Question 2: Is the volatility of coal high or low? According to the use, if the volatility of coal is high, coal appears flammable. The flame is also very high when burning.
Question 3: What effect does the volatile matter of coal have on boiler combustion? What are the requirements for volatile matter in boiler coal blending, the standard of volatile matter in coal and the influence of volatile matter in coal on boiler combustion efficiency?
Volatile matter of coal, that is, the content of water in the substance (gas or liquid) that escapes after coal is heated to a certain temperature without air. The remaining residue is called cinder. Because volatile matter is not inherent in coal, but the product of pyrolysis at a specific temperature, it should be called volatile matter yield. The volatile matter of coal is not only an index to be considered in coking and gasification, but also an important index of power coal and an auxiliary index for pricing power coal according to its calorific value.
Volatile is an important index of coal classification. The volatile matter of coal reflects the degree of coal metamorphism, and the volatile matter decreases from large to small, and the degree of coal metamorphism changes from small to large. For example, the volatile matter of peat is as high as 70%, lignite is generally 40-60%, bituminous coal is generally 10-50%, and high metamorphic anthracite is less than 10%. The volatile matter of coal is related to the composition of coal and rock. The volatile matter of keratin is the highest, followed by vitrinite and bright coal, and silk charcoal is the lowest. Therefore, all countries in the world and China regard the volatile matter of coal as the most important index of coal classification.
The quality of volatile matter mainly depends on the coal you use. If used as power coal, the volatile matter is high and the coal is easy to burn. But if the volatile content of coking coal is too high, it may affect the quality of coke.
Because different coal mines have different coal qualities and different volatiles, they should be mixed and sent to boilers according to different coal ratios. There are 9 boilers in the Northern Suburb Thermal Power Plant, including high temperature and high pressure steam boilers, circulating fluidized bed boilers and hot water boilers. Different boilers have different requirements for volatile matter of coal. There is no best, only coal that can burn more heating is the most suitable.
The content of volatile matter in coal has a vital influence on the ignition and combustion of chain furnace.
When coal burns, volatiles are first separated, mixed with air and burned. Its specific gravity in the air is directly related to the flame propagation speed, and its volatile matter is appropriate and the ignition time is appropriate. When the initial temperature of the furnace increases, the flame propagation speed is accelerated, which makes the furnace temperature higher and is more conducive to the later combustion.
If the volatile matter is too high, it will increase the chemical incomplete combustion loss and reduce the thermal efficiency of the boiler.
The volatile matter is too low, ignition is delayed, and the combustion and burnout stages are relatively shortened, which leads to the increase of mechanical incomplete combustion and some will burn out the rear arch.
For the small chain furnace used in oil field, the best effect is to use coal with volatile content of about 23%.
Question 4: What are the factors that affect the determination of coal volatile matter? What is the effect of 1 and heating temperature?
(1) In a certain temperature range, temperature has a great influence on the yield of volatile matter. When any coal is heated without air, it usually goes through the processes of softening, expansion, gas evolution and solidification (primary pyrolysis). When the secondary pyrolysis is carried out at 700℃-900℃, even the pyrolysis temperature of the same coal sample and the amount of gas decomposed at this temperature are obviously different if the final heating temperature is different. Therefore, the output of volatile substances varies. From the point of view of thermal stability of products, the obtained coke block is thermally stable only when the secondary pyrolysis is over. Practice has proved that coal is not completely decomposed before 900℃. For example, below 850℃, carbonate decomposition is incomplete. The determination error of volatile matter is large, and the result is unstable. When the temperature rises from 850℃ to 900℃, the volatile matter increases greatly, but not much when it rises from 900℃. The results show that the thermal decomposition of most coal samples has been completed at 900℃.
(2) At present, the coking temperature of most coke ovens is (900-950)℃
(3) The International Organization for Standardization (ISO) stipulates that volatile matter should be determined at 900℃.
Therefore, the national standard GB/T26543min8+02-2008 stipulates that the furnace temperature rises to 920℃ and the coal sample is sent back to (910/0)℃ within 3 minutes.
2, the influence of the instruments used in the inspection
(1) Crucibles and Crucible Racks
The quality of volatile crucible has certain influence on the determination results of volatile matter. GB2 12 has always stipulated that the total mass of crucibles is (15 ~ 20) g. In recent years, the quality of volatile crucibles purchased in the market has changed greatly, and it is sometimes difficult to obtain crucibles with the mass of (15 ~ 20) g. In order to explore the possibility of expanding the range of available crucibles, we conducted experiments on the influence of crucible quality on the determination, and concluded that: That is, the greater the difference in crucible quality, the greater the systematic error between volatile matter determination results; B. The volatile crucible with crucible mass of (20 ~ 22) g is used for anthracite, which has no significant effect on the results; C. The use of (20 ~ 22) crucible for bituminous coal has no significant effect on the results; D volatile crucibles with crucible mass greater than 20g cannot be used for lignite. Nickel-chromium wire should be used for crucible frame, and the skin should not be cracked when burning, and the hole should meet the requirements, which is too big and easy to shake; If it is too small, it will stick to the frame after burning, which will affect the smooth progress of the test.
(2) muffle furnace
The muffle furnace required for volatile matter determination must meet the temperature required for volatile matter determination. The constant temperature area of muffle furnace should be measured with the oven door closed at least once a year, and the pyrometer (thermocouple) should be calibrated at least once a year. When measuring, because the muffle furnace is often used, when the thermocouple touches the bottom of the furnace, it should be padded in time, and the position of the thermocouple hot contact should be between the crucible and the bottom of the furnace, 20 ~ 30 nn away from the bottom of the furnace. Before each test, it is necessary to check whether the oven door and chimney are closed and whether the vent hole on the oven door is closed. If the oven door is not properly closed, it will cause air circulation, which will inevitably lead to high grades.
3. Effect of heating time
When coal samples are heated at the same temperature, different heating times will lead to different coke yields within a certain time limit. For example, (900 10)℃ is the final heating temperature, and when this temperature is reached, 1 minute or several minutes is maintained. Although pyrolysis is basically over, the yield of volatile matter is different. Only at this temperature, even if a limit time (7min) is kept, the coke yield will not change obviously. It shows that the secondary pyrolysis has been completed, and within 7 minutes of heating, the first 3 minutes have little influence, and the last 4 minutes have great influence, so the furnace temperature must be raised to (900 10)℃ within 3 minutes, otherwise the test will be invalid. Therefore, the furnace temperature should be controlled flexibly, and the furnace temperature should be restored to 9 10℃ within 3 minutes, and the best test conditions should be found by repeated operations. Generally, when the preheating degree is approaching and the heating time is 7 minutes, the oven door is opened for sample injection 1 ~ 2s in advance, and the time starts from putting the sample into the constant temperature zone, closing the oven door and taking out the crucible when the test is approaching 7 minutes. The action of taking and placing the crucible should be fast and steady, generally 2 ~ 4 seconds can be completed. This method is ideal and reliable, and has little influence on the determination results of different operators. The heating time must be strictly controlled at 7min minutes, including the temperature recovery time. If the time exceeds, it will lead to the result ... >>
Question 5: What is the volatile matter of coal? What are the factors that affect volatiles? Femtosecond detection shows that the volatile matter of coal refers to the volatile thermal decomposition products of organic matter in coal. Besides nitrogen, hydrogen, methane, carbon monoxide, carbon dioxide and hydrogen sulfide, there are some complex organic compounds. The volatiles in coal are mainly composed of water, hydrocarbon oxides and hydrocarbons (mainly CH4), but the physically adsorbed water (including external water and internal water) and mineral carbon dioxide in coal are not included in the volatiles. Determination method of volatile matter (GB/T2 12-200 1). Weigh a certain amount of air-dried coal samples, put them in a porcelain crucible with a cover, and put them in (900? 10), isolated from air and heated for 7 minutes. The reduced mass is taken as the percentage of the mass of the coal sample, and the moisture content of the coal sample is subtracted as the volatile matter of the coal sample.
Question 6: Volatile coal Volatile coal refers to the products (mainly H2, CmHn, CO, CO2, etc.) that some organic substances and minerals in coal decompose and escape when the coal is heated to a certain temperature. ) is called volatile coal. Volatile is the product of coal decomposition at high temperature, and its quantity will change with the change of heating temperature and heating time. Generally speaking, volatile matter refers to the gas production rate of organic matter and minerals heated by coal under certain conditions. That is, the dried coal is heated to 900+10℃ without air, and the gas separated for 7 minutes accounts for the mass percentage of dry ash-free components, which is called dry ash-free volatile Vdaf. Volatiles are gas products of hydrogen, oxygen, nitrogen, sulfur and a part of carbon in coal, most of which are combustible gases. With high volatile content, coal is easy to catch fire and stable in combustion. Therefore, volatile matter is an important index to characterize combustion characteristics, and it also has many influences on boiler work. For example, the size and shape of the furnace should be considered according to the size of volatile matter; Volatile matter affects the selection of burner type and air distribution mode, coal mill type and pulverizing system type. At the same time, volatile matter is also one of the important indexes of coal classification. Volatile is also the main coal quality index, which plays an important reference role in determining the processing and utilization mode and technological conditions of coal. Coal with low coalification degree has more volatile matter. If the combustion conditions are not suitable, the coal with high volatile content will easily produce unburned carbon particles when burning, commonly known as "black smoke"; And produce more pollutants such as carbon monoxide, polycyclic aromatic hydrocarbons and aldehydes, and the thermal efficiency is reduced. Therefore, suitable combustion conditions and equipment should be selected according to the volatile matter of coal.