equipment design - boilers

8/6/2019 Equipment Design - BOILERS

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BOILERS

MU CLARIDAD



BOILER- a device for

generating steam. It

consists of two principal

parts: the Furnace, whichprovides heat, usually by

burning a fuel, and the

Boiler proper, a device in

which the heat changes

water into steam.



Steam Generators are designed to

produce steam for process requirements,

for process needs along with electricpower generation, or solely for electric

power generation.



In the industrial market, boilers have been

designed to burn a wide range of fuels andoperate at pressures up to 12.4 Mpa (1800

psia) and steaming rates extending to 455,000

kg/h (1,000,000 lb/h).

High-capacity shop-assembled boilers

(package boilers) range in capacity from 4545

kg/h (10,000 lb/h) to about 270,000 kg/h

(600,000 lb/h). These units are designed for

operation at pressures up to 11.4 MPa (1650

psia) and 783 K (950°F).



BOILER DESIGN ISSUES

Boiler design involves the interaction of many

variables:

Water-steam Circulation

Fuel Characteristics

Firing Systems

Heat Input Heat Transfer



CIRCULATION AND HEAT TRANSFER

CIRCULATION

as applied to a steam generator, is the

movement of water or steam or a mixture of

both through the heated tubes.

WATER

STEAM



CIRCULATION AND HEAT TRANSFER

HEAT TRANSFERThe rate of heat transfer from the tubes to

the fluid depends primarily on turbulence and

the magnitude of the heat flux itself.

TURBULENCE is a function of mass velocity of the fluid and tube roughness achieved by

designing for high mass velocities, whichensure that nucleate boiling takes place at theinside surface of the tube.



UTILITY STEAM GENERATORS

Steam-Generator Circulation System

Circulation systems for utility applicationare generally classified as natural circulation

and forced of pump-assisted circulation in

drum-type boilers, and as once-through flow

in subcritical- and supercritical-pressure

boilers.





Fuel choice has a major impact on boilerdesign and sizing. Because of the heat transfer

resistance offered by ash deposits in the

furnace chamber in a coal-fired boiler, the

mean absorbed heat flux is lower than in gas-

or oil-fired boilers, so a greater surface area

must be provided.





Coals having a low volatile-matter content

usually require higher ignition temperatures.

In addition, coal

characteristics have a

major impact on the

design and operation of

a coal-fired boiler.




Superheaters and Reheaters

Superheater raises

the temperature of thesteam generated above

the saturation level. An

important function is tominimize moisture in the

last stages of a turbine to

avoid blade erosion.



SUPERHEATER




Economizers

Improve boiler efficiency by extractingheat from the discharged flue gases and

transferring it to a feedwater, which enters the

steam generator at a temperature appreciably

lower than the saturation-steam temperature.



INDUSTRIAL BOILERS

Industrial Boilers

are steam generators

that provide power,steam, or both to an

industrial plant, in

contrast to a utility boiler

in a steam power plant.



INDUSTRIAL BOILERS

Design Criteria

Industrial-boiler designs are tailored to thefuels and firing systems involved.



Design Criteria

Some of the more important designcriteria include:

Furnace heat-release rates both W/m3 and

W/m2 of effective projected radiant

surface

Heat release on grates

Flue-gas velocities through tube banks Tube Spacing



INDUSTRIAL BOILERS

Package Boilers

2 Types of Package Boilers:

Fire-tube Package Boiler

Water-tube Package Boiler



INDUSTRIAL BOILERS

Package Boilers

In a Fire-tube

Boiler, the hotcombustion products

flow through tubes

immersed in the boiler

water, transferring

heat to it.



INDUSTRIAL BOILERS

Package Boilers

The greater safety of water-tube boilershas long been recognized, and they havegenerally superseded fire-tube configurationsexcept for small package boiler designs.



INDUSTRIAL BOILERS

Package Boilers

The majority of water-tube package boilersusenatural circulation and are designed for

pressurized firing. The mostsignificant advantage of shop-assembled or package boilers is thecostbenefit associated with use of standard designsand parts.



FLUIDIZED-BED BOILERS

Although the furnace of a fluid-bed boiler

has a unique design, the system as a wholeconsists mainly of standard equipment items

adapted to suit process requirements.




Bubbling FBCs (Fluidized Bed Combustion)

Bubbling FBC is used primarily for burningbiomass, although coal may be cofired to

maintain heat release rates when feeding high

moisture feedstocks such as sludges.




Circulating FBCs (Fluidized Bed Combustion)

Circulating FBC is the more widelydeployed than the bubbling-bed design and at

far larger sizes.

equipment design - boilers

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