AcidRecovery.com

Consumer Products Manufacturer

Northeast United States

Acid Recovery System

Background:

A major industrial manufacturer of consumer products in the northeast needed to comply with their discharge limits and meet the environmental regulations being enforced by the Federal Environmental Protection Agency (EPA). The solution was to design and install an Acid Recovery System. Mech-Chem Associates, Inc. provided the engineering, design, and construction of an Acid Recovery System for their manufacturing plant.

Problem:

Their process waste contained significant quantities of nitric acid (HNO₃), sulfuric acid (H₂SO₄) and soluble molybdenum compounds. The neutralization and treatment of the process waste streams resulted in high levels of soluble salts and molybdenum being released into the local POTW. Because of the levels of these soluble wastes present in the water, the EPA imposed a fine on the facility for not meeting the discharge limits. However, an agreement was reached with the EPA allowing them to install a system to recover and recycle acids and process wastewater, preventing further releases.

A view of the entire waste recovery system including evaporator, centrifuge, DI system and control panels

Solution:

An Acid Recovery System coupled with a Wastewater Recovery System was designed to reclaim the nitric acid, sulfuric acid, and molybdenum, and provide for the purification and recycling of the process rinse waters. The total system was designed as a closed loop operation with zero wastewater discharge.

The Acid Recovery System engineered and designed by Mech-Chem Associates, Inc. was based on vacuum evaporation technology, and the rinse waters were purified using ion exchange resin bed technology.

The system is fully automated with the appropriate instrumentation and controls including three GE FANUC 90-30 PLCs with Logic Master software. The three PLCs are integrated into one PC by a graphical user interface developed with GE FANUC Cimplicity monitoring and control software.

Technology/Treatment Used

The Acid Recovery System separates the Nitric Acid from the Sulfuric Acid by evaporation using a single effect vacuum evaporator. The vacuum evaporator uses steam heat and has the appropriate materials of construction to handle the varying corrosion conditions as the concentration of the acid (HNO₃/H₂SO₄) mixture changes during distillation. The sulfuric acid/water fraction (still bottoms) are further processed in a glass-lined pressure vessel to precipitate the molybdenum as molybdenum trioxide (MoO₃). The recovered molybdenum trioxide is removed from the sulfuric acid using a solid bowl centrifuge and sent to a metals producer to be reclaimed.

Above: Ion Exchange Resin System for recovering the wastewater.

Left: Control panels for the system.

The rinse water purification and recirculation system treats about 10 million gallons per year of contaminated rinse water using selective anion and cation ion exchange resin beds. The metallic and other contaminants are removed from the rinse waters to produce DI-quality water which is recycled back to the production process.

Results:

The Acid Recovery System has provided a significant environmental and economic impact on the plant's operations. First, by reducing the nitric and sulfuric acid purchases by sixty percent. Second, the recovery of the waste acid solution has eliminated the use of caustic (NaOH) which was required to neutralize the acid. Third, the recovery of the acids has eliminated the discharge of the soluble salts (i.e. sodium nitrate and sodium sulfate) produced by the neutralized waste from the production operation.

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