FI65323C - FOERFARANDE FOER MINSKNING AV NOX-STRAOLNING - Google Patents

Description

2,6323 which oxidize because they are reactive with molecular oxygen, even at relatively low temperatures in the presence of oxygen to NO.

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The reduction of thermal NΟχ formation is therefore achieved above all by lowering the combustion temperature and the holding time at high thermal temperatures. However, since the combustion of fuels with bound nitrogen generates most of the total NO 2 formation due to the fuel NO reaction, for such fuels the above measures are not sufficient to meet the existing radiation reference values in some countries. for this purpose it is necessary to reduce the nitrogen compounds further during the pyrolysis in the absence of oxygen with molecular nitrogen (N2). Experiments have shown that these reduction reactions to molecular nitrogen occur, e.g., when fuels are burned under substoichiometric conditions, i. by adding less oxygen or air than is needed for complete combustion. For optimal results, an air ratio of 0.9 to 0.5 should be selected for the primary combustion zone, depending on the extreme conditions (e.g., the wall temperature of the fire compartment). However, in order to achieve complete combustion of the hydrocarbon compounds in the fuel, the reaction products generated in the substoichiometric range must then be incinerated.

Studies have shown that such combustion, which culminates in post-combustion (two-stage combustion), can significantly reduce both fuel NO 2 formation by simultaneously conducting air out of the substoichiometric range as well as thermal NOx formation. In the experiments with two-stage combustion, the NO 2 emission values decreased by about 70% in relation to the stepless combustion.

A method according to the preamble of claim 1 is known from U.S. Pat. No. 4,023,921. This method uses cold flue gas recirculation to reduce Ν0χ. Although a certain phase division in combustion is thus achieved by dividing the combustion air into primary and secondary streams, which are also mixed into the flame one after the other, but only 2 to 10% of the primary flow is combined. However, this small percentage of air mixing is not sufficient to pyrolyze a substantial portion of the fuel in the primary zone. Therefore, this method only achieves a reduction in thermal Ν0χ: η.

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It has further been found that by slowing down the mixture between the air and fuel flow, a considerable reduction in NO 2 radiation can also be achieved.

In a known low-temperature powder burner (DE design 1868003), a jacket-shaped secondary air flow is conducted in two closely spaced circularly arranged and separately controlled tubes, e.g. The disadvantage of this arrangement is that the flame lengthens, which means that the firebox lengthens, and that the velocity of the secondary air decreases, thereby changing the nature and shape of the flame. Under certain conditions, this may negatively affect ignition.

It is further known from DE-A-2129357 to allow primary combustion to take place under substoichiometric conditions in a pre-chamber, and to mix the air required for complete combustion with the inert gases which leave the pre-chamber. Further, flue gases are sucked from the firebox from the device installed in the burner.

The invention is therefore based on a method as described in the introduction, which still reduces the formation of ΝΟχ: η.

This problem is solved by giving the method according to the preamble of the claim the special features according to the characterizing part of the claim.

The advantages achieved by the method according to the invention, namely reduced ΝΟχ-radiations, are achieved by a special distribution of the secondary air flow in connection directly with the suction of the flue gases from the firebox.

While the second part of the secondary air supplied to the burner immediately can be formed in terms of rotation and velocity so as to ensure efficient ignition over the entire load range, a second part of the secondary air flow is formed. supporting burnout in the secondary zone according to the objective described in the task.

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The method according to the invention will be explained in more detail below with the aid of the burner and the principle of the flame produced by it.

A burner consisting of an indoor air pipe 2, a fuel and a carrier air part 1 and a jacket air part 3 produces a partial combustion zone (primary zone) 6 with an air number 0.9 to 0.5 times the stoichiometry.

The burner is formed in such a way that by certain measures (jacket air circulation, conically expanding burner mouth, closed indoor air) a zone of strong backflow 5 is produced inside the flame from the area of already advancing combustion. This rapidly heats the fuel-air mixture and ignites it. Heating and ignition can be affected by adding indoor air. This ensures the best ignition when the indoor air is closed.

The air required for the final complete combustion is blown as a stage air 4 through a few nozzles into the circumference, so that it distributes oxygen only to the secondary flame or also to the afterburning zone 7 even after the formation. For this purpose, the phase air flow 4 is arranged on a sub-ring corresponding to twice the diameter of the jacket air tube, thus ensuring that the phase air 4 only reaches the actual flame downstream of the burner orifice after about one or two jacket lamp diameters.

For the parts of the circumferential surface of the flame which are not adjacent to the phase air flow 4, flue gas is sucked from the firebox by means of a pulse exchange. This lowers the flame temperature.