Basic knowledge on Steam Engineering

1. Steam Engineering Basics
Engr. Sahadat Hussain
Sr. Consultant, Environmental & Process
Engineering Resources International (ERI)

2. What is steam?
Steam is water in the gas phase, which is formed
when water boils.

3. What is steam? (Cont...)

4. ENTHALPY IN KCal/kg
Gauge
pressure
bar
Specific
Enthalpy of
evap'tion (hfg)
Volume
Dry Sat.
m /kg
Temp.
ºC
Water
(hf)
Steam
(hg) 3
1 120 120 526.2 646.2 0.881
2
3
4
5
6
134
144
152
159
165
133
144
152
159
166
517.6
509.7
504
498.9
493.5
650.6
653.7
656
657.9
659.5
0.603
0.461
0.374
0.315
0.272
7 170 171 489.8 660.8 0.24
0 100 100 540 640 1.673
What is steam?(Cont.…)

5. What is so different about Steam?
Fixing one parameter fixes all others.
Steam at 1 barg pressure will have -
1200CTs - Saturation Temp.
h -
L -
V -
Sensible Heat
Latent heat
Specific Volume
120 Kcal/kg.
526.2 Kcal/kg.
0.902 m3/kg. (steam)
0.0011 m3/kg. (cond.)
Exercise -
What will be the above properties at a pressure of 3.5 Kg/cm2g.

6. What is so different about Steam - contd.
Steam quality is a changing parameter
be measured on-line.
It is indicated by a term called Dryness
and can’t
Fraction.
Dryness fraction ‘x’ indicates fraction of dry steam
present in given total mass
x=0.9
Means 90% steam with SH+LH and 10% water
(only SH)
Exercise - What will be total heat in steam at 3
kg/cm2g pressure and 0.85 dry?

7. What is so different about Steam? - contd.
Steam Quality depends on type of boiler and
effectiveness of steam distribution.
A coil type boiler will deliver wet steam at load
variation as it has no steam space.
A shell type boiler will ensure better quality
under all load conditions
steam
Saturated steam will never be 100% dry

8. What is so different about Steam?-contd.
Steam has higher Specific Volume
Volume of steam at 1 kg/cm2g
Volume of steam at 7 kg/cm2g
at low pressure
0.902m3/kg
0.24m3/kg
376% more volume to be handled at 1 kg/cm2g
(lower pressure) as compared to 7 kg/cm2g.
Always advisable to reduce steam pressure near
the equipment and not in Boiler House.

9. What is so different about Steam - contd.
Saturated steam is a condensing vapor with
instant heat release on phase change.
Latent heat is released when steam condenses
Superheated steam is a gas with very slow release
of superheat before latent heat can be released.
It is ideal to use saturated steam for any indirect
heat transfer.

10. 80%
HP
steam
15% PRV
Flue
losses
3%gases
Fuel
100%
2%
losses
Blow
down
5%
Condensate
20%
Standard Steam Circuit - Energy Balance
Process
Plant
55% to
process
Boiler
Plant
Steam Circuit

11. Actual Enthalpy of Wet Steam
; Dryness fraction is the proportion of dry steam within a given sample.
; The ‘actual’ enthalpy of evaporation of wet steam is the product of the
dryness fraction (x) and the specific enthalpy (hfg) from the steam
tables. This in short means the lower the dryness fraction more
amount of steam would be needed for the providing the same heat
input.
Enthalpy of
evaporation
Dryness
fraction
Actual
enthalpy
; What will be the actual enthalpy of 0.9 dry steam at 3 barg pressure?

12. Advantage Steam
; High heat content, Easily available, Very cheap in comparison.
;
;
Steam lines are relatively light in weight.
Steam flows in response to the pressure drop along the line and
there is no need for circulating pumps.
Steam is flexible and loads can be added or subtracted at will,;
within the limitations of the supply.
Heat transfer coefficients from steam are often twice as high as
those from water.
Constant temperature gradient will occur along the heat emitting
surfaces.
Relatively easy plant maintenance
;
;
;

13. Energy Equivalent Flow rate for 1KW
Hot Water
Flow rate kg/s = 1000W = 0.0217 kg/s
78 Kg/hr.(BDT 10/hr.)4187J/kg K (82ºC - 71ºC)
Hot oil
Flow rate kg/s = 1000W = 0.091 kg/s
550J/kg K (300ºC - 280ºC) 328 Kg/hr. (BDT 9/hr.)
Steam
Taking steam at 6 bar g. Enthalpy of evaporation per kilogram = 2066 kCal/kg
= 1 = 0.00048 kg/s
1.7 Kg/hr.(BDT 1.25/hr)2066
Cost of equivalent electrical energy will be BDT 6.74/hr.
The comparison in flow rates are well in favour of steam !

14. Engineering involved with Steam
• Quality of steam is a constant variable.
Dry steam at boiler end may become wet at equipment.
Process steam demand is fluctuating with time
On an average a process boiler works at 50% load
•
• Steam may not get due importance at ‘Project’ stage.
Sizing and component selection lacks engineering touch.
The problems start during normal operations
High pressure drops, Water-hammer, Air binding, Longer
batch timings, Poor product quality are very common
•

15. Common operational problems
In an average process plant steam load is variable
peaks occurring for short periods.
with
Steam has major ingress of air whenever used for
intermittent heating applications
Equipments use steam intermittently
Plant
Plant
Plant
works only for one/two shifts in a day
has seasonal operations
works for five days or six days in a week.

16. Steam Should Be Supplied At The
Desired Time
Demand Satisfied by
a drop in Boiler
Demand Not
Satisfied
Pressure
Peak
Boiler Maximum Continuous Rating
Average Steam Flow RateSteam
Flow
Rate
Actual Steam
Flow Rate
Time

17. Layers That Reduce Heat
Transfer Efficiency
Scale Film
Air Film
Condensate Film
Stagnant Water
Steam
Metal Wall
Water
Being
Heated

18. Steam Engineering - Related Problems
• Incorrect Basis For Boiler Capacity
• Lack Of Info On Boiler Efficiency
• Flue Gas Not Monitored
• Improper Loading Of Boiler Plant
No Relation With Process Demand
Confusion On Relation Between
Blow-down & Boiler Load
Blow-down & Hardness
•

19. Common Problems in Steam Distribution
High And Abnormal Pressure Drops
Manufacturing Operations Limited To Only Few
Longer Processing Timings’
Lower Productivity On Machines
Steam Starvation At End Points

20. • No Modification In Piping System To Reflect
Changes In Equipment, Etc.
.
• Misconceptions Regarding Flash Steam
• Hot Condensate Cooled Because Pump - Motor
Set Cannot Handle It
• Operating Staff Unaware Of Cost Of Steam And
Its Components
Common Problems In Steam Distribution cont...

21. • Bypass Of Traps/Control Valves Open
• Wrong Trap Selection (Open Bypass) And
Installation
• Use Of Traps For Lifting Condensate
• No Air Vents Except On Headers/Jacketed
Vessels. Mostly Manual Venting
Common Problems In Steam Distribution cont...

22. High - Pressure Steam Necessary For Fast Heating.
Required
PRV Not
Improper Sizing Of PRV Assembly
Absence Of External Pressure - Balancing
Pressure Reduction/Control By Blowing Rather Than
Control Valve
Using
Common Problems In Steam Distribution cont...