Process integration, energy and exergy analyses of a novel integrated system for cogeneration of liquid ammonia and power using liquefied natural gas regasification, CO2 capture unit and solar dish collectors

https://doi.org/10.1016/j.jece.2021.106374Get rights and content

Highlights

  • Integrated Haber-Bosch process, steam methane reforming and air separation unit.

  • CO2 capture unit were employed to hydrogen purification.

  • LNG regasification and solar collectors used to supply the utility of the system.

  • This structure produced 3.042 kg/s ammonia, 13,300 kW power and 2.762 kg/s CO2.

  • Total exergy efficiency & exergy destruction of the system were 57.36% & 116,763 kW.

Abstract

One of the most common methods of ammonia production used in the last hundred years is the Haber-Bosch process. The basis of this process is hydrogen and nitrogen, which must be supplied in different ways. In the present study, a novel integrated structure for tri-generation of liquid ammonia, carbon dioxide, and power through the Haber-Bosch process, amine-based carbon dioxide capture cycle, and absorption-compression refrigeration cycle is developed. The required nitrogen of this process is supplied by the cryogenic air separation system with the help of the liquefied natural gas regasification process and the required hydrogen is supplied through a steam methane reforming process with the help of an amine-based CO2 capture cycle. The needed cooling by the Haber-Bosch process at − 50 °C is also provided by the absorption-compression refrigeration cycle. The required power of the whole system is generated through the organic Rankine cycle. Solar energy heat source and power plant exhaust flue gas are used to supply heat to different parts of the integrated system. Simultaneous design of units and integration of processes reduces the number of required equipment and reduces energy consumption, thus increases the system efficiency. This hybrid structure produces 3.042 kg/s ammonia as the main product, 13,300 kW power, 2.762 kg/s CO2, 3.929 kg/s pure oxygen, and 11.31 kg/s hot water as byproducts. The total energy and exergy efficiencies of the combined structure are 46.95% and 57.36%, respectively. Exergy investigation of the combined system illustrates that the highest rate of exergy destruction includes heat exchangers (46.18%), collectors (18.45%), and towers (14.97%) of the total exergy destruction. Sensitivity analysis is performed on the sensitive parameters of the system and its results are reported.

Introduction

Ammonia is a natural substance that is environmentally friendly. It has excellent thermodynamic and thermophysical properties, but has moderate toxicity and is almost flammable. For this reason, the necessary precautions must be taken to use it. Ammonia is also a chemical with an alkaline property, colorless, lighter than air with a pungent odor, which is widely used in industry and agriculture. Ammonia is the second most-produced chemical in the world, which can be obtained from fossil fuels, biomass, or other renewable sources. Its main advantages are the refrigeration effect, lower cost per unit of stored energy, and high bulk energy density, which is comparable to gasoline in this regard [1]. More than 200 million tons of ammonia are produced annually worldwide. About 80% of the produced ammonia worldwide is used to make nitrogen-based fertilizers. Global ammonia capacity is projected to increase from 205 million tons in 2010 to about 239 million tons by 2020, representing an increase in production to more than 33 million tons, equivalent to a 16% increase over a decade [2]. Also, because ammonia is a good source of hydrogen, it has the potential to play an important role in the future hydrogen economy [3]. Although a large percentage of global ammonia production is currently used in fertilizer production, it can be used as fuel for vehicles and space heating. Ammonia is an excellent energy storage medium that has the necessary infrastructure for its transportation and distribution in many countries [4]. It is a carbon-free substance and also has a high-octane content; there is now a greater tendency to use ammonia as a fuel. Zamfirescu et al. [5] analyzed the potential benefits and technical advantages of using ammonia as a sustainable fuel in vehicles. Also, the cooling effect of ammonia is a valuable side advantage that shrinks the engine cooling system and provides air conditioning. Ammonia is a source of promising energy storage that can meet hydrogen-related challenges. Siddiqui et al. [6] investigated a new ammonia synthesis and solar-based fuel cell system. They also used thermodynamic and exergy tools to analyze the system. The system uses the extra power generated by a solar photovoltaic system to synthesize ammonia, and besides, in the absence of solar radiation, a direct ammonia fuel cell is used to generate electricity. The total exergy efficiency was in the range of 16.44–16.67%, while the total energy efficiency during the year varies between 15.68% and 15.83%. Ammonia is also considered as an energy storage source and hydrogen source because the hydrogen content in liquid ammonia is 17.6% by weight, which is about 12.5% by weight in methanol [7]. Patil et al. [8] proposed a new solution based on ammonia energy buffer to solve the problems caused by solar energy rotation and uncertain energy demand and balancing solar energy production. A completely environmentally friendly system that is no carbon emissions upstream or downstream. If necessary, this ammonia was converted to power through ammonia generators. Also, excess ammonia can be used directly as chemical fertilizers. Lipman et al. [9] studied the use of ammonia as a fuel for transport vehicles in an internal combustion engine and concluded that this fuel has the potential to play an important role in the future hydrogen economy because ammonia is easily broken down and used to produce hydrogen in fuel cells. Rouwenhorst et al. [10] compared and evaluated alternatives to hydrogen production, nitrogen production, ammonia synthesis, ammonia separation, ammonia storage, and ammonia combustion. Also, a conceptual process design, based on temperature and pressure optimization on existing and proposed technologies, is presented for the islanded ammonia energy system. The use of ammonia as fuel in fuel cells has the advantages of low pollutant emissions and high efficiency. Ammonia is a carbon-free fuel that emits no carbon dioxide (CO2) during combustion, thus reduces the risk of NOx emissions in fuel cell applications because no direct mixing between oxygen and ammonia occurs [11]. Yapicioglu et al. [12] discussed the use of ammonia as a fuel in industrial generators. Also, different methods of ammonia production are studied in terms of potential benefits and challenges from economic, social, and environmental perspectives. In addition, ammonia synthesis methods were compared and evaluated based on technical, economic, and environmental performance criteria. Anaerobic ammonium oxidation (anammox) can be turned into an economical and environmentally friendly technology with a high potential for bioenergy recovery. Therefore, Arora et al. [13] thoroughly investigated the inhibition mechanism, threshold concentration and control strategies to ensure the proper functioning of the anammox system. Finally, the main bottlenecks and innovative perspectives for achieving the global application of anammox-based technologies were presented.

For the past hundred years, the Haber-Bosch process has been used to convert nitrogen in the atmosphere into ammonia. Although there are many risks to the Haber-Bosch process due to high temperatures and pressures, the very low cost of iron catalysts makes the Haber-Bosch process more cost-effective than other processes. Therefore, the usual route of ammonia production is by the Haber-Bosch process [14]. As a result, NH3 can be produced through the synthesis of nitrogen and hydrogen in the Haber-Bosch process. The basis of this process is hydrogen and nitrogen, which must be supplied in different ways [15]. To supply the required nitrogen in the Haber-Bosch process, it is possible to do so by separating the air, because the highest percentage of the constituent elements of the air in the atmosphere are nitrogen and oxygen. Other elements such as helium, krypton, xenon, argon, and some hydrocarbons are also reported. Since air is a rich source of nitrogen and oxygen gases, so it can be used to produce high purity of these compounds for industrial purposes. Inlet pressure and boiling points are the main and influential factors in the nitrogen separation process. Therefore, nitrogen can be separated from the airflow by reducing its temperature to the desired boiling point [16]. Giovanni et al. [17] designed an innovative system for the production of green ammonia using renewable energy sources. In the study, an improved Haber Bosch Reactor was used to produce hydrogen, and a solid oxide electrolyzer (SOE) was used to synthesize ammonia. An air separator has also been introduced to provide pure nitrogen. SOE and HBR both operate at 650 °C. Morgan et al. [18] proposed an integrated structure for the production of carbon-free ammonia fuel using wind energy on Monhegan Island. In the proposed system, the climate is used directly by traditional air separation units (ASUs), alkaline electrolyzers, mechanical vapor compression desalination, and a Haber-Bosch synthesis ring. Osman et al. [19] simulated an integrated power plant including desalination, electrolysis, air separation, refrigeration, and storage in ASPEN PLUS software and technically and economically optimized the production of renewable ammonia as a promising carrier option. The specific energy consumption and electrical process of this integrated system were 10.43 kWh/kg-NH3 and 37.4%, respectively.

On the other hand, the required hydrogen for the Haber-Bosch process must be provided. The most important methods of hydrogen production are water electrolysis, coal decomposition, and hydrocarbon conversion. Of course, on an industrial scale, the conversion of hydrocarbons to hydrogen is possible with three methods, which are steam reforming, partial oxidation, and auto thermal reforming. However, in the past, the main source of hydrogen was coal gasification, but the fall in oil prices pushed hydrogen production towards natural gas vapor reform [20]. The proper efficiency and cheapness feed of this process make it more economical than other hydrogen production methods [21]. About half of the world's hydrogen is produced by methane reforming in the presence of water vapor so that in 2007, about 80% of total ammonia synthesis used natural gas as the main material and the remaining 20% from coal [22]. Ghorbani et al. [23] developed a new integrated system including air separation units, Fischer-Tropsch synthesis unit, steam power plant, and Rankine power generation cycle for producing power and liquid fuels using liquefied natural gas regasification and solar collectors. The liquefied natural gas (LNG) regasification and solar collectors were used to provide cooling and heating of the integrated structure, respectively. The integrated system and related processes were simulated and designed using HYSYS and TRNSYS software and MATLAB programming. The results showed that the integrated structure produced 200.6 MW of power and 78.88 kgmol/h of liquid fuel. In addition, total thermal efficiency and total exergy efficiency were 42.36% and 64.72%, respectively. Andersson et al. [24] conducted a technical and economic evaluation of ammonia production through integrated biomass gasification in a pulp mill. In this method, the produced hydrogen was provided through biomass gas supply and as a result, ammonia was produced by using the synthesis of nitrogen and hydrogen in the Haber-Bosch process. Biomass degassing and subsequent NH3 production were modeled using ASPEN PLUS software. Emelin et al. [25] developed the process of bio-ammonia production from syngas resulting from the gasification of the African Rachis palm and performed its technical and economic evaluation. According to the results, 1630,000 metric tons of Rachis palm per year produced a single gas with 99% hydrogen concentration, which annually generates 35,755 million tons of bio ammonia. Hosseini et al. [26] introduced and developed an integrated system consisting of a molten carbonate fuel cell (MCFC) with steam methane reforming (SMR), methanol synthesis process (MSP) with distillation process, and combined heat and power plant (CHP) including gas turbine, Rankine cycle (RC), the organic Rankine cycle (ORC) and the Regional Heating Line (DH). In this system, the SMR unit at 800 kPa and 600 °C was used to generate the required artificial gas by MCFC and MSP. The simulation was performed by ASPEN HYSYS software. This structure produced 110,544 kW of net power, 271.7 kgmole/h of pure methanol (99.9%), and 65,398.7 kgmole/h of hot water at 80 °C.

Nowadays, fossil fuels provide about 80% of the world's primary energy sources and generate more than 60% of the world's electricity. However, the combustion of fossil fuels leads to the emission of air pollutants and the release of large amounts of CO2 into the atmosphere. From a global environmental perspective, CO2 uptake is critical to reducing the threat of global warming. On the other hand, to purify the output hydrogen from the SMR, carbon dioxide must be adsorbed. The best-known way to capture CO2 is by removing CO2 by adsorbing it to amino solutions. Amines are weak alkali compounds that react with CO2 and are easily broken down under gentle heat and amine recovery occurs [27], [28]. As regards most of the world's energy is still supplied through fossil fuels, the need for sustainable development requires the application of effective methods to reduce the environmental impact of fossil fuel use. The CO2 capture and storage technology is currently one of the best ways to directly reduce carbon dioxide emissions into the atmosphere [29]. However, carbon dioxide adsorption systems based on the combustion process are generally divided into three categories: pre-combustion adsorption, post-combustion adsorption, and oxygen combustion [30], [31]. Liu et al. [32] investigated the aggregation effect of carbon dioxide absorption and compression system and compression on a natural gas combined cycle power plant. They reduced the efficiency drop due to systems aggregation to 1.31% by using a 38% ratio of exhaust gas recirculation system as well as the use of shock wave ultrasonic compressors and recovering waste heat from the compressors' intermediate coolers. Daniel et al. [33] evaluated the efficiency, cost of exergy, and cost allocation of CO2 emissions for an integrated syngas and ammonia production plant. This evaluation was performed from steam methane modification (SMR), CO2 capture and compression units, as well as ammonia synthesis and purge gas treatment. The total exergy efficiency of the ammonia project is estimated at 66.36% by recovering the fuel and hydrogen-rich gases in the purge gas treatment process. Biliyok et al. [34] evaluated the integration of a 440 MW natural gas combined cycle with a carbon dioxide capture and compression system. The results showed that by using the exhaust gas recirculation system with a ratio of 40%, it has recovered 10 MW of power plant waste. The use of CO2 as sustainable energy carriers leads to near-zero emissions levels. By performing the hydrogenation process, CO2 was converted to methanol, which has many environmental benefits. Bayomie et al. [35] investigated different process configurations for hydrogenation of CO2 to methanol from industrial flue gases. This process was modeled with ASPEN HYSYS simulation software. In addition, sensitivity analysis was performed to evaluate the effect of different parameters on reactions and total efficiency. Farajollahi et al. [36] used the integration of a thermal power plant with carbon dioxide absorption and compression systems to increase the efficiency of the power plant and also reduced its efficiency loss from 9.29% to 5.1% by applying organic Rankine cycle to recover waste heat sources. Absorption-compression refrigeration systems were widely applied to use waste heat in industrial processes and produce cooling and liquefaction. Ghorbani et al. [37] developed an innovative structure including cryogenic/amine scrubbing biogas upgrading process for cogeneration of CO2 and methane mixed fluid cascade liquefaction cycle. The specific power consumption was 0.476 kWh/kg LNG. The thermal energy and exergy efficiencies were 73.11% and 72.58%, respectively. The return period and prime cost of the product are 3.675 years and 0.2399 US$/kg LNG, respectively. Han et al. [38] proposed a hybrid absorption-compression refrigeration system based on the medium temperature waste heat, the fluid of which is water and ammonia. The novel integrated structure showed proper performance due to the cascading use of waste heat of subsystems. So that with the same entering waste heat, the proposed system produced 46.7% more cooling than conventional water and ammonia absorption refrigeration. Chen et al. [39] proposed a low-temperature novel heat-driven absorption-compression refrigeration system, including a new water/ammonia power cycle, an ammonia/water absorption refrigeration cycle, and a CO2 compression refrigeration unit. In recent years, the development of technologies for waste heat recovery has accelerated. Exhaust gases are one of the largest sources of waste heat in industries. The energy of this type of wasted heat can be recovered and used in three different ways: 1- energy recovery for electricity generation, 2- heating of buildings and processes through heat pumps or heat exchangers, 3- cooling of buildings and refrigeration of processes through thermal-driven systems [40]. As a result, the existing flue gas of power plants can be used for temperature applications. For this purpose, Zhou et al. [41] studied the launching of the organic Rankine cycle using waste heat recovery from flue gas at low temperatures. The results illustrated that the maximum output power of the expander is 645 W. Also, the cycle and heat recovery efficiencies were 8.5% and 22%, respectively.

So far, several studies have been performed to produce liquid ammonia using the natural gas reforming method and the air separation unit. External energy sources are needed to supply power, heat, and refrigeration to the integrated structure of liquid ammonia production, which leads to an increase in equipment. The objective of the studies reported in the literature is the simultaneous optimization of the required thermal energy consumption, power consumption, economic price of the hybrid system, and environmental problems. Based on a recent literature review, so far no comprehensive method has been developed for the production of liquid ammonia using LNG regasification and renewable energy. This research has developed a new method for producing liquid ammonia in order to store it for a long time as a clean and portable fuel to distant places with the methods of thermal integration between processes and pinch analysis in heat exchangers. This paper presents a new integrated cycle of ammonia production using the Haber-Bosch process, air separation unit, LNG regasification, reforming of natural gas obtained from LNG regasification. A carbon dioxide capture (CO2 capture) unit was also installed to increase the degree of hydrogen purity. Also, the required cooling for ammonia liquefaction is provided by the absorption- compression refrigeration cycle, which receives its desired heat from the flue gas leaving the power plants.

Section snippets

Process description

The steam methane reforming process and air separation unit are used to supply hydrogen and nitrogen in the ammonia production process, respectively. High-temperature hot utility, power, and cooling are used in the steam methane reforming process, air separation unit, and ammonia liquefaction cycle, respectively. Fig. 1 shows the process flow diagram (BFD) of the novel integrated structure for the production and liquefaction of ammonia using the Haber-Bosch process, amine-based carbon dioxide

Exergy analysis

Exergy investigation is an engineering tool that is utilized to examine the thermodynamics of the process and specify the maximum amount of useful work that can be achieved from a certain amount of input energy. The exergy analysis, irreversibilities that increase the wasted work of system equipment are identified and their impact on process efficiency is determined. The dead state is the same environmental conditions that are usually considered to be 25 °C and 1 bar [50], [51]. The exergy rate

Results and discussion

In this paper, an innovative combined structure for the tri-generation of liquid ammonia, carbon dioxide, and power using the ammonia production process, amine-based CO2 capture cycle, the cryogenic air separation system based on the LNG regasification, steam methane reforming plant, and absorption-compression refrigeration unit is developed and exergetically is investigated. Thermal integration is utilized to apply waste heat in the combined structure. Solar dish collectors based on

Conclusion

In the present work, a novel integrated system for the production of liquid ammonia, power, pure oxygen, carbon dioxide, and hot water using the Haber-Bosch process, amine-based carbon dioxide capture cycle, and absorption-compression refrigeration was presented. Liquefied natural gas was used as the main feed system so that initially its cooling during the regasification process was applied in the cryogenic air separation unit to produce nitrogen and pure oxygen and then enters the steam

CRediT authorship contribution statement

Mostafa Moradi: Methodology, Investigation, Writing – original draft, Software, Validation.Bahram Ghorbani: Supervision, Conceptualization, Methodology, Investigation, Software, Validation, Original draft.Armin Ebrahimi: Methodology, Investigation, Writing – original draft, Software, Validation.Masoud Ziabasharhagh: Investigation, Methodology, Investigation.

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

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