Limitations of current cooling water treatment processes to control cooling water chemistry in wet cooled power plants

Abstract

In a coal-fired power plant, recirculating cooling water exchanges latent heat energy with the exhaust steam in the condenser and transports the heat to the cooling tower for evaporative cooling. The water lost in the evaporative cooling tower is continuously replenished by make-up water or effluent generated within the power plant processes. Due to the make–up water and effluent generated from the station chemistry quality, challenges relating to the recirculating cooling water, such as scaling, fouling, and, at times, corrosion are experienced. These challenges impact the performance and operation of the cooling system, leading to thermal efficiency losses. The investigation uses quantitative analysis and deductive evaluation to describe the effect of recirculating cooling water on plant performance. Thermal efficiency as a measure of a wet cooled power plant’s overall performance for the past four to five years was assessed on four wet cooled power plants. The condenser and cooling tower performance was the focus area for the investigation. Fouling and scaling (dirty heat transfer surface) has an influence on recirculating cooling water flow, inlet and outlet temperatures, heat transfer leading to vacuum, and back pressure challenges on the condenser. The higher the demands on the plant components with respect to pressure and temperature, the purer the recirculating cooling water must be. To assess the chemistry of the recirculating cooling water, parameters such as calcium carbonate precipitation potential (CCPP), alkalinity, hardness and pH were modelled on power BI and R studio. The observations indicate that operating outside the guidelines has a detrimental effect on the performance of the power plant. Calculated performance indicators like the condenser cleanliness factor and terminal temperate difference contribute to the condenser back pressure, whereas the cooling tower range and approach influence the effectiveness of the tower. The correlation between recirculating cooling water chemistry and plant performance is evident from the results, taking into consideration the time lag between plant exposure and the actual effect on the plant. The management and control of the recirculating cooling water side treatment to control cooling water chemistry will positively influence the power plant performance especially the heat transfer systems in the power plant. The effect of scaling and fouling is revealed to be among the significant parameters that affect the condenser and the cooling tower performance, although further research must be conducted to obtain the actual correlation between recirculating cooling water chemistry and plant performance, particularly condenser back pressure and cooling tower effectiveness. The investigation will be advantageous in addressing major factors contributing to and influencing power plant thermal efficiency decline. The power generation industry in general must extend a significant effort toward the optimal conditioning of cooling systems. A good conditioning method simultaneously reduces scaling, fouling, and corrosion of equipment in the cooling systems. The costs associated with maintaining cooling water chemistry within the recommendations stipulated in the chemistry guidelines are likely to be less than those associated with the maintenance or replacement of heat exchangers and piping, and the outages associated with those efforts.