Vibration Measurements on Foster Wheeler MBF 22 Pulverizers

<strong>Vibration</strong> <strong>Measurements</strong>
on Foster Wheeler MBF 22 Pulverizers
at the
Sines Power Plant / Portugal
on 25./26.05.2000
Project Manager: Dr. G. Hüffmann / GERB Germany
<strong>Measurements</strong> by: M. Maillard / GERB France
14.06.2000

<strong>Vibration</strong> <strong>Measurements</strong> on Foster Wheeler MBF 22 Pulverizers at the Sines Power Plant / Portugal 14.06.2000 / Page 2
1. Introduction
<strong>Vibration</strong> measurements were performed at the Sines Power Plant, Portugal, on Foster
Wheeler MBF 22 pulverizers. Twenty of these mills are operated there since 1982 on
foundations spring supported for vibration isolation by GERB spring and Viscodamper
systems.
The results are going to be compared with those of a theoretical system analysis based on
dynamic load data of IHI/Japan who are making Foster Wheeler MBF 22 coal mills on
licence basis.
The results of these measurements will also be the basis for assessment of vibration
levels in similar existing or future installations.
Fig. 1 shows the foundation system with the spring and Viscodamper arrangement. The
total spring supported weight, foundation plus mill, is 465 + 139 = 604 t. Each foundation
is supported by 22 spring units type GP-8-2715/33 and 12 Viscodampers V5R, both
standard GERB elements.
<strong>Measurements</strong> were performed on different pulverizers, all of unit 1.
2. Measuring System
The measuring system allows to measure velocities as well as displacements and to
calculate and list peak and RMS values. A frequency analysis of the signals is also
possible.

<strong>Vibration</strong> <strong>Measurements</strong> on Foster Wheeler MBF 22 Pulverizers at the Sines Power Plant / Portugal 14.06.2000 / Page 3
3. Sensor Locations
Fig. 2 shows the locations where the sensors were placed during the measurements. All
8 channels were used, 7 sensors were sitting on the mill foundation respectively the mill
top, the 8 th sensor was placed next to the spring supported mill foundations on the boiler
house floor.
Table 1 lists the locations of the sensors and their measuring direction.
Table 1
Sensor Location Direction
Z1 centre of foundation vertical
Z2 rim of foundation * vertical
T2 rim of foundation * lateral
Z3 rim of foundation * vertical
L3 rim of foundation * longitudinal
L4 top of mill longitudinal
T5 top of mill lateral
Z6 outside foundation vertical
* for exact location see fig. 2.
4. Mill Conditions during <strong>Measurements</strong>
<strong>Vibration</strong>s were measured on the following mills and during the following mill operating
conditions:
4.1 Mill 3 - Continuous operation, load 22 t/h
4.2 Mill 3 - Continuous operation, load 30 t/h
4.3 Mill 2 - Start up, empty bowl

<strong>Vibration</strong> <strong>Measurements</strong> on Foster Wheeler MBF 22 Pulverizers at the Sines Power Plant / Portugal 14.06.2000 / Page 4
4.4 Mill 1 - Shut down from load 22 t/h to empty bowl (cleaning)
The measurements cover always a time window of 30 seconds.
A series of a different number of such 30 second intervals were measured for each of the
system conditions 4.1 - 4.4.
5. Results of <strong>Measurements</strong>
5.1 <strong>Vibration</strong> Levels (Velocities)
5.1.1 Mill 3 - Continuous operation at 22 t/h and 30 t/h load
Table 2 and 3 list peak velocities in each recorded 30 second window, table 4 and 5 the
corresponding RMS velocities.
Peak velocities vary only very little in each location with time, which becomes even more
obvious when looking at the RMS velocities. This can also be seen on fig. 3 and 4 where
the RMS velocities are shown versus time for the two load conditions, making it also
obvious that the mill vibration levels are not only quite constant during continuous
operation, but that there is nearly no difference between 22 t/h and 30 t/h load.
Actual velocities are quite low even in horizontal direction at the top of the mill (L4, T5)
with the peaks being in the range of 3 - 3,5 mm/s. The crest factor (ratio of peak and RMS
velocity) is in the range of 3,75 - 4,2 which is typical for mill vibrations.
5.1.2 Start up of Mill 2 - empty bowl
<strong>Vibration</strong>s were measured in a time frame of 42 minutes starting with the shut down and
empty mill until after mill restart the stage of continuous operation according to 5.1.1 was
reached. Table 6 and 7 list again the peak and RMS velocity levels.
<strong>Vibration</strong> levels are in this phase of operation up to 10 times higher than during continuous
operation with horizontal velocities up to nearly 40 mm/s at the top of the mill
corresponding to 7 mm/s RMS.

<strong>Vibration</strong> <strong>Measurements</strong> on Foster Wheeler MBF 22 Pulverizers at the Sines Power Plant / Portugal 14.06.2000 / Page 5
Fig. 5 shows the peak velocities over the whole time frame of 40 minutes where it
becomes obvious that after approximately 30 minutes the mill reaches the state of
continuous operation, here 22 t/h load, when the vibration levels drop drastically down to
the levels recorded and listed in 5.1.1.
The crest factor is during this phase of the same order as during continuous operation
according to 5.1.1.
5.1.3 Shut down operation of mill 1 - cleaning
<strong>Vibration</strong> levels are here as high and vary as much as during start up of mill 2, depending
always on how full the bowl still is.
Recorded peak and RMS velocities are listed in table 8 + 9.
5.2 Displacements
5.2.1 Mills in continuous operation
Fig. 6 shows a typical displacement time history reading at very low amplitudes, which are
even at the top of the mill below 60 microns. The frequencies are mainly the natural
frequencies of the spring supported system and among them mainly the rocking natural
frequencies in lateral and longitudinal direction, both in the range of 2 Hz.
5.2.2 Mills during start up and shut down operation
During start up and shut down operation of the mill, amplitudes will increase by a factor of
approximately 4, but even then the horizontal amplitudes at the top of the mill are still
below ± 200 μm. More important is - see fig. 7 - that these time histories are not anymore
governed by the natural frequencies of the spring supported system, but a random
excitation of frequencies of the mill itself in the range of 5 - 30 Hz.
Fig. 7 is a typical displacement reading at this stage.

<strong>Vibration</strong> <strong>Measurements</strong> on Foster Wheeler MBF 22 Pulverizers at the Sines Power Plant / Portugal 14.06.2000 / Page 6
Table 2, Peak Velocities (mm/s)
Mill 3 Z1 Z2 T2 Z3 L3 L4 T5 Z6 Observations
Continuous Operation
1 25.05.00 14:19:55 1,2 2,8 1,5 2,8 1,3 3,4 2,9 0,2 load = 22 t/h
2 25.05.00 14:23:12 1,1 2,8 1,5 2,8 1,1 3,8 2,7 0,2 load = 22 t/h
3 25.05.00 14:29:00 1,2 2,9 1,4 2,9 1,0 3,3 2,5 0,2 load = 22 t/h
4 25.05.00 14:29:21 1,1 2,7 1,6 3,2 1,1 3,2 3,0 0,2 load = 22 t/h
5 25.05.00 14:29:42 1,0 2,7 1,4 2,8 1,1 3,8 2,7 0,2 load = 22 t/h
6 25.05.00 14:30:37 1,1 2,9 1,5 3,0 1,1 4,0 2,6 0,2 load = 22 t/h
7 25.05.00 14:31:24 1,1 3,0 1,5 2,7 1,1 3,4 2,5 0,2 load = 22 t/h
8 25.05.00 14:31:45 1,2 3,0 1,4 3,0 1,0 3,6 2,5 0,2 load = 22 t/h
9 25.05.00 14:34:03 1,2 3,3 1,6 3,0 1,1 3,5 3,0 0,2 load = 22 t/h
10 25.05.00 14:36:01 1,3 2,9 1,5 3,0 1,2 3,2 2,8 0,2 load = 22 t/h
Table 3, Peak Velocities (mm/s)
mean 1,2 2,9 1,5 2,9 1,1 3,5 2,7 0,2 mm/s
Mill 3 Z1 Z2 T2 Z3 L3 L4 T5 Z6 Observations
Continuous operation
51 26.05.00 10:36:31 0,97 3,50 1,80 2,50 0,96 2,70 2,70 0,26 load = 30 t/h
52 26.05.00 10:37:24 0,98 3,40 1,80 2,50 0,96 3,10 2,60 0,29 load = 30 t/h
53 26.05.00 10:37:46 0,98 3,30 1,40 2,50 1,20 2,80 2,50 0,25 load = 30 t/h
54 26.05.00 10:38:07 1,00 3,60 1,50 2,60 0,99 3,60 2,50 0,22 load = 30 t/h
55 26.05.00 11:01:31 0,96 3,90 1,70 2,90 0,94 3,30 2,70 0,26 load = 30 t/h
56 26.05.00 11:02:13 1,10 3,30 1,70 3,00 1,10 2,70 2,60 0,25 load = 30 t/h
57 26.05.00 11:03:20 1,00 3,30 1,50 1,90 1,10 3,30 2,70 0,27 load = 30 t/h
58 26.05.00 11:04:21 0,99 3,40 1,70 1,90 1,20 2,90 2,80 0,24 load = 30 t/h
59 26.05.00 11:05:02 0,90 3,20 1,50 2,00 1,20 3,10 2,70 0,28 load = 30 t/h
60 26.05.00 11:05:23 0,88 3,30 1,70 2,30 1,20 2,80 2,60 0,22 load = 30 t/h
mean 0,98 3,42 1,63 2,41 1,09 3,03 2,64 0,25 mm/s

<strong>Vibration</strong> <strong>Measurements</strong> on Foster Wheeler MBF 22 Pulverizers at the Sines Power Plant / Portugal 14.06.2000 / Page 7
Table 4, RMS Velocities (mm/s)
Mill 3 Z1 Z2 T2 Z3 L3 L4 T5 Z6 Observations
Continuous Operation
1 25.05.00 14:19:55 0,291 0,764 0,375 0,734 0,272 0,893 0,638 0,069 load = 22 t/h
2 25.05.00 14:23:12 0,290 0,769 0,372 0,725 0,266 0,880 0,639 0,069 load = 22 t/h
3 25.05.00 14:29:00 0,295 0,765 0,377 0,742 0,269 0,909 0,651 0,064 load = 22 t/h
4 25.05.00 14:29:21 0,292 0,770 0,377 0,746 0,272 0,911 0,646 0,067 load = 22 t/h
5 25.05.00 14:29:42 0,289 0,764 0,376 0,740 0,267 0,907 0,633 0,065 load = 22 t/h
6 25.05.00 14:30:37 0,288 0,775 0,381 0,752 0,270 0,926 0,646 0,065 load = 22 t/h
7 25.05.00 14:31:24 0,293 0,766 0,376 0,755 0,271 0,916 0,652 0,066 load = 22 t/h
8 25.05.00 14:31:45 0,288 0,768 0,380 0,749 0,272 0,929 0,649 0,066 load = 22 t/h
9 25.05.00 14:34:03 0,291 0,769 0,377 0,754 0,269 0,924 0,657 0,066 load = 22 t/h
10 25.05.00 14:36:01 0,289 0,773 0,376 0,748 0,266 0,916 0,650 0,066 load = 22 t/h
Table 5, RMS Velocities (mm/s)
mean 0,29 0,77 0,38 0,74 0,27 0,91 0,65 0,07 mm/s
Mill 3 Z1 Z2 T2 Z3 L3 L4 T5 Z6 Observations
Continuous operation
51 26.05.00 10:36:31 0,247 0,925 0,427 0,654 0,250 0,683 0,631 0,073 load = 30 t/h
52 26.05.00 10:37:24 0,246 0,931 0,423 0,674 0,247 0,683 0,634 0,072 load = 30 t/h
53 26.05.00 10:37:46 0,251 0,928 0,423 0,682 0,255 0,702 0,644 0,072 load = 30 t/h
54 26.05.00 10:38:07 0,249 0,938 0,430 0,695 0,257 0,710 0,633 0,070 load = 30 t/h
55 26.05.00 11:01:31 0,251 0,899 0,429 0,759 0,249 0,703 0,661 0,071 load = 30 t/h
56 26.05.00 11:02:13 0,250 0,890 0,430 0,766 0,249 0,703 0,658 0,069 load = 30 t/h
57 26.05.00 11:03:20 0,250 0,902 0,422 0,520 0,259 0,705 0,643 0,071 load = 30 t/h
58 26.05.00 11:04:21 0,253 0,897 0,419 0,535 0,257 0,728 0,658 0,069 load = 30 t/h
59 26.05.00 11:05:02 0,249 0,897 0,419 0,531 0,252 0,691 0,637 0,071 load = 30 t/h
60 26.05.00 11:05:23 0,250 0,896 0,424 0,540 0,252 0,696 0,661 0,069 load = 30 t/h
mean 0,25 0,91 0,42 0,64 0,25 0,70 0,65 0,07 mm/s

<strong>Vibration</strong> <strong>Measurements</strong> on Foster Wheeler MBF 22 Pulverizers at the Sines Power Plant / Portugal 14.06.2000 / Page 8
Table 6, Peak Velocities (mm/s)
Mill 2 Z1 Z2 T2 Z3 L3 L4 T5 Z6 Observations
Start-up
11 25.05.00 15:17:21 0,1 0,2 0,2 0,4 0,2 0,7 0,5 0,2 mill shut down
12 25.05.00 15:33:11 7,6 17,6 9,4 21,6 12,5 26,9 28,8 0,5 start-up
13 25.05.00 15:33:32 7,8 14,4 8,9 22,5 11,5 38,2 31,1 0,4
14 25.05.00 15:33:53 7,7 13,9 7,7 13,1 8,7 33,3 31,2 0,4
15 25.05.00 15:34:13 4,5 11,9 7,1 13,1 7,3 32,9 25,6 0,4
16 25.05.00 15:34:34 5,3 12,3 7,1 13,9 8,5 29,4 23,4 0,4
17 25.05.00 15:34:54 3,8 10,5 6,5 13,5 8,9 30,1 25,2 0,3
18 25.05.00 15:35:35 4,1 11,1 5,9 12,1 6,8 26,2 22,7 0,3
19 25.05.00 15:35:55 3,9 10,9 6,1 15,5 10,1 29,6 22,9 0,3
20 25.05.00 15:36:16 4,8 11,0 5,7 13,7 8,3 27,8 27,3 0,4
21 25.05.00 15:37:17 4,7 11,6 6,6 14,6 8,3 26,5 24,8 0,3
22 25.05.00 15:38:18 5,8 10,9 6,2 15,2 11,6 29,0 24,8 0,3
23 25.05.00 15:38:59 5,6 10,5 6,4 11,7 7,0 25,3 26,1 0,4
24 25.05.00 15:39:59 4,3 10,5 6,4 11,8 8,3 31,4 27,9 0,3
25 25.05.00 15:41:40 5,0 14,2 6,4 13,8 9,2 28,3 24,3 0,4
26 25.05.00 15:44:00 8,6 14,9 8,6 22,3 12,0 34,3 26,1 0,3
27 25.05.00 15:44:21 4,6 11,9 6,7 13,7 9,5 26,0 22,9 0,3
28 25.05.00 15:47:42 5,7 17,0 5,9 17,3 12,3 31,6 23,8 0,4
29 25.05.00 15:48:22 8,1 14,6 6,6 22,6 11,4 36,5 25,2 0,4
30 25.05.00 15:49:40 4,5 11,1 6,7 21,0 10,8 30,1 24,9 0,4
31 25.05.00 15:50:41 4,4 11,8 6,3 18,3 10,1 26,9 22,1 0,4
32 25.05.00 15:52:42 4,6 10,7 6,5 16,3 9,2 26,0 30,9 0,4
33 25.05.00 15:53:02 6,0 13,3 6,9 15,3 9,5 29,6 26,2 0,4
34 25.05.00 15:53:43 4,6 11,4 8,6 18,6 10,3 26,1 27,0 0,4
35 25.05.00 15:55:04 4,3 12,7 5,9 13,2 7,7 30,2 24,7 0,4
36 25.05.00 15:57:24 10,8 23,7 12,9 26,0 15,6 35,6 30,8 0,5
37 25.05.00 15:57:45 11,7 16,5 9,9 23,5 12,3 32,8 31,9 0,4
38 25.05.00 15:58:46 3,3 10,5 4,5 7,9 4,2 18,8 12,2 0,3
39 25.05.00 15:59:07 2,7 8,0 3,5 6,4 2,5 11,0 8,1 0,2
40 25.05.00 15:59:27 2,7 7,1 2,9 4,5 2,0 8,9 6,6 0,2
41 25.05.00 15:59:48 2,7 6,1 2,6 5,2 2,3 9,1 6,2 0,2
42 25.05.00 16:00:28 2,0 5,5 2,5 4,4 2,3 7,6 5,9 0,2
43 25.05.00 16:00:49 2,0 4,4 2,0 4,7 2,2 8,2 4,8 0,2 load 22 t/h
44 25.05.00 16:01:10 1,7 4,2 1,9 3,4 1,8 5,0 4,3 0,2
45 25.05.00 16:01:50 1,9 4,2 2,2 3,1 1,8 5,4 4,7 0,2

<strong>Vibration</strong> <strong>Measurements</strong> on Foster Wheeler MBF 22 Pulverizers at the Sines Power Plant / Portugal 14.06.2000 / Page 9
Table 7, RMS Velocities (mm/s)
Mill 2 Z1 Z2 T2 Z3 L3 L4 T5 Z6 Observations
Start-up
11 25.05.00 15:17:21 0,035 0,044 0,053 0,089 0,053 0,178 0,163 0,041 mill shut down
12 25.05.00 15:33:11 1,099 3,005 1,636 3,037 1,761 6,316 5,168 0,081 start-up
13 25.05.00 15:33:32
14 25.05.00 15:33:53 1,210 3,014 1,655 2,937 1,706 7,163 6,128 0,087
15 25.05.00 15:34:13 1,063 2,732 1,500 2,678 1,485 6,745 5,814 0,084
16 25.05.00 15:34:34 0,979 2,769 1,500 2,535 1,409 6,625 5,674 0,082
17 25.05.00 15:34:54 0,981 2,614 1,438 2,604 1,453 6,855 5,375 0,081
18 25.05.00 15:35:35 0,985 2,676 1,469 2,605 1,446 6,556 5,435 0,083
19 25.05.00 15:35:55 0,992 2,608 1,454 2,578 1,447 6,500 5,391 0,081
20 25.05.00 15:36:16 1,023 2,686 1,496 2,621 1,475 6,672 5,757 0,084
21 25.05.00 15:37:17 0,988 2,643 1,403 2,703 1,493 6,917 5,688 0,079
22 25.05.00 15:38:18 0,990 2,485 1,422 2,488 1,435 6,377 5,427 0,084
23 25.05.00 15:38:59 1,003 2,659 1,427 2,507 1,421 6,389 5,540 0,086
24 25.05.00 15:39:59 0,983 2,638 1,448 2,708 1,556 6,945 5,786 0,080
25 25.05.00 15:41:40 1,048 2,659 1,456 2,631 1,532 6,545 5,531 0,085
26 25.05.00 15:44:00 1,065 2,583 1,460 2,690 1,581 6,733 5,702 0,085
27 25.05.00 15:44:21 1,018 2,646 1,480 2,645 1,591 6,456 5,544 0,084
28 25.05.00 15:47:42 1,071 2,779 1,497 2,870 1,755 6,820 5,649 0,087
29 25.05.00 15:48:22 1,107 2,696 1,488 2,792 1,709 6,737 5,720 0,087
30 25.05.00 15:49:40 1,047 2,696 1,478 2,743 1,727 6,479 5,780 0,085
31 25.05.00 15:50:41 0,970 2,550 1,421 2,581 1,606 6,246 5,423 0,082
32 25.05.00 15:52:42 1,019 2,618 1,440 2,642 1,607 6,578 5,648 0,084
33 25.05.00 15:53:02 1,047 2,633 1,455 2,703 1,639 6,555 5,419 0,085
34 25.05.00 15:53:43 1,033 2,580 1,461 2,612 1,602 6,296 5,697 0,085
35 25.05.00 15:55:04 1,039 2,693 1,473 2,824 1,648 6,705 5,588 0,086
36 25.05.00 15:57:24 1,293 2,813 1,563 3,105 1,797 6,950 6,089 0,090
37 25.05.00 15:57:45 1,334 3,039 1,703 3,374 2,019 7,386 6,452 0,093
38 25.05.00 15:58:46 0,934 2,580 1,067 2,005 0,881 4,224 2,714 0,067
39 25.05.00 15:59:07 0,784 1,899 0,796 1,563 0,666 3,097 1,877 0,056
40 25.05.00 15:59:27 0,669 1,643 0,712 1,307 0,570 2,493 1,583 0,051
41 25.05.00 15:59:48 0,702 1,583 0,672 1,290 0,564 2,496 1,491 0,050
42 25.05.00 16:00:28 0,554 1,282 0,556 1,058 0,495 1,939 1,151 0,048
43 25.05.00 16:00:49 0,479 1,078 0,495 0,933 0,466 1,694 1,099 0,045
44 25.05.00 16:01:10 0,417 1,045 0,472 0,854 0,445 1,458 1,050 0,048
45 25.05.00 16:01:50 0,483 0,879 0,407 0,785 0,415 1,291 0,954 0,046

<strong>Vibration</strong> <strong>Measurements</strong> on Foster Wheeler MBF 22 Pulverizers at the Sines Power Plant / Portugal 14.06.2000 / Page 10
Table 8, Peak Velocities (mm/s)
Mill 1 Z1 Z2 T2 Z3 L3 L4 T5 Z6 Observations
Shut down operation
46 25.05.00 16:15:49 3,2 7,2 4,0 5,8 3,4 21,5 0,2
47 25.05.00 16:18:50 3,9 9,1 5,7 6,3 4,8 25,6 0,2
48 25.05.00 16:26:10 3,4 9,0 6,0 8,3 6,0 26,3 23,4 0,3
49 25.05.00 16:26:32 4,0 10,5 5,7 9,6 6,5 25,6 27,2 0,2
50 25.05.00 16:27:14 4,1 9,5 5,3 9,8 7,6 24,7 23,6 0,3
Table 9, RMS Velocities (mm/s)
Mill 1 Z1 Z2 T2 Z3 L3 L4 T5 Z6 Observations
Shut down operation
46 25.05.00 16:15:49 0,858 1,670 0,835 1,320 0,746 4,308 0,050
47 25.05.00 16:18:50 0,840 2,032 1,099 1,531 0,986 5,400 0,053
48 25.05.00 16:26:10 0,854 2,175 1,125 1,985 1,190 6,338 6,018 0,059
49 25.05.00 16:26:32 0,859 2,229 1,133 1,816 1,130 6,218 6,172 0,058
50 25.05.00 16:27:14 0,840 2,148 1,122 1,888 1,154 6,364 6,004 0,059
6. <strong>Vibration</strong> Isolation Effect
The ratio between the vibration levels next to the foundation (Z6) and on top of the
foundation (Z1) defines the vibration isolation effect of the spring supported foundation
system.
<strong>Vibration</strong> levels next to the mill foundations are extremely low at typically a peak velocity of
only 0,2 mm/s corresponding to a RMS velocity of 0,07 mm/s. This level is, however,
governed by other vibration sources in that area, not by mill vibrations. This becomes
obvious when looking at the vibration level next to the mill 2 foundation during start up of
that mill. <strong>Vibration</strong> levels on top of the foundation increase at this stage by a factor of
nearly 10 (see 5.1.3) while the vibration levels next to the foundation increase only from
0,05 mm/s RMS when reaching the stage of continuous operation to 0,09 mm/s RMS in
the start up time frame.
These figures lead to a vibration isolation effect of more than 90 %, which is even
somewhat higher than typically expected (80 %).

<strong>Vibration</strong> <strong>Measurements</strong> on Foster Wheeler MBF 22 Pulverizers at the Sines Power Plant / Portugal 14.06.2000 / Page 11
7. Summary and General Assessment
7.1 <strong>Vibration</strong> levels (velocities) on the spring supported mill foundation and on top of the mill
during continuous operation are low.
7.2 There is no difference between continuous operation with 22 t/h load and 30 t/h load.
7.3 Displacements during continuous operation, governed by a random excitation of the
vertical and rocking natural frequencies of the spring supported system, are low at less
than ± 10 μm on top of foundation level and in the range of ± 30 μm horizontally on top of
the mill.
7.4 <strong>Vibration</strong> levels increase dramatically by about a factor of 10 during the start up or shut
down phase when the bowl is empty respectively not yet fully filled.
The response of the spring supported system can be seen at this stage as forced
vibrations with frequencies in the range of 5 - 30 Hz, randomly excited by the mill.
The vibration levels of up to 25 mm/s measured on top of the foundation would be the
same on a conventional foundation, but would there be transferred in case of no vibration
control with its full amount into the surroundings.
The duration of the start up procedure until the stage of continuous operation is reached
takes for the mill approximately 40 minutes and the time frame is similar when shutting a
mill down from continuous operation while cleaning the bowl.
7.5 Displacements of mill and foundation during the start up and shut down phase of a mill
increase also compared to continuous operation, but not as much as the velocities. This is
because of the higher frequencies in the response signal at this stage compared to
continuous operation.
Still, displacement levels are even at the top of the mill at less than ± 250 μm - a mean
value would be more in the range of less than ± 130 μm - without any major influence on
coupled chutes or tubes, as the 20 year experience with these mills at the Sines plant has
shown.
7.6 The vibration isolation effect of the spring supported system is at more than 90 %
extremely good and keeps the vibration levels in the boiler house and adjacent areas
extremely low.
This high vibration isolation effect is perhaps not so important during continuous operation
of the mills, but will prevent disturbances and damages during start up and shut down
procedures and will, therefore, reduce maintenance in sensitive neighbouring areas like
switch gear panels, control rooms or even other equipment.

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<strong>Vibration</strong> <strong>Measurements</strong> on Foster Wheeler MBF 22 Pulverizers at the Sines Power Plant / Portugal 14.06.2000 / Page 16

<strong>Vibration</strong> <strong>Measurements</strong> on Foster Wheeler MBF 22 Pulverizers at the Sines Power Plant / Portugal 14.06.2000 / Page 17

<strong>Vibration</strong> <strong>Measurements</strong> on Foster Wheeler MBF 22 Pulverizers at the Sines Power Plant / Portugal 14.06.2000 / Page 18