3.5.1 The blower casing should be constructed
in corrosion-resistant material or alternatively of mild steel but
then its internal surfaces should be stove-coated, or lined with rubber
or glass fibre epoxy resin or other equivalent material to protect
it from the corrosive effect of the gas.
3.5.2 The impellers should be manufactured in
a corrosion-resistant material. Aluminium bronze impellers should
be stress-relieved after welding. All impellers should be tested by
overspeeding to 20% above the design running speed of the electric
motor or 10% above the speed at which the overspeed trip of the turbine
would operate, whichever is applicable.
3.5.3 Substantial drains, fitted with adequate
water seals, should be provided in the casing to prevent damage by
an accumulation of water. The drains should be in accordance with
the provisions of 3.15.4.
3.5.4 Means should be provided such as fresh water
washing to remove the build-up of deposits which would cause vibration
during blower operation.
3.5.5 The casing should be adequately ribbed to
prevent panting and should be so designed and arranged as to facilitate
the removal of the rotor without disturbing major parts of the inlet
and outlet gas connections.
3.5.6 Sufficient openings in the casing should
be provided to permit inspection.
3.5.7 Where separate shafts are provided for the
prime mover and the blower, a flexible coupling between these shafts
should be provided.
3.5.8 When roller or ball bearings are used, due
regard should be paid to the problem of brinelling and the method
of lubrication. The type of lubrication chosen, i.e. oil or grease,
should have regard to the diameter and rotational speed of the shaft.
If sleeve bearings are fitted then resilient mountings are not recommended.
3.5.9 The blower pressure/volume characteristics
should be matched to the maximum system requirements. The characteristics
should be such that in the event of the discharge of any combination
of cargo tanks at the discharge rate indicated in 3.4, a minimum pressure of 200 mm water gauge is maintained in
any cargo tank after allowing for pressure losses due to:
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.1 the scrubber tower and demister;
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.2 the piping conveying the hot gas to the scrubbing
tower;
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.3 the distribution piping downstream of the scrubber;
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.4 the deck water seal;
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.5 the length and diameter of the inert gas distribution
system.
3.5.10 When both blowers are not of equal capacity
the pressure/volume characteristics and inlet and outlet piping should
be so matched that if both blowers can be run in parallel, they are
able to develop their designed outputs. The arrangements should be
such as to prevent the blower on load from motoring the blower that
is stopped or has tripped out.
3.5.11 If the prime mover is an electric motor
then it should be of sufficient power to ensure that it will not be
overloaded under all possible operating conditions of the blower.
The overload power requirement should be based on the blower inlet
conditions of -5°C at -400 mm water gauge and outlet conditions
of 0°C and atmospheric pressure. Arrangements should be provided,
if necessary, to maintain the windings in a dry condition during the
inoperative period.