Technical Publication

Transcription

1 Technical Publication Flare Gas Flow Measurement and Control Jim DeLee, Sr. Member, Technical Staff Fluid Components International (FCI) Visit FCI online at FCI is ISO 9001 and AS9100 Certified FCI World Headquarters 1755 La Costa Meadows Drive San Marcos, California USA Phone: Toll Free (US): Fax: FCI Europe Persephonestraat TT Tilbur, The Netherlands Phone: Fax: FCI Measurement and Control Technoloy (Beijin) Co., LTD Room 107, Xianfen Buildin II, No.7 Kaituo Road, Shandi IT Industry Base, Haidian District Beijin , P. R. China Phone: Fax:

2 In oil/as production, refinin and storae operations around the lobe, flare as systems are used to burnoff and dispose of waste, excess or off-ases, and as a safety system. The accurate, responsive and reliable measurement of flare as is essential in order to assure proper operation of the flare as system, which protects people and equipment from potentially hazardous combustible as to maintain a safe workin environment and to avoid environmental contamination. The Problem Flare as flow meters provide plant operations manaers with an intellient tool to sinal abnormal process chanes, early leak detection and report on flared ases to comply with safety and environmental aency reportin. Flare as systems are installed on offshore platforms and in land-based production fields, on transport ships and in port facilities, at storae tank farms and alon distribution pipelines. The daners of improper hydrocarbon as handlin are well known and are reulated strictly by the United States (U.S.) Occupational, Health and Safety Administration (OSHA) as well as other international safety oranizations. The combustible and flammable properties of hydrocarbons make their handlin a hihly reulated process, requirin flow meter desin certifications from multiple international approval aencies includin FM, FMc, ATEX and IECEx to name a few. In their efforts to reduce lobal warmin, the U.S. Environmental Protection Aency (EPA), the European Union (EU) and aencies at multiple levels of overnment around the lobe are imposin stricter reulations that vary by eoraphic zone for air pollution monitorin, abatement and reportin. The conversion of these waste ases to cleaner burnin electric power eneratin and their interation into the power rid also is bein encouraed at multiple levels of overnments. Many oil and as operations, refineries and chemical plants have flare as system applications that are uniquely challened with two diverse and critically important flow conditions: (1) very low flow under normal conditions and (2) sudden very hih flows durin an upset/blow-down condition. Plant operators, manaers and instrument-and-control enineers are then further challened to comply with the environmental aencies and emissions tradin reulations for their flares stipulatin flow meter accuracy of ± 5% of readin throuhout the entire measurin rane. Flow Meter Challenes Flare as flow measurement applications present several unique challenes to plant, process and instrument enineers when selectin a flow meter solution. In addition to both low flow rates and then sudden hih flow rates durin upset conditions, there several other important criteria to consider when selectin a flow meter for flare as applications: Mixed ases Flow meter calibration specifically for hydrocarbon composition ases and matched to actual process conditions Lare pipe sizes As line sizes increase the effective and suitable flow meterin technoloy options (choices) decrease Lack of available straiht-run Larer line size and limited real estate, particularly on off-shore platforms, are restrictive to providin required straiht run to achieve repeatable flow meterin accuracy Aency approvals for installation in hazardous (Ex) locations The entire flow meterin instrument should carry aency approval credentials for installation in environments with potential hazardous ases; enclosure only ratins are inadequate (and risky) Compliance with local environmental reulations Meet performance and calibration procedures mandated within local reulations such as US EPA s 10 CFR 40; 40 CFR 98; EU Directives 2003/87/EC and 2007/589/EC; US MMR 30 CFR Part 250, Subpart K, Section 250 and others Fluid Components International LLC Pae 2

3 Limited access Pipe access and re-access for installation, maintenance or servicin is difficult; spool-piece flow meters may require proloned process shut-down and extensive on-site labor costs to install and maintain Offshore platforms corrosive salt water Offshore platform may require use of stainless steel on all exposed instrument materials, includin sensors, process connections and enclosures Key Criteria For Flow Meter Selection When selectin a flow meter for flare as applications, plant operators, manaers, process and instrument enineers, will want to have compiled a key criteria check list. There are multiple air/as flow measurement technoloies to choose from and not all of them are well suited to the accuracy, reliability, raneability and rued operatin environment in the oil/as industry. For example, some flow meter technoloies are better at measurin liquids (volume) than air or ases (mass flow). The accuracy of some flow meters is influenced by heat and some sensor technoloies are temperature-compensated to maintain accuracy. Movin parts are acceptable in some operatin environments and in other environments they can require hih levels of maintenance or repair or replacement. Selectin a flow meter can be a complicated process. A check list to select a flare as flow meter should include at a minimum the followin capabilities. Creatin a simple checkbox matrix to compare various flow meters aainst the followin criteria will quickly narrow the choices: Wide turndown for both low flow and hih flow conditions Meet local environmental aency requirements for accuracy and periodic calibration verification NIST certified calibration for mixed hydrocarbon flare ases Multiple calibrations for variations in composition Direct mass flow measurement Easy to install, minimal penetration points Non-cloin, non-foulin, no movin parts desin for lowest maintenance Aency approved for installation in explosive as classified environments Stainless steel wetted parts and optional stainless steel process connections and enclosure housins Fiure 2: ST100 Series flow meters The Solution Owners, operators, manaers and enineers across the petrochemical industry have relied on Fluid Components International (FCI) for as flow measurement solutions for decades. The company s flow meters are installed in flare as systems at both land-based and offshore platform systems throuhout the world, as well as in petrochemical refineries, storae and distribution plants. The company s flare as solutions rane from sinle-line to a lare flarin system with a complex array of tributary lines and mixed ases. From ultra-low flow measurement to detect the smallest of leaks and up to 1000 SFPS [305 NMPS] to measure major upset conditions accurately at very hih flows, the company s flow meters are a proven solution. While the company offers at least three flow meter product lines suitable for flare as system applications, its next-eneration ST100 Series Air/Gas Flow Meter (Fiure 2) provides extensive features and functions that extend and optimize its application in flare flow measurement. The ST100 Series flow meters combine a broad rane of easy to install insertion flow elements with the industry s most powerful and flexible electronics/transmitter and specialized, precision flare as calibrations. With wide turn downs, specific calibrations for mixed as compositions, SR2x split-rane/dual calibration and maximum output flexibility with 4-20 ma analo outputs or bus communications such as HART, Foundation fieldbus, or Modbus, this flow meter delivers a state-of-the-art as flow meter for industrial process, plant and offshore flare applications. Fluid Components International LLC Pae 3

4 Variable Flow Conditions Many oil/as operations, refineries and chemical plants have flare applications uniquely challened with two diverse flow conditions, very low flow under normal conditions and very hih flow durin an upset/blowdown condition. These industries are then further challened to comply with environmental aencies and emissions tradin reulations for their flares stipulatin flow meter accuracy of ± 5% of readin throuhout the entire measurin rane. The answer to this challene is provided with the ST100 Flow Meter s SR2x split rane/dual calibration option that provides: Split ranes Two separate and discrete ranes, one optimized in the low flow rane and one optimized in the hih flow rane (Fiure 3) Double calibration points Strateically placed and optimized in the low flow rane and hih flow rane to achieve ± 0.75% readin, ± 0.5% of full scale to a maximum of ± 5% of readin Dual 4-20mA analo outputs One dedicated to the low flow rane and the other to hih flow rane; this ensures maximum resolution of both the low flow and hih flow rane at the DCS, or, if any of the bus communications are specified, a sinle, contiuous hih accuracy diital value over the entire flow rane is sent to the DCS Lare Pipes In pipe sizes larer than 16 inches [406 mm] a dual-element averain system can provide better measurement performance and a more viable solution when it is impractical or impossible to provide the required straiht-run or installation of a flow conditioner is difficult. The company s dual-element averain system (Fiure 4) available with the ST100 Flow Meter provides Fiure 3: Dual Calibration Performance Fiure 4: Dual Element Systems Fluid Components International LLC Pae 4

5 the solution. Contact the applications enineers at the company to determine if a dual-element averain system will benefit the application. Communicate the Flow Local readout, multiple 4-20 ma analo outputs, diital bus communications includin HART, Foundation fieldbus, Modbus and more, are all available with ST100 Series to provide the flare flow data (Fiure 5). Should the plant need to chane or uprade, the meter is field upradeable to any of the available outputs. VeriCal In-Situ Calibration Verification Many flare meter installations, either per plant edict or for compliance with environmental reulations, require reular validation of calibration. Traditionally this has required a cumbersome and costly project to remove the meter from service and return it to a lab, which is particularly frustratin if the meter is found to still be within calibrated specifications. The VeriCal System (Fiure 6) provides a simple-to-use tool to verify the FCI flow meter is still within calibration without extractin the meter from pipe. The VeriCal system consists of a special VeriCal ready flow sensor, a portable VeriCal Kit (which can be used with any number of VeriCalready ST100 flow meters) and an additional benchmark calibration document to which field verification samples are compared. Fiure 5: Readouts & Diital Communication Conclusions When selectin a flow meter for flare as systems, be sure to start by developin a check list of key criteria that include performance, the operatin environment, environmental and safety criteria. Look for the lowest installed cost, lowest maintenance and lonest life flow meter technoloy. Relyin on these simple suestions will help you reduce the confusion of multiple choices in flow meter technoloies to arrive at a solution that performs as intended to ensure the plant operates efficiently, safely and with the minimum environmental footprint. Fiure 6: VeriCal System Fluid Components International LLC Pae 5