er.1148] y. h. zurigat; b. dawoud; j. bortmany -- on the technical feasibility of gas turbine inlet...

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INTERNATIONAL JOURNAL OF ENERGY RESEARCHInt. J. Energy Res. 2006; 30:291–305Published online 15 August 2005 in Wiley InterScience (www.interscience.wiley.com). DOI: 10.1002/er.1148

On the technical feasibility of gas turbine inlet air cooling

utilizing thermal energy storage

Y. H. Zurigat1, B. Dawoud2,n,y and J. Bortmany3

1Mechanical Engineering Department, The University of Jordan, Amman, Jordan2Chair of Technical Thermodynamics, RWTH-Aachen University, Schinkel Str. 8, D-52062 Aachen, Germany

3Petroleum Development Oman, P.O. Box 81, Postal Code 113, Oman

SUMMARY

The potential of using thermal energy storage (TES) in the form of ice or chilled water to cool gas turbine

inlet air is evaluated for a remote oil field location in the Sultanate of Oman using local hourly typicalmeteorological year weather data. It is found that under the conditions investigated seasonal TES in chilledwater storage tanks or ice bins for the location considered is prohibitively expensive and thus notrecommended. Application of partial TES option shows that the cool storage does not result in anynoticeable reduction in the chiller size. Hence, TES whether seasonal, partial, or full storage is not a viableoption for the considered location, especially in the absence of time-of-use utility rate structure. Copyright# 2005 John Wiley & Sons, Ltd.

KEY WORDS: gas turbine; inlet air cooling; thermal energy storage

1. INTRODUCTION

Ambient conditions influence the performance of gas turbine power plants. As the ambienttemperature is decreased the power output and the efficiency are increased. Hence, inlet air

cooling has been considered for boosting the power output of gas turbine during hot summer

months when the electric power demand is high due to air conditioning load. Depending on the

type of gas turbine, a reduction of about 0.2% in the heat rate and an augmentation of about 0.5

to 0.9% in electrical power production for every degree Celsius drop in the compressor’s inlet air

temperature are achieved (Chaker and Meher-Homji, 2002). Thermal energy storage (TES) is a

technique which may be integrated with gas turbine power generation plants to store chilled

water or ice during off-peak periods to be used for inlet air cooling during peak periods. A

comparison of the ice and chilled water storage systems is shown in Hasnain (1998).

Received 21 August 2004Revised 11 March 2005

Accepted 1 May 2005Copyright# 2005 John Wiley & Sons, Ltd.

yE-mail: [email protected]

Contract/grant sponsor: Petroleum Development of Oman (PDO); contract/grant number: 2002-52

nCorrespondence to: Dr Belal Dawoud, Chair of Technical Thermodynamics, RWTH-Aachen University, SchinkelStr. 8, D-52062 Aachen, Germany.



In their study of overall economics of the gas turbine power augmentation benefits Ondryas

et al . (1991) considered TES as an option for a power generation facility comprised of four GE

Frame 7E gas turbine generators. They investigated the use of chilled water and ice TES systems

for the peak hours of the peak months of the year. For chilled water TES they considered both

full and partial TES options. For an ice TES system of equivalent cooling capacity thecalculated storage tank volume 7–14 times less than the chilled water TES tank volume. Based

on their study they concluded that the size of chilled water TES may result in space constraints

and large costs.

Ice storage has been applied for gas turbine inlet air cooling at different locations

around the world. A system installed at a gas turbine power generation plant (ISO rating of

59.8 MW and a peak rating of 65.2 MW) at a Nebraska company used ice storage to cool the

inlet air from 38 to 48C (Stewart, 1998). A net power increase of approximately 12 MW (21%)

has been achieved (a power boost of 0.59% 8C1). To cool the gas turbine inlet air a study

conducted by Antoniak et al . (1992) examined both seasonal TES of cold water and diurnal TES

of ice. The former termed aquifer thermal energy storage (ATES) was designed to store cold

water during winter time in an aquifer. The water is chilled during winter by cold winter air in a

conventional cooling tower and injected into the aquifer through a number of supply wells. Thecool water is then withdrawn during summer months to supply the cooling load of gas turbine

inlet air cooling system. Economic assessment of the seasonal TES technique showed that under

the climatic conditions of Minneapolis area inlet air cooling with ATES provided lower cost

electricity than installing extra power generation capacity (or installing larger gas turbines) to

meet the same increase in power output. In contrast, diurnal TES of ice showed that inlet air

cooling with ice storage is 5–20% more expensive than installing larger gas turbines to meet the

power demand.

Somasundaram et al . (1993) addressed some of the TES systems that are readily

applicable to be combined with cogeneration systems. With regard to precooling the gas

turbine inlet air with cold water supplied by ATES system, their preliminary results indicated

that the preferred system will depend on site-specific conditions and operating requirements.

The cost effectiveness of the ATES system varies significantly with site-specific geologicconditions.

In his review of cool thermal storage Hasnain (1998) stated that a 1996 U.S. Department of

Energy study showed that a thermal energy storage for turbine inlet air cooling system can be

installed at a cost of 150–250 U.S.$ kW1 of incremental power boosting. In their analysis of

cool storage integrated with a typical commercial building air conditioning system,

Hasnain et al . (1999) concluded that cool storage is a cost-effective tool for both demand and

utility sides, i.e. building air conditioning and gas turbine inlet air cooling, respectively.

However, it must be noted that the cooling load profile used in their analysis perfectly suits

thermal storage, i.e. low night load and high daytime load. This is typical of commercial and

public buildings. The analysis of gas turbine inlet air cooling (Hasnain et al ., 1999) was not

based on detailed calculations of a specific gas turbine or actual local weather profiles. Their

conclusion of the cost effectiveness of cool storage for gas turbine inlet air cooling is basedmainly on the experience of similar systems in U.S.A. where a number of TES systems have been

operated. In fact, a thermal storage system using ice for gas turbine inlet air cooling was

designed to operate on a weekly cycle (Bakenhus, 2000). Table I gives detailed specifications of

the system which was then the largest of its kind in the world. Bakenhus (2000) reported that the

cost effectiveness of the system was based on the lowest first cost option for additional

Copyright # 2005 John Wiley & Sons, Ltd. Int. J. Energy Res. 2006; 30:291–305

Y. H. ZURIGAT, B. DAWOUD AND J. BORTMANY292



Table I. Specifications of a gas turbine inlet air cooling system using ice storage(compiled from Bakenhus, 2000).

Gas turbineGas turbine model (simple cycle) GE MS7001BDesign temperature drop, 8C 37.7 to 4.9=32.8Corresponding power increase, MW From 53.1 to 67.1=14 MWPer cent increase per degree Celsius, % 8C1 0.82Corresponding heat rate improvement, % 6

Ice makerIce maker capacity, kW (ton) 1930 (550)Evaporator type 3 shell and tube evaporatorsCondenser type EvaporativeIce maker power supply Off-peak powerIce maker power consumption (compressor, condenser, pumps, etc.)

per ton of refrigeration, kW ton11.27

Compressor (screw type) motor power, kW (hp) 522 (700)Operation period 148 h week1

Ice storage tank (cylindrical )Volume, m3 (gallons) 4300 (1.15 million)Dimensions (heightdiameter), m 924Buried depth, m 6Construction material Cast-in-place concreteStorage capacity, kWh (ton-h) 131 240 (37 400)

Inlet air cooling systemOperation mode (4 h a day, 5 days a week) Weekly cycleGas turbine inlet heat exchanger

Type Coil bank (24 coils)Surface area, m2 125Inlet air volume flow rate, m3 s1 203.4Inlet air mass flow rate (at 398C and 34% rh), kg s1 250.0

Coil leaving air velocity, m s1

1.5Moisture condensation rate at the coils, ‘ s1 (gpm) 2.5 (40)

Circulating cooling waterEntering temperature, 8C 1.1Leaving temperature, 8C 7.7Flow rate, ‘ s1 612

Cooling water circulating pumps (two centrifugal horizontal split case)Power, kW (hp) 186 (250)Redundancy: one pump is sufficient for the inlet cooling system operating

on a design day at 7.28C inlet air temperature which only results in1 MW less than design power output improvement.

EconomicsGas turbine initial (installed) cost, $ kW1 300

Inlet air cooling system installed cost, $ kW1

165Avoided cost on new peaking generating capacity, $ kW1 100


GAS TURBINE INLET AIR COOLING UTILIZING THERMAL ENERGY STORAGE 293



generating capacity. That is, the TES system installation cost was $165 kW1 of capacity

compared with an initial cost of $300 kW1 of capacity from an additional gas turbine. Table II

gives the details of another project (Anderpont, 2001) for gas turbine inlet air cooling (GTIAC)

system coupled with chilled water TES for a combined cycle power plant with district heating

and cooling. Although he projected attractive project net present value Anderpont (2001) gaveno details on economic assessments.

Based on the literature review presented in the foregoing it is seen that the application of TES

to GTIAC is site specific. Furthermore, most of the studies use a single design day cooling load.

The objective of this study is to examine the technical feasibility of using TES for GTIAC based

on cooling load profiles calculated based on hourly typical meteorological year (TMY) weather

data. The question posed now is whether to use a chiller alone for gas turbine inlet air cooling or

to use a chiller in combination with TES. The analysis is applied to one remote oil field location

(Fahud) in the Sultanate of Oman.

Table II. Chilled water TES GTIAC for a combined cycle power plant (compiled from Andrepont, 2001).

Location Florida/U.S.A.Combined cycle GT power (nominal), MW 40 (32 from GT+8 from ST)Heat recovery steam generator, kg s1 11.34 (40 823 kgh1)Cooling source and capacity, MW (ton) Electric+absorption chillers 5.043 (17 750)

Inlet air cooling system design conditionsDesign inlet air T db/T wb Temperatures, 8C/8C 35/26Design outlet air temperature, 8C 10Chilled water supply temperature, 8C 4Chilled water return temperature, 8C 21 for GT inlet air cooling and 13 for district coolingAir flow rate, m3 s1 103.45Heat exchanger 4 banks of coilsAir side pressure drop, Pa (inch H2O) 30 (1.2)

Chilled water storageType StratifiedVolume, m3 19 000Dimensions (DH ), m 35.420.4Material Welded steelCapacity, MWh (ton-h) for 200.6 (57 000) for}Inlet air cooling, MW }2000}District cooling, MW }3500Discharge duration, h 10

PerformanceIncreased GT power (from 35 to 108C), MW 26 to 34=8Heat rate improvement, % 6

Economics unpublished except ‘the NPV for the project totalling several millions of dollars’ (Andrepont,2001)

RemarksThe chillers+TES are sufficient for cooling the inlet air+district cooling. Inlet air cooling eliminated theneed for two new chillers of combined capacity of 3325 ton.





2. SYSTEM DESCRIPTION

A block diagram of a generic GTIAC system is depicted in Figure 1. The basic building blocks

are the chiller, its cooling tower, the air heat exchanger, and the interconnecting piping. The

exhaust gases of the gas turbine may be used directly to drive the sorption chiller. Some of the

available chillers are hot water or steam driven, while the others are direct fired. For this reason,

a steam boiler is incorporated as optional equipment. Cold fluid from the chiller is pumpedthrough the air heat exchanger, where the coolant is heated and returned to the chiller, while the

inlet air is cooled prior to entering the compressor. A TES system is incorporated to store the

cooling capacity required or the excess cooling generated.

The required cooling water for both the condenser and absorber of the absorption chiller is

provided using cooling tower. Alternatively, evaporative or air-cooled condensers and absorbers

might be used with some types of chillers. Including storage and its associated piping loop

increases the number of system components, but must allow the chiller and cooling tower

components to be downsized.

3. ANALYSIS

It is well known that when thermal loads fluctuate, the potential exists for storing thermal

energy (cooling or heating) to furnish the high load peaks. TES may be designed on seasonal or

diurnal bases. Seasonal cool storage is quite expensive as the volume of storage and thermal

losses are high. For example, assume a cooling load of 1 MW is to be furnished by thermal

storage such that it covers 25% of the summer months of May, June, July and August or 738 h

Figure 1. Generic inlet air cooling system.





[0.25 24 (31+30+31+31)]. Ignoring losses this translates into 738 MWh of cooling energy

stored. About 3 kg of ice is required to store 1 MJ of cooling (Dincer and Rosen, 2002). Hence,

a 7970400kg (738 3600 3) or 7971 m3 of ice is required. For a 2 m deep storage tank the

area needed is 3986 m2. This area is calculated without accounting for thermal losses which for

such a large area are quite significant considering the long storage period.If chilled water is used instead of ice different storage devices exist, their purpose is to separate

chilled water from warm water returning from the load. These are the two-tank system (also called

the empty tank design), the single tank with flexible diaphragm, the labyrinth tank where water is

forced to flow through a maze (a long zigzagging channel) and the single stratified tank. The single

stratified tank is widely used as it is simple, has low cost, and its performance is comparable with

other types. In this design the warm and cold waters are separated due to density difference. A

thermocline region (a region of high temperature gradient) exists which acts as a natural barrier that

inhibits mixing between chilled and warm waters. For tanks with well-designed inlet diffusers the

thickness of the thermocline region is normally small. In U.S.A. chilled water storage constitutes

about 34% of the cooling capacity of all cool storage systems with 60% of these systems utilize

stratified thermal storage tanks as large as 15 140 m3 (4 million gallons) (Musser and Bahnfleth,

1998). A full account of the single stratified tank theory and design is given by Zurigat and Ghajar(2002). As in the above example for ice storage if 1 MW of cooling is to be stored in chilled water

the storage volume required becomes much larger than that for the ice storage. Using the figures

quoted in Hasnain (1998), i.e. 0.089–0.169 m3kWh1 the chilled water volume needed becomes

65700–124 800 m3. Unless there is an aquifer nearby it is too high a price to pay for building a tank

or system of tanks of this volume. Note that these results are for 1 MW of storage cooling capacity.

Based on the above it is seen that under the conditions investigated seasonal storage in chilled water

storage tanks or ice bins for the location considered is seen to be prohibitively expensive.

Thermal storage on diurnal basis is common and many thermal storage installations have

been in use throughout the world. The weather conditions often determine the feasibility of cool

storage as it affects the cooling load profile. It was concluded by Dincer and Rosen (2002) that

cool storage is advantageous where the summer weather profile includes limited number of peak

demand days and large temperature variations during a given 24 h period. In addition to theweather factor the load profile determines the mode of operation of thermal storage system. For

example, office buildings normally have very low cooling loads during the night as they are

unoccupied while during the day they have high cooling load which peaks in the afternoon. This

load profile is ideal for thermal storage application in full storage mode where thermal storage

fully replaces the chiller thereby eliminating the use of electricity during the day where, when

rate schedule applies, high electric charge rates exist. In hotels and residential buildings, on the

other hand, the cooling load profiles are flatter and thus they are not suitable for full storage as

the capacity in excess of the cooling load is not sufficient for charging the storage. In this case,

partial storage or peak shaving (also called load-leveling) storage modes may be employed

depending on whether electricity rate schedule is practiced by the local utilities. It is generally

recommended that cool storage be sized to meet 20% of the peak load (Dincer and Rosen,

2002). Thus, there exist mainly two modes of operation of thermal storage:

1. Operating the chillers or ice makers during the night to charge the chilled water storage

tanks or the ice bins (charge) for day use (discharge). This way, the cooling equipment

works only during the night to make use of the low off-peak electricity charge rates and

relatively cooler temperatures. This is termed full storage option.





2. Operating the cooling equipment all the time. During the peak load, the cooling equipment

and the thermal storage work simultaneously. During off-peak or reduced cooling load

periods the cooling capacity in excess of the cooling load is stored. This is termed partial

storage option.

The second scheme is more economical in terms of investment cost as it results in smallerequipment size (Dincer and Rosen, 2002). Generally, cool storage (chilled water or ice) is

advantageous for cooling applications that have large daytime cooling loads and little or no

cooling loads at night. The next section presents the calculation results based on partial storage.

4. RESULTS AND DISCUSSIONS

As stated previously partial storage has an economic advantage over full storage, both being

applied for diurnal thermal energy storage for shaving or eliminating the peak electric demand.

The applicability of partial storage demands that the load peaks during a number of hours in the

day. A starting point in this study is to inspect the hourly ambient temperature profiles as they

are indicative of the peak air conditioning load and the peak load on electric utility thereafter. In

this work, typical meteorological year data (Zurigat et al ., 2003) were used. Figure 2 shows the

hourly ambient temperature profile for the first day of each month of the year for Fahud.

Although the profiles shown are not in magnitude representative of the temperature in the given

month but what is important here is the shape of the profile. It is seen that most profiles shown

in Figure 2 exhibit flat peaks with over 6 h duration. At first glance, similar patterns would be

Figure 2. Diurnal ambient temperature profile for the first day of each month of the year at Fahud.





expected for the cooling load which is a favourable condition for thermal storage. One must

note, however, that the temperature profiles are indicative only of the sensible cooling load. In

hot and humid conditions the latent load may dominate the total cooling load profile. In this

study, the total hourly cooling load for gas turbine inlet air cooling was calculated as the sum of

the latent and sensible components as given by Dawoud et al . (2004).For the problem at hand, i.e. gas turbine inlet air cooling the hourly total cooling load for the

whole year was calculated by Dawoud et al . (2004) based on a design compressor inlet air

temperature of 88C. It was found that a chiller capacity of 8 MW would satisfy the cooling load

for the majority of the hours of the year. This has been estimated through a sensitivity analysis

for the impact of different chilling capacities on boosting the power of a GE frame-6B gas-

turbine unit at Fahud in Oman (Dawoud et al ., 2004).

Calculations of the mean of the daily cooling load profiles were calculated for the whole year

and showed that the maximum daily average cooling load is 7.7 MW which occurs on the 9th of

June. In technical terms the profile indicates seasonal variation which, in principle, is very

suitable for seasonal energy storage. However, the example discussed at the start of the previous

section shows that this is a prohibitively expensive endeavour. Therefore, emphasis has been

focused on diurnal thermal storage, namely the partial storage. To evaluate this option the firststep is to quantify the storage capacity needed. Recall that in partial storage scheme the chillers

operate continuously. Assume that the chiller is sized at the maximum of the mean daily cooling

load. Then, it would be ideal if the excess cooling produced by the chiller during off-peak hours

is stored and is sufficient (in conjunction with the chiller) to meet the cooling demand during on-

peak hours.

The calculated daily average cooling load profiles indicate that the cooling load peaks during

summer months and there is a distinct variation in cooling load from one day to another.

Hourly cooling load variation for some days exhibit large diurnal variation a condition essential

for the applicability of thermal energy storage. But this is not consistent as in some days the

cooling load profile exhibits flat profile (see Figure 3).

A closer look at the cooling load profiles calculated shows that most of the time the peak

period is wide in span and occupies almost 8 h in the day. In fact, for the 9th of June the profileis almost flat considering the y-axis scale (see Figure 3). The potential for thermal energy storage

is evaluated using the cooling load profiles calculated for each day. For example, for the 3rd of

July (see Figure 4) the daily average cooling load, denoted by % Qc is calculated to be 5.34 MW

while the peak cooling load for that day is 9.25 MW which is the maximum for the year. For

another day in July (see Figure 5) % Qc ¼ 6:06 MW with peak cooling load of 6.8 MW.

To see whether a chiller operating 24 h on 3rd of July at 5.34 MW capacity would satisfy the

cooling load when coupled with cool storage the hourly gas turbine inlet air cooling load profile

is plotted along with the daily mean cooling load (see Figure 4) of 5.34 MW. The (+) regions

indicate excess cooling that can be stored while the () regions indicate cooling load to be

supplied by thermal storage. Clearly, for this particular day, the (+) and () areas are equal and

in case of no thermal losses occur during charge and discharge of thermal storage, then a

5.34 MW chiller would be sufficient as opposed to 9.25 MW chiller needed to satisfy the peakcooling demand. Let us assume for now that the 3rd of July is the design day based on which the

chiller and thermal storage tank sizes are determined. For 3rd of July the cooling produced by

the chiller in excess of the cooling load is 18.52 MWh while the cooling load demand in excess of

the chiller capacity of 5.34 MW is 18.52 MWh, as expected from a chiller operating at the daily

mean cooling load. Therefore, a system consisting of 5.34 MW chiller integrated with an





Figure 3. Cooling load profile for the day with maximum daily average cooling load (9th of June).

Figure 4. Hourly gas turbine inlet air cooling load for Fahud on 3rd of July.





18.52 MWh thermal storage is sufficient. Thus, a reduction in the chiller size of about 43.3% (or

3.91 MW) is achieved. This is a perfect example of the advantage of thermal storage. But, we

should remember that this is based on one specific day with a chiller sized at an average daily

cooling load. Calculations, shown later in this section, show a different conclusion. The above

figure of 18.52 MWh storage is calculated by integrating the (+) areas numerically.

The amount of cooling stored for 3rd of July (18.52 MWh) necessitates a chilled water storagetank volume of 1648–3130 m3 based on storage tank volume given by Hasnain (1998) as

0.089–0.169 m3 kWh1. If ice storage is used instead, ice bin volume of 352–426 m3 is required

based on the figures given by Hasnain (1998), i.e. 0.019–0.023 m3 kWh1. Based on the figure

quoted in Dincer and Rosen (2002), i.e. 3 kg of ice is required per MJ of cooling 200 000 kg of ice

is required or 200m3 volume. This is termed ‘min1’ in Table III below as it is the minimum size

based on the rules used to calculate the ice storage size.

To reduce the storage size one is tempted to follow the recommendation that cool storage be

sized to meet 20% of the peak load (Dincer and Rosen, 2002), i.e. 1.85 MW (0.2 9.25=1.85)

the amount of cool storage becomes 9.25 MWh assuming a time span of 5 h. Then a chilled

water storage tank volume of 735–1564 m3 or an ice bin of 176–213 m3 volume (or 100 000 kg

mass or a 100 m3 based on 3 kg ice per MJ) is required. The chiller size should be increased to

satisfy the peak cooling load when operated simultaneously with thermal storage. Trial anderror calculations based on the peak cooling load less the 9.25 MWh storage give a chiller size of

6.7 MW. If instead, 4 h duration of the peak load is assumed then a 7.5 MWh of cool storage is

required which needs 668–1268 m3 of chilled water storage volume or an ice bin of 143–173 m3

(or 81 100 kg or 81.1 m3 based on 3 kg ice per MJ) is required. A chiller size of 7 MW is needed.

These results indicate that sizing the cool storage to meet 20% of the peak cooling load results in

Figure 5. Hourly gas turbine inlet air cooling load for Fahud on July 6th.





a reduction in the chiller size by 1 MW as 8 MW chiller will do without the need for thermal

storage (Dawoud et al ., 2004). Whether a 7 MW chiller integrated with thermal storage of

7.5 MWh cooling capacity is profitable compared with 8 MW chiller without thermal storage

can only be ascertained by economic assessment. In the absence of time-of-use utility rate

structure in Oman a simple cost comparison is shown in Table III and shows that thermal

storage under the conditions discussed above is not a viable option.It should be noted that assessments based on a single day profile may be misleading. Hence,

problem analysis should consider hour-by-hour calculations as done in this work below.

Based on the above results we may select the size of the chiller to be at the daily average

cooling load of a selected design day. The day with the max hourly cooling load may seem to be

a good selection. However, as will be seen below this is not the case and the cooling load profiles

are detrimental to the success of thermal storage application. So, fixing the chiller size at 5.34

and plotting the difference between the (+) and () areas (see Figure 6) for all the days in the

year shows that a chiller of 5.34 MW capacity would experience insufficient capacity to satisfy

the cooling load during a significant part of summer months (142 days) when cooling is most

needed. So, increasing the chiller size results in less and less number of days with negative

difference (deficit). Figure 7 shows the cumulative distribution function of the deficit for

different chiller sizes. Also, the number of days with deficit is indicated. For example,for a chiller of 6.0 MW cooling capacity there is 102 days experiencing deficit. This is indicated

on the figure as 6.0::102. Based on the results shown in Figure 7 one can find the number

of days experiencing a deficit below or above a certain value. For example, for the 6.0 MW

chiller 70% of the 102 days experiencing deficit experience deficit greater than 10 MWh

(or about 71 days).

Table III. A simple economic evaluation of cool storage for gas turbine inlet air cooling basedon 3rd of July cooling load.

Chilled water storage size (m3) Ice storage size (m3)

Cool storage

(MWh)

Chiller size

(MW) Min Max Min1/Min Max

7.5 7.0 668 1268 81/143 1739.25 6.7 735 1564 100/176 213

18.52 5.34 1648 3130 200/352 426

0.0 8.0n 0.0 0.0 0.0 0.0

Coolstorage(MWh)

Chillersize

(MW)

Chillercost in

k$ at 71$ kW1

Chilled waterstorage cost in

k$ at 18$kWh1

Ice storagecost in k$

at 17$kWh1

Totalcost k$

Ch. W./Ice

7.5 7.0 497 135 128 632/6259.25 6.7 476 167 157 643/633

18.52 5.34 379 333 315 712/694

0.0 8.0n 568 0.0 0.0 568

nWithout cool storage.





Figure 6. Difference between storage and demand cooling load for 5.34 MW chiller.

Figure 7. Cumulative distribution of the difference between storage and demandcooling load for different chiller sizes.





Because the deficit is experienced during summer months calculations on monthly basis are

shown in Figure 8 for a 6.0 MW chiller. The designation month (days) indicate the number of

days with deficit in the month indicated. For example, 8 (27) indicates that for a 6.0 MW chiller

integrated with thermal storage 27 days in August experience deficit. Similarly, 3 days in April

and also in October experience deficit. Clearly, August experiences the highest deficit as 70% of the 27 days (i.e. 19 days) experience deficit of over 25 MWh. The conclusion out of these results

is that higher capacity chiller (>6.0 MW) is needed if one is to satisfy the cooling load during

summer months.

In calculating the size of cool storage and the chiller size it was assumed that no thermal losses

occur. To account for the latter we note that thermal losses are of two types:

1. Heat transfer from the storage tank and piping to the surroundings. This is applicable to

both ice and chilled water storage tanks.

2. Heat losses due to blending in stratified thermal storage during charge and discharge

cycles.

If we introduce thermal storage effectiveness as the ratio of cooling recovered over cooling

stored then the thermal storage size (and the chiller as well) may be sized based on 90%effectiveness (5% loss during charge and 5% during discharge). Hence, the storage size would be

10% higher than the calculated one and the chiller size would also be higher. The chiller size of

8 MW selected for gas turbine inlet air cooling (Dawoud et al ., 2004) would do well without TES

(see also Table III). For proper sizing of both the chiller and the storage detailed dynamic

Figure 8. Monthly cumulative distribution of the difference between storage and demandcooling load for 6.0 MW chiller.





system simulations coupled with economic assessment model would be needed. However, the

simplified analysis done in this work revealed the main characteristics of integration of thermal

storage with gas turbine inlet air cooling for a specific location where hour-by-hour cooling load

and weather data are considered. Hence, based on the results presented and the simple economic

assessment (Table III) TES is not a viable option for gas turbine inlet air cooling as it did notresult in reduction in the chiller size. The main reason behind these results is the shape of the

cooling load profiles as in any given day during summer time gas turbine inlet air cooling is

required all the time. This is in contrast with cool storage applications in commercial or public

buildings where the cooling load profiles have distinct peaks of short duration.

5. CONCLUSIONS

In this work, the thermal storage option for gas turbine inlet air cooling is assessed based on

hourly weather data and cooling load profiles for a remote oil field location (Fahud) in Oman.

The analysis is based on hour-by-hour calculations of the gas turbine cooling load using Typical

Meteorological Year data. Thermal storage capacity was calculated for different chillers sizes. Inthe absence of time-of-use utility rate structure (as in Oman) the only important parameter that

diurnal thermal storage will affect is the reduction in chiller capacity resulting in a reduction in

both the first and operating costs irrespective of the chiller type. It was found that diurnal cool

storage in partial storage mode does not result in reducing the chiller size. Also, despite the

seasonal variation in cooling load, under the conditions investigated seasonal storage in chilled

water storage tanks or ice bins for the location considered is shown to be prohibitively expensive

and thus not recommended. Thus, it is concluded that the cool storage in either ice or chilled

water forms is not viable for the considered location. Also, it must be noted that assessments of

thermal energy storage option based on a single cooling load profile proved to be misleading.

Hence, problem analysis should consider hour-by-hour calculations as done in this work.

ACKNOWLEDGEMENTS

This work is funded by the Petroleum Development of Oman (PDO) under contract No. 2002-52.

REFERENCES

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er.1148] y. h. zurigat; b. dawoud; j. bortmany -- on the technical feasibility of gas turbine inlet...

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