IRIS diaphragm control valve Cost increase due to a wrong regulation We take for example a typical regulation of oxygen in an aeration basin to highlight the importance of analysing the process and the technique used to regulate the system and the corresponding results. When designing a system and selecting equipment, local health and safety laws must always be observed. The conditions and standards employed for this technology: The control value of the oxygen concentration is dependet on the sludge load or the sludge age. Under the assumption of a representative measurement location, the guide values as stated in the German ATV work sheet A131 for the layout of the aeration unit should be used. Higher, unnecessary additional oxygen concentrations will increase energy costs (see drawing 9). Even short time variations of the real oxygen value will increase energy costs therefore these extras should be avoided. The same can be said for other fluids.
Example: - The minimum O2 value should not drop below 2.0 mg/l. However the real O2 value may vary by +/- 0.5 mg/l (when the control valve is not accurate). The value of the conventional valve should then be increased to provide a value of 2.5 mg/l to avoid an under supply. The energy cost will therefore increase by approximately 10% (see drawing 9) - Compressor power requirement for an oxygen concentration of 2.0 mg/l is for example 100 Kw - Electrical cost is for example 0.12 €/Kw Calculation of extra costs in terms of energy/year (Kz) per year and per 100 kW Compressor power at a adjusted set value of 2.5 mg/l: Kz = 100 KW x 0.12 €/KW/h x 24 hours x 365 days x 0.1 = 10'512 € / year
increased relative power demand, referred to power consumption Cx = 0 (%)
With a compressor power of for example 200 kW, the additional energy costs would amount to 21'024 € / year.
env. 10%
Oxygen concentration Cx (mg/l) Source:
Manual ATV (waste water engineering association) - industrial technology; costs and foundations of law concerning sewage clarification, 1996
Illustration 9: Increased relative oxygen demand depending on the oxygen concentration
Dat. 17.05.2006 Emile Egger & Cie SA Cressier/NE (Suisse)
Mannheim(DE) Lyon (FR) Graz (AT)
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BS-953-14gb