Experimental analysis of fouling rates in two small-scale domestic boilers

Abstract

Fouling is a topic of interest in almost all heat production systems. A noticeable fall in thermal efficiency can be caused by accumulated fouled matter, especially in those surfaces where heat exchange takes place. In this research, two domestic-scale commercial pellet boilers were studied (a 24 kW water-tube boiler-stove and a 60 kW fire-tube boiler). Sampling probes were placed in both heat exchangers to measure the deposition rate. Commercial wood pellets were used as fuel. A series of tests were carried out under the same operating conditions. Average fouling rates (FR) of 7–12 g/m2h in the water-tube boiler-stove and 3–5 g/m2h in the fire-tube boiler were measured. The variation of these fouling rates with the position in the boiler side was also analyzed. In addition, measurements of the particulate matter (PM) concentration and flue gas composition were made during the tests. A correlation between the CO emissions and the collected solid particulate (SP) matter was obtained for each case of study. PM values of 110–280 mg/Nm3 were measured for the water-tube boiler and 13–135 mg/Nm3 for the fire-tube boiler. An SP size distribution study provided evidence for the large amount of ultrafine particles in domestic biomass combustion systems.