Design for Blast Furnace Gas Firing Gas Turbine

Toyoaki KOMORI
Gas Turbine Engineering Section Power Systems Headquarters Mitsubishi Heavy Industries, Ltd.
JAPAN

Nobuyuki YAMAGAMI
Gas Turbine Engineering Section Power Systems Headquarters Mitsubishi Heavy Industries, Ltd.
JAPAN

Hiroyuki HARA
Gas Turbine Integration Group Takasago Machinery Works Mitsubishi Heavy Industries, Ltd.
JAPAN

ABSTRACT
In the past natural gas was used as the main fuel for heavy-duty type gas turbine. Because, the natural gas was the best fuel
considering cost and availability. But recently the cost of natural gas presents an increasing trend and its future availability is
not very clear. Therefore, there is a clear trend to use alternative fuels and gas turbines should be capable of burning a variety
of gas fuels including low heating value gases (e.g., Synthetic gas and steel mill gas), landfill gas and others.
Particularly, Blast Furnace Gas (hereinafter abbreviated as BFG) is by-product gas from steel work and its amount is huge.
Therefore, there is a strong requirement to utilize BFG for high efficiency and large capacity Gas Turbine.
Compared with natural gas, BFG vary in hydrocarbon composition, physical properties, impurities and others. In order to use
BFG in the gas turbines, advanced technology modifications to the combustor and combustion system are necessary.
Now, Mitsubishi Heavy Industries, Ltd. (MHI) has developed and delivered BFG firing gas turbine based on many low calorie
gas firing gas turbine experiences and now we are commissioning the world first F class BFG firing GTCC
This paper introduces the MHI design concepts for gas turbines utilizing by product gas in steel works and a recent application
of F class gas turbine firing BFG.

KEY WORD
Gas Turbine, Combustor, BFG, Low Calorie

CONTACT
Mailing Address: 2-1-1 Shinhama Arai-Cho Takasago, Hyogo 676-8686 JAPAN
Tel : +81-794-45-9830
Fax : +81-794-45-6936
E-mail Address: hiroyuki_hara@mhi.co.jp

1. INTRODUCTION
There is growing interest in saving energy by applying modern, high firing temperature gas turbines in electric utility and
industrial facilities.
Japanese industries in particular want to use their by-product gas to best effect, and hereby reduce energy costs. Because, the
energy source such as coal, gas and oil is the limited in Japan. Therefore, the energy cost of Japan is more expensive than the
other countries.
In order to meet this requirement of Japanese industries, has been continuously developing a high efficiency gas turbine,
embodying the state of the art in industrial gas turbine high-temperature turbine technology.
In recent steel industry field, the energy conservation has been expedited and the less oil blast furnace operation has been
achieved. As a result, the balance of energy source in steel work has considerably altered. In this situation, the gas turbine
combined cycle power plant is drawing attention as a high thermal efficiency power generation system, utilizing increased
by-product gas effectively.
Under such circumstances, the design and development work are continuously conducting in MHI since 1950, based on our
extensive experience with the by product gas firing technology in order to develop highly efficient, blast furnace gas firing
combustors.
Based on the successful research & development and existing units we delivered the first unit of Low Calorific Heat (1,050
kcal/m3N) BGF firing F Class gas turbine (1,300C class) to Kimitsu Cooperative Thermal Power Co,. It is will be put into
commercial operation in 2004. The introduction of gas turbine will remarkably improve the overall power generation
efficiency of the power company.
This paper outlines the experiences of the high-efficiency gas turbine combined cycle power plant, firing BFG in the steel
works, and technical key points in the plan of new power plant.

1
2. SUMMARY OF FUEL GAS APPLICICATION
As of April 2004 MHI has gotten orders for a total of 429 units. As can be seen in Table 1, these gas turbines are designed to
burn a variety of fuels.
Table 1. Mitsubishi gas turbine fuel applications (as of April 2004)
Fuel
1. Single Fuel
(1) Natural Gas, LNG 161
(2) Refinery Process Gas, LPG 19
(3) Steel Mill Gas 10
(4) Distillate Oil 63
(5) Other 1
2. Dual Fuel
(1) Natural Gas /Distillate Oil 150
(2) Natural Gas/Crude oil 6
(3) Refinery Process Gas/Distillate Oil 7
(4) LPG/Distillate Oil 7
(5) Steel mill Gas/Distillate Oil 2
(6) Mine Gas/Distillate Oil 1
(7) Synthetic Gas/Distillate Oil 2
Total 429

Figue.1 shows our fuel gas experience depending on the fuel gas heating value. Our gas turbines have operated successfully
burning various fuel gases with heating value ranging from 600 kcal/m3N to 20,000 kcal/m3N. In particular, we have
successfully operating experience in Low heating value gas, such as less than 1,000 kcal/m3N.

COAL & VR GASIFICATION

Air Blown Oxygen Blown LPG & B-B GAS

N.GAS & REFINERY GAS

REFINERY GAS

COG&COAL MINE
BFG/LDG/COG MIXED GAS

BFG

0 500 1,000 2,000 5,000 10,000 20,000 50,000

Calorific Value ( kcal/m3N )

Fig.1 Mitsubishi gas turbine fuel experiences

2
3. DEVELOPMENT AND HISTORY OF BFG FIRING GAS TURBINES
The first BFG firing gas turbine (850 kW) in Japan, of our unique design, was developed in 1958 and delivered as a prime
mover for blast furnace blower to Yawata Steel Corp. (present Nippon Steel Corp.) Yawata Works. NO. 2 larger unit (4000
kW) was delivered in 1964 to the same Works. In 1965, we delivered the model MW171 gas turbine (15000 kW) to
Sumitomo Metal Industries, Ltd. Wakayama Works.
In Europe, about 30 BFG firing gas turbine power plants were reportedly constructed from 1950 to 1965. The inlet
temperature of these gas turbines seems to be about 750C and regenerative cycle is adopted to most of them for the
improvement of thermal efficiency. After then, raising the gas temperature and improving the efficiency of components have
increased the thermal efficiency of the gas turbine itself.
Further, the energy recovery efficiency at the waste heat boiler is improved because of increase of the gas temperature.
Accordingly, the overall thermal efficiency of the gas turbine combined cycle power plant was markedly improved. In 1982,
Mitsubishi high efficiency model M151 gas turbine was delivered to Nippon Steel Corp. Kamaishi Works, with exceeding
1000C of inlet temperature.
After developed M151, we have started to increase the output more than 100 MW with D Class gas turbine (1,150C Class)
depending in the many combined cycle plant operations.
MHI, in 1987, delivered a large capacity (145 MW) high efficiency gas turbine combined cycle power plant to the Chiba
Works of Kawasaki Steel Corporation (present JFE Steel Corporation). This power plant uses low caloric by-product gas
generated within the Chiba Works and has obtained a world record plant thermal efficiency of 46% (LHV base, net).
According to this 145 MW large capacity combined cycle plant operating experience, we have delivered the similar concept
plant to Mizushima Joint Thermal Power Co., and Fukuyama Joint Thermal Power Co., which is 100C higher gas turbine inlet
temperature as DA Class, in 1994 and 1995.
And we delivered the first export unit of BFG firing gas turbine combined cycle plant to UNA, Netherland in 1997 depending
on the successful operating records of above units. Table 2 shows the above experience and Fig. 2 shows the trend of gas
turbine inlet temperature in BFG firing.
Table 2. Experience list of low heating value gas firing gas turbine
GT Unit Fuel
Combined
Customer Application Start-Up Model Rating Stand- Combustor
Plant Rating Main
(Incl.G.C) By
Nippon Steel Co. BFG
Power Supply 1958 - 850 kW - - Single-can
Yahata Works (770kcal/Nm3)
Nippon Steel Co. BFG
Power Supply 1964 - 4,000 kW - - Single-can
Yahata Works (770kcal/Nm3)
Co-generation
Sumitomo Metal Co. BFG
(WHB,G-M,BLO 1965 MW171 15,000 kW - - Single-can
Wakayama Works (750kcal/Nm3)
WER)
Shikoku Elec.Pwr Co. COG
Combined cycle 1970 MW301 34,000 kW 16,000 kW - Multi-can
Sakaide PS (750kcal/Nm3)
Co-generation
Mitsubishi Coal Mining Co. Coal mine
(with 1970 MW101 9,000 kW - OIL Multi-can
Minami Oyubari Plant (4,700kcal/Nm3)
air-preheater)
Nippon Steel Co. Combined cycle BFG
1982 M151 16,000 kW 23,000 kW OIL Single-can
Kamaishi Works with existing STs (670kcal/Nm3)
JFE Steel Co. Combined cycle BFG/COG Multi-can
1987 M701 87,400 kW 145,000 kW -
East Japan Works (Single Shaft) (1,000kcal/Nm3) with BP-V
Mitsubishi Gas-Chemical Co. Co-generation BFG/COG
1988 MF111 16,250 kW - OIL Multi-can
Mizushima-factory (WHB) (2,400kcal/Nm3)
Nippon Steel Co. Co-generation 1989 LDG
M251 30,200 kW - OIL Multi-can
Hirohata Works (WHB) (1,815kcal/Nm3)
Nissin Steel Co. Combined cycle BFG Multi-can
1989 M251 32,000 kW 50,000 kW -
Kure Works with existing STs (700kcal/Nm3) with BP-V
Nakayama Steel Co. Combined cycle BFG/LDG Multi-can
1991 M151 15,000 kW 37,000 kW -
Funamachi Works (Single Shaft) (1,00kcal/Nm3) with BP-V
Mizushima Joint Thermal Combined cycle BFG/M Multi-can
1994 M501 86,250 kW 145,000 kW -
Power Co. (Single Shaft) (965kcal/Nm3) with BP-V
Fukuyana Joint Thermal Combined cycle BFG/M Multi-can
1995 M501 86,250 kW 145,000 kW -
Power Co. (Single Shaft) (965kcal/Nm3) with BP-V
UNA Combined cycle BFG/COG Multi-can
1997 M701 87,400 kW 145,000 kW -
Netherlands (Single Shaft) (1,000kcal/Nm3) with BP-V
Nippon Steel Co. BFG Multi-can
Combined cycle 2001 M251 31,000 kW 65,000 kW -
Ooita Works (700kcal/Nm3) with BP-V
Nippon Petroleum
Combined cycle Syn gas Multi-can
Refining Co. Ltd. 2003 M701F 301,000 kW 431,000 kW OIL
(Single Shaft) (2,680kcal/Nm3) with BP-V
Negishi Refinery
Kimitsu Cooperative
Combined cycle BFG/COG Multi-can
Thermal Power 2004 M701F 180,700kW 300,000 kW -
(Single Shaft) (1,050kcal/Nm3) with BP-V
Company, Inc.

3
 1,300C

(C)
1,300
1,250C (F Class)
(DA Class)
Turbine Inlet Temperature 1,200
1,150C
(D Class)
1,100

1,019C
1,000

85 90 95 00 05
Year
Fig.2 Trend of Mitsubishi BFG firing gas turbine inlet temperature

In Kimitsu Cooperative Thermal Power Co., a newly developed Mitsubishi model M701F gas turbine, firing BFG, has been
installing for the highest thermal efficiency in the BFG firing power plant. The model M701F gas turbine is designed for
firing BFG with an inlet temperature exceeding 1,300C. It is the first gas turbine firing BFG for F Class, in the world.

4
4. DESIGN CONSIDERATION ON BFG FIRING GAS TURBINE
Comparing natural gas as clean fuel, BFG has the special characteristics such as low calorie, dirty dust contents and so, on.
Table 3 shows the fuel gas characteristics comparison.
Table 3. MHI Typical fuel characteristic table
Oxygen Air
Mixed
FUEL LNG BFG Blown Blown
BFG
Syngas Syngas
CH4 88.0 - 2.02 0.21 2.9
C2H6 7.11 - 0.24 - -
Composition (vol.%)

C3H6 3.58 - - - -
C4H10 1.24 - - - -
C5H12 0.05 - - - -
N2 0.02 55.4 51.02 0.51 30.7
CO - 22.4 20.88 50.07 11.0
CO2 - 20.4 19.78 3.21 10.9
H2 - 2.0 6.05 44.66 16.8
Ar - - 0.01 1.03 0.80
LHV (kcal/m3N) 9,762 706 1,000 2,680 1,020
Flammability Range ( - ) 3.2 2.1 4.2 25.8 9.8
Burning Velocity (cm/sec) 37 3 16 169 44

The standard gas turbine is designed for natural gas (i.e., LNG). If the fuel properties as BFG are different from standard
natural gas, suitable modification of the fuel control system, supply system, combustor etc. will be required. Depending on
the long term operating experience, MHI has already established the key technologies for BFG utilizing. Table 4 shows the
summary of them.

Table 4. Development technology for BFG firing gas turbine

BFG CHARACTERISTIC KEY POINT TECHNOLOGY

Narrowed Flammability Zone Suitable Fuel Air Ratio Multi Can Type Combustor
Low Burning Velocity with Air Bypass Valve

Low Calorie Large Capacity Gas Supply Compressor with Variable Pitch
System Vane
Fuel Gas Return System

Dirty Dust Dust Removal Wet Type E.P.

G.C. Cleaning System

Toxic (CO) Prevention of BFG Leak to Gas Cooler

Outside Advanced Shaft Seal
The key technology is the best matching design for compressor, combustor and turbine to maintain the stable operation in low
heating value. The above design considerations are mainly described here in after.

5
4.1 Heating value
The heating value is the key parameter to decide the modification of gas turbine components. In the case of decreasing heating
value, a modification will be necessary. Our design modification concepts are shown on Table.5.

Table 5. Design modification for various heating value

High Standard Medium Low
Heating Value 10,000 to (Natural Gas) 2,000 to 600 to
5,000 kcal/m3N 8,500 kcal/m3N 7,000 kcal/m3N 2,000 kcal/m3N
Air Compressor Standard Standard Standard Modification
Standard Standard
Combustor Standard Modification
(Minor mod.) (Minor mod.)
Turbine Standard Standard Standard Standard
Standard Standard
Fuel system Standard Modification
(Minor mod.) (Minor mod.)

To maintain the reliability and the hot component changeability, the identical turbine parts are applied for the various heating
values. However, the other parts will be modified depending on the heating value. For your reference, we explain the
modifications introducing to BFG.

6
4.1.1 Air Compressor Modification
Huge fuel gas flow is fed to gas turbine when BFG firing since its heating valve is lower. Therefore, if the standard gas
turbine as natural gas is applied, the surge problem on air compressor and over load on turbine will occur. So, to maintain the
same gas flow on turbine, the air compressor is modified to decrease the air flow by adjusting the high of compressor blades
( tip cut ). This air compressor modification is applied in the existing operating units.

Air 98% Air 65%

Comp. Turb. COM

Comp. Turb.
Gen Comb. Gas Comb.
Gen
Comp.
Bypass
N.Gas 2% Gas Cooler BFG 35%

Exhaust Gas 100% EP Exhaust Gas 100%

BFG Line
Natural Gas Line

Fig.3 Flow balance vs. heating value

On the other hand, there is air bleed system to correspond to BFG firing shown on Fig.4. In case of air bleed system, the air
compressor parts are not necessary to be modified. However, the performance is worse than the airflow cut modification shown
on Fig.3 during the normal BFG firing mode, if there is no chance to utilize the bleed air.

Air 98%
Bleed Air 33%

COM
Comp. Turb.
Gas Gen Comb.
Comp.
Bypass
Gas Cooler BFG 35%

EP Exhaust Gas 100%

BFG Line

Fig.4 Bleed air system on BFG firing gas turbine

7
4.1.2 Combustor Modification
When burning BFG for gas turbine, the silo type combustor with pilot-torch is the suitable from the point of view of stable
combustion only. However, considering the total evaluation of gas turbine including the reliability of turbine blades and others,
the multi-cannular type combustor is the best type.
This combustor design with new concept is focused from the following points;
Large amount of the air must be supplied for the combustion because of its substantial lower heating value and this gives the
disadvantage for the control of the fuel to air ratio. Stable and high efficient combustion is required within the turndown ratio
2.5 in the gas turbine combustors. The disadvantage for the combustor basket cooling because only a less air is available for
cooling.
To solve the above, multi-cannular combustor design is selected because of the smaller combustor basket surface area are
available compared with the large silo type combustor design.
The specially designed air bypass valve is applied to compensate the air flow supplied to the combustion area
Combustor configuration is illustrated on Fig.5.
Air bypass valve is equipped on the transition piece and adjusting the valve openings can regulate airflow supplied to the
combustion area.

1. BFG+COG Fuel gas

1 6 2. Spherical elbow
3. Combustor
4. Air for combustion
5. Compressor discharge air
6. Variable ring
3 7. Air bypass valve
2
7 8 8. Bypass air
9 9. Transition Piece
4 10. Turbine
10
5

Fig.5 Combustor configuration

Prior to the combustor detail design, joint combustion development rig tests were carried out befitting the actual blast
furnace/coke oven gas in the Steel Work. Rig test results are summarized as follows;
100
Efficiency%
Combustion

90

80
Full Open 90
Bypass valve
Angle (deg)

45

Full Close 0
0 50 25
75 100
Load (%)
Fig.6 Combustion efficiency improvement using bypass valve

Stable and high efficient combustion can be obtained under the expected operating fuel to air ratio including no-load condition
and the full load condition.
Under the part load condition, the air bypass valve improved the combustion efficiency as shown on Fig.6 .

8
4.2 Performance impact
Comparing natural gas firing gas turbine combined cycle plant, thermal efficiency of BFG firing is reduced. The approx.
10 % as relative is lower for combined cycle plant base and 15% as relative is lower for gas turbine base.
The above efficiency drop could not be recovered since the thermodynamic theory of BFG firing gas turbine is different from
natural gas firing. Main factors for the above is the compressor power and turbine output.
First, we explain the effect of turbine output between natural gas and BFG. Fig.7 shows turbine heat drop for both fuel gases.
K 1

R { 1 ( P 2 / P1) }
K
h = T 1
K

P1 K 1
T1 h ; Heat Drop
T1 ; Turbine Inlet Temp.
h P1 ; Turbine Inlet Press.
P2 ; Turbine Outlet Press.
P2 K ; Specific Heat Ratio
R ; Gas Constant
; Efficiency

N.Gas BFG
Combustion gas CO2 Content % 4.1 16.7
K - 1.31 1.28
R kgfm/kgk 29.91 27.71
h % 100 (Base) 95
[Remarks]
1. =Constant
2. P2/P1=1/15
Fig.7 Effect of turbine output

When firing BFG, CO2 content level in turbine working fluid as combustion gas is increased. As result of CO2 increasing,
turbine output of BFG firing is reduced to be 95% from natural gas firing.
Gen. Output = Lt - Lc=46.9 Gen. Output = Lt Lc - Lgc=37.8
Thermal Efficiency =1.0 Thermal Efficiency =0.85
Lc=52.3 Lt=100 Lc=38.8 Lt=95

Lgc=17.7
Comp. Turb. Comp.
COM Turb.
Lt=95
Gen Gas Gen
Comp.

Heat Input 1.0 Heat Input 0.95

Turbine Comp. Power

Fuel Flow Air Flow Gen. Output Ther.
Output
Gf Gc Lc Lgc Lc+Lgc Ratio Kw=Lt-(Lc+Lgc) Eff.
LT
LHV Heat
Flow Flow
Fuel Kcal/m3 % Ratio Input Ratio % % % - % Ratio Ratio
% %
N Ratio
N. Gas 8,800 100 2.0 1.0 1.0 98.0 1.0 52.3 - 52.3 1.0 46.9 1.0 1.0
BFG 1,000 95.0 28.5 14.3 0.95 71.5 0.73 38.8 17.7 56.5 1.08 37.8 0.81 0.85
[Remarks]
1. Flow balance is Turbine exhaust gas base.
2. Power/Output base is Turbine output of natural gas firing.
Fig.8 Effect on total performance

Fig.8 shows the total performance effect considering compressor power and turbine output. When evaluating total
compressor power coupled with air and BFG, its power is 8% increasing than natural gas firing due to the less compressor
efficiency. Therefore, 19% on generator output is lower. On the other hand, fuel gas heat input is reduced to be 95% since
less compressor efficiency. Combined with the above output and heat input variations, thermal efficiency on BFG firing is
reduced to be 85% than natural gas firing.

9
5. PLANT OUTLINE AND FEATURES OF F CLASS BFG FIRING COMBINED
CYCLE PLANT
5.1 Plant outline
The overall equipment layout shown in Fig. 9 and the plant system flow shown in Fig. 10.

5.2 Plant features

The features of the plant are described below.
(1) A combined cycle power plant system is selected in order to obtain a high thermal efficiency. The design value for plant
thermal efficiency is taken as 50% (LHV base).
(2) A multi-cannular combustor with air bypass valve is developed and installed in order to allow low caloric gas operation
over the entire operating range (from turbine start-up to full load operation).
(3) The gas turbine, generator, steam turbine and gas compressor are coupled on a single shaft. (The gas compressor is
connected to the shaft through step up gear.) (see Fig. 11) The total shaft length is the approx. 60 meters long and in
order to prevent mutual interference resulting from longitudinal thermal expansion of the shaft, both ends of the steam
turbine shaft are fitted with flexible couplings.
(4) The plant is started up by the main steam turbine using steam from an existing boiler. This eliminates the need for
start-up device.
(5) A multi-cannular low NOx combustor with air bypass valve is provided so that low NOx operation could be carried out
without having to inject steam or water into the combustor.
Steam Turbine Gas Turbine
Gas Compressor Generator
Gas Cooler

Approx. 60 m
HRSG
Stack
Gas
Mixer Inlet Air Filter
E.P.
Transformer
Approx. 200 m
BFG COG
Fig. 9 Overall equipment layout

LP
IP
By-pass
HP
Valve

Step up
Gear
Gas ST Gen
Cooler Gas
Turbine
Gas Condenser HRSG
Comp
Filter
Mixer Stack
EP Cold reheat
Air

B COG Condensate Pump

BFG Main Line

Fig.10 Plant system flow

10
 Fig. 11 Shaft arrangement
The gas turbine, generator, steam turbine, and gas compressor are could on a single shaft.
(6) A gas decompression device with direct water cooling system, developed by Mitsubishi, is installed to enable to send
back the high temperature and high pressure gas discharged from the gas compressor outlet to the gas supply line in an
emergency or during normal shutdown.
(7) A full automatic control system makes it possible for one or two operators to control and monitor the plant from a central
control room. This eliminates the need on-site control.

5.3 Equipment features

5.3.1 Gas turbine proper
For this plant, we selected our Model M701F, a simple open cycle, single shaft gas turbine. The reliability of this model has
been well established from the successful operating record with natural gas and distillate oil.
In order to convert this standard model from natural gas firing to low caloric by-product gas firing, the design modifications
shown on Table 5 are made.

5.3.2 Gas compressor

We selected a high efficiency axial flow type gas compressor which was scale designed from a gas compressor model with an
extensive operating record.
In order to minimize a drop in efficiency under partial load, we control the fuel gas flow with variable pitched stator vanes
when operating at loads of 65% or more. A dry-type segment seal is used for the shaft seals. Furthermore, in order to
prevent gas leaks, nitrogen gas is injected between the segment seals at a pressure slightly higher than the ground pressure.

5.4 Status of site

The construction of this world first BFG firing F class combined cycle plant was begun in 2001. This plant is now under the
last stage of trial run and reaches full load operation as scheduled. In this summer, the plant will be put into commercial
operation.

Fig.12 Overall plant view

11
6. CONCLUSION
We presented the experience and design consideration for BFG firing gas turbine.
We have developed and delivered BFG firing gas turbine based on many low calorie gas firing gas turbine experiences and
now we construct the world first BFG firing F class GTCC. This world first BFG firing F class gas turbine combined cycle
plant is now under trial run and this plant will be put into commercial operation in this summer.
For effect utilization of low calorie gas, we will continue the further technical development.

References
(1) Y. Mori, K. Mikata and M. Murono, 1985, High Efficiency Gas Turbine and Combined Cycle Power Plant, Mitsubishi Technical Review 1985.
(2) H. Takano, M. Okishio, and T. Hashi, 1989, Design and Operating Results of 145 MW Low Caloric Gas Fired Combined Cycle Power Plant for Chiba
Works of Kawasaki Steel Corporation, Mitsubishi Technical Review 1989.
(3) H. Hara, T Komori, H Arimura and Y. Kitauchi, 2003, Design for F Class Blast Furnace Gas Firing 300 MW Gas Turbine Combined Cycle Plant,
International Gas Turbine Congress 2003 Tokyo, (November 2-7, 2003).
(4) K. Tanaka, K. Nishida, W, Akizuki and T. Komori, 2003, MHI combustor development for Low Calorie fuel firing, Power-Gen International 2003 Las
Vegas, (December 9-11, 2003).

12