Research reactor uses Coriolis flowmeter and control valve to provide the critical flow control elements for charging with hazardous batch ingredients
Strata Technology is an expanding project and design services company based in Sunbury on Thames, specialising in the petrochemical and pharmaceutical industries.
Synthomer is a major producer of the polyvinyl alcohols used as suspending agents in the polymerisation reactions of vinyl chloride monomer (VCM) to produce PVC.
To aid in the development of these additives, Synthomer needed a pilot reactor at its Harlow plant (formerly Harlow Chemical), and so turned to Strata to provide the best technology available.
The plant is designed to be capable of being tuned to match the technology and production reaction characteristics of the full-scale PVC production units.
A significant challenge included the containment of the toxic and flammable VCM raw material, within a hermetically sealed unit, designed to deliver zero emissions of VCM to the environment.
The plant developed by Strata Technology is based on a highly automated 10 litre reactor vessel, operating at pressures up to 18barg and temperatures to a maximum of 85C.
The whole plant is contained within a ventilated enclosure, and effluent gases are treated within a thermal oxidative facility to destroy any VOCs (volatile organic compounds) produced.
The automated system will also deliver information on batch calorimetry, reaction profiles, foaming levels and agitator power demands.
In handling the raw material feed into the reactor, Strata Technology placed great emphasis on accurate material delivery, fluid containment and integrity of the pipework.
The raw materials, such as VCM, are held in bulk storage tanks.
Charging of the reactor is controlled via interlocks and logic within the PLC control system designed by Strata Technology.
A Bronkhorst Coriolis flowmeter and control valve are used to provide the critical flow control elements. Pivotal to the control system is the precision Cori-Flow mass meter from Bronkhorst.
This flow meter is based on the Coriolis vibrating tube loop technique, which gives accurate fluid mass flow measurement.
Two tube loops are contained within the meter body, and are stainless steel, fully welded, with no seals or shafts to leak.
The tubes are helium leak testedin the factory, as a quality assurance check.
Built-in to the single, neat Cori-Flow package is all the electronic circuitry required to accept the input command signals from the Strata Technology pilot plant control system: the Cori-Flow provides the drive signals and PID control functions to drive the electromagnetic coil in the flow control valve, and establish the mass flowrate requested, whilst also giving an electronic output proportional to actual recorded mass flow.
The unique construction of this control valve uses a plunger and orifice combination: flow is controlled using the magnetic force from an electromagnetic coil encapsulated within the valve body.
There is no gland packing or external connection to the plunger, eliminating all potential VCM leak paths in this area.
The normally closed valve, with a metal-to-metal seal, has excellent resealing capability.
Actual shut-off valves are separate duplicated quarter turn ball valves further down the line.
Paul Fisher, consultant engineer at Strata Technology responsible for this project, appreciated the compactness and complete capability of the Cori-Flow package: "For flow control of a liquid such as VCM, you need a reliable measurement system that is independent of the liquid composition, so requires no special setting up.
"Plus the Cori-Flow PID control package enabled us to concentrate on the overall process design, knowing that this critical flow control package would perform first time, and have no leaks".
The Cori-Flow measures the actual mass flow rate of the VCM and the water flows into the reactor, at rates up to 20kg/hr.
The Cori-Flow range is unique in being capable of monitoring fluid flows from as low as 20gm/hr up to 600kg/hr, with a 1bar maximum pressure drop.
The Strata Technology control system monitors these flows to determine when the required batch quantity is complete, and signals to end the batch at the required volume. The operator and the main system can therefore concentrate on adjustment and optimisation of the ingredient sequence logic, and the timing of the different additions in the polymerisation process.
The system also monitors and records all process reaction mixture temperatures and pressures for later analysis. The Bronkhorst Cori-Flow units on this reactor system are the primary flow measurement devices on the installation.
They control the reactor charge where accurate measurement is very important.
Bronkhorst Cori-Flow mass flow measurement systems have a repeatability of 0.1% of rate.
This measurement is independent of the fluid properties, such as density, viscosity, conductivity, temperature and pressure.
The Cori-Flow range complements the established Bronkhorst range of gas mass flow measurement systems and controllers: the Strata design also employs a Bronkhorst pressure controller on the nitrogen supplies used for the pressure control of the reactor.
The microprocessor based intelligence within the Cori-Flow unit itself can be used for other digital interfaces and communications, as well as computation and control.
The external interface of command signals and monitored mass flow measurement is available as conventional analogue signals of 0 or 4 to 20mA, or 0-5VDC, or 0-10VDC: the microprocessor also offers standard digital protocol communications.
Because of the varied industries that have adopted mass flow control, the available interfaces include both Profibus-DP and DeviceNet, plus standard RS-232 interfaces, plus the Bronkhorst Flow-Bus protocol, which is based on RS485, and has been in use on equipment using such Bronkhorst mass flow controllers for over ten years.
Strata Technology has used Bronkhorst gas pressure and mass flow controllers on previous designs of process plant: here, for hazardous liquid measurement and control, the new compact Cori-Flow unit provided off the shelf flow control, unaffected by the hazardous liquids involved, and made a major contribution to the process measurement accuracy and success of the project.
