Understanding the Types of Burners in Pyro Processing

This article seeks to help production managers and kiln engineers to choose the right type of burner that is best suited to their present and future needs. It is to help the users of these burners to ask the OEMs relevant questions; it also looks into some of the characteristics of burners that are often overlooked.

The average cement producer would prefer an average burner that has a great performance to a ‘best’ burner with a poor performance.  And as a production manager, you should be able to tell the different types of burners available.

Types Of Burners

Some of the reasons why a new burner may be necessary are:

- excessive wear

- to increase production

- to reduce NOx emission, and

- when there are changes to the fuel mix. 

The types of burners in this article have been classified into three categories based on the way the primary air streams distributed and adjusted.

The major difference in these three groups has to do with where and how the axial part of the primary air is injected relative to the fuel, the dial swirl and the secondary air.

Group 1

Here the primary air is split at the burner inlet into three channels- swirl, radial, and axial channels. The volume of air entering each channel is regulated by valves, VDFs, fan dampers and at times by use of multi blowers or fans.

The critical parameters in this first group are the number of primary air jets and their quality. This refers to the ratio between the diameter of the nozzle and the length as well as the number of radial and axial primary air and their locations within the burner.

Group 2

These are burners with a blend of the radial and axial primary air streams situated at the tip of the burners. The number of axial and radial primary air stream and their intensity can be adjusted by sliding the channels at the burner floor. This means there is only one exit for the primary air. Conversely, there could be a single primary air entrance to the burner with two different exits after an adjustable opening within the burner.

Group 3

This group is defined by burners with adjustable radial/axial primary air jets in a mono channel; it may or may not have a swirl component. They usually come with both fixed and adjustable versions. Other minor differences include the location of the primary air jets relative to the coal channel and the presence/absence of extra radial channel.

These categories are a broad reflection of the evolution of burners from coal/petcoke firing to the low, low-low and ultra-low NOx types, to high momentum designs for alternative fuel firing, then all-purpose designs. It should be noted that these categories are not absolute as each group borrows from other groups.

The following parameters are further used to compare each burner design:

- Primary air flow and exit velocity.

- The number of primary air, adjustability and the angles of the primary air outlets.

- Coal injection angle.

- Relative positions of the air and fuel pipes/channels

- The cooling/recirculation/central parts of the primary air burner.

- These could range from none to simple perforated plates to meshes.

When classifying and evaluating the quality of a burner, accessories and peripherals such as a flame scanner, monitoring instruments, igniter, emergency cooling air fans, safety controls, etc. have to be put into consideration. Also, the positions of all the necessary connections, the weight of the burners as well as the physical limitation of the burner floor are equally important factors to take note.

If the blaster/air tank is placed at the rear of the burner, such design is often problematic. If the distance between the exhaust slot and the burner tip is too far, the blast will likely be too weak, and if it is too close, it would only partially remove the rhino horn.

Evolution of Modern burners

New burner designs and concepts originate from a blend of changing needs in the cement industry and sheer marketing skills of the OEMs that aim to distinguish themselves from the rest.

Some of the trends in burners evolution include: ultra low-NOx burners that significantly reduced the amount of NOx emitted,  momentum which refers to the sum-total of all the primary air flow multiplied by the absolute ejection velocities as well as the trend towards a 100% solid alternative fuel.

In conclusion, with the increase in environmental, financial, and quality constraints, the demand for a ‘perfect’ burner designs well as kiln/plant conditions will also increase. Makers of burners with moving parts may assume that one burner can fit into all cases while those with fixed parts will be concerned about the specifics of each application.

Ravi Kumar is a mechanical engineer with over a decade of work experience in the manufacturing industry. He is a key member of the product architecture team at Chanderpur Group. He is always keen to study and try out new technologies.