Black liquor gasifier

A system for producing a product gas, comprising:

• a gasifier reactor having a fluidizing bed located therein with an inlet and an outlet;
• direct means for heating and simultaneously fluidizing the fluidizing bed in said gasifier reactor to a temperature ranging from about 800.degree. F. to 1400.degree. F., said direct heating means providing a heated fluid stream which is used for both heating and fluidizing the bed of said gasifier reactor;
• means for introducing a residual waste liquor into said gasifier reactor to produce a product gas stream;
• dust collector means positioned downstream of said gasifier reactor for removing dust from the product gas stream;
• first heat exchanger means positioned downstream of said dust collector means for recovering heat from the product gas, said first heat exchanger means having tubes covered with an inert covering, said tubes being constructed to be cooled and exposed to the product gas stream to cool the product gas to a first selected temperature range;
• second heat exchanger means operating in a condensing mode positioned downstream of said first heat exchanger means and connected in series by a duct thereto for cooling the product gas to a temperature below an adiabatic saturation temperature of the product gas, said second condensing heat exchanger means having tubes covered with an inert covering, said tubes being constructed to be cooled and exposed to the product gas stream;
• and
• means for spraying a reagent into the product gas stream in an inlet and an exit of said second condensing heat exchanger means for removing an acid gas and particulate from the product gas.