Gas Kiln Design and Firing Integrating Material and Energy Efficiency into Gas Fired Kiln Plans
Learn how to efficiently build and fire a gas kin this FREE PDF!
If you want to build and/or fire a gas kiln, there are several things you need to know before diving in. Whether you plan on doing oxidation, neutral, or reduction firing, and regardless of the type of gas fuel you will be using, knowing how a kiln is designed and put together helps you understand what is happening during the firing. Gas Kiln Design and Firing Integrating Material and Energy Efficiency into Gas Fired Kiln Plans provides guidance and information critical to the success of your ceramic work.
Check out this excerpt:
Principles of Gas Kiln Design: How to Plan and Build a Gas Kiln That Suits Your Needs
by Frederick L. Olsen
Six critical factors must be considered before you begin to design a kiln. This article reviews those considerations, then discusses the principles of good gas kiln design. These basic principles are then incorporated into the four distinct types of kilns discussed in succeeding chapters on crossdraft, downdraft, updraft configurations and multi-directional draft configurations.
Kind of kiln. Will you build an updraft, downdraft, crossdraft, circular dome, or salt glaze kiln? Will the kiln be 10, 20, 25, 45, or 150 cubic feet or larger? You must carefully calculate your requirements before you begin the design.
Clay to be fired. The type of clay you plan to fire will determine the type of kiln you need, its size, the fuel to be used, and so forth. Kilns may be planned and built specifically to fire terra cotta clay, sewer pipe clay, earthenware, stoneware, porcelain, or any of a number of possibilities. In fact, the potter should know the clay and ware so well that he can design the kiln to enhance the pottery and to control the effects of firing.
Atmospheric conditions. The chamber shape will depend on whether the kiln is intended for oxidation, reduction, or perhaps middle fire. Burners and dampers can greatly affect the ability of the kiln to oxidize or reduce. This, in turn, affects clay bodies and glazes and their outcome.
Available fuel. It may be foolish to build a woodburning kiln in the city; it’s a romantic idea but impractical. Therefore, the relative availability of natural gas, propane/butane, oil, wood, coal/coke, and electricity must be considered. Since propane/butane and electricity are available almost anywhere, and are clean burning, they can be used anywhere except where natural gas is provided. Natural gas is a perfect fuel for use in cities or highly populated neighborhoods; however, before one proceeds, ascertain the amount of gas available to the site. Wood, coal/coke, and oil should be reserved for use in the country.
Location of kiln. Whether city, suburb, backyard, garage, manufacturing area, or countryside, all locales tend to “self design” a kiln. By this I mean that each location tends to dictate what kind of kiln is feasible, a wood kiln in a garage is not the best idea, nor is an anagama in a suburb. Many areas will have building code restrictions that affect what kind of kiln you can use. Be sure to check local regulations before spending any money.
Shelf size. Be sure your kiln is designed to accommodate one of the standard shelf sizes.
Once the basic requirements are determined, according to these critical factors, the following nine principles become an integral part of every kiln design:
PRINCIPLE 1: A cube is the best all-purpose shape for a kiln.
The best design for an updraft kiln has the arch on top of the cube, not contained within (figure 1). This allows for the best stacking space. Also, the volume of the arch serves as a collection area for the flue gases. Increasing the height of the cube chamber with a fixed width decreases the efficiency of even-temperature firing (figure 2). I do not know what the ratio factor is between increasing height and uneven temperature. From experience in firing an updraft kiln (2×3-foot base x 5-feet+ high stacking space) with burners in the floor, I have found from to 1 cone difference between top and bottom, no matter what firing schedule was used. However, on the same kiln 1 foot shorter (2x3x4 feet) it can be dead even top to bottom. In a similar kiln (3x3x5-foot stacking space), I found a constant ½ to 1 cone difference in the firing temperature between top and bottom but if the width and length was increased to 4 feet, the temperature evens out perfectly. My conclusion is that equal height and width is extremely important to even temperature when using floor level burners. From my experience, the same findings also apply to the downdraft and crossdraft kiln design.
Increasing the length of the cube has no effect on the even firing efficiency of the kiln, hence the development of tunnel kilns (figure 3), and other long tube-type kilns used commercially. In circle or round-dome kilns, (figure 4), the diameter and height should be nearly equal, depending upon whether it is an updraft or a downdraft kiln. Most small downdraft kilns tend to include the dome in the height measurement, while updraft beehive types tend to add the dome to the height measurement. For firing tall kilns (figure 2), the burner becomes important and should be placed up the sides of the kiln. There are other specialty kiln designs, not based on the cube, like the tube, groundhog and derivative kilns, but follow other principles listed here.
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Efficient Gas Kiln Firing
by Hal Frenzel
Most anyone can figure out how to mix gas and air to produce heat in a kiln. What takes a little more expertise is firing a kiln with efficiency, regardless of what type of firing is being done. Understanding fuel combustion and the kinds of burners and other atmospheric controls that are available will help you understand the processes at work in a gas fired kiln, and will help you determine the best possible approach for your ceramic art.
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Jennifer Poellot Harnetty
Editor, Ceramic Arts Daily
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