A system and method for preparing ultrapure coal from low-ash coal.

Abstract

This invention discloses a system and method for preparing ultrapure coal from low-ash coal. Before feeding the coal powder into the molten alkali leaching tank, the coal powder undergoes microwave pretreatment. This pretreatment causes partial structural fractures in the coal, increasing the contact area between the reactants and the coal, thus accelerating the subsequent acid washing and leaching processes. Instead of directly acid washing after leaching, the system first performs water washing followed by acid washing. This simplifies the acid and alkali recovery steps and improves system economy. The main energy source for this system is high-temperature flue gas. The energy in the high-temperature flue gas is utilized in a cascade manner to power the system, improving energy efficiency. Furthermore, the final pass of the flue gas through the alkali washing solution allows CO2 in the flue gas to be used for alkali regeneration, reducing CO2 emissions and improving environmental benefits.

Description

Technical Field

[0001] This invention relates to the field of ultrapure coal preparation technology, and in particular to a system and method for preparing ultrapure coal from low-ash coal. Background Technology

[0002] The demand for high-purity carbon materials is increasing. Coal-based carbon materials have broad application prospects due to their low cost, good stability, and mature preparation processes. Ultra-pure coal can be used as a raw material for preparing coal-based carbon materials. Ultra-pure coal preparation methods are mainly divided into two categories: chemical methods and physical methods. In terms of physical methods, extensive research has been conducted on ultra-pure coal preparation technology, but many limitations remain, such as high energy consumption, high equipment maintenance costs, and low deep deashing efficiency. Only a few methods have achieved industrial application, with the vast majority still remaining in the laboratory stage. Some chemical methods for preparing ultra-pure coal have been industrialized, but some shortcomings remain in the process. For example, while the acid-base method has high deashing efficiency, strong process adaptability, and high clean coal yield, it uses large amounts of reagents, has low reagent recovery rates, high process costs, and the reagents are highly corrosive, posing a certain environmental impact. The traditional molten alkali leaching method directly mixes coal with molten alkali, causing a series of problems such as low reaction rates between ash in the coal and alkali, and low alkali recovery rates in subsequent processing. Summary of the Invention

[0003] The present invention aims to at least partially solve one of the technical problems in the related art.

[0004] Therefore, embodiments of the present invention propose a system and method for preparing ultrapure coal from low-ash coal.

[0005] On one hand, this invention proposes a system for preparing ultrapure coal from low-ash coal, comprising:

[0006] Molten alkali leaching tank;

[0007] The pretreatment process system is located upstream of the molten alkali leaching tank. The pretreatment process system includes a grinding and screening device, a microwave treatment device, a first acid washing device, a first water washing device, and a first drying device arranged sequentially upstream and downstream. The outlet end of the first drying device is connected to the inlet end of the molten alkali leaching tank.

[0008] The post-treatment process system is located downstream of the molten alkali leaching tank. The post-treatment process system includes a second water washing device, a second acid washing device, a third water washing device, and a second drying device arranged sequentially upstream and downstream. The inlet end of the second water washing device is connected to the outlet end of the molten alkali leaching tank.

[0009] An acid regeneration device and an alkali regeneration device are provided, with a flue gas treatment device installed downstream of the alkali regeneration device.

[0010] In some embodiments, high-temperature flue gas from the power plant provides a heat source for the first drying equipment, the second drying equipment, and the molten alkali leaching tank, wherein the temperature of the high-temperature flue gas is greater than 450°C.

[0011] In some embodiments, the high-temperature flue gas becomes medium-temperature flue gas after heat exchange in the first drying device, the second drying device, and the molten alkali leaching tank. The medium-temperature flue gas provides a heat source for the first pickling device, and the temperature of the medium-temperature flue gas is 380°C to 400°C.

[0012] In some embodiments, the medium-temperature flue gas becomes low-temperature flue gas after heat exchange in the first pickling equipment, and the low-temperature flue gas provides a heat source for the second pickling equipment. The temperature of the low-temperature flue gas is 200°C to 250°C.

[0013] In some embodiments, the low-temperature flue gas is heat-exchanged in the second pickling equipment and then introduced into the alkali regeneration equipment, whereby the alkali regeneration equipment absorbs and utilizes the carbon dioxide in the low-temperature flue gas.

[0014] In some embodiments, the first pickling device, the first washing device, the second washing device, the third washing device, and the molten salt leaching tank all employ paddle mixers.

[0015] In some embodiments, the waste liquid from the first pickling device, the first washing device, the second pickling device, and the third washing device is fed into the acid regeneration device.

[0016] In some embodiments, the waste liquid from the second washing device is fed into the alkali regeneration device.

[0017] In some embodiments, low-ash raw coal is processed by the grinding and screening device to obtain coal powder with a particle size of less than 0.5 mm.

[0018] On the other hand, the present invention proposes a method for preparing ultrapure coal from low-ash coal, comprising the following steps:

[0019] Low-ash raw coal is ground, screened, and microwave treated before entering the first pickling equipment for pickling. After pickling, it enters the first water washing equipment for water washing. After water washing, it enters the first drying equipment for drying and then passes into the molten alkali leaching tank.

[0020] After leaching, leached coal is obtained. The leached coal is washed by a second washing equipment and then acid-washed by a second acid washing equipment. After acid washing, it is washed by a third washing equipment and then dried by a second drying equipment to obtain ultrapure coal.

[0021] The high-temperature flue gas provides a heat source for the first drying equipment, the second drying equipment, and the molten alkali leaching tank. The medium-temperature flue gas obtained after heat exchange of the high-temperature flue gas provides a heat source for the first pickling equipment. The low-temperature flue gas obtained after heat exchange of the medium-temperature flue gas provides a heat source for the second pickling equipment. The low-temperature flue gas after heat exchange is then introduced into the alkali regeneration equipment.

[0022] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0023] This invention pretreats the coal powder with microwaves before feeding it into the molten alkali leaching tank. The microwave pretreatment causes some of the coal's structure to break and form cracks, increasing the contact area between the reactants and the coal, thus accelerating the subsequent acid washing and leaching processes.

[0024] This invention does not directly use acid washing when processing leached coal. Instead, it first performs water washing followed by acid washing. This simplifies the acid and alkali recovery process and improves the system's economic efficiency.

[0025] The main energy source of the system of this invention comes from high-temperature flue gas. The energy in the high-temperature flue gas is used to power the system through a cascade process, which improves the energy utilization efficiency. In addition, the flue gas finally passes through an alkaline scrubbing solution, and the CO2 in the flue gas is used for alkaline regeneration, which reduces CO2 emissions and improves environmental benefits. Attached Figure Description

[0026] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the following description of the embodiments taken in conjunction with the accompanying drawings, wherein:

[0027] Figure 1 This is a schematic diagram of the system for preparing ultrapure coal from low-ash coal according to the present invention. Detailed Implementation

[0028] Embodiments of the present invention are described in detail below, examples of which are illustrated in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.

[0029] The system and method for preparing ultrapure coal from low-ash coal according to embodiments of the present invention are described below with reference to the accompanying drawings.

[0030] like Figure 1 As shown, the system for preparing ultrapure coal from low-ash coal of the present invention includes a molten alkali leaching tank, a pretreatment process system, a post-treatment process system, an acid regeneration device, and an alkali regeneration device. The pretreatment process system is located upstream of the molten alkali leaching tank, and the post-treatment process system is located downstream of the molten alkali leaching tank.

[0031] The pretreatment process system includes a grinding and screening device, a microwave treatment device, a first acid washing device, a first water washing device, and a first drying device arranged sequentially upstream and downstream. The outlet end of the first drying device is connected to the inlet end of the molten alkali leaching tank.

[0032] In the preparation of ultrapure coal from low-ash coal, the raw low-ash coal is first crushed, coarsely ground, and finely ground by a grinding and screening device to obtain coal powder. The particle size of the coal powder obtained after processing by the grinding and screening device is less than 0.5 mm. Then, the coal powder is sent to a microwave processing device for microwave treatment. After microwave treatment, the coal powder enters the first acid washing device for acid washing. The acid washing temperature in the first acid washing device is 70℃~95℃. Acid washing can dissolve most of the minerals in the coal, such as Fe2O3, CaO, MgO, Na2O, and CaCO3. After acid washing, the ash in the coal mainly consists of SiO2, aluminum-containing minerals, and sulfur-containing minerals. Before the coal powder enters the molten alkali leaching tank, the coal is acid-washed. This step removes most of the alkali metals from the coal, and the remaining ash is mainly SiO2, aluminum-containing minerals, and sulfur-containing minerals. After the coal powder enters the molten alkali leaching tank, NaOH can react quickly with these substances, which improves the leaching speed and efficiency. At the same time, it reduces the types of reactants, simplifies the subsequent alkali recovery steps, and improves the system's economy.

[0033] Before feeding pulverized coal into the first acid washing equipment, it undergoes microwave pretreatment. Different substances exhibit different characteristics when exposed to microwave radiation. Some substances absorb microwaves, but their absorption capacity varies; others do not absorb microwaves and may even reflect them. This difference in characteristics results in varying heating rates among different substances in the coal during microwave pretreatment. After a period of microwave heating, phase transitions and expansion occur in the pulverized coal. The phase transition primarily involves the water contained in the pulverized coal, generating internal pressure within the coal matrix, which weakens the structure and causes cracks. Therefore, microwave pretreatment increases the contact area between minerals and acids / alkalis, making it easier to remove ash from the coal and improving deashing efficiency.

[0034] After being acid-washed in the first acid washing unit, the pulverized coal enters the first water washing unit for washing. The purpose of water washing is primarily to remove residual hydrochloric acid and water-soluble substances produced during acid washing. The washing time is 1-2 hours, and the resulting solution should be nearly neutral. Following water washing, the pulverized coal enters the first drying unit for drying. After drying, it enters the molten alkali leaching tank. The dried pulverized coal undergoes leaching in the molten alkali leaching tank. During leaching, the temperature range is 370℃-390℃, and the leaching time is 1-3 hours. Silicon compounds, free SiO2, and most silicates in the coal can react with OH-. -The reaction produces soluble sodium silicate, which is then removed. Kaolin-like compounds and certain silicates react with alkali to produce acid-soluble derivatives, Na2O·Al2O3·2SiO2·xH2O.

[0035] The post-processing system includes a second washing unit, a second acid washing unit, a third washing unit, and a second drying unit, arranged sequentially upstream and downstream. The inlet of the second washing unit is connected to the outlet of the molten alkali leaching tank. After the leaching process, leached coal is obtained. The leached coal undergoes washing, acid washing, re-washing, and drying to obtain ultrapure coal product. Specifically, the leached coal flowing out of the molten alkali leaching tank enters the second washing unit for washing. The main purpose of washing is to remove the alkali mixed in the leached coal, as well as water-soluble substances such as sodium silicate generated during the leaching process. Washing is continued until the washing wastewater is nearly neutral. After washing in the second washing unit, the leached coal enters the second acid washing unit for acid washing. The temperature range of the acid washing solution is 50℃~70℃. The purpose of acid washing is to remove acid-soluble substances generated during the leaching process, achieving a deep ash removal effect. After being acid-washed in the second acid washing unit, the leachate coal enters the third water washing unit for washing. The purpose of water washing is to remove residual hydrochloric acid and various impurity ions. This water washing needs to be repeated until the washing solution is neutral. After being washed in the third water washing unit, the leachate coal enters the second drying unit for drying. After drying, ultrapure coal is obtained.

[0036] The leachate coal undergoes a process of water washing, acid washing, and then water washing again. The water washing step before acid washing allows for the recovery of a large amount of alkali mixed in the leachate coal. If water washing is omitted before acid washing and acid washing is performed directly, the acid and alkali will react, increasing the amount of acid used and significantly increasing the cost of alkali recovery.

[0037] In some embodiments, the first pickling equipment, the first washing equipment, the second washing equipment, the second pickling equipment, the third washing equipment, and the molten salt leaching tank all employ paddle agitators. The paddle agitator uses the rotation of the paddle to thoroughly mix the pulverized coal with the solution, promoting the reaction of relevant substances in the pulverized coal with the corresponding solution or molten alkali. Furthermore, the paddle agitator has a simple structure, reliable performance, and is easily scaled up.

[0038] High-temperature flue gas from the power plant provides a heat source for the first drying unit, the second drying unit, and the molten alkali leaching tank; the temperature of the high-temperature flue gas exceeds 450℃. After heat exchange in the first drying unit, the second drying unit, and the molten alkali leaching tank, the high-temperature flue gas becomes medium-temperature flue gas, which provides a heat source for the first pickling unit; the temperature of the medium-temperature flue gas is 380℃~400℃. After heat exchange in the first pickling unit, the medium-temperature flue gas becomes low-temperature flue gas, which provides a heat source for the second pickling unit; the temperature of the low-temperature flue gas is 200℃~250℃. After heat exchange in the second pickling unit, the low-temperature flue gas is introduced into the alkali regeneration unit, where the alkali regeneration unit absorbs and utilizes the carbon dioxide in the low-temperature flue gas.

[0039] Specifically, the heat source for the entire system is primarily provided by high-temperature flue gas from the power plant, with a temperature exceeding 450°C. In the first drying unit, the second drying unit, and the molten alkali leaching tank, the high-temperature flue gas undergoes heat exchange through heat exchangers, providing heat for heating the molten alkali in the molten alkali leaching tank and maintaining its temperature, while also providing a heat source for the first and second drying units. The flue gas after heat exchange is then medium-temperature flue gas, with a temperature of 380°C to 400°C. In the first pickling unit, the medium-temperature flue gas undergoes heat exchange through a heat exchanger, providing a heat source for the pickling process. The flue gas after heat exchange is then low-temperature flue gas, with a temperature of 200°C to 250°C. In the second pickling unit, the low-temperature flue gas undergoes heat exchange through a heat exchanger, with a temperature of 50°C to 70°C after the heat exchange. The low-temperature flue gas after heat exchange is fed into an alkali regeneration device, which absorbs carbon dioxide from the flue gas for use in the alkali regeneration process. After steps such as gas washing, the flue gas reaches room temperature. A flue gas treatment device is installed downstream of the alkali regeneration device. After exiting the alkali regeneration device, the flue gas enters the flue gas treatment device, and after treatment, it is discharged into the atmosphere. In this process, the flue gas first enters the first acid washing device and then the second acid washing device because the temperature of the leached coal is very high, and it can provide a certain amount of heat. Therefore, the second acid washing device can utilize the lower-temperature flue gas. The system of this invention realizes the cascade utilization of high-temperature flue gas energy, maximizes energy utilization efficiency, achieves deep deashing of low-ash coal, and provides a new approach for flue gas treatment.

[0040] Waste liquids from the first pickling unit, the first washing unit, the second pickling unit, and the third washing unit are fed into an acid regeneration unit. Waste liquid from the second washing unit is fed into an alkali regeneration unit. Specifically, the acid regeneration unit is used in the acid regeneration process. The pickling waste liquids from the first and second pickling units, as well as the washing waste liquids from the first and third washing units, contain a large amount of acid. Passing these waste liquids into the acid regeneration unit yields acid and metallic mineral byproducts. The obtained acid can be reused in the system of this invention, thus achieving acid recycling and reducing energy consumption. In this invention, the waste liquids from the first pickling unit, the first washing unit, the second pickling unit, and the third washing unit are treated together, simplifying the acid recovery process. The alkali regeneration unit is used in the alkali regeneration process. The washing waste liquid from the second washing unit contains a large amount of alkali. Passing this waste liquid into the alkali regeneration unit yields alkali and silicon and aluminum byproducts. The obtained alkali can be reused in the molten alkali leaching process of this invention, thus achieving alkali recycling and reducing energy consumption. The alkali recovery process involves first carbonizing the waste liquid by introducing CO2, causing impurity ions in the waste liquid to precipitate. Then, filtration is performed, with the filtrate primarily containing Na2CO3 and the precipitates consisting mainly of silicon and aluminum. Next, the filtrate is causticized by adding CaO to react with Na2CO3, generating CaCO3 precipitate and NaOH. After a series of further treatments, alkali regeneration is complete. In this invention's system, the CO2 in the flue gas can provide raw materials for the alkali treatment step, reducing CO2 emissions.

[0041] A method for preparing ultrapure coal from low-ash coal, utilizing the system for preparing ultrapure coal from low-ash coal of the present invention, includes the following steps:

[0042] Low-ash raw coal is ground, screened, and microwave treated before entering the first pickling equipment for pickling. After pickling, it enters the first water washing equipment for water washing. After water washing, it enters the first drying equipment for drying and then passes into the molten alkali leaching tank.

[0043] After leaching, leached coal is obtained. After being washed by the second washing equipment, the leached coal enters the second acid washing equipment for acid washing. After acid washing, it enters the third washing equipment for washing. After washing, it enters the second drying equipment for drying to obtain ultrapure coal.

[0044] The high-temperature flue gas provides a heat source for the first drying equipment, the second drying equipment, and the molten alkali leaching tank. The medium-temperature flue gas obtained after heat exchange of the high-temperature flue gas provides a heat source for the first pickling equipment. The low-temperature flue gas obtained after heat exchange of the medium-temperature flue gas provides a heat source for the second pickling equipment. The low-temperature flue gas after heat exchange is then fed into the alkali regeneration equipment.

[0045] In one specific embodiment, the low-ash raw coal is first processed in a grinding and screening device through grinding, crushing, coarse grinding, fine grinding, and screening to obtain coal powder with a particle size of less than 0.5 mm. Then, the coal powder is pretreated using microwave processing equipment. The microwave-treated coal is first processed using a concentration of 2 mol·L⁻¹. -1 The coal was acid-washed in a dilute hydrochloric acid solution at 95°C for 1 hour in the first acid washing unit. Then, the coal was washed and dried in the first water washing unit and the first drying unit, respectively. The washed and dried acid-washed coal was then fed into a molten alkali leaching tank and mixed with molten NaOH for leaching and deashing. After leaching for 2 hours, the leached coal was rinsed in the second water washing unit, and then treated with a 2 mol·L⁻¹ solution. -1 The coal was acid-washed in a dilute hydrochloric acid solution at 70°C for 1 hour in a second acid washing device. The acid-washed coal was then washed and dried in a third water washing device and a second drying device to obtain an ultra-pure coal product with an ash content of less than 1%.

[0046] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms may refer to different embodiments or examples. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0047] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this invention, "a plurality of" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0048] Although embodiments of the invention have been shown and described, those skilled in the art will understand that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the claims and their equivalents.

Claims

1. A system for preparing ultrapure coal from low-ash coal, characterized in that, include: Molten alkali leaching tank; The pretreatment process system is located upstream of the molten alkali leaching tank. The pretreatment process system includes a grinding and screening device, a microwave treatment device, a first acid washing device, a first water washing device, and a first drying device arranged sequentially upstream and downstream. The outlet end of the first drying device is connected to the inlet end of the molten alkali leaching tank. The post-treatment process system is located downstream of the molten alkali leaching tank. The post-treatment process system includes a second water washing device, a second acid washing device, a third water washing device, and a second drying device arranged sequentially upstream and downstream. The inlet end of the second water washing device is connected to the outlet end of the molten alkali leaching tank. The system includes an acid regeneration device and an alkali regeneration device. A flue gas treatment unit is installed downstream of the alkali regeneration device. Waste liquids from the first acid washing device, the first water washing device, the second acid washing device, and the third water washing device are fed into the acid regeneration device, and waste liquids from the second water washing device are fed into the alkali regeneration device. High-temperature flue gas from the power plant provides a heat source for the first drying equipment, the second drying equipment, and the molten alkali leaching tank. The temperature of the high-temperature flue gas is greater than 450°C. After heat exchange in the first drying equipment, the second drying equipment, and the molten alkali leaching tank, the high-temperature flue gas becomes medium-temperature flue gas. The medium-temperature flue gas provides a heat source for the first pickling equipment. The temperature of the medium-temperature flue gas is 380°C to 400°C. After heat exchange in the first pickling equipment, the medium-temperature flue gas becomes low-temperature flue gas. The low-temperature flue gas provides a heat source for the second pickling equipment. The temperature of the low-temperature flue gas is 200°C to 250°C. After heat exchange in the second pickling equipment, the low-temperature flue gas is introduced into the alkali regeneration equipment, where the alkali regeneration equipment absorbs and utilizes the carbon dioxide in the low-temperature flue gas.

2. The system as described in claim 1, characterized in that, The first pickling equipment, the first water washing equipment, the second water washing equipment, the second pickling equipment, the third water washing equipment, and the molten alkali leaching tank all employ paddle agitators.

3. The system as described in claim 1, characterized in that, Low-ash raw coal is processed by the grinding and screening device to obtain coal powder with a particle size of less than 0.5 mm.

4. A method for preparing ultrapure coal from low-ash coal, characterized in that, The system described in any one of claims 1-3 includes the following steps: Low-ash raw coal is ground, screened, and microwave treated before entering the first pickling equipment for pickling. After pickling, it enters the first water washing equipment for water washing. After water washing, it enters the first drying equipment for drying and then passes into the molten alkali leaching tank. After leaching, leached coal is obtained. The leached coal is washed by a second washing equipment and then acid-washed by a second acid washing equipment. After acid washing, it is washed by a third washing equipment and then dried by a second drying equipment to obtain ultrapure coal. The high-temperature flue gas provides a heat source for the first drying equipment, the second drying equipment, and the molten alkali leaching tank. The medium-temperature flue gas obtained after heat exchange of the high-temperature flue gas provides a heat source for the first pickling equipment. The low-temperature flue gas obtained after heat exchange of the medium-temperature flue gas provides a heat source for the second pickling equipment. The low-temperature flue gas after heat exchange is then introduced into the alkali regeneration equipment.

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