Abstract :
Steam
Condenser: It is a device or an appliance in which steam condenses and heat
released by steam is absorbed by water.
Classification
of Condensers
1. Jet
condensers
2. Surface
condenser
Jet
Condensers: The exhaust steam and water come in direct contact with each other
and temperature of the condensate is the same as that of cooling water leaving
the condenser. The cooling water is usually sprayed into the exhaust steam to
cause, rapid condensation.
Surface
Condensers: The exhaust steam and water do not come into direct contact. The
steam passes over the outer surface of tubes through which a supply of cooling
water is maintained.
PARALLEL-FIOW
TYPE OF JET CONDENSER:
The exhaust
steam and cooling water find their entry at the top of the condenser and then
flow downwards and condensate and water are finally collected at the bottom.
Air Leakage
As both the
exhaust of the steam turbine and the condenser are operating under a substantial vacuum, air is bound
to leak into the system. This leakage occurs through the
gland seals on
the steam turbine and through minute holes in the piping connections associated with the surface condenser itself. Over a
period of years, Heat
Exchange Institute has determined the normal quantity of air that should leak through properly designed turbines
and piping systems, and these are specified in their "Standards for
Surface Condensers ." Manufacturers have similarly standardized their ejector sets so that several standard sizes are
available for specific air which are the only moving parts in a surface condenser system
should be supplied in duplicate. Power plant practice
usually requires twin air Ejector sets, one a standby, but for air conditioning
installations, a single set is sufficient.
Materials of Construction
Materials used
in construction of steam surface condensers. Use of copper alloy tube sheets in steam surface
condensers with the Accompanying requirement that tube sheets be bolted to the shell
by Means of collar bolts is a carryover from marine practice. There is No reason why a steel tube sheet cannot be used, in view of the fact That the refrigeration condenser just upstream of
the steam condenser Uses this type of construction. When a steel
tube sheet is used, The specification should indicate that it may be
welded to the shell.
Copper
based alloy(ASTM B 111,B543)
Stainless
steel (ASTM A268, B268, A249, A213, A269)
Titanium(
ASTM B 338 Gr 1&2)
Carbon
steel (ASTM A 179,A214)
REASON FOR
REMOVING AIR/GAS:
The gases
will increase the operating pressure of the condenser. This rise in pressure
will decrease the turbine output and efficiency.
The gases
will blanket the outer surface of the tubes. This will severely decrease the
heat transfer of the steam to the circulating water. Again, the pressure in the
condenser will increase. The
corrosiveness of the condensate in the condenser increases as the oxygen
content increases. Oxygen causes corrosion, mostly in the steam generator.
Thus, these gases must be removed in order to extend the life of cycle
components.
EFFECT OF
AIR INGRESS:
For maximum
thermal efficiency, corresponding to a minimum back pressure, a vacuum is
maintained in the condenser. However, this vacuum encourages air in- leakage.
Thus, to
keep the concentration of non-condensable gases as low as possible, the
condenser system must be leak tight, together with any part of the condensate
system that is under vacuum. Failure to prevent or remove the non-condensable
gases may cause serious corrosion in the system, lower heat transfer
properties, and/or increase plant heat rate due to the back pressure rise
associated with a high in leakage.
The cost of
excess back pressure in terms of additional fuel or increased heat rate.
CONDENSER
TUBE CLEANING:
Macro-fouling
(accumulation of debris), not only reduces the cooling water flow rate through the
tubes it can cause tube corrosion and tube erosion failures.
Micro-fouling
(biological growth) and scaling reduces the heat transfer coefficient and could
cause under deposit corrosion resulting in premature tube failures.
Various tube cleaning
options are available to
reduce or eliminate the micro/macro fouling and scaling.
off-line on-line
methods. — (Sponge balls or brushes may be automatically recirculated through the
condenser).
Cycle
Isolation:
Generating
plants often suffer from power losses/heat rate due to leakages through valves
to condenser.
Check
incoming drain lines, feedwater heater high level dumps, minimum flow valves,
and steam traps for leakage or improper operation which could add unexpected
heat load to the condenser.
To minimize
leakages through valves to condenser ,Select all control valves (e g emergency drain of
heaters) to condenser with leakage class v and Select all isolating /drain
valve to condenser with leakage class MSS SP 61.
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