U.S. patent application number 12/668503 was filed with the patent office on 2010-10-14 for method for the uninterrupted operation of a gas liquefaction system.
Invention is credited to Reiner Balling, Andreas Heinemann, Fritz Kleiner, Ulrich Tomschi.
Application Number | 20100257895 12/668503 |
Document ID | / |
Family ID | 39104484 |
Filed Date | 2010-10-14 |
United States Patent
Application |
20100257895 |
Kind Code |
A1 |
Balling; Reiner ; et
al. |
October 14, 2010 |
METHOD FOR THE UNINTERRUPTED OPERATION OF A GAS LIQUEFACTION
SYSTEM
Abstract
A method for the uninterrupted operation of a gas liquefaction
system is provided, wherein the operation is continuously monitored
for at least those users of the refrigerant compressor component
which represent a two-digit percentage of the total load on the
refrigerant compressor component. A total instantaneously available
negative load reserve is calculated, and at least one predetermined
turbine is switched off when the load reserve reachable via a
frequency regulation of the one or more refrigerant compressors is
lower than the energy demand of the largest of the refrigerant
compressors and either a refrigerant compressor fails or a speed of
frequency change for the power supply network for the gas
liquefaction system exceeds a present threshold.
Inventors: |
Balling; Reiner; (Erlangen,
DE) ; Heinemann; Andreas; (Hirschaid, DE) ;
Kleiner; Fritz; (Munchen, DE) ; Tomschi; Ulrich;
(Neunkirchen am Brand, DE) |
Correspondence
Address: |
SIEMENS CORPORATION;INTELLECTUAL PROPERTY DEPARTMENT
170 WOOD AVENUE SOUTH
ISELIN
NJ
08830
US
|
Family ID: |
39104484 |
Appl. No.: |
12/668503 |
Filed: |
July 8, 2008 |
PCT Filed: |
July 8, 2008 |
PCT NO: |
PCT/EP2008/058821 |
371 Date: |
June 11, 2010 |
Current U.S.
Class: |
62/611 |
Current CPC
Class: |
F25J 1/027 20130101;
F25J 1/0284 20130101; F04D 25/16 20130101; F25J 1/0298 20130101;
F04D 25/04 20130101; F25J 1/0022 20130101; F25J 2240/70 20130101;
F25J 2280/20 20130101; F25J 2230/22 20130101; F25J 2240/80
20130101 |
Class at
Publication: |
62/611 |
International
Class: |
F25J 1/02 20060101
F25J001/02 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 12, 2007 |
EP |
07013711.2 |
Claims
1.-4. (canceled)
5. A method for interruption-free operation of a gas liquefaction
plant comprising a power generation module including a plurality of
turbine sets; a transmission module providing power generated in
the power generation module to the refrigerant compression module;
a refrigerant compression module including a refrigerant compressor
and a drive motor with a rated electrical demand coupled to the
refrigerant compressor as an electrical drive for the refrigerant
compressor; and a control system, the control system being
connected to the power generation module and to the refrigerant
compression module, and in normal operation the power required for
the rated demand is provided by partial- or full-load operation of
all the turbine sets, wherein the plurality of turbine sets exceeds
a minimum plurality of turbine sets necessary to ensure continuity
of operation of the refrigerant compression module, the method
comprising: monitoring continuously the operation of at least those
consumers in the refrigerant compression module representing a two
digit percentage fraction of the total load from the refrigerant
compression module; calculating a total instantaneously available
negative load reserve; and shutting down at least one predetermined
turbine when the negative load reserve achievable by frequency
regulation of the refrigerant compressor is less than the power
demand from the largest of the refrigerant compressors and the
refrigerant compressor goes down.
6. The method as claimed in claim 5, wherein an instantaneously
available positive load reserve is calculated and a compressor
drive speed is lowered in the event of the failure of a turbine set
when the positive load reserve is less than the power provided by
the turbine set before the failure.
7. The method as claimed in claim 6, wherein at least one
predetermined electrical consumer in the gas liquefaction plant is
shut down when, after the failure of a turbine set, even a reduced
compressor speed does not enable the actual power from the turbine
sets to cover the current power demand for the refrigerant
compression module.
8. The method as claimed in claim 5, wherein predetermined loads
are shed when predefined lower threshold values for the network
frequency are reached in the power supply network for the gas
liquefaction plant.
9. The method as claimed in claim 6, wherein predetermined loads
are shed when predefined lower threshold values for the network
frequency are reached in the power supply network for the gas
liquefaction plant.
10. The method as claimed in claim 7, wherein predetermined loads
are shed when predefined lower threshold values for the network
frequency are reached in the power supply network for the gas
liquefaction plant.
11. A method for interruption-free operation of a gas liquefaction
plant comprising a power generation module including a plurality of
turbine sets; a transmission module providing power generated in
the power generation module to the refrigerant compression module;
a refrigerant compression module including a refrigerant compressor
and a drive motor with a rated electrical demand coupled to the
refrigerant compressor as an electrical drive for the refrigerant
compressor; and a control system, the control system being
connected to the power generation module and to the refrigerant
compression module, and in normal operation the power required for
the rated demand is provided by partial- or full-load operation of
all the turbine sets, wherein the plurality of turbine sets exceeds
a minimum plurality of turbine sets necessary to ensure continuity
of operation of the refrigerant compression module, the method
comprising: monitoring continuously the operation of at least those
consumers in the refrigerant compression module representing a two
digit percentage fraction of the total load from the refrigerant
compression module; calculating a total instantaneously available
negative load reserve; and shutting down at least one predetermined
turbine when the negative load reserve achievable by frequency
regulation of the refrigerant compressor is less than the power
demand from the largest of the refrigerant compressors and a rate
of change in the frequency in the power supply network for the gas
liquefaction plant exceeds a prescribed limit.
12. The method as claimed in claim 11, wherein an instantaneously
available positive load reserve is calculated and a compressor
drive speed is lowered in the event of the failure of a turbine set
when the positive load reserve is less than the power provided by
the turbine set before the failure.
13. The method as claimed in claim 12, wherein at least one
predetermined electrical consumer in the gas liquefaction plant is
shut down when, after the failure of a turbine set, even a reduced
compressor speed does not enable the actual power from the turbine
sets to cover the current power demand for the refrigerant
compression module.
14. The method as claimed in claim 11, wherein predetermined loads
are shed when predefined lower threshold values for the network
frequency are reached in the power supply network for the gas
liquefaction plant.
15. The method as claimed in claim 12, wherein predetermined loads
are shed when predefined lower threshold values for the network
frequency are reached in the power supply network for the gas
liquefaction plant.
16. The method as claimed in claim 13, wherein predetermined loads
are shed when predefined lower threshold values for the network
frequency are reached in the power supply network for the gas
liquefaction plant.
17. A gas liquefaction plant, comprising: a power generation module
including a plurality of turbine sets; a transmission module
providing power generated in the power generation module to the
refrigerant compression module; a refrigerant compression module
including a refrigerant compressor and a drive motor with a rated
electrical demand coupled to the refrigerant compressor as an
electrical drive for the refrigerant compressor; and a control
system, the control system being connected to the power generation
module and to the refrigerant compression module, and in normal
operation the power required for the rated demand is provided by
partial- or full-load operation of all the turbine sets, wherein
the plurality of turbine sets exceeds a minimum plurality of
turbine sets necessary to ensure continuity of operation of the
refrigerant compression module.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is the US National Stage of International
Application No. PCT/EP2008/058821 filed Jul. 8, 2008, and claims
the benefit thereof. The International Application claims the
benefits of European Patent Application No. 07013711.2 EP filed
Jul. 12, 2007. All of the applications are incorporated by
reference herein in their entirety.
FIELD OF INVENTION
[0002] The invention relates to a method for the uninterrupted
operation of a gas liquefaction plant, in particular a natural gas
liquefaction plant.
BACKGROUND OF INVENTION
[0003] The term liquefied natural gas (abbreviated to LNG) is
applied to natural gas which has been liquefied by cooling it. LNG
has less than 1/600.sup.th of the volume of natural gas at
atmospheric pressure, and is thus especially suitable for transport
and storage purposes; in this aggregate state it cannot be used as
a fuel.
[0004] In power plants which are upstream of a plant for the
liquefaction of light carbohydrates, such as for example natural
gas, it is conventional to make use of gas turbines fired by
natural gas and if necessary steam turbines in order to provide the
required electrical energy from the generators coupled to them,
which are motor driven.
[0005] In conventional natural gas liquefaction plants, the
turbo-compressors for the refrigerant circuit are driven by
directly coupled gas turbines.
[0006] Generic disadvantages of these plants are production down
times during the regular maintenance work which is required on the
gas turbines, difficult startup or restart of the compressors with
single-shaft gas turbines, together with the direct dependence of
the size and the power output of the refrigerant compressor on the
type-tested gas turbines themselves, the shaft output of which
depends in turn on ambient conditions which fluctuate daily or
undergo seasonal changes.
[0007] For the purpose of avoiding these disadvantages, in newer
plants the refrigerant compressor is driven by maintenance-free
variable-speed electric motors. An electric generator driven by a
gas or steam turbine supplies the electrical power for these
motors; upstream static frequency converters permit a gentle
startup and variable-speed operation. This is then referred to as
an eLNG plant (e for electric).
[0008] U.S. Pat. No. 7,114,351 B2 describes such a plant for the
provision of the electrical power for driving the refrigerant
compressor of an LNG process. By this the electrical power, for the
process of liquefying light carbohydrates in gaseous form from a
source, is provided in a first step, and in a second step a
refrigerant is compressed in a refrigerant compressor which is
driven by an electric motor which makes use of the electrical power
generated in the first step.
[0009] Electric motors supply their nominal power under various
operating conditions, which permits continuous operation of the
refrigerant compressor even under changing ambient conditions, with
a different gas, or input air to the gas turbines at different
temperatures. U.S. Pat. No. 7,114,351 B2 also explains that a gas
turbine which suddenly goes down can be replaced by one, or even
several, additional gas turbines in standby mode or by one, or even
several, turbine sets in standby mode, as applicable. However, the
disadvantage of this method is that the LNG production process has
then already failed, and it takes some hours until the refrigerant
compressor concerned has started up again and become thermally
stable. One must therefore make allowance, in particular, for
interruptions or down times, as applicable.
[0010] The applicant's publication "All Electric Driven
Refrigeration Compressors in LNG Plants Offer Advantages", KLEINER
et al, GASTECH, Mar. 14, 2005, XP-001544023, therefore proposes a
gas liquefaction plant incorporating a power generation module, a
transmission module, a refrigerant compression module and a control
system, where the power generation module has a number of turbine
sets and the refrigerant compression module has at least one
refrigerant compressor and a drive motor, coupled to the
refrigerant compressor, for driving electrically the refrigerant
compressor, the transmission module makes available to the
refrigerant compression module the power generated in the power
generation module, and the control system is connected to the power
generation module and the refrigerant compression module, where the
power necessary for the rated demand in normal operation can be
made available via the control system by partial- or full-load
operation of all the turbine sets, and the number of turbine sets
exceeds the minimum number which will ensure continuity of
operation of the refrigerant compression module.
[0011] The essential thought here is to install a turbine set which
is additional, measured against the total power demand of the eLNG
plant, in accordance with the n+1 principle. This turbine set is
not a standby turbine set. In the uninterrupted or normal state of
the plant, as applicable, all the turbine sets necessary for the
operation of the eLNG plant, including the n+1.sup.th turbine set,
work in partial-load mode, i.e. so much spinning reserve is always
maintained that it is possible to compensate for the failure of one
turbine set by the control engineering. In this situation, one or
more designated turbine sets can undertake the frequency regulation
and in the normal situation all the operational turbine sets are
equally loaded. In the event of the protective shutdown (tripping)
of a turbine or a generator, a control system (dynamic load
computer) will decide whether or not measures must be initiated for
the purpose of stabilizing the stand-alone network.
SUMMARY OF INVENTION
[0012] An object of the invention is to specify a method for the
interruption-free operation of a gas liquefaction plant.
[0013] In the inventive method for the interruption-free operation
of a gas liquefaction plant, incorporating a power generation
module, a transmission module, a refrigerant compression module and
a control system, where the power generation module has a number of
turbine sets and the refrigerant compression module has at least
one refrigerant compressor and, coupled to the refrigerant
compressor, a drive motor with a rated electrical demand, for
driving electrically the refrigerant compressor, the transmission
module makes available to the refrigerant compression module the
power generated in the power generation module, and the control
system is connected to the power generation module and the
refrigerant compression module, and in normal operation the power
necessary for the rated demand is provided by partial- or full-load
operation of all the turbine sets, where the number of turbine sets
exceeds the minimum number which is necessary to ensure the
stability of operation of the refrigerant compression module, the
operation of at least those users in the refrigerant compression
module which represent a two-digit percentage of the total load on
the refrigerant compression module is monitored, an overall
instantaneously available negative load reserve is calculated and
at least one predetermined turbine is shut down if the negative
load reserve which can be achieved by frequency regulation of the
refrigerant compressor or compressors is smaller than the power
demand of the largest of the refrigerant compressors and either a
refrigerant compressor fails or a rate of frequency change (df/dt)
in the power supply network for the gas liquefaction plant exceeds
a prescribed limit.
[0014] It is emphasized at this point that, unlike in conventional
power networks, in the case of stand-alone networks such as for
example the power generation modules of an eLNG plant, the
relationship between load and generator power is such that over 80%
of the current load is distributed across just a few individual
loads. This is not the case for conventional networks, where there
are very many individual loads with a small percentage fraction of
the total load, and the operation of the consumers is therefore not
observed or monitored.
[0015] The best way of all of achieving interruption-free operation
of the gas liquefaction plant is by operating the turbine sets in
such a way that a positive or negative power reserve which is
maintained covers the failure of the largest turbine machine,
whereby the positive power reserve covers the failure of a
generator and the negative power reserve the failure of a
motor-compressor train in the refrigerant compression module.
[0016] In the event of the failure of a turbine set, the
(rotational) speed of the compressor drive will preferably be
lowered if a previously determined overall positive load reserve is
smaller than the power which was being supplied by the turbine set
before its failure. (According to the quadratic load characteristic
curve of the turbine compressor, the power drawn from the electric
motors reduces as the cube of the rotational speed).
[0017] If the current energy demand of the refrigerant compression
module is not covered even by the reduction in the compressor drive
speed, it is expedient to switch off at least one predetermined
electrical consumer in the gas liquefaction plant (load
shedding).
[0018] The most far-reaching way of ensuring interruption-free
operation of a gas liquefaction plant when there are unwanted
shutdowns of subsidiary parts of the plant in the liquefaction
process or when predefined threshold values are reached by the
network frequency and by its rate of change, by the voltage and the
phase angle in the power supply network for the gas liquefaction
plant, is by shutting down predetermined turbines.
[0019] The most serious fault to be expected in the operation of an
eLNG plant is an unplanned failure of a turbine set in the power
generation module, i.e. in the stand-alone power plant--protective
shutdowns of compressor drives are subordinate to this in their
effects, and in the case of emergency shutdowns in the process
plant it may sometimes be impossible to maintain operation.
However, it is even possible in principle to incorporate a partial
emergency shutdown (ESD) of the process plant into the dynamic load
computer's algorithm.
[0020] Due to the elimination of maintenance work necessary on the
gas turbines in the power generation module, the duration of
interruption-free operation for a gas liquefaction plant which this
permits in principle is increased, from the previous one to two
years up to more than five years. The only remaining obstacle to
increasing the expected productive days from around 340 (the value
from historical experience of directly-driven gas liquefaction
plants) up to 365 per year is then unplanned (malfunction)
shutdowns.
[0021] When variable-speed (converter-fed) electric motors are used
and are supplied with power from a modern gas and steam (combined
cycle) power plant, the thermal efficiency of the plant increases
and the emission of greenhouse gases is reduced.
[0022] By a suitable layout of the drive facilities, the
refrigerant compressors can be started up again, after a
process-induced shutdown, within 10 to 30 minutes instead of the 8
to 12 hours for standby turbines or fixed speed electric motors
with start-up converters, without reducing the compressor load and
without burning off refrigerant.
[0023] With an appropriate layout of the supplying stand-alone
power plant, and integration of the automation systems involved
(e.g. power plant, converter drives, compressors), production from
the eLNG plant can also be kept interruption-free during a
malfunction shutdown of a generator in the power plant.
[0024] Potential dangers to personnel are reduced by the relocation
of maintenance work out of the explosion-risk process area into the
power plant area.
[0025] When variable-speed electric motors with an
application-specific layout are used, it is easier to effect
optimization for the process conditions within the limitations on
the criteria for compressor selection relating to the rotational
speed and power of the gas turbines.
BRIEF DESCRIPTION OF THE DRAWINGS
[0026] The invention will be explained in more detail by way of
example with reference to the drawings. These show, schematically
and not to-scale:
[0027] FIG. 1 the eLNG plant concept
[0028] FIG. 2 the control system's load computer algorithm for the
positive load reserve, for realizing a method in accordance with
the invention,
[0029] FIG. 3 the control system's load computer algorithm for the
reduction in the rotation speed of the compressor modules for
realizing a preferred embodiment,
[0030] FIG. 4 the control system's load computer algorithm for the
shutdown of preselected turbines, for realizing a further
embodiment,
[0031] FIG. 5 turbine utilization in the conventional power
generation module of a gas liquefaction plant,
[0032] FIG. 6 turbine utilization in the power generation module of
a gas liquefaction plant with a standby turbine,
[0033] FIG. 7 turbine utilization in the power generation module of
a gas liquefaction plant with n+1 turbines in partial-load
operation, and
[0034] FIG. 8 an alternative turbine utilization in the power
generation module of a gas liquefaction plant with n+1 turbines
DETAILED DESCRIPTION OF INVENTION
[0035] FIG. 1 shows an integrated solution for a gas liquefaction
plant 1 with a stand-alone power plant 23 as the power generation
module 2, a transfer module 3 for distributing the power and a
refrigerant compression module 4. A control system 5 is connected
to the power generation module 2, the transmission module 3 and the
refrigerant compression module 4.
[0036] The power generation module 2 incorporates three turbine
sets 6, each with a turbine 10 and a generator 12, which are
connected via a shaft 11. However, the power generation module 2
can also incorporate less than three or more than three turbine
sets 6.
[0037] The turbine sets 6 are in each case connected via an
electrical transformer 13 to the power plant busbar 15 of the
transmission module 3, which makes the electrical power available
to the motors in the refrigerant compression module 4 and/or other
consumers 26.
[0038] In the refrigerant compression module 4, the variable-speed
electric motors 8 of the refrigerant compressor 7 are actuated via
converter transformers 14 and converters 16. Drive motors 8 and
refrigerant compressors 7 are connected via shafts 17, and form
motor-compressor trains 9, which finally effect circulation of the
refrigerant and cooling of the natural gas 21 in the refrigerant
circuit 18.
[0039] FIG. 1 shows a schematic representation of the closed
refrigerant circuit 18. Refrigerant compressors 7 transport
compressed refrigerant through the lines 19 to the liquefaction
module 25. Used refrigerant in the gaseous state is fed back to the
refrigerant compressors 7 via lines 20.
[0040] FIG. 1 shows further an inlet on the liquefaction module 25
for light gaseous carbohydrates such as, for example, natural gas
21. In the liquefaction module 25 (and other similar stages, not
shown here) the natural gas 21 is transformed by cooling in heat
exchangers from the gaseous state into the liquid phase (LNG)
22.
[0041] FIG. 2 shows the inventive algorithm of a load computer in
the control system 5, for carrying out the method in accordance
with the invention, i.e. for controlling the interruption-free
operation of a gas liquefaction plant 1. For the purpose of
assessing the load conditions, the dynamic load computer receives
data 101 constantly from the power plant management system. The
data includes the instantaneous power output from each gas or steam
turbine, as applicable, the maximum instantaneously possible power
from each gas or steam turbine, as applicable, and the minimum
instantaneously possible load on each gas or steam turbine, as
applicable, expressed in each case as electrical generator power.
From the power output and the maximum instantaneously possible
power, or from the power output and the minimum instantaneously
possible load, it is possible to determine respectively the
positive or the negative load reserve.
[0042] In a first step 102, the dynamic load computer calculates
the overall instantaneously available positive load reserve, taking
into account various parameters such as, for example, the
instantaneous ambient temperature, the air humidity, and the
calorific value of the combustion gas, which are already taken into
consideration in the values 101 from the power plant management
system.
[0043] In a second step 103, the dynamic load computer calculates
the positive load reserve using the power of the largest turbine
set 6. If the total positive load reserve is sufficient to maintain
correct operation of the eLNG plant even if a turbine set 6 is shut
down, the dynamic load computer reports to the power station
maintenance staff and to the eLNG plant the status "n+1 available"
104. If, in this state, a protective shutdown actually does occur
in the power plant, the dynamic load computer remains passive, and
the power plant management system reestablishes a balance between
the available and demanded loads by reallocating the loads on the
remaining generators 12.
[0044] If the dynamic load computer determines that the
instantaneously available positive power reserve is not adequate to
compensate for any possible failure of a turbine set 6, it reports
the alarm status "n+1 not available" 105 to the maintenance office,
as a precaution.
[0045] This enables the operating staff to mobilize any power
reserves which have been shut down (e.g. for maintenance work), or
to reduce the load on the network, e.g. by shutting down other
consumers 26, and thereby to prevent any interruption in production
if a turbine set 6 goes down. Manual load reallocation between the
operational turbine sets 6, and changes in the process steam
consumption, are also suitable for this purpose.
[0046] If a precautionary load reduction is not initiated by the
operating staff of the eLNG plant, e.g. by shutting down
unimportant consumers 26 or by a temporary reduction in production,
the dynamic load computer can intervene, in that it temporarily
reduces the speed of all the operational compressor drives to a
value which ensures the stability of the compressor, and thereby
guarantees the freedom from interruption of the production. For
this purpose the data 106 received from the compressor management
system, about the load reductions which are instantaneously
possible from reducing the compressor speed without endangering the
stability of the compressor operation, is continuously processed
and the sum of the possible load reductions for the individual
compression modules is added to the positive load reserve 107. The
overall load reserve thereby achieved may then possibly cover the
failure of a turbine set 6.
[0047] In the alarm status "n+1 not available" it is then possible
to reestablish the balance between positive and negative load
reserves by a lowering of the compressor drive speed. Since this
operation can be effected very quickly, it will only be initiated
by the dynamic load computer if a protective shutdown in the power
plant actually does take place in the alarm state.
[0048] The associate algorithm is shown in FIG. 3. As already
explained, 107 indicates the sum of the positive load reserve of
the turbine sets 6 and the possible load reduction resulting from a
reduction in the speed of the compressor modules. In the next step
108, the positive load reserve and the possible load reduction are
compared with the instantaneously available power of the largest
turbine set 6. Independently of the result of this comparison, if
there is a failure 109 of a turbine 10, the conjunction 110 is
true, and the speed of the compressor modules will be reduced 111.
If the sum of the positive load reserve and the possible load
reduction is less than the power of the largest turbine set 6, or
at least the one concerned, there will in addition be load shedding
112.
[0049] Apart from the computational determination of the difference
between the positive and the negative load reserve, it is possible
to use an independent determination of the rate of change of the
network frequency (df/dt) for the purpose of recognizing a sudden
change in the load conditions--without regard for its cause. The
rate of change of the frequency is proportional to the step change
concerned in the load, and can thus be used to determine the
necessary protective shutdowns.
[0050] Since a change in frequency is a direct consequence of the
event which triggers it, and the determination of the rate of
change requires more time than a protective shutdown via the direct
shutdown signals, any action based on the calculated frequency
change might come too late. For this reason, this function can be
regarded as a backup to the direct shutdown described. Apart from
this, it is necessary to ensure that actions resulting from the
computational determination of the lower frequency do not cause any
spurious tripping.
[0051] If the measures described are not sufficient to balance out
the difference between the positive and negative load reserves, the
dynamic load computer initiates a chain of preprogrammed load
shedding when a predefined lower frequency threshold is reached, in
order to prevent a further fall in the network frequency--and with
it a protective shutdown of the entire power plant. The consumers
recorded in the load computer, which can if necessary be switched
off at times without interrupting production, are disconnected from
the network as quickly as is required, and to the necessary extent,
to maintain the network frequency.
[0052] In principle, the algorithm applied to the unplanned
shutdown of turbine sets 6 can also be applied to the unplanned
shutdown of large consumers, primarily the large compressor drives.
The layout of the management system for the power plant and
machines is such that it can compensate for load shedding of this
magnitude without the involvement of the dynamic load computer.
FIG. 4 shows the principle. If the total of the negative load
reserve which can be achieved by frequency regulation is larger
than the largest load shedding to be assumed from shutting down
compressor drives, the dynamic load computer will not intervene.
Otherwise, a preselected turbine set 6 will be shut down, and the
resulting positive load reserve balances out the remaining gap.
[0053] Here, 113 identifies the calculation of the negative load
reserve and the determination of the compressor modules with the
largest load. In step 114, these two values are compared. If the
negative load reserve is larger than the larger load from the
compressor modules, the computer reports the status "n+1 available"
115. Otherwise it reports "n+1 not available" 116.
[0054] Using the data from the power plant management system 101
and from the compressor management system 106, an assignment 117 of
turbine sets 6 and compression modules is effected. With the help
of this assignment, preselected turbines 10 are shut down if the
negative load reserve is less 116 than the power demands of the
largest compression modules and 124 either one compression module
goes down 122 or 123 the rate of change of the frequency 120 in the
power supply network for the gas liquefaction plant 1 exceeds 121 a
prescribed limit.
[0055] In the case of even larger load shedding 126, e.g. in the
case of partial emergency shutdowns of the process, it may be
necessary to take several turbine sets 6 out of the network 128. If
the sequence and the scale 118 of such an emergency shutdown is
known, such a procedure can also in principle be controlled by the
load computer, e.g. in that a preselection 119 is made of turbines
10 which are to be shut down, in order possibly to enable operation
of a sub-process to continue. Large load shedding 126 and the
exceeding 121 of a limit for the rate of frequency change 120 are
combined together logically in the sense of a non-exclusive
disjunction 127.
[0056] FIG. 5 shows schematically the turbine utilization in a
conventional power generation module of a gas liquefaction plant 1,
operating as rated. All the turbines 10 of the power generation
module run under nominal full load 27. The power generation module
operated in this way provides no positive load reserve to ensure
interruption-free operation of the complete gas liquefaction plant
is possible in the event of a failure of a turbine set 6.
[0057] FIG. 6 shows schematically the turbine utilization, in the
power generation module of a gas liquefaction plant operating as
rated, described in U.S. Pat. No. 7,114,351 B2. The additional
turbine 24, kept ready on standby, is started up in the event of a
failure of another turbine 10 running under full load when the gas
liquefaction plant is operating as rated. Interruptions and down
times can be the consequence in the LNG production process in the
event of the failure of a turbine 10, and it can take a few hours
until the refrigerant compressor 7 which is affected has been
started up again and the liquefaction process has stabilized
thermally.
[0058] FIG. 7 shows schematically and by way of example the turbine
utilization in the power generation module 2 of a gas liquefaction
plant as described in the applicant's publication "All Electric
Driven Refrigeration Compressors in LNG Plants Offer Advantages",
KLEINER et al, GASTECH, Mar. 14, 2005, XP-001544023 when the
refrigerant compression module 4 is operating as rated. All the
turbines 10 run under partial load 28. There is no standby turbine
24. The positive load reserve is adequate to ensure
interruption-free operation of the gas liquefaction plant 1, if a
turbine 10 fails, by raising the load on the remaining turbines
10.
[0059] FIG. 8 shows schematically and by way of example an
alternative turbine utilization in the power generation module 2 of
a gas liquefaction plant as described in the applicant's
publication "All Electric Driven Refrigeration Compressors in LNG
Plants Offer Advantages", KLEINER et al, GASTECH, Mar. 14, 2005,
XP-001544023 when the refrigerant compression module 4 is operating
as rated. All the turbines 10 run under partial- or full-load
28,27. Here again there is no standby turbine 24. However, the
utilization of the turbines 10 is not necessarily the same. Apart
from other parameters it is possible, for example, to take into
account the operating life of turbines 10 in determining their
utilization on a machine-specific basis.
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