{"id":117,"date":"2010-02-18T22:42:49","date_gmt":"2010-02-19T04:42:49","guid":{"rendered":"http:\/\/beta.solidshandlingtech.com\/?p=117"},"modified":"2017-11-10T14:02:17","modified_gmt":"2017-11-10T14:02:17","slug":"requirements-for-biomass-sampling","status":"publish","type":"post","link":"https:\/\/solidshandlingtech.com\/?p=117","title":{"rendered":"Requirements for Biomass Sampling"},"content":{"rendered":"

Requirements for Biomass Sampling<\/span>
\n<\/span><\/strong>Guest article by Paul Janze, Sandwell Engineering<\/span><\/span><\/h2>\n

Introduction<\/strong><\/span><\/p>\n

\"\"With the current emphasis on the use of biomass for `green\u2019 energy purposes, the importance of having good quality `hog fuel\u2019, cannot be over-emphasized. And to ensure good quality fuel, good sampling procedures must be followed.<\/span><\/p>\n

Woody biomass in chip form has been utilized by the pulp and paper industry for many decades and chip quality has long been recognized as having an important effect on pulp quality; to make good pulp you need good chips. Likewise for a biomass-fired plant to operate efficiently, it needs a reliable, constant supply of consistent quality fuel.<\/span><\/p>\n

Good quality control relies on proper sampling, which must be accurate and precise and truly represent the main body of biomass. Without good sampling, quality control is based on false information. Bulk materials are difficult to sample properly on a production basis. Manual sampling can be done but it is labor intensive, prone to errors and does not easily fit into a production environment.<\/span><\/p>\n

Collecting samples of biomass is one task not always done well, and unless the sample is taken properly, it will not be a true representation of the main product flow.<\/span><\/p>\n

Biomass is not easy to sample. It appears in a myriad of species, forms and sizes; it knits together, doesn\u2019t flow well, consolidates and packs easily; it can have a wide range of moisture contents, basic and bulk densities and calorific values; it will freeze; it is very dusty, catches fire easily and is self-combustible; it can contain all manner of contaminants; it can be quite fragile and care must be taken not to degrade the material.<\/span><\/p>\n

To be of value, biomass samples need to be unbiased, accurate, precise and representative of the main lot or consignment of material.<\/span><\/p>\n

The intent of this paper is to summarize the requirements that must be met in order to provide representative chip sampling and to do so in an easily understood and achievable manner. This paper does not consider chip classification or analysis.<\/span><\/p>\n

1.\u00a0 Features of Good Sampling<\/strong><\/span><\/p>\n

Accuracy – is the ability to obtain samples which represent the true nature of the material supply.<\/span><\/p>\n

Precision – is a statistical term relating to the number of samples taken from a lot or consignment.<\/span><\/p>\n

Biomass is a highly variable product and requires a large number of samples in order to establish sampling precision.\u00a0 Precision can only be increased by increasing the number of spot samples.<\/span><\/p>\n

A single spot sample generally is less likely to be representative of the main body of biomass than is a gross sample, which is a mixture of multiple spot samples.<\/span><\/p>\n

2.\u00a0 Sampling Bias<\/strong><\/span><\/p>\n

Poor sampling can induce systematic errors that skew the results. Two common errors are:<\/span><\/p>\n

    \n
  1. Spot samples are taken where certain properties are over-represented. eg. \u2013 at tail-gate of a truck where fines have settled to the bottom.<\/span><\/li>\n
  2. The sample device is not capable of taking a representative sample. eg. \u2013 the sample device is too small and either rejects large pieces or overflows.<\/span><\/li>\n<\/ol>\n

    Properly designed, operated and maintained automatic samplers can minimize systematic sampling bias.<\/span><\/p>\n

    Fractionation<\/span><\/p>\n

    Fractionation or particle separation can occur from the way in which biomass is loaded \/ stacked and the way in which it is transported. eg. \u2013 fines will settle down to the bottom of a biomass truck over a long haul.<\/span><\/p>\n

    Additionally, fractionation can be produced by the sampling device itself; either by rejecting oversize pieces, failing to pick-up small particles, selectively picking up small particles, or breaking up particles by the sampling motion itself.<\/span><\/p>\n

    Stationary material is not uniform due to fractionation where material stratifies according to size. In order to get a representative gross sample from stationary material, a very large number of increment or spot samples are required.<\/span><\/p>\n

    3.\u00a0 Classification of Sampling Techniques<\/span><\/strong><\/span><\/p>\n

    The quality of the sample depends upon the amount of human discretion involved, the sampling conditions, and the sampling location and timing.<\/span><\/p>\n

      \n
    1. Generally, those samples which do not involve human discretion are more accurate.<\/span><\/li>\n
    2. Accepted sampling conditions, include:<\/span><\/li>\n<\/ol>\n