Enhancing our eco-effectiveness at Ngodwana Mill

Before a team of Sappi finalists in our Technical Innovation Awards (TIA) stepped in, the recovery furnaces were prone to scale build-up at our Ngodwana Mill in South Africa. This reduced furnace efficiency and required the recovery furnace to be taken offline for water washing every quarter. Soot-blower availability and effectiveness are necessary to keep the gas lines of the furnace clean. The TIA team overcame these problems by designing a bespoke soot-blowing system with smart control that improved soot-blowing in critical areas within the furnace.

The design of a new steam and condensate system has allowed for more steam supply to the soot-blowers. The new design also allows multiple soot-blower operations in critical areas by increasing soot-blower operating cycles simultaneously. This strategy reduces the dead time between soot-blowing by keeping the flue lines clean and keeping optimal heat transfer from the fire side to the furnace’s waterside.

Additional benefits include improved steam generation efficiency and reduced flue gas exit temperature, which enhanced precipitator performance. An added advantage of the newly installed system is the reduced risk of smelt/water explosions. This has been achieved by effectively preventing condensate from entering the furnace, while improving sootblowing efficiency.

This eco-effective solution has meant furnace output has increased by 1% due to improved boiler cleaning. This translates into an additional 9.2 tons per day of dissolving pulp production, contributing approximately US$1 million per annum. The benefit of extending the time between furnace cleaning shuts adds savings of just over US$1.1 million per year.