Rolls-Royce is continually investigating means to reduce fossil fuel emissions. The RB211 utilises Dry Low Emissions (DLE) combustion technology. DLE technology guarantees NOx and CO levels less than 25 vppm. DLE technology offers no compromise in performance or reliability. Rolls-Royce DLE technology has amassed over 2 million hours.

DLE development
The conversion of fossil fuels into energy and power and the resulting effects on the environment are of concern to everyone; business, governments and the public. This growing global ecological concern has seen ever-more stringent legislation introduced to control the emissions from gas turbine driven equipment.

As willing participants in the quest for a greener earth, Rolls-Royce has invested over £90 million in DLE development since the programme began in 1989. As the name suggests, this dry solution to nitrous oxide (NOx) and carbon monoxide (CO) production is achieved without the injection of either water or steam. Significantly, not only can the system be fitted to new GenSets but also retrofitted to existing units with years of operational life still remaining.

The RB211 became the world's first DLE gas turbine by pioneering technology which maintained combustion temperature within a narrow band.

This was achieved by developing three processes:

1. premix leanburn combustion controls the combustion temperature
2. fuel staging allows turndown over the load and ambient temperature range without flaming out
3. series fuel staging provides flexible operation with a wide stability range and separate combustion zones

The benefits

• 25 vppm Nox and CO simultaneously
• No effect on performance
• Retrofit capability for mature units
• Proven starting reliability
• Stable low power operation

Following a development programme started in 1989, the first retrofit RB211 DLE was delivered to Pacific Gas Transmission (PGT) in 1994. Within 4 months of arrival at Station 7 in Starbuck, Washington state, the unit entered full commercial gas transmission duty on the expanded PGT pipeline.

Stations 3 and 5 were also soon to benefit from DLE technology as guaranteed emissions levels were consistently demonstrated across the full operating profile. With a fourth unit being added to their fleet, PGT's total DLE experience is now approaching 100,000 hours. Many orders for other gas transmission units followed before ERTISA of Spain chose the DLE RB211 for cogeneration duty at its refinery in Huelva.