4.2 Lignite Specification
4.2.1 Calorific Value
The heating value of the lignite deposit is the most prominent lignite quality parameter as it determines very decisively the economic value of the lignite deposit. It is dependent on the ash content, moisture content, and increasing ligniteification with depth. As the ash content increases, the calorific value decreases.
The distribution of calorific values in the Hongsa deposit is rather different from seam to seam. In the C-seams the heating value tends to increase to the east. The B-seams show extreme low values of around 1,500 kcal/kg in the very west and in some parts to the south, while in the other areas the heating values are mostly somewhat above and below 2,000 kcal/kg. The A-seams are low in heating value in large areas to the west and south (around 1,300 kcal/kg) and relatively high to the east (around 2,000 kcal/kg).
The gross as received (“a.r.”) heating value of the Hongsa lignite deposit in the 11.25 km2 Planned Mine Area is 2,446 kcal/kg (a.r.), slightly better than the 2,430 kcal/kg (a.r.) parameter that the Power Plant was designed to operate on.
4.2.2 Ash Content
Ash distribution within the different seams is somewhat random. C-seams show higher ash contents to the west. Especially C3-seams have extreme high ash contents in that region with more than 45%. The B seams show relative low lignite ash in the centre and to the northeast with values around 20% while especially in the west and south ash values exceed 30%. A-seams are low in ash to the east (20%-25%) and high to the south and west (35%-45%). The ash content of the lignite deposit at Hongsa in the 11.25 km2 Planned Mine Area has an average value of around 26.27%.
4.2.3 Moisture Content
To compensate for the inaccuracies introduced during the transportation of the lignite to the laboratory, an ash-moisture regression analysis was used to reliably generate the in-situ moisture data of the Hongsa lignite. This approach also guarantees that the heating value of the lignite samples are not inflated from the rather low moisture content lignite samples from previous explorations. The Hongsa lignite samples tested shows that as ash content increases, the moisture content decreases.
C-seams and A-seams show high moisture contents to the east with values around 35%, while in the B-seams relative high moisture contents are present in the centre and to the northeast. The average moisture content of the Hongsa lignite in the 11.25 km2 planned Mine area is around 35.03% which is slightly better than the 35.4% lignite moisture parameter that the Power Plant specified.
4.2.4 Sulphur Content
The forms of sulphur found in lignite vary from sulphate sulphur, pyritic sulphur, or organic sulphur. The pyritic sulphate and organic sulphate contents must be taken into account in the design of the desulphurisation facility of the Power Plant as SO2 is formed in their combustion. The concentrations of each sulphur form found in the Hongsa lignite sample are sulphate sulphur 0.11%, pyritic sulphur 0.15%, and organic sulphur 0.45%. The average sulphur content of the Hongsa lignite is 0.71%.
There are variations in the sulphur content of each seam. The C-seams are relatively low in sulphur with values around 0.6%. The B-seams show a trend of increasing sulphur values from the southeast to the west. Especially in the west the sulphur values reach magnitudes of around 1.4%, while in the southeast only about 0.5%-0.6% could be detected. The A-seams are characterised by relative high sulphur contents in large areas to the northeast with values from around 1.0%-1.8%. The average sulphur content of the Hongsa lignite in the 11.25 km2 Planned Mine Area is around 0.67%.
The followings are parameters that are specifically relevant to the Power Plant.
Summary of the Hongsa Lignite Quality in the Planned Mine Area
|Gross Heating Value(a.r.)|