FI81969C - Process for the absorption of sulfur dioxide formed by combustion of sulfur-containing fuels - Google Patents

Description

1 81969

This invention relates to a method for trapping sulfur dioxide from the combustion of sulfur-containing fuels.

It is already known to reduce sulfur dioxide emissions from the combustion of sulfur-rich fossil fuels by feeding suitable material to the combustion plant furnace, which reacts with the sulfur dioxide to prevent it from entering the environment with the flue gases. A suitable material is usually a solid alkali compound which reacts with sulfur dioxide to form solid sulfur compounds, thereby rendering the sulfur more easily removed. This technique is well suited for the use of high-sulfur fossil fuels such as oil and coal. Peat can also contain exceptionally high amounts of sulfur.

Limestone (CaCOg) is used as the most common sulfur retention alkali due to its general availability and low cost. However, the difficulty in sulfur retention is the relatively low sulfur retention efficiency of lime, as the sulfur retention reactions are heterogeneous and therefore the prerequisite for an efficient reaction of a solid is e.g. small particle size, especially when residence times in the furnace are short. The residence times are short when the material is fed into the furnace by injection. Grinding lime into a sufficiently fine amount is expensive.

The object of the present invention is to improve the sulfur retention efficiency of the sulfur retention base and thus to reduce the amount of sulfur dioxide released into the environment with the flue gases.

2,81969

According to the invention, it has surprisingly been found that the sulfur retention efficiency of the sulfur-retaining alkali can be considerably improved by mixing the sulfur-retaining alkali with the peat and feeding this mixture into the furnace of the incinerator.

The main features of the invention appear from the appended claims.

Calcium and / or magnesium compounds such as calcium carbonate, calcium magnesium carbonate or similar oxides are preferably used as the sulfur retaining alkali. A particularly preferred sulfur retention alkali is limestone (CaCOg).

Peat is a decaying plant material that contains humic acids, non-degradable plant material and water resulting from decomposition. The beneficial effect of peat on the sulfur retention properties of lime is due to the fact that lime reacts with the acidic components of peat, i.e. humic acids, to form organic calcium compounds, which upon combustion form small particles of calcium oxide that react efficiently with gaseous sulfur compounds.

The use of peat according to the invention also has the advantage that the lime mechanically mixed with the peat is calcined more efficiently, because as a result of the combustion of the peat particles the temperature rises locally, which at the same time reduces the particle size of the original lime.

Due to these above-mentioned reasons, the lime retention of lime is enhanced and, in addition, lime can be fed together with peat, e.g.

The lime is preferably mixed with wet peat, e.g. for a production run in the autumn, in the germination phase, but the lime can also be mixed with the peat by any other suitable method.

3,81969

According to the invention, wet, moist or dry peat with an average particle size of preferably less than 5 mm can be used.

The mixture of such peat and lime powder can be fed as such to the furnace, but if desired the mixture can be dried to the desired moisture content and / or ground to a desired particle size of less than 5 mm, preferably less than 0.2 mm.

The equilibrium moist mixture of lime and peat preferably contains about 5-50 and particularly preferably about 10-30 pamo% lime.

The invention is further illustrated by the following experiment.

The sulfur retention efficiency of the peat and lime mixture was tested in a drop tube furnace, which is a heated, two meter high vertical tube furnace to which the desired gas mixture (e.g. flue gas) can be introduced. The powdered material under study is fed to the top of the furnace in a steady stream and collected by a cooled probe at a certain distance from the feed point, giving the material a desired residence time selected according to the injection technique. Lime powder (potassium carbonate) with a weight average weight of 47.5 micrometers was used in the experiments mixed with peat so that the amount of lime was 20% by weight of the equilibrium moist lime-peat mixture. The air-dried tur-ve lime mixture was ground for experiments to a grain size of less than 0.2 mm.

o With this mixture ratio, at a temperature of 1000 C and a residence time of 0.5 seconds, an improvement of about twice the sulfur retention efficiency was achieved. When lime powder was used alone, the percentage of sulfur and lime (S / Ca) retained under similar conditions was 4.9%. When using a peat-lime mixture, the corresponding molar ratio <S / Ca> was 11.5%.

Claims (5)

A method for trapping sulfur dioxide from the combustion of sulfur-containing fuels by feeding a sulfur retention element 1 which reacts with sulfur dioxide to form easily removable solid sulfur compounds, characterized in that the sulfur retaining alkali fed to the furnace is mixed with the peat and the sulfur Process according to Claim 1, characterized in that calcium and / or magnesium compounds are used as sulfur retention starting materials. Method according to Claim 1 or 2, characterized in that limestone is used as the sulfur-retaining alkali. Method according to one of the preceding claims, characterized in that the particle size of the mixture of sulfur retention alkali and peat is less than 5 mm, preferably less than 0.2 mm. Process according to one of the preceding claims, characterized in that the equilibrium moist mixture of sulfur-retaining alkali and peat contains from about 5 to 50, preferably from about 10 to 30, by weight of sulfur-retaining element. 5,81969 Patent k rav