ATMOSPHERE PROTECTION IN CASE OF EMERGENCY DURING TRANSPORTATION OF DANGEROUS CARGO Purpose

Purpose. The paper highlights the development of numerical models for prediction of atmospheric pollution in case of burning of the solid rocket propellant in a railway car, situated near the building on railway territory. These models can be used in predicting the effectiveness of neutralization upon the atmosphere protection for this type of accidents. Methodology. To solve this problem the numerical models based on the use of Navier-Stokes equations, to determine the velocity field of the wind flow near cars and buildings, and contaminants-transfer equations in the atmosphere were developed. For the numerical integration of pollutant transport equation was used implicit «change – triangle» difference scheme. When constructing a difference scheme physical and geometric cleavage of the transfer equation is carried out in four steps. Unknown value of pollutant concentration at each step of cleavage is determined by the explicit scheme – the method of «point-to-point computation». For the numerical integration of the Navier-Stokes equations are used implicit difference schemes. When carrying out computing experiment also takes into account: the velocity profile of wind flow; interaction between the building and the wind flow and flame jet of solid rocket propellant; the presence of a railroad car; inside which there is a source of pollution; instability of pollutant emissions. On the basis of constructed numerical models was performed the computer experiment for assessing the level of air pollution at dangerous cargo rail transportation in case of emergency at railway territory.The application calculations for the timely combustion products neutralization of solid rocket propellant were carried out. Findings. The numerical models that let promptly calculate air contamination in case of emergency during solid rocket propellant transportation, as well as calculate the rational parameters of pollutant neutralization process were developed by the researcher. These models can be used for routine calculations of various accident scenarios simulation. Originality. Numerical models were developed; they take into account significant factors, influencing the pollutant dispersion process in the atmosphere. On their base a pollutant neutralization method was offered in emergency situations on the railway transport. Practical value. Efficient numerical models, so called «diagnostic models» were considered for the rapid calculation of the air pollution level and air protection technology in emergency situations, in particular, in the case of railway transportation the solid rocket propellant.

In the case of this propellant burning the great amount of toxic chemicals are dispersed in atmosphere.So it is important to predict the atmosphere pollution in the case of the possible accident and develop methods to protect atmosphere from pollution (Fig. 2) [1,11].
That is why the prediction of the atmosphere pollution in the case of the mighty emissions during transportation is of great interest.1 -building on the territory of station «Pavlohrad-1», 2 -train Nowadays to predict the dimensions of the hitting area in the case of outdoor toxic chemical release the special standard model is used in Ukraine [10].This model is formed on the basis of some empirical models and it has a lot of lacks and is, without doubt, unrealistic.The model does not take into account the influence of the wind velocity and the atmosphere diffusion on the concentration dispersion in the atmosphere.The main lack of this model is that the standard model cannot calculate the change of toxic chemical concentration in the atmosphere after the accident.In some cases Gauss model is used to predict atmosphere pollution level [5][6][7]13].It is very important to develop CFD (Computational Fluid Dynamics) models to solve the problem discussed [1,8,14,15].

Purpose
The purpose of this work is the development of the numerical model to predict the atmosphere pollution in micro scale level in the case of solid propellant burning which also can be used to predict the effectiveness of neutralization for atmosphere protection for this type of accident.

Methodology
When the solid propellant burns different toxic chemicals are emitted in the atmosphere.To compute the toxic chemical (product of propellant burning) dispersion the Navier-Stokes equations and equation of mass transfer are used [14]: 1 Re x y where ψ -is flow function; This model is used to predict the air pollution near railway car with solid rocket propellant (Fig. 2).
To simulate the process of toxic chemical dispersion in the atmosphere (for the distance about 300m) the 2-D transport equation is used [8,14]: where C -is the concentration of toxic chemical; u, v -are the velocity components in x, y direction respectively; ( ) x y µ = µ µ -are the coefficients of turbulent diffusion in x, y direction respectively; σ -is the parameter taking into account the process of toxic gas decay or rain wash out; , ( ) ( ) -is Dirac delta-function.The boundary conditions for the governing equations are discussed in [14].
In the developed numerical model, the following profile of velocity component u and coefficient of diffusion is used [5,6]: where 1 u -is the velocity at height 1 y ; 1 0, 2 k = ; 0 0,1 k = ; 0,16 p = ; 1 m ≈ .Numerical integration.To solve the governing equations the implicit difference schemes were used [14,15].These are so called «change -triangle» difference schemes.

Findings
To minimize the extent of contamination and the risk of toxic defeat people in case of emergency during transportation of solid rocket propellant it is proposed technology, aimed at localization of the source of emission of products of combustion solid rocket propellant.It is proposed to include in the train which transports solid rocket propellant, the car with the pump unit and tank with a stock of neutralizing solution.It is also proposed to include a buffer car between the rail car where solid propellant is transported and the car with the pump unit.This buffer truck will serve as a «screen» for the protection of the car with the pump unit from heat radiation of the combustion solid rocket propellant.With this technology, was organized rapid feed of neutralizing solution into the plume of combustion products and thereby minimizing time the free flow of products of combustion solid rocket propellant in the atmosphere.In addition, unlike the traditional scheme of feeding catalyst in the form of streams offered feed through the sprinkler, which is posted on pull-rod (Fig. 3).This is because the temperature of the combustion solid rocket propellant in the atmosphere is high and if you use a traditional presentation in the form of a jet, there will be rapid evaporation of droplets of reagent on the path of its movement from the installation to the jet plume.The calculation is performed for the following tasks: Scenario 1 -no neutralization; Scenario 2 -supply of reagent is performed at a height of 13,5m and at a distance of 20 m from the source of emission.This distance is constant in all scenarios, catalyst feed rate of 1 kg/s; Scenario 3 -the reagent feed is done at the height of 13,5m, catalyst feed rate of 8 kg/s.On the base of the developed numerical models the special codes were developed.Some results of their application are shown in Fig. 4-6.
The subsequent figures illustrate the area of atmospheric pollution in the case of the options considered.The first figure (Fig. 4) corresponds to the situation when there is no flow of reagent and compares the efficiency of neutralization for each option, comparing to the area of contamination with this picture.The efficiency of neutralization 50% 62% 69% Results from Tabl.1, 2 show that the rate of reagent strongly influences the effectiveness of protection.Also it is clear from Fig. 5, 6 that the height of reagent supply is too high because the region near the railway car and building is still in the plume of toxic chemical.

Originality and practical value
A new numerical model to predict atmosphere pollution and neutralization of toxic chemical after accidents at railways was developed.The model is based on the 2-D transport equation.The developed model takes into account wind profile, diffusion, emission rate.This model allows evaluating the level of atmosphere pollution and effectiveness of neutralization.The model can be useful in the field of transport routes safety prediction.

Conclusions
The article contains results of numerical simulation of air pollution near «Pavlohrad-1» station after the accident at railway.To simulate the process of air pollution the 2-D developed numerical model was used.The developed numerical model takes into account the main physical processes which influences the pollutant dispersion in atmosphere.The developed models allow simulating the process of neutralization of toxic chemical in atmosphere.The future work in this field will be connected with development of fluid dynamics models to simulate the pollutant dispersion over the complex terrain.

Fig. 3 .
Fig. 3. Sketch of toxic chemical neutralization: 1 -vessel with the reagent, 2 -pipeline, 3 -pump, 4 -pop-arrow, 5 -buffer car, 6 -sprinkler Problem setting-to evaluate the effectiveness of the process of neutralization of various intensities of reagent feed and placement of the sprinkler to the source of emission of hazardous substances.The calculation is performed for the following tasks: