Economizer and boiler

Abstract

To improve heat recovery efficiency in a latent heat recovery unit of an economizer.SOLUTION: An economizer is configured such that a heat transfer pipe 2 for heating supply water is arranged in a housing 1 through which exhaust gas circulates, the economizer comprising a nozzle 3 that supplies dropwise condensation accelerator to a latent heat recovery unit in which condensate water is generated on the surface of a heat transfer pipe. The nozzle 3 is arranged so as to supply the dropwise condensation accelerator to a region in which a temperature of the surface of the heat transfer pipe is equal to or less than a thermal decomposition temperature of the dropwise condensation accelerator. The dropwise condensation accelerator contains at least one of a sarcosine compound and long chain aliphatic amine.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to an economizer that heats boiler feed water or the like using exhaust gas from a boiler, etc., and in particular to an economizer that also heats feed water using the heat of condensation (latent heat) of water vapor in the exhaust gas. The present invention also relates to a boiler equipped with this economizer. [Background technology]

[0002] As an economizer that heats feed water using exhaust gas from a boiler or the like, there is one that heats the feed water using sensible heat of the exhaust gas and further heats the feed water using latent heat (heat of condensation) (Patent Documents 1 and 2).

[0003] Patent Document 1 describes providing a means for changing the exhaust gas temperature between a dry economizer for recovering sensible heat and a condensing economizer for recovering latent heat.

[0004] Patent Document 2 describes an economizer that uses fin tubes as heat transfer tubes, recovers sensible heat with the upstream fin tube and recovers latent heat with the downstream fin tube, in which the spacing between the fins of the downstream fin tube is increased to make it easier for condensed water to fall.

[0005] There are two methods of liquefying and condensing steam by contacting it with a solid wall at a temperature lower than the saturation state: film condensation, in which the condensate forms a continuous liquid film on the wall surface, and dropwise condensation, in which the condensate does not wet the wall surface but becomes numerous droplets. Compared to film condensation, dropwise condensation has a thermal transfer coefficient several to several tens of times higher, so a dropwise condensing agent is sometimes used when condensing steam (Patent Document 3). [Prior art documents] [Patent documents]

[0006] [Patent Document 1] JP 2012-57860 A [Patent Document 2] JP 2013-108643 A [Patent Document 3] Patent No. 6506865 Summary of the Invention [Problem to be solved by the invention]

[0007] When a drop-like condensation promoter is added to the exhaust gas introduced into the economizer, depending on the temperature conditions, much of the drop-like condensation promoter may be decomposed by the heat of the exhaust gas, making it difficult to improve the heat recovery efficiency in the latent heat recovery section of the economizer.

[0008] An object of the present invention is to improve the heat recovery efficiency in a latent heat recovery section of an economizer. [Means for solving the problem]

[0009] The economizer of the present invention is characterized in that a heat transfer tube for heating feed water is arranged in an exhaust gas flow section through which exhaust gas flows, and the economizer further comprises a dropwise condensation promoter supply means for supplying a dropwise condensation promoter to a latent heat recovery section where condensed water is formed on the surface of the heat transfer tube.

[0010] In one aspect of the present invention, the dropwise condensation promoter supplying means is disposed so as to supply the dropwise condensation promoter to a region where the temperature of the heat transfer tube surface is equal to or lower than the thermal decomposition temperature of the dropwise condensation promoter.

[0011] In one aspect of the present invention, the dropwise condensation promoter supplying means has a supply amount control means for controlling the amount of dropwise condensation promoter supplying according to the amount of fuel used by a boiler that generates the exhaust gas.

[0012] In one embodiment of the present invention, the dropwise condensation promoter comprises at least one of a sarcosine compound and a long-chain aliphatic amine.

[0013] The boiler of the present invention is equipped with the economizer of the present invention. Effect of the Invention

[0014] In the economizer of the present invention, by adding a dropwise condensation promoter to the latent heat recovery section of the economizer, the dropwise condensation of water vapor is promoted in the latent heat recovery section, and the heat recovery efficiency in the latent heat recovery section is improved. [Brief description of the drawings]

[0015] [Figure 1] FIG. 2 is a cross-sectional view of an economizer according to an embodiment. [Diagram 2] FIG. 4 is a cross-sectional view of an economizer according to another embodiment. [Diagram 3] FIG. 3 is a perspective view of a heat transfer tube of the economizer of FIG. 2. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] Hereinafter, an embodiment will be described with reference to the drawings.

[0017] Fig. 1 is a schematic cross-sectional view of an economizer installed in the exhaust gas duct of a boiler. This economizer has a metal heat transfer tube 2 disposed inside a housing 1. The combustion exhaust gas from the boiler flows into the housing 1 from an inlet 1a at one end thereof, comes into contact with the heat transfer tube 2 to lower its temperature, and then flows out from an outlet 1b at the other end thereof.

[0018] Boiler feed water is introduced into the heat transfer tube 2 from the downstream side in the exhaust gas flow direction (the outlet 1b side), and heated feed water is taken out from the upstream side in the exhaust gas flow direction.

[0019] The upstream side of the heat transfer tube 2 in the gas flow direction is the sensible heat recovery section, and the downstream side of the gas flow direction is the latent heat recovery section. This latent heat recovery section is an area where the surface temperature of the heat transfer tube 2 (hereinafter sometimes referred to as the heat transfer tube metal temperature) is 100°C or less, and a chemical injection nozzle 3 is provided to supply a dropwise condensation promoter as a chemical to this area. By supplying the dropwise condensation promoter from this chemical injection nozzle 3, the heat recovery efficiency in the latent heat recovery section is improved.

[0020] FIG. 2 is a cross-sectional view of an economizer according to another embodiment, and FIG. 3 is a perspective view of a heat transfer tube thereof.

[0021] A heat transfer tube 6 is installed in a housing 5 installed in the exhaust gas flue of a boiler. As shown in Fig. 3, the heat transfer tube 6 is a fin tube having a tubular heat transfer tube body 6a and disk-shaped fins 6b provided so as to spread out in the radial direction from the outer circumferential surface of the heat transfer tube body 6a.

[0022] The exhaust gas flows into the housing 5 through the exhaust gas inlet 5a of the housing 5, comes into contact with the heat transfer tubes 6 to be cooled, and then flows out through the exhaust gas outlet 5b.

[0023] The heat transfer tubes 6 are arranged in multiple rows and stages such that the tube axis direction of the heat transfer tube main bodies 6a is perpendicular to the direction connecting the inlet 5a and the outlet 5b.

[0024] In this embodiment as well, a chemical injection nozzle 7 is provided so as to supply a drop-like condensation promoter to the latent heat recovery section downstream in the gas flow direction.

[0025] By supplying the droplet-like condensation promoter from this chemical injection nozzle 7 to the latent heat recovery section, the heat recovery efficiency in the latent heat recovery section is improved.

[0026] When the thermal decomposition temperature of the dropwise condensation promoter is lower than 100° C., it is preferable that the chemical injection nozzles 3, 7 are provided so as to supply the dropwise condensation promoter to a region of the latent heat recovery section where the metal temperature of the heat transfer tube 2 is equal to or lower than the thermal decomposition temperature. Conversely, when the thermal decomposition temperature of the dropwise condensation promoter is higher than 100° C., the chemical injection nozzles 3, 7 may be provided so as to supply the dropwise condensation promoter to the sensible heat recovery section upstream of the latent heat recovery section.

[0027] In addition, a plurality of injection nozzles may be installed at different installation positions. In this case, the injection nozzle used for injection may be switched depending on the operating conditions of the boiler and the thermal decomposition temperature of the drop-like condensation promoter.

[0028] In the present invention, a dropwise condensation promoter whose distribution ratio for each temperature (concentration of the dropwise condensation promoter in the gas phase / concentration in the water phase), adsorption characteristics for each metal, and decomposition characteristics for each temperature have been examined in advance may be added to the exhaust gas so that the dropwise condensation promoter will be adsorbed onto the heat transfer tube surface (metal surface) even when the pH of the condensed water is on the acidic side. For example, an optimal dropwise condensation promoter is selected as shown in the table below, and one that maximizes the latent heat recovery promotion effect is selected. In addition to the fuels in the table below, ammonia co-firing, which partially uses ammonia, may also be used.

[0029] In a typical small boiler, for example, the exhaust gas temperature at the economizer inlet is 200 to 300° C., and the exhaust gas temperature at the economizer outlet drops to about the temperature of the boiler feed water after passing through the temperature range of the latent heat recovery section. In this case, it is preferable to select a dropwise condensation promoter that does not decompose excessively even at 200 to 300° C. according to the material of the heat transfer tube surface, and for example, the dropwise condensation promoter is preferably at least one of a sarcosine compound and a long-chain aliphatic amine.

[0030] In gas-fired boilers, the sulfur content of fuel is generally low, so the acidity of the condensed water is low. Therefore, from the viewpoint of preventing sulfuric acid corrosion, carbon steel may be used in addition to stainless steel in the heat transfer tube outside the condensed water generation area (latent heat recovery section). In addition, the condensed water generation area may change due to fluctuations in the feed water temperature. Therefore, when carbon steel is used for the heat transfer tube, it is preferable to use oleyl propylene diamine, which is easily adsorbed by carbon steel under weak acidic conditions, as the dropwise condensation promoter. Furthermore, it is more preferable to use a sarcosine compound in addition to oleyl propylene diamine in order to deal with the generation of condensed water on stainless steel. In this case, it can be applied economically without using an alkaline agent, but an alkaline agent may be added depending on the water quality of the condensed water. The alkaline agent is a volatile amine, NH 3 , NaOH, phosphates, etc. The volatile amine may be, for example, ethanolamine, which is a less volatile amine that is soluble in condensed water.

[0031] In heavy oil-fired boilers, sulfuric acid is generated due to the sulfur content in the fuel, so the acidity of the condensed water tends to be high, and as a material for the heat transfer tubes, for example, corrosion-resistant stainless steel (SUS316L) is used. When stainless steel is used, a sarcosine compound is preferable as the dropwise condensation promoter. When the acidity is high due to the fuel properties or when a dropwise condensation promoter other than a sarcosine compound is used, the pH may be adjusted to the optimum range by using the above-mentioned alkaline agent in combination.

[0032] In hydrogen boilers with high flame temperatures, thermal nox is generated from nitrogen in the atmosphere, which is then oxidized to generate high concentrations of nitric acid, resulting in high acidity of the condensed water. Therefore, for example, corrosion-resistant stainless steel is used as the material for the heat transfer tube. In this case, a sarcosine compound is preferred as the dropwise condensation promoter. If the pH of the condensed water is extremely low, the adsorption characteristics change, so it is preferred to maintain the condensed water in the optimal pH range for the dropwise condensation promoter used, for example, by using the above-mentioned alkaline agent in combination.

[0033] In any of the boilers described above, the alkaline agent may be added together with the dropwise condensation promoter or separately, or may be added by spraying boiler blow water containing the alkaline agent.

[0034] [Table 1]

[0035] The surface of the heat transfer tube may be treated to be water-repellent. The water-repellent treatment may be, for example, coating the surface of the heat transfer tube with a highly water-repellent material such as polytetrafluoroethylene (PTFE) which is a fluororesin or silicone to form a resin layer, or physical treatment to give the surface of the heat transfer tube an uneven structure resembling lotus leaves.

[0036] The dropwise condensation promoter used in the present invention preferably contains at least one of a sarcosine compound and a long-chain aliphatic amine.

[0037] As the sarcosine compound, N-oleoyl sarcosine, N-lauroyl sarcosine, N-stearoyl sarcosine, N-cocoyl sarcosine and the like are preferred.

[0038] As the long-chain aliphatic amine, octadecylamine, oleylamine, oleylpropylenediamine, etc. are preferred.

[0039] The amount of the dropwise condensation promoter added may be sufficient to obtain the effect of promoting dropwise condensation on the surface of the heat transfer tube in the latent heat recovery section, and although it varies depending on the type of dropwise condensation promoter, it is usually preferable to add about 0.01 to 10 mg / kg, particularly about 0.1 to 1 mg / kg, relative to the amount of condensed water generated in the exhaust gas. The amount of the dropwise condensation promoter added may be adjusted according to (for example, in proportion to) the amount of fuel used by the boiler.

[0040] The dropwise condensation promoter may be added intermittently or continuously, but is preferably added continuously.

[0041] The dropwise condensation promoter may be dissolved or dispersed in a solvent such as water, methanol, ethanol, or isopropanol and then supplied to the chemical injection nozzle 3 or 7. For example, a solution of the dropwise condensation promoter is stored in a tank, and the dropwise condensation promoter solution is supplied to the chemical injection nozzle 3 or 7 by a pump. A spray tip may be installed at the tip of the nozzle to ensure uniform supply by the chemical injection nozzle. When an orifice-type spray tip is installed, the dropwise condensation promoter solution may be diluted and supplied to the economizer separately in order to adjust the liquid supply pressure and flow rate of the dropwise condensation promoter solution to a range suitable for the spray tip. The dropwise condensation promoter solution may be diluted with filtered boiler blow water or economizer condensate and pressurized to make it suitable for spraying. As described above, the liquid supply amount of this pump may be controlled according to the fuel consumption of the boiler.

[0042] The above-described embodiment is merely an example of the present invention, and the present invention may be embodied in other forms than those described above. [Explanation of symbols]

[0043] 1,5 Housing 2,6 Heat transfer tubes 3,7 Chemical injection nozzle

Claims

1. In an economizer in which a heat transfer tube for heating feed water is arranged in an exhaust gas flow section through which exhaust gas flows, An economizer comprising a dropwise condensation promoter supplying means for supplying a dropwise condensation promoter to a latent heat recovery section where condensed water is formed on the surface of a heat transfer tube.

2. 2. The economizer according to claim 1, wherein the dropwise condensation promoter supplying means is disposed so as to supply the dropwise condensation promoter to a region where the temperature of the heat transfer tube surface is equal to or lower than the thermal decomposition temperature of the dropwise condensation promoter.

3. 2. The economizer according to claim 1, wherein said dropwise condensation promoter supplying means has a supply amount control means for controlling the amount of dropwise condensation promoter supplying according to the amount of fuel used in a boiler which generates said exhaust gas.

4. The economizer according to any one of claims 1 to 3, wherein the dropwise condensation promoter comprises at least one of a sarcosine compound and a long-chain aliphatic amine.

5. A boiler equipped with the economizer according to any one of claims 1 to 4.

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