US3267699A - Atomizer burner - Google Patents

Description

Aug. 23, 1966 N. KNISELEY ATOMIZER BURNER Filed Sept. 18, 1965 a/gzmgglhz 1052/" J nited States Patent 3,267,699 ATOMIZER BURNER Richard N. Kniseley, Ames, Iowa, assignor to Iowa State University Research Foundation, Inc., Ames, Iowa, a corporation of Iowa Filed Sept. 18, 1963, Ser. No. 309,638 2 Claims. (CI. 67-87) This invention relates to an atomizer burner and a method of using thesame, and, more particularly, to a total consumption burner for flame emission and abs-orption spectroscopy.

The invention described herein was made or conceived in the course of or under a contract with the United States Atomic Energy Commission.

Although atomic emission and absorption spectra of many elements are strikingly enhanced in fuel-rich oxyacetylene flames, several problems have limited the application of these techniques. A conventional burner used in this technology is the Beckman-type burner, and among the problems associated therewith are: (l) the turbulent mixing principle employed in the burner gives rise to a high spectral background noise which limits the ultimate sensitivities available; and (2) a deposit tends to form at the capillary-oxygen orifice during a prolonged operation of the burner under fuel-rich conditions. The formation of this deposit affects the atomization efficiency and greatly increases the spectral background.

It is, therefore, a general object of this invention to provide a burner which overcomes these problems and, more particularly, by modifying the Beckman-type burner into the pre-mixed type. :In this fashion, it is possible to circumvent the difliculties associated with deposit formation as well as to improve the sensitivities of detection for many elements by an order of. magnitude or more.

Other objects and advantages of the invention may be seen in the details of construction and operation set down in this specification.

The invention is explained in conjunction with the accompanying drawing, in which:

FIG. 1 is a fragmentary elevational view, partially in section, of the inventive burner;

FIG. 2 is an enlarged transverse sectional view such as would be seen along the sight line 22 applied to FIG. 1; and

FIG. 3 is a fragmentary elevational view, partially in section, of a modified version of the inventive burner.

As shown in FIG. 1, the invention provides a premixing channel generally designated C for the oxygen and acetylene after the sample atomization has occurred. A tube 10, which may be of copper or brass, as illustrated, is attached to the outside of a standard Beckman burner generally designated 11 by means of three sets of aligning screws 12 placed at 120 intervals around the base of the tube. A graphite tubular insert '13, which has an axial bore 14 providing the pre-mixing channel C, is inserted into the tubular casing 10. I have found that it is important that the shoulder 13a on the graphite tube 13 be placed so that there is a chamber 15 provided above the top of the burner 11 and below the bottom surface 13b of the insert 13, the axial dimension of which is optimally in the range of 0.2-1.0 millimeter. The bore 14 is seen to be radially enlarged as at 14a in a conical or flaring fashion.

Three equally-spaced air holes 16 having a diameter 3,267,699 Patented August 23, 1966 "ice of the order of 2 millimeters allow a small amount of air to mix with the gas stream and also provide venting should the burner strike back.

The solution atomized at the tip of the capillary 17 flows axially through the channel C in the graphite rod 13. The alignment of the atomizer capillary 17 with respect to the pre-mixing channel C is an important adjustment. Improper alignment can result in flooding the channel with atomized solution, in an uneven flow of gases, causing the same to flicker and in a tendency for the flame to strike back.

To align the burner conveniently and precisely, the entire assembly, but without the graphite rod 13, is held in an inverted position by clamping onto a ring stand. A distilled water line is connected to the oxygen inlet of the burner as at 18. When the water flow rate through the oxygen inlet is sufficient, a fine jet of water will issue from the oxygen port as at 19. The tubular casing '10 is then centered by means of the aligning screws 12 so that the water jet travels axially through the tubular casing 10. The graphite insert rod 13 is then inserted into the tubular casing 10 and the alignment screws adjusted until the water jet travels axially through the insert '13. A properly aligned burner will not strike back when the acetylene flow entering as at 20 and issuing as at. 21 is turned off first, and the. insert 13 will be cool to the touch even after continued operation. The burner will normally remain aligned for an extended period of time provided the adjustment screws 12 are tightened.

For aid in understanding the practice of the invention, a specific example is set down.

EXAMPLE In this example, the burner 11 employed was manufactured by Beckman Instruments, Inc, Catalog No. 4030, and the tubular casing ltl'was constructed of copper having a 10 millimeter inside diameter and a 12 millimeter outside diameter. The length of the copper tubular casing 10 was 4.5 centimeters, with the air openings 16 being located 1.5 centimeters above the bottom edge 10a of the copper tube 10. The aligning screws 12 were located 0.3 centimeter and 0.6 centimeter above the base 10a. The graphite rod insert 13 had an overall length of 6.0 centimeters and an outside diameter at the top of 12 millimeters, a shoulder being provided at 13a to facilitate insertion within the copper tubular casing 10. The axial bore 14 had a diameter of 2.4 millimeters.

In operation, the burner just described is used in much the same manner as a standard (unmodified) Beckman burner. Relatively high oxygen and acetylene flow rates increased the stability of the flame background. Flow rates of approximately 3.4 liters per minute and 4.2 liters per minute for oxygen and acetylene, respectively, have been found to be satisfactory, although the exact values will vary with the burner used. Sample solutions containing at least 50% ethanol or other flammable solvent are necessary, since burner operation with aqueous solution is not satisfactory.

The inventive burner provides a marked reduction in flame noise as compared with the standard Beckman burner operated under fuel-rich conditions, and there is also a marked reduction in auditory noise. The table below shows that this has made it possible to gain at least an order of magnitude improvement in the detection limits. Comparable increases in detection sensitivity which heretofore have evaded detection in stoichiometric flames.

Table ESTIMATED PRACTICAL DETECTION LIMITS FOR SEV- ERAL ELEMENTS Detection Limit (p-pb Element Line (A) Premixed B urner Standard Beokrnan Burner 5 Using ethanelcontaining solutions. A Harvard Apparatus Oompany infusion pump (Model GUHOO) was used to feed the solution into the atomizer at a uniform rate of 0.5 mljminute.

Expressed as the concentrations (ppm. by weight in solution) which yield line intensities equal to three times the standard deviation of the background fluctuations.

The experiments indicate a corresponding improvement in the atomic absorption detection limits for many elements. This improvement is a result of the lower noise level in the pre-mix burner, thereby allowing the application of scale expansion techniques.

A modified form of the pre-mixing modification to the total consumption burner can be seen in FIG. 3, where the numeral 113 again designates an insert rod. However, in the instance of FIG. 3, the rod is constructed of Teflon, which is a tetrafiuoroethylene marketed by E. I. du Pont de Nemours & 00., Wilmington, Delaware, having a high thermal stability andexcellent resistance to chemical attack. In this instance, the insert 113 is equipped with an axial bore as at 114 and inserted therein is a No. 12 stainless steel hypodermic needle tube as at 114a axially aligned with the palladium capillary 17 of the burner 11the capillary projecting about .0O3-.0O5" beyond the brass oxygen jacket providing the port 1'9. At the upper end of the insert 113, a solution-containing chamber 113a is provided by enlarging the axial bore, the axial bore being enlarged at the lower end also-corresponding to the beveled enlargement A of FIG. 1. The chamber 113a-serves as a reservoir for excess test solution which can be communicated to a waste as at 122, the test solution being introduced at X in FIG. 1. Communication is established through an overflow tube as at 122 in FIG. 3. Additionally, the reservoir chamber 113a provides a means for supporting unburned test solution, whereby the tube 114a is maintained cool.

When using metal tubes such as the tube 114a in the pre-mixing chamber, the atomized solution itself pro- 4 vides a major contribution for cooling the burner tip. Experimental work indicates that previous workers in this area failed to make satisfactory burners because they could not solve the cooling problem. With the instant inVenti0n,'n1etal-lined burners are efiiciently cooled by the atomized solution and no heat problem arises during the time the solution is atomized. If the atomization is stopped, the metal liner tends to overheat and failure occurs. This, however, is avoided through the use of 0 the solution-containing chamber 113a.

It will also be appreciated that the tubular casing 10 may be eliminated if the rod 13 is appropriately drilled so as to fit tightly over the housing of thebore 11.

However, this requires careful machine work to make the pre-mixing tube 13 concentric with the atomizer burner 11 so as to eliminate the need for the aligning screws 12.

While in the foregoing specification a detailed description of the invention has been set down for the purpose of explanation thereof, many variations in the details herein given may be made by those skilled in the art without departing from the spirit and scope of the invention.

Iclaim:

1. A total consumption burner for flame emission and absorption spectroscopy, comprising a tubular burner casing having an open top, means operably associated with said burner for providing an oxygen-acetylene mixture at said open top, and means for providing an atomized test solution at said open top, and a tubular element fixed to said casing in coaxial alignment therewith, a uniform diameter axial bore substantially over the length of said element, said element having a bottom surface spaced from said casing open top to define 'a pre-mixing chamber for said mixture and atomized test solution, said chamber having a height of from about 0.2 to about 1.0 millimeter, said element being equipped with a radially-extending port communicating said chamber with the atmosphere, said element also having an unobstructed open top for positioning a flame for spectroscopic analysis.

2. The burner of claim 1 in which the axial bore is enlarged adjacent said bottom surface.

References Cited by the Examiner UNITED STATES PATENTS 1,922,628 8/1933 Morse 158-409 X 1,946,252 2/1934 Wiles.

2,017,951 10/1935 Dasher 158-111 X 2,714,833 8/1955 Gilbert 158-111 X 2,990,749 7/1961 Thiers et al. 88-14 3,002,819 10/1961 Brace et al.

3,074,308 1/1963 .Perron et al. 88-14 3,141,741 7/1964- Hoel et al 158--1l1 X FREDERICK L. MArrEsoN, lk Primary Examiner.

Claims (1)

1. A TOTAL CONSUMPTION BURNER FOR FLAME EMISSION AND ABSORPTION SPECTROSCOPY, COMPRISING A TUBULAR BURNER CASING HAVING AN OPEN TOP, MEANS OPERABLY ASSOCIATED WITH SAID BURNER FOR PROVIDING AN OXYGEN-ACETYLENE MIXTURE AT SAID OPEN TOP, AND MEANS FOR PROVIDING AN ATOMIZED TEST SOLUTION AT SAID OPEN TOP, AND A TUBULAR ELEMENT FIXED TO SAID CASING IN COAXIAL ALIGNMENT THEREWITH, A UNIFORM DIAMETER AXIAL BORE SUBSTANTIALLY OVER THE LENGTH OF SAID ELEMENT, SAID ELEMENT HAVING A BOTTOM SURFACE SPACED FROM SAID CASING OPEN TOP TO DEFINE A PRE-MIXING CHAMBER FOR SAID MIXTURE AND ATOMIZED TEST SOLUTION, SAID CHAMBER HAVING A HEIGHT OF FROM ABOUT 0.2 TO ABOUT 1.0 MILLIMETER, SAID ELEMENT BEING EQUIPPED WITH A RADIALLY-EXTENDING PORT COMMUNICATING SAID CHAM-

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