Environmental Engineering Reference
In-Depth Information
Figure 2.3: Trends in fuel specifications in European Union [From ref.
25
. Reprinted with
permission].
2.1 Conventional Refinery
Simple refining schemes such as shown in
Fig. 2.4
were adequate for processing light-sweet
crude. They involved atmospheric distillation to obtain fuel fractions. If desirable, vacuum
distillation of atmospheric residue yielded vacuum gas oil (VGO), which could be either the
additional source of fuels or used for production of lubricating oils. In early stages of refining,
the hydrocarbon gases from distillation were simply flared, in spite of their high heating value.
Today, in most of the refineries, the hydrocarbon gases are efficiently utilized on site (e.g., in
preheaters). In some site-specific situations, it was advantageous to use atmospheric residue as
fuel to produce steam and electricity. In other situations, vacuum distillation yielding
additional liquids such as VGO and vacuum residue were added to the overall refining scheme.
Vacuum residue, sometimes termed as asphalt, was used as construction material. In the case
that market for asphalt dried out, a delayed coker was added to produce additional liquids from
the asphalt. The liquids from coking had to be stabilized via a catalytic step. The coke from
delayed coking was suitable for production of various carbon products such as carbon
electrodes, activated carbon, etc. The surplus of delayed coke was utilized on refinery site to
generate steam and electricity via combustion.
