igu2009docswgcfinal00448

1、MONITORING CNG QUALITY IN GERMANYFrank Graf 1, Jrg Riedl 1, Kerstin Krger 1, Rainer Reimert 1, Jrg Meyer 21. DVGW-Research Station at Engler-Bunte-Institut, Universitt Karlsruhe (TH)2. Institut fr Mechanische Verfahrenstechnik und Mechanik,Universitt Karlsruhe (TH)Keywords: 1. CNG; 2. gas quality; 3

2、. oil carry over; 4. particulates; 5. sulphur content1 BackgroundFacilitated by a tax exemption until 2018, currently approximately 80.000 CNG vehicles are operated in Germany. Therefore and as for any other fuel for vehicles a standard for CNG as motor fuel was elaborated and published as DIN 51624

3、 1 in 2008. An extract of the most important parameters being fixed is given in Tab. 1. Beside the composition of the main components, especially to calculate the methane number, sulphurous components and moisture are limited. According to the 10. BImSchV (Tenth Ordinance for the Implementation of t

4、he Federal Immission Control Act (2009) the CNG quality has to be checked by public authorities. Within a random sampling the heating value, the methane number, the total sulphur content and the content of C2+ hydrocarbons as well as moisture have to be analysed. For the sampling of CNG directly fro

5、m the injection nozzle the DVGW standard G 264 “CNG - Sampling and analysis” was introduced.Higher hydrocarbons caused by compressor oil carry-over 2 and particulates are also in the scope of interest. Due to thermodynamic properties the content of higher hydrocarbons can increase dramatically above

6、 pressures of 150 bar 2. Under these supercritical conditions CNG acts as a solvent. Up to now no limit for the oil and for the particles content was fixed in DIN 51624 as no analysis standard is yet available. However, the automotive industry requires quality standards also for these properties bec

7、ause pressure regulators and fuel injection systems could fail with high oil contents in CNG.To provide a basis for including figures for oil and dust content in the standard for CNG the German Association for Gas and Water (DVGW) initiated two research projects. First, a suitable method for the gra

8、vimetric analysis of oil and particle traces in CNG was developed, and second, CNG filling stations are monitored Germany-wide. The second project was co-funded by Initiativkreis Erdgas als Kraftstoff (IEK). Both the projects are executed by the DVGW Research Center at Engler-Bunte-Institut in coope

9、ration with Institut fr Mechanische Verfahrenstechnik und Mechanik, Universitt Karlsruhe (TH).Tab. 1 CNG specification (DIN 51624 (2008)2Objectives of the paperIn this paper the new sampling method willbe presented as well as themain results of themonitoring program focusing on the requirements of D

10、IN 51624. Furthermore, the findings for particulates in CNG will be discussed.parameterunitmin. valuemax. valueCH4Mol.-%80-C2Mol.-%-12C3H8Mol.-%-6C4H10Mol.-%-2C5H12Mol.-%-1C6+Mol.-%-0.5CO2 + N2Mol.-%-15total sulphur (inclusive odorization)mg/kg-10moisturemg/kg-40methane number-70-3Gravimetric analys

11、is method for particles and oils3.1Requirements on the sampling systemIn the past several methods have been developed to quantify higher hydrocarbons in CNG 3-5.However no national or international standard is yet available. To determine the content of liquidhydrocarbons and solid particulates origi

12、nating from oil carry over and abrasion a new sampling method based on filtration and gravimetric analysis was developed regarding the following requirements:1.2.3.4.The duration of the sampling should not exceed 30 min The sampling should be accomplishable by one personThe sample should be taken in

13、tegrally over a complete fuel-filling procedureThe interference of the sampling (e.g. pressure gradient) with the fuel-filling procedure should be minimalNatural gas born gaseous hydrocarbons should not deposit on the filter5.It has to be taken into account that no gaseous hydrocarbons can be analys

14、ed with this method thus only liquid and solid matter are captured.3.2Selection of a filter elementTo select a suitable filter element, extensive theoretical and experimental investigations wereundertaken. Especially the following exigencies had to be fulfilled:1.2.2.The filter element has to be res

15、istant against natural gas at high pressures. Ambient humidity should not affect the sampling and the analysis.The precession of the analysis must be sufficient, thus the total weight of the filter element is limited.Precipitated particles should be embedded in the filter.Higher components of natura

16、l gas should not be precipitated significantly during the sampling.The filtration efficiency has to be adequate over a wide range of particle size.3.4.5.Finally a commercially available filter element (Zander TB 20 CE, Fig. 1) was chosen, fulfilling all the requirements. The filtration efficiency wa

17、s examined by experimental precipitation experiments at ambient pressure (particle size 20 - 1,000 nm) and mathematical filtration modelling. At 200 bar the separation efficiency reaches minimum values of 99.994 % within the mentioned particle size range (Fig. 2). Beside the filtration experiments p

18、ractical aspects like capacity for water vapour and natural gas born hydrocarbons, regeneration behaviour were examined.With the used weighing system (Satorius, Modell LA 1200 S) resolutions of 1 mg can be realized. Typical values for the absolute mass increase per sampling lie between 50 and 500 mg

19、. To avoid temperature induced measurement errors the analysis were carried out in an air-conditioned laboratory.Fig. 1 Filter elementparticle sizeT(x)Fig. 2 Separation efficiency of filter element3.2Sampling systemThe sampling system is modular and consists of the filter system (Module 1, Fig. 3) a

20、nd a tanksystem (Module 2, Fig. 4) which can be used optionally if no CNG car is available when taking the sample. Module I is directly connected to the injection nozzle. To avoid memory effects (e.g. for oil droplets, sulphurous components) the receptacle, which typically consists of a filter eleme

21、nt and a check valve, was bored through. Gas samples can be taken upstream and downstream the filter with high pressure gas cylinders. For the sampling of sulphurous components sulfinert-treated gas cylinders are used.The duration of sampling averages 30 min, inclusive installing and uninstalling of

22、 the apparatus. During the sampling (Fig. 5) the temperature, the system pressure and the pressure drop in the filter are measured and registered continuously (Fig. 6). The run of the different parameters depends significantly on the type of CNG filling station (compressors, banks etc.). The pressur

23、e drop in the filter, that is an important parameter for the filtration efficiency, reaches during the sampling moderate values below 100 mbar. The first results were promising and enable the use of a smaller filter element. Thus the sampling apparatus could be designed compactly (Fig. 7).After the

24、sampling the filter element is removed from the filter housing and weighed in an air- conditioned laboratory (20 C, 40 % relative humidity). For this the filter elements are transported in baggies and stored 24 h in the laboratory before weighing. To quantify the content of gaseous higher hydrocarbo

25、ns (C9 - C40) the gas samples are analysed by GC-FID and GC-HCD. Before the analysis of higher hydrocarbons an enrichment in cyclohexane is necessary. Furthermore, the total sulphur content is determined with a high-resolution UV-detector. The quantitative analysis of selected sulphurous components

26、is undertaken with a pulsed flame photometric detector (PFPD). The moisture content is measured with a mobile device (Michell Cermax EX) at the CNG filling station.separation efficiency T(x)CNG from filling stationCNG to module 2Fig 3 Sampling system (module 1)Fig 4 Gas tanks (module 2)Fig. 5 Sampli

27、ng at a CNG Fuelling stationfilter pressureT upstream filterT downstream filterfilter differential pressure200403516030251202080151040500050100150200250300350400450500550duration of sampling tsampling insFig. 6 Temperature and pressure profiles during samplingtotal pressure ptot in bartemperature T

28、in C, differential pressureDpfilter in mbarFig. 7 Modified sampling system4Results of the monitoring programWith the new sampling system various CNG fuelling stations were monitored from December 2008 toJuly 2009 to evaluate CNG-quality in Germany. After the first six measurements the smaller sampli

29、ng systemwas used to simplify the handling of the sampling. In total approximately 40 CNG-fuelling stations were analysed. Various different types of fuelling stations and operating parameters were regarded (e.g. compressor type, filter media, natural gas quality, maintenance rates). In the followin

30、g the most important results are summarized.In Tab. 2 - Tab.4 the main components and the resulting methane number are shown as well as the moisture and the sampling pressure. It can be stated that all requirements concerning the main components are fulfilled. The calculated methane numbers lie with

31、 a range from 79.4 to 101.3 over the minimum permitted value of 70. In the future the methane number could fall below that limit if heavy LNG will be used in Germany. In contrast the injection of biogas is not crucial for the methane number also if conditioning with LPG might be necessary. Moisture

32、was no problem within the monitoring program. The limit of 40 mg/kg was not reached by far. Typical dew points lie between -40 and -25 C.Tab. 2 Analysis of CNG quality (I)content in Vol.-%123456CH498.3898.1998.4986.1282.6987.27C2H60.630.650.531.702.680.95C3H80.180.190.140.170.350.05C40.0600.0620.040

33、0.0600.1200.020C50.0000.0000.0000.0100.0100.000C6 - C100.0020.0010.0000.0190.0400.013CO2 + N20.750.910.8011.9214.1211.70methane number93.294.094.694.692.0101.3psampling in bar219205205221191218dew point in C-36.5-30.5-38.7-28.9-36.9-30.3moisture in mg/kg0.571.430.441.960.721.66Tab. 3 Analysis of CNG

34、 quality (II)Tab. 4 Analysis of CNG quality (III)The limit for the total sulphur content of 10 mg/kg due to DIN 51624 is under discussion in Germany. Two aspects have to be considered. First there are low calorific gases distributed in some areas in North Germany which could content higher total sul

35、phur concentrations. The biggest part of natural gases in Germany has low sulphur contents below 3 mg/kg. Second the odorization with THT is on a watch as the sulphur limit could be exceeded also for low base sulphur contents by high odorization rates above approximately 24 mg/m3. One alternative to

36、 solve the problem is the use of sulphur free or low sulphur odorants. Otherwise a selective desulfurization at the CNG filling station would be necessary. Up to now no processes are commercially available. Within the monitoring program the values for the total sulphur content vary from 0.29 to 11.8

37、6 mg/kg. Values below 2 mg/kg were reached at CNG-filling stations with sulphur free or low sulphur odorization in combination with natural gas H with a low base sulphur content. The maximum value was analysed in the concerned L-gas area in North Germany. In average, the total sulphur content reache

38、s 5.85 mg/kg.Regarding particles and oil loading a wide range was observed. With total values for regular samplings ranging from 0.67 to 21.29 mg/kg the content of solid and fluid particles exceeds the favoured limits (5 - 10 mg/kg) of the automotive industry considerably in two cases. The average p

39、article content lies at 8.36 mg/kg for the considered samples. The lowest value was measured at a CNG filling station with an oil-free compressor system. In one case an extremely high value of 137.08 mg/kg was analysed. In the corresponding gas analysis a content of higher hydrocarbons of 1,070 mg/k

40、g was measured. The analysis of the higher hydrocarbons was critical in some cases as droplets accumulated in the pipeline system of the sampling apparatus. These droplets lead to a memory effect. To avoid this phenomena the system should be cleaned or reinstalled previously to each sampling which i

41、s not feasible from the practical and economical point of view. Furthermore, sharp edges or internal components should be avoided.content in Vol.-%131415161718CH494.60595.2795.4189.2393.7093.38C2H63.062.452.506.003.913.829C3H80.670.520.521.280.610.61C40.1820.1400.1420.3340.1400.142C50.0100.0100.0100

42、.0300.0100.010C6 - C100.0160.0120.0130.0620.0160.015CO2 + N21.461.601.423.071.622.02methane number86.688.288.179.485.986.0psampling in bar219229230231221221content in Vol.-%789101112CH491.1989.8194.8097.0494.9894.66C2H65.065.302.961.612.812.97C3H80.951.110.670.520.640.65C40.2410.3000.1820.1600.1720.

43、182C50.0300.0300.0100.0100.0100.010C6 - C100.0470.0490.0140.0130.0130.015CO2 + N22.493.411.360.651.381.53methane number82.181.086.789.487.386.8psampling in bar196260230201152213Compared to the results of a former monitoring program 5 in which another sampling method was applied the contents of higher hydrocarbons were significantly higher. In average values of 80 mg/kg were analysed.12 average = 5,85 mg/kg 1086 4 THT/TBM odorization 20123456789101112131415161718sampleFig. 8 Total sulphur content2520151050123456789101112131415161718sampleFig. 9 Particle contentparticl