What Works: Shanghai plant deals with gas oxidation

Gas oxidation had halved capacities of hot, high-power rotary compressors. Learn how the problem was addressed in this What Works case study.

Shanghai Shidongkou Gas Making Co. Ltd, a subsidiary of Shanghai Fuel Gas Group, is a new air/gas supply plant built to implement the city’s five-year gas development plan for domestic and industrial gas production. The facility uses four York RWB II-856 twin-screw compressors, each with a discharge capacity of 6,020 m3/hr (3,540 cfm) at a maximum pressure of 1.4 Mpa (203 psi) and temperature of 110°C to 120°C.

During a production peak at the end of 2004, maintenance engineers noticed an abnormal reduction in compressed air capacity. The unit’s production volume had dropped from normal startup figures of about 5,200 m3/hr to as low as 2,000 m3/hr. With the compressor capacity reduced to less than half of its potential, Shidongkou had to operate three compressors to generate the output normally achieved by one machine.

Another concern was blackening of the compressor oil after only 300 hours of operation. Oil analysis and testing by Anderol Specialty Lubricants (www.anderol.com) determined that premature oxidation was severely undermining compressor performance.

“Detailed checks revealed that the cause of capacity fluctuation was premature thermal-oxidative breakdown of the lubricant,” says a representative of Shanghai Fuel Gas Group. “We tried several synthetic compressor oils, including products from the original manufacturer and other lubricant companies, but unfortunately, the problem persisted.”

Shidongkou asked Anderol to recommend a solution. “Using inappropriate synthetic compressor oil could lead to complications such as heat exchange deficiencies or compatibility issues regarding seal, gaskets and quality of discharge air. Ignoring these problems could imply a safety threat, especially to equipment operators,” points out Francis Hou, general manager, Asia Pacific, Anderol. “We had to be really selective in helping Shidongkou choose the right compressor oil.”

To maximize operational efficiency, Shidongkou had to select a synthetic compressor oil with high viscosity/temperature stability, thermal oxidative stability and thermal conductivity properties for extended service life. Careful matching and consideration led Anderol to recommend its BDC 68 POE synthetic compressor oil, which met Shidongkou’s requirements.

Before integrating the new compressor oil into the production process, Anderol assisted Shidongkou with a changeover procedure to eliminate residual oil, carbon deposit and rust inside the compressor system to ensure equipment cleanliness.
The Anderol BDC 68 synthetic base oil, made from technical grade PE-polyolester, is highly compatible with Shidongkou’s consumable parts. Exhibiting high thermal stability, the oil is especially suitable for screw compressors operating under discharge air temperatures greater than 95°C. Once cleaned and charged with BDC 68, Shidongkou’s four compressor units consistently operated at a smooth air discharging capacity of 5,000 m3/hr to 5,300 m3/hr.

“The outstanding thermal oxidative stability of the BDC 68 virtually eliminated the deleterious byproduct of oxidation, resulting in extended service life of our equipment,” says the Shanghai Fuel Gas Group representative. “This led to substantial cost savings on our resources. Effectively, we were able to do more for less.”

The oil’s detergency and dispersing capabilities remove internal deposits to ensure smooth functioning and help keep the system clean. Its biodegradable properties make it an environmentally friendly product, and a high flash point ensures greater operational safety.

The combination of the right lubricant and proper maintenance strategies has proved fruitful for Shidongkou. After application, the plant was able to increase production efficiency and restore its gas pressure output capacity.

“Anderol BDC 68’s high-quality viscometrics, high temperature stability and sealing capabilities have brought out the best performance in our compressors,” affirms Shanghai Fuel Gas Group’s official representative. “We know that Anderol has helped customers achieve business goals for many years. It’s great to see that success replicated with Shidongkou air compressors.”

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