The introduction
The materials which are in a dispersible state participate in many technological processes. Dispersible materials form aerosols in devices and in air of industrial locations. If such aerosols burn, they represent potential danger and their presence demands observance of certain security measures. In the given operation such aerosols are called "dust". The disperse systems consisting of the gaseous environment and a solid disperse phase are included In this concept. [1] characteristic sign of aerosols is their instability. Fire danger represent both dust clouds, and dust adjournment on building constructions and technology equipment. [1]
The topicality
Now in the world happens more than 7 million fires, and the risk of loss of people on fires exceeds 10-5. This risk fluctuates from 10-3 –10-5at the enterprises of an energetic complex, and risk still above at liquidation and preparation of technology equipment that essentially exceeds requirements of operating standards in the field of industrial and fire safety.
At the given stage of development of mankind, the problem of energetic support of a civilization dares practically, as well as hundred years ago. The main method of obtaining of energy is burning of fossil fuel, and the tendency of growth of consumption of solid types of such fuel recently. In Ukraine this tendency is shown in the form of magnification of consumption of coals of the Donetsk pool which principal lack is high fire and explosion hazard.
Any link of a technological chain from coal mining before its burning in a thermal power station fire chamber is to some extent endangered a fire or explosion. Most sharply this problem costs for the energetic enterprises where any incident connected to a fire or explosion, involves not only the material losses, but also leads to the considerable social disasters. [3-4]
The majority of actions for lowering fire and an explosive situation don't give effect. The unique direction which development can give essential increase of level of fire safety of the energetic enterprises is application of electronic monitoring systems fire and explosive situations.
The purpose and objectives
The purpose is development, a substantiation and research of structure of electronic system which with sufficient confidence figure would notify on origin fire and an explosive situation, for timely detection of process of self-ignition of a coal dust in the conditions of industrial organizations.
The objectives:
- The substantiation of a complex of controllable physical and chemical parameters of individual system pulverization that will allow to find out in time presence and an explosive situation.
- The analysis of methods and monitoring parameters of self-ignition of a coal dust in the conditions of industrial organizations.
- Development of a mathematical model of detection of process of self-ignition of a coal dust.
- Development of a mathematical model of electronic system of detection fire and explosive situations for determination of characteristics of measuring channels.
- Substantiation and development of structure of electronic system of detection fire and explosive situations in the conditions of industrial organizations.
- Development of algorithm of functioning of electronic system of detection fire and explosive situations in the conditions of industrial organizations.
The scientific novelty
The mathematical model of detection of process of self-ignition of a coal dust has had the further development. This model considers kinetic parameters and heat exchange processes, dynamics of temperature and concentration of a dust that will allow to lower risk of origin fire and explosive situations in the conditions of industrial organizations.
The structurally-algorithmic organization of electronic system of detection fire and explosive situations has been implemented in the conditions of industrial organizations.
The preliminary results of researches
The set of controlled parameters:
- The temperature of a coal dust behind a mill.
- The concentration of oxygen in a gas compound.
- The concentration of a dioxide of carbon in a gas compound at drying by smoke gases.
Controllable parameters of process of self-ignition of a coal dust:
- The temperature of adjournment of a coal dust.
- The concentration of the coal dust weighed in air.
Setting of requirements to measuring channels
The main attention is given learning of those physical parameters which inertance of registration is rather small. The range of change of temperature of a coal dust can be found from a condition that the temperature of a carbon dust gradually increases: dT/dτ>0. The range of controllable temperature can be found from a following equation.
where θ=RT/E (R - the general-purpose gas constant, E - an activation energy of substance), θс=RTc/E - the temperature parameter of walls of a tank (camera), α - the heat emission coefficient.
For finding of a range of controllable temperature it is necessary to solve system of equations:
The analysis of the first equation. For coals of Donetsk pool the minimum temperature of self-ignition is equal 1245 K, and the upper temperature limit of self-ignition of a coal dust doesn't exceed 5000 K.
The analysis of the second equation. The temperature range of walls of the camera (tank) at which self-ignition is impossible 1340 K < Tc <18640 K (the theoretical information) is defined.
Necessary condition for origin of process of thermal self-ignition is presence of a sufficient level of concentration of a coal dust.
Minimum explosive concentration of a coal dust, according to [6], it is possible to calculate under the formula:
where Q - warmth of combustion of coal.
Maximum explosive concentration of a coal dust, according to [6], it is possible to calculate under the formula:
where V0ру - theoretically necessary amount of air for burning of a carbon dust of 1 kg in operating conditions.
We receive: Сmin=33 g/m3; Сmax=110/m3.
Dynamics of change of concentration of a coal dust can be defined under the formula [8]:
where С0 - initial concentration of the carbon dust; Т0 - the temperature reference mark.
Dynamics of process of burning-off of substance is presented on figure 1.
Figure 1 – Dynamics of change of concentration of coal dust
The general view of probability dependence of origin fire and explosive situations in the conditions of industrial organizations has been received.
Where TPO - the temperature of adjournment of a coal dust; СDUST - the concentration of a coal dust in a mill-separator; СCO2 - the concentration of a dioxide of carbon behind a mill-separator; СO2 - the concentration of oxygen behind a mill-separator; ТPC - the temperature of a coal dust behind a mill-separator.
Animation of technological process
Animation of several stages of process of self-ignition of a coal dust in a mill-fan is presented on a figure 2.
Figure 2 - Animation of process of origin fire and explosive situations.
The animation parameters: an amount of frames - 8; size - 80 КВ; amount of repetition - 6
The conclusions
- The complex of controllable physical and chemical values of individual system of preparation of a carbon dust is justified.
- The analysis of existing methods and monitoring of processes of self-ignition of a coal dust in the conditions of industrial organizations is made.
- The mathematical model describing process of self-ignition of a coal dust is developed.
- Limits of change of temperature of self-ignition of adjournment of a coal dust and range of change of explosive concentration of the coal dust weighed in air are defined.
The references
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Note
When writing this abstract the masterwork hadn't been completed yet. The deadline of completion is December 1, 2011. Full text of the work and materials on the subject-matter can be obtained from the author or her scientific adviser after that date.