wet vs dry scrubber differentiator

7/28/2019 Wet vs Dry Scrubber Differentiator

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THE REAL DIFFERENTIATOR WET VS DRY SCRUBBERSJan 09

About 95% of all one-ton and 150-cylinder emergency chlor ine scrubbers in theUnited States today are specified as dry scrubbers. Twenty years ago wet

scrubbers were specified 95% of the time. Dry scrubbers have quick ly gainedfavor for a good reason. Dry and Wet scrubbers sell for the same price thesedays. See the Cost Estimate attached. Dry systems save $7K to $10K a year inmaintenance. Dry scrubbers greatly reduce the dangers associated withintroducing another hazardous chemical and the associated liabili ties.

Some of the advantages of dry scrubbing as compared to wet scrubbing are:

1. Secondary containment tanks and/or concrete sumps are not required bythe building codes for dry scrubbers to guard against the release of ahazardous caustic chemical from a leaking or ruptured tank as in the caseof a wet scrubber.

2. Heaters are not required in cold cl imates for dry scrubbers. Dry media

has been tested down to - 40 deg F.

3. Cleaning of wet scrubber mist eliminators is not an issue in dry systems

4. Wet systems require pump maintenance. Dry scrubbers have no pumps.

5. Wet scrubbers require chemical titration, hazardous chemical handlingand hazmat approved personnel. Dry media is non-hazardous in the fresh

& spent forms. Wet caustic soda is hazardous and must be disposed ofas such.

6. Our competitors use high performance packing in vertical towers andcross-flow beds for contacting the gas with the wet caustic soda. The


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In summary, the normal problems associated with wet caustic scrubbers usinghigh performance packing media with 20% caustic soda are:

1. Degrading Caustic - Dried caustic soda reacts with carbon dioxide in the air

and converts to sodium carbonate. This sequesters the CO2 and helps the greenhouse effect but it hurts the wet scrubber long term operation. Thecarbonates will not re-dissolve and cause clogging in the packing, pumpsand spray nozzles and mist eliminators. Frequent acid cleaning of the highsurface area packing and associated down time is maintenance demanding.This is also a dependability issue. In short mist eliminator, packing and

spray nozzle annual cleaning are specific wet scrubber maintenance issuesnot associated with dry scrubbers.

2. Demineralized Water Make-Up - Water naturally evaporates from the causticsolution over time thereby concentrating the solution and accelerating thefoul ing effects stated above. An entire batch can solidify. Constant vigi lmust be maintained of the liquid level and demineralized water added as

required on a regular basis.

3. Disposal of caustic every 5 years - Caustic soda replacement could cost upto $4000 per batch. Disposal of waste caustic , which is normally designatedas a hazardous waste, could cost an addit ional $10,000 per batch. Dry mediadoes not require replacement unless exposed to chlorine.

4. If 1/4 of the caustic solut ion is spent in an event, the entire batch has to bereplaced. The solution concentration can NOT be elevated with the addit ionof stronger caustic as this would lead to reaction salt precipitation problems.Whereas, 1/4 of the dry media can be taken out of the tank and replacedwhi le saving 3/4 of the media that was unaffected by the leak


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operator safety issue. All nuts and bolts have to be re-torqued on a regularschedule many times a year on wet scrubber systems.

7. Wet caustic scrubbers in freezing environments need heating and insulation

and the normal associated maintenance. The dry scrubbing media canoperate at temperatures down to - 40 deg F without heating.

8. Wet scrubbers need caustic leak containment provided either as doublewalled expensive tanks or concrete containment areas around the tank perthe building code.

9. Bleach (NaOCl) is the reaction product in wet caustic soda chlorinescrubbers. Bleach is a hazardous aggressive chemical that can result in ashorter tank life. This is not the case for dry scrubber tanks.

10. Foaming is experienced due to natural caustic contamination over t ime.This is caused by the inability of the air to separate from the thick caustic

solut ion. Special caustic surfactants need to be added to the caustic every2 to 3 months to prevent this problem.

11. Wet caustic scrubbers are NOT user-friendly.

12. The normal maintenance savings of dry scrubbers over wet scrubbers are

$7500 per year considering the total costs associated with one completebed exhaustion over a 20 year scrubber li fe. See the cost estimateworksheet attachment.

Before any specifications are written the specifying engineer should visit some


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Aqua America in PA purchased eleven (11) wet caustic packed scrubbersystems over a 4 year period and is now in the process of converting to drybecause of the many problems they are now facing with the caustic/packingissue. Some operators have described high concentration 20% caustic

scrubbers using packing as cement mixers .

Ken ZarzyckiSevern Trent Water Purifications, Inc./EST Scrubber ProductsOffice: 215 - 997- 3736; Fax: 215 - 997- 4062Email: [email protected]

At tachments:

1. 20 year Installation and Maintenance Cost Estimate Jan 09

2. Carbonate Fouling Photos


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Carbonate Formation on Wet PackingCarbonate Formation on Wet Packing


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EST

Jan

2009

20 Year Operating & Maintenance Cost Estimate

Capital Costs Dry Scrubber

with release

Wet MVP

with release

Dry Scrubber

without release

$ 410,000 $ 335,000

335,000

(16,750/year)

48,000(2,410/year)

$383,000($19,150/year)

410,000

(20,500/year)

200,000(10,000/year)

$610,000($30,500/year)

$ 335,000

335,000

(16,750/year)

102,000(5,110/year)

$437,000($21,850/year)

Wet MVP

without release

Project Subtotal $ 410,000

Depreciation

Cost

410,000

(20,500/year)

Operating &

Maintenances

Costs

186,000(9,300/year)

Total 20-YearCosts

$596,000($29,800/year)


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EST

Capital Costs Dry Scrubber

Installation

Wet MVP

Installation

Equipment Pad

$3,000 $3,000Scrubber System 150,000 175,000

Installation 30,000 40,000Duct Work 15,000 15,000

Electrical Work 15,000 25,000Contractor Over Head

(15%)28,000 39,000

Contingency (15%) 38,000 45,000

Construction Cost 279,000 342,000Engineering and

Administration (20%)56,000 68,000

Project Subtotal $335,000 $410,000

Jan

2009

Cost basis is outdoor installation and double wall containment & heater on MVP


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EST

A) Operating Cost Calculations for Dry Scrubber With Accidental Release:Operating Man Hour= 2 Man Hr /Month X 12 Month /Yr = 24 Hr/Yr X $ 40 /Hr =$ 960/YrPower Supply= 25 KWH / Month X 12 Month /Yr= 300 KWH/Yr X $ .17/KWH = $ 50 /YrYearly Maintenance/Analytical Items Cost = $ 1000/Yr.Misc. Cost= $ 400/Yr.

Media Change and Disposal Cost (assuming 1 time media change in 20 year) = $ 54000/20 yr.=2700/YrTotal Yearly Operating and Maintenance Costs = $ 511020-Year Maintenance Costs ~ $ 102,000

B) Operating Cost Calculations for Dry Scrubber Without Accidental Release:Operating Man Hour= 2 Man Hr /Month X 12 Month /Yr = 24 Hr/Yr X $ 40 /Hr =$ 960/Yr

Power Supply= 25 KWH / Month X 12 Month /Yr= 300 KWH/Yr X $ .17/KWH = $ 50 /YrYearly Maintenance/Analytical Items Cost = $ 1000/Yr.Misc. Cost= $ 400/Yr.Total Yearly Operating and Maintenance Costs = $ 241020-Year Maintenance Costs ~ $ 48,000

C) Operating Cost Calculations for EST MVP Wet Scrubber Without Accidental

Release:Operating Man Hour= 8 Man Hr /Month X 12 Month /Yr = 96 Hr/Yr X $ 40 /Hr =$ 3840/YrPower Supply= 40 KWH / Month X 12 Month /Yr= 492 KWH/Yr X $ .17/KWH = $ 84 /YrYearly Maintenance Items Cost = $ 1000/Yr.Misc. Cost= $ 2000/Yr.Caustic Change and Disposal Cost (recommended once every 5 years, 4 times in 20 year life

time, $ 12,000 per change for disposal and replenishment) = $ 12,000 x 4 /20yr.= $2400/YrTotal Yearly Operating and Maintenance Costs = ~ $ 930020-Year Maintenance Costs ~ $ 186,000

D) With an accidental release for the wet MVP:$12,000 per change x (4 + 1) /20 yrs = $3000/Yr

Total Yearly Operating and Maintenance Costs = ~ $ 10,00020-Year Maintenance Costs ~ $ 200,000

Jan

2009

wet vs dry scrubber differentiator

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