摘要:
The invention relates to methods for producing urea-based fertilizers on the basis of urea and, more specifically, to methods for producing fertilizers containing urea and elemental sulfur. Sulfur-coated granulated urea is produced by introducing urea granules at a temperature of 20-60°C into a drum which has blades mounted on the inside surface thereof and rotates at a speed equal to 81-99 % of the critical speed of rotation of the drum, and by spraying a sulfur melt onto the surface of the urea granules. The melt is sprayed in the direction of the axis of rotation of the drum. The method provides for the even coating of the granules with sulfur.
摘要:
The invention relates to processes for purifying wastewater formed during manufacturing of melamine produced from urea using techniques that involve the use of aqueous solutions of alkali metal hydroxides in order to purify and separate melamine. The invention can be used in the industrial production of melamine. The process for purifying melamine production wastewater involves two stages of wastewater thermal hydrolysis. The thermal hydrolysis of the first stage is performed at a temperature of 180-270°C to decomposition of 95.0-99.9% of triazine derivatives present in a wastewater; the water treated at the first stage at the amount of 20-80% is recycled into the process. The second stage is the final thermal hydrolysis of the other part of wastewater treated at the first stage. It is performed at a temperature of 180-270°C. The technical result that can be achieved by invention is a high level of purification of wastewater discharged into the sewers, reduced amount of treated wastewater discharged into the sewers, reduced consumption of pure water in the process along with simplified process technology and reduced energy consumption.
摘要:
The invention relates to the technique for producing melamine by converting urea into melamine using a non-catalytic method at high pressure, as a whole, as well as to a stage of removing dissolved gases from an aqueous solution of crude Melamine, and can be used in commercial production of melamine. The method for producing melamine comprises a stage of converting urea into melamine at increased temperature and pressure with the formation of a gas-liquid reaction mixture containing melamine, ammonia, carbon dioxide and impurities, and a melamine separation stage. In order to separate melamine, the gas-liquid reaction mixture is cooled with lowering pressure and contacting with an aqueous medium, resulting in the formation of an aqueous solution of crude melamine and the partial removal of dissolved gases. The melamine solution obtained is allowed to stand in order to decompose a part of impurities, the pressure and the temperature are lowered, and the dissolved gases are removed from the aqueous solution of crude melamine using the proposed method by means of blowing water vapour through this solution with simultaneous ammonia introduction. An alkali metal hydroxide solution is added to the resultant melamine solution and melamine is separated from the solution by crystallization. The technical result which can be produced when using this invention involves increase of melamine purity and ensuring independence of its purity from the process parameters fluctuations. Melamine-formaldehyde resins prepared on the base of melamine produced by the proposed method have a high degree of transparency.
摘要:
The invention relates to methods for cooling a melamine melt using water and aqueous solutions. The invention can be used in industrial production of melamine. The method for cooling a melamine melt involves cooling a melamine melt with water to temperature of 130-230°C in a cooling zone, with evaporation of water and formation of solid melamine-water vapour gaseous suspension. Melamine is removed from the cooling zone in form of solid melamine-water vapour gaseous suspension. Before removal from the cooling zone, nitrogen, air or a mixture thereof can be added to the formed solid melamine-water vapour gaseous suspension. The technical result which can be achieved using the invention is lowering degree of hydrolysis of melamine when cooling melamine melt with water as well as a simplification of the process.
摘要:
The invention relates to a process for purifying melamine from condensation products, formed in the process of melamine synthesis and separation, by means of treatment of its aqueous solution. The melamine purification process involves treating an aqueous solution of unpurified melamine at a temperature of 110-170°C for a period of 5-60 minutes in presence of an alkali metal carbonate. Sodium carbonate, potassium carbonate or a mixture thereof is used as alkali metal carbonate. Purified wastewater of melamine production plant containing alkali metal carbonate can be also used as a source of alkali metal carbonate. The technical result which can be achieved by invention is a reduction in the level of melamine decomposition with a high level of decomposition of condensation products.
摘要:
The invention relates to processes for purifying wastewater generated in the production of melamine from urea using techniques that involve the use of aqueous solutions of alkali metal hydroxides in order to purify and separate melamine. The invention can be used in the industrial production of melamine. The process for purifying melamine production wastewater involves the thermal hydrolysis of the wastewater at a temperature of 190-245°C, wherein steam having a temperature 5-60°C greater than the working hydrolysis temperature is bubbled through wastewater, preferably in an amount equal to 5-20% of the amount of unpurified wastewater. The technical result which can be achieved using the invention is an increase in the level of purification of the wastewater and a simplification of the technique.