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Dust Control Handbook for Minerals Processing
For problems with accessibility in using figures and illustrations in this document,
Necessity for Cost Estimates
Since adequate control of dust emissions can usually be achieved by
more than one dust control method, a considerable economic burden may
result if the appropriate method is not selected. This burden can be
higher capital costs, higher operating and maintenance costs, or
both. Preliminary cost estimates can prevent this unnecessary
economic burden by-
please contact the Directorate of Technical Support and Emergency Management at (202) 693-2300.
- Characterizing the costs to be incurred and determining whether they
- Comparing expected costs of alternative dust control techniques to
help identify the optimum control technique
Cost Estimating Procedures
Several methods, with varying degrees of accuracy, are available for
estimating costs. They range from presenting an overall installed
cost on a per-unit basis to presenting detailed cost estimates based on
preliminary designs, schematics, and/or vendors' cost estimates. The
lease accurate method is to equate overall costs to a basic operating
parameter such as tons per hour or cubic feet per minute. This
approach is not recommended. Where possible, detailed cost estimates
should be arrived at by preparing preliminary designs and
schematics. However, if time does not permit this approach,
equipment vendors may be contacted. Based on their current knowledge
of the technology and experience in the industry, they can provide
reasonably accurate cost estimates.
To prepare and analyze cost estimates, a basic knowledge of the cost
components and their relationship to the total cost of the system is
Total costs for any system can be divided into-
- Capital costs
- Operating and maintenance costs
Capital costs consist of the delivered costs for major control
equipment, auxiliary equipment and accessories, and field
installation. Capital costs can be grouped as follows:
Summary of Capital Costs
- Major equipment (35%)*
- Auxiliary or accessory equipment (15%)
- Field installation (20%)
- Project management and engineering (13%)
- Freight, taxes, subcontractor, and so forth (17%)
- Start up cost, working capital, and other capitalized costs (15-20%)**
* Average percent of the capital investment
** Additional costs, expressed as a percentage of
total capital costs
The capital costs of a baghouse depend on the following:
- Major Control Equipment
- Electrostatic precipitators
- Water-spray bars
- Auxiliary or Accessory Equipment
- Air-moving equipment
-- Fans and blowers
- Liquid-moving equipment
-- Electrical motors, starters, wire, conduit, switches, etc.
-- Hoods, ductwork, gaskets, dampers, etc.
- Storage and disposal equipment
-- Electrical motors, starter, wire, conduit, switches, etc.
-- Piping and valves
-- Settling tanks (for wet scubbers)
--Dust storage bins and hoppers
- Supporting construction
--Drag lines, trackway, etc.
-- Structural steelwork
- Instruments to measure or control the following:
-- Cement foundation
-- Thermal insulation
-- Vibration and antiwear materials
-- Protection covers
-- Air and liquid flow
-- Temperature and pressure
-- Operation and capacity
-- Opacity of flue gas
-- Dust concentration
- Field Installation Costs
- Labor required for delivery, assembly, removal or relocation of equipment
- Freight, taxes, and subcontractors' fees
- Engineering supervision
- Startup and performance testing
- Extending or increasing utilities
The capital costs of an electrostatic precipitator depend on the net
plate area (NPA). The NPA, in turn, depends on the efficiency
required of the precipitator.
- Type of filtering media used (cotton, dacron, glass, Teflon, etc.)
- Type of fabric used (felted vs. woven)
- Adopted air-to-cloth ratios
- Type of cleaning mechanism (mechanical shaker, pulse jet, reverse air)
- Type of baghouse (suction type vs. pressure type; continuous duty
- Design and construction (standard design vs. custom design; carbon
steel vs. stainless steel)
- Temperature of exhaust gases (high temperature vs. low ambient
Following are the factors that affect the cost of an electrostatic
The capital costs of a scrubber depend, generally, on the following
- The electrical characteristics of the dust may have a significant
effect on the collection efficiency and the plate area.
- The resistivity of the dust varies with the temperature and moisture
content of the bag. Therefore, in some cases, auxiliary
equipment may be required to precondition the gas stream before it
enters the precipitator.
- The addition of moisture to the gas stream, in combination with a
low operating temperature, may require insulating the precipitator to
prevent condensation and corrosion.
The volumetric airflow rate is the most important factor because the
size of the scrubber and its cost are determined by the actual gas volume
at the scrubber's inlet.
- Volumetric airflow rate
- Operating pressure
Operating pressure also affects scrubber efficiency and price.
The higher the air volume and/or operating pressure, the greater the plate
thickness of the shell must be to prevent buckling of the shell.
The cost of a scrubber can also increase if it is constructed of
special materials, such as stainless steel or fiber-reinforced plastics to
protect against corrosion or lining the scrubber shell with PVC, rubber,
or refractories to protect against erosion.
The capital costs of a cyclone or multiclone are a function of the
particulate-removal efficiency, which, in turn, depends on the inlet gas
velocity and inlet diameter. Theoretically, the higher the velocity
or the smaller the inlet diameter, the greater the efficiency and pressure
The material of construction also affects the cost. For handling highly
abrasive dust, the cyclone/multiclone may have to be constructed of
abrasion-resistant material or lined with ceramic material. For a
highly corrosive gas stream, stainless steel or fiber-reinforced plastic
may be necessary.
Fans and Motors
The capital costs of a fan are based on-
The capital costs of a fan motor are related to-
- Volume handled
- Pressure developed
Although pump prices vary with the design of the pump, they are
generally a function of-
- Fan speed
- Total system pressure
- Gas volume flow rate
- Selected motor housing
The selections of revolutions per minute for these pumps should be
based on the design flow rate:
- Pump head developed, ft
- Pump capacity, gal/min
- Pump speed, r/min
Note: Generally, the capital cost of the pump and motor
combination varies inversely with the revolutions per minute; however,
maintenance costs may be higher as the revolutions per minute increase.
|Flow rate (gal/min)
| 0 - 1,000
|500 - 5,000
|2,000 - 10,000
Operating and Maintenance Costs
Operating and maintenance costs consist of direct expenses of labor and
materials for operating and maintenance, the cost of replacement parts,
utility costs, and waste disposal costs. They may also include
indirect costs of overhead, taxes, insurance, general administration, and
capital recovery charges. However, only direct costs are discussed
Operating costs include-
Direct Labor and Material Costs- Labor and materials costs for
operation and maintenance of dust control systems vary substantially among
plants due to factors such as the degree of automation, equipment age, and
operating periods. Generally speaking, labor costs can be reduced by
increased system automation.
- Direct labor and materials
For small- to medium-size systems with an installed cost of
approximately $100,000 or less, the total cost of maintenance is
approximately 5% of the installed cost.
|Estimated Labor Hours per Shift
||Guidelines for Parts and Equipment Life
||Materials and Parts Life
|Water spray system/wet dust suppression system
- Estimates are based on large plants operating three shifts per day for 365 days. For smaller plants expected to operate
one shift per day, 5 days per week, 50 weeks per year, the labor hours/shift will be higher.
- The guidelines for average life represent a process operating continuously with three shifts per day, 5-7 days per week,
52 weeks per year.
- Estimates are only for performing preventive maintenance.
- The guidelines for low life are based on a continuous process, handling moderate- to high-temperature gas streams,
with a high concentration of corrosive or abrasive dusts.
- Where periodic replacement of major parts are required, such as replacement of filter bags in a baghouse
or replacement of spray nozzles in a wet dust suppression system, the labor cost of replacement will be at least equal to the material
cost of replacement parts.
- Applications having high life expectations for parts and equipment are assumed to be operating
intermittenly or approximately one shift per day with gas streams having ambient temperature and low dust concentrations.
Utility Costs - the utility costs for equipment such as pumps
and electrical motors are a function of power/energy requirements, which
can be calculated as follows:
0.746 (hp) (H)
||= kilowatt hour
||= actual volumetric airflow rate
||= pressure loss, in. wg
||= mechanical efficiency, usually 60-70%
||= hours of operation
||= specific gravity as compared to air at 70°F,
29.92 inches of mercury
0.746 (hp) (H)
Baghouse Power (auxiliaries, motor, etc.)
||= flow rate
||= hours of operation
||= head of fluid (ft.)
||= specific gravity relative to water
Horsepower requirements for baghouse shaker motors, reverse-air fan
motors, etc. can be estimated at approximately 0.5 hp per 1,000 ft2
of cloth area. Power usage depends on dust loading and cleaning
frequency. Assuming a 50% usage factor, power requirements are
approximately 0.2 kW·h for 1,000 ft2 of cloth area.
Electrostatic Precipitator Power
The power requirements for an electrostatic precipitator are
approximately 1.5 W/ft2 of collection plate area. The
range varies from 0.3 to 3 W/ft2.
Once the power requirement is known, the annual power costs can be
calculated using the following equation:
Annual power cost ($) =
Power usage x Cost of
power x Total annual
($/kW·h) operating hrs.
Waste Disposal Costs
The cost of waste disposal included the removal and hauling of dry
contaminants to a nearby site. This cost varies with the
particular plant and available landfill site.
Water costs vary in different areas.
Maintenance costs include-
The annual cost of replacement parts represents the cost of the parts
or components divided by their expected life. Replacement parts are
components such as filter bags and spray nozzles, which have a limited
life and must be replaced periodically.
- Labor and materials for preventive and routine maintenance, such as
lubrication, surface protection, cleaning, and painting
- Replacement of worn-out equipment, parts, or structures due to wear,
abrasion, or corrosion
A 10-15% return on investment is necessary to justify and capital
investment. However, when dust controls are considered, such a
return is not always practical. The following are some tangible
benefits that may assist in economic justification of a dust control
Various federal and state governments provide the following tax relief
benefits for industries that install dust control or pollution control
- Industrial taxes amount to about 50% of net income, which means
business investments result in a tax savings equivalent to
approximately half the expenditure.
- Return on investment before taxes is approximately twice the value
of the return calculated after taxes.
- Section 169 of the Internal Revenue Tax Reform Act of 1969 permits a
faster tax write-off of pollution control facilities. If the
facility is certified by both the Environmental Protection Agency and
the appropriate state agencies, facilities installed after 1968 can be
amortized over a 60-month period. An exception to this is any
control system that recovers the costs by generating a profit in some
- Thirty-seven states provide tax incentives for pollution control
facilities, such as-
- Property tax exemption
- Sales and use tax exemption
- Income tax credit
- Accelerated amortization
Other intangible benefits may further assist in justifying a dust
- All but four states (California, Idaho, New Jersey, and Texas)
authorize the use of industrial revenue bonds to finance pollution
control equipment. These are normally 15-year bonds that provide
tax-free interest to the holders. Although the interest rates
offered by these bonds are about 2% lower than most other bonds, they
can attract investors because of their tax-free status.
- Reducing health hazard possibilities
- Reducing risk of dust explosion and fire
- Reducing equipment wear and damage
- Increasing visibility
- Reducing or eliminating unpleasant odors
- Improving relations with neighbors
- Creating safer and more pleasant working conditions, thus improving
employee morale and productivity
- Possible product or byproduct savings