Greening with natural gas

New bark silo and offloading.

The conversion of Nekoosa Mill’s three main power boilers to natural gas will result in a significant reduction in the facility’s environmental footprint beginning in 2015. This major project was completed in November 2014, ahead of schedule and under budget.

The project removed 172,000 tons/year of greenhouse gas emissions, 3,500 tons/year of SO2, 1,000 tons/year of NOx, 50 tons/year particulates, 100% of mercury resulting from coal, 32,000 tons/year of fly ash from the landfill, and 500,000 gallons per day of water discharges. In addition to meeting future environmental regulations, starting in 2015 the mill is also in a position to lower operating costs and improve plant energy efficiency.

New regulations

National Emission Standard for Hazardous Air Pollutants for industrial power boilers (known as Boiler MACT) placed compliance deadlines for Boiler MACT (Maximum Achievable Control Technology) in January 2016. To meet this deadline, the Nekoosa team began examining methods for compliance beginning in 2012. All three of the main power boilers had to be in compliance in 2016.

The largest boiler (#10) was a coal stoker boiler that also utilized residual bark for combustion. The other two boilers used pulverized coal as the fuel source and were similar in design to each other. The team first examined additional pollution abatement equipment for the boilers and remaining on coal versus the conversion of the boilers to natural gas. This approach of purchasing pollution abatement equipment did not provide an effective solution and significantly raised operating costs. The solution that was reached was to convert boilers #10, #2, and #1 to gas firing and remove the small, older #7 boiler from service. With the assistance of Corporate Purchasing and Engineering, the project was developed and approved in 2013.

Equipment removal

The project consisted of removing the bark feed and coal stoker system from #10, with #2 and #1 boilers, which required the removal of the pulverizing equipment and coal burners. This equipment would be replaced with four new gas burners in #10 boiler and two new burners each in #2 and #1 boilers, and a complete gas delivery system.

#2 boiler before (above) and after (below) conversion.

#10 boiler burner before (above) and burner deck after (below) conversion.

A new bark handling system was also required, with the bark product shipped to Rothschild for consumption in the new biomass unit. In all, the project touched many areas and people, including the power plant and four boilers, controls, wood room and bark system, railroad which transported coal, and the coal distribution system within the facility.

Smooth execution

The $10.2 million project was approved in late 2013. Equipment purchases started in early 2014 with construction scheduled to start July 21 and be finished November 28.

#10 boiler was the first to undergo its conversion and finished a few days early. This was quickly followed by #2 boiler and then #1 boiler. The construction went smoothly and all boilers were on line and operating by Nov. 9, finishing 21 days early and $700,000 under budget.

A key element was that the project was completed by the mill crews and outside contractors with zero first aids or incidents.