Management in technical systems
Relevance of the topic. In recent years, there has been significant progress in the creation and application of new, more economical and environmentally friendly technologies for the treatment of industrial and waste water, which reduces the burden on pollution of water bodies and rivers as a result of the ever increasing industrial and domestic human activity.
Modern requirements for the operation of treatment facilities include:
Automation is designed to fulfill these requirements.
The need to automate treatment facilities was described by scientists in the 60s and 70s of the XX century, and was presented as a mandatory norm in SNiP II —32—74 Sewerage. Outdoor networks and facilities
. When automation is introduced, the number of people involved in the technological process is sharply reduced, labor productivity increases and the likelihood of emergencies decreases, etc.
The technical advantages of automation of industrial wastewater flotation treatment are as follows:
The aim of the work is to improve the quality of the prepared solution by developing an automatic control system for the preparation of flocculant, which will reduce the cost of operation and maintenance of treatment facilities.
To achieve this goal, it is necessary to solve the following research tasks:
Research object — automatic control system for industrial wastewater flotation treatment.
Subject of research — methods of analysis and automatic control systems for flotation treatment of industrial wastewater.
Research methods. When constructing a model, control algorithms and synthesizing the structure of an automatic control system, the following were used: methods of system analysis and decomposition, methods of modern control theory, methods and algorithms for identifying a control object, methods for constructing distributed control systems based on modern network technologies, computer modeling, and analysis of experimental results.
Scientific novelty of the obtained results:
Approbation of the dissertation results at the following conferences: XIX International Scientific — technical conference of graduate students and students
Automation of technological objects and processes. Search for young people
, Donetsk, 2019
Publications. Based on the results of the dissertation, 1 printed work was published, including 1 in the abstracts of reports at scientific and technical conferences.
Structure and scope of work. The work consists of an introduction, six sections and a conclusion, set out on 69 pages of typewritten text, of which 62 pages of the main text, illustrated with 34 figures. The work contains 2 tables, a bibliography of 20 titles and 2 appendices.
Initial water is used for the needs of the main production, for the transportation of technical raw materials, for auxiliary technological processes, as well as for economic — drinking and household needs. The wastewater treatment process consists of the following technological units:
Industrial wastewater in the amount of 600 m 3 per day by gravity flows into the tank — the homogenizer of the treatment plant system, from where it is pumped into the building for mechanical and physical - chemical treatment of industrial wastewater.
Mechanical wastewater treatment is a preliminary stage that necessarily precedes complete wastewater treatment in wastewater treatment plants. The task of mechanical cleaning — remove from the water settled or suspended insoluble solid particles, fibers and coarse impurities. They can damage filters that are not designed for this type of contamination, as well as adversely affect the functioning of other equipment.
Figure 1 – Stages of homogenization and mechanical treatment of waste water
(animation speed - 16.4 number of frames - 5)
A static lattice is used as the 1st – stage. Lattices retain large to medium sized elements. The grates are mounted in the direction of the liquid flow, and the elements can be installed obliquely or vertically, but it is imperative to equip the sinuses of the grates with rake teeth that remove debris and send the waste to the belt. In the first stage, the supply of wastewater to the pressure flotation unit is carried out submersible pumps. The pumps are switched on and off when the preset water level in the averager is reached. To measure the level of wastewater in the averager, a level gauge is provided, which is used to determine the degree of filling of the averager and control the operation of mixers and feed pumps.
Figure 1.2 – Physics — chemical cleaning by reagent flotation
( animation speed - 34.6 number of frames - 12)
Mechanically treated industrial wastewater from the homogenizer is pumped into a tubular flocculator. The flocculator is equipped with samplers for sampling the incoming wastewater to the flotator. In order to increase the efficiency of wastewater treatment, the supply of chemical reagents is provided for the flotation treatment.
Flotation — this is the process of molecular adhesion of particles of a floating material to the interface of two phases, usually gas (more often air) and liquid, due to the excess free energy of the surface boundary layers, as well as surface wetting phenomena [13, 14].
Flotation is used to remove dispersed impurities from wastewater, which spontaneously settle poorly. The process of purification of industrial wastewater containing surfactants (surface - active substances), oils, fibrous materials by the method of flotation consists in the formation of complexes bubble - particle
, floating of these complexes and removal of the formed foam layer from the surface of the treated liquid. The adhesion of the particles in it to the surface of the gas bubble is possible only when non-wetting or poor wetting of the particle by the liquid is observed. The formation of the bubble — particle
complex depends on the intensity of their collision with each other, chemical interaction of substances, excess air pressure in waste water, etc.
Flotation is accompanied by aeration of wastewater, a decrease in the concentration of surfactants and easily oxidized substances, bacteria and microorganisms. This contributes to the success of the following cleaning steps.
Pressure flotation units are simple and reliable in operation. The pressure flotation method has a wider range of applications, since it allows you to regulate the degree of supersaturation in accordance with the required efficiency of wastewater treatment at an initial concentration of contaminants up to 4? 5 g / l or more. To increase the degree of purification, coagulants are added to the waste water.
The process is carried out in two stages:
During pressure flotation, wastewater under pressure of 0.3 - 0.5 MPa is supplied to the pressure tank (saturator). Air is supplied there by a compressor. It is also possible to supply air through a water-air ejector installed on the pump bypass line (Fig. 1.3).
Figure 1.3 – Pressure flotation scheme
The amount of air supplied depends on the initial and final concentration of pollutants, as well as their properties. Air-saturated water from the saturator is fed into the flotation chamber, where air bubbles released from the waste water float together with suspended solids.
The flotation sludge (floating mass) from the surface of the skimmer is collected by scrapers into the pocket for flotation sludge. A screw pump is provided for pumping out flotation sludge from the collection pocket. The flotation sludge is pumped into the sludge tank.
Figure 1.4 – The structure of a pressure head flotation plant
Sludge forms in the bottom of the skimmer during wastewater treatment. A pneumatically operated shut-off valve is installed to remove the sediment. The sludge removal valve operates in a timer mode. Due to hydrostatic pressure, the sediment from the flotator is discharged into a horizontal sand trap, in which heavy mineral impurities settle. The clarified water is discharged into the blending unit.
To increase the efficiency of the flotation unit, a solution of coagulant and flocculant is dosed into the treated water, which contribute to the formation of sludge entering the unit, and a solution of sodium hydroxide is supplied to adjust the pH value.
Membrane pumps — dispensers are used to supply a coagulant solution, sodium hydroxide solution to the flocculator.
Unit for preparation and dosing of flocculant solution consists of a station for preparation of flocculant solution and a screw pump — dispenser for flocculant solution [9].
Figure 1.5 – Scheme node cooking flocculant
The dry flocculant is poured by the operator into the flocculant funnel of the station. To prepare the flocculant solution, water is supplied to the station. The ready-made flocculant solution is prepared in the upper chamber. The selection of the finished solution takes place in the lower chamber. From the upper chamber, the diluted reagent solution, after a certain time of maturation, is ready for further use. When the lower chamber is empty, a signal is received to overflow the finished solution from the upper chamber to the lower one. By pumps - dosing devices, the flocculant solution is fed to the dosing point in the flocculator.
Automation of the flocculant preparation unit allows you to save up to 20-30% of funds in the purchase of chemicals, allows you to ensure that a solution of the desired concentration is obtained at the outlet, as well as to control and predict the consumption of flocculants.
Treated industrial wastewater after physical — chemical treatment at the pressure flotation unit enters the treated wastewater drainage well and is discharged into the city collector.
An important stage in the development of an automatic control system for a flotation plant is its analysis as an object of automatic control.
One of the tasks of wastewater treatment is the removal of impurities into foam. By adding flocculants and coagulants, it is possible to achieve their enlargement, as well as to promote their adhesion. The possibility of formation of a flotation complex bubble — particle
, the process speed and bond strength, the duration of the complex existence depend on the nature of the particles, as well as on the nature of the interaction of reagents with their surface and the ability of the particles to be wetted with water.
The wetting ability of a liquid depends on its polarity, with an increase in which the ability of a liquid to wet solid bodies weakens. An external manifestation of the ability of a liquid to wet is the value of its surface tension at the interface with the gaseous medium, as well as the difference in polarities at the interface between the liquid and solid phases. The flotation process is efficient when the surface tension of water is no more than 60 - 65 mN / m, which is provided by the addition of flocculants.
Figure 2.1 – Education diagram bubble — particle
Of great importance in flotation are the size, quantity and uniformity of distribution of air bubbles in wastewater. Sticking occurs when a bubble collides with a particle or when a bubble forms from a solution on the surface of a particle. For particles well wetted with water, the surface tension of water at the interface with air tends to zero, therefore, cos & # 952; tends to unity, which means that the adhesion strength is minimal. For non-wettable particles, on the contrary, the energy of formation of the bubble — particle
complex will be maximum. The flotation separation effect depends on the size and quantity of air bubbles.
In this case, a high degree of saturation of water with bubbles or a large content of gas in it is required. The specific air consumption decreases with an increase in the concentration of impurities, since the probability of collision and adhesion increases. Stabilization of the bubble size during flotation is of great importance. For this purpose, various foaming agents are introduced, which reduce the surface energy of the phase separation.
Let's describe the process of controlling the preparation of a flocculant during wastewater treatment in a pressure flotation plant is described as follows. Three types of variables are considered, which are physical quantities of the technological process of preparing a flocculant and its dosage into a flotation unit (Fig. 2.2):
Controlled Variables — observable variables that during the implementation of the technological process must take values within the specified boundaries:
Figure 2.2 – Flocculant preparation unit as a control object
In each hydrographic region, enterprises of different types of industry prevail, with significant water consumption and, accordingly, significant costs of discharged wastewater. These enterprises include primarily oil refineries, metallurgical, pulp — paper, chemical, metalworking, machine-building, mining, food enterprises, as well as enterprises of light industry, energy, agriculture.
The main pollutants found in most industrial wastewater are suspended solids, oils and oil products, heavy metal ions, as well as organic pollution characterized by MIC and chemical pollution, characterized by COD.
At many enterprises, treatment facilities have fallen into disrepair from — for a significant period of operation; there are enterprises where industrial sewerage accepts economic — household and fecal wastewater; there are enterprises that do not have local treatment with the reuse of purified water and the disposal of the separated useful components. The lack of local treatment with the combination of wastewater with different pollution often makes it impossible or difficult to treat the general wastewater flow before it is discharged into a city sewer or water body.
The way out of this situation is the introduction of automation systems for the flotation process.
The purpose of the system being created — improving the quality of the prepared solution due to the development of an automatic control system for the preparation of a flocculant, which will reduce the cost of operation and maintenance of treatment facilities.
ACS function — it is a set of actions of the system aimed at achieving a particular goal of management. ACS functions are subdivided into information, control and auxiliary. To achieve this goal, it is necessary that the automatic control system of the flocculant preparation process performs the following functions.
Informational functions of ACS for flocculant preparation:
Control functions of ACS for flocculant preparation:
Auxiliary functions of the ACS for the preparation of a flocculant:
To implement the selected functions, it is necessary to solve the following tasks:
