Natural gas transporter and distributor Distrigaz NV, Brussels, has installed a fifth compressor at its Loenhout mixing plant and underground natural-gas storage site that is powered directly by a diesel engine, eliminating the need for a diesel generating set.
The compressor joins four others whose function is feed air to a membrane air separation unit at 28 bara. The membrane unit vents the oxygen, and the remaining nitrogen is boosted to 80 bara and routed and route the nitrogen for blending with high-calorific natural gas to produce lower calorific gas suitable for residential use during peak-demand winter months.
Supplier Atlas Copco Comptec, New York, and Atlas Copco Energas, Cologne, determined that the new compressor could be powered directly by a diesel-driven engine, eliminating the need for a generating set and thereby reducing capital costs by 50% and lowering power losses.
Meeting demand
To satisfy its legal requirement in meeting consumer demand when temperatures drop below 0° C., Distrigaz' Atlas Copco H-type centrifugal compressors operate at 28 bara (406 psia) to initiate separation of air.
With a flow rate of 9,330 cu m/hr, the H compressors' take air from 1 bara to 28.4 bara. A two-stage air filter eliminates any particles being fed into the high-speed compressors.
Dryers remove any humidity from the compressors' output before passing the air through a membrane unit for further separation.
Here, oxygen mix is vented into the atmosphere. The remaining 50%, pure nitrogen, passes through single-stage reciprocating compressors to ensure a pressure of 80 bara at 100 % nitrogen.
First motor-driven compressor
Atlas Copco says that, as a rural location, Loenhout has only a minimal main power supply, with each of the existing four H-type compressors being powered by a diesel generating set.
Expansion of the system and experience gained by the company proved that the new fifth compressor could be powered directly by a diesel-driven engine, eliminating the need for a generating set and thereby reducing capital costs by some 50% and reducing power losses.
A Caterpillar 16-cylinder 35 Series BTA diesel engine rated 2,374 hp (1,771 kw) at 1,800 rpm was therefore specified. The company says this is the first of its compressors in Europe to be directly powered by a diesel motor.
An electronic injection system is fitted to the engine to minimize emissions. To enhance the installation's environmental features further, it is housed in an acoustic enclosure.
The new installation included a cooling tower and pump unit to recirculate cooling water.
An Atlas Copco Sequential Control System has been fitted automatically to determine start-up operation and sequence of the five units in two steps.
Sequence generally designates electrical motor-driven Units 1 and 2 to start, followed by the new unit and one other electrical-driven unit, with the remaining unit providing standby back-up.
Each compressor driven at 3,000 rpm features an integral speed increasing gear. Supplied as a four-stage H-type compressor, Stages 1 and 2 operate at 23,407 rpm and Stages 3 and 4 at 40,106 rpm.
The latest compressor was installed in August 1999 and was on-line by November to meet winter demand.
