FI76931B - FOERFARANDE FOER RENING AV ROEKGASER. - Google Patents

Description

The invention relates to a method for cleaning flue gases, in which method the substance is conveyed to the boiler furnace absorptloaline and the substance is reacted with flue gas sulfur, the flue gases are further conveyed from the boiler furnace through a discharge duct transport that unreacted product to a separate hydration unit.

Several methods are known for removing sulfur compounds from combustion, in particular sulfur dioxide, from flue gas. Methods are known in which sulfur is bound to a calcine reagent. It is known e.g. wet limestone method and semi-dry lime cleaning method. Also known as. dry desulfurization methods based on the use of a furnace injector. In some processes, desulfurization in the furnace is supplemented by a reactor or hose filter. They have sought to increase the utilization rate of the absorption trough through recycling.

The object of the invention is in particular a method for cleaning flue gases, in which flue gases can be cleaned of sulfur compounds 25 during combustion and, in particular, sulfur dioxide can be removed from the flue gas.

It is also an object of the invention to be able to utilize the heat released in the boiler furnace in the decomposition of carbonate rock into a more reaction-sensitive oxide.

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It is also an object of the invention to provide a method which can be applied to combustion devices for solid, liquid and gaseous fuels.

The process according to the invention is mainly characterized in that the solid separated in the pre-separator is hydrated and reacted with sulfur to form and transferred downstream to a reactor located downstream of the flue gas pre-separator with respect to the direction of flue gas flow.

Numerous advantages are achieved with the feed-in according to the invention. The amounts of fuel to be handled in the hydration remain small, making the equipment simpler and thus cheaper than the prior art equipment. The actual dust separation equipment is not loaded because recycling is not performed. In this case, the method according to the invention can also be easily applied to existing plants without filter changes. With the feed-in according to the invention, the dust content in the gas entering the reactor is considerably reduced due to the pre-separation, whereby the mechanical wear of the parts in contact with the gas of the reactor is small. In addition, the fouling of the reactor with pre-separation is less than in the case where pre-separation would not take place.

15

In the process according to the invention, the sulfur binding takes place in two steps.

According to the invention, an absorbent which is formed in the general embodiment of the invention from a powdered carbonate bath containing alkali and / or alkaline earth metals is conveyed to the firebox of the boiler structure in connection with the flue gases. The carbonate rock decomposes into the corresponding oxide under the influence of the heat of the furnace. In a most preferred embodiment of the invention, calcium carbonate is used, for which the reaction equations for the next step are also shown.

In the first lie, finely ground limestone is blown into the boiler furnace to a temperature of 900 ° C to 1200 ° C, whereby the potassium carbonate decomposes according to reaction equation (1):

CaCO3- »CaO + CC> 2 (1)

Some of the calcium oxide thus formed still reacts with sulfur dioxide (2), 35

CaO + SO2 + l / 202 -> CaSO4 (2) 3 76931 f 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 is used for the sulfur contained in the carbon, the sulfur separation in the furnace is then about 30-50 Z of the total amount of SO2. In order to be below the 5 emission standards, sulfur sequestration must most often be supplemented by post-boiler treatment.

In the second step of the process, unreacted CaO and reaction products travel with the flue gas out of the boiler and enter the pre-separator.

10 All dry dust separators can be used as pre-separators.

The choice and dimensioning of the pre-separator depends essentially on the ash content of the fuel used and the combustion method. If there is little or no ash in the fuel, there are no special requirements for the pre-separator. The degree of separation must be sufficient to separate a sufficient amount of lime 15 from the flue gas for further processing.

If the fuel contains a lot of ash and the combustion method is such that the majority of it is exposed to flue gases (dust combustion), it is advantageous to make the eslerot selective. Preferably, the cyclone separator is then dimensioned so that only particles larger than the appropriate particle size are separated. In this case, it is possible to substantially reduce the mass flow to further processing.

Once the particle size of the limestone to be blown into the furnace has been selected to be suitable for fly ash, only the fraction containing mainly CaO is subjected to further treatment. The ash and CaSO4 particles, which are not necessary for further desulfurization reactions, are instead transported with the flue gas.

The fraction separated in the work-up is hydrated either wet or dry according to the equation below.

CaO + H 2 O -> Ca (OH) 2 (3) 35 · Hydration is necessary to react and remove the remaining SO2 in the flue gases.

4 76931 1 The fraction separated in wet hydration is introduced into a tank and mixed with water, which is kept in a continuous rotation by means of a stirrer. The reaction of equation (3) takes place in the tank. Some of the calcium is soluble in water, but most remains in suspension.

From the tank, the suspension is pumped to a reactor where the SO 2 reacts and the solid dries. Spraying of the suspension into the reactor can be done using known rotary or pressure dispersed nozzles. The amount of liquid entering the reactor is controlled so that the temperature after the reactor 10 is higher than the temperature of the water dew point, but still close enough to it to ensure efficient SO2 absorption. The SC ^ separation takes place mainly according to Equation (4).

Ca (OH) 2 + SO 2 -> CaSO 3 + 1 ^ 0 (4) 15

In the dry hydration alternative, water vapor is introduced into the separated fraction, which causes the reaction (3). During steam blowing, the dust must be mixed intensively, e.g. with a screw mixer as shown in the figure. Grinding before screwing improves the hydration properties of the dust. It is also possible to combine the hydration and grinding steps using a preferably steam-powered jet grinding support. The released steam is led from the hydrator directly to the reactor.

Hydrated dust is blown into the reactor by means of carrier air. Prior to mixing the dust, it is preferred to cool the flue gas by water quenching to create good reaction conditions.

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 using a hose filter, a sulfur slurry reaction also takes place in the dust layer formed on the surface of the hose.

The advantage of the method according to the invention, e.g. over the wet method, is the simple and thus inexpensive equipment, the wastewater resistance 35 and the dry end product. Compared to the semi-dry method, the decisive advantage is a cheaper absorbent and the equipment is constructively simpler and less expensive. A preferred embodiment of the method 5 76931 1 according to the invention is based specifically on the use of limestone as an absorbent, as a result of which the operating costs are considerably lower.

Compared to desulfurization methods based on the use of furnace injection and compared to methods in which the desulfurization in the furnace is supplemented by a reactor or a hose filter, there are advantages and substantial differences between the process of the invention and the controlled activation of the injection product in a separate process. the process according to the invention guarantees good sulfur separation capacity and a coupled solids flow in the process.

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

Figures 1 and 2 show the method schematically.

In a process according to the invention, in a preferred embodiment, the limestone flour is fed so that it is calcined to calcium oxide (CaO). In this case, part of the sulfur reacts immediately with Ca0.

In this case, calcium sulphate CaSO is formed

A

in the process according to the invention, the reaction products and fly ash are conveyed with the flue gases to a post-boiler desulphurisation unit, where first selective escalation of unreacted CaO takes place.

The pre-separated calcium oxide (CaO) is hydrated according to the invention using the downstream principle and performing the hydration as a separate process to produce reactive calcium hydroxide (CaCOH), which is conveyed downstream to the reactor. Only the particles containing the most calcium oxide are introduced into the hydratolntl-30 process according to the invention, as the fly ash and the CaSO 4 -particles generated in the plug pass with the flue gas along the channel α 2 directly to the reactor 16.

In the downstream process according to the invention, the Ca 2 O 4 generated is preferably blown into the flue gas cooled by water injection, whereby the remaining SO 2 reacts mainly with calcium sulphite (CaSO 4). Finally, the solids are preferably purified from the flue gas in an electric and / or hose filter.

In Fig. 1, a silo for an absorptal, most preferably lime-5 stone is denoted by reference numeral 1. At the bottom of the silo there is an absorber dispenser 2. The transport air blower 3 blows carrier air mixed with the absorbent into the furnace of the boiler 4. Combustion and coal are introduced along channels 5. In the most preferred embodiment, the boiler has a dust boiler. But an embodiment is also possible in which the cat-10 state is the so-called a grate boiler or a combined grate / dust combustion boiler, the grate being marked as in the figure with reference number 6. Slag is taken out of the boiler along the duct 7. 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 particle-15 liters are separated into an intermediate silo 9. The closing device 10 is preferably a so-called the feed from the intermediate silo 9 to the mixing tank 11 from the pre-separator 8. to the reactor 16. The reactor 16 can advantageously be supplied with an auxiliary which may be required for spraying, e.g. air or steam along the duct 17. 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 blower 25 sucks the flue gas from the dust separation device 18 and blows it into the chimney 20 and from there on to the outside air. Units 16 and 18 are separated from the separated flue gas contaminants along the discharge line 28.

Figure 2 shows another preferred embodiment of the invention.

30 In this embodiment, the so-called a hydration screw 22. A fraction separated in the separator device is introduced from the intermediate silo 9 to the hydration screw 22 through the closing device 10, to which steam is also fed along the channel 23. The hydrated substance is conveyed by a screw to the supply duct E and the hydrated substance is fed to the reactor 16 together with the carrier air by means of the transport air fan 24. The substance is fed to said reactor 16 via the distribution piping 25. The flue gas wetting water is fed to the reactor 16 via the duct 26. The flue gas is further discharged out of the reactor 16 via the duct 21. According to the invention, a hydrating solution has been implemented on the basis of the principle of 7 76931 l. A certain fraction is recovered from the esler separator point of the flue gas duct and this fraction is treated so as to be reactive with the flue gas sulfur and is then transferred to the reactor 16 specifically downstream of the flue gas transport direction 5.

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Claims (9)

1. A method for the purification of flue gases, in which method an absorption medium is transported to the fireplace by a boiler (4), and one is allowed to react with the evaporator in the flue gases, the flue gases are transported from the boiler fireplace along an outlet channel (a). a pre-separator (8) which separates the part of the absorbent which is not reacted with sulfur from the flue gas and transports the non-reacted product to a separate hydration unit, characterized in that the solid separated from the pre-separator (8) is hydrated is reacted with sulfur and is transported co-stream to a reactor (16), in which the flow direction of the flue gases is located after the pre-separator (8). 15 2. A method according to claim 1, characterized in that from the pre-separator (8), the separated cargo is led to an intermediate shaft (9) and hence to a mixing container (11). 1 Patent Claim 10 76931 3. A method according to claim 1 or 2, characterized in that in the hydration process one uses a mixing vessel (11), to which one the freight charge is separated in the pre-separator and to which one is fed water along the line (15). The connection between the main duct of the flue gases and the mixing vessel (11) then connects an interconnection branch (13) to the mixing vessel (11). 4. A method as claimed in claim 1, characterized in that the freight charge led from the pre-separator (8) in the hydration process is transported to a hydration sealing screw (22), to each screw device which is advantageously also inserted into the meadow along the line (23) and where the freight link is separated. this screw device is advantageously conveyed with the carrier air as blown by the transport air blower (24) to the reactor (16). 35 Process according to any of the preceding claims, characterized in that the use of a reactor (16) is used after the pre-separator (8) for the purpose of conducting the hydrated calcium oxide.