Dust control enclosures

The original design was based on a control velocity recommended by dust control design manuals. The original design of 28 m s exhaust flow induced an inward velocity of about 0.5 m s" through the enclosure entrance and trolley shots. This was not sufficient to overcome plume trajectories aimed outward, or to overcome the effect of moderate wind levels. 

A design based on the enclosure open-area control velocity does not consider all the other variables listed as affecting dust control. Calculation procedures to predict many of the other variables would be very complicated if not impossible to perform. Physical modeling of the problem and solution w as therefore used as the basic design tool. 

The correct application of either sizing technique will result in a duct network that works well on air. It is equally important to ensure that each air flow is adequate to transfer all the particulates from the hood/enclosure to the collection and/or cleaning device. Unfortunately, many dust control systems have been designed and/or are being operated with little or no regard for what actually has to go through the hood-duct network. This can result in ... 

Many operations within the laboratory start with weighing. It is difficult to undertake precise weighing in conventional laboratory fume hoods, as the airflow and vibration inside an operating fume hood often disturb the balance. In order to accommodate the need for an engineered control at this scale of operation, dust control systems have evolved known as ventilated weighing safety enclosures or powder weighing hoods. Key characteristics of a ventilated weighing safety enclosure include ... 

Therefore, an essential requirement in plant design is the stringent application of dust control techniques. Specifically designed enclosures enabling materials to be handled in closed systems and extraction and plenum air systems of sufficient capacity to maintain normal working areas free from contamination are essential. Special plant finishes to facilitate good housekeeping are an added requirement. 

Dust Control/Explosion Protection Raw material feed systems. For materials which are potential sensitizers, (e.g., enzymes), it is advisable to fully enclose the raw material unloading station and feeder system in a booth with dedicated dust control. This ensures that any release of dust is contained. Operators entering the enclosure should do so with appropriate personal protective equipment. 

Screens do not usually present material exposure hazards not already covered in Section 3.11.2. Generation of vapors is small, and dust control, while important, is not fundamentally difficult. Simple enclosures are often used to contain dusts. These range from partial enclosure of a vibrating element to total dust-tight enclosure of an entire system. 

Dust control systems usually include hoods and enclosures connected to a local exhaust ventilation system that discharges to cyclone collectors and scrubbers or a baghouse in series. The most common type of control equipment is the baghouse these are increasing in use as more stringent pollution control codes are adopted. These filters provide excellent collection efficiency with little or no visible emissions and the collected dry fines are sometimes usable in concrete mixes. However, if the exhaust gas temperature is at or near the dew point of the gas, condensation of moisture on the fabric filters is always a possibility and poses a serious fire hazard. The other type of the commonly used control equipment is the venturi wet... 

Preventing Dispersal of Dust The dispersal of respirable dust from crushers, conveyors, and similar equipment can be eliminated in most instances by confining the dust-producing operation within an enclosure and controlling the air contained therein. The air from within the enclosure can be exhausted directly to the upcast airway or, if this is not feasible, it can be filtered. The section of this chapter entitled Minerals Processing Dust Control Devices and Systems gives guidehnes for dust collection systems. 

Crushers Crushers emit dust primarily from two points, the discharge and the feed. Dust control measures are not usually considered in the design of a crusher. However, the use of shrouds or enclosures for crushers can contain the dust so that a dust control system can operate more efficiently. In installing crushers, the following measures are recommended (1) a crusher feedbox with a minimum number of openings should be installed, and rubber curtains should be used to minimize dust escape and airflow and (2) the crusher should be choke-fed to reduce air entrainment and dust emission. Dust escape at the crusher discharge end can be minimized by properly designed and installed transfer chutes. 

An aluminum enclosure housed the working components of the cotton-dust analyzer. The upper section of the enclosure, which was hinged to the lower section, contained the HEPA filter, the spray bar assembly, and the top, hold-down screen for the lint batt. The botton section housed the sizing screen, filter support, fan, and the electrical and pneumatic controls. The entire enclosure was 60 cm wide, 46 cm deep, and 72 cm tall. 

The metallizing unit should be situated as far as possible from other processes, especially if these generate dust or fumes it should be in its own enclosure—which should be constructed from materials that do not give off or retain dust, and preferably fitted with inter-locked double doors. The floor of the enclosure should be level and smooth, and treated or covered with hard-wearing, non-slip material. The temperature and humidity within the enclosure should be controlled. Often the units are built into enclosures with the pumping system outside. Control panels also may be mounted outside, as in Figure 75. 

Isolation of Source—Dust can best be controlled at the source of generation by enclosures, wet methods, or exhaust ventilation. The first of these methods, although obviously the simplest, cannot be used where the process requires attention by an operator. In theory this control method utilizes segregation of the dust-producing source. It is... 

The primary control to protect an employee from dust, mist, fumes, gases, and toxic vapors is the engineering control, such as enclosure or confinement of the operation, general and local ventilation, and substitution of less toxic materials. In addition, appropriate respirators should be provided to protect from occupational diseases. 

In general, dust emission from screening dry, crushed limestone should be controlled by enclosure or extraction. An alternative approach is to suppress the dust using water, preferably containing a wetting agent. This, however, may introduce down-stream problems as a result of carry-forward of fines and contaminants. 

An enclosure intended for outdoor use to protect the enclosed control against windblown dust and water. These enclosures must have provisions for watertight connectors, provisions for mounting external to the enclosure cavity and provisions for locking. 

An enclosure intended for outdoor use to protect the enclosed control against windblown dust and water and to provide for its operation when the enclosure is covered by external ice or sleet. These enclosures do not protect the enclosed equipment from malfunction due to internal icing. These enclosures must have provisions for watertight connectors, for mounting external to the enclosure cavity and for locking. In addition, these enclosures must have the ability to support the additional weight of ice and to withstand the removal of ice by a hand tool to permit access to the enclosure interior. 

---