Contact information:
Danish Energy Agency: Rikke Næraa, rin@ens.dk Energinet.dk: Rune Grandal, rdg@energinet.dk Author: Dansk Gasteknisk Center
Publication date August 2016
Amendments after publication date
Date Ref. Description
January
2018 06 Gas engines Reference sheet have been updated
Qualitative description
Brief technology description
A gas engine for co-generation of heat and power drives an electricity generator for the power production. Electrical efficiency up to 45- 48 % can be achieved. The engine cooling water (engine cooling, lube oil and turbocharger intercooling) and the hot exhaust gas can be used for heat generation, e.g. for district heating or low-pressure steam.
In district heating systems with low return temperatures both sensible and latent heat in the exhaust gas can be recovered by using a condensing cooler as the final cooling of the flue gasses and a total efficiency of approx. 96-98%
can be reached. If applying heat pumps for extra cooling of the exhaust gas system, 5-7% higher total efficiency can be reached. The flue gas heat pumps can be electrical or absorption type.
Two combustion concepts are available for spark ignition engines; lean-burn and stoichiometric combustion engines.
Lean-burn engines have a high air/fuel-ratio. The combustion temperature and hence the NOx emission is thereby reduced. The engines can be equipped with oxidation catalysts for CO-reduction.
In stoichiometric combustion engines, the amount of air is just sufficient for (theoretically) complete combustion. For this technology, the NOx emission must be reduced in a 3-way catalyst. Only few of such engines are used for combined heat and power production in Denmark. These engines are usually in the lowest power range (< 150 kWe).
Pre-chamber lean-burn combustion system is a common technology for engines with a bore size typically larger than 200 mm. This technology helps to maximize electrical efficiency and increases combustion stability along with low NOx emissions.
Another ignition technology is used in dual-fuel engines. A dual-fuel engine (diesel-gas) with pilot oil injection is a gas engine that - instead of spark plugs - uses a small amount of light oil (1 - 6% ) to ignite the air-gas mix by compression (as in a diesel engine). Dual fuel engines can often operate on diesel oil alone as well as on gas with pilot oil for ignition.
More than 800 gas engines for combined heat and power production are installed in Denmark [4].
Figure 1 A gas engine based cogeneration unit with heat recovery boilers and an absorption heat pump to obtain a high heat production and highest possible overall efficiency. The heat pump is steam driven [9].
Input
Gas, e.g. natural gas, biogas, landfill gas, special gas and syngas (from thermal gasification) can be input to gas engines.
Multi-fuel engines are also on the market, and installations are in service in Denmark and abroad.
In recent years, engines have been developed to use gasses with increasingly lower heating values.
Output
Electricity and heat (district heat; low-pressure steam; industrial drying processes; absorption cooling) are output of the gas engine.
Typical capacities
5 kWe - 10 MWe per engine.
Regulation ability and other power system services
Gas engines can start faster than most other electricity production technologies. For many engines 5-15 minutes are needed. Large gas engines have been successfully developed and tested for start to full electrical load in less than one minute. Engines have been developed for fuel switch during operation [7].
Part load is possible with only slightly decreased electric efficiency. The dual-fuel engines have the least decrease of efficiency at part load. Gas engines have better part load characteristics than gas turbines.
To operate a gas engine in power-only mode, the exhaust gas can be emitted directly to the atmosphere without heat extraction (but with de-NOx if required), whereas engine heat (about 50% of total heat) must be removed by a cooler.
Approximately 10% of O&M costs can be saved in power-only mode [7].
Most gas engine based CHP plants installations include a short time heat storage. This leads to more flexibility in production planning.
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Advantages/disadvantages Advantages
Gas engines are known and proven technology making it a highly reliable technology.
Gas engines can operate on moderate gas pressures. Gas engines can be supplied by a gas pressure of less than 1 bar(g).
The pre-chamber lean-burn technology often requires a pressure for the pre-chambers of approx. 4 bar(g).
Disadvantages
Gas engines cannot be used to produce considerable amounts of high-pressure steam, as approx. 50 % of the waste heat is released at lower temperatures.
Environment
Spark ignition engines comply with national regulations within EU by using catalyst and/or lean-burn technology to reduce the NOx emission.
The content of other air pollutants than NOx in the flue gas from a gas engine is generally low.
Research and development perspectives
Multi-fuel or flexible fuel operation has been introduced, and R&D efforts are continuously put into this. Engines with almost instantaneous shift from gas to diesel and vice versa have been developed and demonstrated.
Short start-up, fast load response and other grid services are becoming more important as more fluctuating power sources are supplying power grids. Gas engines have a potential for supplying such services, and R&D efforts are put into this.
R&D in further emission reduction is continuously taking place; biogas and other such gasses may lead to new catalytic post treatment solutions.
Examples of market standard technology
Best available technology from an efficiency point of view will be a large gas engine with approx. 48-50 % electrical efficiency and a total fuel efficiency of some 106% if fitted with an absorption heat pump using the outlet flue gas as heat source.
Engine based cogeneration units can be fitted with a small low pressure steam turbine for extra power generation.
From a grid service point of view (power balancing and backup) engines with a start to full electrical load in less than one minute is the best available technology.
Prediction of performance and costs
Cogeneration based on gas engines is a proven and commercial technology in Denmark and abroad. Development still takes place mostly related to advanced control and diagnostic systems, making gas engines a category 4 technology.
Development also takes place related to efficiency improvements, auxiliary equipment as heat pumps and/or heat driven cooling systems (tri-generation).
Gas engines are now being developed for wider acceptance of various fuel compositions. This includes operation on upgraded biogas.
Even higher electrical production efficiency can be reached by including small low pressure steam turbines to the shaft.
This is being tested and supplied to some larger gas engine makes; it improves the mechanical/electrical efficiency by 2-4 percentage points.
A number of gas engine based cogeneration plants have increased their heat output and the total overall efficiency by including heat driven absorption heat pumps in the cogeneration system configuration. The outlet flue gas can be cooled to a temperature less than the available cooling water, and total efficiencies up to approx. 106% have been achieved.
For shorter start-up time services, new designs/solutions on the water side are needed to avoid sudden temperature disturbances in the heat supply.
The expected market in Denmark is limited and declining as well as the annual operation hours. This means that no significant reductions in investment and/or operation/maintenance cost are expected to be seen in the years to come.
Uncertainty
Uncertainty stated in the tables both covers differences related to the power span covered in the actual table and differences between the various products (manufacturer, quality level, extra equipment, service contract guarantees etc.) on the market.
A span for upper and lower product values is given for the year 2020 situation. No sources are available for the 2050 situation. Hence the values have been estimated by the authors.
Additional remarks
The information given in tables is for gas fired (n-gas and biogas) engines only. The natural gas basis is the natural gas supplied in Denmark according to regulations. The biogas basis is a methane/CO2 mixture (digestion of manure and/or industrial organic waste).
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Data sheets
Technology 06 Spark ignition engine, natural gas
2015 2020 2030 2050 Uncertainty (2020) Uncertainty (2050) Note Ref
Energy/technical data Lower Upper Lower Upper
Generating capacity for one unit (MW) 1 -10 MWe
Electricity efficiency (condensation mode for extraction
plants), net (%) 46 47 48 50 40 48 44 52 A 3, 4
Electricity efficiency (condensation mode for extraction
plants), net (%), annual average 44 45 47 48 38 46 42 50 A 3, 4, 7
Cb coefficient (50oC/100oC) 0.9 0.95 0.99 1.04 0.65 1.02 0.65 1.15 3, 4, 7
Cv coefficient (50oC/100oC) - - - - - - - - G
Forced outage (%) 3 3 3 3 2 5 2 5 5, 6
Planned outage (weeks per year) 0.8 0.8 0.8 0.8 N.A N.A N.A N.A H 5, 6
Technical lifetime (years) 25 25 25 25 25 >25 25 >25 D 4, 5, 7
Construction time (years) 1 1 1 1 0.5 1.5 0.5 1.5 B 3, 6
Space requirement (1000m2/MW) 0.04 0.04 0.035 0.03 0.03 0.05 0.025 0.04
Plant Dynamic Capabilities
Primary regulation (% per 30 seconds) 25 30 35 50 10 40 25 100 12
Secondary regulation (% per minute) 25 30 40 50 20 100 25 100 C 6, 12, 13
Minimum load (% of full load) 50 50 50 50 30 50 25 50 6
Warm start-up time (hours) 0.05 0.05 0.05 0.05 0.015 0.15 0.015 0.15 C 6, 10
Cold start-up time (hours) 0.3 0.3 0.3 0.3 0.2 0.4 0.2 0.4 E 6, 10
Environment
SO2 (degree of desulphuring, %) 0 0 0 0 0 0 0 0 4
NOX (g per GJ fuel) 75 60 60 60 50 100 50 100 4
CH4 (g per GJ fuel) 315 315 280 250 300 400 250 350 4
N2O (g per GJ fuel) 0.6 0.6 0.6 0.6 N.A N.A N.A N.A H
Financial data
Nominal investment (M€/MW) 1 0.95 0.9 0.85 0.9 1.1 0.8 1.1 3, 5, 11
- of which equipment 0.65 0.6 0.55 0.55 N.A N.A N.A N.A H 3, 5
- of which installation 0.35 0.35 0.35 0.3 N.A N.A N.A N.A H 3, 5
Fixed O&M (€/MW/year) 10,000 9,750 9,300 8,500 7,000 20,000 6,000 15,000 F 5
Variable O&M (€/MWh) 5.4 5.4 5.1 4.9 4 12 4 10 F 3, 5, 11
Technology 06 Spark ignition engine, biogas
2015 2020 2030 2050 Uncertainty (2020) Uncertainty (2050) Note Ref
Energy/technical data Lower Upper Lower Upper
Generating capacity for one unit (MW) 1-10 MWe
Electricity efficiency (condensation mode for extraction
plants), net (%), 42 43 45 47 38 44 42 48 A 3, 4
Electricity efficiency (condensation mode for extraction
plants), net (%), annual average 40 41 43 45 36 42 40 46 A 3, 4, 7
Cb coefficient (50oC/100oC) 0.82 0.86 0.92 1 0.59 0.96 0.75 1.1 3, 4, 7
Cv coefficient (50oC/100oC) - - - - - - - - G
Forced outage (%) 3 3 3 3 2 5 2 5 5, 6
Planned outage (weeks per year) 1 1 1 1 N.A N.A N.A N.A H 5, 6
Technical lifetime (years) 25 25 25 25 25 >25 25 >25 D 4, 5, 7
Construction time (years) 1 1 1 1 0.5 1.5 0.5 1.5 B 3, 6
Space requirement (1000m2/MW) 0.04 0.04 0.035 0.03 0.03 0.05 0.025 0.05
Plant Dynamic Capabilities
Primary regulation (% per 30 seconds) 25 30 40 50 10 40 25 100 J 8
Secondary regulation (% per minute) 25 30 40 50 20 100 25 100 C 6, 8, 13
Minimum load (% of full load) 50 50 50 50 30 50 25 50 6
Warm start-up time (hours) 0.05 0.05 0.05 0.05 0.015 0.15 0.015 0.15 C 6, 10
Cold start-up time (hours) 0.3 0.3 0.3 0.3 0.2 0.4 0.2 0.4 E 6, 10
Environment
SO2 (degree of desulphuring, %) (I) (I) (I) (I) 0 99.9 0 99.9 K 8
NOX (g per GJ fuel) 100 100 100 100 90 120 90 120 4
CH4 (g per GJ fuel) 300 300 300 300 300 400 300 400 4
N2O (g per GJ fuel) 1.0 1.0 1.0 1.0 N.A N.A N.A N.A J
Financial data
Nominal investment (M€/MW) 1 0.95 0.9 0.85 0.8 1.2 0.8 1.2 3, 5, 11
- of which equipment 0.65 0.6 0.55 0.55 N.A N.A N.A N.A 3, 5
- of which installation 0.35 0.35 0.35 0.3 N.A N.A N.A N.A 3, 5
Fixed O&M (€/MW/year) 10,000 9,750 9,300 8,500 7,000 20,000 6,000 15,000 F 5
Variable O&M (€/MWh) 8 7.5 7 6 6 13 4 12 F 3, 5, 11
Page 81| 414 Notes:
A Ref 1, 2 and 3 is used for 2015 values for 3 - 10 MWe engine, 1 MWe engine 4-5 % points less. Ref 4 & 5 is used for predictions for the future years.
B The construction time given is for a medium size installation; small installations can be erected in a shorter period C Engines have been build and demonstrated for short start up < 1 minute for full electrical load. This includes large engines D Technical- and design life most often > 25 years
E For a medium size engine; small engines with less thermal mass might be faster F When operating 4000 hours a year
G Only relevant for steam based CHP H No data available
I DGC estimate for years 2030, 2050 J No known use, data from n-gas engines
K Sulphur is removed in the biogas processing, according to manufactures spec. Lower values for biogas from waste water
References
[1] Cogeneration and On-site Power Production, Ltd., Penwell International.
[2] Opportunities for Micropower and Fuel Cell/Gas Turbine Hybrid Systems in Industrial Applications, A. D. Little, US, 2000.
[3] ASUE BHKW Kenndata 2014/2015.
[4] DGC statistics, Efficiency and emission test reports.
[5] DGC analysis, The gas fired cogeneration sector, Bilagsrapport 9, Energiforligsanalyse 2013.
[6] Features and parameters of various power plant technologies, Wartsila In Detail 02-2014 etc.
[7] Dansk Fjernvarme and FDKV reports from CHP installations, the Dansk Fjernvarme information is from a 2012 survey for an earlier version of the report.
[8] Ongoing Sulpur research project at DGC (MUDP).
[9] AEA.dk
[10] Danish Gas Technology Centre, Analysis on gas engine and gas turbine dynamics, 2013.
[11] Blockheizkraftwerke 2013, M. Buller et al, GWF Gas Erdgas, Juni 2014.
[12] Suppliers association information etc.
[13] MAN Turbo Presentation of Gas Engine with fuel switch, 2012