friends we have loesche VRM our max grinding pressure is 100bar. normally we operate mill with 500t/h with 90bar grinding pressure and 24bar counter pressure. but we are facing problem in our nitrogen cylinder in every 24hrz we found one nitrogen cylinder empty sometimes in nitrogen cylinders of grinding pressure and sometimes in nitrogen cylinder of counter pressure.we keep pressure in nitrogen cylinder upto 40bar in nitrogen cylinder of grinding pressure and keep 12bar pressure in nitrogen cylinder of counter pressure.
armankhan
VRM nitrogen cylinder problem
FraMisUS
Dear Sir, let me make some asumptions:
1. The nitrogen accumulators for the grinding pressure side are bladder accumulators, the nitrogen accumulators on the counter pressure side are piston accumulators.
2. We are talking about a raw mill (based on the 500 t/h capacity).
3. The empty accumulators are recharged once and if the same accumulator fails again that accumulator is dismounted and the rubber bladder/filling valve or respectively the piston O-Rings and the filling valve are exchanged with new material.
Here are some general remarks:
a) The reported oil / nitrogen pressures for the grinding and counter pressure sides are within the normal ranges and are not the reason for the problems.
b) One very common reason for a failure within the bladder accumulators is a misoperation in local mode. When the personnel in the field makes the mistake of lifting the rollers, draining the grinding side oil pressure to zero and then lowering the rollers the rubber bladders tend to be sucked into the botoom valves of the accumulators which causes the rubber to be damaged at the metal edges of the valves. Please review the local operation habits of the field operators.
c) A common reason for the failure of the piston accumulators is a neglectance of the air bleeding after installation. Since you report many failures of the accumulators let me assume that accumulators are dismounted / remounted frequently. Not only should air be bled just after the installation but also after 5 to 8 hours of operation and then again after 24 hours of operation. The bleeding of air from the piston accumulators must not be done at more than 5 to 8 bar at the accumulator itself.
d) Another common reason for failure of the piston accumulators is unclean installation. When changing the accumulators a VERY high level of cleanliness throughout the entire exchange has to be maintained.
e) Since accumulators on both sides are frequently without nitrogen also the filling valves may be leaky which can be tested with soap water tests on all filling valves.
f) Once nitrogen has been inserted into the oil within the counter rpessure side it cannot be stressed enough that a repeated an thorough air bleeding must be done over the course of several days.
I hope these remarks help.
Best regards,
Frank Mischorr
General Manager FraMisUS, LLC
armankhan
thanks sir alot for such detailed n valuable reply..... sir you mentioned that local mode operation can also cause failure sir then we need some times its local mode operation at site then whats the best way to operate rollers down or up locally and to avoid failure of bladder