WO2012066153A1

WO2012066153A1 - System and method for non-catalytic reduction of nitrogen oxides

Info

Publication number: WO2012066153A1
Application number: PCT/ES2010/070731
Authority: WO
Inventors: Franscisco J. RODRÍGUEZ BAREA; Enrique Tova Holgado; Miguel A. Delgado Lozano; Enrique Bosch Naval; Julio MONTAÑÉS PÉREZ; Luís CAÑADAS SERRANO; Vicente Jose Cortes Galeano
Original assignee: Inerco, Ingeniería, Tecnología Y Consultoría, S. A.
Priority date: 2010-11-15
Filing date: 2010-11-15
Publication date: 2012-05-24

Abstract

The invention makes it possible to reduce nitrogen oxides in combustion apparatuses (1) with a high level of reduction efficiency as compared with the amount of nitrogenated reducing agent employed. The invention comprises injectors (9a, 9b, 9c, 9d) for the injection of the reducing agent; a system for analysing the concentration of gases (CO, CO₂, O₂ and NO_X1); means for calculating the stoichiometric relationship as a function of the CO, CO₂, and O₂ concentrations; and a control system for, on the basis of the values of CO, CO₂, O₂ and NO_x1 concentration, influencing the supply of fuel and air to the apparatus (1), with the aim of achieving SR values of between 0.8 and 1 at the points and also injecting a flow of reducing agent only at the SR points below 1, where said flow is proportional to the measured NO_x concentrations.

Description

SYSTEM AND METHOD OF NON-CATALYTIC OXIDIZATION

NITROGEN

D E S C R I P C I O N

OBJECT OF THE INVENTION

The field of application of the present invention is that of combustion equipment, such as boilers of thermoelectric groups or as process furnaces existing in a wide range of industrial facilities.

The invention relates to a method and a system optimized for the non-catalytic reduction of nitrogen oxides in flue gases, in order to minimize the emissions of this pollutant.

BACKGROUND OF THE INVENTION

The use of fossil fuels, such as coal, fuel oil or natural gas, in industrial boilers has as a negative consequence the emission of nitrogen oxides into the atmosphere (NO _x ). The NO _x mainly comprise NO and NO ₂ and are among the gaseous pollutants most harmful to health and the environment.

Nitrogen oxides are precursors of photochemical smog and acid rain, phenomena with direct effects on the health of animals, vegetation and humans.

The technologies applied to reduce NO _x emissions In these types of installations, they can be classified mainly into two groups: modifications and adjustments of the combustion process, or primary measures, and post-combustion abatement, or secondary measures.

Secondary measures are applied upon combustion and are based on the selective chemical reduction of the molecule of NO _x that evolves nitrogen (N ₂₎ and water vapor (H ₂ 0) by a reducing agent nitrogenous base, usually ammonia (gas or aqueous solution) or urea solution.

Reaction with ammonia 4 NO + 4 NH ₃ + O ₂ → 4 N ₂ + 6 H ₂ O

Reaction with urea 4 NO + 2 CO (NH ₂₎ ₂ + O ₂ → 4N ₂ + 2 CO ₂ + 4 H ₂ O

For the reaction to occur, the confluence of several factors is necessary:

Contact between NO _x molecules and reagent (conditioned by the distribution and mixing of the reducing agent in the gas stream).

Availability of an optimum temperature range for the selective abatement reaction.

Residence time of the reacting species in the area where the optimum temperature range is established.

To the extent that the above factors are optimized the greater the development of the selective reaction and, therefore, the reduction of NO _x emissions.

In catalytic NO _x chilling systems (SCR) the reaction occurs in a reactor designed specifically, equipped with one or more layers of catalyst. The reducing agent injection systems are installed in the reactor inlet ducts, achieving adequate degrees of mixing between the reactant species through the effective design of the injection and distribution systems of the reducing agent. Also, the presence of the catalyst favors the reaction kinetics for a temperature range between 340 ° C and 400 ° C.

SCR systems, depending on the goodness of their design, allow to achieve reductions greater than 90%, although they require high investments for their implementation that, in many cases, cannot be amortized in facilities with a reduced remaining operating life.

Non-catalytic systems (SNCR) perform a direct injection of the reducing agent into the combustion equipment itself, in the area where the gas stream to be treated is in the temperature range or window from 850 to 1, 150 ° C. For the distribution of the reducing agent, several injection lances distributed on one or several levels are used to adjust the injection to the possible variations in the location of the temperature window, generally associated with the boiler load regulations.

At temperatures below 850 ° C, the abatement reaction does not occur, so that if reducing agent is injected at these points, it is emitted together with the flue gases as unreacted ammonia (in the terminology "ammonia slip"). The ammonia slip precipitates in the presence of SO3 in the form of sulphate and ammonium bisulfate at temperatures below 300 ° C producing jams in equipment located downstream, mainly air preheaters, and ash contamination, conditioning its sale to the cement industry.

If the injection of reducing agent occurs at points with temperature above 1 150 ° C oxidation occurs due to the oxygen remaining in the gases, evolving to NO _x , with the consequent damage to the overall reduction process.

The reduction levels achieved with this technology are significantly lower than those obtained by SCR systems. The origin of this lower efficiency lies, fundamentally, in that the performance of an SNCR system is always conditioned by the design and operation of the combustion equipment in question. Among the main factors that justify this lower performance, the following stand out:

- Bad distribution and low degree of mixing of the reducing agent in the gas stream. The large size of the combustion equipment, especially the boilers of the large thermoelectric groups, together with limitations of access to certain interior points, greatly penalizes the achievement of an adequate concentration of the reducing agent for the specific NO _x levels.

- Short residence time available in the temperature window.

In many cases this window is, for a wide range of combustion equipment load, in the superheater zone. In this area the temperature of the gases decreases rapidly as the gas progresses, offering a reduced residence time for the abatement reaction.

- Poor monitoring of the temperature of the gases at the injection points. The location of the lances is defined by preliminary tests that identify the range of variation of the Temperature window for all operating loads. In the usual operation of boilers and industrial furnaces there are operational variations that can produce changes in the temperature profiles in the injection sections. The lack of monitoring means that the injection strategy cannot be adapted according to the actual temperature conditions. This causes may occur favoring the occurrence of ammonia slip conditions at certain points, and in others, the generation of _NOx by oxidation of the reducing agent.

- Poor monitoring of gas concentration at injection points. In a similar way to the above, this causes that the injection cannot be adapted to the local concentration of NO _x , generating areas with excess reducing agent, ammonia slip enhancers, and areas with reagent defect, which penalize the overall performance of dejection.

The above factors lead to the need to operate SNCR systems with an excess of reducing agent, compared to those demanded by stoichiometry, to achieve significant reductions; being, in any case, a limiting factor the ammonia slip tolerable in each installation. Depending on the type of process, the application of SNCR technology can produce NO _x reductions in the range of 20-60% with ammonia reagent consumptions of the order of 1, 5-3 times those required by SCR technology.

After the development and implementation of the first SNCR systems, a variant of this technology called RRI (Reach Reagent Injection) has been developed consisting of the injection of the reducing agent in a fuel-rich zone (reducing zone) to temperatures between 1300 - 1700 ° C. The result, as in SNCR technology, is the decomposition of NO _x into N ₂ and H ₂ 0. The combustion process is completed with the air supply (OFA) from the English Over Fire Air downstream of the point reagent injection.

The reductions in NO _x emissions obtained with RRI technology in large electric generation boilers reach a maximum of 30%, requiring a greater reagent contribution compared to that required by conventional SNCR systems for the same reduction, mainly due to the greater incidence of competitive reactions in this environment. As a main advantage, it should be noted that this type of system does not practically produce ammonia slip.

RRI systems are usually associated with stratification systems of OFA air intakes, providing an additional NO _x reduction.

This approach constitutes a solution for those cases in which small levels of reduction not obtainable with SNCR technology are required, for example, because there is not enough residence time for the gases in the temperature window 850-1.150 ° C.

The critical parameter that determines the success of RRI technology combined with OFA systems is the stoichiometric ratio or ratio between the combustion air supplied and the air required in stoichiometric conditions (SR) in the injection zone of the reducing agent. In high temperature reducing zones, where reagent injection is performed in RRI systems, this ratio should be less than 1; otherwise the reagent oxidation reaction would occur giving rise to the generation

In the RRI systems known to date, the SR ratio is establishes based on the total combustion air derived from the OFA system. This practice, although it establishes on average a sub-stoichiometric atmosphere in the high temperature zone, it does not allow to ensure the reducing conditions at all points of the section where the injection occurs. Thus, for example, point burner stops can produce high-temperature air-rich areas that enhance oxidation to NO _x of the injected reagent, reducing the efficiency of the blasting process. In this sense, as in SNCR systems, the lack of monitoring of the combustion zone conditions of industrial boilers and furnaces, especially in very high temperature areas, can lead to reagent injection in inadequate areas (generators of ΝΟχ) that penalize the performance of RRI technology.

In recent years, experimental programs have been developed for the reduction of NO _x by stages combining OFA technologies,

SNCR and RRI, in boilers of thermoelectric groups. Dejection degrees greater than 40% have been reported with slip ammonia values below 10 ppm, although at the expense of a high consumption of reducing agent.

Within the framework of this approach, the joint optimization of the previous processes could allow the achievement of higher levels of reduction of NO _x emissions linked to lower reagent consumption, to the point of constituting a reduced cost alternative to the systems SCR when the required reduction levels are below 90%, depending on the type of installation.

There are published patent documents relating to systems and / or methods SNCR control units aimed at optimizing levels of NO _x reduction, the ammonia slip and consumption Agent reducer.

In the case of publications US20050063887, US20060052902 and US7712036, control systems of conventional SNCR plants are detailed, with injection in the temperature window 850-1 150 ° C, in which the injection adjustment is proposed based on concentration measures of the chemical species involved in the abatement reaction, NO _x and unreacted reducing agent (ammonia slip). The effective application of these approaches on an industrial scale is usually very limited since, in most cases, the location of the temperature window occurs in convective tube benches where it is unlikely to obtain meshes from Extensive measurement of the parameters that provide accurate information for zonal injection. DESCRIPTION OF THE INVENTION

The present invention relates to a system optimized for the non-catalytic abatement of nitrogen oxides in boilers and industrial furnaces, as well as a method of non-catalytic abatement of nitrogen oxides that employs said system, with a view to maximizing the reduction of said nitrogen oxides, while minimizing the consumption of reducing agent used.

The preferred field of application of the invention is the optimization of the RRI technology abatement systems which, as previously mentioned, are based on the injection of reducing agent in the sub-stoichiometric zones (with stoichiometric ratio SR between combustion air injected and stoichiometric air less than 1), high temperature (1300 - 1700 ° C) that are generated in industrial furnaces and boilers equipped with OFA or other type air stratification systems. Broadly speaking, the method is based on the determination, by means of direct measurements, of the actual conditions of the gases to be purified at points close to the injection zones of the reducer to, depending on the information obtained, act on two levels :

- 1: Making adjustments to the operating parameters that govern the zonal contributions of combustion and fuel to actively generate the conditions conducive to the application of RRI technology. Examples of such parameters are: load differentials (bias) in fuel injection (for example, those associated with the production of mills in pulverized coal boilers), position of secondary and, where appropriate, tertiary air registers. , primary air flow, air flow derived to OFA registers, etc.

- 2: Establishing a reducing agent contribution strategy discretized by zones, depending on the actual conditions of concentration of the gases at the injection points. More specifically, the method object of the present invention comprises the following steps:

1. - Determination of the concentrations of carbon monoxide (CO), carbon dioxide (CO2), oxygen (O2) and nitrogen oxides (NO _x ) in the gases to be treated measured at points located in the vertical plane that passes through the longitudinal axis of each injector, upstream of the injection point of each injector.

2. - Determination, based on the concentrations of CO, CO ₂ and O ₂ measured above, of the stoichiometric ratio (SR) existing in each of the measuring points, defined as the ratio between air supplied for combustion and stoichiometric air required (SR), in the injection zone. 3.- Adjustment of the elements that govern the zonal contributions of air and fuel of the hip or furnace, establishing as an objective the achievement in the largest possible number of measurement points of values of the ratio SR included in the range 0, 8- one. 4.- Control of the contribution of reducing agent, by acting on the flow controls and flow regulators.

Preferably, the control of the reducing agent contribution comprises injecting reducing agent only in the injectors associated with the measuring points at which values of the SR ratio of less than 1, called active injectors, are determined, establishing flow rates of reducing agent in the active injectors defined as functions of the measured NO _x concentration and the values of the SR ratio determined at each measurement point. In this way, the reducer flow at each point is established proportionally to the concentration of NO _x , taking into account the existence of adequate values of the SR ratio.

It is also object of the present invention for an automated system, based on the above detailed method, so optimize online performance of a non - catalytic system for the abatement of NO _x. This system consists of the following elements:

- A number of reducing agent injectors arranged in one or several planes located upstream of the boiler inlet sections or furnace of the air currents associated with the combustion air stratification systems and in which the temperature of the gases is between 1300 and 1700 ° C, to inject the nitrogen reducing agent, said means injectors equipped to control independently the flow of reducing agent provided.

- A CO, C0 ₂ , 0 ₂ and NO _x gas concentration analysis system measured at points located in the vertical plane that passes through the longitudinal axis of each injector, upstream of the injection point of each injector.

- A control system receiving the values of CO, CO _2, O ₂ and NO _x measured and acts on two levels:

- 1) Making continuous adjustments on the elements that govern the zonal contributions of air and fuel of the hip or furnace for the achievement in the injection points of conditions favorable to the reaction of high-temperature blasting, quantified by values of the ratio SR included in the range 0, 8-1

- 2) Continuously adjusting the flow of reducing agent provided by each injector based on the premises defined in the method detailed above.

DESCRIPTION OF THE DRAWINGS

To complement the description that is being made and in order to help a better understanding of the characteristics of the invention, according to a preferred example of practical implementation thereof, a set of drawings is attached as an integral part of said description. where, for illustrative and non-limiting purposes, the following has been represented: Figure 1 shows a general scheme of a boiler equipped with the elements that constitute the non-catalytic chilling system object of the present invention.

Figure 2 shows a cross-section of the boiler of Figure 1 at the height of the plane where the reducing agent injectors are located.

Figure 3 shows a cross-section of the boiler at the level of the plane of the refrigerated probes for the sampling of gases.

PREFERRED EMBODIMENT OF THE INVENTION

Next, a description of a possible embodiment of the invention for the case of a boiler of a thermoelectric group of pulverized coal is carried out with the aid of the attached figures 1 to 3.

The boiler (1) represented in figure 1 corresponds to a 220 MWe tangential coal boiler, controlled by a master control (not shown) and equipped with twenty-four burners distributed in four groups (2a, 2b, 2c, 2d) (see Figure 2) and in six levels. The groups (2a, 2b, 2c, 2d) are located in each of the four corners of said boiler (1). Each group (2a, 2b, 2c, 2d) of burners comprises six burners arranged on two levels.

The fuel is sprayed in six mills (3) each of which feeds the 4 burners of a level through pneumatic conveying pipes (4). For simplicity, only one of the mills (3) is shown in Figure 1. As can be seen in figure 1, each burner has a secondary air supply duct (5) connected to a common wind box for the burners of each group (2a, 2b, 2c, 2d), equipped with each wind box of a flow regulator (6a, 6d) for the regulation of the flow of air transported by each wind box. There is a flow regulator (6a, 6d) for each group (2a, 2b, 2c, 2d) of burners, although only flow regulators (6a, 6d), corresponding to the burner groups, are shown in Figure 1 (2nd, 2nd).

Additionally, the boiler (1) is provided with OFA air supply means (7) located above the highest level of burners. The flow of the air derived to the OFA (7) is regulated according to a flow regulator (8) common for all OFA air supply means (7).

The mills (3) have a mill control system based on load differentiation signals (bias signals) to generate a differential contribution (positive or negative) of fuel for each mill (3) with respect to the established demand by the master control of the boiler.

The system of the invention additionally comprises four injectors (9a, 9b, 9c, 9d); means of analysis of concentration of gases CO, CO ₂ , O ₂ and NO _x ; and control means (18).

The injectors (9a, 9b, 9c, 9d) (see figures 1 and 2) of aqueous solution of nitrogenous reducing agent, preferably an ammonia reagent, are located in an intermediate plane between the last level of burners and the level of the means of OFA air supply (7). In the area of the injectors, sub-stoichiometric conditions are established, conducive to RRI technology, when operating by deriving a minimum percentage of air to the OFA air supply means (7). Additionally, the temperature of the gases in this The zone is in all operating cases above 1400 ° C.

The injectors (9a, 9b, 9c, 9d) spray the ammonia reagent over an initial coverage area based on the geometric characteristics of the nozzles available to them. Its boiler arrangement is such that it ensures a uniform distribution of the reducing agent in the plane of the injectors (9a, 9b, 9c, 9d). As shown in Figure 2, for the case in question the location of two injectors (9a, 9b, 9c, 9d) has been established on each of two opposite walls of the boiler (1), said injectors facing two to two .

Each of the injectors (9a, 9b, 9c, 9d) is provided with a regulating valve (10) of the flow of the reducing agent provided and a meter (11) of said flow, which allows establishing a differential distribution in each of the points.

The reducing agent is stored in a tank (12) from where it is pumped by means of a drive module (13) to the injectors (9a, 9b, 9c and 9d).

The gas concentration analysis means CO, C0 ₂ , 0 ₂ and NO _x consist of four probes (14a, 14b, 14c, 14d) cooled for gas extraction, connected to a sample conditioning system (15) common and an analyzer (16) multiparametric CO _2, O ₂ and NO _x.

The probes (14a, 14b, 14c, 14d) are located in a plane located between the last level of burners and the plane of the injectors (9a, 9b, 9c, 9d) of reducing agent, the position and depth of said probes being (14a, 14b, 14c, 14d) such that they allow gas extraction at points (17) located in the vertical plane that passes through the longitudinal axis of each injector, upstream of the point of injection of each injector, depending on the spray profiles of the nozzles of the injectors (9a, 9b, 9c, 9d), as shown in Figure 3. This allows the establishment of an injection pattern of differential reducing agent per injector (9a, 9b, 9c, 9d) depending on the actual concentrations of the gases to be purified measured in representative areas associated with the areas of influence of each injection point.

The control means (18) are based on a PLC that, operating continuously, receives the concentration values of CO, CO2, O2 and

ΝΟχ obtained by means of the probes (14a, 14b, 14c, 14d) and the flow rate of reducing agent fed to each injector (9a, 9b, 9c, 9d).

Once all the information is processed by the control means (18), the necessary adjustments are generated: in the first instance, on the elements that govern the zonal contributions of air and fuel, in this case, the flow regulators (6a , 6d), the OFA air flow regulator (8) and the load differentiation signals (bias) of the mills (3), to produce favorable conditions for high-temperature non-catalytic depletion (RRI) and, second instance, about regulating valves

(10) of reducing agent flow rate to each injector (9a, 9b, 9c, 9d).

In order to materialize the application of the NO _x reduction method using the system described above, an example of a situation without NO _x control is used in which boiler operating conditions (1) are defined, defined in this case, due to the opening percentages in% of the secondary air flow regulators (6a, 6d) and the OFA air flow regulator (8), which are shown in table 1. To simplify the approach, it is not possible will act during the optimization process on the distribution of fuel by acting on the signals of load differentiation (bias) of the mills (3).

Regarding this situation, the dejection method comprises the following stages:

1. - Measurement of the concentrations of CO, CO2, O2 and NO _x gases obtained by the 4 probes (14a, 14b, 14c, 14d) and the flow rate of reducing agent fed through each of the injectors (9a, 9b , 9c, 9d) associated with each probe (14a, 14b, 14c, 14d), at points located in the vertical plane that passes through the longitudinal axis of each injector, upstream of the injection point of each injector.

2. - Determination, based on the concentrations of CO, CO ₂ and O ₂ measured above, of the stoichiometric ratio (SR) existing at each of the measuring points. The calculation of SR is executed in the control means (18) solving the known problem of incomplete combustion and is given by the following equation:

where O ₂ , CO and CO _{2 are} the concentrations expressed in%.

Table 1 shows, in addition to the status of the secondary air flow regulators (6a, 6d) and the OFA air flow regulator (8), the concentration values of CO, CO ₂ , O ₂ and NO _x obtained in point 1, the value of the calculated SR ratios associated with each measurement point obtained in point 2 and the measurement of NO _x measured in chimney.

TABLE 1

It is observed that the values of the SR ratio are above 1 at all measurement points.

3.- Adjustment of the flow regulators (6a, 6d) of secondary air and of the flow regulator (8) of OFA air, establishing the objective at the points of measurement of values of the SR ratio in the range 0.8 -one.

Table 2 shows the values of the same parameters in table 1 after the combustion adjustment. It is observed that, after the new regulation scenario, 3 points have been obtained with values of the SR ratio lower than 1, conditions favorable to RRI technology. At the point associated with the probe (14c) the SR ratio has a value greater than 1 due to limitations in the boiler control elements. It should be remembered that the temperature in the injection plane is above 1400 ° C for all operating conditions.

TABLE 2

4.- Establishment of a strategy of differential contribution of reducing agent individualized by injector (9a, 9b, 9c and 9d).

For a given NO _x objective reduction, the total flow rate of the reducer to be supplied is defined according to the NSR parameter (Standard Stoichiometric Ratio) defined as:

In conventional RRI systems, for a reduction objective of ΝΟχ set at 30%, as in the case of the example, and assuming that the initial NO _x values are of the same order as those obtained after the combustion adjustments of point 3 , the NSR values are around 3. This would result in a consumption of reducing agent solution of 500 l / h that would be distributed equally among all injectors (9a, 9b, 9c, 9d).

As observed in Table 2, the value of the SR ratio in the upstream zone of the injector (9c) is greater than 1, so that the reagent supply in this area, far from producing an effective reduction of the NO _x , would produce the generation of said NO _x by oxidation of the reducing agent. This fact significantly penalizes the performance of the global dejection system. Following the criteria defined for the method object of this invention, reagent will not be injected through the injector (9c) and the injection will be adjusted in each of the remaining injectors (9a, 9b, 9d) by adjusting the regulating valves (10 ) based on the NO _x concentration values measured with their associated probes (14a, 14b and 14d).

Table 3 shows, together with the data in table 2 and by way of comparison, the injection strategy that would be used by a conventional or RRI system and that derived from the application of the described method and system.

Is fixed, for comparison in both cases, the same value of initial ΝΟχ (237 mg / Nm ³⁾ and the same final value (165.9 mg / Nm ³⁾ where Nm ³ means cubic meters at standard conditions ( 0 ° C, 1 atm.).

15 TABLE 3

From this table it follows that, for the analyzed case, the saving of reducing agent (reagent) for the same NO _x reduction derived from the invention can be quantified in the environment of 30%. This saving is mainly based on the non-injection of reducing agent in areas not conducive to high-temperature non-catalytic depletion and by the reduction of the contribution of reducing agent at points of lower NO _x concentration.

Claims

1.- Non-catalytic abatement system of nitrogen oxides through a nitrogenous reducing agent, for boilers (1) and industrial furnaces that are equipped with:

- combustion air supply means;

- fuel supply means;

- a plurality of burners (2a, 2b, 2c, 2d) to burn the fuel using combustion air, equipped with flow regulators (6a, 6d); Y

- combustion air stratification systems provided by air currents downstream of the fuel injection zone, equipped with flow regulators (8), which allow generating, in the boiler areas

(I) or furnace in which the temperature of the flue gases is approximately between 1300 and 1700 ° C, sub-stoichiometric conditions defined as those in which the ratio between the combustion air present and the stoichiometric combustion air (ratio stoichiometric, SR) is less than 1;

characterized in that it comprises:

- a plurality of injectors (9a, 9b, 9c, 9d) arranged in one or more planes located upstream of the boiler inlet sections (1) or furnace of the air currents associated with the air stratification systems of combustion and in which the temperature of the gases is between 1300 and 1700 ° C to inject the nitrogenous reducing agent, located in said sub-stoichiometric zones, equipped with said injectors (9a, 9b, 9c, 9d) of individual valves (10) of flow regulation, and of two meters

(I I) of flow, to independently control the flow of reducing agent provided in each injector (9a, 9b, 9c, 9d);

- means for analyzing the concentration of CO, CO2, O2 and NO _x gases measured upstream of the boiler inlet sections (1) or furnace the air currents associated with the combustion air stratification systems at points (17) located in the vertical plane passing through the longitudinal axis of each injector (9a, 9b, 9c, 9d) and in the vicinity of the effective zone (17) injection of each of the injectors (9a, 9b, 9c, 9d); and - control means (18) connected to the gas concentration analysis means, with the flow regulators (6a, 6d) of the burners (2a, 2b, 2c, 2d), with the flow regulators (8 ) of the air stratification system, with the fuel supply means and with the flow regulation valves (10) and the flow meters (11) of the plurality of injectors (9a, 9b, 9c, 9d) and that are, said control means

(18), adapted to receive the measured CO, C0 ₂ , 0 ₂ and ΝΟχ concentration values, calculate the relationship between the present combustion air and the stoichiometric combustion air (stoichiometric ratio, SR) at each of the points measure according to these concentrations and act continuously on the flow regulators (6a, 6d) of the burners (2a, 2b,

2c, 2d), on the flow regulators (8) of the air stratification system, on the fuel supply means and on the flow regulation valves (10) (11) of the plurality of injectors (9a, 9b , 9c, 9d).

2. Non-catalytic nitrogen oxidization abatement system according to claim 1, characterized in that the measuring points (17) of CO, CO ₂ , O ₂ and ΝΟχ are located upstream of the injection point of each injector ( 9a, 9b, 9c, 9d).

3. Non nitrogen catalytic abatement system according to claim 1, characterized in that the nitrogenous reducing agent is an ammoniacal based reagent.

4. Non nitrogen catalytic abatement system according to claim 3, characterized in that the nitrogen reducing agent It is in the form of an aqueous solution sprayable by the injectors (9a, 9b, 9c, 9d) in the gas stream.

5. - Non-catalytic abatement system for nitrogen oxides according to claim 1, characterized in that the CO, CO2, O2 and NO _x gas concentration analysis system comprises a set of so many probes (14a, 14b, 14c, 14d) refrigerated for gas extraction, such as injectors (9a, 9b, 9c, 9d), said probes (14a, 14b, 14c, 14d) being connected to a common sample conditioning system (15) and an analyzer (16 ) multiparameter of CO, CO2, O2 and NO _x .

6. - Non-catalytic abatement system of nitrogen oxides according to claim 5, characterized in that each probe (14a, 14b, 14c, 14d) is located upstream of one of the injectors (9a, 9b, 9c, 9d) the position and depth of said probes (14a, 14b, 14c, 14d) being such that they comprise a gas inlet hole located at a point (17) located in the vertical plane that passes through the longitudinal axis of each injector (9a , 9b, 9c, 9d), upstream of the injection point of each injector (9a, 9b, 9c, 9d).

7. - Method of non-catalytic abatement of nitrogen oxides in boilers and industrial furnaces, using the system described in any one of the preceding claims, characterized in that it comprises the steps of:

- determination, using the means of gas concentration analysis, of the concentrations of carbon monoxide (CO), carbon dioxide (CO ₂ ), oxygen (O ₂ ) and nitrogen oxides (NO _x ) in the gases to be treated measured at points (17) located in the vertical plane that passes through the longitudinal axis of each injector (9a, 9b, 9c, 9d), upstream of the injection point of each injector (9a, 9b, 9c, 9d);

- determination, based on the concentrations of CO, CO ₂ and O ₂ measured above, of the stoichiometric ratio (SR) existing in each one of the measuring points, defined as the ratio between air supplied for combustion and stoichiometric air required (SR), in the injection zone;

- adjustment, by the control means (18), of the elements that govern the combustion air supply means to the burners (2a,

2b, 2c, 2d), the fuel supply means, and the means that constitute the combustion air stratification system in order to achieve, in the greatest possible number of measurement points, values of an SR ratio comprised in the range 0.8-1; Y

- control of the contribution of reducing agent, by acting on the control valves (10) and the flow meters (11) of the injectors (9a, 9b, 9c, 9d), by the control means (18) .

8. - Non-catalytic abatement method of nitrogen oxides according to claim 7, characterized in that the control of the reducing agent contribution comprises injecting only in the injectors associated to the measuring points at which values of the SR ratio are determined. less than 1, called active injectors, establishing flow rates of reducing agent in the active injectors defined as functions of the concentration of ΝΟχ measured and the values of the SR ratio determined at each measurement point.

9. - Non-catalytic abatement method of nitrogen oxides according to claim 8, characterized in that the flow rates of reducing agent in each active injector are proportional to the concentration of NO _x measured.