【Ten Years of Great Progress in Chemical Technology】Successful application of the first domestically developed nitric acid phosphate fertilizer production plant using cryogenic methods from 2012 to 2018

It is understood that the development of phosphate nitrate fertilizers in our country has been fraught with difficulties. Starting in the 1970s, efforts were made to introduce a complete set of manufacturing facilities, and this project was included in the **“Sixth Five-Year Plan.”** Numerous challenges had to be overcome from the stage of construction to actual operation, and the difficulties were far beyond what industry experts had imagined. The high requirements regarding the quality of phosphorus ore, along with various problems related to equipment, processes, and technology, led to difficulties in getting the introduced facilities up and running; it took a full 13 years to overcome these challenges. Domestic imitation devices have also failed, which prevents some domestic companies from pursuing such projects despite their desire to do so. 　　Huang Deming, general manager of Guizhou Batian Company, said that amid the difficult circumstances facing the development of nitrate phosphate fertilizers in China, Batian Company, from the perspective of plant-based nutrition, organized scientific and technical efforts to build the first domestically produced nitrate phosphate fertilizer production facility that can rival those abroad. In June 2012, Guizhou Batian brought in a group of experts in phosphoric acid fertilizers and signed an agreement with Tianjin Huajing New Technology Co., Ltd. to jointly develop technologies related to phosphoric acid fertilizers and calcium nitrate ammoniated processes. On April 18, 2013, the first phase of the Batian Phosphorus Chemical Circular Economy Ecological Industry project, with a total investment of 10.278 billion yuan, was officially launched. This phase involved the construction of facilities for producing 270,000 tons per year of nitric acid (equivalent to 100% HNO3), two plants capable of producing 150,000 tons each of nitric acid-based fertilizers (which, after adding potassium, would result in 200,000 tons per plant of nitric acid-potassium fertilizers); in addition, there were plans to produce 200,000 tons per year of calcium hydroxide as a by-product, as well as two plants capable of producing 300,000 tons per year of high-efficiency compound fertilizers. 　　Zhang Lingyun, the chief engineer at Guizhou Batian, said when introducing technology development that there is no mature technology available at home or abroad for removing the acid-insoluble substances present in the acidic solution resulting from the decomposition of phosphate rocks. With the current separation techniques, the removal rate is only around 10%, which is not sufficient to meet the separation requirements. Faced with pressure, the leaders and key members of the Batian Shares project team, bearing the heavy responsibility for the development of phosphoric acid fertilizers in China, worked day and night to solve one technical challenge after another. Technologies such as flocculation sedimentation, horizontal spiral separation, and pressure filtration were studied successively, and an acid-insoluble matter separation process based on pressure filters and filter aids was developed, achieving a removal rate of over 90% for acid-insoluble matters. China’s first treatment technology for ammonia-containing alkaline wastewater from phosphatic nitrate fertilizers was developed, resulting in no wastewater discharge. The development of a production process technology for *ao acid an calcium resolved the issue of what to do with the by-product Ca(NO3)2•4H2O generated in traditional nitric acid phosphate fertilizer production processes, enabling the complete utilization of phosphate rock resources.

　On March 18, 2015, the process was initiated for feeding materials into the boiler used in the project; on May 18, the entire process of the phosphoric acid fertilizer production unit was operational, and the first batch of phosphoric acid fertilizer was produced； On May 26, the entire process of the calcium nitrate ammoniation plant was operationalized, producing the first batch of calcium *ao acid an. It took only 2 years from the project’s initiation to the completion of the first set of nitrophosphatic fertilizer plants. It marked the birth of China’s first domestically designed set of facilities for producing phosphoric nitrate fertilizer. 　　The entire process was streamlined. Drawing on the experience of their peers in bringing installations online and meeting performance standards, they set goals for achieving such standards in three stages: 70% load in the first stage, 85% load in the second stage, and 100% load in the third stage, with the system required to operate safely and stably for 72 hours. Tests at 100% load were conducted twice, from January 23–25, 2018, and from August 23–25, 2018. The key indicators meet the assessment requirements, and the plant achieves full production capacity and standard compliance. 　　Huang Deming said that the successful development and application of domestic production facilities for frozen nitrogen phosphate fertilizers have fulfilled the vision set forth during the First Five-Year Plan period to promote the use of such fertilizers in China’s fertilizer industry, laying a solid foundation for the country to produce high-quality nitro compound fertilizers using domestic technology in the future.

Internationally, there are mainly two mainstream production processes for phosphorus fertilizers: one is the ammonium phosphate products based on the sulfuric acid method used in the United States, and the other is the nitrate phosphorus fertilizer products based on the nitric acid method used in Europe. Given China’s energy structure characterized by an abundance of coal but a shortage of sulfur, the development of nitric acid phosphate fertilizers is in line with national needs. 　　Phosphoric acid fertilizer refers to a general term for fertilizers containing nitrogen and phosphorus pentoxide, which are produced by decomposing phosphate rocks with nitric acid; it is one of the main types of compound fertilizers used internationally. Its main feature is that when nitric acid is used to decompose phosphate rock, it acts as a acidulant, converting P2O5 in the phosphate rock into a form that can be absorbed by crops ； Moreover, it remains in the product as a nitrogen fertilizer itself, playing a role in transporting phosphorus along with nitrogen. In this way, the cost of nitric acid can be included in the production costs of nitrogen fertilizers, and since it can be used to produce phosphatic fertilizers without the need for sulfuric acid, it offers economic advantages. Calcium nitrate, a by-product of phosphoric acid fertilizers, can be used to produce products such as calcium nitrate; since sulfuric acid is not required, there is no waste in the form of phosphogypsum, which eliminates the pollution associated with storing such waste. Therefore, it also has environmental advantages. 　　The characteristic of phosphate nitrate fertilizer is that it contains both rapidly available nitrate nitrogen and water-soluble phosphorus, as well as ammonium nitrogen and phosphorus soluble in citric acid, which provide a more sustained fertilizer effect ； It has a nitrogen-to-phosphorus ratio of 2:1, which meets the absorption requirements of most crops ； It also activates trace elements and rare earth elements such as S, Ca, Mg, Fe, Mn, Cu, Zn, B, Mo, etc., present in phosphate rocks, to make them water-soluble so that they can be directly absorbed by crops, enabling their balanced utilization. Therefore, phosphoric acid fertilizer is a fully nutrient-rich fertilizer that aligns with the development trends of high efficiency, long-lasting effectiveness, diversity, and multiple functions. 　　Compared with the nitric acid+sulfuric acid and sulfate methods, this technology does not produce \"phosphogypsum\", thereby addressing the challenges associated with the storage, recycling, and reuse of phosphogypsum waste ； Compared with the imported cooling nitrate phosphate fertilizer production plant, the introduced plant produces cement as a by-product along with calcium carbonate; however, the calcium carbonate contains about 1.5% nitrogen, which causes yellow smoke to be emitted from the cement kiln’s exhaust gases and leads to severe excess levels of NOX. This technology addresses the challenge of producing cement under strict environmental regulations. 　　The by-product Ca(NO3)2•4H2O is processed into a new type of fully water-soluble calcium nitrate compound fertilizer, thereby enabling the production of phosphate nitrogen fertilizers in line with the requirements of circular economy development. This domestically developed technical device features good product quality, low steam consumption, a high degree of automation in the operation of the refrigeration unit, and simple operation. All the exhaust emission outlets of the device meet the emission requirements. Wastewater is recycled in a closed loop with no emissions.

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