Survey of unit operations

Survey of unit operations

1. Survey of Unit Operations Nadia Junaid

2. Unit Operations: Introduction Chemical Engineering is study of a group of industrial processes in which raw materials are changed or separated into useful products RAW MATERIALS >>>>>>>> PRODUCTS Chemistry: - to create a new substance - to study its properties - to investigate all possible pathways from one substance to another Chemical Engineering: - to design the most optimal technology for production of a specified substance from raw materials - to develop and discover new technological applications for materials

3. A raw material can be converted into a Product by doing such operations that can cause certain changes/steps, physical or chemical Changes (Steps) Raw Materials Product

4. Operations on Raw Materials The operations may be Physical operations or Chemical Operations .

5. A Physical (Operation) Change or A Chemical Change Convert Water into Ice (Cooling) Is any chemical Change there? NO Make a sugar solution Is any chemical Change there? NO Convert Water in to Vapours / Steam (Heating) This is also a physical Change

6. Differentiate the following as Physical or Chemical changes Combustion of Wood Combustion of Natural Gas Rusting of Iron Drying Heating Cooling Crushing of stones Separation Distillation (First 3 steps/operations are Chemical Changes, and the remaining are Physical Operations)

7. History of the term “Unit Operation” Historically, the different chemical industries were regarded as different industrial processes and with different principles. Arthur Dehon Little propounded the concept of "unit operations " to explain industrial chemistry processes in 1916. In 1923, William H.Walker , Warren K. Lewis and William H. McAdams wrote the book The Principles of Chemical Engineering and explained the variety of chemical industries have processes which follow the same physical laws. They summed-up these similar processes into unit operations. Each unit operation follows the same physical laws and may be used in all chemical industries. The unit operations form the fundamental principles of chemical engineering.

8. Define Unit Operation In chemical engineering and related fields, a unit operation is a basic step in a process . Unit operations involve bringing a physical change such as separation, crystallization, evaporation, filtration etc. For example, in milk processing, homogenization , pasteurization , chilling, and packaging are each unit operations which are connected to create the overall process. A process may have many unit operations to obtain the desired product.

9. Unit Operations are operations that cause Physical Changes only Unit Operations is a method of analysis and design of chemical engineering processes in terms of individual tasks/operations -It is a way of organizing chemical engineering knowledge into groups of individual tasks/operations -A unit operation: basic step in a chemical engineering process that can cause physical change conversions.

10. Examples: Unit Operations Heat Transfer Evaporation Humidification Gas absorption Solvent Extraction Adsorption Distillation Drying Mixing Classification Fluidization Filtration Screening Crystallization Centrifugation Materials Handling Fluid Dynamics

11. unit operations consist of five classes Fluid flow processes, including fluids transportation , filtration , solids fluidization Heat transfer processes, including evaporation , condensation Mass transfer processes, including gas absorption , distillation , extraction , adsorption , drying Thermodynamic processes, including gas liquefaction , refrigeration Mechanical processes, including solids transportation , crushing and pulverization , screening and sieving Chemical engineering unit operations also fall in the following categories: Combination ( mixing ) Separation ( distillation ) Reaction ( chemical reaction )

12. Unit Operations: Classification Fluid flow processes - fluid transport - solids fluidization - mixing Heat transfer processes - heating/cooling - evaporation/condensation Mass transfer processes - absorption - distillation - extraction - adsorption - drying Thermodynamic processes - liquifaction - refrigeration Mechanical processes - crushing - sieving - solid transportation

13. Chemical separation processes: required background B V D - How do we know that at pressure P and temperature T, vapour and liquid phase are present in the system? - What is the composition of the phases? Chemical engineering thermodynamics L a ,x a V a ,y a V b ,y b L b ,x b - How do we know the amount of mass exchanged by two phases? - What is the new composition of the phases? Mass transfer methods

14. Chemical separation processes Very Important to know as bio Chemical Engineers Use Technology maturity Distillation Gas Absorption Crystallization Adsortion Membranes Chromatography

15. What to Know about Unit operations All the unit operations obey simple physical laws, Knowledge of the laws which is governing a specific unit operation is necessary. The information about the Type of equipment capable of operation/conversion at a large scale is necessary

16. Heat Transfer Laws governing heat transfer Modes of heat transfer Conducation Convection Radiation (The above has been discussed in class)

17. Heat Transfer Equipment In daily life Air conditioner Heater Refrigerator Cooking Range Fans

18. Daily life examples of Heat transfer Car radiator Motor Bike engine FINS

19. Heat Transfer In Industry Normally Heating is provided by steam (Boilers) Cooling is by water / air (Cooling Towers)

20. Heat Transfer Equipment Shell & tube type heat exchanger Coil type heater

21. DRYING

22. Drying of Clothes

23. Hair drying

24. Drying of food items

25. Open air drying

26. DRYING Removal of moisture/water from a substance is termed as drying. Moisture drying from a substance depends on many factors, For example: HUMIDITY, During rainy season it is difficult to dry clothes And during summer it takes no time is drying

27. Factors affecting rate of drying The water which is removed from a wet/damp material is evaporated in air. The more is the temperature diff the more is the rate of drying The more is the humidity, lesser would be rate of drying Area of drying, More is area exposed more would be rate of drying

28. METHODS OF DRYING Application of hot air ( convective or direct drying). Air heating increases the driving force for heat transfer and accelerates drying. It also reduces air relative humidity , further increasing the driving force for drying. In the falling rate period, as moisture content falls, the solids heat up and the higher temperatures speed up diffusion of water from the interior of the solid to the surface

29. . Spray drying Dielectric drying (radiofrequency or microwaves being absorbed inside the material) is the focus of intense research nowadays. It may be used to assist air drying or vacuum drying. Drum drying Freeze drying or lyophilization is a drying method where the solvent is frozen prior to drying and is then sublimed , i.e., passed to the gas phase directly from the solid phase, below the melting point of the solvent. It is increasingly applied to dry foods

30. Application of Drying

31. DRYING vs EVAPORATION

32. Evaporation

33. FACTORS INFLUENCING EVAPORATION Temperature : Higher the temperature, greater will be the evaporation (Ex – Alkaloids, Harmones , Enzymes, antibiotics – heat sensitive) Vapour pressure : Rate of evaporation is directly proportional to the vapour pressure of the liquid Lower the pressure, greater will be the evaporation Surface area : Greater the surface area of the liquid, greater will be the evaporation

34. Time of evaporation : Exposure time is longer – more evaporation Density: The higher the density, the slower a liquid evaporates Concentration : Low concentration of the substance – faster evaporation

35.   Moisture Content of Feed: Some drug constituents undergoes hydrolysis readily in presence of moisture at high temperature. To prevent the decomposition, the material is exposed to low temp. initially, then exposed to higher temp. Time of evaporation: If time of exposure is longer, greater will be the evaporation, provided the constituents are thermostable . Exposure of a drug to a relatively high temp. for a short period of time may be less destructive of active principle than a lower temp. with long exposure time

36. Theory For molecules of a liquid to evaporate T hey must be located near the surface, be moving in the proper direction, and have sufficient kinetic energy Since the kinetic energy of a molecule is proportional to its temperature, evaporation proceeds more quickly at higher temperatures. As the faster-moving molecules escape, the remaining molecules have lower average kinetic energy, and the temperature of the liquid thus decreases. This phenomenon is also called evaporative cooling

37. Evaporator

38. Examples Concentration of milk to produce condensed milk Concentration of juices Concentration of NaOH , NaCl from aqueous solutions to produce salt. Ether recovery from fat extraction

39. TYPES OF EVAPORATORS Evaporators with heating medium in jacket – Steam jacketed kettle (Evaporating pan) (II) Vapour heated evaporators with tubular heating surfaces (A)Evaporators with tubes placed horizontally - Horizontal tube evaporator (B)Evaporators with tubes placed vertically (i) Evaporators with short tubes (a) Single effect evaporators - Short tube vertical evaporator - Basket type evaporator (b) Multiple effect evaporator - Triple effect evaporator (ii) Evaporators with long tubes (a)Evaporators with natural circulation - Climbing film evaporator - Falling film evaporator (b)Evaporators with forced circulation - Forced circulation evaporator

40. DISTILLATION

41. Distillation Equipments

42. Types of distillation

43. Application of Distillation Purification of materials : Natural Products Flavors Essential Oils Fragrances Distilled air to separate it’s components like oxygen, nitrogen, and argon Solvent Recycling Xylene Solvent Recycling Alcohol Solvent Separate crude oil fractions

44. Herbal Distillates