Numerous substances and complex chemical agents, as well as various biocides for inhibiting the growth of microbial colonies and algae, are commercially available in the market of water treatment chemicals. In frequent cases, the chemicals offered in the market are not adapted to the water chemistry conditions of power plant circulating cooling systems (CCSs), and attempts of using them may lead to violation of the circulating water or effluent (blowdown) water quality standards. The aims of this study were to investigate the effectiveness of the VTIAMIN EKO-1 chemical agent and to select its optimal dose to reduce the corrosion rate of heat transfer surfaces and prevent mineral deposits from forming on them under the conditions of the experimental bench facility simulating the operation of CCSs for the condensers of steam turbines used at combined heat and power plants (CHPPs) equipped with a PGU-450 combined-cycle power unit. During the bench tests, the circulating and makeup water quality in terms of main indicators was monitored on a daily basis. For evaluating the corrosiveness of circulating water flowing in the experimental bench facility, a pair of corrosion rate surveillance specimens (coupons) made of St. 20 carbon steel and one brass coupon were installed at all test stages. The circulating water scale-forming properties were evaluated based on the results from visual examination and weighing of the thermal electric heater and the surveillance specimen made of stainless steel as well as the stabilization coefficient (calcium transport) calculation results. After having been evaporated, the CHPP makeup water that has not been subjected to corrective (reactant) treatment has increased scale-forming and corrosive properties with respect to carbon steels and medium-level scale-forming and corrosive properties with respect to brass. By using the VTAMIN EKO-1 chemical agent in the optimal dose, the carbon steel corrosion rate was slowed down by a factor of 3.7; the linear deposit-formation rate was decreased by a factor of 27.5, and the stabilization coefficient was kept at a level of 95.72%. In so doing, the requirements posed to the chemical agent’s key components by the standards for fishery water bodies were not violated. With the average content of the VTIAMIN EKO-1 reagent in circulating water at a level of 9.54 mg/dm3, its effectiveness in terms of corrosion protection and prevention of scale formation has been demonstrated. The estimated demand for the chemical agent is 33 397 kg/year.

Water Chemistry Development for a Thermal Power Plant Circulating Cooling System Using the VTIAMIN EKO-1 Chemical Agent

Currently, electro-membrane processes are dynamically developing technologies with many existing and still developing areas. This paper provides an overview of modern developments in the use of electro-membrane processes in the heat-and-power engineering to ensure resource and energy conservation, reduce harmful effects on the environment, and improve energy security. Electrodialysis and electrodeionization are widely used at many thermal power plants in the world and the number of such stations is constantly growing. The main attention is paid to the promising resource-saving areas of membrane technology with an industrial degree of implementation for the development at the treatment of natural water, the production of highly pure water using combined methods (electrodeionization and reverse osmosis), the disposal of highly mineralized wastewater from industrial and energy enterprises (diffusion dialysis, block electrodialysis), and energy-saving electrosynthesis―production of acids and alkalis from salt solutions (bipolar electrodialysis). When using special solutions and membranes and high temperatures, this direction can be promising.

Electro-Membrane Technologies in Energy and Industry

In 2018, combined-cycle power installations equipped with heat-recovery steam generators were commissioned at the combined heat and power plant nos. 1, 2, and 3 (CHPP-1, CHPP-2, and CHPP-3) in the city of Kazan. The content of organic substances in the blowdown water of clarifiers, in chemically demineralized water, in evaporating plant condensate, in heat-recovery steam generator feed water and blowdown water, and in turbine condensate was investigated. Organic substances in dry form were separated from water samples using the extraction method. The physicochemical properties and structures of the separated organic impurities were determined using an elemental analysis, infrared spectroscopy, high-efficient liquid chromatography, chromatography-mass spectrometry, and nuclear magnetic resonance methods. It was found that the content of total organic carbon (TOC) was higher than its standardized value in the heat-recovery steam generator feed water, slightly higher than the standardized value in the condensate of evaporators, and in compliance with the existing standard requirements in the turbine condensate and chemically demineralized water. Humic substances that are not removed from water during its pretreatment and enter in the heat-recovery steam generator feed water were identified as the main organic component. It is shown that ion exchange is an efficient technology for removing organic impurities from makeup water for the heat-recovery steam generator.

Physicochemical Analysis of Organic Impurities in the Coolant of Combined Heat and Power Plants Equipped with Combined-Cycle Power Installations

This article is devoted to optimization of parameters and structure of the industrial-heating vapor-gas facilities (HVGF). The aim of the study is determination of the optimal initial parameters of two-circuit utilization HVGF. The set goal is achieved based on the methods of the mathematical modeling of the thermal schemes, using the elements of thermodynamic economic analysis. As the optimization criterion, the index of a relative fuel economy is used upon the combined generation of the energy and heat. The most significant result of the research consists in revealing a tendency to an increase in the optimal vapor pressure of the HVGF high pressure circuit, compared to a similar parameter of the condensation vapor gas device (VGD CEPP). For the two-circuit HVGF, the optimal initial pressure is 9.8—10 MPa (for the CEPP it is 8 MPa). The tendency is revealed for an increase of the relative fuel economy upon the complication of the HVGF thermal scheme. It was established that for the identic HVGF located in different energy systems, the relative fuel economy differ greatly. The relative fuel economy for the HVGF under consideration compared to analogous VGD CEPP is 27.35 %, and compared to the vapor turbine CEPP, the relative fuel economy will increase by 8.8 %. The importance of the results obtained consists in that their application will make it possible to increase the energy efficiency of the HVGF being constructed, and optimize the structure of the energy systems of separate regions and states.

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Optimization of the Initial Parameters of the Utilization Circuit of Cogeneration Combined Sycle Plant of Two Pressure Levels

An analysis of water utilization systems at thermal power plants (TPPs) shows that highly mineralized effluent waters are mainly generated at these facilities by their water-treatment plants. Highly mineralized alkali liquid waste is presented by the products from continuous and periodic blowdowns of thermal demineralization systems and drum boilers, by spent anion exchange filter regeneration solutions, and by alkali concentrates from reverse osmosis plants. In view of the fact that the alkali used in technological processes has quite a high cost, it is economically expedient to subject alkali effluents to processing with the extraction of alkali for repeatedly using it in the production cycle. The article presents the results obtained at a TPP from experimental investigations into processing of highly mineralized alkali–salt solutions by means of electromembrane technology. The experimental investigations were carried out using the EMA-100 laboratory electromembrane apparatus and included two series of tests: a sequential diffusion–dialysis extraction with concentration by electrodialysis and a single-stage concentration by electrodialysis. As a result, a concentrated alkali solution and partially demineralized softened water were obtained. An analysis of the qualitative and quantitative compositions of the obtained products has shown the effectiveness of the proposed electromembrane processing arrangements, because an alkali solution suitable for its repeated use in the TPP water-treatment cycle was obtained in both series of tests. However, it should be borne in mind that single-stage concentration by electrodialysis is a more economically efficient and simple method, which provides high throughput and yields solutions containing satisfactorily separated alkali and salt components.

Laboratory Investigations of Processing Highly Mineralized Alkali Solutions by Means of Electromembrane Technology

In recent years, combined-cycle units with heat-recovery steam generators have been constructed and commissioned extensively in the European part of Russia. By the example of the Kazan Cogeneration Power Station no. 3 (TETs-3), an affiliate of JSC TGK-16, the specific problems for most power stations with combined-cycle power units that stem from an elevated content of organic impurities in the feedwater of the heat-recovery steam generator (HRSG) are examined. The HRSG is fed with highly demineralized water in which the content of organic carbon is also standardized. It is assumed that the demineralized water coming from the chemical water treatment department of TETs-3 will be used. Natural water from the Volga River is treated to produce demineralized water. The results of a preliminary analysis of the feedwater demonstrate that certain quality indices, principally, the total organic carbon, are above the standard values. Hence, a comprehensive investigation of the feedwater for organic impurities was performed, which included determination of their structure using IR and UV spectroscopy techniques, potentiometric measurements, and element analysis; determination of physical and chemical properties of organic impurities; and prediction of their behavior in the HRSG. The estimation of the total organic carbon revealed that it exceeded the standard values in all sources of water comprising the feedwater for the HRSG. The extracted impurities were humic substances, namely, a mixture of humic and fulvic acids in a 20 : 80 ratio, respectively. In addition, an analysis was performed of water samples taken at all intermediate stages of water treatment to study the behavior of organic substances in different water treatment processes. An analysis of removal of the humus substances in sections of the water treatment plant yielded the concentration of organic substances on the HRSG condensate. This was from 100 to 150 μg/dm3. Organic impurities in boiler water can induce internal corrosion and deposits containing products of their degradation.

Qualitative and Quantitative Analysis of Organic Impurities in Feedwater of a Heat-Recovery Steam Generator

Studies on electrodialysis concentration/desalination of concentrated salt solutions (NaCl) as a model of soft highly mineralized liquid waste have been carried out. The apparatus of the EMA line manufactured by JSC «Membranines Technologijos LT» were used as electro-membrane devices. Apparatus are distinguished by reliable operation in concentrated mineral solutions under high currents. IONSEP-HC/MC ion-selective cation- and anion-exchange membranes intended for work with highly mineralized sewage was used. Studies have shown the possibility of utilization of concentrated electrolyte solutions, as models of highly mineralized VPU waste with high efficiency. To a residual electrolyte concentration in dialysate at a level of 0.2-0.25 g/l, the unit cost of electricity for salt transfer is approximately 1 kWh/kg, the desalination ratio is 100-150. When the concentration of electrolyte in dialysate is less than 0.1 g/l, the process practically stops due to the increasing influence of the reverse diffusional salt transfer. The calculated maximum salt (NaCl) concentration in the concentrate is 15-16 mass. %

https://iopscience.iop.org/article/10.1088/1755-1315/288/1/012006/pdf

Electrodialysis concentration of highly mineralized wastes of water treatment plants modeling

The article presents an overview of experimental layout design solutions and the general operation scheme of combined heat and power systems with a high-temperature solid oxide fuel cell (SOFC). This system is an environmentally friendly and energy-saving way to produce electricity and heat. The use of high-temperature SOFCs makes it possible to obtain an electrical efficiency of 45–55%. Combining the electrochemical and mechanical system can increase the total efficiency by up to 60–65% in a hybrid power plant. This article discusses the structure and relationship between the components of a hybrid power plant and various modification options for efficient power generation. The technological schemes for existing and tested hybrid power plants with an SOFC and gas turbine are presented and described in detail. When designing a hybrid power plant, the key factors are the choice of design, heat source, and fuel-reforming method; the design of a solid oxide fuel cell and the number of modules in a stack; selecting devices for generating electricity with the development of cogeneration or trigeneration cycles (for possible use in thermal power plants and for the energy supply of social facilities); the direction of material flows within the system; pressure and tightness; and the interconnection of the hybrid power system elements. Researchers have accumulated and described in scientific papers extensive experience in designing, theoretical research, and numerical modeling of hybrid power plants with high-temperature SOFCs. It is shown that experimental hybrid power plants based on SOFCs of the megawatt class are in operation. Hybrid systems with an SOFC are designed only for the kilowatt power class. Trigeneration systems with a steam turbine exist only in the form of theoretical calculations. Trigeneration systems show the highest electrical efficiency, but the highest construction and service costs. Systems based on high-temperature SOFCs can be used for autonomous systems, and in combination with gas and steam turbines only at thermal power plants. Experimental laboratory studies are limited by the high cost of installations and the difficulties of testing the possibility of using combined heat and power systems on an industrial scale. Therefore, a more detailed study of the relationship between the units of a combined heat and power system is recommended in order to achieve the high efficiency indicators obtained from theoretical studies.

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Theoretical and Experimental Studies of Combined Heat and Power Systems with SOFCs

A turbine-condensate cooling system is one of the less stable and most hard-to-control systems of maintaining optimal water chemistry. A laboratory recycling cooling water test facility, UVO-0.3, was developed for physical simulation of innovative zero-discharge water chemistry conditions and improvement of technological flowcharts of stabilization treatment of the initial and circulating water of the recycling cooling systems at thermal power plants. Experiments were conducted in the UVO-0.3 facility to investigate the processes that occur in the recycling water supply system and master new technologies of stabilization of the initial and circulating water. It is shown that, when using untreated initial water, scaling cannot be prevented even under low concentration levels. The main reason for the activation of scale depositing is the desorption of carbon dioxide that results in alkalization of the circulating water and, as a consequence, a displacement of the chemical reaction equilibrium towards the formation of slightly soluble hardness ions. Some techniques, viz., liming and alkalization of the initial water and the by-pass treatment of the circulating water, are considered. New engineering solutions have been developed for reducing the amount of scale-forming substances in the initial and circulating water. The best results were obtained by pretreating the initial water with alkalizing agents and simultaneously bypassing and treating part of the circulating water. The obtained experimental data underlie the process flowcharts of stabilization treatment of the initial and circulating TPP water that ensure scale-free and noncorrosive operation and meet the corresponding environmental requirements. Under the bypassing, the specific rates of the agents and the residual hardness are reduced compared with the conventional pretreatment.

Development of the Technologies for Stabilization Treatment of the Water of the Recycling Cooling Systems at Thermal Power Plants

The innovative baromembrane technologies for water demineralization were introduced at Russian TPPs more than 25 years ago. While being used in the power engineering industry of Russia, these technologies demonstrated certain advantages over the traditional ion-exchange and thermal technologies of makeup water treatment for steam boilers. Water treatment units based on the baromembrane technology are compact, easy to operate, and highly automated. The experience gained from the use of these units shows that their reliability depends directly on preliminary water treatment. The popular water pretreatment technology with coagulation by aluminum oxychloride proved to be inefficient during the seasonal changes of source water quality that occurs at some stations. The use of aluminum coagulant at pH 8 and higher does not ensure the stable and qualitative pretreatment regime: soluble aluminum forms slip on membranes of the ultrafiltration unit, thereby causing pollution and intoxication as well as leading to structural damages or worsening of mechanical properties of the membranes. The problem of increased pH and seasonal changes of the source water quality can be solved by substitution of the traditional coagulant into a new one. To find the most successful coagulant for water pretreatment, experiments have been performed on both qualitative and quantitative analysis of the content of natural organic matters in the Volga water and their structure. We have developed a software program and measured the concentrations of soluble aluminum and iron salts at different pH values of the source water. The analysis of the obtained results has indicated that iron sulfate at pH 6.0−10.2, in contrast to aluminum oxychloride, is not characterized by increased solubility. Thus, the basic process diagrams of water pretreatment based on baromembrane technologies with pretreatment through coagulation by iron salts and wastewater amount reducing from 60–40 to 5–2% have been introduced for thermal power stations.

A. A. Filimonova

Papers

Qualitative and Quantitative Analysis of Organic Impurities in Feedwater of a Heat-Recovery Steam Generator

Electrodialysis concentration of highly mineralized wastes of water treatment plants modeling

Theoretical and Experimental Studies of Combined Heat and Power Systems with SOFCs

Development of the Technologies for Stabilization Treatment of the Water of the Recycling Cooling Systems at Thermal Power Plants

Enhancing the ecological and operational characteristics of water treatment units at TPPs based on baromembrane technologies