Welcome to the world of fume and vapor emissions. Today we shall talk about filtration of air at the entry to a workspace or a living zone. It is important to know more about Fume and vapor emissions as we live in an environment that is filled with dust, vapor, and fumes. As there are significant situations where the process of generation of fumes, dust, and vapor cannot be curtailed, but its removal can be simplified.
Why It Is Important For An Employer To Take A Note Of Fume And Vapor Emissions?
An employer is responsible not only towards his workers but also the environment at large. There are strict national regulations in the European Union Directive where the implementation of the workers’ protection in the industry is stringent.
Come to think of it, industrial fumes include dry smoke emitted from the welding operations. People also suffer from the wet smoke aerosols that include oil mist or other liquid products. Such contaminants need to be removed from the atmosphere by the process of extraction. The extraction process will hold effective only when such fumes are collected at the source. It is necessary to do so as the heavily contaminated extraction then goes under the filtration process to supply a non-pollution exhaust.
Types of Ventilated Workstation-
When the question comes about methods of ventilating a workstation, many may not be aware, but there are almost more than six general methods to do so. Let us take a sneak peek to it-
- Natural Ventilation: This is the most simple and easy to do with ventilation. Here you can keep the doors and windows open. You don’t need any fancy exhaust equipment to provide you with fresh air. It means you save on your pockets. Having said this, it is not the direct solution to solve the problem of fume and vapor emissions. Often the heat loss takes place during winter when the heaters are switched on, but the natural ventilation process brings in the cold air back again.
- General Ventilation of The Room: it involves ventilation of the room without filtration of the exhaust. You can succeed in getting ventilation of the room by fixing fans or wall mounted fans. You can see a high volume of air extracted. So, if you own a welding workshop, you must essentially have 3 to 15 air changes in an hour to get the generation ventilation of the room method working. Again talking about investment part of it, the cost part is low. However, it yet does not solve the problem of people inhaling the toxic fumes. Besides, the functioning of the fans loss of heat takes place during the winters. So although it may sound like a good plan, there are pitfalls of it too.
- Forced Ventilation: Here you can use wall mounted flexible fume extractors. These extractors run from the source of the fumes. It then extracts manifold on the wall. It helps the pollutants to get extracted from the source and thus prevents it from spreading all over the workshop. It functions through the exhaust filter. The combined exhaust with the help of the exhaust fan discharges the fumes outside the premises. All this takes place with the help of an exhaust filter. Most employers prefer this as it is cost effective and efficient. It comes with concentrated pollutants that get extracted at the source. This indicates that only a small volume of air gets extracted along with the fumes. The difficulties faced by the users are that the extraction hoods must be placed not more than 50 cm from the source of the fume and vapor emissions. So when one needs to mount such a system for larger scale production areas, it may be difficult to do so. Such large-scale production houses do not have walls that are close to the operation.
- Mobile Fume Extractor with a Built-In Filtered– If you have heard know how a vacuum cleaner works, you will know what I am hinting at. It works on the similar principle of a vacuum cleaner where the extractor extracts the fumes and vapor emission at the source. The USP of such extractor is that it is movable. It is regarded as an energy saving extractor that provides clean air. Its process is efficient. The system re-circulates the clean air inside the work-station once the extraction process is complete. There is no requirement for any wall mounting. It is a machine like a device that is easy to move. The system demands the filtration elements to be cleaned. Now there are two ways to do so, I normally recommend replacing it after a period of use. Some wash it too. Depending on your usage you could take a call.
- General Central Circulation inside the Room– this extraction of fume and vapor emissions is done through a fan-filter unit. The unit is usually mounted on the ceiling. This unit promises to remove 100% of the contaminants providing clean air. This unit extracts a high volume of air. There requires no positioning of any extraction hoods. Besides, while most of the system shows heat loss, under this extraction system, the heat loss is reduced. What can be said as a drawback is that there is no specific extraction at the source! Therefore the employees at the work-station will inhale those toxic fumes much before they are filters. There are special filters, therefore,required where such toxic gases at present can be filters easily. Such filters need special filters that can filter the toxic gases that are present at that very moment. The filters must be cleaned, washed and replaced on a routine basis.
- Wall Mounted Flexible Fume Extractors– These is flexible fume extractors. It has a manifold towards a central extraction unit. The unit works by extracting the contaminants at the source. It gives 100% recycled and filtered air. They are preferred over the other systems as the contaminants are captured before they head to spread in the workshop. The heat is retained in the workstation and these benefits in saving energy. The positioning of the hoods must be positioned as per the operator’s instructions. You will need special filters to remove the noxious gases. The filter elements are washable and replaceable too.
So the idea is to treat the effluent problem from the base. It must be removed before it starts spreading to the surrounding air. With the help of an individual source, getting the work done can be difficult. But with additional methods of extraction of unwanted fumes from the workstation can be done with other methods too.
Knowing the Three Basic Methods of Extraction of Unwanted Fumes from the Workstation-
- Local Exhaust Ventilation (LEV): This system requires hoods to work as the main tool to control the contamination. Hoods need large volumes of air. The problem the LEV 395n faces is that the operation of LEV cannot rely on the operator. The distance from the source of contamination to that of the hood is important. With the LEV being installed, there comes a change in room conditions too. It holds true especially when the enclosed type of hoods is used. You will mostly find cross-draughts and general room air movements are major sources of detraction from the contaminant efficiency. LEV system must be the last option unless the material evolved is innocuous or the process does not need any operator for functioning.
- Fishtails– If you have a small workshop, this process is good to provide a high velocity of extraction. You can expect the fishtail to extract welding fumes and remove all the oil mist from certain types of unguarded machine tools. Fishtails can be mounted. It can be moved either by using a swinging arm or a magnetic clamp. The procedure of moving should be such that it does not affect the operation. The system works on an open and slotted area that is equal to the cross-sectional area of the duct of the extraction. The unit that is 680 and 850 m 3/hr. can extract contaminants up to 225 m away from the source of the fume emission. You may find that when it comes to welding fumes,the rate of extraction becomes slower as 200 m 3/hr., while the extractions slots are more than75 – 25 mm. One thing is important to notice that while the fumes get collected directly at sourced; you must ensure that the solid matter like swarf or liquid droplets is not entrained. You may have to keep experimenting the initial days on the positioning of the fishtail to get optimum results. You must position it in a way that the extraction velocity of approximately 30 m/mm at the source of emission is possible. Thus, cross draughts, heat and all the other factors bear on the positioning and extraction rate.
- Enclosure: In a work zone, the fumes that are created by operations like machine tool must be completely enclosed. It helps to prevent the effects of splashing. Usually the owners of machine tool manufacturers, as a standard rule, fit oil mist extraction and filtration equipment. The idea behind such an arrangement is to have a system that has an extraction rate in a way that it can clean the work-station air into the fume- generating zone. It will preventthe fumes to escape around the sides of the enclosure. So even if the doors are opened, there will not be much of fumes going out. As a tip, it is better to keep that air flow of 4.2 m 3 /hr. for every square meter of open area to keep the working area under the necessary negative pressure. The extraction rate is directly proportionate to that of the enclosure size. For large enclosures, you will require a higher rate of extraction. It is better to place the extraction point away from the working area so that it reduces the possibility of drawing off unwanted solid matter or fluid. There are laminar flow booths that have airborne dust and vapor. They are done by inducing a flow of external air inward through the working zone as well as in the filtration system.
How to Find a Safer Operation for Fume and Vapor Emissions?
Thus the answer to the safer use by an operator is to work at the side of the source. Many may think standing downstream is a good option, but it does not offer any protection from dust or vapor. Standing upstream, in fact, can cause a turbulent wake in the front of the source. This can be a compromising element for operator protection. Having said this, there is no denying the fact that correct inward air velocity is necessary as too low and dust containment will fall out. Nevertheless, if the inward air velocity is too high then the turbulence in the booth will occur. Having an operator exposure level is good as the background factory’s level. It is because such booths require the inward flow of a large volume of factory air. You will also find in few industries there is an increase in the potential product cross-contamination.
Many suggest that the Laminar flow booths are good as it is best suited to operations that need enclosures not more than 1.5 m wide. It is good to handle nuisance particles with a working limit of 5–15 mg/m 3.
Down flow booths are suitable for airborne dust and vapors. These booths are normally used in the food industry. The functioning is based on clean laminar air flow. It is placed vertically downwards from the ceiling. It helps to push the hazardous contamination downwards and keeps it away from the operator’s breathing zone. Before the air is re-circulated back to the work-station, the exhaust air flow is taken through a number of dust filters and HEPA filters. Such an arrangement is okay for low levels only.
Conversely, there are other methods of extraction that are commonly in use. Some use lip extractors that are used around the fume creating tanks. There is a powerful floor mounted ducts. It is easily adopted in certain foundries.
How Does The Ventilation Process Work?
The air resistance in a duct-work system is determined by the velocity of the air in that unit. So basically what happens is when the fumes or dust are being extracted, there is a requirement of maintaining relatively high velocity. The high velocity will aid in the prevention of the dust and fume particles from getting settled in the ducting system. It is ideal to have a velocity of 10-15 m/s.
How Different Is Fume Filtration From Other Filtration Processes?
So when it comes to fume filtration, the process involves the collection of dry smoke particles by the process of impingement filtration. The process requires using pad, pocket or cartridge type of filter, bag or any paper or synthetic media to electrostatic separators. You can mix and match the combination to get high efficiencies.
One important aspect that most of the filter operators forget to do is the timely replacement of the elements. But with the electrostatic type of system, only routine cleaning will do the needful. The market is also well equipped with automatic and semiautomatic wash facilities. It is a costly affair no doubt, but they are worth the deal.
What Happens To Industries That Emit Wet Smokes?
Call it wet smokes, or aerosols, these droplets of liquids ranging from 10 to 0.5 m are suspended in the air. They are often filtered by a bag or a panel type of filters. Some use electrostatic/electro dynamic separators or even centrifugal impaction units to remove the contaminants. Usage of bags or panel filters benefits in giving effective results. They are cheap and easily available. Many employers do not approve of the idea of bag changing. As after the change, the collected solids are required to be disposed of.
If you are someone who wishes to use electrostatic units, they may be costly but are effective holding light contamination. Here, the liquid gets collected and drains off the collection over the plates. On regular accumulation of the liquid, you will find a stain on the plate. You may have to clean it on a regular basis to maintainthe separation efficiency of the process.
Centrifugal Impaction Separators– this may not offer high cleaning process as electrostatic separators but is good for down to 0.5 m without any sort of deterioration in use. In this process, the action imposes about 1000 G on the 399 aerosols. The advantage is the collectors become self-cleaning. It is viable and maintenance cost is low. The process functions on a perforated steel drum that is directly driven by an electric motor. The blades of the drum’s interior produce suction to draw in the oil mist. It is suitable for ducting hence. The blades at velocities excessive of 50 m/s impact a great deal in oil mist. The particles are thereby forced to coalesce much before being thrown by the centrifugal force. In a way, the cleaned air gets returned to the work-station. The pressure that is present within the casing checks that the liquid oil is getting drained continuously through a discharge duct for re-use.
So How Does One Treat Vapor Emissions?
There are many industries that use organic solvents. However, the emissions of these solvents often become hazardous to the health. There could be several that have adverse effects on human health. But the one that hits the global issues are the photo chemically reactive solvents. They are most commonly known as volatile organic compounds (VOCs). This day, the emissions of VOCs are strictly prohibited in many countries. The reason is simple. There are billions of cubic meters of contaminated matter from the solvent that get treated by solvent removal and recovery plants. There are several clean-up systems that are based on different technologies. The story of activated carbon adsorption remains no alien with anybody.
When you think of the process being followed, it includes the passing of solvent laden air through the adsorber vessels. These vessels contain beds of granular or powdered activated carbon too. However, you will require at least two adsorbers to get a continuous flow of the liquid. Every adsorber alternates between the cycle of the adsorption step and the regeneration step. Solvents are then seen to be retained in the carbon during the adsorption step. In the following step, you will find carbon removed. The process is often done with the help of heating. In the regeneration step, steam is used to remove the carbon. You will find condensed steam-solvent after it is cooled.
The mechanical decantation is great for water-insoluble solvents. These water-soluble solvents require further separation, dehydration, and 100% purification before it gets to the re-usable step. Many use alternative carbon adsorption technology to use the cam rotary valve method. This method is different from the conventional adsorption technology where the duplex system is used. The carbon adsorption technology uses only a single unit. The single unit is further divided into multiple compartments.
If You Are Wondering How Does The Rotary Basis Work? Read Further To Know About It-
Rotary basis system means a central valve in the unit that distributes contaminated air to an individual compartment. Here each compartment undergoes the regeneration step and meanwhile others are purifying the solvent-laden air. This system supplied continuous and uninterrupted adsorption. It also uses less activated carbon which is a plus point. To recover VOCs from air streams, membrane systems are employed successfully. This membrane system is used in the vapor recovery process. It includes a combination of compression-condensation and membrane vapor separation. It is the membrane separation stage that uplifts the recovery with compression and compensation alone. It also allows the process to operate at a higher recovery rate. Alternatively, the temperature and pressure connections can also remain relaxed. It is called the new age developing technology where it promises to showcase a resourceful recovery and pollution free element.
Talking About Oxidizer System-
Under this adsorption process it intends to recover the solvent in the air stream. This catalytic oxidizer system destroys the air toxics. The VOCs are discharged in the exhausts of the industrial processing.
The reason why people use catalyst is it allows the oxidation of hydrocarbons to carbon dioxide and water vapor at a considerably lower temperature (Reminds of my school days chemistry sessions!) thus, after this the air stream enters the system fan followed by the heat exchanger.
The catalyst is protected from the heat exchanger as the air then passes through a high temperature –resistant filter. Therefore as a catalyst, an exothermic reaction takes place. It oxidizes the VOCs and other contaminants. On oxidizing the gas temperature automatically raises. The heated gas is used to heat the incoming air before getting exhausted to the atmosphere.
So does the catalyst require any fuel? The Catalytic oxidizer requires little or no added fuel. However, it depends if the solvent content of the air is high or low. If the solvent content is high, the catalytic oxidizer needs no fuel.
If you are wondering what kind of oxidizer can be added, you can add in a thermal oxidizer like the regenerative oxidizer. It has two insulated chambers of vertical thermal energy. These chambers are connected by an inverted U-shaped insulated oxidation chamber. There is a flow diverter valve that is placed under the energy recovery chambers. They act as a diversion to the process air flow into and out of the chambers. There is a recovery up to 95% of the oxidation energy. It comes due to the energy recovery chambers being packed with ceramic material. This entire system is controllable by a programmable logic controller.
Off late there are people talking about Bio-filtration. The technique that is uses micro-organisms for the removal of undesirable components from industrial waste gases. So let us know more about Bio-filtration.
So basically the waste gases go through a layer of filter material on which micro-organisms are made immobile. The active surface layer absorbs the contaminants. The micro-organism breaks them and supplies carbon dioxide, mineral salts, and water. The functioning of the filter works on the similar grounds that of a trickle filter. The principle of working is based on microbiological degradation mechanism. It is essentially used for water wastes.
The method is simple. The gases go through a process of deducting, cooling or dehumidifying before it is ready to enter the filter. It then passes through the layers of the filter material where earlier inoculated with cultured micro-organisms have taken place. It is done to get propelled into the filter. It may require a fan’s assistance too. The propelling allows the gas to get distributed evenly over the filter bed.
According to the components that need to be removed from the gas stream, the strains used vary. So let’s say, Nocardia culture is used for thiobacillus for hydrogen sulphide, styrene fumes, and hyphomicrobium for methylene chloride. In this process, you will find that as the polluted gas stream gets passed through the filter, the pollutants are consumed by the bacteria. You can expect solvents like toluene and acetone or hydrocarbons, alcohols to aromatics for the treatment under this application.
Off late, this process holds best for industries like paint, brewing, food processing, textile manufacture, plastics, pulp, petrochemical, printing, and paper industries. The reason why it stands to be the favorite for the industrialists is that the operation cost is low. There is no requirement for routine maintenance.
Hope the above article has proven fruitful to you in understanding the various concepts on fumes and vapor emissions. Keep yourself updated on this page for more information on filtration related things.