Hanno Carl Rudolf Reuter

Performance Evaluation and Design of a New Cooling Tower Spray System for Uniform Water Distribution

ABSTRACT The performance of wet cooling towers can be improved by installing sprayers that distribute the cooling water uniformly onto the fill while operating at a low pressure head. This paper presents the methodology that was followed to design a new cooling tower spray nozzle. The fluid dynamics of an orifice nozzle, such as the effect of a change in pressure head, spray angle, spray height, orifice diameter, and wall thickness on drop diameter and spray distance, is experimentally investigated, and ultimately a model with which a spray nozzle can be designed is presented. The manufacture and testing of a prototype spray nozzle show that it is possible to enhance the performance of sprayers and thus wet cooling towers by means of the methods presented.

The antifouling effects of copper-oxide filler incorporated into paint-based protective films applied to steam surface condenser tubes

Paint-based protective films (PPFs) are used to protect condenser tubes from corrosion and erosion but have been shown to be susceptible to biofouling. Here the biocidal properties of copper-oxide fillers incorporated into PPFs are explored in this paper. Specifically two PPFs filled with 20% and 50% filler (by weight) are tested in parallel with a non-biocidal ordinary epoxy PPF, and bare stainless steel tube. Using double-pipe co-current flow heat exchangers installed at a thermal power plant, actual cooling water exiting the condenser is evenly distributed between the test tubes. Heat transfer in the condenser is simulated by heated water flowing through each annulus of the double-pipe heat exchangers, thereby maintaining repeatable outer convection conditions. An exposure test of 125 days shows that the 50% biocide filled PPF has the lowest fouling factor of all the tubes. The non-biocidal epoxy has the highest fouling factor and the 20% filled PPF behaves similarly. Both of these are greater than the bare stainless steel control tube. The 50 % filled PPF is compared to the fouling of an existing admiralty brass tube and the shape of the fouling curves are similar. This evidence suggests that provided the filler concentration is sufficiently high, there is the potential for the copper-oxide filler to reduce the asymptotic composite fouling factor by virtue of its antibacterial properties.

Enhancing Turbine Output at Dry-Cooled Power Plants Using a Hybrid (Dry/Wet) Dephlegmator

ABSTRACT This paper examines the benefits to steam turbine output of retrofitting an air-cooled steam condenser with a hybrid (dry/wet) dephlegmator (HDWD) in a coal-fired, reheat, regeneration cycle. A hybrid dephlegmator concept has been proposed and shown to provide enhanced air-cooled condenser cooling performance while consuming only a small amount of water. The hybrid dephlegmator retrofit is shown to be able to increase turbine power output by up to 10.8% in certain cases. A corresponding increase in annual energy output of 2.56% can be achieved for continuous wet operation of the hybrid dephlegmator. A likely operating scenario, where hybrid dephlegmator units are sequentially operated in wet mode in order to maintain rated turbine power output over a wide range of ambient temperatures, results in an annual energy output increase of 1.33%. Based on these results, the payback period for an HDWD retrofit is between 3 and 6 years. The hybrid dephlegmator concept offers a simple, cost-effective, and sustainable solution to the issue of reduced air-cooled condenser performance at high ambient temperatures and is capable of providing clean dispatchable power.

Computational Models for Predicting Cooling Tower Fill Performance in Cross-Counterflow Configuration

In cooling towers packed with trickle or splash fills, which have almost isotropic or anisotropic flow resistance, the air flow through the fill is oblique or in cross-counterflow to the water flow, particularly at the cooling tower inlet when the fill loss coefficient is small or when the fill hangs down into the air inlet region. This results that the fill Merkel number or transfer characteristic for cross-counter flow is between that of purely counter- and crossflow fills. When using CFD to model natural draught wet-cooling tower performance for isotropic fill resistance, two- or three-dimensional models are therefore required to determine fill performance. In this paper, the governing fundamental partial differential equations are derived in cylindrical and Cartesian co-ordinates to determine the cooling water temperature, water evaporation rate, air temperature and air humidity ratio in two-dimensional cross-counterflow fills for both saturated and supersaturated air. To solve these equations, a relation is proposed to determine Merkel numbers for oblique air flows by linear interpolation and extrapolation of purely cross- and counterflow Merkel numbers in terms of the air flow angle. This model is compared to analytical Merkel numbers obtained for different air flow angles using a single drop trajectory model. A linear upwind computational model and an Eulerian FLUENT® model are developed to evaluate fill performance characteristics from test data and to model fill performance in cooling towers respectively. The results of these two models are compared and verified with a FLUENT® Euler-Lagrange model.Copyright

A method to determine the performance characteristics of cooling tower spray zones

Cooling tower spray zones play an important role in cooling tower performance. Ideally they must distribute the cooling water uniformly onto the fill and must produce small drops at minimal pressure head to maximise heat and mass transfer in the spray zone with minimal pumping power. Limited thermal performance characteristic data is found in literature for cooling tower spray zones, since it is virtually impossible to measure spray zone performance accurately. In this paper, the method used to model the performance of cooling tower spray zones and results obtained for a medium pressure swirl nozzle are presented. Water flow distribution and drop size distribution tests are conducted on cooling tower spray nozzles to investigate the effects of varying different operating parameters, such as air and water flow rates, and installation parameters, such as nozzle height, nozzle spacing and direction of spray, on performance. The suitability of superimposing single nozzle flow distribution data to obtain the water distribution for a grid of equally spaced nozzles with variable nozzle spacing is investigated. Furthermore, a single nozzle simulation model is developed and used to model single spray nozzles. The single nozzle model and the superposition model are subsequently used to obtain initial drop conditions to model the spray zone using the commercial CFD package FLUENT® . The proposed modelling approach allows for the evaluation and performance prediction of existing and new nozzle design configurations. Correlations are presented for the Merkel number and loss coefficient for the downspray nozzle investigated.Copyright