With a population of six million, Libya sits on 48 billion barrels of oil and 55 trillion cubic feet of natural gas reserves. Though 80% of the country's GDP and 99% of its government income derive from the energy sector, little of this money found its way into setting up a reliable domestic power grid.
When rolling blackouts became commonplace, General Electric Company of Libya (GECOL) started rebuilding the electrical infrastructure to not only meet current demands but provide a stronger foundation for future economic growth. Rather than waiting for years to plan, build and commission new power plants, GECOL contracted with APR Energy to bring in temporary generators to provide a rapid 450 MW boost. Some of these units were equipped with inlet fogging systems, attaining a 15% increase in output in the hot Sahara operating conditions.
APR provides large-scale, fast-track solutions to provide seasonal peak capacity or for bridging power during new plant construction. Its shipping container-based fleet amounts to 1.2 GW, and includes dual-fuel gas turbines, diesel reciprocating generators and natural gas reciprocating generators. APR provided mobile gas turbines at four key sites in Libya (250 MW) as well as 200 MW of diesel generators at two sites.
Challenges during installation included having to deal with attacks from armed groups, kidnapping of engineers, remote locations, extremely high temperatures, sand storms and lack of water. Despite all the challenges, APR managed to survey twelve sites, select the six that were used, ship or fly in the containers, truck them to their destinations, build crew quarters, install and commission all the equipment, and train more than 80 GECOL staff on maintenance and operations of the turbines and diesel units. The final units came on line within five months of signing the initial contract.
Desert fogging
One of the desert locations chosen was Samnu, where it rains less than 1/2" per year. Afternoon temperatures in Samnu average over 90°F for more than half the year, and over 100°F from June through September.
APR selected Pratt and Whitney FT8 MobilePac gas turbine packages for the site. While the gas fueled, water injected FT8s can generate more than 24 MW at 40°F, the output drops below 20 MW at 113 °F, a typical summer temperature. 0ver that same temperature range, the heat rate rises from 10,000 kJ/kWh to nearly 11,000 kJ/kWh.
Given the output and efficiency losses with high ambient temperatures, it was essential to add inlet cooling to those turbines. The problem was the lack of water. While the FT8s do come with water injection, due to the lack of water in the area APR decided to use inlet fogging systems from Mee Industries.
"APR Operations observed that MeeFog could provide the equivalent amount of power boost as the water injection system while consuming almost half the amount of make-up water," says Michaud. "The quantity of water saved by not running the water injection system while maintaining the required power boost will significantly increase the overall life-cycle of the demineralized water system."
For the Samnu power station, there was a dedicated fog pump skid for each turbine. Each skid has three pumps and two motorized ball valves. These pumps are operated in a sequence that provides fourteen stages of fog output each with 24 operating nozzles. A weather station monitors the temperature and relative humidity and sends this data to a programmable logic controller (PLC). The PLC also connects to the turbines distributed control system (DCS) to receive data on the inlet air volume. The PLC computes, based on ambient conditions and air volume, how many of the 14 fogging stages can be turned on without exceeding the set points.
At Samnu, the fogging system was designed for an ambient dry bulb temperature of 113° F and a wet bulb temperature of 68°F, a difference of 45 °F. The 14 stages could each provide 3.5 °F of cooling, so the entire system can provide the desired 45 °F of cooling, plus one stage of overspray.
"Depending on ambient conditions, the fogging systems can run 100% of the time to maintain the desired increase in output," explainsed Tom Michaud, project manager for APR Energy. "By using the MeeFog system, APR experienced a power boost of approximately 3 to 4 MW per turbine."