How to control and improve steel grade ammonium sulfate Quality
As a synthetic by-product of coke production enterprises, ammonium sulfate is obtained by using sulfuric acid and coke oven gas, a by-product of coke production, to purify and recover, then directly carry out a neutralization reaction, and absorb ammonia in the gas. This article discusses the quality problems of ammonium sulfate products such as discolouration and entrainment of black particles and gives corresponding solutions.
The Process of Coal Desulfurization
The main product of the production enterprise is coke, and the by-products mainly include purified gas and tar, crude benzene, sulfur, ammonium sulfate, etc. purified and recovered from the gas. Coal is a complex polycyclic substance with many benzene rings condensed. It can be coked into coke when heated. It is usually called coking coal. Coking coal undergoes a series of physical and chemical changes in the coke oven under the condition of being isolated from the air and heated at high temperature. In addition to forming coke, it also cracks to generate volatile products, which are called coal gas.
In daily production, the coke oven gas from the blower enters the gas preheater after passing through the electric tar catcher. Coke oven gas is commonly known as raw gas, which contains a large amount of coal tar and ammonia. Coke oven gas is heated in the gas preheater to about 80 ℃ and enters the gas-liquid separator. The gas-liquid separator removes coal tar and ammonia from the coke oven. separated from the gas. The coal tar, ammonia water and oil residue mixture separated from the gas-liquid separator enters the tar ammonia water clarification tank, where gravity separation is carried out. The desulfurized gas enters the saturator after being heated by steam, and the gas is sprayed and washed by the circulating mother liquor containing free acid in the saturator ring chamber, so that the free acid and the ammonia in the gas react to form ammonium sulfate dissolved in the mother liquor, thereby achieving removal The purpose of ammonia gas NH3 in gas.
The process of ammonium sulfate formation
Ammonium sulfate is a by-product in the gas purification process, and its reaction is an exothermic process.
1) H2SO4 + NH3 → NH4HSO4 (excessive acidity in circulating mother liquor, high free acid content)
2) NH4HSO4 + NH3 → ( NH4 ) 2 SO4 (the degree of saturation of liquid ammonia gas in the circulating mother increases, and the content of free acid is low)
The mother liquor circulation pump continuously draws the mother liquor from the upper part of the crystallization chamber of the saturator, and sends it to the upper annular spray chamber for spraying. The circulating mother liquor that has absorbed ammonia flows from the central downcomer to the bottom of the crystallization chamber of the saturator to form larger ammonium sulfate crystals, which are naturally classified according to particle size. The crystallization pump continuously pumps the thick slurry containing ammonium sulfate crystals from the bottom of the saturator and sends it to the centrifuge through the crystallization tank. The centrifuge dries the ammonium sulfate crystals with high humidity and rinses the ammonium sulfate crystals with industrial clean water to reduce free acid. content, the ammonium sulfate crystals from the centrifuge are sent to the vibrating fluidized bed dryer by the screw conveyor, dried with heated hot air, and then cooled by the cold air sent by the cooling fan, and then enter the ammonium sulfate storage hopper. That is the finished product of ammonium sulfate.
The ammonium sulfate section is highly corrosive, and the use of spray saturators to produce ammonium sulfate is conducive to improving the operating environment. The mother liquor discharged from the centrifuge and the mother liquor separated from the crystallization tank flow back to the lower section of the saturator. In addition, the tail gas discharged from the vibrating fluidized bed in the production of ammonium sulfate is further separated from the entrained dust by the cyclone dust collector and the wet dust collector, and then discharged to the atmosphere by the tail gas induced fan.
At present, ammonium sulfate is mainly used as a raw material for the production of nitrogen fertilizer, a catalyst for food caramel, a nitrogen source for cultivating yeast in the production of fresh yeast, a dyeing aid for acid dyes, a deliming agent for leather, beer brewing, battery production, mining of rare earths, protein purification process, etc. Ammonium sulfate is white crystal particles. If the ammonium sulfate has gray, brown, yellow and other discoloration phenomena, it means that its impurity content is too high and it is an unqualified product.
The main reason for the discolouration of ammonium sulfate
- Effect of ferric ion Fe3 +
The ammonium sulfate mother liquor used for ammonium sulfate crystallization comes from the mother liquor circulation tank of the saturator and the high-pressure and high-temperature oxidation solution in the Hax device. The oxidation solution contains SCN – ions, and the ammonium sulfate mother liquor contains Fe3 + ions. These two ions The reaction produces brown Fe(SCN) 3 . This species Fe(SCN) 3 is attached to the ammonium sulfate crystals, making the sulfur
The ammonium acid crystals were impure and discolored. - Influence of phenolic organic compounds
A large amount of phenolic organic matter exists in the gas. During the process of removing hydrogen sulfide and ammonia in the gas, the phenolic organic matter will be absorbed into the ammonium sulfate mother liquor. If these organic matter cannot be removed in time, the phenolic organic matter entering the ammonium sulfate mother liquor will accumulate Discoloration occurs with attached ammonium sulfate crystals. - Effects of acid tar
The coal tar in the gas reacts with the ammonium sulfate mother liquor to form acid tar. If the acid tar in the ammonium sulfate mother liquor cannot be effectively removed, the acid tar particles will dissolve into the ammonium sulfate crystal or become the crystal nucleus of the crystal when the ammonium sulfate crystallizes. Causes discoloration of ammonium sulfate crystals. - Influence of centrifuge washing water
The washing effect of the centrifuge washing water pipe becomes poor, and the impurities attached to the surface of the ammonium sulfate crystal cannot be cleaned, which affects the color of the ammonium sulfate crystal.
Improvement measures
- Concealed ferric ion Fe3 +
Add oxalic acid into the ammonium sulfate mother liquor as a ferric ion Fe3+ sequestering agent, and calculate the amount of oxalic acid added to the ammonium sulfate mother liquor according to the standard of adding 2.3g per 100 mL. - Reduce the content of phenolic organics in the mother liquor
After a certain period of static precipitation of the ammonium sulfate mother liquor, tar and phenolic organic matter will usually float on the upper layer of the mother liquor, and the lower layer is basically a mother liquor without phenolic organic matter. According to this principle, a mother liquor circulation tank can be added, and the two tanks are used in turn. When the tank is in use, the other tank settles still. After a certain period of time, the phenolic organic matter floating on the upper layer after precipitation overflows into the overflow tank, and then the circulation tank that removes the phenols through precipitation is put into use, and another cycle The tank exits the production process and enters the static sedimentation process. - Reduce the formation of acid tar
Acid tar is the product that coal tar and ammonium sulfate mother liquor react to generate, so controlling the tar content in coal gas and ammonium sulfate mother liquor is key, and this is relevant with several procedures: electric catch tar operation, can appropriately improve electric catch voltage, and increase The frequency of cleaning the electric trap is changed from once a month to once every half a month to improve the effect of the electric trap on removing coal tar. In the gas preheating process, when the gas passes through the preheater, a part of the coal tar in the gas will adhere to the preheater. As the amount of adhesion increases, the coal tar in the passing gas will not decrease, but will also Take away the excess coal tar in the preheater, which will increase the tar content in the gas. Therefore, it is necessary to remove coal tar from the preheater frequently to maintain the cleanliness of the preheater and to absorb as much coal tar in the preheated gas as possible.
In the saturator spraying process, the temperature of the gas entering the saturator is appropriately reduced to reduce the gasification rate of coal tar contained in the gas, so that coal tar can form more solid particles, which is convenient for separation from the ammonium sulfate mother liquor. - Maintain efficient centrifuge washing effect
Frequently check the washing water condition of the centrifuge washing water pipe, and replace the washing water pipe immediately if the washing water effect becomes poor due to blockage.
Conclusion
After taking the above measures while producing ammonium sulfate products, the product colour remains normal. After a period of time, the color was found to be repeated. After investigation, some operators on duty did not clean and replace the equipment according to the new requirements. There are many factors in the improvement measures, such as the frequency of cleaning the electric trap, timely replacement of the washing water pipe, etc., depending on human operation.
Therefore, not only the technical requirements but also the quality of the staff is also very important to the quality control of the product. Supplement and improve the post-operation manual, strengthen education and training for operating staff, and strictly implement the responsibility system and assessment management, so that employees can fully understand the importance of fine operation to product quality, and can strictly follow the operating procedures and technology in production positions Requirements to minimize the impact of human factors on product quality.
