White Paper November 12, 2009 FuelsManager and Radar Tank Gauging for Overfill Prevention Considerations for replacing your existing mechanical float switches with radar technology for continuous overfill protection. Automation solutions for oil & gas, defense and aviation applications
Contents Contents Contents... 2 Executive Summary... 3 Single Point and Continuous Measurement... 5 Costs Comparison... 6 New and Upgrade Installations... 6 Additional Benefits... 7 Sharing Data via OPC... 7 Different Gauging Technologies... 8 Testing the Device... 8 Summary... 10 Repeatability with Accuracy... 10 Credits... 11 About Varec... 11 Copyright... 12 2 White Paper
Executive Summary Executive Summary Bulk storage tank overfills are a common cause of product release and pollution at tank farms, terminals and refineries. Some overfills are small and easily contained, but the accumulation of product from repeated overfills or a single large spill can cause significant soil and ground water contamination. Throughout the bulk liquid storage industry, it is increasingly being viewed as good practice, and in some areas it is mandated, that some form of independent overfill prevention be provided on all hazardous material storage tanks. Independence is one key feature of an overfill prevention system. The measurement for overfill is independent of other devices or systems used to monitor tank inventories. Historically, facilities in the U.S. oil and gas industry have implemented single point measuring systems (a mechanical float switch) to measure the Crucial Process Value (CPV), e.g. high and high high level tank alarms. The float switch is generally connected to a system, such as a PLC, that when activated triggers audible and visual alarm systems and controls the shutdown of system devices, such as pumps and valves. In many cases, the primary tank gauges communicate through a separate field interface to an inventory management system, such as FuelsManager. Varec, Inc. 3
Executive Summary The separation of devices, power, communications and automated control by the PLC creates the required independence. Today, the industry is moving to continuous detection as defined by the American Petroleum Institute in their upcoming standard API 2350. For companies utilizing a single point system, this paper provides an upgrade solution that introduces continuous radar technology to increase safety and ensure a facility meets or exceeds current industry guidelines. 4 White Paper
Single Point and Continuous Measurement Single Point and Continuous Measurement As the name suggests, a single point system utilizes a device to tell the PLC (system) when the liquid level in a tank reaches a single point, e.g. high high level. They tend to be simple and very reliable devices with a low cost of ownership. The switch is normally open (not powered) until the liquid reaches the float, at which point the float rises with the liquid level and triggers (closes) the switch. They can be easily installed on any small nozzle set in the tank wall and they generally use two wires for power and communications. Multiple switches are needed to monitor multiple level alarms. Likewise, radar technology now provides a comparable means to continually monitor liquid level on the same two wires. When a configured level set point is reached in the PLC, it triggers an alarm. If multiple level set points are configured in the PLC, then a single radar tank gauge is able to provide multiple level alarms. Varec, Inc. 5
Costs Comparison Costs Comparison Cost is a major issue for any tank gauging installation, more so for a secondary system. List prices for mechanical switches are just under $1,000. Each tank requires 2 4 switches, depending on alarms managed (low low, low, high and high high), while a single Varec radar tank gauge that is applicable to overfill protection is approximately $2200. Alarms Managed vs. Costs per Tank (Float Switch vs Radar) Tank Alarms $ Float Switch $ Radar $ Difference 1 2 (High High) (High) $1,000 $1,200 + $2,200 3 4 (Low) (Low Low) $2,000 $200 + This cost scenario does not take into account the costs for installation on the actual tank. Wiring costs vary significantly from site to site based on the distances to power supplies or control rooms, safe vs. hazardous areas, AC vs. DC, etc. New and Upgrade Installations For new installations, a single radar instrument can take replace up to four float switches. This means one tank entry vs. four, and one set of power/communications cables (2 wires) on the tank vs. four. For upgrade installations, the radar gauge may be able to utilize the existing 2 wires used by the float switch. They would simply need to be extended from the high point on the tank to the entry point on the tank roof. The radar gauge is suitable for installation on a nozzle as small as 1.5 NPT. It can be supplied with a range of ANSI, EN or Tri clamp flange connections very common fittings on most tank roofs. 6 White Paper
Additional Benefits Additional Benefits As you can see, there may be occasions when a radar gauge upgrade may be equally as cost effective as replacing float switches, but if replacing older mechanical float switches with radar technology is more expensive, then there needs to be additional functionality in the system to warrant any additional costs. Additional functionality for this system is realized by way of: Sharing data via OPC Using different gauging technologies Testing the device Sharing Data via OPC In our example system, the PLC system can be easily connected to FuelsManager without losing independence of the overfill system by using an OPC connection between the two. The radar tank gauge measurements can then be duplicated and monitored in FuelsManager by the facility operator and used as an operational status check. The level readings of the primary tank gauge and radar tank gauge should change in parallel; any deviation between the two can be monitored. A Varec, Inc. 7
Additional Benefits single operator screen can be created in FuelsManager to monitor primary level vs. overfill level. If the deviation between the two level readings is out of a tolerance set by the administrator, e.g, +/ 6, an alarm will be triggered in FuelsManager. This tolerance factor not only monitors for reliability and accuracy of instruments over time, but also for instrument malfunction. Different Gauging Technologies An additional factor that should be considered for overfill protection is technology difference. It is suggested that a secondary overfill device of a different technology to the primary level instrumentation be utilized. In this case, an application factor that would adversely affect one technology may not affect the other, and vice versa. For example, if during a tank filling operation the float on a float and tape gauge got caught on the guidewires the primary level reading would be stuck at one value. The secondary continuous radar measurement would continue to operate normally. If the OPC is utilized between the PLC and FuelsManager, the different level readings from the same tank will alert an operator to a potential problem. Testing the Device If a float switch s contacts are normally open, how does the facility operator know that they are functioning correctly? He does not, unless the operation is manually checked at the switch, a time intensive process that requires operators to climb the tank to the location of the switch. This switch checking process has caused some facility operators to create make shift testing systems, such as dropping cables from the switch so an operator pulls the cable at ground level to test the switch, rather than climbing the tank. It is widely accepted that mechanical float switches are very reliable, but what is identified from the checking procedure is the switch worked at that point in time and we trust the device s reliability and hope the 8 White Paper
Additional Benefits switch will work the next time it is needed. As the device increases in age, the confidence factor that the switch will work the next time decreases. If a float switch stops working, chances are an operator will not know about it until it becomes an overfill situation. The Varec radar tank gauges internal operational alarms provide continuous status checking. If a radar gauge loses a level echo for any reason, the gauge can be configured to automatically alarm, thus indicating a problem to the operator, before it becomes a potential overfill situation. This feature also saves time by removing the need for facility operators to enter the facility checking individual switches manually. Varec, Inc. 9
Summary Summary Repeatability with Accuracy The Varec 7240 Radar Tank Gauge offers a unique solution to overfill protection due to: Comparable cost vs. float switches Simple retrofit installation Continuous measurement Built in protection When OPC is utilized between a PLC and FuelsManager, both the primary inventory management tank gauges and overfill gauges can be cross checked for operational status. Lastly, although the system described in this paper is not identified as a SIL system, additional peace of mind is provided by selecting an instrument that has been designed for overfill applications. The Varec 7240 Radar Tank Gauge is approved for applications in a SIL 2 rated system. 10 White Paper
Credits Credits About Varec Varec, Inc. delivers measurement, control and automation solutions and professional services for most major oil companies, defense organizations and airlines worldwide. Varec's FuelsManager software applications and hardware products provide local level management and enterprise visibility of liquid petroleum assets at bulk storage facilities, marketing terminals, refineries, petrochemical plants and military fuel facilities. Varec, Inc. 11
Copyright Copyright Copyright 2009 Varec, Inc. All rights reserved. No part of this publication may be reproduced or transmitted in any form or for any purpose without the express permission of Varec, Inc. The information contained herein may be changed without prior notice. Some software products marketed by Varec, Inc. and its distributors contain proprietary software components of other software vendors. All other product and service names mentioned are the trademarks of their respective companies. Data contained in this document is for informational purposes only. These materials are subject to change without notice. These materials are provided by Varec, Inc. for informational purposes only, without representation or warranty of any kind and Varec, Inc. shall not be liable for errors or omissions with respect to the materials. The only warranties for Varec, Inc. products and services are those that are set forth in the express warranty statements accompanying such products and services, if any. Nothing herein should be construed as constituting an additional warranty. 12 White Paper