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Challenges in producing BS-VI diesel

An Indian refiner describes the technical challenges of meeting a leap in
fuel quality specification.

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Article Summary
BS-VI auto fuel emission standards mandate all Indian refiners to produce diesel with <10 ppmw sulphur content from January 2020 onwards. There are numerous challenges in the design and operation of an ultra-low sulphur diesel (ULSD) producing hydrotreater. Experience is that most of the challenges in a ULSD producer’s operation can be addressed by establishing the appropriate process basis at the design stage.

Cracked gasoil from delayed cokers, FCC units or visbreakers will have two or more times the sulphur, nitrogen, metals and aromatics content of straight run diesel. Therefore the right strategy will be to design the catalyst and hydrogen (make-up and recycle compressors) circuit for a good amount of cracked gasoil feed. The heat integration and feed effluent exchanger design should consider the correct volume of lean olefin and/or cold feed as the design basis for robust operation. Such a feed case, along with key process design aspects which will ensure robust design and operation in a diesel hydrotreater, are discussed in this article. Fail-safe options/strategies for refiners in the event of critical equipment failures, such as in combined feed exchangers, which may call for shutdown or slow-down to enable sustainable production of BS-VI diesel, are described. The article also highlights the challenges in logistics for storage, transfer and despatch of BS-VI diesel along with the means to address these challenges.

The Indian auto industry will move directly from BS-IV to BS-VI emission norms by 2020. BS-VI standards prescribe emission norms that are ‘fuel-neutral’. At BS-VI levels, the gap between emissions from diesel and petrol vehicles narrows. At that level, emissions will become nearly fuel-neutral. India’s Auto Fuel Policy had earlier recommended the implementation of BS-VI norms by 2024. Now India’s Ministry of Road Transport and Highways (MoRTH) has advanced the date to 1 April 2020. Thus, the implementation of BS-VI is to take place from 2020 itself.

Considering the environmental impact, rising pollution levels and health hazards due to vehicular pollution, India will move to the toughest emission standards of BS-VI from the current BS-IV from 2020, skipping an intermediate level, BS-V. By switching to BS-VI, India will join the US, Japan and the European Union, which follow Euro VI emission norms. BS-VI is the Indian equivalent of Euro 

What are BS norms?
In vehicles, emissions depend on fuel and emission control technologies that are regulated through emission standards.

The BS – or Bharat Stage – emission standards are norms instituted by the government to regulate the output of air pollutants from internal combustion engine equipment, including motor vehicles. India has been following the European (Euro) emission norms, though with a time lag of five years. BS-IV norms are currently applicable in 50 cities in which the required grade of fuel is available; the rest of India still conforms to BS-III standards. From April 2017, the entire nation moved to BS-IV emission norms.

A brief history
• India introduced emission norms first in 1991, and tightened them in 1996, when most vehicle manufacturers had to incorporate technology upgrades like catalytic converters to cut exhaust emissions.
• A Supreme Court order of April 1999 notified Bharat Stage I and Stage II norms, broadly equivalent to Euro I and Euro II respectively. BS-II applied to the Delhi National Capital Region and other metros, BS-I for the rest of India.
• In August 2002, the first Auto Fuel Policy was announced. As per the policy, four-wheelers in 13 metro cities moved to BS-III emission norms from April 2005 and the rest of country to BS-II.
• In April 2010, Bharat Stage IV emission standards were put in place in 13 major cities.
• India currently follows Bharat Stage IV norms, but only across 50 major cities. The whole country switched to BS-IV from April 2017.
• The second version of the national auto fuel policy, Auto Fuel Poilcy 2025, laid the road map up to 2025 by announcing the implementation of BS-V by 2021 and BS-VI by 2024. But the government of India mandated the adoption of BS-VI norms, skipping BS-V, by April 2020 (see Table 1).

This jump in standards will make a huge impact and significantly bring down vehicular emissions’ contribution to India’s air pollution levels.

At the BS-VI level, the gap maintained between emissions from diesel and petrol, wherein diesel cars are allowed to emit more particulate matter and nitrogen oxides narrows. For instance, in diesel cars, the jump to BS-VI norms will result in a reduction of nitrogen oxide emissions by 68%, and particulate matter, which has a damaging effect on air quality and human health, by 82%. Similarly, in heavy duty vehicles like trucks, the shift to BS-VI norms will result in a reduction of nitrogen oxide emissions by 87% and particulate matter by 67%.

With BS-IV norms, commercial heavy duty diesel engines are estimated to emit ~70 times the 2019 levels of NOx and particulate matter  emissions in 2030 due to growth in numbers of vehicles. With BS-VI’s implementation, NOx emissions are estimated to be about ~8 times and particulate matter emissions ~30 times the levels of 2020.

Currently, MRPL’s refinery is capable of producing around 1.2 million t/y of BS-IV motor spirit and around 6.5 million t/y of BS-IV diesel. MRPL has received environmental clearance from the Union Ministry of Environment, Forest and Climate Change (MoEFCC) for its BS-VI auto fuel quality compliance project and associated project facilities.

With this clearance, the company will be able to achieve conversion of the existing BS-IV quality motor spirit and high speed diesel facilities entirely to BS-VI quality. This will help to achieve the production of 1.2 million t/y of motor spirit and 7 million t/y of high speed diesel to the higher standards.

Approximately 20 acres of land in the existing refinery complex will be used for the proposed project. MRPL will be spending INR 1810 crore (~$275 million)  for implementation of the BS-VI project. Currently, the company can meet around 80% of its high speed diesel production potential to BS-VI requirements, and will be ready to produce BS-VI motor spirit by January 2020.

Challenges in producing BS-VI diesel (ULSD)
Typical challenges in operating an ULSD producing hydrotreater are:
• Nearing end of run (EOR) period or, at times, the reactor exotherm or weighted average bed temperature or peak temperature is limited due to more cracked (olefinic) gasoil from the bottom upgraders such as a coker or visbreaker.
• Make-up compressor or recycle gas compressor constrained due to high chemical hydrogen consumption to saturate high aromatic feeds from resid crackers when nearing the EOR period.
• Reactor charge heater limitation in hydrotreaters designed for good cracked (olefinic) feed while running with straight run feed.
• Feed/reactor effluent or combined feed exchangers: a minor leak jeopardises 10 ppmw product requirements.
• Product fractionators steam reboiler: leak jeopardises water specification in high speed diesel.
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