Original Date: 05/23/1994
Revision Date: 01/18/2007
Information : OTTO Fuel Reclamation
Naval Undersea Warfare Center (NUWC) Division Keyport has developed an OTTO fuel reclamation process that resulted in substantial savings for the facility. OTTO fuel, used in the external combustion cycle of the MK 48 torpedo engine, is comprised of an energetic compound (Propylene Glycol Dinitrate), a desensitizer (Butyl Sebacate), and a stabilizer (2-Nitro DI Phenylamine). An OTTO fuel and seawater mixture is created during torpedo test firings by the addition of seawater into the fuel tank module. During a torpedo run, seawater is allowed to enter the fuel tank to pressurize the fuel, thus pushing it into the combustion chamber. OTTO fuel, which is heavier than water and with a different polarity, settles out at the bottom of the fuel tank. This chemical property of the mixture is used to aid in separating the mixture in a semiautomatic process.
The separation process begins by transferring the OTTO fuel and seawater mixture from the MK 48 torpedoes to a separation tank equipped with low and high level fuel sensors. A quantity of the mixture is pumped into the separation tank and allowed to settle. After the mixture settles, a water overflow line is opened to transfer the seawater to a separate holding tank. Additional quantities of the mixture are transferred into the separation tank and the seawater is drained until the OTTO fuel level reaches the high level sensor. The high level sensor is located just below the seawater overflow so a minimum of seawater will remain on top of the OTTO fuel at this point. When the high level fuel sensor is reached, actuators shut off the influent mixture flow, shut off the seawater overflow, open the OTTO fuel drain valve, and introduce air into the separation tank to purge the fuel to a Grade B holding tank. The fuel level in the separation tank drops until the low fuel level sensors stop the purging operation and return the system valves to their original configuration. The location of the low fuel level sensor ensures that only OTTO fuel is purged and a small quantity of fuel and the seawater above remain in the separation tank.
The Grade B OTTO fuel is used to refuel torpedoes used for exercise drills only. Following the separation process, the seawater is treated by an activated carbon system and the Keyport Industrial Waste Treatment Facility before being discharged to the sewer.
Recent improvements to the process include the addition of an air dryer tank to further purify the Grade B OTTO fuel by sparging with air. After sparging and filtration, the Grade B OTTO fuel becomes Grade A and is used to fuel torpedoes for combat.
The improved reclamation process has the capacity to process OTTO fuel and seawater mixtures from naval submarines in San Diego and Pearl Harbor that are shipped to Keyport in tanks. The process is also used to reclaim OTTO fuel from MK 46 torpedoes.
A volume of 350,000 pounds of OTTO fuel, at a value of over $1M is being reclaimed at Keyport per year. Factoring in the costs to operate the process and the avoidance of waste disposal costs, the reclamation process results in a net savings of approximately $960K per year.
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