U.S. patent application number 14/411533 was filed with the patent office on 2015-07-09 for method and apparatus for cooling in liquefaction process.
The applicant listed for this patent is Highview Enterprises Limited. Invention is credited to Nicola Castellucci, Daniel Harris, Robert Morgan, Stuart Nelmes.
Application Number | 20150192358 14/411533 |
Document ID | / |
Family ID | 46766260 |
Filed Date | 2015-07-09 |
United States Patent
Application |
20150192358 |
Kind Code |
A1 |
Morgan; Robert ; et
al. |
July 9, 2015 |
Method and Apparatus for Cooling in Liquefaction Process
Abstract
Methods and apparatus are disclosed for efficient cooling within
air liquefaction processes with integrated use of cold recycle from
a thermal energy store.
Inventors: |
Morgan; Robert;
(Shoreham-by-Sea, GB) ; Nelmes; Stuart; (Reigate,
GB) ; Castellucci; Nicola; (Woking, GB) ;
Harris; Daniel; (Feltham, GB) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Highview Enterprises Limited |
London, England |
|
GB |
|
|
Family ID: |
46766260 |
Appl. No.: |
14/411533 |
Filed: |
July 8, 2013 |
PCT Filed: |
July 8, 2013 |
PCT NO: |
PCT/GB2013/051797 |
371 Date: |
December 29, 2014 |
Current U.S.
Class: |
62/606 |
Current CPC
Class: |
F25J 1/0251 20130101;
F25J 1/0202 20130101; F25J 1/004 20130101; F25J 1/0035 20130101;
F25J 1/0045 20130101; F25J 1/0242 20130101; F25J 1/0052 20130101;
F25J 1/0082 20130101; F25J 1/0228 20130101; F25J 2270/06 20130101;
F25J 2205/24 20130101; F25J 2230/06 20130101; F25J 1/00 20130101;
F25J 1/0208 20130101; F25J 1/0012 20130101; F25J 1/0015 20130101;
F25J 1/0037 20130101; F25J 1/0292 20130101 |
International
Class: |
F25J 1/00 20060101
F25J001/00 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 6, 2012 |
GB |
1212056.4 |
Mar 27, 2013 |
GB |
1305641.1 |
Claims
1. A cryogenic liquefaction device comprising: a heat exchanger; a
first phase separator; a first expansion device; a first expansion
turbine; a second expansion turbine; a cold recovery circuit
including a heat transfer fluid; and an arrangement of conduits,
wherein: the operating inlet pressures of the first and second
expansion turbines are different from one another; and the
arrangement of conduits is arranged such that: a first portion of a
pressurised stream of gas is directed through the heat exchanger,
the first expansion device and the first phase separator; a second
portion of the pressurised stream of gas is directed through the
first expansion turbine, then through the heat exchanger in a
counter-flow direction to the first portion of the pressurised
stream of gas, and then through the second expansion turbine, and
the heat transfer fluid is directed through the heat exchanger.
2. The cryogenic liquefaction device of claim 1 wherein the cold
recovery circuit comprises: a thermal energy storage device; a
means for circulating the heat transfer fluid; and an arrangement
of conduits arranged to direct the heat transfer fluid through the
thermal energy storage device and the heat exchanger.
3. The cryogenic liquefaction device of claim 1, wherein the
pressurised stream of gas consists of gaseous air or gaseous
nitrogen.
4. The cryogenic liquefaction device of claim 3, wherein the
pressurised stream of gas is input into the cryogenic liquefaction
device at a pressure greater than or equal to the critical
pressure.
5. The cryogenic liquefaction device of claim 1, wherein the first
portion of the pressurised stream of gas and the second portion of
the pressurised stream of gas are at different pressures.
6. The cryogenic liquefaction device of claim 1, wherein the first
portion of the pressurised stream of gas and the second portion of
the pressurised stream of gas are at the same pressure.
7. The cryogenic liquefaction device of claim 1, and further
comprising a third expansion turbine, wherein: the operating inlet
pressure of the third expansion turbine is different to at least
one of the first and second expansion turbines.
8. The cryogenic liquefaction device of claim 7, wherein the
arrangement of conduits is such that the third expansion turbine is
in parallel with at least one of the first and second turbines such
that at least a portion of the second portion of the pressurised
stream of process gas is directed through the third turbine.
9. The cryogenic liquefaction device of claim 7, wherein the
arrangement of conduits is such that the third expansion turbine is
in series with at least one of the first and second turbines such
that at least a portion of the second portion of the pressurised
stream of process gas is directed through the third turbine.
10. The cryogenic liquefaction device of claim 1, and further
comprising a refrigerant circuit which is connected to an output of
the second expansion turbine via the arrangement of conduits.
11. The cryogenic liquefaction device of claim 1, and further
comprising a second arrangement of conduits that directs a second
heat transfer fluid through a closed cycle refrigeration circuit
and through a localised area of the heat exchanger.
12. The cryogenic liquefaction device of claim 11, wherein the
second heat transfer fluid comprises a gas or a liquid.
13. The cryogenic liquefaction device of claim 7, and further
comprising a fourth expansion turbine, wherein: the arrangement of
conduits is arranged such that: a third portion of the pressurised
stream of gas is directed through the fourth expansion turbine, and
then through the heat exchanger in a counter-flow direction to the
first portion of the pressurised stream of gas.
14. The cryogenic liquefaction device of claim 13, and further
comprising a fifth expansion turbine, wherein: the arrangement of
conduits is arranged such that: the third portion of the
pressurised stream of gas is directed through the fifth expansion
turbine after passing through the fourth expansion turbine and the
heat exchanger.
15. The cryogenic liquefaction device of claim 1, wherein the first
expansion device comprises at least one of a Joule-Thomson valve,
another pressure reducing valve, an expansion turbine and another
work extracting device.
16. The cryogenic liquefaction device of claim 1, and further
comprising a second phase separator and a second expansion device,
wherein the arrangement of conduits is arranged such that at least
a portion of the second portion of the pressurised stream of gas is
directed through the second expansion device and the second phase
separator after having passed through the first expansion
turbine.
17. The cryogenic liquefaction device of claim 16, wherein the
second expansion device comprises at least one of a Joule-Thomson
valve, another pressure reducing valve, an expansion turbine and
another work extracting device.
18. The cryogenic liquefaction device of claim 1, and further
comprising a first compressor, wherein the arrangement of conduits
is arranged such that at least a portion of the second portion of
the pressurised stream of gas is directed through the first
compressor before passing through the first expansion turbine.
19. The cryogenic liquefaction device of claim 18, and further
comprising a second compressor, wherein the arrangement of conduits
is arranged such that the first portion of the pressurised stream
of gas is directed through the second compressor before passing
through the heat exchanger.
20. The cryogenic liquefaction device of claim 19, and further
comprising a cooler, wherein the arrangement of conduits is
arranged such that the first portion of the pressurised stream of
gas is directed through the cooler after passing through the second
compressor and before passing through the heat exchanger.
21. The cryogenic liquefaction device of claim 1, wherein the
output from the second expansion turbine is directed into the first
phase separator.
22. The cryogenic liquefaction device of claim 7, wherein an output
from the third expansion turbine is directed into the first phase
separator.
23. The cryogenic liquefaction device of claim 13, wherein an
output from the fourth expansion turbine is directed into the first
phase separator.
24. The cryogenic liquefaction device of claim 14, wherein an
output from the fifth expansion turbine is directed into the first
phase separator.
25. The cryogenic liquefaction device of claim 1, further
comprising a feed stream compressor adapted to output the
pressurized stream of gas, wherein the arrangement of conduits is
arranged such that: a) a feed stream is directed to an input of the
feed stream compressor; and b) an output stream from the first
phase separator joins the feed stream after passing through the
heat exchanger.
26. The cryogenic liquefaction device of claim 25, wherein the
arrangement of conduits is arranged such that the pressurized
stream of gas output from the feed stream compressor is directed to
a heat storage device before passing through the heat
exchanger.
27. The cryogenic liquefaction device of claim 26, wherein the
arrangement of conduits is arranged such that a pressurized stream
of gas output from the heat storage device is directed to a heat
rejection device before passing through the heat exchanger.
28. A cryogenic liquefaction device comprising: a heat exchanger; a
first phase separator; a first expansion device; a first expansion
turbine; a first compressor; a cold recovery circuit including a
heat transfer fluid; and an arrangement of conduits, arranged such
that: a first portion of a pressurised stream of gas is directed
through the heat exchanger, the first expansion device and the
first phase separator; a second portion of the pressurised stream
of gas is directed through the first expansion turbine, then
through the heat exchanger in a counter-flow direction to the first
portion of the pressurised stream of gas, and then through the
first compressor, and the heat transfer fluid is directed through
the heat exchanger.
29. The cryogenic liquefaction device of claim 28, wherein the
arrangement of conduits is arranged such that an output stream of
the first compressor joins the pressurised stream of gas.
30. The cryogenic liquefaction device of claim 29, wherein the
arrangement of conduits is arranged such that the output stream of
the first compressor is directed into the heat exchanger before it
joins the pressurised stream of gas.
31. The cryogenic liquefaction device of claim 29, wherein the
arrangement of conduits is arranged such that the output stream of
the first compressor joins the pressurised stream of gas before it
is directed into the heat exchanger.
32. The cryogenic liquefaction device of claim 28, wherein the
first compressor is one of a single stage and a multistage
compressor.
33. A cryogenic energy storage device including the cryogenic
liquefaction device claim 1.
34. A method for balancing a liquefaction process with the use of
cold recycle from an external thermal energy source comprising:
directing a first portion of a pressurised stream of gas through a
heat exchanger, a first expansion device, and a first phase
separator; directing a second portion of a pressurised stream of
gas through a first expansion turbine, then through the heat
exchanger in a counter-flow direction to the first portion of the
pressurised stream of gas, and then through a second expansion
turbine; and directing a heat transfer fluid through a cold
recovery circuit and the heat exchanger; wherein: operating inlet
pressures of the first and second expansion turbines are different
from one another.
35. A method for balancing a liquefaction process with the use of
cold recycle from an external thermal energy source comprising:
directing a first portion of a pressurised stream of gas through a
heat exchanger, a first expansion device, and a first phase
separator; directing a second portion of a pressurised stream of
gas through a first expansion turbine, then through the heat
exchanger in a counter-flow direction to the first portion of the
pressurised stream of gas, and then through a first compressor; and
directing a heat transfer fluid through a cold recovery circuit and
the heat exchanger.
36. A method of storing energy including the method for balancing a
liquefaction process of claim 34.
37. A method of storing energy including the method for balancing a
liquefaction process of claim 35.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to cryogenic energy storage
systems, and particularly to methods for the efficient balancing of
the liquefaction process with the integrated use of cold recycle
from an external source such as a thermal energy store.
BACKGROUND OF THE INVENTION
[0002] Electricity transmission and distribution networks (or
grids) must balance the generation of electricity with the demand
from consumers. This is normally achieved by modulating the
generation side (supply side) by turning power stations on and off,
and running some at reduced load. As most existing thermal and
nuclear power stations are most efficient when run continuously at
full load, there is an efficiency penalty in balancing the supply
side in this way. The expected introduction of significant
intermittent renewable generation capacity, such as wind turbines
and solar collectors, to the networks will further complicate the
balancing of the grids, by creating uncertainty in the availability
of parts of the generation fleet. A means of storing energy during
periods of low demand for later use during periods of high demand,
or during low output from intermittent generators, would be of
major benefit in balancing the grid and providing security of
supply.
[0003] Power storage devices have three phases of operation:
charge, store and discharge. Power storage devices generate power
(discharge) on a highly intermittent basis when there is a shortage
of generating capacity on the transmission and distribution
network. This can be signalled to the storage device operator by a
high price for electricity in the local power market or by a
request from the organisation responsible for the operating of the
network for additional capacity. In some countries, such as the
United Kingdom, the network operator enters into contracts for the
supply of back-up reserves to the network with operators of power
plants with rapid start capability. Such contracts can cover months
or even years, but typically the time the power provider will be
operating (generating power) is very short. In addition, a storage
device can provide an additional service in providing additional
loads at times of oversupply of power to the grid from intermittent
renewable generators. Wind speeds are often high overnight when
demand is low. The network operator must either arrange for
additional demand on the network to utilise the excess supply,
through low energy price signals or specific contracts with
consumers, or constrain the supply of power from other stations or
the wind farms. In some cases, especially in markets where wind
generators are subsidised, the network operator will have to pay
the wind farm operators to `turn off` the wind farm. A storage
device offers the network operator a useful additional load that
can be used to balance the grid in times of excess supply.
[0004] For a storage device to be commercially viable the following
factors are important: capital cost per MW (power capacity), MWh
(energy capacity), round trip cycle efficiency and lifetime with
respect to the number of charge and discharge cycles that can be
expected from the initial investment. For widespread utility scale
applications it is also important that the storage device is
geographically unconstrained--it can be built anywhere, in
particular next to a point of high demand or next to a source of
intermittency or a bottleneck in the transmission and distribution
network.
[0005] One such storage device technology is the storage of energy
using cryogen such as liquid air or nitrogen (Cryogenic Energy
Storage (CES)) which offers a number of advantages in the market
place. Broadly speaking a CES system would, in the charge phase,
utilise low cost or surplus electricity, at periods of low demand
or excess supply from intermittent renewable generators, to liquefy
a working fluid such as air or nitrogen. This is then stored as a
cryogenic fluid in a storage tank, and subsequently released to
drive a turbine, producing electricity during the discharge or
power recovery phase, at periods of high demand or insufficient
supply from intermittent renewable generators.
[0006] Cryogenic Energy Storage (CES) Systems have several
advantages over other technologies in the market place, one of
which is their founding on proven mature processes. Means to
liquefy air, necessary in the charging phase, have existed for more
than a century; early systems utilised a simple Linde cycle in
which ambient air is compressed to a pressure above critical 38
bar), and progressively cooled to a low temperature before
experiencing an isenthalpic expansion through an expansion device
such as a Joule-Thomson valve to produce liquid. By pressurising
the air above the critical threshold, the air develops unique
characteristics and the potential for producing large amounts of
liquid during expansion. The liquid is drained off and the
remaining fraction of cold gaseous air is used to cool the incoming
warm process stream. The amount of liquid produced is governed by
the required amount of cold vapour and inevitably results in a low
specific yield.
[0007] An evolution of this process is the Claude cycle (for which
the current state of the art is shown in FIG. 4); the process is
broadly the same as the Linde cycle however one or more streams 36,
39 are separated from the main process stream 31 where they are
expanded adiabatically through turbines 3, 4, resulting in a lower
temperature for a given expansion ratio than an isenthalpic process
and hence efficient cooling. The air expanded through turbines 3, 4
then rejoins the returning stream 34 and aids the cooling of the
high pressure stream 31 via heat exchanger 100. Similar to the
Linde cycle the bulk of liquid is formed via expansion through an
expansion device such as a Joule-Thomson valve 1. The main
improvement with the Claude process is that power produced by the
expansion turbines 3, 4 directly or indirectly reduces the overall
power consumption, resulting in greater energy efficiency.
[0008] The most efficient modern air liquefaction processes
typically use a two turbine Claude design, and at commercial scale
can typically achieve an optimum specific work figure of around 0.4
kWh/kg. Although highly efficient this would not enable a CES
system to achieve a market entry Round Trip Efficiency figure of
50%, without significant reductions in specific work.
[0009] In order to achieve greater efficiencies the liquefaction
process within a fully integrated CES system, such as the one
disclosed in W02007-096656A1, utilises cold energy captured in the
evaporation of the cryogen during the power recovery phase. This is
stored by means of an integrated thermal store, such as the one
detailed in GB 1115336.8, and then used during the charging phase
to provide additional cooling to the main process stream in the
liquefaction process. The effective use of the cold recovery stream
is a prerequisite to achieving an efficient cryogenic energy
storage system.
[0010] The necessary change in enthalpy that an arbitrary high
pressure process stream must undergo to reach the required
temperature to maximise liquid production when expanded through an
expansion device such as a Joule-Thomson valve is shown in FIG. 1.
A typical ideal cooling stream must similarly undergo an enthalpy
change throughout the process as shown by the profile in FIG. 2,
marked `No Cold Recycle`. The second profile in FIG. 2 demonstrates
the dramatic change in required cooling (i.e. relative change of
enthalpy) when large quantities of cold recycle are introduced into
the system, marked `Cold Recycle`. FIG. 2 shows quantities of cold
recycle in the region of 250 kJ/kg (defined as cooling enthalpy per
kg of liquid product delivered), which is consistent with levels of
cold recycle used in a fully integrated cryogenic energy system
such as the one disclosed in W02007-096656A1. As is evident from
FIG. 2, the addition of the cold recycle completely satisfies the
cooling requirements in the higher temperature end of the
process.
[0011] This presents a problem with current state of the art
liquefaction processes which are designed to be used with more
progressive thermal energy profiles, and are much more effectively
handled by a single cooling stream running the extent of the heat
exchanger. As can be seen from FIG. 3 the effective cooling stream
produced by current state of the art processes (indicated by
profile marked `state of the art`), such as the Claude cycle shown
in FIG. 4, is extremely linear in comparison to the required
profile in a system using large quantities of cold recycle
(indicated by profile marked `Ideal Profile`), and a very poor
match. To meet the acute cooling demand at the lower temperature
end, a typical state of the art process must expand a similar
quantity of air through the cold turbine as a system without cold
recycle. This results in poor efficiencies and heat transfer
requirements above the maximum design level of the device within
the process heat exchangers.
[0012] The present inventors have identified that there is a need
for a system that can provide focused non-progressive cooling to
concentrated areas of the process, in particular at the lower
temperature end of the process.
SUMMARY OF THE INVENTION
[0013] A first aspect of the present invention addresses these
needs by providing, in a first embodiment, a cryogenic liquefaction
device comprising: [0014] a heat exchanger; [0015] a first phase
separator; [0016] a first expansion device; [0017] a first
expansion turbine; [0018] a second expansion turbine; [0019] a cold
recovery circuit including a heat transfer fluid; and [0020] an
arrangement of conduits, wherein: [0021] the operating inlet
pressures of the first and second expansion turbines are different
from one another; and [0022] the arrangement of conduits is
arranged such that: [0023] a first portion of a pressurised stream
of gas is directed through the heat exchanger, the first expansion
device and the first phase separator; [0024] a second portion of
the pressurised stream of gas is directed through the first
expansion turbine, then through the heat exchanger in a
counter-flow direction to the first portion of the pressurised
stream of gas, and then through the second expansion turbine, and
[0025] the heat transfer fluid is directed through the heat
exchanger.
[0026] In the context of the present invention, the phrase "a
counter-flow direction" is used to mean that the second portion of
the pressurised stream of gas flows through the heat exchanger in
an opposite direction to the first portion of the pressurised
stream of gas, for at least a part of its path through the heat
exchanger. The first and second portions of the pressurised stream
of gas may enter the heat exchanger at opposite ends, i.e. so that
the temperature difference between the entry points is maximised.
Alternatively, the first and or second portion of the pressurised
stream of gas may enter the heat exchanger at a point between the
ends of the heat exchanger, but flow through the heat exchanger in
an opposite direction to the other of the first and second portion
of the pressurised stream of gas, for at least a part of its path
through the heat exchanger.
[0027] The cold recovery circuit comprises a thermal energy storage
device, a means for circulating the heat transfer fluid (HTF), and
an arrangement of conduits arranged to direct the HTF through the
thermal energy storage device and into the heat exchanger. An
exemplary cold recovery circuit is described in detail in GB
1115336.8. The HTF may comprise a gas or a liquid, at high or low
pressure.
[0028] The configuration of the present invention is such that the
second portion of the cooled process stream can be partially
expanded through the first turbine to provide a high pressure
cooling stream local to the entry point of the cold recovery stream
of the cold recovery circuit. The stream can then be further
expanded through the second turbine to provide significant
additional cooling to the lower section of the process.
[0029] The present invention offers increased work output from the
expansion turbines as a result of the reheating of the expanded
stream, whilst also providing cooling between expansion
turbines.
[0030] The pressurised stream of gas may consist of gaseous air.
Alternatively, the pressurised stream of gas may consist of gaseous
nitrogen. The pressurised stream of gas may be input into the
cryogenic liquefaction device at a pressure greater than or equal
to the critical pressure which, for gaseous air is 38 bar and for
gaseous nitrogen is 34 bar.
[0031] After the pressurised stream of gas is split into two
portions, the first portion of the pressurised stream of gas and
the second portion of the pressurised stream of gas may be at the
same pressure. Alternatively, the first portion of the pressurised
stream of gas and the second portion of the pressurised stream of
gas may be at different pressures. In particular, the first portion
may be above the critical pressure, and the second portion may be
below the critical pressure, or vice versa.
[0032] The cryogenic liquefaction device may comprise more than two
expansion turbines, with turbines in both parallel and series.
[0033] The cryogenic liquefaction device may further comprise a
third expansion turbine, wherein the operating inlet pressure of
the third expansion turbine is different to at least one of the
first and second expansion turbines.
[0034] The arrangement of conduits may be such that the third
expansion turbine is in parallel with at least one of the first and
second turbines such that at least a portion of the second portion
of the pressurised stream of process gas is directed through the
third turbine.
[0035] The arrangement of conduits may be such that the third
expansion turbine is in series with at least one of the first and
second turbines such that at least a portion of the second portion
of the pressurised stream of process gas is directed through the
third turbine.
[0036] The cryogenic liquefaction device may further comprise a
refrigerant circuit which is connected to the output of the second
expansion turbine via the arrangement of conduits.
[0037] The cryogenic liquefaction device may further comprise a
second arrangement of conduits that directs a second heat transfer
fluid through a closed cycle refrigeration circuit and through a
localised area of the heat exchanger. The second heat transfer
fluid within the refrigerant circuit may comprise a gas or a
liquid, at high or low pressure.
[0038] The cryogenic liquefaction device may further comprise a
fourth expansion turbine, wherein the arrangement of conduits is
arranged such that:
[0039] a third portion of the pressurised stream of gas is directed
through the fourth expansion turbine, then through the heat
exchanger in a counter-flow direction to the first portion of the
pressurised stream of gas.
[0040] The cryogenic liquefaction device may further comprise a
fifth expansion turbine, wherein the arrangement of conduits is
arranged such that:
[0041] the third portion of the pressurised stream of gas is
directed through the fifth expansion turbine after passing through
the fourth expansion turbine and the heat exchanger.
[0042] The cryogenic liquefaction device may further comprise a
second phase separator and a second expansion device, wherein the
arrangement of conduits is arranged such that at least a portion of
the second portion of the pressurised stream of gas is directed
through the second expansion device and the second phase separator
after having passed through the first expansion turbine.
[0043] The or each expansion device may comprise a Joule-Thomson
valve, another pressure reducing valve, an expansion turbine or
another work extracting device.
[0044] The cryogenic liquefaction device may further comprise a
first compressor, wherein the arrangement of conduits is arranged
such that at least a portion of the second portion of the
pressurised stream of gas is directed through the first compressor
before passing through the first expansion turbine.
[0045] The cryogenic liquefaction device may further comprise a
second compressor, wherein the arrangement of conduits is arranged
such that the first portion of the pressurised stream of gas is
directed through the second compressor before passing through the
heat exchanger.
[0046] The cryogenic liquefaction device may further comprise a
cooler, wherein the arrangement of conduits is arranged such that
the first portion of the pressurised stream of gas is directed
through the cooler after passing through the second compressor and
before passing through the heat exchanger.
[0047] The cryogenic liquefaction device may further comprise a
feed stream compressor adapted to output the pressurized stream of
gas, wherein the arrangement of conduits is arranged firstly such
that a feed stream is directed to the input of the feed stream
compressor; and secondly such that the output stream from the first
phase separator joins the feed stream after passing through the
heat exchanger.
[0048] The arrangement of conduits may be arranged such that the
pressurized stream of gas output from the feed stream compressor is
directed to a heat storage device before passing through the heat
exchanger.
[0049] The arrangement of conduits may be arranged such that the
pressurized stream of gas output from the heat storage device is
directed to a heat rejection device before passing through the heat
exchanger.
[0050] The first aspect of the present invention further provides a
method for thermally balancing a liquefaction process with the use
of cold recycle from an external thermal energy source
comprising:
[0051] directing a first portion of a pressurised stream of gas
through a heat exchanger, a first expansion device, and a first
phase separator;
[0052] directing a second portion of a pressurised stream of gas
through a first expansion turbine, then through the heat exchanger
in a counter-flow direction to the first portion of the pressurised
stream of gas, and then through a second expansion turbine; and
[0053] directing a heat transfer fluid through a cold recovery
circuit and the heat exchanger; wherein: [0054] the operating inlet
pressures of the first and second expansion turbines are different
from one another.
[0055] Any of the optional features recited above in connection
with the cryogenic liquefaction device may also be incorporated
into the method of the first aspect of the present invention.
A second aspect of the present invention addresses these needs by
providing, in a first embodiment, a cryogenic liquefaction device
comprising: a heat exchanger; [0056] a first phase separator;
[0057] a first expansion device; [0058] a first expansion turbine;
[0059] a first compressor; [0060] a cold recovery circuit including
a heat transfer fluid; and an arrangement of conduits, arranged
such that: [0061] a first portion of a pressurised stream of gas is
directed through the heat exchanger, the first expansion device and
the first phase separator; [0062] a second portion of the
pressurised stream of gas is directed through the first expansion
turbine, then through the heat exchanger in a counter-flow
direction to the first portion of the pressurised stream of gas,
and then through the first compressor, and [0063] the heat transfer
fluid is directed through the heat exchanger.
[0064] The arrangement of conduits may be arranged such that the
output stream of the first compressor joins the pressurised stream
of gas.
[0065] The arrangement of conduits may be arranged such that the
output stream of the first compressor is directed into the heat
exchanger before it joins the pressurised stream of gas.
Alternatively, the arrangement of conduits may be arranged such
that the output stream of the first compressor joins the
pressurised stream of gas before it is directed into the heat
exchanger.
[0066] The first compressor may be either a single stage or a
multistage compressor.
[0067] The second aspect of the present invention further provides
a method for balancing a liquefaction process with the use of cold
recycle from an external thermal energy source comprising:
[0068] directing a first portion of a pressurised stream of gas
through a heat exchanger, a first expansion device, and a first
phase separator;
[0069] directing a second portion of a pressurised stream of gas
through a first expansion turbine, then through the heat exchanger
in a counter-flow direction to the first portion of the pressurised
stream of gas, and then through a first compressor; and
[0070] directing a heat transfer fluid through a cold recovery
circuit and the heat exchanger.
[0071] Any of the optional features recited above in connection
with the cryogenic liquefaction device may also be incorporated
into the method of the second aspect of the present invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0072] Embodiments of the present invention will now be described
with reference to the figures in which:
[0073] FIG. 1 shows a profile of the relative change in total
enthalpy which a process gas undergoes during the cooling process
(Relative Change of Total Enthalpy vs Cooled Stream
Temperature);
[0074] FIG. 2 shows profiles of the relative change in total
enthalpy which the cooling streams must undergo during the cooling
process for systems with and without the use of large quantities of
cold recycle (Relative Change of Total Enthalpy vs Cooled Stream
Temperature);
[0075] FIG. 3 shows profiles of the relative change in total
enthalpy which the cooling streams must undergo during the cooling
process for `ideal`, `state of art` and `present invention` systems
with the use of large quantities of cold recycle (Relative Change
of Total Enthalpy vs Cooled Stream Temperature);
[0076] FIG. 4 shows a typical state of the art air liquefaction
plant arrangement using the Claude cycle;
[0077] FIG. 5 shows a schematic of a cryogenic energy storage
system liquefaction process according to a first embodiment of the
first aspect of the present invention;
[0078] FIG. 6 shows a second embodiment of the first aspect of the
present invention;
[0079] FIG. 7 shows a third embodiment of the first aspect of the
present invention;
[0080] FIG. 8 shows a fourth embodiment of the first aspect of the
present invention;
[0081] FIG. 9 shows a fifth embodiment of the first aspect of the
present invention;
[0082] FIG. 10 shows a sixth embodiment of the first aspect of the
present invention;
[0083] FIG. 11 shows a seventh embodiment of the first aspect of
the present invention;
[0084] FIG. 12 shows a variation of the second embodiment of the
present invention;
[0085] FIG. 13 shows a variation of the seventh embodiment of the
present invention;
[0086] FIG. 14 shows an eighth embodiment of the present
invention;
[0087] FIG. 15 shows a variation of the first embodiment of the
present invention;
[0088] FIG. 16 shows another variation of the first embodiment of
the present invention;
[0089] FIG. 17 shows yet another variation of the first embodiment
of the present invention; and
[0090] FIG. 18 shows a first embodiment of the second aspect of the
present invention.
DETAILED DESCRIPTION OF THE INVENTION
[0091] The first simplified embodiment of the present invention is
shown in FIG. 5. The system in FIG. 5 is similar to that of the
state of the art shown in FIG. 4 in that the main process stream 31
is cooled via cold expanded air from turbines and expanded through
an expansion device such as a Joule-Thomson Valve 1 to produce
liquid, however the warm turbine 3 of FIG. 4 is replaced by a
second cold turbine 6 aligned in series with the first cold turbine
5.
[0092] In the first embodiment of the present invention shown in
FIG. 5, the process gas (in the preferred embodiment air) is
compressed to high pressure, of at least the critical pressure
(which for air is 38 bar, more preferably >45 bar), and at
ambient temperature (.apprxeq.298K) enters the cryogenic
liquefaction device at inlet 31, from where it is directed through
a heat exchanger 100 and cooled progressively by cold low pressure
process gas, before returning through the heat exchanger 100 via
passage 41, 42. Also passing through the heat exchanger 100 is a
cold recovery stream 30, 50 of a cold recovery circuit of the
cryogenic liquefaction device. The cold recovery circuit comprises:
a thermal energy storage device (not shown); a means for
circulating a heat transfer fluid through the cold recovery circuit
(not shown); and an arrangement of conduits arranged to direct the
heat transfer fluid through the thermal energy storage device and
the heat exchanger 100. An exemplary cold recovery circuit is
described in detail in GB 1115336.8
[0093] A proportion of the high pressure process gas input into the
heat exchanger at 31, and now at a temperature of between 150-170K
(in the preferred case 165K), is separated from the main flow 31,
via passage 39, and is partially expanded to between 5 and 20 bar
(more typically 10-14 bar), using expansion turbine 5, before
passing through passage 40, 43 of the heat exchanger 100, where
cold thermal energy is transferred to the high pressure gas in
stream 35. This feature of the present invention provides more
effective cooling than the arrangement of FIG. 4 as a result of the
higher pressure cooling stream 40, 43 around the entry point of the
cold recovery stream 30, better matching the resultant cooling
demand (as shown in FIG. 3) than conventional layouts, where the
warm turbine 3 (of FIG. 4) provides cooling at higher temperatures
which are not required where cold recycle is available.
[0094] The partially expanded gas stream in passage 40, 43 is
heated to a temperature between 120-140K (in the preferred case
125K), as a result of the thermal transfer in passage 40, 43
through heat exchanger 100, and is further expanded through turbine
6, to between ambient and 6 bar where it travels through passage 44
and enters the phase separator vessel 2. The gas fractions of
streams 32 and 44 are combined to form output stream 34, which
travels through passage 41, 42 through heat exchanger 100 which
provides additional cooling to the high pressure process stream 35.
An additional advantage of the present invention is that the
typical composition of the cold process stream in stream 44 is a
mixture of liquid and gaseous air. The liquid fraction from the
final expansion is collected within the phase separator 2 and
output via passage 33.
[0095] The numbered points in FIG. 5 indicate positions in the
system at which typical absolute pressures, temperatures and mass
flows are as follows:
TABLE-US-00001 Temperature Pressure Mass Flow Point (K) (bar)
(kg/hr) 31 298 45 16651 35 165.5 45 7160 38 101 45 7160 32 91.23 4
7160 33 91.23 4 6249 34 91.23 4 911 39 165.5 45 9491 40 113 11.23
9491 43 125.5 11.23 9491 44 95.91 4 9491 41 95.49 4 10402 42 295.3
4 10402 30 115 1.2 8280 50 295.3 1.2 8280
[0096] A second embodiment of the current invention is shown in
FIG. 6 (where like reference numerals refer to the same components
as in FIG. 5), wherein the proportion of air separated from the
main stream 31 via passage 39 is carried out later in the process
and therefore at a lower temperature (between 130-170K). As a
result the subsequent temperature of the cold gas after partial
expansion in turbine 5, is sufficient to provide a high pressure
cooling stream for the bottom end of the process stream 35 via
passage 40, 43, after which it is expanded again through the second
turbine 6 to provide additional focussed cooling in stream 34.
[0097] A third embodiment of the present invention is shown in FIG.
7 (where like reference numerals refer to the same components as in
FIG. 5) wherein a third expansion turbine 7 is provided in parallel
with the second turbine 6 which remains in series with turbine 5.
Similar to the second embodiment shown in FIG. 6, a portion 39 of
the cold high pressure stream 31 is partially expanded by turbine 5
to provide a high pressure cooling stream 40 at the lower end of
the heat exchanger only, before it is split again into two streams
43, 45 and expanded through the two further turbines 6 and 7 in
parallel. The outlet from turbine 7 is introduced typically into
the phase separator 2 via passage 80. In some embodiments where the
cold recycle temperatures are low the outlet from turbine 7 may be
introduced higher up the heat exchanger 100 via passage 46.
[0098] FIG. 8 (where like reference numerals refer to the same
components as in FIG. 7) details a fourth embodiment of the present
invention wherein, similar to the system shown in FIG. 7, a third
expansion turbine 7 is added and placed in parallel to the second
expansion turbine 6 which remains in series with the first
expansion turbine 5. The expansion ratios of the second 6 and third
7 turbines are different from each other, the second expanding from
around 8 bar to 4.5 bar, and the third expanding from around 8 bar
to near ambient. The inventors have realised that by layering
multiple cooling streams in parallel as in FIG. 8, the cooling
profile demand, identified in FIG. 3, can be more closely matched.
In some embodiments, where the outlet pressure of turbine 7 is
substantially equal to the separator pressure 2, the outlet of
turbine 7 is introduced to the phase separator 2 via passage 80
where liquid formed in the outlet of turbine 7 is collected.
[0099] A further embodiment is shown in FIG. 9 (where like
reference numerals refer to the same components as in FIG. 8). This
embodiment is the same as that of FIG. 8 except that the exiting
gases travelling through stream 48 from the second expansion
turbine 6 are removed from the process heat exchanger 100 before
reaching the top. The cold gases in stream 48 are further
compressed, by compressor 8, and the resultant stream 49 is cooled
by a closed cycle refrigeration circuit 10 before exiting the
circuit 10 as stream 51 and mixing with the high pressure process
stream 31. In certain embodiments there is the potential for a
proportion of liquid to be formed in stream 46 from the cold gas on
exiting the third turbine 7, whereby the stream would be directed
via passage 80 to enter the phase separator 2, instead of being
directed straight through the heat exchanger 100 via passageway 46,
47.
[0100] In a further embodiment (not shown but otherwise the same as
FIG. 9), the outlet of turbine 7 may be expanded to near ambient so
that this process stream can be used to drive a low pressure high
grade cold store, such as that detailed in GB1115336.8.
[0101] The embodiment shown in FIG. 10 (where like reference
numerals refer to the same components as in FIG. 5) is the same as
that of FIG. 5 except for the addition of a closed cycle
refrigeration circuit 101 to provide a local potentially high
pressure cooling stream 60 to better match the cooling demand. The
closed cycle refrigeration circuit 101 includes compressor 102,
cooler 103 and expansion turbine 104.
[0102] FIG. 11 shows a further embodiment of the present invention
(where like reference numerals refer to the same components as in
FIG. 5) wherein a warm turbine 14 and cold turbine 5 partially
expand portions 60, 39 of the cold high pressure stream 31. Streams
60 and 39 are at different temperatures and are expanded to
different pressures by turbines 14 and 5 to provide streams 61 and
40, respectively. Gas in streams 61 and 40 provides focussed
cooling to the high pressure stream at points 35 and 69, before
separately being expanded to between 0 and 6 bar, using further
turbines 16 and 6 to provide streams 63 and 44 which are directed
through heat exchanger 100.
[0103] A variation to the second embodiment is shown in FIG. 12
(where like reference numerals refer to the same components as in
FIG. 6) wherein the addition of a second phase separator 18 and
pressure reducing valve 19 enable the removal of additional liquid
produced in stream 40. In some embodiments the outlet pressure of
turbine 6 is equal to the separator pressure 2 and the outlet of
turbine 6 is introduced to the phase separator via passage 80 where
liquid formed in the outlet to turbine 7 is collected.
[0104] A further component (not shown), which can be included in
any of the previous embodiments is a closed loop refrigeration
cycle (similar to cycle 101 shown in FIG. 10), that utilises a
different working fluid to provide additional cooling at a specific
section of the system where the cooling requirements are
particularly high, in particular between 140 and 120K. The
different working fluid may comprise a refrigerant such as
methane.
[0105] A further arrangement, which can be applied to any of the
previous embodiments where the high pressure stream is divided into
two streams of different pressure, includes providing the first
stream (that is cooled and then transferred to the expansion
device) at a pressure above the critical pressure to maximise
liquid production. The second high pressure stream is at a
different pressure (typically above the first stream pressure) and
is cooled and transferred to the two or more expansion turbines to
provide additional cooling to the first stream as described in the
previous embodiments.
[0106] In a further embodiment as shown in FIG. 13 (where like
reference numerals refer to the same components as in FIG. 5) the
second stream 58 is compressed by compressor 20 to stream 59 and is
then divided into a further two or more streams 63, 65. Stream 65
is compressed by compressor 19 and then directed, via a first
stream (66), through two turbines 5, 6 in series. Stream 63 is
expanded through a third turbine 21. The outlet streams 40, 44, 64
of the first, second and third turbines 5, 6, 21 provide additional
cooling for the first process stream 35 prior to expansion in an
expansion device such as a Joule-Thomson valve 1.
[0107] In a further embodiment, as shown in FIG. 14 (where like
reference numerals refer to the same components as in FIG. 5)
applied to the first embodiment, the cooled gas stream 31 is fed
directly from a compressor commonly referred to as a Recycle Air
Compressor (RAC) and a stream 58 is split from the cooled gas
stream 31 and subsequently boosted to a higher pressure by
compressor 19 before being directed through expansion turbines 5
and 6 and heat exchanger 100. This additional booster component can
be incorporated into any of the previous embodiments.
[0108] FIG. 15 (where like reference numerals refer to the same
components as in FIG. 14) shows a variation of the embodiment of
FIG. 16 whereby stream 31 is fed directly from the RAC. Stream 31
is split into two streams 41 and 35; stream 41 is directed through
heat exchanger 100, where it is cooled before being directed
through expansion turbines 5 and 6 and again heat exchanger 100,
while stream 35 is boosted to a higher pressure by booster 19
before being directed through heat exchanger 100 and an expansion
device such as a Joule-Thomson valve 1.
[0109] FIG. 16 (where like reference numerals refer to the same
components as in FIG. 15), shows a variation where stream 31 is
again fed directly from the RAC and compressed to a pressure lower
than the critical pressure (<38 bar). Stream 41 splits from the
main cooled stream 31 prior to the remainder of the main cooled
stream 35 being boosted and subsequently cooled by boosters 19 and
20, and coolers 10 and 22. The sub critical pressure stream 41 is
cooled via heat exchanger 100 before being partially expanded, to
between 5 and 20 bar, but more typically 10-14 bar, through
expansion turbine 5 before passing through passage 40, 43, of the
heat exchanger 100, where cold thermal energy is transferred to the
high pressure gas in stream in passage 73, 38, and being further
expanded by expansion turbine 6. The additional components arranged
in stream 35 can also be incorporated in any of the previous
embodiments.
[0110] In the final embodiment, as shown in FIG. 17 (where like
reference numerals refer to the same components as in FIG. 15)
shows a variation where output stream of the first phase separator
2 becomes low pressure return vapour 42, having passed through the
heat exchanger 100, and merges with a feed stream 401 to form
stream 402. The pressure of stream 402 can be between 3 barA and 15
barA, more typically 8 barA. Stream 402 is directed to a single
stage compressor 400, which boosts the stream 402 to a higher
pressure. The output stream 403 of the single stage compressor 400
therefore has a higher pressure than stream 402. The higher
pressure is at least the critical pressure (which for air is 38
bar, more preferably >45 bar). The temperature of stream 403 can
be between 100 deg C and 400 deg C, more typically 270 deg C.
Stream 403 is directed to a heat storage device 404 which removes
at least some of the heat energy in the stream 403. The temperature
of the output stream 405 of the heat storage device 404 can be
between 20 deg C and 100 deg C, more typically 60 deg C. If the
temperature of stream 405 is above ambient temperature the heat
rejection device 406 may be used to cool the temperature of the
stream. When this liquefaction cycle is used as part of a cryogenic
energy storage plant it is highly preferable that the heat of
compression captured by the heat storage device 404 is used in the
power recovery cycle to boost the temperature of the working fluid
at the inlet of the expansion turbines.
[0111] FIG. 18 (where like reference numerals refer to the same
components as in FIG. 4) shows an embodiment of the invention which
is a further development of the air liquefaction plant arrangement
of FIG. 4. Here, the cold vapour stream 40, which is output from
the expansion turbine 4, is directed to the heat exchanger 100
rather than merging with returning stream 34 to form stream 41 as
shown in FIG. 4. The cold vapour stream 40 thus gains heat as it
passes through the heat exchanger 100 and exits the heat exchanger
as stream 43. The temperature of stream 43 can be between 0 deg C
and -180 deg C, more typically -117 deg C. Stream 43 is directed to
a compressor 300, which boosts the stream 43 to a higher pressure.
The compressor 300 can be a multistage compressor or a single stage
compressor. The output stream 301 of the compressor 300 is directed
back to heat exchanger 100 in one of two arrangements. If the
temperature of stream 301 is near ambient temperature then it can
be directed to merge with stream 35 outside the heat exchanger 100.
This is shown by stream 302. Alternatively, if the temperature of
stream 301 is below ambient temperature then it can be directed to
merge with the stream 35 insider the heat exchanger to form stream
74. This is shown by stream 303.
[0112] It will of course be understood that the present invention
has been described by way of example, and that modifications of
detail can be made within the scope of the invention as defined by
the following claims.
* * * * *