Vacuum tower bottoms, utilization

A possible solution is to gasify the more dilute vacuum tower bottoms product in an oxygen blown gasifier and to convert the excess synthesis gas to methanol. In those cases where a Flexicoker is used the heavy scrubber liquids could be recycled to extinction. Therefore, the plant products are SNG, naphtha, 300-800°F distillate and methanol. All of these products are of high quality or can be hydrotreated to achieve high quality. As a result, they could be easily integrated into the utility fuel mix with a minimum amount of disruption or special product handling facilities. 

In the development of coal liquefaction processes considerable effort has been concentrated on the coal liquefaction part of the process. In contrast, less effort has been directed toward utilization of the coal liquefaction residue or vacuum tower bottoms. 

Crude oil and high-boiling-point, high-viscosity petroleum fractions such as 6 fuel oil, atmospheric tower bottoms, and vacuum gas oil can contain wax which crystallizes at temperatures often above room temperature. It is not unusual for these oils to have base pour points of 100°F (37.8°C) or greater. In order to utilize these heavy oils, the pour point and viscosity of these oils must be reduced. One method which is used to accomplish this is to dilute the heavy oil with lower-viscosity components such as diesel fuel or kerosene. The oil then becomes pumpable at lower temperatures. 

Figure 1 is a schematic section of the Otto sterilization apparatus, the most commonly utilized. It is used generally in combination with Otto plate ozonators. The water to be treated comes under pressure to the emuheur, a sort of water jet pump. The vacuum produced by the water is sufficient to suck in the ozonated air from the ozonator, and the mixture of the two fluids is carried to the bottom of the self-contact column, which is a tower 5 meters (16 feet 4 inches) in depth. The water falls freely from a weir at the top of the tower, where most of the gas escapes. 

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