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COMFLEXKHD's lqtestgrinding system

I(J) I H,Y.*P9"}'T W E DAG

ln this region of Portugal, Lhe marble quarry

rejects have ahvays provided the best qual iry l imestone(CaCO1 >98.2%, MgCO" <0.4%, Fe,O, <0.O1Vc and Al"O,<0.02q.) to many small l ìme producers that used old

furnaces, ut i l is ing cork and eucalyptus wood rejects as

fuel for l imestone burning.

UpgradeSince 1970, Calcidrata Co. has produced l ime using

tradit ional methods - with small single-shaft ki lns

supplied by SIC (Società Impianti Calce S.r. l) - using cork

dust or sawdust as fuel and the residue from the marble

quarry as hmestone.

In 2008, n' i th i ts vast experience in biomass

combustion technology, SIC real ised and started-up

a new DSS 300 double-shaft ki ln for the Portuguese

Figure I Calcidrata's plant in Alcanede.

Figure 2. 5lC D55 300 tpd l ime ki ln.

company. The ki ln represents more efncient

thermodynamic technology for burning large quanti t ies

of l ime, while st i l l retaining the 'winning' factors that

have al lowed Calcidrata to become well-known in the

l ime market, based on the l imestone from the marble

quarry rejects and the bio-fuel avai lable.

The k i ln-fhe

DSS 300 ki ln is a double-shaft ki ln of 6.4 m:

rectangular section, equipped with 24 lances per shaft

suitable for the combustion of both biomass and natural

gasThe trvo fuels can be f ired alternately at 100%, while

natural gas can be used as necessary during periods of

low bio-fuel avaiÌability.

The ki ln has been designed to cope with dif ferent

sizes of l imestone part icle (f iom 20 - 60 mm or from

50 100 mm) to permit maximum exploitat ion of the

available l imestone in the quarry.

The use of a wider range of l imestone means that

the company has to pay part icular attention to the

segregation process during the l imestone charging phase

in the shaft, by enforcing a size re-distr ibution to ensure

homogeneous distr ibution across !he ki ln's cross-section.

L imestoneDuring the commissioning phase i t was confirúed, as

was expected during the project phase, that changing

the size of the l imestone consequently changes the ki ln

capacity.At L.O.L (1.5%) equal values, the prodùcl ion capacity

of the ki ln is 195 tpd with the smaÌÌer part icles, but about

300 tpd with the larger ones.

Fue lThe bark and sawdust that is del ivered to the plant by

truck from dìfferent sources, mainly at <5 mm, is already

suitabìe for use in the kì ln.The inferior calorifrc value of the fuels is

3800 - 4100 kcal/kg with a medium humidity of 6 - 7%.

It has been observed that after one year of ki ln

operation, the variat ion in the calori f ic value of the fuel

does nor heavi ly inf luence the quali ty of the f ired l ime.

This is because large humidity variat ions, due to typical

seasonal factors that are repeatable and easi ly predicred,

and small variat ions in humidity values, which can be

checked in the laboratory analysis of bio-fuel, do not

give appreciable L.O.I. changing or reactivi ty for the

produced l ime.

It has been necessary for the customer to erecl a large

storage faci l i ty for the bio-fuel because i ts avai labi l i ty

is not constant throughout the year. Large quanti t ies

are stored during the summer, which is the period of

maximum availabi l i ty.The fuel from the main storage is del ivered by

a Redler conveyor to a lower part of the screen that

divides the material by size: > 100 mm, 6 100 mm and< 5 m m .

The material >100 mm is rejected because i t is mainly

consti tuted of extraneous agents, such as spal ls thar

adhe re ro rhe m i re r i a l du r i ng eo l l e r r i on .

The 6 - 100 mm material is sent to the mil l , which

reduces i t to <5 mm. The quanti ty ofthis size material

58 worldcement.com [Apr 09]

l f there is excessive fuelconsumpt ion or a defect , thesu perv is ion system in thefo l lowing cyc le wi l l a u tomat ica l lycorrect the mistake.

varies, but geleral ly never represents more than 5 - 67o

of the total treated material.

Material <5 mm from the screen ancì mil l is

pneumatical ly transported to the ki ln main storage sì lo.

Figure 3. Combustion lances.

As bio-fuels are very l ìght, both the screen and the

mil l use negative pressure to faci l i tate the f low of the

material, using the same air that t Ìansports the mater- ial

from the mil l ing and scr-eening system to the top of the

storage si lo.Befrrre ki ln charging, the quanti ty ofbark srorage

in a 400 mj sì lo should be suff icient to fuel the ki ln at

maximum capacìty lor about trvo and a half days.

The salvdust is extr-acted from the si los by a " leaf

spring" expeller that feeds a weighing hopper during the

ki ln combustion " inversion r ime".

Dos ing and we igh ingThe plessule in the dosing and weighing hopper is

maintained by a double valve system, and i t is equipped

with a mixer to guarantee regular f low of the pulverised

f.uel during the îeeding phase of the lances.

The weighing hopper operates using lost t 'eight

technoìogy. The supervision system calculates the fuel

quanti ty necessary lor- each combustion cycle and sets

the speed of the extraction r-otary ceÌl to guarantee that

the correct quanti ty of fuel is fed to rhe shaft during

cornbustion,

If ther-e is excessive fuel consumption or a defèct,

the supervision system ìn the fol lorving cycle wil l

automatical ly correct the mistake.

There are t lveÌve dosing scrervs that feed thepneumatic t)-ansport l ines through Venturi pipes. Each

of these l ines feeds two combustion ìances placed in the

same shaft. Pneumatic valves located along the bio-fuel

t ì_anspor_t pipel ines alternate che luel fèed f ' rom one shaft

!o the other.Even though the division of the salvdust quanti ty

that instantaneously arr ives àt the two lances fecl by the

same pneumatic transport l ine is not exact, ì t has been

seen during the plant running test that distr ibuting

fuel quanti ty between the dif ferent ki ìn lances is not a

systematic mistake, but principal ly a casual one. The

result is that, in the middle, the

calori f ic contr- ibution is suff i ciently

homogeneous to guàÌ-antee

l ime-burning uniformity.

Conclus ioni ime burnt using bark as fuel

has an excel lent reactivi ty and

homogeneity, but i t appears

ro have a "cappuccino" coÌour,

This does not represent the f inal

colour- of the l ime because i t is

a pigmentation exclusively on

surface, rvhi le the inside of rhel ime mass maintains i ts natural

colour.

The calori f i c consumption

when using natural gas is<840 kcal/kg, and CaO and

L .O .L va lues < 1 .5%. W i th b i o -

f irel, i t has been esrimated that

theÌe is a calori f ic consùmptìon

oI abour 865 kcal/kg, and CaO(210/220 kg bio-fuel/kg CaO) and

L .O .L va lues a re be tween 1 .5 and

1.7 6Vc. i ìFigure4.lwo SIC 10 tph hydration plants.

60 worldcement.com [Apr 09]