Avalanches in Cement Kiln Exhaust Fan
Dynamis has been contacted by a cement producer client with a serious issue: the kiln exhaust fan suffered frequent shut-downs due to material accumulation into the upstream hot gas duct.
The plant has a 1000 mtpd (metric tons per day) cement kiln, with a cyclone preheating tower of 4 stages, given that the upper stage has two parallel cyclones. The gas exhaust system is made of one draft fan (J01), one gas cooling tower, one draft fan for the cooling tower (P01) and one electrostatic precipitator. Moreover, given that the hot gases still supply heat for the raw meal mills (mills R4 and R5) and to the petcoke mill, the exhaust system is under influence of the J03 and S02 fans, responsible for the supply of hot gases to the raw meal and pet coke mills, respectively. The figure below illustrates the system:
According to Dynamis' calculation, the accumulation of material was happening in the duct to the raw meal mills, as confirmed by inspections made by the plant personnel. At first glance, the client would prefer to have a bin installed at the botton of the hot gas circuit to retain the material, preventing it from reaching the fan.
Dynamis analyzed the system and the calculation showed that:
- Case both raw meal mills were operational, the hot gas velocity was proper to pneumatic conveying
- Case only one mill was operational, this velocity dropped down below minimum pneumatic conveying values
An alternate solution was proposed by Dynamis and accepted by the client: the installation of a steeper duct with Øi870 mm (45° slope) in place of the Øi1118 mm original duct (30° slope), as shown in the figure below.
A “Gas Crost” (sound wave emitter) was also installed.
The following tables show a comparison between the initial and the adopted solution situation:
| RESUME - Initial Situation | |||||
|---|---|---|---|---|---|
| Condition 1 | Condition 2 | Condition 3 | Condition 4 | Condition 5 | |
| R4 | Raw Meal | Raw Meal | Lime Dust | Lime Dust | Raw Meal |
| R5 | Stopped | Raw Meal | Stopped | Lime Dust | Lime Dust |
| % of maximum flow | 50,0% | 100,0% | 27,5% | 55,0% | 77,5% |
| Is the velocity enough for pneumatic conveying? |
YES | YES | NO | YES | YES |
| RESUME - Adopted Solution Situation | |||||
|---|---|---|---|---|---|
| Condition 1 | Condition 2 | Condition 3 | Condition 4 | Condition 5 | |
| R4 | Raw Meal | Raw Meal | Lime Dust | Lime Dust | Meal |
| R5 | Stopped | Raw Meal | Stopped | Lime Dust | Lime Dust |
| % of maximum flow | 50,0% | 100,0% | 27,5% | 55,0% | 77,5% |
| Is the velocity enough for pneumatic conveying? |
YES | YES | YES | YES | YES |
One of the main concerns of the plant staff was the additional head loss, caused by the reduction of the hot gas duct diameter and the increase of gas speed. The pressure drop on the intake damper (witch operated at 70% opening) of the exhaust fan was measured by Dynamis, and the additional pressure drop (caused by the section reduction) was about the loss caused by the damper. Thus, this equipment is now operating almost fully opened, and no alterations were necessary on the exhaust fan, to maintain the same gas flow, necessary to the mills.
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