Q&A

The following are FAQs regarding recovery system

What is solvent recovery system (hereinafter called "SRP")?
It is a system which causes activated carbon to absorb VOCs (volatile organic compounds) contained in exhaust gas, then desorbs them with steam to recover.(Our system: Fixed-layer granular-carbon steam desorption system)
Since installation of SRP allows reuse of the solvents, which previously is discharged into the atmosphere, it contributes remarkably to cost reduction in product fabrication and resource saving.
Is SRP prospective as a measure for global warming control?
Yes, it is. When solvent-containing gas is treated through combustion, carbon dioxide (hereinafter called CO2 is discharged. Since in SRP, steam is used for carbon desorption, boiler combustion caused CO2 to be discharged as well. It can be said that the system discharges CO2 indirectly, however the emission can be controlled at lower level than in the case of combustion treatment. The following is an example of comparison in CO2 emission of SRP and regenerative combustion equipment:

Requirement for solvent gas: 30,000m3N/h; Toluene:1,000 parts per million, Operation hours: 6,000h/yr
SRP: 770ton/yr (CO2 emission accompanying required steam generation)
Regenerative combustion equipment: 2,500ton/year (CO2 emission accompanying toluene combustion treatment)

As indicated above, the system allows control of CO2 emission at the level approximately less than one third (1/3).
Are the recovery solvents reusable?
Almost all our customers reuse the recovered solvents. In SRP, reuse of the recovered solvents produces substantial merits of introduction of the system. We will consult with you about reusable properties and conditions to reflect them to the planning and the design.
What are the features of "Mitsubishi Power Environmental Solutions" SRP?
Features of our SRP are "fixed layer (absorption tank)", "granular carbon", and "Steam desorption".
Following good points allow actualization of highly efficient recovery, low running cost, and maintenance saving.
Fixed Layer: Since activated carbon is stationary in the absorption tank, abrasion of activated carbon is extremely minor. Without short-passing, solvent gas passes through the activated carbon layer and absorbed Granular carbon: Since the area which contacts the solvent gas is large, deterioration due to clogging is minor compared with other types of activated carbon.
"Steam desorption" : Since the (desorption) process of washing out from upper section with steam is employed, the system is highly resistant to impurities such as paper powder and silicone.
What is absorption on activated carbon and desorption?
When solvents containing gas passes through absorption tank packed with activated carbon, solvents are absorbed on the activated carbon. Activated carbon has holes in micron cold pores, in which solvents are absorbed.
When pouring steam onto the activated carbon with given amount of solvents absorbed, the solvents are washed out (desorbed), becoming distilled air to be recovered.
Onto the regenerated activated carbon, solvent gas is poured again. This cycle of process is repeated in operation of the system.
Are there many types of activated carbon available? If yes, what types are they?
Yes.
We are using activated carbon called "granular carbon".
Besides, there are fiber carbon and bead carbon. For all of them, principles of solvent absorption are the same.
How long is the service life of the activated carbon?
Since it depends on the types of recovered solvents and existence of impurities in the gas, we cannot say sweepingly. However, just for your reference, let us give you an example: in the case of toluene recovery, at a certain plant, to which we supplied the system, absorption performance has been maintained for 10 years without replacing the activated carbon.
Which activated carbon is the best?
It is not a question of good or bad, but suitable or not.
Which activated carbon is suitable is determined according to the types of solvents and existence o impurities. Combination of "granular carbon" and "steam desorption" is superior to deal with impurities.
Furthermore, no activated carbon can absorb solvents which cannot be absorbed by "granular carbon"
What should we do with the activated carbon, of which absorption performance degraded?
Activated carbon with absorption performance being degraded can be subjected to regeneration treatment at the manufacturer's factory to reuse.
However, in some cases, it is difficult to regenerate the carbon depending on the conditions to use. In such a case, we will take back the old carbon when delivering of new one.
What about the risk of explosion or fire, and measures of precaution?
Solvents have explosion lower limit respectively. (When concentration is lower than this value, a solvent does not explode.) We generally recommend system design at the level lower than 1/4 of the explosion lower limit in consideration of uneven raw gas concentration.
Component parts are explosion-proof and various safety interlocks are equipped, securing safe operation.
What is the recovery efficiency of SRP?
It varies with types of solvents.
In case of toluene, efficiency of more than 99 percent can be expected as initial performance for Plant Type.
Do you have systems larger than 22.000m3N/h model available in Package Type?
Fabrication is practicable. However, in connection with the transport limits, assembly range at the system fabrication factory is small. It does not make much difference in the range of installation work at the local site compared with the Plant Type.
We have plural production facilities generating solvent-containing gas. In this case, do we have to install SPRs for respective facilities?
Generally, gas from respective production facilities is collected through duct to treat at one SRP. However, when solvent composition and operating hours are substantially different, in some cases separate installation (by types) may be advantageous. In case production facilities stand away from each other, separate installation of the systems may allow lower investment in plant & machinery than drawing around the duct.
At our production facility, load variation is great. Dose it affect the system?
No. it does not. Options such as raw gas load counter control and inverter control system equipped allows energy-saving operation without trouble.
There are houses in the vicinity of the plant. How intense is the noise of the system?
Let us have the noise values near the system or boundaries of your premises.
We use lagging onto the raw gas blower, duct and piping for noise reduction.
As the case may be, sound-proof chamber is installed to locate noise sources such as raw gas blower indoors.
Does SRP allow settlement of odor problem?
SRP is not a deodorizer and not capable of removing odor. However, for toluene, when employing SRP, its odor is hardly sensed compared with that is discharged into the atmosphere. However, it should be noted that solvent odor intensity varies with types.
Odor problem is referred to as sensory nuisance, and identification of odor source and determination whether the measures taken is effective or not are said to be extremely difficult.
We will consider specifically techniques to solve the problem including sensory test to make suggestions.
We would like to introduce SRP. Is it possible to use it on lease?
Yes it is.
Is it required to submit report about installation of SRP to relevant authorities?
Basically, it is required to report to the competent fire department, Labor Bureau, and Prefecture (Municipality).
Is exclusive staff required for daily operation and maintenance after installation of SRP?
Legally no exclusive staff is required.
Going around two - three times a day, on startup and shutdown, and during operation, is enough.
What should we do about operation control and repair after installation of SRP?
After installation of SRP, we hold an explanatory meeting on the operation procedures and provide instruction manual to leave the operation control to the customer.
For repair ranging from minor work such as repair of piping to retrofitting work for reinforcement of capacity (such as rise in treatment gas volume), we provide attentive support.
Are regular inspections required?
In order to operate the system stably for a long period of time, inspections are required to some extent. We suggest that customers request us to do system inspection every year or every two years after installation.
We conduct operating inspections and shutdown inspections to suggest maintenance including precaution measures.
Is there anything corresponding to legal inspections for SRP?
If you introduce our distillation/purification/Separation system, in most cases a reboiler is included. When a reboiler corresponding to the 1st class pressure vessel is included, the system should be subjected to a legal inspection by the Labor Bureau once a year.
What are included in the repair/maintenance items for SRP?
Repair/maintenance items include housekeeping (general tank, separator, condenser, and instrumentation line), servicing of absorption control valves, and replacement of rotating equipment bearings. Repair/maintenance items and frequency substantially vary with using conditions and utility properties. Daily management such as greasing-up allows operation without trouble for two-three years after installation according to our record.
How long is SRP service life?
Since service life of SRP is not provided for legally, it will follow that of the production facility.
We cannot definitely indicate actual service life, however, there are a number of plants that have been operating for over 30 years since we supplied the system.
How large is SRP?
For Package Type, refer to the page for introduction to products.
For Plant Type, we will consider and design for specific cases according to the gas volume as well as the installation space suggested by the customers respectively.
Just for your information, see the page showing examples of actual application.
Since the installation space is narrow, we would like to install it on the roof.
The system can be installed if your building is sufficient enough. There are a number of examples of installation on the roof.
SRP should be installed outdoors? (Is it possible to install it indoors?)
It is practicable to install indoors. However, careful consideration should be given to the ventilation and room temperature (for example, extending exhaust hole to discharge outdoors).
What is the load of the system by estimate (ton/square meter)?
Package Type is approx. 1ton/square mete r(operating load).
For Plant Type, the load greatly varies with the installation space. We will consider specific cases respectively.
Is it allowed to discharge separator wastewater as it is into the sewerage?
Since the properties of wastewater vary with the types of solvents, we will consider specific cases respectively.
We have trouble with maintenance of existing SRP, which is not Mitsubishi Power Environmental Solutions's. Would you let us have your suggestions about that?
We are ready to deal with your consultation.
There are cases, which can be settled by retrofitting or otherwise depending on the methods of SRP.
We have experience in retrofitting of other companies' SRPs called "fixed bed horizontal method". Ours is "fixed bed upper/lower stream method using flow direction of solvent gas and steam, with which activated carbon is hardly polluted.