Diffusion Coatings for Corrosion-Resistant Components in Coal Gasification Systems

Krishnan, Gopala N. ; Malhotra, Ripudaman ; Alvarez, Esperanza ; Lau, Kai-Hung ; Perez-Mariano, Jordi ; Sanjurjo, Angel

SRI International

关键词: Coal Gasification;    Corrosion;    Scanning Electron Microscopy;    Alloys;    Diffusion;   

DOI  :  10.2172/891455
RP-ID  :  None
RP-ID  :  FC26-03NT41616
RP-ID  :  891455

美国|英语

来源: UNT Digital Library

【 摘 要 】

Heat-exchangers, particle filters, turbines, and other components in integrated coal gasification combined cycle system must withstand the highly sulfiding conditions of the high-temperature coal gas over an extended period of time. The performance of components degrades significantly with time unless expensive high alloy materials are used. Deposition of a suitable coating on a low-cost alloy may improve its resistance to such sulfidation attack, and decrease capital and operating costs. The alloys used in the gasifier service include austenitic and ferritic stainless steels, nickel-chromium-iron alloys, and expensive nickel-cobalt alloys. During this period, we analyzed several coated and exposed samples of 409 steel by scanning electron microscopy (SEM) and energy-dispersive X-ray (EDX). We report here on findings of this analysis: (1) A SS409 coupon that was coated with multilayered combined nitrides of Ti, Al, and Si showed adherent coatings on the surface; (2) A similarly coated coupon, after exposure to simulated coal gas at 900 C for 300 h, revealed that the coating has cracked during the exposure; (3) An SS409 coupon that was coated with nitrides of Ti and Si with a barrier layer of tungsten in between to improve the adhesion of the coating and to prevent outward diffusion of iron to the surface. (4) A porous coupon was coated with nitrides of Ti and Al and examination of the coupon revealed deposition of Ti at the interior surfaces. A similarly prepared coupon was exposed to simulated coal gas at 370 C for 300 h, and it showed no corrosion.