Note: Descriptions are shown in the official language in which they were submitted.
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lOA-68 763
A compressor assembly
The invention relates to a compressor assembly for compressing
gas, especially for operating non-stationary pressure gas con-
sumers, such as pneumatic equipment used in the construction
and building industry.
Many attempts have been made in compressor engineering at
making renewed use of process waste heat either within or
outside of the process so as to improve the energy balance and
thereby achieve a higher overall efficiency.
DE 29 12 190 A1 discloses an arrangement for generating com-
pressed air with which the exhaust gas end of a multicylinder
reciprocating piston internal combustion engine is connected
to the drive portion of an exhaust gas turbocharger. Air
aspired and compressed by a fresh air compressor of the ex-
haust gas turbocharger is supplied through an intermediate
cooler to the suction end of the internal combustion engine.
Downstream of the intermediate cooler, a line branches off
from the manifold leading to the internal combustion engine
and leads to the suction end of a small reciprocating compres-
sor. The latter is not switched on unless required and, there-
fore, is not a constant consumer of power supplied by the in-
ternal combustion engine. The pressure conduit of the recipro-
cating compressor is connected to the usual type o~ accesso-
ries of a motor vehicle which are fed with pressurized air,
for instance, the brakes, pneumatic shock absorption assembly,
door locking system, etc. By virtue of this arrangement the
reciprocating compressor can supply more compressed air of a
given pressure, whereby its operating period is reduced ac-
cordingly.
Likewise known is a method of operating a compressor by a com-
bustion engine to produce high temperature high pressure gas
(EP 0 248 640 A1) where the waste heat of the combustion en-
gine is utilized to raise the temperature of the compressed
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gas. In spite of the overall efficiency thus improved, this
mode of operation is limited to the specific case of applica-
tion and not useful for pressure gas which usually is cooled.
Furthermore, a multistage compressor is known which includes
coolers interposed between its compressing stages and forming
an integral component part of a heat pump (DE 31 34 844 A1).
In this case compression heat generated in the process is con-
verted into heat which is externally useful. Internal use is
not intended of the heat thus provided. Although this does im-
prove the energy balance of the compressor arrangement, still
external processes are required to really make use of the en-
ergy recovered. This kind of improvement of efficiency is not
convenient ~or an autonomous compressor of the type specified
initially.
This invention aims at improving the overall efficiency of
compressor arrangements, especially mobile compressor assem-
blies. The overall efficiency is meant to be the ratio between
the drive energy required and the quantity of gas compressed
at a predetermined pressure ratio.
This problem is solved, in accordance with the invention, as
recited in claim 1. The subclaims present modifications of the
invention. The invention thus relates to a compressor of any
kind, being driven by an internal combustion engine, wherein
energy contained in the exhaust gas from the internal com-
bustion engine is utilized in at least one exhaust gas turbo-
charger for primary and/or secondary compression o~ the com-
pressed gas.
The compressor in question may be a compressor of an~ desired
kind pro~ided it is suitable to compress a gas. That comprises
preferably all compressors having a variable compression cham-
ber, such as reciprocating piston and propeller compressors,
but also includes all compressors operating according to a
different principle of compression, such as turbocompressors.
The internal combustion engines in question are reciprocating
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piston engines, such as diesel and gasoline engines, and also
rotary piston engines and gas turbines of any kind which con-
vert chemical energy contained in a liquid or gaseous fuel
into mechanical energy and pass this on substantially com-
pletely to the compressor. The gas to be compressed especiall~
is air but may be any other gaseous medium adapted to be com
pressed. Suitable intermediate coolers are heat exchan~ers of
any kind as usually provided for cooling a gas, in particular
air. The coolant used may be ambient air or any other medium
suitable for cooling in open or closed systems. Suitable tur-
bochargers especially are those which comprise radial propel-
lers in the compressor and turbine portions, but any other ex-
haust gas turbocharger may also be used at higher performance
rates with multistage design, such as those having an axial
turbine runner.
In accordance with the invention, at least one exhaust gas
turbocharger is associated with a per se known compressor
which is driven by an internal combustion engine and obtains
the gas to be compressed through a filter and a suction con-
duit and feeds it through a pressure conduit into a pressure
tank. The exhaust gas turbocharger is arranged upstream and/or
downstream of the compressor for selective primary and/or se-
condary compression and is operated by the exhaust gas from
the internal combustion engine which outputs substantially all
the mechanical energy it produces to the compressor. This does
not exclude that the internal combustion engine may pass a mi-
nor part of the mechanical energy it generates to an acces-
sory, such as a l~bricant pump.
It is especially advantageous to submit the gas to be com-
pressed both to primary and secondary compression. This pro-
vides even better overall efficiency due to the lower compres-
sion ratio of each individual compression stage. Moreover, the
total efficiency is increased still further by the provision
of respective heat exchangers serving as intermediate coolers
between the individual compression stages. Thus the energy re-
.
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quirement of the compressor assembly is red~ce~ due to thefact that the temperature of the compressed gas is lowered.
Embodiments of the invention will be described in greater de-
tail below, with reference to the accompanying drawings, in
which:
Fig. 1 is a basic diagram of a compressor assembly accord
ing to the invention;
Fig. 2 shows a compressor assembly comprising an exhaust
gas tubocharger arranged upstream of the compressor;
Fig. 3 shows a compressor assembly as presented in fig. 2
in which an intermediate cooler has been inserted;
Fig. 4 shows a compressor assembly comprising an exhaust
gas turbocharger arranged downstream of the compres-
sor;
Fig. 5 shows a compressor assembly as presented in fig. 4
in which an intermediate cooler has been inserted;
Fig. 6 shows a compressor assembly comprising exhaust gas
turbochargers both upstream and downstream of the
compressor;
Fig. 7 shows a compressor assembly as presented in fig. 6
in which an intermediate cooler has been inserted;
Fig. 8 shows a compressor assembly as presented in fig. 6
in which two intermediate coolers have been insert-
ed;
Fig. 9 shows a compressor assembly with a special way of
exhaust gas conduction.
The operational diagrams presented in the drawings merely com-
prise a few of the principal structural components of a com-
prQssor arrangement, illustrating those elements which are es-
sential to the invention. The other structural members and
subassemblies needed to operate a compressor are unaffected by
the invention and may be added, as required, without having
any influence on the essence of the invention.
.
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As shown in fig. 1, a compressor 50 is connected to a per se
known internal combustion engine 40. This compressor is adapt-
ed to take up the entire mechanical energy output of the in-
ternal combustion engine, or the major part thereof, 60 as to
convert this energy into compression work. The compressor
generates a dif~erential pressure P2 between its inlet and its
outlet. The exhaust gas end o~ the internal combustion engine
40 is connected by an exhaust gas pipe 30 to an exhaust gas
turbocharger 20. Another exhaust gas pipe 32 discharges the
exhaust gas upon expansion. The compressor portion of the ex-
haust gas turbocharger 20 generates a differential pressure
Pl. Thus it is made sure that both the mechanical energy of
the internal combustion engine 40 is converted into a dif-
ferential pressure by means of the compressor 50 and the ex-
haust gas energy of the internal combustion engine 40 is con-
verted into a differential pressure by means of the exhaust
gas turbocharger 20. Consequently, by virtue of the arrange-
ment of the compressor stages in series, the total pressure
difference of the compressor assembly equals the sum of all
differential pressures, in the instant case the sum of P1 and
P2. The order of the compressor stages, in principle, makes no
difference.
With a given compressor arrangement, definable energy is re-
quired to produce a predetermined difference in pressures and
this energy may be taken as a constant magnitude from the in-
ternal combustion engine ~0. At a given quantity of energy
converted per unit time in the internal combustion engine 40,
the total efficiency of the compressor assembly according to
the invention is higher than thak of known compressor as-
semblies because of the greater compression ratio. The waste
heat created thus is utilized to advantage within the process.
According to fig. 2 the qas to be compressed is scrubbed in a
filter 10 and aspired by an exhaust gas turbocharger 21
through a suction conduit 60. Then the supercharged gas is
passed through a pressure conduit 70 to the compressor 50. The
internal combustion engine 40 serves to drive the compressor
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50. The exhaust gas from the internal combustion engine 40 is
fed through the exhaust gas pipe 30 to the exhaust gas turbo-
charger 21 and is then discharged through the exhaust gas pipe
32. From the compressor 50, the compressed gas is passed
through a pressure conduit 70 into a pressure tank 80 which is
monitored by a safety valve 81. From the pressure tank 80, the
compressed gas is passed through a pressure conduit 75 via a
pressure maintenance check valve 82 and throu~h a pressure
conduit 76 to taps 83. Fig. 3 in addition shows an interme-
diate cooler 90 inserted between the exhaust gas turbocharger
21 and the compressor 50. The intermediate cooler 90 cools the
supercharged gas and lowers the power requirement of the com-
pressor assembly. The intermediate cooler 90 communicates with
the compressor 50 through a pressure conduit 71.
i
As shown in fig. 4, an exhaust gas turbocharger 22 is disposed
downstream of the compressor 50 to subject the gas stream
leaving the compressor 50 to further or secondary compression.
The drive portion of the exhaust gas turbocharger 22 communi-
cates with the exhaust gas end of the internal combustion en-
gine 40 through an exhaust gas pipe 31. The exhaust gas, upon
expansion, is discharged through an exhaust gas pipe 33. The
exhaust gas turbocharger 22 is connected by a pressure conduit
74 to the pressure tank 80. According to fig. 5 an interme-
diate cooler 91 is arranged in addition downstream of the com-
pressor 50 so as to reduce the power requirement of the com-
pressor assembly, in analogy to fig. 3. The intermediate coo-
ler 91 communicates with the exhaust gas turbocharger 22
through a pressure conduit 73.
Fig. 6 illustrates a compressor assembly in which exhaust gas
turbochargers 21 and 22, respectively, are disposed both ahead
of and behind the compressor 50. Fig. 7 in addition shows a
compressor assembly comprising an intermediate cooler 90 down-
stream of the first exhaust gas turbocharger 21 so as to re-
duce the rate of power input, in analogy to the presentation
given in fig. 6. In addition to fig. 7, fig. 8 comprises an
interme~iate cooler 91 downstream of the compressor 50 to pro-
vide further reduction of the total rate of power inpuk intothe compressor. If desired, provision may be made for conden-
sate draining from each intermediate cooler 90 and 91.
Fig. 9 shows a compressor assembly comprising two exhaust gas
turbochargers 21 and 22 connected in series at the drive ends.
The exhaust gas from the internal combustion engine 40 in this
case first is fed to the drive end of the downstream exhaust
gas turbocharger 22. In the exhaust gas turbocharger 22 the
exhaust gas experiences partial expansion and is then passed
through the exhaust gas pipe 30 to the drive end of the up-
stream exhaust gas turbocharger 21. In the exhaust gas turbo-
charger 21 the exhaust gas experiences further expansion and
is then discharged through the exhaust gas pipe 32. This ar-
rangement has the advantage that the exhaust gas turbocharger
22, taking care of the secondary compression and thus having
to do more work, is supplied directly with the energy-rich ex-
haust gas, without any bypass losses. Subsequently the exhaust
gas, upon partial expansion, is utilized further, namely to
drive the exhaust gas turbocharger 21.
