Українська   Русский
DonNTU   Masters' portal

Abstract

Сontent

Introduction

In the mining, oil, glass, chemical industry, machine building, metallurgy and other industries, large enterprises, of great importance is the problem of cooling the circulating water used in a closed technological cycle, to the desired temperature. The need to maintain the required temperature difference is caused by the specifics of certain chemical industry products, which is necessary to ensure the accuracy of the process cycle. In large enterprises, widespread tower.

The tower – a structure for cooling water with atmospheric air. Hot water in the cooling tower is cooled both by contact with cold air, and as a result so called evaporative cooling during the flow of water evaporation portion.

1. Theme urgency

Water, which departs from the cooling tower can be reused to cool process streams (in heat exchangers). The inclusion of large amounts of water used for cooling, water cycle can significantly reduce the need for fresh water, which in this case is used only for feeding the corresponding water circulation loop. In addition, the use of cooling towers in conjunction with filters allows the use of water in a closed technological cycle, which substantially improves the environmental situation in the region where the enterprise is located.

The temperature of the circulating cooling water in cooling towers, significantly affects the manufacturing equipment. Creating a water recycling systems with cooling towers has become common practice to ensure the production process. Operating experience in the cooling tower circulating water supply systems allows enterprises to reduce costs seriously consumption and discharge of process water (95%), increase the efficiency of the use of the compressor equipment (2–4%) and to ensure environmental safety.

A system of circulating water supply is one of the most important indicators of the technical level of industrial enterprises. The introduction of water recycling systems can dramatically reduce the amount of waste water discharged and reduce the need for fresh water, it gives a great economic and ecological effect.

To improve the efficiency of the process cooling water and ensuring energy savings during periods of reduced load on the cooling equipment is expedient implementation of automated process control systems (APCS) water circulating.

2. The technological process of cooling water in the cooling tower

The technological process of cooling water is as follows: hot circulating water through an underwater pipeline is supplied to each section of the distribution system and spray nozzles uniformly across the entire surface of the sprinkler. Through the input box fan draws air that rises and cools the water running down the corrugated surface of the leaves of the sprinkler. Then, cooling water flows into the tank, and the warm air through a diffuser discharged into the atmosphere. Air rising picks with small droplets of moisture. In order to reduce the loss of recirculated water at the top of the tower is installed eliminator.

Figure 1 – Scheme of the cooling tower

Figure 1 shows a diagram of the cooling tower, in which: 1 – distribution system, 2 – nozzles, 3 – irrigation, 4 – fan, 5 – input window, 6 – eliminator, 7 – difuzor, 8 – a tank

Water cooling towers transfer heat to ambient air due to surface water evaporation and heat transfer collision, the implementation of processes of heat conduction and convection. Vaporization of water caused by the difference of partial pressure of water vapor at the surface and in the core air flow heat transfer – the difference in temperature of hot water and air. Therefore, in the summer due to evaporation will be limited to 90% of heat in the winter to 70% increases the heat transfer. Among the main design features of the equipment – sprinkler polymer that provides a high cooling effect of the water at low aerodynamic drag, not clogged and is resistant against the low temperatures; as well as part of a three phase low – speed fan setting asynchronous motor type RM, impeller with plastic blades (fan) and a diffuser. The frame is made of metal towers, highly processed special anti – corrosion coating. Sheathing consists of galvanized profile sheets with polymer coating.

3. Cooling towers as a control object

In the cooling tower, the magnitude of which is controlled, is the rotational speed of the electric fan (ωф) as regulating it, you can set the initial valuechilled water temperature (tо).

Also on the tower is influenced by various disturbing factors. By perturbing factors include meteorological factors: air temperature and humidity, wind, atmospheric pressure and others - and technological factors: changes in supply (production) circulation pumps and hot water temperature (or the temperature difference of the input / output of water). The greatest influence on the process of cooling give values of the four parameters (perturbation):

• The temperature difference of hot / chilled water;

• The ambient air temperature;

• Humidity;

• Pump flow.

These four parameters are major disturbances as due to them can vary greatly initial value the temperature of the chilled water.

Figure 2 – Cooling towers as a control object

Cooling towers as a control object is shown in figure 2, where ω –  rotation speed of the electric fan (actual),tо – chilled water temperature (actual), β – humidity of the ambient air, tв – ambient temperature, Δtго – temperature drop of hot / chilled water, Q – flow pump.

4.Goals and objectives of the research

Objective is to increase the efficiency of water circulation cooling system of process equipment through the development of the automatic control block cooling towers.

The main objectives of the study:

  1. Explore the block cooling towers as an object of automatic control.
  2. Improved quality control process chilled water temperature at the outlet of the cooling tower under the influence of disturbances due to the modernization of the automatic fan cooling tower.
  3. Simulation process control water temperature at the outlet of the cooling tower when exposed to disturbances.

5. SAU Modeling and analysis of the quality of regulation.

Let's build SAU cooling towers in the package Simulink (figure 3).

Figure 3 – Model ACS cooling tower in Simulink

Simulation system will be done taking into account disturbances. The main disturbances are meteorological factors: air temperature and humidity, wind, atmospheric pressure and other technological factors: changes in supply (productivity), circulation pumps and hot water temperature (or the temperature differential input / output water). In the cooling tower models SAU selected two disturbances: the hot water temperature and humidity. Schedule the first disturbance (hot water temperature) is shown in figure 4. On the chart we see that the water temperature changes abruptly from 52° C to 55° C.

Let's add to the perturbation of the temperature of hot water, outrage humidity (Figure 4). On the chart we see that the humidity changes abruptly from 46% to 52%.

Figure 4 – Reaction SAU cooling tower on indignation hot water temperature and air humidity. (animation: 3 frames, 7 cycles of repetition, 19 kilobytes)

Based on the results: control time tp = 3800 s., overshoot σ = 5.7%, it is clear that the system copes with the disturbance with the necessary levels of quality, and additional adjustment for ACS is not needed.

Conclusion

We investigated the block cooling towers, provides general information about the cooling system circulating water. The basic specifications and design of the cooling tower fan. The analysis of the tower, as a control object.

ACS developed to formulate the purpose of cooling circulating water. The block diagram and the mathematical models of elements designed ACS developed simulation model of the control system in the package MATLAB & SIMULINK. As a control law selected PI controller, the parameters of which are preset.

After analyzing the graphs it can be concluded that the developed system remains stable and quality indicators meet the transients.

References

  1. Пономаренко В. С. Градирни промышленных и энергетических предприятий / В. С. Пономаренко, Ю. И. Арефев. – М.: Энергоатомиздат, 1998. – 376 с.
  2. Рульнов А. А. Автоматизация систем водоснабжения и водоотведения/ А. А. Рульнов, К. Ю. Евстафьев. – М.: МГСУ,–2005. –203–с.
  3. Вахромеев И. Е. Автоматизированное управление процессами в охладительных установках/ И. Е. Вахромеев, Ю. – Б. Евчина. – «Компьютерные технологии, управление, радиоэлектроника», выпуск 8, 2008г.
  4. Киянов Н. В. От электромонтажных работ до систем комплексной автоматизации / «Новости приводной техники». 2006. – № 12. –1 c.
  5. Крюков О. В. Микропроцессорное управление машинами двойного питания: Учеб. пособие / Нижегород. гос. тех. унт. – Н. Новгород, 1999. – 118 с.
  6. Камразе А. І. Контрольно – вимірювальні прилади та автоматики / А. І. Камразе, М. Я. Фитерман. – М.: Вища школа, 1980. – 208 с.
  7. Кузьмінов Г П. Основи автоматики і автоматизації виробничих процесів / Г. П. Кузьмінов. – Л.: ЛТА ім. С. М. Кірова, 1974. – 89 с.
  8. РМ4 – 2 – 78 «Системи автоматизації технологічних процесів. Схеми функціональні. Методика виконання». – М.: Проектмонтажавтоматика, 1978. – 100 с.
  9. Смоляк В. М.  Автоматизація виробничих процесів / В. М. Смоляк. – М.: Наука, 1973. – 240 с.
  10. Клюєв А. С. Проектування систем автоматизації технологічних процесів / А. С. Клюєв, Б. В. Глазов, А. Х. Дубровський. – М.: Енергія, 1980. – 345 с.