Environmentally Sound Steel Making Process and Products

Transcription

1 Environmentally Sound Steel Making Process and Products Toni HEMMINKI Manager, Energy and Env. Rautaruukki Oyj Hämeenlinna, Finland Tarmo MONONEN R&D Manager Rautaruukki Oyj Helsinki, Finland Master of science (eng.) in energy technology, Lappeenranta University of Technology 1999 Master of environmental business management, Helsinki University of Technology, Lifelong Learning Institute Dipoli, 2003 Member of International Iron and Steel Institute LCA Forum since 2001, Jernkontoret LCA committee since 1999 and Teknologiateollisuus Ry environmental committee since Master of science (Civ.Eng.) Helsinki University of Technology 1983 Summary The paper presents long-term environmental development at the Rautaruukki within steel production, processing and product manufacturing and construction. At the paper main focus in the production phase is given for the energy efficiency and principles of industrial ecology and also recycling of iron and steel making by-products are covered. Rautaruukki steel production has been developed to be very energy efficient. Significant amount of the avoided environmental burden is gained, as steel production by-products are recycled. This and steel product good recyclability can be modelled in the LCI according methods used at the International Iron and Steel (IISI) LCI database. This paper concern also the ecoefficiency of steel based products within construction. Case studies are disclosed. Keywords: steel production, steel products, life cycle assessment, LCA, by-products, industrial ecology, recycling, energy efficiency 1 Introduction Today's industry is facing significant change from the process related environmental thinking towards product and/or need based environmental thinking. In practice this is seen for example in the EU integrated product policy, where focus is not any more only on the production phase of the products, but on the total life cycle of the products. For construction sector this will mean more need for the environmental assessment covering the buildings etc. products production, in-use phase, recycling and disposal. At this kind of assessment, which can be done according life cycle analysis method, environmental benefits of different alternatives and solutions will be addressed. Steel products can offer environmentally sound solutions in the construction. To ensure good environmental quality Rautaruukki Group has environmental management systems in all main production units. Steel production has been developed to be very efficient in energy consumption and it follows principals of the industrial ecology.

2 In the paper Rautaruukki Steel Raahe steelworks energy saving activities are discussed. The credit of the by-product recycling is presented with the steel products LCI database established by the IISI. Steel as a material is 100 % recyclable and can be used again and again. The method, recommended by the IISI LCA specialists, to take recycling into account in the steel product life cycle assessment will be presented. Rautaruukki steel products good environmental quality will be discussed with the case studies about the Drytec building system, steel roofs LCA and outer wall LCA. Also the 4R principal for development of the steel structures are presented. 2 Rautaruukki environmental management Rautaruukki Group has about 4,3 Mt annual steel production including both ore and scrap based production. Steel production takes place in Finland, Sweden and Norway. Upgrading of the steel product is done in the different downstream operation unit in 15 countries in North and Central Europe. Rautaruukki Group has extensive environmental management starting from the group level values, environmental policy and management team followed by the site level certified environmental management systems in all sites with significant environmental burdens. On year 2002 about 75 % of the Rautaruukki Group employees were working under verified ISO environmental management system. According the group environmental policy the eco-efficiency of the steel products are taken into account at the development of the steel products and best available technologies are considered as new activities are planned and decided. 3 Environmental aspects of the steel production Raahe steelworks is main source of raw material for the whole Rautaruukki Group. According case studies the steel production forms the main environmental burden of the steel product. But the case is not the same with steel-based products in which also other materials are used. Taking into consideration also the in-use phase of the product, the environmental burden of steel making presents minor role. 3.1 Development of the energy efficiency Raahe steelworks has been under voluntary Ministry of Trade and Industry energy saving agreement since Because of the choice of efficiency process technology from the starting of the steel production at 1960's, site is in the class of the world's most energy efficiency sites. In ore based production most of the energy is coming in to the site in form of coal, which is processed and used as a reduction material in iron ore reduction. Low reduction material consumption per ton of hot metal (iron) at the blast furnaces makes it possible to produce steel with the low CO 2 emission associated to the steel products. As a result of the processing and using this reduction material the large amount of process gases are produced. At the Raahe steelworks all the coke making and blast furnace gas is recovered as a fuel to produce electricity and steam. About 60 % of site total electricity consumption is produced out of the process gases. 3.2 Utilisation of the by-products Steelworks produces the valuable by-products, which are recycled. By this recycling the byproducts are substituting virgin materials and energy consumption. As shown in Figure 1 the LCI database for steel products contains system expansion for the significant by-products.

3 Emission: to air, water and soil Consumption of natural resources Scrap: from other steel works, obsolete etc. Raw material and energy production (incl. extraction) Consumables production (e.g. chemicals) T r a n s p o r t a t i o n Steelworks System boundary By-products Allocated Minus Equivalent byproduct function Saved external operation Steel product Non allocated by-products System expansion Fig. 1 Steel product LCI system [1]. System expansion is LCI modelling method recommended by the ISO standard, if database contains multi-output process units and dividing of the multi-output process unit environmental burden for each functional product is not possible. For more detailed illustration of the LCI model the hot rolled coil produced at the Raahe steelworks is taken as an example product. Utilised by-products (and considered as significant) in the LCI for the hot rolled coil are BF slag, BOF slag, coke (breeze and sand), process gases (if not used in the production system of hot rolled coil), sulphur, tar, benzene, hot water and steam. Blast furnace and basic oxygen furnace slags can be credited according the material production, which it is substituting: soil conditioners in agriculture, embankment material e.g. in road construction or clinker in the cement making. Coke oven by-products coke (breeze and sand), tar, sulphur and benzene are assumed to save similar virgin materials. Net production of the blast furnace and coke oven gas is assumed to substitute heavy fuel oil. Quantitative magnitude of the by-product utilisation is presented with details in the paper "Life cycle inventory of the steel product - byproducts, recycling and credit"[2]. 4 Steel life cycle or cycles One of the original and main goals of the LCA is to compare products environmental performance over it's life cycle. Some benchmarking against different materials can be done only, if same system boundaries and rigorous data collection and database modelling of the LCI data for different materials and products is taking place. Often the benefits of the material reuse and recycling after the first use phase is not properly taken into account. The reason for that is lack of simple methods and clear models to take this into account within the LCA calculations procedure. For steel products this can be taken into account with the method recommended at the IISI World Steel Life Cycle Methodology Report 1999/2000. Steel as a material can be recycled 100 % and scrap can be converted to quality steel (higher or lower crades), thus steel can be recycled over and over again. Because of this, there is large amount

4 of secondary steel making, which present about 40 % of global steel production. Some steel scrap also is used at the primary production, for example at the Raahe steelworks up to almost 30 %, thus overall about 50 % of all steel produced has already at least once been steel. In the figure 2 the system of global steel recycling is presented. Raw material Steel Production (ore based) Upgrading (rolling and manufacturing of the end products) Scrap Arsenal Scrap Yard Steel Production (scrap based) Use of the end products Reuse of the steel parts Recycling of the end products Fig 2. Global system of steel recycling. Disposal and recycling losses of the steel The recycling modelling method recommended by the IISI is based on the ISO LCI standards and presents the general equation to calculate total environmental burden for the steel products produced at the primary route and recycled at the end of the products life. X = X primary + (X recycled - X primary ) RR Y (1) Where RR is the recycling ratio, Y is a measure of metallic yield ratio at the recycling process defined here as the ratio of steel to scrap yield and X, X primary and X secondary are the LCI values for the whole system, the virgin material route and the recycling route respectively. 5 Environmentally sound steel construction 5.1 Ecologically efficient steel construction Rautaruukki supplies ecologically efficient steel construction products and services to the construction industry. Ecological efficiency means the maximisation of functional and economic properties of the product with minimal environmental load. Ecological efficiency is measured by a LCA, which assesses the environmental load of production, transportation, packing, use, recycling and desposal compared to their functional and economic properties over their entire life cycle. Very important property of steel products is their recyclability. Also the reduction of heating and cooling energy is a crucial development target. Steel-based products provide flexibility and an opportunity to modify the building according to their intended use, enhancing functional properties and lifespan. In the development activities of Rautaruukki special 4R strategy is applied. Four important aspects are taken into consideration: Reduce the use of natural resources, Repair (for new use), Re-use and Recycle.

5 5.2 Drytec Construction System Drytec - structural system is based on light, dry and fast construction methods. The system has been developed in particular for low buildings and densely built areas. The system contains lightweight materials, product parts and their fixing parts which are demountable and easy to recycle. A building's heating energy consumtion is about 30 per cent below the limits set by the building regulations. Facilities can be designed to meet the client's demands and are easily adabtable at later phases. Economical life cycle is complemented by roofing sheets and facades with long lowmaintenance sevice life. Fig 3. Adabtable and flexible Drytec - building system for residental and office buildings 5.3 Thermal Frame System Thermal frame exterior walls are composed of C frame structure with perforated profile webs which reduce thermal conductivity considerably, approximately to one tenth compared to a non-perforated web, at the same time improving the normal insulation and moisture-technical properties of the wall. Normal insulation consists of 175 mm of mineral wool (Illustration 1). By adding 50 mm wool to the external surface as a base for i.e. plaster, the U value could be dropped to the level of 0.19W/m 2o C (Illustration 2), reducing energy consumtion during use phase by 30 per cent from the normal level and carbon dioxide emissions by 40 per cent over 100 years period. According to the LCA, environmental impact is reduced by 25 per cent. Excellent thermal and moisture-technical functionality guarantees long service life which, according to the research, is about a hundred years, depending on the environmental conditions. A B Fig 3. Thermal frame and additional insulation in outer wall structures

6 5.4 Steel roofs In LCA study /3/ steel roofs are investigated. Main focus was put on service life and rate of recycling and their influence on evironmental impacts. Also the influence of energy roof was studied. The global warming potential (GWP) and energy consumption were used in the evaluation. From the results it was found, that the product's entire life cycle, steel production accounts for most significant environmetal effects. Steel production account for 97,2%, painting 2,1% and recycling 0,7% for the primary energy consumtion. The degree of recycling and service life have very crucial effects. At 100% degree of recycling the global warming potential is 25% and primary energy consumtion 47% of what they would be without recycling. If service life is from 25 to 45 years, for examble through maintenance painting, and the recycling rate 90%, the GWP is reduced about 55%. Rautaruukki has developed energy roof solutions. In the results of LCA it could be found that "payback time" for the global warming potential is 2.8 years. In other words this mean that the increased GWP that results from manufacturing of energy roof is fully compensated in 2.8 years by the production of electricity. 6 Conclusions Steel products can offer environmentally sound solutions for the variety of applications within construction and other industries. Rautaruukki has ensured the good environmental performance of it's operations with the extensive environmental management. Good examples of the eco effciency are energy efficiency, recycling and the industrial ecology principals followed at the Rautaruukki steel production. Steel is 100 % recyclable material and has good properties to be used in ecoefficient steel construction. Important is to ensure good environmental quality not only in building phase but also within in-use phase. Thus energy efficiency, recycling and adabtable solutions enchances the environmental properties of buildings. References [1] International Iron and Steel Institute LCA Forum, World Steel Life Cycle Methodology Report 1999/2000, IISI second LCI study, available by request from the IISI LCA manager ( 2002, Brussels [2] Hemminki T., Life cycle inventory of the steel product - by-products, recycling and credit, Recycling and waste treatment in mineral and metal processing: Technical and economical aspects, conference proceeding, Published by Luleå University of Technology, MEFOS and The Mineral, Metals & Materials Society, 2002, Luleå [2] Eriksson Niko., Soukka R., The life cycle inventory study for a steel roof. Master's thesis. Lappeenranta University of Technology, 2003