Dry scrubbing with hydrated lime

A dry exhaust gas cleaning system removes sulphur dioxide by passing the exhaust through a bed of calcium hydroxide granulate rather than washing it into a liquid. The product is calcium sulphate, gypsum, which is stored and landed ashore. There is no discharge water, so the whole section 10 criteria set and the entire open-loop discharge restriction question fall away.

The trade is consumables and space. Granulate is consumed and gypsum accumulates, so the system needs bunkering of one and landing of the other, and both need volume that a wet system does not. Resolution MEPC.340(77) is written for wet systems: paragraph 2.2.2 states that EGCS in the Guidelines means a wet system generally, and 2.2.3 allows the Guidelines to be applied to others as appropriate.

The full article will cover the reaction chemistry, the thermal window the process needs, granulate consumption and gypsum production per tonne of fuel sulphur, the arrangement relative to the waste heat recovery economiser, and how an Administration approves a dry unit under a wet-system guideline.