There is not a one-size-fits-all operation in waste. The best combination or system of landfill equipment is the one that allows for the highest densities, lowest fuel burn, lowest cost on maintenance, and allows for everyone to go home safely each night.
By Clay Layne
The landfill business is all about airspace. It is the main thing sold in the landfill. Why is conserving airspace so important? For one, it is good for the environment as there is a substantial difference between the density of dirt/soil and waste. The average density for soil is about 2,550 lbs/yd3 and waste is only about 500 lbs/yd3.
At those densities, 10 tons of soil only consumes a volume of 8 yd3, whereas the same 10 tons of waste is 40 yd3, so about five times more space. From an environmental standpoint, this is why it is critical to achieve good compaction and higher densities.
Fortunately, higher waste compaction densities are not only good for the environment, but also for a landfill’s revenue. Consider the following calculation on the importance of conserving airspace and the cost of a cubic yard.
How much revenue could you generate by selling a cubic yard of airspace? Assuming the landfill makes a $10 profit per ton of waste:
• $10/2000 lbs /ton = profit per lbs
• Compaction density = 1000 lbs/yd3
• Profit per lb x density = 5.00 profit per yd3
Improving compaction by just 100 lbs/yd3 to 1,110 lbs/yd3 increases profit to $5.50 per yd3. Considering airspace savings, assume the landfill takes in, on average, 500 tons per day, which equates to roughly 150,000 tons per year. Compacting the waste stream to only 1,000 lbs/yd3 density consumes 300,000 yd3 of airspace. Increasing densities to 1,100 lbs/yd3, the same amount of waste requires only 272,727 yd3 of airspace.
Just a 10 percent increase in compaction densities delivers annual savings of 27,273 yd3 of airspace. At those numbers, the landfill will gain one extra year of life for every 10 years of operation. From a revenue standpoint, the extra $0.50 profit will generate an extra $75,000 per year or $750,000 over those 10 years. These numbers are on a small scale. Imagine what the savings could be with higher tonnage landfills and if the density numbers were much higher.
Determining the Right Combination
So, what is the best way to achieve the highest densities and meet those goals? The answer lies in compression and shredding the waste. Compression and shredding consist of several factors: running the proper number of passes and patterns, compacting all the area before more waste is added, avoiding double layering, communicating when working with team members, not using the compactor as a dozer, and operator training to use best practices. Before implementing and using these best practices, the proper equipment must be in place at the landfill.
What is the proper equipment to have at every landfill? The truth is every landfill is different and a different mix of equipment is needed at every site. That is what makes the Waste Industry so fascinating. There are a certain criterion of questions regarding the application that must be answered to help determine the proper equipment needed. They include:
• How much tonnage is coming in daily/monthly/yearly?
• What type of waste? (municipal solid waste {MSW}, construction and demolition {C&D}, sludge, green waste, etc.)
• How many days/hours is the site open?
• What are the peak times? How many tons are received during peak periods?
• What is the typical size of slope operated?
• What is the typical working face size?
• What type of truck is delivering the waste? (residential, tippers, or walking floors)
• Will the compactor work alone or with a dozer?
• What is the anticipated growth in waste stream over the next three to five years?
• What type of daily cover is used? (soil, ADCs, or tarp)
• What are the current and desired compaction densities?
Thoroughly considering and answering these questions will start down the path of selecting the proper equipment for the individual landfill.
When purchasing a mix of the more popular equipment used in the landfill, first make sure it is designed as a waste handler. This means extra engineering has gone into the machine to ensure it will hold up for its life in the landfill. Waste is one of the harshest environments for operating equipment. The goal is for the machine to last for 12,000 to 15,000 hours before it needs to be rebuilt, despite the extreme environment. Extra guarding has been designed to protect the vital components of the machine to ensure the longevity to meet the mid-life rebuild phase.
The Right Compactor
The landfill compactor is a vital piece of equipment used tomaximize airspace. The primary purpose of the compactor is to obtain the highest amount of density possible for the waste streambeing compacted. The weight of the compactor works in conjunction with the tips on the wheels to get the compression and shredding that is required for maximum compaction.
To determine the right size compactor, consider the daily or hourly production and the desired density. The size of compactor will also determine what layer depth should be applied to the working face. For example, a 57,000-lb. landfill compactor with a 60-ft push pattern is capable of a 75 ton-per-hour production rate when working alone and up to 145 tons/hour when paired with a dozer. In four passes compacting 12- to 15-inch layers, the 816 will deliver 1,200 lbs/yd3 compaction densities.
Stepping it up, a 90,000-lbs class compactor offers a production range reaching 115 tons/hour alone or up to 145 tons/hour when working with a dozer. It will compact 15- to 18-inch layers, offering 1,550 lbs/yd3 densities in four passes.
Finally, a 123,000-lb. compactor will deliver production rates of 180 tons/hour alone and 250 tons/hour with a dozer. It is capable of compacting 20- to 24-inch layer thicknesses in a four-pass pattern to densities reaching 1,800 lbs/yd3.
These are some compactor capabilities that will be used to help decide which would be the right fit, given the landfill’s needs. As mentioned, weight alone does not optimize compaction densities. Wheel tip type and pattern selection is also important to help achieve the highest densities. Each tip is designed to have a specific purpose.
A paddle tip is designed to shred MSW waste. The very destructive, plus tip, is designed to crush and pulverize the waste, making it good for compacting C&D waste. Its larger footprint also offers good stability on the slope.
The Swiss Army Knife of tips, the combination tip, integrates the paddle design in the center with plus tips on the outside to give the best of both worlds. Chopper tips excel at compacting waste streams with a higher moisture content, while long-lasting diamond tips are designed to last up to the 15,000-hour rebuild mark.
Supporting Equipment and Technology
Nearly at the same level of importance as the compactor for the landfill is the dozer, or track type tractor. These machines work with a compactor to help push and spread the waste, allowing the compactor to focus on running its passes and patterns. Selection of the right size dozer will depend on the desired daily or hourly production.
Another option to consider is the type of blade to place on the dozer. There are several options of blades from which to choose. In waste, a good operator can maintain a good 1.5 fill factor, so that plays into blade and machine selection.
Compact track loaders are not as common at the landfill, but they are a possible option for small- to medium-sized operations. The versatility of a track loader is what makes this a great option for a landfill. The track loader not only can spread the waste, but it can spread daily cover, load trucks, and complete haul road maintenance and general material handling duties.
Articulated trucks are used to haul daily cover. An excavator typically loads them, and they haul the daily cover to the working face. The soft and uneven terrain in the landfill can create a potential safety issue of truck tip-overs for an operator. To help reduce this potential safety hazard, consider an ejector style articulated truck that ejects dirt out the rear of the bed. This truck can still do everything a tipper truck does, but it improves operating safety.
Scrapers are typically used in new cell construction and to haul cover soil, and, once again, scraper size depends on the landfill set up. Excavators are also typically used in new cell construction and, as previously mentioned, to load articulated trucks with cover soil.
Technology on landfill equipment is increasing and improving every day. Technology is designed to make an operator better. For instance, using the pass counter system will not only help train operators on passes and patterns, but it can improve densities by 8 percent or more. The full GPS option can let an operator know that too thick of a layer was just placed, so corrective action can be taken prior to compaction. GPS can also notify the operator that compaction has been achieved, and it is time to move over to the next pass. This system can improve densities by 15 to 18 percent.
Compactor at a landfill in Illinois.
Looking at all the different waste handling configured machines and the many different variables involved in day-to-day operations at a landfill, what is the best combination or system to use in a landfill? Once again, the operation must consider all the variables previously covered. Also, the daily lift height will need to be considered, as will working face dimensions, the number of layers required to achieve that lift height by the end of the day, and how long it will take the compactor to complete a layer with four passes.
The Best Combination
There is not a one-size-fits-all operation in waste. Every site is different from the next and needs that individual attention to determine the best and most efficient combination of equipment needed. The best combination or system of landfill equipment is the one that allows for the highest densities, lowest fuel burn, lowest cost on maintenance, and allows for everyone to go home safely each night. | WA
Clay Layne is the Sales Support Consultant in Waste Applications at Caterpillar Inc. Clay covers landfills, transfer stations and MRFs. He started working for Caterpillar in 2008 as an operator at the Peoria Proving Grounds working with engineers on the Research and Development of Caterpillar Machinery. In 2011, Clay moved to the Edwards Demonstration and Learning Center. It was here that Clay started working in the Waste Industry, conducting onsite operator training for Caterpillar customers all over the world. Clay can be reached at (309) 675-8486 or e-mail [email protected].