Fulton, a manufacturer of steam, hot water and thermal fluid heat transfer systems, has successfully completed a trial of a prototype modulating burner at Cardiff University

Fulton had originally installed two gas fired 60J steam boilers at Cardiff University’s bio-science areas back in 2003. At the point of installation and commissioning, each boiler was fitted with a standard on/off burner. Eight years on, and with energy costs reaching unprecedented levels, the university began reviewing ways to reduce energy consumption and improve its carbon footprint. Following conversations with Fulton, the university agreed to allow the company to conduct trials with the prototype of a modulating burner.

The Fulton boilers (one running 24/7 the other operating on-demand) are used to raise steam for autoclave sterilisation services and supply-air humidification for the university’s research facilities, where ambient humidity must remain constant regardless of external air conditions.

Senior plant attendant John Blakemore explained, “Constant and consistent humidification of the research facility on the main campus is paramount, and is obviously dependant on external air conditions. For example, if it is damp or raining, external humidity levels are high, so steam demand for the supply-air humidification is reduced. Under these conditions, the university’s building energy management system (BEMS) will usually only operate one of the two Fulton boilers. Conversely, if external air conditions are dry (similar to those experienced across much of the country in the spring), the demand for humidification is high and both 60J boilers will be operating to cope with the increased steam load requirements.”

Meeting demand

Before the installation of the modulating burners, the energy graphs produced by the university’s BEMS would show typical peaks and troughs associated with on/off burners due to the boilers firing when steam pressure falls to 7bar and continuing to fire until the required 10bar pressure is met. This constant rise and fall in steam pressure meant that peak demands for steam were difficult to achieve, especially when pressure was approaching 7bar. It also meant that condensate would build up in the steam, making it wetter than required for the humidification and sterilisation processes, and therefore placing a greater reliance on steam traps to remove excess condensate.

To improve steam quality and boiler efficiency, Fulton installed a prototype modulating burner on the primary 60J boiler, subject to Cardiff University agreeing to monitor the installation over a 12 month period and provide feedback and data such as external air temperature, gas meter readings, run hours, feed pump readings etc. The university also provided feedback on alarm conditions, but were happy to report that nothing out of the ordinary was noted during the trial period.

Based on Fulton’s existing on/off burner, the new modulating burner uses a linkage-less burner management system to operate two modulating actuators. One regulates the flow of gas and the other adjusts air flow to ensure that optimum combustion is possible across the full firing range of the boiler. To optimise combustion, each of the valves is capable of being adjusted by as little as 0.1° allowing small adjustments to be made to the burner output.

Gas flow into the burner is controlled by two fuel valves, the first acting as a safety shut-off and the second being a constant pressure governor. Burner output is also regulated via a pressure transducer and controller, which uses a 4-20mA signal to modulate the burner output.

A successful trial

After twelve months the trial installation proved successful and, as Bob Duckett, university estates officer, explained, the energy graphs had changed significantly and within a very short period of time. “Once installed, we were no longer seeing peaks and troughs as steam pressure increased and reduced, but were instead seeing an oscillating wave. In addition, because steam pressure is kept at a more consistent rate, the boiler was more efficient and wasn’t working as hard to achieve peak demand. This was therefore giving us better control of the steam, which meant that steam delivery and condition had improved. This in turn improved the humidification and sterilisation processes and also had additional benefits as it reduced maintenance issues by reducing stress on the steam system and associated equipment, including pressure reducing valves and steam traps.”

At the end of the trial Fulton also presented its findings to the university’s maintenance engineer, Keith Sims, and the decision was made to install another modulating burner on the second 60J steam boiler. This has been operational since May 2011 and, although the university isn’t providing Fulton with the same data as the previous installation, the university is confident that it is achieving similar results.