Exploring Hydrocarbon Depletion
Page added on January 26, 2017
Biking along the Lake Ontario shoreline one autumn afternoon, I passed the new and just-barely operational Durham-York Energy Centre and a question popped into mind. If this incinerator produces a lot of electricity, where are all the wires?
The question was prompted in part by the facility’s location right next to the Darlington Nuclear Generating Station. Forests of towers and great streams of high-voltage power lines spread out in three directions from the nuclear station, but there is no obvious visible evidence of major electrical output from the incinerator.
So just how much electricity does the Durham-York Energy Centre produce? Does it produce as much energy as it consumes? In other words, is it accurate to refer to the incinerator as an “energy from waste” facility, or is it a “waste from energy” plant? The first question is easy to answer, the second takes a lot of calculation, and the third is a matter of interpretation.
Before we get into those questions, here’s a bit of background.
The Durham-York Energy Centre is located about an hour’s drive east of Toronto on the shore of Lake Ontario, and was built at a cost of about $300 million. It is designed to take 140,000 tonnes per year of non-recyclable and non-compostable household garbage, burn it, and use the heat to power an electric generator. The garbage comes from the jurisdictions of adjacent regions, Durham and York (which, like so many towns and counties in Ontario, share names with places in England).
The generator powered by the incinerator is rated at 14 megawatts net, while the generators at Darlington Nuclear Station, taken together, are rated at 3500 megawatts net. The incinerator produces 1/250th the electricity that the nuclear plant produces. That explains why there is no dramatically visible connection between the incinerator and the provincial electrical grid.
In other terms, the facility produces surplus power equivalent to the needs of 10,000 homes. Given that Durham and York regions have fast-growing populations – more than 1.6 million at the 2011 census – the power output of this facility is not regionally significant.
Energy Return on Energy Invested
But does the facility produce more energy than it uses? That’s not so easy to determine. A full analysis of Energy Return On Energy Invested (EROEI) would require data from many different sources. I decided to approach the question by looking at just one facet of the issue:
Is the energy output of the generator greater than the energy consumed by the trucks which haul the garbage to the site?
Let’s begin with a look at the “fuel” for the incinerator. Initial testing of the facility showed better than expected energy output due to the “high quality of the garbage”, according to Cliff Curtis, commissioner of works for Durham Region (quoted in the Toronto Star). Because most of the paper, cardboard, glass bottles, metal cans, recyclable plastic containers, and organic material is picked up separately and sent to recycling or composting plants, the remaining garbage is primarily plastic film or foam. (Much of this, too, is technically recyclable, but in current market conditions that recycling would be carried out at a financial loss.)
If you were lucky to grow up in a time and a place where building fires was a common childhood pastime, you know that plastic bags and styrofoam burn readily and create a lot of heat. A moment’s consideration of basic chemistry backs up that observation.
Our common plastics are themselves a highly processed form of petroleum. One of the major characteristics of our industrial civilization is that we have learned how to suck finite resources of oil from the deepest recesses of the earth, process it in highly sophisticated ways, mold it into endlessly versatile – but still cheap! – types of packaging, use the packaging once, and then throw the solidified petroleum into the garbage.
If instead of burying the plastic garbage in a landfill, we burn it, we capture some of the energy content of that original petroleum. There’s a key problem, though. As opposed to a petroleum or gas well, which provides huge quantities of energy in one location, our plastic “fuel” is light-weight and dispersed through every city, town, village and rural area.
The question thus becomes: is it an economic proposition to drive up and down every street gathering up bags of plastic fuel for an electricity generator?
The light, dispersed nature of the cargo has a direct impact on garbage truck design, and therefore on the number of loads it takes to haul a given number of tonnes of garbage.
Because these trucks must navigate narrow residential streets they must have short wheelbases. And because they need to compact the garbage as they go, they have to carry additional heavy machinery to do the compaction. The result is a low payload:
Long-haul trucks and their contents can weigh 80,000 pounds. However, the shorter wheelbase of garbage and recycling trucks results in a much lower legal weight — usually around 51,000 pounds. Since these trucks weigh about 33,000 pounds empty, they have a legal payload of about nine tons. (Source: How Green Was My Garbage Truck)
By my calculations, residential garbage trucks picking up mostly light packaging will be “full” with a load weighing about 6.8 tonnes. (The appendix to this article lists sources and shows the calculations.)
At 6.8 tonnes per load, it will require over 20,000 garbage truck loads to gather the 140,000 tonnes burned each year by the Durham-York Energy Centre.
How many kilometers will those trucks travel? Working from a detailed study of garbage pickup energy consumption in Hamilton, Ontario, I estimated that in a medium-density area, an average garbage truck route will be about 45 km. Truck fuel economy during the route is very poor, since there is constant stopping and starting plus frequent idling while workers grab and empty the garbage cans.
There is additional traveling from the base depot to the start of each route, from the end of the route to the drop-off point, and back to the depot.
I used the following map to make a conservative estimate of total kilometers.
Because most of the garbage delivered to the incinerator comes from Durham Region, and the population of both Durham Region and York Region are heavily weighted to their southern and western portions, I picked a spot in Whitby as an “average” starting point. From that circled “X” to the other “X” (the incinerator location) is 30 kilometers. Using that central location as the starting and ending point for trips, I estimated 105 km total for each load. (45 km on the pickup route, 30 km to the incinerator, and 30 km back to the starting point).
Due to their weight and to their frequent stops, garbage trucks get poor fuel economy. I calculated an average .96 liters/kilometer.
The result: our fleet of trucks would haul 20,600 loads per year, travel 2,163,000 kilometers, and burn just over 2 million liters of diesel fuel.
Comparing diesel to electricity
How does the energy content of the diesel fuel compare to the energy output of the incinerator’s generator? Here the calculations are simpler though the numbers get large.
There are 3412 BTUs in a kilowatt-hour of electricity, and about 36,670 BTUs in a liter of diesel fuel.
If the generator produces enough electricity for 10,000 homes, and these homes use the Ontario average of 10,000 kilowatt-hours per year, then the generator’s output is 100,000,000 kWh per year.
Converted to BTUs, the 100,000,000 kWh equal about 341 billion BTUs.
The diesel fuel burned by the garbage trucks, on the other hand, has a total energy content of about 76 billion BTUs.
That answers our initial question: does the incinerator produce more energy than the garbage trucks consume in fuel? Yes it does, by a factor of about 4.5.
If we had tallied all the energy consumed by this operation, then we could say it had an Energy Return On Energy Invested ratio of about 4.5 – comparable to the bottom end of economically viable fossil fuel extraction operations such as Canadian tar sands mining. But of course we have considered just one energy input, the fuel burned by the trucks.
If we added in the energy required to build and maintain the fleet of garbage trucks, plus an appropriate share of the energy required to maintain our roads (which are greatly impacted by weighty trucks), plus the energy used to build the $300 million incinerator/generator complex, the EROEI would be much lower, perhaps below 1. In other words, there is little or no energy return in the business of driving around picking up household garbage to fuel a generator.
Energy from waste, or waste from energy
Finally, our third question: is this facility best referred to as “Energy From Waste” or “Waste From Energy”?
Looking at the big picture, “Waste From Energy” is the best descriptor. We take highly valuable and finite energy sources in the form of petroleum, consume a lot of that energy to create plastic packaging, ship that packaging to every household via a network of stores, and then use a lot more energy to re-collect the plastic so that we can burn it. The small amount of usable energy we get at the last stage is inconsequential.
From a municipal waste management perspective, however, things might look quite different. In our society people believe they have a god-given right to acquire a steady-stream of plastic-packaged goods, and a god-given right to have someone else come and pick up their resulting garbage.
Thus municipal governments are expected to pay for a fleet of garbage trucks, and find some way to dispose of all the garbage. If they can burn that garbage and recapture a modest amount of energy in the form of electricity, isn’t that a better proposition than hauling it to expensive landfill sites which inevitably run short of capacity?
Looked at from within that limited perspective, “Energy From Waste” is a fair description of the process. (Whether incineration is a good idea still depends, of course, on the safety of the emissions from modern garbage incinerators – another controversial issue.)
But if we want to seriously reduce our waste, the place to focus is not the last link in the chain – waste disposal. The big problem is our dependence on a steady stream of products produced from valuable fossil fuels, which cannot practically be re-used or even recycled, but only down-cycled once or twice before they end up as garbage.
Top photo: Durham-York Energy Centre viewed from south east.
APPENDIX – Sources and Calculations
Capacity and Fuel Economy of Garbage Trucks
There are many factors which determine the capacity and fuel economy of garbage trucks, including: type of truck (front-loading, rear-loading, trucks with hoists for large containers vs. trucks which are loaded by hand by workers picking up individual bags); type of route (high density urban areas with large businesses or apartment complex vs. low-density rural areas); and type of garbage (mixed waste including heavy glass, metal and wet organics vs. light but bulky plastics and foam).
Although I sent an email inquiry to Durham Waste Department asking about capacity and route lengths of garbage trucks, I didn’t receive a response. So I looked for published studies which could provide figures that seemed applicable to Durham Region.
A major source was the paper “Fuel consumption estimation for kerbside municipal solid waste (MSW) collection activities”, in Waste Management & Research, 2010, accessed via www.sagepub.com.
This study found that “Within the ‘At route’ stage, on average, the normal garbage truck had to travel approximately 71.9 km in the low-density areas while the route length in high-density areas is approximately 25 km.” Since Durham Region is a mix of older dense urban areas, newer medium-density urban sprawl, and large rural areas, I estimated an average “medium-density area route” of 45 km.
The same study found an average fuel economy of .335 liters/kilometer for garbage trucks when they were traveling from depot to the beginning of a route. The authors found that fuel economy in the “At Route” portion (with frequent stops, starts, and idling) was 1.6 L/km for high-density areas, and 2.0 L/km in low-density areas; I split the difference and used 1.8 L/km as the “At Route” fuel consumption.
As to the volumes of trucks and the weight of the garbage, I based on estimates on figures in “The Workhorses of Waste”, published by MSW Management Magazine and WIH Resource Group. This article states: “Rear-end loader capacities range from 11 cubic yards to 31 cubic yards, with 25 cubic yards being typical.”
Since rear-end loader trucks are the ones I usually see in residential neighborhoods, I used 25 cubic yards as the average volume capacity.
The same article discusses the varying weight factors:
The municipal solid waste deposited at a landfill has a density of 550 to over 650 pounds per cubic yard (approximately 20 to 25 pounds per cubic foot). This is the result of compaction within the truck during collection operations as the truck’s hydraulic blades compress waste that has a typical density of 10 to 15 pounds per cubic foot at the curbside. The in-vehicle compaction effort should approximately double the density and half the volume of the collected waste. However, these values are rough averages only and can vary considerably given the irregular and heterogeneous nature of municipal solid waste.
In Durham Region the heavier paper, glass, metal and wet organics are picked up separately and hauled to recycling depots, so it seems reasonable to assume that the remaining garbage hauled to the incinerator would not be at the dense end of the “550 to over 650 pounds per cubic yard” range. I used what seems like a conservative estimate of 600 pounds per cubic yard.
(I am aware that in some cases garbage may be off-loaded at transfer stations, further compacted, and then loaded onto much larger trucks for the next stage of transportation. This would impact the fuel economy per tonne in transportation, but would involve additional fuel in loading and unloading. I would not expect that the overall fuel use would be dramatically different. In any case, I decided to keep the calculations (relatively) simple and so I assumed that one type of truck would pick up all the garbage and deliver it to the final drop-off.)
OK, now the calculations:
Number of truckloads
25 cubic yard load X 600 pounds / cubic yard = 15000 pounds per load
15000 pounds ÷ 2204 lbs per tonne = 6.805 tonnes per load
140,000 tonnes burned by incinerator ÷ 6.805 tonnes per load = 20,570 garbage truck loads
45 km per “At Route” portion X 20,570 loads = 925,650 km “At Route”
1.8 L/km fuel consumption “At Route” x 925,650 km = 1,666,170 liters
60 km per load traveling to and from incinerator
60 km x 20,570 loads = 1,234,200 km traveling
.335 L/km travelling fuel consumption X 1,234,200 km = 413,457 liters
1,666,170 liters + 413,457 liters = 2,027,627 liters total fuel used by garbage trucks
As a check on the reasonableness of this estimate, I calculated the average fuel economy from the above figures:
20,570 loads x 105 km per load = 2,159,850 km per year
2,079,625 liters fuel ÷ 2,159,850 km = .9629 L/km
This compares closely with a figure published by the Washington Post, which said municipal garbage trucks get just 2-3 mpg. The middle of that range, 2.5 miles per US gallon, equals 1.06 L/km.
Electricity output of the generator power by the incinerator
With a rated output of 14 megawatts, the generator could produce about 122 megawatt-hours of electricity per year – if it ran at 100% capacity, every hour of the year. (14,000 kW X 24 hours per day X 365 days = 122,640,000 kWh.) That’s clearly unrealistic.
However, the generator’s operators say it puts out enough electricity for 10,000 homes. The Ontario government says the average residential electricity consumption is 10,000 kWh.
10,000 homes X 10,000 kWh per year = 100,000,000 kWh per year.
This figure represents about 80% of the maximum rated capacity of the incinerator’s generator, which sounds like a reasonable output, so that’s the figure I used.