Automated Gauging and Metering for Oil Stockpiles

30 July 2019

The loss control covers a wide range of different activities and knowledge that are needed to obtain a correct estimate of actual losses, to identify the cause of the losses, to determine their amount, and whether an investment is justified for their reduction.

It used to be considered that automatic measurement systems are dedicated solutions that are suitable only for large and long-term applications. In ancient times, this may have been the case, but today’s modern technology has allowed manufacturers to add more flexibility to such systems. This makes that systems an excellent choice for several smaller volume applications.

The main advantage of automatic measurement is consistency, since it practically removes any variable associated with the operator from the operation. Three variations in automatic measurement systems are available: flexible оr reusable, dedicated, depending on application requirements.

The standard automatic measurement system consists of a station controller for sequencing of material handling or PLC, tracking, blocking and other functions. The automatic system has an amplifier or display for collecting the output of the measuring inverter and their processing so that the final geometric and dimensional values can be displayed. The system consists of auxiliary equipment that indicates the part for monitoring purposes. This amplifier in the measurement system is actually a small computer running software that processes signal processing and data analysis for filtering raw signals. In this way, the software combines these signals with different readings of the transducer. This generates dimension information. Statistical analysis can also be displayed by the amplifier and can generate compensation signals that can be implemented in machine controls. 

Metering: In the process of identifying and determining the size of losses, the most important activity is measurement, which is divided into:

• Static measurement (Gauging System) in the tank or in other types of equipment for storage, whose main function is to control the quantity of the stored product.
• Metering System primarily to measure the process of moving products from / to the tank, usually in / from a car or wagon tank.

In order to reliably and accurately measure the volume of the product stored in the reservoir, attention must be paid to the following:

1. Calibration (Calibration, Graduation) of the reservoir
2. Determining the level of product in the tank
3. Determining the temperature of the product in the tank
4. Determining the density of products in the tank
5. Calculation based on a correctly chosen method

Calibration of Reservoirs: Earlier, vertical cylindrical tanks were calibrated by the method of determining the tank volume per tank height (Strapping Method – ISO 7507-1), or for small reservoir capacity, by measuring the volume of liquids with approximately the same characteristics as the stored product. Lately, other methods of measurement, such as optical method (Optical-Reference-Line Method – ISO 7507-2), are used.

Tanks, as well as tankers or wagons, when used as measuring materials, must be calibrated as follows:

• before use
• after any deformation during exploitation
• after any modification affecting the capacity
• when required by applicable regulations

According to earlier regulations, the calibration was performed every 5 years, however, as a general position, re-calibration at the time of the main inspection is recommended, for example, every 15 years, provided that there were no deformations or modifications to the capacity of the exploited reservoir.

Correctly prescribed calibration (calibration) tables are those whose fault is within the range ± 0.1%

Manual measurement is often performed with the commission of a major error due to the use of poor equipment and incorrect procedures.

Automatic measurement is applied to frequent-level reservoirs as well as in storage loss control systems, where the automatic level measurement subsystem is mandatory, the accuracy of which must be much better than the accuracy achieved at manual measurement.

The temperature of the stored product is often measured manually with an accuracy not better than:

In order to determine the effect of the temperature influence on the volume of the stored product, as well as the procedure for calculating the mass of the product based on the measured volume, it is necessary to apply the automatic temperature measurement sub-system, the accuracy of which must be much better than the accuracy achieved at manual measurement.

The density must be measured in the case of the volume correction factor (Volume Correction Factor ), in the procedure for determining the volume at a standardized temperature or in determining the mass of the product based on its measured volume or determining the volume based on its measured mass.

When the density is used as the data for determining the mass of the product, the accuracy of the measured density must be significantly greater than the accuracy of the measured density used to determine.

This is the “nature” of the fluid used

In order to determine the reduced or steady amount of the product in or out of a car or wagon of tanks and reservoirs, it is performed, in contrast to direct weighing or filling or discharging to a fixed marker, dynamic measurement using gauges, the accuracy of which must be within the range of their bandwidth with repeatability at a specified flow rate for a minimum of 6 (six) months without the need for frequent adjustments.

The positive displacement gauges were previously the only ones that met the set requirements, however, with the appearance and application of a Coriolis force mass flow meter, the characteristics of which are at least better than required, a very high level of measurement accuracy in the filling systems and discharging the stored product, as well as simultaneously measuring both the current volume and instantaneous mass flow and the current density of the prototype fluid.

Causes of Loss: Losses in the process of storage of products can be divided into physical and apparent losses.

• Physical Loss is a “real” material loss of stored product from the storage system, including loss due to the evaporation process.
• The apparent Loss is not realistic from the physical point of view but arises from such things as: random measurement errors, systematic calibration errors, differences in calculation procedures. Despite the fact of the non-physical phenomenon, i.e. Do not appear as a result of a physical process, however financial loss exists and can be incorrectly attributed to the account at the time of sale or with the delivered invoice.

Physical loss is due to:

• Leaking or spilling
• Evaporation
• Cleaning of the reservoir (drainage of water sediment)
• The problem of “flat substrate” (for transport means)
• Excessive measurement flow (“short” meter)
• Theft and embezzlement

If a leakage of one stroke intensity drops for one second in one connection, we have:

 – loss of 1 hour is 0.3 liters (if 1 liter = 1 Eur), the loss is 0.3 Euro per hour

 – loss for 1 day is 7 liters or 7 Eur / day

 – loss for 1 month is 200 liters or 200 Eur / month

 – loss for 1 year is 2400 liters or 2400 Eur / year

If there is a leaky intensity in the joint “drowsy droplet form”, we have:

 – loss for 1 hour is 4 liters or 4 Eur / hour

 – loss for 1 day is 90 liters or 90 Eur / day

 – loss for 1 month is 2,700 liters or 2,700 Eur / month

 – loss for 1 year is 32,400 liters or 32,400 Euro / year

If there is a leak in the intensity of jets with a width of 3 mm in width, we have:

– the loss for 1 hour is 41 liters or 41 Eur / hour

– loss for 1 day is 1,000 liters or 1,000 Euro / day

– loss for 1 month is 30,000 liters or 30,000 Eur / month

– loss for 1 year is 365,000 liters or 365,000 Eur / year

Conclusion: Good Maintenance is the most important precondition for good and successful loss control

In normal and procedural operation, losses by evaporation can be divided depending on the type of storage equipment, reservoir in which the product is stored:

Fixed Roof Tanks:

1. Loss by Pushing: when the fixed-roof reservoir is refilled (replenished) with a liquid product, the appropriate volume (quantity) of the air mixture and the vapor phase of the product is discharged into the atmosphere.
2. Working Losses: in the process of discharging the tank the air enters the tank, and saturation of this air with the gas phase of the product causes the expansion and suppression of a certain amount of this mixture in the atmosphere.
3. Loss by Breath: With a fixed roof tank, the gas phase is emitted from the tank (outbreak) during the day due to thermal expansion caused by solar energy, and during the night the air into the tank (inbreathing) enters due to cooling and condensation of the gas phase. This daily process is called “breathing the reservoir”, the intensity of which depends on several factors.

Tank:

The tank filling losses are normally significantly lower than the loss by pushing the fixed-roof tank. Typical values are from 0.04% to 0.06% of flow, as a liquid gas equivalent product.

Tank with Floating Roof:

Using internal floating parts (floating), i.e. Their installation in tanks with a fixed roof, tanks with internal float, some type of floating roof tanks; but much more important is that in this way loss of breath and loss by suppression can be reduced by 90%.

Drainage and Cleaning of Reservoirs: These operations require, first, strictly defined procedures and their procedural execution, in order to minimize the possible big losses.

Precious Measuring Protocol: Dynamic measurements, i.e. Measuring systems must operate with correct flow rates and reliably calibrated intervals. The normal wear of the moving parts of the gauge depends on the size of the flow, especially if the flow rate is higher than the registered capacity of the volumetric gauge, which makes many manufacturers to reduce errors and losses, suggesting a more frequent recalibration of meters.

One of the advantages of the mass flow meter is that there are no moving parts and therefore it is insensitive to wear, that is, unnecessary re-calibration measurements.

Stealing and Embezzlement: Theft was and will always be a permanent problem and will certainly never be eliminated.

Security can be improved as follows:

• Automation of the Measurement and Data Processing System, as this will illuminate the illegal movement of the product if it has.
• By automating the charging system, as it will allow the product to be filled only if the driver, tank and transfer point are correctly identified and who will automatically issue the dispatcher with the quantity and quality of the delivered product
• By automating the Discharge System, as it will allow product discharge only if the driver, tank and transfer point are correctly identified and which will automatically issue the receiver with the quantity and quality of the delivered product.
• Integrated Information System, which, among other things, and for the purpose of collecting data across the entire geographically distorted product network, connects and enables the exchange of data between individual systems, provides automatic control, management and control over the process of distribution and storage of products.

The apparent losses, that is, apparent deviations can occur during inventory due to:

• Measurements
• Temperature
• Calibration
• Calculation procedure

In warehouses, where deliveries are made through volumetric or massive meters or scales, such errors are discovered earlier and it is usual that in modern automated systems, static measurement is only used for the monitoring system, while balance is based on data from dynamic measurement!

Acceptable, Target Loss of Loss: If the losses are identified, an estimate of their admissibility can be made or an action to bring losses to an acceptable, targeted level will be undertaken.

So, the losses must be accurately determined and quantified.

In order to improve the work, you need to have properly programmed and designed automated control and measurement systems that are reproducible, very fast and accurate.

Consequently, they eliminate the content of human error in most of the repeatability and reliability studies of manual control and measurement process. Machine cameras can be programmed to automatically verify dozens of features on 100% of products or assemblies produced in just one second. High precision lasers ensure maximum accuracy at the micron level without having to contact with the work. On the contrary, manual control is very intense, so there are many errors. Operators must comply with detailed operating instructions, handheld devices, and may be easily erroneous as they carry out product check controls.