Exhaust hood


Handling of dry acrylamide is hazardous primarily from its dust and vapor, and this is a significant problem, especially in the course of emptying bags and dmms. This operation should be carried out in an exhaust hood with the operator wearing respiratory and dermal protection. Waste air from the above mentioned ventilation should be treated by a wet scmbber before purging to the open air, and the waste water should be fed to an activated sludge plant or chemical treatment faciUty. SoHd acrylamide may polymerize violendy when melted or brought into contact with oxidizing agents. Storage areas for sohd acrylamide monomer should be clean and dry and the temperature maintained at 10—25°C, with a maximum of 30°C.  [c.136]

Offsetting exhaust hood requirements Energy sources  [c.360]

To remove all decomposition products, a "total-capture" exhaust hood is recommended.  [c.370]

Warm-Up. Warm-Up refers to that period of operation beginning immediately after the car has started and continuing until the engine has reached normal operating temperatures, usually after 10 minutes or so of operation. During this period, the vehicle designer wants to get the vehicle equivalence ratio to stoichiometric as soon as possible to minimize emissions. On the other hand, if the mixture is leaned out too soon, the car experiences poor driveability during the warm-up period. Euel system design is critical during this period. With single point fuel metering systems such as carburetors and throttle body injectors, there is generally Hquid fuel on the walls of the intake manifold during warm-up. If this Hquid only reaches the cylinders in bursts the vehicle may experience unwanted surges. Manufacturers employ techniques to use the exhaust heat to rapidly heat up the walls of the intake manifold. Multipoint fuel injectors minimize many of these problems but make the scheduling of the fuel pulses critical.  [c.182]

The compressor can be driven by electric motors, gas or steam turbiaes, or internal combustion (usually diesel) engines. The compressor can also be a steam-driven ejector (Fig. 7b), which improves plant reUabiUty because of its simplicity and absence of moving parts, but also reduces its efficiency because an ejector is less efficient than a mechanical compressor. In all of the therm ally driven devices, turbiaes, engines, and the ejector mentioned hereia, the exhaust heat can be used for process efficiency improvement, or for desalination by an additional distillation plant. Figure 8 shows a flow diagram of the vertical-tube vapor compression process.  [c.246]

Air flotatioa dryers have exceUeat heat-transfer coefficients, give very uniform dryiag across the web, and give excellent web stabiUty. These dryers, which can be used for a wide range of web types and tensions, also tend to be quieter and thus pose less noise problems than higher velocity siagle-sided dryers. Floater dryers are totally eaclosed and compact so that they are clean and cause less dirt defects ia the coatiag. Air dryers can also be coupled with radio frequency or iafrared units to give even higher dryiag rates. Oftea these units are added to existing dryers because no additional dryer length is requited.  [c.315]

For maximum heat economy, recovered exhaust heat is employed for preheating of the incoming sohds and combustion air. The fuels used may be gas, oil, or pulverized coal.  [c.1222]

Information on vibrating conveyors and their mechanical construc tion is given in Sec. 21. The vibrating-conveyor diyer is a modified form of fluidized-bed equipment, in ich fluidization is maintained by a combination of pneumatic and mechanical forces. The heating gas is introduced into a plenum beneath the conveying deck through duc ts and flexible hose connections, passes up through a screen, perforated, or slotted conveying deck, through the fluidized bed of solids, and into an exhaust hood (Fig. 12-93). If ambient air is employed for coohng, the sides of the plenum may be open and a simple exhaust system  [c.1224]

The leaving velocity Co is a measure of the unused energy. For best efficiency Co should have no radial component Co should be straight axial. For all stages except the last one, Co represents a carryover to the next stage. For the last stage, Co is the velocity into the exhaust hood and is referred to as the leaving loss or exhaust loss.  [c.2498]

Grains come in all shapes and sizes, and both shape and size can have a big effect on the properties of the polycrystalline metal (a good example is mild steel - its strength can be doubled by a ten-times decrease in grain size). Grain shape is strongly affected by the way in which the metal is processed. Rolling or forging, for instance, can give stretched-out (or "textured") grains and in casting the solidifying grains are often elongated in the direction of the easiest heat loss. But if there are no external effects like these, then the energy of the grain boundaries is the important thing. This can be illustrated very nicely by looking at a "two-dimensional" array of soap bubbles in a thin glass cell. The soap film minimises its overall energy by straightening out and at the corners of the bubbles the films meet at angles of 120° to balance the surface tensions (Fig. 2.6a). Of course a polycrystalline metal is three-dimensional, but the same principles apply the grain boundaries try to form themselves into flat planes, and these planes always try to meet at 120°. A grain shape does indeed exist which not only satisfies these conditions but also packs together to fill space. It has 14 faces, and is therefore called a tetrakaidecahedron (Fig. 2.6b). This shape is remarkable, not only for the properties just given, but because it appears in almost every physical science (the shape of cells in plants, of bubbles in foams, of grains in metals and of Dirichlet cells in solid-state physics)."  [c.20]

Exit loss. The fluid leaving a radial-inflow turbine constitutes a loss of about one-quarter of the total exit head. This loss varies from about 2-5%.  [c.332]

As an alternate to the drivers mentioned, a gas turbine may be selected as the driver. If exhaust heat recovery or regeneration is used, the efficiency of the gas turbine is quite attractive. Unfortunately, the gas turbine is expensive and in some cases has demonstrated high maintenance cost. It should be understood that gas turbines are relatively standardized even though they cover a wide range of power and speed. They are not custom engineered to the specific application for a power and speed as is customary with st a turbines. In many applications, a speed matching gear must be included, which adds the complication of another piece of equipment, subsequently higher capital cost, and potentially decreased reliability. This gear also inherently has a high pitch-line velocity making for one of the more difficult applications. Despite some of the hurdles just mentioned, the gas turbine i s widely used in offshore installations because of its superior power-to-weight ratio over other drivers. It is quite popular for use in remote locations where the package concept minimizes the need for support equipment. As an example, the north slope of Alaska is estimated to have in excess of 1.5 mil lion horsepower in gas turbine powered compressors.  [c.147]

The need for exact target values relating to processes and products is self-evident in the design phase of process technology, equipment manufacture, and many other areas of engineering. Industrial ventilation is defined as airflow technologies to control the workplace indoor environment and emissions. It is therefore logical that the goals of industrial ventilation are unambiguously quantified. In the past the design goals of industrial ventilation have been expressed in many terms, such as airflow rates, filter classes, control velocity of a local exhaust hood, and surface temperature of a radiator. Although these are indispensable quantities in the design and realization processes, they account only indirectly for the environment within the premises. Therefore, the goal of industrial air quality should be defined using target values of the relevant contaminants occurring in the room.  [c.397]

The following equations separately outline calculating contaminant concentration inside a room with central and local recirculation. The assumptions for the room are that it has one main ventilation system with supply and exhaust air and that the contaminant concentration is the same in the whole volume (except very close to the contaminant source or in the ducts, etc.). The contaminant source is steady and continuous. The model for local ventilation assumes also one main ventilation system to which is added one local exhaust hood connected to a local ventilation system (see Chapter 10) from which all the air is recirculated. In the central system the number of inlets and outlets could vary. The flow rates are continuous and steady.  [c.613]

Local ventilation in industry usually differs from the description above in that it is connected to a local exhaust hood (Chapter 10), which has a capture efficiency less than 100%. The capture efficiency is defined as the amount of contaminants captured by the exhaust hood per time divided by the amount of contaminants generated per each time (see Section 10.5). Figure 8.3 outlines a model for a recirculation system with a specific exhaust hood. Here, the whole system could be situated inside the workroom as one unit or made up of separate units connected with tubes, with some parts outside the workroom. For the calculation model it makes no difference as long as the exhaust hood and the return air supply are inside the room.  [c.617]

This latter equation can also be used for systems without a local exhaust hood by setting the capture efficiency to zero. It could also be used to show the result of recirculation from, e.g., a laboratory fume hood with immediate recirculation. In such a hood all contaminants are generated within the hood and usually also all generated contaminants are captured, so the capture efficiency is 1. The equation demonstrates that if the  [c.617]

The principal classification made here is from the functioning point of view, i.e., how the different flow fields are intended to eliminate the contaminants. When using an exhaust hood the intention is to suck the contaminant into the hood (or prevent it from escaping the hood into the surroundings) by proper design of the flow field and the hood. When using a supply inlet, the intention is to blow the contaminant away (to an exhaust quite close or by spreading the air to an exhaust situated far away) from the volume (breathing zone, etc.) and the air inlet. With a combined system, the intention is to combine the effects of an exhaust outlet and a supply inlet to get a higher efficiency than either of them could achieve separately.  [c.812]

Walls of exhaust hood/supply inlet  [c.813]

FIGURE 10.1 Principles for the three different ways of protecting a volume by using an exhaust hood (above), a supply inlet (middle), and a combined exhaust hood and supply inlet (below).  [c.813]

An exhaust hood requires an adequate supply airflow rate (direct supply or indirect from another room and transported through a transfer opening) inside the room where the exhaust is situated. This means that the supply airflow rate should be approximately equal to the exhaust rate and that the supply devices should be placed in such a way that the incoming air does not  [c.814]

FIGURE 10.6 Definition of capture efficiency, a, M = contaminant source rate, m = contaminant transport (directly) into the exhaust hood, a — m/M.  [c.819]

The first step in designing an exhaust hood is to select the geometry of the hood. As described above, the hood should enclose the process as much as possible. Where enclosures are not possible the hood should be located as close as possible to the source. The next step is to select an appropriate hood flow rate. The most common methods are  [c.831]

This type of dependence of capture efficiency on the exhaust flow rate and cross-draft velocity has also been seen by Fletcher and Johnson who determined the capture efficiency of a flanged square exhaust hood in a cross flow.  [c.841]

It has long been recognized that the presence of a worker close to an enclosure, especially a fume cupboard, can have a significant effect on the exhaust hood performance (see Section 10.2.3.3). However, one aspect of  [c.879]

To choose a supply inlet as the local ventilation system is not common because it is difficult to design for the specific spreading of contaminants. This is usually easier with an exhaust hood. However, there are moments when large flow rates or specific flow fields are necessary to transport contaminants or for shielding from contaminants.  [c.916]

Supply inlets are also used when there is no room for an exhaust hood or when the contaminant-generation process has a form such that an exhaust  [c.916]

When using supply inlets it is more important than for exhaust hoods how the person, working with a process, is placed, relative to the contaminant source and to the inlet. It is nearly always better to keep the person between inlet and source than source between inlet and person. For supply systems it is even more efficient than for exhausts to have the flow passing in front of the person instead of from back to front. The airflow from behind the person could generate a wake, which includes the source or the generated contaminant and thereby increases the person s exposure. This phenomenon is more common with large flow rates and large supply openings than with small flow rates and small inlets. Placing the worker beside the path from the inlet to the source and on to the exhaust is a general rule. It is possible to counteract the wake around a person by using supply air, directed downward around the worker. In this case, the air is normally sucked into an exhaust hood (see Section 10.4).  [c.918]

These systems can be inside large halls and may have no fixed limits for their influence, except for some parts of the system (inlet device surface, etc.) They can also be situated inside small rooms, where walls, floors, and ceilings are the natural boundaries. The systems usually consist of one exhaust hood and one supply inlet, which interact. There are also special combinations, as two or more inlets and one exhaust hood, or one supply inlet and two or more exhausts. All of these combinations need careful design and an accurate relation between supply and exhaust flow rates and velocities. Some systems also need stable temperature conditions to function properly. All combinations are dependent on having a defined contaminant concentration in the inlet air. This usually implies clean supply air, but some systems may use recirculated air with or without cleaning.  [c.935]

Similar to supply inlets, no measurements exist for evaluating the inlets specific influence on contaminant concentration. The available measurements for the combinations are the same as for exhaust hoods, i.e., capture efficiencies and similar measures. Sometimes the performance of a combined system can be approximated from the performance of the incoming supply inlet and exhaust hood.  [c.935]

For workbenches or laboratory fume hoods with auxiliary supply it is the working person w ho could break the shielding curtain, and in that way contaminants are transported from the interior of the exhaust hood to the space where the person is situated.  [c.936]

The California Energy Commission, Energy Technology Advancement Program, and the U.S. Departmant of Energy jointly sponsored a project for reducing diesel engine fuel use and NO particulates (18). An engine-driven electrical generator uses up to 2200—3700 W (3—5 hp) from the engine drive shaft, whereas a thermoelectric generator uses only exhaust heat and coolant from the radiator. In the latter instance there is very Httle degradation of the engine power output. The unit is about 1-meter long and 25-cm in diameter, and uses bismuth teUuride thermoelectric modules. Initially more expensive than the engine driver alternator, at 1997 fuel costs, however, the device could recover this cost differential in two years in the United States or 6—8 months in Europe. It is beHeved that on-board electrical usage in tmcks for powering computer NO reduction systems, particulate trapping, etc, is only to increase in the future, making the gains from the thermoelectric system even better.  [c.509]

Goal Gasification Combined Cycle. Coal gasification combined cycle (CGCC) integrates two commercially proven technologies the manufacture of a clean-burning fuel gas from coal and the highly efficient use of that gas to produce electricity in a combined cycle power generation system. The combined cycle system has two basic components (/) high efficiency gas turbines, which bum the clean fuel gas to produce electricity (4,5), and (2) exhaust heat, which is recovered to power traditional high efficiency steam turbines to generate additional electricity. The overall system is shown in Figure 1. The combination of the gas turbine and steam turbine cycles gives CGCC systems a coal-to-power efficiency of 41—43%, based on coal higher heating value (HHV), compared with about 34—35% achieved by conventional coal combustion steam cycle power plants. Additional efficiency gains are being pursued in CGCC systems using innovations such as hot-gas cleanup in the gasification island and improved gas turbines in the power block.  [c.267]

Because fuel costs are high, the search is on for processes with higher thermal efficiency and for ways to improve efficiencies of existing processes. One process being emphasized for its high efficiency is the gas turbine combined cycle. The gas turbine exhaust heat makes steam in a waste heat boiler. The steam drives turbines, often used as lielper turbines. References 1, 2, and 3 treat this subject and mention alternate equipment hookups, some in conjunction with coal gasification plants.  [c.340]

As an example of using a Mollier diagram in defining the state of air, we can take a typical measurement from the local exhaust hood of a paper machine. Tbe temperature of the exhaust air is 82 C and its wet bulb temperature 60 "C. In Fig. 4AQd we move from the saturation curve at the point 60 °C straight up along the constant enthalpy line ( = 460 kj/kg d.a.) until we reach the isotherm  [c.91]

Braconnier, R. 1988. Bibliographic review of velocity field in the vicinity of local exhaust hood openings. American Industrial Hygienists Association Journal, vol. 49 no. 4, 18.5-198.  [c.553]

FIGURE 8.3 Model of a local recirculating system with a local exhaust hood, used for calculating the connection between contaminant concentrations, airflow rates, contamirtartt source strength, q , air cleaner efficiency, n and hood capture efficiency, a. is the concentration in the supply (outside) air c (equal to c h) is the concentration in the room Is the concentration in the returned air is the supply flow rate to the room equal to the exhaust flow rate, the recirculated flow rate (through the cleaner) is T is the time constant for the room and V is the room volume.  [c.618]

The more enclosed a process is, the easier it is to keep a low concentration in the workroom. It is usually necessary for the workers or for some equipment to have physical contact with the process, w hich could make it difficult to use complete enclosures. If it is possible to enclose the contaminant source and the tool, a total enclosure is recommended, especially if the workers only need to access the process during pauses in operation. Total enclosures may also be necessary for processes that generate highly toxic contaminants. Where total enclosures are not practicable, partial enclosures may be used. F xterior hoods are the least effective exhaust hood.  [c.815]

Flow Past a Point Sink A simple potential flow model for an unflanged or flanged exhaust hood in a uniform airflow can be obtained by combining the velocity fields of a point sink with a uniform flow. The resulting flow is an axially symmetric flow, where the resulting velocity components are obtained by adding the velocities of a point sink and a uniform flow. The stream function for this axisymmetric flow is, in spherical coordinates.  [c.840]

Rim exhausts, being one type of slot hood, use the same basic principles as given in the section on basic exhaust openings. The recommendation is to use the equations ven in the Basic Exhaust Openings section for unflanged or flanged slot hoods or elliptical openings. The most common design method, howevei uses Method B, capture velocity. The design procedure involves selecting a capture velocity. The selection depends on the generation rate and toxicity of the contaminant as well as some consideration of disturbances near the local exhaust hood. For the case of open surface tanks, the generation rate and toxicity are usually combined to determine the class of contaminant. The class is then used to select an appropriate capture velocity. The ACGIFf gives recommended capture velocities for a number of open-tank processes. F.quation (10.55) is applicable  [c.849]

One w ay to minimize or eliminate exposure to contaminants is to have a completely closed box wdth a glass or plastic panel to look through and gloves mounted in one or more walls. This type of local exhaust hood makes it possible to have a completely shielded workplace available nearly anyw here.  [c.910]

L. M. Conroy. Field Study of Local Exhaust Hood Performance Retdsed Final Report. National Institute for Occupational Safety and Health (NIOSH) Grant 5 KOI OH00078-03. February 19, 1996.  [c.914]


See pages that mention the term Exhaust hood : [c.348]    [c.254]    [c.2474]    [c.443]    [c.294]    [c.613]    [c.617]    [c.809]    [c.823]    [c.917]   
Industrial ventilation design guidebook (2001) -- [ c.0 ]