New oil burning furnace build

It's interesting to note the different concrete building methods: the 12" PVC tube I have was an offcut from a building site where it was used to cast round concrete columns for buildings. They just leave it in place after the concrete has set and maybe paint the PVC. It looks like Sono tubes are used the same way but cut off the concrete after casting.

 

I'm wondering if commonly available American dense castables have enough strength to cast a liner the way I've been doing?. I'd researched dense castables available in the USA like "mizzou" and if it's the same stuff I'm using over here which is calcium aluminate based concrete or ciment fondu which is a high strength fast setting cement. Does mizzou behave like concrete, does it set after a certain time period like concrete?. More careful handing may be needed than I'm getting away with.

 

Hi Kelly, it's a different chemistry to the usual portland cement but made the same way in a large rotary kiln which causes a chemical reaction between lime and aluminium oxide (could be bauxite, could be pure oxide). It forms a type of concrete that is fast setting and has a green strength of 80 MPa/ 11600 PSI which is 3-4 times that of normal concrete. After firing the strength drops to 60 MPa which is still 3 times normal concrete. It's used to patch airport runway holes as it sets up in 30 minutes. It ages poorly and several buildings around 50 years old made from the stuff have collapsed or been knocked down. The refractory is a mix of the fine ground powder as well as small stone sized aggregate lumps of the same white material.

From Wikipedia:
Manufacture
The cement is made by fusing together a mixture of a calcium-bearing material (normally calcium oxide from limestone) and an aluminium-bearing material (normally bauxite for general purposes, or refined alumina for white and refractory cements).

The melting of the mixture is achieved at 1600 °C and is energy demanding.[8][9] The more elevated temperature explains a part of its higher production costs than for the clinker of ordinary Portland cement sintered at 1450 °C.[citation needed]

The liquified mixture cools to a vesicular, basalt-like clinker which is ground alone to produce the finished product. Because complete melting usually takes place, raw materials in lump-form can be used. A typical kiln arrangement comprises a reverberatory furnace provided with a shaft preheater in which the hot exhaust gases pass upward as the lump raw material mix passes downward. The preheater recuperates most of the heat in the combustion gases, dehydrates and de-hydroxylates the bauxite and de-carbonates the limestone. The calcined material drops into the "cool end" of the melt bath. The melt overflows the hot end of the furnace into molds in which it cools and solidifies. The system is fired with pulverized coal or oil. The cooled clinker ingots are crushed and ground in a ball mill. In the case of high-alumina refractory cements, where the mix only sinters, a rotary kiln can be used.[citation needed]

 

I don't know anything about the science of these materials, but being young and impressionable in the 1970's, I would really like a t-shirt with the
word 'fondu' on it for the word play off of 'fondue' ...

 

The high alumina content white ciment fondu seems to be a specialist refractory material, I haven't seen it for sale at all, just brown and grey versions with less alumina content and lower temperature handling. When cleaning up any excess refractory, I washed the fines off to reveal the aggregate lumps and they are snow white ceramic stones which I assume is also uncrushed ciment fondu clinker from the kilns. Looking at the blue label stuff, I could see a film about some street concretors called the "The Fast and the Fonduriest".

There must be thousands of fondue sets used maybe twice and lurking in cupboards for the last 50 years . The bore formwork has been reconfigured into the top ring formwork now: I used grey epoxy grout to add draft to the inner plywood ring and fill some gaps, it'll need a good sand and a lot of wax to guarantee release. I added the black plywood ring to position the colorbond sheet steel at the new diameter which will leave 10cm/4" space for insulation. A bit of calculating shows I have about 18 litres of volume if the ring is 7.5cm/3" deep which equates to 40 kilograms of refractory concrete. So already we are up to 100 Kilograms. The base doesn't need to be full diameter so I can save some material there.

 

The top ring has been poured now, it took about a bag and a half or 40Kg of refractory. I had to overdose the water content as it was too stiff to ram up initially. I sanded down all the epoxy grout from yesterday, wrapped it with grey stretchy tape and put a generous coat of paste wax on all surfaces for release. I'll be able to remove the inner and outer walls and then that just leaves the inner plywood socket ring and plywood base.


I think once it's in place I'll support it with steel underneath it. Two bags of refractory left now to make the furnace base and the lid so cutting things a bit fine but I think I can make it by using the silica fibre insulation to back the dense refractory.

 

The inner and outer formwork came off easily, then I made some thin wood wedges to get the ring off the base and stood it on it's edge without disaster. After a few measurements, I manhandled the ring onto the bore tube where it fit snugly and smoothly. I'll weld some sheet steel supports under the overhang for when it eventually cracks over time. I'll start work on the steel base now with the same 69cm/27" diameter to match the ring O.D.. Currently it's 40cm/16" bore and 50cm/20" deep.

 

I have the steel base cut from 3mm/0.125" scrap and I'm looking at using a steel plough disc as the physical support for the furnace refractory. The idea would be to weld some ribs underneath to space it off the main base and stuff the air gap with fiber insulation. The steel would have to provide weight support while hot from whatever heat bleeds through which would be a minimum of 360 deg C/ 680 F based on measuring dense refractory only furnace walls with a laser temp unit. I think I'll cast the furnace base in situ onto the plough disc with some permanent steel form work.

 

I'd been thinking of expanded perlite as a potential cheap backfill insulation, the stuff has to be heated to 1300 deg C or 2372 F to be expanded.

On pondering overnight, I'll cut the plough disc to slightly larger diameter than the refractory tube and weld a strip round the rim, I'll then use a short length of steel waterpipe to connect the center hole to a drilled hole in the round base. The theory is that when inevitable cracks form in the refractory base, any fuel oil that makes it through to the plough disc can drain out the bottom of the furnace base.

 

The steel furnace body is coming along nicely: there are eight square hollow steel uprights supporting the top ring. The ring was cut from the leftover steel after cutting the round base and it will support the refractory ring and lid. The uprights will support the silica fibre insulation while the sheet metal cover is wrapped around the outside.

 

Today the frame was fully welded, the plough disc has four short lengths of square hollow steel around the rim to support it and in the center there is a 75mm length of 50mm water pipe connecting the plough disc hole to a hole in the steel base. The idea is the plough disc can act like a bowl to gather any waste oil that percolates through the cracks in the base and drain it out the bottom of the furnace. This has happened before if the furnace is slow to light at times, soaking the floor with oil. I had to tip the frame on it's side to fit the liner as it's too awkward to lift at 60+ kilos through the hole in the frame. I have about 6mm of air gap between the refractory bore and the refractory ring which I'll grout with clay before use, I'll put a thick ring of the clay and the ring can squish it down to size. The base of the bore liner has an air gap of 12mm/0.5" due to the curve of the plowing disc and it should fill with the vibrated refractory. To save on refractory, I'll put an existing spare refractory disc in the bottom with grout under it and seal the drain hole with tape (will burn away) and cast an inch or more of refractory over it. I'll cut the tuyere hole with some 5 inch diamond masonry wheels, making sure to go anticlockwise to take maximum advantage of the Coriolis effect in the Southern Hemisphere.

 

I've had issues before with tuyere plugs moving during vibration of the refractory in the past, this time round I wasn't sure of the diameter and placement. The furnace will sit out in the backyard next to the existing one, I'll put some stubby legs on it to keep it off the ground. Surprisingly the size isn't much taller or wider than the existing 1.5 beer keg furnace with insulation jacket: it's about knee high at the moment. Long term, I'll need a pivoting lever based crane to lift the crucibles out and keep some distance from the heat.

 

The floor has been installed: A quarter of a bag of refractory leveled off the plough disc curve, then I placed a 5cm/2" thick refractory disc in the center and broke up a second disc into chunks and wet them before setting into place around the first disc. It took half a bag of refractory to cover the wet chunks and I ended up with 6cm thick at the edges and 8cm thick in the center. The vibration worked really well with refractory showing up on the outside of the base in small amounts.