**2. Key problems and status**

The harsh conditions involved in SCWO process, such as high temperature, high pressure, excessive oxygen, corrosive ions, etc., easily induce severe reactor corrosion problems, meaning a shorter reactor life. On the other hand, inorganic salts will precipitate from SCW due to its extremely low dielectric constant, which may result in reactor plugging triggered by deposited salts and further cause expensive and frequent shutdowns of the whole SCWO plant. These two aspects, to a certain degree, are still not effectively solved and seriously hinder the extensive commercialization of SCWO.

### **2.1 Corrosion**

*Advanced Supercritical Fluids Technologies*

matter and oxygen [1].

disposed via SCWO efficiently.

is eliminated. There, SCW can be used as an excellent reaction medium for organic

Supercritical water oxidation (SCWO), which was firstly proposed by Modell in MIT in the middle of 1980s, is an effective and advanced oxidation technology to destruct organic matters by taking advantage of the unique properties of SCW under the typical operation conditions of 450–600°C, 24–28 MPa. A schematic of a typical SCWO process is displayed in **Figure 1**. In SCWO reactor, organic wastes can be thoroughly oxidized and decomposed into harmlessly small molecules, such as CO2, N2, water, etc., under excess oxidants in single-phase SCW. Hetero-atoms in organic matters are mineralized into corresponding acids or inorganic salts, and the formation of nitrous oxides is inhibited owing to the low reaction temperature. SCWO is particularly suitable for disposing organic wastewaters with high toxicity, high concentration, and bio-refractory components [2–4]. It can also recover energy and achieve heat self-sufficiency easily to ensure an economic advantage [5]. When a mass concentration of organic matters in feedstock is in the range of 3–4%, the whole reaction process does not require an extra energy input commonly. Furthermore, compared with incineration, SCWO does not have the problems of high cost, public resentment, and secondary pollutants like dioxins [5]. Hence, SCWO has attracted much attention in the past three decades. Brunner [1] has summarized SCWO results of real waste materials including textile wastewater, wastewater from terephthalic acids, food wastes, municipal excess sludge, and alcohol distillery wastewater. Furthermore, Veriansyah and Kim [5] have also systematically introduced SCWO experiments of toxic organic wastes such as pesticide, bacteria and dioxins, chlorophenol and chlorobenzene, pharmaceutical and biopharmaceutical wastes, solid rocket propellants, military wastes, etc. Some other feedstocks, including landfill leachate [6–9], industrial dyeing wastewater [10, 11], polychlorinated biphenyls (PCBs) [12], chlorinated wastes, oily wastes, etc., have also been

Nowadays, SCWO plants have been commercialized by several famous companies and universities [14–16], such as General Atomics, Chematur AB, HydroProcessing, Supercritical Fluids International (SCFI), SuperWater Solution, Xi'an Jiaotong University (XJTU), etc. In 2001, two commercial-scale SCWO

**132**

**Figure 1.**

*A schematic of a typical SCWO process for sludge treatment [13].*

Corrosion is a key obstacle to limit the commercial application of SCWO, which not only shortens reactor life but also induces a bad treatment effect of feedstock due to the formations of corrosion products. Harsh operation conditions (high concentration of oxidants, extreme pH values, high temperature, and pressure) together with reaction intermediate/ultimate products (high concentrations of ionic species, free radicals, and acids) result in severe corrosion problem in SCWO reactors. Corrosion mainly occurs on reactor's inner wall; it also appears in heat exchanger and cooler on inlet and outlet pipelines of the reactor [19–21].

Materials serving for SCWO include stainless steels, nickel-based alloys, titanium, tantalum, noble metal ceramics, etc. [21–25]. A series of investigations on the corrosion resistances of these materials under supercritical and/or subcritical conditions [20, 24, 26–30], reflected that no one kind of material can withstand corrosion at all conditions, but some exhibit perfect corrosion resistance under specific conditions, as given in **Table 1**. Thus, appropriate reaction conditions such as heteroatom types in feedstock, reaction temperature, and pressure should be optimized in order to minimize corrosion rate for a chosen reactor construction material. Generally speaking, nickel-based alloys show a relatively good corrosion resistance among all the acids listed in **Table 1** under supercritical conditions. Titanium is fit to be employed under subcritical conditions, and is a potential proper liner of preheater and cooler being installed before and after reactor, respectively.

Corrosion in SCWO circumstance also depends on parameters concerning both materials (alloy composition, surface condition, material purity, and heat


### **Table 1.**

*Corrosion resistance of alloys against various media at subcritical and supercritical temperatures [19].*

treatment) and the aqueous solutions (chemical dissolution process, electrochemical dissolution process, and influence of anions) [31]. Under the same condition, various alloys always display different corrosion resistances, which mainly depend on the intrinsic content of alloying elements, especially iron, chromium, nickel, and molybdenum. Iron is usually used to improve economy of iron-based alloys, nickel-based alloys, and titanium-based alloys. In SCW, Fe shows the highest oxidation rates to form stable oxide among the interested metal elements (Fe, Ni, Ti, Mo, and Cr). The corrosion rate of Fe in the oxidizing HCl solution is three times higher than that in SCW without HCl, indicating that the oxidizing acidic chlorinated solution can promote dealloying Fe of alloys in high density systems [32]. Fe always has a faster diffusion velocity than other elements so that the Fe oxides make up the majority of the outer layer of corrosion scales formed on alloys at temperature higher than 400°C [33]. The common Fe oxides includes Fe2O3, Fe3O4, and α(γ)- FeOOH under the SCWO condition. The mass loss of Fe is higher than that of Mo at 300–350°C and lower than that of Mo at 400–450°C in SCW with NaCl [34].

The Cr is considered as the most important alloying element to improve corrosion resistance [35]. The Cr2O3 presented the lowest solubility and the best oxidation resistance among the oxides of chromium, iron, and nickel [29, 32, 35–38]. The higher chromium-containing alloys presented the lower thicknesses of the formed oxide scales. The NiCr25 alloy performed the best corrosion resistance among the interested binary Ni-Cr alloys (0–25 mass% Cr) in an aqueous solution resulting from the oxidation of CH2Cl2 at 40 MPa and temperatures of 100–415°C [39]. The cracking susceptibility of nickel-based alloys also decreased with an increase in Cr content of the substrate exposed to SCW containing HCl or NaOH [40]. The oxygen affinity of chromium is higher than those of iron and nickel, and thus Cr generally may be selectively oxidized to Cr(OH)3 and Cr2O3. The Cr(III) of Cr2O3 can be transformed into Cr(VI) by further oxidation in the oxidizing high temperature water, and unfortunately the Cr(VI) possibly loss by the dissolution. A more continuous and stable Cr2O3 layer was formed at higher temperatures (450 and 500°C) than at 400°C in oxidizing SCW [41]. A series of results indicate that alloys generally suffer the more serious corrosion in high temperature subcritical water rather than in SCW at low density. Mo improves the resistance to pitting corrosion in subcritical salt solution obviously [42]. In nickel-based alloys, the synergistic effect of Mo and Cr on improving the corrosion resistance is remarkable [43]. The nickel-based alloys often show a severe depletion of nickel in high-density aqueous systems [32, 37], while NiO, which is an effectively protective oxide, covers the alloy substrate in SCW environments at low density [44].

For a specific reactor material, the corrosion behavior is commonly influenced by the dissociations of acids, salts, and bases, the solubility of corrosion products and gases, and the stability of protective oxide scales. All these characteristics are

**135**

*Supercritical Water Oxidation for Environmentally Friendly Treatment of Organic Wastes*

affected by density and ionic product of the solution [11, 20]. In order to decrease corrosion rate, it is better to adjust the solution density to be below 200 kg/m3 [31], which may result from the variation in corrosion mechanisms at high- or low density aqueous systems. Lots of studies have been carried out on the mechanism of corrosion scales grown on metal materials in SCW [29, 45, 46]. Two typical mechanisms, such as solid-state growth mechanism and mixed model (formation of the inner layer by solid-state growth process and formation of the outer layer by a metal dissolution-oxide precipitation mechanism) depending on the water density below

mechanism has been used successfully in corrosion problems of various materials such as alloys and ceramics in high temperature gaseous environments such as single gas (O2, N2, and CO2), air, high temperature steam, and a series of mixture gases. According to the diffusion rate of metals involved in the substrate, some alloying elements with relative slow rate are retained and enriched in the inner layer, while the outer layer grows outwards resulting from that the metal ions, especially irons, transport along oxide grain boundaries outwards and then react with gas species at scales/environment interface [29, 38, 45]. However, the mixed model, obtaining satisfying application in condensed aqueous systems, emphasizes that the outer layer is formed by a metal dissolution-oxide precipitation mechanism, and the precipitated metal ions are released from the corroding metal itself or originate elsewhere in the system [27]. The dissolved metal cations combine with anions such as OH<sup>−</sup> in aqueous environments to form oxides or hydroxides; they then precipitate on specimens surface to form and/or thicken the outer layer [49]. Li et al. [30] reported that the corrosion of Inconel 600 and Incoloy 825 in low density SCW containing sulfides

Salt management was identified as a critical issue for the success of SCWO technology. Except for the inorganic salts initially present in the feedstocks, a majority of inorganic salts derive from the SCWO treatment of high-concentration, stubborn organic matters including hetero-atoms such as chlorine, sulfur, and phosphorus [50]. Solubility of salts is reduced evidently in SCW, which is usually lower than 100 mg/L, and thus they are prone to deposition. In addition to corrosion issues, plugging triggered by salts precipitation is another main obstacle to hinder SCWO commercialization, which is induced by sticky salt agglomeration and deposition on

When plugging takes place, the SCWO plant has to be shut down, washed, and restarted, which will directly decrease the reliability of the plant and increase its running cost. Inorganic salts, whether soluble or not, may come from feedstock or reaction byproducts, and their viscosities decide the tendency of depositing on the reactor wall. In general, different salts own different deposition characteristics [51]. Salt deposition principles and the corresponding solutions have been systemically presented in the previous literatures [50, 52, 53]. In a commercialized SCWO plant, reactor plugging can be avoided by particular reactor designs, special instruments, and operation means [18]. Possible solutions are to adopt reverse flow tank reactor, reverse flow tubular reactor, transpiring wall reactor, centrifuge reactor, mechanical brushing, rotating scraper, reactor flushing, crossflow filtration, density separation, additives, high flow velocity, homogeneous precipitation, and extreme pressure [17]. In fact, precipitated salts are relatively difficult to be removed out of SCWO plant during the operation process; thus, most SCWO plants do not have salt removal function. Salts in SCWO are classified into Type 1 or Type 2, according to their solubility [54], Type 1 salt has a high solubility in the

, have been proposed [24, 29, 45, 47, 48]. Solid-state growth

*DOI: http://dx.doi.org/10.5772/intechopen.89591*

also follows the solid-growth mechanism.

**2.2 Salt precipitation**

the internal surface of reactor.

or above 100–200 kg/m3

*Supercritical Water Oxidation for Environmentally Friendly Treatment of Organic Wastes DOI: http://dx.doi.org/10.5772/intechopen.89591*

affected by density and ionic product of the solution [11, 20]. In order to decrease corrosion rate, it is better to adjust the solution density to be below 200 kg/m3 [31], which may result from the variation in corrosion mechanisms at high- or low density aqueous systems. Lots of studies have been carried out on the mechanism of corrosion scales grown on metal materials in SCW [29, 45, 46]. Two typical mechanisms, such as solid-state growth mechanism and mixed model (formation of the inner layer by solid-state growth process and formation of the outer layer by a metal dissolution-oxide precipitation mechanism) depending on the water density below or above 100–200 kg/m3 , have been proposed [24, 29, 45, 47, 48]. Solid-state growth mechanism has been used successfully in corrosion problems of various materials such as alloys and ceramics in high temperature gaseous environments such as single gas (O2, N2, and CO2), air, high temperature steam, and a series of mixture gases. According to the diffusion rate of metals involved in the substrate, some alloying elements with relative slow rate are retained and enriched in the inner layer, while the outer layer grows outwards resulting from that the metal ions, especially irons, transport along oxide grain boundaries outwards and then react with gas species at scales/environment interface [29, 38, 45]. However, the mixed model, obtaining satisfying application in condensed aqueous systems, emphasizes that the outer layer is formed by a metal dissolution-oxide precipitation mechanism, and the precipitated metal ions are released from the corroding metal itself or originate elsewhere in the system [27]. The dissolved metal cations combine with anions such as OH<sup>−</sup> in aqueous environments to form oxides or hydroxides; they then precipitate on specimens surface to form and/or thicken the outer layer [49]. Li et al. [30] reported that the corrosion of Inconel 600 and Incoloy 825 in low density SCW containing sulfides also follows the solid-growth mechanism.

### **2.2 Salt precipitation**

*Advanced Supercritical Fluids Technologies*

**a**

H3PO4, HF, alkaline solutions

**Good resistance Poor** 

**Materials T<Tc**

*The critical temperature of water.*

Nickel-based alloys

*a*

**Table 1.**

treatment) and the aqueous solutions (chemical dissolution process, electrochemical dissolution process, and influence of anions) [31]. Under the same condition, various alloys always display different corrosion resistances, which mainly depend on the intrinsic content of alloying elements, especially iron, chromium, nickel, and molybdenum. Iron is usually used to improve economy of iron-based alloys, nickel-based alloys, and titanium-based alloys. In SCW, Fe shows the highest oxidation rates to form stable oxide among the interested metal elements (Fe, Ni, Ti, Mo, and Cr). The corrosion rate of Fe in the oxidizing HCl solution is three times higher than that in SCW without HCl, indicating that the oxidizing acidic chlorinated solution can promote dealloying Fe of alloys in high density systems [32]. Fe always has a faster diffusion velocity than other elements so that the Fe oxides make up the majority of the outer layer of corrosion scales formed on alloys at temperature higher than 400°C [33]. The common Fe oxides includes Fe2O3, Fe3O4, and α(γ)- FeOOH under the SCWO condition. The mass loss of Fe is higher than that of Mo at

**; high density T>Tc**

**resistance**

HCl, HBr, H2SO4, HNO3

Titanium All acids F<sup>−</sup> HCl H2SO4, H3PO4

*Corrosion resistance of alloys against various media at subcritical and supercritical temperatures [19].*

**a**

**Good resistance**

**; low density**

**Poor resistance**

All acids [H3PO4] > 0.1 mol/kg, NaOH

300–350°C and lower than that of Mo at 400–450°C in SCW with NaCl [34].

substrate in SCW environments at low density [44].

The Cr is considered as the most important alloying element to improve corrosion resistance [35]. The Cr2O3 presented the lowest solubility and the best oxidation resistance among the oxides of chromium, iron, and nickel [29, 32, 35–38]. The higher chromium-containing alloys presented the lower thicknesses of the formed oxide scales. The NiCr25 alloy performed the best corrosion resistance among the interested binary Ni-Cr alloys (0–25 mass% Cr) in an aqueous solution resulting from the oxidation of CH2Cl2 at 40 MPa and temperatures of 100–415°C [39]. The cracking susceptibility of nickel-based alloys also decreased with an increase in Cr content of the substrate exposed to SCW containing HCl or NaOH [40]. The oxygen affinity of chromium is higher than those of iron and nickel, and thus Cr generally may be selectively oxidized to Cr(OH)3 and Cr2O3. The Cr(III) of Cr2O3 can be transformed into Cr(VI) by further oxidation in the oxidizing high temperature water, and unfortunately the Cr(VI) possibly loss by the dissolution. A more continuous and stable Cr2O3 layer was formed at higher temperatures (450 and 500°C) than at 400°C in oxidizing SCW [41]. A series of results indicate that alloys generally suffer the more serious corrosion in high temperature subcritical water rather than in SCW at low density. Mo improves the resistance to pitting corrosion in subcritical salt solution obviously [42]. In nickel-based alloys, the synergistic effect of Mo and Cr on improving the corrosion resistance is remarkable [43]. The nickel-based alloys often show a severe depletion of nickel in high-density aqueous systems [32, 37], while NiO, which is an effectively protective oxide, covers the alloy

For a specific reactor material, the corrosion behavior is commonly influenced by the dissociations of acids, salts, and bases, the solubility of corrosion products and gases, and the stability of protective oxide scales. All these characteristics are

**134**

Salt management was identified as a critical issue for the success of SCWO technology. Except for the inorganic salts initially present in the feedstocks, a majority of inorganic salts derive from the SCWO treatment of high-concentration, stubborn organic matters including hetero-atoms such as chlorine, sulfur, and phosphorus [50]. Solubility of salts is reduced evidently in SCW, which is usually lower than 100 mg/L, and thus they are prone to deposition. In addition to corrosion issues, plugging triggered by salts precipitation is another main obstacle to hinder SCWO commercialization, which is induced by sticky salt agglomeration and deposition on the internal surface of reactor.

When plugging takes place, the SCWO plant has to be shut down, washed, and restarted, which will directly decrease the reliability of the plant and increase its running cost. Inorganic salts, whether soluble or not, may come from feedstock or reaction byproducts, and their viscosities decide the tendency of depositing on the reactor wall. In general, different salts own different deposition characteristics [51]. Salt deposition principles and the corresponding solutions have been systemically presented in the previous literatures [50, 52, 53]. In a commercialized SCWO plant, reactor plugging can be avoided by particular reactor designs, special instruments, and operation means [18]. Possible solutions are to adopt reverse flow tank reactor, reverse flow tubular reactor, transpiring wall reactor, centrifuge reactor, mechanical brushing, rotating scraper, reactor flushing, crossflow filtration, density separation, additives, high flow velocity, homogeneous precipitation, and extreme pressure [17]. In fact, precipitated salts are relatively difficult to be removed out of SCWO plant during the operation process; thus, most SCWO plants do not have salt removal function. Salts in SCWO are classified into Type 1 or Type 2, according to their solubility [54], Type 1 salt has a high solubility in the

range of water's critical temperature, while Type 2 salt has a low solubility in this region. Type 2 salt can be separated by properties of SCW [50], and the suitable supercritical conditions should be controlled at approximately 400°C and 25 MPa according to the solubility of salts mentioned in the previous studies [52, 55]. Hydro cyclone or centrifugal reactor helps to remove soluble salts under the abovementioned supercritical conditions, but severe wearing problem is inevitable. Of course, low salt concentration in feedstock is helpful for avoiding reactor plugging. Appropriate reactor configuration and pre-desalination before reactor may solve reactor plugging problem effectively and economically.

In addition, when the preheating temperature of feedstock is in the range of 200–450°C [56], some undesired intermediate products like tar and char will be generated, which may also plug preheating pipeline. To overcome this problem, the following options are taken into consideration, which include enlarging the inner diameter of the preheating pipeline, adding a small amount of oxidant into the preheating pipeline to inhibit the formations of tar and char, increasing the heating rate of feedstock, and preheating feedstock up to a lower temperature even not preheating [57]. However, the improvement of the heating rate is limited by setting space of heating part, heating methods, and withstanding temperature of preheater wall. The above fourth approach means that a large amount of heat will not be recovered into the SCWO system, which will undoubtedly reduce the energy efficiency and increase the running cost.

Salt deposition also accelerates catalyst inactivation rate and reactor corrosion rate, and reduces heat transfer coefficient [22, 58]. The potential catalysts for SCWO reactions may be poisoned and/or polluted quickly by precipitated salts in SCW [59]. It is also difficult to replace catalyst in traditional reactor configuration. That may be the reason why Savage has reported that no catalyst is implemented commercially for catalytic SCWO for organic waste treatment [60]. Thereby, it is important to separate these precipitated salts before they contact heterogeneous catalyst. Comparing with salt of ion form in subcritical water, salt in the form of molecule in SCW is relatively less corrosive [19, 21–23, 61]. Salt precipitated out from SCW mainly results in chemical corrosion through oxidation reaction. Salt in subcritical water or high density SCW mostly promotes electrochemical corrosion [58, 62], and may result in inter-granular corrosion starting from the edge of metal grain [49]. Nowadays, two contradictions of preventing salt deposition and minimizing reactor corrosion rate are displayed as follows: first, preventing salt deposition needs high SCW density because it will exhibit a relatively improved solvent property for precipitated salts. However, minimizing corrosion rate requires low SCW density to decrease the content of ionic salts [31]. Kritzer et al. [63] controlled SCW density at less than 250 kg/m3 in order to reduce reactor corrosion rate. Second, adding alkali compounds independently or in feedstock before reactor is helpful for inhibiting reactor corrosion, but the possibility of reactor plugging increases because of salt deposition [19]. That is why some alkali compounds are delivered into reaction system from reactor outlet.

Salt deposition control achieves significant improvement through the innovation of research methods, the studies of salt deposition and separation performance, the evolution of salt control techniques, and new reactor configuration designs. However, several challenges such as the transport properties, deposition mechanisms, and practical salt control techniques, still restrict the technology application. Operation parameters play important roles in salt deposition processes, and various ions in the mixture may exhibit mutual influence or common effect. Thus, the prediction of salt deposition is quite difficult and needs extensive information on salts phase behavior in SCW. Moreover, the mechanisms of salt deposition in the multi-component system have not been recognized deeply, and the entire evolution

**137**

*Supercritical Water Oxidation for Environmentally Friendly Treatment of Organic Wastes*

process of salts from microscopic nucleation to macroscopic deposition in SCW requires to be further revealed. Hence, it is necessary to gain more phase behavior data for analysis in depth. The combination of the experiment and numerical

In future, salt deposition control in a SCWO system requires global considerations and designs instead of previous single or local protection. Certainly, reactor configuration design has the priority to the whole SCWO system due to its crucial roles in salt control. Wise reactor concept combines with appropriate operation techniques before the reactor, in the reactor and/or after the reactor, forming multiple control and security units. Notably, the determination of salt control schemes should also consider the characteristics of wastewater and each technique, as well as the economic costs. With the solution of salt deposition problems and the development of reactor corrosion resistant materials, SCWO will be able to achieve

Since the occurrence of SCWO technology firstly proposed by Modell at the Massachusetts institute of technology in the early 1980s, a number of researcher and industrial engineers have been devoted to related research on prevention and control of corrosion and salt precipitation, enhancement of SCWO economy, safety, automation control, etc. A series of effective solutions, technologies, and equipment were proposed, and some have been applied to the actual industrial SCWO plants, which are not focused in this chapter. Here, several latest or typical

Beyond all doubt, reactor is the most important core equipment of SCWO plants. The produced salts due to SCWO reaction together with those initially contained in feedstock may result in reactor plugging and increase corrosion rate of equipment. In terms of whether or not the precipitated solid-state salt is promised to accumulate on reactor's internal surface, the precipitated salt and the internal surface of reactor have two kinds of relations in reactor [53]. For the former case, salt removal can be accomplished by special instruments such as mechanical brushing, rotating scraper, reactor flushing, etc. For the latter case, it can be achieved by particular reactor designs and operation means. They include reverse flow tank reactor with brine pool, reversible flow tubular reactor, transpiring wall reactor, centrifuge reactor, crossflow filtration, density separation, additive, high velocity flow, and homogeneous precipitation. Moreover, extreme pressure is provided to avoid salt precipitation in SCW. Philip et al. [53] have objectively reviewed the properties of the above specific reactor configurations and operational approaches in commercial applications. Furthermore, there are some other special reactor configurations such as cool wall reactor reported by Cocero and Martinez [64] and two pipes reactor introduced by Baur et al. [65]. Calzavara et al. [66] set a stirrer in their reactors. Príkopský [67] installed a protective metal sleeve replaced easily to prevent salt from depositing on the internal surface of their axial reactor in SCWO. There is no doubt that no one reactor design or operation mean has been

Next, three kinds of typical reactor configurations are given to introduce the development of the novel reactors. MODAR reactor or its variation belongs to a reverse flow tank reactor with brine pool, which separates/removes salt by SCW

simulation is a desired method for the investigation of salt deposition.

*DOI: http://dx.doi.org/10.5772/intechopen.89591*

large-scale commercial applications.

**3.1 Development of novel reactor**

**3. Advanced technologies and equipment**

advanced technologies and equipment are introduced in detail.

proven to be clearly superior to the others in all aspects.

*Supercritical Water Oxidation for Environmentally Friendly Treatment of Organic Wastes DOI: http://dx.doi.org/10.5772/intechopen.89591*

process of salts from microscopic nucleation to macroscopic deposition in SCW requires to be further revealed. Hence, it is necessary to gain more phase behavior data for analysis in depth. The combination of the experiment and numerical simulation is a desired method for the investigation of salt deposition.

In future, salt deposition control in a SCWO system requires global considerations and designs instead of previous single or local protection. Certainly, reactor configuration design has the priority to the whole SCWO system due to its crucial roles in salt control. Wise reactor concept combines with appropriate operation techniques before the reactor, in the reactor and/or after the reactor, forming multiple control and security units. Notably, the determination of salt control schemes should also consider the characteristics of wastewater and each technique, as well as the economic costs. With the solution of salt deposition problems and the development of reactor corrosion resistant materials, SCWO will be able to achieve large-scale commercial applications.
