Latest technologies for Alternative solid fuels feeding

Luc Rieffel

Walter Material Handling – A division of ATS Conveyors (I) Pvt. Ltd.

Many years of experience is of great help for handling solid secondary fuels for firing in cement kilns. The properties of the material used, the options and conditions of the material to be used, conditions of material supply, requisite degree of processing, the feed position in the kiln, the degree of automation and specific condition at the cement works all have to be considered when working out a successful technical solution. It is well known that properties, nature of secondary fuel is never constant & is always heterogeneous in nature. In a country like India it is difficult to get only one type of secondary fuel throughout whole year.This calls for use of equipment that is very flexible in operation. Walter material handling a division of ATS group has developed appropriate equipment specifically for reliable and safe feeding of solid secondary fuels, such as shredded tyres, plastic, paper, agro waste, impregnated saw dust etc. All these some of the examples of secondary solid fuels have tendency to bridge when stored in silos. Covered stores have proved successful everywhere for the handling.These stores are best served by fully automatic grab crane, inclined metallic apron extraction conveyors with integral mass flow measurement, belt conveyors, and bucket elevator for vertical transport, double valve airlocks and safety gate that ensures safe feeding of secondary solid fuel into kiln almost without introducing any false air. Example of completed projects for handling solid secondary fuel in cement works in India and several projects across globe proves flexibility of the technical solution by Walter-ATS. Following six important criteria’s have to be taken into account while searching for a suitable solution for handling solid alternate fuel for firing cement kilns.

The nature of the material to be co-processed The conditions of achieving constant material flow The position where material is fed into kiln/Calciner The level of automation The type of material delivery and storage The specific conditions/layout on site.

I Automated Storage, Metered extraction & Transport: The equipment has been developed specifically for automated storage management by grab crane, extraction and transport of alternate solid fuel such as shredded tyres, agro waste, impregnated saw dust etc which as a light weight have a tendency to bridge. The extraction conveyor which has been protected by Walter with international patent is capable of producing a constant mass flow between 0.5 and 20 t/h with an accuracy of ±1%.

                                                                                                                           

  

I-a Metallic apron extractor This patented extractor is composed of a loading hopper and a frame. The metallic apron is tilted at 35 degree and is made of overlapping blades bolted on two/three strands of chains. The constant layer thickness is ensured by a calibrator with coils. The height of the output section between the metallic apron and the calibrator is adjustable depending on the different products. The dosing is done by loss of weight using weight cells under the extractor frame. The flow is controlled by comparing loss of weight with flow set point through the four load cells every 500 milliseconds. The flow is defined

Fig-1, Extractor schematic arrangement with the metallic apron speed, the width of product on the metallic apron, the thickness of the layer. This measured flow is compared to the flow set point. The regulation unit will send information to the metallic apron motor in order to regulate the speed accordingly and get an accurate dosing with a constant flow. The big advantage of this metallic apron dosing extractor is its high flexibility regarding the big range of accepted grain size (1…500mm) and density (0,1…..1,5T/m3). After metered extraction material is conveyed with Belt conveyor or any other means to the introduction point in preheater tower. Belt conveyor is most popular and flexible for all type of alternate solid fuel handling. II Electrical Double Valve Airlock (For safe introduction of ASF in Kiln): The double valve airlock unit consists of two electrical valves and a pneumatic sliding gate. The opening and closing of valves is realized by pendulum of a single flap. An electrical motor ensures a very short cycle time, efficient closing and opening. VFD regulates the acceleration and deceleration of the valves, so that flaps open and close smoothly and rapidly. Sensors are used to indicate each position of flap. Technical advantage of such electrical drive over pneumatic valve is more than 50% reduction in cycle time. Such double valve system enables safe introduction of alternate solid fuel of different grain size (Grain size 1 to 400 mm) into Calciner / Kiln Inlet with short cycle time and minimizing introduction of false air. Regarding security, the double valve airlock offers three safety levels. Level 1 and 2 are in case of power failure, the mechanical flap closing is ensured with integrated counterweights. Level 3 – in case of pressure drop from plant, air tank placed on electro pneumatic cabinet ensure that safety gate is closed. Excessively high temperature or pressure will be detected by sensors located between top and bottom valves & complete valve with safety gate is closed.

Metallic apron extractor

Hopper

Calibrator

Main chute

Tire rack

Spillage chute 

                                                                                                                           

  

Mechanical performance of double valve airlock is also due to right choice of material. This new concept of double valve airlock is very compact and can be mounted easily on the Calciner. It has generated a great deal of interest by cement producers. Many of them qualified this equipment as the most advanced and secured double valve airlock on the market today. Several cement plants, in India and worldwide have already been equipped with these new generations of electrical double valve airlock. Since their commissioning, the installations have been running to the full satisfaction of client. Upper Valve Bottom Valve Safety Gate

Expansion Joint Fig-2, Electrical Double Valve Airlock Single Flap Electrical Drive Counter weight Fig-3, Electrical Valve Details