Unit Operations Dr. Dongyun Zhang A

Unit Operations Chapter 3 Separation ( 分离 ) Chapter 5 Evaporation ( 蒸发 ) Chapter 8 Gas Absorption ( 气体吸收 ) Chapter 9 Distillation ( 蒸馏 ) Chapter 10 Leaching and Extraction ( 浸析 / 萃取 ) Chapter 11 Drying ( 干燥 ) Physical process Enthalpy balance Mass balance Mechanical energy balance Principles

Chapter 3 Separation ( 分离 ) Screening ( 筛分 ) Separate particles based on size or shape sieving diameter

settlement ( 沉降 ) p138 Separate solids from fluids depending on difference of density Gravitational settling process ( 重力沉降 )

Centrifugal settling process ( 离心沉降 )

Filtration ( 过滤 ) p140 Separate solids from liquids by passing suspension through a permeable medium ( 过滤介质 ) which retains the particles four types of driving force: 1.Gravity ( 重力 ) 2.Vaccum ( 真空 ) 3.Pressure ( 压力 ) 4.Centrifugal ( 离心 )

Chapter 5 Evaporation ( 蒸发 ) p245 concentrate a solution consisting of a nonvolatile ( 非挥发性 ) solute and a volatile ( 挥发性 ) solvent. Evaporation is conducted by vaporizing a portion of the solvent to produce a concentrated solution of thick liquor ( 浓缩液 ). classificate by usage of vapor: 1.single-effect evaporation( 单效蒸发 ) 2.multiple-effect evaporation ( 多效蒸发 )

the solute balance F=the rate of thin liquor, or feed, kg/h W=the rate of vapor flow to the condenser x 0 =a solids content of mass fraction of feed x 1 =a solids content of mass fracton of feed Enthalpy (Heat) balance q s =rate of heat transfer through heating surface from steam q=rate of heat transfer from heating surface to liquid p256

 circulation evaporators ( 循环型蒸发器 ) 中央循环管式蒸发器外热式蒸发器 forced-circulation ( 强制循环 ) evaporator natural circulation ( 自然循环 ) evaporator

climbing film evaporator 升膜式 蒸发器 Agitated-film evaporator 刮板式 蒸发器 falling-film evaporator 降膜式 蒸发器  once-through evaporators ( 单程型蒸发器 )

Chapter 9 Distillation ( 蒸馏 ) p348 α relative volatility ( 相对挥发度 ) The larger of α, the easer for components to separate separate resulting from differences in vapor- and liquid-phase compositions arising from the partial vaporization of a liquid mixture or the partial condensation of a vapor mixture. The vapor phase becomes enriched in the more volatile components ( 易挥发组分 / 轻组分 ) while the liquid phase is depleted ( 脱 除 ) of those same components.

 flash distillation ( 闪蒸 / 平衡蒸馏 ) vaporize a definite fraction of the liquid in such a way that the evolved vapor is in equilibrium with the residual liquid, separating the vapor from the liquid, and condensing the vapor.

 continuous distillation with reflus( 精馏 ) P356 separate components of comparable volatility rectifying section 精馏段 heavy components light components stripping section 提馏段

青海格尔木炼油厂年产 100 吨常压蒸馏装置 兰州石化年 550 万吨常减压蒸馏装置

Chapter 8 Gas Absorption ( 气体吸收 ) p321 During the contact of the two phases (a gas and a liquid) the components of the original mixture redistribute themselves between the two phases. It is based on the solubility difference of the component in two phases. The phases are then separated by simple physical method. Gas absorpt ion stripping / desorption pure solute

Chapter 10 Leaching and Extraction ( 浸析 / 萃取 ) leaching ( 浸析 ) p393 Removing one constituent from a solid by means of a liquid solvent is called leaching or solid extraction. It is used to dissolve soluble matter from its mixture with an insoluble solid.

liquid extraction ( 液液萃取 ) p399 Removing one constituent from a liquid by means of a liquid solvent is called liquid extraction. It is used to recover a valuable product from a multicomponent solution by contact with an immiscible solvent that has a high affinity for the product. liquid extraction can be used to separate close-boiling liquids that would be difficult to separate by distillation.

Chapter 11 Drying ( 干燥 ) p426 remove relative small amounts of water or other liquid from the solid material to reduce the content of residual liquid to an acceptably low value. Drying is usually the final step in a series of operations, and the product from a dryer is often ready for final packaging.

1.What are the differences between evaporation and drying? 2.What are the differences between evaporation and distillation? 3.Which unit operations are working based on the property of solubility? 4.What are the differences between screening and filtration? Questions & Homework 5.What are the differences between absorption and extraction?