Mathematical modeling of the impact of emergency situations on atmospheric air

. The aim of the work is to assess the impact of oil and gas industry production on the environment, taking into account emergency situations using mathematical modeling of the impact of emergency situations on atmospheric air. In order to solve this problem, the situation with fires in the oil and gas industry facility is considered. During the combustion of oil and gas, the contained carbon and hydrogen atoms are oxidized. In addition, there are some sulfur-, nitrogen, oxygen-containing compounds in the oil. To determine the quantitative indicators of the formation and consumption of all substances involved in the process of obtaining energy from the combustion of oil and from the environment, the equations of material balance are used. In the case considered by us, the zone of active air pollution in case of an emergency fire of a gushing well does not exceed the sanitary protection zone of the 1st hazard class, despite the aeroclimatic conditions of the region


Introduction
Atmospheric pollution in emergencies is inevitable.Sources of pollution in emergency situations are: oil, toxic or flammable gas emissions; liquefied gas emissions and ignition, oil ignition, explosions [1][2][3].
Material balance equations are used to determine the quantitative indicators of formation and consumption of all substances involved in the process of obtaining energy during oil combustion and from the environment.Below we give information on material balances of fuels, the elemental composition of which is close to the composition of oil (Table 1).
Note: according to reference data the carbon content in oil is 83-87% by weight.Therefore, the table shows fuels with similar carbon content.
The material balance is formed according to the elemental composition of oil, which expresses the relative mass content of individual elements at complete and incomplete combustion of oil.Working mass of oil containing impurities of nitrogen, sulfur, ash, moisture is determined by the formula: wC +wH +wO +wN +wS +wA +wW = 1 (1) For the fuels listed in Table 1, the content of ash (A) and moisture (W) in fuel oil is up to 0.2 and 9 % (low-sulphur fuel oil).Mass fractions w of separate elements in 1 kg of oil CxHyOz are found according to known ratios: here MT is molar mass of a "conventional" oil molecule; 12х, у, 16z -mass of carbon, hydrogen, oxygen in an oil molecule; In most commercial grades of petrol and diesel fuels the presence of oxygen can be neglected (conditional "molecule" of fuel CхHу, MT=12х+у).A mixture of gas fuels of the following composition CxHyOz+N2 with volume (molar mass) fraction of each gas (j) has the following elemental composition for 1 kmol (1m 3 ) -molar mass of the gas mixture: and gas mass fractions

Results
Total oil oxidation.The ratio between the amount of initial products (oil plus air) and combustion products is determined from chemical reaction equations under the following assumptions: all chemical compounds consist of atoms of individual elements bound together in certain numerical ratios; during chemical reactions atoms retain their individuality and only their rearrangement takes place.The complete oxidation (combustion) of the CxHy molecule to the final products (carbon dioxide CO2 and water vapour H2O) is described by the equation (initial and final products of the reaction are given in kilomoles).

Discussion
Table 2 shows data on oxygen consumption and release of carbon dioxide and water vapour as a result of complete combustion of fuels.
As a result of complete combustion of oil consumes 1.5-7.9kg of air oxygen, and the release of CO2 (for currently used fuels) is about 3 kg, water -0.8-2.3 kg, nitrogen -10.4-13.3kg.Note: According to reference data, the carbon content of oil is 83 to 87 per cent by weight.Therefore, fuels with similar carbon content are given in the table.
Incomplete oxidation.If the amount of oxygen will be less than stoichiometric, the oxidation will be incomplete: part of the carbon will be oxidised only to CO, and part of the hydrogen will not burn at all.Oxidation of hydrocarbon molecule CхHу goes according to the equation: CxHy +[wx/2 +(1-w)x +y(1-1)/4]O2 = wxCO +(1-w) xCO2 +y 1 H2/2 +y(1-1)H2O/2 Here: w defines mass fraction of carbon oxidised to CO; 1 is mass fraction of unburnt hydrogen.
Per 1 kg of oil (kmol): With decreasing amount of oxygen in the combustion products the content of CO and H2 will increase, and the content of H2O and CO2 will decrease.At w1 = w = 1, the combustion products will contain only CO and unburned hydrogen H2.The corresponding oxidation equation is as follows: The amount of oxygen (kmol) NO2 =x/2 corresponds to the condition when the number of carbon atoms is equal to the number of oxygen atoms, i.e., C/O=1.At further reduction of oxygen content (C/O>1) unburned carbon (soot) appears in combustion products.

Conclusions
In summary, the magnitude of pollutant emissions depends on several factors: -the hydrocarbon composition of the crude oil; -the rate at which the crude oil is released; -the timing of the crude oil release; -the weather conditions in the area of the accident; -combustion temperature.Fires occur during drilling when a spark created by a grain of sand or pebble that rubs against metal structures ignites an escaped oil or gas fountain.This usually occurs when a well cannot be immediately capitulated.
A small fire burns about 30-40 tonnes of oil and 1.5-2 thousand cubic metres of gas per hour.This consumes approximately 180 tonnes of oxygen (about 30,000 cubic metres of air) per hour.Everything in the vicinity is in danger of fire and death: drilling wells and oil tanks, compressor units and oil pipelines, workshops, garages, residential houses and forest areas.
Temperatures reach 1400-18000 C. Average surface concentrations of pollutants in the fire area exceed the maximum permissible concentration (MPC) dozens of times.Fire produces: aerosols, carbon dioxide, carbon monoxide, nitrogen oxides, soot, hydrocarbons, sulphur oxides.
The pressure drop with altitude causes a corresponding lift of air from the surface layer of the atmosphere into the rarefied space of the fast-moving stream.Gaseous pollutants are forced to participate in the upper air flow and participate in long-range atmospheric transport.
Thus, the zone of active pollution of atmospheric air at the emergency fire of the flowing well does not exceed the sanitary protection zone (SPZ) of the 1st class of danger, despite the aeroclimatic conditions of the region (1000 m).

Table 1 .
Physical and chemical properties of fuel

Table 2 .
Amounts of air oxygen consumption and emission of various substances at complete combustion of 1 kg of fuel, kg