U.S. patent application number 14/674319 was filed with the patent office on 2015-10-01 for method for automatically controlling a vapor content of a working medium heated in a vaporizer of a system for carrying out a thermodynamic cycle, control unit for a system, system for a thermodynamic cycle, and arrangement consisting of an internal combustion engine and a system.
The applicant listed for this patent is MTU Friedrichshafen GmbH. Invention is credited to Gerald FAST, Tim HORBACH, Max LORENZ, Mathias MULLER, Jens NIEMEYER, Daniel STECHER, Niklas WAIBEL.
Application Number | 20150275699 14/674319 |
Document ID | / |
Family ID | 52780743 |
Filed Date | 2015-10-01 |
United States Patent
Application |
20150275699 |
Kind Code |
A1 |
WAIBEL; Niklas ; et
al. |
October 1, 2015 |
METHOD FOR AUTOMATICALLY CONTROLLING A VAPOR CONTENT OF A WORKING
MEDIUM HEATED IN A VAPORIZER OF A SYSTEM FOR CARRYING OUT A
THERMODYNAMIC CYCLE, CONTROL UNIT FOR A SYSTEM, SYSTEM FOR A
THERMODYNAMIC CYCLE, AND ARRANGEMENT CONSISTING OF AN INTERNAL
COMBUSTION ENGINE AND A SYSTEM
Abstract
A method for automatically controlling a steam content of a
working medium heated in an evaporator of a system for carrying out
a thermodynamic cycle with the following steps: carrying out a
phase separation for the working medium downstream from the
evaporator, wherein liquid components are separated from vapor
components of the working medium; conducting the separated liquid
components to a reservoir; determining a level in the reservoir;
and varying a control variable for automatically controlling the
steam content as a function of the level.
Inventors: |
WAIBEL; Niklas;
(Friedrichshafen, DE) ; STECHER; Daniel;
(Pfulldendorf, DE) ; NIEMEYER; Jens;
(Friedrichshafen, DE) ; LORENZ; Max;
(Friedrichshafen, DE) ; HORBACH; Tim;
(Friedrichshafen, DE) ; FAST; Gerald; (Markdorf,
DE) ; MULLER; Mathias; (Friedrichshafen, DE) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
MTU Friedrichshafen GmbH |
Friedrichshafen |
|
DE |
|
|
Family ID: |
52780743 |
Appl. No.: |
14/674319 |
Filed: |
March 31, 2015 |
Current U.S.
Class: |
60/615 ; 60/651;
60/667; 60/671 |
Current CPC
Class: |
F01K 7/165 20130101;
F01K 25/10 20130101; Y02E 20/14 20130101; F01K 23/065 20130101;
F01K 13/02 20130101 |
International
Class: |
F01K 23/06 20060101
F01K023/06; F01K 7/16 20060101 F01K007/16; F01K 25/10 20060101
F01K025/10; F01K 13/02 20060101 F01K013/02 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 31, 2014 |
DE |
10 2014 206 012.5 |
Claims
1. A method for automatically controlling a steam content of a
working medium heated in an evaporator of a system for carrying out
a thermodynamic cycle, comprising the steps of: carrying out a
phase separation for the working medium downstream from the
evaporator, wherein liquid components are separated from vapor
components of the working medium; conducting the separated liquid
components to a reservoir; determining a level in the reservoir;
and varying a command variable to control the steam content
automatically as a function of the level.
2. The method according to claim 1, including varying a mass flow
of the working medium in the system as a function of the level.
3. The method according to claim 2, including determining a change
in the level in the reservoir, and varying the mass flow is varied
as a function of the change in level.
4. The method according to claim 2, wherein the mass flow is varied
by variation of an output of a conveying device, wherein the
conveying device is used to convey the working medium in the
system.
5. The method according to claim 1, wherein a pressure and/or a
temperature of the working medium downstream from the evaporator
and/or upstream from a separation device and/or upstream of an
expansion device of the system is determined and used as input for
the automatic control of the steam content.
6. The method according to claim 1, wherein the automatic steam
content control is calibrated by operating the system on or beyond
a saturated steam curve of the working medium and by intentional
deviation from the saturated steam curve into a wet steam
region.
7. The method according to claim 1, wherein a withdrawal of liquid
from the reservoir is used as an input for the automatic steam
content control.
8. A control unit for a system for a thermodynamic cycle, wherein
the control unit is set up to carry out a method for automatically
controlling a steam content of a working medium heated in a
evaporator of the system according to claim 1, wherein the control
unit is operatively configured to determine a level in a reservoir,
which is located downstream from the evaporator and is connected to
a separation device, and to vary a command variable for
automatically controlling the steam content as a function of the
level.
9. A system for a thermodynamic cycle, comprising a control unit
according to claim 8.
10. The system according to claim 9, wherein the system comprises a
evaporator, a separation device, an expansion device, a condenser,
and a conveying device for the working medium, arranged in series
in a flow direction of the working medium through a circuit,
wherein a reservoir, to which liquid components of the working
medium separated in the separation device are conducted, is
connected to the separation device.
11. The system according to claim 9, wherein the expansion device
is configured as a helical screw expander.
12. The system according to claim 9, wherein the system is arranged
to use waste heat of an internal combustion engine.
13. An arrangement, comprising: an internal combustion engine; and
a system for a thermodynamic cycle according to claim 9.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] The present application claims priority of DE 10 2014 206
012.5, filed Mar. 31, 2014, the priority of this application is
hereby claimed and this application is incorporated herein by
reference.
BACKGROUND OF THE INVENTION
[0002] The invention pertains to a method for automatically
controlling a vapor content of a working medium heated in a
evaporator of a system for carrying out a thermodynamic cycle, to a
control unit for a corresponding system, to a system for a
thermodynamic cycle, and to an arrangement with an internal
combustion engine and a system.
[0003] Thermodynamic cycles of the type in question here are known.
A working medium is conveyed through a circuit by a conveying
device, wherein the medium is vaporized in a evaporator and sent to
an expansion device, wherein it performs mechanical work. The
expanded working medium is cooled in a condenser and thus
condensed, after which it is sent back to the evaporator by the
conveying device. A typical example of a thermodynamic cycle of
this type is the Clausius-Rankine cycle. Very similar to it is the
organic Rankine cycle (ORC), which, because of the lower
temperature level in the evaporator thanks to the use of an organic
working medium, is especially adapted to the use of waste heat in
stationary applications such as geothermal power plants or to the
use of the waste heat of an internal combustion engine. Whereas, in
classical steam-powered machines and/or steam power plants, the
steam is usually superheated after the vaporization of the working
medium, so that dry steam can be expanded in the expansion device,
it has been found, especially in conjunction with the use of waste
heat and with the ORC process, that it can be advantageous to
operate in the wet steam region. To ensure that the process can be
carried out in stable fashion, however, it is necessary to work
with a defined steam content, which means in particular that this
content must be automatically controlled. The working medium is
typically vaporized at a constant pressure and a constant
temperature. There is thus no clear correlation between these
variables on the one hand and the steam content on the other. It is
therefore impossible to determine the quality of the steam directly
by means of the rudimentary measuring techniques which would
normally be present in any case. It is possible to make use of
capacitive moisture measurements to determine the steam content,
but this approach is complicated and expensive.
SUMMARY OF THE INVENTION
[0004] The invention is based on the goal of creating a method for
automatically controlling a steam content, namely, a method which
is easy to carry out and at the same time allows stable and
accurate control. The invention is also based on the goal of
creating a control unit for carrying out a process of this type, a
system for a thermodynamic cycle which can be automatically
controlled by means of such a method, and an arrangement consisting
of an internal combustion engine and a system of this type.
[0005] The goal is achieved in a method in which a phase separation
is carried out for the working medium downstream from the
evaporator. Liquid components are therefore separated from the
vapor components of the working medium. The separated liquid
components of the working medium are conducted to a reservoir, and
the level reached in the reservoir is determined. As a function of
this level, a control variable is adjusted to control the steam
content. This means that the level of the separated liquid working
medium is used as the measurement value for the automatic control
process, which ultimately represents the indirect control of the
wet steam content. Because the amount of liquid separated during
the phase separation step will be larger or smaller as a function
of the steam content of the wet steam generated in the evaporator,
it is possible, by determining the level in the reservoir, to infer
the steam content. This content can thus be determined very easily
and without complicated and expensive measuring devices. The
automatic control method makes it possible to achieve robust
control behavior especially in the face of changes in the boundary
conditions and/or disturbances, wherein the reaction of the
thermodynamic state of the process always occurs reliably within
the wet steam region. This applies above all to load changes in the
system, which will therefore never lead outside the wet steam
region, which means that the process as a whole remains stable.
This also makes partial load control easier to implement, and the
behavior of the system when the load increases quickly is improved.
This is especially important in conjunction with the use of waste
heat of an internal combustion engine, where the operating state of
the system changes as a function of the operating state of the
engine, because the exhaust gas temperature and thus the amount of
heat available depend on the operating state of the internal
combustion engine. Depending on the manner in which the internal
combustion engine is being used, load changes occur more or less
frequently and at more or less regular intervals. Against this
background, stable automatic control of the steam content makes it
possible for the first time to operate the process in the wet steam
region, which in turn makes it possible to increase the power yield
of the system, especially when this is configured as an ORC
system.
[0006] The possibility of operating the system, i.e., the cycle, in
the wet steam region offers additional advantages with respect to
long-term service life and/or component stress: Larger wetted
surfaces in the evaporator prevent inhomogeneous temperature
distributions in the area of the evaporator wall, which
considerably reduces the thermal load on the material of the
evaporator. At the same time, the wetting prevents oil from being
coked in the evaporator. In addition, the fluid-dynamic stability
of the process is increased: As a result of operation in the wet
steam region, the phase discontinuity in the evaporator occurs at a
later point, which means a smaller gas volume and a slower flow
rate in the evaporator. Associated with this is a reduced pressure
loss, as a result of which ultimately the tendency to develop
fluid-dynamic instabilities, especially a tendency to develop the
Ledinegg instability, is decreased. Finally, the amount of
circulating lubricant provided to lubricate the expansion device
can be reduced, because the circulating lubricant has less of a
tendency to form deposits in dead volumes and on the walls of the
system. The lubricant is washed away by the liquid components of
the working medium and transported further along the circuit. The
liquid components therefore have an advantageous washing effect, so
that ultimately a greater amount of lubricant can be circulated
permanently through the system while at the same time the total
amount of lubricant can be reduced.
[0007] The advantageous effects of automatic wet steam control with
respect to the service life of the system components are important
criteria in particular for so-called off-road applications, that
is, couplings of the system with an internal combustion engine for
use of its waste heat in areas separate from conventional highway
traffic such as in stationary systems or in special types of
vehicles, so that the acceptance of this type of waste heat use is
considerably increased by the method proposed here.
[0008] The phase separation for the working medium is preferably
carried out directly downstream from the evaporator, especially
upstream of the expansion device. Thus it is possible to control
the fresh steam content at the evaporator outlet very precisely,
wherein at the same time saturated steam as free as possible of
liquid components is sent to the expansion device.
[0009] An embodiment of the method is especially preferred in which
an ORC process is carried out. In this type of process, the
advantages of the method are realized in a special way, wherein the
process at the same time is especially adapted to the use of waste
heat, especially to the use of the waste heat of an internal
combustion engine. In a preferred embodiment of the method, ethanol
is used as the working medium. Other organic working media are also
possible, of course.
[0010] It is possible for the level in the reservoir to be
determined intermittently, that is, at certain times. Under certain
conditions this can be sufficient for the stable automatic control
of the steam content. As an alternative, it is preferable, however,
for the level in the reservoir to be determined, especially
monitored, at all times. In this way, the automatic control of the
steam gas can be carried out with particular precision.
Intermittent determination, however, leads to a less complicated
method and therefore offers certain cost advantages.
[0011] A preferred embodiment of the method is characterized in
that a mass flow of the working medium in the system is varied as a
function of the level. The mass flow of the working medium in the
system is, to this extent, used as a control variable. This makes
it possible to regulate the steam content very efficiently and
precisely. It has been found that the pressure at the evaporator
outlet is essentially dependent on the mass flow on the one hand
and on the rotational speed of the expansion device on the other.
When the amount of heat entering the system increases because, for
example, an internal combustion engine coupled to the system comes
under load and its exhaust gas temperature increases, there is a
tendency for the fresh steam to become a superheated, wherein the
temperature at the evaporator outlet increases at the same time.
The pressure and/or the volume flow rate in front of the expansion
device also increases. Simultaneously, the level in the reservoir
either falls, increases with at least a reduced separation rate, or
remains constant. The level falls especially when working medium is
being withdrawn continuously from the reservoir. In any case, the
level changes, or the change in level is different, which means
that the change in the steam content can be determined. The mass
flow in the system is then increased so that the increased amount
of heat can be absorbed while keeping the steam content as constant
as possible. If, conversely, the amount heat being supplied to the
evaporator falls, because, for example, the load on the internal
combustion engine decreases significantly, thus leading to a drop
in the exhaust gas temperature, the steam content falls
simultaneously. As a result, more liquid is separated, and the
level in the reservoir rises. In this case, the mass flow in the
system is reduced and thus adapted to the smaller amount of
available heat.
[0012] Within the scope of the method, preferably the steam content
at the evaporator outlet is regulated. In particular, this
corresponds to a regulation of the wet steam at the evaporator
outlet. The steam content is preferably regulated automatically to
match a constant, previously determined value. What this regulation
preferably does, therefore, is to maintain a constant steam
content.
[0013] Another embodiment of the method is characterized in that a
change in the level in the reservoir is determined, wherein the
mass flow is varied as a function of the change in level. This
takes into account the knowledge that the absolute level of the
reservoir, in and of itself, typically says little about the steam
content. In contrast, an increase in the level in the reservoir
indicates an increase in the separation of liquid components and
thus a decrease in the steam content, whereas a decrease in the
level--as working medium is being withdrawn continuously from the
reservoir--or a reduction in the separation rate and possibly even
a constant level indicates an increase in the steam content. To
this extent, a method is also preferred in which the rate at which
the level changes is determined and evaluated with respect to the
steam content or a change in the steam content. On this basis, it
is possible to achieve an especially precise automatic control of
the steam content.
[0014] Another embodiment of the method is characterized in that
the mass flow is varied by variation of an output of a conveying
device, wherein the conveying device is used to convey the working
medium in the system. In this way, the mass flow can be varied
directly, very precisely, and easily. A pump is preferably used as
the conveying device, especially a feed pump. To vary the mass
flow, preferably the rotational speed of the pump, especially of
the feed pump, is varied. A further embodiment of the method is
characterized in that a pressure and/or a temperature of the
working medium is determined downstream from the evaporator and
used as input for the automatic control of the steam content.
According to one embodiment of the method, therefore, it is
provided that the pressure of the working medium is determined
downstream from the evaporator, preferably directly downstream from
the evaporator, in particular at the evaporator outlet, and used as
input for the automatic control. Alternatively or in addition, it
is provided that a temperature of the working medium downstream
from the evaporator, especially directly downstream from the
evaporator, preferably at the evaporator outlet, is determined and
used as input for the automatic control. By determining or
acquiring at least one of these measurement variables, the
thermodynamic state of the working medium downstream from the
evaporator and upstream of the expansion device, especially at the
evaporator outlet, can be determined.
[0015] Under certain circumstances, this allows, in and of itself,
conclusions to be drawn concerning the steam content. In
particular, it is thus possible under certain conditions to
determine a superheating of the working medium at the evaporator
outlet. In any case, the accuracy of the automatic control can be
increased by combining the determination of the level, especially
the determination of a change in the level, with the evaluation of
the pressure and/or the temperature of the working medium
downstream from the evaporator.
[0016] Alternatively or in addition, it is possible to determine
the pressure and/or the temperature of the working medium upstream
of a separation device, which is provided to separate liquid
components of the working medium from the vapor components. The
pressure and/or the temperature is preferably determined directly
in front of the separation device. Alternatively or in addition, it
is possible for the pressure and/or the temperature of the working
medium to be determined upstream of an expansion device of the
system, especially directly in front of the expansion device.
[0017] Another embodiment of the method is characterized in that
the automatic control of the steam content is calibrated by
operating the system on or beyond the saturated steam curve of the
medium and by intentional deviation from the saturated steam curve
into the wet steam region. The phrase "beyond the saturated steam
curve" means that the working medium is superheated, so that dry
fresh steam is produced. The reservoir is preferably completely
emptied prior to the calibration, so that no liquid is present in
the reservoir. For the calibration, preferably pure working medium
without any lubricant components in the circuit of the system is
used. The system is then operated initially on or beyond the
saturated steam curve, wherein no liquid components of the working
medium separate in the reservoir. By intentional deviation of the
operating state of the system from the saturated steam curve into
the wet steam region, it is then possible to determine how the
level in the reservoir changes when the steam content changes in a
defined manner. The data on the level and/or on the change in level
in the reservoir as a function of the absolute and/or changing
steam content thus acquired are preferably used as input for
drawing up a characteristic diagram, which is then used later for
automatic control during operation of the system.
[0018] Alternatively it is also possible for the calibration to be
carried out when the system is operating with a mixture of working
medium and lubricant. It is possible to include the lubricant
separating in the reservoir during the operation of the system in
the data used to draw up the characteristic diagram. This can
increase the accuracy of the calibration and ultimately also the
accuracy of the automatic control.
[0019] In another embodiment of the method a withdrawal of liquid
from the reservoir is used as input for the automatic control of
the steam content. Liquid is withdrawn from the reservoir, first,
to prevent the reservoir from overflowing. Liquid is therefore sent
back, preferably continuously, from the reservoir to the circuit of
the working medium. Exact knowledge of the amount of liquid
withdrawn makes possible the precise automatic control of the steam
content as a function of the level or change in level.
[0020] It has also been found that at least some of the lubricant
used to lubricate the expansion device is typically conveyed around
the circuit together with the working medium. The lubricant is not
vaporized in the evaporator and is thus separated together with the
liquid components of the lubricant as part of the phase separation
process in the reservoir. These amounts of separated lubricant are
preferably also used as input for the automatic control of the
steam content. Lubricant or a mixture of working medium and
lubricant is withdrawn from the reservoir--preferably by means of a
metering pump; this is then sent to the expansion device by way of
lubricant pathways separate from the circuit. The lubricant demand
depends on the operating point of the expansion device, especially
on its rotational speed, and thus also on the operating point of
the system. This operating point-dependent withdrawal of liquid
from the reservoir is preferably stored in a characteristic diagram
and can thus be used for the automatic control of the steam content
as a function of the level. Under steady-state operating
conditions, i.e., a constant withdrawal of lubricant or mixture
from the reservoir, it is possible to detect a change in the steam
content quickly and easily by detecting a change in the level in
the reservoir.
[0021] The goal of the invention is also achieved in that a control
unit for a system for a thermodynamic cycle is created. This is set
up to carry out a method for automatically controlling a steam
content of a working medium heated in a evaporator of the system,
wherein the control unit is set up to determine a level in a
reservoir, which is located downstream from a evaporator and is
connected to a separation device for separating liquid components
of the working medium, wherein the control unit is also set up to
vary a control variable for automatically controlling the steam
content as a function of the level. The control unit is preferably
set up to carry out a method according to one of the previously
described embodiments. Thus, in conjunction with the control unit,
the advantages already explained in connection with the method are
realized.
[0022] The method can be permanently implemented in an electronic
structure, i.e., in the hardware, of the control unit.
Alternatively, it is preferred that a computer program product be
loaded into the control unit, namely, a program which contains
instructions on the basis of which the method is carried out when
the computer program product is running on the control unit.
[0023] The control unit is preferably set up to vary a mass flow of
the working medium in the system as a function of the level,
especially to vary an output of a conveying device in the
system.
[0024] The control unit is preferably set up to acquire a change in
the level, wherein it is also set up to vary the mass flow as a
function of the change in level.
[0025] The control unit is also preferably set up to acquire a
pressure and/or a temperature of the working medium downstream from
the evaporator, in particular upstream of an expansion device, and
especially preferably at the evaporator outlet.
[0026] The control unit is set up to use at least one of these
measurement values for the automatic control of the steam
content.
[0027] The control unit is also preferably set up to use the
withdrawal of liquid from the reservoir as input for the automatic
control of the steam content.
[0028] The control unit comprises appropriate interfaces to
appropriate sensors and actuators.
[0029] The goal of the invention is also achieved in that a system
for a thermodynamic cycle is created. This is characterized by a
control unit according to one of the previously described exemplary
embodiments. Thus, in conjunction with the system, the advantages
previously explained in connection with the control unit and
especially the advantages already explained in connection with the
method are realized.
[0030] The system preferably comprises a evaporator; a separating
device, set up to separate liquid components of the working medium
from the vapor components of the working medium; an expansion
device; a condenser; and a conveying device for the conveying the
working medium in the circuit--arranged in series in the flow
direction of the working medium through the circuit of the system.
The system is preferably set up to carry out an organic Rankine
cycle (ORC), especially with ethanol as the working medium. This
makes it possible to employ the system especially effectively as a
means of using waste heat.
[0031] A reservoir is preferably connected to the separating
device, so that the liquid components separated in the separating
device can be conducted to it. The system preferably comprises a
level sensor, by means of which the level or the change in level in
the reservoir can be detected. The control unit of the system is
preferably functionally connected to the level sensor for
determining, preferably for monitoring, the level in the reservoir.
The control unit is also preferably functionally connected to the
conveying device for varying its output and thus in particular for
varying a mass flow in the system.
[0032] The system also preferably comprises a pressure sensor
and/or a temperature sensor downstream from the evaporator,
especially at an evaporator outlet. The control unit is preferably
functionally connected to at least one of these sensors and is set
up to determine a thermodynamic state of the working medium
downstream from the evaporator, especially at the evaporator
outlet. The control unit is also preferably set up to use at least
one of these measurement values for the automatic control of the
steam content.
[0033] Another exemplary embodiment of the system is characterized
in that the separating device is configured as a cyclone separator.
Baffles cause the working medium to flow in circles in the cyclone
separator, as a result of which liquid components strike the
baffles and run down them. The cyclone separator makes highly
efficient phase separation possible while simultaneously having an
extremely low pressure loss.
[0034] Another exemplary embodiment of the system is characterized
in that the expansion device is configured as a helical screw
expander. A helical screw expander has been found to be especially
favorable in terms of power yield especially in the case of an ORC
process. This is especially true for ORC systems which operate
without superheating, i.e., which operate in the wet steam region.
A helical screw expander is a displacement machine free of dead
spaces, the working chambers of which are formed by the spaces
between the teeth of two helical gear wheels, also called rotors.
The teeth of one rotor, which preferably extend in spiral fashion
over the rotor's circumferential surface, which is elongated in the
axial direction, engage in the tooth spaces of the other rotor.
When the two rotors are in relative rotation, working chambers of
variable volume are thus formed, in which the working medium
expands as it passes through the helical screw expander from the
inlet to the outlet.
[0035] Alternatively, it is also possible for the expansion device
to be configured as a continuous-flow machine, especially as a
turbine, as a displacement machine of some other type, or as a
volumetric expansion device, in particular as a reciprocating
piston machine, a scroll expander, a rotary vane machine, or a
Roots expander.
[0036] Finally, an exemplary embodiment of the system is
characterized in that it is set up to use the waste heat of an
internal combustion engine. This makes it possible to employ the
system advantageously for the mobile or stationary use of waste
heat and to increase the efficiency of the internal combustion
engine.
[0037] The goal of the invention, finally, is also achieved by an
arrangement that comprises an internal combustion engine and a
system according to one of the previously described exemplary
embodiments. The system is functionally connected to the internal
combustion engine for the use of its waste heat. It is possible for
the exhaust gas of the internal combustion engine to be conducted
to the system so that use can be made of the waste contained in
that gas. Alternatively or in addition, coolant of the internal
combustion engine can be conducted to the system so that use can be
made of the waste heat contained in the coolant. In this way, the
overall efficiency of the internal combustion engine can be
increased, and beneficial use can be made of its waste heat. It is
possible for the mechanical work performed in the system to be
returned directly to a crankshaft of the internal combustion engine
to support the work of the engine. Alternatively or in addition,
the mechanical work can be used elsewhere in directly mechanical
fashion. It is also possible for a generator to be functionally
connected to the expansion device, so that the mechanical work is
converted to electrical energy. This can be sent, by means of an
electric motor, for example, back to the crankshaft of the internal
combustion engine to support it. Alternatively or in addition, the
electrical energy thus generated can be used elsewhere such as in
an on-board power supply system, or it can be fed into a power
grid.
[0038] The internal combustion engine of the arrangement is
preferably configured as a reciprocating piston engine. In a
preferred exemplary embodiment, the internal combustion engine
serves in particular to drive heavy land vehicles such as mining
vehicles and trains or water craft, wherein the internal combustion
engine is used in a locomotive or motor coach or in a ship. The use
of the internal combustion engine to drive a vehicle serving
defensive purposes such as a tank is also possible. In another
exemplary embodiment of the internal combustion engine, it is
stationary and used for stationary power generation to generate
emergency power or to cover continuous-load or peak-load demands,
wherein the internal combustion engine in this case preferably
drives a generator. The stationary use of the internal combustion
engine to drive auxiliary units such as fire-fighting pumps on
offshore drilling rigs is also possible. An application of the
internal combustion engine in the area of the recovery of fossil
materials and especially fossil fuels such as oil and/or gas is
also possible. The internal combustion engine can also be used in
industry or in the construction field for the production of
construction vehicles such as cranes and bulldozers. The internal
combustion engine is preferably configured as a diesel engine; as a
gasoline engine; or as a gas engine for operation with natural gas,
biogas, customized gas, or some other suitable gas. Especially when
the internal combustion engine is configured as a gas engine, it is
suitable for use in block-type thermal power stations for
stationary power generation.
[0039] An especially preferred exemplary embodiment of the
arrangement is provided for marine applications, especially for use
on board a ferry, wherein the internal combustion engine is
provided preferably to drive the ship. Electrical energy for an
on-board power system of the ship can be recovered by means of the
system.
[0040] The description of the method on the one hand and of the
control unit, the system, and the arrangement on the other hand are
to be understood as complementary to each other. Features of the
control unit, of the system, and/or of the arrangement which have
been explained explicitly or implicitly in conjunction with the
method are preferably steps, individually or in combination, of a
preferred embodiment of the control unit, of the system, and/or of
the arrangement. Method steps which have been explained explicitly
or implicitly in conjunction with the control unit, the system,
and/or the arrangement, are preferably steps, individually or in
combination, of a preferred embodiment of the method. The method is
preferably characterized by at least one method step which is
required by at least one feature of the control unit, of the
system, and/or of the arrangement. The control unit, the system,
and/or the arrangement are characterized preferably by at least one
feature which is required by at least one method step of the
method.
[0041] The various features of novelty which characterize the
invention are pointed out with particularity in the claims annexed
to and forming a part of the disclosure. For a better understanding
of the invention, its operating advantages, specific objects
attained by its use, reference should be had to the drawings and
descriptive matter in which there are illustrated and described
preferred embodiments of the invention.
BRIEF DESCRIPTION OF THE DRAWING
[0042] In the Drawing:
[0043] FIG. 1 shows a schematic diagram of an exemplary embodiment
of an arrangement with an internal combustion engine and a system
for carrying out a thermodynamic cycle; and
[0044] FIG. 2 shows a schematic diagram of an embodiment of the
method in the form of an automatic control circuit.
DETAILED DESCRIPTION OF THE INVENTION
[0045] FIG. 1 shows a schematic diagram of an exemplary embodiment
of an arrangement 1, which comprises an internal combustion engine
3 and a system 5 for a thermodynamic cycle. The system 5 is set up
here to carry out an organic Rankine cycle and to use waste heat of
the internal combustion engine 3. For this purpose, waste heat of
the internal combustion engine 3 can be conducted to a evaporator 7
of the system 5, especially the waste heat contained in the exhaust
gas and/or in a coolant of the internal combustion engine 3.
[0046] The system 5 comprises a circuit 9 for a working medium,
preferably ethanol, wherein a separation device 11, an expansion
device 13, a condenser 15, and a conveying device 17 for conveying
the working medium through the circuit are provided around the
circuit 9 downstream, in the flow direction of the working medium,
from the evaporator 7. The separation device 11 is preferably
configured as a cyclone separator. The expansion device 13 is
preferably configured as a helical screw expander. The conveying
device 17 is preferably configured as a feed pump with variable
speed. In any case, the conveying device 17 comprises variable
output, wherein the mass flow of the working medium in the system 5
is adjustable by varying the output of the conveying device 17.
[0047] The system 5 is set up to operate the thermodynamic cycle,
especially the ORC process, in the wet steam region, so that,
downstream from the evaporator 7, in particular at the evaporator
outlet, wet steam containing both liquid and vapor components of
the working medium is present. To guarantee a stable cycle, the
system 5 comprises automatic control for the steam content of the
working medium downstream from the evaporator 7 and upstream of the
expansion device 13, especially in the area of the evaporator
outlet. In the separation device 11, liquid components of the
working medium are separated from the vapor components, wherein the
separated liquid components are conducted to a reservoir 19.
Lubricant, which is provided to lubricate the expansion device 13,
is also preferably separated in the separation device 11. At least
some of this lubricant is conveyed together with the working medium
around the circuit 9, but it is not vaporized in the evaporator 7.
It is therefore in liquid form downstream from the evaporator and
therefore is also separated in the separation device 11. It then
arrives in the reservoir 19 along with the liquid components of the
lubricant.
[0048] The system 5 comprises a level sensor 21, by means of which
the level and in particular a change in the level in the reservoir
19 can be detected. To regulate the steam content of the working
medium downstream from the evaporator 7, the system 5 is set up to
vary a control variable as a function of the level detected by the
level sensor 21, especially as a function of a change in level
detected by the level sensor 21.
[0049] For this purpose, a control unit 23 is provided, which is
functionally connected to the level sensor 21 to determine,
especially to monitor, the level, especially a change in the level.
The control unit 23 is set up to vary a mass flow of the working
medium in the system 5 as a function of the level, especially of
the change in the level. For this purpose, in the exemplary
embodiment shown here, it is functionally connected to the
conveying device 17 to vary its output and thus the mass flow of
the working medium through the circuit 9 as a function of the
signal acquired from the level sensor 21.
[0050] If, for example, more heat is being supplied from the
internal combustion engine 3 to the evaporator 7, the steam content
at the evaporator outlet increases, so that less liquid working
medium is separated in the separation device 11 and thus conducted
to the reservoir 19. The level therefore increases more slowly, no
longer changes, or perhaps even falls. These data are acquired by
the control unit 23 and evaluated quantitatively as an increase in
the steam content. The conveying device 17 is actuated by the
control unit 23 to increase its output, so that the mass flow in
the circuit 9 increases. Thus the increased amount of heat supplied
to the evaporator can be absorbed by the system 5 while the steam
content remains at least approximately the same.
[0051] If, conversely, the amount of heat supplied by the internal
combustion engine 3 decreases, less vaporization will occur and
thus the amount of liquid component of the working medium will
increase, wherein more liquid is separated in the separation device
11, which liquid is then conducted to the reservoir 19. Thus the
level in the reservoir 19 rises, which is again detected by the
level sensor 21 and quantitatively evaluated by the control unit 23
as a decrease in the steam content. The control unit 23 then
actuates the conveying device 17 in such a way that its output is
reduced, so that the mass flow in the circuit 9 decreases. It is
thus adapted to the smaller amount of available heat in the
evaporator 7, as a result of which the steam content again can be
kept at least approximately constant. The control unit 23 is
preferably set up automatically to keep the steam content at the
evaporator outlet constant. The control unit 23 is also preferably
configured to control the rotational speed of the conveying device
17, configured as a feed pump.
[0052] A sensor device 25 for detecting a pressure and/or a
temperature of the working medium is preferably provided downstream
from the evaporator 7, especially at the evaporator outlet. The
control unit 23 is preferably functionally connected to this sensor
device 25 and is set up to determine a thermodynamic state of the
working medium at the evaporator outlet on the basis of the at
least one measurement value of the control unit 25. This
information is preferably used as input for the automatic control
of the steam content, as a result of which the precision of the
control process is increased.
[0053] It has been found preferable to send the lubricant separated
in the reservoir to the expansion device 13 to lubricate it by way
of a lubricant route 27, which is indicated only schematically.
Alternatively or in addition, liquid present in the reservoir 19 is
preferably returned to the circuit along a drain route 29,
preferably downstream from the expansion device and upstream of the
condenser 15. This option is preferably used especially to prevent
the reservoir 19 from overflowing. In addition, it is possible in
this way to ensure a high lubricant concentration--and thus a small
amount of working medium--in the reservoir, which functions to this
extent as a lubricant tank.
[0054] In any case, it has been found preferable for liquid to be
withdrawn from the reservoir 19 continuously and/or at regular
intervals. In particular, the removal of lubricant to lubricate the
expansion device 13 depends on the operating state of the system 5,
especially on the rotational speed of the expansion device. In the
control unit 23, preferably at least one characteristic diagram is
stored, in which the operating point-dependent removal of liquid
from the reservoir 19 is entered. Alternatively or in addition, it
is possible for the system 5 to comprise a withdrawal sensor 31,
preferably in the form of a flow sensor, by means of which the
withdrawal of liquid from the reservoir 19 can be detected
directly. In this case, the control unit 23 is functionally
connected to the withdrawal sensor 31 to detect the withdrawal of
liquid from the reservoir 19. In any case, the withdrawal of liquid
from the reservoir is preferably used as input for the automatic
control of the steam content, which increases its accuracy yet
again.
[0055] It has also been found that, in the case of the exemplary
embodiment of the system 5 illustrated here, the expansion device
13 is functionally connected to a generator 33, so that the
mechanical work performed by the working medium in the expansion
device 13 can be converted into electrical energy by the generator
33.
[0056] It is especially preferable to provide the arrangement 1 for
marine applications, especially for ferries. In this case, the
internal combustion engine 3 preferably serves to drive the ship,
especially the ferry. The electrical power generated by the
generator 33 is especially preferably sent to, i.e., fed into, an
on-board power system of the ship, especially of the ferry. Other
applications of the use 1, especially stationary applications or
other mobile applications--as previously described in conjunction
with the internal combustion engine--are also possible.
[0057] FIG. 2 shows a schematic diagram of an embodiment of the
method in the form of an automatic control circuit. The automatic
control illustrated schematically here is preferably carried out in
its entirety in the control unit 23. A nominal value 35 for the
steam content of the working medium downstream from the evaporator
7, especially at the evaporator outlet, is sent to the automatic
control circuit. In a comparison member 37, this value is compared
with an actual value 39 of the steam content, from which a control
deviation 41 is obtained. This is sent to an automatic control
device 43, which calculates from it a control variable 45, in
particular in the form of an actuation signal for the conveying
device 17, to adjust its output. It is possible for the output of
the conveying device 17 to be controlled on the basis of the
control variable 45 alone. Alternatively, it is preferable,
however, for the output of the conveying device 17, especially the
rotational speed of the feed pump, to be regulated to match the
control variable 45 by means of a subordinate control process. This
increases the accuracy of the method.
[0058] The command variable 45 acts on a controlled system 47,
which comprises in particular the conveying device 17, the
evaporator 7, the separation device 11, and the reservoir 19. On
the basis of a change in the control variable 45, the mass flow of
the working medium in the circuit 9 is changed by variation of the
output of the conveying device 17, which influences the steam
content of the working medium at the evaporator outlet and thus
also the level in the reservoir 19, which can be detected by the
level sensor 21. The controlled system 47 therefore results
ultimately in a measurement value 49, which represents the level or
the change in the level, preferably detected by the level sensor
21. The measurement value 49 is therefore in particular a
measurement signal produced by the level sensor 21. The measurement
value 49 is sent to a calculation member 51, which is set up to
calculate the steam content of the working medium downstream from
the evaporator 7, in particular at the evaporator outlet, as a
function of the measurement variable 49. What therefore results
finally from the calculation member 51 is the actual value 39 for
the steam content, which is itself sent back to the comparison
member 37.
[0059] Additional variables are preferably also input into the
calculation member 51. It is preferable for a pressure 53 of the
working medium downstream from the evaporator 7, especially at the
evaporator outlet, to be entered. Alternatively or in addition, it
is provided that a temperature 55 of the working medium downstream
from the evaporator 7, especially at the evaporator outlet, is
entered. By means of at least one of these measurement variables, a
thermodynamic state of the working medium at the designated point
can be determined, as a result of which also--and possibly as a
complement to the measurement variable 49--the steam content of the
working medium can also be inferred. This increases the accuracy of
the automatic control.
[0060] Alternatively or in addition, preferably a withdrawal 57 of
liquid from the reservoir 19 is entered into the calculation member
41, wherein the withdrawal 57 is read out from a characteristic
diagram and/or measured by means of the withdrawal sensor 31. This
also increases the accuracy of the method.
[0061] Overall, it has thus been found that, by means of the
method, it is possible to regulate the steam content automatically
in a very stable, accurate, and low-cost manner, which ultimately
makes it possible to operate the system economically in the wet
steam region with all its associated advantages.
[0062] While specific embodiments of the invention have been shown
and described in detail to illustrate the inventive principles, it
will be understood that the invention may be embodied otherwise
without departing from such principles.
* * * * *