The influence of the steam-side characteristics of a modular air-cooled condenser on CSP plant performance

Limited water supplies in proposed concentrated solar power (CSP) plant locations have instigated the need for air-cooling of the condensers in the Rankine cycle. The current industry standard for air-cooling in power plants is the A-frame air-cooled condenser (ACC), the installation of which has increased exponentially in the last 15 years. This has occurred despite the fact they suffer from significant inefficiencies and weather effects. This paper introduces a modular air-cooled condenser (MACC) design which seeks to minimise these inefficiencies. A thermodynamic analysis is carried-out to determine the outcome of installing this MACC design in a CSP plant. Firstly, a series of measurements performed on a full-scale prototype MACC under vacuum conditions representative of an operational ACC are presented. Condenser temperature and pressure were measured as fan speed was varied, for a range of steam flow rates, to determine the qualitative and quantitative relationship between fan rotational speed and condenser steam-side conditions. Results show that for a fixed steam flow rate and constant ambient temperature, condenser temperature and pressure decrease as fan speed increases. The relationships, developed from the measurements, between fan speed and condenser temperature-pressure were then used to evaluate the gross output from a 50 MW steam turbine and, ultimately, evaluate the net plant output. Results show that increasing fan speed leads to an increase in plant output up until a certain point, at which further increases in output are offset by larger fan power consumption rates. Thus, an optimum operating point exists. The effects of ambient temperature were also examined and were seen to have a significant impact on firstly, steam-side conditions and consequently, plant output. Increases in ambient reduce plant output. However, by varying the fan speed to achieve the optimum operating point for any given ambient, the losses can be minimised.