Does it Make Sense to Recycle Plastic?

Factual Questions
1

What if your trash is going to an electricity co-generation plant? Isn’t the plastic just another form of hydrocarbon fuel? Aren’t you saving oil or coal by burning hydrocarbon polymer instead? And what about all the energy required to transport, clean, sort and process the waste plastic compared to using virgin plastic?

And suppose your waste goes to a landfill? What is so bad about that? Are we really running out of space? If we were, why isn’t it more expensive to dispose of waste? In my town, it only costs $165 a YEAR to cart away all your household waste from your curbside.

I’d love to hear some solid facts to address these issues. Otherwise I feel like not helping the environment when I put out my blue bin - I’m afraid I’m just playing with garbage.

2

I really hate seeing GQ threads like this that are lonely and abandoned.

First, some problems with recycling plastic is that it is still more expensive to sort and get a high enough quality stream to compete with virgin plastic. There sometimes have to be large subsidies to make the collection, sorting, cleaning, and re-use process viable.

Even though it’s from the NYT, here is an article that has an overview that does not have any huge factual errors:

http://www.spaceship-earth.org/Letters/Editor/Plastics_recycling_in_US.htm

Also, several types of plastics are not really “recyclable” at all, due to their chemical nature. Reputedly, the “Type 1” (i’ll skip chemical terms to keep it simple) plastics can be very easily recycled and do make economic sense, and “Type 2” can be recycled if they are cleaned well enough, but even then are still more difficult than “Type 1”.

Now, on burning: you’re not saving much oil at all, at least not in the US, as barely 2-3% of US electricity production dervies from oil. You could be saving some on coal and other fossil fuels, but burning plastic is somewhat problematic for a few reasons:

  1. Plastics have handling and sorting problems at the start - metal removal, removal of other trash. While power plants can be very flexible in accepting large amounts of carrier and inert material, they still have to be careful on this. And, of course, non-burnable items reduce the efficiency of the process.

  2. Plastics don’t lend themselves to being burned in high-efficiency pulverized furnaces, as they clog the pulverziers. Even when hogged or fluffed or ground, they can melt in the coal pipes and build up on the lower-temperature portions of the burners, clogging them and bringing the unit down. They can be burned in cyclone furnaces, but only in small amounts so as not to disturb or change the slag tapping rate outside of the boundaries you need. So much of the time they are burned in stoker furnaces, which are much lower efficiency than a conventional coal furnace.

  3. Plastics can pose environmental problems when being burned. While most consumer plastics aren’t filled with mercury or lead or other yummy heavy metals, some industrial plastics are contaminated with them. Burning plastics at the lower temperatures and poorer air distribution levels found in stoker furnaces can result large amounts of unburned hydrocarbon emissions, which is not something a power plant typically has, and which is very problematic from a local air quality standpoint.

  4. The ash or waste from the plastic is generally not saleable. Many coal power plants are able to recycle their fly ash for use in concrete, and their bottom ash for use in sandblasting and aggregate. When plastic is combusted over a certain level, the colour and chemical quality of the ash can quickly change an ash from something you can sell at $5 a ton, to something that must be landfilled at $15 a ton. If your plant makes 100,000 tons/year of fly ash…you can see that is a $2M differential cost.

In addition, co-firing of plastics with coal has resulted in some small level of extra deposits on the cooler portions of the furnace walls and tubes, which require additional sootblowing to remove. Generally, air sootblowing does not work well with these, and steam sootblowing is required. This equates to a net additional cost.

  1. Then of course there is the public perception issue. Tell the average person at their door that the local power plant is going to be burning trash, and they get that deer on the first day of hunting season look. It’s bad enough that there have to be all those evil power plants running around threatening their children, but burning trash at one?

So there are some issues with burning the plastics. They do have a good heat content level - between 7000 Btu/lbm to as high as 17,500 Btu/lbm IME (partially because there is little to no water and ash content in them), with most of them being about the same level of heat per pound as a very good bituminous coal (12,000 - 14,000 Btu/lbm).

And, of course, your point in the OP regarding landfill space is somewhat on the money - there is an abundance of landfill space, but the key problem is finding landfill space that is close and convenient to the town, such that it does not involve a 20-mile round trip for the dump trucks. The same soccer Dads and Moms who sign the petition to move the new landfill 50 miles out of town where those “farmers” can deal with it are the same ones that will bitch and moan to high heaven over having caravans of dump trucks on the highway and $500 a year tipping bills.

3

Thank you for your thoughtful and informative reply. The general concerns you raise with respect to plastics incineration seem theoretically valid but how do they square with the reality of various regional co-gen facilities that are operating successfully on a municipal waste stream? In my area of eastern Massachusetts, many municipalities are sending their mixed municipal waste to a waste-to-energy plant called SEMASS. They have been operating for about 15 years steadily adding capacity. They shred and recover ferrous and aluminum for resale. They say their ash goes for use in paving aggregate. Biggest complaint seems to be about trucking all that volume all that distance. In the northeast, I think it is a fair assumption that waste is substituting for coal because we still use coal in many sites of the power grid. So my question is: is this kind of situation, does it make sense to recycle plastic?

My fear is that recycling has become somewhat of a religion the premise of which cannot be questioned.

4

The main probelm is that plastic is very poor at being recycled unless you have a very pure stream. Most plastics hate being mixed with a plastic of another kind. so if so 5% of polypropylene got in with polyethylene, the reulting plastic would have little strength and be useless for most things. the ink, pigments and the additives they add to stabilise the plastic also means that reusing it gives an inferior product. As most plastic articles often have a mixture of plastics already (e.g. Polyethylene bottle but polypropylene screw top which stops the screw top getting welded to the base) seperating then can be a nightmare.

If possible, the best way of extracting the energy back from most plastics is to burn them if possible.