Note: Descriptions are shown in the official language in which they were submitted.
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DEVICE AND METHOD FOR RECOVERING FRACTIONAL HYDRO-
CARBONS FROM RECLAIMED PLASTIC MATERIALS AND/OR FROM
OILY RESIDUES
Field of the invention:
The invention relates to a method for recovering fractional hydrocarbons
from reclaimed plastic materials and/or from oily residues, said reclaimed
plastic materials and/or residues being sorted according to type and corn-
pacted using a feed system, after which the compacted mass is fed to a
melting tank where it is heated; the invention likewise relates to a device
for carrying out the method for recovering fractional hydrocarbons from
reclaimed plastic materials and/or from oily residues.
Description of related art:
Plastics are used in almost all realms of life nowadays and they have to be
recycled and/or disposed of after being used. Disposal that takes health
aspects into account poses considerable difficulties. Plastics such as poly-
propylene (PP), polyethylene (PE) or polystyrene (PS), which consist of
long-chained macromolecules, have to be cleaved into small molecules in
order to be recycled. A conversion system can perform a low-temperature
cracking process to convert such reclaimed plastic materials into an oil-like
product containing gaseous admixtures and a solid residue.
The gas formed during the cracking process consists of a mixture of meth-
ane, ethane, ethylene, propane, propylene, 1-butene, 1-butane, 1-butene,
1-butane, pentane, etc. as well as a small residue of water vapor. The oil
obtained from polystyrene consists of over 50% styrenes and also con-
tains 2-methyl-styrenes, toluenes, ethyl benzenes and benzenes. The oil
obtained from polyethylene and polypropylene consists mainly of paraffins
and olefins, and only contains small amounts of aromatic compounds. The
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low-volatility residues consist of cokes, long-chained hydrocarbons, that
are similar to heavy oil. In a subsequent process step, the oil-like residue
can be mixed with water. In this process, an oil-water emulsion is formed
that can be used for the conversion of refuse to energy, for example, it can
be burned as fuel.
Chinese patent specification CN 1284537A describes a method for recov-
ering hydrocarbons such as gases or oils from reclaimed plastic materials,
comprising a melting and cracking process with subsequent oil-gas sepa-
ration as well as distillation of the oil mixture. For this purpose, plastic
raw
materials are melted and evaporated in a tank (melting and cracking
reactor). The plastic raw materials are heated to 280 C to 380 C [536 F to
716 F] and cracked. The drawback here is the one-stage input of the req-
uisite heat energy. Due to the high heat flow density, severe overheating
occurs in certain areas. This then leads to the formation of encrustations
that have a negative impact on the further heat input. As a result, the heat
consumption is high relative to the yield. Chinese patent specification CN
2435146Y has also disclosed a similar method.
Technical objective:
The invention is based on the objective of refining the above-mentioned
method and device in such a way that the energy input is improved and
that the efficiency of the method and of the device is improved, especially
through an optimal and systematic energy utilization and through heat
recuperation in various areas.
Disclosure of the invention and of its advantages:
This objective is achieved according to the invention by a method for
recovering fractional hydrocarbons from reclaimed plastic materials and/or
from oily residues, said reclaimed plastic materials and/or residues being
sorted according to type and compacted in the absence of air using a feed
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system, after which the compacted mass is fed to a melting tank where it
is heated, so that a separation occurs into a first liquid phase, a first gas
phase and a residue fraction, after which the liquid phase and the first gas
phase are transported into an evaporation tank in which a second liquid
phase and a second gas phase are formed under continued heat input,
whereby the second liquid phase is transferred to a re-heater and addi-
tionally heated there under further heat input so that a third gas phase is
formed, after which the second gas phase from the evaporation tank and
the third gas phase from the re-heater are conveyed to a cracking tower
where further cracking of the long-chained hydrocarbons into short-
chained hydrocarbons takes place, and the resulting oil gas is then con-
veyed to a condenser in which the oil gas is condensed to form liquid oil,
whereby the oil constitutes the target product.
In another embodiment according to the invention, the method is carried
out using a multi-circuit, indirect heating system that generates the proc-
ess heat for the melting tank, for the evaporation tank and for the re-
heater, whereby oil or salt or gas can be used as the heat-transfer
medium. For this purpose, a non-condensable fraction of the oil gas can
advantageously be fed to the heating system where it can be burned for
purposes of thermal recovery. Consequently, the heating system com-
prises all components for supplying the melting tank and the evaporation
tank with energy. The thermally recyclable by-products that are formed in
this process ¨ for instance, a fraction of an oil-water emulsion from the
residue fractions from the melting tank as well as other non-recyclable gas
fractions from the cracking tower as well as a gas fraction from a flame
overvoltage protector ¨ are advantageously used in the heating system for
generating the primary process heat.
In addition, a maximum amount of heat from the area where the oil gas
and residue are pre-cooled and from a cooling system is returned to the
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heating system. For this purpose, the condenser can consist of a pre-con-
denser and a main condenser, which can be connected to a multi-circuit
cooling system. The excess heat from the pre-condenser, main condenser
and residue pre-cooling tank is thus fed to the heating system. By the
same token, the oil-water emulsion can be fed to the heating system
where it can be burned for purposes of thermal recovery.
The method according to the invention advantageously has a low energy
expenditure as well as an optimal energy utilization through heat recu-
peration, relative to the yield. In particular, the heat circulation system
advantageously provides indirect and targeted heat in the various process
areas. In particular, the method according to the invention can utilize
reclaimed plastic materials in accordance with the waste utilization regula-
tions.
In another embodiment according to the invention, a pre-condenser and a
main condenser are used as the condenser, whereby the excess heat
from the pre-condenser, main condenser and residue pre-cooling tank is
fed to the heating system, and the main condenser is connected to a multi-
circuit condensation system.
In another embodiment according to the invention, the reclaimed plastic
materials and/or the oily residues are comminuted in a pretreatment proc-
ess after having been sorted and, if applicable, they are dried before the
cracking process is carried out. The reclaimed plastic materials are sorted
into PP, PE and PS into hard and soft plastic fractions. Since the water
fraction in the plastics should be less than 1% for energy-related reasons,
plastics with a higher water fraction should be dried first. In order to feed
the reclaimed plastic materials and/or the oily residues into the melting
tank, a tamping auger or tamping mechanism that compacts the residues
in order to remove the oxygen can be used within the feed system. By the
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same token, the reclaimed plastic materials should be fed to the tamping
auger or tamping mechanism in finely shredded form.
In another inventive embodiment of the method, the residue fraction is
transported inside the melting tank into a sedimentation compartment
located underneath where the residue fraction is concentrated and subse-
quently the concentrated residue fraction is transferred into a residue pre-
cooling tank where the residue fraction is cooled by means of a cooling
medium, preferably to a temperature below 120 C [248 F]. The cooled
residue fraction can be fed to an emulsion unit in which an oil-water emul-
sion is produced from the residue fraction.
In another embodiment of the method, a pre-condenser is arranged
between the cracking tower and the main condenser, whereby the pre-
condenser pre-cools the oil gas and recovers heat at a high temperature
level and also reduces the temperature gradient between the cracking
tower and the main condenser. Moreover, the main condenser and option-
ally the pre-condenser can be connected to a multi-circuit cooling system.
The method according to the invention is preferably carried out between
300 C and 450 C [572 F and 842 F] and between normal pressure and
overpressure of up to 2 bar.
A device according to the invention for recovering fractional hydrocarbons
from reclaimed plastic materials and/or from oily residues, said reclaimed
plastic materials and/or residues being sorted according to type, is char-
acterized by a feed system for compacting the reclaimed plastic materials
and/or the oily residues in the absence of air, as well as by a downstream
melting tank for heating and melting the compacted mass in order to cre-
ate a first liquid phase, a first gas phase and a residue fraction, whereby
an evaporation tank is arranged downstream from the melting tank in order
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to create a second liquid phase and a second gas phase under continued
heat input, said evaporation tank being upstream from a re-heater for pur-
poses of feeding and further heating the second liquid phase so as to cre-
ate a third gas phase, and a cracking tower is connected to the evapora-
tion tank and to the re-heater in order to separate the resulting oil gas from
the heavy oil as well as from non-evaporated reclaimed plastic materials,
and a main condenser is connected to the cracking tower in order to con-
dense the oil gas to form liquid oil.
In another embodiment of the device, in order to feed the reclaimed plastic
materials and/or the oily residues into the melting tank, a tamping auger or
tamping mechanism for compacting the reclaimed plastic materials and/or
the oily residues is arranged within the feed system and, if applicable, a
spherical transfer tank is located upstream from said tamping auger or
tamping mechanism for purposes of transferring material into the tamping
auger or tamping mechanism. The outlet of the tamping auger or tamping
mechanism opens into the melting tank below the liquid level of the melted
mass.
In another embodiment of the device, it has a multi-circuit heating system
for generating the necessary process heat at a temperature level that has
been optimized for this purpose, whereby oil or salt or gas serves as the
heat-transfer medium.
In another embodiment of the device, a sedimentation compartment is
arranged underneath the melting tank in order to receive the residue frac-
tion. A residue pre-cooling tank with an emulsion unit connected to it can
be arranged on the sedimentation compartment in order to produce an oil-
water emulsion from the residue fraction.
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In another embodiment of the device, the condenser consists of a main
condenser and a pre-condenser, whereby the pre-condenser is arranged
between the cracking tower and the main condenser in order to pre-cool
the oil gas. Moreover, a multi-circuit cooling system can be connected to
the main condenser.
In another embodiment, the device has a multi-circuit heating system for
generating the process heat for the melting tank, evaporation tank and re-
heater.
Furthermore, the melting tank and the evaporation tank as well as, if appli-
cable, the re-heater, have an exterior heating jacket and/or interior heating
coils, which can be heated up by means of the shared heating system for
the heat-transfer medium.
Brief description of the drawings, in which the following is shown:
Figures la, lb and lc a
processing installation distributed over three
figures, for recovering fractional hydrocarbons from
reclaimed plastic materials and/or from oily residues,
Figure 2 a feed system that has been modified as compared to that of
Figure 1,
Figure 3 a processing installation similar to that of Figures I
a, lb and
1 c, in which the heat-transfer medium circuit and the cooling
circuit are shown in greater detail,
Figure 4 another feed system of a processing installation
Figure 5 another feed system of a processing installation
having a
cooling jacket around the feed pipe and a tamping screw
jacket upstream from another melting tank,
Figure 6 another example of a main condenser and
Figure 7 another processing installation, similar to that of Figure 3.
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Preferred embodiment of the invention:
The processing installation for recovering fractional hydrocarbons from
reclaimed plastic materials and/or from oily residues, as shown in the fig-
ures, consists of a silo 1 in which the reclaimed plastic materials to be
processed are stored, preferably in the shredded state. They can also be
stored in a bunker. In order to remove the reclaimed plastic materials, a
motor-driven trough conveyor screw 2 that is designated with the letter "M"
is connected to the silo 1, and said trough conveyor screw 2 conveys the
material into a transfer tank 3, for example, a flanged spherical housing
that allows a flexible adaptation to differing local circumstances. The
transfer tank 3 is upstream from a tamping auger 4 or tamping mechanism
that compacts the reclaimed plastic materials, thereby largely expelling the
air and thus the oxygen. The lower end of the tamping auger 4 or tamping
mechanism opens into a melting tank 7, above or below its filling level. A
pneumatically actuated throttle-check fitting 5 is arranged between the end
of the tamping auger 4 or tamping mechanism and the mouth that opens
into the melting tank 7, and said throttle-check fitting 5 is upstream from a
feed fitting 6 in the form of a ball valve 6.
The lower end of the melting tank 7 has a sedimentation compartment 10
in order to receive and concentrate a residue fraction that precipitates out
of the liquid phase of the compacted mass. The sedimentation compart-
ment 10 is connected through piping to a residue pre-cooling tank 15 via
three residue discharge fittings 11, 12 and 13 arranged consecutively in a
row, said residue pre-cooling tank 15 having a cooling jacket 14 on the
outside. The residue is collected from a cooling system 34 and cooled
inside the residue pre-cooling tank 15 by means of a cooling medium,
preferably to below 120 C [248 F]. The residue is pre-cooled with the pos-
sibility of heat return into the heating system, resulting in a reduction of
the
temperature gradient between the melting tank 7 and an emulsion unit 16
located downstream.
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The cooled residue is fed through piping to the emulsion unit 16 in which
an oil-water emulsion is produced from the residue fraction by means of a
motor-driven agitator. The reduction of the temperature gradient also
reduces the necessary water seal in the emulsion unit 16, as a result of
which a higher oil concentration is possible in the oil-water emulsion and
consequently, its calorific value is raised.
The melting tank 7 has an agitator 9 for homogenizing the melted plastic
mass as well as a scraper 17 for scraping off the inner wall of the melting
tank 7 in the area of the mouth of the tamping auger 4 or tamping mecha-
nism. Moreover, the melting tank 7 is closed at the top and has a lateral
outlet A in its upper section. As a result, the bottom area of the upper tank
is very strong, thanks to the reduction in the number of openings. More-
over, the melting tank 7 is surrounded by an exterior heating jacket 8
which is constructed in such a way that the heat input is homogenous and
especially heat peaks are avoided during operation. By the same token,
the exterior heating jacket 8 allows heat discharge and condensation
before maintenance work or else in case of a breakdown.
Moreover, the melting tank 7 and the evaporation tank 20 can be fitted
with, for example, two suspended concentric tubular coils. The use of
tubular coils for heat transfer translates into a larger surface area for the
transfer.
The plastic mass is heated up inside the melting tank 7 so that a separa-
tion into a first liquid phase, a first gas phase and a residue fraction
occurs, after which the liquid phase and the first gas phase are transported
through piping via the outlet A into an evaporation tank 20 in which, under
further heat input into the mass, a second liquid phase and a second gas
phase are created. The evaporation tank 20 serves to evaporate reclaimed
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material fractions with higher evaporation temperatures. The outlet A of
the melting tank 7 or the inlet A of the evaporation tank 20 can have an
additional heating unit 18 such as an electric immersible heater that can
be followed by another intermediate heater 19 in order to increase the heat
input into the intake of the evaporation tank 20.
The heat input into the evaporation tank 20 is regulated in a controlled
manner via a heating jacket 21 and/or heating coils at a higher level than
in the melting tank 7 and the heat input goes into a reduced quantity of
plastic, resulting in a reduction in the amount of energy at the high tem-
perature level. The evaporation tank 20 also has a motor-driven agitator
22 for homogenizing the melted reclaimed material. A second liquid phase
and a second gas phase are formed inside the evaporation tank 20.
Parallel to the evaporation tank 20, a re-heating tank 23 is connected
through piping and it has its own heating unit 24, which can be an electric
heater E. The re-heating tank 23 serves to further re-heat and evaporate
an even smaller amount of reclaimed material fractions than in the evapo-
ration tank 20 at the highest evaporation temperatures of the reclaimed
material fractions, so that a third gas phase is formed there. The evapora-
tion tank 20 is closed at the bottom by means of a residue discharge fitting
25, for example, of the ball valve type, so that residues can be discharged.
The re-heating tank 23, in turn, has a drain fitting 26 at its lower end in
order to drain the re-heating tank 23.
A cracking tower 27 is mounted on the evaporation tank 20 and said
cracking tower 27 serves to break up the long-chained molecules into
short-chained molecules; the resultant oil gas is separated from the high-
boiling constituents in the cracking tower 27. The re-heating tank 23 is also
connected through piping to the cracking tower 27 so that the second gas
phase from the evaporation tank 20 as well as the third gas phase from
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the re-heating tank 23 are fed into the cracking tower 27. Via a product
gas line 28, namely, a pipeline 28, the product gas being formed in the
cracking tower can be branched off into a pre-condenser 29 that functions
as a heat exchanger in order to recover heat at a high temperature level,
so that this pre-cooling of the product gas takes place with the possibility
of heat recuperation to return to the heating system. The oil gas is then fed
to the main condenser 30 in which the oil gas is condensed to form liquid
oil.
The main condenser 30 has two cooling circuits, namely, a sump cooling
condenser 31 and a head cooling condenser 32. The main condenser 30
has an inlet line and an outlet line with a circulation pump 35 for
circulating
the oil. In the line, there are likewise two automatic fittings with a
throttle
function in order to switch over and divert the circulating flow to the main
condenser 30 or into a transfer line 37 to a separator (not shown here).
The line also has a metering point 40 as an inoculation point for metering
in additives, for example, in order to condition and stabilize the product oil
as well as to set the product properties.
The additive can also be added in the line between the cracking tower and
the main condenser.
Moreover, the main condenser 30 is connected through piping via a resid-
ual gas exhaust 39 to a heating system 38 of the processing installation,
whereby the non-condensable fraction of the product gas is bled off via the
residual gas exhaust 39 into the heating system 38 of the processing
installation for purposes of thermal recovery in the heating system.
By using the processing principle of quenching, the main condenser
achieves a very fast cooling and condensation of the hot product gas
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(shock cooling) to a mean temperature level of 80 C to 200 C [176 F to
392 F].
Cooled condensate (product oil) is used as the quenching medium. The
Consequently, an arrangement having two packed columns allows one
column to be regenerated while the other is in regular operation, whereby
in order to carry out the regeneration, the circulating flow is switched off
in
the packed column that is to be regenerated and the hot gas flow coming
condenser do not necessarily have to be arranged inside the condenser,
for example, as a sump cooling condenser and a head cooling condenser,
but rather, it is sufficient to install a heat exchanger in the line of the
circu-
lating flow.
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The heating system preferably has multiple circuits in order to generate
the necessary process heat at the temperature level optimized for this
purpose. Oil or salt or gas can be used as the heat-transfer medium in
order to transport heat at a regulatable maximum heating temperature.
The efficiency of the heating system is maximized in that heat is returned
into the system, making use of the residual gas as fuel for the heating
system. Thus, the method according to the invention can do without the
separate gas combustion and gas flares that are needed with the state of
the art. Maximum energy utilization is also ensured because, due to sev-
eral optimized temperature levels, a flexible heating of the heating system
is possible, namely, by the product oil, by the product gas and by an oil-
water emulsion as well as electrically or through a combination of the vari-
ous above-mentioned energy sources. Moreover, the occurring tempera-
ture differences, the different pressures and the different flow quantities of
the heat-transfer medium circuits can be used in order to ascertain and to
monitor the energy quantities.
Figure 2 shows a feed system that has been modified in comparison to the
one shown in Figure 1. The connection pipe of the melting tank 7 for con-
necting the tamping auger 4 or tamping mechanism is shaped here onto
the melting tank at an acute angle; otherwise, the configuration is the
same.
Figure 3 shows a processing installation that is very similar to Figures la,
lb and 1 c and in which the heat-transfer medium and cooling circuits are
shown in their entirety. The heating system 38 is divided into five heat-
transfer medium circuits, WTI to 1NT5. WTI is connected via lines to the
melting tank 7 and supplies it with heat energy; by the same token, VVT2 is
connected to the evaporation tank 20. 1NT3 and VVT4 and VVT5 are con-
nected to the pre-condenser 29, to the cooling system 34 and to the resi-
due pre-cooling tank 15, respectively.
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Figures 4 and 5 show two additional examples of different feed systems of
a processing installation according to the invention. The melting tanks 7
shown here have an upper filling vent 40 through which a feed pipe 41
passes, whose opening is below the liquid level 42 of the liquid melted
mass. In Figure 5, the feed pipe 41 and the tamping auger are additionally
surrounded with a cooling jacket 43 through which cooling water flows.
Figure 6 shows another example of a main condenser 44 of the process-
ing installation according to the invention. The hot gas enters through the
opening 45 into the main condenser 44 and flows through packing col-
umns 46 in which packings are present, for example, rings made of
stainless steel. Liquefied condensate is withdrawn from the sump 54 via a
line 47 and fed by a pump 48 to two series-connected heat exchangers 49,
50 and cooled off further, said heat exchangers 49, 50 being connected to
two cooling circuits, namely, cooling circuit I and cooling circuit II. Via a
return line 51 downstream from the second heat exchanger 50, cooled
condensate is fed in a countercurrent back to the main condenser 44, as
can be seen in Figure 6. As a result, the gas flowing through the packing
columns 46 is cooled off abruptly. Via the outlet 53 situated at the top,
which corresponds to the outlet 39 in Figure 1c, non-condensed residual
gas is either used as combustion gas or else another condenser can be
installed here by means of which any fractions of hydrocarbons still pre-
sent in the residual gas are condensed. The liquid oil, the target product of
the processing installation, is withdrawn via a branch-off line 52 down-
stream from the second heat exchanger 50 and upstream from the return
line 51.
Figure 7 differs from Figure 3 essentially only in that additional heating
coils 56, 57 are installed in the melting tank 7 as well as in the evaporation
tank 20 in order to increase the introduction of heat into the masses. As
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shown in Figure 7, in order to obtain a heat supply, these heating coils 56,
57 are connected to their own heat-transfer medium circuits, namely, WT-
circuit 1 and WT-circuit 2 of the heat-transfer medium heating system 58
which is either gas-oil-fired ¨ for example, with the residual gas from the
5 main condensers 30 or 44 ¨ or else heated electrically. When heating
coils
are used, the outer heating jacket can also be omitted.
An amount of 100 kg of dry, clean and pure reclaimed plastic materials
give rise to about 75 to 90 kg of product oil, 2 to 12 kg of residues and 2 to
10 15 kg of non-condensable gases for thermal recovery in the heating sys-
tem. The yield of product oil depends, among other things, on the types of
plastic that served as feedstock.
Commercial applicability:
15 The method or cracking method and the device according to the invention
can be used commercially in the branches of industry involved in the hygi-
enic processing in order to recover reclaimed plastic materials and/or oily
residues or plastic waste and/or oily waste.
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List of reference numerals
1 silo
2 trough conveyor screw
3 transfer tank
4 tamping auger or tamping mechanism
5 throttle-check fitting
6 feed fitting
7,39 melting tank
8,21 heating jacket
9,22 agitator
10 sedimentation compartment
11,12,13,25,26 residue discharge fittings
14,43 cooling jacket
15 residue pre-cooling tank
16 emulsion unit
17 scraper
18 heating unit of the intermediate heater 19
19 intermediate heater
20 evaporation tank
23 re-heating tank
27 cracking tower
28 pipeline
29 pre-condenser
30,44 main condenser
34 cooling system
38 heating system
53 outlets
40 upper filling vent
41 feed pipe
42 liquid level
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45 opening of the main condenser
46 packing columns
47 line
48 pump
49,50 heat exchanger
51 return line
52 branch-off line
56,57 heating coils
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Figure la
Feed system
type 1
Figure lb
WT-circuit 1
WT-circuit 2
Heat-transfer medium heating system
gas-oil-fired or electrically heated
Figure lc
Cooling circuit 1
Cooling circuit 2
Cooling system
Figure 2
Feed system
type 2
Figure 3
WT-circuit 1
WT-circuit 2
WT-circuit 3
WT-circuit 4
WT-circuit 5
Heat-transfer medium heating system
gas-oil-fired or electrically heated
Cooling circuit 1
Cooling circuit 2
Cooling system
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Figure 4
Feed system
type 3
Figure 5
Feed system
type 3
Cooling water
Figure 6
Cooling circuit 1
Cooling circuit 2
Cooling system
Figure 7
WT-circuit 1
WT-circuit 2
WT-circuit 3
WT-circuit 4
WT-circuit 5
Heat-transfer medium heating system
gas-oil-fired or electrically heated
