FR2647479A1 - METHOD FOR ADJUSTING THE INJECTION OF A BITUMINOUS BINDER DURING THE CONTINUOUS MANUFACTURE OF ROAD COATINGS - Google Patents

Abstract

The aggregates 7 are fed continuously into a drying and mixing installation 1 at a point from which the binder injection is carried out. The adjustment method consists in measuring the weight flow of aggregates 7 at a weighing point 11 outside the drying and mixing installation 1. The flow rate of binder required to coat the flow of aggregates measured and the time is determined. transfer of aggregates between the weighing point 11 and the injection point. Finally, the injection is carried out as a function of the determined flow rate and transfer time. During the start-up and shutdown phases of the installation, the determined bituminous binder flow rate is injected with a time shift greater than the transfer time of the aggregates 7 and in a progressive manner.

Description

The invention relates to an adjustment method

  injection of a bituminous binder during manufacture

  continuous cation of asphalt for road surfaces

  by mixing aggregates and bituminous binder.

  It is known to manufacture. bituminous mixes for road surfaces by mixing aggregates

  and a binder such as liquid bitumen.

  Prior to mixing with bitumen

  liquid, the aggregates are dried and heated to

  ensure a good coating with bitumen.

  It is well known to carry out the drying, heating and kneading of the aggregates in the same installation such as a drum-dryer-coater

  consisting of a cylindrical envelope of large di-

  mensions rotating around its axis which is slightly

  inclined to the horizontal plane.

  The cold and wet aggregates are brought to one end of the drum and then poured into it by a continuous handling device, such as a

conveyor.

  A burner enters through one end of the drum, so that hot gases circulate in the drum, in its axial direction. The burner

  can be inserted through the inlet end of the drum

  bour into which cold and wet aggregates penetrate or by the outlet end of the drum

  opposite the inlet end.

  In the first case, the hot gases and the aggregates circulate in the same direction inside the

  drum, this circulation being designated as

lation with parallel currents.

  In the second case, the hot gases and the aggregates circulate in different directions, this

  circulation being designated as counter circulation

current.

  The binder generally consisting of bitu-

  the liquid is introduced through an injection rod,

  the interior of the drum at an interjection point

  medial between the inlet end and the outlet end of the drum. It is necessary to adjust the injection of bitumen, so that the proportion of bitumen in the

  mixture constituting the bituminous mixes remains

  aunt and equal to a determined value.

  To do this, the weight flow of the aggregates introduced into the drum is measured and the corresponding bitumen flow which must be introduced is determined.

by the injection lance.

  The weight flow of the aggregates introduced into the drum is determined by continuous weighing,

  on a weighing conveyor, cold and humid aggregates

  des, at a point which can be relatively far from

the entrance to the drum.

  To determine the bitumen flow rate that it is necessary to add to the aggregates at a given time, the weight flow rate of dry aggregates corresponding to the flow of wet aggregates measured on

  the weighing conveyor. For this, we determine the pro-

  average portion of water contained in humus aggregates

  and a correction is made on the measurement of the

weight bit.

  In addition, the weighing point being far from the bitumen injection point, it is necessary to take into account the time of transfer of the aggregates between the weighing point and the injection point, so that the

  bitumen flow rate determined as a function of the flow rate of

  gats is effectively incorporated into aggregates whose

  weight flow was measured at the weighing point.

  In the current technique, for a function-

  operation of the coating plant in permanent

  However, an average travel time of the aggregates between the weighing table of the weighing conveyor and the injection point is taken into account. Bitumen injection

  with a flow corresponding to the flow determined from

  shot of the aggregate weight flow is deferred in

  the time of a duration corresponding to the time of

average price of aggregates.

  This technique is entirely satisfactory.

  te in the case where the coating plant operates in steady state, as well as during changes

  of the installation, in the direction of an increase

  tation or a decrease in the flow of aggregates or in the case of changes in the composition formula of the mixes, if these changes take place without interrupting the circulation of the flow of aggregates at

through the installation.

  On the other hand, this technique for adjusting the injection of bitumen is no longer satisfactory,

  during transitional regimes and in particular during

  during the start-up and shutdown phases of the installation

  lation at the beginning or at the end of which the drum is

completely empty of aggregates.

  During the start-up phase of the installation

  tion, if the average travel time TO of the aggregates between the weighing table and the bitumen injection point is set too high, a recovery is obtained, at the outlet of the drum, at the start of the operation of the installation, significant amount of aggregates not coated with bitumen, generally referred to as

of "white materials".

  If the time TO is set too low, white materials are not collected at the outlet of the drum, at the start of operation of the installation, but materials overdosed in bitumen whose fluidity is abnormally high (phenomenon designated by specialists under the name of "soup") When the time TO actually corresponds to the average journey time of the aggregates, we may find ourselves, depending on the start-up phases, in the presence of one or other of the manufacturing defects described above. In all cases, the use of the prior art results in the production of asphalt of unsatisfactory quality during the start-up phases of the installation. The result

  loss of materials and energy and therefore

your financials.

  Likewise, during the shutdown phase of the ins-

  tallation, if the time TO is evaluated at too high a value, the mixes produced exhibit the phenomenon of "soup" and if the time TO is evaluated at a value too

  low, we produce a quantity which can be important

aunt of white materials.

  In addition, if the average travel time TO is set to an incorrect value, the installation is

  likely to produce poor quality asphalt

  during changes in gait or changes

  elements of formula "on the fly" that is to say without inter-

  break the flow of aggregates in the drum.

  The object of the invention is therefore to propose

  a method of adjusting the injection of a bitu-

  during the continuous manufacture of asphalt for road surfaces by mixing aggregates and bituminous binder, the aggregates being fed continuously into a drying and kneading installation at a point from which 1 injection of binder and the adjustment process consisting of measuring the weight flow of aggregates at a weighing point outside the drying and kneading installation, determining the flow of binder necessary to coat the measured flow of aggregates and the transfer time of approvals - gats between the weighing point and the injection point and to carry out the injection as a function of the flow rate and of the transfer time, this process making it possible to obtain a correct dosage of the binder in the asphalt mixes, in steady state, during the changes in gait or formula as well as during the start and stop phases

of the installation.

  For this purpose, during the start-up and shutdown phases of the installation at least, the determined flow rate of bituminous binder is injected with a time lag greater than the

  transfer of aggregates and gradually.

  In order to clearly understand the invention,

  we will now describe, by way of nonlimited example

  tative, with reference to the attached figures, the implementation of the method according to the invention, in

  the case of an asphalt mixing plant with a drum-

  parallel flow circulation dryer.

  Figure 1 is a schematic representation

  and functional of the information adjustment device

  bitumen junction in a drum-dryer-wrapper.

  Figure 2 is a representative diagram

  variations in aggregate flow and bi-flow

  tume introduced into a drum-drier-wrapper, during

  during the operation of this drum in perma-

  nent. Figure 3 is a representative diagram

  variations in aggregate flow and bi-flow

  tume introduced into a drum-drier-wrapper, during

during the start of this drum.

  Figure 4 is a representative diagram

  variations in aggregate flow and bi-flow

  tume introduced into a drum-drier-wrapper, during

  during a stop phase of this drum.

  In Figure 1, we see a drum-dryer

  wrapper 1 shown schematically and com-

  bearing a first zone 2 in which the drying and heating of the aggregates is carried out and a second zone 3 in which the kneading of the dried and heated aggregates is carried out with bitumen introduced

with a lance 4.

  The flame 5 of a burner enters the

  first drying and heating area from the outside

  drum inlet unit through which are introduced

aggregates 7.

  The drum, generally cylindrical,

  is rotated around its axis during operation

  operation of the installation. Aggregates 7 are often

  lifted inside the drum, by solid blades

  of the inner surface of the cylinder casing

  drique of this drum, until constituting an oc-

  cutting the whole section of the drum and separating the drying zone 2 from the coating zone 3. The aggregates 7 are thus exposed to the hot gases coming from the burner

  and circulating inside the drum according to its di-

  axial rection, between its inlet end and its outlet end which penetrates inside a hopper 8 for recovering the mixes produced in the

  drum to which an exhaust chimney is connected

  cuation of gases having passed through the drum.

  The cold and wet aggregates are brought to the inlet end of the drum by conveyors 9 and 10 ensuring a continuous supply of the drum

in aggregates.

  A weighing table 11 is associated with the conveyor 9 in order to determine the weight of aggregates

  carried by the conveyor at the weighing table

  ge. The conveyor 9 also includes a speed measurement device 12, the indications combined with those of the weighing table make it possible to determine

  the flow of cold and wet aggregates by weight

carried by the conveyor 9.

  The bitumen injection lance 4 is connected, via a valve 13. to a circuit

bitumen supply 14.

  Circuit 14 includes a main branch

  the on which are placed a bitumen pump 15 and

  a counter 18 and a branch branch 19.

  The two branches of the bitumen circuit 14 are connected to a reservoir, not shown, in which the bitumen is kept at temperature. The valve 13 allows

  connect the main branch of the circuit

  cooked 14, either with the injection lance 4, or with

  branch 19 in derivation ensuring the return of bi-

tumes towards the tank.

  The bitumen pump 15 is driven by a variable speed motor 16 controlled by a variator 17. The installation further comprises an assembly

  regulator computer 20 consisting of several modules

calculation and comparison.

  A first calculation module 21 receives in the form of signals the information coming from the

  weighing table 11 and the vi measuring device

  size 12 and makes it possible to determine, from these in-

  formations the flow of wet aggregates by weight

carried by the conveyor 9.

  A second calculation module 22 receives the si-

  output of the first module 21 and a signal

  from a humidity measurement probe 23 shown

  of the moisture content of the wet aggregates transported by the conveyor 9. The calculation module 22 determines the flow of dry aggregates corresponding to the flow by weight

  wet aggregate measured on the conveyor 9.

  A third calculation module 24 determines from the flow of dry aggregates coming from the

  calculation 22 and a signal from an input module

  very 25 representative of the proportion of bitumen to in-

  troduire in the aggregates, the weight flow of bitu-

  me which must be injected by the lance 4.

  It should be noted that the weighing point corresponding to the weighing table 11 is at a relatively large distance from the injection point corresponding to the end of the lance 4 opening at

inside the drum 1.

  Aggregates 7 travel this distance in

  a time TO which can be evaluated from the speed

  average of the aggregates between the weighing table 11 and

  the injection point inside the drum.

  A shift register 28 receives a signal representative of the transfer time TO, from an input module 26. The register 28 also receives a signal representative of the bitumen flow rate calculated by the

module 24.

  Register 28 provides an output to a

  parateur 30, a value of the bitumen weight flow

  corresponding to the weight flow of the aggregates, in te-

  taking into account a time offset equal to TO. This bitumen weight flow theoretically corresponds to the weight flow of aggregates arriving at the injection point

in the drum.

  g The bitumen counter 18 allows you to

  reach module 31 of the regular computer unit

  reader 20. a signal developed in a module 32 and re-

  presentation of the instantaneous value of bit rate

  me injected by the lance 4. This value of the instant bitumen flow is sent to comparator 30 which generates a signal

  output according to the two input signals represented

  bitumen bit rate which must be calculated

  thrown by lance 4 and the actual measured flow rate

  vement. The output signal from the comparator 30 controls the variator 17 and the motor 16 in a manner a. adjust the value of the flow injected by the lance 4 to

  the value developed by the calculation module 28.

  In Figure 2, the

  variations over time in the bi-weight flow

  tume injected into the drum, during operation

  ment of the installation and the variation during the same time of the weight flow of aggregates introduced into the drum.

  At an instant t1, the weight flow rate of

  gats introduced into the drum and measured by the weighing table 11 is increased by an amount t Q.

  The corresponding bitumen flow remains constant.

  both until an instant t2 = tl * TO. to take into account

  te of the transfer time of the aggregates between the table

  weighing 11 and the bitumen injection point.

  At time t2, the bitumen weight flow

  is increased by a quantity A 'Q corresponding to the ac-

  Q increase in aggregate flow at time tI.

  In the case of continuous drum operation. if the transfer time TO of

  aggregates between the weighing point and the injection point

  tion is correctly determined, the variations in the bitumen flow corresponding to the variations in the aggregate flow are implemented at the desired time so that the proportion of bitumen in the mixes remains constant. In the case of an operation of the drum in such a way that only changes in shape take place, resulting in a variation in the flow rate of aggregates entering the drum, the technique of the prior art consisting of differing from a time TO

  variations in the flow rate of corresponding liquid bitumen

  wavering at variations in aggregate flow leads to quite satisfactory results with regard to maintaining a constant proportion of

bitumen in asphalt products.

  FIGS. 3 and 4 show the variations in the weight flow rate of the aggregates entering the drum and in the corresponding weight flow rate of the

  injected bitumen, during a start-up phase and during

  during a shutdown phase of the drum-drier-wrapper,

  using the process according to the invention.

  In FIG. 3, it can be seen that the flow rate of the aggregates measured at the level of the weighing table 11 changes at time tl, from a value O to a value Qn corresponding to the feed flow rate of the drum under normal conditions of operation. The instant tl corresponds to the arrival of the flow of wet aggregates, on the conveyor 9, at the weighing table 11. After the instant tl, the aggregate flow is maintained at its value On throughout the period of

operation of the installation.

  According to the invention, the bitumen flow rate Q ′ is maintained at a zero value until a time t3 = tZ +

  Tg, the time t2 being itself equal to ti + TO.

  The time t2 theoretically corresponds to the ar-

  the first aggregates in the injection area, these aggregates having reached the weighing table at

instant tl.

  In reality, as it is visible on the fi-

  gure 1, the front part of the drum 1 circulating

  tion with parallel currents in which the

  drying zone 2 has an increased diameter compared to

  port to the remaining part of the drum and its filling

  age by aggregates delays the arrival of aggregates at

  injection point with a duration Tg. The time Tg corresponds to

  pond the filling time of the head part at

  large diameter of the drum-dryer-coating.

  It is obvious that the time Tg depends

  of the morphology and dimension characteristics

the drum used.

  From time t3 (t3 = t2 + Tg), the bitumen flow rate Q 'changes from the value O to the value Q'n which represents the weight flow rate of bitumen in the installation in normal operation. This Q'n flow

  bitumen is calculated according to the flow rate Qn of

  gats, so that the proportion of bitumen in the mix produced by the drum-dryer-coating is

  fixed at a predetermined value.

  As can be seen in FIG. 3, from time t3 to time t4, the bitumen flow rate Q'n is established in successive stages during each of which the bitumen flow rate varies linearly as a function of time. This linear variation mode in successive stages makes it possible to carry out the adjustment.

  bitumen in a relatively simple way, while

  putting a progressive and modulated increase in the

bitumen bit.

  This drum operating phase of duration Tm = t4 - t3 corresponds to a phase of

  ramp up of bitumen injection.

  This ramp-up is carried out in three successive stages, each resulting in a linear variation in the bitumen flow as a function of the

  time, with a different proportionality factor.

  This gradual increase in the bitumen flow injected is necessary to take into account the progressive constitution of the vein of materials in

  circulation in the injection area, after filling

  complete age of the drum head part.

  This gradual establishment of the normal bitumen injection flow rate can result in any number of successive phases during which the bitumen flow rate varies linearly as a function of

time.

  In reality, the gradual establishment of the

  bitumen flow depends on the characteristics of the drum

  bour-dryer-coating and the variation of the flow of bi-

  tume injected as a function of time can be represented

  ted by a different curve from a succession of seg-

* right, as shown in Figure 3.

  The process according to the invention makes it possible to add to the aggregates, at the desired time, the quantity

  of bitumen necessary to obtain bituminous mixes

  neux presenting a proportion of bitumen perfectly

  constant and corresponding to the desired value.

  The delay time Tg due to the filling of the head part of the drum can be determined from the mass of aggregates necessary to ensure the filling of this head part and the flow rate of aggregates in the installation. The weather

  Tg is equal to the ratio of these two parameters.

  The time Tm of ramp-up of the installation

  The rate and shape of the variations in the flow rate of aggregates at the level of the injection zone, after filling of the head part of the drum can be determined experimentally at the time of the putting into service of the drum-dryer-wrapper.

  In FIG. 4, the varia-

  the aggregate flow measured at the table

  weighing system 11 and the corresponding variations

  bitumen flow rate correspondents, at the point

  injection, during a stopping phase of the following drum

  life of a complete drain of it.

  At time tl, the aggregate flow rate measured at the weighing table 11 changes from the value

  Qn corresponding to the flow during normal operation

  drum hurt at value 0, the conveyor 9 not being

no longer supplied with aggregates.

  A halt to the injection of bitumen at the

  as long as it would result in the production of a large quantity of white materials at the outlet of the drum,

  that is to say, uncoated aggregates.

  The weight flow Q'n of bitumen corresponds to

  Dant at the flow Qn of aggregates is therefore maintained until time t2 such that t2 = tl + TO. TO representing the average time of transfer of aggregates between the table

weighing point and injection point.

  However, as can be seen in the fig-

  re 4, the bitumen flow Q'n is only brought to the value 0

  only gradually from time t2 to time t3.

  This phase with a duration Td equal t3 - t2 corresponds to a fall in speed during which the flow

  of aggregates at the injection point decreases pro-

  gressively. This phase of descent in the duration regime Td corresponds to the emptying of the large diameter head portion of the drum, this emptying occurring

  gradually over time, which

  ceases a gradual decrease in the Q'n flow rate of the bitumen.

  In Figure 4, we see that this decrease

  Progressive tion can be represented by a curve consisting of a succession of straight line segments with different slopes. This curve can be determined

  experimentally and include for example three pha-

  successive linear variation.

  It should be noted that the time Td of emptying

  ge of the large diameter head portion of the drum is substantially greater than the filling time Tg of this head portion. This results from the fact that the emptying of the large diameter head part is not influenced by the thrust of other materials,

unlike filling.

  After the installation has been stopped by inter-

  break in the supply of aggregates, the aggregates remaining in the drum present after a certain

  time a disparate particle size and are little used

  sands for making asphalt; on the other hand their

  transit time in the drum is extremely long.

  This part of the materials including the coating

  not of great interest can be used to

cleaning the drum.

  However, it is not desirable to stop injecting bitumen too abruptly after stopping the supply of aggregates to the drum, to

  avoid producing too much ma-

white materials.

  The scheduled and progressive shutdown as re-

  presented in Figure 4 avoids this inconvenience

  deny. In general, the process according to the invention makes it possible to obtain a satisfactory dosage of bituminous binder, both under steady conditions and during changes of gait or changes of formula "on the fly" during the operation of the coating plant. This assay is obtained by using the average travel time of the aggregates TO between the weighing table and the binder injection point, as a basis for determining the

bitumen injection delay.

  In addition, the process according to the invention makes it possible to carry out the starting and stopping phases of the coating installation without loss of materials and while maintaining a correct bitumen dosage in the

coated products, at any time.

  Finally, the method according to the invention allows

  to take into account the morphology of the drum-

  dryer-coater, for example, in the case of a drum

  Bour-dryer-enrober with parallel currents having a large diameter head portion in which the drying and heating of the aggregates are carried out, this form is taken into account by establishing the required bitumen flow rate, at the start of the installation with additional delay time due to filling the

large diameter head.

  The invention is not limited to the mode of realization

which has been described.

  This is how we can consider varia-

  bitumen flow over time during the start and stop phases of the installation of a

  different form from those which have been described and re-

  presented. These variations depend in particular on the morphology of the drum-dryer-coating, its

  operating conditions and the nature of the approvals

  gats. It is possible to apply the process of

  adjustment according to the invention in the case of a dry drum

  cheur and enrobeur with circulation against the current. In this case, the burner enters through the outlet of the drum and optionally includes an elongated body whose end from which the flame develops is distant from the ends of the drum. Such a drum generally does not have a zone for entering the aggregates with a large diameter and the terminal zone for the drum in which the mixing of the aggregates and the bitumen can on the contrary have an enlarged diameter. In this case, when the installation starts, the bitumen flow rate is gradually established

  without the injection being delayed by a corresponding time

  laying out a filling time of the part of

  drum trée. The gradual establishment of the bitumen flow takes into account the progressive constitution of a constant-flow material flow in the area

mixing.

  The bitumen flow rate can be established according to any law of variation in

function of time.

  The invention applies to any installation for the continuous production of bituminous mixes by methane.

mixture of aggregates and binder,

Claims (5)

  1.- Method for adjusting the injection of a bituminous binder during continuous production   of asphalt for road surfaces by mixing of   gats (7) and bituminous binder, the aggregates (7) being fed continuously into an installation (1) of   drying and kneading at a point from which   performs a binder injection and the adjustment method consisting in measuring the weight flow of aggregates (7) at a weighing point (11) outside the drying and kneading installation (1), in determining the binder flow necessary to coat the measured flow of aggregates (7) and the transfer time of the aggregates between the weighing point (11) and the injection point and to carry out the injection as a function of the flow and transfer time, characterized by the fact that, at least during the start-up and shutdown phases of the installation, the determined flow rate is injected   bituminous binder with a time difference greater than   less than the TO transfer time of aggregates and ma- progressive.   2.- Adjustment process according to the claim   tion 1, in the case of a drying and kneading installation constituted by a drum-dryer-coater   (1) having a large diameter head portion (2),   characterized by the fact that during the start-up phase   age of the drum-dryer-wrapper (1), the injection of bi-   tume in the drum (1) is deferred for a time greater than the transfer time TO of the aggregates between the weighing point (11) and the injection point, by a   duration Tg corresponding to the duration necessary for the replacement   pleating of the large-diameter head portion (2) of the drum (1) by the aggregates,   3.- Adjustment process according to the claim   tion 2, characterized in that the bitumen flow Q'n corresponding to the normal operation of the drum   supplied with aggregates with a flow rate Qn is established   gressively, in successive phases during which the bitumen flow varies linearly by in relation to time.   4.- Adjustment method according to any one   conch of claims 1 to 3, in the case where the ins   drying and mixing plant is constituted by a wrapping drum-dryer (1) comprising a large diameter head part (2), characterized by the fact   that during the shutdown phases of the drum-dryer-enro-   beur, the bitumen flow Q'n corresponding to the function   normal operation of the installation in which   calculates a flow of aggregates Qn is brought in a pro   decreasing from value Q'n to value 0, after a time at least equal to the time for transfer of the aggregates between the weighing point (11) and the injection point, from time tl o the weight flow of the aggregates   at the weighing point (11) takes a zero value the.   5.- Adjustment process according to the claim   tion 4, characterized by the fact that the bitumen bit rate changes progressively from the value Q'n to the value 0, in successive phases during   of which the bitumen flow varies linearly re with respect to time.