Chemistry of inorganic compounds – Modifying or removing component of normally gaseous mixture – Halogenous component
Reexamination Certificate
1996-09-06
2001-01-09
Griffin, Steven P. (Department: 1754)
Chemistry of inorganic compounds
Modifying or removing component of normally gaseous mixture
Halogenous component
C110S345000
Reexamination Certificate
active
06171567
ABSTRACT:
The invention relates to the purification of gases containing hydrogen chloride.
It more particularly relates to a reactive composition based on sodium bicarbonate which can be used for purifying a gas from hydrogen chloride.
Incineration is a technology which is increasingly necessary for the disposal of household or municipal waste. The incineration of household waste is accompanied by the formation of smoke generally containing hydrogen chloride. It is imperative to remove the hydrogen chloride from the smoke before discharging the latter to the atmosphere.
A known process for purifying smoke containing hydrogen chloride consists in treating the smoke with sodium bicarbonate, so as to decompose the hydrogen chloride and to form sodium chloride.
A process has more particularly been provided in which sodium bicarbonate is injected in the form of a powder into the smoke exiting from the incinerator and the smoke, thus treated, is then conveyed to a filter (Solvay & Cie, brochure TR. 895/5c-B-1-1290). In this known process, the smoke is at a temperature of 260° C. at the point of injection of the sodium bicarbonate. The latter is used in the form of a graded powder, obtained by milling, of which 90% by weight is in the form of particles with a diameter of less than 16 &mgr;m.
In practice, the sodium bicarbonate powder used in this known process contains sodium monocarbonate.
It has now been found that it is possible to optimize the efficiency of the known process which has just been described by selecting sodium bicarbonate of well-defined quality.
The invention consequently relates to a solid powdered reactive composition for the purification of a gas containing hydrogen chloride, the said reactive composition comprising more than 98% by weight of sodium bicarbonate and less than 2% by weight of sodium mono-carbonate and exhibiting a particle size distribution defined by an average particle diameter of less than 0.050 mm and a particle size slope of less than 5.
In the reactive composition according to the invention, the sodium bicarbonate and the sodium mono-carbonate are regarded as in the anhydrous state.
According to the invention, the reactive composition comprises more than 98% (preferably at least 99%) by weight of sodium bicarbonate and less than 2% (preferably at most 1%) by weight of sodium mono-carbonate. It can also comprise other impurities commonly found in commercial sodium bicarbonate, in particular sodium chloride.
The reactive composition according to the invention is a powdered solid. An important characteristic of the reactive composition according to the invention lies in its particle size distribution which is characterized by an average particle diameter D
m
of less than 0.050 mm (preferably at most equal to 0.030 mm) and a particle size slope &sgr; of less than 5 (preferably at most equal to 3).
In the reactive composition according to the invention, the average diameter D
m
and the particle size slope &sgr; are defined by the following relationships
D
m
=
∑
n
i
·
D
i
∑
n
i
,
σ
=
D
90
-
D
10
D
50
in which n
i
denotes the frequency (by weight) of the particles with diameter D
i
, and D
90
(D
50
and D
10
respectively) represents the diameter at which 90% (50% and 10% respectively) of the particles of the reactive composition (expressed by weight) have a diameter of less than D
90
(D
50
and D
10
respectively). These particle size parameters are defined by the method of analysis by diffraction of laser beams using a Sympatec model Helos 12LA measuring device manufactured by Sympatec GmbH.
The reactive composition according to the invention is especially intended for the purification of smoke originating from furnaces for the incineration of household waste. This smoke generally contains, in addition to hydrogen chloride, sulphur dioxide. It has been observed that the reactive composition according to the invention efficiently purifies the smoke, both from hydrogen chloride and from sulphur dioxide.
In the reactive composition according to the invention, the sodium bicarbonate is the main active compound. The sodium carbonate content and the particle size distribution are, moreover, two interdependent parameters. On the one hand, it has been observed that, everything else being equal, an excessive sodium carbonate content tends to cause the particles of the reactive composition to stick together, reducing the efficiency of the composition. On the other hand, the particle size distribution of the reactive composition has to be a compromise, as it is known that a fine particle size will promote the reaction with the hydrogen chloride in the treated gas, whereas a coarse particle size will promote the subsequent separation of the solid reaction products. In practice, reactive compositions which are especially recommended are those in which the sodium bicarbonate content by weight is from 99 to 99.9%, the sodium monocarbonate content by weight is from 0.1 to 1%, the average particle diameter is from 0.010 to 0.030 mm and the particle size slope is from 1 to 3. The optimum values of the particle size parameters are related to the means used to separate the solid products from the reaction of the reactive composition with the hydrogen chloride and, if appropriate, the sulphur dioxide in the treated gas. In fact, it has proved to be the case that these reaction products have a particle size distribution which is directly related to that of the reactive composition.
An embodiment of the reactive composition according to the invention, which is especially suited to the specific case where an electrostatic filter is used as means for separating the abovementioned reaction products, is that in which the average particle diameter is from 0.020 to 0.030 mm and the particle size slope is from 1.25 to 2.50. A preferred alternative form of this embodiment of the invention is that in which at least 90% by weight of the particles have a diameter equal to or less than 0.055 mm and at most 10% by weight have a diameter of less than 0.006 mm.
Another embodiment of the reactive composition according to the invention, especially suited to the specific case where a filter of the filter-cloth type (for example a bag filter) is used as means for mechanical separation of the abovementioned reaction products, is that in which the average particle diameter is from 0.010 to 0.020 mm and the particle size slope is from 1 to 3. A preferred alternative form of this other embodiment of the invention is that in which at least 90% by weight of the particles have a diameter equal to or less than 0.035 mm and at most 10% by weight have a diameter of less than 0.005 mm.
The reactive composition according to the invention is generally obtained by milling a coarse commercial sodium bicarbonate powder. The composition of the powder and its particle size grading play an important role in the quality of the reactive composition according to the invention.
According to an especially recommended embodiment of the reactive composition according to the invention, the latter is obtained by milling a powder which comprises more than 98% (preferably at least 99%) by weight of sodium bicarbonate and less than 2% (preferably at most 1%) by weight of sodium monocarbonate and which exhibits a particle size distribution such that at least 85% by weight of its particles have a diameter of less than 0.500 mm and such that at most 25% by weight of its particles have a diameter of less than 0.040 mm. In accordance with a preferred alternative form of this embodiment of the invention, the powder used for the milling exhibits a particle size distribution such that, per 100 units by weight of its particles, 85 units have a diameter of less than 0.250 mm, from 50 to 70 units have a diameter of less than 0.125 mm, from 30 to 50 units have a diameter of less than 0.090 mm and less than 25 units have a diameter of less than 0.045 mm.
In the especially recommended embodiment which has just been described, the milling conditions are an important parameter. In particular, it is important to a
Di Mauro Peter
Griffin Steven P.
Solvay ( Societe Anonyme)
Venable
LandOfFree
Process for the purification of a gas containing hydrogen... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Process for the purification of a gas containing hydrogen..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Process for the purification of a gas containing hydrogen... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2517367