Thermal Oxidizer & Enclosed Flare Retrofits
Why retrofit or upgrade an oxidizer, combustor, or enclosed flare?
Quite simply, because it saves money over buying a new system. Also, it may avoid re-permitting the thermal
oxidizer and/or burner.
Our retrofits will allow you to operate your oxidizer as required to destroy VOC, CO, meet NOx requirements,
decrease fuel usage, allow for a stable burner operation, and eliminate refractory problems.
Why is discovering the "root cause" critical?
Because the last thing we want to do is mistake a symptom of a problem as the actual problem. Or even worse, to fix
something that is not broken in the first case. For example, a thermal oxidizer loosing refractory may appear to
have a problem with the type of refractory used or the method in which the refractory was attached. However after further research, we may find the
root cause may be that the oxidizer is shaking from a burner related problem and the shaking is the root cause of
the refractory problems with the method of attachment or type of attachment only a contributing factor.
Depending upon the complexity or nature of the retrofit needed, we generally start by evaluating the basics of the
equipment design. The purpose of this is to determine the 'root cause' of the problem before we go to fixing anything.
Brief review of common problems and causes
Based upon our previous experience these are some of the most common problems. However, there are a multitude of
other problems and related causes. If yours is not listed, contact an MRW associate and we will be glad to
help you with a cost effective solution.
- High NOx Levels - Especially when operating above 1550°F for efficient CO destruction. Thermal NOx is caused from excess high peak flame temperatures. Certain types of burners are susceptible to producing excess high peak flame temperatures and high NOx levels. This is especially true for older burners and burners manufactured by "standard" or "packaged" burner suppliers.
- Burner Problems - Fluttering, lack of air/oxygen, poor mixing, or unstable flame. All of these problems are a result of poor mixing of air, waste gas, and fuel gas. When the flame is lacking sufficient oxygen, the flame flutters causing the oxidizer to shake. Over time, this can cause the combustion chamber to lose parts or all of the refractory.
- CO Destruction Efficiency - The thermal oxidizer may not be able to destroy CO efficiently because there is insufficient mixing of air, waste gas, and fuel gas, it cannot reach high enough temperatures, insufficient retention time, or has an undersized or improper burner design. There is an inverse relationship between CO and NOx. When temperatures are lowered to meet NOx requirements, the amount of CO increases. When temperatures are raised, the amount of CO decreases but the NOx increases. This indicates that the burner produces too high of peak flame temperatures when operating at temperatures necessary to destroy CO. This can be fixed - i.e. CO destruction while meeting low NOx - by changing the burner type used and/or by changing the method and mixing of the air, waste gas, and fuel gas.
- Shaking - This is usually caused from an unstable burner under high firing rates and running lean on oxygen. A rectangular or asymmetrical shape may also contribute to shaking. A rectangular shaped combustion chamber can cause poor or un-uniform flow distribution and therefore may also be contributing to any shaking and/or acoustical vibrations
- Lack of Capacity - This is usually caused from incorrect design criteria or changes in processes. In any case, an undersized combustion chamber may be the culprit. This is especially the case if the original thermal oxidizer was designed for one-second residence time at
a lower temperature than required for vapor destruction. Also, if the combustion chamber is rectangular, the manufacturer may have inappropriately used the total volume of the rectangle for flow calculations.
- Refractory Problems - The oxidizer may have refractory problems including burning, not staying attached, and losing refractory out the stack. This is caused from shaking, flame impingement, and/or method of attachment.
- Flame Impingement - Flame from burner is either too long or too wide and directly contacting and burning refractory or attachments. (Refractory is usually rated for 2100°F to 2600°F. Peak flame temps are likely to be above that with some types of burners.)
Common services and retrofits
I. A complete system evaluation includes:
II. Modification of introduction, quantity, and/or ratio of waste gas, fuel gas, and air to thermal oxidizer:
- Review original design requirements and specifications
- Combustion chamber size and shape
- Evaluate burner design, burner type, burner size, and burner configuration
- Introduction of waste stream, air, and fuel gas into the thermal oxidizer or combustor
- Oxygen and fuel requirements
- Residence time, temperature, and mixing
- Review all other necessary design elements relating to cause of problems
- Refractory type and method of attachment
- Burner design, type, and size
III. Combustion chamber replacement:
- If VOC destruction, CO destruction, or NOx is not in compliance, the culprit is likely to be either with the burner
and/or the method in which the waste gas, air, and fuel gas is introduced/injected into the thermal oxidizer or
burner. It is also very crucial that the ratio of fuel, air, and waste gas be optimized in order to have the most
efficient and complete combustion. This can be the most important factor to meeting DRE while meeting low NOx requirements.
- MRW's proprietary waste gas injection system and nozzle design contribute to efficient CO destruction at 99%+ while
maintaining exceptionally low NOx as low as .04 lb per mmbtu or less depending upon requirements.
IV. Replacement of pilots and igniters with proprietary MRW components:
- If the combustion chamber is undersized or is deteriorating, replacing the combustion chamber may be necessary.
MRW uses cylindrical combustion chambers due to superior flow patterns and uniform mixing. MRW is able to replace
part of the chamber or the entire chamber depending upon the condition of the combustion chamber and the plant's
needs. We design replacement combustion chambers to match up to existing flanges and bolt patterns. If a new
burner or staged injection system is used waste gas is diverted into a plenum at the base of the new combustor.
The outlet of the new MRW vapor combustor would exhaust into the top or side of the existing or remaining combustion chamber.
- MRW uses many different types of refractory, anchors, and attachment systems depending upon the application and needs of the customer.
V. Control system modifications
- MRW pilots are proven in hundreds of applications across the world. Our pilots are reliable, fast, and easy to operate and maintain.
- MRW uses a proprietary thermocouple design and location to safely and accurately monitor the pilot status while
also extending the life of the thermocouples. Pilots are made of 309/310 stainless steel for reliability and extended life.
Burner retrofits or replacement
Different options may be pursued depending upon the type, size, and condition of burner.
Also, the environmental and NOx regulations for your plant may dictate which type of burner to be used.
Following are some common solutions to many burner problems:
- Replace burner w/custom Low NOX proprietary burner(s) from MRW
- Staged combustion analysis or approach
- Change waste gas, air, and/or fuel gas injection and/or ratios
- Multiple and proprietary MRW burner arrangements
Email firstname.lastname@example.org for a quote for your retrofit needs.