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March 6, 2025

Steam is a vital energy source on cruise ships, serving a wide range of purposes that contribute to both operational efficiency and passenger comfort.

It is used for heating, hot water production, fuel treatment, freshwater generation, laundry, galley operations, and waste management. Due to its high energy-carrying capacity and efficient heat transfer properties, steam is the most effective medium for shipboard thermal energy needs.

A key characteristic of steam is its ability to store and transfer large amounts of heat through latent heat of vaporization. Unlike hot water, which gradually loses heat as it cools, steam releases a significant amount of energy as it condenses, making it an efficient and uniform heat source. Steam can also be distributed through insulated piping systems with minimal loss, allowing for effective heating across the entire ship.

The method of steam production varies depending on whether the ship is at sea or in port. While sailing, waste heat from the main diesel engines is used to generate steam via exhaust gas boilers (EGBs), ensuring high energy efficiency. When in port, where the main engines are either shut down or operating at low loads, steam must be produced using fuel-fired auxiliary boilers. Both methods have their own advantages and operational considerations, which will be explored in detail.

What is steam and why is it a powerful energy carrier?

Steam is the gaseous phase of water, formed when liquid water is heated beyond its boiling point. The key reason why steam is such an effective energy carrier is due to its latent heat of vaporization—the significant amount of energy absorbed during the phase change from liquid to gas. This makes steam an efficient means of transferring heat, as it carries a large quantity of thermal energy in a relatively small volume.

In thermodynamic terms, steam possesses two primary energy components:
– Sensible Heat (Specific Enthalpy of Water): The heat required to raise the temperature of water to its boiling point.

– Latent Heat of Vaporization: The energy absorbed during phase transition without a temperature change, allowing steam to store and transport substantial heat energy.

For example, heating water from 0°C to 100°C requires approximately 419 kJ/kg. However, converting it into steam at 100°C requires an additional 2,257 kJ/kg, which is over five times the energy required to heat the water. When steam condenses back into liquid, it releases this stored latent heat, making it an excellent medium for heat transfer in shipboard systems.

Why ships use steam instead of other heat transfer mediums

Compared to hot water or thermal oil, steam offers several advantages, like:

– Higher Energy Density: Steam carries more energy per unit mass than hot water, reducing the volume required for heat distribution.
– Self-Pressurizing System: Steam naturally moves through the piping system due to pressure differences, eliminating the need for pumps in many applications.
– Uniform Heating: Steam condenses at a constant temperature, ensuring even heat distribution, unlike heated water, which cools gradually.
– Reusability: Condensed steam (condensate) can be collected, reheated, and reused, making it a sustainable heat source. By recovering and reusing condensate, ships improve fuel efficiency, conserve freshwater, and minimize energy waste. Condensate is collected from steam consumers then returned to the boiler feedwater system. Since condensate is already purified and preheated, it reduces thermal shock in boilers and prevents scaling caused by mineral deposits. Efficient condensate recovery lowers operational costs, enhances sustainability, and ensures continuous steam availability for shipboard systems.

Steam Producers on a Cruise Ship

On board a cruise ship steam is primarily generated through two main systems:
– Auxiliary Fuel-Fired Boilers – These produce steam by burning marine fuel, mainly when the ship is in port.
– Exhaust Gas Boilers (EGBs) – These utilize waste heat from the main engines while the ship is at sea.

Auxiliary Fuel-Fired Boilers – Steam Production in Port

When a cruise ship is docked in port, its main engines are either operating at low loads or shut down, meaning that exhaust gas boilers cannot generate sufficient steam. Instead, fuel-fired auxiliary boilers produce steam by burning marine gas oil (MGO) or low-sulfur fuel oil (LSFO), which complies with port emission regulations.

The process works as follows:
– Fuel is burned in a combustion chamber, heating water inside the boiler tubes.
– The heat converts water into steam, reaching temperatures of 170–190°C at 7–10 bar pressure.
– The steam is distributed to various onboard systems.
– The used steam condenses into water and is returned to the boiler for reuse.

These units provide a steady and controllable steam supply but require additional fuel consumption, increasing operational costs. Environmental regulations in some ports restrict emissions, sometimes requiring ships to rely on shore power for electricity. However, since shore power does not supply steam, auxiliary boilers often remain necessary.

Exhaust Gas Boilers (EGBs) – Steam Production at Sea

While the ship is sailing, exhaust gas boilers recover waste heat from the ship’s propulsion engines, making steam production energy-efficient. The exhaust gases from these large diesel engines reach temperatures of 300°C to 450°C, and instead of being expelled directly into the atmosphere, this heat is captured and used to convert water into steam.

The process works as follows:
– Hot exhaust gases from the ship’s main engines flow through a series of water-filled tubes inside the boiler.
– Heat is transferred to the water, turning it into saturated steam at approximately 7–10 bar (170–185°C).
– The cooled exhaust gases are then released through the funnel.
– The generated steam is distributed to various systems, including heating, fuel treatment, and evaporators.
Since this method relies on engine exhaust, the amount of steam produced depends on the engine load. If the ship is cruising at lower speeds or maneuvering, the exhaust temperature may not be sufficient for full steam production, requiring supplementary fuel-fired boilers.

Steam Consumers on a Cruise Ship

Steam is distributed throughout the ship to various consumers, including:
– Heating Systems – Cabin, corridor, and public space heating.
– Hot Water Production – Steam heats freshwater for showers, sinks, and kitchens.
– Fuel Heating – Heavy fuel oil (HFO) must be preheated to reduce viscosity.
– Evaporators – Seawater is converted into freshwater for drinking and washing.
– Laundry Operations – Industrial washers, dryers, and pressing equipment.
– Galley and Food Preparation – Cooking, dishwashing, and sterilization.
– Waste Management – Sterilization of biohazardous waste and volume reduction.

Each consumer requires steam at specific temperatures and pressures, depending on its operational function. Ships use different steam pressures for various applications because pressure determines the steam’s temperature and energy content. Higher-pressure steam contains more energy, but it also requires stronger piping and safety measures. The steam distribution system is designed with multiple pressure levels to optimize efficiency and safety.

– High-Pressure Steam (7–10 bar, 170–190°C): Used for high-energy applications such as fuel heating, high-capacity evaporators, and heavy-duty laundry operations.
– Medium-Pressure Steam (4–6 bar, 140–160°C): Used for general heating, hot water production, and steam ovens in the galley.
– Low-Pressure Steam (1–3 bar, 100–130°C): Used for air humidification, low-temperature heating, and delicate laundry applications.
– Steam in Heating Systems

Cruise ships need to maintain a comfortable indoor climate for passengers and crew, especially when sailing through colder regions. Steam is used in heating coils, fan coil units, and heat exchangers to transfer heat to the ship’s ventilation system.

– Heating Coils and Fan Coil Units: Steam at 6–8 bar (160–175°C) passes through heating coils, warming the air that is circulated throughout the ship’s ventilation system.
– Deck and Window Heating: To prevent condensation or freezing in colder climates, heated pipes running beneath external decks and around windows maintain temperatures above freezing.
– Steam in Hot Water Production

Steam is used to heat freshwater for showers, sinks, and kitchen use through hot water heat exchangers, with the following process:

– Steam at 4–6 bar (140–160°C) enters a heat exchanger.
– Cold freshwater absorbs heat, reaching a final temperature of 60–70°C.
– The hot water is stored in insulated tanks before distribution.
– Steam in Fuel Heating

Heavy fuel oil (HFO) is highly viscous at ambient temperatures and must be heated to 120–140°C before being used in the engines. To do that, steam at 6–8 bar (160–175°C) is circulated through heat exchangers in fuel tanks and pipelines. This way, the heated fuel reaches the correct viscosity for efficient atomization and combustion in diesel engines.

– Steam in Evaporators (Freshwater Production)

Cruise ships can produce their own freshwater using evaporators, which use steam to remove salt from seawater. This process is done only when the ship is at sea and mostly of the steam used in this condition is produced by the EGBs. The process consists in using steam at 5–6 bar (150–160°C) to heat seawater inside a vacuum chamber. The vacuum lowers the boiling point to 40–60°C, allowing the water to evaporate efficiently, then the vapor is condensed into freshwater, leaving the salt behind. The condensed freshwater is stored for drinking, cooking, and washing.

– Steam in Laundry Operations

A cruise ship’s laundry facility processes thousands of linens, towels, and uniforms daily. A standard marine laundry includes:

– Industrial Washing Machines: Steam at 4–5 bar (130–150°C) heats water to 90°C for effective cleaning.
– Steam Dryers: Steam at 6–8 bar (160–175°C) dries fabrics faster and more evenly than electric dryers.
– Steam Pressing and Ironing Equipment: Steam at 4–5 bar (130–150°C) removes wrinkles and sanitizes fabrics.
– Steam in the Galley (Ship’s Kitchen)

The galley on a cruise ship can operate 24/7 to serve thousands of passengers and crew. A marine standard galley includes:

– Steam Ovens: Steam at 4–5 bar (130–150°C) provides even heat distribution for large-scale cooking.
– Dishwashing Equipment: Steam at 5–6 bar (140–160°C) ensures high-temperature sanitization of utensils.
-Steam Kettles: Steam at 6 bar (160°C) is used to cook soups, sauces, and stews efficiently.
-Steam in Waste Management

Cruise ships produce significant waste, including food scraps, packaging, and biohazards. Steam is used in:

– Biohazard Waste Sterilization: Steam at 6–8 bar (160–175°C) sterilizes medical and organic waste.
– Compaction and Drying: Steam reduces moisture content, minimizing waste volume before disposal.

Conclusion

Steam is an essential component of cruise ship operations, serving a wide range of critical functions. While at sea, exhaust gas boilers efficiently produce steam by recovering waste heat, whereas in port, fuel-fired boilers generate steam when the engines are not running. Steam consumers, such as heating systems, evaporators, laundry facilities, galleys, and waste management systems, rely on carefully controlled steam temperatures and pressures.

As cruise ships continue to evolve toward greater energy efficiency, advancements in waste heat recovery, alternative fuels, and environmental regulations will play a key role in optimizing steam production and utilization. Understanding the intricate relationship between steam producers and consumers is crucial for maintaining smooth and efficient maritime operations.

Don’t miss more updates, news and informations about the world of cruises on Cruising Journal.

Luca Paglia

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