Abstract—Absorption process is normally used for chilled

water production at district cooling plants. Besides enhancing

the efficiency of the plant, the process assists in reducing the

emission of CO2 to the environment. The absorption system is

also installed at a district cooling plant at Universiti Teknologi

Petronas. The system is operated using waste heat from the gas

turbine to produce chilled water. During the process heat loss is

generated and emitted to the environment. This study analyzed

the amount of heat loss and CO2 released to the environment

using the First Law of Thermodynamics. It is estimated 70 887

kg of CO2 released to the environment due the absorption

process. However the economic impact to the environment is

not covered in the scope of this study. It is recommended the

Life Cycle Assessment (LCA) should be undertaken due to CO2

emission by the plant.

Index Terms—Absorption process, CO2 emission, District

Cooling, Energy analysis.

I. INTRODUCTION

Cogeneration plant can be defined as the simultaneous

production of electrical or thermal energy from a single

energy source, by capturing waste heat from the gas turbines

which would otherwise be rejected to the environment [1].

Cogeneration plant is useful to enhance the efficiency of

energy of the conventional plant. The enhancement is

achieved through the utilization of waste heat from the gas

turbine to generate additional energy. The waste heat

normally is converted to steam or chilled water. The

absorption process is used to convert the waste heat to chilled

water. The process involved the conversion of waste heat

released by Gas Turbine Generator (GTG) to steam by Heat

Recovery Steam Generator (HRSG) and then from steam to

chilled water by Steam Absorption Chiller (SAC). The

absorption process assists in enhancing efficiency of the

cogeneration system as well as reduced the emission of waste

heat to the environment thus reducing CO2 emission.

Ukur Cakir et. al. [2] reported that cogeneration system

could lead to consistent energy conversion when compared to

fossil-fired generation of heat and power. In addition the

system helps in reducing CO2 emission, similar to the amount

of energy saving. Gianfranco Chicco and Pierluigi

Mancarella [3] noted that, to assess the emission reduction of

CO2 and other Greenhouse Gas (GHG) from cogeneration

systems it should be broken up to a subsystem which are

represented with block diagram models. From the

experience, M. Kanoglu et. al. [4] on the evaluation of energy

systems, the assessment of the cogeneration systems, should

be based on thermodynamic principles.

Many authors have done analyses of cogeneration system

at University Teknologi Petronas (UTP) covering Gas

Turbine [5], Electric Chillers and Steam Absorption Chillers

[6] and Thermal Energy Storage [7]. However, there is no

specific study on evaluation of the amount of CO2 emission

from this plant. The objective of this study is to evaluate the

amount of CO2emitted by the plantin the absorption process.

II. METHODOLOGY

The approach used for this study covers the following:

1) The Universiti Teknologi Petronas District Cooling

(UTP-DC) plant is taken as a case study.

2) The data of chilled water generated by the UTP-DC

plantin August 2011 is used for this study.

3) The analysis on the energy is based on total energy

input and output for both HRSG and SAC. Energy

loss by HRSG and SAC during the process are also

evaluated.

4) The validation of the findings is based on the earlier

researches as well as on published literatures.

III. CASE STUDY

The absorption system of UTP-DC plant consists of 2 units

4.2 MW Gas Turbines Generator (GTG), 2 units Heat

Recovery Steam Generator (HRSG) and 2 units Steam

Absorption Chiller (SAC). The plant uses natural gas as fuel.

The schematic flow of the systems is shown in Fig. 1.

Fig. 1. Flow of Absorption Process System

The plant started operation in April 2003. The plant

operates on a 24 hour basis. During peak periods, the

absorption system is operated with full load capacity. The

waste heat from GTG is used to generate steam by HRSG.

This study only confine to one unit HRSG and one unit SAC.

As shown in Fig. 2, the waste heat from the GTG is diverted

Evaluation of Carbon Dioxide Emission Using Energy

Analysis Approach: A Case Study of a District Cooling

Plant

Adzuieen Nordin, Norsheila Buyamin, M. Amin A. Majid, and S. Amear S. Ariffin

International Journal of Computer and Electrical Engineering, Vol. 5, No. 3, June 2013

284DOI: 10.7763/IJCEE.2013.V5.713

Manuscript received October 18, 2012; revised November 21, 2012.

Adzuieen Nordin, Norsheila Buyamin, are

Engineering Department, Politeknik Ungku Omar, Perak, Malaysia.(e-mail: auieen@jkm.puo.edu.my/adzuieennordin@gmail.com,

nsheila@jkm.puo.edu.my).

M.Amin A. Majid is with the Mechanical Engineering Department, University Teknologi Petronas, Perak, Malaysia (e-mail:

mamin_amajid@petronas.com.my).

S. Amear S. Ariffin is with the Mechanical Engineering Department, Politeknik Ungku Omar, Perak, Malaysia.(e-mail: amear@jkm.puo.edu.my).

Mechanical with the

(4) (3)

to HRSG to generate steam. The steam is used by SAC to

generate chilled water. For the analysis, only 66.6% of

exhaust heat is captured to produce the steam while the

remaining 33.4% is emitted to the environment [8]. The

temperature of chilled water generated and distributed to

campus building is 6ºC with a flow rate of 1.53kg/s and the

returned chilled water temperature is 13.5ºC.

Fig. 2. Energy system circulation

The analysis covers HRSG and SAC. The energy model of

the analysis for HRSG is shown in Figure 3. Figure 4 shows

the energy model for SAC. Three assumptions were used to

analyze the model namely:

1) The temperature of steam coming out from HRSG is

kept constant at 177℃.

2) The flow rate of steam from HRSG is 5.5T/h.

3) The total steam generated by HRSG is to be taken as

energy input to SAC.

Fig. 3. Energy balance model for HRSG

Fig. 4. Energy balance model for SAC

Thermodynamic analysis:

Thermodynamic First Law states that energy can neither

be created nor destroyed but can only alter the form. The

thermodynamics models are based on fundamental mass and

energy balances. Using the mass and energy balance

equations for each component in the power plant model, it is

possible to compute energy contents and flows at each device

of the plants and efficiency of the plants [9]. Energy balance

equations used for the analysis as shown by equation (1) [10].

Energy Balance Equations:

𝑄 − 𝑊 + 𝑚 𝑕𝑖 − 𝑕𝑜 + 𝑉𝑖

2−𝑉𝑜2

2 + 𝑔 𝑧𝑖 − 𝑧𝑜 = 0

(1)

𝑄 = heat rate into the system

𝑊 = rate of work done by the system

𝑚 = mass flow rate

𝑕𝑖 = specific enthalpy of the working fluid entering

the system

𝑕𝑜 = specific enthalpy of the working fluid leaving the

system

𝑣𝑖 = velocity of mass inlet

𝑣𝑜 = velocity of mass outlet

𝑔 = accelerationdue to gravity

𝑧𝑖 = elevation of mass inlet

𝑧𝑜 = elevation of mass outlet

For the analysis, the velocity and elevation components are

assumed zero. Using mass and energy balance equations,

equations for HRSG and SAC are formulated as follows;

1) For the Case of HRSG:

The HRSG generates steam by utilizing the energy in the

exhaust heat from the gas turbine. The energy balance

equations model with reference to Fig. 3:

𝐸𝑛𝑒𝑟𝑔𝑦𝑖𝑛 𝑜𝑓 𝐻𝑅𝑆𝐺 𝑄𝑖𝑛𝐻𝑅𝑆𝐺 = 𝑚 𝑤𝑕𝐶𝑝𝑤𝑕𝑇𝑤𝑕 (2)

𝐸𝑛𝑒𝑟𝑔𝑦𝑜𝑢𝑡 𝑜𝑓 𝐻𝑅𝑆𝐺 𝑄𝑜𝑢𝑡𝐻𝑅𝑆𝐺 = 𝑚 𝑠𝑡𝐶𝑝𝑠𝑡𝑇𝑠𝑡 (3)

Therefore,

𝐸𝑛𝑒𝑟𝑔𝑦𝑙𝑜𝑠𝑠 𝑓𝑜𝑟 𝐻𝑅𝑆𝐺 𝑄𝐿𝐻 = 𝐸𝑛𝑒𝑟𝑔𝑦𝑖𝑛 − 𝐸𝑛𝑒𝑟𝑔𝑦𝑜𝑢𝑡

(4)

2) For the Case of SAC:

Energy out from the HRSG is used to generate chilled

water for steam absorption process. The energy balance

equation with reference to Figure 4;

𝐸𝑛𝑒𝑟𝑔𝑦𝑖𝑛 𝑆𝐴𝐶 𝑄𝑖𝑛𝑆𝐴𝐶 = 𝑚 𝑠𝑡𝐶𝑝𝑠𝑡𝑇𝑠𝑡

=𝐸𝑛𝑒𝑟𝑔𝑦𝑜𝑢𝑡 𝑜𝑓 𝐻𝑅𝑆𝐺 (5)

𝐸𝑛𝑒𝑟𝑔𝑦𝑜𝑢𝑡 𝑜𝑓 𝑆𝐴𝐶 𝑄𝑜𝑢𝑡𝑆𝐴𝐶 = 𝑚 𝑐𝑕𝑤𝐶𝑝𝑐𝑕𝑤𝑇𝑐𝑕𝑤 (6)

Therefore,

𝐸𝑛𝑒𝑟𝑔𝑦𝑙𝑜𝑠𝑠 𝑓𝑜𝑟 𝑆𝐴𝐶 𝑄𝐿𝑆 = 𝐸𝑛𝑒𝑟𝑔𝑦𝑖𝑛 − 𝐸𝑛𝑒𝑟𝑔𝑦𝑜𝑢𝑡 (7)

Steam

(177°C)

SAC

66.6% of

exhaust

heat

33.4% of

exhaust

heat

HRSG

Gas

Turbine

GeneratrChilled

water

out

(6°C)

Chilled

water in

(13.5°C)

𝑄𝑜𝑢𝑡𝐻𝑅𝑆𝐺

(𝑚 𝑠𝑡𝐶𝑝𝑠𝑡𝑇𝑠𝑡)

𝑄𝑖𝑛𝐻𝑅𝑆𝐺

(𝑚 𝑤𝑕𝐶𝑝𝑤𝑕𝑇𝑤𝑕)

𝑄𝐿𝐻

HRSG

G

𝑄𝑜𝑢𝑡𝑆𝐴𝐶

(𝑚 𝑐𝑕𝑤𝐶𝑝𝑐𝑕𝑤𝑇𝑐𝑕𝑤)𝑄𝑖𝑛𝑆𝐴𝐶

(𝑚 𝑠𝑡𝐶𝑝𝑠𝑡𝑇𝑠𝑡) SAC

𝑄𝐿𝑆

International Journal of Computer and Electrical Engineering, Vol. 5, No. 3, June 2013

285

where:

𝑄inHRSG = energy in to HRSG (kWh)𝑄outHRSG = energy out from HRSG kWh 𝑄inSAC = energy in to SAC (kWh)𝑄outSAC = energy out from SAC kWh 𝑄LH = energy loss from HRSG kWh 𝑄LS = energy loss from SAC kWh 𝑚 wh = flow rate of waste heat (kg/s)𝑚 st = flow rate of steam (kg/s)𝑚 chw = flow rate of chilled water (kg/s)𝐶𝑝wh = enthalpy of waste heat (kJ/kg)𝐶𝑝st = enthalpy of steam (kJ/kg)𝐶𝑝chw = enthalpy of chilled water (kJ/kg)𝑇wh = Temperature of waste heat (℃)

where:

𝑇st = Temperature of steam (℃)𝑇chw = Temperature of chilled water (℃)

IV. RESULTS AND DISCUSSION

Using historical data for August, 2011 and equations (2) to

(7), the total amount of Qin (input), Qout (output) and Qloss

(loss) for both HRSG and SAC were calculated. The plots of

the results are shown in Figure 5 and Figure 6 for the case of

the HRSG. While in the case of SAC the plots are shown in

Figure 7 and Figure 8.

Fig. 5. Energy in of HRSG for August, 2011.

Fig. 5 shows the total energy that was supplied to HRSG. It

assumed the input energy to the HRSG is constants which is

around 10 000 kWh. However, the output energy is about

5500 kWh as shown in Figure 6. Thus energy loss during the

process within HRSG is about 57%.

Fig. 6. Energy loss of HRSG for August, 2011.

In the analysis of SAC, Figure 7 and 8 shows the amount of

energy out and energy loss respectively in August 2011. It is

assumed that the total steam generated by HRSG is taken as

input to SAC. The amount of chilled water generated and the

heat loss to the environment is calculated based on the

equation (5), (6) and (7).

Fig. 7. Energy out of SAC for August, 2011.

Fig. 8 shows the total of energy loss to the environment is

around 1800kWh while the energy out from SAC remains

2600 kWh. It is estimated that, the energy loss is about 40%

during the absorption process.

Fig. 8. Energy loss of SAC, for August, 2011.

The results are summarized in Table 1.

TABLE I: RESULTS FROM ENERGY ANALYSIS FOR HRSG AND SAC

HRSG SACQin

(kWh)

Qout

(kWh)

Qloss

(kWh)

Eff.

(%)

Qin

(kWh)

Qout

(kWh)

Qloss

(kWh)

Eff.

(%)

Min 9582 4245 5607 0.59 4245 2374 1871 0.44

Max 9926 4245 5681 0.57 4245 2644 1601 0.34

Mean 9893 4245 5648 0.57 4245 2526 1719 0.40

SD 104 N/A 104 0.02 N/A 88 88 0.02

For the case study of HRSG, the minimum of 𝐸𝑛𝑒𝑟𝑔𝑦𝑖𝑛 is

9582 kWh while the maximum of 𝐸𝑛𝑒𝑟𝑔𝑦𝑖𝑛 to HRSG is

9926 kWh. The 𝐸𝑛𝑒𝑟𝑔𝑦𝑖𝑛 to SAC is constant whereas 4245

kWh. The minimum of 𝐸𝑛𝑒𝑟𝑔𝑦𝑜𝑢𝑡 from SAC is 2374 kWh

while the maximum of 𝐸𝑛𝑒𝑟𝑔𝑦𝑜𝑢𝑡 is 2644 kWh. The

equation (6) also reveals the minimum of 𝐸𝑛𝑒𝑟𝑔𝑦𝑜𝑢𝑡 from

SAC is 1601 kWh and the maximum value is 1871 kWh.

From the analysis, it is estimated that the total energy loss

from HRSG and SAC due to absorption process is 149 551

kWh, equivalent to 70 887 kg of CO2. This is based on 474

g/kWh of CO2 as reported by R. Kannanet. al. [11] which is

lower in the case of coal fired power 1kWh electricity

generation will emit around 1 kg of CO2 [12]. This amount of

CO2 is released to the environment and contributed to Global

Warming Potential (GWP). However, if the waste heat

generated by GTG is not used for absorption process, it is

estimated that about 98 473kg CO2 will be generated. Thus

the absorption process assists in reduction of CO2 emission in

the environment by 28%.

V. CONCLUSION

The production of chilled water using the absorption

process of the district cooling plant enhanced the productivity

of the plant. In addition, it also assists in reducing the amount

of CO2 emission to the environment. However, to ascertain

economic feasibility of the plant, LCA study is needed. This

is recommended to be undertaken in the future study.

ACKNOWLEDGMENT

The authors would like to express their appreciation to the

International Journal of Computer and Electrical Engineering, Vol. 5, No. 3, June 2013

286

support by Center of Technology, Politeknik Ungku Omar,

Perak, Malaysia, University Teknologi PETRONAS (UTP),

Malaysia and Ministry of Science, Technology and

Innovation (MOSTI).

REFERENCES

[1] B. T. Aklilu and S. I. Gilani, “Mathematical Modeling and Simulation

of a Cogeneration Plant,” Applied Thermal Engineering, 2010, pp.

2545-2554.

[2] U. Cakir, K. Comakli, and F. Yuksel, “The Role of Cogeneration

System in Sustainability of Energy,” Energy Conversion of

Management, 2012.

[3] G. Chicco and P. Mancarella, “Assessment of the greenhouse gas

emissions from cogeneration and trigeneration systems,” Part I:

Models and indicators, 2008, PP. 410–417.

[4] M. Kanoglu, I. Dincer, and Y. A. Cengel, “Exergy for better

Environment and Sustainability,” Environment Dev. Sustain., 2009, pp.

971-988.

[5] B. T. Aklilu and S. I. Gilani, “Exergetic Performance Analysis of a

Cogeneration Plant at Part Load Operation,” Journal of Energy and

Power Engineering, 2010, ISSN 1934-8675 USA.

[6] C. Rangkuti, A. M. M. Amin, and S. I. Gilani, “Operation and

Performance Analysis of Steam Absorption Chillers of the GDC Plant,”

International Conference on Energy and Environment, 2006.

[7] S. I. Gilani, A. M. M. Amin, and C. Rangkuti, “Chillers Operating

Strategies of a Thermal Energy Storage System: Case Study of a Gas

Distrct Cooling Plant,” International Conference on Energy and

Environment, 2006.

[8] M. A. A. Majid, S. A. Sulaiman, I. Ibrahim, and Z. Baharddin, “Causal

Model for Peak and Off Peak Waste Heat Recovery for Chilled Water

Production,” Journal of Applied Science, 2012, ISSN 1812-5654.

[9] F. J. Wang, J. S. Chiou, and P. Wu, "Economic Feasibility of Waste

Heat to Power Conversion," Science Direct, vol. 84, no. 4, pp.

442-454, 2007.

[10] Y. A. Cengel and M. A. Boles, Thermodynamics: an engineering

approach, McGraw-Hill Higher Education, 2006.

[11] R. Kannan, K. C Leong, R, Osman, H. K. Ho, and C. P. TSO, “Gas

Fired Combined Cycle Plant in Singapore: Energy Use, GWP and

Cost- A Life Cycle Approach,” Energy Conversion and Management,

vol. 45, 2005, PP. 2145-2157.

[12] R. Zevenhoven and A. Beyene, “The Relative Contribution of Waste

Heat from Power Plants to Global Warming,” Energy, vol. 36, 2011, pp.

374-3762.

Adzuieen Nordin is a senior lecturer in the Mechanical

Engineering Department of Politeknik Ungku Omar,

Malaysia since 2003. She graduated with bachelor

degree B.Sc. (Hons.) Mechanical Engineering

(Manufacturing) 2002 from Universiti Teknologi

Malaysia, Malaysia and M. Ed. Technical and

Vocational 2003 from Kolej Universiti TeknologiTun

Hussein Onn, Malaysia. Currently she is pursuing Ph.D

in Life Cycle Assessment for cogeneration plant. Her research interest is on

Air Conditioning and Life Cycle Assessment.

Besides, she is registered as an ASHRAE member since 2011. She is also a

Graduate Member (Mechanical Engineering) of the Institution of Engineers,

Malaysia (IEM), since 2011.

Norsheila Buyamin is a lecturer in the Mechanical

Engineering Department of Politeknik Ungku Omar,

Malaysia since 2010. She graduated Bachelor degree in

Mechanical Engineering 2009 from

UniversitiTeknologi Malaysia, Malaysia. She is a

researcher at Centre of Technology of Politeknik Ungku

Omar, Malaysia. Her current research interests are

cogeneration plant, district cooling and indoor air

quality (IAQ). She is registered as an ASHRAE member since 2011.

M. Amin A. Majid received Ir. (1976), in Mechanical

Engineering from Institut Teknologi

Bandung-Indonesia, M. Eng. (1981) from Asian

Insitute Technology, Thailand and Ph.D (1994) from

University Malaya, Malaysia. He is Associate Professor

in Mechanical Engineering Department, Universiti

Teknologi Petronas (UTP), Malaysia. His current

research interests include energy system,

manufacturing optimization and asset management.

Syed Amear Syed Ariffin is currently a senior lecturer

at Mechanical Engineering Department of Politeknik

Ungku Omar, Malaysia. He has been attached to this

polytechnic since 1995 and now holding the position as

the Program Head of Refrigeration and Air

Conditioning course. He graduated with Bachelor

Technology and Education specializing in Mechanical

Engineering from University Technology of Malaysia,

Malaysia in 1995. From September 2009 till now, he is in-charged by the

Centre of Technology of Politeknik Ungku Omar specializing in

Refrigeration and Air Conditioning course. His current research interests are

human comfort, thermal energy storage, absorption chiller and systems

design. Besides, he is also a registered ASHRAE member since 2011.

International Journal of Computer and Electrical Engineering, Vol. 5, No. 3, June 2013