AU654632B1 - Reactor for the production of ammonium nitrate solution - Google Patents

Description

654632 1

AUSTRALIA

PATENTS ACT 1990 COMPLETE SPECIFICATION FOR A STANDARD PATENT

ORIGINAL

o Name of Applicant: Actual Inventor: Address for Service: UHDE GmbH Robert NEBEL SHELSTON WATERS 55 Clarence Street SYDNEY NSW 2000 "REACTOR FOR THE PRODUCTION OF AMMONIUM NIT .rE SOLUTION" Invention Title: The following statement is a full description of this invention, including the best method of performing it known to us:- -2 "Reactor for the-production of aminonium nitrate solution" The invention relates to a reactor for the production of ammonium nitrate solution by neutralization of aqueous nitric acid with the aid of pure ammonia or a gas containing ammonia.

Ammonia reacts rapidly and completely with nitric acid in aqueous solutions to form ammuonium nitrate:

NH

3 HN0 3

=NH

4

NO

3 reaction. heat A small amount of sulphuric acid serving as a stabilizer of the final product during solidification (improvement of the storage 10 life) can be co-neutralized.

The acid is neutralized with the aid of ammonia in an exothermic reaction, either under vacuum or at pressures up to 10 bar abs., in natural circulation or forced circulation reaction loops and in one or two steps at acidic or alkaline conditions. For all neutralization processes it is necessary to recycle ammonium nitrate solution that has already formed (recycle ratio 5-40 tonnes of solution per tonne of production) and serves as buffer for the reaction heat. The recycle ratio depends on the maximum allowable reaction temperature (ranging from 140 to 185 0

C).

The differences between the various processes are mainly related to the method of recovery and utilization of the reaction heat, for example in the cases listed below: fresh steam generation (4-8 bar abs.) final concentration of the melt (96-98 w/w) in an evaporator with the aid of the solution from the reactor process steam generation (2-5 bar abs.) for intermediate or final concentration of the solution (93-96 w/w) total or partial flashing of the solution after reaction (93-96 wiw).

Said heat recovery methods are also combined.

3 A typical process, combining fresh steam generation, flashing of the produced solution as well as concentration with the aid of process vapour is described in the German patent application DE-A-33 47 404.

The known process operates as follows: The feedstock, i.e. gaseous ammonia and aqueous nitric acid containing 56 up to more than 60% w/w HNO 3 are preheated by means of process vapours before being fed to the reactor where the reaction takes place at a pressure of approx. 3.5 bar in an ammonium nitrate solution that has already formed. The reaction heat liberated in this process causes the solution to boil and the resulting vapour bubbles cause the solution to be conveyed through the reactor, the vertical steam boiler and the process steam separator, from which the solution produced is extracted and 15 returned to the reactor. Part of the reaction heat is utilized in the steam boiler for generating fresh steam (about 6 bar abs.), the remaining reaction heat is then available for preconcentration of the ammonium nitrate solution. The 3.5-bar process vapours are used for further concentration of the ammonium nitrate solution.

The generation of pure steam is controlled so as to ensure that a sufficient quantity of process vapours is available for final concentration to, for example, 95 w/w.

The aim of the invention is to improve the reactions with a view to minimizing the nitrogen losses.

4 According to a first aspect, the present invention consists in a reactor when used for the production of ammonium nitrate solution by neutralization of aqueous nitric acid with the aid of an ammonia containing gas, said reactor comprising in sequence: a bottom cone for receiving recycled ammonium nitrate solution, said cone having injection nozzles arranged about the perimeter of the cone for introducing aqueous nitric acid for admixture with the recycled ammonium nitrate solution; a premixing zone located adjacent said bottom .cone and adapted to receive the admixture and initially mix the recycled ammonium nitrate solution and aqueous nitric acid; a final mixing zone located adjacent said premixing zone and adapted to receive and homogeneously mix the premixed recycled ammonium nitrate solution and aqueous nitric acid; a downstream tubed chamber located adjacent the final mixing zone, said chamber containing a bundle of perforated tubes for introducing the ammonia containing gas for admixture with the mixed recycle ammonium nitrate solution and aqueous nitric acid in a gas-to-liquids admixing zone; and a reaction chamber located adjacent the downstream tubed chamber for reaction in a reaction zone i of the mixed recycle ammonium nitrate solution and 4a aqueous nitric acid with the ammonia containing gas to produce an ammonium nitrate silution.

Preferably the reactor is a vertical reactor with circular cross-sections comprising a bottom conical section, a cylindrical main section and a top conical section.

The bottom cone of the reactor serves as an intake chamber for recycled ammonium nitrate solution and is provided with injection nozzles on its S 10 perimeter. Preferably the injection nozzles are located equidistantly about the perimeter. The injection nozzles are provided for admixing aqueous nitric acid to the recycled ammonium nitrate solution in order to o •prepare an initial liquid mixture.

The reactor internals are arranged in a manner such that the initial liquid mixture passes (typically in an upward direction) through a mixing zone (PML), a final mixing zone, a gas-to-liquids admixing zone and a reaction zone (RL) Typically the premixing zone is enclosed by the walls of the upper part of the bottom cone and cylindrical walls of a first mixing chamber, the final mixing zone is enclosed by the cylindrical walls of a downstream mixing chamber, the gas-to-liquids admixing zone is located on the tube side of the downstream tubed chamber, and the reaction zone (RL) is enclosed by the cylindrical wall of a reaction chamber and an upper conical reaction chamber.

4b Preferably the bundle of perforated tubes (typically vertically oriented) admit the ammonia containing gas to the shell-side cavity of the tubed chamber at a pressure sufficient to permit the gas that enters through the perforated walls and the gas entrained in the mixed liquid to flow through the gas-to-liquids admixing zone.

Preferably mixing elements are provided in the final mixing zone. Preferably the mixing elements are 10 provided in the downstream mixing chamber and the mixing elements act on the entire cross-sectional area of the downstream mixing chamber. 9 O 5 Another embodiment of the invention provides for a reactor according to one of the preceding embodiments, in which mixing elements are arranged on the outlet side of the reaction zone.

This shortens the residence time of the reactants in the reaction zone without affecting the conversion rate of the reaction, thus ensuring a product partially free of non-reacted ingredients.

A further embodiment of the invention provides for a reactor according to one of the preceding embodiments characterized in that the perforated tubes are fixed .n flanged-type tubesheets.

This facilitates the inspection and maintenance of the perforated tube walls.

An embodiment of the invention consists of a reactor according to one of the preceding embodiments characterized in that the nozzles for injecting the aqueous nitric acid are provided with integrated 15 acid-proof nozzle heads shielded with sleeves of corrosionresistant metal.

A further embodiment of the invention, which comprises a reactor according to one of the preceding embodiments, incorporates acidproof nozzle heads which are screwed into the shielding sleeves of 20 corrosion-resistant material and which can thus be easily unscrewed, and hence said heads can be easily replaced in case of wear and tear.

Another embodiment of the invention provides for a reactor according to one of the preceding embodiments characterized in that the injection nozzles are directed upwards at an angle of 0° to 100, the angle being measured within a radial plane through the vessel centre axis and measured against the plane perpendicular to the vessel centre axis, and/or eccentrically at an angle of 0° to 300 from the vertical centre axis of the cross-sectional area of said bottom cone, the angle of excentricity being measured in a horizontal plane.

-6 Due to this arrangement, the injection nozzles induce a vortextype circumferential flow in the premixing zone which flattens the local concentration profile. Thus, the length of the premixing zone (Pl4L) can be kept below 2xD, D representing the inside diameter of the first mixing chamber. A short premixing zone length significantly reduces cost of manufacture significantly because the reactor vessel is made of high-alloy corrosionresistant stainless steel, which is considerably more expensive than ordinary stainless steel grades.

A further embodiment of the invention provides for a reactor according to one of the preceding embodiments, said reactor being characterized in that the reactor vessel sections are cif the flanged type to be stacked, thus ensuring ease of assembly and maintenance.

S 15 An embodiment of the invention comprising a reactor according to one of the preceding embodiments is characterized in that each tube of the tube bundle in the tubed chamber is provided with penetration holes arranged in a spiral manner on the perimeter and is intended for admitting ammonia-bearing gas to the mixed liquid treated in the gas-to-liquids admixing zone.

Provijsion is made for flash evaporation taking place between the neutralization and the final concentration steps. in order to reduce ammonia losses, the ammoniumu nitrate .solution in the reaction loop is adjusted so as to obtain a small surplus of acid.

in order to reduce nitrogen losses, the process vapours are treated in scrubbers. The concentrated scrubbing condensate is returned to the process. The concentration of the ammnonium nitrate solution requires a temperature of 175-180 0 C sufficient to generate pure 4- to 8-bar fresh steam and to allow reliable process control with a view to optimizing the utilization of the reaction heat. This -process demonstrates that a sophisticated type of reactor is required to permit a homogenous reaction, a uniform heat distribution over the entire cross-sectional area of the reactor as well as lower nitrogen losses and to deploy suitable materials of construction.

7 The invention is described below in greater detail on the basis of the example illustrated in the following drawings; Figure 1 shows a simplified design layout of a vessel according to the invention (sectional view).

Figure 2 shows a large sectional view of the nozzle for injecting aqueous nitric acid into the reactor (section marked 11 in Fig. 1).

Figure 3 shows the section marked 111-111 in Fig. I (simplified design layout).

Figure 4 shows the lateral view of a single tube of the tube bundle.

Figure 5 shows the enlarged detail section of said -tube.

The device 1 illustrated in the example consists of stacked flanged cylindrical modules. Inlet pipe 2 is connected to bottom cone 3 which communicates with the first mixing chamber 4 and a downstream mixing chamber S. The latter is flanged to a tubed chamber 6 which communicates with reaction chamber and finally with a fu-ther conical reaction chamber 8 equipped with outlet pipe 9.

Accordi-ng to Figure 1, bottom cone 3 has a ring tube 10 (not completely shown) with a multitude of injection nozzles arranged on the line perimeter, said nozzles being detailed in Fig. 2 and marked 11.

In order to achieve a thorough mixing, it is possible to provide mixing elements 12 in mixing chamber 5, refer to Fig. 1.

Tiubed chamber 6 has two tubesheets 13 with a multitude of tubes 14 placed in a stream of NH 3 gas fed via gas inlet nozzle 15 of tubed chamber 6. Fig. 3 shows a plan view of the tube arrangement which can of course be varied and the two related gas feed pipes 15a. and 15b. Tubes 14 have penetration holes 16 on the external perimeter, 8which are dotted in Fig. 4 whereas the penetration layout is illustrated in Fig. S.

Figure 2 shows the detail section of injection points 11.

As nitric acid is a very corrosive agent at elevated temperatures, it is necessary to provide an "ai injection layout" that avoids di;:-.ct contact; hence the ammonium nitrate solution (100-170 0

C)

does not come into contact with the tubes, flanges etc. feeding the nitric acid to the injection nozzle 3.6 made of PTFE, other acid-proof plastics, titanium, tantalum or ceramics. The nozzle housing 17 is made of highly corrosion-resistant material for ,.boosafety reasons.

To ensure proper inspection, maintenance etc the arrangement corresponds to Fig. 2.

The reactor designed according to the invention operates as follows: The recycled ammonium nitrate (AN solution) enters the bottom cone 3 of the reactor via inlet 2. The aqueous nitric acid distributed by ring tube 10 to several acid injection points 11 is injected into the ammoniumn nitrate solution. In view of the corrosion at 20 temperatures between 100 and 170 0 C the acid feed system avoids direct contact. The acid is admixed by 1-12 special injection nozzles (Fig. equally spaced on the perimeter of the mixing to tube. The nozzle 11 can be ai'ranged in such a way that the jets are directed upwards (gradient 0-l0*) and/or eccentrically 0-300 from the vertical centre axis and cause an angular momentum acting on the mixed stream. Hence, the acid is distributed to a certain extent across the reactor section.

Downstream of the acid injection device there is a premixing zone (PML) (0.5 1 3 mn), followed by 1-4 static mixing elements 12 (multi-orifice plates, packings, fluid mixers). The aim of the static mixer is to optimize the homogenity of the acid distribution in the mixture. The coefficient of variance /r should range from 0.01 to 9 The finally mixed acidic ammonium nitrate solution enters a multitube reactor bundle 6 (3-200 tubes) arranged in such a way that the ammonia gas is also homogeneously distributed (Fig. The tubes 14 are of the perforated type as described above. The individual tubes (50 d i 200 mm of the bundle have penetration holes d2 5 mm 1) arranged in a spiral manner as shown in Fig. The tubes are of a limited length because of vibration unless one or two grids are provided. The tubes must be tightly welded into the tube plates 13. The pressure inside the reactor bundle 6 should be 0.02-2.5 bar higher than the boiling point of the ammonium nitrate solution at the given temperature. Reaction zones 7,8 (with or without guiding channels) of empirical length (RL) followed by a postmixing element 12a, similar to the premixing 15 elements 12 ensure completion of the reaction so that the nitrogen 22 *losses are very low during further process steps, for example flashing. Via outlet 9 the hot ammonium nitrate solution leaves the reactor.

go•

Claims (12)

1. A reactor when used for the T uction of ammonium nitrate solution by neutralization of aqueous nitric acid with the aid of an ammonia containing gas, said reactor comprising in sequence: a bottom cone for receiving recycled ammonium nitrate solution, said cone having injection nozzles arranged about the perimeter of the cone for introducing aqueous nitric acid for admixture with the recycled S" 10 ammonium nitrate solution; a premixing zone located adjacent said bottom cone and adapted to receive the admixture and initially mix the recycled ammonium nitrate solution and aqueous S: nitric acid; 15 a final mixing zone located adjacent said premixing zone and adapted to receive and homogeneously mix the premixed recycled ammonium nitrate solution and aqueous nitric acid; a downstream tubed chamber located adjacent the final mixing zone, said chamber containing a bundle of perforated tubes for introducing the ammonia containing gas for admixture with the mixed recycle ammonium nitrate solution and aqueous nitric acid in a gas-to-liquid admixing zone; and a reaction chamber located adjacent the downstream tubed chamber for reaction in a reaction zone of the mixed recycle ammonium nitrate solution and aqueous nitric acid with the ammonia containing gas to 11 produce an ammonium nitrate solution in a reaction zone.

2. A reactor according to claim I, wherein the injection nozzles are located equidistantly on the perimeter of the bottom cone.

3. The reactor according to claim 1 or 2, wherein mixing elements are provided in the final mixing zone.

4. The reactor according to any one of claims 1 to 3, wherein mixing elements are provided on an outlet side of the reaction chamber.

5. The reactor according to any one of the preceding claims, wherein the perforated tubes are arranged in flanged-type tubesheets.

6. The reactor according to any one of the preceding claims, wherein the injection nozzles for the aqueous 15 nitric acid are provided with integrated acid-proof nozzle heads shielded with sleeves of I•corrosion-resistant metal. ••co

7. The reactor according to claim 6, wherein the acid-proof nozzle heads are removable from the sleeves of corrosion-resistant metal for easy replacement.

8. A reactor according to any one of the preceding claims, wherein the injection nozzles are directed upwards at an angle of from 00 to 100 from the inlet stream of ammonium nitrate solution and/or eccentrically at an angle of 00 to 300 from the vertical centre axis of the cross-sectional area of said stream.

9. A reactor according to any one of the preceding claims, wherein the reactor comprises a number of 12 reactor sections which are of a flanged type and capable of being stacked.

A reactor according to any one of the preceding claims wherein the reactor comprises a bottom conical section incorporating the bottom cone and a part of the premixing zone; a main cylindrical section incorporating a first mixing chamber incorporating the other part of the premixing zone, a downstream mixing chamber incorporating the final mixing zone, the downstream 10 tubed chamber and part of the reaction chamber; and a top conical section incorporating the other part of the reaction chamber and an outlet for resulting ammonium nitrate solution.

11. A reactor according to any one of the preceding 0 15 claims, wherein each perforated tube of the tube bundles is provided with penetration holes arranged in a spiral "manner on the perimeter of the tube for admitting the ammonia containing gas into the reactor.

12. A reactor when used for the production of ammonium nitrate solution, substantially as herein described with reference to any one of the accompanying drawings. DATED This 9th Day of September 1994 UHDE GmbH Attorney: RUTH M. CLARKSON Fellow Institute of Patent Attorneys of Australia of SHELSTON WATERS ABSTRACT The invention relates to a reactor of the vertical vessel type for the production of ammonium nitrate, aqueous nitric acid with a concentration of to 65% by weight being neutralized in said reactor with the aid of pure ammonia gas or a gas containing ammonia with a concentration of 30 to 60%. Such a gas is, for instance, obtained as off-gas in a urea plant. o'o The reactor internals are arranged in such a manner S 10 that the liquid mixture subsequently passes in an upward direction through a first premixing zone (PML), a second final mixing zone, then through a gas-to-liquids admixing zone and finally a reaction zone (RL) 8). 9 9