Hand Out Kuliah Boiler Fuels and Combustion

8/9/2019 Hand Out Kuliah Boiler Fuels and Combustion

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Boiler Fuels and Combustion

Boiler Fuels.

Differs to other heat engines such as the internal combustion engines, practicallyboilers can use all kind of fuels, as solids, liquids, and gasses. However, most boilers

are using fossil fuels, and small numbers use other fuels such as waste materials.

1

Fuel types for boilers.

11. Solid fuels:

a. ossil fuel : coal !anthracite, semi" anthracite, bituminous, semi"bituminous,

sub"bituminous, lignite#.

$ b. Solid waste fuels and by products: waste wood, bagasse, forest wastes.

%. &iquid fuels:

1 a. ossil fuels: diesel and petroleum products, residual fuel oil.

% b. Synthetic biofuels' c. (aste and by product: waste oils

'. )as fuels.

a. ossil fuel: natural gas

b. *arious process gasses.

Fuels Properties.

+he main property of fuels is the Calorific Value, which could be defined as is the

quantity of heat produced by its combustion " at constant pressure and under normal

conditions !i.e. to 0oCand under a pressure of 1,013 mbar#.

+he combustion process generates water vapor and certain techniques may be used to

recover the quantity of heat contained in this water vapor by condensing it. +he

Higher Calorific Value!or )ross -alorific *alue " )-*# suppose that the water of

combustion is entirely condensed and that the heat contained in the water vapor is

recovered.

uel

Higher -alorific *alue

!)ross -alorific *alue " )-*#

kJ/kg Btu/lb

nthracite '%,/$$ " '0,$$$ 10,$$$ " 10,/$$

Semi anthracite %,2$$ " '%,/$$ 11,/$$ " 10,$$$

3ituminous coal 12,$$$ " %',%/$ 2,'$$ " 1$,$$$

&ignite 1,'$$ 2,$$$

4eat 1',5$$ " %$,/$$ /,/$$ " 5,5$$

(ood !dry# 10,0$$ " 12,0$$ ,%$$ " 2,/$$

Diesel 00,5$$ 16,'$$

)asoline 02,'$$ %$,0$$

kJ/m3 Btu/ft3


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3utane -0H1$ 1'',$$$

7atural gas 0',$$$

Methane CH4 39,820

Propane C3H8 101,000

kJ/l Btu/gal Heavy fuel oil 41,200 177,000

Kerosene 35,000 154,000

+heLower Calorific Value !or 7et -alorific *alue " 7-*# suppose that the products

of combustion contains water vapor and that the heat in the water vapor is not

recovered. 8n general it is possible to use the appro9imation:

net calorific value = gro calorific value ! 10"

ther properties of fuels depend on the type of the fuels either solid fuel, liquid fuel,

or gaseous fuel

Solid uels: -oal 4hysical properties

; !moisture B volatile matter B ash#

; -arbon B hydrogen, o9ygen, sulphur, nitrogen residues

; Heat generator during combustion

4ro9imate analysis of coal

; Determines only fi9ed carbon, volatile matter, moisture and ash

; Cseful to find out heating value !)-*#

; Simple analysis equipment

Cltimate analysis of coal

; Determines all coal component elements: carbon, hydrogen, o9ygen,

sulphur, other; Cseful for furnace design !e.g flame temperature, flue duct design#


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Fuel oil type')0

!&ight Diesel il#Furnace oil

'SHS!&ow Sulphur

Heavy Stock#

Specific 1ra+ity 2.3-42.35 2.3642.6- 2.3342.63

7iscosity

; 8easure of fuel*s internal resistance to flow

; 8ost important characteristic for storage and use

; )ecreases as temperature increases

Flash point

; 'owest temperature at which a fuel can be heated so that the

+apour gi+es off flashes when an open flame is passes o+er it

; Flash point of furnace oil# 99oC

Pour point

; 'owest temperature at which fuel will flow; Indication of temperature at which fuel can be pumped

Specific heat

; &Cal needed to raise temperature of &g oil by oC :&cal&goC$

; Indicates how much steamelectricity it ta&es to heat oil to a

desired temperature

Sulphur content

; )epends on source of crude oil and less on the refining process

; Furnace oil# ;4< % sulphur

; Sulphuric acid causes corrosion

=sh content

; Inorganic material in fuel; >ypically 2.2 4 2.25%

; Corrosion of burner tips and damage to materials e(uipments at

high temperatures

Carbon residue

; >endency of oil to deposit a carbonaceous solid residue on a hot

surface

; "esidual oil# ?% carbon residue

@ater content

; Aormally low in furnace oil supplied :% at refinery$

; Free or emulsified form; Can damage furnace surface and impact flame

Storage of fuels

; Store in cylindrical tan&s abo+e or below the ground

; "ecommended storage# ?2 days of normal consumption

; Cleaning at regular inter+als

>ypical specifications of fuel oils

!adapted from +herma9 8ndia &td.#


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; Hydrocarbons are gaseous at atmospheric pressure but can be

condensed to liquid state

; &4) vapour is denser than air: leaking gases can flow long distances

from the source

7atural gas

;


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4roses pembakaran bahan bakar industri mempunyai beberapa karakteristik sbb.

1.


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c. Cntuk membakar 3elerang:

S B % B 7% S% B 7%

'% kg S B '% kg % B 26J%'1 9 '% kg 7% 0 kg S% B

B 26J%'1 9 '% kg 7%

Setiap 1 kg S membutuhkan: 1 kg %, dan 26J%'1 kg 7%.

tau kebutuhan udara: 1$$$J%'1 kg A 1J$,%'1 kg

pabila setiap 1 kg bahan bakar mengandung - kg -arbon, H kg Hydrogen, S kg

3elerang, dan kg ksigen, maka kebutuhan udara stoichiometri untuk reaksi

pembakaran sempurna setiap kg bahan bakar tersebut !)u#:

%'1,$%'1,$%'1,$

.5

%'1,$1%

.'% )%H

*

C+

u ++=

atau: )u A 11,/' - B '0,/ !H"J5# B 0,'% S kgJkg b.b.

Dalam ukuran volumetris, apabila density udara 1,%6' kgJm' !dalam kondisistandar atmosfir# maka kebutuhan udara stoichiometri !*u#:

%)HC+u

Vu

'//,'#5J!6,%65,5%6',1

++== m'Jkg b.b.

Cntuk bahan bakar yang tidak diketahui komposisi unsur kimianya, maka

kebutuhan udara stoichiometri dapat diperkirakan berdasarkan 7ilai 3akar +inggi"

nya !HH*#:

$$$.1$

/,2 HHV+

u = kgJkg b.b.

%. )as sap Hasil 4embakaran.

Dalam proses pembakaran stoichiometri, produk gas asap hasil pembakarannya

adalah: -%, H%, S%, dan 7%. 3erdasarkan reaksi kimia diatas maka umlah

produk gas asap setiap 1 kg bahan bakar adalah:

a. 3erat -%: )"-% A 00.-J1% A ',2 - kgJkg b.b.

Density -% !S+4# A 1,622 kgJm'K sehingga volumenya:

*"-% A ',2J1,622 - m'Jkg b.b. A 1,5 - kgJkg b.b.

b. 3erat H% !uap air#: )"H% A '.HJ0 A 6.H kgJkg b.b.

Density H% !S+4# A $,5$0 kgJm'K sehingga volumenya:

*"H% A 6,$J$,5$0 H m'Jkg b.b. A 11,1 H m'Jkg b.b.

pabila setiap kg bahan bakar uga mengandung ( kg air, maka umlah uap

air didalam gas asap:

)"H% A !6.H B (# kgJkg b.bK dan volumenya:

*"H% A !6.H B (#J$,5$0 H m'Jkg b.b.

c. 3erat S%: )"S% A 0.SJ'% A %.S kgJkg b.b.

Density S% !S+4# A %,6%2 kgJm'K sehingga volumenya:

*"S% A %,$J%,6%2 S m'Jkg b.b. A $,5$ S m'Jkg b.b.


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d. 3erat 7%: )"7% A $,26 )u A $,26L11,/' - B '0,/ !H"J5# B 0,'% SM A

A 5,5/ - B %,0!H " J5# B ','1 S.

*olume 7%: *"7% A $,26 *u A $,26L5,56.- B %,6!H"J5# B ','// SM A

A 2,1 - B %1,' !H > $J5# B %,/ S

Dengan demikian umlah berat !)ga# dan volume !*ga# gas asap yang dihasilkan

dari proses pembakaran stoichiometri 1 kg bahan bakar:

)ga A )"-$% B )"H%$ B )"S% B )"7% A

A ',2 - B 6H B ( B % S B 5,5/ - B %,0!H > J5# B ','1 S A

A 1%,/% - B 6 H B %,0!H"J5# B /,'1 S B ( kgJkg b.b.

*ga A *"-% B *"H% B *"S% B *"7% A

A 1,5 - B !6 H B (#J$,5$0 B $,5 S B 2,1 - B %1,'!H " J5# B %,/ S A

A 5,6 - B 11,1 H B %1,'!H > J5# B ','' S B 1,%0 ( m'Jkg b.b.'. 4roses 4embakaran dengan @9cess"ir.

ungsi dari udara lebih yang diberikan diantaranya:

a.


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pabila dalam proses pembakaran menggunakan koefisien e9cess air maka

koefisien kelebihan udara pembakaran terhadap udara stoichiometri A "1.


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the proportion of various gasses content in the flue gas. 8f the chemical composition

of the fuel is known, then e9cess air can be calculated analytically.

+he maor constituents in flue gas are -%, -, %, 7% and H%. @9cess air is

determined by measuring the % and -% contents of the flue gas. 3efore proceeding

with measuring techniques, consider the form of the sample. flue gas sample may

be obtained on a wet or dry basis. (hen a sample is e9tracted from the gas stream, the

water vapor normally condenses and the sample is considered to be on a dry basis.

+he sample is usually drawn through water near ambient temperature to ensure that it

is dry. +he maor constituents of a dry sample do not include the water vapor in the

flue gas.

+o ensure a representative average gas sample, samples from a number of equal area

points should be taken. or normal performance testing, equal areas of appro9imately

6 ft% !$.5 m%# up to %0 points per flue are adequate. or continuous monitoring, the

number of sampling points is an economic consideration. Strategies for locating

permanent monitoring probes should include point by point testing with different

burner combinations. s a guideline, four probes per flue located at quarter pointshave been used successfully on large pulveriEed coal"fired installations.

(hen evaluating the performance of a steam generator firing a heterogeneous fuel

such as municipal solid waste !


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tau kelebihan udara %/= diatas kebutuhan udara teoritis.

Efisiensi dan Deseimbangan Panas pada Detel /ap.

@fisiensi Ietel Cap

Iinera efisiensi boiler adalah:

A energi bergunaJenergi input, atau dapat disederhanakan menadi:

A !@nergi dalam uap produksi# J !@nergi kimia bahan bakar#

@fisiensi boiler biasanya berkisar antara: 2/= " 5/=.

Ieseimbangan panas 3oiler atau sering disebut sebagai neraca panas, menunukkan

aliran panas dari energi kimia bahan bakar menadi energi berguna dan semua losses

dan aliran lain yang teradi selama proses dalam boiler. 7eraca panas boiler sangatpenting untuk di analisis karena dapat menunukkan:

1. Iinera efisensi boiler.

%. 3esar dan arah semua kehilangan energi yang teradi selama proses.

'.


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. )iagram &eseimbangan energi pada boiler

Bahan4ba&ar# 22% /ap# 3; %

1as asap# %

'osses# -,-% ,- %.

;. )iagram &eseimbangan energi pada P'>/.

D0A)EAS0"#% 'IS>"ID# /"BIA 1EAE"=>0"

/=P# 32 %

=I" PEA1ISI

B=H=A B=D=" S/PE"HE=>E"

EC0A08ISE"

,- %

'0SSES PE8B=D="=A )IA)IA1# -,- %

/A4=CC0/A>E) '0SS# ,-%

B0I'E"

B0I'E"

22%

%

>/"B041EA.

'0SS# 5 %


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'. )iagram San&ey pada P'>/

Gin 2,-%

Gboiler 32 %

Gloss - ,-%

Gloss < -,-%

Gloss %Gloss; 5%

G'


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+he amount of % in the flue gas is significant in defining the status of the

combustion process. 8ts presence always means that more o9ygen !e9cess air# is being

introduced than is being used. ssuming complete combustion, low values of %

reflect moderate e9cess air and normal heat losses to the stack, while higher values of

% mean needlessly higher stack losses. +he quantity of e9cess % is very significant

since it is a nearly e9act indication of e9cess air.

+he current industry standard for boiler operation is continuous monitoring of % in

the flue gas with in situ analyEers that measure o9ygen on a wet basis. or testing, the

preferred instrument is an electronic o9ygen analyEer. +he rsat unit, which measures

!-% B S%# and % on a dry volumetric basis, remains a trusted standard for

verifying the performance of electronic equipment. +he rsat uses chemicals to

absorb the !-% B S%# and %, and the amount of each is determined by the

reduction in volume from the original flue gas sample.

+he rsat has several disadvantages. 8t lacks the accuracy of more refined devices, an

e9perienced operator is required, there are a limited number of readings available in a

test, and the results do not lend themselves to electronic recording. (hen -% is

measured, by rsat or a separate electronic analyEer, it is best to calculate e9cess air

based on the % result due to the insensitivity of e9cess air versus % results in the

fuel analysis.

3oiler @fficiency

3oiler @fficiency may be indicated by

Combution fficienc-" indicates a burners ability to burn fuel measured by

unburned fuel and e9cess air in the e9haust

(hermal fficienc- " indicates the heat e9changers effectiveness to transferheat from the combustion process to the water or steam in the boiler, e9clusive

radiation and convection losses

.uel to .lui$ fficienc-" indicates the overall efficiency of the boiler

inclusive thermal efficiency of the heat e9changer, radiation and convection losses

" output divided by input.

3oiler @fficiency is in general indicated by either +hermal @fficiency or uel to luid

@fficiency depending the conte9t. 3oiler efficiency related to the boilers energy

outputto the boilers energy inputcan be e9pressed as:

Boiler efficienc- " = heat carrie$ b- the team / heat 'rovi$e$ b- the fuel

Heat deli+ered from the Boiler to the Fluid

8f a fluid like water is used to deliver heat from the boiler, the delivered heat can be

e9pressed as:

= m / t c'$(

where2 = heat $elivere$ kJ/, k

m / t = ma flow kg/

m = ma kg

t = time

c'= 'ecific heat ca'acit- kJ/kgoC

$( = tem'erature $ifference between inlet an$ outlet of the boiler oC


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or a steam boiler the heat e9ported as evaporated water at the saturation temperature

can be e9pressed as:

= m / t he 3

where2 m = ma flow of eva'orate$ water kg

t = time he= eva'oration energ- in the teamat the aturation 'reure the boiler i

running kJ/kg

Fuel Combustion E(uipments.

-ombustion of Solid uels.

+hree methods for combustion solid fuels in boilers.

1. Stokers combustion%. 4ulverised coal combustion

'. luidiEed bed combustion

Stokers combustion.


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installation requires selecting the correct type and siEe of stoker for the fuel being

used and for the load conditions and capacity being served.

+here are two general types of systems: un$erfee$ and overfee$ toker. Cnderfeed

stokers supply both the fuel and air from under the grate while overfeed stokers

supply fuel from above the grate and air from below the grate. verfeed stokers arefurther divided into two types: ma fee$ and'rea$er. 8n the mass feed stoker, fuel is

continuously fed to one end of the grate surface and travels horiEontally across the

grate as it burns. +he residual ash is discharged from the opposite end. -ombustion air

is introduced from below the grate and moves up through the burning bed of fuel.

8n the spreader stoker, combustion air is again introduced primarily from below the

grate but the fuel is thrown or spread uniformly across the grate area. +he finer

fraction of the fuel burns in suspension as it is lifted by the upward moving flue gas

flow. +he remaining heavier fraction of the fuel lands and burns on the grate surface

with any residual ash removed from the discharge end of the grate. +here is little

demand in todays market for the underfeed and small mass overfeed coal"fired unitsbecause of cost and environmental considerations. +his market has been replaced with

shop assembled oil" and gas"fired units and to some e9tent, by overfeed spreader

stoker systems.

+he stokerJgrate systems are provided in many mechanical configurations depending

upon the manufacturer. +able 1 summariEes several variations of basic stoker designs

by type, fuel, heat release rate and appro9imate largest capacity available. )rate heat

release rate is the fuel input divided by the active or effective area of the grate upon

which fuel burning is intended to occur.

or a given boiler steam capacity, the typical fuel burning rates in +able 1 generally

determine the plan area of the grate and furnace in which it is installed. 4ractical

considerations limit stoker siEe and, consequently, the ma9imum steam generation

rates. or coal firing, this ma9imum steam generation rate is about 06.1 kgJsK for

wood or biomass firing it is about 11'.0 kgJs. lmost any coal can be burned on some

type of stokers.


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Underfeed stokers

+here are two general types of underfeed stokers: the horiEontal feed side ash

discharge type shown in ig. 1 and the gravity fed rear ash discharge type shown in

ig. %. 8n the side ash discharge type, coal is fed from a hopper to a central trough,

called a retort, by a screw or ram pusher. ir is admitted through the tuyTres or air

noEEles as shown. 8n the larger units, a ram assisted by pusher blocks or a sliding

retort bottom !fuel distributors# moves the fuel upward and into the retort.

s the coal moves upward and over the retort edges and spreads out over the active

grate area, it is e9posed to air and radiant heat. Drying occurs and distillation ofvolatiles begins. s the coal moves to the sides andJor rear, the distillation is

completed, leaving coke which is burned out near the edges or end of the grate. High

pressure is used to produce high turbulence and reduce smoke. 3urning coal in

this fashion increases the probability of clinkering !producing large agglomerates of

ash slag# or matting !layers of ash slag#.

+o reduce this tendency, alternate fi9ed and moving grate sections are applied to the

underfeed stoker design to agitate the fuel. -oal characteristics are critical to

underfeed stoker performance. +able % outlines coal specifications for stationary and

moving grates, although underfeed stokers have burned coals outside of these

guidelines. +o burn these coals, some deviation from the normal ma9imum graterelease rate may be required. reduction in the percentage of fines helps to keep the

feed bed porous and e9tends the range of coals with a higher coking inde9.

(ith suitable coal, single and double retort units are generally limited to '.% to '.5

kgJs steam flow. +ypical grate release rates are 1.'0


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8ass feed sto&ers

+wo types of mass feed stokers are used for coal firing: the water"cooled vibratinggrate and the moving !chain and traveling# grate stokers.


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combustion inherently produces low ash carryover. However, it is more sensitive to

variations in fuel characteristics that affect ignition without a larger ignition arch

!discussed below#.


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+he moving chain stoker requires more maintenance than the water"cooled vibrating

grate. -hain and traveling grate stokers can burn a wide range of solid fuels including

peat, lignite, subbituminous, bituminous and anthracite coals and coke breeEe. +ypical

coal characteristic ranges are provided in +able %. )enerally, these stokers use furnace

arches !front andJor rear, not shown in ig. 0# to improve combustion by reradiating

heat to the fuel bed. (hen burning low volatile anthracite or coke breeEe, rear archesdirect the incandescent fuel particles and combustion gases toward the front of the

stoker, where they assist ignition of the incoming fuel.

3urning rates on chain and traveling grate stokers vary with different fuels. +he lower

ash !5 to 1%=# and lower moisture !1$=# fuels permit rates to /$$,$$$ 3tuJ h ft%!1./5


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%. specifically designed air metering grates,

'. dust collection and reinection equipment,

0. a combustion air system including forced draft fans for undergrate and overfire air,

and

/. combustion controls to coordinate fuel and air supply with steam demand.

Feeders for spreader sto&ers

Spreader feeders have the capability to uniformly feed coal into a device that can

propel it along the depth of a grate in an evenly distributed pattern.


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traveling grate shown in ig. / is a high resistance air metering grate. +he resistance

air metering concept eliminates the need for undergrate air plenum compartmentation

for good air distribution and control.


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+he combustion rate of coal as a solid fuel is, to a large e9tent, controlled by the total

particle

surface area. 3y pulveriEing coal to a nominal /$ micron diameter or smaller !see

-hapter 1'#, the coal can be completely burned in appro9imately one to two seconds.

+his approaches the rate for oil and gas. 8n contrast, the other technologies discussed

in subsequent chapters use crushed coal of a larger siEe and require substantiallylonger combustion Eone residence times !up to $ seconds or longer#.

4ulveriEed coal was first used in the 15$$s as a cost effective fuel for cement kilns.1

+he ash content enhanced the properties of the cement and the low cost resulted in the

rapid displacement of oil and gas as a fuel. However, early pulveriEing equipment was

not

very reliable and, as a result, an indirect bin system was developed to temporarily

store the pulveriEed coal prior to combustion, providing a buffer between

pulveriEation

and combustion steps. Cse in the steel industry followed closely. 8n this application,

the importance of coal drying, particle siEe control and uniform coal feed wererecogniEed.

Success for boiler 4- firing applications required modification of the boiler furnace

geometry to effectively use the 4- technology. 8n the early 16$$s, firebo9es and

crowded tube banks had to be e9panded to accommodate 4- firing. 3y the late 16%$s,

the first water"cooled furnaces were used with pulveriEed coalfired systems. 3urner

design progressed, providing improved flame stability, better mi9ing, and higher

combustion efficiency. -oupled with improvements in pulveriEer design and

reliability, improved 4- burners permitted the use of direct firing with coal

transported directly from the pulveriEer to the burner.

+he e9ponential increase in the C.S. electric power generation and the increase in

boiler siEe from 1$$


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the moisture laden 4. Secondary air is introduced through a burner to the 4J4-

mi9ture, in a controlled manner to induce air"fuel mi9ing in the furnace. s a coal

particle enters the furnace !see ig. '#, its surface temperature increases due to

radiative and convective heat transfer from furnace gases and other burning particles.

s particle temperature in

creases, the remaining moisture is vaporiEed and volatile matter is released. +hisvolatile matter, which ignites and burns almost immediately, further raises the

temperature of the char particle, which is primarily composed of carbon and mineral

matter. +he char particle is then consumed at high temperature, leaving the ash

content and a small amount of unburned carbon. +he volatile matter, fi9ed carbon

!char precursor#, moisture and ash content of the fuel are identified on a percentage

basis as part of the pro9imate analysis discussed in -hapter 6.

7olatile matter content

*olatile matter is critical for maintaining flame stability and accelerating char

burnout. -oals with minimal volatile matter, such as anthracites and low volatile

bituminous, are more difficult to ignite and require specially designed combustion

systems. +he amount of volatile matter evolved from a coal particle depends on coal

composition, the temperature to which it is e9posed, and the time of this e9posure.

+he merican Society for +esting and


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+he moisture content of the coal also influences combustion behavior. Direct

pulveriEed coal"fired systems convey the moisture evaporated during pulveriEation to

the burners. +his moisture plus that remaining in the coal particles present a burden to

coal ignition. +he water must be vaporiEed and superheated during the early stages of

the combustion process. urther energy is absorbed at elevated temperatures as the

water molecules dissociate.


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the furnace shaft. inal burnout of the char depends on the coal properties, particle

fineness, e9cess air, airfuel mi9ing, and thermal environment. +he products of

combustion proceed out of the furnace after being cooled sufficiently and enter the

convection pass. 4roperly controlled furnace e9it gas temperature is critical for

achieving the required steam conditions and efficiency, and to limit slagging and

fouling on downstream tube surfaces.

Combustion system and boiler integration

+he most fundamental factors that determine the boiler design are the steam

production requirements and the coal to be fired. +he thermal cycle defines the heat

absorption requirements of the boiler which supplies the rated steam flow at design

temperature and pressure. )as"side parameters, based on the design coal, are used to

estimate boiler efficiency. Heat input requirements from the coal can then be

determined, setting the coal firing rate at ma9imum load. +he number and siEe of

pulveriEers are then selected. requently, the pulveriEer selection is based on meeting

ma9imum requirements with one mill out of operation. +his permits maintenance on

one pulveriEer without limiting boiler load.

+he siEe and configuration of the furnace are designed to accommodate the

combustion characteristics and the slagging tendencies of the coal ash as discussed in

-hapter %1. 79 emission control factors are also incorporated into the layouts of

modern combustion systems. urnace volume must provide sufficient residence time

to complete combustion. Heat input per plan area is a key parameter to gauge thermal

loading, and has to be moderated with high or severe slagging coals. 4eak flame

temperatures can e9ceed '$$$ !106-# in the burner Eone, well in e9cess of ash

fusion temperatures.


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loading and tends to reduce 79 formation. However, taller burner Eones tend to

reduce upper furnace residence time and pose problems for completing combustion

for a given furnace volume. +he best overall furnace design takes into consideration

many cross"related factors and is strongly influenced by e9perience.

+he number of burners and the heat input per burner are selected to minimiEe flameimpingement on the furnace walls.


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4ulveriEers can typically operate at grinding rates down to %/ to 0$= of ma9imum

capacity, depending on the design, coal variability, and control system. 3urners are

e9pected to operate with stable flames over the normal turndown range of the

associated pulveriEer. +his can usually be accomplished with good coal, but can be

problematic with difficult to ignite coals.

4rimary air is supplied to the pulveriEer to facilitate coal drying, for circulation within

the mill, for classification of coal particles, and for transport of the coal through the

coal pipes to the burners. 4rimary air temperature to the mill depends on the air

preheat capability, moisture content in the coal, primary air to coal ratio in the mill,

and the required mill outlet temperature.


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Secondary air supply orced draft !D# fan!s# supply the secondary air !S# for

combustion. +otal air to the boiler is basically the sum of primary air and secondary

air. +he D fans must supply secondary air in sufficient quantity to achieve the

intended e9cess air at the boiler outlet.


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induce localiEed mi9ing from the secondary air.


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e9pansion and maintain integrity at high temperature. 3urner parts subect to 4-

erosion should

be protected with wear resistant ceramic materials.

/. Safety must be paramount under all operating conditions. utomated flame safety

and combustion control systems are recommended, and often required.

Con+entional PC burners

4rior to 79 emission regulations introduced in 1621 in the C.S., the primary focus

of combustion system development was to permit the design of compact, cost

effective boilers. s a result, the burner systems developed focused on ma9imiEing

heat input per unit volume to enable smaller furnace volumes using rapid mi9ing

burners which generated very high flame temperatures.

n unintended side effect was the production of high levels of 79. 3urners used on

such boilers include the conventional circular burner, the cell burner, and the S"type

burner.


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Cell burner

+he cell burner combines two or three circular burners into a vertically stacked

assembly that operates as a single unit !ig. 2#. 8n the 16$s and 162$s, the cell burner

was applied to numerous utility boilers which had compact burner Eones. (hile

highly efficient, the

cell burners produced high levels of 79 emissions and tended to be mechanically

unreliable.

S4type burner

+he S"type burner was developed in the early 165$s as a functional and mechanical

upgrade for the circular burner. +he S"type burner separates the functional attributes

of the circular burner for improved S control in a mechanically superior

configuration.

!See ig. 5.# +he burner noEEle is generally the same as that in the circular burner.

However, secondary air flow and swirl are separately controlled. Secondary airquantity is controlled by a sliding disk as it moves closer to or farther from the burner


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barrel. Secondary air swirl is provided by adustable spin vanes positioned in the

burner barrel. n air"measuring pitot tube grid is installed in the barrel ahead of the

spin vanes. +his provides a local indication of relative secondary air flow to facilitate

sliding disk adustments to balance S among burners. Swirl control for flame

shaping is controlled separately by spin vanes. +he S"type burner provides higher

combustion efficiency and mechanical reliability than the circular unit and requires nopressure part replacement.

'ow A0 combustion systems A0 formation

79 is an unintended byproduct from the combustion of fossil fuels and its emissions

are regulated in the C.S. and many other parts of the world. (hile a number of

options are available to control and reduce 79 emissions from boilers, as discussed

in -hapter '0,

the most cost effective means usually involves the use of low 79 combustion

technology, either alone or in combination with other techniques. +he effectiveness of

the pulveriEed coal 79 control technology depends primarily upon the fuel

characteristics and the combustion system design. or pulveriEed coal wall"fired units,

79 emissions from older conventional combustion systems discussed above

typically range from $.5 to

OFA it* all&fired syste!s

+he description above illustrates the advantages of air staging for 79 reduction, butalso reveals potential problems which may result. pplication of to an e9isting

wall"fired system reduces burner"induced mi9ing, which tends to impair flame

stability and slows the combustion process. +his occurs due to lower burner throat

velocities and lower secondary air to primary air ratio. ?esulting reductions in burner

S momentum and mi9ing energy can best be compensated for by raising burner

throat velocity. Deep staged systems therefore necessitate the use of new, smaller

burners for good

combustion performance. )reater amounts of swirl, for at least a portion of the S,

further assist in flame stabiliEation.

+he burner arrangement andJor swirl orientation may need to be altered to present amore uniform flow field to the system. dvanced low 79 burners with


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improved S control measures can compensate for these issues with air staged

systems, and have demonstrated equal or less furnace slagging tendencies compared

to some unstaged conventional designs.

fter properly dealing with the wall"fired burners, the design of the air staging system

can proceed. +he maor functional issue concerns proper distribution of the within the furnace, in a manner which minimiEes 79 reformation, -, and

unburned char.


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@ach windbo9 is divided along its height into alternating compartments of air and coalas shown in ig. 12. @ach pulveriEer serves one complete coal elevation !i.e., all four

or eight corners#. +he windbo9es distribute secondary combustion air as fuel air and

au9iliary air. uel air is the portion of the secondary air admitted to the furnace

through the coal compartments and air annulus around each coal noEEle tip and is

used to support combustion and stabiliEe flames.

u9iliary air is the balance of the secondary air which is admitted into the furnace

through air noEEles located in the compartments above and below each coal elevation

to complete the combustion. 4rimary air is the balance of air entering through the coal

pipes and noEEles and serves in the same manner as in wall"fired burner arrangements.

Secondary air is distributed in the windbo9 by a system of dampers located at the inlet

of each compartment as shown. uel air dampers are controlled based on pulveriEer

feed rate whereas au9iliary air dampers are controlled based on windbo9 to furnace

differential pressure. 8n conventional applications, all of the secondary air enters

through the corner windbo9 assemblies. However, these cornerfired combustion

systems embody air staging technology by virtue of the layered introduction of fuel

and air. +his lowers 79 by slowing the mi9ing of air and fuel as they proceed into

the flame vorte9.

pplication of overfire air to a corner"fired system involves diverting a portion of the

au9iliary air to an overfire air Eone located above the combustion Eone. Depending onthe required 79 reduction, can be introduced at the top of the windbo9 through

two

or more air compartments andJor through separate ports located some distance above

the top coal elevation.

8ncreasing the separation between the combustion Eone and the ports reduces

79 emissions most effectively. +herefore, for a given quantity of , separated

is generally twice as effective as windbo9 for reducing 79. lso, since

separated

ports require new openings in the upper furnace, they can be made larger than

windbo9 overfire air for greater 79 reduction, as windbo9 compartment siEes arelimited by the e9isting windbo9 width and compartment heights.


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proven approach for retrofitting a separated low 79 system involves the

addition of one level of four to ten ports depending on furnace type. or smaller four"

corner furnaces, the ports are typically located on furnace corners since adequate

coverage can be achieved as these furnaces have smaller, more square cross"sections

than the larger eight"corner units. lso, ductwork for four"corner units is simplerwhen the ports are located on the corners. or larger eight"corner furnaces with center

division walls, the ports may be located on the front and rear walls. +hey are arranged

in an interlaced fashion from front to rear and offset in the direction of fireball

rotation. +his

effectively reduces 79 while providing more complete coverage of the furnace plan

area and corners for better carbon burnout and - control. 8n both furnace types, the

ports are located several feet above the highest coal elevation to allow separation

distance for effective 79 control but low enough to allow ample furnace residence

time for good carbon burnout after overfire air inection. +he location and siEing of

ports are also set to avoid or minimiEe buckstay modifications when possible. 8f

necessary, computer modeling serves to optimiEe port arrangement and performance.

+he typical 3W( separated port for corner firing shown in ig. 15 uses an all

welded !no refractory#, deep throat, perpendicular opening to cool the air noEEles

from the intense radiant heat in the Eone. +he port normally has two air

compartments

with integral turning vanes and independent flow control dampers to ma9imiEe

velocity and penetration over the load range. +he air noEEles can be manually tilted

andJor yawed on line for enhanced emissions control. small pitot tube grid is

located near the inlet of each noEEle for relative air flow indication and balancing.

ddition of an system reduces secondary air flow to the main windbo9. +o

compensate for this, the e9isting au9iliary air compartment and damper siEes are

reduced using blocking plates and the au9iliary air noEEles are replaced with smaller

ones. +hese modifications are required to maintain e9isting inection velocity,

pressure drop and thus, damper controllability over the load range. dding only

has proven to be the most cost effective and reliable combustion system modification

for reducing 79 emissions in corner"fired boilers.

79 reduction for units with only windbo9 overfire air typically ranges from %$ to

'$=. or additional 79 reduction, separated can be added to units with or

without windbo9 overfire air. 79 reduction with these arrangements typically rangesfrom 0$ to $=, depending on initial 79 levels, boiler siEe, furnace type, heat

release rate, separation distance and coal reactivity.

+ypical of other air staged systems, 79 reduction on corner"fired units may be

accompanied by some increase in - emissions and unburned carbon. However,

with careful system design and field tuning, e9isting - emissions can normally be

maintained with reasonable unburned carbon !C3-# results.

=uiliary e(uipment

0ilgas firing e(uipment


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8n some cases, 4-"fired furnaces are required to burn fuel oil or natural gas up to full

load firing rates. +hese fuels can be used when the 4- system is not available for use

early in the life of the unit, due to an interruption in coal supply, or as a 79 control

strategy.

Some operators avoid installing a spare pulveriEer by firing oil or gas when a mill is

out of service. +o fire oil, an atomiEer is installed a9ially in the burner noEEle. @rosionprotection for the atomiEer is recommended. source of air is needed when firing oil

or gas to purge the noEEle and improve combustion. +his air system must be sealed off

prior to 4- firing. Steam"assisted atomiEers are recommended for best performance.

)as elements of several designs can be used in 4-fired burners. +hese include

designs with manifolds which supply multiple elements in the air Eone, or single

element designs mounted a9ially in the coal noEEle. )as manifolds can be located

inside or outside of the windbo9. 8nstallation in the windbo9 clears the burner front of

considerable hardware but prevents on"line adustment or repair of gas elements.

@9ternal manifolds are more comple9, but enable rotational adustment or

replacement of the gas inection spuds.

n"line adustability is very useful for optimiEing emissions and to counteract any

tendency toward burner rumble. single a9ial high capacity gas element !H-)@# in

the coal noEEle offers the most effective 79 control in use with advanced low 79

4-fired

burners. +he H-)@ !see -hapter 11# has to be inserted for operation and has to be

retracted and supplied with seal air when out of service. ?egardless of gas element

type, the issue of compatibility with the combustion system has to be considered.

?etrofit of gas or oil elements increases the forced draft fan load in many cases.

4rimary air is eliminated which results in higher quantities of secondary air compared

to 4- firing. s a result, fan flow and static margins need to be considered. See

-hapter 11 for more information on oil and gas firing equipment.

Igniters

n igniter is required to initiate combustion as pulveriEed coal is first introduced to

the burner, as the burners are being normally shut down, and as otherwise required for

flame stability. dditionally, the igniters may be used to warm the furnace and

combustion

air prior to starting the first pulveriEer. 8n some cases they are used to synchroniEe the

turbine prior to firing coal. 8gniters typically use a High @nergy 8gnition spark systemto ignite the fuel, which is usually natural gas or 7o. % fuel oil. 8gniters on utility

boilers and most large industrial boilers are operated with an input capacity of

appro9imately 1$= or more of the main 4-"fired burner. Such igniters are

categoriEed by 74 !7ational ire 4rotection ssociation# as -lass 8. +he use of

-lass 8 igniters reduces the comple9ity

of the flame detection system and permits operation of the igniters as desired under

any boiler conditions.


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absorbed by the limestone, and 79 formation is limited by lower operating

temperatures and staged combustion, when used. +his technology is now used in a

variety of industrial and utility boiler applications.

+oday, bubbling fluidiEed"bed !33# boilers, with a bed of fluidiEed particles that

remain in the lower furnace, are used primarily in specialty fuel applications such ascoal wastes and biomass fuels. -irculating fluidiEed"bed !-3# boilers, with solids

circulating through the entire furnace volume, address most larger steam generator

applications and a broader range of fuels.

>he fluidi!ed4bed process

+he fluidiEing process induces an upward flow of a gas through a stacked height of

solid particles. t high enough gas velocities, the gasJsolids mass e9hibits liquid"like

properties, thus the termflui$i4e$bed.

+he following e9ample helps illustrate the process. ig. 1a shows a container with an

air supply plenum at the bottom, an air distributor that promotes even air flow through

the bed, and a chamber filled with sand or other granular material. 8f a small quantity

of air flows through the air distributor into the sand, it will pass through the voids of

an immobile mass of sand. or low velocities, the air does not e9ert much force on the

sand particles and they remain in place. +his condition is called a fi*e$bed and is

shown in ig. 1b.

3y increasing the air flow rateJvelocity, the air e9erts greater forces on the sand and

reduces the contact forces between the sand particles caused by gravity. 3y increasing

the air flow further, the drag forces on the particles will eventually counterbalance thegravitational forces, and the sand particles become suspended in the upward stream.

+he point where the bed starts to behave as a fluid is called the minimum flui$i4ation

condition. +he increase in bed volume is insignificant when compared with the non"

fluidiEed case !ig. 1c#.


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Fig. +ypical fluidiEed"bed conditions.

s the air flow increases further, the bed becomes less uniform, bubbles of air start to

form, and the bed becomes violent. +his is called a bubbling fluidiEed bed !33#,

shown in ig. 1d. +he volume occupied by the airJsolids mi9ture increases

substantially. +here is an obvious bed level and a distinct transition between the bed

and the space above. 3y increasing the air flow further, the bubbles become larger andbegin to coalesce, forming large voids in the bed. +he solids are present as

interconnected groups of high solids concentrations. +his condition is called a

turbulent fluidiEed bed.

further increase in air flow causes the particles to blow out of the bed and the

container. 8f the solids are caught, separated from the air, and returned to the bed, they

will circulate around a loop, defined as a circulating fluidiEed bed !ig. 1e#. Cnlike

the bubbling bed, the -3 has no distinct transition between the dense bed in the

bottom of the container and the dilute Eone above. +he solids concentration gradually

decreases between these two Eones. +he pressure differential between the top and the

bottom of the container changes with air flow, as shown in ig. %. t low air flow, thepressure differential increases with flow through the static bed until reaching the

minimum flui$i4ation velocit-. t this point, the sand is supported by the air, and the

pressure

differential is determined only by the mass of bed material. +he pressure differential is

independent of further increases in air flow until the air velocity becomes high enough

to convey material out of the container.

+hen the pressure differential decreases as mass is lost from the system, which is

represented by the entrained flow portion of the curve in ig. %.


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n important parameter for evaluating hydrodynamic and heat transfer performance

of particle mi9tures is the Sauter !also called volume"surface or harmonic# mean

diameter !S


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+he typical slumped !non"fluidiEed# density of a sand bed is 6$ lbJft' !100% kgJm'#.

+he voidage or volume between the particles in the fluidiEed bed is /= and the bulk

density is /5 lbJft' !6%6 kgJm'#. +he gas flow rate through the bed is defined as the

u'erficial be$ velocit-, which is calculated by dividing the volumetric gas flow rate

at the bed temperature by the plan area of the bed without the solids. typical

nominal design

superficial velocity of 5 ftJsec !%.0 mJsec# is enough to fluidiEe 33 bed material with

a particle siEe distribution between /$$ and 10$$ microns. +he boiler enclosure is

made of water"cooled membrane panels.

3W( offers two air distributor systems for its 33 boilers: o'en bottom andflatfloor systems. +he open bottom system shown in ig. / is characteriEed by the

fluidiEing air bubble caps and pipes mounted on widely spaced distribution ducts !see

also ig. # located in the bottom of the 33 furnace. Stationary bed material fills the

hoppers and furnace bottom up to the level of the bubble caps, above which the bed

material is fluidiEed by the air flow.


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+he open spacing is effective in removing larger rocks and debris from the active bed

area as bed material moves down through hoppers. +his design is particularly

attractive

in biomass and waste fuel applications, which contain non"combustible debris. 8n the

flat floor system shown in ig. 2, the floor of the furnace is formed by horiEontal

water"cooled membrane panels with bubble caps. ir passes from a windbo9 belowthe water"cooled panel through the bubble caps to enter and fluidiEe the bed material.

Separate bed drains are provided. +he membrane panel floor must form an airtight

seal with the furnace walls, must support the weight of a slumped bed, and must resist

the uplift generated from the air pressure drop during operation.

+his design is attractive for firing coal where there is much less large debris present.

-oal"fired bubbling"bed boilers normally incorporate a recycle system that separates

the solids leaving the economiEer from the gas and recycles them to the bed. +his

ma9imiEes combustion efficiency and sulfur capture. 7ormally, the amount of solids

recycled is limited to about %/= of the combustion gas weight.

or highly reactive fuels such as biomass, this recycle system is usually omitted.

+he typical operating temperature range of a bubbling bed is 1'/$ to 1/$ !2'% to

566-#, depending on the fuel moisture, ash content, and alkali content in the ash.

@ven at these low combustion temperatures, the high convective and radiative heat

transfer

from bulk bed material to the fuel particles provides sufficient ignition energy to

evaporate moisture, heat the ash, and still combust the remaining fuel without

significantly changing the instantaneous bed temperature. +his is why the bubbling

bed can burn low"grade fuels, which burn at low combustion temperatures due to their

high moisture and ash contents.

Heat transfer surface may be placed within the bed depending upon the fuel being

burned. or biomass and other low heating value fuels, no in"bed surface is usually

required because other methods of bed temperature control can be used. or coal

firing with its high heat content and lower relative volatility, the heat transfer surface,

in the form of a tube bundle, is placed in the bed to achieve the desired heat balance

and bed operating temperature. +he bed temperature is uniform, plus or minus %/

!10-#, as a result of the vigorous mi9ing of gas and solids.

33 combustion systems are attractive retrofits to older boiler designs where a

change in fuels or wider fuel fle9ibility is required. ig. 5 shows a sectional side viewof a process recovery !4?# boiler that was retrofitted with a 3W( open bottom 33

combustion system. +he black liquor firing capacity was no longer needed and the

owner wanted a power boiler capable of firing wood waste, primary clarifier sludge,

and tirederived

fuel. ig. 6 shows an isometric of the 33 combustion system in the bottom of the

boiler. +he air distributor, fluidiEed bed of material, and overfire air systems

are clearly identified.

ig. 1$ shows a sectional side view of a small 33 boiler firing wood, wood waste

and byproduct sludge. +his +owerpakX boiler design is a version of the StirlingX

power boiler !S43, see -hapter %2# with two drums and bottom support for ease ofinstallation. +his unit is capable of supplying 1%$,$$$ lbJh of steam flow !1/.1% kgJs#.


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ll fossil fuel boilers require closely coordinated control of fuel, air, water and steam

parameters. luidiEedbed boilers require additional control. Selected key parameters

for fluidiEed"bed boiler design include: bed temperature control !fuel dependent#, bed

inventory control, bed density !for heat transfer control#, and emissions.

Bed temperature control and fuel feed

+he most fundamental control function of a 33 combustion process is bed

!combustion# temperature control. +he control method depends upon the fuel Fig. 5

urnace distributor plate and bubble caps for a flat floor system being fired. 3ed

temperature is controlled to limit emissions of 79 and S%, and to limit bed

material agglomeration. gglomeration is caused by sodium and potassium

combining with alumina and silica to form low melting point eutectics that can coat

the bed particles.

8f the alkali concentration in the coating is too high, the coating can start to melt and

cause particles to stick together. s a result, the larger particles do not fluidiEe and, if

the process continues, the bed can solidify and the combustion process can stop. +he

agglomeration process is quite temperature"sensitive and some fuels have strict

requirements for the ma9imum peak bed temperatures. lso, some fuels have such

high alkali contents that the fuel can not be fired in a fluidiEed bed combustion

process. Such fuels are typically agro"based where the plants are fertiliEed or the

ground is rich in alkali. Some process waste can also contain high alkali

concentrations.

Bio!ass firin

3iomass firing begins with an inert bed of solid particles in the bottom of the furnace

preheated to 1/$$ !51-# using oil or gas startup burners. ir flows into this bed at

5 to '6% !%$ to %$$-# and fuel at 5 !%$-#. +he bed material must heat the

incoming air and fuel to the bed temperature and the fuel must release the same

amount of heat back into the bed to maintain a constant temperature. +oo much heat

release increases bed temperature, while too little heat release reduces bed

temperature. +hree methods of bed temperature control are used in biomass firing:

primaryJoverfire air split adustment, flue gas recirculation !)?#, and fuel feeder

selection and operation.

5rimar-/overfire air 'lit a$6utment 3iomass bubbling beds operate

substoichiometrically with less than theoretical combustion air. 8n the bed, all

available o9ygen is completely used. ny additional o9ygen would o9idiEe more fuel

and increase the in"bed heat release, while lower o9ygen levels would have the

reverse effect. 3ecause of this repeatable relationship, an increase in air flow from the

windbo9 through the bed

will raise bed temperature while a decrease in air flow will lower bed temperature at

steady"state conditions. verfire air flow increases or decreases in the opposite

direction to maintain constant total combustion air flow to the boiler.

Shifting the air flow between the bed and overfire air system shifts the combustion orheat release between the two. t steady"state conditions, the flue gas temperature


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8f the fuel is not distributed evenly, some air simply passes through the bed without

contributing to the inbed combustion process. +o obtain the highest amount of in"bed

heat release, the fuel must be distributed as widely and uniformly as possible to match

the uniform air flow. +he lowest in"bed heat release results from dumping fuel to one

spot. +herefore, the fuel feeder should be able to function as either a chute or as an air

distribution feeder. (hen the fuel is dry, the feeder air flow can be reduced and thefuel falls into a small portion of the bed. (hen the fuel is wet, the feeder air flow can

be increased and the fuel distributed over the plan area. +he in"bed heat release

change rate

from low" to high"feeder air flows can be as much as %$= of the fuels heating value.

Coal firin

3ed stoichiometry adustment is not effective for coal"fired 33 combustor

temperature control because carbon builds up in the bed when there is less than

theoretical combustion air. (hen the air flow is increased for load, the bed

temperature increases

rapidly and uncontrollably. 8n an e9treme case, the pressure parts could be damaged,

and more commonly, the bed could agglomerate. +herefore, 33s firing coal are

limited to no less than stoichiometric conditions in the bed.

+he coal can be blown into the bed from below using pressuriEed feed pipes, or can

be fed over the bed using common rotary flipper"type feeders. +he underbed feed

system is more e9pensive and the coal must be dry and less than $.%/ in. !.'/ mm#.

+he feed pipes

are prone to erosion and plugging, and the noEEles at the ends of the pipes erode. +he

in"bed heat release is higher and the carbon loss is lower using the underbed feedsystem, but the disadvantages typically cause the over"bed system to be preferred.

(ith the overfeed system, the in"bed heat release is 2/ to 5/= of the coals heating

value. or the coal falling on the bed, all of the fi9ed carbon and 2$= of the volatile

matter combusts while in the bed. +he fines burn in suspension and reduce the overall

inbed heat release. (ith this high in"bed heat release, the adiabatic bed temperature

would be significantly higher than the desired 1/$$ to 1$$ !51/ to 521-# range. +o

lower the bed temperature to the desired range, tube bundles are submerged in the

bed.

+his in"bed surface can be either steam"generating surface or superheater surface.

(ater circulation in the steamgenerating surface can be either natural or forced.

+he fluidiEing air is provided from a windbo9 mounted below the bed. +he windbo9

is typically compartmentaliEed, with individual air flow control to each compartment.

3ed temperature varies with the firing rate. +herefore, as the boiler load is reduced,

the firing

rate is reduced, and the bed temperature declines. (hen the bed temperature reaches a

certain minimum, an outer portion of the bed is shut down by shutting off the air flow

and fuel flow to that portion of the bed. +he air flow and fuel flow to the remaining

active bed area is increased which raises the bed temperature in the operating beds.

3oiler load is increased by re"fluidiEing out"of"service !slumped# compartments and

firing to larger portions of the bed.


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Pressuri!ed fluidi!ed4bed combustion :PFBC$

33 and -3 boilers discussed above operate effectively at atmospheric pressure and

are generally referred to as atmospheric fluidiEed"bed combustors !3-#.

4ressuriEed fluidiEed"bed combustors !43-# are an outgrowth of this technology.+he underlying concept is to create a combined cycle plant where a coal"fired system

with a steam turbine is combined with a gas turbine to increase overall cycle

efficiency. simplified schematic and process e9planation is shown in ig. 15. 8n its

simplest form, a compressor pressuriEes the combustion air to 1% to %$ atmospheres

!120 to %'% psi or 1.% to %.$


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efficiency. 8n the full combined cycle system, advanced hot gas cleanup technology is

used to clean the gas from the fluidiEed bed at appro9imately 1/5$ !5$-# so that

hotter and higher pressure gas can be sent to the gas turbine. 8n this case, 5$= of the

power is produced in the steam turbine and the balance is produced in the gas turbine.

inally, in the advanced combined cycle, a partial coal gasification process is added.

+he char from gasification isburned in the fluidiEed"bed combustor. +he clean gas leaving the 43- boiler, which

still contains o9ygen, can be mi9ed with the fuel gas !from the partial gasifier# and

then burned in a gas turbine combustor at temperatures of 15$$ to %/$$ !65% to

1'21-# for even higher efficiencies.

+he bubbling fluidiEed bed operating inside the pressure vessel behaves basically the

same as the atmospheric fluidiEed bed although the higher pressure !and higher gas

density# combustion affects three key areas: fluidiEation, heat transfer, and

combustion. +he overall effect is to provide a very compact and cleaner combustion

system. more complete summary of this technology is provided in the 0$th edition

of this te9t.2

3W( designed, fabricated and installed a 2$

Documents

Hand Out Kuliah Boiler Fuels and Combustion