Renewable Energy Technologies I Prof. A. Wokaun 2nd AS 2014 of December Exercise 12: Biomass - Fuel Production Julia Witte, ([email protected]) Vera Tschedanoff, ([email protected]) A detailed solution is provided at the 9th of December. Please see: http://www.psi.ch/ene/ret1 Problem 1: Methanation of Syngas from Biomass An new location for a methanation plant shall be checked. Therefore a scheme of the reactor can be seen in figure 1. For simplification purposes the reactor, where the Water Gas Shift (WGS) reaction and the methanation reaction take place, is divided into 2 parts: WGS and Methanation. The product stream contains 20 kmol/hr methane and 2 kmol/hr carbon dioxide (stream 4). The stream 3 contains 25 kmol/hr carbon monoxide. Stream 7 provides water for the WGS reaction. Stream 5 and 6 are cooling water streams. Figure 1: Process Flow Diagram of the Methanation of Syngas The exothermic WGS reaction can be described by equation (1): 𝐶𝑂 + 𝐻2 𝑂 → 𝐶𝑂2 + 𝐻2 ∆ℎ𝑅 = −41.16 𝑘𝐽/𝑚𝑜𝑙 (1) The exothermic methanation reaction is described by equation (2): 𝐶𝑂 + 3𝐻2 → 𝐶𝐻4 + 𝐻2 𝑂 ∆ℎ𝑅 = −206.28 𝑘𝐽/𝑚𝑜𝑙 (2) Assumptions:  Stream 1 contains only hydrogen and carbon monoxide  Complete conversion of water for the WGS reaction  The ratio of CO and H2 after WGS fits stoichiometrically for the methanation part  The process is isothermal  The heat capacities are approximately equal: cp,2 ≈ cp,3 ≈ cp,4  Heat capacity of water: cp,w = 4.182 kJ/(kg ∙ K)  Steady-state process Table 1 gives an overview of the streams and compounds. The marked fields should be calculated. Streams Compound k H2 CO H2O CO2 CH4 Stream 1 Stream 2 Stream 3 Stream 4 Stream 7 𝑛1𝑘̇ [kmol/hr] 𝑛2𝑘̇ [kmol/hr] 𝑛3𝑘̇ [kmol/hr] 𝑛4𝑘̇ [kmol/hr] 𝑛7𝑘̇ [kmol/hr] 0 0 25 0 0 0 2 20 0 0 Table 1: Streams and Compounds i. What is the CO-conversion of the methanation part? ii. Calculate the molar flows of stream 3. iii. Calculate the molar flows of stream 4. iv. How much water (stream 7) has to be added to the WGS part? What are the molar flows of stream 2? v. The location of the methanation plant allows only a maximum cooling water stream of 50 kg/s. Because of statutory regulations the difference between the cooling water input and output stream should not exceed 10K. Calculate the heat flow from the reactor including WGS and methanation. Is the maximum cooling water stream sufficient to cool the reactor, so that the reactor can operate under isothermal conditions? Problem 2: Resources, Energy Demand and CO2 i. How many cars in Switzerland can run per year with fuel from Swiss wood, produced by the Fischer-Tropsch-Synthesis (FT), if the available wood is used only for fuel production? For how much percent of the cars in Switzerland the fuel production from wood is sufficient?        Lower heating value of wood (LHV): 18.170 MJ/kg Sustainable wood production per year: 4.3 t/(a ha) Area of wood in Switzerland: 1 284 000 ha Percentage of commercially used forest : 70% Efficiency wood to fuel (FT): 0.385 Energy demand of one car per year: 26 614 MJ/a Cars in Switzerland: 4 250 000 The authorities of the Swiss Federation have committed themselves to reduce the CO2emissions of Switzerland in 2020 by 20% in comparison with the CO2-emissions of the year 1990. In figure 2 the CO2-emissions are shown from 1990 until 2013. It can be seen, that the reduction of the emission until 2013 is marginal. Figure 2: CO2 emissions of Switzerland; Bundesamt für Umwelt-Schweiz, 2014 ii. What is the fraction, with which the saved CO2, due to the replacement by fuel from wood, contributes to the overall CO2 reduction aim of 2020? In order to solve the problem calculate also the amount of saved CO2 per MJ of fuel, caused by the replacement by fuel from a Fischer Tropsch process. Consider also given values of task 2.i. year 1990 2013 2020 CO2-emissions [mio tons] 39.10 38.29 ? Table 2: CO2-emissions of Switzerland; Bundesamt für Umwelt-Schweiz, 2014  CO2 emission from diesel from fossil source: 2.68 𝑘𝑔 𝐶𝑂2 𝑘𝑔 𝐶𝑂2 𝑙  CO2 emission for wood harvesting: 0.002 𝑘𝑔 𝑤𝑜𝑜𝑑  2 CO2 emission for wood transportation: 0.005 𝑘𝑔 𝑤𝑜𝑜𝑑  Energy produced per kg of wood in FT process: 7.0 𝑘𝑔 𝑤𝑜𝑜𝑑  Energy density of diesel: 34 𝑘𝑔 𝐶𝑂 𝑀𝐽 𝑙 𝑀𝐽