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Why use dry wood chip as fuel ?

Time:2017年12月05日      Hits:

Firstly the reason for using wood as fuel are as follows:

--- a renewable energy source, grows by converting solar energy

--- leaving wood to decompose releases as much carbon dioxide (CO2) as when it is combusted → wood is therefore CO2-neutral as a fuel 

--- mainly locally-produced energy sources → independence from exported fuels

--- transportation distances are usually relatively short.

--- carbon content ≈ 50 %, nitrogen content ≈ 6 %

--- ash ≤ 1 % (typically)

--- high volatile content (≈ 80 – 85 %) → long flames, big furnace size

--- heating value of wood in average ≈ 19 MJ/kg ≈ 5,3 kWh/kg

--- different forms of wood fuels, e.g. split billets, wood chips and pellets, saw dust, bark, etc.

moisture lowers the net heating value

Why use dry wood chip but not use wet wood chip as fuel ?

--- at harvest the moisture content of wood is around 50 % (total weight)

---  to evaporate 1 kg of water takes about 2,5 MJ/kg H2O (0,8 kWh/kg H2O)

---  e.g. 2 kg of wood chips, moisture content 50 %

= 1 kg dry-matter of wood + 1 kg water

→ net heating value ≈ (19 – 2,5) MJ ≈ 16,5 MJ  → 8,25 MJ/kg of fuel

--- moisture content affects greatly on net heating value of wood fuel (see tables 1 & 2 )

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In practice the heating effect of small-scale boilers decreases even more.

--- the total efficiency of the boiler decreases rapidly when the moisture content rises (boiler tests are usually made with fuel

that contains 30 % or less moisture/water)

--- moisture content decreases conversion efficiency into energy and increases gaseous emissions (incomplete combustion)

--- when using dry fuels the boiler stays cleaner, malfunctions and need for maintenance decreases → uptime increases.

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As a result, in order to increase the calorific value of the wood chips, we have to find ways to reduce the moisture content of wood chips to be about 20%.

The wood chip drying machine of Sunco Machinery can successfully to solve this problem. And it can use waste heat or fuel to generate hot air for the wood chip drying system.

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Wood Chips Dryer mainly consists of a horizontally inclined rotating cylinder, air duct tube, hor air furnace, highpressure draught fan, electric control box, etc.

Wet wood chip are fed at the feed inlet hole, and discharged at the dischaging hole. It is direct-type heated rotary dryers, hot gases move through the cylinder in direct contact with the wet wood chips, either with or against the direction of the wood chips' moving direction. The cylinder is equipped with lifting plates which lift the wood chips, and shower it up and down through the hot flue gas.

For more detail of wood chip dryer machine, please contact us by email to : suncomachinery@hotmail.com 

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