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Improved analytical techniques are helping to ensure that the environmental performance of plants is being fully optimised. Here, a new method of analysing the mercury content of crude oil and an improved system of flue gas analysis are outlined.

Improved analytical techniques are helping to ensure that the environmental performance of plants is being fully optimised. Here, a new method of analysing the mercury content of crude oil and an improved system of flue gas analysis are outlined.

Being able to accurately measure mercury levels in crude oil is vital to ensuring that a plant is operating as safely as possible. However, mercury levels differ from crude to crude, depending on their source. And the analysis process, being laboratory based, takes time.

Now, however, there is a faster solution to the problem.

Developed by ABLE Instruments and Controls, the Jerome 431-XE mercury analyser is a portable, hand-held unit that can easily be carried to locations where mercury might be present.

It uses a patented gold film sensor for accurate detection and measurement and is ideal for applications such as industrial hygiene monitoring, mercury spill clean up and mercury exclusion testing. Simple, push-button operation allows users to measure mercury levels from 0.003 to 0.999 mg/m3 in just seconds.

The gold film sensor is inherently stable and selective to mercury, eliminating interferences common to ultraviolet analysers, such as water vapour and hydrocarbons. When the sample cycle is activated, the internal pump in the 431-XE draws a precise volume of air over the sensor. Mercury in the sample is absorbed and integrated by the sensor, registering it as proportional change in electrical resistance. The instrument computes the concentration of mercury in milligrams per cubic metre or nanograms, and displays the final result in the LCD readout. An improved film regeneration circuit in the 431-XE makes for increased sensor longevity.

Recently Innovene called upon ABLE Instruments and Controls to assist in the detection of mercury contamination in crude oil streams at its Grangemouth site in England.

A Jerome analyser is now used around the Grangemouth site, within many of the different plants, to measure the mercury vapour levels in oil pipelines and storage vessels.

“Levels of mercury in crude oil vary depending on the source of the oil. The Grangemouth site sources its crude oil feedstocks from around the world and these may contain differing levels of mercury within them,” said an occupational hygiene specialist working at the Innovene site. “The main importance of mercury measurement is to protect employees’ health. There are certain strict limits to which we adhere. If the levels detected exceed these, we change the way in which we carry out certain operations, for instance issuing breathing apparatus.”

“The Jerome is used because the analysis is almost instant. With other methods, the samples have to be sent to laboratories for analysis, which simply takes too long,” added the specialist.

Savings from Flue Gas Analysis

Combustion control has always been an important aspect of plant management, both in terms of process efficiency and environmental impact.

As a result, the US-based Electric Power Research Institute (EPRI), one of the world’s leading independent research institutes, has been carrying out trials to verify the suitability of analysers for analysing oxygen and carbon monoxide in a flue gas in order to achieve efficient combustion control.

The EPRI compared the performance of three oxygen and carbon monoxide flue gas analysers from different manufacturers. According to Servomex, its 2700 analyser “demonstrated outstanding results”.

Throughout the six-month duration of the test the Servomex analyser operated reliably. No further calibration was performed after initial start up. Even after an unplanned power down during the tests, the analyser restarted and after warm up continued its analysis without any significant change.

The results of regular checks carried out during the test period indicate that the oxygen sensor only needs to be calibrated on a yearly basis. Similarly, the results also indicated that the combustibles sensor should only need a span calibration every year with a zero calibration every two months. The results were also used to predict seven years as the expected lifetime of the oxygen sensor and five years as the expected lifetime of the combustibles sensor.

The 2700 analyser was fitted with both zirconia oxygen and combustibles sensors for fast simultaneous analysis of both oxygen and carbon monoxide in order to maximise combustion efficiency.

Given that the typical fuel cost for a power station unit of similar size to the one used for the tests is US$2m per month, the Servomex analyser would reduce average oxygen levels of about three per cent by about one per cent. This in turn represents a reduction of at least half a per cent in fuel costs. According to the company, the use of the analyser to control at this new level delivers potential savings of US$10 000 per month on this unit alone. Taking into account the cost of the analysers and their installation, the payback time is much less than a year.

At the end of the trial, with no intervening recalibration, analyser performance tests were carried out which showed that the stability and repeatability of the analyser enabled the carbon monoxide breakthrough point to be readily established. This, together with the fast speed of response and simultaneous analysis of oxygen and carbon monoxide, is why Servomex is confident that the 2700 analyser an ideal tool for combustion control.

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