Fbc Assignment Jeffy

8/16/2019 Fbc Assignment Jeffy

1/17

FANS, BLOWERS AND COMPRESSORS

ASSIGNMENT-1

DESIGN AND APPLICATION OF

BLOWERS

SUMBITTED BY

G.Jeffy Shannon

15227001

M.Tech(R & AC)


2/17

INDUCED AND FORCED FAN APPLICATION IN COOLINGTOWER

Cooling towers are a very important part of many chemical plants. The primary task of a cool-

ing tower is to reject heat into the atmosphere. They represent a relatively inexpensive anddependable means of removing low-grade heat from cooling water. The make-up water source

is used to replenish water lost to evaporation. Hot water from heat exchangers is sent to the

cooling tower. The water exits the cooling tower and is sent back to the exchangers or to other

units for further cooling. Typical closed loop cooling tower system is shown in Figure 7.1.

Cooling Tower Types

Cooling towers fall into two main categories: Natural draft and Mechanical draft.

Natural draft towers use very large concrete chimneys to introduce air through the media.

Due to the large size of these towers, they are generally used for water flow rates above 45,000

m3/hr. These types of towers are used only by utility power stations.

Mechanical draft towers utilize large fans to force or suck air through circulated water. Thewater falls downward over fill surfaces, which help increase the contact time between the water

and the air - this helps maximise heat transfer between the two. Cooling rates of Mechanical

draft towers depend upon their fan diameter and speed of operation. Since, the mechanical draft

cooling towers are much more widely used, the focus is on them in this chapter.


3/17

Mechanical draft towers

Mechanical draft towers are available in the following airflow arrangements:

1. Counter flows induced draft.

2. Counter flow forced draft.

3. Cross flow induced draft.

In the counter flow induced draft design, hot water enters at the top, while the air is intro-

duced at the bottom and exits at the top. Both forced and induced draft fans are used. In cross flow induced draft towers, the water enters at the top and passes over the fill. The

air, however, is introduced at the side either on one side (single-flow tower) or opposite sides

double-flow tower). An induced draft fan draws the air across the wetted fill and expels it

hrough the top of the structure.

The Figure 7.2 illustrates various cooling tower types. Mechanical draft towers are avail-

able in a large range of capacities. Normal capacities range from approximately 10 tons,

2.5 m3/hr flow to several thousand tons and m3/hr. Towers can be either factory built or field

erected - for example concrete towers are only field erected.

Many towers are constructed so that they can be grouped together to achieve the desiredcapacity. Thus, many cooling towers are assemblies of two or more individual cooling

owers or "cells." The number of cells they have, e.g., an eight-cell tower, often refers to

such towers. Multiple-cell towers can be lineal, square, or round depending upon the shape

of the individual cells and whether the air inlets are located on the sides or bottoms of the

cells.

Components of Cooling Tower

The basic components of an evaporative tower are: Frame and casing, fill, cold water basin,

drift eliminators, air inlet, louvers, nozzles and fans.

Frame and casing: Most towers have structural frames that support the exterior enclosures

casings), motors, fans, and other components. With some smaller designs, such as some glass

fiber units, the casing may essentially be the frame.

Fill: Most towers employ fills (made of plastic or wood) to facilitate heat transfer by maximis-

ng water and air contact. Fill can either be splash or film type.

With splash fill, water falls over successive layers of horizontal splash bars, continuously

breaking into smaller droplets, while also wetting the fill surface. Plastic splash fill promotes

better heat transfer than the wood splash fill. Film fill consists of thin, closely spaced plastic surfaces over which the water spreads, form-

ng a thin film in contact with the air. These surfaces may be flat, corrugated, honeycombed, or

other patterns. The film type of fill is the more efficient and provides same heat transfer in a

smaller volume than the splash fill.

Cold water basin: The cold water basin, located at or near the bottom of the tower, receives

he cooled water that flows down through the tower and fill. The basin usually has a sump or

ow point for the cold water discharge connection. In many tower designs, the cold water basin

s beneath the entire fill.


4/17

Figure 7.2 Cooling Tower Types

In some forced draft counter flow design, however, the water at the bottom of the fill is

channeled to a perimeter trough that functions as the cold water basin. Propeller fans are mount-

ed beneath the fill to blow the air up through the tower. With this design, the tower is mounted

on legs, providing easy access to the fans and their motors.


5/17

Drift eliminators: These capture water droplets entrapped in the air stream that otherwise

would be lost to the atmosphere.

Air inlet: This is the point of entry for the air entering a tower. The inlet may take up an entire

side of a tower – cross flow design – or be located low on the side or the bottom of counter flow

designs.

Louvers: Generally, cross-flow towers have inlet louvers. The purpose of louvers is to equal-ze air flow into the fill and retain the water within the tower. Many counter flow tower designs

do not require louvers.

Nozzles: These provide the water sprays to wet the fill. Uniform water distribution at the top of

he fill is essential to achieve proper wetting of the entire fill surface. Nozzles can either be

fixed in place and have either round or square spray patterns or can be part of a rotating assem-

bly as found in some circular cross-section towers.

Fans: Both axial (propeller type) and centrifugal fans are used in towers. Generally, propellerfans are used in induced draft towers and both propeller and centrifugal fans are found in forced

draft towers. Depending upon their size, propeller fans can either be fixed or variable pitch.

A fan having non-automatic adjustable pitch blades permits the same fan to be used over a wide

range of kW with the fan adjusted to deliver the desired air flow at the lowest power consumption.

Automatic variable pitch blades can vary air flow in response to changing load conditions.

Tower Materials

n the early days of cooling tower manufacture, towers were constructed primarily of wood.

Wooden components included the frame, casing, louvers, fill, and often the cold water basin. Ifhe basin was not of wood, it likely was of concrete.

Today, tower manufacturers fabricate towers and tower components from a variety of mate-

rials. Often several materials are used to enhance corrosion resistance, reduce maintenance, and

promote reliability and long service life. Galvanized steel, various grades of stainless steel,

glass fiber, and concrete are widely used in tower construction as well as aluminum and vari-

ous types of plastics for some components.

Wood towers are still available, but they have glass fiber rather than wood panels (casing)

over the wood framework. The inlet air louvers may be glass fiber, the fill may be plastic, and

he cold water basin may be steel. Larger towers sometimes are made of concrete. Many towers – casings and basins – are con-

structed of galvanized steel or, where a corrosive atmosphere is a problem, stainless steel.

Sometimes a galvanized tower has a stainless steel basin. Glass fiber is also widely used for

cooling tower casings and basins, giving long life and protection from the harmful effects of

many chemicals.

Plastics are widely used for fill, including PVC, polypropylene, and other polymers. Treated

wood splash fill is still specified for wood towers, but plastic splash fill is also widely used

when water conditions mandate the use of splash fill. Film fill, because it offers greater heat

ransfer efficiency, is the fill of choice for applications where the circulating water is generallyfree of debris that could plug the fill passageways.


6/17

Plastics also find wide use as nozzle materials. Many nozzles are being made of PVC, ABS,

polypropylene, and glass-filled nylon. Aluminum, glass fiber, and hot-dipped galvanized steel are

commonly used fan materials. Centrifugal fans are often fabricated from galvanized steel.

Propeller fans are fabricated from galvanized, aluminum, or molded glass fiber reinforced

plastic.

Cooling Tower Fans

The purpose of a cooling tower fan is to move a specified quantity of air through the system,

overcoming the system resistance which is defined as the pressure loss. The product of air flow

and the pressure loss is air power developed/work done by the fan; this may be also termed as

fan output and input kW depends on fan efficiency.

The fan efficiency in turn is greatly dependent on the profile of the blade. An aerody-

namic profile with optimum twist, taper and higher coefficient of lift to coefficient of drop

ratio can provide the fan total efficiency as high as 85 –

92 %. However, this efficiency isdrastically affected by the factors such as tip clearance, obstacles to airflow and inlet shape,

etc.

As the metallic fans are manufactured by adopting either extrusion or casting process it is

always difficult to generate the ideal aerodynamic profiles. The FRP blades are normally hand

moulded which facilitates the generation of optimum aerodynamic profile to meet specific

duty condition more efficiently. Cases reported where replacement of metallic or Glass fibre

reinforced plastic fan blades have been replaced by efficient hollow FRP blades, with resultant

fan energy savings of the order of 20 – 30% and with simple pay back period of 6 to 7 months.

Also, due to lightweight, FRP fans need low starting torque resulting in use of lower HPmotors. The lightweight of the fans also increases the life of the gear box, motor and bearing

is and allows for easy handling and maintenance.


7/17

INDUCED AND FORCED DRAFT FOR AIR CONDITIONING PLANTS

Blower System manufacturer unique range of Induced Draft(ID Fans) andForced Draft(F.D.Fans) which are designed by specially developed

software and experienced design head. Induced Draft(ID Fans) and Forced

Draft(F.D.Fans) are use as High Pressure, Medium Pressure and Low

Blowers/Fans. Which generate Low Volume of air at High pressure and Medium?

Volume and Low Pressure and High Volume at very Low Pressure.We also give orSupply Induced Draft (ID Fans) and Forced Draft (F.D.Fans) to the Traders and

Trading Company in different parts in India and outside India .Also as per thereRequirements, we also take Induced Draft(ID Fans) and Forced Draft(F.D.Fans)

ord ers and repairing works. We also supply Induced Draft (ID Fans) and Forced

Draft (F.D.Fans) Spare parts.Induced Draft (ID Fans) and Forced Draft (F.D.Fans)

are suitable for various applications for Cooling, Humidification, Ventilation, Gas

exhaust Fans, Exhausters, fresh air supply, HVAC duties, Recirculation of Fresh

and Uded Air, etc.We manufactures Induced Draft (ID Fans) and Forced Draft (F.D.Fans) from M.S. as well as S.S., MS-FRP, PP-FRP, & other special

materials. Induced (ID Fans) and Forced Draft (F.D.Fans) are also offered with

different surface treatments such as epoxy paint, spray galvanising, Hard facing,

Wear liners Case Carburizing etc.

InducedDraft(IDFans)andForcedDraft(F.D.Fans)are very efficient and made

f or different types of Impellers or Rotors like Backward/forward Curved inclined bl aded, Airfoil designs, Open Type, Multiblade Type, F type, Backward curvedImpell ers/Rotors, Forward curved Impellers/Rotors, etc

Required Specifications for Induced Draft (ID Fans) and Forced Draft

(F.D.Fans):

* Air Volume

* Air Pressure

* Motor H.P.

* Blower R.P.M. * Operating Temp

* Drive Type

* Construction of Material (M.O.C.) Application of Induced Draft(ID Fans) and

Forced Draft(F.D.Fans)


8/17

Ceramic and Refractories Industries, Chemical Factories, Cement Plants, Crucible

F urnaces, Furnaces like Oil, Gas, Cupola ,Furnaces, Flour Mills, Rolling Mills,Boilers, Textile Mills, Cattle Feed Plants, Pharmaceutical Industries, Fertilizer

Industries, Plastic Machinery Plants, Hot Mix Plants, Iron and Steel Plants, and

many more.

USE OF INDUCED DRAFT (ID FANS) AND FORCED DRAFT (F.D.FANS):

As Supply and Exhaustfans in Ventiiation systems, in air handling units for air

Conditioning systems, in cold storage plants, for fume extraction in industrial

Plants, Industrial Blowers/Fans are widely used in Ventilation, Pollution Control,Fume Extraction, Dust collection, I.D/F.D/P.A fans for Boilers and Furnaces, etc.

INDUCED DRAFT(ID FANS) AND FORCED DRAFT(F.D.FANS)

FEATURES:

High efficiency, Low sound level, Compact Design, Large sizes can be dismantled, More Air with less HP, Easy in operation, Smooth

in Running, Several versions available, etc.

INDUCED DRAFT (ID FANS) AND FORCED DRAFT (F.D.FANS) ARE

AVAILABLE IN THREE DIFFERENT DRIVES:

DIRECT DRIVE INDUCED DRAFT (ID FANS) AND FORCED DRAFT

(F.D.FANS):

All direct motor drive Induced Draft (ID Fans) and Forced Draft(F.D.Fans) Are supplied with suitable Electric motor with Fan cooling and alsoFlame Proof. In Induced Draft(ID Fans) and Forced Draft(F.D.Fans), Impeller

are Directly mounted on Shaft of Electric motor. Electric motor in direct drive

Blowes are Mounted on M.S. Fabricated Base Plate.

BELT DRIVE INDUCED DRAFT (ID FANS) AND FORCED DRAFT

(F.D.FANS):

All Belt driven Induced Draft (ID Fans) and Forced Draft (F.D.Fans) are Provided with EN8 Steel shaft extension running in Ball bearing of diffrent types

Like Pillow Block Pedestal, Sleeve Type Pedestal, Single bearing Type, etc.Induced Draft (ID Fans) and Forced Draft(F.D.Fans) are provided with V type or

Flat Pulley of suitable size. Complete Shaft and Bearign systems are mounted onM.S. Fabrica ted Base Plate. Induced Draft(ID Fans) and Forced Draft(F.D.Fans) isalso available Aluminum disc for air cooling of bearings.

Couple Drive Induced Draft(ID Fans) and Forced Draft(F.D.Fans):

All motor coupled Industrial Blowers/Fans are supplied with suitable couple

set as per blower capacity. The Bearing and Shaft system is same as Belt Drive.


9/17

BOOSTER SYSTEM A booster pump is a machine which will increase the pressure of a

fluid, generally a liquid. It is similar to a gas compressor, but generally a

simpler mechanism which often has only a single stage of compression,and is used to increase pressure of an already pressurised gas. Two- stage

boosters are also made.[1] Boosters may be used for increasing gas

pressure, transferring high pressure gas, charging gas cylinders and

scavenging.

CONSTRUCTION AND FUNCTION

Booster pumps are usually piston or plunger type compressors. A single-

acting, single-stage booster is the simplest configuration, and comprises a cylinder,

designed to withstand the operating pressures, with a piston which is driven backand forth inside the cylinder. The cylinder head is fitted with supply and discharge

ports, to which the supply and discharge hoses or pipes are connected, with a non-return valve on each, constraining flow in one direction from supply to discharge.

When the booster is inactive, and the piston is stationary, gas will flow from the

inlet hose, through the inlet valve into the space between the cylinder head and the

piston. If the pressure in the outlet hose is lower, it will then flow out and towhatever the outlet hose is connected to. This flow will stop when the pressure is

equalised, taking valve opening pressures into account.

Once the flow has stopped, the booster is started, and as the piston withdraws along the cylinder, increasing the volume between the cylinder head

and the piston crown, the pressure in the cylinder will drop, and gas will flow in

from the inlet port. On the return cycle, the piston moves toward the cylinder head,decreasing the volume of the space and compressing the gas until the pressure is

sufficient to overcome the pressure in the outlet line and the opening pressure ofthe outlet valve. At that point, the gas will flow out of the cylinder via the outlet

valve and port.

There will always be some compressed gas remaining in the cylinder and

cylinder head spaces at the top of the stroke. The gas in this "dead space" will

expand during the next induction stroke, and only after it has dropped below the


10/17

supply gas pressure, more supply gas will flow into the cylinder. The ratio of the

volume of the cylinder space with the piston fully withdrawn, to the dead space, isthe "compression ratio" of the booster, also termed "boost ratio" in this context.

Efficiency of the booster is related to the compression ratio, and gas will only be

transferred while the pressure ratio between supply and discharge gas is less thanthe boost ratio, and delivery rate will drop as the inlet to delivery pressure ratio

increases.Delivery rate starts at very close to swept volume when there is no pressure

difference, and drops steadily until there is no effective transfer when the pressure ratio reaches the maximum boost ratio.[1] Compression of gas will cause a

rise in temperature. The heat is mostly carried out by the compressed gas, but the booster components will also be heated by contact with the hot gas. Some boosters

are cooled by water jackets or external fins to increase convectional cooling by theambient air, but smaller models may have no special cooling facilities at all.

Cooling arrangements will improve efficiency, but will cost more to manufacture.Boosters to be used with oxygen must be made from oxygencompatible materials,

and use oxygencompatible lubricants to avoid fire.

POWER SOURCES Boosters may be driven by an electric motor, hydraulics, low or high

pressure air or manually by a lever system. Those powered by compressed air are

usually linear actuated systems, where a pneumatic cylinder directly drives thecompression piston, often in a common housing, separated by a seal. A high

pressure pneumatic drive arrangement may use the same pressure as the output pressure to drive the piston, and a low pressure drive will use a larger diameter

piston to multiply the applied force.

MANUFACTURERS Boosters are manufactured by Haskel, Draeger and others. Rugged and

unsophisticated models (KN-3 and KN-4) were manufactured for the Soviet ArmedForces and surplus examples are now used by technical divers as they are

relatively inexpensive and are supplied with a comprehensive spares and tool kit.


11/17

5. SPECIAL DESIGN AND APPLICATION OF BLOWERS

Ore Processing: - Cake Blowing, Combustion air, Vacuum filtration

Distilleries: - Liquor moving, Conveying of grains etc.

Fishery: - Aeration of fish Tanks, Removal of eggs from fish, Agitation of

washing tanks

Glass: -Pneumatic Convey of vac. Holding of sheet glass for transfer, Evacuation of

test chamber

Steel miles – Blast furnace air supply, coke oven exhauster, fly ash collections,

combustion air for open health furnace.

Coal: - Coal Washing, Tunnel ventilation, Dust Collection Conveying :- Pneumatic, Vacuum, or combination for material such as coal, salt,

cement ,sand, feeds, fly ash, sugar, starch, carbon black, transfer material fromtrucks, hoppersFood Processing: - Flower / sugar conveying,

Sugar: - Pneumatic Conveying, sulphdization, Aeration of storage bins, vacuum

Filtration.


12/17

UpcastShaft

DowncastShaft

Mine Ventilation System

Ventilation is the control of air movement, its amount, and direction. Although it contributes noth-ing directly to the production phase of an operation, the lack of proper ventilation often will causelower worker efficiency and decreased productivity, increased accident rates, and absenteeism.

Air is necessary not only for breathing but also to disperse chemical and physical contaminants(gases, dusts, heat, and humidity). In the U.S., as well as in the rest of the world, mineventilation practice is heavily regulated, especially in coal and gassy (noncoal) mines, and other statutes relateto air quantities required to dilute diesel emissions, blasting fumes, radiation, dusts, battery emis-sions, and many other contaminants.

To ensure adequate ventilation of a mine, provision is made for suitable paths (airways oraircourses) for the air to flow down the mine to the working places and suitable routes out of themine when it has become unsuitable for further use. The primary ventilation system thus consistsof an intake or intakes (or downcasts) through which the fresh air passes, the mine workings, andan exhaust or exhausts (or upcasts) where the air passes after having ventilated the working placesof the mine. Mine fans can be installed on the intake airshaft, return airshafts, or both, either on the

surface or underground (Figure 9-1).

Mine Fan

Mined out Area

D 1

R2

R Main Levels 3

D

Figure 9-1. Basic ventilation system underground where D is a ventilation door or airlock, R is a mine regulator and 1, 2, 3 are working places with a surface exhaust fan.

To maintain adequate ventilation through the life of a mine, careful advance planning isessential. Advance ventilation planning involves the consideration of two principal factors: (1) thetotal volume flow rate of air required by the mine, and its satisfactory and economic distribution,and (2) the pressure required by the mine fan(s). A well designed ventilation system should beeffective, flexible, and economical.


13/17

1 . Mine System and Control Devices

A well designed and properly implemented ventilation system will provide beneficial physiologicaland psychological side effects that enhance employee safety, comfort, health, and morale. In planning a ventilation system, the quantity of air it will be necessary to circulate to meet all healthand safety standards must be decided at the outset. Once the quantity required has been fixed, thecorrect size of shafts, number of airways, and fans can be determined. As fresh air enters the

system through the intake airshaft(s) or other connections to the surface, it flows along intakeairways to the working areas where the majority of pollutants are added to the air. These includedust and a combination of many other potential hazards, such as toxic or flammable gases, heat,humidity, and radiation. The contaminated air passes back through the system along returnairways. In most cases, the concentration of contaminants is not allowed to exceed mandatorythreshold limits imposed by law. The return (or contaminated, exhausted) air eventually passes back to the surface via return airshaft(s), or through inclined or level drifts.

Air always flows along the path of least resistance, but this may not be where it is required foruse. To direct the air where it is needed, ventilation devices are necessary; the primary means of producing and controlling the airflow for the entire system are mine fans (either in the form ofsingle fan installation or multiple fans). In addition, many other control devices also are necessaryfor effective underground air distribution:

1. Stoppings - Temporary or permanent Stoppings are simply air walls made of masonry, concrete blocks, pre-fabricated steel, gob

walls, fire-proofed timber blocks, or any other material used to channel airflow for effective airdistribution. Depending on the size of mining entries, stopping sizes range from as small as 4-ft by 20-ft in low coal to as large as 30-ft by 40-ft in limestone mines.

2. Overcast/undercast Overcasts are air bridges where intake and return airways are required to cross each other

without mixing. They could be constructed of masonry, concrete blocks, or pre-fabricated steel.

3. Regulator Regulators are commonly used to reduce the airflow to a desired value in a given airway or

section of the mine. Depending on its permanency and the pressure differential to beexperienced across the regulator, materials used in the construction of regulators range from asimple brattice sheet blocking the airway to a sliding shutter in a stopping.

4. Man-doors These are generally steel access doors mounted in stoppings between intake and return

airways.

5. Air locks When access doors between intake and return airways are necessary and their pressure

differential is high, man-doors generally are built as a set of two or more to form an air-lock.This prevents short-circuiting when one door is opened for passage of vehicles or personnel.

The distance between doors should be capable of accommodating the longest train of vehiclesrequired to pass through the air-lock.

6. Line brattice/Vent tubing As a short term measure, fire-resistant line brattices may be tacked to roof, sides, and floor

in underground coal mines to provide temporary stoppings where pressure differentials are lowin and around working areas. For metal and non-metal mines, vent tubing is generally used in


14/17


15/17

9. Mine Ventilation Systems

Workings

Workings

Intakes

Returns

Intakes

(a) (b)

Figure 9-2. Basic ventilation systems (a) U-tube and (b) through-flow (McPherson, 1993).

For Stratified Deposits

The vast majority of underground mines extracting tabular forms of orebodies (coal, potash, salt,limestone, etc.) normally use one of two methods, longwall or room-and-pillar mining. While ac-tual layouts can vary significantly from mine to mine and region to region according to localgeological conditions, the basic design for these two methods remains the same. The followingsections describe the airflow distribution system usually employed.

a) Longwall systems

Two factors that have significantly influenced the design of the longwall ventilation systems are thecontrol of methane or other gases that accumulate in the gob area (Haake, et al., 1985; Highton,1980; McPherson, 1993; den Drijver, et al., 1997; Diamond, 1997; Dziurzynski and Nawrat,1997) and the increasing high rate of rock breakage on heavily mechanized longwalls that has ex-

acerbated the production of dust, gas, heat, and humidity (Uchino and Hirago, 1984; Battino andMitchell, 1985; Organiscak and Jankowski, 1996; Colinet, et al., 1997; Stokes and Tuck, 1997).

Figure 9-3 depicts some of the commonly used ventilation layouts used on longwall sections.In the U.S., a minimum of two entries is required, while single entry longwalls are primarily employed in European coal mines (Fuller, 1989; McPherson, 1993).

System layouts become more complex when mining under inclined, thick, and gassy coalseams with frequent faults. Narrower and shorter panels are necessary to cope with these difficultconditions. There also have been other type of layouts to accommodate specific geological condi -tions (Fuller, 1989 and Tien, 1995).


16/17


+

+

+

+

(a) (b) (c) (d)

Figure 9-3. Classifications of longwall ventilation systems (a) single-entry advancing; (b) single-entry retreating; (c) single-entry retreating with back bleeder; (d) double-entry retreating with back bleeder (after McPherson, 1993).

(e) (f) (g)

Figure 9-3a. Classifications of longwall ventilation systems (e) Y-system; (f) double-Z system; (g) W-system. (after McPherson, 1993).

b) Room and pillar systems

Figure 9-4 shows the two methods of ventilating a room and pillar development panel in a coalmine where multiple entries are driven. Figure 9-4a is the directional, or W-system, in which in-take air courses are airways in the central portion of the panel, with return airways on both sides,often referred to as the fish-tail method. The method in Figure 9-4b is the unidirectional system inwhich intake and return are located on both sides of neutral airway (belt and track).

In both cases, the conveyor belt and/or track are located in the middle, with a brattice curtain atthe end to regulate the airflow. In U.S. coal mines, unless a special petition is approved by MSHAin advance, air in these entries is not supposed to be used to ventilate working areas under normalcircumstance, so they are directed directly to the return airway through a regulator. Advantages ofthis system include: the airflow splits at the end of the panel, with each airstream ventilating the op-erational rooms sequentially over one half the panel only, resulting in less leakage due to less pres-sure differential across the stopping; and any gas emission will be flowing automatically to returnairways. An obvious disadvantage is that the number of stoppings required is double that of theuni-directional system. The air leakage also is twice as much due to the extra stoppings(McPherson, 1993).


17/17

R e t u r n A i r

I n t a k e A i r

I n t a k e A i r

R e t u r n A i r

I n t a k e A i r

R e t u r n A i r


(a) (b)

Figure 9-4. Room and pillar development with line brattices to regulate airflow in conveyorbelt entry: (a) bi-directional system; (b) uni-directional system.

A uni-directional system should offer a higher volumetric efficiency at the face because of thereduced number of stoppings. A disadvantage is that the higher volume also has a higher ventila-tion pressure, which in turn offers higher leakage.

c) Mine with large-size entries

Typically, mines with large-size entries (e.g., limestone, salt, and oil shale) require large volumesof ventilating air (between 350,000 to 500,000 cfm, depending on specific conditions) to ade-

quately ventilate underground workings. In trying to meet this requirement, two major problemsare usually encountered: (1) excessive air leakage through stoppings and (2) local air recirculation, both of which are caused by improperly constructed (and maintained) stoppings, or the lack ofstoppings in many cases, and both can adversely affect the underground working environment.Oftentimes, mine management are reluctant to construct an adequate number of stoppings, either because of technical problems or the associated expenses.

Air is used to dilute diesel exhaust and to maintain a minimum air velocity in large-dimensionairways in order to avoid air stratification, and every reasonable measure has to be taken to ensurethat fresh air is effectively delivered to working places where air is needed. The cost of not main-taining adequate ventilation results in a poor working environment that not only is in violation offederal and state regulations, but can adversely affect worker performance and morale. To deliverfresh air to working places over large distances, effective air distribution system is essential. They

can either be: (1) conventional large-scale stoppings using pipes with metal sheeting, brattice andwire, a muckpile, etc. or (2) adopting a modular type pillar layout.

Date post:	06-Jul-2018
Category:	Documents
Upload:	jeffy-shannon
View:	218 times
Download:	0 times

Fbc Assignment Jeffy

Documents