Ammonia Production during LTSC reduction period

[Ammonia Engr]

Kindly share your experience on subject topic
Can we get ammonia production without LTSC? i.e. during LTSC reduction activity.
What will be the challenges if we proceed for Ammonia Production duringLTSC reduction period. Specifically tell about effect on CO2 absorption system with higher CO contents

[Edmondson Bob]

Hi, Yes-depending on some plant details this is easily done. To keep the methanator below trip temperature S/C should be kept high, at >5.0 I think I recall. One trick to this is LTS inlet and outlet valves hold tight and we would overhaul them for the catalyst change turnaround. In that way removal of blinds can be safely done. If the carrier gas for LTS reduction is natural gas, as it was in our case, it can be recovered to fuel. In our case solvent was Sulfinol but I suspect all solvents would be fine with higher CO. Rough figures with HTS at 360 deg and S/C of 5.0is 1.5% ex HTS so at methanator, creates an exotherm of 140 deg C, so with 260 deg inlet, 400 deg outlet, if we go to 7:1 S/C we have 93 deg exotherm. This has been done many times with good success. One small warning, -in one case the sudden cooling of the methanator outlet when the LTS was put on line, flanges leaked resulting in fires but they were easily extinguished.

[Satyajit Mahapatra]

You should not bypass LTS to produce ammonia as explained by Bedmonds above. The major risks of high CO content in the syngas are as following:
1. Formation of Formic acid and Heat stable salts (HSS) which cause corrosion and foaming in CO2 removal system.
2. Carry over of CO along with CO2 to Urea plant, CO forms explosive mixture similar to H2 in CO2.

Satyajit

[Edmondson Bob]

Hi Zohaibadeel and Satyajit,
I continue to believe this can be easily, and safely done -but could be wrong.
For CO issue, while S/U of the urea plant was not the primary topic I think, steam balance permitting, it can be done. CO is more readily oxidized in the H2 removal reactor than H2 and in the incoming CO2 would be around.19% while H2 is 0.7% and CH4 0.1% hence some methane but the H2 in the ammonia supply is normally far greater than H2 from the CO2 after the removal reactor and H2 has a far wider explosive range than CO and CH4.
For formic acid, this is one day out of a 1200 day LTS charge life and in that day there would be <0.25 mols of formic acid entering the CO2 removal (depending on CO2 removal process since Benfield tends to have a hotter raw gas separator which, I would guess, is not so different from normal operation at high load . At least in my experience the main formate issue to droplet carryover from the raw gas separator and for this operation we are at low plant rate (80% or so) hence reduced carryover of liquid droplets from the demister. The vast majority of formic acid leaves with the condensate and because of the high steam/gas the amount of condensate per mol of gas is more than 50% higher . I don’t have good formic acid solution VLE data but this observation is based on operation at very high load and with significant water carryover and Raoult’s law extrapolation .
I may well be wrong and perhaps others can offer more experience and data. The advantage to Zohaibadeel’s proposal is a 24 hour headstart on ammonia production which does offer significant return. In my Kellogg plant days this was done for every LTS reduction, which in those days, were every two year. For stand alone plants the front end is run to make the H2 so lots of gas consumed and it seems a shame to waste it if not required. In recent years LTS’s I’ve been involved with, are always done off line with tube trailers of H2 which is even nicer but depends on accessibility of tube trailers. With that method startup is not delayed at all

[AHMAD IRFAN]

1) In plants where main gas is N2, you cannot run B.E as N2 is circulated through air compressor
2) In plants where DS gas is used, you can run by taking precautions like HTS out CO slip should be in control range to keep methanator temperatures within limits. For this low, FE load and high S/C is recommended
3) For format formation as said by Satyajit, process gas is already venting at methanator downstream because we require sny gas/H2 for reduction which means CO2 removal system is already online at low load. But with increase of load, CO to absorber will also increase

[Pattabathula Venkat]

Yes, NH3 could be produced while LTS catalyst was in progress and we did this successfully as long you maintain CO+CO2 <10ppm exit methanator. But it could be at very low rates.

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