Inconel 625 for use in waste to energy plants

18 June 2020

Inconel 625 has a high magnitude of nickel, and NiO is noticed as precipitates in the sulfate melt; however no extensive layer of NiO is noticed. A less bulky layer is due to high concentrations of chromia on the nickel-based alloy. 

Due to the vast variety of municipal, chemical and hospitals solid waste, sulfur and chlorine in waste to energy plants are always present. When volatilized chloride salts in the combustion gases come into contact with the cooler tube surface, they condense and produce liquid or solid deposits that may comprise sulfates and alkali chlorides. Accumulated metal chlorides interact with gaseous SO2 or SO3 to produce condensed alkali sulfates. 

So, the presence of sulfates induces the interaction with chromium oxide, causing the dissolution of this security oxide. A specific reaction that is advantageous is decreasing the corrosive effect of chlorine and chloride salts is the sulfating of volatilized alkali salts in the flue gases. This interaction converts chlorides into sulfate salts and chlorine released interacts with water vapor to produce HCl gas. Sulfate salts are less vigorous as sulfate corrosion requires high temperature. 

It is found that corrosion resistance of Inconel wire 625 in dry chlorine is significant and hence it can offer regular service, and the alloy can be used in increasing temperatures going up to 540°C, the highest temperature at which Inconel 625 can perform without any corrosion issue.

When the conditions are more vigorous involving a mixture of HCl, HBr and SO2, Inconel 625 still offers suitable performance at the maximum temperatures. Although it refers that alloys having cobalt or higher chromium concentration than in alloy 625, offer superior resistance against oxidation and sulfidation. 

Inconel 625 can also be used as coatings for service in molten chloride salts and dry HCl or SO2 conditions up to 650°C. 

Courtesy of Heanjia Super Metal Co. Ltd.