Oil-free compressors increase glass production

One of the world’s leading float glass manufacturers, China’s Shenzhen Southern Floating Glass Co is achieving increased glass production in its process using nitrogen produced by recently installed Atlas Copco ZH Series oil-free centrifugal compressors. Since it’s inception in 1993, the Shenzhen Southern Float Glass Co Ltd (SFG) has invested some 1.5 billion Renminbi (180 million Euro) in two of the world’s most advanced float glass production lines; aided by two new Atlas Copco ZH Series oil-free centrifugal compressors in the critical annealing stage process to ensure increased production. Capable of producing the highest quality float glass in a variety of colours and from thicknesses ranging from 0.55mm to 19mm, the lines produce over 26 million tonnes of glass product per annum. Since its discovery in the 1970s, the float glass manufacturing process has been steadily improving, especially in the last decade with the introduction of new technology in the control, coating and annealing procedures. The introduction of new technology has enabled super thin float glass (0.55mm to1.1mm) to be produced and SFG’s Guandong manufacturing plant has facilitated China’s entry into a selective club of producing countries. Applications for super thin float glass range from telecommunications to optics, automotive and LCD’s/PDP’s for the giant electronics industry. Production of float glass involves six separate processes, which commence with the charging of the raw materials. Melting of these materials in a furnace at 1550C leads to pouring the molten glass onto a bath of liquid tin where glass sheet is formed by floatation. Critical annealing process The fourth process coats the hot sheet glass strip with metal oxide. At the fifth stage, considered the most critical, the continuous glass strip is passed through an annealing tunnel. The tunnel cools the hot glass in a controlled process to ensure perfect flatness whilst at the same time eliminating any internal stresses, which could weaken the finished product. Finally, after cooling to ambient temperature, the glass is cut and made ready for shipment. The annealing stage of the production process relies upon the continuous and uninterrupted operation of two Atlas Copco ZH7000-5 oil-free centrifugal compressors. Working on a 24 hour/7 day duty/standby basis, the ZH7000-5 compressors each produce up to 5000Nm3/hr at a working pressure of 7 bar. The compressed air is chilled to 12C and passed through a moisture separator where condensate is removed. The chilled air passes through molecular sieves to further reduce moisture and any carbon dioxide present. The treated air is passed through a series of heat exchangers where it is progressively cooled to –170C becoming liquefied. Further processing separates oxygen and nitrogen into separate components and the latter is transported to the float glass annealing tunnel where it is used to protect the hot glass strip and liquid tin. Continuous operation of the production line is essential as any non-planned shutdown will cause severe disruption and possibly major damage to processing machinery. Since coming on-line at the beginning of 2002, the ZH7000-5 compressors have not missed a ‘beat’. According to Mr Huang Jin, who is the plant manager for N2 & H2 production, the Atlas Copco ZH7000-5 oil-free compressors were chosen for their low energy consumption and efficiency at part loading. Mr Huang also placed great emphasis upon the quality of after sales support provided by Atlas Copco’s local office in Guangzhou which enabled him to "sleep soundly at night". Atlas Copco’s ZH Series oil-free compressors feature an interactive PLC control system including a surge anticipation feature and plant control system integration facility, installation friendly baseplate/vibration damping and for critical process engineering – 100% oil-free air supply. SFG’s emphasis upon high technology processing equipment combined with many years of production experience has won widespread customer credibility both domestically and internationally. The company has extensive export markets in the USA, South East Asia & Europe.