U.S. patent application number 14/878186 was filed with the patent office on 2016-04-14 for vertical multiple passage drainable heated surfaces with headers-equalizers and forced circulation.
The applicant listed for this patent is Stanislav V. POLONSKY, Vladimir S. POLONSKY. Invention is credited to Stanislav V. POLONSKY, Vladimir S. POLONSKY.
Application Number | 20160102926 14/878186 |
Document ID | / |
Family ID | 55653850 |
Filed Date | 2016-04-14 |
United States Patent
Application |
20160102926 |
Kind Code |
A1 |
POLONSKY; Vladimir S. ; et
al. |
April 14, 2016 |
VERTICAL MULTIPLE PASSAGE DRAINABLE HEATED SURFACES WITH
HEADERS-EQUALIZERS AND FORCED CIRCULATION
Abstract
The present invention discloses improved heated surfaces (HS)
with vertical multiple passage panels or vertical serpentine coils
from straight tubes with connections between them by top and bottom
bends. In HS with tube bends there is not any mixing headers--each
circuit has a single tube from inlet header to outlet header. This
increases mass velocity of flow and improves stability and
temperature regulation of tubes. The bottom bends have holes. The
bottom bend holes of the adjacent passes are connected with drain
header by drain stubs. Each header serves to drain the adjacent
tube passes and as equalizing header of pressure/flow. It will help
to decrease multivaluedness and maldistribution of flow between
parallel tubes of the module. Such design of HS noticeably
decreases the corrosion of tubes.
Inventors: |
POLONSKY; Vladimir S.;
(Moscow, RU) ; POLONSKY; Stanislav V.; (Moscow,
RU) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
POLONSKY; Vladimir S.
POLONSKY; Stanislav V. |
Moscow
Moscow |
|
RU
RU |
|
|
Family ID: |
55653850 |
Appl. No.: |
14/878186 |
Filed: |
October 8, 2015 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
62062055 |
Oct 9, 2014 |
|
|
|
Current U.S.
Class: |
165/110 |
Current CPC
Class: |
F01K 7/16 20130101; F01K
7/32 20130101; F22D 1/32 20130101; F28F 9/22 20130101; F28D 21/0003
20130101; F22B 1/18 20130101; F28D 7/085 20130101; F22B 29/067
20130101; F22B 1/1815 20130101; F01K 7/30 20130101 |
International
Class: |
F28F 9/22 20060101
F28F009/22 |
Claims
1. Heated surfaces (HS) with forced circulation of liquids/gases,
comprising: a vertical multiple passage panel or serpentine coil
comprising rows of vertical straight tubes with connections between
them by top and bottom bends; each bottom bend having a drain stub;
each drain stub being connected to a header; all headers are
located below the bottom bends; each header being connected to at
least one bypass line for circulating water; thus providing a
stable operation of heat exchange elements of boilers and steam
generators; wherein each HS absorbing heat from exhaust gas.
2. The heated surfaces of claim 1, wherein the drain stub is
connected to the header, which is an elemental header; further
comprising: at least one integral header receiving the bypass from
the elemental header and outputting at least one drain pipe for
water draining into a water accumulator.
3. The heated surfaces of claim 2, further comprising drain stubs
entering the integral header.
4. The heated surfaces of claim 2, wherein the accumulator is
located outside a casing; and the drain pipes go through the casing
via holes.
5. The heated surfaces of claim 4, wherein the holes in the casing
have larger diameter than the drain pipes allowing thermal
expansion of the drain pipe.
6. The heated surfaces of claim 2, wherein both types of
headers--integral and elemental serve as equalizers thus regulating
a pressure and a flow liquid/vapor in parallel circuits.
7. The heated surfaces of claim 2, wherein water always passes
through the headers to cool down the bypass lines and the drain
pipes.
8. The heated surfaces of claim 1, wherein a diameter of the stub
is smaller than a diameter of the bottom bend.
9. The heated surfaces of claim 1, wherein a diameter of the stub
is at least twice smaller than a diameter of the bottom bend.
10. The heated surfaces of claim 1, further comprising: a drain box
covering the bottom bends, the drain stubs, the drain pipes, the
bypass lines and the headers; the box including water cooled wall
tubes to keep proper temperature conditions in the drain box.
11. The heated surfaces of claim 1, wherein each water cooled wall
tube is connected to an inlet header and an outlet header.
12. The heated surfaces of claim 1, wherein a pressure inside the
panel or the coil is a subcritical pressure.
13. The heated surfaces of claim 1, wherein a pressure inside the
panel or the coil is a supercritical pressure.
14. The heated surfaces according to claim 1, where the sizes of
holes in the bottom bends and in the headers of multiple passage
panels or serpentine coils are adjusted in such manner to have an
equal pressure drop in all parallel circuits.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] The present application claims priority to U.S. provisional
application No. 62/062,055 filed on Oct. 9, 2014.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention is the heated surfaces (HS) for
application in the different technical fields--power industry,
metallurgy, chemical industry, etc. Below the invention is
considered in the context of power industry.
[0004] 2. Background Art
[0005] For units of power industry which are based on Brayton and
Rankine cycles the general tendency is increasing, the initial
parameters--pressure and temperature to improve, the thermal
efficiency (TE) and decrease carbon dioxide emissions. In the
modern conventional units the pressure is well above the critical
pressure. The boilers of such units are once through type.
[0006] The same tendency with pressure increasing can be seen in
the case of Combine Cycle Power Plants (CCPP) as well. At present
time the pressure in steam generators of CCPP is below of critical
pressure. However in the future heat recovery steam generators
(HRSG) the pressure will be above critical pressure. The cycle of
CCPP with HRSG of supercritical pressure (SCP) can have the thermal
efficiency well above 60%. The SCP HRSG could be realized as once
through boilers (OTHB) only. The subcritical conventional boilers
and HRSGs can be as once through (circulation ratio is equal one)
units and with forced circulation (circulation ratio is above one)
as well. These two types of units are the subject of invention. The
conventional boilers and the HRSGs of subcritical pressure with
natural circulation are not considered here based on essence of
invention.
[0007] The main problems of once through units and units with
forced circulation are corrosion/erosion, temperature regime of
heated surfaces, and hydrodynamic instability. In accordance with
Electrical Power Research Institute data the main failures of
boilers and HRSGs are as result of corrosion of heated surfaces.
The suggested invention can improve the effectiveness and
reliability of multiple passage heated surfaces and increase TE of
whole units.
SUMMARY OF THE INVENTION
[0008] A principal peculiarity of suggested heated surfaces with
forced circulation are the vertical multiple passage panels
(usually used in conventional boilers) and vertical serpentine
coils (usually used in HRSGs) from some rows of straight tubes with
connections between them by top and bottom bends. Such types of HS
can be used for different elements of boilers and HRSGs--water
preheaters (WPHTR), economizers (EC), evaporators (EV),
superheaters (SH), and reheaters (RH).
[0009] In HS with tube bends there are not any mixing headers--each
circuit goes like a single tube from inlet header to outlet header.
It allows increasing mass velocity of steam/water or steam-water
mixture for subcritical pressure (or supercritical fluid) and
improves stability of flow and temperature regime of tubes.
[0010] To have opportunity for water drain at the lower point of
bottom bends there are the holes. The bend holes of the adjacent
passes are connected with drain header by pipe stubs. Each header
serves for drain of the adjacent tube passes. At the same time the
header can serve as equalizing header of pressure/flow. In the case
of the different thermal-hydraulic characteristics of parallel
tubes there is opportunity for bypass flows. It will help to
decrease multivaluedness and maldistribution of flow between
parallel tubes of the module. Besides such design of HS noticeably
decreases the corrosion when the units are not in operation.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] The present invention will now be discussed in further
detail below with reference to the accompanying figures in
which:
[0012] FIG. 1 is a scheme of Benson HRSG with once through
evaporator;
[0013] FIG. 2 is a scheme of conventional boiler with N-shaped
evaporator panel and forced circulation;
[0014] FIGS. 3a-3h are multiple passage panels of conventional once
through boilers;
[0015] FIG. 4 is a typical vertical serpentine drainable coil with
bottom header and forced circulation;
[0016] FIG. 5 is a vertical serpentine coil of HRSG with drainable
header-equalizer;
[0017] FIG. 6 shows varying drain stub and drain pipe diameters for
a vertical serpentine coil of HRSG with drainable
header-equalizer;
[0018] FIG. 7 is a multiple passage panel of convention once
through boiler with drainable header equalizer.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0019] All types of thermal power plants are emitting a lot of
waste heat into the atmosphere. To improve the thermal efficiency
and decrease carbon dioxide emissions a noticeable portion of waste
heat can be captured and used for the different goals. Let's
consider the issue in the context of Combine Cycle Power Plants
(CCPP) as one of the most effective cycles in power industry. In
this case the heat of exhaust gas after gas turbines (GT) can be
used in heat recovery steam generators. The steam after HRSG goes
into steam turbine (ST) which drives electrical generator. The
thermal efficiency of such combined cycle (Brayton and Rankine
cycles) can be above 60%. In contrast a single ST cycle of
subcritical pressure is limited around 40%, the best modern GTs
have thermal efficiency about 45%. The modern units with ST cycle
of supercritical pressure have achieved 43-44%. In this respect the
future tendency in this branch of power industry should be the CCPP
with HRSG of supercritical pressure (SCP). The SCP HRSG could be
realized as once through boilers (OTHB) only (it means a forced
circulation in all elements of boiler including zone of maximum
thermal capacity). At the same time the conventional boilers of
supercritical pressures are in operation during many years
already.
[0020] There are some publications regarding SCP HRSG with
horizontal design of heated surfaces and vertical gas flow. However
there is no information about any practical application of this
approach. The most common technology of subcritical horizontal OTHB
is Benson HRSG licensed by Siemens (FIG. 1, prior art). FIG. 1
shows the Benson HRSG with feed water inlet 104, star distributor
105, downcamera 106, a first evaporator 103, a second evaporator
102, separator 107, and super heater 101. Unfortunately Benson HRSG
has some serious problems with evaporator (EV) design--the very
small velocities of flow in cold section and EV instability; a very
complex design of hot EV section with not good temperature regime
of tubes; two-phase flow distribution by star-distributor on the
hot EV section inlet is very complex and not reliable, etc.
[0021] One of the most important and key element in once-through
boilers and HRSGs is evaporator (pseudo EV in the case of SCP). It
is a reason for consideration below of HS as the EVs in the first
turn. In subcritical EV there is two-phase flow (steam/water
mixture) in all range of operational parameters. In supercritical
boilers two-phase flow could be under partial loads. Two-phase
flows have very complex structure, hydrodynamics, and very complex
behavior of heat transfer and hydraulic resistance coefficients.
The stratification of two-phase flows, deposition of salts,
corrosion/erosion issues, critical heat fluxes, and instability are
the major concerns for designers of once-through HRSGs and
conventional boilers.
[0022] There is a good experience in design and operation of
conventional once through units and units with forced circulation
(FIG. 2, prior art) with different levels of pressure. The working
fluid (water for subcritical pressure or supercritical fluid for
supercritical pressure) from inlet manifold goes throw high
pressure (HP) economizer to HP evaporator (for subcritical
pressure) or pseudo evaporator PEV (for supercritical pressure).
FIG. 2 shows a scheme of a conventional boiler with N-shaped
evaporator panel and forced circulation having a feed water pump
201, economizer 202, evaporator 203, circulation pump 204, second
stage evaporator 205, super heater 206, outlet for super heater
207, separator 208, and valve 209. As a result of heat absorption
from hot exhaust gas an enthalpy of working fluid will change from
water inlet value up to value of slightly superheated steam in EV
outlet and strong superheated steam in SH coils. As rule, the
modern units have a reheat system as well.
[0023] The tube panels of conventional boilers with forced
circulation (EC, EV, SH and RH) have the very different layouts.
For example, on FIG. 2 the EV panel was implemented as N-shaped
panel with vertical tubes. Different manufactures are used the
different types of tube panels (FIG. 3, prior art). FIGS. 3a-3h
show multiple passage panels of conventional once through steam
generators. FIG. 3a show a N-shaped panel with vertical tubes. FIG.
3b shows a modified N-shaped panel. FIG. 3c shows a standard panel
with horizontal tubes. FIG. 3d shows a modified panel with
horizontal tubes. FIG. 3e shows a vertical multiple passage panel.
FIG. 3f shows a modified vertical multiple passage panel. FIG. 3g
shows vertical panels with even number of passages. FIG. 3h shows
vertical serpentine panels. Each type of panels has the advantages
and disadvantages. Many problems were resolved regarding heat
transfer and hydrodynamics of flows in such panels. One of the main
problems of multiple passage panels with vertical tubes (types--a,
b, e, f, g, and h) is corrosion of internal surface of tubes. As it
can be seen from FIG. 3 in these panels there are some
non-drainable passages. During the shutdown period some water can
accumulate in the bottom bends of these passages that result in
strong corrosion.
[0024] In the coils of HRSGs there is similar problem. For example,
in the earliest types of serpentine coils there were some
non-drainable bottom bends. Because of strong corrosion the bottom
bends were replaced with bottom headers (FIG. 4, prior art). It
helps to decrease a rate of corrosion. However the hydrodynamics of
such vertical serpentine drainable coils is complex enough. Besides
such type of coils can't be used for EVs because of possibility for
maldistribution of two-phase flows between parallel tubes.
[0025] The tubes of HRSG heated surfaces are the finned tubes
usually. In the case of relatively big heat fluxes some rows of
HRSG can be manufactured from the bare tubes. A principal
peculiarity of suggested heated surfaces for HRSG conditions is the
vertical serpentine coil from some rows of straight tubes with
connections between them by top and bottom U-bends 506 (FIG. 5). A
direction of water flow in the coil could be counter flow or
parallel flow with exhaust gas flow. A tube (finned or bare) layout
could be a staggered or an inline.
[0026] FIG. 5 shows gas baffle keeper 515 connected to gas baffle
516. An inlet header 502 and outlet header 501 are contained within
gas baffle 516. Inlet header 502 and outlet header 501 are
connected by evaporator coil 503. The evaporator coil has bottom
U-bends 506. The bottom U-bends 506 are connected to drain stubs
507 which are connected to elemental header-equalizer 509 which are
connected to drain bypass 508 which are then connected to bellows
513. The bottom U-bends 506, drain stubs 507, elemental
header-equalizers 519, drain bypasses 508, integral
header-equalizers 509, water cooled wall inlet header 510, water
cooled wall outlet header 511, and water cooled wall tubes 504 are
all contained within drain box 517. Water cooled wall inlet header
510 and water cooled wall outlet header 511 are connected by water
cooled wall tubes 504. Drain box 517 has water cooled wall 505
(which is adjacent to water cooled wall tubes 504) which is
connected to a gas baffle keeper 510 sitting on top of liner 518.
Liner 518 sits on top of casing 514. The drain bypasses 508 pass
through the liner 518 and casing 514 into the bellows 513.
[0027] Let's consider the specific of suggested HS for EV of HRSG
because the physics of two-phase flow is more complex as the single
flows. In case of EV with tube bends (FIG. 5) there are not any
mixing headers--each circuit goes like a single tube from inlet
header to outlet header. It allows increasing mass velocity of
steam-water mixture (or supercritical liquid) and improves
stability of flow and temperature regime of tubes. To have
opportunity for water drain at the lower point of bottom bends
there are the holes. The bend holes of the adjacent rows are
connected with drain header by pipe stubs. The pipe stub diameter
is noticeably less than EV tube diameter. It means that water flow
goes mainly through the EV tubes. Each header serves for drain of
two adjacent tube rows. The sizes of such headers should be smaller
than regular bottom headers of standard design.
[0028] At the same time the header can serve as equalizing header
of pressure/flow. In the case of the different thermal-hydraulic
characteristic of parallel tubes there is opportunity for bypass
flows. It will help to decrease multivaluedness and maldistribution
of flow between parallel tubes of the module. There is sense to
underscore that bottom portion of coil (from the hole in bottom
bend to drain pipes) will be filled in with water (for subcritical
EV) or heavy phase (for supercritical EV). It is a result that in
bottom bends there is a centrifugal force, which in many times more
than force of gravitation. Besides in the bottom bend the both
vectors of centrifugal force and force of gravitation are coincided
(both are acting in downward direction). Both forces are
proportional to density of medium. It means that integral force for
water will be more than for steam (for subcritical pressure) or for
heavy phase will be more than for light phase (for supercritical
pressure). Besides, in vertical downward two-phase flows, as rule,
velocity of droplet is more than velocity of steam. It means that
centrifugal force for droplet in bottom bend will be more than for
steam. This results in that all operation conditions the bottom
portion of coil (from drain stubs and below) will be filled in with
water (for subcritical EV) or heavy phase (for supercritical EV).
This is very important for thermal-hydraulic processes in the
coil.
[0029] In some HRSG design conditions drain system is situated in
the area of relatively hot exhaust gas. To avoid thermal-mechanical
problems the drain system should have the proper temperature
regime. It can be achieved by circulation of small amount of water
(or supercritical liquid) through drain system. For this goal two
adjacent drain lines are connected by drain cross over (drain
bypass) pipe (FIG. 5). The diameter of drain cross over pipe is
noticeably less than EV tube diameter and should be calculated in
such a way to guarantee the proper temperature regime of the drain
system. To decrease the number of drain pipe penetrations through
the casing the design of drain assembly could be as it is shown on
FIG. 5. All pipe penetrations are realized with help of bellows. Of
course for sizing of cross over pipes (drain bypass pipes) it is
needed to take into account the difference in pressure drop between
the proper headers. On FIG. 5 the drain headers are depicted for
cold conditions (unit is not in operation). In hot conditions (unit
in operation) the headers will move down to bottom liner as result
of coil expansion with temperature. In the case the temperature
regime of drain system will be normal even with relatively small
water flow in drain bypass lines.
[0030] Temperature regime of drain system can be reliable under
small water bypass if it is situated out of the main exhaust gas
flow (in the area of relatively stagnant gas flow). Such scenario
can be realized with help of gas baffle plates (FIG. 5). Upper
portion of plates should be fixed on the EV (EC, SH, etc.) tubes
above bottom bends. Lower part should be situated in the baffle
keeper. On this figure EV (EC, SH, etc.) coil is fixed on the top
of HRSG (at some designs a coil can be fixed in the bottom). In
this case the coil will expand in downward direction. A height of
the sealing assembly (baffle keeper) should guarantee the coil
expansion in all operational conditions. The upper portion of
baffle plates should have such height to minimize exhaust gas flow
through the box with drain system. The drain box includes bottom
bends, drain stubs, headers-equalizers, drain pipes and confined by
gas baffle plate. The box of drain system has to have the gas
baffle plates on all four sides. In the case of multi wide HRSG the
gas baffle plates are installed between the modules as well to
decrease the gas bypass.
[0031] In the case, when the coil is situated in very high range of
gas temperatures, the temperature regime of drain system can be
kept on reliable level with help of water cooled walls. The walls
could be fabricated from membrane tubes to minimize gas bypass.
Water for the wall is used after EC before going to EV. It is
possible as well to take water for the wall between the sections of
EC. Thermodynamic efficiency is taken into account in each case. A
direction of water flow in the wall could be counter flow, parallel
flow, or perpendicular with exhaust gas flow. Designer has to take
into account the peculiarities of temperature regimes of the coil
and water cooled wall in the contact area of tubes with different
wall temperatures. In the case of multi wide HRSG the gas baffle
plates should be installed between the water cooled boxes of the
different modules. In most cases the water cooled walls will not be
necessary.
[0032] Temperature regime of once-through HRSG EV tubes could be
different from HRSG EV tubes with natural circulation. In OTH HRSG
EV subcritical or supercritical pressures could be a zone with
deterioration of heat transfer. It means that under any enthalpy of
fluid there is a jump in tube wall temperature. The value of
temperature jump depends on parameters of exhaust gas flow, as well
of water pressure, mass velocity, and heat flux for given geometry
of coil tubes. For any combination of these parameters temperature
jump could be strong enough. To improve the tube temperature regime
the different types of intensificators can be used (rifled tubes,
inserts, etc.).
[0033] A special attention should be paid to bottom bends and
connections with drain stubs (FIG. 5). To avoid excessive stresses
the material and geometry of the transition tees should be designed
properly. The drain system should be a flexible enough to
compensate the possible difference in expansions of the coil and
drain system.
[0034] The HRSG can be operated under supercritical and subcritical
pressures. Under nominal conditions a unit can be supercritical but
under part loads the pressure in system can be subcritical. Besides
on the EV outlet a two-phase flow could be, but not superheated
steam. To prevent a steam-water mixture going in superheater the
special separators should be on the outlet of EV (see FIG. 2). At
the same time the assembly of the separators and the water tanks
can help to manage the proper temperature regime of EV under
partial loads of HRSG. A control of water mass velocity and steam
quality on the EV outlet can be done by the feed water pump(s) or
by the special recirculation pump(s). Exploitation of the feed
water pump(s) or the special recirculation pump(s) should be chosen
based on technical/economical evaluations of the proper schemes
(price of pumps, price of electricity, relative duration of part
loads, etc.).
[0035] FIG. 5 shows an inlet and outlet header that may be
connected to one or more vertical evaporator coils. The evaporator
coils have bypass drains connected to the bottom of the evaporator
coil. The drain bypasses ultimately lead to a bellows on the other
side of the casing. The vertical evaporator coil may further have a
water cooled inlet header and water cooled outlet header connected
by water cooled wall tubes contained within a water cooled wall and
connected to the casing by a gas baffle keeper.
[0036] FIG. 6 shows the bottom U-bend 606 of the vertical
evaporator coil. The bottom U-bends 606 can be connected by drain
stubs 607. The drain stubs 607 do not all need to be the same
diameter, the drain stubs 607 and bypass lines 608 can vary in
diameter across the vertical evaporator coil. The widest diameter
drain stub 607 can be either on the inlet header or outlet header
side of the vertical evaporator coil. The drain stub 607 and the
bypass line 608 are connected at the elemental header-equalizer
609.
[0037] Relatively simpler thermo-mechanical situation is in the
header--equalizer and the drain system of multiple passage panels
of conventional boilers (FIG. 7). The tubes 719 of the panel are
connected by tube stubs 707 with header-equalizer 709. The
headers--equalizer are situated outside of casing. The drain pipes
708 are also situated outside of combustion chamber (or gas duct).
In this sense the temperature regime of drain system will be
reliable because of there is no the additional sources of heat.
[0038] Special attention should be paid to the position of
header--equalizer. The header should be a horizontal orientation to
avoid the effect of possible gravitational component in pressure
drop (it is specific of vertical and inclined headers). Header
should be situated below the lowest row of the panel. It can
guarantee that header will be filled in with water (for subcritical
pressure) or heavy fluids (for supercritical pressure). This
provision is very important for stability of flow.
[0039] The length of heated tubes and pipe stubs of panel different
circuits in the connection points with headers could be different.
In this respect the special attention should be paid to equal
pressure drop. The possible way to do it is to adjust the sizes of
the holes in the bottom bends and in the header--equalizers in such
manner to have the equal pressure drop in all parallel
circuits.
[0040] While the foregoing written description of the invention
enables one of ordinary skill to make and use what is considered
presently to be the best mode thereof, those of ordinary skill will
understand and appreciate the existence of variations,
combinations, and equivalents of the specific embodiment, and
examples herein. The invention should therefore not be limited by
the above described embodiment, and examples, but by all
embodiments within the scope and spirit of the invention.
* * * * *