Estimate of Methane Emission in Startup and Shutdown Process of Siemens Gas Compressors Using PHAST Software

Journal of Environmental Treatment Techniques

2018, Volume 6, Issue 3, Pages: 66-71

J. Environ. Treat. Tech.

ISSN: 2309-1185

Journal weblink: http://www.jett.dormaj.com

Estimate of Methane Emission in Startup and

Shutdown Process of Siemens Gas Compressors

Using PHAST Software

Abdolrasoul Shahpari ¹^،²،Farham Aminsharei Ph.D.¹^،²^*، Majid Ghashang Ph.D.¹^،²

- Department of Chemical Engineering - Health, Safety & Environment, Najafabad Branch, Islamic Azad University, Najafabad, Iran

- Human Ecology and Sustainable Development Research Center, Najafabad Branch, Islamic Azad University, Najafabad, Iran

Received: 10/6/2018

Accepted: 4/11/2018

Published: 30/11/2018

Abstract

Methane is the main component of natural gases which has a potential for global warming of more than 25 times that of Carbon

dioxide. Methane is the second greenhouse gas to be released by human activities, and almost a third of these emissions are in

different sections of oil production and processing, transfer and storage of natural gas. The purpose of this study is to estimate the

amount of Methane emission to the atmosphere due to the startup and shutdown of Siemens gas compressors in Gas Transmission

Operation District No. 2. For the present study, first the total number of Siemens compressors, model and type of each compressor

in District No. 2 were determined. Then the similar compressors were placed in the same group and for each group the compressor

information of one station was collected as a pilot and transferred to the PHAST software, and the modeling and outputs were

received and recorded. The amount of Methane emission in year 2017 in the process of startup and shutdown of Siemens

compressors was found as below: type C compressors the amount of 202814 kg, type D compressors 183841 kg, and type E

compressors 227098 kg of Methane emission to the atmosphere. According to the obtained information, it can be concluded that

in 2017, this gas transmission District has released a total of 613.753 tons of Methane gas from the above-mentioned process in the

atmosphere, which has a global warming potential of 15343.825 tons of Carbon dioxide equivalent.

Keywords: Methane emission, Gas compressors, Global warming, PHAST software, Greenhouse gases.

Introduction¹

such as yellow fever and foot-and-mouth disease, also

become more common with global warming [4]. Regarding

the importance of the issue in the National Climate Change

Adaptation Strategy (NSP) program, healthy policy

vulnerability assessment has been addressed to climate

change impacts, as well as part of the Sixth Development

Plan is also dedicated to identifying vulnerable areas

affected by the effect of extreme and gradual climate change

Climate change is caused by an increase in the

concentration of the greenhouse gases in the atmosphere. It

is a very complex atmospheric phenomenon on a global and

long- term basis. Climate change will take place in the next

few decades as a global warming [1]. It makes some regions

more humid and some areas dry up, and the severity and

frequency of extreme events such as floods and droughts will

increase. Nowadays, the fact that humans change the state of

the Earth's atmosphere is clear, and this phenomenon is the

motivation and focus of extensive activities across countries

and the United Nations [2].

[

5].

The Intergovernmental Panel on Climate Change (IPCC)

in a study conducted on the basis of simulations predict that

global temperature changes on Earth’s surface will increase

to 1.5 degrees by the end of 21 century than 1850. The 2 ºC

limit is considered to be a risk limit in global warming.

Scientists say that even if we reduce greenhouse gases

emission dramatically, its effects will continue, as large parts

of the climate system need hundreds of years to respond to

changes. In addition, it takes decades to clear greenhouse

gases emission from the atmosphere [6].

The direct effects of climate change on health can be seen

in increasing the incidence of tropical diseases, including

carrier disease (such as malaria). Other infectious diseases

(such as cholera) are also indirect effects of climate change.

Direct damage can also be caused by extreme changes in

temperature and the incidence of related diseases, such as

respiratory and cardiovascular disease [3]. Other diseases,

¹Corresponding author: Farham Aminsharei (Ph.D), (1) Department of Chemical Engineering - Health, Safety & Environment,

Najafabad Branch, Islamic Azad University, Najafabad, Iran and (2) Human Ecology and Sustainable Development Research Center,

Najafabad Branch, Islamic Azad University, Najafabad, Iran. E-mail: farham.aminsharei1@gmail.com.

Journal of Environmental Treatment Techniques

2018, Volume 6, Issue 3, Pages: 66-71

According to studies conducted, in 2014, Canada had

2.1 Data collection

34,000 tons of carbon dioxide equivalent emission in the

form of Vent and Escape From gases transmission stations

7]. Also, according to the US Environmental Protection

All Siemens gas compressors in District No. 2 is a two-

stage centrifuge, known as the SIEMENS 10MV2A. This

compressor model has several types that three types of C, D

and E are used in this district. The number of startup and

shutdown of Siemens turbo-compressors in 2017 is

summarized in Table 1.

[

Agency’s research (EPA), the natural gas industry

transmission and storage section has accounted for 37% of

the total waste gas, with the largest share in all sections

(

production, processing, transmission and distribution [8].

In a study conducted by the Department of Atmospheric

By visiting all Siemens stations of District No. 2, the

documents related to the startup and shutdown of the

compressors of each station were identified, considering that

the same type of compressors were designed and

manufactured in exactly the same way, and in terms of

operating conditions they installed in the same gas pipelines

in operating parameters operate the same, so all compressors

of the same type have the same emission. Siemens

compressors at station are grouped in the Table 2.

Program in climate change section, the amount of emission

in U.S Gas Transmission section in 2014 was estimated

about 22million tons of Carbon dioxide equivalent, of which

million tons of Carbon dioxide is due to the emission of

Methane from gas compressors [9]. Also, in studies carried

out by the EPA in 2011, it was found that with the change in

the design of the blow down system and shutdown

management of the compressors at gas stations, the amount

of Methane emissions could be reduced to 1,800 million

cubic feet per year [10].

Gas Transmission Operation District No. 2 has different

compressor types with different manufacturers, and in each

station according to the conditions of the gas transmission

line has been used from an appropriate compressor that was

available at the time the station was established. This Gas

Transmission Operation district has 17 active gas pressure

boost stations and has a total of 74 turbo compressors active

in its stations. Gas compressors in this district have different

manufacturers such as Summy, Nuovo Pignono, Siemens,

Nevsky.

A total of 25 Siemens gas compressors have been used at

different stations of District 2, which is more than the other

types of gas compressors in this district, and furthermore,

given that the most of these compressors are located on third

and fourth gas pipelines and operating maneuvers on these

gas transmission lines are more than the other lines, so the

highest startup and shutdown rates related to this type of

compressors. As a result the amount of Methane emission to

the atmosphere in the process of startup and shutdown of

these compressors are more than the other types of

compressors in the District No. 2.

2.2 Reviewing How to Emit During the Process

In order to review the process and operational procedures

for startup and shutdown of Siemens gas compressors, first

it is necessary to be familiarize with the method of

connecting the lines and the position of the relevant valves.

When the compressor is in operation service the gas cleaned

by the scrubbers enters the entrance line through the inlet

valve and from there enter the gas compressor booster. In the

booster, the pressure of the gas increases in two steps and

then enters to the compressor exit line, then through the

outlet valve to the gas coolers. The full description of how

the compressor emit in startup and shutdown process is

explained in the following.

2.2.1 Start-up process

At the time of startup of Siemens gas compressors, no air

should be present in the compressor boosters and the lines

leading to it before pressurized. Therefore, prior to launching

the unit, purge operations must be performed. To do this,

through a 2-inch bypass inlet valve, the gas is injected into

the compressor booster and the lines connected to it, and

blow down from the Vent line at the outlet of the compressor

into the atmosphere.

With regard to the goal of reducing 10% of the emissions

during the Sixth Development Plan (2016-2020) and the

high share of gas vent in the gas transmission company, any

prevention of gas losses at the booster station will have a

significant effect [11]. Therefore, accurate calculation of

Methane emission in different parts of gas stations is

important. In this study, the amount of emission was

computed from Siemens gas compressors, and for modeling

the software PHAST 7.11 was used. This software is based

on the most practical and reliable software for calculating

and modeling of emission and distribution of gases in the

world's oil and gas industry.

2.2.2 Shutdown process

By issuing a shutdown command for the Siemens turbo-

compressor, the rotation of the shaft is reduced to a

minimum, first. By approaching the work point to the surge-

line, the unit anti- surge valve starts opening as a percentage

by reaching the unit round to the ideal (5390 rpm) the valve

of the anti- surge will be open completely. For about 4

minutes, the unit remains in the ideal round, then the flame

is turned off and the close command issued for the inlet and

outlet valves of the unit and the isolation valve of the anti-

surge line and simultaneously the unit round is reduced again

and the rotation of the gas compressor stops. . After this step

and after about 25 minutes, while all the valves are closed,

the gas contained in the compressor booster and the lines

connected to it for some reasons, including safety issues

through the 2-inch Vent line blow down to the atmosphere.

Methodology

In order to implement the present study, a framework

consisting of 5 stages, according to the type of compressor

and operation conditions was developed.

Journal of Environmental Treatment Techniques

2018, Volume 6, Issue 3, Pages: 66-71

Table 1: The number of startup and shutdown of Siemens turbo-compressors in 2017

/builder

Total sta rtup

Number

Row

normal

shutdown

SIEMRNS

479

TOTAL

25 devices

437

Table 2: Grouping of Siemens compressors at stations

Main Pipeline Name Number of u nits

Row

type

Model

SIEMRNS

10MV2A

Third

The Fourth

Second and third

.3 Scenario selection

To interpret the results, the data for each type of Siemens

pipe connected to the input header of the units, and because

the header is connected to the main pipeline, this amount of

blow down rate does not have any effect on the main header

pressure. But in the process of shutdown of the compressor,

which emission is due to the blow down of the compressor

booster and the lines connected to it, the rate of blow down

varies from the unit vent and, as time passes, the rates of

blow down decreases and this effect also affects the tank

pressure. To simulate such cases, the software uses a Time-

varying short pipe release scenario.

gas compressors in Gas Transfer Operations District No.2,

according to the operational parameters and design, were

loaded in the software and by selecting appropriate scenario;

the results were obtained from the software.

To simulate the gas emission in the process of startup of

the compressor in the software, the “Pressure vessel” and the

“

Short pipe” scenario were used and to simulate the

compressor shutdown process, the “Pressure vessel” and

Time varying short pipe release” scenario were used.

“

Therefore the software considers the compressor and

pressure pipelines as a pressure vessel. Also, with the Short

pipeline scenario, blowing down from a pipe connected to

the tank is simulated in a state in which rate of blow down is

constant and it rate does not reduce the pressure of the tank.

In the process of startup of the gas compressor, the

compressor purge operation is carried out through a 2-inch

2.4 Receiving reports from the software

After entering the data for each type of compressor, in

according to the specifications and operating conditions,

the output of the software is extracted from the Reports

section. For example, the results of the Type C Siemens

compressors are shown in Figures 1 and 2.

Journal of Environmental Treatment Techniques

2018, Volume 6, Issue 3, Pages: 66-71

Figure 1: Extraction of software results for startup mode (Type C compressor)

Figure 2: Extraction of software results for shutdown mode (Type C compressor)

.5 How to calculate

.5.1 Startup mode

To calculate the emission in the startup process, the results

in Figure 1 (Type C compressor) and Equation

The total amount of Methane emission in the process of

startup of each type of Siemens gas compressor calculated

by equation 2-2 and tables 1 and 2:

퐦_푪_푯_ퟒ_풔_풕_풂_풓_풕= 퐦

퐦_푪_푯_ퟒ_풔_풕_풂_풓_풕: Mass of Methane released at one startup (kg)

̇ _N_A_T_U_R_A_L_G_A_S

: Mass flow rate of gas output (Kg/s)

T: Gas blow down time (s)

^푪^푯ퟒ : Percentage of Methane in natural gas

composition:

̇ _N_A_T_U_R_A_L_G_A_S

. 풕. %푪푯_ퟒ

Eq. (1-2)

퐦

⁄

= 퐦

. 푵

Eq. (2-2)

푪푯ퟒ 풚풆풂풓_ퟐ_ퟎ_ퟏ_ퟕ풔풕풂풓풕

ퟒ

푪푯 풔풕풂풓풕

퐦

퐦푪푯ퟒ⁄풚풆풂풓_ퟐ_ퟎ_ퟏ_ퟕ풔풕풂풓풕 : Total amount of Methane emission in

startup process in 2017 (kg)

퐦_푪_푯_ퟒ_풔_풕_풂_풓_풕: Mass of Methane released at one startup (kg)

N: Number of startup in 2017

Journal of Environmental Treatment Techniques

2018, Volume 6, Issue 3, Pages: 66-71

.5.2 Shutdown mode

퐦

⁄

= 퐦_푪_푯_ퟒ_풔_풕_풐_풑. 푵

푪푯ퟒ 풚풆풂풓_ퟐ_ퟎ_ퟏ_ퟕ풔풕풐풑

To calculate the emission in shutdown process, the results

in Fig. 2 (for type C compressor) and Equation 2-3 were

used.

Equation (4-2)

_ퟐ_ퟎ_ퟏ_ퟕ_풔_풕_풐_풑: Total amount of Methane emission in

퐦

⁄

푪푯ퟒ 풚풆풂풓

017(kg)

퐦_푪_푯_ퟒ_풔_풕_풐_풑: Mass of Methane released at one shutdown

kg)

N: Number of Shutdown in 2017

퐦_푪_푯_ퟒ_풔_풕_풐_풑= (퐦_N_A_T_U_R_A_L_G_A_S_._푻

−

퐦_N_A_T_U_R_A_L_G_A_S_._푹). %푪푯_ퟒ

Equation (2-3)

(

^퐦푪푯ퟒ풔풕풐풑 : Mass of Methane released at one shutdown

(kg)

Total mass of natural gas in the compressor

Results

^퐦NATURAL GAS.푻

According to the calculations, the amount of Methane

퐦_N_A_T_U_R_A_L_G_A_S_._푹: The mass of the remained natural gas in

the compressor

Also, the total amount of Methane emission in the

shutdown process of each type of Siemens gas compressor

were calculated as follows in Table 2-4 and Tables 1 and 2:

emission in all three types of Siemens gas compressor

inShutdown and startup process, as well as the total

emission from this process in12017, is presented in Table

푪푯 : Percentage of Methane in natural gas composition

ퟒ

Table3: The amount o f Methane emission in startup and shutdown process of the Siemens compressors in 2017

Compressor t ype

Shutdown

kg)

CO Equivalent of

total emission (T)

Row

Startup(kg)

Total (kg)

Total emission (T)

(

44614

47789

57824

158200

136052

169274

202814

183841

227098

613/753

15343/825

According to the results, the highest share of emission

among different types of Siemens compressor is related to

type E, although the lowest number of compressors (5

devices) is of this type. This emission is due to the following

reasons:

Iran Gas Transmission Operation District No.2 according to

our research in 2017, is equal to 55.91 tons. The main

reasons for the difference are:

’

• The Ojito station s compressors are a reciprocating, but

Petaveh station’s compressor are centrifugal type, that the

booster of these compressors are much higher volume than

reciprocating type of compressors.

•In Ojito station input and output Compressor’s lines are 24

inches, but in Petaveh are 30inches.

•

Number of startup and shutdown: In 2017, these types of

compressors have a total of 154 startups and shutdowns,

which is equivalent to 30.8 times of startup and shutdown

for each unit. While the type C compressors, which are12

units, have 185 times startup and shutdown, which means an

average of 15.4 times startup and shutdown for each unit.

• The Ojito station has 3 gas compressors, while the G3

station has 4 gas compressors.

•

Another reason is the high volume of the booster and the

In 2015, Subramanian et al. measured the Methane

emissions from 45 gas compressor stations in the United

States. They conducted their research with direct

measurements of escape and blow down sources and divided

the sites according to Methane emission, and concluded that

the Methane emission level in these sites varies from 200 to

880 standard cubic feet per minute. The blow down of the

compressors, leakage from isolating valves, exhaust gas

combustion engines and leakage from other equipment were

recognized as the main sources of emission [13]. As

mentioned above, direct measurement was used in this study,

but in our study, due to the lack of suitable measuring

equipment, high volume of emission at blow down time, and

the absence of accurate blow down time, there was no direct

measurement of the rate of emission.

input and output lines of this type of compressor. In C and D

types, the diameter of the lines connected to compressor is

0 inches and in type E is 36 inches.

According to above discussion, the effect of the number

of startup and shutdown is quite clear on the emission of the

gas compressors. To reduce emission, as much as possible

and in according to the conditions of operation, the

compressors must not be shut down and restarted in cases

where it is less urgent.

Discussion

In 2017, Dr. Erica LeDoux of the US Environmental

Protection Agency (EPA), in cooperation with Williams

Company, conducted a research on greenhouse gases

emission from the Ojito Gas Pressure Boost Station in New

Mexico. This station uses three gas compressors to increase

the pressure of the pipeline. In this study, the calculation

method was used to calculate Methane emission in shutdown

and startup process of gas compressors using emissions

coefficient. It was determined that the emission of Methane

from the process of startup and shutdown of the gas

compressors at this station was 32.2 tons per year [12]. For

comparison, the rate of Methane emission at G3 station of

Acknowledgements

The present study is based on the research project of Iran

Gas Transmission Operation District No.2 and conducted by

the support of this company and The Islamic Azad

University of Najafabad, whereby the authors express their

immense gratitude to all persons who have given their

invaluable support and assistance.

Journal of Environmental Treatment Techniques

2018, Volume 6, Issue 3, Pages: 66-71

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