Colloids and Surfaces A: Physicochem. Eng. Aspects 375 (2011) 237–244 Contents lists available at ScienceDirect Colloids and Surfaces A: Physicochemical and Engineering Aspects journal homepage: www.elsevier.com/locate/colsurfa Modified jet flotation in oil (petroleum) emulsion/water separations M. Santander 1, R.T. Rodrigues, J. Rubio ∗ Laboratório de Tecnologia Mineral e Ambiental, Departamento de Engenharia de Minas, PPG3M, Universidade Federal do Rio Grande do Sul (UFRGS), Av. Bento Gonc¸ alves 9500, Prédio 75, Porto Alegre, RS 91501-970, Brazil article info abstract Article history: This work presents results of a rapid emulsified oil (petroleum) removal from water by flocculation Received 20 August 2010 followed by flotation in a modified jet (Jameson) cell (MJC). The modification is such that the downcomer Received in revised form 2 December 2010 was sealed at the bottom (by a concentric blind-end tube) to allow floated particles to enter immediately Accepted 10 December 2010 into the frothy phase after the capture of the oily flocs by the bubbles. Also, a packed bed (crowder) Available online 23 December 2010 was placed at the upper part of the concentric tube to stabilize the froth and facilitate the rise of the oil floc/bubble aggregates. The work was divided into two parts: a detailed laboratory study (1.3 m3/h) and a Keywords: pilot plant trial in an offshore platform. Parameters studied were flocculation (type and concentration of Jet flotation Oily pollutants polymer), oil concentration, oil droplets size distribution and flotation cell design. Results of laboratory Petroleum separation studies showed mean separation efficiencies of the order of 80% when used as a conventional jet cell Platform (CJC) with feed emulsions (droplets size of about 20 ␮m) ranged between 100 and 400 mg/L petroleum concentration. The oil removal increased up to 85% in the MJC. These studies allowed optimizing the design and process parameters: chemical, physico-chemical and operating. A MJC (5 m3/h) was then projected, built and installed in an offshore platform, after the oil extraction–production point. At optimal conditions, in a single flotation stage, discharges varied between 20 and 30 mg/L oil concentration or 81% removal at 24.7 m3/h m2 loading capacity. Because this jet cell operates with a high air hold-up, it presented a very good efficiency (capture of oil droplets by bubbles) at low residence time (high-rate separation) and showed to be simple, compact and easy to operate. It is believed that the MJC has a great potential for treating polluted oily high flow wastewaters, at high separation rate. Results and mechanisms involved are discussed in terms of interfacial phenomena and design factors. © 2011 Elsevier B.V. All rights reserved. 1. Introduction commonly discharged into the ocean environment and may cause severe environmental petroleum contamination especially when Mining, metallurgical, petroleum and chemical industries gen- reaching surface, ground and coastal waterways. erate huge amounts of wastewater usually polluted by solids, Therefore treatment of these effluents is required and must process chemicals, organic and other compounds [1–4]. Table 1 result in improved oil/water rapid separation, improved water summarizes main oil/organic sources reported. quality, oil recovery, water reuse, amongst others. The conventional During crude oil exploration and production large volumes of technology for the treatment of oily produced water on offshore petroleum hydrocarbon bearing effluents, the so-called produced platforms usually includes a degasser (to remove the natural gas waters, are concurrently recovered. These waters usually contain that accompanies oil) and oil–water separators (mainly gravity set- high salinity, suspended solids (clay, sand, scale corrosion prod- tlers). ucts), total dissolved solids and the oil may range between 100 and Many techniques for separation of oil–water emulsions are 1000 mg/L or still higher depending on oil separation process effi- available, namely filters [5], ultra-filtration [6], micro-filtration [7], ciency and nature of crude oil. Crude oils are a complex mixture reverse osmosis, gravity separation, activated sludge treatment of many hydrocarbons which vary in their toxicity to aquatic and [7], dissolved air flotation [8,9], column flotation [10], flotation terrestrial life. These produced waters (after treatment) are more with gas-aphrons [11], electroflotation [12], induced air flotation [13], membrane bioreactor [14], carbon adsorption, chemical coag- ulation, electrocoagulation. The advantages and disadvantages of these processes have been already fully discussed by Bande et al. ∗ Corresponding author. Tel.: +55 51 33089479; fax: +55 51 33089477. [12]. E-mail address: [email protected] (J. Rubio). The efficiency of these techniques depends on feed concentra- URL: http://www.ufrgs.br/ltm (J. Rubio). 1 Permanent address: Departamento de Metalurgia, CRIDESAT, Universidad de tion but mainly on the form of oil in the aqueous phase; if disperse Atacama, Av. Copayapu N◦ 485, Copiapó, Región de Atacama, Chile. (oil droplets > 50 ␮m), emulsified (oil droplets < 50 ␮m) and dis- 0927-7757/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.colsurfa.2010.12.027 238 M. Santander et al. / Colloids and Surfaces A: Physicochem. Eng. Aspects 375 (2011) 237–244 Table 1 a feed line and forms a liquid jet. Air is entrained into the liq- Main organic pollutants in different industrial activities. uid in the downcomer by a vacuum effect and sheared into Petroleum exploration and oil Hydrocarbons, alcohols, ethers, phenols, many bubbles. Thus a very good environment for particle collec- refineries carbon disulfide, sulfonic acids, etc. tion by bubbles (air hold-up >40%) is created in the downcomer Beneficiation of agates and Minerals oils, dyes, diesel oil, etc. [42,43]. amethysts Treatment of ores and Organic solvents of solvent extraction This cell has shown a great potential, nor only in mineral pro- metallurgy processes flotation reagents: foaming, cessing but also for solid/liquid separations and for liquid/liquid collectors and surface modifiers separations [40,42]. Its main advantage is its high rate process effi- Process metallurgy Cutting oils, solvents ciency and moderate equipment cost [41,44]. Chemical and petrochemical Various oils and fats, organic reagents, Problems with process efficiency have been recently solved surfactants with low-shear mixing head, recycle of treated water and use of polymeric flocculants in the downcomer. This allowed its use in wastewater treatment and recovery of solvent extraction liquors solved. The selection process for the treatment of oily produced [37], municipal waters [45], treatment of wastes from a variety of water oil platforms offshore will depend also on the equipment industries, such as dairy factories, abattoirs, metal finishing, rolling foot-print and performance because the space of the platform is mills, coke ovens. reduced. Advantages recognized, amongst others, are: Yet, the flotation efficiency will be determined mainly by the degree of emulsion destabilization stage. Poor performance has • Compact design and low capital cost; always been observed when flocculation was incomplete. The flota- • More, with no moving parts, the jet cell has low power con- tion of organic rich waters such as oil spills on water, oily sewage sumption and low maintenance costs: (air self-entrained, no or oil-in-water emulsions has been used for a number of decades compressor or blower required); in various fields. • Improved performance in a number of specific areas: mineral pro- Because of collection and adhesion problems, the separation of cessing, solvent extraction, industrial (treatment of effluents) and the very fine oil droplets (<50 ␮m) by flotation requires fine bub- municipal wastewater industries; bles, quiescent hydrodynamic conditions in the cell and emulsion • Low residence times (<3 min), high throughput and high effi- breakers prior to flotation [15]. ciency. Table 2 summarizes most of the flotation processes applied to oily effluents including organic liquors and solvents. In the CJC modification to the basic design [46], for effluents 1.1. The Jameson flotation cell – background containing fragile flocs, the feed containing suspended particu- lates is mixed with a bubbly flow generated by a plunging jet The cell (originally from the mineral processing field) consists of recycled clean liquid, in a relatively quiescent zone in the of an aeration/contact zone (the downcomer), a bubble-particle downcomer. or aggregate disengagement zone (the tank proper pulp area) The flotation separation of very fine oil droplets (2–30 ␮m) is and a cleaning or froth forming zone (the tank proper zone). In even more complicated and usually requires fine bubbles, qui- contrast to conventional mechanical flotation units, the Jameson escent hydrodynamic conditions in the cell separation zone or cell was designed to accomplish fast flotation based on a high emulsion breakers prior to flotation [32]. This is due to collection bubble surface area flux, as a result of the very many fine bub- and adhesion factors, which makes the process very slow, espe- bles generated by high shear rate in the downcomer. The bubbles cially when, treating high flow-rates. IAF (induced air flotation) and (medium size) formed in this cell may have 100–600 ␮m in diam- DAF, have been used extensively in the removal of stable oily emul- eter [40,41]. sions [15,20,23]. IAF utilizes bubbles between 40 and 1000 ␮min In a Jameson