Hydrogen Cools Nicely, however Security is Essential

By Nancy Spring, Senior Editor

Working an electrical energy generator produces giant quantities of warmth that should be eliminated to take care of effectivity. Air, water and oil have all been used for cooling. However hydrogen’s low density, excessive particular warmth and thermal conductivity make it a superior coolant for this utility. Plus, it’s plentiful and due to this fact comparatively cheap.

The issue is, hydrogen may be harmful. In its pure state, hydrogen is okay, however a mix of air and hydrogen may be explosive. So why hydrogen?

Steve Kilmartin, director of merchandise and markets for Atmosphere One Corp.’s utility programs enterprise, has requested himself the identical query. The writer of quite a few papers on generator monitoring and upkeep, together with co-authoring the Electrical Energy Analysis Institute’s “Turbine-Generator Auxiliary Methods, Quantity 3: Generator Hydrogen System Upkeep Information,” Kilmartin mentioned one of many questions he requested when he first obtained into the enterprise was “who got here up with this concept? He needed to be a madman.”

However hydrogen is an efficient strategy to cool the generator and permits energy plant operators to get much more megawatts out of a smaller generator.

In line with John Speranza, vice chairman, hydrogen product gross sales, Proton Vitality Methods, virtually 70 % of all electrical energy turbines over 60 MW worldwide use hydrogen cooling. And there are two methods to fill the generator’s hydrogen demand: have it delivered in cylinders or make it on web site.

“Hydrogen fuel stock turns into the chief security concern due to the potential power in hydrogen,” mentioned Speranza.

For instance, Speranza mentioned an ordinary transportable cylinder full of hydrogen at 2,400 psig is equal to 35 kilos of TNT by way of explosion potential. A 12-pack of cylinders represents 420 kilos of TNT and a typical tube trailer, 5,585 kilos of TNT.

“Hydrogen is a important plant useful resource and its provide and use must be handled with care,” mentioned Speranza. “Hydrogen fuel security continues to be a priority at energy vegetation because the fuel was first used greater than 70 years in the past, regardless of a usually good security document.”

Energy vegetation utilizing hydrogen-cooled turbines should preserve advisable hydrogen purity and strain within the generator casing for effectivity, security and tools reliability. Fixed monitoring and use of licensed tools for hazardous areas are essential first steps.

Enjoying It Protected

Hydrogen in a pure state is okay, however when blended with air, it turns into flamable. What makes it particularly harmful is that the explosive vary of hydrogen in air is broad, from concentrations that vary from 4 % to 74 %. “Any combination in that vary is explosive,” mentioned Kilmartin.

Not solely does hydrogen have a large flammability vary, ignition takes little power, mentioned Stephen Phelps, fastened programs product line supervisor for Sensidyne LP. Hydrogen burns with a pale blue, virtually invisible flame that may severely injure personnel, in addition to trigger extreme tools harm. A standard technique of detecting a hydrogen hearth is to make use of a brush to “sweep” the suspected space.

Making hydrogen keep put is sort of unimaginable, too, as a result of it’s gentle and its molecules are small.

“It’s tough to seal hydrogen, so there’s a excessive likelihood you’ll have leaks,” mentioned Kilmartin. All hydrogen-cooled turbines leak and have an appropriate leakage fee, he mentioned.

Fortunately, when hydrogen does leak, it’s so gentle that it dissipates rapidly, in contrast to pure fuel, for example, which is heavy and can sink to the ground and keep there.

“Typically, if hydrogen leaks out of a generator, it rises and must have some place to build up,” he mentioned.

One harmful space to be careful for is below the generator’s flooring. Hydrogen could kind there as a result of turbines are sometimes constructed proper onto the turbine deck, mentioned Kilmartin. “Half of the generator is above the ground and half is under so on the flooring degree the hydrogen can construct up and accumulate.”

Hydrogen can even construct up within the oil used to seal it within the generator. The oil/hydrogen combination then turns into explosive.

Monitoring hydrogen purity is essential for 2 causes, mentioned Kilmartin. The primary is effectivity: The purer the hydrogen the extra environment friendly the generator, as a result of hydrogen has much less windage loss than air does. “It takes extra horsepower to show a fan in air than hydrogen,” he mentioned.

The second cause is the explosive combination ratio—the purer, the safer.

Sadly, there’s no scarcity of how to trigger a hydrogen hearth. Kilmartin estimated that maybe 5 hydrogen fires a 12 months happen at energy vegetation with hydrogen-cooled turbines.

“You will have an exciter that’s connected to the generator and it might have arcing and sparking units in it,” mentioned Kilmartin. As a result of hydrogen is so dry, static buildup can develop and discharge, inflicting its personal inside arc.

“You will have a filter on a system that it is advisable to blow down and if it’s not correctly grounded you’ll be able to construct up a static cost that may ignite the hydrogen.”

Licensed Security Sandards

Thirty or 40 years in the past, auxiliary tools didn’t have to satisfy certification to be used in a hazardous space. At the moment, nevertheless, Kilmartin mentioned tools needs to be licensed by North American Electrical Code. He estimated he doubtless would discover tools that shouldn’t be utilized in an space with hydrogen in 75 % of right this moment’s energy vegetation. Even fluorescent lights, for example, shouldn’t be used within the space as they don’t fulfill code.

Designs have modified, too.

“One of many issues they used to do within the previous days was put the electronics in a single enclosure and hydrogen in one other enclosure,” he mentioned. Though that helps, designers didn’t think about that if hydrogen begins to leak it might find yourself within the different enclosure. And though the follow of separating electronics from hydrogen was safer than having the 2 collectively, it nonetheless didn’t fulfill code.

Kilmartin recommends inspecting the entire tools in an space with hydrogen to confirm that programs are both licensed for use in a hazardous space or are designed to satisfy the intent of the code for that space. He additionally recommends utilizing screens, known as low explosive restrict detectors, in confined areas. “Put them within the cupboard they usually’ll inform you when hydrogen will get above that 4 % vary,” he mentioned.

Ambient fuel detection is used to detect hydrogen leaks, mentioned Sensidyne’s Phelps. Hydrogen leaks happen on the generator bearings and shaft seals, within the seal oil provide system and from the hydrogen provide piping, mechanicals and purity/purging cupboard. Many vegetation monitor the seal oil system space and hydrogen purity cupboard. Older producing items could require bearing journal monitoring the place entry is obtainable, he mentioned.

Battery rooms may be infamous hydrogen turbines, in line with Phelps. Monitoring the rooms to activate a air flow fan is an effective follow, typically required by hearth code. A single hydrogen sensor excessive contained in the battery room, with annunciation exterior the door and supervisory notification, is a generally accepted resolution, he mentioned.

A situation monitor tracks insulating supplies’ thermal breakdown within the generator, mentioned Kilmartin. When thermal breakdown happens, it provides off thousands and thousands of submicron particles. Beneath regular circumstances within the generator, no submicron particles are current. Plant personnel ought to search for them as an indicator the generator will fail. “It’s not a security problem, it’s a reliability problem,” he mentioned.

Tools Detection Choices

Sensidyne producers and provides fuel detection and air monitoring programs. Based mostly in Clearwater, Fla., the corporate additionally affords restore and calibration companies.

Older detector varieties consisted of a non-specific catalytic detector delicate to all combustibles, mentioned Phelps. Through the use of a hydrogen-specific fuel detector no confusion exists about whether or not or not the detected leak is tramp methane, so corrective measures may be taken rapidly. The detector is mixed with the corporate’s 2-Wire Common Transmitter.

Phelps mentioned fuel sensors have reached a brand new expertise degree within the final 15 years. P.c remaining sensor life, prolonged calibration intervals, absolutely configurable electronics, real-time clocks with time-stamped information, giant illuminated shows, a number of communication modes and “calibrate sensors within the store—sizzling swap within the plant,” have all contributed reliability and added worth for the top person.

Ambient fuel sensors may be put in above the tools the place leaks are probably, resembling generator bearing assemblies, valves, fittings and the carbon dioxide purging system. Different fuel sensor mounting choices embody inserting the sensor distant from the transmitter or drawing a pattern from a distant or inaccessible location. Within the latter case, a calibration adapter is equipped.

Sensidyne trains personnel to deal with the routine upkeep related to clever plug-in fuel sensors. Coaching often takes two or three hours and is completed through the fuel detection tools’s start-up and commissioning.

Atmosphere One’s common situation monitor (GMC) makes use of real-time detection to offer early warnings of generator overheating and potential failure. The explosion-proof monitor’s ion chamber detects pyrolytic merchandise—submicron particles produced each time supplies within the generator are heated sufficiently to provide thermal decomposition—if they’re current within the hydrogen. The GCM-X warns of impending failure. An alarm verification sequence is carried out and if the alarm is confirmed, a hard and fast quantity of the hydrogen move mechanically passes by way of the sampling system. Particles are collected for laboratory evaluation to find out their supply.

E/One’s generator fuel analyzer (GGA) for hydrogen-cooled turbines is a triple-range sensor/analyzer that gives steady monitoring of fuel purity throughout all phases of generator operation. E/One says the system eliminates the problems of drift and want for frequent recalibration seen in some thermal conductivity programs.

See Also

Mild attribute – Wikipedia

Yokogawa Corp. is an industrial automation-and-control, test-and-measurement firm with services in 40 international locations. The corporate has utilized a vibrating aspect (VBE) fuel measurement expertise utilized in quite a lot of course of management environments to energy generator hydrogen purity measurement.

A vibrating aspect system works on the precept that the resonant frequency of a thin-wall cylinder will change because the density of the encompassing fuel varies—the “tuning fork technique.” The lighter the fuel, the quicker the cylinder vibrates. Yokogawa says VBE is well-suited for area measurement circumstances as a result of it doesn’t require reference fuel, an isothermal atmosphere, warm-up or temperature stabilization time.

Generator hydrogen purity had traditionally been measured with thermal conductivity analyzers or mechanical fan differential units, Yokogawa says. And whereas situations exist the place conventional fuel measurement can’t be changed, vibrating aspect expertise is viable and confirmed for fuel properties measurement for density, particular gravity or fuel % focus.

In the previous couple of years, Yokogawa mentioned GE Vitality turbines totaling virtually 1,300 MW have been transformed to VBE at Southern Co.’s Georgia Energy Plant Yates. The Tennessee Valley Authority’s Kingston Fossil Plant changed 9 thermal conductivity analyzers with VBEs on 5 GE 200 MW and 4 Westinghouse 150 MW turbines.

MediVac Applied sciences’ leak testing companies may be utilized to hydrogen-cooled turbines, steam generators, condensers, warmth exchangers and buried pipelines. MediVac’s technicians use the detector probe technique of helium leak testing, which, in line with the corporate, can find leaks on hydrogen-cooled turbines that may go undetected by bubble options and different much less delicate strategies. If a generator fails to carry strain after upkeep or previous to start-up, MediVac says it’s not essential to pressurize or check the generator with hydrogen. Utilizing two or three commonplace cylinders of helium blended with air or carbon dioxide as a tracer fuel, the generator may be examined, repaired and re-tested earlier than being full of hydrogen for operation.

MediVac additionally performs helium leak detection on the tubes and tube sheets of the hydrogen coolers to establish the precise location of the leakage.

Security and Onsite Hydrogen Manufacturing

The standard mode of hydrogen provide differs from plant to plant relying on a number of components, resembling distance from the central hydrogen provide and allow restrictions on the amount of saved hydrogen, mentioned Proton’s Speranza. Some vegetation use single cylinders or transportable cradles of six, 12 or 18 high-pressure (2,400 psi) hydrogen cylinders. Others use giant bulk programs which are both stationary high- or low-pressure tanks or transportable high-pressure tube trailers. Some vegetation have a cryogenic liquid hydrogen provide.

The potential for accidents will increase each time hydrogen is transported, transferred or a bulk hydrogen connection is dealt with, mentioned Speranza. In energy vegetation with a bulk hydrogen provide, it’s common to exchange a tube trailer each one or two weeks, whereas vegetation with cylinder packs could require alternative and reconnection each 4 to seven days. When a leak happens, it probably could contain your complete bulk stock, releasing your complete stock inside seconds. Provide and siting necessities per Nationwide Fireplace Safety Affiliation (NFPA) requirements require programs higher than 15,000 scf to be situated outside or in a “devoted, ventilated, noncombustible and indifferent constructing.” NFPA 55 additionally prescribes clearances of fifty toes from public meeting areas, electrical areas, air intakes and traditional building. The set up web site turns into a labeled space, restricted in use and sophisticated to allow.

In distinction to conventional bulk hydrogen programs, an on-site hydrogen generator resolution, resembling a Hogen Proton Change Membrane (PEM) water electrolyzer, has comparatively insignificant (<1.5 scf) inside hydrogen stock, allowing location inside virtually any ventilated construction that complies with NFPA requirements, mentioned Speranza.

Within the occasion of an onsite generator leak, the speed is not going to exceed the hydrogen generator’s most manufacturing capability. This low quantity, sometimes lower than 4 scf/min, is diluted regionally in air flow air to a protected degree.

An onsite hydrogen generator is usually sized to supply the entire every day hydrogen make-up necessities, leaving the re-gas requirement to be met by bulk supply strategies.

A Hogen onsite hydrogen generator requires minimal operator coaching as a consequence of its absolutely automated operation and requires lower than eight man-hours of annual upkeep.

Hydrogen’s Advantages as a Cooling Medium for Turbines

Hydrogen has top-of-the-line warmth switch properties of any fuel, with a particular warmth of three.4 Btu/lb-F at commonplace circumstances. On a mass foundation, hydrogen is 14 occasions extra environment friendly than dry air for eradicating warmth and hydrogen’s superior cooling properties improve because the hydrogen strain will increase.

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Hydrogen, as the lightest gas, has the lowest density of any stable gas. Wind resistance losses are kept to a minimum because the rotor’s wind resistance in a hydrogen-cooled generator is far less than in a similarly sized air-cooled generator. And unlike air, hydrogen is not an oxidizing agent.

While hydrogen can be an effective cooling medium for large turbo generators, it can also be hazardous and proper practices must be followed for safe operation.

Source: “Turbine-Generator Auxiliary Systems, Volume 3: Generator Hydrogen System Maintenance Guide,” EPRI.