Patent Description:
In an asphalt mixing plant an asphalt mixture is produced by a thermal mixing process of mineral rocks, fillers, bitumen and possibly additives. The production of an asphalt mixture is a complex procedure which is usually controlled by a central control unit.

There are generally two main production methods.

According to a continuous production method, the mixing process takes place in a continuous manner. More particularly, the individual components of the asphalt mixture are added continuously to the mixing process. This method is particularly suitable for large volumes with the same asphalt mixing recipe.

According to a discontinuous production method, pre-weighed components of the bituminous mixture are batch mixed in an asphalt mixer. This method is more flexible as it allows batch-by-batch changes of the asphalt mixing recipe. In addition, a higher mixing quality and subsequently a higher quality of the asphalt mixture is achieved.

Asphalt mixing plants comprise one or more drying drums for drying and heating process materials. This usually includes a first drying drum for drying and heating virgin aggregate, i.e. the new mineral, as well as a second drying drum for drying and heating reclaimed asphalt.

In order to achieve a high quality of the asphalt mixture, it is important to perform the drying and heating of the materials in the drying drum(s) at predefined as constant as possible material temperatures. However, the predefined as constant as possible material temperatures depend on the respective mixing recipe of the respective asphalt. Due to the large number and bandwidth of process parameters, the control of the desired material temperature is a challenge. Such process parameters include e.g. the composition of the material, fluctuating humidity as well as variable dosages and others.

In addition to the control of the material temperatures, it is desirable to keep the raw gas temperature leaving (or exiting) the dryer at predefined levels, in particular in view of the filter performance of a subsequent downstream filter. For this purpose, it is known to equip the drying drums with frequency converters which allow an operator of the asphalt mixing plant to manually adapt the raw gas temperature by changing the rotational frequency of the drying drum.

<CIT> and <CIT> disclose a dryer performance optimization system comprising a dryer being adapted to rotate at variable speeds and a variable frequency drive being adapted to vary the rotational speed of the dryer. The disclosed system also comprises a baghouse being adapted to receive exhaust gas from the dryer and a controller being adapted to control the temperature of the exhaust gas from the dryer by varying the rotational speed of the dryer. However, the system of <CIT> and <CIT> does not disclose a control of the material temperature.

<CIT> discloses a process and apparatus for heating particulate solids in a rotary kiln. The rotary kiln is provided with an axial burner comprising a burner body having an axial nozzle supplied form a first fuel line and a ring of surrounding nozzles supplied from a second fuel line. Separate flow control means are provided in the first and second fuel lines. The flow rate of fuel to the axial nozzle is regulated to control stack gas temperature and the flow rate of fuel to the ring nozzles is regulated to control the temperature of heated solids egressing from the kiln.

The document by <NPL>, doi: <NUM>/<NUM>. , discloses a predictive PI controller with dead-time compensation. The advantage of the described controller compared with the other dead time compensating controllers is that although it contains five parameters, only three are adjusted by the operator, namely, the gain, the integral time and the dead time.

<CIT> discloses a burner combustion controlling method of an asphalt plant. A necessary amount of combustion is calculated from the detected aggregate supply amount and aggregate temperature set point on the basis of theoretical combustion. The temperature variation is calculated from an aggregate temperature successively detected at an outlet of the dryer, a trend of the aggregate temperature is forecasted from the temperature variation, and a tolerance between the forecasting value and aggregate temperature set point is obtained. A correction amount of combustion for correcting the current amount of combustion is calculated on the basis of the tolerance amount and necessary amount of combustion, and an amount of combustion of a burner is corrected by the correction amount of combustion.

One problem of an aspect of the invention is to provide an asphalt mixing plant that allows to control the drying and heating of materials in a drying drum of the asphalt mixing plant in an advantageous manner, in particular in view of ecological worthwhile aspects.

According to an embodiment of a first aspect of the invention, there is provided an asphalt mixing plant according to claim <NUM>, 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 comprising a first control loop configured to control the first aggregate temperature of the first aggregate and a second controller comprising a second control loop configured to control a first raw gas temperature of a first raw gas of the first drying drum. The first controller and the second controller are configured to operate independently from each other. The first controller is configured to control the first aggregate temperature by controlling or in other words adapting the burner load or in other words the thermal output power of the first burner. The first drying drum is configured to rotate at a first rotational speed. The second controller is configured to control the first raw gas temperature of the first raw gas exiting the first drying drum by controlling or in other words adapting the first rotational speed of the first drying drum.

Such an embodied asphalt mixing plant allows to operate the asphalt mixing plant in such a way that both the temperature of the first aggregate as well as the first raw gas temperature of the first raw gas is automatically controlled. This allows to keep both the first aggregate temperature as well as the first raw gas temperature at desired levels or within desired ranges without a manual control of an operator of the asphalt mixing plant.

Investigations of the applicant have shown that such a separate control of the first aggregate temperature and the first raw gas temperature by means of separate and independent controllers provide advantageous results. Furthermore, such a solution with separate controllers may be implemented with reduced complexity compared with a single multi-value controller.

Embodiments of the invention are based on a unexpected discovery of the inventors that despite the fact that there are interdependencies between control parameters of the first controller and its corresponding first control loop and the second controller and its corresponding second control loop, these interdependencies may be purposely ignored by providing two separate controllers and by operating these controllers independently.

The mentioned interdependencies between parameters of the first controller and its first control loop and parameters of the second controller and its second control loop are as follows: An increase of the burner load of the first burner results in an increase of the first aggregate temperature as well as in an increase of the first raw gas temperature. Accordingly, the burner load of the first burner is positively correlated with both the first aggregate temperature as well as the first raw gas temperature.

However, an increase of the first rotational speed of the first drying drum results on the one hand in an increase of the first aggregate temperature, but on the other hand in a decrease of the first raw gas temperature. Accordingly, the first rotational speed of the first drying drum is positively correlated with the first aggregate temperature, but negatively correlated with the first raw gas temperature.

These complex interdependencies make a control of both the first aggregate temperature and the first raw gas temperature very challenging and would usually indicate the use of a complex multi-value controller.

The unexpected discovery by the investigations of the applicant have resulted in a solution that according to embodiments purposely ignores these complex interdependencies and uses two independent controllers that operate independently from each other, but nevertheless provide an advantageous and efficient control solution with low complexity.

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

Such an embodied method comprises four independent controllers and four independent control loops that control the first and the second aggregate temperature and the first and the second raw gas temperature independently from each other.

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

According to embodiments having only one drying drum, the first aggregate may be a virgin aggregate, i.e. new mineral, or reclaimed asphalt.

According to embodiments having two drying drums, the first aggregate may be in particular a virgin aggregate and the second aggregate may be reclaimed asphalt or vice versa.

According to an embodiment, the first controller may be configured to compensate a deadtime of the first control loop and/or the third controller may be configured to compensate a deadtime of the third control loop. The deadtime may also be denoted as process deadtime.

Such controllers with deadtime compensation show advantageous control results for the first and the third control loop. This is based on the finding that there is some deadtime between a change in the burner load and a corresponding change of the first or the second aggregate temperature.

According to an embodiment, the first controller is a predictive Proportional-Integral controller. According to an embodiment, the third controller is a predictive Proportional-Integral controller
Investigations of the applicant have discovered that such predictive PI-controllers show particularly advantageous control results for the first and the third control loop.

According to embodiments, the second controller may be a Proportional-Integral controller. According to embodiments, the fourth controller may be a Proportional-Integral controller.

Investigations of the applicant have discovered that such pure PI-controllers show particularly advantageous control results for the second and the fourth control loop.

Furthermore, investigations of the applicant have discovered that in particular the combination of using predictive PI-controllers for the first and the third control loop and using pure PI-controllers for the second and the fourth control loop show particularly advantageous overall control results.

According to embodiments the first drying drum and/or the second drying drum may be direct flow drums.

According to embodiments, the first drying drum and/or the second drying drum may be counter flow drums.

According to embodiments, 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 a downstream filter. The first temperature sensor may be arranged at a predefined first distance to an outlet for the first raw gas of the first drying drum. According to embodiments, the predefined first distance is at least <NUM> meter. According to preferred embodiments, the predefined first distance is at least <NUM> meters, in particular at least <NUM> meters.

According to embodiments, 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 predefined second distance to an outlet for the second raw gas of the second drying drum. According to embodiments, the predefined second distance is at least <NUM> meter. According to preferred embodiments, the predefined second distance is at least <NUM> meters, in particular at least <NUM> meters.

With such an arrangement of the first and/or the second temperature sensor, the temperature profile of the first raw gas leaving the first drying drum and/or the temperature profile of the second raw gas leaving the second drying drum have equalized/mixed/evened out in the corresponding ducts or tubes until the raw gas arrives at the respective temperature sensor(s).

According to an 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 efficient. According to embodiments, the first temperature sensor for sensing the first raw gas temperature of the first drying drum is arranged within a predefined third distance upstream to an inlet of the common filter. According to embodiments, the predefined third distance is less than <NUM> meter. According to further embodiments, the predefined distance is less than <NUM> meter.

Such an arrangement of the temperature sensor close to the common filter provides the particular advantage that the temperature sensor may also be used to observe and measure the raw gas input temperature at the filter. This is particularly cost efficient.

It should be noted that the first, the second and the third distance shall refer to the travel distance or in other words the flow distance that the raw gas travels or flows within the corresponding duct or tube of the asphalt mixing plant.

According to an embodiment of another aspect of the invention, a method for operating the asphalt mixing plant according to claim <NUM> is provided.

According to an embodiment of another aspect of the invention, a computer program product for operating a control unit of the asphalt mixing plant according to claim <NUM> is provided.

Features and advantages of one aspect of the invention may be applied to the other aspects of the invention as appropriate.

In the following description abbreviations as follows may be used:.

The use of RAP may reduce the production costs and avoids asphalt waste.

Reclaimed asphalt may be added to the asphalt mixing process via a separate drum, e.g. a parallel drum, or a drum with ring addition.

Reclaimed asphalt may also be added directly into a mixer and/or a hot elevator of the asphalt mixing plant.

The term "Raw gas" shall denote the exhaust gas which exits the drying drum(s) of an asphalt mixing plant. The raw gas comprises the burned gas mix of the burner comprising a fuel gas, an oxidizer such as the ambient air or supplied oxygen and fine aggregate particles. The raw gas exits the drying drum at an outlet and may hence also be denoted as exhaust gas. The raw gas temperature shall denote the temperature of the raw gas at a predefined measurement point, in particular as measured by a corresponding temperature sensor.

A predictive Proportional-Integral (PI) controller is a specific controller with dead-time compensation as suggested by <NPL>.

Such an embodied controller contains five process model parameters, while two of the process model parameters are determined automatically based on the three other process parameters, namely based on the proportional term (gain), the integral term (integral time) and the dead time. Hence for such a controller, only three process model parameters need to be tuned, namely the proportional term, the integral term and an estimate of the process dead time. Referring e.g. to page <NUM>, column <NUM> of the above referenced document, parameters K, Ti, and L are determined by the operator, while parameters Kp and T are calculated as functions of the K and Ti. Conceptually, the predictive Proportional-Integral (PI) controller may be considered as a special case of a Smith predictor.

<FIG> shows a schematic diagram of a first drying drum <NUM> according to an embodiment of the invention. The first drying drum <NUM> may be configured to dry and heat a first aggregate A1 to a first aggregate temperature TA1. The first drying drum <NUM> comprises a first burner <NUM>. The first drying drum <NUM> further comprises a first controller <NUM> configured to control a first control loop <NUM> to control the first aggregate temperature TA1 of the first aggregate <NUM> and a second controller <NUM> comprising a second control loop <NUM> configured to control a first raw gas temperature TG1 of a first raw gas G1 of the first drying drum <NUM>. The first controller <NUM> and the second controller <NUM> are configured to operate independently from each other.

The first controller <NUM> is configured to control the first aggregate temperature TA1 by controlling the burner load P1 of the first burner <NUM>. The burner load P1 corresponds to the thermal output power of the first burner <NUM>.

The first drying drum <NUM> is configured to rotate at a first rotational speed RPM1. The second controller <NUM> is configured to control the first raw gas temperature TG1 of the first raw gas G1 by controlling the first rotational speed RPM1 of the first drying drum <NUM>. The rotational speed of the first drying drum <NUM> may be adapted by frequency converters (not shown) which are arranged between the second controller <NUM> and electric motors <NUM>, <NUM> for rotating the first drying drum <NUM>. The drying drum <NUM> is embodied as counterflow drum. The virgin aggregate A1 enters the drum <NUM> at the right side and leaves at the left side as indicated by the arrows, while the raw gas exits the drum <NUM> at the right side as indicated by a the dashed-dot line.

<FIG> shows a table comprising the complex dependencies between control parameters of the asphalt mixing plant according to embodiments of the invention. More particularly, changes of control parameters of the first control loop <NUM> influence also control parameters of the second control loop <NUM> and vice versa. Column <NUM> comprises the control parameters to be changed, namely the burner load of the first burner and the rotational speed of the first drying drum. Column <NUM> shows the effect which a change of the control parameters of column <NUM> have on the aggregate temperature of the first aggregate, while column <NUM> shows the effect which a change of the control parameters of column <NUM> has on the raw gas temperature of the first drying drum <NUM>. In <FIG> an arrow in an upwards direction indicates an increase of the corresponding parameter, while an arrow in a downwards direction indicates a decrease of the corresponding parameter.

As shown in table <NUM>, an increase of the burner load results in an increase of the aggregate temperature as well as in an increase of the raw gas temperature.

An increase of the rotational speed of the first drying drum results in an increase of the aggregate temperature, but in a decrease of the raw gas temperature.

The influence of the respective control parameter on the other control loop is indicated with a circle.

These dependencies may be explained as follows: An increase of the burner load increases the temperature inside the drying drum and hence increases the temperature of the aggregate/material inside the drying drum as well as the temperature of the gas inside the drying drum. An increase of the rotational speed of the drying drum decreases the raw gas temperature, but increases the temperature of the aggregate/material due to a denser material curtain inside the drying drum and a corresponding improved heat transfer from the hot raw gas to the virgin aggregate/material.

Drying drums for virgin aggregates and reclaimed asphalt show a similar behaviour as described above.

<FIG> illustrates a schematic diagram of the first control loop <NUM> and the second control loop <NUM> according to an embodiment of the invention. The first controller <NUM> receives as input signal an error signal e(t). The error signal may be also denoted as control deviation. The error signal e(t) corresponds to the difference between a target signal TA1tar(t) which represents the target temperature of the first aggregate temperature TA1 and the actual temperature TA1act(t) of the first aggregate. The actual temperature TA1act(t) may be measured by a temperature sensor. In this illustration t represents a point in time to reflect that the parameters of the first control loop <NUM> may change over time.

In dependence on the error signal e(t) the first controller <NUM> computes as output a control signal (control output or correcting value) P1(t) which represents the first burner load of the first burner <NUM> and adapts accordingly the first burner load. This changes the temperature in the first drying drum <NUM> and correspondingly the actual temperature TA1act(t) of the first aggregate material.

The second controller <NUM> receives as input signal an error signal e(t)which corresponds to the difference between a target signal TG1tar(t) which represents the target temperature of the first raw gas temperature TG1 and the actual raw gas temperature TG1act(t) of the raw gas/exhaust gas of the first drying drum. The actual temperature TG1act(t) may be measured by a temperature sensor. In this illustration t represents a point in time to reflect that the parameters of the second control loop <NUM> may change over time.

In dependence on the error signal e(t), the second controller <NUM> computes as output a control signal RPM1(t) which corresponds to the rotational speed in rounds per minutes of the first drying drum <NUM> and adapts accordingly the rotational speed of the first drying drum <NUM>. This changes the first raw gas temperature TG1act of the exhaust gas of the first drying drum <NUM>.

The first controller <NUM> and the first control loop <NUM> operate independently from the second controller <NUM> and the second control loop <NUM> despite the interdependencies between them as explained above with reference to <FIG>. More particularly, the control signal P1(t) of the first controller <NUM> changes also the first raw gas temperature TG1 and the control signal RPM1 of the second controller <NUM> changes the first aggregate temperature of the first aggregate.

<FIG> shows a block diagram of a control unit <NUM> which comprises the first controller <NUM> and the second controller <NUM> and the corresponding input and output signals of the first controller <NUM> and the second controller <NUM>.

<FIG> illustrates a schematic diagram of a third control loop <NUM> and a fourth control loop <NUM> according to an embodiment of the invention. The third control loop <NUM> and the fourth control loop <NUM> are used to control a second drying drum <NUM> comprising a second burner <NUM>. The third control loop <NUM> comprises a third controller <NUM> which receives as input signal an error signal e(t). The error signal e(t) corresponds to the difference between a target signal TA2tar(t) which represents the target temperature of a second aggregate temperature TA2 of a second aggregate A2 in the second drying drum <NUM> and the actual temperature TA2act(t) of the second aggregate A2. The actual temperature TA2act(t) may be measured by a corresponding temperature sensor.

In dependence on the error signal e(t) the third controller <NUM> computes as output a control signal P2(t) which represents a second burner load of the second burner <NUM> and adapts accordingly the second burner load. This changes the temperature in the second drying drum <NUM> and correspondingly the actual temperature TA2act(t) of the second aggregate A2.

The fourth controller <NUM> receives as input signal an error signal e(t)which corresponds to the difference between a target signal TG2tar(t) which represents the target temperature of the second raw gas temperature TG2 and the actual raw gas temperature TG2act(t) of the exhaust gas of the second drying drum <NUM>. The actual temperature TG2act(t) may be measured by a temperature sensor.

In dependence on the respective error signal e(t), the fourth controller <NUM> computes as output a control signal RPM2(t) which corresponds to the rotational speed in rounds per minutes of the second drying drum <NUM> and adapts accordingly the rotational speed of the second drying drum <NUM>. This changes the second raw gas temperature TG2act of the raw gas/exhaust gas of the second drying drum <NUM>.

The third controller <NUM> and the third control loop <NUM> operate independently from the fourth controller <NUM> and the fourth control loop <NUM> despite the interdependencies between them as explained above with reference to <FIG>. More particularly, the control signal P2(t) of the third controller <NUM> changes also the second raw gas temperature TG2 and the control signal RPM2 of the fourth controller <NUM> changes the second aggregate temperature of the second aggregate.

<FIG> shows a block diagram of a control unit <NUM> which comprises the first controller <NUM>, the second controller <NUM>, the third controller <NUM> and the fourth controller <NUM> and the corresponding input and output signals of the first controller <NUM>, the second controller <NUM>, the third controller <NUM> and the fourth controller <NUM>. Such a control unit may be used for asphalt mixing plants which comprise two drying drums, namely the first drying drum <NUM> and the second drying drum <NUM>. All four controllers <NUM>-<NUM> operate independently from each other which is illustrated with the separation by the dotted lines.

According to the embodiments which comprises two drying drums, namely the first drying drum <NUM> and the second drying drum <NUM> as illustrated with reference to <FIG>, the first aggregate A1 which is dried and heated in the first drying drum <NUM> may be in particular a virgin aggregate, i.e. a new mineral. Furthermore, the second aggregate A2 which is dried and heated in the second drying drum <NUM> may be in particular reclaimed asphalt or in other words recycled asphalt.

The first controller <NUM> may be in particular configured to compensate a deadtime of the first control loop <NUM> and the third controller <NUM> may be in particular configured to compensate a deadtime of the third control loop <NUM>. The first controller <NUM> and the third controller <NUM> may be in particular predictive Proportional-Integral controllers.

The second controller <NUM> and the fourth controller <NUM> may be in particular Proportional-Integral controllers.

<FIG> illustrates in an exemplary way a simplified flow diagram <NUM> of an asphalt mixing process according to an embodiment of the invention. The asphalt mixing plant comprises a plurality of VA cold feeder units <NUM>, a first drying drum <NUM> embodied as VA drying/heating drum including a first burner <NUM>, a common filter <NUM>, an exhaust gas blower <NUM> and an exhaustion pipe <NUM>. The asphalt mixing plant further comprises a reclaimed filler elevator <NUM>, an intermediate reclaimed filler silo <NUM>, a reclaimed filler silo <NUM>, an imported filler silo <NUM>, a filler scale <NUM> as well as a VA elevator <NUM>, a screen <NUM>, a hot VA silo <NUM> and a VA scale <NUM>. The asphalt mixing plant further comprises a hot reclaimed asphalt (RAH) addition, including a plurality of (cold) RA feeder units <NUM>, a RA elevator <NUM>, a second drying drum <NUM> embodied as RA drying/heating drum including a second burner <NUM>, a RAH buffer silo <NUM> with weighing appliance and a RAH scale <NUM>. Furthermore, the asphalt mixing plant comprises a cold reclaimed asphalt (RAC) addition, including a plurality of (cold) RA feeder units <NUM>, a RA buffer silo <NUM> and a RA belt scale <NUM>. The asphalt mixing plant furthermore comprises a plurality of bitumen tanks <NUM> and a bitumen scale <NUM>. The asphalt mixing plant further comprises a mixer <NUM>, a skip <NUM> and a plurality of asphalt mixture storage silos <NUM>.

The asphalt mixing plant <NUM> may comprise in particular the control unit <NUM> as shown in <FIG> comprising the first controller <NUM> and the second controller <NUM> for controlling the first drying drum <NUM> and the third controller <NUM> and the fourth controller <NUM> for controlling the second drying drum <NUM>.

The common filter <NUM> is configured to filter the raw gas/exhaust gas of the first drying drum <NUM> and the raw gas/exhaust gas of the second drying drum <NUM>.

The asphalt mixing plant <NUM> comprises a first temperature sensor <NUM> for sensing the first raw gas temperature of the first drying drum <NUM>. According to embodiments, the first temperature sensor <NUM> is arranged at a predefined first distance d1 to an outlet <NUM> for the first raw gas of the first drying drum <NUM>. Furthermore, according to embodiments, the first temperature sensor <NUM> is arranged within a predefined third distance d3 to an inlet <NUM> of the common filter <NUM>.

The asphalt mixing plant <NUM> further comprises a second temperature sensor <NUM> for sensing the second raw gas temperature of the second drying drum <NUM>. According to embodiments, the second temperature sensor <NUM> is arranged at a predefined second distance d2 to an outlet <NUM> for the second raw gas of the second drying drum <NUM>.

The first, the second and the third distance shall refer to the travel distance or in other words the flow distance that the raw gas travels or flows within the corresponding duct or tube of the asphalt mixing plant. This is indicated with the dotted lines for d1, d2 and d3.

<FIG> shows methods steps of a method for controlling an asphalt mixing plant according to an embodiment of the invention.

At a step <NUM>, the operation and control of the asphalt mixing plant is started. For the exemplary embodiment of <FIG> it is assumed that the asphalt mixing plant comprises a first and a second drying drum as shown e.g. in <FIG> as well as a first, a second, a third and a fourth controller. Accordingly, the operation of the asphalt mixing plant comprises drying and heating, by the first drying drum, a first aggregate to a first aggregate temperature and drying and heating, by the second drying drum, a second aggregate to a second aggregate temperature.

At a step <NUM>, the first controller controls the first aggregate temperature TA1 of the first aggregate.

At a step <NUM>, the second controller controls the first raw gas temperature TG1 of the raw gas of the first drying drum.

At a step <NUM>, the third controller controls the second aggregate temperature TA2 of the second aggregate.

At a step <NUM>, the fourth controller controls the second raw gas temperature TG2 of the raw gas of the second drying drum. According to embodiments, the control steps <NUM>, <NUM>, <NUM> and <NUM> are performed in parallel, but independently from each other by their respective controllers.

Aspects of the present invention may be embodied as a system, in particular an asphalt mixing plant, a method, and/or a computer program product. The computer program product may include a computer readable storage medium (or media) having computer readable program instructions thereon for causing a processor, in particular a processor of the control unit <NUM>, to carry out aspects of the present invention.

The computer readable program instructions may execute in particular on the control unit <NUM> of the asphalt mixing plant.

Claim 1:
An asphalt mixing plant (<NUM>), comprising
a first drying drum (<NUM>) for drying and heating a first aggregate to a first aggregate temperature, the first drying drum (<NUM>) comprising a first burner (<NUM>);
a first controller (<NUM>) configured to control by a first control loop (<NUM>) the first aggregate temperature of the first aggregate by controlling the burner load of the first burner (<NUM>); and
a second controller (<NUM>) configured to control by a second control loop (<NUM>) a first raw gas temperature of a first raw gas exiting the first drying drum (<NUM>); wherein
the first drying drum (<NUM>) is configured to rotate at a first rotational speed;
the second controller (<NUM>) is configured to control the first raw gas temperature of the first raw gas exiting the first drying drum by controlling the first rotational speed of the first drying drum (<NUM>); and
the first controller (<NUM>) and the second controller (<NUM>) are configured to operate independently from each other.