Power Plant Energy Efficiency Analysis – An Effective Tool to Reduce Pulp and Paper Mill Energy Production Costs

Poster presented at PulPaper 2004

FROM KYOTO TO POWER PLANT ENERGY EFFICIENCY ANALYSIS

Finnish pulp and paper companies are currently actively promoting energy efficiency and increased use of bioenergy under the Finnish energy efficiency scheme 1 financed by the Ministry of Trade and Industry of Finland and managed by Motiva Oy. The target of the Finnish government is to reduce energy consumption and CO₂ emissions in accordance with the Kyoto Protocol. The energy efficiency scheme was first introduced in conventional industries in the mid-1990s but has now been extended to industrial and utility power plants.

Electrowatt-Ekono was involved in the development of the power plant energy efficiency analysis guidelines 2 , which were published by Motiva in 2002.

ENERGY – MAJOR CONTRIBUTOR TO PULP AND PAPER MILL PRODUCTION COSTS

Energy costs make typically 10-15% of total paper production costs. Energy conservation in the pulp and paper industry has typically focused on the demand side, i.e. the energy consumption of the mill only. The supply side, i.e. the energy production and distribution, has been of less interest to the industry as long as steam and electricity are available whenever needed. Rising energy prices along with environmental pressures have forced the industry to put energy issues higher on their agenda.

COMBINING EXPERIENCE FROM BOTH SIDES OF THE FENCE

Electrowatt-Ekono Oy and Jaakko Pöyry Oy have been involved in numerous energy efficiency improvement projects in the pulp and paper and energy industries over the past few decades. The Jaakko Pöyry Group is now able to offer pulp and paper mills a total energy solution from energy supply to demand-side optimisation. The ultimate target is to reduce the client's energy costs. As part of this service, Electrowatt-Ekono Oy and Jaakko Pöyry Oy have developed a customised Power Plant Energy Efficiency Analysis, aiming at improved energy economy of a pulp and paper mill.

POWER PLANT ENERGY EFFICIENCY IMPROVEMENT PROGRAMME

A Power Plant Energy Efficiency Analysis is the first part of a three-phase work process, the Energy Efficiency Improvement (EEI) Programme for a power plant (Fig.1). Typically the Programme can be carried out in 12-24 months, depending on the required investments.

Major emphasis is placed on operational and control improvements as well as small process changes, which have an immediate positive effect on the cash flow.

Fig. 1. Power Plant Energy Efficiency Improvement Programme – Work Process

HOW TO SUCCEED IN POWER PLANT ENERGY EFFICIENCY ANALYSIS?

Know-how of existing and new technologies, experience from similar projects and access to reliable power plant data are the success factors for the Power Plant Energy Efficiency Analysis (Fig. 2). Electrowatt-Ekono's methodology utilises customised tools developed to meet the success criteria.

Figure 2. Power plant energy efficiency analysis - success factors and tools

CASE STUDY – POWER PLANT ENERGY EFFICIENCY ANALYSIS FOR STORA ENSO, IMATRA MILLS

Background

As part of the Finnish Energy Conservation Scheme, Stora Enso Oyj Imatra Mills, in cooperation with Motiva Oy and Electrowatt-Ekono Oy, carried out a Power Plant Energy Efficiency Analysis for the Imatra Mills. The objective of the Analysis was to identify realistic energy saving and energy production improvement opportunities in the power plant process and to create a model for making corresponding power plant analyses for other Stora Enso mills.

Imatra Mills

Stora Enso Oyj Imatra Mills in Kaukopää and Tainionkoski produce pulp on three production lines, chemi -mechanical refiner pulp on the CTMP line and board and paper on seven board and paper machines. The total production amounts to approximately a million tonnes a year. The Kaukopää power plant produces all heat the mills consume and more than a half of the electricity they need. It also burns wood-based by-product fuels generated in the mills and takes care of the regeneration of cooking chemicals used in pulp production.

In addition to the power plant, the evaporation, caustic and lime kiln processes were briefly reviewed in view of energy efficiency improvement potential.

Analysis

Customised tools were used to optimise the energy production and supply. For example, the power plant process was simulated to optimise the loading of the steam turbines and further to calculate the savings.

Findings

The most significant saving potential was related to more efficient use of secondary heat, increasing of the power-to -heat ratio by means of improved steam control system concept and reduction of natural gas firing. For example, the improved steam control concept suggested would increase the on-site power generation by approximately 14 GWhe/a. Improved preheating of make-up water by means of hot condensates would lead to a total reduction of approximately 74 GWhfuel/a in fuel consumption.

All suggested improvement ideas would improve the overall energy economy of the Imatra mills. The overall energy cost saving potential was calculated to be over EUR 1 million annually.

SIGNIFICANT SAVINGS CAN BE EXPECTED

The results of the Power Plant Energy Efficiency Analyses carried out as part of the Finnish energy efficiency scheme have generally been very satisfactory. At condensing power plants, the identified improvement ideas have resulted typically in an estimated increase of the efficiency by approximately 1%-unit 3 . At pulp and paper mill power plants the recently completed analyses by Electrowatt-Ekono have resulted in an estimated efficiency increase of 1.5 - 2%-units.

EMISSIONS TRADING – HOW DOES IT IMPACT ON ENERGY CONSERVATION?

In Europe the forthcoming CO2 emissions trading will have its effect on the feasibility of energy conservation.

The emissions trading arrangements will most likely raise the electricity market price and improve the viability of energy conservation.

CONCLUSIONS

1. Power Plant Energy Efficiency Analysis can significantly help a pulp and paper mill improve its energy efficiency and reduce its CO2 emissions and/or energy costs.

2. Some energy saving potential ideas are transferable from one mill to another. Specific methodology, know-how and experience are required to be able to capitalize on the saving opportunities since each power plant process and its integration to the mill is different.

3. Rising fuel and electricity prices will increase the energy costs of the industry, which makes efficient energy production and supply increasingly vital for a mill.

4. Emissions trading in Europe will further improve the viability of energy conservation measures. Subsequent effects need to be reviewed carefully case by case.

REFERENCES

1. The Finnish energy efficiency scheme is an informal expression concerning the implementation of energy efficiency and renewable activities within the National Climate Strategy and the associated Action Plan for Energy Efficiency and Action Plan for Renewable Energy.

2. Koski, Pertti, Timonen, Tuomas and Suominen, Markku, 2002, Energy analysis for power plants, Publisher Motiva Oy. ISBN Number: 952-5304-15-9.

3. Hietaniemi, Janne, 2004. Discussion with Janne Hietaniemi of Motiva Oy, February 2004.