Air blaster

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, bins and hoppers walls for all powdery form of materials, and are used for 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 air pressure (60 psi or 400 kPa), 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 passes through a 3/2 way solenoid valve 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.

References

Sources

• PWI Piston type shock blaster New Generation of piston type shock blasters which installed more than 500 pieces in cement indystry
• 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
• INWET website