CONTINUOUS DISTILLATION COLUMN

Distillation has always been and will continue to be one of the most important industrial processes for separating the different components of a liquid mixture. Laboratory scale distillation columns are needed to provide adequate practical training for student engineers and plant operators in a safe environment. They may also be used to acquire process separation data, of use in full-scale plant design.

The UOP3CC allows the study of both batch and continuous distillation, packed or plate column operation, operation under atmospheric pressure or under vacuum, azeotropic distillation, and manual, PID, PLC or computer control of the process. Data logging of the process is also possible.

UOP3CC Continuous Distillation Column

with computer control

Figure 1. Schematic Diagram of Apparatus

Figure 2. Diagram of Distillation Column

Figure 3. Diagram of UOP3CC Process Unit

Figure 4. Diagram of UOP3CC Console

B. DESCRIPTION

Where necessary, refer to the drawings on pages 19 to 22.

1. Overview

The UOP3CCContinuous Distillation Column is a self-contained distillation facility consisting of two interconnected units: a floor standing process unit and a bench mounted control console.

2. Floor-Standing Frame

The distillation column is mounted on a floor standing, welded tubular steel framework (1) fitted with four adjustable feet (2). The frame is designed to allow the use of a fork lift or pallet truck to manoeuvre the unit into position initially.

3. Distillation Column

The 50mm diameter sieve plate column is made up of two glass sections (3) and (4) each containing four sieve plates. The columns are separated by a central feed section and arranged vertically for counter-current vapor/liquid flow. The column is insulated to minimize heat loss.

The glass column incorporates a total of eight sieve plates in two sections (3) and (4) each containing four plates. Each plate (D) is located by a central support rod (E) and incorporates a weir (F) and downcomer (G) to create a liquid seal between successive stages. The liquid seal on the final plate in each section is achieved by U-tube (H).

Feed mixture from either of the feed tanks is pumped by pump (7) to the base, centre or top of the distillation column at connections (A), (B) or (C) respectively. The feed pump incorporates a length of Viton rubber tubing. This tubing is suitable for all of the recommended test mixtures (see “Operational Procedures”). Where other test mixtures are being used, the suitability of this material must be checked.

4. Reboiler

The reboiler (13) situated at the base of the column is manufactured from 316 stainless steel and incorporates a flame-proof immersion type heating element. Either batch or continuous distillation can be carried out using this reboiler.

In continuous operation, valve (V1) is open and bottom product flows from the reboiler through the bottom product cooler (15) to the bottom product tank (9). It is possible to preheat the feed to the column by directing the feed through a spiral coil in the bottom product cooler where heat is transferred from product leaving the reboiler at the boiling point. When feeding cold feed directly to the column, the product from the reboiler is cooled in the bottom product cooler by circulating cold water through the spiral coil.

For batch operation, valve (V1) remains closed so that the reboiler can be filled with the initial charge (10 to 12 litres) of binary mixture. The column and reboiler are both insulated to minimize heat loss. A level sensor (17) inside the reboiler protects the heating element from overheating due to low operating level and a sight glass (18) allows the level in the reboiler to be observed.

5. Condenser

Vapor from the top of the column passes to a water-cooled, coil-in-shell condenser (8), which may be fitted with an insulated jacket to allow heat balances to be carried out.

The shell of the condenser incorporates a pressure relief valve (PRV1) to protect the system in the event of a blocked vent and cooling water failure. Cooling water enters the condenser at a regulated rate through a rotameter (FI1) and the flow rate is controlled by diaphragm valve (V5). A cooling water supply is connected to the inlet nozzle (19) and serves also to operate the vacuum pump (20) when operation at reduced pressure is required. Water supply to the vacuum pump is controlled by valve (V14), which must only be operated when valve (V5) is open.

6. Decanter

Condensate is collected in a glass decanter (11) (phase separator) which is bypassed for normal distillation experiments by opening valve (V10). When the decanter is in use (separation of two immiscible liquids as condensate), valve (V10) is closed so that the overflow (25) and underflow (26) pipes inside the vessel, can take effect.

With valve (V10) open, condensate from the condenser outlet passes directly through the decanter to the inlet of the reflux ratio control valve (12) which is a 3-way solenoid operated valve. Depending on the setting of the reflux timers, condensate is directed by the reflux valve either back to the top of the column or to the top product collecting vessel (10). When directed to the column, the reflux passes through a U-seal where a valve (V3) can be used for measuring boil-up rate or for draining the U-seal. The contents of the top product tank (10) can be drained into the reboiler (13) for re-use viavalve (V12).

7. Thermocouples

Temperatures within the system are monitored by fourteen thermocouple sensors (T1 to T14) located at strategic positions in the system. T1 to T8 are located in the column and measure the temperature of the liquid on each sieve plate. There are seventeen locations for the temperature sensors, three of which do not have sensors installed but which can be fitted with sensors moved from other, less relevant locations when necessary.

8. Manometer

The total pressure drop across the column is indicated on a U-tube manometer (P1) via appropriate tappings in the column fitted with isolating valves (V6) and (V7).

9. Product Receiver

All of the vessels in the system are connected to a common vent on the top product receiver. This vent is normally connected through a 4.0 m length of tubing to a fume cupboard or safe atmospheric vent outlet.

10. Vacuum Pump

Operation at reduced system pressures is achieved using the water powered vacuum pump (20). When in use, the flexible vent pipe from the common connection on the top product receiver is attached to the inlet of this vacuum pump at (23), and motive water admitted via valve (V14), which must only be operated when valve (V5) is open.

The level of vacuum is adjusted using needle valve (V15) and is indicated on pressuregauge (P1).

11. Control Console

The console is attached to the process unit by an umbilical cable which is of adequate length to allow the console to be positioned at least 2.0 m away (outside the “Zone 2” area). See the Safety section at the front of this manual, and the Specifications section on page 15.