ET 494: Senior Design II

Bio-Mass Gasification System - Pyrolysis

Advisors:

Dr. Junkun Ma and Byron Patterson

Spring 2016

Students:

Andrew Gilly and Anthony Perret

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I. Abstract

Southeastern’s Sustainability Center is a building on Southeastern’s north campus

constructed for educational purposes. The Sustainability Center provides opportunities for

students to learn about renewable energy, recycling, waste reduction measures, and other “green”

technologies. One of the Sustainability Center’s goals is to produce a biomass electrical power

plant to be installed by 2018 to cleanly transform campus’ rejected matter into energy. A

biomass gasification downdraft system works by converting bio-mass (organic trash) into a

combustible syngas. With the use of a pyrolysis system, organic matter can be thermo chemically

transformed into combustible substances. By filtering the “smoke” bi-product, a pure syngas is

produced that can fuel an internal combustion engine, which operates a generator, producing

electrical energy. For further educational purposes, Southeastern intends to build a prototype

gasification system with a 5 kW capacity generator placed on a flatbed trailer as a demonstration.

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II. Background

Biomass gasification is the process of converting a solid waste into a product for modern use,

in our case a combustible gas. The main component of our gasification system will be the

pyrolysis. Simplified, pyrolysis is the process of burning matter. Different from a typical fire,

pyrolysis uses minimum oxygen to perform the decomposition, leaving behind the pure chemical

makeup of the matter being decomposed. Most differently, pyrolysis can occur in the absence of

any fire, needing only elevated temperatures to release the chemicals needed, which is similar to

the fermentation process. By increasing the temperature, the biomass changes into organic

vapors, gases, carbon and tars. Filtering systems such as scrubbers and separators then clean the

fuel and remove all the non-combustible particles, leaving behind a syngas.

The Lakos separator works by separating particles with a centrifugal action. It also has a

“vortube” that draws fluid and pressure to positively allow finer solids to be drawn into the solids

collection chamber. A system such as this will be needed to further clean the bio-fuel.

III. Objective

This project will include extensive research in combustible engines, pyrolysis, liquid and

solid filters, and electrical output from modern generators. The objective of the research is to

gain the proper knowledge in order to successfully design and organize the construction of a

prototype system that will demonstrate and model a large-scale system. In particular, the design

is tasked with the technical design of pyrolysis system, as the other components are industrial

units. Proper knowledge of burn ratios and air/fuel mixtures will be important in the process.

Using skills acquired during Mechanical Engineering Technology courses, a design of a

pyrolysis system based on the fuel needs of a previously acquired generator is to be completed.

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The pyrolysis system will be designed to burn 10 lbs. of wood pellets or less to power a 5 kW

generator for 1 hour. The pyrolysis will need to be a continuous flow of input and output. The

final objective of the design phase will be to draw, using Solid Works, a detailed drawing of the

pyrolysis system.

The overall objective of the research and design will be the construction of a gasification

system that will produce 5 kW/hr. of electricity from 10 lbs. of wood pellets.

IV. Progress (Design)

Following the initial and preliminary research needed for the proposal and justification, we

researched deeper to learn more about combustion and the pyrolysis process. This information

would be needed for proper design and construction. During the early stages of research, our

focus was on the chemical makeup of the wood pellets we would use for the process. After

further study, we discovered that using the wood pellet technology the Sustainability Center has

developed and the typical density of the pellets, the chemical makeup would not be as important

as the heat provided. Therefore our focus switched slightly.

Knowing that the thermal conductivity of the air and material used would be influential,

we began, and studied, the basics of fire and heat. Pyrolysis occurs with heat, not necessarily

fire or combustion. Our design is centered on providing enough heat, and also regulating that

heat in order to keep a combustion controlled environment with a high enough temperature to

achieve the optimum syngas production.

Even with modern technology and modeling programs such as MatLab and ComSol,

there was only one way to know what our temperature and volume flow rate would be for our

unique design, and that was to have a complete system built and conduct analysis. Naturally

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“trial and error” methods, while proven to work, can become timely. Our focus was to make a

best assumption of the parameters needed based on our research of heat and combustion.

Three things are needed for combustion, ignition, oxygen, and fuel. Since the fuel we would

be using would consume the entire system above the combustion (the pellets), and the ignition to

be implemented one time and dependent on fuel, our only control of heat and burn rate is to

regulate the oxygen or air flow. Several bottleneck designs were sketched for our solution.

Below, our current design is displayed through a 3D SolidWorks drawing. The main combustion

tube is a 6-inch schedule 40 pipe at 24 inches long. This will hold approximately 10 lbs. of

wood pellets, which is optimal in achieving our goal for fuel consumed in an hour. We have

researched and studied the height on the tube and cone that the air should be pulled into and

came up with approximately 8 inches about the combustion zone. Since oxygen is our

independent variable and we have designed a downdraft system, theoretically there should be no

combustion above the level of the air intake.

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We researched different feed methods for the wood pellets into the pyrolysis system including

gravity fed, chain or conveyor fed, injection, and even hopper with screw conveyor fed. Since

the air intake should be regulated, the fill point for the biomass needed to be sealed. With this in

mind, we sealed of the feed with an airtight manhole cover. This way we know it can hold

pressure and is airtight unless we allow air in through the air intake.

In a downdraft system, the ash is a first stage filter for the gas. Therefore, not all of the ash

would need to be removed. However, once the system has burned out of wood pellets we need a

way to extract the remains of the fuel in order for continued use of this system over time. As the

fuel feeds, the ash extraction method must also prove to be airtight. This is even more important

after pyrolysis has taken place to limit fuel loss to the generator, to prevent vacuum pressure loss,

and internal combustion in the gasifier. Our design for the ash extraction method does just that,

identical to the fuel intake it is also a manhole cover, which is large enough for shovel extraction

of the remaining ash.

V. Progress (Construction/Completion)

On January 4th, we began construction on the gasifier. Most of the parts for the system

did not arrive until late February, therefore the only building we could do was to start with the

materials that were in the Physical Plant. Currently, we have the entire system installed on the

flatbed trailer and running. The component arrangement of the system from the front to the back

of the trailer is the gasifier, Lakos Separator, scrubber box, vacuum air pump, flare tube, and

generator. For better control of the generator’s fuel and air intake, the whole system is a series of

pipes and vales. A bypass line is interpreted into our design to pass up the air pump when the

generator is started since it will pull the draft for itself.

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The gasifier being the focus in our designing stage is the first control we have in fueling

the generator. The gasifier was designed to give us complete control of the combustion and

initial fuel output towards the generator. It consists of two different steel pipes the inner 6” pipe,

the throat, and the outer 16” sch. 40 pipe, the housing.

The throat is where the wood pellets are fed into with a cone sealing off the inside of the

body to the inside throat pipe. At the bottom of the throat pipe is a cast iron reducer that reduces

the throat from a 6” pipe to a 4”. After the reducer is a shaker box that holds a manufactured

screen made out of stainless steel. From the shaker box the smoke will be forced to travel

downward through the ash via ash hood on the bottom of the box and back up around the outside

of the throat into the inside of the body pipe.

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The objective of the body pipe is to be completely sealed to any uncontrolled airflow. We

also have implemented a series of gages on the body to provide a reference of the temperature of

our system. This give us a benchmark of where our system needs to be when running so

adjustments can be made. In order to do so we have installed three metering valves as the air

intake that run through the body into the throat. In addition, to prevent ash build up in the

gasifier a shaker box was designed to take the heat of the pyrolysis and weight of the pellets

supporting the biomass. At the same time the shaker box was designed to have an air tight

handle to allow a small back and forth motion to allow gravity and the downward suction of the

vacuum to cause the ash to fall to the bottom of the gasifier. The gasifier releases smoke to the

rest of the system from the 2” gas outlet located on the top of the body.

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Filtering

The Lakos Separator is the first filtering device after the gasifier. It works using a vortex

to separate the heavier molecules out of the smoke. It was purchased and modified to better

gauge how much tar is being removed at that stage in the system. In order to do so a glass mason

jar with a measuring scale was used as a drip leg to view the amount of tar and particles being

separated from the fuel. Also a metering valve was installed at the waste extraction of the Lakos

if interchanging of mason jars is needed.

The scrubber is the second filtering device after the gasifier. It has two main purposes; to

further filter the smoke and to lower the temperature of the smoke. When designing the scrubber

we considered using as much surface area as we can with the space provided. With this in mind,

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we built a box with a snaking pattern to force the smoke through as much of the medium in the

scrubber as possible. As a medium, we used pine wood chips to maximize the surface area to

filter out the smoke. At the same time, the wood chips absorb thermal energy in the smoke

lowering the temperature.

Creating the Draft

The vacuum air pump and flare are crucial in the flowing and testing of the fuel. In order

to start the system the air pump has to be running to pull a draft from the air inlets of the gasifier

through the flare as a temporary exhaust. As the smoke cools from being pulled through the

scrubber, the temperature changes so drastic condensation begins to form throughout the air

pump and flare portion of the system. In order to gauge the amount of condensation and remove

it, we implemented two more glass mason jars to gauge and catch the condensation to protect the

engine from said condensation. The flare not only serves as a temporary exhaust for the system

but also as a fuel-testing device. The hotter the temperature, the more the particles break down.

Once more carbons have been burned off and the smoke “thins” out this is a sign that the flare if

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ready to be lit. After being lit the color, size, and intensity of the flare will determine the

combustibility or richness of the fuel that we are producing.

The Generator

Our main objective is to get the 5000-watt generator running for one hour from 10

pounds of wood pellets. In order to get the generator running from smoke a few modifications

had to be done to what was once a gasoline engine. The original carburetor for the motor had to

be removed and replace with a manufactured part. The manufactured carburetor is made from a

block of aluminum with a threaded hole bored through the top and bottom of the block towards

one end of the block. Another hole, non-threaded, is connecting the threaded hole through the

center of the block and into the intake. The threaded hole is divided into a fuel intake at the

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bottom, and an air intake at the top. Two metering valves that are installed before the intakes can

be turned manually to regulate both intakes. The air and fuel are then mixed in the hole that runs

along the length of the manufactured carburetor into the engine. To cut back on the generator’s

vibration towards the rest of the system, two flex hoses are mounted in between both metering

valves and the carburetor. Four rubber pads were placed under the generator to help reduce the

vibration to other components.

VI. Conclusion

We proposed to design, construct, and test a 5kW biomass gasifier to be used as a

prototype display for Southeastern Louisiana University’s Sustainability Center. During the Fall

semester, we conducted our design phase. The Spring semester consisted of constructing and

testing the components. Using only a biomass fuel, ignition source, air and filtration, we have

successfully powered an engine that can in return produce 5kW of electrical power.

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With the knowledge of gasification, this system can be scaled up to meet the needs and

proposals of the Sustainability Center. This system will act as an education device for future

students, and a benchmark for future designs.