Expansion turbine
Air and steam vent
Puri ed water
Liquid phase reactor
Flue gas
Vent
NO converter
Liquid NH
Vapour NH
Filter
Steam
Crude HNO storage tank
Vapouriser
Dilute NHO
Ammoni a storage tank
Condenser
NH + O mixer
Molten ammo- nium nitrate
NH + O
Ammo- nium nitrate solution
Prilled ammo- nium nitrate
Air
Catalyst recovery lter
Distillation
60% HNO product
Cooler steam generation
Oxygen + air
Ammonia
Air
Condensate Evaporator
Prilling tower
Compressor
NO + NO
Pure HNO
O
O
60% HNO Absorber
ASU
NO converter x
NO absorber x 1. 6NO + 3H O 3HNO + 3HNO 2. 3HNO HNO + H O + 2NO 3. 2HNO + O HNO 4. 2N O + O + 2H O 4HNO
Ammonium nitrate reactor
Nitrogen to ammonia synthesis
1. 4NH + 5O 2. 2NO + O
4NO + 6H O
H to ammonia synthesis
2NO
1. HNO + NH
NH NO
Electrolyser
3. 2NO
N O
Figure 3 Nitric acid and ammonium nitrate production
together. In this pathway, hydrogen can be produced on a reformer with water gas shift reactors. After the reformer, hydrogen can be separated from unreacted methane, residual CO and CO 2 using a PSA system. Nitrogen can be supplied to the ammonia synthesis process in a variety of ways, depending on the scale required. The ideal choice may be an on-site cryogenic nitrogen generator. It can provide a high volume of high-purity gaseous nitrogen to the ammonia synthesis process and may simultaneously produce liquid nitrogen, which can be stored in a cryogenic vessel on-site as a backup to the cryogenic nitrogen generator. On the other hand, if pure oxygen is required for an ATR or POx reactor, a cryogenic air separation unit (ASU) may be appropriate. It removes argon from the nitrogen, reducing the requirement to purge argon from the ammonia synthesis loop. It also provides nitrogen for ammonia synthesis and oxygen to the reformer. Additionally, it can produce liquid nitrogen and oxygen for back-up storage. Cryogenic nitrogen and oxygen production technologies use electricity as the main energy source. Decarbonisation can be facilitated by sourcing renewable power to run the process. Nitric acid and ammonium nitrate Nitric acid is produced by the Ostwald process. The first stage of this process is to oxidise ammonia to form nitric oxide. The gases from the reactor are passed into an absorber where oxygen is added to further oxidise the nitric
oxide to nitrogen dioxide, which is dissolved in the liquid to yield nitric acid at about 60% concentration. Oxygen enrichment of the air feed to the absorber can achieve process intensification. In an integrated ammonia and nitric acid facility, an ASU can provide oxygen to the nitric acid process and nitrogen to the ammonia process. Alternatively, oxygen-enriched vent gas from a nitrogen generator, containing around 35% oxygen, can be used to feed the nitric acid absorption column. In the future, it is possible that green hydrogen for ammonia production will be produced by the electrolysis of water. Oxygen is produced as a co-product during electrolysis. In such a scheme, the oxygen can be used to enrich the air stream to the absorber for nitric acid production. Ammonium nitrate (AN) is produced by reacting nitric acid and ammonia (see Figure 3 ). AN is one of the main nitrogen-containing fertilisers used worldwide. It can be blended with fuel oil to create ammonium nitrate-fuel oil (ANFO), an explosive in the mining industry. Parallels with ethylene oxide production Around 20 million tonnes of EO are produced each year. The majority of this EO is converted to monoethylene glycol (MEG) and polyethylene glycol (PEG). The modern process to produce EO combines pure oxygen from an ASU with ethylene. The ethylene is generally produced on a steam cracker unit from crude oil or ethane, which is a component of many natural gas
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