GAS TURBINE 2

1

Fuel System

Technology

Off-Base Fuel Systems for Gas Turbines

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2

Fuel System

Technology

Gas Turbine fuels

and Fuel Flexibility

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3

Fuel System

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Need for Fuel Flexibility- Fuel Availability

- Cost of Fuel

- National Interest

3

Gas Turbine Fuels:Gaseous Fuels:

1) Natural Gas

2) Refinery Gases

(High Hydrogen content)

3) Liquified Petroleum Gas

(LPG) [wet gases]

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Gas Turbine Fuels:Liquid Fuels:

1) Distillates

- Naphtha, Kerosene,

Diesel Oils

2) Heavy Oils (ash forming)

- Petroleum Crude Oils,

Petroleum Residual Oils

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Fuel Gas System:1) On-Base fuel gas system - to regulate gas fuel flow based

on load of gas turbine

2) Off-Base fuel gas system - provides necessary fuel gas

conditioning as required by

on-base system

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On-Base Gas Fuel

System requirements:1) The fuel gases shall conform to

spec. GT 10197, fuel gas

supply specifications

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The fuel gas properties

Which are controlled in off-base fuel gas system, as required by

GT

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1) Removal of particulate matter

- sand and clay

- Rust

- Construction debris

Particulate matter to be removed

down to 10 microns

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2) Ensuring 28 Deg. C super heat of fuel

gas at GT inlet

- above hydrocarbon dew point

- above moisture dew point

thus ensuring no condensate will form

in the GT on-base system

3) Prevention of hydrate formation in

fuel gas treatment system

4) Maintaining fuel gas pressure within

the allowable limits of gas turbine.

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Effect of contaminants

on GT operation:1) Particulates:

- Plugging of nozzles

- Erosion

- Deposition

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Effect of contaminants

On GT Operation: 2) Liquid condensates:

- Rapid excursions in firing

temperature and GT load

- Melting of hot gas paths

- Blow out (liquid water)

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Effect of contaminants

On GT Operation:3) Gas Hydrates are crystalline materials that are formed when free water is present in the gas which combines with gas compounds.

Hydrates can plug stagnant areas like

orifice plates, valves,instrumentation

etc. Maintaining fuel gas above water

Dew point temperature ensures prevention of hydrates formation.

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Main Processing equipment

for Fuel Gas Conditioning:1) Dry Gas Scrubber

2) Particulate filter

3) Filter Separator

4) Fuel gas heater (Electric/Steam)

5) Pressure Control Station

6) Fuel gas compressors

(if fuel gas is available at a lower pressure

than required by GT)

7) On-off valves, vent header, drain tanks etc.

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Various configurations of fuel gas conditioning systems

Involving simple particulate filter to most complex systems are engineered to meet the specific requirements of a project.

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If a gas compressor is used, if incoming gas supply pressure is too low to meet the gas turbine pressure requirements, advantage can be taken of heat of compression to avoid the cost of a gas super heater.

A surge vessel is required for on-line

change over of GT to alternate fuel

in case of tripping of fuel gas

Compressor.

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Special Considerations for Refinery gases:

1) If Refinery gas contains more than 5% by

volume of Hydrogen

- alternate startup fuel is required

- No flanged connections are permitted

within GT Hall

- GT requires inert gas purge/blocking

system. Nitrogen shall be made

available at two pressure s 2 Bar (g)

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Special Considerations for Refinery gases: (contd.)

and 30 Bar (g) for the purpose of

purging.

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Fuel Oil System:1) On-Base fuel oil system - to regulate fuel oil flow based

on load of gas turbine

2) Off-Base fuel oil system - provides necessary fuel oil

conditioning as required by

on-base system

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On-Base Fuel Oil

System requirements:1) The fuel oils shall conform to

spec. GT 10505, Gas Turbine Liquid

fuel specification.

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Fuel Oil Properties and

Contaminants that affect

the operation of GT and

Fuel Handling System

System requirements:

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Concerned fuel oil properties: - specific gravity (separation of impurities)

- viscosity (pumping, heating, atomization,

lubrication)

allowable max. limit 10 cst for Distilates

20 Cst for heavy oils

(for proper atomization)

Min. allowable viscosity is 1.8 Cst for proper

lubrication.

- flash point (explosion proofing requirement,

floating roof requirement for tanks)

- wax (plugging of filters)

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Concerned fuel oil contaminants: - solids (sand, rust, metallic oxides which

cause fouling of filters, control

systems, fuel pumps, flow dividers,

and fuel nozzles)

- water (presence of water along with bacteria

in oil will degrade oil creating slimy substance

which can plug the filters and jam the flow

divider)

which can cuse viscosity (pumping, heating, atomization,

lubrication)

allowable limit 10 cst for Distilates

20 Cst for heavy oils

(for proper atomization)

- flash point (explosion proofing requirement,

floating roof requirement for tanks)

- wax (plugging of filters)

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Concerned fuel oil contaminants: (contd.) presence of water can create emulsions which

will plug the filters.

water can also cause corrosion if left in flow

dividers and pumps.

- Trace Metals (Na, K, Va, Ca, Lead)

(hot-temperature corrosion, deposits)

which can cuse viscosity (pumping, heating, atomization,

lubrication)

allowable limit 10 cst for Distilates

20 Cst for heavy oils

(for proper atomization)

- flash point (explosion proofing requirement,

floating roof requirement for tanks)

- wax (plugging of filters)

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- Distillate fuel oils such as Naphtha and

kerosene are generally pure fuels require only

proper maintenance of storage tank and fine

filtration.

- Diesel fuels generally confirm to IS-1460

which has filterable dirt as high as 4 mg/100

ml, thus require a centrifuge to reduce the load

on filtration equipment provided.

- Ash forming fuels contain trace metal

components in addition to impurities found in

distillates in higher proportions, calling for fuel

washing.

will plug the filters.

water can also cause corrosion if left in flow

dividers and pumps.

- Trace Metals (Na, K, Va, Ca, Lead)

(hot-temperature corrosion, deposits)

which can cuse viscosity (pumping, heating, atomization,

lubrication)

allowable limit 10 cst for Distilates

20 Cst for heavy oils

(for proper atomization)

- flash point (explosion proofing requirement,

floating roof requirement for tanks)

- wax (plugging of filters)

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- The minimum allowable viscosity for GT is

1.8 Cst. Viscosity of oil below 1.8 Cst requires

dosing of additive Hitec-580.

Normally Naphtha fuel oil requires above

dosing.

- Trace metal vanadium can not be removed

by washing which requires dosing of an

inhibitor.

- Lead cannot be removed by any process.

Hence, shall be limited in the fuel oil

specification.

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Off-Base Liquid Fuel Handling Systems:

1) Fuel Oil Unloading System

2) Fuel Oil Storage System

3) Fuel Oil Treatment System

4) Fuel Oil Forwarding System

5) Fuel Oil Dosing System

6) Fuel Oil Filtration System

7) Fuel Oil Drain System

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Steps to ensure minimize chances of contaminated oil unloaded at site:

1) Cleaning the tank wagon before loading by

supplier

2) Dedicated unloading tankers (or) trucks

3) Providing Coarse filter at unloading inlet of

tank

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Recommendations on Fuel Oil Storage System:

1) Two Storage tanks are recommended for each fuel. One tank is in use. The other tank is settling. After filling a tank or after adding additional fuel to it, a minimum of 24 hours settling should occur before taking fuel from the tank.

2) Fixed roof tanks are preferred. For volatile fuels fixed cum floating roof tanks are to be provided to avoid ingress of rain water.

3) Water and other sediments should be drained on a regular basis.

2) Dedicated unloading tankers (or) trucks

3) Providing Coarse filter at unloading inlet of

tank

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Such steps as draining water and sediment from the tank regularly, letting a tank settle for 24 hours before use and making sure that the drain is at the lowest point in the tank - All these can reduce problems related to fuel pump, flow divider and check valve and short filter life etc..

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