A package that converts diesel truck engines to dual fuel power units that run primarily on natural gas may have dramatic potential for the stationary gen-set market as well. Clean Air Partners, Inc. (CAP) has already retrofitted 1,500 heavy-duty trucks with the system, which converts diesel engines to run on a blend of diesel and compressed or liquid natural gas, thereby producing substantially less nitrous oxide and particulates than engines burning diesel alone and without sacrificing diesel-like performance. Using only a small amount of diesel fuel as an ignition starter, the modified diesel engines produce equivalent horsepower and torque, while burning mostly natural gas. The company is also currently developing propane as an alternate second fuel source.
In partnership with Caterpillar’s truck engine division, CAP has developed and sells Caterpillar dual-fuel systems for electronically controlled truck engines. Because stationary gen-sets operate at a constant speed, the distributed generation application is simpler to control for optimum efficiency and emissions. The cost to convert a typical standby gen-set to make it meet 2 gram NOx/HP-hr levels is about $100/kW.
A conventional Caterpillar 3412 600 kW standby gen-set can be converted to dual fuel use for about $100/kW. Photo courtesy of Clean Air Partners.
“The process offers distinct advantages when applied to stationary distributed generation installations,” says Daniel Kabel, CAP’s CEO. “While the CAP system is based on the principle of its patented pilot diesel injection, it does not require ultra-high injection pressure, which translates into fewer maintenance requirements and higher overall operating efficiency.”
Kabel says that for DG applications, the CAP system provides a relatively inexpensive way to retrofit an existing standby diesel powered generator and turn it into one that could be used for peak shaving. No change to the diesel engine heads, pistons, or injectors is required. It can also be deployed as a new prime-power dual-fuel gen-set, that can run in 100 percent diesel mode, when natural gas is unavailable.
The system provides near diesel efficiency and power output allowing a lower capital investment than is required with an equivalent spark-gas engine gen-set. With no spark plugs required, operation and maintenance costs are lower also. The proprietary control system maintains close control of all of the engine’s critical combustion parameters, enabling it to always use the leanest fuel mixture possible and allowing maximum substitution of natural gas for diesel fuel and minimal emissions.
Most current emissions requirements limit a reciprocating gen-set to 2 gram/HP-hr of NOx. “All CAP systems meet this level without after-treatment,” says Kabel. The Southern California Coastal District and East Texas both have more stringent requirements than the rest of the country. All reciprocating gen-sets in those locations are required to use after-treatment on the gases they emit to ensure that requirements are met. Kabel foresees that the rest of the U.S., and other developed countries, will eventually move to similar, more stringent requirements.
“CAP knows how to obtain low emissions levels without after-treatment, and is currently developing systems based on this know-how,” says Kabel. “Even at this time, in strict emission areas such as Atlanta, Chicago, Dallas and New York, CAP can retrofit a standby diesel gen-set using its lowest technology system, and run the gen-set as a peak shaver for five times longer than it would be allowed to run as a diesel-only standby unit.”
That’s significant, he says, because standby gen-sets are an under-utilized asset. “If turning these idle assets into peak shavers is relatively inexpensive, doing so can make them very valuable when high peak electricity usage rate adjustments occur, such as in the summertime.”
CAP is presently arranging beta test sites to demonstrate the performance of its dual-fuel solutions for DG. Those sites are scheduled to become operational this year.