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

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 (F-R) of 7-12 g/m(2)h in the water-tube boiler-stove and 3-5 g/m(2)h 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/Nm(3) were measured for the water-tube boiler and 13-135 mg/Nm(3) for the fire-tube boiler. An SP size distribution study provided evidence for the large amount of ultrafine particles in domestic biomass combustion systems. (C) 2016 Elsevier Ltd. All rights reserved.