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WASTE TO ENERGY


TACKLING BOILER CORROSION


High velocity thermal spray stops weld overlay corrosion in waste to energy boiler


alloy 625 weld overlay was showing signs of premature accelerated degradation. IGS was contracted to apply a high


W


velocity thermal spray (HVTS) cladding on top of the weld overlay in situ to stop corrosion and ensure the reliable and safe operation of the boiler. After 10 months in service, the IGS thermal spray solution had no defects. As a result, additional areas of degrading alloy 625 were protected with HVTS.


RENERGIA PERLEN Te Renergia waste incineration plant is a joint effort of all waste disposal associations from Central Switzerland and Perlen Papier. Renergia Zentralschweiz is responsible for more than just recycling waste from Central Switzerland. It supplies Perlen Papier with process steam, the district heating networks Rontal and


44 www.engineerlive.com


hen a waste to energy (WTE) boiler was experiencing fireside corrosion, its operators discovered that shop-applied


Emmen with hot water and provides electricity for approximately 44,000 households. Following two years of construction, the Renergia Waste to Energy plant went into operation in 2015.


WTE BOILER FIRESIDE CORROSION Te Hitachi Zosen Inova (HZI) furnace installed at Renergia is an inclined, moving grate, four-pass WTE boiler with an external economiser. Te boiler’s thermal capacity is 47MW with the steam flow of 58 t/h and steam pressure of 41 Bar at 410°C. Alloy 625 weld overlay was shop- applied on the fireside water wall panels to protect the WTE boiler tubes from fireside corrosion. After months of operation, an inspection revealed accelerated degradation of the Alloy 625 just above the grate. Several solutions were considered to manage the boiler tube metal wastage and improve reliability and lifetime of the water walls, including replacement, field-applied weld overlay and thermal spray.


EVALUATION OF ALTERNATIVES Te replacement of affected water wall sections with new tubes would have been time consuming and expensive, considering the estimated frequency of replacement of five years or less. Like-for-like weld overlay repair is an intensive and time-consuming solution. It requires preliminary grinding of the degraded surface layer prior to the application of new weld overlay. Moreover, both aforementioned solutions wouldn’t exactly solve the problem, as the same corrosive media attacking existing weld overlay would still be present. Te third option was thermal spray


(TS). Tis technology had mixed results in boiler applications and the plant invited four TS vendors to perform test applications on different sections within the boiler. Each vendor was given a side wall inside the two lines. Out of the four claddings applied, only two delivered satisfactory results. IGS’s HVTS solution was found to be the best, both in terms of


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