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 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 -400F 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, designed and manufactured by Powell Fabrication & Manufacturing, Inc, a leader in the chlor-alkali industry for more than 40 years.
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 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 -40oF 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 180psi to 190psi. The unit will automatically fill tank cars in an on/off mode with a minimum of 5psi differential (ie, 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.
Standard Powell Railcar Padding System - Design Summary
Flowrate |
Choice |
Dew Point |
-40oF or below at operating pressure (12 mg/m3) |
| Air Quality |
ISO Class 8573.1 |
| Solids |
0.1 microns solids |
| Oil |
0.01 mg/m3 |
| Control System |
Allen-Bradley CompactLogix processor; NEMA 4X enclosure |
| Operator Interface |
Allen-Bradley PanelView + 400 monochrome screen display |
| Compressor |
Quincy with oil and water separator |
| Dryer |
Hankinson Heatless Desiccant Dryer |
| Back |
Integrated Powell Safety Section |
Powell Safety Section
A 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.
Powell Fabrication maintains a comprehensive inventory of chlorine rated components for quick delivery of critical items. More...
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