Summary of Urine-based Compound Fertilizer Production Technology

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Modern agriculture requires chemical fertilizers not only in sufficient quantity, but also in terms of applicability. In order to meet the requirements of users and obtain better economic benefits, basic fertilizers such as ammonium phosphate, urea, potassium chloride, etc. are generally processed twice to make compound fertilizers. Compound fertilizer is an inevitable trend in the development of modern chemical fertilizers. When the chemical fertilizer industry is developed, * * It accounts for 70% to 80% of the total fertilizer consumption. Compound fertilizers have developed rapidly due to their comprehensive nutrients, easy scientific fertilizer preparation, labor and time saving, and significant fertilizer efficiency. In 2003, my country's nitrogen fertilizer production was 28.79 million tons of N, and the physical production of urea was 36.3 million tons. Urea has accounted for 60% of my country's total nitrogen fertilizer production. The production of NPK ternary compound fertilizer using urea as a nitrogen source has also received increasing attention. The number of single-nutrient urea used in secondary processing to produce high-concentration compound fertilizers is gradually increasing. The advancement of high-concentration urea-based compound (mixed) fertilizer production technology has become very important, which is mainly reflected in the following aspects. ①market: With the expansion of urea production capacity, urea products have shifted from a buyer's market to a seller's market, and the urea market is highly volatile. Due to market changes, many urea production companies have insufficient operating rates and poor economic benefits. They urgently need to adjust their product structure. The main direction of adjustment is the development of high-concentration urea-based compound (mixed) fertilizers. ②Fertilizer utilization rate: As we all know, when urea products are applied alone, due to their high solubility, they can easily cause leaching and volatilization losses, and the fertilizer utilization rate is low, only about 30%. ； And developed * * The utilization rate of urea can reach about 60%, which is a large gap. Practice has proven that when a single nutrient is appropriately formulated into compound (mixed) fertilizer and applied, due to the combined effect of the nutrients nitrogen, phosphorus and potassium, crop yields can generally increase by 10% to 15% compared to single nutrient fertilization. In other words, the application of compound (mixed) fertilizers improves the utilization rate of chemical fertilizers. ③price: Judging from the price comparison of various chemical fertilizers at home and abroad, based on single nutrients, potassium chloride (MOP) is the lowest, heavy calcium (TSP), urea (U), and ammonium phosphate (MAP or DAP) are in the middle, and compound fertilizer (NPK) is the highest. The price ratio abroad is roughly 1: 1.65: 2, while domestically it is about 1: 1.5: 1.9, that is, using urea as raw material to produce compound fertilizers, the economic benefits of enterprises can be increased by 25% to 27%. ④technology: The compound fertilizer process is commonly used to produce high-concentration urea-based compound fertilizers, especially when producing urea-based compound fertilizers with high nitrogen ratios. The elasticity of granulation and drying operations is relatively low, and sometimes the operation becomes very difficult. The product particles also have poor appearance, low particle strength, and serious agglomeration. ⑤Development direction: The development of high-concentration compound (mixed) fertilizers is a worldwide development trend and is in line with the industrial policy for the development of my country's fertilizer industry. In summary, the production and technological progress of high-concentration urea-based compound (mixed) fertilizers will become a hot spot in the development of compound fertilizers in my country and become the focus of attention of various urea production plants. However, due to the low melting point of urea (132.7°C), the critical relative humidity (CRH) and softening temperature of urea-containing fertilizers are relatively low, which brings many difficulties to production and operation and restricts the development of urea-based compound fertilizers. Shanghai Research Institute of Chemical Industry has long been engaged in the research and technology promotion of compound fertilizers. Since the 1980s, the technology of pelletized compound fertilizers has been promoted and applied to more than 300 manufacturers across the country, and complete sets of technology and equipment have been exported to Southeast Asia. * * . In recent years, based on the actual situation of compound fertilizer production by urea manufacturers, new production processes and technologies such as urine slurry method and tower type urea-based compound fertilizer have been developed. The different production processes of NPK granular compound fertilizer are described below. 2. Production process 1. Agglomeration process The basic principle of granulation of the agglomeration process is that the basic fertilizer of a certain fineness wets the surface of the powder particles with the help of the liquid phase and water or water vapor produced by the dissolution of the salts themselves. Under the appropriate conditions of the existence of the liquid phase, mechanical agitation promotes continuous movement of the particles, and the materials collide, squeeze, and roll with each other to form a compact, agglomerate and adhere to form granules. According to different granulation equipment, it can be divided into disc granulation, drum granulation and other processes. The process technology is simple and mature ； Easy to operate and control ； It has relatively strong adaptability to raw materials and easy adjustment of product specifications. Various basic fertilizers can be used for granulation to produce compound fertilizers with different nutrient concentrations. ； Device versatility ； The factory construction conditions are low and there are no restrictions on raw materials. However, the disadvantages of this process are low granulation rate, large energy consumption, poor particle appearance, and poor flexibility in the production of high nitrogen ratio urine base fertilizer. 2. Slurry method process The principle of the slurry method granulation process is that part of the basic fertilizer for granulation is fed into the granulator in the form of slurry. The slurry is used as a liquid phase and is coated or bonded into granules with other powdery and granular raw materials and return materials in the granulator. According to the different forms of granulators, the process can be divided into: (1) Drum granulation process, (2) Disc granulation process, (3) Shot granulation process, (4) Biaxial granulation process, (5) Fluidized bed granulation process and (6) Drum curtain granulation process. According to the raw materials of slurry, it can be divided into urine base, * * base and ammonium phosphate. Domestic phosphate compound fertilizer production includes the imported DAP/NPK production equipment and the dotted slurry ammonium phosphate equipment and the sulfur-based compound fertilizer equipment with phosphoric acid as the head, all of which are based on spray granulation. This method combines granulation and drying, and forms particles through coating, bonding and self-granulation. The resulting granular products have better physical, chemical and mechanical properties. my country's largest single compound fertilizer plant, Tianji Coal Chemical's 900,000-ton nitric acid phosphate fertilizer, is the only one in China that adopts a biaxial granulation process. Partial slurry method urea base ( * * The base) compound fertilizer production technology is a patented technology researched and promoted by the Shanghai Institute in recent years (Patent No. 00116235.7). This process utilizes urea and * * It has the characteristics of greater solubility and lower melting point, and uses the heat of its slurry to spray ≥95% high-concentration solution or molten salt directly into the granulator to agglomerate with other powdery and granular raw materials to form granules. The process flow diagram is shown in Figure 2. This process utilizes low moisture content urea (or * * ) solution is beneficial to the water balance of the entire production unit. During the granulation process, urea (or * * ) solution can release heat of crystallization, which can increase the granulation temperature, reduce the moisture content of the product exported from the granulator, and increase the drying load. The use of solution granulation produces both agglomeration and granulation characteristics and a coating effect during the granulation process, making the product round in appearance, increasing particle strength, and improving the degree of automation in process control. * * improve. Some slurry processes can utilize urea (or * * ) semi-finished products from the production plant are used as raw materials, which saves the operating costs of urea granulation and product packaging and transportation costs, and makes full use of the heat energy of urine, reducing the energy consumption of the production process and the cost of the product. It is urea (or * * ) The production plant can choose the compound fertilizer production process route to improve the product structure. 3. Granular nitrogen-potassium compound fertilizer (nitrogen-phosphorus-potassium blended fertilizer) process. The slurry method without drying granulation process is the compound fertilizer production process recently developed by Shanghai Institute. It can produce either nitrogen-potassium fertilizer (this nitrogen-potassium fertilizer can be used as raw material for blended fertilizer) (see Figure 3 for the process flow) or nitrogen-phosphorus-potassium compound fertilizer (see Figure 4 for the principle process flow). The slurry can be urea solution or melt ； It can also be a eutectic compound produced by urea solution and potassium chloride (or potassium sulfate) ； The slurry is used as a liquid phase and phosphorus raw materials (such as heavy calcium, ammonium phosphate, etc.) and potassium salts (potassium chloride or potassium sulfate) are coated or bonded into balls in the granulator. The granulator can be a drum, a disc or a drum curtain 4. Melt granulation process The melt granulation process is characterized by the material being in a high-temperature molten state, the water content being very low and the flowable melt being directly sprayed into the refrigerant (the refrigerant is usually air or a liquid insoluble in the melt material, such as mineral oil, etc.), and the material solidifies into spherical particles when cooled. ； Or the flowable melt is sprayed onto the returned particles in the mechanical granulator, so that it can be coated or bonded on the surface of the fine particles to form particles that meet the requirements. Evaporation or concentration of solutions requires energy consumption, but the energy utilization is far more efficient than dry granular products. What's more, in some production processes, reaction heat can be fully utilized to evaporate part or even all of the water. ； In the general granulation process, the dryer is usually the largest and most expensive equipment in the granulation device. The melt granulation process does not require drying, saving investment and energy consumption.