US3157487A - Method of making a nitrate-phosphate fertilizer - Google Patents

Description

United States Patent Alfred M. Thomson, 265 Buckingham Way, Apt. 402, San Francisco 27, Calif. Continuation of application er. N 35,783, lune 13, 1969. This application Sept. 19, 1962, Ser. No. 224,618 1 Claim. (Cl. 7139) This application is a continuation of an earlier application having the same title and the Ser. No. 35,783, filed on the 13th day of June 1960, now abandoned. It is the aim and object of the present application to present the same disclosure as that of the earlier application but with such changes in the language employed that particular emphasis is placed upon the novelties that I have introduced, thus solving the difiiculties on which previous attempts to build a satisfactory process have so far universally failed. For this reason I will first review briefly such failures and show why they were foredoomed to failure. I will commence with a statement, also made in the previous application, that in so far as chemical reactions are concerned I am introducing nothing new. The novelty resides not in any of such reactions, nor in the combination of same, but rather in the way in which i have altered and deviated former attempts so as to form a process that is economically feasible and fully operative. When past attempts are analyzed it is obvious that the use of the electric arc, of exceptionally high temperatures produced by the combustion of fuel, of heat recuperation to increase the economy of such use of fuel, of shockcooling to preserve nitric oxide, etc, are all very old items in the fixation of nitrogen. Nevertheless, the ultimate results of virtually any combination of such items has always ended in failure so it is not in the combination, per se, but HOW the combination is efiected that becomes the important item.

It is assumed that the reviewer is familiar with the various processes for nitrogen fixation as thus referred to. Were it otherwise no specification could possibly be understood. It would require literally volumes of technical literature to cover the subject and only the briefest abstracts can be given. However, to one familiar with the subject, applicants descriptions will be found both clear and lucid.

The are processes, known as Birkeland-Eyde, Schoenherr, lauling, etc. were technically a perfect success in so far as producing nitric oxide is concerned. For a time they were important, and in conjunction with very cheap water power they produced notable amounts of nitrates. But when the present cheap synthetic ammonia appeared they became obsolete. My use of the arc is thus manifestly distinct and dififerent from all the old techniques in which the arc was the sole source of heat. By deforming said arc into sorn type of a flaming arc the nitric oxide formed was subjected to a type of shock-cooling in merely escaping from said arc into the relatively cool circumambient air current which was an inescapable condition for satisfactory formation of said arc. The salient fault of the process was the extremely small yield of nitric oxide when compared with the current input, the literature indicating an efficiency of only about 3%. The arc was, of course, the sole source of heat.

inasmuch as most of the energy produced today is based on fuel it is obvious that if the rise in temperature can be produced by the direct combustion of fuel such heat input will cost far less than any possible arc-heating technique. This was originally introduced as early as the turn of the century in the so-called explosion technique of the German investigators who exploded coke-oven gas mixed with air in a type of bomb and then released the resultant pressure almost instantaneously, producing a type of limited shock-cooling due to the expansion of the imprisoned gases. While the literature on the subject is extensive it has shared the same fate as the arc processes previously referred to.

More recently this phase of nitrogen fixation was taken up under the auspices of our government by introducing a highly developed form of heat recuperation to diminish the fuel consumption and simultaneously to achieve a form of so-called shock-cooling, the device used in both cases being a pebble bed heat-accumulator, alternately heated and cooled by the reversal of flow of traversing gases. Like all others it failed, though only after the expenditure of much money, through three difficulties. inasmuch as the formation of nitric oxide is endothermic, it is mandatory to heat the gases initially to a temperature well above the mandatory 4200 F., which introduces the first difficulty. It is very dif icult to reach the latter temperature consistently, let alone exceed it. The second is to preserve intact the walls of the heat accumulators that soon become fissured and thus let gases byy-pass the pebble-packed interiors. The third is due to an actual volatility of the refractory used in both Walls and packing. heoretically, there is quite a margin between the temperature of fusion and of volatilization of the refractory selected, and the temperature of operation; but this vanishes in operation in View of the law of partial pressures when the enormous volumes of the traversing gases is taken into consideration. The fact remains that unavoidable spalling or" the pebbles is complicated by the actual deposition of volatilized MgO in the spaces between the pebbles. The over-all result was failure.

My method of overcoming all the difilculties enumerated in the preceding descriptions is as follows: I do indeed use heat recuperation but NOT at the temperatures used by others. I do use shock-cooling but not by passing nitrous gases through a hot pebble bed, conti'ariwise, I commingle the hot gases issuing from the heating stage with cold air in such an amount that the mixed gases drop to the comfortable approximation to 2800 P. which presents none of the aforementioned difficulties when subjected to heat recuperation. In such commingling there is no actual loss of heat but merely a decrease in intensity, or temperature, compensation for such loss in intensity being found in the increase of mass involved. While the approximation, 2800 F., does not render nitric oxide stable it makes further loss sufiiciently slow so that the heat accumulators will speedily produce complete safety.

It will be obvious that in thus solving the difficulties attending heat recuperation at high temperatures 1 have introduced another. it is impossible to re-introduce all of the air required to cool the heat accua ulators into the actual heat cycle of nitrogen fixation. Assuming a top temperature of 4200 F. it will take about 50% by volume of cold air, both reduced to NTP, to produce 2800 F. in the mixture. Now in cooling these accumulators, by reversal of how, this will yield more heated air than can be re-introduced as before mentioned and some use must be found for this heat discard outside of nitrogen fixation. It will also be obvious that the ENTIRE heat value of the fuel consumed will be salvaged in this manner, thus adding immeasurably to the economics of the operation.

I now come to the use I make of arc-heating. It is used, substantially, only to supply the heat increment needed to sustain the 4200" F. temperature during the formation of nitric oxide thus making it unnecessary to temporarily increase combustion heat above that intensity. Such consumption of electrical energy is quite small. Assuming that the gas leaving the arc contains about 2% of nitric oxide this w'll involve only /2 kw. hr. per pound of fixed nitrogen. It will be obvious that with such a low input of electrical energy and the salvage, as highly a in situ.

made from the weak nitric oxide 'by suitable means as a heated air, of substantially ALL'the fuel burned, the cost of nitrogen fixation can be made very low 'mdeed.

So far I have dwelt only on nitrogen fixation and said nothing about phosphate, but to render-the dilute nitric acid transportable or marketable somethting must be done, Itis true that full strength nitric acid can be that is done every day in malring ammonia the intermedi ate between atmospheric nitrogen and nitric acid. But a glance at any price list will also show that relatively weak nitric acid is far cheaper, per pound of actual HNO contained, than the stronger acids. For this reason I have 7 incorporated the decomposition of tri-calcium phosphate by means of nitric acid as a preferred way to use said acid. Itis true, and I am well aware, that there is nothing new in this application so far as the chemical reactions are concerned but as an additive step in a long process claim it is certainly new as such a process as I shall now describe is found nowhere.

It is obvious that the reaction between the dilute nitric acid produced from the air and rock phosphate will yield a mixture of calcium nitrate and either mono-calciurn phosphate, or di-calcium phosphate, or even phosphoric acid. That is entirely under'the control of the operator as it resides in the relative proportions of acid, and phosphate which said operator sees fit to employ. Inasmuch as all three of these phosphoric acid combinations are acceptable to the plant I have usedthe expression plantimmediately below the combustion chamber, are represented in the discharging phase, cold air entering at the bottom and air at approximately 2860 P. leaving at the top. Such a portion as can be used in the combustion chamber is seen going in this direction, the remainder forming the Heat Discard previously referredto. In

' the event that the ratio between hot arc chamber discharge and cold air be as previously mentioned then about two-thirds of the heated air leaving the heat ac cumulators will pass'to the combustion chamber, the remaining one-third forming the discard. A simple calculation will show that the Btu. content of said air will be practically equivalent to that furnished by the'fuel, thus rendering it possible to recoup almost the entire value of the fuel if said air be used in any other industry. Such:

utilization, while obvious, isnot considered a part of this disclosure, though it is of the utmost economic importance.

Attention will now be tocused'upon the cooled gas with its content of nitric oxide which was discharged from the left hand pair of heat accumulators. I have shown this gas as entering a scrubber which may be of any conventional type suitable to the re-circulation of a slurry. The

slurry is composed'of water and finely ground rockphosphate, tri-calcium phosphate, and their decomposition assimilable-phosphorus compounds as ageneric term for approximately 2800 F. by heat recuperation, is'rnixed' with sufficient fuel to raise the temperature to approximately'42fi0 F. after which the products of combustion pass into the arc-chamber represented just above the combustion chamber. Of course, there is an incipient formation of nitric oxide in these gases but unless something is done to prevent the resultant cooling action, due to the endothermic character of said reaction, there will be a notable decrease in the formation of nitric oxide. For this reason I use the arc to the extent necessary'to prevent such a drop in temperature and I have represented the needed energy as Current entering the arc chamber. The overall result is, therefore, that gases with approximately 2% of NO leave the arc'chamber at substantially 4200? F. and enter the shock-cooler, represented at the upper left hand corner. The three devices so far' referred to are merely empty chambers fit for the high temperatures employing and without any packing whatsoever. They are meant for the thorough mixing of the traversing gases that'the inherent reactions may take place,

' and for substantially no other purpose.

In the shock-cooler I have indicated the admixture of an admixture be in the ratio of 1 part of'cold air with 2 parts of hot. gas, by weight, then the resultant mixture instantaneously as possible so the air will enter through a thehot gases from the arc chamber with cold air. If such 7 plurality of small'jets and create violent turbulence within said'chamber. In this manner there will be butslight decomposition of the resident nitric oxide. 7

The next devices indicated, in the line below the combustion chamber, are four heat accumulators. The two immediately below the shock-cooler are represented in the charging phase, thus storing the heat abstracted from'the traversing gas, and the d'raw'ingshows cooled gas is-= suing from both. ,The righthand set of heatlaccumulators,

. mingling in a state of violent turbulence with cold air in. 7 the amount of 50% by weight of the hot gases, thus cans-- products, and, of'course, the calcium nitrate formed.

No mention has been made of the need of oxidation to convert the nitric oxide to nitric acid, but that is the inevitable outcome of the scrubbing' operation in view' of the large excess of free'oxygen still remaining in the gas that has passed through both combustion and arc chamber; In spite of the conversion of a part ofthe entering oxygen into compounds with carbon, hydrogen,

and'nitrogen, there will still be a large excessof uncon-' sumed oxygen. To this is now added the cold air in the shock cooler so it is evident that there will be no lack of oxygen in the gas involved in the scrubbing operation. As a corollary, it will be equally obvious that if no tri calcium phosphate be added then the final product will be some form of dilute nitric acid dependent essentially on the amount of water tolerated in the scrubbing medium. l Inasmuch as all such material is purely conventional there is no need for any fuller explanation. e

As represented in the drawing, however, rock phosphate is in use and the resultant slurry is shown as entering a drier for dehydration in order that it may be put in a marketable condition. It is obvious that any uncombined nitric acid passing to the drier will at the higher temperaa ture and increased time have'ample opportunity to finish.

any reaction uncompleted in the scrubbing operation. A nitrogen-phosphate fertilizer is thus obtained and the ratio between nitrogen and P 9 can obviously'be varied within wide limits by the operator if he so desires, it being only necessary to increaseor decrease the amount of powdered rock phosphate added to the scrubbing medium. 7 7

Having thus fully described my process and called attention to the specific ditferences between my process and the many previous attempts at the direct fixationof ing sufficient fuel therein until .a temperature of approxi-' mately 4200 F. is obtainedymaintainingsaid tempera ture by the use of the electric arc during sustained for mation' of nitric oxide until substantial equilibrium has been obtained; shock-cooling the resultant gases by coming'a substantially instantaneous drop in temperaturejto yapproximately 2800 F., thusobtaining substantial stability ofthe resident nitric oxide and avoiding all ditliculties in subsequent heat recuperation; storing the heat f i still remaining in said gases in heat accumulators; subsef quently transferring said heat to incoming, traversing air which thus becomes heated to approximately 2300" F.; dividing said air, heated by heat recuperation, into two portions representing approximately one-third and twothirds respectively; re-cycling the larger portion to the combustion step previously prescribed and discarding the smaller portion from the nitrogen fixation cycle for use elsewhere, said discard representing substantially the heat equivalent of the fuel consumed in the combustion step; scrubbing the nitric oxide containing gases that were previously cooled by passage through heat accumulators with a slurry consisting of a Water suspension of finely divided tri-calcium phosphate to produce a mixture of calcium nitrate and plant assimilable phosphates; continuously recycling a portion or" said slurry and drying the remainder to form a nitrate-phosphate fertilizer.

References Qited in the file of this patent UNITED STATES PATENTS Pauling Dec. 13, 1904 Pauling Mar. 13, 1906 Saarbach Aug. 27, 1912 Bundick Apr. 19, 1932 Johnson Sept. 6, 1932 Hechenbleikner June 4, 1935 Pike June 30, 1953 Daniels Oct. 27, 1953 FOREIGN PATENTS Great Britain 1907

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