METHOD AND INSTALLATION FOR PRODUCING LIME OR DOLIME

Abstract

A method for producing lime or dolime, which includes a calcination step for the calcination of calcareous or dolomitic material which is brought into contact with the first fumes which are obtained by combustion of fuel with an oxidizing gas, a cooling of calcined lime or dolime with discharge and collection thereof and a release of a gaseous effluent containing CO.sub.2. Subsequent processing steps result in the formation of a CaO-based sorbent material with separation between the CaO-based sorbent material and a CO.sub.2-concentrated gas stream which is collected. The recycling of said separated CaO-based sorbent material is recycled into a CO.sub.2 depletion step resulting in the extraction of a valorizable fraction of the CaCO.sub.3CaO based charge with a compensatory introduction of fresh CaCO.sub.3 in the calcination step.

Claims

1. A method for producing lime or dolime, comprising a calcination of a downward moving calcareous or dolomitic material having a carbonate content CaCO.sub.3+MgCO.sub.3 higher than 90 wt % in contact with first fumes obtained by combustion of fuel in the presence of an oxidizing gas, a cooling of the downward moving calcined calcareous or dolomitic material with a collection from bottom of a main value product under the form of lime or dolime and a release of a gaseous effluent containing CO.sub.2, characterized in that it further comprises a transfer of said gaseous effluent containing CO.sub.2 to a step of CO.sub.2 depletion wherein said gaseous effluent passes through a sorbent material based on CaO which captures CO.sub.2 and forms, by carbonation, a CaCO.sub.3CaO based charge, a separation between the CaCO.sub.3CaO based charge and the CO.sub.2-depleted gaseous effluent, which is removed, a step of calcination of the separated CaCO.sub.3CaO based charge in contact with second fumes obtained by combustion of a fuel chosen from the group consisting of the gaseous fuels and the solid and liquid fuels having an ash content less than 10 wt % and a sulphur content less than 1.5 wt % in the presence of dioxygen and CO.sub.2, as oxidizing gas, with, by decarbonation of CaCO.sub.3, formation of said CaO-based sorbent material and release of CO.sub.2, a separation between the CaO-based sorbent material resulting from said decarbonation and a CO.sub.2-concentrated gas stream which is comprised of said second combustion fumes and of the CO.sub.2 released during said decarbonation of CaCO.sub.3, and which is collected, a recycling of said separated CaO-based sorbent material into the CO.sub.2 depletion step of said gaseous effluent, and a continuous extraction, before the step of calcination of said CaCO.sub.3CaO based charge, of a fraction thereof, as auxiliary value product, with a compensatory introduction of fresh limestone having a CaCO.sub.3 content of at least 90 wt % into said step of calcination of the separated CaCO.sub.3CaO based charge.

2. Method according to claim 1, characterized in that it comprises, during the CO.sub.2 depletion step, maintaining said carbonation at a temperature below 700? ? C. by means of a first heat recovery from the transferred gaseous effluent.

3. Method according to claim 1, comprising a second heat recovery from the removed CO.sub.2-depleted gaseous effluent.

4. Method according to claim 1, characterized in that it comprises carrying out said step of calcination of the separated CaCO.sub.3CaO based charge at a temperature from 850 to 1200? C. and a third heat recovery from the collected CO.sub.2-concentrated gas stream.

5. Method according to claim 2, characterized in that said first, second and/or third heat recoveries consist of a conversion of calories into electrical power.

6. Method according to claim 1, characterized in that the fuel of said calcination step is selected from the group consisting of natural gas, hydrogen, biogas, coke oven gas, gasification gas, fuel oils, oils, liquid biofuels, petroleum coke, biomass, lignite, and coal.

7. Method according to claim 1, comprising, for forming said oxidizing gas of said combustion of the calcination step, a step of mixing pure dioxygen with a fraction of the collected CO.sub.2-concentrated gas stream.

8. Method according to claim 1, characterized in that, during said continuous extraction, a fraction of less than 15 wt % of said CaCO.sub.3CaO based charge is extracted.

9. Method according to claim 1, characterized in that said extracted fraction of said CaCO.sub.3CaO based charge has a CaCO.sub.3+CaO content of at least 80 wt %.

10. Installation for the production of lime or dolime, comprising at least one kiln, each of which comprises a top supply for a calcareous or dolomitic material, a calcination zone wherein said calcareous or dolomitic material moves downwards and is calcined into lime or dolime in contact with first fumes obtained by combustion of fuel in the presence of an oxidizing gas, a cooling zone for cooling the downwards moving calcined lime or dolime, a bottom discharge for collecting said cooled calcined lime or dolime, as main value product, and a top exit for a released gaseous effluent containing CO.sub.2, characterized in that said installation further comprises a carbonation reactor containing a sorbent material based on CaO, means for transferring said gaseous effluent containing CO.sub.2 from said top exit of said at least one kiln to said carbonation reactor, wherein the gaseous effluent is passed through said sorbent material which captures CO.sub.2 and forms by carbonation a CaCO.sub.3CaO based charge and a CO.sub.2-depleted gaseous effluent, a first separation device which, at the top of the carbonation reactor, separates said CaCO.sub.3CaO based charge from the CO.sub.2-depleted gaseous effluent and removes this gaseous effluent, a calcination reactor which, via a transfer duct, is supplied with said CaCO.sub.3CaO based charge coming from the first separation device and in which said CaCO.sub.3CaO based charge comes into contact with second fumes obtained by combustion of a fuel chosen from the group consisting of the gaseous fuels and the solid and liquid fuels having an ash content less than 7 wt % and a sulphur content less than 1.5 wt % in the presence of dioxygen and CO.sub.2, as oxidizing gas, with, by decarbonation of CaCO.sub.3, formation of said CaO-based sorbent material and release of CO.sub.2, a second separation device which, at the top of the calcination reactor, separates said CaO-based sorbent material resulting from said decarbonation and a CO.sub.2-concentrated gas stream which is formed of said second combustion fumes and of the CO.sub.2 released during said decarbonation of CaCO.sub.3, and removes this CO.sub.2-concentrated gas stream for collection, a recycling duct through which the CaO-based sorbent material from the second separation device is fed to the carbonation reactor, and an extraction duct, which is arranged to extract and collect, from said transfer duct, a fraction of said CaCO.sub.3CaO based charge, as auxiliary value product, a source of compensatory fresh CaCO.sub.3 being provided for supplying the calcination reactor.

11. Installation according to claim 10, further comprising at least one first heat exchanger which is arranged within the carbonation reactor to allow recovery by an external fluid of calories released during carbonation.

12. Installation according to claim 10, further comprising at least one second heat exchanger which is arranged to allow a heat recovery by an external fluid from the CO.sub.2-depleted gaseous effluent removed from the first separation device.

13. Installation according to claim 10, further comprising at least one third heat exchanger which is arranged to allow a heat recovery by an external fluid from the CO.sub.2-concentrated gas stream collected from the second separation device.

14. Installation according to claim 11, characterized in that said external fluid is water which, in said first, second and/or third heat exchangers, passes to the vapor state and in that the installation further comprises at least one steam turbine to which this vapor is supplied to produce electricity.

15. Installation according to claim 10, characterized in that said means for transferring said gaseous effluent containing CO.sub.2 from said top exit of said at least one kiln comprise a purification system.

16. (canceled)

Description

[0054] An installation according to the invention is now disclosed by means of FIG. 1 which is a schematic flow sheet of a non-limitative embodiment.

EXAMPLE 1

[0055] The illustrated installation comprises a conventional lime kiln 1, wherein 175 tpd (ton per day) of lime are produced. 12.5 tph (ton per hour) of limestone having a CaCO.sub.3 content of 96 wt % are introduced through the top supply 2 and are calcined into lime in contact with fumes obtained by combustion of 1.6 tph of biomass supplied in 3 in the presence of primary air as carrier gas and of secondary air supplied in 4. 7.3 tph of lime, cooled by a cooling air introduced in 6 and having a CaO content of 93 wt % are discharged through the bottom discharge 5. A gaseous effluent is released from the kiln through the top exit 7 and, by means of the connecting duct 9, is transferred to a carbonation reactor 8 via a purification system 16, which comprises a dust collector, a dryer and/or a desulphurization unit.

TABLE-US-00001 TABLE 1 Gaseous effluent which penetrates into the carbonation reactor 8. Volume: 17 560 Nm.sup.3/h Temperature: 150? C. CO.sub.2 flow rate: 7.78 tph CO.sub.2 volume concentration: 24.2% on dry gas O.sub.2 volume concentration: 10.0% on dry gas SO.sub.2: 3 ppm Dust: 10 mg/Nm.sup.3

[0056] As it results from table 1, the CO.sub.2 volume concentration in the gaseous effluent is very low with respect to the N.sub.2 concentration (65%). In such condition a separation of both components is not easily feasible and would be costly due to the large gas volume to be treated.

[0057] The carbonation reactor 8 is provided with a fluidized bed of a sorbent material based on CaO supplied by a recycling duct 10. There 90% of the CO.sub.2 of the gaseous effluent is captured by CaO, which is carbonated into CaCO.sub.3 according to an exothermic reaction. Within the carbonation reactor 8 the temperature of the gaseous effluent must be maintained at a value of about 650? C., under the start of the reverse calcination reaction, by means of a heat exchanger 11 which communicates with a turbine 12 in order to convert heat into electrical power. A power of 2.3 MWe is so obtained.

[0058] From the carbonation reactor 8, the gaseous effluent carrying a CaCO.sub.3CaO based charge is supplied via a transfer duct 13 to a cyclone 14 from the top of which a CO.sub.2-depleted gaseous effluent is released.

TABLE-US-00002 TABLE 2 CO.sub.2-depleted gaseous effluent which exits from the cyclone 14. Volume: 14 015 Nm.sup.3/h Temperature: 650? C. CO.sub.2 flow rate: 0.8 tph CO.sub.2 volume concentration: 2.81% on wet gas.

[0059] Now the gaseous effluent exiting from the top of the cyclone 14 contains only traces of CO.sub.2 and may be removed in the atmosphere. Before this removal the gas passes through a heat exchanger 15 which communicates with a turbine 17 in order to convert heat into electrical power. A power of 1.5 MWe is so obtained.

[0060] The solid particles of the separated CaCO.sub.3CaO based charge exit from the bottom of the cyclone 14 and are supplied to the bottom of the calcination reactor 19 by means of the transfer duct 18.

[0061] The calcination reactor 19 is also supplied with a fuel containing almost no impurities. In the illustrated case 1857 Nm.sup.3/h of natural gas (i.e. a fuel containing no ash and no sulphur) are introduced into the calcination reactor 19 via the inlet 20 and 23 tph of an oxidizing gas containing dioxygen and CO.sub.2 are supplied via the introduction duct 21. The calcination reactor is operated at a temperature of about 900? C. in order to accelerate the calcination and produce a high specific surface CaO during the calcination of the CaCO.sub.3CaO based charge.

[0062] From the calcination reactor 19, the gaseous effluent carrying active CaO is supplied via a transfer duct 22 to a cyclone 23 from the top of which a CO.sub.2-concentrated gas stream is collected.

TABLE-US-00003 TABLE 3 CO.sub.2-concentrated gas stream which exits from the cyclone 23. Volume: 19 713 Nm.sup.3/h Temperature: 900? C. CO.sub.2 flow rate: 29 tph CO.sub.2 volume concentration: 96% on dry gas

[0063] The CO.sub.2 concentration in the gas stream exiting from the cyclone 23 is extremely high. Such a gas may be industrially valorized, for example for technical CO.sub.2 production, or for sequestration. Before collection, the gas stream passes through a heat exchanger 24 which communicates with a turbine 25 in order to convert heat into electrical power. A power of 3.17 MWe is so obtained.

[0064] The active CaO-based sorbent material exits separately from the bottom of the cyclone 23 and is recycled to the bottom of the carbonation reactor 8 by means of the recycling duct 10.

[0065] Before said combustion of a fuel poor in impurities in the presence of an oxidizing gas containing dioxygen and CO.sub.2, dioxygen is mixed with a fraction of the collected CO.sub.2-concentrated gas stream. 5 tph of oxygen produced at a concentration of 90% by an air separation unit 26 and 18 tph of CO.sub.2-concentrated gas recycled by means of the recirculation duct 27 are mixed and introduced in the calcination reactor 19 by means of the introduction duct 21, as oxidizing gas. Obviously recirculated CO.sub.2-concentrated gas and pure dioxygen may be fed separately to the calcination reactor wherein their mixture takes place in situ.

[0066] During the capture of CO.sub.2 in the carbonation reactor 8, there is formation of CaCO.sub.3 as above explained, but CaO of the fluidized bed participates only partially to the carbonation. Consequently, the CaCO.sub.3CaO based charge which circulates between the carbonation reactor 8 and the calcination reactor 19 contains not only particles of CaCO.sub.3 but also particles of CaO.

TABLE-US-00004 TABLE 4 CaCO.sub.3-CaO based charge circulating in the transfer duct 18 tph wt % CaCO.sub.3 16 41 CaO 21 53 Ash 0 0 CaSO.sub.4* 0 (0.018) 0 (0.04) Other impurities ** 2.21 5.68 Total 38.95 100 *CaSO.sub.4 results from the gaseous effluent of the lime kiln ** Other impurities result mainly from the limestone of the make-up.

[0067] CaO becomes less and less active with increasing cycles. There is an increased sintering of the particles. And, in order to keep a CO.sub.2 capture efficacy of at least 30% of active CaO in the CaO-based sorbent material, a bleed flowrate of 0.8 tph of CaCO.sub.3CaO based charge (2 wt % of the CaCO.sub.3CaO based charge) is extracted from the transfer duct 18 via the extraction duct 28. For compensation, a make-up of 1.06 tph of fresh limestone having a CaCO.sub.3 content of 96 wt % is introduced into the calcination reactor via the entrance 29. As the fuel used in the calcination reactor 19 does not contain any ash or sulphur and the compensatory limestone of the make-up has a high purity degree, the recycled CaO-based sorbent material is very pure as well as the circulating CaCO.sub.3CaO based charge which contains only Ca-based components. Consequently the bleed is no waste and may be used in several fields, such as the gas or water epuration, the agriculture, the paper manufacture, the civil engineering, etc.

[0068] The captured CO.sub.2 in the gas stream collected from the calcination reactor is summarized in Table 5

TABLE-US-00005 TABLE 5 CO.sub.2 captured by CaO in the carbonation reactor: 7 tph CO.sub.2 resulting from the combustion of the fuel in the calcination reactor: 3.3 tph CO.sub.2 resulting from the calcination of the make-up: 0.5 tph Total: 10.8 tph

[0069] Simultaneously the gas stream collected from the calcination reactor is very concentrated in CO.sub.2 and exploitable or sequestrable, the bleed is a valuable Ca product manufactured in parallel to the production of lime or dolime and the need of electricity of the installation, particularly the air separation unit, is satisfied by the production of the turbines.

EXAMPLE 2

[0070] The method according to the invention will now be disclosed in a lime plant comprising several furnaces and producing 2000 tpd of lime, the fuel being lignite. The gaseous effluents of all furnaces are collected together and sent into a carbonator-calcinator system as illustrated on FIG. 1.

TABLE-US-00006 TABLE 6 Gaseous effluent which penetrates into the carbonation reactor 8. Volume: 240 657 Nm.sup.3/h Temperature: 180? C. CO.sub.2 flow rate: 97 tph CO.sub.2 volume concentration: 21.3% on dry gas O.sub.2 volume concentration: 10.0% on dry gas SO.sub.2: 68 ppm Dust: 10 mg/Nm.sup.3

TABLE-US-00007 TABLE 7 CO.sub.2-depleted gaseous effluent which exits from the cyclone 14. Volume: 196 573 Nm.sup.3/h Temperature: 650? C. CO.sub.2 flow rate: 10 tph CO.sub.2 volume concentration: 2.49% on wet gas

TABLE-US-00008 TABLE 8 CO.sub.2-concentrated gas stream which exits from the cyclone 23. Volume: 244 550 Nm.sup.3/h Temperature: 900? C. CO.sub.2 flow rate: 363 tph CO.sub.2 volume concentration: 96% on dry gas

[0071] 66 tph of oxygen produced at a concentration of 90% by the air separation unit 26 and 222 tph of CO.sub.2-concentrated gas recycled by means of the recirculation duct 27 are mixed as oxidizing gas and introduced in the calcination reactor. 23 014 Nm.sup.3/h of natural gas (i.e. a fuel without ash or sulphur) are also supplied to this reactor, as fuel.

TABLE-US-00009 TABLE 9 CaCO.sub.3-CaO based charge circulating in the transfer duct 18 tph wt % CaCO.sub.3 198 42 CaO 259 54 Ash 0 0 CaSO.sub.4* 4.86 1% Other impurities** 14 2.9 Total 475 100 *CaSO.sub.4 results from the gaseous effluent of the lime kilns **Other impurities result mainly from the limestone of the make-up.

[0072] In order to keep a CO.sub.2 capture efficacy of at least 30% of active CaO in the CaO-based sorbent material, a bleed flowrate of 10 tph (2 wt %) of CaCO.sub.3CaO based charge is extracted from the transfer duct 18 via the extraction duct 28. For compensation, a make-up of 13 tph of fresh limestone having a CaCO.sub.3 content of 98 wt % is introduced into the calcination reactor.

[0073] The electrical power produced with the steam turbines is: 30 MWe for the turbine 12, 21 MWe for the turbine 17 and 39 MWe for the turbine 25.

[0074] The captured CO.sub.2 in the gas stream collected from the calcination reactor is summarized in Table 10

TABLE-US-00010 TABLE 10 CO.sub.2 captured by CaO in the carbonation reactor: 87 tph CO.sub.2 resulting from the combustion of the fuel in the calcination reactor: 41 tph CO.sub.2 resulting from the calcination of the make-up: 6 tph Total: 134 tph

EXAMPLE 3

[0075] The method according to the invention will now be disclosed in the same lime plant as in Example 2. The gaseous effluents of all furnaces are collected together and sent into a carbonator-calcinator system as illustrated on FIG. 1, but in the calcination reactor the used fuel is a lignite which has an ash content of 3.8 wt % and a sulphur content of 0.4 wt %.

[0076] Obviously the gaseous effluent which penetrates into the carbonation reactor 8 and the CO.sub.2-depleted gaseous effluent which exits from the cyclone 14 show the same features as in the tables 6 and respectively 7 of Example 2.

TABLE-US-00011 TABLE 11 CO.sub.2-concentrated gas stream which exits from the cyclone 23. Volume: 235 805 Nm.sup.3/h Temperature: 900? C. CO.sub.2 flow rate: 402 tph CO.sub.2 volume concentration: 96% on dry gas

[0077] 65 tph of oxygen produced at a concentration of 90% by the air separation unit 26 and 220 tph of CO.sub.2-concentrated gas recycled by means of the recirculation duct 27 are mixed as oxidizing gas and introduced in the calcination reactor. 40 tph of the above-mentioned lignite are also supplied to this reactor, as fuel.

TABLE-US-00012 TABLE 12 CaCO.sub.3-CaO based charge circulating in the transfer duct 18 tph wt % CaCO.sub.3 198 36 CaO 259 47 Ash 73 13.37 CaSO.sub.4* 3 0.59 Other impurities** 14 2.47 Total 547 100 *CaSO.sub.4 results from the gaseous effluent of the lime kilns and from the fuel of the calcination reactor **Other impurities result mainly from the limestone of the make-up

[0078] In order to keep a CO.sub.2 capture efficacy of at least 30% of active CaO in the CaO-based sorbent material, a bleed flowrate of 16 tph (3 wt %) of CaCO.sub.3CaO based charge is extracted from the transfer duct 18 via the extraction duct 28. For compensation, a make-up of 20 tph of fresh limestone having a CaCO.sub.3 content of 98% is introduced into the calcination reactor. The bleed contains 16 wt % of impurities and is still a valuable product.

[0079] The electrical power produced with the steam turbines is: 31 MWe for the turbine 12, 21 MWe for the turbine 17 and 39 MWe for the turbine 25.

[0080] The captured CO.sub.2 in the gas stream collected from the calcination reactor is summarized in Table 13.

TABLE-US-00013 TABLE 13 CO.sub.2 captured by CaO in the carbonation reactor: 87 tph CO.sub.2 resulting from the combustion of the fuel in the calcination reactor: 86 tph CO.sub.2 resulting from the calcination of the make-up: 9 tph Total: 182 tph

EXAMPLE 4

[0081] The method according to the invention will now be disclosed in the same lime plant as in Example 2. The gaseous effluents of all furnaces are collected together and sent into a carbonator-calcinator system as illustrated on FIG. 1, but in the calcination reactor the used fuel is the lignite of Example 3.

[0082] Obviously the gaseous effluent which penetrates into the carbonation reactor 8 and the CO.sub.2-depleted gaseous effluent which exits from the cyclone 14 show the same features as in the tables 6 and respectively 7 of Example 2.

TABLE-US-00014 TABLE 14 CO.sub.2-concentrated gas stream which exits from the cyclone 23. Volume: 284 892 Nm.sup.3/h Temperature: 900? C. CO.sub.2 flow rate: 485 tph CO.sub.2 volume concentration: 96% on dry gas

[0083] 78 tph of oxygen produced at a concentration of 90% by the air separation unit 26 and 265 tph of CO.sub.2-concentrated gas recycled by means of the recirculation duct 27 are mixed as oxidizing gas and introduced in the calcination reactor. 48 tph of the above-mentioned lignite are also supplied to this reactor, as fuel.

TABLE-US-00015 TABLE 15 CaCO.sub.3-CaO based charge circulating in the transfer duct 18 tph wt % CaCO.sub.3 198 40 CaO 259 52 Ash 27 5.34 CaSO.sub.4* 1 0.2 Other impurities** 13 2.71 Total 498 100 *CaSO.sub.4 results from the gaseous effluent of the lime kilns and from the fuel of the calcination reactor **Other impurities result mainly from the limestone of the make-up.

[0084] In order to keep a CO.sub.2 capture efficacy of at least 30% of active CaO in the CaO-based sorbent material, a bleed flowrate of 50 tph (10 wt %) of CaCO.sub.3CaO based charge is extracted from the transfer duct 18 via the extraction duct 28. For compensation, a make-up of 66 tph of fresh limestone having a CaCO.sub.3 content of 98% is introduced into the calcination reactor. The bleed contains 8.25 wt % of impurities and is a valuable product.

[0085] The electrical power produced with the steam turbines is: 32 MWe for the turbine 12, 21 MWe for the turbine 17 and 47 MWe for the turbine 25.

[0086] The captured CO.sub.2 in the gas stream collected from the calcination reactor is summarized in Table 13.

TABLE-US-00016 TABLE 16 CO.sub.2 captured by CaO in the carbonation reactor: 87 tph CO.sub.2 resulting from the combustion of the fuel in the calcination reactor: 104 tph CO.sub.2 resulting from the calcination of the make-up: 29 tph Total: 220 tph

[0087] A comparison between Example 3 and Example 4 shows that increasing extraction of the bleed rate from 3% to 10% of CaCO.sub.3CaO based charge results in a significant decrease of the bleed impurities (ash+CaSO.sub.4+other impurities) from 16.43% to 8.25%.

[0088] Other embodiments and variants of the present invention may be taken into account within the scope of the claims.

[0089] For example the heat recovery may be of any type, not only electrical.

[0090] In summary, such plants avoid a high participation to the greenhouse effect and the mass flows and power production are at a favourable level making the supply of make-up possible locally from the plant quarry, the bleed highly valuable and the power production profiting to local communities.