EP0507711A1 - Apparatus for controlling the continuous operation of a convective dryer for drying products in the form of webs, in particular those of the textile type - Google Patents

Abstract

This apparatus comprises a central treatment unit (13) which gathers all the information communicated through different measuring means (9, 11) and, more particularly, the consumption of energy by the heating means (7) and the speed of passage of the web (3) in the dryer (2), and which, starting from reference data, such as the temperature of the hot air insufflated into this dryer (2), controls, through suitable control means (14) and by means of extraction means (8), the rate of extraction of air charged with water vapour from the dryer (2) with a view to guaranteeing optimum functioning of the latter, taking account of its energy consumption and its maintenance cost. <IMAGE>

Description

The invention relates to a device for regulating the continuous operation of a convective dryer intended for drying strip products, in particular of textile type, device according to the preamble of claim 1.

The present invention will find its application in the context of convective dryers which, by continuous operation, ensure the drying of a strip product. Thus, this invention will relate, more particularly, to textile materials in the form of a strip.

In fact, in this area, two parameters should be taken into consideration essentially because of their influence on the speed of drying.

Thus, this drying speed is proportional to the temperature difference between, on the one hand, the air blown into the dryer and arriving at the level of the strip and, on the other hand, the temperature of this strip itself even.

Furthermore, the lower the degree of humidity inside the dryer, the greater the aforementioned temperature difference and therefore the greater the drying speed.

However, we observe that if we also take into account at the level of these data, the energy consumption of the dryer, we see that it represents a factor antagonistic to that of the drying speed.

• 10 % pour les cartes par les parois ;
• 40 % pour les pertes par les fumées (air chaud évacué avec les vapeurs) ;
• 50 % pour l'évaporation de l'eau ;
• il en découle que plus la concentration en vapeur d'eau de l'air extrait du séchoir est grande, c'est-à-dire plus le degré d'hygrométrie est important, plus l'énergie consommée par le séchoir est faible.

Indeed, if we take into account the fact that the consumption of a dryer is distributed around the following values:

• 10% for cards by the walls;
• 40% for smoke losses (hot air evacuated with vapors);
• 50% for water evaporation;
• it follows that the higher the water vapor concentration of the air extracted from the dryer, that is to say the higher the degree of humidity, the lower the energy consumed by the dryer.

There is therefore an operating optimum which cannot be determined theoretically, as the calculation involves parameters that are sometimes difficult to predict or measure and fluctuate over time.

Thus and in the context of fabrics, these parameters are, in particular, the nature of the fibers but also their provenance, the spinning world, the fabric's texture, the surface mass of this fabric, the dimensions of the width, the permeability to 'air.

Of course, to these parameters, linked to the strip product, proper, are added many others which are dependent on the dryer technology. Thus, for the determination of this optimum operation of the dryer, account should also be taken, and this by way of example, of the fouling of the filters.

To return now to the operation of dryers known at present, it is necessary, initially, to recall their structure. Thus, these dryers, outside of the enclosure which constitutes them, comprise means for ensuring the drive and the running of the product in a band inside this enclosure, these drive means being provided with speed motor means. variable.

Furthermore, these dryers comprise, on the one hand, temperature-controlled heating means for the production of hot air intended to be blown into the enclosure of the dryer in order to ensure drying and, on the other hand , extraction means, with adjustable flow rate, to guarantee the evacuation at the level of this enclosure, of the air charged with water vapor.

Such known dryers are also provided with a number of means for measuring the operating conditions. Thus, there are means for measuring energy consumption by the heating means. For example, it can be an electric meter in case of an electric energy heating system or a flow meter when the energy consumed is a fluid, such as gas or fuel.

Furthermore, there are means for measuring the residual humidity at the level of the strip product at the outlet of the dryer, as well as means for measuring the running speed of this strip product.

Thus, after having displayed, as setpoint data, a residual humidity rate, servo means are able to adjust the speed of movement of the strip in order to precisely reach this humidity rate at level of this strip at the outlet of the dryer.

Until now, the management of the operating conditions of this dryer was under the control of an operator who, to ensure this function, used, on the one hand, the data communicated to him by the various measurement means and, on the other hand, from his experience in the field.

However, this manual management method only very rarely achieves the dryer operating optimum, in particular, if one wishes to take account, also, for the determination of this optimum, of maintenance costs and, more particularly , labor costs which, of course, are linked to the duration of use of the equipment.

This maintenance and operating cost is of little importance when the company is in a position of production under-capacity. In fact, under these conditions, the labor costs are constant and cannot be minimized.

On the other hand, in the event of an overcapacity of production, only the metering of the product in strip which it is advisable to dry is imposed and it is under these conditions that it is necessary to take into account both energy consumption and maintenance costs and driving knowing that the greater the length of dried strip per unit of time, the more energy is consumed, but the lower these maintenance and driving costs will be.

However, it is precisely under these conditions that the operator is not able to guarantee the operation of the dryer at an optimum.

The present invention therefore proposes to remedy this drawback.

• des moyens d'entraînement de la bande munis de moyens moteurs à vitesse variable ;
• des moyens de chauffage à régulation de température pour la production d'air chaud destiné au séchage ;
• des moyens d'extraction à débit réglable de l'air charge en vapeur d'eau du séchoir ;
• des moyens de mesure de la consommation en énergie par les moyens de chauffage ;
• des moyens de mesure de l'humidité résiduelle de la bande en sortie du séchoir ;
• des moyens de mesure de la vitesse de défilement de cette bande ;
• et des moyens permettant d'asservir cette vitesse de défilement de la bande en fonction de l'humidité résiduelle mesurée ;

The invention as characterized in the claims, solves the problem and consists of a device for regulating the continuous operation of a convective dryer intended for drying a strip product, in particular of the textile type, comprising:

• belt drive means provided with variable speed motor means;
• temperature controlled heating means for the production of hot air intended for drying;
• means for extracting the air charged with water vapor from the dryer at an adjustable flow rate;
• means for measuring the energy consumption by the heating means;
• means for measuring the residual moisture of the strip leaving the dryer;
• means for measuring the running speed of this strip;
• and means making it possible to control this speed of movement of the strip as a function of the residual humidity measured;

• de la consommation en énergie de ce séchoir 2 exprimée par la fonction : $$\text{F2 = b x Q / V}$$
  
  où
  b : est le coût de l'unité de combustibles
  Q : la consommation en combustible par unité de temps
  V : est la vitesse de production en métrage par unité de temps
• et du coût de maintenance et de conduite exprimé par la fonction $$\text{F1 = a / V}$$
  
  où
  a : est le coût de maintenance et de conduite par unité de temps.

This device further comprising a central processing unit collecting all the information communicated through the various measurement means and, more particularly, the energy consumption by the heating means and the speed of travel of the strip and which, consequently setpoint data such as the temperature of the hot air blown into the dryer, ensure through appropriate control means and by means of the extraction means, the adjustment of the extraction rate of the air charged in water vapor from dryer 2 in order to guarantee optimum operation of the latter, taking into account:

• of the energy consumption of this dryer 2 expressed by the function: $$\text{F2 = bx Q / V}$$
  
  or
  b: is the cost of the fuel unit
  Q: fuel consumption per unit of time
  V: is the production speed in meters per unit of time
• and the cost of maintenance and operation expressed by the function $$\text{F1 = a / V}$$
  
  or
  a: is the cost of maintenance and operation per unit of time.

The advantages obtained thanks to this invention consist, of course, in that it makes it possible to ensure, automatically, the optimum operation of a convective dryer of strip products.

The invention is set out below in more detail using a drawing representing only one embodiment.

FIG. 1 shows the diagram of a strip product dryer incorporating a device for regulating its operation, according to the invention.

The present invention as shown in this figure 1 relates to a device 1 for regulating the operation of a convective dryer 2 intended for the continuous drying of products in strip 3 in particular of textile type.

Thus, this dryer 2, outside the enclosure 4 which composes it, comprises means 5 for ensuring the drive of the strip 3 to the tarvers of the dryer 2, these drive means 5 comprising variable speed motor means 6 .

Furthermore, this dryer 2 is provided with heating means with temperature regulation 7 ensuring the production of hot air intended to be blown into the enclosure 4 in order to guarantee the drying of the product in strip 3.

In addition, extraction means 8 overcome the enclosure 4 of this dryer 2 in order to ensure the evacuation of the air loaded with water vapor at a rate which can be adjusted.

Said dryer 2 is also provided with a certain number of measurement means through which it is possible to determine its operating level or even the quality of the drying produced.

Thus, it comprises means 9 for measuring the energy consumption by the heating means 7. By way of example, such measuring means 9 can be constituted either by a flow meter when the fuel used is gas or fuel oil , or by a simple electric meter when the energy used to heat the air intended for drying is electrical energy.

This dryer 2 further comprises means 10 for measuring the residual moisture of the product in a strip 3 at the outlet of the enclosure 4. Thus, to such measurement means 10 can be associated servo means capable of control the speed of travel of the strip 3 so that, precisely, at the outlet of the dryer 2, the humidity rate corresponds to a setpoint value displayed.

Finally, it should be noted that this speed of travel of the product in strip 3 is itself detected through appropriate measurement means 11.

Of course, one can find in the middle of the dryer 2 many other detectors or measuring means which could be decisive for its operation. Thus, means for measuring the temperature 12 placed inside the enclosure 4 of the dryer 2 will, through continuous monitoring, guarantee perfect regulation of the temperature of the hot air blown into this enclosure 4 via the heating means 7.

In fact, the object of the present invention is to guarantee optimized operation of this type of convective dryer 2, this with regard to a certain number of parameters but also imposed operating data.

Thus, the regulating device 1, according to the present invention comprises a central processing unit 13 collecting the information at the output of the measuring means and, more particularly, means 9 for measuring the energy consumption by the heating means 7 thus that means 11 for measuring the running speed of the strip 3 and which, starting from setpoint data such as the temperature of the hot air blown into the dryer, ensure, by means of appropriate control means 14 and by intermediate of the extraction means 8, the adjustment of the extraction rate of the dryer 2 of the air charged with water vapor in order to guarantee an optimum operation of this dryer 2, this as a function of the parameters that constitute the consumption in energy of the latter and its cost of maintenance and operation.

où
b : est le coût de l'unité de combustibles
Q : la consommation en combustible par unité de temps
V : la vitesse de production en métrage par unité de tempsIn fact, energy consumption is expressed by the following function: $$\text{F2 = bx Q / V}$$

or
b: is the cost of the fuel unit
Q: fuel consumption per unit of time
V: the production speed in meters per unit of time

où
a : est le coût de maintenance et de conduite par unité de tempsAs for the cost of maintenance and operation, this is expressed by the function: $$\text{F1 = a / V}$$

or
a: is the cost of maintenance and operation per unit of time

In this regard, it should be noted that this maintenance and operating cost per unit of time can include labor costs, but also all the costs which are linked to the operation of the dryer 2.

Consequently, the function for which the central processing unit 13 proposes to determine the minimum through the management of the operation of the dryer 2 is as follows: $$\text{F = F1 + F2}$$

In fact, in order to achieve this goal, this central processing unit 13 performs a recurrence calculation. More precisely, through the information communicated to it via the measurement means 9, 11, the central processing unit 13 determines the value of F, ie CO. Then, this central processing unit 13, by means of said control means 14 intervenes on the extraction means 8 with a view to increasing or decreasing the flow rate DO for evacuating the air loaded with water vapor an increment I whose module is also a setpoint data (D1 = DO + I).

Then he comes to evaluate the new value of F or C1 which corresponds, in a way, to the new operating cost of the dryer 2. This cost C1 is then evaluated with respect to the previous CO cost through a test consisting of subtracting from the cost CO cost C1.

In the event that the test C = CO - C1 is greater than zero the central processing unit 13 keeps in memory the lowest cost (CO = C1) then proceeds to a new change of the flow rate via said control means 14 this in the same increment and in the same direction of change as above. So if during the previous cycle the flow D1 had been increased by an increment I, this new flow D1, when the test is greater than zero, is again increased by the same increment I.

On the other hand, if the test C = CO - C1 is less than zero, which corresponds to an operating cost of the dryer 2 greater than the cost evaluated previously before changing the flow rate, the central processing unit 13 makes a new change of this flow, taking into account the last value D1 given to the latter and modifying it this time by two 2 x I increments but in the opposite direction to the direction of change chosen during the previous modification of the flow.

By way of example if, to determine the operating cost of the dryer 2, the processing unit 13 had just increased the flow rate D1 for extracting the air loaded with water vapor and the test C = CO - C1 was found to be negative, this central processing unit 13 will reduce this flow D1 by a module corresponding to twice the 2 x I increment.

Finally, if the test determines a value lying in an interval close to zero, the central processing unit detects the optimum operating point of the dryer 2 and maintains the adjustment of the extraction rate of the air charged with steam from water, this for a period which can be extended before restarting the cycle.

As for the control means 14 on which the central processing unit 13 intervenes, these are, of course, adapted to the extraction means 8.

Thus, in the case where the latter are in the form of at least one motorized shutter, said control means 14 will advantageously consist of a stepping motor actuated by means of an impulse command from the control unit. central processing 13.

In the case of extraction means 8 in the form of at least one fan, such control means 14 are constituted, essentially, by a speed variator which comes to convert a voltage signal coming from the processing unit central unit 13, either in a new voltage signal when the motor of this fan is of the direct current type, or in frequency in the context of an asynchronous technology.

The main advantages obtained thanks to this invention consist, essentially, in that it is no longer the responsibility of the operator to determine the optimum operating mode of the dryer 2 which leads to a more rational management of this dryer 2 and , therefore, to better results.

Claims (3)

Device for regulating the continuous operation of a convective dryer (2) intended for drying strip products (3), in particular of textile type, comprising: - drive means (5) of the strip (3) provided with variable speed motor means (6); - heating means (7) with temperature regulation for the production of hot air intended for drying; - Extraction means (8) with adjustable flow rate of the air loaded with water vapor from the dryer (2); - means for measuring (9) the energy consumption by the heating means (7); - Means for measuring (10) the residual moisture of the strip (3) at the outlet of the dryer (2); - Measuring means (11) of the running speed of this strip (3); - And means making it possible to control this running speed of the strip (3) as a function of the measured residual humidity; device characterized in that it comprises a central processing unit (13) collecting all the information communicated through the various measurement means (9, 11) and, more particularly, the energy consumption by the heating means (7 ) and the speed of travel of the strip (3) and which, on the basis of setpoint data such as the temperature, of hot air blown into the dryer (2), ensure through appropriate control means (14) and by means of the extraction means (8), the adjustment of the extraction rate of the air charged with water vapor from the dryer (2) in order to guarantee an optimum operation of the latter taking into account: - the energy consumption of this dryer (2) expressed by the function: $$\text{F2 = bx Q / V}$$

or
b: is the cost of the fuel unit
Q: fuel consumption per unit of time
V: is the production speed in meters per unit of time; - and the cost of maintenance and operation expressed by the function: $$\text{F1 = a / V}$$

or
a: is the cost of maintenance and operation per unit of time. Control device according to claim 1 characterized in that the extraction means (8) consist of at least one motorized flap and that the control means (14) are in the form of a stepping motor actuated at through an impulse command from the central processing unit (13). Control device according to claim 1, characterized in that the extraction means (8) are in the form of at least one fan and that the control means (14) consist of a variable speed drive which converts a voltage signal from the central processing unit (13) into a new signal, either in voltage or in frequency.

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