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Sodium Tripoly Phosphate (STTP) Plants
System solutions for the production of highest grade polyphosphates (as additives for detergents and foodstuffs) of all particle sizes, bulk densities and phase compositions that are in demand on the market.
Since the early 1970s Grenzebach BSH has been active in the design and construction of plants for the production of sodium tripoly phosphate (STTP) as a base material for detergents. Although various substitutes (zeolithes and phyllosilicates) were favoured for some time, STTP phosphate has become an important component of modern detergents again. We supply the process technology and the major equipment components required for the production of STTP. We have so far built some 28 plants with an overall production capacity of some 880,000 tonnes per year. The plants are mostly located in Europe, Africa and Asia.
Plant concepts
An STTP production plant essentially consists of a neutralisation part where phosphoric acid is neutralised with soda or soda lye to an orthophosphate solution (also called mono-di-lye), and a drying part where, by drying, polycondensation and calcination, the solution is converted into STTP. As far as the drying part is concerned, a distinction is made between single-stage and two-stage processes.
In a single-stage process the orthophosphate solution is converted from a liquid phase in one process step to become marketable STTP in its solid free-flowing form. The single-stage Grenzebach BSH process uses a rotary kiln in which granulation, drying, polycondensation and calcination of the orthophosphate solution to finished STTP take place in a single step. This process yields so-called "heavy product" with a bulk weight of 700 to 1,050 kg/m³.
In a two-stage process the orthophosphate solution is first transferred into the solid free-flowing phase of an orthophosphate mixture by drying and crystallisation of the salts and subsequently converted to finished STTP by means of a separate heat treatment (polycondensation/calcination). For the two-stage process Grenzebach BSH offers two different key equipment arrangements: a) Spray tower and rotary kiln – or, alternatively b) Two rotary kilns. Mechanical finish treatment of the product is also covered by Grenzebach BSH's product range. The two-stage process offers a wider range of STTP bulk weights, for "light product" (400 - 700 kg/m³) and "heavy product" (700 - 1,050 kg/m³). In addition to the process steps described above, we also supply machines and systems for finish treatment of the STTP. These include coolers (such as the Sectional Cooler or the Moving Bed Cooler), hydration, grinding (such as the Whirlwind Mill ) and screening systems.
Advantages
The choice of the process and apparatus is mostly determined by the STTP quality required on the market. For the benefit of our customers, we can rely on a wide range of experience with various reference plants when proposing and selecting the respective processes and equipment. Grenzebach BSH's proven technology and its know-how and experience gained from practical operation also provide the customer with a maximum safety and reliability in the operation of the plant, which, among other things, is demonstrated by the constant, high product quality and the high availability of the plants supplied. When defining the process stages and dimensioning the equipment, we allow for sufficient flexibility in the control of the process so that the STPP producer can quickly adapt to changing market requirements in terms of the product specification. With the technology available today it is possible to built plants with lower capacities that nevertheless yield an optimum economic benefit. Especially in countries possessing the necessary raw materials, specifically adapted modern STTP production plants provide opportunities for exporting processed products or alternatives to expensive imports of such products.
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