Multi-objective optimization of sulfur recovery units for enhanced sulfur recovery and reduced natural gas consumption
The low and fluctuating demand and sales price of sulfur and its increasing production due to the discovery of new sour fields have mandated optimization studies to reduce the production cost in sulfur recovery units. Natural gas (mainly methane) is continuously co-fired with acid gas (H2S and CO2) in the Claus furnace to maintain temperatures above 1050°C, which adds to the operating cost. This study aims at optimizing the usage of natural gas in sulfur recovery units and enhancing sulfur yield simultaneously using a detailed reaction mechanism for Claus feed combustion, while ensuring complete BTEX destruction. An optimal combination of feed-preheating using natural gas and its co-firing in the furnace is determined through furnace and fired heater simulations. Through simulation studies by varying natural gas flow rates into the Claus furnace and to the air preheater, it is observed that a considerable amount of natural gas can be saved to maintain the required furnace temperature, if air is preheated to a higher temperature rather than natural gas co-firing (also validated in an operational sulfur recovery plant), (b) a reduction in natural gas to the furnace improves the sulfur recovery efficiency, and (c) the destruction of aromatic contaminants (that are harmful for the catalysts present downstream) in the furnace is enhanced with decreasing natural gas co-firing and increasing feed temperature. With multi-objective optimization, further increase in sulfur yield by 8% and a reduction in fuel gas demand is achieved.