Abstract:
The invention relates to a method for temperature-dependent setting of a sealing gap between an adjustable seal and a revolving rotor of a regenerative heat exchanger by means of at least one actuating apparatus which comprises at least one rod body which is thermally influenced in an alternating manner and whose temperature-dependent change in axial length is converted into an actuating movement for the seal. It is provided in accordance with the invention that this rod bod is arranged at least in sections in a chamber and a control medium flows through or about this chamber at least in part, which medium acts in a direct or indirect manner in a thermally alternating fashion on said rod body, with the temperature level of the control medium corresponding to a temperature level of a gas volume flow flowing through the rotor, so that a change in axial length of this rod body is produced depending on a temperature change of this gas volume flow and a respective actuating movement for the seal is brought about.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims priority to EP application EP filed May 28, 2009. The contents of EP are incorporated herein by reference in their entirety. 
       BACKGROUND 
       [0002]    1. Related Field 
         [0003]    The invention relates to a method for the temperature-dependent setting of a sealing gap between an adjustable seal and a revolving rotor of a regenerative heat exchanger, according to the preamble of claim  1 . The invention further relates to an actuating apparatus concerning the same according to the preamble of the alternative independent claim. The invention further relates to a regenerative heat exchanger. 
         [0004]    2. Related Art 
         [0005]    Regenerative heat exchangers of the kind mentioned above are used for air preheating (APH) and/or gas preheating (GPH). For this purpose, a heat-emitting and a heat-absorbing gaseous medium are guided in counter-flow along heat storage bodies. The heat storage bodies, e.g. heating element packs, are arranged in a stator or rotor. 
         [0006]    When the heat storage bodies are arranged in a rotor (Ljungström principle) they are rotated through the cold and hot gas flows, so that a continuous exchange of heat between the gas flows is enabled. In the arrangement in a stator (Rothemühle principle), the heat exchange is enabled in such a way that rotating gas conduit connections, so-called rotary hoods, are arranged on both stator face sides, so that the gas flows rotate through the stator. In both variants, all existing gas flows flow through the heat storage bodies in an alternating fashion. 
         [0007]    In order to prevent leakages, various rotor seals are required both on a stator as well as especially on a rotor. These are radial seals, circumferential seals and axial or jacket seals on a rotor. As a result of changing thermal conditions, a continuous readjustment of these seals is necessary in operation in order to obtain defined sealing gaps. The following possibilities are known for setting or readjusting the sealing gap: 
         [0008]    Adjustment by hand (manual readjustment) 
         [0009]    Multi-point adjustment via an actuator system with actuating cylinders 
         [0010]    Electric actuating drives which are controlled automatically 
         [0011]    A thermally controlled actuating apparatus for temperature-dependent setting of a sealing gap is known from DE 2 162 248 A. The seals are then connected via spring bolts with bellows which are influenced in a thermally alternating manner. An enclosed gas volume is disposed in the closed bellows, which volume is heated or cooled by the ambient operating gases, thus changing the gas pressure, which can be utilized as an actuating force for a seal. Furthermore, rod bodies are known from the state of the art which are influenced in a thermally alternating manner and whose temperature-dependent change in axial length is converted into an actuating movement for the seal. These concepts are disadvantageous in many respects. 
         [0012]    In some embodiments, a an aspect of providing a simple, automatic and cost-effective possibility for setting seals in a regenerative heat exchanger is present. 
         [0013]    This may be achieved by a method described herein. This is further achieved by an actuating apparatus and a regenerative heat exchanger with the feature of the alternative independent claims. Preferred and advantageous further developments form the object of the dependent claims. 
         [0014]    Advantages may be achieved in respect of the method by a method for temperature-dependent setting of the sealing gap between an adjustable seal and a revolving rotor of a regenerative heat exchanger by means of at least one actuating apparatus which comprises at least one rod body which is thermally influenced in an alternating manner and whose temperature-dependent change in axial length is converted into an actuating movement for the seal. It is provided that this rod body is arranged at least in sections in at least one chamber a control medium flows through or about this chamber at least partly or in sections, which medium acts in a direct or indirect manner in a thermally alternating fashion on said rod body, with the temperature level of the control medium corresponding to a temperature level of a gas volume flow flowing through the rotor, so that a change in axial length of this rod body is produced depending on a temperature change of this gas volume flow and a respective actuating movement for the seal is brought about. 
         [0015]    A rod body is a solid body which is characterized by an axial longitudinal extension which is a multiple of its cross-sectional dimensions. A rod body that is influenced in a thermally alternating manner is made of a material which is subjected to a change in volume determined by the thermal expansion coefficient in the case of a change in temperature, leading, among other things, to a change in the axial length. 
         [0016]    A rod body that is influenced in a thermally alternating manner is arranged at least in sections in a chamber. The respective rod body is enclosed at least in sections by at least one chamber or penetrates at least one such chamber. The walls of such a chamber are preferably arranged to be fluid-tight. A control medium can be introduced into such a chamber for a direct influence in a thermally alternating manner, which control medium represents in accordance with the invention a thermal level of the gas volume flow passing through the rotor. The surface of the rod body can be arranged accordingly for better heat exchange. It is similarly possible to protect the surface of the rod body by a coating from a control medium that acts aggressively for example. The control medium can flow about this chamber for the purpose of an indirect influence of the rod body in a thermally alternating manner, as will be explained below in closer detail. Both possibilities can be combined with one another. 
         [0017]    The revolving rotor is used preferably for the heat transfer from a first gas volume flow, e.g. a flue gas volume flow, to a second gas volume flow such as a fresh-air or air-volume flow. Such a technology is used especially in power plants. 
         [0018]    A control medium can be a gaseous or fluid medium, which needs to be arranged in such a way that it can flow through a conduit system or the like. It is provided in accordance with the invention that the temperature level of this control medium corresponds with a temperature level of a gas volume flow flowing through the rotor, which means that there is a mutual correspondence. It can concern the first or second gas volume flow. It is preferably provided that it concerns the second gas volume flow, i.e. the air-volume flow, and its temperature level is relevant for setting the sealing gap after flowing through the rotor or at the rotor outlet (on the hot rotor side). 
         [0019]    One basic principle of some embodiments of the invention consists in the recognized correlation between the temperature level of a gas volume flow flowing through the rotor and a rotor deformation occurring at a specific temperature. Such a rotor deformation is a crown of a rotor for example, as described in detail in DE 2 162 248 A for example. This requires a setting of the sealing gap by readjusting the seals. This concerns the radial seals and the circumferential seals on both rotor sides and the axial and jacket seals. This invention enables a simple, but highly effective readjustment of rotor seals, through which the sealing gap can be set in an optimal manner at any time in a quasi automatic way under a large variety of operating conditions. 
         [0020]    It is provided in accordance with some embodiments of the invention that a temperature level of the control medium corresponds to a temperature level of a gas volume flow flowing through the rotor. This can be realized technically in different ways. It is possible for example that the control medium is in thermal connection with the gas volume flow via a heat exchanger. It is further possible that a partial volume flow used as a control medium is branched off from the gas volume flow. It is further possible to detect a temperature of the gas volume flow by means of measuring technique and thereafter to set the properties of the control medium in a purposeful way. These possibilities can also be combined with one another. A number of the possibilities will be explained below in closer detail as preferred further developments. 
         [0021]    Some embodiments of invention may have many advantages such as:
       The rod body/rod bodies that are influenced in a thermally alternating manner and the chamber or chambers enclosing the same can be arranged with independent location from one another;   the rod body/rod bodies that are influenced in a thermally alternating manner are substantially subjected to only one specific control medium;   the invention can be implemented for radial, circumferential and axial seals;   the respective seals automatically follow the rotor deformation in all load changes;   no electric, pneumatic, hydraulic and/or comparable actuating drives are required;   no electric wiring is necessary;   the sealing gaps can be adjusted individually in a location-dependent manner also during operation;   the sealing gaps remain the same during operation, i.e. there is very little leakage;   long service life, and   low maintenance costs.       
 
         [0032]    It is provided according to a preferred further development that a partial volume flow is branched off as a control medium from a gas volume flow flowing through the rotor and is supplied to at least one such rod body, for which purpose this rod body is arranged in sections in at least one chamber, with the branched-off partial volume flow flowing at least partly through and/or around said chamber, so that depending on a change in temperature this gas volume flow produces a change in axial length of this rod body and a respective actuating motion for the seal. The partial volume flow is preferably branched off at the hot rotor side from the second gas volume flow, i.e. the air volume flow. After the branching, the partial volume flow can further be subdivided into several partial volume flows. 
         [0033]    It is provided according to a preferred further development that the branched-off partial volume flow is recirculated to the same gas volume flow after having flowed through and/or about the chamber or is introduced into another gas volume flow flowing through the rotor. As a result, a partial volume flow branched off from the air volume flow is recirculated to the air volume flow or is introduced into the flue gas volume flow. The recirculation or introduction can occur before the entrance of the respective gas volume flow into the rotor or after the same. As a result of skilled recirculation or introduction, a pressure difference against the branch-off can be utilized which drives the partial volume flow. Such a measure is further advantageous from an energy point of view. 
         [0034]    It is provided according to a preferred further development that additionally a sealing gap measurement is performed by means of at least one sensor, on the basis of which at least one relevant property of the control medium or partial volume flow is changed under determination or control of a control unit in order to bring about a required change in axial length of this rod body and a respective actuating motion for the seal. Relevant properties of the control medium or partial volume flow are especially its pressure, temperature and flow volume. These properties can be influenced for example by heating and/or cooling and by a fan. It is the idea that by influencing the control medium or the partial volume flow, a defined change in length of a rod body is produced or controlled, thus causing a defined actuating motion for the seal. 
         [0035]    It is provided according to a preferred further development that an actuating apparatus comprises several such rod bodies which, by cooperation, produce an actuating motion for the seal, with at least two of these rod bodies being separately controllable via respective chambers by means of the control medium or partial volume flow in a thermally alternating manner. This will be explained below in closer detail in connection with the drawings. 
         [0036]    It is provided according to an especially preferred further development that a firstly cold control medium is supplied to at least one rod body and is heated thereafter in order to be supplied to further rod bodies. A good control precision can thus be achieved with respect to the sealing gap. This will be explained below in connection with the drawings. 
         [0037]    This object is achieved in respect of the apparatus by a thermally controlled actuating apparatus for a regenerative heat exchanger for setting a sealing gap between an adjustable seal and a revolving rotor, with the actuating apparatus comprising at least one rod body that is influenced in a thermally alternating manner and whose temperature-dependent change in axial length is converted into an actuating motion for the seal. It is provided that at least one rod body that is influenced in a thermally alternating manner is arranged at least in sections in at least one chamber and this chamber can be supplied directly or indirectly with a control medium which causes the (direct or indirect) influencing in a thermally alternating manner of this rod body. 
         [0038]    The statements made above in connection with the method in accordance with the invention apply to this actuating apparatus analogously and vice-versa. A branched-off partial volume flow of a gas volume flow heated by the rotor is preferably provided as a control medium. The actuating apparatus in accordance with the invention is especially suitable for performing the method in accordance with the invention and is provided for this purpose. 
         [0039]    It is provided according to a preferred further development that the control medium can flow at least partly or in sections through the chamber, for which purpose it comprises at least one inlet and at least one outlet. This leads to a direct or indirect influencing of the rod body in a thermally alternating manner. Such a chamber can be arranged as a through-flow chamber. This will be explained below in closer detail in connection with the drawings. 
         [0040]    It is provided according to a preferred further development that the control medium can flow about the chamber at least partly or in sections, for which purpose its walls are arranged to have double walls (i.e. with an enclosed cavity) and/or with a conducting jacket. This leads to an indirect influence of the rod body in a thermally alternating manner. 
         [0041]    It is provided according to a preferred further development that a relative motion is enabled between this rod body and the chamber. Alternatively, no relative motion is enabled between this rod body and the chamber. 
         [0042]    It is provided according to a preferred further development that this rod body is arranged as a tube. Preferably, the tube has a cross section in the shape of circular ring, with other cross-sectional shapes being possible. Massive arrangements are also possible. 
         [0043]    It is provided according to a preferred further development that the chamber is placed on the rod body. Preferably, the chamber is fixed to this rod body and completely encloses the same in the radial direction. The length of the chamber corresponds to approximately 60 to 80% of the axial length of the rod body in the axial direction, so that it preferably projects or protrudes beyond the chamber at both axial ends. Several chambers can also be provided in the axial direction of the rod body which can be supplied differently with control media for example. 
         [0044]    It is provided according to a preferred further development that the walls of the chamber are provided with at least one bellows-like section which enables a temperature-induced volume compensation. This will be explained below in closer detail in connection with the drawings. 
         [0045]    It is provided according to a preferred further development that several of these rod bodies are comprised which are arranged at least in sections parallel and/serially in a chamber. It is also possible that several such chambers are provided in which one group each of rod bodies is arranged. The number of the rod bodies jointly arranged in a chamber can be different. It is provided alternatively and/or additionally that several of these rod bodies are comprised which are arranged at least in sections in separate chambers. As a result, this encompasses all technically possible combinations of arrangements. 
         [0046]    If a plurality of rod bodies is comprised, it is provided according to a preferred further development that at least two rod bodies are made of the same material. In particular, all rod bodies are made of the same material. Even in the case of a similar choice of material, the rod bodies can expand or contract differently as a result of different axial lengths and/or temperature stresses. It is provided alternatively and/or additionally that at least two rod bodies are made of different materials. 
         [0047]    It is provided according to a preferred further development that at least one first chamber is provided with an inlet for non-heated or cool control medium such as air and at least one second chamber with an inlet for a heated control medium, so that the rod bodies that are arranged in said chambers can be subjected to a defined temperature difference by a respective supply of a control medium (air). It is the idea that an independent system is created with an adjustable temperature for the control medium or an adjustable flow volume, with which the axial change in length can be influenced in a purposeful manner. This will be explained below in closer detail in connection with the drawings. 
         [0048]    It is provided according to a preferred further development that the first chamber and the second chamber are in flow connection and the first chamber is provided upstream of the second chamber with respect to a preferred direction of flow of the control medium. The flow connection is realized by means of a tubing system. A preferred tube diameter of this tubing system is approximately 20 mm. This will be explained below in closer detail in connection with the drawings. 
         [0049]    According to a preferred further development, the system comprises at least one heating and/or cooling device. It is especially provided that a heating device for auxiliary heating of the control medium is arranged between an outlet of the first chamber and the inlet of the downstream second chamber. Preferably, such a heating device is embedded in a possible tubing system. Preferably, this heating device can be bridged for example by means of a bypass for example. This is especially considered in the case that the control medium is at least partly a warm or hot partial volume flow which is branched off or derived from a gas volume flow passing through the rotor. An additional heating might not be necessary in this case. Cooling might be necessary however. This will be explained below in closer detail in connection with the drawings. 
         [0050]    At least one blower device is comprised according to a preferred further development. It is especially provided that between the outlet of the first chamber and the inlet of the downstream second chamber a blower device is arranged for auxiliary conveying of the control medium. Preferably, such a blower device is embedded in a possible tubing system. The blower device can possibly be used to increase the pressure in the control medium. This will be explained below in closer detail in connection with the drawings. 
         [0051]    At least one valve device is comprised according to a preferred further development. It is especially provided that at least one valve device is comprised for controlling the volume flow of the control medium. Preferably, such a valve device is embedded in a possible tubing system. This will be explained below in closer detail in connection with the drawings. 
         [0052]    At least one filter device is comprised according to a preferred further development. It is especially provided that this filter device is arranged before the rod bodies in the direction of flow and should prevent potential dirt deposits on the rod bodies. Preferably, such a filter device is embedded in a possible tubing system. 
         [0053]    At least one sensor for measuring the sealing gap is comprised according to a preferred further development. 
         [0054]    A control unit is comprised according to a preferred further development. It is especially provided that this control unit or control device controls a heating device and/or a cooling device, a blower device and/or a fan device on the basis of the sensor measurement signal. The control unit preferably concerns an electronic control unit which especially comprises a software-based control algorithm. 
         [0055]    The object is further achieved in respect of the apparatus by a regenerative heat exchanger, comprising at least one thermally controlled actuating apparatus in accordance with the invention. It is especially provided that this regenerative heat exchanger is or can be operated according to the method in accordance with the invention. The statements made above apply in an analogous manner to this regenerative heat exchanger. 
         [0056]    According to a preferred further development of this regenerative heat exchanger, it is provided that the seal which is adjustable by means of the actuating apparatus is a radial seal, a circumferential seal and/or a jacket seal. It is especially provided that the seal which is adjustable by means of the actuating apparatus in accordance with the invention is a radial seal and/or a circumferential seal on the cold rotor side and/or the hot rotor side. 
         [0057]    The will be explained below by reference to the drawings that show schematically: 
     
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         [0058]      FIG. 1  shows the rotor of a regenerative heat exchanger in a side view; 
           [0059]      FIG. 2  shows an embodiment of an actuating apparatus in accordance with the invention in a sectional view; 
           [0060]      FIG. 3  shows an alternative embodiment of an actuating apparatus in accordance with the invention in a sectional view; 
           [0061]      FIG. 4  shows a further embodiment of an actuating apparatus in accordance with the invention with an exemplary wiring, and 
           [0062]      FIG. 5  shows the progress over time of the rod body temperature at a temperature jump of the control medium in a diagram. 
       
    
    
     DETAILED DESCRIPTION 
       [0063]      FIG. 1  shows a rotor designated in its entirety with reference numeral  1  of a regenerative heat exchanger. Rotor  1  comprises a vertical rotation axis  2 . The rotation direction is indicated by way of example with the arrow R. A first gas volume flow  3 , which can concern a hot flue gas volume flow for example, and a second gas volume flow  4 , which can concern a cool air volume flow for example, flow in opposite directions through the rotor  1 . Heat from the first gas volume flow  3  is transferred to the second gas volume flow  4  by means of rotor  1 , through which the first gas volume flow  3  cools off during passage through the rotor  1  and the second gas volume flow  4  is heated up during the passage through the rotor  1 . As a result of the existing temperature conditions, the upper rotor face side can be designated as the hot face side (or rotor side) A and the bottom rotor face side as the cold face side (or rotor side) B. A sealing gap is designated with U by way of example. 
         [0064]    Circumferential seals  7   a  and  7   b , radial seals  8   a  and  8   b , and axial seals or jacket seals  9   a  and  9   b  are provided to prevent leakages on the rotor  1 . These seals  7   a ,  7   b ,  8   a ,  8   b ,  9   a ,  9   b  can be arranged in a segmented manner. As a result of the changing thermal conditions, it is necessary to continually readjust these seals in operation in order to maintain defined sealing gaps. This readjustment of the seals  7   a ,  7   b ,  8   a ,  8   b ,  9   a ,  9   b  occurs by means of at least one actuating apparatus  10  in accordance with the invention, as will be explained below in closer detail. Several such actuating apparatuses  10  can be provided for a seal  7   a ,  7   b ,  8   a ,  8   b ,  9   a ,  9   b , which actuating apparatuses are operated in an autonomous fashion or in agreement with one another. 
         [0065]      FIG. 2  shows a simple embodiment of an actuating apparatus  10  in accordance with the invention in a schematic sectional view. The actuating apparatus  10  is fixed in a stationary manner to a housing section or frame  5  of the regenerative heat exchanger. The actuating apparatus  10  comprises an actuating unit  11  and an actuating section or actuating drive  12 . Several rod bodies  13  and  14  are arranged in the actuating section, the axial length of which varies depending on a momentary temperature. The rod bodies  13  are provided with the same axial lengths and shorter than the rod body  14 . 
         [0066]    The outer rod bodies  13 , the arrangement of which on the outside is merely exemplary, are fixed with their axial ends on the left side to a fixed bearing  15 . In the case of a temperature-induced change in axial length of the rod bodies  13 , these changes in length are transferred to the floating bearing  16  on the right side. The translational movement V on the floating bearing  16  is transferred via the rod body  14  to a tilting lever  20  which moves the respective seal via an adjusting bolt  21 , which is indicated by a double arrow X. The threaded nuts  22  are used for manually adjusting the seal. The illustrated lever mechanism is merely exemplary. Other mechanical actuating drives can thus be readily realized. Similarly, the illustrated diagonal arrangement of the rod bodies  13  and  14  is merely exemplary. 
         [0067]    The rod bodies  13  are made of a material which has a large amount of volume change in the case of changes in temperature. The rod body  14  is made of a material which has a considerably lower change in volume at the same amount of change in temperature, so that changes in length of the rod bodies  13  are not compensated by a change in length of this rod body  14 . The actuating mechanism can also be described as follows: the rod bodies  13  with a high thermal expansion initiate an actuating movement which is transferred via at least one rod body  14  with a low thermal expansion to the actuating drive  12 . The number of the individual types of rod bodies is merely exemplary, with it being preferable that several rod bodies  13  are provided which can produce high actuating forces. The rod bodies  13  are subjected to pressure and can therefore be designated as pressure rods. The rod body or bodies  14  are subjected to tensile stress and can therefore be designated as tension rods. 
         [0068]    The rod bodies  13  and  14  are arranged in a chamber  17  which is formed by a fluid-tight wall  17   a . In the illustrated embodiment, the rod bodies  13  and  14  are completely enclosed by the chamber  17 . Chamber  17  comprises an inlet  18  and an outlet  19  by way of example. A control medium can flow through the chamber  17  via the inlet  18  and the outlet  19 , which is indicated by the flow arrows. The control medium flows directly around the rod bodies  13  and  14 , which subsequently assume the current temperature of the control medium. A change in temperature in the control medium causes a change in axial length of the rod bodies  13 , through which an actuating movement X for the seal is initiated, as already explained above. 
         [0069]    A gaseous medium is preferred as a control medium. It is especially provided that a partial volume flow is used as a control medium which is branched off from the second gas volume flow to be heated or the air flow  4  after its passage through the rotor  1 , i.e. on the hot face side A of rotor  1 . As a result of a correlation between the temperature of this gas volume flow  4  on the hot face side A of rotor  1  and an obtained rotor deformation, the actuating apparatus  10  can be set mechanically in such a way that the respective seal is readjusted at a specific change in temperature with a defined path, which then occurs in a quasi automatic manner. A specific actuating path length X can be determined for example by the transmission ratio in the mechanical actuating drive  12  or by choosing the material of the rod body  13  and  14  or its geometric dimensions. 
         [0070]    If necessary, the reaction time can be varied via the flow volume and/or the flow pressure of the control medium in the chamber  17 , which reaction time is needed by the rod bodies  13  and  14  in order to adjust to the current temperature of the control medium. In order to enable changing the flow volume and/or the flow pressure, a heating and/or cooling device and a fan device can be comprised. It can further be necessary under certain circumstances to change the properties of the control medium in a purposeful way in order to thus produce a desired actuating movement X for the seal. This will be explained below in closer detail in connection with a further embodiment on the basis of  FIG. 3 . 
         [0071]      FIG. 3  shows an alternative embodiment of an actuating apparatus  10 . Its configuration is substantially identical to the configuration as shown in  FIG. 2 . It is provided in a deviating manner in this case that the control medium does not flow directly about the rod bodies  13  and  14  and there is thus no direct influence in an alternating thermal manner, but that the control medium is guided through a hollow chamber  17   b  in wall  17   a  and thus does not come into direct contact with the rod bodies  13  and  14 , for which purpose the wall  17   a  is provided with a double wall. The rod bodies  13  and  14  are influenced in an alternating thermal manner only indirectly in that the control medium transfers its temperature level to the air (possibly also a gas or a fluid) enclosed in chamber  17 . Such an arrangement offers advantages concerning sealing for example. Furthermore, aggressive control media can also be used without having a negative effect on the seals and/or the rod bodies  13  and  14 . Instead of a hollow chamber  17   b  or in addition thereto, the wall  17   a  of the chamber  17  can also be enclosed at least in sections by a sheath of lines such as spiral flow line through which the control medium will flow. 
         [0072]    In accordance with  FIG. 4 , an alternative actuating apparatus  10  comprises a rod body  14  arranged as a tension rod and several rod bodies  13  arranged as pressure rods. They are each enclosed in a fluid-tight chamber  171  and  172  which are arranged in this case as hollow-cylindrical jackets with circular face sides. The chambers  171  and  172  are arranged as through-flow chambers with direct flow through the same. The chambers  171  and  172  are quasi placed from the outside on rod bodies  13  and  14 . The chambers  171  and  172  are part of a flow or tubing system which comprises an inlet  181 , several connecting lines  40 , one outlet  192 , several valves or valve devices  51  to  54 , a filter device  60 , a controllable fan device  60 , and a controllable electric heating device  70 . The two through-flow chambers  171  and  172  are switched behind one another. The connecting lines  40  of the tubing system have an inside diameter of approx. 20 mm for example. 
         [0073]    The pressure rods  13  and the tension rod  14  are arranged parallel with respect to one another and enable a temperature-dependent adjustment of a seal in the manner as explained above, with a circumferential seal  7  being concerned in this case by way of example. The sealing gap to rotor  1  is designated with U. Whereas the pressure rods  13  are held in a rigid manner on a fixed bearing  15  at their upper axial ends, the bottom axial ends can move in a floating bearing  16 . This movement in the floating bearing  16  is transferred via the tension rod  14  and a lever rod assembly (not shown in closer detail) as an actuating movement to the seal  7 , which is designated in lieu with U. The pressure rods  13  and the tension rod  14  have different coefficients of thermal expansion for this purpose. Alternatively or in addition, they can be arranged with different cross sections. In the illustrated example, the rod bodies  13  and  14  are further arranged with different axial lengths. 
         [0074]    In a preferred constructional arrangement, the rod bodies  13  and/or  14  are arranged as round rods with a rod diameter of approx. 10 to 20 mm. Their axial length is approx. 2 m for example. The chambers  171  and  172  are preferably arranged in a circular-cylindrical manner and have an inside diameter of approx. 100 mm for example. 
         [0075]    The chambers  171  and  172  have a substantially unchanged volume. A control medium can be guided through these chambers  171  and  172  (through-flow chambers), which medium has a direct thermal influence on the pressure rods  13  and the tension rod  14 . the chambers  171  and  172  are rigidly connected at their face sides with the associated tension and pressure rods  13  and  14 . In order to compensate the temperature-induced changes in length, the walls of the chambers  171  and  172  comprise bellows  173  and  174 . 
         [0076]    In the illustrated embodiment, unheated ambient air is drawn at a temperature of 20° C. for example via the inlet  181  at one end into the chambers  171  which enclose the pressure rods  13 . This “air” is used subsequently as a control medium. It flows about the pressure rods  13  virtually over their entire complete length and is then discharged via the outlet  191  at the other end. From there it reaches the electric heating device  70  via a connecting line  40  where it is heated before it is supplied to the inlet  182  of the chamber  172  which encloses the tension rod  14 . If required, the heating device  70  can also concern a cooling device or a combined heating/cooling device. The output of the heating device  70  is controlled by a control unit  80  which communicates with a sensor  90  for example for measuring the sealing gap U. A fan device  60  is further arranged in the connecting line  40 , which is used to produce the flow in the tubing system or at least to support the same. The fan device  60  can also be controlled by the control unit  80 . Moreover, a filter unit  50  is arranged upstream of the heating device  70  which especially removes solids from the control medium or the air. 
         [0077]    The air heated by means of the heating device  70  and/or the fan device  60  is finally discharged via the outlet  192  after having flowed along the tension rod  14  over virtually its entire length, and is preferably supplied to the gas volume flow  4  to be heated (not shown). 
         [0078]    The rod bodies  13  and  14  can be subjected to different temperatures with the illustrated arrangement. This leads to a good controllability. Furthermore, it is possible to provide an indirect control of a sealing gap depending on the temperature of the gas volume flows and a partial volume flow which is possibly branched off from the same. It thus offers the advantage that a flow along the rod bodies  13  and  14  specifically predetermined by the chambers  171  and  172  can be produced, so that a defined heat transfer to the rod bodies  13  and  14  is ensured. It is thus also possible to easily determine the dependence on the changes in axial length or the flow volume of the air (or the control medium) and to set the sealing gap U on seal  7  in this way. Since the invention can be arranged as an independent system, it can be used in many ways. Because of the relatively simple components, the system works reliably and can be built at low cost. 
         [0079]    As an alternative to or in support of the heating device  70  and/or the fan device  60 , the heated air can also be branched off from the hot face side of the rotor  1  and be supplied via a further inlet  41  to a node  42  in the connecting line  40 . The feeding is controlled by the valves  51  and  52 , which can also be controlled by the control unit  80 . It is generally prevented by closing the valve  51  that an undesirable return flow of the heated air to the pressure rods  13  occurs. 
         [0080]    A bypass  44  with a valve  53  arranged therein leads about the heating device  70 , with which the air can optionally be guided past the heating device  70 . The flow volume of the air through the heating device  70  can be blocked off partially or completely via the downstream valve  54 . The valves  53  and  54  are also used for determining the flow volume and optionally the temperature of the air at the inlet  182  by the mixing ratio. The valves  53  and  54  are also controlled by the control device  80 . A bypass is also possible on the fan device  60  and/or the filter device  50 . 
         [0081]      FIG. 5  shows the time progression of the rod body temperature S at a jump of the temperature L of the control medium in a diagram. It can be recognized that the rod body temperature S approaches the temperature L of the control medium flowing through the chamber  17  (or  171  and/or  172 ) in a temporally sluggish manner, with the axial change in length occurring in synchronicity with this progression S. This temporal behavior must ideally be considered in the configuration of the actuating apparatus  10 . The temporal behavior can be influenced for example via the fan device  60  and/or the heating/cooling device  70 , which is then optionally initiated by the control device  80 .