A model of wet limestone flue gas desulfurization (WLFGD) system has been developed based on the use of the number of transfer units (NTU) and height of transfer unit (HTU) focused to full-scale coal-fired power plants. The model describes the process occurring in the absorber as the most important step in the WLFGD system by establishing what increase in SO2 removal can be achieved as the higher levels of nozzles come progressively into service when initially the first spray header is operating alone, and keeping the other operating conditions under control. This relative improvement of the SO2 removal can be obtained from only one datum: the number of mass transfer units when only the first spray level is on service (N-1). The model computes the gains in both the volumetric overall mass transfer coefficient and the number of transfer units. The model can be used to evaluate data or changes in an existing full-scale system as well as to evaluate proposed system designs and even as a pre-design tool in relation to the number of spray levels on service under controlled operating conditions. The model is tested on the basis of some data taken from a power plant and from the literature. The model results agree well with the real and published data. (C) 2010 Elsevier B.V. All rights reserved.