PTQ Q1 2023 Issue

Ammonia vapour to incineration

Ammonia incineration

Cooling water

Anhydrous liquid ammonia

Water

Caustic

Ammonia vapour from a mmonia stripper

Anhydrous ammonia production

Refrigeration unit

Scrubber

Anhydrous liquid ammonia

Water

Aqueous ammonia production

Ammonia absorber

Aqueous ammonia

Figure 2 Production of anhydrous and aqueous NH 3

the column bottoms stream. After being heat exchanged with the feed and cooled, this stripped water is suitable for many plant reuse needs or may be discharged. The H 2 S and NH 3 content of the stripped water is tailored to individual client requirements. Typically, this is in the range of 10-50 ppmw NH 3 and 1-25 ppmw H 2 S. Stripped water from SWSPlus plants can be used in hydroprocessing unit injection water, in crude unit desalter water, for coke drum quenching, or may be sent to effluent treating for discharge. The NH 3 and residual H 2 S stripped from the water in the NH 3 stripper are passed through an overhead condenser and recovered as a vapour and liquid. The liquid is used as column reflux.  NH 3 purification and liquefaction The vapour product is an NH 3 -rich gas that may be handled in a variety of ways. Depending on the final use, additional purification of the NH 3 -rich stream is required. This additional process may require water wash and/or caustic wash to remove various impurities. For small plants where NH 3 recovery is not desired or economic, the overhead product may be sent to a specialised thermal oxidation unit for heat

recovery, typically as high-pressure steam. However, in most cases, the choice is to purify the gas and produce either anhydrous or aqueous NH 3 suitable for sale, as shown in Figure 2 . For production of anhydrous NH 3 , the gas is passed through a two-stage scrubbing system to remove resid- ual contaminants. It is then liquefied using compression and cooling to produce anhydrous NH 3 . For production of aqueous NH 3 , a one- or two-stage scrubber may be used to remove the contaminants, depending on purity require- ments. The NH 3 gas is then dissolved in water to yield the desired product grade. Because of how a SWSPlus operates, incremental air permits are not required for recovery of anhydrous NH 3 or aqueous NH 3 . In the existing thermal oxidation unit, some- times called an incinerator, the net mass flow decreases, causing a decrease in fuel gas firing rate. This, in turn, reduces the operating cost and NOx, SOx and particulate emissions from the unit. When the extra capacity provided by a SWSPlus unit is consumed by incremental sulphur pro- cessing, these values tend to return to their original state. However, NOx will be lower due to the reduced nitrogen content of the waste gas.

Acid gas to SRU

Stripped water

Ammonia-free water

Sour water feed

Concentrated feed to smaller SWSPlus

Sour water s tripper (existing)

Bolt- O n A bsorber (new)

Figure 3 Addition of Bolt-On Absorber to an existing sour water stripper

PTQ Q1 2023