SAG Mill Stoppage

7/25/2019 SAG Mill Stoppage

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14/02/2016

Job Mateus

Mill Shut down and SAG Discharge pumps blocage

!n "rida# 12 "ebruar# 2016 at around 22$00 on A%ternoon Shi%t& the process

water pump 600'((')*6 %ailed due to a sha%t that broe+ A sudden loss o% process

water ,ow to the grinding area was e-perienced& which e.entuall# led to the

stoppage o% the SAG Mill and blocage o% the SAG Discharge pump 200'(('16+

elow is the detailed seuence o% e.ents that led to the stoppage o% the mill+

As indicated in "igure 1 below& at 22$16& the process water pump 600'((')*6

sha%t broe& resulting in a sudden %all o% ,ow o% process water to the grinding

area+

Figure 1: Process Water Flow

An instruction was gi.en %or the grinding operator to go open the manual .al.es

o% the standb# process water pump 600'((')*)& in order o% the acting ontrol

3oom !perator to mae the switch o% the process water pumps+ he grinding

operator then disco.ered a huge leaage o% water at pressure relie% line o% the

standb# process water pump+ $e then announced the una.ailabilit# o% the

standb# pump citing the huge leaage+ 5n the meantime& the 3! was instructed

to stop %eed to the mill as there is no water going into the mill as well as the SAG

Mill discharge pump bo-+ he sudden loss o% process water has resulted in the

sudden increase o% slurr# densit#& both in the mill and pump bo-+ "igure 2 below

indicates the stoppage o% %eed to the mill at 22$22+


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he con.e#or was stopped howe.er the SAG mill was le%t running to grind out

the dr# ore in the mill+ 5n the meantime& the SAG discharge pump lost ,ow due to

the sanded pump resulting %rom the high densit# slurr# in the pump bo-+ ith a

nown histor# o% the SAG discharge pumps blocing& o%ten a .aried speed %or the

pump can easil# resol.e the blocage problem+ he speed %or the pump was

.aried as in most usual pump 7am to tr# and get ,ow+ A%ter se.eral attempts& it

was then decided to switch to a standb# SAG discharge pump 200'(('166+

Figure 2: SAG Feed Tonnage

he standb# pump 8200'(('1669 did not immediatel# gi.e ,ow a%ter start'up+ he

speed was similarl# .aried to tr# and get ,ow howe.er it too time be%ore 200'

(('166 de.eloped ,ow+ 5n the meantime the SAG discharge pump bo- was

o.er,owing since the SAG mill was still running+ During this appalling moment& a

mill started showing signs o% o.erload& as it can be seen in "igure * b# the mill

bearing pressure o% 6100 :(a+ here%ore stopping the mill in that state due to the

pump bo- o.er,ow was not an option+ he standb# process water pump 600'(('

)*) was started in its alarming state to assist in grinding out the mill and lower

the densit# inside the mill and pump bo-+

At 2*$00& the mill started showing good signs that it is not o.erloaded and ha.e

success%ull# grinded out as the bearing pressure read )00 :(a+ 5t was the

decided to stop the SAG mill to control the o.er,ow o% the SAG discharge pump

bo-+


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Figure 3: SAG FE Bearing Pressure, Power and Torque

A%ter se.eral attempts to get the SAG Discharge pump 200'(('166 running&

success was recorded at 2*$04 when it started gi.ing ,ow 8See "igure 49+ "igure

4 also indicates that the pump 200'(('166 was actuall# partiall# bloced as it

continued running on ;ight Shi%t+ he a%ter'e.ents o% 200'(('166 be#ond 2*$10

are unnown as it happens on ;ight Shi%t& considering that the plant was

e.entuall# started up+

Figure 4: SAG ill !isc"arge Flow

5n onclusion& the stoppage o% the mill as well as the SAG discharge pump

blocage was mainl# due to the sudden una.ailabilit# o% process water to thegrinding+ his was mainl# caused b# the process water pump that broe the sha%t


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and una.ailabilit# o% the standb# pump due to the barrel that sei

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SAG Mill Stoppage