This investigation aims to compare the experimental and theoretical ammonia boiling heat transfer coefficient in a plate heat exchanger (PHE). Measured data were gathered during functioning of a single stage vapor mechanical compression refrigeration system placed in the Thermal Systems Research Center of the Technical University of Civil Buildings Bucharest (TUCEB). Experimental values fall within the range of 1377−3050 W/m2K. Theoretical values were obtained from 12 correlations confirmed by the literature to date, developed for similar working conditions. The experimental values are close to the theoretical ones for Shah and Jokar correlations applied for a vapor quality of 0.5. The theoretical values are in the range of 1440−2076 W/m2K and 1558−2318 W/m2K, respectively. Shah correlation predicted 82.35% of all data within the ±30% error band at an MAE value of 14.23%, and Jokar et al. predicted 76.47% of all data within the ±30% error band with an MAE value of 17.7%.

The impact of adding H2O2 in the fuel stream on the structure of non-premixed opposed-flow NH3/O2 flames was investigated numerically using a verified computational tool and validated mechanism. The results illustrate the dual role of the added H2O2 within the fuel jet. A small amount of H2O2 within the NH3 stream acted as a fuel additive that enhanced the reaction rate via reducing the kinetic time scale. However, a novel flame structure appeared when the H2O2 mole fraction within the fuel stream increased to χH2O2 > 16%. Unlike the pure NH3/O2 flame, a premixed reaction zone was discerned on the fuel side, in which H2O2 reacts with NH3 and played the role of an oxidizer. Then, the remaining NH3 that survived premixed combustion continues reacting with O2 and forms a non-premixed flame. As a result of this structure, it was shown that the well-established conclusion of “near-equilibrium” non-premixed flame analysis in which the strain on the flame is determined by the momentum fluxes... [more]

Anaerobic digestion (AD) and sewage sludge digestion (SD) plants generate significant quantities of ammoniacal nitrogen in their digestate liquor. This article assesses the economic viability and CO2 abatement opportunity from the utilisation of this ammonia under three scenarios and proposes their potential for uptake in the United Kingdom. Each state-of-the-art process route recovers ammonia and uses it alongside AD-produced biomethane for three different end goals: (1) the production of H2 as a bus transport fuel, (2) production of H2 for injection to the gas grid and (3) generation of heat and power via solid oxide fuel cell technology. A rigorous assessment of UK anaerobic and sewage digestion facilities revealed the production of H2 as a bus fleet transport fuel scenario as the most attractive option, with 19 SD and 42 AD existing plants of suitable scale for process implementation. This is compared to 3 SD/1 AD and 13 SD/23 AD existing plants applicable with the aim of grid inje... [more]

In this paper, a new integrated system of solid oxide fuel cell (SOFC)−gas turbine (GT)−steam Rankine cycle (SRC)−exhaust gas boiler (EGB) is presented, in which ammonia is introduced as a promising fuel source to meet shipping decarbonization targets. For this purpose, an SOFC is presented as the main power-generation source for a specific marine propulsion plant; the GT and SRC provide auxiliary power for machinery and accommodation lighting, and steam from the waste heat boiler is used for heating seafarer accommodation. The combined system minimizes waste heat and converts it into useful work and power. Energy and exergy analyses are performed based on the first and second laws of thermodynamics. A parametric study of the effects of the variation in the SOFC current density, fuel utilization factor, superheat temperature, and SRC evaporation pressure is conducted to define the optimal operating parameters for the proposed system. In the present study, the energy and exergy efficien... [more]

Micro gas turbines fit perfectly with the energy roadmap to 2050: on-site, small scale power generation, combined with heat recovery from exhaust gas, offers an opportunity to deploy primary energy saving and pollutant emission reduction. Moreover, their flexibility enables fuel switching from natural gas (NG) to carbon-free fuels such as hydrogen and ammonia. This study aims to explore the potential of direct combustion of ammonia in a micro gas turbine (MGT), from a thermodynamic point of view. A modeling procedure was developed to simulate the behavior of a 100 kW MGT operating at full and part-load. After validation with NG as fuel, an increasing fraction of ammonia was fed to the combustor to predict performance variations in terms of electric, thermal and total efficiency, as well as exhaust gas composition, for a load range between 40% and 100%. Additional relevant details, related to the interaction between compressor and turbine in the single-shaft arrangement, were discussed... [more]

One of the consequences of the conflict in Ukraine relates to the growing shortfall in global ammonia production. There are additional negative global impacts on the availability of fertilizers and prices of ammonia (NH3). The shortage in ammonia production does not only influence the agroindustry but also the global shipping industry, as ammonia is positioned as a promising zero-carbon fuel and as a storage and transport medium for hydrogen. There are plans underway to start ammonia production in Estonia to minimize the consequences of the import stop of Russian ammonia in the context of the Ukrainian crisis. This study investigated the Baltic Sea Region (BSR) ammonia market and analyzed the economic implications of building an ammonia plant within the BSR. Using fuzzy real options models as the conceptual framework, together with secondary data analysis, case studies and expert interviews, the authors chart possible courses for the construction of ammonia production facilities within... [more]

Three vanadium-based catalysts were used to remove high concentrations of nitrogen oxides, and the catalysts’ performance of de-NOx and anti-H2O under the high concentrations of NOx were investigated. The V-Mo-W/TiO2 catalysts were tested under 1500 mL/min gas flow (GHSV = 500 h−1, 2.4% NO2, 4.78% NH3, 13% O2, 4% H2O, 5% CO2) and characterized by BET, SEM, EDS, XRD, XPS, H2-TPR, and NH3-TPD; then, their physical and chemical properties were analyzed. The results showed that under the influence of H2O, the NOx conversion of the V-Mo-W/TiO2 catalysts remained above 97% at 200−280 °C indicating that the catalysts had high catalytic activity and strong water resistance. The analysis of the characterization results showed that the larger specific surface area of the catalyst, the higher acid content, stronger redox ability, and higher V4+ and V3+ content were the reasons for the high NOx conversion. The surface area decreased and the microstructure become smoother after the reaction, which... [more]

This study proposes a fuel supply system for dual-fuel propulsion engines using liquefied natural gas (LNG) and ammonia to control carbon emissions. The independent fuel supply system of LNG and ammonia is configured as a hybrid system. The operating pressure of the re-condenser is determined as a process variable according to the power consumption and flow rate of the non-condensable boil-off gas. The independent and hybrid systems are compared and evaluated through thermodynamic analyses, including specific power consumption (SPC) and exergy analyses, with respect to the fuel ratio and engine load. When the engine load is 100% in Case 1 for a 40% carbon reduction by 2030, the hybrid system exhibits an SPC reduction of 70% and exergy efficiency increase of 16% compared with the independent system.

Increased renewable energy production and storage is a key pillar of net-zero emission. The expected growth in the exploitation of offshore renewable energy sources, e.g., wind, provides an opportunity for decarbonising offshore assets and mitigating anthropogenic climate change, which requires developing and using efficient and reliable energy storage solutions offshore. The present work reviews energy storage systems with a potential for offshore environments and discusses the opportunities for their deployment. The capabilities of the storage solutions are examined and mapped based on the available literature. Selected technologies with the largest potential for offshore deployment are thoroughly analysed. A landscape of technologies for both short- and long-term storage is presented as an opportunity to repurpose offshore assets that are difficult to decarbonise.

The rising technology of green hydrogen supply systems is expected to be on the horizon. Hydrogen is a clean and renewable energy source with the highest energy content by weight among the fuels and contains about six times more energy than ammonia. Meanwhile, ammonia is the most popular substance as a green hydrogen carrier because it does not carry carbon, and the total hydrogen content of ammonia is higher than other fuels and is thus suitable to convert to hydrogen. There are several pathways for hydrogen production. The considered aspects herein include hydrogen production technologies, pathways based on the raw material and energy sources, and different scales. Hydrogen can be produced from ammonia through several technologies, such as electrochemical, photocatalytic and thermochemical processes, that can be used at production plants and fueling stations, taking into consideration the conversion efficiency, reactors, catalysts and their related economics. The commercial process i... [more]

Recently, the research interest regarding ammonia applications in energy systems has been increasing. Ammonia is an important hydrogen carrier that can also be obtained starting from renewable energy sources. Furthermore, ammonia can be used as a carbon-free fuel in combustion systems. In particular, the behavior of internal combustion engines (ICEs), fueled by ammonia, needs to be further investigated. The main disadvantage of this kind of fuel is its low laminar flame speed when it is oxidized with air. On the other hand, considering a spark-ignition (SI) engine, the absence of knock phenomena could allow a performance improvement. In this work, a 1D numerical approach was used in order to assess the performance and the operating limits of a downsized PFI SI engine fueled with pure ammonia. Furthermore, the reliability of the 1D model was verified by means of a 3D approach. Both throttled and unthrottled engine operation was investigated. In particular, different boost levels were an... [more]

Recently, ammonia is emerging as a potential source of energy in power generation and industrial sectors. One of the main concerns with ammonia combustion is the large amount of NO emission. Air staging is a conventional method of reducing NO emission which is similar to the Rich-Burn, Quick-Mix, Lean-Burn (RQL) concept. In air-staged combustion, a major reduction of NO emission is based on the near zero NO emission at fuel-rich combustion of NH3/Air mixture. A secondary air stream is injected for the oxidation of unburned hydrogen and NHx. On the other hand, in fuel-staged combustion, NO emission is reduced by splitting NH3 injection, which promotes the thermal DeNOx process. In this study, NOx emission characteristics of air-staged and fuel-staged combustion of partially cracked ammonia mixture are numerically investigated. First, the combustion system is modeled by a chemical reactor network of a perfectly stirred reactor and plug flow reactor with a detailed chemistry mechanism. Th... [more]

The constant development of civilization increases environmental pollution as a result of industrial activity and transport. Consequently, human activity in this area is restricted by regulations governing the permissible emission of harmful substance components into the environment. These include substances emitted by combustion engines, the use of which remains high in many industries. Consequently, research is being conducted to reduce the emissions of harmful exhaust components from existing and newly manufactured internal combustion engines. This research presents a used semi-truck engine, in which an innovative Compressed Natural Gas (CNG) supply system was applied. Using this fuel supply installation allows a mass exchange of the base diesel fuel to natural gas of up to 90%. The study evaluated the effect of the diesel/CNG exchange ratio for different engine operating conditions (engine load, speed) on the concentration of toxic components, such as CO, NO, NO2, NOX, as a sum of... [more]

This work presents an experimental study on the influence of the pilot flame characteristics on the flame morphology and exhaust emissions of a turbulent swirling flame. A reduced-scale burner, inspired by that fitted in the AE-T100 micro gas turbine, was employed as the experimental platform to evaluate methane (CH4) and an ammonia-methane fuel blend with an ammonia (NH3) volume fraction of 0.7. The power ratio (PR) between the pilot flame and the main flame and the fuel composition of the pilot flame was investigated. The pilot power ratio was varied from 0 to 20% for both fuel compositions tested. The NH3 volume fraction in the pilot flame ranged from pure CH4 to pure NH3 through various NH3−CH4 blends. Flame images and exhaust emissions, namely CO2, CO, NO, and N2O were recorded. It was found that increasing the pilot power ratio produces more stable flames and influences most of the exhaust emissions measured. The CO2 concentration in the exhaust gases was roughly constant for CH4... [more]

Nitrogen reduction reaction (NRR) and nitrate reduction reaction (NO3−RR) provide a potential sustainable route by which to produce ammonia, a next-generation energy carrier. Many studies have been conducted over the years, mainly emphasizing material design and strategies to improve catalytic performance. Despite significant achievements in material design and corresponding fundamental knowledge, the produced ammonia is still very limited, which makes it prone to bias. The presence of interferants (e.g., cations and sacrificial reagents), the pH of the solution, and improper analytical procedure can lead to the over or underestimation of ammonia quantification. Therefore, the selection of the appropriate ammonia quantification method, which meets the sample solution condition, along with the proper analytical procedures, is of great importance. In this review, the state-of-the-art ammonia quantification method is summarized, emphasizing the advantages, limitations, and practicality fo... [more]

Analyzing the entire liquefaction cycle, using a large temperature span with many degrees of freedom, may not always result in a practical solution. The objective of this paper is to investigate the feasibility of using an environmentally friendly refrigerant compound, ammonia, in the mixed refrigerant (MR) for the liquefied natural gas (LNG) pre-cooling cycle through thermodynamic performance, economic analyses and environmental impact. Fifteen cases studies within three major mixed refrigerants groups of MR-1, MR-2 and MR-3 were developed by adding ammonia to various molar compositions of lighter and heavier hydrocarbons. The thermodynamic analysis shows increasing ammonia’s concentrations in the mixed refrigerant by 10% had the largest enhancement on coefficient of performance (COP) of MR-1 by 0.67 and decreased the specific energy consumption of the pre-cooling cycle by 128 kJ/kg compared to the base case. Economic analyses revealed that the mixed refrigerant MR-1, with ammonia, me... [more]

In the future, ammonia is expected to become a carbon-free fuel for internal combustion engines. However, the flammability of ammonia is poorer compared to conventional fuels such as gasoline and diesel fuel. Pre-chamber jet ignition may be an effective way to ensure stable ignition and enhance the combustion of ammonia. In this paper, the effects of pre-chamber geometric parameters, including volume and orifice diameter, on the jet ignition and combustion processes were studied using visualization methods, combined with pressure acquisition. The results showed that ignition energy increased and the jet duration was prolonged with the increase in pre-chamber volume, resulting in a higher maximum pressure and pressure rise rate in the main chamber. The jet characteristics of a larger volume pre-chamber exhibited higher stability when the ambient parameters were changed. The smaller volume pre-chamber showed the superiority of a shorter flame propagation distance inside the pre-chamber,... [more]

The purpose of this study was to evaluate the performance of laboratory-scale biotrickling filters (BTFs) packed with composite filler and pine bark filler under different operating conditions in purifying mixed gas containing H2S and NH3. The composite filler was prepared with modified activated carbon and loaded with functional microbes, using the microbial immobilization technology combined with a nutrient sustained-release composite filler. The results showed that the composite filler could better adapt to low empty bed retention time (EBRT) and high inlet concentration than the pine bark filler. When EBRT was 40 s and the inlet load was 41 g/m3·h, the NH3 removal efficiency of the composite filler was kept above 80%, and when the inlet load was 61.5 g/m3·h, it could be stabilized at about 60%. When EBRT exceeds 34 s, the H2S removal efficiency of the two BTFs was maintained at 100%. Yet, when EBRT was 34 s, the H2S removal efficiency of the bark filler BTF dropped to <80%. The... [more]

Ammonia and phosphate, which are present in large quantities in waste streams such as livestock manure, are key compounds in fertilization activities. Their recovery will help close natural cycles and take a step forward in the framework of a circular economy. In this work, a lab-scale three-chambered microbial electrolysis cell (MEC) has been operated in continuous mode for the recovery of ammonia and phosphate from digested pig slurry in order to obtain a nutrient concentrated solution as a potential source of fertilizer (struvite). The maximum average removal efficiencies for ammonium and phosphate were 20% ± 4% and 36% ± 10%, respectively. The pH of the recovered solution was below 7, avoiding salt precipitation in the reactor. According to Visual MINTEQ software modelling, an increase of pH value to 8 outside the reactor would be enough to recover most of the potential struvite (0.21 mmol L−1 d−1), while the addition of up to 0.2 mM of magnesium to the nutrient recovered solution... [more]

The paper investigates the stability and bifurcation phenomena that can occur in membrane reactors for the production of hydrogen by ammonia decomposition. A simplified mixed model of the membrane reactor is studied and two expressions of hydrogen permeation are investigated. The effect of the model design and operating parameters on the existence of steady state multiplicity is discussed. In this regard, it is shown that the adsorption-inhibition effect caused by the competitive adsorption of ammonia can lead to the occurrence of multiple steady states in the model. The steady state multiplicity exists for a wide range of feed ammonia concentration and reactor residence time. The effect of the adsorption constant, the membrane surface area and its permeability on the steady state multiplicity is delineated. The analysis also shows that no Hopf bifurcation can occur in the studied model.

Slaughterhouse waste (SW) is potentially a good source of biomethane; however, its excessive ammonia content quickly causes inhibition of microbial processes. Our aim was therefore to remove ammonia from SW before putting it into a biogas reactor. Experimental 120 L pressure container was constructed to observe NH3 removal from diluted slaughterhouse waste at constant air flow of 144 NL/min, temperature 130 °C, and at different pressures: 300 kPa, 600 kPa, and 900 kPa. SW was first allowed to hydrolyze for 14 days at 38 °C. The SW was diluted with water (DSW) to 8.4% dry matter (DM) and forcibly aerated for 334 min. From the DSW, 0.7%, 3.8%, and 9% of initial total N were removed at 300 kPa, 600 kPa, and 900 kPa, respectively. However, the C/N ratio changed only slightly, from the initial 4.38 to 3.17, which is not a promising result for biomethanization. Further research on the presented system with the addition of bases might be promising to remove more ammonia.

Ammonia, which has advantages over hydrogen in terms of storage and transportation, is increasingly expected to become a carbon-free fuel. However, the reduction of fuel NOx emitted from ammonia combustion is an unavoidable challenge. There is the report that two-stage combustion with parallel independent jets could achieve Low-NOx combustion under ammonia/methane co-firing conditions. In order to further improve NOx reduction, we experimentally evaluated the effects of secondary air nozzle parameters, such as nozzle diameter and nozzle locations, on combustion characteristics in two-stage combustion of ammonia/natural gas co-firing using parallel independent jets. As a result of the experiments under various secondary air nozzle conditions, it was found that under the conditions where NOx was significantly reduced, the peak temperature in the furnace was observed at 300−500 mm in the axial direction from the burner, and then the temperature decreased toward the downstream of the furna... [more]

Methanol and ammonia are important chemical materials in the chemical industry. During the production of methanol and ammonia, a large amount of waste heat is released. The waste heat can be used to save energy and reduce CO2 emissions. In this study, pinch analysis is used to design the heat exchanger network (HEN) of pulverized coke (PC) chemical looping gasification coupled with coke-oven gas (COG) to methanol and ammonia (PCCLHG-CGTMA). The heat integration process is accomplished in two ways, as mentioned below. (1) The HENs in each of the three heat exchange units are designed individually; (2) the HENs of the three heat exchange units are treated as a whole and designed simultaneously. Compared to the HEN designed individually, when the HENs are designed as a whole, a total of 112.12 MW of hot and cold utilities are saved. In the HENs designed as a whole, the reduction in operating cost is sufficient to offset the increase in capital cost; the total annual cost (TAC) is reduced... [more]

CO2 biomethanisation is a rapidly emerging technology which can contribute to reducing greenhouse gas emissions through the more sustainable use of organic feedstocks. The major technical limitation for in situ systems is that the reaction causes CO2 depletion which drives up pH, potentially leading to instability and even digestion failure. The study aimed to test fundamentally derived predictive equations as tools to manage H2 addition to anaerobic digesters. The methodology used data from the literature and from experimental digesters operated with excess H2 to a point of failure and subsequent recovery. Two equations were tested: the first relating pH to CO2 partial pressure (pCO2), and the second extending this to include the influence of volatile fatty acids and ammonia. The first equation gave good agreement for data from studies covering a wide range of operating conditions and digester types. Where agreement was not good, this could usually be explained, and in some cases impr... [more]

The continuous increase in the number of stringent exhaust emission legislations of marine Diesel engines had led to a decrease in NOx emissions at the required level. Selective catalyst reduction (SCR) is the most prominent and mature technology used to reduce NOx emissions. However, to obtain maximum NOx removal with minimum ammonia slip remains a challenge. Therefore, new mixers are designed in order to obtain the maximum SCR efficiency. This paper reports performance parameters such as uniformity of velocity, ammonia uniformity distribution, and temperature distribution. Also, a numerical model is developed to investigate the interaction of urea droplet with exhaust gas and its effects by using line (LM) and swirl (SM) type mixers alone and in combination (LSM). The urea droplet residence time and its interaction in straight pipe are also investigated. Model calculations proved the improvement in velocity uniformity, distribution of ammonia uniformity, and temperature distribution... [more]