Some Problems of Recycling Industrial Materials

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JOURNAL OF IRON AND STEEL RESEARCH, INTERNATIONAL. 2008, 15(5): 37-41, 55

Some Problems of Recycling Industrial Materials CAl Jiu-ju,

LU Zhong-wu ,

YUE Qiang

(SEPA Key Laboratory on Eco-Industry, Northeastern University, Shenyang 110004, Liaoning, China) Abstract: The industrial system should learn from the natural ecosystem. The resource utilization efficiency should be increased and the environmental load should be decreased, depending on the materials recycled in the system. The classification of industrial materials from the viewpoint of large-scale recycling was stated. Recycling of materials, on three different levels, was introduced in the industrial system. The metal flow diagram in the life cycle of products, in the case of no materials recycled, materials partially recycled, and materials completely recycled, was given. The natural resource conservation and the waste emission reduction were analyzed under the condition of materials completely recycled. The expressions for the relation between resource efficiency and material recycling rate, and the relation between eco-efficiency and material recycling rate were derived, and the curves describing the relationship between them were protracted. The diagram of iron flow in the life cycle of iron and steel products in China, in 2001, was given, and the iron resource efficiency, material recycling rate, and iron eco-efficiency were analyzed. The variation of iron resource efficiency with the material recycling rate was analyzed for two different production ratios. Key words: recycling; industrial material; product life cycle; resource efficiency; eco-efficiency , material recycling rate

The ecological problems of the industrial system must be studied by imitating the ecosystem in nature (see Fig. 1), which is a crude example of sustainable development. The components in the ecosystem depend on and influence each other, and constitute a close cycle of materials, The whole ecosystem neither takes any resources from the nature nor emits any wastes to the nature, and can operate continually relying on only solar energy. If a manmade system can constitute a close cycle of materials similar

,----

Solar energy

•

to the ecosystem in nature, it will undoubtedly be sustainable. However, it is impossible for an industrial system to achieve this goal. It will be better if it can take fewer resources (this includes energies) from nature, and simultaneously increase the output of products and wealth, depending on the materials recycled in the system. Recycling of materials is the basic measure of increasing resource efficiency and decreasing environmental load. After coming into the industrial system, natural resources flow in the following stages: production, fabrication" manufacture of products, and products used by customers. When the products become obsolete, some materials in the obsolete products are reclaimed and returned to the industrial system as raw materials, and the others are not reclaimed, and are emitted into the environment as wastes and contaminants'<' .

Fig. 1

Ecosystem in the nature

The recycling of industrial materials is contributing to conservation of natural resources and environment improvement. However, it is a pity that

Foundation Item: Item Sponsored by National Key Fundamental Research and Development Project of China (2005CB724206); National Natural Science Foundation of China (50334020) Biography:CAl Jiu-ju0948-). Male. Doctor, Professor;

E-mail: rcjj@mail. neu. edu. en;

Revised Date: June 29, 2007

• 38 •

Journal of Iron and Steel Research. International

only a small part among them is recycled. The metal recycling level is not high. although it is easier to regenerate. About 50 % of them are emitted into environment even in developed countries. The recycling rate of several metals in Japan and Canada is shown in Table 1 [z].

It must be pointed out that only a part of the materials contained in industrial products can be recovered and recycled. In this respect. industrial materials are classified into three groups. as follows[3] : (1) materials economically and technologically compatible with recycling under the present prices and regulations. such as most structural metals. industrial catalysts. paper. glasses. and some kinds of plastics; (2) materials economically not compatible with recycling. but technically feasible. such as some structural and packing materials. most refrigerants. and solvents; (3) materials for which recycling is inherently not feasible. including coatings. pigments. pesticides. herbicides. preservatives. explosives. detergents. fertilizers. fuels. and other chemical products. Therefore. the contents in this article are fit for the materials in group one and two. More materials may become suitable for recycling with the development of technology. Theoretical study on the recycling of industrial materials should be based on the life cycle of the products. Some essential principles of material recycling are obtained from studying the quantitative relationships among each substance flow. Here. the products are designated to an element or a steady compound; furthermore. the life span of products from production to obsolescence and the variation of product output with time are considered. Table 1

Recycling rate of several metals in Japan and Canada Al

Japan Canada

1

Pb

Cd

20%

66%

28%

19%

55%

Cu

Zn

54%

66%

32%

43%

Fe 45%

Three Scales of Recycling Industrial Materials

In the industrial system. there are three kinds of recycling flows of materials-'". (1) Small-scale recycling-recycling of materials within an enterprise. For instance. the wastes of downstream unit processes return back to upstream unit processes for retreatment , such as water recycling in an enterprise. other expendables. byprod-

Vol. 15

ucts , and so on. recycled in an enterprise. (2) Middle-scale recycling-recycling of materials among different industrial sectors. For instance. the wastes of downstream industrial sectors return back to upstream sectors for retreatrnent , or wastes of one of the industrial sectors go to another sector for utilization. (3) Large-scale recycling-when the industrial products become obsolete after their use. some materials containing the obsolete products are returned to the original industrial sectors to be used as raw material. These three kinds of recycling are beneficial in increasing resource efficiency. It is true that large-scale recycling is the most efficient way to increase resource efficiency in the case of a constant volume of economy. Nevertheless. in China. for the sake of rapid growth of its economy. the situation is quite different. It seems that the material recycling on three scales is of equal importance in the case of China. Reduce is in the first place in an enterprise or between enterprises. That is to say that reducing the generation of wastes and natural resource consumption should be first paid attention to. Recycling of wastes comes second. Besides this. reuse must come prior to recycling. That is to say. products should be first reused after their first use stage and the use life span of products should be extended. In addition. it should be pointed out that the priority order of 3R (reduce. reuse. recycling) should be kept in mind during the process of developing circular economy. This is extremely important for China, because there is still a lot of study to do on reduce and reuse.

2 Diagram of Metal Flow in Life Cycle of Products A simplified model of metal flow in the life cycle of products without metal recycling is shown in Fig. 2[5J. The import and export of metal scraps and products are not taken into consideration in the model. All the flow rates indicated in Fig. 2 are not those of materials in kind; instead. they are the flow rates of iron contained in the flowing materials. The year of interest is designated as the year t:» when the annual output of the metal of the nation is (l b) P t/a, and CPT t/ a represents the losses by means of metal wastage during the production stage. The output of

+

T

metal products is P T t/a. and bP T t/a of metal scraps are generated in the manufacturing stage. The span of a product life cycle is assumed to be 6.r years. ThE

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"Some Problems of Recycling Industrial Materials

(I+c+b)Pr (I+c+b)Pr

Fig. 2

Diagram of metal flow in life cycle of products without metal recycling (t/a)

products become obsolete after 6.r years (Assuming no metal wastes are generated in the products' use stage). The metal wastes, metal scraps, and obsolete products are not recycled. The metal loss in the products' life cycle is (l c b) P r' which is the same as the input of natural resources. The model of metal flow in the life cycle of products with metal recycling is shown in Fig. 3. Here, it is assumed that: (1) in the small-scale recycling, metal wastes recycled are c' P r and those emitted into the production stage are (c-c')P r, whereas, in the middle-

+ +

scale recycling, metal wastes recycled are b'P t: and those emitted in the manufacturing stage are (b - b') P r ; (2) all recovered post-use scraps go to the production stage in the same year of their generation, that is, the year (r+6.r); (3) the recycling rate a does not

vary with time. If c=c', b=b', that is to say, that there is no emission of wastes in production and manufacturing stages. Under these circumstances, Fig. 3 changes into Fig. 4. Comparing Fig. 2 and Fig. 4, it can be· found that if the wastes are all recycled, the natural resources required are P, -aPr-Ar' The saving amounts of natural resources are: (l +c+b)P r - CP, -aPr-Ar) = (c+b) P, +aP r- Ar (1)

The reducing amounts of wastes losses are: (l+c+b)Pr-(l- a)Pr=(c+b+a)P r (2) It seems that in the case of constant output of products CP, = P r- Ar) , the recycling rates of three scales (a, b , c) are of equal importance for saving

[I+(c-c')+ (b-b')-a]Pr

(I-a)P,

To metal production in the year (Htir) a-Recycling rate of large-scale recycling;

Fig. 3

b'-Recycling rate of middle-scale recycling;

c'-Recycling rate of small-scale recycling

Diagram of metal flow in the life cycle of products with metal recycling (t/a)

From metal products of the year (r-Ar)

(I-a)Pr

(l-a)Pr

To metal production in the year (Htir)

Fig. 4

Diagram of metal flow in the life cycle of products with zero emission (t/a)

Journal of Iron and Steel Research, International

• 40 •

natural resources and reducing wastes losses.

3. 1

'u


6

'-

4

5.00

.;::


'::l"' Ul

0.2


0::

0

0.2

r

uct output decreases, t/> 1.

Resource efficiency

Resource efficiency, r , can be defined as the output of products per unit of natural resource inputr ' : 1 r= (l +c-c' +b-b') -aPr-t"r! P, (4) where if the product output keeps constant, that is, Pr-t>r!P; = 1, large-, middle- and small-scale recycling have equal influences on resource efficiency; if the product output increases, that is, Pr-t>r/Pr
tha t is, P r - t>r / P r > 1, large-scale recycling has more influences on resource efficiency than middle- and small-scale recycling. When c' = c, b' = b , Eqn. (4) can be expressed

as

1 r= I-ap

2.50 1.67 1.25

2

0

(3)

where p is the factor of nonsteady state of substance flow; if the product output keeps constant, p = 1; if the product output increases, p
3. 2

8

<::

The variation of product output in a product's life cycle can be described as follows:

P

~ (.)

Variation of product output

p= Pr-t"

10

~

3 Relation Between Resource Efficiency and Recycling Rate

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Fig. 5

0.6 0.4 Recycling rate/a

0.8

1.0

Relation between resource efficiency and recycling rate

for p = 1. When a = 0.7, the values of r tend to 6.25 and 50 in the case of p=1. 2 and 1. 4, respectively. Besides, it should be pointed out that the values of r are not necessarily larger than 1. 0, if the wastes in the production and manufacturing stages are not all recycled. The values of r may be smaller than 1. 0, particularly when a is low.

4 Relation Between Eco-Efficiency and Recycling Rate Eco-efficiency, q, can be defined as the output of products per unit emission of wastes to the environrnent'f ", 1 q= 1 +c-c' +h-b' -a

(6)

When c' = c, h' = b , Eqn, (6) can be expressed as 1 q=-

(7)

I-a

Eco-efficiency is a function of a, where the (5)

Resource efficiency. is a function of a and p when the wastes in the production and manufacturing stages are all recycled. Fig. 5 can be obtained from Eqn. (5), in which each curve corresponds to a different p. The curves in the case of p 1 show that the .values of r increase even more rapidly than the curve

wastes in the production and manufacturing stages are all recycled. Fig. 6 can be obtained from Eqn, (7). It can be seen from Fig. 6 that the values of q increase inconspicuously when a is low; but q increases obviously when a is high. Hence, recycling rate should be higher to get high eco-efficiency. 10

S ~<::

8 6


'u <;::: '-

0/0 (.)

'"

4 2

o Fig. 6

0.2

0.4 0.6 Recycling rate/a

0.8

1.0

Relation between eco-efficiency and recycling rate

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Some Problems of Recycling Industrial Materials ~~~_.-~~~----------

5 Diagram and Analysis of Iron Flow in Life Cycle of Iron and Steel Products in China in 2001 The iron flow diagram in the life cycle of steel products in China, in 2001, is shown in Fig. 7. For Fig. 7, the average life span of steel products is 20 years[7] . The output of steel in China, in 2001, was 154 X 106 t. 12 X 10 6 t of iron from old scraps (from steel products produced in 1981) and 167 X 10 6 t of iron from iron ore input were needed for the production. The output of the steel products was 142 X 10 6 t. In the recovery stage, 56 X 10 6 t (from steel products produced in 2001) of old scraps would be recovered from retired steel products. These old scraps would go to the production stage in 2021. According to Fig. 7, (1) Iron resource efficiency 142 r= 16-7 =0.850

recycling rate can be derived from Fig. 7, which is expressed as 1 r= (8) 1. 262-ap When p = 0.25, it matches the case in China, as shown in curve 1 in Fig. 8. It can be seen that even if the recycling rate increases much higher, the increase in iron resource efficiency would be very limited. When p = 1. 00, it is described in curve 2, in Fig. 8. It can be seen that if the recycling rate increases a little, the increase in iron resource efficiency will be very obvious; and if the recycling rate decreases a little, the decrease in iron resource efficiency will also be very obvious.

~

t

~

"o "... ;; 0

...'"

56 a=142=0.394

~

0 ~

7

(3) Iron environmental efficiency

142

q= 123 = 1. 154 (4) Variation of iron resource efficiency versus recycling rate The equation between iron resource efficiency and

Curve 1 0.5

6

0.2

0

Fig. 8

b = 142 =0.049

I 10 c = 142 =0.070

1.5

Q)

12 b= 142 =0.085

42 c= 142 =0.296

3.82

3.5

" 'u S 2.5

(2) Iron recycling rate

I

4.5

0.4 0.6 Recycling rate/a

0.8

0.09

1.0

Iron resource efficiency versus recycling rate

Conclusions

(1) In the industrial system, there are three kinds of recycling flows of materials. Increasing material recycling is a basic measure for increasing resource efficiency and ceo-efficiency. (2) The recycling rate has an influence on resource efficiency, and the variation of product output also ha-s an influence on resource efficiency. (3) The output of China's steel is increasing rapidly; hence, large-; middle- and small-scale recycling are of equal importance. So the iron resource efficiency and the environment of steel enterprises should be improved. References: [IJ

Flow in Steel Manufacturing Process on Atmosphere Environ-

To steel

mental Load

production in 2021

I -Production; II -Manufacturing; ill -Using; N -Waste recovery Fig. 7 Iron flow diagram in life cycle of steel products in China in 2001 (unit: 10· t)

DU Tao, CAl j iu-ju , LU Zhong-wu. Influence of Material

[n.

Journal of Iron and Steel Research, Interna-

tional, 2004,11(2): 38.

[2J

Ayres R U. Industrial Metabolism: Theory and Policy, the Greening of Industrial Ecosystems [M]. Washington: National Academy Press, 2001.

(Continued on Page 55)

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Frictional Heat-Induced Phase Transformation on Train Wheel Surface

therefore, they easily became the channel of crack initiation and propagation. (4) The increased speed could result m an mcreased probability of wheel tread phase transformation, but it did not lead to a significant increase in the peak temperature of the wheel tread or the thickness of the martensite layer. (5) The austenitizing temperature of low alloyed steels increased with the decrease in carbon contents, which was helpful in limiting the size of the phase change area on the wheel surface. When the carbon contents decreased from O. 7 % to O. 4 %, the thickness and sectional area of the martensite layer significantly decreased by 30 % and 45 %, respectively. The decreased carbon contents also Improved the toughness and elongation properties of the martensite layer and helped to reduce the probability of wheel tread spalling. The authors would like to thank Professor ZHANG Bin for his help of providing a great deal of

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