ERCIM News No.46, July 2001 [contents]

The Possible Effect of a Turbine Testing Plant on the Quality of the Air — A Case-study for Air Pollution Transmissions

by Sándor Márton and Tamás Rapcsák

The amelioration of the state of environment is a key-issue for the countries belonging to the European Union (EU) and for those wishing to join EU. One of the most serious problems is air pollution, caused mostly by industrial plants. Based on the Hungarian National Standards, scientists at SZTAKI have been studying the transmission of pollutants emitted by point-sources (stacks), linear sources and surface sources, for several years, elaborating numerous case-studies in the field.

The expected effect of a future turbine testing plant on the air quality has been studied in the framework of a case-study ordered by General Electric Ltd. This project was carried out with the help of the ATP program-system developed in course of our research.

The future plant is to be based on the model of a US plant working in a desert belt. The location in Hungary, however, is surrounded by inhabited settlements, therefore, in the interest of a safer forecast, the transmission calculations were prepared in circle representation as well, besides the most frequent wind direction. By circle representation modelling the concentration at every point of the map can be obtained in case the wind blows towards the examined point from the point of emission. Following the stipulations of the Hungarian Standards, also the level-differences in the surface were considered, by the help of the relevant relief digital map.

The composition and the volume of the emitted gas in course of the planned turbine testing will change, depending on the type of the turbine and the test loading. Testing would run exclusively during day-time, and the turbines will be in operation for 2 hours as an average, as per loading levels. On the effect of the high speed of the exhaust output and its high temperature, an effective stack-height of 160-300 meters develops. Consequently, in the case of a stack designed as 6-10 m high, on the basis of the calculations, the difference of some meters in the height would result a practically negligible (1-2%) difference in the effective stack-height and in the developing concentrations. According to the agreement with the Consigner, calculations regarding short averaging time were done based on the most unfavorable emission- and meteorological parameters, and regarding long averaging time, we calculated yearly dispersion. To determine the sphere of effect to be expected, we considered two methods. More than 50 different cases were examined, and the results were visualized in the form of tables, diagrams and on 30 digital maps annexed to the study.

Computations were done regarding three pollutants: nitrogen oxides (NO_x), sulphur dioxide (SO2) and carbon monoxide (CO). Out of these, NO_x is the most significant. However, the ground-surface concentration to be expected, regarding this pollutant didnít attain or got at the limit value for short averaging time (30 min) stipulated by the Hungarian Standard, either in the most unfavorable meteorological state. The maximum value to be expected at populated areas is the concentration corresponding to the 65% of the limit value, but this concentration zone almost ends at the settlement, and is gradually reduced under 10% onsite. The developing maximum concentration, related to the limit value of 24 hours is the 1,5% of the limit value, and the yearly dispersion is almost zero, consequently, practically insignificant in both cases. The effects of SO₂ and CO emissions calculated for short averaging time are insignificant, and in daily and yearly dispersion cannot be detected.

It derived from the results that:

• the increase in wind-speed results in the increase of the developing maximal concentration, and at the same time, the significant attenuation of the smoke-tail departing from the stack. This is due to the fact that in case of rather intense wind blow, the effective stack height is lower, ie, the smoke-tail precipitates sooner
• a smoke-tail of bigger size (wider and longer) belongs to smaller wind-speeds
• an increase of 15^oC in the temperature results in a concentration increase of 1-2% in relation to the limit value, thus air-temperature makes influence on the concentrations developing on the ground-surface, only to a small extent
• by the increase of the stability indicator of the meteorological state, the developing maximum concentration decreases
• a wind-speed increase of 3 m/s has a bigger influence on the concentrations (intensifying them) than the increase of the Pasquill stability indicator by a unit (decreases the concentrations).

Figure 1 shows NO_x in circle representation, developing in the most frequent meteorological condition. The deviation of the isoconcentration zones from the regular concentric circles derives from differences in the altitude. The isoconcentration zones increase with concentrations corresponding to the 10% of limit value regarding air quality, defined by the Hungarian Standard. Consequently, the value of the concentration in the innermost and the outermost zones is between the 10-20% of limit value, and 50-60% in the maximum concentration zone, in W-NW direction from the stack. The stack position is denoted (indicated) by the point marked inside the concentration zones, on the site of the planned plant.

Figure 1: Isoconcentration zones in circle representation for the planned turbine testing plant, for the most frequent meteorological condition (9,7o C air temperature, 2 m/s wind speed, B stability indicator), NOx, emission: 362,2 kg/h, imission limit value: 150 µg/m3.	Figure 2: Concentration tail in W wind-direction for the planned turbine testing plant, for the critical meteorological condition (35o C air temperature, 5 m/s wind speed, B stability indicator), NOx, emission: 362,2 kg/h, imission limit value: 150 µg/m3.

Figure 2 shows the concentration tail developing in case of W wind-direction and in critical meteorological condition. The modelling calculations were made for maximum NOx emission, in both figures. Consequently, the concentrations in the figures show the highest values to be expected, based on the calculations.

This research was supported in part by the Hungarian Research Foundation.

Links:
Department and Laboratory of Operations Research and Decision Systems, SZTAKI: http://www.oplab.sztaki.hu

Please contact:
Tamás Rapcsák — SZTAKI
Tel: +36 1 209 5266
E-mail: rapcsak@oplab.sztaki.hu