GRATE COOLER

DEAR ENGINEERS....

WE HAVE A PROLEM IN OUR COOLER (CLAUDIUS PETERS). WE ARE FREQUENTLY FACING THAT PROBLEM, THE PROBLEM IS , AT THE KILN DISCHARGE END OF GRATE COOLER MORE RED HOT CLINKER IS LEAKING TO THE HOPPER. DURIING SHUT DOWN WE ARE CHECKING THE CONDITION OF GRATE PLATES, AND IN THESE AREAS WE CAN SEE MORE GRATE PLATES AND SIDE SEALING PLATES ARE BURNING. THIS PROBLEM IS FREQUENTLY HAPPENING AND UPTO NOW WE COULDNT DETECT THE ACTUAL PROBLEM. THE CLINKER LEAKAGE IS SAME LIKE WATER FALL. DUE TO THIS WE HAVE TO STOP OUR KILN ONCE IN A MONTH. 

SO IF YOU HAVE AN IDEA ABOUT THIS PROBLEM PLEASE LET ME KNOW..

THANKING YOU

AFSAL KANNIYAN

DOHA- QATAR 

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Re: GRATE COOLER

Hello Afsal,

What you are describing is a common problem in clinker coolers and is generally called a "Red River".

I found this passage in a book called "Clinker Coolers" by Hans E. Steuch (Chapter 3.8, p494-495), which may be helpful to you;-

"The fact that especially large diameter type kilns tend to discharge fine clinker on the kiln’s load side and coarse clinker on the opposite side can make it difficult to get good clinker distribution. Due to the high air resistance of a fine clinker bed, “red rivers” often are inevitable. Studies show that “red rivers” can cause a variation in air distribution of 1:6 between the fine and coarse clinker side and can even cause clogging of the bed. This is why grate plates sometimes become red hot in places. “Red rivers” also cause an increase in clinker discharge temperature. Measures for improving the clinker distribution should start at the cooler inlet. Where “snowmen” cause poor clinker distribution, the cooler back and sidewalls can be kept clean with the help of compressed air cannons. Some improvements are possible by slowing down the movement of the fine clinker bed and diverting more fine clinker to the coarse cooler side, thus increasing the overall clinker bed resistance which pushes more air through the fine clinker bed. This diversion can be done by using wedge-type grates with 125-mm or 200-mm high faces. The grates are arranged in a checkerboard pattern as shown in Figure 3.8.17. An often successful way to improve the situation is to narrow the cooler grate area on the fine clinker side. By doing so, the clinker bed becomes narrower and often eliminates a severe segregation of fine and coarse clinker. It is recommended that the cooler inlet grate width not exceed 2.5 m for kiln capacities up to 2,500 metric tons per day of clinker. Figure 3.8.17 shows that some air holes in corner grates are blanked off. Corner areas often have a low clinker load which results in heavy air channeling and bypassing the clinker load. Blanked off air holes ensure that cooling air is diverted into the clinker load. When severe “red river” conditions exist and loss of cooler grates are experienced, “Ondufin” grates can be applied. The grates have cooling fins on the underside which increase the cooling surface. The grates stay cooler and last longer. In addition, if a grate is burned through, the fins prevent large clinker spillages for a considerable time. When “red river” conditions in a pre-1990’s style cooler are extremely severe, compartments can be divided into two sections. Two cooling fans, one on each cooler side, assure that both grate areas, the fine and the coarse side, receive the proper amount of air. Or, the design can be upgraded to one with airbeams or mechanical air flow regulators for small groups of grates. Some suppliers, borrowing from the airbeam technology, offer a grate plate design for pre-1990’s coolers where the air has to travel through a labyrinth in the grate – first up, then down – before exiting into the clinker bed. This provides an effective clinker seal that reduces the amount of clinker falling through the grate plates to the undergrate compartment. Increasing the clinker bed thickness generally improves the overall clinker distribution and heat transfer. Good results have been experienced with clinker beds up to 1 meter deep. In addition, lower grate speed has had a positive effect upon grate wear rates. High undergrate pressures and airflows adversely affect the conveying action of a reciprocating grate. High air pressures can reduce the friction between the clinker and the grate, which in turn can speed up the movement of the clinker toward the cooler discharge. The air, which expands as it rises in the bed, causes the clinker at the surface to be fluidized. The result might be that clinker flows down the slope if the grate area is inclined or that the clinker can only be moved with extremely high reciprocating speed on horizontal type coolers. To prevent clinker from flowing forward, the single grate surface should be at least horizontal. Experience has shown that the best results can be attained with a maximum of 4.7 to 5.5 kPa undergrate pressures in horizontal and 3 degree inclined coolers.

AIR DISTRIBUTION VERSUS OVERALL COOLER EFFICIENCY

Optimized air distribution also improves the overall thermal cooler efficiency and prevents damage to grates due to overheating. To achieve this goal, predefined amounts of cooling air need to be established for every cooler compartment. Coolers with airbeams or mechanical air flow regulators can refine the air distribution even more to sections of grate plates or to individual plates. The optimization of airflow is especially important for the heat recuperating zone. Too high amounts of air do not give maximum secondary air temperature. Too low amounts of air elevate the clinker discharge temperature. Too high amounts of air also promote fluidization of the clinker. As the finer clinker particles are likely to be entrained in the locally intensified air flow, high amounts of dust cycles between kiln and cooler are likely. Dust particles might also be picked up from highly fluidized areas and concentrate in others, thereby intensifying any “red rivers.” Extremely high airflows also promote heavy air channeling, giving a poor heat exchange for a grate cooler of 1970’s to mid-1990’s vintage. It is recommended that maximum airflow not exceed approximately 140 normal cubic meters per minute per square meter of cooler grate area. Figure 3.8.18 shows a chart of optimized cooling air distribution for a typical eight-compartment reciprocating grate cooler. The first five compartments (including quench compartment) supply secondary air and tertiary air if applicable; compartments #5 through #8 cool the clinker to a final temperature of approximately 100°C. Lowering the clinker discharge temperature further with more air increases the electrical power consumption considerably. Depending upon the total amount of cooling air used, the power consumption for the cooling fans can run between 3 and 8 kWh/ton of clinker, plus up to 4 kilowatt-hours for venting.coolers, and 2.0 to 2.5 kPa in old 10 degree inclined coolers."

Regards,

Ted.

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Re: GRATE COOLER

Dear Mr.Kanniyan,

The followings are may be the reason for your problem:

1) In your plant are you encountering frequent snow man problem? If yes, Try to adjust the Kiln feed chemical composition, so that you can avoid snow man formation.

2) Please check and confirm the cooler fans air flow displayed in CCR are matching with actual readigs. Secondary air temperature is the best indicator.

3) Is there any alignment problem in the first grate?  If yes, repair it immediately.

4) Analyse the grate plates quality. Are they matcing with the recommendations of OEM?

Try to purchase from other supplier.

Regards,

G.S.M.Subramanian

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GRATE COOLER

Hi Afsal,

This is not a surpirse to hear material spillage in the 2nd generation grate coolers.When the grate plates are installed/ commissioned the minimum gap between plates are measured and the correction is done accordingly. As days move the gap between the plates and side seals starts to increase and after some time they open up so badly to allow red hot material spillage into the bottom hoppers (loss in thermal energy when the red hot clinker is not shredding the heat in the recuperation region). 

Now in our modern 4th generation clinker coolers from Fons Technology International, we are offering moving lanes of grate plates along the length. These coolers come in modular type so the same module with with different cooler sizes shall support 300 TPD - 13000 TPD with less downtime for upgrade, providing 75 -80% recuperation efficiency. Hydraulic drive increases the availability and also the lane technology allows mixing of fine and coarse clinker by varying the stroke length of the individual lanes across the width of the coolers.

Apart from this Iso Kinetic Inlet ( static inlet) is offered to avoid snowman and minimise compressed air consumption in the inlet. With the snowman free inlet the secondary and tertiary air temperatures are acheived to the best level.

If you need mor information, please contact us jayaram@fons.dk or refer www.fonstechnology.com/

Regards,

Ram

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