The gas pipeline extends from the west coast of Myanmar, formerly Burma, to Kunming in Yunnan province and is intended to cover part of China’s huge energy requirement and make the country less dependent on sea transportation. The pipeline is a joint venture between the state-owned China National Petroleum and Myanmar Oil & Gas Enterprise. This ambitious project was launched in 2009; the gas pipeline has been operating since July 2013. Around 30 billion cubic metres of gas now flow annually from west to east; a crude oil pipeline planned concurrently is under construction.
14 compressor and transmission stations along the pipeline are responsible for transferring the gas smoothly and failure-free. The automated processes are linked to defined safety levels, which are intended to keep the risks for people, the environment and the plant as low and improbable as possible. In order to transport the gas reliably and safely over long distances, a certain pressure and related minimum temperature must be maintained in the line. If the pressure falls, the temperature will drop. Due to the specific properties of the gas, this increases the risk of ice formation – with negative impacts on the gas flow and the pipeline system.
Guo Peng Technical Co., Ltd. is based in Beijing, China. As one of the consortium of project partners, it was responsible for preventing icing and maintaining a continuous gas flow using an electrically heated system. Multiple sensors monitor the temperature and flow rate in the pipeline network: if the values fall below a defined minimum, the heating system starts up. The supply of heat is switched off again when a defined maximum value is reached. The pipeline operator specified that this safeguard should run automatically and absolutely reliably. Yet, what type of safety device is suitable for monitoring the execution of the switching signals accurately enough? In extreme cases, if the temperature and gas flow exceed or fall below the limit values without being detected, this could cause an explosion with harmful effects for people and the environment as well as long-term loss of the gas supply. The consequential costs would quickly run into millions.
Safety integrity level (SIL) 3 was stipulated. Zhu Yi Ming is the engineer at Guo Peng Technical Co. responsible for the development and reliable operation of the heating system. He recalls one of his early visits to Germany: “I was struck by what at the time was an outstanding safety solution on a large hydraulic press; it was built by Pilz”, he says. Zhu Yi Ming contacted Pilz’s subsidiary in Beijing. Since a gas pipeline is basically nothing more than a complex production plant with an array of control and safety requirements, it was worth considering the PSS 4000 automation system for this project, as it had already been used successfully in numerous mechanical engineering applications.
The automation system supplied by Pilz, a one-stop manufacturer of safe automation technology, enables optimum interaction between the hardware and software components, the network devices and the real-time Ethernet SafetyNET p. It provides a variety of functions and possible combinations which distinguish it from classic automation solutions. This applies to both stand-alone machines and interlinked plants: owing to the efficient distribution of control functions, projects can be implemented more flexibly and therefore more easily with the PSS 4000 automation system. “Classic” automation structures with a centralised PLC can also be realised.
Safe monitoring of PID controllers
A mandatory requirement when it comes to safe monitoring of gas temperature and flows was that the envisaged solution should facilitate safe PID controllers. Although many automation systems in the market are able to monitor non-safety-related PID controllers, only very few PLCs currently allow safe process control. The
PSS 4000 automation system offers reliable safety and automation in one system: PID control is achieved via a special software block in the PAS4000 software platform.
The PSSuniversal PLC belonging to the
PSS 4000 automation system communicates with the higher level plant control system via Modbus / TCP and is used in each of the 14 compressor stations. It can safely monitor the gas flow, temperature, pressure and E-STOP pushbuttons, and it also monitors and controls automation functions such as sirens or signal lamps. “The key factor for us was that PSS 4000 provides safety and automation in one system: the whole thing is easy to implement using intuitive software and it gives us unbeatable value for money”, Zhu Yi Ming explains. And any future changes or adjustments which are necessary are a simple matter thanks to the various software editors for programming in accordance with EN/IEC 61131-3 or for configuration. “Pilz not only supplied the technology for this project but was also an equal partner in the search for the optimum solution, a safety expert and an adviser whose programming and ramp-up support was invaluable”, he adds in conclusion.
Überschrift std : Überschrift std
AutHor : Hans Xu