GRATE PLATE FOR COOLING AND CONVEYING CLINKER

Technical Field

The present invention relates to a grate plate for cooling the hot clinker with air injected through the opening of grate plate to the hot clinker for rapid cooling, meanwhile the clinker was conveyed to further processing stages. The volume of hot air occurred from heat transfer between hot clinker and cooling air can be reused as process heat in the system.

Background Art

A typical process of clinker production for the cement industry is a mixture of raw materials according to the desired proportions. Then, it has been heating in a rotary kiln to a sintering temperature of approximately 1,450 degrees Celsius, resulted in a chemical reaction takes place to form a new substance called clinker. Then the clinker is discharged from the rotary kiln in the form of a bulk materials bed, which is called clinker bed. This clinker bed of clinker moves onto a grate plate where it is rapidly cooled by heat transfer with cooling air. The cooling air is blown pass through the opening of grate plate allowing of cooling air pass through clinker bed. This rapid cooling of clinker results in higher cement strengths. On top of the heat exchange that we mentioned above, we require to transport clinker concurrently in forward direction by the grate plate, which was installed on support devices. These support devices allow forward-backward movement. Also this support device is aligned adjacent into rows. The rear part of each row is overlapped by the front part of the preceding row. When the grate plate movement forward- backward, hot clinker on the grate plate move forward as a way to transport clinker. While the grate plates move forward, it pushes the clinker down to front row and then move backward to get clinker from the rear rows. When this movement continue repeatedly, the clinker gradually move forward with temperature decreases respectively until the clinker come out from cooler outlet after the last row of the grate plate. The temperature of clinker at outlet reduces down to 80 - 120 degrees Celsius. It is then conveyed to stock to prepare for next cement processes. The cooling air, which got heat transfer from hot clinker in this process, will become a hot air, which can be reused in heating process in the system. It gives energy saving as it reduces fuel requirement. Thus, the production cost will be reduced.

Therefore, we can say that the efficiency of grate plate depends on how efficient of heat exchange with that grate plate. The cooling air that passes through the air opening of grate plate must be strong enough to penetrate from bottom to top surface of clinker bed. If the grate plate can allow more the cooling air to penetrate the clinker bed, heat exchange will be better, causing the increase of productivity as well as more hot air to be reused in the system. As a result, the inventor focus on designing the opening of grate plate, which create air with high velocity with Trumpet venturi opening design. This shape brings the highest velocity at the end of the air opening and directs the air flow in the same direction of clinker movement for helping move forward. This design allow increasing of heat exchange compared to the normal design that has air flow pass through the opening of grate plate in perpendicular direction. The previous invention has appeared for different grate plate design as follows.

E.P. Pat. No. 0,120,227 A1 discloses a grate plate with several circle opening in the same size and direction of air flow that pass through these opening is perpendicular direction with materials conveying direction. So the air will pass through the clinker vertically. These air openings are large. Hence, the air velocity will be low. Hence, it will not be able to penetrate through the clinker bed, which is formed with high density. As a result, it gives low clinker production and low volume of hot air from heat exchange. Note that this hot air will be reused as process heat in the system. So low volume will yield higher production cost.

U.S. Pat. No. 5,575,642 discloses a grate plate with several pockets which air opening at the lateral faces of the pockets. The hot clinker to be filled in these pockets and cooled by air pass through the opening on two side of the pockets which is different direction from clinker conveying direction. Hence, it will not support the transportation of clinker. Moreover, the air opening is still large opening. Hence, the cooling air from this opening will not be able to penetrate through the clinker bed which has formed densely above. As a result, the heat exchange cannot take place effectively.

U.S. Pat. No. 5,947,719 discloses a grate plate with the narrow air opening with the same width throughout the opening until the top surface of grate plate. It has inclined opening in the same direction as clinker conveying direction. But it does not have trumpet venturi opening, which enable high air velocity at the end of the air opening. As a result, the clinker could fall down and clog the air opening. After clogging, it creates problems such as inefficient heat exchange, corrosion of the plate that shorten the lifetime of grate plate. Moreover, this opening without high air velocity design, it will be difficult to penetrate the high clinker bed.

U.S. Pat. No. 9,677,816 B2 discloses a grate plate with air opening in cross section is right triangle with a fin-shaped bottom. It has been assign the angles that influence shape. It has large opening and does not consider the relative distance of opening parts to form the air opening. The shape of the opening does not allow the high air velocity area at the end of opening. Hence, our invention gives improve air velocity and better penetration of the air into the clinker bed.

U.S. Pat. No. 9,513,058 B2 discloses a grate plate with cooling air jets opening. At inlet or lower part of the air opening has width and gradually narrow until the outlet or upper part of the air opening. It is difference from this invention, which design of Trumpet venturi opening, which has wide lower part of the air opening and gradually narrow until the second part, which is the narrowest section and then gradually widen until the top of grate plate. The trumpet venturi opening has been proven to create the highest the air velocity at the end of the air opening. The higher air velocity leads to better heat exchange and the better penetrate high clinker bed.

The inventor foresees the above weakness that can be improved to achieve the better efficiency. This invention reflects the requirements of clinker manufacturing process both in terms of product quality and reducing the cost of clinker production. It gives longer lifetime of grate plate and yield higher volume of hot air to be used in the system. It also gives a good heat exchange through higher clinker bed depth, enabling higher production. Hence, we can increase the production without high investment such as expansion of machine or major modification of machine. As a result, the design of the grate plate should consider both shape and size of the air opening, which effects on the heat exchange and transportation of clinker.

Aims of the invention

The objective of this invention is to improve the efficiency of a grate plate to meet requirements of operation process as much as possible. The efficiency should consider both in terms of heat exchange (cooling hot clinker to reduce temperature by heat transfer between hot clinker and cool air more efficiently for obtaining the high volume of hot air that can be reuse as process heat in the system) and conveying of clinker. The clinker should be transported smoothly without material clogging at the air opening which is cause many problems, such as inefficient heat exchange as well as the corrosion of the grate plate resulted in shortening the lifetime.

This main design of this invention is the grate plate with an air opening with cross section of the trumpet venturi. It also has smooth surface, which means that no sharp corner causing turbulence air distribution. The lower part of the air opening is wide and gradually narrow toward the second part, which is the middle part of the air opening. This second part is the narrowest section with constant opening until it reaches last part, which is the upper part of the air opening. The last part will gradually widen toward the top of grate plate. This design gives a maximum air velocity at the end of the air opening or outlet end of the cooling air. The designed air opening with inclined trumpet shape also control air blowing toward the same direction with clinker conveying direction

This present invention optimizes efficiency of heat transfer between cool air and hot clinker. When the cooling air blow pass through the opening of grate plate with shape of trumpet venturi opening giving higher air velocity and will be better penetrate the thick clinker bed. It means the cool air can have better heat exchanged with thicker the clinker bed depth. Better heat exchange will in turn increase production capacity. Moreover, heat exchange will give higher volume of hot gas to be used in system. As a result, it reduces the fuel consumption in heating up hot air. With the maximum air velocity at the end of the air opening give benefit not having material clogging at the air opening. Moreover, with direction of air flow toward the same direction of clinker conveying direction, it will better help clinker forward movement for better clinker transportation.

Brief Description of drawing

Figure 1 is a perspective view of the grate plate position in cement production process.

Figure 2 is a perspective view to shows arrangement of grate plate within rows.

Figure 3 is a cross-sectional view of the grate plate to shows overlapped arrangement in each row.

Figure 4 is a cross-sectional view of the grate plate and conveying direction of materials.

Figure 5 is a detail cross-sectional view of Figure 4 to shows the details of trumpet venturi opening.

Figure 6 is a simulation of cooling air flow pass through the opening of grate plate varying XI distance to show its effect in air velocity area at opening.

Figure 7 is a simulation of cooling air flow pass through the opening of grate plate varying Xout distance to show its effect in air velocity area at opening.

Disclosure of Invention

In the present invention is a grate plate (1) that installed next to the rotary kiln (2) for clinker cooling, shown in Figure 1. The process starts from the hot clinker out of the rotary kiln (2) at approximately 1,450 degrees Celsius to the grate plate (1) for rapid cooling getting an air from cooling fan (3) blows through air opening of grate plate. The heat transfer will take place between very hot clinker and cooling air out of opening of grate plate.

Figure 2 and Figure 3 show method of the grate plate (1) installation, which located on top of grate support (4) with a drive to be able to move forward and backward. Each grate plate adjacent arranged in row and each row will be overlapped at least one row. Overlapped part of grate plate (5) is the part with no opening for the passage of cooling air. The grate plate moves forward to push the clinker to drop down to the front row of grate plate and then move backward. The clinker from the rear row will replace on such grate plate, which was pushed to its front row. This movement continue repeatedly and the clinker will gradually move forward toward the direction according to clinker conveying direction (8).

Figure 4 shows cooling air direction (6) that pass through trumpet venturi opening (7) with inclined control air direction toward forward movement the same as clinker conveying direction (8). The trumpet venturi opening (7) can be divided in 3 parts; lower part, middle part, and upper part. The lower part of the air opening (9) is wide and gradually narrow toward the second part, which is the middle part of the air opening (10). This middle part (10) is the narrowest section with constant opening until it reaches last part, which is the upper part of the air opening (11). This upper part (11) will gradually be widen toward to the top of grate plate.

Figure 5 shows the detail of the air opening including of lower part of the air opening (9), middle part of the air opening (10) and upper part of the air opening (11). It also shows the front surface of the air opening (12) and rear surface of the air opening (13), which have smooth surface, that is, no sharp comer along the surface. As shown in the figure, Xin is distance from midpoint end at the air inlet of lower part of the air opening (9) to beginning of the middle part of the air opening (10). XI is the distance of middle part (10) from beginning to the end of middle part (10) connecting with beginning of the upper part (11). Xout is a continued distance from XI to the midpoint end at air outlet of the upper part of the air opening (11).

Figure 6 shows simulation result of grate plate design with trumpet venturi opening (7) and how the distance of each air opening part affects air velocity at the area end of the air opening. This invention aims is to achieve the maximum air velocity at the end of trumpet venturi opening (7). Hence, simulation of air flow pass through trumpet venturi opening (7) has been modeled and it shows air velocity throughout the air opening with different parameters. As seen the legend in Figure 6, the different patterns are used to represent the range of air velocity; from minimum air velocity section(14) until maximum air velocity section (15). In the Figure 6, we compared 3 different XI distances in sub-picture (a), (b) and (c). The result showed that the sub-picture (b), gives the optimal XI distance because we can notice the patten of maximum air velocity section (15) at the outlet end of the air opening. The sub-picture (b) has the largest area of maximum air velocity section (15), in which we can call such area as “the maximum- velocity-area of the air opening (16)”. If we increase XI distance more as shown in sub-picture (c), the maximum- velocity-area (16) become smaller. Therefore, XI distance must not be too small or too large. Figure 7 shows simulation result of grate plate design with trumpet venturi opening (7) by comparing with various Xout distance. In this Figure 7, the sub-picture (d) shows the maximum- velocity-area of the air opening (16) while sub-picture (e) has no such area. These two sub-pictures demonstrate that Xout distance affect air velocity. If Xout distance is too short, it will result in decreasing air velocity at the end of the air opening.

The present invention uses XI and Xout in Trumpet venturi opening at optimal distance, which lead to the highest velocity at the end of the air opening. The higher velocity will enable cooling air to penetrate further in the clinker bed. As a result, the operation can keep the clinker bed thicker and hence make the heat exchange between cooling air and clinker better. The design also supports the clinker transport by direct the high velocity air in the clinker transport direction. So the cooling air help clinker transportation as well. Moreover, the high velocity air will prevent the clinker to fall into the opening and get the clogging. All of above points improves efficiency of a grate plate.

List of reference numbers

1. grate plate

2. rotary kiln

3. cooling fan

4. grate support

5. overlapped part of grate plate

6. cooling air direction

7. trumpet venturi opening

8. clinker conveying direction

9. lower part of the air opening

10. middle part of the air opening

11. upper part of the air opening

12. front surface of the air opening

13. rear surface of the air opening

14. minimum air velocity section

15. maximum air velocity section

16. maximum-velocity-area of the air opening