World Cement - July 2020

upgrade, the entire subgrate compartment of the

cooler and the sealing were optimised. The final

result brought greater advantages than just easier

maintenance.

One target was to update the cooler sealings.

The sealings make up the juncture between the

aeration floor units and conveying elements, the

latter being connected to the hydraulic system

in the subgrate compartment. They ensure that

no clinker falls under the grate at the interface

between the static aeration floor and the moving

tracks. While the original flat guide sealings

proved to be very effective in many plants, due

to a shift towards fuels with an increased sulfur

content, the clinker size decreased significantly

in some kiln lines. In these plants, increased

maintenance, especially for the spring system,

was required to keep the sealings spillage

free. The spring system is needed to keep the

horizontal sealing aligned and tight against the

structures above the grate, and to prevent clinker

from trickling under the grate into the aeration

chambers. It requires regular maintenance,

especially in plants with very fine clinker, to

ensure spillage-free operation.

A simplified sealing, as illustrated in Figure 2,

was designed to tackle this challenge. The new

sealing arrangement was tested successfully

under challenging operating conditions. It is a

vertical, continuous sealing, without springs,

made out of hardened steel to withstand the

friction resulting from the movement of the tracks.

It has fewer components, and it is faster and

easier to install.

Another significant issue related to maintenance

is accessibility. For this reason, the substructure

of the grate was completely redesigned

(Figure 3) to allow unhindered access to the

bearings and hydraulic cylinders located under

the grate for inspection and maintenance. The

distribution of forces was optimised, allowing the

weight of the support structures to be reduced.

The new substructure consists of bent metal

sheets instead of profiles, which has the added

benefit of allowing faster, easier manufacturing

without machining. The reduction in weight of

the grate substructure has a positive impact on

the overall cooler cost. The investment costs for

the new product design become more attractive,

especially for conversion projects, where the

cooler modules make up the majority of the

scope of supply.

Finally, the bearing design was also altered

to improve maintainability. The entire bearing

position is lighter and is fixed to the grate

substructure with only two bolts, which makes

installation quick and easy. High quality materials

are used to manufacture the bearing components

in order to increase wear and temperature

resistance.

This new design opens up the possibility

of recirculating hot gases under the grate

of the cooler. This technology has possible

applications, for instance, for simplified emission

control. Strict NO

emissions limits pose

difficulties for plants with high RDF utilisation

rates, especially if a highly variable mixture

is used, leading to continuously changing

combustion conditions. This causes significant

concentration fluctuations in both the

main gas stream and the bypass stream, which

usually reaches the stack without undergoing

reduction, making precise control of

the NO

concentration at the stack more

challenging. Recirculating the bypass stream

under the cooler grate reduces the complexity of

the emissions control task.

Conclusion

The clinker cooler is a key component of any

clinker production line, and its performance

weighs heavily on the final economic performance

of a cement plant. The improvement programme

for the polytrack has resulted in optimisations in

many areas and greater customer benefit.

About the author

Valentina Bordei has five years of experience in

the cement industry, where she worked first in the

development of emission reduction technologies

and is currently a part of the pyro-processing

equipment design and technical sales team. She

holds M.Sc. titles in Environmental Engineering

and Process Engineering and Energy Technology.

Figure 3. New grate structure.

Figure 4. Old grate structure.

World Cement

July 2020