Rezultaty
Straw gasification in fluidised bed must be done in a relatively low temperature. In higher temperatures straw ash starts to melt and molten ash prevents the bed fluidisation.
When gasification is done in low temperature, the carbon conversion to gas is not 100%. Typically the carbon conversion is 95 97%. So there is some carbon left in the fly ash separated from gas in the filter. There is about 20 30% carbon in the ash. This ash contains also Polyaromatic Hydrocarbons (PAH), which prevents its recycling.
According to the tests, it is possible to incinerate this ash in Circulating Fluidised Bed below ashes melting point and to reduce the ashes carbon content to 3%. The tests confirm, that the amount of PAH, dioxin and furan in incinerated ash prevent this material from being recycled.
Straw gasification in fluidised bed must be done at relatively low temperatures. In higher temperatures straw starts to melt and molten ash prevents bed fluidisation.
When gasification is done in low temperature, the carbon conversion to gases is not 100 %. Typically the carbon conversion is 95-97%. So there is carbon left in the fly ash separated from gas in the filter. There is about 20-30% carbon in the ash. This ash contains Polyaromatic Hydrocarbons (PAH), which prevents recycling it.
According to the tests, it is possible to incinerate this ash in Circulating Fluidised Bed below the melting point of the ash and attain less than 3% carbon content in the ash. The tests confirm, that the PAH, dioxin and furan contents in the incinerated ash are below the limits thus allowing for recycling of this material.
Straw is a major biomass resource in large parts of Europe. This development will help increase the share of renewable energy in the energy system, and also improve economy and employment in the agricultural sector.
To first produce clean gas from straw and then burn the gas in power plants is the development of this procedure.
The chemical composition of the straw ash makes it necessary to use a special gasification process to prevent the risk of bed sintering. Due to high contents of alkali and chlorine, it is necessary to clean the low calorific gas before it can be safely co-fired in a power plant boiler using coal as the main fuel.
When limestone and sand is used as bed material and steam and air as gasification agents, loose straw can be gasified in the fluidised bed.
When gas is cooled in the waste heat boiler, where heat is recovered to feed water preheating, the gas can be filtrated through the baghouse filter and clean from alkalies and chlorines.
To build up the straw gasification plant connected to the existing power plants is the fastest way to reduce fossil fuel consumption with biomass in power production. The same gasification plant can also be used for wood.
Straw is a major biomass resource in large parts of Europe. This development will help to increase the share of renewable energy in the energy system, and to improve economy and employment in the agricultural sector.
This development has been obtained by producing clean gas from straw and then burnin the gas in the power plants.
The chemical composition of the straw ash makes the use of a special gasification process necessary to prevent the risk of bed sintering. Due to high contents of alkali and chlorine, it is necessary to clean the low calorific gas before it can be safely co-fired in a power plant boiler using coal as main fuel.
When limestone and sand are used as bed material and steam and air as gasification agent, loose straw can be gasified in the fluidised bed.
When gas is cooled in the waste heat boiler, where heat is recovered to feed water preheating, the gas can be filtrated in the baghouse filter clean from alkalies and chlorines.
To build up the straw gasification plant connected to the existing power plants is the fast way to reduce fossil fuel consumption with biomass in power production. Same gasification plant can also be used for wood.
Straw is a very low energy-density fuel (straw 0.4GJ/m{3} and coal 23GJ/m{3}). Therefore new developments were required to able the handling of this very large material flow.
Straw pellets are easy to handle, but their production is very expensive. For the storage and transport straw is packed in large bales (ca 2.4 x 1.3 x 1.2m). The bales must be shredded to be able to receive enough reaction surfaces between the straw and gasification agent. However there is a small over pressure in the gasifier, which means that the gas can escape via straw feed.
In the wood gasification rotary feeders are used to prevent gas leakages in the feed, but the size of rotary feeders needed for straw is so large, that the leakage will be too large.
The system where plug screw forms first a gas tight plug and then a cutter screw cuts the plug into pieces seems to be working.
The wear in this system must be taken into consideration and easy replace of the worn parts must be planned.
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