The main objective of this operation is to estimate the time for loading a column (if not specified by the user) and estimate the number and size of columns required (when the equipment is in Design Mode). The same operation handles loading of cation exchange, anion exchange, and mixed bed columns.
● Ion Exchange Procedure (for Demineralization)
The specified binding fraction for each component of the feed stream is used to determine the total fraction of ions that bind to the resin. The remaining fraction of ions that do not bind to the resin exit through the outlet stream.
In Design Mode, the following equations are used for the calculation of total bed volume required by the operation:
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where:
● FD is the equipment’s overdesign factor,
● VF is the total feed volume per procedure cycle,
● tp is breakthrough (process) time,
● EBCT is the empty-bed contact time,
● Ns is the service volume (expressed as number of bed volumes),
● mion is the total mass of ions that bind to the resin(s) per procedure cycle, and
● Wb is the resin binding capacity (expressed as mass of ions per bed volume).
The value of EBCT is usually in the range of 1.5 to 7.5 min (Clifford, 1990).
The total bed volume is calculated from the above equations depending on the specified option for the breakthrough time. The following specification options are available:
● Set by User,
● Calculated Based on Binding Capacity, or
● Calculated Based on Service Volume.
If the breakthrough time is Set by User, the total bed volume is estimated from the specified breakthrough time and empty-bed contact time. If the breakthrough time is Calculated Based on Binding Capacity, the total bed volume is estimated from the specified binding capacity. If the breakthrough time is Calculated Based on Service Volume, the total bed volume is estimated from the specified service volume.
Dividing the bed volume by the ‘Bed to Column Height’ ratio yields the column volume. When the bed height, Hb, is specified, its diameter, D, is calculated using the following equation:
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If D > Dmax, then multiple columns are assumed in parallel. Alternatively, the user may specify the ‘Bed Height to Diameter’ ratio and have the model calculate the bed and column dimensions.
If the Plant Operation Mode is Batch, VF is calculated by dividing the corresponding feed volume per batch of the feed stream by the procedure’s Number of Cycles per Batch. Similarly, mion is calculated by summing-up the product of mass per batch and binding percentage for all components of the feed stream for which the ‘Ignore in Sizing?’ check-box is not checked, and dividing the sum by the Number of Cycles per Batch.
If the Plant Operation Mode is Continuous, VF is calculated by multiplying the volumetric flow rate of the feed stream with the procedure’s Holdup Time. Similarly, mion is calculated by summing-up the product of mass flow rate and binding percentage for all components of the feed stream for which the ‘Ignore in Sizing?’ check-box is not checked, and multiplying the sum with the procedure’s Holdup Time. Note that the specified holdup time must be greater than or equal to the procedure’s Cycle Time divided by 1 + M, where M is the number of extra sets of equipment units in stagger mode; for more details on the use of holdup time, see Holdup Time; for more details on the use of stagger mode, see Staggered Mode.
The binding capacity of the resin refers to all the compounds that bind to the resin and whose ‘Ignore in Sizing?’ check-box is not selected. The binding capacity can be specified based on:
● Ion Mass, or
● CaCO3 hardness.
If the resin binding capacity is specified based on CaCO3, then, the ion mass flow refers to equivalent CaCO3. The CaCO3 ratio can be specified for a pure component through the ‘Aqueous’ tab of the Pure Components Properties page; for more details on viewing/editing the properties of a pure component, see Pure Component Properties. Please refer to the literature for a straightforward explanation of water hardness expressed on the basis of CaCO3 (Kemmer, 1988 – Chapter 4).
In Design Mode, as well as in Rating Mode, the program will check that the specified binding capacity is adequate for retaining the specified binding fractions of all feed stream components that are not ‘ignored in sizing’.
The following equation may be derived from eq. (A.178) for the calculation of breakthrough time with respect to empty-bed contact time and service volume:
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If the breakthrough time is Set by User, then, if the equipment sizing option is in Design Mode, the above equation is used to calculate the service volume from the specified breakthrough time and empty-bed contact time. If the equipment sizing option is in Rating Mode, the service volume is calculated from eq. (A.178) and the above equation is used to calculate the empty-bed contact time from the service volume and the specified breakthrough time.
If the breakthrough time is Calculated Based on Binding Capacity, the service volume is calculated from eq. (A.178) and the above equation is used to calculate the breakthrough time from the service volume and the specified empty-bed contact time.
If the breakthrough time is Calculated Based on Service Volume, the above equation is used to calculate the breakthrough time from the specified service volume and empty-bed contact time.
Note that in Rating Mode, FD is equal to one in eq. (A.178).
1. Clifford, D.A. (1990). Ion Exchange and Inorganic Adsorption. in “Water Quality and Treatment”, American Water Works Association, 4th Edition, McGraw-Hill, Inc., Edited by: F. W. Pontius.
2. Kemmer, F.N. (1988). The NALCO Water Handbook, 2nd Edition, McGraw-Hill Book Company.
● The feed stream must carry material of non-zero flow and of liquid/solid phase. If the material is found to be of mixed phase, then only the liquid/solid portion is considered in column size calculations.
● The total volume-specific mass of ions that bind to the resin per cycle must not exceed the binding capacity of the resin.
The interface of this operation has the following tabs:
● Oper. Cond’s, see INX Column Loading: Oper. Conds Tab
● Labor, etc, see Operations Dialog: Labor etc. Tab
● Description, see Operations Dialog: Description Tab
● Batch Sheet, see Operations Dialog: Batch Sheet Tab
● Scheduling, see Operations Dialog: Scheduling Tab
