Slow-rotating machinery condition monitorin in pulp mill

Written: Juha Hautala

Case 1. Examining condition of pulp disc filter and vacuum drum pulp washer

Need

Customer wanted to check the condition of pulp disc filter and drum pulp washer machines.

Challenges

Slow rotating devices are challenging targets for vibration measurements. Measuring targets with handheld devices is slow. In addition, the measurement settings for most manual measuring devices are poorly suited for slow-rotating machinery. In many organisations, listening the sound has been chosen as the method of controlling slow rotating machinery. Listening is an effective method, but diagnosis and documentation are challenging in all sensory methods.

In our experience, the vibration analysis of slow rotating machinery differs in part from vibration analysis of fast rotating machinery. For measurements and analysing, we divide the machinery in four different categories. Of these four categories, measuring the slow and very slow rotating machinery demand longer monitoring period than the regular route measurements.

 

  1. Very fast rotating machinery (i>6000 rpm)
  2. Fast rotating machinery (300 rpm > i > 6000 rpm)
  3. Slow rotating machinery (60 rpm > 300 rpm)
  4. Very slow rotating machinery (1 rpm > i > 60 rpm) 

 

Solution

The customer presented a problem to nome´s experts. As part of the development of the nome´s nmas (nome measuring and analyzing system) measurement device, the system has built-in characteristics for long time levels and very slow-rotating equipment analysis.

The customer did not have the opportunity to invest for online monitoring system. An agreement was reached with the client to rent the nmas equipment for the duration of the measurements. Nome guided customer with the use of the device and the customer transferred the measuring device to the new measurement position according to the agreed schedule.

Analysis

Analysis of the condition of the bearings of pulp disc filters and pulp washers was agreed to be done by nome´s experts. Among several monitored targets, one pulp washer was found, which, based on the analysis, was in need of maintenance. The analysis method developed by nome to evaluate the severity of the very slow rotating devices was used to classify and monitor the severity of the defect. The target was at a 5-tier scale level of four and the recommendation was to maintain the subject at the next downtime.

 

 

Picture 1. and 2. Damaged bearing parts

Result

The measurements gave an indication of a serious bearing damage in pulp disc filter. If the defect had progresses, the target would be very likely to be severely damaged and caused a production shutdown of several days.

Based on the measurements and analysis carried out, the target was overhauled at the annual maintenance standstill. There was no need of service for other measured items.

The bearing removed from the disc filter was checked and found to have cracked roll and damage to the inner and outer rim.

Mobile online health surveillance enabled all items to be measured and analyzed without any major investment.

Used remote monitoring system:

nmas Simple monitoring device

– nmas connection point

Cables, sensors and magnets

– Tacho meter

nmas Analysator program

Picture 3. and 4. Used nmas Easy measurement device