WOOD TUB GRINDERS

Revision Date: 9/03
Process Code: Navy/Marines: SER-005-00; Air Force: FA06; Army: N/A
Usage List: Navy: Medium; Marines: Medium; Army: Low; Air Force: Low
Alternative For: Landfilling or incineration
Compliance Impact: Low
Applicable EPCRA Targeted Constituents and CAS Numbers: N/A
Overview: A wood tub grinder is used to reduce wood or other organic matter into small particles. The larger-sized output material from the tub grinder can be used as a biomass fuel or bulking agent to balance high nitrogen loads in composting operations, while the smaller-sized material is composted. The upper section of a tub grinder is a large, revolving tub and the lower section is a stationary hammer mill. Typically, the tub grinder is fed by a front-end loader or stationary grapple, while a conveyor carries away the continuous stream of shredded material. Tub grinders are not limited in opening size like smaller chippers and shredders, and can process large and odd-shaped wood including stumps, pallets, and waste lumber.

Normal tub widths range from 6 to 14 feet in diameter. Most Navy buyers prefer an 8-foot tub width. Engine horsepower can range from 100 hp to 800 hp. A 575 hp tub grinder is capable of providing a throughput of up to 120 tons per hour. Grinder weight varies from 5,000 pounds to 60,000 pounds. The entire tub grinder assembly is usually moveable from one site to another.

According to MCB Camp Lejeune, in 1998 wood waste and yard waste comprised approximately 18%-20% of the total waste stream. Complete recovery of yard waste will reduce the amount of waste disposed by an average of 12% while the addition of wood waste will divert another 3.8% (U.S. EPA, 2000).
Compliance Benefit: Wood tub grinders are used to reduce wood into smaller particles for composting or biomass fuel, thereby helping facilities to meet the requirements of Executive Order (EO) 13101, which call for executive agencies (e.g., Department of Defense) to incorporate waste prevention and recycling into their daily operations. Composting practices may also help facilities to meet the environmentally beneficial landscaping requirements outlined in EO 13148.

Use of a loader may increase the quantities of fuels and related hydraulic fluids on site that may, in turn, increase a facility's need to comply with SARA (40 CFR 355, 370) and EO 13148 reporting requirements as well as spill plan requirements under 40 CFR 112. In addition, a wood tub grinder may increase electricity consumption. Under EO 13123, federal facilities are required to reduce energy consumption.

The compliance benefits listed here are only meant to be used as general guidelines and are not meant to be strictly interpreted. Actual compliance benefits will vary depending on the factors involved, e.g., the amount of workload involved.
Materials Compatibility:


 No materials compatibility issues were identified.


Safety and Health: Safety concerns regarding tub grinder use include issues related to the operation of power equipment. Operators should be specifically trained to use the grinder. Machinery should not be used if workers are on medication. Proper personal protection equipment including gloves, eye protective, and hearing protection should be used if needed.

Consult your local industrial health specialist, your local health and safety personnel, and the appropriate MSDS prior to implementing this technology.


Benefits:
  • Produces usable products such as landscape mulch, fuel, and compost agents.
  • Grinds material to a fine, even texture that will compost quickly.
  • Can process large trees and finished lumber.
  • If all yard waste is ground and diverted, there is a possible 15.9% reduction in waste (U.S. EPA 1994) disposed in landfills.
  • If all wood is ground and diverted, there is an additional 6.6% possible reduction in waste (U.S. EPA, 1994) disposed in landfills.


Disadvantages:
  • Capital costs may be high.
  • Maintenance costs may be high and tend to increase after 3-4 years of steady use.


Economic Analysis: Typical application: 8 foot tub grinder, 110 hp diesel; capital cost - $40,000; operating cost - $70/hour (includes labor, fuel, and maintenance). MCB Camp Lejeune operates a 12-foot tub grinder. Capital costs for a typical 12-foot tub grinder with a capacity of 500-650 horsepower range between $300,000 - $375,000. These grinders can process between 100-250 yards/hr.

Chipper applications: at 25 to 50 cubic yards per hour; capital cost: $10,000 to $40,000 (with replacement blades at approximately $70 to $200).

The following economic analysis is based on the experience at Seymour Johnson Air Force Base. The wood chipping program is relatively new and has been improving each year. The recycling coordinator at the base reported that currently the program is breaking even and that he expects in a few years, the program will cost much less than landfilling wood wastes. Currently, labor and maintenance are the biggest costs associated with operating the tub grinder. As the staff is educated and operation improves, these costs should decrease.

Assumptions:

  • Process 200 tons/yr. of wood waste.
  • Produce 200 tons/yr. of mulch.
  • Capital Costs: $75,000
  • Solid waste disposal costs: $33/ton
  • Labor: 150 hrs/yr. at $30/hr.
  • Maintenance: $30,000/yr.
  • Avoided mulch purchases: $25/ton

Table 1. Annual Operating Cost Comparison of Diversion and Disposal for Wood Using Tub Grinders

 
Diversion
Disposal
Operational Costs:    
Labor: $4,500 $0
Landfill costs: $0 $6,600
Maintenance: $30,000 $0
Total Operational Costs: $34,500 $6,600
Total Recovered Income: $5,000 $0
Net Annual Cost/Benefit: -$29,500 -$6,600

Economic Analysis Summary:

  • Annual Savings for Diversion Method over Disposal: -$22,900
  • Capital Cost for Diversion Equipment/Process: $75,000
  • Payback Period for Investment in Equipment/Process: N/A

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NSN/MSDS:
Product NSN Unit Size Cost MSDS*
Tub Grinder 3660-01-385-1908 ea. $90,000.00  

*There are multiple MSDSs for most NSNs. The MSDS (if shown) is only meant to serve as an example. To return from the MSDS, click the Back arrow on the Tool Bar.


Approving Authority: Appropriate authority for making process changes should always be sought prior to procuring or implementing any of the technologies identified herein.


Points of Contact: For more information
Vendors: This is not meant to be a complete list, as there may be other manufacturers of this type of equipment.

DuraTech Industries International
P.O. Box 1940
Jamestown,  ND   58402-1940
Phone: (701) 252-4601 
FAX: (701) 252-0502
  Diamond Z Manufacturing
1102 Franklin Boulevard
Nampa,  ID   83687
Phone: (208) 585-2929 

Rotochopper, Inc.
P.O. Box 295
St. Martin, MN 56376
Phone: (320) 548-3586
FAX: (320) 548-3372
Contact: Mr. Bob Schuning
E-mail: bschuning@meltel.net
URL: http://www.rotochopper.com
  Morbark Sales Corporation
P.O. Box 1000
Winn,  MI   48896
Phone: (800) 233-6065 or (989) 866-2381
FAX: (989) 866-2280
  Precision Husky Corp
P.O. Drawer 507
Leeds,  AL   35094-0507
Phone: (205) 640-5181 
FAX: (205) 640-1147
  Vermeer Manufacturing Co, Inc.
P.O. Box 200
Pella,  IA   50219
Phone: (641) 628-3141
FAX: (641) 621-7734
Contact: Mr. Daryl Bouwkamp, Contact for Government Contracts
Related Links:

Tub Ginder
Shredder/Chipper Unit


Sources: U.S. EPA, Municipal Solid Waste in the United States: 2000 Facts and Figures.
Mr. Chuck Schwingler, Seymour Johnson Air Force Base, February 1999
Mr. Kirk Kropinack, MCB Camp Lejeune, February 1999.
DuraTech Industries International, March 1995.
Morbark Sales Corp., March 1995.


Supplemental: Picture of an Electric Tub Grinder
Picture of an Electric Tub Grinder