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Comment PDF Processing & Handling

Technology Profile: Calcium Carbide Production from Limestone

By Intratec Solutions |

This column is based on “Calcium Carbide Production from Limestone – Cost Analysis,” a report published by Intratec. It can be found at: www.intratec.us/analysis/calcium-carbide-production-cost.

Calcium carbide is the most industrially relevant carbide because of its important role as the basis of the acetylene industry. In locations where there is a shortage of petroleum, calcium carbide is used as the starting material for the production of acetylene, which, in turn, can be used as a building block for a range of organic chemicals, such as vinyl acetate, acetaldehyde and acetic acid.

Figure 1. The process diagram shown here outlines a process for the production of calcium carbide from limestone

The process

The following describes a process for calcium carbide production from limestone and coke (Figure 1).

Feed preparation. Initially, coke is dried with hot air in a tray dryer to reduce moisture in the coke. After drying, the coke is transferred to the electric furnace. Limestone is crushed in a jaw crusher into a uniform particle-size range. Some gross impurities originating from the limestone are separated in a screener.

Lime kiln. The crushed limestone is calcined in a vertical-shaft lime kiln. The calcium carbonate present in the limestone is decomposed into calcium oxide (CaO, or lime) and carbon dioxide, which is used to preheat the limestone feed. The resulting CaO is passed through a screener for the removal of gross impurities. Then the CaO is conveyed, along with dry coke, to an electric furnace, which contains electrodes through which high current passes to provide heat.

Electric furnace. The lime-coke mixture flows down the furnace until reaching the high-temperature reaction zone, where molten CaO reacts with coke and generates molten calcium carbide. The reaction zone is a packed bed of coke, where empty space is filled with molten calcium carbide and gaseous byproduct carbon monoxide. The CO gas from the electric furnace is fed to a water scrubber for removal of any residual particles. The gas is then temporarily stored in a gas holder before it is fed through a blower to the dryer and the lime kiln upstream, where it is used as fuel.

The molten calcium carbide product is removed from the furnace by means of continuous tapping, and it falls into a water-cooled cylinder, where the products solidifies.

Finishing. The solid calcium carbide is transferred to the carbide crusher, where it is sieved and crushed until it reaches the desired particle size for the final product. The crushed product is screened to remove impurities and then conveyed to silos that feed the packing section.

 

Other production pathways

Calcium carbide production consists of the reaction of CaO (obtained from limestone) with a carbon material. There are several different routes to manufacturing, related to the different sources of carbon (Figure 2).

Economic performance

The total operating cost (raw materials, utilities, fixed costs and depreciation costs) estimated to produce calcium carbide was about $1,000 per ton of calcium carbide in the first quarter of 2015. The analysis was based on a plant constructed in the U.S. with the capacity to produce 80,000 metric tons per year of calcium carbide.

Edited by Scott Jenkins

Editor’s note: The content for this column is supplied by Intratec Solutions LLC (Houston; www.intratec.us) and edited by Chemical Engineering. The analyses and models presented are prepared on the basis of publicly available and non-confidential information. The content represents the opinions of Intratec only. More information about the methodology for preparing analysis can be found, along with terms of use, at www.intratec.us/che.

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