Chemical processes date from several centuries ago. These are mature and have established methodologies for their design and evaluation. Process design may have many solutions depending on the design goals. According to Mody and Strong [36], the goals of process design must be to eliminate non-optimal solutions with as little effort as possible. One of the most common group of methodologies combines the conceptual design and the hierarchical decomposition, to determine the step that most affects each process and to use this critical step as the base point for the design of the rest of it [20]. Due to this, the methodologies for designing biotechnological processes had to be reconsidered in terms of specific analysis of processing stages that differ considerably from chemical processes [35]. This type of hierarchy is generally represented through an “onion” diagram, as it is shown in Figure 4.

Figure 4.

“Onion” diagram for the hierarchical design of process [35]

Officially as the United Nations states, biotechnology is any technological application that uses biological systems, living organisms or derivatives thereof, to make products or processes for specific uses [37]. These processes open a new spectrum of possible raw materials, which were currently considered as mere residues (e.g., biomass). During the last decade, biotechnological processes aimed at a wide variety of processes. Several products (biofuels, bioenergy, food products, biomaterials, biomolecules and chemical products) have been developed [38] and different raw materials have been explored, mainly coming from agroindustrial processes. Due to this, the methodologies for designing biotechnological processes had to be reconsidered in terms of specific analysis of processing stages that differ considerably from chemical processes [39]. In this regard, the most advanced concept up to date is the biorefinery, producing different products such as biomolecules, biomaterials, bioenergy and biofuels through an efficient technological scheme [40]. The design of biorefineries and further considerations will be described as follows.

For the design of biorefineries, multiple models have been proposed. Moncada et al. [38] proposes the design and evaluation of biorefineries from the knowledge-based approach. Kelloway et al. [41] propose a guided approach to biorefineries optimization. Pham et al. [42] discuss this approach as an improvement of the process synthesis. Kokossis et al. [43] use the same strategy but considering biomass conversion systems as the basis of any analysis. Patel et al. [44] propose an Early-stage approaches approach. In the design of a biorefinery, it is necessary to consider technical, social, and political aspects as well as logistics and laws, among others. The most common methods of design described by the mentioned authors are studied hereinafter:

• Optimization. This design method aims to maximize the yield or the economic potential based on the limitations, chosen technology, conversions, reactants and products [27]. First, it is necessary to define the desired goal to achieve, for example, maximum production yield or minimum production cost [45]. Then, it is necessary to perform an analysis of the technology alternatives (conversion routes), defining the critical steps in the biorefinery, to integrate technologies and establish the bases of the economic analysis [46];

• Early-stage approaches. This design method focuses on a preliminary assessment without requiring detailed process modelling. Then, the results are compared with the petrochemical equivalent process [47]. Therefore, it is necessary to perform a detailed assessment of the reaction system assuming a 100% recovery of the products [24];

• Knowledge-based approach. This design method applies three concepts: hierarchy, sequencing and integration. These elements will be described as follows:

• Hierarchy. The first level in a biorefinery is raw materials. A given raw material will allow obtaining certain type of products. Depending on the components of the raw material, it is only possible to obtain certain chemical building blocks that can be converted in specific products. Moncada proposed five families of products that can be obtained from biomass: biofuels, bioenergy (e.g., power and heat), food products, biomaterials and biomolecules [19]. Figure 5 shows the linkage between the types of biomass, obtained chemical building block and possible products. The second level of a biorefinery is the technologies. Hierarchy in this regard focuses on the step that most affects each process. This is a modification of the onion diagram [36], which considers the critical stage of the process in the center [19]. Depending on the desired platform, the critical stage may vary in a lignocellulosic-based biorefinery; Figure 5.

  Distribution of biomass types, building blocks (platforms) and possible products

  

• Sequencing. This stage aims to establish a logical order and relation between technologies and products [29]. Therefore, the first step must be the selection of desired products, definition of a main product and by-products and the available technologies. It is very important to define clearly the purpose of the biorefinery. To exemplify, from the production process of sugarcane, it is possible to obtain sugar and molasses as by-product. If the aim of the biorefinery is the production of ethanol, both products could be used for this end. However, if the aim is to produce both sugar for human consumption and ethanol, only molasses should be directed for the production of the alcohol [22];

• Integration. This stage aims to take advantage of all the mass and energy streams within the process. Therefore, in this stage mass and energy balances become transcendental. Mass integration can refer to the optimization of the use of reactants and their recycle, extractive processes of recirculation, pervaporation processes for the separation of different components [48], for example. Roffler et al. [49], studied the extractive fermentation of acetone and butanol. Energy integration focuses on the design of a heat exchange network or the implementation of power cycles in order to improve the efficiency of each stage into the biorefinery [50];

• Sensitivity analysis. This stage aims to identify the trends and tendencies of the biorefinery in terms of its economic and environmental performance in terms of a given input. This information is very important because it gives information about the scale and the feasibility of the process. This stage varies the percentage of the given input (e.g., feedstock flow) in a positive and negative margin and determines the margins of economic and environmental feasibility of the process.

Manufactured chemicals generally are classified in three groups according to the production volume. Bulk or commodity chemicals are produced in very large quantities and tend to have a low sales price. Fine chemicals are obtained in small amount and the price is higher. Specialty chemicals have the highest price per gram and their production volume is the lowest. Generally, commodity chemicals are produced through continuous operation mode and these processes are characterized by large plants, low profit margins, and high-energy consumption [51]. For specialty and fine chemicals, the most common operation mode is batch. These chemicals provide higher profit margins and have less cyclicality in their business cycle, generally, they are produced in volumes lower than 1,000 tons per year [38].

Necessarily, high production volumes will require high amounts of feedstock. However, the scale is not only related to the amount of generated product, but to the amount of processed raw material (processing scale). It is important to note that from the latter perspective, it is possible to obtain both bulk and specialty chemicals in small scale and large scale of production. Nonetheless, the benefits associated to a large scale of production would not be the same as in the case of a large scale of feedstock processing.

According to production capacity, biorefineries can be classified into small and large scale. The size of a biorefinery is influenced by important factors: government and environmental policies and market conditions [52]. These elements influence directly on supply chain decisions, technology selection and integration levels. To exemplify both types, a small-scale biorefinery is the extraction of essential oil, colorants and pectin from fruit peel, a large-scale biorefinery is the production of biodiesel, ethanol and electricity from palm. This definition of scale includes both perspectives (raw material and product), because it depends on the amount of feedstock and hence this limits the production of a given product.

The small or large scale concept is something very confused when biorefineries are designed and specific references or rules are needed. For this purpose, it is necessary to look for another reference that considers certain types of processes or stages of a process with respect to the processing/production scale, which will be addressed in the following section. The aim of this section would be to identify some ranges of raw material flow or capacity that define the scale of the process.

In coffee production different residues such as pulp, husk, leaves, and coffee grounds are produced mainly during the coffee harvesting, processing and final consumption [58]. Other residues that are obtained in high volumes are coffee leaves and Coffee Cut-Stems (CCS). These last are obtained when coffee trees are cut to obtain a younger tree with higher coffee productivity. These wastes are seasonally produced and stockpiled for their burning or, in most of the cases, for their auto-degradation.

In García et al. [59], three possible scenarios for the processing of CCS are analysed. From the diagram shown in Figure 6, 3 scenarios were proposed. Scenario 1 is the production of hydrogen, scenario 2 the production of hydrogen and electricity and scenario 3 the production of hydrogen, electricity and ethanol. The configuration with the best economic and energy performance was the multiproduct portfolio (scenario 3). The most relevant results of this study are shown in the Table 4.

Figure 6.

Biorefinery flowsheet based on coffee cut stems

In this case most of the residues were valorized. However, an integral analysis was not applied. The logistics analysis developed at coffee industry level (confidential results and access) demonstrated later that the implementation of this project is practically impossible for Colombian context based on high inclination fields and the existence or more than 100,000 small farmers that dramatically increases the transport costs and the raw material price, even if it is a residue. Here the crude-oil refinery strategies cannot be used to improve these results. However, additional work is needed to demonstrate the lower scale possible to have a feasible project including the logistics restriction. It is important to note that this is mainly a simulation work and no experiments supported the results.

Pinus Patula is a soft wood grown widely and used in industry for producing important amounts of residues with just a small portion for specific purposes (for example, the sawdust is used in cement industry). The idea of a second-generation biorefinery based on lignocellulosic feedstocks (i.e., Pinus Patula bark) leads to the formulation and evaluation of biorefining alternatives to obtain different and new products.

Wood residues as Pinus Patula bark are an alternative feedstock for producing ethanol and furfural in Colombia as it was demonstrated through assessments developed in Moncada et al. [33]. Different pretreatment alternatives were tested (i.e., dilute acid, alkali, liquid hot water) as well as the fermentation of cellulose hydrolysate to produce ethanol (using S. Cerevisiae), and the dehydration of hemicellulose hydrolysate to obtain furfural. The chemical composition of Pinus Patula and the yields obtained from the experimental assessment were used to feed a biorefinery simulation (see Figure 7) using Aspen Plus to carry out the techno-economic and environmental assessment. Three scenarios were assessed and compared based on different levels of energy integration.

Figure 7.

Biorefinery design based on Pinus Patula bark

The alkali method showed the highest yield (50%). The pentose rich hydrolysate was used as substrate to produce furfural using sulphuric acid as catalyst (yield 91%). The cellulose saccharification was done enzymatically (max. concentration 63 g/L), and the hexose hydrolysate was used as substrate to produce ethanol using S. Cerevisiae as strain (0.42 g ethanol/g sugars). For the three scenarios based on different levels of heat integration (i.e., non-integration, full energy integration, full energy integration plus cogeneration). The fully integrated scenario plus cogeneration system was the configuration with the best economic and environmental performance. For this case, the economic margin was 37.96%, and the potential environmental impact was 0.063 PEI/kg products. This result served as basis to draw recommendations on the technological, economic and environmental feasibility to implement such type of biorefinery in Colombia. Table 5 shows the most representative results in the simulation of the biorefinery described.

This biorefinery was designed through experiments at laboratory level and simulations with last tools for process design and analysis. The logistics in this case is not a restriction but some questions appear: is it really the best combination of products? Is there a real and stable market for the so called fertilizers and animal feed? It is important to note that the crude-oil refineries for example have a very defined and well-studied market to decide what kind of products will be involved in the plant. It looks today that most of the biorefineries proposed at scientific world are very weak in terms of market justification. It could be very dangerous because the errors at this stage can mean a future non sustainable business.

Andes Berry (Rubus glaucus benth) is a common fruit in many countries, especially in Colombia and other tropical countries. This fruit has an important composition in phenolic compounds, specially anthocyanins using an enhanced-fluidity liquid extraction process with CO₂ and ethanol [60]. In 2011, Colombia had a production of 94,000 tons of Andes Berry fruits [61], which is used to produce concentrates, jams and juices among other products. However, the fruit processing leaves significant amounts of residues, which can be used in the extraction of anthocyanins with chemical, cosmetic, food and pharmaceutical purposes.

Spent Blackberry Pulp (SBP) is a waste product of blackberry juice extraction with a high potential as a raw material for valuable compounds. In Dávila et al. [62] a biorefinery is proposed for producing phenolic compounds extract, ethanol and xylitol from SBP (Figure 8). Techno-economic and environmental assessments were developed in order to analyse both, total production costs and potential environmental impact of the proposed biorefinery. Four potential scenarios were evaluated:

• A biorefinery without mass and heat integrations as well as without a cogeneration system;

• A biorefinery with heat integration but with neither mass integration nor cogeneration system;

• A biorefinery with mass and heat integrations but without cogeneration system;

• A biorefinery with mass and energy integrations as well as with cogeneration system.

Table 6 shows the results obtained in scenario 1.

Figure 8.

Biorefinery design based on SBP

Results indicated that the integration significantly affected the total production cost obtaining a reduction of 16.1%, 32.97% and 30.90% for scenarios 1, 2 and 3 while scenario 4 (with cogeneration system) increases the total production cost of the biorefinery. The sale to total production cost ratio was calculated, finding that the scenarios with mass and heat integration with very high values (close to 25) become the most promising for obtaining value-added products. The environmental assessment reveals that potential environmental impact can be reduced according to the level of integration in the biorefinery.

The crude-oil refineries in the world are mainly high scale facilities. Just in the beginning some small scale companies existed. The biorefineries can be high scale, but the small scale cases are not so common given that energy is usually the main purpose. The only solution to the scale problem is the added value. It is possible to affirm that the crude-oil refineries products are low added value and in the biorefineries case together with biofuels some high value chemicals can be produced. In the SBP biorefinery analysed here, the low scale is compensated with very high profits (sale to production costs ratio higher than 25). These values can be achieved in practice when molecules like antioxidants or pharmaceutical products can be obtained. Very high added values in crude-oil industry is something impossible today, but the market for any added value product is also very limited.

In Rincón et al. [63], two biorefineries based on oil palm were designed, assessed and compared to transform this feedstock into biodiesel, alcohols and other added value products. The first scenario considers the simultaneous production of biodiesel and ethanol from lignocellulosic biomass and glycerol. The second scenario includes palm oil fractionation, biodiesel production and biomass fired cogeneration using a gasification technology. Figure 9 presents the flowsheet for the two biorefineries. These two integration alternatives were analysed according to their potential income (total sales/total production cost ratio), and environmental impact (WAR algorithm). Table 7 shows the most relevant results obtained.

Figure 9.

Oil palm biorefinery

The total sales/total production cost ratio obtained for the integrated approaches were 1.88 and 3.33, respectively. The economic and environmental assessment revealed a better global performance for the second integrated approach. In this sense, a biorefinery with a major number of products and low energy consumption is an important option for the development of oil palm industry. The latter is due to the maximum utilization this feedstock.

Palm is an interesting example of total integration of feedstocks in the framework of bioenergy production. The question about the use of methanol (mainly produced in crude-oil refineries) or ethanol (possible to be obtained from the lignocellulosic residues produced in the oil extractions units) demonstrated the competition between crude-oil and biomass industry. Additionally, the logistic problems for energy production in rural areas are also solved through this approach if considering that ethanol, biodiesel and electricity can be produced without dependency on supplies in raw materials from crude-oil refineries.

The actual Amazon Region is more than any natural region with high biological and ethnic biodiversity, of fragile ecosystems. It is an essential supplier into the global climate change and source of riches without exploitation. It is a large Cuenca that is shared for seven south-American countries. But, first and foremost, it is the scenario of the most serious social, environmental and territorial conflicts derived to the people movements without organization, resources exploitation and extraction, and public programs and mistaken regulation or lack of them. Last statements discussed in detail in Correa et al. [64] involves the justification for new proposals for boosting the economy in this region. In a biorefinery based on an exotic fruit as Makambo at low scales to produce: pasteurized pulp, seed butter, residual cake (it is a paste that should be used as an ingredient in a food industry) as a substitute for cacao, phenolic compounds, biogas and biofertilizer. This fruit belongs to Sterculiaceae family as Theobroma cacao (Cocoa) and Theobroma grandiflorum (Copoazú). It grows in different regions of Central and South America. Pulp is used for direct consumption as food. Seeds are used as a kind of cocoa. Peel is usually a waste. In Figure 10, the biorefinery is disclosed. Table 8 shows the material balance for the biorefinery described.

Figure 10.

Amazonian fruit biorefinery: Makambo case

As a result of the analysis, a positive NPV was found with a payout period of 5.1 years and a profitability index of 1.35. For this small scale it is a very representative result. On the other hand, the environmental analysis carried out with the WAR software resulted indicator total the contamination of 3E-2 PEI/kg product, in which the category that contributes most to this value is acidification potential.

The case analysed can be considered as very low scale project (2-5 tonnes a day as maximum). The solutions for small scale projects should integrate natural not very well processed products (with no sophisticated technologies) and very high added value products as antioxidants (with very sophisticated technologies). The crude-oil refineries at fractionation steps also use very simple technologies as distillation with plates and only to obtain very high special chemicals complex catalytic reactors and sophisticated separation units are used. But the most important result of this work, where experimentally and theoretically the feasibility of this biorefinery was demonstrated, is the possible use of a biorefinery concept at small scale to solve problems in small rural communities.

Oil palm is grown in Colombia in four different zones, which are southwestern, northern, central and eastern. The oil palm crop became one of the most important oil crops in the world due to the following features: steady and continuous oil production, adsorption of large amounts of CO₂, low biodiversity compared to the crops that it replaces. In addition, its production yields are higher than those achieved by other oil crops such as soybean, rapeseed and sunflower. Oil Palm Rachis (OPR) is a residue coming from the oil palm tree. Oil palm fronds are the largest lignocellulosic biomass that is produced during the oil palm tree harvesting activities. This one can have a length from 7 m to 8 m. Also, oil palm fronds can constitute a 70% of the total amount of lignocellulosic residues generated in the oil palm industry. The oil palm frond is the set composed of the rachis, petiole and leaves. The petiole is the transition between the stem (rachis) and the leaves. The rachis is the stem that supports all the leaves of the oil palm tree. In Cardona Alzate et al. [66], a techno-economic analysis for an OPR biorefinery is presented for the Colombian case. The first biorefinery involves ethanol, lactic acid, xylitol and biogas production. These compounds are biochemical products obtained from fermentation and anaerobic digestion processes. The second biorefinery considers ethanol, lactic acid, n-pentane, methanol and ethyl levulinate as final products. Figure 11 shows the flow chart of biorefineries. Table 9 shows the mass balance for the biorefineries. The mass flow rate considered is 250 tons/day of OPR.

As a result of the analysis, a positive NPV was demonstrated with a payout period of 4.07 and 4.55 years as well as profitability indexes of 1.50 and 1.43 for biorefineries I and II, respectively. The internal rate of return for both cases was close to 50%.

Figure 11.

OPR biorefinery proposed in Cardona Alzate et al. [66]

The two biorefineries analysed in this paper compare different product configurations from the same raw material. The analysis is carried out to implement catalytic processes, both homogeneous and heterogeneous. The effect of the catalytic processes implemented in the biorefinery design is mainly reflected in the total raw material and utilities costs. The implementation of catalytic processes into biorefineries increases the number of products that can be obtained from lignocellulosic biomass. Therefore, the inclusion of these types of processes could supply products to different production chains. An advantage of the catalytic processes is their facility to be implemented in any part of a biorefinery because these can be used to upgrade the main biomass components or convert the products obtained from biochemical and thermochemical pathways to other added- value products.

In Moncada et al. [40], a techno-economic analysis for a sugarcane biorefinery is presented for the Colombian case. Two scenarios for different conversion pathways for sugar, fuel ethanol, PHB, anthocyanins and electricity production are shown. The first scenario considered all the products and the second just the Colombian base case producing sugar, fuel ethanol and electricity. A simulation procedure was used in order to evaluate biorefinery schemes for all the scenarios, using Aspen Plus software that included mass balances, energy calculations and economic evaluation for each process configuration. Table 10 shows the mass balance for the scenario that involves all products.

The results showed that the configuration with the best economic, environmental and social performance is the one that considers fuel ethanol and PHB production from combined cane bagasse and molasses (see Figure 12).

One important result to discuss in this work is that a very high profit margin is reached when all the products in an integrated biorefinery are considered (scenario 2 32.94%, see Figure 12). Another important social aspect to consider is the land requirements to ensure the needed feedstock for production. In the case of Colombia, the average crop yield per hectare is 93 tons (but in the main producing regions, it is about 120-140). Therefore, in this project a high scale is necessary and the sugarcane needed to cover the biorefinery capacity is 1,725,000 tons/year, with a land area requirement of 18,839 hectares. This land requirement represents the 8.6% of the total planted area reported for 2010 [67]. It ensures greater capacity of sugar production to keep food security, larger ethanol production for the oxygenation programme, acceptable GHG emissions, low stillage effluent and positive social aspects through job generation. PHB production would open new markets to consider second-generation feedstocks and anthocyanin production would innovate in the national market. The term sequence can be easily used for analysing other combinations of technologies, feedstocks distribution and inclusion of other products.

Figure 12.

Scenario 2 (ethanol, PHB, sugar, energy and anthocyanins as products) for sugarcane biorefinery proposed in Moncada et al. [40]

One very important topic to discuss in the sugarcane biorefinery above mentioned is the status quo that characterizes the crude-oil refineries and the sugar cane sectors. In many refineries the flexibility for a quick introduction of new products line with new equipment or revamping is really low. The same existing sugarcane factories are also very conservative and the addition of new products or conversion lines is practically impossible, even if it is a really new and lucrative business. What was learned after these statements is the importance of flexibility, especially for very big biorefineries is to be prepared for changes in the market and then in technologies or products needed to continue with the same profitability.

Beta Renewables’ commercial-scale production at the Crescentino plant in Italy is one of the most important biomass projects in the world. Beta Renewables uses lignocellulosic biomass technology called Proesa. Giant reed, agricultural and wood residues are used as raw materials. The Italy plant was designed to produce biofuels from wheat straw and corn straw in the summer, rice straw in the winter and in between winter and the summer, eucalyptus. As the web page informs [68] PROESA™ combines an enzymatic pretreatment process with fermentation. This process has a shorter residence time than other enzymatic hydrolysis technologies. It is acid and alkali-free and has minimal byproducts. The technology is protected by 26 patent family applications, 14 of which are public.

The design promised biofuel sas ethanol, bio-jet, butanol and biochemicals as fatty alcohols 1,4 butanediol, farnasene, acrylic acid, succinic acid and others. Additionally, lignin derivatives were considered as phenols, xylene, terephthalic acid. However, in 2017 it was reported that the Beta Renewables plant in Crescentino, Italy with costs of about 250 million euros, has been closed. The biorefinery had a capacity to produce 40,000 tons of bioethanol per year. This biorefinery of ethanol was the first on a commercial scale in the world. The Beta Renewables biorefinery was established at the end of 2011 as a joint venture between the subsidiary of M & G, Biochemtex and the Findo from Texas Pacific Group. Novozymes acquired 10% of the shares of Beta Renewables in 2012 [69]. In this case, logistic and some design failures can be addressed as the reasons for the operation and financing problems of this biorefinery.

Raizen is a biorefinery located in Piracicaba – SP, Brazil.

The USD 100 million plant is located adjacent to a sugar cane mill and will produce 40 million litres of cellulosic ethanol a year from sugarcane bagasse and straw. The plant construction was completed on schedule, and production of cellulosic ethanol began in late 2014. Initially, the project considered the use of bagasse as the feedstock and the return of lignin residue to the on-site boiler. The project involves Iogen technology (pretreatment, enzymatic hydrolysis and fermentation) and clearly uses the advantages of integration with a sugarcane mill [70].

The company POET-DSM Advanced Biofuels raised in 2014 is a production plant, in Emmestsburg, Iowa, United States called Project Liberty. POET is one of the largest producers of ethanol in the world. Moreover, this company is considered as a pioneer in renewable fuels. On the other hand, DSM is a recognized company in the expansion of industrial and biotechnological operations. Also, it is a leader in conversion technologies (yeast and enzymes) for cellulosic biomass to ethanol. POET-DSM is based on the strengths of both companies for the purpose of producing cellulosic bioethanol [71]. Project Liberty is now running pretreatment at 80% uptime [72]. Project Liberty, as it has been named, will process 770 tons of corn cobs, leaves, husk and some stalk daily to produce 20 million gallons of cellulosic ethanol per year, later ramping up to 25 million gallons per year. Project Liberty will be the flagship plant in POET-DSM Advanced Biofuels’ plan to license this technology to companies across the US and around the world. The company ‘announced the construction of an on-site enzyme manufacturing facility’ to directly pipe DSM enzymes into the process and ‘ramped up biomass purchasing’ in anticipation of increased production levels in 2018 [73]. Additionally, Project Liberty produces biogas and combined heat and energy [74].

Abengoa Bioenergy Biomass of Kansas (ABBK) is a company of Abengoa Bioenergy that operated a biomass-to-ethanol biorefinery located in Hugoton, Kansas, USA. This commercial scale biorefinery facility was implemented to produce 25 million-gallon/year of ethanol from nearly 350,000 tons of biomass annually and the residues to be combusted along with 300 tons/day of dry biomass material (feedstock) to produce 18-21 megawatts of electricity [75].

However, this project as one of the biggest in the world was shut down after one year of launch. The so called biorefinery, built by a Spanish company with financing from the US Department of Energy never lived up to its billing. Construction of Abengoa’s bio-refinery finished in mid-August 2014. In late November 2015, Abengoa SA, the parent company of Abengoa Bioenergy, filed for creditor protection in Spain, prompting fears it might default on nearly USD 10 billion of debt. Then the company shut down the Hugoton plant USA. Abengoa received a USD 132.4 million loan guarantee and a USD 97 million grant through the Department of Energy to support construction of the Hugoton facility. According to the Department of Energy’s website, Abengoa fully paid back its loan guarantee in March.

This is a very good case for further analysis. The financial aspects of biorefineries are still very influenced by the governments and policies. This is a very dangerous support that in this case demonstrates that the sustainability of the projects at every scale should be considered rigorously and the risks accounted before any nice project will be developed.

Biomass gasification has been widely researched since the Second World War to use hardwood as fuel for vehicles. This technology provides a relative low-cost energy production due to the amount of fuel gas that can be obtained. On the other hand, many types of gasifiers and designs have been proposed to increase the energy efficiency of the process. Solids flow, gases flow as well as the heat and mass transfer issues are considered the biomass gasification due to the feedstock properties. The main product that is obtained from the biomass gasification is a gas mixture called syngas (mainly hydrogen and carbon monoxide), which can be used as chemical platform and energy source.

Biomass gasification has not been implemented at industrial level widely. Only coal gasification has been applied to produce syngas as chemical platform. Nevertheless, co-gasification has emerged as alternative for using lignocellulosic feedstocks at industrial level in this process. Actually low-scale applications related with the heat and power production has been implemented in the world [76]. Figure 13 present the flow diagram for the gasification process.

Figure 13.

Gasification process

Table 11 shows some developers or projects in which different raw materials are used to produce energy. Most of these projects or plants are considered as biorefineries due to the production of syngas as biofuel, electricity from syngas and in some cases the use of syngas as platform to obtain different chemicals.

Pyrolysis is one of the most promising thermal conversion technologies for biomass. It can decompose biomass into solid bio-char, liquid bio-oil, and combustible gas to meet different energy needs approaching the biorefinery concept. Pyrolysis processes are carried out in the absence of oxygen, at atmospheric pressure, and at temperatures ranging from 300 to 600 °C. Biochar is the main product of the traditional slow pyrolysis process, in which the biomass (usually wood) is heated slowly to temperatures between 300 and 400 °C. Fast pyrolysis, on the other hand, involves very high heating rates to temperatures around 500 °C followed by rapid cooling and condensation of the vapours produced. This yields a maximum quantity of dark-brown mobile liquid with a heating value roughly equal to that of wood, which is approximately half the heating value of fossil fuel oil [77]. Figure 14 presents a flow diagram for the process of pyrolysis.

Figure 14.

Pyrolysis to bio-oils

Table 12 shows some companies in which different raw materials are used to produce energy and bio-oils.