Patent Application
20080028932
The invention will now be described in more detail with reference to an example.
A sorbent, obtained by thermal conversion from paper production residue is introduced into a waste gas stream comprising a known amount of mercury and also having a known temperature. The method of obtaining such a product is described in the Dutch Patent NL 1009870. In the example for the sorption of mercury with the aid of the above mentioned sorbent the temperature in the gas stream is varied from 50° C. to 500° C. [800]. The gas stream consists of nitrogen containing metallic mercury. In the various experiments a fixed sorption bed comprising the above mentioned sorbent was used. Both the ingoing and the outgoing mercury concentrations were measured by means of a commercially available “Buck analyzer”. This device is exclusively suitable for determining metallic mercury. The concentration of ionogenic mercury was determined by, prior to measuring, leading the mercury-comprising gas through a bubbler containing stannouschloride. Stannouschloride is known to convert any ionogenic mercury that may be present into metallic mercury. In this way the total of both the metallic and ionogenic mercury is determined.
Table 1 shows the mercury concentration applied in the gas stream in the various experiments. The temperature indicated in Table 1 is the temperature at which mercury was removed with the aid of the sorbent. The percentage of captured mercury shown in Table 1 was calculated by dividing the difference between the ingoing mercury concentration and the outgoing mercury concentration by the ingoing mercury concentration. The mercury was fed to the gas stream at 100° C. by means of a Dynacal permeation tube, as known in the art. The nitrogen was preheated. Subsequently the mixed gas stream was heated to the temperature indicated in Table 1, after which it was lead through the sorption bed and subsequently to the analyser described above in order to measure whether any, and if so how much, mercury was still present in the gas stream.
The amounts of mercury used in the experiments are compatible with the sensitivity of the analyzer.
From Table 1 it can be seen that with an increase in temperature, the sorption of mercury by means of the sorbent according to the invention is enhanced.
The original uncorrected values were as follows:
The foregoing Table 1 and the
The sorption of mercury on the sorbent according to the invention may be further improved by adding a suitable amount of calcium hypochlorite to the sorbent prior to contacting the mercury with the sorbent. This may be achieved, for example, by introducing hypochlorite into the gas stream at a position upstream from the sorbent, for example, by placing the hypochlorite on the sorbent-comprising bed, when the mercury-comprising gas stream passes from the top through the bed. Experiments performed in this manner showed that at an equal amount of sorbent according to the invention, to wit 60 grams, the mercury removal was increased from approximately 11% to 100%, at 300° C. [500]. Other temperatures also produced removal percentages of 100%, as can be seen from the results shown in
At such temperatures the hypochlorite will dissociate completely. It was shown, however, that an improved activity of the sorbent that was placed downstream of the hypochlorite was prolonged even after the hypochlorite had long since been completely dissociated, hypochlorite that had not reacted with the sorbent being removed from the experimental set-up by means of the gas stream. The absence of the hypochlorite after the completion of the experiment is confirmed by measuring with the aid of the TGA/DTA analysis and a coupled mass spectrometer whether any chlorine or chloride compounds of the sorbent used were present in the gases leaving the TGA/DTA characterization. The result of this measurement was that the amounts of of any chlorine or chloride compounds were below the detection limit of the mass spectrometer. These measurements were verified by releasing chlorine with the aid of the so-called Gordinne basic fusion technique, after which the escaping chlorine was detected with the aid of photometric analysis. A more detailed description of this method can be found in ASTM C114. The result of this analysis which was carried out on two sorbents treated with hypochlorite was, that the chlorine content was below the detection limit of 100 ppm-weight, while the chlorine content of the initial calcium hypochlorite/sorbent mixture was more than 4% by weight, or 40,000 ppm-weight. It is concluded therefore, that the sorbent used no longer contains chlorine or chloride compounds. Since the activity enhanced by calcium hypochlorite (from 11% to 100% mercury adsorption at 300° C.) was maintained during the entire duration of the experiment, thus also after the chlorine was removed with the mercury-comprising gas stream, it is further concluded that the sorbent treated with the oxidator at elevated temperature possesses a permanently improved mercury-removing activity.
In the present cases an amount of 10 grams of calcium hypochlorite appeared to be sufficient.
The mercury-polluted gas stream may be contacted with the sorbent by placing the sorbent as fixed bed into the stream. The sorbent may optionally be dispersed in the gas stream. According to a first embodiment, the oxidator is added to the sorbent directly. According to a second embodiment, the oxidator may be added to the gas stream upstream from the sorbent, for example, by dispersing the same in the gas stream, and according to a third embodiment, an oxidator may be added to the gas stream simultaneously with the sorbent. The contacting time must in any case be such as to allow a desirable activation and sorption to take place. If the gas stream originates from, for example, an incineration plant, the above-mentioned substances may be added to the gas stream preceding a dust collector, so that the dust collector can remove the solid components from the gas stream all at the same time. The method according to the invention is also applicable to gases or vapors from the petrochemical and chemical industry, for example, for the removal of mercury from natural gases and natural gas condensate, from naphtha and other base materials used in the said industries.
According to a preferred embodiment, the sorbent may be added to a waste gas stream at various positions having different prevailing temperatures. This means that due to the choice of the location for adding a sorbent, different types of metal, irrespective of their condition (metallic or ionogenic), can be sorbed in a desirable condition. This condition depends on the temperature. Components such as SO2, HCl and Cl2 may also be removed with the aid of the method according to the invention.
The method according to the invention may be applied in an existing system where a cleaning apparatus for gas streams, for example a scrubber, is already present. Optionally only a small amount of sorbent may be added, just sufficient to convert the mercury in the gases into the ionic form (Hg2+). This improves the mercury capturing performance in the scrubber.
The invention is not restricted to the above-described embodiment. Amounts of sorbent other than those mentioned above may be used in practice. Likewise, it is possible to use other kaolin-comprising sorbents.
The results of the measurements on prior art sorbents as indicated in
W. A. Rosenhoover et al., US ICCI project 98-1/1.2B-2
R. A. Hargis et al., US DOE; Mercury control by injection of activated carbon, 17th Int. Pittsburgh Coal Conf., 2000
J. R. Butz, C. Turchi, T. E. Broderick, J. Albiston, ADA techn, Littleton, Options for mercury removal from coal fired flue gas streams, pilot scale research on activated carbon and alternative and regenerable sorbents, 17th Int. Pittsburgh Coal Conf., 2000
Sid Nelson Jr., High temperature sorbents to lower mercury control costs, 17th Int. Pittsburgh Coal Conf., 2000
J. Montgomery, D. Battleson, S. Bryson, Mercury removal from incineration offgas by carbon injection, MSE technology applications Inc., Butte.
| Number | Date | Country | Kind |
|---|---|---|---|
| 1017206 | Jan 2001 | NL | national |
| Number | Date | Country | |
|---|---|---|---|
| Parent | PCT/NL02/00052 | Jan 2002 | US |
| Child | 10470437 | US |
