This operation models the washing of impurities out of a feed stream using a washer. One type of washer consists of a belt conveyor feeder with a spraying system on top. As the belt conveyor transports a solids feed, an aqueous detergent is sprayed to wash away impurities in the feed stream.
If the option to consider solids is not checked (default), then for every component you must specify the component’s removal percentage from the feed stream to the wash-out stream. Based on the specified component data, the program will do the component mass balances to determine the component flows of the product and wash-out streams. In that case, the program will solve the following component mass balances:
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where:
● mF,i is the mass flow rate of pure component i in the feed stream (kg/s),
● mP,i is the mass flow rate of pure component i in the product stream (kg/s),
● xi is the removal fraction of the mass of pure component i from the feed stream to the wash-out stream.
● mw-in,i is the mass flow rate of pure component i in the wash-in stream (kg/s),
● mw-out,i is the mass flow rate of pure component i in the wash-out stream (kg/s), and
● r is the fraction of wash-in stream flow that is retained by the product stream.
If the option to consider solids is checked, then the component removal data table is be used to specify component removal data only for particulate solid components (i.e., undissolved solids, suspended or precipitated). Only pure components that are set as solid through the Pure Component Properties dialog can be set as particulate solids in the components table. Based on the specified component removal percentages, the program can solve the mass balances for the particulate solid components in order to calculate the flows of those components in the product and wash-out streams. In addition to setting one or more solid components as particulate solids and specifying the removal percentages of those components to the wash-out stream, you must also specify either the total (particulate and dissolved) or particulate solids percentage of the product stream. Based on this information, the program will calculate the total removal percentage of all other components besides particulate solids (i.e., dissolved solids, liquids and gases), assume that the removal percentage of each of those components is the same as the total removal percentage of those components, and solve the component mass balances for those components to calculate the flows of those components in the product and wash-out streams.
Three options are available for specifying the product stream temperature:
● Set Approach To Equilibrium,
● Set Temperature, and
● Set Approach To Ambient Temperature.
In the first case, it is assumed that the feed stream and the wash-in stream are mixed adiabatically and they reach a certain degree of thermal equilibrium. The approach to thermal equilibrium factor is used as a measure of heat transfer between the feed stream and the wash-in stream. It is defined as the difference of the actual product stream temperature from the feed stream temperature divided by the difference of the equilibrium temperature from the feed stream temperature. The equilibrium temperature is calculated based on the VLE data specifications for the corresponding procedure state stream. In mathematical terms, the approach to equilibrium factor can be expressed as follows:
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where:
● f is the approach to thermal equilibrium factor,
● TF is the temperature of the feed stream (K),
● TP is the temperature of the product stream (K), and
● Teq is the equilibrium temperature of the product and wash-out streams (K).
In the second case, you must specify the product stream temperature directly. In the third case, you must specify an approach to ambient temperature factor .This is defined as the difference of the actual product stream temperature from the feed stream temperature divided by the difference of the equilibrium temperature from the feed stream temperature. It can be calculated from the above equation if the equilibrium temperature is replaced with the ambient temperature.
After determining the product stream temperature, the temperature of the wash-out stream can then be calculated from the energy balance around the washer, which can be written as follows:
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where:
● hF is the enthalpy of the feed stream (J),
● hP is the enthalpy of the product stream (J),
● hwi is the enthalpy of the wash-in stream (J), and
● hwo is the enthalpy of the wash-out stream (J).
The operating throughput is calculated based on the non-gaseous mass flow rate of the feed stream.
If the equipment size option is in Design Mode, the user specifies the maximum equipment throughput per unit. If the calculated operating throughput exceeds the maximum throughput per unit, then, the program assumes multiple, identical units operating in parallel with an operating throughput per unit of less than the maximum and a total operating throughput equal to the mass flow rate of the feed stream.
If the equipment size option is in Rating Mode, the user specifies the rated throughput and the number of units. If the calculated operating throughput per unit exceeds the rated throughput, a warning message is displayed advising the user to increase the equipment power or number of units, or reduce the mass flow rate of the feed stream.
● 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 washing calculations. The gaseous portion is transferred directly to the product stream.
● The wash-in 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 washing calculations. The gaseous portion is transferred directly to the wash-out stream.
● If you specify a value for the outlet temperature, then this value must be between the feed stream temperature and the wash-in stream temperature.
The interface of this operation has the following tabs:
● Oper. Cond’s, see Bulk Washing: Oper. Conds Tab
● Power, see Throughput Operations: Utilities 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
