Case Study #13:
Acid Recovery Systems
Initial situation
Industrial acid recovery systems are essential for reducing chemical waste and operating costs in metal finishing and pickling lines. These systems operate under highly corrosive conditions, handling sulfuric acid or hydrochloric acid at varying temperatures. Historically, metallic heat exchangers failed quickly due to corrosion, leading to costly downtime and constant maintenance. The customer needed a long-term, corrosion-resistant solution for both heating and cooling steps in their acid recovery process.
Challenge
A customer approached Calorplast USA with a requirement for high-performance heat exchangers for their acid recovery system. The system included:
- Large acid tanks (over 2,500 ft³ volume, bath temperature up to 160°F)
- Continuous operation at elevated temperatures with aggressive chemical solutions
- Reliable, energy-efficient cooling and heating of acids using process water or steam
- Long-term durability to reduce operational costs and maintenance
The key challenge was selecting the right plastic material for each application—cooling vs. heating—based on chemical compatibility and temperature resistance.
Solution
Material Selection – Technical Rationale:
Cooling:
For cooling steps, where the acid temperature is moderate and chemical exposure is constant, high-performance polyethylene (PE or PE-RT) is ideal. PE provides excellent corrosion resistance and is cost-effective for temperatures up to approximately 176°F. It is well-suited to cooling sulfuric acid and similar process solutions.
Heating:
For heating acid to higher temperatures (such as 160°F in the pickling tank), PVDF (polyvinylidene fluoride) was selected. PVDF offers superior chemical resistance and withstands both the elevated temperatures and the aggressive nature of concentrated or oxidizing acids. This ensures reliable, long-term operation and eliminates concerns of premature failure or contamination from metallic components.
Implementation
Calorplast USA supplied immersion-type heat exchangers specifically engineered for acid recovery. For this project:
- PVDF heat exchangers were installed in the high-temperature acid heating stage.
- PE heat exchangers were recommended for cooling duties, ensuring the right balance of performance, longevity, and cost.
Each unit was custom-sized for tank dimensions and duty requirements, maximizing efficiency and minimizing pressure drop. The plastic construction provided complete immunity to corrosion, virtually eliminating maintenance needs.
Result
The acid recovery system now operates with:
- Consistent, efficient heating and cooling of acid solutions at every stage
- No metal contamination or heat exchanger failures due to corrosion
- Reduced operational costs and increased uptime, thanks to the durability of all-plastic construction
- Optimized material use, with PVDF and PE selected precisely for their respective strengths in heating and cooling applications
This approach has delivered long-term reliability and value for the customer’s acid recovery process—backed by sound technical reasoning and real-world results.
