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limestone charging system for controlling segregation in lime shaft kilns

CARGO loading and feeding system

correct conveying and distribution of the limestone in pieces inside a vertical lime kiln is a determining factor for a homogeneous firing of the material and an excellent quality of the finished product.

QualiCal
QualiCal
Jun 11 · 5 min read

Introduction

Much of the world lime production is carried out nowadays in PFR kilns, where greater product quality and reduce operating cost in term of energy and by using a wide size range of material, are becoming key factors in the lime market.

QualiCal, following its own guide line of the #neverstopinnovating philosophy, is continuously developing the kiln technology to meet these challenging requirements.

After the proper evaluation of the problems and limitation of the system available in the market, has been decided to design a complete new system for limestone feeding, to obtain more consistent quicklime quality from the Synthesis PFR kilns, particularly for larger kilns.

Known technique

As is well known, the correct conveying and distribution of the limestone in pieces inside a vertical lime kilns is a determining factor for a homogeneous firing of the material and an excellent quality of the finished product.

Currently, many systems (static and dynamic) are known and normally used: some of them are mainly used to improve the distribution of limestone stones in order to homogeneously cover the section of the kiln; other systems are also used to avoid the segregation of the material in pieces, that is to say to prevent the separation and the inhomogeneity between large and small stones.

  • For example, in static loading systems, through which limestone is generally brought to height by a vertical elevator, skip or conveyor belt, the stones are directed by means of chutes and valves in one or more shafts of the kiln. These systems, which are rather simple from a plant engineering point of view, involve a rather important segregation of the size, especially in kilns with a large section.
  • In hybrid systems, the material is conveyed into the shaft or shafts through the use of fixed or mobile distribution and conveying chutes, valves and plates. In this way, a good coverage of the surface of the shaft is obtained, but the segregation of the size is not prevented.
  • Finally, in mobile and dynamic systems of the known type, buckets, “skips” or rotating hoppers are used, which are filled during rotation. This movement allows to mix the limestone in pieces, trying to avoid segregation, before the vertical and direct discharge in the shaft takes place. These systems are more complex from the manufacturing point of view and do not allow a control of the conveying and distribution of the pieces along the section of the shafts.

As already mentioned, the correct limestone loading system inside a vertical kiln is one of the most important aspects for lime preparation, especially when the size can be fine and/or very variable. Also to be taken into consideration are the cost, the overall dimensions and the height that this entails for the plant, the ease of installation, calibration and programming. There are also limestones and raw materials that are chemically and mechanically critical, so the choice of a loading system that can reduce the stress of the stones during their conveying and the subsequent crumbling with production of fine, becomes very important and strategic.

There is therefore a need to obtain an efficient system, which allows to solve the technical problem mentioned above and able to have control of the load and size of the incoming raw material, especially in critical industrial contexts, such as those of regenerative kilns with two or more shafts for firing limestone.

CARGO operating principles

The idea of CARGO (patent pending) is a limestone loading system for vertical lime kilns which, thanks to the rotation on the vertical axis of its loading hopper and the parameterization of a motor controlled by an inverter, allows the hopper to be positioned precisely and the limestone to be unloaded in the kiln shaft, at different angles from cycle to cycle, controlling the segregation of the size at each loading phase, thus being able to guarantee an overall homogeneous distribution of the size within the volume of the kiln.

CARGO operating principles

A further purpose is given by the possibility, in regenerative kilns with two or more shafts, to move the hopper from one shaft to another in the kiln or from one kiln to another (in the case of one or more batteries of vertical furnaces with single shafts), by means of a rack-and-pinion translation system. In particular, for the large and modern regenerative kilns with two shafts, with double entry of material for each shaft, this system (including two hoppers for conveying and distributing the limestone) allows you to load the raw material needed for each burning cycle, alternately 100% in the same shaft or 50% in both shafts. Thanks to the inverter-controlled motor and absolute encoder control, the hopper can be positioned with extreme precision on the shaft to be loaded.

Advantageously, this configuration allows to have a single loading point of the hopper (through “skip”, bucket elevator or conveyor belt), avoiding the installation of additional machines and simplifying the loading configuration of the kiln.

A further advantage of the system which is the subject of this invention, thanks to the use of a double plate discharge valve, consists in being able to project the limestone in the desired direction (opening both or partially the single plates) inside the shaft, covering adequately and homogeneously the section of the kiln. This type of valve also allows the plates to be moved (unlike the more commonly used conical valves) by means of hydraulic cylinders installed outside the valve itself, which simplify installation and maintenance and allow for more space inside the hopper. In addition, the inside of the hopper and the valve is lined with high-strength rubber panels, which reduce the impact force of the input material and reduce the formation of fines and noise.

Advantageously, the machine provides, already in the construction phase, the electrical and hydraulic systems in order to simplify the connections on the plant and commissioning.

Finally, the machine is parameterized and programmed directly during the construction phase, with the need to configure only the simple basic operations at the time of installation in the plant.

Cargo OPEN DAY

Presentation to QualiTeam of the new CARGO loading system for Synthesis lime kilns

Thanks to RONDIFER, ASPEX, SAE-FLEX and SYSWARE — Davide Beretta for the co-operation and the technical support.

Here is our publication in the International Cement Review Magazine: “Innovative feeding for Lime Kiln”.
Read our article here:

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QualiCal

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