Diesel Hydrotreating Segmentation for Cetane and Cost
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Solution Overview
Problem
Current hydroprocessing methods at lower pressures are cost-effective but fail to sufficiently saturate aromatics, resulting in diesel products with lower cetane values and higher sulfur content, which do not meet stringent regulatory standards for ultra-low sulfur diesel.
Innovation Solution
A process and apparatus involving a hydrotreating reactor followed by stripping sections to remove light gases and poisons, a saturation reactor to enhance cetane through aromatic saturation, and a fractionation column to produce low-sulfur, high-cetane diesel, utilizing noble metal catalysts and specific operating conditions to maintain catalyst effectiveness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If high pressure processing (12.4-17.2 MPa) is used for hydrotreating to saturate aromatics and increase cetane number, then cetane number is improved, but capital and operational costs increase due to more robust metallurgy and compression systems
Solution Approach 1:
The process is divided into two distinct stages: a first hydrotreating stage operating at lower pressure (3.4-6.9 MPa) for sulfur removal, and a second hydrotreating stage operating at higher pressure (6.9-13.8 MPa) for aromatic saturation. This segmentation allows each stage to be optimized for its specific function, reducing overall capital costs while achieving the desired cetane number improvement.
Solution Approach 2:
The first hydrotreating stage performs preliminary sulfur removal and partial aromatic saturation before the feed enters the second stage. By removing sulfur and nitrogen heteroatoms in advance, the process prepares the feedstock for more effective aromatic saturation in the second stage, reducing the burden on the high-pressure system and associated costs.
2Ease of manufacture
If lower pressure processing is used for hydrotreating to reduce capital and operational costs, then capital and operational costs are improved, but aromatic saturation effectiveness decreases, resulting in lower cetane number
Solution Approach 1:
The hydrotreating process is segmented into two pressure stages, with the second stage specifically dedicated to aromatic saturation at elevated pressure. This ensures sufficient cetane number improvement while limiting the extent of high-pressure processing to only what is necessary, thereby controlling capital and operational costs.
Solution Approach 2:
The process utilizes parameter changes by adjusting pressure from the first stage (3.4-6.9 MPa) to the second stage (6.9-13.8 MPa). This parameter adjustment optimizes aromatic saturation effectiveness in the second stage while maintaining cost efficiency through the lower-pressure first stage.
3Manufacturing precision
If hydrotreating is performed to remove sulfur from hydrocarbon feedstock, then sulfur content is reduced, but hydrogen sulfide and ammonia are produced which can poison downstream catalysts
Solution Approach 1:
A stripping section is introduced between the two hydrotreating stages to extract and remove hydrogen sulfide and ammonia from the liquid hydrocarbon stream. This prevents the harmful gases from poisoning the catalysts in the second stage while maintaining the sulfur removal benefits of the first stage.
Solution Approach 2:
The stripping section acts as an intermediary between the two hydrotreating stages, removing harmful byproducts (hydrogen sulfide and ammonia) generated in the first stage before the feed enters the second stage. This protects the downstream catalysts from poisoning while allowing continuous sulfur removal.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The process effectively reduces sulfur content to below 10 wppm and increases cetane number, producing diesel that meets stringent regulatory standards while minimizing operational and capital costs by operating at lower pressures.
Implementation Method 1
Hydroprocessing is a process that contacts a selected feedstock and hydrogen-containing gas with suitable catalyst(s) in a reaction vessel under conditions of elevated temperature and pressure
Implementation Method 2
Hydrotreating is a type of hydroprocessing active for the removal of heteroatoms, such as sulfur and nitrogen, and saturating unsaturated compounds in the hydrocarbon feedstock
Implementation Method 3
Ammonia is a catalyst poison for hydroprocessing catalyst such as hydrocracking catalyst and saturation catalyst, particularly, noble metal saturation catalyst. Hydrogen sulfide and ammonia gases are stripped from liquid hydrocarbon streams
Implementation Method 4
At higher pressures, such as 12.4 MPa (1800 psig) to 17.2 MPa (2500 psig), hydrotreating can also saturate aromatic compounds to increase the cetane number of diesel produced from a hydrocarbonaceous feed
Implementation Method 5
a fractionation column in communication with the second stripping section
Data Source
Figure 1
AI summary
A process and apparatus is provided to produce desulfurized diesel at low pressure with high cetane rating. A hydrotreated stream is stripped and fed to a saturation reactor. The saturated stream is stripped again and fractionated to provide diesel product. Unconverted oil may be hydrocracked and stripped with the saturated product.