. Finally, the insoluble
compound HgS can be disposed safely due to its advantageous
properties. However, in previous studies it is reported that increasing
the pH-value of HgCl2 containing FGD slurries promotes the
re-emission of Hg0 [12–15]. This could result in uncontrolled desorption
of Hg0 during the first stage of waste water treatment, limiting
the actual Hg removal rate of the plant and causing unnoticed
safety issues [12]. In order to overcome this problem, the approach
of this study is to take advantage of the redox characteristics of dissolved
Hg2+ compounds. In concrete terms, the desorption of Hg0
by aeration of the waste water during alkalization is intentionally
triggered in a controlled process. The resulting small gas flow with
high content in Hg0 is directed to a suitable fixed bed adsorber (e.g.
activated carbon) for environmentally safe Hg removal. There, the
adsorption of Hg0 takes place at ambient temperature, high Hg0 gas
phase concentration, small gas flow rate and thus low pressure
drop and long retention time. Under such conditions, the loading
capacity of the sorbent is maximized. Hence, in comparison to
dry sorbent injection in hot flue gas, by magnitudes higher Hg
loadings and corresponding lower operating costs for the sorbent
are to be expected. Since the alkalization of FGD waste water is
state of the art for cost effective heavy metal precipitation and utilized
in most plants, no additional processing steps are required by
the proposed process. The concept of aerated alkalization is rather
a modification of the existing process and thus retro-fit capable
. Finally, the insolublecompound HgS can be disposed safely due to its advantageousproperties. However, in previous studies it is reported that increasingthe pH-value of HgCl2 containing FGD slurries promotes there-emission of Hg0 [12–15]. This could result in uncontrolled desorptionof Hg0 during the first stage of waste water treatment, limitingthe actual Hg removal rate of the plant and causing unnoticedsafety issues [12]. In order to overcome this problem, the approachof this study is to take advantage of the redox characteristics of dissolvedHg2+ compounds. In concrete terms, the desorption of Hg0by aeration of the waste water during alkalization is intentionallytriggered in a controlled process. The resulting small gas flow withhigh content in Hg0 is directed to a suitable fixed bed adsorber (e.g.activated carbon) for environmentally safe Hg removal. There, theadsorption of Hg0 takes place at ambient temperature, high Hg0 gasphase concentration, small gas flow rate and thus low pressuredrop and long retention time. Under such conditions, the loadingcapacity of the sorbent is maximized. Hence, in comparison todry sorbent injection in hot flue gas, by magnitudes higher Hgloadings and corresponding lower operating costs for the sorbentare to be expected. Since the alkalization of FGD waste water isstate of the art for cost effective heavy metal precipitation and utilizedin most plants, no additional processing steps are required byการนำเสนอ แนวคิดของ alkalization อากาศจะค่อนข้างการปรับเปลี่ยนที่มีอยู่ประมวลผล และ พอย้อนยุคจึงสามารถ
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