This depends on where the tanks are sited. In hot countries some operators specify insulated tanks but, in turn, some don&#;t. It&#;s down to project specific requirements.

Click here to get more.

The thickness of insulation for each tank is determined by the

• hydraulic retention time (HRT), ie, the time when productivity could start to decline (while the organic fermentable substrate remains in the digester)
• type of process; thermophilic or mesophilic.

We have supplied tanks with insulation as thin as 50mm and as thick as 150mm. Thicker insulation is available but we have rarely been asked to supply this.

Ultimately, the insulation specification is the responsibility of the biogas plant designer.

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Experience with Epoxy coating for interior of large diameter tanks

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Experience with Epoxy coating for interior of large diameter tanks

Experience with Epoxy coating for interior of large diameter tanks

GRRR

(Chemical)

(OP)

Goto zhaoyang to know more.

27 May 03 18:04

Waste will contain less than 10% NaOH, water, and less than 40% organic, some of which (5-10% total) will separate out in an upper layer during storage.

Waste may be stored from several months to 2 years before disposal facility can be constructed.  Iron contamination for one of the potential treatment processes is an issue.

Organics will consist of a relatively large-chained mercaptan, Ethylmethyl Phosphonic Acid (EMPA), Methyl Phosphonic Acid (MPA),  relatively large-chained disulfide, and other organics of small concentration. Tanks will have nitrogen blanketing.

Designer is recommending a epoxy lining (Plasguard ) concern has been raised about epoxy coating failures with respect differences in thermal expansion of the coating versus underlying carbon steel (tank diameter is 42 ft), coating rigidity, and/or acceration of epoxy coating adhesion loss with respect to "hot water" acceration.   

I am interested in hearing from someone with experience with coating large tanks storing similar materials.

Thanks

We are in design process of for a large tank farm (4-tanks, 300K gallons each, one spare), for use in RCRA waste tank farm on a fast-tracked project. Tanks will be insulated and heated to maintain fluid temperature of 100F.Waste will contain less than 10% NaOH, water, and less than 40% organic, some of which (5-10% total) will separate out in an upper layer during storage.Waste may be stored from several months to 2 years before disposal facility can be constructed. Iron contamination for one of the potential treatment processes is an issue.Organics will consist of a relatively large-chained mercaptan, Ethylmethyl Phosphonic Acid (EMPA), Methyl Phosphonic Acid (MPA), relatively large-chained disulfide, and other organics of small concentration. Tanks will have nitrogen blanketing.Designer is recommending a epoxy lining (Plasguard ) concern has been raised about epoxy coating failures with respect differences in thermal expansion of the coating versus underlying carbon steel (tank diameter is 42 ft), coating rigidity, and/or acceration of epoxy coating adhesion loss with respect to "hot water" acceration.I am interested in hearing from someone with experience with coating large tanks storing similar materials.Thanks

Replies continue below

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RE: Experience with Epoxy coating for interior of large diameter tanks

cub3bead

(Chemical)

3 Jun 03 09:02

I have used another Plasite product for lining demineralized water tanks and have experienced no failures to date.  Demineralized water is very corrosive.

Surface preparation is the most important step.  White metal blast and a good QA/QC program is mandatory for a long service life.  

Insulating the tank and heating the contents would minimize my concern about coating adhesion.  You are minimizing differential heating as the sun tracks across the sky.  

Have you considered a vinyl ester coating?  Or field erected FRP tanks?   

RE: Experience with Epoxy coating for interior of large diameter tanks

azertyuiop

(Mechanical)

14 Jun 03 17:32

I had a similar problem with demin water storage in a 30 feet diameter tank , 15 feet high. The most economical solution was to buy an epoxy coated tank , fabricated from small pannels , bolted together to create the tank.

I had major quality problems during construction , the construction crews being 'imported' unqualified people , who managed to let gear fall on the surface of the pannels and mishandle the stored pannels.

Luckily for them , all surface damages were on the oustide of the pannels , and a new protective coating was sufficient to permanently repare the damages.

However , the whole construction process is a very tedious and carefull job , not leaving me with a confortable feeling , even now. If I had to redo the whole thing , I probably would have settled for a big concrete 'swimming pool' covered with several layers of an adequate internal lining , even when this was more expensive.

RE: Experience with Epoxy coating for interior of large diameter tanks

rembrandt

(Specifier/Regulator)

23 Jun 03 11:44

Guys,
The difference between the latter 2 tanks and the original owners query is that your tanks are in Demin water service, and his isnt. I would suggest a far better solution to the original problem is to line the tanks with a solvent free (100% Volume Solids) Glass flake reinforced Vinyl Ester coating applied in 2 coats at 500-750 microns per coat
(20 to 30 mils.) This will be more suitable to the environment you will experience. There are some very valid points about surface preparation and stringent independent QA/QC. Do not rely on the application contractor to provide this on your behalf.

RE: Experience with Epoxy coating for interior of large diameter tanks

lafdot

(Chemical)

29 Jun 03 20:18

Before applying coating to floor of tank, re-pressure wash to remove any environmental contamination and overspray that occurred while applying to the top and walls. Then dry and apply polyurea to metal. Make sure all termination points are outside of tank. In other words, spray out the flanges and tie back on the exterior of the tank by a 6 inch margin. Otherwise there is a possibility for coating to delaminate from intrusion of liquid. The tank should be cured for at least 3 days before opening to service.

See:

We have coated the internal sections of waste water (RCRA) tanks with polyurea (100% polyurea aromatic) and have good success. Polyurea is a fast (less than 15 seconds) curing high performance coating. Highly chemical resistant. It exhibits high adhesion characteristics on steel, concrete, wood, fiberglass, etc. The key (repeat "KEY") to a successful application is surface preparation. It is important that the surface be cleaned, blasted to a 2 to 4 mil profile, cleaned again with a hot solution of TSP (trisodium phosphate), pressure washed with + psi water. If steel is new this should get it prepared for coating. If the steel was in service, it should be checked for chloride residual. If none dry, and apply 120 mils of polyurea. The application should be from the top down in a cross/hatch pattern to get even coverage of coating.Before applying coating to floor of tank, re-pressure wash to remove any environmental contamination and overspray that occurred while applying to the top and walls. Then dry and apply polyurea to metal. Make sure all termination points are outside of tank. In other words, spray out the flanges and tie back on the exterior of the tank by a 6 inch margin. Otherwise there is a possibility for coating to delaminate from intrusion of liquid. The tank should be cured for at least 3 days before opening to service.See: www.rapidcoating.com

RE: Experience with Epoxy coating for interior of large diameter tanks

JimMetalsCeramics

(Materials)

24 Jul 03 15:44

www.devcon.com

If an epoxy winds up not being adequate, you might consider a thermally sprayed metallic coating.

You might check with Devcon:If an epoxy winds up not being adequate, you might consider a thermally sprayed metallic coating.

RE: Experience with Epoxy coating for interior of large diameter tanks

ghopkins

(Chemical)

29 Jul 03 11:40
For manufacturers to build this type of equipment, see:
www.rl-industries.com
www.ershigs.com

With straight fiberglass construction, there are no concerns with chipping, peeling, or other degradation of a liner.  The corrosion barrier as well as the structure are all resistant to chemical attack.

Has 100% FRP construction been considered? There are a few companies that can build FRP tanks as large as you require. Resistance to organics is of primary concern, but a novalac epoxy vinyl ester resin (i.e. DEREKANE 470) should suffice.For manufacturers to build this type of equipment, see:With straight fiberglass construction, there are no concerns with chipping, peeling, or other degradation of a liner. The corrosion barrier as well as the structure are all resistant to chemical attack.

RE: Experience with Epoxy coating for interior of large diameter tanks

JimMetalsCeramics

(Materials)

29 Jul 03 13:24 http://www.belzona.com/polymers.html

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