US20100242504A1

US20100242504A1 - 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

Info

Publication number: US20100242504A1
Application number: US12/749,304
Authority: US
Inventors: Andreas Fredenhagen
Original assignee: Kaeser Kompressoren GmbH
Current assignee: Kaeser Kompressoren AG
Priority date: 2009-03-31
Filing date: 2010-03-29
Publication date: 2010-09-30
Also published as: DE102009002047B4; DE102009002047A1

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.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

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

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.
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.
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.
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.
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.
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.
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.
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.
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

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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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

The figures show:

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;

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;

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;

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

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

A preferred embodiment of the present invention is explained below in greater detail with the aid of FIGS. 1 and 2.
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_Cool,outof 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_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_Cp-Cton a correspondingly dynamic basis.
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_Cool,inof 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.
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_Cp-Ctby 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 ΔT_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_Cp-Ctfrom this data, whilst taking into account the respective adiabatic increase in temperature using a pre-defined algorithm. This is explained in greater detail below.
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_Cp-Ctor any reference values or similar values which are used are stored and can be used by the control unit for appropriate cooling phase control.
The adsorption system according to the present embodiment also has a temperature sensor to measure the current outlet temperature T_Cool,outof 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.
For example, as shown in FIG. 1, the current inlet temperature T_Cool,inof 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_Cool,inof 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_Cool,inis 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_Cool,inof 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.
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_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.
The adiabatic adsorption temperature T_Adis calculated or estimated by means of a pre-defined algorithm based on measured and/or estimated variables, or the adiabatic increase in adsorption temperature ΔT_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 ΔT_Adin FIG. 1 corresponds to the difference in temperature on the y axis between the dotted line for the inlet temperature T_Cool,inof the incoming cooling gas and the dashed line for the adiabatic adsorption temperature T_Ad.
The following process can for example be used to calculate the adiabatic increase in adsorption temperature ΔT_Ad. The adiabatic increase in adsorption temperature ΔT_Adis 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 ΔT_Adis 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.
For example, the adiabatic increase in adsorption temperature ΔT_Adcan 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:
$\begin{matrix} Δ T_{Ad} = \frac{{dM (t)}_{Water, ad} Δ h_{Ad}}{{dM (t)}_{Air} c_{P, air} + {dM (t)}_{Water, ad} c_{P, Water, Ad}} \\ \approx \frac{{dM (t)}_{Water, in} Δ h_{Ad}}{{dM (t)}_{Air} c_{P, Air} + {dM (t)}_{Water, in} c_{P, Water, Ad}} = \\ = \frac{x Δ h_{Ad}}{c_{P, air} + {xc}_{P, Water, Ad}} \\ \approx \frac{x Δ h_{Ad}}{c_{P, air}} \end{matrix}$ $where :$ $x = \frac{{dM (t)}_{Water, in}}{{dM (t)}_{air}}$
and where:

- dM(t)_Water,adrepresents the mass of adsorbed water over time;
- dM(t)_Water,inand dM(t)_Airrepresent 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)_Water,incan be assumed to be equal to the mass of adsorbed water over time dM(t)_Water,ad;
- Δh_Addefines 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
- c_P,airand c_P,water,adrepresent the heat capacities of air and adsorbed water.

As a result, the adiabatic increase in adsorption temperature ΔT_Adis 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 ΔT_Addynamically 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.
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 ΔT_Adcan 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 ΔT_Adcan 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 ΔT_Adand 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_Ador the adiabatic increase in adsorption temperature ΔT_Ad.
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_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 ΔT_Ad.
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 ΔT_Adcan be saved as a clear function of the inlet temperature T_Cool,inof 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.
Once the adiabatic increase in adsorption temperature ΔT_Adhas 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_Cp-Ctis determined. For example, the cooling phase cut-off temperature T_Cp-Ctis defined as the sum of the measured or calculated inlet temperature T_Cool,inof the incoming cooling air, the defined adiabatic increase in adsorption temperature ΔT_Adand a previously defined cut-off temperature difference ΔT_Rin the following manner:
T _Cp-Ct =T _Cool,in +ΔT _Ad +ΔT _R
In FIG. 1 the cut-off temperature difference ΔT_Ris set at 9 K by way of example. However, an expert will realize that the cut-off temperature difference ΔT_Rcan be preset accordingly as a function of the relevant application.
FIG. 1 also shows measurement points for the outlet temperature T_Cool,outof 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 ΔT_Rcould accordingly be set initially at 9 K in order to calculate the cooling phase cut-off temperature T_Cp-Ct.
FIG. 2 illustrates the changes in the outlet temperature T_Cool,outof 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_Cool,outand the adiabatic adsorption temperature T_Adat 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 ΔT_Rand thus the cooling phase cut-off temperature T_Cp-Ctcan accordingly be defined dynamically on the basis of this information. In general terms, the cooling phase cut-off temperature T_Cp-Ctshould for reasons of expediency be slightly higher than the defined adiabatic adsorption temperature T_Ad. According to the present embodiment of the invention, the selected cooling phase cut-off temperature T_Cp-Ctis a constant 9 K higher than the adiabatic adsorption temperature T_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_Adcan 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.
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.
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.
As already explained above, the adiabatic adsorption temperature T_Adis 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_Ad.
Calculated values for the adiabatic adsorption temperatures T_Adat 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_Cp-Ctshould preferably be above these illustrated values, as already described in detail above.
Finally, the control unit terminates the cooling phase when the current measured outlet temperature T_Cool,outof the emerging cooling gas falls below the dynamically determined and currently applicable cooling phase cut-off temperature T_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_Cool,outof the emerging cooling air does not fall below the currently defined cooling phase cut-off temperature T_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.
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.
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.
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_Cool,outof 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_Cool,out. As shown in FIG. 2, the gradient of the cooling air outlet temperature is lower as the cooling air outlet temperature T_Cool,outgets closer to the minimum achievable limit temperature.
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_Cool,outcan 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.
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.
The cooling air outlet temperature T_Cool,outis 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.
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.
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.
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.
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.
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.
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.
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.

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.