EP-4737420-A1 - METHOD OF PRODUCING A POZZOLANIC MATERIAL IN A CEMENT MANUFACTURING PLANT

EP4737420A1EP 4737420 A1EP4737420 A1EP 4737420A1EP-4737420-A1

Abstract

Method of producing a pozzolanic material in a cement manufacturing plant, comprising: - providing a silico-aluminous mineral material susceptible of pozzolanic reactivity upon calcination, - introducing the silico-aluminous mineral material into the rotary kiln via the kiln feed installation without having been thermally treated in the combustion chamber and calcining the silico-aluminous mineral material in the rotary kiln at a temperature of 400-900°C, preferably 600-900°C, in order to obtain said pozzolanic material, combusting a non-fossil, alternative fuel by means of the main burner for providing thermal energy to the calcination process, - guiding the combustion gas from the kiln inlet chamber into the combustion chamber and combusting a fuel in the combustion chamber, thereby raising the temperature of the combustion gas to an elevated temperature of above 850°C and keeping the combustion gas at said elevated temperature for at least 2 seconds.

Inventors

DAMLJANOVIC, Dejan
MILICEV, Dejan
GARAI, Gergely
BARBARULO, Rémi

Assignees

Holcim Technology Ltd

Dates

Publication Date: 20260506
Application Date: 20241029

Claims (13)

Method of producing a pozzolanic material in a cement manufacturing plant, the plant comprising a rotary kiln having an inlet end with a kiln inlet chamber and an outlet end, a main burner arranged at the outlet end, a combustion chamber connected to the kiln inlet chamber and a kiln feed installation opening into the kiln inlet chamber for feeding a raw material into the rotary kiln, wherein the rotary kiln is configured to calcine a raw material travelling from the inlet end to the outlet end in counter current to a combustion gas, the method comprising: - providing a silico-aluminous mineral material susceptible of pozzolanic reactivity upon calcination, - introducing the silico-aluminous mineral material into the rotary kiln via the kiln feed installation without having been thermally treated in the combustion chamber and calcining the silico-aluminous mineral material in the rotary kiln at a temperature of 400-900°C, preferably 600-900°C, in order to obtain said pozzolanic material, - combusting a non-fossil, alternative fuel by means of the main burner for providing thermal energy to the calcination process, - guiding the combustion gas from the kiln inlet chamber into the combustion chamber and providing an additional source of heat in the combustion chamber, thereby raising the temperature of the combustion gas to an elevated temperature of above 850°C and keeping the combustion gas at said elevated temperature for at least 2 seconds.
Method according claim 1, wherein the additional source of heat in the combustion chamber is obtained solely from the use of electrical energy.
Method according claim 1, wherein the additional source of heat in the combustion chamber is from combusting a fuel or from a combination of the combustion of a fuel and the use of electrical energy.
Method according to claim 3, wherein a non-fossil waste material, such as a waste solvent, is used as said fuel in the combustion chamber.
Method according to claim 3 or 4, wherein the total fuel used in the combustion chamber and the main burner has a chloride content of less than 0.2 wt.-%.
Method according to any one of claims 1 to 5, wherein the combustion chamber is a precalciner of the cement manufacturing plant.
Method according to any one of claims 1 to 6, wherein the combustion gas is withdrawn from the combustion chamber and used to dry and/or preheat the silico-aluminous mineral material before the silico-aluminous mineral material is introduced into the rotary kiln.
Method according to claim 7, wherein the cement manufacturing plant comprises a preheater tower having at least one string of cyclone preheaters, wherein the combustion gas is led through the at least one string of preheaters in counter-current to a flow of silico-aluminous mineral material for preheating the silico-aluminous mineral material.
Method according to any one of claims 3 to 8, wherein an additional alternative fuel is introduced into the rotary kiln via the kiln inlet chamber and, preferably being in a mixture with the silico-aluminous mineral material, is subjected to a gasification in order to obtain a syngas.
Method according to claim 9, wherein the syngas is guided into the combustion chamber and used as the fuel in the combustion chamber or constitutes a partial amount of the fuel in the combustion chamber.
Method according to any one of claims 1 to 10, wherein the cement manufacturing plant comprises a cooler arranged at the outlet end of the rotary kiln for cooling the pozzolanic material, wherein ambient air is led through the cooler as a cooling medium and, after having been preheated in the cooler, is used as combustion air in the combustion chamber.
Method according to any one of claims 1 to 11, wherein a raw clay material is used as said silico-aluminous mineral material.
Method according to any one of claims 1 to 12, wherein the combustion gas from the combustion chamber and the kiln contains SOx, which is removed from the combustion gas by contacting the combustion gas with a calcium source.

Description

Various types of mineral components may be added to Portland cement in order to obtain composite cements. In particular, it has become common practice to use pozzolanic and/or latent hydraulic material as supplementary cementitious materials in Portland cement mixtures. By substituting supplementary cementitious materials for Portland cement the specific emission of CO2 in the production of cement will be reduced. During the production of Portland cement clinker a considerable amount of CO2 per ton of Portland cement clinker is emitted by the decarbonation of the raw materials and from the oxidation of the fuels that occur during calcination of the raw materials in rotary kilns. Supplementary cementitious materials comprise a broad class of siliceous or siliceous and aluminous materials which, in finely divided form and in the presence of water, chemically react with calcium hydroxide at ordinary temperature to form compounds possessing cementitious properties. Examples of supplementary cementitious materials include granulated blast-furnace slag, fly ash, natural pozzolans, burnt oil shale, or calcined clay. Cement is a product that in most cases is used in locations relatively close to where it is manufactured. Therefore, in case of composite cements, its production requires the availability of a source of a supplementary cementitious material, this source being either natural or synthetic. However, the local availability of such source is not guaranteed in all regions where cement is produced, mainly because of the decreasing availability of some synthetic sources of supplementary cementitious materials. Synthetic supplementary cementitious materials are in most cases a byproduct of various industrial processes, such as fly ash from coal-fired power plants or blast-furnace slag from steel mills. The decreasing supply of fly ash from the power industry is encouraging the search for new sources of supplementary cementitious materials for the cement and concrete production. Therefore, increasing efforts are undertaken to use widely available sources for producing supplementary cementitious materials, such as calcined clays. Various types of silico-aluminous mineral materials, such as raw clay, can be treated thermally by heating to a temperature high enough to alter the structure of the clay minerals by dehydroxylation, but low enough to avoid recrystallization and the formation of chemically inert phases such as mullite. A particularly useful type of clay is kaolinite that has a layered silicate structure, composed of alternating layers of tetrahedral sheets of silica and octahedral sheets of alumina linked with each other by oxygen atoms. When kaolinite is heated during a calcination process, dehydroxylation and transformation of the kaolinite into a material known as metakaolin are occurring. Various methods have been proposed for producing calcined clay. One option is to use an existing rotary kiln of a cement manufacturing plant in order to calcine raw clay. When calcining raw clay, the calcination temperature shall be maintained in a range of 600-900°C in order to achieve dehydroxylation of the clay minerals while preserving the reactive structure of the calcined product. Dehydroxylation, which occurs between 400-900°C, preferentially between 600-900°C, involves the removal of chemically bound water (hydroxyl groups) from the clay minerals, transforming them into a reactive state. However, if the temperature is too high (above 900°C), chemical reactions will occur and the calcined clay may begin to recrystallize, forming less reactive crystalline phases such as mullite or cristobalite. When using a rotary kiln for calcining raw clay, the raw material is travelling from an inlet end of the kiln to an outlet and, while combustion gases are flowing in counter current from the outlet end to the inlet end, which results in that the combustion gas leaves the rotary kiln at a temperature of about 500°C. If an alternative fuel is used in the rotary kiln to provide the thermal energy needed for calcining the raw material, volatile organic compounds (VOC) contained in the alternative fuels may be released and/or transformed to undesired pollutants that would be released into the environment as part of the combustion gas. An alternative fuel is here defined as a fuel that is not a fossil fuel, i.e. not a natural fuel such as coal or gas, formed in the geological past from the remains of living organisms. In order to minimise air pollution, the EU Industrial Emissions Directive (IED) 2010/75/EU requires cement kilns co-incinerating waste to comply with the provision that the temperature of the combustion gases resulting from the co-incineration of waste shall be raised in a controlled and homogeneous fashion and even under the most unfavourable conditions to at least 850°C for at least two seconds after the last injection of air. The high temperature and sufficient residence time help to ensure complete combustio