General
- Lime” is a
general term referring to burned or calcined limestone (burnt lime
or quicklime) and its secondary products, including slaked lime and
hydrated lime (or calcium hydroxide). In the calcining process,
quicklime (CaO or CaO.MgO) begins to form when the dissociation
temperature of the limestone occurs. (This occurs from 402°C for
the magnesium carbonate component to 898°C for the calcium
carbonate portion.) Temperatures are maintained sufficiently long
until there is a complete breakdown of the limestone and a release
of the carbon dioxide content.
-
Lime
is the high-temperature product of the calcination of limestone.
Although limestone deposits are found in every state, only a small
portion is pure enough for industrial lime manufacturing. To be
classified as limestone, the rock must contain at least 50 percent
calcium carbonate. When the rock contains 30 to 45 percent magnesium
carbonate, it is referred to as dolomite, or dolomitic limestone.
Lime can also be produced from aragonite, chalk, coral, marble, and
sea shells. The Standard Industry Classification (SIC) code for lime
manufacturing is 3274. The six-digit Source Classification Code (SCC)
for lime manufacturing is 3-05-016.
Lime
Kilns
-
There
are an estimated 6,000 operational lime kilns in India. Most of the
kilns exist in clusters near limestone deposits. The major clusters
are spread across the western region (Gujarat, Rajasthan,
Maharashtra), northern region (Uttaranchal, Uttar Pradesh, Himachal
Pradesh), southern region (Andhra Pradesh, Karnataka, Tamil Nadu),
central region (Madhya Pradesh), and eastern region (Jharkhand,
Meghalaya).
-
Rotary
kiln will achieve a daily production of some 600 to 2,000 tonnes.
The heat consumption of a rotary kiln is markedly higher than that
of vertical shaft kilns. This "disadvantage" is frequently
compensated for by the flexibility with which the kiln can be
operated.
Technology
-
The
most prominent technology is the process that uses an aqueous slurry
of lime, Ca(OH)2, or limestone, CaCO3, for control of SO2. The
systems of the 1970s and early 1980s typically operated at 90
percent SO2 capture at a calcium/absorbed sulfur molar ratio of
about 1.1 Ca/S. While most of these scrubbers did produce the
desired result, uncontrolled, natural oxidation of the sulfite
species produced a slurry containing a mixture of CaSO3·1/2H2O
platelets and blocky crystals of CaSO4·2H2O (gypsum) that was
difficult to dewater.
-
The
process hinges around the use of limestone precipitate as a
neutralisation agent The use of limestone to treat acid effluent
offers the mines a financially attractive alternative to lime dosing
technology The CSIR s limestone process offers a substantial cost
saving and performs exactly the same function.
Market
Reports
-
Industrial
markets for lime mainly include the pulp and paper industry, the
mining industry, chemicals manufacturing, and environmental control.
The pulp and paper industry is one of the major consumers of lime,
mainly for the preparation of digesting liquor for manufacturing
kraft or sulphate paper, and for pulp bleaching during a primary
stage of production. Most of the input lime is recovered by
calcining dewatered calcium carbonate sludges; however, an important
volume of lime is required as “make-up.” The increasing use of
precipitated calcium carbonate in coated and uncoated printing and
writing papers in North America has led to major growth in the
demand for lime.
-
In
2004, Japan’s industrial production, as measured by the indices of
mining and manufacturing, increased by 5.6% compared with 3.3% in
2003. The number of unemployed workers in Japan decreased to 3.2
million from 3.5 million in 2003, and the total labor force
decreased to 66.4 million from 66.67 million in 2003. As a result,
the unemployment rate in Japan decreased to 4.7% from 5.3% in 2003.
Japan’s merchandise trade surplus rose to $110.5 billion from
$87.9 billion in 2003. The Japanese yen appreciated by 7.2% to
¥108.17 against $1.00 in 2004.
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