**1. Introduction**

Ammonia is a key hydrogen carrier with the potential to be utilised as a fuel, an intermediate product, and also a combo product (of hydrogen and nitrogen) for agricultural and pharmaceutical applications. The current chemical pathway for generating ammonia is through the Haber-Bosch (HB) methane reforming process [1, 2] which is highly dependent on the quality and price of natural gas. The Haber-Bosch process includes consecutive stages of methane reforming, followed by water-gas shift improvement and catalytic nitrogen fixation at high pressure and low temperatures

[3, 4]. All these stages are energy-intensive, far from equilibrium and release CO2 as part of the process due to the number of reformers existing in the process [5]. Hence, the HB process is not a sustainable cycle for nitrogen fixation [6] and ammonia production considering the technical challenges associated with environmental pollution and global warming [7].

The main issue with CO2 formation is the presence and adjacency of oxygen and carbon that can generate either CO2 via complete combustion, or CO through partial oxidation reactions as represented below:

$$\text{C}(\text{s}) + \text{O}\_2(\text{g}) \rightarrow \text{CO}\_2(\text{g}),\\\Delta G = -\text{394.3 kJ/mol}\,\Omega 27\text{\AA},\tag{1}$$

and

2*C s*ðÞþ *O*2ð Þ!*g* 2*CO g*ð Þ,Δ*G* ¼ �269*:*9 kJ*=*mol@273 K*:* (2)

Reactions 1 and 2 can proceed depending on the availability of the oxygen in the reactor, referred to as the "O/C" molar ratio. In conventional combustors and gaseous reactors, these reactions will always occur due to the direct contact of oxygen and carbon. Therefore, new combustion systems should be developed to avoid the production of Green House Gases (GHGs). Chemical looping technology [8] is a promising thermochemical pathway by which the direct contact between air and fuel is inherently hindered, thereby avoiding the production of CO2 and/or CO. In a chemical looping system, oxygen is transported between two reactors via an oxygen carrier (OC), which has the following properties:


A general chemical looping system includes reactors (for combustion [16], reforming [17], or gasification [18]) or as will be investigated here, it has three reactors (for ammonia/hydrogen production) [19] in which cyclic reduction and oxidation occurs.

There has been extensive research conducted on the potential of chemical looping systems for hydrogen production. For example, steam chemical looping gasification [20] or Co2-chemical looping gasification [21, 22] is one potential configuration that

#### *Green and Sustainable Chemical Looping Plasma Process for Ammonia and Hydrogen Production DOI: http://dx.doi.org/10.5772/intechopen.104095*

has been extensively investigated for H2-enrich fuel production. For example, He et al. [23] recently, proposed a new concept for steam chemical looping gasification to decrease the exergy destruction and to improve the cold gas efficiency of the gasifier. They used coal as the source of fuel and demonstrated that the efficiency of the cold gas can be as high as 86% in a three-stage chemical looping system. Also, the energy efficiency of 62.3% was calculated for the proposed plant. Pan et al. [24] used industrial waste such as gypsum and steel slag as the oxygen carrier to operate a steam chemical looping gasification system for generating H2-enriched fuel. Based on the FactSage calculation [25] and experimental validation, they found that the optimum temperature for the gasification is around 1023 K, with a feedstock/oxygen carrier ratio of 1 and steam to oxygen carrier of 0.6. In a similar study, Zhao et al. [26] assessed a novel chemical looping gasification concept in which NiFe2O4 and CuFe2O4 particles were synthesised and utilised as an oxygen carrier for hydrogen production. They identified the optimum operating conditions for both reduction and oxidation reactions and showed that the gas yield can be as high as 64.98 mol/kg and syngas quality can reach 2.79 which is suitable for gas to liquid and Fischer-Tropsch processes [27, 28].

CO2-chemical looping gasification is another process similar to dry gasification or pyrolysis which is used to generate syngas from coal or biomass. Recently, Xu et al. [22] developed thermodynamic models followed by conducting a series of experiments to assess the gasification of rice husk char sourced from pellet pyrolysis. They investigated the effect of various operating parameters including temperature, CO2 concentration, and quantity of the oxygen carrier on the performance of the system. They showed that the presence of CO2 can influence the performance of the gasification process. Also, they identified a mass transfer resistance within the char particles due to the change in the pore structure of the feedstock, which affected the gasification conversion. Zhang et al. [29] evaluated the effect of the red mud as the active oxygen carrier on the pyrolysis and gasification in a chemical looping gasification process. They utilised a fluidised bed reactor and investigated the effect of temperature (750–900°C) and also the ratio of the oxygen carrier to fuel (0.1–0.7) onthe syngas quality and chemical conversion extent of the fuel. The results indicate that red mud promoted the pyrolysis reaction and also intensified the gasification reaction. However, increasing the temperature decreased the syngas quality from 7.26 to 4.83. In another study, Zhang et al. investigated a novel hydrogen production process with integration of CaO - Ca(OH)2 thermal storage unit for gasification of coal and biomass using chemical looping of calcium. The thermal storage unit decreased the quantity of oxygen carrier required for the process and also improved the rate of hydrogen production. at optimum conditions of temperature and pressure, the gas yield was 17% higher than a normal process. The process was reported to have an energy conversion efficiency of 42.1% together with an exergy efficiency of 39.4%.

**Figure 1** represents schematic diagrams of two-stage and three-stage chemical looping technologies. In a three-stage chemical looping, it is assumed that the third reactor can dissociate the metal oxide into reduced metal directly and without any side reaction with air or other chemicals. However, in the two-stage chemical looping, the second reactor requires air to regenerate the oxygen content of the oxygen carrier.

As represented in **Figure 1a**, for combustion/gasification chemical looping systems, a reduction reaction occurs, in the fuel reactor between a metal oxide and a fuel, which is an endothermic reaction requiring an external energy resource to drive the reaction to its equilibrium. For example, for alumina oxide as an oxygen carrier in a

**Figure 1.**

*Chemical looping systems for a) two-stage reforming/combustion/gasification and b) three-stage ammonia/ hydrogen production.*

chemical looping reforming system for CH4, in the fuel reactor, methane reacts with aluminium oxide according to the following reaction:

$$\text{\ $}\text{\$ }\text{CH}\_4(\text{g}) + \text{Al}\_2\text{O}\_3(\text{s}) \rightarrow \text{2Al}(\text{s}) + \text{6H}\_2(\text{g}) + \text{\text{\ $}\text{CO}(\text{g})},\\\text{\Delta}\text{\text{\$ }\_{1773\text{K}}} = \text{5.1 kJ/mol} \tag{3}$$

or

$$\text{1.5}\text{CH}\_4(\text{g}) + \text{Al}\_2\text{O}\_3(\text{s}) \rightarrow 2\text{Al}(\text{s}) + \text{3H}\_2(\text{g}) + \text{1.5}\text{CO}\_2(\text{g}), \Delta\text{G}\_{1773\text{ K}} = \text{5 kJ/mol} \tag{4}$$

The Gibbs value (ΔG) of both reactions are relatively the same. Hence, to determine the dominant reaction in the fuel reactor, the thermodynamic condition of the reactor must be studied, which includes the operating temperature and pressure of the fuel reactor, and the quantity of Al/aluminium oxide (oxygen availability, i.e., the O/C ratio). In the air reactor, the reduced metal (Al for our reactor) reacts with an abundant amount of air via an exothermic reaction to generate aluminium oxide particles and vitiated air. The vitiated air can then be utilised for electricity generation via gas combined power cycles, while the re-generated metal oxides can be fed into the fuel reactor again to be reduced over reforming reaction. As shown in the literature review section, it was identified that chemical looping gasification (either with steam or CO2) is mainly used for generating syngas fuel. Accordingly, gasification includes the emission of CO2 and CO as the products of the process. However, in the present work, the chemical looping technology will be utilised to generate hydrogen and ammonia instead of hydrogen and carbon monoxide, thereby either reducing or eliminating the carbon footprint from the process.

With process modifications, as represented in **Figure 1b**, the chemical looping technology can be utilised for the co-production of ammonia and hydrogen referred to as "3-stage chemical looping ammonia production, 3CLAP". In the nitridation reactor, a metal nitride can be formed by a direct exothermic reaction between a metal and a pure nitrogen stream. Pure nitrogen steam can be sourced from an air separation unit or any vitiated air from other industrial processes that have 99% nitrogen purity. In the ammoniation reaction, the metal nitride reacts with steam to generate ammonia and/or hydrogen depending on the availability of the steam, temperature of the reaction, and quantity of metal nitride in the reactor. The metal oxide produced from the ammoniation reactor is then fed into a dissociation reactor to be dissociated into

*Green and Sustainable Chemical Looping Plasma Process for Ammonia and Hydrogen Production DOI: http://dx.doi.org/10.5772/intechopen.104095*

pure metal and oxygen. While metal is fed into the nitridation reactor, oxygen can be chilled, stored and used for other industrial/health applications.

The main bottleneck of the 3CLAP system is the dissociation reactor. This is because dissociating metal oxides, such as Al2O3, requires high temperatures (6273 K) to provide sufficient thermal driving force for such a highly positive Gibbs free energy of the "metal oxide to reduced metal reaction". Such high temperatures cannot be maintained by conventional reactors; hence, thermal plasma is suggested as a potential technology that can be utilised in this process.

In this chapter, the use of thermal plasma technology as a disruptive method is proposed to push the boundaries of dissociation reactors, and increase the chemical efficiency and performance of the process. Also, a renewable energy-friendly concept has been designed and simulated to demonstrate the feasibility of co-production of hydrogen and ammonia when integrated with photovoltaic solar energy generation. For the proposed process, Al/Al2O3 pair was used as it has reasonably large Gibbs free energy and a tendency to participate in the reaction, favourable thermophysical properties and stable thermodynamic phases during cyclic reduction and oxidation reactions. The Gibbs minimisation method coupled with thermochemical analysis was utilised to quantify the thermodynamic performance of the proposed system including hydrogen/ammonia ratio, exergy partitioned in the gas products, 1st law thermodynamic efficiency, self-sustaining factor, exergy partitioning factor, and renewable energy share (solar share).

## **2. Conceptual design of 3CLAP and its configuration**

#### **2.1 Process design**

**Figure 2** represents a detailed illustration of a three-stage chemical looping ammonia production system [19] designed for integration with a photovoltaic solar farm. In this process, three reactors for nitridation, ammoniation and thermal plasma

#### **Figure 2.**

*An illustration of the proposed process for hydrogen and ammonia production using the aluminium chemical looping process.*

are utilised amongst which thermal plasma is integrated with solar PV, while a heat recovery system is designed to recover heat from the reactors' outlets.

As already discussed, the energy of the thermal plasma is proposed to be supplied from renewable energy sources, such as solar photovoltaic combined with the electricity that can be generated from a built-in power cycle (steam combined cycle from the recovered heat of the processes), thereby improving the process sustainability and its energetic performance.

**Figure 3** shows the process model developed using the Aspen Plus software package for simulating the 3CLAP process operating with alumina. Alumina was selected because it has high thermal conductivity, good thermal response, and high Gibbs free energy. Also, in the model, the aluminium/aluminium oxide pair was assumed to remain solid in all process stages. Also, the separators were assumed to have 100% separation efficiency and a capacity to separate solid materials from gases. The steam flow rate in the steam power cycle was varied depending on the thermal loading of the heat recovery thereby enabling the steam turbine to operate at a constant stream inlet temperature.

The simulations were performed with the Aspen Plus software package coupled with Matlab and Homer [30–32] to simulate the photovoltaic panels. To simulate the reactors, the Gibbs minimisation method [33] was utilised for the nitridation, ammoniation, and thermal plasma reactors. Also, thermochemical equilibrium analysis [34] was used to conduct sensitivity analysis of the reactors against operating parameters such as temperature or feed ratios. All Gibbs's free energy parameters, enthalpy of reactions, and thermodynamic properties were extracted from Barin's Handbook [35]. In addition, the following assumptions were considered in the model:


**Figure 3.** *The Aspen plus model was developed for simulating the 3CLAP system.*

*Green and Sustainable Chemical Looping Plasma Process for Ammonia and Hydrogen Production DOI: http://dx.doi.org/10.5772/intechopen.104095*


These assumptions are used to simplify the analysis and provide a benchmark of an ideal process, However, in practice, an adjustment based on the specific design is required in the model to account for the effect of imperfections and non-ideal conditions on the physical performance of the system.

#### **2.2 Aluminium-oxygen-nitrogen thermodynamic system**

As a preliminary step, the change in the Gibbs free energy of each reaction must be evaluated at equilibrium conditions to ensure reactions are thermodynamically feasible in fuel or air reactors. Accordingly, to assess the thermodynamics of the 3CLAP system at equilibrium conditions, it is necessary to consider aluminium, nitrogen and oxygen and any oxidation states such as Al2O3 as part of the thermodynamic system. Since all reactors work at atmospheric pressure, the Gibbs minimisation analysis is assumed to be only a function of temperature. In the nitridation reactor, the following reaction occurs:

$$Al(s) + N\_2(g) \to AlN(s) \\ \Delta G = 579.1 \text{ kJ/mol} \tag{5}$$

The AlN formed in the reactor is then fed into the ammoniation reactor in which the following reaction is expected to occur:

$$2\text{AlN}(\text{s}) + 3\text{H}\_2\text{O}(\text{g}) \rightarrow \text{Al}\_2\text{O}\_3(\text{s}) + 2\text{NHS}(\text{g}), \Delta\text{G}\_{298\text{ K}} = \text{59.6 kJ/mol} \tag{6}$$

The key operating parameter here is the molar ratio of the reactants (steam/AlN ratio) which determines the final product of the reactor. Hence, depending on the availability of nitrogen and steam in the reactor, the following reaction can occur in the ammoniation reactor:

$$2AlN(\text{s}) + 3H\_2O(\text{g}) \rightarrow Al\_2O\_3(\text{s}) + 3H\_2(\text{g}) + N\_2(\text{g}), \Delta G\_{298\text{ K}} = 321.8\text{ kJ/mol} \tag{7}$$

The produced Al2O3 particles from both reactions are then fed into the thermal plasma reactor to be dissociated to aluminium and oxygen according to the following reaction:

$$Al\_2O\_3(s) \rightarrow 2Al(s) + 1.5O\_2(g) \\ \Delta G\_{6373\text{K}} = -16.4 \text{ kJ/mol} \tag{8}$$

The pure aluminium is then returned to the nitridation reactor, completing the cycle, while oxygen can be chilled and stored for industrial and/or hygienic applications. This reaction is endothermic, thereby high energy is required in the thermal plasma reactor. Also, there is a need to utilise a rapid quenching system to be able to create aluminium particles in a plasma environment. The rapid quenching system must be robust, with a small response time close to that of a plasma reactor (i.e., microseconds to milliseconds). Considering the existing

utilisation of plasma reactors for carbon black particle production [36], and the maximum temperature that a plasma reactor can reach [37], an arc thermal plasma is proposed. Combined with electricity produced via renewable energy sources, it decreases the emission of CO2 and carbon footprint to the environment. As shown in **Figure 4**, a comparison between the equilibrium mole percentages of gaseous products in the thermal plasma reactor before and after the quenching shows that a rapid quenching system can operate at T > 6373 K to avoid recombination of oxygen and alumina. As shown in **Figure 4b**, the stable thermodynamic components after rapid quenching are Al2O3 and Al, while before quenching, O(g), O2(g) and various solid phases of alumina are the dominant products of the thermal plasma.

#### **2.3 Calculation of the thermodynamic parameter**

To calculate the Gibbs free energy of the reactions and the change in the enthalpy of the proposed reactions, the following equation was utilised:

$$
\Delta G\_{R\_i} = \sum \Delta G\_{pm.} - \sum \Delta G\_{Rct.} \,. \tag{9}
$$

In this equation, G is the Gibbs free energy (kJ/mol), *pro* and Rct are acronyms for the products and reactants. If Δ*GRi* >0, it shows that the reaction is not thermodynamically feasible, while Δ*GRi* < 0 shows that the reaction will proceed towards equilibrium without any thermodynamic barrier.

The same equation was utilised for the enthalpy of reaction, which is as follows:

$$
\Delta H\_{R\_i} = \sum \Delta H\_{pm.} - \sum \Delta H\_{Rct.} \tag{10}
$$

In this equation, H is the enthalpy of reaction (kJ/mol). Δ*HRi* > 0 shows that the reaction is endothermic thereby requiring thermal energy to proceed to the equilibrium state. However, Δ*HRi* < 0 simply shows that reaction is exothermic, thereby releasing thermal energy during the reaction.

The self-sustaining parameter is defined as the ratio of the energy recovered and produced by the power block to the energy demand from the thermal plasma reactor defined with the following equation:

#### **Figure 4.**

*Formation and stability of different phases and compounds in the thermal plasma reactor before and after the rapid quenching process for metals and powders [38].*

*Green and Sustainable Chemical Looping Plasma Process for Ammonia and Hydrogen Production DOI: http://dx.doi.org/10.5772/intechopen.104095*

$$\text{SSF} = \frac{\mathcal{W}\_{Tur.}}{E\_{TPR}}.\tag{11}$$

In the above equation, *WTur:* is the amount of energy recovered and converted to electricity using a multi-stage turbine from a built-in power block and *ETPR* is the energy demand from a thermal plasma reactor.

The exergy partitioning factor is the amount of energy that can be stored in form of chemical exergy in the products of the plant and can be calculated using the following equation:

$$EPF = \frac{\dot{n}\_{H2}LHV\_{H2} + \dot{n}\_{NH3}LHV\_{NH3}}{\sum \Delta H\_{net, reactants,1,2,3}}.\tag{12}$$

Here, *n*\_ *<sup>i</sup>* is the mole flow of component I, LHV is the acronym defined for the lower heat value for either hydrogen or NH3. The molar ratio of the steam to AlN is also defined as φ according to the following equation:

$$\text{op} = \frac{[H2O]\left(\frac{kmol}{h}\right)}{[AlN]\left(\frac{kmol}{h}\right)}\,. \tag{13}$$

The above thermodynamic parameters were used in the calculations to assess the energetic performance and thermodynamic potential of the system.

### **3. Result and discussion**

#### **3.1 Nitridation reactor**

**Figure 5** represents the effect of temperature on the Gibbs free energy of the reaction in the nitridation reactor. As can be seen, by increasing the temperature of the reactor, for example from 250 K to 1000 K, the Gibbs free energy is decreased by �25% recorded at atmospheric pressure. Also, the enthalpy of the reaction shows a

**Figure 5.** *Variation of the Gibbs free energy and enthalpy of the reaction with the temperature of the nitridation reactor.*

linear weak dependence on the temperature of the reactor because it is an exothermic reaction. For example, increasing the temperature from 250 K to 1000 K causes only a 1.4% decrease in the enthalpy of the reaction. Also observed, was a slight drop in the enthalpy around T = 750 K due to the phase change in the AlN (solid) to the eutectic and liquid phase. Notably, to avoid complexity in the operation and reduce potential plant costs associated with maintaining the operating pressure, all reactors are designed at atmospheric pressure. This is advantageous as it can reduce erosion and corrosion related to high-pressure gaseous reactions in the reactors. It is worth mentioning that reaction 5 is spontaneous, hence it is not energy-intensive and does not require a continuous energy source to maintain its temperature. It can proceed to equilibrium due to the heat released during the reaction. Also, considering the melting temperature of the aluminium, the operating temperature of the nitridation reactor is set to the minimum with a 50 K buffer zone to avoid any liquid metals and clogs forming inside the pipes and walls of the nitridation reactor. Thus, T < 700 K is designated as a suitable temperature for the operation of the reactor. These findings are in good agreement with the results obtained in the literature for the hydrolysis reactors. Wang et al. [39] showed that a similar reaction can be driven with a non-equilibrium hydrolysis reactor in a system referred to as "Chemical Looping Ammonia Generation" (CLAG).

#### **3.2 Ammoniation reactor**

The generated AlN from the nitridation reactor is fed into the ammoniation reactor to be blended and react with steam for ammonia generation. As already elaborated in Section 3, reactions 6 and/or 7 occurs in this reactor depending on the operating conditions and molar ratio of steam to AlN feed. As represented in **Figure 6**, the results of the equilibrium analysis for the ammoniation reactor showed that while the dominant reaction in the reactor is reaction 6, it is an exothermic reaction. Also, there is a weak dependence of the performance of the reactor on temperature. Also, the Gibbs free energy for the reactions showed that with an increase in the temperature of the reactor, the ΔG value increases by 30%.

For example, at T = 900-1000 K, 300 kJ/mol < ΔG < 400 kJ/mol. This shows that the reaction is highly spontaneous in the reactor at this operating temperature

**Figure 6.** *The variation of the Gibbs free energy and enthalpy of reaction with the temperature of the ammoniation reactor.* *Green and Sustainable Chemical Looping Plasma Process for Ammonia and Hydrogen Production DOI: http://dx.doi.org/10.5772/intechopen.104095*

region while at any other operating temperature < 1000 K, the reaction is still feasible and can reach equilibrium without any phase change occurring inside the reactor. Hence, the temperature of the reactor must be chosen wisely to avoid phase change and melting in the reactor. Overall, the upper limit operating temperature for the reactor is 1000 K in which particles are still solid, the Gibbs free energy is negative and the reaction is exothermic.

As shown in **Figure 7**, the molar ratio of steam/AlN (φ value) is another key operating parameter that can control the chemical performance of the ammoniation reactor. Production rates of H2 and NH3 are nonlinearly dependent on the temperature of the ammoniation reactor, and it is proportional to the value of the steam to AlN ratio. For example, the final product from the ammoniation reactor could be determined by the φ value. As an example, at T = 540 K, for 0.5 < φ < 1, the dominant product of the reactor is hydrogen with H2/NH3 ratio 25, while at 1 < φ <3, the H2/NH3 ratio significantly increases from 25 to 50 showing that production of ammonia is severely suppressed by increasing the amount of steam in the system. This is because, for larger φ values, the hydrogen and oxygen content in the reactor is increased which drives reaction 7 towards equilibrium. As a result, hydrogen production increases in the reactor. The best operating temperature range and φ values for producing hydrogen were at T > 500 K and φ = 3. While for ammonia production, not only the temperature of the reactor should be close to 300 K, but also the φ value should be below 0.5. The aluminium oxide produced in this reactor is then fed into the thermal plasma reactor to re-generate the reduced aluminium particles for completing the cycle and to provide the feed for the nitridation reactor. It is worth mentioning that in the hydrogen dominant operating region, still ammonia is produced, however, the mole fraction of the H2: NH3 is 1:300 or (less than 0.3%) that can be separated from the hydrogen stream using a robust aqua-ammonia condenser already developed in the literature [40] or hydrogen/ammonia membrane separators [41]. It is worth mentioning that alumina has already been identified as an oxygen carrier in a two-stage chemical looping ammonia production at 1773 K and 0.1 MPa using steam hydrolysis reaction. Galvez et al. [42] showed that both reactions can occur at atmospheric pressure without any added catalysts. They also advised that steam hydrolysis, which is an endothermic reaction, can be driven using concentrated solar thermal.

**Figure 7.** *Variation of the H2/NH3 ratio with φ values at various operating temperatures inside the ammoniation reactor.*

#### **3.3 Thermal plasma reactor**

In a plasma reactive system, the reactions are driven by a non-conventional energy source. A plasma stream includes (but is not limited to) ions, charged particles, neutral species, radicals, and spinning-vibrational excited species with relatively high Gibbs free energy (ΔG) that participate in the reaction. The bombardment of any neutral species by electrons (electron avalanche) and charged species in plasma can stimulate the material to aggressively participate in the reaction. A thermal plasma is a type of reactive plasma configuration in which reactions occur at very high temperatures typically in the range 6000 K < T < 10,000 (for example for arc plasma reactor). The high temperature of the plasma reactor ensures that the reactions can proceed to equilibrium, thereby reaching a high chemical conversion extent and chemical efficiency (generally >99%). The results of the modelling for the Gibbs free energy and enthalpy of reaction, **Figure 8**, shows that at T > 6273 K, there is an inflexion point for the Gibbs free energy to a negative ΔG making the reaction thermodynamically feasible in the plasma reactor. For temperatures above 6273 K, an increase in the temperature of the thermal plasma reactor leads to an increase in the magnitude of the Gibbs free energy indicating that this reaction is more favourable at high-temperature conditions. Also, the enthalpy of the reaction is >0 (across the entire temperature range) implying the reaction is endothermic and requires thermal energy to be driven towards equilibrium. At such high temperatures, it is expected that all species exist in the gaseous phase thereby requiring a quenching system to generate solid particles from gaseous metals.

#### **3.4 Effect of pressure**

The proposed 3CLAP process at atmospheric pressure has several advantages:

1. there is no complexity associated with maintaining the pressure and temperature of each reactor. Since pressure and temperature can have a synergic or nonsynergic effect on the performance of the reactors (e.g., nitridation and ammoniation), the operation of the reactors at atmospheric pressure can minimise the complexity and technical challenges due to the temperature– pressure interaction in the reactors.

*Green and Sustainable Chemical Looping Plasma Process for Ammonia and Hydrogen Production DOI: http://dx.doi.org/10.5772/intechopen.104095*


#### **3.5 Thermodynamic characterisation of the process**

The performance of the system based on the 1st law efficiency, nitrogen economy, steam consumption, exergy partitioning factor and self-sustaining factor are depicted in **Figure 9**. As can be seen, the 3CLAP process transport exergy in form of chemical exergy by partitioning it in hydrogen and ammonia as the main products of the system. Hence, a parameter is defined as Exergy Partitioning Factor to account for the fraction of energy that is partitioned in the ammonia and hydrogen. Additionally, using a heat recovery system, the energy recovered from outlet products and streams are recovered and converted into steam to produce electricity for supplying the energy demanded by the thermal plasma reactor. Hence, a parameter is defined as the Self-Sustaining Factor (SSF) defined as the ratio of electricity produced by the heat recovery block to the energy demand of the thermal plasma reactor. The results showed that the designed process can achieve an SSF value of 0.11 without incorporating renewable energy or external energy resources.

Also, it was found that the nitrogen and steam economy of the process is >1.8 and < 1 showing that the proposed system can deliver 1 mol of ammonia at cost of

**Figure 9.** *The effect of the temperature of the thermal plasma reactor on self-sustaining and exergy partitioning factors.*

consuming 2 mol of nitrogen and < 1 mol of steam. Since steam production costs vary depending on the source of water, the proposed system can offer a plausible Levelized Cost of Energy and techno-economic value for ammonia production. Notably, to produce ammonia, the temperature of the ammoniation reactor should be as low as 300 K to promote the economic viability aspects of the ammoniation reactor.

#### **3.6 Renewable energy penetration - integration with solar energy**

In this section, an example of hybridisation of the 3CLAP with solar photovoltaic energy is represented to calculate the solar share and to obtain the installation capacity required for the PV panel. It further elaborates on which fraction of solar energy can penetrate the system, thereby reducing the CO2 emission from the plant. While the entire thermodynamic plant is a zero-carbon process, energy demands for the reactors can contribute greenhouse gases to the environment. Thus, it is critical to demonstrate how the proposed process can operate with renewable energy. **Figure 10** represents the frequency of energy demand (**Figure 10a**) and its diurnal/annual fluctuations (**Figure 10b**) from the plant calculated for a case study to produce 1 tonne/day of ammonia. The energy algorithm of the plant was defined such that using renewable energy and energy produced by the built-in power cycle are prioritised. However, if both sources cannot meet the demand of the process, the energy from the grid is ramped up to meet the demand.

A 2.1 MW generator was calculated for the grid network to adapt to demand fluctuations. Considering a chain of 4 kW DC to AC converters, the performance of the system for a location at Geelong, Victoria in Australia (where solar reception is moderate) was evaluated. As can be seen, the solar share increases with an increase in the PV installation capacity reaching 28.4% at PV installation capacity of 5 MW and 33.6% at installation capacity of 10 MW. Notably, the solar share can be improved by adding battery storage units to the system to address the intermittent behaviour of solar irradiance. However, a detailed assessment of renewable energy penetration is not part of the main goal of this study.
