Process Engineering Equipment Handbook 2009 Part 10 pdf

TABLE F-9 Liquid Fuels for Gas Turbines Typical Lower Heating Fuel Value, MJ/kg Btu/lb Comments* Distillate No... As these fuels have a dew point that is higher than ambient temperature

Solids removal efficiency: 100 percent for particles of 8 microns and larger, 99

percent for particles of 6 to 8 microns, 90 percent for particles of 4 to 6 microns,and 85 percent for particles of 2 to 4 microns See Fig F-32

Vertical absolute separators

Definition: Vertical single or two-stage separator for removal of solids and very fine

mists with liquid removal efficiency of 100 percent for particles 3 microns andlarger, and 99.98 percent for particles less than 3 microns

Solids removal efficiency: 100 percent for particles of 3 microns and larger, and 99.5

percent for particles of 0.5 to 3 microns

Line separators

Definition: Vertical vane-type separator with liquid removal efficiency of 100

percent for removal of particles 10 microns and larger

Fuel Systems; Fuel Flow Control

One* of the most common types of fuel flow control is electrohydraulic control Thereare electrohydraulic control solutions for differing environments, including low-pressure and potentially explosive conditions

FIG F-32 System installed in Saudi Arabia includes one vertical dry scrubber followed by two pressure regulating valves and a line separator A condensate drain tank is mounted alongside (Source: Peerless.)

* Source: J.M Voith GmbH, Germany Adapted with permission.

Modern industrial gas turbine systems require precise fuel dosage for the lowestpossible NOx emissions Each application requires the right actuator and valvecombination to achieve exact, uniform fuel distribution to the burner See Figs F-

33 and F-34

The controller needs to be:

1 Inherently reliable (robust construction and low-pressure hydraulics)

2 Equipped with single-stage signal conversion which results in fast, accurateresponse times

3 Equipped with an oscillating magnet and minimized bearing forces to avoidstatic friction effects

4 Easy to install because the magnet and control electronics are all one unit

5 A control with availability of 99.9 percentThe actuator is only one of the components necessary for accurate flow control Somecontrols OEMs cooperate with leading valve manufacturers to offer a total controlsystem All valves and actuators are factory mounted and aligned to reduce labor-intensive adjustments during commissioning

Balanced valves have low force demands Trip time of the complete valveassembly is less than 200 ms and the related increase in pressure is absorbed bythe valve

Valves are available with soft seals as well as with bellows for gaseous fuels.For optimum performance and safety, electrical components face a burn testoperated under “cold” conditions (See Figs F-35 and F-36.)

Electrohydraulic actuators utilize an integrated position regulator that provides

a true position signal

Other assembly features generally provided by actuator OEMs include:

1 Minimal interfaces

2 Valves designed to run without additional breakaway thrust, even after long, continuous operation

3 Flange mounting for easy assembly

FIG F-33 Electrohydraulic actuator in a U.S power station (Source: J.M Voith GmbH.)

with integrated control electronics; 2, control piston; 3, position sensor; 4, clamp magnet; 5, drive piston; 6, piston rod; 7, stem; 8, stuffing box packing; 9, body; 10, trim; 11, fuel inlet; 12, seat (Source: J.M Voith GmbH.)

F-31

4 Fail-safe design

5 Explosion-proof design

6 Controlled emergency trip

7 Ease of commissioning and installation

8 Low maintenance

9 Compact design

FIG F-35 Schematic of gas turbine fuel system – = control valve assembly, G = generator, T =

gas turbine (Source: J.M Voith, GmbH.)

FIG F-36 Functional schematic of control valve assembly X 0 = pressure P A at I = 0 or 4 mA; X 1=

pressure P A at I = 20 mA; K p = proportional amplification; F M = magnetic signal/force; F 1 = feedback

force/signal to controller; F A = hydraulic cylinder force (Source: J.M Voith, GmbH.)

10 Inherent long-life design

11 Failure indication signal

12 Insensitive to dirt due to encapsulated design

13 Control and performance insensitive to temperature

14 Precise repetition

15 Fast, hysteresis-free processing of signal

16 Friction free due to oscillating solenoid force

17 Compensation of different expansion factors with internal position regulator

18 Not affected by disturbance factors such as air gap, magnetic hysteresis, andvoltage fluctuations

19 Open loop control, PID configuration

Typical range of valve actuators for gas turbines*

Control, emergency trip, and relief valves can be equipped with electrohydraulicactuators:

Natural gas Up to 200 mm (8 in) Up to 63 bar (914 psig)Diesel oil Up to 100 mm (4 in) Up to 160 bar (2320 psig)

 Design of the valves to: ANSI or DIN specifications

 Internal fittings: Perforated or solid cone

 Flow curve characteristics: Linear, same percentage, open-closed, or specific

 Installation: Flanges or welded ends

 Valve tightness: Up to 0.001% of nominal KVSvalue

Actuators*

Performance features include:

 Standard actuator stroke 50 mm (2 in) to maximum stroke 200 mm (8 in)

 Explosion-proof design is standard

 Operation with hydraulic or pneumatic auxiliary energy

 Low- and high-pressure designs up to 170 bar (2,500 psig) available

 Accuracy: ±0.1 mm absolute

 Tripping force at a stroke of 0 percent: ≥15.000 N

* Source: J.M Voith GmbH, Germany Adapted with permission.

is supplied with a turbomachinery package Typical valves in the system areindicated in Fig F-38; they perform metering, isolation (shutoff), or stagingfunctions Figure F-39 illustrates a typical hydraulic-actuated modulating sleevevalve Note the mechanical feedback on this valve type Figure F-40 illustrates aservo motor actuated plug metering valve and its performance parameters.

FIG F-37 Universal all-electric DLE and SACn gas test cell fuel skid used with LM engines (DLE and SACn are Whittaker model designations; LM refers to GE LM series gas turbines.) Approved to CSA, Ex standards (Source: Whittaker Controls.)

FIG F-38 Some typical fuel system components (Source: Whittaker Controls.)

FIG F-39 Typical 3-in hydraulic actuated modulating sleeve valve (Source: Whittaker Controls.)

FIG F-40 Typical 2-in servo motor actuated plug metering valve (Source: Whittaker Controls.)

OPERATING FLUID:

Natural gas APPLICATION:

Aeroderivative TEMPERATURE:

Ambient: -65 °F to 350 °F Fluid: 32 °F to 400 °F ELECTRICAL:

Motor Voltage: 170 VDC servo motor Current: 0.3 amp max steady state Resolver

Voltage: 4 VAC Current: 25 to 60 ma max Position switch

Voltage: 28 VDC Current: 2.5 amp Connector: Terminal block INSTALLATION DATA:

Flanges: Per ANSI B16.5, 1.5 inch pipe, Class 600 both ends

WEIGHT:

80 lb max PERFORMANCE:

Flow: 0 to 4.0 lb/sec, in direction shown effective area linearly propertional to valve stroke Accuracy ±1% from 1.0 to 4.0 lb/sec Pressure:

Operating: 100 to 600 psig Proof: 1,440 psig DP: 15 psid at 4 lb/sec, 500 psig at 60 °F Hydrostatic: 2,160 psig at room temperature Leakage:

Internal: ANSI class IV Operating time:

Open to closed: 100 msec max Closed to open: 100 msec max Fail safe closed: 500 msec max

* Source: Whittaker Controls, USA Adapted with permission.

Fuel System Testing

Part of a typical test routine is outlined here The end user concerned about fuelsystem malfunction needs to question the supplier, often a subvendor, about theresults of some of these tests Typically, the OEM adds its own nameplate to thesystem provided by the subvendor

Typical fuel systems test specification* (for dual fuel machines or DLE systems)

A typical test specification would call for performance of the following tests:

 Fuel pressure cycle testing (DAT)

Expected results vary based on line size For instance, typical nominal testcapabilities for a 3-in line size cover three ranges.

1 Static bench test for leakage (100 gpm at 1300 psig)

2 Self-contained dynamic test (low flow) (150 gpm at 600 psig)

3 Self-contained dynamic test (high flow) (300 gpm at 1300 psig and 1800 gpm at

600 psig)

Fuels, Alternative; Fuels, Gas Turbine*

The term fuel in process engineering generally means fossil fuel The most common

fossil fuels in use today are natural gas, oil, and coal The latter two have manyvarying grades and sulfur contents The emissions evolved from combustion of thefossil fuels are dealt with under other subject headings in this book, includingEmissions and Turbines

Common Gas Turbine Fuels

In broad terms, gas turbine fuels can be classified as gaseous or liquid fuels Theterms “gaseous” and “liquid” indicate the state of the fuel as it enters the gas turbineand not the state it is stored in at the site The most commonly encountered gaseousfuels include:

 Natural gas

 LNG (liquefied natural gas)

 LPG (liquefied petroleum gas; typically a blend of propane and butane)

 Refinery gas

 Blast furnace gas

 Coke oven gas

 Coal gas

 HydrogenSuitable liquid fuels include:

 Distillate No 2 (diesel fuel)

 Heavy fuel oil

* Source: Adapted from extracts from Narula, “Alternative Fuels for Gas Turbine Plants—An Engineering, Procurement, and Construction Contractor’s Perspective,” ASME paper 98-GT-122.

Tables F-8 and F-9 list the lower heating values of these fuels and provide a briefcommentary on each fuel While many of these fuels have some unique applicationsfor on-site use, they are not economically viable fuels for large-scale developmentprojects Therefore, this section only focuses on the four alternative fuels that aretypically being considered on power projects worldwide: LNG, LPG, naphtha, andcrude/heavy fuel oil.

Liquefied Natural Gas

Logistics

Natural gas is often found in remote locations far from the point of end use Largereserves have been found in Siberia, Alaska, Sumatra, the Middle East, Australia,Indonesia, the Sahara Desert, and the North Sea Where economically viable, thegas is transported by pipeline to the end user Where the gas source and end userare separated by oceans and continents, the only viable alternative is to liquefy thenatural gas and transport it via insulated LNG tankers

TABLE F-8 Gas Fuels for Gas Turbines

Typical Lower Heating Fuel Value, MJ/Nm 3 (Btu/SCF) Comments*

Natural gas 35.5 (900) (1), (2), (4)

LPG (typical blend) 104.8 (2,700) (2), (3), (5) Propane 91.2 (2,300) (2), (5) Butane 118.5 (3,000) (2), (5)

Blast furnace gas 3.6 (90) (7), (8), (17) Coke oven gas 11.8 (300) (7), (11), (14), (16) Hydrogen 10.8 (270) (9), (10), (16)

* Refer to comments nomenclature below Table F-9.

TABLE F-9 Liquid Fuels for Gas Turbines

Typical Lower Heating Fuel Value, MJ/kg (Btu/lb) Comments*

Distillate No 2 42.7 (18,400) (1), (2) Kerosene (K-1) 43.0 (18,500) (2)

Naphtha 44.2 (19,000) (2), (12), (13), (14) Condensate fuel 45.2 (19,400) (2), (12), (13), (14) Methanol 19.9 (8,555) (2), (12)

Ethanol 26.8 (11,522) (2), (12) Crude oil 41.2 (17,700) (7), (13) Heavy fuel oil 39.6 (17,000) (7), (15)

* Comments nomenclature: (1) standard fuel; (2) clean burning; (3) needs vaporization; (4) low transportation and storage cost; (5) medium transportation and storage cost; (6) high transportation and storage cost; (7) needs scrubbing of contaminants; (8) needs enrichment with a higher heating value fuel; (9) high flame temperature results in high NO x ; (10) needs

a separate startup fuel; (11) fuel needs heating to preclude condensate dropout; (12) poor lubricity; (13) low flash point; (14) high vapor pressure (highly volatile), needs a separate startup fuel; (15) needs preheating and treatment; (16) high (>40 percent) hydrogen fuel; (17) difficult fuel-to-air control because of large mass of air due to very low heating value.

Given the recent advancements in liquefaction technology, even the once-strandedgas fields are turning out to be economically viable sources of fuel supply From the source the gas is piped to a coastal location where it is processed to removeimpurities and inerts After extracting heavy ends, the processed gas is finallyrefrigerated to make LNG and stored at atmospheric pressure and at a temperature

 Well head price of gas

 Liquefaction technology

 Size and tanker age

 Need for a breakwater at the receiving terminal

 Seismic classification of receiving terminal location

 Applicable safety criteria

Combustion considerations

Vaporized LNG is similar to, if not a little lighter and cleaner than, pipeline naturalgas There are no significant combustion concerns with this fuel since it burns justlike natural gas

BOP and energy integration considerations

Site selection, facility design, and energy integration are so critical that in manyprojects they can make a difference in the project being economically viable or not.The major considerations in this category include the following

Plant site selection. A 2500 MW combined cycle facility with the associated harborfor the LNG receiving terminal and storage facility may require on the order of 60hectares (150 acres) of geotechnically good quality land

The harbor should be well protected from rough sea conditions to preclude theneed for an expensive breakwater It should have sufficient water depth (about

15 m) for the 125,000 m3

(or larger) LNG carrier The ship channel should besufficiently deep for the LNG ship traffic and have a large ship turning basin (900 mdiameter) Good seabed geotechnical conditions are also very important Availability

of fresh water for the process and fire protection systems is also very important, asthis can preclude the need for, or reduce the size of, desalination facilities Finally,the site should be compatible with the applicable environmental criteria

Safety. Public health and safety and property protection are important issues thatmust be addressed at the initial stages of a project Thus a hazards review studymust be conducted The three main aspects of this study are:

 Fire radiation analysis—Addresses ignition of the pool of LNG and levels of radiation at specified points This is used to determine the minimum separationdistances and the amount of fire water needed to cool the adjacent equipment.

 Gas dispersion analysis—Determines the dispersion of vaporized LNG for variousclimatic conditions The extent of a vapor cloud is used in determining theminimum distance to sources of possible ignition

 Detonation analysis—Addresses the resultant blast from unconfined or confinedvapor explosions This determines blast protection requirements and the safedistance for structures and equipment

The results of the above-listed analyses are used to determine the exclusionzone—the area outside of which is considered safe for public access The results are also used to determine in-plant separation distances The hazards study must

be conducted before finalizing the relative locations of storage tanks, liquefactionfacilities, and other power plant facilities From a capital cost viewpoint, these facilities should be kept as close as possible to each other; however, safetyconsiderations mandate minimum safe distances anywhere between 200 and 800 m.Enlarging the exclusion zone by 1 to 2 km from any public facility such as a school,

a hospital, or a highway may be necessary

LNG cold utilization. As stated earlier, LNG is stored at a temperature of -160°C (-256°F) To use it as a fuel in a gas turbine, it must be vaporized in a heatexchanger by adding heat The amount of energy transfer required is commonlyknown as LNG cold or LNG chill Theoretically the amount of heat required has to

be equal to the amount of energy required for vaporization Further, we also knowthat the lower the temperature of the ambient air entering the gas turbine, thegreater the amount of power it can produce Thus, if we utilize the LNG coldeffectively to cool the air entering the gas turbine, thereby increasing power plantoutput, we can improve the overall economics of the entire facility Experienceindicates that at a practical level we can boost the plant output by as much as 5percent Many other uses of LNG cold have been examined, but they are outsidethe scope of this book It is, however, important to note that cost-effective use ofLNG cold is heavily dependent upon the annual profile of the ambient airtemperature and relative humidity at the site

Energy and project integration. Historically, LNG trade across the Atlantic betweenAlgeria and the U.S or in the Pacific to Japan has been to keep the gas pipelinesflowing predominantly for residential, industrial, and some limited thermal powerplant use The large-scale use of LNG for gas turbine–based power production is afairly recent phenomenon and is predicted to accelerate in the near future Because

of the liberalization of the region’s electricity market, the fastest demand for LNG

is expected to be in the Asia-Pacific region in South Korea, Japan, Taiwan, India,and China Thus, integration of the LNG receiving terminal and power plant hasnow become an important consideration Having performed numerous studies andconceptual designs for a number of our domestic and international customers, theauthor is convinced that tens of millions of dollars can be saved by integrating thedesign, procurement, and construction of the two facilities The factors contributing

to these huge savings include:

 Optimization of LNG cold utilization

 Optimum layout of the entire facility based on safety and design considerations

 Integration of fuel unloading pier and water intake structure/discharge structure

 Integrated site development plan

 Common facilities for fire fighting, cooling water, electrical systems, andadministration and warehouse facilities

 Common nonmanual construction staff

 Integrated schedule (this is important as LNG tank construction schedule is generally on the critical path)

Emissions. Emissions control when using LNG is analogous to natural gas, wherelow NOx and CO emissions can be achieved However, the actual allowableemissions may vary from country to country and from state to state within eachcountry While modern gas turbines are capable of meeting fairly low emissions,many states within the U.S have very stringent emissions limits requiring the use

of external devices such as selective catalytic reduction (SCR) and CO removalmodules Therefore the facility design must either be optimized up front toaccommodate these devices or have the flexibility to incorporate such devices laterdepending on the site-specific emissions criteria

Liquefied petroleum gas

Many of the design considerations discussed under LNG are equally applicable tothe use of LPG as a fuel for gas turbine–based power plants The discussion below

is, therefore, limited to considerations unique to LPG

 LPG is a by-product of natural gas treating processes or an incidental gasrecovered during the oil extraction process It generally comprises propane,butane, or a combination of both As the spot market price for propane and butanevaries with the seasonal demand, the receiving terminal and power plant facilitiesmust be designed to handle 100 percent propane, 100 percent butane, or anycombination of the two

 Neither propane nor butane is as cryogenic as LNG Propane and butane arestored at atmospheric pressure at temperatures of -42°C (-44°F) and 0°C (32°F),respectively The LPG tankers are generally smaller (80,000 m3) and lessexpensive than LNG tankers The higher boiling temperatures of these gases(relative to LNG) and the owner’s desire to use 100 percent propane, 100 percentbutane, or a mixture of both has a significant impact on the size and design

of the refrigeration system for storage tanks as well as on the design of thevaporization facility It also impacts the design of gas turbine combustor andchoice of startup fuel

 Because these gases are heavier than air, proper attention must be paid to theplant design with respect to selection of the fire detection and protection system

To detect fuel leaks and prevent vapor access to drains, gas detectors must belocated near floor level

 As these fuels have a dew point that is higher than ambient temperature at the maximum expected gas turbine fuel system pressure, the fuel must besuperheated, and fuel lines must be properly heat traced Likewise, all the valves

in fuel-forwarding stations need sufficient heat tracing The design must avoidfuel collection by eliminating low points and by providing adequate venting toprevent two-phase flow into the gas turbine

 The LPG cold utilization considerations are similar to those of LNG The amount

of cold energy, however, is smaller, especially with butane Depending on the mix

of propane and butane, a study must be conducted to establish the economicpayoff.

 It should be noted that because of limited LPG market, not all gas turbinesuppliers are currently offering dry low NOxcombustors for their advanced gas turbines for this fuel Use of moisture injection to control oxides of nitrogen canworsen thermal efficiency and increase BOP water treatment cost, especially atsites where desalination is necessary to make fresh water Further, since it is arelatively new fuel for gas turbines, the emissions requirements with this fuel arenot clearly defined by regulatory agencies The actual emissions from the gas turbines when burning LPG are closer to those with liquid fuels than those with gaseous fuels

Overall, because an LPG receiving terminal is not as expensive as an LNGterminal, a plant size as small as 500 to 700 MW is economically viable with thisfuel In smaller or island countries where total electric demand is modest, LPG may

be a more viable fuel than LNG

Naphtha

Logistics. Naphtha is a generic, loosely defined term that covers a wide variety

of light distillates It is processed from crude oil through distillation towers inpetroleum refineries and is a primary ingredient in gasoline It also has wideapplications in the pharmaceutical, dry cleaning, painting and coating, rubber, and textile manufacturing industries In developed countries, naphtha is usuallycracked to produce ethylene, which commands a premium market price Indeveloping countries such as India, the market for cracked products is not as robust.Further, limited availability of natural gas has forced power plant operators to usenaphtha as an alternative gas turbine fuel

The naphtha classification includes common fuels such as gasoline, mineralspirits, and many petroleum solvents In general, liquids classified as naphtha have

a low flash point and high volatility and require special design and operating safetyconsiderations Naphthas are low viscosity liquids having poor lubricating qualitiescompared to No 2 or heavier oils They have been widely used as primary or back-

up fuels for gas turbine plants in India Other countries that have used naphtha

as gas turbine fuel include Pakistan, Venezuela, Spain, Angola, France, Slovenia,Morocco, Italy, Saudi Arabia, Malaysia, Philippines, U.K., U.S., and the VirginIslands

Combustion considerations. In general, naphtha is a relatively clean fuel (cleanerthan No 2 oil) and can be used in gas turbines with minimum modifications to thegas turbine accessory equipment As the fuel composition for naphtha variessignificantly, its suitability for a given application must be confirmed with the gasturbine suppliers The gas turbine suppliers generally require a fuel additive toincrease the fuel lubricity As with high-hydrogen gas fuels, naphtha, with its lowflash point, requires special consideration in combustor design and an alternatestartup fuel Generally distillate No 2 oil is used as the startup fuel

BOP considerations

General. Hazardous operation design criteria must be considered for the fuelunloading, storage, treatment, and fuel forwarding/sendout systems It isrecommended that applicable piping and instrument diagrams, hazardous areaclassification drawings, and other design drawings be reviewed by the gas turbine

supplier to ensure that all criteria established by the gas turbine supplier are fullycomplied with.

Country-specific codes and standards must also be followed For example, Indiancodes and standards dealing with hazardous area classification are more stringentthan U.S standards regarding separation criteria and air movement It should benoted, however, that some of these requirements are based on extreme hazards thatmay not exist for a particular application The designer must exercise judgment toensure that an appropriate level of safety is achieved and that all requiredapprovals by local authorities are secured

Fuel storage system. Bulk storage of naphtha presents greater risk than isexperienced with less volatile liquids such as distillate oil Special precautionsassociated with storage and handling of Class I flammable liquids must be followed.Vented atmospheric tanks cannot be used Selection of the appropriate storagetankage depends on the properties (vapor pressure, etc.) of the naphtha underconsideration Options include low pressure tanks or pressure vessels One way tocost-effectively minimize vapor formation and prevent accumulation of vapors is touse a floating roof design

The use of Class I liquids such as naphtha may affect plant layout with regard

to separation of storage tanks, structures, and other plant facilities

Fuel handling system. The gas turbine supplier specifies the acceptable viscosityrange for the fuel system, recommends the lubricity additive, and usually suppliesthe lubricity additive system If site topography requires fuel storage tanks andsendout pumps to be located higher than the gas turbines, and/or if fuel deliverypiping is fairly long, a transient analysis must be performed to determine the needfor a surge chamber (or other measures such as controlling valve stroke times) toensure that release of naphtha does not occur

Emissions. In general, gas turbine emissions when burning naphtha are similar

to emissions experienced with burning distillate oil Moisture injection and use ofexternal devices such as SCR and CO modules may be required depending onallowable emission limits The water treatment and storage system design is often dictated by the demineralized water requirements for NOxcontrol

Crude/heavy fuel oil

Logistics. Heavy fuel oil is basically what comes out the bottom of the distillationcolumn after all the lighter oils have been removed Lower grade fuel oil,particularly crude oil, has historically been used as a fuel for gas turbines in oil-producing countries with limited refinery capacity The economic driver for usinglower grade fuel oil is the fuel price difference between distillate oil and crude/heavyfuel oil While spot market prices for these fuels can vary significantly, anapproximate rule of thumb is that the price of crude oil is about 70 percent of theprice of distillate oil, and the price of heavy fuel oil is approximately 60 percent ofthe distillate price Thus, there is big cost incentive to use these fuels Dueconsideration must, of course, be paid to the higher operating and maintenancecosts associated with these fuels and the attendant lower plant availability Also,the applicable environmental regulations may limit or preclude their use It isinteresting to note that the bulk of operating experience with crude oil is in theMiddle East and Africa; with heavy fuel oil, it is in North and South America andAsia; and with blends of crude/distillate, it is in Europe With the emergence ofVenezuela as an oil giant, use of crude as a gas turbine fuel may increase in SouthAmerica

Combustion considerations. While fuel and machine design issues can best beaddressed by gas turbine suppliers, the generic concerns with the heavy, ash-bearing fuels are:

 Corrosion of high-temperature materials due to presence of trace metalcontaminants such as vanadium, sodium, and potassium

 Proper fuel atomization to ensure complete combustion and smoke-free stack overthe entire operating range of the gas turbine

 Ash deposition and fouling of turbine and heat recovery steam generator components

Because of these concerns, use of crude/heavy fuel oil has been prohibited in hightemperature (2400°F) “F Class” gas turbines by major gas turbine suppliers.Experience to date is with machines operating at firing temperatures of about2000°F and below For reliable operation of gas turbines with these fuels, it isimportant to follow the fuel procurement, fuel additive, and maintenancerequirements imposed by the equipment suppliers

BOP considerations

General. Crude oils typically have flash point temperatures lower than distillateoils and thus need provisions for explosion proofing Heavy oils have high pourpoints that are characteristic of paraffin-based oils and dictate the need for higherstorage temperatures

Thus special consideration needs to be given to design criteria for the fuelunloading and storage, fuel treatment, fuel heating, and fuel forwarding systems

Fuel storage system. In order to make the fuel pumpable, the fuel temperatureshould be at least 10°C (18°F) higher than its pour point While crude oil is generallypumpable without preheating, this is not the case with heavy oils Heavy oil storagetanks are typically maintained at approximately 30°C (86°F) with a bottom coilheater In addition, an outlet heat exchanger heats the exiting oil above 60°C(140°F) as it leaves the storage tank Further, fuel recirculation lines are provided

to establish and maintain the desired operating temperatures

Use of multiple storage tanks enables sufficient settling time for the water andother contaminants Use of fixed roof–type frame design minimizes salt and othercontaminants from the atmosphere from entering the fuel The storage tank bottom

is sloped to an area from which water and other settled material can be removedperiodically to avoid buildup of microorganisms at the fuel/water interface Thetreated fuel tank should have a floating suction in the fuel line feeding the gasturbine

Fuel handling system. The transfer piping is heat traced to maintain the fuel at theelevated temperature to reduce pumping costs Further, fuel recirculation lines areprovided to establish and maintain the desired operating temperatures The plantlayout considerations and need for hydraulic transient analysis listed in the section

on naphtha are also applicable here

Fuel treatment system. Heavy fuels are frequently contaminated with trace metalsand usually require both treatment to remove sodium and potassium, and injection

of additives to inhibit corrosion Crude oil requires washing to remove the sodiumand potassium Water washing of crudes in power plants is generally done by acentrifugal or electrostatic treatment system Centrifuges are preferred becausethey remove contaminants more reliably Electrostatic separators are moreappealing, however, because they do not have high-speed rotating parts

Emissions. From an emissions viewpoint, crude/heavy fuel oil is the leastdesirable fuel of the four fuels discussed in this paper These fuels generally containhigh levels of fuel-bound nitrogen, which increases NOx emissions Moistureinjection may bring the NOxemissions to acceptable levels For sites with stringent

NOx emissions limits, however, this fuel may not be an acceptable alternative.Generally, because of the higher sulfur content in this fuel, SO2emissions are alsohigher than the other fuels

Reference and Additional Reading

1 Soares, C M., Environmental Technology and Economics: Sustainable Development in Industry,

Butterworth-Heinemann, 1999.

Gas Turbine Cleaning or Washing (see Turbines)

Gas Turbines (see Turbines)

Gearboxes (see Power Transmission)

Reference and Additional Reading

1 Bloch, H., and Soares, C M., Process Plant Machinery, 2d ed., Butterworth-Heinemann, 1998.

Gears (see Power Transmission)

Generators; Turbogenerators*

This section is written with reference to specific models made by the Alstomcorporation Most generator original equipment manufacturers (OEMs) use similiarstandards

Standard Design

The modular design of the turbogenerator permits the selection of a standardversion with either an open or closed cooling system and static or brushlessexcitation systems

The generators satisfy the requirement of IEC-34 and other relevant standardssuch as SEN, ANSI, NEMA, CSA, etc This means that the generators can be used

in countries in which these or comparable standards apply Generators can becustom built to satisfy other standards

Configuration

The turbogenerators are two-pole, air-cooled synchronous generators withcylindrical rotor and direct air-cooled rotor winding They are intended for bothbasic and peak-load operations and designed to withstand high short-circuitingstresses The configuration with journal bearings in the end shields permits delivery

of the machines as a single unit which considerably simplifies installation andcommissioning See Fig G-1

Degrees of Protection and Methods of Cooling

The design of the generators provides for the following degrees of protection andmethods of cooling in accordance with IEC 34-5 and 34-6, 1983

Degrees of

parts inside the machine and drip-proof

G-1

* Source: Alstom.

Methods of Descriptions Cooling

through a screen-protected opening for differenttypes of air filters on the long sides of the statorand is exhausted through a flanged opening.This is located at the middle of the generatorhousing and can be connected to a hood for theexhaust air The method of cooling is then IC21

is cooled in turn by a water-cooled heatexchanger

These combinations of degrees of protection and methods of cooling are standardfor this information source

The different cooling methods require two fans mounted on the generator rotor.The use of the IC 01 and IC 21 methods of cooling presupposes that the coolingair supplied is cleaned by thorough filtration For this reason, IC 01 and IC 21

FIG G-1 An installed generator package (Source: Alstom.)

should be avoided when the cooling air available contains corrosive gases or largequantities of other pollution.

Arrangement Forms

The machines can be supplied in the following versions:

Arrangement

bearing end shields, one free shaft extensionend with coupling flange

bearing end shields, two free shaft extensionswith one coupling flange This version permitspowering of the generator from two directions.The stator is, in both cases, intended for footmounting If required, for example with anelevated turbine centerline, the above machines can be delivered with a base frame

Excitation System

The generators can be delivered with one of two alternative excitation systems

1 Rotary brushless excitation system. The winding of the generator rotor issupplied via a rectifier mounted on the shaft, from a directly connected 3-phase

AC exciter The system includes a pilot AC exciter

2 Static excitation system. This system consists of a static thyristor rectifier unitsupplied from an external power source The excitation current is connected tothe rotor windings via conventional sliprings The static thyristor rectifier unitcan be supplied on request

Accessories

The following accessories can be supplied on request:

 Fire extinguishing system

 Base frame

 Lubricating oil system

 Sound insulating enclosure

 Current transformer

 Voltage regulation system

The following information and requirements should be provided by the end user

to the OEM with any request for a bid

 Relevant standards and recommendations

 Rated power

 Temperature of the cooling medium

 Power factor with rated power

 Rated voltage and voltage range

 Rated main power supply frequency

 Rated rotational speed and overspeed

 Rotation direction (as seen from the exciter end)

 Generator power in relation to the maximum and minimum ambient temperatures

 Degree of protection and method of cooling

 Arrangement form

 Excitation system

 Application

 Cooling air quality (for methods of cooling IC 01 and IC 21)

 Cooling water quality (for method of cooling IC 71)

 Special requirements, e.g., thrust bearings

 Extra testing and documentation

Technical Data on Typical Available Generators

 Power range, 20–200 MVA (40°C cooling air, temperature rise in accordance withclass B)

 Insulation class F (155°C)

 Power factor 0.8 for 50 Hz, 0.85 for 60 Hz

 Standard voltage up to 80 MVA is 11 kV for 50 Hz and 13.8 kV for 60 Hz.Equipment for other voltages can be provided on request

Design Description

Stator frame

The stator frame is of welded steel construction See Fig G-2

The side plates are dimensioned to bear the weight of the complete generatorduring lifting Openings are provided in the top or sides for cooling air supply andexhaust Longitudinal foot plates are provided at the bottom of the long sides of thestator frame for fixing the stator to the foundation

Stator core

The stator core is built up of segments stamped from thin silicon-steel sheets thatgive high permeability and small losses See Fig G-2

The segments are varnished on both sides with a heat-resistant varnish to form

an effective and permanent insulation between the sheets

The segments are stacked to form a number of axial packages Radial cooling airchannels are formed between the packages by means of support plate segmentsprovided with spacers

The sheet segments are guided into place by axial guide bars The stator core ispressed with the upper pressure ring installed to give the sheet pressure specified.The pressure ring is then locked

The pressure rings and the superimposed pressure fingers are sprung into placeduring the pressing to maintain the necessary pressure in the stator core

Stator winding

The stator winding is a diamond winding installed in open slots with two coil sidesper slot The coils are manufactured in two halves that are brazed together.The strands are transposed alternately through roebling in the slot section of thecoil or by transposition, group by group, in the connections between the coils Thestrands are insulated with impregnated glass fiber yarn

The conductor insulation consists of MICAFOLD®.The insulation of the coil sides is built up as continuous tape isolation, i.e., boththe straight sections of the coil and the core ends are wound with tape Theinsulation consists of epoxy-impregnated mica glass-tape Both the preimpregnatedMICAREX® system and the vacuum-pressure impregnated MICAPACT® systemsatisfy the requirements for temperature class F (155°C) The insulation systemsused are described in more detail in separate brochures

The straight sections of the coils are fixed in the winding slots in the stator core

by means of contra-wedging Spring elements are inserted in the slots to hold thecoils in the winding slots, also after long service These exert uniform pressure onthe complete length of the straight section of the coil

FIG G-2 Generator stator (Source: Alstom.)

The ends of the stator coils are supported against the pressure rings in the statorcore by radial support plates of insulating material The coil ends are anchored

to the support plates and braced against each other The bracing system isdimensioned to withstand the stresses that can develop during normal operationsand following a sudden short-circuiting of the generator

Stator terminals

The connections to the busbars are located outside the generator casing (see Fig.G-3) The terminal bushings are connected to the terminal connections in the statorwinding with clamps with generously dimensioned contact areas The clamps areeasily accessible for removing the stator terminals for, e.g., transport

Fan covers

The covers are manufactured of heat-resistant, glass-fiber-reinforced polyester.Each cover is divided into removable segments to simplify inspection of the coilends

The fan covers are mounted against the stator frame over the coil end area andlead the incoming cooling air to the axial fans on the rotor shaft

Bearing end shields

The bearing end shields consist of a very stiff lower half with bearing housing (seeFig G-4) The upper half of the bearing housing is easily removed to facilitateinspection of the bearing Holes for supply and drainage of oil are drilled in thelower half The bearing housing is provided with connections for air extraction.The upper half of the bearing end shield consists of a sound insulating screenplate divided into three parts to simplify removal for inspection

FIG G-3 Stator terminal (Source: Alstom.)

Each bearing housing contains a radial bearing (see Fig G-5) for the generatorrotor The radial bearings are pressure-lubricated slide bearings with white-metallinings divided into staggered upper and lower segments Lubricating oil is supplied

to the bearing through drilled channels

Where the bearings must take up axial forces, one is provided with axial bearing pads The thrust bearing is double-acting, i.e., it takes up forces in bothdirections One of the bearings is insulated from the bearing end shield to preventthe development of damaging bearing currents

thrust-When the generator is to be driven from both ends, both bearings are insulated.The support bearing is always insulated The shaft seals prevent oil leakage fromthe bearing housing and consist of a divided seal of oil-resistant insulation material

An air extraction system is connected to the bearing space to prevent oil leakagethrough the external seals The internal shaft seals are provided with sealing capsand the intermediate space is connected to blocking air from the pressure side ofthe fan

FIG G-4 Bearing end shield (Source: Alstom.)

FIG G-5 Fan bearing assembly (Source: Alstom.)

The rotor body (see Fig G-6) is manufactured from a cylindrical forging of alloy steel with suitable magnetic properties A hole is drilled into the shaftextension for terminal conductors The terminal conductors carry excitation currentfrom the exciter to the rotor winding

high-A number of axial winding slots for the excitation windings of the rotor are milled

on both sides of the pole sections

each other The connections from the terminal conductor and radially outward tothe winding consist of contact screws The design of the contact screws eliminatesthe risk of fatigue failure in the connection details caused by the differentialmovement of the rotor winding and the shaft.

All joints are provided with gold-plated spring-contact elements to ensureeffective current conduction between the contact surfaces

Rotor winding

The conductors in the rotor winding consist of silver-alloyed copper Each conductorconsists of two strands The conductors are brazed to the rotor coils with silversolder

The rotor coils are installed in the winding slots in the rotor body with conductorinsulation of epoxy resin-impregnated glass fiber fabric between each conductorlayer The spaces at the side of the rotor coils function as ventilation channels.The straight sections of the winding are supported tangentially with a number

of bracing pins mounted in holes in the conductors and the coil insulation Thestraight sections are fixed radially by means of pressure bars filled with syntheticresin under high pressure The windings are thereby fixed radially and all play inthe winding slots is eliminated

The rotor coil ends are supported with blocks of glass fiber fabric laminate.Impregnated glass fiber fabric is used as insulation between the retaining rings

FIG G-7 Rotor terminal (Source: Alstom.)

and rotor coil ends of the winding The coil end insulation is provided with coolingchannels after hardening.

The insulation system satisfies the requirements for temperature class F (155°C)

Rotor retaining and support rings

Rotor retaining rings of high alloy nonmagnetic steel are shrunk on the rotor body

to provide radial support of the rotor coil ends against centrifugal forces duringrotation

The retaining ring material is not affected by stress corrosion To ensure that theretaining rings are sufficiently stiff to remain circular, a support ring is shrunk inthe outer end of the retaining ring, free from the rotor shaft

The retaining rings and the other parts of the bracing system are dimensioned to withstand the stresses that develop with short-circuiting andoverspeeding

Axial fan

A number of aluminum fan blades are mounted on a fan hub, shrunk on each shaftextension on the rotor The fan blades are easily removed and replaced when therotor is to be installed

Balancing and overspeed running

The rotor is balanced when the rotor winding, insulation, and retaining rings are

in place It is then heated to a high temperature and test-run at overspeed Thisresults in the winding adopting its final form before the rotor is finally balanced tosatisfy the relevant requirements The normal overspeed is 120 percent of the ratedspeed Certain of the balancing planes remain accessible when the rotor is installed

in the stator

Rotor cooling

The rotor winding (see Fig G-8) is directly air-cooled by ventilation channels indirect contact with the winding slots Cooling air is drawn in between the supportring and the shaft extension by the centrifugal fan effect of the rotor

The air cooling the coil ends passes out radially through holes in the coil endinsulation to the retaining ring and axially in channels under the retaining ringthrough holes in the support ring

The cooling air in the winding slots is drawn in under the coil ends and into theaxial cooling air channels between the sides of the slots and the conductor package.The rotor slot wedges and the beams between the winding slots are provided with

a number of exhaust openings, connected in parallel, for the cooling air

Cooling Systems

The generator is provided with two axial fans The main task of the fans is toventilate the stator (see Fig G-9); the rotor itself functions as a centrifugal fan Thegenerator can be provided with an open or closed cooling system The air circulation

in the different cooling systems is shown in Figs G-9 through G-11

In closed cooling systems (see Fig G-10), the cooler housings are mounted, withthe air/water coolers, on the long sides of the generator The cooler housings arewelded steel constructions that lead cooling air from the coolers to the axial fans

The air/water coolers are of the lamellar tube type The materials chosen for thetubes and water chamber are dependent on the quality of the cooling wateravailable.

Compensation air is drawn in through a filter to replace air leakage from themachine

With an open cooling system (see Fig G-11), the incoming air is to be filtered.The choice of filter is determined by the site conditions Recommendations forfilter selection are based on the information regarding the environment providedwith the request to tender

Figure G-12 illustrates a generator assembly that has not been installed

FIG G-8 Rotor winding (Source: Alstom.)

Rotating rectifier

The purpose of the rectifier is to rectify the AC current from the main exciter andprovide the rotor winding of the turbogenerator with DC current via connectors inthe center of the shaft

The electrical equipment in the rectifier consists of silicon diodes and RC protection.The rectifier is built of two steel rings that are shrunk on the shaft of the exciterrotor with intermediate mica insulation The steel rings are connected to theterminal conductors in the center of the shaft

All contact surfaces are specially processed to guarantee a high degree of rectifierreliability and stability during operations

FIG G-9 Cooling air direction (Source: Alstom.)

FIG G-10 Closed cooling system (Source: Alstom.)

FIG G-11 Open cooling system (Source: Alstom.)

G-12 Generator assembly (Source: Alstom.)

Pilot exciter

The pilot exciter is a synchronous generator with permanent magnets on the rotor.The rotor magnets are enclosed in a short-circuited aluminum ring that preventsdemagnetization of the poles because of short-circuiting in the stator winding.The stator winding insulation satisfies the requirements for temperature class F(155°C)

of a split seal of oil-resistant insulation material An air extractor is connected tothe bearing space to prevent oil leakage through the external seals Internal shaftseals are provided with sealing caps and the intermediate space is connected to theblocking air from the pressure side of the fan

FIG G-13 Main exciter (Source: Alstom.)

The exciter can be provided with either an open or a closed cooling system.With an open cooling system, a housing with filter cassettes is mounted on oneside of the exciter housing for the incoming cooling air The cooling air exit isdirected downward under the exciter housing

With a closed cooling system, the filter housing is replaced with supply andexhaust air channels connected to the cooler housing of the generator

Surface Treatment

In its standard version, the generator is painted with a lacquer of two-componenttype based on ethoxylized chlorine polymer The generator is primed inside andoutside and then finished externally in a neutral blue color The paint is resistant

to corrosive, tropical, and other aggressive atmospheres

The sliprings are manufactured of steel and have generously dimensioned contactsurfaces for the carbon brushes The spiral-machined contact surface is carefullyground and polished This prevents current concentrations and reduces brush andslipring wear The sliprings are shrunk on the shaft extension on a cylinder ofinsulating material The radial connections from the sliprings to the terminalconductors consist of insulated contact screws through holes in the shaft extension.The terminal conductors in the slipring shaft and the rotor shaft are connectedwith contact screws

The carbon brushes in the handle parts are mounted in holders of coil-spring typethat give a constant brush pressure during the service life of the brush The handleparts are insulated and the brush holders can be removed from the brush holderpockets by hand when the brushes are to be replaced Brush replacement is thuspossible during operations

Slipring housing

Openings are formed in the side walls of the housing for service These are coveredwith hatches provided with air filters The opening in the end wall of the housing,

towards the generator, through which the slipring shaft passes, is provided with aseal.

Inspection and Testing

General basic inspection and testing points performed during the fabrication of thegenerators are included in a check plan Each manufacturing operation is subject

its result is used as a reference for the subsequent machines of the same type Amore extensive test can be offered separately.

Control and Protection

Temperature monitoring

A number of platinum wire resistance elements installed in different parts of the machine are used for continuous monitoring of the temperature of the parts.The connection cables of the elements are routed to junction boxes on the outside

of the stator housing The number and location of the elements are shown in thefollowing list:

FIG G-15 Slipring assembly detail (Source: Alstom.)

Number Location

As a standard, the resistance elements have a resistance of 100 ohms at 0°C

Bearing vibration measurement

Vibration transducers of seismic type for bearing vibration measurement can bedelivered mounted on the bearing shields of the generator

 Negative phase-sequence current protection

 Stator earth fault protection

 Rotor earth fault protection

 Underexcitation protection and/or underexcitation limiter

 Reverse power protection (depending on the drive machine type)

TABLE G-1 Normal Testing

Measurement of generator losses (through run-down test) ¥

Loading point with cos j = 0 overexcited ¥

 Overexcitation and/or overexcitation limiter

 Loss-of-excitation protection; in installations where there is a risk of highovervoltages, a surge diverter is to be installed and, in certain cases, protectivecapacitors

Operating Characteristics

Operations with constant winding temperature

With gas turbine operations, the principle described as follows is applied Thisprovides an optimum relation between the permitted power output of the generatorand the power available from the turbine at varying cooling medium temperatures

In accordance with international standards, particularly for gas turbine–poweredgenerators, the generator can be loaded so that the maximum winding temperaturepermitted remains the same with a cooling air supply temperature other than 40°C The winding temperature rises permitted increase or decrease as much asthe temperature of the cooling medium falls below, or exceeds, respectively, thevalues given previously

Synchronous compensator operation

The generators are particularly suitable for synchronous compensator operation Topermit such operation, however, mechanical disconnection of turbine and generator

is usually required and one of the main bearings must be provided with thrust bearings

Operation at low ambient temperatures

With very low temperatures the generator can be provided with a recirculationarrangement for cooling air or water

Noise Reduction

When there are special acoustic requirements, the generator can be installed in asound-absorbing enclosure consisting of a steel frame with panels of perforated steelsheets with sound-absorbing mineral wool in-fill

The sealing against water leakage between the panels and the supportingstructure consists of a self-adhesive rubber strip and silicon-rubber caulking.The roof and walls of the enclosure are provided with service openings

Base frame

The stator frame of the generator is self-supporting and therefore requires no baseframe to provide stiffness If the center height is required to be higher thanstandard, the generator can be provided with a separate, welded, steel base frame

Grinding (see Abrasives; Some Commonly Used Specifications, Codes, Standards,

and Texts)

Grinding Wheels (see Abrasives)

Hazards (see Color Coding; Explosion; Some Commonly Used Specifications,

Codes, Standards, and Texts)

Heat Exchangers (see also Cogeneration; Regenerator; Vaporizers)

A heat exchanger basically removes or adds heat to a fluid The most common types

in process plants are shell and tube exchangers Plate types (consisting of conducting fins), cascade types (single pipe bent back and forth many times), andspiral plate and extended surface types are less common The working principle

heat-behind the heat exchanger is well illustrated in the section on condensers (see

Condensers) A heat exchanger is usually custom designed for a large process plant

by the overall contract designer Builders of items such as condensers andseparators generally also make related items such as heat exchangers and will have

a catalog on smaller items that can be bought without a custom order

Some information on different commonly available heater types follows

Heat Pumps; Heat Pumps, Geothermal; Heating Systems with

a Renewable Energy Source*

Working Theory behind Geothermal Heat Pumps

How earth loops work

A system of high-density polyethylene pipes is buried in the ground or installed in

a body of water to exchange heat between the building and earth An antifreezesolution is circulated through the pipes by low wattage pumps The plastic pipe wallbecomes a heat exchanger between the fluid and the surrounding earth In theheating mode the liquid in the pipe is cooler than the surrounding earth In thecooling mode the opposite condition exists Since heat flows from a warm area to acooler one, heat exchange occurs under both conditions

Pond and lake loops

Short polyethylene loop coils are stretched horizontally and attached to a plasticmesh to form a mat-style anchored heat exchanger Several mats are connectedtogether, and once in position the pipes are filled with fluid, possibly weighted, andthe mats sink to the bottom See Fig H-1

Open loops (well systems)

In areas where a good supply of clean ground water and an accessible waterdischarge system is available, an earth loop becomes unnecessary Well water ispumped directly through the unit and heat is either extracted from or rejected back

to the water table See Fig H-2

H-1

* Source: Enertran, Canada Adapted with permission.

Earth loop configurations

Earth loops (Figs H-3 and H-4) are installed in either horizontal or verticalconfigurations; the choice depends upon geographical location and the land areaavailable [This information source’s systems are sized to meet or exceed CSAStandard—M445 (sizing requirements), fulfilling the stringent energy efficiencyrequirements of the North American Building Codes.] Earth loop lengths arecalculated using a sophisticated computer program that predicts annual loopperformance, energy consumption, and operating costs

Horizontal loops. Horizontal loop designs vary from a single, in-series pipe tomultipipe parallel systems Pipes are laid in trenches 4–6 ft deep, using a backhoe

or trencher, and pressure tested, and then the trench is backfilled See Fig H-3

Vertical loops. Vertical loops usually require less pipe than horizontalconfigurations Vertical loops are connected in series or parallel or both Drillingequipment produces small diameter holes, 75 to 300 ft deep Two pipes are joined

FIG H-1 Pond and lake loops (Source: Enertran.)

FIG H-2 Open loops (well systems) (Source: Enertran.)