Background

There are three dual fuel steam boilers in a government hospital. Boiler feed water is treated by water softener and chemicals including pH booster, anti-corrosion agent and oxygen scavenger.

There was an additional chemical for descaling which is not used in other hospitals due to the cost issue. Even though the feed water was treated in this way, there was a thin layer of mineral scale deposited on boiler tubes which is the major cause of energy inefficiency to the boilers.

After knowing the descaling performance of HydroFLOW from another hospital, it was decided to replace the descaling chemical by HydroFLOW for cost saving. The boiler tubes were inspected before the installation of HydroFLOW and shown in picture 1.

Result

After one year of operation without pre-cleaning of the tubes, it was found that the scale deposit on tubes was much thinner than one year ago as shown in picture 2. However there was a remaining deposit which is pale-pink in colour. Without any guesstimation, sample was collected and sent to MRC of Hong Kong Polytechnic University for SEM/EDX analysis.

It was found that the major composition of the sample is phosphate which was confirmed by the chemical supplier to be the anti-corrosion agent. The function of it is to coat on the tube surface for a direct protection. Therefore the descaling performance is demonstrated and no side effect is produced to other chemicals such as the anti-corrosion agent.

The installation of HydroFLOW can be paid back in 24 months with the cost saved by the elimination of descaling chemical. However the saving in fuel consumption surprised everyone as 15.0% of fuel was saved in one year which shortened the payback period to just 3 months. The performance chart is shown below.