An acid cabinet (sometimes called a smoke or cupboard cupboard) is a type of local ventilation device designed to limit exposure to hazardous substances or fumes toxic, steam or dust.
Video Fume hood
Description
Acid wardrobes are usually large appliances that surround five sides of the work area, the bottom most commonly located at standing height.
Two main types exist, channel and recirculate (ductless). The principle is the same for both types: air is taken from the front side (open) of the cabinet, and is removed from outside the building or made securely through filtration and put back into the room. This is used for:
- protects users from inhaling toxic gases (acid cabinets, biosafety cabinets, glove boxes)
- protect the product or experiment (biosafety cabinet, glove box)
- protect the environment (circulating acid cabinets, certain biosafety cabinets, and other types when fitted with appropriate filters in the exhaust air stream)
The secondary functions of this device may include protection against explosions, spill containment, and other functions necessary for work performed within the device.
Acid cabinets are usually retrofitted to the wall and often installed with the contents above, to cover the exhaust channels. Because of their hidden shape they are generally less illuminated by general room lighting, so many have internal lamps with anti-steam covers. The front is the sash window, usually on the glass, can move up and down on the balancing mechanism. In the educational version, the sides and sometimes the back of the unit are also glass, so some students can look into the acid cabinets at once. The low airflow alarm control panel is common, see below.
Acid cabinets are generally available in 5 different widths; 1000 mm, 1200 mm, 1500 mm, 1800 mm and 2000 mm. The depth varies between 700 mm and 900 mm, and the height between 1900 mm and 2700 mm. This design can accommodate one to three operators.
For highly hazardous materials, closed gloveboxes can be used, which completely isolates the operator from all direct physical contact with materials and work tools. Enclosures can also be maintained at negative air pressure to ensure that no one can escape through minute air leaks.
Liner material
- Phenolic resin (for general applications)
- Fiber-reinforced Plastics (FRP)
- Epoxy resin
- Square square steel (for durability and heat resistance)
- Angular funnel steel (easier decontamination, for radio-chemical and biohazard applications)
- Cement board (for rough use)
Control panel
Most fume hoods are equipped with an electric powered control panel. Typically, they perform one or more of the following functions:
- Warn about low airflow
- Warn a too large opening on the front of the unit ("high sling" alarm is caused by the sliding glass at the front of the raised unit higher than it deems safe, due to the decreased air velocity generated)
- Lets you turn on or turn off the exhaust fan
- Allows turning on or off the internal lights
Special additional functionality may be added, for example, a switch to enable or disable the water system.
Maps Fume hood
Acrided cabinets
Most industrial acid cabinets are supplied. A wide assortment of sour cabinets is present. In most designs, conditioned air (heated or cooled) is taken from the lab room to the acid cabinet and then dispersed through the conduit into the outer atmosphere.
The acid cabinet is only one part of the laboratory ventilation system. Because laboratory air recirculation to all facilities is not allowed, air handling units serving non-laboratory areas are kept separate from laboratory units. To improve indoor air quality, some laboratories also use a single-pass air handling system, in which heated or cooled air is only used once before disposal. Many laboratories continue to use air systems back into laboratory areas to minimize energy and operational costs, while still providing adequate ventilation levels for acceptable working conditions. The acid cupboard serves to evacuate the level of harmful contaminants.
To reduce laboratory energy ventilation costs, a variable air volume system (VAV) is used, which reduces the volume of exhausted air when the cover of the acid cabinet is closed. This product is often perfected by the automatic cover sling device, which will close the shroud of the acid cabinet when the user leaves the face of the smoke hood. The result is a veil operating at a minimum disposal volume whenever no one actually works in front of them.
Because the special acid cabinets in the US climate use 3.5 times more energy than homes, the reduction or minimization of disposal volume is strategic in reducing the facility's energy costs as well as minimizing the impact on facility and environmental infrastructure. Particular attention should be paid to disposal sites, to reduce risks to public safety, and to avoid withdrawal of exhaust air into the building's air supply system.
Additional air
This method is outdated technology. The premise is to bring the unconditioned outer air directly in front of the hood so that it is the exhausted air. This method does not work well when the climate changes because it pours cold or hot and humid air into the user so it is very uncomfortable to work or affect the procedure inside the tent. The system also uses additional channel channels that can be expensive.
Volume of air constant (CAV)
In a survey of 247 lab professionals conducted in 2010, Lab Manager Magazine found that about 43% of the acid cabinets are conventional CAV acid cabinets.
Non-cut CAV
Closing the sling on a non-bypass CAV cap will increase the face speed ("pull"), which is a function of the total volume divided by the opening area of ​​the sling. Thus, the performance of a conventional hood (from a safety perspective) depends heavily on the sling position, with increased safety when the hood is pulled closed. To solve this problem, many conventional CAV hoods set the maximum height that the acid cabinet can be opened to keep the flow rate safe.
The main disadvantage of a conventional CAV hood is that when the sash is closed, the velocity can increase to the point where it interferes with fine instrumentation and apparatus, cold hot plate, slow reaction, and/or creating turbulence that can force contaminants into the room.
Bypass CAV
Bypass CAV hoods (sometimes referred to as conventional hoods) were developed to overcome the high-speed problems affecting conventional smoke hoods. This hood allows air to be pulled through the opening of "bypass" from above when the sling closes. The shortcut is located so that when the user closes the sling, the opening opens becomes larger. The air passing through the hood maintains a constant volume wherever the sash is positioned and without changing the fan speed. Consequently, the energy consumed by CAV cabinets (or more precisely, the energy consumed by the building's HVAC system and the energy consumed by the exhaust fan) remains constant, or close to constant, regardless of the position of the sling.
Low flow/high performance cut CAV
High-performance or low-flow bypass CAV hoods are the newest type of CAV hoods bypass and typically feature improved containment, security, and energy conservation features. Low-flow/high performance CAV hoods generally have one or more of the following features: sash stops or horizontal-sliding sashes to limit openings; position sensors and airflow sensors that can control mechanical baffles; small fans to create an air curtain barrier in the operator's respiratory zone; enhanced aerodynamic design and variable dual-baffle systems to maintain laminar flow (undisturbed, unwilling) through the hood. Although the initial cost of the high performance hood is usually more than that of the conventional cutting hood, the increase in containment and flow characteristics allow this hood to operate at face speeds as low as 60 fpm, which can translate into $ 2,000 per year or more in energy savings, depending on the size of the hood and the sling arrangement.
Reduce air volume (RAV)
Reduced air volume hoods (variations of low-flow/high-performance hoods) incorporate cut blocks to partially close the bypass, reducing air volume and thus saving energy. Typically, this block is combined with a sash stop to limit the opening height of the sling, ensuring a safe facial speed during normal operation while lowering the air hood volume. By reducing the air volume, the RAV hood can operate with a smaller blower, which is another cost savings advantage.
Because the RAV hood restricts sling movement and reduces air volume, the hood is less flexible in what can be used and can only be used for certain tasks. Another disadvantage to RAV hoods is that users can theoretically override or release a sash stop. If this happens, the face speed can go down to unsafe levels. To overcome this condition, the operator must be trained not to overwrite the sash stop when in use, and only to do so when loading or cleaning the hood.
Variable air volume (VAV)
VAV veil, the latest generation of acid cabinets, vary the amount of room air that runs out while maintaining the facial speed at a set rate. Different VAV veils change the exhaust volume using different methods, such as dampers or valves in open drains and closing by sling positions, or blowers that change the speed to meet the air volume demands. Most VAV hoods integrate a modified passenger block system that ensures sufficient airflow in all sling positions. VAV veil is connected electronically to laboratory building HVAC, so the disposal of hood and room supply is balanced. In addition, the VAV hood has a monitor and/or alarm that warns the operator of unsafe airflow conditions.
Although VAV hoods are much more complex than traditional constant volume hoods, and thus have a higher initial cost, they can provide considerable energy savings by reducing the total volume of air-conditioning consumed from the laboratory. Since most of the veils are operated all the time, an open laboratory, this can quickly add significant cost savings. This savings, however, depends entirely on user behavior: the less open the hood (both in terms of height and in terms of time), the greater the energy savings. For example, if laboratory ventilation systems use 100% once-through outside air and air-conditioning values ​​are assumed to be $ 7 per CFM per year (this value will increase with a very hot, cold or humid climate), 6 foot VAV fume hood in the open full for the experiment set 10% of the time (2.4 hours per day), at 18 inch opening work 25% of the time (6 hours per day), and completely covered 65% of the time (15.6 hours) per day) saving about $ 6,000 each year compared to a fully open hood 100% of the time.
The potential behavioral savings of the VAV acid cabinets are highest when the density of the smoke hood (the number of hoods per square foot of laboratory space) is high. This is because the smoke hoods contribute to the achievement of the required air exchange rates of laboratory space. In other words, the savings from the fume hood cover can only be achieved when the level of smoke hood exhaust is greater than the air exchange rate required to reach the required ventilation level in the lab room. For example, in a lab room with a required air exchange rate of 2,000 cubic feet per minute (CFM), if the room has only one fume hood that delivers the air at 1,000 square feet per minute, then covering the sash in a smoke hood will only cause handling laboratory air space increased from 1000 CFM to 2000 CFM, so there was no net reduction in exhaust level, and thus no net reduction in energy consumption.
In a survey of 247 lab professionals performed in 2010, Lab Manager Magazine found that about 12% of the acid cabinets are VAV acid cabinets.
Canopy fume hoods
Canopy fume hoods, also called exhaust canopies, are similar to the range hood found on commercial stoves and some residential kitchens. They have only a canopy (and no cage and no sling) and are designed for ventilation of non-toxic materials such as smoke, steam, heat, and non-toxic odors. In a survey of 247 lab professionals conducted in 2010, Lab Manager Magazine found that about 13% of the fume hoods are supplying the canopy smoke hoods.
Ductless acid cabinet (recirculation)
Especially for educational or testing use, these units generally have a fan mounted on the top (soffit) of the hood, or under a part shelf. The air is sucked through the front opening of the hood and through the filter, before passing through the fan and put back into the workplace. With ductless smoke hoods it is very important that the filter media can eliminate the hazardous or toxic materials used. Because different filters are required for different materials, recirculating acid cabinets should only be used when the dangers are known and unchanged.
Air filtration of ductless acid cabinets is usually divided into two segments:
- Pre-filtration: This is the first stage of filtering, and consists of a physical barrier, usually an open cell foam, which prevents large particles from passing through it. This type of filter is usually not expensive, and lasts for about six months depending on usage.
- Primary filtering: After pre-filtering, the smoke is sucked through an activated charcoal layer that absorbs most of the chemicals that pass through it. Ammonia and carbon monoxide will, however, pass through most of the carbon filter. Additional special screening techniques may be added to combat the chemicals to be pumped back into the room. The main filter will generally last for about two years, depending on usage.
Ductless acid wardrobes are often unsuitable for research applications where activities, and materials used or produced, are subject to change or are unknown. As a result of this and other shortcomings, several research organizations, including the University of Wisconsin, Milwaukee, Columbia University, Princeton University, the University of New Hampshire, and the University of Colorado, Boulder either prevent or ban the use of ductless acid cabinets.
The benefit of ductless acid cabinets is that they are mobile, easy to install as they do not require ductwork, and can be plugged into a 110 volt or 220 volt outlet.
In a survey of 247 professional labs conducted in 2010, Lab Manager Magazine found that about 22% of the acid cabinets are ductless acid cabinets.
Custom design
Acid digestion
These units are usually made of polypropylene to withstand acid corrosive effects at high concentrations. If hydrofluoric acid is being used in the hood, transparent sheath should be made of polycarbonate that holds etchings better than glass. The pipeline works should be coated with polypropylene or coated with PTFE (Teflon).
Downflow
Downfume fume hoods, also called downflow work stations, are usually ductless acid cabinets designed to protect users and the environment from harmful vapors produced on the work surface. Upstream air flow is generated and hazardous vapors are collected through a gap in the work surface.
Perchloric acid
These units have a waterwash system in need of ducts. Because solid perchloric acid fumes settle and form explosive crystals, it is essential that the air ducts are cleaned internally with a series of sprays.
Radioisotope
This acid cupboard is made with stainless steel coating and reinforced reinforced stainless steel table that is reinforced to handle the weight of a brick or lead beam.
Scrubber
The type of fume hood absorbs smoke through a room filled with a plastic form, which is watered with water. These chemicals are washed into a container, often filled with a neutralizing fluid. The smoke is then dispersed, or disposed of, in a conventional manner.
Waterwash
This acid cabinet has an internal washing system that cleans the inside of the unit, to prevent the buildup of hazardous chemicals.
Energy consumption
Because acid cabinets constantly release large volumes of conditioned air (heated or cooled) from the laboratory room, they are responsible for large amounts of energy consumption. Key statistics laid out in the 2006 article by Evan Mills et al.:
- For the standard hood of two meters (six feet), the energy costs of the hoods range from $ 4,600/year for temperate climates such as Los Angeles, up to $ 9,300/year for extreme cold climates such as Singapore.
- With about 750,000 veils used in the US, aggregate energy use and a potential savings are significant. Mills et al. estimates the annual operating cost of a US cabinet of about $ 4.2 billion, with a peak of 5,100 megawatts of electricity demand.
- As a result, acid cabinets are a major factor in making typical laboratories four to five times more energy intensive than ordinary commercial buildings.
- With the new technology, 50% to 75% per capita savings can be achieved safely and cost-effectively while overcoming the limitations of existing strategies.
Most of the energy responsible for the smoke hood is the energy needed to heat and/or cold air sent to the laboratory. Depending on the type of HVAC system (heating, ventilation, and air conditioning) installed, this energy may be electricity, natural gas, heating oil, coal or any other type of energy. Additional electricity is consumed by fans in HVAC systems and fans in the smoke exhaust system.
Calculate energy consumption
Lawrence Berkeley National Lab has developed the Fume Hood Energy Laboratory Model which estimates annual energy usage of fatty acids and the cost for climate and user-defined assumptions about the operation and efficiency of the equipment.
Program behavior to reduce energy usage
Acid Cupid Treatment may involve daily, periodic, and annual examinations:
- Examination of the daily acid cupboard
- The acid closet area is visually inspected for material storage and other visible blockages.
- Examination of periodic smoke hood function
- Capture or facial speed is usually measured by a velometer or anemometer. Veils for the most common chemicals have an average speed of at least 100 feet (30 m) per minute on an 18-inch (460 mm) sling opening. Face speed reading should not change more than 20%. A minimum of six readings can be used to determine the average speed of the face.
- Other local exhaust devices are tested to determine whether contaminants designed to be removed are sufficiently captured by the hood.
- Annual maintenance
- Maintenance of the exhaust fan, (ie lubrication, voltage belt, blade blade deterioration and rpm), is performed in accordance with the manufacturer's recommendations, or adapted to appropriate hood functions.
- Safety & amp; Increased Energy must be performed by professionals as required from time to time to meet the requirements.
History
The need for ventilation has been evident from the early days of research and chemistry education. Some initial approaches to the problem are adaptations of conventional chimneys. A fireplace built by Thomas Jefferson in 1822-1826 at the University of Virginia is equipped with a sandbox and a special chimney to vent toxic gases.
In 1904, the Faculty of Chemistry at the Technical University at Gda? Sk is equipped with a fume hood. The harmful and corrosive gas side effects are actively removed using the natural draft of the fireplace chimney. The initial design is still functioning after more than 100 years.
The chimney draft is also used by Thomas Edison as the so-called "first acid cabinet". The first modern "closet closet" design known as the rising belt was introduced at the University of Leeds in 1923.
Modern acid cabinets are distinguished by methods of regulating airflow independently of combustion, increasing efficiency and potentially disposing of volatile chemicals from exposure to flames. The acid cabinets were originally made of wood, but during the 1970s and 1980s, epoxy epoxy coated steel became the norm. During the 1990s, pulp derivatives treated with phenolic resins (plastic laminates and solid-grade laminates) for chemical resistance and flame retardation began to be widely accepted.
See also
- Laminar flow cabinet
- Vented Balance Safety Enclosure
- ECO funnel
References
External links
- Northwestern University Office for Security Research - The Chemical Fume Hood Handbook
- Lab Manager Magazine : CAV, RAV & amp; VAV
- Hood Chemical User's Guide from University of Louisville
- Information from the University of Bath in England
- Fume Hood Resource Center by Lab Manager Magazine
- University of Toronto guide to run sash-shutting campaign
Source of the article : Wikipedia
0 Comments