Why does cement factory SO2 discharge exceed standard?
Date：2019-08-23 15:31 Source：cementepcViews:
A company's 5000t/d clinker production line was put into production in March 2010, and the emission concentration of SO2 was relatively high at the beginning of production.Therefore, the company has been trying various measures, such as optimizing the ratio, adjusting the process operation, strengthening the raw material index control, strengthening the process management, selecting the appropriate alkaline raw materials, absorbing sulfur in the waste gas in the raw material grinding system, etc., which has greatly reduced the emission concentration of SO2.
1 the necessity of controlling SO2
When the discharge concentration of SO2 is high, in order to control the discharge, the company has to reduce production and reduce coal operation, and the kiln condition fluctuates greatly. The minimum output of the clinker table is about 150t/h (daily output is 3600t/d), and the standard coal consumption, clinker power consumption, power generation power and other important indicators are poor, so the clinker cost increases a lot.
2. Mechanism analysis
The sulfur in the raw materials exists in the form of sulfur compounds, of which the sulfur compounds are divided into organic sulfur compounds and inorganic sulfur compounds. The decomposition temperature of these sulfur compounds is between 300 and 600℃, which has a great influence on sulfur in the exhaust gas of kiln tail.The other type of sulfur, in the form of sulfate, has little or no effect on sulfur in the exhaust due to its high decomposition temperature.
Sulfur existing in sulfide in raw materials is one of the most critical factors affecting SO2 emission.The reactions of this part of sulfide include: inorganic sulfide reacts with oxygen to form corresponding oxides and SO2;Organic sulfide generates SO2, CO2 and water.The above reactions were carried out between 300 and 600℃, mainly concentrated in the interior of C2 and C3.In order to prove this theory, we sampled and analyzed C2, C3, C4 and C5 skids during the maintenance and stopping of kiln, and found that the SO3 content in C2 and C3 skids was the highest, up to 36.8%.Since the decomposition rate of CaCO3 in C2 and C3 is low, and the content of active CaO is also low, most of these SO2 are discharged with waste gas.
3. Internal circulation of sulfur
SO2 decomposed by various sulfide compounds will also be absorbed by CaO and other substances in decomposition furnace and preheater, forming the inner cycle of high-temperature chemical enrichment of SO2.Research shows that CaO solid sulfur reaction efficiency is low, we worked in controlled trials, the sulfur content in coal rises, the growth in the exhaust gas of sulfur is more obvious), most will enter the waste gas, part of SO2 gas condensation in the raw material of low temperature, along with the raw materials into the next level of preheater, yet again at high temperature decomposition, the formation of SO2 circulate in the enrichment of low temperature physics, chemistry.
The final solution to the excessive sulfur content is to add calcium carbide residue and other alkaline substances in the waste gas for absorption.
4. Production practice
In 2010, when the production line was put into production, the company used limestone, sandstone, high-alumina ore and sulfuric acid slag as ingredients. The discharge amount of SO2 in this charging scheme was relatively high, reaching 200~400mg/m3. Subsequently, silica sand was used to replace sandstone and wet ash was used to replace high-alumina ore as ingredients.
One of the effective ways to reduce SO2 is to mix limestone well.The first thing the company does when it lowers SO2 is grab limestone from the mines.When the new production line was put into production, the emission of SO2 in the waste gas continued to be on the high side, and it fluctuated greatly. We had gone through many detours, but finally found a solution, which was to strictly control the collocation of limestone in mines.Therefore, the company has repeatedly carried out comprehensive and detailed planning and analysis on each mine site, so as to find the best scheme for matching limestone. The limestone used can be divided into eight parts for matching.SO2 emission concentration is reduced by about 100~150mg/m3 after combined use of limestone.
Increasing the restriction of sulfur in the raw material and burning material to create conditions for the control of SO2.Due to the limitation of reaction time, reaction concentration and other conditions, the absorption efficiency of CaO generated by the decomposition of SO2 from coal combustion by CaCO3 in the decomposition furnace is low.Therefore, the sulfur content in the raw and burning materials of clinker is also limited, especially the sulfur content in the raw coal, the sulfur content of the raw coal used by the company ranges from 0.3% to 1.0%.The sulfur content in raw coal is basically controlled at about 0.3%.It has been proved that the content of sulfur in coal has an important influence on the emission of sulfur in waste gas, especially when the kiln is in bad condition and the excess coefficient of air in the kiln system is low.
At the beginning of replacing high-alumina ore with wet ash, sulfur in wet ash also fluctuates greatly, ranging from about 0.5% at low sulfur content to more than 6% at high sulfur content.After the company limits the sulfur in wet ash, the probability of kiln ring formation is greatly reduced. Although most of the sulfur in wet ash exists in the form of sulfate, limiting the content of sulfur can not only reduce the introduction of sulfur, but also reduce the occurrence of technological accidents.
Good process management of preheater system is also a way to reduce sulfur emission.Around the process management, the main work we do has the following aspects.
1) clean the skin of the preheater.
2) seal and seal the system well.
3) match the ventilation ratio of kiln and furnace.Ensure reasonable air surplus coefficient of smoke chamber, decomposition furnace outlet and C1 outlet.
4) adjust the position of burner to ensure the thermal system of kiln flame and kiln system.
5) clean the coal pipe of kiln head to ensure the full combustion of coal.
6) control the quality of pulverized coal, raw materials easy to burn, etc.
The sulfur emission concentration in the waste gas of the production line decreased from about 300mg/m3 to less than 100mg/m3. The air volume in the working condition was calculated as 450,000 m3/h, and 135kg of SO2 was discharged per hour.After the effective control of sulfur, cement enterprises can make better use of limestone resources, especially the limestone resources with high sulfur content, which also changes the passive production situation. The kiln system is more stable, and there is no sharp decline in output when the kiln is in Taiwan.Jiangsu LVSSN more products, about the Raymond mill can consult our online customer service