Microwave treatment has successfully treated slop oils and sludges of light and medium crude. This paper reports its extension to slops derived from heavy crude oil. Scientific and industrial treatments using microwaves are usually limited to frequencies of 2450 MHz and 915 MHz. However, this study used a variable frequency microwave to examine the effect of applying radiation between 5800 and 7000 MHz. Microwave treatment of an unusually stable, high-solids slop oil from the Elk Point region did not break the slop oil, but it did improve oil-solids detachment by up to 29%. The frequency centered on 6400 MHz was the most effective. Although preliminary, these results certainly warrant a closer look at variable frequency microwave treatment of slop oils, particularly for more typical slop oils of lower stability, as a way to significantly reduce oily waste volumes and disposal costs.
Slop oil is a term often used for field-produced mixtures of oil, water, and solids. The slop can derive from interface pads from heater-treaters; solidscontaminated oil from the top of skim tanks; and oily sludges from desand tanks. It is characterized by its stability and high-solids content. The traditional treatment at many sites is to add more demulsifying chemicals and increase settling time. However, these steps are rarely completely effective. Producers must still dispose of the oily wastes.
Road spreading offers the cheapest disposal costs, estimated at $40/m3. However, liability concerns have limited the use of this alternative. Field operators now report less road spreading and land farming than was used five years ago. More common disposal options are now salt cavern disposal and transportation to commercial oil reclaimers for recovery and landfill disposal. At disposal costs of $40 to $140/m3, and typical disposal amounts of 1300 m3/year, slop oils represent a considerable cost to producers.
Microwave treatment of slop oils offers an on-site treatment method which could substantially reduce the disposal volume of oily wastes.
Wolf was awarded the first patent for using microwaves to assist the demulsification of emulsions.1 Wolf claims all microwave frequencies used to assist the separation of any hydrocarbon/water emulsion or dispersion. However, his examples cite only the preferred usefulness of microwaves of frequencies between 2000 and 3000 MHz, applied to synthetically produced emulsions. Other patents were awarded to addon apparatuses for treaters using microwaves. 2–4 Like Wolf, Masliyah's group examined the separation effectiveness of 2450 MHz microwaves only on synthetically created emulsions. 5,6 In fact, only two groups have published reports of successfully using microwaves to separate crude oilfield emulsions and sludges. Fang et al used microwaves of 915 MHz frequency to break slop oils/sludges of medium crude. 7,8 Perhaps the best known use of microwave separation of slop oils is by the Imperial Petroleum Recovery Corporation. 9–11 They report a high degree of success in breaking high-solids refinery sludges. Extending their application to western Canadian slop oils needs to take two factors into account: their published case histories report successes only on oil of 35 ° API, and the microwave treatment is always used in conjunction with centrifugation.
