RWE npower raises CHP plant efficiency with flue gas monitors

London -- RWE npower’s combined heat and power plant in Barry, South Wales is achieving an overall efficiency rate of about 75% following installation of systems to monitor flue gas oxygen levels.

Since fitting Rosemount Analytical Oxymitters, the plant uses substantially less fuel than conventional methods for generating heat and power - and the efficiency level has prompted Defra to rate the plant as a “Good Quality CHP”.

The CHP unit supplies electricity, steam and treated process water to Dow Corning’s adjacent manufacturing facility for silicone-based materials. The 28MW of generating capacity is developed from two 6.5MW Tornado gas turbines and a 15MW Thermodyn steam turbine. Multiple high-pressure waste heat recovery boilers and low-pressure boilers supply up to 250t/h of steam capacity.

After experiencing problems with existing flue gas analyser equipment, an Oxymitter 400 unit was installed on a trial basis. This zirconium oxide-based oxygen transmitter is designed to be mounted directly into high temperature flues, allowing burner air/fuel ratios to be fine tuned for maximum efficiency and reduced NOx emissions from analysis of its measurements.

Further Oxymitter 400 units were installed after the successful trial, with npower Cogen appreciating particularly the fact that the sensors mount directly into the flue gas duct, eliminating the need for separate sampling systems. Operator and display electronics can be installed up to 60 metres away from the sensor, so there is no need for personnel to have to climb up through the plant to reach the flue gas head unit and make any adjustments.

“It is far more convenient, and safer, not to have to send engineers right up to the head unit,” said site engineer Paul Gardner. “The Oxymitter local operator interface gives us a display of flue gas oxygen level and temperature, and with the sealed push buttons, we can carry out any calibration routines needed on the sensor from ground level.”

The instrument’s on-line diagnostics determine when calibration is needed and signal a warning on the ground-level display. Any unusual readings trigger a warning on the interface and suggest a recalibration.