Using gas analysis to cut costs and improve RATA performance

Paul Boughton

Although its existing equipment did a reasonable job in many respects, Kosmos Cement was finding that every few days there would be an alarm situation in the coal mill at its plant in Sugar Land, Texas, USA.

Carbon dioxide in the form of liquid and vapour was required to inert the atmosphere and avoid a fire hazard. This was very costly in terms of both carbon dioxide consumption and the fact that the coal mill and downstream processes had to shut down, which caused lost production. Each inert situation cost thousands of dollars.

Kosmos was also coming under pressure for failing RATA tests on the plant’s emissions. This was as a direct result of the underperformance of the continuous emissions monitoring system (CEMS) that was operating at that time.

The company was getting a poor response from its instrumentation supplier and had to take urgent action, so opened discussions with what it saw as the two major players in the US, one of which was Servomex. Kosmos felt that Servomex had a strong reputation for its products and customer support and heard good feedback first-hand from other end users of its products.

Darrell Wiley, the lead electrical engineer for the upgrade project, said: “We held a pre-bid meeting with Servomex and they were clearly well prepared. It was also reassuring that senior management were involved and it was obvious that Servomex was committed to working in the cement industry. Overall we got a good impression and were confident that Servomex would be the better partner for this project.”

As a result, a number of different systems were supplied to the Kosmos plant. Two Servomex4900 analysers were provided to meet the company’s state-mandated CEMS requirements. In addition, an air-conditioned stainless steel cabinet was delivered with a sampling system to monitor two coal mill exhausts. This was necessary because a switching system enables one analyser to monitor two sampling points. This system is equipped with a Servomex1800 oxygen analyser and a Servomex2500 analyser for measuring carbon dioxide.

A second similar cabinet contains a sampling system for use with the pre-heater, this time switching between three sampling points. This system also has 800 and 2500 analysers. Both cabinets are fully controlled by Allen-Bradley PLCs so that stream switching, blow-back to clean the sample probe filters, and calibration are automated.

Alarms are triggered if temperatures or pressures stray outside specified limit; even the pressure in the calibration gas bottle is monitored so that plant operators are automatically notified when supplies are running low. This level of automation keeps the equipment easy to use, despite its inherent sophistication.

The two 4900CEMS analysers, which are each capable of making up to four measurements, are used here to measure oxygen, carbon monoxide, nitrogen dioxide and sulphur dioxide. The system it replaced could only measure carbon monoxide.

Because Kosmos now has data for oxygen as well as carbon monoxide, the plant operator is able to make better informed decisions about combustion that enable the plant to be operated at a higher efficiency. Further, Kosmos has passed every RATA inspection since the new instruments were installed, whereas failures were a common occurrence beforehand.

In the systems monitoring the coal mill exhausts and preheater, carbon monoxide reading is used to indicate a possible smouldering fire and the level of oxygen is monitored for safety purposes. Nevertheless, accurate measurements of these gases allow alarm levels to be set such that remedial action can be taken prior to a shutdown being necessary. With the previous system, inerting of the coal mill was required every few days, costing thousands of dollars every time. But now the new instruments are installed, there is only one such event every five or six months – a year-on-year savings of tens of thousands of dollars to Kosmos.

Another aspect of the project was good communication. “They kept asking the right questions and made sure we were involved at every step,” said Wiley. “Right throughout the specification and design phases the Servomex team worked closely with us to make sure we got what was right for our plant.”

Although Kosmos carried out the installation work, Servomex provided guidance and subsequently came on site to commission the equipment. “This is highly specialised instrumentation and we were anticipating some initial teething problems. But Servomex always gave us very prompt support and made sure we solved every issue satisfactorily as quickly as possible. We could not have asked for better support than that.”

Following the success of this project, Kosmos Cement is now in discussions with Servomex for a second phase of the plant upgrade that will involve a further two gas analysis systems. 

More about these and other systems can be found at http://www.servomex.com  

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