Flow Industries’ Silo-Flow system employ a technology using a new, proven concept of cyclical sudden, high-pressure air discharges (up to 3000 PSI or 200 bars) for eliminating blockages and accumulations in all types of silos, hoppers, bins and bunkers at cement, chemical and steel plants as well as at power stations.
Limitation of existing solutions
Existing solutions of bulk material flow are usually air blasters or cannons and Cardox. An air cannon consists of a fast-acting normally-closed valve and a pressure tank. The tank may be of various capacities and is filled with air compressed up to 100 PSI (7 bar). The cannon releases the compressed air from the pressure tank into a storage or process vessel and this discharge is supposed to break down accumulations and blockages.
In many cases, the maximum pressure amplitude of 100 psi of traditional air blasters is not sufficient to do the job effectively. To overcome the disadvantage of low power discharges, plants usually install a great number of cannons. Since bulk material has usually cracks and holes, a part of the air released by the cannon immediately escapes over the paths of the least resistance, causing immediate pressure drop and making the process even less efficient. For hard buildups like in high-temperature facilities, air cannons slightly reduce the rate of buildup formation but are very inefficient to clean them or maintain the surface clean.
Cardox is a method of converting liquid carbon dioxide into gas inside the tube containing at one end a bursting disc. Gas rapidly expanding in the tube breaks the disc and creates a blast outside the tube. The method is used mostly to clean hard buildups in high-temperature facilities and creates only a single blast per charge. The method is inconvenient and expensive while has a potential to damage the refractory.
General. The Silo-Flow™ patented technology has been developed and marketed worldwide by Flow Industries Ltd. Silo-Flow™ devices (SFDs) are pneumatic devices for sudden multi-pulse release of air compressed at up to 3000 psi (200 bar) into the plant storage or process vessel to meet unique application requirements.
Operation. Silo-Flow™ system consists of SFD, a control panel (CP), one or two standard high-pressure tanks and a dedicated high-pressure compressor (Figure 1). The compressor supplies air to the high-pressure tanks, which are connected to the SFD by a high-pressure tubing through a normally closed CP valve, so that in the standby mode the SFD is not under pressure. The SFD is attached to the vessel wall by a mounting socket enabling insertion of the SFD nozzle into the vessel. The system can be activated from the control room by a standalone timer or manually by opening the CP valve and allowing the compressed air from the cylinders to flow freely into the SFD. As soon as compressed air reaches the SFD, it continuously creates powerful air pulses (blasts) with the frequency of one pulse per three or four seconds as long as the air supply is activated. Each such pulse results in a shock wave followed by a high velocity air stream. The shock wave and air stream inside the plant vessel dislodge any blockage or build-ups inside. The SFD is programmed to ‘fire’ at predetermined intervals, depending on the application. In addition, air pressure is fully controlled from as low as 300 psi (20 bar) to 3000 psi (200 bar).
Silo-Flow™ Device working principle. The SFD working principle is based on a unique innovative concept of continuous firing of blasts triggered by the incoming high-pressure gas. Pressure of the gas flowing into the device governs the firing power. The higher the gas pressure, the stronger the firing pulse. In general, the SFD consists of two chambers separated by a piston. When air is fed into the device, the inlet chamber is filled more quickly and has a higher pressure than the pressurized chamber. This keeps the piston in a closed (charged) position. As gas continues to fill the SFD, the pressure in the pressurized chamber increases and becomes close to that of the Inlet chamber. Because of the different piston surfaces exposed to the chambers, the piston is eventually forced towards the inlet chamber and opens the discharge ports releasing the energized compressed air stored in the pressurized chamber. This burst of air is directed into the storage or process vessel through release tunnels alongside the SFD body. When the compressed air reaches the vessel and atmospheric pressure inside, the sudden jump in pressure inside the vessel creates an instant shock wave and a strong turbulent air flow throughout the material inside.
Silo-Flow replacing natural gypsum with synthetic gypsum
The availability and low cost of synthetic gypsum (a by-product of power plant activity) has enabled cement producers to reduce the demand for mined (natural) gypsum. But synthetic gypsum is a cohesive material and has much more problematic properties than natural gypsum, causing severe flow and operational problems industrywide, regardless of the gypsum bin design or cover. These flow problems significantly impact productivity, to the extent that cement manufacturers avoid replacing natural gypsum with synthetic.
Like many other cement plants, the Lehigh plant in Alabama tried to replace natural gypsum with synthetic, but experienced severe problems with the flow of synthetic gypsum in its feeder bins although there was no problem with natural gypsum flow. Despite the installed air cannons (several per bin), the gypsum bins would severely clog with the synthetic gypsum, so the plant continued using the more expensive natural material. The plant engineers were frustrated with the continued inability to use to the synthetic gypsum. When they heard that Silo-Flow technology assured continuous and stable material flow, they decided to try it at the plant.
The plant had the device fire for 25 seconds (5 ‘shots’) every 20 min at about half its maximum power (1500 psi). After several trials with various mixtures of synthetic and natural gypsum, they moved to 100% synthetic gypsum. The SFD maintained continuous material flow of 100% synthetic gypsum at all times. The plant achieved huge savings with the move to 100% synthetic gypsum and paid back the investment in less than a year.
Silo-Flow eliminates fly ash and coal blockage in power plant hoppers.
Ashkelon power station in Israel, like many other plants, experienced severe flow problems with their fly ash and coal hoppers. These problems affected process efficiency, raised maintenance expenses, and caused costly process interruptions. Air cannons (several per hopper) couldn’t solve the problem. The plant searched for an efficient and safe method to prevent such problems, and chose Silo-Flow system.
The plant installed one Silo-Flow device per hopper and that was enough to solve completely the plant material flow problems.