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Abstract

Сontent

Introduction

Currently, water is widely used in various industries as a coolant, including heat and energy, but it can not be used in thermal power plants without pre-treatment, as modern thermal power plant (TPP) in the energy cycle using high-quality water. TPP modern equipment operated under high thermal loads, which requires strict limits on the thickness of deposits on the heating surfaces, the temperature range of metal working for the campaign. Such deposits are formed from substances coming in power cycles, including with added water, therefore ensuring a high quality water-cooled thermal power plants is essential. Using high quality water coolant also simplifies the tasks of obtaining pure steam, minimize corrosion rates of structural materials of boilers, turbines and equipment condensate-feed circuit.

When operating thermal power equipment may occur various undesirable phenomena associated with the quality of water and steam. The first phenomenon leads to the release of water from the solids (deposits) deposited predominantly on the metal surface of the boiler, turbines, heaters. The second phenomenon leads to the separation of suspended particles (sludge), which over time may form deposits on the surface of the partition. Water or vapor upon interaction with structural elements may be partly dissolve them, and then precipitating the corrosion products. Furthermore, there are chemical compounds and gases contained in the water and entering the trace the contour of TPP priming water, and as a result vnutrikonturnyh corrosion processes. The most common of these are dissolved in water, sodium and potassium chlorides, sulfates and carbonates of calcium, magnesium, silica, iron ions, oxygen, oils, petrochemicals, and others.

Thus, the quality of water treatment on the TPP closely connected with reliable and economical operation of modern high energy boiler and turbine equipment, security of energy installations.

1. Theme urgency

The problem of automation of processes of chemical water treatment thermal power plants (TPP) is relevant due to the following circumstances:

  1. Workflow chemical water to a significant degree is crucial for the effective operation of the main equipment of combined heat and power (CHP) and heating systems, which, in particular, indicates a high social significance of this process. Chemical water quality is one of the most significant factors that directly form the main characteristics of electricity and heat to the public and industry.

  2. Backfeed of heating equipment is very cumbersome, is spread over a large area of chemical plant and partly outside it, making it difficult to effectively manage the organization manually.

  3. Workflow chemical water belongs to a class of discrete-continuous processes , while long-haul traffic flows operational decisions without automated and efficient distribution of information difficult.

  4. Availability streams containing aggressive components, requires continuous monitoring of the state of correct valve and piping.

This work is relevant, since the chemical water treatment is widely used in practice with regard to the energy industry is not only in thermal power plants, but also in nuclear power plants and, of course, equipped with the appropriate automation. In some such TPP ACS absent, although the process of chemical water treatment is carried out, gives products, but manually controlled operators. Why we need to design and put into operation the SAR chemical treatment of water.

2. Analysis automation object

2.1 Flow diagram of the facility

Chemical water treatment complex process, which is a combination of the following processes: heating source water; clarification, the produced water; Mechanical cleaning, which is carried out by mechanical filters; Chemical cleaning, which is an ion exchange; deaeration process (getting rid of the air molecules). It is the sequence of these processes in terms of automation is presented in Figure 1.

Figure 1.1 - Process flow chart demineralizer
(анимация: 5 кадров, интервал 500 мс, 96 килобайт)

In Figure 1 are designated: 1 – control unit performance (flow of raw water); 2, 4 – control valves; 3 – raw water heater; 5 – temperature controller; 6 – clarifier; 7 – storage tank; 8 – pump; 9 – mechanical filter; 10 – demineralizer; 11 – chemical softening filters; 12, 14 – bleeders (Installations for the disposal of oxygen); 13, 15 – nourishing and suction pumps.

2.2 Principle of operation of the system

Water is supplied to the internal needs of TPP, including for the preparation of additional water to make up demineralizer. One of the main factors contributing to the efficiency of deposition processes is heating water. Feed water enters the paropodogrevatel where served and couples. Since the temperature to which the raw water needs to be heated strongly set (30ºC), the flow of steam is carried out at a constant pressure, and heating occurs by changing the flow of steam. The output of paropodogrevatelya obtain a predetermined water temperature which is fed to the clarifier, where it is the initial stage of water purification.

The initial stage of water treatment – pre-treatment – needs to improve the technical and economic indicators of subsequent stages of water treatment, and also because in the absence of pretreatment use many methods in subsequent stages purification meets with considerable difficulties.

Presence of various impurities in the raw water is the reason for the cooking water feeding and filling outlines several steps. First out of the water removed and coarsely dispersed colloidal particles by precipitation, which includes the processes of coagulation and liming conducted in the clarifier.

Source water flows through the dispenser in an air, thence the outlet line through regulating nozzle is directed into the mixing portion of the bottom cone clarifier. This also lime milk is fed and a coagulant solution. Mixing water and the reagents is ensured by the tangential supply of water into the conical housing part. Regulating nozzle allows you to change the rate of flow of water into the mixing portion of the housing. As head of the treated water in the clarifier rotational motion is damped due to the presence of vertical walls and soothing mixing lattice. The interaction of the input reactants from the treated water, a precipitate (sludge). The treated water, having an upper distribution grid via a collecting box is displayed in the interim from the clarifier tank. Evolved in the tailings pond sediment partially compacted and drained water from the purge. Shlamouplotnitelya purging is carried out continuously. Sand that accumulates in the bottom of the cone clarifier is periodically removed through a drain clarifier.

After putting in a certain natural water coagulant dose turbidity occurs first, then over time formed loose of visible flakes settling down and drags the suspended solids. At the same time an increase in the transparency of source water.

As a coagulant used ferrous iron sulfate (iron sulfate). Treating water with slaked lime, calcium hydroxide, called liming. The main purpose of liming – reduced bicarbonate alkalinity of water. Simultaneously decreasing stiffness TDS concentration grubodisperstnyh impurities of iron compounds and silicic acid. Increasing pH of the water to reduce the bicarbonate alkalinity produced slaked lime that is fed into the water as a suspension (milk of lime).

Thus, as can be seen from the clarification process, it becomes apparent that it is necessary to regulate the amount of water supplied to the clarifier, the amount of coagulum and the amount of alkali. According to the technology necessary to lighten the water initially loaded into the clarifier fed alkaline solution, and after 5 minutes apply coagulant solution. The main task is to provide brightening pH-specified parameter.

Coming bleach water flows into the intermediate tank, whose main task is to control the system performance. This is done by changing the water level in the tank of the clarified water. Thus, at this stage it is necessary to maintain the predetermined water level in the tank.

Intermediate tanks softened water is pumped for further treatment on the mechanical filter. Water clarification when skipping through mechanical filter is the result of sticking to the particles of the granular filter media particulate pollutants source water under the action of the molecular forces of attraction. The intensity of adhesion is greater than the stability of the particles is less aggressive. Last reduced as a result of water pretreatment coagulant. Thus formed flakes easily stick to grain loading and high bleaching effect is achieved at a relatively high speed filtration. Currently mechanical filter loaded titanium chips.

Water subjected to pre-treatment, almost does not contain impurities grubodisperstnyh largely exempt from the colloid. Thus, the produced water should be characterized by the following parameters:

3. Goals and objectives of the research

Proceeding from the above, for making common tasks you need to apply the system decomposition into three subsystems, as the solution of the problem is not solved water treatment chemical research, monitoring and control of a single process. Thus, clearly distinguished the three subsystems:

  1. Water Heater;
  2. Dodge;
  3. Storage tank.

Clearly, the challenge is to develop a heater control system for automatic monitoring of the heating source of water that enters the heat exchanger. Necessary to provide hot water to the optimum level, meaning that for the considered process, defined on the basis of the research and operational experience of the heat exchanger in the chemical treatment and is 30º С.

The objective of the illuminator is to develop a system of stabilization of pH-parameter, which is estimated at the outlet of the clarifier. The optimum value must match 10,0 for the process that was defined by the research.

The object of controlling the flow of source water is maintaining the water in the intermediate tank at the desired level with a possible deviation from the range of 20 межуточном баке на необходимом уровне с возможным отклонением 20 – 30 %, which will characterize the system performance.

Based on the above problems, it is clear that the pretreatment process management objective generally is to provide adequate flow at its desired water temperature and pH-value of the parameter. Achieving this goal can be done manually, semi-automatically or automatically. In any case, the main objective is to obtain a desired control performance and subordinate objective is to achieve the required temperature at the outlet of preheater and the pH of the parameter at the outlet of the clarifier.

In accordance with the plan should aim to automate the process of maintaining the desired temperature at the outlet of paropodogrevatelya, pH-parameter output of the illuminator and water flow in paropodogrevatel what will affect the water level in the intermediate tank.

The aim of this work is to improve the performance demineralizer and improving the quality of the water received through the introduction of a new automated control system.

4. Design of automatic control system

4.1 Overview and analysis of known solutions

Overview and analysis of known solutions In this section, carry out a study of existing automated facilities, consider their structure in terms of technological devices, as well as to identify shortcomings and advantages. Process control chemical treatment of water Novogorkovskaya TPP performed APCS based on microprocessor technology Siemens. Controller SIMATIC 417-4H is a senior in the lineup duplicate controllers SIEMENS, ie has maximum resources (processing power, memory, etc.). In particular, working memory controller FirmWare latest version is 30 MB. Nevertheless, the software operating system support the controller lags behind, for example, in a given controller is stored in the limit 8191 data blocks. Habitual service providing commissioning simulation I/O mapping and step by step process of washing and regeneration of the filter units HVO, led the project for the restriction on DB. Had to sacrifice convenience and partly reconstruct the program to fit within the constraints of the processor. Thus, in actual use, less than 10 % of the working memory of the controller allowable number of data blocks is already exhausted.

Characteristics of the automation system :

Lower level:

Considered automated system has several advantages, but the main drawback is the fact that it is designed for larger than the system we developed requires. The system is a PLC Siemens, which imposes significant financial embezzlement.

4.2 Justification for directions

To achieve this goal it is necessary to design the automation system, which will receive all necessary information about the system parameters that characterize and influence on her work.

The main objective of the ACS – increased productivity due to changes in water level in the intermediate tank. Secondary objectives are – water heating to a predetermined temperature and maintaining the pH-value parameter in unstable water consumption.

Measurement of the current value of the temperature is performed by means of temperature sensors, pH-value setting – using pH-meter, the flow rate – using a flow meter. Data processing and issuing control signals to the valves will be made by a programmable logic controller (PLC).

Similarly, will be monitored in the condensate level paropodogrevatele; temperature steam, water and raw water in an illuminator; flow of water and chemical reagents, as well as the pressure in the tanks. This will be installed following encoders:

To eliminate the emergency on exceeding the maximum water level in the intermediate tank minimum level required to enable/disable the pump. When you exit the allowable limit pH is necessary to block/open the appropriate valves. When temperature falling outside the permissible value is necessary to block/open the appropriate valves.

Conclusion

In the course of the work was designed ACS chemical cleaning process water to the power station. ACS effectively solves the tasks assigned to it, thus achieving the goal set for the system – to maintain a given level of water temperature, pH-setting and water flow. Analysis of the current state of the problem of automation systems, chemical cleaning large TPP showed that the developed system is more effective and cheaper to build, than the use of ready-made options from leading companies.

As a result of developments obtained economical and reliable system.

According to the results of this project, you can examine in more detail the strengths and weaknesses of the resulting ASC for further improvement of the system, eliminate defects and improve system efficiency.

This master's work is not completed yet. Final completion: December 2014. The full text of the work and materials on the topic can be obtained from the author or his head after this date.

References

  1. Лукас В. А. Теория управления техническими системами. Учебный курс для вузов. Екатеринбург: Издательство УГГГА, 2002. – 675 с.
  2. Дорф Р., Бишоп Р. Современные системы управления. – М.: Лаборатория Базовых знаний. – 2002 – 832 с.
  3. Федюн Р. В., Попов В. А., Найденова Т. В. Принципы построения динамической модели процесса биохимической водоочистки. Наукові праці ДонНТУ. Серія: Обчислювальна техніка та автоматизація. Випуск 20 (158). – Донецк, ДВНЗ “ДонНТУ”, 2010. – с. 30 – 37.
  4. Федюн Р. В., Найдьонова Т. В., Юрченко Р. В. Математична модель технологічного процесу біохімічного водоочищення. Наукові праці Донецького національного технічного університету. Серія: Обчислювальна техніка та автоматизація. Випуск – 22(200) – Донецьк, ДонНТУ, 2012. – с. 48 – 55.
  5. Федюн Р. В., Попов В. О., Бунєєв В. О. Автоматичне управління гідравлічними параметрами системи водопостачання. Наукові праці ДонНТУ. Серія: Обчислювальна техніка та автоматизація, Випуск 14 (129). – Донецк, ДонНТУ, 2008. – с. 54 – 63.
  6. Плановский А. Н., Рамм В. М., Каган С. З. Процессы и аппараты химической технологии – 2е здание, дополн. – М.: Госхимиздат, 1962. – 846 с.
  7. Рыбалев А. Н. Автоматическое управление энергетическими установками А. Д. Качан. – Благовещенск, 2007 – 94 с.
  8. Иванова Г. В. Автоматизация технологических процессов основных химических производств: Методическое пособие/ СПбГТИ(ТУ). – СПб., 2003 – 140 с.
  9. Федюн Р. В., Попов В. О., Бунєєв В. О. Автоматичне управління гідравлічними параметрами системи водопостачання. Наукові праці ДонНТУ. Серія: Обчислювальна техніка та автоматизація, Випуск 14 (129). – Донецк, ДонНТУ, 2008. – с. 54 – 63.
  10. Ефимов В. Т., Молчанов В. И., Ефимов А. В. Методы расчетов в автоматизации химико-технологических и теплоэнергетических процессов: Учебное пособие. Харьков, 1998.