CO2 as a control index of pollution levels generated by underground operation of Diesel mounted equipments. Keywords: mine, air, pollution degree, quality ...
Air Pollution and Climate Change
UNDERGROUND AIR POLLUTION IN METAL MINES: NEW CONTROL METHOD AND CASE STUDY IN TWO ROMANIAN MINES FROM BAIA MARE ORE BASIN Assoc. Prof. Dr. Gabriel Bujor Băbuţ, Assoc. Prof. Dr. Roland Iosif Moraru, Monica Crinela Băbuţ University of Petroşani, Romania ABSTRACT Heat and exhaust emissions are representing two of the major health and safety issues induced by the presence of Diesel-mounted equipments in underground mines. The first one has greater effects in deep mines, while the second one requires a careful dimensioning of ventilation airflows in all mines. Taking into consideration the higher exposure level of Diesel mounted equipment drivers at the noxious products contained in the exhaust emissions, it clearly appears as a major safety concern the need for an expeditious method of assessing the pollution degree. The paper presents the legal requirements regarding the Diesel exhaust emissions in Romanian underground mines, a new expeditious method aimed at assessing the mine air pollution degree and the results of measurements and experimental data processing at Baia-Sprie and Şuior mines. The measurements carried out in two metal mines from Baia Mare basin and the plotting of individual and cumulated dependence curves, have confirmed the feasibility of using the CO2 as a control index of pollution levels generated by underground operation of Diesel mounted equipments. Keywords: mine, air, pollution degree, quality index INTRODUCTION Heat and exhaust emissions are the major problems raised by the presence of Dieselmounted equipments in underground mines. The first one has greater effects in deep mines, while the second one involves a careful dimensioning of ventilation airflows in all mines. The provision of proper control of Diesel exhaust emissions is an intricate issue, while pollutant composition and levels directly depends upon various factors, such as [4]: •
working conditions and technical state of the engine;
•
parameters of the underground environment;
•
skills and ability of vehicle's operator.
Measuring all the exhaust components is practically very difficult to achieve due to the narrow, humid and dusty underground environment. An expeditious method for quantifying the air quality is needed.
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International Multidisciplinary Scientific GeoConference SGEM 2010
DIESEL ENGINES EXHAUST EMISSION COMPOSITION The fuel One of the most important factors related to Diesel engines operation in mines is the fuel. Diesel oil is, normally, distillated petroleum, significantly less volatile than gasoline, having a slight tendency to form an explosive mixture when mixed with air, at normal temperatures. The sulphur content in Diesel oil should not exceed 0.5 %. Limiting this compound, the concentration of toxic sulphur oxides will remain under the Treshold Limit Value. This reason represents a main issue regarding the prescriptions for a fuel to be used underground. The pure Diesel oil molecules are consisting of carbon and hydrogen atoms, and the medium composition can be epitomized by the C8H16 formula. Exhaust emissions As a result of combustion, carbon and hydrogen are oxidized, generating in the case of complete combustion, carbon dioxide. Owing to the process rapidity of (a few miliseconds, usually), the combustion is not complete and new gases are generated, such as carbon monoxide and nitrogen oxides, due to partial oxidation of nitrogen. Consequently, in the exhaust duct will be eliminated a mixture of harmless gases (N2, vapors, rare gases and a part of CO2) and noxious substances, presented in table 1 [1]. Table 1. Harmful substances in the Diesel engine exhaust Nitrogen oxides
Carbon monoxide Hydrocarbons Sulphur compounds
Particles
- NO (nitric oxide) - NO2 (nitrogen dioxide) - NOx (oxides mixture) - CO - HC (including aldehydes) - S (free sulphur particles) - SO2 (sulphur dioxide) - other sulphur compounds - RCD (Respirable Combustible Dust) - PNA (Poly-nuclear-aromatics, especially benzo-alpha-pyren)
Legal restrictions regarding the Diesel exhaust emissions In Romania, the safety legal acts are giving the minimum requirements to be fulfilled in order to provide the worker’s health and safety [6]. The Government Decisions which are transposing the EU directives are than particularized by each company, who develops his own safety and health regulations [7]. Consequently, it is established that a Diesel engine mounted equipment will not be maintained in operation, when the measurement results are leading to one of the following situations: •
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carbon monoxide concentrations exceeds 20 ppm in mine air;
Air Pollution and Climate Change
•
Bosch smoke index 3 or Hartridge smoke index of 36 % are exceeded;
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in engine's vicinity, carbon dioxide concentration exceeds 5000 ppm and nitrogen oxides (NOx) concentration is over 3.9 ppm.
In table 2 there are given the Treshold Limit Values for exhaust pollutants in several countries which are using Diesel equipment in mines, on a large scale. Table 2. Threshold limit values for Diesel exhausted gasses in several countries Country
U.S.A. Germany Poland South Africa Australia Canada Great Britain Romania
CO [ppm] In exhaust duct In mine air 3000 50 500 50 20 2000 100 1500 50 2000: coal mine 1500: non-coal 50 2000 50 20
CO2 5000 10000 10000 5000 12500 5000 5000 5000
In mine air [ppm] NO2 NOx 5 25 5 2.5 5 5 5 5 3 -
25 100 3.9
SO2 5 10 7 5 5 5 3.5
The research conducted in U.S.A [5], led to certain changes of maximal values, as presented in table 3. Comparing the values in table 2 and 3, it results that in U.S.A. the limitations regarding the Diesel equipment operation in the underground environment, are much more complex than in Romania. Table 3. Threshold limit values reassessed in U.S. underground mining Exhaust emissions
U.M.
CO CO2 NO NO2 SO2 Coal dust Metal mine dust
ppm % vol. ppm ppm ppm mg/m3 mg/m3
Long-term exposure (8 h) 50 0.5 25 3 2 2(1) 10(2)
Short-term exposure (15 min.) 400 3 N.Ap. 5 5 N.Ap. N.Ap.
Remarks: (1) - respirable dust; (2) - total dust; N.Ap. - not applicable limits. THE AIR QUALITY INDEX METHOD The method was verified in mines of U.S.A. and Canada [2] and consists, in principle, in covering the following main steps: •
establishing the pollutant characteristic curves, as a function of carbon dioxide concentrations measured in same location, at the same time.
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International Multidisciplinary Scientific GeoConference SGEM 2010
•
determination of an Air Quality Index which allows to establish a value of CO2 concentration under which all the other pollutants can be considered as having values not involving health hazards.
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recurrently, measurements of exhaust emissions in order to verify that the predetermined correlation is maintained.
Pollutant characteristic curves are diagrams illustrating the average concentrations for each pollutant, as a function of carbon dioxide concentration, measured in the same location and at the same time. This curves represents the evolution of each pollutant (CO, NO, NO2, SO2, Diesel Particulate Matter) versus the CO2 concentration. Such a curve, as an example, is presented in Figure1, where the dashed horizontal line illustrates the Treshold Limit Value for a specific pollutant.
Figure 1 Pollutant characteristic curve The ratio between pollutant concentration and CO2 concentration is the slope of the characteristic curve and, consequently, the ideal, theoretical characteristic curves will be straight lines passing through the coordinate system origin. As mentioned before, in order to quantify the air quality into a single numerical value, taking into account the combined effects of pollutants, in Canada and then in U.S.A. [2] , an Air Quality Index (A.Q.I.) was introduced, which can be expressed by the following relations: A.Q.I.( gases ) =
A.Q.I.( dust ) =
CO NO NO 2 + +
