High-Temperature Gas Burners For Microcombustion Methods of Ultimate Analysis VETO A. ALUISE Hercules Experiment Station, Hercules Powder Company, Wilmington 99, Del. Coil and ring gas burners are described which fulfill the requirements of the thermal decomposition method for the direct determination of oxygen in organic compounds. The coil burner is designed for pyrolyzing the sample at 900" to 1000" C.; however, it is capable of producing a temperature of 1300" to 1350"C. inside the reaction tube. The ring burner is designed to provide a temperature of 1100"C. near
the end of the furnace used for conversion of the pyrolj-sis products to carbon monoxide. These gas burners have also been found useful in other microcombustion methods of ultimate analysis. The burners, which utilize a mixture of propane gas and air, are inexpensive, heat and cool the reaction tube rapidly, and provide a uniform distribution of heat around the tube.
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PIT T H E thermal decomposition method for the direct detertemperature to ensure complete removal of all oxygen from the mination of oxygen in organic compounds, first proposed by pyrolysis products. Because of the thick wall insulation necessary Schutze ( 2 ) )the substance is pyrolyzed in a clear quartz tube in a in a high-temperature electric furnace, a zone of lower temperastream of pure nitrogen a t a temperature of 900" to 1000" C. ture always exists in the reaction tube in this insulated area. I n a recent investigation of this method (1) a Fisher high-temThis low-temperature zone introduces the problem of the conperature burner was used to provide this temperature. In order densation of oxygen-containing pyrolysis products, which are to maintain this temperature uniformly around the tube the difficult to remove and necessitate special provision for lateral flame was confined by mounting a U-shaped Xichrome wire movement of the furnace ( I ) . gauze hood over the top of the burner, in the manner described This objectionable feature a a s overcome b j installing a ring by Schutze and Unterzaucher ( 2 , 3). Holvever, even with a burner adjacent to the wall of the furnace, as shoivn in Figure 1. hood over the burner, a considerable amount of heat was wasted I n making this burner, holes, 0.05 to 0.06 inch in diameter and 0 25 inch apart, are drilled in a straight line through one wall of and the temperature of the heated portion of the reaction tube a suitable length of seamless nickel tubing 0.25 mch in diameter. was not uniform. The drilled section is then bent into a ring so that the holes !i the I n the course of an investigation for a more efficient device for ring are directed away from the center of an angle of 45 , in pyrolyzing the substance, electric combustion furnaces were order to direct the flame of the burner toward the interior of the furnace. considered. Electric furnaces wound with base metal resistance To provide maximum conductance of heat and a t the same wire ordinarily do not have a long life when operated continuously time to protect the reaction tube, a sheet of platinum rolled into at 900" to 1000" C., and furnaces vound with noble metal resistcylindrical shape, about 1.5 inches long. is slid over the reaction ance wire are expensive,, especially as the type needed for tube to a point where it projects about 0.5 inch from the furnace microcombustion methods is not available as a stock item. In view of these FURNACE SHELL factors, attention was directed to more efficient gas burners. After the difficulties of preliminary models had been overcome, two satisfactory high-temperature gas burners were designed by the author and made i n t h i s l a b o r a t o r y : coil a n d ring burners. Each has a specific use. The burners uttlize a mixture of propane gas and air, are inexpensive, heat and cool APART AROUND the reaction tube rapidly, and can be made in various lengths and coil diamL I N E A S SHOKN eters. .Ilthough originally designed for use in the thermal decomposition method for the direct determination of oxygen in organic compounds ( I ) , these burners have been found very useful in other microcombustion methods of FULL SCALE ultimate analysis, such as t,he determinat'ion of carbon and hydrogen and Dumas nitrogen. R I S G BURNER
In the direct determination of oxygen by the thermal decomposition method it is necessary to have a sufEciently high
FRONT VIEW
Figure 1.
END VIEW OF BURNER
SECTIONAL VIEW OF BURNER THROUGH AA
Sectional View of Furnace with Ring Burner in Position
746
J U N E 1949
147 inserted into a hole drilled in the bottom of the vertical arm of the T-shaped brass base, and also brazed. Iron pipe or any other metal tubing may be used instead of nickel tubing for the gas feed. The drilled T-shaped brass base supplies gas-air mixture to both ends of the coil, thereby providing a uniform flame. One method of mounting-this burner to dlaw for close adjustment around the reaction tube is shown in Figure 3. I n order to obtain maximum &rienrv ~~~~.~ .... with thir "___" burner, the ends of the coil are closed by two silica (Vitreosil) disks, having dimensions shown in Fieure 4. A roll of Nichrome wire gauze, approximately 0.625 inch in diameter, is inserted in the coil, through the holes in the silica disks, and the ends of the SRUZP n- -. -7 ~ flared to hold it in Place. A lamer roll of zauze is placed around the outside of the coir and the e&es are bent down over the silica disks (Figure 4). In addition mmve to holdine the silica disks in d a c e . bot,h rolls of .~ o__._ aid in cozfiniue the heat to ihat bection-of-the ~ P R , C tion tube covered by the burner. Operation of the burner is simple. After t,he gas is turned on by means of a needle-type valve and lighting, the air is turned on until a nonluminous flame is praduced. The intensity of the flame can he varied as in any burner by regulating the gas and air supply. At the completion of the combustion the gas is shut off and the air flow is increased to cool the reaction tube rapidly. In this way the waiting period before the introduction of the next sample is greatly reduced.
;o ORlLL 1'' APART
OF COIL
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BRAZE,
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wall. Tests showed that prior to the installation of this burner, the temperature in the reaction tube at a point 0.5 inch inside the furnace (Figure 1) was only 650" to 700" C.; after installation of the burner the temperature wil&sraised to 1100" C.
In laboratory tests the coil burner produced a maximum temperature of 1300" to 1350" C., as measured inside the reaction tube, using a mixture of propane gas and air. These burners have been in daily use a t 900" to 1000" C. for one year and are still in excellent condition. No tests were made in this laboratory to determine the maximum number of spirals that could be effectively incorporated into a coil burner of this type.
COIL BURNER
LITERATURE CITE1
The essential features of construction of the multiplecoil burner are shown in Figure 2.
(1) Aluise. V. A., Hall, R. T..Staats, F. C., and Beeker, W. W., ANAL.Cnmx., 19,347-51 (1947). ( 2 ) Sohutue, M., Z. anal. Chem., 118,241-5(1939) (3) Unterzauoher. J.. Ber.. 73B,391-404(1940).
END V I E W OF BURNER LII.yI
I
UDINAL VIEW
OF BURNER
Figure 2.
High-Temperature Coil Gas Burner
I n making this burner, holes. 0.05 to 0.06 inch in diameter and approximately 0.25 inch apart, are drilled in 8. straight line through one wall of a suitable length of seamless nickel tubing 0.25-inch in diameter. (Gases other than urouane will require
RECEIVED October 2, 1948.
,SILICA I
ENO Rnrc
NICHROML Gn
L SECTIONAL VIEW THROUGH HH
LONG ITU0 INA
sure 4.
H i g h - l e m p e r a t u r e Coil t i a s burner Shown in Assembly
