Diesel engines comprise more than 80 percent of all on-site generation in the United States. But few diesel engine owners probably realize the advantages of converting their engines to use natural gas in combination with diesel fuel. Dual fuel conversion can help manufacturers, hospitals, hotels and other facilities that rely on dependable backup power systems to cope with weather-related disruptions to diesel fuel supplies for their on-site generators. Dual fuel users also avoid the cost and liability of large diesel storage tanks. On top of that, such conversions afford the opportunity for significant utility power savings through peak shaving.
Joe Renner, director of business development for Innovative Technology Group (ITG)’s Dual Fuel branded engines, explains bi-fuel means the ability to burn one fuel or another, whereas dual fuel means the ability to burn both simultaneously in various mixture percentages. “We guarantee a 50-50 mix, but in most cases you’ll get a 60 percent natural gas, 40 percent diesel mix,” he says. “You can run them at 80-20 and some conversion companies advertise that, but there’s a sweet spot where you maximize efficiency for both fuel and engine. This normally occurs below the 80-20 substitution rate.”
ITG’s conversion consists of a very detailed combustion analysis and a customized delivery system. “We analyze the engine and then build a complete customized system to meet the specialized needs of the client, for that engine, and its related operating conditions,” says Renner. “That’s important because two seemingly identical engines off the same assembly line will show different operating characteristics. Although several providers offer conversions, they do not offer in-depth combustion analysis, control methodologies or individualized customer service.”
The system uses an exclusive technology, known as Controlled Gas Release Combustion. The system mixes natural gas with air before it is drawn into the engine, where it combusts just like ordinary diesel fuel.
Shown atop this diesel engine is the Dual Fuel conversion system’s gas train that leads to the diffuser in the air intake. Photo courtesy of ITG.
The other key component is the programmable load control (PLC). “We use input sensors on the engine and exhaust gas temperatures,” he says. “We monitor everything we can around and on that engine and are the only ones that evaluate the system itself from a fuel dynamics and system dynamics standpoint before we do the conversion so we know how to set it up for maximum benefit.”
The system uses ITG’s eNRGy Pac PLC Controls System, which allows operators to either run the engine on the optimum mix of diesel and natural gas or choose 100 percent diesel. It also allows engines to operate at full horsepower and at their normal temperature and enables manufacturers’ warranties on original diesel engines to remain completely in effect. Among other advantages, the system lowers operating cost by extending the interval between oil changes up to three times longer with proper oil analysis control and, because natural gas is a cleaner burning fuel than diesel, conversion can help meet clean air regulations without expensive pollution control equipment.
Renner says that a 300 kW diesel engine costs about $9,000 to $12,000 to convert. “If you have a diesel engine and have to add more storage versus the cost of conversion, the cost of conversion will always be less than half,” he says. “And typically getting the gas to it won’t be that big of an issue because everyone has gas delivery somewhere to the building.”
He explains that the conversion is not intrusive to the engine. “We’re not opening the engine up or doing anything to it. So after the conversion, if a cylinder is supposed to run at a specific temperature, it will continue to run at that temperature after the conversion. If there is a failure and something goes outside the engine manufacturer’s spec, the first thing that happens is the PLC shuts the natural gas down. So the natural gas is not causing any issues with the engine at all.”
Renner cites the hospital sector as a customer segment that can benefit from dual fuel conversions. “Hospitals have a significant amount of backup power, but most of their load is not connected to it – only critical life support and other essentials. But with all the hurricanes and extended power outages, the health care facilities are discovering they need to be able to run longer and may even need backup for less critical equipment. And storage becomes a problem with diesel.”
ITG is currently finishing a project in Manhattan based on two Caterpillar 3516 engines and one Caterpillar 3512. The engines are located on a terrace on the 38th floor of an office building, meaning they have issues related to fuel storage, emissions and the high cost of power in New York. The client has an opportunity, even with the high cost of diesel and natural gas, to recognize savings through peak shaving arrangements.
“Not only do these conversions reduce fuel costs in general, but they facilitate peak shaving,” says Renner. “At the time of day when electricity rates are at their peak, facilities can make their own power and save 10 to 30 percent on their utility bills.” p