Thermal Deaerators Research Articles

Modeling of the process of retaining the concentration of aggressive gases during the operation of deaerators

In this article, in the process of deaeration of feed water in thermal deaerators in the saturation temperature range of 20-105 °C, a method is proposed for determining changes in partial pressure, absorption coefficient and concentration values of aggressive gases such as carbon dioxide, oxygen and nitrogen in the gas phase and dissolved in water is modeled according to Henry’s law, and the results obtained are graphically depicted; conclusions are given on how the correspondence of the saturation temperature to an increase in pressure affects the change in the concentration of aggressive gases.

Degassing Dissolved Oxygen through Bubbling: The Contribution and Control of Vapor Bubbles

An innovative yet sustainable approach for industrial deaeration is proposed, with demonstrated results and analyses, to contribute to finding solutions to improve energy efficiency in this field. Vacuum bubbling deaeration, sharing the same working principles of solubility control and the mass diffusion through vapor (or steam) with conventional thermal deaeration processes, works, however, at lower vacuum pressures. It neither resorts to heating nor requires any third-party materials such as membranes or gases, achieving orders of magnitude of reduction in the expected energy consumption in a simple and concrete way. In this study, the mechanisms of vapor bubble generation and retention were discussed by employing a vacuum bubbling model based on the experimental apparatus at Kongju National University, which uses a venturi-nozzle bubbler. The four parameters influencing vapor bubble generation and retention were identified as vessel pressure p1, nozzle depth Δh, nozzle performance p4−p3, and water temperature Tw. A series of deaeration experiments using the present approach for a tap water sample of 360~400 L were conducted under four different conditions to investigate the effects of the water temperature, vessel pressure, and bubbler nozzle depth. Final dissolved oxygen (DO) concentrations close to zero could be achieved with a vessel pressure of p1=1 kPa, with different bubbling times to reach a zero mg/L reading of DO concentration (case 2 and 3), which demonstrates the vital roles of the vapor bubble generation condition of (psat−p3) and retention condition of (p4−psat) in achieving the lowest DO concentration. Analysis of the test results, based on the discrete-bubble model with the measured DO concentrations and degassing rates, showed promising results in reproducing the experimental data. Though the potential of vacuum bubbling deaeration is demonstrated, for the first time, to its full extent, further research efforts are encouraged in many areas, including more case-specific validation test cases with optimum operating conditions along with the study of more detailed modeling for performance prediction, including energy analysis.

Evaluation of the cost-effectiveness of solutions to improve the efficiency of atmospheric deaeration in boiler plants

The reliable and economical operation of equipment for thermal power plants, heat supply systems and boiler houses has been a relevant problem in the field of thermal power engineering for many years. In many industries, industrial steam is often used, for which steam boilers are used at thermal power plants. The water consumed by the boilers undergoes pre-treatment, which, in addition to its softening, includes thermal deaeration — the removal of aggressive gases that lead to equipment corrosion. Atmospheric deaerators are often used for this purpose. They are easy to use, quite effective, but have a disadvantage — a considerable amount of heat is lost with the removed flash steam. The article is dedicated to evaluating the cost-effectiveness of the technology for additional heating of return system water using deaerator steam and considering a method for improving the efficiency of atmospheric deaeration by partial closure of flash steam output in boiler plants. The paper presents a calculation of the scheme of operation of a deaeration plant, which makes it possible to increase the efficiency and effectiveness of the boiler house of the AB InBev Efes brewery in Ulyanovsk due to additional heating of return system water with atmospheric deaerator flash steam. The article also discusses the scheme of operation of an atmospheric deaerator, in which the flash steam will be discharged into the atmosphere only if it is necessary to remove aggressive gases. Thanks to the developed scheme, when the deaerator operates with a closed flash steam removal pipeline and without being fed with chemically purified water, the consumption of industrial steam is reduced, especially with a significant return of condensate, which increases the efficiency of the entire boiler room as a whole. According to preliminary calculations, assuming the average return of condensate from production per day of about 300 m3, the production steam savings will be 0.8 tons.

Simplified dynamic model of a nuclear reactor

The article is devoted to the issues of nuclear energy. It considers a simplified dynamic model simulating the main processes occurring in a nuclear power plant. The basis of the proposed model is a model of heat release in the reactor, simulating the relative neutron power and temperature of the coolant in the hot thread of the circulation circuit. The position of the absorbing assemblies, which determines the reactivity introduced by them, is formed in an operational control model that simulates bringing the assemblies into a pre-start state, displacement of the control assembly under the influence of a power regulator, as well as under the action of protections of various levels. The purge/recharge model describes the dynamics of the concentration of boron absorber during water exchange between the deaerator and the circulation circuit. Models of thermal deaeration, pressure compensation and heat exchange in the circuit simulate the pressure and temperature of the coolant.

Using the heat of deaerator flash steam for additional heating of return system water in boiler installations

Reliable and economical operation of the equipment of thermal heat supply systems and boiler installations is an important and challenging task. High-quality water treatment directly affects the efficiency of boiler installations. The main stages of water treatment at thermal power plants are pretreatment, desalination and thermal deaeration — removal of aggressive gases that lead to corrosion of equipment. Currently, there are a significant number of manufacturing enterprises that are equipped with their own boiler plants. In boiler houses used for steam generation, as well as heating boilers serving heating system, water deaeration is a mandatory process. The article is dedicated to the development of a technology to make the boiler installations more economical and efficient due to additional heating of the return system water with deaerator flash steam. In this paper, the process of water deaeration is considered on the example of the boiler room of the AB InBev Efes brewery in Ulyanovsk, where the heating station is equipped with automation systems, and the regulation of steam supply for heating is carried out automatically depending on the temperature of the return system water. Due to the designed arrangement and depending on the amount of flash steam of the atmospheric deaerator, the return water of the heating system can be heated by 3 - 10°C. Besides, during periods of warm winters at the Ulyanovsk-based brewery of AB InBev Efes, with minimal loads of the boiler plant, heating of the return system water in the heat exchanger with the flash steam of the atmospheric deaerator may be used as the main or additional stage of heating.

Determining the Efficiency of Desorption of Corrosive-Active Gases in Columns with Chaotic and Regular Nozzles

The process of removing corrosive gases from water at TPPs in packed columns of calciners and in columns of thermal deaerators with a storage tank in film mode is considered and a mathematical model is presented for calculating the efficiency of the desorption process. A cell model of the flow structure and an equation for calculating the mass transfer coefficient for a wave flow of a water film over the surface of a packing with artificial roughness are used. The value of the required height of the packing layer is obtained for the given density of irrigation with water and the efficiency of extracting gases dissolved in water. Formulas are given for calculating the parameters of a mathematical model: the coefficient of mass transfer in the wave film, the average velocity of water in the film, the dynamic retention of the liquid in the packing layer and the number of cells for complete mixing of the liquid phase. The possibility of using metal chaotic and regular packings is considered, and the results of calculations of the efficiency of mass transfer and the required height of the packing layer at various operating parameters of the desorption process are presented. The graphs of the required layer height for the given efficiency of mass transfer and the power spent on air supply to the desorber when using various nozzles of domestic and foreign production are presented. The article describes the operation of a thermal deaerator with a storage tank and outdated contact devices in a deaerator column at a TPP. The main mass transfer and hydraulic characteristics of modern nozzles for thermal deaerators are presented. Technical solutions have been developed that can be used when choosing a highly efficient metal chaotic packing with a rough surface, which provides an increase in the mass transfer coefficient in a liquid wave film and, accordingly, the efficiency of mass transfer. A variant for modernization of the deaeration column of the DSA-300 deaerator at the Kazan CHPP-3 by replacing outdated contact devices with a modern chaotic packing is shown. As a result of its application, compliance with the standards of water purification from dissolved oxygen is ensured at various loads on water and steam.

Dynamic Operational Characteristics for Condenser and Correlative Equipment

Effective control of condenser backpressure and outlet supercooling plays important role in thermal deaeration process. The back pressure model of condenser is established to analyze the influence of condenser pressure and temperature on circulating water flow, circulating water temperature and suction capacity of air ejector. The dynamic control characteristics and ability of the above factors to backpressure are analyzed.

The Vapor of Thermal Deaerators as a Factor of their Energy Efficiency

The effect of the vapor of thermal deaerators on the energy efficiency of these heat-and-mass transfer apparatus and the thermal power plant as a whole is considered. Problems of reducing the vapor flow rate and its use in design and operation of Russian thermal power plants are neglected. Unjustified fuel losses in thermal deaerators of poor design and the lack of control over the vapor and its recovery are exemplified. The theoretical vapor flow rates necessary for different flow patterns of deaerated water and desorbing agent in deaerators are determined. A significant advantage in the energy efficiency of the countercurrent design over the once-through design is demonstrated. It is shown that the standardized specific vapor flow rates for thermal deaerators of different types are justified inadequately. The possibility of effective deaeration of water at a specific vapor flow rate that is substantially lower than the standard one and very close to the theoretically necessary value is proved based on experimental data. It is demonstrated that there is a wide margin to improve the energy efficiency of thermal power plants by rationally using the vapor heat of thermal deaerators. A necessary condition for increasing the energy efficiency of thermal power plants is shown to be the recovery of the vapor heat and mass of thermal deaerators. To this end, the vapor coolers should be made of corrosion-resistant materials and the vapor condensate should be used in the water-steam cycle of the power plant. Another important way to improve the efficiency is to maintain the vapor flow rate consistent with the operating mode of the deaerator, which can most effectively be done by monitoring the residual content of corrosive gases in the deaerated water. A schematic of a deaeration plant with the vapor flow rate controlled by monitoring the residual oxygen content in the deaerated water is proposed. The vapor flow rate in such a plant is kept necessary and sufficient to maintain the rated desorption efficiency of dissolved oxygen in all thermohydraulic deaeration modes, thus preventing the operation of the deaerators at insufficient or excessive vapor flow rate.

Steady-state Operational Characteristics for Condenser and Correlative Equipment

Effective control of condenser backpressure and outlet supercooling plays important role in thermal deaeration process. The backpressure model of condenser is established to analyse the pressure and temperature impact of circulating water flow, circulating water temperature and suction capacity of air ejector. The steady-state control characteristics and ability of the above factors to backpressure are analyzed.

Evaluation of the efficiency of cavitation-jet deaerator in condensate return systems of remote external consumers of thermal power plants

Thermal power plants (TPPs) operate technological systems for the steam condensate return from remote external consumers. In such systems, it is necessary to protect the metal from corrosion. This will allow ful-filling the regulatory requirements for the concentration of iron compounds in the condensate entering the power plant. Such systems do not use thermal deaerators operated by using heating steam. The aim of the undertaken study is to assess the efficiency of superheated water deaerator use in such conditions, in par-ticular cavitation-jet deaerators. It means determining the effect of a new element of the system – the de-aerator – on the normalized chemical parameters of the returned condensate. A mathematical model of superheated water deaerators is used. The employed model is based on the theory of similarity of heat and mass transfer processes. The methodology for calculating the corrosion rate of return condensate pipelines was used, as well as experimental data on medium pressure TPPs. The efficiency of cavitation-jet deaerators in condensate return systems of external consumers has been estimated. A mathematical description of the system has been developed, which allows determining the required performance of deaerators and the required ratio of water recirculation through them in each mode. Recommendations for effective practical applications of the proposed technical solution have been developed considering the actual conditions at thermal power plants. It is advisable to install a deaerator according to the recirculation scheme through the condensate collection tank. This scheme, compared to a sequential scheme, enables to reduce capital costs and ensure that the deaerator operates in the highest efficiency mode. The choice of the nominal capacity of deaerators should be carried out taking into account the graphs of the change in the flow rate of incoming condensate and the concentration of dissolved oxygen in it during the day. In most operating modes of the system, it is possible to ensure compliance with the regulatory requirements for the mass concentration of corrosion products in the condensate returned to the TPP. The obtained results can be used in the design of new and improving the efficiency of existing TPPs that supply steam to external consumers.

Efficiency of Water Purification from Dissolved Gases under Weak and Strong Phase Interaction in Film Degassers

Water purification processes in film decarbonizers and thermal deaerators with different contact arrangements in the modes of weak and strong interaction between phases are considered. Weak interaction is characterized by a separate movement of phases, wherein a gas or vapor flow hardly affects the hydrodynamics of a liquid film. Such a mode is most often implemented in the case of countercurrent phases. At a gas or vapor velocity greater than 8 m/s and an atmospheric pressure, the gas flow carries the liquid film in an ascending or descending flow. In this mode, mass and heat transfer processes are greatly intensified. The modes are considered by the example of removal of aggressive corrosive gases at TPPs and industrial enterprises. Expressions are given for the calculation of the mass exchange characteristics of degassers and for the efficiency of water purification from oxygen and carbon dioxide. It is shown that a strong interaction occurs in the tubes with discrete-rough walls and a ribbon swirler, whereas a weak one takes place in irregular (chaotic) packed beds and regular corrugated packed beds with a rough surface. To calculate the efficiency of mass transfer (the extraction of dissolved gases from water), we used such flow structure models as a diffusion model and a cell model with bulk mass sources. Expressions for the calculation of model parameters—dispersion coefficients, number of cells, mass transfer coefficients in the liquid phase—are presented. The results of calculations of the mass transfer efficiency in packed columns and channels with discrete-rough walls and swirling flows are given. An example for mounting a packed bed in a DSA-300 deaerator is presented. Conclusions are drawn concerning the most rational designs and operating modes of thermal deaerators and decarbonizers.

Hydraulic resistance of thermal deaerators of thermal power stations (TPS) with jet-film contact devices

One of the methods of solving the problem of improvement of heat-mass efficiency of thermal deaerators of TPSs is application of jet-film contact devices for interaction of vapor and liquid flows. The design of these devices has been studied. Estimate calculations of hydraulic resistance have been carried out. We have obtained the equation for calculation of resistance coefficient, depending on the height of element of contact device.

Improving the efficiency of water purification from dissolved gases at TPP

The method for increasing the efficiency of thermal deaerators and calciners of a TPP is considered; it consists of the use of a turbulent mass transfer device with random small packing. Before entering the packed bed in water, air (decarbonization) or water vapor (deaeration) is supplied. Chaotic nozzle creates intense turbulent interaction mode of air (vapor) with water and splitting it into small bubbles; thus the specific surface area of the contact of phases significantly increases, and high efficiency of mass transfer (extraction of dissolved gases) is ensured. A turbulent mass transfer device is a circular channel with connections for connecting of the source water to a pipeline. Inzhekhim chaotic nozzle is used with large free volume (95%) and the specific surface area of 150–300 m2/m3. The nozzle is made of a thin metal strip that may have a rough surface and is retained in the channel by means of two grids. For the calculation of turbulent mixer, mathematical model of the flow structure is presented, which is built with the use of a one-parameter diffusion model and a semiempirical reverse mixing ratio. Accounting of interphase transfer of dissolved gases is carried out via volume source of weight. The equation to determine the weight source and calculation of its parameters is presented. In the particular case, transition to the cell model is made and an expression for calculating the profile of concentrations of dissolved gas is obtained along the channel with a nozzle. An example of calculating the efficiency of turbulent mixer upon removing dissolved carbon dioxide from water at a TPP is shown. Recommendations on the use of the considered technical device are given.

Domestic atmospheric pressure thermal deaerators

Based on many years of experience and proven technical solutions, modern atmospheric pressure deaerators of the capacity of 0.4 to 800 t/h were designed and developed. The construction of such deaerators is based on known and explored technical solutions. A two-stage deaeration scheme is applied where the first stage is a jet dripping level (in a column) and the second one is a bubble level (in a tank). In the design of deaeration columns, low-pressure hydraulic nozzles (Δp < 0.15 MPa) and jet trays are used, and in deaerator tank, a developed “flooded” sparger is applied, which allows to significantly increase the intensity of the heat and mass exchange processes in the apparatus. The use of the two efficient stages in a column and a “flooded” sparger in a tank allows to reliably guarantee the necessary water heating and deaeration. Steam or “superheated” water of the temperature of t ≥ 125°C can be used as the coolant in the deaerators. The commissioning tests of the new deaerator prototypes of the capacity of 800 and 500 t/h in the HPP conditions showed their sustainable, reliable, and efficient work in the designed range of hydraulic and thermal loads. The content of solved oxygen and free carbon dioxide in make-up water after deaerators meets the requirements of State Standard GOST 16860-88, the operating rules and regulations, and the customer’s specifications. Based on these results, the proposals were developed on the structure and the design of deaerators of the productivity of more than 800 t/h for the use in circuits of large heating systems and the preparation of feed water to the TPP at heating and industrial-heating plants. The atmospheric pressure thermal deaerators developed at NPO TsKTI with consideration of the current requirements are recommended for the use in water preparation schemes of various power facilities.

Numerical simulation of mass transfer in the liquid phase of the bubble layer of a thermal deaerator

On the basis of one-dimensional diffusion model of the flow structure and boundary layer theory, a method for calculating the mass transfer of dissolved oxygen in the liquid phase of the bubble layer of a thermal deaerator is developed. Mass transfer with the bulk source of mass has been considered, wherein the basic parameter is mass-transfer coefficient. A model of pseudo laminar boundary layer on the bubble surface is proposed, and the possibility of calculating of mass-transfer coefficient from bubbles in the mass source of diffusion model is shown, taking into account the gas content and external turbulence. A comparison of the calculation results of mass-transfer coefficient is given from the bubbles with known experimental data. It is shown that taking into account gas content results in an increase of the mass-transfer coefficient by 2–4 times. Expressions for calculations of gas content, dynamic speed, and inverse stirring coefficient in the liquid phase of the bubble layer are presented. In the special case, transition from the diffusion model of the flow structure to cell model is made, and comparison of the calculation results on the concentration of oxygen in water at the output of DSA-300 bubbling thermal deaerator with experimental data is performed. The developed mathematical model and calculation algorithm can be used in the design, diagnosis, and modernization of thermal deaerators.

Predicting the indicators characterizing the water decarbonization efficiency when using atmospheric-pressure thermal deaerators without subjecting water to steam bubbling in the deaerator tank

The results obtained from combined numerical and experimental investigations of the water decarbonization process carried out in atmospheric-pressure deaerators without subjecting water to steam bubbling in the deaerator tank are presented. More exact values of the hydrocarbonate thermal decomposition rate have been obtained, and the hypothesis about a change of the process governing mechanism in shifting to low total alkalinity values of deaerated water has been proven in the course of these investigations. A procedure for predicting the indicators characterizing the water decarbonization efficiency in using deaerators is proposed based on the obtained study results. The developed procedure features the maximally possible accuracy that can be achieved at the metrological characteristics of the standard alkalinity measurement methods.

Simulation and optimization of transients in thermal deaerators

A cellular matrix approach is proposed for calculating transients that occur during thermal deaeration with possible variations in the level of system decomposition due to the available support by empirical data. Matters relating to optimal control of the process are discussed.

Water treatment for steam generators with the aid of ion exchangers

A method for simultaneous desalting and deoxygenation of feed and extra water was developed for through steam generators using ion-exchange mixed bed filters and the filter with ferrous hydroxide electron ion exchanger which eliminates the stage of thermal deaeration.

A study of the electret state of polyethylene formulations with a ferroelectric

A method for simultaneous desalting and deoxygenation of feed and extra water was developed for through steam generators using ion-exchange mixed bed filters and the fi lter with ferrous hydroxide electron ion exchanger which eliminates the stage of thermal deaeration.

Enlarged thermal deaerators with a horizontal column for large units at nuclear power stations

We describe the new enlarged deaerators for 1000-MW power units and for a BN-800 power unit equipped with an enlarged-volume tank with one horizontal deaeration column.