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www.<strong>petrofed</strong>.org Prof. Hamid Ali Director of Petroleum Studies, Aligarh Muslim University An Energy Saving Option in Process Industry Energy resources will continue to play an important role in India's future, being a major growing economy and having large boundaries. However it is heavily dependent upon imported crude oil for its energy requirements affecting its balance of payment adversely. The majority of India's population is still living in rural areas and has no access to modern forms of energy which is central to economic development. Thus there is a need to examine other alternatives. One option is to conserve energy by replacing and installing energy efficient equipments which should be cheap and require little or no maintenance as energy saved is, energy Table - 1 Process Reboiler name/column Alkylation Sulfuric Depropanizer Desiobutanizer Alkylation (HY) Acid Rerum Depropanizer Acid Stripper Deisobutanizer Debutanizer Catalytic Reformer Stabilizer Aromatic Recovery Stripper Pre-extractor Gas Plant Stabilizer Stripper De-ethanizer/ Absorber Stripper Debutanizer Rerun (naptha splitter) Depropanizer Depentanizer Stabilizer Sulfur Sour water stripper Recovery Amine regeneration Miscellaneous Vaporizer Splitter 22 generated. In view of these aspects, Vertical Tube Thermosiphon Reboilers have proven to be highly effective and efficient equipment in heating as well as cooling circuits for multiple applications of all the reboiler types. Vertical tube thermosiphon reboilers are most widely used in petroleum refining, natural gas, petrochemical and chemical processing industries where significant capital investment is represented by vaporizers, evaporators and reboilers due to a number of advantages over the other types. In these industries about 60% of their total operating costs are represented by these systems. What is a Thermosiphon? Thermosiphon reboiler is essentially a closed loop circulation system where movement of fluid takes place due to the density difference of liquid and two-phase mixture in cold and hot legs respectively. Thermosiphon boiling of liquids in vertical tubes also play a decisive role in power plants and nuclear reactors and offers a potential means of storage and transportation of solar energy. The vertical tube thermosiphon reboilers (recirculating type) when designed and operated properly provide an efficient and economical Purpose Remove and collect from alkylate system Recycle acid stream to remove contaminants Remove and collect propane from alkylate stream Remove acid from propane stream Produce low vapor pressure alkylate gasoline Remove and collect butane from deisobutanizer stream Remove butane and lighter hydrocarbons from reformer stream Remove and collect aromatics from solvent hydrocarbon stream Remove butane and lighter hydrocarbons from reformate charge Remove water from solvent Remove and collect benzene from aromatics stream Remove and collect toluene from aromatics stream Remove and collect xylene from aromatics stream Remove butanes and lighter hydrocarbons from gasoline product Remove very light hydrocarbons such as methane and ethane Produce low -vapor pressure alkylate gasoline Stabilize gasoline component Recycle to polish lean oil (solvent) of lighter gasoline fraction Remove and collect propane Remove butane and lighter hydrocarbons from gasoline stream Remove butane and lighter hydrocarbons from gasoline stream Remove and collect H2S and NH3 from water stream Regenerate amine for recycle Normally found in fuel system to remove butanes Separation of two or more hydrocarbon fractions by distillation
23 www.<strong>petrofed</strong>.org means of excellent heat transfer rates, short receives the heat from the heat flux supplied and residence times of liquids in the reboiler tube its temperature rises as it moves upward. When which minimizes the risk of thermal degradation, vaporization takes place in the tubes, the specific most compact dimensions, simple in construction, volume of the fluid is increased resulting in its low manufacturing cost, easy to support, ease of upward movement while the liquid is siphoned cleaning and maintenance and since the reboiler from the adjoining cold leg. Depending upon the can be set close to the column, the frictional losses heat flux applied the flow regimes which may in the inlet and outlet piping and cost of vapor occur in boiling two-phase flow is out lined in lines are minimized. Thus this reboiler type is very Figure 2. Thus the heat transfer to the liquid reliable, has far lower operating costs than other reboiler tube generates a changing two-phase reboiler and can be used in a wide range of flow with various flow regimes spread along the operating pressures and temperatures. However tube length depending upon wall heat flux, inlet in the design of thermosiphon reboilers, special liquid temperature, liquid level in the column and care for low pressure drop has to be taken as the physical properties of the fluids. The heat transfer circulation is due to the density difference of liquid and hydrodynamics interact with each other in the & two-phase mixture. Some important thermosiphon reboiler under the influence of applications of reboilers found in a typical various governing operating parameters. The petroleum processing units have been point at which two-phase flow begins is known as summarized by Huchler as given in Table – 1. incipient point of boiling (IPB). The IPB divides the tubes into two distinct regions with significantly In a process industry, the equipment is generally a different modes and heat transfer coefficients. 1 – 1 exchanger placed vertically, with upper tube Non-boiling single phase (convection dominated sheet close to the liquid of the bottoms in the sub-cooled boiling with low heat transfer column as shown in Figure 1. The process fluid coefficient) and boiling (fully developed saturated entering the vertical tubes of heat exchanger boiling with very high value of heat transfer
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