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Application of ARDIS hardware-software system for weighing railcars while taking into account the air buoyancy force

Transportation by railcars most often domestically is the most flexible and economically viable way to deliver the petroleum products from enterprises to the end consumers. Such transportation, however, always requires volume measurement. In the case of petroleum products, it is necessary to take into account the Archimedes’ buoyant force, which cannot be accounted for by scales themselves. The following article reviews how ARDIS hardware-software system, including the Archimedes’ Buoyant Force module, solves this task.

Specificity of petroleum products logging

Measuring the volume of petroleum products transported by rail tank cars can be performed during the loading and unloading processes with the help of flow meters. However, their use is not always possible and convenient, especially while operating at open-gallery overhead rail facilities. It is also can be challenging to use the volume of the tank cars in calculations due to technical, metrological and organizational reasons. Therefore, the task of logging the petroleum products during shipment is often solved with the help of railcar scales.

Due to domestic regulations, the enterprise should follow the requirements of GOST (i.e., domestic quality standard) about methods of measuring weight of oil and petroleum products. According to GOST, when weighing petroleum products, it is necessary to take into account the air buoyant force that acts on the transported product. A number of technical means and measures are required to ensure this. They enable to compensate for irrecoverable losses, which, according to practical calculation cases, account to 0.09-0.19% of the product mass. In financial terms, the accounting of Archimedes' buoyant force provides a substantial saving of funds of the enterprise, while accounting for this effect is rather quick.

Next, let us consider technical means that can provide automation of dynamic railcar scales.

System composition

According to GOST, the following data are required for the mathematical calculation for taking into account the air buoyant force:

  • mass of product in the railcar
  • density of the product in the railcar
  • ambient temperature
  • atmospheric pressure

ARDIS hardware-software system with the optional Archimedes’ Buoyant Force module enables to automatically measure these parameters and calculate the correction.

ARDIS is a system for recognition the railcar identification numbers, capable of working in challenging conditions of industrial production, such as reverse movement of cars in the control zone, limited-spacing conditions for installing cameras, entry of railcars and platforms of various types into the control zone, login of articulated railcars, recognition of non-standard identification number of internal standards, etc.

ARDIS hardware-software system includes:

  • video cameras, illuminators and wheelset sensors
  • server with software for recognition identification number of railcars
  • specialized computer with installed software operator's workstation

Besides recognition functions, the system with the help of additional modules can perform automation tasks of technological operations with railcars (e.g., weighing, loading, unloading, etc.). Specifically, the hardware-software system provides an integration module with railcar scales and software automated workstation (AWS) for the scale operator (see image below). It enables to calculate the net weight of each railcar in automatic, semi-automatic or manual mode, depending on the specifics of railcar movement at the enterprise.

Separate specialized module required by the oil-refinery industry is the Archimedes’ Buoyant Force module. It includes:

  • ambient air temperature sensor
  • atmospheric pressure sensor
  • programmable logic controller (PLC), which calculates the correction at the level of a separate railcar
  • Archimedes’ Buoyant Force program module, which is integrated with the information systems of particular enterprise, and it controls the calculation of correction for each corresponding railroad train.

System operation algorithm

As the starting point of considering ARDIS algorithm and Archimedes’ Buoyant Force module operation in integration with dynamic railcar scales, it is necessary to describe the basic sequence of actions for weighing railcars:

  • The automatic subsystem for railcar identification number recognition performs video recording, counting and recognition of railcars of the moving railway train. At the same time, dynamic railcar scales weigh each railcar passing through the control zone.
  • After the last railcar has passed, the railcar scales integration module combines the data from the scales with the recognized numbers.
  • When the train returns through the video control zone after loading (or unloading) the tank cars, the net weight of the product is determined.

To automatically synchronize data from the railcar scales and recognized identification numbers, the recognition system is installed in close proximity to the scales (see image below).

After determining the net mass, the Archimedes’ Buoyant Force module performs the calculation of correction. Overall, the system operates according to the following algorithm:

  • Sensors measure temperature and atmospheric air pressure at the time of weighing of loaded tank cars.
  • The density value of petroleum products in the tank car is supplied into the module program from the external information system connected to the laboratory of plant.
  • The mass of the filled petroleum product, corrected for the air buoyant force, is calculated automatically using the formulas from GOST. For this, if all the initial data for the calculation of correction (i.e., net weight, product density, air pressure and temperature) are available, the Archimedes’ Buoyant Force module transfers these values to the PLC, which consequently calculates the corrected net weight.

In some cases, this algorithm may be adopted further in order to take into account the specifics of a particular implementation site. For example, at an implementation site, density values may be received late or may not be received for each individual tank car, but only for the storage container that is used to fill all tank cars.

Economic effect

As an example of the economic efficiency of the system, we present a fragment of a report on calculating the correction for the air buoyant force below. These measurements are obtained at one of the ARDIS and Archimedes’ Buoyant Force module implementation site.

As we can see, the correction in those conditions was about 0.1%, which, however, can vary depending on product density and environmental conditions. To put it simply, the correction will be greater if the product density and temperature are low, and the atmospheric pressure is high.

Let us suppose that the company ships about 1 million tons of petroleum products through the railcar scales per year. Then, taking 0.1% as the average value of the correction, we will get an increase of 1,000 tons of product. Suppose that the cost of 1 ton of petroleum product is 30 thousand rubles, then the annual economic effect will be about 30 million rubles (or 310 thousand USD aproximatelly), and the payback period of the project on automation of railcar scales will be just a few months.

Currently, ARDIS system developed by Mallenom Systems LLC is implemented and successfully operates at more than 70 large industrial facilities in Russia and CIS. The systems with the Archimedes’ Buoyant Force module are used at LUKOIL, Gazprom Neft and Rosneft weighing stations, helping the enterprises to increase their profits.

Conclusion

In this article we have highlighted the technical aspect of the task of taking into account the correction for the air buoyant force when weighing petroleum products. In conclusion, we would like to emphasize the important role of the recognition system and its specialized modules since it operates at a level of individual railway trains, meeting the large demand of cases where companies process specifically individual trains rather than independent railcars during logistics operations.

In addition, it should be noted that issues related to metrological certification of such systems, their integration into customer information environments and automation of direct weighing have been out of the scope of the present publication. These are broad topics which require detailed consideration in separate future articles.

Published in Control Engineering Russia magazine, July 2023

24.10.2023