EP2805111B1

EP2805111B1 - Cylindrical gas premix burner

Info

Publication number: EP2805111B1
Application number: EP13700009.7A
Authority: EP
Inventors: Dirk Ten Hoeve; Geert Folkers
Original assignee: Bekaert Combustion Technology BV
Current assignee: Bekaert Combustion Technology BV
Priority date: 2012-01-19
Filing date: 2013-01-03
Publication date: 2018-07-04
Anticipated expiration: 2033-01-03
Also published as: WO2013107661A3; WO2013107661A2; EP2805111A2

Description

Technical Field

The invention relates to a cylindrical gas premix burner with a cylindrical burner deck comprising a perforated metal plate. The cylindrical gas premix burner deck is particularly suited for use in a burner system with air to gas ratio control via ionization current measurement by means of an ionization pen. Application of such gas premix burners is e.g. in boilers or in instantaneous water heaters.

Background Art

US5,215,457 discloses an atmospheric burner that has rows of small groups of slots in the burner deck, wherein the groups are separated at varying distances. This allegedly makes it possible for the flame halo of the burner to follow the shape of the heat exchanger.
DE9209134U discloses
Cylindrical gas premix burners with a perforated metal plate functioning as cylindrical burner deck are known, e.g. from EP 1337789 , EP2037175 , WO2009/077333 , WO2009/065733 and WO2011/069839 . It is a general objective to have a burner that is as energy efficient as possible while minimizing emissions, e.g. of NOX and of CO. Cylindrical gas premix burners are used e.g. in boilers or in instantaneous water heaters. WO2011/069839 discloses a cylindrical gas burner with a burner deck that has an overall porosity being equal to or lower than 11 percent. The document discloses cylindrical burners with a burner deck with different porosity along the length of the burner. A disclosed example is wherein the first 11.8 mm of the burner deck length has a porosity of 15 percent, thereafter is a zone of 46.8 mm of the burner deck length with a porosity of 7.3 percent and the last zone with a length of 5.8 mm of the burner deck length having a porosity of 16.5 percent. WO2011/069839 discloses a cylindrical gas premix burner according to the preamble of claim 1.
Premix burners are known that are operating according to a control system: an ionization signal, which is obtained via measurement of the flame current by means of an ionization pen, is used to obtain a measure for the air to gas ratio. Control methods aim at keeping the air to gas ratio constant (so-called lambda control) via controlling the supply to the burner, thereby obtaining clean combustion throughout the whole combustion range via adapting compositions of the combustion gas and/or adapting composition and/or temperature of the combustion air.
It is a problem when using such control systems to optimize the air to gas ratio using ionization pen measurement, that the control cannot be done in an effective way over a broad load (or power) range of the cylindrical gas premix burner, with problems occurring especially at low burner load.

Disclosure of Invention

It is the objective of the invention to provide a cylindrical gas premix burner that:

has high efficiency and low emissions, and that
allows the use of a control system via ionization current measurement by means of an ionization pen in a broad range of burner power (or burner load) to control the air to gas ratio of the burner in an efficient way, and especially at low burner loads.

A first aspect of the invention is a cylindrical gas premix burner. The gas premix burner comprises

a cylindrical burner deck. The cylindrical burner deck is comprising a metal plate (and preferably wherein the cylindrical burner deck is formed by the metal plate), and wherein the cylindrical burner deck has a perforated zone, the perforated zone being the part of the cylindrical burner deck that is foreseen with perforations in the metal plate,
an end cap. The end cap can be a metal plate devoid of perforations (meaning no combustion is taking place on the end cap). Alternatively, the end cap can be perforated to form an additional burner deck on which combustion takes place.
an inlet for gas premix at the opposite side of the end cap.

The perforated zone is comprising - seen along the axis of the cylindrical gas premix burners - at least three sections, wherein a first section at the inlet, a third section located towards the end cap, and a second section located between the first and the third section. The porosity of the second section of the cylindrical burner deck is at least 50% higher (and preferably between 50 and 200% higher, more preferably between 75 and 150% higher, even more preferably between 75% and 125% higher) than:

the porosity of the burner deck in the first section of the perforated zone of the cylindrical burner deck,
the porosity of the burner deck in the third section of the perforated zone of the cylindrical burner deck.

With porosity is meant the percentage of surface which is covered with through holes through which gas premix will flow that will be combusted at the external surface of the burner deck.
The cylindrical gas premix burner is having excellent energy efficiency, low emissions combined with reliable use with ionization pen measurement control systems for the air to gas ratio control over a broad load range of the burner, including at low loads.
It is the objective that the burner will be used in blue flame mode (and not in red flame mode which is useful when heat is transferred via infrared radiation) whereby hot flue gas is generated that will transfer its energy via conductivity and via convection, e.g. to a fluid (e.g. water) in a heat exchanger (e.g. a cast heat exchanger or a plate heat exchanger or a spiral tube heat exchanger).
Preferably, the gas premix burner of the invention is a fully premixed burner, meaning that the full amount of air required for combustion is available in the premix, and that no secondary air is required to participate via diffusion to the combustion.
The gas premix burner of the invention can comprise a fan supplying the combustion air (such a burner with an air fan is not an atmospheric burner). Combustible gas is then added to the air, e.g. via an injector, making up the gas premix which comprises the full amount of air required for the combustion; no secondary air is required nor added for the combustion (and thus the burner is a fully premixed gas burner). The gas premix flows through the inlet for gas premix and through the cylindrical burner deck after which the gas premix is combusted.
A cylindrical gas burner is a burner that has perforations substantially around the full circumference of the cylindrical burner deck. Preferably, the cylindrical gas burner of the invention has perforations around the full circumference of the cylindrical burner deck.
In a preferred embodiment the cylindrical gas premix burner has a porosity of the second section of the cylindrical burner deck that is 100 % higher (to be understood within manufacturing tolerances of a 100% higher porosity) than:

the porosity of the burner deck in the first section of the perforated zone of the cylindrical burner deck,
and/or than the porosity of the burner deck in the third section of the perforated zone of the cylindrical burner deck.

It means that in this embodiment the porosity of the second section of the cylindrical burner deck is double the porosity (meaning 100% higher) than the porosity of the first section and/or than the porosity of the third section of the perforated zone.
In an even more preferred embodiment the porosity of the second section is double the porosity of the first section and then the porosity of the third section. The shape of the perforations in the first, second and third section of the perforated zone of the cylindrical burner deck can be the same, but with a double density of the perforations in the second section compared to in the first section and to in the third section. It is a benefit of this embodiment that the burner deck can be produced more easily: the perforations in the burner deck are made by punching. A plate is moved with a certain displacement (in the direction that will become the axis of the cylindrical burner) into the punching unit. For punching the second section, the plate is moved half of the distance compared to when punching the first and/or the third section.
Preferably, the gas premix is fed into the cylindrical gas premix burner with a minimum of flow restriction at the inlet of the cylindrical gas premix burner. Preferably, the inlet for gas premix has a circular shape, with a diameter as high as possible, preferably equal to at least 80%, preferably 90% of the internal diameter of the cylindrical gas premix burner. The inlet can be e.g. of a ring shape.
This has as benefit that pressure drop of the gas premix is reduced, beneficial especially to operate the burner at high loads.
In a preferred embodiment, the cylindrical gas premix according to the invention is devoid of a diffuser inside the space enclosed by the cylindrical burner deck.
Preferably, the gas premix is flowing from the inlet to and through the burner deck without the presence of another object inside the cylindrical gas premix burner that would create a pressure drop of the gas premix. This includes that preferably no diffuser (as e.g. a cylindrical perforated plate with smaller diameter than the cylindrical burner deck) is installed inside the space delimited by the cylindrical burner deck.
This has as benefit that pressure drop of the gas premix is reduced, beneficial especially to operate the burner at high loads, contributing to the extension of the load range of the burner.
Preferably, the external diameter of the cylindrical burner deck is smaller than 60 mm, e.g. 50 mm. Cylindrical burner decks with an external diameter less than 60 mm have the benefit that the gas premix is distributed better over the surface of the cylindrical burner deck, certainly at higher burner loads, which contributes in a synergetic way in the invention for a cylindrical gas premix burner that can be used in a larger load range and that is operating with air to gas ratio control via an ionization pen measurement.
In a preferred embodiment, the porosity pattern in each of the first, second and third section of the perforated zone of the cylindrical burner deck is fully repeated along the circumference of the cylindrical burner deck. With porosity pattern is meant the pattern of the perforations in the burner deck that create the porosity. The porosity pattern can comprise different types of perforations, e.g. circular holes and slits. Slits are preferably of rectangular shape, possibly with rounded corners. With the porosity pattern is fully repeated is meant that a perforation pattern is repeated along the circumference of the cylindrical burner deck.
In a preferred embodiment, the porosity of the first section and/or of the third section of the perforated zone of the cylindrical burner deck is between 5 and 10%.
In a preferred embodiment, the porosity of the second section of the perforated zone of the cylindrical burner deck is between 10 and 20%.
Preferably, the average porosity of the perforated zone of the cylindrical burner deck is below 11%, more preferably between 7% and 11%. It is a benefit of the cylindrical gas premix burners according to this embodiment of the invention that the distribution of the gas premix is improved, resulting in an improved performance of the burner over a larger load range of the burner.
Preferably, the length - measured along the axis of the cylindrical gas premix burner - of the first section of the perforated zone of the cylindrical burner deck is between 25% and 40% of the length of the perforated zone of the cylindrical burner deck.
Preferably, the length - measured along the axis of the cylindrical gas premix burner of the second section of the perforated zone of the cylindrical burner deck - is between 20% and 50% of the length of the perforated zone of the cylindrical burner deck.
Preferably, the length - measured along the axis of the cylindrical gas premix burner - of the third section of the perforated zone of the cylindrical burner deck is between 25% and 40% of the length of the perforated zone.
Preferably, the first section and the second section of the perforated zone of the cylindrical burner deck have the same length. With length is meant the length as measured along the axis of the cylindrical gas premix burner. Even more preferred is when the first, second and third section of the perforated zone of the cylindrical burner deck have the same length. These embodiments facilitate the production of the burner deck.
In a preferred embodiment, the first section, the second section and the third section of the perforated zone of the cylindrical burner deck form the complete perforated zone of the cylindrical burner deck.
A second aspect of the invention is a gas premix burner system. The gas premix burner system is comprising:

a cylindrical gas premix burner as in the first aspect of the invention,
an ionization pen installed parallel with the axis of the cylindrical gas premix burner. Preferably the ionization pen is installed at a distance between 5 and 10 mm, more preferably at a distance between 7 en 8 mm from the burner deck of the cylindrical gas premix burner.

The perforations in the burner deck can be of different shapes. E.g. circular holes and slits (preferably of rectangular shape, preferably with rounded edges) can be present. Slits can be positioned with their longest dimension in circumferential direction of the cylindrical burner deck. Slits can be positioned in such a way that one or more virtual lines on the cylindrical burner deck that are parallel with the axis of the cylindrical gas premix burner cross slits in at least one of the first, second or third section of the perforated zone of the cylindrical burner deck, preferably in each of the first, second and third section of the perforated zone of the cylindrical burner deck. Preferably, the ionization pen is positioned in front of slits of the cylindrical burner deck, creating a synergetic effect with the porosity arrangement of the burner deck according to the invention to enable use of the cylindrical gas premix burner over a broad load range with air to gas ratio control via use of an ionization pen.
Preferably, the ionization pen is extending along the cylindrical burner deck into the second section of the perforated zone of the cylindrical burner deck over at least 25%, and preferably over more than 50%, and even more preferably over 100% of the length - measured in the direction along the axis of the cylindrical burner deck - of the second section of the perforated zone of the cylindrical burner deck.
When the ionization pen is covering a longer length of the second section of the perforated zone of the cylindrical burner deck, a better result is obtained in terms of quality of the measurement of the ionization pen and hence better air to gas ratio control is possible, even better (and hence more preferred) is when the ionization pen is covering the full length of the second section.
Even more preferred is when the ionization pen is extending along the cylindrical burner deck into the third section of the perforated zone of the cylindrical burner deck, and preferably over at least 25%, and more preferably over more than 50%, and even more preferably over 100% of the length - measured in the direction along the axis of the cylindrical burner deck - of the third section of the perforated zone of the cylindrical burner deck.
An improvement of air to gas ratio control over a broad load range is obtained (and especially beneficial for lower loads of the cylindrical gas premix burner) where the ionization pen is covering at least part of the third section of the perforated zone of the cylindrical burner deck.
A third aspect of the invention is a method for the operation of a cylindrical gas premix burner, wherein

a cylindrical gas premix burner is used as in the first aspect of the invention, or a gas premix burner system is used as in the second aspect of the invention.
an ionization pen is mounted along the cylindrical gas premix burner,
the premix gas supply is controlled in order to optimize the air to gas ratio, wherein the control is using the measurement of the flame current by the ionization pen.

A fourth aspect of the invention is a boiler or an instantaneous water heater comprising

a gas premix burner as in the first aspect of the invention, or a gas premix burner system as in the second aspect of the invention,
a heat exchanger in order to exchange heat between the hot flue gas and a fluid flowing through the heat exchanger. The heat exchanger can be a cast heat exchanger, a plate heat exchanger, a tube heat exchanger, a spiral tube heat exchanger, a fabricated (e.g. welded) heat exchanger or any other type of heat exchanger. The heat exchanger can e.g. be made out of aluminium, stainless steel or copper or out of alloys comprising such metals.

A fifth aspect of the invention is the use of the method of the third aspect of the invention in a boiler or in an instantaneous water heater.
The cylindrical gas premix burners are used in blue flame mode, the hot flue gas generated by the combustion is transferring its heat via conduction and via convection in a heat exchanger (e.g. in a cast aluminum heat exchanger) onto a fluid (e.g. water).
It is a benefit of the invention that such boilers or instantaneous water heaters according to the fourth and fifth aspect of the invention can work with effective air to gas ratio control by means of using measurement with an ionization pen over a broad load range.

Brief Description of Figures in the Drawings

Figure 1 shows a cylindrical gas premix burner according to the invention.
Figure 2 shows test results for the ionization current measured as a function of burner load.

Mode(s) for Carrying Out the Invention

Figure 1 shows an example of a cylindrical gas premix burner 100 according to the invention. The cylindrical gas premix burner 100 is having a metal plate forming the cylindrical burner deck 110, an end cap 115, a flange 117 and an inlet 120 for gas premix (a mixture of combustible gas and air, preferably the burner is a fully premixed burner). In the example the end cap is welded to the cylindrical burner deck and the end cap is not perforated (no combustion is taking place at its surface). In the example, the cylindrical burner deck 110 is having an external diameter DIAM of 50 mm. The cylindrical gas premix burner 100 of the example is devoid of a diffuser inside the space enclosed by the cylindrical burner deck 110.
The metal plate forming the cylindrical burner deck 110 is having - seen along the axis of the cylindrical burner - different zones. A first zone 130 (with length A measured along the axis of the cylindrical burner) at the inlet 120 is devoid of perforations; and the zone 170 (with length E) at the end cap 115 is also devoid of perforations. The cylindrical deck is having a first section 140 (with length B) of the perforated zone, a second section 150 (with length C) of the perforated zone and a third section 160 (with length D) of the perforated zone. Gas premix will flow through the perforations in the metal plate and the gas premix will be combusted on the external surface of the cylindrical gas premix burner 100. The first section 140 of the perforated zone, the second section 150 of the perforated zone and the third section 160 of the perforated form together the perforated zone of the cylindrical burner deck in the example of a cylindrical gas premix burner according to the invention.
In the example the perforation pattern of each of the first section 140, the second section 150 and the third section 160 of the perforated zone is repeated over the circumference of the cylindrical burner. The perforation pattern can comprise different types of perforations, e.g. circular holes and slits, as illustrated in figure 1. For instance, circular holes can have a diameter of 0.8 mm. For instance, the slits can be rectangular with a length of 4 mm and a height of 0.5 mm.
As an example the length A of the unperforated zone 130 is 19.2 mm, the lengths B (of the first section 140 of the perforated zone), C (of the second section 150 of the perforated zone) and D (of the third section 160 of the perforated zone) are each 24 mm and the length E (of the unperforated zone 170) is 23.2 mm, meaning that the total length of the burner deck - measured along the axis of the cylindrical gas premix burner is 114.4 mm. In the example, the porosity of the first section 140 of the perforated zone is 7.8%; the porosity of the second section 150 of the perforated zone is 15.6% and the porosity of the third section 160 of the perforated zone is 7.8%. Hence, in this example, the average porosity of the perforated zone of the burner deck is 10.4%. In the example, the porosity of the second section (150) is double (meaning 100% higher than) the porosity of the first section (140) and of the third section (160). In the example, the double porosity is obtained by a double density of the perforations in the second section (150) compared to in the first section (140) and compared to in the third section (160).
Figure 1 shows an ionization pen 190 installed parallel with the axis of the cylindrical gas premix burner 100. In the example, the distance between the ionization pen and the burner deck is 5 - 9 mm, preferably between 7 - 8 mm. The ionization pen 190 is positioned such that it covers at least part of the second section (150) of the perforated zone of the burner deck.
The length of the ionization pen along the axis of the cylindrical burner and measured from the inlet (120) is indicated with F. Preferably, the ionization pen 190 covers at least half, even more preferably the full length, of the second section (150) of the perforated zone of the burner deck. It is even more preferred when the ionization pen 190 covers at least part (e.g. 25% or 50% or 75% of the length) of the third section (160) of the perforated zone of the burner deck. Most preferred is when the ionization pen 190 covers the full length of the third section of the perforated zone of the burner deck.
Figure 2 shows test results for the ionization current measured by an ionization pen. The ionization current is measured as a function of burner load in the low range of the burner load (load range of the burners goes up to 25 kW). The results for three burners are compared:

the burner indicated with BU1 is the burner according to the invention described in the example and as shown in figure 1.
the burner indicated with BU2 is a burner of the same diameter and height as burner BU1, but with a burner deck with a uniform porosity over the length of the cylindrical burner deck of 7.8%.
the burner indicated with BU3 is a burner of the same diameter and height as burner BU1, but with a uniform porosity of 15.5% over the length of the perforated zone of the cylindrical burner deck and with a cylindrical diffuser with 7% porosity inside the cylindrical burner deck.

Figure 2 indicates in X-axis the load of the burner (in kW), whereas the Y-axis shows the electrical current (ionization current in microampere) measured by an ionization pen. The ionization pen was placed at a distance of 8 mm from the cylindrical burner deck. The ionization pen was extending over the full length of the perforated zone of the cylindrical burner deck, meaning that for burner BU1 the length F (as indicated in figure 1) is 91.2 mm.
The results of figure 2 clearly indicate that the burner according to the invention results in a higher ionization current than the other burners, meaning that air to gas ratio control is facilitated and made possible over a broader load range, especially in the low load ranges. Furthermore burner BU1 (burner according to the invention) showed low emission values of NOX and of CO.

Claims

Cylindrical gas premix burner (100), comprising
- a cylindrical burner deck (110), wherein said cylindrical burner deck (110) is comprising a metal plate, and wherein said cylindrical burner deck (110) has a perforated zone, the perforated zone being the part of the cylindrical burner deck (110) that is foreseen with perforations in the metal plate,

- an end cap (115),

- an inlet (120) for gas premix at the opposite side of said end cap (115); and wherein said perforated zone is comprising - seen along the axis of the cylindrical gas premix burners - at least three sections, wherein a first section (140) at said inlet, a third section (160) located towards said end cap, and a second section (150) located between said first section (140) and said third section (160), characterized in that the porosity of said second section (150) of the perforated zone of the cylindrical burner deck (110) is at least 50% higher than the porosity of the burner deck in said first section (140) and than the porosity of the burner deck in said third section (160).
Cylindrical gas premix burner as in claim 1, wherein the porosity of said second section is 100 % higher than:
- the porosity of the burner deck in said first section

- and/or than the porosity of the burner deck in said third section.
Cylindrical gas premix burner as in any of the preceding claims, wherein the cylindrical gas premix burner is devoid of a diffuser inside the space enclosed by said cylindrical burner deck.
Cylindrical gas premix burner as in any of the preceding claims, wherein the porosity pattern in each of the first, second and third section of the perforated zone is fully repeated along the circumference of said cylindrical burner deck.
Cylindrical gas premix burner as in any of the preceding claims, wherein the porosity of said first section and/or of said third section is between 5 and 10%.
Cylindrical gas premix burner as in any of the preceding claims, wherein the porosity of said second section is between 10 and 20%.
Cylindrical gas premix burner as in any of the preceding claims, wherein the length - measured along the axis of said cylindrical gas premix burner - of said first section is between 25% and 40% of the length of said perforated zone.
Cylindrical gas premix burner as in any of the preceding claims, wherein the length - measured along the axis of said cylindrical gas premix burner of said second section - is between 20% and 50% of the length of said perforated zone.
Cylindrical gas premix burner as in any of the preceding claims, wherein the length - measured along the axis of said cylindrical gas premix burner - of said third section is between 25% and 40% of the length of said perforated zone.
Cylindrical gas premix burner as in any of the preceding claims, wherein said first section, said second section and said third section form the complete perforated zone of said cylindrical burner deck.
Gas premix burner system comprising
- a cylindrical gas premix burner (100) as in any of the preceding claims,

- an ionization pen (190) installed parallel with the axis of said cylindrical gas premix burner.
Gas premix burner system as in claim 11, wherein the ionization pen is extending along the cylindrical burner deck into said second section over at least 25% of the length - measured in the direction along the axis of said cylindrical burner deck - of said second section of the perforated zone of the cylindrical burner deck.
Gas premix burner system as in claim 11, wherein the ionization pen is extending along the cylindrical burner deck into said third section, and preferably over at least 25% of the length - measured in the direction along the axis of said cylindrical burner deck - of said third section of the perforated zone of the cylindrical burner deck.
Method for the operation of a cylindrical gas premix burner, wherein
- a cylindrical gas premix burner as in claims 1-10 is used, or a gas premix burner system as in claims 11-13 is used,

- an ionization pen is mounted along the cylindrical gas premix burner,

- the premix gas supply is controlled in order to optimize the air to gas ratio, wherein the control is using the measurement by said ionization pen of the flame current.
Boiler or instantaneous water heater comprising
- a gas premix burner as in any of the claims 1 - 10, or a gas premix burner system as in claims 11 - 13, for the production of hot flue gas,

- a heat exchanger in order to exchange heat between said hot flue gas and a fluid flowing through said heat exchanger.