US2013809A - Production of nitrogen - Google Patents

Description

INVENTOR. Ehuwj n E m. W m w W 5 3 4 T K /O w m w W v A l M .njfzoz vw I C C 2 ,M K A f N. JH@ lim. o ,//IHIIIIHI M -9%- i 9 y .AuJPDO Qu@ omxOO I m `H Ilv Sept. 10, 1935.

Eril: Hall 55h Patented Sept. 10, 1935 UNITED STATES lA'rEN-r trice PRODUCTION F NITROGEN" Application October 14, 1932, Serial Nov.637,8144

In Great-Britain October 20, v.1931

3 Claims.

drogen. It is known that ammonia will decompose atan elevated temperature in the presence of a catalyst to yield a mixture of nitrogen and hydrogen and it has been proposed to prepare a gas containing nitrogen for use in metallurgical operations by burning this nitrogen-hydrogen mixture with air and subsequently separating the Water formed from the residual nitrogen.

We have now found that a particularly suitable method for carrying out such a process 5 consists in arranging for the heat generated in the combustion step to be returned to the cracking step, thus dispensing with the need of auxiliary heating.

The invention consists accordingly in the partial or complete decomposition of ammonia into its elements and the combustion with air of the completely or partially decomposed gas, the two reactions being performed in heat exchange with each other. 'Ihe amount of air supplied for combustion may be varied according as the final gas is to consist substantially of nitrogen or is to contain small amounts of hydrogen.

A suitable apparatus for carrying out the invention consists in a cylindrical combustion chamber in one end of which is situated a coiled iron tube which acts as a decomposing or cracking chamber. Instead of an iron coil, a chamber filled with an ammonia decomposing catalyst may be used, such chamber being arranged in thermal contact with the products of combustion in the combustion space. Thus the catalyst chamber may be an annular space surrounding the combustion chamber. A supply of ammonia gas is admitted to the coil or catalyst space from a cylinder of anhydrous ammonia or other convenient source, and in starting up the apparatus heat is supplied by burning in the combustion chamber a coal gas or hydrogen flame, o-r a flame of ammonia burning in oxygen may be employed. An electric heater may also be employed if desired in starting up. When the coiled iron tube or catalyst space has been raised to a suiciently high temperature, decomposition of the ammonia commences and the partially cracked gas is then admitted into the combustion chamber, together with the necessary amount of air. It is necessary that approximately per cent of the ammonia should be cracked in order that combustion may occur and providing this limit has been attained in the initial start-up the heat developed (Cl. ,Z3-277) by combustion-of the hydrogen is suflicient to maintain reaction between ammonia and the. air and 4there isanet balance of heat which istransmittedV to the. cracking chamber, that is the coiled iron tube or catalyst space. perature will ultimately be set upand depending on the particular form of apparatus and the eiciency of the thermal` insulation present,.,the degree of cracking will vary. The final products, however, are independent of the degree of crack- 10 ing and are treated for the removal of water and the production of a substantially pure nitrogen gas in any suitable manner. When equilibrium has been attained it is necessary to adjust the air supply in order that no ammonia 15 appears in the products of combustion. Excess of air should be avoided as it leads to the presence of free oxygen in the final gas, and the air supply to the combustion chamber is suitably controlled by making test analyses from time to time of the issuing gases.

In addition to the production of pure nitrogen, the apparatus described is particularly suitable for the economical production of gases containing up to about 10 per cent. hydrogen, the re- 25 mainder being substantially pure nitrogen. The economic production of such a gas is important for purposes such as bright annealing of metals, particularly non-ferrous metals. In certain circumstances the presence of even small amounts of oxygen in annealing furnace atmospheres is highly undesirable but by the production of a gas containing hydrogen as described above, no free oxygen is possible in the products of combustion delivered from the apparatus. In order to produce hydrogen-nitrogen mixtures it is only necessary to vary the proportion of air which is introduced into the combustion space of the apparatus, the ratio of air to ammonia being reduced according to the percentage of hydrogen which is required in the final gas mixture.

An apparatus answering to the above description is illustrated in the accompanying drawing, which is a sectional elevation. In this drawing, the combustion chamber consists of two cylinders I and 2, xed end to end by bolted flanges 3 and 4. The top cover 5 of the chamber is bolted to flanges on the cylinder I and has a central outlet 6 for the combustion products, which are led away by a branch pipe 1. Ammonia is introduced by pipe 8, which passes through the cover 5 and is then developed into a coil 9 terminating in an outlet pipe ID which passes through the cover 5 and is connected to an external pipe Il which leads the cracked gas to the lower end of tbe An equilibrium tem- 5 combustion chamber and terminates in the bottom cover I2. The cover I2 is provided with air ports I3 and a rotary perforated plate I4 which controls the air supply. The cylinder 2 is lined internally with refractory material I5 to protect the walls from the initially very hot gases, and the lining is bevelled as shown so as to allow of the entrance of air through the ports I3. The gases pass upwardly into the space enclosed by the coil 9, which is closed at the top by a plate I6, and owing to the tapered form of the coil fractions of the gas are successively by-passed through the coil towards the walls of the cylinder, thus ensuring as far as possible that each turn of the coil is swept by the gases. For this purpose the external diameter of the turn of the coil first encountered by the combustion gases approximates to that of the internal diameter of the cylinder I, as shown in the drawing.

I claim:-

1. An apparatus for the decomposition of ammonia into its elements and -for the combustion with air of the resulting gases, comprising a cylindrical combustion chamber, a coiled iron tube located in one end thereof and adapted to be swept externally by the combustion products, means for admitting ammonia to said coil and for withdrawing the decomposition products therefrom, means for passing the said decomposition products to the other end of the combustion chamber, and means for admitting air into said combustion chamber in amounts controllable with respect to the rate of ow of said gases.

2. An apparatus as set forth in claim 1, in which the coil is co-axial with the combustion chamber and the turn of the coil rst encountered by the combustion products is in contact with the wall of the combustion chamber, while the succeeding turns of the coil are spaced progressively further apart from said wall.

3. An apparatus for the decomposition of ammonia into its elements and further combustion with air of the resulting gases, comprising two separably connected cylinders placed end to end, the first of said cylinders containing a coiled cracking tube adapted to be traversed internally by the ammonia to be decomposed and to be swept externally by the gaseous products resulting from the combustion of the decomposed gas, o

the first cylinder, and means for withdrawing the combustion products vfrom the remote end of the iirst cylinder.

ERIC HALL SALISBURY.

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