EP2084455A1

EP2084455A1 - Combustion apparatus for a gas boiler

Info

Publication number: EP2084455A1
Application number: EP07746197A
Authority: EP
Inventors: Yong Bum Kim
Original assignee: Kyungdong Navien Co Ltd
Current assignee: Kyungdong Navien Co Ltd
Priority date: 2006-12-01
Filing date: 2007-04-26
Publication date: 2009-08-05
Also published as: JP2010511143A; CN101553692B; EP2084455A4; US20100047728A1; KR100805630B1; WO2008066223A1; CN101553692A; JP4792112B2

Abstract

Disclosed is a combustion apparatus of a gas boiler. The combustion apparatus of the gas boiler includes a structure that can improve a TDR of a burner, and can increase an efficiency of a gas boiler by preventing oxygen concentration of exhaust gas from being rapidly increased in a low output area. The combustion apparatus includes: an air blower for supplying air required for combustion; a proportion control valve for controlling a supply flow rate of gas; a nozzle part connected to the proportion control valve, the nozzle part supplying gas according to opening and closing of auxiliary valves and including a plurality of nozzles connected in parallel with one another; a mixing chamber for mixing the air supplied from the air blower and the gas passed through the nozzle part, and then supplying the mixed air and gas to a burner surface; and a controller for controlling the number of rotations of the air blower according to opening and closing of the proportion control valve and the auxiliary valves, so as to supply only an amount of air as much as that required for combustion.

Description

Description COMBUSTION APPARATUS FOR A GAS BOILER

Technical Field

[1] The present invention relates to a combustion apparatus of a gas boiler, and more particularly to a combustion apparatus of a gas boiler, which can improve a Turn- Down Ratio of a burner and can prevent sudden increase of oxygen concentration included in exhaust gas in a low output area, thereby maintaining a high efficiency. Background Art

[2] In general, a Turn-Down Ratio (TDR) is set in a gas boiler. The TDR refers to a ratio of a maximum amount of consumed gas to a minimum amount of consumed gas in a gas combustion apparatus capable of controlling the amount of supplied gas. For example, when a maximum amount of consumed gas is 24,000kcal/h and a minimum amount of consumed gas is 8,000kcal/h, the TDR is 3:1. The TDR is limited by the lowest value to which the minimum amount of consumed gas for maintaining a stable flame can be controlled.

[3] In the case of a gas boiler, the convenience in use of heating facilities and hot water is increased according to an increase of the TDR. That is, when a burner operates in an area that has a small TDR (i.e. a case where a minimum amount of consumed gas is high) and a small load of heating and hot water, on/off states of a boiler frequently occur, which increases variation in the temperature control and reduces the durability of the boiler. Therefore, a method for improving a TDR of a burner applied to a gas boiler has been proposed.

[4] FIG. 1 is a graph showing a relation between an amount of consumed gas and a gas supply pressure, FIG. 2 is a schematic perspective view showing a conventional combustion apparatus, and FIG. 3 is a graph showing a relation between an oxygen concentration and a dew point temperature. Problems of the conventional combustion apparatus will be described with reference to FIGs. 1 through 3.

[5] Basic factors limiting the TDR of a gas burner include the relation between the amount of consumed gas (Q) and the gas supply pressure (P), as shown in FIG. 1. In general, the relation between pressure of fluid and a flow rate is defined as follows.

[6]

[7]

[8]

[9] That is, in order to increase the flow rate of fluid by two times, the supply pressure should be raised by four times. Therefore, in order to set the TDR to be 3: 1, the supply pres sure should have a ratio of 9 : 1. Further, in order to set a TDR to 10 : 1 , the supply pressure should have a ratio of 100: 1. However, it is impossible to unlimitedly increase the supply pressure of gas.

[10] In general, a standard gas supply pressure of city gas for home is 200mmH O with an allowable tolerance of +50 and -lOOmmH O. Therefore, it is preferred to set the maximum gas pressure to lOOmmH O or lower in consideration of the allowable tolerance, in order to guarantee stable burning of a burner.

[H] Further, a gas valve (i.e. governor) for proportionally controlling the quantity of supplied gas can perform a minimum gas amount control only above a predetermined pressure. Although the range of the minimum gas amount control depends on characteristics of gas valves, it is preferred that the gas valve for the proportional control is used at a pressure of lOmmH O or higher.

[12] When the gas pressure is changed within a range of 10 to lOOmmH O in consideration of the conditions as described above, the TDR is about 3.15: 1. Accordingly, only by changing the gas pressure, the TDR is limited to be approximately 3: 1.

[13] To solve the above-mentioned problems, a method has been proposed where the burner is partitioned into several areas and a gas passage for spraying gas to each of the partitioned areas is opened and closed, so as to increase the TDR of a gas burner, as shown in FIG. 2.

[14] In the combustion apparatus shown in FIG. 2, the area of the burner 20 is divided into a one- stage area 21 and a two- stage area 22 at a ratio of 4:6, and then valves 31 and 32 are installed on the gas passage of each divided area. Then, it is possible to obtain proportion control areas as listed in Table 1 below. In Table 1, it is assumed that a TDR for each of the divided areas in the burner is 3: 1.

[15] [16] Table 1

[17] [18] That is, when the maximum gas amount is 100 %, it is possible to achieve proportional control within a range of 13% to 100%, and it is thus possible to obtain a TDR of approximately 7.7 to 1. However, when the combustion apparatus having the above-described structure is applied to a condensing boiler, the following problems occur. [19] A condensing boiler condenses steam included in exhaust gas and then collects the latent heat of the condensed steam through a heat exchanger, thereby increasing an efficiency of a gas boiler. Therefore, the higher the dew point temperature of the exhaust gas is, the more easily the steam is condensed and thus the higher the efficiency of the boiler is.

[20] However, the higher the volume proportion (%) of steam included in the exhaust gas, the higher the dew point temperature of the exhaust gas. Further, in order to increase the volume proportion of the steam, the amount of surplus air (i.e. oxygen and nitrogen that do not participate in combustion reaction among H O + CO + O + N components of the exhaust gas) included in the exhaust gas is required to be as small as possible.

[21] However, as shown in FIG. 3, if concentration of oxygen in the exhaust gas increases (i.e. if the amount of surplus air increases), the dew point temperature rapidly lowers, so as to degrade the efficiency of the condensing boiler.

[22] Accordingly, in the case where the area of the burner 20 is divided into the one- stage area 21 and the two-stage area 22 as shown in FIG. 2, even when combustion occurs only in the one-stage area 21, an air blower 10 supplies air even to the two- stage area 22 of the burner 20. As a result, the concentration of the oxygen in the exhaust gas becomes very high.

[23] Therefore, in the case of applying the combustion apparatus of FIG. 2 to a condensing boiler, it is impossible to achieve a high efficiency in a low output area (i.e. a case where combustion is carried out in only the one-stage area or only the two-stage area).

[24] Reference numerals 33 and 34 not described above denote a proportion control valve and a solenoid valve, respectively. Disclosure of Invention Technical Problem

[25] The present invention has been made in view of the above-mentioned problems, and the present invention provides a combustion apparatus of a gas boiler, which has a structure for improving a TDR of a burner and can prevent oxygen concentration of exhaust gas from being increased in a low output area, so as to increase an efficiency of the gas boiler. Technical Solution

[26] In accordance with an aspect of the present invention, there is provided a combustion apparatus of a gas boiler including: an air blower for supplying air required for combustion; a proportion control valve for controlling a supply flow rate of gas; a nozzle part connected to the proportion control valve, the nozzle part supplying gas according to opening and closing of auxiliary valves and including a plurality of nozzles connected in parallel with one another; a mixing chamber for mixing the air supplied from the air blower and the gas passed through the nozzle part, and then supplying the mixed air and gas to a burner surface; and a controller for controlling the number of rotations of the air blower according to opening and closing of the proportion control valve and the auxiliary valves, so as to supply only an amount of air as much as that required for combustion. [27] Preferably, the nozzle part includes a plurality of nozzles having different diameters of a portion through which the gas passes.

[28] Preferably, the mixing chamber includes an air distribution plate disposed therein.

[29] The gas passed through the nozzle part is introduced into an inlet of the air blower and is then mixed with air.

Advantageous Effects [30] By a combustion apparatus of a gas boiler according to the present invention, it is possible to improve a TDR of a burner and to pre-mix gas with air, so as to prevent the supply of surplus air and prevent oxygen concentration of exhaust gas from being increased in a low output area, which can increase an efficiency of a gas boiler.

Brief Description of the Drawings [31] The foregoing and other objects, features and advantages of the present invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings in which: [32] FIG. 1 is a graph showing a relation between an amount of consumed gas and a gas supply pressure; [33] FIG. 2 is a schematic perspective view showing a conventional combustion apparatus; [34] FIG. 3 is a graph showing a relation between oxygen concentration and dew point temperature; [35] FIG. 4 is a view schematically showing a combustion apparatus according to one embodiment of the present invention; and [36] FIG. 5 is a view schematically showing a combustion apparatus according to another embodiment of the present invention.

Mode for the Invention [37] Hereinafter, exemplary embodiments of the present invention will be described with reference to the accompanying drawings. [38] FIG. 4 is a view schematically showing a combustion apparatus according to one embodiment of the present invention. [39] The present invention provides a structure of a combustion apparatus, which can improve a TDR of a burner and can reduce surplus air, so as to maintain a high efficiency in a low output area. One example of the construction of the combustion apparatus according to the present invention will be described with reference to FIG. 4. The combustion apparatus includes an air blower 110 for supplying air required for combustion, a proportion control valve 153 for adjusting the supply flow rate of gas, a nozzle part 140 which is connected to the proportion control valve 153, supplies gas according to opening and closing of the auxiliary valves 151 and 152, and includes a plurality of nozzles 141 and 142 connected in parallel with each other, a mixing chamber 120 for mixing air supplied from the air blower 110 with a gas passed through the nozzle part 140 and then supplying the mixed air and gas to a burner surface 130, and a controller (not shown) that controls the number of revolutions of the air blower 110 according to opening and closing of the proportion control valve 153 and the auxiliary valves 151 and 152 so as to supply only an amount of air as much as that necessary for combustion.

[40] The structure of the burner shown in FIG. 4 includes the mixing chamber 120, which corresponds to a combustion structure of a pre-mixed burner. The pre-mixing burner injects air and gas that have been mixed in advance for complete combustion to the burner surface 130, so that the burner can burn the mixed air and gas. The pre- mixing burner can achieve combustion at a lower surplus air ratio than that of the Bunsen burner, and thus can increase dew point temperature. Therefore, the pre-mixing burner is widely used especially in a condensing boiler.

[41] The proportion control valve 153 controls a supply flow rate of gas in a proportion control combustion system 153 for combustion with a control of an air amount and a fuel amount based on the heating power of a necessary burner.

[42] A main valve 154 is installed on a gas inlet side of the proportion control valve 153.

The main valve 154, which corresponds to an on/off valve, supplies gas by open/close operation.

[43] According to the present embodiment, the nozzle part 140 includes a first nozzle

141 and a second nozzle 142. The first nozzle 141 and the second nozzle 142 may have the same diameter, but it is preferred that the first nozzle 141 and the second nozzle

142 have different diameters, for example, with a ratio of 4:6, so as to increase the TDR.

[44] Although only the first nozzle 141 and the second nozzle 142 are shown in FIG. 4, three nozzles or four nozzles can be also constructed to further increase the TDR.

[45] A first auxiliary valve 151, which corresponds to an on/off valve for opening or closing a gas supply path to the first nozzle 141, is installed on the gas inflow side of the first nozzle 141, and a second auxiliary valve 152 having the same function as the first auxiliary valve 151 is installed on the gas inflow side of the second nozzle 142. [46] The mixing chamber 120, corresponding to a room where air and gas are mixed, is connected to each of the air blower 110 to which air is supplied and the nozzle part 140 to which gas is supplied. Moreover, an air distribution plate 121 is installed inside of the mixing chamber 120, so as to prevent air and gas from moving upward directly to the burner surface 130, thereby enabling smooth mixing of the air and the gas.

[47] A general pre-mixing burner surface can be used as the burner surface 130. For example, a metal fiber, a ceramic or stainless honeycomb plate, etc., may be used. [48] FIG. 5 is a view schematically showing a combustion apparatus according to another embodiment of the present invention. [49] The only difference between the combustion apparatus of the present embodiment and the combustion apparatus of FIG. 4 lies in the location where air and gas are mixed. That is, a pipe line is constructed such that the gas passed through the nozzle part 140 is introduced into an inlet 111 of the air blower 110 and is then mixed with the air.

[50] Hereinafter, an operation of a combustion apparatus according to the present invention having the above-mentioned construction will be described with reference to Table 2 below.

[51] It is assumed that the ratio between the diameters of the first nozzle 141 and the second nozzle 142 is 4:6 and the TDR through control of gas pressure is 3: 1.

[52] [53] Table 2

[54] [55] When loads of heating and hot water are small, the first auxiliary valve 151 of the first nozzle 141 is opened and the second auxiliary valve 152 of the second nozzle 142 is closed. In this case, the amount of gas controlled by the proportion control valve 153 has a value between a maximum of 40% and a minimum of 13%.

[56] In this case, the controller controls the number of revolutions of the air blower 110 according to opening and closing of the proportion control valve 153 and the auxiliary valves 151 and 142, so as to supply only an amount of air as much as the amount necessary for combustion.

[57] The supplied gas and air are mixed in the mixing chamber 120 and are then burned in the whole area of the burner surface 130. Therefore, it is possible to prevent dew point temperature from being lowered due to supply of surplus air to a low load area, which may be caused by combustion only in a partial area of a burner surface as is in the prior art.

[58] When loads of heating and hot water have medium values, the first auxiliary valve

151 of the first nozzle 141 is closed and the second auxiliary valve 152 of the second nozzle 142 is opened. In this case, the amount of gas controlled by the proportion control valve 153 has a value between a maximum of 60% and a minimum of 20%.

[59] When loads of heating and hot water are large, both the first auxiliary valve 151 of the first nozzle 141 and the second auxiliary valve 152 of the second nozzle 142 are opened. In this case, the amount of gas controlled by the proportion control valve 153 has a value between a maximum of 100% and a minimum of 33%.

[60] According to the above-described structure, when a maximum gas amount is 100%, the proportional control can be achieved within a range from 13% to 100%. Therefore, it is possible to maintain a TDR of approximately 7.7:1 as in a case of the prior art and to prevent lowering of the dew point temperature, so that it is possible to drive a condensing boiler with a high efficiency.

[61] According to the present invention, it is also possible to increase the number of nozzles of a nozzle part to three or four, thereby further increasing a TDR without lowering the dew point temperature, as compared with the prior art. Industrial Applicability

[62] By a combustion apparatus of a gas boiler according to the present invention, it is possible to prevent oxygen concentration of exhaust gas from being increased in a low output area, thereby improving the efficiency of the gas boiler.

[63] Although several exemplary embodiments of the present invention have been described for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims.

Claims

[1] A combustion apparatus of a gas boiler comprising: an air blower for supplying air required for combustion; a proportion control valve for controlling a supply flow rate of gas; a nozzle part connected to the proportion control valve, the nozzle part supplying gas according to opening and closing of auxiliary valves and including a plurality of nozzles connected in parallel with one another; a mixing chamber for mixing the air supplied from the air blower and the gas passed through the nozzle part, and then supplying the mixed air and gas to a burner surface; and a controller for controlling the number of rotations of the air blower according to opening and closing of the proportion control valve and the auxiliary valves, so as to supply only an amount of air as much as that required for combustion. [2] The combustion apparatus as claimed in claim 1 , wherein the nozzle part includes a plurality of nozzles having different diameters of a portion through which the gas passes. [3] The combustion apparatus as claimed in claim 1, wherein the mixing chamber includes an air distribution plate disposed therein. [4] The combustion apparatus as claimed in one of claims 1 to 3, wherein the gas passed through the nozzle part is introduced into an inlet of the air blower and is then mixed with air.