EP2291231A1

EP2291231A1 - Process for the combustion of coal with use of an absorbent agent in aqueous dispersion, ashes obtained and uses thereof

Info

Publication number: EP2291231A1
Application number: EP09750152A
Authority: EP
Inventors: Yves Kensicher
Original assignee: Coatex SAS
Current assignee: Coatex SAS
Priority date: 2008-05-21
Filing date: 2009-05-06
Publication date: 2011-03-09
Also published as: US20110092617A1; FR2931367A1; CN102036738A; CA2724445A1; WO2009141695A1; FR2931367B1

Abstract

The invention consists of a process for manufacturing ashes from the combustion of coal, this process comprising at least one step of bringing the coal into contact with an absorbent agent on the one hand, this absorbent agent being, on the other hand, contained in an aqueous phase in the presence of a (meth)acrylic dispersant, preferably a (meth)acrylic comb polymer. Thus the emissions of carbon dioxide and likewise the compounds based on sulphur, nitrogen or mercury which result from the combustion of coal are effectively combated.

Description

PROCESS FOR COMBUSTING COAL WITH IMPLEMENTATION OF ABSORBENT AGENT IN AQUEOUS DISPERSION, ASHES OBTAINED AND

THEIR USES

The use of coal in thermal power plants is very important; these plants provide 40% of the world's electricity production. For a long time considered as outdated, the coal becomes again of topical because the energy needs are such that the maximum capacities of production of oil or natural gas are about to be reached: this contributes to reduce the natural reserves of these products and causes a soaring prices that directly affect the end consumer.

However, there is a first issue, which is the sustainability of coal as a natural resource to provide energy to our planet: it is the reduction of greenhouse gas emissions, as required by the protocol of

Kyoto. However, a current coal plant emits significantly less CO ₂ per kilowatt-hour of burnt product than an old one (because of its better efficiency) but twice as much as a gas-fired plant. In order for technologies from coal combustion not to contribute adversely to global warming, it is therefore essential to limit the release of CO ₂ .

In addition, when the coal is burned in order to produce energy, it also seeks to enhance the products resulting from this process: it is solid residues, resulting from this combustion, also called ash. For many years, this ash has been used in the manufacture of cement, including type I cement - still known as Portland cement - which is one of the basic materials for the global construction industry. On this subject, see the documents "Concrete of high C3A slag cernent using coal ash as raw material" (Semento Gijutsu Nenpo, 1983, (37), pp. 514-17), "Use of coal-mining wastes as "(Cernent-Wapno-Gips, 1983, (12), pp. 326-8)," Manufacture of a new type of blended cernent using limestone and coal ash as main raw materials "( Semento Gijutsu Nenpo, 1988, (42), pp. 48-51). This valorization of the ashes resulting from the combustion of coal, gives birth to a second stake: it turns out that the obtaining of these ashes, via temperatures sometimes higher than 1 000 ° C, causes the emission of compounds at the same time toxic and dangerous for the environment, especially based on sulfur, nitrogen or mercury. These compounds, although they do not contribute to global warming, remain undesirable: both harmful to humans, they can also harm animal and plant species and, more generally, our ecosystems.

In order to combat both greenhouse gas emissions, such as carbon dioxide, while limiting the presence of other compounds based on sulfur, nitrogen and mercury, the skilled person has initially thought of developing solutions from a process point of view. In this respect, mention may be made of absorber-neutralizer devices intended to absorb and then neutralize toxic fumes (see document EP 1 059 112) and the so-called RSC or Selective Catalytic Reduction (see EP 1 687 567) . However, these methods remain expensive and need to be adapted according to the constraints of each industrial site.

Those skilled in the art have also turned to the introduction of various additives, which act as absorbers with respect to undesirable compounds resulting from the combustion of coal. It is thus known to use cement, slaked lime or not, calcium oxide (see EP 0 292 083, JP 9 173 768 and CN 1 962 034), halogenated compounds such as in particular calcium bromide (see WO 07 149867), or alternatively aluminosilicates (see US 4,116,705). As pointed out in the documents WO 2006 099 611 and WO 2007 092 504, these additives are used in the form of powders, previously mixed with the coal or introduced directly into the combustion chamber.

Continuing its research to effectively fight against the emissions of carbon dioxide, mercury, nitrogen and sulfur compounds during the industrial combustion of coal, the Applicant has developed a method of making ash from the combustion of the coal, by contact with the coal before combustion and / or during its combustion, and / or by contact with the fumes resulting from the combustion of the coal, of at least one absorbent compound, characterized in said absorbent compound is in the form of an aqueous dispersion containing at least one dispersing agent.

Unlike the state of the art which taught the implementation of such compounds in the form of powders, it was possible to observe the quite unexpected effects related to the implementation of these additives in the aqueous phase and in the presence of a dispersant: the emissions of harmful compounds, and especially carbon dioxide, are advantageously reduced. Preferably, when the dispersing agent is a (meth) acrylic comb polymer, the CO ₂ emissions are reduced even more significantly. Nothing in the prior art described or suggested such a result.

Without wishing to be bound by any theory, we believe that the effective surface area available for absorbing the harmful compounds is increased by the presence of a dispersing agent in the aqueous phase: the absorbent particles, dispersed stably and uniformly , have a larger effective area for the absorption mechanisms, than in the case of a powder where the individual particles are subject to phenomena of agglomeration and / or association.

In the present Application, the term "absorbent" here means any compound capable, through surface physicochemical mechanisms, of absorbing all or part of the compounds released during the combustion of coal, such as in particular carbon dioxide, compounds based on sulfur, nitrogen or mercury. These compounds are described not necessarily exhaustively, but to a large extent in EP 0 292 083, JP 9 173 768, CN 1 962 034, WO 07 149867, US 4 116 705, WO 2006 099 611 and WO 2007 092 504 mentioned above.

The term "aqueous dispersion" denotes a medium in which water constitutes the liquid continuous phase, particles of solids being in dispersion therein: it is in this case particles of the aforementioned absorbent agent.

The term "dispersant" refers to a chemical additive whose function is to regulate the viscosity of a liquid medium containing at least one solid species, with a view to achieving the dispersion in a stable manner over time and homogeneous in the medium under consideration. solid species (the absorbing agent) in the continuous phase (water). The term "(meth) acrylic polymer" refers to a polymer consisting of at least one acrylic and / or methacrylic monomer.

The term "(meth) acrylic comb polymer" refers to a polymer consisting of an essentially linear and acrylic and / or methacrylic backbone, on which at least two lateral segments consisting of at least one "macromonomer" are grafted. The term

"Macromonomer" means a polymer or copolymer which is not soluble in water and which has at least one end group having an unsaturated ethylenic function.

In this sense, the expression "(meth) acrylic comb polymer" refers both to structures as described in the documents WO 2007/052122 and in the French patent application having the deposit number 07 00086, as in the documents

US 7,232,875, US 6,815,513 and US 6,214,958.

Also, a first object of the invention consists of a process for producing ash from the combustion of coal, comprising the steps of:

a) producing an aqueous dispersion of at least one absorbent compound with a dispersant,

b) to carry out the combustion of the coal and this: bl) by putting said dispersion in contact with the coal and this, before its combustion and / or during its combustion,

b2) and / or by contacting said dispersion with the fumes resulting from the combustion of the coal.

Concretely, therefore, we begin by making an aqueous dispersion, by mixing in the proportions defined by those skilled in the art, both the absorbent compound, the dispersing agent and water. Then, this dispersion is brought into direct contact with the coal before combustion (typically on the storage areas, or during the possible coal granulation step that may precede combustion) or during combustion (i.e. say by injection inside the combustion chamber). It can also be brought into contact, at the outlet of the combustion chamber, with the fumes resulting from said combustion of the coal. This process is also characterized in that said dispersant is a (meth) acrylic polymer.

According to a preferred variant, this process is characterized in that said dispersant is a (meth) acrylic comb polymer.

This process is also characterized in that said (meth) acrylic comb polymer contains at least one monomer selected from acrylic acid, methacrylic acid, esters and mixtures thereof.

This process is also characterized in that said (meth) acrylic comb polymer contains at least one monomer of formula (I):

or

m, n, p and q are integers and m, n, p are less than 150, q is greater than

0 and at least one integer from m, n and p is nonzero,

R has a polymerizable vinyl function, preferably methacrylic,

R ₁ and R ₂ are identical or different and represent hydrogen atoms or alkyl groups,

R 'represents hydrogen or a hydrocarbon radical having 1 to 40 carbon atoms, preferably 1 to 12 carbon atoms, and very preferably 1 to 4 carbon atoms, R' being extremely preferably the methyl radical.

This process is also characterized in that said (meth) acrylic comb polymer consists of, expressed as a percentage by weight of each of its constituents: 1) 1% to 20%, preferably 2% to 15%, very preferably 3% to 12% of at least one monomer chosen from acrylic acid, methacrylic acid, esters and mixtures thereof,

2) 80% to 99%, preferentially 85% to 98%, very preferably 88% to

97% of at least one monomer of formula (I).

This process is also characterized in that said (meth) acrylic polymer and said (meth) acrylic comb polymer are totally or partially neutralized by at least one neutralization agent, chosen from hydroxides and / or oxides of calcium, magnesium, barium, of lithium, among hydroxides of sodium, of potassium, or ammonia, of primary, secondary and tertiary amines, and mixtures thereof.

This process is also characterized in that the absorbing agent is chosen from cement, oxides and / or hydroxides of calcium, magnesium, sodium, potassium and lithium, and mixtures thereof, halogens and preferably calcium bromide. alumino silicates and mixtures thereof.

This process is also characterized in that said aqueous dispersion contains from 0.01% to 0.3% by dry weight of absorbent agent relative to its total weight.

This process is also characterized in that the dry weight of dispersing agent is between 0.02% and 0.5% of the weight of absorbent agent.

This process is also characterized in that the molecular weight of the dispersing agent, as determined by Gas Chromatography, is between 10,000 g / mol and 80,000 g / mol, preferably between 15,000 g / mol and 40,000 g / mol. 000 g / mol.

Another object of the invention resides in the ashes obtained by the combustion of coal and this, by implementing the method according to the present invention.

A final object of the invention is the use of these ashes in the manufacture of compositions based on hydraulic binders, preferably cement compositions, very preferably Portland cement compositions. EXAMPLES

In all the examples, as well as throughout the present application, the molecular weight of the polymers used is determined according to the method explained below, by Steric Exclusion Chromatography (CES).

A test portion of the polymer solution corresponding to 90 mg of dry matter is introduced into a 10 ml flask.

The mobile phase, added with 0.04% THF, is added to a total mass of 10 g.

The composition of this mobile phase is as follows: NaNO ₃ : 0.2 mol / L, CH ₃ COOH:

0.5 mol / L, acetonitrile 5% volume.

The CES chain is composed of a Waters ™ 510 type isocratic pump, the flow rate of which is set to 0.8 mL / min, a Waters 717+ sample changer, an oven containing a precolumn type "Guard Column Ultrahydrogel Waters ™", followed by a set of columns of 7.8 mm internal diameter and 30 cm length type

"Ultrahydrogel Waters ™", whose nominal porosities are, in the order of their connection: 2000, 1000, 500 and 250 A.

Detection is provided by a Waters ™ 410 differential refractometer. The temperature of the oven and detector is regulated at 35 ° C.

Acquisition and processing of the chromatogram is performed using the PSS WinGPC Scientific v 4.02 software.

The CES is calibrated by a series of sodium polyacrylate standards supplied by Polymer

Standard Service under PAA 18 K, PAA 8K, PAA 5K, PAA 4K, PAA 3K. The calibration curve is of linear type and takes into account the correction obtained thanks to the flow rate marker (THF).

Example 1

This example illustrates the ability of a mineral mixture, subjected to a gaseous mixture containing carbon dioxide, to absorb CO ₂ . Several tests are carried out including a control where the mineral is in powder form and free of any additive, a test according to the prior art where the mineral is additive of an absorbent in the form of a solid particulate, and two tests according to the invention wherein the mineral is put in aqueous dispersion in the presence of two acrylic dispersants including a comb type.

Test No. 1 - Reference: preparation of a mineral powder mixture for the reduction of carbon dioxide in a gaseous effluent.

The mineral mixture is prepared by homogenization in a powder mixer of 747 g of slaked lime (Ca (OH) ₂ ) and 253 g of calcareous marl, the two minerals being previously crushed and screened in order to have a maximum particle size of 250 micrometers.

The homogeneous mixture is then placed in a cylindrical chamber whose bottom consists of a sintered glass with a porosity of between 16 and 40 microns. The bottom of the chamber is connected to a source of a gaseous mixture of air enriched with carbon dioxide and having a content of 5% by volume of CO ₂ . The flow rate of the gaseous mixture is regulated to 1 liter per minute and the composition of the gas leaving the chamber analyzed by means of gas chromatography coupled with a mass spectrometer, according to the methods well known to those skilled in the art, all 5 minutes after a 10-minute operation (in the following tests, the carbon dioxide contents are determined according to this method). The carbon dioxide content of the exiting gas mixture stabilizes at around 2.5% by volume during the 40 minutes of the test. 50% of the carbon dioxide is absorbed by the mineral mixture.

Test No. 2 - Prior Art: Preparation of a mineral mixture in aqueous suspension without dispersing agent for the reduction of carbon dioxide in a gaseous effluent.

A mineral mixture identical to that used for test No. 1 is prepared and then suspended in water at a rate of 1000 g of mixture per 2333 g of water, the Brookfield ™ viscosity of the mixture being 350 mPa.s (at 10 rpm and 25 ° C). A higher solids content is not possible, the viscosity increasing very rapidly with the dry extract.

The dispersion thus prepared is introduced into a solid bottom cylindrical chamber provided with a sintered glass bubbler with a porosity of between 16 and 40 microns. The bubbler is connected to a source of a gaseous mixture of air enriched with carbon and having a content of 5% by volume of CO ₂ . The flow rate of the gaseous mixture is regulated at 1 liter per minute and the composition of the gas leaving the chamber analyzed every 5 minutes after starting at 10 minutes.

The carbon dioxide content of the outgoing gas mixture stabilizes at around 0.5% by volume and then slowly increases during the test period to finish at 0.7% by volume after 40 minutes.

90% of the carbon dioxide is absorbed by the mineral mixture at the beginning of the test, the ratio rising to 86% after 40 minutes.

Example 3 - Invention: Preparation of a mineral mixture in aqueous suspension with a dispersing agent of the sodium polyacrylate type for the reduction of carbon dioxide in a gaseous effluent.

A mineral mixture identical to that used in test No. 1 is prepared and then suspended in water at a rate of 1000 g of mixture for 666 g of water and 5.8 g of an aqueous solution. of sodium polyacrylate of 43% dry matter and an average molecular weight of 3500 g / mol, the Brookfield ™ viscosity of the mixture being 400 mPa.s (10 rpm and 25 ° C). The dispersion thus prepared is introduced into a solid bottom cylindrical chamber provided with a sintered glass bubbler with a porosity of between 16 and 40 microns. The bubbler is connected to a source of a gaseous mixture of air enriched with carbon dioxide and having a content of 5% by volume of CO ₂ . The flow rate of the gaseous mixture is regulated at 1 liter per minute and the composition of the gas leaving the chamber analyzed every 5 minutes after starting at 10 minutes. The carbon dioxide content of the exiting gas mixture stabilizes at around 0.4% by volume and then slowly increases during the test period to finish at 0.52% by volume after 40 minutes.

92% of the carbon dioxide is absorbed by the mineral mixture at the beginning of the test, the ratio rising to 89.6% after 40 minutes.

Example 4 - Invention: Preparation of a mineral mixture in aqueous suspension with a dispersing agent of the comb-polymer type for the reduction of carbon dioxide in a gaseous effluent. A mineral mixture identical to Example 1 is prepared and then suspended in water at a rate of 1000 g of mixture for 666 g of water and 2.25 g of an aqueous solution of a comb polymer of 40 % of dry matter and an average molecular weight of 800 g / mol, the Brookfield ™ viscosity of the mixture being 330 mPa.s (at 10 revolutions / minute and at 25 ^° C.).

Said comb polymer is composed of:

10% by weight of methacrylic acid, 90% by weight of methoxypolyethylene glycol methacrylate with a molecular weight of 2000 g / mol,

It is totally neutralized by sodium hydroxide and its molecular weight is equal to 28,000 g / mol. It is obtained from a conventional polymerization process, as is well known to those skilled in the art.

The dispersion thus prepared is introduced into a solid bottom cylindrical chamber provided with a sintered glass bubbler with a porosity of between 16 and 40 microns. The bubbler is connected to a source of a gaseous mixture of air enriched with carbon dioxide and having a content of 5% by volume of CO ₂ . The flow rate of the gaseous mixture is regulated at 1 liter per minute and the composition of the gas leaving the chamber analyzed every 5 minutes after starting at 10 minutes.

The carbon dioxide content of the outgoing gas mixture stabilizes at around 0.36% by volume and then slowly increases during the test period to finish at 0.41% by volume after 40 minutes.

92.8% of the carbon dioxide is absorbed by the mineral mixture at the beginning of the test, the ratio rising to 91.8% after 40 minutes.

These results demonstrate that the amount of carbon dioxide absorbed is greater when the mineral mixture is dispersed in water in the presence of an acrylic dispersing agent (tests 3 and 4): the absorption capacity of such a mineral mixture will therefore be increased when it is implemented in a coal combustion process according to the invention. It is also demonstrated that, according to the preferred embodiment of the invention, the best results are obtained when using a comb-type acrylic polymer (test No. 4).

Claims

1 - Process for producing ash from the combustion of coal, comprising the steps of:

(b) burn coal and

bl) by contacting said dispersion with the coal and this, before combustion and / or during combustion, b2) and / or by contacting said dispersion with the fumes resulting from the combustion of coal.

2 - Process according to claim 1, characterized in that said dispersant is a (meth) acrylic polymer.

3 - Process according to claim 2, characterized in that said dispersant is a comb (meth) acrylic polymer.

4 - Process according to claim 3, characterized in that said (meth) acrylic comb polymer contains at least one monomer chosen from acrylic acid, methacrylic acid, esters and mixtures thereof.

5 - Method according to one of claims 3 or 4, characterized in that said (meth) acrylic comb polymer contains at least one monomer of formula (I):

or : m, n, p and q are integers and m, n, p are less than 150, q is greater than 0 and at least one of m, n and p is non-zero,

- R comprises a polymerizable vinyl function, preferably methacrylic, - R ₁ and R ₂ are identical or different and represent hydrogen atoms or alkyl groups,

6 - Process according to one of claims 3 to 5, characterized in that said (meth) acrylic comb polymer consists of, expressed as a percentage by weight of each of its constituents:

1) 1% to 20%, preferably 2% to 15%, very preferably 3% to 12% of at least one monomer chosen from acrylic acid, methacrylic acid, esters and mixtures thereof,

2) 80% to 99%, preferentially 85% to 98%, very preferably 88% to

97% of at least one monomer of formula (I).

7 - Method according to one of claims 2 to 6, characterized in that said (meth) acrylic polymer and said comb polymer (meth) acrylic are totally or partially neutralized with at least one neutralizing agent, selected from hydroxides and / or oxides of calcium, magnesium, barium, lithium, among hydroxides of sodium, potassium, or ammonia, among primary, secondary and tertiary amines, and mixtures thereof.

8 - Process according to one of claims 1 to 7, characterized in that the absorbent agent is selected from cement, oxides and / or hydroxides of calcium, magnesium, sodium, potassium, lithium and mixtures thereof halogens and preferentially calcium bromide, alumino silicates and mixtures thereof. 9 - Process according to one of claims 1 to 8, characterized in that said aqueous dispersion contains from 0.01% to 0.3% by dry weight of absorbent agent relative to its total weight.

10 - Process according to one of claims 1 to 9, characterized in that the dry weight of dispersing agent is between 0.02% and 0.5% of the weight of absorbent agent.

11 - Process according to one of claims 1 to 10, characterized in that the molecular weight of the dispersing agent, as determined by Gas Chromatography, is between 10 000 g / mol and 80 000 g / mol, preferably between 15,000 g / mol and 40,000 g / mol.

12 - Ash characterized in that they are obtained by the method according to one of claims 1 to 11.

13 - Use of the ash according to claim 12, in the manufacture of compositions based on hydraulic binders, preferably cement compositions, very preferably Portland cement compositions.