Reactor weblab

Experimental Equipment

This page describes the experimental equipment that is controlled via the user interface.

The reactor is mounted on the front of a cabinet containing supply tanks, pumps, measuring devices, control hardware and plenty of wiring and piping. The reactor and cabinet have been designed and built by Promech, Sweden. All control hard- and software, flow meters and temperature probes have been donated by Siemens.

This is the experimental rig shown from the front. The reactor and its ancillaries are mounted in a cabinet for convenience and safety. The reactor itself and the peristaltic pumps are mounted in the front face of the cabinet, whereas supply tanks, flow meters, heater, dosing unit etc are enclosed with easy access provided through rear doors. The three supply tanks (T1, T2, T3) are shown schematically on the top left, below them are the displays for the flow meters and below them the peristaltic pumps. The reactor is to the right. The reactor is manufactured from Perspex, has a variable volume of 100-300ml and can be operated at controlled temperatures up to 50°C. A dead-zone can be created in the bottom of the reactor by a movable effluent pipe and by varying the depth and speed of the stirrer. The three feed streams can be controlled individually by Siemens coriolis flowmeters and the peristaltic pumps.

This is the experimental rig shown from behind with the doors open. Here the supply tanks are visible and above them the Siemens coriolis flowmeters. The flowrate is displayed both on the display units mounted on the front of the rig and the in the user interface on the operator station.

The signal from the flowmeters is used to control the pump speed and therefore maintain the desired flowrate. The pumps being used are peristaltic pumps, which are ideal for small scale lab work. In this picture the pump is opened up to show how it works.

Sodium Hydroxide (NaOH) and Phenolphthalein in dilute aqueous solutions are used as reactants. One of the products is bright pink, and the progress of the reaction is monitored by measuring the intensity of light at 550nm passing through a flow cell with a spectrophotometer. For residence time experiments, Rose Bengal which absorbs light at the same wavelength, is used. The reactants from the supply tanks enter the reactor, mix and react. The mixing is not always ideal depending on the reactor setup

On exiting the reactor, the mixture passes through a flow cell. Because the reaction we are investigating changes the colour of the solution, we can use a spectrophotometer to measure the intensity of the light that is transmitted through the solution and therefore the concentration (using the Beer-Lambert law). This picture shows a close up of the flow cell used for this purpose. Light is transmitted into the right of the flow cell via a fibre optic cable, passes through the solution and is collected (via the other fibre optic cable) by a spectrophotometer. Of course, the flow cell is covered up under normal operation, to prevent ambient light affecting the results. Once the mixture has passed through the flow cell it is sent to the drain.

Network Camera

A network camera donated by Axis is mounted in front of the experimental rig. This camera can be accessed at http://labcam.cheng.cam.ac.uk.

Siemens Hardware

The Siemens Coriolis flow meters are so called 'intelligent devices' communicating with the system, together with the temperature probes, via a Profibus PA network (wiring shown in picture to the left). These devices are easier to install and configure, and can provide a lot more information than traditional devices.

The peristaltic pumps and the stirrer are connected to an analogue output module and the relays for the dosing unit, heater element and heater circulation pump to a digital output module. The intensity signal from the spectrophotometer is entered into the system via an analogue input module. The Profibus PA signal is converted to a Profibus DP signal in a DP/PA coupler and all inputs and outputs are then communicated to the S7-400 PLC via a Profibus DP link. All of these are mounted in the cabinet and shown on th photo to the right.

To program, broadcast and operate the system, three industrial PCs are used. On the engineering station the operating system is programmed and the operating interface designed and uploaded to the PLC. The operating system server communicates with the PLC and broadcasts the operating system to the local Ethernet network. The web server runs a html-based version of the operating system and broadcasts this to the Internet. The photo shows the S7-400 PLC on top of the tree industrial PCs.

Siemens Software

After configuring and networking the PCs, connections are established between the devices in the experimental setup and the controller using the SIMATIC manager. In the CFCs the properties and controls for the devices are configured. The corresponding Block Icons are combined with a visual representation of the experimental setup in the Mimic, the working area for the operator. For more information on the Mimic please refer to the Interface section. For further information on the Siemens Simatic PCS7, two brochures are available here for download: The Process Control System for all industry sectors SIMATIC PCS7 Process Control System

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