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Novel reactor design allows better control

22 June 2009

The Constant Flux (or Coflux®) reactor incorporates improved temperature control and process analytical features, which together can significantly improve the performance of batch processes.

Coflux reactor arrangement
Coflux reactor arrangement

The U.S. Food and Drug Administration’s (FDA) Process Analytical Technology (PAT) initiative (see sidebar box at end of this article) has elevated the need for improved real-time monitoring and process control, thus making processes more efficient and repeatable.

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RIGHT: Coflux® reactor arrangement

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AM Technology claims its new Coflux reactor design offers more precise temperature control with no overshoot. In addition, it allows operators to more precisely monitor and control important PAT variables such as enthalpy, U-value, process power and wall temperature.

• Enthalpy (J) is used to monitor yield in chemical reactions, crystallisation and biomass.

• U-value or heat transfer coefficient (W.m-2.K-1) is used to monitor wall fouling, viscosity changes and agitator performance.

• Process power (W) is used to monitor rates of reaction, initiation, crystallisation, nucleation and cell growth.

• Wall temperature (K) monitoring allows the user to employ maximum heating and cooling power without causing damage to the product.

Unlike conventional reactor designs, Coflux reactors use a number of individual coils instead of a standard jacket for heating / cooling. The heat transfer fluid valve (TC) controls the HTF supply temperature. The heat transfer surface area is controlled by an actuated valve (CV) which allows heat transfer fluid (HTF) through the separate coils.

Typical PAT variable trends
Typical PAT variable trends

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LEFT: Typical PAT variable trends

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This has many advantages including faster response, better temperature control, improved energy efficiency and reduced HTF volume. The number of coils can be regulated in relation to the process level thus eliminating dry wall burning or freezing effects.

This is particularly important for processes such as crystallisation, evaporation and distillation. The heat transfer fluid valve (TC) controls the jacket temperature and the Coflux valve (AC) controls the heat transfer area. The Coflux reactor typically operates between -50 and + 200°C although higher temperatures are achievable. Reactor volumes range from labscale to 10,000 litres.

Off-the-shelf instruments

At the heart of the Coflux control system is a Honeywell HC900 hybrid controller with Experion PKS SCADA.

The PAT control variables are achieved in real-time by using the HC900 to perform heat balance measurements across the Coflux reactor. The HC900 generates PAT process variables which can be used to evaluate and control batch progress and to detect events such as process end point.

These new process variables can also be incorporated into PAT control strategies. The flexibility of the control system allows process invasive instruments such as NIR analysers, particle size analysers, and Raman spectroscopes to be connected to the HC900 for PAT control and monitoring purposes if required.

Typical Experion process power trend
Typical Experion process power trend

Unusually for PAT control solutions, the Coflux control system uses standard off-the-shelf instrumentation and can be located in hazardous areas. Indeed a recent 400 litre glass-lined Coflux vessel developed under licence by Pfaudler has been built to ATEX standards for zone 1 use.

Although the Coflux and PAT software has been designed to run as an independent solution on the HC900 platform, the system can be installed alongside and communicate with existing non-Honeywell DCS or PLC systems via OPC server over Ethernet.

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right: Typical Experion process power trend

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—Kevin Poole MIEE, Control & Automation Engineer, AM Technology For more information, visit www.amtechuk.com CLICK HERE

Sidebar: Process Analytical Technology (PAT)

Process Analytical Technology (PAT) is defined by the U.S. Food and Drug Administration (FDA) as a mechanism to design, analyse, and control pharmaceutical manufacturing processes through the measurement of Critical Process Parameters (CPPs). PAT aims to better understand the process by defining the CPPs and monitoring them on-line. The goal is to be more efficient in testing while at the same time reducing over-processing, enhancing consistency and minimising rejects. The FDA’s PAT initiative is contained within the broader initiative Pharmaceutical Current Good Manufacturing Practices (cGMPs) for the 21st century — A risk based approach. To view the FDA paper CLICK HERE


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