FI83166B - RENINGSMETOD FOER ROEKGASER OCH ANLAEGGNING FOER RENING AV ROEKGASER. - Google Patents

Description

83166 ^ Flue gas cleaning method and apparatus for flue gas cleaning Renewal methods for flue gas cleaning and flue gas cleaning for flue gas cleaning 5

The invention relates to a method and an apparatus for purifying flue gases, in which an absorbent substance is conveyed to the boiler flue and reacted with flue gas sulfur, the flue gases are further conveyed from the boiler furnace through an outlet duct to a pre-separator separating the to the unit where the product is activated mechanically.

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Applicant's prior publication No. 76,931 discloses a process in which a solid separated from a pre-separator is hydrated and converted to a sulfur-reactive form and transferred downstream to a reactor located downstream of the flue gas pre-separator with respect to the flue gas flow direction 20.

The object of the invention is to improve the above-mentioned process and in particular its hydration process. The aim is to have a method and a device which have made it possible to considerably increase the flue gas desulphurisation after the boiler furnace 25.

The object of the invention has been achieved by a solution in which the CaO and CaSO 4 separated from the flue gases are treated mechanically, e.g. by crushing, with an activating device, whereby the CaSO 4 shell surrounding the CaO particles breaks and CaO 3 is released into the hydration reaction. Preferably, an after-separator is used after the activating device, in which the reactive CaO is separated from the rest of the material and from which the CaO dust separated from the after-separator is fed to the reactor, where the actual hydration takes place. The hydrated CaO further reacts with the flue gas introduced into the reactor, effectively binding the flue gas SO 2.

The following is a step-by-step description of the entire cleaning process.

35 2 83166 ^ In the first stage, finely ground limestone is blown into the boiler furnace to a temperature of 900 ° C to 1200 ° C, whereby the calcium carbonate decomposes according to reaction equation (1): 5 CaCO 3 -----> CaO + CO 2 (1)

Some of the calcium oxide thus formed still reacts with sulfur dioxide (2), 10 CaO + SO2 + 1/202 -----> CaSO4 (2) This gives calcium sulphate. The proportion of reacting sulfur in the furnace can be 10-70% of the total sulfur. When an economically reasonable amount of reagent relative to the sulfur contained in the carbon is used, the sulfur separation in the furnace is then about 30-50% of the total amount of SO2. In order to meet the set emission standards, sulfur sequestration must in most cases be supplemented by post-boiler treatment.

In the second stage of the process, the unreacted CaO and the reaction products travel out of the boiler with the flue gas and enter the pre-separator. All dry dust separation devices can be used as pre-separators.

Once the particle size of the limestone blown into the furnace has been selected to be suitable for fly ash, only the fraction containing mainly CaO is subjected to further processing. However, CaO particles coated with a CaSO 4 layer are always subjected to further processing, whereby CaO is activated according to the invention in an activating device, most preferably in a press by crushing the CaSO 2 shell surrounding the CaO and releasing the CaO into the Hydration Reactor.

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In the further processing, the separated and ground fraction is hydrated in the reactor according to the equation below.

CaO + H 2 O -----> Ca (OH) 2 (3) 35 3 83166 ^ Hydration is necessary to react and remove the remaining SC> 2 in the flue gases according to reaction equation (2).

5 After the reactor, fly ash and reaction products are separated from the flue gases. The separator can be, for example, an electric or hose filter. When a hose filter is used, a sulfur binding reaction also takes place in the dust layer formed on the surface of the hose.

The process according to the invention is mainly characterized in that the solid separated from the pre-separator is transferred to an activation bed after the pre-separator, which crushes the pre-separated material particles, whereby the CaSO 4 shell around CaO is broken and CaO is released downstream of the activator to a reactor downstream of the flue gas pre-separator, and that the method substantially hydrates the CaO particles in the reactor by introducing the CaO particles through the nozzles into the reactor droplet zone, face and CaO reacts immediately with water and the resulting Ca 2 O 4 further reacts; with the flue gas flowing in the reactor, binding the SO 2 contained in the flue gas.

The apparatus according to the invention is mainly characterized in that the apparatus comprises, after the esler separator, an activating device which crushes the pre-separated material particles, whereby the CaSO 4 shell around CaO is broken and CaO is released into the hydration reaction, the apparatus comprising a channel for passing CaO-containing particles for hydration in a reactor located downstream of the flue gas escalator relative to the flue gas flow direction, the apparatus comprising nozzles through which the CaO particles are introduced into the reactor with the water spray nozzles located substantially in the vicinity of the nozzles.

The invention will now be described with reference to some preferred embodiments of the invention shown in Figures 35 * 83166 1 of the drawings, to which, however, the invention is not intended to be exclusively limited.

Figure 1A shows a press used as an activating device.

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Figure 1B schematically shows the release of CaO in a compression event.

Figures 2 and 3 show the method and apparatus schematically.

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In the flue gas cleaning process shown in Figures 1A-3, limestone flour is fed to the furnace so that it first cesps into calcium oxide (CaO) and then reacts with the sulfur compounds of the flue gases to form calcium sulfate CaSO 4.

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CaO + SO 2 + 0.502 -> CaSO 4

The proportion of CaO involved in the reaction is 5-30%, usually 15%. The reason for the poor use of calcium is the CaSO 4 shell formed in the reaction, which hi-20 slows down the course of the reaction after a certain layer thickness, so that the reaction, when available for 0.5-5 s, usually does not have time to take place in less than 2 s. Excessive temperature, usually <1150 ° C, causes Sint cracking on the surfaces of lime particles, which impairs reactivity.

The reaction products and fly ash are transported with the flue gases to a desulphurisation unit after the boiler, where the unreacted CaO is first pre-separated.

The method according to the invention reactivates the calcium-containing CaO particle separated from the flue gas stream by breaking the surrounding CaSO4 shell. This takes place after the pre-separation of CaO in the activating device, preferably in a press. In the activator, the comminuted product is fed to the droplet zone of the flue gas humidification reactor, whereby CaO is hydrated to Ca (OH) 2, which efficiently binds SO 2 to form cesium sulfite CaSO 4. The comminuted product is fed, for example, by means of carrier air, so that the powdered product is fed through the nozzles to the droplet zone of the flue gas humidification reactor. Thus, CaO is hydrated to CafOH essentially in the flue gas humidification reactor.

Only the particles containing the most calcium oxide CaO 5 are introduced into the hydration process and, for example, fly ash is separated in a post-separator after the activator.

The following reactions thus take place in the droplet zone of the flue gas humidification reactor: CaO hydrates to Ca 2 O 3 and CaCO 3) reacts with the sulfur oxide SO 2 of the flue gases to form calcium sulphite CaSO 4.

Water injected into the droplet zone of the flue gas humidification reactor not only provides a hydration process but also cools the flue gas and.

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Figure 1A shows an activating device 11 according to the invention, which is most preferably a press. From the pre-separator, the pre-separated CaO-containing material stream J is conveyed to the press 11, where it is conveyed by the press discs and the rotating discs Ε ^, Ε ^ pulling the material 20 into the space between the discs, whereby the material is subjected to strong compression.

Figure 1B shows a CaO particle surrounded by a CaSO 4 shell that substantially slows CaO from hydration in the hydration reaction.

According to the invention, this CaSO 4 shell is broken by pressing the CaO-CaSO 2 particle between the mechanical press discs Ε ^, Ε ^ on the CaO-CaSO 4 interface, fracture lines F 2 2, F 2 and Ca 2 O 2 are released along the interface from the surface of the CaO component. , whereby CaO is released into the hydration reaction.

In Fig. 2, a silo for an absorbent, preferably a limestone, is denoted by reference numeral 1. At the bottom of the silo there is an absorbent dispensing device 2. The transport air blower 3 blows carrier air into which the absorbent mixes with the boiler 4 furnace. Combustion air and carbon _- · are introduced along ducts 5. In a preferred embodiment, the boiler is a dust combustion boiler. But it is also possible an embodiment in which the boiler is a so-called a grate boiler or a combined grate / dust combustion boiler, the grate being indicated as in the figure by reference numeral 6. Along the channel 7 83 8366 1, slag is taken out of the boiler. The flue gases are led from the boiler structure along the flue gas duct a to the flue gas pre-separator 8. In the most preferred embodiment, the pre-separator 8 consists of a cyclone. The sorted particles are separated into an intermediate silo 9. The closing device 10 is preferably a so-called a shut-off 5 feeder, distributes the fraction from the intermediate silo 9 to the pre-separator 8 to the activating device 11, most preferably to the press. The flue gas from the reactor 16 is conveyed along the duct 21 to the dust separation device 18. The dust separation device may comprise an electric or hose filter device for separating the dust. The flue gas fan 19 sucks the flue gas 10 from the dust separation device 18 and blows it into the chimney 20 and from there on to the outside air. The separated flue gas impurities are removed from the units 16 and 18, e.g. along the CaSO 4 removal line 28.

In the activator 11, the sintered pre-separated CaO as well as the 15 CaSO 4 particles are mechanically reactivated into a CaO particle by breaking the CaSO 2 shell surrounding the CaO so that the CaO is released for hydration. From the activating device 11, the activated particle is conveyed along the duct 12 to the after-separator 13 and along the duct 14 to the reactor 16. The duct 14 is supplied with carrier air or carrier gas by a fan arrangement 15.

The substance can also be introduced from the activating device 11 directly into the reactor 16, in which case the after-separator 13 is not used. The dusty activated CaO-containing material is sprayed through the nozzle 14a into the droplet zone A of the reactor 16. Water is also sprayed onto the droplet zone A of the reactor 16, which causes the CaO to be hydrated to CaCl 2. Another purpose of the water supply is to cool the flue gases. Hydrated CaO reacts efficiently with Ca 2 O 2 as flue gas SO 2 to form calcium sulfite CaSO 4. Water is introduced along the channel 17 and sprayed in droplets through the end nozzles 17a of the channel 17 into the reactor 16. The end nozzles 17a are located right next to the dust nozzles 14a, thus ensuring immediate encounter and reaction of the components involved in the hydration reaction.

The reactive CaO dust separated from the flue gas stream is efficiently directed to the area of the water mist A of the reactor 16, thus ensuring good water / solids contact. The flue gas is flowed in the reactor 16 so that the flue gas and the Ca (OH) 2 particles formed during the hydration meet as efficiently as possible. In this case, a good alignment of the Ca (OH) .particles with the flue gas SC is ensured. Preferably, the inlet directions of the CaO-containing dust and water from their nozzles 14a, 17b are perpendicular to the flue gas flow direction (S).

5 The water and dust supply can be concentrated in the middle of the reactor 16 so that the reactor walls remain dry.

Water is supplied through nozzles 17a so that the heat of the flue gases has time to evaporate all the water and no wet solid suspension 10 or wastewater is formed at any stage.

Figure 3 shows in more detail the method and apparatus according to the invention. When treating the CaO-CaSO 4 mixture mechanically with an activating device 4 11 e.g. a press, mill, grinder, crusher, the shell of CaSO 4 surrounding the 15 CaO is broken so that the CaO is released for hydration. As shown in Fig. 2, the mechanically treated CaO and CaSO 4 are further conveyed along the channel 12 to the after-separator 13. The after-separator 13 classifies the fly ash or CaSO 4 from the active CaO dust stream and thus reduces the dust load of the reactor 20 16 Figure

3, the treated activated dusty CaO material is fed through the nozzle 14a of the duct 14 to the flue gas stream S in the reactor 16 and said feed takes place to the droplet zone A of the flue gas reactor, to the droplet zone A at the same time as the water mist D fed from the nozzles 17a

With 25. Water mist D is produced from the nozzles 17a of the channel 17. The nozzles 17a are located in the droplet zone A of the reactor 16 near the dust nozzles. By droplet zone A is meant that area inside the reactor 16 in which the ignited water H 1 O has not yet evaporated from the flue gas S.

the effect of thermal energy.

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Claims (11)

A method for purifying flue gases, wherein the absorber is conveyed to the furnace of the boiler (4) and reacted with the flue gas sulfur, and the flue gases are further conveyed from the boiler furnace via the exhaust duct (a) to a pre-separator (8) separating the sulfur-unreacted absorber of the substance flue gas and some of the absorbent particles which have already reacted with the flue gas sulfur, characterized in that the solid separated from the pre-separator (8) is transferred to an activator (11) after the pre-separator (8), which crushes the pre-separated alna particles the shell breaks and CaO is released into the hydration reaction, in which the crushed dusty CaO-containing substance is transferred from the activator 15 (11) downstream to the reactor (16) located downstream of the flue gas pre-separator (8), and that we in the method, the CaO particles are substantially hydrated in the reactor (16) by introducing the CaO particles through the nozzles (14a) into the droplet zone (A) of the reactor (16), to which water is also introduced through the nozzles 20 (17a), causing CaO and water droplets to meet and The CaO reacts immediately with water and the resulting Ca 2 OH 2 reacts with the flue gas flowing in the reactor (16) to bind the SO 2 contained in the flue gas. 25 Method according to Claim 1, characterized in that before the CaO-containing material crushed in the activation bed (11) is transferred to the reactor (16), the components containing the most CaO are separated in a post-separator (13) after the activator (11) and transferred to the reactor (16). ). 30 Process according to Claim 1 or 2, characterized in that the CaO dust-containing substance is introduced into the reactor (16) together with the carrier air or carrier gas. Method according to one of the preceding claims, characterized in that the hydration is started before the reactor (16) by supplying steam or water to the CaO-containing material stream after the activating device (11). 9 83166 Method according to one of the preceding claims, characterized in that the CaO-containing dusty substance is fed to the droplet zone (A) of the reactor (16) in the central region of the reactor (16) and flows from the nozzles towards the flue gas (S) 5 so that the flue gas and the flow directions and velocities of the dust are as favorable as possible to achieve good contact contact of the reactants. Method according to one of the preceding claims, characterized in that water is sprayed from nozzles (17a) located immediately adjacent to the dust nozzles (14a), allowing the best possible contact between the reactants and that water and CaO-containing dust are sprayed in such a way that their flow directions are somewhat opposite to the flue gas flow direction (S). 15 Method according to one of the preceding claims, characterized in that the activating device (11) used in the method is a mechanical activating device and most preferably a press. 20 .! An apparatus for cleaning flue gases, which comprises a flue gas duct (a) discharged from the furnace of the boiler (4) and a branch point therein for a pre-separator (8) separating the sulfur-unreacted boiler (4) from the flue gas 25 and some of them reacted with flue gas sulfur, characterized in that the apparatus comprises, after the pre-separator (8), an activating device (11) which crushes the pre-separated material particles, thereby rupturing the CaSO 4 shell around CaO and releasing CaO into the hydration reaction, the apparatus comprising a channel (14) ), through which the CaO-containing particles are transferred to a hydrated trough in a reactor (16), which reactor (16) is located downstream of the flue gas pre-separator (8) and which comprises nozzles (14a) through which the CaO particles are introduced into the reactor (16) water spray-35 the nozzles (17a) being located substantially in the vicinity of the nozzle (14a). ίο 83166 Apparatus according to claim 8, characterized in that the apparatus comprises an after-separator (13) between the activating device (11) and the reactor (16), whereby only the particles containing the most CaO are transferred to the reactor (16). 5 Apparatus according to one of the preceding claims 8 or 9, characterized in that the apparatus comprises a blower (15) or the like, by means of which a flow of carrier air is produced to the substance fraction transferred along the duct (14). 10 Apparatus according to one of the preceding claims 8, 9 or 10, characterized in that the activating device (11) is a press. 15 20 25 30 35 n 83166