Jan-2012

New crude oil basket for hydrogen 
savings

The processing requirements of opportunity crudes are considered for the operations of the Indian refineries

Rajeev Kumar, Prashant Parihar and Ravi K Voolapalli
Corporate R&D Centre, Bharat Petroleum Corporation Ltd

Article Summary

In the world of petroleum refining, optimal use of hydrogen is the key to maximising a refiner’s profitability. In fact, the presence of hydrogen in petroleum oils and/or fractions should decide the actual value of hydrocarbons. The deficiency of hydrogen in crude oil is normally compensated by the addition of hydrogen in hydroprocessing units in order to meet stringent fuel specifications. In this scenario, refiners need to understand the balance of hydrogen and carbon for achieving the best margin. The hydrogen content of crude oils and their straight-run products for low-API and high-sulphur, and for high-API and low-sulphur, crude oils have been studied (see Figure 1).¹ The hydrogen content of distillates is higher than crude oil and has a higher monetary value than crude oil. On the other hand, the hydrogen content of residues is lower, as is their value.

This directly implies that hydrogen addition to upgrade crude oil to produce valuable distillates will result in increased product value, but at the cost of additional hydrogen. Therefore, it is essential to characterise feedstock crude oils for hydrogen content so that excessive hydrogen addition is not added on to the cost of crude processing.

Crude oils mainly contain carbon, hydrogen and many undesirable components. In petroleum refining, maximum effort goes into dealing with impurities, which results in higher processing costs. The cost of crude oil amounts to 80–90% of the total cost to a refiner; hence, the selection of an appropriate crude oil basket is of the highest importance.²

In the current refining climate, processing opportunity crude oils and meeting critical product specifications such as Euro III, IV and V is the real challenge for improving refinery margins. As the word “hydrocarbon” suggests, only hydrogen and carbon are the desirable components in their different forms. All other components, in any structural or free form, are undesirable impurities. These impurities imbalance the hydrogen content of petroleum and are colloquially known as “hydrogen guzzlers” in the course of hydroprocessing to meet product specifications.³

Vacuum gas oils (VGO) derived from high-sulphur and low-API crude oils consume lots of hydrogen during hydroprocessing and, thus, it results in exorbitant cost. In order to minimise hydrogen consumption in the hydrocracking unit, a new crude basket has been proposed. The characteristics of VGO, such as aromatic and sulphur content and other impurities that consume maximum hydrogen for saturation, are minimised in the new crude basket. These properties also affect catalyst activity and, in turn, the run length, which restricts the throughput capacity of the hydrocracking unit, with hydrogen unit capacity being constant. The methodology for hydrogen consumption is based on the balance of carbon, hydrogen and impurities to screen the new crude oils in comparison with the high-sulphur crude oils typically processed as the base case for estimating their benefits. As the costs of crude oils and distillate yields are the most important variables for achieving overall benefit, a detailed techno-economic study is essential.

Processing low-API and high-sulphur crude oils
The world over, processing opportunity crude oils is the current refining trend for targeting higher refining margins. These crude oils are available at a lower cost with a compromise on factors such as API, sulphur content, TAN, and others. These crude oils produce inferior- quality atmospheric, vacuum gas oil and lots of residues that require either additional refining processes and/or evacuation at a lower cost. Hydroprocessing such streams  consumes large quantities of hydrogen at a high cost.⁴

Although it is known that the cost of crude oils has a large influence on the economics of the refining business, the cheaper crude oils add lots of processing costs in order to meet the critical product specifications of Euro III, IV and V product grades. This results in a squeezing of benefits and may lead to a reversal in the trend of processing opportunity crude oils.

Since opportunity crude oils not only influence processing costs because of their deficiency in hydrogen but also produce lots of residues, refiners are forced to sell fuel oils with additional distillate as cutter. Other, secondary units such as fluid catalytic cracking units suffer feedstock availability and frequently have to run at lower capacity as a result of the high residue yields obtained from cheaper crude oils. And the distillates produced from cheaper crude oils consume large quantities of hydrogen during hydroprocessing, which means further additional cost. Therefore, the increasing criticality of product specifications requires selection of a new crude oil basket for minimising processing costs through hydrogen savings. In the present study, the selection of a new crude oil basket has been carried out to enlarge a refinery’s existing crude basket.

The VGO drawn from low-API, high-sulphur crude oils is streamed towards hydroprocessing, which leads to high levels of hydrogen consumption. The characteristics of VGO as a feedstock are the key factors influencing hydrogen consumption and so it is essential to evaluate them. The characteristics of VGO are mainly influenced by vacuum tower operations, endpoints and types of crude oils processed in crude distillation units.5 The main culprits among poor characteristics of VGO are aromatics, sulphur and other impurities such as vanadium, nickel and nitrogen, which either consume hydrogen for saturation and/or are a serious threat to catalyst life, run length and unit capacity. Thus, there is a need to select new crude oils, which can minimise hydrogen consumption.

To reduce hydrogen consumption, a superior-quality VGO needs to be sourced, perhaps from costlier crude oils (high API, low sulphur). It is a challenge to meet the 
requirement of current trends and the processing opportunity crude oils to minimise 
hydrogen consumption in hydroprocessing.

In order to save hydrogen in hydroprocessing, a study has been carried out at the Corporate R&D centre, BPCL, for the selection of a basket of crude oils. The characteristics of VGO are the basis for estimating hydrogen savings in the hydrocracker. The present approach to selecting a crude basket is based on the cost of processing VGO in the hydrocracker. For the present study, operation of the hydrocracker at a refinery  has been considered for selection of a new crude basket. The cost savings derived are in comparison with the processing of Arab Mix crude oil as a base case. Since the cost of new crude oils is not fixed, a detailed techno-economic study would be required before selecting them for processing in the refinery.