FR2490107A1 - SOLVENT AIR CONTENT CONTROL FACILITY - Google Patents

Abstract

THE COST AND TIME OF REGENERATION OF THE SOLVENT STOPPING FILTERS IS MINIMIZED, AS IS THE FILTRATION CAPACITY INSTALLED. FILTERING UNITS 3 OPERATING IN TURN BY FILTRATION ARE CONNECTED TO THE AIR SUCTION DUCT 2 5 OF THE PREMISES. WHEN THE SOLVENT (S) CONTENT MEASURED (IN 7) AT THE AIR OUTLET OF ONE OF THE FILTERING UNITS 3 REACHES THE MAXIMUM TOLERATED, THIS FILTERING UNIT IS REGENERATED, WHILE FILTRATION IS ASSUMED BY THE OTHER UNIT. THE SOLVENT CONTENT (S) OF WHAT COMES OUT OF THE UNIT UNDER REGENERATION IS MEASURED (IN 13), AND THE END OF REGENERATION OF THIS UNIT IS COMMANDED ACCORDING TO THIS MEASUREMENT. CONTROL, FIGHT AGAINST AIR POLLUTION, SAFETY AT WORK, USE OF SOLVENTS.

Description

The invention relates to an installation for controlling the air content in

  solvents, in particular for the control of the trichlorethylene content and / or the perchlorethylene content of the air in the premises of workshops or chemical cleaning installations, this installation comprising, connected by an air duct to the premises to be inspected, filtering means having at least one filter unit and followed by a measuring assembly with a solvent indicator, itself followed by a processing or interpretation module, the filter unit being regenerable when

  of a regeneration cycle by application of a regenerating agent

  controller, and the regeneration cycle is controlled according to the measurement of the solvent content of the outgoing air.

of the filter unit.

  The expression "control of the content of air in solvents" refers, in the context of the invention, to measurements, provisions and operations relating to the detection and determination of the nature and the quantity of solvents present. in the air and / or the respect of certain

  specifications concerning the limitation of this quantity.

  Such control is necessary, on a regular basis, when substances harmful to health, or in other respects, are emitted into the atmosphere, this applies in particular

  solvents that are encountered, for example, in

  chemical cleaning shops or workshops.

  As indicated above, the invention relates, in the first place, to the control of the solvent content of the air, in particular of the air of workshop premises or chemical cleaning installations. However, the invention can also be applied as such to other areas of control and preservation of air quality, and may involve other agents (other than solvents).

problematic topics.

  It is particularly necessary, in the context of the aforementioned control, to suck the solvent-laden air out of the premises and to replace it with fresh air. The air sucked up, loaded with solvents, can not generally be sent as it is in the atmosphere, but must be previously

2490107.

  purified to meet certain regulatory or legal specifications. For this purpose, the air sucked into

  the premises is first sent to a filtering facility.

  For example, in the case of the monitoring of the content of solvents such as perchlorethylene or trichlorethylene, filtering installations are used which

  Filter units are equipped with activated carbon filters.

  During filtering, these filter units are loaded with solvents and need to be regenerated from time to time. Regeneration can be carried out in various ways, for example by passing as a regenerating agent

  hot steam in the filter units.

  The installation of the invention has already been widely used successfully. However, it has the disadvantage that it does not optimize the duration of the regeneration cycle. Regeneration is usually carried out for a fixed, established duration, with a

  more or less accurate, based on experience.

  However, the time required to properly regenerate a filter unit is subject to fluctuations since it depends, for example, on the quality, the age, the solvent charge, etc., of the filters. As a result, with the instalation of the type indicated at the beginning, the regeneration of the filtering units is inevitably either incomplete or sometimes excessively long, which is disadvantageous because, as the filter units are not available when they are in regeneration, it is necessary to install a very large filtering capacity. In addition, the energy expenditure related to the regenerating agent (for example water vapor)

  are greater than the actual needs.

  The object of the invention is to improve and develop an installation of the kind indicated at the beginning, so as to optimize the regeneration while minimizing its

  duration and cost, thanks to an appropriate order.

  According to the invention, this object is attained by the fact that the measurement of the solvent content (s) takes place during the regeneration cycle, and that the end of this cycle is controlled according to the measurement of the solvent content. (s) air leaving the filter (s). In the context of the invention, the beginning of the regeneration cycle, as a rule, as explained above, controlled according to a measurement of the solvent content of air leaving the filters. If this solvent content reaches a predetermined limit value during filtration, this indicates that the maximum permissible solvent load of the filter unit has been reached and that this filter unit will be "slammed" (ie say will stop retaining the solvent (s) if it continues to operate in filtration mode. The regeneration of this unit is then initialized

  According to one essential aspect of the ivention, this cycle of regeneration

  ration is performed not for a predetermined time but depending on the measurement of the solvent content (s) of the air leaving the filter (s). The conduct of the regeneration cycle is thus optimized taking into account the condition of each filter unit, and the nature and amount of the solvents therein. Of course, the air leaving the filter (s) during the regeneration is no longer, stricto sensu, "air" but a mixture of air, solvent vapor and regenerating agent (for example steam hot), the latter generally being the dominant component of this mixture. The invention takes advantage of this important fact that a perfect measurement of the solvent content (s) is possible not only in the air usually leaving the filters during the filtration but also in the air or fluid (consisting mainly of the agent

  regenerator) coming out of the regenerating filters.

  Regeneration is usually countercurrent to the filtration regime. As a result, there is on the one hand, in known manner, a set or measurement module at the output of the filter or filters and, on the other hand, according to the invention, another measurement module at the input of the filter or filters, the words "input" and "output" being understood by considering the direction of flow in the filtration regime. The following description, with reference to the accompanying drawings as non-limiting examples, will make it possible to understand clearly how the present invention can be

put into practice.

  Figure 1 schematically represents a

  installation of control of the content of the air in solvents.

  FIG. 2 is a diagram illustrating the progress, over time, of the control of the regeneration cycles in the case of the installation

according to Figure 1.

  The installation shown in FIG. 1 serves to control the trichlorethylene content and / or the perchlorethylene content of the air of the premises of a chemical cleaning installation or workshop. The air containing solvents leaves the installation or cleaning workshop 1 via an air evacuation pipe 2 and sent to a filtering installation which, for the most part, consists of two filtering units 3 equipped with filters in activated charcoal. The filtered air in the filter units 3 is evacuated via a suction pipe 4 to which are connected unrepresented suction means. The direction of flow of air during filtration is represented by arrows in solid lines in FIG. 1. The air supply to the filtering units 3 is controlled by valves or registers 6 installed on the air channels. input and output of the filter (s). In FIG. 1, the positions in which the valves 6 are shown immediately show that the filter unit 3 on the left is traversed by the exhaust air and

  therefore works in filtration mode.

  Insofar as the filter units 3 in the filtering stage are loaded with solvents, the filtration efficiency decreases and, consequently, the air leaving the filtering units 3 has an increasing solvent content. If this solvent content of the air coming out of the filters exceeds a limit value, generally between 50 and 100 vpm (1 vpm corresponds to a volume proportion of 106), then we come to a "breakdown" of the filtering units 3. A set 7 is arranged on the output path of each filter ("output" considering the direction of the flow in filtration mode) In the present example, each measuring unit 7 can be a solvent indicator

  in the form of a heated metal oxide semiconductor.

  If the solvent content (s) of the outgoing air, measured at the outlet of one of the filtering units 3 by the measurement unit 7 thereof, exceeds a predetermined limit value, this filtering unit 3 is then put into operation. regeneration regime; Switching from one regime to another

  using a module or set of processing or interpreting

  tation (not shown) mounted as a result of the measuring assemblies 7 and itself followed by a non-represented control unit by which the valve actuations

appropriate actions are triggered.

  In the regeneration regime, the corresponding filter unit 3 is traversed by a regenerating agent which, in the present example, is water vapor supplied via a hot steam pipe 8 and discharged through a hot steam pipe 9. The Vapor supply and discharge pipes are controlled by valves 10 which are arranged on the inlet and outlet channels of the filtering units 3. The direction of the flow of the water vapor during the regeneration step is

  indicated by arrows 11 drawn in broken lines.

  The positions in which the steam valves 10 are shown in FIG / show that the regeneration takes place at co-current, that is to say with a direction of flow opposite that of the air in the filtration regime. The hot steam loaded with solvent leaving the filter unit 3 is further normalized in a cooling and drying device 12 in which the solvent can optionally be recovered. In the condition corresponding to FIG. 1, it is the filtering unit 3 located on the right

  which is in regeneration regime.

  On each inlet (considering the direction of filtration flow) is another measuring assembly 13 which also operates with a solvent indicator in the form of a heated metal oxide semiconductor. As the regeneration progress of a filter unit 3 progresses, the solvent content of the gaseous agent, essentially consisting of the hot vapor, decreases. This solvent content is measured by the relative measurement unit 13 during the regeneration cycle, and the end of this cycle occurs as a function of this measurement, namely when the solvent content passes

  below a predetermined value.

  The modulus c processing or interpretation of the measurements is constituted so that the measuring assemblies 7.13 of the filtering unit 3 concerned are also switched during the transition from the filtration regime to the regeneration regime, and this so that the measuring unit 7 is activated for the filtration regime, and that the measuring unit 13 is activated for the regeneration regime of the corresponding filter unit 3. This switching is accompanied by a corresponding change of calibration and measuring range. This switching is carried out as part of a control system, by a comparison "actual value / set value". For this purpose, the processing module has, for each measuring assembly 7.13, a measuring channel which is specific to this assembly and in which there is a reference value emitter or reference value specific to a solvent content. given. The reference solvent content for initiating the regeneration is given by the setpoint emitters assigned to the sets c measure 7, and the solvent content serving as a reference for the end of the regeneration cycle is given by the value emitters.

  setpoints assigned to measurement sets 13.

  The two filter units 3 of the installation shown in FIG. 1 operate intermittently, in turn, as explained in detail with reference to FIG. 2. FIG. 2 represents a step diagram showing in the form of a timing diagram. with several superimposed time axes, the evolution of the operating parameters

  of the two filter units 3 of Figure 1. From bottom to -

  up: the ordinates B relate to the operating mode

  neatly, the ordinates A correspond to the measured solvent content, by the measuring assembly 7, at the outlet of the filters, whereas the ordinates E correspond to the solvent content measured by the measuring assembly 13 at the input filters. The indices I, II indicate which filter unit it is (the index I is relative to the filter unit 3 on the left in FIG. 1, while the index II is relative to the filter unit

  III located on the right in Figure 1).

  At the beginning, that is to say at time "a", the filtering unit 3 operates in filtration mode,

  while the filtering unit on the right, 3, is in regeneration

  ration. This corresponds to the operating position shown in FIG. 1. As the regeneration of the filter unit 3 on the right progresses, the measuring assembly 13 relating thereto measures a content E II of decreasing solvent. At the instant "b" this content reaches a limit value set in advance, that is to say that the filtering unit 3 on the right is regenerated. As a result, the regeneration cycle / right unit 3 is terminated by closing the hot steam supply, and a door circuit, provided in the treatment module, is assigned to this filter unit 3. right, is open (or "unlocked"). The filter unit 3 on the right is then again ready to operate in filtration mode F, while the filter unit 3 on the left continues to filter. This being the case, the solvent content AI measured by the measuring assembly 7 at the outlet of the filter unit 3 of the left crott as a function of the load thereof and, at the instant "c", reached an upper limit whose value has been fixed in advance. At this instant "c", the control unit switches directly, on the regeneration regime, the filter unit 3 on the left, which is done by appropriate actuation of the outgoing air valve, 6, and the valve 10 hot steam. As the filter unit 3 on the right is already "busy", the filtration continues with it. The content of solvent E: I measurement unit 13 of the filter unit 3 of left measures in what comes out of it, that is to say at the hot vapor outlet of this filter unit, decreases then up to the limited value fixed to the door, for which there is unlocking of the door system assigned to the unit

filter 3 left.

  FIG. 2 shows that the regeneration cycle of the filter unit 3 on the left requires less time than the regeneration cycle of the filtering unit 3 on the right, for example because the active carbon filters of the filter unit 3 on the right, older, have less filtering capacity. The end of the regeneration cycle of the filter unit 3 on the left, and therefore the availability thereof, is carried out at time "d", while the filter unit 3 on the right is still in operation. filtration step. At time "e", the solvent content A II at the outlet of the filter unit 3 on the right, measured by the measuring unit 7, reaches its upper limit, so that this filtering unit on the right is switched on "regeneration, while filtration continues

  with the filter unit 3 on the left that is available.

  From the foregoing, it emerges that the air leaving the filters in the regeneration regime first passes the measuring assemblies 13 arranged at the filter outlets and is only then normalized in the cooling and drying means 12. However, it would also be possible to first standardize the air leaving the filters and then to measure the solvent content. This may be advantageous because standardization makes it possible to establish

  determined measuring conditions, fixed in advance.

  In addition to the last mentioned provisions, another possibility can be considered in this context: In the foregoing, for simplicity, the invention has been explained by considering an exemplary embodiment in which a measuring assembly 7 and a measuring assembly 13 are associated with each filter unit 3. However, it is

  possible to arrange, respectively in the suction line

  4 and in the hot steam duct 9 (these ducts being common to all the filter units), a measuring unit 7 and, respectively, a measuring unit 13, the effect of which on the various filter units 3 varies according to that of these units. the last which is in filtering step and, respectively, the one which is in regeneration. In particular, it is also possible, as mentioned above, to mount the measuring unit

  13 downstream of the cooling and drying means 12.

  In summary, in an installation according to the invention, the processing or interpretation module presents at least two calibrations and / or switchable measuring ranges,

  knowing at the same time that the control of the regeneration cycle

  ratior, on "filtering" or "regeneration", as appropriate.The filtering means may comprise at least two filtering units 3 each followed by a set of measurement 7.13 which is specific to it. In this case, when the processing or interpretation modules are provided with adjustable set point transmitters, comparators "value of actual / value / setpoint" and, possibly, alarm and / or control means, the sets measuring 7.13 are from

  preferably connected to a processing module or

  a common measurement which has, for each filtering unit 3, at least one measuring channel specific thereto and at least two switchable setpoint transmitters, while, preferably, the regeneration cycles R of the filtering units 3 are controlled in order to run intermittently, in turn. Each filter unit 3 can then be assigned a gate circuit which, at the end of the regeneration cycle R of the corresponding filtering unit 3, is brought into the open condition by the processing or interpretation module, and which, when the solvent content (s) of the air leaving a filtering unit in filtration mode F reaches a value that can be selected in advance (content A), switches this

  filter unit 3 on the regeneration cycle R, -

  while the filtering unit 3, or one of the filtering units 3, whose gate circuit is open, is then switched to the filtration mode F.

Claims (6)

  1.- Installation for the control of the content of air in solvents, in particular for the control of the trichlorethylene content and / or the perchlorethylene content of the air in the premises of workshops or chemical cleaning installations, this installation comprises, connected by an air duct to the premises to be inspected, filtering means having at least one filtering unit and followed by a measuring assembly with a solvent indicator, itself followed by a tracing or interpretation module the filter unit being regenerable during a regeneration cycle by application of a regenerating agent, and the regeneration cycle being controlled as a function of the measurement of the solvent content of the air leaving the filter unit, this installation being characterized in that the measurement of the content (E) of solvent (s) takes place during the regeneration cycle (R), and in that the end of this cycle (R) is controlled as a function of measuring the content (E) of solvent (s) what comes out of the filter (s).   2.- Installation according to claim 1, characterized in that the processing module or interpretation has at least two calibrations and / or switchable measuring ranges, and in that these two calibrations and / or measurement ranges are switchable at the same time as the control of the regeneration cycle (R),   on "filtering" or "regenerations, as appropriate.   3.- Installation according to claim 1 or 2, characterized in that the filtering means comprise at least two filter units (3) each followed by a   measuring set (7, 13) of his own.   4. Installation according to claim 3, in one embodiment in which the processing or interpretation modules are provided with adjustable set point transmitters, comparators "actual value / set value" and, optionally, alarm means. and / or control, characterized in that the measuring assemblies (7, 13) are connected to a common processing or interpretation module which has, for each filtering unit (3), at least one measurement channel specific to this one and at least two transmitters of switchable setpoint.   5.- Installation according to claim 3 or 4, caraeterized in that the regeneration cycles (R) of the filter units (3) are controlled so as to   take place intermittently, in turn.   6. Installation according to claim 5, characterized in that at each filter unit (3) is assigned a door circuit which, at the end of the   Regeneration cycle (R) of the filter unit (3) -   corresponding, is put in open condition by the processing module cu interprétation, and that-, when the solvent content (s) of the air leaving a filter unit in the filtration regime (F) reaches a value which can be selected in advance (content A), switches this filter unit (3) over the regeneration cycle (R), and by the fact that the filter unit (3), or one of the filter units ( 3), whose door cireuit is open   is then switched to the filtration regime (F).