New high-reliability cement kiln gas analysis system overcomes tough sampling conditions to deliver significantly better process control and more reliable emissions monitoring.
Servomex has successfully tested and supplied a new design of gas analysis system to the Lafarge Calcium Aluminates specialist cement plant in Purfleet, just East of London, which produces approximately 150 tonnes of calcium alumina compounds per day. Marketed under the Secar brand, this high-value cement is used for refractory linings and other applications where high or freezing temperatures are encountered.
The Purfleet plant burns low sulphur fuel oil of less than 1%, and has done so since 1999. As with all cement plants, the gases produced in the kiln can be a challenge to analyse reliably. To avoid acidic gases condensing and damaging the analyser, a cooler has to be incorporated within the gas sampling system. However, after the plant’s original gas analysis system suffered a series of cooler failures, combined with the supplier no longer responding in a timely manner to Lafarge’s requests for support, Lafarge sought a more customer-focused supplier that could build a system with better reliability.
Lafarge approached Servomex, based upon Servomex’s experience in other cement plants around the world, including another specialist one owned by Lafarge in Tianjin, China. At that time Servomex had just completed the development of a new gas analysis system for cement works, so offered Lafarge the use of a trial system.
The key component of this new system is a 19 inch rack-mounted Servomex 4900 multi-gas analyser installed in a sealed and heated enclosure, which provides protection against dust ingress and the formation of condensation. Furthermore, two new features are incorporated in the sampling system to enhance reliability and accuracy: a membrane filter that stops water reaching the analyser and damaging it in the event of a cooler failure; and a calibration gas hydration unit that enables gas composition changes, due to water loss, to be calibrated out - which is particularly important for SO2 analysis.
Benefits of the 4900 include a low cost of ownership, minimal maintenance and easy integration with other systems. Oxygen is measured using a non-consumable magnetodynamic paramagnetic sensor cell, while gas filter correlation (Gfx) infrared technology is used for SO2, NO and CO. These technologies have both been proven as fast response, accurate and highly reliable on cement plants.
At Purfleet, Lafarge is using the 4900 analyser to monitor SO2 in the kiln exhaust to ensure that emissions do not exceed permitted levels. In addition to this, O2, CO and NO are measured both for environmental compliance and process control. These last three readings are fed into the expert control system that automatically optimises the kiln’s performance; measurements of CO and O2 are used for combustion control, and NO is used as an indication of flame ’quality’.
When the plant was reliant on the previous gas analyser, frequent failures in the cooler, led to costly repairs being required, which cost hundreds of pounds in parts and labour each time. In addition, the plant control would have to be switched from the control system to manual and, unless a highly skilled operative was on hand to take control immediately, manual operation would sometimes lead to less efficient operation of the plant, lower product quality and, in some cases, lost production. Each failure of the cooler therefore had the potential to cost Lafarge thousands of pounds.
In contrast, the Servomex gas analysis system has been 100 per cent reliable over an 18-month period, requiring nothing more than weekly calibration checks and routine maintenance such as filter changes.
Keith Stanley, the Automation Technician at Lafarge, comments: "Kiln exhaust gases are extremely difficult to analyse due to their hot, dusty and corrosive nature, so we would not have expected any instrument to last this long. But the Servomex system has given us no problems whatsoever, with the added advantages of very low drift and a simple calibration procedure. The filters are also easy and quick to change."
Indeed, Lafarge was so impressed with the trial rig (system) that it decided to purchase it from Servomex. Keith Stanley adds: "We believe the cost of ownership is extremely attractive, and the high reliability has meant that we have been able to produce consistently high quality cement, with no stoppages attributable to the gas analysis system."
As well as being pleased with the analyser, Keith Stanley also was especially impressed by the support from Servomex: "The people there are always quick to respond, and they have demonstrated a good understanding of the cement production process. Compared with our previous supplier, the service we get from Servomex is substantially better."