Analysis of Large Dry Cooling Towers With Power-Law Heat Exchanger Performance

1976 ◽  
Vol 98 (3) ◽  
pp. 345-352 ◽  
Author(s):  
F. K. Moore ◽  
C. C. Ndubizu
Keyword(s):  
Heat Exchanger ◽  
Heat Exchangers ◽  
Ambient Pressure ◽  
Tube Length ◽  
Cooling Towers ◽  
Tube Size ◽  
Best Value ◽  
A Chain ◽  
The Cost ◽  
Dry Cooling

An analysis is presented for heat exchanger area, tower exit area, and exchanger tube length and number, for heat exchangers in large dry cooling towers, having performance parameters given by powers of Reynolds number, but otherwise under very general cooling-cycle constraints. The calculation method is illustrated for a “spine-fin” heat exchanger which, in a tube size of about 3/8 in., seems capable of achieving low tower size in a practical device. Calculations, over ranges of water pumping power, approach, ITD, number of passes, tube size, tower shape (natural draft) or fan power (mechanical draft), and ambient pressure altitude are shown to be well represented by a chain of powers of these variables, and certain functions of the ratio of real to ideal tower exit area. This ratio is shown to have a best value, depending on the cost coefficients of heat exchange and exit areas, and it is pointed out that typical cost proportions lead to a fluid-mechanical “packaging” problem for the shallow heat exchangers which would be preferred.

Addressing Fouling by Qualifying Chemical Additives Using Novel Technologies

2021 ◽  
Author(s):  
Andrew Robert Farrell ◽  
Dario Marcello Frigo ◽  
Gordon Michael Graham ◽  
Robert Stalker ◽  
Ernesto Ivan Diestre Redondo ◽  
...  
Keyword(s):  
Heat Exchanger ◽  
Heat Exchangers ◽  
Emulsion Stability ◽  
Ambient Pressure ◽  
Screening Tests ◽  
Process Conditions ◽  
Screening Methods ◽  
Chemical Additives ◽  
Laboratory Techniques ◽  
Prediction And Prevention

Abstract Fouling of heat exchangers and production of stable emulsions in desalting units can present significant challenges in refinery operations. Often these difficulties occur due to the concurrent processing of two or more crude oils that are incompatible under process conditions. This paper describes a significant development in laboratory techniques for studying these issues and evaluating mitigation strategies. Asphaltenes compatibility was evaluated for oil mixtures that may be co-processed in the refinery using a deposition flow rig, and the results were compared with those obtained with more conventional tests: blending stability analysis by light scattering and various screening methods. The flow rig mimics the process conditions (elevated pressure, high temperature, flow-induced shear) and identifies whether deposition or precipitation will occur. The former can cause fouling of heat exchangers whereas the latter produces solids that can stabilize emulsions in the desalter. By varying the proportions of oils that were co-injected into the deposition flow rig, the range within which mixtures were unstable was found. By flowing through a capillary (to mimic a heat exchanger) and in-line filter, it was possible to identify whether precipitation of suspended flocs or fouling of the heat exchanger itself was the likely issue for each mixture. Emulsion-stability tests were conducted using a pressurized rig with an ersatz separator to mimic the desalting unit; results were compared with those obtained in conventional, ambient-pressure bottle tests. Oil(s) and refinery wash water were injected, mixed under representative shear, and allowed to separate within the typical residence time of the desalter. Chemical additives were tested to identify those that were effective at controlling any observed problems. Results obtained in either flow rig (using representative pressure, temperature, and shear) did not always match those obtained using conventional methods. Asphaltenes fouling occurred under conditions where it was not predicted by screening tests that were conducted at conditions not representative of the process and did not occur under conditions where it was predicted. Differences were also observed between the emulsion stability observed in bottle versus rig tests, though these should be viewed as complementary techniques. This paper presents new laboratory techniques for the prediction and prevention of refinery fouling and emulsion stability. They mimic conditions in the facilities much better than those typically used to date.

Analysis of the efficiency of hydrocarbon propellant cooling using liquid nitrogen and a combination of recuperative heat exchangers

2020 ◽  
Author(s):  
A.A. Aleksandrov ◽  
I.V. Barmin ◽  
A.V. Zolin ◽  
V.V. Chugunkov
Keyword(s):  
Heat Exchanger ◽  
Liquid Nitrogen ◽  
Coming Out ◽  
Heat Exchangers ◽  
Cooling System ◽  
Design Parameters ◽  
Nitrogen Gas ◽  
Double Pipe ◽  
The Cost ◽  
Pipe Heat

The paper describes the propellant cooling system using liquid nitrogen and a combination of recuperative heat exchangers, including sections of the double pipe heat exchanger and a twisted heat exchanger located in a tank with antifreeze, cooled by nitrogen gas coming out of the sections of the double pipe heat exchanger. Mathematical models of cooling processes for two variants of movement of propellant and liquid nitrogen in the channels of the double pipe heat exchanger sections are considered. Their using makes it possible to analyze the efficiency of propellant cooling operations depending on its mass, design parameters of the system tanks and heat exchangers, consumption characteristics of nitrogen and propellant, as well as to predict the required mass of liquid nitrogen and the time of propellant cooling during the operation of launching complex propellant-feed systems. Calculated dependences and simulation results of propellant and antifreeze cooling in a tank with a twisted heat exchanger are presented. The influence of variants of arranging propellant cooling processes and liquid nitrogen consumption on the efficiency of the cooling system is analyzed. Comparing to the available systems the capability of reducing the cost of liquid nitrogen are identified as well as reducing time of the propellant cooling operations by means of equipping launch complexes.

scholarly journals Numerical and Experimental Study of the Thermal Efficiency of an Air-Soil Heat Exchanger in the Sahelian Zone

2021 ◽  
pp. 8-16
Author(s):  
Boureima Kaboré ◽  
Germain Wende Pouiré Ouedraogo ◽  
Adama Ouedraogo ◽  
Sié Kam ◽  
Dieudonné Joseph Bathiebo
Keyword(s):  
Experimental Study ◽  
Heat Exchanger ◽  
Thermal Efficiency ◽  
Heat Exchangers ◽  
Air Conditioning ◽  
Electrical Energy ◽  
Tube Length ◽  
Air Velocity ◽  
June July ◽  
Sahelian Zone

In the Sahelian zone, air conditioning in house by air-soil heat exchangers is an alternative in the context of insufficient of electrical energy. In this work, we carried out a numerical and experimental study of thermal efficiency of an air-soil heat exchanger. This study provided an estimation of thermal efficiency of an experimental air-soil heat exchanger during June, July and August 2016. Numerical results provided a better understanding of the influence of parameters such as tube length, air velocity and soil temperature on the thermal efficiency of this system.

Details Study of Ambient Wind Effect on Heat Dissipation Capacity of Thermal-Powerplant Dry Cooling-Towers

2014 ◽  
Author(s):  
Masoud Darbandi ◽  
Ali Behrouzifar ◽  
Ahmad Mirhashemi ◽  
Hossein Salemkar ◽  
Gerry E. Schneider
Keyword(s):  
Heat Exchanger ◽  
Heat Exchangers ◽  
Heat Dissipation ◽  
Cooling Tower ◽  
Wind Effect ◽  
Circulating Water ◽  
Wind Velocities ◽  
Computational Fluid Dynamics Cfd ◽  
Dry Cooling Tower ◽  
Dry Cooling

Thermal powerplants report a reduction in their dry cooling tower performances due to surrounding wind drafts. Therefore, it is very important to consider the influence of wind velocity in cooling tower design; especially in geographical points with high wind conditions. In this regard, we use the computational fluid dynamics (CFD) tool and simulate a dry cooling tower in different wind velocities of 0, 5 and 10 m/s. To extend our calculations; we also consider the temperature variation of circulating water through the tower heat exchanger or deltas one-by-one. We show that some heat exchangers around the tower cannot reduce the circulating water temperature sufficiently. This causes an increase in the mean temperature of those heat exchangers. The worst performances can be attributed to heat exchanger located on side wind places. We will discuss the detail performance of each delta and their assembly in draft wind conditions. This study suggests some effective ways to overcome thermal-performance of cooling tower in wind conditions.

scholarly journals A Simple Method for Finding Optimal Paths of Hot and Cold Streams inside Shell and Tube Heat Exchangers to Reduce Pumping Cost in Heat Exchanger Network Problems

2020 ◽  
Vol 34 (3) ◽  
pp. 131-148
Author(s):  
V. Sadri ◽  
Hadi Soltani ◽  
S. Rahimzadeh
Keyword(s):  
Linear Programming ◽  
Heat Exchanger ◽  
Heat Exchangers ◽  
Continuous Variables ◽  
Simple Method ◽  
Optimal Paths ◽  
Network Problems ◽  
Pumping Cost ◽  
Minlp Models ◽  
The Cost

In this paper, a simple method is presented for the synthesis and retrofit of heat exchanger networks (HENs) by considering pressure drop as well as finding proper path of streams inside heat exchangers (HEs) to reduce the pumping cost of network. Generally, HEN problems lead to MINLP models which have convergence difficulties due to the existence of both continuous and integer variables. In this study, instead of solving these variables simultaneously, a combination of Genetic Algorithm (GA) with Quasi Linear Programming (QLP) and Integer Linear Programming (ILP) was used for solving the problem. GA was used to find optimal HENs structure and streams paths, whereas continuous variables were solved by QLP. For the retrofit of HENs, a modified ILP model was used. Results show that the proposed method has the ability to reduce the cost of annual pumping due to considering optimal paths for streams in the HEs compared to the literature.

scholarly journals Reduction of Biofilm Formation on Cooling Tower Heat Exchangers using Nano-silica Coating : Environmentally sustainable antifouling coating demonstrated on stainless steel heat exchanger tubes

2020 ◽  
Vol 64 (4) ◽  
pp. 419-424
Author(s):  
Irfan Turetgen
Keyword(s):  
Heat Exchanger ◽  
Heat Exchangers ◽  
Biofilm Formation ◽  
Epifluorescence Microscopy ◽  
Total Biomass ◽  
Cooling Towers ◽  
Nano Silica ◽  
Coated Surfaces ◽  
Control Surfaces ◽  
Steel Heat

Cooling towers are industrial cooling units operating to dissipate heat. As with any surface in contact with aqueous systems, biofilm formation appears on the surface of heat exchangers. Although biofilm formation on plastic tower fill in wet cooling towers has been studied widely, no studies were found regarding biofilm formation on steel heat exchangers in closed-loop systems. In this study, heat exchangers were coated with nano-silica, which is known to reduce the formation of biofilm. Natural biofilm formation was monitored for six months. Biofouling was examined monthly using epifluorescence microscopy by assessing the numbers of live and dead bacteria. It was observed that the biofilm layer formed on the nano-silica coated heat exchanger surfaces was significantly lower than on the control surfaces. 3 log microbial reduction was recorded on coated surfaces in the first month. After six months, total biomass on control surfaces reached 1.28 × 1012 cell cm−2, while the biomass on nano-silica coated surfaces was 6.3 × 104 cell cm−2.

A Method to Achieve Robust Aerodynamics and Enhancement of Updraft in Natural Draft Dry Cooling Towers

2009 ◽  
Author(s):  
Christopher C. M. Chu ◽  
Md. Mizanur Rahman
Keyword(s):  
Heat Exchanger ◽  
Power Plants ◽  
Substantial Part ◽  
Cooling Towers ◽  
Time Data ◽  
Unstable Flow ◽  
Flow Area ◽  
Cross Sectional ◽  
Cold Air ◽  
Dry Cooling

A method to stabilize the draft through natural cooling towers is introduced. Natural draught dry cooling towers are widely used in arid regions of the world for the power industry especially those employing nuclear reactors. Their presence has become iconic of the process industry for their dominance of the landscape. These towers control the overall efficiency of power plants, and with the ongoing energy crisis it is desirable to raise efficiency by stabilising the draught through the tower. Energy comsumption is a substantial part of the overall cost of plant operation, and therefore even with a conservative 5 per cent improvement is feasible. It has been noted by some researchers like Baer, Ernst and Wurz (1980) that cooling towers do experience unstable flow with breezes. This phenomenon can be explained by Jo¨rg and Scorer (1967) to occur even in a still ambience with cold air inflow down into the tower shell from exit. Jo¨rg and Scorer (1967) developed a correlation to predict cold inflow to a glass tube for various fluids in a laboratory. By using their formula, it is found that under typical exit bulk velocities, of 3–5 m/s or below, cold air is liable to ‘sink’ into the shell, even in a quiescent surrounding. Indeed this phenomenon was demonstrated in the laboratory using a duct of size 457 × 457 mm2 of a heat exchanger by employing a smoke generator to detect that cold air did flow into the duct rather than the hot air filling the entire cross sectional area of the duct exit. A device was applied by Chu (1986) to prevent this cold air from sinking into the duct and enhance the stability and quantity of the updraft. In this paper, for the first time data obtained from a 700 × 700 mm2 cross-sectional flow area model air-cooled heat exchanger are presented that proves the air flow rate enhancement due to this device. It is hoped that more tests can be conducted to optimize the design for application in boiler chimneys and natural draught dry cooling towers.

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