MeeFog Boosts Power Output by 15% at Sahara Power Station | APR Energy Case Study

The Installation

APR Energy began operations in 2004, when cofounders John Campion and Laurence Anderson purchased the Alstom Power Rentals subsidiary of Paris-based Alstom Power, Inc. APR provides large-scale, fast-track solutions to provide seasonal peak capacity or for bridging power during new plant construction. In the spring of 2013, anticipating high summer peak demand exceeding available generation capacity, GECOL and Libya’s Ministry of Electricity and Renewable Energy contracted with APR to provide mobile gas turbines at four key sites, with a total of 250 MW. Then in June, when other vendors had failed to deliver, APR agreed to provide GECOL with an additional 200MW of diesel generators at two sites.

One of the locations chosen was Samnu. 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 5°C (40°F), the output drops below 20 MW at 45°C (113 °F), a typical summer temperature. Over 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 is essential to use inlet cooling on those turbines. The problem was the lack of water. While the FT8s do come with water injection, because of the lack of water in the area, APR decided to use MeeFog inlet cooling systems.

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 demin water system and its associated filters and mixed beds.

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 and to communicate to the DCS how much water is being injected. The PLC then computes, based on ambient conditions and air volume, how many of the 14 fogging stages can be turned on without exceeding the set points. To control the MeeFog system, the user inputs the desired amount of overcooling or undercooling as compared to saturation. Set points over 100% will result in the fog system injecting more water into the air stream than can actually be evaporated at the current ambient conditions. The excess water droplets (called overspray) are carried by the air stream into the compressor section where the heat of compression causes them to evaporate and further augment the power output.