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Exergy destruction in ammonia scrubbers

Author:
Zisopoulos, Filippos K., van der Goot, Atze Jan, Boom, Remko M.
Source:
Resources, conservation, and recycling 2018 v.136 pp. 153-165
ISSN:
0921-3449
Subject:
air flow, ammonia, evaporation, exergy, latent heat, mixing, neutralization, scrubbers, sulfuric acid
Abstract:
A theoretical ammonia scrubbing process by sulfuric acid solution is assessed with the concept of exergy. The exergy destruction of chemical neutralization is mainly (75–94%) due to changes in the chemical exergy of streams and thermal effects from the reaction while mixing effects have a limited contribution (6–25%). The minimum exergy consumption to remove one mole of ammonia chemically from an airstream could be two to eight times larger than the latent heat of evaporation of one mole of water depending on whether a concentrated (98% w/w) or a dilute (1% w/w) sulfuric acid solution is used. The exergy destruction per mole of ammonia scrubbed could be reduced by up to 75% when both the sulfuric acid solution and the ammonia at the inlet airstream are highly concentrated. The use of sulfuric acid concentration in the range of 10–50% w/w could lead to a very low exergy efficiency (<50%). The exergy efficiency could be improved up to ∼87% by introducing an ammonia pre-concentration step right before the scrubbing process. The extension of system boundaries shows that the cumulative exergy loss rate for neutralizing a heavily loaded ammonia airstream with a flowrate of 1 kg s⁻¹ ranges between 0.3–1.5 MW depending on the way sulfuric acid is produced. Consequently, an exergy-efficient scrubber design should balance between the minimization of the consumption of exergy-intensive resources, the minimization of the exergy destruction occurring in the separation process, and the maximization of output stream utilization.
Agid:
6037319