The demand for emissions monitoring equipment grows unabated, with new technologies delivering mobile solutions and ever more accurate results. Sean Ottwell reports.

BP Chemicals has invested £20million in a refurbishment project at its acetic acid production plant in Hull, UK. One element of the upgrade to the steam reformer is the installation of six Servomex 2700 combustion gas analysers and a manual calibration and control panel, which have contributed to reduced fuel consumption and savings of £500 000 per year.

Four of the gas analysers have been employed in the arch section. Two are installed to ensure accuracy on each of the east and west furnaces. This is due to the length of each furnace and the resultant potential for changes in the air register openings along that length. A further two have been installed to monitor the flue gases. All six analysers measure both oxygen and combustibles (COe), whereas the analysers they replaced only measured oxygen. This ability to measure COe gives the plant operators the confidence needed to run the furnace with lower oxygen levels, which helps to reduce the amount of natural gas burnt.

One of the reasons why BP Chemicals chose to purchase these combustion gas analysers was that one Servomex 2700 analyser had already been used successfully elsewhere on the plant. Furthermore, prior to placing the order the engineers at BP Chemicals had established that Servomex was the only company able to supply an analyser that would permit the transmitter to be mounted sufficiently far from the control unit. In the Hull plant, the control units had to be mounted at ground floor level, while the sensor heads were at fourth floor level.

Two different technologies are employed within the Servomex 2700 sensor head; oxygen is measured using a zirconium oxide sensor, giving high accuracy and a fast response, while levels of carbon monoxide equivalents are monitored using a thick film catalytic sensor that gives a precision of ±25ppm, with sufficient sensitivity and speed of response to enable the combustion process to be continuously fine-tuned.

Both of these sensing technologies are highly reliable, non-depleting, and can operate for extended periods without requiring attention. Furthermore, the thick film catalytic combustibles transducer is considerably less affected by cross-interference from other background gases such as water and carbon dioxide than transducers using alternative sensing technologies.

Gary Garner, analyser performance engineer at BP Chemicals’ Hull plant, comments: “BP Chemicals has used Servomex analysers since the 1970s and we have always been pleased with the systems’ performance and reliability, as well as the technical support from Servomex. Given the excellent experience we already had with the initial Servomex 2700 combustion gas analyser, we had no hesitation in specifying them for the steam reformer refurbishment. Furthermore, these were the only combustion gas analysers on the market that enabled us to separate the control units and sensor heads by 70 metres.”

Servomex worked with BP Chemicals to ensure that the probes and control units were correctly matched to the application, and Servomex also designed and built a bespoke manual calibration and control panel system to serve all six analysers.

In a separate development, a major Middle Eastern petrochemical plant has also selected Servomex gas analysers for continuous emissions monitoring (CEM) and safety-related applications.

The Saudi Arabia-based production facility is one of the largest of its type in the world, with an annual ethylene capacity of 1.6m t/y, plus another 2m t/y of derivatives such as polyethylene, polypropylene and ethylene glycol.

The plant’s CEM analysers that were originally installed to monitor sulphur dioxide and nitrous oxides were suffering badly from drift, which was having a small but appreciable impact on the plant's profitability due to the plant running inefficiently.

Although it is common practice in the Middle East to install analysers that use chemiluminescence technology, Servomex suggested the site trial two 4900 analysers, which use photometric infra-red technology, confident that their solution could deliver improved long-term performance.

At the end of the 12-month trial, the drift problem had been eliminated and the engineers at the plant have enjoyed additional benefits relating to operating efficiency, ease of use and maintenance.

Safety is another top priority at the site, and the plant’s owners have entrusted several safety-related functions to Servomex oxygen analysers, such as monitoring oxygen levels during ethylene oxide production. On the back of previous performance, Servomex secured an order for eight 2200 process oxygen analysers and sampling systems for use in controlling oxygen levels in the plant.

Pinpointing emissions

Meanwhile US company Picarro has launched an ultra-trace gas analyser for precisely measuring isotopic carbon dioxide, a marker for this type of carbon dioxide and its origin.

The instrument is based on cavity ring down spectroscopy (CRDS) technology licensed from Stanford University.

According to the company, Picarro’s CRDS analysers deliver parts-per-billion to parts-per-trillion gas sensitivity at high speed and without interference to meet the requirements of the most demanding applications.

The isotopic carbon dioxide application was originally developed for the Los Alamos National Laboratory where the instruments are used to study carbon dioxide ratios and concentration in plants and the atmosphere.

“Fast response, continuous isotope measurement systems allow us to better understand carbon dioxide flow through ecosystems, water usage, the biochemistry of plants, and in a multitude of other temporal and spatial studies,” said Nate McDowell, Earth and Environmental Sciences Division, Atmospheric and Environmental Dynamics Group,Los Alamos National Laboratory.

“Many studies of plant, ecosystem and global carbon and water cycling are based on a number of assumptions because we could never before analyse stable isotopes of carbon dioxide or water rapidly and continuously. With this analyser, we can get fast and continuous results which will allow studies to be based on facts.”

Additional applications for isotopic carbon dioxide systems include monitoring of carbon sequestration programmes and measuring mud-gas samples collected during the natural gas exploration process. Carbon sequestration is a process of capturing carbon emissions from power plants, compressing them, and putting them underground instead of into the atmosphere. Mud-gas analysis is done to help energy service providers pinpoint the quality and potential quantity of natural gases.

The new analyser incorporates a platform first introduced by Picarro in 2005. It measures single spectral features in a compact flow cell with an effective path length of up to 12 km which produces huge advantages in sensitivity, selectivity, precision, and data quality. It is an exceptionally rugged analyser, making it ideal for deployment in any environment. The instruments are essentially drift and maintenance free, and require no consumables, potentially offering significant ease of use and cost of ownership benefits for customers.
“Compared to isotopic ratio mass spectrometers, our instruments are considerably smaller, exceptionally simple to run, and inexpensive to operate. We designed our instruments to run unattended for days on end in some pretty remote locations making them an ideal solution for both field-based and laboratory-based applications,” explained Picarro president and ceo Michael Woelk.

Going mobile

For over 25 years, UK company ET has been designing and building mobile air quality monitoring stations for clients around the world.

It most recent contract involves a vehicle with instrumentation equipped for the measure of nitrogen oxides, sulphur dioxide, hydrogen sulphide, carbon monoxide, ozone and VOCs, to name but a few. A pneumatic meteorological mast has been fitted which can be raised to a height of six metres to measure wind speed, wind direction, temperature, relative humidity, solar radiation and pressure.

According to technical director Mike Webley: “This is perhaps one of the most comprehensive mobile stations we have ever built and I am confident that the end client will be extremely happy with the performance of the equipment and the overall quality and standard of ET's work.”

Interestingly, the company has seen a huge increase in the number of air quality and monitoring projects it has undertakne between October last year and February 2008. “Our throughput of air quality monitoring projects represents a 50 per cent increase on the same period last year, with increases in both UK and overseas,” confirmed project manager Frazer Livingstone.