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Opportunities for improved heat integration in average Scandinavian kraftliner mills: A pinch analysis of a model mill

Erika Axén
Göteborg : Chalmers tekniska högskola, 2010. 43 s.
[Examensarbete på avancerad nivå]

Energy savings and increased efficiency is important to a large energy consuming industry such as the pulp and paper industry. To give industries incentives to do something about their energy consumption, policy instruments are used and research in the pulp and paper field show that large savings can be achieved. One way to save steam is process integration and a tool to find steam saving opportunities is pinch analysis. The method is used in this thesis where a pinch analysis of a modelled average Scandinavian Kraftliner mill has been done. The mill is modelled within the national research program FRAM (Future Resource Adapted Pulp Mill) and the results in this thesis might act as a guideline for possible steam saving opportunities for a mill of this size and type. The pinch analysis shows that theoretically, 20 MW of steam can be saved through improved heat exchanging, which is about 11% of today’s steam demand. By making a retrofit analysis, two steam saving proposals with possibility to save 13.7 and 19.6 MW of low pressure steam were worked out. Other investigated steam saving alternatives were flue gas heat recovery, upgrading of the evaporation plant, and energy savings in the paper machine. The steam saving opportunities were put together to eight different investment alternatives with steam savings between 120 and 420 GWh/yr. The economic evaluation of those alternatives shows an investment cost in the range 1–15 M€, depending on the investment. The largest investment cost is an upgrade of the evaporation plant, 10.4 M€. The steam surplus can be used for fuel savings and thereby achieve annual earnings. To analyze this, two levels of bark and electricity prices were used and the resulting earnings lie between 2.5–10 M€/yr depending on investment alternative, bark and electricity prices. An interesting concept within process integration and the biorefinery field is lignin separation. In this thesis it is investigated what lignin price is required for lignin to be equally profitable as saving fuel. The same levels of fuel and electricity prices as for the fuel savings were used and consequently two lignin price levels were achieved. The achieved lignin prices vary between 30 and 51 €/MWh. Depending on the investment alternative and thereby achieved lignin price, this is comparable to the price of high-grade biofuels as well as the oil price. Conclusions that can be drawn are; considerable savings can be achieved in the mill, it is clearly profitable to save fuel and the estimated lignin price implies that lignin separation can be an interesting alternative to fuel saving.

Nyckelord: pinch analysis, steam savings, retrofit, lignin separation, kraft pulp mill, fuel savings

Publikationen registrerades 2010-07-02. Den ändrades senast 2013-04-04

CPL ID: 123625

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