Gas Chromatography monitors Green House Gas (GHG) emission from flares

Transcription

1 Gas Chromatography monitors Green House Gas (GHG) emission from flares International regulations increasingly call for on-line monitoring of Green House Gas emissions from flare stacks Flaring produces Green House Gases Partly as a consequence of the Kyoto protocol of December 1997, climate change is one of the most discussed issues worldwide. International regulations and restrictions have been implemented in order to reduce the impact of human activities on the environment including the emission of greenhouse gases (GHG). A considerable contribution to the world s total GHG emission originates from gas flaring: According to a World Bank estimation, an amount of around 150 billion cubic metres of natural gas is flared around the world annually, contaminating the environment with 400 million tons of CO2. This is equivalent to around 25 % of the United States gas consumption, or 30 % of gas consumption in the European Union. It is not surprising, therefore, that governments around the world are taking action to reduce gas flaring and venting. As a result, regulation of gas flaring is becoming more stringent for energy-intensive installations, especially those in the power generation sector. Current legislation focuses on CO2 emissions, but this is likely to be widened in the future to include other greenhouse gases and additional industry sectors. Regulations for flare gas monitoring In the European Union (EU), the key instrument to regulate the monitoring of flare gas emissions is the EU Emissions Trading Scheme (ETS) and its Monitoring and Reporting Guideline. Originating in 2005 and now in its third phase, the EU ETS requires operators to measure, monitor and report the flare GHG emissions of their relevant plants on the basis of a Carbon Credit Trading principle. Offshore flaring was included in 2008 and the aviation and maritime sectors in In the USA, (1) in 2009, the EPA promulgated a new rule affecting GHG emissions from numerous industries and (2) according to the Bureau of Ocean Energy, Regulation and Enforcement, gas quantities must now be accurately measured by facilities in the Gulf of Mexico region and US outer continental shelf. Effective regulation of gas flaring and venting relies on accurate measurement. This is reflected in rigorous flare measurement guidelines introduced by countries to support flaring legislation. ABLE Instruments is a key provider of complete solutions for flare gas monitoring, including Process Gas Chromatography and Ultrasonic Flare Gas Flow Metering. About Flaring Flaring is a controlled, open-flame combustion process to burn unwanted or surplus gases from different sources and for various reasons: (1) natural gas associated with crude oil when it is pumped up from the ground and/or (2) gases from industrial operations such as refineries, petroleum production, chemical plants and others, where another use of the gases is not possible or intended. The primary aim of flaring or venting is to act as a safety method to protect vessels or pipes on a plant from over-pressuring. In this case, pressure relief valves automatically release gas to the flare where it is burned or vented. Flares are also used as an outlet for gas during maintenance and repairs. In these cases, the flare is operated temporarily until the emergency situation is resolved or maintenance has been completed. 1

2 Emission of CO2 and methane Natural gas, propane, ethylene, propylene, butadiene, butane and potentially sulphur are the main constituents of waste gases from the oil and gas industry. During combustion, these hydrocarbons react with atmospheric oxygen to form carbon dioxide and water leading to emission of CO2, the most active green house gas. Venting the gas also releases even larger quantities of methane, the second main greenhouse gas, directly to the atmosphere. In some cases flared gas also contains hydrogen sulphide (H2S), which combusts to form SO2, a critical pollutant in terms of acid rain contribution. Flue gases from coal-fired power stations contain mostly uncombusted N2 and up to 25 volume % CO2. Environmental concerns and regulations Many countries, such as the United States and those of the European Union, have established, or plan to establish, regulations to limit and reduce the amount of GHG emission. Flares are specifically mentioned as a source of GHG emissions and are included in those regulations. The following chapters refer to the EU regulations. It covers more than 11,000 facilities in 31 countries which translates to around 45 % of the total greenhouse gas emissions from these countries. (See the 2003/87/EC Directive, the EU Commission Decision 2007/589/EC and the EU Commission Regulation 601/2012). The EU ETS is now in its third phase, running from 2013 to 2020 with a major revision approved in 2009 in order to strengthen the system. The Carbon Credit concept The main instrument used to regulate the measurement of flare gas emissions is the EU Emissions Trading Scheme s (ETS) Monitoring and Reporting Guideline. The European commission allocates Carbon Credits (gas emission permits) as tradable commodities to the countries which limit the amount of CO2 that can be released to the atmosphere by each country. In order to ensure that the countries comply with their allocated allowances, they must monitor and report emissions. In each country, this allocated limit ( cap ) is spread over the various industrial installations, which have to report their individual emissions at the end of a year. Depending on whether they have emitted less or more CO2 than allocated, they can sell or must buy credits. Phase 3 regulations Almost all types of industry need to comply with emissions monitoring and reporting: Refineries and petrochemical plants, oil and gas production plants, power plants using fossil fuels, coke, metal ore roasting and sintering, iron and steel, cement, lime, glass, ceramic, and pulp and paper facilities. The revised Monitoring and Reporting Regulations (MRR 601/2012) replaces the previous Monitoring and Reporting Guidelines (2007) and reinforces the need to demonstrate compliance with uncertainty targets, setting more rigorous verification requirements and guidance for auditors. Fig 1. Typical flares in process plants The EU Emission Trading Scheme Following the Kyoto protocol, the ETS is central to the European Union s policy to reduce climate change and a key tool for reducing industrial greenhouse gas emissions. Introduced in 2005, it has become the biggest international system for trading greenhouse gas emission allowances. Phase 3 also includes flaring from chemical production sites, and the allocation for routine and maintenance flaring, to be purchased through auction. Besides emissions of carbon dioxide, nitrous oxide emissions from the production of certain acids and emissions of perfluorocarbons from aluminium production are now also included in phase 3 which also accommodates the aviation and maritime sector. 2

3 Methodologies to determine emissions Effective regulation of gas flaring and venting relies on accurate and reliable measurements. This is reflected in measurement guidelines introduced to support flaring legislation. In the EU, the regulatory guidelines allow a number of approaches and methods to determine the amount of gas flared. However, the guidelines are not prescriptive in terms of specifying a type of measuring technology. The two main approaches are Calculation based approach which involves the measurement of the quantity of gas flared (precombustion) and a calculation of the total amount of CO2 emitted using emission and oxidation factors Or Measurement based approach which involves emission determination by means of continuous measurement of the concentration of the relevant greenhouse gas in the flue gas and of the flue gas flow. Combinations of these approaches are allowed, under the condition that the operator demonstrates that neither double counting nor data gaps in the emissions will occur. Gas analysis both approaches In the measurement based approach in addition to determining the gas flow through the stack continuous emission monitoring systems (CEMS) or other accepted analysis methods such gas chromatography (GC) are used once the operator has received approval from the competent authority. Even in case of calculation based methodology, gas analysis instrumentation may be used according to article 32 of regulation (EU) No 601/2012:...where online gas chromatographs or extractive or non-extractive gas analysers are used for emission determination, the operator shall obtain approval from the competent authority for the use of such equipment. The key advantages of online analysis are both practical and economical. In cases when blow-down activities are recorded (flow rate increase) without on line GC, the plant operator must collect a sample of flare gas typically within 15 minutes. This has to be done at anytime day and night, no matter if it happens during working days or at the weekend. In some countries cost savings of several hundred thousand Euro or significantly more could be achieved per annum for both central but decentralized flare installation (e.g. by avoiding the costs of EU emission credit trading). Measurement uncertainty Regulations dictate that operators report flare emissions to a high degree of accuracy and stipulate the need to ensure that all equipment is appropriately applied, maintained and calibrated. Regarding measurement uncertainty, the EU ETS applies a tiered approach: Larger installations (category C, fig. 2) are required to meet a lower level of measurement uncertainty (higher accuracy) compared with smaller installations. Online Process Gas Chromatographs are able to support these requirements. With regard to measuring flare gas, the regulation considers this to be a more difficult task and allows a higher threshold of ± 7.5 % in type C category and ± 12.5 % and ± 17.5 % for type B and A category installations respectively. Installation Category Annual emission [kilotons of fossil CO2] Uncertainty for total annual emission value Uncertainty for flare gas measurements A 50 ± 7.5 % ± 17.5 % B > 50 < 500 ± 5.0 % ± 12.5 % C > 500 ± 2.5 % ± 7.5 % Fig 2. Measuring uncertainty thresholds Calculation of emissions In the calculation based approach the calculation of emissions is done by means of activity data, e.g. the amount of fuel or process input material consumed, multiplied by an emission factor, multiplied by an oxidation or conversion factor (see formula top of next page). 3

4 Calculation of CO2 emission CO2 Emissions = Activity data x Emission factor x Oxidation/Conversion factor Activity data represents material flow, consumption of fuel, input material or production output. Emission factors are based on the carbon content of fuels or input materials. Oxidation factor for combustion emissions (or Conversion factor for process emissions reflect the proportion of carbon which is not oxidised or converted in the process. In the measurement based approach, the greenhouse gases in the installation s off-gases are themselves the object of the measurement requiring gas composition and gas volume flow. Detailed information regarding the various calculation procedures is contained in the respective guidelines. Gas Chromatography is a key method Determining composition of flare gases can only be achieved by using appropriate gas analysis instrumentation. Different techniques can be used such as gas chromatography or spectroscopic methods. While traditional CEMS (Continuous Emission Monitoring Systems) using continuous gas analysers monitor post combustion gases, which contain only a limited number of gas components, flare gas emissions are determined by analysing the gas composition prior to combustion where typically many more gaseous components exist. This requires analysers such as gas chromatographs which are able to perform a multicomponent analysis including calculation of the calorific value. The measuring results are then used to assess the total CO2 emission. Fig 3. Flare Gas Monitoring key measurements 4

5 The typical measuring point is located after all knock-out drums and liquid separators (fig. 3). Before the liquid drum the blow-down gases are usually too dirty and are mixed with liquid. Taking gas at this point is not representative and too difficult to process. In order to maintain a high level of quality assurance, recognized standards such as of ISO, CEN or ASTM should be applied. EU ETS regulation requires compliance with a number of standards as listed in fig. 4. EN 15984: 2011 ISO 6974, DIN ISO 6976, DIN EN ISO 17025: 2005 EN ISO 10723: 2012 EN ISO 9001: 2000 ISO 12039: 2001 ISO 10396: 2006 ISO 14164: 1999 Fig 4. Relevant Standards Relevant Standards Determination of composition of refinery heating gas and calculation of carbon content and caloric value Gas chromatography method Natural Gas Description of the measuring method by gas chromatography Calculation of caloric value and other physical properties Requirements for the competence of testing and calibration laboratories Performance evaluation for online analytical systems Natural Gas Quality management systems Requirements Stationary source emissions ABLE Instruments & Controls Ltd as a key partner As a long time provider of analytical solutions, ABLE Instruments & Controls Ltd is uniquely qualified to assist plant sites in meeting these new requirements. ABLE has developed, tested and validated analytical solutions that exceed the requirements of the regulations today and provide flexibility for tomorrow. ABLE has available a wide range of products and services ranging from detailed up-front engineering assistance, provision of tested and validated analytical solutions and flare gas flow metering instrumentation, as stand alone or as part of a packaged system, as well as delivering startup assistance, field validation and maintenance services to ensure regulatory compliance. A core technology for online flare gas monitoring is process gas chromatography (PGC) which has the capability to provide data for a wide range of constituents with varying concentration levels whilst giving the best measurement uncertainty. Beside the performance of the online GC itself, optimal performance depends upon the careful selection of the sample probe, the sample lines and the sample conditioning system. The use of the MAXUM or MicroSAM GC provides options for the determination of calorific value as well as H2S and Total Sulphur. Another required measurement is oxygen safety monitoring which can be achieved by using an in-situ tunable diode laser (TDL) gas analyser type SITRANS SL. Flare Gas Monitoring for simple applications using MicroSAM (Calorific Value) MicroSAM is an outstanding compact online gas chromatograph. The GC hardware is based on micromachined analytical components on the scale of microchip technology, which permits the compact design associated with high resistance against environmental influences. Protection against moisture, dust and corrosion (IP65, NEMA 4X), operation at extreme ambient temperatures (-20 to +55 C), as well as explosion protection without purging (EEx d) are indispensable for field installations. The analyser comprises three modules (analytics, pneumatics and electronics) which are modular in design and interface to enable easy replacement and a reduced spare parts requirement. 5

6 Fig. 5 shows a typical gas specification for an elevated flare in a polyethylene plant. The gas includes volatile organic carbons (VOC) including highly reactive substances such as ethylene and propylene and other individual constituents which are required to calculate the calorific value (CV) and molecular weight (MW). Component Concentration [Vol%] Measuring range [Vol%] Repeatability [%] H Calculated N CH Ethane Ethene Propane Propylene Butane C H Not meas. Fig 5. Gas specification Elevated PE flare well as a wide range of detectors options such as TCD, FPD or FID. The analyser is therefore extremely flexible when it comes to meeting varied user requirements with an economic approach This applies to flare gas applications in determination the calorific value from the gas composition, the H2S concentration or even the total sulphur content. Often plant operators are interested in combining single or multi-point flare gas monitoring systems with other measurements for economic reasons. Combinations of process flare (high ranges most components) online analysis with other applications such as tank flare (high ranges nitrogen and ethane), furnaces or boilers (high ranges hydrogen, methane and ethane) or heating gas to burners for steam production are often used in practice on site. Therefore powerful analytical solutions are feasible from simple off-gas compositions from one plant section to more complex applications by using just one MAXUM analyser for multiple sample extraction points. This analyser concept allows also standardized system solutions for less complex flare gas specifications (fig. 6). Despite the sample extraction point being downstream of the liquid separators, it is mandatory to keep the sample at defined temperature levels (standard is 60 or 120 C) to avoid water condensation when the sample is introduced into the analyser. This could result in fluctuations in the analyser s repeatability. Furthermore filtration and pressurization of the sample is intrinsic to reliable functionality of the complete analytical solution. Flare gas monitoring using MAXUM edition II (Calorific Value, H2S and Total Sulphur) MAXUM edition II is very well suited to deployment in rough industrial environments and hazardous areas and meets a wide range of applications in refineries and the chemical and petrochemical industry. The key analytical features of the MAXUM edition II are a flexible, energy saving single, dual or modular oven concept, maintenance-free valve less column switching and parallel chromatography using multiple single trains as Fig 6. Cabinet mounted flare gas system using a smart Micro GC 6

7 Analytical solutions Solution GC 1: Determination of major gas components including H2S for calorific value calculation Fig. 7 shows the measuring components of a multiple use flare gas application and fig. 8 the respective analytical configuration of the total of 4 analytical trains by one MAXUM gas chromatograph. Each analytical train is standardized by using a 10-port diaphragm valve (Model 50), two separation columns (typically micro-packed type) and a multi-tcd detector (8-cell TCD). For standard vapour applications (component concentrations in the percentage level) as for flare gas applications the model 50 valve (10- port membrane valve) combines sample injection and column switching for reconditioning of the analytics by back flushing into one unit. This in combination With the multi-cell TCD simplifies the analytical train and reduces maintenance requirements significantly. The deployment of a robust Teflon coated stainless steel diaphragm allows up to 10 million switching cycles on clean samples without maintenance. Application (Components) Required Instrumentation Basic Configuration CV and C6+ application: Four Analytical Trains: Optional Extensions to Basic Configuration Optional Extensions to Basic Configuration H2, N2, O2, CO, CO2 4 injection/backflush valves CH4, C2H2, C2H4, C2H6 Sum C3, Sum C4, Sum C5, Sum C6+ C3s individual C4s individual H2O or H2S Benzene, Toluene, Xylenes (BTX) CV and C5+ application incl. H2S CV and C5+ application Fig 7. Flexible measurement tasks for various flare gas monitoring approaches 4 sets of micropacked columns Two 8-cell-TCDs 1 additional train (max. 6 trains/maxum) 1 additional train (max. 6 trains/maxum) 1 additional train (max. 6 trains/maxum) 1 additional train (max. 6 trains/maxum) 3 Analytical trains, meets US flare gas regulation 2 Analytical trains, meets US flare gas regulation Fig 8. 4-train configuration of MAXUM 7

8 Solution GC 2: Total Sulphur Determination (fig. 9) The Siemens Flare Total Sulphur Analyser is built around the proven process gas chromatograph MAXUM edition II. The analyser uses a vapour sample valve to deliver the sample to the burner. A Flame Photometric Detector then measures the resulting SO2. The sample amount introduced to the burner is matched to the analyser operational requirements. To achieve a specific sample dilution, the carrier flow that pushes the sample into the burner is adjusted for each range. The measuring range is determined and automatically controlled using software. Depending on the requirements, measuring ranges can be realized from low ppm levels (10 ppm to 500 ppm) up to high % (10 to 100 %) Total Sulphur measuring ranges. The cycle time to results is 4 minutes. Extensive field evaluation and installed analyser systems have proven system efficiency, with excellent linearity, stability, and repeatability. Key benefits by using Siemens Gas Chromatographs MAXUM and MicroSAM Simple analytical solutions by modular GC design facilitate user friendly operation and optimize plant personal maintenance works. Rapid measurements secure the availability of analyser data to the control and reporting system in accordance to the Emissions Trading Scheme. Flexible GC analytics enable cost effective standard as well as customized flare gas applications. Widely used field proven solutions guarantee high reliability of the measurement system. The tested and validated solution guarantees best measurement uncertainty and contributes to reliable reporting of the emission data. Safety monitoring with TDLS O2-analyzer Infiltration of air into the flare stack through leaks or the stack exit is critical as it can lead to a flame flashback resulting in a destructive detonation in the system. Therefore the oxygen level is typically measured and monitored in the flare drum (see fig. 3) for safety. Historically, paramagnetic oxygen analysers have been used in flare systems for this purpose. Unfortunately the paramagnetic O2 measurement technique is subject to interference by hydrocarbons which, in many cases, cannot be calibrated out or otherwise compensated for because the amount and type of hydrocarbon vary over time. The analytical solution for interference-free O2 measurement in flares is the in-situ TDL (Tunable Diode Laser) SITRANS SL. This analyser is not affected by varying hydrocarbons in the flare feed stream. The analyser has no moving parts and the sensors are intrinsically safe for Class 1, Division 2 installations. Since the SITRANS SL is an in-situ type analyser it has no sample system, reducing initial capital costs and long term cost of ownership due to extremely low maintenance. Sample Dilution Flame Oxidation Separation/ Removal of Optical Interferences Optical Detection of SO2 Fig 9. Sulphur measurement concept (using MAXUM Total Sulphur Gas Chromatograph) 8

9 Analytic Solution Sets The analytic solution set integrates the analyser and the appropriate sample transport and conditioning system in the plant environment and allows reliable long-term usage of the equipment. Various options are available from a simple 3-sided shelter, free-standing cabinet (as illustrated for MicroSAM solution, fig. 6) to walk-in type shelters with or without air conditioning (HVAC, fig. 10). Analytical solution sets from ABLE as a single source supplier provide remarkable user benefits ranging from single source responsibility to single-point FAT inspection. It also means lower project costs due to ABLE s long-term expertise in project planning, engineering and execution. Fig 10. Typical flare gas system package for multiple flare gas monitoring using the MAXUM As the exclusive UK channel partner for Fluenta AS, we are pleased to offer the renowned FGM160-II ultrasonic flare gas flow meter. The FGM160-II has been developed to specifically measure flare gas in pipes where pressure, velocity and large pipe diameters represent a real challenge. Flare Gas Flow Monitoring As accurate flow metering is also vitally important in helping companies calculate the carbon loading of their operations, it is appropriate within this document to discuss the best way to meter the flow of gases in flare stacks. Flare stacks are a well-established way to dispose of flammable The Fluenta FGM 160 as provided by ABLE waste gases safely. Before the issue of climate change edged its way up the political agenda, measuring the flow of gas as it exited the flare stack used to be primarily a safety issue a question of checking whether or not there was enough gas emerging to maintain a reliable flame. However, as the focus on industrial emissions intensifies, it has become more important to quantify flare gas emissions precisely so that companies and regulators can reliably calculate the greenhouse gases that industrial operations are releasing into the environment. This has a significant cost implication for companies, which are taxed on emissions under the Climate Change Levy. Offshore oil and gas platforms and sewage treatment plants are the sites where flares can be spotted most frequently, although they are also used to a lesser extent in other applications, such as landfill sites. As well as improving safety in these industries, flares also reduce the impact of emissions by converting methane into carbon dioxide, which has a much smaller global warming potential. Although safety remains the most immediate consideration when opting for a flare, the environmental case for flaring is increasingly important. The impact of methane on global warming is about 21 times greater than that of carbon dioxide. Since flares effectively burn methane to produce carbon dioxide, they can have a major benefit on the environmental impact of an industrial operation. For example, if 90% a gas volume is flared and 10% is vented, the vented gas would still have approximately twice the global warming potential of the flared gas. 9

10 The efficiency of flares varies, with the least efficient converting only 90% of methane into carbon dioxide and the most efficient converting 98%. So opting for the most efficient flare can reduce the potential impact on global warming by almost half. The situation is further complicated by the variability of flare gases, which may be rich in heavier hydrocarbons, such as propane, butane or pentanes. These produce more smoke than pure methane. The presence of other impurities, such as nitrogen, sulphur compounds or carbon dioxide will also play a role in determining the impact that a flare has on the environment. Natural gas is a normal by-product of oil production, but the gas output can be variable. Flares are therefore vital on all platforms for dealing safely with potential surges in production. Furthermore, some platforms produce gas in quantities too small to make it economical to transport back to shore, in which case flaring is the best alternative. Offshore companies are therefore issued with flare permits by the DECC. As the exclusive UK channel partner for Fluenta AS, ABLE Instruments & Controls Ltd offer the renowned FGM160- II ultrasonic flare gas flow meter. The FGM160-II has been developed to specifically measure flare gas in pipes where pressure, velocity and large pipe diameters represent a real challenge. The non-intrusive design of the FGM160-II does not penetrate the flow stream, providing a longer transmit path for improved turn down and longer life expectancy. The Fluenta flare gas meter is the most robust and accurate flare monitor on the market today. An essential tool for E&P operators. With over 1400 flare metering systems in operation worldwide, Fluenta is a world leader in ultrasonic flare gas metering. Features Optimized signal processing and acoustic sensors enabling Flow measurement up to 100 m/s Automatic Gain Control (AGC) for enhanced performance Digital Signal Processing (DSP) Software based interface (Operator Console) Easy and fast to install Field mounted flow computer Low maintenance costs Serial interface based on modbus protocol ABLE offer additional system options for Fluenta Ultrasonic Flare Gas Flow Meters including system integration, hot tapping, calibration & upgrade options. System Integration A flare gas metering installation not only requires a world class flare gas meter, but for most installations an integrated metering system. Whilst the Fluenta ultrasonic transducers can be installed directly onto the flare pipe, including hot tapping without shut down of the flare, often the meter is supplied spool mounted with integrated pressure & temperature measurement. To ensure the entire flare metering system is supplied to meet customer installation and project specifications, full design and fabrication services, project management and documentation control is provided by ABLE as part of the ABLE-Fluenta relationship. Valve Isolation Whilst the FGM160-II utilises a pair of non-intrusive ultrasonic transducers, provision has always been made to allow for transducer withdrawal from the process under pressure for inspection or maintenance without shut down of the flare. The traditional design to achieve this using a single ball valve, whilst providing adequate isolation, does not offer the increased safety delivered by double block and bleed valves (DB & B). This type of valve achieves both primary and process isolation and the means to safely dispose of unwanted gas and liquid trapped within the assembly. ABLE instruments offer double block and bleed valves with all flare gas meter proposals as an important additional safety feature. 10

11 Operator Interface SOFTFLOW Basic The SOFTFLOW Basic system is designed to control and monitor Fluenta Flare Gas Metering systems (FGM). This user-friendly solution improves the way critical information is acquired and combined by using advanced graphs and customizable alarm features. SOFTFLOW Basic allows for communicating with multiple FGMs from every computer inside the local network and is compatible with many web browsers. Advantages: Easy-to-implement no need to install or calibrate the Operator s Interface The Operator s Interface is accessible via a web browser therefore also available from portable devices PDAs, laptops, tablets, mobile phones, etc. Constant remote control and diagnosis of multiple FGM systems performed in parallel in the safe area Storing historical records of measured and calculated data Customizable graphs for up to four parameters presented simultaneously with the option to save the graph template FGMs and SOFTFLOW Basic appliance s uptimes displayed for any pre-selected period Immediate downtime detection Remote alarm setting for all instruments or a specific FGM 11