Chemistry of hydrocarbon compounds – Purification – separation – or recovery – By plural serial diverse separations
Reexamination Certificate
1999-06-16
2001-09-18
Griffin, Walter D. (Department: 1764)
Chemistry of hydrocarbon compounds
Purification, separation, or recovery
By plural serial diverse separations
C208S347000, C208S351000, C208S363000, C202S158000, C169S060000
Reexamination Certificate
active
06291734
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to an apparatus and method for the depropanization and debutanization in an olefin plant processing propane and heavier feedstocks, and particularly to the use of an integrated column which combines both the low pressure depropanizer and debutanizer into a single column.
BACKGROUND OF THE INVENTION
A typical process for the separation and recovery of olefins from pyrolysis furnaces operated with feedstocks heavier than ethane, is known as the front end depropanizer and front end acetylene hydrogenation scheme. A brief review of the typical front end depropanizer process is in order.
Starting with the separation section
2
after the water quench, as shown on the simplified process flow diagram of
FIG. 1
, there are three stages
4
,
6
,
8
of conventional compression to raise the pressure of the process gas from just above atmospheric to a pressure of about 15 bars (210 psia). Condensed liquids, i.e. hydrocarbons and water, are separated.
The gas is then treated in a conventional two or three stage caustic wash tower
10
as shown in
FIG. 2
for the removal of carbon dioxide and hydrogen sulfide. The gas is cooled and mildly chilled before entering the dryers
12
,
14
. Water is removed completely.
The gas is then further chilled in propylene refrigerant exchanger
16
seen in
FIG. 3
, and enters the high pressure depropanizer
18
which does not really operate at high pressure but is only called that because there is also a low pressure depropanizer
20
. The high pressure depropanizer
18
typically operates at a pressure of 12 bars (170 psia), and the low pressure depropanizer
20
at a pressure of 8.5 bars (120 psia).
The overhead of the high pressure depropanizer
18
is usually compressed in compressor
22
to a pressure of 38 bars (550 psia) and is then sent to the acetylene hydrogenation system
24
which typically consists of two or three adiabatic reactors in series with inter-cooler for the removal of the heat of reaction. The reactor effluent is cooled in cooling water exchanger
26
and partially condensed in propylene refrigerant exchanger
28
. A portion of the condensate is used as reflux via line
30
for the high pressure depropanizer
18
. The rest is sent to the demethanizer stripper
32
(see
FIG. 4
) via line
34
.
In the stripping section
36
of the high pressure depropanizer
18
only ethane and lighter components are removed, resulting in a fairly low bottoms temperature of 56° C. (133° F.). The bottoms product is sent via line
38
to the low pressure depropanizer
20
where it is separated into C
3
's and C
4+
. The C
3
is used as reflux in the high pressure depropanizer
18
via line
30
, while the C
4+
is sent to the debutanizer
86
via line
40
. Due to the low operating pressure, the bottoms temperatures in the depropanizers
18
,
20
are quite low, namely 56° C. (133° F.) and 71° C. (160° F.). Therefore, there is no fouling in either tower
18
,
20
or their respective reboilers
42
,
44
.
Debutanizer
86
separates the C
4+
stream via line
40
into overhead vapor stream
85
comprising C
4
's and bottoms stream
88
comprising C
5+
. The debutanizer
86
is heated with 2.2 bar steam in reboiler
90
. Overhead vapor is condensed in condenser
92
with cooling water. Condensate is refluxed to the debutanizer
86
via line
94
and valve
96
. A C
4
product stream is recovered via line
98
.
The acetylene hydrogenation unit
24
is highly efficient and selective. The acetylene removal easily results in acetylene concentrations of less than 1 ppm in the final ethylene product while the ethylene gain amounts to 50% or more of the acetylene. Due to the high hydrogen content of the feed gas, no carbonaceous material is deposited on the catalyst. The catalyst needs no regeneration and thus the reactors
24
need no spares. Green oil formation is miniscule.
In the acetylene hydrogenation reactor
24
about 80% of the methyl-acetylene and 20% of the propadiene are converted to propylene. If the olefins plant produces polymer grade propylene the remaining C
3
H
4
can be easily fractionated into the propane product; the high conversion of methyl-acetylene and propadiene in the acetylene hydrogenation reactors obviates the need for an additional separate C
3
H
4
hydrogenation system.
The operational stability of the acetylene hydrogenation reactor
24
is enhanced by its location in the gross overhead loop of the depropanizer
18
and in the minimum flow recycle circuit of the fourth stage of compression
22
. These factors reduce the acetylene concentration in the inlet to the reactor
24
and stabilize the flow rate irrespective of the furnace throughput.
The vapor and liquid from the reflux accumulator
46
of the high pressure depropanizer
18
flow to the chilling and demethanization section
48
(see FIG.
4
). The liquid plus the condensate formed at −37° C. (−35° F.) is sent via respective lines
34
and
50
to the demethanizer stripper
32
. The overhead vapor from the demethanizer stripper
32
plus the liquids formed at lower temperatures are sent to the main demethanizer
52
via respective lines
54
and
56
. The tower
52
is reboiled by reboiler
58
with condensing propylene refrigerant, and reflux is condensed in heat exchanger
60
with low temperature ethylene refrigerant.
The respective bottoms products
62
,
64
of the two demethanizers
32
,
52
, after some heat exchange which is not shown, enter the prior art deethanizer
66
. The tower
66
recovers approximately 40 percent of the ethylene contained in the two feeds as high purity product. Sixty percent of the ethylene and all the ethane leave the tower
66
as a side stream
68
and proceed to the ethylene fractionator
70
. The deethanizer
66
is reboiled by reboiler
74
with quench water and reflux is condensed in exchanger
76
with −40° propylene refrigerant. The bottoms product
72
of the deethanizer
66
is a stream containing propylene, propane and the remaining C
3
H
4
. It flows to a conventional propylene fractionator (not shown). Because of the ethylene fractionation in its top section
78
, the deethanizer
66
has fifty more trays than a conventional deethanizer (without the side draw) which produces a mixed ethylene and ethane overhead product in line
80
.
The ethylene fractionator
70
is a relatively low pressure tower typically operating at 4 bars (60 psia) with approximately 100 trays. It uses an open heat pump. Ethylene refrigerant is condensed in the reboiler
82
and is then used as reflux via line
84
. Effectively, the reboiler
82
also serves as the reflux condenser. There are no reflux pumps and there is no reflux drum.
Another possible deethanizer/ethylene fractionator arrangement is disclosed in U.S. Pat. Nos. 5,678,424 and 5,884,504 both to Nazar which are hereby incorporated herein by reference.
A deethanizer and ethylene fractionator integrated into a single column is disclosed in my earlier U.S. Ser. No. 09/266,214 filed Mar. 10, 1999, which is hereby incorporated by reference for purposes of U.S. patent practice.
Other references of interest are U.S. Pat. Nos. 5,709,780 and 5,755,933, both to Ognisty et al.
SUMMARY OF THE INVENTION
The present invention combines the low pressure depropanizer and debutanizer of the prior art into a single fractionation column, reduces the pressure of the low pressure depropanizer to that of the debutanizer and locates the debutanizer and the stripping section of the low pressure depropanizer in the bottom portion of a single distillation column divided by a vertical wall. Locating the debutanizer and the stripping section of the low pressure depropanizer in the bottom section of a single distillation column divided by a vertical wall has the capital cost savings of replacing two large columns with a slightly larger column; eliminates the debutanizer reflux condenser, drum and pumps; and employs a much smaller debutanizer reboiler.
In one aspect, the present invention provides an integrated low pres
Griffin Walter D.
Kellogg Brown & Root Inc.
Kellogg Brown & Root, Inc.
Nguyen Tam M.
LandOfFree
Integrated low pressure depropanizer/debutanizer column does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Integrated low pressure depropanizer/debutanizer column, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Integrated low pressure depropanizer/debutanizer column will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2435944