Steam Distribution

1
80
HP steam
PRS unit
15
Flue gases
losses

3
Power PRDS Plant Unit
Fuel 100
Boiler Process Plant Plant
55 to process
2
losses
Blow down
Condensate
20
5
Standard Steam Circuit - Energy Balance
2
Selection of Working Pressure

• What is the right pressure for given process
• Objective should be process temp.
• Heating water to 850C can be achieved using
• steam at any pressure above atmospheric.
• Would you use steam at -
• (a) 2 barg.sat.
• Or (b) at 7 barg.sat.
• Or (c) superheated at 2barg.2000C?
• For indirect heating, latent heat released will
  be -
• (a) 517.6 Kcal/Kg.
• (b) 489.9 Kcal/Kg. 5.3 more consumption
• (c) 517.6 Kcal/Kg. At a very slow rate

3
Selection of Working Pressure - contd.
For indirect heat transfer process - The right
choice is the lowest possible. Rule of thumb -
Pressure giving T(steam) 350C For Direct heat
transfer process - It does not matter so long as
you ensure thorough mixing of steam with the
product.
4
Distribute at High Pressure

• This will have the following advantages
• Smaller bore steam mains needed and therefore
  less heat (energy) loss due to the smaller
  surface area.
• Lower capital cost of steam mains, both
  materials such as pipes, flanges and support
  work and labour. Lower capital cost of
  insulation (lagging).
• Dryer steam at the point of usage because of the
  drying effect of pressure reduction taking
  place near the equipment.
• The boiler can be operated at the higher
  pressure corresponding to its optimum operating
  condition, thereby operating more efficiently.
• The thermal storage capacity of the boiler is
  increased, helping it to cope more efficiently
  with fluctuating loads, and a reduced risk of
  priming and carryover
• How much reduction in thermal storage capacity
  of a 10.5 barg rated boiler operated at 7 barg.?

5
How Do We Pipe Size?
Spirax Customer

• On the basis of
• Fluid Velocity
• Pressure Drop

6
Pipe Sizing

• Greater Cost
• Greater Heat Loss
• Greater Volume of Condensate Formed
• Lower Pressure to Steam Users, or
• Not Enough Volume of Steam
• Water Hammer and Erosion

7
Methods of Steam-pipe Sizing

• Velocity Method
• For saturated steam system
• Ideally suited for Process use
• Pressure Drop Method
• For superheated steam
• Ideally suited for Power Plants Co-gen units

8
Methods of Steam-pipe Sizing - contd.

• Factors governing the method to be used -
• Steam Pressure and Temperature
• Size of distribution network
• Longer lengths
• Larger pipe sizes
• Criticality of pressure drop th.stresses
• Mostly for Power plants and HP cogen

9
Methods of Steam-pipe Sizing

• Rules of thumb to be followed -
• Maximum velocity 15 m/s for LP wet steam(flash
  steam)
• 25 m/s for sat.steam long lengths
• 30 m/s for sat.steam short tappings
• 40 m/s for superheated steam
• Normal Pressure Drop Less than 10 inlet
  pressure
• Less than 1 Kg/cm2 for given length of
  piping.
• Equivalent length of piping - Add 10 for
  fittings in the line.

10
Pipeline Capacities at Specific Velocities
Pressure Velocity kg/h bar
m/s 15mm 20mm 25mm 40mm 50mm
80mm 100mm 150mm 1.0
15 8 17 29 65 112
260 470 1020
25 12 26 48 100
193 445 730 1660
40 19
39 71 172 311 640
1150 2500 4.0
15 19 42 70
156 281 635 1166
2460 25
30 63 115 270 450
1080 1980 4225
40 49 116
197 456 796 1825 3120
7050 10.0 15 41
95 155 372 626 1485
2495 5860
25 66 145
257 562 990 2205 3825
8995 40
104 216 408 910 1635
3800 6230 14390
11
Steam-pipe Sizing Examples

• Size the line to carry -
• (a) 300 kgs/hr.steam at 1 barg to FWT 150 m.away
• (b) 1100 kgs/hr.steam at 10 barg to a drier
  300m.away
• (c) Superheated steam 2TPH at 15 barg.300C to
  turbine at a distance of 50 m.

12
Waterhammer - a phenomenon

• Steam has low density but high velocity
• WP 10 barg Density 5.5 Kg/m3 Velocity 25m/s
• Condensate has high density but low velocity
• WP 10 barg Density 909 Kg/m3 Velocity 3m/s
• Impact or Momentum Mass X Velocity
• Condensate having 160 times mass density
  travelling
• at 10 times its normal velocity will exert
• 1600 times greater impact.

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Waterhammer
SAGGING MAIN
Condensate
Vibration and noise caused by waterhammer
Slug of water from condensate
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What is water-hammer?
Water-hammer is the hammer like impact due to
fluid flow in a pipeline. This can happen in
any line carrying two-phase flow Steam lines with
lot of condensed steam not properly
drained Condensate lines with flashing of
condensate in the line. The effect would be -
Severe mechanical vibrations Heavy
leakages from joints Ruptured pipelines
15
Ineffective, and Proper Drain Points
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Steam Line Reducers
Correct
Steam
Condensate
Incorrect
Steam
17
Branch Connections
Condensate
18
Drop Leg
Main
Shut off Valve
Trap Set
19
Warm Up Loads/Running Loads(kg)per 50m of Steam
Main
Figures in italics represent running loads
Ambient temperature 200C, insulation efficiency
80
20
Calculation of Pipe Expansion
21
Recommended Support Spacing for Steel Pipes
22
Rollers for Steel Pipework
Twin Pipe Support Bracket
Chair Roller
Chair Roller Saddle
23
Air Venting
Balanced Pressure Air Vent
Steam Main
Thermodynamic Steam Trap with optional Blowdown
and for ease of maintenance a universal coupling
Air
24
Heat Emission from Bare Pipes
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Calculation of Heat Transfer
Where Q heat transfer rate (W) U overall heat
transfer coefficient (W/m2K) A mean surface
area (m2) ?t temperature difference (K)
26
THERMAL INSULATION

• TO REDUCE HEAT LOSS
• TO PROTECT FROM DAMAGE/BURNS
• TO PROVIDE WEATHER PROOFING

27
DESIRED PROPERTIES

• THERMAL
• TEMP.RESISTANCE
• LOW CONDUCTIVITY
• MECHANICAL
• SHOCK RESISTANCE
• POROSITY FOR AIR BINDING
• CHEMICAL
• INERT ACTIVITY

28
INSULATION MATERIALS

• MINERAL WOOL (IS-3677)
• - Most commonly used
• GLASS WOOL
• - Specified as
  alternative
• CALCIUM SILICATE OR MAGNESIA
• - Use as Refractory
• ASBESTOS
• - Used for small lines

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INSULATION MATERIALS

• WIRENETTING
• - TO KEEP INSULATION IN PLACE
• SURFACE COVERING
• - TO PROTECT INSUL. FROM DAMAGE
• - GI/AL SHEET OF 22/24g THK.
• - CEMENT PLASTER
• - THERMOSETTING COMPOUND

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INSULATION APPLICATION METHODS

• WIREBRUSHING HOT SURFACES
• PREPARATION OF INSULATION MATTRESSES OF CORRECT
  DENSITY
• (USUALLY 120 OR 150 Kg/M3)
• WRAPPING WITH WIRENETTING
• (USUALLY 24g GI WIRENET USED)
• BINDING THE LINEAR JOINTS

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APPLICATION (contd.)

• SURFACE COVERING WITH METAL
• (USUALLY AL.CLADDING WITH 22g OR 24g SHEET)
• JOINT PREPERATION WITH OVERLAP TO AVOID WATER
  SEEPAGE.
• MAKING BOXES FOR FITTINGS SUCH AS VALVES AND
  FLANGES.
• MITER CUT SHAPES FOR BENDS.

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INSULATION STANDARD

• CURRENTLY IS-7413 IS APPLICABLE
• SPECIFIES METHODS OF
• MATERIAL SELECTION
• APPLICATION OF INSULATION MATERIALS
• MEASUREMENTS OF FINISHED SURFACES.

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HEAT LOSS FROM UNINSULATED SURFACES

• INTERNAL TEMP. HEAT LOSS
• IN DEG.C IN KCAL/HR.M2
• 291
• 894
• 200 3065
• 6690
• 400 12115

34
HEAT LOSS FROM INSULATED SURFACES
Temp.in deg.C Thk. In mm. and Heat Loss in
Kcal/hr/sq.mtr.
35
ECONOMIC THICKNESS OF INSULATION