An air blaster or air cannon is a de-clogging device composed of two main elements: a pressure vessel (storing air pressure) and a Triggering mechanism (high speed release of compressed air). They are permanently installed on silos

Storage silo

A silo is a structure for storing bulk materials. Silos are used in agriculture to store grain or fermented feed known as silage. Silos are more commonly used for bulk storage of grain, coal, cement, carbon black, woodchips, food products and sawdust. Three types of silos are in widespread use...

, bins and hoppers walls for all powdery form of materials, thus preventing caking and allowing maximum storage capacity.

Air blasters do not need any specific air supply. Available plant air is enough with a minimum of 4 bar

Bar (unit)

The bar is a unit of pressure equal to 100 kilopascals, and roughly equal to the atmospheric pressure on Earth at sea level. Other units derived from the bar are the megabar , kilobar , decibar , centibar , and millibar...

 air pressure (60 psi

Pounds per square inch

The pound per square inch or, more accurately, pound-force per square inch is a unit of pressure or of stress based on avoirdupois units...

 or 400 kPa

Pascal (unit)

The pascal is the SI derived unit of pressure, internal pressure, stress, Young's modulus and tensile strength, named after the French mathematician, physicist, inventor, writer, and philosopher Blaise Pascal. It is a measure of force per unit area, defined as one newton per square metre...

), although 5 to 6 bar are preferred for better results (75 to 90 psi). The average air consumption is moderate, and depends on the number of firings per hour, size of the pressure vessel, and number of air cannons installed. For instance, a 50-liter air cannon consumes 0.60 Nm³/hour at 6 bar air pressure (90 psi or 600 kPa), with 2 firings per hour.

The compressed air contained in the pressure vessel is instantly released, and the achieved blast, called the impact force, evacuates material sticking to the walls (rat holing), as well as breaking potential bridging thanks to the shock wave obtained.

The blast are usually organized by using an automatic sequencer

Operating principle

• Phase 1: Air feeding: Air supply from the air compressor
  Air compressor
  An air compressor is a device that converts power into kinetic energy by compressing and pressurizing air, which, on command, can be released in quick bursts...
  
   passes through a 3/2 way solenoid valve
  Solenoid valve
  A solenoid valve is an electromechanical valve for use with liquid or gas. The valve is controlled by an electric current through a solenoid: in the case of a two-port valve the flow is switched on or off; in the case of a three-port valve, the outflow is switched between the two outlet ports...
  
  feed, the Quick Release Valve (QRV), and reach the triggering mechanism with its piston disc in closed position. The air reservoir is then pressurized in less than 15 seconds, depending on the air pressure and air volume used.
• Phase 2: Waiting: An air pressure equilibrium between air circuit, triggering mechanism, and pressure vessel is created.
• Phase 3: Blasting: When activated, a solenoid valve purges the air circuit, thus creating an air vacuum. Then, the piston inside triggering mechanism is abruptly pushed back by negative pressure, thus creating a sudden blast from the air contained in the pressure vessel. This phase is measured in milliseconds.
• Then the cycle repeats again at Phase 1.

Design criteria and construction

An efficient air blaster should be designed to ensure:

• Complete safety for the operators, thus avoiding harsh rodding or other manual cleaning methods;
• A sturdy design, able to cope with the most severe operating conditions;
• Easy maintenance, due to an easily accessible triggering device;
• A metal-to-metal construction design, making the air blaster extremely reliable even in harsh environment (such as exposed to heat and/or dust);
• A cost effective solution to all customers that prevents hopper, bin, and silo discharge interruption, as well as process disruption.

Construction

Usually 2 versions exist:
• High temperature version: mainly for heat exchanger and cooler applications to remove clogging and to avoid costly plant stoppages and downtime;
• Low temperature version: to eliminate build-up and dead stock for powdery and granular materials thus preventing caking and allowing optimization of storage capacity.

Installation

Air blasters solves problem occurring in Cement factories among other industries, with blockages occurring in preheater towers (Kiln inlet, Cyclones, riser ducts...etc.) and in grate coolers, thus providing substantial savings.

• BIVIKA Shock Blaster
• Vortex Air Blastair website The technology and specifications used in the article are provided by Staminair Corporation.
• AirBoost website
• Martin Engineering website
• Standard Industrie website