Green Ammonia’s Role in Decarbonizing Many Sectors: Its Global Impact and Optimization Associated With Renewable Energy Ammonia: Production and Diversity of Applications

Storing and transporting hydrogen is very expensive, thus its conversion to ammonia is very useful, due to its capacity to be stored in liquid form (-33.4ºC), at atmospheric pressure, or at room temperature (20ºC) at 8.59 bar. When liquefied, ammonia contains near 50% more hydrogen by volume than liquid hydrogen. There are several methods to produce hydrogen [1]. Green ammonia is obtained from green hydrogen from water electrolysis, nitrogen achieve in an air separation unit. The reputable Haber Bosch synthesis process produces ammonia via the chemical reaction 3H2 + N2 → 2NH3 [2]. The conversion rate for obtaining ammonia, after several passes, is close to 97% [3]. The gases employed must have a high degree of purity [4]. The before chemical reaction is reversible, as ammonia can be dissociated or “cracked” back into hydrogen and nitrogen via endothermic reaction. The cracker efficiency is estimated at around 80% [5,6].

The electrolysis process consumes most electricity, by a considerable margin [7]. For this reason, it is both much more efficient to obtain green hydrogen in locations that have a high renewable resource, like sun or wind. Today in the Canary Islands, due to the little flexibility of conventional generation and the lack of energy storage systems, some of the renewable generation is wasted, which gives this installation added value.

To obtain high levels of decarbonization, green hydrogen and ammonia need to be produced in large quantities (currently, global ammonia production is high, around 176 million tons per year). In particular, this can then be used in the manufacturing of cement, steel, ethylene and fertilizers [2]. As well as many other applications such as cleaning products, refrigeration, pharmaceuticals, and textile manufacturing [8], [9]. Ammonia is expected to be a competitive carbon neutral marine fuel [10].

Furthermore, ammonia can be used in gas turbines, fuel cells or as a combustion group [11]. Recently considerable research effort has been dedicated to combustion engines and fuel cells that employ ammonia and produce H2O and N2; thereby avoiding any greenhouse gas. The emission of NOX is negligible when reduction catalytic selection and reused ammonia are employed.

We must aspire to a complete decarbonization, for this reason we must use renewable electricity to recharge vehicles and operate heat pumps with which to obtain low temperature at high performance. There are other types of transport, which due to their size, or route, will not be easy to be electric. Just as there will be thermal processes that, because they need medium or high temperature, it will not be possible to use a heat pump. In addition, natural resources follow a seasonality, so they will be more abundant at one time and less at another.

An installation where many chemical components linked in the aforementioned processes are produced simultaneously is of great interest. Some components are input to form other components, thus the diversification of both production and storage will lead to a more efficient and profitable installation. Recent publications present a study in this line, although still in the context of steady-state modelling and optimization, taking into account the fluctuations of renewable energies [12].

The energy in multi-production will be stored in various ways and for different time frames, using comprehensive management software, and a SCADA network that will monitor all production systems, making optimal decisions in real time. The products can go directly to the market or be used as ‘ingredients’ in a subsequent refurbishment. Fresh water, N2 and O2 wouldn´t be used for energy purposes; but specifically, it could use in business requirements. Anyway, it is easy to find many papers that link desalination and storing water, as a way to store energy. A complete experimental multi-production plant has been recently proposed for Gran Canary, because the island has a strong water shortage and an abundance of sun and wind resources with locations near to the port, to the airport, and to the electricity grid [13].

Ammonia is an energy vector that is easy to market, store, transport and use in different ways and in many economic sectors. In order to achieve complete decarbonization, it is necessary to use sustainable electricity as renewable energy in all the processes involved in the production of ammonia. In particular, green hydrogen production. We emphasize that it is important to incorporate all the productions of the chemical components linked to the production of ammonia as possible. Optimal management of these integral installations requires the use of advanced multiobjective methods and artificial intelligence.

The author wishes to sincerely thank Canary institutions for their support.

No conflict of interest.

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