Pre-calculated API Gravity Tables as an Alternative to the Standard Equation

1.       Introduction

    The American Petroleum Institute (API) gravity value is a key indicator of crude oil quality and its selling value. Accurate measurement of API gravity is essential for classifying crude oil and petroleum products. Existing crude oil API prediction methods are difficult and time-consuming because they rely on numerous parameters [1]. In the oil industry, the API gravity test is an important method for determining product type [2]. API gravity is a significant quantity in the crude oil sector; nitrogen compounds are not directly related to API gravity, which causes conceptual confusion [3]. The large quantities of oil originate from the upstream and downstream processes, which cause differences in specifications, specialists in specific gravity (Sp. gr) [4]. North refinery company NRC Baiji produced about 200,000 barrels/day. These quantities to be produced must be calculated in accordance with the specification [5]. The world has recently turned to solving problems through scientific research, including the oil industry, as this opportunity has justified reducing the number of workers and the effort expended [6]. Fossil fuels are the largest source, accounting for more than 75% of global energy demand. Various fuels, including diesel fuel, gasoline, and kerosene, can be generated in petroleum refineries using several petrochemical processes [7]. Crude oil is a complex of hydrocarbon that contains organic and inorganic materials.

2. Materials and methods

2.1. Oil samples and equipment

Four types of petroleum products were used in this study, which are gasoline, kerosene, gas oil, and lubricating oils. In this work were used 16 samples, 4 samples of gasoline, 4 samples of kerosene, 4 samples of gasoil, and 4 samples of lubrication oil, these samples were different and Sp.gr to find different API gravity depending on it. These samples were brought from North Refineries Company (NRC) in Baiji. The testes of these samples were evaluated for specific gravity, temperature, and American Petroleum Institute (API) gravity. Four different samples were tested for each model, bringing the total number of samples examined to sixteen. Samples were taken from the loading arms of petroleum products from the dispatch warehouse (Baiji), concentrated in the laboratories of the Petroleum Products Distribution Company (OPDC), Salahuldeen branch, and cooled at room temperature (15 °C). The equipment employed in this work (cylinder 100 ml, thermometer range from 0 to 100 °C, and hydrometers range 0.600 to 0.650, 0.650 to 0.700, 0.700 to 0.750, 0.750 to 0.800, 0.800 to 0.850, 0.850 to 0.900, 0.900 to 0.950, 0.950 to 1.000).

2.2 Testing methods

The Sp. gr. was determined according to ASTM D1298 [12], while the API gravity was determined according to ASTM D 5002 [13] and calculated according to Equation 1 [14]. These tests were done at the laboratory of Salahuddeen branch, Western Authority, Oil Product Distribution Company (OPDC), Ministry of oil Iraq.

API=141.5/Sp.gr-131.5   (1)    Figure 1: The Sp.gr apparatus

3.       Results and discussions

3.1.  Gasoline test

        Table 1 presents the data on specific gravity, temperature, and API gravity for gasoline samples. As a result, the range of specific gravity was from 0.700 to 0.750 while the range of API gravity was from 75.6 to 57.2. The results also showed that the gasoline samples had the lowest temperatures, at approximately 20 °C, compared with kerosene and gasoil, which reached 20-21 °C. These results are attributed to the presence of light volatile aromatic compounds in gasoline. Therefore, these results will contribute to strengthening the findings that constitute the final Table of this research [15].

Table 1: Sp.gr, temperature, and API results of gasoline samples

3.2. Kerosene test

      Table 2 presents the data on specific gravity, temperature, and API gravity for kerosene samples. As a result, the range of the specific gravity was from 0.750 to 0.800, while the range of API gravity was from 57.2 to 45.4. The results also showed that the temperatures of the kerosene product were average compared to gasoline and gasoil, ranging between 22 and 23 °C. This is attributed to the mixture that makes up the kerosene. These results are attributed to the presence of light volatile aromatic compounds that contribute to the composition of gasoline products. Therefore, these results will contribute to strengthening the results that are the basic components of the final Table of this research [16].

Table 2: Sp.gr, temperature, and API results of kerosene samples

3.3. Gasoil test

       Table 3 presents specific gravity, temperature, and API gravity for gasoil samples. As a result, the range of specific gravity was from 0.800 to 0.850, while the range of API gravity was from 45.4 to 35.0. The results also showed that the temperatures of the gas oil product were reasonable compared to other products, as they ranged between 23 and 25 °C. This is attributed to the mixture that makes up the gas oil, which is a mixture of linear organic hydrocarbon compounds that extend up to C30. These results are attributed to the presence of light volatile aromatic compounds that contributed to the composition of the gasoline product. Therefore, these results will contribute to strengthening the results that are the basic components of the final Table of this research [17].

Table 3: Sp.gr, temperature, and API results of gasoil samples

3.4. Lubrication oil

     Table 4 presents the specific gravity, temperature, and API gravity for lubrication samples. As a result, the range of specific gravity was from 0.850 to 0.900 while the range of API gravity was from 25.4 to 25.7. The results also showed that the temperatures of the lubrication product were low compared to other products, ranging between 20 and 25 °C. These results are attributed to the presence of lubricating oils are heavy hydrocarbons compounds that contribute to the composition of the lubricant product. Therefore, these results will contribute to strengthening the results that are the basic components of the final Table of this research [18].

Table 4: Sp.gr, temperature, and API results of lubrication oil samples

3.5. API gravity tables

     Table 5 presents the ranges of Sp. gr. and API gravity for oil products. Tables 6, 7, and 8 present the API gravity data, which range from 0.600 to 0.795, corresponding to API gravities of 104.3 to 46.5. In addition, the API gravity ranges from 0.800 to 0.995, corresponding to API gravities of 45.4 to 35.0. Furthermore, API gravity was initially set at a specific gravity (Sp.gr) of 1.000 to 1.025, corresponding to API gravities of 10 to 7.0, respectively [19].

Table 5: Range of Sp.gr and API gravity ranges of oil samples

Table 6: API gravity started of Sp.gr from 0.600 to 0.795

Table 7: API gravity started of Sp.gr from 0.800 to 0.995

Table 8: API gravity started of Sp.gr from 1.000 to 1.025

Figure 2: API gravity curve, relationship with sp. gr of oils

4.Conclusions

The Tables of all API gravity values by their relationship with specific gravity has successfully in this work. Extracting the weight value through the equation may take about five minutes, while extracting it from the table does not take half a minute, which saves time in the oil sector. Therefore, these Tables will be of great importance in all aspects of oil extraction, production, refining and distribution, as the API gravity values will be taken directly from the specific gravity via these Tables. As well as there is no need to calculate the equation or the possibility of being exposed to error after these Tables. While statistical analysis, which included standard deviation, error bars, or confidence intervals, was not found because the current work was done according to the API gravity equation.

5. Acknowledgment

    The authors would like to thank Hussain Talib Abood, General Director of the Oil Products Distribution Company (OPDC), The authors would like to express their appreciation to Eng. Raad Ahmed Abdulaah, Head of Salahudeen Branch (OPDC). At the same time, the author would like to express her thanks to AlNoor University for supporting the research.

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جداول الكثافة النوعية وفق معيار API المحسوبة مسبقًا كبديل عن المعادلة القياسية

هشام قنبر علي¹، محمود عبد الكريم عبدالقادر^3،2*

¹شركة مصافي الشمال بيجي، ²شركة توزيع المنتجات النفطية، فرع صلاح الدين، تكريت، وزارة النفط، العراق، ³ قسم هندسة النفط، كلية الهندسة، جامعة النور، العراق

يعَدّ كثافة معهد البترول الأمريكي (API) معيارًا أساسيًا لتصنيف النفط الخام والمنتجات النفطية اعتمادًا على الكثافة. يقدّم هذا البحث تطوير جداول لكثافات الزيوت تتراوح بين 0.600 إلى 1.025، يمكن من خلالها اشتقاق كثافة API مباشرةً دون الحاجة إلى استخدام معادلة الحالة. كما تناولت الدراسة فحص أربع كثافات لأربعة منتجات نفطية (البنزين، الكيروسين، زيت الغاز، وزيوت التزييت)، مما أسفر عن 16 نموذجًا إجمالًا. وأظهرت نتائج الاختبارات المختبرية تقارب كثافات الزيوت؛ فعلى سبيل المثال، تتراوح كثافة البنزين بين 0.700–0.750، وتتراوح كثافة الكيروسين بين 0.750–0.800، بينما تتراوح كثافة زيت الغاز بين 0.800–0.850، وأخيرًا تتراوح كثافة زيوت التزييت بين 0.850–0.900. وخلاصة القول، فإن الجداول التي أُنتجت في هذه الدراسة تُمكّن من القياس المباشر لكثافة API، مما يوفر وقت الفاحصين، ويُحسّن الدقة، ويُقلّل الأخطاء.