Catalysis 2024 Issue

Experimental study on diesel fuel haziness

Understanding the exact reasons behind haziness in diesel fuel facilitates quality control strategies

Dhiraj Gondaliya, Murthy Nelakanti, Kinjal Patel and Shailesh Gadhvi Nayara Energy Ltd Research & Development Centre

N ayara Energy Limited operates a 20 million metric tonnes per annum ( MMTPA) petroleum refinery and produces valuable fuels, including l iquefied petro - leum gas (LPG), naphtha, motor spirit (petrol), kerosene, avi- ation turbine fuel (ATF), and diesel. The refinery can produce around 30 kilo tonne per day (KTPD) ultra low-sulphur die- sel (ULSD) products. The diesel hydrodesulphurisation unit (DHDS), diesel hydrotreater (DHDT), and vacuum gasoil mild hydrocracker (VGOMHC), all catalytic conversion processes, are primarily used to produce low-sulphur diesel fuel. Steam is added after hydrotreatment to strip out the hydrogen sulphide (H 2 S) and ammonia generated during the process. Hence, the saturated moisture will always remain with hydrotreated diesel fuel. The hydrotreatment units are provided with a techno-vacuum dryer or a coalescer facility to remove moisture from diesel and improve haziness. Test method ASTM D4176, procedure-1 (P-1) was used to measure appearance per the specification for rundown and final diesel fuel certification. It was observed that diesel products from the unit and rundown samples intermittently had a hazy appearance, which could lead to failure of the final diesel product specification during certification. Hence, an experimental study was conducted to evaluate the problem. Improvement opportunities The haziness and moisture content were monitored reg- ularly as per scheduled frequency. The detected moisture increased but remained within the acceptable limit of speci- fication, which is a maximum of 200 ppm. The hazy appear - ance of diesel improved upon increasing retention time, and the product became clear after some time. However, it was an alarming situation that could worsen if the problem was further aggravated, hampering diesel production. After a period, haziness was observed even after utilis- ing the techno vacuum dryer and coalescer in sequence. An upgrade to the existing system was discussed, which could require high capital investments. Hence, there was an opportunity to study the haziness; accordingly, an upgrade could be planned to address the problem. Experimental Nayara’s Research and Development team conducted com- prehensive studies and a literature review to support and

resolve the diesel haziness problem. Theoretically, it may be due to the inherent properties of the surfactant type of mol- ecules in the fuel or to moisture present in fine aerosol form. Steam is used as part of the process; hence, moisture comes from the diesel product, which is removed by the techno vacuum dryer and/or coalescer. The following aspects were studied during experimental work to understand the exact reason behind the haziness: • Techno vacuum dryer operation simulation study at the laboratory • Measurement of haziness by various test methods • Stability of haziness • Impact of sample storage container on haziness • Moisture content vs haziness correlation study • Haze rating correlation between two test methods • Removal of haziness by alternate techniques. Techno vacuum dryer operation simulation study The moisture content and haziness are correlated properties of diesel fuel. The moisture content is controlled by optimis- ing the dryer operational parameters such as vacuum, tem- perature, and residence time. A bench-top diesel vacuum dryer was developed in the laboratory using a glass assem- bly with a vacuum pump and heating mantle to study the dryer’s operation performance parameters (see Figure 1 ).

Thermometers

Diesel dryer glass assembly

Vacuum system

Heating system

Figure 1 Lab-scale bench-top vacuum dryer system

Catalysis 2024