HELSINKI, March 7, 2011 (RISI) -In part I of a two part special report, energy efficiency at mills comes under the spotlight, highlighting the fact that operational staff at mills will have to take on more responsibility in the future.
The monitoring and reporting of energy efficiency is a very recent topic in the papermaking context. Integrated paper mills traditionally know their overall energy consumption at a very general level, but the energy efficiency of individual paper machines is tracked only through a handful of indicators. A set of energy efficiency tools will be needed to bring energy efficiency within the reach of operators. In fact, energy efficiency should be considered already at the line engineering stage to make all required information available to process operators.
Making energy efficiency more tangible and disseminating information:The concluding report of a committee on energy efficiency appointed by the Finnish Ministry of Employment and the Economy lists three items that also constitute an integral part of energy efficiency monitoring for the paper industry:
- Identification, dissemination and implementation of best practices
- Further development of product and process engineering expertise
- Increased supplemental training in energy efficiency.
Comprehensive energy efficiency monitoring can help to identify and disseminate best practices within companies and beyond. Training is correspondingly needed for both process operators and designers. This raises various forms of collaboration between industry participants to a key role.
The many definitions of energy efficiency:While energy efficiency is discussed a lot, it lacks a commonly accepted definition. At a general level, energy efficiency can be defined as the ratio of value added to the amount of energy consumed within a specified process. This, however, is not very informative in many cases since the amount of value added may be difficult to determine in practice. Nevertheless, energy efficiency indicators can be categorized in practical terms as presented in Table 1.
Energy efficiency indicators
||W, J, %
||J/kg, MWh/t, W/kg
In looking at paper machinery related indicators, we notice that many of the parameters in Table 1 are relatively unknown or unused. Paper machinery indicators tend to relate either to specific energy consumption (e.g., kilograms of steam per amount of water evaporated) or to indirect measures of energy efficiency (such as hood supply air temperature). Additional new energy efficiency indicators and tracking methodologies will also be needed to facilitate comprehensive efficiency measures.
Process instrumentation facilitates energy efficiency improvements:The monitoring of pertinent indicators will provide a basis for energy efficiency improvements, but it is not possible without sufficient measurement instrumentation. In practical terms, one should be able to compute consumption balances for various usage locations. General level balances help to understand the magnitude of various energy flows, but true efficiency measures require that this balanced thinking is taken much deeper inside the process.
Starting with electricity usage, consumption figures need to be available both at the power distribution and process levels. The overall electric power consumption of a papermaking line would first need to be measured at each distribution transformer and this data should then be transferrable to the energy efficiency monitoring system employed. As we know, these types of usage locations are in practice operated through a separate control system, but utilizing the OPC interface, for example, facilitates the transfer of data for use in other systems as well. This also applies to sectional drives, which are typically governed by a drive control system that is separate from the actual machine control system, but data can still be transferred from this system to other systems.
Very little energy consumption information is generally available for the hundreds of separate motors found on a papermaking line. Major displays typically provide power consumption information as a percentage of dimensioning values. The inclusion of this area within reliable and comprehensive control would require power measurement instrumentation also for motors with less than 30 kW of rated power. These under 30 kW motors are predominant in number but they represent only a fraction of a line's overall power requirement, which means that rather comprehensive energy monitoring can be implemented at limited expense, Fig. 1.
Distribution of paper machine motors by number and power rating
In terms of thermal energy, one should be able to determine a thermal balance and major usage locations for each papermaking line. In practice this requires flow measurements at each heating and cooling location and comprehensive air and water system temperature measurements.
Water consumption has been noted to have a significant effect on energy efficiency. For this reason attention also needs to be paid to a line's water balance along with its energy balance. Just as in the case of thermal balance, water balance determination also requires flow and temperature measurements, both before and after each usage location/process.
Additional measurements that expand the comprehensiveness of energy efficiency monitoring include:
- Flow measurements for compressed air
- Compressed air pressure and pressure differential between line end points
- Forming and press section dewatering measurements
- Forming and press section dry content measurements
- Outdoor temperature measurements
- Machine hall temperature and humidity measurements.
Energy efficiency indicators do not always need to provide specific readings, in some cases it is sufficient to know the direction in which the process should be steered to move closer to the optimum. Visual edge trim monitoring, for example, can increase energy efficiency since well-functioning trimming improves machine runnability and thereby also enhances energy efficiency.
Operator in key role:One recurrent claim made in recent years is that technology has isolated people from the consequences of their actions. This is probably true, to a certain extent, and new technology will actually be increasingly needed for such purposes as making energy consumption more readily apparent and putting control and responsibility back in the hands of people. This will facilitate greater environmental awareness and therefore increased tendency and willingness among operators to also reduce the energy consumption of the process they operate. Operators must also be properly motivated since a simple underscoring of green values will not be sufficient incentive everyone.
Operating approach example for increased energy efficiency
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