Chemistry of inorganic compounds – Modifying or removing component of normally gaseous mixture – Sulfur or sulfur containing component
Patent
1992-09-28
1994-07-12
Heller, Gregory A.
Chemistry of inorganic compounds
Modifying or removing component of normally gaseous mixture
Sulfur or sulfur containing component
42324408, B01J 800, C01B 1700
Patent
active
053286740
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
This invention relates to a process for desulfurizing combustion gas.
The strict regulations limiting in many countries and many regions the emissions of sulfur oxides through the gaseous effluents of heat generators forbid the use of fuels with a high sulfur content which, besides, may show definite economical advantages: it is the case of some coals having certain similarities to lignites, and of petroleum residues stemming from refining processes.
French patent 2,609,150 describes a process for reducing the emissions of sulfur oxides and particularly the ones of sulfur dioxide coming from a heat generator accepting fuels with a high sulfur content. According to this process, a powdered desulfurizing agent is injected into the combustion gases and the resulting mixture is circulated in a desulfurization zone, then the at least partially desulfurated gases are partly separated from the powdered desulfurizing agent which can be recycled or discharged.
A similar process is described in the French patent application EN. 88/12,363. In this patent application, the mixing of the desulfurizing agent particles with the combustion gases is carried out in a turbulence zone located upstream from the desulfurization zone.
With this type of desulfurization, the rate of use of calcic or magnesian absorbents such as calcium and magnesium oxides and carbonates remains limited. The reason for this phenomenon has not been totally cleared up, but it seems that a skin which partly prevents the reagents from getting into the grains, forms at the surface of these grains.
A process allowing to remedy the drawbacks mentioned above and particularly allowing to obtain high desulfurization rates and to increase the rate of use of the absorbent, at a lower cost, has been discovered.
SUMMARY OF THE INVENTION
More precisely, this invention is directed to a process for desulfurizing combustion gases, wherein a grained (i.e. particulate) desulfurizing agent is injected into a flow or stream of combustion gases, has been discovered; said process comprises the following stages: two streams, desulfurizing agent towards one another, in order to cause the meeting and the mixing thereof, streams, cause the meeting and the mixing thereof, and desulfurizing agent.
After the separation, the particles can be recycled if they still show a sufficient desulfurizing power, but this is not always necessary because of the improvement of the rate of use per pass obtained according to the invention.
The grain or particle size of the particles usually ranges from 1 to 100 micrometers, preferably from 2 to 25 micrometers, and the density thereof ranges from 500 to 4,000 kg/m.sup.3.
The desulfurization temperature, that is the temperature obtained after mixing the gases with the desulfurizing agent acting as an absorbent, can be selected between 700.degree. and 1,100.degree. C.
An important element is the rate of the flow of the suspension of the gas and of the particles. This rate advantageously ranges from 10 to 80 m/s, preferably from 20 to 30 m/s. These rates lead to turbulence levels which are high enough to provide a homogeneous mixing of the absorbent in the fumes and thereby to obtain high rates of use of the absorbent.
The concentration of the particles in the gas can, for example, range from 0.02 to 1 kg/Nm.sup.3, preferably from 0.05 to 0.2 kg/Nm.sup.3.
According to a preferred embodiment procedure, additional particles of a desulfurizing agent are injected in the flows of stage (f) and the resulting mixture of gas and particles is carried off following a direction substantially perpendicular to the one of said flows. Stage (g) is carried out thereafter.
It is clear that the carrying off of the gases at each stage of the process where such a discharge is planned, is performed following the normal direction of flow of the combustion gases, that is from the combustion zone towards the zone of discharge of the gases of the process.
After stage (f), the suspension of particles in the gas can advantageously be let flow
REFERENCES:
patent: 4726940 (1988-02-01), Kobayashi
patent: 4909161 (1990-03-01), Germain
Bouju Jean-Louis
Martin Gerard
Babcock Entreprise
Heller Gregory A.
Institut Francais du Pe'trole
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