FI123021B - Combustion boiler with superheater - Google Patents

Description

FIELD OF THE INVENTION The present invention relates to a combustion boiler for producing and recovering thermal energy.

BACKGROUND OF THE INVENTION Combustion boilers contain a large amount of compounds which are harmful to the materials of the heat transfer surfaces of the boiler. In particular, when burning biofuels and waste fuels, corrosion, i.e. corrosion, of the heat transfer surfaces of the boiler, in particular of the superheaters and their heat transfer surfaces, has been observed. In addition, it has been found that ash from combustion accumulates in heat transfer surfaces, which impairs heat transfer and thus the utilization of thermal energy.

The above biofuels include naturally occurring plant-based materials such as wood chips, bark, field biomass, sawdust, black liquor and the like. Examples of waste fuels are sorted household waste, industrial and commercial waste and demolition wood. These fuels contain significant amounts of chlorine. Together with the sodium and potassium released from the fuel, they form gaseous alkali chlorides in the flue gases, which condense and deposit on heat transfer surfaces, in particular on superheater surfaces. Deposition and condensation occurs particularly at sites where the surface temperature of the heat transfer surfaces is less than 650 O. When the surface temperature of the heat transfer surface is greater than 450 Ό, the chlorides cause chlorine corrosion.

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9 To overcome the corrosion problems caused by chlorides, various additives have been introduced to the furnace. WO-2006/134227-A1 discloses that a solution in the form of a solution is injected into the superheater area of a steam boiler.

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sulfate-containing compound that binds alkali chlorides formed in the furnace. 3 According to WO-02/059526-A1, a solution of sulfate

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° product or sulfuric acid to flue gases before superheaters. EP-c32071239-A2, for its part, discloses that the 35 additives required to prevent corrosion are fed to the boiler flue gases by means of a cooled beam.

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It is also known to reduce nitrous oxide emissions from various types of boilers by supplying to their furnace various additives that reduce the amount of nitrogen oxides produced in combustion in the flue gases. Such a solution is disclosed, for example, in WO-9813649-A1, where cooled tube panel surfaces with separate additive channels for the additive are installed in the furnace of the fluidized bed boiler 5.

WO-96/02792, in turn, discloses a heat exchanger located in a pocket-like compartment that collects particles and is separated from the fluidized bed at the bottom of the cat-space in the center of the boiler. The material in the pocket is fluidized with a gas that is non-aggressive and substantially oxygen-free to avoid corrosion problems in the heat exchanger. WO-03/104547-A1, in turn, discloses a boiler with a separate compartment with a superheater and also with combustion in progress. The objective is to burn fuel-15 materials that do not cause corrosion problems in the superheater located in the chamber.

According to the prior art, combustion boiler superheaters are located either in the combustion boiler furnace, typically at the top of the furnace, or in the post-furnace flue gas duct 20 to which the furnace flue gases are fed. The superheaters may be located either in the same flue gas duct or in parallel flue gas ducts. The superheaters are located in the flue gas stream, and the heat energy of the flue gas is transferred to the superheater, through heat radiation and heat convection, which can be referred to as combination superheaters. It is also possible to use 25 special radiant heaters, the use of which is mainly based on the utilization of the thermal radiation of the flame, and special convection heaters, the use of which is mainly based on contact between the superheater and the flue gases.

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9 thermal convection. The radiation superheater is generally located in the flames at the top of the casing, e.g. in the wall of the furnace, and is in direct contact with the thermal radiation of the g flame. There is a direct line of sight between the flame and the superheater

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(line-of-sight). The convection suppressor is generally protected from the heat of the flame and is located outside the furnace, e.g. in the flue gas duct. The type of superheater also influences the structure of the superheater, whereby, for example, in the irradiator, the tubes are placed very close together and form a plate-like surface or plane.

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The superheaters act as heat exchangers, which typically comprise a structure constructed of interconnected tubes that transfer heat energy to a fluid flowing inside the tube, such as a gas, liquid or mixture thereof.

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The above means of eliminating the corrosion problems of superheaters are often impractical, especially if a separate supply of additive or separate supply of gas is required to protect the superheaters in order to avoid the harmful effects of the flue gases.

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Brief Description of the Invention

It is therefore an object of the present invention to provide a system which avoids the above problems, which are specifically related to corrosion and corrosion caused by flue gases.

The combustion boiler of the invention is set forth in claim 1.

The principle of the invention is the utilization of heat radiation in the superheater and at the same time the prevention of the damaging effects of the flue gases on the superheater, whereby no attempt is made to utilize heat transfer by convection.

In one embodiment, the principle is that the superheater is located in a chamber where access to the harmful gas, corrosive or corrosive substances contained in the flue gas, and thereby the flue gas, is significantly restricted, thereby preventing access completely or nearly completely. The aim

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9 is to prevent or severely restrict the access of these compounds and substances to the heat transfer surfaces of the superheater. There are different ways to avoid flue gas circulation at the superheater.

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3 According to one example, the chamber is constructed so that there is no continuous flow of flue gas through the superheater within the chamber. thermal energy

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The transfer of the c / j to the superheater is mainly based on thermal radiation, and the possibility of the 35 energy transferring to the superheater by convection is completely or almost completely prevented.

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In one example, the chamber is made only from the bottom or only one side open so that the flow of flue gases into the chamber, and in particular through the chamber, past the superheater, is prevented as much as possible.

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In one example, the chamber is constructed such that the gas in the chamber is retained in the chamber by the dynamic pressure of the flue gas rising in the furnace. The gas pours into the chamber and remains in the chamber. In this way, flue gases are not continuously flowing past the superheater and the gas in chamber 10 is not exchanged. Preferably, the chamber is located at the top of the furnace and is open at the bottom. Preferably, a radiation list is disposed within the chamber. Further, it is most preferable for the superheater and its heat transfer surfaces to have a direct line of sight with the flame so that heat energy recovery is based on heat radiation, since heat transfer by convection is avoided. Convection is thus not intended to be possible by the flow of flue gas, nor, for example, by particles, particles or bed material in the furnace.

Direct vision in this specification refers not only to the visible flame of the combustion in the furnace 20, but also to the source of thermal radiation, of which the visible flame forms only a part, whereby the thermal radiation is invisible and mainly in the infrared region.

Nor is it a chamber for separate combustion of the fuel 25, the flue gases of which are combined with the flue gases of the boiler furnace so that the separate combustion flue gases are led through a superheater or ™ chamber. The chamber is mainly focused on thermal radiation and smoke.

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9 gases produced during combustion in the furnace. This ^ combustion is the primary source of thermal energy.

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In one example, the flow of flue gases, and also the flow of various particles and particles, is controlled by a gas, powder, or liquid jet of one or more nozzles at the open bottom or side of the chamber so that gas is formed in front of the open mouth of the chamber. a powder or liquid curtain that directs the flow of flue gases away from the chamber orifice and prevents the flue gases from entering the chamber. Furthermore, the gas, powder or liquid to be injected may be an additive according to the prior art which reduces the corrosion problems caused by the flue gases. The gas to be injected may be a gas known in the art to reduce corrosion problems, or e.g. a gas which is free of corrosive substances, e.g. an inert gas. It may also be air or gas from a combustion boiler.

One or more jets of gas, powder or liquid can also form a curtain or barrier which is located in front of the open mouth of the chamber 10 and prevents the flow of flue gases through the mouth of the chamber.

In another example, one or more nozzles are provided inside the chamber or directly adjacent to the mouth of the chamber to fill the chamber with gas to reduce corrosion and corrosion problems, to dilute flue gases entering the chamber, or to completely replace the gas in the chamber with another gas, e.g. with inert gas. Filling occurs, for example, once when the boiler starts or, if necessary, at certain intervals. In this way, flue gases will never enter the chamber. The gas supplied to the chamber by the nozzles is retained in the chamber 20, preferably by the dynamic pressure of the rising flue gas stream. The aforementioned additives may also be sprayed into the chamber by means of a liquid or powder jet.

The above nozzles may be located within or near the chamber as required.

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In one embodiment, the chamber is located at the top of the furnace

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o inside the beak so there is no need to make any changes to the boiler walls.

? The beak is a structure at the top of the furnace which narrows the upper portion of the furnace to a size smaller than the lower portion of the furnace. At the same time, the beak directs the flue gases to the superheaters and to the flue gas duct above the beak. The chamber is typically rectangular in shape, comprising a side in wall of tubes carrying the medium, one or more of which are the same side wall of the furnace, or one or more of which are the same side wall of the beak. The chamber has no bottom or is 35 open at the bottom. The chamber has a ceiling that can be part of the beak.

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In one example, the chamber is positioned outside the furnace such that the mouth of the chamber is on a horizontal or vertical wall of the furnace and extends into the chamber either through the bottom of the chamber or through one of its sides. Again, the chamber has a radiation superheater having a direct line of sight to the flame. In one example, the chamber is positioned inside the furnace such that one or more of the side walls of the chamber are simultaneously the side wall of the furnace. The roof of the chamber may also be the roof of the furnace.

The flow of gases in the chamber is avoided. With respect to the structure of the chamber 10, it is often possible that the chamber is not completely sealed but allows leakage of gases and flue gases through various gaps and holes. However, significant efforts are made to limit these leaks and to keep them insignificant. However, it may be necessary to provide continuous ventilation of the chamber by leakage. The chamber may also be provided with a separate ventilation duct 15 which can be opened and closed as required, for example by means of a controlled valve, through which the gases or flue gases in the chamber can be removed from the chamber.

One or more of the chamber walls are formed using fluid-carrying tubes to recover the heat energy of the furnace by radiation and / or convection. The inner bulge of the chamber walls is preferably covered with an insulating compound.

BRIEF DESCRIPTION OF THE DRAWINGS In the following, the invention will be further described with reference to the accompanying drawings, o ™, in which:

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Fig. 1 is a schematic side view of a fluidized bed boiler, in which the fluidized bed boiler is provided with a chamber with superheater;

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Fig. 2 is a more detailed view of the chamber and superheater shown in Fig. 1, while Fig. 3 is a schematic view of an inside chamber insert 35, viewed from the side, 7 Fig. 4 is a schematic view of a chamber outside the furnace, Fig. Fig. 6 schematically shows the lower part of the recovery boiler, in which the recovery chamber can be applied to the superheater 10.

DETAILED DESCRIPTION OF THE INVENTION

In the drawings, like-function parts are denoted by the same reference numeral -15a.

Figure 1 shows an example of a steam boiler applying the above chamber and superheater solution. As a steam boiler and as a location for the chamber and superheater solution, a fluidized bed boiler, in particular a fluidized bed boiler (BFB) shown in Figure 1, or a circulating fluidized bed boiler (CFB) shown in Figure 5 can be used. . Alternatively, the recovery site may be a recovery boiler, shown in Figure 6, based on black liquor combustion, or a combustion boiler where the fuel is burned on a grate, or another steam boiler.

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δ ™ Figure 1 shows a combustion boiler 1, which in this example is a

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9 a boiler with a furnace 2. The walls of the furnace are formed by water-cooled pipes which are joined by fins to each other. At the bottom of the furnace are nozzles 3 for supplying fluidizing air, i.e. primary air, from the air box 4

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2. The fluidization layer 5 5 in the lower part of the furnace is made to float by the fluidizing air, i.e. continuous movement in the furnace 2. Fuel is supplied from the fuel supply means 6 and secondary air per second from the sparger air nozzles 7. In this boiler the tertiary is also fed. air nozzles 8. The fuel used is, for example, biofuels and / or waste fuels. The flame 12 generated by the combustion of the fuel is located above the fluidized bed and extends, for example, above the secondary air nozzles 7 and often also up to the tertiary air nozzles. Combustion of the fuel by oxygen-containing gas in the lower part of the furnace 2 is the primary source of thermal energy.

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At the top of the furnace are superheaters 9 and 13 which serve to produce superheated steam, which is typically used in a turbine (not shown in the figure). As shown in the figure, the tubes forming the furnace wall are bent inwardly from the rear wall 2b so as to form a cam 10 towards the furnace front wall 2a. The cam 10 serves to direct the flue gases as desired to the superheater 9 and 13. The superheater 9 is , the operation of which is based on heat radiation and heat convection, and the superheater 13 is, for example, a convection superheater. The superheaters, and the cam, are drawn in a simplified diagram illustrating the rotation of the medium.

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The flue gases 19 formed in the furnace are directed forward through the flue gas duct 11 in connection with the furnace. Heat transfer surfaces or heat exchangers 14 may be provided in the flue gas duct.

In the example of Figure 1, the chamber 17 for the superheater 15 is disposed inside the beak 10 at the top of the furnace. The bottom of the chamber 17 is open and at the same time forms the orifice 18. The superheater located in the chamber has a direct line of sight 16 to the primary heat source represented in Figure 1 by a flame 12. Visual contact is provided by the orifice 18 or the like.

The mouth opening 18 may consist of one or more separate openings. If the orifice extends from a plurality of apertures, the size of the apertures, for example, may be suitably

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o by selecting to prevent the flow of flue gas into the chamber while still allowing 2 heat radiation to enter the chamber and the heat transfer surfaces of the superheater.

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5 In the example shown in Figure 1, the flue gases are prevented from entering the chamber

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o so that the gas in the chamber remains in the chamber due to the rising flow of flue gas S, so that the gas is trapped in the chamber. Thus, no substitute gas, especially flue gases, can enter the chamber.

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The example shown in Fig. 2 also utilizes a nozzle 20, which in this example is located in the furnace wall 2b, near the chamber. A suitably directed liquid, powder, or gas blown out of the nozzle directs the flue gases 19 away from the chamber and its orifice. In addition, it is difficult for the flue gases to pass through the shower 5 into the chamber.

The example shown in Fig. 2 also utilizes a nozzle 21 which in this example is located inside the chamber 17. The liquid, powder or gas blown out of the nozzle and, if necessary, appropriately directed, neutralizes or dilutes the gas in the chamber, e.g., flue gas entering the chamber, or fills the chamber with the desired gas so that the gas in the chamber is replaced. The gas is, for example, a non-corrosive or non-corrosive gas, e.g. an inert gas. The gas remains in the chamber due to 17 recovery. The gas can also maintain a pressure in the chamber which is higher than the pressure outside the chamber in the furnace, whereby the gases flow only outwardly from the chamber, e.g. through an orifice.

In the various examples, only one or both of the nozzles 20 and 21 are used.

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Fig. 3 shows an example in which the chamber 17 is disposed inside the furnace 2 with the rear of the chamber bordering the furnace wall, for example its front wall 2a, rear wall 2b or a side wall. The chamber is open on at least one side that forms the same mouth opening 18. The superheater 15 disposed within the chamber has a direct line of sight 16 to the primary heat source. The nozzle 21 in this example is located on the chamber ™ wall. The operation of the nozzles 20 and 21 corresponds to that described in Figure 2

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9.

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g 30 Figure 4 shows an example in which chamber 17 is disposed within the furnace

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2, so that the front of the chamber abuts the wall of the furnace, for example its front wall 2a, the rear wall 2b or one of the side walls. The chamber is open at least on one side, which at the same time forms an orifice 18.

The chamber is connected from the furnace through the furnace wall and the mouth 18 is formed in the wall. The superheater 15 located in the chamber has a direct line of sight 16 to the primary heat source. In this example, the nozzle 21 is located on the wall of the furnace, near the chamber. The operation of the nozzles 20 and 21 corresponds to that described with reference to Figure 2.

The chamber and superheater solution shown can also be applied in a circulating fluidized bed boiler 5, as well as a recovery boiler or grate furnace. Figure 5 shows a combustion boiler 1 which is a circulating fluidized bed boiler. The boiler comprises a furnace 2, a flue gas duct 11 and a cyclone 25. In the cyclone, particles of fluidized bed entrained by the flue gases are separated. The fluidized bed particles separated from the flue gases are returned to the furnace 2. Fluidized air is fed into the furnace from the bottom of the furnace 10. The velocity and volume of the fluidizing air are adjusted such that it causes the fluidized bed particles to substantially fill the entire furnace. The furnace is supplied with fuel, which may be biofuel, waste fuel, or carbon from the fuel supply means 6 and the fuel air from the air nozzles 7. The fuel air may be supplied from a use level of up to 15. The boiler also has several superheaters 9, 22, 23 and 24.

The combustion boiler is provided with a chamber 17 and a superheater 15 shown in Figure 3. Alternatively, the chambers of Examples 2 or 4 may be applied to that combustion boiler.

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Figure 6 shows a combustion boiler which is a recovery boiler. The baking boiler uses fuel from chemical pulp production and a solution containing wood dissolved particles, ie black liquor. The boiler has a furnace 2 to supply black liquor from the fuel supply means 6 and the furnace 25 from air nozzles 26, 7 and 8 located at different heights of the boiler. Melt 27 generates molten 27 which is discharged from the furnace for further processing. At the top of the furnace are superheaters and flue gases

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9 is discharged from the furnace through a flue gas duct.

σ> 30 The combustion boiler is provided with a chamber 17 and a superheater 15 shown in Figure 3.

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Alternatively, the chambers according to the examples of Figures 2 or 4 can be applied to the said boiler.

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The invention is not intended to be limited to the exemplary embodiments set forth above, but is intended to be widely applied within the scope of the features defined in the claims which follow.

Claims (13)

A combustion boiler for the production and recovery of thermal energy, the combustion boiler (1) comprising at least: 5. a combustion chamber (2) which is limited by walls, a bottom and a roof and on whose lower part the combustion functions as a primary source of the combustion boiler heat energy is arranged to take place; - means (6) for feeding a fuel into the combustion chamber for combustion; means (3, 7, 8, 26) for supplying combustion gas into the combustion chamber for combustion; - one or more flue gas ducts (11) located on the upper part of the combustion chamber and controlling the flue gases (19) formed during combustion out of the combustion chamber; characterized in that the combustion boiler further comprises: - at least one chamber (17) to which has been placed at least one superheater (15) for steam to utilize the heat energy; - said chamber being adapted to allow a direct visual contact (16) between said superheater and said primary cold, to enable the receipt of heat energy by means of heat radiation; and wherein said chambers are further arranged to prevent the supply of said flue gases (19) to said superheater either completely or almost completely to avoid the receipt of thermal energy by convection. C \ J o Combustion boiler according to claim 1, characterized in that the marble is coupled to the combustion chamber via an orifice (18), via g 30 which comprises a direct visual contact between the superheater and said primary source. O 3. Combustion boiler according to claim 2, characterized in that the bottom of the chamber is open and forms said orifice. 35 4. Combustion boiler according to any one of claims 1-3, characterized in that gas contained in the chamber is adapted to lean into the chamber under the influence of a dynamic pressure of the flow of the flue gases. 5 The combustion boiler according to any one of claims 1-4, characterized in that the combustion boiler further comprises a comb (10) located in the upper part of the combustion chamber which controls the flue gases, said chamber being located within the comb. 10 Combustion boiler according to any one of claims 1-4, characterized in that the chamber is located outside the combustion chamber and it controls a connection thereto through the wall of the combustion chamber, or the chamber is located within the combustion chamber, the bottom or one side of the chamber being open and forming said mouth. Combustion boiler according to any one of claims 1-6, characterized in that at least one nozzle (20) for blowing gas, powder or liquid into the combustion chamber has been placed in the chamber or in the vicinity of the chamber and it is directed that the flue gases are controlled from the chamber and the access of the flue gases to the chamber is prevented. Combustion chamber according to any one of claims 1-7, characterized in that a nozzle (20) for blowing liquid, powder or gas 3 within the chamber, in which said liquid, powder or liquid, is placed in the chamber or in the vicinity of the chamber, gas has been configured to neutralize the effect of corrosive or corrosive substances in the flue gas, to dilute the flue gas content in the chamber, or to replace the chamber flue gas with a gas that does not corrode or corrode. | 30 Combustion boiler according to claim 7 or 8, characterized in that ID 3 as gas is used air or an inert gas. m o S Combustion boiler according to claim 7 or 8, characterized in that said liquid, powder or gas is iron (III) sulphate Fe2 (SO4) 3 or aluminum (III) sulphate AI2 (SO4) 3 or a mixture thereof. Combustion boiler according to any one of claims 1-10, characterized in that the superheater comprises tubes which are attached to each other and within which streams a medium to which the thermal energy collected by the superheater is transmitted. Combustion boiler according to any one of claims 1-11, characterized in that the combustion boiler is a bubbling fluid bed boiler, circulating fluid bed boiler or a soda boiler, or a combustion boiler which applies rust combustion. The combustion boiler according to any one of claims 1-10, characterized in that the combustion boiler is a bubbling fluid bed boiler or a circulating fluid bed boiler, the combustion boiler further comprising a fluid bed (5) located in the lower part of the combustion chamber and means (3). of fluidizing air into the combustion chamber. CM δ CM CD O O) X cc Q. LO • 'ί LO O O CM