AquaCritox® is a hydrothermal oxidation process that involves the use of pressure, temperature and oxygen to effect partial or complete oxidation of the oxidisable components present in a sludge or contaminated water-based waste stream.

Typically, the process operates at minimum pressures of 165 Bar and up to 240 Bar and approximately 300°C to maintain water at near-critical or supercritical phase for the oxidation reaction. This process is achieved through a combination of high-pressure feed pumps and a unique pressure let down system with flow maintained through a series of heat exchangers.

The automation system had to react in a safe way to any deviations from these setpoints, including changes in waste stream viscosity and density. The system also had to maintain temperature, pressure and flow to various setpoints during the injection of liquid oxygen to each reactor to ensure full oxidation.

We developed the system using Siemens GRAPH logic in TIA Portal for an S7 1500 CPU with ET200SP remote rack. To allow each system work alongside the main state controller, we developed novel solutions for pressure control, safety shutdown, pressure let down, PID control loops, interlocks and oxygen injection control.

We designed a SCADA system with WinCC Professional and showed a simplified mimic of the process and key variables and setpoints for the user. We also configured a remote connection to the plant using an eWon Cosey router and VPN to allow for monitoring and support.