FIELD OF INVENTION
The present invention generally relates to feed water heaters. In particular, the
invention relates to low pressure feed water heater. More particularly, the
invention relates to a venting device for 4-pass horizontal condensing type low
pressure feed water heater.
BACKGROUND OF INVENTION
Air venting plays a very important role in efficient functioning of a feed water
heater. Improper venting arrangement may result in following problems in the
feedwater heater:
a) Accumulation of non-condensable gases / air, which cause drop in partial
pressure of the steam vapour leading to a depression of the saturation
temperature. Such a depression in the saturation temperature results in
lowering of temperature difference between the hot and cold medium
which adversely alters the temperature gradient required for heat flow.
b) A blanketing of air/non condensable gases / steam takes place over the
tube bundle of the heater. Thus, any condensation which takes places in
the heater, has to overcome the effect of enveloped/blanketed vapour
layer over tubes thereby increasing the fouling factor. Such a
phenomenon results in poor heat transfer coefficient.

c) Presence of non condensable gases in the heaters, mainly Oxygen and
Carbon-di-Oxide increase the corrosion of various components of the
heater.
d) Presence of pockets / blankets of non-condensable gases results in an
uneven distribution of steam inside the heater. This decreases the
efficiency of the heater.
e) An un-natural vibration of various components of the tube bundle develop
which lead to higher stress values and stress induced corrosion.
In a horizontal condensing type low-pressure feed water heater, venting
extraction is taken from the first pass as it is the coolest part of the heater. In
case of a 2 pass (water side) heater, it's easier to carry-out the venting
extraction from the first pass since at least one complete half of the heater is
available for the venting arrangement. However, incase of a four pass heater,
only 1/4th part of cross section is available for venting arrangement which makes
the venting arrangement in 4-pass heaters quite challenging.
Figure-1 shows a typical 4-pass venting arrangement, having the following
features :-
a) segmental baffles (1) of two types,
b) a Support baffle (3),

c) a close clearance (c) between the outside diameter of the baffles (1) and the
internal diameter of the shell (2),
d) In this type of arrangement, steam flow is governed by both upstream and
downstream steam pressure which may result in uncontrolled steam flow
Fig-2 shows another typical 4-pass venting arrangement having following
features:-
a ) Vent pipe which is not in the center of the tube-layout
b) an Unequal steam flow (S1, S2) due to difference in length of the path
traversed by the different streams of the steam.
As can be seen from figure-1, this type of venting arrangement has the following
characteristics:
i) a plurality types of baffles (1), a vent connection (6) attached to an air
box (7).
ii) a small clearance provided between the outside diameter of the baffles (1)
and the internal diameter of the shell to avoid by-pass of steam. This is
done to eliminate flow of steam towards an air-extraction opening (6)
because of otherwise less resistance through the gap (c). Due to this
small clearance (c), assembling of the Tube system (9) to Shell (2) pose
various difficulties.
As shown in figure-2, another type of prior art venting arrangement is available

in which the air extraction manifold or the vent pipe (4) is not deposed in the
center of the tube bundle (9). Such an eccentric vent pipe (4) results in a
skewed flow of the steam vapour and leads to an in-efficient heat transfer
between the hot and cold medium.
OBJECT OF INVENTION
It is therefore an object of the invention to propose a venting device for a 4-pass
horizontal condensing type low-pressure feed water heater, which eliminates the
disadvantages of prior art.
Another object of the invention to propose a venting device for a 4-pass
horizontal condensing type low-pressure feed water heater, which is enabled to
achieve uniform distribution of steam due to disposition of the venting manifold
in the center of tube layout.
A still another object of the invention to propose a venting device for a 4-pass
horizontal condensing type low-pressure feed water heater, which
accommodates the air baffles in the tube-layout so as to envelope the first pass
on water side and prevents direct steam entry in the first pass.
Yet another object of the invention to propose a venting device for a 4-pass
horizontal condensing type low-pressure feed water heater, which is provided
with a manifold having opening in the first pass only and allows the steam to

ravel maximum possible path before reaching the vent orifices thereby achieving
a complete condensation of the steam.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Figure 1 - shows a prior art 4-pass venting device without vent pipe having small
clearance between baffle OD and Shell ID.
Figure 2 - shows another type of prior art 4-pass venting device having the vent
pipe disposed eccentric to the tube bundle
Figure 3 - shows a 4-pass horizontal condensing type low pressure feed water
heater according to the invention.
DETAIL DESCRIPTION OF THE INVENTION
As shown in figure-3, the novel and inventive device comprises:
- vent pipe (4) disposed at the center of the tube bundle (9);

- a single type of rotatable baffle (1) to envelope the first pass of the tube
bundle (9);
- a pre-defined path off steams flow (s1) formable over the tube-bundle (9)
due to the disposition arrangement of the baffles (1) which ensures that no
steam flow (s1) is directed towards the air-extraction of opening (6);
- a plurality of holes orifice in the vent pipe (4) to ensure the critical flow of
non-condensable gas vents through vent pipe (4); and
- a clearance (c) sufficient enough between the outside diameter of the baffle
(1) and the internal diameter of the shell (2) configured to allow an easy
assembly of the tube bundle (9) and the shell (2).
A steam nozzle (11) directs the steam flow into the shell (2).
WE CLAIM
1. A venting device for 4-pass horizontal condensing type low-pressure feed
water heater, comprising:
- a vent pipe (4) disposed at the center of the tube bundle (9), the vent pipe
(4) being configured with a plurality of shaped orifice holes (10) to allow the
critical flow of non-condensable gas vent only through the vent piper (4);
- at least one single type rotatable baffle (1) disposed in the shell (2) with a
clearance (c) sufficient enough between the outside diameter of the at least
one baffle (1) and the inside diameter of the shell (2) to enable smooth
assembly of the tube bundle (9) and the shell (2); and
- the depositional arrangement of the at least one baffle (1) generating a pre-
defined flow path over the tube bundle (9) for the steam to disallow flow of
the steam towards an air-extraction opening (6).

The invention relates to a venting device for 4-pass horizontal condensing type
low-pressure feed water heater, comprising a vent pipe (4) disposed at the
center of the tube bundle (9), the vent pipe (4) being configured with a plurality
of shaped orifice holes (10) to allow the critical flow of non-condensable gas vent
only through the vent piper (4); at least one single type rotatable baffle (1)
disposed in the shell (2) with a clearance (c) sufficient enough between the
outside diameter of the at least one baffle (1) and the inside diameter of the
shell (2) to enable smooth assembly of the tube bundle (9) and the shell (2); and
the depositional arrangement of the at least one baffle (1) generating a pre-
defined flow path over the tube bundle (9) for the steam to disallow flow of the
steam towards an air-extraction opening (6).