Incineration Process For Disposal Of Waste Propellant And Explosives

Abstract

A process is provided for incineration of waste propellants and explosives. In this process the waste propellant or explosives in particulate form is mixed with water forming an aqueous suspension. The aqueous suspension is burned in a rotary incinerator under conditions which permit sequential evaporation of water from the suspension, drying of the particulate propellant or explosive, and then ignition of the propellant or explosive. The combustion gases are scrubbed with water prior to passing into the atmosphere. The invention herein described was made in the course of or under a contract or subcontract thereunder with Department of the Army.

Description

This invention relates to a process for incineration of waste propellants, and explosives.

The commonly employed method for disposing of propellant and explosive waste generally consists of manually spreading the waste on pads or on the ground and burning the waste in open air. There are several undesirable features associated with this commonly employed method. Open air burning is limited by weather conditions and produces combustion products which are a source of air pollution. Further, personnel are exposed to a potential fire hazard when the propellant or explosive waste is spread on the pads or the ground prior to burning. Space and quantity distance requirements for burning of waste propellants and explosives introduce additional limitations on open-air burning.

The open burning method for solid waste propellants and explosives is a source of pollution. A new method of disposal of waste propellants and explosives must be devised in order to meet present and future air pollution standards. To meet this need, a process has been developed for incineration of waste propellants and explosives, which eliminates many of the hazards inherent in the open burning of waste propellants and explosives and which process is capable of reducing pollution to within limits currently under consideration for pollution standards.

Broadly, in accordance with this invention, a process is provided for incineration of waste propellant and explosives comprising the steps of:

A. forming an aqueous suspension of propellant or explosive waste in water having a dispersed phase comprising solid propellant or explosive waste in particulate form, in which the solid particles have a maximum average length of less than 0.25 inch, and a continuous phase comprising water;

B. introducing air and the suspension of step (a) into one end of a rotary kiln operating at a temperature of from about 1,200.degree.F. to about 2,200.degree.F., said suspension being fed at a rate sufficient to initially form a thin aqueous layer of said suspension on the wall of said incinerator and continuously contacting said layer of suspension with dry surface of said incinerator wall whereby the continuous water phase of the suspension is evaporated and the propellant or explosive particles are sequentially dried and ignited within the rotary kiln;

C. drawing exhaust gases from the rotary kiln and contacting said exhaust gases with water to remove particulate matter and noxious gases from the exhaust gas, and

D. exhausting the resulting gases from step (c) to the atmosphere.

The process of this invention is more fully described with reference to the drawings. In the drawings like numbers refer to like parts where applicable.

FIG. 1 is an overall flow diagram of the process of this invention utilizing both solid and liquid propellant or explosive wastes as feed materials.

FIG. 2 is a schematic diagram illustrating a preferred embodiment of a system utilized in the process of this invention in which a normally solid, waste propellant or explosive is incinerated.

FIG. 3 is a schematic diagram illustrating the interior of a rotary kiln during the controlled burning process of this invention.

FIG. 4 is a schematic drawing illustrating the feed nozzle for introducing the aqueous suspension of waste feed into the rotary kiln.

FIG. 1 illustrates the overall process of this invention in block diagram form. It is seen from FIG. 1 that either solid or liquid waste propellants or explosives can be incinerated in accordance with the process of this invention by forming a suspension of solid or liquid propellant or explosive, in solid particulate form in water, and incinerating the suspension.

As illustrated in FIG. 2, waste solid propellant or solid explosive, is fed into feed hopper 10. The feed hopper 10 is equipped with vibratory means (not shown) for uniformly feeding the waste solids through a bottom opening 12 in said feed hopper 10 onto a fiber glass conveyor 16. Conveyor 16 is used to convey the waste solids through a metal detection and removal device 18 wherein any extraneous metal, i.e., metal which is not associated with or part of either the solid propellant or solid explosive waste feed is detected and after detection said metals are removed from the feed to wet grinder. Extraneous metal-free waste solid propellant or solid explosive is then conveyed into a wet grinder 20 at a controlled rate. In the wet grinder 20, the solid waste is ground in the presence of water. The resulting solid particles have a length or maximum dimension averaging 0.25 inch or less.

The ground water-wet solid waste particles are washed into mixer 22. In mixer 22, the particles are admixed with additional water, as necessary, to form a suspension of solid waste particles in water. This suspension is pumped by pump 24 through feed line 26 into the inlet-end 30 of kiln 32. Flow through the feed line 26 must be maintained in the turbulent range, i.e., at a Reynolds Number of at least about 6,400 to maintain the solid particles in suspension.

Kiln 32 is lined with refractory brick. Kiln 32 rotates about its longitudinal axis through use of drive means (not shown). The aqueous suspension of waste solids is deposited on the wall of the kiln 32 and immediately flows to a thin layer of suspension. Movement of the wall 34 of kiln 32 constantly provides continual contact of a hot-dry surface to the layer of suspension. Air is continuously introduced into the kiln 32 at the inlet-end 30 through air line 36. Air passes through the inner chamber 38 of kiln 32 and through exhaust outlet 40 at the burner-end 42 of kiln 32. A burner 44 is used constantly during incineration to maintain the temperature in the inner chamber 38 of the kiln 32. Exhaust gases from combustion of the waste solid propellant or explosive within inner chamber 38 of kiln 32 pass through exhaust line 40 into a second incinerator 46 consisting of a refractory lined wall 48 and burner 50. The second incinerator 46 functions as an afterburner for further combustion of combustible products contained in the exhaust gas from kiln 32. The resulting exhaust gas passes out of the exit-end 52 of second incinerator 46 through a precooler 54 and through feed line 56 into a wet scrubber 58. In wet scrubber 58 particulate matter and noxious gases are removed from the exhaust gas. An exhaust fan 60 draws the exhaust gas through the wet scrubber 58 and exhausts the resulting product gas to the atmosphere.

In FIG. 3 the sequential nature of the incineration of solid particles as it occurs in the kiln 32 is illustrated. The suspension of solid waste particles in water initially forms a thin layer of suspension along the refractory lined wall 48 of the incinerator. As the layer of suspension is continually contacted with the hot surface of the rotating kiln wall, the water content of the suspension is evaporated. The solids 64 are then heated rapidly to dryness and then are ignited. The various factors which must be controlled to insure that the sequential burning process takes place in the rotary kiln are more fully described hereinafter.

In FIG. 4 the stationary, inlet-end 30 of rotary kiln 32 is shown. The feed inlet 31 to said kiln is close to the lower wall of the kiln. The feed spout 33 is jacketed with water. The cooling provided by the jacketed spout prevents vaporization of the water phase of the aqueous suspension in the feed lines. Any such vaporization is detrimental to sequential burning of the waste particles in suspension.

The following examples further illustrate the process of this invention. In the examples, parts and percentages are by weight unless otherwise specified.

EXAMPLE 1

A waste single base propellant (IMR) charge is passed through a metal detection and removal device wherein extraneous metals are removed from the propellant charge. The propellant is then passed at a controlled rate into a flying blade grinder where it is mixed with water and ground into small particles. The particle size of the ground propellant is determined by Tylers Screen Analysis. The propellant particles have an average length or maximum dimension of about 0.04 inches. The water-wet particles are transferred to a mixing vessel wherein additional water is added. The weight ratio of water to particles in the mixing vessel is 2.8:1. The particles are slurried in the mixing vessel to form a suspension of the propellant particles in water. The propellant suspension is introduced into an incinerator operating at a temperature of 1,600.degree.F. and in which the air flow rate through said incinerator is 1,248 cubic feet per minute. The incinerator consists of a high-alumina refractory brick lined rotating chamber, 6 feet long and having an inside diameter of 5 feet. The chamber rotates at a speed of 1.1 revolutions per minute. The feed line in the rotary incinerator is cooled to maintain the liquid phase of the suspension in the liquid state. The suspension of waste propellant in water is fed at one end of the rotary kiln near the rotating walls. The suspension immediately starts to flow and very rapidly forms a thin layer of suspension on the moving walls of the incinerator. The water phase of the suspension is rapidly evaporated and the propellant particles are sequentially dried and ignited. The product gases from the combustion are exhausted through a second incinerator operating at a temperature of about 1,600.degree.F. The residence time of the exhaust gases in said second incinerator is about 0.3 seconds. The second incinerator which is sometimes referred to as an afterburner is high-alumina refractory lined chamber, seven feet in length and having an inside diameter of 23/4 feet. The hot exhaust gases are drawn through a pre-cooler where the temperature of the gases is reduced to about 250.degree.F. and the gases are then drawn through a wet scrubber in which the gases are in intimate contact with water. In the wet scrubber, water soluble gas contained in the exhaust gases and some particulate matter are removed from the exhaust gas stream. The resulting gases are subsequently exhausted to the atmosphere. The gases being exhausted are analyzed for NO, NO.sub.2, SO.sub.2 , Hcl, CO.sub.2 and hydrocarbons. The analysis of the gases exhausted to the atmosphere is set forth in Table I.

EXAMPLES 2-6

Example 1 is repeated utilizing a mixture of single base and double base propellant as the waste feed charge. This waste feed is ground under water. The resulting particles have an average length or maximum dimension of about 0.08 inches as measured by Tyler Screen Analysis. The particles are admixed with water to form a suspension. The suspension is introduced into the rotary kiln. Processing conditions differing from Example 1 are set forth in Table II. The exhaust gas analysis from incineration of the mixture of single and double base waste propellant is set forth in Table I.

TABLE I __________________________________________________________________________ STACK GAS ANALYSIS EXAMPLE (PPM) CO.sub.2 * No. HYDROCARBON HYDROGEN SULFIDE NO NO.sub.2 HYDROGEN CHLORIDE SULFUR DIOXIDE % __________________________________________________________________________ 1 0 100 80 0 -- 0 2% 2 90 58 170 6 -- 10 2.0% 3 90 0 160 0 -- 83 1.6% 4 50 35 235 0 -- -- 1.0% 5 28 0 200 0 -- -- 3.4% 6 23 80 200 0 0 30 2.1% __________________________________________________________________________ * % Increase of CO.sub.2 in stack gas when burning propellant and fuel as compared to CO.sub.2 in exhaust burning fuel only.

TABLE II __________________________________________________________________________ TEMPERATURE .degree.F. EXAMPLE TYPE FEED RATE PARTICLE SIZE WEIGHT RATIO ROTARY SECOND AIR FLOW NO. MATERIAL LBS./MIN. (average) WATER/SOLIDS KILN INCINERATOR CU.FT./MIN. __________________________________________________________________________ 1 Sgl. Base 4.9 .040 inch 2.8:1 1600.degree.F. 1600.degree.F. 1248 Propel. 2 Sgl. Base 4.2 .080 2.8:1 Dbl. Base Propel. 3 4.2 2.9:1 4 4.2 3.0:1 5 4.2 3.0:1 6 4.1 3.3:1 __________________________________________________________________________

EXAMPLES 7-24

Example 1 is repeated utilizing various waste solid propellants and explosives as feed materials. Operation of the process proceeds satisfactorily in all cases. Water evaporation drying and ignition of propellants and explosives proceeds smoothly in the kiln in all cases. Visual observation of the stack gases shows no visible smoke from the exhaust gas stack. A white exhaust plume of gas saturated with water vapor can be observed. The exhaust gases for each propellant and explosive charge are analyzed. Process conditions and gas analysis for each example are set forth in Tables III and IV, respectively.

TABLE III __________________________________________________________________________ TEMPERATURE .degree.F. EXAMPLE TYPE FEED RATE PARTICLE SIZE WEIGHT RATIO ROTARY SECOND AIR VELOCITY NO. MATERIAL LBS./MIN. (average) WATER/SOLIDS KILN INCINERATOR CU.FT./MIN. __________________________________________________________________________ 7-15 Comp. A-5.sup.(1) 3.0 Granular 3:1 1600 1700 1000 4.2 Sugar-like 1600 1700 1350 3.3 (<0.10 inch) 1600 1700 1800 3.3 1500 1600 1000 3.2 1700 1800 1000 4.2 1800 1800 1000 3.6 1600 1700 1000 -- 1500 1600 1350 1.8 1500 1600 1350 16 Mixture 1.7 0.10 inch 5.5:1 1600 1700 1000 Comp. B.sup. (2) Dbl. Base.sup. (4) Sgl. Base.sup. (3) 17 Sgl. Base.sup. (3) 1.7 0.10 inch -- 1600 1700 1000 18 Sgl. Base.sup. (3) 1.2 >.10 inch 3.7:1 1600 1700 1000 Dbl. Base.sup. (4) 19 TNT.sup.(5) 1.1 Flake .020 inch 4.4:1 1600 1700 1000 thick .times. 1/8 inch length 20-22 3.9 3:1 1800 1800 1000 3.0 3:1 1700 1800 1350 3.0 3:1 1500 1600 1000 23 Aluminized 2.9 3:1 1700 1800 1000 Dbl. Base.sup. (4) 24 Dbl. Base.sup. (4) 3.7 3:1 1700 1800 1000 __________________________________________________________________________ .sup.(1) Composition A-5 is 98.5% cyclotrimethylenetrinitraamine (RDX) an 1.5% stearic acid. .sup.(2) Composition B is 60% (RDX) and 40% trinitrotoluene. .sup.(3) Single Base propellant consists primarily of nitrocellulose. .sup.(4) Double Base propellant consists primarily of nitrocellulose and nitroglycerin. .sup.(5) TNT is trinitrotoluene.

TABLE IV __________________________________________________________________________ STACK GAS ANALYSIS EXAMPLE (PPM) CO.sub.2 NO. HYDROCARBONS HYDROGEN SULFIDE NO NO.sub.2 HYDROGEN CHLORIDE SULFUR DIOXIDE % __________________________________________________________________________ 7 130 41 160 4 0 60 8.4 8 0 42 160 10 0 68 8.2 9 0 80 240 2 0 69 10.5 10 280 130 130 0 0 54 10.5 11 170 29 230 0 0 0 6.6 12 0 15 610 10 0 10 8.3 13 0 9 250 24 0 0 7.2 14 0 5 160 32 0 2 7.2 15 0 10 152 23 0 0 7.6 16 0 29 270 0 0 0 13.5 17 0 16 190 0 0 0 9.7 18 7 55 95 0 0 0 6.0 19 0 130 230 112 0 92 9.0 20 0 11 300 99 0 17 9.2 21 0 0 350 160 0 5 5.7 22 0 25 310 50 0 0 8.3 23 60 21 128 49 0 0 -- 24 170 50 80 0 0 0 -- __________________________________________________________________________

EXAMPLE 25

Example 1 is again repeated utilizing a nitroglycerin slum as explosive liquid. The nitroglycerin slum contains triacetin, acetone and some water. The nitroglycerin slum is poured onto sawdust particles to wet the sawdust with the nitroglycerin slum. The sawdust absorbs all of the slum. The nitroglycerin wet sawdust is then screened to remove any foreign objects, particularly metals, and is then added to a mixer containing water, nitrocellulose, and single and double base propellant to form a suspension of explosive solids (nitroglycerin impregnated sawdust, nitrocellulose and propellant) in water. Some of the nitroglycerin is extracted from the sawdust into the water, up to the limit of the solubility of nitroglycerin in water at the mixing temperature of about 70.degree.F. The suspension is mixed for a minimum of 15 minutes and then pumped to the incinerator under conditions of turbulent flow following steps and conditions for operation of the process as set forth for Example 1. After most of the suspension has been incinerated, additional water-wet solid propellant particles and water is added to the mixer and pumped to the incinerator using the steps and conditions for operation of the process as set forth in Example 1. The process operates smoothly in the incineration of the waste containing nitroglycerin wet sawdust and visual observation of the exhaust gas reveals no smoke.

In the examples heretofore described, a second incinerator is employed in series with the rotary kiln for purposes of achieving more complete combustion of the exhaust gas from the rotary kiln, whereby hydrocarbonaceous particulate matter in the exhaust undergoes further combustion. Also, the level of noxious gases is further reduced in the secondary incinerator. In practice, the need for a secondary incinerator will depend, in part, on the permissible level of noxious gases and hydrocarbonaceous and other particulates in the exhaust stream. In theory, the first incinerator can be designed and operated to avoid the necessity of utilization of a second incinerator. In practice, however, this may not be practical, i.e., the size (length and diameter) of the kiln may become excessive, and the operating temperatures, etc., may not be readily controlled in such a unit. The need for a second or more incinerators in series will be determined on an overall system design basis. When a second incinerator is employed it is generally operated at from about 1,200.degree.F. to about 2,200.degree.F. Residence time of exhaust gas in the second incinerator may vary depending on system design, however, a residence time of from about 0.3 seconds to about 0.5 seconds is generally acceptable.

In the process of this invention sequential evaporation of water from the aqueous suspension of waste propellant or waste explosive is essential. Thus, the operational variables such as feed rate, feed condition (liquid suspension), air flow rate through the incinerator, incinerator temperature, incinerator residence time and the like must be controlled to produce sequential evaporation, drying of the waste feed, and ignition and burning in order to achieve safe and effective incineration of the waste feed while achieving reduction in the level of pollutants in the exhaust gases to acceptable levels.

The waste material which can be incinerated in the process of this invention includes all types of solid and liquid propellants and explosives. Illustrative solid propellants which can be incinerated include single base propellant, double base propellant, triple base propellant, high energy propellant, rocket casting powder, cast propellant grains, rolled sheet propellants, nitrocellulose, trinitrotoluene, inorganic oxidizers such as ammonium perchlorate, ammonium nitrate; organic oxidizers such as HMX (cyclotetramethylenetetranitraamine), RDX (cyclotrimethylenetrinitraamine), and the like. Illustrative waste liquid propellants and explosives which can be incinerated in the process of this invention included nitrate esters such as nitroglycerin, diethyleneglycol dinitrate, triethylene glycol dinitrate, and the like.

When incinerating liquid propellants or explosives in accordance with this invention it is necessary that the liquid propellant or explosive be abosrbed by a particulate absorbent carbonaceous combustible material such as sawdust. The explosive-wet or propellant-wet carbonaceous combustible materials are considered solid propellants or solid explosives for purposes of this specification and claims. These particulate propellants or explosives are admixed with water to form aqueous suspensions and processed in accordance with the incineration process heretofore described. In the step of forming the aqueous suspensions, normally solid propellants which absorb propellant or explosive liquids can be added. Thus, for example, it is oftentimes desirable to admix nitrocellulose or single or double base propellant, in particulate form, to nitroglycerin wet carbonaceous material.

In order to successfully operate the process of this invention it is necessary to have the waste propellant or explosive material reduced to a substantially uniform particle size. Small particle sizes are needed because propellants and explosives burn rapidly and propagate flame easily. In this case of normally solid, waste propellant or explosives, the waste is ground under water for safety purposes and the particle size of the resulting ground particles should average less than about 0.25 inches and preferably the average particle length or maximum dimension shall be less than about 0.10 inches. In the case of normally liquid, explosives or propellants, the explosive is absorbed in particulate carbonaceous combustible material within the size envelope heretofore described. The resulting particulate waste propellant or explosive is then formed into a suspension by mixing the water-wet explosive with water, as necessary, to form a suspension having a weight ratio of water to waste propellant or explosive of from about 19:1 to about 1:1. It is generally preferred to employ a water/propellant-explosive ratio of about 3:1. The suspension of the small particles in water is pumped into the rotary kiln under conditions to maintain turbulent flow within the feed lines. Turbulent flow conditions in the feed lines is necessary for safety purposes. The feed is then discharged into the rotary kiln for incineration. Feed rate must be controlled so that all the explosive or propellant waste is consumed within the incinerator. If feed rate is excessive, unburned propellant can be discharged with ash.

The temerature within the rotary kiln is maintained at between 1,200.degree.F. and 2,200.degree.F. In order to achieve low concentrations of NO.sub.x it is preferred to operate the rotary kiln at a temperature at about 1,500.degree.F. to about 1,800.degree.F. At temperatures of below 1,500.degree.F. and above 1,800.degree.F. the NO.sub.x concentration in the exhaust gases from the incinerator is substantially increased. At temperatures above about 2,000.degree.F., evaporation of the water portion of the suspension of propellant or explosives and ignition of the waste is more difficult to control which can result in incomplete combustion of the propellant or explosive waste. The higher temperature, i.e., above 2,000.degree.F., sometimes prevents the thin layer of aqueous suspension from forming on the chamber wall, allowing unburned propellant and explosive waste to be discharged with the ash. Unburned waste in the ash is a safety hazard, since propellant and explosive waste could ignite and burn outside the rotary kiln.

In the operation of the process of this invention, the rotary kiln is heated by burning of a fuel such as fuel oil, propane, natural gas, or a substitute therefor. The burner fuel does effect the combustion occurring within the rotary kiln. Thus, propane is a preferable fuel to fuel oil to use to fire the rotary kiln because the propane combustion products function as a reducing agent thereby lowering the NO.sub.x content in the exhaust gases. It is understood that the composition of exhaust gases will vary depending on the composition of the waste material being incinerated.

In the process of this invention the air provided to the incinerator should be thoroughly mixed with the exhaust gases prior to exit from the rotary chamber. Therefore, it is preferable to fire the burner in the rotary kiln, countercurrent to the air flow through the kiln. The amount of air in which the waste explosives and propellant is burned should be as near the stoichiometric amount as possible. The stoichiometric amount of air required for each propellant or explosive waste can be readily calculated based on the feed material to be burned.

The wet scrubber employed in the process of this invention is used to reduce particulate matter and water soluble gases in the exhaust stream. Wet scrubbing of the exhaust gases can be achieved by passing the exhaust gas through a scrubbing liquid, for example, a water spray or water bath. The exhaust gas can then pass to an entrainment section to remove the water from the gas, while contaminated scrubbing liquid is drained to the scrubbing section.

Claims

What we claim and desire to protect by Letters Patent is:

1. A process for incineration of waste liquid and solid propellants and explosives comprising:

a. forming an aqueous suspension of propellant or explosive waste in water having a dispersed phase comprising solid propellant or explosive waste in particulate form, in which the solid particles have an average maximum length of less than 0.25 inch, and a continuous phase comprising water;

b. introducing air, and the suspension of step (a) into one end of a rotary incinerator operating at a temperature of from about 1200.degree.F. to about 2200.degree.F., said suspension being fed at a rate sufficient to initially form a thin aqueous layer of said suspension on the walls of said incinerator and continuously contacting said layer of suspension with dry surface of said incinerator wall whereby the aqueous content of the continuous phase of the suspension is evaporated and the propellant particles are sequentially dried and ignited within;

c. drawing exhaust gases from the rotary kiln and contacting said exhaust gases with water to remove particulate matter and noxious gases from said gas, and

d. exhausting the resulting gases from step (c) to the atmosphere.

2. The process of claim 1 in which the solid propellant or explosive particles have an average maximum length of about 0.10 inch.

3. The process of claim 1 in which the particulate solid propellant is ground single base propellant.

4. The process of claim 1 in which the particulate solid propellant is a mixture of ground single base and double base propellant.

5. The process of claim 1 in which the dispersed phases comprises a particulate carbonaceous combustible material which contains absorbed liquid propellant or explosive.

6. The process of claim 5 in which the dispersed phase comprises sawdust impregnated with nitroglycerin.

7. A process for incineration of waste solid propellant or explosive comprising the steps of:

a. removing extraneous metal from said solid propellant or explosive feed material,

b. grinding the substantially extraneous metal-free solid propellant or explosive in the presence of water, to form solid particles, substantially all of said particles having a (maximum) average dimension of less than 0.25 inch,

c. mixing said water wet solid particles and additional water necessary to form an aqueous suspension of said solid particles in water, the weight ratio of water to said solid particles being from about 19:1 to about 1:1,

d. introducing air, and the suspension of step (c) into one end of a rotary incinerator operating at a temperature of from about 1,200.degree.F. to about 2,200.degree.F., said suspension being fed at a rate sufficient to initially form a thin aqueous layer of said suspension on the walls of said incinerator, and continuously contacting said layer of suspension with dry wall surface of the incinerator whereby the continuous phase of the suspension is evaporated and the solid particles are sequentially dried and ignited within said incinerator,

e. drawing exhaust gases from the rotary incinerator, and wet scrubbing said exhaust gases with water to remove particulate matter and to dissolve noxious gases present in said exhaust gases, and

f. exhausting the resulting gases from step (e) to the atmosphere.

8. The process of claim 7 in which the exhaust gases from the rotary incinerator are drawn through a second incinerator prior to wet scrubbing, said second incinerator operating at a temperature of from about 1,200.degree.F. to about 2,200.degree.F., the residence time of said gases in said second incinerator being from about 0.3 seconds to about 0.5 seconds.

9. The process of claim 8 in which the weight ratio of water to said particulate propellant or explosive is about 3:1 and the solid particles have an average maximum dimension of about 0.10 inch.