Monitor Maximises Combustion Efficiency in Ethylene Furnaces

The SERVOTOUGH LaserSP TDLS gas analyser from Servomex (UK), the global specialist in gas analysis, delivers the optimum combustion control solution for ethylene cracker furnaces.

The key to combustion efficiency is minimising excessive air in the combustion chamber, a process which requires fast speed of response when monitoring the flue oxygen concentration at close to the optimum level and for the detection of carbon monoxide in the flue gas. The LaserSP, a high performance combustion monitor which utilises the latest tuneable diode laser (TDLS) technology, combines a response time of less than two seconds with an in-situ measurement location that eliminates any sample system delays.

The ability to measure these gases at up to 1500°C allows the LaserSP to be located close to the furnace burner, delivering the fastest possible speed of response. Additionally, the TDLS analysis technique offers a representative path-averaged measurement of process gas concentrations with a sensitivity that enables it to highlight faults: for example problems with a single burner jet can be detected by the LaserSP, even in furnaces where more than 100 burners may be present.

When utilised for a typical measurement of 0-10% O2 and 0-1000ppm CO respectively, the LaserSP delivers a flue gas analysis solution that enables optimisation of the combustion control process, improving process efficiency by lowering fuel consumption and reducing carbon dioxide emissions. Offering highly stable performance and minimum sample conditioning requirements with no moving parts and consumables, the LaserSP also minimises maintenance costs. With the accurate and reliable measurement delivered through a rugged and reliable Servomex design, the LaserSP is the best solution for in-situ measurements in the extreme and harsh environments of an ethylene furnace.

Servomex’s advanced technology also enables additional cost and process control benefits. In traditional TDLS in-situ installations, it is common practise to flow a dry N2 purge gas over the windows of analysers to protect the optics. Instrument air is not used as the oxygen content would interfere with the O2 combustion chamber measurement. The infra-red scan range of the LaserSP enables the inclusion of additional absorption lines which only appear at greater than 600°C. By using one of these “hot lines” to monitor the process O2, it is possible to use instrument air as the window purge gas without any interference to the measurement. The standard “cold” O2 absorption line is also monitored and the signal utilised for the purpose of checking the LaserSP’s response to a test gas, and to provide an alarm in the event of an interruption of the flow of window purge gas. The LaserSP monitor with air purge typically saves $5000pa (Euro4000pa) compared to a traditional TDL with nitrogen purge.

The thermally induced flexing of furnace walls can cause measurement failure for basic TDL technologies, due to the movement of the wall on which the analyser is mounted resulting in the laser “target” moving. The SERVOTOUGH LaserSP enables the laser transmitter optics to diverge the laser beam, ensuring the receiver remains unaffected by thermal movements of the process. This “receiver overfilling” technique is only made possible as a result of the LaserSP’s advanced second harmonic (2f) wavelength modulated signal (WMS) processing, which operates at a 200kHz carrier signal frequency, providing an order of magnitude improvement in signal to noise ration compared to traditional TDL.

“From reduced emissions and lower fuel costs to vastly improved response and reliability, the advanced technology of the SERVOTOUGH LaserSP delivers ethylene manufacturers overwhelming cost, process and safety benefits”, says Roger Highton, Product Business Manager, Servomex.