Some Common Knowledge About High-Purity Acetylene

      Producing high-purity acetylene from calcium carbide is an essential component and defining feature of the calcium carbide-based polyvinyl chloride (PVC) production process. There are two main processes: wet acetylene production and dry acetylene production. In China, the majority of the domestic calcium carbide-based PVC industry employs the wet acetylene production process. The environmental challenges posed by the "three wastes"—including calcium carbide slag slurry and clean wastewater—generated during the calcium carbide-based PVC production process have long been a major obstacle to the industry's development. Addressing these "three wastes" in wet acetylene production not only represents a key goal for energy conservation and emission reduction but also has become an inevitable necessity for the survival and sustainable development of calcium carbide-based chlor-alkali enterprises.

　　The basic reaction in the wet-process high-purity acetylene production involves calcium carbide reacting with water—in an amount far exceeding the theoretical stoichiometric requirement—in an acetylene generator. This hydrolysis reaction produces acetylene gas and releases a significant amount of heat. Since calcium carbide contains small amounts of impurities, certain side reactions also occur in the aqueous phase of the generator. During production, water (including clarified slurry from calcium carbide residue and waste sodium hypochlorite solution) must be continuously added to the acetylene generator. Meanwhile, the calcium carbide residue slurry is discharged to carry away heat and maintain the temperature, while also replenishing the water that has been consumed.

　　The production of high-purity acetylene mainly involves four processes: calcium carbide crushing, acetylene generation, acetylene purification, and calcium carbide slurry treatment. The block-shaped raw material—calcium carbide—is crushed by a crusher and then subjected to iron and silicon removal using an iron remover. The calcium carbide meeting the required particle size is conveyed by a belt conveyor to a calcium carbide storage bin. During the acetylene generation process, after being metered, the calcium carbide from the storage bin is fed into a feeding hopper via a feeder and a belt conveyor. Under continuous nitrogen purging, the material is sequentially introduced into the upper and lower hoppers through hopper valves, and then intermittently added to the acetylene generator under the control of a vibrating feeder. When calcium carbide comes into contact with water in the acetylene generator, it rapidly decomposes, generating crude acetylene gas that escapes from the top of the generator. This crude acetylene gas then passes through a calcium carbide slurry separator and a positive water seal before entering the acetylene purification stage. The concentrated calcium carbide slurry remaining after the hydrolysis of calcium carbide is periodically discharged from the bottom of the acetylene generator into a calcium carbide slurry pond under the control of a slag discharge valve, while the dilute calcium carbide slurry flows into the slurry pond via an overflow pipe. All of this slurry is subsequently sent to the calcium carbide slurry treatment process.

　　During the high-purity acetylene purification process, the crude acetylene gas is first washed and cooled in a water scrubbing tower and a cooling tower. A portion of the gas then enters the acetylene gas cabinet to balance the system’s consumption of produced gas. The majority of the crude acetylene gas is compressed by a liquid-ring compressor, separated from water, and sequentially fed into Cleaning Towers No. 1 and No. 2, where it undergoes counter-current reaction with sodium hypochlorite solution inside the towers, effectively removing impurities such as sulfur and phosphorus. The gas then proceeds to the neutralization tower. Acidic substances generated during the manufacturing process are neutralized within the tower using a dilute NaOH alkaline solution, producing refined acetylene gas. After being cooled and dehydrated by a high-purity acetylene cooler and an acetylene mist eliminator, the purified acetylene gas is sent to the conversion process for the production of vinyl chloride.

　　During the calcium carbide slurry treatment process, the concentrated calcium carbide slurry from the calcium carbide slurry pond is pumped by a calcium carbide slurry pump into the calcium carbide slurry pond, where it is mixed with dilute calcium carbide slurry. The resulting mixture is then pumped by another calcium carbide slurry pump into the high-level calcium carbide slurry pond and subsequently flows into the thickening pond. After undergoing gravity sedimentation, separation, stirring, and concentration in the thickener, the concentrated calcium carbide slurry at the bottom of the pond is conveyed to the calcium carbide slurry treatment process via a discharge pump. The clear liquid from the upper part of the thickening pond flows over an overflow weir into the secondary settling tank, where it is pumped by a clear liquid cooling pump into the spray cooling tower. Following forced spray cooling, the clear liquid enters the tertiary settling tank. The clarified liquid separated through sedimentation is then pumped by a clear liquid pump back to the generation process, where it is reused as circulating water for the production of high-purity acetylene generators.