With the increasing cost of energy and mounting environmental concerns about emissions, a few pulp mills are installing biomass gasifications as an alternative source of energy. One recent example is the Kruger tissue mill in New Westminster, BC. The mill is installing a gasification system to convert locally –sourced wood residue into syngas, which will be fired into a boiler, replacing natural gas. The system start-up is scheduled for December 2009, and will produce 40,000 lb/hr of process steam and replace around 445,000 GJ of natural gas per year [1]. The gasification process uses 20-30% of the oxygen required for complete combustion. Through pyrolysis, a syngas is produced which mainly consists of carbon monoxide, hydrogen and methane. The main advantage of syngas compared to hog fuel is that it is a clean fuel; hog fuel generates a significant amount of particulate emissions. It is estimated that New Westminster installation will save millions of dollars in energy costs.

Other related projects in the pipeline are an ethanol production plant in Westbury, Quebec that will produce ethanol from old utility poles, and a plant in Edmonton, Alberta, which will produce ethanol from municipal solid waste. These projects indicate another option for wood residues in the pulp and paper industry.

The North American pulp and paper industry, as a whole, is taking a wait-and-see attitude towards biomass gasification, as the industry level of risk tolerance is low and money for capital projects is scarce in these difficult economic times. However, mills can take measures to improve their energy efficiency without spending significant amounts of money. The first step is to do an energy audit, to understand how energy is used at the mill and to take measures to improve efficiency. Process modeling can be used to monitor process changes and optimize energy consumption. The second step is to review how energy is purchased and what options are available from suppliers that may reduce costs. A team made up of people from all areas of the mill that can monitor energy consumption and affect conservation measures is another essential step.

Examples of proven tools to measure and control energy uses are given for a few mills in Quebec [1]. One mill used a two-stage approach to cut down on its energy consumption. In the first stage, a base line cost for heating was calculated and differentiated from the overall mill energy consumption. In the second stage, measures were taken to reduce heating costs based on available technologies. A model was used to isolate the impact of external ambient air temperature changes on energy consumption. The model showed that for a paper mill, heating represented a cost of $4 – $13/ tonne of product and accounted for 2%-10% of the overall energy cost. In one measure, automation of the mill’s economizers, at a cost of $65,000, resulted in a saving of $35,000 per year or a payback of 1.9 year.

In another case an advanced control system was used in a kraft mill to manage electricity demand. The mill used the advanced controls in six applications; one of these was on the turbo-generators. The main objective was to maximize the utilization of the turbo generators, minimize the use of make-up bunker oil and maximize the profitability of the mill’s electricity production. This was achieved by balancing the supply of electricity from both turbo generators to meet mill demand, while optimizing the purchase of electricity.

References:

Pulp and Paper Canada, pp.10-13, April 2009.