Carbon neutral cement

Abstract

A system for producing carbon neutral cement comprising: a carbon neutral energy source; a limekiln comprising a vessel for containing limestone, an inlet for the introduction of limestone into the ve

Description

This invention relates to a system and method for the production of cement and in particular carbon neutral cement. The term “system” is used herein to mean an arrangement of apparatus and, while some of the component parts of the apparatus are conventional and / or known per se, the particular assemblage is novel and wholly inventive. Further, the phrase “carbon neutral” is used herein to mean that the amount of carbon dioxide produced during the process is balanced and negated by the subsequent absorption or capture of an equivalent or even greater quantity of carbon dioxide by calcium oxide produced by the process and / or conversion of carbon dioxide using processes as discussed herein. Carbon neutrality must be distinguished from carbon offsetting; in contrast to carbon neutrality, the process of offsetting requires a reduction in emissions of carbon dioxide to compensate for emissions made elsewhere. Carbon offsetting is subject to the fundamental moral principles of the individuals involved and is fundamentally flawed; there are various investigations and reports that show that even gold and platinum carbon offset schemes are faulty, and in some cases, they are simply scams. Essentially, the financial value of carbon offsets does not cover the sum needed to make processes carbon neutral. In essence, “carbon offset” does not equate to “carbon neutral” or “zero emissions”. Cement is the second largest consumable in the world after water. Conventional cement production is energy intensive and requires the use of fossil fuels and the creation of carbon dioxide. Fossil fuels are non-renewable energy sources. The combustion of fuel manufactured from crude oil creates large quantities of greenhouse gases. With increasing concerns of climate change due to greenhouse gases, there is a need to reduce the amount of air pollution caused by the combustion of fuels and by industrial manufacturing processes. Due to the limited number of oil reserves, it is necessary to transport large quantities of oil from the oil reserves to the consuming areas, often over great distances. The transportation of such oil inevitably enhances the problem of pollution. The environmental impact of carbon dioxide has been a growing concern and the need to reduce such emissions increasingly prevalent. Scientists devoting their lives to, and specialising in, climate science warn us that climate change is the largest of all threats that could bring about the extinction of humankind. Of all living scientists, most now agree that climate change is one of the very largest risks to our continued existence as a species. It is incumbent upon all, including innovators and all those involved in the protection of new ideas to try to do all that we can to encourage solutions that will help in the fight against climate change for the sake of all humanity. In an attempt to reduce fossil fuel use and eliminate pollution caused by the burning of such fuels, there is an increasing need for sustainable energy sources. Processes for producing synthetic fuels using carbon dioxide and hydrogen are well established. However, obtaining carbon dioxide directly from the atmosphere is not only expensive but is also problematic in that the extraction process creates yet more pollution. To address the foreseeable problems associated with global warming, the process of carbon sequestering is used to capture and supposedly store atmospheric carbon dioxide. Again, this process avoids dealing properly with the issue. Carbon dioxide has been found to leak from sequestration sites. As more carbon dioxide is sequestered, there will be more leakage affecting future generations, which defeats the object of trying to make things better for future generations. Several methods have been proposed to deal with atmospheric carbon dioxide, as an alternative to sequestration. One of those proposals is the conversion of carbon dioxide into carbon and oxygen. The process of splitting carbon dioxide is achievable but requires large amounts of energy. Under the principles of thermodynamics, if that energy is supplied by hydrocarbon fuels the net result will be more carbon dioxide than from the outset. Catalysts effectively to convert carbon dioxide into carbon monoxide and oxygen or hydrogen have been identified. Such catalysts have been shown to provide highly effective results, but the process requires large amounts of energy, making such conversion inefficient in practice. It is a principal aim of the present invention to address the environmental damage caused by fossil fuels and the conventional methods of cement production to provide apparatus and a method for producing carbon neutral cement. The invention aims to address the adverse effects of harmful emissions in the manufacture of cement, and so have a smaller impact on the environment and climate change. According to a first aspect of this invention, there is provided a system for producing carbon neutral cement comprising: - a carbon neutral energy source; - a limekiln comprising a vessel for containing limestone, an inlet for the introduction of limestone into the vessel, a heater arranged within the vessel for heating said limestone within the vessel, and an outlet for the release of calcium oxide and carbon dioxide yielded by the heated limestone; and - a cement plant operatively connected to the limekiln outlet to receive calcium oxide therefrom and operatively connected to the energy source, the energy source being configured to provide heat energy and / or electrical energy to the cement plant; wherein the cement plant is configured to process received calcium oxide with clay and one or both of received heat energy and electrical energy, thereby to produce cement. Heat and / or electrical energy may also be supplied from other sources such as those described in earlier patent publications of the applicant. According to a second but closely related embodiment, there is provided a method of producing carbon neutral cement comprising: - providing a carbon neutral energy source; - heating limestone in a vessel of a limekiln, the limekiln having an inlet for the introduction of limestone into the vessel, a heater arranged within the vessel for heating said limestone within the vessel, and an outlet for the release of calcium oxide and carbon dioxide yielded by the heated limestone; and - processing in a cement plant calcium oxide from the limekiln with clay and one or both of heat energy and electrical energy from the energy source to produce cement. The method of producing carbon neutral cement of the present invention utilises the system for producing carbon neutral cement of the invention. As such, features of the method and system shall be discussed collectively and shall relate to both. Calcination of limestone by heating releases carbon dioxide and produces calcium oxide (referred to hereinafter as quicklime). Quicklime produced by the heating of limestone may be collected from the limekiln and used to absorb carbon dioxide from the atmosphere. Such quicklime could be used in vehicle exhaust filters or along motorways or other areas of high carbon dioxide pollution in order to absorb the carbon dioxide. Additionally, or alternatively, the quicklime could be made into mortar-like slabs which could be utilised in sea defences, new quays and the like. Quicklime is particularly good at absorbing carbon dioxide when placed in water and this could be especially beneficial in coastal projects. In fact, quicklime is able to absorb up to twice the carbon dioxide produced in its formation when it is placed in water; thus, quicklime could be used in the sea and coastal works or sewage schemes, to counter any excess carbon dioxide resulting from the system and / or make the system carbon negative. The energy source must be carbon neutral to ensure that the overall system remains net zero. The carbon neutral energy source may comprise carbon neutral electricity from the national grid, such as that described in the Applicant’s UK Patent publication No. 2 477 376. Alternatively, the energy source may be a carbon neutral synthesis gas. This synthesis gas may be generated by a carbon neutral underground fossil fuel seam gasification process, such as that described in the Applicant’s earlier UK Patent Publication No. 2 614 525 or may be generated by processing plastic waste, as described in the Applicant’s earlier UK Patent Publication No. 2 588 414. In one arrangement, the heater of the limekiln may be in communication with the carbon neutral energy source so that at least a portion of the energy is supplied to the heater to facilitate the heating of limestone within the limekiln. Where the energy source is a synthesis gas, an outlet may be provided for the heat energy and the limekiln and / or cement plant may be operatively connected to the outlet such that at least a portion of the heat energy produced by the carbon neutral energy source is transferred thereto. In this way, the heater of the limekiln may be in communication with the outlet so that synthesis gas is supplied directly to the heater to facilitate the heating of limestone within the limekiln. Where the carbon neutral source comprises synthesis gas, the system may further comprise a furnace for combusting the synthesis gas to produce hot gas. The outlet for the heat energy may be configured to transfer hot gas from the furnace to the limekiln. In this arrangement, the heater of the limekiln may be in communication with the outlet so that hot gas from the furnace is supplied directly to the heater to facilitate the heating of limestone within the limekiln. The heater of the limekiln may be an electrical resistance heating element powered by electricity. In this way the heater may be powered by carbon neutral electricity from the national grid. Where the carbon neutral energy source comprises synthesis gas, the system may additionally comprise a heat exchange arrangement for transferring heat from the carbon neutral power source to steam. This may comprise a boiler for converting water to steam, the boiler having an inlet for the introduction of water and an outlet for the steam. In this arrangement a turbine-driven generator set may be provided and means to direct the steam to the turbine of the generator set for the production of electricity. In this way, electricity may be supplied to the heater of the limekiln from the turbine driven generator set. The outlet for the heat energy may be configured to transfer synthesis gas directly to the cement plant to provide heat thereto. Alternatively or additionally, the outlet may be configured to transfer hot gas from the furnace to the cement plant. The cement plant may require very high temperatures (to above 1,450°C) in order to operate efficiently. To meet the temperature demands of the cement plant, or indeed other parts of the system, such heat may be obtained by carbon neutral electricity derived from the national grid. Alternatively (or additionally) the required heat may be obtained by electricity derived from the turbine driven generator set. The heater of the limekiln may be capable of receiving heat energy directly from synthesis gas or hot gas from the furnace and also comprise an electrical heating element to provide additional heat within the limekiln. In such an arrangement if the heat produced by the synthesis gas or hot gas from the furnace is too low, a portion of the synthesis gas or hot gas may be supplied directly to the heater to facilitate the heating of limestone within the limekiln with the remainder of the synthesis gas or hot gas being directed to the boiler to create steam. That steam may then be transferred to the turbine for the production of electricity in order to power the electrical heating element and thus further heat the limestone within the limekiln and also in order to power the limekiln. The system and process of the present invention will inevitably produce carbon dioxide, particularly the processing of limestone in the limekiln. One option for processing the carbon dioxide may be to utilise carbon curing of concrete - a known process involving the injection of waste carbon dioxide into cement in the making of concrete to increase its compressed strength. As an alternative or additional option, the system may further comprise a carbon curing plant configured to receive carbon dioxide produced by the system, the carbon curing plant comprising sand and / or clay to absorb the carbon dioxide. Sand and / or clay contains silica which will absorb carbon dioxide. The same sand and / or clay could be used to assist in the production of cement in the cement plant. Preferably, olivine sand, formed by grinding the mineral Olivine, could be used further to improve the process. Olivine is a relatively inexpensive resource and is particularly effective in absorbing carbon dioxide, absorbing approximately its own weight. The carbon curing plant may thus comprise olivine sand to absorb received carbon dioxide. Excess carbon dioxide produced by the system could be converted to greenhouse neutral gasses. Preferably, it would be advantageous if carbon dioxide could be processed further to ensure that that the system is carbon neutral, and this is possible within the system described hereinafter. Excess carbon dioxide from the process will be pure and measuring and collecting this from the limekiln should be relatively straightforward. This excess can be sequestrated or used in making fuels or other processes on the basis that a proportional amount of calcium oxide produced by the process can be used in marine projects where almost twice the amount of carbon dioxide can be absorbed than the carbon dioxide produced by the system of the present invention. Alternatively, or additionally, this excess carbon dioxide can be processed in the plant described herein to make the whole process carbon neutral if that is what is required. In one method of the present invention 70% of quicklime produced may be sold at world price and 70% of carbon dioxide produced may be sold to industry as carbon neutral carbon dioxide. In this way it is possible to achieve an equilibrium with a percentage of carbon dioxide produced being absorbable by an equivalent quantity of produced quicklime. The remaining 30% of carbon dioxide produced may be utilised in the carbon curing of concrete, as discussed above. The cement plant may be configured to receive the remaining 30% of quicklime produced by the heating of limestone. In an alternative method, which does not utilise a 70%-30% division discussed above, the system of the present invention may further comprise an electrolysis plant arranged to receive excess carbon dioxide produced by the system and to convert the carbon dioxide into carbon and oxygen by electrolysis. The splitting of carbon dioxide into carbon and oxygen is energy intensive, but by utilising energy derived from elsewhere in the system, the process becomes viable. The electrolysis plant may be powered by the carbon neutral energy source. The electrolysis plant may be operatively connected to the furnace to receive excess carbon dioxide and / or heat produced by the combustion of synthesis gas. Alternatively, or additionally, the electrolysis plant may be operatively connected to the limekiln to receive excess carbon dioxide and / or heat produced by the calcination of limestone. Heat reclamation from the system can therefore be used to assist the conversion process in the electrolysis plant. The electrolysis plant may be operatively connected to the turbine and / or the electrical energy source to receive electricity produced thereby to facilitate the conversion process. In an alternative arrangement or in addition to some or all of the methods hereinbefore described in relation to the processing of excess carbon dioxide, the system of the present invention may include means for the processing of excess carbon dioxide into useful carbon-based products. Electricity, excess heat and / or excess steam produced by the system can be utilised for this purpose. There are known processes for the processing of carbon dioxide into carbon neutral products. A selection of those is summarised, as follows: • Researchers at George Washington University have developed a process for the production of carbon wool which can be utilised in the same way as conventional carbon fibres; the process involves the use of sunlight to power apparatus which uses molten electrolysis to produce a carbon nanotube material that can be developed into carbon fibres. Instead of sunlight power, electricity from the plant can be used for this purpose. • Other processes include the combining of carbon dioxide with waste products to form nanoparticles which are subsequently used as additives in the formation of other materials, such as concrete, and material coatings. • Additional processes being established include methods for combining carbon dioxide with a microorganism which extracts the carbon therefrom. The carbon can then be processed with hydrogen and oxygen to produce a synthetic PHA-based biopolymer material which is formed into capsules and can subsequently be melted and formed into desired shapes. • Further processes now exist for this purpose and these do not need to be listed here. It is not controversial to believe that there will be new processes discovered in the future to achieve this desired effect. The present invention utilises power obtained from a carbon neutral energy source to produce carbon neutral carbon dioxide and calcium oxide. The carbon dioxide may be utilised in carbon curing and / or sold to industry (as carbon neutral carbon dioxide) or may be processed by electrolysis in order to produce oxygen and solid carbon products, such as carbon fibre, carbon black, graphene or synthesised diamonds. The calcium oxide may be used in the environment to absorb carbon dioxide and / or may be processed with clay in order to form carbon neutral cement. By way of example only, embodiments of this invention will now be described in detail, reference being made to the accompanying drawings in which:- Figure 1 is a simplified diagram of a first embodiment of the system for producing carbon neutral cement of the present invention; Figure 2 is a simplified diagram of a second embodiment of the system for producing carbon neutral cement of the present invention; and Figure 3 is a more detailed diagram of the second embodiment of Figure 2. Referring initially to Figure 1, a first embodiment of system 10 of the present invention is shown. The system 10 includes a carbon neutral energy source 11 which comprises carbon neutral synthesis gas 12 or carbon neutral electricity. Where the carbon neutral energy source comprises synthesis gas 12, the system 10 includes a furnace 13 to combust the synthesis gas 12. The furnace 13 is operatively connected to a limekiln 14 such that hot exhaust gasses 15 are directed thereto. The limekiln 14 is provided for the production of calcium oxide (referred to hereinafter as quicklime 16) from limestone 17. Calcination of limestone 17 by heating releases carbon dioxide 18 and produces quicklime 16. The limekiln 14 is provided with an inlet 19 for the introduction of limestone 17 into an outer vessel 20 of the limekiln 14, an outlet 21 for the release of carbon dioxide 18 and an outlet 22 for the release of quicklime 16. Co-axially within the outer vessel 20 is an inner chamber 23, having a heater 24, which is arranged to receive hot exhaust gas 15 from the furnace 13 for heating limestone 17 in the outer vessel 20. Carbon dioxide 18 produced by the limekiln 14 is pure, because it is not polluted with combustion gases as is the case with a conventional limekiln, and can be sold to industry and carbon dioxide generated by such industrial use, can be absorbed by quicklime 16 expelled from the limekiln 14. Alternatively, or additionally carbon dioxide may be used in the process of carbon curing of concrete. In the system shown in Figure 1, 70% of quicklime 16 produced is to be sold at world price 25 and 70% of carbon dioxide 18 produced is to be sold to industry as carbon neutral carbon dioxide 26; an equilibrium 27 is achieved in this arrangement with a percentage of carbon dioxide 18 produced being absorbable by an equivalent quantity of produced quicklime 16. The remaining 30% of carbon dioxide 18 produced may be utilised in the carbon curing of concrete 28. The system 10 includes a cement plant 30 which is connected to the quicklime outlet 22 and configured to receive the remaining 30% of quicklime 16 produced by the heating of limestone 17. The cement plant 30 includes an inlet 31 for the introduction of clay and / or sand 32 therein for the processing of the quicklime 16 to produce cement 33. The cement plant 30 is operably connected to the energy source 11 and is configured to receive heat energy and / or electrical energy therefrom. This is shown as hot gas 15 produced by the combustion of carbon neutral synthesis gas 12 in the furnace 13 provided directly to the cement plant 30. An alternative arrangement is illustrated in figures 2 and 3 where the system also includes a turbine generator set 40 for the provision of electrical energy to the cement plant 30 in the form of electricity 48 produced by the turbine generator set 40. Where a turbine generator set 40 is provided, the system of Figures 2 and 3 include a boiler 41. The boiler 41 receives heat from the furnace 13 to convert water 49 into steam 50. The turbine-driven generator set 40 is arranged to receive steam 50 from the boiler 41 and is configured to generate electricity 48 for supply elsewhere in the system. Carbon dioxide 18 produced by the method of the present invention can be processed in various ways. The system shown in Figures 2 and 3 comprises an electrolysis plant 45, arranged to receive carbon dioxide 18 produced by the limekiln 14 and from the furnace 13, to convert the carbon dioxide 18 into carbon 46 and oxygen 47 by electrolysis. Such processes are known by those skilled in the art and are thus not discussed in detail herein. The electrolysis plant 45 is powered by electricity 48 produced by the turbine-driven generator set 40. As with the system illustrated in Figure 1, the quicklime 16 produced by the kiln 14 5 shown in Figures 2 and 3 may be used in the environment 25 to absorb carbon dioxide and may be processed with clay 32 in order to form carbon neutral cement 33. In all arrangements the systems may also incorporate a carbon curing plant 28 which is arranged to receive carbon dioxide 18 produced by the system. 10 Sand and / or clay 32 within the carbon curing plant 28 absorbs the carbon dioxide 18 as they contain silica. The same sand / clay 32 may then be used within the cement plant 30 of the system. The system may be configured to include one or more of the additional features without departing from the invention. The inventive concept relies upon 15 the clever carbon neutrality and potential carbon negative effects which result from the particular configuration.

Claims

1. A system for producing carbon neutral cement comprising:- a carbon neutral energy source;- a limekiln comprising a vessel for containing limestone, an inlet for the introduction of limestone into the vessel, a heater arranged within the vessel for heating said limestone, and an outlet for the release of calcium oxide and carbon dioxide yielded by the heated limestone; and- a cement plant operatively connected to the limekiln outlet to receive calcium oxide therefrom and operatively connected to the energy source, the energy source being configured to provide heat energy and / or electrical energy to the cement plant;wherein the cement plant is configured to process received calcium oxide with clay and received heat energy and / or electrical energy, thereby to produce cement.

2. A system as claimed in claim 1, wherein the heater of the limekiln is in communication with the energy source to supply heat and / or electrical energy to the heater.

3. A system as claimed in claim 1 or claim 2, wherein the energy sourcecomprises a carbon neutral synthesis gas generated by a carbon neutral underground fossil fuel seam gasification process.

4. A system as claimed in claim 1 or claim 2, wherein the energy source comprises a carbon neutral synthesis gas generated by a carbon neutral polymeric waste processing process.

5. A system as claimed in claim 3 or claim 4, further comprising a furnace configured to receive and combust the synthesis gas to produce hot gas.

6. A system as claimed in claim 5, wherein the furnace is operatively connected to the limekiln such that at least a portion of the hot gas is transferred to the heater of the limekiln.

7. A system as claimed in claim 5 or claim 6, wherein the furnace is operatively connected to the cement plant such that at least a portion of the hot gas is transferred to the cement plant.

8. A system as claimed in any of claims 5 to 7 further comprising a boiler for converting water to steam, the boiler being in thermal communication with the hot gas from the furnace and having an inlet for the introduction of water and an outlet for steam.

9. A system as claimed in claim 8, further comprising a turbine driven generator set connected to the boiler and means to direct at least a portion of the steam from the boiler to the turbine of the generator for the production of electricity.

10. A system as claimed in claim 9, wherein the heater of the limekiln comprises an electrical heating element powered by electricity produced by the turbine-driven generator set.

11. A system as claimed in claim 9 or claim 10, wherein the cement plant is powered by electricity produced by the turbine-driven generator set.

12. A system as claimed in any of the preceding claims, further comprising a carbon curing plant configured to receive carbon dioxide produced by the system, the carbon curing plant comprising olivine sand to absorb received carbon dioxide.

13. A system as claimed in any of the preceding claims, further comprising an electrolysis plant arranged to receive carbon dioxide produced by the system and to convert the carbon dioxide into carbon and oxygen by electrolysis.

14. A system as claimed in claim 13, wherein the electrolysis plant is operatively connected to the limekiln to receive excess carbon dioxide and / or heat produced by the calcination of limestone.

15. A method of producing carbon neutral cement comprising:- providing a carbon neutral energy source;- heating limestone in a vessel of a limekiln, the limekiln having an inlet for the introduction of limestone into the vessel, a heater arranged within the vessel for heating said limestone within the vessel, and an outlet for the release of calcium oxide and carbon dioxide yielded by the heated limestone; and- processing in a cement plant calcium oxide from the limekiln with clay and one or both of heat energy and electricity from the energy source to produce cement.

16. A method as claimed in claim 15, further comprising the step of combusting in a furnace carbon neutral synthesis gas, generated by a carbon neutral underground fossil fuel seam gasification process, to produce hot gas.

17. A method as claimed in claim 15, further comprising the step of combusting in a furnace carbon neutral synthesis gas, generated by a carbon neutral polymeric waste processing process, to produce hot gas.

18. A method as claimed in claim 16 or claim 17, further comprising the step of transferring produced hot gas to the heater of the limekiln to heat the limestone within the limekiln.

19. A method as claimed in any of claims 16, 17 or 18 wherein produced hot gas is passed from the furnace to the cement plant to provide heat energy therein.

20. A method as claimed in claim 15 to 19 wherein carbon dioxide is completely absorbed by olivine sand within the carbon curing plant.

21. A method as claimed in clam 20, wherein a portion of the carbon dioxide produced by the system is passed to the carbon curing plant and the remainder of carbon dioxide is sold.

22. A method as claimed in any of claims 15 to 21, wherein carbon dioxide produced by the system is passed to an electrolysis plant and is therein converted to carbon and oxygen by electrolysis.

23. A method as claimed in any of claims 15 to 22, wherein at least a portion of heat energy produced by the energy source is directed to heat water in a boiler to produce steam.

24. A method as claimed in claim 23, wherein the steam from the boiler is directed to a turbine of a turbine-driven generator set for the production of electricity; and wherein the heater of the limekiln is electrically powered by the turbine-driven generator set.

25. A method as claimed in claim 24, wherein the cement plant and / or the electrolysis plant is electrically powered by the turbine-driven generator set.A

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