Keep liquefaction running smoothly with Panametrics

In 2000, the US Geological Survey (USGS) stated that nearly one-third of the earth’s undiscovered oil and gas resources were in the Arctic. These are wild, remote locations where temperatures regularly drop as low as -50°C. The extreme ambient conditions also compound a significant challenge associated with LNG production, flow measurement.

It is no secret that natural gas is compressed 600 times in volume to facilitate easier transport as LNG. Under the best conditions, measurement is a challenge since volume is a function of pressure and temperature, factors that can create havoc in metrology. Panametrics technology is widely deployed on liquefaction trains, including ones located in extreme conditions like the Arctic.

Before natural gas can be supplied to national distribution networks, it needs to be liquefied for transport. LNG terminals are faced with receiving the gas for processing and moving the gas within their facility, storing, and ultimately transferring the now liquid product to vessels that will bring it to market. Natural gas changes physical form within the infrastructure that handles these operations as temperature and pressure conditions vary. For instance, LNG is stored at pressures very close to its boiling point within cryogenic double-walled tanks.

Within these tanks, it is mostly stable. However, once LNG starts moving through a pipeline, there is a risk of it changing to a two-phase flow if there are hot spots along the path or if the pressure drop transforms some of the liquid into gas with a much higher volume. Accurate measurement is essential to minimise lost and unaccounted-for product. Within the LNG facility, Panametrics engineers worked with the customer to identify situations with the greatest potential for product loss and the greatest need for flow measurement. Needs centered around the transport of LNG, backflow of boil-off gas (BOG), and flare.

The LNG facility was built to withstand the harsh environment using a modular design. This approach saved nearly 30% in construction costs but created a compact infrastructure devoid of sufficiently long straight runs, a requirement for accurately measuring flow with ultrasonic meters. Getting accurate measurements was one of the top priorities for the customer to export LNG efficiently. The temperamental nature of LNG demands that it be handled at a very low temperature (around -150°C or lower). Every time LNG moves from a vessel to the processing facility, some BOG needs to be flown in the opposite direction to maintain the delicate pressure equilibrium to prevent the rapid release of LNG vapors, known as ‘rollover’. Here again, there was a need for precise measurement.

The third area requiring careful measurement is the handling of excess gas. Due to the liquefaction process, excess gas (mainly methane) is vented through a flare stack where, as a safety protocol, it is combusted. Depending on where it is released, the excess gas going to the flare can have a vast flow rate range – from 0.03 m/sec. up to 100+ m/sec. – and temperature – from -160°C up to +300°C – making the measurement a big challenge.

With the challenges identified, Panametrics’ experience with similar LNG projects took over. The company immediately set to work on a technical analysis that included a review of isometric engineering drawings and computational fluid dynamics to model the environment mathematically.

This work resulted in a plan that was custom-tailored to the needs of this particular LNG facility and relied heavily on Panametrics’ Sentinel LNG flow meter, the latest addition to its series of advanced ultrasonic flow meters for LNG measurement. The BOG and flare measurements both used the legacy gas and flare meters, of which there are several thousand in operation worldwide. The plan, and Panametrics’ industry-leading expertise in LNG, created a trustful environment with the EPC firm, and the customer.

Valves, elbows, control valves, and other piping components limit the number of straight runs in an LNG facility and can cause flow disturbances. The tight configuration of this facility had more than the usual amount of these to fit within the available footprint.

To address the woefully insufficient straight runs, which create measurement errors due to non-fully developed flow profiles, Panametrics selected its 4-path meter Sentinel LNG flow meter, which reacts to changes in flow rate with incredible speed and accuracy. The flow meter extends the use of ultrasonic technology into cryogenic applications for measuring LNG with unbeatable performance, reliability, and safety and can be calibrated down to ±0.25% of reading. In all, 26 Sentinel units were installed.

Panametrics has a proven track record for BOG measurement in similar LNG projects. For this project, the company recommended its XGM868i, which handles low pressure and cryogenic conditions exceptionally well using ultrasonic technology. Choosing this meter ensured against pressure drops and the maintenance of necessary equilibrium pressure.

The harsh environment of the region also demanded special consideration for handling flare. To ensure that the company's product was up for the task, in addition to using its XGF868i flare electronics, Panametrics conducted extensive testing of our transducers to expose them to extreme temperature cycles. Creating artificial environments using liquid nitrogen and specialized ovens, the company tested the units at -190°C and then at +300°C. The transducers performed at both extremes, enabling certifications for all hazardous area standards while ensuring reliable operations.

Click here to download the Case Study

www.bakerhughes.com/panametrics

Read the article online at: https://www.lngindustry.com/special-reports/13062023/keep-liquefaction-running-smoothly-with-panametrics/