QS Style Steam Assisted Flare

The QS style flare tip uses a single ring of steam injectors around the discharge perimeter of the tip. At low steam flow rates, cold weather will increase the amount of heat energy lost from the steam as it travels to the flare tip. This loss of heat can cause condensation within the piping and significantly lower the temperature of the steam that discharges from the tip increasing its propensity to freeze after discharging from the steam nozzles. The following are required during installation of the flare tip:

  • Install steam traps downstream of the control valve at all low points. Special consideration must be given when designing a condensate trapping system downstream of a flare steam control valve. The pressure downstream of a flare steam control valve can vary from design pressure to atmospheric. The steam trap(s) and condensate handling system must be designed to accommodate this wide range of line pressures.
  • Insulate the steam piping from control valve to flare tip. The insulation of the steam piping should be sufficient to ensure high quality steam reaching the flare tip when steam flow is at the minimum rate and minimum ambient temperature.

Other preventative and reactive actions that can be taken include: 

  • Insulate the steam piping on flare tip. This refers to just the vertical portion of the flare tip steam piping. Due to flame impingement, insulating the circular manifold is not practical.
  • Locate the steam control valve as close to the flare as practical. By minimizing the distance between the control valve and flare tip, the amount of heat loss from the steam after the final pressure reduction is minimized.
  • Increase the steam flow rate to the flare. Increasing the steam flow to the flare will increase the temperature of the steam discharging from the steam injectors. Note: increasing steam flow may require the use or increase of supplemental gas to stay within regulatory requirements.
  • Flow a heated non‐condensable gas, such as air or nitrogen, through the steam injectors in place of steam during cold conditions.

Center Steam

Center steam is steam that is injected into the body of a flare tip. This style of steam injection can be present on many styles of steam assisted flare. Its purpose is to prevent burning inside the flare tip by preventing air from infiltrating down into the tip. At low fuel flow rates, cold weather can cause center steam to condense and form ice on the inside of the flare tip or stack. As ice builds up, the available exit area for discharge of gases is reduced. In such a situation, the potential exists for the flare tip or stack to become completely blocked by ice, which puts all process units which discharge to the flare at risk for over pressure. Even partial blockage of the flare tip can reduce the hydraulic
capacity of the flare and lead to over pressure during a major flaring event. The following are required during installation of the flare tip:

  • Install steam traps downstream of the control valve at all low points. Special consideration must be given when designing a condensate trapping system downstream of a flare steam control valve. The pressure downstream of a flare steam control valve can vary from design pressure to atmospheric. The steam trap(s) and condensate handling system must be designed to accommodate this wide range of line pressures.

  • Insulate the steam piping from control valve to flare tip. The insulation of the steam piping should be sufficient to ensure high quality steam reaching the flare tip when steam flow is at the minimum rate and minimum ambient temperature.

Other preventative and reactive actions that can be taken include:

  • Locate the steam control valve as close to the flare as practical. By minimizing the distance between the control valve and flare tip, the amount of heat loss from the steam after the final pressure reduction is minimized.
  • During periods of cold weather, the center steam can be turned off. If internal burning is a concern during these periods, the amount of purge gas can be increased to the point the flame is external of the flare tip.
  • Flow a heated non‐condensable gas which does not contain oxygen, such as nitrogen, through the center steam injectors in place of steam during cold conditions.

SA/QS & HSA Style Steam Assisted Flares

The SA/QS and HSA style flare tips use an upper ring of steam injectors around the discharge perimeter of the tip as well as a lower ring of steam injectors that discharge into tubes that penetrate inside the body of the flare tip. The upper ring of injectors should be treated the same way as the QS Style Steam Assisted Flares mentioned above. The lower ring of injectors is usually supplied with a muffler that includes a floor and drains. At low steam flow rates, cold weather will increase the amount of heat energy lost from the steam as it travels to the flare tip. This loss of heat can cause condensation within the piping and significantly lower the temperature of the steam that discharges from the tip increasing its propensity to freeze after discharging from the steam nozzles. The following are required during installation of the flare tip:

  • Install steam traps downstream of the control valves at all low points. Special consideration must be given when designing a condensate trapping system downstream of a flare steam control valve. The pressure downstream of a flare steam control valve can vary from design pressure to atmospheric. The steam trap(s) and condensate handling system must be designed to accommodate this wide range of line pressures.
  • Insulate the steam piping from control valve to flare tip. The insulation of the steam piping should be sufficient to ensure high quality steam reaching the flare tip when steam flow is at the minimum rate and minimum ambient temperature.
  • Install muffler drain lines.
  • Insulate and heat‐trace the muffler drain line up to and including the connection point to the muffler floor. If the muffler drain were to freeze up, liquid could accumulate in the muffler floor. This liquid could freeze as well as overflow to form large ice formations on the side of the flare tip and stack.

Other preventative and reactive actions that can be taken include:

  • Heat‐trace and insulate the external surface of the muffler floor. If freezing rain or heavy snows are common, insulating and heat‐tracing the underside of the muffler floor can help reduce the buildup of snow and ice.
  • Insulation of QS steam piping on flare tip. This can include just the vertical portion of the QS piping of the flare tip or it can also include the circular QS manifold. John Zink does not recommend that the lower ring manifold be insulated. This manifold is typically located very near the bottom of the muffler. It provides a heat source that helps keep the muffler floor ice free.
  • Locate the steam control valve as close to the flare as practical. By minimizing the distance between the control valve and flare tip, the amount of heat loss from the steam after the final pressure reduction is minimized.
  • Increase the steam flow rate to the flare. Increasing the steam flow to the flare will increase the temperature of the steam discharging from the steam injectors.
  • Flow a heated non‐condensable gas, such as air or nitrogen, through the steam injectors in place of steam during cold conditions.

XP Style Steam Assisted Flare

The XP style flare uses one or more steam manifolds to inject steam into the base of one or more modules. The XP flare tip has two major variants: warm weather and cold weather. Only the cold weather variant is addressed here. The XP has a tip drain that removes any liquids that accumulate inside the body of the flare tip. The tip also has a condensate catch tray positioned below the steam injectors to catch condensate that can drip from the XP modules. In cold conditions, ice can form from water dripping out of the bottom of the XP modules. Also, steam can work its way into the body of the flare tip where it can condense and form ice. The following are required during installation of the flare tip:

  • Insulate and heat‐trace the underside of the flare body. This will prevent formation of ice inside the flare tip.
  • Install flare tip drain line.
  • Insulate and heat‐trace the flare tip drain. If the drain were to freeze up, liquid would accumulate in the flare body and would eventually flow down the flare stack. Liquid flowing down the flare stack could freeze and eventually plug the flare stack.
  • Insulate and heat‐trace the bottom of the catch tray. This will ensure the catch tray does not become an anchor point for ice formation from condensate dripping from the XP modules.
  • Install catch tray drain line.
  • Insulate and heat‐trace the catch tray drain. If the drain were to freeze up, liquid would overflow the catch tray. Falling liquid could be blown by the wind onto other sections of the flare structure and form ice.
  • Install steam traps downstream of the control valve at all low points. Special consideration must be given when designing a condensate trapping system downstream of a flare steam control valve. The pressure downstream of a flare steam control valve can vary from design pressure to atmospheric. The steam trap(s) and condensate handling system must be designed to accommodate this wide range of line pressures.
  • Insulate the steam piping from control valve to flare tip. The insulation of the steam piping should be sufficient to ensure high quality steam reaching the flare tip when steam flow is at the minimum rate and minimum ambient temperature.

Other preventative and reactive actions that can be taken include:

  • Insulate steam piping on flare tip. This can include both the vertical portion of the flare tip steam piping and the circular manifold.
  • Locate the steam control valve as close to the flare as practical. By minimizing the distance between the control valve and flare tip, the mount of heat loss from the steam after the final pressure reduction is minimized.
  • Increase the steam flow rate to the flare. Increasing the steam flow to the flare will increase the temperature of the steam discharging from the steam injectors.
  • Flow a heated non‐condensable gas, such as air or nitrogen, through the steam injectors in place of steam.

A note on ice formations on flare structures – Once ice forms on a structure, most operators attempt to rectify the cause of the formation but must wait for ambient conditions to change so the ice melts naturally. One operator has used a spray nozzle affixed to the top of a crane to spray an environmentally acceptable aviation de‐icing fluid to melt the ice from their structure. Increasing the size of the flare flame and the associated radiation from the flame could be beneficial depending on the location of the ice formation.

Molecular Seal

A molecular seal (moleseal) is a purge reduction device which causes the waste gas to make two 180° changes in direction. It is equipped with a drain to remove any liquid that accumulates in the bottom of the moleseal. Liquids, especially water, may enter the molecular seal by any of several sources including: rainfall, snowfall, upper ring condensate spray, center steam condensation, liquid seal  carryover, and waste gas condensation. Reliable draining of such liquid is necessary to prevent freezing shut the moleseal and thereby the flare stack. he following is required during installation of the moleseal:

  • Insulate and heat‐trace the moleseal drain line from the moleseal (include the drain line connection) to the sewer or flare drum. (Note: connecting the moleseal drain line to a drum requires the drum connection to be sufficiently below the drum liquid level to prevent bypassing vent gas around the moleseal.) If the moleseal drain were to freeze up, liquid could accumulate in the moleseal. This liquid could greatly increase the pressure loss through the moleseal and possibly increase the backpressure on the flare header above the design limit. Standing liquid inside the moleseal could freeze and totally block the waste gas flow.

Other preventative and reactive actions that can be taken include:

  • Insulate and heat‐trace the bottom plate of the moleseal along with the outer barrel from the bottom to the inspection hand hole.
  • Inject an environmentally acceptable de‐icing fluid through the moleseal drain line. Care should be taken with this option so as to avoid filling the moleseal with liquid to the point it can obstruct waste gas flow.
  • Inject an environmentally acceptable de‐icing fluid through the center steam line. 

Pilots

A pilot is a device that provides a continuous flame as an ignition source for the flare tip. The pilot also enhances main flame stability. Pilots are critical to the safe operation of the flare. While most pilots operate well in cold weather, there are certain atmospheric conditions and operating scenarios that can cause a pilot to be adversely affected by cold eather. 

Hoar‐frost is a type of frost that can form on objects that are colder than the surrounding air. The venturi mixer of the pilot can become colder than the surrounding air due to the drop in pressure experienced inside the mixer. Hoar‐frost typically forms when ambient temperatures are near freezing and the humidity is high. Under such conditions, frost can build up in the pilot mixer and degrade the stability of the pilot allowing it to be easily extinguished. If a location is prone to hoarfrost forming conditions, the following preventative measure can be taken:

  • Use pilots equipped with anti‐hoar‐frost heaters. John Zink supplies pilots that have special heaters bonded to the venturi mixer. During conditions that hoar‐frost can form, these heaters supply enough heat to prevent frost formation.
  • John Zink can supply an “Arctic Pilot” which recycles some of the pilot combustion products to keep the fuel orifice or venturi from freezing.

The burning of fuel gas generates water as a product of combustion. For pilots equipped with flame front generators, some of this water will condense in the ignition hood of the pilot and the ignition line itself. Water typically accumulates in the ignition line during normal pilot operation year round. In cold weather, this water will freeze and block the ignition line, preventing the use of the flame front generator. The following preventative measures can be taken:

  • Inject a small amount of dry instrument air into each pilot ignition line. Typically 35 SCFH per ignition line is sufficient to keep the water vapor from migrating down the ignition line and condensing.

The moisture content of fuel gas can vary from zero to significant. In cold conditions, wet fuel gas can cause the fuel orifice to plug due to ice forming in the orifice. Once this has occurred, it becomes very difficult to melt this ice and re‐open the orifice. Preventative measures that can be taken:

  • Ensure the pilot fuel gas supply is dry with a dew point well below the minimum ambient temperature possible in that region.
  • John Zink can supply an “Arctic Pilot” which recycles some of the pilot combustion products to keep the fuel orifice or venturi from freezing.

Other reactive actions that can be taken after orifices have partially closed due to ice formation:

  • If the orifice is restricted, but still flowing some amount of fuel, a fluid that can melt the ice can be sent through the fuel delivery system. This approach will cause the pilots to extinguish. A possible fluid option is alcohol or any other de‐icing fluid. Once the pilot orifices are cleared, the piping is draining and then the pilots re‐ignited. The sensible heat of the de‐icing fluid can’t be relied on because the low flowrate through the piping will cause the fluid to discharge at near ambient temperature. Consequently, steam is not recommended as a fluid for this service.

Other reactive actions that can be taken after orifices have completely plugged due to ice formation:

  • If the main flame is present, the waste flow to the flare can be increased to the point that radiation from the main flame inputs enough heat into the pilot assembly to cause the ice to melt. This technique may only be viable on the pilots located on the downwind side of the stack.
  • If the main flame is not present, then alternate means of main flame ignition should be employed. Some options include: sending fireballs through a flame front generator, flaming arrow, and incendiary shotgun shells.
  • If the flare can be shut in, the ice can be melted directly through the application of heat such as a propane torch or hot air gun.

Liquid Seals

A liquid seal is a device which forces waste gases to bubble through a certain height of liquid (typically water) before entering the flare stack. This allows a positive pressure to be maintained in the flare header. Liquid is inherent in the liquid seal design and cannot be avoided. Prevention of freezing is necessary to prevent blockage of the flare system. The following are preventative actions that can be taken:

  • Insulate the portion of the liquid seal drum that will be in contact with the water.
  • Include in the design of the drum, a means to add supplemental heat to the water. This could be a steam coil external of the drum, a steam coil internal of the drum, heat tracing external of the drum, electric heater inserted into the drum, or a steam sparger to inject steam directly into the liquid.
  • Add a non‐flammable anti‐freeze compound to the water. Care should be taken that such additives don’t significantly change the specific gravity of the liquid, or if a significant density change is made, the liquid operating levels are adjusted accordingly. Another concern with any additive is its effect on surface tension and viscosity. Surface tension and viscosity impacts bubble formation and thus can have a significant effect on liquid seal performance.
  • Insulate and heat‐trace the skimmer piping (also called an overflow) along with the associated loop seal from the drum to the sewer. The skimmer is used to remove liquid hydrocarbons that can accumulate on top of the water. Some operators run a continuous trickle of water into their liquid seal of which the excess exits through the skimmer piping. If this piping becomes plugged, the liquid seal can overfill. If liquid hydrocarbons are not removed, during high volume releases, the hydrocarbon can be carried out the flare tip and result in burning rain.

A note on drains – Proper drain operation is critical for safe flare operation, especially during freezing conditions. Drains should be periodically checked to ensure free-flowing operation. If the flow from a drain decreases significantly from its normal flow rate, investigate since this could indicate a blockage in the drain line or equipment which feeds the drain line.

Water vapor contained in the flare gas – A major concern with freezing water is the potential to partially or totally block the flare stack/riser. Potential sources of water vapor include wet plant gas, water left in the bottom of a knock‐out drum (evaporates into the flare gas), and a water-filled seal drum. This concern applies to any type of elevated flare. There has been at least one example of an air assisted stack in Canada that had the 24” flare stack plug and seal off with ice from evaporated water.

One potential mitigation for this would be to install a nozzle near the top of the stack (below the tip). Piping up the stack would supply methanol to the nozzle. A spray nozzle would direct the alcohol to the walls of the stack. The purpose would be to spray methanol on the inside surfaces of the stack during cold weather conditions on a periodic basis. Methanol will melt the ice and help prevent ice build‐up on the walls of the stack. Note that the use of a center steam nozzle (if one exists) may be able to accomplish the same thing – block in the steam, fill the line with methanol, flow methanol into the tip/stack, drain the line, and place steam back into service.

Partnering with John Zink

Cold weather brings unique challenges, but with the right expertise and solutions, you can keep your operations running safely and efficiently. John Zink offers decades of experience in combustion and emission control, providing the technology and support needed to mitigate cold weather risks. From tailored solutions to ongoing service, we’re here to help you navigate the toughest conditions.

Reach out to learn how we can support your operations year-round.