CS272565B1 - Sorbent for dry flue gas desulphurisation - Google Patents

Abstract

The essence of the solution is that the sorbent consists of 1 to 6 parts by weight of finely ground limestone, 1 to 3 parts by weight of iron particles and its oxides, and 1 to 3 parts by weight of gypsum. The solution can be used especially in the energy industry when burning sulfurous coal in pulverized, grate and fluidized bed boilers.

Description

The invention relates to sorbents for dry flue gas desulphurisation. Dry sorbents for flue gas desulphurisation make it possible to capture sulfur oxides in a single operation, without significant cooling of the flue gas, so that no costly additional heating is required. Several refeneration methods with different sulfur carriers are known, but degeneration complicates and prolongs the desulfurization process and is adversely affected by the presence of fly ash in the flue gas.

Dry non-regenerative methods of flue gas desulphurisation are also known, namely the so-called dry additive technology, a method using highly reactive sorbents based on calcium hydroxide and a method of desulphurisation with calcium materials in the fluidized bed of combusted coal.

It is known that the application of limestone in the process of dry active technology is a one-time desulphurisation process with a low degree of limestone utilization and low flue gas desulphurisation efficiency.

Methods using a highly reactive calcium hydroxide sorbent remove sulfur oxides from flue gases with high efficiency, for example the solution according to MS. author's certificate No. 217642. They use either waste lime from various productions, or calcium hydroxide is prepared by thermal decomposition of natural carbonates and subsequent hydration of calcium oxide. The use of waste lime has the advantage that its amount does not correspond to the consumption of lime in flue gas desulphurisation processes, the disadvantage of thermal decomposition is considerable energy consumption, which is adversely reflected in the cost of the actual desulphurisation process.

Furthermore, in the case of desulfurization in the fluidized bed of combusted coal, a method is known for reactivating partially reacted calcium sorbents which are in a mixture with fly ash. This method is based on the following reactions

OaCO ₃ -----> CaO + C0 ₂ (1)

CaO + S0 ₂ + 1/2 0 ₂ -> Ca S0 ₄ (2)

CaO + S0 ₃ ------------- Ca S0 ₄ (3) '

CaO + h ₂ 0 ------------ 5 * Ca (OH) ₂ (4)

The deactivation process consists in the hydration reaction of calcium oxide (4), which is formed by the calcination reaction (1) and is converted into calcium sulphate by reactions (2) and (3). Since an excess of input carbonate is used due to the stoichiometry of reactions (2) and (3), a certain amount of calcium oxide remains in the resulting reaction mixture under the given reaction conditions, which is subsequently hydrated. Calcium hydroxide is a very effective sorbent of sulfur oxides. Its use in the flue gas desulphurisation process is adversely affected by the presence of a considerable amount of fly ash, which as an inert very dilutes the active ingredient, ie calcium hydroxide. When dosing into the boiler hearth, the combustion process is negatively affected.

These disadvantages are eliminated by the dry flue gas desulphurisation sorbent according to the invention, which consists in a mixture composed of finely ground limestone with a grain size of 10 to 20% of the residue on a 0.05 M mesh in an amount of 1 to 6 parts by weight. , from a gypsum-based binder in an amount of 1 to 3 parts by weight, and from iron particles and its oxides in an amount of 1 to 3 parts by weight.

The advantage of the sorbents according to the invention over the limestone itself used in the dry additive technology process lies in the substantially higher degree of utilization of sorbents and in the substantially higher efficiency of flue gas desulphurization, caused mainly by the high reactivity of calcium hydroxide formed in the reactivation reaction (4).

The sorbent according to the invention has the advantage over the use of waste lime in that its amount can cover the needs of flue gas desulphurisation processes.

Compared to the method of thermal decomposition of limestones to obtain highly reactive sorbents based on calcium hydroxide, the sorbent according to the invention has the advantage of less expensive preparation, since calcination of calcium carbonate to oxide (1) takes place directly in the boiler during the first activation of sorbents. No special equipment is required for calcination, which is another advantage; already during calcination, sulfur oxides are partially bound.

• CS 272 565 B1 2

Compared to the use of partially reacted and unactivated calcium sorbents, which are mixed with fly ash, the sorbent according to the invention has the advantage that it can be magnetically separated from inert fly ash, which facilitates its reactivation and allows its second addition to the boiler with significantly less negative impact. combustion process.

Example

Finely ground limestone with grain sizes from 0.01 to 0.09 mm was mixed with finely ground iron sawdust with an oxidized surface with grain dimensions below 0.09 mm and with calcium sulphate in a weight ratio of first 1: 1: 1 and later in a ratio 6: 3: 3 »Gradual addition of water and kneading brought both mixtures to a pasty consistency. They were then dried at 120 ° C and crushed to a particle size of 0.3 to 0.6 mm. These materials were added to the fluidized bed along with the power plant fly ash. The weight ratio between fly ash and sorbent was 6: 1. The flue gas from the power plant boiler, partially de-ashed in electrostatic precipitators containing 0.3% by volume of sulfur dioxide heated to 800 ° C, entered the fluidized bed reactor. The sorbent particles were fed to the reactor at such a rate that the stoichiometric excess of calcium oxide relative to the sulfur dioxide flow in the flue gas was 1.1 to 1.2. 5 to 7% of sulfur dioxide was removed from the flue gas by passing the flue gas through the fluidized bed in the case of a mixture with a weight ratio of limestone to iron to gypsum of 1: 1: 1, 12 to 15% in the case of a mixture in a weight ratio of 6: 3: 3. sulfur dioxide from flue gases. The reacted particles in the mixture with the fly ash were discharged by overflow. They were applied to the glass plate in a layer about 3 to 5 mm high. The ferromagnetic additive particles were separated from the fly ash by a permanent magnet. The separated additive was not activated by grinding with water in a ball mill and further by boiling with water.

After drying and crushing to a particle size of 0.3 to 0.6 mm, both sorbents were fed to the fluidized bed reactor under the same conditions as before reactivation. The passage of the flue gases through the fluidized bed has now removed 67 to 73% of sulfur dioxide in the case of sorbents with a component ratio of 1: 1: 1 and 73 to 80% of sulfur dioxide in the case of sorbents with a component ratio of 6: 3: 3.

The invention can be advantageously used in particular in the energy sector in the combustion of sulfur coal in pulverized, grate and fluidized bed boilers.

Claims (1)

OBJECT OF THE INVENTION Sorbent for dry flue gas desulphurisation, characterized in that it consists of a mixture composed of 1 to 6 parts by weight, finely ground limestone with a grain size of 10 to 20% of the residue on sieves with a mesh size of 0,05 mm, of 1 to 3 parts by weight, particles of iron and its oxides and from 1 to 3 parts by weight of gypsum.