| Front page | | Contents | | Previous
| | Next |
Mass Flow Analysis of Chromium and Chromium Compounds
Chromium occurs as a trace constituent in a wide range of raw materials and products.
The most significant of these are;
![](../../_themes/nyt-milj-/dot.gif) | Fossil fuels coal and oil |
![](../../_themes/nyt-milj-/dot.gif) | Aluminium see section 2.2 |
![](../../_themes/nyt-milj-/dot.gif) | Copper see section 2.3 |
![](../../_themes/nyt-milj-/dot.gif) | Cement |
Here, we focus on chromium as a trace constituent in fossil fuels and cement.
Fossil fuels like oil and coal contain a number of heavy metals, including chromium.
The average contents are shown in Table 4.1. If we base our calculations on an annual
consumption of oil and coal of 182 PJ/year and 386 PJ/year, respectively, in 1999 plus
residual product quantities from Danish CHP plants, we can establish a balance for
chromium as a trace constituent in fuels; see Table 4.1. The figures on fuel quantities
describe the gross energy consumption and cover all kinds of coal and oil products. Coal
is, however, primarily used at CHP plants, which means that the residual product
quantities come mainly from coal.
Table 4.1
Balance for chromium as a trace constituent in fuels
|
Quantity5
(tonnes) |
Quantities used
(GJ) |
Chromium concentration
(mg Cr/tonne) |
Emissions factor6
(mg Cr/GJ) |
Chromium quantities
(tonnes chromium) |
Coal1 |
|
182 x 106 |
32 |
802 |
146 |
Oil2 |
|
386 x 106 |
0.055 |
2.21 |
0.85 |
Flue gas3 |
|
|
|
4.33/4.017
0.72/0.668
0.809 |
3.510 |
Fly ash11 |
795 x 103 |
|
78,000230,000 |
|
62183 |
TASP4 |
50 x 103 |
|
|
|
|
Plaster |
366 x 103 |
|
|
|
|
Slag, etc.11 |
72 x 103 |
|
15,00021,000 |
|
1.11.5 |
|
|
1 |
The total quantity of coal used in Denmark. |
2 |
The total quantity of oil used in Denmark. |
3 |
The consumption of coal and oil for energy conversion
(heat and electricity generation) has been calculated to be 185 x 106 GJ coal
and 48 x 106 GJ oil products (The Danish Energy Authority, 2000). In addition
to this, 12 x 106 GJ coal are used directly by production industries, i.e.
without any special flue-gas treatment facilities, and 318 x 106 GJ oil
products are used directly by households and businesses or for transport. |
4 |
Dry desulphurisation product. |
5 |
The residual product quantities constitute 99% of the
quantities produced (The Danish EPA, 2000) |
6 |
Illerup et al. (1999). |
7 |
Emission factors after electro filter and
desulphurisation plant for coal (semi-dry/wet flue gas cleaning). |
8 |
Emission factors after electro filter and
desulphurisation plant for oil (semi-dry/wet flue gas cleaning). |
9 |
Emission factor after SNOX facility for coal. |
10 |
For other combustion of oil, it is assumed that 50% of
the chromium contents are emitted to air. For other combustion of coal, it is assumed that
25% of the chromium contents are emitted to air. |
11 |
Chromium contents in fly ash and slag (ELSAM, 2002). |
A total 0f 99% of the residual products are reused in a wide range of products, e.g.
cement, concrete, lightweight concrete, asphalt, etc. The remaining 1% is sent to
landfills.
It is a well-known fact that cement can contain quite a lot of chromium. To ensure a
safe working environment, there are rules for the content of Cr(VI). In all likelihood,
chromium in cement probably comes from raw materials from specific areas, from coal used
during firing, and from fly ash used as part of the cement. During the period
19982000, Aalborg Portland used 225,171 tonnes coal each year and 187,350 tonnes of
petroleum coke/year on average (Aalborg Portland, 2001a). The chromium content of coal
varies, but is often 32 mg Cr/tonne (ELSAM, 2002). If we assume that coal and petroleum
coke have the same chromium content, we arrive at a Cr input of 0.013 tonnes Cr/year.
During the period, an average of 204,819 tonnes fly ash/year were used. Fly ash from
CHP plants contains 78230 mg chromium/kg (ELSAM, 2002). This corresponds to chromium
contributions to cement of 1647 tonnes/year.
The other raw materials used to make cement, chalk and sand, are not expected to
contain large amounts of Cr. Analyses carried out at Aalborg Portland show that their
"Basis" cement contains 32 ppm Cr-total, of which 56 ppm is chromate
Cr(VI). Other types of cement white cement and low-alkali cement often have
lower contents of Cr(VI) << 2 ppm. It is, however, assumed that the same
relationship between total Cr and Cr(VI) applies (Cementfabrikkernes tekniske
Oplysningskontor, 2002a).
Approximately 1.5 million tonnes of cement are used in Denmark each year. Aalborg
Portland sells 1.3 million tonnes of cement on the Danish market each year and exports
5600,000 tonnes, particularly to the USA (Cementfabrikkernes tekniske
Oplysningskontor, 2002a).
During the period 19982000, the average production at the Aalborg factory was as
follows; 2,487,123 tonnes cement/year, 145,963 tonnes clinker/year, and 3,450 tonnes
filler/year (Aalborg Portland, 2001a). According to Statistics Denmark, the total quantity
of cement produced in Denmark during this period was 2,622,168 tonnes/year on average.
This is to say that almost all of this cement was produced at Aalborg Portland. As a
result, their figures on chromium contents are used for general purposes.
The total quantities of cement produced are divided into grey cement and other cement.
In 2001, Aalborg Portland produced 2.1 million tonnes grey cement (Aalborg Portland,
2001b). As the total production figures were more or less identical for 1999 and 2001, it
is estimated that 2.1 million tonnes of the cement produced in 1999 are also grey cement.
The rest (2,622,168 2,100,000 = 522,168 tonnes) is assumed to be of a kind with
lower contents of chromium (white cement, low-alkali cement). The actual chromium content
is not known, but the content of Cr(VI) is much less than 2 mg/kg. If the content is set
at 0.21 mg Cr(VI)/kg, this leads to chromium quantities of 0.100.52 tonnes
Cr(VI)/year and 0.63.0 tonnes Cr(III)/year.
Production of 2,100,000 tonnes grey cement/year containing 32 mg Cr/kg yields 67.2
tonnes Cr/year. Of this amount, 10.512.6 tonnes are Cr(VI). As far as possible,
Cr(VI) is reduced to Cr(III) by adding Fe(II); this reduces the concentration of Cr(VI) to
less than 2 ppm. Thus, production of 2,100,000 tonnes grey cement/year containing 12
mg Cr(VI)/kg yields 2.14.2 tonnes Cr(VI)/year and 63,065,1 tonnes
Cr(III)/year.
Table 4.2
Supply of cement (19982000) according to Statistics Denmark
CN uh |
Product |
Import
tonnes/ year |
Export
tonnes/ year |
Production
tonnes/ year |
Supply
tonnes/ year |
25232900 |
Portland cement |
221,581 |
530,696 |
1,951,783 |
1,642,668 |
25231000 |
Portland cement, clinker (cement
clinker) |
127 |
106,326 |
111,367 |
5,168 |
25232100 |
Portland cement, White cement |
8,150 |
527,244 |
550,178 |
31,084 |
25233000 |
Portland cement, Aluminate cement |
3,010 |
15 |
0 |
2,994 |
25239010 |
Clinker cement |
1 |
11 |
0 |
10 |
25239090 |
Hydraulic cement |
17,799 |
47,837 |
27 |
30,012 |
|
Total cement |
250,667 |
1,212,130 |
2,613,345 |
1,651,883 |
Chromium occurs as a trace constituent in, for example, fossil fuels coal and
oil and in cement as a result of the use of coal and residual products from energy
production in connection with cement production. Table 4.3 shows the estimated consumption
and dispersal of chromium.
Table 4.3
Estimated consumption and dispersal of chromium associated with chromium as a
trace constituent in Denmark
Use |
Con- sumption
tonnes Cr/year |
Air |
Water |
Soil |
Reuse |
Dangerous waste |
Waste treatment |
Coal and oil |
147 |
3.5 |
|
|
621852 |
|
|
Cement |
671 |
?? |
|
|
|
|
|
Total |
214 |
3.5 |
|
|
62185 |
|
|
|
|
1 |
Of which 24 tonnes Cr(VI). |
2 |
Approximately 20% of the fly ash and slag used are for filler in accordance with
Statutory Order 568 and filler in accordance with Chapter 5 approvals (The Danish EPA,
2000). |
| Front page | | Contents | | Previous
| | Next | | Top | |
|