A Solution to Increase Natuna D Alpha’s Resource Utilization by

Cryogenic Distillation: Conceptual Design & Sensitivity Study

Wijoyo Niti Daton, Ezra Revolin, Siptian Nugrahawan, Prasandi Abdul Aziz, Tutuka Ariadji, Steven

Chandra and J. A. Nainggolan

Petroleum Engineering Program, Institut Teknologi Bandung, Jalan Ganesha No 10 Bandung, Indonesia

Keywords:

Cryogenic Distillation, CO

Separation, CO

Transportation.

Abstract:

Natural gas extracted from its respective reservoir needs to be processed to meet the speciﬁcations of sales

gas. CO

is one of the components that needs to be separated from natural gas. The CO

concentration of

natural gas varies from a content of less than 20 mole % to more than 80 mole%. There is a problem when

the content of CO

is very high so it is necessary to modify the CO

level reduction by modifying the equip-

ment or changing the operating conditions to meet the desired CO

purity. In this study, ﬁeld conditions and

characteristics reviewed is East Natuna Gas Field which has a gas composition of 71% CO

and 29% methane

with modiﬁed pressure based on the capability and capacity of available equipment. From the conditions and

characteristics of the ﬁeld, the CO

method of separation from natural gas using cryogenic distillation was

chosen.This research presents analysis and sensitivity of technical parameters that inﬂuence the method of

separation from natural gas using cryogenic distillation. The sensitivity is done by changing parameters

of pressure and very high feed gas ﬂow rate into the column. In addition, the calculation of the diameter and

height of the distillation column using the calculation of the formula and the results of the simulation using

commercial process ﬂow software. This study applies a CO

separation process with cryogenic distillation

and the desired product speciﬁcation of CH

is 99%. The design of the equipment was simulated using two

distillation columns with operating pressure at the ﬁrst distillation column of 45 bar and the temperature of

19.19 oF, and for the second distillation column the operating pressure was reduced to 35 bar. The results are

for the 8000 MMSCFD ﬂow rate case obtained the ﬁrst number of columns as many as 16 with the size of

7.4 meters diameter and 17.66 meters high, while the number of second column of 4 with the size of 8 meters

diameter and 22.38 meters high. The results presented are still less suitable with the conditions in the East

Natuna Gas Field because offshore constrains so need to be studied further for design and other methods in

application in the ﬁeld.

1 INTRODUCTION

Natural gas is one of most the important energy

sources in the world. Today humans use natural gas

to meet energy needs, where the use of gas is esti-

mated to increase by 1.5% each year (IEA, 2017).

Global gas demand for natural gas increased from

3635 bcm in 2016 to more than 5300 bcm in 2040

(IEA, 2017) Indonesia is one of the archipelagic coun-

tries that has large gas reserves spread across sev-

eral regions, one of which is the East Natuna Block.

Natuna Timur block is one of the gas ﬁelds that has an

abundant source of gas reserves, which makes Natuna

the largest undeveloped gas reserve in Southeast Asia

(Fenter et al., 1996). However, the abundant potential

of gas reserves also has a very high CO

gas content

so that CO

separation technology is needed so that

the gas produced can be utilized properly. Impuri-

ties such as CO

, H2S, and other acid gases need to

be removed from natural gas because in the presence

of water, this content can make pipes and other tools

corroded(Rufford et al., 2012).

At present, various methods of acquisition and

technology have been implemented to increase nat-

ural gas production. The existing technology is ad-

justed to the ﬁeld conditions and characteristics. One

challenge that is often faced is the presence of acid

gas contained in it. Sources of acid gas are natural

gas resources that contain most of CO

and/ or H2S

(Burgers et al., 2011). The separation process can be

designed to overcome differences in molecular prop-

erties or thermodynamic properties and the .

342

Daton, W., Revolin, E., Nugrahawan, S., Aziz, P., Ariadji, T., Chandra, S. and Nainggolan, J.

A Solution to Increase Natuna D Alpha’s Resource Utilization by Cryogenic Distillation: Conceptual Design Sensitivity Study.

DOI: 10.5220/0009427203420348

In Proceedings of the Second International Conference on Science, Engineering and Technology (ICoSET 2019), pages 342-348

ISBN: 978-989-758-463-3

displacement of components in the mixture (Ruf-

ford et al., 2012). Therefore several methods of sepa-

ration of acid gas have been developed, or commonly

called sweetening gas processes for H2S separation,

such as absorption, adsorption, membrane and cryo-

genic methods, each of which is used for different

properties and conditions of ﬂuid and ﬁeld. In this

study, the selection of CO

separation method with

reference characteristics from the East Natuna Gas

Field was carried out and a process simulation was

carried out to obtain the results of the high CO

con-

tent separation by observing the effect of pressure and

the feed rate from CO

gas was very high.

Natuna Gas Field is located in Indonesian waters

precisely in the Natuna Sea. This ﬁeld is 140 miles

northeast of the Natuna Islands and 218 miles north-

west of the island of Borneo. The water depth of this

ﬁeld is around 475 feet. The amount of gas volume

in the reservoir is estimated at 222 TSCF with the

composition of the gas contained among others 71%

, 28% methane and heavy diffraction hydrocar-

bons, 0.5% H2S, and 0.5% N2 (Fenter et al., 1996).

The Natuna Gas Location Map is shown in Figure 1.

Figure 1: Location of Natuna Field (Fenter et al, 1996).

Natuna gas reservoir is interpreted in the form of

carbonate domes which are isolated and contained in

the Miocene Reef Formation (Fenter et al., 1996). If

the formation is a carbonate formation, calcite disso-

lution will form CO

. The high CO

content in the

Natuna gas reservoir is estimated to be the result of

the calcite dissolution process (Suarsana et al., 2010).

This reservoir has a pressure of 5717 psig and a tem-

perature of 340 F which is measured by measuring

the well at the central depth. The estimated gas yield

from this ﬁeld is 75% with recoverable hydrocarbon

gas of 46 TSCF (Fenter et al., 1996).

Natuna Field Reservoir contains more CO

than

hydrocarbons. CO

dominates the aging of the reser-

voir phase and controls the production method. Be-

cause this reservoir ﬂuid contains more hydrocar-

bon components, this reservoir is considered a non-

hydrocarbon reservoir (Suarsana et al., 2010).

2 OVERVIEW OF NATURAL

GAS-CO

SEPARATION

PROCESS

During the requirement of separating CO

from nat-

ural gas, not all available methods can be applied in

every ﬁeld. Considerations of methods available on

separating high levels of CO

is important so that the

selection of the right method will give good results.

In addition, differences also depend on the thermody-

namic and transport properties (interphase), in which

case the properties considered include vapor pressure,

boiling point, solubility, adsorption capacity, and dif-

fusivity (Rufford et al., 2012). Based on the nature

of the components to be separated, the main opera-

tion in the gas separation and puriﬁcation mechanism

follows the mechanism: (1) phase formation by heat

transfer and / or shaft work into or from the mixture,

(2) absorption on liquid sorbents or solids, (3) adsorp-

tion on solids, (4) permeation through a membrane,

and (5) changes in chemical compounds into other

compounds (Kohl and Nielsen, 1997)(Seader et al.,

1998). The direct chemical change in CO

which is

currently under study is an example of dry reforming

process, namely CO

reacts with CH

to form syn-

gas (mixture of H2 and CO

) which can later be used

to produce liquid fuel through a Fischer-Tropsch re-

action (Rufford et al., 2012) Then the selection for

selecting an acid gas treating process can be viewed

from the gas partial pressure, based on references

from Aden (Nexant, 2011) and shown in Figure 2.

Figure 2: CO

Removal Chart Based on Partial Pressure

(Aden, 2009).

Based on the results of Revolin’s (2016) research,

the selection of the CO

method can be done with

the help of the separation process selection diagram

shown in Figure 10. In addition, in this thesis a selec-

tion of CO

separation methods was carried out with

references from (Rufford et al., 2012) based on sev-

A Solution to Increase Natuna D Alpha’s Resource Utilization by Cryogenic Distillation: Conceptual Design Sensitivity Study

343

eral inﬂuential parameters in Table 1. In this study, the

factors that were considered to be the most inﬂuential

in the process of selecting CO

separation methods

from natural gas include:

• The presence or absence of H

S gas content

• Concentration of feed gas CO

• Feed gas ﬂow rate

• The purity of CH

and CO

products

From the Natuna Field case, there are several

characteristics that are owned as consideration of the

choice of methods including:

• The H

S content is small

• The concentration of the gas content is 29%

methane and 71% CO

• Flow rate is very high (more than 1 BSCF, de-

pending on the duration of the contract)

• The desired purity of the product is at least 95%

methane, in this case it is targeted to be 99%.

From the parameters of CO

inlet concentration

above 50%, then based on a summary of the techno-

logical characteristics in Table 1 that may be used are

membrane technology, absorption with amine, and

cryogenic distillation. Then the selection process is

also carried out with the help of a selection diagram

in Figure 3 with the results of technology suitable for

use, namely cryogenic absorption and distillation. In

this study, membrane technology and absorption were

not chosen because there were several considerations

based on (Rufford et al., 2012). Membrane technol-

ogy requires pretreatment processes to remove heavy

liquids or hydrocarbons because it can cause damage

to membranes and blockages. Membrane quality de-

pends on permeability and selectivity that cannot be

obtained simultaneously. In addition, membranes are

sensitive to feed conditions and hydrocarbon loss is

also higher than other technologies. In the absorption

method another unit is needed to regenerate solvents

in the process of CO

gas separation. In this method

it is also often formed loading, foaming, and channel-

ing so that mass transfer is not good. Then, the ab-

sorption method requires a large amount of solvents

to separate the volume of high CO

gas, which makes

energy consumption also higher especially for regen-

erating solvents. Conformity between the character-

istics of the cases and categories in this study resulted

in the selection of cryogenic distillation.

In this study the simulation of CO

separation us-

ing the cryogenic distillation method was carried out

using the Aspen Hysys V10 software. Simulation

of CO

separation was carried out by applying refer-

ence to the cryogenic distillation process by Pellegrini

Figure 3: CO

Separation Guideline (Liu et al., 2015).

(Pellegrini et al., 2015) with simpliﬁcation of one dis-

tillation column and reference from Revolin (2016) as

a simulation baseline with several assumptions used

in the process including simpliﬁed feed gas compo-

nents in the form of binary mixture namely CO

and

methane, and the vapor and liquid phases are consid-

ered ideal. The scheme of the distillation process can

be seen in Figure 4.

Figure 4: Cryogenic CO

Separation (Pellegrini et al.,

2015).

In this CO

separation simulation the most im-

portant component observed is the distillation col-

umn. The distillation design process consists of de-

signing processes and mechanical design. Simulation

with shortcut distillation is used in the design pro-

cess to ﬁnd out the mass balance and the variables

needed. Then, some parameters generated from this

simulation that are needed for mechanical design in-

clude pressure and temperature on the top product (in

the condenser) and the bottom product (in reboiler)

needed, the minimum and actual stage number, the

position of the feed gas stage, and reﬂux ratio early. In

this stage data on composition, pressure, temperature,

and feed gas ﬂow rate are needed, as well as the speci-

ﬁcations of the condenser output and reboiler needed.

The feed gas ﬂow rate obtained also makes the ﬂow

rate data for each component in the feed known.

In mechanical design, rigorous methods are used

(with the distillation column) for more detailed and

detailed simulations to determine and determine the

proﬁle of pressure and temperature in each stage, con-

ICoSET 2019 - The Second International Conference on Science, Engineering and Technology

344

denser and reboiler condition proﬁles, and the com-

position of CO

and methane from separation. It is

necessary to know the variables needed in the distilla-

tion column, including the composition and ﬂow rate

of the feed gas, the pressure and temperature of the

feed gas, the position of the feed gas stage, the num-

ber of stages and the pressure proﬁle, and the spec-

iﬁcations of the desired product or product. Some

of the assumptions used in the distillation column

include each plate in the column having an equilib-

rium with constant pressure reduction with a rule of

thumb of 0.2 psi per plate. The pressure and tem-

perature of the feed gas entering the distillation col-

umn need to be adjusted to match the column op-

erating conditions. The high CO

content is cooled

to a certain temperature and pressure on the distilla-

tion column so that the CO

concentration decreases

to the desired level, which increases the concentra-

tion of methane. Pressure and temperature speciﬁ-

cations are important factors that inﬂuence gas sep-

aration(Suarsana et al., 2010). The column operating

conditions are assumed to be in ideal conditions or in

the sense that the amount of feed gas to the distillation

column is equal to the number that exits the column.

Then the separation simulation is carried out using

two stages of design with several sensitivity studies

that refer to a predetermined base case condition.

From the base case that has been determined, pres-

sure sensitivity and the rate of gas feed production are

carried out into the distillation column. After a simu-

lation and sensitivity study, the reﬂux ratio results and

the number of stages needed to obtain the desired cri-

teria for the methane and CO

content are obtained.

Variations in the condition of the feed gas are carried

out with the condition of the condenser and the re-

boiler being ﬁxed.

3 CASE STUDY

Before the sensitivity study, a base case was sim-

ulated with a composition of 71% CO

and 29% CH

, feed gas ﬂow rate of 8 BSCFD, pressure of 652.7

psia, and temperature of 19.19 oF (at the dew point

point) with the result speciﬁcations in the CH

con-

denser with purity of ≥ 95% and the result of reboiler

≤ 0.001%. From the variable reference shortcut

distillation method obtained, the minimum number of

stages required is 9,643 with rounded up to 10 stages,

the actual number of stages is 17, and the feed gas

ﬂow is optimal in the second stage. Then the results

of the condenser namely CH

composition has a ﬂow

rate of 2,442 BSCFD and from the reboiler obtained

a ﬂow rate of 5,558 BSCFD. The shortcut distillation

operation scheme in the base case can be seen in Fig-

ure 5.

Figure 5: Cryogenic CO

Separation (Pellegrini, 2014).

The results of the number of stages and reﬂux ra-

tios obtained from the shortcut distillation simulation

are entered into the distillation column for rigorous

distillation simulation and the results for this base

case condition are reﬂux ratios of 12.08. Comparison

of reﬂux ratio calculations with the shortcut distilla-

tion method and rigorous distillation gives different

values. This is due to the rigorous distillation simula-

tion, the calculation is done in more detail and detail

that considers many variables and results until the de-

sign of column sizes. The results obtained are in the

form of a static plant simulation and even dynamic

if added to the addition of controls (Biyanto, 2007).

While the distillation shortcut is still a rough calcula-

tion or not done in detail. The CO

separation scheme

uses rigorous distillation in the base case distillation

column attached to Figure 6.

Figure 6: Cryogenic CO

Separation (Pellegrini, 2014).

A Solution to Increase Natuna D Alpha’s Resource Utilization by Cryogenic Distillation: Conceptual Design Sensitivity Study

345

Then a sensitivity study is carried out by review-

ing the variable pressure and feed gas ﬂow rate. The

temperature conditions of the feed gas, gas speciﬁca-

tions produced, and variations in ﬂow rates are made

the same in each case. The feed gas ﬂow rate and

the ﬂow rate of the separation results for each rate are

shown in Table 1.

Table 1: Gas Flow Rate on Distillation Column.

Flow Rate (MMSCFD)

Feed Gas Condenser (Top) Reboiler (Bottom)

8000 2442 5558

1000 305.2 694.8

2000 610.4 1389.6

3000 915.6 2084.4

4000 1221 2779

5000 1526 3474

6000 1831 4169

7000 2136 4864

From Table 2, the ﬂow rate of CH

generated

from the condenser is smaller than the ﬂow rate of

generated from the reboiler because the fraction

of the CO

component in the feed gas is greater than

. And also in this study, the calculation in the

simulation uses the assumption of a 100% efﬁciency

level in the separation process so that the total ﬂow of

the feed gas entering is equal to the amount that comes

out. The following are the operating conditions of the

distillation tower for each case shown in Table 2.

Table 2: Gas Condition in Distillation Column.

Case

Operating Condition

Feed Gas Condenser Reboiler

Base

P = 652.7 psi

T =19.19 F

Pcond = 652.3 psi

Tcond = -109.5 F

Preb = 656.1 psi

Treb = 50.67 F

Case 1

P = 507.6 psi

T =19.19 F

Pcond = 507.2 psi

Tcond =-120.9 F

Preb = 510.2 psi

Treb = 33.3 F

Case 2

P = 362.6 psi

T =19.19 F

Pcond = 362.4 psi

Tcond = -130.1 F

Preb = 364.6 psi

Treb = 33.3 F

Case 3

P = 217.6 psi

T =19.19 F

Pcond = 217.4 psi

Tcond =-140 F

Preb = 219.4 psi

Treb = -17.5 F

Case 4

P = 72.52 psi

T =19.19 F

Pcond = 217.4 psi

Tcond = -163.3 F

Preb = 73.92 psi

Treb = -69.13 psi

In terms of operating conditions, the pressure on

the condenser needs to be made smaller than the re-

boiler pressure. This is so that the steam formed can

rise to the top of the column, according to the prin-

ciple of ﬂuid ﬂow that the gas will ﬂow from high

pressure to low pressure.

From the sensitivity results obtained that the

greater the pressure of the feed gas into the distilla-

tion column, with the same ﬂow rate and tempera-

ture of the feed gas, the more reﬂux ratio is needed.

This is because with high pressure the more steam

formed. Even though the reﬂux system is condens-

ing steam, so if the steam is high then the reﬂux ra-

tio is also high. This applies also with the increasing

pressure of the feed gas, the greater the number of

stages needed. The principle of the stage is to sep-

arate the components in the gas feed, if the pressure

is high then the interaction of the gas component is

also higher, then more stages will be needed for the

separation process. In this study the magnitude of the

feed gas ﬂow rate does not directly affect the magni-

tude of the relux ratio and the number of stages. For

each case carried out, the value of reﬂux ratio and the

number of stages are the same, but the magnitude of

the feed gas ﬂow rate affects the diameter of the dis-

tillation column more and the energy needed, in this

case the condenser duty and reboiler duty. The greater

the feed gas ﬂow rate, the greater the dimension (di-

ameter and height) of the distillation column and the

energy needed. This is because a large ﬂow rate re-

quires a large capacity.

After the sensitivity to the inﬂuential parameters

it was found that in distillation using distillation is

strongly inﬂuenced by pressure and rate feed gas ﬂow.

The smaller the condenser duty feed gas pressure and

the reboiler duty is also greater, but it needs to be ad-

justed again with the existing capacity. In the low

temperature process carried out on the separation of

the natural gas ﬂow with high CO

concentration the

cooling cycle is required in the process. In this condi-

tion, electrical energy needs are one of the important

factors because they are needed in the cooling cycle.

Therefore it would be better to choose the lowest pres-

sure energy conditions, especially in this study the

condenser and reboiler. From the results of the sensi-

tivity obtained the selection of pressure is taken at the

greatest value. In this study the pressure was in the

range of 5-45 bars. In this study cryogenic distillation

was not carried out by a higher pressure review be-

cause of the limitation of temperature determination

of 19.20 F and the feed gas vapor fraction 1 which

could be achieved with higher pressure when the tem-

perature was also raised. Therefore it was chosen, the

feed gas pressure was 45 bar in this study.

The design of the CO

separation process in this

study used the method in the Pellegrini (Pellegrini

et al., 2015) patent with separation using two distil-

lation columns. The feed gas pressure entering in the

ﬁrst column is 45 bar and in the second column 35

bar. The purity results obtained in this study were

99% CH

at the end of the second column. From the

ﬁrst column to the second column a heater and valve

are given to reduce pressure. Then the output of CO

in the second column is pumped back to the ﬁrst col-

umn for re-separation. The design of this process can

ICoSET 2019 - The Second International Conference on Science, Engineering and Technology

346

be seen in Figure 7.

Figure 7: Overall Design of Cryogenic Process.

To validate the results of the calculation of the dis-

tillation column, a reference is needed for compari-

son. In this study a reference to the size of the dis-

tillation column from the RCC Regenerator Column

was used, Balongan reﬁnery with a diameter of about

9 meters and a height of more than 20 meters. Then

the feed gas rate is determined by the length of the

agreed contract. In this study the reference of feed

gas ﬂow rate uses a reference from Nainggolan (2016)

with a ﬂow rate of 8 BSCFD. From these references,

determining the size of the distillation column can be

done.

The variation in ﬂow rate from 1-8 BSCFD pro-

duces a diameter of more than 11 meters. Whereas

the ﬂow rate of 100-800 MMSCFD has the largest di-

ameter at the rate of 800 MMSCFD with a value of

10 meters. For the rate of 8 BSCFD, a diameter of

52.5 meters is produced, in the ﬁeld this condition is

not possible so there is a need for a scenario to di-

vide the ﬂow rate in the column in parallel, more than

one in each column. In the ﬁrst column the maximum

rate that can be accommodated is 500 MMSCFD with

a diameter of 7.4 meters, while for the second col-

umn the maximum rate that can be accommodated is

610.4 MMSCFD from the results of the ﬁrst column

with a diameter of 8 meters. The scenario is based

on the smallest condenser duty and reboiler duty to-

tal requirements is selected so that the ﬁrst scenario

with column 1 (7.4 meters in diameter and 17.66 me-

ters in height) is obtained and 16 pieces are needed

column 2 (with a diameter of 8 meters and a height

of 22.38 meters) requires 4 pieces. From these results

for the next process, it is necessary to consider the ap-

plication of the distillation column in the ﬁeld, with

the limitation of the location of the Natuna Gas Field

which is offshore resulting in the availability of land

and installation of the distillation column equipment

that needs to be reviewed.

Based on the designs presented above, it can be

proposed to be two main distribution/processing hub,

namely the platform based unit processing and on-

shore facility, connected with underwater pipeline. It

is worth noting that applying platform based process-

ing facility requires massive capital due to the size

of the processing facility, while using onshore facil-

ity would require very large pipe with high corrosion

potential. Further study should be done to assess the

economic and technical feasibility of these projects.

4 CONCLUSIONS

The choice of CO

separation technology from natu-

ral gas is based on several factors that are highly de-

pendent on the conditions and characteristics of the

gas ﬁeld being reviewed.

Under pressure and gas ﬂow rates based on the

case of the Natuna Gas Field, the cryogenic distilla-

tion process is chosen in the separation of CO

con-

tent at high ﬂow rates, and is considered capable of

obtaining speciﬁcations of CO

content of less than

or equal to 1%.

In designing CO

separation using cryogenic dis-

tillation at a very high ﬂow rate, a ﬂow rate distri-

bution scenario in parallel with different columns is

needed to meet these needs due to limited location

availability.

With the content of 71% CO

and 29% methane,

the results of separation using two-column cryogenic

distillation obtained by the case of 8000 MMSCFD

ﬂow rate obtained the number of the ﬁrst column as

much as 16 with a diameter of 7.4 meters and height

of 17.66 meters, while the number of second columns

was 4 in diameter 8 meters high and 22.38 meters.

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