Process Modeling to Save Energy

- Source: PA Files

Martin Fairbank
Typography

As everyone knows, it’s difficult to manage a process if you can’t measure it. This is particularly true of energy management in a pulp and paper mill, especially when dealing with steam flow meters, which are notorious for sometimes giving inaccurate measurements.

The steam from a boiler can be used in hundreds of different locations in a large facility, and it is common for many of the steam flow measurements to be wrong, due to sensor drift, corrosion, contamination, non-linearity of calibration or simply broken sensors. Obtaining an energy balance of the mill is difficult if some of the measurements are inaccurate.

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Building a Model

One way to better understand a process and figure out what’s going on is to build a computer model. One useful modeling package, a Canadian product used around the world for over 30 years, is Cadsim Plus from Aurel Systems. The founder of Aurel, Larry Wasik, developed Cadsim Plus with the vision of “living drawings” that mirror the exact process. The software includes modules for common operations such as heat-exchangers, washers, tanks, evaporators and turbines, and asks the user for basic information in order to properly model them. Process data can also be imported directly from the process or the data historian to populate the model. Building a basic Cadsim Plus steady state model, often used by engineering consultants when designing a process to figure out the correct sizing of equipment, can take about a month. With more work, this can be developed into a dynamic model, able to show what happens when input parameters are changed, which can help mills to better understand their process. Aurel, based in the Vancouver area, has grown today to 5 full-time and 4 part-time employees to support their existing clients and find new ones. Larry’s son Andrew Wasik is now in charge of operations, allowing Larry to devote himself to developing new applications.

Real-Time Optimization

While there is value in using a static or dynamic model to learn how the process works, significantly more value can be developed by using Cadsim Plus to generate a real-time model that can be used as a better representation of the process than the actual process measurements. Larry has been developing this capability over the last several years, working with a few facilities that are on the leading edge. As he describes it, a “dynamic data reconciliation” process (DDR) uses engineering first principles to develop several measurements of the same data, and then selects the measurements that are most likely to be correct using a combination of least-squares regression analysis and weighting factors that take into account the reliability of the measurements. For instance, temperature measurements are much more reliable than orifice steam flow meters, and if a temperature increase is seen with the addition of steam, the steam flow can be calculated independently and more reliably than from an orifice meter. The best fitting results are computed, resulting in a full heat and material balance calculated in real time. Requiring a large investment of time from Aurel staff, the DDR process has been used to generate accurate energy reports, to prioritize instruments for recalibration or repair, and to find operating sweet spots to maximize value, but Aurel’s vision is to develop new business in real-time optimization (RTO) of operations using this approach. Their long-term business plan is to sign up clients at an initial low cost to have DDR-based models built by Aurel. Once a model demonstrates the potential to improve profitability through process optimization, the client would enter into a long-term contract with Aurel to help maximize their profitability 24 hours a day.

“Our target clients are mostly kraft pulp mills that operate several boilers and generate power from steam. Many of the operators of these facilities don’t know how to best run their turbogenerators or operate their steam let-down system, and this is because the answer changes with the production rate,” says Wasik. With Aurel’s DDR-based models, many such mills could use RTO to increase their profitability by 1 to 3 million dollars per year, he estimates. Among other potential processes that could benefit from this process are sulfur make-up or load shedding for thermomechanical pulp mills whose purchased power price varies with the time of day.     

Asked for his vision of the future, Wasik said, “I think we are the only company that can do RTO the way it should be done, and that this will be a game-changer in advanced process control.”


Martin Fairbank, Ph.D. Martin Fairbank has worked in the forest products industry for 31 years,
including many years for a pulp and paper producer and two years with
Natural Resources Canada. With a Ph.D. in chemistry and experience in
process improvement, product development, energy management and lean
manufacturing, Martin currently works as an independent consultant,
based in Montreal. He is also an author, having recently published
Resolute Roots, a history of Resolute Forest Products and its
predecessors over the last 200 years.


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