Objective
To demonstrate the operation of the extractor when configured for single stage continuous solid liquid extraction and to assess the efficiency of the process.
Method
By measuring the conductivity and temperature of the final miscella as it leaves the process it is possible to find the percentage weight of extracted Potassium
Bicarbonate (KHCO3) in the final miscella and therefore the degree of extraction
taking place. Similar measurements of the fresh solvent entering the process allow the efficiency of the process to be investigated.
Equipment Required
UOP4 MkII Solid Liquid Extraction Unit
Solid carrier - porous polymer pellets containing Potassium Bicarbonate (prepared in advance).
Stopwatch (not supplied)
Measuring cylinder, typically 250 ml (not supplied)
Optional Equipment
None
Theory/Background
When the system is configured for single stage continuous extraction the fresh solid material is fed into the system using the spiral material feeder. The solid material is moved through the system by the rotating cell and fresh solvent sprinkled onto it continuously drains through it. (Refer to the flow diagram in Equipment Set-up below.) Once the solid material has been processed it discharges into the extracted solids tank. The miscella containing the soluble component is collected in the final miscella tank.
Single stage continuous extraction is an open loop system and the rate of extraction will be dependent on variables such as the solvent temperature, the solvent flow rate, the solids feed rate, the amount of solute in the dry solid and the characteristics of the contact between the solid particles and the liquid.
Because the extraction is continuous the process will stabilise after an initial period; however, transient changes as the process starts up and stabilises will be of interest, as well as the readings when steady state is achieved.
The % weight of KHCO3 in the final miscella can be determined from measurements
of temperature and conductivity of the final miscella using the conversion graphs in
Graphs of Concentration.
When choosing the operating parameters of an extraction process the main objectives are as follows:
a. To make the final miscella as concentrated as possible – to minimise the cost of further processing when recovering the soluble component from the
b. To use the minimum amount of solvent – to reduce operating costs.
c. To lose the minimum amount of solvent – solvent retained in the solids after processing
d. To maximise product output – to process the required amount of product in the minimum time.
e. To extract the maximum percentage of the valuable soluble component from the feed – any soluble component remaining in the solids after processing is wasted.
f. To minimise the energy input to the process (operating at the lowest practicable temperature)– to reduce operating costs.
It is clear that all of these objectives are inter-related and that any attempt to
compare how a system performs with different combinations of settings would require a comprehensive series of tests to determine the individual effects of each
parameter. Such a test is suggested in the Project Work section.
The efficiency of the process can be assessed by considering the following parameters:
Concentration of the final miscella. Amount of soluble component extracted.
Amount of soluble component remaining in the solids after processing. Amount of solvent remaining in the solids after processing.
Energy required to perform the extraction.
Equipment Set Up
Configure the equipment for single stage continuous extraction as depicted in the flow diagram below. Water from the fresh solvent tank is pumped upwards through the first stage heater and sprinkled onto the surface of the solid material which is moved beneath the sprinkler by the rotor. The miscella draining from the bottom of the rotor is collected in the final miscella tank.
Exercise C
Configuration for Single stage continuous extraction
Procedure
Start Up
Check that the UOP4 MkII is switched off, all switches are set to off and all rotary controls are set to minimum on the front panel of the console.
Fill the fresh solvent tank with clean water.
Fill the hopper of the spiral feeder with prepared solid carrier.
Plug in and switch on the UOP4 MkII. Adjust the setpoint of controller 1 to match the temperature indicated on the display (to avoid excessive overshoot when heating is required).
Set pump one to give the required flow rate (typically 5.0 on the speed control, approximately 6 litres per hour).
When solvent appears at the sprinkler bar measure and record the temperature TS of the solvent direct from the fresh solvent tank indicated on the stage 1 temperature controller (T1) before the heater is switched on.
Switch on heater ONE ONLY then adjust the set point on the stage 1 temperature controller to 40oC and allow the temperature to stabilise. Note that the heater must only be on when there is a steady flow of liquid through the heater.
Monitor temperatures T1 and T4 (T1 indicated on the stage 1 temperature controller, T4 indicated on the panel meter via the selector switch) and wait until the
temperatures have stabilised. Once the temperatures have stabilised the extraction can commence as follows.
Extraction
Before commencing the extraction it will be necessary to organise recording of the required data. The following readings will be required:
T1 Temperature of solvent entering rotor T4 Temperature of final miscella
C1 Conductivity of solvent entering the rotor (will remain constant) C4 Conductivity of final miscella
In manual operation it will be necessary to switch the multi function display on the console between C1, C4 and T4 in order to take down these readings on a regular basis (typically once per minute) as the process progresses.
Start the rotor cell and adjust the speed control to give the required rotational speed (typically 5.0 on the speed control, approximately 2 revs per hour).
Turn on the spiral material feeder and adjust the speed control to give the required depth of material in the cells of the rotor (typically 30 -50% full).
When the solid material reaches the aperture in the base at the rear of the extractor it will be necessary to turn on the spray nozzle so that the material is washed into the extracted solids tank. Adjust the position of the nozzle and pressure regulator as required to prevent overspray.
Note: It will be necessary to refill the hopper with prepared solid carrier as the
exercise proceeds.
Start the stopwatch and commence recording the above readings when the first cell containing the solid material reaches the sprinkler bar.
As the solvent extracts the KHCO3 from the solid carrier the output from conductivity
probe C4 will rise and eventually stabilise.
Note: When the system has achieved steady state small cyclic variations will be
observed in the reading from conductivity probe C4 as the individual cells of the rotor present fresh solid material to the solvent stream. This effect can be observed more clearly when logging results continuously using the optional PC logging interface and software (Armfield product code UOP4MkII-303IFD).