Coal gasification with alkali additives to reduce emissions of mercury to the atmosphere

Abstract

Method for removing mercury emissions from the burning of coal or other carbonaceous fuels, such as in a power plant or from coal gasification. Alkali additives are introduced in the coal gasification and staged coal combustion processes to capture the mercury in an alkaline molten slag. The combustor is operated at a stoichiometric air or oxygen to fuel ratio of about 0.40 to 0.80 and a temperature range of about 2200°-3000° F. During the staged combustion process the molten slag containing combinations of alkali and mercury is removed and disposed of to minimize or prevent mercury from escaping in the flue gas.

What is claimed is:  
     
         1 . A method for the removal of mercury of carbonaceous fuel comprising 
 a) introducing any carbonaceous fuel; coal, coke, bio-mass or combinations thereof containing mercury into a first stage partial oxidation (gasifier) unit operating at a stoichiometric air or oxygen air to fuel ratio of 0.40 to 0 0.80, to provide a reducing operating condition for high levels of mercury capture in an alkaline molten fuel ash slag under reducing conditions with carbon, carbon monoxide and hydrogen as the reducing agents for a partial oxidation (gasifier) temperature range of 2200° F. to 3000° F.;    b) introducing an alkali or any alkali or combinations thereof from the class consisting of lime, limestone, dolomite, calcium chloride, nacholite, and trona, with the said fuel or via a separate stream into the first stage oxidation unit, the alkali acting as a flux to reduce molten carbonaceous fuel ash viscosity and to react with the mercury species being liberated from said fuel;    c) fuel gas and molten slag being separated in a first stage cyclonic device following the fuel gas-slag mix section and said molten slag containing combinations of alkalis and mercury compounds being removed to a water quench system and disposed of.    
     
     
         2 . An apparatus for removing mercury during combustion of a carbonaceous fuel as shown in FIG. 1, and operated according to the parameters shown in FIG. 2.