**5. Conclusions**

*Advanced Supercritical Fluids Technologies*

**Figure 9.**

pump (4), preheated in the preheater (5) by high temperature intermediate medium, and then made to enter into reactor (6) when reaching the expected temperature. Liquid oxygen is pressured and its flow rate are regulated by the low temperature oxygen pump (17), subsequently gasified in the vaporizer (18), and then gaseous oxygen is stored in the oxygen buffer tank (19), ultimately entering the reactor (6) after being depressurized by the oxygen pressure regulator (20) and reacting with the feedstocks. Meanwhile, the SCWO reaction releases a certain amount of heat and reaction effluent with high-temperature and high-pressure flows into the inner tube of heat exchanger (6) to heat the intermediate medium in the outer tube, and the effluents are also cooled through the intermediate medium at the same time. Then the cooled effluents are reduced to an appropriate pressure by the capillary depressurization device (8). Gaseous products, liquid products, and solid products are similarly separated in the low pressure three-phase separator (9). The intermediate medium from the water buffer tank (12) pressurized by high pressure booster pump (13), firstly absorbs the heat of the reaction effluent through the regenerator (7); flows through the heater (14); and then, if necessary to further increase the temperature, eventually enters the preheater (5) for preheating the feedstock. Therefore, the corrosive fluid only passes through the inner tube of the preheater and the regenerator, and both outer tubes of the heat exchanger are clean water. Therefore, only inner tubes of the preheater and regenerator require the use of highend corrosion-resistant alloys, and the outer tubes can use cheap carbon steel or low alloy steel, which will greatly reduce the investment cost of heat exchanger for the SCWO process. In addition, the clean water in the outer tube also dramatically avoids the blockage risk compared with dirty fluid containing insoluble solids.

*A Schematic diagram of the indirect heat transfer SCWO comprehensive system: 1—filter; 2—low pressure pump; 3—feedstock tank; 4—high pressure feedstock pump; 5—preheater; 6—reactor; 7—heat exchanger; 8 capillary depressurization device; 9—three phase separator; 10—water storage tank; 11—high pressure water pump; 12—water buffer tank; 13—booster pump; 14—heater; 15—spray desuperheater; 16—liquid oxygen tank; 17—low temperature oxygen pump; 18—vaporizer; 19—oxygen buffer tank; 20—oxygen pressure regulator; 21—caustic tank; 22—low pressure caustic pump; (101—108)—valve; 23—biochemical treatment unit.*

Additionally, in view of specific characteristics of various municipal/industrial sludge and organic wastewaters such as printing and dyeing wastewater, phenolcontaining wastewater, pharmaceutical/pesticide-production wastewater, etc., combining with their individual industrial production processes and customer specific requirements, the Energy and Environment Institute in XJTU has carried out the process integration innovation of large-scale supercritical water treatment system to maximize the efficiency, economy, and safety, and has finished a series of

**150**

mature, reliable SCWO process packages [82].

In virtue of the special physicochemical properties of supercritical water, supercritical water oxidation (SCWO) can efficiently and thoroughly degrade a wide variety of organic pollutants into harmless small molecules, such as CO2, N2, H2O, etc., which has been widely regarded as the most promising, environmentfriendly treatment technology for organic wastes. Not a specific material can withstand all kinds of SCWO conditions; however, the suitable material can be selected for a certain condition considering corrosion resistance, strength, and economy. Abundant corrosion control approaches can mitigate the equipment corrosion effectively. Salts precipitation, possibly resulting in plugging of pipes and instruments and accelerating corrosion, is another main obstacle to hinder SCWO commercialization. Fortunately, pre-desalination, on-line salt separation, novel reactor configuration such as TWM reactor, etc., all exhibit better performances in preventing and controlling salt deposition and corrosion issues occurred in reactors. The global considerations and designs instead of previous single or local protection will be in focus in the future. On the basis of decades of implementation experience of full-scale SCWO plants, considering the incessant emergence of more advanced technologies and equipment which aims to overcome the abovementioned two key obstacles and to further elevate the system economy, safety, and automatic control level, the industrial SCWO plants will achieve the harmless disposal of various organic wastes in a more economical, safe, credible way.
