Eco-efficiency analysis of plasma-assisted nitrogen fixation

Abstract

An eco-efficiency analysis has been conducted, as a sustainability performance indicator, by combining the life cycle costs (LCC) and the environmental impacts of diverse plasma-assisted ammonia and nitric acid synthesis routes, for which a detailed process design for small-scale production has been previously reported. The proposed design of the specific plasma processes involves new upstream and downstream activities, which are independent of conventional natural resources and comprise less equipment. In the context of this study, the impact of the product yield and plasma power consumption on the eco-efficiency profiles of the selected plasma processes is evaluated and benchmarked against that of the established synthesis pathways. Results show a relatively improved environmental profile of the plasma-assisted NH3 (5% NH3 yield), considering a power consumption of 17.2 g NH3 kWh−1 and energy recovery of 5%, against that of the contemporary production route. In the case of the plasma-assisted HNO3 (6% NO yield) synthesis, incorporating a power consumption of 7.77 kWh kg−1 NO and a 20% energy recovery, a better ecological footprint is displayed as compared to the conventional chemical process. Both plasma processes are characterized by higher LCC than the conventional ones, with the plasma-assisted nitric acid displaying a more competitive LCC profile. A clear contribution of the utilities (upstream and downstream equipment) to both the environmental and cost benefits is shown, and the plasma plant is the enabler of such integration. The contribution is related to both the number reduction of equipment (process simplification) and improved operation (process intensification). Given the outcomes of this study, the concept of developing modular plants incorporating the plasma technology and renewable energy sources—e.g. wind power—for synthesizing ammonia and nitric acid demonstrates promising potential and promotes a new window of opportunities for future sustainable decentralized fertilizer production; such as distributed production at the farm site, with the opportunity to react immediately to weather changes and to local conditions (soil, climate, crops, farming business model).

Tri‐fold process integration leveraging high‐ and low‐temperature plasmas: From biomass to fertilizers with local energy and for local use

“…On the other end of the commercial food chain, low-temperature plasma processes have shown promise for the nitrogen fixation to fertilizers. [24,[37][38][39][40] While they seem to be on the way to give an economic pathway to nitric acid as platform material for fertilizers recent plasma technologies did not manage to produce truly green and affordable ammonia. [41][42][43] Having both ammonia and nitric acid would open the full N-based fertilizer plethora from urea, ammonium nitrate, potassium nitrate, and so on.…”

Plasma-fixated nitrogen as fertilizer for turf grass

“…Smaller, decentralized plants could be co-located with fertigation systems to produce and distribute fertilizer only when necessary and could also be adapted for localized climates and conditions. 20 The use of plasma-xated nitrogen systems will allow for the development of sustainable decentralized production on site. These decentralized plants would be able to be integrated into fertigation systems and produce and distribute fertilizer only when necessary.…”

“…Economic analysis of the energy costs and efficiencies have been extensively studied for a variety of plasma xation technologies. 18,20 These past studies have shown potential in realizability of scalable production based on estimated capital expenses and operating costs. The current Haber-Bosch process has been fully optimized over the past century of its use, with an energy consumption of about 0.48 MJ mol À1 ammonia produced.…”

Towards Green Ammonia Synthesis through Plasma‐Driven Nitrogen Oxidation and Catalytic Reduction

“…[20] Adding the energy consumption of reactants production (0.51 MJ mol À1 NH 3 ) and product separation (0.54 MJ mol À1 NH 3 )results in atotal energy consumption of 19.65 MJ mol À1 NH 3 as shown in Figure 2. [21] Theenergy consumption of PNOCRA is an over 4-fold reduction, compared to the current BATf or plasmabased NH 3 synthesis.…”

“…[19] Ther ecovery of NH 3 from such ad iluted product mixture would be very challenging and highly energy intensive.The lowest reported energy cost with areasonable yield (1.4 %) is 18.6 MJ mol À1 NH 3 . [20] Al ow ammonia concentration in the reactor outlet can increase dramatically the overall energy consumption of the ammonia synthesis process.A nastasopoulou et al [21] quantified this energy penalty.F or amixture with 1vol %NH 3 ,the energy needed for NH 3 separation from such ad iluted gas mixture is in the range of the energy consumption of the Haber-Bosch process (0.54 MJ mol À1 NH 3 ). [21] Thehigh energy demand of plasma-driven NH 3 synthesis in its current state calls for an alternative approach.…”