Online shutdown, heating, and purging achieved for the air separation expander in Hubei Fertilizer Plant

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Hubei Fertilizer’s air separation expansion machine underwent online shutdown, heating, and purging – Author/Source: China Chemical Industry News, Date: 2019-02-12, Clicks: 68. Sinopec Hubei Fertilizer Company recently carried out online shutdown, heating, and purging of its air separation expansion machine for the first time; this measure eliminated the bottleneck associated with increased load on the facility, laying a foundation for improving its efficiency and performance as well as for enhancing the overall production system. 　　The cooling capacity provided by the booster turbine expansion mechanism can compensate for the cooling loss in the air separation system, and it is essential for the stable operation of the plant. Over the past few days, ice buildup has occurred in the company’s expanders, resulting in insufficient cooling capacity in the system. This affects the oxygen production of the air separation unit as well as the loads downstream, and it also causes issues such as reduced rotational speed and surging, thereby impacting the operation of the unit. It is urgent to carry out equipment heating and degassing procedures. 　　The company’s 48,000 standard cubic meter domestic air separation unit operates in a single series format, without any backup systems for oxygen or nitrogen; moreover, the heating and purging technique involved is complex and difficult to implement. The company’s technical staff conducted research, communicated with industry experts, systematically calculated the heat load and material balance, evaluated the technical measures needed to achieve system equilibrium, and repeatedly discussed the possibility of shutting down the expander online. 　　Subsequently, the company’s technical staff further refined the process plan for shutting down the unit and heating it up, carried out joint tabletop simulations with relevant departments involved in the upstream and downstream processes, added liquid nitrogen to maintain thermal balance in the system, and coordinated with various departments to closely monitor changes in the load on the units as well as product quality. As a result, the water content in the gas exiting the expander after heating met the required standards, allowing the online shutdown, heating, and purging process of the air separation expander to be completed ahead of schedule.