Tugboats are the tireless workhorses of the world’s rivers and harbors. These powerful watercraft must remain on standby for long periods, ready to assist other vessels at a moment’s notice. The energy required to keep the engines warm and the cabin comfortable in cold climates is usually derived from electrical shore power. That’s expensive and inefficient.
Kotug International BV has developed an on-board system that captures heat produced by the engines and stores it in a tank that contains phase change material. The Dutch company installed the heat recycling system on one of its tugboats, the ZP Bison, in 2016. The result: Shore power consumption has been cut in half on the Hamburg-based tugboat.
Koos Smoor, manager for fleet performance and innovation at Kotug, oversaw development of the system, which won the Maritime Innovation Award 2017 in November.
“The use of PCM technology is new in the maritime industry and has great potential not only for tugboats, but for every type of vessel, as it can be tailored to different spaces and user profiles,” Smoor said. “Kotug is looking into more applications for temperature control purposes.”
Smoor answered a few PCM-related questions by e-mail:
Q: When did Kotug begin developing the heat recycling system?
A: “Two years ago we tested heat storage on our hybrid tugs to reduce the ‘hotel load’ during standby. The hotel load is the generator load in kilowatts when the tug is not working. It is mainly heating or cooling and pre-heating of the main engines.”
Q: What type of PCM is used in the system (salt hydrate, paraffin, biobased)?
A: “We are still testing multiple PCM materials.”
Q: What is the PCM's peak melting point?
A: “85 degrees is the 'coolwater' temperature of the engines. The coolwater of the main propulsion engines is used to heat up the PCM buffer. We also did test to use heat from the exhaust gasses to heat up the PCM buffer. However that is more complicated, and we stopped with that.”
Q: What is the PCM's heat capacity?
A: “The heat capacity is 73 Kwhr/m3.”
Q: How is the PCM tank configured, what are its dimensions, how much PCM is used?
A: “The PCM tank [shown at right] is approximately 2 cubic meters. The PCM is warmed up by the coolwater of the engines. We like to keep the heat exchanger in the buffer for ourselves as we are working on a patent.”
Q: Who is the PCM manufacturer?
A: “The PCM material is manufactured in China.”
Q: How many tugboats are in Kotug's fleet?
A: “Worldwide Kotug and its joint ventures consist of approximately 120 tugboats.”
Q: Are there plans to install the heat recycling system in other Kotug vessels?
A: “Yes, we are looking into more installations on more tugboats. The installation can be done during the five-year maintenance period cycle of the tugboat. Note: Many tugs operate in the tropics where there is no need to preheat the engines. On these tugs there is no application for PCM materials.”
Q: Are there plans to license the technology for use by other towage operators?
A: “We are still looking into this.”