Calcination process
Described is the use of a mineral comprising a metal carbonate fraction and a fuel fraction, such as oil shale or coal shale, in a calcination process. The disclosed process can advantageously result in carbon dioxide being removed from the atmosphere. Further, in the process, heat energy generated during calcination can be used to separate oxygen from air, so that the oxygen can be fed back into the system. Alternatively or in addition, heat energy may also be used to compress the gaseous carbon dioxide generated from the calcination process.
1 . A process comprising:
(a) providing a mineral comprising a metal carbonate fraction and a fuel fraction, wherein the fuel fraction has a calorific value which is at least 50% of the energy needed to calcine the metal carbonate fraction, and combusting the mineral in the presence of oxygen, water vapour and carbon dioxide, to generate a metal oxide, water vapour, carbon dioxide and heat;
wherein the mineral is combusted in a mixture of gases comprising 5 to 20% by volume water vapour, 15 to 25% by volume oxygen, and 60 to 75% by volume carbon dioxide.
2 . A process according to claim 1 , wherein the fuel fraction of the mineral has a calorific value which is sufficiently high to enable to calcination of the entire carbonate fraction.
3 . A process according to claim 1 , wherein the mineral is oil shale or coal shale.
4 . A process according to claim 1 , wherein the metal carbonate fraction of the mineral comprises a group II metal, or a combination of group II metals.
5 . The process according to claim 1 , the process further comprising:
(b) for using the gene rated heat to:
(i) drive a gas se tion process which generates high purity oxygen from air, wherein the generated high purity oxygen is used in step (a); and/or
(ii) compress the carbon dioxide generated in step (a).
6 . A process according to claim 1 , wherein the mixture of gases in which the mineral is combusted comprises nitrogen at a level of 0 to 1% by volume of the gases.
7 . A process according to claim 1 , wherein the mixture of gases in which the mineral is combusted comprises flue gases recycled from step (a) and oxygen.
8 . A process according to claim 1 , wherein the combustion/calcination reaction takes place in the range of 800 to 1350° C.
9 . A process according to claim 5 , wherein the gas separation process of step (b)(i) occurs in a system selected from the group consisting of an Air Separation Unit (ASU), a Pressure Swing Adsorption (PSA) System, and a Vacuum Swing Absorption (VSA) process.
10 . A process according to claim 9 , wherein the gas separation process of step (b)(i) occurs in a Pressure Swing Adsorption (PSA) system.
11 . A process according to claim 1 , the process further comprising an additional step of sequestering the generated carbon dioxide.
12 . A process according to claim 11 , wherein the heat generated is used to both (i) drive a gas separation process which generates high purity oxygen from air and (ii) compress the generated carbon dioxide, in the process of sequestering the carbon dioxide.
13 . A process according to claim 5 , further comprising an additional step of causing hydration of the generated metal oxide to produce a metal hydroxide and heat.
14 . A process according to claim 13 , wherein the heat generated during hydration of the metal oxide is used to drive the generation of high purity oxygen and/or the compression of the carbon dioxide.
15 . A process according to claim 1 , wherein the oxygen and/or carbon dioxide used in the combustion reaction is at least 90% pure.
16 . Use of a process according to claim 1 in carbon dioxide sequestration.
17 . Use of a process according to claim 1 in oxygen generation.