Proper distillate storage, cleanliness, delivery to the burner tip critical to starting reliability

The industry’s on-again/off-again affair with liquid fuels is on again. Not too long ago, very few owner/operators of merchant plants in the Lower 48 powered by gas turbines would have considered burning distillate in gas turbines, except in an emergency. One outcome: Some dual-fuel units were converted to gas-only to (1) simplify maintenance/overhaul, (2) avoid having to deal with distillate prices in the stratosphere, (3) eliminate the fouling of oxidation and SCR catalysts that occurred when oil was burned, (4) soothe headaches associated with maintaining fuel quality in large onsite storage tanks, (5) avoid coking of liquid fuel systems when on standby, etc.

The phrase “never say ‘never’” certainly applies here: Oil prices have dropped precipitously over the last year or so, gas availability has been sporadic in some areas—such as New England in winter, and government-controlled regional grids have a scissor-lock hold on the balance sheets of many generators. These are some of the reasons users are rethinking the value of dual-fuel capability. Regarding the grid’s influence on decision-making, bear in mind it would be difficult for a plant get an ancillary-services contract for emergency or black-start power today without the ability to burn liquid fuel. Given the marginal profitability of the bulk-power business, ancillary-services revenue is critical for many facilities.

Vendorama. One thing the steering committee for the 501F Users Group may do better than others in the industry is to invite technical presentations from a wide variety of product/services providers at the annual meeting because, for F-class combined-cycle owner/operators especially, there’s a lot more in the plant to keep current on than the basic engine. The so-called Vendorama Program, organized for the 2015 meeting at the Westin Savannah Harbor, February 23-27, by 501F Chair Russ Snyder, 501G Chair Steve Bates, and their respective committees, hosted 42 half-hour presentations arranged in seven time slots, each with six presentations conducted in parallel.

JASC’s ZEE system. Two presentations concerned liquid fuel and both had a significant number of owner/operators participating. JASC’s Schuyler McElrath brought attendees up to date on the company’s ZEE system (for Zero Emissions Equipment) which allows users to verify the operational readiness of their gas turbines for liquid-fuel firing without actually burning any distillate. Because grids offer little or no sympathy for failed starts, it behooves owner/operators to exercise their fuel systems regularly. The ability to do this emissions-free and without the possibility of coking oil that might remain in supply lines and valves—despite best efforts to the contrary—is a big plus, McElrath told the group.

ZEE is based on existing, proven components engineered to operate in demanding environments, the fuel-system expert continued. A dedicated instrumentation and data acquisition system controls ZEE activity, alarms, and historical performance data. Limited communication with the turbine controller allows its use with both OEM and aftermarket control systems.

Velcon, today Parker Velcon, like JASC, was a pioneer and leader in the aviation business before migrating to power generation and other industries. Parker Velcon is well respected for its technology focus on maintaining fuel cleanliness to the level required. While most of the references in the presentation pointed to large diesels used in transportation and mining, that was not a negative. The same cleanliness rules apply as well to gas turbines, with particulates and water the biggest culprits.

When offloading distillate from a barge, in particular, plant personnel really don’t know what they are putting in their storage tank. A sample drawn may be representative or not, despite the care taken. Given, too, that oil may remain in a vented steel tank for years there are more unknowns than knowns about the distillate oil you expect to feed your turbine without incident.

The speaker spent some time explaining ISO 4406, the cleanliness standard specified for distillate. Most in the room were familiar with the standard because it also is used in lube-oil analysis. The value of particle-count analyzers were part of the presentation, too. Some attendees were familiar with like equipment used to determine iron transport in condensate/feedwater circuits.

The final part of the Parker Velcon presentation described the type of equipment available for removing undissolved particles and water from oil forwarded from the storage tank. To dig deeper, the company offers several worthwhile documents on its website. A white paper available at the Parker Velcon booth on the exhibition floor, “Guidelines for Fuel Handling,” also offered useful information, and can be downloaded here with a name and email address.

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