Thermosyphon Reboiler & its type with operational parameter.

introduction to reboiler ,its type,.
introduction to thermosyphon reboiler.

1. Technical Seminar On “Thermosyphon Reboiler & It’s Operational Characteristic” In the Partial Fulfillment of the Degree of Bachelors in Technology- Chemical Engineering Submitted By Mr. Govind K. Patil (13GCH43) Under the Guidance of Dr. Ujwal D. Patil (Assistance Professor, U.I.C.T., N.M.U., Jalgaon.) University Institute of Chemical Technology, North Maharashtra University, Jalgaon.

2. OVERVIEW INTRODUCTION TO REBOILER. INTRODUCTION THERMOSYPHON REBOILERS. WORKING PRINCIPLE OF THERMOSYPHON REBOILER. TYPES OF REBOILER. OPERATIONAL CHARACTERISTICS OF THERMOSYPHON REBOILER. CONCLUSION. REFERENCE.

3. 1. INTRODUCTION TO REBOILER The transfer of heat to and from process fluids is an essential part of most chemical process. Reboilers are heat exchangers typically used to provide heat to the bottom of industrial distillation columns. They boil the liquid from the bottom of a distillation column to generate vapors which are returned to the column to drive the distillation separation. The heat supplied to the column by the reboiler at the bottom of the column is removed by the condenser at the top of the column. Well a boiler is an equipment used to convert liquid into high pressure vapor. It is familiarly known as the famous equipment "steam boiler", that produce steam from water. However, a reboiler does the same operation, due to its involvement in the continuous process of boiling the recycling liquid stream in its shell side. The name was given by the reason for boiling the same liquid again and again.

4. Types of Reboiler: The most critical element of reboiler design is the selection of the proper type of reboiler for a specific service. Most reboilers are of the shell and tube heat exchanger type and normally steam is used as the heat source in such reboilers. However, other heat transfer fluids like hot oil may be used. Fuel-fired furnaces may also be used as reboilers in some cases. Commonly used heat exchanger type reboilers are Kettle Reboilers. Thermosiphon Reboilers. Fired Heaters. Forced Circulation type. Internal Reboilers.

5. 2. INTRODUCTION THERMOSYPHON REBOILERS Thermosyphon reboilers play a wide role in the chemical industry. low maintenance design . It has two endearing qualities, mechanical simplicity & attractive high fluxes. Application in petroleum & chemical industries. In the Thermosyphon reboilers no need of pump to transport the Process liquid. Its work on natural circulation. Natural circulation is obtained by using the density difference between. They are characterized by high heat transfer rates and low fouling tendencies. This type of reboiler having the low operating and maintenance cost. * IOCL, Vertical Thermosyphon Reboiler.

6. Thermosyphon reboilers are majorly used in petroleum refining, petrochemical and chemical industries. 95% of the reboilers in petroleum industries are horizontal type. 70% are vertical type in petrochemical industries and in chemical while nearly. 100% are vertical type in chemical industries. There are mainly two types of Thermosyphon Reboilers. Vertical Thermosyphon Reboilers. Horizontal Thermosyphon Reboilers.  

7. 3. WORKING PRINCIPLE OF THERMOSYPHON REBOILER Thermosyphon reboilers is basically a shell and tube heat exchanger. No requiring pumps to pump the vapor into the column back. These reboilers work on a simple principle based on difference of densities of liquid and vapor. Recirculation of these systems is driven by the density difference between the outlet and inlet line.

8. 4. VERTICAL THERMOSYPHON REBOILER. Of all reboiler types, vertical thermosiphon reboilers are most widely used in chemical industry. They are characterized by high heat transfer rate and low fouling tendencies The liquids have short RTD. Minimizes the risk of thermal degradation. This reboiler type is very reliable, lower operating costs. It is an shell & tube heat exchanger type having shell with vertical tube bundle. Vertical thermosyphon reboilers are usually attached directly to distillation columns. 70% are vertical type in petrochemical industries and in chemical while nearly 100% are vertical type in chemical industries. *Vertical Thermosyphon Reboiler, CDU-UNIT, Exxon Mobil.

9. 5. WORKING PRINCIPLE OF VERTICAL THERMOSYPHON REBOILER. The liquid passes from the bottom of the tower into the reboiler, with the evaporation taking place inside the tubes. The heating fluid (typically condensing steam) is on the outside of the tubes. The boiling liquid usually flows through the tubes as shown, but shell-side boiling may be used in special situations, e.g., with a corrosive heating medium. The vertical thermosyphon reboiler is less susceptible to fouling problems. it has higher heat transfer coefficients. * NPTEL, Vertical Thermosyphon Reboiler, Reboiler Section.

10. Setup of Vertical Thermosyphon reboiler. Vertical Thermosyphon Reboiler. Forced Circulation Vertical Thermosyphon Reboiler. Vertical Thermosyphon Reboiler with Fixed Liquid Head. Once-Through Vertical Thermosyphon Reboiler. Once -Through Naturally Forced Vertical Thermosyphon Reboiler. *J. S. Stephan Arneth, "Characteristics of Thermosiphon Reboilers”.

11. Advantages: Vertical thermosyphon reboilers do not required Pump. The main advantage of this reboiler is low fouling factor. It has low maintenance costs. It required low less space and piping. It has high heat transfer rates, thus less powered is used during distillation process. The exchanger is cheap. Low plot area is required. High circulation can be achieved, leading to high heat transfer coefficient and reduced fouling. Disadvantages: These reboiler have reliability issues. cannot be used where a large surface area is needed. The performance tends to be poor under deep vacuum conditions. The performance tends to be poor near critical conditions, where the liquid and vapor have similar densities, thus giving little driving force for the recirculation.

12. 6. HORIZONTAL THERMOSYPHON REBOILER. This is a very common type of reboiler. Horizontal thermosiphon used in refining applications. 95% of the reboilers in petroleum industries are horizontal type. It requires less headroom but have more complex pipework and plot space making it more expensive to install and has a higher fouling tendency. Tube bundles can be more easily withdrawn. This design has the advantage of preserving the natural circulation concept while allowing a lower headroom than the vertical thermosyphon type. Less susceptible to fouling. *Horizontal Thermosyphon Reboiler, ISOM-UNIT, British Petroleum

13. 7. WORKING PRINCIPLE OF HORIZONTAL THERMOSYPHON REBOILER. The process side is on the shell side, and the heating medium is on the tube side. There is recirculation around the base of the column. A mixture of vapor and liquid leaves the reboiler and enters the base of the column where it separates. It has higher circulation rates and lower vaporization fractions in horizontal thermosyphons make them less susceptible to fouling. Horizontal rather thermosyphon should be considered if the feed viscosity exceeds 0.5 cp. * NPTEL, Horizontal Thermosyphon Reboiler, Reboiler Section.

14. Advantages: The exchanger is relatively cheap. Removeable bundles are possible. High circulation can be achieved, More effective at low temperature difference. It is more attractive when the heat transfer area requirement is large due to machinal consideration (e.g. Distillation column height). Fluids with moderate viscosity boil better in horizontal thermosyphon. The static head required is less because of their high circulation rate. It has super thermal performance . Disadvantages: Large plot area is required than vertical unit, especially if the bundled is removed. The process fluid is on the shell side, creating potential problems with fouling or corrosive fluids.

15. 8. COMPARISON BETWEEN HORIZONTAL & VERTICAL THERMOSYPHON REBOILER Advantages of Horizontal Over Vertical Thermosyphon Reboiler: Much more effective at low temperature differences . Vertical thermosyphons are also less attractive than horizontal type when heat transfer area requirements are large due to mechanical considerations Fluids with moderate viscosity boil better The static head requirements are lower Advantages of Vertical Over Horizontal Thermosyphon Reboiler: More-sensitive operation.  More area can be placed in a single shell than with vertical units. Low headroom required.

16. 9. MECHANISMS OF THERMOSYPHON REBOILER. In a thermosyphon reboiler, there exists a complex mutual interaction between two-phase flow and heat transfer. The heat transfer depends on the pressure, the vapor–liquid equilibrium, the flow rates and the system properties, In order to understand the response of the thermosyphon reboiler to it is divide in to the reboiler into two zones: a heating zone & evaporization zone. The heat transfer coefficient is much higher in the evaporization zone than in the heating zone. *J. S. Stephan Arneth, "Characteristics of Thermosiphon Reboilers”.

17. Figure(B) illustrates the principal temperature profile versus the tube length. The liquid entering the reboiler tubes has approximately the same temperature as the liquid in the bottom of the column. Due to the liquid head in the vertical inlet line the fluid is significantly subcooled at the reboiler entrance. Here, the heating zone ends and the evaporation zone begins. Within the evaporation zone the state of the liquid approximately follows the vapor pressure curve. At atmospheric pressure, the length of the heating zone is typically 20–50% of the total tube length. It increases significantly with decreasing pressure.

18. 10. OPERATIONAL CHARACTERISTICS OF THERMOSYPHON REBOILER. Influence of driving temperature difference: At low temperature differences, the specific overall heat flux rises steeply with increasing temperature differences. Since more liquid is evaporated, Therefore heat transfer coefficient increases, evaporation zone increases thus heating zone decreases, heat flux increases. At higher driving temperature differences, the increase of the heat transfer rate slows down a little. Heat transfer rate decreases, then heating zone rise little and evaporation zone decrease small. The mass flow density in a rises sharply at small driving temperature differences It usually reaches its maximum at about 20 K temperature difference and decreases thereafter. At small temp diff liquid circulation is low and at high temp diff liquid circulation is high, Also at high temp diff the mass flow density is decreases. *J. S. Stephan Arneth, "Characteristics of Thermosiphon Reboilers”. *J. S. Stephan Arneth, "Characteristics of Thermosiphon Reboilers”.

19. Influence of operating pressure: The operating pressure strongly influences the performance of a thermosiphon reboiler. At low pressures, the sub cooling of the liquid is high. Adversely at high pressures, the sub cooling of the liquid is very low. The heating zone where the liquid is warmed up to the boiling temperature is much shorter. The increased vapor content in the pipe, larger density difference and higher circulation rate. This increases the length of the evaporization zone. Heat transfer coefficient is higher, higher operating pressures enhance the heat transfer rates. The heat flux as well as the mass flow density rate increase with rising operating pressure *J. S. Stephan Arneth, "Characteristics of Thermosiphon Reboilers”.

20. Influence of pipe diameter: While the specific overall heat transfer rate decreases with increasing pipe diameter, the heat transfer rate per tube rises. With increasing pipe diameter the ratio of heat transfer area to heated pipe volume becomes smaller. Thus, the heating zone is longer and the heat flux smaller. In other words, smaller pipes are more effective in terms of specific heat flux than larger ones. Mass flux is increases with increase in pipe diameter. *J. S. Stephan Arneth, "Characteristics of Thermosiphon Reboilers”. *J. S. Stephan Arneth, "Characteristics of Thermosiphon Reboilers”.

21. 11. THERMOSYPHONE REBOILER ADVANTAGES & DISADVATAGES. Advantage: Cheapest reboiler installation in terms of capital and operating cost. Permits simple, compact piping arrangement. Provide excellent thermal performance. Most economical because no pump is used. It has high heat flux. It has high transfer rate. It has low fouling factor. Disadvantages: Not suitable for viscous and solid bearing fluid. More heat transfer area is required for vacuum operation. Not specified for pressure below 0.3 bar. Column based must be elevated to provide the hydrostatic head required for the thermosyphon reboiler. This increase the cost of the column supporting structure. Its is not suitable for low temperature difference .

22. 12. INDUSTRIAL APPLICATION. Thermosyphon reboilers are extensively used for chemical engineering applications in various industries. They comprise of 70% of evaporation duties in all process industries. Thermosyphon reboilers are majorly used in petroleum refining, petrochemical and chemical industries. 95% of the reboilers in petroleum industries are horizontal type. 70% are vertical type in petrochemical industries and in chemical while nearly 100% are vertical type in chemical industries. Typical applications may be the reduction of monomers or oligomers from a polymer or the recycle of organic solvents from a waste stream.

23. 13. CONCLUSION Conclusions made from this study; In a thermosiphon reboiler, there exists a complex mutual interaction between heat transfer and two-phase flow. Decisive for the operational characteristic of a thermosiphon reboiler is the length of the heating and the evaporation zone, respectively. Since the values of the heat transfer coefficients are much higher in the evaporation than in the heating zone the overall heat transfer rate of the reboiler is governed by the length of the evaporation zone. Thermosyphon reboilers are majorly used in petroleum refining, petrochemical and chemical industries. 95% of the reboilers in petroleum industries are horizontal type, 70% are vertical type in petrochemical industries and in chemical while nearly 100% are vertical type in chemical industries.

24. 14. REFERENCES [1] R. K. Sinnott., "Coulson & Richardson's Chemical Engineering.," in Chemical Engineering Design.Volume-6, 4th Edition., Oxford, UK., Elsevier., 2005, pp. 728-743, . [2] J. S. Stephan Arneth, "Characteristics of Thermosiphon Reboilers.," International Journal of Thermal Sciences, Elsevier., vol. 40, no. 4, pp. 385-391, 2000. [3] F. B. Stephan Scholl, "Intensification of fluid dynamic and thermal performance of thermosiphon reboilers.," Applied Thermal Engineering, Elsevier., vol. 25, no. 16, pp. 2615-2629, 2005. [4] P. A. L. B. J. A. B. N. H. Ezekiel O. Agunlejika, "Sub atmospheric Boiling Study of the Operation of a Horizontal Thermosyphon Reboiler Loop: Instability.," Applied Thermal Engineering, Elsevier., vol. 109, no. Part-A, pp. 739-746, 2016. [5] D. Love, "No Hassle Reboiler Selection.," Hydrocarbon Processing., vol. 71, no. 10, pp. 41-47, 1992. [6] H. Z. Kister., Distillation Operations., New York.: McGraw-Hill., 1990. [7] S. S. Ulrich Eiden , "Use of Simulation In Rating and Design of Distillation Units.," Computers &. Chemical Engineering., vol. 24, no. Supplement, pp. S199-S204., 1997. [8] J. F. R. J. M. Coulson, "Coulson and Richardson's Chemical Engineering.," in Fluid Flow, Heat Transfer and Mass Transfer. Volume-1, 6th Edition., Swansea., Elsevier., 1999, pp. 494-496.

25. THANK YOU