1, leavening agent
The leavening agent will burst when heated in the high temperature area of the furnace, stirring the airflow in the coal seam, and promoting the separation of ash or combustion product CO on the surface of carbon particles and full combustion. The leavening agent used mainly refers to industrial salt and sodium chloride.
2. Oxidant
Oxidant is helpful to provide active oxygen necessary for combustion in preheating stage, combustion stage and final combustion stage, and promote the combustion of combustible volatiles and carbon particles during coal combustion. Commonly used oxidants are potassium permanganate, potassium chlorate and potassium perchlorate. Potassium permanganate can decompose oxygen at 200-240℃; Potassium chlorate can release oxygen at 300-350℃; Potassium perchlorate can decompose oxygen above 400℃; These decomposed oxygen provide the necessary oxygen source for coal combustion. In addition, solid nitrates such as sodium nitrate, potassium nitrate, cerium nitrate and barium nitrate can decompose and release oxygen when heated. Among them, the nitrate of the most active metal only releases a part of oxygen and becomes nitrite, while the nitrate of most other metals decomposes into metal oxide, oxygen and nitrogen dioxide. Nitrate is also a strong oxidant at high temperature.
3. Catalyst
There are manganese dioxide, magnesium oxide, alumina, iron oxide, iron oxide, ferric chloride, rare earth elements, sodium carbonate, bauxite and so on. Among them, alumina can inhibit the decomposition of CaSO4 at high temperature, and at the same time, it can form high-heat stable double salt with CaSO4, CaO and Al2O3. This product covers or wraps the surface of CaSO4 crystal to inhibit the decomposition of CaSO4. Metal oxides play an important role in oxygen transfer. Iron compounds can improve the combustion characteristics of coal by reducing the ignition temperature and reaction activation energy of coal combustion. Its effect is enhanced with the increase of dose. Among them, FeCl3 _ 3 _ 3 can increase the volatile matter in the process of coal combustion, reduce the ignition temperature of coal char, improve the combustion rate at low temperature, and make the ignition and combustion of coal easier. With the increase of addition, the improvement of coal combustion characteristics is also improving. The catalytic effect of FeCI2 on coal combustion is similar to that of FeCI3, but the improvement effect is relatively small; Fe2O3 has little effect on the combustion process of coal. While Fe2O3 can help coal combustion at about 550℃. Adding MnO _ 2 to coal can improve the combustion performance of pulverized coal. The experimental results show that adding 2% ~ 5% MnO 2 can increase the combustion rates of anthracite and bituminous coal by 14% ~ 18% and 3% ~ 8% respectively, and the combination of oxygen enrichment and adding MnO 2 can further improve the combustion-supporting effect. The combustion-supporting mechanism is that the active oxygen released by thermal decomposition accelerates the flame propagation speed in the early stage of ignition, and then improves the combustion rate of pulverized coal.
4. Desulfurization agent or sulfur-fixing agent
There are many kinds of sulfur-fixing agents, such as calcium-based sulfur-fixing agent, barium-based sulfur-fixing agent, magnesium-based sulfur-fixing agent, nano-material sulfur-fixing agent, etc. Sometimes, industrial wastes such as carbide slag, papermaking waste liquid, boron mud, red mud, salt mud and natural minerals such as limestone and dolomite are selected. There are three kinds of calcium-based sulfur-fixing agents: CaCO3, CaO and Ca(OH)2. Ca(OH)2 has the best sulfur fixation effect, followed by CaCO3 and CaO. Adding iron oxide to pure CaCO3 can promote the sulfur fixation reaction, reduce the activity of the reaction, and make the reaction easier. Moreover, the addition of iron oxide can increase the decomposition temperature of CaSO4 to a certain extent and accelerate the oxidation reaction of CaSO4. Simple mechanical mixing method of CaCO3, Fe2O3, CaO, etc. The combustion-supporting effect on coal combustion is weak. Some even have inhibitory effects, while adding CaCO3 or Ca(OH)2 (lime milk) and its mixed salts with a small amount of CaCl2, Fe(NO3)3 and FeSO4, and impregnating Fe(NO3)3 and FeSO4 have obvious combustion-supporting effects on bituminous coal and anthracite.
A large number of experimental results show that the effect of organic calcium-based sulfur fixing agent is better. The experimental results show that the calcination of organic calcium can be divided into three stages: 1 stage is dominated by the precipitation of water, the second stage is marked by the precipitation of organic gas, and the third stage is the decomposition of calcium carbonate. Calcium magnesium acetate is easy to decompose, and acetone gas begins to precipitate at 298℃. While calcium acetate and calcium propionate began to separate out acetone and pentone gas at 390℃ and 392℃, respectively. After adding magnesium calcium acetate or calcium propionate, the pyrolysis temperature of coal is advanced, the maximum volatilization rate is increased, the volatile release characteristic index is obviously improved, the pyrolysis process is more intense and the pyrolysis performance is improved. After adding organic calcium into coal, the sample loses weight quickly at the initial stage of combustion, and the combustion rate is much higher than that of raw coal. In the later stage, the sample burned gently, and the combustion rate was lower than that of raw coal. Organic calcium improves the ignition performance and overall combustion performance of coal. The magnesium-based sulfur-fixing agent includes magnesium carbonate and magnesium oxide. Its action principle is similar to that of calcium-based sulfur-fixing agent, and barium-based sulfur-fixing agent is mainly BaCO3. The decomposition temperature of pure barium sulfate is 1580℃, which is much higher than that of calcium sulfate, showing high thermal stability. Moreover, the metal activity of Ba is higher than that of Ca, and the corresponding oxide is more alkaline, which is more conducive to the reaction with acid oxide SO2. The sulfur-fixing effect of barium-based sulfur-fixing agent in high-temperature coal combustion is obviously higher than that of calcium-based sulfur-fixing agent, which has a good application prospect. Shell sulfur-fixing agent and nano-material sulfur-fixing agent also have applications. Using calcium-based, magnesium-based and barium-based sulfur-fixing agents, the sulfur-fixing reaction occurs between SO2 or SO3 and metal oxides. The general formula of main chemical reactions is: MEO+SO2+1/2o2 = MEO 44 or MEO+SO3 = MEO 4.
5. Smoke suppressants: The early smoke suppressants were mainly inorganic substances, and a small amount of organic substances were also used as smoke suppressants, including manganese ore powder, potassium hydroxide, acetic acid, potassium perchlorate, quicklime, zinc nitrate, aluminum nitrate, lead nitrate, calcium nitrate, cyclohexylamine, methanol, ethanol, Tween, diethyl ether, nitrate aqueous solution, lime milk and other components. In recent years, coal combustion-supporting and smoke-eliminating agents have developed towards organic solvents. In the preparation method described in China patent CN 10 1003759A, polyoxyethylene and clear water are used. The raw materials of the formula are easily available, the preparation method is simple and the cost is low. The main principle of smoke suppression is that the water molecules in the combustion-supporting smoke suppression agent stirred in coal at high temperature are separated into hydrogen and oxygen, which are mixed with coal gas and burned at the same time to improve the combustion calorific value, so that flue gas impurities can be burned at the same time at different combustion temperatures under the same conditions, thus achieving the purpose of smoke suppression. China cn10099690a added C 12 fatty alcohol polyoxyethylene (4) ether to the smoke suppressant. Other organic compound auxiliaries include alkyl alcohol ether, alkyl ester, olefin, aromatic compound, phosphate ester, chlorinated hydrocarbon, alkyl alcohol acyl group, etc.