Archive for October, 2008

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Straw Pellet Ash and Clinker

October 15th, 2008

Through burning biomass pellets, whether they are made from wood, straw, grass or any other form of biomass they produce ash. The percentage of ash and possibly a clinker is specific to that raw material.

Straw Pellets
Wheat, Barley and other types of straw pellets are becoming more popular as fuel pellets. With regards to pellet production at harvest the material is at the correct moisture content for pellet production. This means drying equipment is not required, and this therefore reduces capital expenditure on equipment, and the cost of production. Productivity for straw pellets is also a lot higher than wood pellets, as straw is not as dense as wood, and is more malleable. However straw does have a disadvantage, as it does not have as much lignin as wood. Since lignin is what gives a pellet its strength, straw pellets have less mechanical strength than wood pellets. This means straw pellets tend to produce more fines than wood pellets, and with regards to combustion this causes more sintering and clinkers to form. The reduced percentage of lignin and increased percentage of fines is not the only reason straw pellets produce more ash and clinker. Straw ash has a lower melting point than wood ash, and ash melting is what forms a clinker.

So straw pellets have advantages with regards to higher pellet production, and have a similar heat value to wood pellets. However during combustion they do produce more ash and clinker so can only be burned in a suitable pellet boiler. The final point is straw generally contains a high percentage of chlorine, and chlorine or chloride is a high temperature corrosive. With regards to a suitable boiler to withstand this corrosion, some manufactures have focused on stainless steel. Stainless steel does have good corrosion resistance, however is susceptible to cracking and stainless steel boilers as very expensive. The best advice is just keep it simple, look for a boiler similar to the old coal boilers, these are built like a tank and resist corrosion though the fact of been very thick.

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WoodPelletProductionGuide

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Posted in Burning Pellets

School Wood Pellet Boiler

October 14th, 2008

Below is a video of Glenmoor School, who had to find a replacement for their coal boiler. After looking at all their alternatives with regards to heat pumps, gas, and diesel they decided that wood pellets would be their best option.

They decided the key advantages of wood pellets are that they are sustainable and carbon neutral. Another key advantage was the pellet boiler would use the current infrastructure the school currently had, which keeps the overall cost of conversion and installation low. Price stability compared to fossil fuels is also a key advantage, as schools with budget limitations; they can more accurately forecast future fuel costs. The Efficiency of the wood pellet boiler is far higher than the previous coal boiler, and can get the school to temperature in half the time.

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WoodPelletProductionGuide

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Posted in Burning Pellets, Videos

Wood Pellet Ash

October 14th, 2008

Through burning biomass pellets, whether they are made from wood, straw, grass or any other form of biomass they produce ash. The percentage of ash and possibly a clinker is specific to that raw material.

Premium Wood Pellets
These pellets are currently sold on the open market, and are the most common type of fuel pellet. They are produced from the residue from the wood processing industry. The residue is mainly from softwood, i.e. pine or spruce. The residue contains no or very little bark. These pellets are a pale yellow in colour and tend to be very shiny.

In terms of ash content they will produce very little, in most cases between 0.5% and 1%. If you are using ‘premium wood pellets’ and you are getting more ash than this, there is either some bark in them or other materials. You shouldn’t really experience any clinker (sinter) from these pellets, unless there are a high percentage of fines. Fines are loose particles, which burn too quickly and reach very high temperatures where the ash begins to melt and form a hard deposit (clinker/sinter).

Other Wood Pellets
Other species of wood and wood pellets, which contain bark, will have higher ash content. Generally the percentage will be between 1-3%. For example producing wood pellets from Willow is becoming popular, as coppiced Willow is a relatively fast growing wood species. However you cannot separate the bark, therefore the pellets will produce higher ash content. Again though these pellets should not produce any clinker. However due to the higher ash percentage the ash pot needs to be empted more frequently, and the boiler tubes cleaned more often.

Premium wood pellets due their low ash level and low maintenance currently dominates the fuel pellet market, and the domestic market prefers them. However premium wood pellets do have their issues, for example the video I posted a few weeks ago on the pellet shortage. If the wood processing industry goes into decline, for example with few houses been built, this affects the supply of residue to the wood pellet plants. With less wood pellets been produced and a high demand the price will rapidly increase. For example currently the US has seen wood pellet prices double. This is why when purchasing a pellet boiler or stove I would recommend finding a more flexible burner that can handle more than premium wood pellets.

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Posted in Biomass, Burning Pellets

Measuring Raw Material Moisture

October 13th, 2008

Before pellet production can take place a material needs to be relatively dry. With regards to relatively dry, it means between the ranges of 10-20%. Where between the range of 10-20% produces the best pellets is specific that raw material. For example a softwood raw material may prefer 10-15% and say barley straw may prefer 15-20%. Moisture is needed to create the pressure required, how much moisture is dictated by the materials natural lignin content and density. It’s basically a trial and error test to get the best pellets possible. The pellet mill has maximum and minimum tolerances for material moisture content; again how wide these tolerances are is dictated by the raw material. Adding a lubricating agent to the mixture can increase these tolerances.

If you wish to understand the process in more detail visit www.biomasspelletmill.com

If you currently have a raw material and you would be interested in upgrading it into pellets, you can test the moisture content of the material by following the simple steps below.

This moisture test is called a dry weight test. For this test a measured weight of the raw material is dried, and the weight difference is the moisture content. You will need a small metal container, weigh scales and a heat source.

1. Firstly weigh your metal container with no material in it; you need to know this figure to take away from the final reading.

2. Place 100g of the raw material into the metal container, if you can reduce the material into small particles it will be easier to get 100g and the material will dry quicker.

3. Place the metal container on a heat source. Now this heat source should not be too hot, as you don’t want to cook the material, as you will release more than moisture.

4. Frequently weigh the container, if the weight keeps dropping keep placing it back on the heat source. Once the materials weight remains constant the material is now completely dry.

5. Measure the container, then minus the weight of the container, and then take the remaining figure away from the original 100g. So if the reaming figure was 40g (100g-40g) leaves 60g, so the moisture content was 60% (very wet!).

Clearly if the material has a moisture content of 60% it needs to be dried, or mixed with a very dry material to create a suitable average moisture content.

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Posted in Biomass, Making Pellets

Biomass Pellet Production Guide

October 7th, 2008

We have developed a guide to give more information on the pellet production process as a whole. The guide is not specifically about our unit, it is a general summary of the equipment and processes used in the pellet production industry, in small scale and large scale applications. The guide includes the principles of operation, and how parameters must be changed for different materials to produce quality pellets at maximum productivity. The guide is separated in to 10 steps, which include the following:

STEP 1. Size Reduction
STEP 2. Material Transportation
STEP 3. Drying
STEP 4. Mixing
STEP 5. Conditioning
STEP 6. Pellet Production
STEP 7. Sieving
STEP 8. Cooling
STEP 9. Pellet Transportation
STEP 10. Bagging and Storage

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WoodPelletProductionGuide

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Posted in Biomass, Making Pellets