EP0603708A2

EP0603708A2 - A process for the combustion, separation, and solidification of 3H and 14C from combustible liquids

Info

Publication number: EP0603708A2
Application number: EP93120118A
Authority: EP
Inventors: Steven T. Schaeffer
Original assignee: EI Du Pont de Nemours and Co
Current assignee: EIDP Inc
Priority date: 1992-12-18
Filing date: 1993-12-14
Publication date: 1994-06-29
Also published as: JPH06222196A; EP0603708A3

Abstract

This invention relates to a process for combustion, separation, and solidification of ³H and ¹⁴C from a combustible liquid stream. Gaseous combustion gases containing ³H₂O and ¹⁴CO₂ are processed by absorption of the ¹⁴CO₂ with caustic solution to produce a ¹⁴C salt and condensation and/or removal of gaseous ³H₂O through the use of a desiccating agent. Liquid ³H₂O and a slurry solution containing the ¹⁴C salt are solidified through the addition of a solidifying agent.

Description

Field of the Invention

This invention relates to a process for removing tritium (³H) and carbon-14 (¹⁴C) from combustible liquids, and more particularly to a process for the combustion, separation, and solidification of ³H and ¹⁴C from combustible liquids.

Background Art

The manufacture of radiochemicals for use in various applications such as medical tracer compounds and diagnostic reagents, involves processes including precursor synthesis, radiolabelling, and final purification. Invariably, these processes result in the production of radioactive by-products and radioactive contaminated solvents which are eventually separated from the final product. These radioactive wastes are isolated and, depending on their nature, either disposed of or stored at the site of generation.
Radioactive wastes from the processing of ³²P, ³³P, and ³⁵S can be stored at the site of generation for eventual decay due to their relatively short half-lives. However, the longer half-lives of ³H and ¹⁴C make on-site storage of these radioactive wastes costly and also pose a safety hazard.
Radioactive liquid streams containing ³H and/or ¹⁴C can be disposed of in a variety ways. For example, aqueous wastes containing 0.5% organics may be mixed with cement and subsequently buried. Organic wastes containing less than 0.2 milli Curie (mCi) radioactivity due to the presence of ³H and/or ¹⁴C can usually be burned, and some facilities may provide for combustion of wastes having radioactive contamination as high as 0.2 to 1.0 mCi/gallon.
Various processes for the combustion of radioactive organic liquid waste are known. For example, U.S. Patent No. 4,686,068, issued August 11, 1987, Keishi et al., discloses a batch process for treating radioactive organic waste by subjecting the organic waste to oxidative decomposition in an aqueous solution containing an inorganic fusion preventive agent, such as silicon dioxide, and a catalyst.
Japanese Patent Application 59035197, published February 25, 1984 discloses a controlled process for incinerating organic liquid streams contaminated by radioactive ³H and ¹⁴C which utilizes a liquid valve for regulating the organic solvent waste liquid and/or ignition oil flowing into the burners of the incinerator, so that the ignition oil is fed before or after the end of the incineration of the waste liquid.
U.S. Patent No. 4,655,968, issued April 7, 1987, to Kleinschroth et al., discloses a method for treating radioactive wastes by pyrolysis to reduce the volume of solid radioactive contaminated waste.
Various methods for the removal of radioactive ¹⁴CO₂ from waste streams are also known. For example, Japanese Patent Application J02287299, published November 27, 1990, discloses a method for treating radioactive wastes containing ¹⁴C in which hydrogen peroxide is reacted with the radioactive waste in an aqueous medium in the presence of a water soluble oxygen containing organic compound and copper and/or iron ions to produce a gaseous ¹⁴CO₂ stream which is contacted with barium hydroxide to produce barium carbonate. The remaining ¹⁴CO₂ gas-free solution can be solidified with cement or asphalt. Japanese Patent Application JP04093797, published March 26, 1992, discloses a process for treating gaseous ¹⁴CO₂ generated by nuclear power plants by passing the ¹⁴CO₂ through an organic solvent or by spraying the organic solvent into the ¹⁴CO₂, mixing the organic solvent with a monomer, and forming a plastic product via polymerization.
Various methods for the removal of ³H are also known. U.S. Patent No. 4,555,361 issued November 26, 1985 to Buckely et al. discloses a method for reducing the volume of solid radioactive waste by pyrolysis of the radioactive waste, followed by gasification of residual carbon with superheated steam, so that carbon containing components of the waste are removed as gaseous decomposition products in the form of carbon containing components in the form of carbon monoxide and hydrogen, leaving an ash residue for subsequent disposal. European Patent Application No. Publication EP 265744, published May 4, 1988, discloses a method for removing ³H from gas mixtures by hydrogenation of the ³H with a mono or poly-unsaturated compound such as linoleic acid in a Pt or Pd catalyst.
Japanese Patent Application J53126497, published April 11, 1978, discloses a process for removing gaseous ³H by absorption of the ³H in an absorption tower filled with an intermetallic compound composed of a rare earth metal and Ni, such as LaNi₅.
There are several known processes for the solidification of hazardous wastes. Conner, Jesse, R., "Chemical Fixation and Solidification of Hazardous Wastes", New York, (1990) discloses several such processes including various cement-based solidification processes such as Portland cement and cement-silicate solidification processes (Chapter 10) as well as alternative solidification processes including organic based processes such as urea-formaldehyde systems and thermoplastic process (Chapter 14).
Liquid wastes containing greater than 0.5% organics and further having greater than 1.0 mCi/gallon radioactivity, present novel disposal difficulties. These wastes, hereinafter referred to as "mixed wastes", contain hazardous (organic) components as well as radioactive contamination. New technologies for treating such mixed wastes are under development. Generally, mixed wastes cannot be accepted for burial due to their relatively high organic content and cannot be combusted safely due to their high radioactivity. For example, Dhoogie, P.M. A Catalytic Wet Oxidation Process For Mixed Waste Volume Reduction/Recycling, "Proceedings of the Symposium on Waste Management," Tucson, AZ, March 1, 1992, R. G. Post, Editor p. 1289-1291 (1992), discloses a wet oxidation process using iron (III) as an oxidant in the presence of homogeneous cocatalysts. Some existing technologies have been applied the treatment of mixed wastes. For example, Garcia, Corazon, "Incineration of Radioactive Wastes Containing Only C-14 and H-3", "Proceedings of the Symposium on Waste Management," Tucson, AZ, March 1, 1992, R. G. Post, Editor p. 1271-1273 (1992) disclose an incineration process for treating mixed wastes. However, such known process may not meet regulatory requirements in certain countries, such as the United States.

Summary of the Invention

This invention relates to process for the removal of ³H and ¹⁴C from a combustible liquid stream which comprises:

(a) combusting a combustible liquid containing ³H and ¹⁴C to produce a gaseous stream containing ³H₂O and ¹⁴CO₂;
(b) condensing the gaseous ³H₂O in the gaseous stream to produce a liquid ³H₂O stream;
(c) absorbing the gaseous ¹⁴CO₂ with a caustic solution to produce a ¹⁴C salt; and
(d) solidifying the liquid ³H₂O stream and the ¹⁴C salt through the addition of a solidifying agent.

Additionally, the invention relates to a process wherein after step(b) above, any remaining gaseous ³H₂O is removed by contacting the gaseous stream with a desiccating agent.
Another aspect of the invention relates to a process for the removal of ³H and ¹⁴C from a combustible liquid stream which comprises:

(a) combusting a combustible liquid containing ³H and ¹⁴C to produce a gaseous stream containing ³H₂O and ¹⁴CO₂ gaseous stream;
(b) removing the gaseous ³H₂O by contacting the gaseous stream with a desiccating agent;
(c) absorbing the ¹⁴CO₂ with a caustic solution to produce a ¹⁴C salt; and,
(d) solidifying the ¹⁴C salt through the addition of a solidifying agent.

Yet another aspect of the invention relates to a process for the removal of ³H and ¹⁴C from a combustible liquid stream which comprises:

(a) combusting a combustible liquid containing ³H and ¹⁴C in a furnace to produce a gaseous stream containing ³H₂O and ¹⁴CO₂;
(b) condensing the gaseous ³H₂O in the gaseous stream in a condenser to produce a liquid ³H₂O stream;
(c) absorbing the gaseous ¹⁴CO₂ in a scrubber having a caustic solution contained therein to produce a slurry containing a ¹⁴C salt; and
(d) solidifying the liquid ³H₂O stream and the slurry containing the ¹⁴C salt with a solidifying agent.

Additionally, the invention relates to the above process wherein after step (b) remaining gaseous ³H₂O is removed by passing the gaseous ³H₂O through a desiccating column, the desiccating column having a desiccating agent contained therein.
A final aspect of the invention relates to a process for the removal of ³H and ¹⁴C from a combustible liquid stream which comprises:

(a) combusting a combustible liquid containing ³H and ¹⁴C in a furnace to produce a gaseous stream containing ³H₂O and ¹⁴CO₂;
(b) removing the gaseous ³H₂O by passing the gaseous stream through a desiccating column having a desiccating agent contained therein.
(c) absorbing the gaseous ¹⁴CO₂ in a scrubber having a caustic solution contained therein to produce a slurry containing a ¹⁴C salt; and
(d) solidifying the the slurry containing the ¹⁴C salt with a solidifying agent.

Brief Description of the Figures

Figure 1 depicts a flow chart for a process to remove ³H and ¹⁴C present in a combustible liquid stream. The process depicted includes combustion of the radioactive stream to produce ¹⁴CO₂ and ³H₂O, removal of the ³H₂O by condensation followed by removal of any remaining ³H₂O through the use of a desiccating agent, absorption of the ¹⁴CO₂ by a caustic solution to produce a ¹⁴C salt, and solidification of the ¹⁴C salt and ³H₂O liquid.

Detailed Description of the Invention

This invention relates to a process for the removal of ³H and ¹⁴C from a combustible liquid stream which comprises combusting a combustible liquid containing ³H and ¹⁴C to produce a gaseous stream containing ³H₂O and ¹⁴CO₂, condensing the gaseous ³H₂O to produce a liquid ³H₂O stream, absorbing the gaseous ¹⁴CO₂ with a caustic solution to produce a ¹⁴C salt, and solidifying the liquid ³H₂O stream and the ¹⁴C salt through the addition of a solidifying agent. Alternatively, the gaseous ³H₂O can be removed from the gaseous stream containing the ³H₂O and ¹⁴CO₂ by contacting the gaseous stream with a desiccating agent.
The process of combustion and a discussion of the elements of combustion is described by Perry, R. H., and and Chilton, C. H., Chemical Engineers' Handbook, section 9, New York (1973), the disclosure of which is hereby incorporated by reference.
A furnace system can be used for the combustion process. Such a furnace system includes one or more burners which are the devices used for producing a flame. The burner mixes the combustible liquid stream to be combusted and an oxidizer in proportions that are within the limits of flammability for ignition as well as for steady combustion.
The furnace can be defined as the enclosed space in which the chemical oxidation of the combustible liquid is achieved. The furnace complements the burner or burners firing into it to obtain the desired combustion reaction. The furnace and burner combination should be designed so as to provide for the four elements of good combustion, including intimate mixing of the combustible liquid stream to be combusted and the oxidizer, admission of sufficient oxidizer to burn the combutible liquid stream completely, sufficient temperature to ignite the combustible liquid stream/air mixture and complete its combustion, and the required residence time for combustion to be complete (see Perry, R. H., and and Chilton, C. H., Chemical Engineers' Handbook, New York (1973)).
By "combustible liquid stream" is meant any liquid stream which is combustible or which can be rendered combustible. By "combustible" is meant the ability to be burned (oxidized) to produce the products of combustion, including water (H₂O) and carbon dioxide (CO₂) gases, and any solid ash wastes remaining after completion of the oxidation process. Preferred liquids to be combusted are mixed wastes. By "mixed waste" is meant liquid wastes containing hazardous (organic) components as well as radioactive contamination. The preferred liquid mixed wastes treated by the method of the present invention are those mixed wastes containing greater than 0.5% organics and further having greater than 1.0 mCi/gallon radioactivity. An example of a composition of such a preferred mixed waste to be combusted is shown in Table 1, Flow 1 and depicted in Figure 1, Flow 1.
Drums containing the liquid stream to be combusted are preferably first transferred to a liquid waste feed tank using a liquid transport means such as a drum pump. Upon being opened, these drums can be vacuumed into the furnace air feed system to combust any volatiles.
From the liquid waste feed tank, which is maintained, preferably, under a partial vacuum resulting from the furnace air-feed system, the liquid to be combusted can be pumped as a feed stream into the furnace at various rates depending on known operating parameters including liquid feed stream rate, furnace capacity, and furnace operating pressure and temperature.
There can be more than one phase present in the drum containing the liquid to be combusted, including a heavy aqueous phase and a lighter organic phase. The liquid to be combusted can be withdrawn from the bottom of the drum and from just below the liquid level to form the feed stream to insure that no dramatic transitions in British Thermal Units (BTU) value occur upon feeding of the liquid stream to be combusted to the furnace.
An organic fuel can be added to the liquid stream to be combusted in order to increase the BTU value of the liquid stream to be combusted. Any fuel can be used which, when added to the liquid stream to be combusted has the effect of rendering the liquid stream to be combusted a combustible liquid stream, thereby insuring uniform combustion (oxidation). Such added fuels serve to boost the BTU value of the liquid stream to be combusted. The heat of combustion of the combustible liquid should be about 90,000 BTU/gal or greater. Examples of suitable fuels include propane, ethane, butane, natural gas and fuel oil. Preferably propane is used as the fuel. The desired heat of combustion (approximately 90,000 BTU/gallon) can be used to determine a suitable propane feed rate to the furnace. While this flow rate can be varied to control the furnace operating temperature, the propane addition rate should be minimized to avoid excessive non-radioactive H₂O and CO₂ generation which can lead to increased waste to disposal volume ratio. Similarly, the desired flow rate for other fuels can be determined based on their specific heats of combustion and a liquid combustible stream having a desired heat of combustion of about of 90,000 BTU/gal.
Air can be supplied via an air compressor to the furnace at various rates depending on the scale of design. An air ratio corresponding to 50% excess air over the theoretical amount of air required to burn (combust) the carbon and net hydrogen in the liquid combustible stream is preferred. The air compressor inlet can be dampered to the open air, thereby providing for a means of suction via flexible hose to any storage drums and tanks which could release radioactive volatiles.
The gaseous stream exiting the furnace contains the products of combustion, including carbon dioxide, water, nitrogen, and oxygen. Any ¹⁴C originally in the combustible liquid is in the form of radioactive carbon dioxide (¹⁴CO₂) and any ³H originally present in the combustible liquid is in the form of radioactive water (³H₂O). The flow rate of the gaseous stream exiting the furnace, hereinafter referred to as the "gaseous stream containing ³H₂O and ¹⁴CO₂" can vary widely depending upon scale of design and desired operating conditions. To insure continuous flow of the furnace off-gases, the furnace can be operated under pressure, preferably, at about 10 pounds per square inch gauge (psig).
Preferably, a furnace heat exchanger can be used to cool the gaseous stream containing the ¹⁴CO₂ and ³H₂O combustion gases prior to the removal of the ³H₂O and the adsorption of the ¹⁴CO₂. Preferably, the furnace heat exchanger cools the gaseous stream containing the ¹⁴CO₂ and ³H₂O to 400° F and generates 15.6 pounds/minute (lb/min) saturated steam at 150 psig.
After exiting the furnace or furnace heat exchanger (if used), the gaseous stream containing the ¹⁴CO₂ and ³H₂O is passed through a condenser to cool the gas mixture and condense a portion of the water vapor. Any heat exchanger capable of providing sufficient cooling to condense a substantial portion the water present in the gaseous stream containing the ¹⁴CO₂ and ³H₂O can be used. The heat exchanger can be sized using known heat transfer principles and heat exchanger design parameters to provide, preferably, for cooling the gas mixture to 68°F and condensing 83% of the gaseous H₂O (including ³H₂O) to produce a liquid ³H₂O stream. This stream will also contain nonradioactive H₂O. Cooling can, for example, be provided by counter-current flow of water at 59°F, either from an existing cooling tower or from an independent refrigeration system. Examples of a suitable types of heat exchangers for use with this process include spiral heat exchangers and shell-and-tube exchangers.
The condensate from the exchanger containing the liquid ³H₂O, referred to as the "liquid ³H₂O stream", can be collected for later incorporation into the final solidification step (see below).
Preferably, a desiccating column or columns containing a desiccating agent can be used to remove any of the gaseous ³H₂O remaining after condensation. Alternatively, the desiccating column(s) can be omitted from the process of the present invention. In another embodiment, the condenser can be omitted and the use of a desiccating column or columns can utilized as the sole means for removal of gaseous ³H₂O.
The principles of gas absorption through the use of solid desiccating agents and the design of equipment useful in sorption processes are known and described by Perry, R. H., and Chilton, C. H., Chemical Engineers' Handbook, section 16, New York (1973), the disclosure of which is hereby incorporated by reference. Various known factors to be considered in sizing desiccating equipment such as packed columns include the ultimate capacity of the desiccating agent for the gaseous ³H₂O, the phase equilibrium, the rate behavior, and the process arrangement. Any of several known desiccating agents such as CaSO₄, silica gel, molecular sieves, Na₂SO₄, P₂O₅, CaCl₂, MgSO₄, H₂SO₄, NaOH, and KOH can be used. Sodium sulfate (Na₂SO₄) is the preferred desiccating agent. The ³H₂O will react with the CaSO₄ to a dew point of -99°F (0.0012 mmHg partial pressure = 0.00016 mole% H₂O in gas). A moisture sensor at the column outlet can be used to indicate an increase in the exit gaseous water content which is used as a signal to take a water saturated desiccating column off-line and have it regenerated. If the condenser is operated at 68°F the desiccating column should be regenerated approximately every 3 days; more frequently if the condenser is operated at greater than 68°F. Regeneration of the desiccant can be performed by purging the column either with the furnace exist gas (gaseous stream containing the ¹⁴CO₂ and ³H₂O) or by passing heated air, preferably at about 300°F, through the column. The hot gas releases the water from the desiccating agent, and the released water can be recycled to the condenser inlet. A moisture sensor at the column outlet can be used to indicate completion of the regeneration process. Preferably, two vertical desiccating columns are utilized to allow for the desiccation operation to continue while a water saturated column is being regenerated. In this preferred operation, regeneration is performed in a first desiccating column by purging the column with the furnace exit gas and sending the released water to the condenser inlet, while a second desiccating column downstream of the condenser is utilized to absorb any remaining gaseous H₂O.
Further in accordance with the invention, the gaseous CO₂ present in the stream exiting the desiccating column is then sent through a scrubber or scrubbers, wherein the CO₂ is absorbed (at least some of the CO₂ is ¹⁴CO₂). By absorption is meant the removal of CO₂ (including ¹⁴CO₂) from the gaseous stream by reaction of the CO₂ with a liquid solution to produce a non-reactive non-volatile product. Methods for sizing and optimizing caustic scrubbers for removal of CO₂ are known. Such methods are described by Perry, R. H., and Chilton, C. H., Chemical Engineers' Handbook, section 20, New York (1973), the disclosure of which is hereby incorporated by reference.
By "scrubber" is meant any type of equipment designed for gas-liquid contacting including various types of plate columns, packed columns, falling film (wetted wall columns), fluidized bed columns, spray chambers, agitated vessels, and line mixers. Preferably a vertical scrubber or scrubbers is used, the vertical scrubber having a packed column packed with suitable size packing, such as, for example, one inch Raschig rings. Several types of packing can be used including Raschig rings, pall rings, berl saddles, lessing rings, intalox saddles, and tellerettes.
The type of packing used can be chosen using known packing properties such as those relating to surface availability, interface regeneration, pressure drop, weight, and corrosion resistance. The packed column can be designed as a cylindrical shell containing a support plate for the packing material and a liquid distributing device designed to provide effective irrigation of the packing. Devices can be added to the packed column for redistribution of any liquid that might channel down the sides of the column. Preferably two vertical packed column scrubbers are used in sequence. These scrubber(s) contact the gaseous ¹⁴CO₂ with a caustic solution, preferably NaOH, and preferably in a countercurrent flow with the stream containing gaseous ¹⁴CO₂ so that the ¹⁴CO₂ is reacted with the caustic solution to form a ¹⁴C salt such as sodium carbonate (Na₂¹⁴CO₃) (when the caustic solution utilized is NaOH). Non-radioactive CO₂ will similarly react with the caustic solution to form a non-radioactive salt (Na₂CO₃). The scrubber(s) can be sized using known mass transfer principles and taking into account various factors such as pressure drop and mass transfer of the gaseous ¹⁴CO₂ accompanied by chemical reaction with the caustic solution. When two scrubbers are used sequentially each scrubber can be designed, preferably, to remove 96% of the CO₂ for a total removal rate of 99.84% of the inlet ¹⁴CO₂.
The ¹⁴C salt exiting the scrubber(s) is in the form of a slurry solution which can be fed, preferably, into a common holding tank. Optionally, the slurry can be pumped through any properly sized heat exchanger to remove any heat of reaction generated by reaction with the caustic solution. The slurry can then be filtered. Various filtration processes can be utilized including centrifugal filtration, plate and frame filtration, pressure and vacuum leaf filtration, and rotary drum filtration. Known principles of filtration and factors for sizing filters are described by Perry, R. H., and Chilton, C. H., Chemical Engineers' Handbook, section 19, New York (1973), the disclosure of which is hereby incorporated by reference. Various known factors to considered in choosing and/or designing a suitable filtration device include pressure drop, cake thickness, effect of temperature, effect of pressure, effect of type of filtration medium, effect of particle size, effect of viscosity, and effect of solids concentration. Preferably the filter used is a rotary disk filter. The ¹⁴C salt, for example, sodium carbonate, will be retained in the filter cake and the filtrate can be fed to a holding tank. The rotary disk filter can be designed and the operating parameters chosen, using known methods, such that the filter cake can preferably consist of about 30% solids. The filter cake can be continuously removed from the rotary disk filter and directed to a mixer.
Finally in accordance with the invention, the liquid ³H₂O and/or the 30% solid ¹⁴C salt containing slurry are then combined with a solidifying agent. The solidifying agent is any substance which solidifies or hardens the liquid ³H₂O and/or the 30% solid ¹⁴C salt containing slurry for disposal. The solidifying agent should be chosen so as to insure that no leaching of radiactivity can occur for extended period of time, preferably 500 years or more. A variety of solidifying agents can be used including cement, glass, urea-formaldehyde, polybutadiene, polyester-epoxy, acrylamide gel, polyolefin, and polyurethane. Preferably the solidifying agent utilized is cement. The preferred type of cement mix is a Portland general-use cement (Waldo Brothers, Massachusetts). Portland cement is described by Conner, Jesse, R., "Chemical Fixation and Solidification of Hazardous Wastes", New York, (1990) discloses several such processes including various cement-based solidification processes such as Portland cement and cement-silicate solidification processes (Chapter 10), the disclosure of which is hereby incorporated by reference. Portland cement is basically a calcium silicate mixture containing predominantly tricalcium and dicalcium silicates with small amounts of tricalcium aluminate and a calcium aluminoferrite.
The process of the present invention can be modified for exclusive processing of either ¹⁴C or ³H contaminants.
If only ¹⁴C waste is available, a condenser can be used to cool the gas to 86°F and the desiccating column(s) can be by-passed. However, the waste disposal volume increase will only be slightly affected unless cement recipes othe than the described Portland cement recipe (see Figure 1, Flows 26 and 27) are used.
If ³H-only waste is available, the scrubber(s) can be by-passed and the gas exiting the desiccation column can be fed directly into dilution ducts for subsequent dispersion. The waste disposal volume increase will be reduced considerably by this type of processing.
The present invention thus provides a process for treating liquids containing both organic wastes as well as radioactive contamination due the presence of ¹⁴C or ³H contaminants, in a way that allows for the safe disposal of such liquids in a single process.
Figure 1 depicts a process flow chart for the preferred embodiment of the present invention. The flow streams, and processing equipment are described in the example below.
The following example illustrates the process of this invention.

EXAMPLE

The process of the present invention is exemplified by the process depicted in Figure 1 and described below. A material and energy balance of the process in accordance with the scale of this example is provided in Table 1 below.
The gas flow exiting a furnace 30, (gaseous stream containing ³H₂O and ¹⁴CO₂₎ (Fig 1, Flow 4) is 300 cubic feet per minute (cu. ft./min) at standard operating temperature and pressure (STP). Propane is added at compressor 32 as the auxiliary fuel (Fig 1, Flow 2) to boost the BTU value of the mixed waste. To insure continuous flow of the combustion gas mixture exiting the furnace, 30, the furnace operates at 10 pounds per square inch gauge (psig).
The particular liquid to be combusted is a mixed waste of the composition shown in Table 1 and depicted in Figure 1, Flow 1. Drums containing liquid mixed waste (Figure 1, Flow 1) are first transferred to a mixed waste feed tank at 34 using a drum pump at 36. The opening of these drums is vacuumed into the furnace air-feed system to combust any volatiles which may be present.
From the mixed waste feed tank, 34, maintained under a partial vacuum via the furnace air-feed system (Figure 1, Flow 3), with air being added at compressor 38, the mixed waste is pumped into the furnace, 30, at a rate of 0.178 gal/min. As there can be more than one phase present in the drum, including a heavy aqueous phase and a lighter organic phase, the liquid to be combusted is withdrawn from the bottom of the drum and from just below the liquid level to insure that no dramatic transitions will occur in BTU value.
As noted above, propane is utilized to increase the BTU value of the contaminated liquid stream. The approximate molar ratio of propane to mixed waste is 9:100, thereby yielding a 90,000 BTU/gal liquid fuel. This ratio corresponds to a propane flow rate which is 1.5 cu. ft/min (STP). While this flow rate can be varied to control the furnace operating temperature, the propane addition rate should be minimized to avoid excessive non-radioactive H₂O and CO₂ generation which can lead to increased contaminated waste-to-disposal volume ratio.
Air is supplied to the furnace at a rate of 281 cu. ft/min (STP) corresponding to 50% excess air for the reaction. This air ratio insures complete combustion of the mixed waste. The air compressor inlet is dampered to the open air and permits suction via flexible hose to any storage drums and tanks which could release radioactive volatiles.
The furnace heat exchanger, 40, (Figure 1, HX 1) cools the gaseous stream containing the ³H₂O and ¹⁴CO₂ to 400°F and generates 15.6 lb/min of saturated steam at 150 psig (366°F) (Figure 1 Flow 6). The net heat transferred is 13,600 BTU/min.
The gaseous stream containing the ³H₂O and ¹⁴CO₂ then passes through a first desiccating column, 42, (Fig. 1, DES COL. 1) which is shown in Fig. 1 operating in a regeneration mode. Regeneration of the desiccating agent is completed by purging with the furnace exit gas (Figure 1, Flow 7). Hot air can also be used to purge the desiccating column 42. The hot furnace exit gas releases the water from the desiccating agent for recycle to the condenser inlet. A moisture sensor at the outlet of the desiccating column 42 indicates completion of the regeneration process.
The gaseous stream exiting the desiccating column 42 then passes through a spiral heat exchanger, 44, (80 square feet) (Figure 1, COND, Flow 8) to cool the gas mixture to 68°F and condense 83% of the water vapor. The net heat transfer in the exchanger is 3600 BTU/min. Cooling is provided by counter-current flow of water at the cooler, 48 (Figure 1, COOLER, Flow 11).
The condensate containing liquid ³H₂O from the condenser 44 is collected for later solidification into a cement matrix (Figure 1, Flow 9).
The gaseous stream exiting the condenser 44 then enters a second 3.3' dia x 15' vertical desiccating column, 46, (Figure 1, DES COL 2, Flow 10) packed with 12,100 lbs of calcium sulfate (CaSO₄). The water reacts with the calcium sulfate to a dew point of -99°F (0.0012 mmHg partial pressure = 0.00016 mole% H₂O in gas), corresponding to an annual release rate of ³H₂O of 0.3 Ci/yr. After a moisture sensor at the column outlet indicates an increase in the water content (approximately every 3 days, more frequently if the condenser is operated at greater than 68°F), the column 46 is taken off-line and regenerated.
The gaseous stream exiting the second desiccating column, 46, gas then enters a series of two vertical packed column scrubbers at 50 and 52 (Figure 1, SCRUB COL 1 and SCRUB COL 2, Flows 13 and 15), which are 1.9 feet (') in diameter x 22' in length and packed with 1" Raschig rings. These scrubbers at 50 and 52 contact the entering gaseous stream with 177 pounds per minute (lb/min) NaOH solution (Figure 1, Flows 23, 14, and 17) to provide for the reaction of the CO₂ to produce the ¹⁴C salt, sodium carbonate. Each scrubber at 50 and 52 sequentially removes 96% of the CO₂ for a total removal rate of 99.84% of the inlet CO₂ corresponding to an annual release rate of ¹⁴CO₂ of 3.4 Ci/yr. Exiting the scrubber 52 is 247 cu. ft./min (STP) CO₂-free gas (Figure 1, Flow 18) for dilution in facility main ducts.
The solution exiting each of the scrubbers 50 and 52, (Figure 1, Flow 16 and 19, 20 (combined)) is fed into a common holding tank at 54. The slurry is pumped via pump 55 through a heat exchanger, 56, (Figure 1, HX 2) to remove any heat of reaction and is then passed through a rotary disk filter,58, (Figure 1 FILTER). The sodium carbonate is retained in the filter cake and the filtrate is fed to a holding tank, 62 (Figure 1, Flow 21). The filter cake consisting of 30% solids is continuously removed and directed to a cement mixer, 60 (Figure 1, Flow 24).
The filtrate in the holding tank 62 is adjusted to 2 Normal (N) NaOH by addition of 11 lb/min of 50 weight% NaOH (Figure 1, Flow 22). The tank level is maintained by addition of water to the holding tank 62. The caustic solution is returned to the tops of the scrubbers 50 and 52, by two feed pumps at 64 operating at 177 lb/min (Figure 1, Flow 23 (combined), 14, and 17).
The water from the condenser, 44 (1.9 lb/min) (Figure 1, Flow 9) and the 30% solid slurry from the filter 58 (4.1 lb/min solids, 9.5 lb/min liquid) (Figure 1, Flow 24) are combined with cement (Figure 1, Flow 26) and water (Figure 1, Flow 25) at a rate of 6.6 lb/min in a cement mixer 60. The resulting cement matrix is fed to drums at a rate of 28 lb/min or 2.1 drums (55 gal) per hour (Figure 1, Flow 27).
The rate of drum generation, and therefore the waste-to-disposal volume ratio can be reduced significantly if the filter can further concentrate the solids.
The final drum mixture for the process described averages 5.1 gallons of mixed waste (volume increase of 9.8 fold), and 2.2 Ci ³H and 0.17 Ci ¹⁴C.
Table 1 provides a material and energy balance of the exemplified process. Flow numbers referred to above correspond to the labelled streams of Figure 1.

Claims

A process for the removal of ³H and ¹⁴C from a combustible liquid stream which comprises:
(a) combusting a combustible liquid containing ³H and ¹⁴C to produce a gaseous stream containing ³H₂O and ¹⁴CO₂;

(b) condensing the gaseous ³H₂O in the gaseous stream to produce a liquid ³H₂O stream;

(c) absorbing the gaseous ¹⁴CO₂ with a caustic solution to produce a ¹⁴C salt; and

(d) solidifying the liquid ³H₂O stream and the ¹⁴C salt through the addition of a solidifying agent.
The process of claim 1 wherein after step(b) any remaining gaseous ³H₂O is removed by contacting the gaseous stream with a desiccating agent.
A process for the removal of ³H and ¹⁴C from a combustible liquid stream which comprises:
(a) combusting a combustible liquid containing ³H and ¹⁴C to produce a gaseous stream containing ³H₂O and ¹⁴CO₂ gaseous stream;

(b) removing the gaseous ³H₂O by contacting the gaseous stream with a desiccating agent;

(c) absorbing the ¹⁴CO₂ with a caustic solution to produce a ¹⁴C salt; and,

(d) solidifying the ¹⁴C salt through the addition of a solidifying agent.
The process of claims 2 or 3 wherein the desiccating agent is selected from the group consisting of CaSO4, silica gel, molecular sieves, Na₂SO₄, P₂O₅, CaCl₂, MgSO₄, H₂SO₄, NaOH, and KOH.
The process of claims 1, 2, or 3 wherein the solidifying agent is selected from the group consisting of cement, glass, urea-formaldehyde, polybutadiene, polyester-epoxy, acrylamide gel, polyolefin, and. polyurethane.
The process of claims 1, 2, or 3 wherein the combustible liquid is a mixed waste.
The process of claims 1, 2, or 3 wherein after step (c) the ¹⁴C salt is filtered.
A process for the removal of ³H and ¹⁴C from a combustible liquid stream which comprises:
(a) combusting a combustible liquid containing ³H and ¹⁴C in a furnace to produce a gaseous stream containing ³H₂O and ¹⁴CO₂;

(b) condensing the gaseous ³H₂O in the gaseous stream in a condenser to produce a liquid ³H₂O stream;

(c) absorbing the gaseous ¹⁴CO₂ in a scrubber having a caustic solution contained therein to produce a slurry containing a ¹⁴C salt; and

(d) solidifying the liquid ³H₂O stream and the slurry containing the ¹⁴C salt with a solidifying agent.
The process of claim 8 wherein after step (b) remaining gaseous ³H₂O is removed by passing the gaseous ³H₂O through a desiccating column, the desiccating column having a desiccating agent contained therein.
The process of claim 9 wherein after step (a) the gaseous stream is passed through a regenerating desiccating column having a saturated desiccating agent contained therein.
A process for the removal of ³H and ¹⁴C from a combustible liquid stream which comprises:
(a) combusting a combustible liquid containing ³H and ¹⁴C in a furnace to produce a gaseous stream containing ³H₂O and ¹⁴CO₂;

(b) removing the gaseous ³H₂O by passing the gaseous stream through a desiccating column having a desiccating agent contained therein.

(c) absorbing the gaseous ¹⁴CO₂ in a scrubber having a caustic solution contained therein to produce a slurry containing a ¹⁴C salt; and

(d) solidifying the the slurry containing the ¹⁴C salt with a solidifying agent.
The process of claims 8, 9, 10, or 11 wherein the scrubber is a vertical packed column having packing material therein.
The process of claim 12 wherein the packing material is in the form of Raschig rings.
The process of claims 10 or 11 wherein the desiccating column is a vertical packed column, having a desiccating agent contained therein.
The process of claim 14 wherein the desiccating agent is selected from the group consisting of CaSO4, silica gel,molecular sieves, Na₂SO₄, P₂O₅, CaCl₂, MgSO₄, H₂SO₄, NaOH, and KOH.