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Managing the overlap

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Managing the overlap

December 09, 2012 - 14:00
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BRUSSELS, Dec. 10, 2012 (RISI) -Energy has historically been a major component of an integrated pulp and paper mill's overall operating cost structure. As energy costs have rapidly escalated over the last five years, how well a mill positions itself to manage this spend can be a major determinant in its long-term viability.

To address this priority mills have responded in a variety of ways. To leverage their own internal operational and engineering expertise, many facilities have used on-site staff and resources from other mills within their corporation to identify and evaluate energy optimization (EO) opportunities. Outside energy management consultants are routinely contracted to perform studies on a mill's potential to optimize energy costs. With all of these efforts, expertise and analysis one may wonder if yet another different perspective could generate additional novel and innovative solutions.

Most energy studies whether performed by internal teams or outside consultants have a tendency to specialize in a certain branch of EO whether it is demand-side conservation project identification or power supply-side agreement cost-reduction. As is often the case, when one steps back to take a broader view of the mill production cycles, additional perspectives and solutions may arise. This is the arena where the Nalco approach to EO excels and serves to complement existing, ongoing and previously performed work. The main objective of the Nalco EO approach is to develop a short list of high impact projects that can be easily implemented with little or no capital, Fig. 1.

Many integrated mills are good candidates for the Nalco EO approach. From experience a brief phone interview with mill operations staff members is all that is required to determine if a mill could benefit from the Nalco approach.

Fig. 1 - The fluency in all branches of EO allows Nalco to provide innovative solutions to compliment specialized efforts by the mill and conventional energy management consultants

The need for a thermodynamic model

An integrated pulp and paper mill has one of the most complex industrial utilities operations, burning multiple fuels and supplying varying proportions of mill electrical demand. Simple conservation- minded approaches to energy cost reduction can have the unanticipated effect of actually raising overall facility operating costs. For example, a project to conserve low-pressure steam in a pulp mill could lead the power and recovery department to adjust its operations which could in itself result in a purchase of more electricity at a higher rate because decreased steam demand reduces turbine electrical output. These are the kind of complex inter-relationships that necessitate the development of a comprehensive thermodynamic model (TM) of mill power production, Fig. 2, as the first step in the Nalco EO approach. The main purpose of the model is to easily evaluate the financial consequences of any change in the utility which could be influenced by an increase or decrease in steam demand at a variety of pressures.

In one Nalco EO project the thermodynamic model confirmed that a previous attempt to increase the heat recovery in the boiler make-up water system ahead of a reverse osmosis system was producing a net increase in energy consumption and subsequent cost. An alternate solution, verified by the thermodynamic model, was identified whereby the addition of a vent condenser on the condensate storage tank, would enable the mill to generate the desired increased heat recovery in a more cost effective manner. The mill achieved a net saving of ~$275,000 after recovery of the capital and installation costs associated with the second exchanger.

Figure 2 - The TM of the utility allows complex inter-relationships to be considered and the financial impact quantified when planning a process change that will affect a mill’s energy picture

Where to start: Mining the data for gold

Once the TM has been constructed it is possible to determine how either the production process or the utility can be manipulated and any subsequent impact on energy costs. The next step in the EO process is to establish the correct strategy for the particular mill by asking a series of general questions:

  • Can the mill produce more power internally?
  • If so, what are the implications on fuel costs and power contracts?
  • If more power is produced, what amount of additional steam would be generated and at what pressure?
  • If more steam is produced, how could it be used in the various process areas to provide a process benefit?

This is one example of a typical line of reasoning that is undertaken once the model is constructed.

In addition to the TM model, an energy consumption benchmarking exercise is conducted. There are comprehensive thermal energy consumption benchmarks that have been published for the pulp and paper industry for entire mills and individual production areas, Fig. 3.

Reviewing benchmarks in one case challenged long held views of performance in the mill's evaporator section. The mill had what they thought was an acceptable steam economy and annual steam usage with respect to grade and tons produced. The benchmark exercise revealed comparisons that prompted the mill technical staff to closely inspect the evaporator set during the annual outage. This comprehensive inspection revealed a problem that was able to be corrected and reduce mill steam load to the point that auxiliary No. 6 fuel oil was no longer required.

Figure 3 - Example of using energy consumption benchmarking comparisons by process area. This measure is a useful step in establishing an EO strategy

To be continued ...Click here to read Part II

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