Biogas

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EXERCISE ON BIOGAS SOLAR AND BIOMASS POWER PRODUCTION – AA 2018/19 Prof. Giampaolo Manzolini – Ing. Marco Binotti It is requested to optimize the biogas plant design by maximizing the NPV. The plant is fed with 250 t/d of cheese whey that is paid at a price of 13 €/t. Whey characteristics are as follows: o Composition:  proteins 13.5 g/100 g VS (VS: Volatile solids are a measure of the suspended (particles) and dissolved (salts) solids in water)  carbohydrates 75.2 g/100 g VS  lipids 0.813 g/100 g VS o Solid content: 6.7 gVS/100g o Specific weight: 1 t/m3 o Approximation: VS~TS o Ultimate BMP: 0.35 m3@0°C,1 atm/kgCOD The Biogas Methane Production theoretical can be determined starting from the Chemical Oxygen demand (COD)of the cheese whey which depends on the biomass compositions. Conversion numbers are: • Proteins: 1.42 gCOD/gVS • Lipids: 2.9 gCOD/gVS • Carbohydrates (as lactose): 1.19 gCOD/gVS Another approach to determine the BMP is the adoption of the following equation: BMPth (m3/kgVS) = 0.415·Carbohydrates (%VS) +0.496·Proteins (%VS) +1.014·Fats (%VS) The Biogas Methane Production efficiency (ηBMP) is function of the Hydraulic Retention Time (HRT) of the whey in the digesters assuming the following dependence: From 1 day to day 20: it is linear starting from 1% to 75%; From day 20 to day 30: it is linear starting from 75% to 87.5%; From day 30 to day 40: it is linear starting from 87.5% to 97%; The Organic Loading Rate (OLR) should be between 1 and 3, and the HRT above 15 days. The methane has LHV equal to 9.96 kWh/m3 and it is used as fuel in an internal reciprocating engine with a net electric efficiency equal to 40%. The PB cost: -0.9342 x (power)2 + 1913.2 x (power) + 23759 The digester cost is: -0.0364*(Volume)2+618.18*(Volume)-545455 with a maximum…