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

Transcription

1 Process Analytics 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 Climate changing is one of the most discussed issues worldwide especially as consequence of the Kyoto protocol of December International regulations and restrictions have been implemented in order to reduce the impact of human activities on the environment including the emission of green house gases (GHG). A considerable contribution to the worlds total GHG emission originates from gas flaring: According to a World Bank estimation an amount of around 150 billion cubic meters 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, preferably in the power generation sector. Current legislation focuses on CO2 emissions, but very likely this will be widened in the future to include other greenhouse gases and further industry sectors. Regulations for flare gas monitoring In the European Union (EU), the key instrument to regulate the monitoring of flare gas emission is the EU Emissions Trading Scheme (ETS) and its Monitoring and Reporting Guideline. Started in 2005 and now already in its phase 3, the EU ETS brings operators to measure, monitor and report the flare GHG emissions of their relevant plants on the base of a Carbon Credit Trading principle since Offshore flaring was included in 2008 and aviation and maritime sector 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 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. Process Gas Chromatography is a key method to support flare gas monitoring and Siemens is a key provider of complete solutions for that. Note: Information contained in this document is partly taken from the documentation section of the EU Commission s website at the following address: siemens.com/processanalytics

2 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 safety method to protect vessels or pipes of a plant from overpressuring. In this case, pressure relief valves automatically release gas to the flare where it is burnt or vented. Flares are also used as 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. Emission of CO2 and methane Natural gas, propane, ethylene, propylene, butadiene, butane and potentially sulfur 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 releases as well even larger quantities of methane, the second main greenhouse gas directly to the atmosphere. In some cases flared gas contain also hydrogen sulfide (H2S) which combust to SO2, a critical pollutant in terms of acid rain contributor. Flue gases from coal-fired power stations contain CO2 by itself. Environmental concerns and regulations Many countries as those of the the European Union or the United States have established or plan to establish regulations to limit and reduce the amount of GHG emission. Flares are specifically mentioned as source of GHG emissions and included in those regulations. Besides the USA, the list of relevant countries actually comprizes all EU countries including the non-eu countries Norway, Iceland and Liechtenstein. Furthermore Qatar, Taiwan, Australia (2015), Korea (2015), which all use elements of the EU legislation. The following chapters refer to the EU regulations. The EU Emission Trading Scheme Following the Kyoto protocol, the ETS is the central part of the European Union s policy to reduce climate change and a key tool for reducing industrial greenhouse gas emissions. Introduced in 2005, it became the biggest international system for trading greenhouse gas emission allowances. It covers more than facilities in 31 countries which means around 45 % of total greenhouse gas emissions from these countries. See e.g. 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 to regulate the measurement of flare gas emission 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 whether they have emitted less or more CO2 than allocated, they can sell or must buy credits. Phase 3 regulations Almost all types of industries need to comply with emissions monitoring and reporting: Refineries and petrochemical plants, oil and gas production plants, power plants using fossil fuels, also coke, metal ore roasting and sintering, iron and steel, cement, lime, glass, ceramic, and pulp and paper facilities. The revised Monitoring and Reporting Regulation (MRR 601/2012) replaces the previous Monitoring and Reporting Guidelines (2007) and strengthens the need to demonstrate compliance with uncertainty targets, setting more rigorous verification requirements and guidance to auditors. Third phase 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 as well as the aviation and maritime sector. Fig. 1: Typical flares in process plants 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. But: 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 (pre-combustion) 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 in 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 the calculation based methology, gas analysis instrumentation may be used according to article 32 of regulation (EU) No 601/2012: "... where online gas chromatographs or extractive or nonextractive gas analyzers are used for emission determination, the operator shall obtain approval from the competent authority for the use of such equipment." Measuring uncertainty Regulatory issues require the operators to report flare emissions to a high degree of accuracy and the need to ensure that all equipment are 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 to smaller installations. Online Process Gas Chromatographs are able to support these requirements. Especially for measuring flare gas, the regulation considers that this is 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. 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. amount of fuel or process input material consumed, times an emission factor times an oxidation or conversion factor, see formula below. 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. Very detailed information about the various calculation procedures are contained in the respective guidelines. The key benefit for online vs. offline analysis has often practical and significant economical reasons. 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 weekend. In some countries cost savings of several hundred thousand Euro or even significantly more could be achieved per annum for central but also decentralized flare installation (e.g. by avoiding the costs of EU emission credit trading). 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 prodution 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. 3

4 Fig. 3: Flare gas monitoring (Siemens concept) Gas Chromatogaphy is a key method Determining composition of flare gases can only be achieved by using gas analysis instrumentation. Different techniques can be used such as gas chromatography or spectroscopic methods for example. While traditional CEMS (Continuous Emission Monitoring Systems) using continuous gas analyzers monitor post combustion gases which contain only a limited number of gas components, flare gas emissions are determined by analyzing the gas composition prior to combustion where typically much more gaseous components exist. This requires analyzers 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. 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 mixed with liquid. Taking gas there is not representative and too difficult to handle. 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. Relevant standards EN 15984: 2011 Determination of composition of refinery heating gas and calculation of carbon content and calorific value - Gas chromatography method ISO 6974, DIN Natural Gas - Description of the measuring method by gas chromatography ISO 6976, DIN Calculation of calorific value and other physical properties EN ISO 17025: 2005 Requirments for the competence of testing and calibration laboratories EN ISO 10723: 2012 Performance evaluation for online analytical systems - Natural Gas EN ISO 9001: 2000 Quality management systems - Requirements ISO 12039: 2001 ISO 10396: 2006 Stationary source emissions ISO 14164: 1999 Fig. 4: Relevant standards 4

5 Siemens Process Analytics is a key partner As a long time provider of analytical solutions, Siemens is uniquely qualified to assist plant sites in meeting these new requirements. Siemens has developed, tested and validated analytical solutions that exceed the requirements of the regulations today and have the flexibility for tomorrow. Siemens has available a wide range of products and services ranging from providing detailed up-front engineering assistance, providing tested and validated analytical solutions, stand alone or as part of a packaged system, as well as providing start-up assistance, field validation and maintenance services to ensure regulatory compliance. A core technology for online flare gas monitoring is process gas chromatography (PGC) due to the capability to provide data for a wide range of constituents with flexible concentration levels and best measurement uncertainty. Beside the performance of the online GC itself the reliable and precise operation depends extremely also on the careful selection of the sample probe, the sample lines and especially the sample conditioning system. The GC portfolio by using MAXUM or MicroSAM allows options for the determination of calorific value as well as H2S and Total Sulfur. Another measurement task is the oxygen safety monitoring by using an in-situ tunable diode laser (TDL) gas analyzer type SITRANS SL. Flare Gas Monitoring for simple applications using MicroSAM (Calorific Value) Fig. 5 shows a typical gas specification for an elevated flare in a polyethylene plant section. 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 H2O Not meas. Fig. 5: Gas specification Elevated PE flare This analyzer concept allows also standardized system solutions especially for less complex flare gas specifications (fig. 6). Despite the sample extraction point is downstream the liquid separators it is mandatory to keep the sample on defined temperature levels (standard is 60 or 120 C) to avoid water condensation when the sample is introduced into the analyzer. This could result in fluctuations of the analyzer repeatability. Furthermore filtration and pressurization of the sample is obvious for a reliable functionality of the complete analytical solution. MicroSAM is an outstanding compact online gas chromatograph. The GC hardware is based on micro-machined 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 analyzer comprises three modules (analytics, pneumatics and electronics) which are standardized in design and interfaces to enable easy replacement and reduced needs of spare parts. Fig. 6: Cabinet-mounted flare gas system using a smart Micro-GC 5

6 Flare gas monitoring using MAXUM edition II (Calorific Value, H2S and Total Sulfur) MAXUM edition II is very well suited to be used in rough industrial environments including hazardous areas and performs a wide range of duties in refineries and the chemical and petrochemical industry. MAXUM edition II analytical features are e.g. a flexible, energy saving single, dual or modular oven concept, maintenance-free valveless column switching and parallel chromatography using multiple single trains as well as a wide range of detectors such as TCD, FPD or FID. The analyzer is therefore very flexible to meet user requirements by a best economic approach also for flare gas applications to determine the calorific value from the gas composition, the H2S concentration or even the total sulfur content. Often plant operators are interested to combine single or multi-point flare gas monitoring systems with other measuring tasks due to economic reasons. Combinations of process flare (most components in high ranges) 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 just from one plant section up to more complex applications by using just one MAXUM analyzer for multiple sample extraction points. 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 used flare gas application and fig. 8 the respective analytical configuration of totally 4 analytical trains in 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 vapor 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 backflushing into one unit. This in combination with the multi-cell TCD simplifies the analytical train and reduces maintenance requirements significantly. Due to its design, using a teflon coated stainless steel diaphragm is very robust and allows switching cycles up to 10 million on clean samples without maintenance. Basic Configuration Optional Extensions to Basic Configuration Optional Reductions of Basic Configuration Application (Components) CV and C6+ application: H2, N2, O2, CO, CO2 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 measuring tasks for various flare gas monitoring approaches Required instrumentation Four Analytical Trains: 4 injection/backflush valves 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 6

7 Solution GC 2: Total Sulfur Determination (fig. 9) The Siemens Flare Total Sulfur Analyzer is built around the proven process gas chromatograph MAXUM edition II. The analyzer uses a vapor 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 analyzer 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 Sulfur measuring ranges. The cycle time to results is 4 minutes. Extensive field evaluation and installed analyzer systems have proven efficiency, including linearity, stability, and repeatability. Safety monitoring with TDLS O2-analyzer Infiltration of air into the flare stack through leaks or the stack exit is critical because it may lead to a flame flashback resulting in a destructive detonation in the system. Therefore the oxygen level is measured and monitored in the flare drum (see fig. 3) for safety. Historically paramagnetic oxygen analyzers have been used in flare systems for safety. Unfortunately paramegnetic O2 measurement technique is affected by interference with larger amount of hydrocarbons which cannot be calibrated out or otherwise compensated in many cases because amount and type of hydrocarbon vary over time. The analytical solution for interference-free O2 measurement in flares is the Siemens in-situ TDSL (Tunable Diode Laser) SITRANS SL. This analyzer is not affected by varying hydrocarbons in the flare feed stream. The analyzer 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 analyzer it has no sample system, reducing initial capital cost and long term cost of ownership due to extremely low maintenance. Fig. 9: Sulfur Measurement concept (using MAXUM Total Sulfur Gas Chromatograph) 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. Fast applications secure the availability of analyzer data to the control and reporting system in accordance to the Emission Trading Scheme. Flexible GC analytics enable economic 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 a reliable reporting of the emission data. Analytic Solution Sets The analytic solution set integrates the analyzer and the appropriate sample transport and conditioning system in the plant environment and allows a reliable long-term usage of the equipment. Various options are available from simple 3-sided shelter, free-standing cabinet (as illustrated for MicroSAM solution, fig. 6) up to walk-in type shelters with or without air conditioning (HVAC, fig. 10). Analytical solution sets from Siemens - as single source supplier - provide remarkable user benefits ranging from single source responsibility to single-point FAT inspection. It also means lower project cost due to Siemens longterm expertise in project planning, engineering and execution. Fig. 10: Typical flare gas system package for multiple flare gas monitoring using 8 MAXUM 7

8 Siemens Process Analytics at a glance Leading in process analytics Siemens is a leading provider of process Chromatographs, process analyzers and process analysis systems and solutions. We offer our global customers the best solutions for their applications based on innovative analysis technologies, customized system engineering, sound knowledge of customer applications and professional support. From applications in the chemical and petrochemical industry to emission monitoring in waste incinerators and power plants, the highly accurate and reliable Siemens analyzers and chromatographs will always do a perfect job. The chromatographs and analyzers are easily integrated into the Totally Integrated Automation (TIA) concept making Siemens Process Analytics your qualified partner for efficient solutions that integrate process analyzers into automation systems. Global presence The global presence of the Siemens service organization permits optimum support for our customers through fast response time onsite. Furthermore, our service specialists are acquainted with the local and regional requirements, standards and directives. We can offer our customers tailored service products based on our specific knowledge of the processes involved in the oil & gas, chemical, power, cement and other industries. Plant life-cycle support As a result of our large service portfolio we are able to support our customers throughout the complete product life cycle. We already develop cost-efficient and reliable analytical concepts during plant planning. Using customized service cotracts and competent service onsite we can help to reduce downtimes while simultaneously ensuring optimum operation of the analytical equipment. Our range of services is extended with technical support from experts over the hotline and a comprehensive selection of on-site training courses for service personnel and operators. FEED Front End Engineering and Design (FEED) is part of the planning and engineering phase of a plant construction or modification project and is done after conceptual business planning and prior to detail design. During the FEED phase, best opportunities exist for costs and time savings for the project, as during this phase most of the entire costs are defined and changes have least impact to the project. Siemens Process Analytics holds a unique blend of expertise in analytical technologies, applications and in providing complete analytical solutions to many industries. Siemens AG Industry Sector Sensors and Communication Process Analytics KARLSRUHE GERMANY Subject to change without prior notice 08/2014, Siemens AG The information provided in this Case Study contains descriptions or characteristics of performance which in case of actual use do not always apply as described or which may change as a result of further development of the products. An obligation to provide the respective features shall only exist if expressly agreed in the terms of contract. Availability and technical specifications are subject to change without prior notice. All product designations may be trademarks or product names of Siemens AG or supplier companies whose use by third parties for their own purposes could violate the rights of the owners.