EP0632242B1 - 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 for drying and / or heating free-flowing Material in a drying drum, especially in asphalt plants, and a device to carry out the procedure.

FR-A 2 274 882 is a drying system with a drying drum for dewatering known from agricultural products and animal feed. The drying drum was heated with a burner. According to the state of the art described in this document, the Temperature of the exhaust gas leaving the drying drum measured. Using only this temperature value, one was then Control of the fuel inflow made for the burner.

Free-flowing material consisting of minerals, e.g. for asphalt production must be dried and heated. As a mineral, so-called new material, crushed rock material - limestone, dolomite, granite, etc. - comes out differently Grain and surface properties as well as sands and gravel in question.

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

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

Among the physical, related to the Heat absorption process of the to be dried and / or heated Material parameters are particularly important 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" by the Understanding the firing or drying drum.

The invention solves the problem of heating or Drying process for the material to be used in this way to control that a combustion-technically optimal, Low pollutant process flow is given the operating parameters (burner output, etc.) of the device not because of a too hot or too cold End material are changed, but the device in such a way is operated that such deviations even not or only with the slightest deviations from the norm values occur, causing material deterioration through the heating process can be excluded.

The object is solved by the claims.

In order to achieve the set goal, two control processes, as explained below, with each other e.g. B. connected by evaluating data fields. It can for control and security purposes the "final values" of the dried and / or heated material measured become. However, the main focus is on the input data, such as Moisture, grain size of the material and their Quantity ratio and absolute quantities, composition of the fuel, its flow and the flow of the oxygen carrier (the combustion air) and the composition and amount of exhaust gases u. a. to determine the pollutant content and determining an optimal combustion also in terms of time, especially when moving in and out the device. Because the amounts of the different Grain sizes determined or according to a given "Recipe" with known physical mineral parameters can be mixed together to obtain the optimal one Burner output taking into account the initial material moisture be determined to this mixture then on a specified temperature with the lowest possible residual moisture to heat.

Due to stored data or data fields, which can be continuously corrected by actual exhaust gas data optimal combustion can be set. Hereby there is a high level of combustion efficiency with controlled, minimum possible pollutant emissions, the exhaust gas temperature of the device being so low for this purpose is kept as possible without the dew point in the Exhaust pipes, the chimney or the filter arrangement on their coldest places is reached. Through the ongoing Measurements will also be too high a temperature of the exhaust gases avoided, which also damage the filter arrangement could.

Below the dew point is a pressure-temperature-humidity diagram understood the place where one in itself unsaturated gas-vapor mixture passes into saturation. The droplets of liquid that would fall out would affect the filter arrangement close within a short time and possibly also destroy.

The amount of pollutants emitted by the exhaust gases is achieved by fine adjustment of the feed to the burner Combustion air kept low.

Thanks to the advantageous control of the number of revolutions the drying drum or its inclination to the horizontal as well as the adjustment of the in the drums arranged blades for circulating the material results a stronger or weaker "swirling" of the Materials, as well as a different length of "contact time" with the flame gases or through the burner flame heated drum walls or internals. This is The "heat flow" into the material is adjustable, which makes the process the release of moisture and heat transfer the material can be influenced. The drying and / or Heating process of the material is with the first control process not just by the burner output, but also through the setting options just described can be influenced on the drying drum.

The merger has proven to be particularly advantageous a device for drying and heating new material with a device in which expanded asphalt is dried and is heated. Exhaust gases from the asphalt processing device together with the exhaust gases the device for new material by one and the same Filter arrangement directed, so prefer to store organic vapors from the asphalt during the the drying and heating process of the new material whirled up dust particles and can then together are eliminated in the filter arrangement.

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 shown as the ordinate as a function of the excess air number lambda as the abscissa 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, by means of 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. The negative pressure to be set depends on the burner output and the amount of fine material whirled up from 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 reached at a point in the exhaust pipe 15a ( 15b ) or the chimney 21 , this can cause damage to the latter 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 be temporarily stored for a few hours or used directly for asphalt production by mixing binders and fillers 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 intermediate 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 4a/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 4a / 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 combustion technology Device efficiency.

• 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, H ₂ O, O ₂ .
• 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, a weighting of new data can be undertaken which 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 the devices 1a and 1b to be optimally moved in and out.

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 convey how the sizes of the device with the individual measured values are linked. Furthermore, the calculation to note that volume and mass flows on each other must be coordinated. So z. B. the Oxygen content of the combustion air flow in winter that in summer only because of the higher temperature the spec. Weight of the combustion air is lower and therefore with a constant volume flow less mass is promoted.

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.

G is the amount of water vapor to be expelled contained in standard input cubic meters per unit of time contained in the moist input material. 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: F [kg / h] = A [t / h] · B [%] · 10

The conversion into standard cubic meters per hour [Nm ³ / h] is carried out using the molar volume of 22.4 m ³ / 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 exemplary device, the water vapor 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 / Nm ³ K] (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 [Nm ³ / 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 I [Nm 3rd / kg] = b [Nm 3rd / kg] + ((Lambda) - 1) · a [Nm 3rd / kg] and results in this example with the values listed below and the fuel heating oil extra light (EL) to 29.01 Nm ³ / kg. The combustion air flow a [Nm ³ / kg] and the exhaust gas flow b [Nm ³ / kg] set only for the combustion with the metering device 32a are loaded with water vapor or the dry exhaust gas flow e [Nm ³ / kg] without water vapor is shown in Table 1 below for the different fuels.

The excess air (lambda) in the above relationship can be determined according to the following relationship: (Lambda) = 1 + e / aD / (21 - D), where D is the oxygen content based on the dry exhaust gas flow. It is 12.85%. fuel Combustion air a [Nm ³ / kg] Exhaust gases moist b [Nm ³ / kg] Calorific value c [kcal / kg] Exhaust gases dry e [Nm ³ / kg] CO ₂ 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: P = W/100 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: 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. P [mbar] 42.41 73.75 123.35 199.2 311.6 473.6 578 701.1 845.3 1013.3 T [° C] 30th 40 50 60 70 80 85 90 95 100

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 by means of a second control process ("secondary control") mentioned above. It should be noted here, however, that the risk increases that the dew point will be reached in the filter arrangement 17 .

The relationship between firing efficiency Γ the device, material moisture, amount of pollutants in the exhaust gases and burner output is said to be the following Examples will be demonstrated.

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., the combustion efficiency r of 90.6% results from FIG .

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 exhaust gas temperature is 67 ° C, which then firing efficiency Γ of 91.8% through the Adjustment to this exhaust gas temperature results. At an exhaust gas temperature The firing efficiency would be 74 ° C Γ only 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 figure can now be obtained of 2.0, which results 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 results. The firing efficiency Γ has thus increased by 0.7%, resulting in a reduction the burner output by 0.08 MW is possible.

Is z. B. an increase in exhaust gas temperature by reducing the sand content reached by 30 ° C to 114 ° C and if the burner output were not readjusted, then the final material temperature drops by 11 ° C. However, the Burner output adjusted to 8.29 MW results in an efficiency Γ of 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 the Number of revolutions of the pre-drum and / or the inclination of the Drum to the horizontal as well as the position of the blades the values of the first example can be adjusted can be reached again, whereupon the burner output of the 8.29 MW above to 8.0 MW again 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.m ^-3 with a CO content of 100 mg.m ^-3 and a NO _x content below 50 in the exhaust gases mg · m ^-3 can be observed.

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 in relation 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 the burner in the drying drum integrate, a hot gas can also be generated externally, which is then blown in.

Claims (16)

1. Process for drying and/or heating pourable material in a drying drum (1a/b), particularly in asphalt installations, with a high fuel-engineering efficiency (Γ) of the installation and a minimal pollutant fraction in the waste gases, a final temperature and/or moistness of the material being achieved which is predetermined within a tolerance range, in which process the drying and/or heating of the material takes place in a burner (5a/b) by combustion with the controlled infeeding of a burning medium and an oxygen-carrier, in particular combustion air, the temperature of the waste gases from the burner and/or the drying drum is measured and is kept as low as possible, and in which process the burner capacity necessary for the drying and/or heating of the material to a predetermined temperature is ascertained by a control apparatus (29) using data stored in advance, the dew point of the waste gases at the coldest point in the waste-gas flow, particularly in a waste-gas filter arrangement (17), is calculated, taking into account the burning capacity and also the moistness, quantity and temperature of the material before its entry into the drum as physical measured values of the material, the moisture, the quantity and the temperature of the combustion air and also of the infiltrating air passing into the drum, and then an ideal waste-gas temperature is chosen which is at least five degrees, and preferably ten degrees, above the dew point calculated.
2. Process according to claim 1, characterised in that, at least one of the physical characteristic quantities of the mineral which are connected with the heat-absorption operation of the material to be dried and/or heated is ascertained as a further physical measurement value of the material, and the said measurement value acts, via the control apparatus (29), on the infeed of the burning medium and/or of the oxygen-carrier.
3. Process according to claim 1 or 2, characterised in that the number of revolutions of the drying drum (1a/b) is set in dependence upon at least one of the physical measurement values and/or the waste-gas temperature, in such a way that the dew point of the waste gases is not reached at the coldest point in the waste-gas flow, particularly in the waste-gas filter arrangement (17).
4. Process according to one of claims 1 to 3, characterised in that the inclination of the drying drum (1a/b) in relation to the horizontal is set in dependence upon at least one of the physical measurement values and/or the waste-gas temperature, in such a way that the dew point of the waste gases is not reached at the coldest point in the waste-gas flow, particularly in the waste-gas filter arrangement (17).
5. Process according to one of claims 1 to 4, characterised in that

   the concentration of at least one gas, particularly of oxygen and/or carbon monoxide (CO), in the waste gases is determined, and

   the influx of the oxygen-carrier to the burner (5a/5b) is controlled, in accordance with the said concentration values, in such a way that

   the waste gases have a minimal pollutant concentration.
6. Process according to one of claims 1 to 5, characterised in that the temperature of that transport and/or storage apparatus (35, 37, 39) for the material which is arranged downstream of the drying drum (1a/b) is measured, and
   the burner capacity is finely set in accordance with the measurement value.
7. Device for performing the process according to one of claims 1 to 6 for drying and/or heating pourable material, the said device having

   a burner (5a/b) arranged in a drying drum (1a/b) which is rotatable about its longitudinal axis (2),

   an apparatus (31a/b, 32a/b) for setting the influx of burning medium and oxygen-carrier to the burner (5a/b),

   a first measuring apparatus (22a/b) for determining the temperature of the waste gases from the burner (5a/b) and/or the drying drum (1a/b),

   a second measuring apparatus (24a/b; 25a-f; 27a-f) for measuring at least one physical measurement value, which apparatus is connected to the process for drying and/or heating the material which is to be fed in or has just arrived in the said process,

   a control apparatus (29),

   a data store (43)

   a filter arrangement (17) for the waste gases, and

   a control apparatus (29) which is connected to the measuring apparatuses (22a/b, 24a/b; 25a-f; 27a-f) and the setting apparatus (31a/b, 32a/b) and with the aid of which it is possible to set the influx of burning medium and oxygen-carrier for the burner (5a/b) in dependence upon the waste-gas temperature and the physical measurement value.
8. Device according to claim 7, characterised in that the inclination of the axis (2) of the drying drum (1a/b) in relation to the horizontal can be set during the drying and/or heating process by a first adjusting apparatus (13a/b) connected to the control apparatus (29), in accordance with the value measured with the aid of the first and/or second measuring apparatus (22a/b, 24a/b; 25a-f; 27a-f).
9. Device according to claim 7 or 8, characterised in that the number of revolutions of the drying drum (1a/b) can be set during the drying and/or heating process in accordance with the value measured with the aid of the first and/or second measuring apparatus (22a/b, 24a/b; 25a-f; 27a-f), with the aid of a drive (11a/b) connected to the control apparatus (29).
10. Device according to claims 7 to 9, characterised in that the second measuring apparatus is a moistness-measuring apparatus (25a-f) for the material to be dried and/or heated.
11. Device according to claims 7 to 10, characterised in that the second measuring apparatus has a measuring element (24a/b) for determining the concentration of at least one gas, in particular oxygen and/or carbon monoxide, in the waste gases.
12. Device according to one of claims 7 to 11, characterised in that it is possible to store, in the data store (43) connected to the control apparatus (29), the measurement values of the measuring apparatuses (22a/b, 24a/b; 25a-f; 27a-f) as first data in a time-dependent manner, particularly beginning with the starting-up and/or ending with the running-to-capacity of the burner (5a/b), preferably with the weighting of second data which have already been stored in a time-dependent manner.
13. Device according to one of claims 7 to 12, characterised by a further, second drying drum (1b), which can be rotated about its longitudinal axis, for drying and heating, in particular, asphalt lining material, the said device having a second burner (5b), a second apparatus (31a, 32b) for setting the influx of combustion medium and oxygen-carrier, and just one filter arrangement (17), upstream of which the waste gases from both the first and also the second drying drums (1a/b) are brought together in a waste-gas line (49) and can then be guided through the filter arrangement (17).
14. Device according to one of claims 7 to 12, characterised by a further, second drying drum (1b), which can be rotated about its longitudinal axis, for drying and heating, in particular, asphalt lining material, the said device having a second burner (5b), a second apparatus (31a, 32b) for setting the influx of combustion medium and oxygen-carrier, a waste-air inlet (47) on the first burner (5a) through which the waste gases from the second drying drum (1b) can be conducted into the first burning drum (3a), and just one filter arrangement (17), downstream of the first drying drum (1a), for all the waste gases.
15. Device according to claim 13 or 14, characterised by at least one transport apparatus (7a/b), particularly for the material to be introduced into the second drying drum (1b), which apparatus is controlled, in its material-transporting capacity, by the control apparatus (29), and at least one apparatus (24a/b) for measuring the gas concentration of at least one gas component in the waste gases, which apparatus is arranged upstream of the filter arrangement (17) and is connected to the control apparatus (29), so that the capacity of the transport apparatuses (7a/b) for transporting material into, in particular, the second drying drum (1b) can be set in dependence upon the concentration measured.
16. Device according to one of claims 13 to 15, characterised by a waste-gas quantity-measuring apparatus, upstream of the filter arrangement (17), which is connected to the control apparatus (29) and in dependence upon the measurement-value level of which the transport capacity, particularly into the second drying drum (1b), and/or the burner capacity, particularly of the second burner (5b), can be reset.

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