Heat exchange – Casing or tank enclosed conduit assembly – With distinct flow director in casing
Reexamination Certificate
2002-03-19
2002-12-17
Bennett, Henry (Department: 3743)
Heat exchange
Casing or tank enclosed conduit assembly
With distinct flow director in casing
C165S158000, C165S174000, C126S109000
Reexamination Certificate
active
06494255
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to tubular air heater constructions used in steam generator installations for utility power generation and, more particularly, to an air heater gas inlet plenum for such tubular air heaters which permits retrofit installation of additional flue gas environmental treatment equipment.
BACKGROUND OF THE INVENTION
Increasingly stringent environmental regulations continue to place pressures upon electric utilities which utilize fossil-fueled steam generators to produce electricity. However, modifications to existing steam generators is often problematic due to the limited space available, and the utilities' desire to make such modifications in an efficient manner and at minimum cost.
Many fossil-fueled steam generators used for utility power generation employ recuperative tubular air heaters to transfer heat from the hot flue gases produced during combustion into the incoming combustion air. After this heat exchange process has occurred, the flue gases are eventually conveyed into the atmosphere via a stack. Various types of environmental cleanup equipment are also often provided in between the flue gas outlet of such steam generators and the stack, such as precipitators for particulate control and wet or dry flue gas desulfurization systems.
In addition to controlling sulphur oxide emissions, nitrogen oxides are one of the primary pollutants emitted during combustion processes. As described in Chapter 34 of
Steam/its generation and use
, 40th Edition, Stultz and Kitto, editors, Copyright ©1992 The Babcock & Wilcox Company, at pages 34-1 to 34-9, various methods are used to control nitrogen oxide emissions. One method involves selective catalytic reduction (SCR) systems which catalytically reduce flue gas NO
x
to N
2
and H
2
O using ammonia in a chemical reduction. For further details concerning the basic principles behind SCR systems, the reader is referred to the aforementioned Chapter 34 of
Steam
, the text of which is hereby incorporated by reference as though fully set forth herein.
SCR reactions take place within an optimal temperature range, and the SCR modules used in such systems are typically located downstream of the economizer gas outlet of the steam generator or boiler and upstream (with respect to a direction of flue gas flow through the steam generator) of the air heater devices used to preheat the incoming combustion air. Retrofit applications of SCR systems to steam generators having tubular air heaters present their own particular problems.
Referring generally to
FIGS. 1 and 2
of the present disclosure, there are shown two such typical installations of tubular air heaters as provided at the economizer gas outlet of a utility steam generator (not shown).
FIG. 1
illustrates a first embodiment of a known tubular air heater installation, generally designated
10
. Hot flue gas
12
provided from a boiler economizer gas outlet
14
is conveyed to a tubular air heater
16
for transferring heat from the hot flue gases
12
into incoming combustion air (not shown). Tubular air heater
16
is generally provided with a large gas inlet plenum
18
located at an upper end of the tubular air heater
16
and above a plurality of heat exchanger tubes
20
for receiving and conveying the hot flue gas
12
therethrough while the air for combustion (not shown) passes there across over the outside surfaces of these tubes
20
in a heat exchange relationship. The large gas inlet plenum
18
has a top wall
19
, a rear wall
21
, and side walls
23
. The hot flue gases
12
are cooled as they pass downwardly through the tubular air heater
16
, conveying the heat contained therein to the combustion air. A gas outlet plenum
22
is generally provided at the bottom of the tubular air heater
16
for collecting and conveying the flue gases
12
to a stack (not shown). Since the flue gases
12
contain significant amounts of flyash, a hopper
24
may be provided at a lower portion of the gas outlet plenum to collect flyash particles. As illustrated in the arrangement of
FIG. 1
, the hot flue gas
12
is conveyed from the boiler economizer gas outlet
14
via an outlet gas flue
26
into the gas inlet plenum
18
where the flue gases make a 90° turn downwardly into the plurality of heat exchanger tubes
20
and, after exiting therefrom, make another 90° turn at the gas outlet plenum
22
before exiting the tubular air heater
16
. The tubular air heater
16
is generally top supported via support rods
28
which are hung from top support steel
30
, but it may be bottom supported as well.
Various other arrangements of tubular air heaters are known. For particular details of such arrangements, the reader is referred to Chapter 13 of
Steam/its generation and use
, 39th edition, Copyright ©1978 by The Babcock & Wilcox Company, particularly pages 13-4 to 13-8, and that chapter is hereby incorporated by reference as though fully set forth herein.
FIG. 2
illustrates one such variation, generally designated
50
. Throughout
FIGS. 1 and 2
, as well as in the balance of the present disclosure, like reference numerals designate the same or functionally similar elements throughout the several drawings. In the arrangement of
FIG. 2
, the hot flue gases
12
are again conveyed from the boiler economizer gas outlet
14
into an upper plenum
18
of a U-shaped tubular air heater, generally designated
17
. As shown therein, tubular air heater
17
is provided with a gas downflow section
32
and a gas upflow section
34
containing heat exchanger tubes
20
. While the hot flue gas
12
makes a 90° turn downward into the gas downflow section
32
, at the bottom portion thereof the hot flue gases
12
make a 180° turn up into the gas upflow section
34
by means of an intermediate gas plenum
36
. If desired, hoppers
24
may again be provided to collect particles from the hot flue gas
12
as it makes the 180° turn within the intermediate gas plenum
36
. After passing upwardly through the heat exchanger tubes
20
comprising the gas upflow section
34
, the hot flue gases
12
make another 90° turn in a gas outlet plenum
38
located at an upper portion of the gas upflow section
34
. The hot flue gases
12
then exit from the tubular air heater
17
for eventual exhaust into the atmosphere. At the upper portion of the tubular air heater
17
a flue gas impermeable wall
40
separates the gas inlet plenum
18
from the gas outlet plenum
38
. Similarly, flue gases conveyed downwardly through gas downflow section
32
and upwardly through gas upflow section
34
are separated from one another by another flue gas impermeable wall
44
.
It will thus be readily appreciated that retrofit installation of SCR equipment so that the flue gas
12
exiting from the boiler economizer gas outlet
14
can be treated prior to entry into the tubular air heater configurations illustrated in
FIGS. 1 and 2
can present significant arrangement problems. The present invention provides a solution with a minimum of cost and modification.
SUMMARY OF THE INVENTION
The present invention involves modifications to an air heater gas inlet plenum for a tubular air heater to permit retrofit installation of additional flue gas environmental treatment equipment, such as selective catalytic reduction (SCR) systems for treating flue gas. A divider plate is located within the inlet plenum to subdivide it into first and second flue gas passages. The first flue gas passage created by the divider plate merely conveys the hot flue gas through the inlet plenum and into flues which convey the flue gas to the new equipment. Return flues convey the flue gas back to the second flue gas passage created in the inlet plenum which, in turn, conveys the flue gas into the tubular air heater heat exchanger tubes. By taking advantage of the large size of a conventional air heater gas inlet plenum, the first and second flue gas passages created by the divider plate still have sufficient cross sectional area so that acceptable flue gas velocities are preserved.
Accordingly, o
Lieb Paul James
Nelson Norman D.
Piaskowski Edward J.
Bennett Henry
Duong Tho V
Grant Kathryn W.
Marich Eric
The Babcock & Wilcox Company
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