Gas 2024 Issue

in today’s modern refinery. Gasoline has several specifica - tions that must be satisfied to provide high performance for today’s motor vehicles. Octane, however, is the most widely recognised specification. Molecules are reformed into structures that increase the percentage of high-octane components while reducing the percentage of low-octane components. In doing so, it liberates a significant amount of hydrogen that may be used in desulphurisation and sat- uration reactions elsewhere in the refinery. Table 2 sum- marises the units and operating conditions for potential sources of hydrogen-containing ROG. Where does membrane technology make the most sense? Membrane separation technology has been closely moni- tored for its advantages over traditional separation meth- ods. Membrane separation requires no moving parts, chemical reactions, solvents, or adsorbents. The separation is driven exclusively by the pressure of the feed gas. While purified hydrogen is produced at a lower pressure than the feed gas, it can be reintroduced to units operating at lower pressure or recompressed using existing or new hydrogen recycle compressors. The retentate – typically containing <10% hydrogen and lighter hydrocarbons – is released at near feed pressures and can be easily routed to downstream separation processes (for example, cold box) or even as feed back to the SMR. Due to the feed pressure requirements for membrane separation, the units that make the most sense as ROG feed producers are the high-pressure systems. An eco- nomic analysis of the separation potential for Divi-H will be conducted in Part 2, starting with the highest pressure systems then working to the lower. Divigas has developed a proprietary simulator that uti- lises Aspen Hysys and Matlab to allow for simulations using feed gas pressure, temperature, composition, and flow rate. Results include the make-up of the permeate and retentate streams, as well as the required membrane surface area, end hydrogen purity, and hydrogen recovery. We will ana- lyse the results as follows: • Pressure reduction and module count required for 95%, 99%, and 99.9% hydrogen purity from each potential source. While currently utilised PSA technologies typically produce 99.9% or greater hydrogen, there is significant flexibility in permeate purities with membrane technology. • Opportunities for reintroduction without additional compression. • Recompression of purified hydrogen back to feed pres - sures, allowing recycling back into the same unit. • Cost of separation ($/kg). Several assumptions were made to simplify the analysis: • These streams are rough approximations of ROG com - position, flow rate, and conditions. For an analysis of a spe - cific unit case, precise data from that specific unit should be utilised. • While the compressor duty was considered when look- ing at cases where the purified hydrogen was recom - pressed to feed pressures, it was assumed spare hydrogen recycle compressor capacity would be available. If it is not

Hydrogen-containing ROG producers

Unit name

Operating temp. (F) 600-800 650-800 600-800 600-800 400-500 400-500 250-520 925-975 950-1,020

Operating

pressure (bar)

Gas oil hydrotreater

130-140 105-210 35-100 35-100

Hydrocracker

Kerosene hydrotreater Diesel hydrotreater

Light naphtha hydrotreater unit Heavy naphtha hydrotreater unit

25-45 25-45 17-27

Isomerisation unit Catalytic reformer

7-25

Fluid catalytic cracker (FCC)

1-2

Table 2

potential recovery. For the purposes of this analysis, the following sources of hydrogen-containing ROG will be dis- cussed in Parts 1 and 2: • Hydrotreating is a catalytic process to stabilise products and remove objectionable elements like sulphur, nitrogen, and aromatics by reacting them with hydrogen. Hydrogen reacts with oil to produce hydrogen sulphide from sulphur, ammonia from nitrogen, saturated hydrocarbons, and free metals. Metals remain on the catalyst, and other products leave with the oil-hydrogen stream. • Isomerisation is a type of refinery process that converts linear paraffins with low octane ratings into branched par - affins with higher octane ratings. This process is typically used to upgrade low-quality naphtha into higher-quality gasoline blending components. Due to the feed pressure requirements for membrane separation, the units that make the most sense as ROG feed producers are the high-pressure systems • The fluid catalytic cracker (FCC) is the tool refiners use to correct the imbalance between market demand for lighter petroleum products and crude oil distillation that produces an excess of heavy, high boiling range products. The FCC unit converts heavy gasoil into gasoline and diesel, cracking heavy gasoils by breaking the carbon bonds in large mol- ecules into multiple smaller molecules that boil in a much lower temperature range. • The hydrocracker is like the FCC in that it is a catalytic process that cracks long-chain gasoil molecules into smaller molecules that boil in the gasoline, jet fuel, and diesel fuel range. The fundamental difference is that cracking reactions take place in an extremely hydrogen-rich atmosphere. Two reactions occur. First, carbon bonds are broken, followed by the attachment of hydrogen. Hydrocracker products are sulphur-free and saturated. • Catalytic reforming is the workhorse for octane upgrade

Gas 2024