Pyrolysis gas

The Reactor D experiments are intended to quantify aspects of pyrolysis gas production independent of combusion. The reactor has been fitted with a vent tube so pyrolysis gas can be observed. However, pyrolysis is a complex mixture which is beyond this amateur scientist’s capability to analyze component-by-component. Instead, two-stage crude separation will be attempted. The reactor has proven difficult to seal for creating positive pressure - the paint can lid leaks, the vent tube fittings leak, and the electrical wire entrance leaks. Therefore, the system will be operated at negative pressure, created by a small aquarium pump.

The first stage of separation will be a “cold finger” a small glass jar will be set in an ice bath. The vent tube will enter the jar on one side and be roughly separated from the other side with the outlet tubing by accordion-folded aluminum foil. The foil barrier, it is hoped, will force the gas to take a longer flow path and will create some additional heat transfer area and condensation surface area.

The second stage of separation will be a plastic container loosely filled with cotton batting (salvaged from an abandoned box-spring). The inlet tube is attached to one side of the container, and the outlet tube is attached to the opposite side.

The air pump, which is designed with only a controlled outlet, is enclosed in a third container. The inlet to this container serves as the suction port, and the exhaust is directed to the environment.

Reactor D with the pyrolysis gas separation chain

The cold finger with its foil baffle (but not the lid or associated tubing), and the cotton filter, with its associated tubing will be weighed before and after each test so net mass capture can be calculated. Captured masses will be compared with the mass loss of the pyrolysis sample. Although the air pump itself is not intended as a capture stage, the air pump will be wrapped with filter fabric (old t-shirt cloth) and weighed before and after each test to check for filter stage leakage.

This setup failed on the first attempt: with ice at the cold finger and the air pump seemingly operating (exhaust makes bubbles), at pyrolysis temperature, there was copious smoke escape from the power wires entrance and negligible smoke evident in the condensation stage. This is proving to be a difficult problem: sealing the reactor. There are relatively few commonly available materials that can withstand 500C.

I will mix a small amount of cement with sand and chopped fiberglass to make a plug for the approximately 1.5cm diameter hole around the wire. The calcining temperature for making Portland cement is about 600C. Unfortunately, the Portland-cement-based products I have available all contain “polymers” - though the polymer fraction is likely low. The polymers will decompose and this may compromise the plug integrity. The fiberglass insulation under the reactor base is saturated with pyrolysis oil and must be replaced before I attempt the hole repair.

I made a rough measure of the air pump flow rate and it is only 250 mL/minute - I suspect that fast pyrolysis may produce gas at a higher rate. Boiling of 100g of water took 15 minutes; the density of saturated steam is 0.59 kg/m3, so 100g of water yields 0.169 cubic meters of steam; released over 15 minutes that is a flow rate of 11 L/min; 180 mL/sec. Early pyrolysis experiments exhibited high velocity smoke venting that appeared quite rapid. I will abandon the air pump stage