Method and apparatus for estimating the ash content of a biological material

1. A method for estimating ash contents in a biological material, comprising steps of:

scanning the biological material with X-ray radiation of at least two different energy levels;

determining an amount of X-ray radiation transmitted through a sample of the biological material at the at least two different energy levels;

estimating a moisture content in the biological material based on a relationship between the determined amount of X-ray radiation transmitted through the biological material at the energy levels; and

estimating the ash content in the biological material, based on the estimated moisture content in the biological material, average attenuation coefficients for the biological material without moisture, attenuation coefficients for a combustible part of the biological material, and attenuation coefficients for ash of the biological material at the energy levels;

wherein the moisture content of the sample of the biological material is determined by determination of a K-value for the biological material, the K-value being calculated as:

K

=

ln

⁡

(

N

01

/

N

1

)

ln

⁡

(

N

02

/

N

2

)

wherein N01, N02 are calibrated reference values for transmission at the at least two different energy levels and N1, N2 are transmission values through the biological material at the energy levels, and the estimating of the moisture content of the biological material is done by comparing the calculated K-value with corresponding K-values for a similar material type.

2. The method of claim 1 , further comprising a step of determining the attenuation coefficient for moisture at the energy levels by reference measurements.

3. The method of claim 1 , further comprising a step of determining the attenuation coefficients for a combustible part of the biological material and the ash of the biological material at the energy levels by reference measurements.

4. The method of claim 1 , wherein the scanning of the biological material with X-ray radiation of the at least two different energy levels comprises arranging the biological material in a separated form.

5. The method of claim 4 , wherein the separated form is in the form of chips.

6. The method of claim 5 , wherein the method comprises at least one X-ray radiation source for each specific energy level.

7. The method of claim 6 , wherein there is provided at least one detector for each specific energy level.

8. The method of claim 1 , wherein the scanning of the biological material with X-ray radiation of the at least two different energy levels comprises arranging the biological material in a sample container.

9. The method of claim 1 , wherein the scanning of the biological material with X-ray radiation of the at least two different energy levels comprises scanning the biological material as it is continuously conveyed through a point of measure.

10. The method of claim 1 , wherein the amount of X-ray radiation transmitted through the sample of the biological material at the at least two different energy levels is determined in relation to a calibration reference value.

11. The method of claim 10 , wherein the calibration reference value is determined by measurement of the transmission of X-ray radiation through a reference material of a predetermined thickness, the calibration measurement being made immediately before and/or after each measurement through the biological material.

12. The method of claim 1 , wherein the scanning of the sample of the biological material with X-ray radiation of the at least two different energy levels comprises a first scan with a first energy level, and a subsequent second scan with a second energy level.

13. The method of claim 1 , wherein the at least two different energy levels both are of X-ray radiation wavelengths.

14. The method of claim 1 , wherein the X-ray radiation of both the energy levels are emitted from a single X-ray radiation source operating in an energy range of about 20-150 kVp.

15. The method of claim 1 , wherein a reference material is aluminum.

16. An apparatus for estimating ash contents in a biological material comprising:

a scanning device for scanning a sample of the biological material with X-ray radiation of at least two different energy levels;

a detector for determining an amount of X-ray radiation transmitted through the sample of the biological material at the at least two different energy levels; and

a processor programed to estimate the moisture content in the biological material based on determined amounts of radiation transmitted through the sample, estimate ash content in the biological material, based on the estimated moisture content and average attenuation coefficients for the biological material without moisture, attenuation coefficients for a combustible part of the biological material, and attenuation coefficients for the ash content of the biological material at the energy levels, wherein the moisture content of the sample of the biological material is determined by determination of a K-value for the biological material, the K-value being calculated as:

K

=

ln

⁡

(

N

01

/

N

1

)

ln

⁡

(

N

02

/

N

2

)

wherein N01, N02 are calibrated reference values for transmission at the at least two different energy levels and N1, N2 are transmission values through the biological material at the energy levels, and the estimating of the moisture content of the biological material is done by comparing the calculated K-value with corresponding K-values for a similar material type.

17. The apparatus of claim 16 , wherein there are provided at least two detectors for determining the amount of X-ray radiation transmitted through the sample of the biological material at the energy levels.