Design and evaluation of biomass utilization systems

(1)

Design and Evaluation of Biomass Utilization

Systems

by

Valerie Peng

B.S., Mechanical Engineering, MIT (2017)

Submitted to the Department of Mechanical Engineering

in partial fulfillment of the requirements for the degree of

Master of Science in Mechanical Engineering

at the

MASSACHUSETTS INSTITUTE OF TECHNOLOGY

June 2019

@

Massachusetts Institute of Technology 2019. All rights reserved.

A uthor ...

Certified by...

Walter M. May & A.

Accepted by ...

MASS INTITUTE OF TECKNOLOGY

JUN 1310

9 LIBRARIE$

Signature redacted

Department of Mechanical Engineering

May 19, 2019

Signature redacted

Alexander Slocum

Hazel May Professor of Mechanical Engineering

Signature redacted

Thesis Supervisor

I

Nicolas Hadjiconstantinou

Chairman, Department Committee on Graduate Theses

(2)

(3)

Design and Evaluation of Biomass Utilization Systems

by

Valerie Peng

Submitted to the Department of Mechanical Engineering on May 19, 2019, in partial fulfillment of the

requirements for the degree of

Master of Science in Mechanical Engineering

Abstract

This thesis designs and evaluates systems to utilize two problematic biomass sources, hurricane debris and invasive water hyacinth, and turn costly cleanup efforts into opportunities for biofuel conversion systems. A novel solution is proposed for each biomass source and techno-economic models accounting for economic, energy, and carbon costs are used to evaluate different options for utilization. Hurricane debris is a feedstock that gets generated in vast quantities in an unpredictable manner, thus its main challenge is its supply chain. We propose a 30MW barge-mounted biofuel conversion system, which travels to hurricane-hit ports and converts debris into biofuels. For a 30MW plant, the break-even per-gallon revenue for profitability was found to be $5.28 per gallon of jet fuel for Fischer-Tropsch synthesis, $0.88 per gallon of heating oil for pyrolysis, and $1.07 per gallon of ethanol for fermentation. Using May 2019 US national fuel prices, the pyrolysis and fermentation plants were found to operate at a profit of $363.87 and $166.40 per dry ton of consumed hurricane debris respectively. A supply chain model was also created to calculate debris transport costs and evaluate the economic benefits of chipping debris directly in the field, which was found to be 24% more efficient than status quo stationary chipping operations. Water hyacinth is generated predictably and in huge quantities; however, the weight of water hyacinth is up to 95% water and it is thus inefficient to work with. Thus, we propose a novel roller-crusher harvester which grabs, crushes, and directly bags aquatic plants into digesters in-situ on the water. We find that an anaerobic digestion system with the proposed mechanical harvesting system could make a profit of $5.81 per ton of hyacinth, turning a costly problem into an economic opportunity. Hardware designs, prototypes, and on-water tests then show the viability of the roller-conditioner as a boat-mounted in-situ harvester-crusher. Ultimately, this work shows that careful design and evaluation of utilization systems could turn government aid and charity spent every year on debris and waterway cleanup into a profitable investment.

Thesis Supervisor: Alexander Slocumn

(4)

(5)

Acknowledgments

I would like to give a huge thank you to Professor Alex Slocum for pushing me down a

path of precision engineering for the sake of human goodness, and for teaching me to turn problems (frowns) into opportunities (smiles). Thank you also for showing your students that it is not only possible to balance family, career, and self in harmony, but also possible to have all in full throttle. I have a lot to learn still, and can only hope I will continue to draw from your mens et manus.

Thank you also to Dr. Jason Prapas for wittingly drawing me into the world of using problematic plants as opportunities, and for your never-ending supply of technical insights and support. Your mentorship has helped me scratch the surface of

being a cognizant, entrepreneurial engineer, and I know I will continue to learn from your expertise.

Thank you to Circle C Rollers for your generous donation of the roller-conditioner

display unit, which was critical to the on-water tests of Chapter 5, and your patience in helping a student take a dive into agricultural equipment. Thank you to Country

Gardens of Rowley, Massachusetts, for your supply of water hyacinths at the outset

of this project.

Thank you also to Megan O'Brien for helping me start on the path of evaluating

biomass systems, and to Professor David Hsu for allowing me into the world of urban planning and community engagement when designing systems to help the people of Puerto Rico.

Thank you to my labmates in PERG, whose relentless curiosity and work ethic continue to push me to be a better engineer and a better friend, and thank you

for your never-ending supply of design reviews, gentle nudges, hard questions, and

bridge-loop runs. Thank you also to Ethan Lietch for your curiosity, commitment, and attitude on helping to design and test the bagging section of this thesis.

Thank you to Sarah Wright for the nudges when I needed them, and for your

confidence in me when I had none left.

(6)

to MIT, but thrive here. I would not be here without your years of commitment and

love. And finally thank you to my older sister Lauren, who has always been there to

cheer me on, console me, and laugh with me - you are truly the best sister anyone could ask for.

This material is based upon work supported by the National Science Foundation

Graduate Research Fellowship under Grant No. (1122374). Any opinions, findings, and conclusions or recommendations expressed in this material are those of the

au-thors and do not necessarily reflect the views of the National Science Foundation.

(7)

List of Figures

2-1 The market prices for different RINs, reflecting the per-gallon ethanol

equivalent incentive that producers receive for producing renewable

fuels of different types [123]. . . . . 35

3-1 A picture showing part of the aftermath of Hurricane Maria, which

toppled electricity poles, trees, and lines across Puerto Rico and other

Caribbean islands. Photo by Carlos Giusti - AP, taken from Fortune

(2017) [98. . . . . 38

3-2 A qualitative assessment of conversion methods for hurricane debris.

Solutions range in complexity and in value of final produced product. 43

3-3 The model used to evaluate costs to transport hurricane debris from the vegetative collection sites spread throughout the island to the ports

of San Juan and Mayaguez. The collection sites were modeled to be

spread evenly throughout the island. Distances from the sites to the

ports were taken to be twice the direct-line distance, in order to account

for road winding and other unknowns. . . . . 51

3-4 The two debris cleanup scenarios being evaluated: (1) the status quo, wherein a front-loader and a truck operate in the field, and debris is

brought to a central gathering site. A second front-loader loads the

debris into the chipper. (2) A mobile chipper is brought to the field,

and N front-loaders are used to minimize operation costs. The debris

(12)

3-5 The results showing the specific transport cost for the status quo sce-nario, the mobile chipping scenario with N front-loaders, and the

mo-bile chipping scenario with only one front-loader allowed. . . . . 56 3-6 The results showing the balance of operations

($

per dry metric ton

(dmt)) as a function of the summed fuel revenue

($

per gallon from the market fuel price and the renewable incentive). The range of summed

revenue is different for each fuel, as market prices for each fuel have

varied differently over the last ten years. The market value of heating

oil differs by region, so its fuel price was assumed to range from

$0-2.84 per gallon. For ethanol, the market value fuel prices have ranged

from $1.33-3.25 per gallon over the last ten years, with the May 2019

price being at the low of $1.33. For jet fuel, the price has ranged from

$0.85-3.29 per gallon over the last ten years, with the May 2019 price

being $1.97 per gallon [121]. . . . . 65

4-1 Fishermen stuck in a water hyacinth mat. Dense water hyacinth mats

float and blow with the wind, causing unpredictable movements and

stranding boats that get stuck in them. Picture credit to Denish

Ochieng, Standard Digital; taken from Onyango (2018) [87. . . . . . 68

4-2 A simple decision tree regarding the cleanup of hyacinth. Each decision

- whether to clean it, how to clean it, and what to do with it - should be carefully evaluated. . . . . 71

4-3 A picture of fishermen on Lake Victoria, manually inspecting and

cor-ralling water hyacinth. Picture credit to phys.org [24]. . . . . 77

4-4 A picture of a spray crew treating water hyacinth. Picture source from

Kimball Environmental Inc. webpage [65]. . . . . 78

4-5 A typical aquatic hyacinth harvesting boat. These boats typically cost

more than $50,000, and have long maintenance down times due to

(13)

4-6 The relationship between plant length (stem height) and areal plant

density in kg/rn2. Data from Tucker (1981). . . . . 81

4-7 The areal cost (left) and specific mass cost (right) of shredding and

harvesting water hyacinth, as a function of reported stem height of the

hyacinth. Once changes in plant density are taken into account, the

spread between specific costs narrow significantly. Data taken from

Greenfield et al. (2006) and transformed using densities from Tucker

(198 1). . . . . 8 1

4-8 The effects of contract labor rates on mechanical control. Chemical

control costs are assumed to be $1500 per hectare across the board.

Original data obtained from Greenfield et al. (2005) and Lwasa et al.

(2002). . . . . 85

4-9 A picture of cattle eating water hyacinth. Often only the green leaves

and stems are eaten, and the roots and bulbs are left. Picture source

from http://www.inriodulce.com/ [57]. . . . . 93

4-10 A first-pass evaluation of different utilization pathways, rated as good

(green), neutral (yellow), or not ideal (red). . . . . 93

4-11 A summary of the inputs and outputs required to evaluate each control

method and utilization scheme. . . . . 94

5-1 A figure showing the main steps of the water hyacinth supply chain,

and potential strategies to achieve each step. . . . . 108 5-2 The integrated system of a John Deere combine harvester, which

di-rectly harvests and processes corn crops into clean corn kernels. Picture

source from John Deere webpage [60]. . . . . 112

5-3 Example of a single-screw extruder which conveys, melts, and extrudes plastic material through a die. Picture credit to Dr. Harold Giles, adapted from AZO Materials web page [30]. . . . . 114

(14)

5-4 CircleC rollers, which use spiral rubber rollers and high pressure for full

contact crushing. According to Mel Homer at Circle C Equipment, the

high pressure immediately crushes the plant cells and stops respiration.

Picture source from Circle C Equipment, LLC homepage [21]. . . . . 115 5-5 Alternative urethane and steel rolls, which crush rather than crimp the

incoming stems. Picture source from John Deere product brochure [59]. 115

5-6 Roller mechanisms are used in many types of volume reduction and pretreatment applications. (a) A diagram of a roller mill, which are

used to crush and reduce a wide variety of materials including biomass

or rock ore. Picture from Stedman Machine Company [107]. (b) A

figure taken from Tsapekos et al. (2018), which used steel conditioner

rollers (bottom rollers shown) to mechanically pretreat land grasses

for anaerobic digestion. A crimping conditioner roller used with a road

sweeping brush (top) enhanced methane production by 20% compared

to untreated grasses; a corrugated roller rotating in a corrugated shell

(bottom) enhanced methane production by 22-27% [112]. . . . . 116 5-7 A diagram of a four-roller conditioner, which uses a twined roller to

feed into the roller setup. Picture taken from Shinners [103]. . . . . . 117 5-8 _{A diagram of the roller crushing process and its main parameters: 0ni,,}

the nip angle of the rollers (where friction pulls in the material), Pave, the average crushing pressure on the rollers, R, the roller radius, and

L, the arc length of contact. . . . .

5-9 The two main concepts considered are (a) an auger, which collects and shears the water hyacinth; and (b) a pair of roller-conditioners, which grabs and crushes the water hyacinth. The full system concept

is shown, wherein the harvester boat directly bags the water hyacinth

into anaerobic digester bags. This overall system concept is the subject

of this chapter. . . . . 5-10 The differences between flat rolling and meshed rolling on water

hy-acinth stem s. . . . .

118

119

(15)

5-11 The relationship between compression pressure and volume reduction

of water hyacinth, as reported by Bagnall (1982) [9]. . . . . 124

5-12 The model for a simple flat roller, and associated variable dimensions.

h(6) or A is the thickness of the biomass as it passes through the roller, 0 is the angle through which the biomass passes, with 6 = 0 at

the closest point between the rollers and =m.= 0ip, H, is the initial

thickness or height of the biomass, and H1 is the final thickness of the

biomass, equal to the roller gap spacing. . . . . 125 5-13 The torque required to compress water hyacinth on a one-meter geared

roller, as a function of the volume reduction. As can be seen, there is a

dramatic increase of required torque once volume reduction increases

above 80%. Torque requirements were calculated using pressure-volume

data from Bagnall (1982) [9] . . . . 126

5-14 A diagram showing the pressure distribution on the gear teeth as

biomass gets pulled through the gear-tooth roller and compressed. The

direction and magnitude of force varies greatly throughout the profile. 127 5-15 A diagram showing the two approximate zones of pressure regimes: (1)

the radial-only regime, where plants are compressed against the root

via the top land of the opposing roller tooth (and vice versa), and (2)

the pressure angle regime, where plants are compressed against the

tooth at pressure angle 4. . . . . 128 5-16 An isometric view of the Solidworks model of the designed geared roller

crusher. ... ... 129

5-17 Results from tests run on the geared roller crusher in water. (a) The

number of times a single leaf successfully fed through the rollers, as a

function of water level and travel speed. Three trials were performed

for each combination. (b) A diagram showing the relative water levels

from the experiments run in (a), which are above, at, or below the

mid-plane between the rollers. . . . . 131 5-18 A view of the crusher in the water. . . . . 131

(16)

5-19 The modeled and experimental power required to crush various

feed-stocks. Volume-pressure characteristics of lettuce and turnip tops were

assumed to be similar to water hyacinth above 65% volume reduction, i.e. that lettuce and turnip tops compress similarly to water hyacinth

without air gaps or roots [109]. . . . . 133 5-20 A diagram and picture of the water-displacement gas collection method

used to measure the methane generation of untreated, roller-crushed, and macerated water hyacinth . . . . . 135 5-21 The preliminary results from the anaerobic digestion of uncrushed,

roller-crimped, and shredded water hyacinth, showing the specific

bio-gas production from the three trials. The results show only slight

differences between the different methods. . . . . 136 5-22 The donated Circle C roller-conditioner display unit, before (a) and

after alterations and the addition of the chain drive (b). . . . . 138 5-23 The motorized display unit being drive through the water and hay

using a tractor. . . . . 139

5-24 A view of the loose hay that traveled through the roller, as well as a mat of hay which caused the rollers to clump. The overly-increased

preload force applied by the air bladders caused the key to push out, preventing the motor drive from operating the rollers. . . . . 140

5-25 A picture of a Versa silage bagger, which fills and simultaneously

un-rolls a silage bag. A rolled up bag is placed onto the back of the silage

bagger, and the silage bagger either drives forward or self-propels itself

forward as the bag gets filled. The bag thus unrolls itself as the silage

fills the bag. Picture from Versa Bagger website [128]. . . . . 141

5-26 A picture of the experimental test setup, wherein gradually increasing

number of weights were placed into a bag. The gradual increase

rep-resents the increase of drag forces on the bag as the bag unrolls in the

(17)

5-27 A CAD representation of the proposed large-scale roller crusher system.

The system shown is a 2m-wide roller system that is attached to a

14-foot long pontoon barge. The bag unrolls as the boat drives through the

water hyacinth, and collects the crushed hyacinth behind the rollers.

The hydraulics and other boat apparatus are not shown. . . . . 145

5-28 A comparison of specific energy requirements between towing water

hyacinth mats, towing smooth bags, towing biofouled net bags, and

towing on the back of a standard harvester boat. Results are shown

on a log scale. . . . . 155 5-29 A comparison of economic costs between towing water hyacinth mats,

towing bags, and towing on the back of a boat. . . . . 156 5-30 The calculated difference in profit from anaerobic digestion of cauliflower

leaves of different particle sizes. The assumed harvest cost is $4 per

fresh ton. Data from Sharma et al. (1988) [102]. . . . . 159

5-31 The calculated difference in profit from anaerobic digestion of cauliflower

leaves of different particle sizes. The assumed harvest cost is $40 per

fresh ton. Data from Sharma et al. (1988) [102]. . . . . 160

5-32 The average methane production for five different pretreatment stratgie

of Miscanthus grass: untreated, shredded, roller-milled, ground, and

extruded. Original regressed data from Frydendal-Nielsen et al. (2016)

[3 7]. . . . . 16 1

5-33 The daily profit from anaerobic digestion of Miscanthus with five

differ-ent pretreatmdiffer-ent strategies: untreated, shredded, roller-milled, ground, and extruded. Original regressed data from Frydendal-Nielsen et al.

(2016) [37]. . . . . 162

5-34 The daily profit from anaerobic digestion of untreated Miscanthus, with

differing harvest costs. Original regressed data from Frydendal-Nielsen

(18)

5-35 The annual profit expected from the anaerobic digestion of water

hy-acinth, as a function of volume reduction. The volume reduction

in-creases the mass loading rate, which is directly proportional to annual

revenues. An ultimate methane yield of 194 liters per kg volatile solids

is assum ed. . . . . 164 B-i An example of the measurements taken using a 1 Hz Watts Up Pro

power meter and Logger Lite. The peak power measurements were

used, and the mean and standard deviations of the trials (N=5) were

(19)

List of Tables

2.1 Typical yields from popular energy crops, taken from Mckendry (2002)

[76]. . . . . 26

3.1 The feedstock costs for shipping either unchipped or chipped hurricane debris from 24 vegetative debris collection sites spread evenly

through-out Puerto Rico. The mean travel distance is 78km. . . . . 52

3.2 The main parameters used in the mobile chipping model. Hourly ma-chinery costs are standard FEMA contract costs. The throughput

of the chipper is assumed to be the reported throughput of a 1000hp

Hogzilla chipper [52], and the theoretical throughput of the front-loader

is assumed to be the truck loading rate reported by Zomara-Cristales

et al. (2015) [141]. . . . . 55

3.3 A summary of the component costs for biofuel production as reported by Ekbom et al. and Dimitriou et al., amortized over the lifetime of

the plant. Additionally, Dimitriou et al.'s reported numbers scaled to

30MW show the importance of economies of scale in biofuel plants.

(20)

3.4 The results showing the net balance of operation for producing biojet

fuel, bio-oil, and ethanol from hurricane debris. The studies from

Ek-bom et al. (2009), Cambero et al. (2015), and Humbird et al. (2011) were scaled down to accept approximately 90,000 metric tons of

hur-ricane debris each year, which is approximately 56,000 dry tons and

30MW of biomass input, and US market values from May 2019 were

tabulated for all fuel products in order to directly compare the three

studies . . . . 62 3.5 The results showing the specific carbon emission offset per dry metric

ton (dmt) for producing biojet fuel, bio-oil, and ethanol from hurricane

debris. EPA emissions factors were used [116]. For each product, it is assumed that 1 GJ replaces 1 GJ of offset fuel. . . . . 63

4.1 The primary physical properties of water hyacinth used in this model.

These assumed properties are derived from values reported in literature

- a full list of encountered values and sources are found in Appendix A. 72 4.2 A summary of the cost-effectiveness ratios found for manual, biological,

chemical, and mechanical control methods in a study conducted by

Lwasa and Mwanje (2002) [72]. . . . . 75

4.3 The assumptions used to construct the bottom-up cost estimates for

operating a generic mechanical harvester. . . . . 83

4.4 The transport, gathering, and conveying energy requirements for a

mechanical harvester. . . . . 87

4.5 The reported specific fuel consumption for two different mechanical

harvesters. . . . . 88

4.6 A summary of the production energy, application rate, specific

produc-tion energy (per mass of hyacinth treated), and specific carbon emission

(21)

4.7 A summary of studies on the anaerobic digestion of water hyacinth.

The methane potential shown to be a function of particle size and

pretreatm ent. . . . . 96

4.8 Emissions factors for different sources of energy. Data compiled from

EPA (2014). . . . . 97

4.9 The summary of the economic, energetic, and carbon revenues for the

anaerobic digestion of water hyacinth. The biogas is assumed to offset

wood energy, and fertilizer profits include costs required to transport. 100

4.11 Summary of the evaluated cleanup and harvesting methods, as well as

the utilization methods. . . . . 102 4.10 The summary of the economic, energetic, and carbon revenues for the

decomposition, open-air dumping, and landfilling of water hyacinth. . 102

4.12 A summary of the economic, energetic, and carbon costs for manual, chemical, and mechanical control methods paired with their respective

possible utilization (or non-utilization) scenarios. . . . . 103

4.13 The economic, energetic, and carbon emission cost results from the

case study of Lake Tana, with parameters shown. The results include

costs associated with no maintained coverage (total elimination of

wa-ter hyacinth), 50% of current hyacinth coverage maintained, and 100%

of current coverage maintained. . . . . 104

5.1 A summary of the main criteria and functional requirements of a

de-signed water hyacinth collecting system. . . . . 108 5.2 A summary of the differences between the roller and auger concepts. 120

5.3 A summary of the main design parameters for roller-crusher design. 121 5.4 The pretreatment energy input, approximate energy generated from

anaerobic digestion, and resulting energy balance for the untreated, roller-crimped, and food processed water hyacinth. The methane

(22)

5.5 The functional requirements, design parameters, and relevant analysis for the main modules of a roller-crusher system. . . . . 146

(23)

Chapter 1 Introduction

This thesis designs and evaluates systems to utilize two problematic biomass sources, hurricane debris and invasive water hyacinth, and turn costly cleanup efforts into opportunities for biofuel conversion systems. Both feedstocks present challenges for utilization - hurricane debris because of its unpredictable generation, and water hy-acinth because of its low solid density (95% weight in water). Both also cause great economic harm to the communities impacted by them. A novel solution is proposed for each biomass source and techno-economic models accounting for economic, energy, and carbon costs are used to evaluate different options for utilization. The goal of this work is to show that careful design and evaluation of utilization systems could turn government aid and charity spent every year on debris and waterway cleanup into a profitable investment. Chapter 2 gives background for biomass utilization and conversion technologies.

The motivation for evaluating the feasibility of using hurricane debris comes from the aftermath of Hurricane Maria, which hit Puerto Rico and surrounding Caribbean islands in Fall 2017. The hurricane caused dramatic damage throughout the region, including dumping 1 million tons of debris across Puerto Rico and contributing to almost 3000 deaths. In response, this thesis proposes a barge-mounted biofuel con-version system that travels to hurricane-hit ports and converts debris into biofuels. Chapter 3 presents techno-economic results for converting the debris into bio-jet fuel via Fischer-Tropsch synthesis, heating oil via pyrolysis, and ethanol via fermentation.

(24)

A generic debris transport model is also created, and is used to evaluate the economic

benefits of chipping debris directly in the field as a mobile system that loads, chips, and ships debris as a continuous unit.

The motivation to evaluate systems to clean up invasive water hyacinth comes

from the dramatic spread of water hyacinth throughout the world, which has caused

great economic and ecological harm to waterways and thus far has had costly and

inefficient cleanup methods. Chapter 4 evaluates the different ways to clean up and

use water hyacinth, and we present the costs and revenues associated with the most

promising and common options. An emphasis is given to mechanical harvesting

meth-ods, which have unmet technological needs yet help to avoid chemical herbicides and

allow for plant utilization. Chapter 5 then proposes a new method of cleaning up

water hyacinth and other aquatic plants: a mobile roller-conditioner harvester which

grabs, crushes, and directly bags the plants into digesters in-situ on the water. The

hardware designs, prototypes, and tests that address the highest-risk parts of this

proposal are then presented. Additionally, we create techno-economic models to

eval-uate the different modes of transporting water hyacinth - towed as a plant mat, in bags, or on a boat - and to optimize the mass loading rate of anaerobic digestion systems for maximum profit. Chapter 6 provides a summary of work done and of

(25)

Chapter 2 Background

Biomass energy makes up about 10-14% of the world's energy supply, or about 38 EJ

(1018 J) per year. Plant biomass is generated through the process of photosynthesis,

in which carbon dioxide (C02), water, and solar energy are biochemically converted

into carbohydrates that serve to power plant growth. When the organic carbon bonds

are broken down again, typically back into C02, energy is released; hence, biomass

energy has a cyclical carbon cycle and is considered renewable [76].

This section gives a brief overview of conversion technologies, the current state of

bio-energy globally, the use of waste biomass feedstocks, relevant subsidies and

incen-tives, and the core to this thesis: the use of debris and invasive plants as feedstock.

2.1 Conversion of Biomass into Energy

2.1.1 Biomass Feedstock Characteristics

Before converting a biomass into useful energy, the feedstock itself must be

under-stood. The main biomass feedstock characteristics are the heating value, moisture

content, volatile matter content, ash content and cellulose-lignin ratios.

The heating value of biomass is typically expressed as the lower heating value

(LHV), which represents the usable energy content of the fuel when combusted in air, or the higher heating value (HHV), which adds water vapor energy to the LHV. The

(26)

LHV of dry wood is around 20 MJ/kg, whereas the LHV of green wood can be as

low as 8 MJ/kg - hence the importance of the biomass moisture content, which can affect transportation fuel requirements and available conversion pathways [76].

Volatile matter content, ash content, and cellulose-lignin ratios describe the

con-vertibility of the organic compounds into energy. The volatile matter is the part

of the biomass that can be reacted when heated. The ash content is a portion of

the solid residue left behind after combustion, which creates additional handling and

processing costs. Finally, the biodegradability of cellulose, hemicellulose, and lignin

are very different, and thus in bioconversion pathways, the cellulose-lignin content is

important [76].

Outside of the intrinsic plant properties, the growth rate and yield of a feedstock

also determine suitability and profitability for production of bioenergy. The crop

yield (in kg or tons per hectare per year) and HHV (in MJ/kg) can be combined to

find the energy yield of a given land area (Table 2.1).

Energy yields from selected bionass

Biomass Crop yield HHV Energy yield

(dint/ha/a) (MJ/kg, dry) (GJ/ha) Wheat 7 grain/7 straw 12.3 (straw) 123

(14 total)

Poplar 10-15 17.3 173 259

SRC willow 10-15 18.7 187-280

Switchgrass 8 17.4 139

Miscanthus 12-30 18.5 222-555

Table 2.1: Typical yields from popular energy crops, taken from Mckendry (2002)

[76].

The biomass characteristics are essential to evaluating whether or not a biomass

could and should be used for bioenergy. For instance, road transport for a thermal

power station was found to be 70% of the delivered biomass feedstock cost -a function of bulk density (how dense it is), LHV (how energy dense it is), crop yield (how hard

it is to grow), and crop location.

This thesis focuses on using unconventional biomass sources as feedstocks, which

(27)

hurricane debris and invasive water hyacinth. Both feedstocks generate thousands of tons every year without additional human input, do not require land use conversion, and already require costly cleanup efforts; thus, they are problematic feedstocks which can be turned into economic opportunity.

2.1.2 Biomass Conversion Processes

Biomass can be converted into energy (heat or fuels) and/or physical products. Be-cause physical products are more feedstock-specific, they are addressed specifically for woody debris and water hyacinth in the following chapters. A brief overview of energy conversion pathways is given below.

Broadly, biomass can be converted via biochemical pathways such as anaerobic digestion and fermentation, or via thermochemical pathways such as combustion, pyrolysis, gasification, or liquefaction. In all cases, the basic solid, liquid, and/or gas products can be further upgraded to be used as replacement fuels or drop-in transportation fuels for petroleum products like gasoline, diesel, jet fuel, or natural gas.

Direct combustion of biomass can produce heat for generating steam and thus power, with electrical efficiency around 20-40%. Combustion is a mature technology and already has widespread use, particularly in the incineration of municipal solid waste. The combustion of biomass at a smaller scale, for space heating, cooking, and industrial processes, is the primary form of biomass energy utilization currently. The use of combustion for large-scale biomass power generation is limited to around 25-75 MW due to feedstock availability [25].

Anaerobic digestion (AD) is the degradation of biomass with methanogenic bacte-ria. AD has been commercially successful in agricultural digesters and in landfill gas recovery. AD can be used on a large variety of wet and dry biomass; however, it is not suitable for high-lignin biomass such as wood, due to the limited biodegradability of lignin [41].

Fermentation uses bacteria or yeast to convert sugars from biomass into alcohols such as methanol and ethanol. Most ethanol production in the United States is

(28)

produced by fermenting corn grain. These alcohols are typically drop-in gasoline

fuels, though can be upgraded further to be used as jet fuel blends [132].

Transesterification uses methanol to produce straight chain fatty acids from

veg-etable oils. The process is fairly mature, however it requires catalysts and produces

a number of products and waste streams [104].

Pyrolysis is the heating of biomass in the absence of oxygen, which creates a

carbonized solid residue (like charcoal), gas (typically a mixture of carbon monoxide, hydrogen, methane, carbon dioxide, and nitrogen), and oil-like liquid. Temperatures

and techniques can be changed to optimize one product over the other, and the

products themselves can be further refined [41]. For example, pyrolysis oil can be

refined into renewable gasoline, jet fuel, or diesel [132].

Gasification is pyrolysis at high temperatures, which optimizes the production of

product gases (hydrogen and carbon monoxide) and syngas (carbon dioxide and

wa-ter) over the production of liquid oils. The gases can be burned directly in boilers,

re-acted in combustion engines, or converted further into biofuels using Fischer-Tropsch

synthesis [26] [41].

Hydrothermal liquefaction (HTL) reacts biomass at high pressures and

temper-atures (350 deg C and 200 atm) to form biocrude oil, which can be further refined.

HTL has been a research topic of interest due to insensitivity to particle size and

moisture content; however, despite being studied and tested since the 1970s, HTL

technology has not been proven at a commercial-scale [140].

A number of other conversion technologies have been explored in literature;

how-ever, only technologies that have been tested at a commercial-scale were considered

for this project.

2.1.3 Biomass Pretreatment Overview

Biomass in its natural state is typically resistant to degradation, primarily due to

the presence of lignin. Lignin binds together the cellulose and hemicellulose layers, making the plant structurally rigid, insoluble in water, and resistant to microbial

(29)

and increase reaction-available surface area [1]. This processing is known as biomass

pretreatment, and it is typical for all the major conversion pathways.

The major types of pretreatment are:

" Mechanical: particle size is reduced using physical methods like chipping,

shred-ding, grinshred-ding, or milling. Mechanical pretreatment is widely used, however it

has high energy requirements.

" Biological: lignin and cellulose is broken down using fungi and/or enzymes to

enhance biodegradability. The residence time of biological pretreatment is

typi-cally on the order of 10-14 days, which increases storage requirements, decreases

throughput, increases capital cost, and is generally too slow for industrial

pur-poses.

" Chemical: lignin structure is disrupted via internal swelling, using acids, alkalis, or other liquids. The chemical compounds are typically consumed in the process, requiring an additional input to the system.

" Physicochemical: surface area is increased and structures are broken down using

processes like steam explosion (high pressure, high temperature steam). These

new methods can be low cost input and require no chemicals; however, they

are typically used to optimize conversion efficiency for biomass that has already

been reduced in size.

In microbial processes such as anaerobic digestion, some level of pretreatment is

necessary to increase the surface area of the plant and break up lignin structures, so that the microbes can access the cellulose [1]. The same is true for enzymes

in fermentation. However, particle size reduction past a certain point can inhibit

bioenergy production. For instance, Moorhead et al. (1993) found that anaerobic

digestion of water hyacinth was highest with 6.4mm particle size, compared to both

1.6mm and 12.7mm [80]. For gasification, the plant structure must react with hot

gases and pass through various fixed-bed or continuous reactors - particle sizes too large cannot pass through the reactor and do not react properly with the hot gas,

(30)

and particle sizes too small tend to clog more easily; thus, incoming feedstock particle

sizes typically range from 20-80mm [77].

2.1.4 Biomass Pretreatment Costs and Opportunities

Pretreatment is a major cost of biomass logistics, and the ability to pretreat effectively

and efficiently is a major barrier to large-scale commercial production, even for mature

conversion technologies like anaerobic digestion [81]. For fermentation, now widely

used in the United States and Brazil to produce first-generation ethanol, it has been

suggested that the challenge now is in producing good yields with low energy input, and that pretreatment should be a primary focus of research efforts [13.

Despite these suggestions that pretreatment logistics are an essential component

to bioenergy feasibility, as noted by Hjorth et al. (2010), the energy balance of

pretreatment strategies "has only been considered in a few previous studies." The

shredding of plant biomass is widely used as a precursor in anaerobic digestion studies

[95] [49] without reporting the energy required for such studies, yet other studies note

that the net energy budget from maceration has 'not proven to be positive' [51].

Milling, due to its high energy consumption, has also been questioned as unlikely

to be economically feasible [1]. Thus, it is important to carefully evaluate the most

efficient way for optimal pretreatment with minimal energy consumption.

The economic and energetic costs associated with pretreatment is a motivator

for this thesis, as pretreatment costs can be minimized by integrating into

already-existing supply chains (as with hurricane debris) or by integrating mechanical

pre-treatment with harvesting requirements (as with water hyacinth).

2.1.5 Biofuel Types and Maturity

Biofuels are classified as first, second, and third-generation biofuels based on their

feedstock.

First-generation biofuels are made from edible crops such as corn or sugarcane.

(31)

soy-bean or palm oil, are the only biofuels currently produced at an industrial scale [69].

The conversion of these high-starch and high-sugar feedstocks is more technologically

mature.

Second-generation biofuels are made from any number of other feedstocks, such as

non-edible lignocellulosic woods, agricultural residues, and municipal waste. These

feedstocks typically cost less than corn ($300/ton): $100-120/ton for woods,

$60-80/ton for agricultural and forest residues, and $0-60/ton for municipal waste [69].

The wide availability, low feedstock cost, and potential to integrate into existing

supply chains make second-generation biofuels the main target of current government

subsidies and research studies. However, the homogeneity for these feedstocks can be

significantly lower, and their conversion pathways are often less mature. Currently, landfill gas (LFG) is the most proliferous second-generation "biofuel", with over 600

operational LFG projects in the US [115].

Third-generation biofuels refer to biofuels produced from algae. Algae have high

growth rates and thus the ability to sequester carbon dioxide when co-located with

power plants; however, have growth challenges at an industrial scale.

2.2 Current Utilization of Bioenergy

Biomass energy can make up 35% of primary energy consumption in developing

coun-tries [25], and is typically used in more traditional forms such as fuelwood and manure

[53]. However, in the developed world there has been an increased push for the use

of advanced biofuels made from high-productivity energy crops such as grasses or

willows. Biomass-derived renewable fuels are a promising way to decrease our

depen-dence on fossil fuels and reduce greenhouse gas emissions, as energy crop biofuels can

be used to produce drop-in ethanol, bio-jet fuel, renewable natural gas, and bio-diesel.

However, such crops are often grown on arable land, replacing or following the food

and fodder land needs of the region. For instance, 40% of the corn grain grown in

the United States in 2011 was used for ethanol production [82]. The merits of using

(32)

because deforestation and land use change has been thought to account for 12-20%

of all anthropogenic greenhouse gas emissions.

2.2.1 Utilization of Biomass Wastes

Another class of biomass energy is in biomass wastes, including agricultural residues, woody residues, livestock animal manure, and municipal solid waste. These waste

streams can be low-cost feedstocks with already existing supply chains (such as water

and sewage infrastructure) and do not require useful land to be grown; however, the

feedstock itself can be highly diverse and can contain contaminants. The United

States generates approximately 230 million tons of municipal solid waste (MSW),

318 million tons of agricultural waste fiber (like corn stover and crop residues), 66

million tons of food waste, and 45 million tons of wood and yard waste every year.

The energy potential of these waste streams is significant: the methane potential from

anaerobically digesting domestic livestock manure alone would generate 2.4% of US

electricity requirements. These waste streams are often predictable but difficult to

gather and separate, as they are low density and heterogeneous feedstocks [101].

Of the conversion technologies for biomass wastes, anaerobic digestion of municipal

waste is one of the most mature. Landfills are quasi-anaerobic digesters, and the

utilization of landfill gas is growing [115]. Additionally, wastewater can be treated

with anaerobic digestion: for example, the Massachusetts Water Resource Authority

(MWRA) operates an anaerobic digester on Deer Island which converts human waste

into methane and fertilizer, generating 28 MWh of electricity and saving the MWRA

approximately $15 million in fuel oil costs and $2.8 million in electricity every year

[73].

2.2.2 Biomass Debris and Invasive Plants

There is an entirely other class of biomass that might be described as uncoupled

or unpredictable supply chains - biomass waste streams that are not coupled with existing agricultural, industrial, or urban supply chains. Examples of such biomass

(33)

wastes are invasive plant growth, hurricane debris, and detritus from other invasive

animals (such as beetle infestations). These biomass sources are generated in high

volumes without intentional human input and are often associated with economic

losses and costly cleanup operations. For instance, it is estimated that in India,

1.32 million hectares are covered with 100-200 million tons of aquatic weeds in

post-monsoon season, and this number can increase to 2.1 million hectares in pre-post-monsoon

season [63]. Duncan et al. (2004) estimate that 51 million hectares in the United

States are infested with just 16 species of invasive plants. Additionally, these plants

have spread rates easily over 10% and can cause great environmental harm. For

instance, Tamarix, a flowery plant originating from Eurasia and Africa, has overtaken

between 0.47-0.65 million hectares of grazing and wildlands across the western United

States, projecting to cost $7-16 billion in lost ecosystem function over the next

half-century [29]. These feedstock streams are harder to estimate, are underutilized, and

are the subject of current research.

These invasive and non-agricultural biomass sources present a distinct

optimiza-tion problem because the supply of biomass is created regardless of human input, economic losses can arise because of the biomass growth, and resources are already

used to collect and remove the biomass. The biomass itself may not be optimized for

a given bio-energy process, for instance due to moisture content, lignin content, or

heterogeneity; however, the potential of these biomasses is vast. If the infested plots

of land studied by Duncan et al. (2004) were even 25% as productive as switchgrass, they would produce 1.8 EJ (1018 J) of energy per year, or about 2% of annual US

energy consumption.

Disaster debris is another source of problematic biomass, and it is generated

un-predictably and in enormous quantities. Earthquakes, tsunamis, tornadoes, and

hur-ricanes generate debris depending on the affected location and the strength of the

event. The focus of this work is on hurricane debris, due to the proximity of

hurri-canes to the water and the relative short-term predictability of the storms. In 2005, Hurricane Katrina generated 100 million cubic yards of disaster debris [71] spread

(34)

States in recent years have also left behind major quantities of debris, including

Hur-ricane Michael in 2018 generating an estimated 72 million tons of debris [113] and

Hurricanes Maria and Irma generating approximately 1 million tons of debris in 2017

[14]. Over the last 30 years, an average of 1.6 hurricanes have made landfall in the

United States, with 0.5 hurricanes being Category 3 or above [11]. The frequency

and intensity of hurricanes is also expected to increase due to climate change [131]

-thus, a solution that helps to consume resulting hurricane debris and helps to combat climate change by lowering carbon emissions is required.

The focus of this thesis is on two non-traditional, water-borne feedstocks: woody

hurricane debris and invasive water hyacinth (Eicchornia Crassipes).

2.3 Biofuel Policy Incentives

2.3.1 US Renewable Fuel Standard (RFS)

The Renewable Fuel Standard in the United States was created under the Energy

Policy Act of 2005, and mandates that a certain volume of fossil-fuel transportation

fuel be replaced or reduced with renewable fuels. Each category of renewable fuel

has an annual mandated volume of production (and replacement), and thus each

category and sub-category has a "D-code" identification label attached to it. The different categories are:

" Cellulosic biofuel (D3) or cellulosic diesel (D7)

" Biomass-based diesel (D4)

" Advanced biofuel (D5)

" Renewable fuels (non-advanced/conventional) (D6)

Each producer generates a "renewable identification number" (RIN) for each

gal-lon of renewable fuel produced, and in turn the obligated gasoline importers and

refiners must purchase a certain number of RINs (as renewable fuel or as fuel off-sets). Thus, there is an existing market of RINs for each D-code, and the producers

(35)

get a per-gallon incentive for producing renewable fuels (calculated on a gallon of

ethanol-equivalent basis). The production of each fuel can have added incentives of

$0.20-$3.00 depending on the market and the fuel type (Figure 2-1). The differences

between assigned codes primarily reflect the feedstock, expected lifecycle greenhouse

gas emission declines, and technological maturity - for instance, ethanol produced from corn starch would be considered a standard renewable fuel (D6) and have a RIN

incentive of $0.19 per gallon, whereas ethanol from food waste or crop residues would

be classified as a cellulosic biofuel (D3) and have a RIN incentive of $2.00 per gallon

[123].

Weekly D3, D4, D5 and D6 RINs Prices

-3 -4 -5 -6 $3.00 $2.00 ----z $1.00 2... 2011 2012 2013 2014 2015 2016 2017 2018

Transfer Date by Week, FUEL (D Code)

Figure 2-1: The market prices for different RINs, reflecting the per-gallon ethanol equivalent incentive that producers receive for producing renewable fuels of different types [123].

2.3.2 Incentives for feed-in renewable electricity

Renewable electricity generation can be incentivized with feed-in tariffs - prices for electricity paid on a per-kWh basis. In the Netherlands, a $0.11/kWh subsidy is

(36)

guaranteed for up to 10 years to a plant generating renewable electricity and combined

heat and power (CHP) [40]. In Kenya, there is a $0.12/kWh feed-in tariff for solar

(37)

Chapter 3 Utilization of Hurricane Debris for

Biofuel

On September 20th, 2017, Hurricane Maria traveled right through the middle of

Puerto Rico. The Category 4 hurricane left the entire island without power, wiped

out 80% of the island's crop value, covered roads and bridges with impassable

de-bris, flooded communities, and left many without safe drinking water. It took eleven

months for electricity to be restored to the entirety of the island, and the island

con-tinued to experience blackouts in the following months due to mechanical failures, rainfall, and accidents during the repair process [129]. In an independently

commis-sioned study done by George Washington University, 2975 deaths were attributed to

the hurricane's aftermath [78].

The hurricane's 155 mph winds tore through the densely forested island, and

generated massive amounts of debris throughout the island (Figure 3-1). In the

aftermath, the US Army Corps of Engineers had collected 4 million cubic yards of

debris, and they were still grinding the vegetative debris at eight temporary debris

sites as late as eight months later [14]. The tedious process requires the debris to

be cleaned and collected off the roads, delivered to a central gathering site (typically

near a landfill), shredded into chips, delivered to a landfill, and then buried. Of the

nearly $3.77 billion obligated to Puerto Rico for public assistance, $576 million was

(38)

Figure 3-1: A picture showing part of the aftermath of Hurricane Maria, which toppled electricity poles, trees, and lines across Puerto Rico and other Caribbean islands.

Photo by Carlos Giusti - AP, taken from Fortune (2017) [98].

Furthermore, Puerto Rico, as is the case with most islands, is nearly exclusively

reliant on fossil fuels for electricity generation, transportation, and heating. 98% of

the island's electricity generation comes from imported petroleum, natural gas, and

coal, and Puerto Rico consumes 97,000 barrels of petroleum products per day [122]

- nearly all of which is imported. After a major storm like Hurricane Maria, the damaged port and transportation infrastructure caused major fuel shortages, which

exacerbated the lack of access to electricity as households and hospitals turned to

diesel generators. A week after the hurricane, nearly half of the island's hospitals

were still out of operation, and 58 of 69 hospitals had no access to fuel or electricity

[34].

This chapter evaluates the potential of using post-disaster biomass debris for

en-ergy, and in particular for the production of high-value energy products such as jet

fuel, heating oil, and ethanol. These biofuels could be stored, used as drop-in fuels,

or used in generators to alleviate energy shortages during the hurricane aftermath,

while also alleviating debris buildup on the island. Disaster cleanup presents a unique

(39)

un-wanted biomass debris (which would be otherwise landfilled or burned) and generate

valuable fuels domestically (which would otherwise be imported). Currently, federal

funds allocated to large, organized debris cleanup operations. Instead, we propose

the creation of a debris harvesting operation, wherein a barge-mounted biofuel plant

follows hurricanes and docks at islands and ports where debris is generated. The

barge-mounted plant would integrate into existing debris cleanup operations, with

the added requirement that the debris are transported to the ports, instead of to

landfills, from the typical debris collection sites. This mobile disaster-following plant

would use post-disaster debris as an economic opportunity, and it could turn federal

aid spent every year on debris cleanup into a profitable investment.

A generic biomass transportation model is created to estimate the additional

trans-portation costs and evaluate the benefits of chipping debris directly in the field as

opposed to at collection sites. In addition, a techno-economic model evaluates the

energetic, economic, and greenhouse gas costs for three selected conversion processes

-Fischer-Tropsch synthesis, pyrolysis, and fermentation. The cost accounting includes

the energy conversion processes themselves, feedstock gathering and pre-processing

requirements, and facility and operation requirements. The potential of these

bio-debris utilization processes is presented specifically for Puerto Rico.

3.1 Methods of Debris Disposal and Utilization

The various ways to dispose of and utilize hurricane debris are explored. The debris

itself can have a varied composition, often being a combination of woody wastes, combustible waste, and construction debris mixed together. The USACE estimates

that in general approximately 30% of hurricane debris is clean woody debris, and the

other 70% is mixed construction and demolition debris [32]. On tropical islands, the

ratio of clean woody debris is most likely higher, as FEMA estimated that 60% of the

hurricane debris on the US Virgin Islands after Hurricanes Irma and Maria was clean

woody debris [33]. Additionally, even the clean vegetative debris is often partially

Design and evaluation of biomass utilization systems

Design and Evaluation of Biomass Utilization

Systems

by

Valerie Peng

B.S., Mechanical Engineering, MIT (2017)

Submitted to the Department of Mechanical Engineering

in partial fulfillment of the requirements for the degree of

Master of Science in Mechanical Engineering

at the

MASSACHUSETTS INSTITUTE OF TECHNOLOGY

June 2019

@

Massachusetts Institute of Technology 2019. All rights reserved.

A uthor ...

Certified by...

Walter M. May & A.

Accepted by ...

JUN 1310

9

LIBRARIE$

Signature redacted

Department of Mechanical Engineering

May 19, 2019

Signature redacted

Alexander Slocum

Hazel May Professor of Mechanical Engineering

Signature redacted

Thesis Supervisor

I

Nicolas Hadjiconstantinou

Chairman, Department Committee on Graduate Theses

Design and Evaluation of Biomass Utilization Systems

by

Valerie Peng

Abstract

Acknowledgments

Contents

List of Figures

($

($

List of Tables

Chapter 1

Introduction

Chapter 2

Background

2.1

Conversion of Biomass into Energy

2.1.1

Biomass Feedstock Characteristics

2.1.2

Biomass Conversion Processes

2.1.3

Biomass Pretreatment Overview

2.1.4

Biomass Pretreatment Costs and Opportunities

2.1.5

Biofuel Types and Maturity

2.2

Current Utilization of Bioenergy

2.2.1

Utilization of Biomass Wastes

2.2.2

Biomass Debris and Invasive Plants

2.3

Biofuel Policy Incentives

2.3.1

US Renewable Fuel Standard (RFS)

2.3.2

Incentives for feed-in renewable electricity

Chapter 3

Utilization of Hurricane Debris for

Biofuel

3.1

Methods of Debris Disposal and Utilization