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Railcar Unloading
Powell Railcar Padding System
Pressurized
railcars of chlorine frequently require additional pressure to facilitate the railcar
unloading operation at user production facilities. This practice - often called
pressure padding - introduces air or nitrogen into the vapor space above the liquid
chlorine in the car to force the liquid chlorine out of the liquid angle valve at
the top of the car. Typically air, as opposed to nitrogen, is used as the pad gas.
The air used in any padding system must be of high quality to protect the integrity
of the system. In addition, the air must meet several other criteria:
- The air must be clean to eliminate debris and contamination.
- The air must be oil free to eliminate the possibility of a heat-producing reaction
between the chlorine and any oil that could be present in the stream.
- The air must be dried to an atmospheric dew point of -40°F or below at operating
pressure to ensure moisture does not enter the chlorine system since even a minimal
amount of moisture can result in corrosion and potential failure of the tank car,
piping, chlorine vaporizers and control valves.
- In addition, the air should be provided from an independent source other than the
plant supply to ensure that during the padding operation overall system pressure
is maintained at a level higher than the car pressure to minimize the possibility
that chlorine could backflow into the air supply system.
The system should also include a backflow protection mechanism to prevent the backflow
of chlorine which could also occur if a component should fail.
The easiest, most reliable way to comply with all of these critical requirements
for railcar padding is with the Powell Railcar Padding System.
The Powell Railcar Padding System provides an independent source of clean, oil free,
dry air in accordance with The Chlorine Institute, Inc. Pamphlet 66 guidelines for
chlorine tank car pressure padding. This separate chlorine padding system is completely
isolated from other air supplies to prevent chlorine vapors from accidentally mixing
into the instruments and equipment. Built in redundant features protect equipment
in the event of power loss, compressor failure, or failure of individual components.
The standard Powell Railcar Padding System incorporates an air padding compressor,
air drying system, and backflow prevention sub-assembly mounted on a skid along
with a control system housed in a NEMA 4X box.
The unit provides clean, oil free, dry air with a dew point of -40°F or below
at line pressure. Although flow rate of the system is typically 30 SCFM to 35 SCFM,
the system can be designed with purchaser's choice of flow rates. The typical maximum
outlet pressure is 180 psi to 190 psi. The unit will automatically fill tank cars
in an on/off mode with a minimum of 5 psi differential (i.e., 140#-150#).
An oil and water separator is standard on the Powell Railcar Padding System. After
separation, water can be drained to a waste treatment system and waste oil can be
reclaimed for recycling.
Control System
The control system includes a display screen to indicate high moisture, low primary
differential pressure, low secondary differential pressure, and low compressor oil
pressure. The display also indicates power on for automatic valves. An alarm horn
is included and a common alarm contact is provided.
The Powell Railcar Padding System is shipped completely assembled requiring only
on-site connection to power and external air line piping.
Backflow Prevention Unit Available as Stand-Alone Component
The backflow prevention component of the Powell Railcar Padding System - the Powell
Safety Section - is available as a skid-mounted, stand alone component. The unit
is designed to prevent the back flow of chlorine from the tank car to the air drying
system and to automatically fill the tank car. Built in redundant features protect
the equipment in the event of power loss, compressor failure, or failure of individual
components.
The Backflow Prevention Unit includes all appropriate instrumentation as well as
a control system mounted on the skid.
Powell Safety Section
The subassembly in the Powell Tank Car Padding System is available
as an individual assembly. The unit is designed to prevent the back flow of chlorine
from the tank car to the air drying system and to automatically fill the tank car.
Redundant features are built in to maintain equipment protection in the event of
power loss, compressor failure, or failure of individual components.
Chlorine Line Equipment
Powell Fabrication maintains a comprehensive inventory of chlorine rated components
for quick delivery of critical items. Chlorine Line Equipment
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