Control of NOx reduction in flue gas flows

A method of reducing NOx from a flow of flue gas produced by a burner, comprising the steps of:

• passing the flue gas through a first treatment zone;
• substantially simultaneously with said passing, selectively introducing a nitrogeneous treatment agent into the first treatment zone for the selective non-catalytic reduction of a first portion of the NOx from the flue gas passing through the first treatment zone, said introducing including an excessive amount of such nitrogeneous treatment agent above that required for such non-catalytic reduction of the first portion;
• passing the flue gas, containing such excessive amount of nitrogeneous treatment agent, through a second treatment zone which includes a catalyst therein, wherein a second portion of the NOx within the flue gas is removed therefrom as a result of a reaction thereof with such excessive nitrogeneous treatment agent in the presence of the catalyst;
• detecting the quantity of NOx in the flue gas intermediate the first and second treatment zones;
• detecting the quantity of ammonia in the flue gas exiting from the second treatment zone;
• varying the treatment of the flue gas according to the steps of
• (i) increasing the quantity of nitrogeneous treatment agent introduced into the first treatment zone in response to said first and second mentioned detecting, so long as the following criteria are being met,
• A1. the quantity of NOx indicated at said first mentioned detecting is generally decreasing with an increasing addition of the nitrogeneous treatment agent, and
• B1. the quantity of ammonia detected at said second mentioned detecting is generally below a predetermined maximum limit,
• (ii) selectively introducing a second nitrogeneous treatment agent into the flue gas, said last mentioned introducing being downstream of the first treatment zone and within the second treatment zone, so long as the following criteria are being met,
• A2. the quantity of NOx indicated at said first mentioned detecting is not generally decreasing with an increasing addition of the nitrogeneous treatment agent, and
• B2. the quantity of ammonia detected at said second mentioned detecting is generally below a predetermined maximum limit.

A method of reducing NOx from a flow of flue gas produced by a burner, comprising the steps of:

• passing the flue gas through a first treatment zone;
• substantially simultaneously with said passing, selectively introducing a nitrogeneous treatment agent into the first treatment zone for the selective non-catalytic reduction of a first portion of the NOx from the flue gas passing through the first treatment zone, said introducing including an excessive amount of such nitrogeneous treatment agent above that required for such non-catalytic reduction of the first portion;
• passing the flue gas, containing such excessive amount of the nitrogeneous treatment agent, through a second treatment zone which includes a catalyst therein, wherein a second portion of the NOx within the flue gas is removed therefrom as a result of a reaction thereof with such nitrogeneous treatment agent or its derivatives in the presence of the catalyst;
• detecting the quantity of NOx in the flue gas intermediate the first and second treatment zones;
• detecting the quantity of ammonia in the flue gas exiting from the second treatment zone;
• varying the quantity of nitrogeneous treatment agent introduced into the first treatment zone in response to said first and second mentioned detecting, by
• increasing the quantity of nitrogeneous treatment agent added so long as the following criteria are being met,
• A1. the slope of NOx with increasing addition of the treatment agent at said first mentioned detecting is generally negative, and
• B1. the quantity of ammonia detected at said second mentioned detecting is generally below a predetermined maximum limit, and
• by decreasing the quantity of nitrogeneous treatment agent so long as the following criterion is met,
• C1. the slope of NOx with increasing addition of the treatment agent at said first mentioned detecting is generally positive;
• and
• selectively introducing a second nitrogeneous treatment agent into the flue gas, said last mentioned introducing being downstream of the first treatment zone and no later than the entry of the flue gas into the second treatment zone, so long as the following criteria are being met,
• A2. the slope of NOx with increasing addition of the treatment agent at said first mentioned detecting is not generally negative, and
• B2. the quantity of ammonia detected at said second mentioned detecting is generally below a predetermined maximum limit.

A method of reducing NOx from a flow of flue gas produced by a burner, comprising the steps of:

• passing the flue gas through a first treatment zone and thereafter through a second treatment zone which includes a catalyst for the selective catalytic reduction of NOx in the flue gas;
• controllably introducing a flow of a nitrogeneous treatment agent into the first treatment zone for the selective non-catalytic reduction of the NOx in the flue gas passing through the first treatment zone, the nitrogeneous treatment agent being introduced at a flow rate so as to minimize the quantity of NOx in the flue gas intermediate the first and second treatment zones, subject to the constraint that the quantity of ammonia in the flue gas exiting from the second treatment zone remain below a preselected value;
• and
• controllably introducing a flow of a second nitrogeneous treatment agent into the flue gas at a location between the two treatment zones, the second nitrogeneous treatment agent being introduced at a flow rate so as to further decrease the quantity of NOx in the flue gas exiting from the second treatment zone, subject to the constraint that the quantity of ammonia in the flue gas exiting from the second treatment zone remain below the preselected value.