Total Capital Investment

Total capital investment (TCI) is estimated from a series of factors applied to the purchased equipment cost (PEC) to obtain direct and indirect costs for installation. The TCI is the sum of the direct costs (equipment and installation) and indirect costs. The required factors are given in Table. Because ESPs can vary from small units attached to existing buildings to large, separate structures, specific factors for site preparation or for buildings are not given. However, costs for buildings and materials may be obtained from references such as Means Square Foot Costs 1987. Land, working capital, and off-site facilities are excluded from the table because they are required only for very large installations. However, they can be estimated on an as-needed basis. Note that the factors given in Table  are for average installation conditions, and for example, include no unusual problems with site earthwork, access, shipping, or interfering structures. Considerable variation may be seen with other-than-average installation circumstances. For two-stage precipitators purchased as packaged systems, several of the costs in Table would be greatly reduced or eliminated. These include instruments and controls, foundations and supports, erection and handling, painting, and model studies. An installation factor of 0.25 of the PEC (instead of 0.67 PEC) would be more nearly appropriate for the two-stage ESPs.

                                                 Capital cost factors for ESPs

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Total Purchase Cost

The total purchase cost of an ESP system is the sum of the costs of the ESP, options, auxiliary equipment, instruments and controls, taxes, and freight. The last three items generally are taken as percentages of the estimated total cost of the first three items. Typical values are 10% for instruments and controls, 3% for taxes, and 5% for freight.
 

Costs of standard and other options can vary from 0% to more than 150% of ESP base cost, depending on site and application requirements. Other factors that can increase ESP  costs are given in Table

                                               Items that increase ESP costs

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Costs for Two-Stage Precipitators

Purchase costs for modular, two-stage precipitators should be considered separately from large-scale, single-stage ESPs (see Figure ). To be consistent with industry practice, costs are given as a function of flow rate through the system. The lower cost curve is for a two-cell unit without a precooler, installed cell washer, and a fan. The upper curve is for an engineered package system with the following components: inlet diffuser plenum, prefilter, cooling coils with coating, coil plenums with access, water-flow controls, triple-pass configuration, system exhaust fan with accessories, outlet plenum, and in-place foam cleaning system with semiautomatic control and programmable controller. All equipment is fully assembled mechanically and electrically, and it is mounted on a steel structural
skid.

                              Purchase costs for two-stage, two-cell precipitators

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Retrofit Cost Factor

Retrofit installations increase the cost of an ESP because of the frequent need to remove something to make way for the new ESP. Also, the ducting usually is much more expensive as a retrofit application because the ducting path is often constrained by existing structures, additional supports are required, and the confined areas make erection more labor intensive and lengthy. Costs are site-specific; however, for estimating purposes, a retrofit multiplier of 1.3 to 1.5 applied to the total capital investment can be used. The multiplier should be selected within this range based on the relative difficulty of the installation. A special case is the conversion of a hot-side to a cold-side ESP for coal-fired boiler applications.
 

The magnitude of the conversion is very site-specific, but most projects will contain the following elements:

• Relocating the air preheater and the ducting to it
• Resizing the ESP inlet and outlet duct to the new air volume and rerouting it
• Upgrading the ID (induced draft) fan size or motor to accommodate the higher static pressure and horsepower requirements
• Adding or modifying foundations for fan and duct supports
• Assessing the required SCA and either increasing the collecting area or installing an SO3 gas-conditioning system
• Adding hopper heaters
• Upgrading the analog electrical controls to microprocessor-type controls
• Increasing the number of collecting plate rappers and perhaps the location of rappers
 

In some installations, it may be cost-effective to gut the existing collector totally, utilize only the existing casing and hoppers, and upgrade the ESP using modern internal components. The cost of conversion is a multimillion dollar project typically running at least 25 to 35 percent of the total capital investment of a new unit.

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Recent Trends

Most of today's market (1987) is in the 50,000 to 200,000 ft2 plate area size range. ESP selling prices have increased very little over the past 10 years because of more effective designs, increased competition from European suppliers, and a shrinking utility market. Design improvements have allowed wider plate spacings that reduce the number of internal components and higher plates and masts that provide additional plate area at a low cost. Microprocessor controls and energy management systems have lowered operating costs.
 

Few, if any, hot-side ESPs (those used upstream from an air preheater on a combustion source) are being specified for purchase. Recognition that low-sodium coals tend to build resistive ash layers on the collection plates, thus reducing ESP efficiency, has almost eliminated sales of hot-side units. Of the 150 existing units, about 75 are candidates for conversion to cold-side units (using resistivity conditioning agents) over the next 10 years (U.S. EPA 1990).

Specific industry application has little impact on either ESP design or cost, with the following three exceptions: paper mills, sulfuric acid manufacturing plants, and coke byproduct plants. Because paper mills have dust that can be sticky and difficult to remove, paper mill ESPs use drag conveyer hoppers. These hoppers increase the cost by approximately 10 percent of the base flange-to-flange equipment cost. For emissions control in sulfuric acid plants and coke by-product ovens, wet ESPs are used. In sulfuric acid manufacture, wet ESPs are used to collect acid mist. These precipitators usually are small and use lead for all interior surfaces; hence, they normally cost $65 to $95/ft2 of collecting area installed (mid-1987 dollars) and up to $120/ft2 in special situations. Using Figure , the standard cost for a rigid-frame ESP ranges from $7 to $14/ft2 of collecting area. In addition, a wet circular ESP is typically used to control emissions from a coke oven offgas detarring operation. These precipitators are made from high-alloy stainless steels and typically cost $90 to $120/ft2 installed. Because of the small number of sales, small size of units sold, and dependency of site-specific factors, more definitive costs are not available.

                           Dry-type rigid electrode ESP flange-to-flange purchase price versus plate area

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Impact of Materials of Construction: Metal Thickness and Stainless Steel

Corrosive or other adverse operating conditions may require specifications of thicker metal sections in the precipitator. Metal thickness can be moderately increased with minimal cost increases. For example, collection plates are typically constructed of 18-gauge mild steel. Most ESP manufacturers can increase the section thickness by 25% without significant design changes or increases in manufacturing costs of more than a few percent. Changes in the type of material can increase the purchase cost of the ESP significantly. Using type 304 stainless steel instead of 18-gauge mild steel for collection plates and precipitator walls can increase costs 30-50%. Using even more expensive materials for all elements of the ESP can increase costs up to several hundred percent. Based on the carbon steel 18-gauge cost, the approximate factors given below can be used for other materials.

                                                 ESP costs using various materials

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Impact of Alternative Electrode Designs

All three designs—rigid electrode, weighted wire, and rigid frame—can be employed in most applications. Any cost differential between designs will depend on the combination of vendor experience and site-specific factors that dictate equipment size factors. The rigid-frame design will cost up to 25% more than the wire and plate design if the plate height is restricted to that used in wire/plate designs. Several vendors can now provide rigid-frame ESPs with taller plates, and thus the cost differential can approach zero. The weighted wire design uses narrower plate spacings and more internal discharge electrodes. This design is being used less; therefore, its cost is increasing and currently is approximately the same as that for the rigid electrode ESP. Below about 15,000 ft2 of plate area, ESPs are not normally field-erected (erected at the installation site), and the costs will probably be higher than values extrapolated from Figure

Dry-type rigid electrode ESP flange-to-flange purchase price
versus plate area

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ESP Equipment Cost

Most of the following cost discussion is taken from the EPA OAQPS Cost Control Manual (1990). Costs for rigid-electrode, wire and plate, and flat-plate ESPs can be estimated using Figure . 

Figure  represents two cost curves (the two in the middle) along with their respective equations (outer lines with arrows). Each curve requires two equations for calculating cost: one for total plate areas between 10,000 and 50,000 ft2 and another for total plate areas between 50,000 and 1,000,000 ft2. The lower curve shows the cost for the basic unit without the standard options. It represents the flange-to-flange, field-erected price for a rigid-electrode design. The upper curve includes all of the standard options (listed in Table ) that are normally used in a modern system. All units (both curves) include the ESP casing, pyramidal hoppers, rigid electrodes and internal collection plates, transformer-rectifier (T-R) sets and microprocessor controls, rappers, and stub supports (legs) for 4-foot clearance below the hopper discharges. The costs are based on a number of actual quotes
that have been fitted to lines using the “least squares” method. Don’t be surprised if you obtain quotes that differ from these curves by as much as ±25%. (Significant savings can be obtained by solicitating multiple quotes.) The equations should not be used to extrapolate costs for total plates areas below 10,000 or above 1,000,000 ft2. The standard options included in the upper curve add approximately 45% to the basic cost of the flange-toflange hardware. Insulation costs are for 3 inches of field-installed glass fiber encased in a metal skin and applied on the outside of all areas in contact with the exhaust gas stream. Calculate insulation for ductwork, fan casings, and stacks separately. To obtain more accurate results, solve the equations for the lines instead of reading the values from the graph.

                            Dry-type rigid electrode ESP flange-to-flange purchase price versus plate area

                                                    Standard options for basic equipment

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Estimating Capital and Operating Costs

The total capital investment (TCI) includes costs for the ESP structure, the internals, rappers, power supply, and auxiliary equipment, and the usual direct and indirect costs associated with installing or
erecting new structures.

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