• Feedstocks Analysed at Celignis
    Willow

Background on Willow

Willow is a hardwood that is often grown as an energy crop for utilisation in biomass power stations or, potentially, for the production of advanced (cellulosic) biofuels in second generation biorefineries.

When it is grown as an enery crop it is usually cultivated as a short rotation coppice. Under this practice the willow crop is typically harvested every 3-5 years.

Analysis of Willow at Celignis



Celignis Analytical can determine the following properties of Willow samples:



Lignocellulosic Properties of Willow

Cellulose Content of Willow

Willow is a hardwood and so will have a good cellulose content. The whole-plant cellulose content will depend on: the productivity of the tree; the mass ratio of stem biomass to foliage; the cutting cycle; and the particular willow variety.

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Hemicellulose Content of Willow

Given that it is a hardwood, willows will typically have a lower hemicellulose content than herbaceous energy crops (e.g. Miscanthus). The principal hemicellulose sugar is xylose with small amounts of galactose, mannose, arabinose, and rhamnose present.

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Lignin Content of Willow

As a hardwood willow will have a good lignin content. The whole-plant lignin content will depend on: the productivity of the tree; the mass ratio of stem biomass to foliage; the cutting cycle; and the particular willow variety.

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Starch Content of Willow

The starch content of willows varies between the different anatomical components of the plant. Typically it is highest in the leaves, where photosynthesis takes place, and lower in the stems. The starch content can also vary according to the maturity of the plant.

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Uronic Acid Content of Willow

The uronic acids glucuronic acid and galacturonic acid are present in the hemicelluloses of willows.

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Enzymatic Hydrolysis of Willow

We can undertake tests involving the enzymatic hydrolysis of Willow. In these experiments we can either use a commercial enzyme mix or you can supply your own enzymes. We also offer analysis packages that compare the enzymatic hydrolysis of a pre-treated sample with that of the native original material.

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Bioenergy Properties of Willow

Ash Content of Willow

The ash content of willows is typically reasonably low although this will be dependent on the variety and the amount of foliage present on the standing crop.

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Heating (Calorific) Value of Willow

Willows have good heating values, meaning that they are suitable for utilisation in boilers for the production of heat and/or electricity. However the effective heating value will depend greatly on the moisture content of the crop.

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Ash Melting Behaviour of Willow

Ash melting, also known as ash fusion and ash softening, can lead to slagging, fouling and corrosion in boilers which may reduce conversion efficiency. We can determine the ash melting behaviour of Willow using our Carbolite CAF G5 BIO ash melting furnace. It can record the following temperatures:

Ash Shrinkage Starting Temperature (SST) - This occurs when the area of the test piece of Willow ash falls below 95% of the original test piece area.

Ash Deformation Temperature (DT) - The temperature at which the first signs of rounding of the edges of the test piece occurs due to melting.

Ash Hemisphere Temperature (HT) - When the test piece of Willow ash forms a hemisphere (i.e. the height becomes equal to half the base diameter).

Ash Flow Temperature (FT) - The temperature at which the Willow ash is spread out over the supporting tile in a layer, the height of which is half of the test piece at the hemisphere temperature.



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Major and Minor Elements in Willow

Examples of major elements that may be present in Willow include potassium and sodium which are present in biomass ash in the forms of oxides. These can lead to fouling, ash deposition in the convective section of the boiler. Alkali chlorides can also lead to slagging, the fusion and sintering of ash particles which can lead to deposits on boiler tubes and walls.

We can also determine the levels of 13 different minor elements (such as arsenic, copper, and zinc) that may be present in Willow.

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Analysis of Willow for Anaerobic Digestion



Biomethane potential (BMP) of Willow

Willow coppices are considered to be a somewhat difficult feedstock to process in anaerobic digestion reactors. This is due to their relatively high lignin contents and low concentrations of the more volatile constituents (e.g. starch, water soluble carbohydrates, lipids). As a result, the biochemical methane potential (BMP) of coppice willows is typically significantly lower than that associated with the more conventional anaerobic digestion energy crops, such as maize (corn).

However, there have been a number of studies that have shown that the biochemical methane potential of willows can be significantly increased following a pre-treatment that makes the lignocellulosic matrix of the feedstock more amenable to hydrolysing anaerobes.

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Physical Properties of Willow



Bulk Density of Willow

At Celignis we can determine the bulk density of biomass samples, including Willow, according to ISO standard 17828 (2015). This method requires the biomass to be in an appropriate form (chips or powder) for density determination.



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Particle Size of Willow

Willow coppices are considered to be a somewhat difficult feedstock to process in anaerobic digestion reactors. This is due to their relatively high lignin contents and low concentrations of the more volatile constituents (e.g. starch, water soluble carbohydrates, lipids). As a result, the biochemical methane potential (BMP) of coppice willows is typically significantly lower than that associated with the more conventional anaerobic digestion energy crops, such as maize (corn).

However, there have been a number of studies that have shown that the biochemical methane potential of willows can be significantly increased following a pre-treatment that makes the lignocellulosic matrix of the feedstock more amenable to hydrolysing anaerobes.

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Publications on Willow By The Celignis Team

Hayes, D. J. M. (2011) Analysis of Lignocellulosic Feedstocks for Biorefineries with a Focus on The Development of Near Infrared Spectroscopy as a Primary Analytical Tool, PhD Thesis832 pages (over 2 volumes)

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The processing of lignocellulosic materials in modern biorefineries will allow for the production of transport fuels and platform chemicals that could replace petroleum-derived products. However, there is a critical lack of relevant detailed compositional information regarding feedstocks relevant to Ireland and Irish conditions. This research has involved the collection, preparation, and the analysis, with a high level of precision and accuracy, of a large number of biomass samples from the waste and agricultural sectors. Not all of the waste materials analysed are considered suitable for biorefining; for example the total sugar contents of spent mushroom composts are too low. However, the waste paper/cardboard that is currently exported from Ireland has a chemical composition that could result in high biorefinery yields and so could make a significant contribution to Irelandís biofuel demands.

Miscanthus was focussed on as a major agricultural feedstock. A large number of plants have been sampled over the course of the harvest window (October to April) from several sites. These have been separated into their anatomical fractions and analysed. This has allowed observations to be made regarding the compositional trends observed within plants, between plants, and between harvest dates. Projections are made regarding the extents to which potential chemical yields may vary. For the DIBANET hydrolysis process that is being developed at the University of Limerick, per hectare yields of levulinic acid from Miscanthus could be 20% greater when harvested early compared with a late harvest.

The wet-chemical analysis of biomass is time-consuming. Near infrared spectroscopy (NIRS) has been developed as a rapid primary analytical tool with separate quantitative models developed for the important constituents of Miscanthus, peat, and (Australian) sugarcane bagasse. The work has demonstrated that accurate models are possible, not only for dry homogenous samples, but also for wet heterogeneous samples. For glucose (cellulose) the root mean square error of prediction (RMSEP) for wet samples is 1.24% and the R2 for the validation set ( ) is 0.931. High accuracies are even possible for minor analytes; e.g. for the rhamnose content of wet Miscanthus samples the RMSEP is 0.03% and the is 0.845. Accurate models have also been developed for pre-treated Miscanthus samples and are discussed. In addition, qualitative models have been developed. These allow for samples to be discriminated for on the basis of plant fraction, plant variety (giganteus/non-giganteus), harvest-period (early/late), and stand-age (one-year/older).

Quantitative NIRS models have also been developed for peat, although the heterogeneity of this feedstock means that the accuracies tend to be lower than for Miscanthus. The development of models for sugarcane bagasse has been hindered, in some cases, by the limited chemical variability between the samples in the calibration set. Good models are possible for the glucose and total sugars content, but the accuracy of other models is poorer. NIRS spectra of Brazilian bagasse samples have been projected onto these models, and onto those developed for Miscanthus, and the Miscanthus models appear to provide a better fit than the Australian bagasse models.





Examples of Other Feedstocks Analysed at Celignis



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