AU2003277947A1

AU2003277947A1 - Process for producing carbide lime

Info

Publication number: AU2003277947A1
Application number: AU2003277947A
Authority: AU
Inventors: Emilio Neil Menchetti (Deceased); Florindo Neil executor of the estate of Emilio Neil MENCHETTI Menchetti (deceased); Irene executor of the estate of Emilio Neil MENCHETTI MENCHETTI (deceased); Peter Danny executor of the estate of Emilio Neil MENCHETTI MENCHETTI (deceased)
Original assignee: CONCEPT NOMINEES Pty Ltd
Current assignee: CONCEPT NOMINEES Pty Ltd
Priority date: 2002-10-29
Filing date: 2003-10-29
Publication date: 2004-05-25

Description

WO 2004/039730 PCT/AU2003/001425 "Process for Producing Carbide Lime" Field of the Invention The present invention relates to a process for producing carbide lime. More particularly, the process of the present invention intended for use in the production 5 of carbide lime from carbide lime waste. Background Art Quicklime (CaO) is used in the manufacture of many chemicals, including calcium carbide (CaC 2 ) and hydrated lime (Ca(OH) 2 ). Calcium carbide is, in turn, used in the production of acetylene gas (C 2

H

2 ) by reaction with water. A by-product of 10 this reaction is a product conventionally known as carbide lime residue or waste. It is known that carbide lime waste can be used for raising alkalinity or increasing pH in some industrial applications. However, being a waste product, the material varies in terms of strength (i.e. CaO content) and the level of contaminants it carries. These inconsistencies make its use difficult and therefore the waste is 15 often discarded. There is a need for a process that converts carbide lime waste into a product useful as a replacement for hydrated lime in a variety of chemical and industrial applications. The method of the present invention has one object thereof to overcome 20 substantially, or at least provide a useful alternative to, the above-mentioned problems associated with the prior art. The preceding discussion of the background art is intended to facilitate an understanding of the present invention only. It should be appreciated that the discussion is not an acknowledgement or admission that any of the material 25 referred to was part of the common general knowledge in Australia as at the priority date of the application.

WO 2004/039730 PCT/AU2003/001425 -2 Throughout the specification, unless the context requires otherwise, the word "comprise", or variations such as "comprises" or "comprising", will be understood to imply the inclusion of a stated integer or group of integers but not the exclusion of any other integer or group of integers. 5 Disclosure of the Invention In accordance with the present invention there is provided a process for the production of carbide lime from carbide lime waste, the process comprising the step of: screening the carbide lime waste; 10 thereby producing carbide lime that may be utilised in place of hydrated lime, in chemical and industrial applications. Preferably, the screening of the carbide lime removes material over about 800 tm. In an alternative form of the invention, the screening of the carbide lime removes material greater than about 500 pm. In a further alternate form of the 15 invention, the screening of the carbide lime removes material greater than about 200 pim. The choice of particle screen sizes used in the process of the present invention is in large part dependent upon the initial particle sizes in the carbide lime waste and the intended final application of the carbide lime. However, removal of material 20 over a certain size is generally preferred. Preferably, the solids content of the carbide lime waste is between about 1 to 50 % by weight. More preferably, the solids content of the carbide lime waste is between about 1 to 20 %. Even more preferably, the solids content of the carbide lime waste is between about 2 to 12 %. 25 The process of the present invention may further comprise the additional step of: WO 2004/039730 PCT/AU2003/001425 -3 dilution or enrichment of the screened carbide lime to achieve a desired CaO content. Preferably, the desired CaO content is about 25 % by weight of the carbide lime. Preferably, the step of enriching the carbide lime is performed by settling the 5 solids, vacuum filtration, pressure filtration and/or hydration with quicklime and/or blending with hydrated lime for the purpose of beneficiation. The step of settling the solids may be performed by natural settling or assisted settling. In the context of the present invention, natural settling is understood to mean settling in a tank, dam, silo or other containment vessel or structure under the force of gravity. In 10 one particular form of natural settling, water is passed over the top of the vessel or structure and carbide lime is drawn from the bottom of the vessel or structure. The process of the present invention may further comprise the additional step of: addition of a flocculant to the screened carbide lime to increase the rate of settling. 15 The process of the present invention may further comprise the additional step of: stirring the screened carbide lime to increase the rate of settling. Where the process includes the step of stirring the carbide lime, the stirring is preferably conducted at a rate of between about 0.01 rpm to 5 rpm. In accordance with the present invention there is further provided carbide lime 20 prepared by the process as described hereinbefore. The particle size of the carbide lime is preferably no greater than about 800 Itm. In an alternate embodiment of the present invention, the particle size of the improved carbide lime is preferably no greater than about 500 pm. In another alternate embodiment, the particle size of the improved carbide lime is preferably 25 no greater than about 200 pm.

WO 2004/039730 PCT/AU2003/001425 -4 Preferably, the carbide lime may be used in place of hydrated lime in various industrial applications. In accordance with the present invention there is provided carbide lime prepared from carbide lime waste, wherein the carbide lime comprises particle sizes less 5 than about 800 pm. In an alternative form of the invention, the carbide lime comprises particle sizes less than about 500 ptm. In a further alternate form of the invention, the carbide lime comprises particle sizes less than about 200 pm. Preferably, the carbide lime has a CaO content of about 25 % of the carbide lime. In accordance with the present invention, there is provided an apparatus for the 10 production of carbide lime from carbide lime waste as described hereinabove. Brief Description of the Drawings A process for the production of carbide lime in accordance with the present invention will now be described, by way of example only, with reference to one embodiment thereof and the accompanying drawing, in which: 15 Figure 1 is a schematic flow diagram of a process for the preparation of an carbide lime in accordance with the present invention. Best Mode(s) for Carrying Out the Invention Those skilled in the art will appreciate that the invention described herein is amenable to variations and modifications other than those specifically described. 20 It is to be understood that the invention includes all such variations and modifications. The invention also includes all of the steps, features, compositions and compounds referred to or indicated in the specification, individually or collectively and any and all combinations or any two or more of the steps or features.

WO 2004/039730 PCT/AU2003/001425 In Figure 1 there is shown a process for the production of carbide lime 10 from carbide lime waste 12, in accordance with the present invention. The carbide lime waste 12 comprises CaO, water and one or more of a variety of contaminants. 5 The carbide lime waste 12 has a solids content of about I to 45% and a portion of its particle size distribution of greater than about 800 pm. The carbide lime waste 12 is firstly subjected to a screening step 14 to remove at least a portion of the larger particles present, providing a carbide lime product 10 with a consistent sizing of less than about 800 pm. The screening step 14 may be by way of, for 10 example, rotary or oscillating screening, liquid centrifuge classification and/or flotation. It is to be understood that use of any one or more of such devices is not to be considered to limit the scope of the present invention. The carbide lime is subsequently exposed to either a dilution 16 or enrichment 18 step to achieve a desired CaO content. It is envisaged that this step may be 15 conducted by any number of means, including dewatering by settling the solids, vacuum filtration, pressure filtration and/or dilution with water and/or hydration with quicklime and/or blending with hydrated lime for the purpose of beneficiation. The step of settling the solids may be performed by natural, settling or assisted settling. 20 The desired CaO content will be dictated by the final application of the improved carbide lime for example in water or effluent treatment. The carbide lime waste 12 varies in terms of consistency. For example, it may be collected directly from generators as a by-product of the production of acetylene. This type of carbide lime waste may contain large amounts of carbon and 25 unreacted calcium carbide that need to be removed in order to make the carbide lime a useable product. Carbide lime waste is often also stored in dams or other holding facilities for periods of time resulting in a product with increased solids content.

WO 2004/039730 PCT/AU2003/001425 -6 It is envisaged that the treatment of the carbide lime waste (i.e. the degree of screening and any subsequent dilution or enrichment steps) will be dependant on the nature of the carbide lime waste and the application of the finished product, for example fine pH control , waste water treatment or acid effluent neutralisation. 5 The process of the present invention is adapted to treat carbide lime waste from different sources with different properties in terms of solids content and particle sizes. Further, the process can be altered to provide carbide lime with different specifications depending on the final use of the carbide lime. The process of the present invention provides carbide lime that may be utilised in 10 place of commercially produced hydrated lime, in chemical and industrial applications. In particular, it is envisaged that the carbide lime may offer some benefits over commercially produced hydrated lime, for example a reduced acid insolubles content. The following Examples serve to more fully describe the manner of using the 15 above-described invention, as well as to set forth the best modes contemplated for carrying out various aspects of the invention. It is understood that these Examples in no way serve to limit the true scope of this invention, but rather are presented for illustrative purposes. Example I 20 An example of an application of the present invention is described below and details the preparation of carbide lime with about 35 % CaO to be used in effluent treatment with a process site restricted in area. Inflow of carbide lime waste was 120 L/min at an average of 4.2 % solids. The carbide lime waste was passed through a 0.5 m diameter rotary screen with a 25 mesh size of 800 pm. The resultant product was captured in a surge tank and fed into a cone thickener 2.5 m in diameter and 5.8 m tall. The rake speed was set at 0.02 rpm and the bed depth was between about 1.4 m and 1.6 m. Flocculant was introduced at a rate of 150 g per ton of solids. Underflow was WO 2004/039730 PCT/AU2003/001425 -7 drawn off at a rate of about 3 L/min to 6 L/min so as to maintain a bed depth of between 1.4 m and 1.6 m. The clear water ran into the overflows at the top of the cone and was returned to the process or a water storage area. The product was fed by the underflow pump into a storage tank to await distribution. 5 Example 2 An example of an application of the present invention is described below and details the preparation of carbide lime with about 25 % CaO to be used in water treatment with a process site unrestricted in area. Inflow of carbide lime waste was 270 L/min at an average of 12.2 % solids. The 10 carbide lime waste was passed through a 0.75 m diameter rotary screen with a mesh size of 200 pm. The resultant product was captured in a surge tank and fed into the first of two large settling tanks. The product was pumped into one end of the first tank and allowed to flow to the other end before flowing into the second tank via an overflow pipe. The product then travelled the full length to the other 15 end of the second tank before the clear water was returned to the process. At regular intervals the carbide lime was drawn from the bottom of the first tank and pumped into a storage tank to await distribution. Modifications and variations such as would be apparent to the skilled addressee are considered to fall within the scope of the present invention. 20

Claims

1. In accordance with the present invention there is provided a process for the production of carbide lime from carbide lime waste, the process comprising the step of: 5 screening the carbide lime waste; thereby producing carbide lime that may be utilised in place of hydrated lime, in chemical and industrial applications.

2. A process according to claim 1, wherein the screening of the carbide lime removes material over about 800 [tm. 10

3. A process according to claim 1 or 2, wherein screening of the carbide lime removes material greater than about 500 tm.

4. A process according to any one of the preceding claims, wherein screening of the carbide lime removes material greater than about 200 pm.

5. A process according to any one of the preceding claims, wherein the solids 15 content of the carbide lime waste is between about 1 to 50 % by weight.

6. A process according to any one of the preceding claims, wherein the solids content of the carbide lime waste is between about 1 to 20 % by weight.

7. A process according to any one of the preceding claims, wherein the solids content of the carbide lime waste is between about 2 to 12 % by weight. 20

8. A process according to any one of the preceding claims, wherein the process of the present invention may further comprise the additional step of: dilution or enrichment of the screened carbide lime to achieve a desired CaO content. WO 2004/039730 PCT/AU2003/001425 -9

9. A process according to claim 8, wherein the desired CaO content is about 25 % of the carbide lime.

10. A process according to claim 8 or 9, wherein the step of enriching the carbide lime is performed by settling the solids, vacuum filtration, pressure filtration 5 and/or hydration with quicklime and/or blending with hydrated lime for the purpose of beneficiation.

11.A process according to claim 10, wherein the step of settling the solids is performed by natural settling or assisted settling in a tank, dam, silo or other containment vessel or structure. 10

12.A process according to claim 11, wherein water is passed over the top of the vessel or structure and carbide lime is drawn from the bottom of the vessel or structure.

13.A process according to any one of the preceding claims, wherein the process of the present invention may further comprise the additional step of: 15 addition of a flocculant to the screened carbide lime to increase the rate of settling.

14.A process according to any one of the preceding claims, wherein the process of the present invention may further comprise the additional step of: stirring the screened carbide lime to increase the rate of settling. 20

15.A process according to claim 14, wherein the stirring is conducted at a rate of between about 0.01 rpm to 5 rpm.

16. Carbide lime prepared by the process according to any of claims I to 15.

17. Carbide lime prepared from carbide lime waste, wherein the particle size of the carbide lime is no greater than about 800 pm. WO 2004/039730 PCT/AU2003/001425 - 10

18.Carbide lime according to claim 17, wherein the particle size of the carbide lime is no greater than about 500 tm.

19.Carbide lime according to claim 17 or 18, wherein the particle size of the improved carbide lime is preferably no greater than about 200 pm. 5

20. Carbide lime according to any one of claims 17 to 19, wherein the carbide lime has a CaO content of about 25 % of the carbide lime.

21. Carbide lime according to any one of claims 17 to 20, wherein the carbide lime may be used in place of hydrated lime in various industrial applications.

22.A process for the production of carbide lime from carbide lime waste 10 substantially as hereinbefore described with reference to the accompanying drawing.

23.A process for the production of carbide lime from carbide lime waste substantially as hereinbefore described with reference to the accompanying examples. 15

24. Carbide lime substantially as hereinbefore described with reference to the accompanying drawing.

25.Carbide lime substantially as hereinbefore described with reference to the accompanying examples.