U.S. patent application number 17/593985 was filed with the patent office on 2022-06-02 for method and system for condensing a gas.
The applicant listed for this patent is LINDE GMBH. Invention is credited to Heinz BAUER, Martin KAMANN, Friderike KAMMERMAIER.
Application Number | 20220170695 17/593985 |
Document ID | / |
Family ID | |
Filed Date | 2022-06-02 |
United States Patent
Application |
20220170695 |
Kind Code |
A1 |
BAUER; Heinz ; et
al. |
June 2, 2022 |
METHOD AND SYSTEM FOR CONDENSING A GAS
Abstract
The invention relates to a method for condensing a gas, wherein
the gas is subjected to cooling in indirect heat exchange with a
refrigerant and at least part of the refrigerant is subjected,
after the heat exchange with the gas, to compression by means of a
drive (GT1) that produces waste heat and to a partial or complete
condensing process. After the partial or complete condensing
process, a first portion of the refrigerant is subjected to the
heat exchange with the gas and a second portion of the refrigerant
is subjected, in succession, to pressurization, heating by means of
the waste heat of the drive (GT1) and work-performing expansion and
thereafter is fed back to the partial or complete condensing
process. The invention further relates to a corresponding
system.
Inventors: |
BAUER; Heinz; (Ebenhausen,
DE) ; KAMANN; Martin; (Oberhaching, DE) ;
KAMMERMAIER; Friderike; (Forstinning, DE) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
LINDE GMBH |
Pullach |
|
DE |
|
|
Appl. No.: |
17/593985 |
Filed: |
March 12, 2020 |
PCT Filed: |
March 12, 2020 |
PCT NO: |
PCT/EP2020/025127 |
371 Date: |
September 29, 2021 |
International
Class: |
F25J 1/00 20060101
F25J001/00; F25J 1/02 20060101 F25J001/02 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 1, 2019 |
GB |
1904525.1 |
Aug 2, 2019 |
EP |
19020458.6 |
Claims
1. A method for condensing a gas, wherein the gas is subjected to
cooling in indirect heat exchange with a refrigerant, and at least
a part of the refrigerant is subjected, after the heat exchange
with the gas, to compression using a drive that produces waste heat
and to a partial or complete condensing process, wherein, after the
partial or complete condensing process, a first portion of the
refrigerant is subjected to the heat exchange with the gas, and
that a second portion of the refrigerant is subjected, in
succession, to pressurization, heating using the waste heat of the
drive and to work-performing expansion, and thereafter is fed back
to the partial or complete condensing process.
2. The method according to claim 1, with which a mixed refrigerant
is used as the refrigerant in one or more mixed refrigerant
circuits and/or with which natural gas or a gas mixture formed
using natural gas is used as the gas and/or with which a gas
turbine is used as the drive that produces waste heat.
3. The method according to claim 1, with which work performed
during the work-performing expansion is used in addition to the
drive in the compression of the same refrigerant.
4. The method according to claim 3, with which the compression of
the refrigerant comprises a first compression step to a first
pressure level and a second compression step to a second pressure
level above the first pressure level, wherein the drive is used in
the first compression step and the work performed during the
work-performing expansion is used in the second compression
step.
5. The method according to claim 1, with which the first and second
portions are in each case portions of a first refrigerant, and with
which work performed during the work-performing expansion is used
in the compression of a second refrigerant, wherein the first
refrigerant is a pure refrigerant and the second refrigerant is a
mixed refrigerant, or wherein the first refrigerant is a mixed
refrigerant and the second refrigerant is nitrogen.
6. The method according to claim 4, with which the refrigerant is
at least partially subjected to the first compression step and
subsequently at least partially subjected to a first partial
condensing process to obtain a first liquid fraction and a first
gas fraction, wherein the first gas fraction is at least partially
subjected to the second compression step and subsequently at least
partially subjected to a second partial condensing process to
obtain a second liquid fraction and a second gas fraction.
7. The method according to claim 6, with which after its
work-performing expansion, the second portion of the refrigerant is
at least partially combined with the refrigerant or a part thereof
before the latter is subjected to cooling for the first partial
condensing process.
8. The method according to claim 6, with which before its
work-performing expansion, the second portion of the refrigerant is
at least partially subjected to indirect heat exchange with the
second portion of the refrigerant or a part thereof, after the
latter was subjected to the work-performing expansion and before
the latter is combined with the first gas fraction.
9. The method according to claim 6, with which the second liquid
fraction is at least partially expanded and combined with the
refrigerant compressed in the first compression step.
10. The method according to claim 6, with which a heat exchanger
having a plurality of sections or a plurality of heat exchangers is
used for cooling the gas in indirect heat exchange with the
refrigerant, wherein the first portion of the refrigerant and the
second gas fraction or parts thereof are further cooled to
different temperature levels and reheated after expansion.
11. The method according to claim 1, with which the work performed
during the work-performing expansion is used in addition to the
drive in the compression of a further refrigerant, with which the
gas is subjected to cooling in indirect heat exchange.
12. A system for condensing a gas, wherein the system has means
configured to subject the gas to cooling in indirect heat exchange
with a refrigerant, and at least a part of the refrigerant is
subjected, after the heat exchange with the gas, to compression
using a drive that produces waste heat and to a partial or complete
condensing process, wherein means configured to subject, after the
partial or complete condensing process, a first portion of the
refrigerant to the heat exchange with the gas, and a second portion
of the refrigerant, in succession, to pressurization, heating using
the waste heat of the drive and to work-performing expansion, and
thereafter to feed it back to the partial or complete condensing
process.
13. A system for condensing a gas, wherein the system has means
configured to subject the gas to cooling in indirect heat exchange
with a refrigerant, and at least a part of the refrigerant is
subjected, after the heat exchange with the gas, to compression
using a drive that produces waste heat and to a partial or complete
condensing process, wherein means configured to subject, after the
partial or complete condensing process, a first portion of the
refrigerant to the heat exchange with the gas, and a second portion
of the refrigerant, in succession, to pressurization, heating using
the waste heat of the drive and to work-performing expansion, and
thereafter to feed it back to the partial or complete condensing
process, wherein the system is configured to carry out a method
according to claim 1.
Description
[0001] The invention relates to a method for condensing a gas, in
particular natural gas, and to a corresponding system in accordance
with the respective preambles of the independent claims.
PRIOR ART
[0002] Methods and systems for condensing natural gas are known and
are, for example, described in the article "Natural Gas" in
Ullmann's Encyclopedia of Industrial Chemistry, online publication,
Jul. 15, 2006, DOI: 10.1002/14356007.a17_073.pub2, in particular
section 3, "Liquefaction," or in Wang and Economides, "Advanced
Natural Gas Engineering," Gult Publishing, 2010, DOI:
10.1016/C2013-0-15532-8, in particular chapter 6, "Liquefied
Natural Gas (LNG)."
[0003] In particular, mixed refrigerants consisting of various
hydrocarbon components and nitrogen can be used in natural gas
condensing processes. For example, one, two or even three mixed
refrigerant circuits can be used (single mixed refrigerant, SMR;
dual mixed refrigerant, DMR; mixed fluid cascade, MFC). Mixed
refrigerant circuits with propane precooling (C3MR) or more
generally using a pure refrigerant (see below) are also known.
[0004] Although the present invention is described below
predominantly with reference to the condensing process of natural
gas, the proposed measures are in principle also suitable for
condensing other gas mixtures. Natural gas and corresponding other
gas mixtures may, in particular, have more than 70, preferably more
than 90, mole percent methane and in the remainder (inter alia)
non-hydrocarbon gases, such as nitrogen and acid gases. They may
also contain higher hydrocarbons, in particular ethane. Higher
hydrocarbons, such as ethane, propane, butane, etc. are preferably
contained at less than 10 mole percent. Such higher hydrocarbons
may, for example, be removed upstream of the actual condensing
process. A natural gas used for condensing or another gas mixture
is preferably essentially free of water and/or carbon dioxide.
[0005] Methods for condensing natural gas are energy-intensive.
Depending on the technology selected, between 5 and 15% of the
energy contained in the feed gas are consumed internally, in order
to produce the required cold. Increased process efficiency
frequently leads to additional investments, since technically more
sophisticated systems must be used.
[0006] Large refrigeration circuit compressors are usually driven
by gas turbines, which convert only 30 to 45% of the energy of the
fuel gas, i.e., its calorific value, into mechanical shaft power.
The remainder, i.e., 55 to 70% of the energy, is lost when the
waste heat of the turbine waste gas is not utilized.
[0007] Various concepts for utilizing the waste heat of turbine
waste gases exist. Simple systems comprise the recovery of the
waste heat in the form of process heat, e.g., in a hot oil system,
which transfers the heat from the turbine waste gas at an
appropriate temperature level, for example to reboilers of
regeneration columns in amine washes, regeneration gas heaters for
dryers or any other heat users.
[0008] More complex waste heat utilization systems comprise a
closed steam circuit. The steam produced by the waste heat can be
expanded in a steam turbine in a work-performing manner. Any
refrigeration circuit compressors can be driven with a
corresponding steam turbine, including, for example, those of
precooling circuits with, for example, propane, carbon dioxide or
ammonia as refrigerant. Support of a gas turbine for the main
compressor is also possible.
[0009] Overall, there is the desire to increase the efficiency in
natural gas condensing and other gas condensing methods without the
complex installation of a circuit on the basis of an additional
working fluid, such as steam.
DISCLOSURE OF THE INVENTION
[0010] Against this background, the present invention proposes a
method and a system with the features of the independent claims.
Embodiments of the present invention are respectively the subject
matter of the dependent claims and the following description.
[0011] Within the scope of the present invention, a method for
condensing a gas is proposed, wherein the gas is subjected to a
heat exchange with a refrigerant, and at least a part of the
refrigerant is subjected, after the heat exchange with the gas,
with which the refrigerant can in particular be at least partially
evaporated, to compression using a drive that produces waste heat
and to a partial or complete condensing process. Within the scope
of the present invention, a refrigerant circuit is thus used, which
comprises the steps known per se of heating and evaporation
(against the fluid to be cooled, here the gas to be condensed),
recompression (using the drive that produces waste heat) and
(partial) condensation in the circuit.
[0012] Below, the term "evaporation" generally always refers to
partial or complete evaporation. Accordingly, the term
"condensation" is also to be understood as partial or complete
condensation, even if this is not explicitly indicated in each
case. The heat exchange of the refrigerant "with the gas" can take
place in the form of indirect heat exchange between the gas and the
refrigerant without an intermediate further refrigerant, i.e., via
a common heat exchange surface of a heat exchanger, but also via an
additional refrigerant. Heat exchange "with the gas" thus also
takes place when heat is withdrawn from the gas via a further
refrigerant, and the further refrigerant is precooled with the
refrigerant considered here. The term "heat exchange" is always
used herein synonymously with the scientifically more correct term
"heat transfer" and the term "heat exchanger" is used synonymously
with the term "heat transfer device."
[0013] As also known in this respect, the heating and evaporation,
the recompression and the (partial) condensing process can take
place in the form of any (pressure or temperature) stages or in the
form of a plurality of partial flows in parallel to one another,
wherein corresponding partial flows may be combined with one
another at any locations or formed from an output flow. The present
invention relates in particular to closed refrigerant circuits as
known for condensing natural gas from the aforementioned prior
art.
[0014] According to the invention, after the partial or complete
condensing process of the refrigerant, a first portion of the
refrigerant is subjected to heat exchange with the gas in the sense
just explained, whereas a second portion of the refrigerant is
subjected, in succession, to pressurization (in the liquid state),
heating (in particular superheating) using the waste heat of the
drive, and work-performing expansion and is fed back to the partial
or complete condensing process. In other words, after its
work-performing expansion, with which evaporation in particular
takes place, the second portion of the refrigerant is thus returned
to the refrigerant circuit and is thereby in particular combined
with the first portion of the refrigerant, which was previously
subjected to the heat exchange with the gas and was likewise
evaporated thereby. A partial circuit is thus created. In
principle, the second portion can again be returned to the
refrigerant circuit and combined with the first portion at any
location; specific positions are explained below.
[0015] In other words, the present invention thus relates to a gas
condensing method with which at least one compressor is used in a
refrigerant circuit used to provide cold. A drive of the compressor
produces waste heat. In particular, a gas turbine is used as the
drive, so that the waste heat is provided in particular with the
turbine waste gas that is extracted from an expansion stage of the
gas turbine. In the present invention, work-performing expansion of
a partial flow of the refrigerant, of the mentioned "second
portion," is carried out. The latter is both further pressurized
and heated before the work-performing expansion, so that the
refrigerant is capable of absorbing the waste heat contained in the
turbine waste gas of the gas turbine or in another waste heat
carrier. The heated, in particular superheated, refrigerant, which
is obtained by utilizing the waste heat, is used as an energy
source by the work-performing expansion, so that in this way the
waste heat can be converted into a different energy form. The work
performed during the work-performing expansion can be used as
explained below. The work-performing expansion can also take place
in two or more stages with or without intermediate superheating
using the waste heat.
[0016] Within the scope of the present invention, as explained
below in embodiments, it is in particular provided that the work
performed during the work-performing expansion is used for
compressing the same or a different refrigerant. Although certain
compressors in the embodiments below are driven by means of the
work performed during the work-performing expansion, it is not
excluded that other compressors can also be driven in this way. In
the specific embodiments of the invention, in some cases, the
compressors that compress to the highest pressure in each case in
the refrigerant circuit (designated C2 in the figures) are, for
example, coupled to corresponding expansion machines.
Alternatively, however, any other compressors or compressor stages
that are configured to compress to a lower pressure (designated C1,
C1A or C1B in the figures) can also be driven via the
work-performing expansion. Nevertheless, it is possible to operate
compressors connected in parallel, of which one is driven by means
of the work performed during the work-performing expansion and
another is driven in another way, and which compress parallel
partial flows of the refrigerant.
[0017] In various embodiments of the present invention, the work
performed during the expansion can also be used at least in part to
drive an electric generator.
[0018] In medium-size systems for natural gas condensing with a
capacity of, for example, approximately 0.3 to 2 megatons per year,
the mentioned SMR circuits are frequently used, since a limited
number of components is required in these systems and an adequate
thermodynamic efficiency is present. However, the investment costs
for a steam system to utilize the turbine waste heat are not
necessarily economical for such a system size if the possible
energy savings do not compensate for the additional costs. The
present invention can particularly be used in such cases and
creates an alternative and advantageous possibility for waste heat
utilization here. By the use of the present invention, the
efficiency of an SMR process can be improved by at least 10 to 15
percent points by correspondingly relieving the gas turbine used to
drive the refrigerant compressor.
[0019] On the other hand, the present invention can also be
advantageously used to condense natural gas on a larger scale, for
example in systems with a capacity of approximately 2 to 10
megatons per year. In such systems, more than one refrigerant
compressor is typically required in order to achieve the specified
capacity. The optimal rotational speed of the different refrigerant
compressors is not necessarily similar or identical, so that
transmissions between the individual compressors may have to be
used if the latter are to be driven by means of a common gas
turbine. However, even when a plurality of independent gas turbines
is used, an imbalance in the required shaft power for each
compressor can occur. In certain situations, the present invention
can be used advantageously in that the work performed during the
work-performing expansion is used in support of the drive and
imbalances in rotational speed or power are thus compensated.
[0020] In the method according to the invention, a mixed
refrigerant in one or more mixed refrigerant circuits can in
particular be used as the refrigerant. The refrigerant mixture
typically consists of light hydrocarbons having one to five carbon
atoms and at most 20 mole percent nitrogen. The invention can be
used in the mentioned SMR circuits, but also in DMR, MFC or C3MR
refrigeration circuits, along with other refrigeration circuits in
which, in addition to a mixed refrigerant, a pure refrigerant is
used, as in principle known from the prior art cited at the outset.
The term "pure refrigerant" is understood here to mean a
refrigerant that has or essentially consists of at least 95 mole
percent, in particular at least 99 mole percent, of a single
hydrocarbon, in particular ethane, ethylene, propane or propylene,
or another compound with a suitable vapor pressure curve, such as
ammonia or carbon dioxide. If, for example, "propane" or "propane
refrigeration circuit" is mentioned below, the related explanations
are always to be understood as meaning that they also more
generally relate to a pure refrigerant. Reference to a specific
pure substance is merely illustrative. A corresponding pure
refrigerant can in particular be one that is treated in the manner
explained, i.e., from which the first and second portions are
formed in the form of corresponding partial flows.
[0021] As mentioned several times, within the scope of the present
invention, natural gas or a gas mixture formed using natural gas
(for example deacidified hydrocarbons, dried hydrocarbons and/or
hydrocarbons difficult to boil, in particular hydrocarbons having
three or more carbon atoms, freed natural gas) can be used as the
gas to be condensed, and/or a gas turbine can be used as the drive
that produces waste heat.
[0022] Particular advantages result in embodiments of the invention
if work performed during the work-performing expansion is used in
addition to the drive in the compression of the same refrigerant,
which is also expanded in a work-performing manner and is used to
form the first and second portions. In this way, a drive that is
otherwise used for compression can be relieved by the work
performed during the work-performing expansion, and corresponding
energy savings result, which can be attributed directly to the
utilization of the waste heat. The liquid pressurization of the
second portion of the refrigerant expanded later in a
work-performing manner requires comparatively significantly less
energy as a result. Such embodiments are initially explained
below.
[0023] Within the scope of the present invention, i.e., in a first
group of embodiments, exclusively mixed refrigerants, but no pure
refrigerant in the aforementioned sense, are used. However, these
embodiments can absolutely also be embodiments with which
precooling takes place using a mixed refrigerant. In this first
group of embodiments, the compression of the refrigerant comprises
in particular a first compression step to a first pressure level
and a second compression step to a second pressure level, which is
in particular above the first pressure level, wherein the drive is
used in the first compression step and the work performed during
the work-performing expansion is used in the second compression
step. Thus, the first compression step can in particular be carried
out using one or more first compressors or one or more first
compressor stages that is or are at least partially driven using
the drive, and the second compression step can in particular be
carried out using one or more second compressors or compressor
stages that is or are driven at least partially using the work
performed during the work-performing expansion. The second
compression step is in this case in particular driven without using
the drive that produces waste heat, but advantageously only using
the work performed during the work-performing expansion. In this
way, both compression steps can be realized by machines that can be
operated independently of one another, and no mechanical couplings
are required. As also explained below, however, the work performed
during the work-performing expansion can also be used
correspondingly at any other location.
[0024] Within the scope of the present invention, in a preferred
embodiment, which is also referred to below as "first embodiment,"
the refrigerant can be subjected at least partially to the first
compression step and subsequently at least partially to a first
partial condensing process to obtain a first liquid fraction and a
first gas fraction, wherein in this first embodiment, the first gas
fraction is at least partially subjected to the second compression
step and subsequently at least partially to a second partial
condensing process to obtain a second liquid fraction and a second
gas fraction. In this first embodiment, the entire refrigerant can
in particular be subjected to the first compression step after it
has been evaporated in heat exchange with the gas to be condensed.
The method can thus be used simply and without great additional
effort in connection with known methods for condensing gas, in
which corresponding steps are provided. Reference is made to the
cited prior art.
[0025] In the first embodiment, the first compression step is
carried out in particular using a single, though possibly
multistage, compressor, which however does not compress the
refrigerant to different pressures and which is provided with
reference sign C1 throughout the relevant figures. In this and the
following embodiments, the second compression step is carried out
in particular using a compressor, which is operated independently
of the first compression step and which is provided with reference
sign C2 throughout the figures.
[0026] After its work-performing expansion, the second portion of
the refrigerant in the first embodiment can be at least partially
combined with the refrigerant compressed in the first compression
step, before the latter is cooled for the first partial condensing
process. In this way, the second portion of the refrigerant can be
returned to the refrigerant circuit and can there again be
subjected to the required compression and condensation steps.
[0027] In particular, in the first embodiment, the second portion
of the refrigerant used according to the invention can be brought
in the liquid state from a pressure level of 10 to 40 bar to a
pressure level of 60 to 120 bar for the subsequent expansion. The
heating by means of the waste heat in particular carries out
heating from a temperature level of 10 to 50.degree. C. to a
temperature level of 200 to 400.degree. C. For example, a turbine
waste gas of a gas turbine used as a drive or another substance
flow can be present at 400 to 600.degree. C. In the first
embodiment, the work-performing expansion takes place, in
particular, starting from the mentioned pressure level or a higher
pressure level to a pressure level of 10 to 40 bar, whereby the
temperature is in particular reduced by about 30 to 100.degree. C.
In the first embodiment, the first compression step can in
particular take place to a pressure level of 10 to 40 bar and the
second compression step to a pressure level of 30 to 70 bar. The
respective subsequent partial condensation steps in particular take
place to a temperature level of 10 to 50.degree. C. in each case.
The second portion of the refrigerant, which is ultimately supplied
to the work-performing expansion, comprises in particular 40 to 80%
of the first liquid fraction.
[0028] In the first embodiment, before its work-performing
expansion, the second portion of the refrigerant can be partially
or completely subjected to indirect heat exchange with the second
portion of the refrigerant or a part thereof (i.e., at least
partially "with itself") that has already been subjected to the
work-performing expansion, before the latter is combined with the
first gas fraction.
[0029] If the second portion of the refrigerant is only partially
subjected to the mentioned heat exchange with itself, this takes
place in the form of a first partial flow of the second portion,
whereas a second partial flow of the second portion is not
subjected to this heat exchange with itself. The first and second
partial flows can be subjected separately from one another, and in
particular at different temperature levels, to the heating using
the waste heat and can thereafter, and before the work-performing
expansion, be combined with one another again. For example, the
first partial flow of the second portion can be heated at a higher
temperature level with a turbine waste gas in a first waste heat
exchanger, wherein the already partially cooled waste gas of the
gas turbine is supplied to a second waste heat exchanger, in which
the second partial flow can be heated at a lower temperature level.
In this way, advantageous preheating for the subsequent further
heating or cooling for the subsequent feeding to the first gas
fraction after its compression can take place.
[0030] In the method according to the invention, in the first
embodiment, the second liquid fraction can be at least partially
expanded and, downstream of the first compression step, combined
with the refrigerant or a part thereof after a corresponding
cooling, before the latter is phase-separated.
[0031] In the first embodiment, a heat exchanger having a plurality
of sections or a plurality of heat exchangers can be used for
cooling the gas in indirect heat exchange with the refrigerant,
wherein the first portion of the refrigerant and the second gas
fraction or parts thereof can be further cooled to different
temperature levels and reheated after expansion. The heat exchanger
or the plurality of heat exchangers can in particular be designed
as coiled shell-and-tube heat exchangers or as soldered plate heat
exchangers or can comprise a plurality of such heat exchangers,
even heat exchangers of different types.
[0032] For example, in the first embodiment, the first portion of
the refrigerant and the second gas fraction or respectively parts
thereof (the same also applies, without explicit mention, to the
other fluids mentioned below) can be supplied at an inlet
temperature level of, for example, 10 to 50.degree. C. to the heat
exchanger designed as a coiled heat exchanger and can be cooled by
separate heat exchanger tubes. The first portion of the refrigerant
can be extracted from the heat exchanger at a first intermediate
temperature level, below the inlet temperature level, of, for
example, -20 to -60.degree. C., expanded, and fed back to the heat
exchanger on the shell side. In this case, the second gas fraction
can likewise be extracted from the heat exchanger at the first
intermediate temperature level, at which it is present in partially
condensed form. After phase separation outside the heat exchanger,
the liquid phase and the gas phase are fed back separately from one
another at the first intermediate temperature level to the heat
exchanger and further cooled by separate heat exchanger tubes. The
liquid phase is extracted at a second intermediate temperature
level, below the first intermediate temperature level, of, for
example, -70 to -100.degree. C., expanded, and fed back to the heat
exchanger on the shell side. The gas phase is extracted at a third
intermediate temperature level, below the second intermediate
temperature level, of, for example, -120 to -160.degree. C.,
expanded, and likewise fed back to the heat exchanger on the shell
side. The fluids combined in this way on the shell side are fed
back to the compression.
[0033] If a soldered plate heat exchanger is used, the first
portion of the refrigerant and the second gas fraction or
respectively parts thereof can also be supplied together at an
inlet temperature level in the aforementioned range to the heat
exchanger and cooled in common passages. After extraction at the
cold end of the heat exchanger at an extraction temperature level
of, for example, -120 to -160.degree. C., expansion can be carried
out, and the refrigerant further cooled in this way to a
temperature level of, for example, -130 to -170.degree. C. is
returned through separate passages and fed back to the compression
after heating to a temperature level in the range of the inlet
temperature level.
[0034] In a further preferred embodiment of the present invention,
hereinafter also referred to as the "second embodiment," the first
compression step can in particular be designed differently and can
be carried out using two compressor stages, namely a first
compressor stage and a second compressor stage, which are, however,
advantageously driven together by the drive that supplies waste
heat. The first compressor stage, which may also be structurally
designed in the form of a plurality of compressor stages of a
compressor, is designated throughout the figures with reference
sign C1A, the correspondingly designed second compressor stage with
reference sign C1B. The second embodiment relates in particular to
a DMR process. This process advantageously uses two or three heat
exchangers or heat exchanger sections, which can each be designed
as coiled heat exchangers or corresponding sections of a coiled
heat exchanger. Hereinafter, only for the sake of simplicity, two
or three "heat exchangers" are mentioned, which term, however, also
includes corresponding sections of a common heat exchanger. In the
language used herein, they are a first, a second, and a third heat
exchanger in the direction of decreasing temperature of the gas to
be condensed. In the embodiments with three heat exchangers, the
first and second heat exchangers use the same refrigerant at
different evaporation pressures and may therefore also be combined,
in particular in the case of low-cost systems, or the first heat
exchanger may be dispensed with in such systems. The invention also
relates to such methods and systems, even if reference is not made
separately below and the invention is described with reference to
methods and systems with three heat exchangers.
[0035] In the second embodiment, refrigerant flows evaporated
correspondingly from the first and the second heat exchanger are
supplied to the first compressor stage of the first compression
step at pressure levels of, for example, 5 to 20 bar or 2 to 10
bar. Compression to, for example, 15 to 50 bar takes place in the
first compressor stage of the first compression step; compression
to, for example, 40 to 80 bar takes place in the second compressor
stage of the first compression step. Recooling takes place in each
case downstream of the compression stages. The first or second
portions of the refrigerant previously mentioned several times is
formed from the fluid that is compressed in the first compressor
stage and that can, in addition to the specified refrigerant, also
comprise further refrigerant. The second portion thereof also in
particular comprises 40 to 80%.
[0036] The first portion is initially passed through the first heat
exchanger on the tube side and cooled there to a temperature level
of, for example, 0 to -20.degree. C. A partial flow can be expanded
downstream of the first heat exchanger and fed on the shell side
into the first heat exchanger. This partial flow in particular
represents the entire refrigerant evaporated in the first heat
exchanger. In the mentioned embodiments with only two heat
exchangers, the measures described for the first heat exchanger are
omitted. The non-expanded remainder of the first portion of the
refrigerant can be used to form a further partial flow, which can
be used in a separate further heat exchanger to cool the fluid
compressed in the second compressor stage of the first compression
step and can thereafter be fed to the first compressor stage of the
first compression step. A remainder of the first portion still
remaining thereafter is initially passed through the second heat
exchanger on the tube side and cooled in it to a temperature level
of, for example, -30 to -70.degree. C. This remainder can now be
expanded downstream of the second heat exchanger and fed on the
shell side into the second heat exchanger. This remainder in
particular represents the entire refrigerant evaporated in the
second heat exchanger.
[0037] In the second embodiment, the second portion of the
refrigerant can be essentially treated in the manner explained for
the first embodiment and can in particular be fed to the
refrigerant compressed in the first compressor stage of the first
compression step, before the latter is cooled and condensed. The
second portion is circulated in this way. The refrigerant
compressed in the second compressor stage of the first compression
step can in particular be supplied to the second compression step
and compressed there in principle as explained for the first
embodiment. In particular, compression to a pressure level of 70 to
110 bar takes place. The correspondingly compressed refrigerant is
cooled and initially guided on the tube side through the first to
third heat exchangers for further cooling. Downstream thereof, this
refrigerant portion is expanded and fed on the shell side into the
third heat exchanger. This refrigerant portion in particular
represents the entire refrigerant evaporated in the third heat
exchanger.
[0038] A yet further preferred embodiment of the present invention,
hereinafter also referred to as the "third embodiment," comprises
the first compression step being carried out using two compressors,
which are now advantageously driven by two separate drives that
supply waste heat. These are operated largely similarly to the
corresponding compressor stages in the second embodiment and
therefore bear the corresponding designations. The third embodiment
likewise relates to a DMR process. As in the second embodiment, two
or three heat exchangers or heat exchanger sections are
advantageously used so that the explanations above continue to
apply. The above features and explanations regarding the second
embodiment also relate to the third embodiment, wherein, however,
the remainder of the first portion of the refrigerant not expanded
downstream of the first heat exchanger is optionally not used to
form a further partial flow, which serves to cool the fluid
compressed in the second compressor of the first compression step.
The second portion of the refrigerant, which is ultimately expanded
in a work-performing manner, is heated with the waste heat of both
drives.
[0039] As mentioned, in the embodiments just explained, work
performed during the work-performing expansion is used in addition
to the drive in the compression of the same refrigerant, which is
also expanded in a work-performing manner and which is used to form
the first and second portions, although it is used in different
circuits in the DMR circuits. In contrast, in other embodiments of
the invention, advantages arise if work performed during the
work-performing expansion is used in the compression of a further
refrigerant, i.e., not the same refrigerant, which is expanded in a
work-performing manner and which is used to form the first and
second portions. For better differentiation, the refrigerant
expanded in a work-performing manner and used to form the first and
second portions is referred to as the "first" refrigerant, and the
further refrigerant is referred to as the "second" refrigerant.
[0040] The first to third embodiments are part of the
aforementioned first group of embodiments, in which exclusively
mixed refrigerants are used. These are SMR and DMR circuits, i.e.,
even circuits with which a mixed refrigerant is used for
precooling. A second group of embodiments, which is now explained,
comprises embodiments in which a pure refrigerant is additionally
used in a precooling circuit. These therefore include C3MR
circuits, inter alia.
[0041] In the second group of embodiments, the compression of the
pure refrigerant, which here represents a "first" refrigerant in
the sense just explained, is carried out in the precooling circuit
in a first compressor or a first compressor stage, and the
compression of the mixed refrigerant in the mixed refrigerant
circuit, which in this sense represents the "second" refrigerant,
is carried out using a second compressor or a second compressor
stage and a third compressor or a third compressor stage in the
manner explained below. The work performed during the
work-performing expansion is used to drive the third compressor or
the third compressor stage. Merely for the sake of clarity,
compressors are mentioned below, which are also to be understood as
compressor stages.
[0042] In a corresponding embodiment of the invention, hereinafter
also referred to as the "fourth embodiment," the first and second
compressors (C1A and C1B in the figures) are driven by two separate
drives, wherein only the drive of the second compressor is a drive,
such as a gas turbine, that supplies waste heat (at least to a
considerable and usable extent). The first compressor can be driven
electrically, for example, producing significantly lower (and not
usable) quantities of waste heat.
[0043] In deviation from the second and third embodiments, a
soldered plate heat exchanger and a coiled shell-and-tube heat
exchanger are used in the fourth embodiment to cool the gas to be
condensed. As mentioned, two separate refrigerant circuits are
realized, namely a pure substance circuit with pure refrigerant for
precooling and a refrigerant circuit with mixed refrigerant. As
already mentioned, the pure substance circuit comprises the first
compressor, whereas the mixed refrigerant circuit comprises the
second and the third compressors.
[0044] The pure refrigerant of the pure substance circuit is
supplied to the first compressor in a plurality of partial flows,
which are in particular heated against the mixed refrigerant from
the second compression step and thus precool the mixed refrigerant,
and compressed there. After subsequent cooling and condensing, the
first and second portions of the refrigerant are also formed here.
In distinction from the embodiments explained above, the first and
second portions are thus formed from the pure refrigerant, the
"first" refrigerant, and not the mixed refrigerant, the "second"
refrigerant. The first portion is initially cooled, subsequently
expanded, heated against the mixed refrigerant, and fed back to the
first compressor. The second portion is treated as already
mentioned above and thereby heated with the waste heat of the drive
of the second compressor.
[0045] After its precooling with the pure refrigerant of the pure
substance circuit, in particular to a temperature level of -20 to
-40.degree. C., the mixed refrigerant is cooled further on the tube
side in the coiled heat exchanger, in particular to a temperature
level of -120 to -160.degree. C. Downstream thereof, it is expanded
and supplied on the shell side to the coiled heat exchanger. After
extraction from the coiled heat exchanger and corresponding
heating, further heating is carried out in the soldered plate heat
exchanger, and compression subsequently takes place in the second
and third compressors.
[0046] A variant of the fourth embodiment just explained, referred
to as the "fifth embodiment," comprises the first and second
compressors being driven via a common drive that produces waste
heat.
[0047] In all cases, work performed during the work-performing
expansion can be used in the compression of a further refrigerant,
with which the gas is subjected to cooling in indirect heat
exchange. This may be the case, for example, when using a pure
substance or C3MR refrigerant circuit, or in variants of the first
group of embodiments.
[0048] In a further embodiment of the invention, which is referred
to herein as the "sixth embodiment," a mixed refrigerant is used as
the first refrigerant and nitrogen is used as the second
refrigerant. In this embodiment as well, the first and second
portions are portions of a first refrigerant, namely the mixed
refrigerant, and work performed during the work-performing
expansion is used in the compression of a second refrigerant,
namely the nitrogen.
[0049] In principle, in the sixth embodiment, as previously
explained, for example, for the first embodiment, the mixed
refrigerant can be at least partially subjected to a first
compression step and subsequently at least partially subjected to a
first partial condensing process to obtain a first liquid fraction
and a first gas fraction. The first gas fraction can be at least
partially subjected to the second compression step and subsequently
at least partially subjected to a second partial condensing process
to obtain a second liquid fraction and a second gas fraction. The
further treatment can also be identical.
[0050] Generally speaking, in the fifth embodiment, the nitrogen is
subjected to expansion and compression, wherein the compression of
the nitrogen takes place using the work performed during the
work-performing expansion of the second portion of the mixed
refrigerant. In the fifth embodiment, the expansion of the nitrogen
can take place in a work-performing manner, wherein work performed
during the work-performing expansion of the nitrogen can likewise
be used in the compression of the nitrogen.
[0051] The compressed nitrogen is, in succession, cooled, subjected
to a first indirect heat exchange and thereby cooled, subjected to
expansion, subjected to a second indirect heat exchange and thereby
heated, thereafter subjected to the first indirect heat exchange
and thereby heated, and fed back to the compression. In the second
indirect heat exchange, the gas subjected to the partial or
complete condensing process is supercooled.
[0052] A further embodiment of the present invention, referred to
herein as the "seventh embodiment," differs from the sixth
embodiment in that the compression of the nitrogen is carried out
in two stages in a first and thereafter a second compression step,
wherein the first compression step takes place using the work
performed during the work-performing expansion of the nitrogen and
the second compression step takes place using the work performed
during the work-performing expansion of the second portion of the
mixed refrigerant.
[0053] The invention also extends to a system for condensing a gas,
wherein the system comprises means configured to subject the gas to
cooling in indirect heat exchange with a refrigerant and, after the
heat exchange with the gas, to subject at least a part of the
refrigerant to compression using a drive that produces waste heat,
and to subsequently subject it to a partial or complete condensing
process. According to the invention, the system has means
configured, after a partial or complete condensing process, to
subject a first portion of the refrigerant to the heat exchange
with the gas and a second portion of the refrigerant, in
succession, to pressurization, to heating using the waste heat of
the drive and to work-performing expansion, and thereafter to feed
it back to the partial or complete condensing process.
[0054] Reference is expressly made to the above statements with
regard to features and advantages of a corresponding system, which
is advantageously configured to carry out a method in accordance
with the present invention and any previously explained
embodiments.
[0055] The invention is explained in more detail below with
reference to the accompanying drawings, which illustrate
arrangements in accordance with embodiments of the present
invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0056] FIG. 1 illustrates a method in accordance with an embodiment
of the invention.
[0057] FIG. 2 illustrates a method in accordance with an embodiment
of the invention.
[0058] FIG. 3 illustrates a method in accordance with an embodiment
of the invention.
[0059] FIG. 4 illustrates a method in accordance with an embodiment
of the invention.
[0060] FIG. 5 illustrates a method in accordance with an embodiment
of the invention.
[0061] FIG. 6 illustrates a method in accordance with an embodiment
of the invention.
[0062] FIG. 7 illustrates a method in accordance with an embodiment
of the invention.
[0063] FIG. 7A illustrates a variant of the method in accordance
with FIG. 7.
[0064] FIG. 8 illustrates a method in accordance with an embodiment
of the invention.
[0065] FIG. 9 illustrates a method in accordance with an embodiment
of the invention.
[0066] In the figures, elements corresponding to one another are
indicated by identical reference signs and are not explained
repeatedly for the sake of clarity. Identical elements are not
designated separately in all figures.
DETAILED DESCRIPTION OF THE DRAWINGS
[0067] FIG. 1 illustrates a method in accordance with an embodiment
of the invention with reference to a schematic process
flowchart.
[0068] The method serves to condense a gas that is supplied to the
method in the gaseous state as substance flow 1 and is provided in
condensed form as substance flow 2. An overall highly simplified
heat exchanger or cryogenic part 10 is used here for the condensing
process. In order to illustrate general applicability, the heat
exchanger part 10 is shown in highly simplified form.
[0069] Refrigerant is discharged from the heat exchanger part 10 in
the form of a heated ("warm") refrigerant flow W. Remaining
condensate is separated in a separator D1. The refrigerant of the
substance flow W is compressed in a first compression step using a
compressor C1, which is driven by a gas turbine GT1. In the gas
turbine GT1, air of an air flow A is compressed in a compressor
stage, which is not designated separately, and is combusted with
fuel F in a combustion chamber (not shown). Hot gas is expanded in
an expansion stage, which is likewise not designated separately,
and is discharged via a heat exchanger E4 for heat recovery.
Auxiliary firing using further fuel AF can also take place.
[0070] The refrigerant compressed in the compressor C1 is cooled in
a heat exchanger E1, thereby partially condensed, and subjected to
phase separation in a separator D2. The gas and liquid phases are
supplied to the heat exchanger part 10 in the form of separate
substance flows, wherein a part of the liquid phase is supplied to
the heat exchanger part 10 as the "first portion" of the
refrigerant, which was previously referred to correspondingly
several times, and a further part as the "second portion" in the
form of a substance flow R is increased in pressure by means of a
pump P1, heated in a heat exchanger E3 and thereafter in the heat
exchanger E4, then expanded in a work-performing manner in an
expansion machine X1, passed through the heat exchanger E3, and
subsequently combined with the refrigerant compressed in the
compressor C1 before its cooling.
[0071] A compressor C2 is coupled to the expansion machine X1 via a
transmission G. A mixed refrigerant in the form of a heated
refrigerant flow W1 can be supplied to the compressor C2 from the
heat exchanger part 10, so that utilization of the waste heat of
the gas turbine GT1 is possible in this way. FIG. 1 uses a further
mixed refrigerant with the refrigerant flow W1 in addition to the
refrigerant of the refrigerant flow W and thus relates to a DMR
circuit. The use of such a further mixed refrigerant is likewise
possible in all embodiments of the invention explained below, even
if in each case only one mixed refrigerant circuit, optionally with
partial circuits, is illustrated there.
[0072] FIG. 2 illustrates a method in accordance with a further
embodiment of the invention with reference to a schematic process
flowchart. In particular, FIG. 2 illustrates the heat exchanger
part 10 in more detail. The latter comprises in particular a coiled
heat exchanger 11 and a separator 12, the function of which are
explained below.
[0073] The refrigerant flow W1 in accordance with FIG. 1 or a
comparable substance flow is not provided here, so that the
specific embodiment is an SMR circuit. The refrigerant flow W is
compressed here in a first compression step using a compressor C1
and in a second compression step using a compressor C2, wherein the
first compressor C1 is driven by means of the gas turbine GT1 and
the second compressor C2 is driven by means of the work performed
in the expansion machine X1 during the work-performing
expansion.
[0074] The substance flow W is compressed in the compressor C1
downstream of the separator D1 and subsequently, after cooling in a
heat exchanger E1, is subjected to a partial condensing process in
a separator D2 to obtain a first liquid fraction and a first gas
fraction. The first gas fraction, which is not separately
designated, from the separator D2 is compressed in the second
compressor C2 and subsequently, after cooling in a heat exchanger
E2, is subjected to a partial condensing process in a separator D3
to obtain a second liquid fraction and a second gas fraction.
[0075] The first liquid fraction from the separator D2 is partially
treated in the form of the substance flow R as already explained
above. The remainder, like the second gas fraction from the
separator D2, is supplied to the coiled heat exchanger 11 in the
form of a substance flow which is not separately designated. The
specified refrigerant flows are passed through separate heat
exchanger tubes and cooled.
[0076] The first liquid fraction from the separator D2 not used in
the form of the substance flow R is extracted from the heat
exchanger 11 at a first intermediate temperature level below the
corresponding inlet temperature level, expanded and fed back to the
heat exchanger 11 on the shell side. The second gas fraction can
likewise be extracted from the heat exchanger at the first
intermediate temperature level, expanded and thereby partially
condensed, wherein, however, a phase separation into a liquid phase
and a gas phase is carried out outside the heat exchanger 11 in the
separator 12.
[0077] The liquid phase formed in the separator 12 and the gas
phase are fed back separately from one another to the heat
exchanger 11 at the first intermediate temperature level and
further cooled by separate heat exchanger tubes. The liquid phase
is extracted at a second intermediate temperature level below the
first intermediate temperature level, expanded and fed back to the
heat exchanger 11 on the shell side. The gas phase is extracted at
a third intermediate temperature level below the second
intermediate temperature level, expanded and likewise fed back to
the heat exchanger 11 on the shell side. The fluids combined on the
shell side in this way are fed back to the compression in the form
of the substance flow W.
[0078] After its work-performing expansion, the substance flow R is
combined with the refrigerant that was compressed in the compressor
C1, before the latter is cooled for the first partial condensation.
The second liquid fraction from the separator D3 is expanded via a
valve V1 and returned to the separator D2.
[0079] FIG. 3 illustrates a further embodiment of the invention
that in particular differs from the embodiment in accordance with
FIG. 2 in that a soldered plate heat exchanger 13 is provided
instead of the coiled shell-and-tube heat exchanger 11.
As illustrated here, the portion of the first liquid fraction from
the separator D2 not used in the form of the substance flow R and
the second gas fraction from the separator D3 can be supplied
together to the heat exchanger 13 and cooled in common passages. A
pump 14 boosts the portion of the first liquid fraction thus used
to the pressure of the second gas fraction, so that both fractions
can be fed together to the heat exchanger 13. After extraction at
the cold end, expansion can be carried out via a valve 15 and the
refrigerant further cooled in this way can be returned through
separate passages and, after corresponding heating, can be fed into
the separator D1 again.
[0080] FIG. 4 illustrates a further embodiment of the invention, in
which the first compression step previously carried out in the
compressor C1 is in particular designed differently and is carried
out using two compressor stages (a first compressor stage C1A and a
second compressor stage C1B). These stages are driven together by
the gas turbine GT1.
[0081] Furthermore, three heat exchangers 16, 17, 18, each designed
as a coiled heat exchanger, are used. In the language used herein,
they are a first heat exchanger 16, a second heat exchanger 17 and
a third heat exchanger 18 in the direction of decreasing
temperature of the gas 1 to be condensed. The first heat exchanger
16 may be omitted, as explained in detail above.
[0082] Correspondingly evaporated refrigerant flows are supplied
from the first and second heat exchangers 16, 17 to the first
compressor stage C1A and compressed there. An evaporated
refrigerant flow is supplied from the third heat exchanger 18 to
the second compressor stage C1B and compressed there. Recooling
takes place in each case downstream of the compressor stages. The
first and second portions of the refrigerant previously mentioned
several times are formed from the fluid that is compressed in the
first compressor stage C1A and that, in addition to the specified
refrigerant, can also comprise further refrigerant, which is
extracted from the separator also designated here with D2.
[0083] The first portion is initially passed through the first heat
exchanger 16 on the tube side and cooled there. A partial flow can
be expanded downstream of the first heat exchanger 16 and fed on
the shell side into the first heat exchanger 16. The non-expanded
remainder of the first portion of the refrigerant can be used to
form a further partial flow, which can be used in a separate
further heat exchanger E5 to cool the fluid compressed in the
second compressor stage C1B of the first compression step and can
thereafter be fed to the first compressor stage C1A of the first
compression step. A remainder of the first portion still remaining
thereafter is initially passed through the second heat exchanger 17
on the tube side and cooled therein. This remainder can now be
expanded downstream of the second heat exchanger 17 and fed on the
shell side into the second heat exchanger 17.
[0084] The second portion of the refrigerant can be treated
essentially as described above in the form of the substance flow R
and can in particular be fed to the refrigerant compressed in the
first compressor stage C1A of the first compression step, before
the latter is further cooled and condensed. The second portion is
circulated in this way.
[0085] The refrigerant compressed in the second compressor stage
C1B of the first compression step can in particular be supplied to
the second compression step with the compressor C2 and compressed
there in principle as explained for the first embodiment. The
correspondingly compressed refrigerant is cooled in a further heat
exchanger E6 and initially passed through the first to third heat
exchangers 16, 17, 18 on the tube side for further cooling.
Downstream of the last one, this refrigerant portion is expanded
and fed on the shell side into the third heat exchanger 18.
[0086] Yet another preferred embodiment of the present invention is
illustrated in FIG. 5. This embodiment comprises the first
compression step being carried out using two compressors, which are
designated here for the sake of better comparability as previously
with C1A and C1B but are now driven by two separate drives (gas
turbines) GT1A and GT1B that supply waste heat. Accordingly, the
heat exchangers E3 and E4 previously provided once are now provided
twice in the form of the heat exchangers E3A, E3B and E4A, E4B. The
second portion of the refrigerant, which is ultimately expanded in
the form of the substance flow R, is heated in this embodiment
beforehand with the waste heat of both drives GT1A and GT1B.
[0087] A further embodiment of the present invention is illustrated
in FIG. 6 and is designed in the form of a mixed circuit (e.g.,
C3MR) process precooled with a pure refrigerant.
[0088] The compression of a pure refrigerant (illustrated here by
way of example as propane C3H8) in a precooling circuit is carried
out here in a first compressor C1A, and the compression of a mixed
refrigerant in a mixed refrigerant circuit takes place using a
second compressor C1B and a third compressor C2. The work performed
during the work-performing expansion is used to drive the third
compressor C2. The first and second compressors C1A, C1B are driven
by two separate drives, wherein only the drive of the second
compressor C1B is a drive, such as a gas turbine GT1, that supplies
waste heat (at least to a considerable and usable extent). The
first compressor C1A can, for example, be driven by means of a
motor M, producing significantly lower (and not usable) quantities
of waste heat.
[0089] In deviation from the previously explained embodiments, a
soldered plate heat exchanger 19 in addition to a coiled heat
exchanger 11 is used to cool the gas 1 to be condensed. The
refrigerant of the pure substance circuit is supplied to the first
compressor C1A in a plurality of partial flows, which are in
particular heated and evaporated against the mixed refrigerant from
the second compression step and thus precool the mixed refrigerant,
and compressed there. After subsequent cooling and condensing, the
first and second portions of the refrigerant are also formed here.
The first portion is initially supercooled, subsequently heated and
evaporated against the mixed refrigerant from the second
compressor, and fed back to the first compressor C1A. The second
portion R is treated as already mentioned above and thereby heated
with the waste heat of the drive of the second compressor.
[0090] After its precooling, the mixed refrigerant is cooled
further with the refrigerant of the pure refrigerant circuit on the
tube side in the coiled heat exchanger 11. Downstream thereof, it
is expanded and supplied on the shell side to the coiled heat
exchanger 11. After extraction from the coiled heat exchanger 11
and corresponding heating, further heating is carried out in the
soldered plate heat exchanger 19, and compression subsequently
takes place in the second and third compressors C1B and C2.
[0091] A variant of the embodiment just explained is illustrated in
FIG. 7, which comprises the first and second compressors C1A, C1B
being driven via a common drive GT1 that produces waste heat.
[0092] FIG. 7A again shows a variant of the embodiment illustrated
in FIG. 7, which can, however, also be readily realized as a
variant of, for example, the embodiment shown in FIG. 6 or another
embodiment of the invention. Here, a partial flow R' of the
refrigerant flow R is not passed through the heat exchanger E3 but
through a heat exchanger E4', which is arranged downstream of the
heat exchanger E4 in the turbine waste gas flow of the gas turbine
GT1. As shown in the form of dashed but not separately designated
substance flows and heat exchangers, the precooling of the
refrigerant can also be designed differently and can in particular
comprise fewer heat exchanger stages than previously shown.
[0093] In all cases, work performed during the work-performing
expansion can be used in the compression of a further refrigerant,
with which the gas is subjected to cooling in indirect heat
exchange. This may be the case, for example, when using a mixed
refrigerant circuit precooled with a pure refrigerant, or in
further variants of the invention illustrated in FIGS. 8 and 9.
Further soldered plate heat exchangers 19A and 19B operated using a
nitrogen circuit are used in these variants.
[0094] The treatment of the mixed refrigerant results directly from
FIGS. 8 and 9 and the explanations above and essentially takes
place analogously to, for example, FIG. 3, wherein, however, the
compressors C1 and C2 are operated using the gas turbine GT1
here.
[0095] In the embodiment in accordance with FIG. 8, the nitrogen of
the nitrogen circuit is subjected to an expansion machine X2 and to
a compression in a compressor C3, wherein the compression of the
nitrogen takes place in the expansion machine X1 using the work
performed during the work-performing expansion of the second
portion of the mixed refrigerant. The expansion of the nitrogen
takes place in a work-performing manner in an expansion machine X2,
wherein work performed during the work-performing expansion of the
nitrogen is likewise used in the compression of the nitrogen. The
expansion machines X1 and X2 along with the compressor C3 are
mechanically coupled here.
[0096] The compressed nitrogen is, in succession, cooled, subjected
to a first indirect heat exchange in the heat exchanger 19B and
thereby cooled, subjected to the expansion, subjected to a second
indirect heat exchange in the heat exchanger 19A and thereby
heated, thereafter again subjected to the first indirect heat
exchange in the heat exchanger 19B and thereby heated, and fed back
to the compression. In the second indirect heat exchange in the
heat exchanger 19A, the gas previously subjected to the partial or
complete condensing process is supercooled. A heat exchanger E7 is
provided for recooling the nitrogen in the nitrogen circuit
downstream of the compressor C3.
[0097] In the embodiment in accordance with FIG. 9, which otherwise
essentially corresponds to the embodiment in FIG. 8, the nitrogen
is compressed in two stages in a first and thereafter a second
compression step in compressors C3 and C4, wherein the first
compression step takes place using the work performed during the
work-performing expansion of the nitrogen in an expansion machine
X1, and the second compression step takes place using the work
performed during the work-performing expansion of the second
portion of the mixed refrigerant in an expansion machine X2. In
this embodiment, the expansion machine X1 and the compressor C4 are
coupled on the one hand and the expansion machine X2 and the
compressor C3 are coupled on the other hand.
[0098] The invention described above and its explained embodiments
in particular shown in the figures are described again below in
other words. The terms used below may be synonymous with the terms
used above for the method steps, devices and media referred to in
each case. The following explanations describe the same inventive
concept with corresponding advantageous developments as the above
explanations in at least partially deviating formulation.
[0099] The present invention relates to a method for collecting or
recovering waste heat produced in a gas condensing process,
comprising condensing a gas by a heat exchange process using a
refrigerant fluid, compressing the spent refrigerant fluid from the
condensing process by a method that produces excess heat,
condensing at least a part of the compressed refrigerant fluid,
pumping a part of the condensed compressed refrigerant fluid to a
higher pressure, heating the part of the condensed compressed
compressed refrigerant fluid at a higher pressure by absorbing the
excess heat produced by the compression of the spent refrigerant
fluid, whereby the part of the compressed refrigerant fluid is
superheated at a higher pressure, and using the superheated
compressed refrigerant fluid to supply a mechanical process.
[0100] One embodiment of the present invention applies to a natural
gas condensing method with at least one compressor used in the
refrigerant circuit for the cryogenic process of the natural gas
condensing process. The present invention uses a compressor in the
refrigerant circuit, wherein the compressor is driven by a gas
turbine or a similar energy source that produces waste heat during
the generation of power for operating the compressor. The present
invention uses a work expander, wherein the fluid circuit for the
work expander is used to absorb the waste heat of the gas turbine
or a similar power source that drives the compressor in the
refrigerant circuit. In one embodiment of the invention, the fluid
circuit for the work expander is both pressurized and heated so
that the fluid circuit can absorb the waste heat present in the
waste gas flow of the gas turbine or other waste heat of the power
source that drives the compressor in the refrigeration circuit. The
resulting superheated fluid, which arises from the recovery process
for the waste heat energy, is then used as an energy source for the
drive of the work expander.
[0101] In a further embodiment of the present invention, the fluid
used in the fluid circuit for the work expander is also used for
the refrigerant circuit. In this embodiment of the invention, a
second compressor is additionally used in the refrigerant circuit,
wherein the second compressor is driven by the work expander.
Accordingly, in this embodiment of the invention, the refrigerant
fluid used in the cryogenic process for condensing natural gas is
also used for absorbing waste heat, which is produced for driving
the first compressor in order to provide power for driving the work
expander, which in turn drives the second compressor in order to
further compress the refrigerant fluid. Accordingly, this
embodiment of the present invention offers advantages over other
systems for collecting waste heat energy. This embodiment of the
present invention thus requires neither the introduction of
additional working liquids, such as water, nor the addition of
other liquids (e.g., steam, ammonia, propane, etc.) in closed
circuits.
[0102] In a natural gas condensing process (not illustrated) in
accordance with the prior art, with which a single mixed
refrigerant (SMR) with a two-stage SMR compression process is used,
it can be provided that two compressors C1 and C2 are driven by a
single gas turbine GT1. In this case, a cryogenic part of the
process carries out the condensing process of the natural gas by a
heat exchange process with a mixed refrigerant. In the natural gas
condensing process, the mixed refrigerant is compressed, cooled and
partially condensed before it is recycled in the cryogenic process.
Mixed refrigerant discharged by the cryogenic part can be collected
in a container D1 and is then conducted into the first compressor
C1 and the heat exchanger E1. In a corresponding two-stage
compression process, the liquid portion of the first compressor C1
and of a heat exchanger E1 is collected in a storage container D2,
wherein the vapor portion of the first compressor C1 is fed into
the second stage of the process via the second compressor C2 and a
heat exchanger E2. The resulting portion is combined from the
second compressor C2 and the heat exchanger E2 and collected in a
container D3. The two fractions collected in the containers D2 and
D3 may be fed into the cryogenic part, in order to carry out the
condensing process of natural gas by a heat exchange process.
[0103] FIG. 2 shows an embodiment of the present invention in a
natural gas condensing process in which a single mixed refrigerant
(SMR) is used with a two-stage SMR compression process. In FIG. 2,
the second compressor C2 is driven by a work expander X1 instead of
a gas turbine. The work expander X1 is driven by superheated fluid
supplied by a heat exchanger E4. The fluid discharged by the work
expander X1 is cooled by an economizer or waste heat exchanger E3
and then combined with the refrigerant produced by the first
compressor C1. The combined liquids are then further cooled by a
heat exchanger E1 or the like and collected in a container D2. A
part of the combined liquids collected in the container D2 is then
conveyed by the pump P1 to the heat exchanger E3. The cooled fluid
pumped into the waste heat exchanger E3 is heated and subsequently
conducted into the heat exchanger E4. The heat exchanger E4 is
fluidically connected to the warm waste gas of the gas turbine GT1,
which drives the first compressor C1. In this case, the heat
exchanger E4 utilizes the heat from the waste gas of the gas
turbine GT1, in order to superheat the heated liquid supplied to
the heat exchanger E4 from the heat exchanger E3. The superheated
fluid from the heat exchanger E4 is then conducted into the work
expander X1, in order to drive the second compressor C2.
[0104] In one embodiment of the present invention, the cryogenic
part can be designed with coil-wound heat exchangers (CWHEs),
soldered plate heat exchangers (PFHEs) or a combination thereof.
FIG. 3 is, for example, an illustration of an embodiment of the
present invention using a single mixed refrigerant (SMR)
configuration using soldered plate heat exchangers (PFHEs) in the
cryogenic part.
[0105] In one embodiment of the invention, which is shown in FIG.
1, a partial flow of 30 to 90% by volume of the exiting liquid
container D2 is pumped by means of the pump P1 to at least three
times the pressure in the reservoir D2. The high-pressure flow of
the pump P1 is then heated by a waste heat exchanger E3 and
supplied to the superheater E4. The superheater E4 recovers the
waste heat from the waste gas flow of the gas turbine GT1 and heats
the high-pressure flow from the waste heat exchanger E3 to at least
180.degree. C., preferably at least 200.degree. C. The hot gas from
the superheater E4 is then fed into the work expander X1 and
reduced to a pressure, which is slightly above the operating
pressure of the reservoir D2. In one embodiment of the invention,
the pressure of the flow leaving the work expander X1 is high
enough to overcome the pressure drop in the heat exchangers E3 and
E1, which still encounter the pressure in D2. The flow exiting the
work expander X1 is then cooled and condensed at least partially by
the economizer E3 and the heat exchanger E1 and subsequently
returned to the reservoir D2. The shaft power generated by the work
expander X1 is used to drive the compressor C2 to compress the
refrigerant, which is then stored in the reservoir D3 and then fed
into the cryogenic part of the process.
[0106] As explained with respect to the embodiment of the invention
shown in FIG. 1, the pressure ratio of at least three times the
suction pressure in the container D2 generated by the pump P1 leads
to a similar, only slightly lower pressure ratio in the
work-performing X1, which is a preferred working range for a
work-performing expander. In addition, the inlet pressure of the
work expander X1 can be kept below a pressure of 100 bar, which
enables a cost-effective mechanical construction. In addition, the
increased pressure generated by the pump P1 ensures that the work
expander X1 receives an inlet pressure that is significantly above
the critical pressure of the fluid, and thus avoids two-phase
effects within the fluid. In embodiments of the invention shown in
FIGS. 1 to 9, the refrigerant is used in the process for two
processes, the natural gas condensing process in the cryogenic
region and the process of recovering the waste heat produced by the
gas turbine to drive the refrigerant compression process. Further
improvements can be made in the present invention in order to
improve the performance of the present invention. For example, the
power of the work expander X1 could be increased by additionally
firing an additional heat source into the flue gas channels of the
gas turbine GT1. The work-performing expansion carried out by the
work-performing expander X1 can be divided into successive steps,
with or without the need to reheat the working fluid as
desired.
[0107] In other embodiments of the invention, the shaft power
generated by the work expander X1 could be used to drive other
processes, such as a power generator, a feed gas compression, a
terminal flash gas compression, any type of refrigerant compression
or any other service that requires power.
[0108] The entire cooling system will have at least one refrigerant
consisting of either a pure component or a mixture of components,
wherein the refrigerant in one embodiment of the invention can be
at least partially condensed at ambient temperature. In one
embodiment of the invention, the permissible refrigerant components
could include nitrogen and light paraffinic or olefinic
hydrocarbons of C1 to C5 (such as CH4, C2H4, C2H6, C2H6, C3H6,
C3H8, iC4H10, nC4H10, nC4H10, iC5H12, nC5H12, nC5H12, etc.). The
cooling system can also include more than one circuit, wherein the
additional circuits are pure refrigerant circuits and/or mixed
refrigerant circuits and/or gas expansion circuits.
[0109] FIG. 4 is an embodiment of the present invention using a
dual mixed refrigerant configuration (DMR) with three coil-wound
heat exchangers (CWHEs) in the cryogenic region and a single gas
turbine GT1 used for both mixed refrigerant circuits. As shown in
FIG. 6, the configuration decouples a high-pressure compressor C2
from the low-pressure compressors C1A, C1B, which are driven by a
common shaft, which is driven by the gas turbine GT1. This
embodiment of the present invention also eliminates the need for a
transmission that would be required to operate the compressor C2 at
a higher pressure and at a higher operating speed if the compressor
C2 has a capacity similar to that of the compressor C1A or C1B.
[0110] FIG. 5 is an embodiment of the present invention using a
dual mixed refrigerant configuration (DMR) with three coil-wound
heat exchangers (CWHEs) in the cryogenic part, wherein the
compressors C1A and C1B are driven by independent gas turbines GT1A
and GT1B, wherein the waste heat of the two gas turbines GT1A and
GT1B is used in the heat exchangers E4A and E4B to superheat the
liquid fed into the work machines X1. An advantage of the
embodiment of the invention shown in FIG. 5 is the ability to
achieve a higher power of the work expander X1 for driving the
compressor C2.
[0111] FIG. 6 is an embodiment of the present invention using a
C3MR configuration (propane-precooled mixed refrigerant) with a
single coil-wound heat exchanger (CWHEs) in the cryogenic part. In
FIG. 8, the compressors C1A and C1B are driven by independent power
mechanisms, wherein the waste heat of the gas turbine GT1, which
drives the compressor C1B, is used to superheat the fluid supplied
to the work expander X1. The embodiment illustrated in FIG. 8 would
use a suitable fluid, such as propane, propylene or other
hydrocarbons, for the precooling process. Alternatively, as shown
in FIG. 7, the compressors C1A and C1B can be driven by a common
gas turbine GT1.
[0112] In other embodiments of the invention in which the cooling
system includes more than one circuit, the additional circuits can
be pure refrigerant circuits, mixed refrigerant circuits and/or gas
expansion circuits. In addition, in other configurations, one or
more gas turbines can be operated in parallel or in series. FIGS. 8
and 9 illustrate, for example, an alternative application of the
present invention for a gas condensing process with a two-stage
cryogenic method. In the embodiments shown in FIGS. 8 and 9, a
mixed refrigerant circuit is used for precooling and condensing and
a gas expansion process is used for supercooling the natural gas in
separate stages of the cryogenic process.
[0113] In accordance with a first aspect, the present invention
comprises a method for separating waste heat produced in a gas
condensing process, comprising condensing a gas by a heat exchange
process using a refrigerant fluid, compressing the spent
refrigerant fluid from the condensing process by a method that
produces excess heat, condensing at least a part of the compressed
refrigerant fluid, pumping a part of the condensed compressed
refrigerant fluid to a higher pressure, heating the part of the
condensed compressed refrigerant fluid at a higher pressure by
collecting the excess heat produced by the compression of the spent
refrigerant fluid, whereby the part of the compressed refrigerant
fluid is superheated at a higher pressure, and using the
superheated compressed refrigerant fluid to carry out a mechanical
process.
[0114] In accordance with a second aspect, a method for recovering
waste heat produced in a gas condensing process, according to the
first aspect is provided, furthermore comprising the mechanical
process representing a further compression of the compressed
refrigerant fluid.
[0115] In accordance with a third aspect, a method for recovering
waste heat produced in a gas condensing process, according to the
first aspect is provided, wherein the mechanical process is
furthermore the operation of a work expander.
[0116] In accordance with a fourth aspect, a method for recovering
waste heat produced in a gas condensing process, according to the
third aspect is provided, furthermore comprising heating the part
of the condensed compressed refrigerant fluid at a higher pressure
by heat exchange with the fluid discharged by the work
expander.
[0117] In accordance with a fifth aspect, a method for recovering
waste heat produced in a gas condensing process, according to the
fourth aspect is provided, wherein the fluid from the work expander
used in heat exchange is furthermore combined with the condensed
compressed refrigerant fluid.
[0118] In accordance with a sixth aspect, a method for recovering
waste heat produced in a gas condensing process, according to the
third aspect is provided, furthermore comprising the mechanical
process representing a further compression of the compressed
refrigerant fluid.
[0119] In accordance with a seventh aspect, a method for recovering
waste heat produced in a gas condensing process, according to the
sixth aspect is provided, furthermore comprising the further
compression refrigerant fluid being the refrigerant fluid in the
condensing step.
[0120] In accordance with an eighth aspect, a method for recovering
waste heat produced in a gas condensing process, according to the
first aspect is provided, furthermore comprising the mechanical
method generating electrical energy.
[0121] In accordance with a ninth aspect, a method for recovering
waste heat produced in a gas condensing process, according to the
first aspect is provided, furthermore comprising heating the part
of the condensed compressed refrigerant fluid at a higher pressure,
auxiliary firing of an additional heat source into the collected
excess heat produced by the compression of the spent refrigerant
fluid.
* * * * *