Page 235 - Reciprocating Compressors Operation Maintenance

220 Reciprocating Compressors: Operation and Maintenance

design reduces the pressure along the piston and piston-rod gland and,
thus, achieves the sealing effect.
A "running-in process" and self-centering system provide for optimum
piston clearance, high efficiency and economical operation. Compressed
gas is delivered with unchanged purity, and the risk of carryover of abra-
sives from the piston, rider, or packing rings is virtually eliminated,
either because there is no rubbing or because these components simply
are not part of labyrinth compressors.

Six plants owned by a large corporation and six owned by other firms
in North America and Europe were investigated. Not surprisingly, no two
locations used identical data-collection and data-reporting methods. Some
of the plants monitored repair cost and downtime data; whereas, others
kept track primarily of spare-parts usage, or perhaps, only the number of
outages. However, all of the available statistics did prove relevant.
Exceptionally detailed records have been kept for six machines in
fouling polypropylene services at a U.S. Gulf Coast plant (designated
Plant A) that was commissioned in 1983 (Table 3-13). As illustrated in

TABLE 3-13
EXPERIENCE SUMMARY FOR LABYRINTH-PISTON RECIPROCATING
COMPRESSORS AT PLANT A

Run time before
preventive Maintenance cost, $ Maintenance cost
Compressor maintenance, h Labor Material Total per run-hour, $
_
__
_
___
___
-____
A-2 8,997 8,500 6,280 14,780 L64
A-3 8,545 7,200 9,700 16,900 1.98
A-4 7,000 1,800 5,600 7,400 1.06
A-5 8,300 3,700 6,100 9,800 1.18
A-6 7,545 6,000 17,200 23,200 3.07
Total for plant 47,671 29,000 52,290 81,290
Average annual maintenance expense: $15/hp, or $11/kW
Equipment data:
4 throws, 300-mm (12-in.) stroke, 2 stages, 920 kW, 1,234 hp
4,600 mVh (2,700 cfm)
P s = 1.31 bar abs. (19 psia), P D = 20.7 bar abs. (300 psia)
(conversions are approximate)