Boiler Classification + Components

Natural Circulation

feed water tube goes to the steam drum

- density differences (heat expands water to make it less dense)

Free Circulation

slight angle generating tubes

Accelerated Circulation

steep slope between steam drum and water drum

Forced/Controlled Circulation

pumps

- avoid steam blanketing and prevent tube damage from high heat transfer rates

-pump located along downcomer

Steam Blanketing

when a pump is working too fast, the steam flashes and fills up the generating tubes.

-steam forms a layer on metal and that causes overheating/corrosion

-fix by slowing or stopping pump so tubes can refill with water

Flow Central Orifice

present if forced circulation boilers - used to maintain a constant flow/pressure because there is no feedwater regulator

Natural Circulation Boiler: Drum-Type

recirculation

Natural Circulation Boiler: Header-Type

LP small boilers that use smaller headers to distribute saturation mixture to vertical separators, using centrifugal force to separate

Drum Type Boilers

one or more water drums/water headers

Water Header

a manifold that distributes feedwater and acts as a recirculation point

Header-Type Boiler

no water drum - water header and many tubes act as the water drum

Steam Generation

as the rate of generation increases, it eventually reaches an end point in which the rate can't get any higher

End Point

when steam generation can't increase

-moisture carry-over (max steam)

-water circulation (max water)

-combustion rate (max fuel)

Steam Drum

water reservoir - steam separator - receive + distribute feed

-fore/aft ships

Drum Internal Classes

1st class moisture/impurity removal - 2nd class feed water distribute - 3rd class continuous blow-off

Drum Impurity Removals

scrubbers (collect moisture as steam passes), cyclone

Water/Tube Sheet

steel rolled into circular shape then welded

Upper/Exterior Sheet

wrapper sheet

Lower/Interior Sheet

tube sheet (where tubes enter)

Drumheads

welded at the ends of the drum and one has a manhole

- oval manhole for better sealing

Water Drums/Header

-distribute water to generating tubes

-accumulate scale and solids

-headers=handholes while drums=manholes

Increased Boiler Size

increase in furnace load, water circulation speed, steam temp/pressure, and combustion gas velocity

Sprayer Plates

turns solid streams of oil into fog like particles for burning

Gas FIlm

heat transfer deterrent from fire side to the water side of a boiler

Water Wall Tubes

causes higher combustion rates

- floor, rear, or side

Water Screen Tubes

protect the superheater from furnace temp

- act as generating tubes at high rates of heat transfer

- next to generating tube banks

- protect superheater tube tank for a water tube boiler

Sagged Tube

must be punctured if a water tube boiler to prevent pressure buildup

Water Tracking/Cratering

water trapped between tubes and refractory causes corrosion of tubes

Boiler Tube Pit

forms from dissolved oxygen

Boiler Sliding Feet

accommodates water drum changing length, from temperature

Types of Circulation Tubes

generating/water wall/water screen/downcomers

Tube Location

water wall (start) then screens then the first few rows are closest to the furnace (little to large away from furnace)

Downcomers

3-7 inches AND installed between inner/outer casing to keep water cool

Generating Tubes

multiple rows of 1-1.25 inches

Water Wall/Gas Baffle Tubes Types

studded, finned, and tangent

Studded Tubes

furnace refractory part (plastic/castable chrome)

Tangent Tubes

cool refractory solid tube wall

Finned Tubes

welded insulation longitudinally along the tube

- heat transmission from fin to water in tube

Superheater Tube Location

between screen tubes and generating tube bank

Superheater Support Tubes

support steam drum + superheater

- downcomer at low firing rates

- generating tube at high firing rates

Roof Circulating (Riser) Tubes

on boiler roof with heavy insulation to avoid absorbing heat

- circulates steam that accumulated in upper waterwall headers back to the steam drum

Superheater Important!

during operation, steam must be flowing through the superheater at all times because it is the cooling medium

- must have a vent and a safety valve that can release 25% steam at max firing rate

Economizer

requires relief valves if given feed isolation valves

Hand-Fired Boiler

the user manually loads fuel and manages output

Fusible plug

450-degree melting point, hand-fired boiler, brass/bronze core, and warns about a low water condition

Stays

used on boilers with flat surfaces, diagonal stays for firetube

Manhole Gasket

sealing component that can be 1/4 in thick and is required to cover at least 11/16 inches

Blisters

develop on boiler tubes as a result of waterside scale deposits

Generating Tube Expansion

roll the tube to a depth greater than the drum tube sheet thickness

First End Point

Combustion