US2276690A - Process of producing a purified protective atmosphere - Google Patents

Description

March 17,- 1942. J. H. GERMANY 2,276,690

PROCESS OF PRODUCING A PURIFIED PROTECTIVE ATMOSPHERE Filed Oct. 20, 1939 n a 5* g h ta .9 3 s Y E l2] /6 /6 (0070052700 Uri/f g s /0 *l E *0 Q 5 k k Q: /5-- 61: Q b Q: Q Q U Q Q 3 m g Q E 8 s "a Q Q m m 9 5 a g, A/ifrogen or K5 N/frogen 5 Hydrogen Gas WITNESSES: INVENTOR hibitive.

' producing th protective atmosphere.

ural gas is preferred because it is comparatively Patented Mar. 17, 1942 TES ATENT FFHCE PROCESS OF PRODUCING A PURIFIED PROTECTIVE ATMOSPHERE Pennsylvania Application October 26, 1939, Serial No. 300,379

2 Claims.

This invention relates to a process of pro- 'ducing a purified protective atmosphere of hydrocarbon gas.

Protective gases are widely used in the heat treatment of steels. In the bright annealing of stainless steel and the heat treatment of silicon steel and high carbon alloy steel, it is desired to have a very pure protective atmosphere to prevent contamination of the surfaces of the steel or a change in the alloy composition of the steel itself.

Pure nitrogen, free from all traces of oxygen, or a pure nitrogen-hydrogen mixture free from oxygen, are known to be suitable for use in the heat treatment of the steels referred to hereinbefore. It has been found to be quite difficult to produce such gases free from oxygen or where such gases have been produced that the cost of producing them renders them commercially pro- Heretoiore nitrogen gas has been produced from natural gas by adjusting the gas and air ratio to produce nitrogen with a small amount of carbon monoxide and hydrogen while avoiding complete combustion which, with normal variation in the apparatus employed, would causefree oxygen to be brought over with the processed gas. Such processed gas is unsatisfactory unless the impurities are completely removed therefrom, the removal of the impurties being quite diflicult.

An object of this invention is to provide a process of producing a protective atmosphere free from impurities from hydrocarbon gas, the protective atmosphere being suitable for the bright heat treatment of stainless steel, silicon steel and high carbon alloy steel.

A more specific object of this invention is to rovide a process of producing a protective atmosphere from hydrocarbon gas, such as natural or manufactured gas, by efiecting a complete combustion of the gas with air, combining the free oxygen of the combustion products with hydrogen and removing the impurities of the combustion products to give the purified protective atmosphere.

Other objects of this invention will become apparent from the following description when taken in conjunction with the accompanying drawing, the single figure of which is a diagrammatic sketch of apparatus employed in practicing the process of this invention.

2 In practicing this invention, a hydrocarbon gas, such as city or natural gas, is employed in The natinexpensive as compared to other hydrocarbon gases and is available in most industrial centers of the country.

Referring to the drawing, the hydrocarbon gas is delivered to a pump [0 from any suitable source of supply (not shown) and is mixed in the pump with air in a predetermined amount. The air is admitted to the pump in and mixed with the hydrocarbon gas therein in an amount slightly in excess of the amount necessary for obtaining a complete combustion of the hydrocarbon gas, as will be explained more fully hereinafter.

When the air and gas are mixed as desired, the mixture is delivered from the pump In to any suitable combustion unit l2, where it is burned to eifect a complete combustion of the mixture. In burning the mixture in the combustion unit, it is normally so completely converted that the end product is produced containing only carbon dioxide, water vapor and free oxygen, as impurities. In practicing this process, the presence of only these three impurities is assured by employing the excess of air in the mixture, thereby obtaining complete combustion and preventing the formation of carbon monoxide.

In order to efliciently remove the impurities from the end product, it has been found desirable to bleed pure hydrogen or anhydrous ammonia directly into the combustion unit from any suitable source of supply, such as represented at M. Where ammonia is employed, it is completely dissociated into its nitrogen and hydrogen components in the heated combustion unit.

It is preferred that the ammonia be admitted to the combustion unit near the end thereof from which th combustion products are withdrawn, it being found that the dissociation of the ammonia is more readily effected due to the high heat at this portion of the combustion unit. As the ammonia is dissociated, producing the nitrogen and hydrogen components thereof, the hydrogen of the dissociated ammonia so combines with the free oxygen present as an impurity in the combustion products to form water vapor, that as the combustion products leave the combustion unit I2, they comprise th end products and only carbon dioxide and water vapor as impurities. Where pure hydrogen is employed in place of the anhydrous ammonia, the combining of the hydrogen with the free oxygen is eflicient- 1y efiected in the heated combustion unit.

In order that th combustion products can be efliciently treated to remove the impurities therefrom, the gases are passed immediately from the combustion unit I 2 to any suitable condenser unit i 5, where the water vapor of combustion is condensed to a dew point corresponding to room temperature conditions. With the water vapor at this dew point, it is found that the carbon dioxide and water vapor can be more efficiently removed from the end product of the combustion.

In order to remove the carbon dioxide from the combustion products, they are passed directly from the condenser unit 15 to any suitable carbon dioxide removal system, as indicated at M, where the last traces of carbon dioxide are efficiently removed from the gases. Any of the commercially known carbon dioxide absorbing materials can be employed in the system l6 for removing this impurity.

In order to remove the water vapor from the combustion products, the gases which have been freed of free oxygen and carbon dioxide are delivered directly to a suitable drier l8 where the last traces of the water vapor which has a dew point corresponding to room temperature conditions, are removed from the end product. In practice, it is found that activated alumina, silica gel and Kieselguhr are suitable for use in the drier for removing the water vapor from the end product. Thus, as the end product leaves the drier chamber i8, only the purified protective atmosphere consisting of nitrogen or nitrogen and hydrogen remains.

In introducing the ammonia into the combustion unit IE to convert the free oxygen to water vapor, it is generally desired to supply only enough ammonia to the combustion unit to form sufiicient hydrogen for combining with all of the free oxygen present in the combustion products to form the water vapor. B controlling and so limiting the amount of ammonia supplied to the combustion unit in this manner, it is possible to produce a protective atmosphere of pure nitrogen. However, where the presence of hydrogen is not undesirable, an excess of ammonia can be introduced into the combustion unit, any excess hydrogen of the dissociated ammonia being carried through the systems described and delivered from the drier to give a protective atmosphere composed of nitrogen with small amounts of hydrogen. As explained hereinbefore, pure hydrogen can be employed interchangeably in place of the anhydrous ammonia.

By practicing the process of this invention, an extremely pure protective atmosphere is pro= duced utilizing a minimum amount of equipment, it being quite evident that by reason of the excess of air employed in effecting the combustion only those impurities which can readily be removed from the combustion products are produced. By introducing the hydrogen component selected from the group consisting of pure hydrogen and anhydrous ammonia directly into the combustion unit, the apparatus is greatly simplified, thereby eliminating any necessity for additional apparatus or causing the dissociation of the ammonia or for additionally heating the combustion productions to cause the desired combining of the introduced hydrogen with the free oxygen to form the water vapor. The protective atmosphere produced in accordance with the process of this invention is comparatively inexpensive as compared to the cost of the protective atmospheres produced by known processes.

Although this invention has been described with reference to a particular process, it is, of course, understood that certain changes may be made therein, and this invention, therefore, should not be restricted except in accordance with the description hereof and the appended claims.

I claim as my invention:

l. The process of producing a purified protective atmosphere from hydrocarbon gases comprising the steps of, mixing the hydrocarbon gas with a predetermined amount of air, introducing the mixture into a combustion unit where it is completely combusted to form the end product containing only carbon dioxide, water vapor and. oxygen as impurities, introducing a hydrogen component selected from the group consisting of pure hydrogen and anhydrous ammonia directly into the combustion chamber at a point within the chamber remote from the introduced uncombusted mixture of hydrocarbon gas and air where the hydrogen of the introduced hydrogen component combines with all of the free oxygen to form water vapor, cooling the end products to condense the Water vapor to a dew point corresponding to room temperature conditions, passing the end products containing the carbon dioxide and water vapor through a carbon dioxide removal system to remove the carbon dioxide, and drying the water Vapor having a dew point corresponding to room temperature conditions from the gas to give a purifiedprotective atmosphere.

2. The process of producing a purified protective atmosphere from hydrocarbon gases comprising the steps of, mixing the hydrocarbon gas with a predetermined amount of air, introducin the mixture into a combustion unit where it is completely combusted to form the end product containing only carbon dioxide, water vapor and oxygen as impurities, the air in the mixture which is combusted being slightly in excess of the amount necessary for obtaining the complete combustion, introducing anhydrous ammonia directly into the combustion chamber at a point within the chamber remote from the introduced uncombusted mixture of hydrocarbon gas and air where it is dissociated into its nitrogen and hydrogen components, the hydrogen of the dissociated ammonia combining with all of the free oxygen to form water vapor, cooling the end products to condense the water vapor to a dew point corresponding to room temperature conditions, passing the end products containing the carbon dioxide and water vapor through a carbon dioxide removal system to remove the carbon dioxide, and drying the water vapor having a dew point corresponding to room temperature conditions from the gas to give a purified Drotective atmosphere.

JAMES H. GERMANY.

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