Biomedical Engineering Reference
In-Depth Information
2.6
Ash
In plants, except for carbon, hydrogen, oxygen, and other basic elements, there
are many kinds of other elements that are indispensable materials in living plant
cells, such as nitrogen, sulfur, phosphorus, calcium, magnesium, iron, potassium,
sodium, copper, zinc, manganese, chlorine, and more. When the sample is dried at
105
ı
C and further processed at 750
ı
C in a high temperature furnace, elements
such as carbon, hydrogen, oxygen, nitrogen, sulfur, etc. disappear in the form of
gaseous compounds, and the residue is the ash which contains many types of mineral
elements in the form of oxide. Different types of plants and growth environment
would lead to different types and contents of elements. These elements are absorbed
from soil and generally exist as ions. It is well known that different parts (organs) of
the plants have different functions in the process of plant growth, causing different
distributions of metal ions. Residues from reed and bamboo are mainly parenchyma
cells. Table
2.2
shows that, except Mn and Fe, the content of other metal elements
in the residues of reed and bamboo are all significantly higher than those of wheat
and bagasse. In the process of standard sieve-screening classification of bagasse,
with the increase of the mesh number, the particle size becomes finer, the fiber
content is reduced, the content of parenchyma cells increases (cells through the 80
mesh are mainly parenchyma cells), and the metal contents rapidly increase. The
metal elements and silicon content in the joints, leaves, and ears of wheat straw are
significantly higher than in the internode stem [
2
].
In the combustion process, a small part of the mineral elements may also be
lost through gasification. The content and elemental proportion of ash vary with the
varieties of raw materials, the kind of plant organs, the age of the plants, and so
on. The elements in the growth environment of the plant would also have influence
on the content and elemental composition of ash. Generally, wood has a low ash
content, usually less than 1 % (the majority have 0.3-0.5 %, dry raw material). The
Table 2.2
Comparison of metal ion contents from several grass families [
2
]
Sample
Mn
Cu
Fe
Ca
Mg
Al
Na
Si
Co
Ni
Reed
Reed chip
460:2
9:9
481:4
1,569
625
763
134
9,413
<
0.1
<
0.2
Reed residue
305:2 102:2
243:9
4,285 1,569
1;628
805
24,285
<
0.1
12.1
Bamboo Bamboo chip
251:3
2:5
36:4
593
440
39:1
21
8,674
<
0.1
0.5
Bamboo residue
379:8
11:1
2;181:9
2,901 1,110
353
98
17,810
0.5
4.7
Wheat
Internode stem
9:1
5:4
64
2,325 1,535
63:3 122
14,005
<
0.1
1.78
Joint
16
4:27
106
3,995 3,937
170:9 294
17,827
<
0.1
1.61
Leaf
40
4:61
329
5,061 4,376
54:1 357
4,032
<
0.1
2.35
Panicle
30
3:0
279
1,421 1,421
662:5 132
19,422
<
0.1
1.21
Bagasse
>
20 mesh
65
4:4
90
582 1,060
71:9
44
2,644
<
0.1
0.56
20/40 mesh
98
6:3
267
929 1,490
204:4
57
7,366
<
0.1
0.65
40/80 mesh
161
19:1
547
1,124 1,895
360:4
68
11,551
<
0.1
0.78
Over 80 mesh
312
118:1
3;004
3,084 3,075
138
209
4,408
<
0.1
9.08
