Surge
Control
Vessels
are
Defined
as
Process
Tanks.
Control
Requirements
are
Embedded
in
the
Process
Vent
Definition
and
Require
Emissions
from
These
Vessels
to
Meet
Process
Vent
Requirements.

Paragraph
63.2550(
f)
defines
process
vent
as:

"
process
vent
means
a
vent
from
a
unit
operation
or
vents
form
multiple
unit
operations
within
a
process
that
are
manifolded
together
into
a
common
header,
through
which
a
HAP
 
containing
gas
stream
is,
or
has
the
potential
to
be,
released
to
the
atmosphere."

Following
the
definition,
EPA
provided
examples
of
equipment
that
are
considered
a
process
vent;
surge
control
vessels
are
specifically
identified.
As
a
result,
the
vent
from
a
surge
control
vessel
must
meet
the
process
vent
standards
rather
than
emission
standards
for
storage
tanks.

Including
surge
control
vessels
in
a
sentence
explaining
what
particular
equipment
is
included
in
the
process
vent
definition
contributes
further
ambiguity
to
the
proposed
rule.
Are
emissions
from
the
surge
control
vessel
considered
a
continuous
process
vent,
subject
to
evaluation
using
a
Total
Resource
Effectiveness
(
TRE)
calculation,
or
are
they
considered
a
batch
process
vent
subject
to
control
only
if
a
mass
emission
threshold
is
exceeded?

We
believe
the
concept
and
intent
of
EPA's
process
vent
definition
is
to
capture
many
of
the
mixing,
reaction
and
distillation
operations
associated
with
batch
processing
operations
that
are
vented
to
a
common
control
device.
For
large
continuous
organic
chemical
manufacturing
processes,
this
concept
is
inappropriate.
Many
product
tanks,
surge
control
vessels
and
bottoms
receivers,
associated
with
these
processes
are
large
capacity
vessels,
are
located
outdoors,
and
often
in
a
remote
tank
farm.
The
confusion
surrounding
the
definition
of
a
storage
tank
or
storage
vessel
is
long
standing.
EPA
has
written
many
determinations
to
clarify
this
issue.
In
40
CFR
Part
63,
Subpart
H,
EPA
initially
stipulated
that
surge
control
vessels
and
bottoms
receivers
be
routed
to
the
process
or
to
a
control
device.
Subsequently,
EPA
determined
that
Subpart
H
needed
to
be
changed
in
view
of
the
major
equipment
modifications
or
replacements
that
would
be
necessary
to
comply
with
the
standard
(
see
preamble
discussion
on
this
issue
in
59
Federal
Register
54155,
column
3,
October
26,
1994).
The
preamble
discussion
highlighted
that
a
requirement
to
reroute
the
vent
stream
to
a
control
device
or
return
it
to
the
process
would
require
significant
costs
to
upgrade
existing
equipment.
In
many
situations
existing
surge
control
vessels,
operating
at
atmospheric
pressure,
would
have
to
be
entirely
replaced
with
new
ones
that
could
be
operate
at
a
higher
pressure.
The
higher
vessel
pressure
rating
would
be
needed
to
allow
connection
and
routing
of
the
gases
from
the
tank
vent
to
a
control
device.

EPA
subsequently
concluded
that
surge
control
vessels
should
be
regulated
in
an
identical
manner
as
storage
tanks
in
40
CFR
Part
63,
Subpart
G.
We
believe
that
the
same
logic
should
be
employed
for
continuous
organic
chemical
manufacturing
processes,
since
these
processes
exhibit
a
similarity
to
processes
regulated
under
Subpart
G
of
the
HON
rather
than
batch
processes
regulated
under
the
Pharma
or
PAI
NESHAPs.

Recommendation:
For
continuous
organic
chemical
manufacturing
processes,
surge
control
vessels
should
be
regulated
in
an
identical
manner
as
storage
tanks
under.
This
revision
will
allow
existing
storage
tanks,
considered
surge
control
vessels
in
the
proposed
NESHAP,
to
continue
to
use
internal
and
external
floating
roofs
for
control
of
HAP
emissions.
This
recommended
change
is
also
consistent
with
other
Part
63
standards
for
SOCMI
facilities,
EPA's
New
Source
Performance
Standards,
Subparts
Ka
and
Kb,
and
state
RACT
rules.

DRF;
08/
19/
02
File:
surge
control
vessels
as
process
tanks.
doc
