Biomass Pretreatment Techniques

Renewable Energy


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Biomass, whether forestry or agriculture-based, requires different pretreatments to make the material useful for specific downstream processing. Removal of water, natural resins or other components allow concentration of the carbon in the raw material to prepare it for next steps.

At NRRI, we are developing large-scale demonstrations of biomass pretreatment processes to provide industry-relevant data and support. During the summer of 2016, we initiated commissioning of our Renewable Energy Laboratory located at our NRRI-Coleraine site. The first phase of facility capabilities will include the following techniques:

Torrefaction

This is essentially a “light to dark roast” of woody biomass chips in an oxygen-deprived environment to deliver a uniform, dry solid fuel that contains approximately 90% the BTU content as an equal weight of western coal. This fuel product is to be furnished in tonnage quantities to industrial and power companies interested in offsetting use of coal to meet air standards and reduce ash output. NRRI is commissioning a rotary kiln based system capable of producing 10-12 t/d of torrefied material from 27-32 t/d  green wood chips. In 2017, NRRI will also have a moving bed torrefaction system that will be capable of producing 3 t/d of torrefied product.  Recently, a successful test was conducted using the torrefied fuel as a coal replacement in the steam train at the Milwaukee Zoo. 

Hydrothermal Carbonization (HTC)

This process takes “wet” biomass such as agricultural waste or invasive water plant species and processes it in a process similar to a pressure cooker to produce an aqueous “energy mud” that has energy content similar to the dry torrefied fuel. This material is an excellent binder for the dry fuel to be compressed into briquettes for shipment. NRRI’s HTC process is anticipated in 2017. The concept can be applied to help manage environmental issues associated with nuisance plant materials by providing an economic lever for their harvesting and conversion into useful fuel and chemical products. Some degree of ash and chemical removal can also be attained with this approach.

Steam Explosion

This is a technique of treating woody biomass with high pressure steam followed by rapid release of pressure. This action explodes the wood structure, opening it up for more efficient processing, extraction or torrefaction. NRRI looks forward to having this capability in the Renewable Energy Laboratory in 2017/2018.