Flat Bottom Silo is the most popular design for Grain Storage in bulk because of its capability to store large volumes of grain in a most cost-effective manner. Flat bottom silos have flat concrete base having a row of discharge openings along its diameter to reclaim grain from the Silo. Grain from these discharge openings is received by a grain unloading conveyors that are installed just below these discharge openings in a Tunnel.
Tunnel is integral part of all Flat Bottom Silos foundations. These tunnels are designed to house unloading gates & unloading conveyors. Besides, tunnels provide access to operate, maintain, and clean this equipment in safe manner.
Types of Grain Reclaim Tunnels
There are various types of tunnel options like
1. Equipment Trench: Equipment Trench is just wide enough to house a screw conveyors and top of conveyor is just at the surface of ground.
2. Equipment only tunnel: Equipment only Tunnel is just enough to house the conveyor. There is not enough access for maintenance of conveyor
3. Equipment Tunnel with Man Access: Equipment Tunnel with Man Access is most popular as it is designed to provide easy access to people to do maintenance on conveyors and gates. Besides, cleaning and unplugging of blocked gates can easily be done in this kind of Tunnel system. These tunnels may be constructed below ground level, above ground level or partially above and partially below ground level. Elevation mainly depends upon the site conditions and individual’s layout preference
Among all three options the most popular, safe and maintenance friendly is Equipment Tunnel with Man Access.
Dimensions of Grain Reclaim Tunnel with Man Access
Minimum height of Equipment Tunnel with Man access is 6 feet so that people can walk inside the tunnel with ease without having to bend inside the tunnel.
Width of such tunnel varies depending upon type of unloading conveyor.
If the unloading conveyors is a belt conveyor
Tunnel width = Width of belt conveyor + 5 feet
And, if the unloading conveyor is a chain conveyor
Tunnel width = Width of belt conveyor + 3 feet
Safety Exits from the Tunnel
Grain reclaim tunnels are prone to dust accumulation. Grain dust is highly combustible and may result is dust explosion if it comes in contact with a spark. Long Tunnels should be properly ventilated and well lit with flame proof lighting system.
In case of any dust explosion inside tunnel, people working inside should be able to come out of the tunnel at the shortest possible time. Hence safety exits are planned in tunnels near tunnel joints between two adjacent silos along with louvers for natural light.
Equipment Tunnel with Man access preferably should have clear exits on both its ends and maximum travel distance between two exits ideally not be more than 60 Mtrs. However, in case tunnel has only single exit then maximum safe travel distance to Safety Exit should not be more than 15 Mtrs ideally. However, if a tunnel is having exit on both ends and installed with sprinkler system the maximum allowable safe travel distance can go upto 120 mtrs.
Drainage System inside Tunnel
Water seepage or leakage inside tunnel is not a new problem. Water do get entry inside tunnel and get accumulated on the tunnel floor if proper drainage system is not planned. This becomes a big safety hazard as water accumulation or dampness inside tunnels may result in vegetation and microbiological growth on the walls and floor of the tunnel. A wet or damp tunnel with microbiological growth invites insects and rodents which increases infestation of spilled grains. Sometimes tunnels floor becomes slippery and makes the floor unsafe to walk. Furthermore, a tunnel with standing water may result in electrical accident hence Tunnels must have a proper drainage system to keep the tunnel floor dry and clean. Tunnel floor should always have slope towards one end the tunnel with a sump with a sump pump at this end so that water can be pumped out of tunnel to keep it dry.
Unloading conveyors should be installed above the tunnel floors level on minimum 12” pedestal supports and if possible, the drive unit of conveyor should be kept outside the tunnel. By default, all the conveyors should be sloped upwards a little so that in case water enters inside the conveyor it gets drained automatically through the tail end of the conveyor.
Tunnels if not maintained properly poses safety hazard and hence a lot of care should be taken to design standard operating procedures to ensure the following.
Matches and Cigarettes are strictly prohibited inside tunnels
Shoes with iron studs should be banned in tunnels
No welding and cutting should be carried out inside tunnel while the conveyors are running
Flame proof lights should only be installed inside tunnel
Fire Extinguishers / Sprinkler System should be installed the tunnel
Cell Phones or Wireless Sets with Lithium Batteries should not be allowed
Poking with iron rods or Hammering Spouts when the conveyor is running should be avoided as it creates spark
All maintenance problems that is resulting in metal to metal contact and capable of generating a spark should be resolved immediately.
A portable vacuum system should be available to clear out grains and dust from the tunnel.