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Automated Pressure Control
Reactor Systems
 In Research and Development laboratories of (petro-) chemical companies as well as pharmaceutical companies or life science companies, chemical reactors are used for many different processes.
Bronkhorst has developed a specialized combination of electronic pressure and thermal mass flow controllers for automated pressure control of reactor vessels. This standard solution can be applied for low flow lab reactor systems as well as for high flow industrial applications as for instance in hydrogenation processes in the food and pharma industry or at chemical plants, at either low or (very) high pressure (up to 400 bar).
To optimize a chemical reaction, chemists must find the best combination of compounds and insert these in the optimal proportions into the reaction chamber. This reactor may be kept at a certain pressure and temperature and a catalyst may be added to accelerate the reaction.The input of the reaction gases must be accurately measured at all times, also while pressurizing the reactor. An overshoot in flow (outside the scale of the mass flow meter) should be avoided, because this will introduce inaccuracy.
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Combined Mass Flow - Pressure Control for safe and automated reactor pressure control. |
The proposed set-up may slightly vary per application, since the concept can be applied to both analog and digital systems. Furthermore the instruments used may be in 'laboratory style' or with rugged industrial housing, IP65 protected and optionally with ATEX Zone 2 approval.
 At the inlet of the reactor, a Mass Flow Controller (MFC) takes care of the process gas delivery, while an Electronic PressureTransmitter (EPT) measures the reactor pressure. At the outlet of the system there is a flow restriction which could simply be a (needle) valve or, as shown in the illustration, a Mass Flow Regulator (MFR) with local display. The reactor pressure is controlled by giving a setpoint to the pressure transmitter. In the illustration this is done via RS232 by a script programmed into a PC. The integrated PID-controller of this pressure meter  (Master) controls the valve position of the MFC's control valve (Slave). When building up the pressure in the reactor, the maximum inlet flow is restricted by the MFC, thus preventing a flow peak. By using the 'slave factor' option, the maximum flow can be adjusted. When the process pressure has reached the desired value, it is kept constant while the required amount of reaction gas is controlled with a constant flow. It is also possible to pre-set the total amount of reaction gas allowed into the system by using a batch control function. Once the total amount is reached, the set-point for the MFC can be programmed to be reset to zero, thus switching off the gas supply, independent of the process pressure.
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Another Chance
One More Exhibition in 2013
Bronkhorst USA will be exhibiting at ChemInnovations 2013 in Galveston, TX on September 25-26, 2013.
We will be highlighting the World's Smallest and Lowest Flow Coriolis meters and controllers.
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Under Pressure
EL-PRESS
 The EL-PRESS series electronic Pressure Meters and Controllers have a well-proven compact thru-flow design and are available in pressure ranges from 2...100 mbar up to 8...400 bar, both in absolute and relative (gauge) pressure. A differential pressure transducer can also be supplied in the ranges of 2...100 mbar up to 0,3...15 bar. The pressure controller performs with high accuracy and repeatability and should be specified for forward or backward pressure control.
Today's EL-PRESS series are equipped with a diaphragm type piezoresistive pressure sensor and a digital pc-board as standard and offer high accuracy, stability and reliability. The basic digital pc-board contains all of the general functions needed for measurement and control. In addition to the standard RS232 output, the instruments also offer analog I/O. As an option, an integrated interface board provides DeviceNetTM, PROFIBUS DP®, Modbus-RTU or FLOW-BUS protocols. The latter is a fieldbus based RS485, specifically designed by Bronkhorst High-Tech for their mass flow and pressure metering and control solutions, and with which the company already has over ten years of experience with digital communication.
 | | Forward pressure control |
 | | Back pressure control |
The control valve can be furnished as integral part of an EL-PRESS Pressure Controller (EPC), or as a separate component. It is a proportional, electromagnetic control valve with extremely fast and smooth control characteristics. With reference to the specific field of application there are different series of control valves. There is a standard direct acting valve for common applications, a pilot operated valve for high flow rates, the so called Vary-P valve that can cope with up to 400 bar ΔP and a bellows valve for applications with very low differential pressure.
Fields of application
>Semiconductor processing
>Gas and liquid chromatography
>Vapor pressure control in MOCVD processes
>Protective gas pressure control in extrusion molding processes
>Autoclave / reactor pressure control
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Good to Know
Calibration Schedule
 Mass flow instruments, in fact all process instruments, experience wear from the conditions of the process in which they are installed. Temperature, electronic component tolerance shift, contamination build up over time (even very slight), plus other factors will all contribute to affecting the accuracy of an instrument.
Your instruments should regularly undergo, at a minimum, a calibration check if not a recalibration. But how often? Because the nature of each application is different (conditions, running time, etc) a calibration can last three years or three months.
 Bronkhorst instruments do not have specified due dates for calibration. Bronkhorst suggests that our instruments be calibrated every year. However based on the application conditions, and perhaps your company quality procedures, each customer must determine when they need to send an instrument in for recalibration.
Properly calibrated instruments will be more accurate, more reliable, help ensure consistency, and help improve production yields. |
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Laws And Guidelines
Cole's Axiom
The sum of the intelligence on the planet is a constant; the population is growing.
Cole's Law
Thinly sliced cabbage. |
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