Pressurized water reactors liquid waste processing

Radioactive waste treatment applications have been reported [3-9] for the laundry wastes from nuclear power plants and mixed laboratory wastes. Another interesting application of reverse osmosis process is in decontamination of boric acid wastes from pressurized heavy water reactors (PHWRs), which allows for the recovery of boric acid, by using the fact that the latter is relatively undissociated and hence wdl pass with water through the membrane while most of the radioactivity is retained [10]. Reverse osmosis was evaluated for treating fuel storage pool water, and for low-level liquid effluents from reprocessing plants. 

There are several processes that have been proposed for the direct combustion (oxidation or gasification) of coal within a liquid medium, and three of these are described as follows. The Zimpro process is based on the oxidation of crushed coal suspended in an oxygen-saturated hot-pressurized aqueous medium and is an outgrowth of an attempt to produce oxidized chemical products from paper mill wastes and the development of wastewater reclamation systems. The process involves the injection of high-pressure air into a slurry of hot water and coal under high pressure. High rates of oxidation occur at temperatures between 200°C and 350°C (390°F and 660°F) the exact temperature required to complete oxidation with reasonable residence time is dependent on the coal. Since the energy released is used to vaporize water, there is a direct relationship between the liquid temperature and the reactor pressure to which the air used for oxidation must be compressed. 

This review paper is concentrated on problems in scaling-up multiphase catalytic fixed bed reactors such as trickle-bed or packed bubble column reactors, in which two fluid phases (gas and liquid) pass concurrently through a bed of solid (usually porous) catalyst particles. These types of reactors are widely used in chemical and petrochemical industry as well as in biotechnology and waste water treatment. Typical processes are the hydrodesulphurization of petroleum fractions, the butinediol syntheses in the Reppe process for synthetic rubber, the anthrachinon/hydrochinon process for H202 production, biochemical processes with fixed enzymes or the oxidative treatment of waste water under pressure. 

In upflow bubble operation the consumption of the gas phase by reaction must also be considered in the model if the reactor operates under lower pressure (<20 bar) and if the reactor length is of technical dimensions (L>2 m) additionally gas phase dispersion (radial and axial) may have an influence on conversion [65]. As this reactor type is also used in waste water treatment as well as in fermentation processes, the possible non-Newtonian behavior of the liquid phase as well as the coalescence behavior of the system must be taken into account. Finally, it should be remembered that - comparable to fluidized bed reactors - results from laboratory reactors with small column diameter and/or particle sizes smaller than 0.2 cm usually cannot be regarded as representative for technical upflow units, because capillary force as well as lare scale circulation in the liquid phase may be significantly different. 

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