DE1961048A1 - Desulphurising industrial gases by adsorption - with alkaline earth carbonate or hydroxide - Google Patents

Abstract

After scrubbing industrial waste flue gas, containing SO2 or SO3, with an aqs. suspension of alkaline earth carbonate or -hydroxide, or material containing them, pref. limestone, flue ash, ore processing or-flotation residues, the aqs. suspension is separated in a wet-cleaner into a sludge- and a water-portion, by settling filtration or centrifuging. The sludge portion is sprayed into a drier situated in front of wet-cleaner in gas-flow, to complete reaction of still unreacted carbonate or hydroxide, and is drawn off as fluid. Alkaline earth carbonate or -hydroxide or materials containing them are slurried again into the separated water, after replenishing with fresh water, and suspension is pumped to wet-cleaner to scrub S oxides.

Description

Process for the desulphurization of industrial gases, in particular Exhaust gases such as flue gases To remove harmful sulfur oxides such as sulfur dioxide d and sulfur trioxide, from industrial gases, especially exhaust gases such as flue gases, so-called wet processes are known, in which the flue gases with aqueous sludge, Sunpensions or solutions that contain alkali or alkaline earth compounds contain. The sulfur oxides are in the water portion of the sludge or suspension dissolved and they then react with the alkali or alkaline earth compounds, e.g. I3. Calcium carbonate, with the formation of sulphites and sulphates. These are So about absorption processes.

For such processes, substances containing alkaline earth are also used, like e.g. Fuel ashes, applied, the flue gases being oxygen and the ashes Components that accelerate the conversion of sulfite to sulfate are added.

In this process, the waste product is aqueous sludge or Suspensions that cannot be used in the seizure state, but are also not easy can be drained into the receiving waters of the sewage systems, but a work-up need.

It is known to thicken such suspensions, for example, and to thicken the undissolved ones and to deposit more or less water-insoluble sulphites or sulphates in heaps. But the use of external heat for this is considerable and not economically justifiable.

A new process for the desulphurization of industrial gases, in particular exhaust gases, such as flue gases, proposed in which the gases with aqueous Slurries or suspensions of alkaline earth carbonates or hydroxides or these containing substances are washed, in which the suspension water in the circuit wdeler is used and for the processing of the suspended substance in a Form in which it can be deposited on heaps or further processed, none External heat is required. In addition, the gases to be treated with the new Process before wet washing cooled and moistened or saturated, so for conditioning the wet laundry.

The inventive method is characterized in that one the aqueous suspension of alkaline earth carbonate or hydroxide or containing them Substances after washing the gas in a wet scrubber by settling, filtering off or centrifugation into a sludge fraction and a water fraction and separates the .Sludge portion for reacting the carbonate or hydroxide components that have not yet reacted as well as for drying in a dryer, which is arranged in the gas flow upstream of the wet scrubber is, injected and withdrawn again as a free-flowing product, while separating in <3cm Water after it has been replenished in its quantity by fresh water, again Alkaline earth carbonate or hydroxide or these contain.

tending substances are suspended and the suspension to wash out the sulfur oxides are used in the wet scrubber.

Limestone and calcium hydroxide are particularly suitable for the ncuc Procedure, since calcium sulfite and calcium sulfate schr insoluble in Water, and with the saturated solutions, are not a great deal of these substances be carried around in a cycle. But also the corresponding magnesium compounds with greater solubility of the sulfite and sulfate can be used. In the end Substances that contain alkaline earth carbonate or hydroxide can also be used, e.g. fuel ashes or residues from ore processing or ore flotation. Alkali salts are less suitable for this because of their high solubility in water new procedures.

Another advantage of the new process is the sers cycle, which saves considerable amounts of it, as well as cooling and humidification of the gas before wet scrubbing using the overheating heat of the gas.

There are no problems to weigh up.

The absorbing substances become stoichiometric in the new process loaded with sulfur oxides. Only about fluctuations in the sulfur oxide content of the to be calibrated gases to be treated and the alkaline earth content of the absorption materials used, it is recommended to use such lengths that the calculated mean lengths exceed by lo percent.

For a better understanding of the invention it is illustrated by means of the figure explained.

The hot flue gas is fed to the pre-separator 1 through line 2 and about 80 7th of the fly ash from the flue gas is deposited in it. The fly ash is pulled through lines 3 and 30 and brought to lIalde. The pre-cleaned Flue gas pulls through line 4 into the dryer 5 and from there through line 6 in the wet scrubber 7 and further through line 8, the heating furnace 9, line le, fan 11, line 12 into the chimney 13. Through line 14 water and through line 15 Limestone placed in the pump reservoir 16 and the suspension by Line 17, pump 18 and lines 19 and 20, so the distribution nozzles 21 and 22 in the, wet scrubber 7 sprayed. The suspension, which has largely been converted, collects is at the bottom of the wet washer 7 and is passed through line 23 into the settling basin 24 directed. When the solids content of the suspension settles out and the supernatant Water flows through line 25 into the pump reservoir 16.

The sludge solids content is withdrawn through line 26 and Funded by pump 27, line 28 and distributor nozzle 29 in the dryer 5. here the rest of the alkaline earth compound is converted to sulphite or sulphate and the muddy one The solid has dried to such an extent that a free-flowing product is formed on the bottom by means of a pipe 30 is deducted. For the sake of simplicity and for better curling of the fly ash one pulls the Flucjasche through lines 3 and 30 and the Erdaikalisulfit or sulfate through line 30 together.

Example 20,000 Nm3 flue gas from a boiler system at 120 ° C, with a SO2 content of 3 g / Nm3, a fly ash content of 15 g / Nm3 and a water vapor content of 45 g / Nm3, corresponding to a water dew point of 34 ° C, are after dedusting up to 4 g / SPm3 with So m3 / h of an aqueous suspension in which 90 kg of limestone are suspended, washed in the wet scrubber 22 (Figure).

The suspension draining from the washer is placed in the settling tank 24, in which it separates into a muddy solid fraction and water. The water flows into the pump reservoir 16, while 1,100 kg / h of sulphite sludge small proportions of unconverted KaiIstein and Bo% Wssor in the gas stream before the wet washer arranged dryer 5 are pumped. Be in the dryer the last, not yet converted limestone fractions to sulphite implemented and the sludge is dried by utilizing the superheating heat of the gas to such an extent that that a free-flowing material with a water content of less than lo X at the bottom of the Dryer can be withdrawn through line 3o and deposited on a dump. The humidified flue gas, cooled to 460C in the dryer, moves into the wet scrubber 7 and is completely desulfurized therein; it then only contains traces of S02. The water separated from the suspension and passed into the pump reservoir 16 The amount is around 0.88 m3 / h - that is the proportion that remained with the sludge is - added, 90 kg of limestone suspended in it and the suspension to the wet washer fed.

Claims (3)

Patent languages 1! Process for the desulphurization of industrial gases, in particular Exhaust gases, such as flue gases, the gases with aqueous slurries and suspensions washed from alkaline earth carbonates or hydroxides or substances containing them are, characterized in that the aqueous suspension after washing of the gas in a wet scrubber by settling, filtering or centrifuging in a sludge fraction and a water fraction separates and the sludge in a dryer injected, which is arranged in the gas flow upstream of the wet scrubber, while in the separated one Water, after it has been replenished in its quantity by fresh water, in turn Alkaline earth carbonate or hydroxide or substances containing this are suspended and the suspension is pumped into the wet scrubber. 2. The method according to claim 1, characterized in that the alkaline earth compound Limestone is used. 3. The method according to claim 1, characterized in that as alkaline earth compounds Substances containing fuel or residues from ore processing or flotation be used.