Energy and Environmental Performance of a Dual-Pressure Nitric Acid Plant Under Retrofit of the Tail Gas Treatment Unit

Nitric acid production is among the most significant industrial point sources of nitrous oxide, which is a greenhouse gas with a global warming potential approximately 298 times that of carbon dioxide, yet the large installed base of legacy dual-pressure plants continues to operate with non-selective catalytic tail gas treatment systems that offer limited greenhouse gas abatement and impose rigid thermal constraints on the gas turbine cycle. A validated steady-state process model of an industrial dual-pressure nitric acid plant producing 52.1 t per hour of nitric acid on a 100% HNO3 basis, corresponding to 88.1 t per hour of 59.2 wt.% product acid, is developed, validated against measured plant data, and used to evaluate two selective catalytic retrofit configurations. The first heats raw tail gas to catalyst ignition temperature using the existing process heater, then raises the purified gas to turbine inlet conditions by mixing with flue gas from a newly installed combustion chamber. The second achieves the required temperature rise internally through catalytic fuel gas oxidation within an additional catalyst shelf in a two-bed reactor, eliminating supplementary combustion equipment entirely. The first configuration reduces total greenhouse gas emissions by 42% in carbon dioxide equivalent terms, lowers ammonia slip below 5 ppmv, and enables a 5% production capacity increase worth 5.75 million EUR per year, at a capital cost of 5.25 million EUR and a discounted payback period of 12 months when European Union Emissions Trading System allowance savings are credited; excluding those savings the investment is not recovered within the five-year evaluation horizon. The second achieves a 44% emissions reduction at a capital cost of 1.98 million EUR, reduces annual utility costs by 1.75 million EUR, and recovers its investment within 4 months with allowance savings and 17 months without them, in both cases without increasing electricity demand. The results demonstrate that selective catalytic tail gas treatment retrofit is a value-generating investment rather than a compliance cost. Projected across the global fleet of unabated dual-pressure plants, equivalent adoption could reduce sectoral nitrous oxide emissions by up to 21.6 Mt of carbon dioxide equivalent per year, or 6.5 Mt per year at a 30% adoption rate.