32 Measurement and Testing -
Improving Bottom Line Profits with Real-Time Viscosity Monitoring of Asphalts
Robert Kasameyer, PAC 101 Station Landing, Medford, MA 02155 USA Tel: 781 393-6500 • Email:
pacsales@paclp.com • Web:
www.paclp.com
Tere are more than 700 refineries worldwide with a capacity for 82 million barrels of oil per day operating in almost every country in the world. Of these, 137 operate in the United States with an estimated capacity of 17 million barrels of crude oil per day.1
Demand for energy continues to rise along with pressures on producers to streamline and speed production, increase yield, and operate more efficiently.
A typical barrel of crude yields 50% gasoline, 15% fuel oil, 12% jet fuel, and so on through diesel, asphalt, lubrication oil, and other refined products. However, actual output varies dramatically by refinery. Viscosity is one on the most critical measures of product quality for virtually every refinery product. New developments in viscosity measurement enable refineries to significantly improve production quality, cost, and output.
Quality control in modern asphalt production can be a challenging proposition. Refiners often produce products requiring varying grades and viscosity levels, and the quality of source material—crude oil—can vary vastly depending upon the supplier.
Asphalt
Asphalt is critical for road paving. Roads are subject to radically different environments throughout the world, and throughout the year. Asphalt must be suitable for those local conditions. All customers have asphalt pavement specs that are suitable for their region.
The raw material for making asphalt is basically what is left in the bottom of the barrel of crude oil when all higher value materials have been extracted and refined. That material can be very non-homogenous, and can vary radically in make-up from barrel to barrel depending on the source of the crude. Variations in refinery process conditions can also have an impact.
Refineries utilize in-line measurements to enhance production consistency. Three technologies are commonly used for in-line viscosity measurements: capillary, vibrational and oscillating piston. All require conditioning of the fluid being tested so that it is as consistent as the lab samples are in terms of temperature, flow, and particles. The oscillating-piston technology is preferred for its accuracy, reliability and ease of installation. Capillary systems require high precision pumps for accuracy, which need frequent and costly maintenance and recalibration. Vibrational-based viscometers can cause resonance frequencies in fluids which result in inaccurate measurements; they are also subject to process equipment vibrations which also can cause incorrect analysis.
Controlling viscosity is the key to producing consistent, high quality asphalt. However, lab sampling data often times does not correlate with product run results, making it difficult to accurately monitor viscosity and adjust for fluctuations. To address this issue, a Brazilian refinery implemented an in-line viscosity control system featuring the oscillating-piston technology to better measure asphalt viscosity and achieve higher product quality.
The Challenge
The viscosity and density of in-process asphalt can vary significantly during processing. This is due to fluctuations in raw material characteristics and manufacturing processes. Historically, engineers have controlled the process by periodically sampling the in-process material, testing the samples, and adjusting the process control factors to compensate for any variances.
This method would work fine if the characteristics of in-process material were consistent. Unfortunately, they are not, and as a result, periodic laboratory results are often not representative of the asphalt material being produced as a whole.
In the case of the Brazilian refinery, the company manufactures many different grades of asphalt, including AC-5 asphalt with a viscosity of 500 cP, so it is important for the refinery to produce asphalt as close to the targeted spec as possible. Each grade requires a different viscosity level and needs to be closely controlled.
The company was experiencing inconsistent results when measuring lab samples and comparing them to process samples. Lab samples hardly ever match up with process samples due to the variances in the fluids. When a sample is taken to the lab, it may not be fully representative of the line fluid; it loses volatiles, flow characteristics differ, and it needs to be heated again; thereby changing the characteristics of the fluid.
Asphalt Viscosity Control with Real-time Density In order to better understand this problem, the refinery equipped an asphalt processing line with
Figure 1: Comparison with traditional lab and in-line measurements
Figure 2: Fluctuations in Asphalt Viscosity before and after implementing In-Line Viscosity Control
a new in-line instrument from Cambridge Viscosity to measure viscosity and temperature in real time. They then compared the in-line measurements with periodic lab testing of process samples. Results from this effort are shown in Figure 1.
This figure shows precise agreement between the characteristics of the in-process material at the time the lab samples were taken, between the traditional off-line lab instruments and the new in- line viscometer. The continuous in-process measurements also showed that between the samples taken for the laboratory tests the in-process material showed significant variation. The plant engineers felt the variation shown in the continuous in-line measurements could explain the
April / May 2012 •
www.petro-online.com
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