Navistar's "State Of The Art" Cogeneration Plant
Navistar International Transportation Company's cogeneration facility
in Melrose Park, IL came on line in 1995 and has already demonstrated
the excellent ability of a reciprocating engine cogeneration plant
to operate reliably on a time-of-day basis. The MCA meeting on
September 20, 1995 provided a tour of the facility.
The cogeneration facility was designed by Midwesco Mechanical
and Energy, a division of Midwesco Inc., located in Niles, IL.
Midwesco also acted as construction managers for the project.
The facility consists of twelve (12) Caterpillar, natural gas
fueled, stoichiometric, turbocharged 1200 RPM engine generator
sets producing power at 4,160 V, three phase, 60 HZ. All of the
engines are equipped with catalytic converters for NOx and CO
control. Each engine-generator produces approximately 770 kW;
total capacity of the installation is therefore 9,240 kW. This
installation is one of the larger reciprocating engine projects
in ComEd's territory. Power is interconnected at both 13,800 V
and 4,160 V to the Navistar ring bus and low voltage network power
distribution systems. There are two (2) Plan C interconnects to
ComEd; both include direct transfer trip.
Six of the twelve engines are equipped with heat recovery on the
engine exhaust, enabling the plant to produce 30 psig saturated
steam. The steam supplants or augments steam which would otherwise
have been produced by Navistar's natural gas fired boilers.
The facility is designed for a minimum useful life of 30 years.
It was constructed in a corner of the existing Navistar plant.
The existing floor was completely removed and replaced to provide
the space for the new foundations and enable electrical conduit
to be placed beneath the floor level. Foundations were provided
with special vibration attenuating features so that vibration
is not transferred to nearby sensitive machinery. New interior
walls were provided with sound attenuating masonry block construction.
The engine-generator room is equipped with a balanced ventilation
system including both powered intake and exhaust fans. Intake
fans are equipped with silencers. Also included in the engine
generator room are the catalytic convertors, engine exhaust mufflers,
engine start batteries (2 engines per battery set), heat recovery
boilers, engine heat exchangers, cooling tower water treatment
systems, cooling tower water pumps, various motor control centers
and a 4160 V to 480 V transformer to provide power for the facility
and thereby enable black starts. A separate air compressor system
is also supplied for black start capability. A centralized lube
oil supply and used oil discharge system to facilitate engine
oil changes is also included.
The control room is air conditioned and is elevated to facilitate
viewing the engine room through safety windows equipped with fire
shutters. Control cable enters from both the engine room and switchgear
room via a below control room cable spreading area. Included in
the control room are the computers/CRT's and the control system.
Included in the switchgear room (also air conditioned) are the
generator 4,160 V switchgear, 125 VDC batteries required for the
switchgear and UPS system required for the controls.
Just outside the facility a two (2) cell cooling tower installed
10' above grade, and two (2) 4,160 V to 13,800 kV transformers
for step up (or down) purposes.
The control system allows digital computers to directly control
operation of the governors on each engine so as to meet Navistar's
desired operating scheme. For example, Navistar can choose which
engines to operate and whether each such engine operates in isochronous
load following, base loaded, droop, or auto modes. These choices
allow fuel consumption and emissions to be minimized (by running
most of the engines at full load and taking the swings with the
remaining engines) and also allows the engines to be sequenced
for maintenance reasons. It also allows a minimum of power to
be interchanged to/from ComEd (ComEd's Rider 4 does not provide
economic benefit to export power).
The control system consists of the following:
A Woodward Master Synchronizer and Load Controller (MSLC) and
twelve (12) Digital Sychronizer and Load Controllers (DSLC's).
Six (6) Modicon "Brick" Programmable Logic Controller's
(PLC's), each controlling
Two (2) engines.
Two (2) Modicon 984 PLC's (one in hot backup) for supervisory
control of common systems and performing backup to the MSLC load
control functions.
Two (2) IBM compatible PC's for man-machine interface, supported
by two (2) Modbus Plus and one Echelon 1.25 M baud communication
network for communications and display.
In addition, local hardware manual override of most functions
is included.
The control system provided was the first in the Chicago area
to use the Woodward DSLC/MSLC digital control system. This system
allows load and vars to be digitally controlled and monitored.
This eliminates the need for cross-current CT's, rheostats, dropping
resistors, etc. (which have remained virtually unchanged since
the 1890 exposition first demonstrated AC electricity).
The Factory Link man-machine interface uses more than twenty "screens"
to observe operating parameters. For example, each engine can
be viewed to observe metered fuel consumption, kW, rpm, various
temperatures, pressures and flows. A separate screen views operation
of the cooling tower systems while another displays operating
parameters for the boiler heat recovery system. Finally, overall
screens show the power distribution, electrical interconnection
status and electrical pro-duction summaries and maintenance logs.
Trending is provided for many of the parameters monitored.
How has it worked so far? In a word-"Beautifully".
About the author: David A. Miller is Vice President, Midwesco
Company Inc., Niles, IL.
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