Hydrogen Coolant Purifier

EONE GENERATOR GAS DRYER (GGD II) Justification and Specification Info

GENERATOR H2 BACKGROUND Many generator manufacturers use hydrogen gas as a cooling media for their turbine generators. Older generators could be as small as 10-20MW and be hydrogen cooled. Most, however, are in excess of 100MW machines. While some OEM’s are testing or developing air-cooled generators approaching the 250-300MW range, today’s typical turbine generators above 150MW are, in fact, hydrogen cooled.

Why use hydrogen? Hydrogen is the most abundant gas on the planet. It also is the lightest gas available and has the highest thermal coefficient, or heat carrying capacity, of any gas on earth. In fact, hydrogen’s specific gravity is approximately 0.0696. This means it is roughly 93% lighter than air. The result of this, in generator cooling applications, is a significant reduction in windage or frictional losses on the generator’s rotor/field assembly. An added benefit, aside from the higher thermal capacity of hydrogen, is that hydrogen must be kept at purity levels above the Upper Explosive Limit (UEL = appx 74% H2 in Air) or below the Lower Explosive Limit (LEL = appx 4% H2 in Air). Because ambient conditions (air, dust and other contaminants) are intended to be kept out of the generator environment, the “closed loop” hydrogen environment minimizes the development of contaminant buildup (corona, dirt, etc.). This helps to increase the service life expected from hydrogen cooled generator.

In original generator OEM systems, the typical arrangements required only hydrogen purity monitoring, hydrogen supply and pressure control/regulation, carbon dioxide supply and control (for purge of H2 or air) and gas pressure instrumentation. To keep hydrogen in the generator and air out, these generators are equipped with a shaft/rotor “sealing oil” system. This system incorporates a system of oil containment vessels, pumps, motors, valves, pressure and flow regulation. The seal oil is typically supplied by the turbine lubricating oil system.

As hydrogen cooled machines operated, generating plants and generator OEM’s began to see a need for maintaining dry hydrogen conditions in the machine. As a result, hydrogen dryers were supplied as “optional” equipment which had to be specified/required by the generator end user. Rarely did an OEM provide hydrogen dryers as “standard” equipment on these hydrogen cooled machines.

HYDROGEN DRYER HISTORY Early applications requiring hydrogen dryers incorporated what is referred to as a “single tower” design. While this design was thought to be “better than nothing”, experience has shown that they were problematic in terms of maintenance, and in many cases simply did not work. These dryer systems were of a very small drying volume, and required manual operation to “isolate” the dryer and regenerate the vessel. This led to increased operational costs of the dryer unit, as well as actually introducing moisture and air contaminants into the generator environment (at least one dryer volume full). Furthermore, no hydrogen circulation methods were incorporated. Rather, these single tower dryers could only “work” if the generator was at full speed and relied solely on the generator’s rotor fan differential pressure for the circulation or flow of hydrogen gas. At standstill or turning gear operations, no hydrogen gas was able to be dried. It is during standstill or turning gear operations in which the seal oil system is at its most vulnerable in terms of air or water vapor ingress.

As single tower dryer experience improved, dryer manufacturers developed dual tower hydrogen dryer systems. These were a significant improvement in that the dryer volumes were increased to improve effectiveness, and the towers were “switched” to allow one to dry the generator gas, and the other to be automatically regenerated. These systems, however, had major shortfalls. Most incorporated internally mounted electrical fans in an attempt to provide hydrogen flow during generator standstill or turning gear operations. However, these fans were undersized and could not provide enough flow to overcome system piping losses. This means inadequate circulation of hydrogen during standstill or turning gear operations. In addition, these electrical fans were exposed to potentially high moisture environments, often resulting in fan failures. Such failures required the system to be removed from service, isolated and purged, and the dryer system disassembled to permit repair or replacement of the fan/motor assemblies. Also, these dryers were equipped with “unshielded” heater elements. These elements were continuously in contact with the dryer’s desiccant materials. This lead to high temperature areas significantly reduced desiccant life and function, as well as increased repair costs and down time. The dryer, again, had to be removed from service, isolated, purged, and the desiccant emptied in order to repair or replace these heater elements.

EONE SYSTEM DESCRIPTION

The Generator Gas Dryer (GGD) is a self-contained drying system incorporating a pre- filter, dual chamber desiccant dryer, an after-filter and a positive displacement blower. The system is monitored and controlled by microprocessor-based electronics. The GGD provides clean, dry hydrogen:  During highest contamination loading  During Idle time with less natural circulation boost  While automatically eliminating operator attention  By positively purging contaminants from the hydrogen system

As mentioned above, many dual tower dryer systems are “closed loop” and require a cooling water connection. The intent of this design was to heat the “wet gas”, then rapidly cool the gas causing the water vapor to condense and collect in the bottom of the system to be drained. However, this function is not an effective means of moisture removal, and oftentimes led to the reintroduction of wet gas when the tower was put back in service. Furthermore, many manufacturers utilize an activated alumina as their drying media. Activated alumina is a good drying material for virtually saturated gas environments, but it is not an effective drying material for the lower dew point ranges common to electric generator applications. The EONE GGD is a dual tower system, but incorporates the use of a molecular sieve material as the drying media. Molecular sieve is many times more effective in drying lower dew point gasses than is the activated alumina. Furthermore, mole sieve also has the capacity to remove gas contaminants such as remnant CO2, N2, etc. These gases are commonly present in the generator, especially shortly after purge/fill operations. In addition, to the benefit of the molecular sieve, the EONE GGD is designed as an “open loop” regenerative system. This means that during the regeneration functions of the “wet tower”, the GGD actually exhausts a small amount of H2 gas. By exhausting the H2 gas, which carries water vapor with it, the open loop system guarantees that virtually all water vapor is eliminated from the dryer tower. This is the only way to positively evacuate water vapor contaminants from the generator and dryer systems. The amount exhausted during this regenerative process is typically 2SCFM for duration of 4-6 hours. This is usually much less than typical generators are expected to actually leak in one day.

This open loop regeneration process is controlled by microprocessor control system. This control system uses BOTH an adjustable timer and an adjustable dew point measurement to control the regeneration process. The primary control logic is initiated by a preset dew point level. That is, if the dew point of the H2 gas leaving the GGD and going to the generator reaches a certain threshold, the towers will switch, and the regeneration process initiated. However, if this dew point is never reached, a preset timer (min/max duration) will take over regeneration control. This duplex control method ensures that a) the generator will never see a dew point above the threshold, and b) that the GGD components (desiccant, actuator, heaters, etc.) “share” cyclic duty. This helps to prolong the life of the GGD components, as well as provide long term efficiency of the entire system. The added benefit is reduced operator interface requirements, and reduced maintenance intervals.

A final benefit of the EONE GGD is the use of intrinsically safe wiring practices and the use of explosion proof components. The EONE GGD is, in fact, currently certified for ATEX Zone 2, Group 2 H2. The ATEX hazardous area certification is one of the most stringent certification requirements for electrical systems, and offers the highest level of safety and personnel protection for this equipment.

WHY DRY THE H2?

The Generator Gas Dryer (GGD) is used by electric power generating plants to dry the hydrogen used as a coolant in generators. The presence of water in generator applications can cause corrosion in retaining and zone rings, lead carbonate formation and increased windage losses. The GGD was specifically designed to remove moisture and provide a continuous flow of clean, dry hydrogen throughout all phases of generator operation. While one of the obvious benefits of installing H2 dryers is the long term protection of the generator and its components, one not-so-obvious benefit is the overall improvement of generator efficiency. For example, if we assume a generator contains 20,000 standard cubic feet of 100% pure H2 gas coolant, the resulting weight is 106.3 pounds. If a purity analyzer indicates 95% H2 purity, however, we can assume that the 5% is remaining is either water or oil vapor. The presence of these contaminants reduces the H2 mass to 101 pounds. The remaining water and/or oil vapor would have an approximate mass of 47.3 pounds. With respect to total coolant mass, this is roughly 46.8%.

In April, 1976, General Electric published an article in Power Magazine which discussed the impact of reduced hydrogen purity on the efficiency of electric generators. The premise of the article showed the improvements in generator efficiency simply by increasing the H2 purity from 95% to 98% by the removal of moisture contaminants (water and oil vapors, primarily). The generator used in the example was a 907MW machine, and it was shown that 685kW of increased friction/windage losses were experienced simply by the presence of moisture vapors. Assuming power costs, in 1976, of $.0045/kW-HR, this resulted in a daily operating cost of $74/day or roughly $27,010/year!! Basic ratios comparing today’s power costs and various generator sizes can show estimated windage losses for different machines today. Here are a few examples: (assuming a US average of $.05/kW-HR, according to EIA for 2001)

{(200MW)/(907MW)} X {($.05/kW-HR)/($.0045/kW-HR)} X ($27,010/year) = $66,176/year {(250MW)/(907MW)} X {($.05/kW-HR)/($.0045/kW-HR)} X ($27,010/year) = $82,720/year {(300MW)/(907MW)} X {($.05/kW-HR)/($.0045/kW-HR)} X ($27,010/year) = $99,264/year {(350MW)/(907MW)} X {($.05/kW-HR)/($.0045/kW-HR)} X ($27,010/year) = $115,809/year {(400MW)/(907MW)} X {($.05/kW-HR)/($.0045/kW-HR)} X ($27,010/year) = $132,353/year {(450MW)/(907MW)} X {($.05/kW-HR)/($.0045/kW-HR)} X ($27,010/year) = $148,897/year {(500MW)/(907MW)} X {($.05/kW-HR)/($.0045/kW-HR)} X ($27,010/year) = $165,441/year

These windage loss “costs” are associated to the presence of impurities in the generator cooling gas environment and are strictly results of increased friction, etc. This by no means covers the increased probabilities of failures due to component degradation as a result of exposure to moisture. In any case, by eliminating the presence of moisture contaminants, predominantly water vapor, a GGD can possibly pay for itself within one year, even on smaller generators, 150MW, 100MW, etc.

FEATURES AND BENEFITS  Microprocessor-based electronics.  All electronics are house in explosion proof enclosures  Continuous self-checking diagnostics – all major operating parameters are fully supervised.  Explosion proof, intrinsically safe design (AEX)  Open looped regeneration insures complete contaminant removal.  Dew Point is monitored entering and exiting the system.  High temperature heater shutdown prevents excessive operating temperature.  Chamber relief valves prevent overpressure.  Heaters are housed in explosion proof conduit for safety and to increase the life of the desiccant.  Regeneration flow meter ensures efficient gas flow during periods of regeneration.

RELIABILITY  Complete regeneration of the desiccant is accomplished by multiple low- wattage density heaters. The heaters are housed stainless steel pipe to optimize desiccant life.  Dryer chambers are epoxy painted and have 1/16” corrosion allowance for long service life.  Desiccant quality and life is enhanced by open loop regeneration and down flow drying.

SUPERIOR PREFORMANCE  Maximum contaminant removal is accomplished by a packaged system incorporating a pre-filter to remove trace amounts of oil, a desiccant dryer to remove water vapor and an after-filter to remove particulates.  Positive displacement, gas-tight blower ensures maximum Circulation of hydrogen through the generator and purifier during peak load as well as turning gear operation.  Specially selected desiccant provides maximum moisture removal capacity for low relative humidity gases… 15 times the capacity of activated alumina.  Open-loop regeneration ensures removal of extracted contaminants from the system, unlike closed loop dryers, which actually concentrate contaminants within the hydrogen system. SPECIFICATIONS

Design Operating Conditions: Fluid Hydrogen Gas System Flow Rate 8-12 ACFM Operating Pressure, Min/Max 0/100 psig

Detail Specifications: Pre-filter Cartridge Coalescing

Desiccant Molecular Sieve After-filter Cartridge Particulate Drying Cycle Flow Rate (hydrogen) ≈ 10 scfm Re-Generation Cycle Flow Rate (hydrogen) 2 scfm (4-6hours) System Differential Pressure (hydrogen) > 2 psig Purge Source Dry Hydrogen System Conn. Size 3/4”, 150 lb RF flange Vessel Corrosion Allowance .0625”

Utilities: Area Classification Zone 2, Ex II H2 Electrical Service 460 VAC 60 Hz 3 PH Heater Size 1.8 KW/CHamber Motor Size .6 HP

Outputs: Inlet Dew Point 4-20 mA Outlet Dew Point 4-20 mA Trouble Relay Contacts Dew Point Alarm Relay Contacts

Ordering Information: The Generator Gas Dryer is offered in one size suitable for use with any hydrogen cooled generator.