Pyrolysis, the anaerobic heating of hydrocarbons such as wood, old tires, used engine oil, plastics, tallow and so forth, needs to be economic for it to be undertaken. Below are some suggested ways to increase the financial feasibility of pyrolysis.
Energy conservation
Pyrolysis needs heat energy to cause the various long chain materials to break ('crack', in petrol-chemistry terms) and the applied heat must be at a temperature of about 5000C. But, of course you don't want to be heating the great outdoors. That is a waste of energy/money. Super insulation is needed so that you only use the amount of energy needed to break the bonds. An insulation material that comes to mind is the Aerogel that was used to protect the shuttles during re-entry but cost and availability might be a barrier.
Source of energy
Clearly the energy to heat the retort must be renewable. Energy must come from hydro, wind, geothermal or solar sources. Renewable energy continues to go down in price as the hardware to produce it becomes less expensive. There are a couple of possibilities. With the spot-price-silliness that we have in New Zealand, electric energy is very cheap when it is in excess. Either the pyrolysis unit can operate, only when energy is cheap or cheap energy can be bought and stored in a mega battery to ensure the continual operation of the pyrolysis unit.
It may be worthwhile for the pyrolysis unit to own it's own renewable energy kit and thus be always paying the wholesale price. This 'kit' continues to decrease in price. With a battery as well, excess energy can be sent to the grid when spot prices are high.
Energy is likely to be one of the largest running costs in a pyrolysis factory.
Externalities
Many waste streams can be pyrolyzed to produce either liquid fuels or easily compressed and liquefied fuels. Many waste streams are problematic if not disposed of somehow.
There is now a cost to send waste to land fill and a land fill trashes beautiful pristine wild areas which are then no longer an asset to the community.
Some wastes are direct health hazards such as the leaching of material from them into the ground water or as breeding grounds for mosquitoes (tires). As the world warms, tropical mosquitoes that carry a range of very nasty diseases will be moving poleward.
Many pyrolyzable wastes are a fire hazard and the by product of burning some of them creates the toxic, carcinogenic, dioxane, and fine particulate material. If they are sent overseas, the receiving country may simply dump them into the ocean. There is no need to describe why ocean dumping is problematic.
The point is that the pyrolysis unit has to be credited for the financial cost it mitigates when a solution is not found for that particular waste and/or for the present cost of taking care of the waste. Government action may well be necessary to ensure this.
By products
Depending on the feed stock, there are various valuable by products of pyrolysis.
Wood
The by product of wood-pyrolysis is charcoal. Charcoal can be bagged and sold for barbecues or can be incorporated into agricultural soils, earning carbon credits. See Terra Preta
Plastic (clean or contaminated)
No by products result from the pyrolysis of plastic. It all converts back into alkenes and alkanes. The alkenes can be converted into the more useful alkanes by saturating the double bonds with green hydrogen. Petro-chemical engineers have methods of either bonding low molecular weight fractions into larger molecules or, on the contrary, cracking long molecules into smaller ones to get more of the desired fraction.
Electronic equipment
The pyrolysis of electronic equipment results in a metal rich ash. As battery recycling ramps up, this ash could likely be sent to a battery recycling facility for the separation and recovery of these metals. This sort of ash is a far richer source of metals than any natural ore although it is a rather challenging mix. At present, waste circuit boards are sent overseas for the recovery of their metals. Most of the weight of a circuit board is plastic. With pyrolysis, you don't send the plastic saving on weight and hence expense.
Used tires
By products of the pyrolysis of tires are iron, sulfur and carbon black. Sulfur can be converted into sulfuric acid, using the oxygen which is a by product of the Hydrogen which has been produced for saturating alkenes. Sulfuric acid is a very valuable product used in a plethora of chemical processes. Carbon black is used in air and liquid filters, black paint and in the production of new tires and black plastic. The iron is sent to an iron refinery where it is combined with iron ore in the smelting process.
Used engine oil
Used engine oils are very variable. For instance some of them have additives of materials such as molybdenum sulfide. Presumably this, and any other similar materials would remain after the pyrolysis of used engine oil. In addition, there may be a small concentration of metal from the engines. But I suspect that well north of 99% of engine oil should convert into the usual pyrolysis products. The ash could probably be combined with the ash from electronic equipment and sent to a battery recycling facility.
Tallow
Tallow should not have any by products and rendering is not necessary. It can be directly pyrolyzed. However, if tallow is converted into biodiesel instead of using pyrolysis, glycerine is a by product. One has to work out if it is worth while to build a separate facility for the chemical conversion of tallow to diesel or to simply pyrolyze this waste stream.
Side economic benefit
If this whole process is kept in the eye of the public as it proceeds, it would seem likely that the petrol company responsible would gain a greater share of an ever diminishing market for petroleum products. Parts of the output of pyrolysis can be mixed into conventional petrol and diesel, making them 'greener' and done through already existing distribution channels.
