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Lecture 81 - Hydrocarbon recovery in natural gas systems - III

WEBVTT
Kind: captions
Language: en

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Welcome today we shall be looking into a few
more ah techniques for the recovery of the
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natural gas liquids . So, in this particular
lecture ah what we shall be learning about
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. Is ah two things one is the ah low ethane
recovery and the high ethane recovery . These
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two pertain to the different processes by
which we can recover the ethane ah depending
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on the how much ethane we want to recover
whether we want to recover the .
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The low amount of ethane or high amount of
ethane depending on that we again have a different
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types of recovery processes .
Now, when we talk of the low ethane recovery
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ah what we mean that we want to recover about
60 percent of the ethane that is present in
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the ah original feed gas . And ah this way
we can produce a lean gas lean gas means which
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ah that is having this amount of ethane that
the you know original one . So, that is how
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.
We are producing the lean gas and ah recovering
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up to about 60 percent of the ethane . And
in this ah we ah generally use two types of
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processes one is that ah refrigeration and
ah . It can be by external refrigeration or
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some expansion which is more common and less
common, but it which was historically used
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more is the use of the lean oil absorption
. So, first let us start with .
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The one which is more common and this is the
cooling by the expansion or external refrigeration
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. Now ah we have learned in our earlier lectures
about how cooling can be brought about by
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using expansion ah that is the one we have
studied that we could use turbo expander or
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we can use ah joule Thomson effect .
So, all these principles which we learnt earlier
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it will be now used here for the recovery
of the natural gas liquids and in this case
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it is the ethane recovery we are concerned
about .
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So, here in this particular figure what we
see that the how the temperature affects the
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recovery now here we see that we have drawn
some lines have been drawn.
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Over here and each of these lines represent
in term ah different amounts of the feed content
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and these feed content is given in terms of
GPM that is the gallons per minute . And this
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has been calculated based under C 3 plus ah
fractions that is the propane and higher hydrocarbons
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So, and depending on that these two types
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of lines you can see have been found and this
dashed line is for the propane recovery and
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this solid line is for the ethane recovery
. And we see that ah for a ah this recovery
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is decreasing .
As we increase the ah process temperature
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it is expected because what happens that as
we are increasing the temperature more and
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more of the components are going towards the
ah vapour side and less they are remaining
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in the liquid .
So, that is how we are finding that the recovery
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ah um. Please note that when is a recovery
recovery means that we are trying to recover
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the components in the liquid. So, and the
uh gas we are producing that gas is supposed
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to have more of the methane .
So, ah um as we see from in this ah graphs
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that as we increase the temperature process
temperature for a ah given ah feed content
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or feed ah feed content of the higher hydrocarbons
we find that the these components are going
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more in the vapour vapour so, that we are
getting less and less recovery ah in the liquid
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And the same thing we find that both whether
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we talk of propane or ethane we are finding
that recovery is ah decreasing with the temperature
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for a given feed content . And also what we
find that for a given feed content for example,
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we compare this ah 3 GPM over here and 3 GPM
over here. We find that propane is showing
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more recovery than ethane.
It is also expected because the heavier the
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component the more will be the tendency of
the component to go the liquid phase . So,
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here that is why we find that because propane
has a higher molecular weight than the ethane.
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So, we will find that it will tend to go more
towards the liquid that is why the higher
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hydrocarbons we will have more recovery for
the same operating conditions . And here we
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see that recovery increases with increased
richness at a given temperature. So, that
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is what we find that if you go from for a
given component . So, if you are going from
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3 GPM to 5 GPM to 7 GPM we find for the same
temperature we are uh getting more and more
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recovery .
Now, here we have a typical ah flow chart
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ah for the expansion or external refrigeration
. Here we find the is inlet gas is sequentially
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cooled by the residue gas or the sales gas
and then by the cold liquid from the .
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Cold separator. So, what we find here we have
the inlet stream . So, here the inlet stream
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is first been cooled by these residue gas
which is obtained from the cold separator
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So, first this is ; that means, we are trying
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to recover the cold from the the residue gas.
So, here first it is done there and then we
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take it to this another ah heat exchanger
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So, here we find this is again this inlet
gas is getting further cooled and this is
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getting cooled by the liquid which is coming
out from the cold separator . And then it
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is going to a propane chiller .
Now about the propane chiller we have learnt
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in our previous lecture know please understand
this even though we are showing here with
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single ah symbol , but this is not a single
unit, but its a kind of a cycle it is a refrigerant
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cycle in itself .
So, this is a propane chiller propane representation
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cycle and from there we are making it cold
enough now . So, that we are ah we will be
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getting a liquid and a vapour phase .
Now, what happens this vapour is taken back
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from here and it is now getting as I said
that it is going to cool the inlet gas and
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the liquid is also coming here and is also
cooling the inlet gas . Now what happens that
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after that the cooled gas goes to the cold
separator where the propane chiller as I was
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told you the propane chiller is goes to the
cold separator and liquid from the cold separator
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goes to the fractionators to recover the liquid
product by stripping out the lighter ends.
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So, this liquid which is on a cold separator
it is going from here and it is going to this
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fractionators and in this fractionators we
are stripping of the lighter components from
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whatever it is coming in this liquid lighter
components . And those lighter components
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are going from here and the heavier components
are coming from the ah downwards ok .
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The column operates at a lower pressure than
the cold separator .
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Hence recycle stream has to be recompressed
to feed the feed pressure what it means that
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because this particular thing fractionators
has a lower pressure then the feed pressure
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is the cold separator .
So, when we are passing it through back to
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the inlet gas what we are finding that we
are recompressing it and this by recompression
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we are able to bring the pressure back to
the inlet gas temperature with which we are
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mixing it ok.
So, uh that is why we need the recompression
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of the ah vapour from the fractionators
And to avoid recompression of this recycle
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stream a reflux may be added to the fractionators
or the fractionators pressure may be kept
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higher than the feed pressure in which case
feed needs to be pumped to the fractionators
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Now in this case what we see that suppose
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because each of this extra equipment or the
extra operation we are doing it will incur
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cost. So, if you decide that we do not want
to have any compression because it will involve
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some work to be done on the system .
So, we want to reduce that then one may decide
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that let us keep the fractionators at a higher
pressure. So, that this return stream may
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be sent back to the feed side without any
recompression, but in that case what will
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happen because it is at a higher pressure
than the feed then we need to a pump this
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feed gas ah from this side . So, in either
case we are finding that whether we are going
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to recompress the gas or whether we are going
to compress the inlet gas that will depend
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on the particular situation at hand that at
what pressure the inlet feed is available
00:09:04.470 --> 00:09:08.640
according that we have to decide that whether
we shall be going for compression over here
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or compression over here .
So, it is a typical situation we have shown
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here that where we are recompressing the vapour
from the fractionators .
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And ah if here you you can see that here we
are not ah doing any kind of ah reflux as
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we learnt earlier that reflux helps in ah
increasing the separation of the heavier components
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from the vapour .
So, that thing we are not doing here . So,
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ah that is why we would have to recompress
it. And this may be avoided if we are putting
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some reflux over ah this fractionators .
And there may be possibility of hydrate formation
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that because if there is a substantial amount
of water in the inlet gas then this ah water
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made form hydrate and it may form hydrate
with the hydrocarbons themselves like .
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Methane from hydrate ethane from hydrate . So,
all these gases may inform hydrate with ah
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water and. So, that is why we to reduce the
chances of the hydrate formation it is seen
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to it that we dehydrate the gas before we
go for the NGL . And that is now we can understand
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the importance of dehydration in the natural
gas processing and why we need to maintain
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the particular sequence that we have to first
dehydrate the natural gas before we take it
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for any further processing .
So, this is why that any kind of hydrate formation
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will be avoided if we are ah um taking out
the water initially . Now if there is too
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much ah of water then ethylene glycol may
be used and ah ethylene glycol as we learnt
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that we may use ethylene glycol or other glycols
they may be used to ah do what you call that
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that they are act as hydrate inhibitor .
So, this kind of glycols may be used , but
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if you are putting these external glycols
. First thing is that they also make our stream
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impure and not only that they will increase
the refrigeration duty that means, now we
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will find that the ah uh work or the amount
of refrigeration we need that will also increase
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because of this addition of the glycols . And
one more thing will be there that if we now
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lower the temperature .
What will happen it will increase increase
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the glycol viscosity . And if the viscosity
increase it what it means is this it will
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ah put more resistance to at the flow of the
ah gas streams and in that way what we will
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find that our ah pumping power will also increase
, but ah we have to understand this again
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in many of these things if have to be done
they have need to be done and ah we cannot
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avoid it . And we have to have some kind of
penalty in putting all these kind of .
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Evolving or exploring these various options
. So, these are the various options which
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are followed in the natural gas processing
in the ah recovery of the natural gas . Now
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the temperature is limited to minus 37 degree
centigrade when propane refrigeration is used
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. Now for moderate GPM that is the feed content
the in ethane recovery is about 60 percent
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and expansion expansion may be done by either
joule Thomson valve or trubo expander is used
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to enhance the recovery by lowering the temperature
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Now as we learnt earlier also that expansion
also cause the pressure drop . Now pressure
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drop means we are losing the energy for the
flow . So, then we need to compress the gas
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at higher pressure .
Now if we have the inlet gas ah initially
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at a high enough pressure then expansion is
recommended . Now joule Thomson expansion
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is used for low ethane recovery it is about
10 to 30 percent why because joule Thomson
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gives lower ah cooling.
Than the turbo expander and it can it is also
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used for low gas flow rates below about million
the 10 million ah standard cubic meter per
00:13:30.510 --> 00:13:36.279
day and for fluctuating gas flow rates . Now
for fluctuation gas flow rates ah these trubo
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expanders are not recommended because they
cannot work with too much fluctuations of
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of the gas flow rates . And one more advantage
is this the JT valve is simple and does not
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need any lubricating oil that is needed by
the any kind of ah moving machinery rotating
00:13:54.610 --> 00:13:57.550
machinery . And however, refrigeration obtained
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For a given pressure drop across the expander
is less. So, we get less amount of ah refrigeration
00:14:03.710 --> 00:14:08.130
for a given pressure drop when we are using
the JT valve .
00:14:08.130 --> 00:14:15.300
Next process which is ah there as we said
that this has an historical importance and
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now ah at present this has become quite low
in this application , but still it is there
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at some plants . This is the ah lean oil absorption
and this absorption as we learnt earlier we
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studied about the absorption and how to design
a column for absorption.
00:14:34.120 --> 00:14:40.860
So, in this case we have what we are doing
that we are ah going to use a solvent to take
00:14:40.860 --> 00:14:46.720
out the ah some components from the natural
gas . So, in this case we are the lean oil
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is used .
So, it is less common and being increasingly
00:14:49.880 --> 00:14:56.550
replaced by the refrigeration based system
. Now here we find that inlet gas is cooled
00:14:56.550 --> 00:15:02.241
by the residue gas that a sales gas from the
absorber and in the propane chiller. Now here
00:15:02.241 --> 00:15:07.149
you see that here the inlet gas is coming
and it is to be cooled and this is cooling
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is done from this particular ah inlet gas
this the vapor which is coming from the absorber
00:15:14.100 --> 00:15:17.580
This is a absorber you can see this is the
absorber the gas is coming which is quite
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cold and it is cooling the inert gas initially
and then what is happening that this inlet
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gas is going and it is going to the propane
chiller . As we understand again that this
00:15:27.100 --> 00:15:32.960
propane chiller in itself is a cycle ok .
So, it is going to the propane chiller and
00:15:32.960 --> 00:15:39.370
then it is entering the absorber now cooled
gas is stripped of the C 2 plus component
00:15:39.370 --> 00:15:41.550
from the raw natural gas using a lean oil
00:15:41.550 --> 00:15:49.030
So, when it is going over here we are taking
at the bottom ah of this thing and what will
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happen that here we are putting the ah propane
this lean this lean gas . Now what is happening
00:15:56.170 --> 00:16:00.660
that what we are putting in the bottom because
gas has a tendency to move up the column . So,
00:16:00.660 --> 00:16:05.850
we are putting it at the bottom of the column
and from the top we are putting the lean oil
00:16:05.850 --> 00:16:11.459
. And then what is happening during this contact
this is this particular thing is signifying
00:16:11.459 --> 00:16:14.220
a packed bed .
So, you know this thing what is happening
00:16:14.220 --> 00:16:22.300
that the gas is moving up and as it moves
up this oil is taking up the higher hydrocarbons
00:16:22.300 --> 00:16:28.680
C 2plus that is ethane and higher hydrocarbons
and the gas we are getting here will be richer
00:16:28.680 --> 00:16:31.870
in the methane.
So, here from here we are getting the higher
00:16:31.870 --> 00:16:36.720
hydrocarbons to the rich oil demethanizer
that is in short it is ROD .
00:16:36.720 --> 00:16:43.089
Rich oil demethanizer strips methane and other
lighter components from the ah rich oil . The
00:16:43.089 --> 00:16:49.360
rich oil means this is the the oil which we
are getting from the bottom is rich rich in
00:16:49.360 --> 00:16:53.830
the higher hydrocarbons .
So, which is going in this reach or the demethanizer
00:16:53.830 --> 00:17:00.700
. So, from here what we are doing that we
are able to ah strip of the ah higher this
00:17:00.700 --> 00:17:04.789
right advance and which are taken as the fuel
gas now .
00:17:04.789 --> 00:17:11.470
NGL is recovered in the still and the lean
oil is sent back to the absorber through a
00:17:11.470 --> 00:17:16.380
propane chiller . Now here in this this is
the still . So, here we see that in the still
00:17:16.380 --> 00:17:22.369
what we are doing that we are getting this
ah rich oil from the bottom of the still and
00:17:22.369 --> 00:17:29.070
it is being sent back to the absorber through
this propane chiller over here ok .
00:17:29.070 --> 00:17:34.660
So, this is how and what we are doing that
during this we are also exchanging ah um the
00:17:34.660 --> 00:17:41.690
heat with this ah stream and this is how it
is getting this reboiled and this particular
00:17:41.690 --> 00:17:45.940
stream is getting riboiled is this has the
higher temperature and it is going back to
00:17:45.940 --> 00:17:48.600
this column.
And here we are to the propane chiller we
00:17:48.600 --> 00:17:56.380
are taking it back to the particular absorber
. And gas from the rod is either blended with
00:17:56.380 --> 00:18:00.690
the residue gas from the absorber and or used
as fuel gas as . So, as I was telling that
00:18:00.690 --> 00:18:05.309
from this rich oil demethanizer this here
we are showing this used as fuel gas .
00:18:05.309 --> 00:18:11.239
But this may also be blended with the residue
gas this from residue gas it may blend with
00:18:11.239 --> 00:18:15.999
residue gas it can be connected with this
particular stream and taken out ah. So, this
00:18:15.999 --> 00:18:19.900
because ultimately residue gas is also used
as fuel .
00:18:19.900 --> 00:18:27.059
So, this gas may also be you were taken along
with the residue gas . Now molar mass of lean
00:18:27.059 --> 00:18:32.169
gas is generally between 100 and 130. So,
this is the kind of because there can be many
00:18:32.169 --> 00:18:38.289
valves can be there . So, this is ah the molar
mass is about 100 to 130 . And without refrigeration
00:18:38.289 --> 00:18:44.539
over 75 percent butane and almost all of C
5 plus fraction may be recovered from the
00:18:44.539 --> 00:18:46.580
absorber operating at 38 degree centigrade
00:18:46.580 --> 00:18:51.830
So, it is a typical figure which has been
shown here that the heavier hydrocarbons that
00:18:51.830 --> 00:18:59.200
is the butane and C 5 plus that means, pentane
hexane etcetera they may be completely recovered
00:18:59.200 --> 00:19:05.519
from the natural gas at 38 degree centigrade
and ah butane is about 75 percent of butane
00:19:05.519 --> 00:19:13.010
may be ah recovered .
Now, the high solvent rates can give 50 percent
00:19:13.010 --> 00:19:16.520
recovery of ethane .
So, we can see that the ethane recovery still
00:19:16.520 --> 00:19:21.240
goes up if you are using high solvent rates
and almost full recovery of propane and heavier
00:19:21.240 --> 00:19:26.660
components that means, high flow rate of this
ah solvent is uh preferable, but at the same
00:19:26.660 --> 00:19:31.120
time you have to understand that if you are
increasing the solvent flow rate it is also
00:19:31.120 --> 00:19:37.630
going to increase our pumping costs .
So, propane refrigeration gives over 97 .
00:19:37.630 --> 00:19:42.690
Percent propane recovery and up to 50 percent
ethane recovery. So, this is a comparison
00:19:42.690 --> 00:19:48.770
at this if you are using the propane refrigeration
then we are able to get ah quite high amount
00:19:48.770 --> 00:19:54.170
of the propane in the ah natural gas liquid
and about 50 percent ah we are getting in
00:19:54.170 --> 00:20:00.370
the natural gas liquid and rest of them is
going with the ah overhead gas . Recovery
00:20:00.370 --> 00:20:05.259
increases with cooling of the inlet gas and
a lean oil while heating of the still and
00:20:05.259 --> 00:20:11.940
ROD . Because we have seen that that is why
we are finding that the inlet gas ah is being
00:20:11.940 --> 00:20:16.700
cooled and lean gas is also being cooled as
we have seen from here that here the inlet
00:20:16.700 --> 00:20:21.730
gas is cooled and also this this lean gas
is also getting cooled through this liquids
00:20:21.730 --> 00:20:24.460
here ah.
So, that is why this both these things are
00:20:24.460 --> 00:20:30.639
getting cooled . So, that we can increase
the recovery . Pressure drop is generally
00:20:30.639 --> 00:20:36.539
low and the energy requirement is quite high
because of the compression and chillers we
00:20:36.539 --> 00:20:39.359
are from the chillers we are using ok for
this .
00:20:39.359 --> 00:20:44.559
The energy quantity is quite high and it is
used for capturing fugitive hydrocarbons . Those
00:20:44.559 --> 00:20:51.610
hydrocarbons reach can escape easily . So,
those kind of hydrocarbons are recovered by
00:20:51.610 --> 00:20:58.110
the lean oil absorption .
Now, after learning about the low ethane recovery
00:20:58.110 --> 00:21:03.352
we come to the processes which are used for
the high ethane recovery in this fame it is
00:21:03.352 --> 00:21:09.109
a high it means we want to recover more than
80 percent of the ethane which is present
00:21:09.109 --> 00:21:14.919
in the feed gas . And this can be obtained
at a temperature lower than the one achieved
00:21:14.919 --> 00:21:21.609
by the propane refrigeration system. In the
low ethane recovery we were using the propane
00:21:21.609 --> 00:21:27.840
refrigeration , but ah that and that are temperature
reached by the propane refrigeration ah was
00:21:27.840 --> 00:21:33.380
limiting the recovery of the ethane.
So, if we can make the temperature go still
00:21:33.380 --> 00:21:38.360
less than the propane recovery that is about
minus 37 degree centigrade minus 40 degree
00:21:38.360 --> 00:21:46.940
centigrade . If you can go below that temperature
we can go for higher amount of ethane recovery
00:21:46.940 --> 00:21:49.980
Now if inlet gas pressure is low then direct
00:21:49.980 --> 00:21:55.559
refrigeration may be done either by cascading
the propane cooling with ethane or ethylene
00:21:55.559 --> 00:22:00.409
refrigeration or using mixed refrigerant containing
methane ethane and propane.
00:22:00.409 --> 00:22:06.389
So, this is the case that if we do not have
enough pressure on the feed side then expansion
00:22:06.389 --> 00:22:10.700
should not be done because expansion is going
to create still more pressure drop . So, in
00:22:10.700 --> 00:22:14.669
that case we are ah completely ah dependent
on the .
00:22:14.669 --> 00:22:20.340
Refrigeration either by the cascade refrigeration
and or by the mixed refrigerant . Both these
00:22:20.340 --> 00:22:26.049
things we have done earlier in separate lectures
. So, I am not going to go ah in detail about
00:22:26.049 --> 00:22:32.370
these two types of refrigeration . The substantial
compression of the inlet gas or the refrigerant
00:22:32.370 --> 00:22:37.240
is needed for high ethane recovery .
So, it is the requirement that we need to
00:22:37.240 --> 00:22:41.570
have compress it quite well ah compress to
quite high pressure .
00:22:41.570 --> 00:22:47.429
So, that we can increase the ethane recovery
. And to high ethane recovery would reduce
00:22:47.429 --> 00:22:52.480
the heating value that means, if we are taking
out the ethane too much in the liquid that
00:22:52.480 --> 00:22:57.730
means, less of ethane is going with the overhead
gas then what will happen the heating value
00:22:57.730 --> 00:23:03.669
of the overhead gas will also come down . And
we learnt that why we were doing this whole
00:23:03.669 --> 00:23:10.929
in a NGL recovery was there to keep the heating
value under control because if all the hydrocarbons
00:23:10.929 --> 00:23:15.850
go together they will increase the heating
value , but at the same time if we are taking
00:23:15.850 --> 00:23:20.970
out all the high hydrocarbons that will also
reduce the heating value ah which is below
00:23:20.970 --> 00:23:23.909
the .
Permissible level . So, that is why we also
00:23:23.909 --> 00:23:30.440
need to C 2 it that we are not recovering
all the hydrocarbons high hydrocarbons other
00:23:30.440 --> 00:23:36.539
than the methane ah in the.
NGL process now high recovery is obtained
00:23:36.539 --> 00:23:42.090
using demethanizer as we have seen again this
is the conventional turbo expander based ethane
00:23:42.090 --> 00:23:48.369
recovery system. So, here we are has in demethanizer
this is from where we are getting this ah
00:23:48.369 --> 00:23:53.220
high ethane recovery .
And here we have a five channel gas gas heat
00:23:53.220 --> 00:23:57.619
exchanger is used to cool the feed gas to
the required temperature before in a recovery
00:23:57.619 --> 00:24:04.440
. Now even though it is showing shown as a
gas gas heat exchanger one , but in practice
00:24:04.440 --> 00:24:09.080
signals heat exchanger is replaced by a series
of heat exchanger that means, we generally
00:24:09.080 --> 00:24:14.669
use a heat exchanger network over here .
Which is being compressed and shown in a very
00:24:14.669 --> 00:24:19.830
to show that we are using a simply ah five
channel heat exchanger . It should not be
00:24:19.830 --> 00:24:26.399
taken as the actual one , but should be taken
as a representative of the heat exchangers
00:24:26.399 --> 00:24:32.019
which are used for the cooling of the feed
gas. Now you can see here .
00:24:32.019 --> 00:24:36.549
That the cold inlet gas goes to the cold separator.
Now you see that how the cooling is getting
00:24:36.549 --> 00:24:43.619
done that the feed gas is coming through some
heat exchanger . And here this heat of the
00:24:43.619 --> 00:24:49.869
feed gas is also used in the reboiler to boil
up the liquid in the demethanizer. So, this
00:24:49.869 --> 00:24:54.850
is this that means, this heat is used as boiler.
So, that is why this feed is get is getting
00:24:54.850 --> 00:24:57.399
cooled and it is colder than the initial feed
gas.
00:24:57.399 --> 00:25:04.769
So, it is also used to cool the incoming feed
gas and then it is taken to another reboiler
00:25:04.769 --> 00:25:10.879
over here and again this colder ah feed gas
is again taken back and it is sort of again
00:25:10.879 --> 00:25:16.359
coming back to this heat exchanger and ultimately
it is going into the cold separator. And in
00:25:16.359 --> 00:25:21.659
this code separator what is happening we are
getting the vapour and the liquid the vapour
00:25:21.659 --> 00:25:27.779
is passed through a turboexpander and it is
taken into demethanizer whereas, the liquid
00:25:27.779 --> 00:25:34.999
is expanded through a JT valve and is put
somewhere in the middle of the demethanizer
00:25:34.999 --> 00:25:41.929
ok. And now what we find that a curve in this
case we find the methane will be moving out
00:25:41.929 --> 00:25:46.970
with this particular ah gas stream and then
vapour stream at the top and it will be again
00:25:46.970 --> 00:25:52.779
taken back to before it is taken out ah as
residue gas it is again used to cool down
00:25:52.779 --> 00:25:57.059
the feed gas further through the heat exchanger
network and it is taken as residue gas .
00:25:57.059 --> 00:26:03.659
Well in this case we find this that the from
the bottom we are getting the natural gas
00:26:03.659 --> 00:26:09.909
liquid. So, um this is how and also we are
also using this cold propane liquid in this
00:26:09.909 --> 00:26:13.239
particular heat exchanger to cool the feed
gas .
00:26:13.239 --> 00:26:18.989
So, except the feed gas all the other streams
here we have shown here are cooling the feed
00:26:18.989 --> 00:26:24.929
Now, a JT valve is always used parallel to
00:26:24.929 --> 00:26:29.460
the turbo expander here we are using parallely
to turbo expander JT valve why to help in
00:26:29.460 --> 00:26:35.939
plant start up handle excess gas flow rate
and act, act as standby in case of turbo expander
00:26:35.939 --> 00:26:40.570
So, ah for these reasons we are using a JT
00:26:40.570 --> 00:26:46.299
valve in parallel to the turbo expander and
there may be a problem of freeze out of carbon
00:26:46.299 --> 00:26:50.700
dioxide ah and the maximum ethane recovery
is about 80 percent.
00:26:50.700 --> 00:26:54.929
So, in this particular conventional turbo
expander based ethane recovery is ten we are
00:26:54.929 --> 00:27:00.490
getting about 80 percent recovery .
Now, if you still further want to increase
00:27:00.490 --> 00:27:06.239
the recovery to about say 98 percent . So,
what we are doing it is almost same as the
00:27:06.239 --> 00:27:10.899
conventional among except that we are now
using a reflux. So, here we find that I was
00:27:10.899 --> 00:27:17.809
not explain the ah this uh this things here
because these same remains same as the conventional
00:27:17.809 --> 00:27:21.899
one only thing is we are here shown that here
this there is a extra thing.
00:27:21.899 --> 00:27:27.269
So, what we find this particular ah pole separator
what is happening the vapour which is coming
00:27:27.269 --> 00:27:33.840
out it is again bifurcated a part is going
to the turbo expander and put into the demethanizer
00:27:33.840 --> 00:27:39.220
and the rest of the part is taken to these
two heat exchangers to the J T valve and it
00:27:39.220 --> 00:27:44.019
is taken as one reflux.
And as the reflux is the vapour which is coming
00:27:44.019 --> 00:27:49.109
from the top which is again it is part to
the it is taken out through it is we have
00:27:49.109 --> 00:27:54.840
to cool the incoming feed gas and a part is
again taken through this expander and through
00:27:54.840 --> 00:28:00.980
this ah heat exchanger it goes and it goes
a reflux that means, this there are two reflux
00:28:00.980 --> 00:28:07.360
streams in this particular in particular system
. And rest of the things are remaining the
00:28:07.360 --> 00:28:13.049
same as earlier in the conventional turbo
expander based in a system .
00:28:13.049 --> 00:28:21.140
So, with this this this modification one can
get a still higher ethane recovery when which
00:28:21.140 --> 00:28:28.309
is near about 98 percent . And ah this as
I told you that here also this particular
00:28:28.309 --> 00:28:36.499
ah big heat exchanger ah denotes a series
of heat exchanger or heat exchanger network
00:28:36.499 --> 00:28:39.440
And there are some safety and environmental
00:28:39.440 --> 00:28:43.960
considerations though even though this is
process is not that hazardous ah.
00:28:43.960 --> 00:28:52.009
There may be that insufficient removal of
water BTEX that is the benzene ethyl xylene
00:28:52.009 --> 00:28:57.590
and toluene ah and all these things ethyl
benzene they and their carbon dioxide . They
00:28:57.590 --> 00:29:03.109
may cause plugging by their freeze out and
hence process hazards and either will be some
00:29:03.109 --> 00:29:08.369
environmental pollution may be created if
you are using any kind of lubricating oil
00:29:08.369 --> 00:29:13.669
glycol or methanol.
So, the environmental pollution effect or
00:29:13.669 --> 00:29:21.509
the safety hazards are not very high.
But still some of them may be there in these
00:29:21.509 --> 00:29:28.269
types of angel recovery process .
Further ah details can be found from this
00:29:28.269 --> 00:29:31.309
particular book .
Thank you .

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