Cat introduces low-energy fuel natural gas gen-sets

Caterpillar Inc. has introduced two versions of its Cat G3520C natural gas-fueled generator sets designed specifically for applications using low-energy fuels, such as landfill, digester and coal seam gas.

The generator sets include 20-cylinder, electronically controlled, leanburn natural gas engines coupled with two bearing synchronous generators.

The new gen-sets are available in a 60 Hz configuration operating at 1200 rpm and rated at 1.6 MW, with an ISO mechanical efficiency of 41.5% with water pumps and standard N[O.sub.x] emissions rated at 0.5 or 1.0 g/bhp-hr, Cat said.

Also available is a 50 Hz configuration operating at 1500 rpm and rated at 2.0 MW, with ISO mechanical efficiency of 40.6% with water pumps and standard N[O.sub.x] emissions rated at 250 or 500 mg/N[m.sup.3].

Both models have low-pressure fuel systems (0.5 to 5 psi/3.5 to 35 kPa) designed for efficient operation on low-energy fuels and eliminate the need for fuel compressors. The engines are specially designed to account for fuel variability and fuel impurities and thus operate without intensive fuel treatment systems. "These generator sets are designed to enable highly efficient and reliable operation on low-energy fuels, delivering electricity at extremely competitive cost per kWh, with significantly longer overhaul intervals and lower maintenance costs per kwh," said Michael A. Devine, gas product marketing manager for the Electric Power Group of Caterpillar Inc.

For applications in which fuel purity is a concern, a specially designed cooling system elevates jacket water temperature from the traditional 210[degrees]F to 230[degrees]F, helping to prevent condensation on engine components and the formation of acids in the presence of fuel-borne impurities, such as hydrogen sulfide and halogens.

The elevated jacket water temperature in combination with positive crankcase ventilation also limits acid development in the lube oil, further protecting components and helping to extend oil-change intervals. The low-pressure crankcase ventilation system ejects potentially acidic blow by gases and draws in fresh, filtered air.

To further safeguard against fuel-borne corrosive agents, many components in the engine have been designed to resist corrosion. Aftercooler cores are stainless steel, improving service life and performance in landfill applications, Devine said. He added that rear geartrain bushings have also been modified to improve service life. Valve and valve seat angles have been designed to control the formation of silicon deposits.

Other features of the new G3520C low-energy-fuel generator sets include cylinder-by-cylinder detonation sensing. Further, the SCADA-compatible ADEM III digital microprocessor control is designed for automatic regulation of ignition, engine governing and air/fuel ratio, resulting in what Cat said is optimum fuel economy and stringent N[O.sub.x] emissions control. A patent-pending air/fuel ratio control based on charge-air density, is designed to maintain N[O.sub.x] within tight tolerances under most ambient and load conditions.