Method for simultaneous exhaust gas cleaning and manufacturing of supplementary cementitous material

Abstract

A method for manufacturing a binder of a hydratable material includes providing a starting material from one or more raw materials convertible by tempering at 600 to 1200° C. into the hydratable material and tempering the starting material to provide the hydratable material containing not more than 10% by weight monocalcium silicate and at least 15% by weight hydratable phases in the form of lime and dicalcium silicate. The residence time and the tempering temperature are adapted to obtain the hydratable material by converting not more than 80% by weight of the starting material, and the hydratable material is then cooled to provide the binder comprising the hydratable material. The binder can be mixed with water and optionally one or more of aggregate, additives, admixtures to obtain a binder paste that is placed, hydrated and carbonated to produce a building product.

Claims

1. A method for simultaneous cleaning of exhaust gas from CO.sub.2 and manufacturing a supplementary cementitious material from recycled concrete fines, comprising the steps: providing recycled concrete fines with d.sub.90≤1000 μm in a stockpile or silo as starting material flushing the starting material with the exhaust gas providing a carbonated material, withdrawing the carbonated material and cleaned exhaust gas, and de-agglomerating the carbonated material to form the supplementary cementitious material.

2. The method according to claim 1, wherein the recycled concrete fines are mixed with additional material to form the starting material.

3. The method according to claim 1, wherein the supplementary cementitious material has or is ground to a particle size distribution of D.sub.90 below 90 μm (determined by laser granulometry) and a Rosin-Rammler slope n from 0.6 to 1.4.

4. The method according to claim 1, wherein carbonation is carried out until the supplementary cementitious material contains 1.25 times more CO.sub.2 than the starting material.

5. The method according to claim 1, additionally comprising grinding of the starting material.

6. The method d according to claim 1, wherein the exhaust gas is additionally cleaned of SO.sub.x with x from 0 to 3.

7. The method according to claim 1, wherein the exhaust gas is at a temperature from 10 to 150° C. and at ambient pressure or at 0.01 to 4 bar overpressure.

8. The method according to claim 1, wherein exhaust gas from a cement plant, a coal fired power plant or from waste incineration is cleaned.

9. The method according to claim 1, wherein the exhaust gas is treated to increase a concentration of contained CO.sub.2 and/or SO.sub.x, with x from 0 to 3.

10. The method according to claim 1, wherein sulphur is removed from or diminished in the exhaust gas prior to flushing the starting material with the exhaust gas.

11. The method according to claim 1, wherein the exhaust gas is introduced at a bottom of the stockpile or silo and flows through the starting material in vertical direction.

12. The method according to claim 1, wherein the cleaned exhaust gas is further subjected to one or more of: dust removal, gas cooling, gas conditioning, heat recovery, and/or used for drying of wet materials.

13. The method according to claim 3, wherein carbonation is carried out until the supplementary cementitious material contains 1.75 times more CO.sub.2 than the starting material.

14. The method according to claim 2, additionally comprising grinding of the starting material.

15. The method according to claim 7, wherein exhaust gas from a cement plant, a coal fired power plant or from waste incineration is cleaned.

16. The method according to claim 3, wherein the cleaned exhaust gas is further subjected to one or more of: dust removal, gas cooling, gas conditioning, heat recovery, and/or used for drying of wet materials.

17. The method according to claim 4, wherein the exhaust gas is at a temperature from 20 to 100° C. and at ambient pressure or at 0.1 to 2 bar overpressure.

18. The method according to claim 4, wherein exhaust gas from a cement plant, a coal fired power plant or from waste incineration is cleaned and the exhaust gas is at a temperature from 10 to 150° C. and at ambient pressure or at 0.01 to 4 bar overpressure.

19. The method according to claim 18, wherein the cleaned exhaust gas is further subjected to one or more of: dust removal, gas cooling, gas conditioning, heat recovery, and/or used for drying of wet materials.

20. The method according to claim 8, wherein the exhaust gas is treated to increase a concentration of contained CO.sub.2 and/or SO.sub.x with x from 0 to 3.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention will still further be illustrated with reference to the attached figures, without restricting the scope to the specific embodiments described. The invention includes all combinations of described and especially of preferred features that do not exclude each other.

(2) FIG. 1 is a table of particle size distributions from a ground hardened paste used to create the SCM according to the invention,

(3) FIG. 2 shows a table of strength measurement results of samples prepared according to the invention,

(4) FIG. 3 shows further strength measurement results,

(5) FIG. 4 schematically shows an embodiment of the method according to the invention using a stockpile, and

(6) FIG. 5 schematically shows an embodiment of the method according to the invention using a silo.

DETAILED DESCRIPTION OF THE INVENTION

Example

(7) To simulate RCF a mortar CEM II/B-V containing 20 wt.-% fly ash and a mortar CEM III/A containing 50 wt.-% slag were hydrated at 60° C. for 1 month, crushed and ground. The obtained ground hardened paste had the particle size distributions shown in FIG. 1 and contained the following phases: aggregates from the concrete, unreacted cement phase and unreacted slag/fly ash particles, C—S—H phase, portlandite, AFt and AFm phases, iron bearing hydrates like hydrogarnets, iron hydroxide, goethite, magnesium bearing hydrates like hydrotalcite and brucite and minor phases as known per se. The chemical composition was typical for standard CEM II/B-V as defined in EN 196-1. This hardened paste is comparable to the real industrial RCF in the beginning of the recycling process, i.e. it is only little carbonated.

(8) Natural carbonation was simulated by exposing the obtained ground hardened paste to an atmosphere with 0.04 Vol.-% CO.sub.2 at 65% RH for one week, resulting in two RCF samples from the two used binders. These are also designated naturally carbonated RCF in the following and correspond to the typical RCF at the end of the recycling process, i.e. such that can be sampled from a storage pile for RCF.

(9) According to the invention, the ground hardened paste samples were carbonated in a carbonation atmosphere containing 100 Vol.-% CO.sub.2 at 2 bar above ambient pressure and at ambient temperature for 2 hours to obtain the SCM.

(10) Thermogravimetry was used to determine the amount of bound CO.sub.2. Samples of the ground hardened pastes, the RCFs, and the SCM according to the invention were heated between approximately 20 and 1050° C. The amount of bound CO.sub.2 was calculated from the mass loss between 450° C. and 850° C. and normalized to the ignited cement paste mass. Table 3 presents the results.

(11) TABLE-US-00002 TABLE 3 ground RCF naturally SCM according sample hardened paste carbonated to invention from cement bound CO.sub.2 [g/100 g of ignited cement paste mass] CEM II/B-V 3 7 12 CEM III/A 3 11 22

(12) The results demonstrate that during the time used the ground hardened paste samples simulating RCF could be successfully carbonated. For RCF1 from CEM II/B-V the bound CO.sub.2 in the SCM was 1.7 times that of the sample after simulated natural carbonation, for RCF2 from CEM III/A it was 2.0 times that of the RCF.

(13) Each RCF and SCM was blended with CEM I 32,5 R in a weight ratio 30:70 to obtain binder samples. Three further comparison binder samples were made by blending the same CEM I with 30% limestone (LL according to EN 197-1), 30% fly ash (V according to EN 197-1) and 20% limestone+10% fly ash, respectively. The samples are listed in the following table 4.

(14) TABLE-US-00003 TABLE 4 Sample contains 70% CEM I and designation 30% SCM acc. to invention Inv1 30% naturally carbonated RCF RCF1 30% fly ash Comp3 30% limestone Comp4 20% limestone + 10% fly ash Comp5 30% SCM acc. to invention Inv2 30% naturally carbonated RCF RCF2

(15) Strength measurements were made with all samples according to DIN EN 196-1. The results are presented in FIGS. 2 and 3. FIG. 2 shows the SCM from CEM II/B-V compared to all comparison samples and FIG. 3 that of the SCM from CEM III/A. It is readily apparent that Inv1 and Inv2, the SCMs according to the invention, had a considerable SCM reactivity. Strength obtained was even higher than for Comp3, fly ash as SCM. In contrast, both RCF were much less reactive and not suitable as SCM.

(16) Thus, the present invention allows to turn waste or recycled material into added value products, namely providing high reactivity SCM. The SCM according to the invention allows high clinker replacement and provides an opportunity to increase the composite binder production rate by providing a new source of reactive SCM. In addition, the method according to the invention provides a significant potential for CO.sub.2 sequestration from exhaust gas, especially from cement plant exhaust gas. Since cement plant exhaust gas occurs in close proximity to where the SCM is needed for making composite binders the method needs very little investment. The carbonation device can be placed between the cement plant exhaust gas filter and its stack. It might even be beneficial to place it before the filter to achieve some filtering of the exhaust gas.

(17) In FIG. 4 the recycled concrete fines are stockpiled, optionally after a mechanical pretreatment. The stockpile 1 comprises a gas introduction system 2 comprising conduits 3 and gas distributors 4. Exhaust gas 5 is passed into the conduits 3 and discharged into the stockpile 1 by the distributors 4. The conduits 3 are arranged at the bottom of the stockpile 1. Exhaust gas 5 is introduced into the RCF by the distributors 4, which can be nozzles for example. The exhaust gas 5 flows in vertical direction with respect to the stockpile 1 thereby contacting contained CO.sub.2 and/or SO.sub.x with the waste material. The RCF is carbonated and/or sulphurized by flushing the stockpile bed with the exhaust gases containing CO.sub.2 and/or SO.sub.x.

(18) FIG. 5 schematically shows an embodiment of the method according to the invention, wherein the recycled concrete fines are placed into a silo 10, optionally after the pretreatment. Carbonation and/or sulphurization of the RCF is performed in the silo 10 by exhaust gas 50. This is provided by gas distribution system 20 through conduits 30 arranged at the bottom of the silo 10 and introduced through distributors 40. The exhaust gas 50 flows in vertical direction with respect to the silo 10. The starting material is carbonated and/or sulphurized by flushing the exhaust gas 50 through the starting material. The silo 10 can contain a bottom discharge outlet 60 for withdrawing the obtained carbonated/sulphurized RCF.

LIST OF REFERENCE NUMBERS

(19) 1 stockpile 2 gas introduction system 3 conduit 4 gas distributor 5 exhaust gas RCF waste material 10 silo 20 gas introduction system 30 conduit 40 gas distributor 50 exhaust gas 60 carbonated RCF discharge RCF waste material