| Overview: |
This technology has been used
successfully to recycle wastewater generated during the hydroblasting of
ship’s boilers. Hydroblasting is a time-consuming process that generates
8,000 to 12,000 gallons of wastewater, per boiler cleaning, containing
heavy metals and sodium nitrite. Sodium nitrite is added to the water used
in the hydroblasting process and acts as a surface conditioner that
prevents flash rusting of boiler tube surfaces during the hydroblasting
operations. This water/sodium nitrite mixture can be reused in the
hydroblasting process without adversely effecting the finished product
only if the solids have been removed.
The recycling system consists of collection,
settling, filtration, reconditioning and reuse of the hydroblasting water.
The water is continuously recycled during the hydroblasting operations
until the operation has been completed. Initially, potable water is mixed
with sodium nitrite before being pumped under pressure to high pressure
nozzles. The water is pressurized and sprayed on to the steam side
surfaces of the boiler tubes to remove scale build-up. The wastewater from
the blasting operation is collected and pumped out of the
boiler.
Utilizing the recycling unit, wastewater is
sent to two 650-gallon settling tanks. Once enough water has been
collected, the fresh water is shut off and the wastewater is recycled
through the unit. The wastewater is pumped to the first collection tank,
where it is gravity fed to the second tank, allowing larger, suspended
particles to settle out. It is then pumped from the second settling tank
through a parallel train of six cartridge filters each side rated at 50,
25, and 5 microns, respectively. The recycled water passes through a heat
exchanger before being returned to the hydroblasting operation for reuse.
The filters remove small suspended material that cannot be removed through
gravity settling. The filters do not remove sodium nitrite, which remains
above 1,200 ppm, the level needed to prevent flash rusting. As a result,
no additional sodium nitrite needs to be added to recycled
water.
The recycling unit has resulted in no known
mechanical failures during the hydroblasting operations, nor does it cause
a decrease in the quality of the cleaning operation. The sodium nitrite
stays above the 1,200 ppm threshold, preventing rusting and surface
damage. After inspection, no residuals were observed on the tube surfaces
of boilers cleaned with the hydroblasting recycling unit and the cleaning
operation was completed satisfactorily.
|
| Compliance Benefit: |
Use of a hydroblasting
wastewater recycling system will decrease the amount of water used which
helps a facility meet the requirements of EO 13123 requiring
federal facilities to implement water conservation projects. In addition,
the system will decrease the use of sodium nitrate used at the facility
and therefore, reduce the possibility that a facility will reach any of
the reporting thresholds of SARA Title III for that chemical (40 CFR
370 and EO 12856). Since the volume of wastewater is decreased, the
facility would be decreasing their hazardous waste generation if in fact
the wastewater is considered a hazardous waste (i.e., contains heavy
metals). Decreasing the volume of hazardous waste will help facilities
meet the requirements of waste reduction under RCRA, 40 CFR 262,
Appendix, and may also help facilities reduce their generator status
and lessen the number of applicable regulations (i.e., recordkeeping,
reporting, inspections, transportation, accumulation time, emergency
prevention and preparedness, emergency response) under RCRA, 40 CFR
262.
The compliance benefits listed here are only
meant to be used as a general guideline and are not meant to be strictly
interpreted. Actual compliance benefits will vary depending on the factors
involved, e.g. the amount of workload involved.
|
| Materials Compatibility: |
No materials compatibility
issues were identified.
|
| Safety
and Health: |
Heavy metals and sodium nitrite
are irritants to skin, eyes, and mucous membranes. Inhalation of these
fumes can be toxic. Proper personal protection equipment is, therefore,
recommended.
Consult your local Industrial Health
specialist, your local health and safety personnel, and the appropriate
MSDS prior to implementing any of these technologies.
|
| Benefits: |
- With the use of the recycling unit, the
amount of wastewater generated by hydroblasting operations can be
reduced by 90%.
- Since less potable water is used in the
operation, the amount of sodium nitrite used can be reduced
dramatically.
- No additional personnel are needed to
operate the recycling unit.
|
| Disadvantages: |
- This process generates spent filters that
must be disposed as hazardous waste.
|
| Economic Analysis: |
The process has been used
successfully throughout the Navy for the hydroblasting of ships’ boilers
and may apply to other hydroblasting operations as well. It has been
implemented at several shipyards, Ship Repair Facilities (SRFs), on board
US Navy Tenders, and Shore Intermediate Maintenance Activities (SIMA) by
the former Naval Energy and Environmental Support Activity (NEESA) and
Naval Ship System Engineering Station (NAVSSES).
The cost of the recycling unit is around
$25,000 which includes the equipment, spare filters for a year, training
and support. The savings generated will vary from activity to activity
depending on the number of boiler cleanings performed.
Assumptions:
- 10 boiler cleanings are conducted a
year.
- 10,000 gallons of wastewater are generated
per boiler cleaning.
- Cost to dispose of wastewater is
$2.50/gallon (including transport).
- 2 hours of labor is needed to set up
hydroblast recycling equipment.
- No extra labor is needed to operate
recycling system.
- 80 labor hours are required per boiler
cleaning.
- Labor rate: $45/hr.
- 1,000 gallons of wastewater needs to be
disposed of after hydroblasting boiler using the recycling
system.
- 10 pounds of sodium nitrite is used with the
recycling system and 100 pounds of sodium nitrite is used without the
recycling system.
- Sodium nitrite costs $2.35/lb.
- Water costs $4/1,000 gallons.
- Disposal of used filters costs
$50/cleaning.
- Yearly maintenance cost for recycling
system: $200
Annual Cost Comparison for
Recycling Versus No Recycling of Hydroblast Wastewater
| |
Recycling |
No
Recycling |
|
Capital and Installation
Costs: |
$25,000 |
$0 |
| Operational
Costs: |
|
|
|
Labor: |
$36,900 |
$36,000 |
|
Water: |
$40 |
$400 |
|
Sodium
Nitrite: |
$235 |
$2,350 |
|
Wastewater
Disposal: |
$25,000 |
$250,000 |
|
System
Maintenance: |
$200 |
$0 |
|
Filter
Disposal: |
$500 |
0 |
|
Total Operational
Costs: |
$62,875 |
$288,750 |
| Total
Income: |
$0 |
$0 |
| Annual
Benefit: |
-$62,875 |
-$288,750 |
Economic Analysis Summary
Annual Savings for Secondary Use:
$225,875
Capital Cost for Diversion Equipment/Process:
$25,000
Payback Period for Investment in Equipment/Process: 2
cleanings
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Spreadsheet for this Economic Analysis and Enter Your Own Values. To
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|
| Approving Authority: |
Approval is controlled locally
and should be implemented only after engineering approval has been
granted. Major claimant approval is not required.
|
