Numerical Simulations of Heat and Mass Transfer in Condensing Heat Exchangers for Water Recovery in Power Plants

2011 ◽  
Author(s):  
Kwangkook Jeong ◽  
Harun Bilirgen ◽  
Edward Levy
Keyword(s):  
Experimental Data ◽  
Mass Transfer ◽  
Water Vapor ◽  
Sulfuric Acid ◽  
Heat Exchanger ◽  
Power Plant ◽  
Heat And Mass Transfer ◽  
Flue Gas ◽  
Cooling Water ◽  
Condensing Heat Exchanger

Power plants release a large amount of water vapor into the atmosphere through the stack. The flue gas can be a potential source for obtaining much needed cooling water for a power plant. If a power plant could recover and reuse a portion of this moisture, it could reduce its total cooling water intake requirement. One of the most practical way to recover water from flue gas is to use a condensing heat exchanger. The power plant could also recover latent heat due to condensation as well as sensible heat due to lowering the flue gas exit temperature. Additionally, harmful acids released from the stack can be reduced in a condensing heat exchanger by acid condensation. Condensation of vapors in flue gas is a complicated phenomenon since heat and mass transfer of water vapor and various acids simultaneously occur in the presence of non-condensable gases such as nitrogen and oxygen. Design of a condenser depends on the knowledge and understanding of the heat and mass transfer processes. A computer program for numerical simulations of water (H2O) and sulfuric acid (H2SO4) condensation in a flue gas condensing heat exchanger was developed using MATLAB. Governing equations based on mass and energy balances for the system were derived to predict variables such as flue gas exit temperature, cooling water outlet temperature, mole fraction and condensation rates of water and sulfuric acid vapors. The equations were solved using an iterative solution technique with calculations of heat and mass transfer coefficients and physical properties. An experimental study was carried out in order to yield data for validation of modeling results. Parametric studies for both modeling and experiments were performed to investigate the effects of parameters such as flue gas flow rate, cooling water flow rate, inlet cooling water temperature and tube configurations (bare and finned tubes) on condensation efficiency. Predicted results of water and sulfuric acid vapor condensation were compared with experimental data for model validation, and this showed agreement between experimental data and predictions to within a few percent. The most important parameters affecting performance of the condensing heat exchangers was the ratio of cooling water to flue gas flow rates, since this determines how much heat the cooling water can absorb. The computer program simultaneously calculates both water vapor condensation and sulfuric acid condensation in flue gas along downstream. Modeling results for prediction of sulfuric acid vapor concentration in the flue gas were compared with measured data obtained by the controlled condensation method. An analytical model of sulfuric acid condensation for oil-firing showed two trends — steep reduction within the high temperature heat exchanger and smooth reduction within lower temperature heat exchanger, which is in agreement with experimental data.

Use of Condensing Heat Exchangers in Coal-Fired Power Plants to Recover Flue Gas Moisture and Capture Air Toxics

2013 ◽  
Author(s):  
Edward Levy ◽  
Harun Bilirgen ◽  
Joshua Charles ◽  
Mark Ness
Keyword(s):  
Water Vapor ◽  
Heat Exchanger ◽  
Power Plant ◽  
Flue Gas ◽  
Heat Exchangers ◽  
Power Plants ◽  
Operating Conditions ◽  
Dew Point ◽  
Air Toxics ◽  
Condensing Heat Exchanger

Heat exchangers, which cool boiler flue gas to temperatures below the water vapor dew point, can be used to capture moisture from flue gas and reduce external water consumption for power plant operations. At the same time, thermal energy removed from the flue gas can be used to improve unit heat rate. Recent data also show that emissions of air toxics from flue gas would be reduced by use of condensing heat exchangers. This paper describes results from a slip stream test of a water cooled condensing heat exchanger system at a power plant with a lignite-fired boiler. The flue gas which flowed through the heat exchangers had been extracted from a duct downstream of the electrostatic precipitator. Measurements were made of flue gas and cooling water temperatures, flue gas water vapor concentrations, and concentrations of elemental and oxidized Hg at the inlet and exit of the heat exchanger system. Condensed water was also collected and analyzed for concentrations of H2SO4 and HCl. Results on the effects of the condensing heat exchanger operating conditions on oxidation and capture of Hg and on the capture of sulfuric and hydrochloric acids are described.

scholarly journals The Correlation of Coupled Heat and Mass Transfer Experimental Data for Vertical Falling Film Absorption

1999 ◽  
Author(s):  
William A. Miller ◽  
Majid Keyhani
Keyword(s):  
Experimental Data ◽  
Mass Transfer ◽  
Water Vapor ◽  
Heat And Mass Transfer ◽  
Mass Fraction ◽  
Operating Conditions ◽  
Falling Film ◽  
Design Data ◽  
Vertical Column ◽  
Absorption Chillers

Abstract Absorption chillers are gaining global acceptance as quality comfort cooling systems. These machines are the central chilling plants and the supply for comfort cooling for many large commercial buildings. Virtually all absorption chillers use lithium bromide (LiBr) and water as the absorption fluids. Water is the refrigerant. Research has shown LiBr to be one of the best absorption working fluids because it has a high affinity for water, releases water vapor at relatively low temperatures, and has a boiling point much higher than that of water. The heart of the chiller is the absorber, where a process of simultaneous heat and mass transfer occurs as the refrigerant water vapor is absorbed into a falling film of aqueous LiBr. The more water vapor absorbed into the falling film, the larger the chiller’s capacity for supporting comfort cooling. Improving the performance of the absorber leads directly to efficiency gains for the chiller. The design of an absorber is very empirical and requires experimental data. Yet design data and correlations are sparse in the open literature. The experimental data available to date have been derived at LiBr concentrations ranging from 0.30 to 0.60 mass fraction. No literature data are readily available for the design operating conditions of 0.62 and 0.64 mass fraction of LiBr and absorber pressures of 0.7 and 1.0 kPa. Experiments were conducted on an internally cooled smooth tube 0.01905 m in outside diameter and 1.53 m in length. Tests were conducted with no heat and mass transfer additive. The data, for testing at 0.62 and 0.64 mass fraction of LiBr, were scaled and correlated into both Nusselt (Nu) and Sherwood (Sh) formulations. The average absolute error in the Nusselt correlation is about ±3.5% of the Nu number reduced from the experimental data. The Sherwood correlation is about ±5% of the reduced Sh data. Data from the open literature were reduced to the authors’ Nu and Sh formulations and were within 5% of the correlations developed in the present study. Hence, this study provides correlations for the complex heat and mass transfer process that is validated against extensive experimental data. The study therefore contains useful information for the design of a vertical column absorber operating with no heat and mass transfer additive.

Influence of Flue Gas Turbulence Intensity on the Heat and Mass Transfer and Pressure Drop Inside a TMC Based Heat Exchanger

2021 ◽  
Author(s):  
Saja Al-rifai ◽  
Cheng-Xian Lin
Keyword(s):  
Mass Transfer ◽  
Reynolds Number ◽  
Heat Exchanger ◽  
Pressure Drop ◽  
Turbulent Flow ◽  
Heat And Mass Transfer ◽  
Turbulence Intensity ◽  
Flue Gas ◽  
Condensation Rate ◽  
The Impact

Abstract In this study, a numerical analysis of turbulent flow heat and mass transfer in the cross-flow transport membrane condenser (TMC) based heat exchange was carried out. The heat exchanger under investigation was designed to recover both sensible and latent heat due to transport of heat and mass through a nanoporous ceramic membrane in the bundle of tubes of the heat exchanger. The shear stress transport SST k-ω turbulence model was used to model the turbulent flow of the flue gas mixture. The condensation rate of the water vapor from the flue gas were calculated using a mixed condensation model. The mixed model was based on the capillary condensation and wall condensation in the membrane tube. The numerical study was focused on the investigation of the impact of the turbulence intensity of the flue gas at various inlet conditions, such as Reynolds numbers and temperatures, on the heat and mass transfer and pressure drop characteristics. The numerical results were validated against the experimental results reported in the literature. Different tube diameters were used in the simulation, with the Reynolds number varied from 3000 to 10000. The results showed that an increase in turbulence intensity led to a significant increase in the turbulent kinetic energy, condensation rate, average convective Nusselt number and change on the pressure drop in the heat exchanger. The effects of inlet flow Reynolds number and tube diameter on the heat and mass transfer were also presented and discussed.

A New Approach to Delay or Prevent Frost Formation in Membranes

2018 ◽  
Vol 141 (1) ◽  
Author(s):  
Pooya Navid ◽  
Shirin Niroomand ◽  
Carey J. Simonson
Keyword(s):  
Experimental Data ◽  
Mass Transfer ◽  
Water Vapor ◽  
Numerical Model ◽  
Heat And Mass Transfer ◽  
Moisture Transfer ◽  
Frost Formation ◽  
Permeable Membrane ◽  
New Approach ◽  
Temperature And Humidity

Saturation of the water vapor is essential to form frost inside a permeable membrane. The main goal of this paper is to develop a numerical model that can predict temperature and humidity inside a membrane in order to show the location and time of saturation. This numerical model for heat and mass transfer is developed to show that frost formation may be prevented or delayed by controlling the moisture transfer through the membrane, which is the new approach in this paper. The idea is to simultaneously dry and cool air to avoid saturation conditions and thereby eliminate condensation and frosting in the membrane. Results show that saturation usually occurs on side of the membrane with the highest temperature and humidity. The numerical model is verified with experimental data and used to show that moisture transfer through the membrane can delay or prevent frost formation.

Simulation of Heat and Mass Transfer Involving Vapor Condensation in the Presence of Non-Condensable Gases in Plane Channels

2011 ◽  
Author(s):  
Mohammad Saraireh ◽  
Graham Thorpe ◽  
Jun-De Li
Keyword(s):  
Heat Transfer ◽  
Mass Transfer ◽  
Water Vapor ◽  
Heat And Mass Transfer ◽  
Cooling Water ◽  
Vapor Condensation ◽  
Transfer Coefficients ◽  
Cfd Simulations ◽  
Constant Wall Temperature ◽  
Mass Fractions

Results from computational fluid dynamics (CFD) simulations of heat and mass transfer involving the condensation of vapor in the presence of non-condensable gases in plane channels are presented. The simulations were carried out using FLUENT®. Convective heat and mass transfer and vapor condensation at a constant wall temperature were first investigated with the aim of comparing the CFD results with well established correlations. CFD simulations of heat and mass transfer and water vapor condensation in the presence of non-condensable air were then carried out for constant heat transfer coefficients for the condensation wall and coolant with different mass fractions of water vapor and inlet velocities. The predictions obtained from this are compared with experimental data and reasonable agreement has been found for the condensation rates of water vapor and heat flux. Finally, the condensation of the water vapor was simulated in a heat exchanger including both the cooling water and vapor-air mixture channels separated by solid walls. This simulation is close to reality and no assumptions are required for the temperature or heat transfer coefficient at the condensing wall. The difficulties of simultaneously simulating a gas mixture and liquid flowing in separate channels using commercially available CFD software are discussed and strategies to overcome these difficulties are outlined. Preliminary results from this third simulation will also be presented and compared with available experimental results.

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