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Danish Gas Technology Centre • Dr. Neergaards Vej 5B • DK-2970 Hørsholm • Tlf. +45 2016 9600 • Fax +45 4516 11 99 • www.dgc.dk

Environmental optimisation of gas fired engines in Denmark

Project reportDecember 2013

Measurement of emissions and efficiencies of natural gas and biogas fired engines

Environmental optimisation of gas fired engines in Denmark

Measurement of emissions and efficiencies of natural gas and biogas fired engines

Torben Kvist

Danish Gas Technology Centre Hørsholm 2013

Title : Environmental optimisation of gas fired engines in Denmark

Report Category : Project Report

Author : Torben Kvist

Date of issue : 20-12-2013

Copyright : Danish Gas Technology Centre

File Number : 736-18; h:\736\18 miljøoptimering 2\wp1\rapport målinger736-18_final.docx

Project Name : Environmental optimisation of gas engines

Keywords : kraftvarme, motorer, miljø

ISBN : 978-87-7795-377-4

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Table of Contents Page

1 Introduction ........................................................................................................................... 2

2 Examined engines ................................................................................................................. 3 2.1.1 Natural gas fired engines ......................................................................................... 3 2.1.2 Biogas fired engines ................................................................................................ 3

3 Measurements and operation conditions ............................................................................... 5 3.1 Measurements ...................................................................................................................... 6

3.1.1 Natural gas fired engines ......................................................................................... 6 3.1.2 Biogas fired engines .............................................................................................. 10

3.2 Evaluation of conducted measurements ............................................................................ 11

4 References ........................................................................................................................... 13 Appendices Appendix A: Relation between NOx, UHC, CO emissions and efficiencies at different settings of excess air and ignition timing

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1 Introduction

Emissions of unburned hydrocarbons (UHC), NOx and CO from stationary natural gas fired engines can be reduced by both improved engine design and by modifying the engine settings. Normally, there is a trade-off between low NOx emissions and low UHC emissions. This means that if engine op-eration is changed in order to reduce NOx emissions, higher UHC emissions will often be a negative side effect. Furthermore, it is well known that the electrical efficiency of the CHP engines is affected by varying engine set-tings.

In order to examine how much emissions and efficiencies are affected by

varying engine settings, a number of measurements were conducted on dif-

ferent natural gas fired engines based on CHP units in Denmark.

As a part of this project emission measurements were conducted at two dif-ferent Jenbacher engines and two different Caterpillar engines in operation on local combined heat and power plants in Denmark. The measurements supplement measurements from a previous project “ForskEL 10089”. Dur-ing that project emission measurements were conducted on two Rolls-Royce engines and two Wärtsilä engines. All of these eight engines were natural gas fired. In addition to the natural gas fired engines similar measurements were conducted at three different biogas engines. In order to show a complete and comprehensive picture of the emissions from the main part of natural gas fired CHP engines in Denmark a part of the results given here is obtained as a part of the project “ForskEL 10089”. The participants in this project are:

• GE Jenbacher • PonPower • National Environmental Research Institute, DMU • Danish Gas Technology Centre, DGC.

The project was financially supported by Energinet.dk as a part the PSO ForskEL programme

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2 Examined engines

Eight different natural gas fired engines and three biogas fired engines were chosen for measurement of emissions as well as electrical and heat efficien-cy. 2.1.1 Natural gas fired engines

The eight natural gas fired engines are in operation on local combined heat and power plants (CHP) in Denmark. Makes and sizes of the engines are given in Table 1.

Table 1 Makes and sizes of the examined natural gas engines Unit Make Size #1 Rolls Royce B35:40 4990 kWe #2 Rolls Royce KVGS-G4 2075 kWe #3 Wärtsilä V25SG 3140 kWe #4 Wärtsilä V34SG 6060 kWe #5 Jenbacher J320 1063 kWe #6 Jenbacher J620 3047 kWe #7 Caterpillar G3516 1047 kWe #8 Caterpillar G3616 3845 kWe Measurements on engine units #1-4 were conducted as a part the previous project, but are included in this report in order to show a complete and com-prehensive picture of the possibilities of reducing emissions from natural gas fired CHP engines. The engines were selected in order to be representative of the natural gas engines based on CHP production in Denmark. The eight examined natural gas fired engines represent 85 % of the total natural gas consumption on natural gas engines based on CHP units in Denmark. 2.1.2 Biogas fired engines

In addition to the natural gas fired engines three biogas fired engines were examined. Makes and sizes of the engines are given in Table 2.

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Table 2 Makes and sizes of the examined biogas engines Unit Make Size #9 Caterpillar G3516 1047 kWe #10 Rolls-Royce KVGS-G4 2050 kWe #11 Jenbacher J412 889 kWe Unlike the natural gas fired engines the biogas engines were not selected in order to represent the already installed capacity. Due to the expected expan-sion of biogas production in Denmark it was decided that each of the in-volved engine suppliers should select an engine type that they expected to be the most likely type to be used for biogas operation in the near future. This includes both new engine installations as well as existing natural gas fired engines that will be converted to biogas operation.

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3 Measurements and operation conditions

For all examined engines emissions and efficiencies were measured at dif-ferent combinations of excess air (λ) and ignition timing (IT). The excess air and the ignition timing were set so the following NOx emission levels were obtained for: Natural gas fired engines: 500, 400, 300, and 200 mg/m3(n), ref. 5 % O2 Biogas fired engines: 1000, 800, 600, and 400 mg/m3(n), ref. 5 % O2 The level of NOx emissions is chosen to match threshold limits given in the regulation of biogas and natural gas fired engines, respectively /2/. For each of the examined operational conditions the following measure-ments were conducted:

• O2 - measured by paramagnetic analyser • CO and CO2 – measured by NDIR • NOx and NO2 – measured by CLD • UHC - measured by FID • Natural gas consumption, heat and electricity production. Meters on

the plant were applied. The measurements of emissions were conducted following the same internal procedures as accredited measurements and according to the guidelines of the Danish EPA. The engine settings were chosen by the engine supplier. It was done to fit the scheme shown in Table 3. As shown in the table, four measurements with fixed excess air and fixed time of ignition and four measurements with fixed time of ignition and different excess air were carried out. However, it was not possible to obtain steady operation at all eight chosen engine set-tings for all engines.

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During the previous projects it was found that the negative environmental impact of compounds as HCHO (formaldehyde) and higher hydrocarbons as C2H4, C3H6, C4H10 are negligible compared to the impact of CH4 and NOx. Therefore, the composition of the hydrocarbons in flue gas was not deter-mined as a part of this project. Similarly, no HCHO concentration meas-urements were conducted. For details please refer to /3/.

Table 3 Examined operational conditions. TI denotes the time of ignition, M is numeration of individual measurements.

Unit: mg/m3(n) @

5 % O2

TI1 TI2 TI3 TI4

λ 1 M5 NOx =

200/400

λ 2 M6 NOx =

300/600

λ 3 M1 NOx =

200/400

M2 NOx =

300/600

M3/7 NOx =

400/800

M4 NOx =

500/1000 λ 4 M8

NOx = 500/1000

3.1 Measurements

3.1.1 Natural gas fired engines

Results of the conducted measurement are given below in Figure 1 to Figure 8. As expected, the CO and the UHC emissions increase as the NOx emis-sions decreases. However, there are large differences in the sensitivity of the different examined engines model to the changed engine settings in terms of UHC and CO emissions. For all examined engine models the electrical effi-ciency decreases with decreasing NOx emissions. For some units, the heat efficiency apparently increases, and for some, the heat efficiency decreases with decreasing NOx emissions. In general, the accuracy of the measurement of produced heat is lower than for measurements of both emissions and electricity production. One reason is that the meters for measurement might not be serviced and calibrated as well as required in order to give precise measurement as these meters are

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not used billing purposes, but only as indicative in the daily operation. An-other reason is that whole heating system often responds very slowly to changes in operational conditions compared to emissions and electricity production. For some of the measurements, it is known that heat production rate was not completely stable when the measurement was conducted.

Figure 1 Relation between NOx emissions, unburned hydrocarbon emis-sions (UHC) and CO emissions, and heat and electrical efficiency for a natural gas fired Jenbacher J300 series engine.

Figure 2 Relation between NOx emissions, unburned hydrocarbon emis-sions (UHC) and CO emissions, and heat and electrical efficiency for a natural gas fired Jenbacher J600 series engine

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Figure 3 Relation between NOx emissions, unburned hydrocarbon emis-sions (UHC) and CO emissions, and heat and electrical efficiency for a natural gas fired Caterpillar 3500 series engine

Figure 4 Relation between NOx emissions, unburned hydrocarbon emis-sions (UHC) and CO emissions, and heat and electrical efficiency for a natural gas fired Caterpillar 3600 series engine

Figure 5 Relation between NOx emissions, unburned hydrocarbon emis-sions (UHC) and CO emissions, and heat and electrical efficiency for a natural gas fired Rolls-Royce B engine

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Figure 6 Relation between NOx emissions, unburned hydrocarbon emis-sions (UHC) and CO emissions, and heat and electrical efficiency for a natural gas fired Rolls-Royce K engine

Figure 7 Relation between NOx emissions, unburned hydrocarbon emis-sions (UHC) and CO emissions, and heat and electrical efficiency for a natural gas fired Wärtsilä W34SG series engine

Figure 8 Relation between NOx emissions, unburned hydrocarbon emis-sions (UHC) and CO emissions, and heat and electrical efficiency for a natural gas fired Wärtsilä W25SG series engine

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3.1.2 Biogas fired engines

The NOx emissions from biogas fired engines are known to be higher than for the natural gas fired engine. The installed capacity of biogas fired en-gines is much lower than for natural gas fired engines. However, the biogas production is expected to increase significantly in the near future, and a large fraction of the future biogas production will be used at CHP units. Fur-thermore, biogas fired plants will have a higher number of operation hours per year than existing natural gas fired CHP units. Therefore, it was chosen to conduct emission measurements on biogas fired plants as well. The re-sults of the conducted measurements are given in Figure 9 - Figure 11.

Figure 9 Relation between NOx emissions, unburned hydrocarbon emis-sions (UHC) and CO emissions, and heat and electrical efficiency for a biogas fired Jenbacher J412 engine

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Figure 10 Relation between NOx emissions, unburned hydrocarbon emis-sions (UHC) and CO emissions, and heat and electrical efficiency for a biogas fired Rolls-Royce K engine

Figure 11 Relation between NOx emissions, unburned hydrocarbon emis-sions (UHC) and CO emissions, and heat and electrical efficiency for a biogas fired Caterpillar 3500 engine

3.2 Evaluation of conducted measurements

For all of natural gas fired engines it was possible to obtain NOx emissions as low as 200 mg/m3 @ 5 % O2. However, for some of the engines it was not possible to obtain the low NOx emission level both by varying ignition timing and excess air. Many of the engine models have been on the market for many years. While they have been on the market they have been developed to some extent. For example the Rolls-Royce K engine exists in a G4 version where the “G4” indicates that it is the fourth generation of the engine model.

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When the engines are adjusted to obtain very low NOx emissions, they are operated close to the lean-burn limit. This means that small variations in the operation conditions might lead to further leaning of the combustion condi-tions, and thereby misfire is likely to occur.

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4 References

/1/ Emissionskortlægning for decentral kraftvarme 2007. Energi-net.dk miljøprojekt nr. 07/1882. Delrapport 4. Måleprogram og analyse af emission fra gas- og oliefyrede decentrale anlæg < 25 MWe. April 2010.

/2/ BEK nr 1450 af 20/12/2012

/3/ Environmental optimisation of natural gas fired engines - Measurement on four different engines. DGC report R1005. June 2010.

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Appendix A Relation between NOx, UHC, CO emissions and efficiency at different settings of excess air and ignition timing. In order to assess whether this approach of measurement can be optimised, the measurement data from the previous project as well as measurements conducted as a part this project were analysed further. For all eight engine models shown in Table 1, it was analysed whether obtaining low NOx emis-sion by increasing the excess air or by retarding the ignition have the same effect on the other emissions and on the efficiency. The results are given in the figures below. The red marks and lines show the effect of varying the excess air, and the green marks and lines show the effect of varying the igni-tion timing. The black line showing the effect of reducing NOx emissions is a trend line for all examined operational conditions. It was found that for most engines the CO and UHC emissions as well as efficiencies respond equally, no matter whether NOx was reduced by in-creasing the excess air or by retarding the ignition timing. However, for some cases that is not the case.

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UHC versus NOx emissions at different engine settings Unit #1

Unit #2

Unit #3

Unit #4

Unit #5

Unit #6

Unit #7

Unit #8

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CO versus NOx emissions at different engine settings Unit #1

Unit #2

Unit #3

Unit #4

Unit #5

Unit #6

Unit #7

Unit #8

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Electrical efficiency versus NOx emissions at different engine settings Unit #1

Unit #2

Unit #3

Unit #4

Unit #5

Unit #6

Unit #7

Unit #8

1 Introduction2 Examined engines2.1.1 Natural gas fired engines2.1.2 Biogas fired engines

3 Measurements and operation conditions3.1 Measurements3.1.1 Natural gas fired engines3.1.2 Biogas fired engines

3.2 Evaluation of conducted measurements

4 References