Investigation of woodchip quality: Relationship between the most important chemical and physical parameters
Introduction
Over the past few decades, the level of GHG (greenhouse gases) in the atmosphere has raised [1] causing global warming and climate change. One of the main important causes of GHG emission is energy production [2], which is expected to grow, considering also the continuous worldwide increase in energy demand [3]. The European Union is aware of the importance of finding new way of energy production and of the necessity to limit the dependency on energy imports to improve energy security. This aspect is complex and is influenced by increasing risks of supply disruptions due to a number of factors such as political turbulence, war, financial market turmoil, technical failures, unfavorable weather conditions [4].
Public policies have been set up in order to increase the share of RES (renewable energy source) to the electricity supply, including the target of 20% for the share of renewable in energy consumption in the EU by 2020. For these reasons, most focus should be given to RES for the generation of electricity and heat production.
Among the different types of renewable energy sources, wood biomass is one of the most promising alternative and with the greatest potential. It is available in many forms (dedicated and residual biomass) and in all parts of the world allowing the deployment of bioenergy almost everywhere [5]. It can be used to produce biofuels in solid, liquid or gaseous form and can be stored. Energy from biomass generally has limited weather-related dependencies and hence offers relatively constant and predictable energy output by comparison with wind and solar technologies [6]. Moreover, it is based on well known and proven technologies with good performance.
In particular, woodchips are an appealing alternative being a cheap fuel with low energy requirements for their production and with very stable burning or gasification due to their higher contact surface compared with other solid biofuels [2]. Different studies demonstrate that there is a gap between the amount of biomass resources for energy and the use of these sources; in fact, the energy use from biomass is less than the resources practically in all EU countries [7]. In Europe, Finland and Sweden use the largest volumes of forest woodchips, and it is expected that many other countries will increase the use of this solid biofuel to produce energy [7]. In Italy, although the electricity consumption is decreasing, the solid biofuel power plants for electricity production increased from 75 to 89 in the period 2012–2013. In the same period the CHP (combined heat and power) plants fueled with the same biofuel increased from 104 to 133 [8]. For some countries, like Italy, where the number of power plant is increasing the need to find new sources of supply could lead to a reduction in biomass quality for energy applications.
It is well known that woodchips and woody materials in general present a great variability of characteristics that leads to an indispensable need to employ quality standards to be fulfilled in order to drive the market in a sustainable way. The main international standard for solid biofuels is currently the EN-ISO 17225:2014, which defines different classes of products in relation to their quality. The quality of solid biofuels used for energy generation is defined by different physical and chemical parameters. In particular, one of the most important is the ash content representing a problem because of slagging in furnaces, fouling of heat exchanger surfaces [9], bed agglomeration, corrosion in the combustion device [10] and fly ash emission [11]. EN ISO 17225-4 is the quality standard for graded woodchip for residential, small commercial and public building applications and provides limits for three different woodchip quality classes. The most important discriminant between these classes is the ash content (Ac): classes A1, A2, B are related to a maximum Ac of 1.0, 1.5 and 3.0% respectively. Specific thresholds for elements are set only for B woodchip class.
The moisture content (Mc) is the most important physical characteristic of wood fuels, it depends on different factors [12] and it influences the calorific value. This parameter is a property of a fuel, which determines the energy value of it, and it is relatively constant for wood fuels in their dry status [13]. The contents of nitrogen, sulphur, chlorine and some minor elements are also important parameters for woodchip quality and can represent a burden especially for woodchip produced from crop residues [14].
Considering the raising interest on this solid biofuel, the goal of this paper is to evaluate the quality of woodchip available on the market and employed by Italian power plants. The investigation involved 1790 woodchip samples analyzed from Biomass Lab of Università Politecnica delle Marche. Within the data analysis, particular attention was given to the contents and indications of EN ISO 17225-1 [15] and EN ISO 17225-4 [16]. Moreover, considering the high number of biomass samples studied the paper aims also to investigate the possible correlations between parameters with special attention to net calorific value, Ac and Mc. To this aim, PCA (principal component analysis) was used in conjunction with conventional statistical techniques as reported by other authors [17].
A similar work was carried out by the authors on the wood pellet quality [18], [19] but, as far as we know, no paper based on a comparable sample size are reported in literature for woodchip.
Section snippets
Materials and methods
During the years 2007–2013 chemical and physical analyses (Table 1) were performed on 1790 woodchip samples collected by the Biomass Lab of Università Politecnica delle Marche. The analytical methodologies adopted refer to the standards listed under EN 14961. The woodchip samples originate from power plants (district heating and combined heat and power plants) mainly during the application of a long-term monitoring of biomass quality employed in several installations. The high number of biomass
Results and discussion
The investigation led to different levels of information, which are described separately below.
Conclusions
The results of this work give a good evaluation of the quality of woodchip available on the market and employed by Italian power plants. Many indications emerge from data analysis. There are woodchips with very high Ac on the market, well over the 10%, maximum value to be stated according to EN ISO 17225-1. Ac and Mc variability is highly linked to NCV. A very good relationship (R2 = 0.983) has been found to estimate the NCV from Mc and Ac. Considering the repeatability and reproducibility
References (29)
- et al.
Review of micro- and small-scale technologies to produce electricity and heat from Mediterranean forests' wood chips
Renew Sustain Energy Rev
(2015) - et al.
Influence of storage time on the quality and combustion behaviour of pine woodchips
Energy
(2010) - et al.
Energy security, policy and technology in South East Europe: presenting and applying an energy security index to Croatia
Energy
(2015) - et al.
Physical characterization of commercial woodchips on the Italian energy market
Fuel
(2011) - et al.
The potential impacts of grid-connected distributed generation and how to address them: a review of technical and non-technical factors
Energy Policy
(2011) - et al.
Forest chips for energy in Europe: current procurement methods and potentials
Renew Sust Energ Rev
(2013) - et al.
Ash behaviour and emission formation in a small-scale reciprocating-grate combustion reactor operated with wood chips, reed canary grass and barley straw
Fuel
(2015) - et al.
Chemical forms of ash-forming elements in woody biomass fuels
Fuel
(2010) - et al.
From waste to raw material—the route from biomass to wood ash for cadmium and other heavy metals
J Hazard Mater
(1996) - et al.
Performance of a mobile mechanical screen to improve the commercial quality of wood chips for energy
Bioresour Technol
(2011)
Calorific value estimation of biomass from their proximate analyses data
Renew Energ
Quality of residues of the biodiesel chain in the energy field
Ind Crop Prod
Investigation on wood pellet quality and relationship between ash content and the most important chemical elements
Biomass Bioenerg
Wood pellet quality with respect to EN 14961-2 standard and certifications
Fuel
Cited by (32)
A new concept of a thermal network for energy resilience in mountain communities powered by renewable sources
2023, Sustainable Energy, Grids and NetworksPerformance of a portable NIR spectrometer for the determination of moisture content of industrial wood chips fuel
2022, FuelCitation Excerpt :In some cases, this process can even lead to self-ignition [12], with total destruction of the stored fuel. As a further inconvenience, a high MC strongly reduces the heating value [13], increasing the biomass required for the same energy output. Additionally, when stored in open yards the biomass is exposed to uncontrollable factors (e.g. rain, wind, etc.) that generally lead to MC increase [14,15], but may also dry the stocked fuel if the conditions are favorable [16].
Investigation on woodchip quality with respect to ISO standards and relationship among quality parameters
2020, FuelCitation Excerpt :Table 3 reports the general descriptive statistic carried out on all woodchip samples after removing the outlier samples. The results highlight that woodchip quality is in line or slightly better with respect to the previous study carried out by the authors in the 2007–2013 period [20]. Because of the importance of M and A parameters for the assessment of woodchip quality, the results have been disaggregated for different A and M content ranges.