DESIGN OF ADSORPTION SYSTEMS

Conceptual design of adsorption systems conceptual design has a variety of definitions but is generally understood to lie somewhere between a process concept and final engineering design consisting of detailed plans and specifications

Conceptual design of adsorption system Conceptual design of an adsorption system should consist of the following elements as a minimum: process configuration and adsorbent selection integration of the adsorption process with other processes major items of capital equipment and their sizes

Conceptual design general operating conditions general mass and energy balances scoping cost estimate therefore, the conceptual design of an adsorption system is best undertaken as an iterative process in which the experimental program and the design are conducted simultaneously

Some limitations know thy application. The ultimate application of the adsorption system determines the performance objectives and defines the constraints on the system performance data are necessary to define key design parameters invariably, the required data have not been previously published and must be generated in laboratory experiments the data must always be extrapolated to develop a conceptual design, but one must know the limitations of the data

Experimental data for conceptual design the data can be grouped into a few specific categories: adsorption isotherm loading curves regeneration curves Regeneration curves are similar to loading curves and fulfil the same function for defining the conceptual design of the regeneration cycle

Adsorption isotherms isotherms portray the concentration of solute on the adsorbent as a function of the solute concentration in the feed isotherms can be run to equilibrium in which case they are useful for the selection of an adsorbent based on capacity alternatively, they can be run as a function of time, in which case they can be used to select an adsorbent on the basis of adsorption rate

Loading curves loading curves display the composition of the effluent from an adsorbent column as a function of throughput and are therefore the single best experimental model of column performance many dependent design variables come directly from loading curves:  adsorbent capacity  leakage  throughput

Conceptual design option and criteria main design categories are: adsorbent selection adsorption configuration sizing operating regenerant regeneration cycle regenerant fate pretreatment

Adsorbent selection design option and criteria option granular, powdered, fibre activated carbon, polymeric and other adsorbents criteria highest adsorbent capacity commensurate with desired leakage at minimum residence time economic regeneration process available adsorbent lifetime

Adsorption configuration design option and criteria option batch or continuous process fixed or moving bed countercurrent loading/regeneration criteria highest adsorbent capacity commensurate with an acceptably rapid rate of loading highest solute recovery commensurate with lowest regenerant usage at acceptable capital cost highest adsorbent capacity and lowest leakage at acceptable high residence time

Sizing design option and criteria option  quantity of adsorbent  single column, multiple column  vessel dimensions criteria  minimum residence time to achieve desired  leakage  minimum number of adsorption vessels  highest linear velocity with acceptable hydraulic pressure drop

Operating design option flow rate cycle length time loading level breakthrough/leakage

Operating design criteria flow rate defined by residence time and quantity of adsorbent longest cycle length commensurate with minimum residence time and acceptable leakage highest loading level commensurate with minimum residence time and acceptable leakage breakthrough/leakage defined by application requirements

Regenerant design option and criteria option pressure swing steam thermal chemical solvent bilogical criteria most efficient desorption of solute as a function of regenerant usage solute selection commensurate with desired fate of solute (recovery, incineration)

Regeneration cycle design options flow rate cycle length (time) regenerant throughput regenerant conservation degree of solute desorption backwashing

Regeneration cycle design criteria maximum flow rate commensurate with maximum desorption efficiency and minimum regenerant utilization maximum cycle length commensurate with loading cycle length minimum regenerant usage with maximum solute removal minimum regenerant loss in displacement mixing adsorbent lifetime maintenance of acceptable pressure drop on loading cycle

Regenerant fate design option and criteria option spent regenerant disposal regenerant recovery solute recovery solute recycle criteria minimum disposal cost maximum recovery of regenerant maximum value from recovery of recycle of solute

Pretreatment design criteria suspended solids sufficiently low to prevent pressure drop increase on loading cycle no temperature adjustment unless adsorption/desorption adversely affected bacterial growth must be absent pH adjustment for maximum adsorption efficiency equalize extensive swing of flow and concentration