Research Article Optimization of a Gasoil Vacuum Dryer Using Response Surface Methodology A laboratory-scale vacuum dryer with gasoil as feed was investigated based on response surface methodology (RSM). Dehydration efficiency and gasoil loss in this type of vacuum dryer are significantly affected by residence time, tempera- ture, and pressure as independent variables, therefore, central composite face- centered design of RSM with three levels of these variables was applied to design the experiments. Experimental data of dehydration efficiency and gasoil loss fitted well to the second-order quadratic polynomials using a statistical software pro- gram and predictive models of dehydration efficiency and gasoil loss were ob- tained. An increase in temperature and residence time and a decrease in pressure could improve dehydration efficiency and gasoil loss. The estimated model of gasoil loss was minimized to reach a particular amount of dehydration efficiency. Keywords: Dehydration efficiency, Gasoil loss, Response surface methodology, Vacuum dryer Received: February 17, 2013; revised: July 31, 2013; accepted: August 15, 2013 DOI: 10.1002/ceat.201300123 1 Introduction Vacuum dehydration is one of the most efficient industrial processes used in different chemical plants to dry products whose structures are prone to degrade under high temperature like food, drugs, or even petroleum products. In this process, heat and vacuum are simultaneously applied to promote evap- oration of liquid water from food or other products. Vacuum drying can provide high-quality products, however, it is expensive and time-consuming and requires accurate design and optimization. Vacuum dryers are widely used in petroleum industries and refineries especially in sweetening units including hydrodesul- furization and demercaptanization plants. For example, mer- captans are removed by water-soluble chemicals that react with the mercaptans. In this process, caustic liquid (sodium hydro- xide) or amine compounds (diethanolamine) may be used. Therefore, drying is required to remove water from the prod- ucts. This drying step can significantly influence all parts of the sweetening unit and improve the product quality [1]. The water content is considered as one of the hydrocarbon contaminants that can significantly affect the hydrocarbon sys- tem. As described by Booser [2] and Arizmendi et al. [3], cor- rosion is definitely the most apparent impact that the hydro- carbon water content has on surfaces. Water not only affects the components of hydrocarbons, but it can also change the fluid physically and chemically. Consequently, petroleum industries need to reduce the water content of hydrocarbons. Nowadays, there are different methods to dehydrate gasoil and other petroleum products: dewatering using a coalescer filter, dewatering by a vacuum dryer, and inert gas stripping, to name but a few. The coalescer filters only remove the emulsi- fied water while vacuum dryers separate free and emulsified water as well as dissolved water from hydrocarbons. Indeed, vacuum dryers reduce the water content of hydrocarbon more effectively than other types of dehydrators. In another method described by Pater [4], inert gas stripping was utilized in order to decline the water vapor pressure. Drying is one of the most energy-consuming industrial pro- cesses and it is a combination of material science and transport phenomena. However, the knowledge about drying at micro- scopic level is still rudimentary. A scale-up of the different types of dryer continues to be more complex and empirical due to the nonlinear nature of the governing conservation equations of transport phenomena. Thus, there is no general drying theory and the scale-up of the dryers strongly depends on the planned experiments. However, most models are ap- plicable for specific product-equipment combinations, with notable exceptions, of course. Some 60 000 products need to be dried at different scales in over 100 dryer types. For exam- ple, spray and drum dryers are used to dry pumpable liquids to powder and to classify particles based on their sizes and struc- tures, or vacuum dryers which are available to dry expensive ma- terials that are sensitive to high temperature like fruit, pharma- ceuticals, and petroleum products, to name but a few [5]. Chem. Eng. Technol. 2014, 37, No. 2, 229–239 © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim www.cet-journal.com Elhameh Narimani Javad Alaei Kadijani Research Institute of Petroleum Industry, Refinery Department, Tehran, Iran. – Correspondence: Elhameh Narimani (inspirationj82@gmail.com), Research Institute of Petroleum Industry, Refinery Department, West Boulevard of Azadi Stadium, P. O. Box 14665-1998, Tehran,Iran. Vacuum dryer 229