TubeFeeder key for Gascogne Papier
French pulp and paper maker Gascogne Papier is commissioning a new 59 MW biomass-fired steam boiler. A novel Swedish fuel reclaim system paired with an Austrian fluidised boiler was the solution choice to meet performance needs.
In late 2014 French pulp and paper maker Gascogne Papier qualified for grant from the French Environment and Energy Agency, ADEME, to replace an existing heavy fuel oil (HFO) and bark-fired steam boiler at its Mimizan kraft pulp and paper mill in southwest France. Instead a new 100 percent biomass solution was installed so that Gascogne could ramp up its energy self-sufficiency, use unutilised wood and forest residues and cut its fossil carbon footprint.
Currently under commissioning, the new boiler will use around 110 000 tonnes per annum of biomass fuel consisting of a mixture of bark from the pulp mill and other wood, forest residues and stumps chipped or shredded to P100 specifications and delivered by truck. Some 14 – 16 trucks per day unload into a fuel receiving station, which is open 10 hours per day, five days a week.
The contract to design and install a biomass fuel handling, storage and reclaimer system, from truck receiving to boiler buffer silo infeed, was given to French biomass handling solution providers SERA. The biomass is screened to remove sand, stones, glass and oversized material and passes a metal detector to remove metals before being conveyed to the top front end of a 6 000 m3 A-framed storage silo.
The shredded bark from the pulp mill is conveyed separately and stored in the rear section. The silo is divided by a barrier wall into two separate 3 000 m3 sections, each with its own head-room trip conveyor to evenly distribute the incoming fuel in each section respectively.
The fuel flow rate specified for the new boiler can vary over threefold, from 30 m3 to 100 m3 per hour peaking at 115 m3. Thus selecting a fuel reclaimer system that could supply a well-blended homogenised fuel, meter it out at a rate directly proportional to the boiler demand and provide 100 percent redundancy was a critical design feature of the entire EUR 50 million project.
The heart of the system is the use of two TFL 16 TubeFeeder reclaimers, a proprietary technology developed and manufactured in Sweden by Main Engineering AB and licensed to Jeffrey Rader, a brand of TerraSource Global. These are installed on the floor of each section transversing the silo width.
Both are reversible and can travel the entire length of the silo thanks to a gap at the bottom of the dividing wall. The proportion of each fuel type can vary from 0 to 100 percent meaning that the reclaimers need to work independently from one another and may also need to intermittently start and stop. The two TubeFeeders enable fully homogenised fuel recovery from under the piles in a true first-in, first-out (FIFO) fashion onto a conveyor to boiler buffer silo.
Austrian fluidised bed
The turnkey contract for the 59 MW thermal biomass boiler including auxillaries and boiler house was awarded to Austrian combustion engineers Bertsch Energy GmbH & Co KG, its second biomass boiler delivery to France – the first was a turnkey CHP plant to Sciere Siat-Braun in Urmatt, an integrated sawmill and pellet plant, in 2012. A fluidised bed system, it is designed to provide 20 to 80 tonnes of process steam at 65 bar and 450 oC per hour for the mill.
The challenging point is that we have to respond to the really huge steam demand variations from the paper production. A fluidised bed is the only technology able to do that with biomass, said Carl Christian Redl, Senior Project Manager for Bertsch Energy.
Clearly, it seems that the pairing of the technologies will meet the challenging performance needs of Gascogne Papier for years to come.
This article was first published in Bioenergy International no. 3-2016. Note that as a magazine subscriber you get access to the e-magazine and articles like this before the print edition reaches your desk!