Fuel Flow Monitoring Systems Part 2: Potential Challenges and Best Practices

In Part 1, we looked at a few common types of fuel meters, how they measure flow, how they can be applied, and how they can impact a facility’s operations.  Data from fuel flow meters are fed into regulatory reports, emissions allowance determinations, sustainability metrics, and operations. In Part 2, we will look at the potential challenges around properly operating a fuel flow monitor and best practices to keep your fuel meter data as complete and accurate as possible.

Potential Challenges:

Data from fuel flow meters serves various purposes and is routinely used directly or indirectly by multiple stakeholders at a plant.  Any degradation in data quality materially impacts compliance and operations. You should be mindful of the following items to ensure proper operation of your facility’s fuel flow meters:

Design and Installation: The type and specification of a fuel flow meter affects its ability to meet regulatory or operational requirements. For instance, 40 CFR Part 75 or 40 CFR Part 98 may require fuel flow meters to be designed and installed according to standards such as American Society for Mechanical Engineers (ASME) or American Gas Association (AGA) 3 that contain detailed procedures for the design and installation of flow meters. An applicable air quality rule might require your flow meters to have a certain sensitivity or accuracy. Failure to install the flow meters per applicable standards would invalidate not only the data collected by the meters but also any downstream emissions calculations that use the fuel flow meter output.

Calibrating fuel flow meters: If fuel flow monitoring is regulatory driven, then the meters must be calibrated per the applicable requirements or per your site-specific monitoring plan. Typically, regulatory conditions or plans specify (1) the calibration methodology and (2) the frequency of calibration or verification. Using an incorrect or incomplete calibration methodology could be considered a missed calibration. Failure to comply with the methodology or frequency requirement can result in extended periods of invalid or bad data, which increases the risk of regulatory scrutiny or enforcement. In addition, emissions trading programs and other regulatory programs may require missing data substitution, where invalid or missing data is substituted with conservative emissions rates.  This substitution can increase total emissions and incur additional costs for emissions allowances.

Instrumentation and scaling: A typical flow meter consists of one or more sensors that measure the physical characteristics of the flow. The electronic signals produced by the sensors are converted to volumetric or mass flow rate. The processing and transmission of electronic signals involves several micro-electronic components such as signal conditioners. While mechanical failures are fairly easy to detect, degradation or failure of electronic components may go unnoticed for a long time, specifically when the failure is gradual and does not show large changes in output. Only isolated testing or statistical tools can be used to identify such failures.  Auditing your systems and using data-driven methods can help identify problems before catastrophic failure.

Another common issue with transmitting fuel flow data from one system to another is inconsistent scaling of signals. A 4 to 20 milliamp (mA) signal may be transmitted through several systems (e.g., flow computer to Distributed Control System (DCS) to Programmable Logic Controller (PLC), etc.) before reaching the Data Acquisition and Handling System (DAHS) for emissions calculations. Inconsistent scaling can result in significant under or over reporting of emissions that may result in noncompliance. For instance, if a fuel flow monitor configured to output a 4-20 mA  signal corresponding to 0 – 100 pounds per second (lb/s) transmits the signal to a DAHS that is configured to scale the signal from 0 – 80 lb/s, then the DAHS would be underreporting flow and emissions by 20% at maximum flow.

Using consistent units of measure: Fuel flow meters measure fuel flow in terms of mass or volumetric flow rate. The flow rates are converted from mass to volume or vice versa for regulatory reporting or for operational purposes. A common mistake is inconsistency in the conversion methodology, especially when the fuel flow data is routed through multiple plant data systems before entering a compliance database or a DAHS used for emissions reporting.  For instance, a flow meter may be configured with a density value that is inconsistent with that used in the DCS or the DAHS to convert the fuel flow from mass to volume rate or vice versa. Inconsistent conversion factors can result in erroneous reporting of fuel and emissions data.

Correcting to standard conditions: Most reporting protocols require that the fuel flow is corrected to standard conditions when reported as total usage or used for emissions calculations. The U.S. EPA defines standard conditions as 68°F and 1 atmosphere. Using an incorrect standard leads to erroneous reporting. For instance, correcting fuel flow to 60°F (a common occurrence) instead of 68°F results in an error of 1.52%, which is significant when evaluating long term emissions. The ‘standard’ or ‘reference’ temperature could be different depending on the underlying regulation or reporting protocol. Therefore, it is important to understand the ‘Why?’ – reason for measuring fuel flow and the ‘How?’ – measurement methodology or protocol for fuel flow monitoring.

Best Practices:

Audit your monitoring system: Completing comprehensive audits or assessments of your fuel flow monitoring system will help identify gaps in compliance and catch potential deficiencies and/or inconsistencies. Our experience auditing these systems has shown that routine assessments provide significant value in terms of mitigating compliance risk and ensuring accurate reporting.

Leverage your data: Fuel flow monitoring systems that are correctly operated measure and record high-resolution quality-assured data. By combining statistical analyses and domain expertise, this data resource can be leveraged to identify anomalies and inconsistencies in near real time, mitigating the risk of accruing extended periods of invalid or bad data that may result in regulatory action or penalties.

Recordkeeping and transparency: A well-documented Quality Assurance and Quality Control (QAQC) program and conformance with its procedures are key to having a robust monitoring system that generates good data. Maintaining records of calibrations, maintenance, equipment replacement, and corrective actions reflect transparency and completeness of the QAQC program.

If you have any questions about fuel flow monitoring systems, please contact me at ashivkumar@all4inc.com. ALL4 has supported a variety of industries with implementing monitoring programs and developing data-driven solutions for maintaining compliance, optimizing operations, and meeting sustainability goals.