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Analysing the potential for steam savings in TMP mills using the HLMPP tool

Analysis done for four different TMP mills owned by Holmen

Grègory Michel
Göteborg : Chalmers tekniska högskola, 2010. 95 s.
[Examensarbete på avancerad nivå]

Thermo mechanical pulp (TMP) mills are large consumers of both steam and electricity. Large energy savings can be achieved through investments in thermal process integration or more energy efficient process equipments. Thermal process integration can help to reduce the hot and cold utility consumptions in a mill. A well known thermal process integration method is pinch analysis. This master thesis studies the potential for hot utility savings in four different TMP mills in Norway and Sweden. A detailed pinch analysis requires too much time, mainly for data gathering and especially for four mills so instead, a model named the Heat Load Model for Pulp and Paper (HLMPP) is used. The HLMPP can be considered as a simplified pinch analysis which needs a limited amount of input data and, thus, saves time compared to a detailed pinch analysis. Even though HLMPP gives accurate enough estimations, it does not have the precision of a detailed pinch analysis and does not explain how to upgrade the Heat Exchanger Network (HEN) in order to match the potential of steam savings and warm water available. The results for the four mills studied show promising potentials for steam savings, between 2.1% and 20.3% in total for the four reference cases. Moreover, the results show that large amounts of warm water (excess heat) should be available. However, this excess heat has a fairly low temperature, 65-72°C (for three mills; for the fourth mill, it was even lower). Apart from the reference cases, different sensitivity analyses were studied e.g. a decrease of the fresh water consumption in the Paper Machines (PMs), removal of the internal district heating network, further cooling of waste water, installation of modern dryers with an higher exhaust air moisture content. The results from these sensitivity analyses show that even further steam savings could be possible, between 2.8% and 29.7% in total for the different mills as well as further amount of warm water available. Applications for excess steam and warm water are numerous. With steam savings giving excess steam, the mills can decide to sell it (export to a close mill or a town for district heating), use it on-site for biomass drying or driving a condensing turbine to produce electricity. Steam savings also enable fuel savings in the boilers or the replacement of old refiners by more efficient refiners (which consume less electricity) without having to burn more fuel in the boilers. Excess warm water can, in spite of being at quite low temperature, be either recovered by a heat pump, utilized in an Organic Rankine cycle (ORC) or used for preheating of other (external or new) process streams. According to the results for each mill, one can see the interest of carrying out a complete pinch analysis for all the mills in order to find the most profitable solution between the applications previously mentioned.

Nyckelord: Thermo-mechanical pulp, process integration, pinch analysis, steam saving, Heat Load Model for Pulp and Paper (HLMPP)

Publikationen registrerades 2010-05-10. Den ändrades senast 2013-04-04

CPL ID: 121427

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