Low-carbon transformation method for coal power generation

Abstract

The invention belongs to the technical field of power generation, and relates to a low-carbon transformation method for coal power generation, which is characterized in that metal zinc and aqueous alkaline electrolyte react under the action of a catalyst to produce hydrogen, a reaction product of zinc is electrolyzed by renewable energy electric power to regenerate metal zinc, and reaction hydrogen production and electrolytic regeneration cycle of zinc are formed; the generated hydrogen replaces coal combustion for power generation according to the proportion of 5%-100%; the method has the advantages of being economical, safe and easy to implement, and has wide prospects in application of coal power generation low-carbon transformation and renewable energy waste electricity absorption.

Description

Technical Field

[0001] This invention belongs to the field of power generation technology and relates to a method for the low-carbon transformation of coal-fired power generation. Background Technology

[0002] Coal-fired power generation is my country's largest source of carbon emissions, accounting for more than 40% of the country's total carbon emissions. The low-carbon transformation of coal-fired power plants is a top priority for the entire society in reducing carbon emissions.

[0003] Renewable energy power has reduced the proportion of coal-fired power generation in the power industry, but it is unstable, and a large amount of surplus electricity cannot be utilized. Coal-fired power generation is stable and reliable, and will remain my country's irreplaceable main source of electricity for a considerable period of time. Currently, the average operating age of coal-fired power generating units nationwide is about 12 years, and there are still 20-30 years before the normal retirement of modern coal-fired power plants. Premature shutdown will cause serious economic losses and social problems. In order to stabilize power production, fully utilize the value of coal-fired power plant equipment, and reduce carbon emissions, it is necessary to carry out low-carbon transformation of coal-fired power plants.

[0004] my country faces the challenge of a short timeframe and a heavy workload in carbon reduction. Three pathways have been identified for coal-fired power plants to reduce carbon emissions: biomass co-firing, green ammonia co-firing, and carbon capture, utilization, and storage. Co-firing retrofitting has moved from an elective to a mandatory course for coal-fired power plants.

[0005] The following problems exist with the co-firing of green ammonia: 1. High cost: The production of green ammonia involves many steps, including water electrolysis to produce hydrogen, nitrogen separation from frozen air, high-temperature and high-pressure synthesis, and separation and condensation of liquid ammonia. This process consumes a large amount of resources. In addition, the liquid ammonia needs to be transported to the vicinity of the power plant for gasification before it can be co-fired, resulting in high costs.

[0006] 2. Poor safety: Liquid ammonia is toxic and explosive, with a high accident rate. It is generally not allowed to be stored in the factory area. It needs to be stored in a special device at a certain distance outside the factory area. After being vaporized, it is transported remotely in large quantities through a special pipeline, which poses a risk of gaseous ammonia leakage.

[0007] 3. Limited range of co-firing: If the ammonia content exceeds 10%, harmful NOx will increase significantly; in addition, the slow flame transmission speed of ammonia makes it easy to lose flame, and the low flame stability can reduce the efficiency of the unit; large-scale co-firing is difficult and has many problems.

[0008] 4. Significant Implementation Challenges: Comparing the calorific values ​​of standard coal (29.3 MJ / kg) and ammonia (18.61 MJ / kg), replacing 1 ton of standard coal with the same calorific value would require approximately 1.6 tons of ammonia. China's annual coal-fired power generation consumes over 2 billion tons of coal. If 10% of this coal were blended, replacing 200 million tons of coal would require at least 320 million tons of green ammonia. However, my country's current annual synthetic ammonia production is only around 60 million tons, necessitating the construction of numerous new synthetic ammonia plants to meet the demand.

[0009] Currently, biomass co-firing technology is relatively mature and has obvious cost advantages, but there are still problems such as resource supply, collection radius, and site selection; carbon capture, utilization and storage has problems such as high energy consumption, impact on power generation efficiency and application scenario limitations.

[0010] The low-carbon transformation of coal-fired power generation is crucial to the survival and development of coal-fired power plants and is also a major measure for the country to achieve its "dual carbon" goals. However, low-carbon coal-fired power generation is a global challenge. Existing technologies have problems with economics, safety, and application scenarios, and cannot simultaneously meet the requirements of low cost, high safety, and ease of implementation. In view of this, we propose a method for the low-carbon transformation of coal-fired power generation to supplement and replace the above-mentioned technical routes to solve existing problems. Summary of the Invention

[0011] The purpose of this invention is to provide a method for the low-carbon transformation of coal-fired power plants, which meets the requirements of low cost, high safety and easy implementation, so as to solve the problems mentioned in the background art, make full use of the value of most power generation equipment in coal-fired power plants, and reduce carbon emissions at the same time.

[0012] To achieve the above objectives, the present invention provides the following technical solution: A method for low-carbon retrofitting of coal-fired power generation, characterized by: producing hydrogen through the reaction of metallic zinc and an aqueous alkaline electrolyte under the action of a catalyst; the reaction product of zinc is electrolyzed using renewable energy to regenerate metallic zinc, forming a zinc-based hydrogen production and electrolytic regeneration cycle; the generated hydrogen replaces coal combustion at a ratio of 5%-100% to heat the working fluid of the coal-fired power generation unit, thereby driving the power generation; the zinc-based hydrogen production cycle includes at least the following steps: (1) Hydrogen production by reaction of zinc metal: zinc metal and aqueous alkaline electrolyte are added to a hydrogen production reactor with a catalyst. The zinc reacts with the catalyst to reduce the water in the aqueous alkaline electrolyte to produce hydrogen. (2) Collect and transport the reaction products of zinc and electrolyte together: Collect the reaction products of zinc and electrolyte in the hydrogen generator, store them, and transport them to the location of the next step (3). (3) Electrolytic regeneration of zinc: The reaction products of zinc and electrolyte are added to an electrolytic cell with an anode and a cathode, and electrolysis is performed using renewable energy electricity. Oxygen is released at the anode and zinc is electrodeposited at the cathode. (4) Remove the zinc metal, collect the electrolyte, and store and transport it: Remove the zinc metal from the cathode of the electrolytic cell, collect the aqueous alkaline electrolyte after electrolysis, store it, and transport it to the reaction site of the next step (1).

[0013] Preferably, in the method for low-carbon transformation of coal-fired power generation according to claim 1, the concentration of hydroxide ions in the aqueous alkaline electrolyte is not less than 5 Mol / L.

[0014] Preferably, the method for low-carbon transformation of coal-fired power generation according to claim 1 is characterized in that: the hydrogen generated by the zinc cycle is introduced into the coal-fired boiler in the power plant and co-fired with the coal, and the heating working fluid drives the unit to generate electricity.

[0015] Preferably, the method for low-carbon transformation of coal-fired power generation according to claim 1 is characterized in that: the hydrogen generated by the zinc cycle is fed into the hydrogen-fired boiler to burn the heating medium and generate steam, which is then combined with the steam generated by the coal-fired boiler of the power plant to drive the unit to generate electricity.

[0016] Preferably, the method for low-carbon transformation of coal-fired power generation according to claim 1 is characterized in that: hydrogen generated by the zinc cycle is fed into a hydrogen-fired boiler for combustion, and the heating working fluid drives the unit to generate electricity.

[0017] Preferably, the method for low-carbon transformation of coal-fired power generation according to claim 1 is characterized in that: the zinc-cycle hydrogen production is carried out within the power plant area, and the electricity generated by renewable energy is transmitted to the power plant area through a dedicated transmission line to supply power for electrolysis.

[0018] Preferably, the method for low-carbon transformation of coal-fired power generation according to claim 1 is characterized in that: the zinc-cycle hydrogen production is carried out outside the power plant area, the electricity generated by renewable energy is transmitted to the outside of the power plant area through a dedicated transmission line to supply power for electrolysis, and the hydrogen is transported to the plant area through pipelines.

[0019] Zinc is inexpensive, abundant, and has a high volumetric energy density. It is also safe, environmentally friendly, and non-toxic. Zinc has a lower electrode potential than hydrogen, and in alkaline aqueous solutions, it can reduce water molecules to produce hydrogen gas; however, the reaction rate is normally very slow.

[0020] This invention involves the rapid reaction of metallic zinc with water in an aqueous alkaline electrolyte in a hydrogen production reactor under the action of a catalyst, releasing hydrogen gas. Metallic zinc loses electrons, transforming into divalent zinc, a reaction product. The divalent zinc and the aqueous alkaline electrolyte are collected together, stored to a certain quantity, and then transported to an electrolytic cell. Electrolysis is performed using renewable energy electricity. At the cathode, the divalent zinc gains electrons and is regenerated back into metallic zinc, while at the anode, hydroxide groups lose electrons, releasing oxygen. The zinc and the electrolyzed electrolyte are collected, stored to a certain quantity, and then transported to the hydrogen production reactor for further hydrogen production, thus completing the cycle. Zinc is not lost during the hydrogen production and electrolytic regeneration cycle.

[0021] The cost of co-firing hydrogen generated in this invention is mainly determined by the price of renewable energy electricity. The energy consumption throughout the process is far lower than that of green ammonia, and the cost of producing hydrogen with the same calorific value is only about 40% of that of green ammonia.

[0022] Coal-fired power generation typically uses pulverized coal as fuel, which is burned in a coal-fired boiler to heat water and produce steam. This steam is then fed into a turbine, which drives a generator unit to produce electricity. The steam is condensed into liquid water and recycled. In special cases, the working fluid, water, can be replaced with liquid carbon dioxide or other liquids.

[0023] The hydrogen generated by this invention is fed into a boiler for combustion, replacing coal combustion in a certain proportion to heat the working fluid of the coal-fired power generation system and drive the unit to generate electricity; the proportion of coal replacement is 5%-100%.

[0024] The equipment for implementing the method of the present invention includes a hydrogen production reactor for reacting zinc with an electrolyte and an electrolytic cell for electrolyzing and regenerating zinc.

[0025] The outer shell of the hydrogen production reactor has channels for metallic zinc, catalyst, hydrogen, electrolyte, and the reaction products of zinc. The hydrogen produced by the hydrogen production reactor is purified by a gas scrubbing device before being piped into the boiler for combustion. If necessary, multiple hydrogen production reactors can be connected together with their hydrogen pipelines to increase the hydrogen production and then piped into the boiler for combustion.

[0026] The zinc is preferably zinc granules or zinc powder with a purity of not less than 99.8%.

[0027] Zinc powder produced by electrolysis with an aqueous alkaline electrolyte containing divalent zinc has high purity; preferably, this type of metallic zinc powder is used in the present invention.

[0028] The catalyst may be any of the following: Pt-based catalyst, Pd-based catalyst, transition metal-based catalyst, transition metal sulfide, phosphide, nitride, carbide catalyst, carbon-based catalyst, alloy catalyst; or a combination of the above catalysts.

[0029] Preferably, the aqueous alkaline electrolyte is a strong alkaline aqueous solution formed by dissolving one or more of potassium hydroxide, sodium hydroxide, and lithium hydroxide in water. Preferably, the hydroxide concentration of the aqueous alkaline electrolyte is not less than 5 mol / L.

[0030] The electrolytic cell generally includes an electrolytic cell shell, an anode, a cathode, an electrolyte, and an electrolyte channel. The upper part of the electrolytic cell can be completely open, or it can have an outer cover with an oxygen channel.

[0031] Preferably, the anode of the electrolytic cell is made of a metal material with a low oxygen evolution overpotential, such as stainless steel, nickel, nickel-plated steel sheet, nickel mesh, nickel foam, or a combination of the above materials.

[0032] Preferably, the cathode of the electrolytic cell is made of metals and alloys with a relatively high hydrogen overpotential, such as copper, titanium, and brass.

[0033] Electrolytically deposited zinc is typically removed from the cathode using scraping or powder scraping methods.

[0034] The renewable energy power includes one or more types of power such as wind power, photovoltaic power, hydropower, ocean energy, tidal energy, and thermoelectric power; if it is AC power, it needs to be rectified and regulated before it can be used for electrolysis.

[0035] Metallic zinc reacts with an aqueous alkaline electrolyte under the action of a catalyst to produce hydrogen gas, and electrolytic regeneration of metallic zinc produces oxygen gas. The cycle is equivalent to step-by-step electrolysis of water, and the water consumed can be replenished at any step, preferably in the electrolytic cell.

[0036] This invention can replace up to 100% of coal, while still using most of the power generation equipment in coal-fired power plants.

[0037] If renewable energy electricity reaches 0.1 yuan / kWh, the cost of hydrogen produced by the zinc cycle hydrogen production system, calculated by calorific value, is already lower than the current price of coal in many regions. At this point, not using coal is more economical than using coal. This invention essentially transforms unstable, cheap renewable energy into stable and reliable grid-connected electricity.

[0038] Compared with the prior art, the beneficial effects of the present invention are as follows: Compared with green ammonia co-firing, the present invention has the following decisive advantages: 1. Significant cost advantage: The cost is 40% of that of green ammonia. National coal-fired power generation consumes over 2 billion tons of coal annually. If 10% of this coal is co-fired, at least 320 million tons of green ammonia would be needed. Based on a renewable energy surplus electricity price of 0.25 yuan / kWh and a green ammonia price of 4100 yuan / ton, this would require 1.3 trillion yuan. Under the same conditions, zinc-based hydrogen production would only require 520 billion yuan, saving 780 billion yuan compared to co-firing with green ammonia.

[0039] 2. Safe and simple: It can be carried out at room temperature and pressure without being toxic or odorous, and can be completed within the power plant area without the need for remote vaporization of liquid ammonia.

[0040] 3. Wide range of co-firing: Co-firing results in no NOx emissions, with a replacement rate of up to 100%.

[0041] 4. Easy to implement: Low investment, easy to construct, no need to build large-scale synthetic ammonia plants.

[0042] Compared with biomass co-firing technology, this invention has the following advantages: 1. Renewable energy sources are diverse: they can include wind, solar, and hydropower, ocean energy, and tidal energy. Power plants located some distance from renewable energy power plants can have dedicated transmission lines built to supply power to the zinc-based hydrogen production process, eliminating the need for large-scale material transportation. In contrast, the collection, storage, and transportation of biomass are limited, the supply chain is unstable, and there are resource constraints and seasonality in supply.

[0043] 2. Wide range of co-firing: It can reach up to 100%, with no other emissions. In contrast, co-firing of biomass produces some emissions.

[0044] 3. Easy to implement: Hydrogen can be directly fed into a coal-fired boiler for combustion. Biomass, on the other hand, requires specialized equipment for heating and gasification before being fed into the boiler.

[0045] 4. Promising Future: This invention can absorb renewable energy power off-grid. With the rapid development of wind and solar power, the price of surplus renewable energy will decrease, thus reducing the cost of this invention. However, biomass co-firing poses resource competition issues for existing biomass power plants. Other applications using biomass as a raw material are expanding, and with limited resources, the cost of biomass will likely increase in the future.

[0046] Compared with carbon capture, utilization and storage, this invention has the following advantages: The device is simple, consumes little energy, and does not affect power generation efficiency.

[0047] 2. There are no limitations on the application scenarios for carbon resource utilization and geological storage.

[0048] 3. Better prospects when combined with renewable energy: With the rapid development of renewable energy, a large amount of surplus electricity lacks absorption channels. This invention provides an economical, safe, and easy-to-implement approach; even if coal is no longer used in the future, the equipment will not be idle. Furthermore, carbon capture, utilization, and storage, combined with carbon reduction from coal fuel, may render coal-fired power plants idle when coal fuel is no longer used in the future.

[0049] This invention offers significant cost advantages, high safety, and ease of implementation, solving problems inherent in existing technologies. In particular, it provides a crucial pathway to fully leverage the value of coal-fired power generation equipment, promote its development in conjunction with renewable energy, and facilitate a smooth transition from low-carbon to carbon-free operations for coal-fired power plants. This has significant implications for both the low-carbon transformation of coal-fired power generation and the development of renewable energy, with a very promising future. Major power generation groups and thousands of coal-fired power plants across the country are its users, representing a massive market worth hundreds of billions or trillions of yuan, with extremely broad application prospects.

[0050] For the hydrogen energy industry, other hydrogen energy applications have not yet been promoted on a large scale. This invention is also part of the hydrogen energy industry, and its implementation in the field of coal-fired power generation will be an important starting point for the large-scale application and development of the hydrogen energy industry.

[0051] In summary, this invention has extremely significant beneficial effects, is widely applicable in the low-carbon transformation of coal-fired power generation and the absorption of surplus electricity from renewable energy sources, has significant economic benefits, plays an important role in energy transformation, and has significant industrial and social progress significance. Detailed Implementation

[0052] The technical solution of the present invention will be further described below with reference to specific embodiments.

[0053] Example 1 The aqueous alkaline electrolyte is a 5 mol / L potassium hydroxide solution, and a Pd-based honeycomb catalyst is added to the reactor. The zinc-based hydrogen production process takes place within the power plant area. Electricity generated by solar photovoltaic panels is transmitted to the power plant area via dedicated transmission lines to power the electrolytic cells for zinc regeneration. The electrolytic cells use nickel mesh as the anode and copper sheets as the cathode, with an electrolytic current density of 70 mA / cm². 2 .

[0054] The zinc-cycle hydrogen production process is as follows: (1) Zinc reaction hydrogen production: Add zinc granules and aqueous alkaline electrolyte to a hydrogen production reactor with a catalyst. The zinc reacts with the catalyst to reduce the water in the aqueous alkaline electrolyte and produce hydrogen; (2) Collect and transport the zinc reaction products and electrolyte together: After the reaction, the zinc reaction products and alkaline electrolyte in the hydrogen generator are pumped out together with a magnetic pump and stored in a container. During electrolysis, they are pumped through a pipeline to the next step (3); (3) Electrolytic regeneration of zinc: Add the zinc reaction products and the alkaline electrolyte after the reaction to the electrolytic cell, pass DC current for electrolysis, release oxygen at the anode, and electrodeposit zinc at the cathode; (4) Remove the zinc, collect the electrolyte in the electrolytic cell, and store and transport it: Scrape the zinc from the cathode of the electrolytic cell, collect the electrolyte after electrolysis, store it separately, and then transport it to the reaction site of the next step (1). During the cycle, deionized water is used to replenish the water consumed in the electrolytic cell.

[0055] After being processed by a gas scrubbing device, hydrogen is transported to a coal-fired boiler to mix and burn with pulverized coal. The amount of hydrogen added is controlled according to the amount of coal and pulverized coal, with a coal replacement ratio of 10%. Hydrogen generates 10% of the heat, while pulverized coal generates 90% of the heat. The hydrogen heats water to generate steam, which drives a steam turbine generator unit to generate electricity.

[0056] Example 2 The aqueous alkaline electrolyte is a 5 mol / L sodium hydroxide solution, and an alloy honeycomb catalyst is added to the reactor. Zinc-based hydrogen production is carried out within the power plant area. Alternating current generated by wind turbines is transmitted to the power plant area via dedicated transmission lines, where it is rectified into direct current to power the electrolytic cells for regenerating metallic zinc. The anode in the electrolytic cells is made of nickel foam, and the cathode is made of copper sheet. The electrolytic current density is 80 mA / cm². 2 .

[0057] The zinc-cycle hydrogen production process is the same as in Example 1. Hydrogen gas, after being treated by a gas scrubbing device, is fed into a hydrogen-fired boiler for combustion to heat water and generate steam. Pulverized coal is burned in a coal-fired boiler to heat water as the working fluid and generate steam. The steam channels of the hydrogen-fired boiler and the coal-fired boiler are connected in parallel, and the combined steam drives a steam turbine generator unit to generate electricity. The coal replacement ratio is 50%, with hydrogen generating 50% of the heat and pulverized coal generating 50% of the heat.

[0058] Example 3 The aqueous alkaline electrolyte is a 6 mol / L sodium hydroxide solution, and a carbon-based honeycomb catalyst is added to the reactor. The zinc-based hydrogen production process takes place within the power plant area. Electricity generated by solar photovoltaic panels powers the electrolytic cells to regenerate metallic zinc via dedicated transmission lines. The anode in the electrolytic cells is made of nickel foam, and the cathode is made of copper sheet. The electrolytic current density is 100 mA / cm². 2 .

[0059] The zinc-cycle hydrogen production process is the same as in Example 1. After being processed by a gas scrubbing device, the hydrogen is fed into a hydrogen-fired boiler for combustion, heating water to produce steam, which drives a steam turbine generator to generate electricity. The hydrogen replaces 100% of the coal, and generates 100% of the heat.

[0060] The above specific embodiments are merely several preferred embodiments of the present invention. Based on the technical solutions of the present invention and the relevant teachings of the above embodiments, those skilled in the art can make various alternative improvements and combinations to the above specific embodiments.

Claims

1. A method for low-carbon transformation of coal-fired power generation, characterized in that: Hydrogen is produced by reacting metallic zinc and an aqueous alkaline electrolyte under the action of a catalyst. The reaction product of zinc is electrolyzed using renewable energy to regenerate metallic zinc, forming a zinc-based hydrogen production and electrolytic regeneration cycle. The produced hydrogen replaces coal combustion at a ratio of 5% to 100% to heat the working fluid for coal-fired power generation, driving the generator unit to generate electricity. The zinc-based hydrogen production cycle includes at least the following steps: (1) Hydrogen production by reaction of zinc metal: zinc metal and aqueous alkaline electrolyte are added to a hydrogen production reactor with a catalyst. The zinc reacts with the catalyst to reduce the water in the aqueous alkaline electrolyte to produce hydrogen. (2) Collect and transport the reaction products of zinc and electrolyte together: Collect the reaction products of zinc and electrolyte in the hydrogen generator, store them, and transport them to the location of the next step (3). (3) Electrolytic regeneration of zinc: The reaction products of zinc and electrolyte are added to an electrolytic cell with an anode and a cathode, and electrolysis is performed using renewable energy electricity. Oxygen is released at the anode and zinc is electrodeposited at the cathode. (4) Remove the zinc metal, collect the electrolyte, and store and transport it: Remove the zinc metal from the cathode of the electrolytic cell, collect the aqueous alkaline electrolyte after electrolysis, store it, and transport it to the reaction site of the next step (1).

2. The method for low-carbon transformation of coal-fired power generation according to claim 1, characterized in that: The concentration of hydroxide ions in the aqueous alkaline electrolyte is not less than 5 Mol / L.

3. The method for low-carbon transformation of coal-fired power generation according to claim 1, characterized in that: The hydrogen generated by the zinc cycle is fed into the coal-fired boiler in the power plant and burned together with the coal to heat the working fluid and drive the unit to generate electricity.

4. The method for low-carbon transformation of coal-fired power generation according to claim 1, characterized in that: The hydrogen generated by the zinc cycle is fed into a hydrogen-fired boiler to burn and heat the working medium to produce steam. This steam is then combined with the steam generated by the coal-fired boiler in the power plant to drive the unit to generate electricity.

5. The method for low-carbon transformation of coal-fired power generation according to claim 1, characterized in that: The hydrogen generated by the zinc cycle is fed into a hydrogen-fired boiler for combustion, heating the working fluid to drive the unit to generate electricity.

6. The method for low-carbon transformation of coal-fired power generation according to claim 1, characterized in that: The zinc-based hydrogen production process takes place within the power plant area, and electricity generated from renewable energy sources is transmitted to the power plant area via dedicated transmission lines to power electrolysis.

7. The method for low-carbon transformation of coal-fired power generation according to claim 1, characterized in that: The zinc-cycle hydrogen production takes place outside the power plant area. Electricity generated from renewable energy is transmitted to the outside of the power plant area via dedicated transmission lines to power electrolysis, while hydrogen is transported to the plant area via pipelines.