Proper electric heater for sulfuric acid & hydrochloric acid pickling tanks

A. 1. Quartz heaters seem to be getting rarer in the USA (just based on my impression), due to their fragility and an apparent difficulty in making them as safe as metal heaters. Teflon coated heaters would probably be the ideal solution for your sulfuric acid pickle, but other possibilities might include nickel or titanium. Titanium is tricky stuff in a plating plant, and you should get the supplier to tell you exactly what to do in terms of anodic protection, etc.

2. Incoloy for an alkaline electrocleaning solution strikes me as an expensive & exotic, but poor answer. It may work, but why not steel or stainless steel, like virtually every shop I visit? What are the tank walls made of? I'd guess steel, since you say they are used as electrodes.
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey

A. We have seen significant failure of Titanium heaters lately, in simple caustic cleaners. The failures seem to principally at the welds. Since most titanium is rarely pure, and usually alloyed with some level of Aluminum, we have theorized that it is due to high Aluminum content welding rod. We know what ingredients are in our cleaners, and there is no way that these things can attack Titanium. We have also done testing, and observe how the cleaners attack most Titanium, until the Aluminum in the surface has been eaten away, then all attack ceases ... Hope this helps.

A. This post is a response to the person who was having a problem heating a sulfuric acid pickle tank because of the corrosive effect of the solution on the heater.

Where I currently work, we utilize an over-the-side heater that is essentially a zirconium heat exchanger with hot water as the heat source. The zirconium holds up very well to the environment, but I would not recommend it in an application where the heater can be subjected to any type of shock. We had to replace a heat exchanger after a jam-up in the processing line subjected it to a shock. The zirconium cracked at the weld connecting the tubes to the manifold. The only way we found it was by noticing an unexplainable increase in tank volume and related decrease in concentration. (This took quite some time to find.)

Fabrication of a zirconium heat exchanger can be rather expensive due to the welding and availability of a supplier. A small exchanger (5 feet long by 2 feet wide with 1/2" tubes) can cost several thousands of dollars. You have also have to be extremely careful when installing it. However, if the exchanger will not be subjected to any potential shocks, it might be a good alternative. We've had heaters that have lasted for years in a 10-15% sulfuric acid pickle tank.

A. PVDF heat exchanger with hot water (or steam) circulation is a better way that's very simple. You can make a heat exchanger with PVDF tubs and using hot water or steam for heating. We use this method in hot dip galvanizing pickling process.

A. Dear Jayasenan,
Quartz electric heaters work for HCl. Teflon steam tube heaters also work. Too high of a temperature will give acid fumes in the plant. After drawing the wire you need to take off the lubricant with hot caustic cleaner.
Regards,

A. Teflon coated heaters are an option. Double sided walls and hot water in between is another. Simplest way would be to heat up the wire enough to quickly reach the desired temp. Then, maintain it with suitable heat input from subsequent charges.

A PE-RT or PVDF heater, heated by hot water, mounted on a baffle plate will give you excellent results.

A. I do not think that any common metal heater will last at that concentration and temperature. My guess is that it will take a quartz heater and I will further guess that you probably should use a derated heater or have fairly good solution flow in the tank. The company that you buy the heaters from should be the "authority" on the type and the sizes. A factor that you did not give is allowable warm up time from what temperature to the 135 °C

What kind of a tank is going to stand up to this???

Sir:

Quartz is correct. These usually come in 5KW, 10KW, etc., depending on tank size and tank insulation. I also wonder what the tank construction may be.