LIFE05 ENV/DE/207 Hydromechanical Descaling Process with High Pressure Vacuum Technology using Scale as Abrasive Blast Medium [HVD]

Transcription

1 LIFE05 ENV/DE/207 Hydromechanical Descaling Process with High Pressure Vacuum Technology using Scale as Abrasive Blast Medium [HVD] Layman Report

2 Layman Report EU LIFE Demonstrationsproject EU LIFE05/ENV/DE/207 This report presents the results of the EU Life Environment Demonstration Projects funded project Hydromechanical Descaling Process based on High Pressure Vacuum Technology Using Scale as Abrasive Blast Medium, HVD. The technological aspects of continuous descaling processes of hot rolled steel strip, the application alternatives and the technological, ecological and economical advantages of the new descaling process HVD are pointed out. Introduction During the production of hot rolled steels strips, thick scale layers grow on the surface due to the reaction of metal with the atmosphere at high temperatures. These scale layers have to be removed from the steel surface according to production standards and costumers quality requirements. In modern steel production, continuous pickling lines are used for descaling. The pickle liquors have a maximum temperature of 100 C and are composed of environmentally hazardous mineral acids. The composition of the acids depends on the steel grade. For example, low carbon steels are treated with hydrochloric or sulphuric acids; stainless steels are treated with mixed acids. With this approach, fresh water and energy consumption is rather high. In addition, handling of hot mineral acids results in noxious contamination of indoor air. Furthermore, the heating system is based on natural gas and consequently energy intensive. There are about 600 global existing pickling lines. In addition to the problems regarding the impact on the environment and the high consumption of natural resources, modern steel grades, with high requirements regarding weight, ductility, strength, heat resistance, surface quality, quality of microstructure, resistance against hydrogen embrittlement, magnetizability, etc., need longer pickling times. According to this, the use of operating resources (fresh water, acid, energy) increases with higher requirements in steel quality. Especially these steel grades contribute sustainably to resource efficiency in energy supply, electrotechnology and transport. Hence the production of these steel grades should be sustainable and environmentally friendly as well. It is, according to the abovementioned facts, indispensable to develop new technologies to replace environmentally harmful processes or, at least, reduce chemical process steps in steel production to save energy and operating resources. A integrative technique to meets th requirements for a sustainable steel production is the patented High pressure Vacuum Technology (Airmatic GmbH, Germany). The new High Pressure Vacuum Process, already proven for degreasing and cleaning of steel strips, will be further developed so that it can be used for descaling as well. To achieve this, a two stage demonstration plant was set up. In the first stage, operational tests verified that the process is viable and optimum process parameters were set. In the second stage an industrial demonstration plant was set up on the premises of Airmatic in Hemer, commissioned and demonstrated to international steel operators. Technology The new descaling process based on High Pressure Vacuum Technology (HVD) is a hydomechanical abrasive blasting process for continous descaling of hot rolled steel strips. According to the basic operations blasting and suction, the high pressure vacuum dome cover is divided into two distinct zones. In the blast zone abrasive particles with a defined particle size distribution are blasted onto the material using high pressure water jets. To guarantee a smear free and uniform descaled steel surface the abrasive water jet is applied rotationally. The emerging abrasive suspension is being removed simultaneously in the suction zone of dome cover, leaving behind a descaled and dry surface. After descaling, water and scale are seperated and both media may then be reused in the same process. The scale itself is used as abrasive blast medium. Depending on the application of the new descaling process, alternative abrasive blast media can be used. The compact design in combination with the possibility to easliy integrate the required machinery in an existing production environment makes this innovative process suitable for new plants as well as for retrofit measures. The modular setup of the new process allows a precise adaption of its performance to major figures such as line speed, strip thickness and width, and the individual operation modes. Layman Report LIFE05/ENV/DE/207 2

3 Industrial demonstration plant Industrial demonstration plant: Abrasive and water cycle Layman Report LIFE05/ENV/DE/207 3

4 Application alternatives The compact design and versatility of the new descaling process with high pressure vacuum technology (HVD) allows the application as a pre treatment step in existing and future pickling lines or as an alternative technology to these chemical processes. These application alternatives are determined by steel grade, steel application and the downstream process steps in steel production. Regarding the 600 pickling lines worldwide, the rise in demand of high strength steels, and the conservative attitude of the steel industry towards total process changes,the application of HVD as an integrative pretreatment step offers best prospects in that market. Concerning for example high tensile steels, even small quantities of remaining scale can produce surface defects and evoke a decrease in operational capability. Stress peaks, crack formation, places of preferred local corrosion and consequently reasons of premature material failure result from these surface defects. Hence a complete descaling can only be assured using DD 14 the infiltration and distribution properties of a chemical fluid (pickle liquor). However, the chemical step in the descaling process can be continuously reduced to a minimum using HVD as a pre treatment application. The dissolving rate of the scalelayer in the acid bath is essentially increased by perforating the scale layer with the rotating abrasive water jet. By increasing the dissolving rate, pickling time decreases thus reducing specific amount of energy, acid and water consumption per ton of steel. Regarding the realized descaling experiments the pickling time can be reduced to at least 50 %. Concerning construction steels, surface quality requirements are different and less sophisticated. For example, a surface purity of 95 % is sufficient to guarantee a good zinc adhesion. Considering this, a chemical free descaling can be realized using HVD. In this application, the rotating abrasive water jet completely removes the scale layer without negative impact on surface finish or evoking strain hardening. Using this alternative the energy and water consumption will be considerably reduced and the use of natural gas, hydrochloric or sulphuric acids will be redundant altogether. St 37 untreated untreated pretreated embedding material untreatred descaled scale layer pretreated steel substrate descaled and hot dip galvanised Application alternatives Layman Report LIFE05/ENV/DE/207 4

5 Results and environmental benefit With the two stage demonstration plant, it could be scientifically proven, that the new descaling technology is suitable for industrial production. In the first stage operational tests showed that the process is viable and the optimal process parameters for the industrial second stage plant were set. Particle size, impingement of the abrasive media, water pressure and rotor speed are the vital parameters. It could be ascertained, that fine scale particles deliver an excellent descaling effect without any negative impact on the surface quality. In the second stage, an industrial plant on the premises of Airmatic was constructed, commissioned and demonstrated to international steel operators. 58CrV4 200 bar, µm 200 bar, µm Scale Steel 250 bar, µm 250 bar, µm 300 bar, µm 300 bar, µm The new descaling process HVD was investigated with international steel producers in respect of two different applications; as an alternative for pickling and as a pre descaling process combined with pickling. The steel producer s objective was mostly not to replace the existing pickling plants but to increase the steel output or to reduce the specific consumption of operating resources (fresh water, acid, energy) of the existing pickling lines by using HVD. The reduction of pickling time was considered as quantitative criteria therein. The advantage of this application is the possibility to decrease the chemical part in the whole descaling process continuously to a technological minimum. The technological minimum of the chemical process is determined by the steel grade and the specific steel quality requirements. The following steel grades were tested with/ for five European steel operators: NO Electric strip User: A Objective: Reduction of pickling time (sulphuric acid) Result: 77 % reduction of pickling time St 37 User: B Objective: Replace pickling line (hydrochloric acid) Result: 100 % reduction of pickling time (free from scale, oil, grease) 58CrV4 User: C Result: 77 % reduction of pickling time DX52 User: C Result: 66 % reduction of pickling time H180BD User: C Result: 100 % reduction of pickling time DD14 User: D Result: 50 % reduction of pickling time 12MnCrMo 8 4 User: D Result: 50 % reduction of pickling time St 37 User: E Objective: Replace pickling line (hydrochloric acid) Result: 100 % reduction of pickling time According to the achieved percentage decrease in pickling time the specific consumptions of fresh water, fresh acid and energy per ton steel can be reduced respectively. Regarding a pickling plant with an annual capacity of t using HVD as pretreatment application with a pickling time reduction of 50 %, reductions of m³/a in natural gas, t/a in acid and m³/a in water can be realized. The electricity consumption can be reduced negligibly compared to the essential reductions in natural gas, acid and fresh water. In this case the environmental compatibility will be enhanced for at least 50 %. For some applications (construction steels), it is even possible to descale without any use of water, natural gas or acid (replacement of pickling line). In this case, the rotating abrasive water jet completely removes the scale layer with no negative impact on the required surface finish or the following process steps in steel production. Layman Report LIFE05/ENV/DE/207 5

6 Transferability According to the 6th Commission Environmental Action Programme, a rapidly increasing economic globalisation with substantially higher resource consumption can be expected. Hence, transferability of a new technology plays an important role enabling and pushing a sustainable development, not only in EC Countries, but also in developing countries. Steel industry is an important part of each national economy worldwide, so depending on its market penetration, the new descaling technology HVD can be contributory to the realization of ecological advantages. Due to the compiled results during the project, the currently existing financial and economical crisis and after solving the remaining technological problems, spreading of HVD Technology in the Steel Industry can be expected within 5 years. The impact of this project is not limited to the European Community but can also deliver a tessera to decouple economic growth and environmental damage in emerging and developing countries. For this reason, the export of this environmental friendly technology will not only achieve global environmental relief, but will also enhance the economic growth in the European Community. Summary With the scope of the EU LIFE ENVIRONMENT project Hydromechanical Process based on High Pressure Vacuum Technology using Scale as Abrasive Blast Medium, a new descaling technology has been developed and the suitability for the European Steel Industry has been demonstrated with a twostage demonstration plant. The new descaling technology HVD allows according to article 7, section 1 of the 6 th Commission Environmental Action Programme to substitute dangerous chemicals by safer chemicals or by safer alternative technologies not entailing the use of chemicals. Additionally, HVD realizes an almost closed circuit of processing water with a negligible amount of waste water, so a sustainable use of water will be achieved, article 7, section 1e. Through a substantial reduction in energy consumption compared to the state of art technology, use of resources is minimized. Resource and energy efficiency is drastically increased as postulated in article 8, section 1. At the moment, negotiations with an international steel company are in progress dealing with a first implementation of the new HVD descaling technology into their production line. In addition presentations of the demonstration plant in Hemer and experimental series for the Steel Industry are still in progress and with it the dissemination activities. A distribution partnership with the international reputable company Sundwig GmbH has been started. Sundwigs product range comprises turnkey systems for production and processing of cold rolled strip made of steel, stainless steel, coated metals, non ferrous metals, and special materials. Kontakt Airmatic Gesellschaft für Umwelt und Technik mbh Ostenschlahstraße Hemer Tel.: +49 (0) Fax.:+49 (0) info@airmatic systeme.de systeme.de Lehrstuhl für Energie- und Umweltverfahrenstechnik Univ.-Prof. Dr.-Ing. habil. Wolfgang Krumm Paul Bonatz Str Siegen Tel.: +49 (0) Fax. +49 (0) lehrstuhl@et.mb.uni siegen.de siegen.de/fb11/euvt Sundwig GmbH Stephanopeler Str Hemer Tel.: +49 (0) Fax.: +49 (0) welcome@sundwig.de Layman Report LIFE05/ENV/DE/207 6