Supercritical water oxidation (SCWO) is a promising green technology to completely convert hazardous wastewaters to innocuous products, allowing energy recovery. This process has been extensively applied to many model compounds and real wastewaters at laboratory scale. However SCWO treatments at the pilot plant scale of real wastewaters are much less extensive in literature. Furthermore, the application of this technology to industrial wastewaters has the two main drawbacks of corrosion and salt deposition, and some other problems to be solved related to management of biphasic wastes, presence of suspended solids, high costs, etc., so currently the industrial scale-up and commercialization of the process is still subject to difficulties. This work reviews the main technical solutions studied by numerous authors to avoid the drawbacks mentioned. Besides, since the economic feasibility of the process will depend on the energy recovery of the reactor effluent, this aspect is also presented in this review.

BACKGROUND: Supercritical water oxidation (SCWO) is a promising technology that respects the environment, destroys wastes and allows energy recovery. This process has been applied to many model compounds and real wastewaters at laboratory scale. However, SCWO treatments at pilot plant scale of real wastewaters are scarce. The application of this technology to industrial wastewaters has drawbacks such as corrosion, salt deposition and high cost, so industrial scale-up has been delayed.

The destruction of industrial wastewaters by supercritical water oxidation (SCWO) has been studied intensively in the last two decades due to the powerful and promising advantages of this technology. However, the SCWO process is not yet commercially established due to several drawbacks that limit its application as a general treatment, process costs being one of those limitations. In an effort to enhance the viability of SCWO as a commercial process, a study was performed in a pilot plant (25 kg/h) used to treat industrial oily wastes by SCWO, and a simulation was carried out to evaluate the viability of energy production on an industrial scale. The SCWO pilot plant effluent is good for producing hot water or steam by recovering heat of waste organics. Both alternatives are evaluated for a SCWO industrial plant design with 1000 kg/h, with it being possible to recover a maximum of 118 kW, that is, 71% of the energy content of the wastewater.

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Supercritical water oxidation (SCWO) has been studied for the past three decades and is now a well-known process. However, the commercial development of this technique is currently delayed due to several drawbacks such as corrosion, salt precipitation, and high costs. In an effort to overcome these constraints several authors have studied and designed new SCWO reactor concepts, but these technical solutions involve the use of special materials and complex designs that increase the process costs. However, conventional SCWO could be commercialized for certain wastewaters that satisfy certain requirements, e.g., very low salt and chloride contents, and it is necessary to continue studying the SCWO process at high concentrations and on the pilot plant scale. At present, simulations based on the SCWO of real wastewaters at high concentrations on the pilot plant scale are scarce in the literature. Process simulation is a powerful tool to study processes in depth and to make advances in the scale-up process. Nevertheless, the use of specific chemical engineering software, such as Prosim Plus or Aspen Plus, is not applicable to simulate a complex wastewater. In addition, the use of the kinetic data available in the literature is not straightforward because these kinetic parameters were obtained from experiments conducted under very different conditions (isothermal, low concentration, etc.). In the work described here, the simulation of Biocut 35 cutting fluid SCWO on a pilot plant scale has been conducted satisfactorily. The model was developed using a Microsoft Excel spreadsheet and a kinetic model obtained on the laboratory scale. Fifteen experiments were carried out in order to validate the simulator. These experiments were conducted on a pilot plant scale at a constant pressure of 250 bar and initial temperatures ranging from 388 to 428 °C. The cutting fluid concentration used in these experiments was varied from 19 to 95 g of O2/L. Finally, the simulator was used to check the effect of the operational variables such as wastewater concentration, initial temperature, wastewater flow rate, and thermal insulation.

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