A chemicals technology firm in Belgium recently launched its vision for using green ammonia for “energy harvesting.” The Dualtower is a new kind of wind turbine, under development by Arranged BVBA, that will use wind power to produce and also store hydrogen and nitrogen. These gases are “harvested” as ammonia, which becomes the energy carrier that allows large-scale renewable energy to be transported economically from remote locations with excellent renewable resources to centers of power consumption.
Arranged’s Dualtower is ambitious and, perhaps, futuristic but it illustrates three powerful concepts. First, the vast untapped scalability of renewable power. Second, the benefits of using ammonia as an energy carrier, to improve the economics of large-scale, long-distance energy transportation relative to every other low-carbon technology. The third concept is simply that every idea has its time, and now may be the time for ammonia energy. What was once futuristic, now just makes sense.
What was once futuristic
Ammonia has been proposed as an energy vector for decades because the physical properties of ammonia have always made it an economically competitive energy carrier.
The chart on the right compares the costs of energy delivery via pipeline for hydrogen, natural gas, and ammonia. Ammonia is the cheapest of the molecules for moving energy via pipeline.
Unfortunately, these numbers don’t take into account fossil-based ammonia production: the inefficiencies and capital costs of using natural gas to produce the ammonia in the first place (the ammonia becomes a value-added commodity, priced above its natural gas feedstock), mean that the overall economics are less advantageous. This chart, which supported a nuclear ammonia synthesis project that was well ahead of its time, was produced by the General Atomic Company in 1981, based on data developed by General Electric (GE).
Another project that was ahead of its time was Lockheed’s vision for ocean thermal energy conversion (OTEC, which generates power by using the difference in temperature between warm surface water and cool deep water). Over 40 years ago, in 1977, Lockheed produced the image on the right, which shows a “demonstration size OTEC ammonia plant-ship,” which would have used ammonia as an energy carrier (and also as the working fluid for the OTEC process) because, again, ammonia is the most economical way to produce and then distribute carbon-free energy at a large scale, over a long distance.
Again, in 1977, Lockheed’s economics were disadvantaged because the investment case relied upon concerns over peak oil and peak gas, and the value of conserving those fossil assets, and not upon the intrinsic benefits of carbon-free power generation and energy storage.
Today, we see increasing values for carbon-free energy and, simultaneously, decreasing cost curves for two crucial technologies: renewable (wind and solar) power generation and hydrogen production with electrolyzers. As the costs of both these technologies become more favorable, it suddenly makes commercial sense to synthesize ammonia from renewables instead of using fossil fuels.
This is the context for the Dualtower and its launch in 2018.
[December 2019 update: Arranged has published a new dedicated website for the Dualtower at https://www.dualtower.com]
Duplex Constructive Pressure Vessels
The Dualtower technology represents an innovation upon the traditional wind turbine because it uses “duplex constructive pressure vessels” as both the physical structure of the wind tower and the storage vessels for hydrogen and nitrogen, which it produces on-site using electrolyzers and air separation units. The gases are then periodically “harvested” (pumped onto a plant-ship), converted to ammonia, and transported to industrial areas.
To improve upon these conventional turbine towers, we present the Dualtower concept, built more easily and more efficiently. The Dualtower has the ability to store energy in it.
The Dualtower is made of CPVs, Constructive Pressure Vessels. These CPVs measure up to 13 meters and have diameters of only 1.6 meters. Transportation on standard trucks is therefore easier than when dealing with traditional towers.
The CPVs are interconnected to form four or more legs, stacked on top of each other to reach heights of up to 140 meters or more. Inside the CPV we can store compressed hydrogen gas at 200 bars. For a 100 meter Dualtower, this would result in a storage capacity of 5,000 kg of pure hydrogen.
Arranged BVBA website, Wind-Hydrogen Solutions video, accessed 03/13/2018
The design of these CPVs aims to address a range of challenges with hydrogen storage, including “steel embrittlement, sealing issues, and hydrogen gas permeation.” This is the duplex (double-walled) part of the design: the external parts of the vessel are structural and store nitrogen; the internal parts of the vessel are dedicated to safe and economical hydrogen storage.
Energy Harvesting with Green Ammonia
As with Lockheed’s original concept for OTEC, the Dualtower concept also envisions an ammonia plant-ship. This would visit many Dualtower installations, siphoning off the hydrogen and nitrogen gases, reacting them to produce ammonia on-board, and then distributing it to a center of power consumption.
Of course, as we are learning rapidly, there is nothing futuristic about large-scale renewable power solutions. The 30 GW, 5 km2, artificial energy island being proposed by a multinational consortium, 185 miles into the North Sea at Dogger Bank is no different – except that those project developers have yet to research the energy transportation benefits of ammonia, which would offer significant cost-savings compared to the proposed long-distance, high-loss power cables.