Date post: | 06-Apr-2018 |
Category: |
Documents |
Upload: | vaalgatamilram |
View: | 226 times |
Download: | 0 times |
of 16
8/3/2019 ALTERNATIVE FUEL FOR IC ENGINE
1/16
ALTERNATIVE FUEL FOR IC
ENGINE
FAST PYROLYSIS OF BIOMASS TO BIOOIL FOR
GREEN POWER GENERATION
(OPEN CYCLE GAS TURBINE)
PRESENTED BY,
C.DUSHYANTH (ph no:9994545146)
T.DHIVAHAR
V.M.DHINESH(PH NO:9952893208)
2nd YEAR, B.E (SANDWICH) MECHANICAL,
(TEAM NAME: ZYROXAXIANZ)
P.S.G COLLEGE OF TECHNOLOGY,COIMBATORE-641004
1
8/3/2019 ALTERNATIVE FUEL FOR IC ENGINE
2/16
ABSTRACT
The scientific consensus on global warming is clear. If atmospheric
concentrations of greenhouse gases continue to rise thus it will prove to be a severe
threat to human society. It is also a well-established fact that combustion of fossil
fuels such as coal, oil and natural gas for power generation is a significant contributor
to global warming (1;2;3). On the other hand biomass has long been identified as an
alternate sustainable source of renewable energy.
This paper describes in detail a 'fast pyrolysis' process that has been
developed and used to convert biomass to biofuel to be used as a fuel in open cycle
gas turbine for power generation. The properties of BioOil produced from both forest
and agriculture biomass wastes will be given in detail, particularly in reference to their
application as a fuel for gas turbine engines. Economics of a combined cycle power
generation plant utilizing pyrolysis liquid (BioOil) from biomass in a gas turbine
engine is presented.The nearest term commercial application for BioOil is as clean fuel
for generating power and heat from gas turbines and boilers.
1.INTRODUCTION
Power generation using a solid fuel has had significant limitations with
respect to materials handling requirements and efficient energy conversion.
Converting biomass fuel into a liquid addresses these issues and makes possible the
use of higher efficiency combined cycle systems for power generation. 'Fast
pyrolysis' technology is a unique process that converts these solid biomass waste
materials into a relatively clean burning liquid fuel that is carbon dioxide and
2
8/3/2019 ALTERNATIVE FUEL FOR IC ENGINE
3/16
greenhouse gas (GHG) neutral.
In the sugar production process from cane approximately 30% by weight of the
crop becomes a fibrous residue referred to as bagasse. Traditionally, much of this solidwaste product has been incinerated in stationary boilers to produce steam for the
process. As bagasse contains significant quantities of silica, its application as a fuel
creates many operational problems due to a) the glazing (fouling) of spreader stoker
equipment and high temperature heat transfer surfaces and b) accelerated erosion of
steel tubing exposed to the abrasive particles in the flue gas. As a consequence,
disposal of this residue has been problematic, inefficient and expensive to the industry.
To overcome this problem we opt for fast pyrolysis of biomass to bio oil.
2. FAST PYROLYSIS' OF BIOMASS
Fast pyrolysis (more accurately defined as thermolysis) is a process in which
a material, such as biomass, is rapidly heated to high temperatures in the absence of
air (specifically oxygen). The biomass decomposes into a combination of solid
char, gas, vapors and aerosols. When cooled, most volatiles condense to a liquid
referred to as 'BioOil'. The remaining gases comprise a medium calorific value non-
condensable gas. BioOil is a liquid mixture of oxygenated compounds containing
various chemical functional groups, such as carbonyl, carboxyl and phenolic. BioOil is
made up of the following constituents: 20-25% water, 25-30% water insoluble
pyrolytic lignin, 5-12% organic acids, 5-10% non-polar hydrocarbons, 5-10%
anhydrosugars and 10-25% other oxygenated compounds.
3
8/3/2019 ALTERNATIVE FUEL FOR IC ENGINE
4/16
In this particular fast pyrolysis process, biomass feedstock is introduced into a
thermolysis reactor having a bed of inert material, such as sand, with a height to width
ratio greater than one. The biomass is shredded to sufficiently small dimensions so
that its size does not limit significantly the production of the liquid product fraction.
Simultaneous introduction of pre-heated, non-oxidizing gas at sufficient linear
velocity performs two principal functions: firstly, as a medium for fluidizing the hot
sand bed and secondly, to cause automatic elutriation of the product char from the
fluidized bed reactor. The process includes removing the elutriated char particles from
the effluent reactor stream and rapidly quenching the gas, aerosols and vapors to
produce a high conversion yield of liquid BioOil. For maximum yield of liquid, the
thermolysis reaction must take place within a period of a few seconds at temperatures
ranging from 450C to 500C. The products must then be quenched as soon as
possible to prevent cracking of the newly produced BioOil.
3. FAST PYROLYSIS HEAT AND MASS BALANCE
Feedstock for the fast pyrolysis process can be any biomass waste material
including wood by-products and agricultural wastes. Preparation includes drying the
feedstock to less than 10% moisture content to minimize the water in the BioOil and
4
8/3/2019 ALTERNATIVE FUEL FOR IC ENGINE
5/16
then grinding the feed to small particles to ensure rapid heat transfer rates in the
reactor. When processing wood-derived feedstocks the conversion yield to liquid
BioOil, solid char and non-condensable gas is approximately 70%, 15% and 15% by
weight, respectively, on an as fed basis. When processing bagasse derived feedstocks
(having ash content as high as 10% on an a dry basis), the yields are measured to be
62% BioOil, 26% char and 12% non-condensable gas. These yield rates were identical
to those determined previously in laboratory size apparatus using the same operating
conditions. The heat required for thermolysis is the total heat that must be delivered to
the reactor to provide all the sensible, radiation and reaction heat for the process to
proceed to completion. The heat of reaction for the fast pyrolysis process is marginally
endothermic. When operating the pilot plant using prepared pine/ spruce as feedstock,
the total heat requirement to produce BioOil at a 70% yield rate (including radiation
and exhaust gas losses) is approximately 2.5 MJ per kilogram of BioOil produced.
The net heat required from an external fuel source, such as natural gas, is only 1.0 MJ
per kilogram of BioOil when the non-condensable gas produced in the process is
directly injected into the reactor burner. This represents approximately 5% of the total
calorific value of the BioOil being produced.
4. BIO OIL ANALYSIS
BioOil is a dark brown liquid that is free flowing. It has a pungent smoky odor.
BioOil contains several hundred different chemicals with a wide-ranging molecular
weight distribution.
The following Table I lists the properties of BioOil produced by the
BioTherm pilot plant, derived from three different biomass feedstocks
Table I: BioOil Properties
Biomass
Feedstock
Pine/ Spruce
100% wood
Pine/ Spruce
53%wood
Bagasse
Moisture wt% 2.4 3.5 2.1
Ash Content wt% 0.42 2.6 2.9
BioOil
5
8/3/2019 ALTERNATIVE FUEL FOR IC ENGINE
6/16
PH 2.3 2.4 2.6
Water Content wt% 23.3 23.4 20.8
Lignin Content wt% 24.7 24.9 23.5
Solids Content wt% < 0.10 < 0.10 < 0.10
Ash content wt% < 0.02 < 0.02 < 0.02
Density kg/L 1.20 1.19 1.20
Calorific Value MJ/kg 16.6 16.4 15.4
Kinematic Viscosity
cSt 20C73 78 57
cSt @80C 4.3 4.4 4.0
The density of BioOil is high, approximately 1.2 kg/liter. On a volumetric
basis BioOil has 55% of the energy content of diesel oil and 40% on a weight basis.
The solids entrained in the BioOil principally contain fine char particles that
are not removed by the cyclones. As can be seen, the solids in the BioOil have been
reduced significantly to levels of approximately 0.1% by weight. The ash content in
these solids ranges from 2% to 20%, depending on the ash content in the feedstock
Table II: BioOil Composition
Feedstock Pine/ Spruce 55% wood
45% bark
Bagasse
BioOil Concentrations wt%
Water 24.3 20.8"Lignin" 24.9 23.5
Cellobiosan 1.9 -
Gl oxal 1.9 2.2Hydroxy-acetaldehyde 10.2 10.2
Levo lucosan 6.3 3.0Formaldeh de 3.0 3.4Formic acid 3.7 5.7Acetic acid 4.2 6.6Acetol 4.8 5.8
5. CURRENT BIOMASS CONVERSION TECHNOLOGIES
The most common biomass conversion technology in use today is combustion
6
8/3/2019 ALTERNATIVE FUEL FOR IC ENGINE
7/16
using either stoker fed grates or fluidized bed combustors equipped with a
water/steam cooled boiler utilizing the standard Rankine cycle for electric power
generation. Nominal conversion efficiency for this conversion technology is
approximately 21% based on simple cycle operation and biomass feed supplied at 50%
moisture. By adopting a combined cycle system using a gas turbine engine coupled to
a heat recovery steam generator (HRSG) and steam turbine, the conversion efficiency
can be increased as much as 40% more than that of a simple cycle system.
There have been four main directions of development in utilizing gas turbines for
bioenergy applications:
11 Direct Combustion: Combusting finely ground biomass in a large combustor
and expanding it directly in the turbine.
11 Indirect Combustion: Atmospheric combustion of biomass with the heat
introduced to the turbine through a heat exchanger.
11 Gasification + GT: The conversion of solid biomass to a low or medium
energy gas that is directly combusted in the gas turbine.
11 Fast Pyrolysis + GT: The conversion of biomass to a BioOil that is directly
combusted in the gas turbine.
It is this fourth option that shows significant advantages in its ability to
maintain high efficiency due to direct combustion and the added benefit in the ability
to store the fuel. The advantage of fuel storage is significant since this de-couples the
operation of the engine from the reactor, maximizing the overall availability of the
power generation plant. Downtime of the reactor will not shut down the engine
provided sufficient stores of BioOil are available for continuous operation. As well,
this also permits the economic transportation of fuel as it is in a liquid form and has
a relatively high energy density compared to solid biomass, which has a
significantly lower energy to volume ratio thus making it uneconomical to transport.
6. ECONOMIC ANALYSIS
7
8/3/2019 ALTERNATIVE FUEL FOR IC ENGINE
8/16
Although there are significant technical and logistical advantages to a fast
pyrolysis liquid fueled gas turbine system, the economics of such an installation are
also important. Budgetary numbers have been produced which show the variation in the
cost of electricity (COE) with changing feedstock costs. The flexibility of a gas turbine
installation allows for several types of configurations and for this analysis, the
three most common configurations are considered:
Simple Cycle: Gas turbine turning a generator
Combined Cycle: Configuration 1 + the exhaust heat is used to generate steam
which is expanded through a steam turbine providing more mechanical power to
produce additional electricity.
Co-generation: Configuration 1 + process steam generation for use in industry
or a plant.
The COE is calculated as the ratio of annual expenses to the amount of
energy produced in a given year. The annual expenses are a combination of operating
and maintenance costs and capital costs which are amortized over a 15-year plant
life assuming an 8% net present value. The capital cost includes all equipment to take
'as delivered' biomass and convert it to electricity at the generator terminals. For each
of the configurations, their expected heat and power outputs and efficiencies are
indicated. It is assumed that there are no additional revenues from any charcoal or
chemical products which can also be produced from the fast pyrolysis process.
Typically fast pyrolysis char comprises 15 to 20% of the feedstock, by weight. The
higher heating value is normally in the range of 24 to 28 MJ/kg. From an energy
perspective, if this char were combusted and the gases routed through the HRSG
then the steam turbine generation rate would add to the overall efficiency of thesystem.
These examples represent relatively small installations and, therefore, do
not achieve the economies of scale one would see in a larger plant. However, the
results indicate that the COE is similar to other much larger bioenergy installations.
This is the case for a 30 MWe combined cycle installation where a 20 year plant life
was assumed with an equivalent feedstock cost of 3-4 $US/tonne and the COE was
8
8/3/2019 ALTERNATIVE FUEL FOR IC ENGINE
9/16
estimated to be 0.046 $US/kWhr. As well, there is the potential to reduce the COE
further through a revenue stream from carbon credits. Although not yet clearly
established, this potential commodity could be a significant income source for such a
plant.
7. BIO OIL APPLICATION AS A FUEL IN GAS TURBINE ENGINES
As a clean fuel, BioOil has a number of environmental advantages over fossil
fuels:
CO2 / Greenhouse Gas Neutral - Because BioOil is derived from biomass
(organic waste), it is considered to be greenhouse gas neutral and can generate
carbon dioxide credits.
No SOx Emissions - As biomass does not contain sulfur, BioOil produces
virtually no SOx emissions and therefore, would not be subjected to SOx taxes.
Low NOx - BioOil fuels generate more than 50% lower NOx emissions than
diesel oil in gas turbines.
Renewable and Locally Produced - BioOil can be produced in countries
where there are large volumes of organic waste. As BioOil has unique
properties as a fuel, it requires special consideration and design
modifications. Some of these properties are presented in
Table III: Typical Properties of BioOil Compared to Diesel Fuel
A first generation fuel system and combustion system were designed and
9
Parameter BioOil Diesel
Calorific Value MJ/kg 15-20 42.0
Kinematic Viscosity cSt 3 - 980 C
2 - 420 C
Acidity pH 2.3 - 3.3 5
Water wt% 20 - 25 0.05 v%
Solids wt%
8/3/2019 ALTERNATIVE FUEL FOR IC ENGINE
10/16
tested, demonstrating the capability to operate a 2.5 MW industrial gas turbine on
BioOil These tests not only revealed the feasibility of operation but also
demonstrated that similar performance could be achieved for BioOil and diesel.
Although CO and particulate emissions were higher than diesel, testing revealed that
NOx emissions were about half that from diesel fuel and the SO 2 emissions levels
were so low as to be undetectable by the instrumentation.
The turbine offers distinct technical advantages over other engines. Unlike
aero-derivative engines, it has been designed as an industrial engine with durability
being one of the main design criteria and not weight. In addition to the ruggedness, the
distinct "silo" type combustion system allows for easy access and modifications to the
entire combustion system, which is one of the critical systems for the adaptation of the
engine to BioOil.
COE VS COST OF FEEDSTOCK
1
8/3/2019 ALTERNATIVE FUEL FOR IC ENGINE
11/16
8/3/2019 ALTERNATIVE FUEL FOR IC ENGINE
12/16
Figure 5: Application of Pyrolysis Oil to Gas Turbine Operation. BioOil has an energy
density approximately half of diesel fuel. Therefore, to meet the same energy input
requirement, the flow rate must be double.
Design modification
Injection system:
This requires design changes to the fuel system to be able to control higher
flow rates and also modify the fuel nozzle to accommodate this larger flow. This lower
energy density also can affect combustion since physically there must be twice as
much fuel in the combustion chamber as with diesel. This, however, is another
advantage of using an industrial engine in the fact that the combustion chambers are
designed with a significantly longer residence time (and therefore a larger volume) fora given power output. Higher viscosity of the fuel reduces the efficiency of atomization
which is critical to complete combustion. Large droplets take too long to burn. Proper
atomization is addressed in three ways.
The fuel system is designed to deliver a high-pressure flow since atomization is
improved with larger pressure drops across the fuel nozzle.
The fuel is pre-heated to lower the viscosity to acceptable levels.
The most importantly, the fuel nozzle has been redesigned to improve spray
characteristics. These design improvements are important for complete
combustion and effectively reducing CO emissions.
Water as a remedy for viscosity reduction:
Although looked at as a contaminant for diesel fuel, the water content in
BioOil has some advantages. Firstly, it is helpful in reducing the viscosity, since it
is a relatively low viscosity fluid. As well, it is a factor in lowering thermal NOx
Advanced coatings
hot corrosion
8/3/2019 ALTERNATIVE FUEL FOR IC ENGINE
13/16
emissions.
Material specification:
Due to its relatively low pH, material selection is also critical for all
components wetted by BioOil. This does not require the use of exotic materials,
however, it does eliminate some standard fuel system materials. Typically, 300 series
stainless steels are acceptable metallic materials and high-density polyethylene
(HDPE) or fluorinated HDPE for polymers
Turbine wash system:
The solids content is a combination of ash and char fines which have carried-
over to the liquid part of the BioOil. The effect of these solids is to cause sticking of
close tolerance surfaces and secondly, they can result in particulate emissions because
of the long residence time required to fully combust. It is important that the solids level
in the BioOil is controlled to be less than 0.1 wt%. The ash content in the fuel
represents the material that cannot be combusted. Depending on the elements in the
ash, it can result as a deposit on the hot gas path components that will reduce the
turbine efficiency. This operational problem is a familiar one with the use of low-grade
fuel oils, which also have a high ash content. The solution is a turbine wash system.
This typically consists of two separate systems in which an abrasive medium is
injected during operation to physically 'scrub' off the deposits. This allows turbine
cleaning without any downtime. The second system is an offline process which injects
a cleaning fluid and allows a soak period to loosen the deposits which are then removed
when the engine is started.
Within the ash are alkali elements, which can result in hot corrosion of the hotgas path components with sodium and potassium being the most critical elements
found in BioOil. These elements form low melting temperature compounds, which,
as a liquid, will stick to the hot gas path components and then react and corrode the
component. This effect can be mitigated through the use of fuel additives. As with the
turbine wash systems, this technology was developed for the use of heavy fuel oils in
gas turbines and has been in use for decades. The concept is to inject specific elements,
which preferentially react with the alkali metals such that they do not liquefy.
8/3/2019 ALTERNATIVE FUEL FOR IC ENGINE
14/16
This both reduces the propensity to stick to a surface and also reduces or
completely eliminates its rate of attack. In combination with the additives, hot section
coatings are being developed specifically for the type of attack that may be associated
with BioOil.
Ignition modification:
Due to the poor ignition characteristics of BioOil, one other key design
requirement is a BioOil specific ignition system or process. To overcome this, the
turbine system starts on diesel fuel flowing through the primary channel in the fuel
nozzle. Following a warm-up period, BioOil is fed into the secondary channel at an
increasing rate while the diesel fuel flow is reduced until 100% BioOil flow is achieved.
Polymerization is also a key issue with BioOil. This is the growing of
molecular chains, which can result in an increase in fuel viscosity. This process is
highly dependent on time and temperature. For example, the equivalent change in
properties can be achieved in 6 months at room temperature, compared to 8 hours at
90C .Therefore, as part of the fuel and combustion system design, maximum
temperatures and fuel re-circulating are carefully controlled to ensure
polymerization is maintained at a rate, which is inconsequential to engine operation.
8. GAS TURBINE DEVELOPMENT WORK
'First generation' systems and design modifications have been developed and
tested. This has demonstrated both the feasibility and significant benefits in utilizing
BioOil for the operation of a gas turbine. Efforts are now being placed on the
development of second generation designs to achieve performance and durability
levels required for commercial operation. This means providing high efficiencies,
maintaining high availability, typical time between overhauls and capital cost
comparable with current gas turbine power generating packages. Key to this work is
the use of a variety of BioOils to ensure designs accommodate as wide a range of
fuel characteristics as possible. This will maximize the applicability of the BioOil gas
8/3/2019 ALTERNATIVE FUEL FOR IC ENGINE
15/16
turbine system to a variety of bioenergy applications. Technically, this work is
proceeding down two main avenues:
1)Performance:
Optimization of the combustion system and the determination of the improved
engine operating and emission characteristics.
Develop and test a turbine wash system based on current systems being utilized
on the line of other Mashproekt engines.
2) Durability:
Design and test fuel system equipment and components for long term
operation with BioOil.
Develop hot section coatings specific to the BioOil combustion environment.
Develop a fuel treatment system to upgrade the fuel quality through filtering,
additives injection and alkali removal.
This work is now underway and has led to the development of a
preliminary specification for BioOil. The purpose of this specification is to define an
acceptable envelope of critical fuel parameters such that commercial level operation
can be maintained.
9. CONCLUSIONS
The use of a gas turbine utilizing pyrolysis oil (BioOil) as a renewable energy
source has many significant advantages in both its flexibility in operation and theefficiency that can be achieved. As well, the economics of this type of installation are
very competitive with other gas turbine powered bioenergy technologies and further
prove its commercial viability.
This has provided confidence in the capability of this fuel being utilized for gas
turbine applications. This work has also been key in identifying the required
development necessary for commercial level operation with the majority of the
8/3/2019 ALTERNATIVE FUEL FOR IC ENGINE
16/16
required technologies already developed from the use of heavy fuels in gas turbines.
Additional testing has been carried out and the development of a second-
generation gas turbine BioOil system is under way. It is sure that biooil will contribute
largely for energy generation.
10. REFERENCES
1. United Nations Development Program Global Environment Facility, Climate
Change Information Kit, http: //www. undp. org/gef/new/ccinfo .htm, updated July
1999.
2. International Energy Agency statistics on world CO2 emissions,
http://www.iea.org/stats/files/key stats/stats_98.htm, 1996.
3. Environment Canada , "The Greenhouse Gas Emissions Outlook to 2020",
http://www.ec.gc.ca/climate/fact/greenhou.html,
Global Climate Change, November 1997.
4. J. Yan, P. Alvors, L. Eidensten and G. Svedberg, "Afuture for biomass", Mechanical
Engineering, Vol.119/No. 10, Oct. 1997, pp. 94-96.
11 P. Gogolek and F. Preto, "Status and Potential of Energy from Biomass in
Canada", Proceedings of Combustion and Global Climate Change, Combustion
Canada, May 1999.
11. ENDNOTES
Ratio of electricity and heat output to BioOil energy input.
This type of similar engines are manufactured by Mashproekt in the
Ukraine who has been designing and building industrial gas turbine engines
for over 45 years and has a line of engines ranging from 2.5-25 MW. Orenda
packages these engines for various industrial needs such as power
generation, pumping and bioenergy applications.