Though the mill in Thurso, Quebec is currently a northern bleached hardwood kraft pulp mill and will be transformed into a specialized dissolving pulp mill by 2011, processed pulp isn’t the only commodity produced by the mill.
At several different stages in the pulping process, energy is harnessed and recycled, saving the mill both time and money.
Here are four ways energy is reduced, reused and recycled at the Thurso pulp mill:
#1 – Reusing Cooking Liquors: Two “liquors” are used in the pulping process – white liquor which is a combination of chemicals used to dissolve wood chips, and black liquor which is a runoff liquid created in the actual cooking process. Both liquors are reused thanks to something called a recovery boiler. This machine separates the liquors not only form each other, but also from the pulp once the wood chips have bee dissolved. The white liquor is saved and used for future pulping, and the black liquor is burned off which generates heat, electricity and/or steam for the mill.
#2 – Recycling Steam: At the beginning of July, Thurso’s owners Fortress Specialty Cellulose (FSC) signed an agreement with Forevergreen Energy Inc to use recovered energy at the mill. Steam gathered from the recovery boilers used during the pulping process is channeled through a waste recovery system on site and pumped back into the mill in the form of energy.
#3 – Reducing Waste: Not everything produced in a pulp mill is usable. Wood chips are first cooked and then screened before they can be made into pulp. There is, therefore, some degree of product that ends up as waste. Instead of sending it to landfills, however, the refused parts – biomass – can be incinerated on site and the heat generated from that burning is used as energy for the mill. In the case of Thurso, black liquor (as mentioned in #1) is also biomass.
#4 – Providing Power for the Province: Though it is not up and running yet, FSC is also in the midst of building a cogeneration facility on site that will allow for much of the energy and steam used in the pulping process to be converted into energy and outsourced to the Quebec power grid. Once it is build (late 2012), the cogeneration plant will export 18.8 megawatts (of a possible 25 megawatts) to the province of Quebec. Fortress Specialty Cellulose currently has a 15 year contract with the province for this energy.