American Oil and Gas Reporter - October 2016 - 77

(169 parameters for a four-throw unit)
for every operating point. Needless to
say, this results in a very large database.
The three primary parameters of power,
throughput, and compressor warning
codes were extracted from the CSV file
and written into tables. Finally, the tables
were combined for the solution look-up.
Since this process was applied to a wide
variety of compressors with unique configurations, a Microsoft® Access™ database was incorporated to store the various
unit model tables.
The Access file also contains several
constants for each unique compressor
and tag names, and data paths for both
input and output parameters in the
CygNet™ supervisory control and data
acquisition software. The constants required for determining the solution are
rated driver power, rated driver speed,
auxiliary power, station pressure drop,
and limits of the pressure ranges used
for each unique compressor database.
Input parameters from CygNet are
unit suction pressure, unit discharge pressure, field pressure, current load step,
and actual driver load. Output parameters
are read from the spreadsheet and passed
back to CygNet, and include throughput
at current condition, throughput at optimized condition, optimized load step,
and optimized suction pressure. Several
additional output parameters are passed
through the Access file to enhance the
presentation of recommendations.
Facilitating Changes
The Access file contains all the variables and model tables for the various

compressors, and also has adjustable settings to facilitate changes. This allows
the spreadsheet to remain unchanged if
compressors are added, deleted or modified. The spreadsheet has a macro programmed to read the data path from the
Access file and read/write data from/to
CygNet. Once the input data and database
are written to the spreadsheet, calculations
initiate to both look up data at the current
configuration and solve for the optimal
condition (i.e., maximum throughput).
One key to this logic is that it will not
solve for an unsafe condition by reading
the site-rated power and warning codes
from the Ariel Performance Program incorporated into the database. Another key
that differentiates this method is that it
calculates the maximum available suction
pressure to use in the look-up. Once the
spreadsheet completes the tasks for one
compressor and passes the results to
CygNet, the process repeats for the next
compressor on the list.
To reduce time to complete the process,
all like-kind compressors use the same
model table, and a new table is not written
until a unit with a new compressor configuration is read. The Access file is set
up to easily differentiate like-kind compressors and associated tables.
The final piece of the optimization
tool is a screen developed in CygNet to
allow operations personnel to easily and
visually monitor the compressor fleet. It
contains several parameters, but the primary ones are compressor utilization (the
main parameter to gauge optimization of
each compressor), recommended load
step, and recommended suction pressure.

FIGURE 4
Wattenberg Compressor Utilization Screen

OCTOBER 2016 77

American Oil and Gas Reporter - October 2016

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