38 Flow Level Pressure
Non-Invasive High Temperature Flow Measurements in the Ruhr Oel Gelsenkirchen Refinery
Björg Otte, BP Gelsenkirchen GmbH, Jörg Sacher, FLEXIM GmbH Flexible Industriemesstechnik GmbH, Wolfener Straße 36, D-12681 Berlin Tel: +49 (0) 30 / 93 66 76 60 • Fax: +49 (0) 30 / 93 66 76 80
Due to its practical advantages, external flow measurement with clamp-on ultrasonic transducers has become a standard measuring technique over the past twenty years. Experts are more than happy to resort to non-invasive technology when it comes to measuring the flow of complex media. Te main challenges involved in reprocessing heavy crude oil fractions are high viscosity, solid bodies and high temperatures.
When the city name Gelsenkirchen is mentioned, most contemporaries will initially think of the FC Schalke 04 men dressed in blue and white and then possibly of the extraction and processing of coal, the proverbial black gold of the Ruhr region, but not of the production of liquid fuels from mineral oil. In fact, Gelsenkirchen is a very important refinery location. With a total processing capacity of over 12 million tons of crude oil per year, both plants in Gelsenkirchen’s city districts Scholven and Horst are among Germany’s largest processing plants for mineral oil. The plants belong to Ruhr Oel GmbH and are operated by BP Gelsenkirchen GmbH.
Bottom of the barrel
The objective of every refinery is to process as much the crude oil used as possible into a marketable product. A crucial factor involved is the processing of heavy crude oil fractions, refered to as “bottom of the barrel” in refinery jargon. These are mixtures made of long-chain hydrocarbons that remain as residue during atmospheric and vacuum distillation. Shifts in supply and demand add to the importance of conversion plants for the conversion of distillation residues: due to the fact that raw material supplies are limited, refineries are also willing to exploit low quality sources. As a result, the proportion of deposits in the oil barrel tends to increase. At the same time, worldwide growing mobility, whether it be for global exchange of goods or passenger transport, is leading to an ever-increasing demand for high-quality, pollutant-free fuels.
The Ruhr Oel Gelsenkirchen Refinery manages to make complete use of the crude oil. Here, in the heart of the Ruhr region, experts have unrivalled experience in the field of hydrocarbon chemistry. Both plants in Scholven and Horst, which the BP company runs as a complex, integrated refinery and petrochemical location, began as hydrogenation plants in the thirties where liquid fuels were made from domestic coal. Today, it is the other way around: crude oil from oil production locations all over the world ends up in Gelsenkirchen via pipelines from the oil harbours in Rotterdam and Wilhelmshaven. In 2009, approx. 9 million tons of mineral oil products and a further 3 million tons of petrochemical products were produced from almost 12 million tons of crude oil in Scholven and Horst. Petrol, diesel, jet fuel, heating oil and petroleum coke are among the mineral oil products.
Flow measurements in Delayed Coking
The Ruhr Oel Gelsenkirchen Refinery has three distillation plants and five conversion plants and, as a result, is one of the most complex refineries within the worldwide BP Group. Since 1969, the coker in the Horst plant has been the core for processing distillation residue. From a chemical point of view, coking is a thermal cracking process in which one of the end products is carbon (i.e. coke). The coker in Gelsenkirchen works according to the Delayed Coking method like most other comparable plants in the world. Feedstock, the residue from vacuum distillation, is passed to a furnace under pressure and at a high flow rate and heated to approx. 500°C. The process engineering trick in Delayed Coking is in the short amount of time that the residue mixture stays in the oven so that it is heated above the coking temperature without resulting in significant coke formation. This takes place in a “delayed" manner in downstream chambers. The lighter hydrocarbons that are formed during this thermal process are fractionated and refined into higher-quality end products during further processing stages.
Needless to say, flow measurements are crucial for process control, however they are highly demanding due to the extreme process conditions. The main challenge is due to the fact that solid bodies are constantly present in the form of very fine coke particles which deposit both on the inner pipe wall as well as on the wetted parts of the mechanical measuring devices. For this reason, experts in Gelsenkirchen spent a long time looking for alternatives for conventional flow measurement according to the pressure difference method, where, in particular, tiny pressure tap lines become blocked quickly which in turn prevents the measuring devices from functioning. Measuring orifices that were previously installed had to be rinsed regularly with seal oil which meant wasting valuable end products that could be marketed instead of using them to maintain measuring devices.
Explosion-proof FLUXUS® ADM 8027 ultrasonic measuring systems reliably detect flow rates
© BP Gelsenkirchen Advantage over vortex
Non-invasive, acoustic ultrasonic flow measurement has proven to be an elegant alternative to wetted measuring techniques. This technique is quite literally based on an external method: clamp-on ultrasonic transducers are simply attached to the outside of the pipe, do not come into direct contact with the medium flowing within the pipe and are therefore not subject to mechanical wear and tear by particles which are carried along. Vortex meters, which had proven to be relatively resistant to abrasion, were susceptible to coating formation on measuring devices as well as to disruptions caused by the natural vibrations of the system. This is not an issue for non-invasive flow measurement using clamp-on ultrasonic technology.
August / September 2011 •
www.petro-online.com
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