Limestone production

Abstract

The recycling and waste management process accepts municipal solid waste (MSW) with a substantial organic content and forms a self-sustaining hydrothermal mineralization (HTM) process based on supercritical water oxidation (SCWO), yielding supercritical steam and carbon dioxide with potential for power generation before forming calcium carbonate suitable for concrete production. Hydrothermal mineralization (HTM) rapidly removes organic waste and simultaneously produces a non-emission, thermally stable cement additive that acts as a carbon sink. Hydrothermal mineralization (HTM) provides a rapid disposal route for organic waste, a green power source, and final products that can be combined with conventional and alternative cement production to reduce the carbon footprint of cement production.

Description

[Technical Field]

[0001] Description of federally funded research and development: This invention was developed in collaboration with the U.S. government under contract number DE-EE0009507, granted by the Department of Energy. The government reserves certain rights in this invention. [Background technology]

[0002] background In recent decades, there has been growing concern about carbon dioxide emissions due to their negative impact on the environment. In particular, two industries are substantial sources of carbon dioxide emissions: (1) urban and industrial solid waste management and (2) cement production. Urban waste includes a significant amount of organic material, often referred to as organic urban solid waste (MSW). Cement production is the most energy-intensive stage of concrete production. Both of these processes involve carbon dioxide (CO2) that can be used for energy production and as raw materials for concrete production. [Overview of the Initiative] [Problems that the invention aims to solve]

[0003] overview The recycling and waste management process accepts municipal solid waste (MSW) with a substantial organic content and forms a self-sustaining hydrothermal mineralization (HTM) process based on supercritical water oxidation (SCWO), yielding supercritical steam and carbon dioxide with potential for power generation before forming calcium carbonate suitable for concrete production. Hydrothermal mineralization (HTM) rapidly removes organic waste while simultaneously producing a non-emission, thermally stable cement additive that acts as a carbon sink. Thus, hydrothermal mineralization (HTM) provides a rapid disposal route for organic waste, a green power source, and final products that can be combined with conventional and alternative cement production to reduce the carbon footprint of cement production.

[0004] The configuration described herein is, in part, based on the idea that carbon dioxide sequestration and reduction are beneficial in terms of environmental health. Excessive emissions of carbon dioxide from the combustion of fossil fuels and other sources have become a matter of high concern for governments and environmentalists. Unfortunately, conventional approaches to carbon dioxide reduction have focused on removing CO2 sources by simply reducing emissions through removal at the request or command of the sources, and thus eliminating any benefits of combustion. Therefore, the configuration described herein substantially overcomes the shortcomings of conventional methods by providing a complementary consumer / recipient array for CO2-related processes. MSW, which itself generates environmental problems due to the need for disposal, is supplied to the SCWO process, and once the water reaches a supercritical state, it is supplied to the HTM process for forming calcium carbonate, which is destined for cement (concrete) production, via a hydrothermal mineralization pathway from the CO2 produced in the SCWO. Furthermore, the high-pressure steam and CO2 obtained in the supercritical reaction can be used to power turbines or for other uses of pressurized steam before the HTM.

[0005] In further detail, the configuration provided herein provides a method for obtaining calcium carbonate by mineralization of a waste stream, comprising heating an aqueous waste stream, such as municipal solid waste, to a temperature and pressure to reach a supercritical state of water, and reacting hydrocarbons in the waste stream with oxygen to obtain carbon dioxide and water by supercritical hydroxylation. This mineralization reaction, in which CO2 is combined with calcium in the waste stream to form calcium carbonate, is suitable for industrial and construction purposes such as concrete.

[0006] Brief explanation of the drawing As similar reference letters across different figures indicate the same part in the attached drawings, the above and other objects, features, and advantages of the present invention will become apparent from the following description of specific embodiments of the invention. The drawings are not necessarily to scale, and instead emphasis is placed in the description of the principles of the invention. [Brief explanation of the drawing]

[0007] [Figure 1] This is a diagram illustrating the situation of the disclosed methods for accepting and recycling municipal solid waste (MSW) for carbon dioxide sequestration and concrete production. [Figure 2] This is the energy diagram required to achieve a self-sustaining exothermic reaction in the environment shown in Figure 1. [Figure 3] This is a comparison of the disclosed method with conventional methods for processing MSW as defined herein to produce calcium carbonate or precipitated calcium carbonate (PCC). [Figure 4] The stoichiometric level obtained by the method disclosed when reaching the plateau is shown, while direct air recovery exhibits substantially lower performance. [Modes for carrying out the invention]

[0008] Detailed explanation The following description includes several configurations related to the above method. Examples based on experimental background are disclosed to illustrate the technical details of the conversion from MSW to calcium carbonate, as well as the intermediate steps and compounds.

[0009] Figure 1 is a diagram illustrating the situation of the disclosed method for receiving and recycling municipal solid waste (MSW) for carbon dioxide sequestration and concrete production. Referring to Figure 1, in the recycling environment 100, MSW 101 forms a recycling stream of organic waste with abundant, nonspecific carbon and hydrogen mixed as discarded organic matter. The waste stream from MSW 100 forms precipitated calcium carbonate (PCC) by the method described below. PCC is calcium carbonate (CaCO3) produced by the synthesis described below. The produced calcium carbonate can be used in concrete production 105, consumer goods 107, and any suitable market for calcium carbonate.

[0010] Supercritical water oxidation (SCWO) is operated above the supercritical point of water in an oxidizing environment (T>374°C, P>220 bar), and waste polymers are decomposed to carbon dioxide in minutes. Energy content (HHV) of waste feed material. foodwaste Because of the high heat output (32.1 MJ / kg), the conversion to carbon dioxide is highly exothermic, meaning that once steady-state operation is achieved, the reaction requires no external energy for operation. After conversion, the outflow stream is a high-pressure, high-temperature stream of supercritical carbon dioxide and water vapor. As an additional recovery step, this stream can expand within the turbine to generate excess electricity, which can be returned to the grid and redistributed.

[0011] After utilizing the energy potential of the outflow stream, carbon dioxide is sequestrated in the form of calcium carbonate. This reaction takes place in an aqueous medium under alkaline conditions, thereby converting CO2 into bicarbonate (HCO3). - It is converted to ). From here, HCO3 - Free calcium (Ca 2+) reacts with to produce CaCO3. This conversion is thermodynamically favorable, but CO2 dissolves in water and produces HCO3. - Formation tends to be the rate-determining step. By utilizing the high-pressure and high-purity effluent gas obtained in the SCWO reaction, the disclosed method overcomes the problem of dissolution rate.

[0012] Figure 2 is an energy diagram for achieving a self-sustaining exothermic reaction in the environment of Figure 1. Referring to Figures 1 and 2, the disclosed method for obtaining calcium carbonate 103 by mineralization of waste stream 101 is shown. In a reactor or containment vessel, the aqueous waste stream is heated to a temperature and pressure necessary to reach a supercritical state of water. The waste stream contains large amounts of carbon and hydrogen in the form of organic waste. Due to the heat described above, hydrocarbons in waste stream 101 react with oxygen in an oxidizing environment to form carbon dioxide and water by supercritical hydroxylation. The CO2 obtained from the waste stream dissolves in water to form HCO3. - It forms a substance, which reacts with carbon dioxide to form calcium carbonate. The disclosed pathway for the hydrothermal mineralization of food waste is: [ka] It is determined by.

[0013] Therefore, CO2 combines with calcium in the waste stream to form calcium carbonate. Figure 2 shows that mineralization occurs with a negative Gibbs energy (ΔG value) change as hydrocarbons for chemical utilization are produced by a positive Gibbs energy reaction. A spontaneous or self-sustaining process corresponds to a negative ΔG value as shown in the mineralization step in Figure 2. SCWO relies on the unique reactivity and transport properties that occur when an aqueous waste stream exceeds the critical point of water (374 °C and 218 atm, or 704 °F and 3200 psi). Supercritical water is a dense single phase with transport properties similar to a gas and solvent properties equivalent to a nonpolar solvent. Oxygen is completely soluble in supercritical water and performs a very rapid and complete oxidation of all organic matter to carbon dioxide, clean water (reusable), and some non-leachable inorganic salts.

[0014] Of the 292 million tons of MSW generated in the United States, more than 70% is in the form of organic waste. Most MSW organics retain varying amounts of water. Unlike conventional energy recovery processes from waste such as incineration, hot water processes such as SCWO can use wet organic waste because the operating fluid is water, and a positive energy balance can be obtained when other processes require an energy input.

[0015] The full benefits of integrating the disclosed method depend on the feed materials used. This proposal is based on the use of food waste, which is only 20% of all MSW generated in the United States. When fully converted, food waste could offset nearly 20% of the country's demand for CaCO3.

[0016] Therefore, the disclosed method integrates SCWO and mineralization to produce CaCO3. This method serves at least three requirements or industrial roles: 1) the production of CaCO3, 2) developers of CO2 sequestration technologies, and 3) the waste management industry.

[0017] In the conventional methods, the demand for CaCO3 is mainly satisfied in one of two forms. The first is the direct extraction of limestone. This manufacturing method focuses on extracting limestone in open-pit quarries or underground mines and crushing it to the desired particle size on-site. The second is the precipitation of CaCO3. Typically, precipitated calcium carbonate (PCC) is formed by hydrating or digesting quicklime (CaO) in which CO2 molecules already exist to form calcium hydroxide (Ca(OH)2). Next, CO2 can be converted to HCO3 - and then reacted to form CaCO3.

[0018] In both of these conventional methods, since quicklime is formed by the calcination of CaCO3, the extraction of CaCO3 is ultimately necessary, and about 1.3 kg of CO2 / kgCaO is generated. For the return to CaCO3, the emissions are slightly improved to about 1 kg of CO2 / kgPCC. In contrast, in the disclosed method, the extraction of CaCO3 is unnecessary, and neither any soluble form of calcium nor an alkaline environment is required. In one example configuration, calcium chloride (CaCl2) and sodium hydroxide (NaOH) are used as the calcium source and the base source, respectively. The inventors' model using conventional NaOH production shows a similar emission rate of about 1 kgCO2 / kgPCC. However, when more green energy sources (i.e., solar, wind, biomass, etc.) are considered, it can be seen that this method can actually reduce emissions by 50% to up to 0.5 kgCO2 / kgPCC.

[0019] One of the methods is direct air capture (DAC) / point source capture (PSC), and the purpose of DAC and PSC technologies is to perform either the removal or concentration of dilute CO2 from the atmosphere or process flue gas. These methods are classified into two main chemistries: 1) mineralization and 2) amine-based.

[0020] Mineralization focuses on the permanent removal of CO2 by forming two insoluble, thermally stable inorganic substances, CaCO3 or MgCO3. The facility where it is to be deployed uses mineralization technology for DAC, and it is said that a considerable amount of CO2 is removed per year. However, since carbon is extracted from the highly concentrated feed material in the disclosed method, the removal efficiency is expected to be substantially higher than DAC when the waste is utilized on a sufficiently large scale, although this depends on the moisture and carbon content of the process feed material.

[0021] Figure 3 shows a comparison of the disclosed methods with conventional methods for MSW treatment and the formation of calcium carbonate or precipitated calcium carbonate (PCC), as defined herein. Referring to Figures 1-3, Figure 3 shows a comparison of several methods regarding the ratio of carbon dioxide.

[0022] When landfilled, organic waste decomposes into CO2 and CH4, making it a significant source of greenhouse gas (GHG) emissions, as shown by ratio 302. Conventional PCC production is circular, as it begins and ends with the extraction of CaCO3, as shown by ratio 304. In one of the specific configurations disclosed herein, a linear and finite lifespan of food waste as CaCO3 equivalent to conventional PCC emissions is obtained, as shown by ratio 306, but emissions can be reduced by 50% by using renewable energy sources (i.e., solar, wind, etc.), as shown by ratio 308.

[0023] Returning to Figures 1 and 2 and the corresponding equations, a typical use involves transporting the MSW 101 waste stream or similar to a sealed containment vessel or reactor suitable for pressurized operation. The water is brought to a supercritical state by the use of heat with sufficient pressure increase. After reaching a steady state of supercritical water, the heat source can be removed to allow a self-sustaining exothermic reaction to produce calcium carbonate.

[0024] In the example configuration, the waste stream is an organic waste stream, and a storage container is used to initiate a supercritical water oxidation (SCWO) reaction to produce CO2 by heating to at least 373 °C at a pressure of at least 220 bar in an oxidative environment. The gas streams of carbon dioxide and water can be collected by connecting a container or turbine input to the storage container to power an external load before mineralization. High-pressure steam can be used to power a mechanical load by connecting a container or conduit to the storage container to receive a pressurized gas containing carbon dioxide and steam.

[0025] Amine-based removal has been found to be effective in the stripping of CO2 from gas streams, rather than mineralization. However, since amine reactions are reversible, their CO2 sequestration capacity is limited. Amine-based removal is advantageous for use in the purification and transport of CO2. Furthermore, amines are expensive and corrosive, so they are not practical for many applications. In conventional methods, SCWO is not combined with the mineralization of this method to produce CaCO3. CO2 becomes effectively sequestered in bicarbonates, and mineralization consumes CO2 and free calcium to produce calcium carbonate.

[0026] Figure 4 shows the stoichiometric levels obtained by the method disclosed when reaching the plateau, while direct air capture shows substantially lower performance. Referring to Figure 4, the operating conditions shown by the upper dotted line are for SCWO: ·P CO2 = 150 psi ·T = 20 °C The lower dotted line shows direct air capture (DAC): ·P CO2 = 0.87 psi ·T = 20 °C

[0027] At 150 psi, between 20 and 120 minutes, the process plateaus at approximately 10% conversion. This is the result of the base being stoichiometric and the pH dropping below 5.5. Ca2+ Using a stoichiometric amount of base, a complete or near-complete conversion can be obtained. Once supercriticality is achieved, the mineralization becomes a self-sustaining spontaneous reaction with a negative delta G.

[0028] While the systems and methods specified herein have been described in detail with reference to their embodiments, it will be understood by those skilled in the art that various modifications of their form and detail are possible within them without departing from the scope of the invention as set forth in the appended claims.

Claims

1. A method for obtaining calcium carbonate by mineralization of waste streams: Heating the aqueous waste stream to a temperature and pressure that brings the water in the aqueous waste stream to a supercritical state; The hydrocarbons in the waste stream are reacted with oxygen to form carbon dioxide and water by supercritical hydroxide oxidation; The aforementioned CO ２ The process involves combining the calcium in the waste stream to form calcium carbonate, Methods that include...

2. CO2 from the aforementioned waste stream ２ Dissolve HCO in the water ３ － To form, The HCO formed above ３ － The process involves reacting the carbon dioxide with the calcium carbonate to form the calcium carbonate, The method according to claim 1, further comprising:

3. Transporting the aforementioned waste stream to a sealed containment container suitable for pressurized operation; To bring the supercritical water to a steady state; To carry out the self-sustaining exothermic reaction for producing the aforementioned calcium carbonate, the heating source is removed. The method according to claim 1, further comprising:

4. The method according to claim 3, further comprising recovering gaseous streams of carbon dioxide and water to power an external load.

5. The aforementioned waste stream is an organic waste stream: The supercritical water oxidation (SCWO) reaction is initiated by heating to at least 373°C at a pressure of at least 220 bar in an oxidizing environment, thereby reducing CO2 ２ To generate; The aforementioned CO ２ To isolate it in bicarbonate; the CO ２ and producing the calcium carbonate by mineralizing free calcium The method according to claim 1, further comprising:

6. The method according to claim 5, wherein the mineralization is the result of a negative Gibbs free energy change.

7. The method according to claim 6, wherein the mineralization is a self-sustaining spontaneous reaction having a negative delta G.

8. By mineralization, CO ３ ２－ The method according to claim 6, which yields the following result.

9. Apparatus for supercritical water oxidation and mineralization: A sealed container adapted to pressure and temperature for containing an aqueous waste stream and heating the water in the aqueous waste stream to a temperature and pressure necessary to reach a supercritical state; The hydrocarbons in the waste stream are reacted with oxygen to form supercritical water, which is carbon dioxide and water by supercritical water oxidation; The aforementioned CO ２ A containment vessel that performs a self-sustaining exothermic reaction to combine calcium in the waste stream to produce calcium carbonate, A device including a device.

10. The method according to claim 9, further comprising a container connected to the containment vessel for receiving a pressurized gas containing carbon dioxide and water vapor for supplying power to a mechanical load.

Images