Composition for the Purification of Flue Gas

Abstract

The invention relates to a composition for the purification of flue gas containing 35 to 99 wt. % of a powder of an alkali metal salt of carbonic acid and 1 to 65 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 an alkali metal 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. 35 to 50 wt. % of a powder of an alkali metal salt of carbonic acid; and b. 50 to 65 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 cm3/g, and wherein said absorptive material is an absorbent for sulfur oxides and/or an absorbent for hydrogen chloride and/or hydrogen fluoride, and wherein said alkali metal salt of carbonic acid is selected from the group consisting of sodium hydrogen carbonate, sodium carbonate, sodium sesquicarbonate, potassium hydrogen carbonate, potassium sesquicarbonate, and mixtures thereof.

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

23. The composition according to claim 21, wherein said alkali metal salt of carbonic acid is sodium hydrogen carbonate and/or sodium sesquicarbonate.

24. 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.

25. The composition according to claim 24, wherein said absorptive material is hydrated lime.

26. The composition according to claim 21, wherein said absorptive material has a particle size d.sub.50 of less than 50 m; and/or wherein said absorptive material has a particle size d.sub.97 of less than 150 m; and/or wherein said absorptive material has a surface area that is equal to or greater than 20 m.sup.2/g; and/or wherein said absorptive material has a specific pore volume that is equal to or greater than 0.11 cm.sup.3/g.

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

28. 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.

29. 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: 35 to 50 wt. % of a powder of an alkali metal salt of carbonic acid, and 50 to 65 wt. % of a 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 absorbent for hydrogen chloride and/or hydrogen fluoride, and wherein said alkali metal salt of carbonic acid is selected from the group consisting of sodium hydrogen carbonate, sodium carbonate, sodium sesquicarbonate, potassium hydrogen carbonate, potassium sesquicarbonate, and mixtures thereof.

30. The process according to claim 29, wherein said powder of said alkali metal salt of carbonic acid has a particle size d.sub.50 of less than 50 m; and/or wherein said powder of said alkali metal salt of carbonic acid has a particle size d.sub.97 of less than 180 m.

31. The process according to claim 29, wherein thermal and/or mechanical energy is applied to said powder of an alkali metal salt of carbonic acid and/or to said powder of an absorptive material.

32. The process according to claim 29, 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.

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

34. A method of using the composition according to claim 21 for the purification of flue gas.

35. A method of using a powder of an absorptive material having a specific pore volume that is equal to or greater than 0.1 cm3/g, wherein said absorptive material is an absorbent for sulfur oxides and/or an absorbent for hydrogen chloride and/or hydrogen fluoride, in an amount of 50 to 65 wt. %, based on the total weight of the composition.

36. The method according to claim 35, wherein said powder of 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.

Description

[0082] For the absorptive material for the use of the powder of an absorptive material according to the invention, the above provisions concerning the absorptive material shall apply. In particular, the provisions concerning the type of material used for the absorptive material, the particle size, the surface area, and/or the pore volume of the absorptive material as described above shall apply.

[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 (comparative) 5 95 2 (comparative) 10 90 3 (comparative) 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 4 and 5 and of the comparative composition 3 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 and composition 3 containing 75 wt. % hydrated lime and 25 wt. % sodium hydrogen carbonate as comparative examples.

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

[0097] Moreover, the SO.sub.2 absorptivity of compositions 4 and 5 was significantly higher than for the pure hydrated lime and also for composition 3 containing 75 wt. % hydrated lime and 25 wt. % sodium hydrogen carbonate.

Example 3

Flowability of the Compositions

[0098] The flowability of the compositions 4 and 5 and of the comparative compositions 1 to 3 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. As already mentioned, higher FFC values indicate a better flowability.

[0099] From FIG. 2, the beneficial effect of the admixture of hydrated lime to sodium hydrogen carbonate powder on the flowability after 18 hours can be seen. For the freshly prepared comparative compositions 1, 2, and 3, no significant trend was observed. For the freshly prepared compositions 4 and 5, the admixture of hydrated lime decreased the flowability, as can be seen from the lower FFC value of composition 4 containing 50 wt. % hydrated lime compared to the higher FFC value of composition 5 containing 25 wt. % hydrated lime. However, after 18 hours, it was observed that the FFC values of the compositions decreased compared to the FFC values of the corresponding freshly prepared compositions. Suprisingly, it was observed that after 18 hours, the FFC value of composition 4 containing 50 wt. % hydrated lime was higher than the FFC value of composition 5 containing 25 wt. % hydrated lime. This indicates that the decrease in flowability of the mixture over time depends on the ratio of hydrated lime: sodium hydrogen carbonate. A composition with a particular well balanced property profile was achieved if sodium hydrogen carbonate was present in an amount of approximately 35 to 50 wt. %, based on the total weight of the composition.