Powell Railcar Padding System
for Chlorine and Sulfur Dioxide
Pressurized railcars of chlorine and sulfur dioxide frequently require additional pressure to facilitate
the railcar unloading operation at user facilities. This practice - often
called pressure padding - introduces air or nitrogen into the vapor space above
the liquid in the railcar to force the liquid out of the liquid angle
valve at the top of the car. Typically, dry air, as opposed to nitrogen, is used as 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 system, since even a minimal
amount of moisture can result in corrosion and potential failure of the tank car,
piping, transfer hoses, chlorine vaporizers and valves.
Also, the air should be provided from an independent source other than the
plant supply to ensure that during the padding operation, the overall system pressure
is maintained at a level higher than the car pressure. This minimizes the possibility
that the chlorine or sulfur dioxide could backflow into the air supply system, causing extensive damage to the air dryer, compressor, and other components.
The system should also include a backflow protection mechanism to prevent the backflow
of chlorine or sulfur dioxide which could also occur if a component should fail. This would cause extensive damage to the air dryer, compressor, and other components.
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 stand alone padding system is completely
isolated from other air supplies to prevent 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 Air 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. The flow rate of the system is typically 30 SCFM to 35 SCFM. A Powell Engineer can provide assistance for systems requiring greater than 35 SCFM. The system can be custom 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 (ie, 145#-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.
The control system includes a display screen to indicate line pressures, high moisture, low 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 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.
Chlorine Line Equipment
Powell Fabrication maintains a comprehensive inventory of chlorine rated components
for quick delivery of critical items.
Click to view Powell's Chlorine Line Equipment