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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