Pickling acid is drawn from the tank by means of a chemical pump and fed through a Pre-filter to remove gross particles. Once the acid solution has been filtered, the fluid is passed through a valve and flow meter, allowing the operator to adjust the flow rate and view the clarity of the solution.

The acid solution then enters the Primary Heat Exchanger (1)  where the temperature is reduced by chilled acid traveling counter-currently through the heat exchanger (returning from the end of the process). The digital temperature indicators display the temperatures of the solution entering and exiting the exchanger.

In the Reactor (2) , the acid is agitated and chilled to a level where the iron begins to form an iron sulfate crystal (ferrous sulfate heptahydrate). The special thermoplastic heat exchangers in the solution pass a refrigerant through the inner tubes that absorbs heat from the solution and displaces it in the chiller condenser loop. A specially designed mixer keeps the crystals from forming a cake of solid crystal on the exchanger by violently agitating the solution across the exchange tubes.

The Crystal Settler (3) is a conical-bottomed, fiberglass tank with an overflow port that allows the clarate (solution without iron crystals) to return to one half of the two stage pump back station. This chilled acid is pumped through the Primary Heat Exchanger. The chilled acid is heated by the hot acid coming in from the process tank and uses its own thermal energy to cool the hot acid coming in. In this manner 70,000 to 400,000 B.T.U.s can be utilized in each direction, significantly reducing the operating cost of the system and the cost of re-heating the process acid.

The crystals are gravity fed through the bottom of the Crystal Settler and pumped to the Centrifuge (4). The Centrifuge separates the solution from the crystal and yields a dry product. The centrate (solution with iron crystals) being discharged by the Centrifuge is returned to the other half of the two stage Pump Back Station (5). This solution is then pumped back to the Reactor where the small crystals that could not be spun out by the Centrifuge can reseed and grow. Pickling acid is drawn from the tank by means of a centrifugal chemical pump and fed through a Pre-filter to remove gross particles. Once the acid solution has been filtered, the fluid is passed through a valve and flow meter, allowing the operator to adjust the flow rate and view the clarity of the solution.

The system is equipped with an automatic backwash that is activated when the system is shut down. This prevents crystals from forming as the exchangers cool during shut down.

The system is equipped with an automatic backwash that is activated when the system is shut down. This prevents crystals from forming as the exchangers cool during shut down. A microprocessor based control panel is the heart of the process. The system is highly automated to minimize the need for an operator or even much routine maintenance beyond moving dry crystals and changing filters. Highly corrosion resistant and reliable signal generators are employed throughout the system to feed back information for system response. Automated valves, adjusting liquid and crystal movement throughout the system, respond to the programmed signals generated by the microprocessor. The system is also equipped with alarm lights and a buzzer that refuses to be ignored. Digital temperature controllers track the system's thermal efficiency and indicate potential problem sources.

Optional Design

View our Low Temperature Design for plants which require an unusually low level of iron in the pickle tank -- 50 to 60 grams/liter.  Our conventional sulfuric acid recovery system maintains iron levels at 75 to 95 grams/liter.

last updated May, 2005