Plasma gasifiers use a plasma gun to create an intense electric arc between two elec­trodes. The temperature of the arc can reach extremely high (> 13,000 °C). Biomass, on the other hand, is fed at lower temperatures (2,700-4,500 °C), but still sufficiently high to crack heavy hydrocarbons. Due to its high operating temperature, the plasma

Flow meter

Fig. 10.2 Sketch of a (a) conventional rotating fluidized bed and (b) novel rotating fluidized bed. (Reprinted from ref. [74], Copyright 2008, with permission from Elsevier) gasifier can crack harmful products, such as furan and dioxin, making it suitable for MSW and other types of waste products.

10.6.5 Rotating Fluidized Bed Gasifier

As previously discussed, heat and mass transfer play an important role in the gasi­fication process. As such, fluidized beds are advantageously characterized by high heat and mass transfer rates that will result in temperature homogeneity and the rapid mixing of particulate materials. Heat and mass transfer are maximized by increasing the gas fluidization velocity, but the gas velocity cannot be indefinitely increased. With increasing superficial gas velocity the solid hold up in the bed region decreases causing a short solid residence time and a low conversion or reactor volume increase. To overcome these limitations of conventional fluidized bed gasifiers, the concept of a rotating fluidized bed (RFB) has been introduced. RFB reactors were first patented by Horgan and Morrison in 1979 for a coal combustion application in a centrifu­gal fluidized bed [73]. RFB consists of a cylindrical gas distributor chamber rotating around its axis (shown in Fig. 10.2). The rotating motion of the cylinder is transferred to the particles via fraction and gas is injected inward through the gas distributor. The particles are fluidized uniformly under the action of two opposite forces: the radially inward drag force exerted by the injected gas and the radially outward centrifugal force. The minimum fluidization velocity increases with increasing the reactor rota­tion speeds (rising centrifugal force magnitude). The magnitude of the forces, which can be much higher than gravity, depends on the operating conditions: solid rotating velocity and gas injection velocity.

The rotating motion of RFBs may cause difficulties in design and operation, like severe vibrations of the reactor during operation. To overcome these difficulties, a new concept of a rotating fluidized bed has been proposed where the geometry of the reactor is fixed and the fluidizing gas is injected tangentially via multiple gas inlet slots at the fluidization chamber wall. As a result, the tangential drag force will induce the solid particles into a rotating motion as well as produce a radially outward centrifugal force [74]. The RFB reactor can operate at much higher gas velocities and solid hold-up compared to the fluidized bed. Due to high attrition the novel RFB reactor is suitable for processes where solid is a reactant, like biomass gasification [75].

As discussed above there are several options when choosing and designing a gasifier. The choice of one type of gasifier over another is, however, determined by the type of fuel, its size, the moisture content, the physical limitations of the reactor, its production capacity and the final use of the product gas since one type is not necessarily suitable for the full range of capacities. The different gasifier characteristics are summarized in Table 10.3.

Fluidized beds are widely used in the chemical industry for catalytic cracking and other processes. In fluidized bed reactors, a gas stream (inert gas for pyrolysis) is forced through a bed of powdered material from a distributor plate that supports the bed. At low gas velocities, the bed of particles is non-moving and this is referred to as a fixed bed. As the gas velocity is increased, the drag forces applied on the particles increase until minimum fluidization velocity is reached: the bed is ‘supported’ by the gas and behaves like a fluid. If the gas velocity is increased further, bubbles are formed at the distributor plate and rise through the bed of solids similar (but not identical) to air bubbles in water. Bubbles promote the circulation of solids to ensure a uniform temperature throughout the fluidized bed. A bubbling fluidized bed (BFB) reactor is designed in a way to avoid the entrainment of particles outside the reactor (also called elutriation). The bed zone is narrower to promote the circulation of particles and the formation of bubbles. The gas exits the bed to enter a freeboard zone and a higher diameter disengagement region where the gas velocity is significantly reduced. In the disengagement region, particles that would be entrained in the bed and freeboard zones fall back into the bed by gravity. There is an appreciable amount of established scientific literature on fluidized beds [48,49]. BFB reactors are used for fast pyrolysis by the company Dynamotive, which is operating a pilot-scale unit to convert biomass into bio-oil. The unit has been reported to process at up to 100 tons of biomass per day [50]. Figure 11.3a gives a global view of a possible biomass pyrolysis unit with a BFB.

13.3.2.1 Operation of RCF Facility

Tables 13.2 and 13.3 show the results of refining testing. The average electrical energy consumed by the RCF facility during the testing period was 5.5 kWh. Using the RCF facility, about 44 % of the raw biogas (216.0 Nm3/days) was refined to methane (96.0 Nm3). To increase the methane concentration of the biogas after purification to about 94.5 % and to standardize the caloric content, about 0.5 % propane (1.0 Nm3) was added. This resulted in refined gas (97.0 Nm3) with a caloric content of 9,290 kcal/Nm3 (38.9 MJ/m3).

The gas at the final refining process had a WI of 49.3 and maximum combustion potential (MCP) of 34.3 m/s. These values are the minimum requirement within the specifications of town gas (WI: 49.2-53.8; MCP, 34-47 m/s). In addition, though the amount of raw gas produced per day was 216.0 Nm3, the amount of refined gas was

97.0 Nm3, which satisfied the condition set by the High-Pressure Gas Safety Act of less than 100 Nm3 per day for Class 2 producers.

Heterogeneous catalysts promote reactions at the active sites on their surfaces, so the accessibility of cellulose to internal acidic sites and the dispersion limitation are important limiting factor for the catalytic activity. Heterogeneous catalysts can offer technical advantages related to stability, separation, handling, recycling of catalysts, and reactor design. However, none of the catalysts (metal oxides, zeolites, supported acids, and cation-exchange resins) are highly active and selective under mild conditions [80]. Reaction conditions such as reaction temperature, catalyst loading, and reaction medium are required to be optimized for cellulose hydrolysis with solid catalysts to achieve practical applications.

Chemical pre-treatment such as alkaline (KOH and NaOH) and acid (H2SO4) pre­treatments are carried out in this study. Further study is done where three differently pretreated OPF samples were subjected to sodium chlorite delignification. Lignin content in these three pretreated OPF samples are compared before and after sodium chloride delignification. Alkali pre-treatment assists in the hydrolysis of lignin. The best performance is indicated by the lowest percentage of total lignin content re­mained in the sample after treatment. Study indicated that NaOH pre-treatment coupled with chlorite delignification gave the best performance on lignin removal among the different pre-treatment methods applied, with the lowest total lignin con­tent remained in the sample which accounted for 19.32 % whereby total lignin content in untreated sample was found to have 30.78 % as shown in Fig. 17.4. Chlorite delig — nification can partially remove lignin from biomass [74]. The chlorite treatment was more effective than the organosolv method, as 2.5 % of lignin was left in chlorite treated barley husks as compared to 3.9 % in organosolv treated barley husks [74].

The treated OPF and untreated OPF is subjected to steam and gasified at tem­perature higher than 500 °C. For all experiments, biomass sample weight was approximately 5 mg. N2 was used as inert carrier gas with a constant flow rate of 100ml/min. The micro vacuum pump (650mmHg was applied throughout the experiments) was attached to the gas chromatography (GC) to facilitate gaseous product from thermogravimetric analysis (TGA). Steam was generated by super heater up to 400 °C prior to injection in TGA. The system was purged with N2 gas (100 ml/min) for about 20 min to remove entrapped gases at temperature of 50 °C. All samples were heated at a constant heating rate of 20 °C/min from 50 to 900 °C where it was kept constant for 10 min. To avoid condensation, steam was introduced when temperature inside the TGA reached to 110 °C. The amount of catalyst used was based on biomass-to-catalyst ratio of 3 (mass basis), while steam-to-biomass was kept constant at 1:1 ratio (mass basis). The apparatus used is shown in Fig. 17.5. The biomass steam gasification experiments were performed in a standard TGA (EXS­TAR TG/DTA 6300, from SII) and GC (Agilent 7890A, Agilent Technologies) under non-isothermal conditions.

Balance beam

Fig. 17.5 Experimental Apparatus

Results from TGA-GC analysis reveal that NaOH coupled with chlorite treated OPF was able to produce higher yield of H2 (56.56 vol%) compared to untreated dried OPF (39.48 vol%) as shown in Fig. 17.6. On the other hand, H2 can be produced at a much lower temperature of 550 °C instead of 850 °C if the OPF is treated with NaOH coupled with chlorite; hence, the chemical pre-treatment has improved the biomass quality.

Pyrolysis is the cracking of hydrocarbon molecules into smaller gas molecules without any major reaction with air or any other gasifying medium. The kinetic information of pyrolysis is crucial for the design and scale-up of any gasification process. Extensive investigations have been done on the kinetics of biomass de­volatilization in an inert atmosphere. Table 10.2 shows the most widely used kinetic schemes of biomass pyrolysis.

Earlier kinetic models consisted of simple, single first-order reaction schemes to describe the total volatile yield. Later, more complicated two — and three-step reaction networks containing parallel and series reactions were introduced by different authors [22, 24]. These are empirical models whose parameters are calculated by fitting experimental data generally derived from thermo-gravimetric measurements. Since most of the biomass is composed of cellulose, hemi-cellulose, and lignin, the most accurate models are reported to be a three independent parallel reactions model [25-29].

Most modeling efforts with the three independent parallel reactions model have been conducted using experimental data from a single heating rate [25, 30-33]. The effect of heating rate on the pyrolysis yield is, however, significant because the kinetic parameters derived from a single heating rate cannot be confidently extrapo­lated to other heating rates. Radmanesh and Chaouki proposed an improved model for biomass pyrolysis, which is applicable to different heating rates [27]. The ki­netic parameters were calculated from experimental data obtained at relatively low heating rates (maximum heating rate was 50 ° C/min). Therefore the extrapolation of these kinetic models to actual gasification process conditions yields significant

uncertainties since, in reality, biomass temperature increases very rapidly from am­bient temperature to about 800-1,000 ° C (in less than 1 s) as it is fed into the gasifier [27]. Consequently, the actual heating rates applied to biomass particles in pyrolysis systems are significantly higher than 50 ° C/min or even 100 °C/min.

There are only a few studies on pyrolysis at high heating rates (1,000 °C/s) and the resulting gas production [34-37]. Although it is very important to have knowl­edge about pyrolysis kinetic gasification design and optimization, it is very difficult to obtain reliable data for kinetic constants that can be used for a wide range of biomass at different heating rates. Most models are derived from cellulose pyrolysis experiments, and the available models in the literature are only applicable to specific conditions.

The idea of cultivating trees strictly for energy and biorefining purposes has been proposed. Certain fast growing tree species such as cottonwood, aspen and eucalyptus can grow at rates of around 1 m/yr or even more. The short-rotation woody crop (SRWC) technique can be used to reach yields of about 10 dry metric tons of woody crops per hectare per year can be achieved. However, the economic viability of SRWC is very fragile due to the high costs of preparation and fertilization of the sites [19].

Depending on the maturity of the woody crops, chemical composition will remain close to that of wood and bark (see Sect. 11.2.1.1). The main difference will arise due to the leaves and trimmings, which will accumulate dust and metabolic inorganics up to a few mass per cent during the trees’ growth.

11.2.1.3 Perennial Herbaceous Crops

Perennial crops are vegetal—not edible for humans—which include among others: switchgrass, weeping lovegrass and Napier grass. Herbaceous crops are usually dedicated to alcoholic fermentation because of their high availability of complex sugar content, but pyrolysis of these vegetals has been shown to produce high oil yields [20]. The oil produced contained water-soluble and water-insoluble fractions. Moreover, significant amount of alkanes and phenolic compounds can be found in these oils [21] suggesting a high potential of perennial crops for specialty chemicals production from pyrolysis.

Philip G. Rutberg, Vadim A. Kuznetsov, Victor E. Popov, Alexander N. Bratsev, Sergey D. Popov and Alexander V. Surov

Abstract The chapter is dedicated to a promising method of biomass treatment — plasma gasification. Increased temperatures and energy supply allows significantly in-crease the range of wastes and other carbonaceous materials which could be ef­ficiently processed. Fea-tures of plasma usage in updraft and downdraft bio-mass gasification are described. Several promising re-newable energy sources (wood, en­ergy crops, wastes of livestock, and poultry industry) are examined for the usage in downdraft plasma gasification. The correlation of key parameters of biomass plasma gasification was studied in thermodynamic equilibrium approach along with syn­gas usage for liquid fuel production. Institute for Electrophysics and Electric Power RAS experimental installation is described. Its primary component is a downdraft plasma gasifier for processing of biomass and wastes. Its technical characteristics and functionali-ty are described. A brief survey of existing pilot and in-dustrial projects is given. Methods of energy supply into plasma chemical reactor are described. The review of powerful plasma torches for industrial application is represented. Experi­mental procedures and test results on biomass gasification by air-plasma are presented as well as the comparison with the calculated data.

Keywords Plasma ■ Gasification ■ Syngas ■ Plasma torch ■ Gasifier ■ Energy balance ■ Efficiency ■ Biomass ■ Renewable energy ■ Alternative energy

12.1 Introduction

The importance of the decrease of anthropogenic impact on the environment rises dramatically nowadays. In particular, it is a problem of carbon dioxide emissions [1]. CO2 is the basic component of combustion products of widely used kinds of fuel; it possesses high radiative forcing and is one of the main (and the most dangerous) greenhouse gases [2]. In 2010, the global emission of carbon dioxide increases on

P. G. Rutberg (H) ■ V. A. Kuznetsov ■ V. E. Popov ■ A. N. Bratsev ■ S. D. Popov ■ A. V. Surov Institute for Electrophysics and Electric Power RAS (IEE RAS),

Dvortsovaya nab., 18, St.-Petersburg, 191186, Russia e-mail: rc@iperas. nw. ru

Z. Fang (ed.), Pretreatment Techniques for Biofuels and Biorefineries,

Green Energy and Technology,

DOI 10.1007/978-3-642-32735-3_12, © Springer-Verlag Berlin Heidelberg 2013 ~5.9 % and for the first time exceeds 9 Pg per year [3]. The increase in emission is mainly caused by economic growth of developing economics in which even during a global economic crisis the CO2 emission increased [3]. Economic growth and increase in the living standards of the population invariably lead to growth of energy consumption per capita. According to IEA [4], in 2009 about 80.9 % of mankind energy demands were provided by fossil fuel combustion, about 5.8 %—nuclear energy, about 2.3 % hydroenergetics, and about 10.2 %—energy of biofuels and waste, which in total is 509 EJ. The world’s reserve of fossil fuels is about 35,094 EJ (~23.6 %—oil, ~20.4 %—natural gas, ~56.0 %—coal) [5]. By estimations [6] world oil production will peak before 2020, coal before 2030, and natural gas around 2040. Unfortunately, the comprehension of not only the importance, but also the fact of finiteness of fossil fuels occurs extremely slowly among people defining directions of development both on regional and global level. The citation ideally illustrates the situation: “perpetual growth is often held as a pious belief and fundamental assumption for economists” [7]. The only possibility for humanity to prevent impending energy crisis is usage of renewable energy sources: biomass, solar energy, wind, tidal and wave power, hydroenergetics, and thermal power. Electricity generation from solar energy is very expensive that is why construction of large power plants is unlikely. The wind farms have low efficiency and their applicability is limited. Nowadays, the natural resources for development of hydroenergetics are almost exhausted. In spite of biosphere limits on bioresources generation governed by necessity to sustain the ecological balance and growth of mankind food demand the biomass is one of the most promising types of renewable energy sources. According to the forecasts [8] in 2050, the global potential of biomass energy will be about 1,135— 1,300 EJ (without the use of seaweed as biomass), while the world consumption will reach ~826 EJ (on average under different scenarios). Energy use of biomass does not increase CO2emission, as far as the whole carbon dioxide, formed after bioenergy use, is absorbed by green plants in the process of biomass formation. Other renewable sources hardly will be widely used; in particular, nuclear fusion energy can be practically used not until the end of the century. Nuclear power cost will rapidly increase due to safety issues. Thus, it is clear that if the cultivation requirements of bioresources are met, then the bio-energetic development is one of the most promising ways to form a sustainable and independent economics for both developed and developing countries.

Efficient organosolv pretreatment has been well developed for agricultural residues and hardwoods, rather than softwood biomass because they are considerably more recalcitrant to the pretreatment and enzymatic processes [57, 58]. In order to over­come the problems, organosolv combined with some other approaches have been attempted, such as the two-stage pretreatment approaches as follows:

1. Presoaking/pretreatment of biomass by dilute-acid before the organosolv process. Dilute acid-pretreated sugarcane bagasse was performed prior to an organosolv process using NaOH as a catalyst under the optimized conditions (60 min, 195 °C, using 30 % (v/v) ethanol), where 67.3 % (w/w) of the pretreated solid material was easily converted to glucose in 24 h [59]. The optimized dilute acid presoaking and aqueous ethanol organosolv treatment of Miscanthus led to a better recovery of xylans (~20 % (w/w) of dry mass against ~ 10 % (w/w) without presoaking), en­hanced dissolution of lignin in the aqueous ethanol, and increased enzymatic digestibility (98 % cellulose-to-glucose conversion against 80 % conversion without presoaking) [60].

2. Organosolv pretreatment followed by mechanical milling of pretreated substrates. The subsequent mechanical treatment of the aqueous ethanol-treated lodge — pole pine by mill refining decreased particle size and crystallinity but increased swelling and fiber delamination of the substrate. However, the hydrolysis process was not accelerated remarkably [61].

3. Organosolv pretreatment and substrate sulfonation of the product. After ethanol treatment, sulfonation of lodgepole pine could reduce none of the specific bind­ings of lignin to enzymes. Accordingly, it resulted in obvious enhancement of hydrolysis yields even at low enzyme loadings despite less removal of residual lignin. At the same time, enzyme recovery was increased as well [61].

Though some positive results were achieved with the combined method, it was impossible to check the efficiency of the developed methods such as acid presoaking and sulfonation on other kind of softwood. Additionally, alkali reagent, such as NaOH, NH3H2O, or triethanolamine, which has good ability for delignification rather than the improvement of hydrolysis, can be used in the presoaking prior to acid- catalyzed organosolv treatment [23, 62]. Moreover, it was reported that presoaking of straw by the reaction solvent under mild conditions could improve the subsequent organoslv delignification particularly in high solid-to-liquid ratios. This may account for the higher swelling of the material and increased accessibility of solvents to the reaction sites [63]. However, the effects of combined pretreatment on softwood need to be confirmed.

Anuj K. Chandel, Ellen C. Giese, Felipe A. F. Antunes, Ivy dos Santos Oliveira and Silvio Silverio da Silva

Abstract Sugarcane residues (bagasse and leaves/trash) are the principal feedstock in Asia, South America, Africa, and other parts of the world. The judicious applica­tion of this feedstock into value-added products such as fuel ethanol, xylitol, organic acids, industrial enzymes, etc. may provide a strong economic platform along with clean and safe environment. Pretreatment is an inevitable process to harness the car­bohydrate fraction of sugarcane bagasse and leaves into readily available sugars by cellulase-mediated process for the production of house-hold commodities. Several methods (physical, physico-chemical, chemical, and biological) have been adopted for the pretreatment of sugarcane residues. Pretreatment methods with pros and cons are employed either to depolymerize hemicellulosic fraction or lignin degradation to make cellulose more amenable for improved cellulolytic enzymes action. The choice of pretreatment methods depends upon its precise mechanistic action on lignin or hemicelluloses with fewer inhibitory products, minimal sugar loss by increasing the cellulosic surface area for subsequent enzymatic action to obtain desired sug­ars recovery. Furthermore, economics and environmental impacts are two important considerations for the selection of pretreatment method. This chapter aims to ex­plore a better understanding of multiple pretreatment methodologies applied to the sugarcane residues along with economics and environmental impacts.

Keywords Sugarcane bagasse ■ Sugarcane leaves ■ Pretreatment ■ Enzyme hydrol­ysis ■ Bioethanol ■ Biomass recalcitrance ■ Fermentable sugars

16.1 Introduction

In recent years, numerous efforts have been considered to harness the commercial potential of sugarcane residues (bagasse and leaves) into value-added products of commercial significance such as ethanol, xylitol, organic acids, industrial enzymes,

A. K. Chandel (H) ■ S. S. da Silva (H) ■ E. C. Giese ■

F. A. F. Antunes ■ I. dos S. Oliveira

Department of Biotechnology, School of Engineering of Lorena, University of Sao Paulo (USP), Lorena 12.602.810, Brazil e-mail: anuj. kumar. chandel@gmail. com; silvio@debiq. eel. usp. br

Z. Fang (ed.), Pretreatment Techniques for Biofuels and Biorefineries,

Green Energy and Technology,

DOI 10.1007/978-3-642-32735-3_16, © Springer-Verlag Berlin Heidelberg 2013

and others [1, 2]. The judicious application of sugarcane based feedstock into com­mercial entities is a sustainable process which may influence the economy at the forefront in sugarcane producing countries [3, 4]. Countries in Asia, Asia pacific, SouthAmerica, andAfrica grow a copious amount of sugarcane, which has a key role in their economy [5]. Table 16.1 presents the major sugarcane producing countries in the world.

Production of sugar from cane juice and ethanol from either juice or cane mo­lasses are two major driving forces of agro-economy in these countries. This impact could be wider if the residues of sugarcane (sugarcane bagasse (SB) and sugarcane leaves(SL/ST)) are being used for the production of household commodities em­ploying biotechnological routes [3, 7]. In 2011, the annual worldwide production of sugarcane residues was recorded around 279 million metric tons [2, 5]. From the data of sugarcane production in the world, it can be estimated that a huge amount of sugarcane residue is generated every year which is totally renewable and could be a promising source of bioenergy and other value-added products generation. Each ton of sugarcane yields about 140 kg of humid bagasse, which is a fibrous residue obtained after crushing sugarcane in sugar producing factories, and is currently used for steam generation in boilers [1, 2, 5]. During the harvesting of sugarcane in agri­culture fields, cane leaf residues are removed from the cane stem and left on the fields, causing loss of green energy [2, 8]. SL/ST is generated in huge amount in fields (6-8 tons from one hectare of sugarcane crop) [8]. Sugarcane derived lignocel — lulosic feedstock (SB and SL/ST) are being used in industries now-a-days for steam or electricity generation. Together, both residues constitute a foreseeable amount of biomass, which can be used for bioethanol production and other bio-products of high economic value (Fig. 16.1).

Apart from bioenergy generation from these residues, products of high economic value such as industrial enzymes, organic acids, food/feed products, amino acids, vitamins or cosmetics can also be produced by microbial fermentation. A lot of re­search work is underway in this line. However, a full technological road-map is yet to come for the industrial production of these commodity chemicals from SB/SL. SB and SL contain an appreciable amount of carbohydrates in cell wall along with the lignin. Pretreatment is an inevitable process to break down the carbohydrate fraction into simpler sugars making them readily available for fermenting by microorganisms

[9-11]. The aim of pretreatment of SB/SL is either to remove lignin or hemicellulose for enhancing the amenability of cellulases toward cellulosic fraction of cell wall. Hemicellulose is generally degraded by weak acid catalyzed process removing its heterogeneity by producing monomeric sugars (xylose, arabinose, mannose, galac­tose, and glucose) [12]. Lignin is degraded by alkali based reactions or microbial action by selective lignin degraders and thus leaving cellulose and hemicellulose net­work together, but in less compacted form. The pretreated material is subsequently hydrolyzed by cellulolytic enzymes for sugar recovery toward the fermentation of

other value-added products [1,2, 12, 13]. In past, a number of pretreatment strate­gies (physical, physico-chemical, chemical, and biological) have been developed by researchers considering hemicellulose and/or lignin removal [9-11, 14-17]. An ideal pretreatment method should render lignocellulosics completely susceptible to the action of cellulases, be economic, and pose less environmental pollution load [10, 13, 17]. This chapter describes the various pretreatment strategies applied to the sugarcane residues, process parameters, mechanism of pretreatment methods, economic, and environmental aspects.