Subcritical/Supercritical Water Systems

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 400°C) 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.

Process control for the entire system may be as simple as manual valves with local process parameter display and control, or it may entail complete remote operation with computer process control and data acquisition. The engineering team has leveraged our knowledge base in supercritical fluid carbon dioxide and has specified, designed, and deployed platforms for use with supercritical water.

Pictured is one of the more manually operated supercritical water oxidation systems that was manufactured for one of our clients whose process development interest was developing an oxidative process for the destruction of an isopropyl alcohol waste stream.

SCW can be employed for a wide variety of specialty applications. A process development unit was designed and deployed for a petrochemical company that would allow the use of supercritical water to process “oil heavies” obtained at the end of crude oil cracking processes and conversion of these heavies into usable petroleum products (P&ID).

The US Department of Defense had interest in using supercritical water oxidative processes for the purification of drinking water for soldiers in the field. In conjunction with the DRS SSI C3-Group, SFT specified, designed, and deployed 2 Pilot Scale SCWO units (15 gallons/hour) for the proof of concept work and are currently in the development phase of units capable of 150 gallons/hour. Not only did these units process water in an extremely corrosive environment, but our engineers were able to employ an array of quality sensors to detail the quality of the water flowing into the system and the quality of the water flowing out of the system as part of the complete solution.

Supercritical Fluid Technologies has also provided a custom solution for the use of supercritical water stream with biomass/methanol slurry to produce bio fuels. In conjunction with a US Department of Energy grant to the Iowa State University, Supercritical Fluid Technologies manufactured a Supercritical Bio Reactor for the process development work for this difficult application. Using the equipment featured in the P&ID, Biodiesel has been synthesized under catalyst-free supercritical methanol reactions using a variety of oils at 250 to 325°C in a 1-liter high pressure batch reactor. Multiple experiments were performed at 6 to 80 molar ratios of methanol to oil with excellent results.