Estimating Cooling Towers for Power Plant Applications

It has always been difficult to estimate size and cost of well designed counterflow induced-draught cooling towers due to the interrelationship of approach temperature and cooling range associated with each design. Attempts to estimate the cost of a tower by assessing currency per cell, per square foot, per gallon, or currency per other single metric, have never been sufficiently accurate due to the asymptotic nature of the approach temperature versus the tower size arithmetic function. To determine accurate qualitative metrics for cooling tower estimating purposes requires assessing two-variable second-order equations in water-flow-rate/approach-temperature, temperature-range/approach-temperature, wet-bulb-temperature/approach-temperature, and approach-temperature/cost. The design and therefore cost responds to the following variables; 1) Recirculating Water Flow Rate, 2) Inlet Wet Bulb Temperature (WBT), 3) Approach Temperature, and 4) Cooling Tower Range or Heat Duty. With the proper evaluation of these parameters they can be utilized to determine metrics to estimate the following parameters: 1) Number of Cells, 2) Basin Area, 3) Pump Power, 4) Fan Power, and 5) Costs (at today’s prices only). In addition, a percentage breakdown can be calculated for; 1) Structure, 2) Hardware, 3) Mechanical Equipment, 4) Labor, and 5) Miscellaneous items. Although developed for the power industry, the operative model, design, and qualified costing techniques are also valid for large petroleum and chemical process projects, provided the heat duty dissipated, ambient conditions, water quality and flow rate can be accurately predicted. A set of equations are developed which can be used to estimate the significant costs of a proposed cooling tower. Example calculations and data are presented in Annex A.