EP0632242A1 - Drying and/or heating of bulk material - Google Patents

Abstract

In order to dry and/or heat bulk material in a drying drum (1a/b), in particular in asphalt plants, the temperature of the waste gases of a burner (5a/b) which heats the drying drum (1a/b) is measured. In addition to this measured value, there is determined a measured value in connection with the material to be supplied to the drying and/or heating process and/or already undergoing the latter, and the inflow of the combustible medium and oxygen carrier for the burner (5a/b) is controlled as a function of the measured values. By this procedure, the heating and/or drying process for the material to be used is controlled in such a way that the process proceeds in a manner which is optimal in terms of fuel engineering, with low pollutant content in the waste gases. The apparatus for carrying out the process has a burner (5a/b) arranged in a drying drum (1a/b) rotatable about the longitudinal axis (2), a temperature-measuring device (22a/b) and a filter arrangement (17) for the burner waste gases, an adjusting device (31a/b, 32a/b) for adjusting the inflow of combustion medium and oxygen carrier, a measuring device (22a/b; 24a/b; 25a-f; 27a-f) for measuring at least one physical value of the material to be supplied to the drying and/or heating process and/or already undergoing the latter. <IMAGE>

Description

The invention relates to a method according to the preamble of patent claim 1 and an apparatus for carrying out the method according to the preamble of patent claim 9.

Free-flowing material consisting of minerals such as z. B. used for asphalt production must be dried and heated. Crushed rock material - limestone, dolomite, granite, etc. - of different grain sizes and surface properties as well as sands and gravel can be considered as mineral, so-called new material.

In addition to virgin material, asphalt lining material is also used, especially with the addition of virgin material, for asphalt production.

For the burner, depending on the design gaseous, liquid and solid fuels are used, the inflow of which means the amount of fuel supplied per unit of time.

The physical mineral parameters related to the heat absorption process of the material to be dried and / or heated include, in particular, their grain size, grain size composition, surface quality of the material particles, their material-specific thermal conductivity and heat capacity as well as their "transport properties" through the firing or drying drum Understood.

The invention solves the problem of controlling the heating or drying process for the material to be used in such a way that a firing-technically optimal, in particular low-pollutant process sequence is given, the operating parameters (burner output, etc.) of the device not being called due to or be changed to cold end material, but the device is operated in such a way that such deviations do not occur at all or only with the slightest deviations from the standard values, as a result of which material deterioration due to the heating process is excluded.

The object is solved by the claims.

In order to achieve the set goal, two control processes, as explained below, are z. B. connected by evaluating data fields. The "end values" of the dried and / or heated material can still be measured for control and safety purposes. The main focus, however, is on the input data, such as moisture, grain size of the material and their ratio as well as absolute amounts, composition of the fuel, its flow and the flow of the oxygen carrier (the combustion air) and the composition and amount of the exhaust gases, among other things, to determine the pollutant content and determining an optimal combustion also in terms of time, in particular when starting and extending the device. Since the quantities of the different grain sizes are determined or mixed together with known physical mineral parameters according to a given "recipe", the optimum burner output required can be determined from this, taking into account the initial material moisture, in order to then heat this mixture to a predetermined temperature with the lowest possible residual moisture.

Optimal combustion can be set on the basis of stored data or data fields which are continuously corrected by actual exhaust gas data. This results in a high level of combustion efficiency with controlled, minimal possible emission of pollutants, for which purpose the exhaust gas temperature of the device is kept as low as possible without the dew point in the exhaust pipes, the chimney or the filter arrangement being reached at their coldest points. Excessive temperature of the exhaust gases is also avoided by the ongoing measurements, which could also damage the filter arrangement.

In a pressure-temperature-humidity diagram, the dew point is understood to mean the location at which an unsaturated gas-steam mixture changes to saturation. The dropping liquid would close the filter arrangement within a very short time and possibly destroy it.

The amount of pollutants emitted by the exhaust gases is kept low by fine-tuning the combustion air supplied to the burner.

Due to the advantageous control of the number of revolutions of the drying drum or its inclination with respect to the horizontal, and also the adjustment of those in the drums arranged blades for circulating the material results in a stronger or weaker "vortexing" of the material, as well as a different "contact time" with the flame exhaust gases or the drum walls or internals heated by the burner flame. As a result, the "heat flow" into the material is adjustable, so that the process of moisture release and heat transfer to the material can be influenced. The drying and / or heating process of the material can be influenced with the first control process not only by the burner output, but also by the setting options on the drying drum just described.

The combination of a device for drying and heating new material with a device in which asphalt is dried and heated has proven to be particularly advantageous. If the exhaust gases from the asphalt processing device are passed together with the exhaust gases from the device for new material through one and the same filter arrangement, then the organic vapors from the asphalt preferably accumulate on the dust particles whirled up during the drying and heating process of the new material and can then together in the Filter arrangement are eliminated.

Fig. 1

ein Blockschaltbild der Vorrichtung und

Fig. 2

ein Diagramm zur Bestimmung des feuerungstechnischen Wirkungsgrads der Vorrichtung bei einem Materialdurchsatz von 100t/h, wobei das Eingangsmaterial eine Feuchte von 4% und eine Temperatur von 0°C hat und auf 180°C aufgeheizt wird. Die Abgastemperatur der Vorrichtung ist als Ordinate in Abhängigkeit der Luftüberschußzahl Lambda als Abszisse mit dem feuerungstechnischen Wirkungsgrad der Vorrichtung als Parameter dargestellt.

Exemplary embodiments of the method and the device according to the invention are explained in more detail below with reference to drawings. Show it:

Fig. 1

a block diagram of the device and

Fig. 2

a diagram for determining the firing efficiency of the device with a material throughput of 100t / h, the input material having a humidity of 4% and a temperature of 0 ° C and is heated to 180 ° C. The exhaust gas temperature of the device is as the ordinate as a function of the excess air number Lambda as the abscissa represented with the firing efficiency of the device as a parameter.

In Figure 1 is a block diagram of a device for drying and heating free-flowing new material, for. B. consisting of sand, gravel and crushed mineral and asphalt. The device has a drying drum 1a rotatable about the longitudinal axis 2 for the new material and a drying drum 1b for the asphalt. In the following, the device 1a is first described, which has a pre-drum 4a upstream of a firing drum 3a . A burner 5a for heating oil, gas or heavy oil as the fuel is flanged to the front of the firing drum 3a . A transport device 7a for the free-flowing new material is arranged on the front side of the drying drum 1a opposite the burner 5a . The material is moved in countercurrent mode through the drying drum 1a and exits dried and heated to a predetermined temperature through a material outlet 9a below the burner 5a .

The drying drum 1a has internals (not shown) which mix and circulate the introduced material. The drying drum 1a is set with motors, of which only a single motor 11a is shown schematically, to a predetermined number of revolutions and, via a lifting and lowering mechanism 13a, to a selected inclination with respect to the horizontal.

In the front area of the drying drum 1a - on the left in FIG. 1 - there is an exhaust pipe 15a which is connected to a filter arrangement 17 consisting of several individual filters (three are shown schematically in FIG. 1 ). The filter arrangement 17 is connected to a chimney 21 via a fan 19 which is adjustable in its delivery capacity. The fan output is set in such a way that a negative pressure of about 5 to 15 mm water column results from the environment. Of the The negative pressure to be set depends on the burner output and the amount of fine material whirled up by the new material and is set in such a way that no dust escapes from the openings in the device (material inlet and outlet). The burner output is also dependent on the temperature of the intake combustion air as an oxygen carrier, since warm combustion air (summer) contains less oxygen per unit volume than cold; however, cold combustion air must be heated up more than warm air. The fine regulation of the pressures in the two devices 1a and 1b is carried out by a throttle valve 20a or 20b which can be controlled by the control device 29 .

The filter arrangement 17 serves, among other things, to filter out dusts contained in the exhaust gases, which mainly originate from the free-flowing material and are whirled up during the drying and heating process. These filtered dusts are e.g. B. removed by a blast of compressed air on only one of the three filters that have been shut down for a short period of time and can be added to it later during asphalt production according to the recipe. A measuring arrangement 22a is arranged in the exhaust line 15a in front of the filter arrangement 17 as a measuring device for measuring the pressure, the temperature and the humidity of the exhaust gases enriched with the evaporation products originating from the drying and combustion process. The measuring arrangement 22a serves, among other things, to control the heat absorption, in particular heating (reaching a predetermined final temperature of the new material) and drying of the new material, so that the exhaust gases do not reach the dew point even at the coldest point of the exhaust gas line 15a , the chimney 22 and the filter arrangement 17 to reach. The temperature of the new material is adjusted in particular by controlling the burner output. Reaching the dew point in the filter arrangement 17 would cancel its gas permeability and thus bring the device to a standstill. If the dew point is at a point in the Exhaust pipe 15a ( 15b ) or the chimney 21 reached, this can cause damage to it due to the formation of acid. A measuring arrangement 24a for determining the gas composition of the exhaust gases is also installed in the exhaust line 15a . The measuring arrangement 24a in particular determines the CO and oxygen content in the exhaust gases. However, an NO _x and CH _x measurement could also be carried out.

The free-flowing material to be dried and heated is stored separately in several silos 23a - c according to grain size. In these silos 23a - c , the moisture content of the material in question is measured with moisture sensors 25a - c as a measuring device. The material flow of the material to be discharged from the silos 23a - c in accordance with the prescribed recipe is set by a control device 29 via material metering devices 26a - c and monitored with material flow sensors 27a - c as a further measuring device. The material metering devices 26a - c are not explicitly shown. The material flow conveyed results from the measured partial weight and the belt conveyor speed. The moisture sensors 25a - c and the material flow sensors 27a - c are also connected to the control device 29 for process control, in whose data memory 43 the values for the recipes are also stored. Also connected to the control device 29 are the motor 11a , the lifting and lowering mechanism 13a , the metering devices 31a and 32a for the fuel and the combustion air to the burner 5a , an adjusting device 33 for the fan 19 and the measuring arrangements 22a and 24a .

The temperature of the dried and heated virgin material emerging at the material outlet 9a is measured with a temperature measuring device 28a . The heated material is then conveyed into a hot silo 35a . Here it can now be temporarily stored for a few hours or used directly for asphalt production by using binders and filler are mixed in a mixer 37a . The finished mixed asphalt is now used up directly as a covering or temporarily stored in a asphalt silo 39a for a few hours for later use.

So that the temporarily stored material can be processed at the correct temperature at a later point in time, the downstream silos 35a and 39a , which are to be used in particular for intermediate storage, and their conveying devices are equipped with temperature measuring devices 41a and 41b , which are connected to the control device 29 . The burner output is now set by controlling the metering devices 31a and 32a in such a way that the heated material has the necessary temperature even with possible cooling in the downstream modules 35a, 37a and 39a .

The device 1b for drying and heating recycling material, in particular asphalt, is constructed analogously to the device 1a for the new material. In contrast to the device 1a , which is operated in countercurrent operation, the device 1b operates in direct current operation. The device 1b has, analogously to the assemblies of the device 1a , a firing drum 3b , a pre-drum 4b , a burner 5b , a transport device 7b , a material outlet 9b for the heated and dried lining material, drive motors 11b for the drum 3b / 4b , a lifting and lowering device 13b, an exhaust pipe 15b, a measuring arrangement 22b schematically three silos 23d - f for different to be dried and to be heated proppant, three humidity sensors 25d - f, three Materialflußsensoren 27d - f, three Materialdosiereinrichtungen 26d - f, a temperature measuring device 28b for the final temperature of the heated lining material and analog modules 35b and 41c used for the material storage. The exhaust pipes 15a and 15b are brought together in front of the filter arrangement 17 to form a single exhaust pipe 49 .

As indicated schematically in FIG. 1 by dashed lines, the exhaust pipe 15b of the asphalt processing device 1b can also be connected to an exhaust air connector 47 on the burner 5a of the device 1a . In this case, the exhaust gases are passed through the burner 5a and undergo a combustion and cracking process which affects in particular the organic compounds in the exhaust gases from the asphalt. The heated and dried lining material is conveyed into the hot silo or asphalt silo, possibly by mixing, with new material and filler.

• Materialzusammensetzung und Materialfluß für die betreffende Trockentrommel 1a/1b,
• wärmetechnische Materialeigenschaften,
• vorgegebene und rezeptbedingte Endtemperatur des Neu- bzw. Ausbaumaterials,
• physikalische Taupunktdaten sowie die "Abstandswerte", bis zu denen eine Annäherung an die Taupunktdaten aus Sicherheitsgründen erfolgen darf (eine möglichst geringe Abgastemperatur unter Einhaltung eines Temperatursicherheitsabstands zum Taupunkt wird am Meßort eingehalten, damit der Taupunkt an der kältesten Stelle der Abgasleitung, der Filteranordnung oder des Kamins nicht erreicht wird),
• Richt- und/oder Grenzwerte der Konzentration von Gasen in den Abgasen zur Vermeidung einer Überschreitung insbesondere des zulässigen CH_x-, CO-, und NO_x-Gehalts.

For the control of the device 1a and 1b by the control device 29 , the following data are stored in the data memory 43 , taking into account asphalt production recipes:

• Material composition and material flow for the relevant drying drum 1a / 1b ,
• thermo-technical material properties,
• predefined and recipe-related final temperature of the new or construction material,
• Physical dew point data as well as the `` distance values '' up to which the dew point data may be approximated for safety reasons (the lowest possible exhaust gas temperature, while maintaining a temperature safety distance from the dew point, is maintained at the measuring point, so that the dew point at the coldest point of the exhaust pipe, the filter arrangement or the Fireplace is not reached),
• Guideline and / or limit values for the concentration of gases in the exhaust gases to avoid exceeding in particular the permissible CH _x , CO and NO _x content.

• dem vorgegebenen Rezept unter Berücksichtigung der physikalischen Eigenschaften des Materials, wie Materialart, Materialzusammensetzung, Sandgehalt, Wärmeleitfähigkeit, Wärmekapazität, Transportgeschwindigkeit durch die Trommeln, ...
• der gemessenen Feuchte des Eingangsmaterials,
• der Wärmeaufnahme vom Material in der Vor- bzw. Brenntrommel 4a/b bzw. 3a/b,
• den thermischen Abgasverlusten,
• den thermischen Isolationsverlusten in der Vorrichtung 1a bzw. 1b,
• der Erwärmung und der Feuchte der Falschluft,
• der Temperatur des Brennmittels und der Verbrennungsluft.

The burner output required for drying and / or heating to a predetermined temperature of the new material or of the lining material is determined by the control device 29

• the specified recipe taking into account the physical properties of the material, such as material type, material composition, sand content, thermal conductivity, heat capacity, transport speed through the drums, ...
• the measured moisture of the input material,
• the heat absorption of the material in the pre or firing drum 4a / b or 3a / b ,
• thermal exhaust gas losses,
• the thermal insulation losses in the device 1a or 1b ,
• the warming and humidity of the false air,
• the temperature of the fuel and the combustion air.

• der Wärmeleitfähigkeit des Materials,
• der Wärmekapazität des Materials,
• der zeitlichen Wärmeaufnahmefähigkeit des Materials,
• der Feuchte des Eingangsmaterials,
• der Transportgeschwindigkeit und Durchmischung des Materials in den Trommeln 4a/b und 3a/b,
• der Temperatur der Brennerflamme bzw. den Flammengasen,
• der Brennerleistung.

The heat absorption of the material in the respective preliminary or Firing drum 4a / b or 3a / b depends on

• the thermal conductivity of the material,
• the thermal capacity of the material,
• the temporal heat absorption capacity of the material,
• the moisture of the input material,
• the transport speed and mixing of the material in the drums 4a / b and 3a / b ,
• the temperature of the burner flame or flame gases,
• the burner output.

• die Anordnung und Ausgestaltung der (nicht dargestellten) Schaufeln,
• die eingestellte Neigung der Trommel und/oder deren Schaufeln,
• die eingestellte Umdrehungszahl der Trommel,
• durch die Art des eingebrachten Materials (Neumaterial, Ausbaumaterial, Körnigkeit und deren mengenmäßige Zusammensetzung, Klebrigkeit, ...)

The transport speed and mixing of the material in the drums 4a / b and 3a / b is influenced by

• the arrangement and design of the blades (not shown),
• the set inclination of the drum and / or its blades,
• the set number of revolutions of the drum,
• by the type of material used (new material, finishing material, granularity and their quantitative composition, stickiness, ...)

• vom Verhältnis Brennmittel zu Verbrennungsluft (Luftüberschußzahl),
• von der Art des Brennmittels,
• von der Menge des Brennmittels und der Verbrennungsluft,
• von der Brennkammergestaltung,
• von der Brennerkonstruktion.

The temperature of the flame or flame gases depends

• the ratio of fuel to combustion air (excess air number),
• on the type of fuel,
• the amount of fuel and combustion air,
• from the combustion chamber design,
• from the burner construction.

• den Brennmittelzufluß,
• den Zufluß der Verbrennungsluft gemäß Brennervoreinstellung,
• Korrektur des Zuflusses der Verbrennungsluft.

The burner output is set via

• the fuel flow,
• the inflow of the combustion air according to the burner presetting,
• Correction of the inflow of combustion air.

• dem Verbot, den Taupunkt an der kältesten Stelle in der Abgasleitung 15a/b und 49 in der Filteranordnung 17 oder im Kamin 21 zu erreichen,
• von den Isolationsverlusten in den Abgasleitungen 15a/b und 49, in der Filteranordnung 17, im Kamin 22 und den Trommeln 3a/b und 5a/b,
• der Feuchte, der Menge und der Temperatur des Neu- und Ausbaumaterials vor Eintritt in die betreffende Trommel 3a/b und 4a/b,
• von der Feuchte, der Menge und der Temperatur der in die Trommeln 3a/b und 4a/b eintretenden Falschluft,
• von der Feuchte, der Menge und der Temperatur der Verbrennungsluft,
• der Menge und der Zusammensetzung der abgasenden Produkte aus dem Ausbaumaterial in den Trommeln 3b und 4b,
• der Brennmittelmenge und -art,
• dem Verhältnis Brennmittel zu Verbrennungsluft,
• dem Brennmittel- und Verbrennungsluftzufluß,
• der geforderten Endtemperatur des Neumaterials,
• der geforderten Endtemperatur des Ausbaumaterials,
• der Wärmeaufnahme in den Trommeln 3a/b und 4a/b.

The level of the exhaust gas temperature and the amount of exhaust gas depend on

• the ban on reaching the dew point at the coldest point in the exhaust gas line 15a / b and 49 in the filter arrangement 17 or in the chimney 21 ,
• the insulation losses in the exhaust pipes 15a / b and 49 , in the filter arrangement 17 , in the chimney 22 and the drums 3a / b and 5a / b ,
• the humidity, the quantity and the temperature of the new and finishing material before entering the relevant drum 3a / b and 4a / b ,
• the humidity, the quantity and the temperature of the false air entering the drums 3a / b and 4a / b ,
• the humidity, the quantity and the temperature of the combustion air,
• the quantity and the composition of the exhaust products from the finishing material in the drums 3b and 4b ,
• the amount and type of fuel,
• the ratio of fuel to combustion air,
• the fuel and combustion air inflow,
• the required final temperature of the new material,
• the required final temperature of the lining material,
• the heat absorption in the drums 3a / b and 4a / b .

A low exhaust gas temperature, a small amount of false air and low insulation losses increase the firing efficiency of the device.

• Feuchtegehalt, Menge und Temperatur des Eingangsmaterials,
• Materialzusammensetzung,
• Temperatur und Restfeuchte des erhitzten Ausgangsmaterials,
• Temperatur, Menge, Feuchte und Unterdruck der Abgase in der Abgasleitung,
• Abgaszusammensetzung, insbesondere Gehalt an CO, H₂O, O₂.
• Temperatur der Einrichtungen zur Förderung und Speicherung des erhitzten Materials,
• Temperatur der zugeführten Verbrennungs- und eindringenden Falschluft.

What can be measured in the device for the new material and for the lining material in chronological order or is specified by the recipe:

• Moisture content, quantity and temperature of the input material,
• Material composition,
• Temperature and residual moisture of the heated starting material,
• Temperature, quantity, humidity and negative pressure of the exhaust gases in the exhaust pipe,
• Exhaust gas composition, in particular content of CO, H₂O, O₂.
• Temperature of the devices for conveying and storing the heated material,
• Temperature of the supplied combustion and penetrating false air.

• Zufluß des Brennmittels,
• Zufluß der Verbrennungsluft,
• Neigung der Trommel,
• Verstellung der Schaufeln in den Trommeln,
• Umdrehungszahl der Trommel,
• Saugleistung des Abgasventilators 19.

What the predetermined data and / or the measured values can be adjusted as a function:

• Inflow of fuel,
• Inflow of combustion air,
• Inclination of the drum,
• Adjustment of the blades in the drums,
• Number of revolutions of the drum,
• Suction power of the exhaust fan 19 .

When the device is started up, typical basic values for the control of the metering devices 31a / b , 32a / b and 26a - f are set in a device-specific manner and stored in the data memory 43 . In daily operation, the combustion is now adjusted via the metering devices 31a / b and 32a / b connected to the control device 29 in such a way that a high firing efficiency with minimal pollutant emission results at a predetermined material end temperature. The fine adjustment of the metering devices 31a / b and 32a / b is then carried out continuously during operation by measuring the actual pollutant values with the measuring arrangement 24a / b . The continuously measured pollutant values are also stored in data memory 43 as a function of time. During a later operation of the device, the timing of the metering devices 31a / b and 32a / b is then carried out in accordance with this timing control curve, which in turn is then corrected by the new measured values. This "teach-in" process for burner output and pollutant reduction is intended to determine the best possible operating data. However, in order not to save unrealistic data for later operation due to unusual environmental and short-term plant data, new data can be weighted, which a data change z. B. only causes the same results several times.

The data stored in a time-dependent manner, in addition to adapting to changes in time due to the recipe, material input data, etc., allow devices 1a and 1b to be optimally moved on and off.

In order to achieve a perfect setting of a low-pollutant combustion in the firing drum 3a / b , a firing drum should be used in which no free-flowing material and also no dust or vapors whirled up by it can get into the burner flame. Such a drum is z. B. in the Swiss patent application application no. 01 500 / 93-9.

The pressure of the exhaust gases is determined with the measuring arrangement 22a / b .

As already stated above, the dew point of the exhaust gases depends on their temperature, pressure and moisture content. The exhaust gases must never come near their dew point in the area of the filter arrangement 17 , since otherwise the filter arrangement 17 is no longer effective and can close, as a result of which the device no longer functions.

The following calculation example is intended to provide an insight into how the sizes of the device are linked to the individual measured values. It should also be noted in the calculation that volume and mass flows must be coordinated. So z. B. the oxygen content of the combustion air flow in winter compared to that in summer only in that the spec. Weight of the combustion air is lower and thus less mass is conveyed with a constant volume flow.

wobei hier insbesondere über den unten beschriebenen Abgasfluß I ein zweiter Regelungsvorgang ("Sekundärregelung") einwirkt.The inflow of the fuel M in kg / h required for drying and / or heating the material is determined in a first control process ("primary control") as follows:

a second control process (“secondary control”) acting here in particular via the exhaust gas flow I described below.

   Die Umrechnung in Normkubikmeter pro Stunde [Nm³/h] erfolgt unter Verwendung des Molvolumens von 22,4 m³/k Mol und mit 18 kg für ein Kilomol Wasser gemäß

   Vereinfachend für die nachfolgende Rechnung wird nur ein einziges Material aus den Silo 23a mit einem Fluß A von 100 t/h (Trockengewichtsfluß) mit einer Feuchte B von 4 % m verarbeitet. D. h. in der beispielsweisen Vorrichtung ergibt sich der auszutreibende Wasserdampffluß G zu 4 978 Nm³/h (F = 4 000 kg/h). Die spezifische Wärme g der Abgase beträgt 0,31032 [kcal/Nm³K] (K ≡ Grad Kelvin). Die beispielsweise Temperatur E der Abgase gemessen mit der Meßanordnung 22a liegt bei 74 °C. l ist die spezifische Wärme des aus dem Silo eingebrachten Materials; sie liegt bei 0,21 kcal/kg·K. Die am Trommelausgang 9a mit der Temperaturmeßeinrichtung 28a gemessene Materialausgangstemperatur C beträgt 180 °C. Die Umgebungstemperatur k wird beispielsweise mit 0 °C angenommen. Die Enthalpie i des Wasserdampfs beträgt 650 kcal/kg. Die spezifische Wärme h von Wasser mit 1 kcal/kg. Der untere Heizwert c in [kcal/kg] für verschiedene Brennmittel kann der untenstehenden Tabelle 1 entnommen werden. Der Fluß I [Nm³/kg] der Abgase nur aus dem Verbrennungsprozeß (ohne Feuchte durch das zu trocknende Material), ist mit nachstehender Beziehung bestimmbar

$\text{I [Nm³/kg] = b [Nm³/kg] + ((Lambda) - 1)·a [Nm³/kg]}$

und ergibt sich in diesem Beispiel mit den unten aufgeführten Werten und dem Brennstoff Heizöl extra leicht (EL) zu 29,01 Nm³/kg. Der nur für die Verbrennung mit der Dosiereinrichtung 32a eingestellte Verbrennungsluftfluß a [Nm³/kg] sowie der Abgasfluß b [Nm³/kg] mit Wasserdampf beladen bzw. der trockene Abgasfluß e [Nm³/kg] ohne Wasserdampf sind der untenstehenden Tabelle 1 für die unterschiedlichen Brennstoffe zu entnehmen. G is the water vapor to be expelled in the process from the moist input material introduced into the drying drum 1a by the transport device 7a in order to dry it, in standard cubic meters per unit of time. The water vapor flow G to be expelled is determined from the material inlet flow A [t / h] determined with the material flow sensor 27a and its moisture content B [%] measured with the moisture sensor 25a in accordance with the following relationships:

$\text{F [kg / h] = A [t / h] · B [\%] · 10}$

The conversion into standard cubic meters per hour [Nm³ / h] is carried out using the molar volume of 22.4 m³ / k mol and with 18 kg for one kilomole of water

To simplify the following calculation, only a single material from silo 23a with a flow A of 100 t / h (dry weight flow) with a moisture B of 4% m is processed. That is, In the example device, the steam flow G to be expelled results in 4 978 Nm 3 / h ( F = 4 000 kg / h). The specific heat g of the exhaust gases is 0.31032 [kcal / Nm³K] (K ≡ degrees Kelvin). The temperature E of the exhaust gases, for example, measured with the Measuring arrangement 22a is 74 ° C. l is the specific heat of the material brought in from the silo; it is 0.21 kcal / kgK. The material outlet temperature C measured at the drum outlet 9a with the temperature measuring device 28a is 180 ° C. The ambient temperature k is assumed to be 0 ° C, for example. The enthalpy i of water vapor is 650 kcal / kg. The specific heat h of water with 1 kcal / kg. The lower calorific value c in [kcal / kg] for various fuels can be found in Table 1 below. The flow I [Nm³ / kg] of the exhaust gases only from the combustion process (without moisture through the material to be dried) can be determined using the following relationship

$\text{I [Nm³ / kg] = b [Nm³ / kg] + ((Lambda) - 1) · a [Nm³ / kg]}$

and results in this example with the values listed below and the fuel heating oil extra light (EL) to 29.01 Nm³ / kg. The combustion air flow a [Nm³ / kg] and the exhaust gas flow b [Nm³ / kg], which are only set for the combustion with the metering device 32a , are loaded with water vapor or the dry exhaust gas flow e [Nm³ / kg] without water vapor are shown in Table 1 below for the different types Remove fuels.

wobei D der Sauerstoffgehalt bezogen auf den trockenen Abgasfluß ist. Er beträgt 12,85 %. Tabelle 1 Brennstoff Verbrennungsluft a [Nm³/kg] Abgase feucht b [Nm³/kg] Heizwert c [kcal/kg] Abgase trocken e [Nm³/kg] CO₂ max % Heizöl EL 11,30 12,04 10200 10,76 15,20 Schweröl 10,90 11,56 9700 10,33 16 Erdgas CH 9,57 10,60 8650 7,78 11,90 Erdgas NL 8,41 9,44 7600 7,68 11,90 Propan 12,15 13,12 11070 11,08 13,90 Butan 12 12,89 10920 10,97 14,10 Erdgas CH bzw. NL kennzeichnet in der Schweiz bzw. in Holland üblicherweise verwendetes Erdgas. The excess air (lambda) in the above relationship can be determined according to the following relationship:

$\text{(Lambda) = 1 + e / aD / (21 - D),}$

where D is the oxygen content based on the dry exhaust gas flow. It is 12.85%. Table 1 fuel Combustion air a [Nm³ / kg] Exhaust gases moist b [Nm³ / kg] Calorific value c [kcal / kg] Exhaust gases dry e [Nm³ / kg] CO₂ max% Heating oil EL 11.30 12.04 10200 10.76 15.20 Heavy oil 10.90 11.56 9700 10.33 16 Natural gas CH 9.57 10.60 8650 7.78 11.90 Natural gas NL 8.41 9.44 7600 7.68 11.90 propane 12.15 13.12 11070 11.08 13.90 butane 12th 12.89 10920 10.97 14.10 Natural gas CH or NL denotes natural gas commonly used in Switzerland or the Netherlands.

ermittelbar und aus diesem Ergebnis der Wasserdampfpartialdruck P [bar] gemäß nachfolgender Beziehung bestimmbar:

$\text{P = W/100}$

   Wasserdampfpartialdruck P und der Taupunkt T [°C] von Wasser sind über die nachfolgende Tabelle miteinander verknüpft.

From the input measured values, the total water vapor content W (including moisture expelled from the input material) in the exhaust gases is according to volume percent

can be determined and from this result the water vapor partial pressure P [bar] can be determined according to the following relationship:

$\text{P = W / 100}$

Water vapor partial pressure P and the dew point T [° C] of water are linked with each other in the table below.

In order to achieve a high combustion efficiency Γ of the device - the optimum efficiency is Γ = 1 (or 100%) - the lowest possible exhaust gas temperature E is maintained via a second control process ("secondary control") mentioned above that the risk increases to reach the dew point in the filter arrangement 17 .

The following examples will demonstrate the relationship between the firing efficiency Γ of the device, material moisture, amount of pollutants in the exhaust gases and burner output.

In the following exemplary considerations, a material flow of 100 t / h, an initial material temperature of 0 ° C. and an end heating temperature of the material at the material outlet 9a of 180 ° C. are assumed.

In a first example, the material to be dried and heated has an initial moisture of 4%. With a burner output of 8.08 MW, the exhaust gas temperature is 74 ° C, ie 10 ° C above the dew point temperature of 64 ° C. The relationship between the excess air number lambda, the limit to the condensation area 44 (= dew point line) and the exhaust gas temperature is shown in FIG . On the basis of an excess air number lambda of 2.5, an exhaust gas temperature of 74 ° C. and a dew point at 64 ° C., FIG. 2 results in an efficiency Γ of 90.6%.

In a second example, is the initial material moisture 2% and the burner output set to 6.39 MW, the dew point drops by 7 ° C to 57 ° C and the flue gas temperature is 67 ° C, which then results in a firing efficiency Γ of 91.8% due to the adjustment this exhaust gas temperature results. At an exhaust gas temperature of 74 ° C, the combustion efficiency Γ would only be 91.1%.

In a third example, the initial material moisture is 8% and the burner output is set to 11.46 MW. The dew point is 69 ° C and the exhaust gas temperature is 74 ° C. This difference between exhaust gas temperature and dew point of only 5 ° C is somewhat small. For safety reasons, it should be 10 ° C. so that air flow differences and the thermal insulation of the filter arrangement 17 are not critical.

Based on the first example, an excess air ratio of 2.0 can now be set, resulting in a burner output of 8.0 MW with an efficiency Γ of 91.3% at a dew point of 68 ° C and an exhaust gas temperature of 78 ° C. The combustion efficiency Γ has thus increased by 0.7%, which means that the burner output can be reduced by 0.08 MW.

Is z. B. by reducing the sand content, an exhaust gas temperature increase of 30 ° C to 114 ° C and if the burner output was not readjusted, the final material temperature would decrease by 11 ° C. However, if the burner output is adjusted to 8.29 MW, the efficiency Γ is 87.7% at an exhaust gas temperature of 114 ° C (and as above, a final material temperature of 180 ° C). By influencing the heat absorption, by adjusting the number of revolutions of the pre-drum and / or the inclination of the drum to the horizontal and by the position of the blades, the values of the first example can be reached again, whereupon the burner output increases again from the above 8.29 MW 8.0 MW can be reduced can.

The above examples are intended to show the ways of optimizing a minimal pollutant emission and a good combustion efficiency with the greatest possible protection of the filter arrangement 17 .

Since the moisture content of the material to be dried or the partial materials from the silos 23a - c has already been determined with the moisture sensors 25a - c and the temperature to which heating is to be carried out and the amount of material are predetermined, the burner 3a can be controlled by the control device 29 , as set out above. The measuring arrangement 24a acts via the control device 29 on the metering devices 31a and 32a , so that a total carbon content of approximately 50 mg.m³ with a CO content of 100 mg.m³ and a NO _x content below 50 in the exhaust gases mg · m⁻³ can be maintained.

Instead of sensors 25a to 25f and 27a to 27f , only one moisture and one material flow sensor can be used, which measures the properties of the mixture.

Instead to adjust the inclination of the drying drum 1a / b, can also Figures 3a / b upstream preturret 4a / b arranged blades (not shown) are adjusted in position in the interior of the burning drum. The material to be dried and heated plunges as a "curtain" through the pre-drum 4a / b , through which the hot exhaust gases pass. Preferably, the angular position to the drum axis can now be adjusted so that a denser or less dense "material curtain" results which influences the material dwell time in the drum. The adjustment is carried out by adjusting units (not shown) controlled by the control device 29 in accordance with the measured values of the above-mentioned sensors for the material input and exhaust gas values.

Instead of coupling the two devices 1a and 1b with one another, the two devices can also be operated separately from one another.

The "distance" of the exhaust gas values from the dew point, which in particular endangers the filter arrangement 17, can also be monitored with a psychrometric sensor.

The proportion of "false air" entering the device, which worsens the efficiency Γ of the device, can be reduced by keeping the free material outlet opening 9a / b and the opening for the material inlet as small as possible.

Since the measurement of the exhaust gas composition takes place in the exhaust gas lines 15a and 15b , the air fraction caused by the false air is also recorded. Instead of the two measuring arrangements 22a and 22b for the exhaust gas composition and the two measuring arrangements 24a and 24b for monitoring an approach to the dew point, it is also possible to work with only a single measuring arrangement. However, if two measuring arrangements are used, the burner can be controlled more simply and safely.

Since the setting of the devices by the control device 29 takes place using time-dependent data stored in the data memory 43 , the measuring devices 22a / b and 24a / b can be arranged as only one measuring device behind the filter arrangement 17 .

Based on the data stored in the data memory 43 and the above, monitoring measurements, it is possible to change the fuel and to use so-called multi-fuel burners.

Since there is an upper limit for the ratio of processing asphalt to be processed and new material with respect to the filter arrangement 17 , caused by the vapors the processing asphalt, the amount of processing asphalt to be introduced into the pre-drum 4b can also be regulated by controlling the metering devices 26d - f .

Instead of integrating the burner into the drying drum, a hot gas can also be generated externally, which is then blown in.

Claims (18)

Process for drying and / or heating free-flowing material in a drying drum (1a / b) , in particular in asphalt plants, with a first control process for changing the supply (M) of the fuel and / or the oxygen carrier for the burner (5a / b) and a second control process for changing the firing efficiency (Γ) of the system, the first and second control processes being able to be coordinated with one another in such a way that within a predetermined tolerance range a predetermined final material temperature and / or moisture and a high firing efficiency ( Γ ) of the system minimal pollutant content of the exhaust gases can be reached. A method according to claim 1, characterized in that the temperature of the exhaust gases of the burner (5a / b) which heats the drying drum (1a / b) and a material which is to be supplied to and / or is present in the drying and / or heating process are combined standing measured value is determined, and the inflow of the fuel and the oxygen carrier, in particular the combustion air for the burner (5a / b) is regulated depending on the temperature and / or the measured value. Method according to Claim 2, characterized in that the moisture of the material to be dried and / or heated is determined as the measured value. Method according to Claim 2 or 3, characterized in that at least one of the physical mineral parameters related to the heat absorption process of the material to be dried and / or heated is determined as the measured value. Method according to one of claims 2 to 4, characterized in that the number of revolutions of the drying drum (1a / b) is set in dependence on the measured value or values and / or the exhaust gas temperature such that the dew point of the exhaust gases at the coldest point of the exhaust gas flow , especially in the filter arrangement (17) . Method according to one of claims 2 to 5, characterized in that the inclination of the drying drum (1a / b) with respect to the horizontal is set as a function of the measured value or values and / or the exhaust gas temperature such that the dew point of the exhaust gases is the coldest Location of the exhaust gas flow, in particular in the filter arrangement (17) is not reached. Method according to one of claims 1 to 6, characterized in that the concentration of at least one gas, in particular oxygen and / or carbon monoxide (CO), is determined in the exhaust gases, and the inflow of the oxygen carrier to the burner (5a / 5b) in accordance with the Concentration values are controlled such that the exhaust gases have a minimal pollutant concentration. Method according to one of Claims 1 to 7, characterized in that the temperature of the transport and / or storage device (35, 37, 39) downstream of the drying drum (1a / 1b) is measured for the material and the burner output is fine-tuned in accordance with the measured value. Device for carrying out the method according to one of claims 1 to 8 with a burner (5a / b) arranged in a drying drum ( 1a / b) rotatable about the longitudinal axis (2 ) , characterized by a first measuring device (22a / b) for determining the Temperature of the Exhaust gases from the burner (5a / b) and / or the drying drum (1a / b) , an adjusting device (31a / b, 32a / b) for the inflow of combustion medium and the oxygen carrier to the burner (5a / b) , a second measuring device ( 24a / b; 25a-f; 27a-f) for measuring at least one physical value related to the drying and / or heating method of the material to be supplied and / or currently in the material, a filter arrangement (17) for the exhaust gases and a control device (29) connected to the measuring devices (22a / b, 24a / b; 25a-f; 27a-f) and the setting device (31a / b, 32a / b ) , with which, depending on the temperature and the physical value of the Influx of the fuel and the oxygen carrier for the burner (5a / b) is adjustable. Apparatus according to claim 9, characterized in that the inclination of the axis (2) of the drying drum (1a / b) with respect to the horizontal during the drying and / or heating process by a first adjustment device (13a / b) connected to the control device (29 ) is adjustable according to the value measured with the first and / or second measuring device (22a / b, 24a / b; 25a-f; 27a-f) . Apparatus according to claim 9 or 10, characterized in that the number of revolutions of the drying drum (1a / b) during the drying and / or heating process corresponds to that with the first and / or second measuring device (22a / b, 24a / b; 25a-f ; 27a-f) measured value can be set with a drive (11a / b) connected to the control device 29 . Apparatus according to claims 9 to 11, characterized in that the second measuring device is a moisture measuring device (25a-f) for the material to be dried and / or heated. Apparatus according to claims 9 to 12, characterized in that the second measuring device has a measuring element (24a / b) for determining the concentration of at least one gas, in particular oxygen and / or carbon monoxide in the exhaust gases. Device according to one of claims 9 to 13, characterized by a data memory (43 ) connected to the control device (29) , in which the measured values of the measuring devices (22a / b, 24a / b, 25a-f, 27a-f) are the first data time-dependent, in particular starting with the start-up and / or ending with the extension of the burner (5a / b) , preferably with the weighting of time-dependent stored second data. Device according to one of claims 9 to 14, characterized by a further, second drying drum (1b) rotatable about the longitudinal axis for drying and heating, in particular asphalt lining material, with a second burner (5b) , a second setting device (31b, 32b) for the Combustion agent and the oxygen carrier inflow, only one filter arrangement (17) , in front of which both the exhaust gases of the first and the second drying drum (1a / b) are brought together in an exhaust pipe (49) and can then be passed through the filter arrangement (17) . Device according to one of claims 9 to 14, characterized by a further, second drying drum (1b) rotatable about the longitudinal axis for drying and heating in particular asphalt lining material with a second burner (5b) , a second setting device (31b, 32b) for the combustion agent. and the oxygen carrier inflow, an exhaust air inlet (47) on the first burner (5a) , through which the exhaust gases of the second drying drum (1b) can be introduced into the first burning drum (3a) , and only one filter arrangement (17) after the first drying drum (1a) for all the exhaust gases. Apparatus according to claim 15 or 16, characterized by at least one transport device (7a / b) controlled by the control device (29) in the material transport performance , in particular for the material to be introduced into the second drying drum (1b) , at least one arranged in front of the filter arrangement (17) and measuring device (24a / b ) connected to the control device (29) for the gas concentration of at least one gas component in the exhaust gases, so that the material transport performance of the transport devices ( 7a / b), in particular into the second drying drum (1b), can be set as a function of the measured concentration. Device according to one of claims 15 to 17, characterized by an exhaust gas quantity measuring device connected to the control device (29) in front of the filter arrangement (17) , depending on the measured value, the transport capacity, in particular into the second drying drum (1b) , and / or the burner capacity, in particular of the second burner (5b) can be reset.

Images