Full Length ArticleEffect of steam jet on oil reclamation and purification from layered oily sludge
Graphical abstract
Introduction
Oily sludge is inevitably generated during each process of crude exploitation, storage, transportation, and refining, leading to a worldwide enormous accumulation (over 1 billion tons) [1], [2]. As oily sludge contains a high concentration of petroleum hydrocarbons (PHCs), heavy metals and other toxic components, it is regulated as a hazardous waste in many countries [3]. In recent years, the intense demand for crude oil coupled with the declining conventional oil reserves has resulted in an urgent need of unconventional substitutes, such as heavy and extra-heavy oils, which accounts for two-thirds of total world oil reserves [4], [5]. The exploitation of a considerable volume of heavy oil greatly enhances the challenge of harnessing oily sludge due to its high viscosity, acidity and asphaltene contents [6], [7].
Many efforts have been devoted to treating oily sludge. The reclamation of valuable oil from oily sludge is considered as a primary purpose due to its substantial financial and environmental benefits [2], [8]. Various methods are available for oil reclamation, including solvent extraction [9], [10], [11], thermochemical washing [12], centrifugation [13], freeze/thaw [14], [15], [16], ultrasonic irradiation [17], froth flotation [18], and pyrolysis [19], [20], [21]. However, each method possesses different treatment capacity, efficiency, and costs, which limit their applicability. Moreover, the components of oily sludge vary over a wide range depending on their sources of generation. Even in the same storage pond, oily sludge could be heterogeneous due to various processing schemes and the precipitation of heavier compositions during storage, leading to stratification [22], [23]. Therefore, none of any single method currently used is sufficient to treat all types of oily sludge.
The quality of reclaimed oil is of another concern since it would ultimately be redirected to a refinery for upgrading as a substitute of raw petroleum [10]. Compared with raw petroleum, reclaimed oil may contain more metallic impurities, which may cause installation corrosion and catalyst deactivation during refining [24], [25]. It is therefore essential to remove the metallic impurities to the highest achievable quality. Among current methods, ultrasonic irradiation and centrifugation demonstrate a desirable performance in removing water-soluble salts [26], while solvent extraction can remove oil-soluble metals (e.g. Ni and V) [27]. In addition, supercritical water and methanol can separate Ni, V, Fe and Ca from petroleum emulsion [28], [29]. However, these methods consume a large amount of solvent or require complicated equipment.
Steam-based thermal approaches, such as steam-assisted gravity drainage (SAGD) and cyclic steam stimulation (CSS), are extensively used to enhance recovery of heavy oil [30]. To reduce oil viscosity and improve oil mobility, steam is typically injected with a temperature ranging from 240 to 350 °C and a corresponding pressure ranging from 2.0 to 19.5 MPa [31], [32]. Although steam offers several advantages in terms of comprehensive facilities and sustainable steam source [33], [34], there are few reports about adopting this technique to reclaim oil from oily sludge directly but just as an auxiliary heat source [10], [35], [36]. McCoy et al. [37] disclosed a patent employing a continuous process of steam distillation to deoil and dewater refinery sludge at a temperature varying from 150 to 315 °C. However, some heavy oil fractions could not be vaporized due to their high boiling points. Cheng et al. [38] combined steam injection with the pyrolysis of oily sludge to improve the yield and quality of oil products, but this method is difficult to realize the full utilization of sufficient steam. Accordingly, a more cost-effective and efficient method based on the clean steam source to treat oily sludge could be a significant technique improvement.
In this study, a novel method taking full advantage of sustainable and sufficient steam sources was developed to process layered oily sludge of storage ponds. When steam jet was vertically injected onto the layered oily sludge, lighter oily sludge from the upper layer could be separated rapidly and efficiently from the bottom one. In the meantime, the floated oil was continuously injected by the steam to decontaminate metallic impurities, thus realizing a concurrent effect of oil reclamation and purification. Therefore, it is promising to utilize clean steam jet to alleviate the burden of oily sludge storage as well as reclaim oil with higher refineability in heavy oil production areas.
Section snippets
Materials
Surface oily sludge (S-OS), a highly viscous liquid, as well as bottom oily sludge (B-OS), a semi-solid substance, was collected at different depths from a typical concrete-lined storage pond located in a crude joint station of Shengli Oil Field, China. Samples were sealed in separated buckets at ambient temperature. Each sample was well mixed before experiments. Analytical grade chemicals including toluene, n-hexane, dichloromethane, ethyl alcohol, trichloromethane, nitric acid, perchloric
Characteristics of the oily sludge
Due to the distinct layering phenomenon in the storage pond over several years of precipitation, S-OS and B-OS presented an obvious difference in appearance. From a microscopic perspective, spherical water droplets of diameters less than 30 μm were well dispersed in the oil phase of S-OS, while irregular solid particles (black and bright) of different sizes were distributed in the oil phase of B-OS (Fig. B.1). The differences in the makeup of the three-phase components of these two samples (
Conclusions
Layering is a distinct phenomenon for oily sludge in storage ponds of oil joint stations. Steam jet is efficient to reclaim and purify oil from the layered oily sludge. Higher temperatures and S/OS generate better oil reclamation performance and longer duration improves oil purification. However, taking the economic costs as a factor, the proper condition was determined at 300 °C and S/OS of 6:1, where over 90% of oil was reclaimed within 5 min and over 80% of metallic impurities were removed
Declaration of Competing Interests
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgments
This research was financially supported by the National Nature Science Foundation of China (No. 51778606, No. 21477151) and the National Water Pollution Control and Management Program (No. 2017ZX07107-002). The authors sincerely appreciate the collection support provided by Shengli Oilfield, China. We also would like to thank Dr. Ying Zhou from the University of Chicago for providing many constructive comments.
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2021, Journal of Hazardous MaterialsCitation Excerpt :Huang et al. (2014a) investigated that the water droplets in OS were dispersed uniformly in emulsion, with the diameter of 2.7–3.3 µm. The chemical composition of extracted oil from OS can be further separated into saturates, aromatics, resins and asphaltenes (SARA) for evaluating the oil quality and the possible applications (Xia et al., 2020; Sieben et al., 2017; Handle et al., 2017). Saturates are composed of straight and branched chain alkanes, cycloalkanes, unsaturated alkenes and alkynes (Chen et al., 2020).