The glycol-jacketed ISO tank uses a full external jacket carrying glycol-water mixture or hot water for gentle heating compatible with food-grade applications. The temperature gradient is much smaller than steam jacketing (60 to 80 deg C glycol vs 150 to 175 deg C steam), so the cargo never sees a hot spot at the wall. Eltherm, Holvrieka, Klinge, and Loebbe are the major builders. Used heavily for liquid chocolate, liquid sugar, honey, and edible oils that need gentle heating without the risk of caramelisation or thermal degradation.
What glycol-jacketed is built for
Cargoes that need heating but cannot tolerate the higher wall temperature of steam coils. Liquid chocolate at 45 deg C is the canonical cargo; the chocolate caramelises if it touches a hot steam-coil surface above 60 deg C, but tolerates a 50 deg C glycol jacket indefinitely. Liquid sugar and glucose syrup ship heated to prevent crystallisation; honey ships heated to maintain pourability. Edible oils that need protection against melt-point fluctuations during ocean transit (palm oil, coconut oil, beef tallow).
Construction and materials
316L stainless cylinder, 6 mm reference shell, with a full external glycol or hot-water jacket. The jacket is a second cylindrical shell offset from the cargo shell by 50 to 100 mm, with the annular space filled with circulating glycol-water (typically 30 to 50% propylene glycol). External insulation 100 mm polyurethane foam under aluminium or GRP cladding minimises heat loss. The glycol circulation runs through a pump-and-heat-exchanger system either onboard the tank (electric heater on shore power) or external (steam to glycol heat exchanger at loading and discharge ports).
When glycol-jacketed is the right choice
Glycol-jacketed is the right tank for food-grade cargoes that need heating below 80 deg C and where steam-coil thermal gradients are unacceptable. The build cost premium versus a steam-coil tank is modest (around USD 2,000 to 3,000) and the food-grade compatibility justifies it for the dedicated food-grade fleet.
When glycol-jacketed is the wrong choice
Glycol-jacketed is the wrong tank for cargoes that need higher operating temperatures (above 80 deg C glycol-system limit). Steam-coil or steam-jacketed is the right answer for higher-temperature service. The glycol system also needs more maintenance than steam coils (pump, heat exchanger, glycol-circulation integrity); operators with deep glycol-fleet expertise (Stolt, Hillebrand-Gori) handle this routinely.
How a glycol-jacketed booking is verified
Pre-loading inspection covers the standard food-grade plate stack plus the glycol-system condition: glycol level and concentration, pump operability, heat-exchanger seal integrity, and the operator’s heating-temperature log from prior service. The cargo loads at temperature and the heating system maintains operating temperature through the ocean leg.