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Since 2001, China has had 40 to 50 sets of high-tower compound fertilizer production lines; it is difficult to determine exactly how many companies are currently building or planning to build such production lines. A new wave of enthusiasm for high-tower granulation is growing increasingly strong. So, what are the advantages and strengths of high-tower compound fertilizers that attract so many companies to use them? And what are the shortcomings and concerns that manufacturers should be aware of and address carefully? 1. Introduction to the high-tower granulation process: This process takes advantage of the fact that molten urea, ammonium phosphate, and potassium chloride can form eutectic compounds. Powdered ammonium phosphate, potassium chloride, fillers, and other materials are heated and then added to the molten urea; through a reaction, an eutectic mixture with good fluidity is formed. This mixture is then sprayed into the cavity inside the granulation tower using specialized rotary vibration nozzles. The material sprayed out cools and solidifies into particles in the air, falling to the bottom of the tower. After cooling, these particles are screened, surface-treated, measured, and packaged. Due to the different contraction rates of nitrogen, phosphorus, and potassium components during the cooling process, a shrinkage cavity remains on the product particles. The tower height in the tower-type granulation process generally comes in two specifications: 90–130 m and 35–45 m (i.e., low-tower granulation); depending on the production scale, the tower diameter is usually between 12–18 m. 2 The original intention behind enterprises building high-tower granulation facilities 2.1 Addressing the challenges associated with the production of high-nitrogen compound fertilizers After the success of high-nitrogen compound fertilizers in the Northeast region, such fertilizers characterized by high nitrogen content began to develop rapidly across the country. High-nitrogen compound fertilizers are mainly suitable for top-dressing corn and cotton, as well as for fertilizing leafy vegetables, lawns, forage crops, Chinese herbal medicines, and fruit trees. Especially for corn and cotton, single nitrogen fertilizers were used in the past; now, with the use of high-nitrogen compound fertilizers, yields have increased significantly. Due to its slow-release property, high-nitrogen compound fertilizer helps improve the efficiency of fertilizer use, reduces environmental pollution, prevents soil compaction, and enhances the output-to-input ratio in agriculture. The production of high-nitrogen compound fertilizers requires the addition of large amounts of urea. Since urea is a heat-sensitive substance, it is almost impossible to produce it using conventional granulation processes. To produce high-nitrogen compound fertilizers, the urea melting and spray granulation process is the main method used. Due to the low investment required, it is affordable for most companies, but over time, the advantage of product differentiation gradually fades away. The production of compound fertilizers through high-tower granulation was inspired by the urea production process, and it draws on foreign experience in manufacturing compound fertilizers using this high-tower granulation method. Additionally, due to the high investment required, it is difficult for small enterprises to enter this field. This approach enables the production of compound fertilizers with high nitrogen content; the higher the nitrogen content, the easier it is to produce such fertilizers, thus addressing the issue of low nitrogen content in traditional compound fertilizers. Although BB fertilizer can also achieve high nitrogen production, during transportation, particle segregation easily occurs, leading to an imbalance in nutrients. The mixing of materials for high-tower granulated compound fertilizers is carried out through stirring while in a molten state, thereby ensuring uniform nutrient distribution in the resulting fertilizer particles. Driven by the invisible hand of the market, the domestic production process for high-tower granulated compound fertilizers was thus developed. 2.2 The product features anti-counterfeiting properties. During the production of high-tower compound fertilizers, as the mixture slurry is ejected from the nozzles and cools as it falls, the different contraction rates of the nitrogen, phosphorus, and potassium components result in the formation of contraction pores on the surface of the fertilizer particles. Although this is an unintended effect, it serves as a characteristic that distinguishes melt-type high-tower granulated compound fertilizers from those produced using other manufacturing processes. This is also a helpless measure taken by compound fertilizer manufacturers to deal with fake and substandard compound fertilizers. 2.3 Selling points and drivers of benefits: Due to the differentiation of its products, high-tower compound fertilizers have become a new selling advantage in the market. At first, the selling price of tonnage-based fertilizers was more than 400 yuan higher than that of ordinary compound fertilizers. The high profits led production companies and distributors to be highly optimistic about the prospects of high-tower compound fertilizers, prompting enterprises without such granulation technology to adopt it, while those already using this technology continued to expand their production capacity and scale. 2.4 It provides a way to extend the industrial chain of urea manufacturers. High-tower compound fertilizers are primarily used for producing high-nitrogen compound fertilizers, and urea is the main raw material in such production. This approach can help alleviate the current surplus capacity in urea production, extend the industrial chain of urea manufacturers, and open up new avenues for utilizing urea. 3 Current Status of the Production and Sales of High-Tower Compound Fertilizers 3.1 Current Status of the Production of High-Tower Compound Fertilizers At present, apart from Russia, the high-tower granulation process for producing compound fertilizers is rarely used in other ** countries. As a new process for the production of compound fertilizers in China, there are still many problems with the high-tower compound fertilizer production method: the urine pump is unable to deliver urine to the top of the tower properly ； The temperature of the material at the outlet of the powder heater is too low ； The slurry in the mixing tank has poor fluidity ； Clogging of the granulation nozzle ； Severe wall sticking phenomenon in the granulation tower ； The material exiting the tower tends to become flattened, and the particles tend to stick together ； The urine delivery ducts are prone to blockage ； The finished particles are small ； The content of biuret in the finished product exceeds the specified limit, among other issues. There is another issue that needs to be addressed, namely the handling of the fine particles and oversized particles that are separated out. These materials are difficult to crush and melt, and it is hard to return them to the system for re-grinding. Some manufacturers of high-nutrient compound fertilizers are forced to pack these fertilizers and send them to the drum granulation production line for reprocessing. If the individual nutrient levels and total nutrient content of these reprocessed materials are similar to those of the products produced by the drum granulation line, it is easier to handle them; however, if there are significant differences, it becomes more difficult to deal with them. What’s worse is that from June to August, due to the high temperatures and high air humidity (more pronounced in the south), it is not sufficient for the particles to cool down solely through natural wind as they fall; this makes it easy for the particles to stick together. The compound fertilizer particles that reach the bottom of the tower have not had enough time to cool down, so they tend to stick to the bottom and walls of the tower. As a result, some companies that produce compound fertilizer using high towers are forced to suspend production, which affects their output. Unstable production levels also impact market share and customer loyalty, thereby affecting the development of these companies. If these problems are not properly resolved, it will inevitably affect the adoption of this process (the low-tower air-cooled crystallization granulation process can largely compensate for the shortcomings and defects of the high-tower granulation process). As for the shrinkage pores in high-tower granulated compound fertilizer products, they not only fail to extend the release period of the compound fertilizer but also accelerate its melting rate; even when coated, it is difficult to cover these pores. This is one of the main reasons why, under the same anti-caking treatment, the anti-caking effect of high-tower compound fertilizers is not as good as that of other compound fertilizers; moreover, the claim that high-tower compound fertilizers do not require anti-caking treatment is completely incorrect. 3.2 The production cost of high-tower compound fertilizers remains high. The main reasons for the high production costs of such fertilizers are as follows: 1) The large investment required for plant construction leads to high equipment depreciation costs, thereby increasing manufacturing expenses. For example, the equipment and production facilities for a high-tower compound fertilizer production line with an output of 100,000 tons per year require an investment of 20–25 million yuan, whereas a drum granulation production line of the same scale only needs around 8 million yuan. 2) The device struggles to reach full production capacity, resulting in increased manufacturing costs. 3) The requirements for raw materials are strict, increasing the costs of processing the materials. Ammonium monophosphate, potassium chloride, and the filler must all be in powder form; no caking should occur among these solid materials. After screening, 100% of the material with a particle size of ≤0.8 mm is required, and the water content (w(H2O)) must be ≤1.5%. Among them: the neutralization degree of monoammonium phosphate is required to be between 1.0 and 1.2 ； The w (K2O) of potassium chloride is ≥60% ； The fineness of the filler must be 80 mesh or higher (＜0.175mm) in 100%, to ensure uniform mixing of solids and liquids and to keep the solid materials in a good suspended state after mixing. 4) The process has limited operational flexibility and requires strict process conditions. For example, the mixing time of the slurry must be ≤4 minutes, and so on. 5) Since all raw materials need to be melted, this increases steam consumption. Apart from replacing the dryer and granulator (in the drum granulation line) with a high tower, no other equipment has been reduced; on the contrary, equipment for the pretreatment of raw materials and the preparation of slurries has been added. All materials are lifted to the top of the high tower, which also increases power consumption. 6) Enterprises that are unable to produce urea and cannot obtain urine locally will undoubtedly face increased production costs to a greater extent. Even if a company has its own urea production facilities, it is still almost impossible at present to keep the cost of high-tower compound fertilizers at a level comparable to that of conventional compound fertilizers. 3.3 Current sales situation of High Tower compound fertilizers: Thanks to its attractive marketing features and anti-counterfeiting capabilities, farmers were highly enthusiastic about purchasing these fertilizers under certain circumstances; as a result, both manufacturers and distributors enjoyed large profit margins. The price of High Tower compound fertilizers was more than 400 yuan per ton higher than that of compound fertilizers with similar nutrient content, or even higher in some cases. With the advancement of agricultural services and the gradual improvement in farmers’ knowledge regarding scientific fertilization, it has become clear that what truly boosts yields is the total content of nitrogen, phosphorus, and potassium in compound fertilizers, as well as whether the ratio of these nutrients is appropriate. Farmers’ understanding and consumption of high-nutrient fertilizers are also gradually returning to rationality. Currently, high-nutrient compound fertilizers on the market cost only about 100 yuan more per ton than traditional compound fertilizers with the same nutrient content, and there is a trend toward further price reductions. Therefore, as a company, it is also necessary to conduct careful consideration and scientific analysis to determine whether it is suitable for undertaking high-tower projects. The particle size of high-tower compound fertilizers is influenced not only by the rotation speed and pore size of the nozzles, but also by the height and diameter of the tower; once the height and diameter of the tower are determined, it becomes very difficult to adjust the particle size. The market generally requires compound fertilizers with larger particles, as they are not only easier to use but also have a longer duration of effectiveness. The high-nitrogen compound fertilizer is the main product of this plant; it is very difficult to produce fertilizers with a nitrogen content below 20%. If the particles of such fertilizers are small and they contain a high amount of nitrogen, then they will dissolve more quickly, resulting in a concentrated release of their nutrients. This does not contribute to prolonging the duration of their effectiveness nor to improving the efficiency of their use. Currently, farmers taking into account high-tower compound fertilizers have already paid attention to these factors. In some manufacturers of high-tower compound fertilizers, the urine used as a raw material is obtained through the on-site melting of urea; the melted urine is then pumped to the top of the tower. During the processes of melting and transportation, the content of biuret increases significantly. Even urine coming from the second evaporator in the urea production unit experiences an increase in biuret content during long-distance transportation. Although the GB15063-2001 standard for \"Compound Fertilizers\" does not specify the content of biuret in such fertilizers, it is an established fact that a high level of biuret in compound fertilizers can cause the phenomenon of \"seedling burn.\" Such problems not only cause huge losses to enterprises but also create a negative perception among farmers toward high-tower compound fertilizers. High-Tower compound fertilizer has a high nitrogen content and dissolves quickly, making it suitable mainly for top-dressing. If used as a base fertilizer, its low phosphorus content fails to meet the phosphorus needs of crops, affecting yield increases; this in turn reduces farmers’ willingness to use High-Tower fertilizer in the next growing season. 4 How to Approach the High-Tower Granulation Process Properly: Compared with traditional compound fertilizer production methods, the high-tower compound fertilizer production process is still a new technique in China. Although there are still shortcomings in terms of construction, production processes, market conditions, and agricultural services, which require further improvement, this does not mean that the high-tower granulation process should be completely rejected. Instead, a systematic analysis and evaluation of the existing problems associated with this process are necessary, in order to make breakthroughs in areas such as tower height, diameter, production processes, costs, and agricultural services, thereby improving the high-tower granulation process over time. How should the high-tower granulation process be approached? The author believes that it is necessary to consider the following aspects: 1) First and foremost, it is essential to determine whether the enterprise itself has the conditions to build a high-tower production facility and whether it has sufficient capacity to invest in this granulation process. At present, some companies do not have a clear understanding of the high-tower fertilizer market, nor are they aware of whether they have the capability to handle high-tower compound fertilizer technology; as a result, they invest blindly in building such projects ； It is necessary to draw on the experience of manufacturers that produce high-tower compound fertilizers, learn from their lessons, and conduct a systematic analysis and evaluation of the existing problems with such towers. Factors such as tower height and diameter, the source of urine and its biuret content, costs and funding, as well as environmental temperature and humidity, all must be carefully considered. 2) Conduct a reasonable and accurate positioning of the market demand for high-tower compound fertilizers as well as the corresponding products. High-tower fertilizer is not suitable for all soils, nor for all crops, or for all stages of crop growth. As a company, it is necessary to objectively inform farmers about the characteristics and appropriate uses of fertilizers, so as to gain their recognition and trust. The success of applying high-tower fertilizers in one go to the black soil in the Northeast (the so-called \"one-shot application\") is closely related to the characteristics of this soil: it has good fertility, low temperatures, high humidity, and strong capabilities for retaining nutrients and water. Applying some high-nitrogen compound fertilizer, along with an appropriate amount of seed fertilizer, can ensure one-time fertilization for corn. The black soil in the Northeast is just a special case; soils in other areas do not possess such characteristics, and therefore do not meet the conditions for rapid development. If high-concentration fertilizers are used in large quantities at once, this not only affects crop yields but also hinders the improvement of fertilizer utilization efficiency. Meanwhile, the large amount of fertilizer that is not absorbed by crops ends up in water bodies, causing pollution of rivers, lakes, and seas as well as damage to the ecological environment. 3) Seek methods or approaches to reduce the costs of high-tower compound fertilizers. For farmers, when choosing fertilizers, they consider not only the effectiveness but also the price. No matter how good a product is, if it does not have a price that the market can accept, it will not be able to generate profits for the company. 4) Providing excellent agrochemical services is crucial for promoting high-tower compound fertilizers. 5 Conclusion The high-tower granulation process is a new technique that has emerged in recent years, derived from the urea process. The addition of monoammonium phosphate and potassium chloride leads to a series of changes in the properties of the material used; compared to the urea process, it offers less operational flexibility and presents greater challenges in terms of processing. There are many details in the production process that serve as key factors determining process stability. A long way still remains to go before the problems existing in the construction, production, and sales of high tower fertilizers can be successfully resolved.