How to effectively extract VOCs from solvents?

Volatile Organic Compounds (VOCs) encompass thousands of chemical substances contained in the products, accessories and equipment present at workstations on an industrial site. Among the products used or manufactured by industry, solvents in particular emit vapors and aerosols made up of VOCs.

Pure or included in product formulations, these solvents are used in a variety of industrial processes and in maintenance, cleaning and upkeep operations. They impregnate the resulting waste and soil the accessories and equipment used.

In fact, any use of solvents pollutes the ambient air through the emission of VOCs. But solvents are often toxic and easily ignited. This entails risks for the health and safety of workers, as well as for the environment, with economic and legal consequences.

To prevent these risks, regulations require limit values for the concentration of VOCs in the air. To meet this obligation, one solution is to effectively extract the atmosphere contaminated by solvent vapors, then treat it with a specialized filtration unit.

Solvent categories

We distinguish :

• Organic solvents that emit volatile organic compounds.
• Acidic or basic aqueous solutions. They emit acidic or basic vapors and VOCs (organic acids).
• Detergents that emit acidic or basic vapors, and VOCs if they contain solubilizing agents (alcohols, glycol ethers, etc.), perfumes, dyes, etc.
• Aqueous microbiological solutions emitting biological aerosols

Solvent risks and their impact

Solvents present risks to human health, fire and explosion (ATEX risk), and the environment.

Health risks associated with solvents and their vapors

When humans come into contact with solvents and their vapours, they are exposed to :

• toxic hazards (particularly organic solvents),
• risks of corrosiveness (aqueous acidic and basic solutions),
• biological risks (aqueous microbiological solutions).

Reaches are made by :

• pulmonary (penetration by inhalation of vapours or aerosols),
• skin (contact with solvent),
• digestive (food or beverages contaminated by solvents via the hands, for example).

Other organs can also be damaged: heart, brain, liver, kidneys… The effects can range from mild, reversible symptoms (headache, nausea, irritation, etc.) to serious symptoms or illnesses (loss of consciousness, cirrhosis, cancer, cell mutation, reproductive problems, etc.).

The degree of effect depends on

• the toxicity of the chemical substances making up the solvent,
• the route of penetration into the human body,
• the dose received by the worker at each exposure,
• frequency of exposure to the solvent,
• the physical effort made by the employee at the time ofinhalation exposure, his biological reaction to exposure linked to his genetic make-up, the state of health of the exposed worker, his environment and lifestyle…

Most poisoning occurs through inhalation of solvent vapors or aerosols. A high solvent or room temperature, a large solvent evaporation surface and an air current all favor pulmonary penetration.

Safety hazards caused by solvents and their vapors.

Most organic solvents ignite. If they are not directly explosive, their conditions of use lead to an explosive atmosphere (ATEX). The safety risk depends on the physicochemical characteristics of each solvent: flash point, auto-ignition temperature, explosive range, vapour density; and on the sources of ignition of solvent vapours: flame, hot surface, static electricity… Fires and explosions produce physical and chemical effects on workers and local residents, buildings and thenatural environment of an industrial site and its surroundings.

Environmental risk from solvents and vapors.

The emission of solvent vapors and the discharge of liquid solvents generate direct pollution of the air, water and soil. But also indirect pollution of these 3 ecological compartments via

• atmospheric fallout,
• evaporation of solvents absorbed in soil and water,
• the decomposition of solvents into more dangerous substances
• the absorption of solvents by living organisms and their bioaccumulation.

Solvent pollution directly affects humans, fauna and flora. Discharge from an industrial site indirectly results in the presence of solvents in drinking water, plants and fish.

What regulations affect the use of solvents?

Labor Code to prevent solvent-related risks in the workplace

The use of solvents concerns many aspects of the French Labor Code, in particular articles relating to health and safety in the workplace. The French Labor Code sets out the employer’s obligations with regard to

• capture of workplace emissions, particularly vapours and aerosols
• preventing the risk of fire and explosion (ATEX risk) when using solvents,
• the conformity of equipment in workplaces using or processing solvents or their vapors,
• prevention of chemical, CMR and biological risks, in particular from chemical compounds in solvents…

Environmental Code for the effects of VOC emissions from solvents

The French Environment Code deals with the prevention of pollution caused by the release of solvents into the environment, whether in the normal course of business (diffuse and canalized) or accidentally. It sets environmental emission limit values (ELVs) for each solvent-based VOC. If solvent consumption exceeds a certain threshold, depending on the activity, the company is subject to the regulations governing Installations Classées pour la Protection de l’Environnement (ICPE). The Environment Code also governs the treatment of waste associated with the use of solvents.

The Public Health Code for the effects of solvent emissions on the population

The French Public Health Code deals with the health impacts of solvent use and emissions on the population, particularly in activities not classified as ICPE, in drinking water, in wastewater…

Social Security Code for solvent-related occupational illnesses

The French Social Security Code covers the use of solvents likely to cause occupational illnesses, and the resulting contributions. It defines the employer’s information obligations towards the various social security bodies (health insurance, pension funds, etc.).

ADR regulations for solvent logistics on industrial sites

The European Agreement Concerning the International Carriage of Dangerous Goods by Road (ADR) considers solvents in more ways than one: the transport compatibility of solvent packaging (from can to tank), and the specific handling conditions for unloading and loading solvents on industrial sites.

Different techniques for extracting solvent vapors or aerosols.

Reducing inhalation exposure for people on the industrial site requires the capture of VOCs and solvent aerosols to clean up theambient air. Source capture is preferred to reduce solvent emissions per workstation as much as possible. Residual VOCs are captured by general extraction of the room atmosphere, combined with compensatory ventilation.

Selection criteria for solvent vapour capture technology

The choice of capture technique depends on :

• process constraints,
• of the operator’s task,
• the surface area and evaporation rate of the VOC, and the air density of the VOC emitted.

To effectively capture fumes, we aim to :

• maximum proximity of the device to the emission source,
• total encapsulation of the emission zone and uniform distribution of the suction flow,
• a suction speed enabling both the VOCs and the aerosols derived from them to be drawn into the air stream.

Sensor location and consideration of the natural movement of fumes (depending on vapour density):

• will prevent the operator’s inhalation zone from crossing the solvent emission zone,
• avoids disturbances caused by draughts, thermal discomfort and exceeding regulatory noise levels.

The size of the capture device will meet spatial constraints:

• of the workstation,
• activity,
• maintenance operations.

For emanations presenting an ATEX risk, thecapture device will meet ATEX zoning criteria.

Which local exhaust system to choose for VOCs emitted by solvents?

Several localized suction systems are available for industrial use. The analysis of suction needs and the selection criteria mentioned above will guide its decision.

Swivel and articulated suction or laboratory arms for solvent vapours

Chosen for their flexibility of positioning in space, they respond to the problem of capturing low-toxicity VOCs when working under space constraints, and with low or medium VOC emissions. They aim to achieve :

• Optimized placement of the suction flow in a volume limited both by the workstation and by the footprint of neighbouring installations.
• Maximum proximity of the sensor to the emission source for optimum catchment area.
• Adaptability to a progression of work on parts of a certain size, or to changes in the worker’s position during the operation. However, suction arms are ideal for jobs that don’t require the suction mouth to be changed too often.

The flexible positioning of the suction arms makes it easy to take account of the density of the steam emitted. To achieve this, the suction flow is positioned according to the dispersion or concentration behavior of the VOC in the ambient atmosphere.

Suction arms and laboratory arms have the advantage of being less intrusive for the operator. However, they are more sensitive to air turbulence caused by draughts in the work area, or movements close to the suction arm. Suction flow

Mobile industrial VOC extraction hoods

The more VOCs the operation emits, the larger the extraction port needs to be. Adapting to the articulated, swivel-mounted extraction arm, a rectangular extraction hood offers a large suction surface . In this way, it responds to higher VOC emissions, in conditions of spatial constraints relating to the operation and its environment. The capture hood induces a wider suction flow, while getting as close as possible to the source of VOC emissions. It allows a larger VOC emission surface area than previously.

Suction hood to enclose the VOC emission zone

VOC extraction and capture hoods are used instatic workstation installation configurations, or on industrial machinery. They are designed to enclose the VOC source and prevent any dispersion outside the suction device. Depending on the context of the operation, the hood may or may not have an opening. The size of the opening influences the suction speed of the VOC-laden air stream.

Suction backsplashes to create laminar flow for VOC capture

A VOC suction backsplash has a vertical wall serving as a suction mouth. It is positioned behind or next to the VOC source. A ladder of horizontal suction slots sized to the length of the workspace covers the height of the vertical wall. The vacuum backsplash creates a physical barrier between the operator and the VOC emission zone. To do this, it vacuums the entire work volume horizontally. In fact, suction is evenly distributed over the entire vertical wall, both in height and length.

The homogeneous air flow moves away from the operator towards the suction wall; the source of VOC emissions is located in the flow path. The suction backsplash allows longer operating areas to be suctioned than suction tables. It is well suited to operations on bulky objects, or if the operations involve vertical or horizontal movements of the emission source (e.g.: several operating points on a bulky object). It captures VOCs whose density is close to that of air. These VOCs mix easily with the air, diffusing in all three dimensions of the work volume. By moving the entire atmospheric working volume in a laminar flow, the suction backsplash counteracts the behavior of this type of VOC.

Suction table to capture semi-volatile VOCs

A suction table takes the form of a work surface which, depending on the purpose of the task, has either a horizontal suction slot in the background, or suction slots running lengthwise along the table surface. The aim here is to produce a suction flow evenly distributed over the entire work surface. The aim is also to generate a downward flow of VOCs towards the worktop. The VOC-laden flow is then directed to a centralized or localized filtration system. In the latter case, the suction table is mobile, and can generally release the filtered air back into the workshop.

Suction tables are ideal for jobs requiring a limited work surface. Their use therefore depends on the size of the elements to be worked on, and the space required for operational gestures. They correspond to operations requiring frequent changes in the spatial position of the emission source (e.g. handling of small emitting objects). Furthermore, as they are placed under the emission source, they correspond to the capture of VOCs that are heavier than air (semi-volatile VOCs).

Modular extraction hood for highly volatile VOCs

A solvent fume extractor placed above the workstation, the fume hood is primarily used to capture highly volatile VOCs, or those emitted by a process that generates an upward flow of hot air. The air flow, moving from top to bottom, must not cross the operator’s inhalation zone. This capture device is used in conjunction with other capture systems, or if other localized capture systems cannot be applied in the work situation. The extractor hood is sensitive to draughts, which can be compensated for by the use of flexible vertical louvers. This improves suction performance. If CMR (Carcinogenic, Mutagenic, Reprotoxic) VOCs or other toxic products are to be extracted, the employer will have to choose a different extraction method.

Pouyes ring or annular device for capturing VOCs during operations using circular openings.

VOC-emitting liquids, such as solvents, undergo transfer and handling processes that accentuate VOC emissions. Many operations are carried out within the framework of a circular opening. For example: decanting, filling, sampling, mixing in tanks, drums, reactors… These operations, which increase VOC emissions, can also generate ATEX risks. The aim is to surround as closely as possible the emission source represented by the disc-shaped opening surface.

As a result, the annular collection device consists of a peripheral suction slot. It extracts VOCs from the entire opening surface. A semi-circular hood, or more, open on the side where the worker is operating to facilitate the operation, avoids dispersing vapors into the room. The suction speed ensures that VOCs do not reach the operator’s inhalation zone.

Suction devices integrated into covers for solvent fumes.

They are used for soaking tanks and degreasing fountains with large VOC-emitting surfaces. This device is also used for waste containers or garbage cansthat emit VOCs and odors.

An opening in the cover allows suction air to pass through and maintains an internal vacuum during closing. When the cover is opened, the suction flow rate increases to maintain the efficiency offume capture.

Conclusion

The VOCs emitted by solvents entail health and safety risks for employees and risks for the environment. The multiplicity of emission contexts and the diversity of effects generate regulations established by several legal codes. They oblige the employer to take collective preventive measures, including the extraction of air polluted by VOCs emanating from solvents. There is a wide range of suction techniques. The characteristics and context of VOC emissions will guide the choice of equipment. The advice of an expert in the field will help you make the right decision.