Rail tank cars, tank trucks, and drums are used to transport about 700 different commodities.Rail tank cars and most tank trucks and drums are in dedicated service (carrying one commodity only)and, unless contaminated, are cleaned only prior to repair or testing. Nondedicated tank trucks (about20,000, or 22 percent of the total in service) and drums (approximately 5.6 million, or 12.5 percent of the total) are cleaned after every trip.
4.8.1.1 Rail Tank Cars
Most rail tank cars are privately owned. Some cars, like those owned by the railroads, are operated for hire. The commodities hauled are 35 percent petroleum products, 20 percent organic chemicals, 25 percent inorganic chemicals, 15 percent compressed gases, and 5 percent food products. Petroleum products considered in this study are glycols, vinyls, acetones, benzenes, creosote, etc. Not included in these figures are gasoline, diesel oil, fuel oils, jet fuels, and motor oils, the greatest portion of these being transported in dedicated service.
Much tank car cleaning is conducted at shipping and receiving terminals, where the wastes go to the manufacturers’ treatment systems. However, 30 to 40 percent is done at service stations operated by tank car owners/lessors. These installations clean waste of a wide variety of commodities, many of which require special cleaning methods.
A typical tank car cleaning facility cleans 4 to 10 cars per day. Car capacity varies from 40 to130 cubic meters (m 3 ) (10,000 to 34,000 gallons [gal]). Cleaning agents include steam, water, detergents, and solvents, which are applied using steam hoses, pressure wands, or rotating spray heads placed through the opening in the top of the car. Scraping of hardened or crystallized products is often necessary. Cars carrying gases and volatile materials, and those needing to be pressure tested, must be filled or flushed with water. The average amount of residual material cleaned from each car is estimated to be 250 kilograms (kg) (550 pounds [lb]). Vapors from car cleaning not flared or dissolved in water are dissipated to the atmosphere.
4.8.1.2 Tank Trucks
Two-thirds of the tank trucks in service in the United States are operated for hire. Of these, 80 percent are used to haul bulk liquids. Most companies operate fleets of 5 trucks or less, and whenever possible, these trucks are assigned to dedicated service. Commodities hauled and cleaned are 15 percent petroleum products (except as noted in Part 4.8.1.1), 35 percent organic chemicals, 5 percent food products, and 10 percent other products.
Interior washing is carried out at many tank truck dispatch terminals. Cleaning agents include water, steam, detergents, bases, acids, and solvents, which are applied with hand-held pressure wands or by Turco or Butterworth rotating spray nozzles. Detergent, acidic, or basic solutions are usually used until spent and then sent to treatment facilities. Solvents are recycled in a closed system, with sludges either incinerated or landfilled. The average amount of material cleaned from each trailer is 100 kg (220 lb). Vapors from volatile material are flared at a few terminals, but most commonly are dissipated to the atmosphere. Approximately 0.23 m 3 (60 gal) of liquid are used per tank truck steam cleaning and 20.9 m 3 (5500 gal) for full flushing.
4.8.2 Emissions And Controls
4.8.2.1 Rail Tank Cars And Tank Trucks
Atmospheric emissions from tank car and truck cleaning are predominantly volatile organic chemical vapors. To achieve a practical but representative picture of these emissions, the organic chemicals hauled by the carriers must be known by classes of high, medium, and low viscosities and of high, medium, and low vapor pressures. High-viscosity materials do not drain readily, affecting the quantity of material remaining in the tank, and high-vapor-pressure materials volatilize more readily during cleaning and tend to lead to greater emissions. Practical and economically feasible controls of atmospheric emissions from tank car and truck cleaning do not exist, except for containers transporting commodities that produce combustible gases and water soluble vapors (such as ammonia and chlorine). Gases displaced as tanks are filled are sent to a flare and burned. Water soluble vapors are absorbed in water and are sent to the waste water system. Any other emissions are vented to the atmosphere.
Tables 4.8-1 and 4.8-2 give emission factors for representative organic chemicals hauled by tank cars and trucks.
4.8.2.2 Drums
There is no control for emissions from steaming of drums. Solution or caustic washing yields negligible air emissions, because the drum is closed during the wash cycle. Atmospheric emissions from steaming or washing drums are predominantly organic chemical vapors. Air emissions from drum burning furnaces are controlled by proper operation of the afterburner or secondary combustion chamber, where gases are raised to at least 760°C (1400°F) for a minimum of 0.5 seconds. This normally ensures complete combustion of organic materials.
Note: The information presented herein is our interpretation of certain test results and field experience to date. The information is not to be taken as warranty or representation for which we assume legal responsibility, nor as permission or recommendation to practice any patented invention without a license. It is offered solely for your consideration, investigation and verification.
