AU2009326594B2

AU2009326594B2 - Process for producing cement or cement substitutes

Info

Publication number: AU2009326594B2
Application number: AU2009326594A
Authority: AU
Inventors: Nikola Anastasijevic; Edgar Gasafi
Original assignee: Outotec Oyj
Current assignee: Metso Corp
Priority date: 2008-12-12
Filing date: 2009-10-24
Publication date: 2014-11-27
Anticipated expiration: 2029-10-24
Also published as: AU2009326594A2; BRPI0923335A2; EA201190005A1; AU2009326594A1; JO2988B1; DE102008061743B4; UA103780C2; DE102008061743A1; EA018753B9; BRPI0923335B1; WO2010066316A1; EA018753B1

Abstract

This invention relates to a process for producing cement or cement substitutes on the basis of carbon-containing compounds with a carbon content of more than 10 wt-%, wherein the carbon-containing compounds are burnt in a furnace at a temperature of 600 to 900°C, and wherein beside the carbon-containing compounds at least one additional, inert and/or low-heating-value material, which already before or after a thermal treatment has cement properties, is introduced into the furnace and calcined.

Description

WO 2010/066316 PCT/EP2009/007620 Process for Producing Cement or Cement Substitutes 5 The present invention relates to a process for producing cement or cement substitutes on the basis of carbon-containing compounds with a carbon content of more than 10 wt-%, wherein the carbon-containing compounds are burnt in a furnace at a tempera ture of 750 to 900 0 C. 10 For producing cement or cement substitutes, carbon-containing compounds are used. As such raw material, oil shale frequently is used, which as a collective term designates those clayey rocks which contain bitumen or ultra-heavy oils. Depending on the occur rence, the content of organic material, the so-called kerogen, lies between 10 and 30 wt-%. 15 When producing cement from oil shale, the oil initially is expelled from the oil shale by pyrolysis, as described in DE 385 624. Subsequently, the remaining coal in the oil shale is burnt, and a cement mass free from carbon is formed, which by grinding is converted to cement ready for use. 20 From GB 951,211 it is furthermore known to admix mineral substances such as lime or clay to the oil shale prior to low-temperature carbonization, and to pelletize and then calcine the mixture at a temperature of 400 0 C, in order to remove the organic constitu ents. 25 In connection with the increasing shortage of fossil raw materials, the recovery of energy by combustion of oil shale gains growing importance. As described in DE 38 22 999 C1, combustion for instance is effected by fluidized-bed combustion. This provides for a very good heat exchange and thus a very homogeneous temperature profile over 30 the entire fluidized bed. Combustion of oil shale in the furnace leads to a product which contains clinker phases. The same consist in particular of dicalcium silicate and monocalcium aluminate, but WO 2010/066316 PCT/EP2009/007620 -2 beside free calcium oxide and calcium sulfate there is also found a major amount of pozzolanically reacting oxides such as silica. The resulting product therefore reacts with water and lime to obtain a water-insoluble compound, which opens up applications as cement or cement substitute. 5 For further improvement of the material properties, it is for instance known from EP 0 727 398 B2, to incorporate additives into the product obtained by combustion. Above all, such useful additives include calcium sulfate or calcium sulfoaluminate, but alumina, phosphonic acid derivatives and a number of polymers can also be used. An 10 end product obtained in this way often exhibits attractive properties in terms of con struction chemistry, in particular in its capacity as composite cement with short setting times. In the combustion of oil shale for producing cement or cement substitutes, however, the 15 high energy input of oil shale in the furnace causes problems, since for obtaining a high-grade product temperatures of below 900 0 C are required, in order to ensure the puzzolanic and hydraulic properties for future use for concrete production. Therefore, it has been attempted in various ways to decrease the temperature in the 20 furnace. Temperature control frequently is effected by discharge of energy from the furnace by means of membrane walls or immersed heater surfaces, as they are de scribed in DE 34 47 186 Al. The immersed heater surfaces are immersed into the fluidized bed of the furnace or of a separate fluidized-bed cooler and withdraw energy from the same by evaporating a condensate. The vapor produced can be utilized else 25 where for energy generation. Beside the disadvantage of increased investment costs due to an increased number of components, the contact of these heat-dissipating components with the hot solids, which leads to a fast wear of the cooling elements, is problematic above all. Furthermore, the fluidized bed is cooled locally, which can lead to a less homogeneous product. 30 Similar problems of a non-homogeneous temperature control also arise when cooling with quenching water, which furthermore requires additional devices for venting the steam obtained in a large amount.

- 3 A decrease of the furnace temperature also can be achieved by increasing the amount of combustion air and thus by a reduced local density of the fluidized bed or by flue gas recirculation. What is disadvantageous here, however, is the lower 5 space-time yield and the distinctly enlarged dimensions of the plant. Therefore, it is the object of the present invention to provide for a uniform decrease of the furnace temperature without an additional technical expenditure, when producing cement or cement substitutes from raw materials with a high heating 10 value. This object substantially is solved with the invention in that beside the material to be burnt, at least one additional material, which already before or after a thermal treatment has cement properties, is introduced into the furnace and co-burnt. 15 All additional materials are of such physical quality that they are inert or of low heating value and thereby lower the temperature obtained in the furnace by combustion of the high-carbon raw materials by means of diluting the solid phase. In this way, the space-time yield is decreased in terms of energy input, but the pure 20 yield of energy based on the educt is kept constant. Since all additives are left in the product after the burning operation, potential feedstocks likewise have cement properties already before or after a thermal treatment, so as not to decrease the quality of the resulting product. Cement properties here refer to the fact that it is a hydraulically acting binder in particular for mortar and concrete, which upon addition 25 of water hardens in a volume- and water-stable way by hydration. Due to the admixture of these additional materials, the product output is increased with reference to the amount of high-carbon raw material used. In addition, material properties of the resulting product can be varied selectively. 30 In an embodiment, the present invention provides a process for producing cement or cement substitutes on the basis of carbon-containing compounds with a carbon content of more than 10 wt-%, wherein the carbon-containing compounds are burnt in a furnace at a temperature of 600 to 900'C, and wherein beside the carbon containing compounds at least one additional, inert and/or low-heating value 35 material, which already before or after a thermal treatment has cement properties, is 5899161_1 (GHMatters) P87075.AU JINGT 30/10/14 - 3A introduced and calcined in the furnace, wherein at least one of the admixed materials is in the moist condition and has a water content of up to 25 wt-%. In a particularly preferred aspect of the invention, the carbon-containing material is 5 oil shale, which has a high heating value. It is, however, also possible to use combustion residues such as ashes or soots, in particular also combustion residues from coal-fired power plants, with a comparatively high carbon content. The carbon content is more than 10 wt-%, preferably more than 15 wt-%, and particularly preferably more than 20 wt-%. 10 5899161_1 (GHMatters) P87075.AU JINGT 30/10/14 WO 2010/066316 PCT/EP2009/007620 -4 Lignite as low-grade coal with a high moisture content of mostly more than 50 wt-% likewise is suitable for use in accordance with the invention as material to be calcined when producing cement or cement substitutes. 5 To simplify handling and equipment design, the additional material is mixed with the material to be calcined, before it is introduced into the furnace together with the same, in accordance with a preferred aspect of the invention. As a result, a homogeneous mixture is introduced into the furnace, which also leads to a homogeneous temperature 10 profile in the furnace. In a further aspect of the invention, the furnace temperature can additionally be influ enced by an attached closed-circuit cooling. The prevailing temperatures of the solids streams approximately correspond to those of the desired furnace temperature. In a 15 development of the invention, the inert and low-heating-value material additionally introduced into the process can be introduced into the solid stream at a point of the cooling circuit which is located before, inside or after the cooler. In a preferred embodiment of the invention, clay is added, which in cement production 20 is used as a naturally occurring raw material and has puzzolanic properties. Another preferred aspect of the invention provides the addition of burnt oil shale , which particularly preferably was obtained as a residue of pulverized-fuel firing systems and usually has a residual carbon content of 2 to 5 wt-% or more. Beside hydraulic proper 25 ties as a carrier of aluminate, silicate and iron oxide, the admixture of burnt oil shale provides for the disposal (recycling) of a waste product and therefore offers an eco nomic advantage to a particular extent. Another preferred aspect of the invention relates to the addition of low-carbon combus 30 tion residues from coal-fired power plants, in particular the so-called bottom-ash, which have a similar composition as the burnt oil shale and likewise hydraulic properties. Even more than when using burnt oil shale , the disposal of a problematic waste mate rial must be emphasized here, since such combustion residues currently are disposed WO 2010/066316 PCT/EP2009/007620 -5 of on disposal sites. In accordance with the invention, the carbon content of these compounds is below 10 wt-%, preferably below 5 wt-%, and particularly preferably below 2.5 wt-%. 5 Another preferred aspect of the invention includes the addition of limestone, whereby both the sulfur content is reduced, in that the limestone is calcined, and the calcium oxide formed subsequently reacts with sulfur oxides, and the binding capacity of the product can be increased. 10 Another preferred aspect of the invention describes the addition of gypsum, which in the resulting end product acts as binding retarder. It lies within the scope of the invention that the above-described variants of the addi tional materials also can be admixed to the oil shale in any combination with each 15 other. A development of the invention provides the addition of at least one of the admixed materials in the moist condition. The water content of this material is up to 25 wt-%, preferably up to 15 wt-%, and as a result of calcination and/or evaporation it leads to an 20 additional output of energy from the furnace, whereby the amount of the admixed material can be decreased at the same time. In a preferred embodiment of the invention, it is provided in addition that the solids stream consisting of oil shale and the admixed additional material is heated before 25 entering the furnace. In relation to that, other pretreatments such as a preheating of individual components also are conceivable. Developments, advantages and possible applications of the invention can also be taken from the following description of an embodiment. All features described form the sub 30 ject-matter of the invention per se or in any combination, also independent of their inclusion in the claims or their back-reference. In the drawing: WO 2010/066316 PCT/EP2009/007620 -6 Fig. 1 schematically shows a plant for performing the process of the invention Fig. 2 shows the energy to be dissipated in dependence on the amount of inert 5 material used (clay, moisture 20 wt-%). Fig. 1 schematically shows a plant for performing the process of the invention. In a mixing tank 1, oil shale and an inert and/or low-heating-value material with cement 10 properties are mixed and then supplied to a fluidized-bed furnace 3, in which the mix ture is burnt at a temperature of e.g. 8000C, via a supply conduit 2. Mixing can also be effected by jointly grinding or by an other type of pre-preparation. As inert material, e.g. moist clay is admixed to the oil shale, which is dried and calcined 15 at the temperature generated in the furnace by the combustion of the organic compo nents of the oil shale. The quantities of oil shale and clay introduced into the furnace are determined according the energy amount necessary for combustion, drying and calcination. 20 After combustion and calcination, the solids are withdrawn from the furnace 3 via a discharge conduit 4 and after possible further processing steps, such as grinding and mixing with cement clinker, are employed as cement and used for instance in the pro duction of concrete. 25 Before or after mixing in the mixing tank 3, the solids can for instance be preheated in a Venturi preheater 5. Instead of the illustrated stationary fluidized bed as furnace 3, a circulating fluidized bed, an annular fluidized bed, but also a rotary kiln or some other suitable furnace 30 design can of course also be used for the combustion of the material. Instead of the clay, other inert/low-heating-value materials like limestone, gypsum, burnt oil shale and/or combustion residues from power plants can be added. All these -7 materials have cement properties in the sense of the present invention and can be employed as hydraulically acting binders. Example 5 For the production of 12 t/h of burnt oil shale, 16 t/h of oil shale with a moisture of 7 wt % and an inlet temperature of 25*C are introduced into a furnace, e.g. a fluidized-bed furnace. Assuming a heating value of 3400 kJ/kg, a discharge of 4.3 MW is necessary, in order to keep the furnace temperature below the product-damaging temperature of 10 900 0 C. In accordance with the process of the invention, clay with a moisture content of 20 wt % is admixed to the oil shale. With the available amount of energy of 4.3 MW, about 3200 kg/h of the clay can be dried and calcined in the furnace. 15 In this connection, Fig. 2 shows the decrease rate of energy to be discharged, which is present in the furnace, in dependence on the moist clay amount used for the assumed moisture content of 20 wt-%. 20 Since both burnt oil shale and calcined clay are used as cement substitute, use of the product mixture as cement substitute is also possible. The product quantity achieved can thereby be increased by the invention to 15.2 t/h with the same input of oil shale. However, if the total product quantity of 12 t/h should be kept constant, only about 9.475 t/h of oil shale and 2.525 t/h of clay must be used. 25 In the claims which follow and in the preceding description of the invention, except where the context requires otherwise due to express language or necessary implication, the word "comprise" or variations such as "comprises" or "comprising" is used in an inclusive sense, i.e. to specify the presence of the stated features but not to 30 preclude the presence or addition of further features in various embodiments of the invention. It is to be understood that, if any prior art publication is referred to herein, such reference does not constitute an admission that the publication forms a part of the 35 common general knowledge in the art, in Australia or any other country. 27328261 (GHMatters) P87075.AU 11/07/11

Claims

1. A process for producing cement or cement substitutes on the basis of carbon 5 containing compounds with a carbon content of more than 10 wt-%, wherein the carbon-containing compounds are burnt in a furnace at a temperature of 600 to 900 0 C, and wherein beside the carbon-containing compounds at least one additional, inert and/or low-heating value material, which already before or after a thermal treatment has cement properties, is introduced and calcined in the furnace, wherein at least one 10 of the admixed materials is in the moist condition and has a water content of up to 25 wt-%.

2. The process according to claim 1, wherein oil shale is used as carbon containing compounds. 15

3. The process according to claim 1, wherein ashes with a carbon content of more than 10 wt-% are used as carbon-containing compounds.

4. The process according to claim 1, wherein soots with a carbon content of more 20 than 10 wt-% are used as carbon-containing compounds.

5. The process according to claim 1, wherein combustion residues from coal-fired power plants with a carbon content of more than 10 wt-% are used as carbon containing compounds. 25

6. The process according to claim 1, wherein lignite is used as carbon-containing compounds.

7. The process according to any of the preceding claims, wherein the additional 30 material is mixed with the carbon-containing compounds, before it is introduced into the furnace together with the same via the solids supply conduit.

8. The process according to any of the preceding claims, wherein the furnace includes a closed-circuit cooling and that the additional material is added to the solids 35 stream within this closed-circuit cooling. 2732826_1 (GHNatters) P87075.AU 11/07/11 -9

9. The process according to any of the preceding claims, wherein clay is added as an additional material. 5

10. The process according to any of the preceding claims, wherein burnt oil shale is added as an additional material.

11. The process according to any of the preceding claims, wherein combustion residues from coal-fired power plants, which have a carbon content of less than 10 wt 10 %, are added as an additional material.

12. The process according to any of the preceding claims, wherein limestone is added as an additional material. 15

13. The process according to any of the preceding claims, wherein gypsum is added as an additional material.

14. The process according to any of the preceding claims, wherein the educt stream is preheated. 20

15. A process for producing cement or cement substitutes substantially as herein described with reference to the accompanying drawings and with reference to the Examples. 2732626_1 (GHMatters) P87075.AU 11/07/11