Phosphorus is one of the most important macronutrients in fertilizers. To cater for the worlds growing demand for fertilizers, producers all over the world expand their production capacity and modernise their existing processing facilities to enhance the effectiveness of their processes, e.g. the dehumidification of the production waste.
According to the United Nations, world population will exceed nine billion by the year 2050 – two billion more than in 2016. To feed them all, grain production will have to be increased over the same time period by 46%. But the UN Food and Agricultural Organization (FAO) calculates that the world’s available arable land for food production will only increase by 4% by the year 2050.
Growing Fertilizer Demand
Available arable land will therefore have to produce considerably higher yields. Experts of the German industrial association Agrar e.V. (IVA) are convinced that this higher demand can only be met through the use of mineral fertilizers. In fact, the FAO and the International Fertilizer Industry Association (IFA) both forecast an up to 40% increase in demand for fertilizer by the year 2030 alone.
For phosphorus in particular, the EU Commission even reckons with an increase in demand of around 50 %. Phosphorus is used in both industrial and small-scale agriculture – to the tune of 40 million tons a year. But unlike potassium and nitrogen, phosphorus is a finite resource whose worldwide exploitable reserves are steadily diminishing. And this indispensible fertilizer is irreplaceable by any other substance. For this reason, in May 2014, the European Commission placed phosphate rock on its CRM List of 20 critical raw materials.
The basic material for phosphatic fertilizers is phosphate rock (apatite), which only occurs in a few regions on the planet. For the purpose of fertilizer production, the apatite is crushed and ground into rock flour. But, because raw phosphates are not readily soluble, this rock flour is only used directly on the fields as fertilizer in rare cases. Usually, through addition of nitric, sulphuric or phosphoric acid, the phosphate is dissolved and extracted from the rock flour. In this way, raw phosphate is converted into phosphoric acid of different grades of purity.
The varying characteristics of the particular phosphate rock used is also reflected in the diversity of treatment processes. For example, particle size and process temperatures will vary depending on the particular raw material.
Phosphoric acid production results in the creation of large amounts of phosphogypsum. This contains radioactive and toxic components like uranium and radium due to impurities in the raw material. For this reason, only 2% of this type of gypsum can be recycled. After dewatering on vacuum belt filters, the complete remaining volume is bunkered on piles near the fertilizer production facilities.
Demanding Process Conditions
The world’s largest producers of phosphate fertilizers include companies in Canada, the USA, Russia, Norway and Morocco. To be successful in global competition, their fertilizer production facilities must meet high standards of quality and reliability. At the same time, their efficiency needs to be continuously increased to be able to cater for the constantly rising demand.
A crucial contribution to productivity lies in the stability of the filter belts used in gypsum dewatering. These must be able to withstand massive mechanical and corrosive stress at high throughput rates around the clock in order to ensure the longest possible life cycles. For this reason, more and more companies are using filter belts of the Vacubelt 3354 type, made of polyester monofilaments for the dewatering of their phosphogypsum slurries.
Due to its pore size of 150 µm and an air permeability of 200 cfm (5,67 m3/min), the Vacubelt filter belt excels through efficient dewatering, a low tendency to clog, and very good cleaning properties. In addition, its smooth surface ensures optimal product detachment. Because it is manufactured on special, high-tech industrial looms, the belt mesh is guaranteed to have the required stability to prevent wrinkling, even in the case of extra-large equipment dimensions. Even belts with a length of more than 70 m and up to 4.5 m width maintain the requisite lateral stability to ensure the necessary degree of process reliability.