Exhaust Gas Boilers
Exhaust Gas Boilers also known as Exhaust Gas Economizers, with extended heating surface, used for waste heat recovery in motor ships.
A diesel engine loses approximately 30% of the energy to the exhaust gases.
A turbocharger recover some of it, but there is still heat losses that can be
recovered by means of an Exhaust Gas Boiler, EGB. Utilization of the energy in the exhaust
gas is restricted due to risk of low temperature corrosion on the gas side of
the tubes. The sulphuric acid dew point temperature is assumed to be at
130-140°C. A temperature difference of 40°C must be considered in
order to obtain a certain margin when the gas temperature decreases due to low
load on the main engine. This means that Exhaust Gas Boilers
shall not be designed to reduce the gas temperature at the EGB outlet below
170-180°C at Continuous Service Rating. Besides, at gas temperatures below
170-180°C, the vaporized unburned oil particles in the gas condense to an
adhesive mixture of soot and oil resulting in troublesome deposits on the tubes
and on the heating surface of the Exhaust Gas Boilers.
Exhaust Gas Boilers are normally built to
regenerate heat from comparatively large flue gas quantities at a not very high
temperature and with a limited pressure loss. To fulfill these demands, the
boilers ought to be provided with tubes with extended surfaces on the gas-side.
This can be achieved by means of pinned tubes, as in this example, or finned