CAPS Australia customised a diesel-powered portable back-up air compressor for the highly specialised and hazardous environment of an Australian refinery client to maintain plant operation when electricity failed.
When Compressed Air and Power Services (CAPS) Australia won a contract to supply a back-up air compressor for an Australian refinery, their team recognised the challenges that the very specific requirements would pose. Not only would the Airman PDSE-900-4B1 portable air compressor require significant customisation, it must also be delivered in a very short timeframe. Just eight weeks elapsed between winning the contract and commissioning the modified unit on site.
The client’s existing backup air-compressor was ageing and in need of replacement. As all of their primary fixed air compressors were electrically driven, the refinery was at risk of incurring significant financial losses in the event of power failure. Beau Simon, State Business Development Manager – Portable Product (Queensland) selected the portable Airman model both for its diesel engine and good performance in a similar situation at another refinery customer site.
The compressor supplied is usually sold as a transportable unit. The first challenge was to make it a stationary system. The compressor’s wheels and axles were removed and replaced with a custom-built galvanised skid mounting and roof structure. The construction of the new mounting arrangement was outsourced to local company Extreme Pipe Welding and the final fitting was performed by CAPS Australia.
"As the compressor was to be installed in a fixed position for its entire working life, the wheels would eventually deteriorate and go flat. Galvanising of the skid was required to eliminate any possibility of rust," Simon said.
However, once fitted, the roof structure caused an issue in the operation of the compressor. According to Simon, the compressor’s exhaust fumes were hitting the roof and recirculating through the system. The problem was resolved by extending the exhaust pipe through a hole in the roof structure to remove the fumes completely.
In the event of a primary power failure a requirement was for the compressor to startup immediately at full load to allow refinery operations to continue until mains electrical power was restored.
"The compressor was setup to automatically start as soon as the refinery plant pressure dropped to 55 kPa. Once the refinery’s electrical air compressors started up again, the backup compressor was configured to automatically shut down at 680 kPa," Simon said.
This requirement presented several challenges. In order for the compressor’s diesel engine to start under full-load without a warming-up period, the engine’s glow-plug needed to be kept warm so that the diesel engine was not damaged. This warming needed to be independent of primary electrical power. The automatic detection of start-up and shut-down pressures required an electronic controller which would work in with the compressor’s existing controller. The solution involved installation of an off-the-shelf electronic controller sourced from an auto-electrician. This controller maintains operation of the whole system, from safety devices to auto-restart operation and maintenance of charge to the compressor. The controller is powered by an independent 12-volt battery power supply.
Another challenge was keeping the system’s independent power supply constantly charged so that it was always ready for emergency operation. This was achieved with a DC trickle charger connected to the main 240 volt AC power supply of the refinery. The charger converts mains power to 24 volt and 12 volt DC current to supply power to the heater and all other electrical system components on the back-up compressor.
"When the compressor starts up the trickle charger automatically stops charging and the compressor’s engine alternator takes over to maintain charge while machine is in operation," Simon explained.
"If the machine is there for three to six months the battery will go flat, so the trickle charger maintains power so that emergency startup is guaranteed."
To ensure the safety of maintainers working on the compressor system, Simon also installed an off-the-shelf battery isolator which cuts off all sources of power when required. The pre-heating of the compressor’s diesel engine was achieved by installing a heater block powered by the trickle charger. Simon needed to speak to several suppliers before he found an Australian dealer who stocked a heater that would work with the air compressor’s Mitsubishi engine.
The refinery environment presented several unique challenges, all of which required further customisation by Simon and his team. Due to the risk of a hydrocarbon leak, the customer required that the system include an electronic gas sensor at the compressor’s air intake and electronic shut-off valve to ensure that the compressor’s diesel engine did not continue to operate at high levels of hydrocarbon concentration.
This can be a risk in refinery environments due to the possibility of a diesel engine experiencing runaway operation when the hydrocarbon at the air intake provides an external fuel source and prevents operators from shutting the engine down using conventional methods such as turning off the ignition switch, shutting off the solenoid or disengaging the engine’s load. The consequences of runaway diesel engine operation vary in seriousness from minor engine damage to engine explosion. A sensor was sourced from Prodetect—a company that had supplied a number of other sensors to the site—and this was connected to a Chelwyn engine intake shut off valve.
"This was a whole new thing for us," noted Simon.
"At twenty per cent hydrocarbon concentration, the sensor sends an alarm to the refinery control panel, but the compressor’s engine keeps running. At fifty per cent concentration, the sensor sends a signal to the shut off valve, which closes the inlet valve to the compressor’s combustion engine, choking the engine and shutting it down."
Extra modifications were required to protect the other equipment in the refinery plant from moisture and aerosols in the compressor’s exhaust. The compressor outlet is connected to a moisture separator which uses a centrifuge to settle all moisture droplets to the bottom of the separator. They are then automatically drained. The exhaust is then passed through a pre-filter to remove aerosols. This is then processed by the refinery’s on-site protection: an after-cooler and refrigerator dryer that remove all water from the customer’s plant air system.
Commissioning of the backup compressor system did not end CAPS Australia’s commitment to its customer. A follow-up visit was arranged to install a replacement pressure transducer in the automatic electronic controller so that the refinery’s required pressure tolerances were met.
"The existing pressure transducer had a shut-off range of 550 to 780 kPa, but the customer needed a tolerance of 550 to 680 kPa," Simon stated.
CAPS Australia’s commitment to put in the extra time and effort required to meet the needs of their customer has achieved positive results for supplier and customer alike.
"The customer is really happy," said Simon. "The system is operating exactly as required in the specification."