sistemas de carga y descarga de arena para locomotoras fra

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AREMA

PART 6

LOCOMOTIVE SANDING FACILITIES

2010

TABLE OF CONTENTS

6.1 Introduction 6-6-3 6.1.1 General 6-6-3 6.1.2 Safety Provisions 6-6-3

6.2 Sanding Facility 6-6-4 6.2.1 Capacity 6-6-4 6.2.2 General Platform Layout 6-6-4 6.2.3 Storage 6-6-5 6.2.4 Unloading 6-6-7 6.2.5 Transfer from Storage to Servicing Tanks 6-6-7

6.2.6.1 General 6-6-7 6.2.6.2 Gravity Transfer 6-6-8 6.2.6.3 Pneumatic Transfer 6-6-8 6.2.6.4 Mechanical Transfer 6-6-8

6.3 Sanding System Types 6-6-9 6.3.1 Gravity Overhead Systems 6-6-9

6.3.1.1 General 6-6-9 6.3.1.2 Sand Tower System 6-6-9 6.3.1.3 Design Considerations 6-6-10

6.3.2 Gantry Crane System 6-6-11 6.3.2.1 General 6-6-11 6.3.2.2 Design Considerations 6-6-12

6.3.3 Pneumatic Conveying Systems 6-6-12 6.3.3.1 General 6-6-12 6.3.3.2 Types of Flow 6-6-14 6.3.3.3 Design Considerations 6-6-15

6.4 Sanding Components 6-6-17 6.4.1 Air Supply System 6-6-17

6.4.1.1 Air Requirements 6-6-17 6.4.1.2 Air Pressure 6-6-17 6.4.1.3 Compressor Systems 6-6-18 6.4.1.4 Compressor Building Considerations 6-6-20

6.4.2 Air Dryers 6-6-20 6.4.3 Piping System 6-6-21

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6.4.4 Sand Cocks 6-6-22 6.4.5 Nozzles 6-6-22 6.4.6 Electrical 6-6-22 6.4.7 Lighting 6-6-23 6.4.8 Automation and Instrumentation 6-6-23

6.5 Environmental Considerations 6-6-24 6.5.1 Waste Sand 6-6-24 6.5.2 Air Quality 6-6-24

6.5.2.1 General 6-6-24 6.5.2.2 Tank/Silo Venting 6-6-24 6.5.2.3 System Venting 6-6-25 6.5.2.4 Bag House Venting 6-6-25

6.6 References 6-6-26 6.6.1 Codes 6-6-26 6.6.2 Publications 6-6-27

LIST OF FIGURES

6-6-1 Typical Sanding Tower System Diagram 6-6-28 6-6-2 Overhead Gravity Sand Tower System 6-6-29 6-6-3 Gravity Crane Sanding System 6-6-30 6-6-4 Pneumatic Conveying Sanding System 6-6-31 Dr

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SECTION 6.1 INTRODUCTION

6.1

6.1.1 GENERAL

A. The Federal Railroad Administration (FRA) requires that locomotives have sanders that deposit sand on each rail in front of the first power operated wheel (49CFR229.131). Locomotive sand storage boxes are usually filled in the locomotive service areas of a yard. Sand dispensing systems are often integrated with the fueling facility or diesel repair facility. Many types of systems are available for storing and dispensing sand to the locomotive. Location and capacity requirements for sanding facilities should be considered along with safety and environmental factors when selecting or designing new or reconditioned sanding facilities.

B. In general, sand is received and stored, then transported to the dispensing point by gravity or pneumatic conveying methods. Three types of systems available to accomplish this: 1) sanding tower, 2) gantry crane, and 3) pneumatic conveying system. Combinations of these three systems are also possible.

C. The type of sand used will dictate, to a point, the type of sand facility to be installed (1975). The type of sand used is specified by the individual railroads, and usually depends on local availability. The designer should verify the type of sand used. Recycled materials, including glass, as well as dust suppression chemicals may be in use, and the system must be designed to accommodate them. Delivery time and availability are important and must be determined independently for each yard.

D. Locomotive sand storage boxes vary in capacity. Sand boxes for freight locomotives range from 40 60 cubic feet. Passenger and commuter locomotives range from 20 50 cubic feet. Switcher locomotives typically range from 10 30 cubic feet in capacity. The capacity required should be determined based on the type of equipment used at each location.

6.1.2 ENGINEERED SAFETY PROVISIONS

A. Sand systems should be designed and built in accordance with all applicable workplace safety requirements as well as any requirements of the owner that are more stringent than applicable codes.

B. General issues that should be considered in sanding system installations include fall protection, safe access, electrical hazards, and platform slip, trip, and fall hazards.

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C. Many sanding systems require the operator to climb on top of the locomotive sand tank for inspection and filling. In all cases, the operator must climb onto the locomotive to inspect the level of sand in the sand tank. With some systems, the operator must also climb onto the locomotive sand tank to connect the fill hose. This can be complicated by adverse weather conditions.

D. Access to towers and silos should be provided with caged ladders equipped with a lockout device on the bottom of the cage to prevent unauthorized access. Platforms on towers and silos should be framed of steel or aluminum with open grating used for a slip-resistant walk surface. Platforms should include handrails that, as a minimum, comply with OSHA requirements. On the tops of towers and silos where the installation of grating may be impractical, slip-resistant coatings should be applied.

E. All systems should be designed with either integral fall protection or a platform with railing to access the locomotive sand chambers.

F. Pits used to unload sand from rail cars or trucks present unique hazards. Designers should consider pits to be confined spaces and accommodate them as such. Amenities that can minimize the hazard include adequately sized access points. Pits should be watertight, but they should also include a generous drain to a grit chamber and industrial wastewater treatment system. Pits inevitably fill with runoff from groundwater, storm water, wash water, or snowmelt. Pits should also include adequate lighting with multiple fixtures as well as proper venting to minimize the buildup of hazardous fumes.

SECTION 6.2 SANDING FACILITY

6.2.1 CAPACITY

A. The number of locomotives serviced per day, the amount of sand required for an average locomotive fill operation, and historical data on the amounts of sand used, will help determine the amount of storage required as well as the capacity of the distribution points. Locomotives in mountainous areas generally require more sand at servicing facilities. Some yards only need to fill the lead locomotive sand box, while other facilities service all locomotives in a consist.

B. Other issues that can determine required capacity include delivery distance, cost, quantity of sand deliveries, lead time for delivery after an order is placed, delivery methods (truck or railcar), and unload methods (mechanical, gravity, pneumatic).

6.2.2 GENERAL PLATFORM LAYOUT

A. Knowledge of common consist arrangements in a yard can help determine the configuration and size of a system. Multiple spot sanding systems should provide

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full coverage of all anticipated consist configurations without the need to re-spot a consist.

B. If space is available, the sanding and fueling spots should be on the same track, but no closer than 50 feet. This configuration allows operations to be performed quickly and in sequence without fouling one another (1975).

C. Single sand tower installations can be located at one end of the service platform or on a separate track. If the tower is located at the end of a service track, care should be taken to position the tower so that consists do not require re-spotting for sand filling after receiving fuel and other services.

D. Gantry crane systems can be located along a service platform if space permits, or inside a locomotive servicing shop.

E. Pneumatic systems include distribution stations, which are generally arranged on the platform between other services such as fueling, lube oil, and water. Distribution stations should be spaced out adequately to provide full coverage of the sanding platform.

F. Storage silos can be located away from the distribution points if a conveyance method is in place to move the sand from storage to distribution.

G. Storage silos should be located adjacent to the delivery track if sand is delivered by rail. If sand is delivered by truck, access into and out of the silo area should be considered. Minimize the crossing of tracks by delivery trucks and avoid fouling of track by the truck or operator during the unload process. Consider the truck turning radius when designing access to the silo.

H. For railcar unloading, the unload track should be arranged to cause minimal interference with the movement of trains and locomotives through the yard. It should be an independent track used only for that purpose (1975).

6.2.3 STORAGE

A. The sand requirement at a location is an important factor affecting storage capacity. Availability of the material should also be considered when determining storage capacity (1975).

B. Condensation can be a potential problem when bulk dry sand is stored in large quantities where turnover is slow and humidity is high. Under such conditions, the sand tends to take up moisture, resulting in an unsatisfactory condition for flowing. Where sand turnover is frequent, absorption of moisture is not a serious problem (1975). Consider installation of a dry air purge system in humid climates.

C. For truck-fed gravity silo systems (delivered sand blown up to the silo in dilute phase by truck) the silo should have at least two weeks capacity when the sand order is placed. Preferably, the silo should be at least 25% larger than the volume

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of a delivery truck and trailer (740 cubic feet), but orders should be based on peak usage and delivery time. Silo capacity should include at least one week buffer time in case complications arise with sand delivery.

D. Concrete or steel storage tanks render satisfactory service for dry sand. (1975)

E. The service tank at track side is generally constructed of steel and mounted on a steel column or is an integral part of the sand storage silo, at a suitable elevation to permit loading sand into locomotive sand boxes by gravity through pipe and hose connections. Capacities of 5 to 10 tons are satisfactory for these latter tanks, with the size determined by the quantity of sand handled (1975).

F. The tank should be equipped with approved signals to indicate when the tank is full and when the point of depletion is approaching (1975). Storage tanks should include level sensors to indicate full and empty states. Low alarm points should be placed to allow ample time for sand delivery to the site. High alarm points should be placed to allow time for the fill process to be shut down.

G. Equipment is available to transfer sand automatically from the dry storage tank to the overhead smaller servicing tank. This eliminates the necessity to assign labor to keep sufficient sand in the servicing tank or to delay locomotive sanding because of insufficient sand in the servicing tank. The importance of the operation should determine whether such a refinement is justifiable (1975).

H. Transfer from storage to service tanks is handled by installing the dry sand storage tank at an elevation sufficient to permit the sand to discharge by gravity into an elevating tank for distribution to the servicing tanks. This operation can be handled automatically, thus reducing labor costs (1975).

I. Dry sand storage tanks can be fitted with dry air purge systems to maintain sand integrity, where appropriate. These systems bleed dry air (to a dew point of -40F) into the headspace of the tank to keep the moisture level down.

J. Storage tanks should contain manways and internal ladders for tank maintenance. Manways should be hinged and provide access if sand begins to clump.

K. Below grade storage vaults and pits are not generally used for storage but rather for railcar unloading and placement of transfer equipment.

L. Storage tanks should provide proper air venting during fill procedures, as well as air intake during sand discharge. Tank airspace inbreathing and outbreathing should be considered during temperature changes.

M. The movement of sand from the storage silo may be impeded by common bulk material storage problems including arching, bridging, clinging, and rat-holing. Storage tanks with cone bottoms and bottom discharge points could include a means to get the sand flowing should any of these problems occur. Methods may include mechanical ramming devices that impact the side of the tank, sonic

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devices, and air sweep or air infusion devices that inject air between the tank sidewall and the stored material.

6.2.4 UNLOADING

A. Sand is delivered by truck or railcar. Verify the requirements of each location.

B. If air is used to elevate the dry sand, the elevated tank used in such an arrangement should be equipped with an appropriately sized air release at its top to relieve the air as the tank fills with sand (1975). Service tanks into which sand is loaded by air should be equipped with approved dust arrestors to release the air and retain the dust within the tank (1975).

C. Sand should not be unloaded in the open environment during wet weather (1975).

D. Dilute phase conveyance systems are generally used by delivery trucks to blow sand into elevated storage tanks by means of on-board blowers. Verify the maximum conveyance distance and height with local delivery companies. Distance from the truck to the silo tower determines unload time. Unload time is crucial, because the delivery truck and/or hose may foul a track during delivery. If neither track may be fouled for the delivery time, the fill pipe may be routed to the outside of the sanding tracks.

E. Fill alarms must give the truck operator enough time to shut off the sand supply. If a control valve shuts off sand flow to the tower, as opposed to the operator shutting off the sand supply, the operator must manually remove the sand remaining in the delivery hose. Therefore, operators prefer alarms that notify the truck operator when the silo is nearly full.

F. The availability of sand delivery trucks and distance to the source must be considered when determining whether sand delivery trucks are the proper method of sand delivery and what volume of sand silo to specify.

6.2.5 TRANSFER FROM STORAGE TO SERVICING TANKS

6.2.5.1 General

A. Because sand is generally stored in a storage silo away from the dispensing tower or tank, a method must be employed to transfer the sand from storage to the point of use.

B. If a sanding facility consists of a single gravity sand tower, direct fill lines can be

used to transfer sand from the vendors truck directly to the storage tank on the sand tower. A transporter can also be used to convey sand from storage to a single gravity sand tower.

C. If a sanding facility consists of multiple gravity sand towers, a convenient method

must be employed to fill the towers with sand. Where space and geometry allow,

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direct fill lines can be used to transfer sand from the vendors truck directly to the storage tank on each sand tower. More commonly, a storage silo and transporter are required to transfer sand to each tower on the platform. The storage silo feeds by gravity into a pressurized transporter. Level controls in the individual sand towers determine when the transporter should convey sand.

D. In gantry crane systems, the storage silo is generally placed near the platform so

that the gantry crane can travel to the storage silo. The gantry crane hopper receives sand from the storage silo by gravity. This necessitates storing the sand at an elevation higher than the gantry crane.

6.2.5.2 Gravity Transfer

A. If gravity is used to transfer sand from storage to the distribution point, then the storage silo must be higher than the receiving tank. Care should be taken to design the pipe that conveys the sand at a slope greater than the angle of repose for the type of sand being used.

6.2.5.3 Pneumatic Transfer

A. Sand can be transferred from storage to distribution pneumatically. A common arrangement is a transfer or transport tank (also known as a blow tank or sand pump) located underneath the storage silo. Sand enters the transport tank from the silo by gravity. The transport tank is pressurized, and the sand is conveyed to the distribution point(s).

B. The nozzles for a simple transfer tank arrangement include a sand inlet, vent,

pressurization and sand outlet. The inlet and vent valves are opened and the outlet and pressurization valves are closed during filling. The valve positions are reversed to transfer sand. A valve is usually not needed on the sand outlet because sand flow can be stopped by simply isolating the pressure.

C. Due mainly to differences in sand flow velocities, dilute phase systems generate

more wear on system components. Dilute phase velocities range from 1,000 to 3,000 feet per minute and dense phase velocity is nearly 100 feet per minute. Dilute phase systems are typically more complex, but dense phase flow can be difficult to control and is susceptible to clogging. Dense phase flow typically requires higher pressure and may require varied pressure if multiple receiving tanks and varying distances are used.

6.2.5.4 Mechanical Transfer

A. Mechanical means such as bucket elevators and conveyors can be used to elevate sand from lower storage points to higher distribution or storage silos. Mechanical systems generally require more maintenance due to the movement of parts.

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SECTION 6.3 SYSTEM TYPES

6.3.1 GRAVITY OVERHEAD SYSTEMS

6.3.1.1 General A. Gravity sand systems utilize gravity to transfer sand from an elevated distribution

point to the locomotive sand box. These include single spot towers located between two tracks, single spot towers that straddle a single track, systems that employ multiple towers along a platform, and gantry crane type systems.

B. Height is the primary distinguishing attribute of gravity overhead systems. Care must be taken while maintaining equipment on top of the towers. Hoists or winches may be located outside the handrail. In order to provide a safe working environment for maintenance workers, thought should be given to mounting equipment outside the handrail on retractable arms that can be rotated back inside the handrail for inspection and maintenance.

C. Gravity sand towers should be equipped with load arrest systems to prevent the

uncontrolled descent of a dispensing arm in case of a broken arm support. The load arrest system should be sized for the load of the arm plus any impact load. Care should be taken to design the entire load arrest system for a similar capacity. This could include the mounting brackets, load arrestor, and any additional cables or connections.

D. Occasionally moisture causes the sand in towers to clump, and maintenance

personnel must climb the sand tower to clear the blockage. This usually requires the personnel to climb 20 to 30 feet up the tower and break the sand loose through an access port.

6.3.1.2 Sand Tower System

A. Sanding towers are a common method of filling locomotive sand tanks. Sand is delivered to the tower and fed to a storage silo above and adjacent to the tracks. An arm is lowered, a valve opened, and sand flows by gravity down the inclined arm to the locomotive tank. When the tank reaches the full level, the valve is closed and the arm retracted.

B. Single spot towers located between the tracks generally consist of a lower support

constructed of rolled steel topped by a storage tank constructed of rolled steel. Because the tower is located between the tracks, care must be taken to minimize the exposure to the clearance envelope for each track. This results in a tall and relatively narrow storage tank.

C. Single spot towers that straddle a single track generally consist of a structural

steel support frame erected to hold a large storage tank constructed of rolled steel.

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Because the tower straddles the track, the tank can be much wider and shorter to achieve the same capacities provided by a tower located between the tracks. Care must be taken to minimize the exposure to the clearance envelope for the track being served as well as any adjacent tracks.

6.3.1.3 Design Considerations

A. Gravity dispensing lines should be not less than 2!-inch pipe leading at an angle of 45 degrees from the overhead servicing tank to the sanding platform. These pipes should not encroach on the clearance lines. These delivery pipes are generally supported on posts above the platform or from the tower (1975).

B. Valves should be placed in the gravity dispensing lines at the service tank

connection so that sand can be shut off when necessary to work on the delivery pipe, hose or nozzle. Suitable lines should be provided for reaching top sand boxes on certain types of switcher locomotives (1975).

C. The flow of the sand must be controlled to prevent spillage at the sand box where

it is loaded. Various types of nozzles are available. Care should be exercised to obtain a weatherproof unit. The size of the nozzle should be given consideration to be sure it will fit into the sand box (1975).

D. Swivel connections should be used at the transition from the fixed dispensing pipe

extending from the storage tank to the dispensing line that feeds the locomotive. The connection used is typically a swivel valve or bucket valve. These valves allow the upper pipe to remain fixed while allowing the lower pipe to move both vertically and horizontally.

E. Directional changes of pipe should be accomplished with wye or tee connections

to permit cleaning or rodding of the line in case of stoppage. F. Level controls should be included on the sand tower or storage tank. At a

minimum, the levels to be monitored include high level, low level, and low-low level. The most reliable controls are generally diaphragm switches energized by the pressure of the sand or paddle switches that are raised or lowered by the changing sand level. At the location of the level controls, deflector plates should be installed on the interior of the tank above the flanges to minimize the effect of the sand overhead load on the controls themselves.

G. A cleanout hatch, generally 24 inches in diameter, should be located in the cone

of the tank. This will allow the removal of the entire tank of sand if it gets wet. H. The swivel valve or bucket valve can be a susceptible point for moisture to

infiltrate the tank. Consideration should be given to shrouding the valve in a flexible impermeable boot that will prevent the introduction of moisture into the valve.

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I. A manway should be located on top of the storage tank to allow access to the

interior of the tank for maintenance of equipment and troubleshooting. The tank should be equipped with a fixed ladder on the inside shell of the tank directly below the access point.

J. The fill pipe for the storage tank should be routed through the underside of the

cone core and to the top of the storage tank. At the underside of the top of the storage tank, a replaceable wear plate should be installed to minimize wear on the tank.

K. Where the dispensing arms are raised and lowered, a yoke should be employed to

limit the arms horizontal movement. The yoke also serves to guide the arm back up into the final at-rest position.

L. The vertical position of the arm can be adjusted with cable winches, chain hoists,

hydraulics, pneumatics, or counter weights. Counterweights are considered the least safe of all options and are rarely used in new installations. Hydraulics and pneumatics provide maximum control over the arms movements but can be expensive and require more maintenance. The most common method to raise and lower arms is the use of cable wire winches or chain hoists. Where chain hoists are used, a receptacle should be included to accept the chain as the arm is retracted. The receptacle will prevent the retracted chain from being blown by the wind and becoming entangled with or damaging other equipment. The receptacle should have a perforated bottom that is strong enough to hold the chain but also to allow rain or snow to drain out.

M. The horizontal position of the arms is generally adjusted manually by the operator

on the locomotive. Hydraulic and pneumatic systems are available to adjust the arms horizontally.

6.3.2 GANTRY CRANE SYSTEMS

6.3.2.1 General

A. Power supply is an area of concern for gantry crane systems. Inside a shop or covered service area, the gantry rides on an overhead rail and is powered using bridge conductors routed along the crane runway. Outdoor gantry systems that travel on a rail installed at grade are powered by a cable mounted on a retractable cable drum. Care should be taken to not run over the cable when relocating the gantry.

B. Gantry crane sand system operators must be aware of the activities in the shop or

on the floor below them. Designers should consider the inclusion of a gantry movement warning system that would consist of an enunciator and light to warn shop or platform employees of the potential hazard.

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C. Sand gantries can consist of freestanding structures that traverse a set of rails embedded in a platform or floor. More commonly, a superstructure is constructed along the length of the shop or servicing platform. A set of crane rails is installed on top of the superstructure and the sand gantry traverses this rail.

D. Sand is delivered to a bulk storage silo that may be some distance from the

track(s) where the locomotive sanding is to take place. Sand is delivered to the storage silo mechanically or pneumatically. When the storage silo has sufficient sand available, it is pneumatically conveyed from the base of the storage silo to a surge hopper located above the gantry system at one end of the track. Sand from the surge hopper is fed by gravity to a transfer hopper on the gantry system. An operator travels and controls operations from a control station on the overhead system.

E. When the transfer hopper on the gantry is full from the surge hopper, the operator

moves the unit to a position above a fill hatch. The gantry system has movement in the longitudinal and transverse axes, which allows the operator to position the fill spout above any of the sand boxes on a locomotive. The hatch is opened and the fill hose is inserted. The fill valve opens and the hopper fills. When the hopper is full, the fill hose is retracted and the gantry moved to the next location.


A. The connection between the surge hopper and the transfer hopper should be as waterproof as possible. If rainwater and snowmelt infiltrate the transfer hopper, it can cause the sand to clump and clog.

6.3.3 PNEUMATIC CONVEYING SYSTEMS 6.3.3.1 General

A. Pneumatic systems use compressed air to transfer sand from storage to distribution and then to the locomotive sand box. Compared to gravity flow systems, pneumatic sand conveying systems introduce increased system pressures, potentially higher sand velocities from dispensing systems, increased wear on system components, periodic venting, and modified dispensing equipment.

B. Common arrangements include a storage silo with a transport tank below it,

multiple distribution stations along the service platform, and sand dispensing wands. Compressed air and a venting system are also required.

C. Sand is initially stored in an elevated sand storage silo directly above a transfer

tank. When the transfer tank is empty, the valve between the silo and the transfer tank opens. The vent line valve also opens, and the transfer tank is allowed to vent while sand is gravity fed to the transfer tank. The transfer tank is at

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atmospheric pressure during the fill process. The silo is allowed to vent through a filter located directly on top of the silo or is hard piped to the venting system.

D. When the transfer tank is full, the valve between the silo and transfer tank closes.

The transfer tank is then pressurized. The material being conveyed is extruded from the bottom of the tank into the conveying line. Some transfer tank systems add supplemental air at the exit of the transfer tank to break the extrusion into discrete plugs or pistons. The conveying mode in these systems is known as pulsed-piston or plug flow.

E. Sand is conveyed to distribution tanks located on the service platform. Single- or

multiple-tank arrangements can be used. When the distribution tank is full, it is isolated from the system and pressurized.

F. Sand is dispensed from the distribution tanks to the locomotive sand box through

a hose and sand fill wand. The operator lifts the wand into position and places the end of the wand into the sand fill nozzle. A valve at the base of the wand is opened and sand is dispensed into the sand box.

G. In some systems, sand is stored in a silo and then conveyed by a transfer tank to

other smaller dispensing silos located along the service track. Each dispensing silo is equipped with a filter vent and a proprietary transfer tank beneath. Sand is conveyed from the transfer tanks to the locomotive sand boxes. Multiple dispensing silos, transfer tanks, and filters may drive up capital and maintenance costs.

H. Venting air from the storage silo, transfer tank, and distribution tanks is generally

piped to a bag house. I. Boosters are commonly used to inject air into the conveying line at regular

intervals to help move the sand along.

J. Safety considerations related to pressure are similar to other industrial processes and include noise, system leakage or failure, and isolation during maintenance.

K. The amount and source of pressure required for a pneumatic conveying system

depends upon the type and phase of sand flow: dilute, plug, or dense phase. Generally, pressure requirements range from 10 psig for disbursed phase up to 150 psig for long-range dense phase flow. Pipe runs in long-range systems typically do not exceed 1000 feet.

L. Sources of noise in pressurized systems include air compressor and air drier

mechanical noise, air flow associated with high velocities, possible vibrations or harmonics, venting operations, and leaks. Hearing protection notices should be posted near such sources.

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M. Due to the inherent abrasion associated with sand flow, wear of internal components may be exacerbated. Aggressive system inspection and maintenance is warranted. Thicker pipe walls (schedule 80 or greater) can minimize wear. System design should include manual valves to isolate maintenance areas from pressurized parts of the system. The process should be designed to allow for periods of complete depressurization while minimizing the impact on dispensing schedules.

N. Dispensing and venting cycles typically release dust that must be captured and

collected. If the dispensing method requires close monitoring by the operator, respiratory protective equipment should be considered. Increased dispensing velocities can increase the amount of dust generated at the end of the nozzle.

O. Dispensing equipment such as nozzles and hoses are handled differently than in

gravity systems. Wands, nozzles and hoses are usually filled with sand, and lift-assisting devices such as pulleys, booms or balancers should be considered.

6.3.3.2 Types of Flow

A. Pneumatic transfer systems use pressure as the motive force to move sand from one tank to another. The mode of sand flow can be characterized by defining sand phases as dilute, dense or intermediate. In the dilute phase, sand grains behave independently of each other and are dispersed in air. In the dense phase, sand grains are relatively compact and remain in contact with and experience little motion relative to each other. In the intermediate phase, grains remain mostly in contact but relative flow between grains exists. The mode of flow is determined by the amount of motive pressure applied in the transfer tank and the point of application of the pressurized air.

B. In a typical dilute phase system, pressure is applied on the transfer tank and air is

injected into the outlet nozzle of the tank. The required transfer tank pressure is that which will cause flow into the outlet nozzle. Once in the outlet nozzle, the sand becomes entrained by the air injected into the nozzle. The sand travels in dilute phase at a relatively high velocity in the transfer piping. The required injection pressure needs to generate a sufficiently high velocity in the transfer piping to keep the sand entrained.

C. In a typical dense phase system, the transfer tank pressure provides the sole

motive force to push the sand through the transfer piping. Sand is essentially extruded through the transfer tank outlet nozzle and a dense phase is maintained. The required transfer tank pressure needs to overcome the friction of the sand against the pipe walls. In dense phase flow, the air flow rate is roughly proportional to the sand flow rate.

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D. To reduce friction, air can be cyclically pulsed into the sand to create shorter plugs of sand. The pressurized air gap between each plug generated by the pulse provides motive force to the upstream plug.

E. Intermediate phase flow is caused by conditions that allow sand to settle along the

bottom of the transfer piping while air flows at a higher velocity above the sand. The air interacts with the surface of the settled sand to create a rippled flow. This condition can be developed using air velocities below that required for dilute phase so that sand settles. It can also be developed near the downstream end of a dense phase system as the motive air expands into the vented receiving tank.


A. Elevating tanks should be of the approved unfired pressure type with suitable valves for admitting sand and air. The tank should be fitted with a relief cock to release pressure after the elevating operation when the sand handling is controlled manually (1975).

B. All pressure tanks, including transport tanks and distribution tanks, should be

designed and fabricated in accordance with ASME Section VIII, Pressure Vessels. All pressure tanks should include appropriate overpressure relief and protection.

C. If transport tanks contain internal pipe, consider a flanged connection inside the

tank for easier replacement of worn internal piping. D. Consider using oversized threaded connections at points where valves connect

sand wand hoses to the distribution tanks. Small valves require replacement as they wear out. If oversized connections are used, the reducing bushing will wear out before the tank fitting. It is generally easier to replace the bushing than to repair the tank.

E. Where necessary to use sand shutoff cocks in an elevating line to change the flow

of sand from one servicing tank to another, cocks that are rugged in design and material should be selected to prevent rapid wear by the sand (1975).

F. Items to consider when selecting valve operators include personnel needs, level of

desired automation, durability in an abrasive environment, cycle times, and the availability of power or compressed air for automated valves. Manual valves are adequate for small, non-complex systems. As complexity increases, automation can improve efficiency.

G. Evaluate actuator size or bulkiness to ease overhead installation and maintenance

in areas with interfering piping and equipment. Select valve and actuator combinations that minimize the intrusion of sand and dust into moving parts.

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H. Do not tie pneumatic operator supply lines into the distribution tank air supply lines. The pressure fluctuations in the system will cause valve operator drift and can lead to failure.

I. To reduce wear on system components, the minimum air pressure that can be used

to move sand is desirable. Therefore, it is desirable to place an air-reducing valve in the air supply line (1975). Selection of the operating pressure for a sand transfer or distribution tank should be based primarily on producing the optimum sand flow rate.

J. Dry sand can be moved through 2! inches of pipe for horizontal distances up to

300 feet at 70 lb air pressure (1975). Sand can be transferred several hundred feet in 2!-in pipe using transfer tank pressures between 50 and 100 psi.

K. Sand dispensing rates from distribution tanks should support the shortest on-

station time for a consist with nearly empty sanding bins. Thirty minutes is a typical time for a rapid turnaround of locomotive servicing. In this case, each bin would need to be filled at a rate of approximately 1.5 cfm of sand. If one dispensing hose cannot provide this flow, the platform should be arranged so that multiple hoses can reach one bin. Equipment handling should not inhibit the efficient filling of bins.

L. Sand transfer rates to distribution tanks should support the successive arrival of

consists onto a service platform. M. In dilute phase systems, pressures are generally less than 30 psi. In dense phase

systems, pressures range from 25 to more than 100 psi. System design should allow for a range of possible pressure control set points so that field calibration can be used.

N. Depending upon dispensing hose configuration at the distribution tank, a small

pressure increase can significantly increase flow due to the transition from restricted dense phase flow to intermediate phase flow. Further moderate increases in pressure can cause a transition to dilute phase, generating significant air flow from the hose and causing handling problems. Thus, a narrow range of operating pressures can occur.

O. The pressurized air supply to a transfer or distribution tank can be controlled

based on pressure or volumetric flow rate. Constant-value control (i.e., constant pressure or flow) is usually applied. Variable pressure or flow control is uncommon.

P. Constant pressure control should be applied to tanks from which the discharge

configuration is constant. For example, a distribution tank with multiple, identical distribution hoses would produce a nearly constant sand flow rate for a given pressure regardless of the number of hoses being used at one time.

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Q. Pressure can be controlled manually using a globe or other type of manual valve,

a pressure regulating valve, or an automatic valve that responds to a pressure switch or pressure gauge.

R. A critical flow orifice can be used to create constant flow. For a given inlet

pressure and orifice diameter, there is an associated outlet pressure below which flow is constant. This type of control should be considered where the discharge configuration varies, such as a transfer tank that provides sand to distribution tanks at different distances. The closer tank would require less pressure than the more distant tank. The critical flow orifice would allow for increased pressure to generate the same air and sand flow rate.

S. Distribution tanks and sand silos should contain level instruments. The type

depends on the level of system automation. Paddle-wheel and tuning-fork bulk material sensors are generally used.

SECTION 6.4 SANDING COMPONENTS

6.4.1 AIR SUPPLY SYSTEM

6.4.1.1 Air Requirements

A. Dry Air Bleed System: Dry air (to a dewpoint of 40F) can be continuously bled into sand storage tanks and gravity silos at a rate of 1-2 SCFM as appropriate. This should keep the headspace in the tank dry preventing condensation on the inside walls of the tank which leads to clumping.

B. Bag House Air: Bag houses for sand towers can be the rapper (mechanical

shaker) or reverse pulse jet type. The reverse pulse jet cleans the bags better than the rapper type but requires air to clear the bags. Air used for bag houses should also be dry air.

6.4.1.2 Air Pressure

A. The minimum air pressure that can be used to move sand is desirable, as lower pressures materially reduce the wear in the pipe. Therefore, it is desirable to place an air reducing valve in the air supply line and cut the pressure to the minimum required to move the sand.

B. Dry sand can be moved through 2-1/2 inches pipe for horizontal distances up to 300 feet at 70 lb air pressure (1975).

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6.4.1.3 Compressor Systems

A. Several components of a compressed air system are critical to a properly functioning system. These include the compressor, intercooler, aftercooler, moisture separator, filters, receivers, and air dryer. The air compressors and their critical components are available in multiple configurations, including lubricated or oil-free, single-stage or multi-stage, and air-cooled or water-cooled.

B. Lubricated systems allow traces of lubricant to enter the air stream, as it is present

in the compression chamber. An air-oil separator should be included on these units to minimize the oil carryover in the air stream. Oil-free systems should be used when the system cannot tolerate lubricant, as the lubricant is isolated from the compression chamber and is used primarily for bearing lubrication.

C. Single-stage units consisting of one compressing element or multiple compressing

elements acting in parallel are best suited for pressures of 60 psi or less and airflow below 300 CFM. Large compression ratios in single-stage units may result in excessive discharge temperatures that result in power loss and decreased compressor efficiency. These losses may be reduced or eliminated using a multi-stage unit, which consists of two or more compressing elements working in series, as the discharge air is cooled by an intercooler between the compression stages. Multi-stage units are more desirable when pressures and flows exceed 100 psi and 300 CFM.

D. Air-cooled compressors and oil coolers require ventilation air for proper

operation. Water-cooled compressors require water of an adequate quantity and pressure.

E. Reciprocating air compressors are positive-displacement compressors capable of

delivering up to approximately 6,000 CFM. Reciprocating units are appropriate for base load or partial load applications.

F. Rotary air compressors are positive-displacement compressors well suited for

high-pressure applications, typically 125-250 psi. Several types of rotary compressors are available, with the most common being the oil-lubricated helical screw. This type of compressor may deliver up to 3,000 CFM, and uses air- or water-cooled oil coolers. The oil-free helical screw may deliver up to 12,000 CFM and is air- or water-cooled. The last type of rotary compressor is the oil-free rotary lobe, which is available up to 500 CFM and is also air- or water-cooled. Rotary compressors are best suited for continuous duty applications.

G. Centrifugal air compressors are dynamic compressors that use a rotating impeller

to increase the air pressure. They can deliver very high volumes of air at relatively low pressures up to approximately 125 psi, are water-cooled and oil-free, as the running gear lubrication is sealed off from the air stream. Centrifugal compressors should be used for continuous duty applications.

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H. The cooling system is essential to proper system operation. Compressor oil removes some heat, even more in lubricated compressors because the oil is in the combustion chamber. Multi-stage air compressors are equipped with intercoolers to reduce the discharge air temperature between stages of compression. Compressor systems typically include an aftercooler and moisture separator. The aftercooler can be air- or water-cooled. The aftercooler lowers the compressed air temperature to within approximately 20F of the ambient temperature, condensing the water vapor in the air into liquid. A solenoid-operated moisture separator, composed of a tank and water trap, should be installed with the aftercooler to remove this condensate.

I. Air quality is important to compressor performance as well as downstream

components. Particulates can be abrasive to working parts, resulting in wear on the compressor, and ultimately poor system performance. Intake filters are required to prevent these abrasives from entering the compressor. They should be sized to adequately handle the inlet CFM of the compressor. Dry filters with a minimum removal efficiency of 99 percent for particles 10 microns and larger are usually used for reciprocating and rotary compressors. Two-stage dry filters that provide 99 percent removal efficiency for particles larger than 0.3 microns can be used for centrifugal compressors.

J. Moisture and oil carryover can be detrimental to the downstream components,

especially the air dryer. A coalescing filter should be used prior to the air dryer to prevent these particles from entering. Coalescing filters have efficiencies ranging from 99.98 percent at 0.1-micron particle size to 99.9999 percent at 0.01 micron. The maximum pressure drop is normally around 10 psi, with a maximum wetted pressure drop of 3 to 3.5 psi. Service life for these filters is 6 to 12 months and up to 5 years for high-performance filters. Coalescing filters should have a high-quality automatic condensate drain.

K. Particulates from the air dryer may be added to the air stream during the air

drying process. Thus, a particulate filter should be installed downstream of the air dryer. Particulate filters have a nominal efficiency of 99.95 percent at 1-micron particle size and an initial pressure drop of 1 psi. They should have a differential pressure indicator to evaluate the condition of the filter element.

L. A properly sized air receiver should be installed downstream of the compressor if

the compressor does not run continuously or has constant blow off. The air receiver helps stabilize system pressure, separates moisture and oil carryover, and stores pressurized air in high-demand systems, preventing frequent loading and unloading of the compressor. For compressors using standard induction-duty motors, the air receiver should be sized to prevent the compressor from cycling too often. Compressor manufacturers typically recommend limiting the compressor from cycling more than seven times per hour to prevent the induction motor from burning out. The receiver should be provided with an automatic condensate drain.

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M. All compressor systems should be protected against high temperatures, freezing

temperatures, high pressure, low oil pressure, and excessive vibration. Protection against these events should be provided by alarms, automatic unloading, automatic start/shutdown, and a manual reset.

6.4.1.4 Compressor Building Considerations

A. Adequate ventilation should be provided to rooms housing air compressors and air dryers to prevent room temperatures from exceeding 40C, as well as to accommodate the air compressor load.

B. Outside air intakes should be located at least 6 feet above the ground to prevent

intake of outside contaminants. Ideally, exhaust ducts should be located from the exhaust fans above or in the vicinity of the major heat sources in the building, including the air compressor, to directly remove the heat from the room. Air from the air-cooled aftercooler may also be directly ducted from the building to remove compressor heat during summertime applications. During the winter, the heat from the aftercooler may be used to provide space heating. This may be accomplished by locating a control damper in the exhaust duct that will open to the room when the temperature is low.

6.4.2 AIR DRYERS

A. Air leaving the compressor is saturated with water, and any further drop in temperature causes the water vapor in the air to condense. Air dryers are used to remove the majority of moisture left in the air stream, thus reducing the dewpoint temperature of the air. Air dryers are rated based on pressure dewpoint performance for standard conditions, which typically include inlet air flow, 100F inlet temperature, 100 psi operating pressure, 100F maximum ambient temperature for air-cooled units, 85F cooling water temperature for water-cooled units, and 5 psi maximum pressure drop. Dryer sizing should be adjusted for deviations from the standard rating conditions. Refrigerated and desiccant are the two main types of air dryers most often used in compressed air systems.

B. Refrigerated air dryers are condensation types that use a refrigeration process to

produce dewpoint temperatures in the range of 33 to 39F. Refrigerated air dryers cannot produce dewpoint temperatures below 33F because the condensed moisture could freeze on the coils. Thus, they are better served where the entire air system is located within a warm environment. Refrigerated dryers are available as direct expansion (non-cycling) and cycling.

C. The refrigeration compressor runs continuously on a direct expansion dryer,

regardless of the load on the dryer, and should be used only for constant airflow applications.

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D. Cycling dryers use an intermediate fluid to cool the air, which is in turn cooled by the refrigerant. The refrigeration compressor shuts down until the fluid temperature reaches a temperature requiring cooling. Cycling dryers are ideal for systems with varying airflow and temperature.

E. Desiccant dryers are adsorption-type dryers that use desiccant materials, typically

silica gel or activated alumina, to absorb the moisture in the air until they are saturated, after which the material is regenerated by purging with dry air or adding heat. Desiccant dryers typically have two vessels filled with the desiccant material, one operating in the air drying mode and the other undergoing regeneration. Desiccant dryers can produce dewpoint temperatures down to -40F, or may extend to -100F when silica gel is combined with activated alumina desiccant material, making such systems ideal in cold weather environments.

F. Heatless desiccant dryers use purge air to regenerate the desiccant material. They

provide consistent pressure dewpoints while minimizing maintenance and maximizing desiccant life. However, the use of purge air requires the compressor to deliver excess flow, as much as 15% of the inlet flow.

G. When the compressor cannot supply this excess flow, a heated dryer should be

used. Heated desiccant dryers types available include internally heated, externally heated, blower purge, and heat of compression. Internally and externally heated dryers use a heater and low-rate purge to regenerate the desiccant. The blower purge system uses a heater and small blower rather than the compressed air for desiccant regeneration. In a heat-of-compression process, the hot compressed air is used for regeneration; this process is ideal for oil-free systems.

6.4.3 PIPING SYSTEM

A. A slide gate valve is generally used between the sand silo and transport tank. The valve can include an automated operator

B. Valves and pipelines in pneumatic systems conveying sand are generally 2!

inches in diameter. Pipe is generally schedule 80, ASTM A53, seamless. C. Rubber-lined pinch valves should be used at distribution tank isolation points for

both the vent line and the fill line. Use of quarter-turn valves such as ball valves and plug valves should be discouraged regardless of materials of construction, as the high wear characteristics of the sand can cause high valve failure rates.

D. Sand handled under air pressure is abrasive to the pipe carrier. For such lines, flanged pipe is preferable. The pipe ends should butt at connections so that absolutely no space exists between them that could permit cutting action to begin and wear down the pipe to a point where it enters the fitting. (1975)

E. At points in the line where sharp bends are necessary, either a heavy tee or a wye

connection should be used with a blind flange fastened to the dead end of the fitting. This forms a pocket that fills with sand for deflection purposes. It has

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been determined that where the direction of flow is changed, the ricochet of sand just beyond the fitting causes greater wear there than elsewhere in the pipe. It is good practice to introduce a flanged replacement pipe section not less than 18 inches long immediately beyond the tee or wye fittings. All pipes should be installed to allow access for replacement (1975).

F. Certain conditions may require placing a section of elevating pipe to offset some

obstacle, or space may permit a long-radius curve in the change of direction. Specially manufactured hose is available for such locations, and in some installations such hose has outlasted pipe. If such material is used, the life of the hose will be extended if it is rotated a quarter turn at regular intervals (1975).

G. All pressure components of a system, including tanks and piping, should contain

appropriately ranged pressure indicators. Pressure drops in tanks may indicate a leaking valve. Pressure increases in the system may indicate a system blockage.

6.4.4 SAND COCKS

A. Where necessary to use sand shutoff cocks in an elevating line to change the flow of sand from one servicing tank to another, care should be exercised in selecting a suitable cock, as these units will quickly be worn by the sand if they are not rugged enough in design and material.

6.4.5 NOZZLES

A. Control of flow of sand is desirable to avoid spillage at the sand box where it is loaded. Various types of nozzles are available. Care should be exercised to obtain a weather proof unit. The size of the nozzle should be given consideration to be sure it will fit into the sand box.

B. Sand wands are generally constructed of aluminum because it is lighter than steel and has good wear characteristics.

C. A tool balancer can be used to help lift and store the sand wand and hose assembly.

6.4.6 ELECTRICAL

A. All equipment and materials and the design, construction, installation, and application thereof shall comply with all applicable provisions of the National Electrical Code (NEC), the Occupational Safety and Health Act (OSHA), and any applicable Federal, state, and local ordinances, rules and regulations.

B. Electrical instruments and sensors shall be connected to 24VDC or 120 VAC as

required by instrument type. C. Normal convenience outlets should use 120 VAC.

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D. Panel boards shall supply 120 VAC or 480 VAC depending on the loads served. E. Control cabinets where no 480 VAC is required shall at a minimum be fed from a

120 VAC panel board with the capability to provide 120 VAC and/or 24 VDC to instrumentation.

6.4.7 LIGHTING

A. Suitable lighting should be provided at the sanding platform if night servicing is required (1975).

B. A minimum of 40 foot-candles is required for nighttime work. C. General lighting requirements should include enclosures complete with gaskets to

form weatherproof assembly, and low temperature ballasts, with reliable starting to 0F.

6.4.8 AUTOMATION AND INSTRUMENTATION

A. Simple, compact manual systems can be controlled and operated with pressure gauges and manually operated valves. Compact systems allow the operator to remain in the vicinity of all components to observe and control with little or no automation.

B. Where operators need to monitor or control remote system components, limited

automation should be considered. Remote reading gauges and automatic valves with pushbuttons can assist a limited operating crew. Programmable logic controllers (PLC) may not be necessary, and conventional relay and contact control should suffice.

C. As systems become more complex and cover more facility area, a PLC can

improve efficiency. Because sanding system operation and control is based on discrete inputs, PLC complexity is based on the absolute number of inputs and outputs. A multiple distribution tank pneumatic system can have an I/O count of more than one hundred.

D. Instrumentation and control necessary to support complex sanding systems can

include timing devices, valve position feedback, level detectors, pressure transmitters and gauges, pressure switches, dew point indicators, and compressed air system monitoring.

E. Pressure transmitters and pressure monitoring at multiple locations within the

system should be strongly considered. Pressure is a good overall indication of system performance. High pressures may indicate system clogging, and low pressure may reveal rat-holing or an empty tank with a malfunctioning low-level switch. Because system pressure set points may need adjustment or calibration

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during initial startup, continuously variable pressure signal input to a PLC will allow for programming set points. Otherwise, manual adjustment of pressure switches would be required.

SECTION 6.5 ENVIRONMENTAL CONSIDERATIONS

6.5.1 WASTE SAND

A. Sand spillage is associated with all sanding systems, especially around sand towers, sand unload points, and sand dispensing points. Facility design should incorporate ways to minimize the amount of sand spilled. Old equipment that is prone to leakage should be replaced.

B. Waste sand can damage or impede the performance of storm water and industrial

wastewater systems; consequently, large amounts of sand should not enter any of these systems. An adequately sized grit chamber should be installed on industrial wastewater lines at the platform.

C. Large amounts of spilled sand should be removed either by shovel or machine.

Sand should not be washed down platform drains. Sand should be cleaned up promptly to avoid slip and fall hazards.

6.5.2 AIR QUALITY

6.5.2.1 General

A. Many air pollution agencies require permits for equipment with the potential to emit particulate matter. Potential sources of particulate matter at a sanding facility are tank venting points, system venting points such as bughouses, and the locomotive sand box fill point.

B. Typically it is necessary to contact only the local agency to determine whether a

permit is required. Air quality regulations typically exempt certain equipment or conditions from permit requirements. Before contacting the agency, it is important to estimate the amount of particulate matter that may be released from the sources.

6.5.2.2 Tank/Silo Venting

A. Tanks should never vent directly to atmosphere. B. Tanks can be connected to the system vent piping. Care should be taken to

accurately account for system backpressure on the vent piping and/or the tank venting device.

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C. Tanks can utilize individual vent filters or bag houses. The air is filtered as it leaves the tank. Filters and bin vents are generally located on top of the tank or bin. Filtering devices on each tank cause less waste, but they can be more expensive and require more maintenance than centralized venting systems.

6.5.2.3 System Venting

A. In pneumatic systems, sand is dispensed or transported to other tanks by pressurizing the dispensing or transporter tank. To refill the tanks, the pressure in the tank must be reduced so that the upstream, pressurized source of sand can flow into the tank. To release the pressure, tanks are typically vented to atmosphere via a dust collecting system. Venting system configurations consist of a tank nozzle, vent valve, and a length of piping to route the vented air and dust to the dust collector.

B. Depressurization rates from pressurized tanks depend upon initial pressure, pipe

diameters, valve size and whether flow control devices are used. The volume of air released is a function of the initial pressure in the tank, the total volume of the empty tank, and the volume of sand in the tank when the tank is vented. Sand volume consists of roughly 50% void space.

C. Venting pipe is generally subjected to less wear than sand piping, and schedule 40

carbon steel piping is adequate. 6.5.2.4 Bag House Venting

A. Air is vented to the atmosphere during tank depressurization and sand conveyance and distribution. The vented air contains entrained dust, which may be considered a polluting particulate. Some methods for capturing and collecting dust include the use of bin vents, dust collectors or bag houses, or cyclone separators. The devices can be mounted on top of tanks or silos so that the captured dust falls into the tank or silo. Alternatively, free-standing devices contain a hopper to collect the dust, which can be periodically emptied to a roll-off box, drum, or other container for transport to a dust disposal site.

B. The characteristics of dust generated in typical railroad sanding systems are

compatible with dust removal processes in a bag house. The main component of a bag house is the fabric, cloth or membrane used to filter the dust particles from the stream of air flowing through the fabrics pores. The fabric is typically assembled into bags to increase the surface area of fabric that can be contained in the house. Tubular structures (e.g., mesh, cage, or perforated pipe) support the bags against collapse.

C. Systems that operate at atmospheric or low pressure may require an exhaust fan to

pull the dust from the system. Bag house fans are usually located on the downstream side of the bags, thus pulling the dust to the fabric.

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D. As dust is collected, it adheres to and builds up on the bag, clogging the vent pathway. The dust can be removed using a reverse-flow pulse of air or mechanical agitation. Pulses are applied cyclically, and agitation can be applied cyclically or continuously. The dust removed from the outside of the bag falls into a hopper or the tank or silo onto which the bag house is mounted.

SECTION 6.6 REFERENCES

6.6.1 CODES

A. ASME B19.1, Safety Standards for Air Compressor Systems, and ASME B19.3, Safety Standards for Compressors for Process Industries, both discuss safety standards for the construction, installation, operation and maintenance of air and gas compression equipment.

B. ASME Boiler and Pressure Vessel Code Section VIII address the rules of safety

for design, fabrication and inspection of pressure vessels. C. OSHA Standard 1910.95, Occupational Noise Exposure. D. Atmospheric Storage Tanks: The design of bulk storage tanks is not covered by

any U.S. standards or codes. However, the American Iron and Steel Institute (AISI) has a useful publication entitled Useful Information on the Design of Steel Bins and Silos, which suggests potentially relevant design standards and codes.

E. Pressure Vessels: All pressure tanks, including transport tanks and distribution

tanks, should be designed and fabricated in accordance with ASME Section VIII, Pressure Vessels.

F. Tank Venting: Although American Petroleum Institute (API) standards do not

apply to bulk storage tanks, API 2000, Venting Atmospheric and Low Pressure Storage Tanks, can provide a useful design guide for venting requirements.

G. ASME B31.1, Power Piping.

H. ASHRAE

6.6.2 PUBLICATIONS

A. Pneumatic Conveying Design Guide by David Mills, 1990, University Press, Cambridge. A good source of pneumatic conveying theory, as well as data on the flow of sand.

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B. Pneumatic Points to Ponder, by Paul E. Solt, Powder and Bulk Engineering Magazine, CSC Publishing. Reprints of numerous articles can be purchased. Solt covers many aspects of pneumatic conveying.

C. Useful Information on the Design of Steel Bins and Silos, by John R. Buzek, 1989,

the American Iron and Steel Institute. Contains useful design criteria for the design of bulk storage tanks.

D. Pressure Vessel Design Handbook, by Henry H. Bednar, 1986, Krieger

Publishing Company. Useful guide for pressure vessel considerations.

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Figure 6-6-1 Typical Locomotive Sanding System.

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Figure 6-6-2 Overhead Gravity Sand Tower System

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Figure 6-6-3 Gantry Crane Sanding System Dr

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Figure 6-6-4 Dual Pneumatic Conveying Sand System.

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sistemas de carga y descarga de arena para locomotoras fra

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