SE439009B - WANT TO REDUCE THE EXPLOSIVITY OF CARBAMIDE PRODUCTS - Google Patents

Description

lO 8006001-5 carbon dioxide production and essentially consists of H2, N2, CO, CH4, Ar and He.

The urea installation, the reactor and the decomposer, certain amounts of air or oxygen are fed to protect the reactor, the disintegrator and condenser against corrosive action of the ammonium carbamate.

All non-condensable gases, both those originally present in fresh carbon dioxide and ammonia and those to provide passive protection for exposed devices for corrosion, discharged from the urea synthesis plant and form, after being freed from ammonia, due to the arrival of the oxygen used for the passive protection, an explosive mixture.

The gases in question are usually discharged in part from high the pressure carbamate condenser, from which they are conveniently transferred to the medium-pressure purification column for extraction of ammonia and mixed in this column with the stream coming from the medium pressure carbamate the condenser.

In the said column for the recovery of ammonia the ammonia at the top of the column together with the existing gases and these gases are discharged after separation from condensing ammonia and constitutes the above-mentioned sieve the gas stream.

V It is clear that the corresponding current of uncondensable gases, which constitute an explosive mixture, can also be taken out from other points in the facility without the present problems in any way change.

The measure hitherto commonly used to prevent explosion is that the gas stream is mixed with such volume non-combustible gases, that the resulting gas mixture does not longer is explosive.

It has now been shown that the tendency to explode in a mixture of exhaust gases at the urea production plant can be eliminated without diluting the mixture with non-combustible gases and thus without the gas mixture flammability is reduced. This result can be according to the invention achieved by using the gas streams from the plant ammonia synthesis equipment, which are constantly being 8006001-5 available in urea synthesis plants.

In the case of ammonia synthesis, the following occurs in particular gas flows: l. Natural gas stream, consisting essentially of methane, which goes to a steam plant for the production of ammonia synthesis gas. 2. Gas flow from the plant for the production of the ammonia synthesis gas, consisting essentially of hydrogen, nitrogen, carbon monoxide and carbon dioxide. 3. Gas stream from the steam plant for the production of ammonia synthesis gas, but stripped of carbon dioxide. 4. Stream of nitrogen and hydrogen, saturated with ammonia and optionally with water containing argon, helium and methane, discharged from the plant for ammonia production to prevent enrichment in the stream returned to the ammonia synthesis with argon, helium and methane.

Typical composition ranges for the mentioned streams is the following: Hydrogen from 0.1% to 77% (by volume) Nitrogen from 0.1% to 29% (volume) Inert gases (CO, CO 2, Ar, He) from 0.1% to 50% (by volume) Methane residue up to 10% (volume).

In the currents occupied under 2, 3 and 4 above molar ratios between H2 and N2 in addition between 2.5 and 3.3.

An object of the present invention is to pressure the explosion tendency of the exhaust gas from urea production facility. For this purpose, the method is characterized by mixing these exhaust gases with one or more of them gas streams available in the production plant ammonia and with the composition: hydrogen from 0.1% to 77%, nitrogen from 0.1% to 29%, carbon monoxide and / or carbon dioxide and / or argon and / or helium from 0.1 to 50% and the remainder methane up to 100%, all calculated in volume.

It is quite surprising that by proceeding according to the invention can not suppress the risk of explosion 8006001-5 nb simply because of the change in the composition of the mixture, but also, and completely unpredictably, thanks to narrower look for the explosiveness zone.

It has thus become possible not only to do it gas stream of non-condensable gases emitted from urea plant non-explosive, but also to enable use of the mixture as gaseous fuel in the plant ningen.

The invention is further illustrated by the following example with reference to the accompanying drawing, at which Fig. 1 is a simplified diagram of an urea production plant and Figures 2 and 3 are diagrams regarding explosive limits of current gas mixtures.

EXAMPLE Z The simplified and schematic representation shown in Fig. 1 the urea production plant can be assumed to have a average capacity of 1500 tonnes of urea per day, whereby the volume of the gases dissolved in the reactants is 410 Nm3 / h with the following composition in volume percent: H2 = 51.47, N2 = 40.73, O2 = 7.56, CO = 0.12 and CH4 = 0512.

The high-pressure decomposer is supplied with 333 Nm / h passive ring air.

All these gases are released from the reaction solution and discharged from the plant at the top of the ammonia distillation column, which operates at about 1.8 MPa. Top- the gases from this column go after a first condensation ring of the predominant part of the ammonia through a line 12 to a heat exchanger 8, is separated from the ammonia in a separator 1, from which separated ammonia is taken out via line 9 and is used in other units in the facility. The gases, saturated with ammonia at the prevailing temperature in the separator l (35 ° c) has the following composition in und / h; H2 = 211.0, CH4 = 0.5, CO = 0.5, N2 + Ar = 430.0, 02 = 101.0, and NH3 = 2977.0, and goes via line 2 to an absorber 6, where ammonia is recovered by being absorbed with water, which supplied via line 7.

When stripping the gas on ammonia, a gas mixture with the following composition: 8006001- Combustible gas 28.54% of which H2 = 28.40% CH4 = 0.07 2 CO = 0.07% N2 + Ar 57.87% 02 13.59% Everything in terms of volume.

As can be seen from the diagram Fig. 2, which shows the the activity limits of the gas, where point A represents 100% 02, B 100% is the point representative of the gas, point D, inert gases and C 100% in the field of explosives, represented by the one in triangle ABC horizontal triangle.

In the practice of the present invention, wherein the gases from line 2 are mixed at 11 with the exhaust gases from the ammonia synthesis plant (with a production of ammonia amounting to 865 tons / day), which is added via line 3 receives the exhaust gases in an amount of 7633 Nm3 / h the composition in volume percent: H2 = 54.86, CH = 10.92, N = 21.94 and NH 3 = 12.28. IN The gas mixture which via line 4 goes to the absorber 4 2 the battery 6 in an amount of 11352.0 Nm 3 / h has the composition, in volume percent H2 = 4398.0, CH4 = 833.5, CO = 0.5, N2 + A 2105.0, 02 = LO1n and NH3 = 39l4.0.

After ammonia stripping, the gas has the following saturation in volume percent: H2 = 59.14, CH4 = 11.21, N2 + Ar 28.30 and 02 = 1.35. The total amount of combustible gas is 70.35 volume percent.

Fig. 3, in which A, B and C have the same meaning as in Fig. 2, shows the explosive limits of the latter the gas mixture and its representative point, point D i Fig. 3, is far beyond these limits.

IN' combustible gases, IN'

Claims (2)

8006001-5 šatentkrav l. Ways to reduce the explosiveness of exhaust gases from a urea production plant, characterized in that these exhaust gases are mixed with one or more of the gas streams available in the ammonia production plant and which have components , in volume percent, hydrogen from 0.1 to 77, nitrogen from 0.1 to 29, carbon monoxide and / or carbon dioxide and / or argon and / or helipm from 0.1 to 50 and methane the residue up to 100. 2. A method according to claim 1, characterized in that the gas stream available in an ammonia synthesis plant is one or more of the following: a) natural gas stream, consisting essentially of methane, b) a gas stream from a steam plant for the production of ammonia synthesis gas and consisting essentially of hydrogen, nitrogen, carbon monoxide and carbon dioxide, c) a gas stream according to b) after stripping of carbon dioxide, and d) an ammonia-saturated stream of nitrogen and hydrogen, optionally also saturated with water and containing argon, helium and methane, obtained as an exhaust gas from the ammonia synthesis plant.