Page 222 - Compression Machinery for Oil and Gas

Reciprocating Compressors Chapter 5 211

Noncooled Cylinders
In September 1955, a technical paper was presented at an ASME conference
that offered a contrasting view to the need for cylinder cooling systems and ulti-
mately had a major impact on some future compressor designs. The paper was
titled “Operation of Compressor Cylinders Without Cooling Water” and was
written by H.W. Evans and J.L. Gallagher, two Sinclair Oil and Gas Company
engineers based in Tulsa, Oklahoma [22]. In 1940, while performing mainte-
nance on a cylinder cooling system, the decision was made to keep the compres-
sor running for 3days. During that period, there was no noticeable decrease in
compressor performance or increased discharge temperatures. This led to the
study eventually detailed in the paper. For 2years, the cooling water systems
for all of the compressors at the Sinclair facility were turned off and drained.
The performance of all the compressors was monitored and the following con-
clusion was reached and published in the paper: “After more than two years of
experience in operating plants without the use of jacket water in the compressor
cylinders, we believe there is no measurable loss in gas handling capacity and
no increase in cylinder wear. On all new installations, we have discontinued the
use of cooling water on all gas compressor cylinders and thereby have saved the
installation cost of the pumps, headers, compressor cylinder water piping and
have reduced water usage, treating cost and operating and maintenance cost.”

Capacity Control

Capacity control can be achieved in several ways with a reciprocating gas com-
pressor. In the following discussion a distinction will be made between methods
that are efficient (reduced power with concurrent reduced mass flow so that the
power per unit gas is held constant) and those that are not. The following
methods briefly discussed here include:
– recycle;
– varying rotating speed;
– adding/subtracting fixed clearance;
– end deactivation; and
– suction valve controlled closing

Recycle
Recycle, as summarized in Fig. 5.29, is the simplest and the therefore the most
reliable form of capacity control. It consists of piping that connects the dis-
charge piping with the suction piping through a control valve—a recycle valve.
When the valve is opened discharge gas is allowed to flow back to suction and
not proceed on down the discharge pipe thus reducing the amount of gas the
proceeds down the pipe. While the capacity is changed (lowered when the recy-
cle valve is opened) the power is not, making recycle an inefficient form of
capacity control.