Applications for water as a process media range from subcritical water extraction to supercritical water oxidation to supercritical water reaction processes in this application niche. Supercritical Water Oxidation (SCWO) is among the most challenging applications of supercritical technology. Very high temperatures (over 400oC) and moderately high pressures are required to achieve the critical point of water. An additional difficulty is corrosion, which is a problem for all sub-critical and supercritical water systems. Special materials for vessel linings and tubing are needed to resist the highly reactive chemical species generated during the process.
These challenges demand superior engineering and design expertise for all system components. The water and process streams must both be pumped to high initial pressures under exact flow and pressure control. The heat exchangers are subjected to high heat transfer rates at high temperatures, but must maintain precise temperature control. The reaction vessel requires exact temperature, pressure and flow control. The vessel must seal reliably and be leak free each time it is used, regardless of the harsh operating environment. Downstream processing such as cooling heat exchangers, collection vessels, gas/liquid separation and pressure control must be efficient.
It would be much less expensive to purchase a dedicated supercritical water type unit than go through the detailed modifications needed to change the traditional SFE unit to use water as the supercritical fluid.