Patent Number: 046363360
Section: description

The invention may be better understood by reference to the following examples which are intended to be illustrative of the process of the present invention and not in any way limitative thereof. EXAMPLE 1 The apparatus utilized comprised a commercially available spray dryer constructed of stainless steel. From the spray dryer exhaust, gases with their entrained solids were ducted directly to a fabric filter (commercially available baghouse filter). Sampling locations for gas analysis were, among other places, at the spray dryer inlet before any liquid waste enters the spray dryer and the spray dryer outlet. NO.sub.x measurements were made with a chemiluminescence analyzer. Temperatures also were monitored with the output recorded on a chart recorder. The gas flow rates through the spray dryer were determined by standard pitot tube transfer flow measurements and pressure also was monitored. The average residence time of liquid waste and hot gas in the spray dryer was calculated using the known volume of the spray dryer and flow rates of the waste and gas. A chelate-containing liquid waste was formulated comprising 90 wt. % water and 10 wt. % EDTA in complex with sodium. The waste was introduced into the spray dryer at ambient temperature where it was contacted with a hot gas having an average temperature of approximately 370.degree. C. to produce in a time of about 1.6 seconds an outlet gas having an average temperature of about 173.degree. C. and containing the dried chelating agent. The solid product was collected in the bag filter and recovered as a dry, flowable powder having a density of about 0.39 grams/cc. In contrast, utilizing the same waste and time it was found that if the outlet temperature was allowed to go below 150.degree. that a sticky residue formed on the walls of the spray dryer in such thickness as to necessitate terminating the test. EXAMPLE 2 A simulated copper-containing decontamination liquid waste was formulated. The liquid waste comprised 83.7 wt. % water, 2.5 wt. % EDTA, 5.3 wt. % tetrasodium EDTA, 5.2 wt. % ammonium hydroxide, 2.6 wt. % copper sulfate, and about 0.7 wt. % powdered anion and cation exchange resins. The exchange resins were added to act as abrasives to remove dried residue from the walls of the spray dryer. A finely atomized spray of the waste was introduced into the spray dryer where it was contacted with a hot gas stream having an initial or inlet temperature of 313.degree. C. In a time of about 1.8 seconds the gas temperature (as measured at the outlet of the spray dryer) was about 185.degree. C. The solid product was collected from the filter and found to be a dry, flowable powder having a density of about 0.25 grams/cc. During this test no increase in NO.sub.x was detected, thus demonstrating that the amine chelating agent had not undergone any decomposition. EXAMPLE 3 A simulated iron decontamination liquid waste was formulated. The liquid waste comprised 76.5 wt. % water, 15.4 wt. % EDTA, 1.05 wt. % FE.sub.2 O.sub.3 and 7.05 wt. % NH.sub.4 OH. The liquid waste was introduced into the spray dryer where it was contacted with a hot gas stream having an initial temperature of 313.degree. C. In a time of about 2.1 seconds the gas temperature (as measured at the spray dryer outlet) was reduced to about 172.degree. C. A solid product was recovered from the fabric filter in the form of a dry flowable powder which had a density of about 0.87 grams/cc. Further, throughout the test there was no increase in the NO.sub.x emissions which would have been indicative of any decomposition of the amine chelating agent. It is believed that the foregoing examples clearly demonstrate the efficacy of the present invention to treat a liquid waste containing an organic amine chelating agent to produce a dry, flowable powder of the agent. To demonstrate the benefits obtained from treating an organic amine chelating agent in accordance with the present invention, the following comparison is offered. When an EDTA liquid waste such as is described in Examples 2 and 3 is treated in accordance with the current required practice for such a low-level radioactive liquid waste containing an organic amine chelating agent, one cubic meter of the waste mixed with cement would produce a mixture which upon solidification, would have a volume of 1.7 cubic meters. In contrast, when that same waste from Example 3 is treated in accordance with the present invention it would produce a dry powder product having a volume of only 0.22 cubic meter and when blended with cement would have a volume of 0.56 cubic meter. Further, 1 cubic meter of the EDTA-copper liquid waste from Example 2, while producing a less dense powder, would still only have a volume of 0.48 cubic meter. When wetted and mixed with cement the resulting product would shrink to a volume of 0.21 cubic meter. Thus when the powder product from the present invention is processed in accordance with the current practice, the end product provides substantial reduction in volume and associated disposal cost. Similar benefits are obtainable when the powder product is solidified in other materials, for example, polymers currently used for such purpose. Thus, it is seen that the present invention makes possible what was heretofore believed to be unobtainable; namely, the rapid conversion of a waste containing an organic amine chelating agent into a dry, flowable powder. Further, the practice of the present invention provides a substantial economic benefit. The process of the present invention is capable of substantially reducing the volume of low-level radioactive wastes while producing a dry, flowable radioactive solid product and a gaseous product which contains substantially no NO.sub.x and also retains volatile radionuclides in the solid product. In addition, greater volume reductions can be realized by compression of the spray-dried powder obtained in the process of this invention. It will, of course, be realized that various modifications can be made to the design and operation of the process of this invention without departing from the spirit thereof. For example, waste materials other than those specifically exemplified herein can be spray dried according to the process of this invention. The material to be treated can be introduced into the spray dryer using various single or multiple fluid spray nozzles or other forms of atomizers. Multiple nozzles or atomizers can be used, if desired. In addition, other gas-solid separation means can be used to separate the gaseous and solid products of the process. For example, electrostatic or metal filters or cyclones may be used. Other ways of treating the gaseous and solid products following separation can be used, if desired. Thus, while the principle, preferred design and mode of operation of the invention have been explained and what is now considered to represent its best embodiment has been illustrated and described, it should be understood that, within the scope of the appended claims, the invention can be practiced otherwise than as specifically illustrated and described.