Case History No. 19

Industry & Location:

A pulp and paper mill in the south

Problem:

Excessive horsepower consumption and inadequate draft control of lime kiln

Source of Detection:

Poor quality lime production

Cause of Problem:

Most lime kilns in the paper industry are equipped with high energy scrubbers which are designed to operate at a pressure drop of 25" w.g. In recent years, many of these scrubbers have been replaced with so called low energy scrubbers which operate at a pressure drop of only 5" or 6". However, the reduced horsepower consumption of the I.D. fan as a result of this static pressure reduction is generally offset by pump horsepower consumption.

In this particular case, control problems were encountered with the lime kiln I.D. fan, and the operators could not obtain adequate air flow through the kiln.

Lime Kiln I.D. Fan

Solution:

During a planned outage, a thorough inspection of the I.D. fan was completed and considerable lime build-up was observed in the bottom of the inlet box. This build-up created a flow situation in the inlet box which caused prespinning in a rotation which was opposite to the wheel rotation. Such an inlet box flow condition causes the fan to develop excessive pressure and inadequate volumetric flow.

Lime Accumulation in Inlet Box

In this instance, the fan was improperly selected. The fan had considerably excessive volumetric capacity but only marginal pressure capability. Without the ability to develop adequate static pressure, the volume of gas cannot be drafted from the kiln. Because of the incorrect sizing of the fan, the inlet boxes were oversized and the inlet velocity was so low that lime dust dropped out and settled in the inlet box. In this particular instance, the fan housing and impeller required replacement.

Benefit:

Improved lime production and considerable horsepower savings because of increased fan fficiency of the replacement fan.