By Dr. Cameron Chai
Compressor trains will be supplied by Siemens to China for the biggest propylene plant in the world. Each compressor train is capable of compressing 700,000 m3 of air to 2.4 bar each hour. This flow rate is the highest provided by an axial-flow compressor globally.
The plant will commence production in the year 2013 and generate propylene as the raw material for the plastic polypropylene. Initially, this plants compressor train will be deployed as an axial-flow compressor run by gas turbines. The plant is China’s first propane dehydrogenation project (PDH) and has 600,000 t capacity of propylene every year. The Chinese Tianjin Chemical Industry Group, a plastics processing company will operate the plant.
There is an increasing demand for plastics hence for propylene in China just as in Asia. Along with the PDH plant construction, China satisfies this demand and at the same time, an industry will be developed for the processing of natural gas. Till now, propylene and ethylene have been obtained together due to petroleum cracking in refineries.
Propylene production with propylene selectivity being more than 85% is done as per the Catofin technology of the company, CB&I Lummus. According to this method, dehydrogenation of propane will help manufacture propylene. Propane gas is obtained from natural gas. As per the process, the catalyst will be heated repeatedly and regenerated with heated, compressed air alternately with the dehydrogenation reaction.
In the newly commenced plant, this air is provided by two Siemens compressor trains. Till now, these types of axial-flow compressors have been utilized only in refineries or blast furnaces. In the Bohai project, they are being utilized in the petrol industry in a propane dehydrogenation plant.
Another innovation is the integration of a gas turbine and an axial-flow compressor. Gas turbines at the Chinese plant are a fitting drive system as they can be driven on both natural gas coming from a pipeline as well as propane gas coming from the plant. Axial-flow compressors and gas turbines have superior efficiency rates. Hence the integration of the two systems is highly effective.