(361c) Abfews: An Ammonia-Based System for Food-Energy-Water Sustainability

Since the dawn of the 20th century, industrial agriculture and large-scale commercial power generation have revolutionized society, allowing for less expensive and more plentiful food and electricity. However, these industries are problematic with respect to sustainability, consuming considerable amounts of fossil fuels and withdrawing massive amounts of water, much of which is consumed. The water that is returned to the surrounding environment is often done so at conditions which are damaging to local ecosystems. Examples include the elevated temperature of cooling water used in power generation and excess nutrient (e.g. nitrogen, phosphorus) content in agricultural water runoff, especially in areas such as the U.S. Midwest, where tile drainage is used to more quickly remove excess water from crops.

Ammonia lies at the heart of the food-energy-water nexus. Synthetic ammonia is essential for modern society, allowing for higher crop yield per units of land and water. On the other hand, its conventional production is responsible for more than 1% of global greenhouse gas (GHG) emissions and 5% of global natural gas consumption [1]. This has motivated alternative ammonia production concepts. One such concept is to use biomass to replace conventional sources of hydrogen [2]; this is particularly well-suited to an agricultural setting wherein such biomass is naturally present. Another alternative production scheme uses wind- or solar-derived electricity to obtain hydrogen from electrolysis, nitrogen from air separation and subsequently to power an ammonia synthesis process itself [3]. Apart from the ability to reduce the GHG intensity of ammonia production, renewables-to-ammonia has attracted heightened attention due to the potential of ammonia as a means of energy storage to better enable the use of intermittent renewable energy for power generation, or as a carbon neutral combustion fuel. Our recent work explores these possibilities in the context of a system which uses wind energy to make ammonia as both fertilizer and fuel for a local farm, to meet local electrical power demands and to export power to the grid in a predictable and consistent manner [4].

However, the above-described system and others in the literature of a similar type, for example [5] and [6], do not address water sustainability from neither process consumption nor agricultural runoff perspectives. To our knowledge, less research has been dedicated to combined food-energy-water sustainability, with an exception being an integrated local production system which considers crop allocation for food, energy production from crop waste and rain capture for meeting relevant water demands [7]. However, this system does not account for the energy and water aspects of fertilizer and agricultural fuel production, nor does it address the issue of runoff.

In view of the current state of systems engineering research in this area, we in this work propose an ammonia-based system for food energy water sustainability (ABFEWS). This farm-scale system uses renewable energy and agricultural waste to (i) produce ammonia as fertilizer and agricultural fuels, (ii) meet local power demands, (iii) export excess power to the grid in a predictable and consistent manner, and (iv) extract and purify soil water for use in chemical production. The integrated nature of this system offers synergies which aid with both economic viability and sustainability. As with our previous work, time-varying chemical production can act as controllable load to better balance power supply and demand, and ammonia and hydrogen can be used as energy storage media. Additionally, the use of biomass, whether for power generation or ammonia production, reduces electrical power requirements. , Furthermore, purification of soil water simultaneously reduces process water import and tile drainage to surrounding ecosystems.

In addition to the ABFEWS system concept, we present a mixed integer linear programming (MILP) model for its optimal design. For this system, design and scheduling are inextricably coupled due to the hourly and/or seasonal variation in renewable generation, weather phenomena, and demands for power, ammonia and water. Thus, in addition to design decisions (selection and size of units), the model also determines the optimal hourly operating schedule of the system (e.g. production rates, storage levels) over a representative year. We apply this optimization model to a case study based in Morris, MN which considers the use of two 1.65 MW wind turbines and 196,000 kg of corncob biomass to meet ammonia (used as fertilizer and fuel) demand of 40 tons/year and an hourly average electrical power demand of 985 kWh. This case study provides an initial assessment of the economics, GHG emissions reduction, and water conservation afforded by this integrated approach to sustainability, as well as the most promising areas for future research.

References

[1] Swaminathan & Sukalac. Technology transfer and mitigation of climate change: The fertilizer industry perspective. IPCC Expert Meeting on Industrial Technology Development, Transfer and Diffusion, Tokyo, Japan, 2004.

[2] Demirhan, Tso, Powell, & Pistikopoulos. Sustainable ammonia production through process synthesis and global optimization. AIChE J., 2018, DOI: 10.1002/aic.16498.

[3] Sanchez & Martin. Optimal renewable production of ammonia from water and air. J. Clean Prod., 2018, 325-342.

[4] Palys, Kuznetsov, Tallaksen, Reese, & Daoutidis. An ammonia based system for sustainable energy and agriculture: Concept and design optimization. Chem. Eng. Process, 2019, Accepted.

[5] Wang, Mitsos, & Marquardt. Conceptual design of ammonia-based energy storage system: System design and time-invariant performance. AIChE J., 2017, 1620-1637.

[6] Allman, Palys, & Daoutidis. Scheduling‐informed optimal design of systems with time‐varying operation: A wind‐powered ammonia case study. AIChE J., 2018, DOI: 10.1002/aic.16434.

[7] Hang & Martinez-Hernandez. Designing integrated local production systems: A study on the food-energy-water nexus. J. Clean Prod., 2016, 135, 1065-1084.