Saturday, August 15, 2015

Some Comments on Metal Recovery from Waste to Energy Plant Bottom Ash

In a recent blog, I made some comments on the US market for waste to energy (WTE) plants.   (Click here to read that blog.)   In this blog, I provide some comments on metal recovery in the bottom ash, which results from incinerating waste at WTE plants.

The comments are based on data and information I have found on the Internet and some assumptions I have made in using data to make conclusions.

The following table (Table 1) shows for three regions, the United states (US), the European Union (EU), and Japan (JA), an estimated recent total bottom ash in millions of metric tonnes (mt) generated by WTE plants in those regions (column 6):


Table 1
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Col 5
Col 6

MSW amt m mt
% wte
amt wte m mt
% bottom ash left
amt bottom ash left m mt
US
264
0.095
25.08
0.25
6.27
EU
250
0.205
51.25
0.25
12.8125
JA
63.4
0.75
47.55
0.25
11.8875
individ. wte plant incinerating 1 million MSW/yr
1
1
1
0.25
0.25



The total bottom ash in millions of metric tonnes (mt) (column 6) is based on the following:

1.  The total municipal solid waste (MSW) amounts generated in each region (column 2).   These amounts were computed by multiplying the population of the region (US – 319 million; EU – 503 million; and JA – 127 million) by the estimated per person day-generated waste in each region (US – 5 pounds per day; EU - 3 pounds per day; and JA – 3 pounds per day).  The total MSW amounts are given in column 2.
2.  The percentage of this total waste for each region that is incinerated at WTE plants (US - 9.5%; EU – 20.5%; and JA – 75%).  This percentage is given in column 3.
3.  The total amount (in million mt) of incinerated waste for each region.  This amount is generated by multiplying column 2 by column 3 and shown in column 4.
4.  The percentage of bottom ash left from incinerating the WTE waste.  Twenty-five percent is an average and this amount is shown in column 5.

Column 4 times column 5 gives the amount of total bottom ash in millions of metric tonnes for each region (column 6).

Also in Table 1 is the estimated amount (250,000 mt) of bottom ash generated from one WTE plant incinerating one million mt of waste per year.

Using the bottom ash amounts (column 6) in Table 1, the following 3 tables were generated:


  Table 2   US
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mt bottom ash
% metal in bottom ash
mt metal
recover %
mt metal recover
$/mt at LME
total market value before smelter
sales price - 60% of market value
al
6,270,000
2.0%
125,400
55%
68,970
1550
 $  106,903,500
 $   64,142,100
cu
6,270,000
0.5%
31,350
55%
17,243
5140
 $    88,626,450
 $   53,175,870
steel
6,270,000
8.0%
501,600
85%
426,360
120
 $    51,163,200
 $   30,697,920
ss
6,270,000
0.3%
18,810
55%
10,346
1830
 $    18,932,265
 $   11,359,359
zn
6,270,000
0.2%
12,540
55%
6,897
1810
 $    12,483,570
 $      7,490,142






totals
 $  278,108,985
 $ 166,865,391



Table 3    EU
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mt bottom ash
% metal in bottom ash
mt metal
recover %
mt metal recover
$/mt at LME
total market value before smelter
sales price - 60% of market value
al
12,812,500
2.0%
256,250
55%
140,938
1550
 $  218,453,125
 $ 131,071,875
cu
12,812,500
0.5%
64,063
55%
35,234
5140
 $  181,104,688
 $ 108,662,813
steel
12,812,500
8.0%
1,025,000
85%
871,250
120
 $  104,550,000
 $   62,730,000
ss
12,812,500
0.3%
38,438
55%
21,141
1830
 $    38,687,344
 $   23,212,406
zn
12,812,500
0.2%
25,625
55%
14,094
1810
 $    25,509,688
 $   15,305,813






totals
 $  568,304,844
 $ 340,982,906



Table 4    JA
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mt bottom ash
% metal in bottom ash
mt metal
recover %
mt metal recover
$/mt at LME
total market value before smelter
sales price - 60% of market value
al
11,887,500
2.0%
237,750
55%
130,763
1550
 $  202,681,875
 $ 121,609,125
cu
11,887,500
0.5%
59,438
55%
32,691
5140
 $  168,029,813
 $ 100,817,888
steel
11,887,500
8.0%
951,000
85%
808,350
120
 $    97,002,000
 $   58,201,200
ss
11,887,500
0.3%
35,663
55%
19,614
1830
 $    35,894,306
 $   21,536,584
zn
11,887,500
0.2%
23,775
55%
13,076
1810
 $    23,668,013
 $   14,200,808






totals
 $  527,276,006
 $ 316,365,604



These tables are used to generate the sales prices of five metals (al – aluminum; cu – copper; steal; ss – stainless steel; and zn – zinc), which can be recovered from the generated bottom ash.  A table is provided for each of the three regions.  Column 9 gives the sales prices.

In each table, column 2 comes from column 6 in Table 1.  Column 3 is the estimated percentage amount of the metal in the bottom ash.  The estimated metal amounts (column 2 times column 3), in mt, are provided in column 4.   Column 5 is the estimated recovery percentages of the metals in the bottom ash, and column 6 is the potential amounts of the metals that can be recovered (column 4 times column 5).   Column 7 is a recent (August 2015) price per mt for the metals, found at the London Metal Exchange (LME) website.  Multiplying column 6 times column 7 gives a recent total market value (column 8), before smelter operations, of five metals that can be recovered from the bottom ash.

Column 9 gives the estimated sales price of the recovered metals at the WTE plants.   The plants need to sell the metal to smelters for further processing to pure metal.  It is assume that the smelters will pay the WTE plants 60% of the market value in order to cover their costs and make a profit when the smelters sell the metals. 

Many of the assumptions used above, e.g. the percentages of total MSW sent to WTE plants in each region; the percentages of the incinerated waste remaining as bottom ash; the percentages of metal in the bottom ash; and the percentages of metals that can be recovered from the bottom ash are based on my studying and interpreting European data, information, and comments.  The European Union has been active in developing WTE technology for many years and has more than 470 WTE plants.   By comparison, the US has about 85 plants.  Europe has conducted much study of the technologies and problems in WTE processes, and much can be found on the internet on what they have learned.

Metal recovery amounts from WTE bottom ash depend on many factors that frequently vary from WTE to WTE plant and over time.  So, often only ranges of data, e.g. the percentages of total MSW sent to WTE plants and the percentages of incinerated waste remaining as bottom ash, can convey, correctly, correct amounts.  For those percentages used in the above tables, I have selected a mid-value of the ranges that I have found in the European data.

From the above 3 tables, the approximate total value of the five metals recoverable from bottom ash for all three regions is $1.4 billion (US - $278 million; EU - $568 million; and JA - $527 million).

Perhaps more useful is the data provided in the following table:


Table 5   One WTE Plant Incinerating One Million MT MSW/Year 
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mt bottom ash
% metal in bottom ash
mt metal
recover %
mt metal recover
$/mt at LME
total market value before smelter
sales price - 60% of market value
al
250,000
2.0%
5,000
55%
2,750
1550
 $      4,262,500
 $      2,557,500
cu
250,000
0.5%
1,250
55%
688
5140
 $      3,533,750
 $      2,120,250
steel
250,000
8.0%
20,000
85%
17,000
120
 $      2,040,000
 $      1,224,000
ss
250,000
0.3%
750
55%
413
1830
 $          754,875
 $         452,925
zn
250,000
0.2%
500
55%
275
1810
 $          497,750
 $         298,650






totals
 $    11,088,875
 $      6,653,325

Table 5 show results similar Tables 2, 3, and 4 except the results are for a single WTE plant incinerating approximately one million mt of waste per year.  Table 5 shows an estimated sales price for the recovered metals of $6.7 million, an estimated amount that the plant might obtain from recovering the five metals out of its bottom ash.

The technology for recovering the five metals from bottom ash has been under development for some time, and is fairly advanced and used in several WTE plants.  However, the technology continues to be improved, so that the recovery processes should become even more successfully applied.  The benefits for recovering metals from bottom ash includes not just revenues that can exceed the recovery process costs  but also other benefits such as environmental benefits.  


A good overview of recovering metals from bottom ash is found in a report entitled “Recovery of Metals from Waste Incinerator Bottom Ash” by Rainer Bunge.   (Click here to download the report.)

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