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Energy Savings Via Process Control

British Columbia has more than 4 million residents and 24,000 businesses, but a large portion of the province's electricity is consumed by one easily identifiable group: its 10 mechanical pulp mills. ...


October 1, 2009
By Pulp & Paper Canada

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British Columbia has more than 4 million residents and 24,000 businesses, but a large portion of the province’s electricity is consumed by one easily identifiable group: its 10 mechanical pulp mills. These 10 facilities consume 11% of the province’s connected load. They use, on average, 5,500 GWh/yr.

As such, BC Hydro is in the midst of a long-term Mechanical Pulping Initiative aimed at reducing the electrical energy consumption of these mills. To address the electricity consumption of mechanical pulp mills, BC Hydro has had to delve much further into the process than simply monitoring plant-wide energy use. The utility has concluded it must help TMP mills with measurement and control of the refining process before the industry can fully capitalize on energy saving opportunities.

“One of our biggest issues right now is how to measure and verify the energy savings,” says Norm Wild, program manager, industrial programs, with BC Hydro — Power Smart.

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BC Hydro’s engineers believe they can shave 20% off the energy requirements of each mill with state-of-the-art processes, equipment, and heat recovery. But they can’t do that without a reliable monitoring and quality control system in place to measure their progress and ensure consistent product quality.

Wild notes, however, that the impetus to invest in energy efficiency is not strong right now, given B.C.’s traditionally low electricity costs and the industry’s current woes. His hook line for the program is this: “We will achieve our energy savings targets by helping you build a better process.”

The utility is looking at a suite of projects which could include operational changes, chip conditioning improvements, low energy refiner plates, process simplification, and pumping and screening optimization. “We are hoping to get as much as 1,000 GWh/yr in energy savings,” says Wild.

But BC Hydro has identified a need for advanced process monitoring and control for pulp manufacturing because it needs reliable, consistent data to establish plant KPIs and determine the refining energy vs. pulp quality profile unique to each pulp and paper grade produced at each mill.

“The most significant energy efficiency projects that we can do all affect the refining-energy-to- pulp-quality curve,” says Wild. Therefore, to measure the success suc cess of these energy-efficiency projects, the mill must be able to monitor pulp quality and relate that to refining energy.

Craig Thomson, energy and environmental supervisor supervi sor at Canfor Taylor Pulp,

agrees with the need for greater process control. “Automating the process pro cess control around the refiners will enable potentially huge elec electrical energy savings that will benefit both BC Hydro and the mill,” he says.

One approach BC Hydro has adopted as part of its Mechanical Pulping Initiative is to promote the development of a “tool box” of new technologies that, once proven established, will help mills to monitor and control pulp quality. BC Hydro is offering to bring in its expertise, suppliers, and consultants to test these new technologies in a mill environment.

“Mills are very reluctant to spend money right now. They’re short-staffed, money is tight, there is a lot of uncertainty, and it’s difficult to engage them in new technology,” notes Wild. “We ask them if they’d like to participate in site-appropriate demonstration projects in which BC Hydro shares the financial risk and helps with the testing.”

Continuous pulp quality monitoring is promising

In the past, pulp properties were measured manually in a lab using samples drawn from the production floor — results were reported typically the next day. In recent years there’s been an introduction of automated testing, which is quicker and less labour-intensive, typically returning results in about an hour. But the target, in BC Hydro’s eyes, is inline, continuous pulp quality monitoring.

To this end, the utility has already participated in two demonstrations of a near real-time fibre analyzer called InovoCell. This device uses image analysis of the pulp fibres to determine morphological data, and then estimates the physical properties of the pulp using proprietary software.

BC Hydro’s demonstration projects consisted of taking pulp samples and comparing the results from the fibre analyzer with the results from an independent lab.

Forty samples were taken throughout the process from the secondary refiner discharge through the mainline screening and rejects refining systems and finally the disc filter discharge, at two mills. The participating mills were Canfor’s Taylor mill and Catalyst Paper’s Port Alberni site.

Thomson says the trial at Taylor Pulp emphasized the need for inline monitoring to optimize the use of the refiner quality control system. “The demo raised the awareness of all parties at the mill to push for capital to install the InovoCell analyzer for both quality and energy optimization.

“The lack of a feedback signal to give timely pulp property feedback, such as that provided by the InovoCell inline analyzer, is the current drawback to the QC system we have in place. There’s still much room for improvement through automation in both the refining area as well as bleach plant optimization,” he concludes.

Utility works to help plants reduce demand

It’s a tough climate right now to introduce process changes, but the provincial utility is doing all it can to help mechanical pulping facilities boost their energy efficiency as part of its efforts to reduce the province’s energy needs through demand-side management.

The process control approach that BC Hydro is proposing for mechanical pulp “would require, as a start, metering of all the big process-related drives in the plant, adequate inline instrumentation together with flow measurement and control devices,” Wild explains. “Once you’ve got the power metering and instrumentation in place you can determine what the plant is physically doing. However, this is only half the story — you need continuous pulp quality monitoring and a standardized way to operate to consistently make one pulp grade, one way.

“With this level of process monitoring and control in place we will be able to establish much better energy consumption baselines than we currently do.”

Managing electricity demand is a priority for the provincial utility, so large modernization or expansion projects at pulp mills could be eligible for financial assistance. The potential for energy savings at mechanical pulp mills is so great that the utility “can put quite a bit of money towards a project and still pass all the financial criteria that we have to meet to go forward with it,” says Wild.

Benefits will be felt in the long term

BC Hydro is laying the groundwork for mills to produce optimal pulp quality for minimal input — minimal energy, minimal water, and minimal chemicals.

“Mills will get a much more tightly controlled process out of this,” says Wild. “With less variability in the pulp, mills can lower their quality set-points and still make a comparable product. Then the industry can move to optimize the contribution of each unit process in their mills and investigate energy saving technologies such as low-energy refining plates and targeted refining by means of more effective fibre fractionation.”

For Thomson, the quality control initiative ties in to competitiveness. “In order for mechanical pulp mills in Canada to remain competitive, the need to continually improve and to reduce our dependency on electrical energy and fossil fuels is paramount. There is no magic bullet; hence the sustainable approach, based on structured continual improvement.”

And, as all manufacturers know, measurement is the first step toward improvement.

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BC Hydro’s tool box for pulp mills

BC Hydro is financially supporting research and testing of a portfolio of devices and equipment
that can help mechanical pulp mills to measure and control the refining and screening processes. One device that has shown promise is the InovoCell fibre analyzer.

The device measures important fibre morphological characteristics inline using high-resolution image analysis. Sophisticated software uses this data to compute some of the physical properties of pulp, without the need for sheet-making and testing procedures. It has proven quite accurate in its predictions, when compared with lab results (See table at right).

“I was very impressed with the correlation between the independent lab results and InovoCell, as well as the speed at which the samples from InovoCell were obtained,” remarks Craig Thomson, energy and environmental supervisor, Canfor Taylor Pulp.

Other equipment suppliers offer inline pulp measurement that can be linked to refiner control and BC Hydro is currently looking for mills to demonstrate these comparable technologies as well.