U.S. patent application number 12/592934 was filed with the patent office on 2010-09-16 for chilling economizer.
Invention is credited to Donald Charles Erickson.
Application Number | 20100229594 12/592934 |
Document ID | / |
Family ID | 42729581 |
Filed Date | 2010-09-16 |
United States Patent
Application |
20100229594 |
Kind Code |
A1 |
Erickson; Donald Charles |
September 16, 2010 |
Chilling economizer
Abstract
Chilling is produced from heat that is normally wasted in the
economizer section of a steam boiler. A thermally-activated
ammonia-water absorption chiller is powered by a heat recovery
unit. The heat recovery unit supplies boiler exhaust heat to desorb
the working fluid of the chiller. That can be directly, such that
the heat recovery unit is a heat recovery vapor generator that can
be colocated with an economizer, in parallel or series. The exhaust
heat can alternatively be supplied to the AARC indirectly, via a
heat transfer loop and a separate generator. The desorbed ammonia
vapor is rectified, condensed, and then used to produce the
chilling. The heat released in the chiller when low pressure
ammonia vapor is re-absorbed is used to preheat the boiler
feedwater.
Inventors: |
Erickson; Donald Charles;
(Annapolis, MD) |
Correspondence
Address: |
Donald C. Erickson
627 Ridgely Avenue
Annapolis
MD
21401
US
|
Family ID: |
42729581 |
Appl. No.: |
12/592934 |
Filed: |
December 4, 2009 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61200813 |
Dec 4, 2008 |
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Current U.S.
Class: |
62/476 |
Current CPC
Class: |
Y02A 30/277 20180101;
Y02B 30/62 20130101; F25B 15/04 20130101; F25B 15/02 20130101; Y02A
30/27 20180101 |
Class at
Publication: |
62/476 |
International
Class: |
F25B 15/00 20060101
F25B015/00 |
Claims
1. An apparatus for producing chilling comprised of: a. A steam
boiler; b. An economizer in the exhaust from said steam boiler; c.
A thermally-activated chiller; d. A heat recovery vapor generator
(HRVG) for said chiller that is colocated with said economizer in
said exhaust stream; and e. A thermal heating load that receives
reject heat from the absorber of said chiller.
2. The apparatus according to claim 1 wherein said
thermally-activated chiller is an ammonia-water absorption
refrigeration cycle (AARC), and wherein said thermal heating load
is a preheater for the feedwater supplied to said economizer.
3. The apparatus according to claim 2 wherein said economizer is
comprised of at least two sections, with a section of HRVG between
adjoining economizer sections.
4. The apparatus according to claim 2 wherein said economizer and
said HRVG are in parallel with respect to the exhaust flow
direction.
5. The apparatus according to claim 2 additionally comprised of a
gas turbine that discharges combustion exhaust to heat said boiler,
and a turbine inlet chilling coil that is supplied chilling from
said AARC.
6. The apparatus according to claim 5 wherein said AARC is adapted
to supply heating to said chilling coil in cold ambient
conditions.
7. The apparatus according to claim 5 additionally comprised of a
second generator for said AARC that is supplied steam from said
boiler.
8. The apparatus according to claim 2 wherein working fluid from
said AARC is supplied directly to said HRVG and has countercurrent
flowpath to said exhaust flow.
9. The apparatus according to claim 2 wherein a manufactured
product is heated by steam from said boiler and is chilled by said
chiller.
10. The apparatus according to claim 2 wherein a conditioned space
is heated by steam from said boiler and cooled by said
chilling.
11. The apparatus according to claim 2 wherein said feedwater
preheater is the absorber in said AARC.
12. The apparatus according to claim 11 additionally comprised of a
second absorber for said AARC that is cooled by heat rejection to
ambient, e.g. via cooling water.
13. An apparatus for heating boiler feedwater and for producing
chilling comprised of: a. A steam boiler; b. A thermally-activated
chiller that includes a rectifier; c. A heat recovery unit (HRU)
for said chiller that is located in the exhaust stream of said
boiler, and that transfers exhaust heat to said chiller; and d. An
absorber in said chiller that transfers reject heat to said
feedwater such that the feedwater is heated to at least about
140.degree. F.
14. The apparatus according to claim 13 wherein the chiller working
fluid is an ammonia-water mixture and wherein the feedwater is also
heated by the condenser of said chiller.
15. The apparatus according to claim 14 wherein said HRU supplies
heat to the generator in said AARC.
16. An ammonia-water absorption refrigeration cycle (AARC) that is
powered by waste heat associated with the exhaust of a steam
boiler, comprised of: a. A solution pump and solution heat
exchanger (SHX); b. A rectifier; c. A heat recovery unit that: i.
Supplies heat to the generator of said AARC, ii. Wherein said
generator is supplied pumped solution after heating in said SHX;
and iii. Said generator supplies partially desorbed solution to
said rectifier; d. At least one low pressure absorber that supplies
heat to a heat load; and e. An evaporator that supplies
chilling.
17. The apparatus according to claim 16 wherein at least part of
said heat load is preheating of the feedwater and/or makeup water
for said economizer.
18. The apparatus according to claim 16 additionally comprised of
an intermediate pressure absorber and an intermediate pressure
generator that supplies it vapor.
19. The apparatus according to claim 17 additionally comprised of a
gas turbine combined cycle that includes said boiler, and an inlet
air chilling coil for said turbine that utilizes said chilling, and
wherein said AARC is adapted to provide heating to said inlet air
coil when needed.
20. The apparatus according to claim 16 additionally comprised of
an ammonia expansion turbine that produces work from high pressure
ammonia vapor by expanding it to low pressure.
21. A method for producing chilling and feedwater heating from
steam boiler exhaust comprising: a. Providing an AARC; b.
Transferring boiler exhaust heat to said AARC; c. Desorbing pumped
AARC liquid with said heat; d. Rectifying the desorbed vapor; e.
Condensing the rectified vapor; f. Evaporating the condensed vapor
to produce said chilling; and g. Preheating boiler feedwater to at
least 140.degree. F. with heat rejected from the absorber of the
AARC.
22. The method according to claim 21 additionally comprising using
a three-pressure AARC to cool the steam boiler exhaust to below
190.degree. F.
Description
BACKGROUND
[0001] With steam boilers, it is good practice to include an
economizer or feedwater heater to capture more useful energy from
the exhaust. This increases boiler efficiency and reduces stack
temperature. Thus it is surprising to learn that there is actually
a lot of wasted availability that still remains even when
economizing. The stack temperature is still well above ambient, and
the economizing step employs very large temperature differentials,
thus generating the entropy. The overall purpose of this disclosure
is to make beneficial use of this presently wasted
availability.
[0002] Many steam boilers are found in applications where
refrigeration is also required (or would be useful). Examples
include food processors, hospitals, laundries, hotels, and process
industries. Additional examples are combined cycle plants and
cogeneration plants where the boilers are heated by exhaust from
the prime movers. On warm days those prime movers benefit markedly
from chilling the inlet air. Hence one particular objective is to
convert unused availability associated with current economizers
into chilling.
PRIOR ART
[0003] It is known to chill the inlet air of a combustion turbine
using refrigeration from an ammonia-water absorption refrigeration
cycle (AARC). U.S. Pat. No. 2,322,717 to Nettel discloses that,
using a fired combustion heater to power the AARC. More typically
the AARC is powered by turbine exhaust heat. U.S. Pat. No.
2,548,508 to Wolfner describes one such embodiment. The exhaust
first heats the compressed air in a recuperator, and then directly
heats the aqua solution to desorb it. An alternative configuration
for the AARC is presented in Malewski and Holldorff (1984). In that
disclosure, the turbine exhaust heats a two-pressure steam
bottoming cycle, then heats the aqua solution in a desorber (HRVG).
Ammonia refrigerant is rectified in a rectification column,
condensed, and then is supplied to a heat exchange coil for direct
chilling of the inlet air.
[0004] The 1990 article by Ondryas et al also discloses exhaust
powered ammonia absorption refrigeration as one option for chilling
turbine inlet air.
[0005] U.S. Pat. No. 5,555,738 to Devault discloses chilling the
turbine inlet air of a combined cycle configuration with an AARC
that is powered by steam turbine exhaust or other waste heat
source. The steam condenser 16 is also the aqua desorber, and the
AARC does not have a rectification column or a refrigerant
subcooler.
[0006] U.S. Pat. No. 6,058,695 to Ranasinghe et al discloses a gas
turbine combined cycle wherein extraction ammonia-water fluid from
a Kalina bottoming cycle is condensed to liquid, then is used to
chill the turbine inlet air.
[0007] U.S. Pat. No. 6,173,563 to Vakil et al discloses an
ammonia-water refrigeration cycle for a combined cycle plant.
Exhaust heat in the LP economizer section of the HRSG directly
partially vaporizes the aqua solution, which is then separated in a
separator. The vapor fraction is partially condensed in an
economizer that gives up heat to condensate from the gland seal
condenser. Then it is fully condensed against cooling water, then
depressurized to provide chilling to the inlet air. A small
fraction of the liquid refrigerant is used in the ammonia subcooler
to cool the liquid ammonia before expansion. Finally the low
pressure vapor from the chilling coil and the liquid fraction from
the separator are combined and absorbed against cooling water. This
cycle is similar to the Devault and the Ranasinghe et al cycles in
that there is no rectification column.
[0008] Langreck (2000) discloses an AARC for chilling inlet air to
a combined cycle plant that uses direct exhaust heating of the
desorber, but uses chilled water to cool the inlet air. The AARC
includes a rectification column. Sigler et al (2001) calculate that
a combined cycle plant enhanced by AARC shows improved warm weather
performance even when the penalty of the driving steam for the AARC
is accounted for.
[0009] U.S. Pat. Nos. 6,412,291 and 6,739,119 to Erickson disclose
a gas turbine configuration including an exhaust heat powered AARC
that delivers chilling to the turbine inlet air, plus additional
advantageous features. U.S. Pat. No. 6,715,290 to Erickson
discloses both simple cycle and combined cycle gas turbine plants
having exhaust powered AARC for inlet air chilling, wherein the
AARC has novel advantageous features, e.g. "glide heat".
[0010] The general background of this field of invention is further
defined in EPRI TR-102412 (1994) and in the following U.S. Pat.
Nos. 3,796,045; 5,203,161; 5,632,148; 5,655,373; 5,782,093;
5,790,972; 6,321,552; 6,457,315; 6,460,360; 6,837,056; 7,178,348;
7,228,682; and 7,343,746. These references provide examples of
alternative thermally-activated chillers, including LiBr absorption
chillers; steam-driven mechanical compression chillers; and liquid
desiccant dryer/chillers with thermal regeneration.
[0011] Included among the objects of this invention are to convert
the waste associated with current economizers into useful chilling
and additional feedwater heating. Both will improve the overall
efficiency of the steam boiler.
DISCLOSURE OF INVENTION
[0012] The above and other useful objects are accomplished by
providing a thermally activated chilling unit that is powered by a
heat recovery unit (HRU) located in the boiler exhaust. The HRU can
be directly supplied with working fluid from the thermally
activated chiller, that is desorbed therein, normally referred to
as a heat recovery vapor generator (HRVG). Preferably the HRVG is
colocated with the economizer in the boiler exhaust. Alternatively,
the HRU can be supplied a working fluid that in turn supplies heat
to the thermally activated chiller. The preferred embodiment of
thermally activated chiller is an ammonia-water absorption
refrigeration cycle (AARC). An essential aspect of the invention is
that the AARC reject heat is used to preheat the boiler feedwater
and makeup feedwater, for example before it is sent to the
economizer. That supplies three important benefits: it allows more
of the exhaust heat to be sent to the AARC, thus increasing the
amount of chilling; it reduces the amount of AARC heat that must be
rejected to ambient, through a cooling tower or the like; and it
raises the feedwater temperature above the exhaust dewpoint, so
economizer corrosion is avoided.
[0013] Further to this disclosure, it is desirable to route the
AARC working fluid in direct countercurrent contact with the
exhaust. This allows it to extract more useful heat from the
exhaust, i.e. down to a lower temperature, and also increases the
temperature of the AARC reject heat, thus allowing more reject heat
to be transferred to the feedwater.
[0014] In the combined cycle application, the chilling so produced
is directed to chilling the inlet air of the prime mover that is
producing the exhaust used to make the chilling. Thus the loop is
closed to form an overall integrated cycle, and the chilling is
produced without detracting from either the steam production or the
feedwater heating, and also without the large parasitic electric
load associated with mechanical compression chilling.
[0015] The HRVG can be colocated with the economizer in two basic
configurations--either in parallel, or in series. The parallel
arrangement provides the best thermodynamic results. That is
because each heating load has a temperature glide, and hence the
two in parallel can be sized to match the temperature glide of the
exhaust, such that the driving temperature difference is
essentially constant. However the drawback of the parallel
configuration is that when there are times the AARC is not being
used, e.g. at mild ambient conditions, and is turned off, part of
the exhaust bypasses the economizer. Since the feedwater no longer
receives preheat from the idle AARC, there will be a deficit in
feedwater heating.
[0016] One way to solve that feedwater heat deficit problem is to
leave the AARC always operating whenever the economizer (and
boiler) are operating. That can be done by creating false load
(vapor bypass) on mild days, or even by producing power with that
idle capacity, via the "dual function" cycle. Another way to solve
that problem is with a series arrangement, also referred to as the
"split economizer" arrangement. The economizer is split into two or
more segments, with a HRVG segment alternating with each economizer
segment. The overall objective is to achieve a close match between
the temperature glide of the exhaust and the temperature glide of
heat acceptance. This is the same design objective as that used to
design the entire HRSG of a combined cycle plant. With the series
(split economizer) arrangement, all the exhaust flows through the
economizer even when the AARC is turned off, so there is no
deficit.
[0017] By the same token that adding an economizer to a boiler
increases the backpressure, and hence requires adjustments to the
emissions and other boiler controls, colocating the HRVG with the
economizer will further increase the backpressure, and hence
require further adjustment.
[0018] The terms "economizer" and "feedwater heater" are used in
their broad sense, i.e.
[0019] including functions such as condensate heating, makeup
feedwater heating, etc.
[0020] With single pressure steam boilers, e.g. for steam pressures
in the range of 50 to 100 psig, the exhaust temperature after the
economizer is typically close to 300.degree. F. With multi-pressure
steam plants, more typically encountered in cogen and combined
cycle applications, and very large applications, the exhaust
temperature after the economizer is more typically about
200.degree. F. or lower. Especially in the latter case, it is
desirable to use a more advanced AARC that can beneficially use the
exhaust to lower temperatures. In particular, this would entail use
of a three-pressure absorption refrigeration cycle, with or without
GAX (generator-absorber heat exchange). The three-pressure cycle is
able to extract useful driving energy from the exhaust down to
about 170.degree. F.
BRIEF DESCRIPTION OF THE DRAWINGS
[0021] FIG. 1 illustrates a conventional prior art steam boiler
with a fired burner, a feedwater pump, and a feedwater economizer
in the exhaust stack.
[0022] FIG. 2 illustrates one way to convert the FIG. 1 economizer
to a chilling economizer. Additional heat exchange surface is
colocated in the economizer (parallel in this instance) for a heat
recovery vapor generator that is part of an ammonia absorption
refrigeration cycle, said HRVG receiving pumped liquid from a
solution heat exchanger and sending two phase partially desorbed
fluid to a rectifier. The AARC also has a condenser, a refrigerant
heat exchanger, an evaporator that produces the chilling, and an
absorber that is used to preheat feedwater enroute to the
economizer.
[0023] FIG. 3 illustrates a gas turbine combined cycle plant with
exhaust powered AARC to supply inlet air chilling and feedwater
preheating, where the HRVG is series colocated with the LP
economizer. The AARC is a three-pressure version with exhaust
heating at both pressure levels. The AARC is also adapted to
provide turbine inlet air heating when necessary, and to expand
otherwise unused ammonia vapor for power production when available.
Note that part of the HRVG is at the cold end of the exhaust
flowpath.
[0024] FIG. 4 is a simplified flowsheet for an alternative
three-pressure AARC adapted for firing from a HRVG that is
colocated with a low-pressure economizer. In this case, the HRVG is
shown being in parallel with the feedwater economizer (FWE). The
AARC has internal latent heat exchange in the form of an IP GAX,
part of the "vapor exchange" configuration.
[0025] FIG. 5 illustrates a chilling economizer on a fired steam
boiler wherein a heat transfer loop transfers boiler exhaust heat
to the AARC, and the feedwater is heated by both condenser reject
heat and absorber reject heat from the AARC.
BEST MODE FOR CARRYING OUT THE INVENTION
[0026] It would be possible to mount the HRVG downstream of the
economizer, i.e. at its cold end, and just use the final waste heat
of the exhaust to make chilling. However that would waste about
half of the actual potential of that exhaust to produce chilling.
The features desirable to achieve high levels of chilling are: to
colocate the HRVG of the AARC with the economizer, such that higher
driving temperatures are available to the HRVG; to achieve maximum
useful temperature glide in the HRVG by supplying it directly with
pumped and preheated solution; to rectify the desorbed solution to
higher ammonia purity so as to get more useful chilling from a
given amount of desorbed fluid; and to preheat feedwater with
absorber reject heat. The latter step has two benefits: more of the
exhaust heat becomes available to the HRVG; and the economizer feed
is warm enough (e.g. above 140.degree. F.) that acid condensation
of the exhaust gas is not a concern. Note that this requires that
absorber heat be used, as were the condenser pressure to be
increased high enough to produce that temperature of reject heat in
sufficient amounts to do that heating, the pressure would be
unreasonable and less chilling could be produced. The four critical
features listed above are illustrated in the FIG. 2 flowsheet.
[0027] From the perspective of the heat recovery train for the
exhaust from the boiler, this enhancement entails adding from two
to four more transfer units (NTUs) of heat exchange.
[0028] Beyond the key features recited above, various other
additional features will be found advantageous in particular
applications. For example, when the steam boiler is part of the
HRSG of a gas turbine combined cycle plant, the chilling is
advantageously applied to chill the turbine inlet air. When even
lower exhaust temperatures are desired, the AARC can be a
three-pressure version. This yields more chilling, and can have
other beneficial effects, such as making it easier to recover water
and/or CO2 from the exhaust. The three-pressure cycle can have
external heating at both pressure levels, as in FIG. 3, or can have
internal GAX heating as in FIG. 4. One suitable method of
beneficially applying the third pressure level in the AARC is via
the "vapor exchange" cycle, as disclosed in U.S. Pat. No.
5,097,676, to Erickson. FIGS. 3 and 4 present variants of that.
[0029] Whereas FIG. 3 presents a two pressure steam bottoming cycle
in the combined cycle, it will be recognized that any other
bottoming configuration applies equally well, e.g. three pressure
steam cycle, with or without reheat, etc. Similarly the gas turbine
can optionally have intercooling, recuperation, STIG, and the like.
The bottoming portion of the cycle can be simply for steam
production, i.e. cogeneration, instead of or in addition to power
production.
[0030] With the three-pressure AARC, the exhaust temperature can
readily and beneficially be brought down to the 160.degree. F. to
190.degree. F. range, depending upon ambient temperature. When
using the absorber for feedwater preheating, the feedwater can be
preheated to at least 140.degree. F., and also warmed by at least
30.degree. F. Note that the heat can beneficially be applied to
other loads as well. When the heating is to be applied to cold
water or supply water, the colder condenser reject heat from the
AARC can also be used, in series with the hotter absorber heat.
Note that it is frequently desirable to have more than one
absorber, with the colder one cooled by cooling water, and the
warmer one doing the feedwater heating, as shown in FIGS. 3 and 4.
That makes more chilling and further reduces the exhaust
temperature.
[0031] FIG. 3 illustrates the "split economizer" or series
configuration--there are two sections of LP Econ and two sections
of HP HRVG in alternating sequence. There are also two LP
absorbers--one for heat recovery, and the other rejecting to
ambient. The rectifier has internal heat recovery in both the
stripping section and rectifying section.
[0032] The disclosed chilling economizer can produce approximately
90 tons of energy-free chilling from the exhaust of a 20 million
BTU/hour boiler. In the combined cycle application, it can produce
about 800 tons of energy-free chilling in a 120 MW plant using a
two-pressure steam bottoming cycle. As another example, with a 520
MW combined cycle with three pressure plus reheat bottoming steam
cycle, the chilling economizer can produce up to 3000 tons of
energy-free chilling. That chilling can beneficially be applied to
turbine inlet air chilling.
[0033] FIG. 5 illustrates two alternative features relative to the
FIG. 2 embodiment. First, the boiler exhaust heat is recovered into
a heat transfer fluid, which in turn heats the generator of the
absorption cycle. This variant of the HRU provides some advantages,
such as being able to supply both AARC heating duty and economizing
duty with only a single exchanger in the exhaust path. The downside
is the need for the additional pump to circulate the heat transfer
fluid, plus an expansion tank. Secondly, the feedwater is supplied
heat from both the condenser and the absorber of the AARC, in that
order. This is particularly valuable when the steam boiler requires
a lot of cold makeup water. FIG. 5 also illustrates conventional
features in the feedwater system, such as steam trap, condensate
tank, condensate pump, deaerating feed tank, and feedwater
pump.
* * * * *