American Oil and Gas Reporter - October 2016 - 76

SpecialReport: Natural Gas Update
each step had to be easily measured. The
measurement tool was presumed to be a
tape measure and the position steps were
kept at fractional increments of no less
than one-eighth of an inch.
Figure 3 shows the resulting load-step
schedule for the 3606 packages. Only
the first-stage VVCP was adjusted. The
second-stage VVCP was kept closed because of the very low volumetric efficiency

on first-stage cylinders if the secondstage VVCP was opened. While all the
VVCPs could be adjusted to some infinitely fractional position, this would
defeat the purpose of a straightforward,
repeatable, and robust load-step schedule.
The next part of the procedure was to
define the suction pressure control set
point. Discharge pressures do vary, al-

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Family Owned Since 1945

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though not to the extent seen in field
(suction) pressure. When discharge pressure changes, the operating envelope and
curves shift, causing the maximum suction
pressure point to shift. Therefore, the optimum suction pressure becomes a function
of discharge pressure and load step.
The goal of this effort was to develop
a procedure to achieve maximum compressor throughput and utilization. The
ideal solution was to determine the optimum suction pressure and load step to
achieve this goal, and then be able to run
the performance model in real time. The
Ariel Performance Program has a feature
called "multi-run," which allows load
steps to be created and the model to be
run over a range of suction and discharge
pressures/speeds. The model output at
each condition and each load step is
written to a comma-separated value (CSV)
file. The CSV file became the heart of
the optimization tool.
Optimization Tool

with roots in the Appalachian Basin
Corporate Office and Main Packaging Facility

330-599-5720

3974 Simon Rd, PO Box 6044 Youngstown, OH 44501 www.dearingcomp.com
76 THE AMERICAN OIL & GAS REPORTER

With the basic procedure defined, a
method was needed to provide operations
staff with the recommended suction pressure set point and load step for maximum
throughput. The solution was to copy the
multi-run CSV file into a spreadsheet
and use a "look-up" logic routine to find
the optimum configuration.
The development process involved
defining a modeling procedure to create
performance databases for each compressor. Using the Ariel software's multi-run
feature, each unique compressor was run
through a wide range of suction and discharge pressures at maximum operating
speed to bracket all foreseeable operating
conditions.
Suction pressure was run in 2-psig increments over a 140-psi spread, while
discharge pressure was run in 20-psig increments over a 400-psi spread. The
actual ranges could be adjusted to match
the compressor's service (low pressurehigh pressure, low pressure-intermediate
pressure, or intermediate pressure-high
pressure), but the range spread and increment was held constant.
This resulted in 1,491 calculated points
for each load step. The multi-run CSV
file contains all calculated unit parameters
American Oil and Gas Reporter - October 2016

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