Evolving energy systems in maritime transport: A parameter analysis for hydrogen fueled combined cycle gas turbine - MARPOWER project

1 Evolving energy systems in maritime transport: A parameter analysis for hydrogen fueled combined cycle gas turbine MARPOWER project Lappeenranta–Lahti University of Technology LUT Master’s Program in Sustainable Energy Systems, Energy Technology Master’s thesis 2025 Satu Lehto Examiners: Professor Teemu Turunen-Saaresti Docent Aki Grönman 2 ABSTRACT Lappeenranta–Lahti University of Technology LUT LUT School of Energy Systems Energy Technology Satu Lehto Evolving energy systems in maritime transport: A parameter analysis for hydrogen fueled combined cycle gas turbine MARPOWER project Master’s thesis 2025 85 pages, 35 figures and 5 tables Examiners: Professor Teemu Turunen-Saaresti and Docent Aki Grönman Keywords: MARPOWER project, gas turbine, waste heat boiler, hydrogen, maritime transport, energy system, PPTD Climate change is pressuring the marine transportation section to cut down emissions and fast, starting with 2% in year 2025. The Maritime sector has an important role in the global economies since it is used for exporting goods and transporting people and the sector is only expected to grow. As regulations are set to mitigate emissions, renewable energy sources bring the solution to fueling the sector in the future. Hydrogen properties have made it stand out as the fuel of the future in for marine engines, especially in gas turbines. Combining hydrogen with combined cycle gas turbine optimizes the fuel usage and efficiency of the system. This master’s thesis is done under the EU-funded MARPOWER project. The project aims to bring a combined gas turbine power system to maritime usage that can flexibly use the alternative fuels, including hydrogen. The aim was to see in what state the studies regarding gas turbines in marine sector are and analyze the gas turbine process with two cases that had different TITs. Parameter optimization of the combined cycle gas turbine shows the dependencies of seawater temperature and waste heat recovery boiler’s PPTD on other parameters. With set boundary conditions, a higher turbine inlet temperature results in lower boiler outlet temperature for exhaust gas and higher efficiency. The rising temperature of the seawater used in an intercooler as well as the increase of the PPTD effect negatively on the net electric efficiency. Higher turbine inlet temperature shows increasing ability to convey heat to the steam side in a WHRB to generate electricity. The efficiency of a gas turbine cycle can be improved by adding a WHRS to fully utilize the heat from the exhaust gas. The improvement in net electric efficiency can be over 4 percentage points. 3 TIIVISTELMÄ Lappeenrannan–Lahden teknillinen yliopisto LUT LUT Energiajärjestelmät Energiatekniikka Satu Lehto Meriliikenteen kehittyvät energiajärjestelmät: Parametritarkastelu vedyllä toimivalle kombiprosessille MARPOWER projekti Diplomityö 2025 85 sivua, 35 kuvaa ja 5 taulukkoa Tarkastajat: Professori Teemu Turunen-Saaresti ja Dosentti Aki Grönman Avainsanat: MARPOWER projekti, kaasuturbiini, jätelämpökattila, vety, meriliikenne, energiajärjestelmä, pinch point lämpötilaero Ilmastonmuutos pakottaa meriliikenteen vähentämään päästöjä nopeasti, alkaen 2 %:n vähennyksellä vuonna 2025. Merenkulkusektorilla on tärkeä rooli maailman talouksissa, sillä sitä käytetään tavaranvientiin ja ihmisten kuljetukseen, ja sektorin odotetaan vain kasvavan. Kun päästöjä rajoittavia säädöksiä otetaan käyttöön, uusiutuvat energialähteet tarjoavat ratkaisun alan tulevaisuuden polttoaineeksi. Vedyn ominaisuudet ovat tehneet siitä tulevaisuuden polttoaineen laivojen moottoreissa, erityisesti kaasuturbiineissa. Vedyn yhdistäminen yhdistettyyn kaasuturbiiniin optimoi polttoaineen käytön ja järjestelmän tehokkuuden. Tämä diplomityö on tehty EU-rahoitteisen MARPOWER-hankkeen puitteissa. Hankkeen tavoitteena on tuoda kombiprosessi merikäyttöön, joka voi joustavasti hyödyntää vaihtoehtoisia polttoaineita, mukaan lukien vetyä. Tavoitteena oli selvittää, missä vaiheessa merialan kaasuturbiinitutkimukset ovat, sekä analysoida kaasuturbiiniprosessia kahdella eri turbiinin sisäänmenolämpötilalla. Kombiprosessin parametrioptimointi osoittaa meriveden lämpötilan sekä pinch point lämpötilaeron vaikutuksen jätelämpökattilan muihin parametreihin. Määritetyillä reunaehdoilla korkeampi turbiinin sisäänmenolämpötila johtaa pakokaasun alempaan kattilan ulostulolämpötilaan ja korkeampaan hyötysuhteeseen. Välijäähdyttimessä käytettävän meriveden lämpötilan sekä pinch point lämpötilaeron kasvu vaikuttavat negatiivisesti nettosähköhyötysuhteeseen. Korkeampi turbiinin sisäänmenolämpötila osoittaa parempaa kykyä siirtää lämpöä jätelämpökattilassa 4 pakokaasulta höyrypuolelle. Kaasuturbiiniprosessin tehokkuutta voidaan parantaa lisäämällä jätelämmön talteenottojärjestelmä, joka hyödyntää täysin pakokaasujen lämpöä. Sen avulla nettosähkötehokkuuden parannus voi olla yli 4 prosenttiyksikköä. ACKNOWLEDGEMENTS I want to say the first thank you to the Laboratory of Fluid Dynamics and to my supervisors Teemu Turunen-Saaresti and Aki Grönman and also to Antti Uusitalo for all their help, advice and useful comments during my thesis work. When I came to Lappeenranta, I didn’t know anyone here but after the first day of orientation I found my people and got friends for life. I always say it was one of the best decisions of my life to come to Lappeenranta and that is because of you. I want to also say thank you to my high school friends. It has always been good to know that whether I’m on the other side of Finland or on the other side of the world you have my back, and I can count on you. Finally, I want to say thank you to my family for supporting me through all of my studies. Whether it was prepping me for a language test or helping me with math homework you made it possible for me to come this long of a way. You have always encouraged me to go for what I want and because of you I am now here. These 5 years of university have been quite the journey. It holds the Covid-19 pandemic, countless late-night studies but also incredible student events and an unforgettable exchange. Now I can put my not-so-white overalls away and proudly say, I did it! In Lappeenranta 30.6.2025 Satu Lehto 5 DECLARATION OF AI USAGE Scopus AI has been used to find references. The references have been checked and only ones proven to be correct have been used. Microsoft Copilot has been used to help with structuring of the thesis. 6 SYMBOLS AND ABBREVIATIONS Roman characters p pressure [bar, Pa] T temperature [ºC, K] qm mass flow rate [kg/s] A area [m2] P power [W] Q heat rate [W] k step [ºC, K] U overall HTC [W/m2K] F LMTD correction factor [-] Greek characters θ temperature difference [ºC, K] Φ heat [kW] ε degree of recuperation [-] η efficiency [%] Subscripts a air approach approach temperature B boiler el electric 7 eg exhaust gas fuel fuel in inflow LMTD log mean temperature difference max maximum n n’s value net net value out outflow s steam target target w water Superscripts ' derivative Abbreviations ADP Acid dew point CCS Carbon capture and storage CH4 Methane CII Carbon Intensity Indicator CNG Compressed natural gas CO2 Carbon monoxide CODAG Combined diesel and gas COGAS Combined gas and steam 8 EC European Commission EEDI Energy Efficiency Existing Ship Index EMSA European Marine Safety Agency EU European Union FC Fuel cell GHG Greenhouse gas GT Gas turbine H2 Hydrogen H2O Water HFO Heavy fuel oil HHV Higher heating value HP high pressure HRSG Heat recovery system generator HTPEMFC High temperature polymer electrolyte fuel cell ICE Internal combustion engine IMO International Marine Organization IPPC Integrated Pollution Prevention and Control LFO Light Fuel oil LHV Lower heating value LNG Liquified Natural Gas LOHC Liquid Organic Hydrogen Carrier LP Low pressure MDO Marine Diesel Oil MMT Million metric ton 9 N2 Nitrogen monoxide N2O Nitrous oxide NG Natural gas NH3 Ammonia NOx Nitrogen oxides O2 Oxygen OPS Onshore power supply PCC Post combustion carbon capture SDG Sustainable Development Goals SMR Steam methane reforming SOx Sulfur oxides ST Steam turbine RNG Renewable natural gas TIT Turbine inlet temperature PPTD Pinch point temperature difference WHB Waste heat boiler WHR Waste heat recovery WHRS Waste heat recovery system WtW Well-to-Wake 16 size diesel engines, steam circuit and generators are bulky, the rotational speeds of turbines (thousands of rpm) and the ship’s propellers (around 100 rpm) are not compatible so expensive and bulky speed reducers are needed and reversing requires auxiliary turbine for fixed pitch propellers (Baldi et al., 2022, 33). Internal combustion engines (ICE) have a leading role in the global merchant fleet, nearly 98 % have it as a prime mover. Low price of heavy fuel oil (HFO) makes using ICEs economically interesting. (Mallouppas & Yfantis, 2021). Due to the 1970’s oil crises fuel cells (FC) gained more attention and interest in maritime application as a clean energy technology solution (Baldi et al., 2022, 81). To this day the main factor driving the fuel cells application on vessels is to cut down the emissions. Fuel cells have been proven to work on multiple applications on land such as transportation, but on-board applications come with new challenges. The requirements and challenges for maritime application compared to automobiles can be shortened into four concerns: operational environment, size, emissions and economic consideration. From environmental challenges the number one is fueling. Automobiles are easy to fuel on land but on sea the long voyages don’t offer this option. The salty seawater is also a challenging environment because of seawater corrosion and unpredictable weather. The size of the vessels presents a related problem with fueling. Marine vessels are large so being able to fuel the whole ship with fuel cells is a challenge. Emission wise, it is important to focus on vessels since the individual emissions are more outstanding. From an economic point of view, ships have a longer lifespan when compared to automobiles but require distinct economic considerations. (Wang, 2023) Most promising fuel cell technologies for maritime applications are PEMFC and SOFC. These fuel cells have been used in multiple marine applications on their own or with batteries. The problem today is that they are only capable of producing power up to few megawatts. This limits the exploitation of FCs to vessels voyaging short distances. On larger vessels fuel cells are still only capable of auxiliary power. (Elkafas et al., 2023) Due to strong development of gas turbines (GT) and growing demand in propulsion systems with high power concentration on top of low polluting emissions, it reappeared in maritime transportation at the end of 1990. GT was used before but the oil crisis in 1970’s blocked its use. Gas turbines have advantages over steam turbines and diesel engines. GT has smaller dimensions and is lighter. This is due to the smaller number of auxiliary devices and simpler 17 plant installation. GTs are reliable and can reach the maximum load in less than 5 minutes. It would take a Diesel engine to reach its maximum load about 20 minutes, and a ST would take even longer, up to 4 hours (Baldi et al., 2022, 34). If GT and ICE are compared backto-back GT takes the win in many categories other than the starting time. When the gas turbine is the main engine the noise, vibration, maintenance intervals and the amount of lubricant oil needed reduces. (Barsi et al., 2024) 2.2. Gas turbine technology Gast turbines can be divided into two categories: simple gas turbine and generative gas turbine. Both designs work on open and closed cycles, but popularity is leaning towards the open cycle. In the open cycle the air is constantly being drawn into the compressor and in closed-cycle the exhaust gas is recirculated. The major difference between the two gas turbine categories is that in generative gas turbine the heat from the exhaust gas is used to pre-heat the air before it enters the compressor. This way potential losses are avoided. The gas turbine cycle can be turned into a combined cycle by adding a heat recovery steam generator (HRSG). This bottoming cycle takes the exhaust gas and uses the heat from it to vaporize water to produce more energy via steam turbine. (Li et al., 2021) Gas turbine’s major components are compressor, combustor and turbine. These three parts can be seen clearly in Figure 1. Figure 1. Gas turbine (Donev et al., 2024) 18 First the air enters the compressor where it is compressed to a higher pressure. No external heat is added to the air, but compression increases the air’s temperature. Compressors can be divided into three categories: the positive placement compressors for low flow and high pressure, centrifugal-flow compressors for medium flow and pressure and axial-flow compressors for high flow and low pressure. Most of the compressors used in gas turbines are axial-flow compressors. (Boyce, 2012, 51) An axial-flow compressor has multiple stages. One stage is made of a rotor and a stator. In the rotor blades the air is accelerated and after that diffused in the stator blades. The diffusion has to happen since then the gained velocity in the rotor is converted to pressure increase. Each state increases the pressure slightly. For better control, additional fixed blades can be added to the compressor inlet for making sure the air enters in the right angle. Additional diffuser can also be added to the exit of the compressor. This way it is easier to control the velocity of the air at the end. (Boyce, 2012, 54-55) As axial-flow compressors are popular on large scale gas turbines, centrifugal-flow compressors are used in small scale gas turbines. Centrifugal compressors are known for large tolerance of process fluctuation and high reliability when compared with other compressors. The centrifugal compressor conducts an impeller, and the fluid is forced through it by rotating impeller blades. Centrifugal compressors also have diffusers that conduct of vanes. The vanes are tangential to the impeller and the velocity of the fluid is converted to pressure. (Boyce, 2012, 55-56) There are small gas turbines that operate with both axial and centrifugal compressors. In Figure 2 the difference can be seen. The difference between the exiting fluid flow is easy to visualize from the figure. For axial compressor the fluid enters and exits in axial flow but for centrifugal compressor the fluid enters in axial flow but exits in radial flow to enter the combustor. 19 Figure 2. Small gas turbine (Boyce, 2012, 54) After the fluid exits the compressor, it enters the combustor. There the air is mixed with the fuel. The pressure remains almost constant throughout the combustion phase. High temperatures are reached in the combustor which results in gaseous form of the fuel mix. The hot combustion mixture enters the turbine section. (Poullikkas, 2004). The three major designs for combustors are tubular, tubo-annular and annular. Despite the design, all the combustors have the same features: a recirculation zone, a burning zone and a dilution zone. In the recirculation zone the fuel is evaporated, partly burnt and prepared for the combustion. At the end of the burning zone the fuel should be burnt so that in the final dilution zone the hot gas can be mixed with the dilution air. After the compressor, the mixture enters the turbine (Boyce, 2011, 387). Depending on the usage of the system, turbines are designed to be single-shaft or two-shaft. The difference between the two is that in two-shaft turbine there are two turbines back-to-back: high-pressure and low-pressure. In the maritime sector the ships have to move at a variety of speeds at ports thus implementing the two-shaft turbine is more convenient. (Fatsis, 2019) The turbine section of the GT can have two options, either an axial-flow turbine or a radialflow turbine. Just like the compressor, also turbines are more often axial turbines. The axialflow turbine is used in 95% of gas turbines. With axial turbine the flow enters and leaves in the axial direction. (Boyce, 2012, 76-81) 20 The turbine needs to bear high temperatures because that way the efficiency can be enhanced. Higher temperatures flow through the turbine, the blades are put under enormous thermal stress, and this can cause thermal deformation. (Kim et al., 2024) The blades have a coating that ensures protection in these high temperatures. The coating can act also as a sacrificial layer that can be stripped and recoated. Life of the coating varies from 10 to 15 years. (Boyce, 2012, 49). To ensure the long lifetime of the blades, blade cooling needs to be integrated to the system. Cooling can be divided into surface film and blade internal cooling. Typically, the cooling air is taken from the compressor, but other options are available too. (Kim et al., 2024) The best way to describe the working principle of the whole gas turbine is by the Brayton Cycle (Giampaolo, 2014, 45). Figures 3 show pressure-temperature map for gas turbine. Figure 3. Brayton cycle pressure-temperature map The map in Figure 3 shows that from point a to b the air is compressed in the compressor. Temperature increases a little bit, but pressure growth is more noticeable. From b to c the air enters the combustor, and the process is isobaric, so the pressure remains unchanged. The temperature grows as it is predicted. Expansion takes place from point c to d. Here the gas enters the turbine and the gas expands. Combustion Pressure Temperature 21 2.3. Additional components for complex cycles Additional system components for maritime shipping systems can include heat exchangers such as recuperator or intercooler. Waste heat recovery system (WHRS) can increase the efficiency of the cycle by cutting down fuel intake needed. 2.3.1. Recuperator technology Recuperator can be categorized as a major gas turbine component but is not a necessary part of the gas turbine. Figures 4 and 5 present a gas turbine with a recuperator. Figure 4. Gas turbine with recuperator (Boyce, 2012. s. 41) 22 Figure 5. Air flow in a gas turbine with recuperator (Boyce, 2012. s. 42) In some cases, the exhaust gas exiting the turbine can be significantly higher than the temperature of the air that enters the combustor. In a situation like this, it is more efficient for the fuel consumption to utilize the heat to preheat the compressed air entering the burning chamber. Including a recuperator to the gas turbine is possible with relatively small pressure ratios or high turbine inlet temperature (TIT). The purpose of adding a recuperator to the system is to increase the efficiency. (Poullikkas, 2004) As seen in the figure above the intake air goes through the compressor first, then into recuperator and then into the combustor. Recuperator’s purpose is to increase the efficiency of the process. Recuperator is a heat exchanger that conveys energy from a hot exhaust gas leaving the turbine to compressed air about to enter the combustor. This reduces fuel consumption of the gas turbine and increases electrical efficiency (Xiao et al., 2017). The air entering the turbine is usually above 1200 ℃. (Boyce, 2012, 41) Recuperators are divided into three different categories based on the geometry of the heat transfer surface. The three categories are primary-surface, plate-fin and tubular recuperators (Xiao et al., 2017). Figure 6 shows three types of primary-surface recuperators. 23 Figure 6. Types of primary surface recuperators (Xiao et al., 2017) The primary surface recuperator is a counter-flow heat exchanger. The material is stainless steel. The recuperator is composed of multiple layers stacked on top of one another. One layer has an upper and lower sheet. The metal sheets shown in the figure are welded at the edges leaving an opening for air to enter and exit. The hot exhaust gas follows the patterns of the surface and the air flows between the two sheets. (Xiao et al., 2017) Figure 7 shows the structure of plate-fin recuperator. Figure 7. Plate-fin recuperator (Xiao et al., 2017) This design forms a strong unit of plates, fins, headering bars and manifolds. The gas fin segment has a pattern that the air uses as the heat exchange surface. The exhaust gas enters in a cross-flow to the air flow. The parting plates separate the exhaust gas and air flow. (Xiao et al., 2021) 24 Figure 8. Tubular recuperator (Xiao et al., 2017) Tubular recuperators consist of multiple tubes where the compressed air flows. Outside of the tubes are heated with exhaust gas. The advantages include high resistance to thermal gradient. The tubular recuperator is heavy thus it has a big impact on the total system. (Xiao et al., 2017) An important parameter in recuperators is the degree of recuperation. The degree of recuperation represents the ratio between recuperated heat and waste heat. Degree of recuperation can be calculated as in Equation 1. ε=∆Tmax 𝜃 (1) In the equation ε is the degree of recuperation, ∆Tmax is the temperature difference between outlet and inlet temperatures of the recovered fluid and θ is the difference between the inlet temperature of the heat source and inlet temperature of the recovered fluid. Degree of recuperation works as the criteria for recuperators efficiency. It tells how much heat is possible to recover from theoretical maximum. Energy efficiency is at its highest when ∆Tmax is as high as possible. The size of the heat exchanger surfaces, and the cleanliness of the surface affect the efficiency of heat exchange between the two vapors. (Motiva, n.d.) 25 2.3.2. Intercooler technology Intercoolers are divided to air-to-air and air-to-liquid intercoolers. In marine engines it is more common to use an air-to-liquid intercooler since water is easily accessible due to the environment. The seawater causes easily corrosion so freshwater would be more favorable to use. The seawater wouldn’t only affect the intercooler but also pumps that pump the salty water on board. (Theotokatos et al., 2016) With intercoolers, adding a regenerator such as recuperator before combustor in a gas turbine cycle is crucial for the thermal efficiency and to achieve the set turbine inlet temperature. The advantage that the intercooler gives to the system is that it lowers the amount of power that the compressor would absorb. Compressing cold air takes less power than compressing hot air. This increases the power output of the gas turbine (Beck et al., 1999, 55). Other benefits include lower thermal load to the engine and lower NOx emissions. (Mollenhauer & Tschöke, 2010, 48) 2.3.3. Waste heat recovery system Starting from the 1st of January in 2023, it became mandatory for every vessel to calculate their Energy Efficiency Existing Ship Index (EEDI) and Carbon Intensity Indicator (CII). These are implemented to International Maritime Organization’s (IMO) strategy. As the efficiency of the process and emission reductions are top priorities in the shipping sector, the actions should be lined with them. Implementing a waste heat recovery system on-board answers these demands. (Díaz-Secades, 2023) WHRS’s aim is to take the excess heat from the primary power generation and convert to energy (Erixno, 2021). The waste heat can be classified as high, medium or low quality. The temperature range for low quality heat is 232 ℃ or lower. For medium quality the temperature range is 232-649 ℃ and for high quality 650 ℃ or higher. According to Singh & Pedersen (2016) waste heat in ships usually lies between low and medium quality. Utilizing this heat makes the technology an energy-efficient one that helps with fuel savings (Wang, 2023). With WHRS the demand for propulsion or auxiliary services can be met 32 emissions from international shipping to peak and decline”. Here, the goal was to reduce GHG emissions by 50 % by the year 2050 (IMO b, n.d.). In the new strategy from 2023 there are four levels of ambitions, and the last one is called “GHG emissions for international shipping reaching net zero”. In this level, the new goal for emissions is to reach net-zero by the year 2050. (Annex 15 MEPC 80/17 Add.1, page 6) As mentioned earlier, the European Union and more specifically the European Commission has set regulations and directives for the maritime sector. The European Commission has set up a European Maritime Safety Agency (EMSA) in the early 2000’s. EMSA’s intention is to assist the EC in the fields of maritime safety, maritime security and the prevention of pollution as well as to response to pollution caused by ships. The Agency doesn’t only assist the Member States but also EU neighboring countries (European Commission c, n.d.). The EC and IMO work together to decarbonize the maritime transportation. In July 2023 the Commission welcomed the new climate ambitions by IMO and the parties together ensure that the shipping sector makes a fair contribution to attain the Paris Agreement targets. (European Commission, 2023) 3.3. Maritime fuels: energy carriers and primary energy sources The eventual aim for marine sector and energy systems needed for operation is to be carbon neutral. For shipping industry, achieving this goal means that the industry must have zero environmental impact and must operate by using renewable energy sources (Baldi et al., 2022, 58). The majority of used fuels in the past years are fossil fuels. This can be seen from Figure 13. 33 Figure 13. Quantity of marine fuels in the years 2019 and 2020 (Statista, 2023) The unit for the quantity of the fuel, MMT, stands for million metric tons. One MMT equals 1 000 000 000 kilograms. As seen from the figure above, there are differences between fuel types in both years. The clearest difference can be seen with Light Fuel Oil (LFO). In the year 2019, 6.5 MMT of LFO was used in the marine sector. In one year, its usage grew 10 times, ending up being 65,5 MTT. Even though LNG is the best choice environmentally out of all four fuels, it is also the least used one. To meet the regulations set by the EU and IMO, the usage of renewable and environmentally friendly fuels needs to take its place in the industry. As seen in Figure 12 the first emission mitigation goals are set for this year, the year of 2025. This pushes the industry by force towards alternative fuels. Alternative options for liquid fossil fuels would include hydrogen, ammonia, methane and natural gas, and methanol. (Baldi et al., 2022, 59-65) 3.3.1. Hydrogen Hydrogen, as a fuel, has a big impact on pushing the greener future of energy production closer to the Sustainable Development Goals (Le et al., 2023). That is why it is relevant to explore its suitability for maritime on-board purposes and weight the possible limitations. Hydrogen is the most abundant element on the Earth and in the whole universe. Its 0,00 50,00 100,00 150,00 200,00 250,00 300,00 Heavy Fuel Oil Light Fuel Oil Diesel/ Gas Oil Liquefied Natural Gas (LNG) Quantity of used fuel in MMT Fuel Marine fuels used in 2019 and 2020 2019 2020 34 advantages include that it is colorless, odorless and non-toxic as well as that it is a lightweight gas (Mazloomi & Gomes, 2012). One aspect that makes hydrogen a good alternative for other fuels is its energy content. Hydrogen’s energy content is 120 MJ/kg and when compared with gasoline, which has energy content of 44 MJ/kg, it’s seen that hydrogen’s energy content is almost three times higher than gasoline’s. (U.S. Department of Energy, n.d.) Even when hydrogen is the most abundant element it does not exist in the molecular form in nature hence there are processes that break the hydrogen molecule from other sources. The three methods to produce hydrogen are steam methane reforming (SMR), electrolysis and gasification. In SMR hydrogen is split from methane, in electrolysis the hydrogen is split form water and in gasification coal or biomass can be used for example (Xing et al., 2021). As hydrogen can be classified as a sustainable fuel it is only truly 100% emission free if it is produced with water electolyzer with renewable energy. Today the problem lies in the fact that less than 5 % of hydrogen is produced this way. (Xing et al., 2021) Hydrogen is an appealing fuel since it produces minimal emissions if any. For example, with fuel cell applications only water and heat are the by-products (Baldi et al., 2022, 61). This is presented in Equation 2. 𝐻2+𝑂2=𝐻2𝑂+ℎ𝑒𝑎𝑡 (2) Gas turbine running on 100 % hydrogen eliminates the CO2 emissions. Nevertheless, it will still produce some NOX emissions because of the composition of compressed air. The emissions, however, are below standard values. (Amirouche at al., 2024) Hydrogen has various advantages but also a few challenges as fuel. Even though hydrogen has a high energy density per kilogram, its density per cubic meter is very small in gaseous form. The comparison of different maritime fuels’ volumetric energy density is presented in Figure 14. Hydrogen requires a lot of storage space, and the storage compartment must be able to handle the high pressure needed for storing hydrogen (Mazloomi & Gomes, 2012). The corrosive nature of hydrogen can cause hydrogen embrittlement to the steel materials in the delivery and storage systems. In hydrogen embrittlement hydrogen dissolves into steel causing stress concentration that is greater than the strength limit of the steel which causes small cracks to the steel structure. Hydrogen leaks easily from even a small crack because it has high diffusivity, small molecular weight and low viscosity. There is no cure to hydrogen 35 embrittlement, but the affecting factors are known. They include hydrogen concentration, ambient pressure and temperature, exposure time, stress state, mechanical properties, microstructure, surface conditions and the nature of the material crack front. (Yang et al., 2023) Figure 14. Volumetric energy densities of different marine fuels (Placek, 2023) Figure 14 gives each of the marine fuels their volumetric energy density. Hydrogen doesn’t perform well on the list. However, as stated before when hydrogen and gasoline are compared in mass energy density, hydrogen takes the win with the mass energy density of around 120 MJ/kg with lower heating value (LHV) (Engineering ToolBox, n.d.). Figure 15 shows the mass energy density of most of the marine fuels in Figure 16 with higher heating value (HHV). 0 5 10 15 20 25 30 35 40 Marine diesel oil (MDO) Oleochemical biofuel (HVO) Heavy fuel oil (HFO) Oleochemical biofuel (FAME) Liquefied Petroleum Gas (LPG) Ethanol Liquefied Natural Gas (LNG) Methanol Ammonia (liquid -35C) Hydrogen (liquid -252C) Hydrogen (700 bar) Hydrogen (350 bar) Li ion battery Energy density [MJ/L] Fuels Energy content of marine fuels 2020 36 Figure 15. Mass energy density of different marine fuels (Engineering ToolBox, n.d.) HHV is used since the reference didn’t have the value of LHV for ammonia. The results differ from Figure 14 drastically. Hydrogen takes the first place, and the energy density is almost three times higher than with methane that takes the second place. Even with LHV hydrogen has the highest energy density out of the marine fuels listed. (Engineering ToolBox, n.d.) Table 1. presents the values for molecular hydrogen, H2. The reason behind using molecular hydrogen as a fuel and not atomic hydrogen comes from the chemical properties of these two. Atomic hydrogen or H is much more unstable and very reactive making storage, transportation and usage impossible. H2 on the other hand, is the opposite and makes a great energy carrier and fuel for different energy systems. Table 1 includes molecular hydrogens properties. 020 40 60 80 100 120 140 160 Marine gas oil Biodiesel Light fuel oil (LFO) Heavy fuel oil (HFO) Liquefied petroleum gas (LPG) Ethanol Liquefied natural gas (LNG) Methane Methanol Ammonia Hydrogen Energy density [MJ/kg] Fuels Mass energy density of marine fuels 37 Table 1. Properties of hydrogen (Zhang et al., 2023) Parameters Value LHV [MJ/kg] -118.8 HHV [MJ/kg] 143 Boiling temperature at 1 atm [℃] -253 Melting temperature [℃] -259 Critical temperature [℃] -240.01 Critical pressure [MPa] 1.3 Density (gaseous form) [kg/m3] 0.08987 Density (liquid form) [kg/m3] 70.85 Heat capacity (gaseous form) [kJ/kgK] 14.3 Heat capacity (liquid form) [kJ/kgK] 8.1 As storing hydrogen is one of the main challenges for marine integration, different storage solutions need to be considered. The alternative fuel storage solutions for pure hydrogen are using a hydrogen carrier such as ammonia (NH3) and Liquid Organic Hydrogen Carriers (LOHC), hydrogen produced from methane reforming or using methanol in High Temperature PEM fuel cells (HTPEMFC). (Baldi et al., 2022, 62) Hydrogens usage as a fuel in gas turbine cannot be brought to use on a bigger scale just yet since on top of the other challenges, there is a paucity of the ports where refueling can happen. (Baldi et al., 2022, 61) 3.3.1. Ammonia Ammonia is a good option for fueling the maritime industry and a great fuel for gas turbine application since no major improvements or design changes need to be made. It is produced combining nitrogen and hydrogen in conditions with high pressure and temperature with the help of catalyst. Being compounded of nitrogen and hydrogen means, it doesn’t have molecular carbon thus doesn’t produce CO2 emissions when combusted. To have zero carbon emissions, the used ammonia in marine vessels requires the ammonia to be categorized as 38 green. This means only renewable energy sources such as wind and solar power are acceptable for production. (Thurman, a, 2023) Ammonia has potential to reduce GHG emissions, but it challenges the marine engines with its corrosive nature and this property makes additional maintenance mandatory. Hydrogen and gaseous ammonia share the same problem: storage issues. Ammonia needs a large storage capacity since its volumetric efficiency and energy density are much lower compared to fossil fuels in use. Vessels’ operating range is heavily impacted by the dimensions of the storage unit for ammonia. Ammonia is also toxic, and which makes handling it difficult thus when designing ammonia fuel systems, safety should be in mind. (Thurman, a, 2023) Another challenge with ammonia is its production since it is not sustainable yet (Thurman, 2023). It is possible to use renewable energy to produce green ammonia and generate nearly zero GHGs on a WtW basis. Generality of ammonia used as a fuel is categorized as grey meaning it’s produced with conventional energy sources. Using grey ammonia is less profitable for the environment since its production generates more GHGs than using conventional marine fuels themselves. (European Maritime Safety Agency, 2022) Because of the chemical compound of ammonia, NOx emissions will appear when burnt. Equation 5 presents the chemical reaction when ammonia reacts with oxygen. 4 NH3+ 3 O2→2 N2+ 6 H2O(5) The potential of nitrous oxide (N2O) emissions brings uncertainty to the usage of ammonia since handling it is one of the biggest unknowns. Developing catalysts for N2O emissions is one way to ensure the sustainability of ammonia. (Thurman, a, 2023) To this day there is not much ammonia available for the shipping industry as it is competing with fertilizer and energy industries. Starting up production takes time as building an ammonia plant takes up to six years. On a global scale over 200 low-carbon ammonia facilities are being planned. As the marine industry starts to adopt ammonia as a fuel on a bigger scale, the fuel bunkering network needs to grow with it. The bunkering system can be fixed or mobile. Mobile bunkering systems refer to transportable tanks whereas fixed systems are located at ports or fueling stations. With fixed bunkering the infrastructure needs to be developed to be able to handle both liquid and gaseous ammonia. (Thurman, a, 2023) 39 3.3.2. Renewable methane and natural gas Liquified and compressed natural gases are good options when going towards cleaner fuels since they decrease emissions by 5-21% compared to using HFO. LNG is a drop-in fuel so it can be used on already existing systems and no extra investments are needed (Wärtsilä, b, 2025). Natural gas gains its liquid form in atmospheric pressure and at the temperature of - 162 ℃. It can be stored in insulated tanks. Natural gas can be called compressed natural gas when it is stored in atmospheric temperature and in high pressure, between 300 to 700 bars. Out of the two LNG is more favorable to use in marine propulsion because it has higher energy density than CNG. (Baldi et al., 2022, 59) Natural gas is typically 85-95 % methane. The chemical and combustion properties of the fuel allow SOx emissions to be removed almost completely. The NOx emissions can expect a drop of 85% because of the lean burn combustion process in spark ignited and dual fuel engines. Hence there is no need for emission reduction systems that are needed with oil fuels (Baldi et al., 2022, 59). Natural gas can have its flaws since it’s made with methane. Methane leakage or slip can occur when burning the fuel. If methane gets into the atmosphere, it affects greatly the GHG footprint of the fuel. (Wärtsilä b, 2025) LNG can be used as its own or natural gas and hydrogen can be blended and used as mix. When the ships are at the ports it is more strategic to use a hydrogen mix to obey the emission limits. Transitioning to sustainable shipping LNG is a good choice since it has fairly low WtW GHG emission factor, 76 g/MJ. (Barsi et al. 2024) Renewable methane is also termed as renewable natural gas (RNG) or synthetic natural gas (SNG). Methane would serve the same purpose as natural gas but would be a renewable choice. Chemical composition of natural gas and methane are comparable, and this is why methane can be transported with the same pipelines as natural gas. Because of this there are no concerns about blending limits and reduction in natural gas use. Renewable methane is produced by combining renewable energy powered electrolysis and air-captured CO2 or by removing impurities from biogas that has been produced from waste or landfill gas. Biogas based methane can be also called biomethane. Producing methane from organic waste by anaerobic digestion is a recommended method by the Intergovernmental Panel and Climate Change (IPCC) since it helps to reduce emissions in waste management sector. Methane is very abundant since it takes between 54 and 73 % of biogas’ composition. Methane can be 40 produced with hydrogen and captured carbon dioxide. This methane can only be called renewable if hydrogen is classified as green. (Cha et al., 2024) 4 𝐻2+𝐶𝑂2 →𝐶𝐻4+ 2 𝐻2𝑂 (3) When methane is burnt and reacts with oxygen, carbon dioxide and water are the byproducts. 𝐶𝐻4+ 2 𝑂2 →𝐶𝑂2+ 2 𝐻2𝑂 (4) Including a direct air capture of carbon monoxide, while using renewable methane as a fuel, helps with achieving carbon negative emissions. (Choe et al., 2023) In 2022 the EU released their REPowerEU Plan to phase out Europe’s independency on Russian fossil fuels. In the Plan it was outlined that there is a clear need for scale up in biomethane production by 2030. Production needs to reach a capacity of 35 billion cubic meters per year by 2030. The EU also wants to promote the usage of municipal waste rather than food and feedstock for better land use, just like IPPC. (European Commission d, n.d.) 3.3.3. Methanol Methanol is highly toxic, flammable and colorless biodegradable wood alcohol. As a fuel it still produces emissions but far less than diesel combustion. Switching to methanol from diesel would decrease CO2 emissions by 7 %, SOx emissions by 99 % and NOx emissions by 60 %. These numbers are only reachable if green methanol, which is made from biomass or captured CO2 and green hydrogen, is utilized. (Thurman, b, 2023) Equations 6 & 7 show the chemical reaction when methanol is made with hydrogen and when methanol is burned and reacts with oxygen. When methanol is produced with hydrogen: CO2+ 3 H2 →CH3OH+H2O (6) When methanol reacts with oxygen when burned: 𝐶𝐻3𝑂𝐻+1.5 𝑂2 →𝐶𝑂2+ 2 𝐻2𝑂 (7) Using grey or brown methanol, that are made with natural gas and coal, will only have a worse impact on the CO2 emissions than using diesel. Methanol molecules stay the same 41 despite the production method thus making transition towards green methanol easier over time. (Thurman, b, 2023) Methanol is biodegradable and miscible with water. Unlike gasoline it doesn’t accumulate in water air or soil, making it less of a risk to environment (Candelaresi & Spazzafumo, 2021). Methanol would be very accessible fuel since major ports have storage and handling facilities nearby. Globally over 100 ports have methanol available for fueling. (Thurman, b, 2023) In the study of Cui et al. (2025) methanol and methane were compared as a fuel for gas turbines and the properties were evaluated from a combustor design point of view. As a result, methanol has greater flexibility for the design of the gas turbine and the performance of methanol combustor surpasses methane combustor. The design for methane can be adapted to methanol combustion without structural modification. Production of green methanol is low. Only 0,2 % of the total methanol production is green and is mainly produced with biomass gasification. It has been proposed to produce methanol from municipal waste. The increasing need for sustainable fuels makes producing methanol in an environmentally friendly way more interesting. (Sollai et al., 2022) 48 Figure 17. Ship’s energy system In Figure 17, first the air enters the low-pressure compressor where it is pre-compressed. After that the compressed air enters the air-to-liquid intercooler where the air is cooled down with seawater. Next the air enters a set of high-pressure compressors, where it is compressed more. After a high-pressure compressors, the air flows to the recuperator. Recuperator is a heat exchanger where the air absorbs the heat from the exhaust gas that flows on the other side and then enters the burning chamber. Recuperator’s purpose on the process is to increase the efficiency. Hydrogen is injected to the burning chamber where it reacts with the compressed air. The result is hot water vapor and that enters the high-pressure turbine that has cooled blades. After high-pressure turbine, the water vapor enters a low-pressure turbine. There the vapor goes to the recuperator to cool down as it releases the heat to the compressed air. To maximize the energy usage, the exhaust gas enters a waste heat boiler where it is used to steam up the water into a superheated steam. The superheated steam goes through the waste heat turbine to power a generator. The vapor after the turbine goes through a condenser and the condensed water is pumped back to the boiler with a feed water pump. After the exhaust 49 gas has gone through the boiler, it is released into the air. The exhaust gas mostly consists of water vapor but has some NOx emissions too. After different cases were examined, some adjustments were made. In the previous version there was an intercooler between the two high pressure compressors. This was later left out because of spacing issues on the shaft. The positive gains from the intercooler were not significant so it was better to leave it out. Even though the gas turbine efficiency dropped slightly the complete efficiency of gas turbine and waste heat recovery system increased. Turbine inlet temperature for the vapor was set for one case to be above 1200 ℃ and for another case it is above 1300 ℃. This affects the cooling need of the turbine blades. The cooling vapor is taken from the air after the intercooler. As can be seen from Figure 18, after the cooled air has left the turbine, it is combined with the exhaust gas that leaves the lowpressure turbine. The pressure ratio of gas turbine cycle is 12:1. If referred to the study done by Goswami and Kreith (2019) then the pressure ratio of the gas turbine lies in a very optimum value for high efficiency. Gas turbines can have a pressure ratio as high as 40:1 (Boyce, 2012). Based on that, the pressure ratio of 12:1 in this MARPOWER gas turbine is on the lower side of the pressure ratio range. As recuperators are not used on high pressure ratios, it is applicable to have one is this cycle to increase efficiency. (Sayma, 2017) 5.1.1. Gas turbine: how hydrogen effects the design To understand the importance of proper gas turbine design and especially the combustor design, natural gas can be used as a reference fuel to give some perspective. With natural gas, in gas combustors the fuel is injected to the airflow at an angle and from a specified distance upstream of the flame. If the length of the premixing region for NG combustion is very small, even zero, it results in non-premixed flame and the reaction rate peaks at the stoichiometry. When compared to a more optimal region length, air and NG can form a homogenous mixture before entering the burning chamber. This results in a lean combustion that is the goal. With natural gas the flame stabilization is secured because of the large recirculation zone achieved by highly swirling air. Success is achieved because the flame 50 doesn’t come in contact with the fuel injection point which is ensured with the airflow velocity. (Tingas, 2023, 409-410) Natural gas and hydrogen have very different compositions. If in a gas turbine that works with NG only the fuel is changed to hydrogen and all the other components stay the same, problems will occur. Hydrogen has higher flame speed than natural gas. There is a higher risk that the flame flashes back near the fuel injection point. In flashback the flame speed overtakes the flow velocity. This causes material and safety problems on feeding nozzles. (Cecere et al., 2023). For this reason, it is why either very small injection holes or very high velocity is needed for hydrogen when it is injected, or special care is required to avoid boundary layers and separation. Also splitting the air to flow into many parallel ducts would also be a possible solution. Here hydrogen could be injected in a crossflow to the air flow or parallel configuration. This would help the flame to detach from the injection point because the air and hydrogen both have high velocities. More research needs to be done on the stabilization mechanism (Tingas, 2023, 410). Figure 18 shows how hydrogen is injected to the gas turbine combustion system and the difference between the two techniques. 51 Figure 18. Hydrogen injection techniques (Tingas, 2023, 411) The top picture in Figure 18 shows the situation if hydrogen is injected to the combustor from two spots and cross-flow into the air flow. It shows that the high possibility of a flash back exists, and cooling is needed for the hydrogen feeding nozzles. (Tingas, 2023, 411) The bottom picture shows the situation when hydrogen is injected from many small holes and in a co-flow with air flow. Using small injection holes is a state-of-the-art technology, and multiple variants are under development. Here the idea is to stabilize the flame with burner inlet plate. (Tingas, 2023, 411) As mentioned in Figure 19, here the important factor is low NOx emissions. To achieve that, the significant mixing of air and hydrogen must be accomplished before flame. The relation 52 of the location of injection holes and air flow into the combustion chamber influences the distribution of the mixture. This can have an important effect not only on the shape and location of the flame but also to the NOx emissions (Tingas, 2023, 410). Another characteristic that needs to be noted when working with hydrogen is adiabatic flame temperature. Adiabatic flame temperature refers to the maximum temperature of the heat that is released from the combustion process and that heats up the combustion products. Hydrogen has a quite high adiabatic flame temperature, between 2318 K and 2400 K when other fuels such as methane and propane have an adiabatic flame temperature staying under 2300 K. High adiabatic temperature can also lead to an increased level of NOx emissions. (Cecere et al., 2023) As stated, hydrogen is a much more reactive fuel than for example natural gas. The difference of the flame speed of these two can be seen from Figure 19. When hydrogen is mixed with other fuels the reactivity of the mix increases as well (Cecere et al., 2023). So when changing the composition of the fuel whether it is purely hydrogen or a mix of hydrogen and another fuel the combustion chamber characteristics must be re-evaluated in every case. Figure 19. Laminar flame speed versus equivalence ratio (Dong et al., 2010) Figure 19 presents the laminar flame speeds of H2/air mixture and NG/air mixture. These two fuel mixes have their peak at very different spots. The maximum flame speed for H2 is 2.933 m/s and for NG it is 0.374 m/s. H2 has the maximum value when equivalence ratio is 1.7 and NG has it when equivalence ratio in 1.1. The data is based on the article from Dong 0 0,5 1 1,5 2 2,5 3 0,5 0,7 0,9 1,1 1,3 1,5 1,7 1,9 2,1 Laminar flame speed [m/s] Equivalence ratio [φ] Laminar flame speed versus equivalence ratio H2 NG 53 et al. (2010). As no actual data was available this figure has been made based on their figures. The conditions in the measurement are 293 K and 1 atm and the burner diameter is 2 mm. The high flame speed of hydrogen causes problems with material resistance and safety, increasing the critical strain rate and minimizing the quenching possibilities of the flame. (Cecere et al., 2023) Deutsches Zentrum für Luftund Raumfahrt (DLR) is doing research on the combustion of hydrogen in the MARPOWER project. Cecere (2023) wrote in their paper that with gas turbines there are challenges during testing and operation with thermoacoustic instability. The problem comes from the unsteady phase heat release which leads to large amplitude pressure oscillations (Cecere et al., 2023). In 2024 DLR published an article about successful usage of 100% hydrogen in a micro gas turbine. They have created a new burner and an adapted control system to make it possible to fuel the gas turbine with either 100% hydrogen or mixture of hydrogen and natural gas. The important step on the design was to make sure that the flame would not flash back into the burner nozzles and cause damage to them. DLR’s newest concept on gas turbine design is a jet-stabilised burner that is optimized for hydrogen usage. Success is achieved with air and fuel nozzles that are arranged to ring formation. The ring formation creates a backflow in the burning chamber which makes it possible for the exhaust gases to move back to the nozzles and be mixed with fresh fuel mixture. This doesn’t only stabilize the flame but also lowers the temperature in the burning chamber. (DLR, 2024) 5.1.2. Fuel’s influence on waste heat recovery system In WHRS, pinch point temperature difference plays a vital role in design parameter optimization, but it can also have limiting factors. Acid dew point (ADP) is one limiting factor that sets the range for the PPTD. ADP is the temperature at which the acid vapor in the flue gas begins to condense (Zuo, 2020). Normally acid vapor is referred to as sulfuric acid (H2SO4). As presented in the equations in chapter 3.3, none of the alternative fuels include sulfur thus they won’t produce any emissions containing it. The problem lies more on the conventional fuels in the marine sector as they do include sulfur. Sulphur acid is formed when sulfur trioxide (SO3) reacts with water vapor. Both components are in gaseous form. 54 𝑆𝑂3+𝐻2𝑂→𝐻2𝑆𝑂4 (11) Sulfur acid is corrosive acid. This is why the PPTD in the boiler needs to be carefully determined if fuel contains sulfur. Water isn’t corrosive and since in the boiler the other side is dedicated to handling water in liquid and vapor phase, the pipes should handle the water vapor of the exhaust gas as well. The properties of exhaust gas from hydrogen burning don’t set boundaries to PPTD. 55 6. Design parameter calculation methods This chapter includes the methodology part of the thesis. Here the calculations and chosen methods for the MARPOWER project process are presented. The chapter focuses on how the cycle parameters can be optimized and how they affect the design. The literature for validating the results is also presented in this chapter. 6.1. Seawater temperature The effect of seawater temperature needs to be studied to see its effects on the process parameters. Boundary conditions need to be stated for the cycle since not all parameters can be optimized. Seawater is used in the intercooler to cool down the air from low-pressure compressor. The wanted outlet temperature for the air side in the intercooler is 25℃. To achieve this set value, the water inlet temperature needs to be obtained to set boundaries for the process. The depth where the water used in air-to-liquid intercooler is taken from is assumed to be close to the surface. The water directly from the surface is not used to avoid surface contamination and to ensures a stable water supply to the intercooler. As a methodology used to determinate a seawater temperature for this case, an article from Finnish Meteorological Institute (2023) is used. The article has used data from the Sea of Bothnia which will work as the reference point for the rest of the calculations. Data from both winter and summer time is collected so the intercooler graphs of both seasons can be compared. The smallest temperature difference in the heat exchanger is called the approach temperature. It is also a design parameter for the intercooler and in this case, it is calculated as in Equation 16. 𝑇𝑎𝑝𝑝𝑟𝑜𝑎𝑐ℎ =𝑇𝑎,𝑜𝑢𝑡 −𝑇𝑤,𝑖𝑛 𝑚𝑎𝑥 (16) , where 𝑇𝑤,𝑖𝑛 𝑚𝑎𝑥 is the maximum inlet temperature for seawater, 𝑇𝑎,𝑜𝑢𝑡 is the set air outlet temperature and 𝑇𝑎𝑝𝑝𝑟𝑜𝑎𝑐ℎ is the temperature difference between the first two temperatures, also called as the approach temperature. 56 Mathur (2024) stated in his paper that with liquid-to-liquid heat exchanger, the temperature approach can be as low as 1.1℃. The parameters that are critical for setting the possible approach temperature are mass flow of the cooling liquid and the size of the heat transfer areas and this is linked to the size of the intercooler itself. 6.2. Waste heat recovery boiler Waste heat recovery boiler is added to increase the energy efficiency of the process and to also improve the fuel savings. Boiler calculation originally had 2 pressure levels, highand low-pressure one. It was decided to continue with a single pressure boiler. The stages in the boiler are shown in Figure 20. If evaluated from the water/steam side, the stages start with economizer, next is evaporator and at the end the superheater. The pinch point temperature difference is the smallest temperature difference between the source and the working fluid. It is located between economizer and evaporator. Figure 20. Heat rate in the WHRB One parameter that needs to be optimized is the exhaust gas boiler outlet temperature. As this exhaust gas is released into the air it would be better to use the heat from it to heat the water in the boiler rather than waste it. The exhaust gas outlet temperature is strongly linked to the pinch point temperature difference. Increasing the exhaust gas boiler outlet temperature increases PPTD. If the PPTD is too small, it means that the heat exchanger surfaces have to be large for enough heat to convey from the working fluid to the water. As ships offer only very limited space for the energy system the devices need to be as compact as possible. Based on the literature available, the optimal PPTD for the waste heat recovery 57 boiler is usually between 5 to 20 ℃. This range ensures an efficient heat recovery and economic feasibility. Wu et al. (2014) stated in their paper that in some studies, the range is between 8 to 20 K and in some studies, it is between 3 to 7 K. Their own results show that the optimal PPTD range from the perspective of exergy recovery was 5-12 K 6.2.1. Pinch point temperature difference The pinch point is the point in the WHRS system where the temperature difference is the smallest between the working fluid and the source. Determining the optimal pinch point temperature difference or PPTD is important since it affects the heat transfer areas on the steam side. Achieving an optimal PPTD is also important from an economic point of view. The exhaust gas outlet temperature or the stack temperature in the boiler has a huge impact on PPTD. If the stack temperature is too high this means less heat transfer in the boiler itself. As the outlet exhaust gas isn’t used for energy production after the boiler, it is released into the air. The goal is to have a lower stack temperature since it reflects to the efficiency of the boiler positively and results in higher fuel-to-steam efficiency. (Bhatia, n.d.) In this case Newton’s method is used to find the PPTD. Newton’s method is used for solving equations, but it can be tailored for optimization purposes. As an optimization method Newton’s method is simple and linear. With this method the Excel calculates automatically the boiler outlet temperature for the exhaust gas based on the pinch point temperature that is given to it. Newton’s method is implemented into a macro and a button was created to run the macro when the pinch point temperature was changed (Polyak, 2011). Newton’s method for calculating the next value in the iteration process is shown in Equation 8. 𝑥𝑛+1 =𝑥𝑛−𝑓(𝑥) 𝑓′(𝑥) (8) For the derivative function, the numerical derivative is used. The simple approximation of the first derivative is shown in Equation 9. 𝑓′(𝑥)=𝑓(𝑥+𝑘)−𝑓(𝑥) 𝑘 (9) 64 graphs of intercooler stay the same despite the turbine inlet temperature since the water and the air entering the process are the same in both cases. From the cooled air, a side stream is created to help lower the turbine blade temperatureThis helps to mitigate the damage that high heat can cause. After the turbine the air enters the exhaust gas stream, and this mixture enters the recuperator. The same formula that was used to calculate the degree of recuperation can be used to verify the efficiency of the intercooler, and it results in about 0.90 as well. For the rest of the results, the seawater temperature of 1℃ is used. 7.2. Pinch point temperature difference The exhaust gas entering the boiler goes through the recuperator first to convey the heat from it to the air entering the combustor. Two different cases were compared with the difference being the turbine inlet temperature. In case 1 the TIT is above 1200 ℃ and in case 2 TIT is above 1300 ℃. The degree of recuperation doesn’t change as the PPTD changes. The degree of recuperation can be calculated as in Equation 1 in chapter 2.3.1 Recuperator technology. The result of the calculation is about 0.90, which is a typical value among recuperators (Xiao et al., 2017). Figures 24 and 25 show the recuperator graphs for both cases. 65 Figure 24. Recuperator heat rate, case 1 Figure 25. Recuperator heat rate, case 2 Recuperator graphs are influenced by the turbine inlet temperatures. When comparing the two cases, it’s seen that lower TIT results in lower exhaust gas value that then enters the waste heat boiler. In case 2 more thermal energy is available. The combination of exhaust gas after low-pressure turbine and the cooling flow of the high-pressure turbine blades set the total exhaust gas temperature under 700℃ in both cases. Air entering the recuperator is at the same temperature in both cases. After the recuperator, the exhaust gas enters the waste heat recovery boiler where the PPTD affects how much heat can be recovered from it. 0 100 200 300 400 500 600 700 020 40 60 80 100 Temperature [°C] Relative heat rate [%] Recuperator, case 1 Air Exhaust gas 0 100 200 300 400 500 600 700 020 40 60 80 100 Temperature [°C] Relative heat rate [%] Recuperator, case 2 Air Exhaust gas 66 The calculation for PPTD was run in Excel. The iteration was automated and done with a macro that uses Newton’s method. A button was created to achieve the PPTD for a specific boiler outlet temperature for the exhaust gas. The calculation shows that the pinch point is located between the economizer and evaporator in the WHRB. The results for cases 1 and 2 are presented in Figure 26 to show clearly the differences between them. The boiler outlet temperatures that were calculated based on Newton’s method are on the y-axis. The figure shows the outlet temperature and the PPTD that was used for the calculation. Figure 26. PPTD comparison of two cases The trend in both graphs is growing. In both cases the stack temperature increases about 1.2℃ when PPTD increases 1℃. This indicates that the systems are working stably. Case 2 achieves the same PPTD as case 1 but with lower values. Since case 2 has a higher TIT and lower stack temperatures, a higher efficiency can be reached for the system. The information can be used to form a graph to show the pinch point in the WHRB. Figure 27 presents case 1 and Figure 28 presents case 2. Boundary values for the boiler calculation is set. The temperature difference in the hot end is chosen to be 30℃ which is based on the information from the project. This brings the degree of superheating to about 100 ℃. The temperature difference between exhaust gas inlet temperature and steam outlet temperature also links to the sizing of the boiler 135 140 145 150 155 160 165 5678910 11 12 13 14 15 16 17 18 19 20 Eg boiler outelt temperature [℃] PPTD [℃] PPTD vs. Boiler outlet temperature Case 1 Case 2 67 equipment. With smaller temperature differences the size of superheater is expected to grow which isn’t the ideal solution on marine vessel application. Figure 27. Heat rate of water and exhaust gas for case 1 Figure 28. Heat rate of water and exhaust gas for case 2 0 50 100 150 200 250 300 020 40 60 80 100 Temperature [℃] Relative heat rate [%] Boiler pinch point, case 1 Water Exhaust gas 0 50 100 150 200 250 300 020 40 60 80 100 Temperature [oC] Relative heat rate [%] Boiler pinch point, case 2 Water Exhaust gas 68 The stages in both figures are clear, starting with economizer, then the evaporator and at the end the superheating phase of the steam. The pinch point temperature difference is 5.00 ℃. Exhaust gas graph is a linear line as is should be. When comparing the results it’s seen that while the same PPTD value is achieved, in case 2 it is achieved with higher exhaust gas inlet temperature and lower exhaust gas outlet temperature. This means that more heat is recovered in this case. 7.3. Heat transfer areas Pinch point temperature difference is an important parameter since it is linked to multiple other values. One parameter that PPTD determines is the size of the heat transfer area. The WHRB has three major components: economizer, evaporator and superheater. As stated before, the smaller the PPTD is, the bigger the heat transfer area needs to be to achieve the correct heat conversion between recovered and working fluid. The steam inlet values are set values. The inlet temperature is 50 ℃ and the pressure is 6 bars. Based on these and the pressure losses and mass flow, the parameters in different stages could be calculated. As the temperature difference in the hot end of the boiler is set for 30℃, Figures 29 and 30 show how changing the pinch point temperature difference affects the heat transfer areas of the boiler in both cases. Figure 29. Heat transfer area dependency over PPTD, case 1 0 200 400 600 800 1000 1200 1400 5678910 11 12 13 14 15 16 17 18 19 20 Heat transfer area [m^2] PPTD [℃] PPTD vs. Heat transfer area, case 1 Economizer Evaporator Superheater 69 Figure 30. Heat transfer area dependency over PPTD, case 2 The size of the heat transfer areas decrease while PPTD increases. The difference between the two cases isn’t big. The biggest change can be seen in the evaporator graph while the superheater’s heat transfer area barely changes. Between the first and the last point in the superheater graph there is around 12 m2 difference in both cases. In case 1 the overall heat transfer areas are a bit smaller with the same PPTD than in case 2. The reason behind it is that in case 2 with higher exhaust gas inlet temperature a smaller outlet temperature is reached thus more area is needed to transfer the heat. By the look of the graph the steepest change in both economizer and evaporator happens with smaller PPTD values. This means that the heat transfer area decreases the quickest in the beginning per 1℃ of PPTD increase. For further economic studies of the process this means that the cost of the heat exchanger varies most in the beginning of the graph. The curve is flattening as the PPTD increases and the derivative of the curve doesn’t present as big of a difference at the end of the curve versus at the beginning of the curve. The flattening effect is better seen in the curve representing economizer. 0 200 400 600 800 1000 1200 1400 5 7 9 11 13 15 17 19 Heat transfer area [m^2] PPTD [℃] PPTD vs. Heat transfer area, case 2 Economizer Evaporator Superheater 70 7.4. Exhaust gas thermal power Another value that the pinch point temperature difference adjusts is the heat rate. Heat rate shows how much heat there is for the exhaust gas to give to the steam. With boiler efficiency, the thermal power of the steam can be calculated. In both cases the boiler efficiency is 98 %. The results are based on Equation 12 and 13 and are presented in Figures 31 and 32. Figure 31. Thermal power dependency on PPTD, case 1 Figure 32. Thermal power dependency on PPTD, case 2 1200 1300 1400 1500 1600 1700 1800 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 Thermal power [kW] PPTD [℃] PPTD vs. Thermal power, case 1 Exhaust gas thermal power Heat rate to steam 1200 1300 1400 1500 1600 1700 1800 1900 5678910 11 12 13 14 15 16 17 18 19 20 Thermal power [kW] PPTD [℃] PPTD vs. Thermal power, case 2 Exhaust gas thermal power Heat rate to steam 71 The difference between the cases is noticeable. The higher the PPTD, the lower the thermal power from the exhaust gas to the steam is. This aligns with the expectations since this means that with higher PPTD smaller heat transfer areas are needed in the boiler. The curves are quite linear, and no bigger fluctuation is occurring between the data points. The thermal drop between each PPTD point is between 16 and 17 kW in case 1. Case 2 shows a slightly smaller thermal drop, between 15 and 16 kW. Based on this, in both cases the heat transfer through the boiler is stable. 7.5. Efficiency Pinch point temperature difference as well as seawater temperature affect the net electric efficiency of the process. Figures 33 and 34 show the difference between the two seasons and the PPTD’s effect on the system that has a WHRS. Figure 33. Efficiency dependency on PPTD, winter 50 50,2 50,4 50,6 50,8 51 51,2 51,4 51,6 51,8 5 7 9 11 13 15 17 19 Net electic efficiency [%] PPTD [℃] Efficiency with WHRS, winter Case 1 Case 2 72 Figure 34. Efficiency dependency on PPTD, summer As the two cases are compared some significant changes can be seen between the two seasons. When PPTD increases, efficiency decreases. The graphs aren’t completely linear, and some dips are noticeable after 9℃. The difference between the two cases in both figures is almost 1%pt. Seawater temperature has its impact on achieving higher efficiency. As seen, during winter the efficiency tends to be about 0.1%pt better than during summer. Figure 35 is created to show how much it actually affects the system if the WHRS is installed. Figure 35. Comparison of net electric efficiency 50 50,2 50,4 50,6 50,8 51 51,2 51,4 51,6 51,8 5678910 11 12 13 14 15 16 17 18 19 20 Net electic efficiency [%] PPTD [℃] Efficiency with WHRS, summer Case 1 Case 2 0 5 10 15 20 25 30 35 40 45 50 55 Case 1 Case 2 Efficiency [%] Net electric efficiency Case1 Case 2 73 In case 1 the turbine inlet temperature is above 1200 ℃ and in case 2 it is above 1300 ℃. The two cases show clearly that with higher TIT and with the waste heat recovery system, the efficiency increases. As seen in chapter 7.4, more heat is recovered with lower exhaust gas outlet temperature which leads to higher exhaust gas thermal power. This is why the net electricity efficiency is better in case 2. The impact of pressure ratios change was also studied. With higher pressure ratio, the thermal power increased but the Carnot-efficiency decreased. By increasing the pressure ratio to 13:1, the thermal power increased by 1% and the Carnot-efficiency decreased by 1%. The changing of pressure ratio works in the other direction too. If the pressure ratio is decreased, then the Carnot-efficiency increases but the thermal power decreases. It’s also been noted that lower seawater temperature increases Carnot-efficiency. 80 European Commission, d. n.d. Biomethane. Available: https://energy.ec.europa.eu/topics/renewable-energy/bioenergy/biomethane_en European Maritime Safety Agency. 2022. Update on potential of biofuels in shipping, EMSA, Lisbon. Available: file:///C:/Users/z084922/Downloads/Ammonia%20as%20fuel%20in%20shipping_rev1_Se pt23.pdf Erixno, O. 2021. Energy management of renewable energy-based combined heat and power systems: A review. Sustainable Energy Technologies and Assessments. 51, 101944. Available: https://doi.org/10.1016/j.seta.2021.101944 Fatsis, A. 2019. Design point analysis of two-shaft gas turbine engines topped by four-port wave rotors for power generation systems. Propulsion and Power Research. 8, 183-193. Available: https://doi.org/10.1016/j.jppr.2019.06.001 Faqih, M. et al. 2022. Dry-Low Emission Gas Turbine Technology: Recent Trends and Challenges. Appl. Sci. 2022, 12(21), 10922. Available: https://doi.org/10.3390/app122110922 Finnish Meteorological Institute. 2023. The stratification of the Baltic Sea. Available: https://en.ilmatieteenlaitos.fi/stratification Foretich, A et al. 2021. Challenges and opportunities for alternative fuels in the maritime sector. Maritime Transport Research. 2, 100033. Available: https://doi.org/10.1016/j.martra.2021.100033 GE Vernova, 2025. LM2500 aeroderivative gas turbine. Available: https://www.gevernova.com/gas-power/products/gas-turbines/lm2500 Giampaolo, T. 2014. Gas Turbine systems Theory. Gas Turbine Handbook: Principles & Practice 5th Edition. 45. Portland: CRC Press. Available: ISBN: 9781482228885 Goldmeer, J. & Catillaz, J. Hydrogen for power generation. Available: https://www.gevernova.com/content/dam/gepower-new/global/en_US/downloads/gas-newsite/future-of-energy/hydrogen-for-power-gen-gea34805.pdf Goswami, D.Y. & Kreith, F. 2017. Energy Conversion. 2nd Edition. 219. CRC Press. Available: ISBN:978–1–4665–8482–2 81 Green, D. W. & Perry, R. H. 2008. Perry’s chemical engineers’ handbook 8th Edition. 1154. McGraw-Hill. Available: ISBN 978-0-07-142294-9 Hosseini, S. H. et al. 2023. Use of hydrogen in dual fuel diesel engines. Progress in energy and Combustion Science. 98, 101100. Available: https://doi.org/10.1016/j.pecs.2023.101100 IMO, a. n.d. Introduction to IMO. Available: https://www.imo.org/en/About/Pages/Default.aspx IMO, b. n.d. UN body adopts climate change strategy for shipping. Available: https://www.imo.org/en/MediaCentre/PressBriefings/Pages/06GHGinitialstrategy.aspx Kim, S. et al. 2024. HEAT TRANSFER ENHANCEMENT FOR GAS TURBINE BLADE INTERNAL COOLING WITH LATTICE STRUCTURED RIB. Proceedings of ASME Turbo Expo 2024. GT2024-122753 Le, T. T. et al. 2023. Fueling the future: A comprehensive review of hydrogen energy systems and their challenges. International Journal of Hydrogen Energy. 54, 791-816. Available: https://doi.org/10.1016/j.ijhydene.2023.08.044 Li, J. et al. 2021. Current Status and Prospects of Gas Turbine Technology Application. Journal of Physics: Conference Series. 2108 012009. Available: https://iopscience.iop.org/article/10.1088/1742-6596/2108/1/012009/pdf Li, J. & Li, Y. 2023. Micro gas turbine: Developments, applications, and key technologies on components. Propulsion and Power Research. 12, 1-43. Available: https://doi.org/10.1016/j.jppr.2023.01.002 Mallouppas, G. & Yfantis, E. A. 2021. Decarbonization in Shipping Industry: A Review of Research, Technology Development, and Innovation Proposals. J. Mar. Sci. Eng. 2021, 9(4), 415. Available: https://doi.org/10.3390/jmse9040415 MARPOWER. 2025. MARPOWR-Project. Available: https://marpowerproject.eu/ Mathur, A. P. 2024. Eliminating or Handling Very Close Temperature Approach in Sizing a Heat Exchanger. ASHRAE Journal. 66, 38-42. Available: https://www.proquest.com/docview/3121701597?accountid=27292&sourcetype=Scholarly %20Journals 82 Mazloomi, K. & Gomes, C. 2012. Hydrogen as an energy carrier: Prospects and challenges. Renewable and Sustainable Energy Reviews. 16, 3024-3033. Available: https://doi.org/10.1016/j.rser.2012.02.028 Memet, F. & Faitar, C. 2019. A thermodynamic optimization of a gas turbine cycle with a supplementary regenerator. IOP Conference Series: Materials Science and Engineering. 591 012094. Available: https://iopscience.iop.org/article/10.1088/1757899X/591/1/012094/pdf Mitsubishi. 2023. Mitsubishi Power Successfully Operates an Advanced Class Gas Turbine with 30% Hydrogen Fuel Co-Firing at Grid-Connected T-Point 2. Available: https://www.mhi.com/news/23113001.html Mitsubishi. n.d. H-25 Gas Turbines. Available: https://solutions.mhi.com/power/decarbonization-technology/h-25-gas-turbines/ Mollenhauer, K. & Tschöke, H. 2010. Handbook of Diesel Engines. Springer Heidelberg Dordrecht London New York. DOI 10.1007/978–3–540–89083–6 Motiva. n.d. Energiatehokas lämmönsiirto. Available: https://www.motiva.fi/files/11078/Energiatehokas_lammonsiirto_opas.pdf Placek, M. 2023. Energy density of maritime fuels in 2020, by fuel type. Statista. Available: https://www.statista.com/statistics/1279431/energy-density-of-maritime-fuels/ Polyak, B. T. 2011. Newton’s method and it’s use in optimization. European Journal of Operational Research. 181, 1086-1096. Available: https://doi.org/10.1016/j.ejor.2005.06.076 Poullikkas, A. 2024. An overview of current and future sustainable gas turbine technologies. Renewable and Sustainable Energy Reviews. 9, 409-443. Available: https://doi.org/10.1016/j.rser.2004.05.009 Regulation (EU) 2023/1805. 2023. Regulation (EU) 2023/1805 of the European Parliament and of the Council of 13 September 2023 on the use of renewable and low-carbon fuels in maritime transport, and amending Directive 2009/16/EC. Available: https://eurlex.europa.eu/eli/reg/2023/1805/oj/eng 83 Sayma, I. A. 2017. Gas Turbines for Marine Applications. In: Carlton, J., Jukes, P. & Sang, C-Y. (Eds.), Encyclopedia of Maritime and Offshore Engineering. 1-10. John Wiley & Sons, Ltd. Available: ISBN 9781118476406 Senmatic. n.d. The 5 most relevant marine fuels right now. Available: https://senmatic.com/knowledge/sensor/the-5-most-relevant-marine-fuels-right-now/ Siemens. n.d. Reliable gas turbines. Available: https://www.siemensenergy.com/global/en/home/products-services/product-offerings/gas-turbines.html Siemens Energy. 2025. Zero Emission Hydrogen Turbine Center. Available: https://www.siemens-energy.com/global/en/home/products-services/solutionsusecase/hydrogen/zehtc.html Sollai, S. et al. 2022. Renewable methanol production from green hydrogen and captured CO2: A techno-economic assessment. Journal of CO2 Utilization. 68, 102345. Available: https://doi.org/10.1016/j.jcou.2022.102345 Statista. 2023. Annual fuel consumption by ships worldwide from 2019 to 2020, by fuel type. Available: https://www.statista.com/statistics/1266963/amount-of-fuel-consumed-byships-worldwide-by-fuel-type/ Statista. 2024. Carbon dioxide emissions from international shipping worldwide from 1970 to 2023. Available: https://www.statista.com/statistics/1291468/international-shippingemissions-worldwide/ Theotokatos, G. et al. 2016. Investigation of ship cooling system operation for improving energy efficiency. Journal of Marine Science and Technology. 22, 38-50. Available: https://doi.org/10.1007/s00773-016-0395-9 Thurman, A. a. 2023. Ammonia as marine fuel? It is easier if you do it smart. Wärtsilä. Available: https://www.wartsila.com/insights/article/ammonia-fuel-for-thought-in-ourdeep-dive Thurman, A. b. 2023. Methanol as marine fuel-is it the solution you are looking for? Available: https://www.wartsila.com/insights/article/methanol-fuel-for-thought-in-ourdeep-dive-q-a 84 Tingas, E. 2023. Hydrogen Combustion in Gas Turbines. Gkantonas S. et al. Hydrogen for Future Thermal Engines. 409-411. Cham: Springer Nature Switzerland. Available: ISBN 978-3-031-28411-3 U.S. Department of Energy. n.d. Hydrogen Storage. Available: https://www.energy.gov/eere/fuelcells/hydrogen-storage Wang, Z. et al. 2023. Analysis and evaluation of fuel cell technologies for sustainable ship power: Energy efficiency and environmental impact. Energy Conversion and Management: X. 21, 100482. Available: https://doi.org/10.1016/j.ecmx.2023.100482 Wu, S-Y. et al. 2014. Determining the optimal pinch point temperature difference of evaporator for waste heat recovery. Journal of the Energy Institute. 87, 140-151. Available: https://doi.org/10.1016/j.joei.2014.03.010 Wärtsilä, a. 2025. Onboard carbon capture and storage. Available: https://www.wartsila.com/marine/products/exhaust-treatment/carbon-capture-and-storage Wärtsilä, b. 2025. Future fuels in shipping. Available: https://www.wartsila.com/marine/decarbonisation/future-fuels-development Xiao, G. et al. 2017. Recuperators for micro gas turbines: A review. Applied Energy. 197, 83-99. Available: https://doi.org/10.1016/j.apenergy.2017.03.095 Yang, N. et al. 2023. High pressure hydrogen leakage diffusion: Research progress. International Journal of Hydrogen Energy. 50, 1029-1046. Available: https://doi.org/10.1016/j.ijhydene.2023.08.221 Yu, C. et al. 2021. Analysis of Water-Cooled Intercooler Thermal Characteristics. Energies 2021, 14(24), 8332. Available: https://doi.org/10.3390/en14248332 Zhang, T. et al. 2023. Hydrogen liquefaction and storage: Recent progress and perspectives. Renewable and Sustainable Energy Reviews. 176, 113204. Available: https://doi.org/10.1016/j.rser.2023.113204 Zuo, W. et al. 2020. Review of flue gas acid dew-point and related low temperature corrosion. Journal of the Energy Institute. 93, 1666-1677. Available: https://doi.org/10.1016/j.joei.2020.02.004 85 Öberg, S. et al. 2021. Exploring the competitiveness of hydrogen-fueled gas turbines in future energy systems. International Journal of Hydrogen Energy. 47, 624-644. Available: https://doi.org/10.1016/j.ijhydene.2021.10.035