ES3018086B2 - Procedure and system for the treatment of effluents from the incineration of solid fuels - Google Patents

Description

DESCRIPTION

Procedure and system for the treatment of effluents from the incineration of solid fuels

TECHNICAL SECTOR

The present invention falls within the energy sector, specifically in the production of energy from solid fuels such as coal, biomass, industrial waste and the reject fraction from the treatment and classification plants of Municipal Solid Waste (MSW).

BACKGROUND OF THE INVENTION

Solid fuel power plants are facilities that convert the chemical energy contained in solid materials (such as coal, biomass, municipal solid waste, etc.) into electrical or thermal energy. These plants are an integral part of the energy mix in many regions of the world due to their ability to provide continuous and reliable power.

Power plants that generate electricity from these fuels produce a series of effluents, which have varying degrees of environmental impact. Although most of them (nitrogen oxides, sulfur oxides, particulate matter, methane, carbon monoxide, and volatile organic compounds) are treated through different processes that prevent their release into the atmosphere, others cause significant problems in the sector:

Carbon dioxide (CO2) is the main greenhouse gas due to high levels of emissions into the atmosphere. To prevent emissions of this gas, several Carbon Capture and Storage (CCS) technologies exist, including chemical absorption with amines, adsorption processes, cryogenic separation, and membrane separation, among others [1].

Fly ash (FA) consists of fine particles carried by combustion gases and captured in emission control systems. The main problem with FA is its toxic and hazardous nature, primarily due to the presence of chloride ions (Cl-) and heavy metals such as lead, mercury, copper, and nickel, among others [2]. Various technologies have been developed in the literature for the treatment and stabilization of FA, which can be grouped into separation methods (washing/leaching), electrodialysis, thermal separation [3], and immobilization using cement [4].

The present invention relates to an integrated process and a CO2 and CV treatment system in a solid fuel power plant, based on the inclusion of a sodium chloride (NaCl) electrolysis unit in the system. The most similar prior art is Korean patent KR101549980B1 [5], which describes a method for manufacturing alkali and alkaline earth carbonates using inorganic materials (including CV) and CO2 as raw materials. NaOH and HCl are produced in the electrolysis unit and used in the same process. Additionally, patent EP2136904B1 [6] describes a process for capturing CO2, heavy metals, particulate matter, nitrogen oxides, sulfur oxides, or mixtures thereof in a flue gas unit. This process includes the electrolysis of NaCl for various applications (treatment of acid gases, production of renewable fuels, or similar uses). Also included is patent US10718055 [7], which describes an innovative system for capturing CO2 and producing hydrogen from wastewater, using an electrolytic system in which the cation feed can come from CV.

DESCRIPTION OF THE INVENTION

The present invention describes a system and process that simultaneously captures the CO2 generated in a solid fuel incineration plant and treats the carbon dioxide generated in said plant, utilizing the effluents generated within the plant and the incineration process itself, thus minimizing the need for raw materials and energy from external sources. The novelty of this process lies in the utilization of effluents generated within the process, as well as those from incineration, in order to improve its environmental viability. At the same time, other byproducts are obtained that can be used either for electricity generation, in other process treatments, or even for sale to third parties, representing an improvement in the utilization of this type of facility compared to systems known in the prior art.

Accordingly, in a first aspect, the invention relates to a process for treating effluents from the incineration of solid fuels comprising the following steps:

a) mixing fly ash (11) from a solid fuel incineration unit (0) with a stabilizing agent comprising at least one of sodium carbonate (Na2CO3), sodium bicarbonate (NaHCO3), potassium carbonate (K2CO3), potassium bicarbonate (KHCO3), in any combination thereof;

b) filtration of the resulting mixture to separate it into two streams, one of treated fly ash (12) comprising carbonates and/or bicarbonates of heavy metals, and a residual liquid (21) containing, in addition to chloride ions and alkali cations such as Na and K, various contaminants such as some heavy metals, sulfates, organic matter, or mixtures thereof;

c) capture of sulfates, heavy metals and organic matter from the wastewater (21) by at least one of the following techniques: reverse osmosis, ion exchange, distillation, adsorption, filtration, chlorination, coagulation, addition of oxidants such as ozone or hydrogen peroxide, biological treatment or advanced oxidation processes, alone or in any combination thereof, generating a treated wastewater (22);

d) mixing the treated waste liquid (22) with a NaCl/KCl solution (31) to adjust the concentration of NaCl and/or KCl, generating a feed stream (32) to the electrolyzer that has a NaCl and/or KCl concentration of between 10% and 50% weight/weight;

e) electrolysis of the NaCl and/or KCl from the feed stream (32) to the electrolyzer, generating a NaOH/KOH stream (42) having a NaOH and/or KOH concentration of between 10% and 50% w/w, and two gas streams: one of chlorine (43) and another of hydrogen (44); and

f) carbonation of the NaOH and/or KOH of stream (42) by passing the stream (42) through a plate column or random packing or structured packing in countercurrent with a stream (51) of CO2, generating a product stream (52) comprising at least one of sodium carbonate (Na2CO3), sodium bicarbonate (NaHCO3), potassium carbonate (K2CO3), or potassium bicarbonate (KHCO3), alone or in any combination thereof, product stream (52) being fed back to step a) as a stabilizing agent.

In a second aspect, the invention relates to a system for the treatment of effluents from the incineration of solid fuels comprising the following units:

a) a fly ash stabilization unit (1) comprising:

i. a mixing device for mixing fly ash (11) from a solid fuel incineration unit (0) with a stabilizing agent comprising at least one of sodium carbonate (Na2CO3), sodium bicarbonate (NaHCO3), potassium carbonate (K2CO3), potassium bicarbonate (KHCO3), in any combination thereof; and

ii. a filtration device for separating the resulting mixture into two streams, one of treated fly ash (12) comprising carbonates and/or bicarbonates of heavy metals, and a residual liquid (21) containing, in addition to chloride ions and alkali cations such as Na and K, various contaminants such as some heavy metals, sulfates, organic matter, or mixtures thereof;

b) a wastewater treatment unit (2) for capturing at least some of the heavy metals from the wastewater (21) by at least one of the following techniques: reverse osmosis, ion exchange, distillation, adsorption, filtration, chlorination, coagulation, addition of oxidants such as ozone or hydrogen peroxide, biological treatment or advanced oxidation processes, alone or in any combination thereof, generating as a product a treated wastewater (22);

c) a unit (3) for adjusting the concentration of NaCl and/or KCl, comprising a mixer for mixing the treated waste liquid (22) with a solution (31) of NaCl and/or KCl, generating a feed stream (32) to the electrolyzer having a concentration of NaCl and/or KCl of between 10% and 50% weight/weight;

d) a NaCl/KCl electrolysis unit (4) for carrying out the electrolysis of the NaCl and/or KCl contained in the feed stream (32) to the electrolyzer, the electrolysis being powered by electricity (41) and generating a NaOH/KOH stream (42) having a NaOH and/or KOH concentration between 10% and 50% w/w, and two gas streams: one of chlorine (43) and one of hydrogen (44); and

e) a NaOH/KOH carbonation unit (5) comprising a plate column or random packing or structured packing configured to contact the NaOH/KOH stream (42) countercurrently with a CO2 stream (51) and generating a product stream (52) comprising at least one of sodium carbonate (Na2CO3), sodium bicarbonate (NaHCO3), potassium carbonate (K2CO3), or potassium bicarbonate (KHCO3), alone or in any combination thereof, the product stream (52) being fed back to the fly ash stabilization unit (1).

Figure 1 presents a block diagram of the process in question. The solid fuel incineration unit (0) emits, as effluents, exhaust gases (rich in CO2), fly ash (FA), and electricity. In the present invention, the CVs are treated in the unit (1) by mixing with a solution that can be of Na2CO3, NaHCO3, K2CO3, KHCO3, or a mixture of these, the total concentration of carbonates and bicarbonates being between 2 and 20% weight/weight, the most preferred range being 3 - 8%, at a temperature ranging between 20 and 80 °C, the most preferred range being 25 - 65 °C, at a pressure between atmospheric and 10 bar, atmospheric pressure being the most preferred, and with a stirring speed of the mixture between 100 and 1500 rpm, the most preferred range being 600 - 800 rpm. In this unit, the fly ash will be treated and stabilized through carbonation (immobilization) of the heavy metals it contains, preventing leaching that could contaminate aqueous effluents. This process, which involves the intimate mixing of the fly ash with the specified carbonates and/or bicarbonates followed by filtration, will generate two effluents:

- Treated CV (12), generally carbonates and/or bicarbonates of heavy metals, which must be classified as non-hazardous or inert waste according to current legislation, and which can be deposited in the relevant facilities or used as an addition in construction materials.

- Residual liquid (21), with a significant content of chloride ions and alkali cations such as Na or K, and with traces of heavy metals (Al, Mg, Pb, Hg, Cu, Zn, Cd, among others), sulfates and other components.

The wastewater (21) is treated in a wastewater treatment unit (2), where components that may affect the process, primarily sulfates, heavy metals, organic matter, or others, are removed by at least one of the following techniques: reverse osmosis, ion exchange, distillation, adsorption, filtration, chlorination, coagulation, addition of oxidants such as ozone or hydrogen peroxide, biological treatment, or advanced oxidation processes, alone or in any combination thereof. The purpose is to utilize the treated wastewater (22), rich in chloride ions and alkali cations, in the process of the present invention. Purging a portion of the treated wastewater stream (22) may be necessary to prevent excessive accumulation of unwanted components in the process.

The treated wastewater stream (22) is then fed to a unit (3) for adjusting the alkali chloride concentration, where intimate mixing takes place between the treated wastewater stream (22) and a fresh stream of NaCl, KCl, or both. The objective is to obtain a feed stream to the electrolyzer (32) with a NaCl and/or KCl concentration between 10 and 50% by weight, with the preferred range being 20–30% by weight.

From unit (3), a feed stream is obtained for the electrolyzer (32), which is fed to a NaCl/KCl electrolysis unit (4) after being preheated to the operating temperature (between 60 and 100 °C, with 70 to 80 °C being the most preferable). In this process, thanks to the application of electrical energy (41), which is optionally supplied by the solid fuel incineration unit (0), the products obtained are a NaOH and KOH mixture stream (42), a chlorine gas stream (43), and a hydrogen gas stream (44). Streams (43) and (44) can be used for other processes in the plant or sold.

Stream (42) is sent to the NaOH/KOH carbonation unit (5), where it is contacted with the CO2-rich gaseous effluent (51), optionally from the incineration unit (0), preferably in a countercurrent contact column with trays, random packing, or structured packing, in order to absorb at least some of the CO2 and obtain a carbonate- and bicarbonate-rich stream (52). This process is carried out at a temperature between 20 and 80 °C, preferably between 25 and 65 °C, and a pressure between 1 and 10 atmospheres, preferably between 5 and 7 atmospheres. To achieve the operating pressure, it will be necessary to pressurize streams (42) and (51), which come from processes carried out at atmospheric pressure. As a result of the operation, a gaseous effluent stream (53) is obtained with a reduced CO2 concentration, thanks to the capture of this gas carried out in the absorption process performed in unit (5).

Finally, the liquid stream (52) is mixed with the fly ash stream (11) in the CV stabilization unit (1), described at the beginning of this section.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1. Block diagram of the effluent treatment process from the incineration of Solid Fuels subject to the present invention.

DESCRIPTION OF AN EMBODIMENT OF THE INVENTION

Based on the description in the previous section and the diagram in Figure 1, a preferred embodiment is described below:

- CV stabilization unit (1), consisting of a mixer in which the fly ash stream (11) and the stream (52) are brought into intimate contact, preferably for a time of 5 minutes at a temperature of 30 °C and 700 rpm, and are subsequently subjected to a filtration process, in which the treated CV stream (12) and the residual liquid (21) are separated;

- Wastewater treatment unit (2), in which a heavy metal capture process is carried out. In this unit, the wastewater stream (21) is brought into contact with a separation agent, preferably under ambient operating conditions, in order to obtain the treated wastewater stream (22);

- NaCl/KCl concentration adjustment unit (3), wherein a feed stream to the electrolyzer (32) is obtained by mixing the treated waste liquid stream (22) and an external stream of NaCl/KCl solution (31) preferably under ambient conditions;

- NaCl/KCl electrolysis unit (4), in which the feed stream to the electrolyzer (32) is subjected to an electrochemical decomposition process preferably at 70 °C and ambient pressure, obtaining as products NaOH/KOH (42), Ch (43) and H2(44);

- NaOH/KOH carbonation unit (5), in which the NaOH/KOH stream (42) is contacted with the gaseous effluent (51) from the incinerator (0) by means of an absorption column, preferably under ambient temperature and 5 atmosphere pressure conditions, obtained by pre-pressurization of streams (42) and (51). In this unit, one or more of the following reactions will take place:

Whose products will constitute the main components of the stream (52), which will be sent to the CV stabilization unit (1).

INDUSTRIAL APPLICATION

The present invention aims to improve the processes of incineration of solid fuels from an environmental and economic point of view, thanks to a process in which effluents from said process are used as raw materials, the management and/or treatment of which pose a technical, economic and environmental challenge.

REFERENCES

[1] DECHEMA (2024). Charcoal for Power-to-X. Suitable CO2resources and integration in PtX value chains. [Consultation date: July 31, 2024]. Available in: DECHEMA | Possibilities to capture and utilize carbon dioxide for sustainable production routes [2] E. Atanes-Sánchez et al. A mixed separation-immobilization method for soluble salts removal and stabilization of heavy metals in municipal solid waste incineration fly ash. Journal of Environmental Management 240 (2019), 359. https://doi.org/10.1016/j.jenvman.2019.03.122

[3] A. Ferraro et al. Pre-treatments of MSWI fly-ashes: a comprehensive review to determine optimal conditions for their reuse and/or environmentally sustainable disposal. Reviews in Environmental Science and Bio/Technology 18 (2019), 453. https://doi.org/10.1007/s11157-019-09504-1

[4] Ministry of Transport, Mobility and Urban Agenda (2012). Slag and ash from municipal solid waste (MSW) incinerators. [Accessed: July 31, 2024]. Available at: Slag and ash from municipal solid waste (MSW) incinerators | CEDEX (cedexmateriales.es)

[5] (2014). Manufacturing method carbonates of alkali metal ion or alkali earth metal ion using Electrolysis Unit. KR101549980B1. Korean Intellectual Property Office.

[6] Cooper, H.B.H. et al. (2008). Process and apparatus for carbon capture and elimination of multi-pollutants in flue gas from hydrocarbon fuel sources and recovery of multiple by-products. EP2136904B1. European Patent Office.

[7] Zhiyong, R. & Lu, L. (2016). Carbon dioxide capture and storage electrolytic methods. US10718055B2. United States.

Claims (29)

1. Procedure for the treatment of effluents from the incineration of solid fuels comprising the following stages: a) mixing fly ash (11) from a solid fuel incineration unit (0) with a stabilizing agent comprising at least one of sodium carbonate (Na2CO3), sodium bicarbonate (NaHCO3), potassium carbonate (K2CO3), potassium bicarbonate (KHCO3), in any combination thereof; b) filtration of the resulting mixture to separate it into two streams, one of treated fly ash (12) comprising carbonates and/or bicarbonates of heavy metals from the fly ash, and a residual liquid (21) containing, in addition to chloride ions and alkali cations such as Na and K, contaminants such as heavy metals, sulfates, organic matter, or mixtures thereof; c) capture of sulfates, heavy metals and organic matter from the wastewater (21) by at least one of the following techniques: reverse osmosis, ion exchange, distillation, adsorption, filtration, chlorination, coagulation, addition of oxidants such as ozone or hydrogen peroxide, biological treatment or advanced oxidation processes, alone or in any combination thereof, generating a treated wastewater (22); d) mixing the treated waste liquid (22) with a NaCl/KCl solution (31) to adjust the concentration of NaCl and/or KCl, generating a feed stream (32) to the electrolyzer that has a NaCl and/or KCl concentration of between 10% and 50% weight/weight; e) electrolysis of the NaCl and/or KCl from the feed stream (32) to the electrolyzer, generating a NaOH/KOH stream (42) having a NaOH and/or KOH concentration of between 10% and 50% w/w, and two gas streams: one of chlorine (43) and another of hydrogen (44); and f) carbonation of the NaOH and/or KOH of stream (42) by passing the NaOH and/or KOH stream (42) in a plate column or random packing or structured packing countercurrently with a CO2 stream (51), generating a product stream (52) comprising at least one of sodium carbonate (Na2CO3), sodium bicarbonate (NaHCO3), potassium carbonate (K2CO3), or potassium bicarbonate (KHCO3), alone or in any combination thereof, the product stream (52) being fed back to step a) as a stabilizing agent. 2. A process according to claim 1 wherein, in step a), the total concentration of carbonates and bicarbonates ranges from 2 to 20% w/w. 3. Process according to claim 2 wherein, in step a), the total concentration of carbonates and bicarbonates ranges from 3 to 8% w/w. 4. A process according to any of claims 1-3 above, wherein step a) is carried out at a temperature between 20 °C and 80 °C. 5. Process according to claim 4, wherein step a) is carried out at a temperature between 25 °C and 65 °C. 6. Process according to any of claims 1 to 5, wherein step a) is carried out at a pressure between atmospheric and 10 bar. 7. Process according to claim 6, wherein step a) is carried out at atmospheric pressure. 8. Method according to any of claims 1-7 above, wherein step a) is carried out with a stirring speed of the mixture between 100 and 1500 rpm. 9. Method according to claim 8, wherein step a) is carried out with a stirring speed of the mixture between 600 and 800 rpm. 10. A method according to any of claims 1-9 above, wherein, in step c), a portion of the treated waste liquid stream (22) is purged in order to prevent excessive accumulation of unwanted components in the process. 11. A method according to any of claims 1-10 above, wherein, in step d), the stream of NaCl, KCl or both is fed from outside the system, such as from thermal storage units or seawater. 12. A method according to any of claims 1-11 above, wherein, in step d), the feed stream (32) to the electrolyzer has a NaCl/KCl concentration of between 20% and 30% w/w. 13. Process according to claims 1-12 above wherein step e) is carried out at a temperature between 60 °C and 100 °C. 14. Process according to claim 13, wherein step e) is carried out at a temperature between 70 °C and 80 °C. 15. A process according to any of claims 1-14 above, wherein, in step e), the electrolysis is powered by electricity from the solid fuel incineration unit (0). 16. A process according to any of the preceding claims wherein, in step f), the CO2 stream (51) comes from the solid fuel incineration unit (0). 17. A process according to any of the preceding claims wherein step f) is carried out at a temperature in the range of 25 °C to 65 °C. 18. Process according to claim 17, wherein step f) is carried out at a temperature in the range of 20 °C to 80 °C. 19. A process according to any of the preceding claims wherein step f) is carried out at a pressure between 1 and 10 atmospheres. 20. Process according to claim 19 wherein step f) is carried out at a pressure between 5 and 7 atmospheres. 21. Method according to claims 19 or 20 wherein, in order to achieve the operating pressure, the streams (42) and (51) are pressurized. 22. A method according to any of the preceding claims wherein the solid fuel is selected from coal, biomass, waste-derived fuels (RDF), municipal solid waste (MSW), or mixtures thereof. 23. A process according to any of the preceding claims, wherein the chlorine stream (43) generated in step e) is used in other parts of the solid fuel incineration unit (0) or is separated for commercial sale. 24. A process according to any of the preceding claims, wherein the hydrogen stream (44) generated in step e) is used to produce electricity by means of a fuel cell, or in the electrolysis of NaCl/KCl (4) itself, or is used in other parts of the solid fuel incineration unit (0), or is separated for commercial sale. 25. System for the treatment of effluents from the incineration of solid fuels comprising the following units: a) a fly ash stabilization unit (1) comprising: i. a mixing device for mixing fly ash (11) from a solid fuel incineration unit (0) with a stabilizing agent comprising at least one of sodium carbonate (Na2CO3), sodium bicarbonate (NaHCO3), potassium carbonate (K2CO3), potassium bicarbonate (KHCO3), in any combination thereof; and ii. a filtration device for separating the resulting mixture into two streams, one of treated fly ash (12) comprising carbonates and/or bicarbonates of heavy metals from the fly ash, and a residual liquid (21) containing, in addition to chloride ions and alkali cations such as Na and K, contaminants such as heavy metals, sulfates, organic matter, or mixtures thereof; b) a wastewater treatment unit (2) for capturing at least some of the heavy metals from the wastewater (21) by at least one of the following techniques: reverse osmosis, ion exchange, distillation, adsorption, filtration, chlorination, coagulation, addition of oxidants such as ozone or hydrogen peroxide, biological treatment or advanced oxidation processes, alone or in any combination thereof, generating as a product a treated wastewater (22); c) a unit (3) for adjusting the concentration of NaCl and/or KCl, comprising a mixer for mixing the treated waste liquid (22) with a solution (31) of NaCl and/or KCl, generating a feed stream (32) to the electrolyzer having a concentration of NaCl and/or KCl of between 10% and 50% weight/weight; d) a NaCl/KCl electrolysis unit (4) for performing the electrolysis of the NaCl/KCl contained in the feed stream (32) to the electrolyzer, which is powered by electricity (41) and which generates a NaOH/KOH stream (42) having a concentration of NaOH and/or KOH between 10% and 50% weight/weight, and two gas streams: one of chlorine (43) and another of hydrogen (44); and e) a NaOH/KOH carbonation unit (5) comprising a plate column or random packing or structured packing configured to contact the NaOH/KOH stream (42) countercurrently with a CO2 stream (51) and generating a product stream (52) comprising at least one of: sodium carbonate (Na2CO3), sodium bicarbonate (NaHCO3), potassium carbonate (K2CO3), or potassium bicarbonate (KHCO3), alone or in any combination thereof, the product stream (52) being fed back to the fly ash stabilization unit (1). 26. System according to claim 25, wherein the solid fuel comprises at least one of coal, biomass, waste-derived fuels (RDF), municipal solid waste (MSW), or mixtures thereof. 27. System according to claim 26, wherein, in unit (3), the NaCl/KCl solution (31) is supplied by a source external to the system. 28. System according to claims 25 to 27, wherein, in unit (4), the electricity (41) is supplied by the solid fuel incineration unit (0). 29. System according to any of claims 25 to 28, wherein, in unit (5), the CO2 stream is supplied by the solid fuel incineration unit (0).