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PDVSA has received funding for the project on the condition that it achieves the World Bank limits of 99.98% sulphur removal and 150 mg/Nm3 (approximately 100 ppm) atmospheric release of SO2.

world bank

PDVSA’s expansion of the El Palito refinery in Carabobo is part of the organisation’s drive to strengthen its asset base so that it remains highly relevant to today’s global oil markets.

The objectives of the project, which is now at the detailed engineering phase, are to double the refinery’s capacity, enable processing of the abundant heavy crude oil produced from the Orinoco Belt of the country and increase the production of cleaner fuels. 

PDVSA has received funding for the project on the condition that it achieves the World Bank limits of 99.98% sulphur removal and 150 mg/Nm3 (approximately 100 ppm) atmospheric release of SO2.

These requirements are substantially more challenging than those specified by many local regulators; for example, the United States Environmental Protection Agency limit for SO2 content is typically 250 ppm. 

Shell Global Solutions worked with PDVSA to design a refining configuration that would help the refiner to meet its objectives. To enable the production of diesel and gasoline meeting stringent sulphur targets, the team opted to add two new hydrotreaters. However, state-of-the-art sulphur-removal technologies will also be necessary.

The hydrotreating units are designed to remove impurities such as sulphur and nitrogen from two distinct fractions: the heavy  oil and diesel streams.

The resultant H2S will be sent to the SRU, where it is partly burned to form SO2 and water.

The SO2 reacts with more H2S to form sulphur and more water.

Two distinct streams emerge from the SRU: sulphur, which is cooled to a liquid, and gases, which are sent for further catalytic conversion.

The liquid sulphur recovered from sour crudes contains dissolved H2S, which could be problematic if it were to leave the liquid sulphur and accumulate.

There would be the possibility of explosion or of the gas reaching a lethal (>10-ppm) concentration.

Consequently, the H2S in the sulphur has to be reduced to a lower level, and this is envisaged to be supported by using Shell Global Solutions’ degassing technology. 

In many facilities, the H2S that the degassing units recover is disposed of in an incinerator. However, the lower limits that apply to the PDVSA projects mean that this option is unavailable. Shell Global Solutions’ solution involves degassing the sulphur and returning the H2S to the front of the SRU for a second cycle. 

Limiting the atmospheric release of SO2 to below 100 ppm was especially challenging because a conventional Shell Claus off-gas treating (SCOT) unit would typically be unable to meet this specification, so Shell has devised a solution that features Low-Sulphur SCOT (LS SCOT) technology as part of the sulphur recovery complex. This is Shell’s most advanced sulphur-removal technology and will help PDVSA to meet the tight World Bank limits. 

The complex at the refinery will consist of an integrated SRU, a tail-gas unit, a sulphur degasser, an acid gas removal unit (AGRU) and a water-stripping unit. 

PDVSA has commissioned a similar project at its Centro de Refinación de Paraguaná refinery complex, which is an amalgamation of the Amuay, Bajo Grande and Cardón refineries. With a refining capacity of 940 MMbbl/d, PDVSA claims that this is the largest refining centre in the world: it accounts for more than 70% of the Venezuela’s refining capacity. Again, Shell is licensing hydrotreaters and sulphur-removal technologies to help the complex to process more Venezuelan crudes and comply with tight World Bank limits. Shell is currently working on the basic design package for this project. 

The projects at El Palito and Centro de Refinación de Paraguaná have been vital in helping PDVSA to meet its business objectives and demonstrate that it is possible for refiners to achieve  extremely high levels of sulphur recovery  and very low levels of SO2 emissions. 

Pankaj Desai 

Licensing Sales Manager, Americas, Shell Global Solutions (US) Inc.

The hydrotreating units are designed to remove impurities such as sulphur and nitrogen from two distinct fractions: the heavy oil and diesel streams.

SCENARIO
SCENARIO  
Refinery El Palito
Owner Petróleos de Venezuela SA
Location Carabobo, Venezuela
Refining capacity 140 MM bbl/d rising to 280,000 MM bbl/d on project completion
Objectives
  • Increase capacity
  • Achieve 99.5% sulphur recovery efficiency
  • Comply with 100-ppm SO2 emission limits
  • Process difficult crudes
  • Produce cleaner, high-value fuels
Solution type New units
Conversion facilities to be installed Hydrotreating units
Sulphur recovery facilities to be installed SRU, tail-gas unit, sulphur degasser, acid gas removal unit and water-stripping units
Post-project feed Heavy and extra-heavy crudes from the Orinoco Belt
Post-project product slate Euro V diesel and low-sulphur gasoline