8th

U.S. National Combustion Meeting

Organized by the Western States Section of the Combustion Institute

And hosted by the University of Utah

May 19-22, 2013

Biomass Pyrolysis and Gasification of Different Biomass Fuels

Eric Osgood, Yunye Shi, Tejasvi Sharma, Albert Ratner

Mechanical & Industrial Engineering, University of Iowa, Seamans Center, Iowa City, IA 52240

Abstract

This work explores the gasification and pyrolysis of various biomass fuels such as seed corn,

wood chips, and paper sludge at temperatures between 400°C and 550°C. The gas evolution of

hydrogen, carbon monoxide, and carbon dioxide of the biomass is measured. To achieve the

desired accuracy, a custom experimental setup was constructed with a lab scale gasifier to obtain

time varying gasification and pyrolysis data at high heating rates. Biomass is dropped into a flow

of heated nitrogen where the biomass thermally breaks down and releases various gases. A gas

chromatograph and a CO sensor measure the resulting species concentrations produced from the

various biomass samples. The results show that pyrolysis occurs faster at higher temperatures

and yields higher concentrations of CO, CO2, and H2, as expected. It was found that CO2 and H2

production increases with increasing temperature.

Contents 1 Introduction ........................................................................................................................................... 4

2 Setup & Materials ................................................................................................................................. 8

3 Results & Discussion .......................................................................................................................... 13

4 Conclusions & Future Work ............................................................................................................... 18

5 Acknowledgements ............................................................................................................................. 18

6 References ........................................................................................................................................... 19

1 Introduction

This work explores biomass gasification, which is a process that uses solid or liquid

biomass to create energy through incomplete combustion. Since most of the world uses non-

renewable fossil fuels as energy sources focusing research on renewable energy sources is

worthwhile. Fossil fuels, such as coal, emit carbon dioxide (CO2) and sulfur (S) into the

atmosphere. These gasses and many others released in energy production contribute to global

warming and environmental damage. Biomass gasification uses biomass, material from living or

recently living organisms, and converts it into carbon monoxide (CO), hydrogen (H2), and

methane (CH4) which can later be converted into liquid biofuel through Fischer Tropsch

processes or can be used to generate electrical energy. Through biomass gasification the CO2

originally absorbed by the biomass when grown is released making it a carbon neutral process. A

carbon neutral process is one in which no additional carbon is released. Biomass is also a cost

effective solution in some applications.

There are four main types of biomass gasifiers; they are updraft (counter-flow),

downdraft (co-flow), crossdraft, and fluidized bed. They are fundamentally different in the way

the air and synthesis gas flow through the system. An updraft gasifier has the air injected at the

bottom while the biomass is injected at the top. The gasification products exit through the top.

This is called a counter flow because the fuel flows opposite the air. A downdraft gasifier has the

air and biomass injected at the top and the products of gasification exit at the bottom. This is

called a co-flow gasifier because the air flows in the same direction as the biomass. A cross draft

gasifier has air passing through the fuel from side to side. A fluidized bed gasifier has heated air

flow up from the bottom suspending the biomass particles which creates fluid-like behavior.

Each type of gasifier has different applications, advantages, and disadvantages. Biomass with a

low density should not be used in an updraft gasifier because of the high ash production

associated low density biomass (Sadaka, 2008).

Gasifiers have different zones within them; the zones common to updraft, downdraft, and

crossdraft gasifiers are the drying zone, the pyrolysis zone, the reduction zone, and the

combustion zone. An updraft gasifier with the gasification zones are shown in Figure 1-1

(Verhoeven, 2008).

Figure 1-1. Updraft gasifier.

The gasifier used in the Combustion Laboratory at the University of Iowa is considered a

fluidized bed/updraft gasifier. Heated inert gas, nitrogen, flows up through the biomass which

causes it to gasify. The gasifier at the Oakdale Combined Heat and Power Plant is a downdraft

gasifier while the gasifier at the University of Iowa Main Power Plant is a fluidized bed gasifier.

The main steps in biomass gasification include preprocessing, gasification, gas clean-up

and reforming, and gas utilization (Kumar, 2009). The gasification process can further be split

into three stages as follows:

1 Pre-heating and drying

2 Pyrolysis

3 Char oxidation and gasification

The pyrolysis stage is the main focus of this work. The goal of this work is to

characterize the instantaneous gas concentrations. The gas concentrations in particular of CO,

CO2, CH4, and H2 were closely examined for different materials such as corn kernels, oat hulls,

wet and dry paper sludge, and wood chips at gasification temperatures from 400-550°C.

The combustion equation uses a carbon-based fuel reacting with oxygen in the presence

of heat to form by-products, as shown in Equation 1.1.

(1.1)

In the case of biomass gasification, the amount of oxygen present is not enough to fully

combust the fuel resulting in different products. The gasification reaction with the biomass fuel

in the form of CHxOyNz is shown in Equation 1.2 (Gautam, 2009).

( )

(

) (1.2)

The temperature ranges are directly related to the chemical reactions that take place. At

higher temperatures (600-800°C), Equations 1.3 and 1.4, the rate of steam reforming and dry

reforming reactions, respectively, are dominant and increase the production of CO and H2 whilst

breaking down heavy hydrocarbons such as CH4 and CO2.

(1.3)

(1.4)

Equations 1.5 and 1.6, the boundary and primary water-gas reactions, contribute to the

increase of CO and H2 at higher temperatures.

(1.5)

(1.6)

From the understanding of these previous equations and prior experience it is known that

through the pyrolysis process H2 and CO are produced in higher concentrations at higher

temperatures. However, increasing temperature is not the only factor that affects the product gas.

Several other aspects that affect the product gas are equivalence ratio, heating rate, residence

time, and biomass type.

2 Setup & Materials

i. Materials

This work investigated seed corn, wood, and paper sludge. Corn is quite abundant in

many Midwestern states and is already being used as a renewable energy source in ethanol.

Treated seed corn is considered toxic and must be stored under 18 inches of earth in an isolated

area far from water sources (Ohio State University). The corn is considered toxic because

pesticides and fungicides are applied to the corn before it is planted. Because of this reason

thousands of bushels of corn are wasted every year. If these toxic additives could be removed

then this unused corn could be used as a biomass fuel. Extensive research on how to remove

these chemicals must be conducted before treated seed corn is a feasible energy source.

However, untreated seed corn and corn stover are widely available in Iowa and the Midwest as a

biomass source.

The paper sludge is a byproduct of Weyerhaeuser out of Cedar Rapids, Iowa.

Weyerhaeuser produces the sludge from recycling cardboard and creating cardboard pallets.

They are a company focused on green manufacturing of paper related products. Paper sludge

contains small strands of paper, sand, and a small amount of a plastic contaminant.

Weyerhaeuser creates about 62,000 tons per year of paper sludge at 50% moisture content.

The wood is classified as B12 fine grind wood and has the highest carbon content of all

the materials investigated in this work.

By understanding the chemical formulation of the materials it is much easier to predict

the volatile products formed by gasification. The ultimate and proximate analysis of the materials

can be seen in Table 2-1 and Table 2-2. By examining the ultimate and proximate analysis it can

be predicted that higher levels of CO and CO2 production are the result of using a fuel with

higher carbon content. It can also be predicted that the majority of the permanent gasses are a

result of high carbon and oxygen in the material. A very small amount of hydrogen is expected

since a small amount is present in the fuel.

Table 2-1. Material ultimate analysis (Ratner, 2012).

Seed Corn Wood Paper sludge

Moisture 11.59% 10.60% 46.99%

Carbon 39.13% 44.32% 22.97%

Hydrogen 5.50% 5.23% 2.88%

Nitrogen 1.28% 0.08% 0.05%

Chlorine 0.04% 0.01% 0.01%

Sulfur 0.10% 0.01% 0.07%

Oxygen 41.53% 39.05% 20%

Ash 0.83% 0.71% 7.03%

Total 100% 100% 100%

Table 2-2. Material proximate analysis (Ratner, 2012).

Seed Corn Wood Paper Sludge

Moisture 12.91% 10.60% 46.99%

Volatile Matter 74.42% 77.85% 44.99%

Fixed Carbon 7.46% 10.84% 0.99%

Ash 5.21% 0.71% 7.03%

Total 100% 100% 100%

HV [BTU/lb] 8,910 7,629 3,556

ii. Experimental Configuration

The experimental setup for this work which shows the main components is shown in

Figure 2-1 andFigure 2-2. Figure 2-1 is a schematic of the experimental setup which shows the

main components such as the industrial heater, torch system, thermocouples, flow controllers,

and the gasifier. Figure 2-2 shows a picture of the experimental setup that was used for this

work. Important components not seen in the schematic include particulate filter, gas

chromatograph, CO sensor, and the working environment. A list of the components in their

entirety can be seen in Table 2-3.

A torch and an electric heater were used to jointly heat the reaction chamber to the

desired temperature. The electric heater heated the system to approximately 250°C and the torch

provided additional necessary heating for the reaction chamber. The ratio of O2 and CH4 flow

rates for the torch was set to approximately 2.5 – 2.9 to ensure any excess O2 not burned through

combustion can be accounted for.

Figure 2-1. Schematic of experimental setup.

Figure 2-2. Actual experimental setup.

Table 2-3. Equipment list.

Equipment List

Agilent 490 Micro Gas Chromatograph

Biomass Injection Valve

Biomass Samples

Chromalox Industrial Heater

Computer with LabView

Computer with ChemStation

Exhaust Fan and System

Gas Chromatograph

Gas sampling bags (10)

High Precision Scale

High Tempurate Insulation

Ice Bath

In-line 7 micron filter

IR CO Sensor

Lighter

Nitrogen Tank

NI USB-9162 DAQ Card

Omega FMA-5400 Flow Controller

Omega FMA-A2409 Flow Controller

Oxy-acetylene torch

Oxygen Tank

Particle/moisture Filter

Quartz Tube

Screen Packet

Stainless Steel Mesh

Tubing and Fittings

Type K Thermocouples (2)

iii. Procedure

When the reaction chamber reached the desired temperature the compressed air was shut

off and the N2 was turned on, this was to prevent waste of bottled nitrogen. Then a baseline

sample was collected in one gas sampling bag. This was so the nitrogen and oxygen contents can

be subtracted and the pure synthesis gas content can be known. The ratio of O2 to CH4 for this

work was similar for all samples and temperatures. The ratio was approximately 2.9 for 400°C

and 2.5 for 550°C.

Samples were taken at varying temperatures from 400-550°C for seed corn kernels, wood

chips, and dry paper sludge. For each sample a baseline condition was collected in a gas

sampling bag so the oxygen and nitrogen content could be examined. Then five gas sampling

bags were filled for each biomass sample. These samples were then tested in the GC and

analyzed in ChemStation. The data gathered from the GC is compared to the CO sensor’s result.

3 Results & Discussion

The gas evolution for corn kernels, paper, and wood chips was examined at 400°C and

550°C. It was found that higher temperatures yielded higher amounts of H2, CO2, and CO and

consumed more O2, as expected. These trends were more evident at higher temperatures. This

phenomenon is explained by Equations 1.5 and 1.6, shown above. The results from the GC are

plotted in Figures 3.1-3.6.

Figure 3-1 – 3.6. Gas evolution for corn kernels at 400°C (upper left), corn kernels at 550°C (upper right), paper sludge at 400°C (middle left), paper sludge at 550°C (middle right), wood chips at 400°C (lower left), wood chips at 550°C (lower right).

0

1

2

3

4

5

6

7

8

1 2 3 4 5 6 7 8 9 10

Pe

rce

nt

GC Run #

Corn 400°C

O2

H2

CO

CO2

0

2

4

6

8

10

12

14

16

1 2 3 4 5 6 7 8 9 10 11 12

Pe

rce

nt

GC Run #

Corn 550°C

O2

H2

CO

CO2

0

1

2

3

4

5

6

7

1 2 3 4 5 6 7 8

Pe

rce

nt

GC Run #

Paper 400°C

O2

H2

CO

CO2

0

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Pe

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GC Run #

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O2

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CO

CO2

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1 2 3 4 5 6 7 8 9 10

Pe

rce

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GC Run #

Wood 400°C

O2

H2

CO

CO20

2

4

6

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10

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1 2 3 4 5 6 7 8 9 10

Pe

rce

nt

GC Run #

Wood 550°C

O2

H2

CO

CO2

As shown in the above figures the gasification experiments performed at higher

temperatures yielded clearer trends. Paper sludge and corn at 550°C yielded the highest

concentrations of H2. Paper sludge at 55°0C consumed the most oxygen. Corn at 550°C yielded

the highest amount of CO2.

The data points in these plots are time averaged because of the synthesis gas being mixed

in the gas sampling bags over time. This disrupts the peaks in the data which is why an

instantaneous CO sensor was used. Figures 3.7-3.9 show the plots of the CO gas evolution for

corn, paper and wood chips.

Figure 3.7-3.9. CO evolution from CO sensor for corn at 400°C and 550°C (uppermost), paper sludge at 400°C and 550°C (lower left), wood chips at 400°C and 550°C (lower right).

0

0.001

0.002

0.003

0.004

0.005

0.006

0.007

0.008

0.009

0.01

0 50 100 150

CO

Evo

luti

on

[g

CO

/ g

Co

rn /

s]

Time [sec]

Corn CO Evolution

400C

550C

0

0.001

0.002

0.003

0.004

0.005

0.006

0.007

0 50 100 150

CO

Evo

luti

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[g

CO

/g P

ape

r/s]

Time [sec]

Paper CO Evolution

400C

550C

0

0.005

0.01

0.015

0.02

0 50 100 150

CO

Evo

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[g

CO

/g W

oo

d/s

]

Time [sec]

Wood CO Evolution

400C

550C

The materials at higher temperatures had CO evolution curves that reached higher

maximums but had shorter duration.

Figure 3-10-3.12. CO production from CO sensor for corn at 400°C and 550°C (upper left), paper sludge at 400°C and 550°C (upper right), wood chips at 400°C and 550°C (lower).

To determine the total CO yield, each fuel and temperature series was integrated to find

the total CO production. As shown in the above figures, corn at 400°C yielded the largest CO

concentration and paper sludge at 550°C yielded the lowest amount of CO. This was unexpected

and could be due to the fact that pyrolysis was slower but more complete. This trend was similar

0

0.1

0.2

0.3

0.4

0 50 100 150

CO

Pro

du

ctio

n [

g C

O/

g C

orn

]

Time [sec]

Corn CO Production

400C

550C

0

0.02

0.04

0.06

0.08

0.1

0.12

0 50 100 150

CO

PR

od

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[g

CO

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r]

Time [sec]

Paper CO Production

400C

550C

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0.05

0.1

0.15

0.2

0.25

0.3

0 50 100 150

Axi

s Ti

tle

Axis Title

Wood CO Production

400C

550C

for paper sludge but not for wood. For both temperatures, 400°C and 550°C, paper sludge

produced the smallest amount of total CO. This could be due to the amount of moisture in the

paper sludge. This moisture required more energy to dry the fuel therefore less energy dense gas

was released. The materials gasified at lower temperatures had longer solid residence times than

the higher temperature gasification experiments.

When the results from the CO sensor are compared to the results from the GC, it is seen

that the data is quite similar and yielded the same trends thus providing further validation for the

results.

4 Conclusions & Future Work

The goal of this work was to identify the gas evolution of various biomass fuels in a gas

chromatograph. The results were validated against a CO sensor which showed similar trends in

the data. Corn at 400°C yielded the highest amount of CO, which was unexpected. However,

gasifying at higher temperatures produced more H2 and CO2 signifying that the higher

temperature equations were dominating.

Suggested future work includes performing more gasification experiments at higher

temperatures to further validate these trends. Gasifying several more local fuels would also be

beneficial.

5 Acknowledgements

The author would like to thank Yunye Shi, Tejasvi Sharma, and Albert Ratner for their

help in the lab.

6 References

Gautam G, Adhikari S, Bhavnani S: Estimation of Biomass Synthesis Gas Composition using

Equilibrium Modeling. Energy and Fuels 2009, 24, 2692-2698.

Kumar A, Jones D D, Hanna M A: Thermochemical Biomass Gasification: A Review of the Current

Status of the Technology. Energies 2009, 2 (3), 556-581.

The Ohio State University: Seed Treatment. Bulletin

Ratner: Measurement of Biomass Gasification and Combustion Characteristics in an Upgraded Lab-

Scale Gasification System. 2012

Sadaka S: Pyrolysis Sungrant Bioweb. Sungrant Initive, 15 Nov. 2008. Web.