Archive for October, 2008

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Gasification Challenges

October 27th, 2008

Gasification has its own challenges and issues, as does pellet production. Understanding and respecting these issue will give a more reliable and efficient operation. In this video Ben from Victory Gasworks explains the challenges and issues associated with gasification, and how to resolve them.

Fuel Bridging

In the gasification chamber the material is gravity fed into the pyrolysis section of the reactor. As gravity is what makes the fuel fall downwards, some fuels will not fall and this will create problems, and the process could stop completely.

The advantage with pellets is that they move and fall freely, making them an ideal fuel for gasification. As they have a high energy density, and are much less likely to bridge and stop the combustion process.

Fuel Sensitivity

As Ben states in the video small dense particles of fuel are required for gasification, and pellets provide a uniform dense fuel that will flow well through the gasifier. Agricultural residues for example must be compressed into pellets before they can be used in a gasifier.

Finally moisture content is also crucial to efficient gasification. Excessive moisture vapour will cause problems, particularly if the gas will be used in an internal combustion engine. Low moisture content is also crucial so the gasifier can reach tar-cracking temperatures to reduce the tar percentage in the gas.

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Posted in Burning Pellets, Videos

Measuring Moisture Content

October 26th, 2008

Below is a video from Ben at Victory Gasworks and he is calculating the moisture content of his raw material for the gasifier. The test Ben is carrying out is called the dry weight test. In this test the dry weight of the material it taken away from the original weight, the difference is the materials moisture percentage.

Drying Temperature

When conducting a dry weight test the material must be dried at a constant rate, at a relatively low temperature. If you attempt to dry the material at high temperatures more than just moisture will be released from material, and this will give an inaccurate figure for moisture percentage.

Knowing a materials moisture percentage is important for gasification and pellet production. For pellet production the material moisture content is required to be between the ranges of 10-20%. Generally for most materials the best average moisture content for producing pellets is around 15%. This will give a quality pellet with a moisture percentage at around 10%. Therefore conducting a dry weight test on a raw material will indicate if it is suitable for pellet production.

Pellets for Gasification

As Ben explains in the video, moisture content is important for a gasifier to operate properly. Pellets are a high-density fuel with a uniform shape and low moisture content. This makes pellets ideal for gasification as they produce an efficient and predictable burn.

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Posted in Biomass, Videos

The Case for Biomass

October 23rd, 2008

The video below highlights the need for biomass to be given a more central role in a renewable energy future. When many people think about renewable energy they think of wind or solar, however biomass is rarely mentioned. As described in the video wind and solar will play important roles in our energy future, however they are limited to the supply of wind and sun. Biomass is always available, and particularly in the form of pellets, can be stored in the right conditions indefinitely.

There is definitely a strong case for biomass, and in many cases it solves energy issues, but also a waste issues. Some biomass is purpose grown for energy, however there are large resources of biomass available as a secondary resource from other industries. For example surplus barley and wheat straw and rape seed straw. Rapeseed straw currently has no economic value; once the rape has been harvested the straw is ploughed back into the soil. Another example is forest management; many small and large woodlands and forests today are undermanaged due to the costs involved. However if these resources were properly maintained, huge amounts of woody biomass collected from the woodland floor could be used to create energy and biomass fuel pellets. With regards to green house gases, if the woody biomass is left to decay, this generates methane, which is more than 20 times more effective than carbon dioxide at increasing global warming.

Converting these resources into biomass fuel pellets is the simplest, most efficient and cost effective way to upgrade these resources into a convenient fuel source.

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Raw Material Contamination

October 21st, 2008

When sourcing raw material for pellet production, care must be taken to not process contaminated materials. Contamination in the form of solid particles of stone or metal is the most serious.

Hammer Mill Contamination

When processing materials with contamination such as stones and metal such as nails, need to be taken seriously. For example processing wood chip form waste wood such as old building timber, this may contain nails. The hammer mill runs at high speeds around 4000RPM, if a nail enters the hammer mill this can be dangerous for several reasons. As the nail comes into the contact with the hammers sparks will be made, if the material is relatively dry this could start a fire in the hammer mill. The nail may also be thrown back out of the hammer mill at the user at very high speeds. Contamination from stones gives similar results.

Pellet Mill Contamination

The stones or metal may pass through the hammer mill unnoticed, not starting a fire. However when stones or metal enter a pellet mill, this can seriously damage the pellet mill. The rollers are set a fixed distance over the die plate, usually 1mm. This is a very small clearance and provides no room for a stone or piece of metal to pass under. If the stone or metal was caught between the roller and die, this could either seriously damage the roller and die or break teeth off the bevel gears that run the pellet mill.

Material contamination should be taken seriously and efforts should be made to source uncontaminated materials for the safety of the user and machine.

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Posted in Making Pellets

Biomass Gasification Benefits

October 21st, 2008

This is the second video from Ben at Victory Gasworks. In this video Ben explains how gasification can be used to generate electricity, transportation fuels, soil amendments, heat, waste removal and other fuels.

Stationary power generation or CHP could play an important role in a sustainable energy future. At PelHeat we wish promote the use of our product as a means to be fuel independent. Again a gasification system could take the pellets and use them to provide heat and electricity, giving the user more independence and lower energy prices and energy to sell, either in the form of pellets or by burning the pellets in a gasifier to generate energy which is sold back to the grid.

Pellets are a uniform size and contain larger amounts of energy compared to the uncompressed raw material. Their high energy density and uniform size mean the store of fuel will last for much longer and the fuel hopper can be re-filled with a small screw auger. This gives much more convenience and automation compared to using the original raw material. The low moisture consistency of biomass pellets also plays an important role. Low mositure content pellets provide a more reliable and predictable fuel source in its burning characteristics, producing a more automated and reliable process.

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Crorey Gasifier

October 20th, 2008

Below is a video of the Crorey gasifier demonstration first heating a boiler, and secondly powering an internal combustion system powering a 45Kw generator. As you can see from the video this is an impressive demonstration of the energy contained within dry sold biomass.

The advantages for using pellets in gasification are the same reason they are used in conventional burning equipment; their convenience, automation and efficiency. Pellets are a uniform size and contain larger amounts of energy compared to the uncompressed raw material. Their high energy density and uniform size mean the store of fuel will last for much longer and the fuel hopper can be re-filled with a small screw auger. This gives much more convenience and automation compared to using the original raw material. The low moisture consistency of biomass pellets also plays an important role. Low mositure content pellets provide a more reliable and predictable fuel source in its burning characteristics, producing a more automated and reliable process.

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Posted in Burning Pellets, Videos

Biomass Pellet Ash

October 20th, 2008

Once the pellets have been burnt the ash remains must be removed from the burner and disposed off. However the ash from the pellets is not a waste, It can be used as a soil amendment to improve the quality of poor soils. The ash contains high levels of nitrogen.

Composting
Instead of directly mixing the ash into the soil, it generally is a better idea to create compost, and add to the soil when needed. The compost will be a rich soil amendment with concentrated nutrients.

Wood Pellet Ash and Potash
Wood ash as a soil amendment can be particularly beneficial to fruit trees with stones in the fruit.

PH
Wood ash and potash can raise the PH of the soil to make the soil more alkaline. Through composting with soil and other ingredients like peat, this can reduce the PH. Obviously if the soil already has a high PH the ash should be used else where.

Biomass ash improves soil quality, provides nutrients and improves the soils ability to hold water. The ash should be used a soil conditioner.

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Posted in Biomass, Burning Pellets

Storing Pellets

October 20th, 2008

Storing pellets is as crucial as any other part of the pellet production process. Pellets must be stored properly to maintain their strength, low fines and low moisture. If pellets are not stored properly for later usage they can be damaged even to the extent that they cannot be used.

Pellet Breakage
Moving pellets as little as possible keeps the pellets in a better condition, and reduces the percentage of pellet breaking. The more pellets are moved and external forces are applied to them, the higher probability they will break into smaller pieces. Pellets are not extremely fragile, however careful handling of pellet bags for example can reduce the percentage of fines.

Fines
With excessive external forces being applied to the pellets through rough handling, the pellets will break, and as they break, fines will be produced. Fines are small particles that either did not form a pellet in the pellet mill, or have broken off a pellet. Excessive fines affect the combustion process, reducing fuel efficiency and increase the probability and percentage of clinker formations.

Moisture
Keeping pellets in a relatively dry environment is essential. If the pellets are stored in a damp environment the pellets will absorb this moisture and expand. By absorbing the moisture and expanding the pellets lose all their mechanical strength, and crumble, rendering them useless.

How pellets are stored is up to the user, the pellets can be stored in bags, sacks and silos, however best suits their needs. As long as the above criteria are met, the pellets will remain in top condition to give the highest fuel efficiency and lowest maintenance possible.

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Posted in Biomass

Pellet Burner Maintenance

October 18th, 2008

As discussed in the last few blogs, different types of biomass pellets produce different types and quantities of ash and clinker. Proper pellet burner maintenance is essential to efficient combustion and fuel efficiency. If the pellet burner is not cleaned to a sufficient standard, this can impact the combustion process and reduce efficiency, and result in higher levels of noxious gases, through inefficient combustion. Also if the rest of the burn chamber is not properly cleaned this can reduce the amount of useful heat that is extracted. For example in a pellet boiler if there is a large build up of deposits around the heat exchanger tube, this insulates the tubes and stops heat getting into the boiler. This means more fuel is used to get up to temperature.

Wood Pellet Maintenance
Wood pellets as discussed in earlier articles produce varying levels of ash depending on whether they are premium wood pellets or not. The ash percentage will vary between 0.5-3%, but the chance of sintering or clinker is very low. Some boilers and stoves have heat exchanger tube spring cleaners. The springs are positioned inside the heat exchanger tubes, and a mechanism lift and drops the springs to clean deposit built up. In some pellet burners this is manually carried out by the user, or in some systems is automated and can be set to clean at certain times. Some pellet burners are also water-jacketed, so making sure there is minimal deposit build up in the rest of the burn chamber is also important. Finally fly ash collects within the inside of the chimney, and if not maintained can effect combustion through poor ventilation of the combustion gases.

It is generally recommended that once a year several components should be removed and the burner should be given a thorough clean. This obviously should be carried out during the summer months when the burner isn’t required.

Straw Pellet Maintenance
Straw pellets create a higher ash content than wood pellets, but the same basic cleaning principles apply, however they need to be carried out more regularly. As stated in earlier articles burning straw pellets create clinkers and slag formation on the heat exchanger tubes. The clinker must be removed so that it does not affect combustion. Depending on the type of boiler and burn pot design this may be required every few hours, every 6-8 hours or every day or week. Another factor is slag build up in the heat exchanger tubes. Slag is similar to a clinker, where ash melting has formed a sold deposit to form. Unlike wood ash in the heat exchanger tubes, slag is a hard despot that needs to scraped off. Cleaning springs may not be suitable to remove slag deposits, as they may not provide sufficient force.

Therefore maintenance for straw pellets is more frequent and labour intensive compared to burning wood pellets. However there are sufficient cost incentives and other benefits.

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Posted in Biomass, Burning Pellets

Biomass Gasification

October 17th, 2008

Gasification is one way that biomass pellets can be used to generate heat and energy. The below video is made by Ben Peterson who is developing a 101 guide on the principles of gasification and how it can generate energy for a wide range of uses.

Instead of traditional combustion in a normal burn chamber, a gasifier separates the flammable gasses from the biomass, and then burns the gas. The advantages of this process are that the gas can be used in engines as well as been used to simply heat a property.

The advantages for using pellets in gasification are the same reason they are used in conventional burning equipment; their convenience, automation and efficiency. Pellets are a uniform size and contain lager amounts of energy compared to the uncompressed raw material. Their high energy density and uniform size mean the store of fuel will last for much longer and the fuel hopper can be re-frilled with a small screw auger. This gives much more convenience and automation compared to using the original raw material. Finally as Ben explains in the video, not one gasifier design works for all raw materials. Each system has to be tuned because of raw material differences and different moisture contents. Here the low moisture consistency of biomass pellets also plays an important role. Where for the raw material each gasifier must be changed, once system could be used to burn biomass pellets made from different raw materials.

I will feature the other Gasification 101 videos as Ben makes them available.

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Posted in Biomass, Burning Pellets, Videos