An introduction to integrated biorefineries

Driven by the growing need for a sustainable and secure supply of energy and chemicals, as well as the increasing attention to the environmental consequences of utilizing fossil fuels, there is much interest in the development of cost-effective biorefineries. A biorefinery is a processing facility that converts biomass into chemicals and fuels; the term is derived in reference to analogies with modern refineries that use petroleum as the main feedstock. However, the concept of converting biomass (e.g. agricultural and energy crops, agricultural and forestry waste, municipal solid waste, etc.) into value-added energy and chemical products is well established. For example, ethanol has been produced by humans in alcoholic beverages; it was also used as fuel in early motor vehicles before the era of inexpensive fossil fuels began, in the early 20th century. Despite the dominance of fossil energy, the oil price shock that occurred during the 1970s, and more recently in the late 2000s, triggered renewed interest in biofuels.

The early generation of biofuels was produced mainly using feedstocks derived from food crops, such as sugar, starch and vegetable oils. Such systems are highly inefficient. For example, the conventional production of biodiesel or bioethanol tends to consume large amount of energy, amounting to 30-50 percent of the energy content of the feedstocks; in contrast, optimized oil refineries only consume three to five percent of feedstock’s energy content. In order to improve the overall efficiency of biofuel systems, the concept of the integrated biorefinery, which consists of multiple biomass conversion platforms/technologies, was proposed based on analogy with fossil fuel refineries. Due to the integration of energy and material of different platforms/technologies, the overall energy and fresh resources consumption will be lower, as compared to the processes that operate independently. The parameters and challenges for integrated biorefineries, and the potential of using Process System Engineering (PSE) tools (e,g. modeling, targeting and optimization, etc.) in addressing these challenges is to be further discussed here.

There are a few main criteria, from an extensive list, that will significantly affect the efficiency of an integrated biorefinery. First, an integrated biorefinery needs to be able to accommodate the variation in feedstocks’ availability and quality, especially if the seasonal aspect of biomass availability is in play. Thus, this criterion gives rise to the challenges to establish a sustainable and steady supply of feedstocks for the integrated biorefinery. Feedstocks’ supply is often accompanied by issues of production and transportation cost, as well as difficulties in harvesting and storing for biomass. Besides, designing an integrated biorefinery that has reliable biomass conversion equipment that is able to accommodate such variation is also a crucial criterion in ensuring the feasibility of an integrated biorefinery.

A higher degree of energy and material integration between platforms/technologies is needed to minimize the overall raw material consumption, waste generation, and to maximize overall efficiency, to an extent comparable to that of an oil refinery (note that the latter has had the benefit of efficiency improvements arising from decades of accumulated knowledge). To fulfill this criterion, the challenges involved are to identify the opportunity for process integration and setting the optimum product portfolios. Furthermore, as an integrated biorefinery consists of multiple conversion platforms/technologies, proper integration between them will ensure that the upstream technology is able to produce chemical intermediates with specification which match the requirement of downstream processes. This will reduce the additional process needed to condition the intermediates.

Recent research efforts in this area are focusing on developing tools to design, analyze and optimize biomass logistics, biomass conversion, process efficiency, process scheduling as well as addressing the issues of determining the optimum product portfolio for an integrated biorefinery. The potential of PSE tools is exhibited in optimizing various established biomass-to-energy technologies such as biomass combined heat and power (CHP) plant, polygeneration facilities, biodiesel production and scheduling and bioethanol production. Thus, it is noted that PSE tools are able to aid the conceptual design of an optimal integrated biorefinery and address the abovementioned challenges.

The prevailing doubt in mind when it comes to the prospect of an integrated biorefinery is whether it will be just another biofuel concept that is not sustainable without substantial financial subsidies. Of course, there is still plenty of research and development to be done in this area, especially in the integration of various platforms/technologies and throughout the whole biomass supply chain to achieve maximum efficiency. However, the scientific community made the correct first step in developing the concept of integrated biorefinery in analogy to oil refinery, a highly efficient concept. Again, although the gaps and barriers related to the implementation and commercialization of such a concept are yet to be fully addressed, we are heading down the right path.

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Douglas Tay is a Ph.D. candidate at the University of Nottingham, Malaysia. He is currently a visiting researcher at De La Salle University throughout the month of January 2011. His areas of specialization include development of both insight-based and optimization-based tools for the synthesis of integrated biorefineries. These techniques address many of the challenges in synthesizing an optimal integrated biorefinery using Process Systems Engineering (PSE). Some of his latest work will appear in forthcoming issues of the Industrial and Engineering Chemistry Research and Clean Technologies and Environmental Policy. In addition, he also presented his research works in various international conferences, such as the AIChE Annual Meeting 2009, PRES 2010, PSE Asia 2010 and APCChE 2010. He has been collaborating with well-known PSE researchers from the USA (Prof. Mahmoud El-Halwagi at Texas A&M University and Dr. Mario Eden at Auburn University) and the Philippines (Prof. Raymond Tan at De La Salle University). In 2009, Douglas was a visiting researcher at Texas A&M University and Auburn University. E-mail him at [email protected]. 

Dr. Denny Ng is an assistant professor from the Department of Chemical and Environmental Engineering at the University of Nottingham, Malaysia. Before joining the university, he worked as a postdoctoral research associate at the Chemical Engineering Department of Texas A&M University (US). He obtained his Ph.D. degree from University of Nottingham. His areas of specialization include resource conservation via process integration techniques (pinch analysis and mathematical optimization), process synthesis and design, synthesis and analysis of biomass processing and integrated biorefineries as well as energy planning for greenhouse gas emission reduction. He has published more than 25 journal papers and made more than 40 presentations in various international and national conferences. He has been collaborating with well-known international researchers from the US, the Philippines, Taiwan, etc. throughout his career. He was the recipient of World Federation of Scientists (Malaysia National Scholarship) award in 2007. During his Ph.D. days, he was also a visiting researcher at Texas A&M University, USA; De La Salle University, Philippines; and National Taiwan University, ROC, in the winter of 2006, summer of 2007 and summer of 2008, respectively. E-mail him at [email protected].