Measure Efficiency: Predictive Analytics

Summary 

Predictive analytics describes the process by which measured parameters and models are combined to derive information on flare efficiency. They are analogous to Predictive Emissions Monitoring (PEMS) systems used to track emissions of pollutants such as NOx from gas turbines. For flares, predictive analytics system uses a method based on a parametric modelA Parametric Model is a concept used in statistics to describe a model in which all its information is represented within its parameters. In short, the only information needed to… Learn more… and Computational Fluid Dynamics (CFDis a branch of fluid mechanics that uses numerical analysis and data structures to analyse and solve problems that involve fluid flows. Computers are used to perform the calculations required to simulate… Learn more…) studies with input data coming from flare gas composition, flow rates, flare design and environmental factors such as wind speed. Predictive systems has the advantage of being permanently installed, providing continuous and near real-time feedback on flare performance, allowing adaptations to be made to maintain efficient combustion. Currently available systems are independent of flare vendor and control system provider.

How it Works

• It collects and calculates all influencing parameters such as gas net heating valueThe energy released as heat when a compound undergoes complete combustion with oxygen to form gaseous carbon dioxide and gaseous water (also referred to as lower heating value). Learn more… at the combustion zoneThe area of the flare flame where the gas and vapours found just after a flare tip combine for combustion. Elevated Flare definitions and calculation methods from 40 CFR 63… Learn more… (NHVcz calculated from the MW of the gas mixture itself derived from the speed of sound measured by any ultrasonic flow meterUltrasonic Measurement uses sound waves to interrogate the fluid or object and determine various key properties. The sound waves are typically sent and received by a piezo electric transducer which… Learn more…), flow rate, pressure, temperature, vent gas exit velocity, flare tip diameter, crosswind, nitrogen purge rate and gas analysis (if available).
• The algorithms are based on existing experimental studies, such as TCEQ 2010 flare study where samples of the flare plume were extracted after combustion and analysed to measure both CE% and DRE%. This also served as the basis of the EPA properly designed and operated flares that the model uses as well. ​
• CFD studies have been conducted to run simulations using Eddy Dissipation ConceptEDC model is an extension of the Eddy dissipation model. Detailed Arrhenius chemical kinetics can be incorporated in turbulent flames. However, typical reaction mechanisms are invariably stiff, and their numerical… Learn more…* (EDC) and Probability Density Function* (PDF) and have shown strong correlation. The numerical models can be used in combination with the other parameters for both assisted and non-assisted flares. For assisted flares the system automatically provides DCS steam and fuel gas flow set points.
• Provides a real-time CE calculation.
• For optimal performance, it is required to have available process data to pre-program the system for any type of flares even if fine tuning occurs at site during start up and commissioning.

Assisted flares are often over-steamed leading to incomplete combustion and CH4 slip. Here is a flare incident controlled by the predictive analytics system resulting in staying in compliance with the EPA.

Non-assisted flares: Offshore on one FPSO monitoring both LP and HP flares.

The graph represents the CE from LP flare and HP flare.

HP flare CE% from the system has been post-processed to account for N2 input that was not initially available.