This article by JASC was recently featured in the Combined Cycle Journal, Number 53, Second Quarter. Read the article below or right click to download it here.
Reliable operation of dual-fuel gas turbines on oil demands that owner/operators protect against coking of oil in fuel-system valves and piping. Active cooling is one solution available to users for assuring both reliable starts on liquid fuel and reliable fuel transfers from gas to oil.
“Cool valves, piping improve engine reliability when called to burn oil,” CCJ 1Q/2016 (p 69) and available at www.ccj-online.com (type headline into the search-function box), discusses several cooling options offered by JASC. One of these, the so-called “thermal clamp,” was introduced as that article was in preparation.
Early results available from the first commercial installation (Fig 1, before; Figs 2 and 3, after point to success both in protecting against coking and eliminating the need for “verification” firing of oil monthly to confirm liquid-fuel system reliability.
JASC’s (Tempe, Ariz) Schuyler McElrath told the editors, “With our latest system configuration consisting of rerouting fuel piping, incorporation of heat-sink clamps to keep fuel lines cool, water-cooled fuel controls, and component connections which don’t use O-rings, we are now offering the capability of running on liquid fuel at semi-annual intervals, or longer, without sacrificing back-up liquid-fuel system reliability.
“In the first test of this latest configuration, the second of two 7F gas turbines operated on liquid fuel during commissioning of the fuel-system upgrade in April 2016. The site operated exclusively on natural gas over the next nine months, burning oil only during the second week of January 2017. The next run on liquid fuel was in July 2017. Both times, the turbines started and operated on liquid fuel without incident.”
Thus the two-unit site burned liquid fuel successfully twice in the 15-month period ending in July. The typical site needing to confirm oil firing capability on two units would have paid approximately $60,000 each month the test was conducted. Thus, not having to run tests for 13 of the 15 months since the upgrade was completed saved more than three-quarters of a million dollars.
Based on this success, the owners of other sites currently are upgrading the fuel systems on some of their 7FA engines. These particular upgrades present a variation on the original concept in that they will be using JASC water-cooled 3-way purge valves to replace either standard 3-way purge valves or check-valve and purge-air valve configurations. Piping modifications highlighted here will be incorporated.