Calcining kiln fuel

Multi-stage preheating, pre-calciners, kiln combustion system improvements, enhancement of internal heat transfer in kiln, kiln shell loss reduction, optimize heat transfer in clinker cooler, use of waste fuels Blended cements, cogeneration... 

The monitoring of the calcination process in the production of the rutile-structured titanium dioxide from the anatase structure is recorded as a notable success [28]. A fiber optic probe appropriately positioned in the calcination kiln monitors the composition of the powder undergoing processing. The Raman bands of the two forms of titanium dioxide are quite distinct and as a result the operating conditions of the kiln (fuel and air-flows) can be adjusted to give optimum production. 

Helping to propel capacities upward has been the advent of greatly improved preheaters, which partially calcine the stone and significantly improve thermal efficiency. Modem preheaters improve capacity by 15—20% and decrease fuel consumption a similar percentage. Other kiln appurtenances and accessories that enhance efficiency and lime quahty are the contact coolers, and such kiln internals as metal refractory trefoil systems that act as heat exchangers, dams, and lifters. 

The double-inclined kiln calcines even smaller si2ed stone of 1.88—3.75 cm and at reduced capacity with stone of only 0.63 cm minimum si2e. Most of these kilns operate using gaseous or oil fuels, including propane. An exception is the double-inclined kiln, which appears to operate at optimum efficiency with a mixture of fuel, ie, 60—75% natural gas or oil and 40—25% coke, although it can operate on 100% gas or oil. 

Removal of volatile matter to about 0.5 wt% can be accomplished by calcining in a rotary kiln, rotary hearth, or vertical shaft calciner All of these processes heat green coke to temperatures in excess of 1000°C where shrinkage and subsequent densification take place. The volatile components are comprised primarily of methane, ethane, hydrogen, and hydrogen sulfide gases which can be employed as fuel for process heat. 

The types of reactions involving fluids and solids include combustion of solid fuel, coal gasification and liquefaction, calcination in a lime kiln, ore processing, iron production in a blast furnace, and regeneration of spent catalysts. Some examples are given in Sections 8.6.5 and 9.1.1. 

Nodulizing Mixture of ore fines and fuel, or simply of fusible fines, is passed through a rotary kiln or dryer and agglomerates form by partial fusion, chemical reaction, etc. as the temperature is raised Granulation, calcining Rotary kiln, dryer... 

To improve energy efficiency, refractories with superior K factors are used in lining the kiln, thus reducing radiant heat losses. Moreover, kiln mounted blowers now inject combustion air into the kilns in the zone where the volatiles evolve from the coke, thus permitting utilization of the Btu content in these previously wasted gases. In modern calciners, most of the energy required is obtained by burning the coke volatiles and fine particulate matter in the kiln. In some instances, rotary kilns equipped with kiln mounted blowers actually operate without external fuel (except for start-up). When these units are also equipped with incinerators (to combust the unburned volatiles and emitted coke fines) and waste... 

Figure 7 shows a schematic diagram of the model calciner used for studying an economic continuous two-stage calcining system. The exhaust gas from first stage kiln is fed as fuel for second stage kiln. 

Table VI summarizes a typical heat balance in second stage of the above calcining system (Case A) in comparison with that of an alternative system (Case B) in which the exhaust gas from first stage kiln is not utilized for second stage calcination. The amount, composition and temperature of the exhaust gas from first stage kiln determine the auxiliary fuel requirements for second stage kiln.

When used for ceramic heating, furnaces are called kilns. Operations include drying, oxidation, calcination, and vitrification. These kilns employ horizontal space burners with gaseous, liquid, or solid fuels. If product quality is not injured, ceramic ware may be ejmosed to flame and combustion gases otherwise, muffle kilns are employed. Dutch ovens are used frequently for heat generation. 

The double-inclined kiln incorporates two inclined sections in the calcining zone see Figure 6.13. The offset arches created by the inclines create a void on both sides of the kiln where fuel and preheated combustion air can be fired in combustion chambers. 

By providing air directly to the calciner and not as excess air in the kiln, 60% of the total heat can be burnt in the calciner, allowing more than 90% calcination of the raw meal before entering the kiln. The relatively low temperatures in the calciner (800°C-900°C) indicate that a conventional flame with a defined shape and geometry is not possible. Several factors affect the calciner efficiency, especially the uniformity of air flow, raw meal, and fuel dispersion. With a preheater/ precalciner kiln system, a nominal production of more than 10,000 tpd clinker can be reached with as little as 3 MJ/kg (700 kcal/kg). 

Traditional shaft kilns operate continuously and are fired with fuel introduced into the calcining zone (see section 16.2.2). Various fuels have been used, including bituminous coal, producer gas, fuel oil and natural gas. 

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