Handling Bituminous Crude Oil in Tank Cars

Abstract

Bituminous heavy crude oil is kept at elevated temperatures in order to flow and may be transported in one direction, and light hydrocarbons typically comprising of mixtures of components of which the majority will have molecular chain lengths of 2 to 12 carbon atoms, such as Natural Gas Liquids (NGL), light naphtha, natural gasoline and natural gas condensates may be transported in the opposite direction.

What is claimed is: 
     
         1 . A method for changing a rail tank car from transporting heated bituminous crude oil to transporting light hydrocarbons comprising:
 transporting the bituminous crude oil at a temperature of 70° C. or higher; and   discharging bituminous crude oil from a rail car using light hydrocarbon vapor under pressure.   
     
     
         2 . The method of  claim 1 , whereby, after using light hydrocarbon vapors under pressure to discharge the bituminous crude oil from the rail tank car, refilling the rail tank car with light hydrocarbon liquids of the same or similar composition as the vapors. 
     
     
         3 . The method of  claim 2  including controlling the introduction of light hydrocarbon liquids such that the vapor generated by boil-off when these liquids come into contact with the rail tank car and any remaining bitumen liquids, does not cause the pressure in the rail tank car to exceed its design pressure, whereby the initial vaporization of the light hydrocarbons is used to cool down the rail tank car and its contents. 
     
     
         4 . The method of  claim 1  including emptying multiple rail tank cars simultaneously, with the liquid bituminous crude oil being collected in a common header and led to a collection vessel that is kept under low pressure or partial vacuum by a compressor or vacuum pump in order to assist the viscous flow of the bituminous crude oil. 
     
     
         5 . The method of  claim 2  including pumping the light hydrocarbon vapors, drawing light hydrocarbon liquids from a storage tank, to feed said liquids into a vaporizer where external heat is supplied feeding the generated vapors into a common header that allows connection to multiple rail cars simultaneously. 
     
     
         6 . The method of  claim 2  including transferring the bituminous crude oil, after separation of entrained vapors in the collection drum, from the collection drum to an atmospheric storage tank without risk of a vapor breakthrough leading to emissions of light hydrocarbons from the atmospheric storage tank. 
     
     
         7 . The method of  claim 4  including detecting vapor in the liquid discharge line from the rail car and closing a valve located in said liquid discharge line when a transition from liquid to vapor flow is detected. 
     
     
         8 . The method of  claim 7  including reopening and reclosing the valve in the liquid discharge line, in order to collect any liquids still present in the rail tank car at the time of first vapor breakthrough. 
     
     
         9 . The method of  claim 8  including opening a flow control valve to admit light hydrocarbon liquids into the rail car. 
     
     
         10 . The method of  claim 9  including generating vapors by flashing of light hydrocarbon liquids in contact with the rail tank car and any residual contents in the car, and collecting the vapors displaced by the liquid entering the rail tank car 
     
     
         11 . The method of  claim 9  when the temperature of the contents of the car fall below the atmospheric boiling point of the liquid, introducing air into the vapor space, while preventing back-flow of vapors. 
     
     
         12 . The method of  claim 1  including handling multiple rail tank cars simultaneously with some cars still being emptied from bituminous crude oil, while others are already in the process of being back filled with light hydrocarbon vapors. 
     
     
         13 . The method of  claim 12  including using four separate common headers to allow connection of multiple railcars simultaneously to a bituminous discharge system and a light hydrocarbon liquids system and using a separate pressurized vapor header and a vapor recovery header connected to the vapor space of a rail tank car. 
     
     
         14 . The method of  claim 1  including providing the rail car with external coils that allow the transfer of heat from a suitable heating medium to reheat the bitumen, said coils acting as external stiffeners to enable the rail tank car to withstand full internal vacuum.