U.S. patent application number 12/749304 was filed with the patent office on 2010-09-30 for process for controlling the cooling phase of a container to be cooled for a heat-regenerating adsorption system and a device in a heat-regenerating adsorption system for carrying out such a process.
This patent application is currently assigned to KAESER KOMPRESSOREN GMBH. Invention is credited to Andreas FREDENHAGEN.
Application Number | 20100242504 12/749304 |
Document ID | / |
Family ID | 42732925 |
Filed Date | 2010-09-30 |
United States Patent
Application |
20100242504 |
Kind Code |
A1 |
FREDENHAGEN; Andreas |
September 30, 2010 |
PROCESS FOR CONTROLLING THE COOLING PHASE OF A CONTAINER TO BE
COOLED FOR A HEAT-REGENERATING ADSORPTION SYSTEM AND A DEVICE IN A
HEAT-REGENERATING ADSORPTION SYSTEM FOR CARRYING OUT SUCH A
PROCESS
Abstract
The present invention provides a process for controlling the
cooling phase of a container to be cooled for a heat-regenerating
adsorption system with the following process steps: definition of a
cooling phase cut-off temperature as a function of at least one
parameter which is characteristic of the cooling process, recording
the outlet temperature of a cooling fluid emerging from the
container to be cooled by means of an outlet temperature recording
device, and termination of the cooling phase when the recorded
outlet temperature of the emerging cooling fluid falls below the
defined cooling phase cut-off temperature. The present invention
also provides a device for a heat-regenerating adsorption system
for controlling the cooling phase of a container to be cooled in
accordance with this process.
Inventors: |
FREDENHAGEN; Andreas;
(Coburg, DE) |
Correspondence
Address: |
TRASKBRITT, P.C.
P.O. BOX 2550
SALT LAKE CITY
UT
84110
US
|
Assignee: |
KAESER KOMPRESSOREN GMBH
Coburg
DE
|
Family ID: |
42732925 |
Appl. No.: |
12/749304 |
Filed: |
March 29, 2010 |
Current U.S.
Class: |
62/62 ; 62/176.6;
62/477 |
Current CPC
Class: |
B01D 53/0462 20130101;
F25B 37/00 20130101 |
Class at
Publication: |
62/62 ; 62/176.6;
62/477 |
International
Class: |
F25D 25/00 20060101
F25D025/00; F25B 49/04 20060101 F25B049/04; F25B 15/00 20060101
F25B015/00 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 31, 2009 |
DE |
102009002047.0 |
Claims
1. A process for controlling the cooling phase of a container to be
cooled for a heat-regenerating adsorption system with the following
process steps: definition of a cooling phase cut-off temperature as
a function of at least one parameter which characterizes the
cooling process; recording the outlet temperature of a cooling
fluid emerging from the container to be cooled by means of an
outlet temperature recording device; and termination of the cooling
phase when the recorded outlet temperature of the emerging cooling
fluid falls below the defined cooling phase cut-off
temperature.
2. The process according to claim 1, wherein the cooling phase
cut-off temperature is defined dynamically as a function of at
least one parameter which is characteristic of the cooling process
and recorded continuously, periodically or aperiodically by means
of a recording device, and in particular by means of a parameter
associated with the cooling fluid for cooling the container.
3. The process according to claim 1, wherein the inlet temperature
of the cooling fluid is recorded continuously, periodically or
aperiodically by means of an inlet temperature recording device and
is taken into account when dynamically defining the cooling phase
cut-off temperature, with the cooling process being terminated when
the currently recorded outlet temperature of the emerging cooling
fluid falls below the currently defined cooling phase cut-off
temperature.
4. The process according to claim 1, wherein the adiabatic increase
in adsorption temperature of the cooling fluid is determined
continuously, periodically or aperiodically and taken into account
when dynamically defining the cooling phase cut-off
temperature.
5. The process according to claim 4, wherein the loading of the
cooling fluid when entering the container to be cooled is
determined continuously, periodically or aperiodically and taken
into account in order to determine the adiabatic increase in
adsorption temperature of the cooling fluid, for example by
measuring the inlet temperature of the cooling fluid entering the
container, the relative humidity of the cooling fluid entering the
container, the pressure of the cooling fluid during the cooling
process, the density and/or the absolute humidity of the cooling
fluid entering the container.
6. The process according to claim 4, wherein the cooling phase
cut-off temperature is defined by a pre-specified value above the
defined adiabatic adsorption temperature.
7. The process according to claim 1, wherein one or more of the
parameters which characterize the cooling process are estimated and
these estimates are taken into consideration when dynamically
defining the cooling phase cut-off temperature.
8. A process for controlling the cooling phase of a container to be
cooled for a heat-regenerating adsorption system with the following
process steps: definition of a cooling phase cut-off temperature
gradient; determination of the time-dependent temperature gradient
of a cooling fluid emerging from the container to be cooled by
means of an outlet temperature recording device; and termination of
the cooling phase when the determined outlet temperature gradient
of the emerging cooling fluid falls below the defined cooling phase
cut-off temperature gradient.
9. The process according to claim 8, wherein the outlet temperature
of the emerging cooling fluid is recorded continuously,
periodically or aperiodically and the temperature gradient of the
emerging cooling fluid is defined continuously, periodically or
aperiodically.
10. The process according to claim 8, wherein a pre-defined delay
time, a pre-defined minimum cooling phase length, a pre-defined
coolant flow phase length and/or a pre-defined maximum cooling
phase cut-off temperature are also taken into account when
controlling the cooling process.
11. The process according to claim 8, wherein a cooling gas, for
example ambient air, the compressed and cooled process gas from the
adsorption system or an externally supplied cooling gas is used as
the cooling fluid.
12. The process according to claim 8, wherein termination of the
cooling phase is initiated if a single evaluation or a pre-defined
number of consecutive evaluations for the purposes of a
plausibility check indicate that the temperature has fallen below
the cooling phase cut-off temperature or the cooling phase cut-off
temperature gradient.
13. The process according to claim 8, wherein a control unit for
receiving and evaluating the recorded data and for controlling the
cooling phase accordingly as a function of the recorded data is
provided.
14. The process according to claim 8, wherein reference values for
specific parameters are defined beforehand, stored in a storage
device connected to the control unit and taken into account by the
control unit, for example, pre-defined measurement curves and/or
approximation functions for specific parameters are saved and taken
into account.
15. A device in a heat-regenerating adsorption system for
controlling the cooling phase of a container to be cooled with: at
least one recording device for continuously, periodically or
aperiodically recording at least one parameter which characterizes
the cooling process; at least one outlet temperature recording
device for continuously, periodically or aperiodically recording
the outlet temperature of a cooling fluid emerging from the
container to be cooled; and a control unit for dynamically defining
a cooling phase cut-off temperature as a function of the at least
one parameter recorded continuously, periodically or aperiodically
and for controlling termination of the cooling phase when the
recorded outlet temperature of the emerging cooling fluid falls
below the defined cooling phase cut-off temperature.
16. The device according to claim 15, wherein the device has an
inlet temperature recording device for continuously, periodically
or aperiodically recording the inlet temperature of the cooling
fluid which transfers the recorded data to the control unit for
continuous, periodic or aperiodic evaluation of this data.
17. The device according to claim 15, wherein the device has at
least one additional recording device for continuously,
periodically or aperiodically recording the relative humidity of
the cooling fluid entering the container, the pressure of the
cooling fluid during the cooling process, the density and/or the
absolute humidity of the fluid entering the container or similar
variables.
18. A device in a heat-regenerating adsorption system for
controlling the cooling phase of a container to be cooled with: at
least one outlet temperature recording device for continuously,
periodically or aperiodically recording the outlet temperature and
for continuously, periodically or aperiodically defining a
resulting time-dependent temperature gradient for a cooling fluid
emerging from the container to be cooled; and a control unit for
controlling termination of the cooling phase when the determined
temperature gradient of the emerging cooling fluid falls below a
pre-defined cooling phase cut-off temperature gradient.
19. The device according to claim 18, wherein the control unit has
a data connection with the individual recording devices and
receives the measured data from the individual recording devices,
evaluates it accordingly and controls the cooling phase
accordingly.
20. The device according to claim 18, wherein the device has a
storage facility which is connected to the control unit and, for
example, contains saved and pre-defined reference values for
specific parameters, for example in the form of pre-defined
measurement curves or approximation functions.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims the benefit of German Patent
Application No. 10 2009 002 047.0, filed Mar. 31, 2009, the entire
disclosure of which is herein incorporated by reference.
FIELD OF THE INVENTION
[0002] The present invention relates to a process for controlling
the cooling phase of a container to be cooled for a
heat-regenerating adsorption system and a device in a
heat-regenerating adsorption system for carrying out such a
process.
[0003] Although it can be used in any adsorption processes in which
a heat-regenerating adsorbent requires cooling, the present
invention and the problems underlying this invention are explained
in greater detail with respect to an adsorption system which
constitutes a dryer which uses heat from a compressor.
[0004] Systems for adsorptive gas cleaning involving alternating
flows through at least two containers filled with adsorbent to
remove a component which can be adsorbed from a process gas are
used in many industrial processes. Dehumidification of compressed
air, nitrogen, natural gas or gases from chemical production
processes are examples of such processes. The adsorbed component
must be removed again from the respective adsorbent during the
period of time in which a respective container is not being used
for gas cleaning. This may, for example, be achieved by rinsing
with a very pure regenerative gas flow which is able to take up the
adsorbed component. In the case of non-toxic compressed gases, this
regenerative gas flow can be produced by expanding part of the gas
flow which has already been cleaned. This process is referred to as
pressure-swing adsorption and is performed in cold-regenerative
compressed air dryers amongst other devices.
[0005] More energy-efficient but more complex regeneration
processes in terms of equipment desorb the adsorbed component by
supplying heat, as the adsorption capacity of the adsorbent
decreases sharply at higher temperatures. Either an external heat
source or the compression heat from condensed gases can be used for
this purpose. In the first instance, regeneration is generally
performed at atmospheric pressure using a fan, as described in
document DE 39 15 673 C2 for example, and in the second case it is
performed at operating pressure using the condensed gas directly as
the heat medium, as described in document DE 37 02 845 A1 for
example. On completion of the desorption process, the adsorbent
must be cooled down to the adsorption process temperature once
again. Ambient air, gas supplied to the circuit via a cooler or,
especially when using compressor heat, compressed and cooled
process gas can be used as the cooling medium in this process.
[0006] Before the process gas enters the container in which the
adsorption process takes place, and in processes which use
compressor heat, even during the cooling phase prior to the cooling
gas entering the container to be cooled, some of the component to
be removed can be removed by condensation and precipitation. In the
case of a correspondingly high source concentration, the residual
concentration of the component to be removed after this
precipitation process is directly dependent on the temperature to
which the cooling gas is cooled. As a result, in less favorable
cooling conditions, this residual concentration of the component to
be removed is correspondingly higher than in favorable cooling
conditions, with the result that a greater quantity of the
component to be adsorbed needs to be adsorbed per cubic meter of
process gas. Disadvantageously, the amount of regeneration energy
required per cubic meter of process gas also rises as a result. The
ratio of regeneration time to the available total adsorption time
therefore rises with a constant regeneration temperature and
constant regeneration volume flow.
[0007] This can lead to the disadvantage that the time available
for adsorption is no longer sufficient to regenerate and cool down
the container to be cooled to an adequate extent. A so-called
breach can occur in such cases, where a rise in concentration of
the component to be removed occurs at the system outlet if the
adsorption phase in the additional container cannot be completed on
time as the cooling phase in the container to be cooled has not yet
finished.
[0008] The aim is therefore to achieve as short a minimum cycle
period as possible in order to guarantee switchover in good time
and avoid the risk of such a breach. The minimum cycle period for a
container is essentially made up of the sum of the desorption phase
and the cooling phase. As short a cooling phase as possible is
therefore desirable.
[0009] In the processes known to the applicant in which a constant
cooling phase cut-off temperature is selected, the cooling phase is
thus detrimentally longer, the higher the cooling air inlet
temperature, as it takes longer to balance out the temperature to
below the constant cooling phase cut-off temperature since it is
harder to adapt the outlet temperature to the inlet temperature of
the cooling fluid.
[0010] In practice, to guarantee a certain level of operational
safety even in unfavorable conditions, the cooling phase cut-off
temperature must be set at such a high level to ensure a
sufficiently short cooling period in order to prevent the breach
described above in these unfavorable conditions. However, this
incorporates the disadvantage that terminating the cooling phase at
this high cooling phase cut-off temperature leads to unnecessary
peaks of temperature and pressure dew points in all other operating
situations.
SUMMARY OF THE INVENTION
[0011] The object of the present invention is therefore to provide
an improved process for controlling the cooling phase of a
container to be cooled for a heat-regenerating adsorption system
and a correspondingly improved adsorption system.
[0012] This object is achieved according to the invention by a
process with the features described in claims 1 and 8 and the
devices with the features described in claims 15 and 18.
[0013] The concept behind the present invention initially entails
defining a cooling phase cut-off temperature as a function of at
least one parameter characterizing the cooling process, with the
outlet temperature of the cooling fluid emerging from the container
to be cooled being recorded by an outlet temperature recording
device and where the cooling phase is terminated if the recorded
outlet temperature of the emerging cooling fluid falls below the
defined cooling phase cut-off temperature.
[0014] Compared with the known state of the art methods, the
present invention thus has the benefit that the cooling phase can
be controlled as a function of the cooling conditions which prevail
at any moment, thus preventing an undesirable breach without the
need to set the cooling phase cut-off temperature at unnecessarily
high values. In accordance with the present invention, the
respective cooling phase cut-off temperature is adapted accordingly
to the cooling conditions prevailing at the present time and
guarantees optimum cooling phase control.
[0015] Furthermore, the present invention is based on the similar
concept of defining a cooling phase cut-off temperature at the
outset and then recording the temperature gradient of a cooling
fluid emerging from the container to be cooled over time by means
of an outlet temperature recording device and where the cooling
phase is terminated when the recorded temperature gradient of the
emerging cooling fluid falls below the defined cooling phase
cut-off temperature gradient.
[0016] This process also offers the advantage that just one
constant cooling phase cut-off temperature gradient needs to be
defined at the outset to serve as a threshold for a corresponding
cooling phase control. Additional parameter calculations and
measurements are thus not required. As a result, it has the
advantage of guaranteeing improved cooling phase control in a
simple fashion for defined conditions.
[0017] The sub-claims describe advantageous embodiments and
improvements of the processes described in claims 1 and 8 and the
devices specified in claims 15 and 18.
[0018] In accordance with a preferred embodiment of the invention,
the cooling phase cut-off temperature is defined dynamically as a
function of at least one parameter which is characteristic of the
cooling process and recorded continuously or, at the very least,
periodically by means of a recording device, and in particular by
means of a parameter associated with the cooling fluid for cooling
the container. The parameters which define the cooling conditions
which prevail at a given moment most distinctively are preferably
selected beforehand, these parameters being used to define the
cooling phase cut-off temperature.
[0019] In accordance with a further preferred embodiment of the
invention, the inlet temperature of the cooling fluid is recorded
continuously or, at the very least, periodically by means of an
inlet temperature recording device and taken into account when
dynamically defining the cooling phase cut-off temperature, with
the cooling process being terminated if the outlet temperature of
the emerging cooling fluid recorded at the present time falls below
the cooling phase cut-off temperature which is currently specified.
This thus records an important parameter for the prevailing cooling
conditions, i.e., the cooling fluid inlet temperature, and this is
taken into account accordingly so as to guarantee appropriate and
dynamic cooling phase control.
[0020] In accordance with a further preferred embodiment, the
adiabatic increase in adsorption temperature of the cooling fluid
is determined continuously or, at the very least, periodically and
taken into account when dynamically defining the cooling phase
cut-off temperature. This is an advantageous way of taking into
account the additional rise in temperature of the cooling fluid due
to the resulting adsorption heat if the component to be removed is
present in the cooling fluid. This is particularly so in the case
of dryers which use ambient air or process air to cool the
container to be cooled after the regeneration phase.
[0021] Furthermore, for example, the loading of the component to be
removed in the cooling fluid as it enters the container to be
cooled is defined and taken into account continuously or, at the
very least, periodically in order to determine the adiabatic
increase in adsorption temperature of the cooling fluid by, for
example, continuously or periodically measuring the inlet
temperature of the cooling fluid entering the container, the
relative humidity of the cooling fluid entering the container, the
pressure of the cooling fluid during the cooling process, the
density and/or the absolute humidity of the cooling fluid entering
the container. This thus guarantees a sufficiently accurate
definition of the adiabatic increase in adsorption temperature such
that the cooling phase can be controlled to the optimum extent as a
function of the defined value.
[0022] The cooling phase cut-off temperature is preferably defined
by a pre-specified value above the defined adiabatic increase in
adsorption temperature. For example, a temperature can be selected
for this purpose which is defined as the cooling phase cut-off
temperature which is higher than the recorded adiabatic adsorption
temperature by a pre-defined constant amount.
[0023] Alternatively or additionally, one or more of the parameters
which characterize the cooling process can also be estimated, these
estimates being used to continuously or, at the very least,
periodically define the cooling phase cut-off temperature. This
offers the advantage that just one or a couple of parameters need
to be measured to determine the cooling conditions prevailing at a
given moment, these measured values providing reliable values for
the cooling phase cut-off temperature when used in conjunction with
the estimates.
[0024] In accordance with a further preferred embodiment of the
invention, the outlet temperature and thus the time-dependent
temperature gradient of the cooling fluid emerging from the
container to be cooled are recorded continuously or, at the very
least, periodically, for the purpose of defining a cooling phase
cut-off temperature gradient. In this case, the rate of reduction
of the cooling fluid outlet temperature is established from the
cooling fluid outlet temperature recorded continuously or
periodically and the cooling phase is then terminated accordingly
if the established temperature gradient falls below the previously
defined cooling phase cut-off temperature gradient. This process
offers the advantage that only one constant cooling phase cut-off
temperature gradient needs to be defined at the outset to serve as
a threshold for corresponding cooling phase control. Additional
parameter calculations and measurements are thus not required.
[0025] In accordance with a further preferred embodiment of the
invention, a pre-defined delay time, a pre-defined minimum cooling
phase length, a pre-defined cooling phase starting time and/or a
pre-defined maximum cooling phase cut-off temperature are taken
into account in addition to the outlined threshold criteria when
controlling the cooling process. The use of data which may not be
representative and/or damage to system components can thus be
prevented.
[0026] In accordance with a further preferred embodiment of the
invention, a cooling gas, in particular ambient air, the compressed
and cooled process gas from the adsorption system or an externally
supplied cooling gas is used as the cooling fluid. A corresponding
cooling medium can thus be selected in line with the adsorption
system and the relevant application. In the event of a
heat-regenerating adsorption system, compressed and cooled process
gas is particularly suitable as the cooling gas, which means that
an additional process gas flow is not required.
[0027] In accordance with a further preferred embodiment of the
invention, an adsorbent contained in the container to be cooled is
cooled by the cooling fluid. After cooling the adsorbent, this is
resupplied to the system for the purpose of a new adsorption
process.
[0028] In accordance with a further preferred embodiment of the
invention, a control unit is provided which continuously or, at the
very least, periodically records the recorded data from the
individual recording devices and controls the cooling phase
accordingly as a function of this recorded data. This thus
guarantees automatic cooling phase control without requiring any
great effort on the part of the user. For example, reference values
for specific parameters are defined beforehand, stored in a storage
unit connected to the control device and taken into account by the
control unit when defining the individual values required for
control purposes, for example, pre-defined measurement curves are
stored as reference values in the storage unit and taken into
account.
[0029] The invention is explained below in greater detail with the
aid of embodiments and with reference to the attached figures in
the drawing.
BRIEF DESCRIPTION OF THE DRAWINGS
[0030] The figures show:
[0031] FIG. 1: estimated temperature curves for the incoming
cooling air and the adiabatic adsorption temperature as a function
of the temperature of the cooling medium for cooling the cooling
air as per an embodiment of the present invention;
[0032] FIG. 2: estimated temperature curves for the incoming
cooling air, the adiabatic adsorption temperature and a measured
temperature curve for outgoing cooling air as a function of the
cooling time according to a sample measurement for the present
invention;
[0033] FIG. 3: estimated temperature curves for the incoming
cooling gas and the adiabatic adsorption temperature to establish a
linear approximation of the cooling phase cut-off temperature as a
function of the temperature of the cooling medium for cooling the
cooling gas as per an embodiment of the present invention;
[0034] FIG. 4: temperature curves for the incoming cooling gas and
the adiabatic adsorption temperature as a function of the
temperature of the cooling medium for cooling the cooling gas in
various pressure conditions as per an embodiment of the present
invention; and
[0035] FIG. 5: graphs for the adiabatic adsorption temperature as a
function of the relative humidity of the incoming cooling gas at
different cooling air inlet temperatures as per an embodiment of
the present invention.
DETAILED DESCRIPTION OF THE INVENTION
[0036] A preferred embodiment of the present invention is explained
below in greater detail with the aid of FIGS. 1 and 2.
[0037] As explained above, the minimum cycle time for a container
in a heat-regenerating adsorption system is essentially derived
from the sum of the duration of the desorption phase and the
duration of the cooling phase. The end of the desorption phase is,
for example, defined by the point at which the temperature exceeds
a previously set minimum temperature for the cooling gas emerging
from the corresponding container during desorption. The end of the
cooling phase according to the embodiment described here is defined
by stating that the cooling phase is terminated if the temperature
T.sub.Cool,out of the cooling gas emerging from the container to be
cooled during cooling, for example in the form of the compressed
and cooled process gas from the system, falls below a pre-defined
dynamically defined cooling phase cut-off temperature T.sub.Cp-Ct.
In order to control the cooling phase in accordance with the
principles outlined here, it is thus necessary to define the value
for the cooling phase cut-off temperature T.sub.Cp-Ct on a
correspondingly dynamic basis.
[0038] According to the present embodiment, the heat-regenerating
adsorption system according to the invention has a plurality of
sensors to record the pre-defined parameters which influence the
prevailing cooling conditions at a given moment in time. There is
in particular a temperature sensor for determining the current
inlet temperature T.sub.Cool,in of the cooling gas flowing into the
container to be cooled, data from this sensor being linked to the
central control unit. In the present application, "data" is
understood to mean any type of information, in other words, current
or voltage signals, digital measurement signals, etc.
[0039] If the component to be removed from the adsorbent in the
container is already contained in the cooling gas, the temperature
of the cooling gas rises due to the resulting adsorption heat.
According to the present embodiment, this is determined
continuously in the pre-defined manner and taken into account when
determining the cooling phase cut-off temperature T.sub.Cp-Ct by
dynamic means. Accordingly, additional sensors are provided
according to the present embodiment and these are used to measure
additional variables for determining or at least estimating an
approximate adiabatic rise in the adsorption temperature
.DELTA.T.sub.Ad. To this end, these additional sensors are also
connected to the control unit in such a way that the control unit
evaluates all data received and determines the respective current
cooling phase cut-off temperature T.sub.Cp-Ct from this data,
whilst taking into account the respective adiabatic increase in
temperature using a pre-defined algorithm. This is explained in
greater detail below.
[0040] A storage device is also preferably provided as an integral
part of the control unit or as an external storage unit, in which
previously defined algorithms for determining the cooling phase
cut-off temperature T.sub.Cp-Ct or any reference values or similar
values which are used are stored and can be used by the control
unit for appropriate cooling phase control.
[0041] The adsorption system according to the present embodiment
also has a temperature sensor to measure the current outlet
temperature T.sub.Cool,out of the cooling gas emerging from the
container to be cooled, which in turn preferably has a data
connection to the control unit for the purpose of transferring the
measured data.
[0042] For example, as shown in FIG. 1, the current inlet
temperature T.sub.Cool,in of the cooling gas entering the container
to be cooled is determined indirectly, rather than directly, by
measuring the temperature of the cooling medium for pre-cooling the
cooling gas and the actual inlet temperature T.sub.Cool,in of the
cooling gas entering the container is calculated or estimated from
the measured temperature of the cooling medium. According to the
example shown in FIG. 1 the inlet temperature T.sub.Cool,in is
assumed to be 10 K higher than the recorded temperature of the
cooling medium. This is illustrated in FIG. 1 by the dotted line on
the graph. The current inlet temperature T.sub.Cool,in of the
incoming cooling gas is preferably measured directly. At this point
it should be noted that the individual parameters can be measured
continuously, periodically or even aperiodically or at pre-defined
times. This of course also applies to the corresponding evaluation
and control measures.
[0043] The dashed line in the graph in FIG. 1 also shows the
temperature of the cooling gas and, in the present embodiment, the
temperature of the compressed air which would result if the
compressed air was heated solely by the adsorption heat of the
water contained in the compressed air, in other words the component
to be adsorbed. This temperature is referred to below as the
adiabatic adsorption temperature T.sub.Ad. If we assume 100%
saturation of the cooling air or compressed air with the component
to be adsorbed, it is merely necessary to determine standard
parameters in this case in order to determine the adiabatic
increase in adsorption temperature. For example, in this case, if
we also assume a minimum pressure, the adiabatic increase in
adsorption temperature may be saved as a clear function of the
inlet temperature of the compressed air or cooling air.
[0044] The adiabatic adsorption temperature T.sub.Ad is calculated
or estimated by means of a pre-defined algorithm based on measured
and/or estimated variables, or the adiabatic increase in adsorption
temperature .DELTA.T.sub.Ad, i.e., the temperature increase due to
the formation of adsorption heat for whatever reason is calculated
or estimated. The adiabatic increase in adsorption temperature
.DELTA.T.sub.Ad in FIG. 1 corresponds to the difference in
temperature on the y axis between the dotted line for the inlet
temperature T.sub.Cool,in of the incoming cooling gas and the
dashed line for the adiabatic adsorption temperature T.sub.Ad.
[0045] The following process can for example be used to calculate
the adiabatic increase in adsorption temperature .DELTA.T.sub.Ad.
The adiabatic increase in adsorption temperature .DELTA.T.sub.Ad is
particularly dependent on the loading x of the cooling air in the
case of the compressed process gas with, say, water vapor, i.e., on
the mass of water vapor contained per mass of air in the cooling
air. The loading x is in turn dependent on the prevailing
temperature of the cooling air and the pressure p of the cooling
gas during the cooling process in the event of 100% saturation. In
the event of the adsorption of water by the adsorbent contained in
the container, the adiabatic increase in adsorption temperature
.DELTA.T.sub.Ad is more marked the higher the loading x when the
cooling gas enters or the higher the inlet temperature of the
cooling gas at constant pressure in the container to be cooled.
[0046] For example, the adiabatic increase in adsorption
temperature .DELTA.T.sub.Ad can be estimated as follows, with the
embodiment of the heat-regenerating adsorption system being assumed
below to be a compressed air dryer by way of example:
.DELTA. T Ad = dM ( t ) Water , ad .DELTA. h Ad dM ( t ) Air c P ,
air + dM ( t ) Water , ad c P , Water , Ad .apprxeq. dM ( t ) Water
, in .DELTA. h Ad dM ( t ) Air c P , Air + dM ( t ) Water , in c P
, Water , Ad = = x .DELTA. h Ad c P , air + xc P , Water , Ad
.apprxeq. x .DELTA. h Ad c P , air ##EQU00001## where :
##EQU00001.2## x = dM ( t ) Water , in dM ( t ) air
##EQU00001.3##
and where: [0047] dM(t).sub.Water,ad represents the mass of
adsorbed water over time; [0048] dM(t).sub.Water,in and
dM(t).sub.Air represent the incoming mass flow rates of water and
air in the incoming cooling gas, where the mass flow rate of water
in the incoming cooling gas dM(t).sub.Water,in can be assumed to be
equal to the mass of adsorbed water over time dM(t).sub.Water,ad;
[0049] .DELTA.h.sub.Ad defines the mass-specific adsorption
enthalpy during the adsorption of water by the adsorbent contained
in the container to be cooled and can be assumed to be more or less
constant; and [0050] c.sub.P,air and c.sub.P,water,ad represent the
heat capacities of air and adsorbed water.
[0051] As a result, the adiabatic increase in adsorption
temperature .DELTA.T.sub.Ad is more or less a function of the
loading x of the coolant. There are a number of measurement options
for calculating this loading x and thus the adiabatic increase in
adsorption temperature .DELTA.T.sub.Ad dynamically and/or
continuously. For example, the temperature, pressure p and the
relative humidity of the cooling air entering the container to be
cooled can be determined continuously to establish the loading x.
However, alternatively or additionally, the density and the
absolute humidity of the cooling air entering the container to be
cooled can also be determined continuously.
[0052] In any event, it is also conceivable that it will not be
possible to measure all the variables required to establish the
loading x during the cooling process on a continuous basis, but
that one or more of the necessary variables will merely be
estimated. If, for example, the process pressure or the pressure
inside the container to be cooled is known, for example because the
compressed process gas with a known system pressure is used as the
cooling gas, the adiabatic increase in adsorption temperature
.DELTA.T.sub.Ad can be estimated at the lowest permanently possible
pressure. This is particularly suitable for cooling processes at
atmospheric pressure and in cooling processes with process pressure
if the minimum system pressure is known. The adiabatic increase in
adsorption temperature .DELTA.T.sub.Ad can be shown for a given
pressure with sufficient accuracy, for example by approximation
functions such as second-degree polynomials. Previously defined
measurement curves or approximation functions can also be saved as
reference values and taken into account by the control unit.
Cooling phase control can therefore preferably be adjusted to the
lowest proposed operating pressure due to the relationship between
the adiabatic increase in adsorption temperature .DELTA.T.sub.Ad
and pressure. Alternatively or additionally, the prevailing
operating pressure can also be measured by means of an appropriate
recording device, transferred to the control unit and taken into
account by the control unit when calculating the adiabatic
adsorption temperature T.sub.Ad or the adiabatic increase in
adsorption temperature .DELTA.T.sub.Ad.
[0053] It may also be possible and appropriate to estimate the
loading x if the relative humidity of the cooling air entering the
container to be cooled is known. If, for example, the incoming
cooling air has a very low humidity level, the resulting adsorption
heat will be so low as to be negligible. As a result, when
determining the cooling phase cut-off temperature T.sub.Cp-Ct, a
constant amount can be added to the measured cooling gas inlet
temperature without any further consideration of the adiabatic
increase in adsorption temperature .DELTA.T.sub.Ad.
[0054] If, however, it must be assumed that the relative humidity
of the cooling air entering the container to be cooled is very high
or is approximately 100%, as is the case in adsorption systems
using heat from compressors in the form of dryers, for example, the
adiabatic increase in adsorption temperature .DELTA.T.sub.Ad can be
saved as a clear function of the inlet temperature T.sub.Cool,in of
the cooling air. In this case, a minimum system pressure is also
preferably assumed to be the prevailing pressure in the container
to be cooled.
[0055] Once the adiabatic increase in adsorption temperature
.DELTA.T.sub.Ad has been determined successfully by one of the
methods described above and with the aid of predefined measured
values or estimates, the cooling phase cut-off temperature
T.sub.Cp-Ct is determined. For example, the cooling phase cut-off
temperature T.sub.Cp-Ct is defined as the sum of the measured or
calculated inlet temperature T.sub.Cool,in of the incoming cooling
air, the defined adiabatic increase in adsorption temperature
.DELTA.T.sub.Ad and a previously defined cut-off temperature
difference .DELTA.T.sub.R in the following manner:
T.sub.Cp-Ct=T.sub.Cool,in+.DELTA.T.sub.Ad+.DELTA.T.sub.R
[0056] In FIG. 1 the cut-off temperature difference .DELTA.T.sub.R
is set at 9 K by way of example. However, an expert will realize
that the cut-off temperature difference .DELTA.T.sub.R can be
preset accordingly as a function of the relevant application.
[0057] FIG. 1 also shows measurement points for the outlet
temperature T.sub.Cool,out of the cooling air as established during
tests after 20 minutes cooling time which, in the present
embodiment, more or less corresponds to the time in which a
quantity of air with a heat capacity which is about twice as high
as the heat capacity of the adsorbent passes through the container
to be cooled. The measured temperature values lie on a curve which
runs parallel to the calculated adiabatic adsorption temperature,
as shown in FIG. 1, i.e., on a temperature curve which is displaced
in parallel by 9 K. By way of example, in the present embodiment of
the invention, the cut-off temperature difference .DELTA.T.sub.R
could accordingly be set initially at 9 K in order to calculate the
cooling phase cut-off temperature T.sub.Cp-Ct.
[0058] FIG. 2 illustrates the changes in the outlet temperature
T.sub.Cool,out of the emerging cooling air over time by way of
example, the measurement points from FIG. 2, which are shown in
FIG. 1, being identified by circles and associated numbers in each
case. As shown in FIG. 2, the initial difference between the
cooling air outlet temperature T.sub.Cool,out and the adiabatic
adsorption temperature T.sub.Ad at the time shown in FIG. 1, i.e.,
after 20 minutes, is already reduced by over 90%. However,
extending the cooling period even longer merely brought about a
very slow cooling down process in this particular measurement. In
the present embodiment of the invention, the cut-off temperature
difference .DELTA.T.sub.R and thus the cooling phase cut-off
temperature T.sub.Cp-Ct can accordingly be defined dynamically on
the basis of this information. In general terms, the cooling phase
cut-off temperature T.sub.Cp-Ct should for reasons of expediency be
slightly higher than the defined adiabatic adsorption temperature
T.sub.Ad. According to the present embodiment of the invention, the
selected cooling phase cut-off temperature T.sub.Cp-Ct is a
constant 9 K higher than the adiabatic adsorption temperature
T.sub.Ad, as shown in FIG. 1. As a result of this function, the
temperatures measured after 20 minutes are sufficiently close. The
adiabatic adsorption temperature T.sub.Ad can also be determined
and illustrated with sufficient accuracy for a pre-defined pressure
by approximation functions such as second-degree polynomials. The
parameters for the approximation functions can, for example, be
saved as reference values for various operating pressures in the
control unit storage device.
[0059] Alternatively, using a linear approximation in the relevant
range is also conceivable, as illustrated in FIG. 3 according to a
preferred embodiment of the present invention. It is clear to an
expert that various algorithms can be used by the control unit to
determine the cooling phase cut-off temperature from the measured
or estimated values with sufficient accuracy.
[0060] For example, a previously defined coolant flow phase length
(i.e., a pre-defined minimum cooling period in which an
uninterrupted flow of coolant is present in the container to be
cooled; this may for example start to operate again after the dryer
or the system compressor has been stationary), minimum cooling
phase length (i.e., a time span commencing from the start of the
cooling phase), a pre-defined delay time (i.e., a pre-defined time
span after the condition for termination has been achieved) and/or
a pre-defined maximum cooling phase cut-off temperature can be
defined as an additional criterion for terminating the cooling
phase, with the maximum cooling phase cut-off temperature
preferably being set to no more than the maximum admissible dryer
outlet temperature.
[0061] As already explained above, the adiabatic adsorption
temperature T.sub.Ad is dependent on the pressure of the cooling
gas during the cooling process in addition to the inlet temperature
and humidity of the cooling gas. This relationship is illustrated
in FIG. 4 by way of an example. The cooling phase control process
should therefore preferably be adjusted to the lowest proposed
operating pressure or alternatively the pressure should be recorded
by the control unit and taken into account when calculating the
adiabatic adsorption temperature T.sub.Ad.
[0062] Calculated values for the adiabatic adsorption temperatures
T.sub.Ad at atmospheric pressure as a function of the cooling air
temperature and the relative humidity of the cooling air are shown
in graph form in FIG. 5 by way of example. All the values shown in
the figures for adiabatic adsorption temperatures can vary
according to the adsorbent used. The cooling phase cut-off
temperature T.sub.Cp-Ct should preferably be above these
illustrated values, as already described in detail above.
[0063] Finally, the control unit terminates the cooling phase when
the current measured outlet temperature T.sub.Cool,out of the
emerging cooling gas falls below the dynamically determined and
currently applicable cooling phase cut-off temperature T.sub.Cp-Ct,
taking into account additional criteria such as falling below a
pre-defined maximum admissible dryer outlet temperature, in
particular. In the event that the measured outlet temperature
T.sub.Cool,out of the emerging cooling air does not fall below the
currently defined cooling phase cut-off temperature T.sub.Cp-Ct,
the cooling phase continues accordingly at least until the next
check. Such checks, i.e., the individual measurements, calculations
and approximations of the parameters for determining the cooling
phase cut-off temperature and outlet temperature to be defined, may
be performed continuously or discretely, as required. A number of
consecutive results can also be checked against each other for
plausibility, i.e., termination of the cooling phase is, for
example, only initiated if a pre-defined number of consecutive
evaluations show that the temperature has fallen below the cooling
phase cut-off temperature in each case.
[0064] A further preferred embodiment of the present invention will
be described in greater detail below with particular reference to
FIG. 2. Unlike the embodiments described above, a cooling phase
cut-off temperature is not dynamically defined as a threshold, but
a cooling phase cut-off temperature gradient is pre-defined as a
constant threshold beforehand. In this case, the gradient describes
the rate of temperature reduction as a function of time.
[0065] The versions of the preceding embodiments described above
should be consulted with regard to possible modifications which are
not described in further detail below. All the described
embodiments can of course be used in any combination with each
other, as required.
[0066] In the present embodiment of the invention, a cooling phase
cut-off temperature gradient is now initially defined as a constant
threshold, with the cooling phase being terminated by the control
unit when the gradient of the outlet temperature T.sub.Cool,out of
the emerging cooling air falls below this threshold. As a result,
the progress of the cooling process is defined by the changes in
the cooling air outlet temperature T.sub.Cool,out. As shown in FIG.
2, the gradient of the cooling air outlet temperature is lower as
the cooling air outlet temperature T.sub.Cool,out gets closer to
the minimum achievable limit temperature.
[0067] For example, the maximum dryer outlet temperature, a coolant
flow phase length, a minimum cooling phase length and/or a
pre-defined delay time can also be taken into account in this
instance, as in the embodiment described above. For example, in the
case of coolant flow phase length, this considers whether the
system compressor has operated without interruption over a
pre-defined period of time in order to rule out non-representative
values for the rate of reduction of the outlet temperature or for
the temperature gradient of the emerging cooling air, as the rate
of reduction of the cooling air outlet temperature T.sub.Cool,out
can be very low in the event of a compressor in the adsorption
system coming to a standstill and soon after such a compressor
starts up again, and this can lead to undesirable measurement
results. As a result, by presetting a pre-defined coolant flow
phase length, it should be possible to guarantee that a cooling gas
flow is present over a pre-defined period of time. In the present
embodiment of the invention, it is also advantageous to consider a
minimum cooling phase length from the beginning of the cooling
phase.
[0068] For example, the cooling phase cut-off temperature gradient,
i.e., the threshold for the temperature gradient at which the
cooling phase should be terminated, is defined beforehand and saved
in the control unit storage device. In addition, the gradient of
the cooling air outlet temperature is determined, particularly by
means of an appropriate temperature sensor for the purpose of
measuring the cooling air outlet temperature continuously or
discretely. In the event that the rate of reduction of the cooling
air outlet temperature, i.e., the gradient of the cooling air
outlet temperature, falls below the preset threshold, the control
unit terminates the cooling phase.
[0069] The cooling air outlet temperature T.sub.Cool,out is
preferably measured continuously, periodically or at pre-defined
times and evaluated continuously, periodically or at pre-defined
times, with the temperature gradients from consecutive evaluations
performed once or several times in sequence being required to be
below the preset threshold for the purposes of a plausibility check
before the cooling phase can be terminated. The embodiments
described above are referred to in this respect.
[0070] In this case, under some circumstances, it may not be
necessary to determine the adiabatic increase in adsorption
temperature for the purposes of cooling phase control in order to
guarantee sufficiently satisfactory cooling phase control,
especially when the plant is operated continuously with a constant
volume flow rate without having to continuously measure additional
parameters with the exception of the cooling air outlet
temperature. This represents a particularly simple variation on a
cooling phase control system.
[0071] It is clear to an expert that other algorithms can also be
used as part of the present embodiment of the invention. For
example, a threshold temperature which needs to be determined
dynamically in each instance is defined as a threshold by means of
a constant pre-defined cooling phase cut-off temperature reduction
rate or gradient. If the current measured outlet temperature
exceeds this threshold, this also means that the current rate of
temperature reduction or the current temperature gradient is lower
than the pre-defined constant threshold temperature gradient and
the cooling phase should thus be terminated.
[0072] Although the present invention has been described above by
means of preferred embodiments, it is not limited to the above, but
may be modified in multiple ways.
[0073] The processes described above can in particular be combined
with each other in any way in order to achieve a more reliable
cooling phase control. The respective application determines which
of the parameters determining cooling conditions are ultimately
measured, evaluated and used when determining the cooling phase
cut-off temperature or the cooling phase cut-off temperature
gradient.
[0074] Although the present invention has been substantially
explained by using the example of a compressed air dryer using
compressor heat, the present invention can of course also be used
accordingly for other heat-regenerating adsorption systems and
media other than air and water. Indeed, the present invention is
applicable to all adsorption processes in which the
heat-regenerated adsorbent needs to be cooled in some fashion. The
connection sequence and type of any valves, heat exchangers and
adsorption containers used in the system are not relevant in this
case. Cooling can be achieved both with the total process gas flow,
with part of this flow or equally with another cooling gas, and in
particular with ambient air.
[0075] In the case of dryers which use ambient air for cooling
purposes, the cooling phase cut-off temperature should preferably
not merely be calculated on the basis of the cooling air inlet
temperature alone. It is much better in this case to also measure
the loading of the cooling air entering the container, which has a
much greater influence on the adiabatic adsorption temperature at
atmospheric pressure due to the increased water content per mass of
air than at overpressure, as already explained with reference to
FIG. 5.
[0076] As a result of the invention for cooling phase control
described here, it is possible to simultaneously maintain the
specified pressure dew point under the reference conditions and
also allow emergency operation in excess of these reference
conditions. By increasing the cooling phase cut-off temperature in
this way, it is possible to guarantee a significantly improved
pressure dew point and this has the benefit that only a slight
increase in the temperature peak occurs at the dryer outlet.
* * * * *