Horsepower is a great equalizer. Typically, the smaller the footprint of the RTO, the greater the HP required to overcome the resistance to flow.

While from manufacturer to manufacturer thermal efficiencies should remain constant, the horsepower, and therefore the amount of electric power the system uses, will vary dramatically- sometimes by as much as 250%!

The type of heat recovery media used and the velocity going through that media dictates the fan’s horsepower requirement. The faster the velocity through a device, the smaller the device can be made.  It boils down to fabrication economics. This comes at a price, as the faster the flow moves through the unit, the more HP you need to push or pull it through the RTO. So in the long run, a smaller unit which is less expensive to purchase, may in the end force you to expend your initial saving with never ending additional operating costs.

The amount of fuel consumed depends on true thermal efficiency of the RTO, and the amount of solvent in the process stream. That efficiency should be calculated as the unit’s base line thermal efficiency with no solvent present in the air stream. This is the unit’s true thermal efficiency with all correction factors figured in.

Your RTO was rated on its nominal thermal efficiency, which is the thermal efficiency of the regenerative heat recovery media as if it were a standalone device. But when you add a burner to the system, that efficiency becomes degraded by the amount of combustion air going into the burner. This is known as the RTO’s mass/flow correction factor for thermal efficiency. Typically it degrades the device’s nominal thermal efficiency by about 2%. Unfortunately, to overcome this 2% you must put enough solvent into the unit to eliminate the need for the burner.

The amount of fuel consumed per the proposal was based upon the unit always seeing a constant supply of solvent. As solvent levels decrease, the RTO will augment your solvent with additional natural gas, thereby increasing fuel consumption.

As long as the chlorinated compound total does not exceed 10 ppmv, the catalyst will perform as designed and you should not see a reduction in destruction efficiency of the TPH catalyst. The majority of the chlorinated compounds will pass through untreated and will exit the discharge stack.

If the chlorinated compounds exceed 10 ppmv, the chlorinated compounds start to occupy active catalyst sites.  The chlorinated compounds slowly diffuse, breaking down into inorganic acids, which attack the silica substrate of the catalyst. As this happens, the catalyst loses geometric surface area and the destruction efficiency will start to decline.

Random packed media comes in different structural shapes and is literally placed in the heat recovery chamber randomly. The media can be installed or removed quickly in any geometric tower design. The random arrangement provides both void areas between the media pieces, and excellent heat storage characteristics.

Structured media is manufactured in specific dimensions and must be hand loaded into the heat recovery chamber. Precise fitting with the chamber is required to reduce short circuiting of the air flow. The media is usually thin walled and absorbs and desorbs heat quickly, which can require more frequent RTO valve cycle times.  The more frequent valve cycling increases wear and tear on the valves, as well as increases peak emissions in a 2-chamber RTO.

The premise of Intellishare's RTO design is as simple as 1-2-3:

1. The process stream is pre-heated and enters the RTO's combusiton chamber where the VOC is converted to CO2 and water vapor.
2. As the purified process leaves the combustion chamber, heat is extracted and stored in the heat recovery chamber.
3. After a period of time, the inlet/outlet valves switch positions and the contaminated process gas is redirected through the recovery chamber and the process begins again.

Unfortunately, there is no scientific way to know. Different types of particulate take different amounts of time to plug the RTO. Some particulates pass through the RTO; some lodge in the recovery beds and some, if organic, are oxidized.

All of Intellishare’s RTOs are equipped with a bake out feature to carbonize organic particulate lodged in the system.

Volatile Organic Compounds (VOCs) are a vapor form of hydrocarbons that contribute to air pollution. These hydrocarbon compounds can enter the atmosphere, and when exposed to sunlight, chemically react with elements in the air to produce what is commonly referred to as smog.

A catalyst is a substance that increases the rate of a chemical reaction without being consumed in the process.

In the presence of contaminates, the catalyst active sites can become blinded and as a result, the catalyst surface area and destruction efficiency is reduced.

The following partial list of poisoning agents and inhibitors has been found to have a detrimental effect on the activity of the noble metal catalyst.

Substance	Effect	Remedial Action
Coating Agents rust dirt inorganic oxide	Covers catalyst active site	Non-phosphate detergent washing usually effective for removal.
Glass Forming Coating Agents organic silicates (esters) silicones phosphorus containing materials	Covers catalyst active site	Factory reactivation or replacement usually required. Non-phosphate detergent washing may be effective.
Poisons - Heavy Metal Complexes Mercury Lead Zinc Tin Arsenic Antimony, etc.	Permanent catalyst deactivation	Factory replacement required
Sulfides	Permanent catalyst deactivation	Depending on exposure and sulfide concentration, factory reactivation, non-phosphate detergent washing or replacement is required.
Halogens fluorine chlorine bromine iodine halogenated hydrocarbons	Covers active site-resulting in temporary or permanent deactivation	Activity usually returns if exposed to low concentrations (<10 ppmv) and upon removal of halogen source. Prolonged exposure with water (or protons) can corrode, dissolve the catalyst substrate and require repair or replacement. Note: Does not apply to chlorinated or fluorinated catalysts which have been specifically designed to be tolerant of and/or destroy halogenated hydrocarbons.
Organic Droplets and Aerosols	Covers active site. Possible cause of catalyst hot spot	Such materials may carburize on the catalyst forming a refractory material or become a hot spot source causing substrate deterioration. Factory reactivation or replacement is required.

Catalytic oxidation is a chemical oxidation process in which hydrocarbons (HC) are combined with oxygen at specific temperatures to yield carbon dioxide (CO2) and water (H2O). The formula is:

HC + O2	->	H2O + CO2
400-800°F

As its name suggests, catalytic oxidation uses a catalyst, a substance that accelerates the rate of a chemical reaction without itself being consumed. The catalyst allows the oxidation process to occur at a lower temperature than is required for thermal oxidation.

Key advantages of catalytic oxidation are:

• Much lower operating temperatures
• Longer heat exchange life (less stress because of lower operating temperatures)
• Lower operating costs

It is important to understand the meaning of the term Lower Explosive Limit (LEL), sometimes also referred to as Lower Flammability Limit (LFL).

Lower Explosive Limit: Gases or vapors which form flammable mixtures with air or oxygen have a minimum concentration of vapor in air or oxygen below which propagation of flame does not occur on contact with a source of ignition (LEL).

There is also a maximum proportion of vapor or gas in air above which propagation of flame does not occur (UFL). These boundary line mixtures of vapor or gas with air, which if ignited will just propagate flame, are known as the "lower and upper flammable or explosive limits", and are usually expressed in terms of percentage by volume of gas or vapor in air.

The LEL is based upon location specific normal atmospheric temperatures and pressures. The general effect of an increase of temperature or pressure is to decrease the lower limit and increase the upper limit.

Applicable codes require thermal solvent processing systems to operate no higher than 25% LEL without an LEL monitor and control. Insurance companies may require LEL systems if an oxidation system is added to existing machinery.

For further information concerning the maintenance of safe LEL levels, please refer to NFPA Bulletin 86A and FM Loss Prevention Bulletin No. 14.15. These bulletins will delineate how safety interlocks can be implemented in the operator's system.

Oxidation is a process that causes compounds to break apart and reform into new compounds.

The formula is: Cn CzHy + (z+y/4)O2

->

(z)CO2 + (y/2)H2O

The most effective way to neutralize VOCs is through thermal or catalytic oxidation. On a very basic level, this involves converting the molecules in the VOCs into harmless compounds (carbon dioxide and water vapor) which can then be discharged into the atmosphere.

A two chamber RTO has 2 media beds.  One bed is used as an air inlet and one bed is used as an air outlet.  Every 3-4 minutes the air flow is reversed.  When the flow is reversed, there is a portion of air between the air switching valve and the combustion chamber that does not reach the full oxidation temperature.  This air is exhausted to the atmosphere, often being referred to as a puff or peak emission.

A three chamber RTO has 3 media beds.  One bed is used as an inlet, one bed is used as an outlet, and the 3^rd bed is purged of air and sent back to the inlet of the system.  Once the purge of tower 3 is complete, it becomes the inlet on the next air cycle.  By purging the odd tower, there is no puff or peak emission. 

In many cases RTOs fall under EPA method 25A sampling protocol.  Method 25A is a comparison of RTO inlet and outlet solvent concentrations averaged over 1 hour.  A two chamber RTO will achieve a 1 hour average reduction in solvent concentration of 98% and this is typically acceptable for the US market.

European Union standards are based on a continuous effluent emission, which makes the EU more applicable to 3 chamber RTOs, where in most cases, the puff or peak emission is not allowed.

3 chamber RTO’s are relevant in the US market, and are used on processes that require high removal efficiencies for VOC, HAP and odorous emissions.

Thermal oxidation uses high temperatures to heat the contaminated air, causing the molecules in the VOCs to break apart and yield carbon dioxide (CO2) and water (H2O). The formula is:

HC + O2	->	H2O + CO2
1400-1800°F

Key advantages of thermal oxidation:

• No risk of catalyst poisons
• Can handle higher LEL fume streams
• High temperature refractory reduces manufacturing costs
• Extended residence time for higher destruction efficiencies

Silicone in vapor form will convert to a solid above 1300 degree F and eventually will plug the RTO. How fast depends on how much is contained in the air stream and the void space within the type of heat recovery media used. Typically it adheres as a powder to the heat recovery media radiating above 1300 degree F.