1. BOILERS AND STEAM SYSTEMS ..BOE.ppt

Agro waste fired water tube Boiler

Siphon for Bourden tube Pressure guage

Water level Indicators……types

Blow Down Valve…..Manually Operated

Why Steam ?
 Highest specific heat and latent heat
 Highest heat transfer co efficient
 Easy to control and distribute
 Cheap and inert

Uses
 For power generation
 For process industries
-- For process heating
-- For drying

Some user industries
Sugar
Paper
Fertilizer
Refinery
Chemical
Food
Petrochemical

Length
1 inch =2.54 cm
Weight
1 Kg = 2.205 Lb
Area
1sq inch = 2.54 x2.54 =6.45 cm2

Volume
1 litre = 1000 cc
1 cubic feet = ?
Temperature
0 C = [0 F –32] x 5/9
0 F = [0 C x 9/5 ] + 32
Pressure
1 Kg/ cm 2 = 2.205 / 1/2.54 x 1/2.54
= 2.205x2.54x2.54 =14.23 psi

PROPERTIES OF STEAM
Heating water at constant pressure
Heat
Weight
Piston
Water

Liquid
Enthalpy
Liquid +
vapour
Super heated
steam
Sat temp
Saturation
curve
hf hfg hg
T

Specific heat
The quantity of heat required to raise the
temperature of One Kg of material by 10C
For water =1 Kcal/Kg/ 0C
Sensible heat [hf]
The heat required to change the temperature
of a substance is called sensible heat
[ 1 Kg of water at 250 C is brought to 1000 C by
adding 75 Kcal]

Saturation temperature
The temperature at which the water changes
into steam is called the boiling point or the
saturation temperature
[The temperature of the saturated steam is the
same as the water from which it is generated
and corresponds to a fixed and known
pressure]

Latent heat [hfg ]
To change water to steam an additional 540
Kcal would be required.The quantity of heat
required to change the chemical from liquid to
gaseous state is called latent heat.
The phase change occurs at constant
temperature

Degree of super heat
Super heating is the addition of heat to dry
saturated steam with out increase in pressure
The temperature of super heated steam
expressed as the degrees above the
saturation temperature corresponding to the
pressure is referred to as the Degree of super
heat

Enthalpy of dry steam
This is the total heat content of steam
hg = hf + hfg
Dryness fraction
x = mass of dry vapour / mass of
contents
= mg / mf + mg

Wetness
= mf / mf+ mg
=1-x
Enthalpy of wet steam
h = hf + x hfg

Heat addition due to super heating
=Cp [ tsup –t]
Enthalpy of super heated steam
= hg + Cp [ tsup –t]

Volume of steam
V = Vf + m[Vg-Vf]
= mVg
Superheated steam-volume
Behaves as a Perfect gas
Pg Vg / Tg = Psup Vsup / Tsup
Vsup = Vg Tsup / 273 + t

Question: ???
Boiler operates at 8 Kg/cm2 Steam sat temp
–170 0C
a] Find the total heat
b] If the steam contains 4 % moisture find
the total heat

Ans:
a] Total heat
hg = hf + hfg
=171.35 +489.46 =660.81 Kcal/Kg

b] wetness = 4%
dryness fraction = x = 1- .04 =0.96
Total heat of wet steam
hg = hf + x hfg
=171.35 +0.96 x 489.46 =641.23
Kcal/Kg

Critical Pressure
The pressure at which the latent heat of
vapourisation is zero ie; water will directly
change into steam if the temperature is
raised to the saturation temperature
Psup cr = 3206.2 psi
= 225.3 Kg/ cm 2
Tsup cr = 705.40F
= 374.10C

REMAINING SLIDES FOR
REFERANCE AND ADDITIONAL
INFORMATION

STEAM DISTRIBUTION
Pipe sizing
Mains drainage
General lay out and fittings

Boiler
Equip-1
Equip-3
Equp-2
Too long – radiation loss
high cost
small - starvation

STEAM PIPE SIZING
Pressure drop
Frictional resistance
Fittings
Usual allowance for fittings is 10 % for
30 metres

Velocity
Superheated 50 – 70 m/sec
Saturated – 30 – 40 m/sec
Wet 20 – 30 sec

Inversely proportional to 5th power of
diameter
D = 12√CFM
0.7854F
CFM – Cubic feet /minute
D – Dia inches
F – Velocity f/minute

PIPE REDUNDANCY
Avoid redundancy (usually 10 – 15 %)
Use the shortest route
Care should be taken to include the
thermal expansion

DRAIN POINT
100 mm lagged pipe 30 metres
length 7kg/cm2 can condense
10kg/hr.
may result in water hammer
wet steam

PROVISION FOR EXPANSION
Pipes filled cold will expand when steam
passes
May result in the loss of original slope
Anchorage to be provided for the expansion
fittings
Feed line, main steam line etc. to be
anchored

Types
Loop
Slip bellows
Bellows
Corrugated pipe
Smooth sleeve with slide

LENGTH OF EXPANSION
(t1 – t2) x L x 0.00065) inches
t1= steam temperature
t2= room temperature
L = horizontal length

Expansion joint
Smooth sleeve with slides in an out
through a packing box (Used for LP
steam)

Pipe supports
Side /forward movement – allowed
Vertical movement - not allowed
Supports – to carry full load
Hanger type - have adjustable turn
buckle

BRANCH LINE & FITTINGS
All branch lines should be from top
900 elbow – No
concentric reducer - no
eccentric reducer – yes
900 bend (wide sweeping) - yes

Steam Separator
used for separating moisture carried by
the steam.
centrifugal steam separator
baffle type

STEAM TRAPS
1. bucket traps
-- open bucket
-- inverted bucket
the movement of a bucket as it is
filled and emptied causes the discharge
valve to open and the steam pressure then
forces the condensate out of the traps. As
the bucket empties it returns to the original
position and closes the discharge.

2. Ball and float type
contains a hollow metallic float. As
the trap fills with the condensate the
float rises and open the discharge
valve. As steam pressure empties the
trap the float sinks and the discharge
valve closed.

3. Thermostatic (expansion type)
the expansion and contraction of
metallic element in the trap by oil in
sealed cartridge acting upon a sealed
plunger(usually a metallic bellows to
facilitates to the expansion)

4. Bimetallic trap
the above action is caused
instead of the bellows by a
bimetallic element

5. Thermo dynamic
as the condensate enters it lifts
the disc allowing the condensate flow.
When steam enders the flow velocity
is high resulting in reduced pressure
below valve seat and higher pressure
above the seat, causing it to close.

Valve lifts
p
P
Valve closes
P
p
b) steam
condensate

INSTALLATION OF STEAM TRAPS
Drain point
Pipe sizing
Air lock
Group vs individual traps
Dirt
Water hammer
Condensate lifting

MAINTENANCE
Dirt / scale
Use strainers
Sight glass
Maintenance schedule

POINTS TO BE NOTED FOR STEAM
DISTRIBUTION
-Shortest route, proper size of piping
-Slope to the direction of flow (125 mm to 30
metres)
-Use of eccentric sockets for reduced mains
-Re-laying the mains for long distance
-Provision for expansion – anchoring

-Supports - no vertical movement
-Branching only from top.
-Avoid 900 elbows Use long sweep bends.
-Use reducing valves for low pressure lines
(Install pressure gauge and safety valve)

-Lagging
-Draining points, equal tee, proper traps – 30 –
45 metres interval
-Install separators
-Avoid trapping as far as possible
-Boilers to common header – slope towards
boiler ends with provision for condensate
drain out
-Steam traps – horizontal installations. (open
bucket/TD traps)

ECONOMY MEASURES
--Lowest pressure practicable
--Right quality of steam
--Never supply more than required

--Reduce unnecessary demand by
isolating
--Condensate recovery
--Surface loss to be kept minimum
--Supply to be maintained at steady
pressure

ENERGY SAVING OPPORTUNITIES
1. Monitoring steam traps
Condensate discharge
Flash steam
Continuous blow - leak
Intermittent blow – flash steam
Continuous flow /no flow

2. Steam leakage (avoid)
--3 mm dia hole in pipe 7kg/cm 2
Loss = 33KL of FO /year.
--Plugging all leakes – 5% savings in
steam consumption

Plume length 700mm
Steam loss 10kg/hr

3. DRY STEAM FOR PROCESS
Reduces total heat
Wet film - slow heat treat
Dryness fraction – 0.95 without super
heater
Lagging
Steam separator

4. UTILIZE STEAM AT THE LOWEST
ACCEPTABLE PRESSURE FOR THE
PROCESS
-latent heat (high for LP)
-heat transfer (high at high temperature)
(balance them for indirect heating)

5. PROPER UTILIZATION OF DIRECTLY
INJECTED STEAM.
Cheap equipment
No condensate recovery system
Used only when dilution and agitation
allowed.
Pressure – 0.5 to 1 kg/cm2
2mm – 5mm holes in the distribution pipes.

6. MINIMISE HEAT TRANSFER
BARRIERS
Direct contact
Intermediate heating surface
Barriers
Air film
Condensate film
Inside scale
Metal
Outside scale
Stagnant product

Air - 1500 times resistance than steel
13000 times resistance than copper
air ingress during condensing / start ups
etc.

7. PROPER AIR VENTING
-0.2 mm air film = 330 mm thick copper.
-It reduces the partial pressure
-drops the overall temperature
-provide air venting provisions.

8. CONDENSATE RECOVERY
-25% of the total heat in steam leaves as
condensate.
-600C rise in feed water temperature – 1%
saving in fuel.
-Boiler water to be treated – condensate is
nearly pure.
-Reduces water treatment cost

9. INSULATION OF STEAM PIPE / HOT PROCESS
EQUIPMENT
-Heat loss due to radiation
One un lagged flange = 0.6 m of pipe
If dia = 15cm and 5 flanges, Loss per year = 5
tonnes of coal or 3000 litres of FO
-Insulation – detachable type
-Common materials
-Glass wool, cork, rock wool, asbestos , ceramic
fiber,

ECONOMIC THICKNESS OF
INSULATION
Un insulated 50 mm 100 mm
275 kcal/m 25kcal/m 15kcal/m
heat loss 89MM STEEL PIPE 900C

50 mm insulation  275 – 25
= 250 kcal/m
= 260 litre/year
50 mm to 100 mm  25-15
= 10kcal/m
= 9 litre/year.

10. Flash steam recovery
Produced when condensate at high pressure
is released to lower pressure.
It can be used for low pressure heating
Flash steam % = S1-S2
L2
S1 – sensible heat of HP steam
S2 – sensible heat of LP steam
L2 - latent heat of flash steam. (LP)

Flash vessel
-Large dia to reduce velocity
-Height sufficient to have dry steam at
top.
-Safety valve
-Strainer and float type trap.

11. REDUCING WORK DONE BY STEAM
Reduction in operating hours.
Reduction in steam quantity
Use of more efficient technology
Minimising wastage

1. BOILERS AND STEAM SYSTEMS ..BOE.ppt

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1. BOILERS AND STEAM SYSTEMS ..BOE.ppt