Silo storage and automatic feeding of granules

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Heating with wood pellets: the question to ask before choosing this method of heating?

What pellet tonnage will be needed? See also pellets consumption calculation?

pellet store homemade
pellet store homemade

Once you have your annual heat balance you can infer pellet tonnage required and thus the volume of your silo.

a) from heat balance

Your heat balance gives you need esprimé annual useful energy in kWh.
Each kg of pellets contains between 4,5 and 5kWh. Take 5kWh which corresponds to German standards.

So simply divide your annual energy needs in kWh per 5 to find your pellet needs kg.

It must also be correct and divide by the average efficiency of your boiler, take 90% yield.

Example: a modern house very well insulated from 150 100 m² needs kWh / m².year be 150 000 kWh. Boiler with an efficiency of 90%.

So that's 15000 / (5 0,9 *) = 3333 4 kg or tonnes at delivery (most provider engaged in tonne).

ps: watch your heat balance may already have taken into account your boiler efficiency. In this case the correction of 0.9 be deleted.

b) starting from the consumption of fuel oil or gas

Again this is quite simple: 2 1 kg pellets = L = 1 fuel gas m3.

So if your house 2000L consumed fuel, you would 4000 kg pellets.

A correction is also to be made at the boiler efficiency. But this also depends on the performance of your old boiler.
So if you had a boiler that had 30 years ago, we can estimate the yield to 70%. The performance of your new boiler being 90%, you will use less raw energy for the same useful energy.

Resuming the 2000L raw energy is 20 000 kWh He therefore corresponded to 14 000 kWh (= 20 000 0,7 *) of useful energy is 15 555 kWh (= 14 000 / 0.9) gross energy in your new boiler efficiency 90 3100% in either kg pellets.

What silo volume is needed?

The density of loose pellets is between 650 and 750 kg / m3. Take 700 kg / m3. The required tonnage divided by 0,7 therefore gives the volume required silo.

Take a seat at 10 15% for the dead volumes.

Example: 4 Tons Pellets therefore require: (4 / 0,7) * = 1,15 6.57 m3 be 7m3.

Alternate method: starting from your oil tank, for example 2000L multiply by a factor of 3,5.

technological aspects of the silo

The extraction of the silo is done either by a worm or by suction mouths following brands.

If extraction is done by screws, it is necessary to learn about the living standard lengths to suit.

a) Supply screw

screws automatic pellet boiler feed
Archimedean screw for automatic feeding of a pellet boiler

The internal length of the silo will be higher than in 20 60 cm screw length.
The internal width of the silo must be limited to properly feed screw (1,5 1,8 to m maximum).

Hopper to not mandatory silo

Contrary to what the manufacturers recommend, I advise not to floor shaped hopper. It's complicated if you want to do solid (it should withstand several tons of pellets!) So this means fast and cheap it ultimately serves to not much, if not it is clear to 100% and its silo is obviously illusory to empty the silo until the last granulated before refilling?

Nevertheless, if possible, try to completely empty all 2 fillings so that "stagnant" pellets are consumed. Indeed, after 2 years and according to the conditions of hygrometry, it is possible that the pellets lose their quality (increase of the humidity therefore of the consumption and the polluting emissions of unburned).

I recommend a flat floor at the height of the screw (false floor in chipboard of 22mm on rubble of 5cm laid flat). In this case, two "triangles" of pellets will never be consumed. This is your "reserve" (like on motorbikes): if you arrive at the end of the silo while forgetting to have it filled. In this case, you enter your reserve, give a few shovels to collect the pellets on the screw while waiting for the delivery (attention: sometimes several weeks of delay).

pellet store homemade
Homemade pellet silo: "foundations" of the silo.

The silo will be built in rubble 10 cm, with an open gateway to the outside of the silo with a seal to prevent dust during filling.

pellet store homemade
Homemade pellet silo: "door" to the outside.

Side inside the opening, there must be two angles for inserting boards (27mm thickness) for retaining granules. To find out what remains in the silo, I advocate a window on one of the boards from the top. We must think of the filling port and the air outlet (supplied with the boiler), located on the same side of the silo.

You also need a rubber mat, set free from the ceiling in front of the fill port to prevent the granules explode sawdust on the opposite wall during filling. Be careful not to have water pipes and electrical conduits that pass inside the silo.

If silo inside the house, take care of its construction to the maximum to prevent parts of the silo or rub together or against walls. Indeed, during the operation of the feed screw, the silo can vibrate and resonate throughout the house!

pellet store homemade
pellet store homemade: mouth filling and venting. Please note that this mouth should be outward only if there is a big risk of dust throughout the cellar during filling. Educate yourself, your pellet supplier can be a double pipe that also aspires dust system (much like refueling circuit cars).

To avoid capture moisture from the air (hygroscopic) the silo must be tight as possible with outside air currents, the cavity walls will be pretreated against moisture or covered with a panel.

Depending on your location, your boiler is immediately adjacent to the silo or not. If this is the case, the worm may directly feed the hopper of the boiler. This is the solution which is recommended but not possible all the time, in this case it is necessary to use a vacuum system!

b) Power Aspiration

If your bin is removed from the boiler, you can opt for transport by suction directly from the silo. Nevertheless, even in this case the maximum length of the suction is 20m 6m and height!

You then have a suction turbine (it is a big vacuum in 1000 1400 W about engine) and two hoses 60mm diameter between the silo and hopper of the boiler. The fan circulates air at high speed into the loop return, resulting granules passed.

Boiler side, the flow passes into a cyclone where the granules slow then fall into a hopper, while the air is sucked back into the tube 2eme. One can even go up one floor, and make a maximum length of about twenty meters.

pellet feed by suction
pellet feed by suction

In this case, the boiler has a hopper reserve of about 1 day heating to avoid calling the granules from the silo too often. The suction fan is quite loud.

We program what time it is desired to fill the hopper, it avoids it to happen in the middle of the night. Filling only takes a few minutes.

Importantly, the trap of static electricity: for compelling earth!

Friction dry pellets generate static electricity.

It is essential to ground the filling mouths and the silo-boiler pipes it either with a screw feed but especially with a power vacuum, or the effect of air friction is further increased.

Indeed: dust pellets can be inflamable (we recall that the first diesel engines were walking ... to coal dust!) And a spark in the air can therefore ignite the dust!

A grounding of all metallic parts of the room is more than recommended! The risk is not very important but there all the same!

Read more: hot water ECS and wood boiler or pellet

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