Production process and application range of coal-based activated carbon
The composition of coal ash is relatively complex. It is a product of the conversion of inorganic matter in coal. Its content is related to the original coal-forming plants and coal-forming environment. There is also a small amount of alkali metal K2O, Na2O, etc. in the coal ash. The melting temperature of each component in the coal ash is different, and the melting temperature of the coal ash cannot be measured by a single mineral temperature. Coal ash is actually a composite of various mineral components, which are in the form of silicates and aluminosilicate pots. The composition of the coal ash is complex and, therefore, there is no exact melting temperature. The melting characteristics of the coal ash can only be represented by temperature characteristics.
The ash fusibility of coal is an important coal quality parameter for boiler combustion and activation of coal-based activated carbon. The ash melting point of coal is too low, and it tends to be crusted on the furnace, which affects the normal combustion. If coal-based activated carbon is produced from coal with low ash melting point, in the activation process, the carbonized material is easy to climb on the cremation ballast, and the tumor is affected, which affects the quality of the activated carbon and the life of the activation furnace.
[The burning point of coal affects the quality of coal-based activated carbon]
The action of coal and oxygen raises the temperature of the coal body. When the temperature reaches a certain level, the coal begins to ignite and burn. This temperature is called the ignition point of coal. However, the coal ignition point measured by the laboratory is only a relative value. It is a mixture of NaNO2 and coal samples in a certain proportion. It is heated at a specified heating rate in a burning point test device to deflagrate it. The detonation temperature is the ignition point of coal. . Obviously, the ignition point measured by this method is lower than the ignition point of the actual coal.
The burning point of coal is greatly affected by the type of coal, such as the burning point of peat (225~280 °C), lignite (250~450 °C), anthracite (440-500 °C), and the burning point of coke is higher (700~750 °C). Different coals have different ignition points. Coal with high water content, high oxygen content, high volatile matter and high pyrite content have low ignition points and are easy to spontaneously ignite. Temperature, coal rock composition, and coal particle size are also factors that affect the ignition point of coal.
In the production of activated carbon, the carbonized material prepared by coal with high ignition point is not easily oxidized in carbonization. In the activation furnace, the temperature is easily controlled, which is beneficial to the quality of the activated carbon.
[Acid Activated Carbon Activation and Physical Activation]
Activated carbon is a traditional and modern material. With the continuous development of human society, activated carbon has been widely used in many fields such as food, medicine, chemical industry and environmental protection; the number of applications is also increasing. In recent years, the global use of activated carbon has increased year by year. China's activated carbon production has been ranked in the forefront of the world, but the performance of activated carbon produced in China is generally good, and the performance of activated carbon is mainly dependent on imports.
The raw materials for preparing activated carbon are very rich, such as coal, nut shell, rice husk, petroleum coke, resin, asphalt, used tires and the like. Among them, the shell-shell raw materials have a wide range of sources, low cost, and have a high-quality natural structure, which is conducive to the formation of a developed microporous structure, which has received more and more attention. The preparation methods of activated carbon are mainly divided into two categories: chemical activation method and physical activation method. Chemical activation is a series of cross-linking or polycondensation reactions with carbon materials through chemical reagents such as KOH, Zncl2, etc., to create rich micropores; physical activation is the use of air, carbon dioxide, water vapor and other oxidizing gases at high temperatures and carbon The carbon atoms react in the material. Chemical activation has the advantages of short activation time and low activation temperature. However, the use of a large number of chemical reagents increases the preparation cost, and has a strong corrosive effect on the equipment at a high temperature, and requires a large amount of water in the washing process, and these wastewaters can meet the environmental discharge requirements after a complicated treatment process. For this reason, at present, most of the industry uses steam activation to prepare activated carbon.
The advantage of activation physics is that the process is simple, clean, and does not require washing after activation. The steam activation speed is fast, but it is difficult to obtain high specific surface area activated carbon; activated carbon dioxide can be used to obtain high specific surface area activated carbon, but its activation temperature is high and the speed is slow, so the energy consumption is high, and the activation time usually takes ten hours. Even hundreds of hours. The addition of a suitable catalyst can effectively shorten the activation time, but it is still difficult to meet the industrial production needs.
In short, both chemical and physical activation have their own advantages and disadvantages. On the basis of keeping the preparation process simple and clean, how to further reduce the preparation cost becomes the focus of future research.
[Determination of particle size of coal-based granular activated carbon]
The test method of coal-based granular activated carbon--the measurement standard of particle size stipulates the content of the coal-based granular activated carbon particle size side setting instrument, the side-setting step and the measurement result, and the standard is applicable to the determination of the particle size of the coal-based granular activated carbon.
1, method summary
A certain amount of purified water is sampled by using a coal granular activated carbon sample on a vibrating screen, and the mass of the sample remaining on each sieve layer as a percentage of the mass of the original sample indicates the particle size distribution of the sample.
2, measuring step
a. According to the technical requirements of the product, select a corresponding set of sieve layers, arranged according to the size of the mesh holes, arranged from top to bottom, and placed on the vibrating screen machine.
b. Weigh 100 g of the sample into the uppermost sieve of the vibrating screen, cover the sieve cover, and fasten the complete sieve. Start the vibrating screen and start the timer (or bully stopwatch) at the same time.
c. Vibrating screen (600 ± 10) s.
d. Loosen the shaker clip, take off the screen cover, gently remove the layers in turn and collect the samples in each layer separately. The activated carbon stuck on the sieve hole is gently shaken by a screen frame or brushed, and also sieved on the sieve layer.
e. Weigh each sieve layer and the screening quality in the chassis (accurate to o.1),
f. Repeat steps s. l to s. 5 and make another sample.
3. Calculation formula of particle size of coal granular activated carbon:
Li(%)=mi/m×100%
The mass fraction of the Li-i layer particle size in the formula, %;
Mi—the mass of the sample on the i-th layer sieve, B:
M—the mass of the original sample, g.
[Use function of activated carbon]
Activated carbon is widely used in industrial three waste treatment, solvent recovery, food and beverage purification, carrier, medicine, gold extraction, semiconductor applications, battery and electrical energy storage. Adjusting the pore structure of activated carbon and modifying the surface groups play an important role in improving its special properties and specific adsorption catalysis.
Activated carbon can be prepared from most carbonaceous materials such as wood, sawdust, coal, peat, husk, pit, bagasse and rice husk, petroleum waste, waste plastic, waste leather, waste tires, paper waste, municipal waste. And other waste. At present, it is generally believed that the shell is the best raw material for the preparation of activated carbon, but the nut shell resources in China are very limited, and it is not easy to concentrate, store and expensive. In recent years, various types of wastes with low prices and wide sources have been tested at home and abroad for the preparation of activated carbon [1]. At present, the performance of activated carbon produced from waste is not high, and the practical application is still relatively small, but it is increasingly favored because of its low price, high carbon content, easy availability of materials, sufficient raw materials and green non-toxicity. The effective use of waste to produce activated carbon not only saves resources but also protects the ecological environment.
Among the environmental protection industries, the largest amount of activated carbon is urban water purification projects and sewage treatment projects, accounting for more than 70% of the total amount of activated carbon in the environmental protection industry; followed by air purification, the amount of activated carbon is also increasing year by year. However, there is a certain degree of environmental pollution in the production process of activated carbon. In the case of increasingly strict national environmental protection policies, solving the environmental problems of activated carbon production enterprises is a major issue for the sustainable development of the activated carbon industry. Some experts pointed out that in the next 10-20 years, China's demand for activated carbon will further increase, China's activated carbon industry will develop towards low consumption, low pollution and high quality, high technology [2].
As an excellent adsorbent, activated carbon has a wide range of applications in the purification of drinking water, the advanced treatment of wastewater, purification or storage of gases. Studies have shown that activated carbon mainly has a strong adsorption effect on organic substances with a relative molecular mass of less than 3,000, especially 500-1000. The main factors affecting the performance of activated carbon are specific surface area, pore volume and pore size distribution. Generally, the larger the specific surface area and pore volume, the stronger the adsorption capacity.
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