Note: Descriptions are shown in the official language in which they were submitted.
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TITLE OF THE INVENTION Rynamicaily controlled compressors
FIELD OF THE fl+ VENTION
[00011 The present invention relates to comp(essors. More
specifically, the present invention is concerrted with a qynamOlly controlled
compressor system and method.
, ..
BACKGROLIND OF THE INVENTION
[0002] As well known in the art, centrifugai comprossors have an
operating envelope, referred to as the compressor map, whicN is limited by a
condition calleq choke and another condition called surge
. .~ .
L0,0031 Current centrifugal compressors pump gas tinrhen operating
within the surge and choke points. If a centrifugal compressor !is left
operating
in a surge condition for any length of time, impellors thereof c~n overheat
and
damage the whole machine. Compressor manufacturers go to~ length at trying
to protect the compressor from operating in these damaging clqnditions with a
variety of surge detection devices, which, when they detect aisurge; shut the
machine down to prevent damage=
[00041 ln order to conserve energy, some more recent centrifugal
compressors have added speed control to increase its operat~ing range and in
these cases the compressors control system has become dypamic. While up
until this point, the compressors were either on or off, they h&e thus become
more intelligent and the dynamic nature of the controls causes the compressors
to react to changes in the condition. In a most recent version 1"ow, available
on
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the rnarketplace, by the present applicant, the centrifugal co~npressors may
have totally dynamic controls and continually optimizes their speed and the
positions of their inlet guide vanes to maximize their efficien4y. Up until
this
date, centrifugal compressors have been mainly single compcessor systems,
and in more recent years, when two compressors have been aglplied to the one
machine, have run in parallel and the Ioading atlq unloading hqs been through
the use of the inlet guide vanes (IGV) alone and have peen cortstrotled from
the
one controller and therefore load and unload at the same rate ot1d at the same
time.
1 b t0p45] Currentty, compressors have a compre$sor mop programmed
into a control unit thereof, to adjust their speed and when inecessary also
operate their inlet guide vanes in order to maximize their peqormance. Such
dynamic control system provides that the compressors adapi their operating
'parameters as the conditions in the system change and as the load in the
system varies
[0005] in the case of a system compnsing one qompressor, this
dynamic control of the centrifugal compressor, whereby it ac+ly changes its
speed and inlet guide vane setting to optimize its performonce at various
operating cor<ditions and capacity requirements, is,handled bK an own control
logic of the compressor.
.100071 In systems comprising at least two compressbrs, as shown in
Figure 1 illustrating a first compressor comp 1 and a second cQrnpressor comp
2 in parallel between a!ow pressure side (suction line) and !a high pressure
side (discharge line), operating conditions of the first com~ressor may be
directly effected by a change in pumping capacity of the seo6nd compressor
This may occur for example when one the compressors, afondenser or arl
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evaporaator, is not adequately sized and a pipe work to !ancl from the
compressors is not connected +n an independent fashion, or in hhe case when
multiple compressors are connected in parallel and the point of
interconnection
between the compressors is to a common point or a commom pipe and the
capacity at the conrlecting point is not adequate to compensate ficr the
changes
in the first compressor and therefore has an immediate effect on the second
compressor. (QpQ$] With the event of these compressors haying their own
intelligence, there is now a need in the art for a centrifugal comrressor
system
and methocl allowing a dynamic control of performance therebf over a wide
operating range.
SUIIAMARY OF THF tNV.ENTIOIV
[Q009] More specifically, tlnere is provided a muft,ple compressor
systern, comprising at least a first and a second compres'sors m=parallel
petween a low pressure side and a high pressure side; at loast one inertia
vessel connected to one of soction fines and discharge lines of;the at least
first
and second cbmpressors; wherein, the at least one inertia v4ssel acts as a
means of darnpening changes of operation condition of the ak least first and
second compressors.
[0010] There is further provided a method fot controlling a
compressor system including at least two compressors arranged in parallel
between a low pressure side and a high pressure side, compris'ing the step of
connecting at least one inertia vessel to at least one of: a suotion line and:
a
discharge line of at least one of the at least two compressors.
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[00111 Other objects, advantagQS and features pf thQ pre$ent
invention witl become more apparent upon reading of the,l~ following non-
restrictive description of embodlments thereof, given by way df example only
with reference to the acaampanying drawings
BRlEF DESCRIPTION OF THE DRAWlNGS
[0012] In the appended drawings:
10013] Figure 1, labelled as Prior Art, illusttjates a piping
configuration of multiple compressors piped up in parallel, as krtown tn the
art;
[4014] Figure 2 ipustrates a system according to arl embodiment of
the present invention;
.[00151 Figure 3 illustrates a system accordino to an ather
embodiment of the present invention;
[0016] Figure 4, illustrates a system accordin' to a further
embodiment of the present invention; õ
. , õ
[0017] Figures 5 illustrate altematives to the embqdirnent of Figure
4;
[0418] Figure 6 illustrates a system according to still a further
embodiment of the pmsent invention;
[0019], Figure 7 illustrates an aiternative to the emqodiment of Figure'
6; and
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[0020] Figure 8 iliustrates a system comprising multiRle compressors
piped in parallel to and from a common vessel, i.e. condenser p;nd evaporator,
which most likely does not require inertia tanks.
= !
DESCRIPTION OF EMCi[JDtMENTS OF TUE INVi=NTtON
[00211 In the case of a refrigeration system spch as in air
conditionitig unit for example, the load of the compressor varies'as a
function of
time as well as the temperatures, and therefore pressures. tnese variations
have impacts on the compressor operation and the compresspr, In response,
adjusts Its speed and inlet guide vane.
[0022] Sucth a dynamic control system may te applied to
conventional system using other types of positive dispfacemqnt compressors
su.ah as reciprocating, scroll or screw compressors for exampl?. In the case
of
an air compressor, the compressor may thus respond as tle load demand
ch'anges in the process in which it is being applied, such= as manufacturing
process.
[0023] In systems comprising at least two compres~ors, the present
invention provides an adequately sized vessel or tank in ei~her or both the
suction line or the discharge line of multiple compressors, in such a fashion
that
if the conditions of the first compressor change, it does not have an
immediate
effect on the other compressors, the vessel acting as a mead-s of dampening
the change.
[00241 Figure 2 illustrates a parallel piping systeim comprising a
header arrangement to reduce the Impact of a first compressor changes in
operation on a second compressor: a common low pres~ure tank 12 is
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connected to the suction fine and a high pressure tank 14 is c6nnected to the
discharge line of the compressors Comp 1 and Comp 2.
100251 In the parallel piping system illustrated in; Figure 3, an
expansion tank is installed in the discharge 14a, 14tv and in tCne suction
12a,
12b lines of each compressors Comp I and Comp2 to reduce tFie impact of the
change in the first compressor operation on the second compre$sor.
[ 0251 Figure 4 illustrates a system of hermetic oR semi-hermetic
compressors wherein a compressor housing, 8,16 such as iri a hermetic or
semi-hermetic compressor, is provided, which is adequately si'ed to act as an
inertia tank thus eliminating the need for extemal inertia tanks.
.[0027] . Figures 5 iltustrate a system comprising tvYo compressors
sharirlg a same housing 20 adequately sized to act as an inertia tank thus
eliminating the need for an external inertia tank. This type of sXstem may
have
one or more exit and entry ports (see Figures 5a and 5b).
100281 Figure 6 illustrates an alternative embodim~nt whete a low
and high pressure inertia tanks 22, 24 are provided, these iwtia tanks being
modular in design and connected by flanged connections or co4nections 28, 28
as provided by Victualic Inc. for example,.the inlet and oupet pipes being
connected at either end.
[0029) in Figure 7, the inlet and outlet pipes to the i~ertia tanKs may
be connected into any part of the inertia tanks. When assemqled in a modular
way, the inlet and out{et connections may be installed into t6 middle of the
siacK in order to balance the distributian of the gas and redur~e the size of
the
individual inertia tanKs.
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7 [00301 tt is to be noted that refrigerant may enter anj exit the system
from any of at least one ports.
;
[00311 En a system as illustrated in Figure 8, two compressors, a
condenser and an evaporator, piped in parallel to a common cpndenser vessel
6 32 and from a common evaporator vessel 30, the conqenser and tne
evaporator being adequately sized, inertia tanks are not generally required.
[00321 As people in the art will appreciate, the presept invention may
be used in applications where muttiple dynamically controlled pompressors are
used to replace one large compressor and where the suction and discharge
lines have to be connected to a heat exchanger through either or both the one
entry and one exit points. An example of this would be a water chiller where
there is one entry to the condenser and one exit from the evaporator. if the
compressor only required one compressor, then there would . be no problem,
however where two or more compressors are needed to obtain a required
capacity, then simply piping the compressors as is usually done in the art is:
inefficient. The connecting point of the pipe work needs to be pf adequate
size
as to not have an irnmediate effect on the other compressors: operating in the
system.
[0033} The present invention may be applied to systems comprising
more than two compressors. For example, the systems of Figures 2-8 may be
expanded by adding additional compressors either when the systems are first
installed or at a later date as required. Each of the systems may aiso have
the
capability to bepiped up with single or multiple suction and aiseharge pipes.
[00341 Although the present invention has peen described
hereinabove by way of embodiments thereof, it may be modified, without
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departing from the nature and teachings of the subject invention as described
herein.
AMEN E ~~~E7
