US2212135A - Production of nitric acid - Google Patents

Description

Aug. 20, 1940. N. TlTLEsTAD ET AL PRODUCTION OF NITRIC ACID Filed Jan. 20, 1939 HMH.

Patented Aug. 20, 1940 "Unirse STATES PRODUCTION or Nrrnlc ACID Nicolay Titlestad, White Plains, N. Y., and Arthur C. Bright,Piney River, Va., assignors to Ghemical Construction Corporation, NewYork, N. Y., a corporation of Delaware Application January 20, 1939, serial No. 251,882

3 Claims;

Oxides for the subsequent pressure absorption of the sameto produce nitric acid.

The apparatus involved in a known nitric acid system is comprised essentially and in the order named, of an ammonia burner containing a platvinum `gauze catalyst, a cooler such as a waste heat boiler, a condenser, a compressor, an oxidizer and a pressure absorption tower.

The process of producing nitric acid in such a system comprises the following sequence of steps. Ammonia is oxidized with air on the platinum gauze to produce a hot gas containingnitric oxide and water vapor and this hot gas coming from the ammonia burner is cooled and heat recovered therefrom in the form of steam by passing the hot gas through a waste heat boiler. Thereafter the partially cooled gas is passed through a condenser operated at relatively low temperatures to remove a major part of the water therefrom, whereupon the gases in a separate step are compressed to a high pressure, for eX- ample to several atmospheres, subjected to an oxidation step if necessary, and then absorbed in the tower with a. weak nitric' acid and/or water` underthe pressure produced by the compression step.

In plants employing the above process the gas is ordinarily compressed by a centrifugal or reciprocal type compressor. Centrifugal compressors have been used in large capacity plants, but they are not economical in plants of low capacity, i. e., those having a small gas volume due to `their high initial cost. Reciprocal type compressors have been suggested as a substitute in smaller plants, but the problem of lubricating the pistons of such compressors is still a serious one. One of the chief difculties in the lubrication of this type of compressor is the destruction of the lubricant due to its carbonization by the nitric acid formed when compressing the moist nitrogen oxides.

-trated diagrammatically an apparatus designed for the carrying out of our invention and in which Fig. 1 is a representation of a nitric acid system showing one type of hydraulic compressor and Fig. 2 is a modied form of hydraulic compressor. I It is to be understood that all the parts of such a nitric acid system are not illustrated in the drawing but only those necessary to point out the invention. f

Referring to Fig. 1 there is diagrammatically E10 showntherein an ammonia burner containing a suitablecatalyst such as platinum gauze together with a waste heat boiler, an hydraulic compressor denoted generally at I, an oxidizer and a high pressure absorption4 tower. V'Ihe hydraulic com- "T5,

pressor I consists of an aspirator head 3 of standard construction, a vertical feed pipe It for carry- `ing Ycompressing liquid thereto, a water cooling jacket 5 on pipe Q, and a centrifugal pump 6 connected at its discharge sideV with pipe li. A pipe 'l is shown connected to the discharge side of the aspirator head 3 and with a gas and liquid separation tank 8 of a construction suitable for the disengagement of the compressed gases from the compressing liquid. Pipes 9 and'2`5 l0 are shown as connected to the tank il and to the oxidizer and absorption tower respectively for Athe passage of disengaged and compressed gas on the one hand and a portion of the liquid from tank 8 on the other hand. Pipe I i is provided for the return by means of centrifugal pump 6 of liquid from the tank 8 to the compressing cycle. A means is provided for the introduction of water into the ksystem for use as initial compressing liquid; such a means may be that as indicated on line |.l between the pump 6 and the separation tank 8.

Assuming that ammonia has been oxidized with the reaction proportion of air in the ammonia burner to give a hot gas containing nitrogen oxide and water vapor and that the hot gas has been partially cooled in the waste heat boiler, the operation of the hydraulic compressor to remove water from and to compress the gases in accordance with my inventionis as follows: 45

The hot gas from the waste heat boiler is passed through pipe 2 and enters the aspirator head 3 at an elevated temperature and preferably above the dew point of the gas. In the aspirator' head the hot gas will encounter a stream of cool weak nitric acid supplied by pum-p 6 through pipe 4, the acid moving at a velocity head suflicient for the aspiration and compression of the gas. The centrifugal pump will be operated at a pressure volume of weak acid sufficient 55 to create the necessary velocity head, and the rapidly moving stream of weak nitric acid in the aspirator head will be cooled and mixed therewith, the mixture of gas and acid moving down through pipe 'l into separation tank 8 where the compressed gas will be disengaged from the compressing acid and the condensed water. 'Ihe separated compressed gas will then be passed through pipe 9 to the oxidizer and eventually to the absorption tower while some of the weak acid from the separation tank will be passed to the absorption tower for the absorption therein of the compressed and oxidized nitric oxide under the high pressure resulting from the compression of the gas to produce nitric acid. The oxidizer and absorption tower may be operated in accordance with known practice.

In Fig. 2 we have shown a modiiied design of hydraulic compressor for use in the above described nitric acid systems and in which the 2 from the waste heat boiler will be cooled by a Water jacket i3 and Water condensed therefrom before they enter the aspirator head. A chamber is shown at i4 and a pipe at i5 for the collection and removal of condensed water to an absorption tower. In this modification the gas and liquid separation tank I6 is not provided with a pipe for removal of liquid therefrom to an absorption tower since we contemplate the removal of sufcient water from the gas by cooler I3.

The design of the gas and liquid separation tank is such as to allow of disengagement of the compressed ygas from the acid and it conceivably may take the form of a flash separator or of a single chamber in which may take place the disengagement of the gas from the compressing acid and absorption of the separated gas to produce nitric acid.

From the foregoing it will be seen that a speciiic embodiment of the invention has been described which accomplishes all the objects thereof. This embodiment has been described as operating-on oxides of nitrogen from the catalytic oxidation of ammonia, since this is a representative gas source. It should be understood, however, that the invention is equally well adapted to the compression and subsequent oxidation and absorption of oxides of nitrogen from other sources, such as from the denitration of spent nitrating acid, from the arc process, or in general from any source in which oxides of nitrogen are produced in commercially useful quantities.

It should also be understood that the invention in its broader aspects is not restricted to the specific details which have been described and shown, b-ut that it is limited only by the scope of the following claims.

What we claim is:

1. An apparatus for the production of nitric acid comprising in combination an ammonia burner, a gas cooler, an hydraulic compressor directly connected with the gas outlet of the 'gas cooler, the hydraulic compressor comprising a centrifugal pump, anaspirator head, a vertical conduit connecting the pump with the aspirator head, means for cooling the aqueous compressing liquid, an oxidizer, and a pressure absorption tower.

2. A process of producing nitric acid which comprises condensing water from and compressing a relatively cool gas containing lower oxides of nitrogen in a single operation by hydraulically compressing it with a cool aqueous liquid moving under pressure, disengaging the compressed gas from the compressing liquid, oxidizing lower oxides of nitrogen in the gas to nitrogen peroxide, and absorbing the nitrogen peroxide in an aqueous absorbing medium under pressure to form nitric acid.

3. A process of producing nitric acid which comprises oxidizing ammonia to form a hot gas containing lower oxides of nitrogen and water Vapor, partially cooling saidgas, condensing water from and compressing said partially cooled gas in a single operation by hydraulically compressing. it with a cool aqueousv liquid moving under pressure, disengaging the compressed gas from the compressing liquid,` oxidizing nitric oxide in the compressed gas to nitrogen peroxide, and absorbing the nitrogen peroxide in the gas under high pressure to form nitric acid.

NICOLAY TITLESTAD. ARTHUR) C. BRIGHT.

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