Asphalt Mixing Plant Control

Abstract

According to one embodiment of the first aspect of the present invention, there is provided an asphalt mixing plant 700 comprising a first drying drum 11 for drying and heating a first aggregate to a first aggregate temperature. The first drying drum 11 comprises a first burner 31 and a first controller 41 configured to control a first aggregate temperature of the first aggregate by a first control loop 51. The asphalt mixing plant 700 further comprises a second controller 42 configured to control a first raw gas temperature of the first raw gas of the first drying drum 11 by a second control loop 52. The first controller 41 and the second controller 42 are configured to operate independently of each other. Additional aspects relate to corresponding methods and corresponding computer program products.

Description

[Technical field]

[0001] The present invention generally relates to an asphalt mixing plant comprising a control unit. Additional aspects relate to a method of operating an asphalt mixing plant and a computer program product for operating a control unit of an asphalt mixing plant. [Background technology]

[0002] In asphalt mixing plants, asphalt mixtures are produced by a hot mixing process of mineral rock, fillers, bitumen and possibly additives. The production of asphalt mixtures is a complex procedure and is usually controlled by a central control unit.

[0003] There are two main manufacturing methods.

[0004] According to the continuous manufacturing method, the mixing process is carried out continuously. More specifically, the individual components of the asphalt mixture are added continuously to the mixing process. This method is particularly suitable for large volumes using the same asphalt mixing method.

[0005] According to the discontinuous manufacturing method, pre-weighed components of the asphalt mixture are mixed in batches in an asphalt mixer. This method is more flexible because the asphalt mixing method can be changed from batch to batch. Furthermore, improved mix quality and therefore improved asphalt mixture quality are achieved.

[0006] An asphalt mixing plant includes one or more drying drums for drying and heating the process materials, which typically includes a first drying drum for drying and heating the virgin aggregate, i.e., new mineral, as well as a second drying drum for drying and heating the recycled asphalt.

[0007] To obtain a high quality asphalt mixture, it is important to carry out the drying and heating of the material in the drying drum at a predetermined and as constant as possible material temperature. However, the predetermined and as constant as possible material temperature depends on the respective mixing method of the respective asphalt. The desired material temperature is difficult to control due to the large number and bandwidth of process parameters. Such process parameters include, for example, the material composition, humidity fluctuations as well as changes in dosage.

[0008] In addition to controlling the material temperature, it is desirable to maintain the temperature of the raw gas leaving (or being discharged from) the dryer at a predetermined level, especially taking into account the filter performance of subsequent downstream filters. For this purpose, it is known to equip the dryer drum with a frequency converter that enables the asphalt mixing plant operator to manually adjust the raw gas temperature by varying the rotation frequency of the dryer drum.

[0009] US Patent No. 8,886,340 discloses a dryer performance optimization system that includes a dryer configured to rotate at a variable speed and a variable frequency drive configured to vary the rotation speed of the dryer. The disclosed system also includes a baghouse configured to receive exhaust gas from the dryer and a controller configured to control the temperature of the exhaust gas from the dryer by varying the rotation speed of the dryer. However, the system of US Patent No. 8,886,340 does not disclose controlling the material temperature. [Prior art documents] [Patent documents]

[0010] [Patent Document 1] U.S. Patent No. 8,886,340 Summary of the Invention

[0011] One of the objectives of one aspect of the present invention is to provide an asphalt mixing plant in which the drying and heating of the material in the drying drums of the asphalt mixing plant can be controlled in an advantageous manner, in particular taking into account ecologically valuable aspects.

[0012] According to one embodiment of the first aspect of the present invention, there is provided an asphalt mixing plant comprising a first drying drum for drying and heating a first aggregate to a first aggregate temperature. The first drying drum comprises a first burner. The asphalt mixing plant further comprises a first controller including a first control loop configured to control the first aggregate temperature of the first aggregate and a second controller including a second control loop configured to control a first raw gas temperature of the first raw gas of the first drying drum. The first controller and the second controller are configured to operate independently of each other.

[0013] Such embodied asphalt mixing plants enable the asphalt mixing plant to be operated such that both the temperature of the first aggregate and the first raw gas temperature of the first raw gas are automatically controlled, thereby allowing both the first aggregate temperature and the first raw gas temperature to be maintained at a desired level or within a desired range without manual control by an operator of the asphalt mixing plant.

[0014] Applicant's research has shown that such separate control of the first aggregate temperature and the first raw gas temperature by separate independent controllers provides advantageous results. Furthermore, such a solution using separate controllers may be implemented with reduced complexity compared to a single multi-value controller.

[0015] Embodiments of the present invention are based on the unexpected discovery by the inventors that despite the fact that there is an interdependency between the control parameters of a first controller and its corresponding first control loop, and the control parameters of a second controller and its corresponding second control loop, such interdependency may be intentionally ignored by providing two separate controllers and operating such controllers independently.

[0016] More specifically, according to an embodiment, the first controller is configured to control the first aggregate temperature by controlling, in other words, adapting, the burner load, in other words the heat output of the first burner.

[0017] Further, according to an embodiment, the first drying drum is configured to rotate at a first rotational speed, and the second controller is configured to control the first raw gas temperature of the first drying drum by controlling, in other words adapting, the first rotational speed of the first drying drum.

[0018] The aforementioned interdependence between the parameters of the first controller and its first control loop and the parameters of the second controller and its second control loop is as follows: when the burner load of the first burner increases, the first aggregate temperature increases and the first raw gas temperature also increases. Therefore, the burner load of the first burner is positively correlated with both the first aggregate temperature and the first raw gas temperature.

[0019] However, when the first rotation speed of the first drying drum increases, the first aggregate temperature increases, but the first raw gas temperature decreases, so that the first rotation speed of the first drying drum is positively correlated with the first aggregate temperature but negatively correlated with the first raw gas temperature.

[0020] Such complex interdependencies make control of both the first aggregate temperature and the first raw gas temperature very difficult and would typically require the use of complex multi-value controllers.

[0021] An unexpected discovery from Applicant's research has led, in accordance with an embodiment, to a solution that purposefully ignores such complex interdependencies and uses two independent controllers that operate independently of each other, yet nevertheless provides an advantageous and efficient control solution with reduced complexity.

[0022] According to one embodiment, the asphalt mixing plant comprises a second drying drum for drying and heating the second aggregate to a second aggregate temperature, the second drying drum comprising a second burner. The asphalt mixing plant further comprises a third controller including a third control loop configured to control a second aggregate temperature of the second aggregate, and a fourth controller including a fourth control loop configured to control a second raw gas temperature of the second raw gas of the second drying drum. The third controller and the fourth controller are configured to operate independently of each other.

[0023] Such an embodied method includes four independent controllers and four independent control loops that control the first and second aggregate temperatures and the first and second raw gas temperatures independently of one another.

[0024] The third controller may be configured to control a second aggregate temperature of the second drying drum, in particular by controlling a burner load of the second burner. The second drying drum may be configured to rotate at a second rotation speed, in particular, and the fourth controller may be configured to control a second raw gas temperature of the second drying drum, in particular by controlling the second rotation speed of the second drying drum.

[0025] According to an embodiment having only one drying drum, the first aggregate may be virgin aggregate, i.e. new mineral or recycled asphalt.

[0026] According to an embodiment having two drying drums, the first aggregate may in particular be virgin aggregate and the second aggregate may be recycled asphalt, or vice versa.

[0027] According to an embodiment, the first controller may be configured to compensate for deadtime of the first control loop and / or the third controller may be configured to compensate for deadtime of the third control loop, which may also be referred to as process deadtime.

[0028] Such a controller with dead time compensation provides advantageous control results for the first and third control loops, based on the findings that there is some dead time between a change in burner load and a corresponding change in the first or second aggregate temperature.

[0029] According to one embodiment, the first controller is a predictive proportional-integral controller. According to one embodiment, the third controller is a predictive proportional-integral controller.

[0030] Applicant's research has shown that such predictive PI controllers exhibit particularly advantageous control results for the first and third control loops.

[0031] According to an embodiment, the second controller may be a proportional-integral controller. According to an embodiment, the fourth controller may be a proportional-integral controller.

[0032] Applicant's research has shown that such a pure PI controller exhibits particularly advantageous control results for the second and fourth control loops.

[0033] Furthermore, Applicant's research has shown that, in particular, the combination of using predictive PI controllers for the first and third control loops and using pure PI controllers for the second and fourth control loops exhibits particularly advantageous overall control results.

[0034] According to an embodiment, the first drying drum and / or the second drying drum may be a direct current drum.

[0035] According to an embodiment, the first drying drum and / or the second drying drum may be a countercurrent drum.

[0036] According to an embodiment, such an asphalt mixing plant comprises a first temperature sensor for sensing the first raw gas temperature of the first drying drum. The first temperature sensor may be arranged in a duct between the first drying drum and the downstream filter. The first temperature sensor may be arranged at a predetermined first distance relative to the outlet of the first raw gas of the first drying drum. According to an embodiment, the predetermined first distance is at least 1 meter. According to a preferred embodiment, the predetermined first distance is at least 5 meters, in particular at least 10 meters.

[0037] According to an embodiment, the asphalt mixing plant comprises a second temperature sensor for sensing the second raw gas temperature of the second drying drum. The second temperature sensor may be arranged at a predetermined second distance relative to the outlet of the second raw gas of the second drying drum. According to an embodiment, the predetermined second distance is at least 1 meter. According to a preferred embodiment, the predetermined second distance is at least 5 meters, in particular at least 10 meters.

[0038] With such arrangement of the first and / or second temperature sensors, the temperature profile of the first raw gas discharged from the first drying drum and / or the temperature profile of the second raw gas discharged from the second drying drum is homogenized / mixed / leveled in the corresponding ducts or tubes until the raw gas reaches the respective temperature sensor.

[0039] According to one embodiment, the asphalt mixing plant comprises a common filter for filtering the first raw gas of the first drying drum and the second raw gas of the second drying drum. This is particularly cost-effective. According to an embodiment, a first temperature sensor for sensing the first raw gas temperature of the first drying drum is arranged within a predetermined third distance upstream of the inlet of the common filter. According to an embodiment, the predetermined third distance is less than 1 meter. According to a further embodiment, the predetermined distance is less than 0.5 meters.

[0040] Such a location of the temperature sensor close to the common filter offers the particular advantage that the temperature sensor can also be used to observe and measure the raw gas input temperature at the filter, which is particularly cost-effective.

[0041] It should be noted that the first, second and third distances refer to the travel distance, or in other words the flow distance, that the raw gas travels or flows within the corresponding ducts or tubes of the asphalt mixing plant.

[0042] According to one embodiment of another aspect of the present invention, there is provided a method of operating an asphalt mixing plant. The method includes drying and heating a first aggregate to a first aggregate temperature by a first drying drum and controlling a first aggregate temperature of the first aggregate by controlling a burner load of a first burner by a first controller. The method further includes rotating the first drying drum at a first rotational speed and controlling a first raw gas temperature of a first raw gas discharged from the first drying drum by controlling the first rotational speed of the first drying drum by a second controller. The steps of controlling by the first controller and controlling by the second controller are performed independently of each other via a separate first control loop and a separate second control loop, respectively.

[0043] According to one embodiment of another aspect of the present invention, there is provided a computer program product for operating a control unit of an asphalt mixing plant. The control unit comprises a first controller and a second controller. The computer program product comprises a computer readable storage medium having embedded therein program instructions executable by the control unit to cause the control unit to perform a method including controlling, by the first controller, a first aggregate temperature of a first aggregate, and controlling, by the second controller, a first raw gas temperature of a first raw gas of a first drying drum. The controlling by the first controller and the controlling by the second controller are performed independently via separate first and second control loops, respectively.

[0044] Features and advantages of one aspect of the invention may be applied to other aspects of the invention, where appropriate.

[0045] Further advantageous embodiments are recited in the dependent claims as well as in the following description. [Brief description of the drawings]

[0046] The invention will be better understood and further objects will become apparent from the following detailed description, in which reference is made to the accompanying drawings, in which: [Figure 1] FIG. 1 shows a schematic diagram of a dryer drum according to one embodiment of the present invention. [Diagram 2] FIG. 2 shows a table illustrating correlations between control parameters of a control unit of an asphalt mixing plant according to an embodiment of the present invention. [Diagram 3] FIG. 3 shows a schematic diagram of a first control loop and a second control loop according to one embodiment of the present invention. [Figure 4] FIG. 4 shows a block diagram of a control unit comprising a first controller and a second controller according to one embodiment of the present invention. [Diagram 5]FIG. 5 shows a schematic diagram of the third and fourth control loops according to one embodiment of the present invention. [Figure 6] FIG. 6 shows a block diagram of a control unit with four controllers according to one embodiment of the present invention. [Figure 7] FIG. 7 shows a flow diagram of the asphalt mixing process and associated equipment of an asphalt mixing plant. [Figure 8] FIG. 8 illustrates method steps of a method for controlling an asphalt mixing plant according to one embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0047] In the following description, the following abbreviations may be used: RA: Reclaimed Asphalt RAC: Low temperature recycled asphalt RAH: High-temperature recycled asphalt RAP: Reclaimed Asphalt Pavement VA: virgin aggregate TA1: First aggregate temperature TA2: Second aggregate temperature P1: Burner load of the first burner P2: Burner load of the second burner TG1: 1st raw gas temperature TG2: Second raw gas temperature RPM1: The first rotation speed in revolutions per minute, which corresponds to the rotation speed of the first drying drum. RMP2: Second rotation speed in revolutions per minute, corresponding to the rotation speed of the second drying drum Tar: Target Act: Actual Aggregate: The term aggregate refers to the material that has been dried and heated by the corresponding drying drum. The aggregate may be embodied as virgin aggregate, as recycled asphalt, or any other suitable material for asphalt mix production. A1: First aggregate A2: Second aggregate G1: 1st raw gas G2: Second raw gas

[0048] Using RAP may reduce production costs and avoid asphalt waste.

[0049] Reclaimed asphalt may be added to the asphalt mixing process via a separate drum, for example, a parallel drum or a drum with an additional ring.

[0050] Reclaimed asphalt may also be added directly to the mixer and / or hot elevator of an asphalt mixing plant.

[0051] The term "raw gas" refers to the exhaust gas discharged from the drying drum of an asphalt mixing plant. Raw gas includes the burner combustion gas mixture, which includes fuel gas, ambient air or oxygen supply, and fine aggregate particles. Raw gas is also called exhaust gas, since it is discharged from the outlet of the drying drum.

[0052] The raw gas temperature is intended to refer in particular to the temperature of the raw gas at a given measuring point as measured by a corresponding temperature sensor.

[0053] A predictive proportional-integral (PI) controller is a special controller with dead-time compensation proposed by Tore Hagglund in the article "Predictive PI Controller for Processes with Long Dead-Times" in IEEE Control Systems Magazine, Vol. 12, No. 1, pp. 57-60, February 1992, doi:10.1109 / 37.120455.

[0054] Such an embodied controller includes five process model parameters, two of which are automatically determined based on the other three process parameters, i.e., the proportional term (gain), the integral term (integral time), and the dead time, and thus, for such a controller, only three process model parameters need to be adjusted, i.e., the proportional term, the integral term, and an estimate of the process dead time. For example, see page 58, column 2 of the above reference, where the parameters K, Ti and L are determined by the operator, but the parameters Kp and T are calculated as functions of K and Ti. Conceptually, a predictive proportional-integral (PI) controller can be thought of as a special case of the Smith Predictor.

[0055] FIG. 1 shows a schematic diagram of a first drying drum 11 according to an embodiment of the present invention. The first drying drum 11 may be configured to dry and heat a first aggregate A1 to a first aggregate temperature TA1. The first drying drum 11 comprises a first burner 31. The first drying drum 11 further comprises a first controller 41 configured to control a first control loop 51 for controlling a first aggregate temperature TA1 of the first aggregate 21 and a second controller 42 comprising a second control loop 52 configured to control a first raw gas temperature TG1 of the first raw gas G1 of the first drying drum 11. The first controller 41 and the second controller 42 are configured to operate independently of each other.

[0056] The first controller 41 is configured to control the first aggregate temperature TA1 by controlling the burner load P1 of the first burner 31. The burner load P1 corresponds to the heat output of the first burner 31.

[0057] The first drying drum 11 is configured to rotate at a first rotation speed RPM1. The second controller 42 is configured to control a first raw gas temperature TG1 of the first raw gas G1 by controlling the first rotation speed RPM1 of the first drying drum 11. The rotation speed of the first drying drum 11 may be adapted by a frequency converter (not shown) arranged between the second controller 42 and the electric motors 20, 21 for rotating the first drying drum 11. The drying drum 11 is embodied as a counter-current drum. The unused aggregate A1 enters from the right side of the drum 11 as indicated by the arrows and leaves from the left side, whereas the raw gas leaves from the right side of the drum 11 as indicated by the dashed and dotted lines.

[0058] FIG. 2 shows a table including complex dependencies between control parameters of an asphalt mixing plant according to an embodiment of the present invention. More specifically, changing the control parameters of the first control loop 51 also affects the control parameters of the second control loop 52 and vice versa. Column 201 includes the control parameters that are changed, namely the burner load of the first burner and the rotation speed of the first drying drum. Column 202 shows the effect of changing the control parameters of column 201 on the aggregate temperature of the first aggregate, and column 203 shows the effect of changing the control parameters of column 201 on the raw gas temperature of the first drying drum 11. In FIG. 2, an upward arrow indicates an increase in the corresponding parameter and a downward arrow indicates a decrease in the corresponding parameter.

[0059] As shown in Table 200, increasing the burner duty increases the raw gas temperature as well as the aggregate temperature.

[0060] As the rotational speed of the first drying drum increases, the aggregate temperature increases but the raw gas temperature decreases.

[0061] The effect of each control parameter on the other control loops is shown by a circle.

[0062] Such a dependency can be explained as follows: an increase in the burner load increases the temperature in the dryer drum, which in turn increases the temperature of the aggregates / materials in the dryer drum as well as the temperature of the gas in the dryer drum. An increase in the rotation speed of the dryer drum reduces the raw gas temperature but increases the aggregate / material temperature due to a denser material curtain in the dryer drum and a corresponding increase in heat transfer from the hot raw gas to the unused aggregates / materials.

[0063] Drying drums for virgin aggregate and recycled asphalt behave much the same as above.

[0064] Fig. 3 shows a schematic diagram of a first control loop 51 and a second control loop 52 according to an embodiment of the present invention. The first controller 41 receives an error signal e(t) as an input signal. The error signal is also called a control deviation. The error signal e(t) corresponds to the difference between a target signal TA1tar(t) representing a target temperature of the first aggregate temperature TA1 and an actual temperature TA1act(t) of the first aggregate. The actual temperature TA1act(t) may be measured by a temperature sensor. In this diagram, t represents a point in time reflecting that the parameters of the first control loop 51 may change over time.

[0065] In response to the error signal e(t), the first controller 41 calculates as an output a control signal (control output or correction value) P1(t) representative of the first burner load of the first burner 31 and adapts the first burner load accordingly, thereby causing a change in the temperature in the first drying drum 11 and, accordingly, a change in the actual temperature TA1act(t) of the first aggregate material.

[0066] The second controller 42 receives as input an error signal e(t) corresponding to the difference between a target signal TG1tar(t) representing a target temperature for the first raw gas temperature TG1 and an actual raw gas temperature TG1act(t) of the raw gas / exhaust gas of the first dryer drum. The actual temperature TG1act(t) may be measured by a temperature sensor. In this figure, t represents a point in time reflecting that the parameters of the second control loop 52 may change over time.

[0067] In response to the error signal e(t), the second controller 42 calculates as output a control signal RPM1(t) which corresponds to the rotation speed in revolutions per minute of the first drying drum 11 and adapts the rotation speed of the first drying drum 11 accordingly, thereby causing the first raw gas temperature TG1act of the exhaust gas of the first drying drum 11 to change.

[0068] The first controller 41 and the first control loop 51 operate independently from the second controller 42 and the second control loop 52, notwithstanding the interdependence therebetween as described with reference to Figure 2. More specifically, the control signal P1(t) of the first controller 41 also varies the first raw gas temperature TG1, and the control signal RPM1 of the second controller 42 varies the first aggregate temperature of the first aggregate.

[0069] FIG. 4 shows a block diagram of a control unit 40 comprising a first controller 41 and a second controller 42 and corresponding input and output signals of the first controller 41 and the second controller 42 .

[0070] 5 shows a schematic diagram of a third control loop 53 and a fourth control loop 54 according to an embodiment of the present invention. The third control loop 53 and the fourth control loop 54 are used to control the second drying drum 12 with the second burner 32. The third control loop 53 comprises a third controller 43 receiving an error signal e(t) as an input signal. The error signal e(t) corresponds to the difference between a target signal TA2tar(t) representing a target temperature of the second aggregate temperature TA2 of the second aggregate A2 in the second drying drum 12 and an actual temperature TA2act(t) of the second aggregate A2. The actual temperature TA2act(t) may be measured by a corresponding temperature sensor.

[0071] In response to the error signal e(t), the third controller 43 calculates as output a control signal P2(t) representative of the second burner load of the second burner 32 and adapts the second burner load accordingly, which causes the temperature in the second drying drum 12 to change and accordingly the actual temperature TA2act(t) of the second aggregate A2 to change.

[0072] The fourth controller 44 receives as an input signal an error signal e(t) corresponding to the difference between a target signal TG2tar(t) representing a target temperature for the second raw gas temperature TG2 and an actual raw gas temperature TG2act(t) of the exhaust gas of the second drying drum 12. The actual temperature TG2act(t) may be measured by a temperature sensor.

[0073] Depending on the respective error signal e(t), the fourth controller 44 calculates as output a control signal RPM2(t) corresponding to the rotation speed in revolutions per minute of the second drying drum 12 and adapts the rotation speed of the second drying drum 12 accordingly, thereby changing the second raw gas temperature TG2act of the raw gas / exhaust gas of the second drying drum 12.

[0074] The third controller 43 and the third control loop 53 operate independently from the fourth controller 44 and the fourth control loop 54, notwithstanding the interdependence therebetween as described with reference to Figure 2. More specifically, the control signal P2(t) of the third controller 43 also varies the second raw gas temperature TG2, and the control signal RPM2 of the fourth controller 44 varies the second aggregate temperature of the second aggregate.

[0075] 6 shows a block diagram of a control unit 40 comprising a first controller 41, a second controller 42, a third controller 43 and a fourth controller 44 and corresponding input and output signals of the first controller 41, the second controller 42, the third controller 43 and the fourth controller 44. Such a control unit may be used in an asphalt mixing plant comprising two drying drums, i.e., a first drying drum 11 and a second drying drum 12. All four controllers 41-44 operate independently of each other, as shown by the dotted line separation.

[0076] According to an embodiment with two drying drums, namely a first drying drum 11 and a second drying drum 12, as shown with reference to Figures 5 and 6, the first aggregate A1 dried and heated in the first drying drum 11 may in particular be virgin aggregate, i.e. new mineral. Furthermore, the second aggregate A2 dried and heated in the second drying drum 12 may in particular be reclaimed asphalt, in other words recycled asphalt.

[0077] The first controller 41 may be particularly configured to compensate for dead time of the first control loop 51, and the third controller 43 may be particularly configured to compensate for dead time of the third control loop 53. The first controller 41 and the third controller 43 may be particularly predictive proportional-integral controllers.

[0078] The second controller 42 and the fourth controller 44 may in particular be proportional-integral controllers.

[0079] 7 exemplarily illustrates a simplified flow diagram 700 of an asphalt mixing process according to one embodiment of the present invention. The asphalt mixing plant includes a plurality of VA cold feeder units 701, a first drying drum 11 embodied as a VA drying / heating drum including a first burner 31, a common filter 70, an exhaust gas blower 704, and an exhaust pipe 705. The asphalt mixing plant further includes a recycled filler elevator 706, an intermediate recycled filler silo 707, a recycled filler silo 708, an imported filler silo 709, a filler scale 710, as well as a VA elevator 711, a screen 712, a hot VA silo 713, and a VA scale 714. The asphalt mixing plant further comprises a hot recycled asphalt (RAH) addition section including a plurality of (cold) RA feeder units 715, an RA elevator 716, a second drying drum 12 embodied as an RA drying / heating drum including a second burner 32, an RAH buffer silo 718 with weighing equipment, and an RAH scale 719. The asphalt mixing plant further comprises a cold recycled asphalt (RAC) addition section including a plurality of (cold) RA feeder units 720, an RA buffer silo 721, and an RA belt scale 722. The asphalt mixing plant further comprises a plurality of bitumen tanks 723 and a bitumen scale 724. The asphalt mixing plant further comprises a mixer 725, a skip 726, and a plurality of asphalt mixture storage silos 727.

[0080] The asphalt mixing plant 700 may particularly include a control unit 40 having a first controller 41 and a second controller 42 for controlling the first drying drum 11, and a third controller 43 and a fourth controller 44 for controlling the second drying drum 12, as shown in FIG. 6.

[0081] The common filter 70 is configured to filter the raw gas / exhaust gas of the first drying drum 11 and the raw gas / exhaust gas of the second drying drum 12 .

[0082] The asphalt mixing plant 700 comprises a first temperature sensor 81 for sensing the first raw gas temperature of the first drying drum 11. According to an embodiment, the first temperature sensor 81 is arranged at a predetermined first distance d1 relative to the outlet 71 of the first raw gas of the first drying drum 11. Furthermore, according to an embodiment, the first temperature sensor 81 is arranged within a predetermined third distance d3 relative to the inlet 73 of the common filter 70.

[0083] The asphalt mixing plant 700 further comprises a second temperature sensor 82 for sensing the second raw gas temperature of the second drying drum 12. According to an embodiment, the second temperature sensor 82 is arranged at a predetermined second distance d2 relative to the second raw gas outlet 72 of the second drying drum 12.

[0084] The first, second and third distances shall refer to the travel distance, or in other words, the flow distance, that the raw gas travels or flows in the corresponding ducts or tubes of the asphalt mixing plant, which are shown by the dotted lines d1, d2 and d3.

[0085] FIG. 8 illustrates method steps of a method for controlling an asphalt mixing plant according to one embodiment of the present invention.

[0086] At step 810, operation and control of the asphalt mixing plant is initiated. For the exemplary embodiment of Figure 8, the asphalt mixing plant is assumed to include first and second drying drums as well as first, second, third and fourth controllers, for example as shown in Figure 7. Thus, operation of the asphalt mixing plant includes drying and heating a first aggregate to a first aggregate temperature by the first drying drum, and drying and heating a second aggregate to a second aggregate temperature by the second drying drum.

[0087] In step 820, the first controller controls a first aggregate temperature TA1 of the first aggregate.

[0088] In step 830, the second controller controls the first raw gas temperature TG1 of the raw gas of the first dryer drum.

[0089] In step 840, the third controller controls a second aggregate temperature TA2 of the second aggregate.

[0090] In step 850, the fourth controller controls the second raw gas temperature TG2 of the raw gas of the second dryer drum.

[0091] According to an embodiment, control steps 820, 830, 840 and 850 are performed in parallel by respective controllers, but independently of each other.

[0092] Aspects of the invention may be embodied as a system, particularly an asphalt mixing plant, a method and / or a computer program product. The computer program product may include a computer readable storage medium having computer readable program instructions for causing a processor, particularly the processor of the control unit 40, to perform aspects of the invention.

[0093] The computer-readable storage medium may be a tangible device that can hold and store instructions used by an instruction execution device.

[0094] The computer readable program instructions described herein may be downloaded from a computer readable storage medium into each computing / processing device or downloaded to an external computer or storage device via a network, such as, for example, the Internet, a local area network, a wide area network, and / or a wireless network. The network may include copper transmission cables, optical fiber transmission, wireless transmission, routers, firewalls, switches, gateway computers, and / or edge servers. A network adapter card or network interface in each computing / processing device receives the computer readable program instructions from the network and forwards the computer readable program instructions for storage in a computer readable storage medium in the respective computing / processing device.

[0095] The computer readable program instructions for carrying out the operations of the present invention may be either source code or object code written in any combination of one or more programming languages, including assembler instructions, instruction set architecture (ISA) instructions, machine instructions, machine dependent instructions, microcode, firmware instructions, state set data, or conventional procedural programming languages, such as object oriented programming languages ​​such as Smalltalk, C++, and the like, and the "C" programming language or similar programming languages. The computer readable program instructions may be executed, inter alia, on the control unit 40 of the asphalt mixing plant.

[0096] Aspects of the present invention are described herein with reference to flowchart illustrations and / or block diagrams of methods, apparatus (systems) and computer program products according to embodiments of the invention.

[0097] Such computer readable program instructions may be provided to a processor of a general purpose computer, special purpose computer, or other programmable data processing apparatus to manufacture a machine such that the instructions, executed by the processor of the computer or other programmable data processing apparatus, create means for implementing the functions / acts specified in one or more blocks of the flowcharts and / or block diagrams. Such computer readable program instructions may also be stored on a computer readable storage medium that causes a computer, programmable data processing apparatus, and / or other device to function in a particular manner, such that the computer readable storage medium having instructions stored thereon constitutes an article of manufacture including instructions that implement aspects of the functions / acts specified in one or more blocks of the flowcharts and / or block diagrams.

[0098] The flowcharts and block diagrams in the Figures illustrate the architecture, functionality, and operation of possible implementations of systems, methods and computer program products according to various embodiments of the present invention.

[0099] While presently preferred embodiments of the invention have been illustrated and described, it is to be clearly understood that the invention is not limited to such embodiments, but may be variously embodied and embodied within the scope of the following claims.

Claims

1. An asphalt mixing plant (700), comprising: a first drying drum (11) for drying and heating the first aggregate to a first aggregate temperature, said first drying drum (11) comprising a first burner (31); a first controller (41) configured to control the first aggregate temperature of the first aggregate by a first control loop (51); a second controller (42) configured to control a first raw gas temperature of the first raw gas of the first drying drum (11) by a second control loop (52); An asphalt mixing plant (700), wherein the first controller (41) and the second controller (42) are configured to operate independently of each other.

2. 2. The asphalt mixing plant of claim 1, wherein the first controller (41) is configured to control the first aggregate temperature by controlling a burner load of the first burner (31).

3. The first drying drum (11) is configured to rotate at a first rotational speed; 3. The asphalt mixing plant according to claim 1 or 2, wherein the second controller (42) is configured to control the first raw gas temperature of the first raw gas by controlling the first rotational speed of the first drying drum (11).

4. The asphalt mixing plant (700) comprises: a second drying drum (12) for drying and heating the second aggregate to a second aggregate temperature, said second drying drum (12) having a second burner (32); a third controller (43) configured to control the second aggregate temperature of the second aggregate by a third control loop (53); a fourth controller (44) configured to control a second raw gas temperature of the second raw gas in the second dryer drum (12) by a fourth control loop (54); 4. The asphalt mixing plant according to any one of claims 1 to 3, wherein the third controller (43) and the fourth controller (44) are configured to operate independently of each other.

5. the third controller (43) is configured to control the second aggregate temperature of the second drying drum (12) by controlling a burner load of the second burner (32); the second drying drum (12) is configured to rotate at a second rotational speed; 5. The asphalt mixing plant of claim 4, wherein the fourth controller (44) is configured to control the second raw gas temperature of the second drying drum (12) by controlling the second rotational speed of the second drying drum (12).

6. 4. The asphalt mixing plant of claim 1, wherein the first aggregate is virgin aggregate or recycled asphalt.

7. 6. The asphalt mixing plant of claim 4, wherein the first aggregate is virgin aggregate and the second aggregate is recycled asphalt.

8. the first controller (41) is configured to compensate for dead time in the first control loop (51); and / or 8. An asphalt mixing plant according to any one of claims 1 to 7, wherein the third controller (43) is configured to compensate for dead time in the third control loop (53).

9. the first controller (41) is a predictive proportional-integral controller; and / or 9. The asphalt mixing plant of any one of claims 1 to 8, wherein the third controller (43) is a predictive proportional-integral controller.

10. the second controller (42) is a proportional-integral controller; and / or 10. The asphalt mixing plant of any one of claims 1 to 9, wherein the fourth controller (44) is a proportional-integral controller.

11. 11. Asphalt mixing plant according to any one of claims 1 to 10, wherein the first drying drum (11) and / or the second drying drum (12) are direct current drums.

12. 12. Asphalt mixing plant according to any one of the preceding claims, wherein the first drying drum (11) and / or the second drying drum (12) are countercurrent drums.

13. The asphalt mixing plant comprises: a first temperature sensor (81) for sensing the first raw gas temperature of the first drying drum, the first temperature sensor (81) being arranged at a predetermined first distance relative to an outlet (71) of the first raw gas of the first drying drum (11), the predetermined first distance being at least one meter; and / or 13. The asphalt mixing plant according to claim 1, further comprising a second temperature sensor (82) for sensing the second raw gas temperature of the second drying drum (12), the second temperature sensor (82) being arranged at a predetermined second distance relative to the second raw gas outlet (72) of the second drying drum (12), the predetermined second distance being at least one meter.

14. The asphalt mixing plant comprises: a common filter (70) for filtering the first raw gas of the first drying drum (11) and the second raw gas of the second drying drum (12); 14. The asphalt mixing plant of claim 13, wherein the first temperature sensor (81) for sensing the first raw gas temperature of the first drying drum is disposed within a predetermined third distance to an inlet (73) of the common filter, the predetermined third distance being less than one meter.

15. A method of operating an asphalt mixing plant (700), the asphalt mixing plant comprising a first dryer drum (11) having a first burner (31), a first controller (41) and a second controller (42), the method comprising: drying and heating a first aggregate to a first aggregate temperature by the first drying drum (11), the first drying drum comprising a first burner (31); controlling the first aggregate temperature of the first aggregate by the first controller (41); controlling a first raw gas temperature of the first raw gas in the first drying drum (11) by the second controller (42), wherein the steps of controlling by the first controller (41) and controlling by the second controller (42) are performed independently of each other via a separate first control loop (51) and a separate second control loop (52), respectively.

16. A computer program product for operating a control unit (40) of an asphalt mixing plant (700), the asphalt mixing plant comprising a first drying drum (11) for drying and heating a first aggregate to a first aggregate temperature, the first drying drum (11) comprising a first burner (31), the control unit (40) comprising a first controller (41) and a second controller (42), the computer program product comprising a computer readable storage medium having program instructions embodied therein, the program instructions being executable by the control unit (40), the control unit being configured to: controlling the first aggregate temperature of the first aggregate by the first controller (41); controlling, by the second controller (42), a first raw gas temperature of the first raw gas of the first drying drum (11), wherein the steps of controlling by the first controller (41) and of controlling by the second controller (42) are performed independently of each other via a separate first control loop (51) and a separate second control loop (52), respectively.

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