Improved storage practices will limit the risk of spontaneous combustion of bark piles during storage and support optimized planning of fuel intake at biomass conversion facilities.
Boiler efficiency can be improved by over 5% if biomass moisture can be reduced to 40% from 50%. For a boiler using 34 oven-dry tonnes (ODt)/h of biomass, improved feedstock management can save ~$1.8million/year.
Reducing biomass moisture content by 10% can increase heat value by $9.90/ODt. For a 10-Mw CHP plant purchasing ~50,000 ODt/yr savings would be $495,000 per year.
The 60 MW Nova Scotia Power (NSP) plant installed on the Port Hawkesbury Paper (PHP) mill site in Point Tupper, delivers power and required steam input for the paper mill. NSP manages the boiler operations and PHP serves as the main feedstock supplier, which includes handling the storage of the biomass on site. In April 2016, the Nova Scotia Government amended the provincial law that designated the facility as one that must run 24/7, regardless of electricity market prices. The Nova Scotia Utility and Review Board along with NSP estimated it could save $9 million in 2017 by running the Point Tupper power facility on an as-needed basis (CBC, 2016).
At a monthly energy requirement of 440 000 gigajoules (GJ), the feedstock supply needed to meet plant demand is 45 000 green metric tonnes (GMt), with a target average moisture content of 50.4% (MacLellan, 2015). The estimated available fuel energy from feedstock with a target moisture content of 50.4% is 9.93 GJ/tonne (GJ/t) (using boiler efficiency data). The estimated monthly supply requirements for the boiler are therefore equal to 45 000 GMt, or 540 000 GMt/year based on full power output. Since the April 2016 law amendment, the planned production output is 55%, with the main product being steam for the paper mill. The annual required supply to run the boiler will be approximately 300 000 GMt, as of July 2016. PHP plans to supply the boiler entirely with bark from three sources:
100 000 GMt from the Bear Head legacy pile
90 000 GMt from the paper mill’s woodroom
110 000 GMt from sawmill purchases
The goal of this bark storage trial was to measure the impact of quality (moisture content, dry matter loss) and fire risk over time for innovative pile management techniques (shape, cover, ventilation). The winter supply of bark was targeted as it is the most difficult period in the year to gain access to good quality biomass.