Introduction

Distillation is a form of physical separation. Typically, a mix of two miscible liquids is subjected to enough heat to cause the more volatile of the two liquids to evaporate and then condense in a separate unit. Because the two liquids are typically very alike in many physical and chemical properties, the separation needs to take place over a number of stages aligned up the length of the column. In a distillation column, these stages are actually trays of various configurations where the vapours rising up the column come in contact with a portion of the condensed liquids running back down. At the site of each of these trays, good mixing of the vapour and liquid occurs and a vapour-liquid equilibrium is established. In going up the height of the column, there is a an increasingly higher concentration of the more volatile component. At the top of the column, the percentage of the more volatile component can be as high as 96%.

Equipment

In the distillation column in the E030 laboratory, the trays contain a bubble-cap. With this design, there is an overflow that maintains a level of liquid on a tray. Vapour rises up the column and is forced by the cap to pass through slots that are below liquid level and thus to bubble through the liquid. There are 15 DN50 bubble cup trays distributed through the 3 sections of the column. Industrial units have many caps on each tray and usually many more trays. Alternatively some industrial units feature packed columns.

Unlike many industrial units, the lab apparatus has five sampling valves across the column with the first one at the bottom of the instrument (the heating kettle) three along the column and one on the top of the unit to allow for sampling the final distilled product. A thermocouple at each sampling level enables recording the temperature.

The HMI of the system is positioned on the control cabinet on the right hand site of the unit. The distillation process can be also controlled from the remote computer connected through the Ethernet cable or through the wireless network.

Figure 1: DVI/300 Pignat Distillation unit

Principle Elements

Figure 2 below shows a schematic of the unit with all principle elements identified. A listing of the principle elements follows after the Figure.

Figure 2: DVI/3000 distillation unit principal element identification

  1. Storage tank of the mixture to distillate: capacity 20L
  2. Dosing pump: adjustable flow rate from 0 to 16 L/h. Flow rate adjustment by frequency variation device.
  3. Preheater using 1000-Watt electric resistance. Includes:
    1. Temperature measurement
    2. Safety discharge valve and draining valve level detection by stainless steel float
    1. Temperature measurements
    2. Charging hole Draining valves
    3. Level detection by stainless steel float
    1. 15 DN50 bubble cap trays distributed into 3 column sections
    2. Three intermediate plates with temperature measurement and sampling valve.
    3. Column differential pressure measurement
    4. Removable heat insulation mantle.
    1. Cold water circulation into the coil
    2. Measurement of water inlet and outlet temperatures
    1. Cooling by stainless steel Liebig exchanger
    2. Draining valves and distillate sampling valves
    1. Pressure reducing valve and general isolating valve
    2. Condenser inlet and outlet water temperature
    3. Needle valve for the flow rate oriented to the Liebig exchangers
    4. Control valve and t flow transmitter on the condenser feeding water circuit

    Valve and Sensor Identification

    Figure 3 below shows another schematic of the equipment with all valves and sensors identified. A listing of these elements follows after the figure.

    Figure 3: : DVI/3000 distillation unit principal valve and sensor identification

    Manual valves

    Temperature Measurements

    Flow rate measurements

    Pressure measurements

    Level detection

    Control Cabinet

    The equipment includes the control cabinet shown in Figure 4.

    Figure 4: Control Cabinet

    The main operations of the control cabinet, as highlighted in the picture, are listed below:

    1. A main switch with locking possibility and a white light indicator
    2. General power on push button and green light indicator
    3. An emergency kill circuit breaker
    4. Two light push buttons green and red to power up and stop the dosing pump
    5. Two light push buttons green and red to power up and stop the kettle heating device
    6. Two light push buttons green and red to power up and stop the preheater device
    7. A three-way switch “reflux / cycle / draw off” to select the reflux conditions in the column

    HMI User Interface

    The HMI of the apparatus, shown in Figure 5, is accessible either through the control cabinet or through the PC connected to the apparatus.

    Figure 5: HMI User Interface

    The HMI contains five electronic controllers to control the following process parameters:

    In these controllers, green is the current parameter value, yellow is the set point, and red is the position of the actuating device. There are also six electronic displays for the indication of the following data:

    Functions

    The main functions that can be performed through the control cabinet are: