So I wanted see how much energy I could generate from the gas burner on my stove. I found out how much energy the stove would put out from the specification plate on the underside of the stove. It worked out to be around 3.5KW. To harness this energy I decided to build a simple boiler with a turbine to power an electric motor.
I made the boiler out of a high pressure fire extinguisher which had an absolute maximum pressure of 600PSI. I was planning on having the boiler operate around the 150-200PSI range. I found the fire extinguisher and a nice stainless steel tap which will control the steam released into the turbine at a local salvage yard for about $50 AUD, along with a few other stainless steel odds and ends for the turbine. I welded some stainless steel fittings onto the side of the fire extinguisher to connect the Thermosiphon (heat siphon). The reasoning behind using a Thermosiphon is instead of heating the boiler directly (which would reduce the maximum operating pressure of the boiler by weakening the steel) heat a copper pipe which would be much less catastrophic if it were to fail, but still would cause some damage and steam burns. The copper pipe that I used is rated to 600-700PSI not all pipe is rated to this pressure, some may have a higher or lower rating depending on a few variables. After a few tests of the boiler I added some insulation to the boiler and the pipes, which significantly reduced the heat loss of the system. The insulation had to be tested to see if it could handle the temperatures the boiler would reach which could be as high as 180°C. Some of the insulation failed the test so I had to source a higher rated insulation. The black insulation for the copper tubing can reach 200°C before it starts to melt.
I started off by making a Stainless steel turbine which would harness the energy from the steam, I made the turbine to tight tolerances within half a Millimeter but this was not enough. Upon operation the turbine was vibrating which could be dangerous and a waste of energy. Then I realised the air powered dremel that I was using may be able to do what I wanted if it could handle the temperature of the steam. I tested it and it worked perfectly, I hooked a small electric motor up to the dremel and made a makeshift base for it. I joined it up to the copper pipe, all the fittings had Loctite put on the threads prior to tightening to stop any leaks.
I filled the boiler up with water until it was a about 4 CM form the top and put the Thermosiphon over the burner on the stove (the copper thermosiphon coil was covered with a stainless steel strainer to increase the efficiency ). These are some of the readings taken:
Time taken to reach 100 °C = 1HR 19MIN
After 2HR 45MIN = 140 °C @ 58PSI
(temperatures taken at lower Thermosiphon connection)
Time Taken to reach 165°C = 2HR 50MIN (lower connection)
Time Taken to reach 178°C = 2HR 50MIN (top connection)
A hazard identified with the thermosiphon is that it could get vapor locks, when this vapor lock released itself it could cause the pressure to go up very rapidly, so a suitable pressure relief valve is required to reduce any risk of over pressure. E.g the pressure increased within a minute to 300PSI from 70PSI.
In the video below the multi-meter is reading in amps, the motor generated 7.2 Amps @ 7 Volts.
Project completed: 04/2016