Simulation of a counter current refrigeration system for a SCWO reactor

Resumen

Severa types of reactors ha ve been designed in the last years to avoid or reduce the drawbacks derived from the Supercritical Water Oxidation (SCWO) process. For example, the high pressure and temperature achieved in SCWO reactors require materials with special characteristics to resist those severe conditions, as nickel based alloys such Inconel 625 and Hastelloy. But even using those alloys, it is always needed to prevent temperatures above 600°C anda refrigeration system is required, especially to treat high concentration wastewaters. According to those premises, ditferent reactors have been designed to work at supercritical conditions, for example transpiring wall reactor, cool wall reactor or tubular reactor with cooling water injections.This work proposes the design of a SCWO reactor with a counter curren! refrigeration system. The set consists of two concentric pipes, being the inner tu be the reactor itself, where exotherrnic reactions take place and the heat produced is transmitted through the reactor wall by heat conduction. In the external concentric tube, a cross current flow of water will dissipate part of the energy transmitted, preventing an excess in the maximum value of temperature allowed for the material. Depending on the wastewater concentration fed, and therefore the heat produced by its oxidation, the tlowrate of cooling water is controlled to maintain stable temperature profiles along the reactor (always below 600°C). In order to design the reactor, a model is built up to simulate the desired conditions as a previous step to the experimental system construction. Simulation allows us to know easily the behaviour of the system at ditferent conditions with the aim of optimize the reactor design. The software used in this work have been Engineering Equation Solver (EES) and Matlab, both widely used in many engineering problems and simulations involving themodynamical processes. The main development of the model has been carried out with Matlab, while EES,that counts on a huge therrnodynamical properties and models database for many compounds, has been used to determinate the properties of compounds.