This study was carried out on an absorber in the body of flue gas desulphurization system (FGD) of a coal-fired power plant. In this study, efficiency losses caused by the clogging or breaking of the spray nozzles were examined. These abovementioned problems of spray nozzles are the most common among the many factors affecting the sulfur retention efficiency. Although energy and exergy analysis is very common to optimize the system efficiency of FGD units, failure of spray nozzles in absorbers might be the main reason in terms of low FGD units efficiency and low SO2 removal rates. In this study, firstly locations of clogged or damaged nozzles are determined by examining a total of 240 nozzles (3 x 80). After the replacement of the broken spray nozzles, increase in the efficiency of A-B, B-C, A-C and A-B-C spray lines were observed as 9.14%, 3.77%, 10.56%, 9.72%, respectively. Depending on the washing zone of the nozzles, if one nozzle is damaged, it causes the efficiency to decrease between 0.24% and 0.36%.