petrochemical company reduces risk of lost production

White Paper

Petrochemical comPany reduces risk of lost Production using coriolis meter With meter VerificationBy tonya Wyatt, micro motion, inc. and Brian reagan, rosemount measurement

Micro Motion, Inc.White Paper

abstractA former Ethylene supplier to a petrochemical plant caused interruptions in their supply by shutting off the supply below a certain dP. The petrochemical plant chose a new supplier that installed an Emerson Coriolis meter which offered a full range of flow rates resulting in ceasing the supply interruptions and improving the uncertainty from 0.75% to 0.35%. In addition, the company did not want to have to pull the meter for proving during operations, so Smart Meter Verification was utilized to extend the calibration interval to coincide with plant turnarounds and to continuously monitor meter health. The meter was pulled for calibration after two years of service and found to have -0.06% difference from a lab prover. The solution eliminated replacement during operation, reduced proving costs, improved safety and reduced risk of lost production.

introductionEthylene is used as a critical feedstock for many petrochemical products including polyethylene, ethylene oxide and polyvinyl chloride. Ethylene is typically transferred in mass flow units (lbs, kg, etc.). Ethylene has a critical temperature of 9.5°C (49°F) which is lower than many fluids. Above the critical temperature of a fluid, no matter how high the pressure goes, the fluid does not pass from a gas to liquid phase. There is essentially no phase difference and the fluid acts as a supercritical fluid. Supercritical fluids behave similarly to gas (fill all available space in a container), yet have much higher densities than typical gases; more similar to liquid densities. Another property of supercritical fluids just above the critical temperature is that with small changes in pressure and temperature, there can be large changes in density. As a result, ethylene can be very difficult to measure with traditional volumetric meters.

Background

A large petrochemical company in the gulf coast was purchasing ethylene through a pipeline from an ethylene supplier. They were purchasing 9-12 million lbs/year of ethylene as a critical feedstock for their process. The ethylene supplier was using a 1” differential pressure meter (orifice) that had limited turndown in the application. The ethylene supply contract was written in such a way that when the ethylene usage went below a minimum value or the measurement fell below a specific dP, the supply would be shut off until more ethylene could be used. While this was not typically an issue during production, during start-up

the flow rates varied significantly and were occasionally low enough to trigger an interruption in supply.

Measurement Requirements

The risk of lost production was enough to cause the petrochemical company to seek out a new supplier and a different measurement technology for their custody transfer of ethylene. They established certain criteria for the new measurement technology including:

1. Custody transfer accuracy - measurement that is accepted for gas and has accuracy that would suitable for billing

2. Wide rangeability - no loss of measurement during start-up or production even under varying flow conditions

3. Diagnostic capabilities - immediate notification to critical personnel if health of the meter is compromised

4. Verification of performance - verify measurement accuracy in line on a monthly basis and pull meter out of the line during scheduled turnarounds to prevent loss of measurement or downtime due to proving

Solution

After evaluating multiple measurement technologies, the company partnered with a new ethylene supplier and both parties agreed to install a ½” Micro Motion ELITE® sensor (see figure 1). Coriolis meters measure mass flow directly, so pressure and temperature compensation due to fluid density changes is unnecessary. The American Gas Association (AGA) Report Number 11 “Measurement of Natural Gas by

Figure 1. Ethylene skid with Micro Motion CMF050 Coriolis meter installed


Coriolis Meter” written in 2003, further validated Coriolis meters for use in gas custody transfer applications. The incumbent dP technology specified a lab accuracy of around +/-0.75% whereas the ELITE meter was able to perform at +/-0.35% representing over 50% improvement in measurement accuracy. In addition, the ELITE meter has a much wider turndown than a traditional orifice measurement, virtually eliminating the low flow shutoff risk.

Continuous Health Monitoring

In order to monitor the health of the sensor after it was installed in the line, the petrochemical company chose to retrieve the Modbus status/health information from the transmitter and bring it directly into their SCADA system. The health register would notify them of any of the following errors:

• EEPROM checksum failure

• RAM diagnostic failure

• Sensor failure

• Temperature sensor failure

• Input overrange

• Frequency/pulse output saturated

• Transmitter not configured

• Real-time interrupt failure

• Primary/Secondary mA output saturated or fixed

• Density overrange

• Flowmeter zeroing failure

• Zero value too low or too high

• Transmitter electronics failure

• Flowmeter zeroing in progress

• Slug flow

• Power reset occurred

• Transmitter configuration changed

• Transmitter initialization/warming up

Consequently, any of these errors would also send an e-mail or text to the appropriate technician(s). In addition to continuously monitoring these health registers, the ethylene supplier and end-user chose to order the Micro Motion

sensor with Smart Meter Verification.

Meter Verification

A Coriolis mass flowmeter generally has one or two tubes (straight or bent) that are vibrated at their natural frequency by using a drive coil and magnet to move the tube(s) at a specific amplitude. When there is no fluid flowing through the tube(s), the inlet and the outlet of the tube(s) are moving at the same time. Sensing coils located on the inlet and outlet sections of the tube(s) oscillate and produce a sinusoidal electrical wave as the coil passes through a magnetic field. When there is flow through the tube(s), because of the Coriolis Effect, the gas causes the tube to twist. The inlet of the tube and the outlet of the tube will no longer be moving at the same time. The time difference between the inlet and the outlet of the tube is proportional to the mass flow of the gas. This is true for compressible and non-compressible fluids.

Coriolis flowmeters are well known for their long term stability. There is no time dependent shift in the calibration factor due to the lack of moving or wearing parts. However, if meters are misapplied to applications and are subject to erosion or corrosion or over pressurization of the tubes, the stiffness of the tubes can change and result in a change in the Flow Calibration Factor (FCF) and consequently result in incorrect mass flow measurement.

Smart Meter Verification measures the stiffness of the tubes and compares that measurement to the stiffness of the tubes when they left the factory. Each meter with the Smart Meter Verification option is given a unique fingerprint or baseline of stiffness results prior to leaving the factory. That information is stored within the electronics of the sensor. Smart Meter Verification uses the stiffness of the flow tubes as a secondary variable to verify the validity of the FCF. The FCF is used to relate the measured time delay to the mass flow rate.

All of this is done without taking the meter out of line or losing measurement from the meter. There is no flow interruption and the entire verification can be completed in less than two minutes.


Results

The petrochemical company and the ethylene supplier purchased and installed a Micro Motion ELITE Model CMF050 ½” sensor equipped with Smart Meter Verification and began measuring the ethylene immediately (see figure 2 for installation photo). Due to concern over risk of lost production, the petrochemical company asked the supplier not to remove the sensor from the line except during plant turnarounds for calibration checks. They mutually decided to run Smart Meter Verification on a monthly basis to flag any potential change in the FCF. After running the sensor with no issues for two years, the petrochemical company had a plant turnaround. During this time, they removed the sensor from the line and sent it to a third party lab to be proved. The result of the proving was that the sensor was with -0.06% of the prover, well within the specifications of the meter and the uncertainty of the prover.

Based on the consistent results from Smart Meter Verification and the lack of FCF shift when compared to a lab prover, the customer has decided to extend their Smart Meter Verification interval to quarterly instead of monthly. They have also decided to continue with the practice of only proving the meter during plant turnarounds unless they see an issue with Smart Meter Verification results.

The petrochemical company has also seen an improvement in their measurement performance versus the former measurement technique. Based on the spot prices for ethylene and their usage, the improved accuracy of the system provided payback of the meter in approximately four months, not including the cost savings of removing the meter for periodic proving.

conclusionSmart Meter Verification is a robust option for in-situ verification of a Coriolis flowmeter and can improve measurement confidence. With no moving parts, gas mass flow accuracies as good as +/-0.35% of rate, no need for gas calibration (manufacturer dependent), and no flow conditioning needed, Coriolis meters make an excellent choice for many gas applications including those requiring custody transfer performance.

This paper was presented at the Texas A&M Instrumentation Symposium in January 2013

Figure 2. Micro Motion CMF050 with Smart Meter Verification measuring ethylene


The contents of this publication are presented for informational purposes only, and while every effort has been made to ensure their accuracy, they are not to be construed as warrantees or guarantees, express or implied, regarding the products or services described herein or their use or applicability. All sales are governed by our terms and conditions, which are available on request. We reserve the right to modify or improve the design or specification of such products at any time without notice.

WP-001960 Rev A ©2014 Micro Motion, Inc. All rights reserved.

emerson Process management micro motion 7070 Winchester Circle Boulder, Colorado USA 80301 T: +1 800 522 6277 T: +1 (303) 527 5200F: +1 (303) 530 8459 www.micromotion.com

about micro motionFor over 35 years, Emerson’s Micro Motion has been a technology leader delivering the most precise flow, density and concentration measurement devices for fiscal applications, process control and process monitoring. Our passion for solving flow and density measurement challenges is proven through the highly accurate and unbeatable performance of our devices.

references:

1. Allow Coriolis Meter Verification to Reduce Your Proving and Proof-Test Costs, Cunningham T., O’Banion T., 8th International Symposium of Fluid Flow Measurement, June 2012

2. Using Structural Integrity Meter Verification, Cunningham T., Stack C., Connor C., Micro Motion White Paper WP=00948, www.micromotion.com, 2007

3. An In Situ Verification Technology for Coriolis Flowmeters, Cunningham T., 7th International Symposium of Fluid Flow Measurement, August 2009

petrochemical company reduces risk of lost production

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