THE STANDARDS FOR BIOMASS SUPPLY CHAIN RISK

4.1.1 CONSISTENCY OF FEEDSTOCK QUALITY REQUIREMENTS WITH LOCAL AVAILABILITY

Rationale

If specifications of biomass feedstock do not reflect what is currently or historically produced in the supply basin, supply chain resiliency decreases and risk increases.

Reporting

Reporting Requirements

  1. Proponent feedstock specifications shall be consistent with feedstock quality widely available in the supply basin.

 

Reporting Recommendations

  1. Where feedstock specifications are not typical, mitigating factors shall be demonstrated.
Guidance

Guidance for Reporting Requirements 1

Suppliers often supply more than one market and, despite contracting for a stricter specification, may deliver traditional feedstock specifications (i.e., sub-standard) that are acceptable for existing markets. That is, some suppliers may believe that the Proponent will in fact tolerate the typical regional specification despite written contract specifications to the contrary.

Thermochemical and biochemical refineries have different requirements for the quality of feedstock used for producing fuels or energy. Quality parameters include ash, moisture and hydrocarbon contents (e.g., sugar, lignin, etc.). Current fast-pyrolysis and hydrotreating biofuel facilities require feedstock with low ash content (~0.9%, on a dry basis), 30% moisture content and ~50% hydrocarbons (Jones et al. 2013). For biochemical conversion of feedstocks to biofuels, current designs require 5% ash content on a dry basis, 20% moisture content, and total structural carbohydrates at 59% (Davis et al. 2013).

As technologies develop, these requirements will get more specific and optimal quality range parameters will become clearer. It is important for a Proponent to be aware of changing requirements and compare them to the available feedstock quality parameters.

Guidance Source

Abt (2018, interview); Davis et al. (2013); Jones et al. (2013); Muth (2017, interview); Spikes (2017, interview); Smith (2017, interview); Tumuluru (2016)

4.1.2 DENSIFICATION AND PRE-PROCESSING

Rationale

Non-homogeneity of feedstock can be a major risk during plant scale-up. Densification and pre- processing of feedstock can de-risk scale-up by reducing feedstock variability through size reduction, drying, ash removal, densification, pelletization, or other unit operations to convert to feedstock or required quality, shape and other specifications.

Projects relying upon pre-processing (particularity in the form of pellets with consistent physical and chemical properties and high durability) have fewer quality, homogeneity and flowability issues.

Reporting

Reporting Requirements

  1. The type of pre-processing and densification used shall be identified (i.e., baling, pelletizing or briquetting), including whether densification or pre-processing is done by suppliers or Proponent, and the types of equipment used.
  2. Proponent shall verify steady operation of all steps of the pre-processing operation at scale.
  3. The bounds of variability of key quality specification variables post-pre-processing or densification shall be identified.
  4. The ratio of densified or pre-processed feedstock to natural feedstock shall be determined and such ratios shall be shown to be suitable and appropriately applied to the Proponent.
Guidance

Guidance for Reporting Requirement 3

Densification has been tested for numerous feedstocks with different physical and chemical properties at Idaho National Laboratory (INL) (Tumuluru 2018). Results are available to the public.

Guidance Source

Solomon (2019, interview); (Tumuluru (2018, interview)

4.1.3 FEEDSTOCK DEGRADATION

Rationale

Dry matter is important for bio-processes and losses of such typically results in lower product quality or less product being produced. Incorrect or insufficient information on feedstock degradation during storage can lead to the overestimation of quantities, quality or cost of available feedstock.

Reporting

Reporting Requirements

  1. Proponent shall demonstrate understanding of dry matter losses in feedstock during storage.

Reporting Recommendations

  1. If feedstock is stored at suppliers’ facilities, an understanding of suppliers’ storage methods and its effect on feedstock degradation should be demonstrated.
Guidance

Guidance for Reporting Requirement 1

In general, feedstock stored indoors has a lower rate of degradation than feedstock stored outdoors.

Agricultural Residues. Historical data indicate that corn stover stored outdoors results in higher dry matter losses than when stored indoors, with considerable variability depending on moisture content and storage conditions. Richey et al. (1982) reported dry matter loss increases from 10% up to 23% upon outdoor storage of baled stover. Shinners et al. (2007) reported average dry matter losses of 3.3% for dry stover bales stored indoors and 18.1% for dry stover bales stored outdoors after 8 months, with that figure adjusting to 10.0%, 13.9% and 30.4% when bales were stored outdoors using net wrap, plastic twine and sisal twine, respectively. Emery and Mosier (2012) summarize dry matter losses from a number of publications and report that among baled hay and corn stover stored indoors, the dry matter losses were consistently less than 6% compared to losses between 10% and 20% from bales stored outdoors and baled under a 20% moisture threshold. Occasionally, losses are reported as high as 35-40%. They also summarize the results from various studies statistically into percentile values for indoor and outdoor dry storage. Shah et al. (2011) report dry matter losses from bales stored outdoors of 5-11% and 14-17%, with tarp and breathable film covers, respectively.

Shinners et al. (2007) report about 3% loss in ensiled storage of wet stover. Emery and Mosier (2012) summarize the dry matter losses from wet storage using data from multiple studies into distribution with a 90% confidence interval of 2.8% and 20.6%, and a median of 7.8%.

Athmanathan (2013) provides a detailed analysis of experimental results on the impacts of moisture content and temperature on dry matter loss from corn stover, switchgrass and sweet sorghum bagasse. His research indicated threshold temperatures and moisture contents below which there was little degradation. It also showed that increasing temperatures up to 35°C resulted in increased dry matter loss along with increases in moisture content above 20%.

Feedstock degradation in storage can be mitigated by a plant’s ability to procure feedstock just- in-time. This requires maximizing the time in a year during which feedstock can be harvested and delivered to the plant. This can be achieved through expanding harvesting seasons by allowing a mix of feedstock types (e.g., agricultural with woody materials), or processing feedstock that can be harvested year-round.

Energy Crops. Mooney et al. (2012) estimated dry matter losses for switchgrass, canary grass and sorghum from multiple sources. For outdoor storage of switchgrass, they report dry matter loss from 8.2-13.0%; for canary grass and switchgrass, 15%; for sorghum and switchgrass, 8.2-13.0%; and for sorghum 18%. For indoor storage, they report dry matter loss for switchgrass of less than 2%-3%; for canary grass and switchgrass, 3%; for sorghum and switchgrass, 4.7-5.6%; and for sorghum 10%. For switchgrass stored in rectangular bales in Tennessee, they report 90.8% dry matter loss outdoors and 15% indoors

Guidance Source

Athmanathan (2013); Dujmovic (2019, feedback); Ebadian et al. (2011); Emery & Mosier (2012); Gebreslassie et al. (2012); Lamers et. al. (2015a); Mooney et al. (2012); Nguyen (2017, interview); Richey et al. (1982); Shah et al. (2011); Shinners et al. (2007)

4.1.4 QUALITY MEASUREMENT METHODS

Rationale

In order to understand feedstock quality; moisture content, ash content and other specifications have to be measured accurately. Measurements need to be based on recognized testing and sampling procedures which should be specified and followed by the Proponent.

Reporting

Reporting Requirements

  1. Feedstock quality sampling and measurement methods shall be clear and consistent with industry standards.

 Reporting Recommendations

  1. Suppliers’ acceptance of sampling and measurement methods shall be demonstrated.
Guidance

Guidance for Reporting Requirement 1

Three general categories of sampling and measurement techniques have been developed by Idaho National Laboratory (INL). The first methods use cylindrical core samples from bales, however this constitutes an invasive process. The second method uses a probe to directly measure and report moisture at different locations within a bale. The third process uses microwaves to obtain moisture distributions at a resolution of one inch.

 Agricultural Residue and Energy Crops. It is important to know both the average values for various biomass quality parameters (e.g., moisture and ash content) as well as the variances from the averages in a consignment of bales. However, inherent heterogeneity associated with moisture and ash content distributions within bales makes this difficult. Moisture content can change as climatic conditions such as humidity and temperature influence the moisture movement and evaporation/condensation processes differentially. Therefore, the credibility of sampling and measurement techniques is critical.

Guidance Source

Abt (2018, interview); Smith (2017, interview); Spikes (2017, interview)

4.1.5 GEOGRAPHIC LOCATION INFLUENCE ON FEEDSTOCK VARIABILITY

Rationale

Feedstock from different regions may differ in quality due to variations in soil quality, topography, harvest practices, weather, fertilizer applied, etc.

Reporting

Reporting Requirements

  1. Proponent shall demonstrate understanding of geographic regions from which feedstock will be sourced, and the effect on feedstock quality.
Guidance

Guidance for Reporting Requirement 1

Because of the variability associated with supply from multiple regions, blending or pre- processing may be required to attain the desired raw material specifications.

Variability in herbaceous feedstock quality parameters is typically much higher than in woody feedstocks. Blending of herbaceous materials to produce a single feedstock with a narrow range of desired quality parameters is therefore a bigger challenge than with woody feedstocks.

Guidance Source

Spikes (2017, interview); Swan (2018, interview)

4.2.1 VARIABILITY IN MOISTURE CONTENT

Rationale

Some degree of moisture content variability is unavoidable. Accurate bounds of moisture variation within feedstock should be known. Feedstock with high moisture variation can pose a risk of fire, as well as create operational risks associated with delayed processing (e.g., grinding and/or clogging).

Reporting

Reporting Requirements

Proponent shall demonstrate understanding of:

  1. Moisture content variation typical in available feedstock
  2. Factors that influence moisture content variability
  3. Mitigation strategies to control impact of moisture content variation.
Guidance

Guidance for Reporting Requirement 1

Proponent should determine upper and lower limit of acceptable moisture content in feedstock. Cross-reference these limits with feedstock moisture content data acquired from sampling. The vast majority of the variation (i.e., 95-99%) should be within the upper and lower limit (Ecostrat 2017).

INL’s Bioenergy Feedstock Library (BFL) and ORNL’s Knowledge Discovery Framework (KDF) are valuable resources to understand the spatial and temporal variabilities in moisture content and other properties of feedstock.

Main factors affecting moisture content variability are harvest timing, age, type of biomass, region of origin, water availability and irrigation practices.

Guidance for Reporting Requirement 2

The integrity of the tarps used to cover feedstock during storage is important. Tarps are prone to friction and damages due to atmospheric conditions. Using a high-quality tarp lowers the risk of tarp damage and therefore moisture movement throughout the bale.

Guidance for Reporting Requirement 3

Driers on Proponent site are effective mitigants against moistures risks.

Guidance Source

Ecostrat (2017); Nguyen (2017, interview); Smith (2017, interview); Spikes (2017, interview); Tumuluru (2016); Webster (2017, interview)

4.2.2 VARIABILITY IN ASH CONTENT

Rationale

Some degree of ash content variability is unavoidable. Accurate bounds of ash variation within feedstock should be known. Feedstock with high ash variation can pose a risk of throughput requirements as well as additional costs associated with removing ash from the system.

Reporting

Reporting Requirements

Proponent shall demonstrate understanding of:

  1. Typical ash content variation in available feedstock
  2. Factors that influence ash content variability
  3. Mitigation strategies to control impact of ash content variation.
Guidance

Guidance for Reporting Requirement 1

Proponent should determine upper and lower limit of acceptable moisture content in feedstock. Cross-reference these limits with feedstock moisture content data acquired from sampling. The vast majority of the variation (i.e., 95-99%) should be within the upper and lower limit (Ecostrat 2017).

INL’s Bioenergy Feedstock Library (BFL) and ORNL’s Knowledge Discovery Framework (KDF) are valuable resources to understand the spatial and temporal variabilities in ash content and other properties of feedstock.

Guidance for Reporting Requirement 3

Consistent low ash content in harvested biomass can be maintained by using methods such as washing, leaching and acid or alkali pretreatment. Limitations of these pre-processing steps can be associated with equipment and chemical costs, but these costs can be offset by reducing the operational costs of bio-refineries because the pre-treatments can result in lower maintenance costs (Tumuluru et al. 2016b).

Guidance Source

Ecostrat (2017); Spikes (2017, interview); Tumuluru et al. (2016a); Tumuluru (2016)

4.2.3 VARIABILITY IN PARTICLE SIZE

Rationale

Some degree of particle size variability is unavoidable. Accurate bounds of particle size variation within feedstock should be known. Large variations in particle size and texture result in the need for multiple size reduction techniques.

Reporting

Reporting Requirements

Proponent shall demonstrate understanding of:

  1. Size variation typical in available feedstock
  2. Factors that influence size variability
  3. Mitigation strategies to control impact of size variation.
Guidance

Guidance for Reporting Requirement 1

Proponent should determine upper and lower limit of acceptable particle size in feedstock. Cross- reference these limits with feedstock particle size data acquired from sampling. The vast majority of the variation (i.e., 95- 99%) should be within the upper and lower limit (Ecostrat 2017).

Feedstock plant species, management practices and time of harvest play significant roles in controlling the shape and size of particles supplied as feedstock. INL’s Bioenergy Feedstock Library (BFL) and ORNL’s Knowledge Discovery Framework (KDF) are valuable resources to understand the spatial and temporal variabilities in particle size and other properties of feedstock.

Guidance for Reporting Requirement 3

Variability in particle size arise from multiple sources and multiple locations along the supply chain. Screeners and grinders on Proponent site are effective mitigants against sizing risk.

Alternative to pelletization, particularly for herbaceous biomass, is the use of unit operations such as drying and grinding. These operations can be used to produce particles with desired maximum sizes. However, the size distribution below the maximum size could still have large variability and therefore pose multiple challenges at bio-refineries.

Guidance Source

(Tumuluri 2018, interview)

4.2.4 VARIABILITY IN CHEMICAL CONTENT

Rationale

Some degree of variability in the chemical content of feedstock is unavoidable. Accurate bounds of chemical content variation within feedstock should be known. High variability in chemical contents in feedstock (e.g., lignin, carbohydrates, sugar, etc.) increases the likelihood that feedstock will not be optimal for a conversion process.

Reporting

Reporting Requirements

Proponent shall demonstrate understanding of:

  1. Chemical content variation typical in available feedstock
  2. Factors that influence chemical content variability
  3. Mitigation strategies to control impact of chemical content variation.
Guidance

Guidance for Reporting Requirement 1

Carbohydrate and lignin content are important in the conversion of lign-cellulosic material into biofuels through biochemical conversion processes. While carbohydrates are converted to biofuels, lignin functions as a recalcitrant. In thermochemical conversion, both lignin and carbohydrates are available for thermal conversion and power production.

INL’s Bioenergy Feedstock Library (BFL) and ORNL’s Knowledge Discovery Framework (KDF) are valuable resources to understand the spatial and temporal variabilities in chemical content and other properties of feedstock.

Guidance for Reporting Requirement 3

Pelletization can have a positive effect on the control of feedstock chemical content variability.

Guidance Source

Dujmovic (2019, feedback); Tumuluru et al. (2016a); Tumuluru (2016)

4.2.5 FEEDSTOCK BALE DENSITY

Rationale

High density bales of feedstock can decrease transportation costs, but density can cause problems during pre-processing. Bale density has been linked with feedstock issues such as low flowability, clogging, slow-down and equipment shut downs, particularly when it is associated with high moisture and/or ash contents. It has also been linked to sampling issues when probe samples cannot pierce bales due to high density.

Reporting

Reporting Requirements

  1. Risks related to feedstock bale density shall be assessed and an optimal bale density established.
  2. Availability of feedstock at optimal bale density shall be established.
Guidance

Guidance for Reporting Requirement 1

Bale density has an impact on road weight; the higher the density, the heavier the road weight. Most regions have upper weight limits on roads. If bale density causes trucks to exceed weight limits, or to run at less than cubic capacity, then bale density should be re-examined.

Guidance Source

Spikes (2017, interview)