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05 Jul 2018

How to deal with the coking in the combustion of biomass-fired boiler?

Question details (performance):

Coking.

Answer:

(1) During combustion, the temperature of fuel layer is higher than the softening temperature of ash, which is an important reason for slag formation. Under the deformation temperature of the ash, the ash particles generally do not form slag, but when the softening temperature is reached, the eutectic formed by the melted ash slag is not sufficiently cooled, so it will stick to the water-cooling wall and cause slag formation.

(2) Roughness of boiler wall pipe surface is another important cause of slag formation. rough surface is easy for ash bonding, so that the combustion chamber temperature and pipe wall temperature rise due to heat up, then the fuel ash melting point temperature is reached, thus went into a state of melting or softening, adjacent high temperature melt bonding together, which causes slagging.

(3) Air is insufficient during combustion process, ferric iron in the fuel layer is reducing into bivalent iron, and iron with the melting point of Fe exists less than exists in the form of Fe+2, so that the fuel ash melting point is greatly reduced and cause coking.

(4) Inadequate fuel mixing with air, even if the amount of air supply is enough, it can still cause partially air quantity shortage, where will appear a reducing atmosphere, reduce fuel ash melting point and causing coking.

(5) The unreasonable wind speed causes the flame in the furnace to deviate to one side, causing the partially temperature too high, which increases the temperature of some fuel layers to the ash melting point, and causes coking if the cooling is slow.

(6) The combustion device is overloaded running and the furnace temperature is too high, which increases the temperature of the fuel layer to reach the ash melting point of the fuel and leads to slag formation.

(7) Big fuel diameter and thickness of the fuel layer in the furnace layer combustion furnace will cause the partial temperature of the layer combustion center too high, and the ash melting point of the fuel will lead to slag formation.

Troubleshooting:

(1) The producer of biomass fuel particles should control the material impurities, as well as sand and other debris should be as less as possible.

(2) Adjust the compression ratio. Under the condition of ensuring the particle forming rate, reducing the compression ratio will increase the combustion surface.

 

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