Back-pressure steam turbines reduce Princeton’s carbon footprint by 1,200 pounds annually.


In 2008, Princeton University developed a sustainability plan to reduce its carbon dioxide emissions to 1990 levels by the year 2020. To ensure emission reductions and economic goals are met, the university needed to measure and document energy, carbon dioxide, and life-cycle cost performance of each project.

Energy plant manager Ted Borer, who is involved with the university’s sustainability efforts, sought methods to improve energy performance and implement projects that use alternative fuel sources, upgraded controls, heat recovery, cogeneration, and improvements to existing HVAC systems. One idea considered was to produce power from the energy consumed by pressure reduction in the campus steam distribution system using back-pressure steam turbines.

“I first saw Carrier’s Microsteam power system at the International District Energy Association (IDEA) meeting,” said Borer. “The opportunities for large campuses that have existing steam pressure reduction points were immediately evident.”

USING STEAM FOR ELECTRICITY

The university’s facilities engineering department hired Carrier Corporation’s Dome-Tech business, an energy engineering firm that specializes in energy optimization studies to analyze various solutions on the market. Kevin McCarthy, manager, of Dome-Tech’s Energy Advisors group, considered both conventional horizontal steam turbines and the Carrier vertical shaft solution. The Microsteam power system by Carrier was ultimately recommended for several reasons.

“First, the Carrier arrangement had superior turn-down capability, which provides better low load performance, while providing ample generating capacity for high steam flows,” said McCarthy. “Another key consideration was obtaining a rebate through New Jersey’s Clean Energy Program. The rebate program is a competitive selection process and project distinctiveness is as important a factor as energy use and emission reduction. Carrier’s cutting edge technology had a better chance of receiving a rebate than a conventional turbine.”

Carrier sales engineers worked with Borer and McCarthy to develop the project around two Microsteam units with back-pressure turbines. The turbines operate in parallel and are able to provide 550 kW at peak. The turbines use a steam inlet pressure that varies between 180 psig to 220 psig. They are anticipated to produce 4 million kWh annually for the university.

When steam pressure is stepped down through a pressure reducing valve (PRV), the exiting low-pressure steam essentially has the same energy content as the high-pressure steam. Steam with this type of excess energy is called superheated steam. The radial-flow Microsteam turbine takes this superheat and converts it to power, generating up to 275 kW of electricity per unit.

REDUCED CARBON FOOTPRINT

Borer commented on the Microsteam turbine’s design and engineering, “The Microsteam has a small footprint, which allowed us to fit it through a standard doorway and use a regular elevator. The unit was pre-engineered and pre-packaged, allowing us to quickly fit it with our existing plant.”

Analyses performed by the university and Dome-Tech expect the turbines to reduce the plant’s greenhouse gas emissions by over 1,200 tons of carbon dioxide annually. ES