Method of and plant for combustion of water-vapor generating fuels

A plant for recovering energy from flue gases created during the combustion of a sulfur-containing, water-vapor generating fuel, in which pressurized flue gases are cooled while recovering a major part of the latent heat of evaporation of the water contained therein and while at least partially removing sulfur impurities contained in the flue gases, before the flue gases are expanded to atmospheric, comprising

• a combustion chamber for combustion of the fuel,
• a scrubber, connected to the combustion chamber via a first conduit, for the flue gases,
• means to feed coolant liquid in drop form to the scrubber to effect cooling of the flue gases while recovering latent heat of evaporation of water contained in the flue gases and while at least partially removing sulfur trioxide and other impurities,
• a heat exchanger connected to the scrubber via a second conduit for the flue gases, for heating the flue gases,
• a third conduit connected to the second conduit for mixing, with the scrubbed flue gases, a proportion of heated flue gases which were scrubbed previously and had its temperature raised, so that the temperature of the flue gases after such mixing exceeds the dew point for sulfuric acid in the flue gases under the prevailing conditions, and
• an expansion machine connected to the heat exchanger via a fourth conduit for expanding the flue gases to atmospheric pressure under conditions in which the temperature reduction produced by the expansion does not cause the flue gas temperature to fall below the dew point for sulfuric acid in the flue gases under the then prevailing conditions.

In a method of recovering energy from flue gases resulting from the combustion of a sulfur-containing water-vapor generating fuel in which heat energy is extracted from and sulfur impurities are removed from, the flue gases as these are cooled under pressure,

• the improvement which comprises
• effecting some heat energy extraction and impurity removal by contacting the flue gases with liquid droplets,
• bringing the flue gases, upstream and downstream of said droplet contact into heat exchange relationship in a heat exchanger, and
• returning a proportion of the flue gases flowing downstream of the heat exchanger back into the flue gases at a location upstream of the heat exchanger but downstream of the said droplet contact.

Combustion plant for burning a water-vapor generating fuel that contains sulfur which comprises

• a combustion chamber in which the fuel is burnt to create flue gases,
• means to supply fuel and combustion air to the combustion chamber,
• a first flue gas conduit leading from the combustion chamber,
• a scrubber connected to the first flue gas conduit with means therein to contact flue gases passing therethrough with drops of a liquid coolant,
• a second flue gas conduit leading from the scrubber to lead scrubbed flue gases away therefrom,
• a heat exchanger thermally interconnecting flue gases in said first and second flue gas conduits,
• a third flue gas conduit adapted to feed a proportion of the flue gases leaving the heat exchanger from the second flue gas conduit back to the second flue gas conduit at a point of the second flue gas conduit position between the scrubber and the heat exchanger,
• an expansion machine receiving the residue of the flue gases from the heat exchanger, and
• a waste stack receiving flue gas from the expansion machine.