7 replies to this topic

[Olaniyi]

Hi all,
I work with an LNG company and one of our main targets obviously is to flare as little gas as possible. When methane is flared, the least oxygen is required and generally combustion is clean. In contrast, when C2, C3 or C4 are flared, more oxygen is required per molecule of fuel for complete combustion.
At the flare tip, mixing of air with the fuel (C2, C3, C4, etc) is not very efficient, since fuel comes out of a nozzle and the air is coming from the surrounding atmosphere. Due to incomplete mixing of oxygen for combustion, there is incomplete combustion of the fuel, resulting in soot formation.

I am aware that in a refinery, there is usually high pressure steam available, and at the flare tip, steam is injected into the fuel to disperse the fuel and get more complete combustion with oxygen from the atmosphere. Unfortunately, most LNG plants, including us, do not have a steam system. So we use high pressure fuel gas at 22barg (consisting of mostly CH4) to inject in to the flare to disperse the C2 or C3 or C4 to get better combustion. The high pressure (HP) fuel gas (FG) is called “assist gas”. The downside is that this method of assisting combustion for the flare consumes fuel gas and makes for more flaring.

An alternative to using HP fuel gas would be to buy an air blower and blow the air up the pipes currently used for assist gas. This could save a lot of flaring and money for fuel gas. By my calculation at peak rates we would need a air blower that would deliver at least the HP fuel gas pressure (22bar) and a flow-rate of up to 3-4000m3/hr during peak flaring. Does anyone have experience with using an air-blower for assist gas in a flare system, or with construction, installation, usage, sizing and cost of air-blowers in general? Which companies are considered the industry leaders in this field to contact for ideas or recommendations?

Apologies for the long mail.

Thanks
Ogeds

[ankur2061]

Hi all,
I work with an LNG company and one of our main targets obviously is to flare as little gas as possible. When methane is flared, the least oxygen is required and generally combustion is clean. In contrast, when C2, C3 or C4 are flared, more oxygen is required per molecule of fuel for complete combustion.
At the flare tip, mixing of air with the fuel (C2, C3, C4, etc) is not very efficient, since fuel comes out of a nozzle and the air is coming from the surrounding atmosphere. Due to incomplete mixing of oxygen for combustion, there is incomplete combustion of the fuel, resulting in soot formation.

I am aware that in a refinery, there is usually high pressure steam available, and at the flare tip, steam is injected into the fuel to disperse the fuel and get more complete combustion with oxygen from the atmosphere. Unfortunately, most LNG plants, including us, do not have a steam system. So we use high pressure fuel gas at 22barg (consisting of mostly CH4) to inject in to the flare to disperse the C2 or C3 or C4 to get better combustion. The high pressure (HP) fuel gas (FG) is called "assist gas". The downside is that this method of assisting combustion for the flare consumes fuel gas and makes for more flaring.

An alternative to using HP fuel gas would be to buy an air blower and blow the air up the pipes currently used for assist gas. This could save a lot of flaring and money for fuel gas. By my calculation at peak rates we would need a air blower that would deliver at least the HP fuel gas pressure (22bar) and a flow-rate of up to 3-4000m3/hr during peak flaring. Does anyone have experience with using an air-blower for assist gas in a flare system, or with construction, installation, usage, sizing and cost of air-blowers in general? Which companies are considered the industry leaders in this field to contact for ideas or recommendations?

Apologies for the long mail.

Thanks
Ogeds

Ogeds,

I did a FEED project for Saudi Aramco for High Pressure Assist Gas flares (27 nos.) using high pressure compressed air. The more common system is the one involving low pressure air from a blower.

The best way to start understanding air-assisted flares is go through section 6.4.3.2 of API STD 521 & section 5.1.5 of API STD 537.

Also you can look up the following to get some details of the design concept for flare tips using air assit:

US EPA - CFR title 40, Section 60.18

Hope I could be of some help.

Regards,
Ankur.

[Olaniyi]

Ankur,
Many thanks Ankur for your response. Pls do you have copies of these documents? I've looked through the API 521 copy I have but it only describes air blowers for use as assist gas very briefly in section 4.4.3.1.5.

Warm regards
Ogeds

Hi all,
I work with an LNG company and one of our main targets obviously is to flare as little gas as possible. When methane is flared, the least oxygen is required and generally combustion is clean. In contrast, when C2, C3 or C4 are flared, more oxygen is required per molecule of fuel for complete combustion.
At the flare tip, mixing of air with the fuel (C2, C3, C4, etc) is not very efficient, since fuel comes out of a nozzle and the air is coming from the surrounding atmosphere. Due to incomplete mixing of oxygen for combustion, there is incomplete combustion of the fuel, resulting in soot formation.

I am aware that in a refinery, there is usually high pressure steam available, and at the flare tip, steam is injected into the fuel to disperse the fuel and get more complete combustion with oxygen from the atmosphere. Unfortunately, most LNG plants, including us, do not have a steam system. So we use high pressure fuel gas at 22barg (consisting of mostly CH4) to inject in to the flare to disperse the C2 or C3 or C4 to get better combustion. The high pressure (HP) fuel gas (FG) is called "assist gas". The downside is that this method of assisting combustion for the flare consumes fuel gas and makes for more flaring.

An alternative to using HP fuel gas would be to buy an air blower and blow the air up the pipes currently used for assist gas. This could save a lot of flaring and money for fuel gas. By my calculation at peak rates we would need a air blower that would deliver at least the HP fuel gas pressure (22bar) and a flow-rate of up to 3-4000m3/hr during peak flaring. Does anyone have experience with using an air-blower for assist gas in a flare system, or with construction, installation, usage, sizing and cost of air-blowers in general? Which companies are considered the industry leaders in this field to contact for ideas or recommendations?

Apologies for the long mail.

Thanks
Ogeds

Ogeds,

I did a FEED project for Saudi Aramco for High Pressure Assist Gas flares (27 nos.) using high pressure compressed air. The more common system is the one involving low pressure air from a blower.

The best way to start understanding air-assisted flares is go through section 6.4.3.2 of API STD 521 & section 5.1.5 of API STD 537.

Also you can look up the following to get some details of the design concept for flare tips using air assit:

US EPA - CFR title 40, Section 60.18

Hope I could be of some help.

Regards,
Ankur.

[ankur2061]

[quote][quote name='ogeds' date='07 January 2010 - 09:11 PM' timestamp='1262884879' post='35297']
Ankur,
Many thanks Ankur for your response. Pls do you have copies of these documents? I've looked through the API 521 copy I have but it only describes air blowers for use as assist gas very briefly in section 4.4.3.1.5.

Warm regards
Ogeds
[/quote]


Ogeds,

I presume you have an older copy of API STD 521. The latest edition is January 2007. This gives some more details. However, if you are looking for finer details then you may not find them in any textbooks or standards. Most of the technology is still proprietary & finding open literature on the subject is difficult.

My suggestion would be to contact some reputed flare manufacturers / vendors and ask them for a budgetary quote based on your specific requirements. Some of the them are listed below:

1. John Zink

2. Flare Industries

3. Callidus Technologies

Additionally you can go to a chemical engineering blog established by one of our very respected & veteran members of this forum 'Joe Wong' who has provided dozens of articles on flares on his blog. Here is the address:

http://webwormcpt.blogspot.com/

Hope this helps.

Regards,
Ankur.

[Olaniyi]

Thanks again!!

[quote name='ankur2061' date='07 January 2010 - 01:46 PM' timestamp='1262890588' post='35300']
[quote][quote name='ogeds' date='07 January 2010 - 09:11 PM' timestamp='1262884879' post='35297']
Ankur,
Many thanks Ankur for your response. Pls do you have copies of these documents? I've looked through the API 521 copy I have but it only describes air blowers for use as assist gas very briefly in section 4.4.3.1.5.

Warm regards
Ogeds
[/quote]


Ogeds,

I presume you have an older copy of API STD 521. The latest edition is January 2007. This gives some more details. However, if you are looking for finer details then you may not find them in any textbooks or standards. Most of the technology is still proprietary & finding open literature on the subject is difficult.

My suggestion would be to contact some reputed flare manufacturers / vendors and ask them for a budgetary quote based on your specific requirements. Some of the them are listed below:

1. John Zink

2. Flare Industries

3. Callidus Technologies

Additionally you can go to a chemical engineering blog established by one of our very respected & veteran members of this forum 'Joe Wong' who has provided dozens of articles on flares on his blog. Here is the address:

http://webwormcpt.blogspot.com/

Hope this helps.

Regards,
Ankur.
[/quote]

[laypipe79]

Hi all,
I work with an LNG company and one of our main targets obviously is to flare as little gas as possible. When methane is flared, the least oxygen is required and generally combustion is clean. In contrast, when C2, C3 or C4 are flared, more oxygen is required per molecule of fuel for complete combustion.
At the flare tip, mixing of air with the fuel (C2, C3, C4, etc) is not very efficient, since fuel comes out of a nozzle and the air is coming from the surrounding atmosphere. Due to incomplete mixing of oxygen for combustion, there is incomplete combustion of the fuel, resulting in soot formation.

I am aware that in a refinery, there is usually high pressure steam available, and at the flare tip, steam is injected into the fuel to disperse the fuel and get more complete combustion with oxygen from the atmosphere. Unfortunately, most LNG plants, including us, do not have a steam system. So we use high pressure fuel gas at 22barg (consisting of mostly CH4) to inject in to the flare to disperse the C2 or C3 or C4 to get better combustion. The high pressure (HP) fuel gas (FG) is called “assist gas”. The downside is that this method of assisting combustion for the flare consumes fuel gas and makes for more flaring.

An alternative to using HP fuel gas would be to buy an air blower and blow the air up the pipes currently used for assist gas. This could save a lot of flaring and money for fuel gas. By my calculation at peak rates we would need a air blower that would deliver at least the HP fuel gas pressure (22bar) and a flow-rate of up to 3-4000m3/hr during peak flaring. Does anyone have experience with using an air-blower for assist gas in a flare system, or with construction, installation, usage, sizing and cost of air-blowers in general? Which companies are considered the industry leaders in this field to contact for ideas or recommendations?

Apologies for the long mail.

Thanks
Ogeds

Hey I know a guy who works with roots air blowers and other air blowers
check out his website and give him a call Roots Blowers Chicago

[ashetty]

Ankur,
Many thanks Ankur for your response. Pls do you have copies of these documents? I've looked through the API 521 copy I have but it only describes air blowers for use as assist gas very briefly in section 4.4.3.1.5.

Warm regards
Ogeds

Hello Ogeds,

Please see API 521 (January 2007) Section 6.4.3.2.4

Best Regards,

A.Shetty

[alanjoe]

Many thanks.
I would like to say few points about blowers.
Blowers are used to produce large volumes of air at lower pressures as compared to compressed air. Although there are some applications where compressed air is necessary (air cylinders, pneumatic tools), a large number of industrial applications can use either compressed air or air generated by blowers. Blowers excel at producing large volumes of air needed for many industrial drying, cleaning, ventilation and vacuum applications.
Blowers provide clean air, Since blowers do not use oil as a lubricant, there is no danger of oil droplets or residue in the air blower system.

Ankur,
Many thanks Ankur for your response. Pls do you have copies of these documents? I've looked through the API 521 copy I have but it only describes air blowers for use as assist gas very briefly in section 4.4.3.1.5.

Warm regards
Ogeds

Hello Ogeds,

Please see API 521 (January 2007) Section 6.4.3.2.4

Best Regards,

A.Shetty