Steam Condensers and their performance measurement.pdf

Steam condensers and their classification, difference between Jet and Surface Condensers, Sources of air leakage and its effects, performance parameters of a steam condensers.

1. Steam Condensers

2. Elements of a Steam Condensing Plant
•Condenser
•Supply of cooling water
•Condenser cooling water
pump
•Air extraction pump
•Make up water pump
•Condensate extraction pump
•Boiler feed pump
•Hot well
•Cooling tower

3. Condenser
•Steam condensers are devices in which the
exhaust steam from the steam turbine is
condensed using cooling water.
•Condensation can be done by removing heat
from exhaust steam using circulating cooling
water.
•During condensation, the working substance
(steam) changes its phase from vapour to liquid
and rejects latent heat.
•Objectives:
•To create low back pressure for turbine
exhaust.
•To condense the exhaust steam from the
turbine.

4. Advantages of Using a Condenser
•It increases the efficiency of the power plant due to increased enthalpy drop.
•It reduces the back pressure of the steam which results in more work output.
•It reduces the temperature of the exhaust steam which also results in more work
output.
•The condensed steam can be reused as feed water for the boiler which reduces the
cost of power generation.
•The temperature of the condensate is higher than that of the fresh water which
reduces the heat supplied per kg of steam produced.

5. Classification of Condensers

6. Jet Condensers
• A jet condenser is a condenser in which the condensate gets mixed with the cooling water. That’s why it is
also called as mixing type condenser.
•It is further classified based on the direction of flow of the condensate and the arrangement of the tubing
system.
•Types:
• Low-level jet condenser:
➢Parallel flow type
➢Counter flow type
•High-level jet condenser
•Ejector jet condenser

7. Low-Level Jet Condensers
•Low level jet condenser is the one which is placed at a low level such that vacuum inside
the condenser draws cooling water into the condenser from the river/pond/cooling tower.
•Difference between atmospheric pressure (at which cooling water is available) and
condenser pressure causes flow of cooling water from cooling water reservoir to condenser
i.e. (p
atm – p
cond).
•There is provision for the extraction of air and dissolved gases from the condenser by
using an air extraction pump.
•Condensate extraction pump is used for taking out condensate from the condenser and
sending it to a hot well.
•There are two types of low-level jet condensers: Parallel-flow type and Counter-flow type.

8. Low Level Jet Condensers
(Parallel Flow Type)
•In parallel flow jet condenser, the steam and water
enters into the condenser at the top and leaves at the
bottom.
•The cooling water and steam enters at the top.
• As both steam and cooling water mix with each
other, the steam gets condense.
•The condensate, cooling water and air moves
downward and it is removed by two separate pumps
known as air extraction pump and condensate
extraction pump.
•The condensate pump transfers the condensate to the
hot well and from there the extra water is made to
flow in cooling water tank or pond through overflow
pipe.

9. Low Level Jet Condensers
(Counter Flow Type)
•In counterflow type low level jet
condensers, the steam enters at the
bottom and the cooling water at the top.
•The steam flows upward and meets the
cooling water coming downward.
•In these types of steam condensers, the
air pump is located at the top.
•Air pump creates a vacuum and this
vacuum draws water from the cooling
tower.
•The cooling water enters the condenser
and falls on the perforated conical plate.

10. High Level Jet Condensers
•High level jet condenser is the one which is
placed at a height more than that of water
and water is to be injected into condenser
using a pump and the condensate will flow
out of condenser because of gravity.
•Here no condensate extraction pump is
required, instead pump is required for
pumping water upto the condenser inlet.
•High level jet condenser is also called as
‘barometric condenser’.
•Jet condenser placed above the hotwell by
10.34 m shall be high-level jet condenser or
barometric condenser

11. Advantages and Disadvantages
of Jet Condensers
Advantages:
•Lower quantity of cooling water required
•Simple in design
•Require less floor space
•Lower capital and maintenance cost
•Due to direct contact heat transfer is more effective
Disadvantages:
•Condensate cannot be directly used as feed water
•Power consumption in the pump is more
•Piping cost is high.

12. Surface Condensers
•Surface condenser is a type of steam condenser in which the steam and cooling water do not mix with
each other and the heat transfer occurs between two fluids through the surface in between.
•There is no contamination of feed water and the whole condensate can be used as boiler feed water. It is
also called as non-mixing type condenser.
•Generally, cooling water flows through the pipes/tubes and steam surrounds them.
•These condensers are preferred in the locations where a large quantity of poor quality cooling fluid
(impure water) is available and condensate is to be recirculated.
•It is further classified as follows:
•According to number of cooling water passes
➢Single pass
➢Multi pass
•According to direction of condensate flow
➢Down flow condenser
➢Central flow condenser

13. Single and Multi-Pass Surface Condensers
Two Pass Surface CondenserSingle Pass Surface Condenser

14. Down-flow and Central-flow Surface Condensers
Down flow condenser has steam and air entering from top and flowing
downwards across the bundle of tubes having cooling water flowing through
them.
•Air is extracted from bottom and before being handled by air pump it is
flown through air cooler so as to reduce the temperature of air.
•Low temperature of air enhances the air handling capacity of pump. With
the flow of steam down and simultaneous heat exchange the condensate is
taken out by condensate extraction pump.
Central flow condenser has air cooling section in the center of condenser.
•Steam enters from top and passes over the tube banks of similar type as in
case of down flow condenser.
•As air is being sucked from center so the flow of steam is radially inwards
towards the center. Condensate is collected from the bottom.
•In this type of condenser, there is better contact between steam tubes
because of the radial flow of steam in the whole of the condenser, the
arrangement is better as compared to the down-flow condenser.

15. Comparison between
Jet Condensers and Surface Condensers

16. Air Leakage in Steam Condensers
•Generally, inside the condenser pressure less than atmospheric pressure is maintained, thereby
increasing the chances of air leakage into condenser.
•The presence of air inside a condenser is always undesirable as it causes many adverse effects on
condenser performance and efforts must be made to detect the source of air leakage.
The main sources of air leakage are:
•Joints of the various parts in the condenser body
•Air dissolved in feed water
•A small quantity of air dissolved in injection water (Jet Condensers)
The effects of air leakage are:
•Reduced Thermal Efficiency
•Increased Requirement of Cooling Water
•Reduced Heat Transfer
•Corrosion

17. Performance Measurement of Condensers
•Absolute pressure (in mm of Hg) in condenser
= (Barometric head in mm of Hg) – (Vacuum pressure in mm of Hg)
•Vacuum pressure (in mm of Hg) = 760 – Absolute pressure in condenser (in mm of Hg)
•Corrected Vacuum (in mm of Hg) = 760-(Actual barometric height – Actual vacuum).
Vacuum Efficiency:
•It indicates the ability of a steam condenser to produce vacuum within itself.
•It is defined as the ratio of actual vacuum to maximum obtainable vacuum inside the condenser.
•p
b = Barometric pressure
•p
s = Partial pressure of steam
•p
a = Partial pressure of air

18. Performance Measurement of Condensers
•Condenser Efficiency: It is defined as the ratio of the actual rise in cooling water
temperature to the maximum possible temperature rise.

19. Numerical Problems
Q. During a trial on a steam condenser, the following observations were recorded :
•Condenser vacuum= 680 mm Hg, Barometer reading =764 mm Hg, Mean condenser temperature =
36.2°C, Hot well temperature = 30°C, Condensate formed per hour = 1780 kg, Circulating cooling
water inlet temperature = 20°C, Circulating cooling water outlet temperature = 32°C, Quantity of
cooling water = 1250 kg/min.
•Determine : (i) Condenser vacuum corrected to standard barometer, (ii) Vacuum efficiency, (iii)
Undercooling of condensate, (iv) Condenser efficiency, (v) Condition of steam as it enters the
condenser, (vi) Mass of air present per kg of condensed steam.
•Assume : R for air = 0.287 kJ/kg K, Specific heat of water = 4.186 kJ/kg K

20. Solution
1. Condenser Vacuum corrected to standard barometer

21. Solution

22. Solution