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Most of the solid residue from a utility boiler, defined as Fly Ash, is carried away by the Flue Gas. Coarse particles typically drop out of the gas stream at changes of direction like in the Economiser and in the Air Preheater. The fine particles, which constitutes the largest part, are captured by air cleaning devices (ESP or Fabric Filters) and from there must be conveyed to storage silos.
Fly ash is almost always collected and transferred by one of the following types of system:
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Vacuum Type Pneumatic Conveying System (Dilute Phase) |
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Pressure Type Pneumatic Conveying System (Dilute Phase or Dense Phase) |
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Fluid Channel Type System |
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Screw or Chain Conveyor System |
Nowadays pneumatic systems are almost exclusively used on utility boilers, while mechanical or combined systems are often considered for industrial boilers or incinerators.
The recent diffusion of Dry Bottom Ash Extraction Technologies has created an increasing demand for Dry Bottom Ash Conveying Systems and Termokimik has already installed several Bottom Ash Pneumatic Conveying Systems on units rated up to 600 MW.
Termokimik's experience consists of more than 27.000 MW of Fly and Bottom Ash Pneumatic Conveying Systems.
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Vacuum Systems
In a Vacuum System each pick-up point is equipped with an Ash Intake Valve to smoothly feed ash into the conveying line.
The system is normally arranged in branches with a number of pick-up points collected together. Automatically controlled segregating valves isolate the single branches allowing each of them to be activated independently.
Specially designed air inlet valves at the heads of each branch provide additional conveying air.
An Ash/Air separating device receives the dusty flow and separates the ash, that falls into the silo, from the conveying air, which is induced through a mechanical exhauster.
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Pressure Systems
There are two main Pressure System technologies at present. These are known as Dilute (or Lean) Phase Systems and Dense Phase Pystems.
The difference between the two technologies can be summarised in a parameter defined as Concentration which is the ratio between the mass of product being conveyed and the mass of conveying gas.
Dilute Phase Systems operate at lower concentration than Dense Phase Systems.
For this reason Dilute Phase Systems operate with low pressure conveying air (typically produced by positive displacement blowers), while Dense Phase Systems require Air Compressors (Screw type or Reciprocating) to produce air at the required pressure.
A typical Pressure System can convey flow rates over 100 t/h on distances of several hundreds meters.
In Pressure Systems the ash is collected into Air Locks (for Dilute Phase) or Blow Tanks (for Dense Phase).
Inside these vessels the ash is kept fluidised until it is discharged into the conveying pipeline for transportation up to the target silo. |
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The main advantages of Termokimik's Fly Ash Pneumatic Conveying Systems are:
Complete Technology Portfolio
The availability of such a wide range of technologies allows an optimised design customised to our Customers’ needs. For example, we can provide combinations of vacuum and pressure systems joining together the advantages afforded by the vacuum systems in terms of simplicity and ease of discharge, with the advantages of pressure systems as regards the capacity of transfer over long distances.
Proven and Reliable Components
The key components of our Pneumatic Conveying Systems, from Ash Intake Valves to abrasion resistant pipes and bends, from Pressure Vessels to Ash Collectors, come from a 40 year continuous development process and can now be considered as the State of the Art in Pneumatic Conveying.
Experience on Different Fuels
Termokimik's wide experience on different type of coals and fuel oils enables us to select the best configuration according to any specific project requirement. |
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