Low NO.sub.x cogeneration process and system

A system for low NO.sub.x cogeneration of electricity and useful heat comprising in combination:

• an electrical generator;
• an internal combustion engine connected to drive said electrical generator to produce electricity, said internal combustion engine providing a hot gaseous exhaust stream including elevated NO.sub.x levels and unburned oxygen;
• means for introducing to said internal combustion exhaust stream sufficient fuel to create a fuel-rich mixture;
• an afterburner connected to receive the fuel-enriched exhaust stream from said engine and burn out substantially all of the said oxygen;
• a first heat exchanger connected to receive the gaseous flow from said afterburner and cool same to provide an output stream having a temperature below 1250.degree. F., while extracting useful heat from the input stream;
• means for adding controlled quantities of conversion oxygen to the cooled output stream proceeding from said heat exchanger;
• an overall reducing catalyst bed connected to receive the oxygen-augmented cooled air stream from said heat exchanger and pass said flow through said bed;
• the conversion oxygen acting upon the gaseous flow at the forward end of said bed to oxidize NO to NO.sub.2, and the excess fuel present in said stream acting in the remainder of said bed to reduce the NO.sub.2 to innocuous compounds;
• a second heat exchanger positioned and connected to receive the flow proceeding from said reducing catalyst bed and cool same to a temperature of 450.degree. to 650.degree. F.;
• means to add excess oxygen to the flow proceeding from said reducing catalyst bed while further reducing the temperature of said flow to about 400.degree. to 600.degree. F.;
• and
• an oxidizer catalyst bed positioned and connected to receive the oxygen-enriched flow from said reducing catalyst bed as cooled by passage through said second heat exchanger and by said addition of excess oxygen, and oxidize remaining combustibles therein;
• said catalyst bed having an outlet for the NO.sub.x -reduced and combustibles-reduced gases.

A process for low NO.sub.x cogeneration to produce electricity and useful heat, which comprises:

• providing fuel and oxygen to an internal combustion engine connected to drive an electric generator, to thereby generate electricity;
• recovering from said engine an exhaust stream including elevated NO.sub.x levels and combined oxygen;
• adding to said exhaust stream sufficient fuel to create a fuel-rich mixture, the quantity of fuel being sufficient to react with the available oxygen and reduce the NO.sub.x in said exhaust stream;
• providing said fuel-enriched exhaust stream to a thermal reactor and reacting therein said fuel, NO.sub.x and available oxygen, to provide a heated oxygen-depleted stream;
• cooling said oxygen-depleted stream by passing same through a first heat exchanger;
• adding conversion oxygen to said cooled stream from said heat exchanger, and passing the cooled oxygen-augmented stream over a first catalyst bed operated at a temperature of about 750.degree. to 1250.degree. F. under overall reducing conditions, the quantity of conversion oxygen added being in stoichiometric excess of the amount of NO.sub.x, but less than the amount of combustibles;
• whereby the NO.sub.x is first oxidized to NO.sub.2, and then the NO.sub.2 is reduced by the excess combustibles;
• cooling said stream from said first catalyst bed and adding air to the stream to produce a cooled stream at a temperature of about 400.degree. to 600.degree. F., and having a stoichiometric excess of oxygen;
• and
• passing said stream having said stoichiometric excess of oxygen over an oxidizing catalyst bed at said temperature 400.degree. to 600.degree. F. to oxidize remaining excess combustibles, to thereby provide an effluent stream having environmentally safe characteristics.