Blast furnace plant Dolni Vitkovice
In this series we look into industrial and utility plants that benefit or could benefit from the usage of medium voltage variable frequency drives. Today our excursion leads us to a former blast furnace plant Dolni Vitkovice in Ostrava, Czech Republic [1].
The blast furnace plant Dolni Vitkovice is located in Vitkovice district of Ostrava, the third largest city in Czech Republic. The area of approx. 150 hectars is registered in the list of European cultural heritage. It is divided into three sections: mine Hlubina, blast furnace and coke plant. The site displays a unique collection of industrial architecture. Nowadays it is used as “open air” industrial museum with guided tours. It is also the location of famous music festival Colours of Ostrava [2].
History
The plans to build a steel plant in Vitkovice were made in 1820s. Reasons for selecting the location were a nearby river (transport purpose) and coal deposist in the surroundings. The Vitkovice ironworks were established already in 1828. Smelter operation was launched in September 1830. The coke plant followed a year later. The first blast furnace coke was ignited in 1836, the second two years later. Over the years the number of blast furnaces was growing and finally reached six in its golden era. The most famous one is blast furnace #1. Its extension is nowadays also called Bolt Tower after the famous sprinter.
The industrial production was terminated in 1998 after 162 years of operation. In following years the area was closed and its fate was quite unsure. In 2002 the Ministry of Culture proclaimed the area as national cultural heritage. The revitalization started in 2005 and in 2012 the gates opened for public.
During the 162 years of operation the plant in Lower Vitkovice produced:
– 42 million tonns of coke
– 91 million tonns of raw iron
– 82 million tonns of aglomerat
VFDs in metals plants
The steel production in Dolni Vitkovice ended more than 20 years ago. Back then VFDs were not as widely spread as today. For the process control DC drives were often used. These drives allow simple speed control.
The advancement in VFD technology (i.e. AC variable frequency drives) and the benefits in energy savings and process optimization make it an attractive solution today [3, 4]. We can find VFDs throughout the steel production process. The variety of drive applications in metals industry includes:
– Sinter fans
– Blast furnace blowers
– Hot rolling mills
– Cold rolling mills
Sinter fans are relatively simple general purpose drives. The main motivation of using a VFD is energy efficiency (commercial and environmental benefits). The fans have quadratic torque load. A small reduction of speed means considerable power reduction. This fact turns into cost savings and reduction of emissions. The use of VFDs is not limited to new installations. Existing plants can benefit from drive retrofits.
Blast furnace blowers are also fairly simple from application point of view. However, these drive systems are very critical. Therefore, highest reliability is required. Redundancy of components or complete drive systems is nothing unusual. Additionally, the VFDs might be equipped with a bypass allowing direct on-line operation. Blast furnace blower drives can reach impressive high power. 6 to 10 MW is quite common and some of the largest steel plants require more than 50 MW. Due to such high power there is a huge potential for energy savings when using modern VFD instead of purely mechanical solutions such as blowers with inlet guide vanes. A case note on replacing inlet guide vanes with medium voltage VFD is presented in [5]. The case note reports 10% energy savings and 90% maintenance cost reduction. Another case note with significant energy savings in reported in [6].
Rolling mill drives belong to the most dynamic industrial drive applications. Their performance and dynamic response directly impacts the quality of output product. Precision is the key word. The motors are specifically designed machines working in harsh environmental conditions. The nominal electrical frequency is in the range of 20 Hz. The machines often have heavy duty overload up to 200…250%. Direct torque control is used to achieve fastest torque response. The multidrive concept (one VFD with multiple inverters controlling several motors) allows to further improve the efficiency, reduce the footprint and minimizes the sizing of input transformer. Advantages of multidrive solution will be described in depth in future post. In the past the rolling mill drives were realized with dc drives due to their simple and efficient way of speed control. Due to advancements in power electronics and control dynamic AC drives are the standard solution nowadays.
Benefits of VFDs in metals
The VFDs in metals industry offer several benefits for the end user. One of them is the energy efficiency and potential for energy savings. As the metals industry is very competitive and there is currently a production overcapacity it is important to reduce cost in order to ensure sustainability. Environmental regulations also require reduction of carbon emissions. VFDs help to achieve both targets. Another advantage, particularly important for rolling mills, is high dynamics and precise control. The precision directly impacts the quality of the product. VFDs featuring dynamic torque regulation such as Direct Torque Control (DTC) are the perfect match for customer’s demands. The electric drives require low maintenance which also helps to reduce cost and increase productivity. Personal safety is a must and modern VFDs support the requirements with features such as emergency off / emergency stop / safe torque off or arc resistant design.
Requirements on VFDs in metals
Metals plants use VFDs in multiple applications. Fan and pump drives are common general purpose drives. Rolling mills are special purpose drives with high dynamics and precision. Although these two groups are quite different some requirements are common for all of them:
– Reliability
– Safety
– Efficiency
– Easy maintenance
References
[1] Lower Vitkovice – Wikipedia, Wikipedia_Lower_Vitkovice
[2] Colours of Ostrava (music festival), https://www.colours.cz/?lang=en-US
[3] Drives and PLCs for metals, https://new.abb.com/drives/segments/metals
[4] ABB drives in metals, ABB Drives in Metals
[5] Case note: ACS5000 Variable speed drive increases efficiency of steel mill’s blast furnace blower, Case note to download
[6] Case note: ACS6000 Variable speed drive increases efficiency of metals plant, Case note to download
