The Mixing Challenge
The production of phosphoric acid is one of the most challenging in the mixing industry. The production process involves a series of reaction tanks where phosphate rock is reacted with sulfuric acid. Agitators and wetted parts are exposed to corrosive liquids and vapors that degrade rotating equipment. The phosphoric rock crystallizes and becomes trapped in dead zones in each vessel allowing particles to agglomerate and leave a core of unreacted rock that reduces process yields and tends to adhere to vessel walls and impeller surfaces. Accumulations can become large enough to break off and destroy impellers, shafts or mixer drives with sudden shock loads. The result is an inefficient mixing process with uncertain raw material yields and chronic equipment failures.
In Phosphic Acid production using the industry accepted process, fine particle phosphate rock is distributed based on the level of mixing across the tank. Conventional mixing processes allow dead zones to form near vessel walls and gypsum crystal agglomerates, forming larger particles with unreacted rock at their core. The large particles often coat the walls of the vessel, where chunks can fall and break impellers or cause dangerous working conditions during maintenance. As gypsum builds up on the wall, output decreases, cutting into profitability.
The Process Solution
The best mixing solution for phosphoric acid production involves modeling a full system mixing process that eliminates dead zones in the early reactor tanks. The dead zones are caused by incomplete mixing at the walls of the tanks that encourage particle agglomeration. As particles grow in size they adhere to vessel walls, impellers and shafts. By improving active mixing at the margins of the tanks, agglomeration is minimized. The phosphate rock has a larger surface area to react to the acid. This increases raw material yields and improves overall profitability of the plant.
The illustration shows the results from an existing installation. The customer experienced no accumulation on the walls of the attack tank or on the over or under flows of the attack tank. This contributed to no rebuild or replacements since our experts teamed up with our customer to improve phos acid mixing at their plant.
The Mechanical Solution
The ability to improve in-tank mixing early in the process is critical to improving the mechanical reliability of reactor mixers. The performance of our purpose-designed impellers, mechanical design criteria, and rigid coupling designs continue to withstand the test of time. Our success is no accident. Our process performance eliminates the root causes that lead to failures.
We have developed an industry standard mixer drive—The “Rock” (PVED-13S3) — to operate in the abusive phosphoric mixing process tanks. The drive has extra heavy duty bearings, seals and increased output shaft diameters to resist corrosion and withstand shock loads caused by the impact of phosphoric rock during blending operations. Drive housings have been designed with increased rigidity to keep the bearings and gearing in proper alignment in high shock load applications for long life service.
Our purpose-built PVE Series drives have been in continuous phosphoric acid production service since 2004 and can be deployed new or retrofitted worldwide through our production facilities in the United States or United Kingdom.
Contact us today to see how we can help you.