УПРАВЛЕНИЕ КАЧЕСТВОМ ОБОРОТНОЙ ВОДЫ ТЕПЛООБМЕННОГО ОБОРУДОВАНИЯ
Лебедик Е.А.1, Шариков Ю.В.2 , Железнов В.В.3
1 аспирант 3 – го года обучения, Национальный минерально-сырьевой университет «Горный», 2 Профессор, доктор технических наук, Национальный минерально-сырьевой университет «Горный», 3 инженер-технолог, ООО «Научно-инженерный центр «Креон»
УПРАВЛЕНИЕ КАЧЕСТВОМ ОБОРОТНОЙ ВОДЫ ТЕПЛООБМЕННОГО ОБОРУДОВАНИЯ
Аннотация
В этой статье, рассмотрена значимость оборотной воды на промышленных металлургических предприятиях. Описаны методы прогнозирования свойств воды по индексам Ланжелье, Ризнара, Ларсона-Скольда. Определены основные возникающие проблемы – накипь, биообрастания и коррозия. Предложена технологическая схема коррекционной обработки воды системы оборотного водоснабжения.
Ключевые слова: автоматизация, реагент, контроль, оборотное водоснабжение, коррекционная обработка, качество.
Lebedik E.A.1, Sharikov Y.V.2, Zheleznov V.V.3
1 Postgraduate student, National Mineral Resources University (Mining University); 2 Professor, PhD in Engineering, National Mineral Resources University (Mining University); 3 processing engineer, Ltd Research and Engineering Center "Creon"
QUALITY CONTROL OF CIRCULATING WATER OF WATERHEAT EXCHANGE EQUIPMENT
Abstract
In this paper, we have considered the importance of recycled water in industrial steel mills. Methods have been described for predicting the properties of water in the indices Langelier, Riznar, Larson-Skold. The main problems that the paper arises are scale, biofouling and corrosion. The flowsheet of water correction of circulating water supply is proposed.
Keywords: automation, reagent, control, water recycling supply, correctional treatment, quality.
Water plays a huge role and is widely used in most industries, including metallurgical. Industrial enterprises of metallurgy are subject to strict control to protect the environment, water consumption, quantity and quality of wastewater discharged.
A large volume of water from industrial smelting facilities after use for industrial purposes is not soiled at all or very slightly contaminated and heated. In case of insufficient power of a natural source of supply or a large cost of required amount of water is necessary or economically viable the discharged water by an enterprise to cool and apply again for use on the same site [1].
The consumption by industrial enterprises of the cooling water is very high (65-80% of water consumption in the industry). In this regard a water recycling system plays a major role in water supply companies [2].
As a result of the evaporation of the water in coolers the concentration of mineral salts dissolved in the circulating water recycling systems increases. At certain concentrations of salt dissolved in water temporary hardness (mainly calcium carbonate СаСО3) may precipitate out of it in heat exchangers which dramatically reduces the heat transfer coefficient of heat exchange equipment and degrades its performance indicators. To prevent loss of hardness is made constant purging water recycling system, i.e. a removal of part of the circulating water [1].
The balance of water must be drawn for circulating of water supply systems, taking into account the losses must be reset and the addition of water to the system to compensate for the loss of it [5].
In addition to hardness salts in the tubes of heat exchangers can be deposited oxygen corrosion, mechanical suspension and biological organisms contained in the water, which also drastically reduces the coefficient of heat transfer tubes. In view of this water treatment is important in cooling aimed to prevent scaling, biofouling, corrosion of devices and pipes and to ensure optimal conditions for the operation of [7]. The main types of water quality problems are interrelated and are presented in Figure 1.
Fig. 1. Principal types of water quality problem and interrelation between them.
To fight corrosion in closed systems is recommended chromate to be added into distilled or demineralized water [7].
To control fouling circulating water treatment with chlorine, bromine and biocidal agents are used [1].
The purification of entering water into the system from mechanical impurities is generally carried out by grids, sometimes via sinkers, mechanical or sand filters.
The need for cooling water treatment to combat scale occurs mainly for circulation systems. To do this these methods are used: acidification, recarbonation, phosphate treatment [7].
Maintaining the quality of water in circulating systems takes into account evaporation as an important factor in optimal operation of metallurgical production. Deterioration of water quality leads to the "inferiority" of the equipment reducing the efficiency and productivity of steel production. In the long run it leads to deterioration in the quality of the product and economic losses.
Accurate knowledge of the requirements to water requirements, providing systems industrial water supply with optimal water consumption, to evaluate possible areas and promising areas of application of the method of water treatment for certain types of natural and waste waters, reaching for production purposes, to choose the optimal flow diagram of decontamination [2].
Today there are different methods to control the quality of recycled water. The stability of the composition of water is one of the main indicators of its quality [6]. The most well-known and well-designed method of assessing corrosion corrosive-scale properties of water is the method of Langelier.
This method of qualitative evaluation of the properties of water was developed by chemist Langelier in the 30 years of the twentieth century. According to chemical analysis it is calculated Langelier Index (IL), whose magnitude is to evaluate the ability of water to cause the corrosion of steel, or a tendency to scale formation.
Langelier index is proposed to consider the (digital indicator) properties of water such as:
 |
(1) |
- hydrogen ion exponent measured with a pH meter;
- hydrogen ion exponent in terms of saturation of water with calcium carbonate.
If, 
, i.e.it has negative value, such water causes corrosion of steel. If 
, this water is neutral, stable. It does not cause corrosion or scaling. If 
, i.e. is a positive magnitude, this water tends to cause scale formation on the surface of pipes, heat exchangers and equipment. The sign and magnitude of IL characterizes corrosive-scale properties of water.
The next method of assessing corrosive scale properties of water is stability index by Riznara (ISR). As well as the Langelier Index, ISR is based on accounting solute concentration. Riznar offers to determine the relationship between the solubility of calcium carbonate scale formation. Riznara index is calculated by the equation:
 |
(2) |
Findings from the evaluation of ISR according to the equation (2):
- ISR < 6 water tends to form deposits. This tendency increases with decreasing values of ISR;
- ISR> 7 - calcium carbonate is deposited, but the surface of the steel from corrosion not protect;
- ISR> 8 - with increasing intensity increases in proportion to the ISR corrosion [3].
Index Larson-Skold (ILS) characterizes the corrosion ability of water with respect to the low-carbon steel and stainless steel designs.
 |
(3) |
ILS establishes a causal relationship between the usual corrosion rates and a sharp increase in its speed. ILS is interpreted as follows:
- ILS <0.8 - chlorides and sulfates have no effect on the natural formation of a protective film;
- 0.8 <ILS <1.2 - chlorides and sulfates are difficult formation of a protective film. There is a higher, in comparison with the normal rate of corrosion of steel;
- ILS> 1.2 - high speed pitting with increasing index values [4].
In order to achieve the stability of the water and the required quality control system is used. Under the control of the quality of recycled water means the automation of the processes of the correctional process and purge the SOC, solves the problem of maintaining the optimal operation of heat exchange equipment of metallurgical production. The control system solves the main problems of the SOC - scale, corrosion, scale and fouling [8].
The company Nalco which is part of the corporation Ecolab has got great achievement in the field of automatic control system of water quality.
Its technology 3D TRASAR cooling water includes a unique monitoring in real-time pollution with patented active substances, patented resistance to stress chemical composition and information services, working 24/7 to detect, identify and ensure effective control of scale and corrosion and microbiological control of cooling systems [8].
It is actual the creation of automated control system, based on a new technological solution - creating a system of controlling the supply of stabilization reagents and purge the system of water recycling on the basis of the developed method for the trouble-free operation of heat exchange equipment.
In view of the major water quality problems in heat exchangers proposed flowsheet correction water treatment circulating water supply in Figure 2.
Fig. 2. A flowsheet of water correction of circulating water supply.
The circulation loop of circulating water cooling system provides lateral mechanical cleaning of the bypass line from mechanical impurities and suspended solids. After passing through the purification step is a stream through conduit with sensors mounted thereon. In the pipeline input points of the reactants are set up. Reagent dosing unit includes 4 plastic tank level sensors, metering pumps. Dosing monitoring and visualization reagent level in the tank is carried out by a programmable controller.
According to the main bypass line back purging system is provided, the flow purge valve is adjusted manually on the device according to a visual inspection. Opening/closing of the solenoid valve (SV) located on the line purge is carried out by command of the controller. The program recorded two independent control algorithms SV, as well as the desired range of values of indicators, supported by the system in working circuit.
The pulse flowmeter transmits a certain number of pulses depending on the volume passed through the purge water.
The program controlling the growth of microorganisms in circulating water controls the operation of two pumps, metering primary and preventive biocide. This program consists of two parts:
- program main biocide dosing is carried out on the value of the concentration, transmitted through the transmitter signal from the sensor to the controller;
- program preventive biocide dosing is carried out by the controller's built-in programmable timer. The program data are entered, namely: the necessary dose of the month and time of day to run the operation.
The proposed scheme - the purpose of the control in the operation of automation systems corrective treatment of circulating water supply to ensure reliable operation at the circulating water supply integrated equipment and, consequently, of the industrial enterprise.
Development of technical solutions for the control of water quality parameters, through the use of new techniques will significantly reduce the number of required reagents and water for scavenging. The proposed system solves the problem of maintaining the optimal operation of heat exchange equipment in which provides reliable and durable operation.
References
- Abramov N.N. Water supply. Textbook for high schools. Ed. 2, revised, recast and corrected. M. Stroyizdat, 1974. - 480 p.
- Zhurba M.G., Sokolov L.I., Govorov J.M. Water supply. Design of the systems and structures: 2nd Edition, revised and corrected. Publisher. - M .: Publishing house DIA, 2003. - 288 p.
- Allowance for design automation and control systems of water supply (to the SNIP 2.04.02-84)
- Prysyazhnyuk V.A. Water analysis: objectives, methods, forecasting properties. «SOK» №№ 6-7 / 2005. Journal of Plumbing, Heating, Air Conditioning.
- SNIP 2.04.02-84. Water supply. External networks and facilities. - M .: Stroyizdat. 1986. – 120 p.
- Sukhotin A.M., Bogachev A.F., Palmsky V.G. and others. The corrosion resistance of the equipment of chemical plants. Corrosion under the influence of heat transfer fluids, refrigerants and working fluids: Right. Ed .// Ed. A.M. Sukhotina, V.M. Berenblit. - L.: Chemistry, 1988 - 360 p.; with illustrations.
- Frog B.N., Levchenko A.P. Water: Training. manual for schools. - Moscow: Moscow State University Press, 1996. - 680, 178, ill.
- Technology 3D TRASAR® cooling water: [electronic resource] // NALCO, 2013. URL: http://ru-eu.nalco.com/eu/services/3d-trasar-cooling-water.htm (Date of treatment 09.15.2014)