Overcoming measurement challenges in downstream oil and gas

When it comes to tough operating environments, they don’t come much tougher than the oil and gas industry. Les Slocombe, Marketing Manager for ABB’s UK Measurement Products business, explains how instrumentation can help deliver enhanced performance and production in downstream oil and gas applications.

The challenge of plugged impulse lines
Plugged impulse lines can be a real maintenance headache. As blocked impulse lines will not directly affect the operation of the transmitter itself, the problem can be difficult to detect. If the problem goes untraced, it could result in a process being based on incorrect information, impacting on both production costs and quality.

Plugged impulse line detection (PILD) can help operators to quickly find a blockage so that it can be dealt with.

Some of the latest pressure transmitters not only have built-in PILD, but can also guide operators through a simple process to “train” the transmitter to give accurate results under different process conditions and detect variations in process conditions that indicate a plugged impulse line.

Minimising flow measurement errors
Accurate metering is vital for helping to track product yields, losses and measurement discrepancies.

Oil and gas operators generally prefer volumetric flow meters for continuous measurements, but volumetric meters need to factor in temperature and pressure to deliver an accurate calculated mass or standard volumetric rate, which has the potential to introduce errors.

Impervious to temperature and pressure and offering a wide turndown, coriolis mass flow meters are ideal for liquid mass flow measurement, especially in applications subject to variations in product density or where a product is priced by weight.

pH measurement in condensed water
Distillation is the most fundamental step in crude oil processing, separating the oil into fractions and removing water and other contaminants from the process stream.

Non-hydrocarbon contaminants and water vapour concentrate in the upper part of the distillation column and the overheads system. Vapours from the top of the column pass to a condenser and then to a vessel that separates gas and hydrocarbons from the water. The contaminants tend to collect in the separated water, turning it acidic, which can damage piping, condensers and the upper portion of the column. To minimise corrosion, neutralisation chemicals are added, based on the pH of the water from the separator. Residual hydrocarbons mixed with the condensed water can plug the porous reference junction used in most pH electrodes and hydrogen sulphide (H2S) can also poison pH electrodes, reducing sensor life.

The operating life of a pH sensor can be greatly prolonged by installing a sample conditioning system to cool the condensed water and reduce its pressure.

Using a sensor with a wooden reference junction can also help to prevent the problem of plugging, as wood resists plugging by hydrocarbons much better than Teflon or other man-made materials.

Gas analysis
Close control of ethylene cracking processes is crucial. Process gas analysers provide the data needed to achieve the right cracking severity, while zirconia oxygen probes can help operators achieve the correct air/fuel ratios by monitoring stack emissions. Measuring the output gases from the process and measuring the naptha feedstock quality with an FT-NIR (Fourier Transform Near Infrared) analyser can also help to optimise the cracking process.

Operators can optimise furnace decoking using NDIR (Non-Dispersive Infrared) analysers to monitor carbon dioxide in the effluent gas during burn-off.

Optimised blending
Gasoline and diesel blending demands fuel quality and legislative targets to be met while producing the product at the lowest possible cost. To meet these targets, various properties are measured and controlled such as RON (Research Octane Number), MON (Motor Octane Number), RVP (Reid Vapour Pressure), olefins, ASTM D86 distillation points and oxygenates.

Using FT-NIR analysers enables rapid multi-stream and multi-property analysis of gasoline and diesel blending components and final product streams. By accurately measuring properties in real time, the analysers provide the data needed to optimise the blend, minimise product re-blends and meet product quality targets.

The right partner
With extensive experience in oil and gas applications worldwide, ABB can help operators to keep their plants working safely, productively and profitably. For more information, email moreinstrumentation@gb.abb.com or call 0870 600 6122 ref. ’Oil & Gas’.

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