Composition for the Purification of Flue Gas

Abstract

The invention relates to a composition for the purification of flue gas containing 1 to 99 wt. % of a powder of a sodium salt of carbonic acid and 1 to 99 wt. % of a powder of an absorptive material, wherein the powder of an absorptive material has a specific pore volume that is equal to or greater than 0.1 cm.sup.3/g. The invention also relates to a process for dry flue gas purification and the use of an absorptive material to improve the flowability and/or storability and/or HF absorptivity of a sodium salt of carbonic acid.

Claims

1.-20. (canceled)

21. A composition for the purification of flue gas, said composition containing, in each case based on the total weight of the composition: a. 13 to 30 wt. % of a powder of a sodium salt of carbonic acid; and b. 70 to 87 wt. % of a powder of an absorptive material, wherein said powder of said absorptive material has a specific pore volume that is equal to or greater than 0.1 cm.sup.3/g and wherein said absorptive material is an absorbent for sulfur oxides and/or an absorptive material for hydrogen chloride and/or hydrogen fluoride, and wherein said powder of said sodium salt of carbonic acid has a particle size d.sub.50 of less than 50 m.

22. The composition according to claim 21, wherein said composition contains 13 to 20 wt. % of said powder of said sodium salt of carbonic acid, based on the total weight of the composition, and/or wherein said composition contains 80 to 87 wt. % of said powder of said absorptive material, based on the total weight of the composition.

23. The composition according to claim 21, wherein said powder of said sodium salt of carbonic acid has a particle size d.sub.50 of less than 45 m, and/or wherein said powder of said sodium salt of carbonic acid has a particle size d.sub.97 of less than 180 m.

24. The composition according to claim 21, wherein said sodium salt of carbonic acid is selected from the group consisting of sodium hydrogen carbonate, sodium carbonate, sodium sesquicarbonate, and mixtures thereof.

25. The composition according to claim 24, wherein said sodium salt of carbonic acid is sodium hydrogen carbonate and/or sodium sesquicarbonate.

26. The composition according to claim 21, wherein said absorptive material is selected from the group consisting of limestone, quicklime, hydrated lime, dolomite, dolomitic quicklime, dolomitic hydrated lime, magnesium carbonate, magnesium oxide, magnesium hydroxide, and mixtures thereof.

27. The composition according to claim 26, wherein said absorptive material is hydrated lime.

28. The composition according to claim 27, wherein said hydrated lime has a particle size d.sub.50 of less than 50 m, and/or wherein said hydrated lime has a particle size d.sub.97 of less than 150 m, and/or wherein said hydrated lime has a surface area that is equal to or greater than 20 m.sup.2/g, and/or wherein said hydrated lime has a specific pore volume that is equal to or greater than 0.11 cm.sup.3/g.

29. The composition according to claim 21, wherein the composition contains at least one of clay, active carbon, and zeolites in an amount of up to 30 wt. %, based on the total weight of the composition.

30. The composition according to claim 21, wherein the composition has an FFC value determined using an RST-XS ring shear tester of 0.2 or more.

31. A process for the manufacture of said composition for the purification of flue gas according to claim 21, comprising: a. providing a composition containing, in each case based on the total weight of the composition: 13 to 30 wt. % of said powder of a sodium salt of carbonic acid, and 70 to 87 wt. % of said powder of an absorptive material; and b. applying mechanical and/or thermal energy to the composition, wherein said powder of said absorptive material has a specific pore volume that is equal to or greater than 0.1 cm.sup.3/g and wherein said absorptive material is an absorbent for sulfur oxides and/or an absorptive material for hydrogen chloride and/or hydrogen fluoride, and wherein said powder of said sodium salt of carbonic acid has a particle size d.sub.50 of less than 50 m.

32. The process of claim 31, wherein the composition in step a. contains 13 to 20 wt. % of said powder of said sodium salt of carbonic acid, based on the total weight of the composition; and/or wherein the composition in step a. contains 80 to 87 wt. % of said powder of said absorptive material, based on the total weight of the composition.

33. The process according to claim 31, wherein said sodium salt of carbonic acid has a particle size d.sub.50 of less than 45 m; and/or wherein said powder of said sodium salt of carbonic acid has a particle size d.sub.97 of less than 180 m.

34. The process according to claim 31, wherein thermal and/or mechanical energy is applied to said powder of said sodium salt of carbonic acid and/or to said powder of said absorptive material.

35. The process according to claim 31, wherein step b. comprises a mixing and/or grinding step, and wherein, in the grinding step, the composition is ground to a particle size d.sub.50 of equal to or less than 50 m, and/or wherein the composition is ground to a particle size d.sub.97 of less than 180 m.

36. A process for the purification of flue gas, wherein the flue gas is brought into contact with said composition according to claim 21.

37. A method comprising using said composition according to claim 21 for the purification of HF containing flue gas.

38. A method comprising using a powder of an absorptive material having a specific pore volume that is equal to or greater than 0.1 cm.sup.3/g, wherein said absorptive material is an absorbent for sulfur oxides and/or an absorptive material for hydrogen chloride and/or hydrogen fluoride, in an amount of 70 to 87 wt. %, based on the total weight of the composition, to improve the flowability after some storage time, and/or storability and/or HF absorptivity of a powder of a sodium salt of carbonic acid having a particle size d.sub.50 of less than 50 m.

39. The method according to claim 38, wherein said powder of said absorptive material is used in an amount of 80 to 87 wt. %, based on the total weight of the composition.

Description

[0083] FIG. 1 shows the relative SO.sub.2 absorption (called SO.sub.2 abatement) in % versus the fraction of milled sodium hydrogen carbonate for different absorbent compositions with different sodium hydrogen carbonate and hydrated lime contents.

[0084] FIG. 2 shows the dependency of the FFC value of fresh samples of absorbent compositions and of 18 hour old samples of absorbent compositions for different fractions of sodium hydrogen carbonate and hydrated lime, respectively.

[0085] In the following, the invention shall be further explained by examples that are illustrative only and not to be construed as limiting in any way.

[0086] Materials Used

[0087] Sodium hydrogen carbonate, NaHCO.sub.3, (Bicar, Solvay); hydrated lime Ca(OH).sub.2, (Sorbacal SP, Lhoist). The Sorbacal SP had a BET specific surface area of about 40 m.sup.2/g, a specific BJH pore volume of about 0.2 cm.sup.3/g, and a particle size d.sub.50 of about 6 m.

EXAMPLE 1: PREPARATION OF COMPOSITIONS FOR FLUE GAS PURIFICATION

[0088] Sodium hydrogen carbonate was milled using a pin mill to a powder with a d.sub.50 value of 28.9 m as determined by laser light scattering in ethanol suspension using a Helos particle analyzer from Sympatec. The particle size analyzer had a Sucell equipment, the sample was subjected to ultrasound treatment for 120 seconds with a pause of 120 seconds and the suspension was stirred at 70 rpm. The milled sodium hydrogen carbonate was subsequently mixed homogeneously with hydrated lime at the ratios shown in Table 1 to obtain compositions for flue gas purification. Mixing of the powders was carried out using a rotor mixer.

TABLE-US-00001 TABLE 1 Ratios of the compositions for flue gas purification Amount of Composition number NaHCO.sub.3 [wt. %] Amount of Ca(OH).sub.2 [wt. %] 1 5 95 2 10 90 3 25 75 4 50 50 5 75 25

EXAMPLE 2: DETERMINATION OF THE SO.SUB.2 .ABSORPTIVITY

[0089] The SO.sub.2 absorptivities of compositions 3, 4, and 5 were determined in a flue gas treatment pilot plant that is principally described in WO 2007/000433 A2, pages 10 to 12 and FIG. 2 therein. The compositions were injected in co-current flow to purify a model flue gas with the following gas conditions: [0090] temperature 220 C., [0091] SO.sub.2 inlet concentration 1500 mg/Nm.sup.3, [0092] H.sub.2O content 10%, [0093] CO.sub.2 concentration 9%, [0094] average stoichiometric ratio of absorbent composition to SO.sub.2 (expressed versus the inlet) of 2.5.

[0095] The results of the SO.sub.2 absorption tests are compiled in Table 2 and displayed in FIG. 1 together with the results for pure hydrated lime as a comparative example.

TABLE-US-00002 TABLE 2 Absolute SO.sub.2 SO.sub.2 absorptivity NaHCO.sub.3 absorptivity relative to 100% Composition content [wt. %] [% abs.] Ca(OH).sub.2 [% rel.] 100% Ca(OH).sub.2 0 23 100 (comparative) 3 25 32 139 4 50 46 200 5 75 59 257

[0096] During the test, no blockage or abnormal clogging of the dosing equipment were observed. Thus, the dosing device was not affected by the presence of milled sodium hydrogen carbonate. This may indicate the beneficial effect of the hydrated lime on the milled sodium hydrogen carbonate.

[0097] Moreover, the SO.sub.2 absorptivity of compositions 3, 4 and 5 was significantly higher than for the pure hydrated lime.

EXAMPLE 3: FLOWABILITY OF THE COMPOSITIONS

[0098] The flowability of the compositions 1 to 5 and of pure hydrated lime as a comparative example were investigated by determining their FFC values using an RST-XS ring shear tester. The results are displayed in FIG. 2, using diamonds for the FFC values of samples of the freshly prepared composition and using squares for the FFC values of samples measured 18 hours after preparation of the compositions.

[0099] From FIG. 2, the beneficial effect of the admixture of hydrated lime to sodium hydrogen carbonate powder on the flowability after some storage time can be seen. For freshly prepared compositions, the FFC value of compositions with a low amount of hydrated lime was higher than for compositions with a high amount of hydrated lime. After 18 hours, however, the FFC of compositions with a low amount of hydrated lime was lower than for composition with a high amount of hydrated lime. In particular, an FFC value of more than 1 was maintained even after 18 hours for compositions containing more than 70 wt. % hydrated lime. Moreover, the decrease in the FFC value was greater for compositions 4 and 5 containing 50 wt. % and 25 wt. % hydrated lime, respectively, than for compositions 1 to 3 containing 95 wt. %, 90 wt. %, and 75 wt. % hydrated lime, respectively. This indicates that the decrease in flowability over time depends on the ratio of hydrated lime:sodium hydrogen carbonate. A particularly well balanced property profile with FFC values of approximately 1 or greater and an improved sulfur dioxide absorptivity was achieved if sodium hydrogen carbonate was present in an amount of approximately 10 to 25 wt. %, in particular in an amount of approximately 15 to 25 wt. %. As already mentioned, higher FFC values indicate a better flowability.

[0100] Importantly, it was also observed that compositions containing more than 25 wt. % hydrated lime could at least be temporarily stored without exhibiting the disadvantageous handling properties of pure ground sodium hydrogen carbonate.