Non-invasive ultrasonic flowmeter technology is helping plant operators to optimise processes, without the risk of leaks in high-pressure piping systems.
Ethylene and propylene are plentiful gaseous feedstocks for the most common base polymers. Gases are highly compressed and heated during the polymerisation process – pressures can peak at around 3000 bar. This is where inline metering is prone to heavy wear and tear, often causing high pressure drops, which in turn leads to excessive operational cost and time consuming maintenance.
Using sound waves to measure the flow of media within the pipe, ultrasonic flowmeters work by alternately transmitting and receiving pulses of ultrasound waves between two transducers. This allows the flowmeter to accurately and reliably determine the flow rate. And because measurement is carried out safely from outside the pipe, there is absolutely no risk of contamination or leakage.
Transducers are simply clamped to the pipe’s outer surface, meaning there is no contact with the medium flowing, and they are completely independent of the pressurisation levels within the pipe. The entrained particles do not affect measurement accuracy, and the system can be installed without any interruption to production.
Non-invasive flow measurement solution –
At a high-pressure polymerisation and oxidation plant for the manufacture of specialty ethylene-based products, FLEXIM was tasked with flow measurement of ethylene gas, along with ethylene-copolymer gas mixtures under high pressure.
A steam cracker is located within the plant, and longer-chain hydrocarbons from the distillation of crude oil are thermally cracked in the presence of steam. This produces, among other things, ethylene and propylene. Polyethylene and ethylene-vinyl acetate copolymers from ethylene (ethene, C2H4) are produced with precisely specified product properties for a wide variety of applications. The high pressures required of over 1500 bar are typical of the polymerisation processes in ethylene chemistry.
Orifice plates installed to measure quantities were subject to a great amount of wear and tear due to wax particles carried along in the gas flow, and they demanded a high level of maintenance. These wax deposits reduced measuring accuracy by clogging the impulse lines for recording the differential pressure, causing measurement failure. Therefore, the process engineers needed a more accurate and reliable measurement solution.
Practical advantages –
A key advantage of non-invasive clamp-on flowmeters is that they can be thoroughly tested for suitability prior to permanent installation, without any process disruption.
Following a successful demonstration measurement, the operator made the decision to replace the high-maintenance orifice plates with fixed FLEXIM ultrasonic flowmeters.
Because the gas flow is routed through two lines of identical pipe geometry (DN32, wall thickness 23.5 mm) behind the intermediate-pressure compressor, the two-channel version of the transmitter was chosen, meaning flow could be measured on both lines simultaneously with a single flow instrument. Two lines on the pressure side of the high-pressure compressor have now also been identically instrumented.
Thanks to the extraordinary dynamics of clamp-on ultrasonic flow measurement technology, it’s now possible to record the start-up and shut-down phases of the ethylene cracker system. And as well as optimising process control, the flow measurements enable predictive maintenance capability through the delivery of crucial information on compressor performance – effectively reducing downtimes.
For more detailed information on the benefits of non-invasive ultrasonic flow measurement in the petrochemical industry, contact Simon Millington – www.flexim.co.uk | firstname.lastname@example.org | +44 (0)1606 781 420
By FLEXIM Instruments UK Ltd