Driving Innovation in Product Design and Manufacturing Using 3D Printing
consumes around 150 grams / day of lime products( EuLA, 2013b). Lime products are important in the steel industry and important to produce construction materials, paints, paper and plastics as well as cosmetics, rubber, food and glass. The principal use of quicklime is in the steel industry where it serves as a media to remove impurities( silica, phosphorus, and sulphur) during the refinement of steel 16.
To give an estimate of the Lime market,“ Revenue from the sales of lime in the U. S. market is estimated to be valued at US $ 2,538.1M by the end of 2016. The U. S. lime market is estimated to register a value CAGR of 3.7 % during the forecast period 2016 – 2026.” 17
2.2 Kilns: The Hub of the Lime Plant
How do you go from limestone to lime? The calcination process takes place in a lime kiln, where limestone is burned to produce the form of lime called quicklime. The reaction is endothermic and requires approximately 760 kcal / kg to start. An ideal thermal decomposition of 100 % pure
CaCO3 has a theoretical loss of weight of 44 %, in terms of released CO2.
There are several types of lime kilns, commonly divided into Vertical and Rotary Kilns. Rotary Kilns are generally used for firing coal, oil and natural gas. The next common type of kiln is a Vertical Parallel Flow Regenerative Kiln, or Vertical PFR Kiln. Vertical PFR Kilns, consist of two steel, cylindrical, vertical( refractory-lined furnace) shafts, connected by a single arch( as depicted in figure 1).
The term Parallel refers to the way the fuel and the oxidizers flow into the Kiln while the term Regenerative refers to the fact that the two shafts are fired in sequence to achieve excellent energy efficiency. While one shaft calcines the product, the other preheats the stone. In the burning shaft, the lime is calcined in parallel flow. The hot combustion gases are then transferred through the crossover channel to the non-burning shaft where they preheat the limestone in counter flow in the upper area of the shaft. The flow direction of the gases is reversed at regular intervals. This allows the regenerative preheating of the stone to take place( the stone in the preheating zone of the kiln acts as a heat exchanger) and thus for the maximum use of the heat contained in the kiln gases.
Because the kiln is the hub of the lime plant, it is necessary to monitor the level of the limestone inside the kiln during operation. Through limestone level monitoring, the operator can adjust kiln operation( i. e., adjust waste gas outlet temperature or fine-tune the quicklime discharge system) to optimize final product quality and reduce the unplanned downtime of the whole plant 18.
In a Vertical PFR Kiln, the two shafts are loaded from the top, alternatively, with the appropriate quantity of raw limestone, while the final product( lime) is discharged at the bottom. The kiln
16
Stork, Michiel, et al. A competitive and efficient lime industry- Technical Report by Ecofys. www. eula. eu. [ Online ] July 2014. http:// www. eula. eu / file / 475 / download? token = 5lpX8a3h
17 http:// www. futuremarketinsights. com / reports / us-lime-market
18
Qualical International Srl. How QualiCal Produces Lime: Quicklime Calcination. 2014
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