Method of calculating gas volume and its travel direction in a sewer

Summary

In the process of operating deep sewers some problems arise such as corrosion of reinforced concrete structures of the sewerage network, saturation of the gas phase of the underground space with corrosive toxic substances, accidental emissions of these gases from the network into the atmosphere. Solving these problems is possible by arranging air exchange between the sewerage network and atmosphere. The available methods of calculating the amount of gas travelling in the sewerage network do not take into account the gas density, dynamic viscosity and other parameters that depend on the chemical composition of the gas phase. The lack of the recommendations does not allow estimating the network ventilation in relation to providing the required gas exchange rate. Consequently determining, estimating and substantiating the required capacity of the ventilation equipment are not possible. Possible flow redistribution is not considered either; and, hence, adjusting the gas exchange systems to the definite network parameters is not possible. A method of calculating gas amount and flow direction induced by fluid entraining capacity and natural draft with account of the physical and hydraulic parameters of wastewater and gas, network design features, daylight surface temperature is presented. The method provides for making calculations at the design stage with account of retrofitting ventilation units, filters and vent pipes. The following parameters are determined: the amount and direction of gas flow in the network, gas exchange rate, anticipated background concentration of corrosive gases at the preset gas exchange rate, network corrosion rate, overhaul period.

Key words

collector , sewerage network , calculation method , ventilation , gas exchange , corrosive toxic substances