Options for net zero emissions hydrogen from Victorian lignite. Part 2: Ammonia production

Abstract

This the second of a two-part study investigating the feasibility of producing export quantities (770 t/d) of blue hydrogen meeting international emissions standards, by gasification of Victorian lignite plus carbon capture and storage (CCS). Part 1 focussed on the resources, energy requirements, and greenhouse gas emissions associated with the production of gaseous and liquefied hydrogen, while Part 2 focusses on the production of ammonia as an alternative hydrogen carrier for export.In this study, an Aspen Plus simulation of a conventional 1500 t d−1 iron-based catalyst Haber-Bosch ammonia synthesis process is developed and incorporated into the earlier lignite-to-hydrogen process model. Development of the simulation involves (i) estimation of the instantaneous rate kinetics, (ii) calibration against test data for a reactor of known dimensions, (iii) scaling up the bed dimensions to achieve a target production capacity, (iv) selecting an appropriate feed gas composition to optimise performance, (v) adjusting purge gas flowrates to achieve stable operation, and (v) incorporation into the previous lignite-to-hydrogen simulation.This study finds that 178.2 t h−1 liquid ammonia and all electricity required to support the process can be produced from 1050 t h−1 Victorian lignite. Surprisingly, the simulation results show that the electrical power requirement for ammonia synthesis (176.4 MW) is essentially the same as that needed for liquefaction of an equivalent output of hydrogen (175.5 MW). On this basis both options are equally attractive, although ammonia synthesis is at a higher level of technological maturity than large-scale hydrogen liquefaction.This is the first study to quantify the greenhouse gas emissions intensity of ammonia production from lignite, accounting for the full production chain from lignite mining to CO2 sequestration. It is found that ammonia can be produced from Victorian lignite with very low CO2 emission intensity (0.49 kgCO2-e kgNH3−1) equivalent to that of next-generation natural gas reforming with CCS processes. If required, the emission intensity can be reduced to 0.05kgCO2-e kgNH3−1 with a post-combustion CO2 capture system, and then made carbon neutral by co-gasification with ≤1.4% biomass.For comparison, this study also examines the implications of producing the same quantity of green ammonia using renewable energy alone. It is estimated that production of 178.2 t h−1 green ammonia would require 1946 MW renewable energy and associated transmission infrastructure. In Victoria, this could be supplied by a wind farm with a 5.4 GW rated capacity, occupying an area of over 72,000 ha. This is highly unlikely to be a viable option.This analysis indicates that clean hydrogen in the form of ammonia, produced in Victoria by lignite gasification with CCS, can be consistent with global emissions reductions targets over the next few decades. The unique combination of low-cost lignite and high-quality CO2 storage geology means that Victoria is well placed to become a significant exporter of low-emissions ammonia to the world market. Further research is recommended on recovery of energy from the low grade waste heat streams and opportunities for additional electricity generation using the organic Rankine cycle.