Production Process and Characteristics of High-Purity Acetylene

      Although wet-process high-purity acetylene has a long history of production, requires relatively low investment, and enjoys wide applications, it suffers from high energy consumption, severe pollution, and significant environmental protection pressures. The wet-process acetylene production chain is lengthy, involves numerous rotating equipment, features simple control systems, has a low degree of automation, imposes high labor intensity on operators, and offers poor working conditions.

　　In the production process, large amounts of calcium carbide dust are generated during the crushing, conveying, and feeding stages. During the production of high-purity acetylene, significant quantities of calcium carbide slurry are produced, and during acetylene purification, substantial volumes of clean wastewater are generated. These “three wastes”—dust, slurry, and wastewater—are highly challenging to treat, requiring enormous investments in subsequent treatment processes. In particular, the treatment of calcium carbide slurry is a critical factor for PVC enterprises in managing their “three wastes.” Moreover, in calcium carbide-based PVC production, the cost of calcium carbide accounts for approximately 75% of the total PVC production cost. Therefore, energy conservation and emission reduction in acetylene production are of great significance, yet they present considerable implementation challenges while offering substantial development potential.

　　When calcium carbide slag slurry is used for ashing, a considerable amount of high-purity acetylene gas can be distilled out upon entering the slurry distillation tower. However, bubbles still persist in the concentration tank, indicating that the calcium carbide slag slurry still contains significant amounts of unrecovered acetylene gas. There are three main reasons for the dissolution of acetylene in the calcium carbide slag slurry: (1) incompletely reacted small particles of carbide; (2) acetylene dissolved in the calcium carbide slag slurry in a supersaturated state; and (3) the presence of numerous fine particles of Ca(OH)₂ in the composition of the calcium carbide slag. Ca(OH)₂ has a strong adsorption capacity and can readily absorb large quantities of acetylene. Currently, domestic enterprises have adopted negative-pressure steam stripping and flash evaporation technology to recover acetylene from calcium carbide slag slurry, achieving excellent economic benefits and drawing widespread attention within the industry.

　　The waste liquids generated in the wet-process high-purity acetylene production mainly include the clear liquid from the calcium carbide slurry, the washing liquids discharged from the water scrubbing tower and cooling tower, the waste sodium hypochlorite solution discharged from the scrubbing tower, the waste alkaline liquor discharged from the neutralization tower, the coolant from pumps, and the working fluid used in liquid-ring pumps. After being cooled, the clear liquid from the calcium carbide slurry is returned to the acetylene generator and reused as process water in a closed-loop system. From a compositional analysis perspective, the remaining waste liquids have little adverse impact on acetylene production—especially the waste sodium hypochlorite solution. After the impurities such as hydrogen sulfide and phosphine are oxidized and removed from the crude acetylene gas in the purification tower, some of the resulting waste liquid remains partially oxidized. This oxidized waste liquid can be mixed with the supernatant and fed back into the generator, thereby further removing a portion of the hydrogen sulfide and phosphine from the supernatant. Even if certain unoxidized impurities from the supernatant enter the crude acetylene gas, they can still be effectively removed during the purification stage, so no accumulation of these impurities will affect the quality of the acetylene gas. Considering all factors comprehensively, the waste sodium hypochlorite solution is concentrated in the generator, while the rest is directed to the calcium carbide slurry pool, thus achieving a closed-loop recycling system and comprehensive utilization. This approach not only makes full use of water resources but also ensures zero emissions.

　　The concentrated clear liquid from calcium carbide slurry is used for high-purity acetylene generation. It not only provides the large volume of production water required for calcium carbide hydrolysis but also ensures that the water remains saturated with acetylene, thereby reducing the consumption of acetylene dissolved in the water and effectively recovering acetylene.