No abstract

Two supercritical water oxidation (SCWO) plants that utilize transpiring wall reactor designs for processing organic wastes are undergoing testing and operation. One plant is designed to destroy Navy excess hazardous materials (EHM). The EHMs represent organic materials found aboard Navy ships. The plant has a nominal waste feed rate of 45 kg/h and utilizes compressed air as the oxidant. Corrosive wastes, including chlorinated solvents (diluted with kerosene) and lube oils, and a salt-producing photographic solution simulant have been processed at feed rates between 45 and 95 kg/h. Tests have been conducted at an operating pressure of 24.1 MPa and reactor temperatures between 594 and 816 °C. Destruction removal efficiencies of better than 99.99% have been obtained. Priority air pollutants NO X and CO are below 25 and 100 ppm, respectively. Liquid effluent total organic carbon (TOC) levels are consistently below 3.5 ppm. Post-test inspections have not revealed any obvious reactor liner corrosion or salt deposition. A second SCWO plant designed for the destruction of obsolete, colored smokes/dyes and pyrotechnic munitions has been fully commissioned and is currently undergoing validation testing. The plant is designed to process 145 kg/h of a 25 wt % basis slurry of smokes and dyes. The plant uses oxygen as the process oxidant. The reactor operating pressure is 26.3 MPa, and operating temperatures are between 575 and 750 °C. Off-site plant skid fabrication was completed in 1997, site preparation and construction were completed in 1998, and commissioning was completed in 1999. Validation testing will be completed in the fourth quarter of 2000. Production demilitarization processing of smokes and dyes will follow.

Several researchers have determined that water (H2O) and sulfur dioxide (SO2) in a flue gas stream have an impact on the amount of elemental mercury (Hg0) that is homogeneously oxidized by a chlorine-containing species. Generally, it is concluded that H2O inhibits Hg oxidation by chlorine (Cl2). However, doubt remains as to whether SO2 promotes or inhibits Hg oxidation. Further, most published results seem to indicate that nitric oxide (NO) does not have a significant impact on Hg oxidation. This paper will present data taken in a laboratory-scale apparatus designed to test these observations. In this work, Cl2 is intentionally added to a synthetic flue gas stream containing known amounts of elemental mercury. This gas blend is similar to a flue gas obtained by burning Powder River Basin coal in a pulverized coal fired power plant and is subject to a time−temperature profile similar to a power plant. The results obtained show that H2O, SO2, and NO all have an inhibitory effect on the homogeneous oxidation of Hg by Cl2. Further, the presence of H2O increases the inhibitory effect of SO2 and NO. Two new reactions are proposed to explain these results, in which SO2 and NO react with Cl2. The consequences of these reactions are a reduction in the oxidative interactions that take place between Hg and Cl2, thus decreasing the amount of Hg oxidation that occurs.

Chemical looping combustion (CLC) is an advanced technology with inherent CO 2 capture in which a solid oxygen carrier circulates between an air reactor and a fuel reactor. For coal-fueled CLC, the existence of solid impurities requires the oxygen carrier not only to have good reactivity but also to be contaminant-resistant, low-cost, and readily available. Therefore, the development of cost-effective and well-performing oxygen carriers is very meaningful for the coal-fueled CLC process. Natural red mud, a byproduct from the aluminum industry, was found to function well as an oxygen carrier and has also been found to have in situ coal catalytic gasification behavior. A thorough study on the longterm cyclic performance of red mud with coal char in a fluidized reactor was conducted in this work. For the purpose of comprehensively understanding the functions of inert supports as well as the sodium content in red mud, the effect of various inert oxides (Al 2 O 3 , SiO 2 , TiO 2 , and CaO) and the addition of sodium was evaluated. It has been proven that inert supports, Al 2 O 3 , SiO 2 , and TiO 2 , have a positive effect on both the reduction and oxidation reactivity of iron-based oxygen carriers by developing a porous structure in the particle. Al 2 O 3 and SiO 2 show the ability to stabilize the reactivity of iron oxide with a gaseous reductant (CO), even under fluidized conditions. Both Al 2 O 3 and TiO 2 can assist in maintaining the mechanical strength of the oxygen carrier after many cycles in a fluidized-bed reactor. The addition of sodium (Na) to red mud does not exhibit much effect on the reactivity of OC with CO as the fuel. However, it can significantly enhance the char gasification rate due to its catalytic function. Additionally, interaction between the active iron oxide and inert supports or sodium in the form of red mud at high temperatures leads to the formation of spinel phases. The growth of spinel phases results in the reduction of the oxygen carrying capacity. However, it helps fix sodium as a relatively stable chemical compound (NaAlSiO 4 or NaFe 0.25 Al 0.75 O 2 ). Both inert supports and sodium in natural red mud play critical roles in the performance of red mud as an oxygen carrier from either physical or chemical aspects.