Note: Descriptions are shown in the official language in which they were submitted.
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SYSTEM AND METHOD TO INTEGRATE CONDENSED WATER WITH
IMPROVED COOLER PERFORMANCE
REFERENCE TO RELATED APPLICATIONS
[0001] This application claims the priority benefit of United States Patent
Application
62/375,705 filed August 16, 2016 entitled SYSTEM AND METHOD TO INTEGRATE
CONDENSED WATER WITH IMPROVED COOLER PERFORMANCE, the entirety of
which is incorporated by reference herein.
[0002]
This application is related to U.S. Provisional Patent Application No.
62/375,700
titled "SYSTEM AND METHOD FOR LIQUEFYING NATURAL GAS WITH TURBINE
INLET COOLING", having a common assignee as this application and filed on the
same day
herewith. The disclosure of this related application is incorporated by
reference herein in its
entirety.
BACKGROUND
Field of Disclosure
[0003] The
disclosure relates generally to gas turbines, and more particularly, to inlet
air
cooling of a gas turbine or another process component.
Description of Related Art
[0004]
This section is intended to introduce various aspects of the art, which may be
associated with the present disclosure. This discussion is intended to provide
a framework to
facilitate a better understanding of particular aspects of the present
disclosure. Accordingly, it
should be understood that this section should be read in this light, and not
necessarily as an
admission of prior art.
[0005]
Many industrial processes use a gas turbine or turbines to generate power or
drive
a mechanical load. For example, hydrocarbon production facilities use
combustion gas
turbines to drive the compressors needed to refrigerate the natural gas from a
gaseous to a liquid
state. More specifically, LNG production facilities typically use two or more
refrigeration
circuits to at least pre-chill the incoming natural gas and then to liquefy
it. Often the use of the
various refrigeration circuits in these facilities is not optimized and spare
refrigeration capacity
in one or more of the refrigeration circuits cannot be fully used for all
operating conditions.
Operating at a wide range of ambient temperatures may be a factor that can
result in such an
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imbalance of the various refrigeration circuits.
[0006]
Further, the combustion gas turbine drivers are also sensitive to ambient
temperature and can lose about 0.7% of available power for each 1 degree
Celsius increase of
the ambient temperature. This means that most LNG plants have to be
significantly
overdesigned to ensure the required horsepower is available regardless of
ambient temperature.
[0007]
U.S. Patent No. 6,324,867 to Fanning, et al. describes a system and method to
liquefy natural gas that utilizes the excess refrigeration capacity in one
refrigeration circuit to
chill the inlet air for the gas turbine driver or drivers of another
refrigeration circuit and thus
increase the overall capacity of the LNG plant. The disclosure of Fanning is
incorporated by
reference herein in its entirety. By maintaining the inlet air for the
turbines at a substantially
constant low temperature, the amount of power generated by the turbines
remains at a high
level regardless of the ambient air temperature. This allows the LNG plant to
be designed for
more capacity and allows the plant to operate at a substantially constant
production rate
throughout the year. Further, since the system of Fanning uses the first
refrigerant circuit, for
example a circuit comprising propane as a refrigerant, already present in LNG
systems of this
type, no addition cooling source is required.
[0008] U.
S . Patent No. 8,534,039 to Pierson, et al. describes using moisture condensed
via
gas turbine inlet air chilling for psychometric cooling to improve the
performance of an organic
Rankine cycle condenser and refrigerant condenser. This refrigerant condenser
is part of the
system that provides the gas turbine inlet air chilling. In Pierson, the
condensed moisture is
collected in a basin located below a wet air fin cooler and a pump sprays the
collected water
onto the tubes of the air fin. Pierson also describes adding makeup water to
maintain a
minimum level in the basin. It is desired, however, to provide a such a
cooling system that
does not require the use of a basin as disclosed in Pierson, and that
minimizes possible
contamination of the cooling water from atmospheric contaminants.
SUMMARY
[0009] The
present disclosure provides a method for cooling a process fluid according to
disclosed aspects. An inlet air stream of a turbine is cooled with an inlet
air cooling system.
Moisture contained in the cooled inlet air stream is condensed and separated
from the cooled
inlet air stream to produce water stream in an open-loop circuit. The water
stream is sprayed
into an air cooler air stream. The combined air cooler air stream and sprayed
water stream is
directed through an air cooler. Heat is exchanged between the process fluid
and the combined
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air cooler air stream and sprayed water stream to thereby condense, chill, or
sub-cool the
process fluid.
[0010] The
present disclosure also provides a system for cooling a process fluid in a
hydrocarbon process processing natural gas to produce liquefied natural gas. A
chiller is
located at an inlet of a gas turbine. The chiller is configured to chill an
inlet air stream from
about its dry bulb temperature to a temperature below its wet bulb
temperature. A separator is
located downstream of the chiller and is configured to separate water in the
chilled inlet air
stream and produce a water stream in an open-loop circuit. A wet air fin
cooler combines the
water stream with an air cooler air stream to condense, chill, or sub-cool the
process fluid
passing through the wet air fin cooler.
[0011] The
present disclosure also provides a method for cooling a process fluid. An
inlet
air stream of a process component is cooled with an inlet air cooling system.
Moisture
contained in the cooled inlet air stream is condensed. The moisture is
separated from the cooled
inlet air stream to produce water stream in an open-loop circuit. The water
stream is sprayed
into an air cooler air stream. The combined air cooler air stream and sprayed
water stream is
directed through an air cooler. Heat is exchanged between the process fluid
and the combined
air cooler air stream and sprayed water stream to thereby condense, chill, or
sub-cool the
process fluid.
[0012] The
foregoing has broadly outlined the features of the present disclosure so that
the
detailed description that follows may be better understood. Additional
features will also be
described herein.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013]
These and other features, aspects and advantages of the disclosure will become
apparent from the following description, appending claims and the accompanying
drawings,
which are briefly described below.
[0014]
Figure 1 is a schematic diagram of an LNG liquefaction system according to
aspects
of the present disclosure.
[0015]
Figure 2 is a schematic diagram of a detail of Figure 1 according to aspects
of the
present disclosure.
[0016] Figure 3 is a schematic diagram of an inlet air cooling system used
with an LNG
liquefaction system according to aspects of the present disclosure.
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[0017] Figure 4 is a graph showing the relation between refrigeration
duty of a chiller, gas
turbine inlet air temperature, and ambient air flow rate as a percentage of
base air flow,
according to aspects of the present disclosure.
[0018] Figure 5 is a schematic diagram of an inlet air cooling system
according to aspects
of the present disclosure.
[0019] Figure 6 is a method according to aspects of the present
disclosure.
[0020] It should be noted that the figures are merely examples and no
limitations on the
scope of the present disclosure are intended thereby. Further, the figures are
generally not
drawn to scale, but are drafted for purposes of convenience and clarity in
illustrating various
aspects of the disclosure.
DETAILED DESCRIPTION
[0021] To promote an understanding of the principles of the disclosure,
reference will now
be made to the features illustrated in the drawings and specific language will
be used to describe
the same. It will nevertheless be understood that no limitation of the scope
of the disclosure is
thereby intended. Any alterations and further modifications, and any further
applications of
the principles of the disclosure as described herein are contemplated as would
normally occur
to one skilled in the art to which the disclosure relates. For the sake of
clarity, some features
not relevant to the present disclosure may not be shown in the drawings.
[0022] At the outset, for ease of reference, certain terms used in this
application and their
meanings as used in this context are set forth. To the extent a term used
herein is not defined
below, it should be given the broadest definition persons in the pertinent art
have given that
term as reflected in at least one printed publication or issued patent.
Further, the present
techniques are not limited by the usage of the terms shown below, as all
equivalents, synonyms,
new developments, and terms or techniques that serve the same or a similar
purpose are
considered to be within the scope of the present claims.
[0023] As one of ordinary skill would appreciate, different persons may
refer to the same
feature or component by different names. This document does not intend to
distinguish
between components or features that differ in name only. The figures are not
necessarily to
scale. Certain features and components herein may be shown exaggerated in
scale or in
schematic form and some details of conventional elements may not be shown in
the interest of
clarity and conciseness. When referring to the figures described herein, the
same reference
numerals may be referenced in multiple figures for the sake of simplicity. In
the following
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description and in the claims, the terms "including" and "comprising" are used
in an open-
ended fashion, and thus, should be interpreted to mean "including, but not
limited to."
[0024] The
articles "the," "a" and "an" are not necessarily limited to mean only one, but
rather are inclusive and open ended so as to include, optionally, multiple
such elements.
[0025] As used herein, the terms "approximately," "about," "substantially,"
and similar
terms are intended to have a broad meaning in harmony with the common and
accepted usage
by those of ordinary skill in the art to which the subject matter of this
disclosure pertains. It
should be understood by those of skill in the art who review this disclosure
that these terms are
intended to allow a description of certain features described and claimed
without restricting the
scope of these features to the precise numeral ranges provided. Accordingly,
these terms
should be interpreted as indicating that insubstantial or inconsequential
modifications or
alterations of the subject matter described and are considered to be within
the scope of the
disclosure.
[0026] The
term "heat exchanger" refers to a device designed to efficiently transfer or
"exchange" heat from one matter to another. Exemplary heat exchanger types
include a co-
current or counter-current heat exchanger, an indirect heat exchanger (e.g.
spiral wound heat
exchanger, plate-fin heat exchanger such as a brazed aluminum plate fin type,
shell-and-tube
heat exchanger, etc.), direct contact heat exchanger, or some combination of
these, and so on.
[0027] The
present disclosure is a system and method of using an open loop circuit of the
condensed water collected in an inlet air cooler (IAC), and transferring the
water to a wet air
fin cooler to increase the effective heat transfer relative to a traditional
fin fan cooler with no
water spray. The disclosed method and system results in improved overall
process efficiency.
The water condensed downstream of at least one filter element in an IAC is
expected to be
chilled and generally clean, but additional water treatment may be required in
the water spray
system to reduce corrosion, biological growth, and the like.
[0028] In
an aspect of the disclosure, the disclosed system and method may be used in
any
process that uses a gas turbine, such as (for example) air separation,
pharmaceutical processing,
integrated gasification combined cycle power plants, other power generation
processes,
pharmaceutical manufacturing, organic and/or non-organic chemical
manufacturing, other
.. processes in the oil and gas industry, and the like. As a non-limiting
example, the disclosed
system may be used in a natural gas liquefaction process where using the
excess refrigeration
capacity in one refrigeration circuit to chill the inlet air for the gas
turbine driver or drivers of
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another refrigeration circuit, and thus increase the overall capacity of an
LNG plant. The
disclosed aspects improve upon previous solutions in which moisture condensed
via gas turbine
inlet air chilling is used for psychometric cooling to improve the performance
of a refrigerant
condenser that forms part of the system that provides the gas turbine inlet
air chilling. Such
previous solutions collected condensed moisture in a basin located below a wet
air fin cooler
and sprayed the collected water onto the tubes of the air fin. According to
aspects of the present
disclosure, no basin is required to collect condensed moisture, and
essentially all of the
moisture collected from the gas turbine inlet air chilling system is
subsequently vaporized
within the wet air fin air stream to minimize overspray. The condensed
moisture is collected
downstream of at least one air filter element within the gas turbine air inlet
to minimize
contamination of the water by atmospheric contaminants. Each of these measures
is intended
to minimize the risk of corrosion and fouling of the wet air fin device, the
gas turbine inlet air
chiller and the gas turbine inlet air moisture separation device. Furthermore,
optional control
of the air flow to the wet air fin via adjustable fan speed, pitch, louvers,
or the like, can be used
to improve the air fin performance by trading between lower air temperature
due to
psychometric cooling at lower air flows and velocities vs. higher air
temperature and higher
velocities.
[0029] The
present disclosure improves upon known cooling systems by sub-cooling the
refrigerant slipstream used for gas turbine inlet air chilling, and further by
using psychometric
cooling using moisture condensed during the inlet air chilling to improve the
performance of
this refrigerant sub-cooling.
[0030]
Figures 1 and 2 illustrate a system 10 and process for liquefying natural gas
(LNG)
according to aspects of the present disclosure. It is to be understood that
system 10 is a non-
limiting example of how the disclosed aspects may be applied. In system 10,
feed gas (natural
gas) enters through an inlet line 11 into a preparation unit 12 where it is
treated to remove
contaminants. The treated gas then passes from preparation unit 12 through a
series of heat
exchangers 13, 14, 15, 16, where it is cooled by evaporating the first
refrigerant (e.g. propane)
which, in turn, is flowing through the respective heat exchangers through a
first refrigeration
circuit 20. The cooled natural gas then flows to fractionation column 17
wherein pentanes and
heavier hydrocarbons are removed through line 18 for further processing in a
fractionating
unit 19.
[0031] The
remaining mixture of methane, ethane, propane, and butane is removed from
fractionation column 17 through line 21 and is liquefied in the main cryogenic
heat exchanger
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22 by further cooling the gas mixture with a second refrigerant that may
comprise a mixed
refrigerant (MR) which flows through a second refrigeration circuit 30. The
second refrigerant,
which may include at least one of nitrogen, methane, ethane, and propane, is
compressed in
compressors 23a, 23b which, in turn, are driven by a process component such as
a gas
turbine 24. After compression, the second refrigerant is cooled by passing
through air or water
coolers 25a, 25b and is then partly condensed within heat exchangers 26, 27,
28, and 29 by the
evaporating the first refrigerant from first refrigerant circuit 20. The
second refrigerant may
then flow to a high pressure separator 31, which separates condensed liquid
portion of the
second refrigerant from the vapor portion of the second refrigerant. The
condensed liquid and
vapor portions of the second refrigerant are output from the high pressure
separator 31 in lines
32 and 33, respectively. As seen in Figure 1, both the condensed liquid and
vapor from high
pressure second refrigerant separator 31 flow through main cryogenic heat
exchanger 22 where
they are cooled by evaporating the second refrigerant.
[0032] The
condensed liquid stream in line 32 is removed from the middle of main
cryogenic heat exchanger 22 and the pressure thereof is reduced across an
expansion valve 34.
The now low pressure second refrigerant is then put back into the main
cryogenic heat
exchanger 22 where it is evaporated by the warmer second refrigerant streams
and the feed gas
stream in line 21. When the second refrigerant vapor stream reaches the top of
the main
cryogenic heat exchanger 22, it has condensed and is removed and expanded
across an
-- expansion valve 35 before it is returned to the main cryogenic heat
exchanger 22. As the
condensed second refrigerant vapor falls within the main cryogenic heat
exchanger 22, it is
evaporated by exchanging heat with the feed gas in line 21 and the high
pressure second
refrigerant stream in line 32. The falling condensed second refrigerant vapor
mixes with the
low pressure second refrigerant liquid stream within the middle of the main
cryogenic heat
exchanger 22 and the combined stream exits the bottom of the main cryogenic
heat exchanger
22 as a vapor through outlet 36 to flow back to compressors 23a, 23b to
complete second
refrigeration circuit 30.
[0033] The
closed first refrigerant circuit 20 is used to cool both the feed gas and the
second
refrigerant before they pass through main cryogenic heat exchanger 22. The
first refrigerant is
compressed by a first refrigerant compressor 37 which, in turn, is powered by
a process
component such as a gas turbine 38. The first refrigerant compressor 37 may
comprise at least
one compressor casing and the at least one casing may collectively comprise at
least two inlets
to receive at least two first refrigerant streams at different pressure
levels. The compressed
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first refrigerant is condensed in one or more condensers or coolers 39 (e.g.
seawater or air
cooled) and is collected in a first refrigerant surge tank 40 from which it is
cascaded through
the heat exchangers (propane chillers) 13, 14, 15, 16, 26, 27, 28, 29 where
the first refrigerant
evaporates to cool both the feed gas and the second refrigerant, respectively.
Both gas turbine
systems 24 and 38 may comprise air inlet systems that in turn may comprise air
filtration
devices, moisture separation devices, chilling and/or heating devices or
particulate separation
devices.
[0034]
Means may be provided in system 10 of Figure 1 for cooling the inlet air 70,
71 to
both gas turbines 24 and 38 for improving the operating efficiency of the
turbines. Basically,
the system may use excess refrigeration available in system 10 to cool an
intermediate fluid,
which may comprise water, glycol or another heat transfer fluid, that, in
turn, is circulated
through a closed, inlet coolant loop 50 to cool the inlet air to the turbines.
[0035]
Refering to Figure 2, to provide the necessary cooling for the inlet air 70,
71, a slip-
stream of the first refrigerant is withdrawn from the first refrigeration
circuit 20 (i.e. from surge
tank 40) through a line 51 and is flashed across an expansion valve 52. Since
first refrigeration
circuit 20 is already available in gas liquefaction processes of this type,
there is no need to
provide a new or separate source of cooling in the process, thereby
substantially reducing the
costs of the system. The expanded first refrigerant is passed from expansion
valve 52 and
through a heat exchanger 53 before it is returned to first refrigeration
circuit 20 through a
line 54. The propane evaporates within heat exchanger 53 to thereby lower the
temperature of
the intermediate fluid which, in turn, is pumped through the heat exchanger 53
from a storage
tank 55 by pump 56.
[0036] The
cooled intermediate fluid is then pumped through air chillers or coolers 57,
58
positioned at the inlets for turbines 24, 38, respectively. As inlet air 70,
71 flows into the
respective turbines, it passes over coils or the like in the air chillers or
coolers 57, 58 which, in
turn, chill or cool the inlet air 70, 71 before the air is delivered to its
respective turbine. The
warmed intermediate fluid is then returned to storage tank 55 through line 59.
Preferably, the
inlet air 70, 71 will be cooled to no lower than about 5 Celsius (41
Fahrenheit) since ice may
form at lower temperatures. In some instances, it may be desirable to add an
anti-freeze agent
(e.g. ethylene glycol) with inhibitors to the intermediate fluid to prevent
plugging, equipment
damage and to control corrosion.
[0037] One
aspect of the present disclosure is illustrated in detail in Figure 2, in
which a
wet air fin cooler 104 is connected to the first refrigeration circuit 20. As
used with the present
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disclosure, wet air fin cooler 104 combines the cooling effectiveness of (a) a
conventional air
fin heat exchanger, which may use a fan 108 to pass ambient air over finned
tubes through
which pass the fluid (e.g. liquid or gas) to be cooled to near ambient
temperature (e.g. dry bulb
temperature), with (b) psychometric cooling by vaporizing a liquid, typically
water, within the
ambient air stream using, for example, nozzles 110 in a spray header 112, to
approach the lower
wet bulb temperature of the ambient air.
[0038] Wet
air fin cooler 104 is used to sub-cool the slip-stream of liquid first
refrigerant
in line 51 from surge tank 40. The sub-cooled first refrigerant is directed
through line 105 to
heat exchanger 53. Sub-cooling this propane increases both the refrigeration
duty of heat
exchanger 53 and the coefficient of performance of the refrigeration system.
This coefficient
of performance is the ratio of the refrigeration duty of the heat exchanger 53
divided by the
incremental compressor power to provide that refrigeration. The wet air fin
cooler 104 is
positioned to cool the slip-stream of first refrigerant in line 51 in Figures
2 and 3. Alternatively,
the wet air fin cooler 104 could be incorporated as part of the one or more
condensers or coolers
39 to sub-cool liquid propane that serves the other parts of the liquefaction
process before the
slip-stream of first refrigerant in line 51 is removed to provide a source of
cooling (direct or
indirect) to air chillers or coolers 57, 58. However, it is preferred to sub-
cool only the slip-
stream of propane in line 51 to maximize the benefit with respect to gas
turbine inlet air chilling.
[0039]
According to disclosed aspects, separators 101 and 102 are positioned in the
gas
turbine air inlet following the air chillers or coolers 58, 57, respectively.
These separators 101,
102 remove the water that is condensed from the inlet air 70, 71 as the inlet
air is cooled from
its ambient dry bulb temperature to a temperature below its wet bulb
temperature. Separators
101, 102 may be of the inertial type, such as vertical vane, coalescing
elements, a low velocity
plenum, or any other type of moisture separator or de-mister known to those
skilled in the art.
The gas turbine air inlet may include filtration elements, such as air filters
41, that may be
located either upstream or downstream or both up and downstream of the air
chillers or coolers
57, 58 and the separators 101, 102, respectively. Preferably, at least one
filtration element is
located upstream of the chiller(s) and separator(s). This air filtration
element may include a
moisture barrier, such as an ePTFE (expanded PTFE) membrane which may be sold
under the
GORETEX trademark, to remove atmospheric mist, dust, salts or other
contaminants that may
be concentrated in the condensed water removed by separators 101, 102. By
locating at least
one filtration element or similar device upstream of the chiller and separator
associated with
gas turbines 24 and/or 38, atmospheric contaminants in the collected moisture
(water) can be
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minimized, fouling and corrosion of the chiller(s) and separator(s) can be
minimized, and
fouling and corrosion of the wet air fin cooler 104 can also be controlled and
minimized.
[0040]
During the chilling of the gas turbine inlet air 70, 71, a significant portion
of the
refrigeration duty is used to condense the moisture in the gas turbine inlet
air 70, 71 rather than
simply reducing the dry bulb temperature of the inlet air. As an example, if
inlet air with a dry
bulb temperature of 40 Celsius and a wet bulb temperature of 24 Celsius is
chilled, the
effective specific heat of the air is about 1 kJ/kg/ C between 40 C and 24 C
but increases
dramatically to about 3 kJ/kg/ C below the wet bulb temperature of 24 C as
the dry bulb
temperature is reduced and moisture is condensed from the air. From this, one
could conclude
that about two-thirds of the refrigeration duty used to chill the air below
the wet bulb
temperature (dew point) is wasted since the small compositional change of the
air to the gas
turbine 24 and/or 38 has only a small effect on the available power of the gas
turbine. This
condensed moisture is essentially at the same temperature as the chilled inlet
air to the gas
turbine and could be used to provide some precooling of the inlet air 70, 71
using another
chilling coil similar to air chillers or coolers 57 or 58 that is positioned
ahead of the air chillers
or coolers 57 or 58 in the air flow. However, this arrangement can only recoup
the part of the
refrigeration duty used to reduce the temperature of the water but not the
part used to condense
it. That is, the heat of vaporization of the water cannot be recouped by heat
transfer or
psychometric cooling with the gas turbine inlet air.
[0041] A much greater portion of the refrigeration duty used to cool and
condense the
moisture from the gas turbine inlet air 70, 71 can be recouped by collecting
this chilled water
from separators 101 or 102, pumping it with a pump 103 and spraying the water
onto the tubes
of the wet air fin cooler 104 or otherwise mixing the water with the air flow
106 to the wet air
fin cooler 104. Based on the ambient conditions and the actual flow rate of
air conveyed by the
fan associated with the wet air fin cooler 104, the water pumped by pump 103
may be sufficient
to saturate the air flow of wet air fin cooler 104 and bring it to its wet
bulb temperature. Excess
water flow from separators 101, 102 may be available that could be used for
another purpose,
or may be insufficient to saturate the air flow. In this later case,
additional water from another
source may be provided. Additionally, the water separated by separators 101,
102 is supplied
to the wet air fin cooler 104 in an open-loop circuit, or in other words, the
water is not recycled
or re-used by the wet air fin cooler 104. As the cooling of the gas turbine
inlet air 70, 71
provides a constant source of chilled water to be used by the wet air fin
cooler 104, it is not
necessary to recycle or re-use the water after it has been sprayed in the wet
air fin cooler.
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Employing such an open-loop water circuit reduces the need to re-cool and/or
filter the water
after being used by the wet air fin cooler, thereby reducing the cost and
complexity of system
or any other system using the disclosed aspects. Additionally or
alternatively, as the water
sprayed in the wet air fin cooler has been filtered and is relatively clean,
it may be either
5 disposed of with minimal additional processing required, or may be used
as a water source for
other processes within system 10.
[0042] An
example of the effectiveness of the use of water collected from separators 101
or 102 to improve the air inlet cooling is shown in Table 1. The three columns
show the impact
of no cooler such as wet air fin cooler 104, an air fin cooler with no water
spray, and a wet air
10 fin cooler 104 using condensed moisture from separators 101 or 102.
TABLE 1.
No cooler Air fin cooler Air fin cooler
without water with water
spray spray
Ambient temperature (dry bulb) 40 C Same Same
Ambient wet bulb temperature 24 C Same Same
Gas turbine inlet air flow rate (at 1,528,000 Same Same
wet condition) kg/hr
Compressor refrigeration power 4,000 kW Same Same
Condenser (39) outlet 47.8 C Same Same
temperature (with propane used
as first refrigerant)
"Wet" air fin outlet temperature 41.5 C 32.4 C
(stream 105)
Refrigeration Duty of Chiller (53) 18,000 kW 19,450 kW 21,400 kW
Temperature of inlet air 70, 71 16.1 C 14.9 C 13.2 C
Moisture condensed in 101 or 102 11.1 tons/hr 12.4 tons/hr 14.1 tons/hr
Power increase (per Gas 20.8% 22.0% 23.5%
Processors Suppliers Association)
from ambient
Heat rate decrease per GPSA 7.9% 8.2% 8.5%
from ambient
[0043] As
an example of the effectiveness to control the air flow rate of the wet air
fin
cooler, for the same example above, a wet air fin cooler with a fixed UA
(surface area combined
with heat transfer coefficients) is used. For this example, the same 40 C dry
bulb, 24 C wet
bulb ambient air is assumed to provide the cooling air for this wet air fin
cooler. As a base, the
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air flow is set to 1,000,000 kg/hr and all of the water condensed from the gas
turbine inlet air
is used for psychometric cooling of the wet air fin cooler 104. As the water
is sprayed onto the
air fin tubes or into the air flow stream (or a combination of both), part of
the water vaporizes
to cool the tubes or the air flow and approaches the wet bulb temperature of
the air stream.
However, as this water is vaporized, the water content of this wet air stream
also increases and
so also increases the wet bulb temperature of this wet air stream above the
ambient wet bulb
temperature. As such, it is not possible to vaporize the water to reach a wet
air stream
temperature that approaches the ambient wet bulb temperature; the water can
only approach
the "wet-wet bulb temperature" (WWBT), which is the wet bulb temperature of
the ambient
air with the moisture added to the gas composition at the local conditions.
[0044]
Figure 3 illustrates another aspect of the present disclosure that adds a
dedicated
supplemental compressor 114 to compress the vapor leaving heat exchanger 53 to
the pressure
similar to the outlet pressure of first refrigerant compressor 37. This may
provide an
improvement to the system of Figure 2 to provide control of the inlet air
chilling system that is
independent of the control of the first refrigerant circuit required to manage
the LNG
liquefaction system. To ensure no icing of the inlet air chillers or inlet air
that enters the gas
turbine inlet, it may be advantageous to adjust the temperature of the
intermediate fluid to
ensure that the inlet air temperature can be managed to avoid icing. To
control the intermediate
fluid temperature, the pressure of the first refrigerant slip-stream leaving
heat exchanger 53
may need to be adjusted such that the temperature of the slip-stream is
between -5 C and
20 C. This may be done by use of a control valve at the exit of heat
exchanger 53 as shown
in Figure 3. However, it may be more efficient and provide more precise
control to adjust the
performance of the supplemental compressor 114. The aspect depicted in Figure
3 may also
be an especially good solution if the inlet air chilling system is retrofitted
to an existing LNG
liquefaction system.
[0045]
Figure 4 is a chart 400 showing the effect of air flow rate on the
effectiveness of the
cooling as the wet air fin ambient air flow rate is varied from 80% to 120% of
the base value.
In this case, any excess moisture not required to reach the WWBT of the air
upstream of the
wet air fin cooler 104 is neglected or in essence is allowed to drip away.
Figure 4 demonstrates
that the maximum refrigeration duty of the chiller 402 is reached at an air
flow (about 101% in
this example) that corresponds roughly with the full vaporization of the
available water supply.
This is the optimum air flow required to maximize the refrigeration duty with
the restriction
that excess moisture is separated upstream of the wet air fin cooler 104. This
optimum air flow
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may be determined by several means, including but not limited to 1) measuring
the relative
humidity of the air stream after the water spray and targeting about 100%
relative humidity; 2)
measuring the gas turbine inlet air temperature 404 and performing a real time
optimization to
minimize the gas turbine inlet temperature by air fin air flow adjustments; 3)
measuring the
refrigerant outlet temperature from the wet air fin cooler 104 and performing
a similar real time
optimization; 4) constructing a physics based or empirical model of the system
to optimize the
air flow across the wet air fin cooler 104; 5) another optimization technique
generally known
to those skilled in the art or 6) a combination of (1) to (5). Those skilled
in the art will
understand that a physics based model may be as simple as one that
incorporates psychometric
air data and at least one of ambient temperature, relative humidity, air fin
air flow temperature,
barometric pressure, spray water flow rate and spray water temperature to
estimate or determine
the amount of moisture that can be vaporized into the air fin air flow to
reach saturation.
[0046] The
example in Figure 4 was restricted to psychometric cooling of the air fin air
stream prior to any heating of this air stream by transfer of any heat from
stream 51. With an
adequate mixing area ahead of the air fin tube bundle, this air stream would
be dry but saturated
with moisture at the local conditions with any excess moisture separated.
However, if the air
flow is reduced below the optimum of Figure 4 and it is assumed that any
excess moisture is
not separated but rather travels with this air stream, then a new optimum air
flow can be
determined that is characterized by full vaporization of the available
moisture at the local air
stream conditions downstream of the air fin bundle. Similar to the original
example, this new
optimum air flow may be determined by similar techniques as described in (1)
to (6) above
except that any humidity measurement is preferably performed on the air stream
downstream
of the wet air fin cooler.
[0047]
Figure 5 schematically depicts a cooling system 500 according to aspects
disclosed
herein. System 500 includes a turbine 502 operatively connected to a load 504,
which may be
a compressor, a generator, or the like. Air 506 entering the turbine may be
filtered by one or
more filters 508 and cooled using chillers or coolers 510, which in an aspect
a refrigerant (not
shown) is run through. One or more separators 512 may remove condensed water
in the cooled
air as previously described. The water may be directed through a conduit 514
to a storage tank
516, and may then be pumped using one or more pumps 518, through a conduit
520, to a wet
air fin cooler 522. The water may then be directed to a spray header 524 and
sprayed through
nozzles 526 into ambient air 528 that is being directed into the wet air fin
cooler 522 using a
fan 530. The combined water spray and ambient air are directed over or around
finned
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tubes 532. The finned tubes 532 are configured to permit a process fluid 534
to pass
therethrough. As explained previously with respect to Figures 1 and 2, the wet
air fin cooler
522 cools the process fluid, which exits the wet air fin cooler at 536. The
process fluid may be
any fluid to be cooled, which in the oil and gas industry may include
refrigerants, solvents,
natural gas liquids, natural gas, or other fluids. The water spray in the
ambient air may be
recovered by collecting condensed water on the finned tubes 532 or other
means, and may be
disposed of or used in another process. In the aspect shown in Figure 5, the
open-loop circuit
of water may be depicted by the path of the water from the separator 512
through the wet air
fin cooler 522.
[0048] It can be seen that using condensed water collected in an inlet air
cooler (IAC), and
transferring the water to a wet air fin cooler in an open-loop circuit,
increases the effective heat
transfer relative to a traditional fin fan cooler with no water spray. The
water condensed
downstream of at least one filter element in an IAC is expected to be chilled
and generally
clean, but additional water treatment may be required in the water spray
system to reduce
corrosion, biological growth, and the like.
[0049] The
disclosed aspects have particular applicability to the to the oil and gas
industry
or other industries where water usage is often less critical than with large
power plants having
high capacity steam systems. For example, the disclosed aspects may be
installed in any heat
transfer service requiring additional capacity or process debottlenecking,
such as process
compressor discharge temperature control. The disclosed aspects increase the
effective heat
transfer of any air fin cooler in any service. The disclosed aspects may be
used in the discharge
of a process compressor to reduce the load of the driver, i.e. reduce firing
temperature, as a
means to extend maintenance intervals. The disclosed aspects may also be used
to improve
natural gas liquids processes whereby auxilliary refrigerant systems are used
to reduce the mole
weight of the gas. The capacity of such auxiliary refrigerant systems is often
the limiting factor
in process capacity. Using the disclosed wet air fin cooler, the capacity of
these auxiliary
refrigerant systems is greatly increased, leading to additional available
capacity in the primary
compression process. The disclosed aspects may also be used to improve
efficiency of a
turbine/generator emissions system, where condensed water from an exhaust gas
recirculation
.. cooler is used as a wet spray onto associated steam system condensers
and/or the process stream
coolers.
[0050] The
scope of the disclosed aspects is not limited to use in the oil and gas
industry.
The disclosed aspects may be advantageously applied in other industrial
processes that may
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include but are not limited to air separation, integrated gasification
combined cycle (IGCC)
power plants, other power generation processes, pharmaceutical manufacturing,
organic and
non-organic chemical manufacturing, and the like. Furthermore, the scope of
the disclosed
aspects is not limited to processes in which a gas turbine is used. For
example, the inlet air
stream to an air separation unit (ASU) compressor may be cooled to below the
dew point, and
the water condensed thereby may be used to cool another process fluid in a wet
air fin cooler
as described herein. While cooling the inlet air of the compressor reduces the
required
compression energy and enables improved process efficiency, using the
condensed water in a
wet air fin cooler as described herein will further improve the process
efficiency. In another
example, gas turbines may be integrated with with an ASU for for IGCC and gas-
to-liquids
plants by extracting part of the compressed air from the gas turbine as an
input stream to the
ASU. In this case, the input stream could be cooled to below the dew point
using the aspects
described herein.
[0051]
Figure 6 is a flowchart of a method 600 for cooling a process fluid acording
to
disclosed aspects. At block 602 an inlet air stream of a process component,
such as a turbine,
is cooled with an inlet air cooling system. At block 604 moisture contained in
the cooled inlet
air stream is condensed. At block 606 the moisture is separated from the
cooled inlet air stream
to produce a water stream in an open-loop circuit. At block 608 the water
stream is sprayed
into an air cooler air stream. At block 610 the combined air cooler air stream
and sprayed water
stream is directed through an air cooler. At block 612 heat is exchanged
between the process
fluid and the combined air cooler air stream and sprayed water stream to
thereby condense,
chill, or sub-cool the process fluid.
[0052]
Disclosed aspects may include any combinations of the methods and systems
shown
in the following numbered paragraphs. This is not to be considered a complete
listing of all
possible aspects, as any number of variations can be envisioned from the
description above.
1. A method for cooling a process fluid, comprising:
cooling an inlet air stream of a turbine with an inlet air cooling system;
condensing moisture contained in the cooled inlet air stream;
separating the moisture from the cooled inlet air stream to produce water
stream in an
open-loop circuit;
spraying the water stream into an air cooler air stream;
directing the combined air cooler air stream and sprayed water stream through
an air
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cooler; and
exchanging heat between the process fluid and the combined air cooler air
stream and
sprayed water stream to thereby condense, chill, or sub-cool the process
fluid.
2. The method of paragraph 1, wherein the air cooler includes a tube
bundle, and wherein
the step of exchanging heat comprises:
passing the process fluid through the tube bundle; and
directing the combined air cooler air stream and sprayed water stream over or
across
the tube bundle.
3. The method of paragraph 1 or paragraph 2, wherein directing the combined
air cooler
air stream and the sprayed water stream is accomplished using a fan.
4. The method of paragraph 3, wherein a flow rate or velocity of the air
cooler air stream
is adjusted using one or more of a fan speed control, a fan blade pitch
control, and a damper
adjustment.
5. The method of paragraph 4, wherein the air cooler air stream flow rate
or velocity is
adjusted based on at least one of: relative humidity of the air cooler air
stream, flow rate of the
sprayed water stream, ambient temperature, barometric pressure, psychometric
air data,
ambient relative humidity, air stream temperature, and temperature of the
sprayed water stream.
6. The method of any of paragraphs 1-5, wherein separating the moisture is
accomplished
by a separating device selected from an inertial separator, a vane separator,
a plenum, and a
coalescer.
7. The method of any of paragraphs 1-6, further comprising at least
partially filtering the
inlet air stream before cooling the inlet air stream.
8. The method of any of paragraphs 1-7, wherein the process stream is a
hydrocarbon
process stream requiring heat rejection.
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9. The method of any of paragraphs 1-7, wherein the process stream is a
process stream
in one of a pharmaceutical manufacturing process, a power generation process,
and a chemical
manufacturing process.
10. The method of any of paragraphs 1-9, wherein the inlet air stream, the
turbine, and the
inlet air cooling system are a first inlet air stream, a first turbine, and a
first inlet air cooling
system, respectively, the method further comprising:
cooling a second inlet air stream of a second turbine with a second inlet air
cooling
system;
condensing moisture contained in the second cooled inlet air stream;
separating the moisture from the second cooled inlet air stream; and
directing the water into the water stream.
11. The method of any of paragraphs 1-10, wherein cooling the inlet air
stream of the
turbine with the inlet air cooling system comprises chilling the inlet air
stream from about a
dry bulb temperature of the inlet air stream to a temperature below a wet bulb
temperature of
the inlet air stream.
12. A system for cooling a process fluid in a hydrocarbon process
processing natural gas to
produce liquefied natural gas, the system comprising:
a gas turbine;
a chiller located at an inlet of the gas turbine, the chiller configured to
chill an inlet air
stream from about its dry bulb temperature to a temperature below its wet bulb
temperature;
a separator located downstream of the chiller and configured to separate water
in the
chilled inlet air stream and produce a water stream in an open-loop circuit;
and
a wet air fin cooler that combines the water stream with an air cooler air
stream to
condense, chill, or sub-cool the process fluid passing through the wet air fin
cooler.
13. The system of paragraph 12, wherein the wet air fin cooler comprises:
a tube bundle through which the process fluid passes;
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a spray header configured to spray the water stream into the air cooler air
stream; and
a fan that forces the air stream and sprayed water stream over or across the
tube bundle.
14. The system of paragraph 13, further comprising a fan controller that
controls at least
one of a speed of the fan, a pitch of a blade of the fan, and a damper
associated with the fan.
15. The system of any of paragraphs 12-14, wherein the separator is one of
an inertial
separator, a vane separator, a plenum, and a coalescer.
16. The system of any of paragraphs 12-15, further comprising a filter
arranged to at least
partially filter the inlet air stream before the inlet air stream is chilled
by the chiller.
17. The system of paragraph 16, wherein the filter comprises a moisture
barrier.
18. The system of any of paragraphs 12-17, wherein the gas turbine, the
chiller, the inlet
air stream, and the separator are a first gas turbine, a first chiller, a
first inlet air stream, and a
first separator, and further comprising:
a second gas turbine;
a second chiller located at an inlet of the second gas turbine, the second
cooler
configured to chill a second inlet air stream from about its dry bulb
temperature to a temperature
below its wet bulb temperature; and
a second separator located downstream of the second chiller and configured to
separate
water in the chilled second inlet air stream and deliver the separated water
into the water stream.
19. A method for cooling a process fluid, comprising:
cooling an inlet air stream of a process component with an inlet air cooling
system;
condensing moisture contained in the cooled inlet air stream;
separating the moisture from the cooled inlet air stream to produce water
stream in an
open loop circuit;
spraying the water stream into an air cooler air stream;
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directing the combined air cooler air stream and sprayed water stream through
an air
cooler; and
exchanging heat between the process fluid and the combined air cooler air
stream and
sprayed water stream to thereby condense, chill, or sub-cool the process
fluid.
20. The method of paragraph 19, wherein the air cooler includes a tube
bundle, and wherein
the step of exchanging heat comprises:
passing the process fluid through the tube bundle; and
directing the combined air cooler air stream and sprayed water stream over or
across
the tube bundle.
21. The method of paragraph 19 or paragraph 20, wherein directing the
combined air cooler
air stream and the sprayed water stream is accomplished using a fan.
22. The
method of paragraph 21, wherein a flow rate or velocity of the air cooler air
stream
is adjusted using one or more of a fan speed control, a fan blade pitch
control, and a damper
adjustment.
23. The method of paragraph 22, wherein the air cooler air stream flow rate
or velocity is
adjusted based on at least one of: relative humidity of the air cooler air
stream, flow rate of the
sprayed water stream, ambient temperature, barometric pressure, psychometric
air data,
ambient relative humidity, air stream temperature, and temperature of the
sprayed water stream.
24. The method of any of paragraphs 19-23, wherein separating the moisture
is
accomplished by a separating device selected from an inertial separator, a
vane separator, a
plenum, and a coalescer.
25. The method of any of paragraphs 19-24, further comprising at least
partially filtering
the inlet air stream before cooling the inlet air stream.
26. The method of any of paragraphs 19-25, wherein cooling the inlet air
stream of the
process component with the inlet air cooling system comprises chilling the
inlet air stream from
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about a dry bulb temperature of the inlet air stream to a temperature below a
wet bulb
temperature of the inlet air stream.
[0053] It
should be understood that the numerous changes, modifications, and
alternatives
to the preceding disclosure can be made without departing from the scope of
the disclosure.
The preceding description, therefore, is not meant to limit the scope of the
disclosure. Rather,
the scope of the disclosure is to be determined only by the appended claims
and their
equivalents. It is also contemplated that structures and features in the
present examples can be
altered, rearranged, substituted, deleted, duplicated, combined, or added to
each other.
