Nature protection technologies

1.1.2.2. Modernization of the furnace process

Part 1. AIR PROTECTION FROM POWER INDUSTRY EMISSIONS

1.1. Nitrogen oxide emission reduction

1.1.2. Technological methods for reduction of nitrogen oxide formation in boilers at combustion of different types of organic fuel

1.1.2.2. Modernization of the furnace process

1.1.2.2.1. Low-NOx burners

Kotler V.R., Open JSC “VTI”

A feature of these burners is their structural details, which regulate the intensity and sequence of mixing the fuel with the air flow. Using a ratio of velocities and swirl of inside and outside flows of secondary air, the authors of low-emission burners actually arrange the staged air supply in the flame of a certain burner, and in some cases even the staged fuel supply with the partial NO reduction in each flame.

Part 1. AIR PROTECTION FROM POWER INDUSTRY EMISSIONS

1.1. Nitrogen oxide emission reduction

1.1.2. Technological methods for reduction of nitrogen oxide formation in boilers at combustion of different types of organic fuel

1.1.2.2. Modernization of the furnace process

1.1.2.2.2. Flue gas recirculation (FGR)

Kotler V.R., Open JSC “VTI”

This method consists in selection of the flue gas part (5…30 %) from the flue duct at 300…400 °С and feeding these gases into the active combustion zone (preferably through the burners, using selected nozzles or in the air mixture, supplied for combustion). Flue gases reduce the maximum temperature in the flame core and oxygen concentration in the combustion zone. The first factor affects a rate of thermal NOх formation and the effect is higher with increase in the maximum temperature before recirculation input.

Part 1. AIR PROTECTION FROM POWER INDUSTRY EMISSIONS

1.1. Nitrogen oxide emission reduction

1.1.2. Technological methods for reduction of nitrogen oxide formation in boilers at combustion of different types of organic fuel

1.1.2.2. Modernization of the furnace process

1.1.2.2.3. Over fire air (two-staged combustion)

Kotler V.R., Open JSC “VTI”

A method of Over fire air is called two-staged combustion, because in the furnace two combustion zones are formed: the first – feeding through the burner all the fuel with oxygen deficiency (α < 1), and the second zone, in which the rest air is supplied, required for reburning of incomplete combustion products from the first zone. Even in cases when additional air is fed at two or three levels throughout the furnace height, this method is to be called as two-staged combustion. Its effectiveness is determined by the presence of zones with reducing medium (before supply of additional air), a degree of air deficiency in this zone and time of residence of combustion products in the same zone (i.e., duration of reducing reactions).

Part 1. AIR PROTECTION FROM POWER INDUSTRY EMISSIONS

1.1. Nitrogen oxide emission reduction

1.1.2. Technological methods for reduction of nitrogen oxide formation in boilers at combustion of different types of organic fuel

1.1.2.2. Modernization of the furnace process

1.1.2.2.4. Concentric combustion

Kotler V.R., Open JSC “VTI”

This method also intends creation in the furnace of a zone with a lack of oxidizer, in which nitrogen-containing components don’t convert into NO, but into the molecular nitrogen. In this zone partial conversion of the formed NO into N2 is possible. Reducing zone in this diagram is provided by a change of construction of direct-flow burners, already mentioned in it. 1.1.2.2.1.

Part 1. AIR PROTECTION FROM POWER INDUSTRY EMISSIONS

1.1. Nitrogen oxide emission reduction

1.1.2. Technological methods of nitrogen oxides reduction in boilers at combustion of different types of organic fuel

1.1.2.2. Modernization of the furnace process

1.1.2.2.5. Three-staged combustion

Kotler V.R., Open JSC “VTI”

One of the most effective methods, providing a partial reduction of the already formed NOx to N2, is a three-staged combustion method, called in the U.S. and Western Europe as a reburning process. An essence of the method is that into the primary burners (working with the optimum excess air in terms of efficiency) only 75 ... 85% of all fuel is supplied. The remaining 15 ... 25% is fed into the intermediate zone of the flame (above the primary burners) with a great lack of air. This results in formation of the reducing zone, in which due to hydrocarbons and nitrogen-containing components (eg, amines) NOx is reduced.