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MP5040 Lecture 5.pdf- Process engineering

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The document discusses different types of evaporators used in process engineering, including open kettle evaporators, horizontal tube natural circulation evaporators, vertical tube natural circulation evaporators, long tube vertical evaporators, and methods of operation for single effect and multiple effect evaporators. Multiple effect evaporators use a series of effects where the latent heat from one effect is used to evaporate water in the next effect, improving steam economy compared to single effect evaporators. Forwarded feed multiple effect evaporators feed the concentrate from one effect directly into the next effect to further concentrate the product using residual heat.

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MP5040: PROCESS ENGINEERING Lecturer: Miss. J Sajeeva Lecture Number 05
RECAP 1. Define evaporation? 2. What is mean by degree of freedom in process design? 3. What are the three types of flow diagrams, differentiate them. 4. Elaborate the way to select the pipe, for a suitable application? 5. The purpose of evaporations?
BASIC PROCESS OPERATIONS EVAPORATION
PROCESSING FACTORS 1. The liquid concentration 1. Viscosity Vs Mass transfer rates 2. For high viscosity liquids, adequate circulation or turbulence must be provided 2. Solubility 1. Solubility Vs temperature 2. Crystallization may occur after cooling down process 3. The sensitivity for the temperature 1. Products can degrade at higher temperature rates
PROCESSING FACTORS 4. Foaming/ frothing 1. Food stuffs like milk, or fatty acid solutions can form foam/ forth when boiling 5. Pressure and temperature 1. Boiling point depends on the operating pressure 6. Scale deposition and materials of construction 1. the aggregation of different materials within unwanted parts/areas in the oil/gas production system
TYPES OF EVAPORATION EQUIPMENT 1. Open kettle or Pan 2. Horizontal tube natural circulation evaporator 3. Vertical type natural circulation evaporator 4. Long tube vertical type evaporator 5. Falling film type evaporator 6. Forced circulation type evaporator 7. Agitated film evaporator 8. Open pan solar evaporator
OPEN KETTLE OR PAN EVAPORATOR Steam is supplied to the jacketed kettle in which the aqueous extract is placed. Heat is transferred to the extract by conduction and convection Construction Copper is the excellent material for the kettle because of its conductivity Iron is used for construction of jackets since it has the minimum conductivity
OPEN KETTLE OR PAN EVAPORATOR Working Aqueous extract to be evaporated is placed in the kettle. Steam is supplied through the inlet Steam gives out its heat to the contents and condensates leaves through the out let Advantages Used for both small and large scale operations Simple and easy to operate Low maintenance and installation costs Cheap Wide variety of materials can be used
OPEN KETTLE OR PAN EVAPORATOR Disadvantages Less heat economy Not suitable for heat sensitivity material Vapor can passes to atmosphere Low scale evaporation Advantages Concentrating aqueous and thermos stable liquors
HORIZONTAL TUBE NATURAL CIRCULATION EVAPORATOR
HORIZONTAL TUBE NATURAL CIRCULATION EVAPORATOR Steam is passed through the horizontal tubes, which are immersed in a pool of liquid to be evaporated. Heat is transferred through the tubes and solvent evaporates Concentrated liquid is collected Construction Large cylindrical body doomed shaped at the top and the bottom, made of cast iron or plate steel. Stainless steel tubes are used in steam compartments
HORIZONTAL TUBE NATURAL CIRCULATION EVAPORATOR Working Feed is introduced into the evaporator until the steam compartment is immersed. The horizontal tubes receives the heat and conduct it to the liquid. The feed absorbs heat and solvent gets evaporated. Concentrated liquid is collected. Uses Non viscous solution extraction (Eg Cascara extract) Uses Not good for foamy liquids Not good for the liquids which deposit in the surface The liquor circulation is poor.
VERTICAL TUBE NATURAL CIRCULATION EVAPORATOR
VERTICAL TUBE NATURAL CIRCULATION EVAPORATOR Liquid is passes through the vertical tubes and steam is supplied from outside tubes. Heat transfer is take place through the tubes and liquid gets heated The solvent evaporates, vapor escapes from the top and concentrated liquid is collected from the bottom. The liquid flows up because of the prevailing density gradient. Liquid-vapor disengagement occurs above the upper tube sheet. The liquid flows down through the central open space of the calandria called the down take or the downcomer , thus the continuous circulation occurs.
LONG TUBE VERTICAL TYPE EVAPORATOR
LONG TUBE VERTICAL TYPE EVAPORATOR This is another widely used natural circulation evaporator It has a long vertical tube bundle fitted with the shell The shell is projected into a larger diameter chamber or vapor head top. The feed enters the tube bundle at the bottom, flows through the tubes once, while undergoing vigorous boiling and discharges into the vapor head and impacts on a deflector plate above the free top end of the tube bundle. The concentrated liquor leaves the vapor chamber through a pipe and is withdrawn
LONG TUBE VERTICAL TYPE EVAPORATOR Advantages Large heating surface area in one body Low holdup Small floor surface Good heat transfer coefficients at reasonable temperature (rising Film) Good heat transfer coefficients at all temperature (falling Film) Disadvantages High head room Not suitable for salting kind of process Circulation required for falling film Poor feed distribution in rising film Uses Clean liquids, foaming liquids, corrosive solutions
METHODS OF OPERATION OF EVAPORATORS 1. Single effect evaporators 2. Forwarded feed multiple effect evaporator 3. Backward feed multiple effect evaporator 4. Parallel feed multiple effect evaporator
SINGLE EFFECT EVAPORATORS OF OPERATION OF EVAPORATORS
The feed enters The saturated steam at enters the heat exchange section Condensed steam leases as condensate The solution is the evaporator is assumed to be completely mixed Hence, the concentrated product and the solution in the evaporator have the same composition Temperature 1 is the boiling point of the solution Temperature of the vapor also, 1 since it is in equilibrium with the boiling solution The pressure is 1 where is the vapor pressure of the solution at 1 If the solution to be evaporated is assumed to be diluted and like water, then 1kg of steam condensing will evaporate approximately 1 kg of vapor. SINGLE EFFECT EVAPORATORS OF OPERATION OF EVAPORATORS
SINGLE EFFECT EVAPORATORS OF OPERATION OF EVAPORATORS
Single effect evaporators are often used when the required capacity of operation is relatively small and or the cost of the steam is relatively cheap compared to the evaporator cost However, for large capacity operation, using more than one effect will Markley reduce steam cost. SINGLE EFFECT EVAPORATORS OF OPERATION OF EVAPORATORS
FORWARDED FEED MULTIPLE EFFECT EVAPORATOR
FORWARDED FEED MULTIPLE EFFECT EVAPORATOR A single effect evaporator is wasteful of energy The latent heat of the vapor leaving is not used but is discarded Much of these latent heat, however can be recovered and reuses by employing a multiple effect evaporator A simplified diagram of a forward feed triple effect evaporation system is shown here
FORWARDED FEED MULTIPLE EFFECT EVAPORATOR If the feed to the first effect is near the boiling point at the pressure in the first effect, 1 kg of steam evaporate almost 1 kg of water. The first effect operates at a temperature that is high enough that the evaporated water, serves as the heating medium to the second effect. Here again almost, another kg of water is evaporated, which can then be uses as the heating medium to the third effect. As a very rough approximation, almost 3 kg water will be evaporated for 1 kg of steam in a third effect evaporator.
FORWARDED FEED MULTIPLE EFFECT EVAPORATOR Hence, the steam economy which is kg vapor evaporated/ kg steam used is increased. This also holds approximately for more than three effects. However the increased steam economy of a multiple effect evaporator is gained at the expense of the original first cost of these evaporators. This is used when the feed is hot or when the final concentrated product ,might be damaged at high temperature.

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MP5040 Lecture 5.pdf- Process engineering

  • 1. MP5040: PROCESS ENGINEERING Lecturer: Miss. J Sajeeva Lecture Number 05
  • 2. RECAP 1. Define evaporation? 2. What is mean by degree of freedom in process design? 3. What are the three types of flow diagrams, differentiate them. 4. Elaborate the way to select the pipe, for a suitable application? 5. The purpose of evaporations?
  • 4. PROCESSING FACTORS 1. The liquid concentration 1. Viscosity Vs Mass transfer rates 2. For high viscosity liquids, adequate circulation or turbulence must be provided 2. Solubility 1. Solubility Vs temperature 2. Crystallization may occur after cooling down process 3. The sensitivity for the temperature 1. Products can degrade at higher temperature rates
  • 5. PROCESSING FACTORS 4. Foaming/ frothing 1. Food stuffs like milk, or fatty acid solutions can form foam/ forth when boiling 5. Pressure and temperature 1. Boiling point depends on the operating pressure 6. Scale deposition and materials of construction 1. the aggregation of different materials within unwanted parts/areas in the oil/gas production system
  • 6. TYPES OF EVAPORATION EQUIPMENT 1. Open kettle or Pan 2. Horizontal tube natural circulation evaporator 3. Vertical type natural circulation evaporator 4. Long tube vertical type evaporator 5. Falling film type evaporator 6. Forced circulation type evaporator 7. Agitated film evaporator 8. Open pan solar evaporator
  • 7. OPEN KETTLE OR PAN EVAPORATOR Steam is supplied to the jacketed kettle in which the aqueous extract is placed. Heat is transferred to the extract by conduction and convection Construction Copper is the excellent material for the kettle because of its conductivity Iron is used for construction of jackets since it has the minimum conductivity
  • 8. OPEN KETTLE OR PAN EVAPORATOR Working Aqueous extract to be evaporated is placed in the kettle. Steam is supplied through the inlet Steam gives out its heat to the contents and condensates leaves through the out let Advantages Used for both small and large scale operations Simple and easy to operate Low maintenance and installation costs Cheap Wide variety of materials can be used
  • 9. OPEN KETTLE OR PAN EVAPORATOR Disadvantages Less heat economy Not suitable for heat sensitivity material Vapor can passes to atmosphere Low scale evaporation Advantages Concentrating aqueous and thermos stable liquors
  • 10. HORIZONTAL TUBE NATURAL CIRCULATION EVAPORATOR
  • 11. HORIZONTAL TUBE NATURAL CIRCULATION EVAPORATOR Steam is passed through the horizontal tubes, which are immersed in a pool of liquid to be evaporated. Heat is transferred through the tubes and solvent evaporates Concentrated liquid is collected Construction Large cylindrical body doomed shaped at the top and the bottom, made of cast iron or plate steel. Stainless steel tubes are used in steam compartments
  • 12. HORIZONTAL TUBE NATURAL CIRCULATION EVAPORATOR Working Feed is introduced into the evaporator until the steam compartment is immersed. The horizontal tubes receives the heat and conduct it to the liquid. The feed absorbs heat and solvent gets evaporated. Concentrated liquid is collected. Uses Non viscous solution extraction (Eg Cascara extract) Uses Not good for foamy liquids Not good for the liquids which deposit in the surface The liquor circulation is poor.
  • 13. VERTICAL TUBE NATURAL CIRCULATION EVAPORATOR
  • 14. VERTICAL TUBE NATURAL CIRCULATION EVAPORATOR Liquid is passes through the vertical tubes and steam is supplied from outside tubes. Heat transfer is take place through the tubes and liquid gets heated The solvent evaporates, vapor escapes from the top and concentrated liquid is collected from the bottom. The liquid flows up because of the prevailing density gradient. Liquid-vapor disengagement occurs above the upper tube sheet. The liquid flows down through the central open space of the calandria called the down take or the downcomer , thus the continuous circulation occurs.
  • 15. LONG TUBE VERTICAL TYPE EVAPORATOR
  • 16. LONG TUBE VERTICAL TYPE EVAPORATOR This is another widely used natural circulation evaporator It has a long vertical tube bundle fitted with the shell The shell is projected into a larger diameter chamber or vapor head top. The feed enters the tube bundle at the bottom, flows through the tubes once, while undergoing vigorous boiling and discharges into the vapor head and impacts on a deflector plate above the free top end of the tube bundle. The concentrated liquor leaves the vapor chamber through a pipe and is withdrawn
  • 17. LONG TUBE VERTICAL TYPE EVAPORATOR Advantages Large heating surface area in one body Low holdup Small floor surface Good heat transfer coefficients at reasonable temperature (rising Film) Good heat transfer coefficients at all temperature (falling Film) Disadvantages High head room Not suitable for salting kind of process Circulation required for falling film Poor feed distribution in rising film Uses Clean liquids, foaming liquids, corrosive solutions
  • 18. METHODS OF OPERATION OF EVAPORATORS 1. Single effect evaporators 2. Forwarded feed multiple effect evaporator 3. Backward feed multiple effect evaporator 4. Parallel feed multiple effect evaporator
  • 19. SINGLE EFFECT EVAPORATORS OF OPERATION OF EVAPORATORS
  • 20. The feed enters The saturated steam at enters the heat exchange section Condensed steam leases as condensate The solution is the evaporator is assumed to be completely mixed Hence, the concentrated product and the solution in the evaporator have the same composition Temperature 1 is the boiling point of the solution Temperature of the vapor also, 1 since it is in equilibrium with the boiling solution The pressure is 1 where is the vapor pressure of the solution at 1 If the solution to be evaporated is assumed to be diluted and like water, then 1kg of steam condensing will evaporate approximately 1 kg of vapor. SINGLE EFFECT EVAPORATORS OF OPERATION OF EVAPORATORS
  • 21. SINGLE EFFECT EVAPORATORS OF OPERATION OF EVAPORATORS
  • 22. Single effect evaporators are often used when the required capacity of operation is relatively small and or the cost of the steam is relatively cheap compared to the evaporator cost However, for large capacity operation, using more than one effect will Markley reduce steam cost. SINGLE EFFECT EVAPORATORS OF OPERATION OF EVAPORATORS
  • 23. FORWARDED FEED MULTIPLE EFFECT EVAPORATOR
  • 24. FORWARDED FEED MULTIPLE EFFECT EVAPORATOR A single effect evaporator is wasteful of energy The latent heat of the vapor leaving is not used but is discarded Much of these latent heat, however can be recovered and reuses by employing a multiple effect evaporator A simplified diagram of a forward feed triple effect evaporation system is shown here
  • 25. FORWARDED FEED MULTIPLE EFFECT EVAPORATOR If the feed to the first effect is near the boiling point at the pressure in the first effect, 1 kg of steam evaporate almost 1 kg of water. The first effect operates at a temperature that is high enough that the evaporated water, serves as the heating medium to the second effect. Here again almost, another kg of water is evaporated, which can then be uses as the heating medium to the third effect. As a very rough approximation, almost 3 kg water will be evaporated for 1 kg of steam in a third effect evaporator.
  • 26. FORWARDED FEED MULTIPLE EFFECT EVAPORATOR Hence, the steam economy which is kg vapor evaporated/ kg steam used is increased. This also holds approximately for more than three effects. However the increased steam economy of a multiple effect evaporator is gained at the expense of the original first cost of these evaporators. This is used when the feed is hot or when the final concentrated product ,might be damaged at high temperature.