WO 2009/082090 PCT/KR2008/006788 Description HEAT EXCHANGER OF UPWARD COMBUSTION TYPE CONDENSING BOILER Technical Field [1] The present invention relates to a heat exchanger of an upward combustion type condensing boiler, and more specifically, to an upward combustion type condensing boiler in which a sensible heat exchanger and a latent heat exchanger are sequentially disposed above an upward combustion type burner. Background Art [2] Boilers currently produced are boilers including a heat exchanger to increase heat ef ficiency. Such a heat exchanger is composed of a sensible heat exchange unit and a latent heat exchange unit. The sensible heat exchange unit absorbs sensible heat of exhaust gas generated from a combustion chamber, and the latent heat exchange unit absorbs residual heat and latent heat from the exhaust gas which has been heat exchanged in the sensible heat exchange unit. Such a type of boiler is referred to as a condensing boiler. [3] Such condensing boilers have been put to practical use as oil boilers which use oil fuel as well as gas boilers which use gas fuel such as LNG or LPG, thereby con tributing to an increase in boiler efficiency and a reduction in fuel cost. [4] FIG. 1 is a schematic view of a conventional downward combustion type condensing boiler. [5] Referring to FIG. 1, exhaust gas generated from a downward combustion type burner 12 is cooled down to about 200C while passing through a sensible heat exchanger 13. Then, the exhaust gas is further cooled down to about 40-70C while passing through the latent heat exchange unit 14. [6] Heating water, which is heated while passing through the heat exchange units 13 and 14, is transferred to the interior of a room through a supply pipe 15 so as to deliver thermal energy, and is then cooled down so as to return to a recovery pipe 16. The heating water returning to the recovery pipe 16 must be introduced into the latent heat exchange unit 14 such that the latent heat exchange unit 14 can effectively absorb latent heat. This is because when the exhaust gas passing through the sensible heat exchange unit 13 is set to be equal to or less than a dew point temperature, vapor (H20) included in the exhaust gas can be condensed so as to deliver latent heat to the heating circulation water. [7] In the downward combustion type condensing boiler, a direction where the condensed water falls due to gravity (i.e. a downward direction) naturally coincides WO 2009/082090 PCT/KR2008/006788 with the flow direction of the exhaust gas passing through the sensible and latent heat exchange units. This is a very important factor for increasing the efficiency of the condensing boiler. [8] That is, while the exhaust gas passes through the latent heat exchange unit, vapor in the exhaust gas is condensed so as to deliver latent heat to the heating circulation water, and the exhaust gas is significantly cooled down. Therefore, since the internal temperature of a condensed-water tray 17 considerably decreases, it is possible to minimize a heat loss caused by regasification of the vapor liquefied into the condensed water. [9] The downward combustion type condensing boiler is considered to have an optimal condensing-boiler structure in that the recovery of latent heat can be maximized. However, the downward combustion type condensing boiler must be equipped with a downward combustion type burner. [10] In general, burners which are applied to boilers can be divided into a Bunsen burner and a premixed burner. In the Bunsen burner, a nozzle unit for jetting gas supplies the minimum primary air required for combustion, and supplies excess secondary air to a portion where flames are formed, thereby implementing perfect combustion. The Bunsen burner has high combustion stability. However, since the flames are formed by the secondary air, the flames lengthen, and downward combustion is impossible. That is, since the length of the flames (outer flames) reacting with the secondary air is large and the flame density is low, the flames tend to face upward. Therefore, the Bunsen burner can be applied only to an upward combustion type condensing boiler. [11] The premixed burner burns premixed gas which is obtained by premixing combustion gas and air in a mixing chamber. In the premixed burner, excess air does not exist in a portion where flames are formed. Further, the length of the flames is very small, and the flame density is high. Therefore, the burner can be installed regardless of combustion directions (upward, downward, and sideward). However, since a prede termined amount of air required for combustion should be premixed, combustion control is very complicated. Further, since the premixed burner is easily affected by disturbance, its combustion stability is low. [12] As described above, it is important to cause the falling direction of condensed water and the flow direction of exhaust gas to coincide with the direction of gravity, in order to maximize the efficiency of the condensing boiler. Therefore, the premixed burner which can perform the downward combustion is generally used. [13] However, the premixed burner has low combustion stability, and an expensive control system should be used to implement complicated combustion control. [14] To overcome such a problem, a variety of methods for constructing a heat exchanger of a condensing boiler by using the upward combustion type Bunsen burner have been WO 2009/082090 PCT/KR2008/006788 proposed. An example of one such heat exchanger is illustrated in FIG. 2. [15] FIG. 2 is a schematic view of a conventional upward combustion type condensing boiler. [16] Referring to FIG. 2, a latent heat exchange unit 24 is disposed above a sensible heat exchange unit 23 so as to be inclined, and exhaust gas passed through the sensible heat exchange unit 23 passes through the latent heat exchange unit 24 via a side portion of a condensed-water tray 27. For the latent heat exchange unit 24, an aluminum rolled pipe or stainless flexible tube have been proposed. [17] In FIG. 2, as the latent heat exchange unit 24 is disposed above the sensible heat exchange unit 23, the condensing boiler can be constructed relatively easily and can be reduced in size. [18] However, the condensation efficiency of the upward combustion type condensing boiler is reduced by as much as 3-5%, compared with that of a traditional downward combustion type condensing boiler. The reduction in condensation efficiency happens for the following two reasons. [19] (1) As the condensed-water tray 27 is positioned right above the sensible heat exchange unit 23, the condensed-water tray 27 is heated to a high temperature. Therefore, although condensed water which is generated while the exhaust gas passes through the latent heat exchange unit 23 falls to the condensed-water tray 27, a con siderable amount of condensed water is evaporated by the heated condensed-water tray 27. Therefore, since latent heat recovered by the condensation is discharged in the form of evaporation heat, it is impossible to obtain the maximum condensation ef ficiency. To overcome such a problem, a heat insulating plate 25 may be used in the condensed-water tray 27. However, it has only a limited effect. [20] (2) The fundamental reason for the reduction of the condensation efficiency is that high-temperature wet exhaust gas (exhaust gas including vapor) passed through the sensible heat exchange unit 23 comes in contact with the condensed water. This in evitably occurs, because the falling direction of the condensed water is set per pendicular to the flow direction of the exhaust gas. Therefore, the condensation hardly occurs in a portion that comes in contact with high-temperature wet exhaust gas. As a result, a great part of the latent heat exchange unit 24 does not reliably carry out its primary function of condensation recovery. Accordingly, as the size of the latent heat exchange unit 24 considerably increases in comparison with that of the sensible heat exchange unit 23, the economic efficiency of the condensing boiler decreases. [21] FIG. 3 is a schematic view of a general fin-tube type heat exchanger. [22] There are difficulties in applying a fin-tube type heat exchanger (refer to FIG. 3), which is generally used as a sensible heat exchange unit, to the conventional upward combustion type condensing boiler.
WO 2009/082090 PCT/KR2008/006788 [23] The fin-tube heat exchanger is composed of a heat exchange tube 31 and heat transfer fins 32. The fin-tube heat exchanger is typically formed of copper (Cu) or stainless steel and is bonded by brazing. Since the fin-tube heat exchanger has a small size and can secure a large heat-transfer area, the fin-tube heat exchanger is widely used as a heat exchanger for boilers. When the fin-tube heat exchanger is used, it is natural for the flow direction of exhaust gas to be set perpendicular to the paper surface of FIG. 3. [24] However, when the fin-tube heat exchanger is applied to the latent heat exchange unit of the conventional upward combustion condensing boiler, the flow direction of exhaust gas is set to the horizontal direction (direction A of FIG. 3) or the vertical direction (direction B of FIG. 3) where the exhaust gas serially flows in several tubes. Then, since a pressure loss of the exhaust gas excessively increases, the application is impossible in practice. Therefore, since a heat exchanger having a different structure from the heat exchanger used in the sensible heat exchange unit should be separately manufactured, the economic efficiency of the condensing boiler decreases. [25] The condensed water of the condensing boiler is discharged to the outside through a condensed-water discharge port 28 and a separate hose connected to the condensed water discharge port 28. However, when the condensed-water discharge hose is bent or frozen such as in the winter, the condensed water is not discharged smoothly. [26] In this case, as shown in FIG. 2, the condensed water is filled up to more than the height of the surface A of the condensed water, which corresponds to the upper end 27a of the condensed-water tray 27, so as to overflow the condensed-water tray 27. The condensed water overflowing the condensed-water tray 27 falls to the combustion unit of the burner 22 through the sensible heat exchange unit 23. Since the sensible heat exchange unit 23 is typically formed of a material having no corrosion resistance to the condensed water, the sensible heat exchange unit 23 may corrode, so that its lifespan is reduced. [27] In a typical boiler, a safety device such as a wind pressure switch or sensor is mounted, which detects whether an exhaust flue 29 is closed or not and then gives an instruction to stop the boiler. As shown in FIG. 2, however, since the upper end 27a of the condensed-water tray 27 is positioned at a lower position than an entrance portion 29a of the exhaust flue 29, a path communicating with the exhaust flue 29 is not closed, even when the condensed water is filled up to the surface A. Therefore, the wind pressure switch or sensor does not generate a signal indicating that the exhaust flue 29 is closed. [28] To solve such a problem, the conventional upward combustion type condensing boiler should include a separate safety device which detects whether the condensed water discharge portion is closed or not, for example, a level sensor which detects the WO 2009/082090 PCT/KR2008/006788 level of condensed water staying in the upper portion of the condensed-water tray and stops the operation of the boiler when the level of the condensed water exceeds a pre determined value. Therefore, the structure of the condensing boiler becomes complex, and the manufacturing cost increases. [29] Reference numerals 11 and 21 represent a blower, reference numeral 18 represents a condensed-water discharge port, reference numeral 19 represents an exhaust flue, and reference numeral 22 represents a burner. Disclosure of Invention Technical Problem [30] The present invention is directed to a heat exchanger of an upward combustion type condensing boiler, which can maximize latent-heat recovery efficiency by causing the flow direction of exhaust gas to coincide with the flow direction of condensed water in a latent heat exchange unit. [31] The present invention is also directed to a heat exchanger of an upward combustion type condensing boiler, in which the same fin-tube type heat exchanger is applied to both a sensible heat exchange unit and a latent heat exchange unit, so that the sensible heat exchange unit does not need to be separately manufactured. [32] The present invention is also directed to a heat exchanger of an upward combustion type condensing boiler, which can safely stop an operation without a separate device, even when the boiler is clogged with condensed water. Technical Solution [33] According to an aspect of the present invention, a heat exchanger of an upward combustion type condensing boiler comprises a sensible heat exchange unit that absorbs sensible heat generated from an upward combustion type burner; a latent heat exchange unit that absorbs latent heat of vapor included in exhaust gas which has been heat-exchanged in the sensible heat exchange unit; and a condensed-water tray that discharges condensed water generated from the latent heat exchange unit. An upward flow of exhaust gas passed through the sensible heat exchange unit is converted into a downward flow so as to pass through the latent heat exchange unit, and the latent heat exchange unit is installed in such a manner that the flow direction of the exhaust gas passing through the latent heat exchange unit vertically coincides with the falling direction of condensed water generated from the latent heat exchange unit. [34] The latent heat exchange unit may include a box-shaped body, of which the top and bottom surfaces are opened and the side surfaces are closed, and a plurality of heat exchange tubes which are installed inside the body so as to be spaced a predetermined distance from each other in a horizontal direction. [35] The sensible heat exchange unit and the latent heat exchange unit may respectively WO 2009/082090 PCT/KR2008/006788 have fin-tube type heat exchange tubes installed therein, the fin-tube type heat exchange tube being coupled to heat transfer fins. [36] The height of an upper end portion of the condensed-water tray may be set to be equal to or more than that of an exhaust-flue entrance portion through which exhaust gas is discharged. Advantageous Effects [37] According to the present invention, as the flow direction of exhaust gas in the latent heat exchange unit is caused to coincide with the falling direction of condensed water, it is possible to maximize latent heat recovery efficiency. Further, as the same fin-tube type heat exchanger is applied to the sensible heat exchange unit and the latent heat exchange unit, the sensible heat exchange unit does not need to be separately manu factured. Further, since the size of the latent heat exchange unit can be reduced, the size of the entire boiler can be reduced. Furthermore, although the condensed-water discharge port is clogged with condensed water, the condensed water can be prevented from falling to the sensible heat exchange unit, which makes it possible to safely stop an operation without a separate device. Brief Description of the Drawings [38] FIG. 1 is a schematic view of a conventional downward combustion type condensing boiler. [39] FIG. 2 is a schematic view of a conventional upward combustion type condensing boiler. [40] FIG. 3 is a schematic view of a general fin-tube type heat exchanger. [41] FIG. 4 is a schematic view of an upward combustion type condensing boiler according to an example embodiment of the present invention. Best Mode for Carrying Out the Invention [42] Hereinafter, example embodiments of the present invention will be described in detail with reference to the accompanying drawings. [43] FIG. 4 is a schematic view of an upward combustion type condensing boiler according to an example embodiment of the present invention. [44] The condensing boiler according to the present invention includes an upward combustion type burner 120 which is installed directly above a blower 110 so as to form flames upward, a sensible heat exchange unit 130 which absorbs sensible heat generated from the burner 120, and a latent heat exchange unit 150 which absorbs latent heat of vapor included in exhaust gas which has been heat-exchanged in the sensible heat exchange unit 130. [45] For the burner 120, any one of a Bunsen burner and a premixed burner may be used. The Bunsen burner supplies the minimum primary air, which is required for WO 2009/082090 PCT/KR2008/006788 combustion, to a nozzle unit, and supplies secondary air to a portion where flames are formed. The premixed burner premixes gas and air and then burns the gas and air. [46] The sensible heat exchange unit 130, which is installed directly above the burner 120, has a plurality of heat-exchange tubes 131 which are arranged in parallel so as to be spaced a predetermined distance from each other in a horizontal direction. FIG. 4 shows a state in which the heat-exchange tubes 131 are installed in one line. However, the heat-exchange tubes 131 may be installed in two or more lines. The sensible heat exchange unit 130 is a fin-tube type heat exchanger in which heat-transfer fins as shown in FIG. 3 are coupled to the outer circumferential surfaces of the heat-exchange tubes 131. [47] The exhaust gas passed through the sensible heat exchange unit 130 is introduced into the latent heat exchange unit 150 through a gas flow path unit 140 of which the width is narrowed. [48] A housing 141 composing the gas flow path unit 140 is formed in a shape of which the lower side is wide and the width is narrowed toward the upper side. Therefore, a flow of the exhaust gas is inclined to the right side by the housing 141. [49] The flow direction of the exhaust gas flowing upward along the inside of the housing 141 is switched to the left direction at an upper end portion of the housing 141, and is then switched to the vertical direction such that the exhaust gas is introduced into the latent heat exchange unit 150. [50] The latent heat exchange unit 150 includes a box-shaped body 152, of which the top and bottom surfaces are opened, and a plurality of heat-exchange tubes 151 which are installed inside the body 152 so as to be spaced a predetermined distance from each other in the horizontal direction. The heat-exchange tubes 151 may be installed in one or more lines. [51] The latent heat exchange unit 150 is a fin-tube type heat exchanger in which heat transfer fins as shown in FIG. 3 are coupled to the outer circumferential surfaces of the heat-exchange tubes 151. The fin-tube type heat exchanger can be applied, because since the heat-exchange tubes 151 are installed so as to be spaced a predetermined distance from each other in the horizontal direction as shown in FIG. 3, the flow of the exhaust gas flowing in the latent heat exchange unit 150 is not affected by the heat transfer fins. [52] Therefore, since the heat-exchange tubes 141 and 151 of the sensible heat exchange unit 140 and the latent heat exchange unit 150 are constructed in a fin-tube type, the latent heat exchange unit 150 does not need to be separately manufactured, which makes it possible to reduce inconvenience. Further, since the size of the latent heat exchange unit 150 can be reduced, it is possible to reduce the total size of a product. [53] The top and bottom surfaces of the body 152 are opened, but the side surfaces thereof WO 2009/082090 PCT/KR2008/006788 are closed. Therefore, the flow of the exhaust gas is not inclined in the right and left direction, but is induced so as to be directed to the vertical direction. [54] Therefore, a flow of condensed water, which is generated from the heat exchange tubes 151 so as to fall in the vertical direction, coincides with the flow of the exhaust gas. [55] To obtain the maximum condensation efficiency in the latent heat exchange unit 150, a possibility of wet exhaust gas coming in contact with condensed water needs to be minimized, and only low-temperature dry exhaust gas should come in contact with the condensed water. That is, when the number of contacts between the exhaust gas and the condensed water generated from the surfaces of the heat exchange tubes 151 increases, an amount of heat transferred between the exhaust gas and the heat exchange tubes 151 decreases, and the regasification of the condensed water occurs due to the heat exchange between the high-temperature exhaust gas and the condensed water. Therefore, the condensation does not reliably occur. [56] Therefore, as the flow direction of the exhaust gas is caused to coincide with the falling direction of the condensed water so as to reduce the possibility of the exhaust gas coming in contact with the condensed water, the condensation reliably occurs, and the latent recovery efficiency can be maximized. [57] The exhaust gas passing through the latent heat exchange unit 150 from the upper side to the lower side thereof is sufficiently cooled, and vapor included in the exhaust gas is condensed in the heat exchange tubes 151 of the latent heat exchange unit 150 so as to transfer latent heat to heating circulation water. [58] The condensed water generated from the latent heat exchange unit 150 falls so as to be collected by an inclined condensed-water tray 160, and is then discharged to the outside. [59] The flow direction of the exhaust gas passed through the latent heat exchange unit 150 is switched to the upward direction such that the exhaust gas is discharged to the outside through an exhaust flue 170. [60] To maximize the recovery of condensation latent heat, the condensed-water tray 160 forming the boundary between the latent heat exchange unit 150 and the sensible heat exchange unit 140 may be formed of stainless steel of which the inside is filled with a heat insulator 180. Therefore, although the boundary surface is heated by the high temperature exhaust heat passing through the sensible heat exchange unit 140, some of the condensed water falling on the condensed-water tray 160 can be prevented from being regasified. [61] Meanwhile, the height of the upper end portion 160a of the condensed-water tray 160 is set to be equal to or more than that of an exhaust-flue entrance portion 171 through which the exhaust gas is discharged.
WO 2009/082090 PCT/KR2008/006788 [62] Therefore, even when a hose through which condensed water is discharged is closed so that condensed water is filled up to the height of the exhaust-flue entrance portion 171, the condensed water is prevented from falling onto the sensible heat exchange unit 130, which makes it possible to prevent the durability of the sensible heat exchange unit 130 from being degraded. [63] Further, when the condensed water is filled up to the height of the exhaust-flue entrance portion 171, it has the same effect as when the exhaust flue 170 is closed. In this case, a typical exhaust safety device such as a wind pressure switch or sensor may be used to detect whether the condensed-water discharge portion is closed or not. Therefore, a separate safety device such as a level sensor does not need to be used. [64] In this case, as shown in FIG. 4, the body 152 of the latent heat exchange unit 150 may be fixed and coupled to the exhaust-flue entrance portion 171 and the upper end portion 160a of the condensed-water tray 160. [65] Industrial Applicability [66] The heat exchanger of the upward combustion type condensing boiler according to the present invention can maximize latent-heat recovery efficiency by coinciding a direction where the condensed water falls with the flow direction of the exhaust gas in the latent heat exchange unit, and thus has industrial applicability.