Reactor for oxidation of ammonia in the production of nitric acid

Abstract

A method for the production of nitric acid, comprising a step of oxidation of ammonia in the presence of a catalyst, comprising a step of monitoring the temperature of said catalyst by at least one contactless infrared sensor.

Claims

1. A method for the production of nitric acid, comprising a step of oxidation of ammonia in the presence of a catalyst, comprising a step of monitoring the temperature of said catalyst by at least one infrared sensor.

2. The method according to claim 1, wherein said catalyst is a platinum catalyst or a platinum-rhodium catalyst.

3. The method according to claim 2, said catalyst being in the form of a gauze.

4. The method according to claim 1, wherein: said sensor is positioned away from the catalyst and the method comprising the step of switching said sensor between at least a first position wherein the sensor points a first region of the catalyst, and a second position wherein the sensor points a second region of the catalyst, so that the sensor can selectively detect the temperature of said first region and second region of catalyst.

5. The method according to claim 4 wherein: an alarm signal is generated when the temperature difference between different regions of catalyst exceeds a predetermined alarm threshold.

6. The method according to claim 1, wherein said step of oxidation is carried out with a ratio of ammonia to an oxidant which is continuously adjusted as a function of the temperature of the catalyst detected by said at least one infrared sensor.

7. The method according to claim 1, comprising the use of a plurality of infrared sensors to monitor the temperature of said catalyst.

Description

DESCRIPTION OF FIGURE

(1) FIG. 1 is a simplified scheme of some items of a plant for the production of nitric acid.

(2) FIG. 2 is a detail of the ammonia oxidation reactor of FIG. 1, according to an embodiment of the invention.

(3) FIG. 3 illustrates a detail of a preferred embodiment of the invention.

DETAILED DESCRIPTION

(4) FIG. 1 illustrates the basic steps of industrial production of nitric acid. A reactor 1 contains a gauze 2 of a PtRh catalyst, suitable to catalyse oxidation of gaseous ammonia 3 in the presence of air. Said oxidation of ammonia in the reactor 1 produces a product gas 4 containing nitrogen oxides including NOx and N.sub.2O. Said product gas 4, usually after heat recovery through a heat exchanger 5, is treated in a tower 6 where the oxides are absorbed by water 7, to form an aqueous solution 8 containing nitric acid and an overhead gas 9. Said solution 8 is further purified to obtain nitric acid and the gas 9 is usually treated in a De-NOx unit to remove nitrogen oxides; all the above follows known techniques which are not essential to this invention and are not described in detail.

(5) FIG. 2 illustrates a detail of said reactor 1. The reactor 1 comprises a vessel 10 with a cover 11 held in place by flanges 12, 13. The reactor 1 contains the PtRh catalyst gauze 2 and a basket 14 for Raschig rings and/or a secondary catalyst; the figure also shows tubes 15 of a waste heat boiler.

(6) The reactor 1 comprises at least one infrared (IR) sensor 16 fitted in a sight window 17 of the pressure vessel 10. More particularly FIG. 2 illustrates a preferred embodiment wherein the sight window 17 is made on the cover 11. Said IR sensor 16 faces the gauze 2 and, hence, is able to sense the temperature of the catalyst.

(7) Preferably, multiple IR sensors are provided in order to monitor the temperature over the gauze 2.

(8) Even more preferably, the infrared sensor or each infrared sensor is mounted on a moving socket (e.g. a ball joint socket) so that the sensor can be oriented to target different regions (areas) of the gauze 2. For example, FIG. 3 illustrates an IR sensor 16 mounted on a moving socket 18 and illustrates a first position of the sensor 16 pointing to a first region 2 of the gauze 2, and a second position (dotted line) pointing to a second region 2 of said gauze.

(9) According to some embodiments, the IR sensor 16 may include a built-in moving socket 18.

(10) Preferably a moving sensor 16 as in FIG. 3 is controlled to detect the temperature over a continuous region of the catalyst between two end position, for example between points 2 and 2 of FIG. 3.

(11) The signal of the one or more infrared sensor(s) is sent to a monitoring and control system of the reactor or of a plant comprising the reactor. A deviation of the measured temperature from the expected value, or a non-uniform temperature over the gauze 2, may generate an alarm signal such as, for example, an alarm of contamination of the catalyst.

(12) It shall be noted that the IR sensor 16 is positioned away from the gauze 2; nevertheless, it provides an accurate measure thanks to the infrared sensing. In addition, thanks to the installation in the sight window 17, the IR sensor 16 is in a protected position, being not directly exposed to the input flow 3, which reduces the risk of failure.

(13) The sight window 17 is made with a known technique and can comprise, for example, a flange with a glass cover and a suitable gasket.

(14) An aspect of the invention is the installation of one or more infrared sensor into existing sight windows of a pressure vessel. Accordingly, the reactor 1 can be retrofitted by adding one or more infrared sensors into available sight windows, such as the window 17, to monitor the temperature of the gauze 2. In some embodiments, existing temperature probes can be replaced by newly-installed IR sensors, or the new IR sensors may be in addition to conventional temperature probes.

(15) According to preferred embodiments, the revamping can also comprise the implementation of a control of the ammonia to oxidant (typically ammonia to air) ratio in the feed of the reactor, as a function of the temperature detected by the IR sensor(s).