Environmental compliance for flare operations has been updated with changes to 40 CFR §63.670/1. The primary goal of the control algorithms on flare steam and supplemental gas is to maintain destruction efficiency of 98% by keeping the combustion zone net heating value above a minimum threshold, and to simultaneously maintain operation without visible emissions. The algorithms used for process control (63.670) differ from those used to demonstrate compliance (63.671). From a controls perspective to maintain integrity of the flare’s operation, the controls algorithms use the most current data the moment it’s available. Emerson has developed solutions to control these parameters to maintain compliance on any control system platform.
Dustin opened explaining that flares use combustion to convert hydrocarbons and other toxic or combustible compounds into compounds more acceptable for emission. The flare system is a critical system and needs to be always available. Flare systems are required to handle a variable load with unexpected changes. Historically, few controls have been used and they are often manually controlled by inspection of the flare.
Some challenges are incomplete combustion causing the release of unconverted compounds. Another challenge is when the combustion is smoky. These challenges can cause regulatory issues and problems within the local community.
He described the U.S. federal flare regulations, 40 CFR 63.670 & 63.671. 670 define requirements for flare control devices and 671 define requirements for flare monitoring systems. The requirements are designed to have the flare meet its primary object—complete combustion.
Multiple objectives—net heating value, velocity of material through the combustion zone, pilot presence, and dilution—must be met. When a demand comes, the operational staff ideally needs to be focused on the source of the problem.
The solution to satisfy these objectives must be always available, robust, intelligent, concurrent, and autonomous.
From an intelligent and concurrent standpoint, the system must be able to detect a flare event and work through multiple constraints and resolve operational mode. It must handle computation and validate multiple inputs and outputs against each other. Relief systems can bounce or oscillate which if the controls are not correctly designed can lead to an inadequate solution.
Control strategies can be developed in several ways. Sequential logic is one way and state-based control another way.
For flare control, state-based control provides a more robust approach to handle the multiple constraints.
The SmartProcess Flare Control solution provides a standardized solution for managing the flare system and presenting the information to the operators for action. This application is one of the many SmartProcess Optimization applications using turnkey, off-the-shelf advanced control and monitoring applications from Emerson.