A kiln is a furnace that is used to dry or burn materials. A lime kiln, then, is a kiln used to burn the impurities out of limestone. Pure lime–known as “quicklime”–is produced in the process. Here at Captain Zipline, you can view the remains of lime kilns from the 1890s, structures that were operational more than a century ago.
The trick is, though, you will have to look down into the canyon after stepping off the cliff and while flying across our zip line cables to see these historic treasures!
Well, for the most part. But, if you are not brave enough to look down while in flight, consider taking a peek of these structures from one of the zip line platforms once you get across the canyon…with both feet firmly planted on the ground.
In many places throughout the world, old lime kilns (pre-industrial era) are predominantly found at seaports, places where transportation of the materials into and out of the kilns was more easily managed. Remnants of the historic kilns at Captain Zipline lie at the bottom of the canyon, close to what was once a road. Initially, the access to this site was probably via a mule or donkey trail which later became a wagon road. Raw limestone was hauled into the site and deposited in the kiln in alternating layers of fuel (initially wood; later replaced by coal) and rock. It was important that the limestone rock be of a certain size and fairly uniform. Before modern times, limestone was often crushed by hand with the goal of producing rocks that were approximately 1 to 2.5 inches in size. If the rocks were too large, the burning within the rock would be uneven; if too small, the load “could not breathe.” Temperatures of 2000 degrees Fahrenheit were required for this process, one in which the carbon dioxide was driven off. At the end, the quicklime was raked out from the bottom of the kiln. Two thousand pounds of limestone produced 1000 pounds of quicklime. Pure lime is white in color, caustic, and reacts violently with water. Once mixed with sand and water, it will adhere to brick and stone.
Since ancient times, lime kilns have produced much of the lime used in construction, particularly mortar and plaster. The old, pre-industrial era kilns themselves were made of rock and mortar and resembled a chimney. These types of structures date back as far as 7,000 to 14,000 years ago, having been identified in places such as Turkey. The Mayans used lime mortar in their construction of monuments, stone buildings, and roads. In North America, however, lime was not used until after the European settlers arrived.
Uses over the years have evolved from bleaching and tanning in the earliest years, as well as building materials as described above, to more modern applications in manufacturing. Lime has a long history of being used in agriculture as well. A more macabre use was that it served as a means of preserving dead bodies before refrigeration was available.
Batch processing of limestone was the norm in the old times, a process deemed inefficient given the time and energy required to heat up the oven and then cool it down. In some operations, it could take a 1 week turnaround time to produce a load of quicklime–1 day to load, 3 days to burn, 2 days to cool, and 1 more day to unload. In light of this, some lime kiln operations were built with a series of 7 kilns, allowing a continuous rotation of the process and daily production of pure lime. The romantic brick structures that once were used to produce pure lime have been replaced with reinforced steel structures, fired by gas, oil, and sometimes coal. Today’s kilns are much more efficient, although they still leave a considerable “carbon footprint.” For example, the manufacture of 1 ton of lime results in the emission of 785 kg of carbon dioxide. Additionally, if coal is used as the fuel, 295 kg of carbon dioxide is released/ton; for natural gas, 206 kg of carbon dioxide is released/ton. Modern day designs and technology such as preheaters have greatly improved the efficiency of lime production. This is important since the applications of the product have expanded dramatically as well. Today, lime has a multitude of chemical and industrial uses–it is used as an ingredient in glass, paints, caulks, plastics, and pharmaceuticals; it is used in the sugar refining process as well as in water treatment, steel production, and the manufacture of paper.