Hydrocarbon Processing - March 2022 - 70

Environment and Safety
a single vessel. Developed in the 1970s,
more than 400 of these versatile reverse jet
scrubbers are in use around the world to
treat emissions generated in a wide range
of industrial processes with many of these
systems in operation for more than 20 yr.
The proprietary reverse jet scrubber
consists of an inlet barrel in which a reagent
solution is injected countercurrent
to the gas flow through very large openbore
spray nozzles (FIG. 2). A standing
wave of highly turbulent flow-called the
" froth zone " -is created at the point where
the liquid is reversed by the gas. The froth
zone produces a very high rate of liquid
surface renewal, efficiently quenches the
gas to the adiabatic saturation temperature,
absorbs acids such as sulfur dioxide (SO2
)
and efficiently removes particulate matter.
After contacting the gas with the liquid reagent,
the gas-liquid mixture enters a disengagement
vessel where the liquid drops
to the sump of the vessel and the gas exits
the vessel through a demisting device.
TABLE 1. SO2 removal effi ciency of the proprietary reverse jet scrubber systema
during startup test runs
Test Run 1
Gas pressure drop, mmWC
pH of the liquid
SO2
, ppm
Test Run 1
Gas pressure drop, mmWC
pH of the liquid
SO2
, ppm
Inlet
200
7-8
1,700
Inlet
200
7-8
1,500
< 1
TABLE 2. Refi nery inlet conditions to the proprietary reverse jet scrubbera
Inlet condition
/hr
Flue gas fl owrate, Nm3
Flue gas temperature, °C
Flue gas pressure, kg/cm2
Barometric pressure, kPa
Normal
10,000
(G)
Flue gas composition, vol%
Nitrogen
Oxygen
Water
SO2
Sulfur trioxide (assumed)
A
Incinerator
B
Lime
Bag filter
Incinerator
Lime scrubber
Proprietary
reverse jet
scrubber
systema
FIG. 3. Typical scrubbing/baghouse flow diagram downstream of a mud incinerator (A)
vs. the integration of the proprietary reverse jet scrubbera
to increase SO2 and particulate removal (B).
70 MARCH 2022 | HydrocarbonProcessing.com
Lime
130-150
-0.04
101.325
Balance
11
10
0.2
< 7
Outlet
Outlet
There are no moving parts or narrow
passages that could restrict gas flow, which
prevents plugging issues. The required
maintenance and operator attendance is
minimal and these tasks can be handled
during any scheduled turnaround of
the refinery.
Mud incineration offgas treatment
case study. The following reviews a
case study regarding SO2
removal.
SO2
and particulate
removal. A refiner had installed
a semi-dry lime scrubber and a baghouse
for an existing mud incinerator to reduce
SO2
While the semi-dry lime scrubber was
able to attain an SO2
and particulate emissions (FIG. 3A).
removal efficiency
to achieve required
of approximately 90%, the plant needed
to further reduce SO2
Maximum
12,000
150
-0.04
101.325
Balance
11
10
0.2
levels below 20 ppm. To solve this issue,
the refinery installed the proprietary reverse
jet scrubber downstream of the bag
filter (FIG. 3B). The objective was to have a
highly efficient system that would also be
simple to operate, as only two operators
were available at a time and the scrubber
was sited a long way from the plant.
The flowrate of the incoming gas varied
from 10,000 Nm3
/hr-12,000 Nm3
/
hr. Although the proprietary reverse jet
scrubber can be designed to handle much
higher incinerator temperatures, in this
instance, a pre-existing quench tower upstream
of the scrubber meant that the inlet
gas temperature to this 1.8-m-diameter
scrubber vessel was approximately 150°C
(302°F). The acid content on entry of the
gas was roughly 2,000 ppm SO2
, which
had to be reduced to below 20 ppm.
At the startup of the jet scrubber, two
test runs were conducted. The first run had
1,700 ppm SO2
with the incinerator offgas and measured
less than 7 ppm SO2
Bag filter
Lime scrubber
run recorded 1,500 ppm SO2
coming into the scrubber
on exit. The second
on entry,
with no SO2 detected on exit (TABLE 1).
Particulate removal. The proprietary
downstream of the mud incinerator
reverse jet scrubber is also capable of efficient
particulate removal from mud incinerator
offgases. Particulate removal
depends on two things: the gas-side pressure
drop and the particulate size. FIG. 4
shows the relationship between the two
and the resulting removal efficiency. The
removal efficiency of the particulate depends
on the particle size distribution.
In the refinery example, the gas leaving
the bag filter still contained a certain
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