Example 12-1. (Horse Power Requirements for Size Reduction)

Example 12-1. (Horse power requirements for size reduction)

Estimate the horse power required to reduce commingled MSW to a final size of about 3 in for a plant with a capacity of 80 ton/h using the represented data in fig. 2.6.

Given:

Fig 12-6 is a curve between production (ton/h) and the horse power hp. => so you can use 20 hp. hr / ton. or 10 hp. hr / ton. curve to compute the hose power needed.

Product size factors
6 in product / 1
4 in product / 1.39
2 in product / 1.64
1 in product / 2.38

Solution:

Using a conservative value of 20 hp. ton/hr as given in the fig

ü  Horsepower = 80 ton/hr × 20 hp. hr / ton = 1600 hp. (1194KW)

Using an estimated product size factor of 1.5 (from table)

ü  The required horsepower = 1600 × 1.5 = 2400 hp. (1790 KW)

Example 12-4.

Estimate the composition of the recovered materials in a curbside recycling system in which mixed paper, cardboard, mixed plastics, glass, tin cans, and aluminum cans are to be collected. Also estimate the composition of recycled materials if 60 percent of the aluminum cans are removed prior to curbside recycling. The aluminum cans removed by the homeowners are returned to buyback centers. Assume that the following conditions apply:

1. Composition of the MSW is assumed to be the same as in column 4 table 3-7.

2. Recovery rates for recycled materials are as given in Table 12-16.

Solution

1. Set up a computation table to estimate the composition of recovered materials.

Recyclables
% / Weight recovered
lb / Recovery factor / Weight before recycling
lb / MSW
% / Component
_ / _ / _ / 8.0 / 8.0 / Food wastes
52.2 / 17.9 / 0.50 / 35.8 / 35.8 / Paper
5.5 / 1.9 / 0.30 / 6.4 / 6.4 / Cardboard
10.2 / 3.5 / 0.50 / 6.9 / 6.9 / Plastics
_ / _ / _ / 1.8 / 1.8 / Textiles
_ / _ / _ / 0.4 / 0.4 / Rubber
_ / _ / _ / 0.4 / 0.4 / Leather
_ / _ / _ / 17.3 / 17.3 / Yard wastes
_ / _ / _ / 1.8 / 1.8 / Wood
_ / _ / _ / _ / _ / Misc. organics
17.2 / 5.9 / 0.65 / 9.1 / 9.1 / Glass
13.4 / 4.6 / 0.80 / 5.8 / 5.8 / Tin cans
1.5 / 0.5 / 0.90 / 0.6 / 0.6 / Aluminum
_ / _ / _ / 3.0 / 3.0 / Other metals
_ / _ / _ / 2.7 / 2.7 / Dirt, ashes, etc.
100.0 / 34.3 / 100.0 / 100.0 / Total

2. Set up a computation table to estimate the composition of recovered materials, taking into account the removal of 60 percent of the aluminum cans by the buyback center

Recyclables
% / Weight recycled
lb / Recovery factor / Weight after aluminum removed, lb / Weight before aluminum removed, lb / Component
52.6 / 17.9 / 0.50 / 35.8 / 35.8 / Paper
5.6 / 1.9 / 0.30 / 6.4 / 6.4 / Cardboard
10.3 / 3.5 / 0.50 / 6.9 / 6.9 / Plastics
17.4 / 5.9 / 0.65 / 9.1 / 9.1 / Glass
13.5 / 4.6 / 0.80 / 5.8 / 5.8 / Tin cans
0.6 / 0.2 / 0.90 / 0.24 / 0.6 / Aluminum
100.0 / 34.0 / 64.24 / 64.6 / Total

Example 12-5.

Prepare a materials balance for the process flow diagram given in the accompanying figure. Assuming that the MRF is to be designed to handle 150 ton/d, estimate the hourly loading rates for the various separation processes based on a 7 hr/d operation. Determine the quantities recovered. Determine the number of workers required for manual sorting. Assume that the following conditions apply:

1.  Composition of source-separated materials:

Old newsprint (ONP) / 71.0%
Mixed paper / 14.0%
Old corrugated cardboard (OCC) / 13.0%
Contaminants / 2.0%

2. The baler has a capacity of 16 ton/h. It is also used to process plastics from another process line, so it is fed in batches by a front-end loader when a minimum of 4 tons of paper has been accumulated (about 15 minutes of operation).

3. An average worker can manually sort approximately 2.5 ton/h of paper.

4. The recovery factor for mixed paper, OCC, and contaminants is 95 percent. ONP does not carry over into mixed paper or OCC.

Solution

1. Determine the materials mass balance quantities using the foregoing information

Component / Material composition, % / Materials delivered, ton/d / Recovery factor / Materials recovered, ton/d
Old newsprint (ONP) / 71.0% / 106.5 / 108.6
Mixed paper / 14.0% / 21.0 / 0.95 / 20.0
Old corrugated cardboard (OCC) / 13.0% / 19.5 / 0.95 / 18.5
Contaminants / 2.0% / 3.0 / 0.95 / 2.9
Total / 100.0 / 150.0 / 150.0

2. Percent impurities in ONP = [(108.6 – 106.5)/108.6]*100% = 1.9%

3. Determine the number of workers needed on sorting line:

Workers = 150 ton/d * (1d/7h) * 1 worker/2.5 ton/h = 8.6 workers (9 workers will be required; thus, the estimated output per worker 2.4 ton/h.)

4. Determine the materials sorting rate and time to accumulate 4 ton:

(a) ONP

i. Recovery rate = 108.6 ton/d * (1 d/7 h) = 15.5 ton/h

ii. Time to accumulate 4 ton = 4ton/(15.5 ton/h) = 0.26 h

(b) Mixed paper

i. Recovery rate = 20.0 ton/d * (1 d/7 h) = 2.9 ton/h

ii. Time to accumulate 4 ton = 4ton/(2.9 ton/h) = 1.4 h

(c) OCC

i. Recovery rate = 18.5 ton/d * (1 d/7 h) = 2.6 ton/h

ii. Time to accumulate 4 ton = 4ton/(2.6 ton/h) = 1.5 h

Example 12-6.

A community generates 1000 ton/d of MSW and has decided to build a MRF that will process commingled MSW, source-separated recyclables, and commingled recyclables. A portion of the wastestream, 15 percent, is being diverted to a curbside recycling program. An additional 4 percent diversion is achieved through a commingled recycling program, in which homeowners place recyclable materials in special clear plastic bags for later sorting at the MRF.

Prepare a materials balance for the process flow diagram given in the accompanying figure. Determine the quantities of materials recovered. Estimate the hourly loading rates for the various separation processes based on a 7-h/d operation. Determine the number of workers required for manual sorting. Assume that the following condition apply:

1. The wastestream delivered to the MRF contains 4 percent by weight of commingled recyclables separated in transparent bags. The bagged materials have the same composition as the materials collected by the curbside recycling program.

(a) Bulky materials and other contaminants = 1.0 percent of total MSW generated in the community.

(b) Presorting operation includes two front end loaders and six workers on the presorting floor.

(c) First-stage presorting recovers 75 percent of cardboard and 100 percent of bagged commingled recyclables.

(d) Second-stage presorting recovers 75 percent of the remaining cardboard.

2. Sixty percent of the aluminum cans are recovered and delivered to buyback centers by the residents of the community.

3. An average worker can manually sort approximately 2.5 ton/h of MSW on a conveyor belt sorting line.

Solution

1. Determine the materials balance quantities for the presorting operation:

(a) Amount of material received at MRF less bulky goods, and other contaminants removed during first-stage manual presort:

Material remaining = 1000 ton/d * (1 – 0.01) = 990 ton/d

(b) Set up a computation table to determine the quantities of each component delivered to the MRF, based on 990 ton/d. Also determine the total adjusted quantities, taking into account the aluminum that is returned to buyback programs.

Component / MSW
% / Total MSW,
ton/d / Total adjusted MSW, ton/d
Food wastes / 8.0 / 79.2 / 79.2
Paper / 35.8 / 354.4 / 354.4
Cardboard / 6.4 / 63.4 / 63.4
Plastics / 6.9 / 68.3 / 68.3
Textiles / 1.8 / 17.8 / 17.8
Rubber / 0.4 / 4.0 / 4.0
Leather / 0.4 / 4.0 / 4.0
Yard wastes / 17.3 / 171.3 / 171.3
Wood / 1.8 / 17.8 / 17.8
Misc. organic / _ / _ / _
Glass / 9.1 / 90.1 / 90.1
Tin Cans / 5.8 / 57.4 / 57.4
Aluminum / 0.6 / 5.9 / 2.4
Other metal / 3.0 / 29.7 / 29.7
Dirt, ashes, etc. / 2.7 / 26.7 / 26.7
Total / 100.0 / 990.0 / 986.5

(c) Set up a computation table to determine the quantities of each component in terms of commingled MSW, source-separated recyclables, and commingled, bagged recyclables.

Component / Total MSW,
ton/d / Recycled materials, %* / Source-separated recyclables, ton/d / Commingled recyclables, ton/d / Remaining MSW, ton/d
Food wastes / 79.2 / _ / _ / _ / 79.2
Paper / 354.4 / 52.6 / 77.8 / 20.8 / 255.8
Cardboard / 63.4 / 5.6 / 8.3 / 2.2 / 52.9
Plastics / 68.3 / 10.3 / 15.2 / 4.1 / 49.0
Textiles / 17.8 / _ / _ / _ / 17.8
Rubber / 4.0 / _ / _ / _ / 4.0
Leather / 4.0 / _ / _ / _ / 4.0
Yard wastes / 171.3 / _ / _ / _ / 171.3
Wood / 17.8 / _ / _ / _ / 17.8
Misc. organic / _ / _ / _ / _ / _
Glass / 90.1 / 17.4 / 25.7 / 6.9 / 57.5
Tin Cans / 57.4 / 13.5 / 20.0 / 5.3 / 32.1
Aluminum / 2.4 / 0.6 / 0.9 / 0.2 / 1.3
Other metal / 29.7 / _ / _ / _ / 29.7
Dirt, ashes, etc. / 26.7 / _ / _ / _ / 26.7
Total / 986.5 / 100.0 / 147.9 / 39.5 / 799.1

* from example 12.4

(d) Set up a computation table to determine the quantities of each component recovered during presorting.

Component / Total MSW,
ton/d / Recovered cardboard 1st presort, ton/d / Recovered cardboard 2nd presort, ton/d / Remaining MSW, ton/d
Food wastes / 79.2 / _ / _ / 79.2
Paper / 255.8 / _ / _ / 255.8
Cardboard / 52.9 / 39.7 / 9.9 / 3.3
Plastics / 49.0 / _ / _ / 49.0
Textiles / 17.8 / _ / _ / 17.8
Rubber / 4.0 / _ / _ / 4.0
Leather / 4.0 / _ / _ / 4.0
Yard wastes / 171.3 / _ / _ / 171.3
Wood / 17.8 / _ / _ / 17.8
Misc. organic / _ / _ / _ / _
Glass / 57.5 / _ / _ / 57.5
Tin Cans / 32.1 / _ / _ / 32.1
Aluminum / 1.3 / _ / _ / 1.3
Other metal / 29.7 / _ / _ / 29.7
Dirt, ashes, etc. / 26.7 / _ / _ / 26.7
Total / 799.1 / 39.7 / 9.9 / 749.5

2. Set up a computation table to determine the quantities of each component recovered during first-stage manual sorting:

Component / Total MSW,
ton/d / Manual sorting recovery factor / Recovered materials, ton/d / Remaining MSW,
ton/d
Food wastes / 79.2 / _ / _ / 79.2
Paper / 255.8 / 0.80 / 204.6 / 51.2
Cardboard / 3.3 / 0.75 / 2.5 / 0.8
Plastics / 49.0 / 0.80 / 39.2 / 9.8
Textiles / 17.8 / _ / _ / 17.8
Rubber / 4.0 / _ / _ / 4.0
Leather / 4.0 / _ / _ / 4.0
Yard wastes / 171.3 / _ / _ / 171.3
Wood / 17.8 / _ / _ / 17.8
Misc. organic / _ / _ / _ / _
Glass / 57.5 / 0.75 / 43.1 / 14.4
Tin Cans / 32.1 / 0.90 / 28.9 / 3.2
Aluminum / 1.3 / 0.90 / 1.2 / 0.1
Other metal / 29.7 / _ / _ / 29.7
Dirt, ashes, etc. / 26.7 / _ / _ / 26.7
Total / 749.5 / 319.5 / 430.0

3. Set up a computation table to determine the quantities of each component as separated by the disc screen.

Component / Total MSW,
ton/d / Disc screen unders (-6 in), recovery factor / Disc screen unders (-6 in), ton/d / Disc screen overs (+6 in), ton/d
Food wastes / 79.2 / 1.0 / 79.2 / 0
Paper / 51.2 / 0.75 / 38.4 / 12.8
Cardboard / 0.8 / 0.75 / 0.6 / 0.2
Plastics / 9.8 / 0.75 / 7.4 / 2.4
Textiles / 17.8 / 0.75 / 13.4 / 4.4
Rubber / 4.0 / 0.75 / 3.0 / 1.0
Leather / 4.0 / 0.75 / 3.0 / 1.0
Yard wastes / 171.3 / 1.0 / 171.3 / 0
Wood / 17.8 / 0.75 / 13.4 / 4.4
Misc. organic / _ / _ / _ / _
Glass / 14.4 / 0.75 / 10.8 / 3.6
Tin Cans / 3.2 / 0.75 / 2.4 / 0.8
Aluminum / 0.1 / 0.75 / 0.1 / 0
Other metal / 29.7 / 0.75 / 22.3 / 7.4
Dirt, ashes, etc. / 26.7 / 1.0 / 26.7 / 0
Total / 430.0 / 392.0 / 38.0

4. Set up a computation table to determine the quantities of each component recovered during second-stage manual sorting, assuming an 85 percent recovery factor for recyclables.

Component / Disc screen overs (+6in), ton/d / Source-separated recyclables, ton/d / Commingled recyclables, ton/d / Total materials 2nd stage, ton/d / Recovered materials, ton/d / Remaining materials, ton/d
Food wastes / 0 / _ / _ / 0 / 0 / 0
Paper / 12.8 / 77.8 / 20.8 / 111.4 / 94.7 / 16.7
Cardboard / 0.2 / 8.3 / 2.2 / 10.7 / 9.1 / 1.6
Plastics / 2.4 / 15.2 / 4.1 / 21.7 / 18.5 / 3.2
Textiles / 4.4 / _ / _ / 4.4 / 0 / 4.4
Rubber / 1.0 / _ / _ / 1.0 / 0 / 1.0
Leather / 1.0 / _ / _ / 1.0 / 0 / 1.0
Yard wastes / 0 / _ / _ / 0 / 0 / 0
Wood / 4.4 / _ / _ / 4.4 / 0 / 4.4
Misc. organic / _ / _ / _ / 0 / 0 / 0
Glass / 3.6 / 25.7 / 6.9 / 36.2 / 30.8 / 5.4
Tin Cans / 0.8 / 20.0 / 5.3 / 26.1 / 22.2 / 3.9
Aluminum / 0 / 0.9 / 0.2 / 1.1 / 0.9 / 0.2
Other metal / 7.4 / _ / _ / 7.4 / 0 / 7.4
Dirt, ashes, etc. / 0 / _ / _ / 0 / 0 / 0
Total / 38.0 / 147.9 / 39.5 / 225.4 / 176.2 / 49.2

5. Set up a computation table to determine the quantities of each component sent to the landfill or shredded for compost.

Component / Disc screen unders (-6in), ton/d / Remaining materials from sorting, ton/d / Materials to landfill or composting, ton/d
Food wastes / 79.2 / 0 / 79.2
Paper / 38.4 / 16.7 / 55.1
Cardboard / 0.6 / 1.6 / 2.2
Plastics / 7.4 / 3.2 / 10.6
Textiles / 13.4 / 4.4 / 17.8
Rubber / 3.0 / 1.0 / 4.0
Leather / 3.0 / 1.0 / 4.0
Yard wastes / 171.3 / 0 / 171.3
Wood / 13.4 / 4.4 / 17.8
Misc. organic / 0 / 0 / 0
Glass / 10.8 / 5.4 / 16.2
Tin Cans / 2.4 / 3.9 / 6.3
Aluminum / 0.1 / 0.2 / 0.3
Other metal / 22.3 / 7.4 / 29.7
Dirt, ashes, etc. / 26.7 / 0 / 26.7
Total / 392.0 / 49.2 / 441.2

6. The overall mass balance for the system is shown in the accompanying table and the following figure.

Materials in / Quantityton/d / Materials out / Quantity ton/d
Community MSW / 1000.0 / Aluminum can buyback program / 3.5
Bulky items / 10.0
Cardboard (1st stage presort) / 39.7
Cardboard (2nd stage presort) / 9.9
Recovered materials (1st stage presort) / 319.5
Recovered materials (2nd stage presort) / 176.2
Waste to landfill or composting / 441.2
Total / 1000.0 / 1000.0