RDIC Kiln Heater Specifications
Resource Development International - Cambodia (RDIC) kilns are simple in design and operation. Ceramic filters are produced in a batch process. The kilns are loaded with 96 filters, slowly heated to an initial 100C, to evaporate the water content, then up to 866C at which temperature the clay vitrifies and ground rice husks burn out. The kilns are heated using two fire chambers under the kiln chamber, in which timber fuel is combusted. Hot gases, smoke, and heat rise into the kiln chamber via two internal chimneys, pass around the filters, and exit through a central exhaust slot in the floor before rising out the chimney in the rear of the kiln.
RDIC currently has 5 kilns installed. These are generally operated in pairs to maximise time and labour efficiencies. The kilns are all housed within a larger roofed shed to protect the brick body of the kilns from rain. The exhaust chimney of each kiln passes through the roof to release smoke and heat above the building.
The raw materials used in the furnace construction include:
The construction process is relatively simple, and can be completed using relatively unskilled labour and simple tools. There are four core steps in the process:
1. Foundation
2. Fire chambers and exhaust chute
3. Kiln chamber and chimney
4. Arched kiln roof.
Dimensions: Fire Chambers: 370mm wide x 2030mm long x 620mm high Fire Chamber opening: 620 high x 370 across (though rounded) Kiln Chamber: 1850mm high x 1660 mm wide x 1760mm long
Figure 3 and 4: Entry door to the oven area (upper), two fire boxes (lower) (left image), and rear chimney (right image).
Figure 5: The dried ceramic filters are carefully loaded into the kilns and stacked in a formation in order to maintain uniform heat distribution.
Figure 6: Worker inside kiln stacking filters (left); Figure 7: stacked filters inside kiln (right)
Figure 8: Once all filters are stacked in the kiln (96 fit in RDICs kilns), the door is covered with bricks and mud. Figure 9: A mud mixture is applied to cover the remaining gaps in order to keep as much heat in as possible.
Pyrometric cones and a pyrometer (thermocouple attached to a voltmeter) are used to measure the temperature inside the kiln. The thermocouple is used to determine when the temperature reaches 100C. One of the pyrometric cones melts at 830C while the other melts at 866C.
The kilns are fired up and maintain at 100C for two hours to dry off any excess water. Temperatures above this may cause excess water to crack the filters.
The temperature is gradually increased by adding more fuel. When the first pyrometric cone melts, the operator knows the required temperature has almost been reached. Once the second cone has melted, the required temperature has been reached. It usually takes between 8 and 10 hours to reach the maximum temperature. The pyrometer isnt used to measure these temperatures since it is not accurate at these levels.
Once 866C has been reached, the fuel and cover with the damper doors is put in place. The kiln is left in this state for 9 hours.
After this main firing time, the damper doors are removed and the kiln is left to cool over 24 hours.
