Synthesis HFS: Hybrid Combustion into PFR lime kiln
Lime firing processes with the regenerative system are carried out in vertical kilns with two shafts. These PFR kilns, mainly developed to optimize the specific heat consumption, have the advantages of producing a quality of quicklime of high and very high reactivity which is excellent in steelmaking.
On the other hand, this type of kiln in the configuration produced up to now, is ill-suited when medium or low reactivity limes are required, such as those required today, for example, by certain industries producing prefabricated lightweight construction products based on lime and cement, forcing lime producers to adopt different kiln technologies to wide the product reactivity range.
QualiCal Synthesis HFS kiln
To solve this problem QualiCal developed since the 2000 the HFS Hybrid Firing System to produce quicklime with controlled reactivity from high to medium-low. HFS is embedded into Synthesis PFR kiln combining traditional firing system with lance burners operating in co-current, with an additional beams firing system able to operate in counter-current.
In the upper part of both shafts, the lances of the traditional firing system of the PFR kiln are immersed. In the lower part of the combustion zone of both shafts as well, two liquid-cooled beam burners are inserted transversely to them.
How HFS Kiln works
During a combustion cycle, in which the lance firing system is injecting fuel in the co-current shaft, the beam burners are injecting fuel in the opposite shaft rising hot gases in counter-current to the material flow.
With this hybrid firing system, it is possible to distribute the heat supplied to the limestone in such a way that its total decarbonization occurs after receiving part of the heat in countercurrent and part in co-current. The computerized firing control system allows the correct distribution of the fuel administered in the two modes to obtain, with the same degree of calcination, different grades of reactivities according to the limestone properties.
Contrary, switching off the beam firing system, the kiln can be operated as a traditional PFR kiln to soft burn the raw material and get very high reactive lime.
Advantages of the QualiCal HFS kiln
“Beam burners, contrary to any other type of radial burners, permits to reach the center of the shaft, heating homogeneously all over the cross section of the kiln.
The beam firing system fit perfectly in Qualical Synthesis kiln where the shafts are increasing in section area, passing from rounded to rectangular section, assuring proper material flow.” says — Francesco Cella QualiCal CTO
“Having the beam burners positioned in the burning zone, just above the shaft interconnecting cross over channel, the refractory arches are not directly exposed to the hot gases generated by this new additional firing system.
Moreover, thanks to the high preheating zone of the Synthesis kiln, the increasing of temperatures in the fumes can be properly managed with Metro and, together the possibility to vary the high of the burning zone through the lance burners length, the temperature profile inside the kiln can be tuned to reach the desired product reactivity.”
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This contributes to have a kiln practically identical to the traditional PRF kiln that combines two proven technologies lowering the overall investment and operating costs instead operating different specific kilns for every type of desired product quality.
Last but not least, beam firing system can be implemented on the existing QualiCal Synthesis PFR kiln to permit lime producers to meet, in flexible way, the wide market requirements.
QualiCal Digital Lime Kiln
The Digital Lime Plant is QualiCal’s vision for the future of lime production.
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