Page 35 - Compression Machinery for Oil and Gas

Equipment Overview Chapter 2 25

risk of catastrophic failures, and potential for process improvements leading to
greater efficiency and profitability.
Relative historical service lives of the prime mover categories before exten-
sive and expensive unit overhauls are:

l slow-speed gas engine (300–600rpm): 75,000 operating hours,
l high-speed gas engine (900–1800rpm): 25,000–50,000 operating hours,
l gas turbine: 30,000 operating hours, and
l electric motor: 100,000h.

Pulsation and Vibration Considerations
Most positive displacement compressors (primarily reciprocating and screw-
type compressors) can be subject to significant pulsation and vibration-related
concerns and consideration of these issues should be included in the overall
design effort. Centrifugal compressors inherently have lower unbalanced forces
and are typically less susceptible (but not immune) to pulsation and vibration
related issues. See Chapter 11 for detailed discussion on this topic.

Automated/Manual Controls
The wide variation of compressor station size, complexity, type, and yearly uti-
lization affects the sophistication and configuration of manual versus automated
control systems selected. Generally compressor stations can be divided into
three types or modes of operation. The classification of each mode depends
on the degree of automation required by the company. Usually as the degree
of automation increases the sophistication of the controls and instrumentation
also increases. Typical terms used in three “modes of operation” at varying
levels for compressor stations are: “local—manual,” “local—automatic,” and
“remote—automatic.” The complexity and selection of the control mode varies
with the amount of remote controlled automatic operation required. They may
range from simple manually operated actuators to remotely controlled comput-
erized systems with data logging/reporting and remote diagnostic capabilities.
Regardless of complexity, control systems should be modular and constructed
to facilitate expansion, troubleshooting, and ease of maintenance. Controls are
becoming increasingly electronically operated or activated. There are also
numerous options in the industry for preengineered “off the shelf” mechanical
and electropneumatic individual unit control panels for a shorter list of critical
monitoring and safety shut-down functions specific to standard industry com-
pression packages allowing on-off control tasks and monitoring/alarming of key
machine package operations. Controls of this nature are relatively inexpensive
and can be interfaced easily with engine and compressor equipment. They are
also advantageous in that they can be used safely in locations classified as hav-
ing hazardous atmospheres.