GAS MARKET LIBERALIZATION IN GERMANY AND THE POSSIBLE CONSEQUENCES FOR GAS TURBINE OPERATION

Size: px

Start display at page:

Download "GAS MARKET LIBERALIZATION IN GERMANY AND THE POSSIBLE CONSEQUENCES FOR GAS TURBINE OPERATION"

Claud Harrington
6 years ago
Views:

Gas Market Liberalization & GT Operation OMMI (Vol. 2, Issue 3) Dec. 03 www.ommi.co.

ON Energy Projects GmbH, Germany Dipl.-Ing. Christian Arnold is project manager at KEMA-IEV Dresden GmbH, a German supplier-independent engineering company.

Hubert Skiba is power plant manager for GEW RheinEnergie AG Cologne. He is responsible for the CHP plant Cologne-Merkenich.

1 Gas Market Liberalization & GT Operation OMMI (Vol. 2, Issue 3) Dec GAS MARKET LIBERALIZATION IN GERMANY AND THE POSSIBLE CONSEQUENCES FOR GAS TURBINE OPERATION Christian Arnold, KEMA-IEV Dresden GmbH Hubert Skiba, GEW RheinEnergie AG Köln Alexander Walke, E.ON Energy Projects GmbH, Germany Dipl.-Ing. Christian Arnold is project manager at KEMA-IEV Dresden GmbH, a German supplier-independent engineering company. He is expert in vibrations of turbo-machines, thermodynamic evaluation of power plant facilities and performance tests of CHP plants. Dipl.-Ing. Hubert Skiba is power plant manager for GEW RheinEnergie AG Cologne. He is responsible for the CHP plant Cologne-Merkenich. In April 2004, a gas preheating facility will be erected, on this site, as a cooperative effort between GE VAM-Anlagentechnik and GEW RheinEnergie. Dipl-Ing. Dipl-Wirtsch.-Ing. Alexander Walke is a project leader in the German based company E.ON Energy Projects. He has over 10 years experience, working in the area of thermal power plant issues. His previous experience includes working for Siemens Power Generation and Gerling Industrie Service. Furthermore he is a lecturer at the Cologne University of Applied Science. Keywords: Liberalized Gas Market in Germany; Guidelines; Gas Quality; Compatibility of different Gases; Operation of Gas Turbines

2 Gas Market Liberalization & GT Operation OMMI (Vol. 2, Issue 3) Dec Introduction Germany currently imports about 80% of its required natural gas [1]. Meanwhile, efforts are being made to liberalize the gas market in much the same way as the electricity market. In contrast to electricity, natural gas is - as its name implies - a product derived from nature. Quality is dependent upon the drilling region. With this considered, three points (among others not mentioned here) are of interest: In the process of gas market liberalization, the quality of natural gas in the gas distribution system will experience changes. What consequences will a change in gas quality have on burners of gas-fired turbines? The gas turbine supplier needs to adjust to the conditions of a liberalized gas market. 1. RULES AND STANDARDS FOR GAS MARKET LIBERALIZATION AND GAS QUALITY IN GAS DISTRIBUTION SYSTEMS 1.1 Management of various Natural Gas States before Liberalization of Gas Market The main portion of natural gas used in Germany is imported from the Netherlands, Norway and Russia. The entry points for grid gas pipelines are distributed along Germany s borders and there are no dominant directions of transport. Additionally, domestic gas production (primarily from northern German regions) comprise just under 20% of the market share. The differing gas compositions cause dispersion of gross calorific values up to 25% in the gas distribution system [1], [2]. Shuttle and mixture zones are currently employed to fulfill natural gas demand using varying gas qualities. So called rigid shuttle zones are zones in which gases with varying qualities are serially fed in. In contrast to rigid shuttle zones, open shuttle zones are zones in which two gases with identical gross calorific values, but differing Wobbe-Index values, are fed-in against each other. The feeding in occurs via spatially separated feeding points, whereby the ratio can be adjusted according to demand. In the mixture zones, two gases with differing qualities are mixed at a specific volumetric flow at a defined feeding point in the gas distribution system. The gross calorific value of the mixed gas is determined by the weighted average of the two gas qualities. 1.2 Future Process Management under conditions of the Liberalized Gas Market A precondition for effective competition between various providers in the liberalized gas market is the assurance of interchangeability between gases of differing quality. The association

3 Gas Market Liberalization & GT Operation OMMI (Vol. 2, Issue 3) Dec agreement for access to the natural gas distribution system, Verbändevereinbarung zum Netzzugang bei Erdgas, [3] (VV Erdgas II) that was enacted on 1-October-2002 and runs until 30-September-2003, replaced the former agreement VV Erdgas I [4] (with both supplements [5] and [6]). It defines the guidelines for gas industry services and also defines the technical regulatory environment for the liberalized gas market in Germany. Regarding the requirements for composition and determining a billable amount for the fed-in gases, VV Erdgas refers to the technical regulations, Technischen Regeln der DVGW-Arbeitsblätter G 260 (Gas Composition) [7] and G 685 (Gas Billing) [8]. Provider-supplied natural gas to the feed-in point is deemed compatible when--considering safety, application engineering and accounting--no additional condition and ratio adjustments need to be made by the operator to the relevant sections of the gas distribution system. The stipulated allowable ranges [7], regarding the fuel characteristics of natural gas, are named in VV Erdgas II as compatibility criteria for the natural gas to be transported [3], [4], [6]. If the gas distribution system operator determines that compatibility is not realized, then the provider has to be offered a competitive price to achieve compatibility using adjustment procedures. To adjust the deliverable natural gas to the characteristics of the fuel in the gas distribution system, the operator can--according to availability--mix it with other gases from the provider or condition it with additive gases or inert gases. The special gas conditioning requirements are set forth in DVGW-Arbeitsblatt G 260 [7]. 1.3 Gas Quality Requirements A basic arrangement for combustible gases in the public gas supply is described in DVGW- Arbeitsblatt G 260 [7]. It sets forth guidelines for gas quality with regard to fuel characteristics and content of components and additives. Natural gas in Germany s public gas distribution system will be classified in the second gas family (methane-rich gases) according to DVGW guidelines. Origin-dependent and -differing composition of fed-in natural gases determines combustion properties and thereby gas quality. The Wobbe-Index serves as a substantial measure (for the interchangeability of gases regarding heat load on gas devices) that is normally based on ISO conditions (Index n, by ISO at pressure p n = 1,01325 bar and temperature t n = 0 C): Ho, n Gross Wobbe-Index Wo, n =, with H o,n = gross calorific value and d = specific d gravity of natural gas relative to air at ISO conditions, Hu, n Net Wobbe-Index Wu, n =, with H u,n = net calorific value. d Depending on the size of the Wobbe-Index, the second gas family is divided between group L (low) and group H (high). Gases that conform to combustion characteristics of the second family (i.e. DVGW-Arbeitsblatt G 260 [7]) are displayed in abstract in Table 1.

4 Gas Market Liberalization & GT Operation OMMI (Vol. 2, Issue 3) Dec Descriptions Symbols Units Group L Group H Gross Wobbe-Index, W o,n kwh/m³ 10,5 to 13,0 12,8 to 15,7 Aggregate Range MJ/m³ 37,8 to 46,8 46,1 to 56,5 Gross Calorific Value H o,n kwh/m³ MJ/m³ 8,4 to 13,1 30,2 to 47,2 Specific Gravity 1) d - 0,55 to 0,75 1) Specific gravity of natural gas relative to dry air at same temperature and same pressure (usually ISO conditions) Table 1: Characteristics of gases from the second gas family based on DVGW- Arbeitsblatt G 260 [7] (abstract) 2. IMPACT OF GAS QUALITY ON COMBUSTION 2.1 Description of Studied Natural Gases For the study, three different European natural gas types (from Norway, Netherlands and Russia) were considered. The most important quality indicators (calorific value, Wobbe-Index) and gas components are given in Table 2. They are based on laboratory tests. Further components have only slight shares of aggregate mass and aggregate energy release; they are summarized in the row Remainder. Characteristics Units Norway Netherlands Russia Gross Calorific Value H o,n MJ/m³ 43,96 35,80 40,01 Net Calorific Value H u,n MJ/m³ 39,79 32,32 36,08 Gross Wobbe-Index W o,n MJ/m³ 54,17 44,44 52,67 Methane CH 4 mol % 84,668 81,654 96,661 Ethane C 2 H 6 mol % 9,365 3,225 1,220 Propane C 3 H 8 mol % 2,323 0,608 0,393 Nitrogen N 2 mol % 0,822 12,534 0,968 Carbon Dioxide CO 2 mol % 1,719 1,624 0,539 Remainder mol % 1,103 0,355 0,219 Table 2: Natural gas characteristics and compositions (Examples from analyses) Of the three natural gas types in Table 2, two (from Norway and Russia) are categorized in Group H of the second gas family. Natural gas from the Netherlands belongs to group L and is not compatible with gas from Group H.

5 Gas Market Liberalization & GT Operation OMMI (Vol. 2, Issue 3) Dec Calculation Basis The effects of natural gas on combustion were analyzed independently of specific gas turbine and burner construction. For this, a reaction progress calculation serves as an adequate procedure. The software program CHEMKIN II [9] was applied. It realistically models conversion from the initial combustion components (fuel and air) to the final products (flue gas). The conversion is characterized by a breaking down of gas components, the combining into intermediate products and ultimately -- through a chain of various reactions -- a forming into the final product. In total, 325 reactions are considered. The functionality and background of the reaction progress calculation and the assumed simplifications are covered in [9] and [10]. 2.3 Calculation Results In Figure 1, the combustion processes of the examined natural gases (from Norway, Netherlands and Russia) are compared with respect to energy release at constant Lambda (= 3.0). The expected basic result of the examination is that every natural gas burns differently. Russian natural gas reacts later than gases from Norway and the Netherlands. It is interesting to note the sequence; while gross calorific value and gross Wobbe-Index produces Norway--Russia-- Netherlands, ignition delay produces Norway--Netherlands--Russia. The ignition delay of individual natural gases is apparently arranged according to the ratio of C-atoms to H-atoms (Norway: 0.276; Netherlands: 0.263; Russia: 0.255; see [9], [10]). The less hydrogen atoms per carbon atom, the faster the reaction. However, the aggregate ratios of the ignition delays don t correspond directly to the actual flame lengths (e.g. tripling the ignition delay doesn t mean a tripling of the flame length). But an impact on the flame zone s shape is almost certain. Further results are shown in [10].

6 Gas Market Liberalization & GT Operation OMMI (Vol. 2, Issue 3) Dec L-Gas Netherlands W o,n = 12,34 kwh/m 3 H-Gas Russia W o,n = 14,63 kwh/m 3 H-Gas Norway W o,n = 15,04 kwh/m 3 Energy Release Reaktion Time (Ignition Delay) in ms Figure 1: Local Energy Release for Various Natural Gases using a Constant Initial Temperature (1200 K) and Lambda = 3.0 over the Reaction Time 3. GAS TURBINE SUPPLIER S REQUIREMENTS FOR GAS QUALITY The suppliers of gas turbines analyze the quality of the available natural gas on site before delivery of the system. Burners and their nozzle cross sections are designed and manufactured accordingly. As a rule, they are kept in this state for the lifetime of the gas turbine. With the liberalization of the gas market, the whole fuel range is allowable (see terms of compatibility according to G 260). Also to be considered are the requirements of the gas turbine manufacturer. An example is the GE-specific set of fuel requirements for gas turbines [11]. An equation for the modified Wobbe-Index (MWI) is formulated that is based on the net calorific value and includes the fuel temperature:

7 Gas Market Liberalization & GT Operation OMMI (Vol. 2, Issue 3) Dec W MWI d * ϑf value in BTU/SCF). u, n = (with ϑ F as fuel temperature in degrees Rankin and the net calorific For ignition and start up of the gas turbine, a MWI fluctuation of ± 5% is allowed. By operating the machine at full speed, more than no-load (FSNL) the allowable fluctuation in the Wobbe-Index can be considerably larger than ± 5%... [11]; but this fluctuation is not more precisely quantified. In Figure 2, a example with a Design-MWI of 47.8 is used to illustrate GE-requirements merged with those of ranges possible under G 260. Clearly, gas quality based on DVGW guidelines falls widely outside of GE requirements for ignition and start up. 60 W o,n in kwh/m 3 15,70 55 Modified Wobbe Index = MWI ,00 12,80 10,50 Example for allowable ± 5%- range (according to GEI 41040E for ignition, startup) Allowable aggregate range for H-gas (according to DVGW- Arbeitsblatt G 260) Gas Temperature in C Allowable aggregate range for L-gas (according to DVGW- Arbeitsblatt G 260) Figure 2: GE Range for Ignition and Start-up with the Aggregate Ranges for H- and L-Gases relevant to DVGW G 260

8 Gas Market Liberalization & GT Operation OMMI (Vol. 2, Issue 3) Dec KÖLN-MERKENICH GAS AND STEAM COGENERATION PLANT a. Fuel Specifications The 6FA-Gas Turbine (GEW RheinEnergie, Köln) from GE was designed in 1999, based on characteristics of H- and L-gas that were ascertained in 1996 (i.e. probes on site were analyzed). Gases with uniform qualities were assumed. b. The Operating Range of 6FA In Year 2001, movement in the gas market was realized. The operating range is shown in Figure 3 is insufficient for the prospective liberalized gas market. If measures aren t taken there is a danger that, in the simplest case, the gas turbine will fail. In the long run, damages can t be ruled out. Operating Range 6FA L-Gas RG (Feb/96) Wo,n = 12,69 Wo,n kwh/m3 15,70 H-Gas RG (Sep/95) Wo,n =13,83 WG 08/29/01; RG Feb/00 Wo,n =14,7 WG Eynattten (Jun/00) Wo,n = 14,59 North Sea Gas Wo,n = 15,0 WG Mattnow (Aug/00) Wo,n = 14,81 H-Gas Wo,n = 15, , ,59 Modified Wobbe Index = MWI ,83 13,26 12,69 12,38 12, , , Gas Temperature in C Figure 3: Operating Range of the Köln-Merkenich 6FA Gas Turbine

9 Gas Market Liberalization & GT Operation OMMI (Vol. 2, Issue 3) Dec c. Measures taken on the way to the Liberalized Gas Market For the protection of the 6FA, a second Wobbe-Index measuring device -- in addition to the one located directly at the gas turbine -- was installed at a point far ahead of the gas turbine. - Distance between gas turbine and second Wobbe-Index measuring device is approximately 360 m. - Measurement time totals 120-seconds - Remaining reaction time is 4-minutes (time that gas at base load needs for 360 m.) Gas preheating should be used to widen the gas turbine s range of operation (Figure 3) and to protect it from damages. Presently, the ordering of a gas preheating unit is problematic. Suppliers have already successfully implemented gas preheating with fixed fuel temperatures for increased efficiency. However, preheating, whereby fuel temperature is controlled by gas quality, is a new concept. Our procedure for gas preheating involves two steps: 1. Analyzing the transition function of a change between 2 qualities of gas. 2. Determining the gas temperature caused by slow changes in gas quality. The results of both steps are summarized to determine the future strategy. 5. SUMMARY The possible gas quality fluctuations, due to gas market liberalization, can result in gas turbine operation using fuels that deviate widely from design specifications. Hence, the following questions are raised: Which types of operating problems are caused by heavy deviations in gas quality? Can failure be prevented with heavy deviations in gas quality? Are protective devices for gas turbines necessary? From the gas turbine operator s point-of-view, it must be determined how their gas turbines are prepared for fluctuating gas qualities (within the allowed bandwidths for H- respective of L-Gas according to the DVGW-Guidelines). If gas turbine suppliers determine that fully utilizing the fluctuation range of the Wobbe-Index (based on DVGW-Arbeitsblatt G260) causes significant changes to flame geometry with respective operating restrictions or damage potential, then they should provide plant-specific suggestions to gas turbine operators.

10 Gas Market Liberalization & GT Operation OMMI (Vol. 2, Issue 3) Dec REFERENCES [1] Ströbele W., Zur Verbändevereinbarung zum Netzzugang für Erdgas. Gutachten im Auftrag von BGW und VKU Münster Dec [2] Schulz W., Hallaschka I., Perner J., Schuppe T., Zander W., Borowka J., Kirchenbauer J.M. and Möller A., Analyse und wettbewerbliche Bewertung der Verbändevereinbarung Gas zum Netzzugang Gutachten im Auftrag des Bundesministeriums für Wirtschaft und Technologie, Endbericht Nov. 9, [3] Verbändevereinbarung zum Netzzugang bei Erdgas (VV Erdgas II) May 3, 2002 (valid from Oct. 1, 2002). [4] Verbändevereinbarung zum Netzzugang bei Erdgas (VV Erdgas I) Jul. 4, 2000 (valid until Sep. 30, 2002). [5] 1. Nachtrag Verbändevereinbarung zum Netzzugang bei Erdgas (VV Erdgas I), Jul. 4, [6] 2. Nachtrag zur Verbändevereinbarung zum Netzzugang bei Erdgas (VV Erdgas I), Sep. 21, [7] DVGW-Arbeitsblatt G 260 Gasbeschaffenheit (Jan. 2000). [8] DVGW-Arbeitsblatt G 685 Gasabrechnung (Apr. 1993). [9] Zschunke T. and Neumann M., Einfluss der Gasqualität auf die Verbrennung TU Dresden, Institut für Thermodynamik und Technische Gebäudeausrüstung, Vorstudie Apr. 16, [10] Arnold Ch. and Seyffarth J., Studie zum Einfluss der Gasqualität auf die Verbrennung KEMA-IEV Dresden, Bericht-Nr P, May 30, [11] GEI 41040E Prozess-Spezifikationen Brenngase für die Verbrennung in Hochleistungsgasturbinen GE Industrieal & Power Systems, Gasturbine, Aug

CHAPTER 2 COMBUSTION PROPERTIES

CHAPTER 2 COMBUSTION PROPERTIES Combustion Properties 1. Calorific value (CV) 2. Specific Gravity (SG) 3. Wobbe Number 4. Heat of Combustion 5. Flammability Limit 6. Flame Speed 7. Ignition Temperature