Safe Storage and Handling of Liquid Waxes
Safe Storage and Handling of Liquid Waxes
This section contains recommendations for safe and efficient storage and handling of bulk waxes in liquid form. One should review this information with respect to their own processes to ensure that any storage and handling practices adopted are in conformance with local or federal safety rules and regulations as well ensuring specific local conditions are addressed in a safe manner.
The main topics in this section include:
- Shipment Methods - delivery & unloading
- Storage Tanks
- Maintenance of Storage Facilities
Storing and handling wax in liquid form offers more convenience and economy than wax stored in solid form. Some customers have found that they can realize substantial savings when purchasing bulk (liquid) wax vs. slabbed (solid) wax. Liquid wax transfers easily using a closed piping system from the delivery vehicle (either tank truck or tank car) to storage tanks and then to the process equipment. This type of closed system affords protection against product loss, degradation, and contamination.
One can take delivery of bulk waxes from either tank trucks or tank cars. The economics of shipping, based on bulk quantity and distance and proximity to rail facilities determine the better method of delivery.
Tank Truck: Tank trucks, generally used for shorter hauls, usually contain 7,000 gallons (45,000 lbs) of wax. Depending on the ambient temperature, trucks may prove the better choice for deliveries within a radius of 600 miles of the refinery or storage facility. When trucks deliver the wax, it requires immediate unloading while hot and still fluid.
When unloading tank trucks, customers can choose between using the truck's pump, their own pump, or air pressure unloading. Using the truck's pump allows customers to avoid the expense of purchasing their own pumping equipment. However, trucking companies usually charge a small fee for this service. One must take caution when using this method. There can be trace contamination from a prior load in the truck pump. Flushing the truck pump with a little wax prior to unloading can prevent this from happening.
Air unloading represents a good alternative, but requires the customer to have plant air available at a pressure of at least 10 psi. The truck should have an air valve that will regulate the air pressure to 5 psi inside the truck tank. The air pressure forces the wax out of the truck and into the storage tank. Customers should request "air unloading" at time of order placement so that the common carrier will bring the proper equipment and fittings.
Using any of these unloading methods requires about one hour. Trucks generally come equipped with standard two-inch-diameter-hose 40 ft in length. The customer can request longer hose if needed, although some carriers may charge for this service.
Tank Car: Tank cars (or rail cars) usually contain 23,000 gallons (150,000 lbs) of wax, with larger and smaller sizes also available in the market place. Tank cars work best for long distance shipment to large storage facilities at a railroad siding.
Many suppliers use insulated tank cars equipped with steam coils, which connect to steam or hot water at the destination. These allow reheating of the wax for pumping into storage tanks.
At the refinery or other supply point, wax is loaded into tank cars at approximately 25-30° F above the melting point. It remains in the molten state for a considerable period of time. Depending on the miles traveled and temperature in transit, the wax will cool and start to harden. However, in an insulated rail car, even after 2 weeks exposure to freezing temperatures, the core of a shipment may remain fluid.
The volume of wax increases when heated. Table 1 below shows the volume expansion in a 23,000 gal (150,000 lb) rail car during the heating process. Primarily because of volumetric expansion, never heat wax more than 35° F above the melting point. Overheating can cause hot wax to overflow a rail car as well as cause product degradation.
Typical Effect of Temperature on Volume Expansion for 150,000 lbs Rail Car of Wax
|Temperature,oF||Density, lbs/gal||Volume, gal|
When receiving a tank car of wax, open the dome on the top of the car to inspect the area around the cap for wax plugs. Do this before heating the car. During shipment, wax can splash into this area and form a plug. Heating the tank car can cause pressure build up behind this plug. When opening the top for unloading a heated , plugged car, pressure due to wax expansion can blow this plug or cause it to crack, spraying hot wax. To reduce the risk of incident or injury to personnel, always check for wax plugs prior to heating. If you discover a plug, make a large hole in it or break it up. Push it back into the tank car so that pressure will not build up.
Prepare the tank cars for unloading by applying steam or hot water through the internal coils to soften the wax. Time required to liquefy the wax for pumping or draining will normally vary from about eight hours to a day or more depending on the type of wax, ambient temperature, and time in transit. It is important to completely melt the wax before unloading to ensure a homogeneous product transfer.
The wax must reach a temperature range of 25°F to 35°F above the melting point before unloading. Avoid higher temperatures to minimize the risk of oxidation, a detrimental chemical process caused, in part, by overheating. Check the wax temperature by lowering the thermometer into the tank to a point near the steam coils. See detailed information about oxidation in the next section titled "Storage Tanks."
Prior to offloading any tank truck or tank car cargoes the first few gallons of product should be removed to ensure a clear and bright product is in the line. Water can accumulate in transit due to condensation.
Wax storage, indoor or outdoor, requires insulated storage tanks at a temperature 20° F to 30° F above its melting or congealing point. Maintain waxes containing additives at 10° F to 15° F above the cloud point. This ensures that the additives remain in solution and do not precipitate or "cloud" out. Maintaining wax at temperatures higher than this can lead to oxidation.
Oxidation, a detrimental chemical reaction that waxes and other organic materials undergo when overheated, will cause changes in the odor and color of the wax. The wax takes on an unpleasant burnt smell and the color darkens. Oxidation life of wax is inversely proportional to storage temperature. As a general rule, every 20° F rise in temperature will cut the oxidation life of wax in half. Other contributing factors to oxidation include surface of exposure and contact with metals that provide a catalytic oxidative affect.
Oxidation acts like a catalytic chain reaction in wax storage. Once initiated, remove all oxidized wax from the system to halt the degradation. Any oxidized wax left in the storage system will interact with other wax particles and the oxidation process will continue shortening the life of any fresh wax added to the system.
Many suppliers protect fully refined wax products by injecting a food grade oxidation inhibitor at the refinery. The amount of oxidation inhibitor protects wax under normal operating conditions for reasonable storage periods.
Generally, a two tank system or a single tank with two compartments is beneficial. This allows one tank for receiving product while the other tank supplies the process as well as allowing greater flexibility in scheduling, maintenance and in emergencies. Ideally, each tank or compartment should have the capacity to unload a full tank truck or tank car to permit independent operations. Always consume all wax from a single tank or compartment before adding a new load. For operations that may require a higher process temperature, using a smaller day tank may reduce the time the wax stays at a higher temperature, thereby further mitigating the risk of oxidation.
Tanks should be placed taking into consideration ease of receipt of tank cars or tank trucks as well as production issues. To facilitate cleaning tanks should be fitted with manholes. It is important to avoid the use of copper, brass and their respective alloys in wax storage and handling systems to avoid catalytic oxidative affect they have on wax. Agitation should never be done by air blowing. Blanketing with an inert gas such as carbon dioxide (CO2) or nitrogen (N2) can be beneficial.
Storage Tank Maintenance
Cleanliness in storage facilities protects wax quality. Clean storage tanks every year or as local conditions or throughput dictate. The following procedures are recommended:
Storage Tank Cleaning:
- Drain wax completely from tanks, sumps, valves and lines. Isolate lines, sumps and valves to prevent cleaning water from collecting there during the cleaning process.
- Wire brush all rusted areas.
- Rinse walls of tank with hot water and flush rust, scale and wax remains out of tank through drains.
- Pipe hot water to heating coils to expand pipe and check for leaks. After filling coils with water, apply pressure by means of air to ensure that welds and piping have no cracks or leaks.
- Open manholes and visually inspect the tank. Wipe the walls dry and remove excess water from the bottom of the tank.
- Wipe down tank with USP white mineral oil to prevent rusting prior to filling with the next load of wax. Do not leave mineral oil tailings or accumulation on the tank bottom.
- Close tank to prevent contamination.
After cleaning, some foreign matter may still reside in the line. Collect the first wax pumped from the tank in a bucket until it runs clear and bright. This will help prevent any foreign matter still in the line from passing into the process.
After cleaning tanks, monthly or more frequent screen and filter inspection and cleaning should be performed.
General Wax Precautions
In addition to following local safety rules, personnel handling wax should familiarize themselves with the wax product Safety Data Sheets (SDS). Some general precautionary guidelines include:
EYE CONTACT: Flush thoroughly with water. Contact a physician.
SKIN CONTACT: Wash contact areas with soap and water or waterless hand cleaner. If burned by contact with hot material, cool molten material adhering to skin as quickly as possible with water, and see a physician for removal of adhering material and treatment of burn.
INHALATION: Remove from further exposure. If respiratory irritation, dizziness, nausea, or unconsciousness occurs, seek immediate medical assistance. If breathing is irregular or has stopped, assist ventilation with bag-valve-mask device or use mouth-to-mouth resuscitation and seek immediate medical assistance.
INGESTION: Do not induce vomiting; seek immediate medical assistance.
VENTILATION: Use local exhaust over heating operations. Use in well ventilated area. Refer to current product MSDS.
RESPIRATORY PROTECTION: No special requirements under ordinary conditions of use and with adequate ventilation. Refer to current product MSDS.
EYE PROTECTION: When handling wax in liquid form, wear chemical-type goggles or face shield.
SKIN PROTECTION: Gloves, chemical aprons or other impervious clothing, as required to handle hot materials. Always follow good personal hygiene practices. Refer to current product MSDS.
EXPOSURE LIMITS: Refer to current product MSDS.
Handling FDA Food-Grade Waxes
When handling FDA food-grade waxes, ensure that the procedures and facilities are in compliance with applicable FDA regulations contained in Title 21 Code of Federal Regulations (21 CFR)
General Safety Precautions
- Wear protective clothing including, but not limited to long sleeve gloves, safety glasses or shields, a hard hat and other locally required equipment.
- Brake and choke the tank car or tank truck.
- Ground the tank car or tank truck.
With respect to the information provided herein, neither National Petroleum Refiners Association nor its member companies nor any of its employees makes any warranty, express or implied including warranties of fitness for a particular purpose, or assumes any legal liability or responsibility for the accuracy, completeness or usefulness of any apparatus, product or process disclosed or represents that its use would infringe on privately owned rights. In no event shall National Petroleum Refiners Association nor its member companies nor any of its employees be liable for any direct, indirect, incidental, punitive, or consequential damages of any kind whatsoever with respect to the materials and the products referenced in this document.