Very Large Diesel Engines for Independent Power Producers and Captive Power Plants
Contents
Page Abstract . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3
Preface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . · · · · · · . . . . . . . . . . . .
3
The Diesels and their Competitors. . . . . . . . . . . . . . . . . . . . . . . . . . . . .
4
Diesel Engines in Stationary Applications . . . . . . . . . . . . . . . . . . . . . . .
5
Load Flexibility . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
6
Fuel Linkage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
6
Fuel Flexibility . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
8
Emissions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9
Two-stroke Engine Driven Plants. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9
The Bahamas Project . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 Literature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
1
Very Large Diesel Engines for Independent Power Producers and Captive Power Plants
Abstract During recent years, an increasing demand has been experienced in the stationary diesel engine market for large diesel units for reliable and fuel efficient power plants in the range of 30-250 MW, based on cost effective refinery residuals. This demand is being met by modern marine-derivative medium speed diesel GenSets and, for the larger units, by two-stroke low speed crosshead uniflow scavenged diesel engines, the latter capable of burning almost any fuel available on the market, whether liquid or gaseous. This paper will deal with service experience gained from two-stroke low speed diesel engines and their fuel capability, as well as describe the latest 30 MW extension of the Clifton Pier plant on the Bahamas, owned by the Bahamas Electricity Corporation (BEC).
Engine output Pmech (kW) 70,000
60,000
50,000 Four-stroke Medium speed
Two-stroke Low speed
40,000
30,000
20,000
10,000
0 300
200
100
400
500
600
700
Engine speed, r/min
Fig.1: MAN B&W engine programme
Preface Diesel engines for power generation from MAN B&W Diesel are offered in the following categories, see Fig. 1: • High speed and medium speed engines, ranging from 0.5 to 22 MW per unit, from MAN B&W Diesel’s companies in Germany, Denmark, France and the UK. • Two-stroke MC engines from MAN B&W Diesel, Copenhagen, Denmark. These are low speed engines with unit outputs of up to 68 MW. The engines are built by MAN B&W licensees as listed in Fig. 2.
China HHM ! Shanghai HHM DMD YMD
Korea Hyundai HSD Ssangyong
1980 1994 1980 1989
1976 1983 1984
Croatia Uljanik Split
1954 1984
Poland Cegielski
1959
Spain IZAR- Manises
1941
Japan Mitsui ! Makita Hitachi Kawasaki
Russia Bryansk
1926 1981 1951 1981
1959
Fig. 2: MAN B&W two-stroke licensee family
3
The low speed two-stroke engines match any requirements of medium to large size projects, whether for island utilities or large IPP or captive plants, up to say 250-300 MW, Fig. 3. Guam, Enron units Availability Reliability Scheduled outage Unscheduled outage Load factor
% % hrs. hrs. %
D8 96.3 99.0 234 84 82
D9 95.1 97.6 217 207 83
Low speed engines are particularly suited to digest any fuels with high efficiency and good reliability. Engineers are well acquainted with the technology through wide experience from the world merchant fleet, which is dominated by MAN B&W low speed two-stroke engines.
The Diesels and their Competitors Looking at the prime mover options available to the end-user today, and comparing their efficiencies, we can see that in the relevant range, say 12-68 MW per unit, Fig. 4, the two-stroke diesel engine is unrivalled as the most fuel efficient prime mover, whether compared with medium speed engines, steam turbines or single-cycle or combined cycle gas turbines.
Fig. 3: Guam, 90 MW Enron power plant
Thermal efficiencies % 55 Low speed diesel engine
Combined cycle gas turbine
50 45 Medium speed diesel engine
40 35
Gas turbine 30
Steam turbine
25 20 1
5
10
Fig. 4: Power efficiency comparison at ISO 3046
4
50
100
500 Unit capacity (MW)
Diesel Engines in Stationary Applications The MAN B&W Diesel engines are always matched to the actual climatic conditions of the site, with due allowance for seasonal variations. With demanding site conditions, medium speed engines sometimes call for slight derating, whereas this is not required for low speed diesels in which an acceptable combustion chamber heat load is maintained by modification of the heat rate of the engine. A comparison of deratings, as a function of ambient conditions for the various combustion engines on the market, is shown in Fig. 5, revealing the insensitivity of the low speed diesel engines to ambient conditions, when compared with other internal combustion machines. When one is comparing the various prime movers, differences in the various ISO standards should be considered, Fig. 6.
% Power
Low speed diesel
Power restriction
100 Medium speed diesel
90 Gas turbine
80 20
% Power 100
25
30
35 45 40 o Ambient temperature C
Overall efficiency (%) Low speed diesel 50 Medium speed diesel 49
Efficiency, low speed diesel
90
48 80 47 Efficiency, medium speed diesel
25 35 Min.
35 42 Design
46
Air inlet temperature oC Cooling water temperature oC Ambient conditions
45 52 Max.
Fig. 5: Influence of ambient conditions on rating of internal combustion engines
Gas turbines ISO 3977
Diesel engines ISO 3046
Air temperature
oC
15
25
Coolant temperature
oC
15*)
25
Barometric pressure
mbar
1013
1000
%
60
60
Relative humidity
*) If applicable Fig. 6: Comparison of ISO conditions
5
Load Flexibility To cater for load variation in plants, say up to 300 MW, it is quite common to install a number of equally-sized units. The load fluctuations called for by users are then managed by sequential starting and stopping of the units. This configuration and running principle is very often seen with the traditional gas turbines, because of their poor part-load efficiency behaviour. As shown in Fig. 7, the efficiency of diesel engines, and especially of two-stroke low speed diesels, is almost independent of load over a wide load range. Furthermore, low load running without any limitation is possible down to approx. 20% of Maximum Continuous Rating (MCR), and the engines are able to run at 10% overload for one hour every 12 consecutive hours. It is therefore fully feasible to install the largest two-stroke diesel units applicable, i.e. as few units as possible for a given plant size, thereby shortening plant construction time, reducing the space requirement, as well as reducing first cost, running cost and maintenance load, while still ensuring high efficiency and reliability, irrespective of the plant running programme.
Fuel Linkage As most diesel plants are installed in areas which depend on liquid fuels with scarce and unstable supplies of high quality fuels, it is of paramount importance for the feasibility of a project that the acceptable range in the guideline fuel oil specifications of the various prime movers is considered at a very early stage. Fig. 8 shows the difference in fuels that can be used in gas turbines and diesel engines in general. Essentially, diesel engine combustion comprises a series of batch processes, whereas the gas turbine uses continuous combustion. In the batch process, higher initial temperatures and pressures can be used than in the gas turbine, since the exposed components are cooled at the end of each process and between processes. The thermal
6
% Thermal efficiencies 60
Low speed diesel 50 Medium speed diesel 40 Combined cycle gas turbine 30
20
Steam turbine
Gas turbine
10
Load %
0 50
60
70
80
90
100
Fig. 7: Typical part load efficiencies of prime movers
Diesel engines CIMAC-H55
Designation Density at 15 oC Kinematic viscosity at 100 oC Flash point Carbon residue Ash Water Sulphur Vanadium Aluminium + Silicon API gravity (min) Sodium plus potassium Calcium Lead
kg/m3 cSt o C % (mm) % (mm) % (mm) % (mm) ppm (mm) mg/kg o API ppm (mm) ppm (mm) ppm (mm)
1010 55 > 60 22 0.15 1.0 5.0 600 80
* 200 200 10
* experience, no limitations in official specification ** Incl. sediment *** on 10% destillation
Fig. 8: Diesel engine and gas turbine liquid fuel guideline specification
Gas turbines ASTM 2880 876 50 66 0.35 *** 0.03 1.0 ** 1.0 0.5-2 (10) 35 1 1 1
Cylinder pressure
Low speed (two-stroke) 60/103.4 = 0.58 sec/rev.
A
Medium speed (four-stroke) 60/600 = 0.10 sec/rev. A: Fuel injection period (~22 deg. crankshaft) ~35 msec for two-stroke ~ 9 msec for four-stroke B: Possible max. ignition delay ~ 20 msec for two-stroke and four-stroke B
Sec 1 rev
In medium speed engines all fuel may have been injected before ignition, i.e. detonation may occur if delay is long due to fuel quality.
Fig. 9: Fuel acceptance
efficiency can therefore be higher in the diesel than in the gas turbine. Each piston stroke constitutes a batch process, and the slower it can be while still maintaining its adiabatic thermodynamics, the more efficient it can be. An added advantage of the slow process that takes place in a low speed engine is that the ignition delay which
may occur, depending on fuel quality and engine geometry, has less impact on a low speed engine. While a low speed engine often gives a longer ignition delay than its medium speed counterpart with the same fuel, the ignition delay is still proportionally shorter in a low speed engine, in terms of degrees crankshaft angle.
As illustrated in Fig. 9, the typical fuel injection period in terms of milliseconds is 3-4 times longer in a low speed engine, i.e. up to 35 msec. Typical ignition periods are up to 10 msec in a medium speed engine and up to 20 msec in a low speed engine. Hence, in a worst-case situation using a fuel with a tendency towards long ignition delay, all the fuel for a stroke may have been injected in a medium speed engine before ignition takes place. Ignition can then take the form of a detonation which harms the piston, piston rings and bearings. In the low speed engine, even with a long ignition delay, less fuel is injected before ignition. Thus, the risk of detrimental detonation is over. This is one of the reasons why a low speed engine is considered more forgiving than other types of machinery when low-quality, low-cost fuels are used, as outlined later.
Fuel No.:
Units
1
2
3
4
5
6
7
8
9
10
11
12
13
Guiding fuel specification
Viscosity
cSt/50 oC
2.27
3.8
84
85
141
198
255
470
520
560
690
710
50,000
700
Density
kg/m3 at o
843
968
995
970
993
938
977
985
983
1,040
991*
65
98
84
80
103
100
106
90
95
90
79
84
> 60
60
Flash point
15 C o
C
1,010 1,008 1,030
Conradson carbon
% weight
0.01
0.3
17.2
12.1
13.3
9.4
14.5
16.8
14.8
17.3
22.1
24.7
24.2
22
Asphalt
% weight
0.00
0.78
15.1
8.9
9.2
3.7
10.0
11.3
12.8
14.6
19.3
29.0
-
14
Sulphur
% weight
0.22
0.10
2.72
1.16
0.91 0.83
0.87
0.90
1.18
2.22
3.52
3.30
4.8
5
Water
% weight
0.00
0.01
0.01
0.01
0.00 0.01
0.02
0.02
0.01
0.00
0.00
0.00
0.05
1.0
Ash
% weight
0.00
0.00
0.065 0.025 0.03 0.03 0.025 0.03 0.035
0.04
0.07
0.09
0.035
0.2
Aluminium
mg/kg
-
-
-
-
-
-
-
-
-
-
-
-
2.0
30
Vanadium
mg/kg
0
0
220
20
23
12
17
24
45
122
300
370
149.0
600
Fig. 10: Examples of liquid fuels burned in MAN B&W two-stroke low speed diesel engines
7
Fuel Flexibility
Composition:
Most power plants built today are based on the use of one or two fuels. Such fuels are typically natural gas or light fuels for gas turbines, coal or heavy fuel for steam turbines, and diesel oil, heavy fuel oil or natural gas for diesel engines. The two-stroke low speed diesel engines of MAN B&W design are able to run on virtually any commercially available liquid or gaseous fuel. Fig. 8 shows a typical guideline fuel oil specification of today for such engines. The basic data are dictated by the logistics of the marine market, which require that the fuel can be transported to the ship. This requirement, in principle, does not apply to stationary plants which can be placed close to the source of energy and connected to it by a pipe that is heated by waste heat from the engine. Various types of refinery waste can thus be used in low speed diesels. Such fuel oil specifications are normally quoted by the majority of diesel engine designers on the market, regardless of the number of strokes. Nevertheless, in this connection it should be noted that most medium speed designers specify a max. design temperature of HFO at injection in the range of 130-150 °C, resulting in a max. fuel viscosity of 700 cSt at 50 °C. For the two-stroke engines of MAN B&W design, the max. design temperature of the fuel preheating is 250 oC, corresponding to a specific fuel viscosity of approx. 70,000 cSt at 50 oC, i.e. a factor of 100 in admissible fuel viscosity.
Gas No.
1
2
3
CH4
Vol %
88.5
91.1
26.1
C2 H6
Vol %
4.6
4.7
2.5
C3 H8
Vol %
5.4
1.7
0.1
C4H10
Vol %
1.5
1.4
-
CO2
Vol %
-
0.5
64.0
N2
Vol %
-
0.6
7.3
kg/kmol
18.83
17.98
35.20
Higher calorific value
kJ/kg
49,170
48,390
11,120
Lower calorific value
kJ/kg
Molar mass
o
Density at 25 C/1 bar abs o
Density at 25 C/200 bar abs
41,460
38,930
7,050
3
0.762
0.727
1.425
3
194
179
487
kg/m kg/m
Fig. 11: Examples of gaseous fuels burned in MAN B&W two-stroke low speed diesel engines
Fig. 10 shows examples of liquid fuels burnt or tested successfully in MAN B&W two-stroke low speed diesels, while Fig. 11 shows similar data for gaseous fuels. Fig. 12 shows the fuel flexibility of the MAN B&W MC-GI-S type high-pressure gas injection, dual fuel, two-stroke engines, which are able to burn both liquid and gaseous fuel in almost any ratio without influencing their power rating or efficiency.
Fuel 100%
Fuel-oil-only mode
Fuel
100% load Fuel 100%
Dual-fuel mode
Gas 8%
Fuel 100%
Fuel 40%
100% load
Fixed-gas mode
Gas 8%
Fuel 100% load
Fig. 12: MAN B&W two-stroke low speed diesels, fuel type mode
8
Emissions In response to the increasing demand for environmental protection, the twostroke low speed diesels can be delivered with internal and external controls to comply with virtually any emission restriction requirements, including the 1998 World Bank Guideline for diesel-driven plants.
Two-stroke Engine Driven Plants An example of a 40 MW medium-load high-injection pressure two-stroke crosshead diesel engine plant is the Chiba plant in Tokyo (Fig. 13). This plant is based on a 12K80MC-S engine, developing 40 MW at 102.9 rpm
Main particulars Prime mover:
at an ISO efficiency of 49.3%. The plant is equipped with extensive SCR control of NOx emission in order to fulfil the local NOx limit of 13 mg/Nm3.
De-NOx NOx limit
MAN B&W 12K80MC-GI-S Dual fuel high-pressure gas injection engine 40 MW 103.4 r/min 17 bar 800 mm 2300 mm 12 Main fuel: LNG Pilot fuel : Low-sulphur diesel oil Thomassen recipro. four-stage Suction: 4.5 bar Delivery: 300 bar Meidensha Output: 40,000 kW Voltage: 3.2 kV Frequency: 50 Hz Ammonia SCR 13 mg/Nm3
Main data 1994-1999 Average reliability: Average availability: Average load factor: Average efficiency, gross: Average efficiency, net:
97% 97% 71% 46.1% 42.6%
MCR: Engine speed: Main effective pressure: Cylinder bore: Stroke: Number of cylinders: Fuels: Gas compressor: Pressure: Generator:
Fig. 13: 40 MW Chiba plant in Japan
9
In November 1996 after an extensive international call for tenders, Bahamas Electricity Corporation, decided to extend the plant with a new 30 MW unit, Figs. 14 and 15.
The Bahamas Project At the beginning of the seventies, four 10 MW two-stroke units were installed at the Clifton Pier power plant by Bahamas Electricity Corporation. In 1992 the plant was extended with two 9K80MC-S engines (units DA 9 and DA 10), built by MAN B&W Diesel’s Japanese licensee Mitsui Engineering & Shipbuilding Co. Ltd and supplied by Burmeister & Wain Scandinavian Contractor A/S, Mitsui’s contracting division.
The prime mover selected was an MAN B&W type 10K80MC-S diesel engine, developing 33.5 MW at 102.9 r/min at an ISO efficiency of 49%. The engine was built by Manises Diesel Engine Company S.A., Spain, and the plant order was awarded to a group of companies led by Alstom Power S.A., Madrid, Spain (Fig. 16).
33 kV BIG POND SWBD A 132 kV S/S
BLUE HILLS 132 kV S/S
80 MVA
80 MVA
30 MVA
The project was financed by the InterAmerican Development Bank and the European Investment Bank. The new plant, called unit DA 11, was successfully commissioned and handed over to the owner, Bahamas Electricity Corporation, in October 1999. The plant is equipped with a large exhaust gas boiler, utilising the exhaust gas waste heat energy down to some 180 ° C. The energy is utilised for the production of 10-bar steam, partly used for heating the fuel oil, and mainly
SPARE OHL 132kV SPARE OHL No. 2 LINE No. 1 80 MVA
33kV SWBD C
33 kW SWBD B
13.5 MVA
13.5 MVA
13.5 MVA
13.5 MVA
6.3 MVA
10MW 10MW 10MW 10MW DA8 DA7 DA6 DA5
6.9 kV STATION SWBD 1 2.5 MVA 1.25 MVA
1.25 MVA
35 35 MVA MVA 26.5 26.5 MW MW DA10 DA9
SITE BUILDING SERVICES S/S 1&2
40 MVA 30 MW DA11
80 MVA
30 MW approx. DA12
6.9 kV STATION SWBD 2 FIRE PUMPS
2.5 MVA
EMERG. D.G. 840kVA
415 V 2000A 415 V BH PUMP STN PUMP SWBD 1 SWBD 1
415 V BH PUMP SWBD 2
415 V STN AUX. SWBD 2
POWER STATION’A’ 415 V DA9 SWBD
Fig. 15: Bahamas, single-line diagram
10
415 V CAMCC
415 V DA10 SWBD
415 V 415 V DA11 SWBD CAMCC
415 V DA12 SWBD
Alstom Power S.A., Spain - Main contractor - Generator - Mechanical and electrical aux. systems - Logistics - Site erection - Commissioning
Manises Diesel Engine Co. S.A., Spain - Diesel engine supply - Site erection - Commissioning
MAN B&W Diesel A/S, Denmark - Diesel engine design Foundation design Conceptual plant engineering Commissioning assistance
Fig. 16: Bahamas, project organisation
Fig. 14: Bahamas DA 11, plant view from outside and inside
for the production of drinking water, which is being supplied to the local municipality (Fig. 17).
Engine data: 10K80MC-S shaft power = 33,410 kW at 100% MCR Ambient conditions: Air at blower inlet: 35 oC Air pressure at blower inlet: 1000 mbar o Charge air colant 32 C Heat balance data: Energy in fuel: 100%
Non-utilized energy
Utilized energy
Low temp.
High temp.
The main data of the engine and Alstom generator are shown in Fig. 18. During commissioning, extensive measurements were taken of all guaranteed plant values, and fulfilment has been ascertained, ref. Fig. 19 comparing the guaranteed and the actually obtained data. Of course, no plant of such size has been commissioned without teething troubles. In connection with the engine itself, tear of compensators between turbocharger and air cooler was experienced, as well as repeated accelerated wear on two out of ten cylinders. The difficulties have been investigated in detail, resulting in realignment of the compensators and the introduction of the latest development of ceramic-coated piston rings. Since these modifications were carried out, the engine has been running without any unplanned stoppage.
Radiation:
0.8%
Lub. oil cooling:
4.0%
Jacket water cooling: 6.4%
Charge air cooling:
20.3%
Exhaust gas:
21.0%
Mechanical output 45.4% Generator output 44.0%
2.2% Generator cooling:
Net Electrical output 42.0%
Station use of aux. systems:
1.4% 2.0%
Total energy utilization: Electrical output = 42.0% Thermal output = 2.2% Total energy utilization = 44.2%
Fig. 17: Bahamas DA 11, plant heat balance
11
MAN B&W engine type Number of cylinders MCR r/min Bore Stroke Mean piston velocity Mean effective pressure Length Width Height Total weight Heaviest weight for maintenance
K80MC-S 10 33,410 102.9 80 230 7.89 16.8 18 7.5 14.3 1,200 6.3
From its commissioning in October 1999 until 31 December 2000, the engine has accumulated 9500 running hours, and a total of 280 hours have been spent on scheduled and unscheduled maintenance, resulting in a total plant availability of 90% in the period.
W 950/76/70 41,092 0.8 11 2,156.8 60 70 102.9 124 3,150,000 (1) 4.43 F IM 7325 IP 44 ICW-37A97 (air to water) 400 9
As shown, the two-stroke low speed diesels of MAN B&W design are a viable option to be investigated and chosen by owners anywhere where reliable, fuel-efficient diesel plants are required, especially if the fuel is of a poor quality and available in scarce amounts.
kW rpm cm cm m/s bar m m m t t
Alstom generator type Rated output, kVA Power factor (overexcited) Rated voltage (± 5%), kV Rated current, A Frequency, Hz Number of poles Rated speed, rpm Overspeed, rpm 2 Mass moment of inertia (I), kgm Inertia constant kWs/kVA Insulation class (stator, rotor) Design Enclosure Cooling system Total weight, tons Heaviest weight for maintenance, tons Fig. 18: Bahamas DA 11, engine and generator main data
Plant net efficiency 100% MCR 80% MCR 50% MCR Plant emissions at 15% O2 CO2 mg/Nm3 (2% sulphur in fuel) CO mg/Nm3 NOx ppm/Nm3 (incl. 0.3% fuel bound nitrogen) HC mg/Nm3 PM mg/Nm3 Noise 1 m from engine, dB (A) 2 m above floor level and 1 m from engine, dB (A) At boundary of plant, dB (A) Fig. 19: Bahamas DA 11, plant performance
12
Guaranteed % 40.7 40.8 38.8
Measured at commissioning % 42.0 42.4 40.8
1,900 150 1,300 150 150
1,110 72 1,020 31 140
105 95 70
105 95 60
In February 2001, BEC awarded an order for an identical diesel generator unit to the same group of companies for delivery in 2002.
Conclusion
The future development of such engines will be dictated by the market, in particular by the future fuel oil prices and qualities, and the trend seems to point in the direction of even more efficient and ever larger units.
Literature ‘Diesel Engines for Independent Power Producers and Captive Power Plants’, issued by MAN B&W Diesel A/S, Copenhagen, Denmark. Publication No. P.352-99.01 ‘Waste Heat to Water’, by N. Pearce of Alfa Laval Ltd., published in ‘The Power Engineer’, Vol. 3, No. 2, April 1999.
