Importance of Flow Measurement
The fast-track pace of the project, coupled with the requirement for almost 2000 flow data points, necessitated that we use flow technologies with which we had experience and which we knew could meet the many plant requirements. The aggressive planning timelines meant we had to deal quickly with undefined process data, while balancing this against known plant and operational constraints.
Many of our applications were for demineralized water used for cooling the reactors, where the low conductivity would not allow the use of magnetic flowmeters. Also, the piping around the deposition reactors was congested. Because it was known that space would be at a premium at the facility, differential pressure flow or vortex flowmeters were ruled out, too, because these instruments require significant straight runs of pipe work before and after each instrument.
Another factor for consideration was pressure drop. Our process design did not allow for significant differential pressure loss at the flow measurement points. Generally, the closer a meter is to line size, the smaller the drop. We knew that Micro Motion meters have a large, 50:1 turndown, so we could confidently install line size (or one size below) meters and know that they would be able to measure the required flow rate when it was finally specified.
If we'd chosen alternative technologies, which have a lower turndown, we would also have to wait for the final process data before we could select a meter. Lower turndown means that, in order to accurately measure the flow, we would have had to choose a smaller size meter than the Micro Motion meter required for the same application. In addition, this meter would have to be installed between reducers, creating a restriction in the pipe. The resulting pressure drop would very likely have been larger than the 5 psi specified by the process group.
Our experience with the polysilicon process alerted us to a requirement that many safety instruments would need a SIL 2 rating. At that time, Micro Motion Coriolis mass flowmeters were the only Coriolis flow measuring devices rated to this safety level. If we'd used another technology, we'd have needed two measurements in series to meet the SIL 2 rating, and, as we knew, space would simply not permit this.
After we decided to use Micro Motion Coriolis meters, we then passed the established dimensional data and installation requirements to piping designers for development of isometrics—months ahead of customary schedules. We only had to ensure that the meters were installed in their proper orientation.
Summary of Success
Consequently, more than 1800 Micro Motion Coriolis flowmeters were used on LDK's polysilicon project, which is the world's largest concentrated installation of Micro Motion meters. By considering each application and prioritizing production lines, Emerson was able to begin delivering instruments in June 2008, and be ready for the September 2009 start-up.
Emerson's Micro Motion meters made a big contribution to the success of this project. From an installation point of view, the meter was perfectly suited to the application. Availability of dimensional and performance data meant the pipe work team could start work early, and product was delivered on schedule—months ahead of what we expect with a conventional design. Feedback from the site confirms that correct engineering decisions that were made. The engineers have access to accurate mass flow data at every stage of the process, enabling the operation and systems to be optimized to give the best efficiencies.
LDK's polysilicon project also has been a huge success for all its stakeholders (Figure 3). At the peak of construction, there were more than 8000 craft workers at the jobsite. Their safety record was impeccable, and, in spite of the hurdles, the plant was constructed in a very short time. With the support of Fluor and Emerson's personnel and the technology providers, the commissioning effort has gone smoothly. Production Line 1 is underway, and the result is a world-class facility that will employ many people in a remote region of China.
Charlie Henderson is senior control systems design engineer at Fluor Corp.