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Conversion from kraft pulp into dissolving pulp production is an interesting development since it allows the production of a pulp with higher market value, as well as the production of valuable by-products, for example, hemicellulose, lignin, electricity, and/or heat. In this paper the major energy consequences of converting a modern kraft pulp mill into dissolving pulp production were investigated. Three critical choices for process configuration were examined: a) export the hydrolysate (extracted hemicellulose liquor) to an upgrading plant vs. combustion of the hydrolysate b) level of heat integration c) type of by-products produced (electricity or lignin) The results show that conversion into dissolving pulp production affects the energy balance of the mill considerably and can drastically affect the pulp production capacity of the mill, e.g. if the recovery boiler is the bottleneck. Sending the hydrolysate to combustion decreases the pulp production capacity, whereas lignin separation can debottleneck the recovery boiler and allow for higher pulp production. A higher level of heat integration increases the possibilities for debottlenecking and/or producing by-products. The conclusion is that an economic assessment is necessary in order to identify the most attractive process configuration. This assessment will be presented in the second part of this study.

Within the FRAM programme, two models of average Scandinavian mills producing bleached market pulp have been analysed from an energy perspective. The aim was to explore the opportunities for heat integration in order to create a steam surplus. The steam surplus gives opportunities for increased power generation or lignin extraction. The technical and economic consequences of using the steam surplus in this way are explored in a continuation of this project. Two different approaches for creating a steam surplus have been investigated: 1) conventional measures and 2) processintegrated evaporation (PIvap). The former approach includes improved heat integration and new equipment. The latter approach means that excess heat from the mill is used for evaporation to partly replace live steam. The two model mills created within FRAM both produce 1000 ADt/d softwood pulp. The mills differ in the level of water usage, since it is expected that the amount of excess heat for PIvap will increase with decreasing water usage. By investing 11 M€ in conventional measures it is possible to create a steam surplus of 53 MW (about 26% of the total consumption), independent of the level of water usage. For the PIvap approach, the level of water usage matters, since there is more excess heat for PIvap in the mill with lower water usage. As a result, the total steam surplus with the PIvap approach differs in the two mills: up to 52 and 56 MW, respectively. Hence, the steam savings for the PIvap approach are similar to those in the approach with conventional measures; and so are the investments needed (10-12 M€). Even though the two approaches give approximately the same savings with the same investment, the PIvap approach might be easier to implement in an existing mill.

For increased production in pulp mills, the recovery boiler is often a bottleneck. Two different approaches to debottleneck the recovery boiler have been investigated in two model mills that represent typical Scandinavian pulp mills. As a reference approach, the recovery boiler was upgraded. In connection with this, the turbine system was also upgraded to enable increased electricity production. As an alternative to this conventional approach, the load of the boiler was kept constant by extracting lignin from the black liquor in proportion to the production increase. To keep the steam balance, the specific steam consumption at the mill was reduced through steamsaving measures to such an extent that the amount of steam produced from burning the lignin-lean black liquor was sufficient. Consequently, the extracted lignin was not needed in-house and could be sold as a biofuel. The net profit of implementing lignin separation was calculated for different conditions. The result was that, depending on the conditions, the lignin price had to be 2-17 €/MWh for lignin separation to be equally profitable as boiler upgrade. With an assumed lignin price of about 15 €/MWh, the conclusion is that lignin separation should be an economically attractive alternative for debottlenecking the recovery boiler. With a high power price and a long-term investment strategy, however, upgrading the recovery boiler and the turbine system can be more profitable.

Lignin separation and increased power generation are two alternatives for utilising a steam surplus at a kraft pulp mill. Lignin can be separated from the black liquor by using CO2 in a precipitation process. The resulting lignin can be sold as a biofuel. In this study, lignin separation and increased power generation have been compared by using computer models representing typical Scandinavian mills (327,000 ADt/a). In the studied mills, the steam surplus was up to 437 GWh/a (4.82 GJ/ADt) which enabled either increased power generation by 126 GWh/a(+65%) or extraction of 500 GWh/a lignin. A consequence of extracting this amount of lignin was that the power generation decreased by 59 GWh/a (-30%), which means that the profitability of lignin separation was dependent on the electricity price. Moreover, the profitability was mainly dependent on the lignin price and the cost for CO2 to precipitate the lignin. For lignin separation to give the same annual earnings as increased power generation, the ratio between the electricity price and lignin price had to be 1.9-2.3. For ratios below 1.9, lignin separation was economically preferable, while ratios above 2.3 meant that increased power generation was preferable. It was noticeable that the profitability under all studied conditions was considerably lower for lignin separation than for power generation at high electricity prices. Lignin prices around 15 €/MWh implied that the electricity price had to be below 33 €/MWh for lignin separation to give higher annual earnings than increased power generation. For a high electricity price (55 €/MWh, e.g. including policy instruments), the lignin price had to be above 23.8 €/MWh for lignin separation to give higher annual earnings. These lignin prices are significantly higher than equivalent biofuel prices today. However, the lignin price would probably be higher than 25 €/MWh if lignin were used e.g. as raw material for specialty chemicals or as a replacement for fossil fuels.

A model of a modern magazine paper mill has been investigated from an energy perspective. The mill’s refining process has a power demand of 100 MW (3050 kWh/ADt pulp), and 86 MW of this is recovered as steam. Since the steam demand of the mill is low, there is a steam surplus of 21.5 MW. The steam surplus could be increased by 41 % through thermal process-integration. Simultaneously the cooling demand decreased by 13.2 MW or 49 %, resulting in reduced cooling costs and decreased thermal pollution. The financial evaluation, for which a grass-root situation was assumed, shows promising economy if the mill can sell the surplus heat (e.g. to a district heating system): the marginal payback period for increasing the steam surplus would be less than a year, even with low energy prices. If the surplus steam has to be used on site, power generation in a condensing steam turbine is an option. The financials for increasing the power generation are very dependent on the power price, but with current Swedish power prices the marginal payback period would be 3 to 4 years. Energy exports, whether heat or power, would presumably replace fossil fuel. Consequently, the greenhouse gas emissions in society would decrease by thousands of tons per year. In the future it might be possible to decrease the power consumption in the refining process, resulting in a decrease of the steam surplus. With process integration, the power input can be decreased by 30 % before there is a steam deficit. This option offers a good opportunity for profit as well as decreased environmental impact.