EP3419770A1

EP3419770A1 - Method and apparatus for controlling occupational hygiene in machine tool environment

Info

Publication number: EP3419770A1
Application number: EP17752727.2A
Authority: EP
Inventors: Pirkko PIHLAJAMAA; Matti Niemeläinen; Arto Säämänen
Original assignee: Tampereen Ammattikorkeakoulu Oy
Current assignee: AEROFF OY
Priority date: 2016-02-15
Filing date: 2017-01-09
Publication date: 2019-01-02
Also published as: WO2017140941A1; DE17752727T1; EP3419770A4; DE202017007216U1

Abstract

The invention relates first of all to a method for controlling occupational hygiene in machine tool environment, wherein the machine tool environment includes one or several machine tools in at least one machining booth (1), based on the use of a machining fluid, such as coolant, cutting fluid and/or the like, wherein exhaust air exhausted from the machining booth through an exhaust duct (2) is being controlled by depressurizing the machining booth with a fan setup (3) and being purified with a filtering and purification setup (4), such as one or several HEPA filters, activated carbon filters and/or the like, to permit the further processing of the exhaust air, such as its recirculation, heat recovery and/or the like. The exhaust air of the machining booth (1) is being processed with a pre- separator, such as a rotating separator utilizing centrifugal force (X) or the like, in order to reduce the amount of pollutants in the exhaust air before it is directed to the exhaust duct (2). The invention also relates to an apparatus operating in accordance with the method.

Description

Method and apparatus for controlling occupational hygiene in machine tool environment

The object of the invention is a method and an apparatus for controlling occupational hygiene in a machine tool environment, as defined in the preambles of the independent claims directed thereto.

In connection with machine tools, air being exhausted is typically purified with e.g. fiber filters of various grades, cyclones that are dependent on the velocity of air flow and/or electrostatic precipitators, after which the filtered air is recirculated into a workspace. In practice, however, the situation is that there has yet been little research on the effects or the economic viability of recirculating local exhaust ventilation air into a workspace. The general basis is that by recirculating local exhaust ventilation air, the flow rate of outside air circulated into a workspace can be reduced, thus saving energy. In practice, the local exhaust ventilation air may even after filtering be so unclean that its recirculation to the workspace only increases the need for ventilation, and therefore no concrete savings are in fact achieved unless the quality standards of workspace air are simultaneously lowered. The energy savings achieved by recirculating local exhaust ventilation air are dependent on the quality and quantity of the impurities produced, the penetration ability of filters and purifiers, and the standards set on workspace air quality.

In practical field tests done on the subject, it has, for example, emerged in relation to welding work that the operating costs for local exhaust ventilation filtering alone surpassed expenses saved on energy at prices at the time of the study in question in 1991. It has therefore been considered simpler and often more economical to direct local exhaust ventilation air to outside than to recirculate it into a workspace. However, apparatuses based on the recirculation of local exhaust ventilation air are necessary at sites where local exhaust ventilation air cannot be directed to outside, such as during installation work.

It has also been observed, especially in relation to metalworking fluids, that both solid and liquid aerosols can quite efficiently be removed from local exhaust ventilation air. In practice, however, the strain put on the used filters may become a problem. Long-term tests have for example shown that especially HEPA filters, used as exhaust filters for filter units, have become clogged fairly quickly, and that the efficiency of 95DOP filters used for a comparable purpose has dropped notably as a result of usage. Therefore, when planning the filtering of air exhausted from a machine tool environment, the particle size distribution of the formed aerosol and the efficiency of the filter must be known. Additionally, the amount of aerosol formed inside the machine tool, which in turn determines the total strain put on filters, must be known.

Some of the compounds contained in metalworking fluids are volatile; thus they pass through particle filters as vapors. Practical tests have shown that a notable part of cutting oils or emulsions (measured as concentrations) pass through particle filters as vapors. Furthermore, it has been observed that the emission of volatile compounds from filters continues even if no new aerosols are introduced, if there is airflow in the filter unit. Compounds that pass through the filter may enter the workspace air (e.g. formaldehyde) or reattach themselves to various surfaces in the workspace. In practice, it is often observed at for example machine shops that metalworking fluids have become attached to the surfaces of machines and equipment, even if HEPA filters are being used. After some months of operation, a layer of cutting fluid has also been discovered on the recirculation vent of the local exhaust ventilation system. Aerosols have also often become accrued inside the filter unit, leading to clogged draining openings etc.

The Finnish Institute of Occupational Health (FIOH) has measured the practical quality of recirculated air produced by filter systems as part of its research into exposures, and it has been found that air recirculated into workspace was, in the case of gaseous compounds in certain circumstances, almost invariably less clean than the general air in the workspace of the air within the employees' breathing zone. The concentrations of alkanolamines, contained in metalworking fluids, in the recirculated air have often been observed to be many times above average, and the total concentration of volatile, organic compounds to be one and half times above average. In these cases, especially the concentration of alkanolamines in recirculated air has been measured to clearly surpass (average 0.45 mg/m3) the target level set by FIOH on alkanolamines in machine shop air of 0.1 mg/m3. However, in practice the filter units have been able to contain the particulate pollutants of breathable alveolar fractions. Their concentrations in recirculated air have been mostly lower than in general workspace air, when the filter and ventilation systems have been used and maintained as instructed.

In relation to the controlling of local exhaust ventilation air, it has been presented in e.g. application publication US 2014/0366721 a filtration system used specifically for local exhaust for welding work, based on a fine filter installed to the welding hood's exhaust duct, with its operation controlled by using the exhaust fan based on the pollutant concentrations measured from the hood by a sensor system.

The problem with utilizing this kind of solution in controlling especially e.g. exhaust air containing cutting fluid aerosol is its insufficiency of usage rate, as the wet fiber filter will ultimately become a source of pollutants, which is why a used fine filter should be replaced on short intervals. Furthermore, the US patent 4,985,057 presents a purification system related specially to asbestos work, based on a HEPA filter as well as a condensation filter used in conjunction with it, with which pollutants are bonded to the condensed fluid.

By itself, this solution is inadequate specifically for the controlling of local exhaust ventilation air removed through an exhaust duct from the object of machining, due to the fact that pollutants in the local exhaust ventilation air can build up in the exhaust ventilation duct. This requires the regular cleaning of the exhaust duct in order to maintain the efficiency of local exhaust ventilation flow, and especially to maintain the exhaust ventilation flow velocity of the machining booth at an adequate level in order to permit the optimal purification of local exhaust ventilation air. The basis of the method and apparatus for controlling occupational hygiene in a machine tool environment, according to the present invention, is to achieve a decisive improvement to the aforementioned problems and thus to essentially improve the level of technology used in the industry. For this purpose, the main characteristics of the method and apparatus according to the invention are presented in the characterizing parts of the independent claims directed thereto. The most important advantages of the method and apparatus for controlling occupational hygiene in machine tool environment, according to in the present invention include their efficiency, the simplicity of the hardware used in their implementation, and their low maintenance costs. The invention is enabled by its use of a pre-separator, such as a rotating separator utilizing centrifugal force or the like, by which the local exhaust ventilation air is cleaned sufficiently during exhaustion from the target so as to keep the exhaust duct used to direct the local exhaust ventilation air clean. This, particularly when used in conjunction with a condensation filter, enables optimal conditions for maintaining the adequate efficiency of local exhaust ventilation, owing especially to the HEPA filter staying continuously dry. In this way, the risk of the HEPA filter ultimately becoming a source of pollutants after long-term use is averted.

The main prerequisites for the optimal operation of the method and apparatus according to the invention are, firstly, that the sufficiency of local exhaust ventilation flow rate of e.g. the machining booth is monitored and adjusted by a computing unit through the use of a fan setup and controlled e.g. by a pressure sensor setup or the like, ensuring that pressure conditions in the machining booth and its environment are continuously correct, with no risk of air inside the machining booth "leaking out" due to, for example, insufficient negative pressure or even excess pressure. The second main prerequisite of the invention is that the velocity of exhaust ventilation air flow in the machining booth's exhaust duct is monitored and adjusted by the computing unit through the use of a fan setup controlled by a flow sensor setup or the like, whereby the achieved sufficient velocity of the exhaust ventilation air flow permits the minimal accumulation of pollutants in the exhaust duct, despite the presence of pollutants in the local exhaust ventilation air.

A crucial advantage of the invention is also its versatility of applications, firstly, in connection with an existing machining booth in a machine tool environment, utilizing existing ventilation and filtering equipment, by permitting e.g. the recirculation of local exhaust ventilation air and/or recovering its heat. Secondly, the invention also enables the centralized controlling of several machining booth units through an integrated air-processing device, which processes exhaust air specially to permit its recirculation, through means of condensation filtering, recovering condensing heat, mechanical filtering and/or further chemical filtering.

Other advantageous embodiments of the method apparatus according to the invention are presented the dependent claims directed thereto.

In the following description, the invention is presented in detail in conjunction with the accompanying drawings, in which figure 1 illustrates an example of one of the invention's applications in the controlling of local exhaust ventilation air in a machine tool environment of several machining booths, by utilizing an existing filter unit, fan and a separate heat recovery unit, figure 2 illustrates a advantageous embodiment of the invention, used in connection to a single machining booth, based on the utilization of an integrated air-processing device, figure 3 illustrates an application comparable to figure

2, used in connection to several machining booths, figures 4a and 4b

present some measurement results from the local exhaust ventilation duct implemented in accordance with the invention, showing the total concentrations of alkanolamines and volatile organic compounds, measured at varying points in the process, figure 5 illustrates an example of a mist eliminator, which is a rotating separator based on centrifugal force, advantageous for application in the invention, and figure 6 illustrates an advantageous, integrated set of dehumidifying devices, applicable for use in the invention .

The invention relates, firstly, to a method for controlling occupational hygiene in machine tool environment, wherein a machining environment comprises at least one machining booth 1 containing one or several machine tools that utilize machining fluids, such as coolants, cutting fluids and/or corresponding substances. Exhaust air directed from the machining booth through an exhaust duct 2 is being controlled by depressurizing the machining booth with a fan setup 3 and being purified with a filtering and purification setup 4, such as one or several HEPA filters, activated carbon filters and/or corresponding means, in order to permit the further processing of the exhaust air, such as its recirculation, heat recovery and/or a corresponding purpose. The exhaust air of the machining booth 1 is being processed with a pre-separator, as illustrated in principle in the accompanying drawings, such as a rotating separator utilizing centrifugal force X or like, in order to reduce the amount of pollutants in the exhaust air before it is directed to the exhaust duct 2. As a advantageous embodiment of the method according to the invention, the ventilation of a machining booth is being controlled specially on the principle illustrated in figure 1 with a computing unit 5, such as one or several microprocessors, programmable logic controller and/or the like, wherein sufficient flow rate of exhaust ventilation air from the machining booth 1 is being monitored and adjusted by the computing unit 5 by using the fan setup 3 controlled by a pressure sensor setup 6 or the like.

By controlling the sufficiency of exhaust ventilation flow in the machining booth, it is ensured that air inside the machining booth cannot be uncontrollably transferred to the machining booth's environment. Additionally, monitoring the sufficiency of exhaust ventilation flow assists in monitoring the condition of the local exhaust ventilation system.

As a further advantageous embodiment of the method according to the invention, the velocity of the exhaust ventilation flow in the machining booth's 1 exhaust duct 2 is being monitored and adjusted by the computing unit 5 by using the fan setup 3 controlled by a flow sensor setup 7. In this case, as a further advantageous embodiment, the velocity of exhaust ventilation air in the machining booth's 1 exhaust duct 2 is maintained between 20-30 m/s, favorably between 23-25 m/s, as a ventilation air efficiently eliminates the risk impurities accumulating in the exhaust duct 2 despite the concentrations of pollutants present in the exhaust air .

As a further advantageous embodiment of the method according to the invention, specially the pollutants present in aerosol form in the exhaust air from the machining booth 1 are minimized, in reference to the advantageous embodiments illustrated in figures 2 and 3, with a condensation filter unit 4a and, as a further advantageous embodiment, with a condensing heat recovery device 4a' connected thereto. In this context, as a further advantageous embodiment, condensation fluid N separated with the condensation filter unit 4a is recovered on the principle illustrated in figure 3 to a separate storage setup V and/or transmitted on the principle illustrated in figure 2 for reuse in the machining booth 1. In a corresponding manner, it is possible to arrange the recycling z of fluid separated by a rotating separator X, on the principle illustrated in figure 5. Furthermore, as an advantageous embodiment of the invention, referring to figures 2 and 3, the exhaust air from one or several machining booths 1 is processed centrally with an integrated air-processing device Y, wherein exhaust air is processed specially to permit its recirculation through condensation filtering 4a, heating 4a¹, mechanical filtering 4b, such as a HEPA filter or the like, and if necessary further through chemical filtering 4c, such as with an activated carbon filter or the like.

Figures 4a and 4b present measurement results, measured in practical conditions at different phases, of total concentrations of alkanolamines and volatile organic compounds in local exhaust ventilation air processed in accordance with the invention. Figure 1 illustrates an example of the invention's application e.g. in an existing machine tool environment, where the machining booths 1 are connected to the exhaust duct 2, with which local exhaust ventilation air is exhausted by means of the fan setup 3 and the filter setup 4 connected to it, of which the most typical practical examples are filtering equipment available on the market by brands Dantherm or Nedermann. Local exhaust ventilation air is by means of the fan setup directed further to the heat recovery device LTO, where its heat is extracted to the replacement air K, to be vented into the workspace, and where the resulting unclean condensation fluid KN is removed.

The invention relates, secondly, to an apparatus for controlling of occupational hygiene in a machine tool environment, where the machine tool environment comprises at least one machining booth 1 containing one or several machine tools that utilize machining fluids, such as coolants, cutting fluids and/or corresponding substances. The apparatus contains a fan setup 3 for the controlling of sufficient exhaust ventilation flow from the machining booth 1 through an exhaust duct 2 by means of de-pressurizing the machining booth and the filtering and purification setup 4, such as one or several HEPA filters, activated carbon filters and/or the like, to purify exhaust air in order to enable the further processing of the exhaust air, such as recirculation, heat recovery and/or the like. The apparatus also includes a pre-separator setup in the machining booth 1, such as a rotating separator X utilizing centrifugal force or the like, which functions to reduce the amount of pollutants in the exhaust air before it enters the exhaust duct 2.

As an advantageous embodiment of the apparatus according to the invention, referring in particular to figure 1, it includes a computing unit 5, such as one or several microprocessors, programmable logic controller and/or the like for the controlling of the machining booth's 1 ventilation, whereby the machining booth 1 is equipped with a pressure sensor setup 6 or the like in order to monitor the sufficiency of exhaust air flow in the machining booth 1 and the exhaust duct 2 is equipped with a flow sensor setup 7 in order to monitor the rate of exhaust air flow, whereby the aforementioned exhaust air flow rate and flow velocity can be adjusted by the computing unit 5 through the use of the fan setup 3. Through monitoring the de-pressurization of the machining booth 1, it is ensured that air inside the machining booth may not get drifted to the work environment by other means, in addition to which the monitoring of de-pressurization gives indication on the condition of the ventilation ducts and equipment, thus allowing for their timely repair and maintenance. Maintaining the velocity of the local exhaust ventilation air at a sufficient level in the exhaust duct in turn ensures that the pollutants present in the local exhaust ventilation air are unable to accumulate on the surfaces of the exhaust duct 2. As a further advantageous embodiment of the apparatus according to the invention, it contains a condensation filter unit 4a, and most favorably a condensation heat recovery device 4a' connected thereto, to further minimize pollutants in the machining booth's 1 exhaust air. Herein, condensation fluid N separated with the condensation filter unit 4a is recovered on the principle illustrated in figure 3 to a separate storage setup V and/or transmitted on the principle illustrated in figure 2 for reuse in the machining booth 1. In a corresponding manner, it is possible to arrange the recycling z of fluid separated by a rotating separator X, on the principle illustrated in figure 5.

As a further advantageous embodiment of the apparatus disclosed in the invention, it contains an integrated air-processing device Y connected to the suction side of the fan 3, implemented e.g. on the principle illustrated in figures 2 and 3, in order to centrally process the exhaust air from one or several parallel machining booths 1 specially to permit its recirculation. The air- processing device comprises a moisture-resistant pre- filter 4p, a condensation filter unit 4a, a heating unit 4a' , a mechanical filter 4b, such as a HEPA filter or the like, and if necessary a chemical filter 4c, such as an activated carbon filter or the like.

As an especially advantageous embodiment, the pre- separator has been set up in reference to the advantageous embodiment illustrated in figure 5 by means of a rotating separator X utilizing centrifugal force. This is possible to implement with for example the rotating separator marketed as "TurboSwing" (www.jeven.fi), which was originally designed for use in local exhaust ventilation in professional kitchens to extract grease from the air with a separator placed in the hood above the stove. This type of separator contains a rotor, which by rotating crosswise in relation to the local exhaust ventilation air flow generates a powerful vortex in the exhaust air, whereby the grease contained in it is separated by centrifugal forces to the vat A in the separator, after which the cleaned exhaust air is removed to the exhaust duct connected to the hood.

The compact air-processing device Y that is installed to the exhaust duct 2 comprises the fan 3 and several different filters 4 connected to it (or separate from it) e.g. on the principle illustrated in figures 2 and 3. Firstly, the pre-filter 4p ensures that the heat transfer surfaces of the condensation filter unit 4a that follows it remain clean. In turn, the condensation filter unit dehumidifies the local exhaust ventilation air by cooling it and binds pollutants to the condensation fluid N. The condensation filter 4a may therefore be e.g. an air cooler connected to for example the factory's cooling water system, or it may be a separate so-called direct evaporator. The recovered condensation fluid is either returned directly to the machine tool as illustrated in figure 2 or to a separate container V for reuse as illustrated in figure 3. Following after the condensation filter unit is the heating unit 4a', e.g. a condenser or separate heater, which heats the exhaust air in order for it to be sufficiently dry before reaching the HEPA filter 4b and possible additional chemical filter 4c. After this, the purified air can be recirculated to e.g. the working area .

An alternative application to the ones illustrated in figures 2 and 3 is illustrated in figure 6, wherein the pre-filter 4p, the condensation filter unit 4a and its heating unit 4a', and the fan 3 have been replaced with an energy-efficient, so-called dehumidifying washer i.e. a heat-recovering refrigerant air dryer, which operates in principle as a heat pump, so that exhaust air with its water vapors and chemicals in aerosol form, being sucked therein with the fan 3, is first pre-cooled in a heat exchanger LS, then cooled in a direct evaporator 4a, producing condensation fluid. Finally, the dehumidified local exhaust ventilation air is heated in a heat exchanger LS and in a condensing unit 4a' , after which the exhaust air, having been purified in the aforementioned manner, can be recirculated to the working area or processed further with the filter units 4b and/or 4c.

In the aforementioned application, it is possible to place the fan 3 before the mechanical filter 4b, unlike illustrated in e.g. figures 2 and 3. These applications have utilized a pre-filter 4p, which is however not necessary in all circumstances. This type of pre-filter is typically a washable metal filter, and its purpose is to ensure that heat transfer surfaces remain clean if the result produced by the pre-separator is inadequate. It is clear that the invention is not limited to the previously illustrated or described applications, but that it can be adapted within its basic framework in multiple ways, by modifying the plethora of filtering and ventilation equipment used in connection with machining processes, or by replacing existing systems with setups that are in accordance with the invention. For example, the air-processing device illustrated in figures 2 and 3 can be utilized together with modules connected together as illustrated, or its different sections can be used as separate parts. Correspondingly, the fan setup can be placed to e.g. immediately follow the pre-filter etc.

Claims

Claims :

1. Method for controlling occupational hygiene in a machine tool environment, wherein the machining environment includes one or several machine tools, in at least one machining booth (1) , based on the use of a machining fluid, such as coolant, cutting fluid and/or the like, wherein exhaust air exhausted from the machining booth through an exhaust duct (2) is being controlled by depressurizing the machining booth with a fan setup (3) and being purified with a filtering and purification setup (4), such as one or several HEPA filters, activated carbon filters and/or the like, to permit the further processing of the exhaust air, such as its recirculation, heat recovery and/or the like, characterized in that, the exhaust air of the machining booth (1) is being processed with a pre-separator, such as a rotating separator utilizing centrifugal force (X) or the like, in order to reduce the amount of pollutants in the exhaust air before the exhaust air enters the exhaust duct (2) .

2. Method according to claim 1, wherein the ventilation of the machining booth is being controlled by a computing unit (5), such as one or several microprocessors, programmable logic controller and/or the like, characterized in that, negative pressure in the machining booth (1), the sufficiency of exhaust ventilation air flow and/or the flow rate of air in the machining booth are being monitored and adjusted by the computing unit (5) through the use of the fan setup (3) controlled by a pressure sensor setup (6) or the like.

3. Method according to claim 1 or 2, characterized in that, the flow rate of exhaust air in a machining booths (1) exhaust duct (2) is being monitored and adjusted by the computing unit (5) through the use of the fan setup (3) controlled by a flow sensor setup (7) .

4. Method according to claim 3, characterized in that, the velocity of exhaust air flow in a machining booths (1) exhaust duct (2) is being maintained between 20-30 m/s, preferably between 23-25 m/s.

5. Method according to any of the preceding claims 1-4, characterized in that, by condensing the residual moisture of the machining booths (1) exhaust air the air is being removed of pollutants specially in aerosol form through the use of a condensation filter unit (4a) preferably together with a condensing heat recovery device (4a') connected to it.

6. Method according to any of the preceding claims 1-5, characterized in that, the condensation fluid (N) separated by a condensation filter unit (4a) is being collected to a separate storage setup (V) and/or transferred to the machining booth (1) for reuse.

7. Method according to any of the preceding claims 1-6, characterized in that, the exhaust air of one or several parallel machining booths (1) is processed centrally by an integrated air processing device (Y) , by which the exhaust air is processed specially to permit its recirculation by condensation filtering (4a) , heating (4a'), mechanical filtering (4b), such as by a HEPA filter or the like, and if necessary by chemical filtering (4c) , such as by an activated carbon filter or the like.

8. Apparatus for controlling occupational hygiene in a machine tool environment, wherein the machining environment includes one or several machine tools, in at least one machining booth (1), based on the use of a machining fluid, such as coolant, cutting fluid and/or the like, wherein the apparatus is comprised of a fan setup (3) for the management of exhaust air exhausted from the machining booth (1) through an exhaust duct (2) by de-pressurizing the machining booth and a filtering and purification setup (4), such as one or several HEPA filters, activated carbon filters and/or the like, for the purification of exhaust air to permit the further processing of the exhaust air, such as its recirculation, heat recovery and/or the like, characterized in that, the apparatus comprises in the machining booth (1) a pre-separator, such as a rotating separator utilizing centrifugal force (X) or the like, in order to reduce the amount of pollutants in the exhaust air before the exhaust air enters the exhaust duct (2) .

9. Apparatus according to claim 8, including a computing unit (5) , such as one or several microprocessors, programmable logic controller and/or the like, for controlling the ventilation of a machining booth (1, characterized in that, the machining booth (1) is equipped with a pressure sensor setup (6) or the like for the monitoring of the machining booth's (1) internal conditions, such as negative pressure, sufficiency of exhaust air flow and/or flow rate of air entering the machining booth, and the exhaust duct (2) is equipped with a flow sensor setup (7) for the monitoring of exhaust air flow rate and for the adjusting of conditions in the machining booth (1) based on monitoring done by the flow sensor setup (7) by the computing unit (5) through the use of the fan setup (3) .

10. Apparatus according to claims 8 or 9, characterized in that, it comprises an integrated air processing device (Y) for the centralized processing of the exhaust air of one or several parallel machining booths (1) specially to permit its recirculation, wherein it comprises a condensation filter unit (4a) , a heating unit (4a^f ) , a mechanical filter (4b) , such as a HEPA filter or the like, and if necessary a chemical filter (4c) , such as an activated carbon filter or the like .