Ethanol from corn: a technical and economical assessment based on different scenarios

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Abstract

A dry-grind ethanol from corn process analysis is performed. After defining a complete model of the process, a pinch technology analysis is carried out to optimise energy and water demands. The so-defined base case is then discussed in terms of production costs and process profitability. A detailed sensitivity analysis on the most important process and financial variables is carried out. The possibility to adopt different alternatives for heat and power generation combined to the process is evaluated.

Introduction

Bioethanol is presently the most important biofuel for automotive transportation. In 2006 about 40 million tonnes of ethanol was produced worldwide (compared to about 6 million tonnes of biodiesel). The United States is the world top producer (about 15 million tonnes in 2006 and a projected production of over 18 million tonnes in 2007); Brazil is a close second. The European Union produced about 2.5 million tonnes in 2006, but probably this number will significantly increase in the years to come. The industry will keep on investing in new plants and increasing the production capacity and it is clear that ethanol will become a global commodity (Jacques et al., 2003).

Ethanol is obtained by the fermentation of energy crops, either sugar cane or cereals (corn, wheat, or rice): a favourable climate allows Brazil to grow and ferment sugar cane, whereas the U.S. ethanol production is based on corn. In the EU both corn and wheat are used depending on the specific country. In this work, we will consider the Italian situation. In Italy, although ethanol production has a long tradition in the beverage industry (i.e. wine and spirits), the production of ethanol as biofuel is just being initiated. The first plants are supposed to come into operation by early 2009; corn will be the obvious choice as a raw material, considering the very high yields which can be obtained in Northern Italy (10–14 tonnes/ha).

The ethanol production from corn is definitely a mature process, but its optimisation potential and economics have become a real issue only very recently, i.e. as soon as the production scale has dramatically increased and has determined a great price variability.

Since the energy costs to obtain bioethanol are second to the raw material costs only, the industry has continued to improve its energy efficiency profile (e.g., U.S. Environmental Protection Agency, 2006) and to assess new technological solutions for heat and power generation (Morey et al., 2006). The use of process simulators (e.g., Kwiatkowski et al., 2006) and optimisation techniques (Peschel et al., 2006) has recently been applied to evaluate new processing alternatives and products from starch-based commodities. We believe that the world panorama allows for a reliable analysis of the business potential and risks and that real data can be used to assess the economics of the business by taking into account possible technological improvements and price variations.

The aim of this work is to provide a snapshot on the present business situation and to evaluate a number of potential short-term scenarios. Data from the Italian ethanol industry will be used, but the results will be representative of a more generic European context.

This paper is divided in two parts. In the first one, process simulation will be used to describe a “standard” production process. Pinch technology will be applied to identify some limiting operating conditions. The process sensitivity to a number of critical variables will be analysed.

In the second part, a financial analysis will be carried out to evaluate the present profitability of ethanol production from corn in EU country, referring to an Italian production plant as a case study. Actual capital costs will be used. The sensitivity of process economics on the raw material costs, products’ costs and technological changes will be assessed. Besides, different options for combined heat and power (CHP) generation will be analysed. In particular, the possibility of using one co-product, i.e. the Distiller's Dried Grains with Solubles (DDGS), to produce electricity, will be incorporated in the financial analysis. Eventually, the potential effects of green credits on investment choices will be discussed.

Section snippets

Process description and flowsheet

The most common processes in conventional corn-based ethanol production are known as dry grind (DGP) and wet mill. The DGP is usually the preferred choice and also in this work it is adopted as a reference. A generic simplified ethanol plant is simulated by means of a process simulator (Aspen Plus™) in order to have a sensible base case for the sensitivity and financial analyses.

The process block flow diagram is shown in Fig. 1: the raw material (corn) is turned into the two products, ethanol

Pinch technology analysis

The energy optimisation of the bioethanol process has been achieved by using Pinch Technology Analysis (PTA, Linnhoff and Flower, 1978), through the definition of the heat exchangers network, the classification of the hot and cold streams, the determination of the pinch point (by composite curves), and eventually the setting up of the final heat exchangers network.

The hot (i.e. to be cooled) and cold (i.e. to be heated) streams can be represented on a temperature–enthalpy diagram in the form of

Process financial analysis

As reported above, one goal of this study is to assess the business scenario of a “first generation” bioethanol production process and, afterwards, the convenience of making the process self-sufficient in terms of the energy demand. The quantification in terms of cost savings and returns in a short-term time horizon has been conducted by means of a financial analysis for both the base case and the alternative solutions proposed. A financial model (Douglas, 1988) capable of both evaluating

Concluding remarks

The paper has analysed a dry-grind process for the production of bioethanol in Italy. A rigorous process simulation was carried out to assess the overall yield and the energy and water requirements. The process was optimised adopting a pinch technology analysis that demonstrated the possibility of reducing both energy and (particularly) water requirements.

A financial analysis was then implemented and carried out to highlight costs and profitability of an investment on bioethanol production. A

Acknowledgement

F.B. and A.B. gratefully acknowledge Triera S.p.A. for financial support.

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