Pellets produceras av sågspån som är en restprodukt från sågverk. Tillverkningen av pellets är en energiintensiv process. Mest energi används för att torka det fuktiga sågspånet från ca 50 till ca 11 % fukthalt. Torkningen är inledningsvis effektiv men vid torkning av sågspån under 20 % fukthalt minskar torkningens energieffektivitet. Efter att det torkade sågspånet malts i en kvarn konditioneras det med överhettad ånga innan det pressas till pellets. Ångan värmer sågspånet vilket ger pelletsen bättre hållfasthet. Förutom att sågspånet blir varmt tillsätts också fukt. Genom att värma sågspånet utan att tillsätta fukt, och istället bara torka sågspånet till 15 % fukthalt kan därmed ineffektiv torkning undvikas och energi sparas. I den här studien har temperatur och fukthalt mätts på pelletsfabriken Stora Enso Timber AB i syfte att kartlägga tillförseln av fukt och energi i ångkonditioneringen. Detta har gett ett underlag för försök att tillverka pellets utan ånga, men med förvärmning av sågspånet innan det pressas till pellets. Målet med studien är att beräkna ångkonditioneringen och sågspånet fukt- och energitillförsel samt undersöka hur pelletsens hållfasthet påverkas om konditionering av sågspånet med överhettad ånga ersätts med förvärmning av sågspånet och tillsats av lignin. Resultatet av mätningarna och beräkningarna visar att energitillförseln i konditioneringen är 48 kWh per ton producerad pellets. Ungefär 10 % av ångan kondenserade inte i sågspånet och endast hälften av ångans energiinnehåll tillkom sågspånet efter konditioneringen. Att värma sågspån med ånga kan därför ifrågasättas. Pelletstillverkning med förvärmning av sågspånet gjordes i en försöksanläggning på Karlstads universitet. 7 test med olika koncentrationer av lignin och inställningar på förvärmning och ångtillförsel genomfördes. Resultatet visar att förvärmning av sågspånet ger högre hållfasthet än enbart ångkonditionering. Förvärmning tillsammans med högre fukthalt i sågspånet gav pelletsen ökad hållfasthet. Lignin gav inte högre hållfasthet, vilket motsäger tidigare forskning visat. / Wood fuel pellets is made of sawdust, which is a byproduct from sawmills. The production process is energy-intense and a large part of the energy is used in drying the moist sawdust from about 50 % to 11 % moisture content. Initially, the drying process is quite efficient, but when the sawdust reaches a moisture-content below 20 %, the efficiency of the process drops. The dried sawdust is grinded before superheated steam conditions it. The superheated steam warms the sawdust, which results in a more durable pellet, but also adds moisture to it. By warming the sawdust, without adding moisture, and producing pellets at 15 % moisture content, superheated steam production and inefficient drying can be avoided. In this study, the temperature and moisture content of the sawdust in the pellet plant Stora Enso Timber AB in Grums was measured with the aim to study the moisture and energy supply in the conditioning process. The aim is also to analyse how the mechanical durability of the pellet is affected if the superheated steam conditioning is replaced by preheating the sawdust and adding lignin. The results from the conditioning process shows that the energy use is 48 kWh per ton produced pellets. About 10 % of the steam did not condense in the sawdust and only half of the energy content of superheated steam is absorbed by the pellets. Therefore, heating sawdust with superheated steam can be questioned. Pellet production with pre-heated sawdust took place in a production unit at Karlstad's university. 7 tests were made with different concentration of lignin and settings for the pre-heater and steam supply. The result showed that pre-heating the sawdust before the pellet press gave a higher durability than only superheated steam conditioning. Pre-heating and high moisture content of the sawdust combined, gave higher pellet durability. Adding lignin did not increase the durability of the pellets, which previous research has shown.

<p>Abstract</p><p>This report is the result of an examination work at the University of Karlstad. The purpose of this project is to examine how the condition of the steam affects the efficiency of the steam consumers and how variations in that condition affect a pulp and paper mill.</p><p>This report is meant to describe the main components regarding steam production, steam conditioning and steam consumption. It should also be able to give basic information about the significance of steam conditioning in the pulp and paper industry. It is aimed to people working with steam conditioning to increase their understanding and knowledge about it.</p><p>The aim of this report is to:</p><p>• Describe the function of the most commonly used steam generators and the difference between these.</p><p>• Identify the main steam consumers and describe their function.</p><p>• Give an introduction to steam conditioning and its role at a pulp and paper mill.</p><p>This report will try to answer the following questions:</p><p>• How does the generated power from back-pressure steam turbines vary with grade of superheat of outlet steam?</p><p>• What are the advantages with steam conditioning?</p><p>• Are the steam conditioners at Gruvöns bruk able to deliver steam at the right condition?</p><p>The conclusions from this report are that;</p><p>• If the steam conditioning valves are able to reduce small steam flows to the correct temperature, more power can be produced. The design condition of the steam turbines can than be nearer saturation.</p><p>• The temperature variations are more critical at the turbine inlet than downstream the steam conditioning valves. The valves at Gruvöns bruk who are studied in this report, are fully functioning.</p><p>• Common for the main steam consumers at pulp- and paper mills are that they are all sensitive for variations of steam temperature, especially high temperature.</p>

Abstract This report is the result of an examination work at the University of Karlstad. The purpose of this project is to examine how the condition of the steam affects the efficiency of the steam consumers and how variations in that condition affect a pulp and paper mill. This report is meant to describe the main components regarding steam production, steam conditioning and steam consumption. It should also be able to give basic information about the significance of steam conditioning in the pulp and paper industry. It is aimed to people working with steam conditioning to increase their understanding and knowledge about it. The aim of this report is to: • Describe the function of the most commonly used steam generators and the difference between these. • Identify the main steam consumers and describe their function. • Give an introduction to steam conditioning and its role at a pulp and paper mill. This report will try to answer the following questions: • How does the generated power from back-pressure steam turbines vary with grade of superheat of outlet steam? • What are the advantages with steam conditioning? • Are the steam conditioners at Gruvöns bruk able to deliver steam at the right condition? The conclusions from this report are that; • If the steam conditioning valves are able to reduce small steam flows to the correct temperature, more power can be produced. The design condition of the steam turbines can than be nearer saturation. • The temperature variations are more critical at the turbine inlet than downstream the steam conditioning valves. The valves at Gruvöns bruk who are studied in this report, are fully functioning. • Common for the main steam consumers at pulp- and paper mills are that they are all sensitive for variations of steam temperature, especially high temperature.