Near zero-emissions method to produce lime and / or cement

Abstract

The invention relates to lime and cement production processes using a gaseous CO2 stream as heat transfer fluid. The processes incorporate a heat supply section, a calcination section and a power cycle section, in the heat supply section, an external heat supply is furnished to produce a first heated CO2 stream, which is fed into a reactor in the calcination section, the first heated CO2 stream serves as the principal heat carrier, driving a calcination reaction of limestone to form a heated lime product and releasing a heated CO2 stream from limestone, a combined first CO2 stream, second CO2 stream and heated CO2 stream from limestone are used to drive a power cycle in the power cycle section for power generation. A near zero emission can be achieved at a lower energy and cost penalty than a post-combustion CO2 capture and sequestration applied to conventional lime and cement production processes.

Description

[0001] NEAR ZERO-EMISSIONS METHOD TO PRODUCE LIME AND / OR CEMENT

[0002] Field of the Invention

[0003] The present invention relates to the production of lime and cement from limestone using a gaseous CO2 stream as heat transfer fluid. This invention facilitates CO2 sequestration without necessitating CO2 separation processes. Furthermore, power production using the CO2 stream from the entire production process has the potential for a surplus of power generation beyond meeting all process power requirements.

[0004] Background of the Invention

[0005] Lime is a versatile mineral. Various forms of lime are used in environmental, metallurgical, construction, chemical, industrial applications, and other applications. Lime can be combined with certain additives to produce other materials and is also a key ingredient in mortar and plaster in lime slurry form. Lime is also a key building block of cement.

[0006] Cement, sometimes referred to as Portland cement, is a key ingredient in concrete and has shaped much of the built environment, because concrete is the most widely used man-made material in existence. Cement is second only to water as the most-consumed resource on the planet.

[0007] Green House Gas (GHG) emissions from lime and cement industries are very high and no economically reasonable methods have been applied to limit these emissions. According to the data published by Chatham House, also known as the Royal Institute of International Affairs, an independent policy institute headquartered in London, cement is the source of about 8% of the world’s CO2 emissions.

[0008] Lime production process and the cement production process share a common chemical reaction that is at the heart of the GHG emissions in these industries. This shared chemical reaction is the calcination reaction, wherein limestone (CaCCL), subjected to a temperature of 840 °C, undergoes transformation to lime (CaO) while releasing CO2, as shown below:

[0009] CaCCh (solid limestone) + Heat —> CO2 (gas) + CaO (solid lime) The term “calcinations of limestone” refers to the process of thermal decomposition into quick lime and carbon dioxide. It is frequently referred to as “calcinations” or “lime calcination”.

[0010] Dolomite, containing both calcium and magnesium carbonates, can also be used as a fraction of the feedstock, depending upon the requirements of the final product. Dolomite is in the same family as limestone and shares similar CO2 emission, as shown below:

[0011] CaMg (CO3)2(s) + Heat 2CO2(g) + MgO(s) +CaO(s)

[0012] The existing lime and cement production processes are air-fired direct contact processes.

[0013] In these existing processes, air-fired combustion generates flue gas, which comprises CO2, N2and moisture as shown below:

[0014] Combustion: CH4(g) + 2O2(g) + 7.52N2(g) CO2(g) + 2H2O(g) + Heat + 7.52N2(g)

[0015] The CO2generated from the calcination reaction then combines with the flue gas resulted from the air-fired combustion that also contains some CO2.

[0016] Calcination: CaCO3(s) + Heat —> CO2(g) + CaO(s)

[0017] As a result, the overall exhaust gas of the lime production process and the cement production comprises a mixture of CO2produced from the calcination reaction, and the CO2produced from the air-fired combustion.

[0018] To capture the CO2in the exhaust gas, post-combustion CO2capture technology, utilizing a chemical absorption-based process with aqueous amine solution, can be used. However, separating the CO2from the large amounts of nitrogen in the exhaust gas poses a considerable challenge. The post-combustion CO2capture technology involves high parasitic power consumption, making it energy inefficient and economically costly. For example, there are several problems associated with the post-combustion CO2capture and sequestration technology for the lime and cement production processes, including: • the exhaust gas needs to be scrubbed to remove particulate and impurities,

[0019] • moisture needs to be removed from the exhaust gas,

[0020] • treatment with amines and need to replenish the amines intermittently,

[0021] • post-combustion CO2 capture and sequestration equipment is complex and expensive.

[0022] Therefore, there is a continuous need for improving lime and / or cement production processes with more effective CO2 handling methods.

[0023] Summary of the Invention

[0024] According to the present invention, instead of using direct contact air-firing in the calcination reaction and cement formation, which introduces N2 and moisture into the CO2 stream resulting from the lime and cement production processes and complicate the CO2 capture, an external heat supply, achieved through fuel combustion or electrical heating, is employed.

[0025] This external heat supply is used to heat a stream of relatively pure CO2, which serves as the direct contact heat transfer fluid for the calcination reaction and cement formation. Subsequently, this heat transfer CO2 stream is straightforwardly mixed with the CO2 that is generated during the calcination and cement formation.

[0026] The heat transfer gaseous CO2 stream can be obtained in the following scenarios:

[0027] (1) The heat transfer CO2 stream is heated indirectly using a heat exchanger with the heat provided by an external heat supply, the external heat supply can be achieved through air-firing (where N2 will be present) or oxy-firing (with no N2 present) fuel combustion;

[0028] (2) The heat transfer CO2 stream is heated directly by an external heat supply, the external heat supply can be achieved through electrical heating or by using a near pure CO2 hot stream provided by oxy-firing (with no N2 present) fuel combustion. This heated gaseous CO2 stream then is in contact with the limestone directly and performs the calcination reaction and cement formation in a CO2 environment. In this manner, the CO2, produced from the calcination reaction and cement formation, mixes with the hot CO2 fluid which is resulted from the heated gaseous CO2 stream, thereby keeping the exhaust gas as pure with CO2 as possible so as to enable the ease of CO2 sequestration without the need for CO2 separation. Furthermore, power production using the CO2 stream from the entire production process is realized through heat-to-power cycles.

[0029] As noted above in scenario (1) disclosed in the present invention, the case of using air-firing will require CO2 separation, and it will be limited to the combustion flue gas only.

[0030] In contrast, in other cases in the above two scenarios disclosed in the present invention, a relatively pure CO2 stream is produced, eliminating the need for CO2 separation when releasing the exhaust CO2 stream for sequestration.

[0031] According to the present invention, the lime and cement production processes incorporate an external heat supply to separate (i) the combustion of fuel side of the process from (ii) the lime calcination and cement process side, diverging from the conventional lime and cement production processes.

[0032] On the combustion of fuel side of this invention, or external heat supply side of this invention, there are the following options: a. Indirect air-firing heat supply, at ambient pressure or a pressure higher than ambient pressure, to produce an impure CO2 stream mixed with N2 and moisture, which is then treated with conventional post-combustion CO2 capture means to produce a pure CO2 stream, b. Indirect oxy-firing heat supply, at ambient pressure or a pressure higher than ambient pressure, to produce a pure CO2 stream without the need for CO2 separation, or c. Direct oxy-firing heat supply, at ambient pressure or a pressure higher than ambient pressure, to produce a pure CO2 stream without the need for CO2 separation, the resulted pure CO2 stream is then mixed with the CO2 stream from calcination reaction and cement formation. All resulting CO2 streams are suitable for treatments such as compression, dehydration, O2 scavenging, and sequestration.

[0033] Furthermore, on the lime and cement side of this process, all resulting CO2 streams from the calcination reaction and cement formation are relatively pure and suitable for additional utilization, including feedstock preheating, power production and products cooling, as well as for treatments such as compression, dehydration, O2 scavenging, and sequestration.

[0034] According to one aspect of the invention, there is provided a lime production process incorporating a heat supply section, a calcination section and a power cycle section, wherein: a first CO2 stream is circulated among the heat supply section, the calcination section and the power cycle section, a second CO2 stream is circulated between the calcination section and the power cycle section, in the heat supply section, an external heat supply is furnished to heat the first CO2 stream, the first heated CO2 stream is fed into a reactor in the calcination section, the first heated CO2 stream serves as the principal heat carrier, driving a calcination reaction of limestone (CaCCh) to form a heated lime product (CaO) and releasing a heated CO2 stream from limestone, a combined first CO2 stream, second CO2 stream and heated CO2 stream from limestone are used to drive a power cycle in the power cycle section for power generation resulting in a cooled CO2 stream, and the second CO2 stream as part of the cooled CO2 stream is used to cool the lime product while being heated and returned to the calcination section for temperature moderation, the cooled CO2 stream from limestone exits for sequestration after compression, the power cycle section provides power for compression and other requirements

[0035] According to an embodiment of the invention, the external heat supply is indirect air-firing at ambient pressure or a pressure higher than ambient pressure, to produce a combustion product, the combustion product treated with a post-combustion CO2 capture means to produce a pure CO2 stream for sequestration. According to another embodiment of the invention, the external heat supply is indirect oxy- firing, at ambient pressure or a pressure higher than ambient pressure, to produce the first heated CO2 stream, the combustion product requires no CO2 capture and is suitable for power production. The combustion product is suitable for CO2 compression, dehydration, O2 scavenging, and CO2 sequestration.

[0036] According to an embodiment of the invention, the external heat supply is direct oxy -firing, at ambient pressure or a pressure higher than ambient pressure, to produce the first heated CO2 stream.

[0037] According to an embodiment of the invention, temperature for the calcination reaction is 875 °C and above.

[0038] According to another aspect of the invention, there is provided a cement production process, wherein a third CO2 stream circulates among the heat supply section, a Portland cement kiln and the power cycle section, the heated lime product produced in the calcination section as described above is fed into a Portland cement kiln, with the addition of aluminosilicate materials to produce a mixture, the mixture is heated by the third CO2 stream to produce a heated clinker, the heated clinker is fed into a clinker cooler to produce a cold clinker and processed through a clinker grinder to produce a Portland cement.

[0039] According to an embodiment of the invention, the third CO2 stream utilizes the same external heat supply as the first CO2 stream, and the CO2 stream released from the cement production process follows the same pathways for power generation and sequestration as the CO2 stream released from the calcination reaction, the power cycle section provides power for CO2 compression and other requirements.

[0040] According to an embodiment of the invention, in the cement production process, the mixture is heated to about 1450 °C and above to produce the heated clinker.

[0041] Other features and advantages of the present invention will become apparent from the following detailed description and the accompanying drawings, which illustrate, by way of example, the principles of the invention. Brief Description of the Drawings

[0042] By way of example only, embodiments of the present invention are described hereinafter with reference to the accompanying drawings that define the CO2 streams, wherein:

[0043] Figure 1 is a schematic representation of an embodiment of a lime production process with an external air-firing furnace which indirectly heats the first CO2 stream according to the present invention,

[0044] Figure 2 is a schematic representation of an embodiment of a lime production process with an external oxy-firing furnace which indirectly heats the first CO2 stream according to the present invention,

[0045] Figure 3 is a schematic representation of an embodiment of a lime production process with an external oxy-firing furnace which directly heats the first CO2 stream according to the present invention,

[0046] Figure 4 is a schematic representation of an embodiment of a cement production process with an external air-firing furnace which indirectly heats the first and the third CO2 streams according to the present invention,

[0047] Figure 5 is a schematic representation of an embodiment of a cement production process with an external oxy-firing furnace which indirectly heats the first and the third CO2 streams according to the present invention, and

[0048] Figure 6 is a schematic representation of an embodiment of a cement production process with an external oxy-firing furnace which directly heats the first and the third CO2 streams according to the present invention.

[0049] Detailed Description of the Invention

[0050] It is to be understood that the disclosure is not limited in its application to the details of the embodiments as set forth in the following description. The invention is capable of other embodiments and of being practiced or of being carried out in various ways. By way of example only, preferred embodiments of the present invention are described hereinafter with reference to the accompanying drawings.

[0051] Furthermore, it is to be understood that the terminology used herein is for the purpose of description and should not be regarded as limiting. Contrary to the use of the term “consisting,” the use of the terms “including”, “containing”, “comprising”, or “having” and variations thereof is meant to encompass the items listed thereafter and equivalents thereof as well as additional items. The use of the term “a” or “an” is meant to encompass “one or more.”

[0052] Fuel is a solid, liquid, or gaseous hydrocarbon, or carbon, or hydrogen, or a mixture thereof. Biomass material or hydrogen when used as fuel has negative CO2 emissions. Carbon can be the waste carbon black generated from a natural gas pyrolysis system that produces hydrogen, or another source of carbon, such as petroleum coke. Electricity is also an energy resource.

[0053] Heat supply can be realized by fuel combustion with air (air-firing or air-fired), or fuel combustion with oxygen (oxy-firing or oxy-fired), or simply electrical heating.

[0054] Lime production process and cement production process share a common chemical calcination reaction. The difference is that cement formation requires additional ingredients of aluminosilicate and cementitious materials.

[0055] Lime Production Process

[0056] According to the present invention, the lime and cement production processes incorporate an external heat supply to separate (i) the combustion of fuel side of the process from (ii) the lime calcination and cement process side, diverging from the conventional lime and cement production processes.

[0057] By implementing this separation, CO2 from calcination (representing 60% of the CO2 emissions in conventional approaches) does not require CO2 separation. CO2 from fuel combustion (constituting 40% of the CO2 emissions) can undergo treatment with postcombustion CO2 capture and sequestration in the case of air-firing while requiring no CO2 separation in the case of oxy-firing. This approach improves the efficiency of the CO2 handling process which is more economical compared to other CO2 handling approaches.

[0058] As noted above, on (i) the combustion of fuel side (or the heat supply section) of this process, users have the following options: a. Indirect air-firing heat supply, at ambient pressure or a pressure higher than ambient pressure, to produce an impure CO2 stream, which is then treated with conventional post-combustion CO2 capture means to produce a pure CO2 stream, b. Indirect oxy-firing heat supply, at ambient pressure or a pressure higher than ambient pressure, to produce a pure CO2 stream without the need for CO2 separation, or c. Direct oxy-firing heat supply, at ambient pressure or a pressure higher than ambient pressure, to produce a pure CO2 stream without the need for CO2 separation, which is then mixed with the CO2 stream from calcination reaction and cement formation.

[0059] Furthermore, on (ii) the calcination side of this process (or the calcination section), the exhaust stream of the relatively pure CO2 from the calcination reaction is used to drive a power cycle for power generation (the power cycle section) resulting in a cooled relatively pure CO2 stream. Part of the cooled CO2 stream is used to cool the lime product or cement clinker depending on the product requirements and at the same time this CO2 stream is heated and returned to the calcination section for temperature moderation. Another part of the cooled CO2 stream is ready for additional treatments such as compression, dehydration, O2 scavenging, and sequestration.

[0060] List of the CO2 streams referenced in the Figures:

[0061] COi_l: The first CO2 stream circulates between the heat supply section and the calcination section, then to the power cycle section, and finally back to the heat supply section. CO2 I serves as a heat transfer fluid to drive the limestone calcination process.

[0062] CO2 2: The second CO2 stream circulates from the calcination section to the power cycle section. CO2 2 serves as a heat transfer fluid, cooling lime or cement clinker. C€>2_3: The third CO2 stream circulates from the heat supply section to the Portland cement kiln, then to the power cycle section, and finally back to the heat supply section. COi_3 serves as a heat transfer fluid, driving the Portland cement process.

[0063] CO2 L: The CO2 stream produced during calcination exits from the calcination section, enters the power cycle section, undergoes compression, and then exits for sequestration.

[0064] CO2_P: The CO2 stream produced during Portland cement process exits from the Portland cement kiln, enters the power cycle section, undergoes compression, and then exits for sequestration.

[0065] CO2_c: The CO2 stream produced during fuel combustion, exits from the furnace, enters the power cycle section, undergoes compression, and then exits for sequestration.

[0066] CO2_s: The CO2 stream circulates to convey fuel to the furnace.

[0067] CO2_f: The CO2 stream exits the furnace, a combination of CO2_c and CO2_s.

[0068] CO2_t: The total CO2 stream exits the calcination section, enters the power cycle section, and is used for power generation while being cooled with ambient coolant.

[0069] Figure 1 shows a lime production process where lime (CaO) is produced from limestone (CaCCh) with an external air-firing furnace (option a) which indirectly heats the first gaseous CO2 stream to provide the required heat for calcination reaction according to the present invention.

[0070] Referring to Figure 1, there are three (3) sections in this configuration: a heat supply section, a calcination section, and a power cycle section.

[0071] (1) In the heat supply section, there are the combustion of fuel that occurs in an airfiring furnace 10 and a post-combustion CO2 capture and sequestration process that captures the stream CO2 C from fuel combustion. (2) In the calcination section, there is shaft reactor 20 that has a preheating zone (with first stage preheat and second stage preheat), a calcination zone and a cooling zone (with first stage cooling and second stage cooling). A CO2 stream (CCh t) exits the reactor 20 at high temperature and enters the power cycle section.

[0072] (3) In the power cycle section, there is a heat-to-power Rankine cycle 30 or any heat- to-power process that produces power while cooling the C02_t stream.

[0073] A loop is used to transfer heat via the first CO2 stream (CO2 I) out of the cooled CCh t stream. This stream is blown to the heat supply section, where it undergoes indirect heating through the external air-firing furnace 10.

[0074] Subsequently, the heated CO2 I stream is returned to the calcination zone within the calcination section. The heated CO2 I stream serves as the principal heat carrier, driving the calcination reaction of CaCCh to form lime (CaO) and releasing CO2 in the calcination zone. The CO2 produced from the calcination reaction is CO2 L.

[0075] The required calcination temperature starts at around 875 °C under a pure CO2 environment for limestone according to a thermogravimetric analysis (TGA) test, which is higher than in air environment where it is approximately 840 °C.

[0076] The lime (CaO) stream, formed in the high temperature calcination zone, undergoes cooling through counter-flow interaction with the second CO2 stream (CO2_2) out of the cooled CO2_t, and exits as a product. The second CO2 stream (CO2_2) ascends to the calcination zone to moderate the calcination temperature. The combined C02_t stream, including CO2 L from calcination, the first CO2 stream CO2 I, and the second CO2 stream CO2_2, ascends to preheat the limestone feedstock at the upper part of the shaft reactor 20, passing through the preheat zone. Then the CO2J: stream enters the power cycle section again for cooling to near ambient temperature for power generation.

[0077] CO2 I and CO2_2 undergo circulation within the process, while CO2 L from calcination is pressurized via compressor 40 for sequestration purposes. The power required by the CO2 compressors is offset by the power generated in the power cycle section, with the possibility of surplus power generation beyond meeting all process power requirements. In shaft reactor 20, the stream CCh t flows upwards. It could be taken out before the preheat zone (dotted line), or after the preheat zone, or at different temperature points in the preheat zone according to the system energy balance. The cooled stream CC>2_2 enters the cooling zone and flows upwards. It could enter the cooling zone at different temperature points according to the system energy balance.

[0078] The process as shown in Figure 1 makes the green house gas emissions from calcination ready for compression and sequestration without the need for CO2 separation.

[0079] A post-combustion CO2 capture and sequestration process is only needed to be applied to the combustion side to capture CO2 C from fuel combustion, then a near zero emission can be achieved at a much lower energy and cost penalty than a post-combustion CO2 capture and sequestration that is applied to a conventional lime production process to capture not only the CO2 C from fuel (40% of GHG), but also the CO2 L from calcination (60% of GHG).

[0080] Figure 2 shows a lime production process where lime (CaO) is produced from limestone (CaCCF) with an external oxy-firing furnace (option b) which indirectly heats the first CO2 stream to provide the required heat for calcination according to the present invention.

[0081] Oxy-firing, or oxy-fuel combustion, is the process of burning a fuel using pure oxygen, or a mixture of oxygen and recirculated CO2 stream, instead of air. Since the nitrogen component of air is no longer present, a pure CO2 stream is produced, fuel consumption is reduced, and higher flame temperatures are possible.

[0082] For instance, the combustion of solid carbon C(s) with oxygen O2 produces a CO2 stream as per the reaction below:

[0083] C(s) + O2(g) - CO2(g)

[0084] The oxy-firing can occur under ambient pressure or under a higher than ambient pressure, resulting in a near pure CO2 stream at ambient pressure or pre-pressurized. Therefore, the combustion GHG emissions CO2 is ready for sequestration without separation, and a prepressurized CO2 stream can reduce power consumption of the CO2 compressor. For the same amount of fuel, oxy-firing produces a higher flame temperature than air-firing, compensating for the higher starting temperature (-875 °C) required by calcination under a pure CO2 environment.

[0085] The lime production process in Figure 2 keeps the same configuration for the calcination section and the power cycle section as depicted in Figure 1.

[0086] In Figure 2, however, the heat supply section uses oxy-firing to produce a pure CO2 stream (CO2 C) from fuel combustion, and an air separation unit (ASU) 60 is employed to produce oxygen. A recirculation CO2 stream (CO2_s) is used to convey solid fuel to furnace 10. Subsequently, a power cycle 30a is integrated to produce power while cooling the combined CO2_f stream (CO2_c + CO2_s) before undergoing compression, dehydration, O2 scavenging and sequestration. The power generated from the power cycle 30a can compensate for the power consumed by the compressor in the heat supply section. When combined with the power generated from the power cycle 30 within the power cycle section, it offsets the power required by the CO2 compressors and the air separation unit 60, potentially resulting in a surplus of power generation beyond meeting all process power requirements.

[0087] In the configuration depicted in Figure 2, nearly 100% of CO2 produced by the entire production process can be sequestrated without the need for CO2 separation.

[0088] The configurations in Figure 1 and Figure 2 allow dehydration and O2 scavenging to be applied only to the combined CCh f stream from the combustion.

[0089] There is the option to keep the CO2 I heating loop in Figure 1 and Figure 2 at ambient pressure, or at a higher than ambient pressure to increase the heat transfer rates to the calcination zone.

[0090] There is also the option to operate furnace 10 in Figure 1 and Figure 2 at ambient pressure, or at a higher than ambient pressure to increase the heat transfer rates in the furnace.

[0091] Figure 3 shows a lime production process where lime (CaO) is produced from limestone (CaCCh) with an external oxy-firing furnace (option c). This furnace directly heats a heat transfer CO2 stream to provide the required heat for calcination according to the present invention.

[0092] In the heat supply section of Figure 3, there is an oxy -firing furnace 50 used to combust fuel, such as carbon, to produce a pure CO2 stream (CCh c) as a result of the combustion process.

[0093] Unlike Figure 1 and Figure 2, where the heat supply section includes a process to deal with CO2 C or CO2_f streams from combustion separately, Figure 3 features a heat supply section containing only the oxy -firing furnace 50.

[0094] The CO2 I stream, acting as the principal heat carrier, is directly fed into the oxy-firing furnace 50 and mixed with CO2 C from the fuel combustion and the CO2 S conveying stream to reach the required temperature. The combined CO2 stream (CO2_1 + CO2_c + CO2_s) is then injected into the calcination zone in the shaft reactor 20, driving the calcination reaction of CaCCh to form lime (CaO) and release CO2. The CO2 C stream from fuel is included in stream C02_t, entering the power cycle section to produce power. Subsequently, it is directed along with stream CO2 L from calcination for dehydration, O2 scavenging, and sequestration. To prevent non-CCh gases from entering the oxy-firing furnace 50, liquefied CO2_s can be employed as a means to transport solid fuel into the oxy-firing furnace 50. The remaining configuration in Figure 3 remains unchanged from Figure 2.

[0095] In this setup, nearly 100% of CO2 produced by the entire production process can be sequestrated without the need for CO2 separation. The power generated from the power cycle 30 within the power cycle section offsets the power required by the CO2 compressors and the air separation unit 60, potentially resulting in a surplus of power generation in addition to meeting all process power requirements.

[0096] There is an option to operate the oxy-firing furnace 50 at ambient pressure, or at a higher than ambient pressure. This choice aims to increase the heat transfer rates in the furnace and calcination zone while also reducing the power consumption of compressor 40.

[0097] The configurations for limestone calcination and lime production in Figures 1, 2 and 3 result in a CO2 stream ready for sequestration. This eliminates the need for complicated and costly C02separation processes when using oxy-firing or reduces the required capacity of CO2separation when using air-firing.

[0098] The present invention provides the lime industry with a method to achieve the goal of zero carbon emissions. Furthermore, power production using the CO2 stream from the entire production process results in the potential for a surplus of power generation beyond meeting all process power requirements.

[0099] Cement Production Process

[0100] According to the present invention, a two-step process is used for cement production.

[0101] Figure 4 shows the cement production process, wherein cement is produced from limestone (CaCCh) using an external air-firing furnace 10. This furnace indirectly heats the first and the third CO2 streams to provide the required heat for calcination and cement formation according to the present invention.

[0102] This novel cement production process depicted in Figure 4 takes the hot lime (CaO) generated in the lime process shown in Figure 1 without cooling, adds the other cement ingredients, such as aluminosilicate materials in a Portland cement kiln 70, and then heats the mixture to around 1450 °C to produce molten / hot clinker. It is then fed into a clinker cooler 80 to produce cold clinker. This cold clinker can be further processed through a clinker grinder 90 to yield Portland cement. The cooled CO2_2 stream from the power cycle section is directed to the cement process to cool clinker instead of lime.

[0103] The heat supply section in Figure 4, containing an air-firing furnace 10 and a postcombustion CO2 capture process to capture CO2_c from fuel combustion, indirectly provides heat to the heat transfer CO2_1 stream for the calcination reactor 20 and the heat transfer CC>2_3 stream to the cement kiln 70. The cement kiln 70 can also use direct oxy-firing (indicated by dotted lines) to provide the necessary heat through a pure CO2 stream instead of relying on the CCh S stream from the air-firing furnace 10. Then the pure CO2 stream out of the cement production process, including CCh S. CO2_P that is produced in cement kiln 70, and CO2_2 stream out of clinker cooler 80, can join the CO2 stream out of the calcination reactor 20 and enter the power cycle section. The power cycle section is the same as that in Figure 1, except that the cooled CC>2_2 stream is used to cool clinker instead of lime. In this configuration, the CO2 stream produced by the cement formation process can be captured and sequestrated without the need for CO2 separation. The power generated from the power cycle 30 within the power cycle section offsets the power required by the CO2 compressors, potentially resulting in a surplus of power generation beyond meeting all process power requirements.

[0104] Figure 5 illustrates the cement production process, wherein cement is produced from limestone (CaCCh) using an external oxy-firing furnace 10. This furnace indirectly heats the first and the third CO2 streams to provide the required heat for calcination and cement formation according to the present invention.

[0105] The cement production process in Figure 5 maintains the same configuration for the calcination section and the power cycle section as in Figure 4.

[0106] In Figure 5, however, the heat supply section uses oxy-firing to produce a pure CO2 stream (CO2 C) from fuel combustion, and an air separation unit (ASU) 60 is employed to produce oxygen. Additionally, a recirculation CO2 stream (CO2_s) is used to convey solid fuel to furnace 10. Then a power cycle 30a is integrated to cool the combined CCh f stream before undergoing compression, dehydration, O2 scavenging and sequestration. The power generated from the power cycle 30a can compensate for the power consumed by the compressor in the heat supply section. When combined with the power generated from the power cycle 30 within the power cycle section, it offsets the power required by the CO2 compressors and the air separation unit 60, potentially resulting in a surplus of power generation beyond meeting all process power requirements.

[0107] In this configuration, nearly 100% of CO2 produced by the entire production process can be sequestrated without the need for CO2 separation.

[0108] The configurations in Figures 4 and 5 allow dehydration and O2 scavenging to be applied only to the combined CCh f stream from the combustion. There is the option to keep the CO2 I and CO2_3 heating loops in Figures 4 and 5 at ambient pressure, or a pressure higher than ambient pressure to increase the heat transfer rates to the calcination zone.

[0109] There is also the option to operate furnace 10 in Figures 4 and 5 at ambient pressure, or a pressure higher than ambient pressure to increase the heat transfer rates in the furnace.

[0110] Figure 6 shows a cement production process where cement is produced from limestone (CaCCh) using an external oxy-firing furnace. This furnace directly heats the first and the third CO2 streams to provide the required heat for calcination and cement formation according to the present invention.

[0111] Unlike Figures 4 and 5, where the heat supply section includes a process to handle CO2_c or CO2_f streams from combustion separately, Figure 6 features a heat supply section containing only the oxy-firing furnace 50. This furnace directly provides heat to the heat transfer CO2 I stream for calcination reactor 20 and heat transfer CCh S stream for cement kiln 70. The remaining elements are the same as in Figure 5, except that the CCh-f stream from fuel combustion is included in stream CCh t. CCh t then proceeds to the power cycle section to produce power through power cycle 30, which can be used for an air separation unit (ASU) 60 and a CO2 compressor 40, with the possibility of surplus power generation beyond meeting all process power requirements. In this configuration, nearly 100% of CO2 produced by the entire production process can be sequestrated without the need for CO2 separation.

[0112] To prevent non-CCh gas from entering the oxy-firing furnace 50, a liquefied stream CO2 S can be used to transport the solid fuel into the oxy-firing furnace 50.

[0113] There is the option to operate the oxy-firing furnace 50 at ambient pressure or a pressure higher than ambient pressure. This choice aims to increase the heat transfer rates in the furnace and calcination zone while also reducing the power consumption of compressor 40.

[0114] The configurations for limestone calcination and cement production in Figures 4, 5 and 6 result in a CO2 stream ready for sequestration. This eliminates complicated and costly CO2 separation processes when using oxy-firing or reduces the required capacity of CO2 separation when using air-firing. This invention provides the cement industry with a method to reach the goal of reducing carbon emission to zero. Furthermore, power production using the CO2 stream from the entire production process results in the potential for surplus power generation beyond meeting all process power requirements.

[0115] Although the present invention has been described in considerable detail with reference to certain preferred embodiments thereof, other embodiments and modifications are possible. Therefore, the scope of the appended claims should not be limited by the preferred embodiments set forth in the examples but should be given the broadest interpretation consistent with the description as a whole.

Claims

Claims:

1. A lime production process incorporating a heat supply section, a calcination section and a power cycle section, wherein: a first CO2 stream is circulated among the heat supply section, the calcination section and the power cycle section, a second CO2 stream is circulated between the calcination section and the power cycle section, in the heat supply section, an external heat supply is furnished to heat the first CO2 stream, the first heated CO2 stream is fed into a reactor in the calcination section, the first heated CO2 stream serves as the principal heat carrier, driving a calcination reaction of limestone (CaCCh) to form a heated lime product (CaO) and releasing a heated CO2 stream from limestone, a combined first CO2 stream, second CO2 stream and heated CO2 stream from limestone are used to drive a power cycle in the power cycle section for power generation resulting in a cooled CO2 stream, and the second CO2 stream as part of the cooled CO2 stream is used to cool the lime product while being heated and returned to the calcination section for temperature moderation, the cooled CO2 stream from limestone exits for sequestration after compression, the power cycle section provides power for compression and other requirements.

2. The lime production process according to claim 1, wherein said external heat supply is indirect air-firing at ambient pressure or a pressure higher than ambient pressure, to produce a combustion product to heat the first CO2 stream, the combustion product treated with a post-combustion CO2 capture means to produce a pure CO2 stream for sequestration.

3. The lime production process according to claim 1, wherein said external heat supply is indirect oxy-firing, at ambient pressure or a pressure higher than ambient pressure, to produce a combustion product to heat the first CO2 stream, the combustion product requires no CO2 capture and is suitable for power production.

4. The lime production process according to claim 3, wherein the combustion product is suitable for CO2 compression, dehydration, O2 scavenging, and CO2 sequestration.

5. The lime production process according to claim 1, wherein said external heat supply is direct oxy-firing, at ambient pressure or a pressure higher than ambient pressure, to produce the first heated CO2 stream.

6. The lime production process according to any one of claims 1 to 5, wherein temperature for the calcination reaction is 875 °C and above.

7. A cement production process, wherein: a third CO2 stream circulates among the heat supply section, a Portland cement kiln and the power cycle section, the heated lime product produced in the calcination section according to any one of claims 1 to 5 is fed into a Portland cement kiln, with the addition of aluminosilicate materials to produce a mixture, the mixture is heated by the third CO2 stream to produce a heated clinker, the heated clinker is fed into a clinker cooler to produce a cold clinker and processed through a clinker grinder to produce a Portland cement.

8. The cement production process according to claim 7, wherein the third CO2 stream utilizes the same external heat supply as the first CO2 stream according to any one of claims 1 to 5, and the CO2 stream released from the cement production process follows the same pathways for power generation and sequestration as the CO2 stream released from the calcination reaction, the power cycle section provides power for CO2 compression and other requirements.

9. The cement production process according to claim 7 or claim 8, wherein the mixture is heated to about 1450 °C and above to produce the heated clinker.

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