Sea Water Desalination Using Waste Heat: A Desalination System for Small and Medium Ships Using Exhaust Heat of the Engine

Abstract

Marine engine-generated waste heat presents a great potential for efficient desalination. In this research, the investigators explore a desalination system that uses the exhaust gas of a marine engine to convert seawater into fresh water. The configuration includes a heat exchanger that transfers the exhaust heat to a thermal desalination unit, where seawater is vaporized and condensed into freshwater. By tapping into waste heat, this system not only cuts down on fuel consumption but also lessens environmental impact and boosts the availability of fresh water onboard. This makes it a perfect fit for fishing vessels, cargo ships, and offshore platforms. The study emphasizes the design, efficiency, and economic viability of merging desalination with marine engines, presenting a sustainable approach to producing fresh water at sea.

Introduction

The project aims to develop a desalination system that utilizes waste heat from marine engine exhaust and cooling water to produce freshwater for small ships without conventional freshwater generators. This approach reduces fuel use, increases onboard sustainability, and supports long-term operations in remote maritime areas.

Key Features

• No external energy required: Uses waste thermal energy already generated by the ship.

• Sustainable & efficient: Enhances fuel efficiency, reduces emissions, and boosts freshwater self-sufficiency.

• Target vessels: Small fishing boats, cargo ships, offshore platforms.

System Design & Operation

A. Heat Sources

• Engine exhaust gases (up to 1050°C).

• Cooling water from the engine jacket.

B. Desalination Process

• Multi-effect distillation (MED) or multi-stage flash (MSF).

• Steps:

  1. Preheat seawater using cooling water.

  2. Further heat it using exhaust gas via heat exchanger.

  3. Evaporate and condense to extract freshwater.

  4. Collect and store freshwater onboard.

  5. Dispose brine back to the sea.

Material Selection

• Heat exchangers: Stainless Steel 316L, Titanium, or Copper-Nickel alloy for corrosion resistance and thermal conductivity.

• Pipes: PVC or HDPE for seawater intake and internal flows.

Performance Testing

• Heat transfer efficiency: Measured with sensors; real values compared to theoretical.

• Freshwater output: Measured in liters/hour; water quality checked.

• Fouling & scaling: Assessed to ensure long-term system reliability.

Energy & Time Calculations

• Energy needed to desalinate 10L seawater: ~26,182 kJ.

• Energy available from engine exhaust (Cummins 6.7L, 300 HP): ~167.3 kW.

• Time to boil 10L under ideal conditions: ~2.6 minutes (real time: 5–10 minutes due to losses).

System Components

1. Seawater intake & pre-treatment filter

2. Exhaust gas heat exchanger

3. Evaporation chamber

4. Condenser & freshwater tank

5. Brine discharge system

Conclusion

Utilizing waste heat from the engine exhaust for seawater desalination on small ships is a practical and energy-efficient solution. Based on calculations, the exhaust gases from a Cummins 6.7L marine engine can provide sufficient energy to boil 10 liters of seawater in about 5–10 minutes, depending on heat exchanger efficiency.

References

Books & Research Papers: [1] \"Waste Heat Recovery in Shipboard Systems\" – A technical paper on using engine exhaust for heat recovery. [2] \"Seawater Desalination: Conventional and Renewable Energy Processes\" by Andrea Cipollina, Giorgio Micale, and Lucio Rizzuti. [3] \"Marine Diesel Engines: Maintenance, Troubleshooting, and Repair\" by Nigel Calder – Covers heat recovery applications. Industry & Technical Reports: [1] International Maritime Organization (IMO) reports on energy efficiency in shipping. [2] U.S. Department of Energy (DOE) reports on industrial waste heat recovery. [3] American Bureau of Shipping (ABS) Guidelines on marine heat exchangers. Online Sources & Manufacturers: [1] Cummins Marine Engine Manuals – Available from Cummins official website. [2] Waste heat desalination case studies from research journals like ScienceDirect and IEEE Xplore.

Copyright

Copyright © 2025 Ayush Pudke, Aditya Krupan, Somsen Rahagdale, Prof. Vijayshree Mohabiya. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.