Leveraging modern flow technologies to improve safety in refineries
The refining industry is facing increased pressures, such as crude oil supply changes, changing product distributions and increasing regulations. These pressure points create a highly competitive market where refiners are looking for options that include digitally transforming operations and adapting new technologies to enhance safety and improve uptime, flexibility and efficiency, while securing their competitive position in a dynamic market. Improving personnel and process safety remains a top focus area for refiners.
The refining industry is facing increased pressures, such as crude oil supply changes, changing product distributions and increasing regulations. These pressure points create a highly competitive market where refiners are looking for options that include digitally transforming operations and adapting new technologies to enhance safety and improve uptime, flexibility and efficiency, while securing their competitive position in a dynamic market. Improving personnel and process safety remains a top focus area for refiners.
While many factors are evaluated when improving safety in refineries, selecting the right flow measurement technology can be an overlooked factor, despite the multiple benefits that a single-flow device can deliver beyond process control. Traditionally, refineries would select cost-effective flow measurement technologies to ensure measurement repeatability, primarily for process control purposes. In certain applications, refiners are now realizing the benefits of having more than just repeatability in a flow measurement device. Attributes found in newer flow technologies—such as accuracy, inline meter health verification and integral design—have proven beneficial to enable refineries to optimize processes, ensure environmental compliance and improve process safety, while ensuring reliable and repeatable measurements for process control. These newer technologies include Coriolis meters, vortex meters and density meters.
In addition to adapting newer flow measurement technologies, the increased processing and asset integrity challenges for processing opportunity crudes are driving the use of more online flow assurance technologies for corrosion monitoring purposes.
Leveraging more modern flow and density measurement and assurance technologies is a simple way that refiners can significantly improve personnel safety, ensure asset integrity and reliability, and increase process safety.
IMPROVED PERSONNEL SAFETY
Automating density and concentration sampling
Density and concentration measurements are commonly needed across the refinery to measure American Petroleum Institute (API) gravity for crude oil import, and to provide spent sulfuric acid concentration measurements in alkylation units—converting volumetric measurements to mass measurements for material balances, measuring hydrogen purity and measuring product quality in blending.
To obtain these measurements, personnel are often required to go into the field, open tap points and manually pull samples to send to the lab. In addition to risks due to time in the field and potential exposure to harmful chemicals, it is difficult to get a consistent representative sample. Often, samples are only taken once per day or once per shift. However, refinery process conditions are constantly changing, especially as refiners change crude slates and alter process conditions. Therefore, manual samples are not always representative of the fluid properties and, as a result, they can impact process optimization decisions or accurate closure of mass balances, as well as contribute to safety risks.
Installing an insertion meter or in-line density or concentration meter in the process line or on a slipstream can be a simple, cost-effective way to improve safety while providing continuous online gas or liquid density readings. These meters not only monitor output density but also other variables, such as API gravity, percent concentration and specific gravity.
In certain applications where fluid flow and liquid density readings are needed, a Coriolis meter (FIG. 1) can provide online readings in a single device for the measurement of mass flow, volumetric flow and liquid density. Process unit mass balance points are a great application area where Coriolis meters can provide safety and optimization benefits with the highly accurate, continuous measurements needed to close balances, assess unit performance and develop optimization models.
FIG. 1. Coriolis meters are multivariable devices providing mass measurement, liquid density and temperature. Using these meters for combustion control of fuel gas on a mass basis can improve process safety by stabilizing fired equipment operations.
Measuring hydrogen purity
One of the application areas where many refiners have added more online measurements is hydrogen purity. Due to clean fuel regulations and increased use of sour crudes, the demand for hydroprocessing has increased the importance of the allocation, usage and material tracking of hydrogen. Many methods exist for determining hydrogen purity, but using a specific gravity meter (SGM) can provide a cost-effective and highly accurate, fast-responding, continuous measurement that can be used to optimize hydrogen usage and reduce manual sampling (FIG. 2). Depending on the manufacturer, some SGMs are designed to be virtually maintenance free, further reducing the time for personnel in the field.
FIG. 2. SGMs can reduce time in the field for manual sampling by providing online measurements for the specific gravity of a gas, along with molecular weight, relative density and base density. Additionally, SGMs can be configured for hydrogen purity, calorific value/Btu and the Wobbe Index.
Automating tank dewatering
Several methods are used to dewater hydrocarbon storage tanks. Some methods are manual, and others can be automated with the use of flowmeters and control valves. Traditional level measurement systems are less reliable and can lead to hydrocarbon release into the water, resulting in potential environmental regulatory issues. Some refineries have used nuclear density meters to dewater tanks; however, these devices are hazardous, heavily regulated and expensive to operate due to licensing, documentation, leak testing and training. A refinery recently replaced these nuclear density meters with a fork density meter in an automated loop to control the opening and closing of the control valve as density changes were detected. As a result of installing a fork density meter, the refinery avoided penalties from environmental agencies, reduced operating costs for the nuclear device and improved safety.
In addition to fork density meters, Coriolis meters can be used to automate the operation. Coriolis meters provide the added benefit of flow measurement of the water discharged from the tank, which can be used for mass balance purposes.
Meter health verification
Another area for digitally transforming operations to improve safety and efficiency is the utilization of meter health verification methods to verify meter health and accuracy for process monitoring and control, and compliance reporting. One method involves using diagnostic software with Coriolis meters. One such diagnostic software toola is an automatic meter diagnostic software that monitors the entire flowmeter’s performance and integrity online. The meter diagnostic tool provides information in real time to ensure flow measurement accuracy and reliability, thereby reducing the need for manual calibration of flowmeters. This is especially important for hard-to-reach processing areas where scaffolding may be needed to access and maintain the measurement devices.
This Coriolis meter diagnostic tool has also been used for refiners’ compliance strategy, with the software providing an audit trail for each meter and capturing data for visual analysis and reporting on demand. Agencies—including the U.S. Environmental Protection Agency (EPA), the American Gas Association, the API, the International Electrotechnical Commission (IEC) for safety instrumented systems, and the International Organization for Standardization (ISO)—and other third parties recognize that using this diagnostic tool in lieu of some or all calibrations and provings is a valid work practice.
One example where refiners have used this diagnostic tool is with reporting unit charge rates and calculations for greenhouse gas emissions reporting. An accurate charge rate for the crude and other unit feedrates, as well as the accuracy of the charge meter, must be verified and calibrated periodically to avoid fines and ensure compliance. Differential pressure (dP) orifice meters are often utilized to measure charge; these tend to be 2%–5% accurate at best. Verifying the accuracy of dP orifice meters often involves significant density sampling and potential pulling of plates to be sent for specification tolerance validation. With Coriolis meters and the diagnostic software, verification can be done online without requiring a shutdown, thereby reducing the time needed in the field for sampling.
The diagnostic software is not only for Coriolis meters. It is also used with magnetic flowmeters, which are often used to measure water. If refineries are using water from public sources, the U.S. EPA requires the amount of water usage to be reported and for the meter to be calibrated periodically to ensure accuracy. Like Coriolis meters, the diagnostic software on magnetic flowmeters provides a digital audit trail and extends calibration cycles through online verification, reducing the need to take meters offline for calibration.
ENSURE ASSET INTEGRITY
Asset integrity for piping
According to the EPA’s National Response Center database, approximately 40% of process safety incidents can be tied to mechanical integrity across all processing industries. According to “2012–2016 Tier 1 and Tier 2 Safety Events” reported by the American Fuel and Petrochemical Manufacturers Association (AFPM), 43% of safety events were caused by piping failures. The leading causes often involved fixed-equipment mechanical integrity issues caused by corrosion, erosion, cracking and less-than-adequate inspection.
Corrosion monitoring has become more important and challenging due to the increased use of opportunity crudes, which tend to be more acidic than traditional feedstock and can lead to accelerated corrosion. Refiners are discovering that different crude blends have different rates of corrosion. Having accurate ways to monitor the corrosion for each type of blend is important. A blend of different corrosion monitoring technologies offers the most comprehensive way to avoid unexpected problems with piping or vessel integrity. Wall thickness can be monitored using two non-intrusive techniques. Clamp-on ultrasonic devices, which monitor the corrosion directly below the device, are easy to install and can be combined with a field signature method of detecting corrosion over a larger surface area.
Both methods detect the impact of corrosion on vessels or pipes. This should be combined with a method that detects the corrosion of the process fluid itself, which is frequently accomplished using electrical resistance probes inserted into the piping. Probes are 100 times more sensitive than the non-intrusive techniques, so they can be used to evaluate the corrosivity of specific crude blends to avoid corrosion before it is detected by the non-intrusive devices. Together, these technologies can provide a holistic view of crude blend impacts and enable proactive asset integrity management.
Surge protection for compressors
Improving the safety, efficiency and reliability of rotating equipment—such as compressors—is another focus area for refiners. When operating compressors, it is common for surges to occur when compressors are operated near their peak efficiency point. Surges can result in an increase of stresses, damage to the compressor’s parts or, at worst, complete catastrophic failure of the compressor. To avoid surges, the compressor should operate below a given surge limit or within an operating margin with anti-surge control. Operating within this margin will result in reduced operating efficiency, so it is beneficial to operate as close to the surge limit as possible. A key to implementing anti-surge control is knowing the molecular weight of the gas. With changes in the volumetric flow of the gas during a surge, the composition will change as well. Measuring these composition fluctuations in real time is critical. A refinery was recently able to accurately determine the surge limit, operate with increased efficiency and reduce the risk of damage due to surge by using a specific gravity gas meter to continuously measure specific gravity and molecular weight measurements of the gas, independent of process conditions.
Leak detection for pipelines
Another area of ensuring asset integrity is leak detection for pipelines. Refineries where the terminal is some distance away from the plant, or where feedstocks or products travel through pipes over public roads or bodies of water, often require some form of leak detection to ensure environmental compliance and public safety. Although these systems are often sophisticated and involve additional measurements beyond flow and leak-detection software, there are cases where flow reconciliation between two points in the pipe is enough to meet requirements. In both cases, accurate flow measurement, even through changing temperature and pressure conditions, is beneficial and will provide the most reliable method of detecting leaks quickly and effectively, while preventing false alarms. Coriolis meters that can simultaneously measure mass and volumetric flow, and monitor density of the fluid, are especially beneficial in leak detection applications.
IMPROVED RELIABILITY
Vortex meters
A newer trend has been the increased adoption of vortex meters over dP orifice meters in newly built refineries and unit upgrade projects. Traditionally utilized for steam and utility flows, vortex meters are now used for hydrocarbon measurement, as well. Newly designed vortex meters provide high reliability with an integral design, resulting in no moving parts, leak points, ports, gaskets or impulse lines, which is especially valuable in safety instrumented system (SIS) applications. Plugging of impulse lines with dP orifice meters results in increased safety risks, as flow can be falsely reported, causing undue shutdowns or unsafe conditions for shutting down. Vortex meters eliminate impulse lines. In addition, some vortex meters have online-removable sensors to keep the process up and running while the sensor is changed out, thereby maximizing availability. Due to the lower total cost of ownership, lower capital cost in some applications and improved device reliability, vortex meters are gaining popularity over traditional dP orifice meters.
SIS applications
For reasons previously mentioned, vortex meters have proven extremely beneficial in SIS applications. Dual- and quadruple-vortex meters can be used in SIS applications for up to 1 out of 2 (or 2 out of 3) voting, respectively. The dual- and quadruple-vortex systems provide a cost-effective safety improvement by providing measurement redundancy in a single meter body, thus reducing the need for multiple flowmeters (FIG. 3). Common uses for dual- and quadruple-vortex meters in refineries include furnace pass measurements, along with measurements of areas where impulse lines are prone to plugging. Coriolis meters offer SIS capabilities, as well.
FIG. 3. Vortex meters offer safety and reliability features, such as online-removable sensors to reduce process downtime, which increases personnel safety by preventing exposure to hazardous fluids. Quadruple-vortex meters provide four independent flow measurements in a single meter body for SIS applications.
IMPROVED PROCESS SAFETY
Stabilized combustion control of fired equipment
One significant area for improving process control with flow measurement technology is the combustion control of fuel gas in fired heaters and boilers. According to “2012–2016 Tier 1 and Tier 2 safety events” reported by AFPM, 4% of safety events were caused by fired heaters. The control strategy of fired heaters and boilers impacts safety, environmental compliance and efficiency. Fuel gas is used in most refinery heaters and boilers for combustion. Since fuel gas is made up of refinery offgases, the composition of the gas—and therefore, the energy content of the gas—can vary frequently and rapidly. Although many refineries operate with high excess oxygen as a safety margin, in many cases, a rich fuel gas results in oxygen rapidly depleting and reaching low limits, resulting in a trip of the heater or a shutdown. These trips or shutdowns most often occur when volumetric- or pressure-based control schemes are used to control the fuel gas.
Utilizing Coriolis meters for mass-based control of fuel gas has proven to reduce oxygen variability and provide more stabilized control of the fuel gas, resulting in increased uptime and safer operations. This is because the energy content and stochiometric air required for combustion of fuel gas are more proportional on a mass basis than on a volumetric basis. In this application, Coriolis meters also provide the added benefits of lower nitrous oxide (NOx) emissions and increased energy savings. Many refiners have avoided trips and unsafe conditions by installing Coriolis meters on fuel gas combustion lines.
Continuous improvement
Device selection can be critical for improving safety and provide more benefits in terms of the reliability inherent in the device itself, along with reduced maintenance, online verification and digital audit trails. Evaluating flow measurement technologies beyond repeatability can result in significant benefits for refining operations. Improving reliability, increasing personnel and process safety, and asset integrity can be impacted significantly by utilizing more modern flow, flow assurance and density-related technologies. These are key to remaining agile in today’s dynamic market. HP
NOTES
a Refers to Emerson’s Smart Meter Verification diagnostic software
The Authors
Jha, M. - Emerson, Houston, Texas
Meha Jha is a Refining Industry Marketing Manager for Emerson Flow Solutions. Since joining Emerson, she was selected for Emerson’s Engineers in Leadership Program, where she broadened her refining expertise by working on projects related to mass balance, fuels blending and utilizing flow measurement solutions to optimize production. She earned a BS degree in chemical engineering from Auburn University.
Valentine, J. - Emerson, Reno, Nevada
Julie Valentine is Director of Global Refining Flow Solutions for Emerson. She first joined Emerson in 1993 and worked as the Refining Industry Marketing Manager for Micro Motion products for 14 yr. In 2015, she became responsible for all of Emerson’s flow technologies for the refining industry. Ms. Valentine has authored numerous technical papers on various applications of flow technology in the refining industry and is a co-inventor on two U.S. patents. She is a member of several working committees for the instrumentation and control group of API’s Refining and Equipment Standards program. She holds a BS degree in chemical and petroleum refining engineering from the Colorado School of Mines.
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