Condenser

SubCooling
• Sub-cooling of steam and condensate like in a surface condenser or
any heat exchanger is caused by additional cooling below the
saturation temperature of vapor to liquid phase.

• We can get sub-cooling from radiation loss at pipe walls that are
below the liquid level or condenser sub-cooling employing excess
heat transfer surface area or a lot of tubes with significant coolant.
Vacuum efficiency
• Taking standard atmospheric pressure as 1.01325 bar
• Vacuum Efficiency = (1 .01325 - condenser pressure)/(1.01325 - condenser
pressure corrected to condensate temperature) x 100
• Consider the following example for a modern condenser of the regenerative type:
• Circulating water inlet temp. 21°C
• Circulating water outlet temp. 28 oC
• Condenser pressure 0.05 bar
• Condensate temperature 31.5" C
• Condenser pressure corrected to 28 C 0.038 bar
• Condenser pressure corrected to 3 1.5 C 0.045 bar
• (Vacuum Efficiency) = 0.96325/0.96825 x 100 = 99.4%
Condenser Efficiency
• Taking standard atmospheric pressure as 1.01325 bar Condenser Efficiency = (1
.01325 - condenser pressure)/( 1 .01325 - condenser pressure corrected to
circulating water outlet temperature) x 100

• Consider the following example for a modern condenser of the regenerative type:
• Circulating water inlet temp. 21°C
• Circulating water outlet temp. 280 C
• Condenser pressure 0.05 bar
• Condensate temperature 31.5" C
• Condenser pressure corrected to 28 C 0.038 bar
• Condenser pressure corrected to 3 1.5 C 0.045 bar
• (Condenser Efficiency) = 0.96325/0.97525 x 100 = 98.8%
Limitation on water velocity
• The maximum tube velocity which it is possible to use is however limited by one
or both of two factors, viz.
• 1.The tube material
• For any one tube material, there is a limiting velocity above which there is a
danger of erosion. This risk can be aggravated if there is sand or other abrasive
matter in the circulating water.
• For these reasons, the maximum velocities generally in use with various tube
materials are as follows:
• Admiralty brass 1.5-1.8 m/s
• Aluminium brass 1.8-2.4 m/s 90/10
• copper nickel 3.0 m/s
• 70/30 copper nickel 3.6-4.0 m/s
Limitation on water velocity
• Although 70/30 copper nickel should permit the use of the higher
tube velocity shown above, there is in practice a reluctance to use
tube water velocities much above 3.0 m/s even with this material,
since in the event of partial blockage of a tube or tubes, the local
water velocity past the partial blockage could well approach or
exceed 5.5 m/s at which, for 70/30 copper nickel, adverse high
velocity effects become significant.
The outstanding advantages of titanium for
condenser tubes are:
• 1. It has a high strength/mass ratio. The density of titanium is about half
that of 70/30 copper nickel, while the tensile strength is about the same.
Hence for equal size, strength and number off, titanium tubes would have
about one half the mass of 70/30 copper nickel tubes.
• 2. It has a very high resistance to corrosion, erosion, abrasion and all other
forms of attack on both the steam and water sides, in a wide range of
aggressive media, and at water velocities far in excess of the present
accepted maxima for copper-based alloy tubes.
• 3. Its thermal conductivity is about 70.0 per cent of that of 70/30 copper
nickel, hence for equal thermal performance, a titanium tube should have
a wall thickness 0.7 of that of a 70/30 copper nickel tube of the same
external diameter.
Limitation on water velocity
• Second factor limiting the water velocity is
• Pumping power
• The pressure loss due to water friction in the condenser tubes varies
directly as the square of the water velocity through the tubes. The
condenser pressure loss is part of the pressure which has to be
generated by the circulating pump, so that the power required to
drive the circulating pump increases as the condenser tube velocity is
increased, and there comes a point at which, in the overall
economics, the benefit of the increased tube velocity is offset by the
increased pumping power.
Pumping Power
• by running the circulating pump faster, to reduce the condenser
pressure such that the steam consumption of the main engines is
reduced by 1000 kg/h. This however, would be useless if the engine
driving the circulating pump required an additional 1000 kg/h of
steam to circulate the increased water quantity
Re-Generative Condenser
Re-Generative Condenser
• Figure 6.11 also illustrates divided water ends, which permit one half of the
condenser tubes to be cleaned on the water side while the other half is
condensing the steam. Each half of the condenser has its own c.w. inlet and
discharge pipes and its own air suction.
• The c.w. inlet and discharge valves and the air suction valve of that half of
the condenser which is to be cleaned are closed, and the water boxes
drained prior to opening up for cleaning.
• The cold tube surface and the air suction of the half condenser remaining
in service attracts all the steam preferentially to that half.
• This means that only one half of the condenser surface is being used to
condense all the steam, hence during condenser cleaning in this manner,
either reduced power or increased condenser pressure must be accepted.
Condenser Efficiency on dry air volume
• The air pump, designed for 10.0 kg/h of dry air in our example, has a
volumetric capacity of 886.32 m3/h of air/vapour mixture. Any
increase of dry air above 10.0 kg/h causes an increase in the total
volume of air/ vapour mixture, above the volumetric capacity of the
air pump, and the air pump is therefore incapable of removing the
increased volume of mixture. This causes air to accumulate in the
condenser, causing the condenser pressure to rise to the point which
will reduce the total volume of the mixture to 886.32 m3/h, at which
conditions will stabilise. This increase in condenser pressure can be
very serious from the efficiency aspect.
Air Cooling in Condenser
This means that if the mixture is cooled to only 1°C below
the condenser steam temperature instead of to 4°C below,
then the required volumetric capacity of the air pump is
3328 m3/h instead of 886.32 m3/h, i.e. nearly four times
as much.
Figure 6.17, from which it will be evident that cooling the
mixture in the condenser before extraction results in quite
a dramatic reduction in the required volumetric capacity of
the air pump.
Air Cooling in condenser
Increase of condenser pressure
• 1. Increased sea temperature
• 2. Failed or inadequate c.w. supply
• 3. Excessive air in-leakage (First check should be the turbine gland
sealing system)
• 4. Fouled tubes
• 5. Failed or damaged air pump
• 6. Insufficient air cooling
 REQUIREMENTS OF A GOOD SURFACE CONDENSER
• 1. The steam should enter the condenser with least possible resistance for its easy flow.
• 2. For effective condensation the steam should be well distributed in the vessel and there
should be minimum pressure drop.
• 3. The circulating cooling water should fl ow through the tubes with least friction. The rise in
temperature of cooling water should be limited to 10°C for obtaining better thermal
efficiency.
• 4. There should be no undercooling of the condensate, so the steam should lose only its latent
heat to the circulating water. This is made possible by regulating the quantity of circulating
water in such a way that its exit temperature is same as the saturation temperature of steam.
• 5. To obtain maximum heat transfer rate the tubes should be made of high thermal
conductivity material. The water should fl ow through tubes and steam outside so that the
outer surface of the tubes does not get deposited with sediments. If the cooling water is dirty
then sediments will get deposited inside the tubes. These sediments can be cleaned by motor
driven brushes after removing the end cover plates.
• 6. There should be no leakage of air from the condenser.
• 7. Minimum energy should be spent to extract the air from the condenser. This is achieved by
fitting a baffle plate at the coolest section where air pump is fitted. This arrangement reduces
the specific volume of air and thus reduces the size of the pump.
Protection of Condenser against corrosion
• Polluted waters can be very corrosive in condenser tubes, and condensers
should never be allowed to remain full of such waters for any length of
time. Tubes have been known to corrode through when not running and
containing polluted water during the fitting out period in dock
• For prolonged shutdown in estuarial waters or dockside waters the main
condenser should be emptied on the sea water side, to prevent corrosion.
• Protective measures will be more fully discussed in a later part of this
series dealing with condensers, but briefly, the situation can be controlled
by the injection of ferrous sulphate solution, which helps to form a
protective coating on the tubes particularly during the early life of the
machinery.
Operational defect on Condenser
• The most important defects in the machinery operation which can be
attributed to the condenser are,
• sudden and serious loss of vacuum,
• a gradual but slight deterioration in vacuum
• an increase in feed water salinity
• Vibration
Sudden Loss of Vacuum
• This will most probably ari:;e from the incidence of an air leakage, but
could also be due to a rapid, though unlikely, reduction in the cooling water
rate or to deterioration in air ejector performance.
• Sources of leakage which should be investigated are the small bore piping
connections between the condenser and the kenotometer ( Vacuum
gauge) and defects in any of the joints on the pads and flanges mounted on
the condenser casing
• Cooling Water Circulation Failure of the pump or even uncontrolled partial
reduction in the cooling water flow rate is not considered a normal hazard
but blockage has been known to occur due to weeds or polythene
sheeting. Vacuum willdeteriorate rapidly ifthe flow rate isnot maintained
and this condition may normally be detected by a substantial increase in
the cooling water temperature rise across the condenser
Sudden Loss of Vacuum
• Air Ejector- Failure of the air ejector will most likely be due to
reduction in the flow of driving steam to the ejector nozzles.
• Efficient performance of an air ejector is inherently somewhat critical
for a particular design duty, partial blockage of the nozzles due to
small flakes of scale or other material can curtail performance
sufficiently to result in serious loss of vacuum.
Gradual Deterioration of Vacuum
• Gradual, though slight deterioration of vacuum over a relatively long
period, is almost certainly due to reduction of the heat transfer rate
between the cooling water and the tubes.
• This arises from a slow build up of deposits which foul the inside tube
surface.
• The rate of fouling will mainly depend on the sea trade route.
• If such condition is suspected, the tubes may be brushed using nylon
bristles.
• The frequency at which attention is given must be largely governed by
experience.
Salinity of Feed Water
• If the degree of feed water salinity exceeds the permissible amount, a
leakage of sea water into the steam side of the condenser may be
suspected.
• Leakage can occur due to tube rupture caused by erosion and by
failure of tube end packing rings if fitted.
• Tube erosion is usually most severe near to the water entry end of the
tube, but may not be easily detected without water test.
• Tubes which are known to be damaged may be temporarily plugged,
pending replacement at the earliest opportunity.
Condenser inspection
• Routine inspection inside the water boxes should be carried out by examination of the
tube plate for signs of tube or tube packing failure and erosion pitting of the tube plate
surface.
• One should also examine the mild steel anti-corrosion plates. In the case of fabricated
mild steel water boxes, which are protected by rubber lining, an excessive rate of
wastage may be due to a defect in the rubber lining.
• They should be replaced if they reduce to 50 per cent of the original size.
• The plates should be cleaned of corrosion products and organic growth every 3 to 4
months.
• The rubber lining of the water boxes and doors should be checked to ensure that it-
shows no signs of having "lifted off" the parent metal and that it has not ruptured. Any
such defects should be rectified at the earliest opportunity.
• The same remarks apply to epoxy coatings.
• Remove sludge accumulation from water boxes.
Vibration
• Hull transmitted vibration to the condenser and tubes could cause
the tubes to resonate with possible necking at the fixed ends, necking
and thinning in way of the division support plates.
• It is not good practice to allow a tube length greater than 100
diameters between supports, also a support should not divide the
tube length in an exact ratio so as to make the support a vibration
node.