GAZ FLOW MODELING OF AN NON-CONVENTIONAL STACK (GA2)

ISSUE

Stack sampling of different contaminants requires state-of-the-art technology. It also requires a laminar flow at the sampling location with an even velocity profile at all sampling points. This latter parameter ensures representative results which are mandatory for compliance with any environmental regulation.

Indeed, government authorities require the use of isokinetic stack sampling methods. Only an even flow will comply to this requirement; the presence of cyclonic flow and flow inversion is not permitted. A flow will be recognized as isokinetic if the average deviation from the mean velocity is within ± 20% and if the ratio of the maximum flow to the minimum flow does not exceed 3:1.

However, in some cases, an isokinetic sample is not possible, such as when a non-conventional stack is used. For example, this will occur when the stack is too short and when the flow is turbulent. In this case study, the plant has a short stack provided with three independent gas inlets that create a vortex instead of an isokinetic profile.

TECHNOLOGICAL CHALLENGE

The goal of this project was to study the use of insertion plates that could be installed inside the stack to correct the velocity profile and allow an even flow at the stack sampling platform. This would allow stack sampling in accordance with standard methods and valid reporting of emissions to the environmental authorities.

RECOMMENDED SOLUTION

STS Canada designed a set of baffles to correct the gas velocity profile; this included the installation of perforated baffle plates close to the gas inlets and a flow vortex breaker downstream, underneath the sampling platform. These devices were optimized using computer flow modeling software.

RESULTS

The results obtained by the computer flow simulation allowed to obtain an isokinetic flow at the stack sampling platform. The average deviation from the mean velocity varied between 5% and 23% for the range of flow tested and the ratio of maximum to minimum velocity was always less than 3:1. This modification thus enabled sampling in compliance with environmental standards without having to replace the stack.