Process and plant design of ethanol synthesis from steel industry flue gas

Moreno Fernández-Villamil, Javier (2017). Process and plant design of ethanol synthesis from steel industry flue gas. Proyecto Fin de Carrera / Trabajo Fin de Grado, E.T.S.I. Industriales (UPM).


Title: Process and plant design of ethanol synthesis from steel industry flue gas
  • Moreno Fernández-Villamil, Javier
  • Jimeno Aguilar, Nieves
Item Type: Final Project
Degree: Grado en Ingeniería Química
Date: July 2017
Faculty: E.T.S.I. Industriales (UPM)
Department: Ingeniería Química Industrial y del Medio Ambiente
Creative Commons Licenses: Recognition - No derivative works - Non commercial

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Will we let Europe degenerate into the world’s backyard? No. We are difference makers. In Lappeenranta University of Technology, we are committed to building an alternative path with innovative solutions to energy problems that involve recycling as much as possible, leading to a waste-free world through sustainable and smart business models. The ultimate goal I want to achieve is to make a difference by proposing an innovative method of ethanol production through bacterial fermentation from waste gases in the steel industry. Ethanol obtained through this method falls under the category of second generation biofuels, this is, fuels made from waste. The growing industry of second generation biofuels is starting to play a major role in the efforts of the participants of the Paris Agreement to reduce carbon emissions. As such, it is clear that the motivation behind this work is environmental preservation, but before discussing technical issues, it must be studied whether there is any potential economic benefit to this project. This is why the work opens with a brief market review from which it can be concluded that Finnish and European legislation are to ensure stability and prosperity for those involved in making commodity fuels and chemicals from waste gases. Once the economic opportunities of the project are analyzed, a rough draft of the basic design of the process is presented as a result of an extensive literature review. The goal is to determine the most efficient and simple solution for the process, which consists of 4 stages: gas pretreatment, bacterial growth, fermentation and product separation. Feedstock information was supplied by Outokumpu, whereas process variables and equipment are obtained from the information found in the articles. On the other hand, the variables that remained unknown are either calculated or analyzed through sensitivity analysis using Aspen Plus ®. It is important to understand that the key to the process relies in the fermentation stage. The small gas to liquid mass transfer rates mean that only a small percentage of the gas is transferred to the liquid and transformed into ethanol. As a result, gas pretreatment and reactor conditions must favor high gas to liquid mass transfer rates. This is why the gas is compressed before entering the reactor, with subsequent cooling to maintain stable temperature in the reactor for bacteria to be alive. The reactor is also continuously fed with bacteria, which belong to the strain Clostridium Ljungdahlii, and water, most of which is recycled in the process. After fermentation, the broth is taken to a distillation column where ethanol is obtained as top product with 84 % purity in mass. Water, a small quantity of acetic acid, and bacteria are obtained at the bottom, where a membrane unit separates the bacteria and allows the permeate to be recycled back to the reactor. The main obstacles found when making the basic lay out of the process were: designing of a mathematical model to simulate gas to liquid mass transfer rates, selecting an appropriate reactor model for this innovative process, defining which pressure the gas should be compressed to before entering the reactor and defining the capacity of production. The model developed to simulate mass transfer in the reactor is based on an equation where the rate of transfer of gaseous substrate into the liquid is driven by the difference in partial pressure between the gas and the liquid phases. This corresponds with the idea of previously compressing the gas before fermentation. The reactor model selected is Outotec’s OKTOP 9000 ®, an airlift reactor currently being investigated by LUT University. Finally, both the pressure of compression and the capacity of production were fixed by the fact that the bacteria do not allow a concentration of ethanol above 50 g/L within the bioreactor, otherwise they die. As a result, sensitivity analysis were performed using Aspen Plus ® in order to determine the total amount of flue gas to use for the process and its pressure. These values were fixed at 13800 Nm3/h and 3,8 bar, respectively. Initial process description from the literature review and analysis allowed running simulations with Aspen Plus ® to further specify process variables and flow conditions, as well as equipment specifications. All in all, simulation results show an annual productivity of 4888 tons of ethanol. The simulation stage took the longest time, as several modifications had to be made until the simulation converged. Together with the simulated process, a preliminary study of the control of the bioreactor is presented. A basic piping and instrumentation diagram (P&ID) supports this study. Safety sheets for the compounds involved in the process and environmental considerations regarding waste streams are also presented. Along these lines, results show that as much as 1737 tons of carbon are captured yearly in the process. Finally, the economic viability of the project is estimated without taking into account any aid from the EU or the Finnish government for a more conservative approach. According to this analysis, cash flow of the plant considering a 100 % productivity is 720 000 €. This results in a payback period of 10 years. Sensitivity analysis for the biggest contributors to costs and benefits are also included. The use of the waste gases for ethanol productivity is also proved to be more economically viable than its current use: electricity generation. Through the use of waste gases as feedstock to make fuel, domestic economic growth is promoted in a sustainable way by avoiding competition with land, food, and water resources. As a result, the overall economic, environmental and social impacts of the project are expected to be beneficial.

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Item ID: 49069
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Deposited by: Biblioteca ETSI Industriales
Deposited on: 15 Jan 2018 11:03
Last Modified: 24 Apr 2018 10:06
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