Claims:We Claim:

1. A pellet car assembly for induration systems comprising:

plurality of rows of grate bars;
each row of said grate bars having plurality of centre grate bars and a pair of end grate bars at the end regions thereof ;
said pellet car having side walls/end castings at the ends in operative contact to the respective end grate bars;
lock pin extending from the side wall/end casting on top of said end grate bar at the respective sides;

wherein each said end grate bar and the respective centre grate bars have a substantially flat top for pellet support and downwardly extending legs and each said canter grate bar provided with a side projection for selective spacing of the canter grate bars for passage for hot gases to flow through;
each said end grate bar adapted for tilt free operation during use comprising cooperative tilt arresting means in working interaction with its adjacent side wall/end casting and/or the adjacent centre grade bar.

2. A pellet car assembly for induration systems as claimed in claim 1 wherein said end grate bar adaptation for tilt free operation comprises bossing projections at the side facing the said side wall/end casting to stabilize the end grade bar with respect to the stationary side walls/end castings .

3. A pellet car assembly for induration systems as claimed in anyone of claims 1 or 2 wherein said end grate bar adaptation for tilt free operation comprises bossing/projections in the legs of the end grate bar facing the adjacent legs of the canter grate bars for blocking any tilting movement between the end grate bar and its adjacent canter grate bar.

4. A pellet car assembly for induration systems as claimed in anyone of claims 1 to 3 wherein said end grate bar adaptation for tilt free operation comprises matching the length of the legs of the end grade bras with the leg length of the adjacent centre grade bars enabling self locking for tilt free operation.

5. A pellet car assembly for induration systems as claimed in anyone of claims 1 to 4 wherein said end grate bar construction features include:

Top pellet carrying surface (pellet car as assembly) width in the range of 4000mm to 4000mm and length in the range of 1500mm to 1500mm;
Leg portions having length of 62.5mm to 100mm;
Side projections near the top facing the end of the centre grate bars of dimensions 37mm to 64.5mm & length from 0mm to 30mm;
Projected bossing in the leg end portions of dimensions 32.5mm to 41.5mm;

6. End grate bar of pellet car assembly for induration systems comprising:
a substantially flat top for pellet support and downwardly extending legs having cooperative tilt arresting means adapted for tilt free operation during use in working interaction with its adjacent side wall/end casting and/or the adjacent centre grade bar.

7. End grate bar as claimed in claim 6 comprises bossing projections at the side facing the said side wall/end casting to stabilize the end grade bar with respect to the stationary side walls/end castings .

8. End grate bar as claimed in anyone of claims 6 or 7 comprises bossing/projections in the legs of the end grate bar facing the adjacent legs of the canter grate bars for blocking any tilting movement between the end grate bar and its adjacent canter grate bar.

9 . End grate bar as claimed in anyone of claims 5 to 7 comprises matching the length of the legs of the end grade bras with the leg length as per adjacent canter grade bars enabling self locking for tilt free operation.

10. End grate bar as claimed in anyone of claims 5 to 9 with construction features including :

Top pellet carrying surface (pellet car as assembly) width in the range of 4000mm to 4000mm and length in the range of 1500mm to 1500mm;
Leg portions having length of 62.5mm to 100mm;
Side projections near the top facing the end of the centre grate bars of dimensions 37mm to 64.5mm & length from 0mm to 30mm;
Projected bossing in the leg end portions of dimensions 32.5mm to 41.5mm.

Dated this the 21st day of March, 2018
Anan Sen
Of Anjan Sen & Associates
(Applicants Agent)
IN/PA-199
, Description:FIELD OF THE INVENTION
The present invention relates to pellet car (pallet) assembly for induration systems incorporating modified end grate bars to arrest tilt during operation. More particularly, the present invention is directed to provide pellet car assembly for induration systems wherein each said end grate bar adapted for tilt free operation during use comprising cooperative tilt arresting means comprising projections on side and leg portions configured for working interaction with its adjacent side wall/end casting and/or the adjacent centre grade bar. The above modification helped in avoiding problems in existing pellet plant associated with reduced hearth layer (<80mm) & side layer, this intern lead to exposure of rest of the grate bars to very high temperature, resulting in irreparable damages, in addition to generation of unfired pellets and consequently improving pellet plant productivity and efficiency at reduced production cost thus favouring advantageous application in steel plant.

BACKGROUND OF THE INVENTION

It is well known that the green iron ore pellets are indurated in pellet plant for subsequent use in melting furnace. There are 4 rows of grate bar in one pellet car with each row having 90 Nos. of centre grate bars and 2 Nos. of end grate bars. End grate bars are locked in position by the locking pins. In existing practice, it was observed that the pellet car end grate bars of indurating machine of pellet plant were getting tilted from its position.

Problem in the system is due to improper locking of end grate bar resulting in its tilting, which in turn will provide access to the centre grate bars to change its orientation, creating uneven gaps between grate bars. Such a phenomenon has detrimental effect on pellet (product) quality as areas of excess gaps between grate bars will become a gateway of hot indurating gases to pass through (least resistance path), resulting in loss of heat, production of partially fired pellets, which has huge financial implications in pellet downstream operation.

According to the existing design bottom portion of the end grate bar is having 62.5mm total leg length, as compared to that of centre grate bar is 100mm. As a result, the end grate bar, which has shorter leg length and no supporting bosses at the sides, will have improper locking and will result in tilting during pellet car reversal at feed station or discharge station of indurating furnace and while moving inside the furnace also.

In existing design, each centre grate bar is provided with bossing (extended projection) of 3.0 mm for creating passage for the hot gases to flow through, while 4.0 mm Bossing is provided only on top side end grate bar in the original design. This leaves behind a free gap of 4.0 + 3.0 mm = 7 mm, which is creating gap between end grate bar and centre bar at the bottom and above stated problems are identified as root cause for poor quality and productivity of pellet and damage of equipments due to tilting of end grate bar causing excess gap.

All the straight grate indurating pellet plants operating worldwide have this problem of tilting of end grate bar in different magnitude. Due to the continuous expansion and contraction of grate bars during heating and cooling cycles inside the indurating furnace, gap of more than 15mm will be formed between end grate bar and adjacent centre grate bar. Normally gap of 5 to 8mm is needed for the hot gases between grate bars for the hot gases to pass through the iron ore green pellets to be heat treated. Tilting of end grate bars due to continuous expansion and cooling is resulting in excess gas formation which will result in loss of hot gases leading to poor quality of product pellets in that zone.

Due to tilted end bars & centre grate bars, grate bar rapping device was not operational; (Pellet car grate bar rapping device is a system for light hammering of centre grate bars to get rid of broken pellets trapped between grate bar gaps to improve bed permeability. It is essential to clear this gap as; otherwise, hot gas passage will be blocked by broken pellets trapped between grate bars). To operate the rapping device of the grate bar, end bars & grate bars shall be in perfect position, which otherwise will result in fall of centre grate bars, which is a more serious problem.

There has been thus a need in the pellet plant operation to arrest the tilt of end grate bar to avoid excess gap with adjacent centre bar and consequential loss of heat or unfired pellet for efficient operation of pellet plant.

OBJECTS OF THE INVENTION

The basic object of the present invention is directed to provide pellet car(pallet) assembly for induration systems incorporating selective modified end grate bar configuration to arrest tilt during operation in working interaction with its adjacent side wall/end casting and/or the adjacent centre grade bar .

A further object of this invention is to provide an end grate bar configuration in pellet car(pallet) assembly for induration systems which would avoid tilting due to movement of grate bars, which in turn would arrest widening of gap between end grate bar and adjacent centre grate bar due to continuous expansion and contraction of grate bars during heating and cooling cycles inside the indurating furnace.

A still further object of the present invention is directed to provide a pellet car(pallet) assembly for induration systems which would prevent escape of hot gases through unwanted gap in between end grate bar and adjacent centre grate bar causing poor quality of indured pellet product or partially fired pellets.

A still further object of the present invention is directed to provide a pellet car(pallet) assembly for induration systems which would avoid red hot pellet discharge from indurating machine which is prone to fire hazards in downstream conveyor.

A still further object of the present invention is directed to provide a pellet car(pallet) assembly for induration systems which would avoid spillage of fired pellets through increased gaps causing reduced hearth layer and side layer, which intern lead to exposure of rest of the grate bars to very high temperature, resulting in irreparable damages.

A still further object of the present invention is directed to provide a pellet car(pallet) assembly for induration systems which would ensure longer pellet plant operation free of maintenance, reduce heat loss, improved pellet product quality and enhanced plant productivity.

SUMMARY OF THE INVENTION

The basic aspect of the present invention is directed to a pellet car assembly for induration systems comprising:

plurality of rows of grate bars ;

each row of said grate bars having plurality of centre grate bars and a pair of end grate bars at the end regions thereof ;

said pellet car having side walls/end castings at the ends in operative contact to the respective end grate bars;

lock pin extending from the side wall/end casting on top of said end grate bar at the respective sides;

wherein each said end grate bar and the respective centre grate bars have a substantially flat top for pellet support and downwardly extending legs and each said canter grate bar provided with a side projection for selective spacing of the canter grate bars for passage for hot gases to flow through;

each said end grate bar adapted for tilt free operation during use comprising cooperative tilt arresting means in working interaction with its adjacent side wall/end casting and/or the adjacent centre grade bar.

A further aspect of the present invention is directed to said pellet car assembly for induration systems wherein said end grate bar adaptation for tilt free operation comprises bossing projections at the side facing the said side wall/end casting to stabilize the end grade bar with respect to the stationary side walls/end castings .

A still further aspect of the present invention is directed to said pellet car assembly for induration systems wherein said end grate bar adaptation for tilt free operation comprises bossing/projections in the legs of the end grate bar facing the adjacent legs of the centre grate bars for blocking any tilting movement between the end grate bar and its adjacent centre grate bar.

Another aspect of the present invention is directed to said pellet car assembly for induration systems wherein said end grate bar adaptation for tilt free operation comprises matching the length of the legs of the end grade bras with the leg length of the adjacent centre grade bars enabling self locking for tilt free operation.

Yet another aspect of the present invention is directed to said pellet car assembly for induration systems wherein said end grate bar construction features include :
Top pellet carrying surface (pellet car as assembly) width in the range of 4000mm to 4000mm and length in the range of 1500mm to 1500mm;
Leg portions having length of 62.5mm to 100mm;
Side projections near the top facing the end of the centre grate bars of dimensions 37mm to 64.5mm & length from 0mm to 30mm;
Projected bossing in the leg end portions of dimensions 32.5mm to 41.5mm.

A further aspect of the present invention is directed to end grate bar of pellet car assembly for induration systems comprising:
a substantially flat top for pellet support and downwardly extending legs having cooperative tilt arresting means adapted for tilt free operation during use in working interaction with its adjacent side wall/end casting and/or the adjacent centre grade bar.

A still further aspect of the present invention is directed to said end grate bar comprising bossing projections at the side facing the said side wall/end casting to stabilize the end grade bar with respect to the stationary side walls/end castings .

A still further aspect of the present invention is directed to said end grate bar comprises bossing/projections in the legs of the end grate bar facing the adjacent legs of the canter grate bars for blocking any tilting movement between the end grate bar and its adjacent canter grate bar.

Another aspect of the present invention is directed to said end grate bar comprises matching the length of the legs of the end grade bras with the leg length as per adjacent centre grade bars enabling self locking for tilt free operation.

Yet another aspect of the present invention is directed to said end grate bar with construction features including :

Top pellet carrying surface (pellet car as assembly) width in the range of 4000mm to 4000mm and length in the range of 1500mm to 1500mm;
Leg portions having length of 62.5mm to 100mm;
Side projections near the top facing the end of the centre grate bars of dimensions 37mm to 64.5mm & length from 0mm to 30mm;
Projected bossing in the leg end portions of dimensions 32.5mm to 41.5mm;

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

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Figure 1: Illustrate the photographic image showing shape configuration of existing end grate bar and centre grate bar.
Figure 2: shows a 3-D view of the conventional pellet car assembly of indurating machine wherein the positions of its various components like end grate bar, centre grate bar, lock pin, side wall, end casting etc have been shown.
Figure 3: shows the location of increased gap created in existing operation between the end grate bar and the centre grate bar of a conventional pellet car assembly.
Figure 4:shows the bend locking pin and increased gap of end grate bar near side wall in pellet car, as front view and top view, in existing operation of pellet plant.
Figure 5: shows the photographic image of the end grate bar with modified configuration to prevent tilting.
Figure 6: shows the line diagram of different views of modified end grate bar illustrating the increased leg length and boss thickness at specified location to prevent tilting.
Figure 7: shows graphically the improvement in SIP dust generation before and after modification.
Figure 8: shows graphically the improvement in cumulative % Dust generation before & after modification.
Figure 9:shows boxplot of average SIP dust generation before and after modification.
Figure 10: shows the boxplot of improvement in CCS 0-100% of pellets produced before and after modification.
Figure 11: shows the boxplot of improvement in CCS 100-150% of pellets produced before and after modification.

DETAILED DESCRIPTION OF THE INVENTION WITH REFERENCE TO ACCOMPANYING DRAWINGS

The present invention is directed to provide a pellet car(pallet) assembly for induration systems incorporating selective modified end grate bar configuration to arrest tilt during operation in working interaction with its adjacent side wall/end casting and/or the adjacent centre grade bar. The modified end grate bar configuration in pellet car(pallet) assembly for induration systems which would avoid tilting due to movement of grate bars, which in turn would arrest widening of gap between end grate bar and adjacent centre grate bar due to continuous expansion and contraction of grate bars during heating and cooling cycles inside the indurating furnace.

According to the existing design bottom portion of the end grate bar is having 62.5mm total leg length, as compared to that of centre grate bar is 100mm. As a result, the end grate bar, which has shorter leg length and no supporting bosses at the sides, will have improper locking and will resulting in tilting during pellet car reversal at feed station or discharge station of indurating furnace and while moving inside the furnace also. Accompanying Figure 1 illustrate the photographic image showing shape configuration of existing end grate bar and centre grate bar.

In existing design, each centre grate bar is provided with bossing (extended projection) of 3.5 mm for creating passage for the hot gases to flow through, while 4.5 mm Bossing is provided only on top side end grate bar in the original design. This leaves behind a free gap of 4.5 + 3.5 mm = 8 mm, which is creating gap between end grate bar and centre bar at the bottom and above stated problems are identified as root cause due to tilting of end grate bar causing excess gap. Accompanying Figure 2 shows a 3-D view of the conventional pellet car assembly of indurating machine wherein the positions of its various components like end grate bar, centre grate bar, lock pin, side wall, end casting etc have been shown.

Due to the continuous expansion and contraction of grate bars during heating and cooling cycles inside the indurating furnace, gap of more than 15mm will be formed between end grate bar and adjacent centre grate bar. Normally gap of 5 to 7mm is needed for the hot gases between grate bars for the hot gases to pass through the iron ore green pellets to be heat treated. Tilting of end grate bars due to continuous expansion and cooling is resulting in excess gas formation which will result in loss of hot gases leading to poor quality of product pellets in that zone. Accompanying Figure 3 and Figure 4 shows the location of increased gap created in existing operation between the end grate bar and the centre grate bar and bending of locking plate in a conventional pellet car assembly.

Problems were thus faced in existing pellet plant operation including Often we were facing wind box jamming, lock pin bending, damage to hearth layer gate, damage to side layer chutes, even overheating of the grate bars, reduced hearth layer <80mm, more unfired pellets, more spillage from the gap between end bar and grate bar. Even grate bar rapping device was also not operational due to the same issue.

The present invention thus attempt to develop an end grate bar configuration to arrest the above stated tilting problem through successive trials as follows:
To arrive at the final configuration following stage by stage modification were under taken through successive trials:

1st trial: Both the bottom portion length of the end grate bar is increased by 37.5mm. The 37.5mm length is considered for the trial by keeping in the mind that, the length of end grate bar and centre grate bar to match, so that tilting movement of the end grate bar is restricted due to locking of end grate bar leg. For trial purpose, welding is done in-house by using high chrome grate bar material.

After increasing the length of bottom portion (as described above), problem of tilting of end grate bar reduced but not completely. With this first trial, condition of grate bars in pellet cars of indurating machine was at par with other straight grate pellet plants, with minor tilting problem still continuing. There was further scope for improvement.

2nd trial: In order to minimize the tilting tendency completely, a projection length of approximately 27.5mm is welded on side casting side at the centre of the end bar, which is. This projected part rests on the end casting beam & along with extended leg length as mentioned above, it provided resistance to tilting.

Results of 2nd trial was better than the previous but the tilting was still observed in the range of 9 to 10mm.

3rd trial: Improvements are observed after providing the single projection. To take advantage of side projection, centre projection provided in 2nd trial was removed and instead, two projections are made at either ends of end grate bar on side casting side. This ensured more stability of end grate bar.

4th trial: In order to totally arrest the movement of end grate bar at the leg portion, it was decided to provide an additional bossing of 9mm thickeness on either leg at centre grate bar side. This proposed bossing will lock the leg of the end grate bar with adjacent centre grate bar leg, thereby avoiding any further tilting tendency of end grate bar.

All the changes mentioned from trial 1 to trial 4 above are incorporated in modified drawing of end grate bar and instead of welding, same is being casted as integral part of end grate bar.

The final shape of end grate bars decided through above trials ultimately provided the following end characteristics of the modified end grate bar configuration of Pellet car of straight grate indurating machine:

1. 2 Nos. of Bossings (side projections) provided on the top portion of end grate bar on side casting side.
2. 2 Nos. of bossings (side projections) provided at bottom portion in the end grate bar leg on centre grate bar side.
3. Extended leg length of end grate bar to meet the requirements of self-locking to avoid tilting.

The above modified configuration of end grate bar obtained by of the present invention are illustrated in accompanying Figure 5 as image and Figure 6 as line diagram.

This is the first time in history of pellet plant operation that a low cost innovative solution is found out to prevent tilting problem of end grate bar of pellet car used for pellet induration.

As already indicated that excess gap created due to tilting of end grate bar in existing pellet plant operation causing unfired pellets and these unfired pellets get crushed easily during transferring from conveyor to conveyor and finally lead to high dust generation after reduction in the customer plant SIP (Sponge iron plant). Accompanying Figure 7 shows graphically improvement in the targeted SIP dust frequency Vs actual before and after modification. It is noted that in conventional pellet products obtained before the end grate bar modification, actual avg. Also the comparative advantage in cumulative dust generation in the SIP before and after modification is shown in accompanying Figure 8 and average dust information in Figure 9.

Accompanying Figure 10 & 11 shows the CCS of indured pellet product before and after modification. CCS-Cold crushing strength of the pellet (Unit of measurement-kg/ Pellet), it’s one of the most important quality parameter of the pellet. Which is measured as amount of weight (in kg/pellet) individual pellet can withstand before crushing. The good quality pellet will have a higher strength >250 kg/Pellet. As indicated in the graph <100kg/pellet is 4.1%(before) and 2.9%(after) modification, while CCS 100-150% is 5.3(before) and 4.0(after) modification.

It is thus possible by way of the present invention to provide a pellet car(pallet) assembly for induration systems incorporating selective modified end grate bar configuration to arrest tilt during operation in working interaction with its adjacent side wall/end casting and/or the adjacent centre grade bar. The modified end grate bar configuration in pellet car(pallet) assembly for induration systems would avoid tilting due to movement of grate bars, which in turn would arrest widening of gap between end grate bar and adjacent centre grate bar due to continuous expansion and contraction of grate bars during heating and cooling cycles inside the indurating furnace and adapted to achieve the following operational advantages in pellet plant:

a. No maintenance of end grate bars & locking pins is needed. Which gives a productive time of 36hrs in two to three months.
Appr. Profit due to increased availability: Rs. 10.8Crores/ annum.
b. No wind box jamming is observed due to the above issue.
c. Lock pin bending & damage is avoided, which is a saving of Rs. 7.5lakhs/yr.
d. One time savings by developing in-house solution to the problem (as compared to the solution
provided by OEM) is Rs.55 crore.
e. Problem of overheating of the grate bars is resolved.
f. No reduction in side layer height is observed due to tilting of end grate bar.
g. Rapping device is made operational, which is intangible benefit.
i. Savings by avoiding missing (falling) locking pins, end grate bars & centre grate bars, Rs. 6.64 Lakhs/ yr.
j. Reduced unfired pellets favouring reduced dust generation in SIP and increased CCS of indured pellets.