This is a § 371 National Stage Application of International Application No. PCT/IB2016/001493 filed on Oct. 14, 2016, claiming the priority of Italian Patent Application No. UB2015A005050 filed on Oct. 19, 2015.
This invention relates to a method for reducing harmful gas emissions from gas-fired boilers having a sealed forced-draught combustion chamber and a boiler operating according to the said method, in accordance with the corresponding independent claims.
The invention relates to a boiler with a sealed forced-draught combustion chamber, in which the said boiler may have a burner of the atmospheric type where the combustion air in an air-gas mixture is predominantly secondary or the air which is already in the combustion chamber does not already form part of the mixture before entering therein; this air is delivered via piping from the outside of the boiler to the combustion area where a burner is present. The invention also relates to the case of a boiler using a suitably developed burner (specifically known as a low-NOx burner) for reducing NOx emissions, and to predominantly primary air and improved mixing in comparison with those of the “atmospheric” type.
As is known, the requirement that boilers of the aforesaid type usually in use in buildings for domestic use should comply with increasingly restrictive parameters with regard to harmful gas emissions (mainly NOx or nitrogen oxides) and performance is increasing. Recent European regulations are tending in this direction.
With specific reference to the problem of reducing harmful gas emissions, only solutions equipped with premixed combustion or intermediate solutions including those with an atmospheric burner and those with premixed combustion, defined as “low NOx”, based on an improved mixing technique (in comparison with atmospheric combustion), and other techniques such as cooling the burner flame, are available on the market. Although they achieve the object, these intermediate solutions nevertheless have a high cost which limits their extensive use, to the advantage of premixed applications, also because of the need to cool the burner through water circulating within it (making construction more expensive). The most recent regulation restrictions relating to harmful emissions no longer permit the use of equipment with an atmospheric burner, given that it is impossible to reduce the NOx level below the imposed limits through the techniques in use.
It is also known that combustion conducted in an environment having an oxygen concentration below atmospheric (approximately 21%), even at a very high temperature (which encourages the formation of nitrogen oxides), limits the production or generation of these nitrogen oxides (NOx).
Applications in which the burner-combustion chamber assembly is designed with a view to causing some (uncontrolled) part of the combustion products to be recirculated within the combustion chamber itself by working on the geometry, with effect of diluting the mixture, reducing the formation of NOx, are also known.
However, apart from possible variations in the process and the result, these applications have a high cost to the user (for reasons of a construction nature). Also, this principle based on the recycling of combustion products in the combustion chamber is difficult (or impossible) to achieve technically in a low cost application, such as for example a wall-mounted gas-fired boiler with a burner of the atmospheric type.
The object of this invention is to provide a method for reducing the generation of harmful emissions in a boiler of the abovementioned type, and to provide a boiler operating according to this method which uses the knowledge mentioned above so that the boiler is able to function in such a way as to limit generation of the said harmful emissions.
In particular the object of the invention is that of providing a method through which it is possible to achieve the aforesaid reduction in harmful emissions (mainly NOx) in a controlled way which can be adjusted during the stage of manufacturing the equipment, installation of the equipment or during its use, manually, semi-automatically or automatically.
Another object is to provide a boiler of the aforesaid type which does not give rise to excessively high costs for the end user.
Another object is to provide a boiler of the type mentioned in which the reduction in harmful gas emissions is achieved safely and reliably over time.
This and other objects which will be obvious to those skilled in the art will be achieved through a method and device according to the corresponding appended independent claims.
For a better understanding of this invention the following drawings are provided purely by way of non-limiting example, in which:
With reference to the said
Along second conduit or exhaust conduit 6 there is a conventional fan 7, and a post-condenser 10 of a conventional type (to increase efficiency), may be located between this and combustion chamber 2.
Burner 3 is connected to a gas feed conduit 11 on which is located a valve 12 controlled by a organ 13 (for example), which may be mechanical and operated manually (such as by a handle) or operated electrically (with a relay closing valve 12) or by an automatic electronic device controlling the equipment (130).
In exhaust conduit 6 there is a generally positive pressure, while in the feed conduit or first conduit 5 there is a generally negative pressure; in each case the pressure difference between conduit 6 and conduit 5 is always positive. This situation (pressure difference) is made use of by the invention which provides for a connection between first conduit 5 and second conduit 6 to allow a portion of exhaust gas F to be transferred into the combustion air directed towards combustion chamber 2 before it reaches the latter. This portion of flue gases reduces the oxygen content of the combustion air and as a consequence results in a reduction in the nitrogen oxides generated during combustion.
More particularly the connection between first conduit 5 and second conduit 6 may be made by connecting them through an opening 15, close to fan 7 (
As an alternative the two conduits 5 and 6 are connected together by a connecting conduit 17 on which a valve member 18 is fitted. This solution is mainly used in the case where the abovementioned two conduits are separate (
Valve member 18 may be of the manually adjustable type (
As an alternative flue gases F may be drawn directly from the body of fan 7 when this is located (as in
The quantity of flue gases F which can pass between the first conduit or feed conduit 5 is defined by the cross-section of hole 20 (in addition to the pressure difference).
More particularly the solution in the figure in question comprises an electronic control unit 23 which is capable of monitoring the combustion taking place in chamber 2 through sensors 24 and 25 which detect the pressures of the flows of fluids passing respectively through feed conduit 5 and exhaust conduit 6 and a flame signal detector 27 (in itself known) which enables such units to detect the operating characteristics of burner 2. As an alternative, or in addition, control may be applied through one or more combustion sensors 24, 25, that is sensors which measure a datum identifying the composition of the flue gases, such as for example an oxygen sensor, a carbon monoxide sensor, or the like. Electronic unit 23 is connected to and controls electric actuator 18A (for example a motor) in a manner in which it is connected to the regulator, in this case, electric/electronic regulator 130 for valve 12 located on gas conduit 11.
In this way, unit 23 controls the opening and closing of valve 18 on the basis of the data obtained by aforesaid detector 27 (and/or the data obtained by pressure or flow or combustion sensors 24 and 25) acting on electric actuator 18A so as to allow controlled and “calibrated” passage of part of the pressure of the flue gases present in second conduit 6 into first (feed) conduit 5; this with the object of controlling the emission of harmful gases from boiler 1 continuously and in real time, having regard to the actual feed of gas to the burner and the latter's operating characteristics (obtained through detector 27).
The solution in question does not therefore require any manual adjustment of valve 18 and on the basis of data stored in a memory of unit 23 in respect of correlations between the monitored parameters (pressure of the flows of fluid monitored through sensors 24, 25, the flow of gas controlled through the adjustment of valve 12, the quality of combustion monitored through detector 27) and the actual composition of flue gases F in order to control the level of NOx present in exhaust flue gases F through adjusting the opening (or closing) of the aforesaid valve. All this in real time. This takes place by comparing the data obtained from each sensor with data defined during the design stage deriving from characterisation of the application.
In
The solution in
The solutions in
In equipment with burners known on the market and defined above as being “low NOx”, without premixing but using predominantly primary air, the invention overcomes one of the major problems limiting their use. Use of the invention provides advantages for this type of application in that injection of some of the combustion products upstream of the burner helps to cool its surface making it possible to use it with a range of adjustment which is sufficient for the burner to be used without the need to pass tubes carrying cooling water within it; this simplifies construction and reduces the final cost of the product.
Various embodiments of this invention have been described. Yet others are however possible. For example a flow reducer 38 (for example a fixed opening diaphragm or shutter with an adjustable opening) located in the second conduit or exhaust conduit 6 may be provided in addition to or as an alternative to valve member or valve 18 located in conduit 17 to vary (or increase) the value of the pressure in conduit 6 and assist passage of a portion of the flue gases into conduit 5. This solution is illustrated in
According to another variant illustrated in
This flow regulator 38, 38A located in exhaust conduit 5 and/or feed conduit 6 may be manually adjusted or electrically operated (for example motor-driven) in order to automatically adjust the recycling of exhaust flue gases (in addition or as an alternative to valve member 18 alone operated by motor 18A) through unit 23 and the use of one or more sensors (24, 25, 27) in a similar manner to that described previously.
As a further characteristic, the automatic system providing for control unit 23 may have no pressure or flow or combustion sensors (24, 25) and use only sensor 27 which measures the flame signal (a technique in itself known); the signal detected by this sensor is used by unit 23 as an element for checking the combustion process (flue gas composition) with consequent action, if necessary, on the opening or closing or partial opening of valve 18 and/or on the speed of the fan in order to achieve the desired result in terms of combustion, or simply stopping the system if combustion should depart from the optimum parameters. This is achieved through comparing the data obtained by flame sensor 27 with those defined during the design stage or deriving from characterisation of the application. The same result can be achieved using a combustion sensor (O2, CO, etc.) in addition or as an alternative to the flame sensor, as a measure of the quality of combustion (or the fact that the latter has parameters falling within the limits specified by current regulations).
Finally the system for determining the amount of flue gases which have to be recycled may have automatic regulation of the “mechanical-pneumatic” type. The recycling flow regulator may be constructed so as to vary the quantity of recycled flue gases in relation to the flow of combustion air (for example by varying the pressure, or delta-pressure, in the conduit). In this way, for example, it is possible to vary (reduce) the quantity of recycled flue gases automatically if the flow of combustion air is reduced either deliberately, through adjusting the rotation speed of the fan by means of electronic control, or undesirably, for example, through (partial or total) blocking of the conduit.
Further variants and embodiments of the invention may be made by those skilled in the art on the basis of the above description and are therefore to be regarded as falling within the scope of the following claims.
Number | Date | Country | Kind |
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UB2015A5050 | Oct 2015 | IT | national |
Filing Document | Filing Date | Country | Kind |
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PCT/IB2016/001493 | 10/14/2016 | WO | 00 |
Publishing Document | Publishing Date | Country | Kind |
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WO2017/068407 | 4/27/2017 | WO | A |
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9593846 | Kuczynski | Mar 2017 | B2 |
20020090583 | Cain | Jul 2002 | A1 |
20130340658 | Liao | Dec 2013 | A1 |
Number | Date | Country |
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0271111 | Jun 1988 | EP |
1504804 | Feb 2005 | EP |
1504804 | Sep 2005 | EP |
9961839 | Dec 1999 | WO |
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Entry |
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International Search Report and Written Opinion dated Jan. 31, 2017 for PCT/IB2016/001493 to Bertelli & Partners S.R.L. filed Oct. 14, 2016. |
Number | Date | Country | |
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20180299122 A1 | Oct 2018 | US |