Hydrochloric acid is a highly corrosive acid
Hydrochloric acid is a highly corrosive acid. This acid is commonly produced in conjunction with the chlorination of organic chemicals. The concentration of these acids ranges from dilute solutions through to fuming types at approximately 40% HCL.
Approximately 20 million tonnes of hydrochloric acid are produced each year, making it an important chemical for many processes. It is both produced by chemical manufacturers and onsite as a byproduct from other processes.
- In steel pickling where the acid is used to remove iron oxide and scale from the metal surface prior further processing such as coating.
- The extraction of crude oil requires hydrochloric acid for injection into rock and for cleansing of impurities in the well.
- Hydrochloric acid is also used in the production of many food ingredients such as corn syrup, gelatine, sauces and preservatives.
- The production of leather products
- PVC material
- The production of household cleaning products.
- Producing organic and inorganic compounds in waste water treatment, polymers and battery manufacture.
The two main considerations for the handling of hydrochloric acid are containment and chemical compatibility.
The containment element often derives from chemical compatibility.
Hydrochloric acid is highly corrosive, particularly on metals. Metals such as aluminium, cast iron and even some stainless steels are unsuitable for hydrochloric as it will drastically corrode the material. Metals are used with hydrochloric acid where higher temperatures and pressures are required.
Typical metals used for handling hydrochloric acid include Hastelloy-C and Titanium at lower concentrations and Hastelloy-C at higher temperatures. Although these metals will handle strong acids, they are not impervious to corrosion. Many pumps are specified with a short life cycle due to the tolerated corrosive wear expected. For some pumps this may be as little as a matter of months as no matter what material is selected, the pump will inevitably fail.
Where the hydrochloric acid has impurities reacting in the fluid such as circulation applications the pump may see an exponential rate of corrosion from the particles being oxidised.
Where the temperature and pressure allows, non-metallic materials are favoured due to the excellent chemical resistance, even at higher concentrations. Materials such as PTFE, Viton, PVDF, Kalrez and ceramic/silicon are excellent for handling hydrochloric.
Where pumps are chemically resistant, the best principle for containment is a mag-drive pump. This is principally due to the absence of mechanical seals and wearable parts separating the acid from the environment.
Mag drive technology
A mag drive pump uses o-rings to seal the casing of the pump so providing the fluid is as specified it should work indefinitely.
An excellent example of this would be a mag drive pump with a metallic casing for strength under high pressures with a non-metallic lining such as ETFE with high quality magnet and bearing assembly. Providing the fluid is as stated when specified, the pump life cycle should be in the decades.
Air diaphragm pumps
Where solids are present, such as in circulation applications, an air diaphragm pump may be more suitable due to the wide range of materials, the ability to handle a higher S.G. and resistance to abrasion.
A third option for solids handling, particularly where there may be a more viscous product or slurry/sludge like substance may be using a peristaltic pump.
An industrial hose type material such as EPDM will handle more dilute concentrations such as 20-30%. Although the acid will corrode the hose, it is expected to fail mechanically before the pump can breakdown chemically.
This pump type is also excellent for the accurate dosing of hydrochloric acid as the flow rate is directly proportional to the speed of the pump.