Method for operating a nitric acid plant and nitric acid plant

Abstract

The invention relates to a method for starting a nitric acid plant (1), wherein: at least one operating point is approached on the basis of a process pressure and a volume flow of the nitric acid plant; at least part of the process pressure is adjusted via at least one exhaust gas expander (2); and at least part of the volume flow is adjusted via at least one compressor (3). The method, which significantly simplifies start-up in comparison with the state of the art, is characterised in that, for permitted operating points, a lower limit (4) is defined on the basis of pressure and volume flow and an upper limit (5) is defined on the basis of pressure and volume flow, and in that a signal is provided when the lower limit (4) or the upper limit (5) has been reached during the adjustment of the pressure and / or the volume flow.

Description

[0001] Method for operating a nitric acid plant and nitric acid plant

[0002] The invention relates to a method for starting up a nitric acid plant or for driving into a partial load range, wherein at least one operating point is approached as a function of a process pressure and a volume flow of the nitric acid plant, wherein at least part of the process pressure is adjusted via at least one exhaust gas expander, wherein at least part of the volume flow is adjusted via at least one compressor.

[0003] In addition, the invention relates to a nitric acid plant with at least one compressor and at least one exhaust gas expander.

[0004] Nitric acid is an important basic material in the chemical industry and is used, for example, as a basis for the production of fertilizers, explosives and for the nitration of organic substances in the production of dyes and disinfectants.

[0005] Since the beginning of the 20th century, nitric acid has been produced using the so-called Ostwald process, which is still the basis for large-scale industrial production today. This reaction involves a catalytic reaction of ammonia. The resulting nitrogen monoxide reacts to form nitrogen dioxide, which reacts with water to form nitric acid, which can be separated in trickle towers.

[0006] To produce nitric acid, ammonia NH3 is first reacted with air to produce nitrogen oxide NO, which is then oxidized to nitrogen dioxide NO2. The nitrogen dioxide NO2 thus obtained is then absorbed in water to produce nitric acid. To ensure that as much of the nitrogen dioxide NO2 as possible is absorbed by the water, the absorption usually takes place at elevated pressure, preferably at pressures between 4 and 14 bar. The oxygen required for the conversion of the ammonia used as a raw material is usually supplied in the form of atmospheric oxygen. For the purpose of supply, the process air is compressed in a compressor and brought to a pressure that is suitable for both the oxidation reaction and the absorption reaction.

[0007] Typically, the energy for compressing the air is obtained by expanding the residual gas emerging from the absorption process to ambient pressure in a residual gas expander, also known as a residual gas turbine, and by utilizing the heat released during the conversion. Nitric acid plants, constructed in various designs, are adapted to the specific requirements of their respective locations.

[0008] Nitric acid can be produced using the pressure process or the dual-pressure process. In the pressure process, both combustion and absorption are carried out at medium pressure (< 8 bar) or high pressure (> 8 bar).

[0009] Pressure-pressure processes are particularly used when the required daily production is low. In these cases, the nitric acid plant is preferably operated using the mono-high-pressure process or the mono-medium-pressure process. In the mono-high-pressure process, the ammonia combustion and the nitrogen oxide absorption occur at approximately the same pressure of > 8 bar. The advantage of the mono-high-pressure process is that it ensures a compact design.

[0010] In the mono-medium-pressure process, the combustion of ammonia and the absorption of nitrogen oxides take place at approximately the same pressure of < 8 bar. The advantage of the mono-medium-pressure process is that it ensures optimal combustion yield.

[0011] However, if large nominal capacities and / or higher acid concentrations are required, a nitric acid plant designed according to the dual-pressure process represents the more economical solution. In the dual-pressure process, the ammonia used is burned at a first pressure, namely at a lower pressure than the absorption pressure. The nitrous gases formed during combustion, also called nitrous gases, are generally cooled and compressed to the second pressure, the absorption pressure, by means of nitrous gas compression. The advantage of the dual-pressure process is that the pressure levels are adapted to the respective reactions, thus ensuring both optimal combustion yield and compact absorption.

[0012] In general, the plants for carrying out the processes discussed above comprise at least one air compressor and at least one expansion turbine for the residual gas (also called "residual gas turbine" or "exhaust gas expander").

[0013] In contrast to steady-state operation, the existing equipment does not operate under normal conditions during the start-up and shut-down processes of nitric acid plants and often requires additional control. When starting up from a shut-down / cold state, the nitric acid plant is typically first filled with air using external energy (e.g., external steam or electricity) ("air operation"). Initial NOx emissions occur as soon as the absorption tower is filled with nitric acid from a storage tank during the start-up process, and the nitrogen oxides contained in the acid are blown out through the air. In today's plants, the NOx generated during the filling process is emitted. Upon completion of the filling process, NOx emissions initially cease until the NH3 oxidation of the nitric acid plant is started ("ignited").After ignition, the temperature and NOx concentration in the plant rise steadily to the steady-state operating value and the individual plant components can be operated as planned from a certain point in time.

[0014] During start-up, the so-called "machine train," i.e., the compressors and exhaust gas expanders / turbines required to operate the nitric acid plant, are put into operation. This is a sensitive system in which changes to the settings of a compressor affect the entire system just as much as corresponding settings of an exhaust gas expander / turbine. Starting up the nitric acid plant therefore requires constant and sensitive manual readjustment of the settings of the individual parts of the machine train.

[0015] The difficulty lies in approaching an operating point via the compressors and exhaust expanders / turbines in such a way that no areas are reached that could disrupt the production process or cause a trip (safety shutdown) of the machine train, thus halting nitric acid production. The same applies to the transition from normal or full-load operation to partial-load operation. Here, too, it is important to avoid areas that could disrupt the production process or even trigger a machine trip.

[0016] It is therefore an object of the present invention to provide a method for starting up and driving into the partial load range of a nitric acid plant as well as a nitric acid plant in which the starting up and setting of the partial load operating points is simplified compared to the prior art.

[0017] This object is initially achieved by patent claim 1 in that for permissible operating points both a lower limit (4) is defined, which depends on a first pressure-dependent process variable and a second flow-dependent process variable, and an upper limit (5) is defined, which depends on the first pressure-dependent process variable and the second flow-dependent process variable, and that a signal is given when the lower limit (4) or the upper limit (5) is reached when the first process variable and / or the second process variable is set.

[0018] The first pressure-dependent process variable can be, for example, a pressure, a pressure ratio, a delivery head or similar pressure-dependent variables. Accordingly, the second flow-dependent process variable can be a delivery flow, a mass flow, a volume flow, an orifice plate or mass flow signal or a similar flow-dependent variable.

[0019] The lower limit is understood to be points at which the pressure and / or volume flow are too low. The upper limit is understood to be points at which the pressure and / or volume flow or mass flow are too high. The final pressure or the polytropic delivery head can be used as parameters. The lower and upper limits can therefore be viewed analogously to characteristic curves. In compressor characteristic curves, for example, the relationship between the delivery head and the corresponding volume flow or delivery flow is shown graphically in a coordinate system. The volume flow can be plotted on the x-axis. It is also conceivable to display a flow signal, a mass flow, a dimensionless flow rate coefficient, a Delta P signal via a flow measuring device or similar suitable quantities. The y-axis can represent the delivery head.It is also conceivable to represent a pressure, a pressure ratio, a pressure change energy, a dimensionless pressure coefficient, or similar suitable quantities. The lower and upper limits define a characteristic map containing the permissible operating points of the nitric acid plant.

[0020] The machine set of the nitric acid plant according to the invention comprises at least one compressor and at least one exhaust gas expander. The at least one compressor is an air compressor. Additionally, the machine set can also have at least one further compressor (NOx compressor) and another drive machine, for example in the form of a drive steam turbine or drive gas turbine or an electric motor. The additional drive machine serves to provide the remaining energy required for the operation of the machine set.

[0021] The advantage of the method according to the invention is that it provides the operator with a kind of "parking assistant," analogous to driving a car. The approach to the lower or upper limit can be signaled to the operator acoustically and / or visually or in another suitable manner. Additionally, the approach to one of the limits can be signaled. The signals can be clearer or more forceful the closer the current operating point is to the upper or lower limit. For this purpose, a range can be provided from which a first signal is issued before the lower or upper limit is reached.

[0022] To convert the required characteristic map values, volume flow, pressure, and temperature signals are required, which can be processed, for example, by a machine control system. These can be recorded using suitable sensor data.

[0023] For the operation of the aforementioned dual-pressure process, a first embodiment of the method according to the invention provides for a second compressor to set a second pressure level in a part of the nitric acid plant process. Accordingly, the second compressor is also part of the machine train and must be taken into account when starting up the nitric acid plant. The second compressor can be a compressor for compressing nitrogen oxide (NO).

[0024] In a further preferred embodiment of the method according to the invention, the setting of the second flow-dependent process variable is adjusted via the at least one compressor using control elements. The control elements can be designed in the form of an adjustable guide vane and / or a throttle valve. Further conceivable embodiments of the control elements can also be adjustable control valves or similar suitable control elements that enable the control of a volume flow. Control elements for adjusting the speed of the compressor, for example, would also be conceivable. Opening the control elements increases the volume flow or mass flow. Closing the control elements decreases it.

[0025] Accordingly, in a further embodiment of the method according to the invention, the setting of the first pressure-dependent process variable is adjusted via the at least one exhaust gas expander using control elements. The control elements can be in the form of an adjustable guide vane and / or a throttle valve. Conceivable further embodiments of the control elements can also be adjustable control valves or similar suitable control elements that enable the regulation of a pressure. The process pressure is regulated via an inlet-side throttle valve and / or via adjustable guide vanes upstream of or in the exhaust gas expander. Opening reduces the process pressure and thus also the outlet pressure from the NO and air compressor, while closing increases it. Conceivable further embodiments of the control elements can also be adjustable control valves or similar suitable control elements that enable the regulation of a volume flow.For example, control elements for adjusting the speed of the exhaust gas expander would also be conceivable.

[0026] Furthermore, a further embodiment of the method according to the invention provides that the second flow-dependent process variable is partially adjusted via the speed of the at least one compressor. The volume flow or mass flow increases when the speed of the compressor is increased and decreases when the speed is correspondingly reduced.

[0027] In a further preferred embodiment of the method according to the invention, a warning is issued when the lower limit or the upper limit is reached when setting the first pressure-dependent process variable and / or the second flow-dependent process variable. The warning clearly signals to the operator that action is required before the machine is driven into areas where operation of the nitric acid plant is no longer possible and production must be interrupted. This allows the operator to control corresponding parts of the machine train in the opposite direction.

[0028] In a further advantageous embodiment of the method according to the invention, it is further provided that the adjustability of the at least one compressor and / or the at least one exhaust gas expander is blocked if, when setting the first pressure-dependent process variable and / or the second flow-dependent process variable, a previously defined lower approximation limit to the lower limit or a previously defined upper approximation limit to the upper limit is reached.

[0029] Since the machine train system reacts very slowly during adjustment, it is advisable to define an approach limit. Upon reaching this limit, the control option is blocked, as the system tends to overshoot. The approach limit may then cause the lower or upper limit to be reached after the blockage, but this limit will not be exceeded, thus eliminating the risk of the nitric acid plant being driven into a range where safe operation is no longer possible.

[0030] In this way, control by the operator in the wrong direction can be prevented. This mechanism is comparable to an automatic braking system in a motor vehicle when the vehicle is driven too close to an obstacle. In a particularly preferred embodiment of the method according to the invention, the start-up is carried out in stages and automatically. This means that although the start-up is carried out fully automatically by a machine control system, the step-by-step start-up is necessary because an adjustment of the above-mentioned control elements, i.e. throttle valve, adjustable guide vanes or a change in the speed, can quickly lead to an overshoot of the lower and / or upper limit due to the sluggish process. The adjustment of the control elements is therefore carried out in small steps or in steps. The control system takes over step by step and monitors the activation of the control elements.

[0031] In order to further improve the starting behavior and partial load driving behavior, a further embodiment of the method according to the invention provides that an approach speed to the lower limit and / or the upper limit is monitored.

[0032] Furthermore, a further embodiment of the invention provides that if a previously defined first approach speed is exceeded, the adjustability of the at least one compressor and / or the at least one exhaust gas expander is blocked. Similar to the blocking of the adjustment option upon reaching the lower or upper limit, reaching a certain approach speed is also potentially damaging to the nitric acid plant, since if the approach speed is too high, it can no longer be assumed that the system will not overshoot the lower and / or upper limit.

[0033] Furthermore, in a further embodiment of the method according to the invention, it can be provided that, when a previously defined second approach speed is exceeded, the at least one compressor and / or the at least one exhaust gas expander is controlled in the direction opposite to the lower or upper limit. If the approach speed is so great that an overshoot beyond the lower and / or upper limit can no longer be prevented if no action is taken, then active control is performed in the opposite direction. The degree of control can depend on the value of the approach speed.

[0034] The above-mentioned object is also achieved by a nitric acid plant with at least one compressor and with at least one exhaust gas expander, characterized in that the plant comprises a control device which is designed to carry out the method according to the invention. All previous statements concerning the method also apply accordingly to the nitric acid plant.

[0035] The nitric acid plant according to the invention is characterized in that the control device is designed to detect the movement of the operating points and to act when the nitric acid plant is operated automatically, in that the control device sets a signal to L when the operating point of the compressor crosses the upper limit, and in that the control device resets a signal to R when the operating point of the compressor falls below the lower limit, wherein the adjustable guide vane of the exhaust gas expander or the compressor is opened or closed according to the signals L or R.

[0036] In particular, the invention provides that the signals of the control device

[0037] - the adjustable guide vane of the compressor is opened and the adjustable guide vane of the exhaust gas expander is blocked if the operating point is to be shifted in the direction of an increase in the second flow-dependent process variable, or

[0038] - to shift the operating point towards an increase in the first pressure-dependent process variable, the adjustable guide vane of the exhaust gas expander is gradually closed, whereas the adjustable guide vane of the compressor is blocked,

[0039] - where for a shift of the operating point in the opposite direction the steps are carried out in exactly the opposite way, i.e.

[0040] - that the adjustable guide vane of the compressor is gradually closed if the operating point is to be shifted towards a reduction of the second flow-dependent process variable, or

[0041] - the adjustable guide vane of the exhaust gas expander is gradually opened in order to shift the operating point towards a reduction of the first pressure-dependent process variable.

[0042] In detail, there are numerous possibilities for designing and developing the method and system according to the invention. Reference is made to the claims subordinate to claim 1 as well as to the following description of preferred embodiments in conjunction with the drawings. The drawings show:

[0043] Fig. 1 is a schematic representation of part of a nitric acid plant, Fig. 2 is a schematic representation of the partial load operation of a nitric acid plant with an embodiment of the method according to the invention and

[0044] Fig. 3 is a schematic diagram of a controller logic for automatic start-up and partial load operation of the nitric acid plant.

[0045] Fig. 1 shows a schematic representation of a nitric acid plant 1 with an exhaust gas expander 2 and a compressor 3 in the form of an air compressor. The compressor and exhaust gas expander are combined to form a machine train. In order to set the correct operating point when starting up the nitric acid plant 1, limits are defined, namely a lower limit 4 and an upper limit 5, which are explained in more detail in Fig. 2. The nitric acid plant shown in Fig. 1 is operated according to the dual-pressure process. Therefore, a second compressor 6 is provided, which is used to compress nitrogen oxide NO to a second pressure level. The compressors 5, 6 and the exhaust gas expander 2 can be controlled via control elements 7.

[0046] In general, in the nitric acid plant 1 shown in Fig. 1, ammonia NH3 is first reacted with air compressed by compressor 3 in reactor 8. This produces nitrogen oxide NO, which is oxidized to nitrogen dioxide NO2 and brought to a second pressure level by the second compressor 6. The nitrogen dioxide NO2 thus obtained is then absorbed with water in an absorber 9, producing nitric acid. The resulting residual gas is expanded via the exhaust gas expander 2. Compressors 3, 6, and exhaust gas expander 2 are controlled, among other things, by adjustable guide vanes 10 as control elements.

[0047] Fig. 2 shows a schematic diagram of the start-up of the nitric acid plant 1. The volume flow (i.e. the second flow-dependent process variable) is plotted on the x-axis. The y-axis represents the final pressure downstream of the compressor 3 (in the impression process) or the compressor 6 (in the dual-pressure process) (i.e. the first pressure-dependent process variable). In this exemplary embodiment, the start-up is automated and carried out in small steps. The gradual closing of the adjustable guide vane 10 on the exhaust gas expander 2 leads to an increase in the compression ratio. The operating point moves from point 100 to the left, along a first working line in the form of the upper limit 5 to point 200. After leaving this point, the adjustable guide vane 10 of the exhaust gas expander 2 is blocked by a control device (not shown), and the adjustable guide vane of the compressor 3 is gradually opened to increase the flow.The operating point moves to the right until a second operating line, the lower limit 4, is reached at point 300. At this point, the adjustable guide vane of compressor 3 is blocked by the control device, and the adjustable guide vane of exhaust gas expander 2 is further closed until the upper limit 5 is reached again at point 400.

[0048] This sequence continues until the setpoint of a part-load point 500 ("part-load operating value") or the setpoint pressure of the normal / full-load point is reached at point 600. Compressor 3 has reached a setpoint operating value line at point 600. This sequence can also be operated in reverse to safely control part-load operating points, e.g., part-load point 500, with smaller volumes and possibly lower process pressures. During a manually operable mode, the adjustable guide vanes 10 of compressors 3, 6, and the flue gas expander 2 can be operated manually. However, the control device remains active and takes priority over manually set operating points.

[0049] From the normal / full load point 600 onward, compressor 3 only follows a horizontal "target operating value line" to reach the overload point 700 of the nitric acid plant 1 by further opening the guide vane of compressor 3. From this point onward, the system is no longer limited by limits 4 and 5. The inlet guide vane of the exhaust gas expander 2 is also not adjusted.

[0050] During manual start-up of the nitric acid plant 1, blockades are provided that prohibit the operator from controlling beyond the upper limit 5 or the lower limit 4. The upper limit 5 prevents, for example, a machine trip caused by: a drastic mass flow reduction due to excessive closing of the adjustable guide vanes 10 of compressor 3. As soon as the operating point reaches this upper limit 5, the adjustable guide vanes 10 of compressor 3 are blocked in the closing direction by the control device and, if necessary, reopened slightly by the control device until stable process conditions are reached. a drastic pressure increase due to excessive closing of the adjustable guide vanes 10 of the exhaust gas expander 2.As soon as the operating point reaches the upper limit 5, the adjustable guide vane 10 of the exhaust gas expander 2 is blocked in the closing direction by the control device and, if necessary, reopened slightly by the control device until stable process conditions are reached. Drastic mass flow reduction due to excessive reduction in the speed of the machine train. As soon as the operating point reaches the upper limit 5, the speed controller of the exhaust gas expander 2 is blocked downwards by the control device.

[0051] - if necessary - the speed is increased slightly again by the control device until stable process conditions are reached.

[0052] The lower limit 4 prevents, for example, a process disruption caused by: an overly drastic increase in mass flow due to the adjustable guide vanes 10 of the compressor 3 being opened too wide. As soon as the operating point has reached the lower limit 4, the adjustable guide vanes 10 of the compressor 3 are blocked in the opening direction by the control device and then closed again to a minimal extent by the control device until stable process conditions are reached. an overly drastic reduction in pressure due to the adjustable guide vanes 10 of the exhaust gas expander 2 being opened too wide. As soon as the operating point has reached the lower limit 4, the adjustable guide vanes 10 of the exhaust gas expander 2 are blocked in the opening direction by the control device and - if necessary - closed again to a minimal extent by the control device until stable process conditions are reached. an overly drastic increase in mass flow due to the speed of the machine train being increased too much.As soon as the operating point has reached the lower limit 4, the speed controller of the exhaust gas expander 2 is blocked upwards by the control device and.

[0053] - if necessary - the speed is reduced slightly by the control device until stable process conditions are reached.

[0054] Fig. 3 shows how the control device detects the movement of the operating points and acts accordingly when the nitric acid plant 1 is operated automatically. If the operating point of the compressor 3 crosses the upper limit 5, a signal is set to "L". If the operating point of the compressor 3 falls below the lower limit 4, the signal is reset to "R". The adjustable guide vane 10 of the exhaust gas expander 2 or the compressor 3 is opened or closed according to the signals. The adjustable guide vane 10 of the compressor 3 is opened if the operating point is to be shifted in the direction of an increase in the second flow-dependent process variable, i.e. to the right in Fig. 2 and 3. Accordingly, the adjustable guide vane 10 of the exhaust gas expander 2 is blocked. For a shift of the operating point in the direction of an increase in the first pressure-dependent process variable, i.e. to the right in Fig.2 and 3 upwards, the adjustable guide vane 10 of the exhaust gas expander 2 is gradually closed, whereas the adjustable guide vane 10 of the compressor 3 is blocked. For the opposite direction, the steps are carried out in exactly the opposite way, i.e. the adjustable guide vane 10 of the compressor 3 is gradually closed if the operating point is to be shifted in the direction of a reduction in the second flow-dependent process variable, i.e. to the left in Fig. 2 and 3. The adjustable guide vane 10 of the exhaust gas expander 2 is gradually opened in order to shift the operating point in the direction of a reduction in the first pressure-dependent process variable, i.e. downwards in Fig. 2 and 3.

[0055] List of reference symbols

[0056] (1) Nitric acid plant (2) Flue gas expander

[0057] (3) Compressor

[0058] (4) lower limit

[0059] (5) upper limit

[0060] (6) second compressor (7) control element

[0061] (8) Part of the nitric acid process, including ammonia oxidation reactor

[0062] (9) Part of the nitric acid process, including absorption and residual gas purification

[0063] (10) Adjustable guide grille

Claims

Patent claims 1. Method for starting up or driving into a partial load range of a nitric acid plant (1), wherein at least one operating point is approached as a function of a process pressure and a volume flow of the nitric acid plant, wherein at least part of the process pressure is set via at least one exhaust gas expander (2), wherein at least part of the volume flow is set via at least one compressor (3), characterized in that for permissible operating points both a lower limit (4) is defined, which depends on a first pressure-dependent process variable and a second flow-dependent process variable, and an upper limit (5) is defined, which depends on the first pressure-dependent process variable and the second flow-dependent process variable, and that a signal is given when the lower limit (4) or the upper limit (5) is reached when the first process variable and / or the second process variable is set.

2. Method according to claim 1, characterized in that a second pressure level is set with a second compressor (6) in a part of the process of the nitric acid plant (1).

3. Method according to claim 1 or 2, characterized in that the setting of the flow-dependent second process variable is set via the at least one compressor (3, 6) via control elements.

4. Method according to one of claims 1 to 3, characterized in that the setting of the first pressure-dependent process variable is set via the at least one exhaust gas expander (2) via control elements (7).

5. Method according to one of claims 1 to 4, characterized in that the second flow-dependent process variable is partially adjusted via the speed of the at least one compressor (3, 6).

6. Method according to one of claims 1 to 5, characterized in that a warning is issued when the lower limit (4) or the upper limit (5) is reached when setting the first pressure-dependent process variable and / or the second flow-dependent process variable.

7. Method according to one of claims 1 to 6, characterized in that the adjustability of the at least one compressor (3, 6) and / or the at least one exhaust gas expander (2) is blocked if, when setting the first pressure-dependent process variable and / or the second flow-dependent process variable, a previously defined lower approach limit to the lower limit (4) or a previously defined upper approach limit to the upper limit (5) is reached.

8. Method according to one of claims 1 to 7, characterized in that the start-up is carried out in stages and automatically.

9. Method according to one of claims 1 to 8, characterized in that an approach speed to the lower limit (4) and / or the upper limit (5) is monitored.

10. Method according to claim 9, characterized in that when a previously defined first approach speed is exceeded, the adjustability of the at least one compressor (3, 6) and / or the at least one exhaust gas expander (2) is blocked.

11. Method according to claim 9, characterized in that when a previously defined second approach speed is exceeded, the at least one compressor (3, 6) and / or the at least one exhaust gas expander (2) is controlled in the direction opposite to the lower limit (4) or upper limit (5).

12. Nitric acid plant (1) with at least one compressor (3) and with at least one exhaust gas expander (2), characterized in that the plant (1) comprises a control device which is designed to carry out a method according to one of claims 1 to 11.

13. Nitric acid plant (1) according to claim 12, characterized in that the control device is designed to detect the movement of the operating points and to act when the nitric acid plant is operated automatically, in that the control device sets a signal to L when the operating point of the compressor (3) crosses the upper limit (5), and in that the control device resets a signal to R when the operating point of the compressor (3) falls below the lower limit (4), wherein the adjustable guide vane (10) of the exhaust gas expander (2) or the compressor (3) is opened or closed according to the signals L or R.

14. Nitric acid plant (1) according to claim 12 or 13, characterized in that the signals of the control device - the adjustable guide vane (10) of the compressor (3) is opened and the adjustable guide vane (10) of the exhaust gas expander (2) is blocked if the operating point is to be shifted in the direction of an increase in the second flow-dependent process variable, or - for a shift of the operating point in the direction of an increase of the first pressure-dependent process variable, the adjustable guide vane (10) of the exhaust gas expander (2) is gradually closed, whereas the adjustable guide vane (10) of the compressor (3) is blocked, - where for a shift of the operating point in the opposite direction the steps are carried out in exactly the opposite way, i.e. - that the adjustable guide vane (10) of the compressor (3) is gradually closed if the operating point is to be shifted in the direction of a reduction of the second flow-dependent process variable, or - the adjustable guide vane (10) of the exhaust gas expander (2) is gradually opened in order to shift the operating point towards a reduction of the first pressure-dependent process variable

Images