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WO O D Y BI O M A S S

Woody biomass is the accumulated mass, above and below ground, of the roots,

wood, bark, and leaves of living and dead woody shrubs and trees. Woody biomasscan be used for heat, power, and electricity generation; biofuels production; and

biochemicals production (e.g., adhesives, solvents, plastics, inks, and lubricants). Wood;

wood residue and byproducts; and bushes, shrubs, and fast-growing trees, grownspecifi cally for energy, are all considered woody biomass. The principle sources for

woody biomass in the United States are harvest residues; mill residues; small diameter

trees; cull trees; trees damaged by or at risk of wildfi re, insects, and disease; urbanwood waste, short rotation woody crops, and fuelwood, Handout 2: Woody Biomass

Basics, found in the back of this chapter, provides a condensed overview of woody

biomass and may be a useful handout for your audience or clientele.

Harvesting and Other ResiduesResidues from forest harvesting operations include logging residues (i.e. branches,

tops, and stumps) left on-site, low-quality commercially grown trees, dead wood, and


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other noncommercial tree species. Other residues include wood that has been cut and

burned during land conversion, precommerical thinnings, and other management

techniques such as a crop tree release and timber stand improvement (TSI). Harvestingresidues and other removals are routinely left behind at the harvest site because

they are expensive to transport and there are few markets for the material. However,

harvesting residues and other removals amount to approximately 67 million dry tonsannually, and of this, approximately 41 million dry tons are economically and physically

available for recovery and use, according to the United States Department of

Agriculture Forest Inventory and Analysis (FIA) programs Timber Product Output(TPO) Database Retrieval System, (U.S.DOE and USDA, 2005).

The possibility of using woody biomass for energy production and other products has

the potential to create markets for these harvesting residues. As a feedstock source,

harvesting residues are generally delivered in one of the following three forms:unconsolidated material, comminuted material, and bundled material. It can also be

converted, in-woods, to a higher value product.

Biomass is any organic matterwood, crops, seaweed, animal wastes

that can be used as an energy source. Biomass is probably our oldestsource of energy after the sun. For thousands of years, people have

burned wood to heat their homes and cook their food.Biomass gets its energy from the sun. All organic matter contains

stored energy from the sun. During a process called photosynthesis,

sunlight gives plants the energy they need to convert water and carbondioxide into oxygen and sugars. These sugars, called carbohydrates,

supply plants and the animals that eat plants with energy. Foods rich in

carbohydrates are a good source of energy for the human body!


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Wood and Agricultural BiomassMost biomass used today is home grown energy. Woodlogs, chips,

bark, and sawdustaccounts for about 53 percent of biomass energy.

But any organic matter can produce biomass energy. Other biomasssources include agricultural waste products like fruit pits and corncobs.

Wood and wood waste, along with agricultural waste, are used to

generate electricity. Much of the electricity is used by the industries

making the waste; it is not distributed by utilities, it is co-generated.Paper mills and saw mills use much of their waste products to generate

steam and electricity for their use. However, since they use so much

energy, they need to buy additional electricity from utilities.Increasingly, timber companies and companies involved with wood

products are seeing the benefits of using their lumber scrap and sawdust

for power generation. This saves disposal costs and, in some areas, mayreduce the companies utility bills. In fact, the pulp and paper industries

rely on biomass to meet half of their energy needs. Other industries

that use biomass include lumber producers, furniture manufacturers,agricultural businesses like nut and rice growers, and liquor producer

Solid Waste

Burning trash turns waste into a usable form of energy. One ton (2,000pounds) of garbage contains about as much heat energy as 500 pounds

of coal. Garbage is not all biomass; perhaps half of its energy content

comes from plastics, which are made from petroleum and natural gas.Power plants that burn garbage for energy are called waste-to-energy

plants. These plants generate electricity much as coal-fired plants do,

except that combustible garbagenot coalis the fuel used to firetheir boilers. Making electricity from garbage costs more than making

it from coal and other energy sources. The main advantage of burning

solid waste is that it reduces the amount of garbage dumped in landfillsby 60 to 90 percent, which in turn reduces the cost of landfill disposal. Italso makes use of the energy in the garbage, rather than burying it in a

landfill, where it remains unused.


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Unconsolidated

Unconsolidated material, or woody biomass in its raw form, is

what remains after the trunk of the tree has been harvested. Thismay include stumps, bark, leaves, needles, branches, and even

the trunk itself. Historically, this material was considered unmerchantable (unsellable)

and in most harvest operations was leftin place on the logging site or piled up at the landingthe place

where wood is delimbed, sorted, and loaded onto trucks for transport. However, advances

in biomass utilization promise new opportunities for the utilization of unconsolidatedwoody biomass

feedstock. In many cases, unconsolidated harvesting residue is

used as hog fuel at wood manufacturing facilities. (Hog fuel is a

combination of ground wood and wood waste used to generatepower or produce on-site heat and power.) For more information

on conversion to heat and power, please see chapter 3, Products

and Possibilities.

One obstacle that remains in the broader use of unconsolidated material is the cost oftransportation. Bulky by nature, this material has a low bulk density, in other words, a

high volume-to-mass ratio (Figure 1). Compressing the material, although not widelyperformed, helps increase bulk density. A more conventional method of increasing the

bulk density of woody biomass is to reduce its size signifi cantly, either by chipping,

grinding, or shredding.

Comminuted

Comminution is the process of making woody material smaller. Reducing the size of

logging residue usually occurs in the woods or at the landing but is sometimes delayeduntil the feedstock reaches the processing facility. Of the three types of reduction

(chipping, grinding, and shredding) chipping is the most common.This is because

chippers are well integrated into conventional harvesting systems. Chippers have highoutput, high-speed cutting knives,

and in most cases the ability to throw chipped material into truck

vans for hauling

Bundled

One recent innovation involves the compaction of logging residues

into cylindrical bales called composite residue logs (CRL) or biomass bundles (Figure 3).

Typically, these bundles have a diameterof about 2.0 to 2.5 feet and are about 10 feet long. One of the most

appealing aspects is that they can be handled similarly to round

logs; however, production of the logs requires specialized machinery. Unlikecomminuted material, these bundles can be stored for

longer periods of time without decomposing.

Although technically feasible, the current market price for woodbased fuel in the U.S.does not support the cost of bundling. And

at the other end, the current price of wood-based fuel does not

support the transport of unconsolidated material, especially with

the fl uctuation of prices for petroleum-based fuels. At this time,


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comminuted biomass is the most economically feasible form

In-woods Conversion

In areas where the cost of transporting wood remains a challenge,portable wood-to-energy conversion units may be an option.

Small-scale, portable pyrolysis (a system that turns wood directly

into an oil and char) and gasifi cation (a system that turns wooddirectly into a gas) units can be towed to a harvesting site and utilized to produce fuel on-

site. It is important to note, however, this

technology is still largely in its experimental stages. See chapter 3,Products and Possibilities for more details on biomass conversion processes.

Municipal and Construction Wastes

The two major sources of urban wood residues are the woody portion of municipalsolid waste (MSW) and construction and demolition debris. Of the 62.1 million dry

tons of urban wood residues generated annually, about 28.3 million dry tons are

economically and physically recoverable

Municipal Solid Waste

The portion of MSW that is wood includes items such as discarded furniture, pallets,packaging materials, processed lumber, and

yard and tree trimmings. Of the 13 million dry tons of woody MSW

generated annually, approximately 8 million dry tons are available

for recovery (McKeever, 2004). This material is generally recycledas mulch or compost; sent to a landfi ll; or burned for heat, power,

and electricity.

In recent years, small, portable wood chippers and bailing unitsthat press yard debris into logs similar in appearance to that of

traditional fi rewood have emerged. Some municipalities provide

large yard debris carts, which are collected weekly. Other areaswork with local businesses to ensure collection options such as

drop-off bins and designated collection facilities.

Landfi ll Gas

Landfi ll gas (LFG) is a natural byproduct of decomposing organic matter. It is

approximately 50 percent methane (CH4

) and 50 percent carbon dioxide (CO2). Landfi lls can

be signifi cant sources of greenhouse gas emissions because they contain a signifi cant

amount of organic matter, and over time the organic matter breaks down and releasesits gases into the atmosphere. These emissions can be captured and used to produce

heat, power, electricity, and biofuels. Approximately 400 landfi ll gas-to-energy projects

exist in the U.S. today (Riat, et al. 2006). Fairfax County, Virginia, has been usingLFG since 1989 to power three electricity generating facilities, one pollution control

plant, and the on-site landfi ll maintenance buildings


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Construction and Demolition

Residential and commercial wood frame construction and demolition generates cut-offs,

scraps, and waste that constitute arelatively clean and homogeneous waste stream that can make an

excellent feedstock for biomass fuel and energy production. Moreover, this particular

waste is relatively easy to access. Wood wasteprocessors can coordinate with construction contractors to designate an area for discarded

wood waste or set up drop boxes on

site for scraps. Of the 39.3 million dry tons of construction anddemolition debris generated annually, approximately 20.3 million

dry tons are available for recovery (McKeever, 2004).

It is important to note that the end-use of the feedstock determines

how clean and consistent it is. Sometimes, urban and construction wood waste cancontain too many contaminants to be used for certain applications. For example, air

quality regulations may prevent creosote-treated telephone poles from being burned

for heat and power. Another example is wood waste from demolition activities. This

material can contain contaminants such as paints, plastics, and known carcinogensand may not be suitable for some applications. In other cases, the wood material may

be in such poor condition that the cost of cleaning limits the economic viability ofprocessing and reusing the material.

Natural Disasters

Clean up operations after natural disasters, such as hurricanesand ice storms, produce large amounts of debris that have traditionally been piled up to

burn or rot (Figures 7 and 8). Debris from

these disasters is largely underutilized, but changes have occurredin recent years. After Hurricane Ivan blew through the Florida

panhandle in 2004, Escambia County managed 6.5 million cubic

yards of woody debris, 60 percent of which it exported to Italy forenergy generation. A company called American Biorefi ning shredded millions of tons of

tree debris the following year after Hurricane Rita affected thousands of acres of eastern

Texas forests anddestroyed a number of roofs and homes. The material was then

shipped to European countries for biomass fuel (Yepsen, 2008).

Animal Waste

Beef cattle, dairy cattle, hogs, and poultry all producemanure, which can be used to produce energy. Manure is

typically categorized as liquid, slurry, or solid. In its solid

state, manure can be burned for heating and cooking or toproduce a gas for energy production. As a slurry, manure

releases methane (CH4

), which can be captured to produceheat, power, electricity, and biofuels.


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AG R I C U L T U R A L BI O M A S S

Agricultural biomass is a relatively broad category of biomass that includes: thefoodbased portion of crops (corn, sugarcane, soybeans, beets, etc.), the nonfood-based

portion of crops (e.g., corn stover [leaves, stalks, and cobs], orchard trimmings, rice

husks, perennial grasses, animal waste, and landfi ll gases. Traditionally, costs forrecovering most agricultural residues are high, and therefore, they have not yet been

widely used as an energy source; however, they can offer a sizeable biomass resource

if technology and infrastructure are developed to economically recover and deliverthis type of biomass to energy facilities. It is important to note that not all agricultural

biomass residuals following harvest can be utilized for energy. Some portion

(often as much as 50 percent) must be left on the ground to replace soil nutrients

and to protect from soil erosion. Handout 3: Agricultural Biomass provides an overviewof agricultural biomass you may fi nd useful as a handout when presenting this topic

to an audience.

Food-based Portion of Crops

The food-based portion of crops is the part of the plant that iseither oil or simple sugars. Rapeseed (used for canola oil), sun-

fl ower, soybeans, corn, sugarcane, and sugar beets are all examples of this type ofagricultural biomass (Figure 12). Corn, sugar

beets, and sugarcane are commonly fermented to produce ethanol. Oilseed crops can be

refi ned into biodiesel.

Nonfood-based Portion of Crops

The nonfood-based portion of crops is the portion of the plant

that is commonly discarded during processing and consists of

complex carbohydrates. This category includes materials such ascorn stover, wheat, barley, and oat straw, and nutshells. Stover

and straw are fermented into ethanol. Nutshells are typically re-

fi ned into biodiesel or combusted for heat. Due to the importantfunction of crop residues in erosion protection and overall soil

quality, their sustainable use is accomplished through the planning

and monitoring of harvest rates specifi c to a given site.

GasificationGasification is a process which can be used to turn a wide variety of substances intogas, by partially combusting these substances and reacting them with air to make ablend ofcarbon monoxide and hydrogen which is known as syngas or synfuel. Synfuelcan be used to run an assortment of engines from gas turbines which generateelectricity to the engines found in cars. Many proponents of clean and sustainable

energy have promoted gasification as a process which should be considered, since itcan be made carbon neutral and it can utilize a wide range of materials as fuel.

What is Gasification?

Gasification is the thermal treatment of solid fuels ("feedstock") into a gaseous form whileretaining most of the energy in the original fuel.
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In contrast to incineration, where fuel is burned under high temperatures to produce heat energy,gasification converts the hydrocarbons in solid fuels under controlled temperature and oxygenconditions to produce viable fuel known as syngas.

Syngas contains most of the energy potential of the original fuel and can drive a variety of energygenerating applications.

Introduction (BOOK)

The manufacture of combustible gases from solid fuels is an ancient art but by no

means a forgotten one. In its widest sense the term gasification covers the conversion ofany carbonaceous fuel to a gaseous product with a useable heating value.This definition excludes combustion, because the product flue gas has no residual

heating value. It does include the technologies of pyrolysis, partial oxidation, and

hydrogenation. Early technologies depended heavily on pyrolysis (i.e., the applicationof heat to the feedstock in the absence of oxygen), but this is of less importance in

gas production today. The dominant technology is partial oxidation, which produces

from the fuel a synthesis gas (otherwise known as syngas) consisting of hydrogenand carbon monoxide in varying ratios, whereby the oxidant may be pure oxygen,

air, and/or steam. Partial oxidation can be applied to solid, liquid, and gaseous

feedstocks, such as coals, residual oils, and natural gas, and despite the tautology

involved in gas gasification, the latter also finds an important place in this book.We do not, however, attempt to extend the meaning of gasification to include

catalytic processes such as steam reforming or catalytic partial oxidation. These

technologies form a specialist field in their own right. Although we recognize thatpyrolysis does take place as a fast intermediate step in most modern processes, it is

in the sense of partial oxidation that we will interpret the word gasification, and the

two terms will be used interchangeably. Hydrogenation has only found an intermittentinterest in the development of gasification technologies, and where we discuss


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it, we will always use the specific terms hydro-gasification or hydrogenating

gasification.

HISTORICAL DEVELOPMENT OF GASIFICATIONThe development of human history is closely related to fire and therefore also to

fuels. This relationship between humankind, fire, and earth was already documented

in the myth of Prometheus, who stole fire from the gods to give it to man. Prometheuswas condemned for his revelation of divine secrets and bound to earth as a punishment.

When we add to fire and earth the air that we need to make fire and the water to keep

it under control, we have the four Greek elements that play such an important role inthe technology of fuels and for that matter in gasificationThe first fuel used by humans

was wood, and this fuel is still used today by millions of people to cook their meals and

to heat their homes. But wood was and is

also used for building and, in the form of charcoal, for industrial processes such asore reduction. In densely populated areas of the world this led to a shortage of wood

with sometimes dramatic results. It was such a shortage of wood that caused iron

production in England to drop from 180,000 to 18,000 tons per year in the period of

1620 to 1720. The solutionwhich in hindsight is obviouswas coal.Although the production of coal had already been known for a long time, it was

only in the second half of the eighteenth century that coal production really tookhold, not surprisingly starting in the home of the industrial revolution, England. The

coke oven was developed initially for the metallurgical industry to provide coke as a

substitute for charcoal. Only towards the end of the eighteenth century was gas produced

from coal by pyrolysis on a somewhat larger scale. With the foundation in1812 of the London Gas, Light, and Coke Company, gas production finally became

a commercial process. Ever since, it has played a major role in industrial development.

The most important gaseous fuel used in the first century of industrial developmentwas town gas. This was produced by two processes: pyrolysis, in which discontinuously

operating ovens produce coke and a gas with a relatively high heating value

(20,00023,000 kJ/m3), and the water gas process, in which coke is converted into amixture of hydrogen and carbon monoxide by another discontinuous method

(approx. 12,000 kJ/m3 or medium Btu gas).

The first application of industrial gas was illumination. This was followed byheating, then as a raw material for the chemical industry, and more recently for power

generation. Initially, the town gas produced by gasification was expensive, so most

people used it only for lighting and cooking. In these applications it had the clearest

advantages over the alternatives: candles and coal. But around 1900 electric bulbsreplaced gas as a source of light. Only later, with increasing prosperity in the twentieth

century, did gas gain a significant place in the market for space heating. The use of

coal, and town gas generated from coal, for space heating only came to an endoftenafter a short intermezzo where heating oil was usedwith the advent of cheap natural

gas. But one should note that town gas had paved the way to the success of the latter in

domestic use, since people were already used to gas in their homes. Otherwise theremight have been considerable concern about safety, such as the danger of explosions.

A drawback of town gas was that the heating value was relatively low, and it could

not, therefore, be transported over large distances economically. In relation to this

problem it is observed that the development of the steam engine and many industrial


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processes such as gasification would not have been possible without the parallel

development of metal tubes and steam drums. This stresses the importance of suitable

equipment for the development of both physical and chemical processes. Problemswith producing gas-tight equipment were the main reason why the production

processes, coke ovens, and water gas reactors as well as the transport and storage were

carried out at low pressures of less than 2 bar. This resulted in relatively voluminousequipment, to which the gasholders that were required to cope with variations in

demand still bear witness in many of the cities of the industrialized world.

Until the end of the 1920s the only gases that could be produced in a continuousprocess were blast furnace gas and producer gas. Producer gas was obtained by

partial oxidation of coke with humidified air. However, both gases have a low heating

value (35006000 kJ/m3, or low Btu gas) and could therefore only be used in the

immediate vicinity of their production.The success of the production of gases by partial oxidation cannot only be attributed to

the fact that gas is easier to handle than a solid fuel. There is also a more

basic chemical reason that can best be illustrated by the following reactions:

C + O2= CO 111 MJ/kmol

CO + O2= CO2 283 MJ/kmolC + O2= CO2 394 MJ/kmol

These reactions show that by investing 28% of the heating value of pure carbon

in the conversion of the solid carbon into the gas CO, 72% of the heating value ofthe carbon is conserved in the gas. In practice, the fuel will contain not only carbon

but also some hydrogen, and the percentage of the heat in the original fuel, which

becomes available in the gas, is, in modern processes, generally between 75 and88%. Were this value only 50% or lower, gasification would probably never have

become such a commercially successful process.

Although gasification started as a source for lighting and heating, from 1900onwards the water gas process, which produced a gas consisting of about equal

amounts of hydrogen and carbon monoxide, also started to become important for the

chemical industry. The endothermic water gas reaction can be written as:

C + 2(REVERSIBLE)C + 2 +131 J/kmol

By converting part or all of the carbon monoxide into hydrogen following the COshift reaction

CO + H2O(REVERSIBLE) H2+ CO241 MJ/kmol

it became possible to convert the water gas into hydrogen or synthesis gas (amixture of H2

and CO) for ammonia and methanol synthesis, respectively. Other

applications of synthesis gas are for Fischer-Tropsch synthesis of hydrocarbonsand for the synthesis of acetic acid anhydride.

It was only after Carl von Linde commercialized the cryogenic separation of air

during the 1920s that fully continuous gasification processes using an oxygen blast

became available for the production of synthesis gas and hydrogen. This was the


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time of the development of some of the important processes that were the forerunners

of many of todays units: the Winkler fluid-bed process (1926), the Lurgi moving-bed

pressurized gasification process (1931), and the Koppers-Totzek entrained-flowprocess (1940s)

With the establishment of these processes little further technological progress in

the gasification of solid fuels took place over the following forty years. Nonetheless,capacity with these new technologies expanded steadily, playing their role partly in

Germanys wartime synthetic fuels program and on a wider basis in the worldwide

development of the ammonia industry.This period, however, also saw the foundation of the South African Coal Oil and

Gas Corporation, known today as Sasol. This plant uses coal gasification and

Fischer-Tropsch synthesis as the basis of its synfuels complex and an extensive

petrochemical industry. With the extensions made in the late 1970s, Sasol is thelargest gasification center in the world.

With the advent of plentiful quantities of natural gas and naphtha in the 1950s, the

importance of coal gasification declined. The need for synthesis gas, however, did not.

On the contrary, the demand for ammonia as a nitrogenous fertilizer grew exponentially,a development that could only be satisfied by the wide-scale introduction of steam

reforming of natural gas and naphtha. The scale of this development, both in totalcapacity as well as in plant size, can be judged by the figures in Table 1-1. Similar, if not

quite so spectacular, developments took place in hydrogen and methanol production.

Steam reforming is not usually considered to come under the heading of gasification. The

reforming reaction (allowing for the difference in fuel) is similar to thewater gas reaction.

CH4+ H2O(REVERSIBLE) 3H2+ CO +206 MJ/kmolThe heat for this endothermic reaction is obtained by the combustion of additional

natural gas:

CH4+ 2O2= CO2+ 2H2O 803 MJ/kmolAn important part of the ammonia story was the development of the secondary

reformer in which unconverted methane is processed into synthesis gas by partial

oxidation over a reforming catalyst.CH4+ O2= CO + 2H2 36 MJ/kmol

The use of air as an oxidant brought the necessary nitrogen into the system for the

ammonia synthesis. A number of such plants were also built with pure oxygen as

oxidant. These technologies have usually gone under the name of autothermal reformingor catalytic partial oxidation.

The 1950s was also the time in which both the Texaco and the Shell oil gasification

processes were developed. Though far less widely used than steam reforming forammonia production, these were also able to satisfy a demand where natural gas or

naphtha were in short supply.

Then, in the early 1970s, the first oil crisis came and, together with a perceivedpotential shortage of natural gas, served to revive interest in coal gasification as an

important process for the production of liquid and gaseous fuels. Considerable

investment was made in the development of new technologies. Much of this effort

went into coal hydrogenation both for direct liquefaction and also for so-called


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hydro-gasification. The latter aimed at hydrogenating coal directly to methane

as a substitute natural gas (SNG). Although a number of processes reached the

demonstration plant stage (Speich 1981), the thermodynamics of the process dictate ahigh-pressure operation, and this contributed to the lack of commercial success of

hydro-gasification processes. In fact, the only SNG plant to be built in these years

was based on classical oxygen-blown fixed-bed gasification technology to providesynthesis gas for a subsequent methanation step (Dittus and Johnson 2001).

The general investment climate in fuels technology did lead to further development

of the older processes. Lurgi developed a slagging version of its existing technologyin a partnership with British Gas (BGL) (Brooks, Stroud, and Tart 1984). Koppers

and Shell joined forces to produce a pressurized version of the Koppers-Totzek gasifier

(for a time marketed separately as Prenflo and Shell coal gasification process, or

SCGP, respectively) (van der Burgt 1978). Rheinbraun developed the high-temperatureWinkler (HTW) fluid-bed process (Speich 1981), and Texaco extended its oil

gasification process to accept a slurried coal feed (Schlinger 1984).

However, the 1980s then saw a renewed glut of oil that reduced the interest in

coal gasification and liquefaction; as a result, most of these developments had towait a further decade or so before getting past the demonstration plant stage.

GASIFICATION TODAY

The last ten years have seen the start of a renaissance of gasification technology, as

can be seen from Figure 1-1. Electricity generation has emerged as a large new market

for these developments, since gasification is seen as a means of enhancing the

environmental acceptability of coal as well as of increasing the overall efficiency ofthe conversion of the chemical energy in the coal into electricity. The idea of using

synthesis gas as a fuel for gas turbines is not new. Gumz (1950) proposed this

already at a time when anticipated gas turbine inlet temperatures were about 700C.And it has largely been the development of gas turbine technology with inlet

temperatures now of 1400C that has brought this application into the realm of reality.

Demonstration plants have been built in the United States (Cool Water, 100 MW,1977; and Plaquemine, 165 MW, 1987) and in Europe (Lnen, 170 MW, 1972;

Buggenum, 250 MW, 1992; and Puertollano, 335 MW, 1997).

A second development, which has appeared during the 1990s, is an upsurge ingasification of heavy oil residues in refineries. Oil refineries are under both an economic

pressure to move their product slate towards lighter products, and a legislative pressure

to reduce sulfur emissions both in the production process as well as in the products

themselves. Much of the residue had been used as a heavy fuel oil, either in the refineryitself, or in power stations as marine bunker fuel. Residue gasification has now

become one of the essential tools in addressing these issues. Although heavy residues

have a low hydrogen content, they can be converted into hydrogen by gasification.The hydrogen is used to hydrocrack other heavy fractions in order to produce lighter

products such as gasoline, kerosene, and automotive diesel. At the same time, sulfur is

removed in the refinery, thus reducing the sulfur present in the final products (Higman1993). In Italy, a country particularly dependent on oil for power generation, three

refineries have introduced gasification technology as a means of desulfurizing heavy

fuel oil and producing electric power. Hydrogen production is incorporated into the


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overall scheme. A similar project was realized in Shells Pernis refinery in the

Netherlands. Other European refineries have similar projects in the planning phase.

Introduction 7

An additional driving force for the increase in partial oxidation is the developmentof Gas-to-liquids projects. For transport, liquid fuels have an undoubted advantage.

They are easy to handle and have a high energy density. For the consumer, this

translates into a car that can travel nearly 1000 km on 50 liters of fuel, a rangeperformance as yet unmatched by any of the proposed alternatives. For the energy

company the prospect of creating synthetic liquid fuels provides a means of bringing

remote or stranded natural gas to the marketplace using existing infrastructure.

Gasification has an important role to play in this scenario. The Shell Middle DistillateSynthesis (SMDS) plant in Bintulu, Malaysia, producing some 12,000 bbl/d of liquid

hydrocarbons, is only the first of a number of projects currently in various stages of

planning and engineering around the world (van der Burgt 1988). environmental

acceptability of coal as well as of increasing the overall efficiency ofthe conversion of the chemical energy in the coal into electricity. The idea of using

synthesis gas as a fuel for gas turbines is not new. Gumz (1950) proposed thisalready at a time when anticipated gas turbine inlet temperatures were about 700C.

And it has largely been the development of gas turbine technology with inlet

temperatures now of 1400C that has brought this application into the realm of reality.

Demonstration plants have been built in the United States (Cool Water, 100 MW,1977; and Plaquemine, 165 MW, 1987) and in Europe (Lnen, 170 MW, 1972;

Buggenum, 250 MW, 1992; and Puertollano, 335 MW, 1997).

A second development, which has appeared during the 1990s, is an upsurge ingasification of heavy oil residues in refineries. Oil refineries are under both an economic

pressure to move their product slate towards lighter products, and a legislative pressure

to reduce sulfur emissions both in the production process as well as in the productsthemselves. Much of the residue had been used as a heavy fuel oil, either in the refinery

itself, or in power stations as marine bunker fuel. Residue gasification has now

become one of the essential tools in addressing these issues. Although heavy residueshave a low hydrogen content, they can be converted into hydrogen by gasification.

The hydrogen is used to hydrocrack other heavy fractions in order to produce lighter

products such as gasoline, kerosene, and automotive diesel. At the same time, sulfur is

removed in the refinery, thus reducing the sulfur present in the final products (Higman1993). In Italy, a country particularly dependent on oil for power generation, three

refineries have introduced gasification technology as a means of desulfurizing heavy

fuel oil and producing electric power. Hydrogen production is incorporated into theoverall scheme. A similar project was realized in Shells Pernis refinery in the

Netherlands. Other European refineries have similar projects in the planning phase.

GRAPH FROM BOOK..1

An additional driving force for the increase in partial oxidation is the development

of Gas-to-liquids projects. For transport, liquid fuels have an undoubted advantage.

They are easy to handle and have a high energy density. For the consumer, this

translates into a car that can travel nearly 1000 km on 50 liters of fuel, a range


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performance as yet unmatched by any of the proposed alternatives. For the energy

company the prospect of creating synthetic liquid fuels provides a means of bringing

remote or stranded natural gas to the marketplace using existing infrastructure.Gasification has an important role to play in this scenario. The Shell Middle Distillate

Synthesis (SMDS) plant in Bintulu, Malaysia, producing some 12,000 bbl/d of liquid

hydrocarbons, is only the first of a number of projects currently in various stages ofplanning and engineering around the world (van der Burgt 1988).

1.1 HISTORICAL DEVELOPMENT OF GASIF

INTRODUCTION

Modern agriculture is an extremely energy intensive process. However high agricultural

productivities and subsequently the growth of green revolution has been made possibleonly

by large amount of energy inputs, especially those from fossil fuels

1With recent price rise .

and scarcity of these fuels there has been a trend towards use of alternative energy

sourceslike solar, wind, geothermal etc.

2

However these energy resources have not been able toprovide an economically viable solution for agricultural applications

3

.

One biomass energy based system, which has been proven reliable and had beenextensively

used for transportation and on farm systems during World War II is wood or biomass

gasification4

.

Biomass gasification means incomplete combustion of biomass resulting in production ofcombustible gases consisting of Carbon monoxide (CO), Hydrogen (H2) and traces of

Methane (CH4). This mixture is called producer gas. Producer gas can be used to run

internal combustion engines (both compression and spark ignition), can be used as

substitute


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for furnace oil in direct heat applications and can be used to produce, in an economically

viable way, methanol an extremely attractive chemical which is useful both as fuel for

heatengines as well as chemical feedstock for industries

5

Since any biomass material can .undergo gasification, this process is much more attractive than ethanol production or

biogas

where only selected biomass materials can produce the fuel.Besides, there is a problem that solid wastes (available on the farm) are seldom in a form

that

can be readily utilized economically e.g. Wood wastes can be used in hog fuel boiler but

theequipment is expensive and energy recovery is low

6

As a result it is often advantageous to .

convert this waste into more readily usable fuel from like producer gas. Hence theattractiveness of gasification.

However under present conditions, economic factors seem to provide the strongestargument

of considering gasification

7, 8

In many situations where the price of petroleum fuels is high .or where supplies are unreliable the biomass gasification can provide an economically

viable

system provided the suitable biomass feedstock is easily available (as is indeed the casein

agricultural systems). 2

II HISTORICAL BACKGROUNDHISTORICAL BACKGROUND

The process of gasification to produce combustible from organic feeds was used in blast

furnaces over 180 years ago. The possibility of using this gas for heating and powergeneration was soon realized and there emerged in Europe producer gas systems, which

used

charcoal and peat as feed material. At the turn of the century petroleum gained wider use

as afuel, but during both world wars and particularly World War II, shortage in petroleum

supplies led to widespread re-introduction of gasification. By 1945 the gas was being

used topower trucks, buses and agricultural and industrial machines. It is estimated that there

were

close to 9000,000. Vehicles running on producer gas all over the world9

.

After World War II the lack of strategic impetus and the availability of cheap fossil fuels

led


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to general decline in the producer gas industry. However Sweden continued to work on

producer gas technology and the work was accelerated after 1956 Suez Canal crisis. A

decision was then made to include gasifiers in Swedish strategic emergency plans.Research

into suitable designs of wood gasifiers, essentially for transport use, was carried out at the

National Swedish Institute for Agricultural Machinery Testing and is still in progress10

.

The contemporary interest in small scale gasifier R&D, for most part dates from 1973 oilcrisis. The U.S. research in this area is reviewed by Goss

11

The manufacturing also took off .

with increased interest shown in gasification technology. At present there are about 64gasification equipment manufacturers all over the world

11,36

The present status of .

gasification technology and R&D activities will be discussed in chapter VII.INTRODUCTIONBiomass gasification is an endothermic thermal conversion technology where a solid fuelis converted into a combustible gas. A limited supply of oxygen, air, steam or a

combination serves as the oxidizing agent. The product gas consists of carbon monoxide,

carbon dioxide, hydrogen, methane, trace amounts of higher hydrocarbons (ethene,

ethane), water, nitrogen (with air as oxidant) and various contaminants, such as smallchar

particles, ash, tars, higher hydrocarbons, alkalies, ammonia, acids, alkalies, and the like.

When undertaken with air as the oxidizing agent, the produced gas has a net calorificvalue (NCV) of 4 6 MJ/Nm

3

The heating value of this gas makes it suitable for boiler and .engine use, and for turbine use with burner modifications (for turbine use, the gas must

be

partially cooled to protect valve control materials and cleaned to protect turbine blades).When oxygen is used, the produced gas has a NCV of 10-15 MJ/Nm

3

, sufficient for

limited pipeline transport and synthesis gas conversion.

PROCESS3.1 ChemistryThe substance of a solid fuel is usually composed of the elements carbon, hydrogen and

oxygen. In the gasifiers considered, the biomass is heated by combustion. Four different

processes can be distinguished in gasification: drying, pyrolysis, oxidation and reduction.From a chemical point of view, the process of biomass gasification is quite complex. It

includes a number of steps like

thermal decomposition to non-condensable gas, vapors and char (pyrolysis); subsequent thermal cracking of vapors to gas and char;


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gasification of char by steam or carbon dioxide;

partial oxidation of combustible gas, vapors and char.

A schematic presentation of these processes is shown below.

Reactions

Gasification parameters

Equivalence ratio

The water gas, water gas shift, Boudouard and methane reactions provides the

opportunity to calculate the product gas composition of a gasifier, but only in case thisequilibrium can really be reached. Models can be used to calculate the gas composition

as

function of the temperature and/or the equivalence ratio (ER), which is the oxygen usedrelative to the amount required for complete combustion. This dimensionless parameter

shows that curves of several parameters like chemical energy in the gas and the gas

composition change significantly at ER = 0,25.

GRAPH

A value of zero (left side) corresponds to pyrolysis while combustion is shown at the

right

hand side. At ER = 0.25 all the char is converted into gas giving the highest energy

density of the gas; at lower values char is remaining and at higher values some gas isburned and the temperature will increase

Superficial velocity and hearth load

The superficial velocity is one of the most important parameters determining theperformance of a gasifier reactor, controlling gas production rate, gas energy content, fuel

consumption rate, power output, and tar/char production rate. The superficial velocity is

defined as the gas flow rate (m3

/s) divided by the cross sectional area (m

2

). A low


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superficial velocity causes relatively slow pyrolysis conditions and results in high

charcoal yields and a gas with high tar content.

3.3.3 Turn-down ratioFor every gasifier there is an optimum range of operating conditions corresponding to a

certain turn-down ratio, i.e. the ratio under which gas is produced of sufficient quality for

its application. This quality criterion is in particular related to the tar production level.For

gasifiers the turn-down ratio is typically 2-3, although some technology developers claim

higher values.3.3.4 Gas heating value

The gas heating value is usually expressed in MJ/Nm

3

A normal cubic meter is referring .to the gas volume at 1 atmosphere and 0 C.

3.3.5 Gas flow rate and gas production

The gas flow rate can be calculated from the primary air flow if the nitrogen content in

the producer gas is known, or measured by orifice plates, venturies, pitot tubes orrotameters.

Gas flow rate and gas productionThe gas flow rate can be calculated from the primary air flow if the nitrogen content in

the producer gas is known, or measured by orifice plates, venturies, pitot tubes or

rotameters.

3.3.6 EfficiencyThe efficiency of a gasifier reactor can be expressed on cold or hot gas basis.

3.3.7 Fuel consumption

The fuel consumption is needed to determine the gasifier and overall efficiency. The fuelconsumption can be measured by a balance or automatically by metering bins.

3.3.8 Tar and entrained particles

The amount of tar and entrained particles depends on the gasifier design and operatingconditions, in particularly the load level (actual power output to the maximum rated

power output)

Important biomass characteristics related to gasificationEach type of biomass has its own specific properties, which determines its performance

as

a fuel in gasification plants. The most important properties for gasification are:

moisture content ash content and ash composition

elemental composition

heating value bulk density and morphology

volatile matter content

other fuel related contaminants like N, S, Cl, alkalies, heavy metals, etc.


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Advantages of producergas fuels

> Producer gas obtainedfrom gasificationof biomass can be usedin dryers, kilns,furnaces and boilers> Producer gas obtained isfree from noxioussubstances andcontaminants.> The internalcombustion engine fueled

by fuel gas from gasificationhave feweremission compared topetroleum derivatives fueledengines.> Sulphur dioxide and NOxare normally absent in fuelgas from biomassgasification.> Using this producer gas it

is possible to operate adiesel engine on duel fuelmode.Diesel substitution of theorder of 80-85% can beobtained at nominal loads.> Mechanical energyderived from the producergas can be used for drivingwaterpumps, irrigation purposes

or for coupling with analternator for electricalpowergeneration

Salient featuresof Biomass Gasifier


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* High conversion efficiencyof 70 - 80% fromsolid biomass to gaseousfuel

* Each Kilogramof Biomass producesaround 2.5 to 3.0 cubicmeters of gashaving a calorific value of1000 - 1100 kilocalories percubic meter.

* A Liter of liquid fuels(diesel / gasoline) can besaved with only 3 to 4

kilograms of biomass.

* Extremely clean andcomplete combustion of gasdue high hydrogencontent.

* Positive environmentalimpact through savingof biomass in mot cases.

* Positive impact on globalclimate i.e. reduced threat ofglobal warming.

Industrial usesof biomass gasifier

Thermal applications( Drier )

Brick / tile kiln runningon Biomass GasifierIsland electrification andalso for running of cottageindustries onsmall islandsGrid parallel operation / gridfeeding


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Chilling / cold storageapplications

CONCLUSION

Biomass gasifier is a veryimportant equipment inpresent days. It can removethe present energy crisisand enviornmental

Reference: http://www.seminarprojects.com/Thread-biomass-gasifier-full-report#ixzz1FKNrIahW
http://www.seminarprojects.com/Thread-biomass-gasifier-full-report#ixzz1FKNrIahWhttp://www.seminarprojects.com/Thread-biomass-gasifier-full-report#ixzz1FKNrIahWhttp://www.seminarprojects.com/Thread-biomass-gasifier-full-report#ixzz1FKNrIahWhttp://www.seminarprojects.com/Thread-biomass-gasifier-full-report#ixzz1FKNrIahW

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