Objetivo
To demonstrate the performance of the Montedison IDR urea process, developed by Fertimont. This features a high conversion per pass through the synthesis reactor, easy isobaric recycle of the unreacted matter to the reactor and relatively low steam consumption (40 % less than requirements for conventional processes).
The overall consumption of feed stock, referred to 1 metric ton of prilled urea produced, are as follows :
- ammonia.................................570 kg
- carbon dioxide..........................740 kg
- steam at 25 kg/cm2 abs. sat.............600 kg
- electric power (CO2 compressor driven...
by electric motor).....................130 KWh
- cooling water (temperature rise 10 C)... 60 m3
Before the modification of the urea line the steam consumption was 1,700 kg/tonne urea. After the conversion to IDR section the steam consumption has been recorded at about 600 kg/tonne urea, with saving of 1,100 Kg/tonne urea.
For urea production of 90,000 tonne/year, the energy saving for San Giuseppe di Cairo plant is about 6,500 TOE/year. For a urea plant, having a production capacity of 300,000 tonnes/year and using a conventional process, the adoption of the IDR process would allow the following energy saving rates
to be achieved :
Steam consumption Steam consumption Saving
at present with IDR process in
kg/tonne kg/tonne TOE/yr
2,000 600 27,300
1,500 600 17,550
1,000 600 7,800
Recoveries - steam at 7/9 Bars abs. sat 100 kg/T urea.
The above figures are also valid for the production of 98.5 % urea solutions to be sent to a granulation section, except for the L.P. recovered steam that increases to 150 kg/t urea.
The results obtained to date on a commercial scale (more than 360,000 Tonnes of urea have been produced in the demonstration plant till now) show that the process is viable and efficient and enough know-how has been acquired to design new plants or modify old ones.
Montedison is ready to licence the urea IDR process fully backed by guarantees. The first licence has been granted in February 1986 to China National Chemical Construction Corporation for the modernization and debottlenecking from 500 TPD to 750 TPD of an urea plant in Luzhou Factory.
Performance on commercial scale operation may be summarised as follows:
- high reactor conversion/pass in the 70%-75% range;
- effective operation of the isobaric recycle from the two decomposers;
- complete recovery of the reaction heat as well as of the heat supplied to the decomposers, as steam at 6-6.5 kg/cm2 abs;
- steam consumption significantly lower than in the best current technologies: even prior to the fine tuning of the process variables, net steam consumption of +/- 600 kg/ton of urea was recorded;
- no corrosion, even minimal, has been detected after one year of 'severe' operation, a satisfactory result which is due to the proper selection of construction materials, and to careful and original surface passive technique.
The trial testing of the new process, on an industrial scale, has been carried out at the Fertimont urea plant in San Giuseppe di Cairo, modifying one of the two existing lines of 300 tpd/each. The new IDR section (the high pressure loop-synthesis reactor, I and II stripper, carbamate condenser) was connected to the raw material feed and the finishing section of urea solution, of the existing plant. At present Fertimont produces +- 3 million tonnes of fertilizers amounting to 40 % of italian consumption and exports more than 30 % production.
The high conversion of ammonium carbamate to urea (70 to 75 %) is obtained by operating at fairly high NH3/CO2 molar ratio (4 to 5), whilst the recycle of most of the unreacted matter including the large amount of free ammonia, is effected by two strippers operating in series at the synthesis pressure, the first in excess NH3 and the second one in excess CO2 conditions.
The outgoing urea solution from the reactor at 180-210 bars flows to the first falling film stripper from which part of the ammonium carbamate is recycled in vapour phase to the reactor using about 40 % of the feeding ammonia as stripping agent; the heat is supplied by condensing M.P. steam. The solution thus obtained is sent to the second falling film type stripper, where it is stripped by CO2. It is possible to distil the urea solution coming out from the second stripper in the medium pressure section using recovered steam at 7/9 Bars abs. as a heat source, so minimising M.P. steam supply and further reducing overall steam consumption. The urea solution leaving the second stripper is flashed to +- 25 Bars abs. and fed to a distiller heated by recovered steam.
A solution with low CO2 and NH3 content is obtained by supplying heat and sent downstream for final purification. The vapours arising from the second stripper are sent to the carbamate condenser, also fed by the recycled carbonate solution.
The heat released is recovered by generating 7/9 Bars abs. steam, whilst the condensed carbamate is sent back to the reactor. This steam is utilized on the sections downstream of the IDR loop. The reactor is divided into two sections by a partition plate, the reactants, being fed to the bottom of the upper and larger section rise to the top, reach the bottom of the lower section through a downcomer and flow up to the outlet. This flow arrangement allows the reactor to be placed at grade level avoiding costly superelevation. In the demonstration plant the falling film version of the exchanger was tested with +- 40 % of the feeding ammonia as stripping agent. The ammonia is pre-heated to 200 C prior to entering the decomposer.
Pay back is estimated at three years.
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Coordinador
28138 Milano
Italia
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