such as cold crushing strength comparable to actual plant environment involving the pellet charging system in muffle furnace as described above comprising:

loading of said pellets in thin layer there between said container internal wall and said core/central blank maintaining core/ center part of the of the container/basket completely blank to facilitate efficient heat transfer and effective sampling.

Yet another aspect of the present invention is directed to said method comprising providing a thin ring of pellets 15 to 80 mm preferably about 70 mm depth to accommodate preferably about 5-7 pellets of mean size 10-12 mm.

A still further aspect of the present invention is directed to said method comprising providing there between said peripheral wall and the blank core/central region a thin ring of pellets 15 to 80mm preferably about 70 mm depth to accommodate preferably about 5-7 pellets of mean size 10-12 mm.

The above objects and advantages of the present invention are described hereunder in greater details with reference to following accompanying non limiting illustrative drawings.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Figure 1: show details of heat cycle A & B used for experiments (Furnace end cooling for both muffle cycle).
Figure 2:shows arrangement & data for experiment 1 relating to designing heating cycles.
Figure 3:shows arrangement & data for experiment 2.
Figure 4:shows arrangement & data for experiment 3.
Figure 5:shows arrangement & data for experiment 4.
Figure 6:shows arrangement & data for experiment 5.
Figure 7 :shows arrangement & data for experiment 6.
Figure 8: shows perspective view of core empty new basket design developed at final step.
Figure 9a-b: shows the details of dimensional requirement of the basket configuration of figure 8.

DETAILED DESCRIPTION OF THE INVENTION WITH REFERENCE TO THE ACCOMPANYING DRAWINGS
Present invention is directed to pellet charging system in muffle furnace providing for pellet arrangement for pellet heating to achieve best possible sample pellet quality which can be reproduced on plant scale operation.

Proposed arrangement requires use of a muffle furnace with the capacity to achieve desired temperature cycle. The invention is related to the arrangement of pellets inside the muffle furnace so that the desired output of the pellet quality can be achieved after heating the pellets through designed heat treatment cycle. Contrary to the existing disadvantage of wide variation within a batch and poorer average properties compared to the pellet plant, this invention attempts to arrive at a solution incorporating specific arrangement of pellets inside the muffle furnace.

Cold crushing strength (CCS) is one of the most important pellet property which indicates its cold strength. CCS is measured as per ISO 4700: 2007 where CCS is measured for 60 pellets and average values are reported Grade of pellet product is determined based on CCS values. Pellet product should have CCS >250 kg/pellet for use in large blast furnaces. Standard deviation is also a critical quality parameter which indicates deviation and spread of properties, it should be minimized for a good quality pellet product.

The proposed solution is achieved after a series of carefully designed experiments directed towards breaking down the problem into smallest component to understand the root cause and experiments with various simple &easy to implement solutions.
In each of these experiments, green pellets were taken out from regular pellet plant operation. These samples were treated in lab scale muffle furnace and these results were compared with the results of the plant scale output. These results are compared for the average and standard deviation. Objective of this series of experiments was to arrive at the arrangement with difference of average & standard deviation is minimum between lab scale trial and corresponding plant scale (industrial scale) results.

Experiment 1: This experiment was conducted to establish baseline data of the gap between lab & industrial scale data using two different heat treatment cycles A & B as follows in muffle furnace:
Pellet heating cycles:
Time in min Industry Muffle Cycle A Muffle Cycle B
7 250 250 310
12 350 350 310
16 950 950 1000
20 1330 950 1000
26 1330 1330 1330
29 1250 1330 1330
38 700 1330 1330
41 200 1330
46 1330
106 500

Accompanying Figure 1 illustrates graphically the details of heat cycle A & B used for experiments (Furnace end cooling for both muffle cycle).

Observations: In both the trials, lab scale data is having much lower average CCS compared to industrial data as shown in Figure 2. A cylindrical basket as shown in Figure 2 was used for pellet loading in furnace.
Subsequent experiments are intended to minimize this gap.

Experiment 2: In this experiment, heat treatment cycle ‘B’ was used and procedure was same as experiment 1. Samples were analyzed in a novel way to identify the root cause of low CCS and high standard deviation. Entire basket samples was divided into 9 zones: 3 vertical zones x 3 radial zones as per Figure 3. Sampling was done from each zone and results are compared.

Observations: The novel approach of experiment and data analysis clearly establishes the root cause of the problem. Data clearly indicates that the pellets placed on the inner side of the basket are having inferior properties indicating that poor heat transfer. Because of this, the average CCS is significantly lower and standard deviation is higher in lab scale studies using muffle furnace. Further, it is observed that Edge samples from all the layers are having better CCS compared to inner zone samples

Experiment 3: Based on the findings from experiment 2, and with cycle ‘B’ experiment was designed making ID of the basket as dummy by using a 1 inch diameter stainless steel pipe and data was compared using heat treatment cycle B.
Observations: Use of 1 inch pipe as blanking has avoided very poor quality of pellets with insufficient heat input. These pellets were mainly responsible for lower average & higher standard deviation in overall sample.Figure 4shows arrangement & data for experiment 3.

Experiment 4: Based on the findings from experiment 3, and with cycle ‘B’ experiment was designed making ID of the basket as dummy by using a 2 inch diameter stainless steel pipe and data was compared using heat treatment cycle B.
Observations: Slight improvement over experiment 3 on average & standard deviation at specific locations. Overall, no significant advantage over experiment 3. Figure 5shows arrangement & data for experiment 4.

Experiment 5: Combining learning from all the above experiments, it was concluded that if a pellet is surrounded by all sides from pellets, heat transfer will get affected and it may lead to inferior pellet quality. A new experiment was designed where core/ centre part of the basket was kept completely blank and pellets were charged only in one layer to facilitate efficient heat transfer. Heat treatment cycle B was used.
Observations: Standard deviation in single layer charged pellet in muffle furnace is closed to industrial data but average CCS is significantly higher. Figure 6shows arrangement & data for experiment 5.
Experiment 6: Based on results of Experiment 5 where strength after heating of pellet is much more than industrial data. This trial populated pellet in basket with more controlled layered quantity and with muffle cycle ‘B’. For this experiment, a new basket was fabricated with core less/empty design. Average of 6 experiments with results vary minimum 3 % deviation from industrial data. Porosity of lab scale samples matches with industrial data. Figure 7 shows arrangement & data for experiment 6.

To summarize the findings from experiments, a single layer charging of pellets and avoiding pellets in the core of the basket, uniform heating of pellets can be ensured leading to average & standard deviation very close of the industrial scale. This arrangement of lab experiments using muffle furnace can be extremely useful in doing blend optimization studies.

Further to match up industrial quality strength, controllably populated quantity of pellet arrangement was done, continuing core empty via new basket design as shown in Figure 8. Figure 9 shows the details of dimensional requirement of the basket configuration of Figure 8.

Following Table shows average CCS values with 3, 4 & 5 layers and with centre blocking & continuous (without centre blocking arrangement):

Table: Average CCS values for various arrangements

Layer Centre block Without centre block
3 295 232
4 295 210
5 218 195

It was found during the trials, results(CCS value) are acceptable upto 1-4 layers that too with centre blocking. With either increasing layer or with continuous pellet stacking in basket, results deteriorates.

During the experimental trials, basket with 220 mm dia and 80 mm dia core blank were used. In the initial trials, around 25 mm core blanking was used and results were not good.

Looking at the results and photo images of the baskets, it can be understood that the pellets in the exposed layers (outer & top layers) receives the heat through radiation. If basket is completely filled (without core blanking), inside pellets receives less heat through radiation because of no exposure.

When 80 mm dia is blanked in 220 dia basket, pellets are placed in a ring shaped formation with around 70 mm depth, which places 5-7 pellets (pellet mean size 10-12 mm) along the diameter which receives radiation heat from external surface of the basket and through the blanked core which is exposed.

Elevation of basket from floor level was provided with the objective of providing sufficient gap from bottom so that if air flow from bottom will facilitate convection heat transfer. Another objective of the design is to provide space, in case trial is to be done with hot air inflow from the bottom, either for convection heat transfer or to maintain oxygen potential inside the chamber.

Finally, lab scale set up was arrived in which pellet heat hardening takes place with heat cycle B and pellet quality obtained matching near to industrial level.
Through trial and error inventors have kept central area vacant just to match up pellet strength profile similar to that of plant values. Following are some general understanding while designing the basket:

• Basket is to be made using rods made up of high temperature material like INCONEL.
• Instead of using a closed container (e.g. pipe of similar diameter) a cage like construction (similar to one shown in drawing) is to be preferred for effective heat transfer.
• For basket of 220 mm OD, approx. 80 mm of centre blocking is to be used.
• Difference in outer and inner radii of cage should be below 75 mm.

Configuration/arrangement of pellets inside a muffle furnace is the inventive step. This arrangement is critical because the above series of experiments clearly highlight the importance of the pellet arrangement inside the muffle furnace and its impact on product quality parameters.

Highlights of inventive finding include single layer charging arrangement in contrast to established practice of multiple layer charging. Additionally, core/center of the basket should be kept blank as heat transfer is not adequate due to the surrounding pellets.

Thus while designing the basket/container configuration, following parameters are given due importance:

Central blocking is most important since it has reduced variance in quality of pellet. Extent of blocking set is done by tests with different setting of central block. Centre core blocking will not only block the zone of poor heat transfer but also improve radiation heat transfer by exposing the centre thus improve consistency in properties.

Optimizing pellet layers is next in importance list. A full packed basket will not be able to provide adequate heat transfer to all the pellets in a finite cycle time, when heat transfer mode is primarily radiation, pellets in the central core will receive very less heat through radiation& convection and mostly through conduction only. Using single or 3-4 layer charging ensures exposure of each pellet to the radiation and gives more uniform and consistent properties.

Elevation from bottom is next important, which is primarily designed to provide space in the bottom to increase possibility of convective heat transfer if hot air is supplied from bottom or

The present invention thus establishes the Pellet charging arrangement for achieving best possible pellet properties in a lab scale muffle furnace under radiation heat transfer conditions.