Bioenergy systems for the future 2 technological aspects of nonfood agricultural lignocellulose transformations

Bioenergy systems for the future 2 technological aspects of nonfood agricultural lignocellulose transformations Bioenergy systems for the future 2 technological aspects of nonfood agricultural lignocellulose transformations Bioenergy systems for the future 2 technological aspects of nonfood agricultural lignocellulose transformations Bioenergy systems for the future 2 technological aspects of nonfood agricultural lignocellulose transformations Bioenergy systems for the future 2 technological aspects of nonfood agricultural lignocellulose transformations

Technological aspects of nonfood

agricultural lignocellulose

transformations

H Honkanen, J Kataja

JAMK University of Applied Sciences, Tarvaala, Finland

Abbreviations

BFB bubbling fluidized bed

BIGCC biomass integrated gasification combined cycle

CFB circulating fluidized bed

CHP combined heat and power

dmt/a dry matter tons per year

HEC herbaceous energy crops

SRWC short-rotation woody crops.

Biomass stands for the biodegradable fraction of products, waste, and residues of biological origin from agriculture (including vegetable and animal-based matter), forestry, and related industries, including fisheries and aquaculture, as well as the bio-degradable fraction of industrial and municipal waste Research and development activities have been focused on identifying suitable type of biomass fractions from agriculture and rural areas, which can provide high-energy efficiency, to replace fossil fuel energy sources The type of biomass fractions required is largely determined by the energy conversion process and the form in which the energy is required

2.2.1 Classification of biomass

Researchers characterize the various types of biomass in different ways, but one sim-ple method is to define four main types, woody plants, herbaceous plants, aquatic plants, and manures Within this categorization, herbaceous plants can be further subdivided into those with high- and low-moisture contents Apart from specific Bioenergy Systems for the Future http://dx.doi.org/10.1016/B978-0-08-101031-0.00002-8

© 2017 Elsevier Ltd All rights reserved.

applications or needs, most commercial activity has been directed toward the lower-moisture-content types, woody plants, and herbaceous species, and these will be the types of biomass described in this chapter Aquatic plants and manures are intrinsi-cally high-moisture materials and, as such, are more suited to “wet” processing tech-niques (McKendry, 2002)

Based primarily on the biomass moisture content, the type of biomass selected subsequently dictates the most likely form of energy conversion process On the basis

of the moisture content, herbaceous biomasses can be divided into two groups—green biomass and yellow biomass, as shown in Fig 2.1 Green biomasses are high-moisture-content raw materials, such as the herbaceous plants (grasses by growing season harvesting) or sugarcane and clovers, which lend themselves to a wet/aqueous conversion process, involving biologically mediated reactions, such as fermentation Yellow biomasses are dry raw materials such as straw, corn stover, or reed canary grass (spring harvesting) that are more economically suited to gasification, pyrolysis,

or combustion (Table 2.1)

Both woody and herbaceous plant species have specific growing conditions, based on the soil type, soil moisture, nutrient balances, and sunlight, which will determine their suitability and productive growth rates for specific, geographic locations Many types of perennial grasses, such as sugarcane and cereals like wheat and maize, have widely dif-ferent yields, depending on the growing conditions: Thus, wheat can be grown in both hot and temperate climates with a wide range of rainfall, whereas sugarcane can be grown successfully only in warm, moist climatic conditions (McKendry, 2002) Required characteristics of cultivated biomass crops will also depend on local climate and soil conditions, as you can seeFig 2.2 Precipitation and effective tem-perature sum of the growing season are major constraints in many areas of the world Other important characteristics are drought resistance, pest resistance, and fertilizer requirements of the biomass crops

All the cultivation of biomass (green biomass, yellow biomass, and woody bio-mass) should have moderate requirements concerning soil and fertilization and still

Press juice

Green biomass

Yellow biomass Straw / stover

dedicated energy crops

Wood based residues / dedicated energy crops

Nonfood agricultural lignocellulose biomass

Cellulose

Hemicellulose

Lignin Grain

Woody biomass

Pulpwood/

timber

Press cake

Fig 2.1 The feedstocks of nonfood agricultural lignocellulose biomass

Green biomass Yellow biomass Woody biomass

Other biomass

Grasses (summer

harvesting)

Clovers (summer

harvesting)

Miscanthus (HEC) Branches and

logging residues

Sunflower Sugar beets/bagasse/tops Switchgrass (HEC) Wood processing

residues

Ethiopian mustard

Reed canary grass (HEC)

HEC, herbaceous energy crops; SRWC, short-rotation woody crops.

Fig 2.2 Climate zones and recommended biomass crops for each one

Modified from Alexopoulo, E., Kretschmer, B Mapping biomass crop options for EU27 Biomass Futures Policy Briefings.http://www.biomassfutures.eu/work_packages/WP6%

26 June 2016); Metzger, M.J., Bunce, R.G.H., Jongman, R.H.G., Mucher, C.A., Watkins, J.W.,

2005 A climatic stratification of the environment of Europe Global Ecol Biogeogr 14, 549–563

produce high biomass yield with a minimum need of weeding; high tolerance for pests, diseases, frost, drought; or excess of water that enables cultivation in areas not suited for more demanding food crops Energy consumption is dependent on various parameters, including transportation of the raw material and nitrogen fertilizer used A maximal benefit of the land area could be obtained when the crop would be primarily used for production of food and secondarily as a source of biomass residue for biofuels However, also in the future, the main aim will be to produce the maxi-mum amount of biofuels with the minimaxi-mum environmental consumption (McKendry,

2.2.2 Biomass properties

Numerous crops have been proposed or are being tested for commercial energy farming Potential energy crops include woody crops (poplar and willow) and grasses/herbaceous plants (all perennial crops), starch and sugar crops, and oilseeds

In general, the characteristics of the ideal energy crop are

- high yield (maximum production of dry matter per hectare),

- low energy input to produce,

- low cost,

- composition with the least contaminants,

- low nutrient requirements

However, there are other factors that must be taken into consideration in determining the election of the conversion process, apart from simply moisture content, especially

in relation to those forms of biomass that lie midway between the two extremes of

“wet” and “dry.” Examples of such factors are the ash, alkali, and trace component contents, which impact adversely on thermal conversion processes, and the cellulose content, which influences biochemical fermentation processes (Table 2.2)

Biomass contains varying amounts of cellulose, hemicellulose, lignin, and small amount of other extractives, as you can seeFig 2.3 Woody plant species are typically characterized by slow growth and are composed of lightly bound fibers, giving a hard external surface, while herbaceous plants are usually perennial, with more loosely bound fibers, indicating a lower proportion of lignin, which binds together the cellulosic fibers: both materials are examples of polysaccharides and long-chain natural poly-mers The relative proportion of cellulose and lignin is one of the determining factors

in identifying the suitability of plant species for subsequent processing as energy crops

It is the inherent properties of the biomass source that determines both the choice of conversion process and any subsequent processing difficulties that may arise Equally, the choice of biomass source is influenced by the form in which the energy is required, and it is the interplay between these two aspects that enables flexibility to be intro-duced into the use of biomass as an energy source As indicated above, the categories

of biomass considered in this study are woody and herbaceous species; the two types are examined by most biomass researchers and technology providers

For dry biomass conversion processes, the first five properties are of interest, while for wet biomass conversion processes, the first and last properties are of prime

Table 2.2 Agronomic characteristic of selected nonfood agricultural lignocellulose biomass

Sugarcane bagasse

Maize stover

Wheat

Photosynthesis

mechanism

Annual/

perennial plant

3–7 years Harvesting

equipment

agri

Normal agri

Normal agri

Special Nutrient

requirements

HEC, herbaceous energy crops; SRWC, Short-rotation woody crops; dmt/a, dry matter tons per year.

Modified from Davis, S., Hay, W., Pierce, J., 2014 Biomass in the energy industry: an introduction Energy Biosciences Institute http://www.bp.com/energysustainabilitychallenge ; Faaij, A., 2008 Bioenergy and global food

security, WBGU Hauptgutachten 2008, Welt im Wandel: Zukunftsf €ahige Bioenergie und nachhaltige Landnutzung, Berlin http://www.wbgu.de/fileadmin/templates/dateien/veroeffentlichungen/hauptgutachten/jg2008/wbgu_jg2008_ ex03.pdf (referred to 26 June 2016); Pakarinen, A., Maijala, P., Stoddard, F., Santanen, A., Kym €al€ainen, M., Tuomainen, P., Viikari, L., 2011 Evaluation of annual bioenergy crops in the boreal zone for biogas and ethanol production Biomass Bioenergy 35, 3071 –3078.

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

0%

Sugarcane

bagasse

Corn stover Straw SRWC HEC 35%

25%

20%

20%

53%

15%

16%

16%

38%

36%

16%

10%

50%

23%

22%

5%

45%

30% 15% 10%

Cellulose Hemisellulose Lignin Others

Fig 2.3 The averaging composition of selected nonfood agricultural lignocellulose biomass feedstocks.HEC, herbacenous energy crops; SRWC, short ration woody crops

Data from McKendry, P., 2002 Energy production from biomass (part 1): overview of biomass Bioresour Technol 83, 37–46; Hamelick, C., Hooijdonk, G., Faaij, A., 2005 Ethanol from lignocellulosic biomass: techno-economic performance in shot-, middle- and long-term Biomass Bioenergy 28, 348–410

concern The quantification of these material properties for the various categories of biomass is discussed in the following section (McKendry, 2002)

Looking from the perspective of nonfood agricultural lignocellulose, biomass engi-neering is particularly interested in the partitioning among cellulose, hemicellulose, and lignin

The importance of understanding the chemical composition and structure of crops used as raw materials for bioenergy production cannot be overestimated To achieve the best possible conversion efficiency of different crops from field to fuel, knowledge

on the effects of preservation, pretreatments, and used parameters in enzymatic hydro-lysis, for example, is essential The selection of suitable crops in the existing climate conditions and how to convert the raw materials into the most convenient energy car-riers are nationally and internationally important issues (McKendry, 2002; Pakarinen,

2.3.1 Biomass to bioenergy

Bioenergy production is regarded as renewable energy The use of biomass, many times from local origin, as energy source, supports energy self-sufficiency and helps tackling with greenhouse gas (GHG) emission load and with other negative environ-mental effects to air and water quality Bioenergy currently accounts for two-thirds of renewable energy in Europe Bioenergy is the only renewable energy source able to provide green fuel for all the following energy applications: heating and cooling, power generation, and transport applications (European Biomass Association,

2016) The global potential from agriculture is still largely underexploited, and this sector is expected to grow The global potential of agricultural and forestry residues and organic waste in bioenergy production is essential during forthcoming decades (International Energy Agency, 2012)

Increasing the production of liquid biofuels supports the growth of low-carbon societies along with solar power use in smart energy systems, new energy storage technologies, and distributed energy generation Also the importance of biogas pro-duction and the use of waste-derived fuels will continue to grow in the future mean-while cutting down the use of fossil fuels

Bioenergy stands for energy produced from biomass, so it excludes, for example, wind, solar, or hydroenergetic power Biomass energy products are generated from agricultural crops and residues, herbaceous and woody materials, and biodegradable wastes These feedstock materials can be either directly combusted for energy produc-tion or processed into energy products or carriers such as biodiesel, bioethanol, and biogas, which are then used as transportation fuels or for the production of steam, heat, and electricity

Bioenergy production is strongly promoted by different drivers and sustainability including legislation, economic, and environmental perspective (Fig 2.4) In addition

to environmental incentives, energy supply system has to meet expectations such as undisturbed availability and competitive price Costs of biomass-derived energy are expected to decrease over time, due to both technology development and economies of

scale in larger commercial plants Social and cultural aspect of sustainability so-called human factor refers to consumers’ voice and acceptance, local decision-making, labor, and well-being Human factor aspect plays an important role in the bioenergy field and business in accordance with realization of implementation of new technol-ogy and processes

Local production of raw materials, fuels, and bioenergy offers income for agricul-tural industry However, if traditional thinking of bioenergy is linked closely to coun-tryside, new refinery processes and transformations have expanded operating range and integrated processes with forest and chemical industry and business Whereas long-distance transportation reduces economic and environmental attractiveness of biomass, conversion into higher energy density product, for example, bio-oil, could facilitate also international trade

As presented above, lignocellulosic biomasses contain cellulose, hemicellulose, and lignin, which can be used in different ways in refining processes Plant species differ in the relative amounts and in the chemical structures of these main polymers, depending strongly on its origin As being raw material for higher value bio-based products such as fuels, chemicals, polymers, or materials, hemicellulose and lignin are also suitable for lower value use for combined heat and power (CHP) applications Also residues of cellulose for sugar processes can be used in energy production

2.3.2 Integration of energy use, new biobased products and

nutrient recovery

There are numerous ways to process and utilize agricultural lignocellulose-based biomass Processes result in energy, products, by-products, and residues These prod-ucts include solid, liquid, and gaseous materials to be used as fuels, chemicals, and other materials for industry, agriculture, and municipalities Ash and treated sludge

Drivers: legislation, economy, environment

Refining processes

Dedicated crops,

by-products and

residues from

agriculture

• Quality

• Volumes

• Properties

Bioenergy production Fuels Other solid, liquid and gaseous products Direct use

Human factor: awareness

Fig 2.4 The use of biomasses from agriculture to energy with drivers and incentives

from wastewater treatment and from anaerobic digestion process contain nutrients to

be used for fertilizing in suitable target of application in cultivation and forestry There are also other thermal, biological, and chemical processing technologies to stabilize and disinfect material streams for further use Nutrient recovery option may bring operators and process owner’s possibilities to offer new products and to enhance feasibility

lignocellulose-based biomass The main raw material flows are dedicated energy wood crops, wood-based residues mainly from farming and rural area industries, field and grass crops, biodegradable waste, and sludges like manure from agriculture Biodegradable waste stands in great parts for agricultural residues, which constitute the part of the crop that is discarded after the useful products have been extracted from the harvest Also yard and municipal waste can also be considered as source for energy production Further, sludge from wastewater management refers to sludge originated either from sparsely populated areas treated locally or from centralized wastewater management plants By-products from industry refer mainly to forest industry or other large-scale industry using lignocellulose-based biomass, with own circulation and utilization routes for their, for example, stem-wood-based by-products These by-products and peat and sludges are acknowledged as possible bio-based material flows for combina-tions depending on, for example, the volume requirements or quality restriccombina-tions Woody and herbaceous biomass from agriculture and rural areas is processed via several routes to produce energy In this case, biomass has optional exploitation paths

Bioenergy and nutrients recovery from agricultural lignocellulose based biomass

Origin: agriculture and rural areas

Dedicated energy wood crops

Pyrolysis/thermal gasification

Anaerobic digestion Thermal drying Chemical treatment Composting Combustion

Peat

Raw

material

flows

Processing /

utilization

Product /

by-product

Ash (many types)

- fertilizing fields and forests

1 Biofuels for renuwable energy production

2 Sources of nutrients

Compost Ethanol

(motor fuel) Methanol

(motor fuel, fuel cells)

Methane (combustion, motor fuel)

Biogas + reject (hygienic)

Treated sludge (hygienic) Torrefaction Fermentation Hydrolysis

Wood based residues Field and grass crops Biodegradable waste Sludges from agriculture Sludge from waste water treatment

By-products from industry

Fig 2.5 Bioenergy and nutrient recovery routes for agricultural lignocellulose-based biomass

to be processed or utilized in combustion, gasification, pyrolysis, fermentation, hydro-lysis, or anaerobic digestion to produce biofuels of energy Some of the optional routes are in parallel and some in series, for example, when biomass is firstly processed into biofuel and then utilized in energy production plant Feedstocks may be combined if preferable; also processing technologies may be integrated and centralized, for exam-ple, in biorefineries Some of the mentioned processes are discussed further later on in this chapter and in some later chapters of this book Thermal drying, chemical treat-ment, and composting are presented as alternative processing, aiming to further use and utilization of their nutrient content

Combustion processes for producing steam and power produce ash as sidestream containing mainly inorganic material as result of fuel oxidation With poor combus-tion efficiency, ash contains also unburnt fuel Ash output from combuscombus-tion could be used in fertilizing purposes depending on the chemical composition and composition

of feedstock, combustion technology, possible use of chemicals in the process, and ash collection technology

Torrefaction is a thermal process to enhance the energy density and durability of biomass Produced biochar or traditionally charcoal can be used as energy carrier with versatile use Charcoal is considered as the most important processed biomass fuel

example, used as soil conditioner or as fertilizer (Alakangas et al., 2016)

Biogas, a mixture of methane and carbon monoxide, is the most important gaseous biomass-based fuel Biogas is produced in a digester by anaerobic process using mainly sludges and wet biodegradable waste as feedstock Anaerobic processing com-bines waste disposal with energy and fertilizer production, in small and large central-ized scale, in both developed and developing countries The use of reject of the process

as material for fertilizer depends on the contents of the original feedstock For exam-ple, wastewater treatment may restrict fertilizing use of the reject

Presented solid, liquid, and gaseous fuels can be used in suitable energy production, for example, boilers or motors Also, other hydrocarbons and hydrogen can be prod-ucts from the different processing routes

2.3.3 Energy production technologies and fuel characteristics For energy recovery, solid biomass is processed with combustion, gasification, or pyrolysis With combustion, biomass can be converted into steam for industry pur-poses, heating energy, or electricity with turbine and generator Gasification produces syngas, mainly mixture of carbon oxide and hydrogen, to be used in heat and power generation and in other processes, for example, production of methanol or dimethyl ether Via pyrolysis, biomass can be converted into bio-oil, which can be used for heating or producing biodiesel

Wet biomass originated in agriculture is processed with anaerobic digestion for producing biogas Biogas is used widely for heat and power production It can also

be used as vehicle fuel in many kinds of applications

2.3.3.1 General about refining bio fuels

A wide range of new conversion technologies are under continuous development to produce bioenergy carriers for energy production both small- and large-scale applica-tions Converting biomass feedstock into secondary fuels aims to better adaptation to long-distance transport and application in modern energy converting systems (van

available on seasonal basis, have low physical and energy density and high-moisture content and require processing for efficient further use Many of the conversion technologies are close to commercial maturity but are awaiting further technical breakthroughs to increase the process efficiency, followed by large-scale demonstra-tions to help reduce the risks and cut down the costs

Biochemical technologies are expected to be used to convert the cellulose to sugars that in turn can be converted to bioethanol, biodiesel, dimethyl ester, hydrogen, and chemical intermediates in biorefineries In addition, biochemical and thermochemical synthesis processes could be integrated in a biorefinery such that the biomass carbo-hydrate fraction is converted to ethanol and the lignin-rich residue gasified and used to produce heat, electricity, or fuels In general, biorefinery may contain combination of physical, chemical, and biological conversion steps, producing variety of products such as food and feed, materials, chemicals, fuels, fertilizers, heat, and power (van

In anaerobic treatment process, the feedstock is partially digested to form a methane-rich biogas Biogas is generally produced from organic waste materials such

as sewage sludge, agricultural wastes, industrial wastes, and municipal solid wastes Agricultural residues consist of either crop residues or processing residues Crop residues refer mainly to disposed parts of crops after harvest Processing wastes are leftovers from the processing of the harvested portions of agricultural crops for uses such as food, fiber, and feed Leftover grasses such as those grown in buffer zones protecting water systems are suitable feedstocks to anaerobic digestion process How-ever, process has to have sufficient retention time for grass-type biomass

Biodiesel is produced from vegetable oils and animal fats and used as an alternative fuel of petroleum diesel for vehicles

Biological and chemical biomass refining processes are further discussed in forth-coming chapters of this book

2.3.3.2 Mechanically and thermally treated solid biofuels

Biomasses like small-diameter wood from forest management, energy willow, straw, and agricultural waste such as low-quality grain and sorting waste can be utilized as energy by combustion or gasification to produce heat, electricity, syngas, or other products Agricultural biomass waste can be mixed and processed with other biomass

to suit better its use Usually, solid biofuel is produced with pretreating the biomass mechanically, for example, drying, chipping, crushing, chopping, baling, shredding, pelletizing, or briquetting Usually, pellets are made from by-products of the