(191a) Selecting Right Flare System to Meet Regulatory Requirments

Flare is considered as last line of defense in any process plant. This is one equipment which must be available at all time when the plant is in operation including during emergency cases. The purpose of the flare system is to reliably and safely dispose any and all hydrocarbon releases from the plant during startup, normal operation, maintenance and emergencies. The Federal Regulation (40 CFR 60.8) requires that emissions, except for emergency cases, shall be smokeless. ‘Smokeless’ flare operation is defined as generating emissions within 20% opacity levels, also known as Ringelmann#1 (R1) on Ringelmann smoke Chart. Typically, this smokeless flow tends to fall within 10 to 15% of the emergency flaring load for an LNG (Liquefied Natural Gas) plant. The apparent darkness or opacity of a stack plume depends upon:

• Concentration and size of the particulate matter in the effluent

• Depth of the smoke column being viewed

• Natural lighting conditions such as the direction of the sun relative to the observer, and Color of the particles

There are several limitations to select the right flare system. In the case study presented in this paper, four major criteria have been considered for evaluation. (a) total plot space availability / usage, (b) Flaring noise during normal operation, start-up & maintenance cases (c) Equipment cost and (d) Ease of maintenance. Smokeless characteristic depends on many factors including turbulence (characterized by exit velocity and mixing), molecular weight, heating value and chemical structure of waste gases and time available for combustion.

In the case study presented in paper for an LNG plant, the following type of flares are evaluated to optimize the flare selection, design, and cost.

• Elevated pipe flare including air / steam assisted flaring.

• Multi-point Ground flare (MPGF).

• Totally Enclosed Ground Flare or Enclosed Ground Flare (TEGF or EGF).

The project team needs to get a very good estimate of the amount of plot required for the flare system even in the Front End Engineering phase of the project. A detailed flare study is required to determine the type and cost of the flaring system.

This paper discusses various flare system designs available to achieve smokeless flaring during normal operation, start-up, and maintenance. Selection of right flare or right combinations of flare types are very important and must be evaluated carefully for overall plant reliability and cost effectiveness.