Heating Skid for OCCS Solvent Preheating

The Jacket Water Heat Recovery Skid for OCCS Solvent Preheating is a compact, purpose-built auxiliary unit designed to harvest low-grade thermal energy from the engine’s jacket water (JW) cooling circuit and redirect it into the Onboard Carbon Capture System (OCCS) process as a pre-heating stage for the rich amine solvent stream. Rather than replacing the primary solvent regeneration heat exchanger, this skid acts as an upstream thermal conditioner — delivering a meaningful temperature boost to the cold rich solvent before it enters the main (exhaust-gas-driven) regeneration heat exchanger. This reduces the thermal duty incumbent on the primary heat source, improving overall cycle efficiency and reducing wear on the high-temperature heat exchange equipment.

Engine coolant circulates continuously through the engine block, absorbing combustion heat to maintain safe operating temperatures. After leaving the engine, this water typically sits in the 75–85 °C range — too cool for effective solvent regeneration, but perfectly suited for pre-heating. The JW enters the skid at temperature element TE-101 (mounted at the engine outlet) and is directed toward the plate heat exchanger via the main supply header. Temperature transmitter TT-102 confirms the supply-side temperature immediately upstream of the heat exchanger. After giving up heat to the solvent, the cooled jacket water exits via the bottom of the plate heat exchanger, its temperature recorded at TT-103, and is returned to the engine’s thermal management circuit.

On the Rich Amine Solvent Side, CO₂-laden (rich) amine solvent arrives at the skid from the base of the absorption column at a relatively low temperature. It enters the plate heat exchanger from the bottom port, absorbs thermal energy from the jacket water flowing on the opposing plate faces, and exits the top port at a meaningfully elevated temperature. Temperature transmitter TT-104 monitors solvent inlet temperature and TT-105 confirms the pre-heated outlet temperature. The warmed rich solvent then continues forward to the main regeneration heat exchanger, entering it with reduced thermal deficit and thus demanding less high-grade heat input for full regeneration.

The heat exchanger is a gasketed or semi-welded plate type, selected for its high surface-area-to-volume ratio and ease of cleaning — both important considerations given amine fouling tendencies. The two fluid streams pass on alternating plate faces in a counter-flow arrangement, maximising the mean temperature difference and therefore thermal transfer efficiency even at the relatively modest 75–85 °C driving temperature available from the jacket water. The exchanger is sized to transfer the maximum allowable heat extraction rate permitted by the engine manufacturer’s thermal management guidelines, ensuring the engine outlet temperature never drops below its minimum operational threshold under any operating condition.

The most critical control element on the skid is the modulating bypass valve MV-101, located on the jacket water supply side. This valve continuously splits the JW flow between two paths: one through the plate heat exchanger (heat extraction path) and one bypassing it entirely, rejoining the cooled return stream before re-entering the engine. By modulating the proportion of flow through each path, the valve governs precisely how much heat is extracted from the engine coolant at any given moment.

This bypass is not merely a convenience — it is a safety-critical engine protection mechanism. All marine engines have a minimum jacket water temperature requirement; if coolant is over-cooled, thermal shock, lube oil viscosity changes, and cylinder condensation risks arise. The modulating valve ensures that heat extraction from the JW circuit is automatically curtailed whenever the jacket water return temperature (measured at TT-103) approaches the engine’s lower operating setpoint, protecting engine integrity at all times.