Patent Application
20160305655
This application claims priority of the Finnish national application number FI20155279 filed on Apr. 14 2015, the contents of which are incorporated herein by reference in entirety.
The invention relates to a methods and devices to reduce nitrogen oxide(s) and carbon monoxide from flue gasses of industrial burners as well as to flue gas compositions.
The invention relates to a method as set forth in the claim 1 for reducing nitrogen oxide(s) and carbon monoxide from flue gases of an industrial burner which is intended for a gaseous and/or liquid fuel.
The invention relates also to a flue gas composition in the claim 17.
The invention relates further to burner automation, which can be used in the burner of the invention.
One generally known industrial burner model, which is intended for gaseous and/or liquid fuels, comprises in connection with the windbox a fuel supply conduit for the combustion head and opening to the combustion head, as well as a combustion air supply conduit opening into the windbox. The windbox is associated with a combustion chamber, such as a boiler, which opens into a flue gas conduit.
The burner operation is controlled by burner automation, comprising measuring instruments which include in particular a lambda sensor that measures the amount of residual oxygen in flue gases.
In another generally known, so-called monoblock industrial burner, intended for gaseous and/or liquid fuels, the air is supplied directly to the combustion head of a burner with an air blower included in the burner.
When an industrial burner is used for the combustion of liquid or gaseous fuels, there is a problem that the thermal combustion process always generates nitrogen oxides (NOx) because, at a high temperature (>1000° C.), the atmospheric nitrogen or organic nitrogen contained in fuel reacts with combustion air or oxygen contained in fuel. The higher the temperature and the longer the burn time, the more NOx emissions are produced. Another problem in the thermal combustion process is that thermal combustion is never complete, but the flue gas is always left with unburned hydrocarbons (VOC) and carbon monoxide (CO) as a result of incomplete combustion. The resulting amount of these is the higher, the lower the temperature and the shorter the burn time.
Therefore, the emissions resulting from reducible (NOx) and oxidizable (HC and CO) reactions are generated in conflicting temperature conditions, hindering the reduction thereof. Authorities have started to introduce stricter emission regulations based i.a. on BAT (Best Available Technology) resolutions in Europe BAC (Best Available Control) standards in the USA.
One possibility of reducing the amount of emissions is to use catalytic post-combustion known from the Applicant's WO application No. 2014/154931 in connection with the above-described burner by placing a catalytic converter in a combustion chamber, such as a boiler or flue gas conduit, present in association with the burner. In one embodiment of the above-mentioned patent application, the fuel is pre-combusted partially in at least one thermal pre-combustion zone of the burner and thereafter the post-combustion of pre-combustion-generated gases is carried out in at least one post-combustion zone provided with a catalytic converter for burning the pre-combustion-generated gases, for the reduction of pre-combustion-generated NOx's, and/or for the oxidation of hydrocarbon and carbon monoxide emissions. The post-combustion is conducted in at least one catalytic zone. In one embodiment of the above-mentioned application, the apparatus comprises a thermal burner which is supplied with a liquid or gaseous fuel, and the apparatus is further provided with at least one catalytic converter for the reduction of NOx's present in flue gases generated in thermal combustion, as well as for the oxidation of hydrocarbon and carbon monoxide emissions.
In case the aforesaid burner is adjusted without a feedback from flu gases, the oxygen content of flue gases shall vary roughly +/−1%, which corresponds to about 10% of the amount of combustion air. In a non-feedback system, 3% of residual oxygen (lambda=about 1.15) is in practice the minimum residual oxygen level to which the burner can be adjusted. The excess air of a burner can also be adjusted to a lower level by a feedback of the oxygen measurement conducted from flue gases. With oxygen measurement, the combustion air or fuel of a burner is controlled by burner automation so as to maintain the oxygen content of flue gas at about 2-3%. In addition to oxygen control, it is possible to employ carbon monoxide control which adjusts the residual oxygen to a lower level until small amounts of carbon monoxide begin to appear. This adjustment may enable an achievement of the residual oxygen level close to about 1% (lambda=about 1.05).
The use of a catalytic post-combustion method as described in the above-mentioned application has been said to require that an approximately stoichiometric air-fuel ratio during the thermal combustion process be maintained consistently.
It was now unexpectedly discovered in the invention that the stoichiometric fuel and air ratio required by the discussed method is practically unreachable with existing automation and fuel supply solutions in a design, wherein the accompanying flue gas conduit or boiler is provided with a so-called three-way catalytic converter. Even with several possible burner adjustment methods available, there is none that would achieve a sufficiently low residual oxygen level required for flue gases by the method described in the discussed application.
By just regulating the rate of total fuel flow and total combustion air flow, it will be difficult to reach the required concentrations of residual oxygen prior to the catalytic zone as a result of physical, burner control technology-related, as well as hardware-related limitations.
Additionally, it was discovered, that while it was sometimes possible to attain stoichiometric fuel and air ratio in a mixer zone of a burner and thereafter a proper flue gas composition before delivering this flue gas composition into catalytic zone with above “existing technology” for example by regulating the air/fuel ratio supplied into a burner conventional technology, “it was practically impossible to maintain said proper composition of flue gases except for a very short time span.
With the aforesaid, thus far unrecognized problems as a starting point, it was a main objective of the invention to provide a catalytic converter-equipped industrial burner, in which the above-discussed method is applied and which consistently and continually enables a major reduction of nitrogen oxides NOx, as well as unburned hydrocarbons (VOC) and carbon monoxide (CO), present in flue gases generated in the thermal combustion process of a burner.
It was a second principal objective of the invention to provide an industrial burner, which has its combustion chamber or flue gas conduit provided with a catalytic converter, and which burner enables a stoichiometric air-fuel ratio to be sustained during thermal combustion.
One important further objective of the invention relates to a method, which enables the amounts of air and fuel for a burner to be adjusted in a (thermal) combustion process of the burner so as to reach low residual oxygen prior to a catalytic zone.
The term “industrial burner” in this application refers to an apparatus, which is capable of being connected to a combustion chamber such as a boiler and which comprises all devices needed for a combustion operation and its monitoring. These comprise fuel and air mixers, air supply means, including air blowers that can be incorporated in the burner (a so-called monoblock burner) or separate (a so-called duoblock burner). In this disclosure, the burner is considered to contain a main portion of burner automation such as combustion process monitoring and control devices, including measuring instruments for the composition of flue gases. After the combustion chamber but before the flue gas conduit is usually a heat exchange area. The industrial burner has nominal output at least 3 MWh.
Present disclosure relates specifically to industrial burner which comprises a fuel and air mixing zone, a fuel supply conduit which is adapted to supply the mixing zone with a given inlet flow of fuel, as well as a combustion air supply means which is adapted to provide the mixing zone with a given inlet flow of combustion air, as well as burner automation which contains measuring instruments. The burner has its mixing zone accompanied by a combustion chamber which is in communication with measuring instruments in a flue gas conduit, said combustion chamber or flue gas conduit being provided with at least two catalytic zones. After the combustion chamber but before the flue gas conduit is a heat exchange area.
Term “combustion chamber” means herein furnace, combustion chamber or other limited space where combustion with industrial burner takes place.
Above mentioned objectives can be reached by a method of claim 1.
More specifically, the invention relates to a method according to claim 1, which comprises adjusting the fuel and air ratio in a burner intended for a gaseous and/or liquid fuel.
The method comprises:
a) providing an industrial burner adapted to burn gaseous and/or liquid fuel, and comprising a burner automation containing measuring instruments (6), and a mixing zone accompanied by a combustion chamber, said burner automation being in communication with a measuring instruments of a flue gas conduit, said combustion chamber or flue gas conduit being provided with at least two catalytic zones of at least one three-way catalytic converter(s), which catalytic zones are successive in progressing direction of flue gases;
b) delivering an inlet flow (QI, QItot) of combustion air and an inlet flow (QPA, QPAtot) of fuel into the mixing zone;
c) generating flue gases in the combustion chamber by combusting air and fuel delivered into the mixing zone in step b);
d) measuring the amount of residual oxygen, in flue gases (flue gas oxidation/reduction potential) by a lambda-sensor;
e) directing the flue gases to said at least one three-way catalytic converter(s) (401);
f) adjusting the inlet flow (QI, QItot) of combustion air and the inlet flow (QPA, QPAtot) of fuel arriving in the mixing zone in step b) by means of said burner automation, so that the mean amount of residual oxygen (O2, in moles) compared to mean amount of carbon monoxide (CO, in moles), is 0.5/1 (mole/mole), oxygen being additionally within the range of 0.01-0.50 vol-%, preferably in the range of 0.01-0.25 vol %, in flue gases prior to or at the three-way catalytic converter;
g) delivering supplementary air between the first and the second catalytic zones of the three-way catalytic converter, or between catalytic zones (40, 40) of two successive three-way catalytic converters, so that concentration in the flue gases after said catalytic zones is within range of 0-9 ppm for NOx and within a range of 0-100 ppm, preferably in the range of 0-40 ppm for CO.
In the above-discussed method the low amount of residual oxygen of 0.01-0.50%, preferably of 0.01-0.25% in flue gases prior to the catalytic zone is achieved by using a system with feedback for regulating the ratio between a fuel flow arriving in a fuel and air mixing zone, particularly in a combustion head, and a combustion air flow arriving in a windbox present in association with the combustion head. In the system with feedback, the amount of residual oxygen is measured prior to a catalytic zone and the measured residual oxygen is used as a basis for adjusting the air/fuel ratio.
However, the delay in controlling air/fuel based on O2/lambda measurement is relatively long due to large volume of combustion chamber and flue gas conduit in an industrial burner (nominal power over 3 MWh). Therefore the present invention contains also step of delivering supplementary air between the first and the second catalytic zones of said at least one three-way catalytic converter (step g above). This adjustment reacts very quickly to variation in O2/CO-ratio.
In the preferred method of this disclosure the O2/lambda measurement for controlling air/fuel rate is performed inside the catalyst. Then the amount of supplementary air supplied between the catalytic zones of said at least one three-way converter is based on measured oxygen amount measured by a lambda-sensor located after the second catalytic zone of said at least one three-way catalytic converter.
When delivery of combustion air between catalytic zones of a three-way catalytic converter depends of the measured oxygen present after the second catalytic zone the method is very accurate; the measurement of O2 in flue gases after the three-way catalytic converter is much more accurate compared to situation wherein the O2 would be measured prior to the first catalytic zone of at least one three-way catalytic converter.
These both adjustment steps, mentioned above, will bring the concentration of CO and NOx in flue gases before said catalytic converter consistently in a very low level. This consistency and low levels of CO and NOx prior or after catalytic converter has not been achieved before: the measured NOx should be within a range of 0-9 ppm and CO within a range of 0-100 ppm, preferably in the range of 0-40 ppm after the second catalytic zone of three-way catalytic converter(s). The proportion of O2 to CO should be stoichiometric, about 0.5/1 (mole/mole), oxygen being additionally within the range of 0.01-0.50, preferably in the range of 0.01-0.25 vol % in flue gases prior to or at the first catalytic zone of at least one three-way catalytic converter;
The above mentioned stoichiometric oxygen/CO-proportion prior to catalytic converter is achieved in a preferred embodiment of the invention by first controlling the air/fuel—proportion in the main inlet flow of fuel. The air/fuel-proportion of this main fuel portion is based on a predetermined amount of residual oxygen in flue gases (preferably 1.0-2.5%). Additionally one should control the amount of second inlet portion of fuel which is based on defining the residual oxygen content of gases prior to the first catalytic zone of—at least one catalytic converter(s) in a combustion chamber or in a flue gas conduit and then adjusting the secondary inlet flow of fuel and combining this second inlet portion to main portion. In this connection it should be noted that defining the oxygen content of flue gases prior to the first catalytic zone can be performed by a lambda sensor located at the catalytic converter, for example after the first catalytic zone.
Thus the mixing zone, such as a combustion head, may be supplied with a secondary inlet flow of fuel or air, the supply rate of which is in turn based on measuring the amount of residual oxygen prior to first catalytic zone of at least one three-way catalytic converter(s) and on a precise control of the secondary inlet flow rate conducted on the basis of these measurements.
It is alternatively possible to regulate in a respective manner the rate of a combustion air flow arriving in an windbox (i.e. by dividing the combustion air flow into a primary flow and a secondary flow, with just the secondary flow being regulated in a feedback manner).
The above mentioned feedback system is achieved by a burner automation which uses so called Smith predictor for adjusting the amount of the ratio of fuel and air arriving to said mixing zone. To be more precise, the Smith predictor adjusts the secondary inlet flow of air or fuel.
In a more preferred embodiment, the low amount of residual oxygen in flue gases is nevertheless achieved by regulating the delivery of a primary inlet flow of fuel and a flow of combustion air to the flame by setting for these such supply rates that, based on estimates and calculations, it can be presumed that a given predefined amount of residual oxygen (1.0-2.5%) is reached prior to first catalytic zone of the at least one three-way catalytic converter(s) having at least two catalytic zones in successive order
In addition to this, the mixing zone, such as a combustion head, is supplied with a secondary inlet flow of fuel or air, the supply rate of which is in turn based on measuring the amount of residual oxygen prior to first catalytic zone of at least three-way catalytic converter(s) and on a precise control of the secondary inlet flow rate conducted on the basis of these measurement. Again in this connection it should be mentioned that measurement of residual oxygen before first catalytic zone can be performed also after said first catalytic zone.
The residual oxygen level prior to first catalytic zone should be kept in the range of 0.01-0.50%, preferably 0.01-0.25% which means that the proportion of O2 to CO should be stoichiometric or about 0.5/1 (mole/mole).
As the amount of residual oxygen is reduced in flue gases with the above-described method, as well as with a burner employed therein, there is simultaneously provided a capability of both enhancing efficiency of the burner and of keeping emissions at an extremely low level that is under 0.025% in flue gases prior to the first catalytic zone.
The level of O2 in flue gases should be nearly stoichiometric as to amount of CO. The mean level of O2 in moles (or vol %) compared to mean level of CO in moles (or vol %) should be 0.5/1 and variation of said proportion should be kept in the range of 0.998-1.002. This means, that if the concentration of CO in flue gases is about 6000 ppm, the concentration of O2 should be correspondingly 1000-4000 ppm and mean value of 02 concentration should be about 3000 ppm.
This method comprises additionally:
More specifically, such a preferred method comprises additionally the following steps of:
The actuator-equipped control valve is for example a control valve adjustable with an electric motor, pneumatically or hydraulically.
Accordingly, in the method according to a another embodiment of the invention:
In the invention, one catalytic converter with at least two catalytic zones or at least two three-way catalytic converter with one catalytic zone, are successive in the traveling direction of flue gases and between said two catalytic zones can be introduced supplementary air by way of an extra supply conduit of air arriving in the flue gas conduit.
This way, the catalytic converter can be provided with an expanded operating range, such that the flue gas arriving at first catalytic zone can have a lambda of less than 1, specifically 0.95-1.
In this case, the reduction of nitrogen oxides, as well as the oxidation of hydrocarbon and carbon monoxide emissions, is still adequately effective in the first catalyst regardless of sub-stoichiometric conditions prior to the first catalytic zone, and the remaining unoxidized CO and VOC emissions shall then be oxidized by means of supplementary air in the latter catalyst. As mentioned before the adjustment of level of unoxidized CO and VOC emissions can be performed very quickly in said catalytic converter.
In another preferred embodiment of the invention, the flue gas comprising O2, CO, NOx gases which arrives to said first catalytic zone of said at least one catalytic converter(s) have been homogenized by a mixer located in flue gas conduit or in a heat exchange area after burner's combustion chamber for delivering a homogenous flue gas mixture into said catalytic converter. Homogenization of flue gases is needed before they enter the catalytic zone(s) because combustion chamber of and industrial burner is relatively large and therefore there it has a tendency to include pockets of high concentration of CO.
In yet another preferred embodiment, the ratio of a combustion air flow arriving in the windbox to a fuel flow arriving at the combustion head is adapted to oscillate within a specific steadily constant range. Since the ratio of a fuel flow intended for the flame to a combustion air flow varies from slightly lower than stoichiometric to slightly higher than stoichiometric, there is provided a capability of further expanding the effective operating range of a catalytic converter, i.e. the maximum accepted quantity of residual oxygen prior to a catalytic zone. Preferably, the rate of air flow delivered into a burn zone is maintained constant and the amount of fuel is allowed to oscillate so as converge towards a desired air/fuel ratio.
In one preferred embodiment, it is possible to have the amount of combustion air I adjusted by one or more blowers present in the transfer pipe system, well as by dampers with adjustable opening degrees or by control valves. In this case, to the blower is preferably connected a frequency transformer that enables an adjustment of the blower motor's input power and thereby the rotational speed of the blower motor, as well as the air flow velocity, depending on a utilization rate of the burner.
Having the blower equipped with a frequency transformer enables lower amounts of residual oxygen in flue gases to be reached, the burner efficiency to be enhanced, as well as the power consumption of blowers to be reduced.
In another preferred embodiment, the rate adjustment of a secondary inlet flow of fuel takes place by means of at least one actuator-equipped control valve and at least one actuator-equipped on/off valve.
The actuator-equipped control valve is for example a valve adjustable with an electric motor, pneumatically or hydraulically.
Thus, the measuring instruments may include a lambda sensor which measures residual oxygen and which is located upstream (prior) or preferably after the first catalytic zone of the catalytic converter with at least catalytic zones (or after the first catalytic zone of two catalytic converters), and additionally a sensor which measures the amount of nitrogen oxides NOx from flue gases, and/or a sensor which measures the amount of carbon monoxide from flue gases. The NOx as well as CO sensors may be present upstream of downstream of the first catalytic zone of at least one three-way catalytic converter(s. In one implementation of the invention, these are located downstream of the second catalytic zone in a flue gas conduit. In this case, the adjustment of a secondary inlet flow of fuel traveling in a second section of the transfer pipe system is additionally based on the amount of carbon monoxide measured from flue gases and/or on the amount of nitrogen oxides, such that the burner automation regulates, on the basis of nitrogen oxides and carbon monoxide measured from flue gases, the rate of the secondary inlet flow of fuel by means of actuators, such as actuator-equipped control valves, included in the second section of the transfer pipe system.
This preferred embodiment of the invention provides a capability of further reducing the amount of NOx, CO, and hydrocarbon emissions
The invention and benefits attainable thereby will now be elucidated further with reference to the accompanying figures.
As can be seen from
Main oxidation reactions:
CO+0.5O2—CO2
CH4+2O2-CO2+2H2O
Main reduction reactions:
2NO+2CO-N2+2CO2
4NO+CH4-2N2+CO2+2H2O
As can be seen from
This means that if CO concentration in flue gases just before entering catalytic zone of a three-way catalytic converter is typically 3000 ppm, the amount of O2 may vary 1500 ppm+−1000 ppm. Lambda should be in the range of 0.997-1.003.
In usual CO-levels in exhaust gases generated by an industrial burner before said three-way converter, said exhaust gases (flue gases) may contain only 0.01-0.50% or even only 0.01-0.025% of O2 to enable catalytic conversions of CO and NOx to take place optimally in said three-way catalytic converter. In addition, it was detected in a separate test that, in case the amounts of fuel and oxygen were allowed during thermal combustion to oscillate in such a way that the ratio of fuel and combustion air in thermal combustion was alternately sub-stoichiometric and alternately over-stoichiometric, there was provided a capability of increasing the maximum acceptable amount of residual oxygen prior to a catalytic zone so as to allow the presence of 0-0.50% residual oxygen in flue gases prior to the catalytic zone. This means that the amount of residual oxygen is only allowed to be not more than about a half of what has been reached with prior known adjustment methods applied to the ratio of oxygen and combustion air in a burner.
The stoichiometric O2/CO-ratio in exhaust gases before a three-way catalytic converter, demanded for an efficient conversion of NOx- and CO-gases cannot be reached by normal industrial burners because this requires nearly stoichiometric air/fuel ratio in burner and strict O2 levels (0.01-0.50 preferably 0.01-0.25) before the first catalytic zone of at least one three-way catalytic converter.
Next follows a brief survey of the main structures and functions shown in
Each of
The boiler 3 or the flue gas conduit 4 is provided with two catalytic zones 40, 40. In this case, the three-way converter 401 of the boiler 3 or the flue gas conduit 4 comprises two catalytic zones 40,40 in two separate three-way catalytic converters (401) for the afterburning of gases generated in thermal combustion conducted in the boiler 3. It is possible to deliver supplementary air into a space between the catalytic zones 40, 40 of a catalytic converter having at least two catalytic zones or between series of catalytic converters 401 having one catalytic zone each by way of an extra air supply conduit 222. The catalytic converter 401 is a three-way catalytic converter, which is selected in view of being suitable for the catalytic burning of combustion gases and for the reduction of NOx's generated in thermal combustion conducted with the combustion head 1 and the windbox 10 associated therewith and for the oxidation of hydrocarbon as well as carbon monoxide emissions in resulting flue gases.
By delivering supplementary air between the first and the second catalytic zones of at least one three-way catalytic converter one can adjust very quickly to variation in the amount of NOx and CO in the flue gas arriving said catalyst.
In addition, the burner 100 includes burner automation 5, 6, 7 whose operation is more closely illustrated in
As can be seen from
In
In
It is by way of a supply conduit 210 for fuel PA, opening onto the combustion head 1, that the combustion head 1 is supplied with a given fuel inlet flow QPA, or QPAtot (cf.
In the burner 100 according to a first embodiment of the invention, shown in
The first inlet flow portion QPAA comprises a so-called primary inlet flow, which is adapted to travel in a first section 216 of the transfer pipe system that is in fluid communication with the supply conduit 210, and which makes up 70-100% of the inlet flow, preferably 80-100% of the total inlet flow QtotPA. The primary inlet flow QPAA has its rate regulated with an actuator-equipped control valve, such as with a servo motor-operated control valve 7; 71.
The second inlet flow portion comprises a secondary inlet flow QPAB, which is adapted to travel in a second section 215 of the transfer pipe system that is likewise in fluid communication with the supply conduit 210, and which makes up 0-30% of the total inlet flow, preferably 0-20% of the total inlet flow QtotPA (cf.
In an exemplary embodiment of the invention shown in
The burner according to the exemplary embodiment shown in
The amount of a combustion air inlet flow QI arriving in the windbox 10 is regulated with burner automation 5, 6, 7 (cf.
The amount of a primary inlet flow QPAA of fuel is regulated by means of burner automation 5, 6, 7 and an actuator-equipped control valve, such as an electric motor-operated control valve 7; 71, present in a first transfer pipe system 116, likewise on the basis of a predetermined amount of residual oxygen in flue gases S, preferably on the amount of 1-2.5% residual oxygen in flue gases. This indicates that the adjustment of the primary inlet flow QPAA of fuel is based on estimating or determining by way of calculation how much fuel should be introduced with a given utilization rate of the burner when it is desirable to reach the amount of 1-2.5% residual oxygen in flue gas prior to said first catalytic zone 40.
The secondary inlet flow QPAB of fuel is regulated by means of burner automation 5, 6, 7 and actuators 7 present in a second transfer pipe system 215, i.e. by way of two actuator-equipped control valves such as servo motor-operated control valves 7; 71 and one actuator-equipped on/off valve such as an on/off solenoid valve 7; 70 present in a section of the transfer pipe system 215.
The adjustment of the secondary inlet flow QPAB of fuel is based on the amount of residual oxygen measured with a lambda sensor 63 from flue gases, by way of which the burner automation 5, 6, 7 regulates the secondary inlet flow QPAB, of fuel, which combines with a total inlet flow QPAtot of fuel arriving by way of a supply conduit 210 at the combustion head 1, such that the ratio of the (total) inlet flow QPAtot of fuel arriving at the combustion head 1 to the combustion air flow QPAB, arriving in the windbox is such that said amount of residual oxygen is 0.01-0.50%, preferably 0.01-0.25%, in flue gases S prior to the catalytic zone 40 of said first three-way converter 401.
The burner embodiment shown in
The first portion QIA of a combustion air inlet flow comprises a primary inlet flow QIA of combustion air, which is adapted to travel in a first section 226 of the transfer pipe system that is in fluid communication with the supply conduit 220, and which makes up 70-100%, preferably 80-100%, of the combustion air inlet flow QtotI. The rate adjustment for the primary inlet flow QIA of combustion air takes place by means of burner automation 5, 6, 7 (cf.
The second portion QIB of a combustion air inlet flow comprises a secondary inlet flow, which is adapted to travel in a second section 226 of the transfer pipe system that is in fluid communication with the supply conduit 220, and which makes up 0-30%, preferably 0-20%, of the combustion air inlet flow QItot. The rate adjustment for the secondary inlet flow QB of combustion air takes place by means of burner automation 5, 6, 7 and actuators 7 present in the second transfer pipe system 225.
In an implementation of the invention shown in
The adjustment of a (primary) inlet flow QIA of combustion air is similar to the adjustment of a fuel inlet flow QPA shown in the exemplary embodiment of
On the other hand, the adjustment of a secondary inlet flow QB of combustion air is based on the amount of residual oxygen, which has been measured or for flue gases S prior to the first catalytic zone 40, and by way of which the burner automation 5, 6, 7 regulates the secondary inlet flow QIB, of combustion air which travels through the second transfer pipe system 225 and which changes the amount of a combustion air inlet flow QItot arriving in the windbox 10 by way of a supply conduit 220.
The secondary combustion air inlet flow QIB can be adjusted for example in such a way that the amount of combustion air, returned in normal condition by way of the second transfer pipe system 225 to an intake side of the blower 7; 72, will be constricted with an appropriate actuator 7 present in the transfer pipe system. Such an actuator can be for example an extra damper 7; 73 shown in the exemplary embodiment of
There are also other options for constricting the amount of combustion air in the second transfer pipe system 225, whereby the second transfer pipe system 225 may include for example a return branch 225′ used for returning air by way of an appropriate actuator-equipped control valve 7; 71 to the intake side of a blower 7; 72 present in a main line 229, as shown in
In a minor malfunction, the amount of air traveling by way of the transfer pipe system 225 is increased by increasing constriction of the secondary inlet flow QIB.
Therefore, the adjustment of the secondary inlet flow QIB of combustion air is based on the amount of residual oxygen measured with lambda sensors 63 from flue gases S upstream of the catalytic zone 40 of the first catalytic converter (in the traveling direction of flue gases). Preferably residual oxygen is measured after the first catalytic zone.
Based on this, the burner automation 5, 6, 7 regulates the secondary inlet flow QIB of combustion air, which changes the amount of a total inlet flow QtotI of combustion air arriving in the windbox 10 by way of a supply conduit 220. The adjustment takes place in such a way that the ratio of the (total) inlet flow QtotI of combustion air (secondary inlet flow QIB of combustion air+primary inlet flow QIA of combustion air) to the total inlet flow QPA of fuel arriving at a combustion head remains to be such that the measured amount of residual oxygen is 0.01-0.50% preferably 0.01-0.25% in flue gases S upstream of the first catalytic zone 40.
The exemplary embodiments of both
The burner automation according to the invention is in turn elucidated by
The burner 100 according to the invention is provided with integrated burner automation. The burner automation comprises a central processing unit 5, measuring instruments 6, and data transfer elements for providing appropriate control instructions 710 for operating actuators 7 which control the supplies of fuel PA and combustion air I for the burner 100.
The central processing unit comprises a processor 52 and at least one memory element 51. The memory elements 51 contain various software products 510 for controlling the burner operation, especially for adjusting the total amounts QI, QItot, QPA, QtotPA of air and fuel as well as for regulating the primary and secondary inlet flows QPAA, QPAB, QIA, QIB of fuel or air by means of respective actuators present in transfer and supply pipe systems.
The software products 5101-5104 are associated with control instructions 7101-7104, which are used for controlling the supply of air I to the windbox 10 and a supplementary inlet flow in a pipe system 222 into the flue gas conduit 4 by way of actuators 7. In the exemplary embodiment according to
The software products 5105-5108, on the other hand, are associated with control instructions 7105-7108 to be established for adjusting the supply of fuel PA by way of respective actuators 7. In the exemplary embodiment according to
The control instructions 7105, 7106, 7107, on the other hand, are used for adjusting the secondary inlet flow QPAB of fuel by way of actuators 7 present in a second section 215 of the transfer pipe system. Said actuators of the transfer pipe system's section 215 include two actuator-equipped control valves 7; 71 and one actuator-equipped on/off check valve 7; 70.
The control instruction 7109 is generated by software products 5109 associated with the supply of combustion air. These software products and control instructions are related to the adjustment of a secondary inlet flow QPIB of combustion air. The adjustment of secondary inlet flow is elucidated in the exemplary embodiments of
The measuring instruments 6 of burner automation are used for gathering information about the combustion process of a burner 100. Visible in an embodiment of the invention shown, in
The data transfer elements are used for collecting measurement data from the measuring instruments 6 and for communicating the same to a processor 52 of the central processing unit 5 and to software products 510, comprising the reception of a data item regarding the amount of residual oxygen O2 from the lambda sensors 63; 631-634 which are present in flue gases and measure the oxidation/reduction potential of a flue gas and from the CO sensors 62; 621, 622 which measure the amount of carbon monoxides, as well as from the NOx sensors 61; 611, 612 which measure the amount of nitrogen oxides NOx.
The transfer elements supply the processor 5; 52 as well as the burner control software 510 with the measurement data collected from the sensors 6. The burner control software 510 as well as the central processing unit 5 provide control instructions 710 for actuators 7 used for regulating the amount of air I and fuel PA.
In one preferred exemplary embodiment of the invention, which illustrated by
1) the control instructions 7105, 7106, 7107 relating to the amount of a secondary fuel inlet flow QPAB and used for regulating the secondary fuel inlet flow QPAB in such a way that the amount of secondary inlet flow QPAB in a fuel inlet flow QtotPA to be delivered to a combustion head (1) is such that the amount of residual oxygen is 0.01-0.50%, preferably 0.01-0.25% in flue gases prior to first catalytic zone 40 of at least two catalytic zones.
These control instructions 7105, 7106, 7107 are used for controlling the operation of actuators which regulate the rate of a secondary fuel inlet flow. The actuators are located in a pipe system 215 for the secondary inlet flow, and these include for example an actuator-equipped control valve 7; 71 such as a servo motor-operated control valve, as well as an actuator-equipped on/off valve such as an on/off solenoid valve 7; 70 (a check valve).
2) the control instructions 7108 relating to the amount of a primary fuel inlet flow QPAA and based on a predetermined amount of residual oxygen in flue gases S, preferably on the amount of 1-2.5% residual oxygen in flue gases 40.
The control instruction 7108 is used for controlling the operation of an actuator 7 which regulates the amount of primary inlet flow with an actuator-equipped control valve 7; 71, such as a servo motor-operated control valve.
3) the control instructions 7101, 7104 used for the inlet flow of combustion air I and for regulating the amount of a combustion air inlet flow QI arriving in an windbox 10 by way of a combustion air supply conduit 220, based on a predetermined amount of residual oxygen in flue gases S, preferably the amount of 1-2.5% residual oxygen in flue gases.
The control instructions 7101, 7104 are used for controlling by way of actuators 7 the amount of combustion air I arriving in the windbox 10, said actuators being preferably a blower 7; 72 as well as a damper 7; 73, the former regulating said amount of combustion air in a combustion air transfer pipe system 229 and being fitted with an inverter.
The invention encompasses also the following examples:
1. A method for reducing nitrogen oxide(s) and carbon monoxide from flue gases of an industrial burner (100), said method comprising the steps of:
a) providing an industrial burner (100) adapted to burn gaseous and/or liquid fuel, and comprising a burner automation containing measuring instruments (6), and a mixing zone accompanied by a combustion chamber, said burner automation being in communication with measurement instruments of flue gas conduit, said combustion chamber or flue gas conduit being provided with two catalytic zones of at least one three-way catalytic converter(s), which catalytic zones (40, 40) are successive in progressing direction of flue gases;
b) delivering an inlet flow (QI, QItot) of combustion air and an inlet flow (QPA, QPAtot) of fuel into the mixing zone;
c) generating flue gases in the combustion chamber by combusting air and fuel delivered into the mixing zone in step b);
d) measuring the amount of residual oxygen, in flue gases (flue gas oxidation/reduction potential) by a lambda-sensor;
e) directing the flue gases to said at least one three-way catalytic converter(s) (401);
f) adjusting the inlet flow (QI, QItot) of combustion air and the inlet flow (QPA, QPAtot) of fuel arriving in the mixing zone in step b) by means of said burner automation, so that the mean amount of residual oxygen in moles compared to mean amount of carbon monoxide in moles, is 0.5/1 (mole/mole) and O2 within the range of 0.01-0.50 vol-% preferably in the range of 0.01-0.25 vol % in flue gases prior to or at the first catalytic zone of said at least one three-way converter;
g) delivering supplementary air between the first and the second catalytic zones (40, 40) of the three-way converter (401) or between catalytic zones (40, 40) of two successive three-way catalytic converters, so that concentration in the flue gases after said catalytic zones (40, 40) is within range of 0-9 ppm for NOx and within a range of 0-100 ppm preferable in the range of 0-40 ppm for CO.
2. A method defined in example 1 wherein the delivery of supplementary air is based on lambda measurement after the first catalytic zone (40) of at least one three-way catalytic converter (s) (401).
3. A method defined in example 1 wherein the catalytic three-way converter reduces oxides of nitrogen (NOx) to nitrogen (N2) and oxygen (O2) and oxidizes hydrocarbons (HC) and carbon monoxide (CO) to carbon dioxide (CO2) and water (H2O).
4. The method defined in example 1 wherein the flue gas comprising O2, CO, NOx gases which arrives to the first catalytic zone of said at least one catalytic converter (401) has been homogenized by a mixer located prior to said first catalytic zone (40) in the flue gas conduit or in heat exchange area.
5. The method defined in example 1 wherein flue gas comprises prior the three-way catalytic converter O2 in the range of 0.01-0.50 preferably in the range of 0.01-0.25%, CO under 6000 ppm, NOx under 100 ppm and the mean proportion of O2 to CO is 0.5 mole/1 mole.
6. The method defined in example 1 wherein the amount of residual CO and NOx is measured from flue gases and measured NOx concentration is within a range of 0-9 ppm and measured CO concentration within a range of 0-100 ppm preferable within the range of 0-40 ppm and wherein the CO sensor that measures the amount of carbon monoxides, as well as the NOx sensor that measures the amount of nitrogen oxides (NOx), are located downstream of the catalytic zones (40,40) of the at least one three-way catalytic converter(s) (401) in the flowing direction of flue gases (S).
7. The method defined in example 1, wherein the amount of residual oxygen in flue gases arriving to said three-way catalytic converter is 0.01-0.25%, measured downstream or at the first catalytic zone (40) of said catalytic converter (s) by a lambda-sensor.
8. The method defined in example 7, wherein the amount of residual oxygen in flue gases has been measured by a lambda-sensor located between first and second catalytic zones (40, 40) but before the delivery of supplementary air between said two catalytic zones (40, 40).
9. The method defined in example 1 wherein the ratio of fuel (PA) delivered to the combustion head (1) compared to the combustion air (I) delivered into the windbox (10) is adapted to be almost stoichiometric, i.e. within the lambda range of 0.998-1.002.
10. The method defined in any of the previous examples wherein the method further comprises adjusting the amount of fuel and air arriving in said mixing zone by adapting the ratio of a combustion air flow (QI, QItot) arriving in a mixing zone to a fuel flow (QPA, QPAtot) arriving by way of a fuel supply conduit (210) to be to be such that the amount of residual oxygen is within the range of 0.01-0.25%, in flue gases prior to said first catalytic zone (40) of at least one three-way catalytic converter(s).
11. A method according to example 10, characterized in that the ratio of the combustion air flow (QI, QItot) arriving in a mixing zone, such as the combustion head (1), to the fuel flow (QPA, QPAtot) arriving in a mixing zone, such as the combustion head (1), is adapted to oscillate within a certain constantly steady range, preferably by adapting the amount of the combustion air flow (QI, QItot) to remain constant and by causing the amount of the fuel flow (QPA, QPAtot) to oscillate within a certain range so as to approach a desired ratio of the combustion air flow (QI, QItot) arriving in the mixing zone with respect to the fuel flow (QPA, QPAtot) arriving in the mixing zone.
12. A method according to example 1 wherein
13. The method defined in example 1 wherein the measuring instruments (6) include at least one sensor (63), such as a lambda sensor, measuring the amount of residual oxygen in flue gases (flue gas oxidation/reduction potential), said method further comprising following steps of:
14. The method of example 13, wherein the measurement of the amount of residual oxygen of flue gases (S) prior to the first catalytic zone of at least one three-way catalytic converter(s), is performed by a lambda-sensor located after said first catalytic zone and the burner automation (5, 6, 7) adjusts the amount of the secondary inlet flow (QPAB) in the inlet flow (QtotPA) of fuel to be delivered to the combustion head (1) on the basis of said residual oxygen measurement.
15. The method of example 14, wherein additionally the amount of supplementary combustion air supplied between the first and the second catalytic zones (40, 40) of said at least one three-way converter (401) is based on measured oxygen amount which measurement is performed by a lambda-sensor located after said second catalytic zone of said at least one three-way catalytic converter.
16. A flue gas composition, in a space defined by walls of combustion chamber or a flue gas conduit immediately after a three-way catalytic converter of an industrial burner said flue gas composition comprising, CO and NOx gases in which NOx concentration is in the range of 0-9 ppm, CO within a range of 0-40 ppm and wherein said flue gas composition have been made by:
(a) providing an industrial burner (100) adapted to burn gaseous and/or liquid fuel and comprising a burner automation containing measuring instruments (6), and a mixing zone accompanied by a combustion chamber which is in communication with a flue gas conduit, said combustion chamber or flue gas conduit being provided with at least one three-way catalytic converter having at least two catalytic zones (40, 40) or with at least two three-way catalytic converters (401, 401) which are successive in the progressing direction of flue gases and each converter (401) having at least one catalytic zone (40), which flue gases comprise O2, CO, NOx gases and are generated by
b) delivering an inlet flow (QI, QItot) of combustion air and an inlet flow (QPA, QPAtot) of fuel into the mixing zone;
c) generating flue gases in the combustion chamber by combusting air and fuel delivered into the mixing zone in step b);
d) directing the flue gases to said at least one three-way catalytic converter (s);
e) adjusting the inlet flow (QI, QItot) of combustion air and the inlet flow (QPA, QPAtot) of fuel arriving in the mixing zone in step b) by means of said burner automation, so that the amount of residual oxygen in flue gases (S) will be within the range of 0.01-0.50 preferably in the range of 0.01-0.25% prior to or at the first catalytic zone of said at least one three-way converter,
(f) delivering supplementary air between the first and the second catalytic zones (40, 40) of the three-way converter (401) or between catalytic zones (40, 40) of two successive three-way catalytic converters.
17. A flue gas composition defined in example 16 wherein catalytic converter for reducing oxides of nitrogen (NOx) to nitrogen (N2) and oxygen (O2) and oxidising hydrocarbons (HC) and carbon monoxide (CO) to carbon dioxide (CO2) and water (H2O).
18. The flue gas composition defined in example 16 wherein the flue gas mixture comprising O2, CO, NOx gases which arrives to catalytic zone of said at least one three-way catalytic converter is a homogenous flue gas mixture, produced by a mixer located prior to said first catalytic zone (40) in the flue gas conduit or in the heat exchange area.
19. The flue gas composition defined in example 16 wherein the flue gas after the both catalytic zones (40, 40) of at least one three-way catalytic converter(s) has NOx concentration in the range of 0-5 ppm, CO within a range of 0-9 ppm and O2 within a range of 0-0.25%,
20. The flue gas composition defined in example 16 wherein flue gas comprises prior to said first catalytic zone (40) of at least one three-way catalytic converter O2 in the range of 0-0.25%, CO under 4000 ppm, NOx under 100 ppm.
21. The flue gas composition defined in example 16, wherein the amount of residual oxygen in flue gases arriving to said first catalytic zone (40) of at least one three-way catalytic converter is 0-0.25%, measured upstream, downstream or at the catalytic zone (40) of said at least one catalytic converter by a lambda-sensor.
22. Burner automation (5, 6, 7) used in a method according to example 1 comprising
23. Burner automation defined in example 22 wherein said burner automation uses Smith predictor for adjusting the amount of the secondary inlet flow.
24. The method defined in example 1 wherein said industrial burner has output of at least 3 MWh.
| Number | Date | Country | Kind |
|---|---|---|---|
| 20155279 | Apr 2015 | FI | national |
